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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: [email protected])

The 5th Asian Petroleum Technology SymposiumJakarta, Indonesia, January 23 to 25, 2007



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.



• 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



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.



Various types of S-containing organic

compounds incrude oils

(Adapted from Shennan 1996, J.Chem. Tech. Biotechnol. )



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



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



Alternative Option:

Biocatalysts,Biodesulfurization



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)



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



I . Literature ReviewSulfur Biochemistry of Bunker Oil

• Bunker oil contains heterocyclic sulfur compounds likethiophenes (TH), benzothiophenes (BTH), and mostpossibly dibenzothiophenes (DBT) and its derivatives.



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



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.)



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.



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



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



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

500000

1000000

1500000

2000000

2500000

3000000

3500000

4000000

4500000

Time-->

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



DBT and the intermediates

0

500000

1000000

1500000

2000000

2500000

3000000

3500000

4000000

4500000

0 2 4 6 8

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 !



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



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



Experimental Approach

Schematic of experimental approach with bunker oil



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)



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

2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

200000

400000

600000

800000

1000000

1200000

1400000

1600000

1800000

Time-->

Abundance

TIC: D0#1.D Bunker Oil #1

0 hr

Abundance



2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

55000

60000

65000

70000

75000

80000

85000

90000

Time-->

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

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

55000

60000

65000

m/z-->

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)



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



Sulfur

decreased 21.4%Sulfur decreased

49.3%

Bunker Oil Biodesulfurization – First Trial



• However, C/S ratio

decreased, i.e., C-Ccleavage happened

• Destructive BDS

B k Oil #1 ( t 1 3 V l R ti )



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)





Ratio 1:3 is better than 1:10 for Bunker Oil #1

B k Oil #2 ( t 1 3 V l R ti )





B k il #2 ( t 1 10 V l R ti )



Bunker oil #2 (at 1:10 Volume Ratio)


Ratio 1:10 is better than 1:3 for Bunker Oil #2

Elemental Analysis for Total Sulfur:



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:



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



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.



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.



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



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.



THANK YOU… .

And any questions?

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