Butanol production from sweet sorghum bagasse with high solids content: Part I – comparison of liquid hot water pretreatment with dilute sulfuric acid

Authors: Qureshi, Nasib; Saha, Badal; Klasson, K Thomas; Liu, Siqing

Submitted to: Biotechnology Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2018
Publication Date: 4/25/2018
Citation: Qureshi, N., Saha, B.C., Klasson, K.T., Liu, S. 2018. Butanol production from sweet sorghum bagasse with high solids content: Part I – comparison of liquid hot water pretreatment with dilute sulfuric acid. Biotechnology Progress. 34(4):960-966. https://doi.org/10.1002/btpr.2639
DOI: https://doi.org/10.1002/btpr.2639

Interpretive Summary: Butanol is a superior biofuel and contains more energy than ethanol. It can be mixed with gasoline in any proportion. This biofuel can be produced from numerous feedstocks including corn, sugarcane juice, and molasses. Since the cost of these feedstocks is high, it is suggested that butanol be produced from much economically available feedstocks such as agricultural biomass (Sweet Sorghum Bagasse – SSB). The cost of agricultural biomass is much lower than corn and molasses and is expected to result in economical production of butanol. However, use of biomass requires breaking down (also known as hydrolysis) to simple sugars such as glucose, and xylose prior to butanol production. In these studies we used an economical method to hydrolyze SSB to simple sugars prior to production of butanol. Production of butanol from SSB would benefit United States farmers.

Technical Abstract: In these studies we pretreated sweet sorghum bagasse (SSB) using liquid hot water (LHW) or dilute H2SO4 (2 g·L-1) at 190 deg C for zero min (as soon as temperature reached 190 deg C, cooling was started) to reduce generation of sugar degradation fermentation inhibiting products such as furfural and hydroxymethyl furfural (HMF). The solids loading were 250-300 gL-1. This was followed by enzymatic hydrolysis. After hydrolysis, 89.0 gL-1 sugars, 7.60 gL-1 acetic acid, 0.33 gL-1 furfural, and 0.07 gL-1 HMF were released. This pretreatment and hydrolysis resulted in the release of 57.9% sugars. This was followed by second hydrolysis of the fibrous biomass which resulted in the release of 43.64 gL-1 additional sugars, 2.40 gL-1 acetic acid, zero gL-1 furfural, and zero gL-1 HMF. In both the hydrolyzates, 86.3% sugars present in SSB were released. Fermentation of the hydrolyzate I resulted in poor acetone-butanol-ethanol (ABE) fermentation. However, fermentation of the hydrolyzate II was successful and produced 13.43 gL-1 ABE of which butanol was the main product. Use of 2 gL-1 H2SO4 as a pretreatment medium followed by enzymatic hydrolysis resulted in the release of 100.6-93.8% (w/w) sugars from 250-300 gL-1 SSB, respectively. LHW or dilute H2SO4 were used to economize production of cellulosic sugars from SSB.