Enhanced adipic acid production from sugarcane bagasse by a rapid room temperature pretreatment

Adipic acid is an important precursor for manufacturing Nylon-66, and various efficient renewable routes for adipic acid from lignocellulosic biomass are being explored. To effectively valorize biomass into adipic acid, a novel aqueous solution NaOH/ChCl:TH/water (6:24:160, wt/wt/wt) was firstly applied to pretreat sugarcane bagasse (SCB) at a room temperature (25 C) for a short pretreatment time (1 min) for improving its saccharification efficiency. A deep eutectic solvent ChCl:TH was synthesized by mixing choline chloride (ChCl) and thiourea (TH). The cellulose structure changes of SCB were characterized by FTIR, XRD, SEM, TEM and LSCM. Composition analysis and reducing sugar yield were used to evaluate pretreatment efficiency. Hydrolysis for 72 h, the yields of reducing sugars and glucose from 40 g/L NaOH/ChCl:TH-SCB with complexed cellulases were obtained at 90.2 % and 94.1 %, respectively. Finally, the obtained SCB-hydrolysate was used for adipic acid production by E. coli MG1655 K12. Glucose in SCB-hydrolysate was consumed within 72 h, with a productivity of 0.39 g adipic acid/g glucose, accounting for 72.2 % of the theoretical yield. Further discovery, xylose in SCBhydrolysate was also consumed for adipic acid fermentation, which contributed to an increase in adipic acid production. In view of transcriptome data, most of the genes involved in carbohydrate metabolism were most significantly up-regulated, which was conductive to improve the yield of adipic acid using biomass-hydrolysate as carbon source. Therefore, the NaOH/ChCl:TH-SCB hydrolysates were a better carbon source for adipic acid fermentation compared to commercial glucose. Obviously, this established rapid room temperature pretreatment with NaOH/ChCl:TH was proven to be effective for enhancing saccharification efficiency of SCB, and the hydrolysates had excellent adipic acid fermentability.