(671d) Simulating Microwave-Heated Open Systems: Tuning Competitive Sorption in Zeolites

Zeolites are nonporous crystalline structures used as catalyst in many industrial processes. Over the past years, studies on the effects microwave radiation on zeolite properties have offered very interesting results. For example Turner et al.(1) found that MWs affect the selectivity of cyclohexane and methanol adsorption in silicalite. In this work we try to explain the qualitative differences found between conventional heating and MW heating on competitive mixtures adsorption. To do this, we have developed a new Grand Canonical Molecular Dynamics (GCMD) algorithm, and have applied the method to methanol and benzene sorption in silicalite zeolite. The new algorithm combines MW-driven molecular dynamics with Grand Canonical Monte Carlo (GCMC). We simulated single-component and mixture adsorption isobars for conventional and MW-heated systems. In the case of the single component isobars, we found that for methanol, both the MW and conventional heated isobars show similar desorption behavior, displaying comparable loadings as a function of molecular temperature. In contrast, nonpolar benzene showed no desorption upon exposure to MWs, even for relatively high field strengths. In the case of methanol/benzene mixtures, the fact that benzene is transparent to the MW field allows the selective desorption of methanol from the zeolite framework. Finally, we can say that MW heating produces new steady states that are not reachable through conventional heating. Furthermore, this new MW approach to adsorption may grant us with a new tool for mixture separation using molecular sieves, or even modify the selectivity of reaction taking place inside catalysts.

1.Turner M. D.; Laurence R. L.; Conner W. C.; Yngvensson K. S.; J. AIche 2000, 46, 758.