Syngas fermentation

Syngas fermentation, also known as synthesis gas fermentation, is a microbial process. In this process, a mixture of hydrogen, carbon monoxide, and carbon dioxide, known as syngas, is used as carbon and energy sources, and then converted into fuel and chemicals by microorganisms.[1]

The main products of syngas fermentation include ethanol, butanol, acetic acid, butyric acid, and methane.[2] Certain industrial processes, such as petroleum refining, steel milling, and methods for producing carbon black, coke, ammonia, and methanol, discharge enormous amounts of waste gases containing mainly CO and H
2 into the atmosphere either directly or through combustion. Biocatalysts can be exploited to convert these waste gases to chemicals and fuels as, for example, ethanol.[3]

There are several microorganisms, which can produce fuels and chemicals by syngas utilization. These microorganisms are mostly known as acetogens including Clostridium ljungdahlii,[4] Clostridium autoethanogenum,[5] Eubacterium limosum,[6] Clostridium carboxidivorans P7,[7] Peptostreptococcus productus,[8] and Butyribacterium methylotrophicum.[9] Most use the Wood–Ljungdahl pathway.

Syngas fermentation process has advantages over a chemical process since it takes places at lower temperature and pressure, has higher reaction specificity, tolerates higher amounts of sulfur compounds, and does not require a specific ratio of CO to H
2.[2] On the other hand, syngas fermentation has limitations such as:

References
  1. Brown, Robert C. (2003). Biorenewable resources: engineering new products from agriculture. Ames, Iowa: Iowa State Press. ISBN 0-8138-2263-7.
  2. Worden, R.M., Bredwell, M.D., and Grethlein, A.J. (1997). Engineering issues in synthesis gas fermentations, Fuels and Chemicals from Biomass. Washington, DC: American Chemical Society, 321-335
  3. Abubackar, H.N.; Veiga, M. C.; Kennes, C. (2011). "Biological conversion of carbon monoxide: rich syngas or waste gases to bioethanol" (PDF). Biofuels, Bioproducts and Biorefining. 5 (1): 93–114. doi:10.1002/bbb.256.
  4. Klasson, K.T.; Ackerson, M. D.; Clausen, E. C.; Gaddy, J.L. (1992). "Bioconversion of synthesis gas into liquid or gaseous fuels". Enzyme and Microbial Technology. 14 (8): 602–608. doi:10.1016/0141-0229(92)90033-K.
  5. Abrini, J.; Naveau, H.; Nyns, E.J. (1994). "Clostridium autoethanogenum, sp. nov., an anaerobic bacterium that produces ethanol from carbon monoxide". Archives of Microbiology. 161 (4): 345–351. doi:10.1007/BF00303591.
  6. Chang, I. S.; Kim, B. H.; Lovitt, R. W.; Bang, J. S. (2001). "Effect of CO partial pressure on cell-recycled continuous CO fermentation by Eubacterium limosum KIST612". Process Biochemistry. 37 (4): 411–421. doi:10.1016/S0032-9592(01)00227-8.
  7. Ahmed, A; Lewis, R.S. (2007). "Fermentation of biomass generated syngas:Effect of nitric oxide". Biotechnology and Bioengineering. 97 (5): 1080–1086. doi:10.1002/bit.21305. PMID 17171719.
  8. Misoph, M.; Drake, H.L. (1996). "Effect of CO2 on the fermentation capacities of the acetogen Peptostreptococcus productus U-1". Journal of Bacteriology. 178 (11): 3140–3145. PMC 178064. PMID 8655492.
  9. Henstra, A.M.; Sipma, J.; Reinzma, A.; Stams, A.J.M. (2007). "Microbiology of synthesis gas fermentation for biofuel production". Current Opinion in Biotechnology. 18 (3): 200–206. doi:10.1016/j.copbio.2007.03.008. PMID 17399976.


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