Confinement-Induced Suppression of Vapor Pressure in Hydrocarbons: Elevated-Pressure DSC Measurements and Molecular Simulation

Abstract Phase behavior of hydrocarbons in nanosized porous media is important for understanding fluid behavior in confined environments, yet direct experimental validation under elevated-pressure conditions remains limited. In this work, elevated-pressure differential scanning calorimetry (DSC) was used to measure boiling points of n-heptane and toluene confined in well-defined mesoporous silica materials (SBA-15 and SBA-16) at pressures up to 1300 kPa. The experimentally derived vapor pressure curves show a systematic suppression relative to bulk fluids across all pressures. Kelvin equation predictions and Gibbs Ensemble Monte Carlo (GEMC) simulations provide thermodynamic and qualitative molecular-level support for the observed confinement-induced phase behavior. In contrast, shale samples with low pore volumes and broader, more heterogeneous pore structures did not show a distinct confinement peak under the present experimental conditions. These findings provide elevated-pressure experimental data for confinement-induced phase behavior in well-defined mesoporous model systems and offer a benchmark for comparison with thermodynamic models and molecular simulations.