(509bd) Shell Thickness Optimization for Silicalite-1 Encapsulated Ni/Mg Catalysts for Hydrocarbon Reforming: A Modeling Study

Current trends indicate a continued dependence on hydrocarbon fuels for the coming decades. As a result, an area of critical importance is the development carbon neutral means of producing liquid fuels. One method is “biomass to liquid” wherein biomass is gasified to produce a stream of steam, methane and carbon dioxide which can be further reacted through hydrocarbon reforming to adjust the ratio of syngas for use in the Fischer Tropsch Synthesis reaction. Various tars and contaminants are produced through this process which much be removed prior to further reaction, however it is physically infeasible to achieve complete removal of tars. These hydrocarbon tars can poison the catalyst resulting in reduced efficiency or complete catalytic deactivation. One method to restrict the access of tars and contaminants to the catalyst is the introduction of a microporous zeolite shell. Zeolites, such as the Silicalite-1 studied here, have shown promise as size selective barriers which allow smaller species such as methane to pass through while blocking larger tars. We explore the creation of a reaction/diffusional CFD model to simulate the reforming of methane in the presence of toluene acting as a model tar. The model is used to determine the optimum zeolite shell thickness which balances the selectivity toward lighter hydrocarbons while minimizing the diffusional limitations introduced through the zeolite shell. The model is verified through experimental data for both an uncoated and encapsulated Ni/Mg catalyst pellet with varying shell thicknesses as well as a range of reaction temperatures and pressures to ensure accuracy of the model. We also investigate the control of bed density and packing factor to further minimize diffusional limitations. The model can also be applied to study other scenarios such as the effect of different kinds of zeolite, and situations in which the zeolite actively contributes to the reaction.