Supercritical water gasification of biomass: a state-of-the-art review of process parameters, reaction mechanisms and catalysis
The global energy demand has laid emphasis on the exploration of alternate sources of energy. With the application of many thermochemical and biochemical technologies, waste biomass can be converted into green fuels. Gasification is one of the most effective thermochemical (biomass-to-gas) technologies that can transform organic substrates into combustible syngas. Supercritical water gasification is an iteration of conventional gasification that uses water as the reaction medium to efficiently decompose biomass to hydrogen-rich syngas. The yields and composition of products from supercritical water gasification largely depend on the process parameters such as temperature, pressure, residence time, and feed concentration, biomass particle size, reactor configurations as well as reaction pathways and catalysis. These factors also determine the gasification efficiency, carbon conversion and heating value of the gas products. This paper reviews different homogeneous and heterogeneous catalysts involved in supercritical water gasification of biomass. Several reaction mechanisms occurring during gasification of biomass in supercritical water have also been illustrated and discussed, and research gaps for future studies have been identified. Overall, this review is an update to the compiled literature and the aspects involved in supercritical water gasification of different biomass feedstocks.