Development of a perturbed hard sphere equation of state for non-polar and for polar/associating fluids

A perturbed hard sphere equation of state was developed for both non-polar and polar associating fluids. First, a hard sphere equation of state, based on the Carnahan-Starling equation, with an empirical mean field attractive term was developed for non-polar fluids. The volume dependency of the attractive term was determined in order to reasonably describe volumetric properties of hydrocarbons. Hard sphere based equations of state have an almost temperature independent α(T) for spherically symmetric fluids compared to cubic equations. Thus, the α(T) expression used was the product of a term representing the slight temperature dependency for spherical fluids and a term, a function of the acentric factor, representing effects of shape for non-polar fluids. For polar fluids, a third polar factor was added to α(T) that used an effective acentric factor and a polar parameter.