separacion de parafinas y asfaltenos.pdf

7/28/2019 separacion de parafinas y asfaltenos.pdf

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INGEPET 2002 (EXPR-1-RP-30)

SEPARATION OF WAXES AND ASPHALTENES IN CRUDE OILS

R. Paul Philp, M. Hsieh

School of Geology and Geophysics, University of OklahomaUSA

ABSTRACT

Heavy organics are the primary culprits of deposition problems encountered during the production and

transportation of crude oils, and are important constituents in the formation of tar mats. In general, highmolecular weight hydrocarbons (HMWHCs >C40) and asphaltenes are the principal classes of heavyorganics associated with crystallization, agglomeration, and other deposition-related problems. The

traditional method for isolating asphaltenes is by precipitation with excessive amounts of low boiling pointsolvents such as pentane, hexane, or heptane, which can result in the co-precipitation of a significantamount of microcrystalline waxes (>C40). The presence of microcrystalline waxes (>C40) in the asphaltene

fraction potentially can provide misleading and ambiguous results affecting any modeling or treatmentprogram. The sub-surface phase behavior of an asphaltene fraction will be quite different from the sub-surface behavior of a wax-contaminated asphaltene fraction. Similarly accurate modeling of wax drop-out

requires information on pure wax fractions and not asphaltene dominated waxes. Hence the goal of this

paper is to describe a novel method for the preparation of wax-free asphaltenes and asphaltene-freewaxes. In addition, this method provides a quantitative subdivision of waxes into pentane soluble and

insoluble waxes which, when correlated with physical properties of crude oil such as viscosity, pour point,cloud point, etc., may help to explain causes of wax deposition problems during production, transportationand storage of crude oils.

Oils from a variety of basins worldwide, including examples from Peru, will be used to illustrate theapplication of this method to the determination of their wax and oil content and how this information may

be used for production purposes. In addition the significance of the distribution of individual compoundswithin the wax fraction will be discussed in detail with the use of appropriate examples.

1. INTRODUCTION

The development of high temperature gas chromatography (HTGC) has permitted the geochemist toenter the realm of high molecular weight hydrocarbons (HMWHCs) in the range C40-C120in crude oils, andto lesser extent, source rock extracts (LIPSKY and DUFFY, 1986a and b; PHILP, 1994; HEATH et al.,

1997; MUELLER and PHILP, 1998; HSIEH and PHILP, 2001). A number of papers have already beenpublished on this topic including those by CARLSON et al. (1993), DEL RIO et al. (1992a and b) andWAVREK and DAHDAH (1995). These papers generally have been concerned with the characterization

of waxes isolated from crude oils and pipelines and discuss the potential use of this type of information. Inmost crude oils these compounds typically extend to about C70 with only a few oils that have beenanalyzed containing compounds in the C70-C120range. The distribution of HMWHCs in a crude oil will be

primarily determined by source materials with factors such as migration distances, pressure, andtemperature gradients between reservoir and well-head also playing an important role in determining thedistribution of HMWHCs observed in produced oils. Hydrocarbons with more than 20 carbon atoms are

solid at room temperature and thus crude oils containing large amounts of hydrocarbons above C20, andmore importantly above C40, have the potential to give rise to serious wax deposition problems duringproduction, and in some cases in the reservoir itself (TRINIDADE et al., 1997). Waxes may be

precipitated in the production tubing or anywhere along the pipelines and production facilities until the oilsreach the storage tanks. Even in storage tanks, wax deposition may be a problem and co-mingling of twoor more oils, neither of which have paraffin problems when produced separately, may lead to precipitation

of waxes. Movement and shearing may prevent deposition in the pipeline but the wax crystals formed willreadily be deposited in the storage tank. Although the terms micro- and macro-crystalline waxes havebeen in use for many years to differentiate wax-types on the basis of their carbon number distributions

and other properties, detailed molecular characterization of waxes were rarely undertaken in the past dueto the lack of suitable analytical techniques.

