Perturbed-Chain SAFT:  An Equation of State Based on a Perturbation Theory for Chain Molecules

Abstract

A modified SAFT equation of state is developed by applying the perturbation theory of Barker and Henderson to a hard-chain reference fluid. With conventional one-fluid mixing rules, the equation of state is applicable to mixtures of small spherical molecules such as gases, nonspherical solvents, and chainlike polymers. The three pure-component parameters required for nonassociating molecules were identified for 78 substances by correlating vapor pressures and liquid volumes. The equation of state gives good fits to these properties and agrees well with caloric properties. When applied to vapor-liquid equilibria of mixtures, the equation of state shows substantial predictive capabilities and good precision for correlating mixtures. Comparisons to the SAFT version of Huang and Radosz reveal a clear improvement of the proposed model. A brief comparison with the Peng-Robinson model is also given for vapor-liquid equilibria of binary systems, confirming the good performance of the suggested equation of state. The applicability of the proposed model to polymer systems was demonstrated for high-pressure liquid-liquid equilibria of a polyethylene mixture. The pure-component parameters of polyethylene were obtained by extrapolating pure-component parameters of the n-alkane series to high molecular weights.

Experimental study and a proposed new approach for thermodynamic modeling of wax precipitation in crude oil using a PC-SAFT model

“…In this theory, molecules are modeled as chains of bonded spherical segments and the properties of a fluid are obtained by expanding about the same properties of a reference fluid. Gross and Sadowski (2001) proposed the perturbed-chain modification (PC-SAFT) to account for the effects of chain length on the segment dispersion energy, by extending the perturbation theory of Barker and Henderson (1969) to a hard chain reference (Koyuncu et al 2002). This version of SAFT properly predicts the phase behavior of mixtures containing high molecular weight fluids such as the large wax molecules.…”

A Survey of Equations of State for Polymers

“…Gross and Sadowski [28]- [29] developed a modification to the SAFT equation referred to as PC-SAFT (Perturbed-Chain SAFT). In the structure of the PC-SAFT equation, molecules are assumed to be chains of spherical segments, freely linked and exhibiting attraction forces among them.…”

“…After the work of Gross and Sadowski [28]- [29], some applications of the PC-SAFT model may be found in literature. Table 2 presents a summary of some of the applications of the PC-SAFT model for systems consisting of homopolymers and copolymers.…”

“…Gross et al [146] extended the PC-SAFT model [28]- [29] for copolymers. The authors modeled phase equilibrium for ethylene copolymer systems with random alternating chains in a wide range of compositions (including homopolymer) and with molecular weights ranging between 709 and 242000 g/mol.…”

Phase Equilibria Calculations of Polyethylene Solutions from SAFT-Type Equations of State

“…Recently, Gross and Sadowski 15 have developed a variation of the SAFT model (PC-SAFT) in which the reference term is a hard chain fluid instead of a hard sphere fluid. This feature makes this equation very attractive to model polymer phase equilibria since the particular connection between the different segments is already taken into account in the reference term.…”