Role of sea salt in modulating biomass-to-biocrude conversion via hydrothermal liquefaction

Abstract

Hydrothermal liquefaction (HTL) employs subcritical water as a reaction medium for the conversion of biomass into biocrude, however, most research relies on freshwater as the reaction medium, posing a critical resource challenge. Although preliminary investigations have demonstrated the viability of seawater as an alternative medium for HTL, the mechanistic role of sea salt in HTL of biomass remains poorly understood. In the present study, individual biomass components—carbohydrate, lignin, protein, and lipid—were subjected to HTL under varying sea salt concentrations and temperatures. Sea salt exerted an inhibitory effect on biocrude yield during carbohydrate HTL process, but no inhibitory effect was observed in HTL of lignin, protein, and lipid. As for the impact of sea salt relative to that of sodium chloride (NaCl), it was found that at a moderate sea salt concentration (13.5 wt% relative to feedstock mass) and temperature (270 °C), the minor constituents in sea salt were favorable for HTL of protein and lipid in terms of biocrude yield, energy recovery, and carbon recovery. Our findings offer valuable insights into the benefits and challenges of employing seawater as a reaction medium and illuminate the complex roles that sea salt and its minor constituents play in HTL processes.