Total component transformation of corn stalk to ethyl levulinate assisted by ionic liquid pretreatment

The conversion from widely available and inexpensive crop stalk to high-value platform chemicals through highly selective catalytic liquefaction under mild conditions is one of the effective ways for biomass utilization. In this work, a two-step "lignin-first" process was used to remove lignin from corn stalk (CS) with protonic ionic liquid [B2-HEA][OAc] as the pretreatment agent, followed by targeted conversion of lignocellulosic biomass to ethyl levulinate (EL) using alcoholic liquefaction technology. The optimal pretreatment conditions of CS and liquefaction conditions for the conversion of pretreated CS to EL were investigated. The highest recoveries of cellulose and hemicellulose were 83.78% and 67.20% as well the delignification rate of lignin was 70%, respectively, at the maximum biomass loading (liquid-solid ratio of 10:1), pretreatment temperature of 130°C and pretreatment time of 5 h. And the maximum EL yield of was up to 39.93% at the liquefaction temperature of 190°C with the liquefaction time of 90 mins. Meanwhile, the crystallinity, thermal stability, functional group and morphology of CS, pretreated CS and liquefied residue were carried out using x-ray diffractometer, thermal gravimetric analyzer, fourier transform infrared spectrometer and scanning electron microscope. It was suggested the lignin was effectively removed from corn stalk by ionic liquid pretreatment. Compared to original CS, the cellulose crystallinity index (CrI) of pretreated CS was reduced from 37.17–35.39%, and the surface of the pretreated CS became rough because of regular structure in cellulose broken by the ionic liquid.