Phase behavior of polypropylene + n-pentane and polypropylene + n-pentane + carbon dioxide: modeling with cubic and non-cubic equations of state

The phase behavior of polypropylene (PP) + n-pentane (nC5) binary mixtures was modeled in order to determine the molecular weight influence by finding the cloud point pressures of PP (MW = 50,400 and 95,400) in high-pressure nC5. Besides, the cloud point pressure of PP (50,400) in nC5-CO2 mixtures was also determined. In this work, the non-cubic equation of state (EoS) perturbed chain statistical associating fluid theory (PC-SAFT) [J. Gross, G. Sadowski, Application of perturbation theory to a hard-chain reference fluid: an equation of state for square-well chains, Fluid Phase Equilib. 168 (2000) 183] and Sanchez and Lacombe (SL) [I. Sanchez, R. Lacombe, An elementary molecular theory of classical fluids. Pure fluids, J. Phys. Chem. 80 (1976) 2352] and the traditional Peng-Robinson (PR) [D.Y. Peng, D.B. Robinson, A new two constant equation of state, Ind. Eng. Chem. Fundam. 15 (1976) 59] cubic EoS were used to predict the cloud point pressures from experimental data [T.M. Martin, A.A. Lateef, C.B. Roberts, Measurements and modeling of cloud points behavior for polypropylene/n-pentane and polypropylene/n-pentane/carbon dioxide at high pressure, Fluid Phase Equilib. 154 (1999) 241; A. Leu, D.B. Robinson, Equilibrium phase properties of selected carbon dioxide binary systems: n-pentane-carbon dioxide and isopentane-carbon dioxide, J. Chem. Eng. Data 32 (1987) 447], by fitting one temperature-dependent binary interaction parameter (κij) for each binary system. The pure-component parameters of all models were obtained by fitting pure-component data [P.A. Rodgers, Pressure-volume-temperature relationships for polymeric liquids: a review of equations of state and their characteristic parameters for 56 polymers, J. Appl. Polym. Sci. 48 (1993) 1061; DIPPR, Information and Data Evaluation Manager, Public Version 1.2.0, 2000]. The estimation of pure-component and binary interaction parameters was performed by using the maximum likelihood method. Good results were obtained with the PC-SAFT EoS, while the performance of the SL and PR EoS were less satisfactory.