Role of Confinement on Adsorption and Dynamics of Ethane and an Ethane-CO2 Mixture in Mesoporous CPG Silica

Ethane is found confined to mineral and organic pores in certain shale formations. Effects of confinement on structural and dynamic properties of ethane in mesoporous controlled pore glass (CPG) were studied by gravimetric adsorption and quasi-elastic neutron scattering (QENS) measurements. The obtained isotherms and scattering data complement each other by quantifying the relative strength of the solid fluid interactions and the transport properties of the fluid under confinement, respectively. A magnetic suspension balance was used to measure the adsorption isotherms at two temperatures and over a range of pressures corresponding to a bulk density range of 0.01-0.35 g/cm(3). Key confinement effects were highlighted through differences between isotherms for the two pore sizes. A comparison was made with previously published isotherms for CO2 on the same CPG materials. Behavior of ethane in the smaller pore size was probed further using quasi-elastic neutron scattering. By extracting the self-diffusivity and residence time, we were able to study the effect of pressure and transition from gaseous to supercritical densities on the dynamics of confined ethane. A temperature variation QENS study was also completed with pure ethane and a CO2 ethane mixture. Activation energies extracted from the Arrhenius plots show the effects of CO2 addition on ethane mobility.