oil bunkering
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Bunker Oil Biodesulfurization
⎯ A Feasibility Study
Presented by :Dr. Rong YAN
Institute of Environmental Science and Engineering
Nanyang Technological University, Singapore(email: ryan@ntu.edu.sg)
The 5th Asian Petroleum Technology SymposiumJakarta, Indonesia, January 23 to 25, 2007
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Background
• Singapore has a thriving maritime business, in particularbunker industry. The amount of bunker oil provided bySingapore as ship fuels is about 20 million tons annually,which is equivalent to S$ 6 billion per year.
• However, combustion of bunker oil has caused a significant
release of gaseous pollutants (SOx), leading to marine airpollution. In Singapore, the regulation of sulfur content inbunker fuels is 4.5% on weight basis.
• The new regulation with a stricter limit of 1.5% sulfur might beadopted by Singapore in future, which would cause a greatimpact on Singapore’s maritime business.
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• In 2006, the coming into force of Annex VI of the International MaritimeOrganization (IMO)'s MARPOL convention, as well as European Union(EU) Directive 2005/33/EC, has imposed a 1.5% sulfur cap on marinefuels used by ships in the Baltic Sea and on passenger vessels onregular services to EU community ports.
• In 2007, the 1.5% sulfur cap will be expanded to the second SulfurEmissions Control Area (SECA) for the North Sea and English Channel.
• Both the IMO and EU legalization are, however, subject to further
review in the near future, opening the possibility of further sulfurreductions. The Directive, for example, envisages a future extension ofthe sulfur limit to all EU waters, and also a stricter sulfur cap, possibly
just 0.5%.
Driving Force – New Cap
on Sulfur Contents
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Why Biodesulfurization?• Currently, hydrodesulfurization (HDS) is the most widely used
method in refineries to desulfurize crude oil.
• The HDS process requires high temperature and pressure, thus iscostly and consumes lots of energy. Moreover, HDS has not beenproven to remove the heterocyclic sulfur compounds likedibenzothiophene (DBT) and its derivatives efficiently.
• Limitations of the HDS technology can be overcome by BDS, ascertain microorganisms could use organosulfur in oil as their soleenergy source.
• Biodesulfurization (BDS) of bunker oil is expected to be a moreviable option, as it is more energy efficient, and environmentallyand economically favorable.
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Various types of S-containing organic
compounds incrude oils
(Adapted from Shennan 1996, J.Chem. Tech. Biotechnol. )
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However, DBT and methyl-substituted DBT (4-MDBT and 4,6-DMDBT) wereparticularly refractory to HDS and were not converted even at 390 ºC.
--- Prof. Atsushi Ishihara, Tokyo Univ. of Agriculture and Technology, presentation at the
4 th JPEC Asian Petroleum Technology Symposium, Jan. 2006, Cambodia
Bunker oil(residue) mostly
contains heavymolecules oforgano-S witharomatic rings
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Claus process: 2H2S + SO2→ 3S(s) + 2H2O
HDS process:
• It requires generally high temperature (200-425°C) and pressure (150-250
psi), and consumes hydrogen — extremely high energy consumption.• It requires novel catalysts: (a) new support, (b) noble metal based catalyst,(c) zeolites, (d) new compositions — high cost.
• It has not proven yet to desulfurize DBT and its derivatives — no efficiency.
HDS and I ts Limitations
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Alternative Option:
Biocatalysts,Biodesulfurization
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Objectives of Our Study
• Feasibility of bunker oil biodesulfurization — to
biodegrade the organosulfur species present in bunkeroil using suitable microorganisms (1st phase)
• To develop an advanced biodesulfurization process,
aiming to demonstrate the biotechnology of improvingbunker oil quality in the near future (2nd phase)
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Scope of 1st Phase Study
• I - Literature review on bunker oil, sulfur distribution inbunker oil, and the key issues related to
biodesulfurization of oil
• II - Biodesulfurization of selected model sulfur species
• III - Biodegradation of organic sulfur species present inbunker oil
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I . Literature ReviewSulfur Biochemistry of Bunker Oil
• Bunker oil contains heterocyclic sulfur compounds likethiophenes (TH), benzothiophenes (BTH), and mostpossibly dibenzothiophenes (DBT) and its derivatives.
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Sulfur Biodegradation Pathways
• Oxidative C-C cleavage
• Oxidative C-S cleavage (4S pathway): non destructive BDS
DBT degradation by R. erythropolis IGTS8Source: Vazquez-Duhalt, 2002
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Key Issues in Sulfur Biodegradation
(1)Selection of seed – to be capable to biodesulfurize bunker oil atan improved efficiency and also with no disturbance to theorganic fraction (i.e., heating value); mixed culture, isolation andbioaugmentation
(2)Model sulfur species – to represent bunker oil
(3)Bioreactor / Culturing media(4)Temperature (bioactivity of bacteria / physical properties of
water/oil system)
(5)Mixing ratio of bunker oil and water / Emulsion product(6)Separation of biomass and oil
(7)Others (working time, mass transfer rate, kinetic behavior etc.)
