Modeling polyethylene fractionation using the perturbed-chain statistical associating fluid theory equation of state

This paper illustrates how polymer fractionation can be characterized using the perturbed chain version of the statistical associating fluid theory equation of state, a computationally efficient algorithm, and pseudocomponents. We reparametrize the PC-SAFT equation of state and propose an efficient method of generating pseudocomponents to describe polydisperse polymer molecular weight distributions from the results of size exclusion chromatography analysis by numerical integration. We perform rigorous phase equilibrium calculations to investigate the effects of temperature, pressure, and feed composition on polyethylene fractionation. In these calculations, the polyethylene molecular weight distribution is treated as an ensemble of pseudocomponents consisting of chemical homologues of varying size. The simulation results are compared with plant data from an industrial solution polymerization process using cyclohexane as the solvent to demonstrate the applicability of the method to an industrial situation. The results indicate versatile representation of the polymer polydispersivity as well as accurate prediction of the liquid-liquid, vapor-liquid, and fluid-liquid fractionation process.