Experimental Study on Effect of Thermodynamic Characteristics of Gas Adsorption of Coal Samples with Different Particle Sizes

In order to reveal the thermodynamic characteristics of gas adsorption of coal samples with different particle sizes，the isothermal adsorption experiments of coal samples taken from typical mines were carried out under the conditions of different particle size and temperature，and the Clausius－Clapeyron equation was used to calculate the equivalent adsorption heat of each coal sample; based on the Langmuir equation，the free energy equation of gas adsorption containing the standard equilibrium pressure constant was established，and with this equation，the free energy of gas adsorption was calculated; with the Gibb－Helmholtz equation，the adsorption entropy of each coal sample was obtained．The results showed that the gas adsorption process of coal particles affected by different particle size and temperature can still be represented by Langmuir equation; the equivalent adsorption heat，the free energy of adsorption and the adsorption entropy of coal samples with different particle size were all less than 0，the variation range of the equivalent adsorption heat was from －14．19 kJ/mol to －22．27 kJ/mol，the variation range of the free energy of adsorption was from － 4．83 kJ/mol to －6．72 kJ/mol，and the variation range of the adsorption entropy was from －28．20 J/(mol·K)to －51．32 J/(mol·K); with the increase of the particle size of coal samples，the equivalent adsorption heat，the free energy of adsorption and the adsorption entropy all increased; with the increase of temperature，the free energy of gas adsorption and the adsorption entropy of coal samples decreased gradually．The experimental results showed that the gas adsorption of coal samples was a physical adsorption process of the heat release，natural heating and entropy decrease of them．