(466e) Comparison of Gas and Liquid Transport Properties for Diffusion of Gases Dissolved in Hydrocarbon Liquids inside Mesoporous Silicas with Different Pore Sizes

Quantification and fundamental understanding of diffusion of two-component mixtures consisting of gases dissolved in hydrocarbon liquids under condition of confinement in mesopores is essential for the development and optimization of many applications including heterogeneous catalysis, separations, and sensor development for gas detection. While a significant amount of data was already accumulated on self-diffusion of single component sorbates in mesoporous solids, much less is known about relationship between diffusion of gas and liquid molecules for gasses dissolved in liquids inside mesopores, especially for relatively large gas-to-liquid molar ratios in the range of 1.0. In the current work, this gap is addressed by performing systematic experimental study of self-diffusion inside mesoporous silicas for two-component mixtures consisting of a hydrocarbon liquid component (hexane or hexadecane) and a C-13 labelled gas component (CO₂ or CH₄ or C₂H₆) dissolved in the liquid component. The diffusion studies were carried out by pulsed field gradient (PFG) NMR at a high field up to 17.6 T and large magnetic field gradients up to 25 T/m. The mesoporous silicas with narrow pore size distributions and average pore sizes ranging between 3 and 10 nm were provided by Fuji Silysia Chemical, Ltd. For each silica sample the self-diffusion of a liquid and a ¹³C-labelled gas was quantified separately by ¹H PFG NMR and ¹³C PFG NMR, respectively. The diffusion measurements were performed for gas/liquid molar ratios up to 1.0, different diffusion times, and temperatures ranging between 29 and 80 °C. For selected mixtures, in addition to self-diffusivities also activation energies of self-diffusion were obtained separately for each component in the mixtures. All diffusion data will be presented as a function of average pore size and discussed in detail.