Butanol Production From Lignocellulosic Feedstocks By Acetone Butanol Ethanol Fermentation With Integrated Product Recovery

Abstract: n-Butanol has been attracting research attention as a liquid biofuel recently, in addition to its current application as an industrial chemical and solvent. With the concerns of diminishing fossil reserves, environmental issues caused by greenhouse gas emission, and unstable supply and price spike of crude oil, renewed interest has returned to pursue biobutanol production through acetone-butanol-ethanol (ABE) fermentation as opposed to petrochemically-derived butanol. However, the conventional ABE fermentation suffers from many limitations, including low butanol titer, high cost of traditional food-based raw materials, end-product inhibition and high butanol recovery cost by distillation, which negatively impacts the process efficiency and economics. Fortunately, these hurdles are being overcome by technological advances on ABE fermentation in the past few decades. Research on genetic modifications and chemical mutation of solventogenic Clostridia has focused on obtaining mutant strains with enhanced butanol producing ability. Adequate research success in utilizing renewable and sustainable lignocellulosic biomass has identified a novel group of cost-effective feedstocks for ABE fermentation in replacement of the traditional costly starch and sugar-based substrates. Novel fed-batch and continuous fermentation processes with cell immobilization and cell recycle have been developed for more efficient substrate conversion and butanol production. When further integrated with alternative energy-efficient butanol recovery techniques, such as gas stripping and pervaporation, the integrated ABE fermentation process can achieve high overall butanol production, reactor productivity, sugar conversion, and simplified downstream separation. Therefore, the overall goal of this project was to develop a process to produce butanol through ABE fermentation by hyper-butanol-producing mutants using lignocellulosic biomass, and integrate online product recovery to achieve enhanced overall butanol production and process efficiency. Corn fiber, cassava bagasse, wood pulp and sugarcane bagasse were investigated as potential feedstocks for butanol production from ABE fermentation, and gas stripping as the online butanol recovery technique was evaluated and integrated with ABE fermentation. In batch fermentations, immobilized mutant strain C. beijerinckii JB 200 produced 12.7 g/L and 15.4 g/L ABE from corn fiber hydrolysate and cassava bagasse hydrolysate in a fibrous bed bioreactor, respectively. C. beijerinckii CC101 produced 11.35 g/L ABE from wood pulp hydrolysate, and its recombinant mutant CC101-SV6 produced 9.44 g/L ABE from sugarcane bagasse hydrolysate in free-cell batch fermentations. ABE production from wood pulp hydrolysate was further enhanced to 17.73 g/L in a gas stripping integrated ABE batch fermentation process, with a higher ABE yield of 0.44 g/g compared with 0.39 g/g from non-integrated batch process. Concentrated cassava bagasse hydrolysate containing 584.4 g/L glucose was utilized by C. beijerinckii JB 200 in an integrated fed-batch ABE fermentation process, and 90.3 g/L ABE were produced with a productivity of 0.53 g/L. h, which was further improved to 108.5 g/L with nutrient supplementation. This project demonstrated that butanol can be produced from various lignocellulosic feedstocks, from agricultural biowastes to woody biomass residues. By employing mutant strains of solventogenic Clostridia bacteria, different fermentation modes, and online product recovery, an integrated process was developed for the production of n-butanol that can potentially replace petroleum-based butanol.