MODELING PHASE-EQUILIBRIA USING AN EQUATION OF STATE INCORPORATING ASSOCIATION

A previosly proposed equation of state incorporating association in an explicit form (AEOS = Association + Equation of State) is applied to the calculation of vapor-liquid and liquid-liquid equilibria in mixtures containing water or alcohols and hydrocarbons. The AEOS model consists of two terms: a chemical one based on an association model and a physical one which is equivalent to an equation of state for nonassociating fluids. Attention is focused on the evaluation of pure component parameters which are crucial for mixture calculations. It is shown that the parameters should not only accurately reproduce pure component properties but also ensure the correct magnitude of the chemical and physical terms. A how algorithm is proposed to simplify the evaluation of pure component parameters. The AEOS equation, coupled with the new algorithm, is convenient for routine engineering calculations. It is capable of very accurately representing vapor-liquid and liquid-liquid equilibria over large temperature ranges. Only one binary parameter is needed. Moreover, the accuracy of predicting ternary equilibria using only binary parameters is very similar to the accuracy of correlating binary data.