Molecular Dynamics Simulation on Permeation of Acetone/Nitrogen Mixed Gas through Al2O3 Microporous Membranes

In this work, molecular dynamics (MD) was performed to simulate the dynamic processes of 1:4 acetone/nitrogen permeating through different Al2O3 membranes by Materials Studio 2.2 software package. Three modeling systems were constructed applying different modeling box lengths as well as different hollow size and texture of Al2O3 membranes to compare different permeation behaviors. In each system, initial mixed gas contained 20 acetone molecules and 80 nitrogen molecules and its density was set to 0.1g/cm of which could be seen as a high-pressure fluid. Analysis on the concentration profiles of three systems at different sampling time was implemented to discuss the permeation behaviors of smaller nitrogen molecules (N2) and larger acetone molecules (Ace). In each system, we had found that: (1) adsorption and diffusion occurred synchronously but adsorption was dominant in acetone case; (2) adsorption was easier to reach equilibrium than diffusion; (3) during the simulation time period 2ns, none of acetone was found to diffuse into the vacuum region; (4) when elevating the systematic temperature, adsorptive amount of nitrogen gas decreased whereas their diffusion rate increased, while both adsorptive amount and diffusion rate of acetone increased, which means that higher temperature is favor to the adsorption of acetone by the membrane; (5) larger microporous of the membrane is favor of diffusion against adsorption; (6) when applying COMPASS force field, adsorptive layer was found to be double-layer which up was acetone layer and down was nitrogen gas dominant layer, while monolayer mixed adsorption of nitrogen and acetone molecules was found when applying pcff force field.