Estimation of the Binary Interaction Parameters of the aNRTL Model using Molecular Simulations

The adsorption Non-Random Two-Liquid (aNRTL) model captures the non-idealities in the adsorbed phase for mixed gas adsorption equilibria. The underlying premise of the model is based on the dominance of adsorbate-adsorbent interactions in the adsorbed phase. It regresses the binary interaction parameter which is used to calculate the adsorbed phase mole fractions and the activity coefficients. The binary interaction parameter is a measure of competitive adsorption of a binary gas mixture. This model requires regression of model parameters using experimental data. Unavailability or unreliability of experimental datasets in terms of missing uncertainties and fewer data points affects the regression process, thus impacting the model output.  Therefore, it is extremely important to develop a methodology to estimate such parameters that do not make use of experimental adsorption data. Such an approach has been developed for the estimation of binary interaction parameters of the NRTL model using molecular dynamics simulations. In this study, we follow a similar approach to estimate the binary interaction parameters for a pair of adsorbate molecules in zeolites and MOFs using Monte Carlo and Molecular Dynamics Simulations. We derived equations relating the binary interaction parameters to the molecular parameters of the adsorbate-adsorbent interactions in the first coordination shell of each distinct adsorption site. The binary interaction parameters computed from molecular simulations gave an accurate prediction of the binary adsorption equilibria for the systems that were studied.