A consistent and precise alpha function for cubic equations of state

- Using Taylor series expansion a general exponential form of the Soave α-function is proposed.
- Proposed α-functions and its 1st, 2nd and 3rd derivatives meet all the requirements of consistent alpha functions.
- The proposed general α-functions have superior accuracy in vapor pressure correlations.
- At supercritical temperatures the proposed and the Soave α-functions showed best level of accuracy.
- For asymmetrical mixtures thermodynamic packages with new α-functions demonstrate precise predictions.

Generalized form of alpha function to acentric factor is established for alpha function introduced in our recent study (P. Mahmoodi, M. Sedigh, Second derivative of alpha functions in cubic equations of state, J. Supercrit. Fluids. (2016). doi:10.1016/j.supflu.2016.05.012.). It is shown that proposed generalized alpha function meet all suggested criteria of consistent alpha function by Le Guennec et al. and also it gives correct predictions for Cv and Cp values. Moreover in subcritical and supercritical temperature ranges thermodynamic packages (combination of a CEoS and an alpha function) with the proposed alpha function have superior accuracy.Eventually, results demonstrate that thermodynamic package consist of the SRK EoS, the proposed generalized form of alpha function in this study and classical mixing rule by binary interactions hired from PPR78, is very accurate in vapor-liquid equilibria prediction of highly asymmetrical hydrocarbon mixtures.

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