Study on the surface structure development of porous char particles in catalytic supercritical water gasification process

Abstract

Porous structure and its development have significant influence on the heat and mass transfer between char particle and surrounding fluid, and the unique properties of supercritical water might make this process different. In this work, the catalytic supercritical water gasification experiments of semi-coke were conducted with K2CO3 as the catalyst at 650 °C to 750 °C, and the porous structure was characterized by nitrogen adsorption and SEM. Both micropores of 1.8 nm and mesopores that were enlarged in the gasification process were detected. K2CO3 addition was found to obviously promote the development of mesopore structure, while temperature had no obvious influence on structure development. Specific surface area and pore volume increased after gasification by one to two orders of magnitude, most up to 600 m2∙g−1 and 0.57 cm3∙g−1, respectively. Fractal dimension D increased sharply firstly due to the formation of a large amount of pores in the initial stage and then began to decrease because of the plasticity of char. The obtained structure evolution rules would be used for the establishment and optimization of kinetic models and the study of heat and mass transfer characteristics between char particle and surrounding fluid.