Submitted to: Bioresource Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/22/2007
Publication Date: 12/3/2007
Citation: Qureshi, N., Ezeji, T.C., Ebener, J., Dien, B.S., Cotta, M.A., Blaschek, H.P. 2008. Butanol production by Clostridium beijerinckii. Part I. Use of acid and enzyme hydrolysed corn fiber. Bioresource Technology. 99:5915-5922. Interpretive Summary: Approximately 4-5 million tons of corn fiber are produced annually from corn processing in the United States. Corn fiber is a low value byproduct and is sold for approximately 2 cents/lb. Corn fiber can be converted into a superior liquid fuel called "butanol." Successful conversion using this process would lead us to foreign independence of oil and stimulate our economy. Currently, 2.6 billion pounds of butanol are produced in the United States. Once this conversion process of corn fiber to butanol is successful, 5 million tons of corn fiber could be used to produce 2.36 billion pounds of butanol. In addition to production of 2.36 billion pounds of butanol, this conversion process would also result in the production of 1.18 billion pounds of acetone and 3.9 billion pounds of ethanol as co-products. Butanol has 33% more energy content than ethanol. Currently, we are studying various factors that influence efficient and economic bioconversion of corn fiber to butanol. Conversion of corn fiber to butanol is a two step process. Step one is breaking down of corn fiber to simple sugars, and the second step is conversion of sugars to butanol using Clostridium beijerinckii. Results on breaking down of corn fiber to sugars and their (sugars) conversion to butanol using C. actobutylicum are encouraging. This conversion process will improve farmer's economy and create employment opportunities.
Technical Abstract: Corn fiber was hydrolysed using dilute sulfuric acid (0.1-0.5%, v/v) at 121 deg C, enzymes (cellulose and cellobiases), and a combination of both (acid and enzyme). Sulfuric acid (0.3-0.5%, v/v) resulted in releasing 29.2-29.9 g/L total sugars from 63 g/L corn fiber. Further treatment with enzymes enhanced total sugar level from 29.9 g/L to 54.3 g/L. Based on corn fiber loading of 63 g/L, corn fiber moisture and lignin contents of 16% and 10%, respectively, a sugar concentration of 54.3 g/L was maximum that can be achieved. This represents releasing 103.6% of sugars of that available in corn fiber. Use of enzymes alone represents a hydrolysis of 46.4% of that available in corn fiber and resulted in a sugar concentration of 24.3 g/L. Fermentation of corn fiber hydrolysate suggested that dilute sulfuric acid treatment released inhibitory components that inhibited cell growth and fermentation of C. beijerinckii BA101. It could be possible that salt formed during corn fiber hydrolysate neutralization inhibited cell growth. Enzyme hydrolysed corn fiber did not show any signs of cell inhibition and resulted in the production of 8.1 g/L total ABE from 23.9 g/L total sugars. The ABE concentration in enzyme hydrolysed corn fiber fermentations was low due to initial low sugar concentration. It is suggested that inhibitory components be removed from the dilute sulfuric acid corn fiber hydrolysate prior to fermentation. Another possibility could be that a new culture capable of fermenting such a hydrolysate be developed.