Two-Stage Hydrothermal Liquefaction of Sweet Sorghum Biomass-Part 1: Production of Sugar Mixtures

A two-stage hydrothermal liquefaction (HTL) process was developed for sweet sorghum biomass to improve carbon conversion, to avoid repolymerization reactions between hemicellulose and lignin derivatives that impair the yield of HTL biocrude oil, and to improve the quality of upgraded biocrude oil while producing sugar mixtures as coproducts. In this paper, the first-stage HTL experiment was carried out using sweet sorghum bagasse at various temperature and time conditions to produce sugar mixtures. Under the optimum conditions of 170 degrees C and 60 min, 94.1% of hemicellulose and 49.2% cellulose, respectively, were hydrolyzed into C5 and C6 sugars with the maximum sugar yield of 28.14% at the concentration of 28.52 g/L. The sugar stream can be used as a stand-alone or blended with sorghum juices to produce either biofuels or value-added chemicals and products. The remaining solids fraction mainly consisted of lignin, cellulose, and a trace amount of hemicellulose that can be further converted for use as a high-quality biocrude oil.