An economic evaluation of biological conversion of wheat straw to butanol: A biofuel

A cost estimation study was performed for a biological butanol production plant with a capacity of 150 × 10⁶ kg butanol/year. Wheat straw (WS) was used as a feedstock. In addition to butanol, acetone (78.05 × 10⁶ kg/year) and ethanol (28.54 × 10⁶ kg/year) would also be produced. The total capital cost for this plant was $193.07 × 10⁶. This exercise was based in part on data generated in our laboratory and in part on data obtained from literature. The design, mass balance, and energy balance simulations were performed using SuperPro Designer (Version 8.5003, 2012). For butanol production wheat straw would be pretreated with dilute (1% v/v) sulfuric acid at 121 °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 (49.18%) followed by raw materials (26.81%). Based on batch fermentation of wheat straw hydrolysate and distillative recovery of acetone butanol ethanol (ABE), butanol production cost was estimated to be $1.30/kg for a grass-rooted/green-field plant. Application of a membrane recovery process could reduce this price to $1.00/kg for a plant annexed to an existing distillery.