Adsorptive Separation, Interfacial Configuration, and Mechanism of Dimethyl Carbonate-Methanol Azeotrope onto α-Al2O3: Experimental and Molecular Simulations.

Experiments and molecular simulations were combined to investigate the adsorption mechanism of dimethyl carbonate (DMC) and methanol (MeOH) azeotrope onto α-Al2O3 while the differences and similarities between pure and azeotropic components were discussed. Static experimental results have shown that α-Al2O3 exhibited capacities in an unexpected order as azeotropic MeOH > pure DMC > pure MeOH > azeotropic DMC. MeOH-DMC and pure MeOH both fitted the PFO model with proximal kinetic constants, while the pure DMC exhibited a different behavior with a diffusion-controlled stage followed by chemisorption. The interfacial configuration as well as the mechanism at the molecular level was studied by molecular dynamics and density functional theory. Molecular simulation results indicate that a multilayer adsorption conformation is formed on the α-Al2O3 (0 0 1) surface for MeOH-DMC with most Al sites being occupied by MeOH followed by DMC constructing a bilayerlike structure with the preadsorbed MeOH molecules. Moreover, the adsorption of DMC can further reduce the dissociation of preadsorbed MeOH. This factor seems to promote the adsorption of more MeOH molecules on the α-Al2O3 (0 0 1) surface, leading to DMC aggregation outside the MeOH layer.