Development of multi-component kinetic models based on the reaction behaviors of glucose, glycine and their mixture in a flash-heating continuous hydrothermal liquefaction system

In this work, hydrothermal liquefaction (HTL) experiments with glucose, glycine and their mixture were conducted in a flash-heating continuous HTL system (with the heating time and quenching time both ≪ 1 s) at various reaction temperatures (300–360 °C) and reaction times (4–10 s), to investigate their reaction pathways and kinetics in detail. The overall activation energies of HTL for glucose, glycine, and the mixture were 83.0, 52.3 and 11.9 kJ/mol, respectively, indicating that the energetic barriers for glucose and glycine decomposition decreased significantly in co-fed HTL. According to the rate constants of the reactions, dehydration was the main reaction path of glucose at mild temperatures, but with increasing temperature, the C-C bond breaking rate accelerated and then dominated. Glycine primarily produced glycylglycine and amides by dehydration and decarboxylation at low temperature. However, when the temperature exceeds 320 °C, the glycylglycine was hydrolyzed to glycine again. Direct deamination of glycine was relatively slow below 340 °C, with ammonia mainly generated by secondary decomposition. In the co-fed HTL process, the Maillard and direct deamination reactions replaced the original decomposition reactions in individually-fed HTL, with their rate constants being about five times those of other pathways.