(260c) Modeling Alkane Partitioning and Phase Behavior on Graphite Pores: A Discussion on Dispersion Free Energy Formalism
AIChE Annual Meeting
2017
2017 Annual Meeting
Computational Molecular Science and Engineering Forum
Applications of Molecular Modeling to Study Interfacial Phenomena
Tuesday, October 31, 2017 - 8:45am to 9:00am
We model the mixed alkane fluid adsorption on graphite slit pores with interfacial Statistical Associating Fluid Theory (iSAFT) and study the phase behavior of pure and mixed alkanes in different pore sizes. The excess free energy is a summation of intermolecular repulsion and attraction contributions where the repulsion is accounted for by hard sphere volume exclusion and chain connectivity that is consistent with the SAFT equation of state for a bulk fluid. However, the contribution due to long range attraction is more challenging since the pair correlation function is unavailable for inhomogeneous fluids. There are two types of approximation mainly used by people, which are the mean field approximation (MFA) and a weighted density approximation (WDA).In this study, we compare the performance (accuracy and efficiency) of three schemes, which are MFA, WDA and a combination of these two, in predicting the fluid structure and adsorption isotherms. While MFA is the simplest and most widely used method, the accuracy of bulk fluid property prediction is limited, which makes the confined fluid property also shifted systematically. Thus we explore the performance of different types of WDA or a combination of MFA and WDA in approximating the local dispersion free energy and predicting fluid phase behavior in a wide temperature, pressure, pore size and species range. The accuracy of different methods will be evaluated by comparing to simulation data and computational time of each method will also be shown.