(525e) Molecular Modeling of the Gas Separation in Hybrid Inorganic-Organic Polymeric Membrane

In industry polymeric membranes are widely used for gas separations. To design membranes with high selectivity, excellent thermal stability and good permeability, multiple types of materials have been investigated. However, it is not clear the physics behind bulk gas separation and the active mechanisms at the molecular level. To address the latter, we employ molecular modeling to study gas separation in the membrane; this understanding will help us predict separation related properties of the membrane at the bulk level. Specifically, the hybrid inorganic-organic membrane, which has silicon dioxide as the sieve and organic groups dispersed, is simulated using molecular dynamics (MD).

We proceed as follows. A bulk alpha crystal of silicon dioxide with some of the atoms removed randomly is used as the starting structure. The BKS force field is used within the MD to convert the crystal structure to the amorphous type. Phenyl groups are then systematically attached to the silicon atoms. Next, the Dreiding force field is used to get the equilibrium conformation of the hybrid inorganic-organic membrane. To investigate the performance of the membrane, the separation of CO2 and CH4 mixture is simulated using non-equilibrium molecular dynamics (NEMD). The selectivity, density of two types of gases in the membrane session, the permeability and other properties are then calculated at different pressures and temperatures. The results are compared with our experimental data.

We are currently modifying the organic groups, changing the radius of the hole and processing other kinds of gas mixtures to see if we can reproduce what we have obtained experimentally. The final intent is to use the MD to predict favorable experimental conditions.