Utilization of N , N -Dimethylethanolamine for Deconstruction of Lignocellulose by Removing Lignin to Enhance Enzymatic Hydrolysis Efficiency and Microbial Fermentability for Bioalcohol Production

Amine compounds have attracted attention in biomass valorization due to the ideal solvent recovery yield for recyclable pretreatment. Compared with primary/secondary amines, tertiary amines such as N,N-dimethylethanolamine (DMEA) have certain nucleophilicity and higher basicity, which might remove lignin for enhancing bioconversion efficiency. However, using pure DMEA to pretreat lignocellulose, lignin removal was generally <50%. Here, we tried to improve the pretreatment performance of DMEA by changing the polarity with the addition of water. Using the cosolvent of DMEA/H2O at a ratio of 40:60 (w/w) to pretreat corn stover (CS) at 130 °C, 0.5 MPa for 2 h, 91.18% lignin was removed with glucan recovery of 89.73%. The enzymatic yield of glucose reached 95.96% at 2% solid load, which was 4.66-fold to untreated CS. The recovered DMEA had excellent deconstruction performance for CS after 4 cycles. Then, the hydrolysates were used for bioalcohol production by a Clostridium-yeast two-stage fermentation that first used Clostridium acetobutylicum to produce butanol and then added Saccharomyces cerevisiae to consume glucose for producing ethanol. Under this process, bioalcohol production reached 11.93 g/L with a proportion of >95% over total solvents. Overall, we proposed a tertiary amine pretreatment with superior efficiency of lignin removal and fermentability for producing advanced biofuels.