Corncob Biorefinery for Platform Chemicals and Lignin Coproduction: Metal Chlorides as Catalysts

A facile approach to a corncob biorefinery, focusing on both carbohydrate valorization and lignin stabilization, was proposed to coproduce platform chemicals (glucose, xylose, arabinose, and furfural) and lignin. Different metal chloride prehydrolyses of corncob in the biphasic system (2-methyltetrahydrofuran/H2O) were first carried out, followed by enzymatic hydrolysis of treated corncob. It was found that the dissolution and recovery of carbohydrate and lignin were dependent on the prehydrolysis conditions (metal chloride concentration, temperature, and time); 82.9% xylose with 56.2% arabinose was produced at 140 °C for 20 min using 25 mM FeCl3, and subsequently, furfural was generated in a yield of 60.0% from this hydrolysate-containing biphasic system by increasing the temperature to 180 °C for 120 min. The FeCl3 prehydrolysis of corncob released 99% xylan, retained 91% cellulose, and showed a significant enhancement in the cellulose enzymatic hydrolysis rate of 4.9-fold as compared to that for raw corncob. The chemical structure of the leftover lignin-linked tricin was similar to that of native lignin according to gas permeation chromatography and two-dimensional 13C–1H correlation heteronuclear single-quantum coherence nuclear magnetic resonance characterization, which provided a useful substrate for the production of fine and bulk chemicals.