In many cases the concentration of these HMWHCs may be relatively low, hence techniques may be

required to enhance the concentration of these compounds. PHILP and BISHOP (1995) and PHILP et al.(1995) described one such concentration technique and another standardized method involving acetone

precipitation was published several years ago (BURGER et al., 1981). One of the major problems


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INGEPET2002 (EXPR1-RP-30) 2

associated with this work is the separation of wax es from non-hydrocarbons dominated by resin andasphaltene fractions. Precipitation of asphaltenes with n-pentane will, in many cases, produce fractions

containing high concentrations of microcrystalline waxes (>C40), whose presence can lead to themisinterpretation of geochemical characteristics of asphaltenes. Asphaltenes exist as suspensions incrude oils and are stabilized by peptizing agents such as resins and other aromatic compounds.

Destabilization of asphaltenes will result in its deposition and agglomeration. Asphaltene particulateshave the potential to act as nucleation points from which wax growth/crystallization can occur (HSIEH,

1999). Asphaltene flocculants acting as sites for wax crystallization have been demonstrated to increasecrude oil cloud point and also interfere with wax inhibitors (GARCIA, 2000). Likewise when waxes areconcentrated, they often contain significant amounts of asphaltenes. In this paper, a method for thequantitative and qualitative separation of waxes from asphaltenes will be described and used to illustrate

the approach with results obtained from its application to oils from a variety of sources.

It should be noted that waxy oils are not necessarily limited to those sourced from terrigenous, or higher

plant, source materials as previously suggested by HEDBERG (1968) but many oils from lacustrine andmarine sources also contain significant quantities of high molecular weight hydrocarbons. TheHEDBERG (1968) paper also noted that waxy oils typically originated from stratigraphic sequences of

non-marine origin, shale-sandstone lithology, water salinities less than that of marine waters, and agesranging from the Devonian to Pliocene. KINGHORN (1983) also suggested that petroleum waxes wererestricted to terrigenous sources; however, since those studies evidence has appeared suggesting that

waxy crude oils may also be derived from marine or lacustrine source materials (MOLDOWAN et al.,1985; TEGELAAR et al., 1989; CARLSON et al., 1993; HSIEH, 1999). The wax fractions isolated fromoils are not simply composed of n-alkanes, but also include complex mixtures of long chain

alkylcycloalkanes, methylbranched alkanes, and alkylaromatic hydrocarbons. The presence ofalkylcyclopentanes, extending beyond C40, can be used to predict the depositional environments of theoriginal source material.

Possible sources for these compounds include indigenous components of living organisms (e.g.cuticularwaxes preserved in kerogen), fatty acids, or wax esters (TISSOT and WELTE, 1984; KISSIN, 1990). N-

Alkanes and fatty acids sourced from blue-green algae and various types of bacteria are associated with

hypersaline, carbonate environments (DEMBECKI et al., 1976). Significant fractions of organicsedimentary matter are comprised of algaenans in various classes of marine microalgae. Catagenesis ofaliphatic algaenans in the sediments can provide an important source of n-alkanes in marine oils (GELIN

et al., 1999). HMW mono-, di-, and trimethylalkanes have been observed in Holocene cyanobacterialmats from Abu Dhabi and are believed to originate from insects that grazed on the cyanobacterial mats(KENIG et al., 1995). Complex mixtures of waxy compounds are widespread in many varieties of insects

and are commonly encountered as cuticle/surface lipids and internal lipids. These lipids are present ascomplex mixtures of long-chain n-alkanes, methylbranched alkanes, wax esters, aldehydes, fatty acids,long-chain alcohols, ketones, and sterol esters (NELSON and BLOMQUIST, 1995).

It is important that we improve our understanding of these HMW compounds (i.e. their structures,physical/chemical properties, and origin) in order to alleviate and better address production problems that

result in reduced production, clean-up and remedial expenses, elevated operations costs, andinvestigative/research expenses (TUTTLE, 1983; ESCOBEDO and MANSOORI, 1992; LEONTARITIS,1996).

