Pore structure and its evolution in char during supercritical water gasification process

Pore structure and its evolution provide key information for the heat and mass transfer in char particles and are important for supercritical water gasification reactor design. Supercritical water gasification was conducted in an autoclave, and nitrogen adsorption and scanning electron microscopy were applied for pore characterization in char. Specific surface area and pore volume showed an increasing tendency, but the growth of the specific surface area obviously slowed down as the reaction proceeded. Micropores with pore size of about 1.8 nm in original char increased obviously in quantity but remained nearly constant in size in the gasification process, whereas mesopores showed an increasing trend in both quantity and size from 3 to 5.5 nm. The surface fractal dimension calculated through the Frenkel–Halsey–Hill equation increased first and then decreased. These evolution characteristics may provide useful information for the establishment and optimization of kinetic models for supercritical water gasification.