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A generalized method for predicting vapor-liquid equilibrium



Vapor-liquid equilibrium distribution ratios for hydrocarbons can be computed by the new equations presented in this work with higher accuracy than is possible by previous generalized methods. In this proposed new method, the three coefficients of the combination Viγii are newly developed and generalized functions.

The vapor-phase fugacity coefficient ϕi was formulated via a new generalized equation of state, and the liquid-phase activity coefficient γi is predicted via a proposed new equation that contains three generalized binary interaction coefficients for each binary set in a mixture. These interaction coefficients were developed from experimental K value data. Two expressions are employed in predicting the liquid fugacity coefficient Vi, one for the real liquid state and one for the hypothetical liquid state, the latter being developed empirically from experimental K value data also. These two Vi equations are also generalized.

This new K value prediction method gave an average absolute deviation of 5.25% on a total of 3,504 data points on 19 hydrocarbons in binary and ternary mixtures, these data points being selected so that they cover the range of pure component Tr = 0.5 and up and pressures up to 0.9 of the true mixture critical pressure. Inclusion of nonhydrocarbon-hydrocarbon systems in the evaluation gave an overall absolute deviation of 6.33% for 4,290 K value data points on 23 components.

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