The Effect of Confinement on the Phase Behavior of n-Pentane in Nanoporous Media: An Experimental Investigation at Varying Pore Sizes and Temperatures

n-Pentane, a key component of crude oil and gas condensate, exhibits altered phase behavior under nanoconfinement, affecting enhanced oil recovery (EOR) and hydrocarbon production in shale reservoirs. While its bulk phase properties are well-known, n-pentane’s behavior in nanoscale pores is not fully understood. This study investigates n-pentane’s phase behavior in silica nanopores using a gravimetric apparatus. Adsorption and desorption isotherms were measured in mesoporous MCM-41 (pore sizes: 7, 10.2, 11.3 nm) across temperatures from 24.8 to 98 °C to explore the effects on n-pentane’s phase behavior. Results show significant adsorption occurs prior to capillary condensation due to fluid–solid interactions within nanopores. Capillary condensation pressures increase with pore size and temperature, but suppression of saturation pressure under confinement decreases at higher temperatures and larger pore sizes. Hysteresis between adsorption and desorption was observed at all temperatures and pore sizes, with loops diminishing as temperature increased, indicating an impact on pore critical parameters. Application of the Kelvin equation revealed discrepancies between calculated and experimental capillary condensation pressures, highlighting the limitations of macroscopic models at the nanoscale. These findings provide novel data critical for understanding n-pentane thermodynamics under confinement, aiding the development of advanced simulation models.