Supercritical water gasification in a ceramic wall reactor

Purpose Due to the severe reaction conditions characteristic of biomass gasification in supercritical water (T>374.15°C, P>221 bar), special metallic alloys have been used in order to resist both high pressure and corrosion. Such materials are quite expensive and, moreover, they lead to errors in the evaluation of kinetics, due to the catalytic reactor wall effect which is often a priori unknown. In this work, the possibility to use a ceramic reactor to overcome these problems is explored. Methods Tests were conducted by means of micro-autoclaves made of ceramics (alumina), stainless steel and Inconel. Different types of biomass, as well as model compounds, were used. Tests were conducted at supercritical conditions, 400°C and 300 bar, at a biomass concentration of 15% wt. Solid, liquid and gas samples were taken, quantified and analyzed. Scanning electron microscopy (SEM) pictures of the rector ceramics were also taken. Results Results showed that metallic and ceramic reactors do not behave in a significantly different way. SEM images showed micro-spheres of char and no damages to the ceramic surface. Main conclusions Ceramic alumina reactors could be of interest for supercritical water gasification of biomass, since they can resist the severe reaction conditions, give comparable yields of gas and be much more economic than metallic materials.