Supercritical Water Gasification of Biomass for Hydrogen Production: Variable of the Process

Abstract

Waste biomass has various origins, such as agricultural crops, food waste, animal waste, municipal solid waste, and has the potential to be converted into energy and applied in biorefineries, thus contributing with lignocellulosic material. The emerging technology "Supercritical Water Gasification" has a great potential for recycling biomass for the production of synthesis gas with a higher percentage of hydrogen. The supercritical water gasification (SCWG) does not require drying; thus, the problem of drying is largely avoided by the SCWG and can be used for biomass with high percentage of humidity. The conversion efficiency of the SCWG is generally higher when compared with conventional technologies. This paper reviews known and emerging key supercritical water properties that influence the SCWG of biomass (viscosity, density, dielectric constant and ionic product), the advantages of the SCWG with respect to conventional gasification, the economic viability of the process, and the kinetics of the biomass in the process, this review describes the factors that influence the process (temperature, pressure, residence time, concentration, effect of the catalyst, effect of the reactor geometry, reactor design, heating rate of the biomass particle and type of biomass). Finally, this article concludes that the technology "supercritical water gasification" has great potential for a cleaner biogas production, with a high percentage of hydrogen, by different types of biomass, thus reducing the pollution and CO2 emissions.