Advanced Analytical Study of Process Streams for a Rational Optimization of Hydrothermal Gasification

Hydrothermal processesare promising technologies for an efficientvalorization of wet biomass feedstocks or wastes. Their performancestrongly depends on the composition of the feedstock, and methodsto analyze such complex mixtures along with the produced effluentsare in constant progress. Herein, catalytic hydrothermal gasification(cHTG) was used to valorize process water produced from the hydrothermalliquefaction of pine wood. A detailed analysis of the effluents andstreams at various points of the process was performed. About 54%of the feed's chemical energy could be transferred to syntheticnatural gas while an excellent extraction of minerals (98%) into aconcentrated brine (27 wt % dry matter) could be achieved. The lowgasification efficiency observed and the origin of the 41% and 44%loss of chemical energy and carbon in the brine, respectively, wereinvestigated by high-pressure liquid chromatography-high-resolutionmass spectrometry (HPLC-HRMS) analysis of the feed and theeffluents from the salt separator. This allowed for identifying mono-and polycarboxylates accounting for 71% of the carbon in the brine.Increasing temperature in the salt separator to favor decarboxylationreaction was identified as pivotal to improve synthetic natural gasyields, with a 20-fold decrease of carboxylate concentration beingreached with a temperature rise from 723 to 768 K. The use of twonew approaches to estimate the high heating value (HHV) of this feedrich in volatile organic compounds is also reported.