Capillary Condensation Measurements in Multimodal Nanoporous Media and Pore Critical Point Determination: Methane/Propane Mixture

The effect of pore size distribution on the phase transition of confined mixtures in nanoporous media is a field of study that still has a significant knowledge gap in the literature. This study presents experimental measurements on the phase transition of a methane/propane gas mixture confined in multimodal nanoporous media with independent domains, marking the first measurements of its kind. Accurate experiments are conducted by employing the isochoric cooling procedure using differential scanning calorimetry (DSC). The capillary condensation conditions occur at distinct temperatures and pressures in accordance with the pore size, which agrees well with the independent domain theory. The thermogram peaks for multimodal pores with independent domains are observed to be a linear combination of the peaks measured for each individual pore size. This supports the superimposition principle, which is shown to be valid for both pure gases and gas mixtures. Additionally, for the first time, the three-line approach is employed to pinpoint the pore critical point (PCP) of the gas mixture. Although the pore critical pressure of confined fluids is consistently lower than the bulk critical pressure, this study demonstrates that the pore critical temperature of a confined mixture can be higher than the bulk critical temperature.