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

Lignocellulosic biomass from crop residues is an abundant and inexpensive resource that can be converted into high-value platform chemicals. An effective approach is a two-step and “lignin-first” process, utilizing ionic liquid pretreatment followed by ethanol–water liquefaction. In this work, the corn stalk (CS) was pretreated with the ionic liquid [B2-HEA][OAc] to remove lignin. The optimal pretreatment conditions were determined to be 130 °C for 5 h at a liquid–solid ratio of 10:1, achieving delignification of 85.88 wt% while recovering 52.22 wt% of cellulose and 30.18 wt% of hemicellulose. The pretreated CS was then converted into ethyl levulinate (EL) via ethanol–water liquefaction at 190 °C for 90 min. This resulted in a maximum EL yield of 39.93 wt%. Furthermore, the structural and thermal analyses via XRD, FTIR, TGA and SEM revealed the effective lignin removal and increased cellulose accessibility in the pretreated CS, as well as significant changes in chemical structure following liquefaction. Compared to the original CS, the crystallinity index of pretreated CS increased from 66.85% to 74.87%. The combination of ionic liquid pretreatment and ethanol–water liquefaction serves as an efficient process to convert the lignocellulosic residue corn stalk into value-added platform chemicals.