2. EXPERIMENTAL

The method, summarized in Fig.1, was developed to concentrate waxes in crude oils, separatemicrocrystalline waxes from macrocrystalline waxes, and to provide a method for separating waxes from

asphaltenes. The initial step in this method involves adsorption of the oil on alumina (1-these numbersrefer to the steps numbered in Fig.1), using approximately 1g of oil dissolved in 10 ml of hot iso-octane (atleast 80

oC) to ensure complete dissolution of any wax crystals. Following adsorption, the alumina is

extracted with iso-octane for a period of 48hrs (2) although this time period can be significantly reduced ifthe microcrystalline wax content (>C40) of the oil is low. Following the extraction, the iso-octane extract isconcentrated and the wax precipitated with acetone at -21

oC (3, BURGER et al., 1981). Cold pentane (-

21oC) is added to the precipitate to a concentration of about 2mg/ml and the solution allowed to stand

overnight (4). Following stirring and centrifugation with cold n-pentane, two fractions are obtained with the


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macrocrystalline waxes being in solution (5) and microcrystalline waxes with predominance of HMW HCsbeyond C40being present as precipitate (6). The material that remains adsorbed to the alumina after the

initial extraction step is extracted with a mixture of chloroform/methanol (95:5) for at least 6hrs (7). Thisprocedure will effectively extract the adsorbed asphaltenes and resins from the alumina which cansubsequently be separated by pentane precipitation (8).

The end products of this procedure are: (i) A wax-free asphaltene fraction; (ii) an asphaltene-free wax

concentrate which, if desired, can be subdivided into micro(5)- and macrocrystalline(6) wax fractions.GC Analysis

All GC analyses described in this paper were performed using a Carlo Erba GC8000gas chromatograph

equipped with an on-column injector and a SGE HT-5 column (25m x 0.32mm I. D. x 0.1?m film). Heliumwas used as the carrier gas and the column was programmed from 60

oC to 380

oC with a program rate of

4oC/min.

3. RESULTS AND DISCUSSION

The work described in the first part of this paper is specifically concerned with a method for the qualitativeand quantitative separation of waxes from asphaltenes, and macrocrystalline waxes from microcrystalline

waxes. The procedure has been designed to work on samples of approximately 1g in size but can bescaled down depending upon the amount of oil available and how much material is required from theseparation step. The wax extraction time with iso-octane is mainly dependent upon the amount of

microcrystalline waxes in the crude oil, and can be significantly reduced if a preliminary idea of the natureof the waxes (micro vs macro) is available.

The importance of such a wax isolation is illustrated in Fig.2a which shows the high temperature gas

chromatogram of a crude oil with HMWHCs extending to at least C65. Precipitation of asphaltenes by theclassical pentane precipitation method produced a precipitate, whose chromatogram is shown in Fig.2b.

A significant part of the asphaltene fraction in this case was present as a microcrystalline wax, which it

should be noted is a more common occurrence than has been noted in the past. In most casesasphaltenes are not routinely analyzed by HTGC so the presence of these waxy components is notobserved. Further purification of the asphaltenes would not necessarily remove the wax component

simply because of their HMW and extremely poor solubility in solvents such as pentane commonly usedto purify the asphaltenes. In Fig.2c the HTGC trace is shown for the asphaltene fraction isolated from thesame oil using the procedure shown in Fig.1 and clearly the asphaltene fraction no longer contains any

wax component, indicating complete separation of the wax from the asphaltene fraction. Thecorresponding wax fraction isolated from this oil using the procedure in Fig.1 is shown in Fig.3a, which isfurther separated into n-pentane soluble and insoluble waxes (Fig.3b and c, respectively). The pentane-

soluble waxes contain predominantly n-alkanes (C40) whose extremely poor solubility may potentially cause wax depositionproblems, especially in storage tanks. The quantitation of these higher carbon number components can

be correlated with other physical properties such as pour point, cloud point or viscosity, to help explaincauses of wax deposition problems. Case studies have demonstrated that a wax content as low as 2%can potentially result in wax deposition problems (HOLDER and WINKLER, 1965; TUTTLE, 1983;

AJIENKA and IKOKU, 1990).

