PRECIPITATION OF ASPHALTENES,
QUANTIFICATION OF MALTENES, UV AND FTIR
SPECTROSCOPIC STUDIES OF C7 AND
C5 + C7 ASPHALTENES FROM 350OC ATMOSPHERIC
RESIDUUM CRUDES.
BY
ANIGBOGU, IFEOMA VERONICA
PG/M.Sc/08/49193
DEPARTMENT OF PURE AND INDUSTRIAL
CHEMISTRY,
FACULTY OF PHYSICAL SCIENCES
UNIVERSITY OF NIGERIA, NSUKKA.
NOVEMBER, 2011
i
PRECIPITATION OF ASPHALTENES, QUANTIFICATION OF
MALTENES, UV AND FTIR SPECTROSCOPIC STUDIES OF C7 AND
C5 + C7 ASPHALTENES FROM 350
OC ATMOSPHERIC RESIDUUM
CRUDES.
BY
ANIGBOGU, IFEOMA VERONICA
PG/M.Sc/08/49193
DEPARTMENT OF PURE AND INDUSTRIAL CHEMISTRY,
FACULTY OF PHYSICAL SCIENCES
UNIVERSITY OF NIGERIA, NSUKKA.
NOVEMBER, 2011.
ii
CERTIFICATION
Anigbogu, Ifeoma V. a postgraduate student of the Department of Pure and
Industrial Chemistry with registration number, PG/M.Sc/08/49193 has
satisfactorily completed the requirements for the course and research work for
the award of the degree of Master of Sciecne (M.Sc) in Fossil Fuel (Petroleum
and Coal) Chemistry. This research project has been approved for the
Department of Pure and Industrial Chemistry, Faculty of Physical Sciences,
University of Nigeria, Nsukka.
By
____________________ ____________________
Prof. C.A. Nwadinigwe Dr. P.A. Obuasi
Project Supervisor Head of Department
iii
DEDICATION
I dedicate this work firstly, to the saviour of my life, Jesus Christ, whom by His
grace, favour and help kept me alive after the terrible sickness that befell me,
and helped me to be able to complete this programme. Even when the going was
tough, he encouraged me and taught me that only the tough gets going.
Secondly, I dedicate this work to my beloved husband Mr. Emmanuel
Anigbogu, who has always been a source of great support and inspiration all
through the cause of this programme.
iv
ACKNOWLEDGEMENTS
I wish to acknowledge the assistance of some individuals who have contributed
to the success of this work. First and foremost, my appreciation goes to my
project supervior Prof. C.A. Nwadinigwe whose advice and helpful suggestion
and support have directed the progress of this programme especially this project
work from its insception to the conclusion. His instructions, criticisms and
contributions greatly improved this work both in scope and in quality. My
appreciation also goes to my Head of Department Dr. P.A. Obuasi.
I will ever remain grateful to my beloved husband, who is God’s gift to me. God
will not disappoint us in Jesus name. I appreaciate my father Mwogeoffery
Ugwu (Rtd), my sliblings, Obinna Ugwu, Mrs. Ngene Chizoba, Mr. Valentime
Ugwu and Ejike for their prayers.
My special thanks go to the senior laboratory technician Mr. Cliford Ezeugwu
(Food Chemistry Department), Mr. Uba and Mr. Menakaya (Laboratory
Attendants), Dr. Parka E. Joshua (Biochemistry Department), who were
instrumental to the success of this work. Also to my special friends. Mrs. Ngozi
Alumona, Obiageli Egbu, Amara Chukwuneke, Mr. Emmanuel Okon, Mr. Alifa
David, Ikenna, Adika, C.C., Madam Gloria, Mr. Oformater, Mrs. Vivian
Okonkwo and others. I say thank you. I have learnt so much from you all
collectively and individually.
I will not forget Jesus Reigns Catholic Charismatic Renewal UNN, a place
where I encountered God as God. I express my thanks to the members of the
singing ministry. I express my gratitude to all my roommates in 330 Odili (PG)
Hall, You all have been like sisters to me.
Lastly my special appreaciation goes to my Darling friend and sister Dr. to be
Miss Phidelia Waziri who with perseverance carefully typed my work.
ANIGBOGU IFEOMA VERONICA
v
TABLE OF CONTENTS
Approval page - - - - - - - - - - i
Certification - - - - - - - - - - ii
Dedication - - - - - - - - - - iii
Acknowledgements - - - - - - - - - iv
Abstract - - - - - - - - - - v
Table of contents - - - - - - - - - vi
List of figures - - - - - - - - - - x
List of tables - - - - - - - - - - xi
Chapter one
1.0 Introduction - - - - - - - - - 1
1.1 Background of the study - - - - - - - 1
1.1.1 Types of crude oil - - - - - - - - 1
1.1.2 Fractions of crude oil - - - - - - - - 2
1.2 Origin of asphaltene from petroleum/crude oil - - - - 5
1.3 Statement of the Asphaltenes/Resins problem - - - - - 8
1.4 Aims and objectives - - - - - - - - 10
1.5 Scope of the study - - - - - - - - 12
CHAPTER TWO
2.0 Literature review - - - - - - - - 13
2.1 Occurrence and nature of asphaltenes and resins - - - - 15
vi
2.2 Composition of asphaltenes and resins - - - - - 17
2.3 Structure and chemistry of asphaltenes and other heavy organic deposits - 22
2.4 Asphaltene chemical structure under pyrolysis condition - - - 26
2.5 Molecular weight of asphaltene particles - - - - - 29
2.6 Influence of resins constituents on asphaltene constituent - - - 33
2.7 Causes of asphaltene problem, asphaltene self-association
and micelle / colloid concept. - - - - - - - 36
2.8 Economic effect and relevance / significance of asphaltene precipitation - 42
2.9 Prevention and remedies of asphaltene precipitation - - - - 43
CHAPTER THREE
3.0 Materials and Methods (Methodology) - - - - - 47
3.1 Experimental Methods - - - - - - - 47
3.2 Materials and Methods - - - - - - - 47
3.3 Distillation of Each of the Three Crudes - - - - - 49
3.4 Precipitation of Asphaltene, Purification of Asphaltenes and Various Analysis Carried
out on the Pure Asphaltenes Precipitate - - - - - 50
3.4.1 Precipitation of Asphaltenes - - - - - - - 50
3.4.2 Purification of Extracted Asphaltenes - - - - - 51
3.5 Fractionation of Maltenes - - - - - - - 53
3.5.1 Activation of the Silica Gel - - - - - - - 53
3.5.2 Chromatography Procesure - - - - - - - 53
vii
3.5.3 Extraction of Each of the Saturates, Aromatics and Resins (Maltene) from
their various Effluents - - - - - - - - 55
3.6 Physical Methods for Analysing the Asphaltene Fraction - - - 56
3.6.1 Infrared Spectra Analysis - - - - - - - 56
3.6.2 The Ultraviolet Visible Spectra Analysis - - - - - 56
3.6.3 UV – Specroscopic Procedure - - - - - - 57
3.6.4 Melting Point Analysis - - - - - - - 57
CHAPTER FOUR
4.0 Results and Discussions - - - - - - - 60
4.1 Results of Bonny Export, Bodo and Mogho Crude oils before and after Distillation at
350OC - - - - - - - - - 60
4.2 Results from Asphaltene Precipitation - - - - - 62
4.3 Comparism of the weight of the Precipitated Asphaltene with Time Using N-heptane
and n-pentane + n- heptanes Mixed Solvent - - - - - 71
4.4 Summary of the results of FTIR Spectrophotometric analysis - - 74
4.5 Summary of the results of UV/Visible Spectrophotometric Analysis- - 76
4.6 Results of the chemical physical properties - - - - - 78
4.7 Result of the effect of resins on asphaltene precipitation - - - 81
viii
CHAPTER FIVE
Conclusion - - - - - - - - - - 83
New knowledge arising from this work - - - - - - 85
Literature Citied - - - - - - - - - 86
Appendix - - - - - - - - - - 96
ix
LIST OF TABLES
2.2a Elemental Composition of Asphaltenes from World Sources [23] - 19
2.2b Elemental Composition of Various Asphaltenes[23] - - - 20
2.2c Elemental Composition of Petroleum Resins[10] - - - 21
2.5a Total nC5, nC7, nC9 Asphaltene Content of Crude oil [75] - - 32
2.9 Optimizing Asphaltene – Dispersant Dosage in the Adiatic Sea.[8] - 46
4.1 Physical properties of Bonny Export, Bodo and Mogho crude oils before and after
distillation at 350OC - - - - - - - 60
4.2a Composition of Asphaltenes in Bonny Export Crude- - - 62
4.2b Physical Properties of Maltenes (filtrate) from Bonny Export Crude- 63
4.3a Composition of the Asphaltenes from Bodo Crude - - - 65
4.3b Physical Properties of Maltenes from Bodo Crude - - - 66
4.4a Composition of the Asphaltenes in Mogho Crude - - - 68
4.4b Physical properties of Maltenes from Mogho Crude - - - 69
4.5a Summary of the results of IR Analysis of Asphaltenes from Single Solvent
System (Sample A) - - - - - - - 74
4.5a Summary of the results of IR Analysis of Asphaltenes from Mixed Solvent
System (Sample B) - - - - - - - 75
4.6 UV Spectra of the Asphaltene Fractions of Crude Oil - - 76
x
4.7 Chemical and Physical Properties of Crude oils as obtained
from n-heptane single solvent (80mins) - - - - - 78
4.8 Effect of resins on asphaltene precipitation - - - - - 81
xi
LIST OF FIGURES
1: Classification Procedure for Heavy Crude oil Fractions
(>350° boiling Fraction) [3,8,13] - - - - - 3
1.2a: Examples of Some organic Compounds in Petroleum (organic origin of
Petroleum)[26] - - - - - - - - 5
1.2b: Continued Buried of Sediment and Rock layers in Subsiding Basin - 7
1.3a: Asphaltene Precipitation and Deposition in Subsec Flowing, near Wellbore
Region, Seperators e.t.c.[8] - - - - - - 9
1.3b Deposition and plugging of petroleum flow conduits due to streaming
potential generated and sticking of asphaltene particules to the walls [34] 10
2.0(a) Simplified Petroleum Fractionation Method[9] - - - 13
2.0b Continum of Aromatics, Resins and Asphaltenes in Petroleum[37] - 14
2.3a Molecular Structure of Asphaltene Proposed for Maya crude (Mexico) by Altamirano, et al IMP Bulletin.[46] - - - - 23
2.3b Molecular Struture of Asphaltene Proposed for 510c Residue of venezuelian
Crude by Carbognani[46] - - - - - - 24
2.3c Resin fraction with two subgroups (i,ii) - - - - 26
2.4a Proposed Asphaltene Struture Model: Condensed Aromatic
Cluster Model[47 - - - - - - - 27
2.4b Proposed Asphaltene Struture based on Bridged Aromatic Model[47] - 28
2.5a The Molecular Weight of this Asphaltene[45] - - - - - 30
xii
2.5b “Long Diagram shows that the Asphaltene include the Crude Oil
Material Highest in Molecular Weight, Polarity, and/or Aromaticity[13] 31
2.6 Schematic Illustration of Archipelago Model of Asphaltene Monomers,
Asphaltene Aggregate in absence of Resins, and Asphaltemic Aggregate in
presence of Resins[64] - - - - - - - 34
2.7a: Formation of Asphaltene Micelles in the Presence of Excess Amounts of
Aromatic Solvent [34] - - - - - - - 40
2.7b: Asphaltene Flocculation due to Excess Amount of Paraffins
in the Solution[34] - - - - - - - 41
2.7c: Steric-colloid Formation of Flocculated Asphaltene with Resins[34] - 42
3.4 Flow chart of the separation scheme of the atmospheric residuum - 52
3.5: Flow Chart of the Seperation Scheme of Maltenes - - - 55
4.2a % Weight of Asphaltenes from Bonny Export Crude (Single Solvent)
with stirring time - - - - - - - 64
4.2b: % Weight of Asphaltenes from Bonny Export Crude (mixed Solvent)
with stirring time - - - - - - - 64
4.3a: % Weight of Asphaltenes from Bodo Crude (Single Solvent)
with stirring time - - - - - - - 67
xiii
4.3b: % Weight of Asphaltenes from Bodo Crude (mixed Solvent system)
with stirring time - - - - - - - 67
4.4a: % Weight of Asphaltenes from Mogho Crude (Single Solvent)
with stirring time - - - - - - - 70
4.4b: % Weight of Asphaltenes from Mogho Crude (mixed Solvent)
with stirring time - - - - - - - 70
4.5: Effect of n – heptane Single Solvent with stirring time for Bonny, Bodo
and Mogho Crudes (mixed graph) - - - - - - 72
4.6: Effect of n – pentane + n - heptane mixed Solvents with stirring time for
Bonny, Bodo and Mogho Crudes (mixed graph)- - - - 73
Bodo and Mogho Crudes (mixed graph) - - - - 80
4.9: Barchart of the Weight of Heavy Fractions of each of the Three Crude Oils
Studied and their Asphaltene content. - - - - 80
4.10: Effects of Resin on Asphaltenes Stabilization. - - - 82
xiv
LIST OF PICTURES
3.1 Weighing balance(Model:Adventurers) - - - - - 49
3.4 Magnetic stirrer - - - - - - - - 50
3.5 Centrifuging apparatus - - - - - - - 50
3.6 Oven/Incubator (Model – mini/50 Genlab limited - - - - 51
3.7 Fractionation setup (column chromatography) - - - - 54
3.8 Water bath with resin + dichloromethane + methanol effluent during evaporation of
Bonny Export maltenes - - - - - - - 56
3.9 UV/Visible Spectrophotometer - - - - - - 57
3.10 Melting point analyser - - - - - - - 57
xv
ABSTRACT
Asphaltenes behave like blood cholesterol in that they deposit on the inner walls of crude oil
transportation pipes thereby narrowing the internal diameters. This poses great dangers,
including pipe bursts. This work aims at removing asphaltenes from light crudes by solvent
precipitation. Three different Nigerian crude oils sourced from Bonny Export and Mogho in
Rivers State and Bodo in Delta State were studied. The crude oils were first distilled at 350OC
to remove the lighter fractions leaving behind a dead crude known as 350OC atmospheric
residuum which consist mainly of high molecular weight saturates, aromatics, resins and
asphaltenes. Asphaltenes were precipitated from each of these atmospheric distillation
residues at different stirring time intervals using n-heptane (single solvent) and n-pentane +
n-heptane (mixed solvent system). The corresponding yields of asphaltenes were determined
for each time duration. It was found that asphaltene precipitation was more in Mogho crude
oil for both n-hepane single solvent and n-pentane + n-heptane mixed solvent system and
least in Bonny Export crude oil. Physical parameters such as FTIR (Fourier transform infra-
red spectroscopy), uv-vis spectroscopy and melting point analysis were used to characterize
the precipitated asphaltenes while the maltenes (i.e. crude oil minus the asphaltenes:
saturates, aromatics, and resins) were fractionated in other to quantify the ratio of aromatics
to saturates and resins to asphaltenes as parameters that control the stability of asphaltenes in
crude oils. From the results, the FTIR data revealled that the asphaltene fraction of crude oils
was made up of both saturated (cyclic aliphatic hydrocarbons etc.) and unsaturated (e.g.
substituted aromatic hydrocarbon etc) parts as supported by our uv/vis spectra on the
asphaltene precipitates. Also the ratio of aromatics to saturates and resins to asphaltenes was
higher in Bonny Export crude and lower in Mogho crude. This indicated that Bonny Export
crude has the lowest asphaltene precipitation risk while Mogho crude had the highest
asphaltene precipitation risk. Addition of resins (extracted from each of the crudes) to a
mixture of 1ml crude + 40ml n-heptane brought about a reduction in asphaltene precipitate
for all the crudes. This indicated that resins solubilize asphaltenes in crude oil. On the basis of
these findings: it was shown that asphaltenes precipitated more using the mixed solvent
system. These findings also showed that asphaltenes precipitate in crude oil, but other
constituents of crude oil especially the resins, influence asphaltene precipitation.
1
CHAPTER ONE
3.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Crude oil is a complex mixture of hydrocarbons and other compounds of varying
molecular weight and polarity. [1] [2] Alternatively crude oil can be said to be a collective term
used to described a hydrocarbon rich mixture of compounds that is usually found as a
subterranean deposit that accumulated over millions of years. The physical and chemical
characteristics of crude oil vary widely from one production field to another and even within the
same field.[3]
1.1.1 TYPES OF CRUDE OILS
(i) LIGHT CRUDE AND VERY LIGHT CRUDE OIL: This is liquid petroleum that has low
density and that flows freely at room temperature. It has low viscosity, low specific gravity
and high API gravity (34 – 39OAPI) due to the presence of a high proportion of light
hydrocarbon fractions. It generally has a low wax content. [4a] very light crude is defined with
API gravity above 40OAPI.[4b]
(ii) MEDIUM CRUDE OIL: This is any liquid petroleum with an API gravity between 22 –
33OAPI.[4b]
(iii) HEAVY CRUDE OIL AND EXTRA HEAVY CRUDE OIL: is any type of crude oil
which does not flow easily. It is refered to as “heavy” because its density or specific gravity
is higher than that of light crude oil. Heavy crude oil is defined as any petroleum with an API
gravity less than 20° [5] Heavy oil is asphaltic and contains asphaltenes and resins. It is
“heavy” (dense and viscous) due to the high ratio of aromatics and napthenes to paraffins and
2
high amounts of NSO’s (Nitrogen, Sulfur, Oxygen and heavy metals). Heavy oil has a higher
percentage of compounds with over 60 carbon atoms and hence a high boiling point and
molecular weight.[5] Heavy oil typically contains very little paraffin and may or may not
contain high levels of asphaltenes. Extra heavy crude oil is defined with API gravity below
10.0° API (i.e. with density greater than 1000kg/m3 or, equivalently, a specific gravity
greater than 1), with a specific gravity of greater than one, extra heavy crude oil is present as
a dense non-aqueous phase liquid when spilled in the environment. [6]
1.1.2 FRACTIONS OF CRUDE OIL
LIGHTER FRACTIONS: The compound and compound classes present in the lighter fractions
of crude, which is typically the fraction that can be recovered by atmospheric distillation, can be
identified by chromatographic and spectroscopic techniques. [7]
HEAVY FRACTION OF CRUDE OIL: This fraction is classified based on solubility, [7] with
maltenes (i.e. saturates, resins and aromatics) being soluble in n-alkanes such as n-heptane [8] and
asphaltenes being soluble in benzene/toluene and insoluble in n-alkanes such as n-heptane or n-
pentane. [8] This heavy fraction is non-distillable and remain in the residue fuels as the distillable
fractions (lighter fractions) are removed.[9]
The addition of a low boiling point alkanes example n-pentane, n-heptane or other
alkanes to crude oils originates the selective precipitation of the most aromatic and highest
molecular weight compounds present in the crude oils.[10][11] The crude oil fractions that
precipitates under such conditions is known as asphaltenes. Being a complex mixture of a wide
array of different molecular types.[12] The amount and characteristics of the asphaltene
constituents in crude oil depends to a greater or lesser extent on the source of the crude oil. [9]
3
Asphaltenes Resins Aromatics Saturate
s
The asphaltene content of crude oil varies from 0.1% to more than 20% depending on the
production field.
