Microbial Desulfurization
CHBE446: Process Economics and Design 2
6 February 2014
Heather Cook
Savannah Green
Dave Weglein
Mike Wellen
Outline
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Introduction & History
Mechanisms
Current Uses in Industry
Major Challenges & Advantages
Current Research
Introduction: What is
Microbial Desulfurization?
● Also known as Biodesulfurization (BDS)
● Biological desulfurization process where
microbial catalysts are used to oxidize sulfur
in crude oils
Introduction: Why is BDS
important?
● Combustion of sulfur compounds leads to
production of sulfur oxides
● High concentrations of sulfur oxides in the
atmosphere can lead to health issues such as
asthma, bronchial irritation, and lung cancer
● Ability to “desulfurize compounds that are
recalcitrant to the current standard
technology in the oil industry” (Abin-Fuentes,
et al)
New Regulations
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Sulfur content in crude oil ranges from
0.03% - 7.89%
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Many crude oils are increasing in sulfur content
Clean Air Act Amendments introduced by
EPA in 1990 to restrict sulfur concentrations
in fuels
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Reduce annual SO2 emissions
BDS Overview
● Increased interest over last 20 years
○ Desulfurizes wider range of compounds then
conventional hydrodesulfurization (HDS)
● Three pathways
○ Kodama (destructive)
○ Anaerobic (selective)
○ 4S (specific oxidative)
● 4S is the most popular/effective
Mechanisms
Kodama Pathway
● Sulfur not selectively
cleaved from
dibenzothiopene (DBT)
Carbon-carbon bonds
broken
Metabolize DBT’s &
convert to water soluble
compounds
Water soluble products
inhibits further microbial
growth & DBT oxidation
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Anaerobic pathway
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Anaerobic strain can degrade some of DBT
Products: biphenyl & H2S
o Makes this a selective pathway
Advantage:
o Oxidation of hydrocarbons to undesired compounds
is minimal
Disadvantage:
o Reduced caloric content in fuel
o Specific activity for most isolated strains are
insignificant for alkylated DBTs
4S Pathway
● Carbon-sulfur bond selectively cleaved
Bacteria Used
4S Pathway Enzymes
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Reaction is energy-intensive and needs
cellular metabolism
The 4S pathway involves sequential
oxidation of the sulfur part and cleaving of
the C–S bonds
Four main enzymes used in the 4S pathway
DszC Enzyme
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45 kDa protein
Catalyzes DBT->DBTO->DBTO2
Step uses oxygen, NADH, and FMNH2 for
activity
DszA Enzyme
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50 kDa protein
Transforms sulfone
into sulfinate
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Uses FMH2 as cosubstrate
Step requires
oxygen and NADH
as well
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Oxygen from
molecular oxygen
DszB Enzyme
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40 kDa protein
Final step in the reaction
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Rate limiting step
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Present in cells in smaller amount in cytoplasm
DszD Enzyme
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Uses FMN as a
substrate
Couples the
oxidation of NADH
to substrate
oxidation
Produces FMNH2 to
allow DszC and
DszA to work
Currents Uses in Industry
Thiopaq
• Biogas
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Vent air
Refinery Gas
Hydrogen Sulphide
120 Installations World-wide
Reduces to under 25 ppm
Fluctuating Gas Flows
Low maintenance
Ambient Pressures an Temperatures
• Produces Elemental Sulfur
Benefits of System
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Deep H2S removal and recovery as elemental S, extremely low
SO2 emissions are achieved
Special costly equipment such as burners and reboilers are not
required. The regeneration and sulphur recovery section always
operate at atmospheric pressure and ambient temperature
Reliability of a natural process coupled with the efficiency of
dedicated engineering
Simple process configuration- and control with stable operation
Broad and flexible operating range with short system start-up
times
Expensive chemicals such as those required for liquid redox
processes are not required. Only sodium hydroxide and nutrients
are needed
More Benefits
● Limited utility requirements
● Ease of operation. Produced biosulphur is hydrophilic and behaves like a
relatively stable suspension without clogging or other nuisances
● Environmentally friendly process based on naturally occurring bacteria
● Inherently safe operation:
○ no free H2S downstream absorber
○ ambient temperatures for the whole system (solution
temperatures of 25 – 40 °C)
○ bioreactor and sulphur recovery at atmospheric pressure.
