Experimental Study on the Confined Phase Behavior of n-Butane/n-hexane Binary Mixture: The Effect of the Amount of Nanoporous Material at Varying Pore Sizes and Temperatures

The confinement-induced phase transition of fluids has crucial implications for numerous industrial and scientific applications, such as enhanced hydrocarbon recovery from unconventional reservoirs, gas storage, and phase separation in nanoporous media. Most real-world confined systems, including those in subsurface geological formations, typically contain more than one chemical species of fluids. However, studies in the literature providing insights into the effect of confinement on the phase behavior involve mainly single pure components. The knowledge about the confined phase behavior of mixtures remains scarce and warrants more in-depth investigations. The present work endeavors to fill this gap by examining the thermodynamic properties of the binary mixture of n-butane/n-hexane confined in the nanopores of ordered mesoporous material MCM-41. To this end, experiments were conducted to measure isotherms using an upgraded version of the patented gravimetric apparatus. The impact of the amount of nanoporous material on the confined phase behavior of the n-butane/n-hexane binary mixture was investigated in MCM-41 samples with two different pore sizes at varying temperatures. The results show that the confinement-induced vapor-liquid phase transition of the binary mixture was more noticeable from the isotherms measured using the higher volume fraction of the MCM-41 material. The relatively large porous-medium volume fraction slightly increased the capillary condensation pressure of the fluid mixture, especially at high temperatures. In addition, it is evident from the findings that, depending on the amount of nanoporous material, capillary condensation pressure could reside within either the vapor phase or the two-phase regions of the fluid mixture phase diagram. The results from this work enrich the literature on the confined phase behavior of complex fluid mixtures with a better understanding of the impact of the amount of nanoporous material on measured capillary condensation pressures.