A convenient laboratory method has been developed to quantify the asphaltene fraction.
This technique separates “dead” oil that has lost its gaseous components, into saturates,
aromatics, resins and asphaltenes (SARA) depending on their solubility and polarity, (figure 1.)
[8]
Atmospheric residue
Extract with n – heptanes (C7: oil = 30:1)
Maltenes
Adsorbed on silica, elute with Precipitation
n-alkane Toluene Toluene/methanol
Figure 1: Classification procedure for heavy crude oil fractions (>360°C boiling fraction)
[3],[8],[13]
This SARA method is a reasonable first step for categorizing dead oil, it is also a simple
procedure that can be performed in many laboratory because of its simplicity, SARA analysis
has become a widespread means for comparing oils. However, SARA analysis has several
disadvantages that becomes apparent when it is used for purpose beyond its original intent. [8] In
addition laboratory methods varies greatly and the yield of asphaltenes varies with the type of n-
4
alkane (i.e. precipitant) used, liquid precipitant to oil volume ratio, contact time, pressure and
temperature. [8,14,15,16]
A single oil could have two or more SARA results depending on precipitant used. [8] A
commonly accepted view in petroleum industry is that asphaltenes form micelles which are
stabilized by adsorbed resins kept in solution by aromatics. Two key parameters that control the
stability of asphaltene micelles in a crude oil are the ratio of aromatics to saturates and that of
resins to asphaltenes. When these ratios decrease, asphaltene – micelles will flocculate and form
larger aggregates. [17][18] This fraction is well known for its tendency to precipitate during
production and refining operations causing significant losses to the oil industry every year.[19-20]
The asphaltene precipitation depends mainly on the stability of the asphaltenes and
stability depends not only on the properties of the asphaltenes fraction but on how good a solvent
the rest of the oil is for its asphaltene. As recognized by de Boer et al. (1995), light oils with
small amounts of asphaltenes are more likely to cause problems during production than heavy oil
with larger amounts of material in the asphaltene fraction. The heavier oil also contains plenty of
intermediate components that are good asphaltene solvents whereas the light oil may consist
largely of paraffinic materials in which, by definition, asphaltenes have very limited solubility.
Asphaltenes in heavier oils can also cause problems if they are destabilized by mixing with
another crude oil during transportation or by other steps in oil processing.[12,13]
In particular, the characteristics of the disperse phase and the peptizing power of the
resins [18,19] are considered fundamental factors for stabilization of asphaltenes in crude oil.[12]
Crude oil can be classified by chemical compositon, density, viscosity and distillation
characteristics to name a few. [23] The classification system based on composition refers to only
5
the hydrocarbon nature of oils namely paraffin (alkanes) naphthenic or cycloalkanes and
aromatic hydrocarbons namely Sulphur containing compounds, Nitrogen containing compounds,
organomettallic compounds, oxygen containing compounds. [24][25]
1.2 Origin of asphaltene from petroleum/crude oil
Crude oil is a naturally occurring substance consisting of organic compounds in the form
of gas, liquid, or semisolid. The simplest of these compounds is methane.
Figure 1.2(a) Examples of some organic compounds in petroleum
Figure 1.2(a) shows some examples of organic compounds in petroleum, from the
simplest (methane) to the most complex (asphaltene). Asphaltenes are the most complex and
most polar fractions found in crude oil, with more than 36 carbon atoms bound to more than 167
hydrogen atoms, three nitrogen atoms, two oxygen atoms, and two sulphur atoms. [26][27]
Semisolid petroleum is tar, which is dominated by larger complex hydrocarbons and
asphaltenes (Figure 1.2a).[25] Petroleum formation takes place in sedimentary basins, which are
6
areas where the earth crust subsides and sediments accumulate within the resulting depression.
Throughout geologic time, the world oceans have expanded and receded over the earth’s land
surfaces and contributed sediment layers to subsiding sedimentary basins. [26] Development of
stagnant water conditions in some of the expanded oceans caused the bottom waters to be
depleted in oxygen (anoxic), which allowed portion of the decaying plankton to be preserved as
a sediment layer enriched in organic matter. Methane producing microorganisms referred to as
methanogens may thrive under certain favorable condition within the organic rich sediment layer
during its early burial. There microorganisms consume portions of the organic matter as food
source and generate methane as a byproduct. This methane, which is typically the main
hydrocarbon in natural gas, has a distinct neutron deficiency in its carbon nuclei which allows
microbial natural gas to be readily distinguished from methane generated by thermal processes
later in the basin’s subsidence history. The microbial methane may bubble up into the overlying
sediment layers and escape into the ocean waters or atmosphere. If impermeable sediment layers,
called seals, hinder the upward migration of microbial gas, the gas may collect in underlying
porous sediments, called reservoirs.
Burial of the organic-rich rock layer may continue in some subsiding basins to depths of
6,000 to 18,000 feet, exposing the rocks to temperatures of 150 to 350°F (66 to 177°C) for a few
million to tens of billions of years. The organic matter within the organic rich rock layer begins
to cook during this period of heating and portions of it thermally decompose into crude oil and
natural gas. If the original source of the organic matter is plankton (i.e. algae, bacteria e.t.c)
crude oil will be the dorminant petroleum generated with lesser amounts of natural gas
generation.
7
Petroleum has a lower density, than the water that occupies pores, voids and cracks in the
source rock and the overlying rock and sediment layers. This density difference forces the
generated petroleum to migrate upwards by buoyancy until sealed reservoirs in the proper
configurations serve as traps that concentrate and collect the petroleum Figure 1.2(b).
Figure 1.2(b): Continued buried of sediment and rock layers in subsiding basin.
In some basins, petroleum may not encounter a trap and continue migrating upwards into
overlying water or atmosphere as petroleum seeps. Crude oil that migrates to or near the surface
of a basin will lose a considerable amount of its hydrocarbons to evaporation, water washing,
and microbial degradation leaving a residual tar enriched in large complex hydrocarbons and
asphaltenes.[25]
Asphaltene is an important constituents in crude oils. While it is also a major factor that
causes difficulties in oil recovery.[28][29] During the evolution and migration of oil reservoirs, the
8
asphaltenes may be flocculated or precipitated out from crude oils due to the changes of pressure,
temperature and/or the composition of reservoir fluid. [30]
Owing to the alteration of ambient conditions, asphaltenes are liable to be precipitated out
during oil recovery, transportation and post-processing. It can make oil production more arduous
and costly because of the partially plugging in oil well- and pipeline by asphaltenes. It may
further decrease recovery efficiency or even stop oil production due to the shutoff of oil pore
throat or even of the whole oil well. [30]
1.3 STATEMENT OF THE ASPHALTENES/RESINS PROBLEMS
Asphaltenes are best known for the problems they cause as solid deposit that obstruct
flow in the production system.[31] In asphaltene self associate and/or precipitate, the self
association and precipitation is mediated by other solubility fractions particularly the resins.[32]
Hence asphaltenes and their related compounds resins have often been lumped together as
residue in crude oil [8] causing reduction in crude oil production as they can block the pores of
reservoir rocks and can also plug the wellbore tubing, flowlines, separators, pumps, tanks and
other equipment and as a result, causing barrier to the flow of oil as shown schematically below:
[33][34]
9
Figure 1.3(a): Asphaltene precipitation and deposition in subsea flowlines, near wellbore region,
Seperators. e.t.c. [8]
Not only do asphaltenes increase fluid viscosity and density, they also have the potentials
to derail upstream activities, and can also cause downstream disruptions, such as adhering to hot
surfaces in refineries. [8] As mentioned earlier asphaltene precipitation can make oil production
more arduous and costly because of the partially plugging in oil well and pipeline by asphaltene.
It may further decrease recovery efficiency or even stop oil production due to the shut off of oil
pore throat or even of the whole oil well. [30]
At reservoir conditions, the adsorption of asphaltene to mineral surfaces causes a reversal
in wettability of the reservoir from water wet to oil wet and also results in insitu permeability
reductions. Both factors also reduce oil production. Apart from the production loss, the cost of
removing precipitated asphaltene from equipment and flowlines can be very expensive and
significantly alter the economics of a project. Examples of this cases have been reported in the
prinos field, Greece, Hansimessaoud field, Algeria, Ventura Avenue field, California, and other
places throughout the world.[35][33]
10
Furthermore, flocculation of asphaltene was found to reduce the effectiveness of wax
inhibitors, due to the formation of complex asphaltene paraffin solid aggregate. [36] Asphaltene
precipitation can cause major problems during the transportation of bitumen and heavy oil. The
flow of paraffin diluted bitumen through transportation pipelines and processing equipment can
result in deposition of precipitated asphaltenes. This deposition causes higher pumping rates and
can lead to a build up of internal pipeline pressure.[37] as shown in figure 1.3b below.
Figure 1.3b: Deposition and plugging of petroleum flow conduits due to streaming potentail generated and sticking of asphaltene particles to the walls.[34]
Some other examples of problems that arise due to asphaltene flocculation and/or
sedimentation are: Destabilization of asphaltene constituent as a result of the change in medium
during fuel oil-heavy crude oil blending. Ignition delay and poor combustion (often caused by
high content of asphaltene constituent (≥6%) in crude oil) leading to boiler fouling, diminished
heat transfer, stack (particulate) emissions, and corrosion.[9] e.t.c. Thus, with all these and other
problems – that arise as a result of asphaltene precipitation, it can be seen that there is need for
predicting the conditions for asphaltene precipitation.
1.4 AIMS AND OBJECTIVES
The definition of the non-volatile constituents of petroleum (i.e., the asphaltene
constituents, the resin constituents and to some extent, part of the oils fraction, insofar as
11
nonvolatile oils occur in residue and other heavy feed stocks) is an operational aid. It is difficult
to base such separations on chemical or structural features. This is particularly true for the
asphaltene constituents and the resin constituents, for which the separation procedure not only
dictates the yield but can also dictate the quality of the fraction. The technique employed also
dictates whether or not the asphaltene contains coprecipitated resins. This is based on the general
definition that asphaltene constituents are insoluble in n-pentane (or in n-heptane) but resins are
soluble in n-pentane (or n-heptane). To date, little or no effort has been made to study asphaltene
precipitation from crude oil using mixed n-pentane/n-heptane solvent system. Since the use of
different hydrocarbon liquids influences the yield of asphaltenes as well as resins fraction,
The objectives of this present work are as follows:
� To investigate the effect of the pure solvent i.e., n-heptane and also the mixed n-
pentane/n-heptane solvent systems, on asphaltene precipitation.
� To investigate the effect of stirring time on asphaltene precipitate.
� To fractionate the resulting maltenes obtained – after precipitation of asphaltenes and
compare their ratios (i.e. of aromatics to saturates and resins to asphaltenes) with the
extent of precipitation of asphaltene.
� Determine the melting point of the asphaltene precipitate obtained.
� To ascertain the functional group properties (i.e., using IR and UV) of each asphaltene
precipitate, in other to elucidate if the compound is truly asphaltene.
� To determine the role resins play, if any, in asphaltene stability which may help chemists
develop better methods for preventing and remediating asphaltene problems.
12
1.5 Scope of the Study
� Three different crude oil samples will be used for this work.
� The samples will be collected and distilled at 350°C to strip off lighter fractions.
� For each oil sample (3500C atmospheric residuum), asphaltene precipitation reaction will
be carried out, keeping crude oil/solvent constant, varying stirring time and also weighing
asphaltene yield in each case.
� Functional group properties of each asphaltene precipitation will be ascertained (IR and
UV). Also melting point analysis will be carried out on the asphaltenes precipitated.
� To fractionate the resulting maltenes obtained after precipitation of asphaltenes and
compare their ratios (i.e. aromatics to saturates and resins to asphaltenes ) with the extent
of asphaltenes obtained.
13
CHAPTER TWO
2.0 Literature Review
Crude oils can be fractionated and classified in a number of ways. Standard laboratory
methods have been defined for the fractionation of petroleum. The older ASTM D – 2006
method and ASTM D-2007 method are no longer in official use but may still find use in private
laboratories. Indeed, these methods found such wide use that many modifications have been
proposed that are still in use.[32] The overall product of these fractionation methods, which with
the ensuing sub-fractionation, provides the representation of petroleum a composite of the four
fractions (saturates, aromatics, resins and asphaltenes).[9][2] Fig 2.0(a) below:
Figure 2.0 (a): Simplified petroleum fractionation method [9]
Feedstock
n - heptane
Asphaltenes
(insoluble)
Deasphalted oil
percolate through alumina
Asphaltenes
(soluble in toluene)
Resins (pyridine wash)
Aromatic (Toluene wash)
Saturates (n – heptanes
wash)
Carbenes / carboids (insoluble in toluene)
Carbenes
soluble in CS2
Carboids
insoluble in CS2
14
Figure 2.0(a) above shows the four major solubility fractions (i.e. Asphaltenes, resins,
aromatics and saturates). However, the heavier components, asphaltenes and their related
compounds resins have often been lumped together as residue and deemed unworthy of or too
challenging for further examination.[8] Details of the methods used to separate them are markedly
different from the other three fractions as they mainly contain paraffins and naphthene therefore,
are termed non polar. While, aromatics, resins and asphaltenes form a continuum with increasing
polarity, molar mass and heteroatom content (Figure 2.0(b) below.
Figure 2.0(b): Continuum of Aromatics, Resins and Asphaltenes in Petroleum[37]
15
Asphaltenes are the heaviest and most complex fraction in a crude oil sample, which
appears as brown or black solid particles precipitated from a crude oil by using a low boiling –
point alkane e.g. n-pentane or n-heptane. The asphaltene yield decreases as the carbon number of
an alkane increases, while it increases monotonically and finally reaches a plateau if the liquid
precipitant –to – oil volume ratio increases up to 20-40 for n-pentane and n-heptane,
respectively. Some would argue that the n-C7 asphaltenes are the “real” asphaltenes, whereas the
n-C5 material is a mixture of asphaltenes and resins [13]. Resins are primarily good arphaltene
solvents, and are not known to deposit on their own, but they deposit with asphaltenes. [34],[39]
The reasons for the asphaltene deposition (precipitation) can be many factors including
variations of temperature, pressure, composition, flow regime, and wall and electrokinetic
effect.[34] The precipitation is mediated by other solubility fractions. Therefore it is evident that
petroleum is a delicately balanced physical system where the asphaltenes depend on the other
fractions for complete mobility and phase stability. [9]
Considering that the major barrier in a profitable deposition – free oil production scheme
is the presence of asphaltene, this literature review focuses on what follows the role of other
solubility fractions such as aromatics, saturates and resins in crude oil and most expecially the
role resins play if any in solubilizing asphaltene in petroleum fluids.
2.1 Occurrence and Nature of Asphaltenes and Resins
Asphaltenes are molecular substances that are found in crude oil, along with resins,
aromatic hydrocarbons and alkanes (i.e., saturated hydrocarbons). [40],[41]
Asphaltenes are today widely recognised as soluble chemically altered fragments, of
kerogen which migrated out of the source rock for the oil, during oil catagenesis. Asphaltenes
16
had been taught to be held in solution in oil by resins (similar structure and chemistry, but
smaller).[42] but this (i.e. the role that the resin fraction plays in stabilizing asphaltene) has been a
major topic of debate. A contrary view holds that specific interactions between asphaltenes and
resins are not required to explain asphaltene stability,[43] that resins are primarily good solvents
for asphaltenes and that non – vanderwalls forces are primarily responsible for flocculation of
asphaltenes. [44] Another reference [45] state that there is no implied genetic relationship between
asphaltenes and resins, that resins may polymerize to form asphaltenes and asphaltenes may
break down into resins. However, no matter how resins are defined, they still include species that
contribute to the overall solvent quality of the oil with respect to its asphaltenes. [13]
Asphaltenes appear as brown or black solid particles precipitated from crude by using a
low boiling point alkane.[4] The colour of dissolved asphaltene is deep red at very low
concentration in benzene as 0.003% makes the solution distinctly yellowish. The colour of crude
oils and residues is due to the combined effect of neutral resins and asphalteness. [46]. Heavier,
black oil crudes will typically have higher asphaltene content. The black colour of some crude
oils, and residues is related to the presence of asphaltenes which are not properly peptized [46],[47]
In nature, asphaltenes are hypothesized to be formed as a result of oxidation of neutral
resins. On the contrary, the hydrogenation of asphaltic compound – products containing neutral
resins and asphaltene produces heavy hydrocarbon oils, i.e. neutral resins and asphaltenes are
hydrogenated into polycyclic aromatic or hydroaromatic hydrocarbons. They differ, however,
from polycyclic aromatic hydrocarbons by presence of oxygen and sulfur in varied amounts.