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Challenges in Bunker Oil Sulfur
Biodegradation
(1)Biodesulfurization of heavy oil (including bunker oil) has so
far rarely been reported, although quite some researcheson crude oil and diesel biodesulfurization have beenconducted.
(2)There is limited information on the dominant organosulfur
species of bunker oils.
(3)High viscosity of bunker oil could be a major concern inwater/oil bio-systems.
(4)Efficient separation of the three phases (biomass, oil andwater) is essential but very challenging.
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II . Biodesulfurization of ModelSulfur Species
• As the first step of our overall experiment plan, biodesulfurization of threeselected model sulfur species (TH, BTH, and DBT) were carried out, to get thesuitable bacteria and familiar with essential analytical approaches.
• Bacterial seed: oily sludge
• Culture medium: sulfur-freebasal salt medium consistingof (in g L-1) KH2PO4 2.44,Na2HPO4 5.57, NH4Cl 2.00,MgCl2·6H2O 0.36, FeCl3·6H2O0.001, MnCl2·4H2O 0.004 andglycerol 1.84. The final
medium pH was 7.0• Instrument and identification:GCMS, IC, Plate counting,biomass and sulfur content,and TOC analyzer
Batch Reactor
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Dibenzothiophene
0
0.05
0.1
0.15
0.2
0.25
0.3
0 2 4 6 8
Operation Time (d)
C o n c e n t r a t i o n
( m M )
seed
control
Bacterial CFUnumber increasing
Change of DBT
conc. in seed andcontrol reactors
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GCMS Identification of BiodesulfurizationProducts
ControlDay 0
3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.0011.0012.0013.0014.0015.00
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Abundance
TIC: 021006S.D
Seed
Day 0
SeedDay 6
In seed reactor, DBT-sulfone andhydroxybiphenyl (HBP) were found
with relatively high abundance at12.466 min and 9.036 min. No DBT.
ControlDay 6
DBT
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DBT and the intermediates
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operation time (d)
G
C
a r e a c o u n t
dibenzothiophene sulfone
p-hydroxybiphenyl
dibenzothiophene
Confirmation of 4S Pathway withidentifying DBT Sulfone and HBP
The bacteria within the mixed culture cancarry out the non-destructive BDS !
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Sulfur Mass Balance
Five probable sinks of sulfur:
(1) non-degraded thiophenic compounds
(2) organic metabolites (i.e., DBT sulfone, DBT sultine etc.)
(3) soluble inorganic ions (i.e., sulfite, sulfate and thiosulfate)(4) cellular material in bacteria
(5) surrounding atmosphere
Biomass Concentration
3
3.2
3.4
3.6
3.8
4
4.2
4.4
4.6
0 1 2 3 4 5 6 7 8
Operation Time (day)
B i o m a s s C o n c ( g / L )
seed
Total sulfur content (mg) in biomass= Sulfur content per unit suspended
solids (%)× Suspended solidsconcentration in the sample (g L-1)× Operation volume of the samplereactor (500 mL)× 0.001 (L mL-1)
× 1000 (mg g-1)
Most likelysulfur is
enriched in
biomass
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Enrichment of Bacteria & Bioreactor Setup
Bun k e r o i l t o r ep lace m ode l
su l fu r species
Enrichment reactors –
cultivation of desulfurizers
• Culture medium• Organosulfur solution
• Oil sludge• Sequential batch process• 1 L Erlenmeyer flask - 2 Nos(Enrichment reactor + Control)
• Head space aeration• Bioreactor - 50 mL centrifuge tube• Bunker Oil - 2 types:Bunker Oil #1 and Bunker Oil #2
Bioreactors
III . Bunker Oil Biodesulfurization
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Experimental Approach
Schematic of experimental approach with bunker oil
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Critical ParametersAdjusted(1) Volumetric ratio of bunker
oil - culture medium: 1:3 ;1:10
(2) Bunker Oil types: Bunker
Oil#1 & Bunker Oil#2
(3) Biodegradation time [hrs]:0, 48, 72 & 96
Analytical Methods• Bunker Oil: GC-MS (volatile
organic sulfur); Elementalanalysis (total organic
combustible sulfur)• Aqueous medium: ICP-
OES (total dissolved sulfur)
• Biomass: Elementalanalysis (total organiccombustible sulfur)
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Identification of Organosulfurs in Bunker Oil
Compound Retention time[min]
Main MS Peak
Methyl BTH 7.733 147,74,45
Dimethyl BTH 8.208 162,28,147
Trimethyl BTH 8.616 176,161,115
Diethyl BTH 8.933 175,190,147,160
DBT 9.7 184,139,152
Methyl DBT 10.085, 10.172 198,99,165
Dimethyl DBT 10.513~10.822 212,105,197
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Abundance
TIC: D0#1.D Bunker Oil #1
0 hr
Abundance
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2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00
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Ion 184.00 (183.70 to 184.30): D0#1.D
20 40 60 80 100 120 140 160 180 200 220 240 260 2800
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Abundance
Scan 2404 (9.680 min): D0#1.D184
57
71
8543
139
97 152113 19616512728 218
246230 260 282
Extracted IonChromatogram for
DBT in Bunker
Oil#1 (0 hr)
Mass Spectrum of
DBT in BunkerOil#1 (0 hr)
