Capillary Condensation of Binary and Ternary Mixtures of n-Pentane–Isopentane–CO₂ in Nanopores: An Experimental Study on the Effects of Composition and Equilibrium

Abstract

Confinement in nanopores can significantly impact the chemical and physical behavior of fluids. While some quantitative understanding is available for how pure fluids behave in nanopores, there is little such insight for mixtures. This study aims to shed light on how nanoporosity impacts the phase behavior and composition of confined mixtures through comparison of the effects of static and dynamic equilibrium on experimentally measured isotherms and chromatographic analysis of the experimental fluids. To this end, a novel gravimetric apparatus is introduced and validated. Unlike apparatuses that have been previously used to study the confinement-induced phase behavior of fluids, this apparatus employs a gravimetric technique capable of discerning phase transitions in a wide variety of nanoporous media under both static and dynamic conditions. The apparatus was successfully validated against data in the literature for pure carbon dioxide and n-pentane. Then, isotherms were generated for binary mixtures of carbon dioxide and n-pentane using static and flow-through methods. Finally, two ternary mixtures of carbon dioxide, n-pentane, and isopentane were measured using the static method. While the equilibrium time was found important for determination of confined phase transitions, flow rate in the dynamic method was not found to affect the confined phase behavior. For all measurements, the results indicate qualitative transferability of the bulk phase behavior to the confined fluid.

Effect of Pore Size Distribution on Capillary Condensation in Nanoporous Media

“…All measurements are directly recorded on a computer. Although the configuration of the apparatus is different, its functionality is identical to that described in our previous work …”

“…This apparatus has the unique capability to measure isotherms in large masses of porous media (more than 300 grams) enclosed in core holders over a wide range of temperature and pressure conditions . In our previous study, we utilized this apparatus to measure isotherms with one core holder at any given time . In this study, however, we present an updated version of the instrument that is capable of measuring the phase behavior in multiple core holders simultaneously.…”

“…Three different pore sizes of MCM-41 were obtained from Glantreo, Ltd. These are the same samples of MCM-41 that were used in our previous work. ,, Table lists some key properties of these samples. Note that we label each sample S, M, or L to indicate the small, medium, and large pores, respectively.…”

Effects of Temperature and Pressure on Interfacial Tensions of Fluid Mixtures. I. CO2/n-Pentane Binary

“…The PC-SAFT equation of state (EOS), which is known to be accurate in estimating both liquid and vapor densities, was employed to calculate the required densities at various experimental pressure and temperature conditions. The EOS parameters were taken from Barsotti et al…”

“…The PC-SAFT equation of state (EOS), 31 which is known to be accurate in estimating both liquid and vapor densities, was employed to calculate the required densities at various experimental pressure and temperature conditions. The EOS parameters were taken from Barsotti et al 32 Experimental Procedure. Prior to conducting any IFT measurements, all wetted parts in the experimental setup were cleaned using toluene, methanol, and distilled water.…”