On heating above 300-400oc, asphaltenes are not melted but decompose leaving a
carbonaceous residue [9] (or carbon and volatile products).[46] While the resin fraction becomes
17
quite fluid on heating but often show pronounced brittleness when cold. Being a polar molecule,
asphaltenes adsorb to formation surfaces, especially clay. They can oil wet formations, which
will increase water flow. With their aromatic ring structure, asphaltenes are not soluble in
straight chain alkanes (hexane, heptanes, pentane). They are soluble in aromatic solvents like
xylene and toluene. [47]
Heavy oils, tar sands and biodegraded oils (as bacteria cannot assimilate asphaltenes, but
readily consume saturated hydrocarbons and certain aromatic hydrocarbon isomers –
enzymatically controlled) contain much higher proportions of asphaltenes than do medium API
oils or light oils. Condensate are virtually devoid of asphaltenes.[42]
2.2 Composition of asphaltenes and resins.
Asphaltenes constitutents isolated from different sources are remarkably constant in
terms of ultimate composition, although careful inspections of the date shows extreme ranges for
the composition. Asphaltene constitutents from different sources have never before been
compared with any degree of consistency. The composition of the resins fraction can vary
considerably and is dependent on the kind of precipitating liquid and on the temperature of the
liquid system.[9]
Asphaltene and resins consist primarily of carbon, hydrogen, Nitrogen, oxygen, sulphur
as well as trace amounts of vanadium and nickel, including condensed polynuclear aromatics and
other metallic elements. [10],[42,[47]
There are indication which shows that the condensed aromatic nuclei carry alkyl, and
alicyclic systems with heteroatoms (that is N, O, and S) scattered throughout in various, aliphatic
18
and heterocyclic locations. With the increasing molar mass of the asphaltene fractions, both
aromaticity and proportion of the heteroelement increases.[18]
The elemental composition of asphaltene constituents isolated by use of excess (greater
than 40) volumes of n-pentane as the precipitating medium show that the amounts of carbon and
hydrogen usually vary over only a narrow range. These values corresponds to a hydrogen-to-
carbon atomic ratio of 1.15+ 0.5% (as shown in figure 5 below)[32], although values outside this
range are sometimes found.[9] Furthermore, it is still believed that asphaltene constituents, are
precipitated from petroleum by hydrocarbons solvents because of this composition, not only
because of solubility properties.[9]
19
Table 2.2a Elemental composition of asphaltenes from world sources (Speight, 1999)
Source Composition (wt %) Atomic ratios
C H N O S H/C N/C O/C S/C
Canada 79.0 8.0 1.0 3.9 8.1 1.21 0.011 0.037 0.038
Iran 83.7 7.8 1.7 1.0 5.8 1.19 0.017 0.009 0.026
Iraq 80.6 7.7 0.8 0.3 9.7 1.15 0.009 0.003 0.045
Kuwait 82.2 8.0 1.7 0.6 7.6 1.17 0.017 0.005 0.035
Mexico 81.4 8.0 0.6 1.7 8.3 1.18 0.006 0.016 0.038
Sicily 81.7 8.8 1.5 1.8 6.3 1.29 0.016 0.017 0.029
USA 84.5 7.4 0.8 1.7 5.6 1.05 0.008 0.015 0.025
Venezuela 84.2 7.9 2.0 1.6 4.5 1.13 0.020 0.014 0.020
In contrast to the carbon and hydrogen contents of asphaltenes, notably variations occur in the
proportions of the hetero elements, in particular in the propotions of oxygen and sulfur. Oxygen
contents vary from 0.3 to 10.3%. On the otherhand, the nitrogen content of the asphaltenes has a
somewhat lesser degree of variation (0.6-3.3%).[37]
The use of n-heptane as the precipitating medium yields a product that is substantially
different from the n-pentane insoluble material as shown below [32]
20
Table 2.2b Elemental composition of various asphaltenes
Source Solvent
medium
Composition (wt %) Atomic ratios
C H N O S H/C N/C O/C S/C
Canada n-pentane 79.5 8.0 1.2 3.8 7.5 1.21 0.013 0.036 0.035
n-heptane 78.4 7.6 1.4 4.6 8.0 1.16 0.015 0.044 0.038
Iran n-pentane 83.8 7.5 1.4 2.3 5.0 1.07 0.014 0.021 0.022
n-heptane 84.2 7.0 1.6 1.4 5.8 1.00 0.016 0.012 0.026
Iraq n-pentane 81.7 7.9 0.8 1.1 8.5 1.16 0.008 0.010 0.039
n-heptane 80.7 7.1 0.9 1.5 9.8 1.06 0.010 0.014 0.046
Kuwait n-pentane 82.4 7.9 0.9 1.4 7.4 1.14 0.009 0.014 0.034
n-heptane 82.0 7.3 1.0 1.9 7.8 1.07 0.010 0.017 0.036
For example, the hydrogen-to-carbon atomic ratio of the n-heptane precipitate is lower
than that of the n-pentane precipitate. This indicates a higher degree of aromaticity in the n-
heptane precipitate. Nitrogen - to – carbon, oxygen – to – carbon, and sulfur - to – carbon ratios
are usually higher in the n-heptane precipitate, indicating higher proportions of the hetero
elements in this material. [32][37]
Elemental constituents of a suite of petroleum resins isolated by the same procedure, and
therefore comparable,[32] show that the proportions of carbon and hydrogen, like those of the
asphaltenes, vary over a narrow range: 85± 3% carbon and 10.5 ± 1% hydrogen. The proportions
21
of nitrogen (0.5 ± 0.15%) and oxygen (1.0 ± 0.2%) also appear to vary over a narrow range, but
the amount of sulfur (0.4 to 5.1%) varies over a much wider range. [9][32]
There are notable increases in the H/C ratios of the resins relative to those of the
asphaltenes. Indeed, where as the asphaltenes may have in excess of 50% of the total carbon as
aromatic carbon, in the resins the proportion of the total carbon occurring as aromatic carbon is
significantly lower.[18][48] Presumably this indicates that aromatization is less advanced in the
resins than in the asphaltenes. There is also a tendency to decreased proportions of nitrogen,
oxygen, and sulfur in the resins relative to the asphaltenes. [37]
Table 2.2(c) Elemental composition of petroleum resins [10]
Source Composition (wt%) Atomic ratios
C H O N S H/C O/C N/C S/C
Canada 86.1 11.9 1.1 0.5 0.4 1.66 0.009 0.005 0.002
Iraq 77.5 9.0 3.1 0.3 10.1 1.39 0.03 0.003 0.048
Italy 79.8 9.7 7.2 Trace 3.3 1.46 0.067 - 0.016
Kuwait 83.1 10.2 0.6 0.5 5.6 1.47 0.005 0.005 0.025
USA 85.1 9.0 0.7 0.2 5.0 1.27 0.006 0.002 0.022
Venezuela 76.6 9.6 -- 4.5-- 6.3 1.45 - - 0.030
22
2.3 STRUCTURE AND CHEMISTRY OF ASPHALTENES AND OTHER HEAVY
ORGANIC DEPOSITS.
Asphaltenes and resins are two of the several, but important, heavy organics present in
petroleum fluids. There exact molecular structure are not generally known in a particular oil field
and they could vary from well to well.[34][46] The molecular nature of the asphaltene fractions of
petroleum and bitumens has been subject to numerous investigations. However, determining the
actual structure of the constituents of the asphaltene fractions has proven to be difficult because
they are a mixture of many thousands of molecular species.[37]
Asphaltenes are lyophilic with respect to aromatics, in which they form highly scattered
colloidal solutions. Specifically asphaltenes of low molecular weight are lyophobic with respect
to paraffins like pentanes and petroleum crudes. There have been considerable efforts by analytic
chemists to characterize the asphaltenes in terms of chemical structure and elemental analysis as
well as by the carbonaceous sources.[46]
Attempts have been made to describe the total structure of asphaltenes, resins and other
heavy fractions based on physical and chemical methods. [34][37][46] Physical methods include IR,
NMR, ESR, mass spectrometry, x-ray, ultracentrifugation, electron microscopy, VPO, GPC,
e.t.c. Chemical methods involves oxidation, hydrogenation, elemental and pyrolysis GC – FID –
GC – MS. The chemical structures of asphaltenes, are difficult to ascertain due to the complex
nature of the asphaltenes.[34][42][46] Nevertheless, the various investigations have brought to light
some significant facts about asphaltene structure.[37]
It is undisputed that the asphaltenes are composed mainly of polyaromatic carbon i.e.,
polycondensed aromatic benzene units with oxygen, nitrogen and sulfur, (NSO) compound
23
combined with minor amounts of a series of heavy metals, particularly vanadium and nickel
which occur in porphyrin structures. Further more, asphaltene rotational diffusion measurements
show that small PAH (polycyclic aromatic hydrocarbon), chromophores (blue fluoreseing) are in
small asphaltene molecules while big PAH chromophores (red fluoreseing) are in big molecules.
This implies that there is only one fused polycyclic aromatic hydrocarbon (PAH) ring system per
molecule. [42]
The various figures below shows some of the representative structures of asphaltenes:
Figure 2.3a: molecular structure of asphaltene proposed for Maya crude (Mexico) by
Altamirano, et al IMP Bulletin, 1986 [46]
24
Figure 2.3b: Molecular structure of asphaltene proposed for 510c residue of Venezuelan crude
by carbognani [INTEVEP S.A Tech. Rept., 1992) [46]
Petroleum asphaltene have a varied distribution of heteroatom (N, O, S) functionality.
Nitrogen exist as varied heterocyclic types but the more conventional primary, secondary and
tertiary aromatic amines have not been established as being present in petroleum asphaltenes.[50]
There are also reports in which the organic nitrogen has been defined in terms of basic and
nonbasic types. [37] Spectroscopic investigations suggest that carbazoles occur in asphaltenes,
which supports, earlier mass spectroscopic evidence for the occurrence of carbazole nitrogen in
asphaltenes. [37] The application of x-ray absorption near-edge structures (XANES) spectroscopy
to the study of asphaltenes has led to the conclusion that a large portion of the nitrogen is present
in aromatic systems, but in pyrrolic rather than pyridinic form.[51] Other studies have brought to
light the occurrence of four – ring aromatic nitrogen species in petroleum.
Evidence for the presence and nature of oxygen functions in asphaltenes has been derived
from infrared spectroscopic examination of the products after interaction of the asphaltenes with
25
acetic anhydride. Thus, when asphaltenes are, heated with acetic anhydride in the presence of
pyridine, the infrared spectrum of the product exhibits prominent absorptions at 1680, 1730, and
1760cm-1. These observations suggest acetylation of free and hysdro-bonded phenolic hydroxyl
groups present in asphaltenes.[50][52] Oxygen has been identified in carboxylic, phenolic and
ketonic locations but is not usually regarded as being located primarily in heteroaromatic ring
systems.[37]
Sulfur occurs as benzothiophenes. More highly condensed thiophene – types may also
exist but are precluded from identification by low volatility. Other forms of sulfur that occur in
asphaltenes include the alkyl – alkyl sulfides, alkyl – aryl sulfides and aryl – aryl sulpfides.[37]
Nickel and vanadium occur as porphyrins but whether or not these are an integral part of
asphaltene structure is not known. Some of the porphyrins can be isolated as a separate stream
from petroleum.
In accordance with the Nuclear Magnetic Resonance (NMR) data and results of chemical
analysis, attempts have been made to describe the total structure of asphaltenes.[37] Strausz et al
identified a host of structural units in Alberta asphaltenes from detailed chemical and
degradation studies. He also showed that the extent of aromatic condensation is low and that
highly condensed pericyclic aromatic structures are present in very low concentrations. From his
work he concluded that petroleum asphaltenes were mainly derived through the catalytic
cyclization, aromatization and condensation of n – alkanoic (probably fatty acids) precursors.
He came up with a hypothetical asphaltene molecule consisting of large aromatic clusters.[54]
It must be remembered that asphaltene constituents are a solubility class and, as such may
be an accumulation of life (literally) thousands of structural entities. Hence caution is advised
26
against combining a range of identified products into one (albeit – hypothetical) structure. An
often ignored but extremely important aspect of asphaltene chemistry and physics, is the micelle
structure, which represents the means by which asphaltene constituents exists in crude oil.
The large variety of functional groups and heteroatom content in the asphaltenes indicates
that asphaltene molecules have the potential to form links with other similar molecules in a
number of ways. Their links may be formed through acid-base interactions, aromatics (П-П)
stacking, hydrogen bonding, dipole – dipole interactions or even weak van – der waals
interactions. However, П-П bonding is considered the prevalent theory.[55]
Investigations have shown that a variety of hydrocarbon types and functional types occur
in resin fractions.[18][32][56][57] In addition, the resin constituents contain a variety of functional
groups, including thiophene, benzothiophene and dibenzothiophene systems, hydrogen – bonded
hydroxyl groups, pyrrole (and indole) N – H functions, ester functions, acid functions, carbonyl
(ketone or quinine) functions, and sulfur – oxygen functions. [9][52] Figure 2.3c below shows a
representation of a resin structure.
Figure 2.3c: Resin fraction with two subgroups (i, ii)
27
2.4 Asphaltene chemical structure under pyrolysis condition
Here, two different views of the asphaltene structure have been proposed. The first,
following Yen, T,F [47] who assumes extensive condensation of the aromatic rings into large
sheets. These sheets are assumed to be soluble, because of the saturated rings and side chains
around the molecular periphery as shown in figure 2.4a below
Figure 2.4a: Proposed asphaltene structural model: condensed aromatic cluster model[47]
This type of structure, with lower molecular weight, has been proposed by groenzin and
Mullins,[58] on the basis of spectroscopic studies. In a complex mixture, structure such as this
cannot be left out, particularly when the fraction of aromatic carbon approaches 70%, however,
such a chemical structure cannot account for the average amount of volatile product evolution
under the pyrolysis conditions from a range of asphaltenes.
28
A very different structural organization, illustrated in figure 2.4b below was proposed by
Speight and by Strausz and co–workers (e.g. Murgich et al) on the basis of pyrolytic and
selective oxidation studies to determine the building blocks of asphaltenes.
Figure 2.4b Proposed asphaltene structure based on bridged aromatic model [47]
A structure of the type in figure 2.4a cannot give significant mass yields of volatile
products in a pyrolysis experiment. The side chains would crack off readily, and the naphthenic
rings then would undergo a combination of dehydrogenation (to form aromatics) and cracking
29
(to give mainly light ends). On the contrary, a structure of the type in figure 2.4b can give a wide
range of product sizes, from methane to toluene – insoluble carbon residue, depending on the
balance between cracking, product release, and molecular rearrangements.
Data on the nature of product from the cracking of asphaltenes give further support to the
diversity of asphaltenes from different crude oils and indicate that the chemical structures in
asphaltenes must be consistent with the evolution of a significant yield of volatile products
during pyrolysis.[59] Chemical characterization of the products from the pyrolysis of asphaltenes
depends strongly on the analytical methods selected and, possibly on the chemistry of the
asphaltene selected. When the cracked products are analysed by gas chromatography (GC), the
dominant components in the cracked products are n–alkanes and n- alkenes for a wide range of
asphaltenes. For example, Arkok et al.[33] used curic – point pyrolysis to analyse products from
asphaltenes from an Arabian crude. Paraffins, Olefins, and aromatics were identified by gas
chromatography – mass spectroscopy (GC-MS), but only up to C21. In this range, n– alkane and
n – alkene products dominated.[60][47]
2.5 MOLECULAR WEIGHT OF ASPHALTENE AND RESIN PARTICLES
The physical and physico-chemical properties of asphaltenes are different from those of
neutral resins. The reported molecular weight of asphaltenes varies considerably depending upon
the method and conditions of measurement. These methods include ultracentrifuge, vapour
pressure Osmometry (VPO), electron microscope, solution viscometry, cryoscopic methods,
e.t.c. Reported molecular weight from ultracentrifuge and electron microscope studies are high.
To the contrary, those from solution viscometry and cryoscopic methods are low. The prevalent
method for determining asphaltene molecular weights has become vapour pressure 0smometry
30
(VPO). However, the value of the molecular weight from VPO must be weighed carefully, since
in general, the measured value of the molecular weight is a function of temperature, the solvent
molecular properties.
Asphaltene particles can assume various forms when mixed with other molecules
depending on the relative sizes and polarities of the particles present. The molecules of
asphaltene constituents span a wide range from a few hundred to several million leading to
speculation about self-association.[9][34][46]
Figure 2.5a: The molecular weight of this asphaltene is 7819 [45]
Asphaltene molecular weights are variable because of the tendency of the asphaltene constituents
to associate even in dilute solution in nonpolar solvents. However, data obtained using highly
polar solvents indicate that the molecular weights, in solvents that prevent association, usually
fall in the range 2000 ± 500.[9][55] It should be noted that although the results with asphaltene
constituents available from several crude oils suggest that molecular weight varies with the
dielectric constant of the solvent, there may be other factors which may in part also be
responsible for this phenomenon. The final phenomenon that influences the molecular weight of
31
n-C5 asphaltene
Polarity = N,S,O
Aromaticity =
n-C7 asphaltene
Mo
lecu
lar
wei
gh
t
Polarity and aromaticity
the asphaltene is the relative polarity of the solvent used in the precipitation technique. Figure
2.5b below.
Figure 2.5b: Long diagram shows that the asphaltenes include the crude oil
material highest in molecular weight, polarity and/or aromaticity.[13]
Both polarity and molecular weight of aspahltene constituents in a solvent define the
solubility boundaries and explains conceptually how asphaltene constituents are precipitated
from the mixture in crude oils that can be considered a type of continuum of molecular weight
and polarities.
Also, Auflem 2002 observed that the molecular weight, polarity and aromaticity of
precipitated asphaltene generally decrease with increasing carbon number of n-alkane
precipitant. He compared the wt % of Asphaltene precipitates of the n-C5, n-C7 and nC9 fractions
of crude oil.
32
Table 2.5a: Total nC5, nC7, nC9 asphaltene content of crude oil [75]
Paraffin solvent Wt % Asphaltene
n-pentane (C5) 1.0833 ± 0.0050
n- heptane (C7) 0.5167 ± 0.0059
n-nonane (C9) 0.3982
This is an additional confirmation that asphaltene precipitation decreases with increase in
carbon chain length of precipitating solvent.
The molecular weights of resin fractions in benzene are substantially lower than the
molecular weights of the corresponding asphaltenes in benzene. Compared to the molecular
weights of the asphaltenes, the molecular weight of the resins do not vary, except for the limits
of experimental error, with the nature of the solvent or the temperature of the determination
indicating that there is no association in non polar solvents such as benzene.
The molecular weights of resin fractions, as determined by various methods, are true
molecular weights and that forces that result in intermolecular association contribute very little,
if anything to their magnitude. [9]
One area of investigation that has shed some light on the behaviour of resins during
refining is the construction of molecular weight and polarity maps based on gel permeation
chromatographic data.[61]
33
2.6 INFLUENCE OF RESIN CONSTITUENTS ON ASPHALTENE CONSTITUENTS
The behaviour of asphaltene in petroleum has been complicated by another solubility
class called the resins [9] which have similar structure and chemistry like asphaltene.[42] There is
evidence that the structural aspects of the constituents of the resin fraction may differ very little
from those of the corresponding asphaltene fraction, the main difference being the proportion of
aromatic carbon within each fraction.[18][32][62] It has also been postulated that resin constituents
and asphaltene constituents are small fragments of kerogen [63] or atleast have the same origins as
the kerogen and therefore, a relationship might be anticipated. The analogy is to lock and key
mechanism in which the asphaltene constituent and resin constituents with similar structural
features form a bonding union.[9]][42] As mentioned earlier, resins are structurally very similar to
asphaltenes but have a higher hydrocarbon ratio and lower heteroatom content, polarity and
molar mass. Hence, the number of links they can form through hydrogen bonding, aromatic
stacking or acid – base interactions is lower than those formed by asphaltenes.[37] It has been
suggested that resins contributes to the enhanced solubility of asphaltenes in crude oil by
solvating the polar and aromatic portions of the asphaltenic molecules and aggregates. The
solubility of asphaltenes in crude oil is mediated largely by resin salvation and these resins play a
critical role in precipitation, and emulsion stabilization phenomena[64]
Asphaltenes may be dispersed in the crude oils by the action of resins. The polar resin
molecules may form micelles with asphaltene molecules as the nucleus. Figure 2.6
34
Figure 2.6: Schematic illustration of archipelago model of asphaltene monomers, asphaltene
aggregate in absence of resins, and asphaltenic aggregate in presence of resins.[64]
(a) In a resin poor environment micelles may form from multiple asphaltene molecules.
