This paper proposes a theoretical approach aimed at evaluation of fluid compression factor, activity, and cohesion energy at near-critical and overcritical temperatures, for the fluid molar volumes ranging from 40% of the critical value. Such data are necessary in the theoretical description of sorption processes, developed in our previous papers. The approach is based on separate analysis of fluid entropy and cohesion energy. A theoretical model is used, which makes possible to derive a formula for the athermal compression factor of hard sphere fluids. It involves using a correction for the fluid accentric factor. Also applicability of other expressions is discussed. In turn, the mathematical model for the fluid cohesion energy was obtained by high accuracy approximation of universal compression factor data, with critical point conditions being taken into account. It is recommended to complete the compression data with empirical orthobaric compression factors. The coefficients of the model are expressed as functions of the fluid accentric factor. As the result, a state equation applicable for fluids of accentric factor less than 0.45 and reduced molar volume larger than 0.5 is proposed. For methane and carbon dioxide, the equations of better accuracy are proposed, with coefficients adjusted individually by nonlinear optimization. They are applicable for the reduced volume ranging from 0.4.

No abstract

No abstract

The paper presents a numerical approach to the analysis of the statistical effect of functional groups on the sorption of methanol and water on hard coal samples. The material used for the analysis was obtained from numerous samples of hard subbituminous and bituminous coals up to anthracite from different Polish coal mines and includes sorption isotherms of water and methanol vapors, as well as carbon dioxide and methane on these samples. Measurements were made of the sorption isotherms of water and methanol vapors and the data set has been supplemented with the sorption isotherms of water, methane and carbon dioxide taken from the literature for the precise estimation of the model parameters. More precise estimation is reached by using a strong setting of the coal structure parameters for a bigger number of sorption system, and in each case the same parameters of coal geometry are constant with an exact fitting of sorption isotherm. The adsorption-absorption model of the sorption in coal (Multiple Sorption Model-MSM) is used in the numerical experiments and the parameters of hard coal structure and the sorption systems are estimated. It has been stated that water as a polar substance together with methanol, as well as carbon dioxide and methane give good estimates of coal structure and let us quantify the polar effect of surface groups present in hard coal. The polar effect is introduced in the model in the range of adsorption and expansion subprocesses. The presence of oxygen groups in the bulk of coal matter has no significant effect and can be neglected. A weak decreasing tendency of polar factors ratio for water and methanol is discovered.