Assessment of the optimal reaction conditions and catalyst combinations for production of carbon negative hydrogen from supercritical water gasification of microalgae

Supercritical water gasification of microalgae offers a solution to hydrogen production that can simultaneously capture carbon from the atmosphere as both CO2 and solid biochar, without some of the negative environmental impacts of other biomass sources. Investigation into the influences of temperature (400–600 °C), biomass concentration (1-3 wt%), Oxidant Coefficient (0–0.5), heterogenous catalysts (Ru/C) and homogenous catalysts (KOH, 0-1 wt%) was carried out by integrating experimental results into a system model in ASPEN plus®. High temperatures and ruthenium catalyst were found to be preferable for both experimental and whole system approaches at maximising hydrogen yield and efficiency. However, despite being favourable in the reaction, low concentrations were not favourable in the integrated system, due to differences in heat recovery and pumping power. Similarly, the influence of oxidant and KOH showed a more complex influence on the whole system than is currently understood in SCWG reactions. As a result, a maximum hydrogen yield of 12.7 mg/g was achieved, with 38 % and 30 % of the carbon being captured as gas and solid respectively, at 600 °C, 2 wt% algae, 1 wt % KOH, Ru/C catalyst and a 0.3 oxidant coefficient.<p></p>