Interaction mechanism between cellulose and hemicellulose during the hydrothermal carbonization of lignocellulosic biomass

Abstract The fuel properties of the solid product obtained from hydrothermal carbonization (HTC) are substantially influenced by the interaction reactions of the lignocellulose components. This study focused on the interaction reactions of cellulose and hemicellulose (represented by glucose and xylose, respectively) and the formation mechanism of the hydrochar through experiments and density functional theory methods. Results indicated that furfural was the main intermediate product of xylose and then converted into benzenes, which were seldom produced from the hydrothermal conversion of glucose. When glucose and xylose were co‐carbonized hydrothermally, more benzenes were generated because glucose and xylose exhibited a synergistic effect in forming alkenes, which were then cracked remarkably into C 2 H 2 . Furthermore, C 2 H 2 reacted with furan that transformed from furfural and formed benzenes. The aqueous product of co‐HTC also contained a high concentration of 5‐hydroxymethylfurfural (5‐HMF). The 5‐HMF could polymerize with benzenes and furfural to form insoluble furan−benzene polymers, gradually aggregating into organic micronucleus. Subsequently, 5‐HMF, furfural, and benzenes in the aqueous phase were immobilized on the surface of the organic micronucleus through surface binding sites, eventually causing the growth of organic micronucleus into hydrochar particles. The polymerization between furan−benzene polymers could also increase the aromatization degree of the hydrochar, thereby enhancing the energy density of the hydrochar.