Acetone-Butanol-Ethanol Production from Fermentation of Hot-Water-Extracted Hemicellulose Hydrolysate of Pulping Woods

In the kraft pulping process, the hemicellulose portion of wood is usually discharged as a waste stream into the black liquor, representing a highly underutilized sugar source. In this study, the hemicellulose prehydrolysate is investigated as a liquid sugar source for production of acetone, butanol, and ethanol by ABE fermentation. For this purpose, hot-water treatment is applied to poplar (hardwood) and southern pine (softwood) for hemicellulose extraction. The acquired hemicellulose prehydrolysate was analyzed to contain, in addition to the carbohydrates in the form of oligosaccharides, various degradation compounds. The toxicity test with model compounds indicates phenolic compounds exert tremendous inhibition on the cell growth. Therefore, detoxification is required prior to fermentation. Adsorption with activated carbon is an effective detoxification method greatly reducing the phenolic content and alleviating the phenol-induced inhibition. Upon detoxification, simultaneous saccharification and fermentation (SSF) of concentrated poplar prehydrolysate with 43.3 g/L sugar produced a total of 10.8 g/L ABE giving a solvent yield of 0.25 g of solvent/g of sugar. Comparatively, SSF of concentrated southern pine prehydrolysate with 46.6 g/L sugar resulted in an ABE production of 13.2 g/L and productivity of 0.28 g of solvent/g of sugar. The details of hot-water-extraction conditions, the performance of detoxification, and the fermentation profiles are discussed. The technical feasibility of utilizing the hemicellulose prehydrolysate as feedstock for biobutanol production has proposed an example of the concept of an integrated biorefinery.