Formation of CH4 during K2CO3-Catalyzed Steam Gasification of Ash-Free Coal: Influence of Catalyst Loading, H2O/H2 Ratio, and Heating Protocol

Abstract

Potassium-catalyzed steam gasification experiments of ash-free coal were conducted in a drop-down reactor to study the influence of the catalyst loading, temperature, H2O/H2 ratio, and heating protocol. The higher the catalyst loading, the faster the carbon conversion; however, at an initial K/C ratio of 0.1, a saturation effect (decrease in reactivity per potassium atom) was observed. At higher gasification temperatures, this saturation effect was more pronounced and likely caused by increased potassium mobility. The catalyst accelerated predominately the oxygen transfer reactions and not the methane formation. Methane is produced via direct hydrogenation of the carbon surface. The selectivity to methane and carbon monoxide was increased by reducing the H2O/H2 ratio, which would represent conditions in a gasifier away from the gas inlet. Lastly, the heating protocol influenced mainly the initial rate of gasification up to 20% carbon conversion; beyond that, the rates were similar.