Calculation of vapor–liquid equilibria of polymer solutions and gas solubilities in molten polymers based on PSRK equation of state

Abstract

A simplified EOS- g E mixing rule is applied for the predictive Soave–Redlich–Kwong (PSRK) equation of state (EOS). The combinatorial term Σ x iln( b/ b i ) is skipped with the Flory–Huggins term of the UNIFAC activity model in mixing rule of parameter a of the PSRK model. To take into account the free volume contribution to the excess Gibbs energy in polymer solution, a quadratic mixing rule is applied for the cross co-volume b ij with an exponent equals to 1/2 is used ( b i j 1 / 2 = 1 2 ( b i 1 / 2 + b j 1 / 2 ) ). The PSRK model with the modified mixing rule is used to calculate the vapor–liquid equilibrium (VLE) of 37 solvent–polymer systems, the solvent activity coefficients at infinite dilution of 28 polymer solutions over a large range of temperature and pressure, as well as the gas solubilities and the Henry's constants of nitrogen and carbon dioxide in polyethylene and polypropylene with satisfactory results.