(b) As a result of these physico-chemical shifts the chemistry of asphaltenes is extremely
difficult to establish as it changes with the composition of the crude oil.[45] In addition
when resins and asphaltenes are present together, resin-asphaltene interactions appear to
be preferred over asphaltene – asphaltene interactions, resin – resins interactions appear
to be inconsequential in petroleum.
Numerous analytical techniques have been employed to work on asphaltene and oil
fraction of the crude oil, while only few studies to determine the role resins play in
asphaltene stability has only been briefly documented in the literature. For instance, Chang
and Fogler [65] studied the interactions between asphaltenes and resins. In their study, two
types of oil soluble polymers, dodecylphenolic resin and poly (octadecene maleic anhydride)
35
were synthesized and used to prevent asphaltenes from flocculating in heptanes media
through the acid-base interactions with asphaltenes. The results indicated that there polymers
could associate with asphaltenes to either inhibit or delay the growth of asphaltene
aggregates in alkane media. However, multiple polar groups on a polymer molecule make it
possible to associate with more than one asphaltene molecule, resulting in hetero –
coagulation between asphaltenes and polymers. It was found that the size of the asphaltene-
polymer aggregates was strongly affected by the polymer-to-asphaltene weight ratio. At low
polymer-to-asphaltene weight ratios, asphaltenes were found to flocculate among themselves
and with polymers until the flocs precipitated out of solution. On the other hand, at high
polymer-to-asphaltene weight ratios, small asphaltene polymer aggregates formed that
remained fairly stable in solution.
Moschopedia and Speight showed that dilute solutions (0.01 -0.5% w/w) of Athabasca
asphaltenes in a variety of non-polar organic solvents exhibit the free hydroxyl absorption
band (c. 3585cm-1) in the infrared. At higher concentration (> 1% w/w) this band becomes
less distinquishable, with concurrent onset of the hydrogen–bonded hydroxyl absorption (c.
3200 – 3450cm-1). Upon addition of a dilute solution (0.1 – 1%) of the corresponding resins
to the asphaltene solutions, the free hydroxyl absorption was reduced markedly or
disappeared, indicating the occurrence of intermolecular hydrogen bonding between the
asphaltenes and resins. Therefore, hydrogen bonding may be one of the mechanism by which
resin-asphaltene interactions are achieved. Also resin – asphaltene interactions appear to be
stronger than asphaltene – asphaltene interactions. Thus, in petroleums and bitumen’s it is
believed that asphaltenes exist not as agglomerations but as single entities–that are dispersed
by resins.[50]
36
In a recent work by Murgich et al (1999), the conformation of lowest energy of an
asphaltene molecule of the Athabasca sand oil was calculated through molecular mechanics.
Molecular aggregates formed from the asphaltene with nine resins from the same oil, in an n-
octane and toluene medium were studied. The resins showed higher affinities for the
asphaltene than toluene and n-octane and also exhibited a noticeable selectivity for some of
the external sites of the asphaltene. This showed that this selectivity depended on the
structural fit between the resins and the site of the asphaltene. The selectivity explains why
resins of one oil may not solubilize asphaltenes from other crudes.[66]
2.7 Causes of asphaltene problem, asphaltene self-association and micelle/colloid
concept
The mere presence of asphaltenes in crude oil does not portend asphaltene-related
production problems. [8] As mentioned earlier, what is important is the stability of those
asphaltene and stability depends not only on the properties of the asphaltene fraction, but on how
good a solvent the rest of the oil is for its asphaltenes. As recognized by de Boer et al (1995),
light oils with small amounts of asphaltenes are more likely to cause problems during production
than heavy oil with large amount of material in the asphaltene fraction. [8][9][13] The heavier oils
also contains plenty of intermediate components that are good asphaltene solvents whereas the
light oil may consist largely of paraffin materials in which, by definition, asphaltene have very
limited solubility. Asphaltenes in heavier oil can also cause problems if they are destabilized by
mixing with another crude oil during transportation or by other steps in oil processing.[13] The
problem appears to be that asphaltene self associate and form aggregates.[37]
37
Measurement of asphaltene molar mass was the first indication of asphaltene self –
association –[37] Leon et al performed surface tension and stability measurements to study the
self – association behaviour of two different association samples, one from a stable crude oil
(non-precipitation) and the other from an unstable crude oil were characterized by high
aromaticity. Low hydrogen content, and high condensation of the aromatic rings. Asphaltenes
from stable crude oils showed low aromaticity, high hydrogen content, and low condensation of
their aromatic rings. They showed that these structural and compositional characteristics of the
asphaltenes strongly influence their self-association behaviour. They found that asphaltenes from
unstable oil begin to aggregate at lower concentrations than asphaltenes from stable oils. Self
association appears to be related to a high content of condensed aromatics, which supports a П –
П bonding mechanism. However, the role of heteroatoms in asphaltene self – association was not
investigated by this group of researchers.[67]
As mentioned earlier, asphaltene self-associate and other constituents especially resins,
influence the association. The associated asphaltenes can be considered as micelles, colloidal
particles and / or macromolecules. [37]
An early hypothesis of the physical structure of petroleum indicated that asphaltenes are
the centre of micelles or colloids formed by association or possibly adsorption of part of the
maltenes (i.e., resins) onto the surfaces or into the interiors of the asphaltene aggregates.[68]
It is widely accepted that at low concentrations asphaltene appear as non associated
molecules (monomers), but with changes in temperature, pressure, or concentration, monomers
associate to form aggregates or micelles. At higher concentrations, asphaltenes aggregate and
38
form non dissolved larger particles that at a later stage agglomerate and precipitate, forming the
undesirable deposits.[17]
The term “micelle”, “colloid” and “aggregate” are often used interchangeably in the
literature. A micelle is an aggregate that remains constant in size and aggregation number for a
given set of environmental constraints. The concentration at which asphaltene molecules start to
aggregate is called the critical micelle concentration (CMC).
In the micellar view of asphaltenes, asphaltene-monomers form micelles above a CMC.
Researchers have focused on identifying a CMC with interfacial tension measurements[69][70]
However, Yarranton et al (2000) demonstrated that asphaltene self-association occurs in the
absence of any evidence of micelle formation.[71] Recent work by Alboundoware et al (2001)
suggested that apparent asphaltene CMC’s may result simply from a change in asphaltene molar
mass, without involving the micelle model. Hence, the micelle model is not supported by strong
experimental evidence.[72]
A better supported model of asphaltene structure is the colloidal model. According to the
colloidal view (Leontaritis and Mansoori, 1998), a crude oil is composed of asphaltene
molecules (colloids with their surface covered by resin molecules) suspended in the crude oil.
Figure 2.6 above. The adsorbed resins prevent aggregates and disperse the asphaltene. The
colloids can aggregate upon a change in the system temperature, pressure, concentration and
composition that causes resins to desorb from the asphaltenes. The colloidal view is consistent
with small–angle neutron scattering (SANS) and small–angle X-ray scattering (SAXS) evidence
of asphaltene aggregate in the nanometer size range. The colloidal model is the prevalent view of
asphaltenes in crude oils.[64][73]
39
According to this alternative school of thought, asphaltenes exist as free molecules in a
non-ideal solution (Hirschberg et al,). Hirschberg et al assumed that “pure” asphaltenes
aggregate by a linear “polymerization” process. The asphaltene monomer they considered
corresponded to asphaltene sheet defined by Yen. They proposed that in crude oil the
“polymerization” is blocked (reduced) by the association of asphaltenes with similar but less
polar hetero-components, the resins.[74]
The greatest difference between the polymer/macromoleculer view and micelle/colloidal
view of asphaltene is the fact that the latter considers asphaltene aggregates to be solid particles.
There is no convincing evidence to explain which if any of the views correctly describes the
nature of the asphaltenes.[37]
The different views of an asphaltene aggregate have led to two types of asphaltene
solubility models: the continous thermodynamic models and colloidal models [37]
(i) The continous thermodynamic models: this is based on the assumption that
asphaltene precipitation process is thermodynamically reversible. This may happen
since it is assumed that the asphaltene particles can be dispersed and stabilized in the
oil. The complete dissolution of asphaltenes in some organic solvents such as toluene
supports this assumption.
(ii) Thermodynamic colloidal model: this approach is based on the assumption that
asphaltenes are solid particles colloidally suspended in crude oil. Asphaltene
particles may undergo aggregation to form larger flocculation under Vander waals
attraction forces. This concept is based mainly on titration experiments,, which
demonstrate that once the adsorption equilibrium of resins between solid (asphaltene)
40
and liquid phases is disturbed by adding paraffin solvents, the asphaltene particles
flocculate irreversibly.[75]
(iii) Reversibility of asphaltene aggregation: Hirseberg et al assumed that aggregation was
reversible, but probably very slow, Joshi et al found the precipitation from a live
crude oil to be reversible in a matter of minutes, except for a subtle irreversibility
observed for the first depressurization of crude oil.
Hammani et al also found that the aggregation was generally reversible, but that the
kinetics of the reticulation varied significantly depending on the physical state of the system.
Peramary et al reported differences in the reversibility of solvent and temperature induced
aggregation.[75]
Finally, whether the asphaltene particles are dissolved in crude oil, in steric colloidal state
or in micellar form, depends to a large extent, on the presence of the other particles (parafins,
aromatics, resins e.t.c) in the crude oil.[34]
Various investigators, have established the existence of asphaltene micelles when an
excess of aromatic hydrocarbons is present in a crude oil as shown below
+ +
Figure 2.7a: formation of asphaltene micelles in the presence of excess amounts of aromatic
solvents.[34]
41
The figure above shows three forms of asphaltene micelle and this indicates the fact that
in the presence of excess amounts of aromatic hydrocarbon, asphaltene particles cannot
flocculate but self associate, and form micelle.[34]
In a petroleum fluid, due to excess amounts of paraffins in the solution, small asphaltene
particles can be dissolved while relatively large particles of asphaltene may flocculate out of the
solution and then form steric colloids. Flocculation of asphaltene in paraffinic crude oil are
known to be irreversible, because of their large size and their adsorption affinity to solid
surfaces.
Asphaltene and its flocculates are said to be surface active agents. However, if there is enough
resin in the solution so that they can cover the surface of the asphaltene particles by adsorption,
asphaltene steric colloids are formed. Figure 2.7c below.
Figure 2.7b : Asphaltene flocculation due to excess amount of
paraffins in the solution.[34]
42
Figure 2.7c: Steric – colloid formation of flocculated asphaltenes with resins.[34]
2.8 ECONOMIC EFFECT AND RELEVANCE / SIGNIFICANCE OF ASPHALTENE
PRECIPITATION
Heavy organic deposition during oil production and processing is a very serious problems
in many areas including Venezuela, the Persian Gulf, the Adriatic Sea and the Gulf of Mexico
and other areas throughout the world;[8][34] causing several undersea pipeline plugging with
substantial economic loss to the oil production operation.[76] In one example from eastern
Venezuala, severe asphaltene deposition problems caused a high volume production well to plug
within seven months of treatment.[77] Several cleaning methods has been attempted, including
physically scraping the wellbore and injecting xylene down the tubing. Each cleaning event cost
approximately US $50,000 and two days of shut-in production. After squeeze treatment (2.9)
with activator and inhibitor, the oil production rate increased and frequency of well cleaning
decreased to every eight months. The combination of increased production and less frequent
cleaning generated an annualized gain of 60,882 barrels (9,674m3), and a return on investment of
more than 3,000%.[8] Also in the prinos field in North Aegean Sea, there were wells that,
especially at the start of production, would completely cease flowing in a matter of few days
after an initial production rate of up to 3,000 BPD.[34] Heavy organic deposition in the North Sea
43
and in the Gulf of Mexico oil fields, in recent years have caused several under – sea pipeline
plugging with substantial economic loss to oil production, operation.[76]
The economic implications of this problems were tremendous considering the fact that a
problem well workover cost could get as high as a quarter of a million dollars.[32]
Although asphaltenes are a major concern in production operations, because of their role in
emulsion stabilization and fouling, this fraction of crude oil is also important [47] in the following
ways:
• The conversion of vacuum residues by processes such as coking, catalytic cracking and
hydrogenation.[32]
• Asphaltene in the form of distillation products from oil refineries are used as “tar – mats”
on roads.[42]
• Asphaltene materials – are used for water proofing and roofing.[42]
2.9 Prevention and remedies of asphaltene precipitation
Asphaltenes can deposit anywhere in the production system, but perhaps the most
damaging place is in the near – wellbore region where asphaltene – blocked pores are difficult to
access for remediation.[8]
Flocculation and deposition of asphaltenes can be controlled through better knowledge of
the mechanisms that cause its flocculation in the first place.[34] It can also be controlled using
various methods such as:
44
1. Production techniques
2. Chemical treating techniques.
1. Production techniques includes:
i. Reduction of shear
ii. Elimination of incompatible materials from asphaltic crude streams
iii. Minimization of pressure – drops in the production facility and
iv. Minimization of mixing of lean feed stock liquids into asphaltic crude streams
2. Chemical treating techniques
i. Solvents
ii. Dispersants/solvents
iii. Oil/dispersant/solvents
The dispersant/solvent approach is used for removing asphaltenes from formation
minerals. Continuous treating may be required to inhibit asphaltene deposition in the tubing.
Batch treatments are common for dehydration equipment and tank bottoms. There are also
asphaltenes precipitation inhibitors that can be used by continuous treatment or squeeze
treatments.[34][42] Conventional asphaltene flocculation inhibitor treatments involve either
periodic intervention with solvent soaks or continuous injection of chemicals into wellbore.
These methods are effective at presenting agglomeration and deposition of asphaltenes in
flowlines and tubular, but they do not protect the producing formation, because the chemicals
interact with the oil after it has left the formation, potentially leaving asphaltenes behind.
An improved method developed by Nalco Energy Services adds chemicals to the crude
oil while it is still in the formation.[78] The method entails squeezing as asphaltene deposition
inhibitor into the formation to stabilize the asphaltenes before flocculation occurs. However,
45
tests have shown that squeezing inhibitors alone does not, produce long-term benefits;
formations do not absorb inhibitors adequately, allowing inhibitors to be quickly released from
the formation as oil is produced. Pretreating the formation with an activator chemical enhances
absorbtion of the inhibitor into the formation without changing formation wettablity.
The general squeeze procedure includes cleaning out and flowing back the well, pumping
in activator, a spacer of crude oil, inhibitor, and then more crude oil, and shutting in the well for
12 to 24 hours before resuming production. [77]
The activator prepares the formation and reacts with the inhibitor to make a complex that
remains in place for a prolonged period as the well produces oil.[8]
Asphaltene – dispersants are substitutes for the natural resins and works much in the
same way as resins. That is, dispersants will keep the asphaltenes well dispersed (peptized) to
prevent their flocculation / aggregation. Dispersants will also clean up sludge in the fuel system
and they have the ability to adhere to surface of materials that are insoluble in the oil and convert
them into stable colloidal suspensions. [27]
Laboratory analysis of fluid samples indicated that asphaltene deposition could be
controlled only by continuous downhole injection of asphaltene dispersant. The appropriate
treatment program was designed and initiated with the desired results.
Once a successful treatment program was underway, additional laboratory work on
samples collected as part of a monitoring program helped the operator optimize dispersant
dosage. It was clear from surface – samples analysis that as dosage increased, the volume of
46
stable asphaltene dispersed in the crude increased. This indicated that fewer asphaltenes were
available to deposit in the well.
Asphaltene deposition Condition of crude
0 to 1% Crude strongly stabilized; dosage reduction
indicated
1 to 2% Crude well – stabilized; treatment adequate;
no dosage change indicated.
2 to 3.5% Crude not perfectly stabilized; small increase
in dosage indicated
> 3.5% Crude not stabilized; insufficient dosage
Table 2.9: Optimizing asphaltene – dispersant dosage in the Adriatic Sea. [8]
The volume of asphaltene deposition decreased as dispersant dosage increased.
However, over treatment with dispersant increases cost. Optimization requires a compromise that
allows a tolerable level that allowed deposition of only 1% to 2% of the asphaltene volume
enabled the wells to operate for several years without asphaltene deposition problems.[77]
A treatment level that optimized cost and sufficiently stabilized the asphaltene was shown
to provide a protection level that was 98% to 100% effective. Continuous treatment at this level
has enabled the wells to operate for several years without any plugging problems.[8]
Cleaning the pipeline of asphaltene required a technique that would be environmentally
acceptable, cost effective and successful in the complex pipeline geometry. [79]
47
CHAPTER THREE
MATERIALS AND METHOD (METHODOLOGY)
3.0 Sample Collection
In this present work, a total of three Nigerian crude oils were studied. The crude oils were
sourced from Bodo in Delta State, Bonny Export and Mogho (Port Harcourt) in Rivers State as
shown in the map in appendix 1.
3.1 Sample Treatment
The three crude oils were employed for precipitation of asphaltenes using pure n-heptane
solvent and n-pentane + n-heptane mixed solvent with respect to stirring time, in a solvent to oil
volume ratio of 40:1 and also for fractionation of maltenes. Detailed results of this work are
provided in chapter four.
3.2 Materials and reagents
All the analysis in this work was performed using high purity solvents and
chemicals that were of analytical reagent grade. For distillation of crude oil at
350°c an appropriately calibrated thermometer(3600 c), a heating mantle (that heats
more than360°c) with thermal regulator, cotton wool to lag exposed portion of
flask, a round bottom flask (250ml), antibumping chip (porcelane chips) to avoid
spilling of the crude, distillation chamber, water for cooling the distillation
chamber, analytical balance (weighing with an accuracy of 0.001g and of maximum
capacity 310g), reagent bottle (for storing crude oil before distillation and
atmospheric residuum after distillation), conical flask, a stopper.
