One-pot saccharification and extractive fermentation of biobutanol from sorghum straw using protic natural deep eutectic solvents

Deep eutectic solvent-assisted delignification followed by a one-pot process of saccharification and extractive biobutanol production via ABE fermentation was achieved with sorghum straw biomass (SSB). Six protic natural deep eutectic solvents (PNADES) were synthesized and applied for the delignification of SSB. The eutectic mixture formed with choline chloride and citric acid was observed to have a significantly higher degree of lignin (90% w/w) and xylan (83% w/w) removal which was confirmed by observation under a scanning electron microscope. The cellulose-rich biomass was holistically exposed to enzymatic hydrolysis (Cellulase CTEC 21) and inoculated with Clostridium acetobutylicum (11,274) to facilitate biobutanol production. Response surface methodology optimization of influential parameters like inoculum size (9.75% v/v), biomass feed (24.5 mg/ml), and incubation time (122.5 h) has resulted in effective biobutanol productivity of (0.284 g L-1 h(-1)). Further, scale-up of the process carried out in a 2-L stirred tank bioreactor operated under anaerobic conditions resulted in a higher degree sugar utilization rate of 80% (w/w) enabling better butanol recovery (0.36 g L-1 h(-1)). This study successfully demonstrated sustainable operation conditions for the effective large-scale production of biobutanol through delignification followed by saccharification and extractive bioconversion of sorghum straw biomass.

Automated summary

In this study, the delignification of sorghum straw biomass was achieved using protic natural deep eutectic solvents (PNADES), followed by saccharification and extractive biobutanol production via ABE fermentation. Among the synthesized PNADES, the eutectic mixture of choline chloride and citric acid showed a significantly higher removal of lignin (90% w/w) and xylan (83% w/w). The cellulose-rich biomass was then subjected to enzymatic hydrolysis and fermentation with Clostridium acetobutylicum to produce biobutanol. Optimization of influential parameters resulted in effective biobutanol productivity, and scale-up of the process in a 2-L bioreactor further improved sugar utilization rate and butanol recovery. Overall, this study demonstrated sustainable operation conditions for large-scale biobutanol production from sorghum straw biomass.