Potassium catalyzed hydrogasification of low-rank coal for synthetic natural gas production

Potassium catalyzed isothermal coal hydrogasification was investigated, as an alternative route for synthetic natural gas production. Potassium chemisorption occurred on oxygen sites in the coal structure and was strongly affected by the solution pH and followed the Cation Exchange Capability (CEC) which is also pH-dependent. A quadratic function described the relation between the solution pH and the fraction of the chemisorbed potassium, while; the cumulative distribution function of two Weibull probability density functions correlated the solution pH with the CEC that was linearly correlated with the fraction of the chemisorbed potassium. Coal hydrogasification is strongly affected by the increased alkalinity of the impregnating solution and increased methane yields were obtained while carbon conversion was slightly affected. This was attributed to the formation of profuse K+ substituted active sites that decompose under H-2 attacks and trigger scission of the aromatic rings followed by K+ migration to neighboring complexes, thus, the hydrogasification reaction continuous to yield CH4, as codified in a three stage reaction mechanism. The relative specific hydrogasification rate was found to increase linearly with the CEC of the coal samples, suggesting that the oxygen functional groups, on which potassium is chemisorbed, act as "active sites" and are linked with the carbon's reactivity.