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Characterization of Sulfur in Bunker oil
Comparison of intensities of organosulfurcompounds in two Bunker Oils
• Bunker oil #1has higher Scontent
• Bunker oil #2is heavier andhas a higherviscosity
B k Oil Bi d lf i ti
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Sulfur
decreased 21.4%Sulfur decreased
49.3%
Bunker Oil Biodesulfurization – First Trial
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• However, C/S ratio
decreased, i.e., C-Ccleavage happened
• Destructive BDS
B k Oil #1 ( t 1 3 V l R ti )
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Bunker Oil #1 (at 1:3 Volume Ratio)
Change in intensity of organosulfur species over timecourse for Bunker Oil #1 (Vol. ratio: Oil/Water 1:3)
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Bunker Oil #1 (at 1:10 Volume Ratio)
Change in intensity of organosulfur species over timecourse for Bunker Oil #1 (Vol. ratio: Oil/Water 1:10)
Ratio 1:3 is better than 1:10 for Bunker Oil #1
B k Oil #2 ( t 1 3 V l R ti )
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Bunker Oil #2 (at 1:3 Volume Ratio)
Change in intensity of organosulfur species over timecourse for Bunker Oil #2 (Vol. ratio: Oil/Water 1:3)
B k il #2 ( t 1 10 V l R ti )
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Bunker oil #2 (at 1:10 Volume Ratio)
Change in intensity of organosulfur species over timecourse for Bunker Oil #2 (Vol. ratio: Oil/Water 1:10)
Ratio 1:10 is better than 1:3 for Bunker Oil #2
Elemental Analysis for Total Sulfur:
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Elemental Analysis for Total Sulfur:Bunker Oil #1
Sulfur Content
Ratio 1:3 is better than 1:10for Bunker Oil #1
Carbon/Sulfur
Elemental Analysis for Total Sulfur:
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Elemental Analysis for Total Sulfur:Bunker Oil #2
Carbon/Sulfur
Sulfur Content
Ratio 1:10 is better than 1:3
for Bunker Oil #2
Elemental Analysis: Sulfur in Biomass
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Elemental Analysis: Sulfur in Biomass
Sulfur content in biomass when degradingbunker Oil #2 with oil/water ratio of 1:10
(1) Cells break up duringseparation?
(2) Oil contamination onbiomass due toinsufficient separation?
Key Challenge —
the separation of theindividual phasesnamely bunker oil,
biomass and aqueousmedium
Poor sulfur massbalance observed
Aqueous medium was analyzed for Total Dissolved Sulfur (TDS) usingICP-OES and no dissolved sulfur species were detected.
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Conclusions
• Bacteria suitable for degrading DBT and their derivatives weresuccessfully cultured and enriched from the study using modelsulfur species. Essential analytical approaches were also
established and intermediates of DBT biodegradation wereidentified to confirm the 4S pathway.
• Organosulfur compounds in bunker oil like BTH, DBT and their
derivatives were identified using GC-MS technique.
• Bunker oil biodesulfurization was confirmed highly feasible, the
reduction of total sulfur content reached 49.3% in 1st
trial ofbunker oil biodesulfurization.
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Conclusions (cont’d)
• It is also evidenced that the biodesulfurization of bunker oil by bacteriaare highly dependent on several parameters like ratio of bunker oil/culturemedium, degradation time, and type of bunker oil.
• Bacteria desulfurized bunker oil #1 more efficiently when the volumetricoil/water ratio was maintained as 1:3 whilst bacteria desulfurized bunkeroil #2 more efficiently when the ratio was maintained as 1:10, on the basisof elemental and GC-MS analysis.
• In bunker oil trials, the C/S ratio decreased over time for both fuel typesand oil/water ratios, indicating possibly a destructive BDS. Further studieson bacterial enrichments and degradation pathways are recommended.
• Sulfur balance was not achieved due to most likely inefficient separationof biomass and bunker oil. Further investigation is needed to achieveeffective separation.
Recommendations
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Recommendations
A further investigation (i.e., the 2nd phase study) is highlyrecommended.
This further study will contain:• New batch studies to further explore bunker oil BDS and to solve the
problems encountered in Phase I.
• Investigation of BDS in a larger scale reactor operated in a semi-continuousor continuous mode. Optimization of process parameters such as
temperature, mixing ratio of oil and water, separation of biomass and oil,working time, kinetic behavior, and others.
• A full investigation on the microbial ecology and functional diversity within themixed culture, the isolation and characterization of bacteria, metabolicpathways, increasing the abundance of bacteria capable of non-destructive
BDS in the mixed culture.• A pilot scale demonstration work, targeting at a real industrial application of
bunker oil biodesulfurization.
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THANK YOU… .
And any questions?
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