Cellulosic butanol production from agricultural biomass and residues: Recent advances in technology

Abstract

This chapter details the recent advances made on bioconversion of lignocellulosic biomass to butanol, a superior biofuel that can be used in internal combustion engines or transportation industry. It should be noted that butanol producing cultures cannot tolerate or produce more than 20-30 g/L of acetone-butanol-ethanol (ABE) in batch reactors of which butanol is of the order of 13-18 g/L. This is due to toxicity of butanol to the culture. In order to overcome this challenge, two approaches have been applied: (1) developing more butanol tolerant strains using genetic engineering techniques and (2) employing process engineering approaches to simultaneously recover butanol from the fermentation broth thus not allowing butanol concentrations in the reactor to accumulate beyond culture's tolerance. By the application of the first approach, a number of butanol producing strains have been developed; however, none of these accumulated greater than 1,200 mg/L (1.2 g/L) butanol, while using the second approach total ABE up to 461 g/L has been produced. Attempts to improve the newly developed strains are continuing. Lignocellulosic substrates have been used to produce butanol due to their abundant availability and economical prices usually in the range of $24-60/ton as opposed to corn prices which have been in the range of $153-218/ton during recent months. It should be noted that lignocellulosic substrates require separate hydrolysis prior to fermentation. In a more recent approach, hydrolysis and fermentation (and simultaneous recovery) have been integrated or combined to reduce the cost of butanol production from cellulosic substrates. Using such an approach, up to 192 g/L ABE was produced from 430 g/L cellulosic biomass/sugars. Additionally, this chapter provides details of process integration and simultaneous product recovery technologies for butanol production.