Confined phase behavior of ethane in nanoporous media: An experimental investigation probing the effects of pore size and temperature

Abstract

Ethane is rapidly becoming an efficient and dependable clean energy source for fast-growing and developing countries. It is the second most abundant natural gas after methane. However, it poses a major problem for ozone pollution and plays a significant role in greenhouse warming once released into the atmosphere. Therefore, understanding the mechanisms that govern its behavior during storage in natural and artificial nanoporous materials is essential for numerous industrial and environmental applications. In this work, the confined phase behavior of ethane was investigated in ordered mesoporous silica material MCM-41 at varying nanoscale-pore sizes and temperatures. Adsorption and desorption isotherms were experimentally measured for a wide range of nanopore diameters (7, 10.2, 11.3, and 12.3 nm) and temperatures (varying from −65 to −20 °C) using an automated gravimetric nanocondensation apparatus. This system enabled direct quantification of the mass of ethane adsorbed onto the surfaces of nanopores. We examined the impact of the pore diameter and temperature on the adsorption, capillary condensation, and evaporation of ethane in nanoporous media. The capillary condensation and evaporation pressures were determined using the Lorentzian functions. The accuracy of the measurements was confirmed by comparing the experimental bulk condensation pressures with those reported by the National Institute of Standards and Technology (NIST).The results demonstrate that the capillary condensation pressures increased with ascending pore diameters and temperatures. They also indicate that the degree of suppression of the saturation pressure due to confinement is predominant at low temperatures. The percent reduction in the pressure of vapor-liquid phase change decreased with an increase in temperature. A similar trend was observed with respect to changes in the pore size. The results showed that the effect of confinement was weakened as the nanopores became wider. Furthermore, insights were developed about the effects of pore diameter and temperature on the occurrence of the supercritical-like behavior of ethane in nanopores. A good agreement was evident between our results and the examples available in the literature.To the best of our knowledge, we present the first experimental study that describes the confined phase behavior of ethane using a patented gravimetric apparatus. This work presents a systematic approach to understand the effects of confinement in nanoporous media. Furthermore, it can aid the development of new ethane storage applications, especially the characterization of natural and artificial porous materials for energy and environment-related solutions.