Monte Carlo Informed Modification of Peng–Robinson Equation of State for CO2/Hydrocarbon Mixtures Confined in Nanopores

Abstract

Understanding the vapor–liquid equilibrium (VLE) and critical behavior of carbon dioxide (CO2) and alkane mixtures under confinement is crucial for optimizing CO2 enhanced oil recovery (EOR) and mitigating greenhouse gas emissions. This study investigates the VLE of CO2/n-heptane and methane/n-heptane binary mixtures confined in amorphous silica pores using Monte Carlo (MC) simulations and a modified Peng–Robinson Equation of State (mEoS). The results show that confinement decreases the bubble point pressure while increasing the dew point pressure for both binary systems. The maximum pressure along the composition-dependent critical locus is also reduced under confinement for both binary systems. To improve predictive accuracy, a temperature-dependent modification to the Peng–Robinson EoS is introduced by parametrizing the model coefficients. These findings establish a quantitative framework for predicting phase behavior of confined hydrocarbon mixtures, with direct implications for subsurface energy and carbon management applications.