Computational chemical study on separation of benzene and cyclohexane by a NaY zeolite membrane

Separation of benzene and cyclohexane by a NaY zeolite membrane was studied via grand canonical molecular dynamics (GCMD). The GCMD technique was recently developed by simulation methods and effective for the study of the membrane separation process at the molecular level since it can simulate the dynamics of the permeants at a constant pressure gradient. From the simulation results of benzene single-component permeation, benzene molecules were preferably located at the C site in a NaY membrane. Distribution of benzene molecules around sodium ions on the SII site in a binary mixture system was almost the same as that of the single component, whereas the distribution of cyclohexane molecules around SII sodium ions in a single-component and binary mixture system was different. Calculated permeation flux of cyclohexane showed a higher value than that of benzene in a single component. On the other hand, in the binary mixture system, the cyclohexane flux was reduced significantly compared to the singlecomponent one. A derived separation factor was completely reversed for the single-component and binary systems. This tendency is the same as observed in experiments.

The GCMD simulation of the permeation in benzene/cyclohexane mixture by a NaY zeolite membrane was successfully performed. From the radius distribution analysis, distribution of cyclohexane molecules around the sodium ions at site II in a binary mixture system was different from the distribution in the single-component system. This can be attributed to benzene molecules preferably located at C sites excluding the cyclohexane from their stable sites. In the permeability analysis, selective permeation of benzene and the reversing of the separation factors for the single-component and binary mixture systems were successfully described. It is successfully demonstrated that the computer simulation technique is able to analyze the details of the permeation phenomena occurring inside the membrane at the atoministic level.