Exploring HTL pathways in carbohydrate–protein mixture: a study on glucose–glycine interaction

The hydrothermal liquefaction (HTL) of biomass is a strategic process to convert wet and waste feedstocks into liquid biofuel. In this work, we investigated the hydrothermal liquefaction of glucose and glycine, alone and together, to mimic the composition of low-lipid content biomass. Experimental tests were performed in a batch setup in the temperature range of 200–350 °C. As the feeding composition and temperature changed, the distribution among the different phases (gas, solid, biocrude, and aqueous phase) and their compositions were evaluated through different analytical techniques (GC–MS, µ-GC, HPLC). Glucose–glycine showed strongly different interactions with reaction temperature: increased biocrude production at high temperature and increased solid production at low temperature, following a proportionally inverse trend. Biocrude, as well as all the other phases, was observed to be completely different according to the feedstock used. To study how their formation and mutual interactions were affected by the composition of the starting feedstock, consecutive reactions of the generated phases were innovatively carried out. The solid phase generated from glucose–glycine interaction at low temperatures was experimentally observed to be mostly converted into biocrude at high temperatures. Furthermore, no interaction phenomena between the different phases were observed with glucose–glycine, while with glucose alone the co-presence of the molecules in the different phases seemed to be the cause for the lowest biocrude yield at high temperatures. The results obtained in this work can provide new insights into the understanding of hydrothermal liquefaction of low-lipid biomass, pointing out synergetic phenomena among both the biomolecules and the resulting phases.