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 CO 2 emissions.

A Technical and Environmental Evaluation of Six Routes for Industrial Hydrogen Production from Empty Palm Fruit Bunches

“…As shown in Figure 13, supercritical water achieved the highest hydrogen yield because of the changes in ionic product, polarity, and electrical conductivity of water at a high pressure and temperature. 21 Steam also reported better results compared to air, which is attributed to the absence of nitrogen leading to a shift in chemical equilibrium of the gasification reaction. 47 In addition, it was found that hydrogen production was not enhanced by increasing the oxygen-to-biomass ratio in the direct gasification process.…”

“…As shown in Figure 11, the supercritical water gasification exhibited the highest biomass conversion as temperature increased. Lachos-Perez et al 21 pointed out that biomass in a supercritical environment favors the rapid fractionation of hemicellulose and cellulose due to the properties of water at a high temperature and pressure. Sivasangar et al 22 obtained conversions around 50% of EFBs into hydrogen using a supercritical water reactor at 240 bar.…”

“…The gasification in supercritical water is an emerging process for biomasses with high content of moisture, which has reported to show high conversion rates despite of its dependency with operation conditions, feedstock, and reactor design. 20,21 Sivasangar et al 22 studied the production of hydrogen-rich gas from empty fruit bunches via supercritical water gasification and obtained improvements in hydrogen concentration with reaction time and biomass-to-water ratio.…”

A Critical Review of SCWG in the Context of Available Gasification Technologies for Plastic Waste

“…Therefore, water is a highly polar solvent at room temperature and a non-polar solvent in supercritical conditions. SCW is, therefore, an excellent solvent for non-polar organic compounds [96,97] such as lignin. Thanks to these properties SCW provides a homogeneous and rapid reaction environment for gasification.…”