Abstract
A combination of Flory-Huggins and non-equilibrium lattice fluid models are utilized for predicting the solubility coefficients of CO2, CH4, N2, n-C4H10 and i-C4H10 in low and high-density polyethylene, polysulfone and polycarbonate. The genetic programming has been used to acquire the appropriate function for this model. The solubility coefficients at infinite dilution are calculated based on non-equilibrium lattice fluid theory and the gas-polymer interaction is expressed by the Flory-Huggins interaction parameter. The solubility coefficients at infinite dilution, Flory-Huggins interaction parameter and pressure were selected as terminal sets and some simple mathematical functions and operators such as multiplication, division, summation, power and absolute value were regarded as mathematical function sets. The adjustable parameters of the proposed function were determined for each gas-polymer system based on nonlinear data fitting. The first adjustable model parameter was in the form of constant power and the second was obtained as a variable coefficient in the form of quadratics function of temperature. The results of the presented model demonstrate improved ability to predict the solubility of investigated gases in the considered polymers at high pressures in comparison to non-equilibrium lattice fluid and Sanchez-Lacombe equation of state models. In some cases, the absolute errors between experimental and predicted values of solubility coefficients were below 1% at the considered conditions.
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