Catalytic Biomass Gasification in Supercritical Water and Product Gas Upgrading

The gasification of biomass with supercritical water, also known as SCWG, is a sustainable method of hydrogen production. The process produces a mixture of hydrogen, carbon oxides, and hydrocarbons. Upgrading this mixture through steam or dry reforming of hydrocarbons to create synthesis gas and then extra hydrogen is a viable way to increase hydrogen production from biomass. This literature review discusses combining these two processes and recent experimental work on catalytic SCWG of biomass and its model compounds and steam/dry reforming of produced hydrocarbons. It focuses on catalysts used in these processes and their key criteria, such as activity, selectivity towards hydrogen and methane, and ability to inhibit carbon formation and deposition. A new criterion is proposed to evaluate catalyst performance in biomass SCWG and the need for further upgrading via reforming, based on the ratio of hydrogen bound in hydrocarbons to total hydrogen produced during SCWG. The review concludes that most catalysts used in biomass SCWG trap a large proportion of hydrogen in hydrocarbons, necessitating further processing of the product stream

Comparison of Experimental Results with Thermodynamic Equilibrium Simulations of Supercritical Water Gasification of Concentrated Ethanol Solutions with Focus on Water Splitting

Supercritical water gasification (SCWG) is a process in which biomass reacts with supercritical water to produce H2 and CH4-rich gas. The water-to-biomass ratio is a crucial variable in SCWG that affects the energy efficiency of the process. Despite the clear concept, systematic studies on water consumption during the formation of gaseous products are lacking. This study aims to determine the water consumption in SCWG of organic feedstock. Ethanol was used as an organic model compound since mass balances of complex biomasses like lignocelluloses are often incomplete due to the formation of solid deposits. The ethanol concentration ranged from 1.2 to 72 wt %, and complete gasification was achieved in all cases. Water consumption decreased with an increase in ethanol concentration due to enhanced methanation reactions with increasing organics. Stoichiometric calculations and ASPEN HYSYS simulations confirmed the experimental results, showing equilibrium gas compositions in the reaction system