Phase equilibrium modeling for interfacial tension of confined fluids in nanopores using an association equation of state

Abstract

Two novel interfacial tension (IFT) models are presented, and four thermodynamic models—CPA-G, PCPA-G, CPA-P, and PCPA-P—based on the cubic-plus-association (CPA) equation of state and four IFT models are presented to predict the IFTs of fluids in bulk and nanopores. Among three association schemes of H2S that were studied, the 0d-1a association scheme is suitable for predicting mutual solubility of H2S-H2O system. The CPA-G and PCPA-G models can accurately describe the IFTs of H2S-H2O, CO2-H2O, CO2-n-C10H22, and CH4-n-C10H22 systems, whereas the CPA-P and PCPA-P models are inappropriate for IFTs of systems containing H2O. The IFTs of confined fluids in nanopores are lower than those in bulk. Under the same condition, IFTs of confined fluids decrease with an increase in pressure, but increase with the pore radius. Further, the effects of nanoconfinement for IFTs of confined fluids mainly occur at a pore radius below 100 nm.