Modelling LLE and VLE of methanol + n-alkane series using GC-PC-SAFT with a group contribution kij

The fluid phase diagrams (LLE and VLE) of methanol + n-alkane mixtures series (from C4 up to C16) were modelled using GC-PC-SAFT EOS (Tamouza et al., Fluid Phase Equilibria 222–223 (2004) 67–76) combined with a recent method for computing kij based on the London theory (NguyenHuynh et al., Industrial & Engineering Chemistry Research 47 (2008) 8847–8858). This latter method requires pure compound adjustable parameters: pseudo-ionization energies J that may be calculated by group contribution in the case of n-alkane series. Jalkane is calculated from group parameters JCH3JCH3 and JCH2JCH2.SAFT group contribution parameters for the n-alkanes previously determined by Tamouza et al. (cited above) were re-used here without further treatment. Methanol was regarded here as a specific polar and associative compound. Two sites (one hydrogen donor and one acceptor on oxygen) and three sites (one donor and two identical acceptors) association schemes were considered and compared from a thermodynamic point of view. Methanol EOS parameters were adjusted on pure methanol and selected mixture phase equilibrium data.The phase diagrams of the whole methanol + n-alkane mixtures series were represented within a reasonable accuracy using a two sites association scheme. The modelling is however disappointing when using a three sites model.The kijs could be accurately correlated using the group contribution method of NguyenHuynh cited above, provided that the values of JCH2JCH2, JCH3JCH3 and Jmethanol be adjusted. A comparison with CPA EOS is also given.The comparison between the two association schemes is also made by predicting the second virial coefficient of pure methanol and unbonded fractions of methanol in the methanol + C6 system.