An efficient microwave-assisted method using ethyl lactate/water cosolvent for lignocellulosic biomass fractionation

Biorefinery of lignocellulosic biomass to produce biofuels for replacing fossil resources is a major topic of energy conservation and carbon reduction. The efficiency of such biorefinery processes relies on the pretreatment of biomass, which is, however, the most energy-consuming step in the bio-conversion processes. To answer the demand of clean and efficient production in modern era, this study proposed a microwave (MW)-assisted route to pretreat corn stover (for fractionation) using a green cosolvent system consisting of ethyl lactate (EL) and water, and sulfonated activated carbon particles (AC-SO₃H) were used to improve the MW absorbing ability and process efficiency. Based on the systematic investigation of the effect of operating parameters on fractionation of corn stover, 81.7 % of hemicellulose and 85.3 % of lignin were separated from the raw corn stover with 80.9 % of cellulose retained under optimal conditions of 160 ℃ for 40 min with 0.3 g AC-SO₃H catalyst in EL/H₂O cosolvent (EL/H₂O = 3/2). The proposed EL/water cosolvent showed much higher efficiency than that using either pure EL or water, and in situ production of lactic acid (LA) and ethanol (EtOH) (via EL hydrolysis under acid environment) can benefit the pretreatment process. Compared to conventional heating, the MW method shortened the treatment time by half to obtain similar separation results. The improvement of the MW absorption ability and catalytic activity for this proposed pretreatment method was proven by control experiments, achieving effective disruption of the biomass structure and the accessibility of solvents to hemicellulose and lignin.