The development of the above method has permitted detailed analyses of the isolated wax fractions to be

undertaken. This is an extremely important aspect of the work since in many engineering and modelingstudies the molecular composition of the waxes has been overlooked. For the most part it has beenassumed that waxes all have similar compositions. This is clearly not the case and it is important to

investigate the molecular composition of the isolated waxes to get a more comprehensive picture of theirproperties. The melting points of branched hydrocarbons are dramatically lower than n-alkanes andhence the relative concentrations of these compounds in a wax can have a significant effect on the pour

point of a crude oil. GARCIA et al.,(2000) have demonstrated that iso- and cycloalkane concentrations>40 wt.% can hinder wax crystal arrangements and increase the cloud point of an oil. It is also importantto note the ubiquity of HMWHCs in oils from all types of source materials.


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Wax components are not simply restricted to oils sourced from any one type of environment or sourcematerial. As part of our on-going research a wide range of oils from marine, freshwater lacustrine, saline

lacustrine, and terrigenous environments; with shale or carbonate source rock lithologies; and agesranging from Ordovician to Pliocene have been examined (Fig. 4a-c). The majority of these oils haveseveral homologous series of compounds in the HMW region (Fig. 5). In an effort to identify these

compounds, selected fractions have been analyzed by GCMS which revealed at least seven homologousseries of compounds with major fragment ions at m/z 56, 57, 68, 70, 82, 84, and 92 (Fig. 6). The precise

structures for each of these compounds is still the subject of an on-going investigation. Homologousseries that have been identified to date however, include methylbranched alkanes (m/z 57),alkylcyclopentanes (m/z 68), alkylcyclohexanes (m/z 82), and alkylbenzenes (m/z 92), and are discussedin more detail by HSIEH (1999) and HSIEH et al. (2000). More recently two additional series of methyl-

branched alkanes have been identified by comparison of retention times and mass spectra for similarcompounds present in microbial mats from Abu Dhabi.

The homologous series of alkylcyclopentanes extending beyond n-C40 in crude oils have predominancepatterns that can be associated with source environments as observed by CARLSON et al. (1993), andWAVREK and DAHDAH (1995). Predominance patterns of alkylcyclopentanes between C40 and C46

were observed to be most consistent in relation to depositional environments, whereas patterns aboveC46were sometimes unclear or changed to an opposite pattern (HSIEH, 1999; HSIEH and PHILP, 2001).Oils demonstrating a high even/odd predominance pattern were found to be associated with saline

lacustrine environments (Fig. 7a); freshwater lacustrine oils were characterized by a low even/odd to noclear predominance pattern (Fig. 7b); and marine oils had distinct odd/even predominance patterns (Fig.7c). These compounds along with the other complex mixtures of methylbranched- and alkylcycloalkanes

(>C40) have the potential to be used as supplemental tools in biomarker studies.

Quantitative and qualitative differences are not necessarily restricted to samples coming from differentgeographical areas or source materials. Wax composition can be highly variable in oils as observed in

Fig. 8a and b, illustrating wax fractions from two oils collected from the same formation, equivalent depthsof production, but different well locations. The oil in Fig. 8b contains a bimodal distribution ofhydrocarbons in the range C20-C35and C40-C60; whereas the oil in Fig. 8a is dominated by hydrocarbons

in the C20-C45 range. Such a variation in wax distribution may be related to temperature gradients alongthe migration pathway, with the oil located closer to the source (Fig. 8b) having a higher microcrystallinewax content. As indicated these chromatograms are obtained from the wax concentrates since in many

oils, the hydrocarbons above n-C35 are present in relatively low concentrations (~2%) and need to beconcentrated prior to analysis. In another study published some years ago, HEATH et al. (1998) noted thestability of these HMWHCs towards biodegradation. As an extension to that observation it should be

noted, heavily biodegraded oils may indeed contain trace amounts of these HMWHCs which cannot beseen in the whole oil GC but become evident upon isolation of the wax fraction as illustrated for a heavilybiodegraded oil in Fig. 9a and b.

