ARS | Publication request: An economic evaluation of biological conversion of wheat straw to butanol (a biofuel)

Submitted to: Energy Conversion and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 9, 2012
Publication Date: October 17, 2012
Citation: Qureshi, N., Saha, B.C., Cotta, M.A., Singh, V. 2013. An economic evaluation of biological conversion of wheat straw to butanol (a biofuel). Energy Conversion and Management. 65:456-462.

Interpretive Summary: Butanol, a novel biofuel, can be produced from corn. However, the cost of corn is high ($218/ton), and for that reason production of this biofuel would not be economical. In order to economize production of this biofuel, we attempted to produce it from wheat straw (WS) which costs about $24/ton. Prior to production of butanol from this material (WS) using a microbial culture, the straw is broken down to simple sugars using a treatment with dilute acid and degradation with enzymes. These studies on breaking down to simple sugars and microbial fermentation were encouraging and for that reason we performed cost estimation on the production of butanol from WS for a 50 million gallon/year plant. Based on laboratory scale data, it was projected that the cost of utilities (steam, high pressure steam, cooling water, and chilling water) would cost 59% of the total cost of production. This exercise indicated that the cost of utilities be reduced for economical production of butanol. It also indicated that a new plant would result in the production price of butanol of $4.26/gal while expansion of an existing distillery and economical recovery would cost $2.55/gal. We are attempting to produce this biofuel economically so that the U.S. public, farming community, and the biofuel industry can benefit from these investigations and we become independent of foreign oil.

Technical Abstract: A cost estimation study was performed for a biological butanol production plant with a capacity of 150 x 10**6 kg butanol/year. Wheat straw was used as a feedstock. In addition to butanol, acetone (78.05 x 10**6 kg/year) and ethanol (28.54 x 10**6 kg/year) would also be produced. The total capital cost for this plant was $209.59 x 10**6. This exercise was based in part on data generated in our laboratory and in part on data obtained from literature. The design, and mass and energy balance simulation was performed using SuperPro Designer (Version 7.5, 2010). For this process wheat straw would be pretreated with dilute (1%, v/v) sulfuric acid at 121 deg C for 1 h followed by separate hydrolysis (using enzymes), fermentation, and recovery. Enzyme cost for wheat straw hydrolysis was adapted from literature ($0.16/kg butanol). Utilities which included steam/high pressure steam, cooling/chilling water, and electricity represented the major cost of the operation (59.09%) followed by wheat straw (21%). Based on batch fermentation of wheat straw hydrolysate and distillative recovery of acetone butanol ethanol (ABE), butanol production cost was estimated to be $1.37/kg for a grass-rooted/green-field plant. Application of a membrane recovery process could reduce this price to $0.82/kg for a plant annexed to an already existing distillery.