Microbial Desulfurization

1. Microbial Desulfurization CHBE446: Process Economics and Design 2 6 February 2014 Heather Cook Savannah Green Dave Weglein Mike Wellen

2. Outline • Introduction & History • Mechanisms • Current Uses in Industry • Major Challenges & Advantages • Current Research

3. Introduction: What is Microbial Desulfurization? • Also known as Biodesulfurization (BDS) • Biological desulfurization process where microbial catalysts are used to oxidize sulfur in crude oils

4. 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)

5. New Regulations • Sulfur content in crude oil ranges from 0.03% - 7.89% • Many crude oils are increasing in sulfur content • Clean Air Act Amendments introduced by EPA in 1990 to restrict sulfur concentrations in fuels • Reduce annual SO2 emissions

6. 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

7. Mechanisms

8. 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

9. Anaerobic pathway • Anaerobic strain can degrade some of DBT • Products: biphenyl & H2S • Makes this a selective pathway • Advantage: • Oxidation of hydrocarbons to undesired compounds is minimal • Disadvantage: • Reduced caloric content in fuel • Specific activity for most isolated strains are insignificant for alkylated DBTs

10. 4S Pathway • Carbon-sulfur bond selectively cleaved

11. Bacteria Used

12. 4S Pathway Enzymes • 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

13. DszC Enzyme • 45 kDa protein • Catalyzes DBT->DBTO->DBTO2 • Step uses oxygen, NADH, and FMNH2for activity

14. DszA Enzyme • 50 kDa protein • Transforms sulfone into sulfinate • Uses FMH2as co-substrate • Step requires oxygen and NADH as well • Oxygen from molecular oxygen

15. DszB Enzyme • 40 kDa protein • Final step in the reaction • Rate limiting step • Present in cells in smaller amount in cytoplasm

16. DszD Enzyme • Uses FMN as a substrate • Couples the oxidation of NADH to substrate oxidation • Produces FMNH2 to allow DszC and DszA to work

17. Currents Uses in Industry

18. Thiopaq • Biogas • 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

19. Benefits of System • 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

20. 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

21. Steps of Process • 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

22. 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

23. Ben & Jerry’s • Hellendoorn, Netherlands • Ice cream waste products converted into electricity • Desulfurized with Thiopaq • 40% of factory's energy requirements • Operational 2011

24. Cargill • Starch processing company • Sulfate rich water treated with anaerobic bioreactor

25. Lenzig Ag • Viscose Fiber Production • 2009 produced 568,600 tonnes • Produces range of secondary compounds • Some streams need to be discharged. • SULFATEQ system installed in 2002

26. McCain • 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.

27. Other Examples • WaterStromen • Hulshof Royal Dutch Tanneries • Weltec BioPowr GmbH • Tempec • Nine Dragons • Smurfit Kappa

28. Challenges, Advantages & Current Research

29. 5 Step Process • Production of active resting cells with high 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

30. Major Challenges • Biocatalyst activity improvement • Biocatalyst longevity improvement • Phase contact and separation • Process engineering research

31. Current Research • Reduction in biocatalyst activity associated with the generation of the end product (2-hydroxybiphenyl) • Increase of bacterial desulfurization rate through identification of certain genes • Overexpression of FMN reductase • Change in host strain for dsz genes

32. Advantages of BDS • Requires less energy and hydrogen • Operates at ambient temperature and pressure with high selectivity • Decreased energy costs • Low emissions • No generation of undesired products

33. Questions?

34. 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.