48
For asphaltene precipitation and Fractionation of the maltenes, reagent grade solvents and
materials used were n-pentane (95% purity, sigma Aldrich laborchemical), n-heptane (99.5%
FSA Laboratory supplies meadow road, Lough – borough, LEII ORG, England), Toluene
(99.96% purity BDH laboratory supplies, chemical Ltd poole BH15 17D, England), methanol
(99% purity Fisher Chemicals), Silica gel (99.5% purity, BDH Laboratory supplies, chemical ltd
poole BH-1517D England). Dichloromethane (99% purity, BDH Laboratory supplies), Magnetic
Stirrer (constant temperature magnetic stirrer 78 HW - 1). Spatula, weighing balance (capable of
weighing with an accuracy of 0.001g and a maximum capacity of 310g), filter paper (Whatman
number 2 with pore size of 2µm), graduated cylinders, Centrifuge (model no. 80-2B with
maximum speed 4000rpm serviced and maintained by Finlab Nig. Limited), beakers, petridish,
oven (model-mini/50 Genlab Limited), 50ml standard laboratory burrette with a glass stopper.
For melting point analysis, the material and apparatus used were capillary tubes and the
melting point analyser (electrothermal melting point analyser, melts with a maximum capacity of
400-4500c). For UV/vis spectrophotometer the reagent grade solvent and apparatus used were
Toluene and UV spectrophotometer (Jenway England, model 6405 UV/vis spectrometer), and
printer. For Ir the apparatus used was FTIR Spectrophotometer.
49
Picture 3.1: Weighing balance (Ohaous; Model: Advanturers)
3.3 DISTILLATION OF EACH OF THE THREE CRUDES
The simple distillation process was conducted at the Department of Food Science and
Technology, Post - Graduate laboratory, University of Nigeria Nsukka. For each distillation
process that took place, the set up was first made.Then 200mls of the particular crude to be
distilled was poured into a 250ml round bottom flask containing porcelain chip and corked with
a stopper to prevent bubbling off of the crude. The heating mantle was then plugged to the source
of electricity and set at 3500c, with a thermometer inserted to the stopper. As the temperature
rises, the lighter fractions of the crude oil distilled off and was collected in the receiver (conical
flask with cotton wool to lag off exposed portion of the flask). At 350°C the lighter fractions of
the crude had been distilled off leaving a heavy organic rich residue known as the dead crude oil
(Atmospheric residuum). The whole system was allowed to cool, and the dead crude was stored
in the reagent bottle. The process was repeated until a reasonable quantity for each of the crude
oil was obtained. The results of this process are shown in chapter four.
50
3.4 PRECIPITATION OF ASPHALTENES, PURIFICATION OF ASPHALTENES
AND VARIOUS ANALYSIS CARRIED OUT ON THE PURE ASPHALTENES
PRECIPITATE.
3.4.1 PRECIPITATION OF ASPHALTENES
The precipitation of asphaltenes was conducted at the Energy Commission Research Centre,
University of Nigeria Nsukka. In this present work 40mls of n-heptane single solvent was mixed
with 1ml of each of the crudes also 40mls of n-pentane + n-heptane (mixed solvents in the ratio
20:20) was added to 1ml of each of the crudes. The mixture of dead oil (i.e. atmospheric
residium) and the n-heptane solvent and also the mixture of
the dead crude and the n-pentane + n-heptane mixed solvent
was agitated by using a magnetic stirrer for 20mins, 40mins,
60mins and 80mins respectively and allowed to equilibrate for
48hrs. The stirring time was varied with same quantity of
liquid precipitant to oil volume ratio for the n-heptanes
solvent and the n-pentane+n-heptane solvent in other to study
the stirring time effect on the asphaltene yield.
Picture 3.4: Magnetic Stirrer (Constant temperature magnetic stirrer 78 HW-1)
After 48hrs equilibration, the mixture was centrifuged for 30mins at 2000rpm using a
centrifuging apparatus. After this procedure the
supernatant (maltene) was decanted and kept
separately while the solid residue, which was
mainly composed of precipitated asphaltenes, was
kept rinsing with the liquid precipitant (about
40mls) until a clear solvent was observed.
51
Picture 3.5: Centrifuging apparatus (model no. 80-2B with maximum speed 4000rpm)
The precipitated asphaltenes were slowly dried in a vacuum oven at about 80°c (as shown
below) until no change in weight was observed.
Picture 3.6: Oven/incubator (model – mini/50 Genlab Limited)
These asphaltenes are refered to as C7 asphaltenes since n-heptane was used for the
precipitation and C5+C7 asphaltenes since C5+C7 mixed solvent system (i.e. in the ratio 20:20)
was used for the precipitation.
3.4.2 PURIFICATION OF EXTRACTED ASPHALTENES
The dried C7 and C5+C7 asphaltenes were purified to remove any non asphaltenic solids
(i.e clay, sand, some adsorbed hydrocarbons e.t.c.) that co-precipitated along with the
asphaltenes. To remove these solids, each of the asphaltenes were dissolved in 10mls of toluene
in which asphaltene is soluble, this mixture was filtered and to the filterate (composed mainly of
asphaltenes) 20mls of n-alkanes was added to reprecipitate asphaltenes. The fractions of the C7
and C5+C7 asphaltenes that did not desolve in toluene were discarded (i.e. non asphaltenic
52
solids). Finally, the reprecipitated asphaltenes were dried for 80mins in an oven, the dried
asphaltene from the oven was washed and dried until no change in weight was observed. The
melting point, ultraviolet and infrared analyses were carried out. The UV and IR spectroscopy
were used for final assessment of the precipitated asphaltenes as shown in subsequent sub topics
below.
The maltenes were further separated into saturates, aromatics and resins (by a process
termed SAR method) by first exposing the maltenes at room temperature to evaporate the n-
alkane that was used to precipitate asphaltene, the volume, weight and density of the maltenes
were obtained and the results are as shown in chapter 4.
Figure 3.4: below shows the flow chart of the separation of the atmospheric residuum from Bonny Export, Bodo and Mogho crudes.
Figure 3.4: Classification procedure for the various heavy crude oil fractions (350OC
boiling fraction)
This is refered to as NAMAL method for the separation of atmospheric residuum into
asphaltenes and maltenes.
Non aspaltenic solids
Atomospheric residuum
Extract with C5 and C7
C7: oil = 40:1 & C5 + C7: oil = 40:1
Malteness
Soluble Insoluble
Extract with pentane
Insoluble Soluble
Asphaltenes
53
3.5 FRACTIONATION OF MALTENES
The fractionation of maltenes was conducted at the department of Pure and Industrial
Chemistry. The maltenes obtained from the n-heptane single solvent (ie 80mins only for each of
the crudes) were fractionated into saturates, aromatics and resins.
The separation into these petroleum fractions was performed using chromatographic
method. This technique is described in detail below.
3.5.1 ACTIVATION OF THE SILICA GEL
Approximately 200g of silica (granulated) gel was spread evenly on a tray and dried in an
oven for 24hrs at a temperature of 105°C. Aproximately 40.34g of the dried silica gel was
packed in a 50ml standard laboratory burette and used to carry out the column chromatography
and 50mls of dichloromethane was added gradually in other to prepare the slurry and also to
wash off any trace of impurity in the silica gel. After this procedure, the silica gel was ready for
use in chromatography.
3.5.2 CHROMATOGRAPHY PROCEDURE
5ml of maltene sample was added to the top of the activated silica gel (granulated) in the
standard laboratory burette with the help of a funnel and allowed to percolate as shown below.
54
Picture 3.7: Fractionation setup (Column chromatography)
After the entire sample has entered the gel, 30mls of n-heptane was added to maintain a
liquid level well above the silica gel until saturates were washed off from the adsorbent.
Approximately 30mls of heptane effluent (i.e. n-heptane + saturates) was collected from the
column. After the collection, the flask was replaced with another flask for the collection of
aromatics.
Immediately after all the heptane effluent has eluted toluene in the amount of 200mls (for
aromatics from Mogho crude) and 150mls (for aromatics from Bodo Crude) and 130mls (for
aromatics from Bonny crude) was added to the column through a separatory funnel. The column
was allowed to drain and approximately 200mls, 150mls and 130mls of toluene effluent was
collected for Mogho aromatics, Bonny export aromatics and Bodo aromatics respectively. At this
point, resins have adsorbed on the gel.
To recover the resins, a solvent mixture of dichloromethane and methanol (in the ratio
50:50) in the amount of 100ml was charged slowly to the top of the gel column. At this point
approximately 100ml of dichloromethane + methanol effluent (r
After each effluent has been collected for a particular crude, the
replaced with a fresh activated s
three crudes studied.
Figure 3.5: below shows the flow chart of the separation
and resins
This is referred to as SAR methodthree crude oil studied.
Figure 3.5: Flow chart of the separation scheme
3.5.3 EXTRACTION OF EACH OF THE SATURATES, AROMATICS AND RESINS
(MALTENE) FROM THEIR VARIOUS EFFLUENTS
The drying of the various affluents were c
of Nigeria Nsukka. The n-heptane effluent
romethane + methanol effluent (resin + solvent) was collected.
collected for a particular crude, the silica gel was removed and
th a fresh activated silica gel. This procedure was carried out for the maltenes in
: below shows the flow chart of the separation of maltenes into saturates,
R method for the recovery of the components of the maltenes in the
Flow chart of the separation scheme
EXTRACTION OF EACH OF THE SATURATES, AROMATICS AND RESINS
(MALTENE) FROM THEIR VARIOUS EFFLUENTS
us affluents were conducted at the department of Biochemistry University
heptane effluent (saturates + n heptane) was evaporated at room
55
esin + solvent) was collected.
ilica gel was removed and
the maltenes in the
saturates, aromatics
mponents of the maltenes in the
EXTRACTION OF EACH OF THE SATURATES, AROMATICS AND RESINS
epartment of Biochemistry University
was evaporated at room
56
temperature, while the dichloromethane + methanol effluent (resin + dichloromethane +
methanol) and the tolune effluents (aromatic + toluene)were evaporated at 65°c in a water bath
as shown below. After solvent evaporation each fraction was weighed until no change in
weighed was observed.
.
Picture 3.8: Water bath (Model DK) with resin + dichloromethane + methanol effluent during
evaporation of Bonny Export crude
3.6 PHYSICAL METHODS FOR ANALYSING THE ASPHALTENE FRACTION
3.6.1 INFRARED SPECTRA ANALYSIS: The FTIR analysis was conducted at the National
Research Institute for Chemical Technology (NARICT), Federal Institute for Science and
Technology, Zaria. The infrared spectra analysis of asphaltenes (from 80mins stirring time) were
obtained by carrying out the analysis without interacting the asphalting with any solvent (termed
neat). The procedure was carried out using an FTIR Spectrophotometer. Specify the model of the
Spec.
3.6.2 THE ULTRAVIOLET VISIBLE SPECTRA ANALYSIS: This analysis was conducted
at the department of Pure and Industrial Chemistry. The ultraviolet visible Spectra analysis of the
57
precipitated asphaltene fractions were recorded on a Jenway England, model 6405 UV/Vis as
shown in picture 3.9 below.
3.6.3 UV – SPECTROSCOPIC PROCEDURE
0.01g of each of the precipitates from Bonny Export, Bodo and Mogho crude (ie 80mins
only for both n-heptane and n-pentane+n-heptane mixed solvent ) was dissolved in 3mls of
toluene and poured into a cuvet then placed in the sample compartment of the UV/vis
spectrophotometer as shown below. The sample was then scanned in the UV region. Details of
this report is shown in chapter 4.
Picture 3.9: UV Visible spectrophotometer (Jenway England, model 6405 UV/vis spectrometer)
3.6.4 MELTING POINT ANALYSIS: This analysis was carried out in Pharma-chem
laboratory (U.N.N). It was done by putting a pinch of the asphaltene precipitate in a capillary
tube and dropped in one of the three compartments in the melting point analyser (electrothermal
melting point analyser, which heats up to the range of 350-450°C) as shown in picture 3.10
below
58
Picture 3.10: Melting point analyser (Electrothermal melting point analyser) Cat no.: 1A6304,
For all these analysis, the samples decomposed between the range of 350-410OC to a darker
material (carbonaceous material).
EXPERIMENTAL PROCEDURE TO DETERMINE THE ROLE OF RESINS IN
STABILISING (SOLUBILISING) ASPHALTENES IN CRUDE OIL USING n-HEPTANE
SINGLE SOLVENT ONLY.
To 1ml of each of Bonny Export, Bodo and Mogho crudes (atmospheric residium) 40mls
of n- heptane was added and to this mixture, the same quantity of resins extracted from the
fractionation of n-heptane maltenes (that was obtained from 80mins asphaltenes
precipitation)from Bonny Export, Bodo, and Mogho crudes respectively were added to the same
crude from which they were extracted and stirred with a magnetic stirrer for 80minutes and the
mixtures (resins+1ml of crudes + 40mls of n-heptane) were allowed to age (ie equilibrate) for 2
days (48hours).
After 48hours equilibration (aging) the mixture was Centrifuged for 30minutes at
2000rpm using a Centrifuging apparatus (model no: 80 – 2B). after this procedure the
Supernatant (maltenes) was decanted and kept seperately while the solid residue composed
59
mainly of asphaltenes was kept rinsing with the liquid precipitant (about 40mls) until a clear
solvent was observed. The precipitated asphaltenes were slowly dried in a vacuum
oven/incubator (model; mini/50) at about 80°C until no change in weight was observed .Details
of this result is as shown in chapter 4.
PURIFICATION OF PRECIPITATED C7 – ASPHALTENES WHEN RESINS
WAS ADDED TO THE CRUDE OIL: The dried C7 – asphaltenes were purified to remove any
non asphaltic materia that co-precipitated along with the asphaltenes. To remove this solids the
asphaltenes were dissolved in 10ml of toluene and filtered to remove any solid particles, the
fraction of the C7 – asphaltenes that did not desolve in toluene (non aspaltenic) was discarded.
To the soluble part (composed of asphaltenes) 20ml of n-heptane was added, and then dried in a
vacuum oven at 80°C until no change in weight was observed. Detailed result of this experiment
is shown in chapter 4.
60
CHAPTER FOUR
4.0: RESULTS AND DISCUSSIONS
Asphaltenes has been precipitated from Bonny, Bodo and Mogho (Porth Harcourt) crudes
using n-heptane and n-pentane+n-heptane mixed solvent at various reaction time (20mins,
40mins, 60mins and 80mins). The results of the distillation and composition of the asphaltenes
and maltenes in each of the three different crudes and the role resins play in solubilising
asphaltenes in crude oils are shown in table 4.1, 4.2a, 4.2b.
4.1 RESULTS OF THE PHYSICAL PROPERTIES OF BONNY EXPORT, BODO
AND MOGHO CRUDE OILS BEFORE AND AFTER DISTILLATION AT 350O
C
Table 4.1: PHYSICAL PROPERTIES OF BONNY EXPORT, BODO AND MOGHO
CRUDE OILS BEFORE AND AFTER DISTILLATION
Source of the crude oils Bonny Export Bodo Mogho
Weight of crude used (g) 528.5 632.7 415.8
Weight of atmospheric residuum (g)
182.02 211.7 126.17
Volume of crude (ml) 675 750 500
Volume of atmospheric residuum (ml)
224 250 140
Density of crude (g/ml) 0.78 0.84 0.83
Density of atmospheric residuum (g/ml)
0.81 0.85 0.90
API gravity of crude 49.91 o 36.95 o 38.89 o
API gravity of atmospheric residuum
45.3 o 34.97 o 25.72 o
61
COMMENTS
As accepted generally, there are various types of crudes, the extra heavy crude oil, the heavy
crude oil, the medium crude oil, the light crude oil and the very light crude oil.
� Extra heavy crude oil is any liquid petroleum with an API gravity less than 10°API.
� Heavy crude oil is defined as any liquid petroleum with an API gravity less than 20°API.
� Medium crude oil is any liquid petroleum with an API gravity between 22 - 33° API.
� Light crude oil is any liquid petroleum with an API gravity between 34 - 39°API.
� Very light crude oil is defined as any liquid petroleum with an API gravity above
40°API.
This shows that from the results obtained for API gravity in table 4.1 above Bonny Export is
a very light crude i.e. with an API gravity of 49.91°, Bodo crude is a light crude because its API
gravity is 36.95°API also Mogho crude is a light crude because its API gravity is 38.98° API.
However, after distillation when all the lighter fractions of the various crudes has been
removed, Bonny Export (atmospheric residuum) still behaved like a very light crude but its
density became slightly higher than normal. Bodo (atmospheric residuum) behaved like a light
crude with a slightly raised density compared to its original density but in the case of Mogho
crude though a light crude but after distillation it behaved more like a medium crude and its
density increased greatly compared to its original density. This shows that the heavy organics in
Mogho crude oil will be more compared to that in Bonny Export and Bodo crudes, indicating the
presence of a very high paraffinic material which light crude oils are known for meaning that
Mogho crude may probably have the highest asphaltene content compared to Bodo and Bonny
Export crude, because asphaltene have very limited solubility in paraffinic materials
62
It is a well known fact that density measurement is the simplest way to estimate the
cohesive forces and, therefore, the interaction energies of a particular material. The density is
also a measurement of the molecular parking of the solid, and in the case of aromatic
compounds, this parking strongly depends on the structural molecular topology of the molecules.
This indicates that Mogho crude and Bodo crude with higher densities are likely to have higher
aromaticity, therefore higher asphaltene precipitates and more complex structures than Bonny
Export crude.[80]
4.2: RESULTS FROM ASPHALTENE PRECIPITATION
Detailed result of the compositions of asphaltene and the physical properties of the
maltenes from each of the three crude oils are as shown in the tables below.
Table 4.2a: Composition of Asphaltenes in Bonny Export crude for both n-heptane single
solvent and n-pentane + n-heptane mixed solvent.
Stirring Time
(solvent+ crude)
Solvent Weight of
asphaltenes after
drying (g)
% weight of
asphaltenes (%)
20mins n-heptane 0.001 0.69
40mins n-heptane 0.006 1.33
60mins n-heptane 0.007 1.67
80mins n-heptane 0.009 2.14
20mins n-pentane + n-heptane 0.003 0.88
40mins n-pentane + n-heptane 0.007 1.60
60mins n-pentane + n-heptane 0.008 2.05
80mins n-pentane + n-heptane 0.010 2.90
Table 4.2(a): Shows clearly that the weight / weight 0/0 of asphaltenes increased with increase in stirring time for both single n-heptane solvent and the mixed n-pentane + n-heptane solvents. This is also shown in figure 4.2a and b.
