The modified group contribution PC-SAFT has been extended in this paper to predict phase equilibrium of carboxylic acids and their mixtures. This work will focus on acetic and other linear organic acids due to their importance to the chemical industries. The new association energy parameter of acetic acid and carboxylic acids shows better agreement with the experimental results at approximately 300 K compared to all previously published SAFT-type parameters. New functional group parameters for carboxylic acids were regressed on selected pure compound data, and the binary interaction parameter (k ij ) of binary mixtures was fitted using their liquid–liquid phase equilibrium data. The association schema and dipolar interaction of acetic acid were investigated using PC-SAFT EoS, with an emphasis on the difficulties in predicting liquid–liquid equilibrium of acetic acid and alkanes mixtures. The computation results were improved clearly when acetic acid was considered as dipolar and 1A associative molecule. The polar parameters obtained for acetic acid were then transferred to other linear carboxylic acids to determine the COOH group parameters. Good vapor–liquid equilibrium prediction results were obtained for acid + acid, acid + hydrocarbon mixtures, without using binary interaction parameter, k ij = 0.

The modified group-contribution perturbed-chain statistical associating fluid theory (PC-SAFT) has been extended to model the phase equilibria of alcohols, branched alcohols, aromatic alcohols, and their mixtures. The parameterization has been implemented based on some physical arguments. The association energy of linear alcohols was fixed to the average experimental value, while this parameter for aromatic alcohols was directly estimated from the trimer hydrogen binding energy as evidenced by several experimental investigations. The dipolar moment of aromatic alcohols was reused from that reported experimentally. The importance of the association and the dipolar terms was investigated using the PC-SAFT equation of state by applying the model to represent liquid−liquid equilibrium (LLE) and vapor−liquid equilibrium (VLE) of several mixtures. The results obtained in this work suggest that including the dipolar term does not clearly improve the VLE prediction of linear alcohol-containing mixtures. It was possible to obtain good prediction results of VLE of alcohol-containing mixtures by using a nonzero binary interaction parameter to compensate for omitting the dipolar term (k ij = 0.012, within a 5% deviation on bubble pressure for 95 mixtures with 2616 experimental data). However, the addition of a dipolar term with the 2B association scheme to the PC-SAFT has been proven necessary to correctly describe the LLE/VLE of aromatic alcohol-containing systems. Good LLE and VLE computation results were obtained for almost considered mixtures.

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