Incorporating critical divergence of isochoric heat capacity into the soft‐SAFT equation of state

Abstract

In the critical region, widely used equations of state, including molecular‐based statistical associating fluid theory (SAFT) equations, fail to quantitatively describe the critical anomalies affected by the diverging fluctuations of density due to their classical mean‐field approximation. Description of some properties in the critical region, in particular vapor‐liquid coexistence and isothermal compressibility, can be improved by fitting (multi) parameters of an equation of state to the properties obtained in accurate computer simulations. However, some anomalies in the critical region, which are caused exclusively by critical fluctuations, cannot be readily generated by this procedure. An example of a critical anomaly, completely absent in the mean‐field approximation, is the divergence of the isochoric heat capacity. A simplified methodology for modifying the original soft‐SAFT equation of state to take into account these anomalies is explored. Possible procedures for further improvement are mentioned. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3073–3080, 2015