● Produced biosulphur is the basis for a range of new agricultural
products designed to act as (ingredients for) liquid fertilizers and liquid
fungicides
Steps of Process
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Sulfide rich solution loaded to flash drum
Loaded to bioreactor
Lean solution returned to absorber
Lean solution returned to absorber
Elemental Sulfur seperated out
Bioreactor contents are recycled over settler
Concentrated slurry dewatered in centrifuge
Filtrate is cycled back
Small slipstream of clear solvent
Industrie Eerbek
• Netherlands treats water from three
neighboring paper mills
• Biogas used to produce electricity
• 1% to 25 ppm
• Thiopaq system was installed in 1993
Ben & Jerry’s
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Hellendoorn, Netherlands
Ice cream waste products converted into electricity
Desulfurized with Thiopaq
40% of factory's energy requirements
Operational 2011
Cargill
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Starch processing company
Sulfate rich water treated with anaerobic bioreactor
Lenzig Ag
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Viscose Fiber Production
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2009 produced 568,600 tonnes
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Produces range of secondary compounds
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Some streams need to be discharged.
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SULFATEQ system installed in 2002
McCain
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Potato processing company
Receives biogas from anaerobic water treatment and
solids digester
To prevent corrosion of gas engine, Thiopaq converts
hydrogen sulfide to elemental sulfur
Longer life for gas engine.
Other Examples
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WaterStromen
Hulshof Royal Dutch Tanneries
Weltec BioPowr GmbH
Tempec
Nine Dragons
Smurfit Kappa
Challenges, Advantages
& Current Research
5 Step Process
• Production of active resting cells with high
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specific activity
Preparation of biphasic system containing oil
fraction, aqueous phase and biocatalyst
BDS of wide range of sulfur compounds at
acceptable rate
Separation of desulfurized oil fraction, recovery
of biocatalyst and return to bioreactor
Efficient wastewater treatment
Major Challenges
• Biocatalyst activity improvement
• Biocatalyst longevity improvement
• Phase contact and separation
• Process engineering research
Current Research
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Reduction in biocatalyst activity associated
with the generation of the end product (2hydroxybiphenyl)
Increase of bacterial desulfurization rate
through identification of certain genes
Overexpression of FMN reductase
Change in host strain for dsz genes
Advantages of BDS
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Requires less energy and hydrogen
Operates at ambient temperature and
pressure with high selectivity
Decreased energy costs
Low emissions
No generation of undesired products
Questions?
References
Abin-Fuentes, A., M. E.-S. Mohamed, D. I. C. Wang, and K. L. J. Prather.
"Exploring the Mechanism of Biocatalyst Inhibition in Microbial
Desulfurization." Applied and Environmental Microbiology 79.24
(2013): 7807-817. Web. 6 Feb. 2014.
Mohebali, G., and A. S. Ball. "Biocatalytic Desulfurization (BDS) of
Petrodiesel Fuels."Microbiology 154.8 (2008): 2169-183. Web. 6 Feb.
2014.
Ohshiro, Takashi, and Yoshikazu Izumi. "Microbial Desulfurization of Organic
Sulfur Compounds in Petroleum." Bioscience, Biotechnology, and
Biochemistry 63.1 (1999): 1-9. Web. 6 Feb. 2014.
Paqell | THIOPAQ O&G - Biological Gas Desulpherisation and Sulphur
Recovery | Paqell."Paqell | THIOPAQ O&G - Biological Gas
Desulpherisation and Sulphur Recovery | Paqell. Paqell BV, n.d. Web
. 05 Feb. 2014.
Soleimani, M., Bassi, A., and Margaritis, A. 2007. Biodesulfurization of
refractory organic sulfur compounds in fossil fuels. Biotechnol. Adv.
25(6):570-96.