A new state equation for sorptives in near-critical and overcritical temperature regions

This paper proposes a theoretical approach aimed at evaluation of fluid com pression factor, activity, and cohesion energy at near-critical and overcri tical temperatures, for the fluid molar volumes ranging from 40% of the cri tical value. Such data are necessary in the theoretical description of sorp tion 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 compres sion factor of hard sphere fluids. It involves using a correction for the f luid accentric factor. Also applicability of other expressions is discussed . In turn, the mathematical model for the fluid cohesion energy was obtaine d by high accuracy approximation of universal compression factor data, with critical point conditions being taken into account. It is recommended to c omplete the compression data with empirical orthobaric compression factors. The coefficients of the model are expressed as functions of the fluid acce ntric factor. As the result, a state equation applicable for fluids of acce ntric factor less than 0.45 and reduced molar volume larger than 0.5 is pro posed. For methane and carbon dioxide, the equations of better accuracy are proposed, with coefficients adjusted individually by nonlinear optimizatio n. They are applicable for the reduced volume ranging from 0.4.