The alkylcyclopentanes predominate in the HMW region of some oils and are suspected to be thepredominant series in cases where precipitation has already begun (HSIEH and PHILP, 2001), as shown

in Fig. 10 which illustrates an oil where the n-alkanes predominate over the alkylcyclopentanes in theHMW region. When wax precipitation is induced, it is observed that the n-alkanes are preferentiallyprecipitated while the alkylcyclopentanes in solution are enhanced. N-Alkanes have higher melting points

than iso-alkanes and lower melting points than cycloalkanes. But, when we add a long alkyl- side chain

to the cycloalkane, the melting point will become lower than the n-alkanes due to steric interference. Inthis case, it is reasonable that we observe the n-alkanes (>C40) to precipitate at higher temperatures than

the alkylcyclopentanes.

4. SUMMARY

Waxes are common to most oils regardless of the depositional environment of original source materialsand have been observed in oils sourced from marine, freshwater lacustrine, and saline lacustrine

environments. A method is described which permits the qualitative and quantitative separation of waxesand asphaltenes from crude oils. The quantity and nature of waxes vary from one oil to another, including


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oils produced from different wells of the same reservoir. HTGC and GCMS analyses have revealed thepresence of complex series of compounds comprised of long-chain alkylbenzenes, methylbranched

alkanes, and alkylcycloalkanes. These compounds are very resistant to biodegradation and are presentin significant amounts, but have yet to be utilized to their full potential.

While we do not know the exact structures or origins of wax compounds (>C40), it is apparent that theyare present in most crude oils regardless of source environments, they have the potential to be useful

tools for biomarker studies, and they will continue to hinder oil production until we gain a betterunderstanding of these compounds. Further improvements in extraction techniques for HMWHCs insource rocks will result in better oil-source rock correlations of high-wax oils, and also give greaterinsights into the origin of HMWHCs in crude oils.

5. REFERENCES

AJIENKA, J. A., IKOKU, C. U., 1990. Waxy crude oil handling in Nigeria: practices, problems, andprospects. Energy Sources, 12, 463-478.

BURGER, E. D., PERKINS, T. K., STRIEGLER, J. H., 1981. Studies of wax deposition in Trans AlaskaPipeline. J. Petrol. Tech. , 33, 1076-1086.CARLSON, R. M. K., TEERMAN, S. C., MOLDOWAN, J. M. JACOBSON, S. R. CHAN, E. I.,

DORROUGH, K. S., SEETOO, W. C., MERTANI, B., 1993. High temperature gas chromatography ofhigh-wax oils. Indonesian Petroleum Association, 22

nd Annual Convention Proceedings , Jakarta,

Indonesia, 483-507.

DEMBICKI, H. J., MEINSCHEIN, W. G., HATTIN, D. E., 1976. Possible ecological and environmentalsignificance of the predominance of even-carbon number C20-C30 n-alkanes. Geochim. et Cosmochim.

Acta, 40, 203-208.ESCOBEDO, J., MANSOORI, G. A., 1992. Heavy organic deposition and plugging of wells (analysis of

Mexicos experience). Paper SPE 23696 -Proceedings of the II LAPEC, Richardson, TX.,349-362.GARCIA, M. C., 2000. Crude oil wax crystallization. The effect of heavy n-paraffins and flocculatedasphaltenes. Energy and Fuels, 14, 1043-1048.

GARCIA, M. C., CARBOGNANI, L., OREG, M., URBINA, A., 2000. The influence of alkane class-typeson crude oil wax crystallization and inhibitors efficiency. J. Petrol. Sci. and Engineering, 25, 99-105.GELIN, F., VOLKMAN, J. K., LARGEAU, C., DERENNE, S., SINNINGHE DAMSTE, J. S., DE LEEUW, J.

W., 1999. Distribution of aliphatic, nonhydrolyzable biopolymers in marine microalgae. Org. Geochem.,30, 147-159.HEATH, D. J., LEWIS, C. A.,ROWLAND, S. J., 1997. The use of high temperature gas chromatography

to study the boidegradation of high molecular weight hydrocarbons. Org. Geochem., 26, 769-786.HEDBERG, H. D., 1968. Significance of high-wax oils with respect to genesis of petroleum. AAPGBulletin, 52, 736-750.

