Comparative study on the characteristics of hydrothermal products from lignocellulosic wastes

The chemical constitutions in biomass have a key effect on the development for the diverse valorization products by hydrothermal technology. In this work, the typical lignocellulosic wastes, i.e., fir wood (FW) and corn stalk (CS), were selected to study the effect of chemical constitutions on the characteristics of the hydrothermal solid and liquid products at 180–280 °C. The CS hemicellulose content is higher, and the CS cellulose and lignin contents are lower compared with FW. The yields of hydrothermal solid and liquid products from FW are higher and lower than that from CS, respectively. Hemicellulose was decomposed completely below 230 °C. The amorphous cellulose in FW was decomposed at 180–230 °C, of which the amount is less than the amorphous cellulose in CS decomposed below 230 °C. The crystalline cellulose was mainly decomposed into hydrochar at 230–280 °C. Besides, the interaction between the crystalline cellulose and lignin in CS is stronger than that in FW. The carbon microsphere clusters were formed due to that the monosaccharides from hemicellulose and cellulose in CS were easier converted than that in FW. Hemicellulose and cellulose were mainly decomposed into the furan derivatives at 200–260 °C. The amorphous domains in CS cellulose were mainly decomposed to the acids at 200–230 °C. Lignin in FW and CS were decomposed into the phenols by demethoxylation and the cleavage of C-O-C and C-C/CC bonds starting below 180 °C and above 180 °C, respectively. The acids and ketones were formed by decarboxylation and decarbonylation, respectively.