Modeling phase equilibria in mixtures containing hydrogen fluoride and halocarbons

Recently, much attention has been focused on the production of environmentally acceptable refrigerants, which not only offer desirable physico-chemical properties, but do not deplete the ozone layer and do not cause the greenhouse effect. The production of such refrigerants involves the separation of multicomponent mixtures containing hydrogen fluoride, hydrogen chloride, and various chlorinated and fluorinated hydrocarbons. Therefore, it is indispensable to know the phase behavior of these mixtures. While the phase behavior of refrigerant mixtures can be adequately modeled in the absence of HF using standard thermodynamic techniques, drastically increases the complexity of the mixture because of its unusually strong association. The association of HF manifests itself in its significantly reduced gas-phase compressibility factor and the strong nonideality of mixtures containing HF and hydrocarbons or halocarbons. In this work, the authors develop an accurate, yet simple, association model for HF and compare it with simulation data. The model is combined with a simple equation of state to yield a closed-form expression that is applicable to both pure fluids and mixtures. In addition to representing the pure-component data for HF, the theory accurately predicts phase equilibria in HF + halocarbon systems.