HOLDER, G. A., WINKLER, J., 1965. Wax crystallization from distillate fuels, parts 1, 2, and 3. J. Inst.Petrol., 51, 228-252.HSIEH, M., PHILP, R. P., 2001. Ubiquitous occurrence of high molecular weight hydrocarbons in crude

oils. Org. Geochem., 32, 955-966.HSIEH, M., PHILP, R. P., DEL RIO, J. C., 2000. Characterization of high molecular weight biomarkers incrude oils. Org. Geochem., 31, 1581-1588.

HSIEH, M., 1999. Characterization of waxes in high pour-point crude oils. M.S. Thesis, University of

Oklahoma, 113p.KENIG, F., SINNINGHE DAMSTE, J. S., KOCK-VAN DALEN, A. C., RIJPSTRA, W. I. C., HUC, A. Y., DE

LEEUW, J. W., 1995. Occurrence and origin of mono-, di-, and trimethylalkanes in modern and Holocenecyanobacterial mats from Abu Dhabi, United Arab Emirates. Geochim. Cosmochim. Acta. , 59, 2999-3015.KINGHORN, R. R. F., 1983. An introduction to the physics and chemistry of petroleum. John Wiley &

Sons Ltd., Chichester, 420p.KISSIN, Y. V., 1990. Catagenesis of light cycloalkanes in petroleum. Org. Geochem., 15, 575-594.LEONTARITIS, K. J., 1996. Offshore asphaltene and wax deposition: problems/solutions. World Oil, 217,

57-63.LIAEEN-JENSENN, S., 1990. Marine carotenoids-selected topics. New J. Chem., 14, 747-759.LIPSKY, S. R., DUFFY, M. L., 1986a. High temperature gas chromatography: the development of new

aluminium clad flexible fused silica glass capillary columns: Part I. J. High Res. Chromatog. , 9, 376-381.


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LIPSKY, S.R., DUFFY, M. L., 1986a. High temperature gas chromatography: the development of newaluminium clad flexible fused silica glass capillary columns: Part I. J. High Res. Chromatog. , 9, 725-730.

MUELLER, E., PHILP, R. P., 1998. Extraction of high molecular weight hydrocarbons from source rocks-An exaple from the Green River Formation, Uinta Basin, Utah. Org. Geochem., 28, 625-631.MOLDOWAN, J. M., SEIFERT, W. K., GALLEGOS, E. J., 1985. Relationship between petroleum

composition and depositional environment.AAPG Bulletin, 69, 1255-1268.NELSON, D. R., BLOMQUIST, G. J., 1995. Insect waxes. In: R. J. Hamilton (ed.) Waxes: chemistry,

molecular biology and functions.The Oily Press, Scotland, 1-90.PHILP, R. P., 1994. High temperature gas chromatography for the analysis of fossil fuels: A review. J.High Res. Chrom., 17, 398-406.PHILP, R. P., BISHOP, A. N., 1995. Exploration and reservoir geochemistry: Concepts, applications and

results. In: Proceedings of PETROTECH-95, New Delhi, India, January 1995., 57-77.PHILP, R. P., BISHOP, A. N., DEL RIO, J. C., ALLEN, J., 1995. Characterization of high molecularweight hydrocarbons (>C40) in oils and reservoir rocks. In: The Geochemistry of Reservoir Rocks, (Eds.

J.M. Cubitt and W.A. England) Geological Society Special Publication No. 86, London. 71-85.DEL RIO, J. C., PHILP, R. P., 1992a. Nature and Geochemistry of High Molecular Weight Hydrocarbons(Above C40) in Oils and Solid Bitumens. Org. Geochem. 18, 541-553.

DEL RIO, J. C., PHILP, R. P., 1992b. High Molecular Weight Hydrocarbons: A New Frontier in OrganicGeochemistry. Trends in Anal. Chem., 11, 187-193.TEGELAAR, E. W., MATTHEZING, R. M., JANSEN, J. B. H., and HORSFIELD, B., DE LEEUW, J. W.,

1989. Possible origin of n-alkanes in high-wax crude oils. Nature, 342, 529-531.THANH, N. X., HSIEH, M., PHILP, R. P., 1999. Waxes and asphaltenes in crude oils. Org. Geochem., 30,119-132.

