(601b) Self-Diffusion of Mixtures of Hydrocarbon Gases and Liquids in Mesoporous Silicas with Different Pore Sizes By High Field Diffusion NMR

Development of novel mesoporous catalysts, sensors, and supports intended for controlled release or capture of liquid or gas molecules emphasize the need for a detailed fundamental understanding of diffusion of gas/liquid hydrocarbon mixtures in porous solids. In this work, we report study of self-diffusion liquids and gases dissolved in liquids in several mesoporous silicas with narrow pore size distributions and different average pore sizes between around 3 and 10 nm. The mesoporous samples were provided by Fuji Silysia Chemical, Ltd. The diffusion study was performed with two-component hydrocarbon mixtures, where one component was liquid (hexane or hexadecane), and the second was gas (methane or ethane) dissolved in the first liquid component. Complementary diffusion measurements of liquid diffusion in the corresponding gas-free samples that contain only one component liquid (hexane or hexadecane) were also performed. The diffusion measurements were carried out by pulsed field gradient (PFG) NMR at high field up to 17.6 T and large magnetic field gradients up to 25 T/m. An application of high field facilitated C-13 PFG NMR observation of a relatively weak signal of C-13 labelled gas molecules in two component confined phases, while large gradients enabled measurements of the diffusion process for displacements much smaller than the sizes of porous particles. The diffusion of liquid and gas components inside mesopores was quantified, respectively, by H-1 PFG NMR and C-13 PFG NMR. We will demonstrate that this approach allows for an independent measurement of self-diffusion of liquid molecules and gas molecules confined together in mesopores. Using this approach, the self-diffusivities were obtained for each component separately in each measured mixture sample under the same experimental conditions. These diffusion data were analyzed as a function of the average pore size as well as the size of diffusing molecules. The data and their analysis will be presented and discussed in detail.