Accurately modeling benzene and alkylbenzenes using a group contribution based SAFT approach

In recent work, the GC-SAFT-VR equation, which combines the SAFT equation for potentials of variable range (VR) with a group contribution (GC) approach, was proposed. Parameters for key functional groups (such as CH₃, CH₂, CH, CH₂CH, CO, C₆H₅, ether, ester, OH, NH₂, CHO, COOH) were obtained by fitting to experimental vapor pressure and saturated liquid density data for selected low molecular weight fluids and then used to predict the phase behavior of both pure non-associating and associating fluids and their mixtures, generally without adjusting the group parameters to binary mixture data. In the GC-SAFT-VR approach the benzene ring was modeled as a single group (C₆H₆ for benzene and C₆H₅, for alkylbenzenes) however, in common with other group-contribution based SAFT approaches, this approach fails to reproduce the correct curvature seen in the experimental liquid density of alkylbenzenes. In this work, to improve upon the model adopted for ring molecules, the benzene ring is explicitly considered through the connectivity of several smaller groups to more accurately capture the π-π interactions. We demonstrate that the improved model better captures the curvature present in the experimental saturated liquid density data of pure alkylbenzenes. Additionally, mixtures of several non-associating and associating fluids with benzene and alklybenzenes are studied.