TISSOT, B. P., WELTE, D. H., 1984. Petroleum Formation and Occurrence. New York, Springer-Verlag,699p.TUTTLE, R. N., 1983. High pour-point and asphaltic crude oils and condensates. J. Petrol. Tech. , 35,1192-1197.

TRINDADE, L. A. F., PHILP, R. P., MIZUSAKI, A. M. P., DOS SANTOS, R. L. A., TCHOUPAROVA, E.,SIAMAK DJAFARIAN, M., 1996. Geochemical characterization of waxy oils from the Dom Joao oil field,Reconcavo Basin, Brazil. In: Proceedings of the 5th Latin American Organic Geochemistry Congress,

Cancun, Mexico, October 1996, 281-283.WAVREK, D. A., DAHDAH, N. F., 1995. Characterization of high molecular weight compounds Implications for advanced-recovery technologies. SPE 28965, 207-210.


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Fig.1. Proposed scheme for the qualitative and quantitative separation of asphaltenes, micro-, and

macrocrystallinewaxes. The numbers of each important step are given and these are referred to in thetext.

CRUDE OIL (1g)

Dissolved in 10ml hot iso-octane

1. ALUMINA ADSORPTION

2. FIRST SOXHLETEXTRACTION

with iso-octane, 48hrs

ISO-OCTANE EXTRACT ADSORBED MATERIAL

7. SOXHLET EXTRACTION

with CHCl3:CH3OH (95:5, v/v),

at least 6hrs

CONCENTRATE

3. WAX PRECIPITATIONACETONE, -21

OC, at least

2hrs

ELUATE ADSORBED

MATERIAL

CONCENTRATE

PRECIPITATE

(TOTAL WAX)

SOLUBLES

4. n-PENTANE, -21 Cwith concentration of

2mg/ml

solution stands overnight

8. PENTANE

PRECIPITATION

5. PRECIPITATE

(MICROWAXES, >C 40)

6. SOLUBLES

(MACROWAXES)

ASPHALTENES RESINS

STIR &CENTRIFUGE

with cold pentane


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FIG.2a

15

20

30

40 50 60

4050 60

FIG.2b

0 12 24 36 48 60 72 84 96 108 120Minutes

FIG.2c

Fig. 2a. HTGC chromatogram of a crude oil from the Uinta Basin. GC conditions are described in the textand this oil had lost the light ends through evaporation. However for the purposes of this study that wasnot a major problem.

Fig. 2b. HTGC chromatogram of the asphaltene precipitate isolated from the crude oil used for Fig. 2aand isolated by the classical pentane precipitation method.Fig. 2c. HTGC chromatogram of the asphaltene fraction isolated from the same oil using the procedure

described in this paper. Note the complete absence of any wax components in this sample illustrating thequantitative separation of the wax from the asphaltene.


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0 12 24 36 48 60 72 84 96 108 12 Minutes

C5- INSOLUBLEMICROCRYSTALLINEWAXES

C5- SOLUBLEWAXES

20

30

4050

ACETONE WAXES50

40

50

60

40

60

40

45

FIG.3a

Fig.3a. HTGC chromatogram of the total wax fraction isolated using the procedure described in thispaper. This corresponds to the total wax isolated at step 3 of the procedure shown in Fig. 1. Fig. 3b and3c respectively show the chromatograms for the macro- and micro-crystalline waxes recovered from

steps 5 and 6 shown in Fig. 1.


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Fig. 4. Wax components are not simply restricted to oils sourced from any one type of environment orsource material, and have been observed in oils sourced from marine, freshwater lacustrine, and salinelacustrine environments as illustrated here in chromatograms 4a-c respectively.


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Fig. 5. An expanded region of the higher molecular weight compounds clearly show the presence ofseveral homologous series of compounds, some of which have been identified, some of which remainunknown.

