Ethylene and propylene sorption kinetics on hard coals

Abstract

Ethylene and propylene are gases released to the mine air together with the increase in the temperature of coal as part of self-heating. The concentrations of these hydrocarbons in the mine air are used as indices to assess the development of the coal self-heating process.This paper presents the results of tests involving coal adsorption capacity as well as ethylene and propylene sorption kinetics, conducted on five samples of Polish hard coals collected from coal beds under extraction in Polish mines.The adsorbed hydrocarbon quantities depend on the degree of metamorphism, the pore volume and the internal structure accessibility of the coals. Based on the performed kinetic measurements, it was concluded that propylene sorption is a process more rapid than ethylene sorption – the time required to reach the propylene sorption equilibrium is shorter. A decrease in the time required to reach the sorption equilibrium of both the hydrocarbons was also observed together with the increase in pressure, primarily for coals with low adsorption capacity. Using kinetic data made it possible to determine diffusion coefficients based on a unipore model and kinetic parameters based on modified unipore model. The values of above-mentioned parameters depend on the pressure and type of gas. As the pressure increases, their increase is observed. The values of both diffusion coefficients and kinetic parameters are higher for propylene than for ethylene.