(433e) Toward a Process-Based Molecular Model of SiC Membranes. III. Thermo-Mechanical Properties and Application to Transport and Separation of Gaseous Mixtures in SiC Membranes

Sahimi, M., University of Southern California
Naserifar, S., University of British Columbia
Tsotsis, T., University of Southern California

We have developed a quantum-mechanically trained reactive force field, ReaxFF, to carry out reactive molecular dynamics simulation of hydridolycarbosilane (HPCS) to form amorphous SiC nanoporous membranes, mimicking the experimental pyrolysis process used for fabrication of the membranes. To test the validity of the generated membrane layer, extensive molecular dynamics ( MD) simulations are carried out to compute the self-diffusivities of H2, CO2 and CH4 gases in the SiC membranes at various temperatures. Atomistic models are generated by inserting gaseous molecules in the structure of SiC model using energy minimizations, MD simulations, and the universal force field. The computed self-diffusivities of H2 gas are much larger than other gases and increase with increasing temperature. Next, we use the model and non-equilibrium molecular dynamics simulations in order to study transport and separation in the membrane of two binary gaseous mixtures, namely, H2/CO2 and H2/CH4, and test the accuracy of the results by comparing them with our own experimental data. The model is demonstrated to provide accurate predictions for various properties of interest, and in particular for the separation factors of the mixtures. The effect of the temperature and pressure drop applied externally to the membrane is also described. Finally, we also study the structural, mechanical, and thermal properties of the amorphous SiC film. The bulk properties, such as the thermal expansion coefficient and elastic moduli are calculated and compared with experimental data. In addition, the morphology of the SiC film is characterized by its accessible free volumes. The distributions of the cavity volumes are computed using the Voronoi tessellation method.