Gasification Kinetics in Continuous Supercritical Water Reactors

Abstract

Supercritical water gasification (SCWG) is an emerging technology with synergistic applications in renewable energy and waste processing. Supercritical water (SCW) functions as a green reaction medium during the gasification process, serving to dissolve and decompose complex organic molecules via ionic, radical, hydrolysis, and pyrolysis reaction mechanisms. Researchers investigate the decomposition of model compounds in order to predict product yields and conversion efficiencies during the gasification of heterogeneous biomass waste, food waste, sewage sludge, and other available feedstocks. Continuous, laboratory-scale reactors are often employed to study reaction kinetics, pathways, and mechanisms. This chapter synthesizes previous work investigating model compound gasification in continuous supercritical water reactors (SCWRs). A summary of continuous reactor design strategies is presented for practical benefit, followed by a discussion on reaction chemistry in the supercritical water environment. Reaction pathways and mechanisms have been investigated for several model compounds, lending insight toward the conditions needed for the complete conversion of real-world feedstocks. Several studies assume first-order reaction kinetics and propose Arrhenius parameters for the decomposition reaction. The first-order rate assumption must be carefully evaluated, and the applicable temperature range must be specified. Opportunities for further research are discussed.