Molecular Simulation Of Adsorption And Diffusion In Epoxidation Of Propylene By Catalysts

The Propylene Oxide (PO) is an important chemical material. The traditional way to produce PO always wastes a lot of energy and cause serious pollution. Propylene epoxidation catalyzed by the Titanium silicate zeolite (TS-1) also has some problems such as the deactivation of the catalyst. Used the supercritical carbon dioxide (SC-CO₂) as the solvent of the epoxidation could make better results, and this paper is to discuss how the supercritical condition affects the epoxidation of propylene.Considering the complex structure of zeolite, the molecular simulation was used in this study. First the adsorption and diffusion of the reaction components were calculated used the Sorption and Forcite module of Materials Studio (MS) respectively at 333K, 400KPa, and with the methanol as the solvent. Then the calculations were carried out correspondingly at 328K, 10MPa and with the SC-CO₂ as the solvent. From the results we can get such conclusions:1. The reaction components such as C₃H₆ and H₂O₂ can get a higher loading under the supercritical condition. And for the reaction that catalyzed by the zeolite, the more the components loading, the faster the reaction could perform.2. The C₃H₆ prefers to adsorb in the straight channels under the both conditions. And the distributing of the H₂O₂ is more uniform, but it prefers to adsorb in the zigzag channels when adsorb with C₃H₆ together because of the adsorption competition. 3. Because the volume of the CO₂ molecule is smaller than the methanol, the reaction components can adsorb in the channels more easily, so the loading of the components under the supercritical condition are higher than that under the traditional condition.4. The infinite dilute diffusion coefficients of the reaction components in SC-CO₂ are almost 10 times more than that in the methanol. The excellent diffusion performance of SC-CO₂ can help PO to remove from the zeolite quickly, and restrain the deactivation of the catalyst.5. The PO prefers to diffuse in the zigzag channel under the traditional condition and in the straight channel under the supercritical condition because of the effect of the solvent. And the straight channel is bigger than the zigzag channel, so PO in the straight channel can remove from the TS-1 more easily.