Ethanol Production From Synthesis Gas

Ethanol is the only renewable liquid fuel made in commercial quantities and supplies about 1% of the gasoline type transport fuels used in the USA. Approximately 95% of the commercial production of ethanol in the USA is currently by direct fermentation of com-sourced carbohydrates. However, fermentation of synthesis gas has the advantage over direct fermentation of sugars from cellulose and the hemicelluloses in that all wood components, including lignin and bark, are suitable feedstocks. 

The first step in the process is gasification of wood followed by conditioning and cleaning of the synthesis gas to give a mixture rich in CO and H2. The synthesis gas is sparged into a broth-filled tank fermentor where bacteria Clostridium ljungdahlii, for example) convert CO and CO2 to ethanol via the following two reactions  

The resulting fermentation broth is quite dilute, 2% ethanol or less. The ethanol can be recovered from the broth using distillation schemes developed for the existing com to ethanol manufacturing process (Spath and Dayton, 2003). 

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Kundiyana, D.K., et al., 2011. Effect of temperature, pH and buffer presence on ethanol production from synthesis gas by Clostridium ragsdaleC. Bioresource Technology 102 (10), 5794-5799. 

Saxena, J., Tanner, R., 2011. Effect of trace metals on ethanol production from synthesis gas by the ethanologenic acetogen, Clostridium ragsdalei. Journal of Industrial Microbiology Biotechnology 38 (4), 513—521. 

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