Cornstalk liquefaction in sub- and super-critical ethanol: Characterization of solid residue and the liquefaction mechanism

Cornstalk liquefaction in sub- and super-critical ethanol was carried out in an autoclave at various temperatures. The characteristics of solid residue were investigated by XRD and sugar analysis. Milled solid residue fraction was isolated from the solid residue, and its chemical characteristics were comparatively investigated with milled wood lignin of cornstalk by gel permeation chromatography, FT-IR, and 2D HSQC NMR. The results showed that the structure of xylan in cornstalk was not broken down completely under the reaction temperatures and those liquefaction conditions were unable to break effectively apart the inter/intra chain hydrogen bonding in cellulose fibrils. Characterization of milled solid residue showed that the de-polymerization of lignin was more dominant than the re-polymerization as reaction temperature increased from 180 to 300 °C. The β-O-4, ferulate, tricin substructures almost disappeared from the spectrum of milled solid residue, which indicated the re-polymerization or decomposition of those bonds in lignin during cornstalk liquefaction process. The result showed that characterization of solid residue fractions provided some new information of the mechanisms about cornstalk liquefaction in ethanol.