Synergistic citric acid-surfactant catalyzed hydrothermal liquefaction of pomelo peel for production of hydrocarbon-rich bio-oil

Citric acid showed good performance of hydrothermal liquefaction (HTL) of biomass waste via promoting the depolymerization of macromolecules. The synergistic effects of citric acid-surfactants/solid catalysts in the low-temperature (200 °C) catalytic hydrothermal liquefaction of pomelo peel (PP) were studied for the first time. It turned out that citric acid-surfactants promoted the conversion of pomelo peel to bio-oil with a higher yield (26.10–67.72 wt%), higher heating value (17.79–24.77 MJ/kg) and energy yield (33.53–114.11 %), while citric acid-solid catalysts were more conducive to the formation of gas and other products. FT-IR and GC–MS analysis testified that citric acid-surfactants increased the selectivity of hydrocarbons from 49.99 % to 74.19 %. Additionally, the chemical functional groups of bio-oil were characterized by 1H NMR and 13C NMR, indicating that the highest aliphatic content of bio-oils was 89.67 %. Moreover, citric acid-surfactant more environmentally friendly for low temperature liquefaction of biomass.