63
FILTRATE (MALTENES) FROM BONNY EXPORT CRUDE AS SHOWN BELOW:
Table 4.2b: Physical Properties of maltenes (filtrate) from Bonny Export crude
Stirring Time
(solvent+ crude)
Solvent Weight of
maltenes
Volume of
maltenes
Density of
maltenes (g/ml)
20mins n-heptane 5.962 9.00 0.662
40mins n-heptane 6.559 9.40 0.698
60mins n-heptane 6.706 9.60 0.699
80mins n-heptane 7.248 10.2 0.711
20mins n-pentane + n-heptane 4.564 7.60 0.6005
40mins n-pentane + n-heptane 4.907 7.20 0.6815
60mins n-pentane + n-heptane 5.066 7.20 0.7036
80mins n-pentane + n-heptane 3.917 5.40 0.7254
Table 4.2 (b): Shows that the densities of the maltenes from Bonny Export crude increased with
increase in asphaltene yield.
Fig. 4.2a(i): % weight of asphaltens for bonny Export Crude (n
Fig. 4.2a(ii): % weight of asphaltenes from Bonny Export Crude (n
solvent system) versus time
0
0.69
0
0.5
1
1.5
2
2.5
3
3.5
0 20mins 40mins
0
0.88
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 20mins 40mins
weight of asphaltens for bonny Export Crude (n-heptane solvent) with time
% weight of asphaltenes from Bonny Export Crude (n-pentane + n
1.33
2.08
3.2
40mins 60mins 80mins
% weight of asphaltene vs
time
1.71
2.9
3.85
40mins 60mins 80mins
% weight of asphaltenes vs
time
64
heptane solvent) with time
pentane + n-heptane
% weight of asphaltene vs
% weight of asphaltenes vs
65
Table 4.3a: Composition of the asphaltenes from Bodo Crude for both n-heptane single
solvent and n-pentane + n-heptane mixed solvent.
Stirring Time
(solvent+ crude)
Solvent weight of
asphaltene
after drying (g)
% weight of
asphaltene
(0/0)
20mins n-heptane 0.012 5.850
40mins n-heptane 0.013 6.191
60mins n-heptane 0.040 7.390
80mins n-heptane 0.039 6.500
20mins n-pentane + n-heptane 0.014 6.830
40mins n-pentane + n-heptane 0.030 7.850
60mins n-pentane + n-heptane 0.043 8.600
80mins n-pentane + n-heptane 0.041 7.523
Table 4.3 (a) : shows that the weight / weight 0/0 of the asphaltenes increased from 20mins to 60
mins but decreased slightly at 80mins stirring time for both the single n-heptane solvent and
mixed n-pentane + n-heptane solvent system. This is also shown in Figure 4.3 a and b.
66
FILTRATE (MALTENES) FROM BODO CRUDE AS SHOWN BELOW:
Table 4.3b: Physical Properties of maltenes (Filtrate) from Bodo Crude for both n-heptane
single solvent and n-pentane + n-heptane mixed solvent.
Stirring Time
(solvent+ crude)
Solvent Weight of
maltenes
Volume of
maltenes
Density of
maltenes (g/ml)
20mins n-heptane 0.838 6.800 0.120
40mins n-heptane 0.837 5.800 0.144
60mins n-heptane 0.811 4.840 0.169
80mins n-heptane 0.820 7.900 0.104
20mins n-pentane + n-heptane 0.836 8.400 0.100
40mins n-pentane + n-heptane 0.818 7.200 0.114
60mins n-pentane + n-heptane 0.820 3.600 0.228
80mins n-pentane + n-hepta ne 0.817 5.000 0.163
Table 4.3(b), shows clearly that the densities of the maltenes from Bodo crude increased
with its resulting asphaltenes (Table 4.3a).
Fig. 4.3a(i) % weight of asphaltenes from Bodo Crudes (n
Fig. 4.3a(ii) % weight of asphaltenes from Bodo Crudes (n
solvent)
0
5.8546.191
0
1
2
3
4
5
6
7
8
0mins 20mins 40mins
0
6.829
7.850
0
1
2
3
4
5
6
7
8
9
10
0mins 20mins 40mins
% weight of asphaltenes from Bodo Crudes (n-heptane single solvent)
% weight of asphaltenes from Bodo Crudes (n-pentane + n
6.191
7.390
6.500
60mins 80mins
% weight of
asphaltene vs time
7.850
8.600
7.520
60mins 80mins
% weight of
asphaltene vs time
67
heptane single solvent)
pentane + n-heptane mixed
68
Table 4.4a: Composition of the asphaltenes in Mogho crude for both n-heptane single
solvent and n-pentane + n-heptane mixed solvent.
Stirring Time Solvent Weight of
asphaltene after
drying (g)
% weight of
asphaltene
20mins n-heptane 0.029 10.623
40mins n-heptane 0.027 10.189
60mins n-heptane 0.018 6.590
80mins n-heptane 0.024 9.877
20mins n-pentane + n-heptane 0.036 11.688
40mins n-pentane + n-heptane 0.029 10.546
60mins n-pentane + n-heptane 0.024 6.838
80mins n-pentane + n-heptane 0.025 10.081
Table 4.4(a), shows clearly that the weight / weight 0/0 of the asphaltenes decreased from
20mins to 60mins but increased slightly with 80mins stirring time giving a precipitate slightly
higher than the precipitate obtained from 60mins stirring time for the n-heptane single solvent
and the n-pentane + n-heptane mixed solvent. This is also shown in Figure 4.4 a and b.
69
FILTRATE (MALTENES) FROM MOGHO CRUDE AS SHOWN BELOW:
Table 4.4b: physical properties of maltenes from Mogho crude for both n-heptane single
solvent and n-pentane + n-heptane mixed solvent.
Stirring Time Solvent Weight of
maltenes
Volume of
maltenes
Density of
maltenes (g/ml)
20mins n-heptane 0.871 10.20 0.085
40mins n-heptane 0.873 10.60 0.082
60mins n-heptane 0.876 12.00 0.073
80mins n-heptane 0.882 11.20 0.0788
20mins n-pentane + n-heptane 0.864 4.80 0.180
40mins n-pentane + n-heptane 0.876 5.00 0.175
60mins n-pentane + n-heptane 0.871 6.00 0.145
80mins n-pentane + n-heptane 0.875 6.20 0.14
Table 4.4b, shows clearly that the densities of the maltenes increased along side with
their corresponding asphaltenes, but decreased at 60mins stirring time for n-heptane single
solvent and also decreased at 80mins stirring time for n-pentane + n-heptane mixed solvent.
Fig. 4.4a(i) % weight of asphaltenes from Mogho Crude (n
Fig. 4.4(ii) % weight of asphaltenes from Mogho Crude
vs time
00
2
4
6
8
10
12
0mins 20mins
00
2
4
6
8
10
12
14
0mins 20mins
% weight of asphaltenes from Mogho Crude (n-heptane single solvent) vs time
% weight of asphaltenes from Mogho Crude (n-heptane + n-pentane mixed solvent)
10.62310.189
6.59
9.877
20mins 40mins 60mins 80mins
% weight of
asphaltenes vs time
11.688
10.546
6.838
10.081
20mins 40mins 60mins 80mins
% weight of
asphaltenes vs time
70
heptane single solvent) vs time
pentane mixed solvent)
asphaltenes vs time
asphaltenes vs time
71
4.3 COMPARISM OF THE WEIGHT OF THE PRECIPITATED ASPHALTENE
WITH STIRRING TIME USING N-HEPTANE SINGLE SOLVENT AND N-
PENTANE + N-HEPTANE MIXED SOLVENT.
It is generally accepted that asphaltene precipitation depends mainly on the stability of
the asphaltenes and stability depends not only on the properties of the asphaltene fraction but on
how good a solvent the rest of the oil is for its asphaltenes.
In comparism of the weight of the asphaltene precipitated using n– heptane single solvent
and n–pentane + n-heptane mixed solvent with respect to stirring time for Bonny Export, Bodo
and Mogho crudes:
Table 4.2 (a-b), table 4.3 (a-b), and table 4.4 (a-b) shows the percentage weight of
asphaltenes precipitated from Bonny Export, Bodo and Mogho crudes and their resulting
maltenes using n-heptane single solvent and n-pentane + n-heptane mixed solvent for 20, 40, 60
and 80 minutes stirring time for each of the crudes.
Table 4.2 (a-b) from Bonny Export crude shows that the weight of asphaltenes precipitate
increased with increase in stirring time, for both the C7 – asphaltene and the C5 + C7 –
asphaltenes (Figure 4.2 a - b), also the densities of their maltenes increased with increase in
stirring time.
In the case of Bodo crude (Table 4.3 a-b) and Mogho crude (Table 4.4 a-b), their
asphaltene precipitate do not follow the same trend as in Bonny Export crude (Figure 4.3 a-b and
Figure 4.4 a-b), but the densities of their maltenes increased alonge with their corresponding
asphaltene precipitate. According to these results, it is possible to suppose that asphaltene
precipitation depends on stirring time but due to the presence of other solubility fractions (i.e. the
saturates, aromatics and resins) which may not be present in the right ratios, Bodo and Mogho
crudes did not depend on stirring time. It may also be because the other solubility fractions
as saturates, aromatics and resins)
asphaltenes, therefore making their asphaltenes unstable and so prec
were more and did not depend on stirring time.
It was also noticed that Mogho crude (though a light crude) precipitated more asphaltenes
followed by Bodo crude and then Bonny Export crude for both single and mixed solvent system
(Figure 4.5 and 4.6 below). This indicates that the amount and characteristics of the asphaltene
constituents in crude oil depends to a greater
MIXED GRAPH OF ASPHALTENE PRECIPITATE FROM BONNY
AND MOGHO CRUDES USING N
TO TIME.
Figure 4.5: Effect of n-heptane single solvent with
and Mogho Crudes
0
2
4
6
8
10
12
20mins 40mins
0.691.33
5.856.191
10.62310.189
not depend on stirring time. It may also be because the other solubility fractions
as saturates, aromatics and resins) in Bodo and Mogho crude oils are not good solvents for their
asphaltenes, therefore making their asphaltenes unstable and so precipitation in these crudes
not depend on stirring time.
Mogho crude (though a light crude) precipitated more asphaltenes
followed by Bodo crude and then Bonny Export crude for both single and mixed solvent system
. This indicates that the amount and characteristics of the asphaltene
l depends to a greater extent on the source of the crude.[9]
HALTENE PRECIPITATE FROM BONNY EXPORT, BODO
CRUDES USING N-HEPTANE SINGLE SOLVENT WITH RESPECT
heptane single solvent with stirring time on Bonny
Crudes
40mins 60mins 80mins
2.08
3.2
6.191
7.390
6.5
10.189
6.59
9.877
% weight of asphaltenes
for Bonny Export crude
using single solvent
% weight of asphaltenes
for Bodo crude using
single solvent
% weight of asphaltenes
for Mogho crude using
single solvent
72
not depend on stirring time. It may also be because the other solubility fractions (such
not good solvents for their
ipitation in these crudes
Mogho crude (though a light crude) precipitated more asphaltenes
followed by Bodo crude and then Bonny Export crude for both single and mixed solvent system
. This indicates that the amount and characteristics of the asphaltene
[9]
EXPORT, BODO
SOLVENT WITH RESPECT
Bonny Export, Bodo
% weight of asphaltenes
for Bonny Export crude
% weight of asphaltenes
for Bodo crude using
% weight of asphaltenes
for Mogho crude using
MIXED GRAPH OF ASPHALTENE PRECIPITATE FROM BONNY
AND MOGHO CRUDES USING N
WITH RESPECT TO STIRRING
Figure 4.6: Effect of n-heptane
Bodo and Mogho Crudes
COMMENT
For both Bonny Export, Bodo and Mogho crudes as shown in
mixed solvent precipitant (n-pentane + n
solvent (n-heptane) precipitant. This is due to the addition of n
made up the mixed solvent system as
asphaltene precipitation increases with decrease in the carbon chain
solvent. [75] This increase in asphaltene yield for precipitation using mixed solvent system is also
indicative of the fact that for a given crude oil sample, the yield and properties of the precipitated
20mins
0.88
6.82911.688
% weight of asphaltenes for Bonny Export Crude using mixed solvent
% weight of asphaltenes for Bodo Crude using mixed solvent
% weight of asphaltenes for Mogho Crude using mixed solvent
ALTENE PRECIPITATE FROM BONNY EXPORT, BODO
USING N-PENTANE + N-HEPTANE MIXED SOLVENTS
STIRRING TIME.
heptane + n-pentane mixed solvent precipitant on
Bodo and Mogho Crudes
, Bodo and Mogho crudes as shown in figures 4.5 and 4.6 above, the
pentane + n-heptane) precipitated more asphaltenes than single
This is due to the addition of n – pentane to n
made up the mixed solvent system as in agreement with the generally accepted fact that
asphaltene precipitation increases with decrease in the carbon chain – length of the precipitating
This increase in asphaltene yield for precipitation using mixed solvent system is also
cative of the fact that for a given crude oil sample, the yield and properties of the precipitated
40mins 60mins 80mins
1.71
2.93.85
7.8508.600
7.52310.546
6.838
10.081
% weight of asphaltenes for Bonny Export Crude using mixed solvent
% weight of asphaltenes for Bodo Crude using mixed solvent
% weight of asphaltenes for Mogho Crude using mixed solvent
73
EXPORT, BODO
MIXED SOLVENTS
on Bonny Export,
figures 4.5 and 4.6 above, the
heptane) precipitated more asphaltenes than single
pentane to n – heptane which
in agreement with the generally accepted fact that
length of the precipitating
This increase in asphaltene yield for precipitation using mixed solvent system is also
cative of the fact that for a given crude oil sample, the yield and properties of the precipitated
74
asphaltenes strongly depend on the specific precipitation method and precipitant used. This
means that a single oil could have two or more results depending on the precipitant used.[8]
4.4 SUMMARY OF THE RESULT OF FTIR SPECTROPHOTOMETRIC
ANALYSIS
Table 4.5a: RESULT OF IR ANALYSIS OF ASPHALTENES OBTAINED USING
SINGLE N-HEPTANE SOLVENT
Samples (A)
Asphaltenes Precipitation
using Single Solvent (n-
heptane)
Approximate
characteristic
frequencies (cm-1
)
Bonds
Bonny Export Crude
733.94
1264.38
3056.31
Substituted aromatic hydrocarbon.
C – H bending.
C – H of aromatics.
Mogho (Port Harcourt) Crude
734.90
1265.35
1441.84
2930.9
3080.
Substituted aromatic hydrocarbon.
C – H bending.
C – H bending.
Cyclic aliphatic hydrocarbon.
C-H of aromatics.
Bodo Crude
734.9
971.19
1271.13
1373.36
1456.30
1601.93
1718.63
2933.83
3060
Substituted aromatics hydrocarbon
C = C – H bending out of plane.
C–H bending.
C-H bending.
C – H bending.
C = C of aromatic
C = O (acid, aldehydes, ketones and esters
Cyclic aliphatic hydrocarbon. C-H of aromatics.
75
TABLE 4.5b: RESULTS OF IR ANALYSIS OF ASPHALTENES OBTAINED USING N-
PENTANE + N-HEPTANE MIXED SOLVENT SYSTEM.
Samples B
Asphaltenes Precipitated
using mixed Solvent (n-
pentane+n-heptane)
characteristic
frequencies (cm-1
)
Bonds
Bonny Export Crude at
733.94
1264.38
2932.86
Substituted aromatic hydrocarbon
C – H bending
Cyclic aliphatic hydrocarbon.
Mogho (Port Harcourt) Crude
736.83
1266.31
1450.52
2931.9
Substituted aromatic hydrocarbon.
C – H bending.
C – H bending.
Cyclic aliphatic hydrocarbon.
Bodo Crude 734.90
1276.92
1459.2
1726.35
2929.97
Substituted aromatic hydrocarbon.
C – H bending.
C – H bending.
C = O (acid, aldehydes, ketones and esters
Cyclic aliphatic hydrocarbon.
IR INTERPRETATION
Data from IR as shown in figure I-VI in the appendice is summarized in table 4.5a and b,
obtained from Bonny Export, Bodo and Mogho crudes shows characteristic frequencies at
3056.31,3060,3080 that are due to C-H stretch for aromatic hydrocarbon. This is supported by
the absorptions at 733.94, 734.90, 736.83 that are due to substituted aromatic hydrocarbon. This
confirms the same class of crude oil composition, this class of crude oil composition consist of
the unsaturated part of asphaltenes, that is that part of asphaltenes that consist of fused benzene
rings. However, absorption frequencies at 2933.83, 2930.93, 2932.86, 2929.97 and 2931.9 are
76
due to cyclic aliphatic hydrocarbon. This is supported by the absorptions at 1264.34, 1271.17,
1265.35, 1276.92, 1266.31 that are due to C-H bending. These suggest the same class of crude
oil composition. These classes of crude oil consist of the saturated part of asphaltenes structure.
The IR reveals that asphaltenes fraction of crude oil is made up of both saturated and unsaturated
part as supported by our UV spectra on the asphaltene precipitates.
4.5 RESULTS OF UV/VISIBLE SPECTROPHOTOMETRIC ANALYSIS.
Table 4.6: UV Spectra of the Asphaltene Fractions of Crude Oil.
Samples UV Spectra Data
Asphaltenes precipitated using single solvent
(n-heptane) for 80 minutes
λ (nm) A λ (nm) A
Bonny Export Crude (C7 asphaltenes) 389.8 1.935 418.2 1.366
Bodo Crudes (C7 asphaltenes) 388.9 2.389 509.6 2.906
Mogho Crude (C7 asphaltenes) 389.8 2.303 510.0 2.888
Asphaltenes precipitated using mixed solvent
(n-pentane+n-heptane) for 80 minutes
Bonny Export Crude (C5 + C7 asphaltenes) 388 2.149 449.4 2.389
Bodo Crudes (C5 + C7 asphaltenes) 387.2 2.833 482.6 2.791
Mogho Crude (C5 + C7 asphaltenes) 388.6 2.977 432.8 2.193
UV/VISIBLE INTERPRETATION
Table 4.6 shows the summary of the UV-visible spectra data of asphaltene fractions from
Bonny Export, Bodo and Mogho crudes using n-heptane single solvent and n-pentane + n-
heptane mixed solvent system for 80mins stirring time as shown in figure vii - xii (Appendix 14
– 19). Each of the asphaltene fractions shows absortion maxima in the visible region of the
77
electromagnetic spectrum, indicating that the C7 and C5 + C7 asphaltenes are largely unsaturated
as supported by the asphaltene structure in figures 2.3a, 2.3b, 2.4a and 2.4b.
