The adsorption heat of methane on coal: Comparison of theoretical and calorimetric heat and model of heat flow by microcalorimeter

Various methods have been proposed to determine the heat of adsorption indirectly from adsorption isotherms or directly through calorimeter, whereas authors rarely compared different models for calculating isosteric heat of methane adsorption on coal and seldom studied adsorption thermodynamics related to calorimetric heat flux. In this work, for better probing thermodynamics of adsorption of methane on coal, seeking a reliable model to describe adsorption heat, and predicting the adsorption heat at given temperatures and pressures from heat flow, isothermal adsorption experiments of methane on anthracite at temperatures of 298 K, 308 K and 318 K were conducted, with both calorimetric and volumetric method. The calorimetric results indicate that isosteric heat decreases with the increase of adsorption capacity and temperature. Then the calorimetric heat was compared with the isosteric heat using four adsorption models, in the fitness sequence of D-A > Toth > C-C > Virial. To be noted that the heat flux measured calorimetrically increases to the crest rapidly, then gradually decreases to the initial state. This tendency is proposed to be described by the exponential function with the fitting parameters estimated by empirical formulas proposed. The predicted heat flows were thus acquired, agreeing well with the experimental data except for the low coverage or pressure stage. Furthermore, it is revealed that the temperature evolution of adsorption can also be expressed by an exponential-like polynomial solution, induced from the proposed thermal flux prediction model based on the Tian's equation.