Prediction of phase equilibria for binary systems of hydrogen chloride with ethane, propane and n-dodecane

In many industrially important processes hydrogen chloride occurs as one of the major constituents. Due to its corrosive nature, hydrogen chloride is not an easy substance to handle in industrial or experimental facilities an d, as a consequence, accurate basic data of its mixtures is scarce. In this study, we examine the ability of two theoretical approaches, PACT (perturb ed anisotropic chain theory), and SAFT (statistical associating fluid theor y), to predict the phase behaviour of three binary mixtures of hydrogen chl oride with n-alkanes, In the PACT approach, the molecules are modelled with Lennard-Jones spherical segments with a contribution to describe the dipol e of the hydrogen chloride molecule. The non-sphericity of the n-alkane mol ecules is accounted for via Prigogine's approximation for the external degr ees of freedom. In the SAFT approach, the molecules are represented by chai ns of spherical repulsive segments with attractive short-range sites. Hydro gen chloride is represented by a single sphere, with two attractive sites t o model the dipole of the molecule. Chain molecules, such as the n-alkanes, are modelled fusing together a number of spherical segments. No attractive sites are included as these molecules are non-polar. We treat the long-ran ge dispersion forces via variable-range square-well potentials; with the SA FT-VR approach. We find that both approaches accurately reproduce the exper imental phase behaviour of the three mixtures for wide ranges of temperatur e and pressure. In the case of the SAFT-VR approach, both the critical regi on and the low temperature region are well represented with one set of para meters. However, the PACT approach requires two different sets of parameter s: one for the critical region and one for lower temperature regions. (C) 1 999 Elsevier Science B.V. All rights reserved.