Sugarcane Bagasse Conversion in Water-Ethanol under Pre-Hydrothermal Liquefaction Conditions

Abstract

Hydrothermal liquefaction (HTL) uses compressed water at high temperatures (≥250 °C) to convert wet biomass into a synthetic crude oil (bio-crude). Here, sugarcane bagasse was treated in batch mode using water, ethanol, and a water+ethanol (1:1, w/w) mixture at a 1:9 biomass-to-solvent mass ratio to evaluate the effects of solvent, non-isothermal heating, temperature (180, 210, and 240 °C), and holding time at the setpoint temperature (0 to 60 min) on product distribution under pre-HTL conditions. With water at 240 °C and 60 min holding time, solid recovery was 48% and non-volatile liquor products were 16%. Under the same conditions, the water+ethanol mixture improved fractionation, yielding the highest extraction (35%) and the lowest solid recovery (36%). Ethanol addition inhibited humins formation and favored lignin and hemicellulose fractionation (solid recoveries of 27% and 1% at 240 °C and 60 min), while 56% of glucans remained in the residual solids. Under the best sugar recovery treatment (water, 180 °C, 0 min), 62% of hemicelluloses were recovered in the liquor at a 1:6 mono-to-oligosaccharide ratio. Under harsher conditions, even in the presence of ethanol, slow heating promoted depolymerization but also substantial sugar degradation, with acetic acid being identified as the main component of liquid streams.