Similar absoptions at the following wavelengths: 389.8, 388.9, 387.2 and 388.6nm which
are supported by absorptions at 418.2, 509.6, 510.0, 449.4, 482.6 and 432.8nm suggest the same
class(es) of crude oil composition which is the presence of fused benzene rings or polynuclear
aromatics in asphaltenes which indicate unsaturated and highly conjugated systems. These are
similar to the absorptions found in the literature. The range of the absorption bands for both the
C7 and C5 + C7 asphaltenes are about 400 – 500nm which corresponds to benzenoide band for
highly polynuclear aromatics. This is in agreement with the asphaltene structure. In addition the
uv visible absorption bands are similar to those shown else where (Evdokimov and Losev).[81]
This range (400-500) of absorption band for all the asphaltene precipitates obtained from
Bonny Export, Bodo, and Mogho crudes, which corresponds to the benzenoid bands for
polynuclear aromatics, implies the existence of chromophores in the asphaltenes. These
asphaltenes as a consequence are coloured the chromophores very likely available in these
asphaltenes are: conjugated double bonds involving aromatic hydrocarbons as supported by the
infrared spectra on the asphaltenes from Bonny Export,Bodo and Mogho crudes.
From molecular orbital theory, the allowed possible transitions are: σ →σ*, n→σ*,
П→П*, and n→П* where n= non bonding, σ = sigma, П = pie and those with asterisk are anti-
bonding. The wavelength absorption range is consistent with fundamental molecular orbital
theoretical assumption or specification. This assumptions is that the energy difference ∆E =
HOMO – LUMO is small, and also the longer the wavelength of absorption, the smaller the
energy of irradiation. Thus, exposure of these compounds with small ∆E values and long
78
wavelengths of absorptions to high irradiation energies will destroy these compounds. Hence,
under these conditions, they can decompose.
Our UV and IR spectra are consistent and reveal the presence of some Island and
Archipelago architectures (Sabbah et al, 2011)[82]: 2,3,7,8,12,13,17,18 – octaethyl - 21H, 23H –
porphine; 5,10,15,20 – Tetra – p- tolyl – 21H, 23H-porphine; 5,10,15,20 – Tetrakis (4-
methoxyphenyl) -21H, 23H – porphines; 5,10,15,20 – Tetrakis [4 – (allyloxy) phenyl] – 21H,
23H – porphine; phenanthrene; 1,3,6,8 – tetradecyl pyrene; 2,7 –Bis (2-pyren-1-yl-ethyl) -9, 9 –
diethyl – 9H – fluorene; 1,4 –Bis (2-pyren-1-yl-ethyl) – benzene; 1,4 –dipyren – 1 yl- butane.
4.6 RESULT OF THE CHEMICAL AND PHYSICAL PROPERTIES OF CRUDE OILS
OBTAINED FROM N-HEPTANCE MALTENES
Table 4.7: Chemical and Physical Properties of Crude oils as obtained from
n-heptane maltenes ( 80minutes).
Source
of crude
API
gravity
of crude
Density of
atmospheric
residuum
Wt of
saturates
Wt of
aromatics
Ratio of
aromatics
to
saturates
Wt
of
resin
s (g)
Wt of
asphalt
enes
Ratio of resins
to asphaltenes
Bonny
Export 49.91 0.81 0.364 0.114 0.313 0.121 0.01 12.1
Bodo
crude 36.95 0.85 0.574 0.159 0.277 0.085 0.039 2.180
Mogho
crude 38.98 0.90 0.643 0.17 0.264 0.100 0.050 2.000
Table 4.7 shows the physical and chemical properties of the studied crudes. As
mentioned earlier, it is generally accepted that a high ratio of resins to asphaltenes and aromatics
to saturates is indicative of low asphaltene precipitation risk.[2] As recognized by De Boer et al,
79
the heavier oil also contains plenty of intermediate component that are good asphaltene solvents
whereas the light oil may consist largely of paraffinic materials in which, by definition,
asphaltenes have very limited solubility.[13]
In this present study, the composition factor mentioned were examined and shown in
Table 4.7. The three crudes shows very high values of saturates, indicating the presence of
paraffinic material. Also, according to these results, it is possible to suppose that the crude oils
with higher densities also show the higher cohesive energies and, therefore, the lower solubility
in the crude oil generating unstable crude oils. This result also shows that the density and
aromaticity of the crudes increases simultaneously as the asphaltene precipitates increases from
Bonny Export, Bodo and Mogho crudes. This shows that crude oil with higher aromaticity,
higher saturates and higher density like in Bodo and Mogho crude oils precipitate more
asphaltenes, and are likely to be problematic, most times such crudes are termed unstable crudes.
Infact, it was observed that the ratio of saturates to aromatics and the ratio of resins to
asphaltenes decreases as the asphaltene precipitate increases. This can be shown in the chart
below (figure 4.9).
Figure 4.9: Weight of heavy fractions of each of the three crude oils
studied and their various asphaltene content.
Figure 4.9 shows a bar chart which can be interpreted in terms of asphaltene stability and
stabilization properties of the maltenes.
From the bar chart above Mogho crude has the highest precipitation of asphaltenes
because of the presence of saturate which indicates high paraffinic material in which by
definition asphaltenes has limited solubility also the weigh
crude indicating higher asphaltene precipitation than in Bonny Export and Bodo crudes. Also as
mentioned earlier the ratio of saturates to aromatics and resins to asphaltenes is highest for
Bonny Export crude indicating t
lowest for Mogho crude, indicating the highest asphaltene precipitation risk. All these shows
that Mogho crude is likely to be more problematic followed by Bodo crude.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Bonny Export
0.364
0.114
0.121
0.01
eight of heavy fractions of each of the three crude oils
studied and their various asphaltene content.
Figure 4.9 shows a bar chart which can be interpreted in terms of asphaltene stability and
erties of the maltenes.
From the bar chart above Mogho crude has the highest precipitation of asphaltenes
because of the presence of saturate which indicates high paraffinic material in which by
definition asphaltenes has limited solubility also the weight of aromatics is higher in Mogho
crude indicating higher asphaltene precipitation than in Bonny Export and Bodo crudes. Also as
mentioned earlier the ratio of saturates to aromatics and resins to asphaltenes is highest for
Bonny Export crude indicating the lowest asphaltene precipitation risk and these ratios are
lowest for Mogho crude, indicating the highest asphaltene precipitation risk. All these shows
that Mogho crude is likely to be more problematic followed by Bodo crude.
Bodo Crude Mogho Crude
0.574
0.643
0.159 0.17
0.085 0.1
0.039 0.05
wt of saturates (g)
wt of aromatics (g)
wt of resins (g)
wt of asphaltenes (g)
80
eight of heavy fractions of each of the three crude oils
Figure 4.9 shows a bar chart which can be interpreted in terms of asphaltene stability and
From the bar chart above Mogho crude has the highest precipitation of asphaltenes
because of the presence of saturate which indicates high paraffinic material in which by
t of aromatics is higher in Mogho
crude indicating higher asphaltene precipitation than in Bonny Export and Bodo crudes. Also as
mentioned earlier the ratio of saturates to aromatics and resins to asphaltenes is highest for
he lowest asphaltene precipitation risk and these ratios are
lowest for Mogho crude, indicating the highest asphaltene precipitation risk. All these shows
wt of saturates (g)
wt of aromatics (g)
wt of resins (g)
wt of asphaltenes (g)
81
4.7 RESULT OF THE EFFECT OF RESINS ON ASPHALTENE PRECIPITATION
Addition of resins to crude oil reduced the precipitation of asphaltenes in the crude oil as
shown in Table 4.8 below.
Table 4.8: Effect of Resins on Asphaltene Precipitation.
Weight % of asphaltenes without resins Weight % of asphaltenes with
resins
Source of
crude
Final weight
of asphaltenes
Weight % of
asphaltenes
Final weight
of asphaltenes
after
purification
Weight % of
asphaltenes
Bonny Export 0.013 3.2 0.008 1.663
Bodo crude 0.039 6.5 0.018 3.035
Mogho Crude 0.050 9.877 0.023 5.425
In the experiment reported in table 4.8 Above, resins separated from Bonny Export crude
oil were added to the n – heptanes solution (i.e. 1ml crude + 40ml of n – heptane) of Bonny
Export crude oil, also the resins separated from Bodo crude and Mogho crudes were added to
their various n-heptane solutions (ie 1ml crude + 40ml n –heptane). From table 4.8 shown
above, 3.2% of asphaltene was precipitated from Bonny Export crude, 6.5% from Bodo crude
and 9.877% from Mogho crude before addition of the resins extracted from each of the crudes
but after the addition of resins to these crude oils, asphaltene precipitation in Bonny Export
crude, Bodo crude and Mogho crude reduced to 1.663%, 3.035% and 5.425% respectively
indicating that resins stabilize (solubilize) asphaltenes in crude oil.
Figure 4.10 shows the effectiveness of
To estimate the relative contribution of the resins to the stability of the crude oil, a plot of
the effectiveness of the resins and the asphaltene precipitation reduction as a function of the
stability of the crude oils is shown in Figure 4.10 above.
Figure 4.10 shows that the percentage weight of asphaltenes in Mogho, Bodo and Bonny
Export crudes (when resins extracted from the crude was added) reduced from 9.877
and 3.20/ 0 respectively to 5.425
Bonny Export). Indicating that resins stabilize (solubilize) asphaltenes in crude oil.
0 2
Bonny Export
Bodo crude
Mogho Crude
.10 shows the effectiveness of resins to stabilize their corresponding asphaltenes.
To estimate the relative contribution of the resins to the stability of the crude oil, a plot of
effectiveness of the resins and the asphaltene precipitation reduction as a function of the
stability of the crude oils is shown in Figure 4.10 above.
Figure 4.10 shows that the percentage weight of asphaltenes in Mogho, Bodo and Bonny
resins extracted from the crude was added) reduced from 9.877
to 5.4250/0( for Mogho crude), 3.0350/0( for Bodo), and 1.663
Bonny Export). Indicating that resins stabilize (solubilize) asphaltenes in crude oil.
2 4 6 8 10
3.2
6.5
9.877
1.663
3.035
5.425
Weight % of asphaltenes
with resins
Weight % of asphaltenes
without resins
82
resins to stabilize their corresponding asphaltenes.
To estimate the relative contribution of the resins to the stability of the crude oil, a plot of
effectiveness of the resins and the asphaltene precipitation reduction as a function of the
Figure 4.10 shows that the percentage weight of asphaltenes in Mogho, Bodo and Bonny
resins extracted from the crude was added) reduced from 9.8770/0, 6.50/0
( for Bodo), and 1.6630/0(for
Bonny Export). Indicating that resins stabilize (solubilize) asphaltenes in crude oil.
Weight % of asphaltenes
Weight % of asphaltenes
83
CHAPTER FIVE
Conclusion
Asphaltene precipitation with stirring time using n–heptane single solvent and n-pentane
+ n-heptane mixed solvent from 350OC atmospheric residuum (dead crude oils) is a useful
method to study the stability of crude oils. It was also found to be an important technique for the
study of the chemical factors that affect asphaltene precipitation.
As said earlier De Boer et al, recognized that light crude oils may consist largely of
paraffinic material in which by definition asphaltenes has very limited solubility.[13] This
indicates why the weight of saturates (composed mainly of paraffinic material) obtained from
these studied crude oils were very high compared to the weights of their aromatics, resins and
asphaltenes.
In this present study, it was also found that the density and the aromaticity of the
atmospheric residium increases simultaneousely with increase in asphaltenes from Bonny
Export, Bodo to Mogho crudes. There was a noticeable decrease in the ratio of aromatics to
saturates and resins to asphaltenes with Bonny Export having the highest ratio and Mogho the
least, there was also a noticeable increase in the ratio of asphaltenes to maltenes with Bonny
Export having the least ratio and Mogho the higest ratio. This shows that Mogho crude has the
highest asphaltene precipitate and Bonny Export the least. Therefore, Mogho crude with the
highest amount of density, saturate, aromaticity and asphaltenes is likely to be more problematic.
Further more, the drastic reduction of asphaltene precipitate in Bonny Export, Bodo and
Mogho crudes with additional resins extracted from the same crudes showed that resins from one
crude oil solubilise asphaltenes from the same crude oil.
84
This study also shows generally that the maltenes from Bonny Export crude oil exhibits higher
asphaltene stabilization effectiveness compared to the maltenes from Bodo and Mogho crude oils
indicating that Bonny Export crude is a more stable crude compared to Bodo and Mogho crudes
(unstable crudes).
Finally, this study shows clearly that asphaltene precipitation occurs in crude oil but other
constituents of crude oil especially resins, influence this precipitation. Thus resins play a critical
role in asphaltene precipitation.
85
NEW KNOWLEDGE ARISING FROM THIS RESEARCH WORK
For the first time precipitation of asphaltenes from 3500C atmospheric residuum (dead crude oil)
using mixed solvent system is reported.
This research work confirmed that the length of stirring time affect the yield of asphaltenes. This
has not been reported before.
Apart from the generally accepted fact that high ratio of aromatic to saturates and resins to
asphaltenes is indicative of low asphaltene precipitation risk. It was found from this work that
high ratio of asphaltenes to maltenes is indicative of high asphaltene precipitation risk.
This work showed that NAMAL method was an effective method for the separation of
atmospheric residuum into asphaltenes and maltenes.
This work showed that SAR method was an effective and cheap method for the separation of
maltenes into saturates, aromatics, and resins.
It was found that increasing resin content of one crude oil solubilizes the asphaltenes from the
same crude oil.
86
LITERATURE CITED
1. Jianxin, Wang, and Jill Buckley S. (2003). “Asphaltene stability in crude oil and aromatic
solvents: The influence of oil composition,” New Mexico. Energy and fuels Vol 17, 1445
– 1446.
2. Diallo MS, Cagin T, Faulon JL and Goddard W. A III. (2003). “Thermodynamic
properties of asphaltenes: A predictive approach based on computer assisted structure
elucidation and atomistic simulations,”103.
3. Favennec, J-P. (2001). “Ed Petroleum Refining, Refinery operation and Management”
Editions Technip: Paris, Vol 5,Pg 62 – 69.
4a.Light crude oil ‘‘From wikipedia, the free encyclopedia’’ :http://www.indexmundi.
Com/commodities/glossary, light – vs – heavy crude oil. Retrieved on 12th May, 2011.
4b.Nwadinigwe C.A. and Alumona T.N. (2010). Quantitative assessment of n-Alkanes
asphaltenes and resins in different crudes. Unpublished M.Sc. Thesis. Department of Pure
and Industrail Chemistry University of Nigeria, Nsukka. Pg 119.
5. Dusseault, M.B. (2008). “Comparing Venezuelan and Canadian Heavy oil and Tar
Sands”. (PDF). Calgary, Canada: Canadian International Petroleum Conference.
http://www. energy .gov .ca / oilsands /pdfs/RPT chops app3
6. Heavy crude oil. (2011) ‘‘From Wikipedia, the free encyclopedia’’.
File///C:/users/e/Desktop/Heavy-Crude-oil.htm.
modified on 31 March 2011 at 3.56.
87
7. Roussel, J.C. and Boulet, R. (1995). Composition of Crude oils and Petroleum Products.
In Petroleum Refining vol 1 crude oil Petroleum Products. Process flowsheets: Wauguier,
J-P. Ed.; Editions Technip, Paris: pg 1.
8. Kamran A, Ahmed H, Abdel K, Dan Z, Stophen A, Jefferson C, Shah K, Jamaluddin A,
Alvan G-M, Ryan PR, Olive C M, Tronds S, (2007). “Asphaltenes – Problematic but rich
in potential” Pgs 1-2, 40-43.
9. Speight J. G: (2004), “Petroleum asphaltenes part 1: Asphaltenes, resins and the structure
of Petroleum,” oil and gas science and technology Vol 59, pg 467 – 477
www.editionstechnip.com/source/liste - IfpFiche.asp. Retieved November, 20th 2010.
10. Peng luo, Xiaogi Wang, yongan Gu (2010). “Characterisation of asphaltenes precipitated
with three light alkanes under different experimental conditions: fluid phase equilibria,”
journal 291 pg 103 – 110.
11. Mullins O.C (1990). “Analytical Chemistry pgs 62, 508.
12. Bestougeff, M. A., and Byramjee R. J Yen T. F (1994). Chilingarian G.V: Chemical
constitution of asphaltenes, asphaltenes and asphalts.
13. Asphalteneshttp://bearuan.nmt.edu petro – physics/gp/intro pdf NMT Asphaltene FAQ
Pg 1 Retrieved on
14. Aquinos, Olivos M.A, Andersen S.I, Liran Galeana C: (2003). “Comparisons between
asphaltenes from the dead and live oil samples of the same crude oils, Petrol: Science
Technvlogy 21 1017 – 1041.
15. Miller J.T, Fisher R.B, Thiyagarajan P, (1998). “Subfractionation and characterisation of
Mayan asphaltenes, Energy fuels 12, 1290 – 1295.
88
16. Speight J.G, Long R.B, Trowbridge T.D (1984). “Factors influencing the seperativn of
asphaltenes from heavy pet. Feedstocks” Fuel 63, 616.
17. Anisimov, M.A., Yudin, I.K, Niktin, V., Nilolaenko, G., Onernoustan, A., Toulhoat H.,
and Briolant Y. (1995). Asphalten aggregation in hydrocarbon solutions studied by
photon correction spectroscopy. J. phys Chem. 99: 9576.
18. Koots, J.A, and Speight, J.G.(1975). Relation of Petroleum asphaltene to resins. Fuel, 54
179.
19. Taylor S. (1992). “Resolving crude oil emulsions. Chem. Industry, 770.
20. Galoppin M. and Tambini M. (1994). “SPE European production operations conference
and exhibitions” Aberdeen UK: SPE 27622.
21. Leontariris K.J. 01 (1998). Oil and Gas, Journal 01122
22. Taylor, S.E. Fuel (1998), 77, 821
23. Speight, J.G.(2007). “The Chemistry and Technology of petroleum” 4th edition; CRC
Pree: boca Raton.
24. Irion, W.W; (2001) Newbirth, O.S. Oil Refinin. In Ullmanns Encyclvpedia of Industrial
Chemistry, 6th Edition; Wiley – VCH: Weinhein.
25. Nwadinigwe C.A. 2008/2009 session “Crude oil formation, distribution and Refining
“CHM 543: Lecture note.
26. Organic Origins of Petroleum http://www.google.com.ng/=q= origin + of + asphaltenes
and hl = en and prmd = ivnsb and ei = Xg3 Retrieved 11th May, 2011.
27. Bycosin (2011) “More about asphaltenes, Solving heavy fuel related problems.
http://www.bycosin.Sc/Asph-more.htm.. Retrieved 11th May, 2011
89
28. Speight J.G., “Asphlatene in Crude oil and Bitumen: Struture and Dispersion, Advance
Chemical Society”. Suspension: Fundamantals and Applications in Petroleum Industry:
(1996) 377
29. Mansoori G.A. Modelling of Asphaltene and other heavy organic depositions. (1997)
Journal of Petroleum Science and Engineering. 17:[6].