E+05

2.433

25:00 26:40 28:20 30:00 31:40

10

20

C37H74

C37H68

C39H80

C36H72

n-C38 n-C39

C36H72

C38H78

C35H70

C38H70

C40H82

C37H74

C37H74

C38H76

C39H78

C39H78

C40H80

C38H76

C39H78

C40H80

Retention time (min)

C38H76

alkylcyclopentane

alkylcyclohexane

methylbranched alkane

alkylbenzene


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E+07

4.750

E+04

9.132

E+05

4.179

E+05

8.427

E+06

1.085

E+05

7.416

E+06

3.997

E+06

1.076

23:20 26:40 30:00 33:20

20

50

100

10

50

10

20

20

10

m/z:92

m/z:84

m/z:82

m/z:70

m/z:68

m/z:57

m/z:56

n-C36 n-C37 n-C38 n-C39n-C40

C34H62 C35H64 C36H66 C37H68 C38H70

C35H70 C36H72

C36H72C37H74

C33H66 C34H68

C37H74 C38H76

C36H74 C37H76

C34H68 C35H70 C36H72C37H74 C38H76

C38H78C39H80 C40H82

C39H7

8 C40H80 C41H82

C35H70C36H7

2C37H74

C38H76

C38H76 C39H78 C40H80 C41H82

C37H74 C38H76C39H78

C40H80

Fig. 6. In an effort to identify these compounds, selected fractions have been analyzed by GCMSwhich revealed at least seven homologous series of compounds with major fragment ions at m/z 56,57, 68, 70, 82, 84, and 92 as shown in these single ion chromatograms.


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Fig. 7. Oils demonstrating a high even/odd predominance pattern were found to be associatedwith saline lacustrine environments (Fig. 7a); freshwater lacustrine oils were characterized bya low even/odd to no clear predominance pattern (Fig. 7b); and marine oils had distinct

odd/even predominance patterns (Fig. 7c).


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Fig. 8a and b. Wax composition can be highly variable in oils, as illustrated by the wax fractions isolatedfrom two oils collected from the same formation, equivalent depths of production, at different welllocations.

Fig. 9. The HMWHCs are relatively resistant to biodegradation as illustrated in this example of a heavilybiodegraded oil (Fig. 9a). Isolation and concentration procedures led to the isolation of the wax fractionshown in Fig. 9b.

0 10 2

030 40 50 60 70 80 90 100

Pr

40Ph


(a) Biodegraded Oil

0 10 20 30 40 50 60 70 80 90 100

30

25

20

40

n-C40

44a

48a


(b) Wax Fraction

0 10 20 30 40 50 60 70 80 90 100

Minutes

(b) Anadarko Basin

30

35

25

20

40

45

45

50

Oil #2 - Wax Fraction

Depths: 10530ft - 10546ft

0 10 20 30 40 50 60 70 80 90 100

Minutes

(a) Anadarko Basin

40

45

50

55

6065

30

25

20

Oil #1 - Wax Fraction

Depths: 10160ft - 10210ft

(a) Anadarko Basin

Oil #1 Wax Fraction

Depth: 10160-10210ft

(b) Anadarko Basin

Oil #2 Wax Fraction

Depth: 10530-10546ft

Retention time min



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Fig. 10. The alkylcyclopentanes predominate in the HMW region of some oils and are suspected to be the

predominant series where precipitation has already begun as illustrated by this oil where the n-alkanespredominate over the alkylcyclopentanes in the HMW region indicating precipitation has been initiated.

0 12 24 36 48 60 72 84 96 108 120Minutes

(a) Original Whole Oil

*

40 50 60

30

25

20

15

40 5060

0 12 24 36 48 60 72 84 96 108 120Minutes

(b) Residual Oil

*

30

25

20

15

40

40

0 12 24 36 48 60 72 84 96 108 120Minutes

(c) Precipitated Fraction

30

40

45

50

55

60

65

(c) Precipitated Fraction

(a) Original Whole Oil

(b) Residual Oil

alkylcyclopentanes

alkylcyclopentanes




**

*C36D74

separacion de parafinas y asfaltenos.pdf

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