(29d) Modeling the Influence of Dean Vortices in Improving the Performance of Catalytic Membrane Microreactors

Porous membrane microchannels are used for controlling heterogeneous reactions over catalyst embedded in the annular region of membrane microchannel. In this work, a mathematical model is developed for a heterogeneously catalysed reaction in a porous membrane micro-reactor. Hydrogenation of an aqueous nitrite contaminant in water is analysed as a model reaction. For a straight micro-reactor a numerical algorithm is developed to predict the behaviour for non-linear kinetics. This is benchmarked with an analytical solution and later compared with the experimental observations reported in the literature. Results depict that the straight reactor is inefficient and catalyst utilization is poor when higher throughputs are required because the system is diffusion limited.

A modified design is proposed which incorporates curving of the microchannel to induce passive mixing by generating “Dean Vortices”. The velocity fields are obtained using a perturbation analysis. This is incorporated in solving the convection-diffusion-reaction system which governs the species transport. The non-linear system of equations in core and the membrane is solved using an operator splitting technique. An effective regularization treatment is devised to numerically deal with the singularity at the center for non-axisymmetric systems. Reactor intensification is characterized using conversion, effective length of the reactor and utilization of catalyst inside the membrane. The non-monotonic enhancement in Sherwood number is interpreted by analysing the dynamics of the concentration depletion layer.