30. Liao Zewen and Geng Ansong. ‘Asphaltene in oil Reservoir Recovery.” Chinese Science
Bulletin. Vol 45 No. 8 April 2000 Pg 1 – 4.
31. Auflem I.H.(2002). “Influence of Asphaltene Aggregation and pressure on Crude oil
Emulsion Stability,: Doktor Ingenior Thesis, Norwegian University of Science and
Technology, Trondheim.
32. Speight J.G.(1999) “The Chemistry and Technology of Petroleum” 3rd Marcel Dekker
Inc; New York.
33. Leontaintis K.T. and Mansori G.A.: “Asphaltene Deposition during oil Production and
Processing: A thermodynamic colloidal Model”, SPE Paper. No. 16258 Processings from
the 1987 SPE Symposium on oil field Chemistry, Richardson, Texas.
34. “Arterial Blockage in the Petroleum and Natural Gas Industries Project (Asphaltene
Deposition and its Control). Internet Publication mhtn/:file: Asphaltene (5/3/2008) Pgs 1
of 24.
35. Korseek A.R., Wong H and Radke C.J.(1993)“A Pore – Level Scenario for the
Development of Mixed Wettability in oil Reserviors, “American Institute of Chemical
Engineers Journal 39, No. 6: 1072 – 1085. Yang and Czarnecki, reference 12.
36. Garcia M.D.C. Carbognani L.(2001) Energy Fuels 15, 1021 – 1027.
90
37. Mayor, Agrawala. (2001) “Measurement and modelling of Asphaltene Association. “A
Thesis Submitted to the Faculty of Graduate Studies in Partial Fulfillment of the
Requirements for the degree of Master of Science in Chemical Engineering. Calgary,
Alberta. Pg 1.http://www. Collections Canada.gc.C/obj/S4/fs/lsk3/ftp05/mg64992.pdf.
38. Miller, R. (1998) Hydrocarbon Fractionation with bonded Phase liquid Chromatography.
“Analytical Chemistry, 54: 1742
http://www.collectionscanada.gc.ca/obj./s4/fs/dsk3/ftpo5/mq64992.
39. Buckley, J.S., Hirasaki, C.J., Liu Y., Von Drasek., Wang J. X., Gill B.S. (1998).
Asphaltene Precipitation and Svlvent Properties of Crude oil, Petroleum science
Technology. 16 (384), 251 – 285.
40. Mullins Oc(2007) “Asphaltene Heavy oils and petroleomics Springer New York, chapter
23 ) Pg 700.
41. “Asphaltene Aggregation from Crude oils and Model Systems,” Studied by High
Pressure NIR Spectroscopy. http://www.(amo.com/downloads/Asphaltene-Aggregation
from crude oils and Model systems studied by Highpressure_NIR_Spectroscopy.pdf
(Source:American Chemical Society)
42. Asphaltene from Wikipedia, the free encyclopedia.
http://en.wikipedia.org/wiki/Asphaltene (3/12/2010) Page 1 of 2and 2 of 2.
43. Cimino,R, Correra S,et al.(1995) “Solubility and Phase Bahaviour of Asphaltene in
Hydrocarbon Media. Asphaltene: Fundamentals and Applications. New York Pg 97 –
130.
91
44. Buckley, J.S, Hirasaki G.J, Lui, Von Drasek., Wang J. X., Gill B.S..(1998) “Asphaltenes
Precipitations and Solvent Properties of Crude oils. “Petroleum Science Technology 16
Pp 251 – 285.
45. “Waxes and Asphaltenes – their Chemistry, Analysis and Relevance to Production
Problems.”http://www.ghgeochem.com/documents/waxes_and_asphaltenes.pdf Retrirved
June 12, 2009
46. “Nanoscale Strutures of Asphaltene molecule, Asphaltene Steric – Colloid and
Asphaltene Micelles and Vehicles”
http://tigger.uic.edu/¬mansoori/asphaltene.molecule_html. Retrieved June 12, 2009
47 Muray R. Gray. (2003).Consistency of Asphaltene Chemical Structure with pyrolysis and
Coking Behaviour.” Energy and Fuels.
48.Mc Lean, J.D, and Kilpatrick.(1997) “Journal Colloid and Interface Science, 189, 242.
49. Yen T.F. “The Role of Asphaltene in Heavy Crudes and Tar Sands”.
http://www.oildrop.org/i.b/conf/isttoc.htm/Nsec 1 chapter 22. Pp174 to 176
50. Moschopedis S.E., Fryer, (1976). “Investigation of Asphaltene molecular Weight,” Fuel,
55 Pg 227.
51. Mitra – Kirtley, S. Mullins, O.C., Brathanver J.F., Gam S.P. (1993). “Nitrogen Chemistry
of Kerogen and Bitumens from X-Ray Absorption Near – Edge Structure Spectroscopy,
Energy and Fuels. 7(6) Pg 1128.
52. Moschopedis, S.E and Speight J.G. (1976). “Oxygen Functions in Asphaltenes” Fuel 55,
222.
53. Branthaver, J.F.(1990). “In Fuel Science and Technology handbook: Marcel Dekker Inc.,
New York.
92
54. Strausz, O.P., Mojelsky, T.W, and Lown E.M. (1992). “The Molecular Struture of
Asphaltene: An Unfolding Story”, Fuel 71, 1355.
55. Yen,T.F. (1997) “Structure of Petroleum Asphaltene and its Significance Energy Sources,
1(4), 447.
56. Li M., Christy A.A and Sjoblom, J. (1992). “Emulsions: A Fundamental and Practical
Approach” J Sjoblom (ed, Khuwer Academic Publisher, Amsterdan Publisher,
Amsterdan, The Netherlands, pg 157.
57. Mc Lea, J.D and Kilpatrick, P.K (1997). “Journal Colloid and Interface Science,” 189 Pg
242.
58. Groenzin, H., Mullins, O.C.(200) Energy Fuels Vol 14, Pp 677 – 684
59. Chung, K.H., Xu, C.M.; Hu, X.Y., Wang R., N. (1997). Oil Gas J. 95 (1), Pp 66 – 69.
60. Artok, L., Hirose, Y.(1999). hosokawa, M.; Murata, S.;Nomura, M. Energy Fuels (13)
Pp 287 – 296
61. Long R.B and Speight J.G.(1998). “Petroleum chemistry and refining” Speight (ed.),
Talor and Francis Washington DC.
62. Selucky, M.L., K.S.S., Skinner F., Strausz O.P. (1981) “The Chemistry of Asphaltene
Constituents. In Advances in chemistry Series No. 195, J.W. Bunger and N.C. Li (eds),
American Chemical Society, Washington DC.
63. Tissot, B.(1984) “Characterization of Heavy Crude oils and Petroleum residues, “Edition
Tecnip, paris France.
64. Mattew Spiecker P, Keith Gaways L., Chad Trail B., Peter Kilpatrick K. (2002). “Effects
of Petroleum Resins on Asphaltene Aggregation and Water – in – oil Emulsion
93
Formation,” Pp 1 to 25.http://www.ncnr.nist.gov/programs/sans/pdf/publications/0157
retrieved on december 10th 2010
65. Chang, V – L and Foger, H.S.(1996) “Peptization and Caogulation of Asphaltenes in a
polar media using oil – soluble polymers “Fuel Science and Technology International,
14(1&2), Pg 75.http://www.ncnr.nist.goo/programs/sans/pdf/publications/0157
66. Murgich J., Abanero, J.A., and Strusz O.P. (1999). Molecular Recognition in Aggregates
formed by Asphaltene and Resin Mvlecules from the Athabasca oil Sands,” Energy and
Fuels 13, Pg 278.
67. Leon O, Rogel E, Wspidel J., and Torres G. (1998) “Structural Characterisation and Self
Association of Asphaltenes of Difference Origins,” 3rd International Symposium on the
Thermodynamics of Heavy oils and Asphaltenes, Houston, TX, Pp 37.
68. Pfeiffer, J.P, Saal, RNJ.(1940). “Asphalt. Bitumens as Colloid System,” Journal of
Physical Chemistry, 44, Pp. 140.
69. Mohammed, R.S., Ramos, A.C.S and Loh W. (1999). “Aggregation Behaviour of Two
Asphaltene Fractions in Aromatic Solvents,” energy and Fuels 13, 323.
70. Rogel, E., Leon, O., Torres, G., and Espidel J. (2000). “Aggregation of Asphaltenes in
organic Solvents using Surface Tension Measurements,” Fuel, 79, 1393.
71. Yarranton, H.W., Alboudrone; H. and Jakher R. (2000). “Investigation of Asphaltene
Association with Vapour Pressure Osmometry and Interfacial Tension Measurement,”
Industrial and Engineering Chemistry research, 39(8), 2916.
72. Alboudiwerj, H, Akkarzadeh, K and Yarranton, H.W. Personal communication, 2001.
73. Leotaritis, K.J., and Mansoori G.A.,(1998) “Asphalten Deposition: A Survey of Field
experiences and Research Approach “Petroleum Science and Eng. Pp 1 – 229.
94
74. “Influence of Temperature and pressure on Asphaltene Flocculation,” Society of
Petroleum Engineering Journal (24) (1994), pp 283
75. Onomaka O.R.(2008). “Solubility of Crude oil Solids in organic Solvents”. Unpublished
M.Sc. Thesis Submitted to Faculty of Sciences, Department of Pure and Industrial
chemistry. University of Port Harcourt Nig, Pp 4 and 13.
76. Escobedo, J. Mansoori, G.A., Balderan – Joers C, Carranza Bocerra L.J., and Mendez-
Garcia M.A.. (1997) “Heavy Organic Deposition during oil Petroleum from a hot Deep
Reservior: A Field Experience “Proceedings of the 5th Lattin American and Caribbean
Petroleum Engineering conference and Exhibition, SPE Paper , Pp 9.
77. Ceregy L.M.(2001). “Survey of Successful World _ Wide Asphaltene reinhibitor
Treatments in oil Production Fields” Paper SPE 71542, Presented at the SPE Annual
Technical Conference and Exhibition, New Orleans.
78. “Problems Found in oil Production,” Paper SPE 37286 Presented at the SPE
International Symposium on oil – field Chemistry, Houston, (Feb 18th – 21st ) 1997.
79. Terres C.A., Treint F., Alonso C., Milins A and Locomte A. (2005). “Asphaltenes
Pipeline cleanont: An Horizontal Challenge for Coiled Tubing. “ Paper SPE 93272,
Presented at the SPE/ICOTA Coiled Tubing Conference and Exhibition. The Woodlands,
Texas.
80. Rogel E, Leon O et al. (2003). ‘’Assessment of Asphaltene Stability in Crude oils using
Conventional Technique.(17) Pp 1583-1590.
81. Igor N Evdokimov and Aleksandr P.Losev ‘’On the Nature of UV/Vis Absorption
Spectra of Asphaltenes. http://eee.gubkin.ru. Retrieved on July 16 2011.
95
82. Sabbah, H., Morrow, A.L., Powerantz, A.E. and Zare, R.N. (2011) R.N. Evidence for
Island Structures as the Dominant Architecture of Asphaltenes. Energy Fuels, 25, 1597 -
1604.
96
APPENDIX 1
MAP OF THE SOURCE OF BONNY EXPORT, BODO AND MOGHO CRUDE OILS
▼
◄
►
97
APPENDIX 2
DENSITY OF CRUDE OIL IN g/ml
Bonny Export Bodo Mogho
0.78 0.84 0.83
Density of crude (g/ml) = ������ � �� �(�)
������ � �� �(��)
Bonny Export crude = ���.�
���= 0.78�/�
Bodo crude = �!�.�
��"= 0.84�/�
Mogho crude = $%�.�
�""= 0.83�/�
DENSITY OF ATOMPHERIC RESIDUUM
Bonny Export Bodo Mogho
0.81 0.85 0.90
Density of atmospheric residuum in g/ml = ������ � '���()���� ��(� ���(�)
������ � '���()����(��)
Bonny export = %��."�
��$= 0.81�/�
Bodo = �%%.�
��"= 0.85�/�
Mogho = %��.%�
%$"= 0.90�/�
98
APPENDIX 3
API GRAVITY OF THE CRUDE OILS
Bonny Export Bodo Mogho
49.91O 36.95O 38.89O
OAPI gravity = %$%.�
-)��� ��'���. − 131.5
Bonny Export = %$%.�
".�� − 131.5 = 49. 910
Bodo = %$%.�
".�$ − 131.5 = 36.950
Mogho = %$%.�
".�! − 131.5 = 38.890
API GRAVITY OF ATMOSPHERIC RESIDUUM
Bonny Export Bodo Mogho
45.3O 34.97O 25.72O
OAPI gravity = %$%.�
-)��� ��'���. − 131.5
Bonny Export = %$%.�
".�% − 131.5 = 45.300
Bodo = %$%.�
".�� − 131.5 = 34.972
Mogho = %$%.�
".3" − 131.5 = 25.720
99
APPENDIX 4
PERCENTAGE WEIGHT OF ASPHALTENES FROM BONNY EXPORT
ATMOSPHERIC RESIDUUM
Stirring time Solvent Weight of asphaltenes before drying (g)
Weight of asphaletenes after drying (g)
Percentage weight of asphaltenes (%)
20mins n-heptane 0.144 0.001 0.69%
40mins n-heptane 0.450 0.006 1.33%
60mins n-heptane 0.385 0.008 2.08%
80mins n-heptane 0.312 0.010 3.20%
20mins n-pentane + n-heptane 0.343 0.003 0.88
40mins n-pentane + n-heptane 0.410 0.007 1.71
60mins n-pentane + n-heptane 0.345 0.010 2.90
80mins n-pentane + n-heptane 0.312 0.012 3.85
Percentage weight of Bonny export asphaltenes = 56789: 2; <=>9<?:6@6= <;:6A BAC7@8
������ � '()�'���D�( E���� �.�D� × 100
Density of Bonny Export maltenes = ������ �'���D�( (�)
G����� � �'���D�( (��)
100
APPENDIX 5
PERCENTAGE WEIGHT OF ASPHALTENES FROM BODO ATMOSPHERIC
RESIDUUM
Stirring time Solvent Weight of asphaltenes before drying (g)
Weight of asphaletenes after drying (g)
Percentage weight of asphaltenes (%)
20mins n-heptane 0.205 0.012 5.850
40mins n-heptane 0.210 0.013 6.190
60mins n-heptane 0.541 0.040 7.390
80mins n-heptane 0.600 0.039 6.500
20mins n-pentane + n-heptane 0.205 0.014 6.830
40mins n-pentane + n-heptane 0.382 0.030 7.850
60mins n-pentane + n-heptane 0.500 0.043 8.600
80mins n-pentane + n-heptane 0.545 0.041 7.523
Percentage weight of Bodo asphaltenes = 56789: 2; <=>9<?:6@6= <;:6A BAC7@8
������ � '()�'���D�( E���� �.�D� × 100
Density of Bodo maltenes = ������ �'���D�( (�)
G����� � �'���D�( (��)
101
APPENDIX 6
PERCENTAGE WEIGHT OF ASPHALTENES FROM MOGHO ATMOSPHERIC
RESIDUUM
Stirring time Solvent Weight of asphaltenes before drying (g)
Weight of asphaletenes after drying (g)
Percentage weight of asphaltenes (%)
20mins n-heptane 0.273 0.029 10.623
40mins n-heptane 0.265 0.027 10.189
60mins n-heptane 0.273 0.018 6.590
80mins n-heptane 0.243 0.024 9.877
20mins n-pentane + n-heptane 0.308 0.036 11.688
40mins n-pentane + n-heptane 0.275 0.029 10.546
60mins n-pentane + n-heptane 0.351 0.024 6.838
80mins n-pentane + n-heptane 0.248 0.025 10.081
Percentage weight of Mogho asphaltenes = 56789: 2; <=>9<?:6@6= <;:6A BAC7@8
������ � '()�'���D�( E���� �.�D� × 100
Density of Mogho maltenes = ������ �'���D�( (�)
G����� � �'���D�( (��)
102
APPENDIX 7
WEIGHT OF MALTENES AND RATIO OF ASHALTENES TO MALTENES
Source of crudes
Weight of
saturate (g)
Weight of
aromatics (g)
Weight of
resins (g)
Weight of
asphaltenes
(g)
Weight of
maltenes (g)
Ratio of
asphaltenes
to maltenes
Bonny Export
0.364 0.114 0.121 0.010 0.599 0.017
Bodo 0.574 0.159 0.085 0.039 0.818 0.048
Mogho 0.643 0.170 0.100 0.050 0.913 0.055
Weight of maltenes (g) = wt of saturates + wt of aromatics + wt of resins
Ratio of asphaltenes to maltenes = 56789: 2; <=>9<?:6@6=
������ � �'���D�(
PERCENTAGE WEIGHT OF ASPHALTENE FROM 350O
C ATMOSPHERIC
RESIDUUM WITH ADDITIONAL RESINS EXTRACTED FROM EACH OF THE
CRUDES
Source of crudes Solvent Initial weight of
asphaltenes before
drying (g)
Final weight of
asphaltenes after
drying (g)
Percentage weight
of asphaltenes
(%)
Bonny Export n-heptane 0.481 0.008 1.663
Bodo n-heptane 0.018 0.593 3.035
Mogho n-heptane 0.023 0.424 5.425
Percentage of weight of asphaltenes when resins was added to the atmospheric residuum =
HD���'� ������ � '()�'���D�( E���� �.�D� (�)
I�D'� ������ � '()�'���D� '��� �.�D� × 100
103
APPENDIX 8
Figure 1: C7 asphaltene from Bonny Export Crude
104
APPENDIX 9
Figure II: C7 asphaltene from Bodo Crude
ANIGBOGU IFEOMA V.
105
APPENDIX 10
Figure III: C7 asphaltene from Mogho Crude
106
APPENDIX 11
Figure IV: C5 + C7 asphaltene from Bonny Export Crude
107
APPENDIX 12
Figure V: C5 + C7 asphaltene from Bodo Crude
ANIGBOGU IFEOMA V.
108
APPENDIX 13
Figure VI: C5 + C7 asphaltene from Mogho Crude
109
APPENDIX 14
Figure VII: C7 asphaltene from Bonny Export Crude (UV)
110
APPENDIX 15
Figure VIII: C7 asphaltene from Bodo Crude (UV)
111
APPENDIX 16
Figure IX: C7 asphaltene from Mogho Crude (UV)
112
APPENDIX 17
Figure X: C5 + C7 asphaltene from Bonny Crude (UV)
113
APPENDIX 18
Figure XI: C5 + C7 asphaltene from Bodo Crude (UV)
114
APPENDIX 19
Figure XII: C5 + C7 asphaltene from Mogho Crude (UV)