OP-II-3

OP-II-25MULTISCALE ANALYSIS OF A COATED-WALLMICROCHANNEL REACTORLopes J.P. 1 , Cardoso S. 2 , Rodrigues A. 11 Associate Laboratory LSRE/LCM, Faculty of Engineering, University of Porto,Porto, Portugal, deq07006@fe.up.pt2 Department of Chemical Engineering and Biotechnology, University of Cambridge,Cambridge, UKMicroreactor technologies have been object of intense research due to thereduced mass/heat transfer resistance compared with conventional equipment[1].Applications of these microsystems range from production of fine chemicals,pharmaceuticals and energy-related compounds (e.g. synthesis gas and hydrogenfor fuel cells) to biotechnological products (from e.g. immobilized enzymes in acoated-wall biomicroreactor), catalyst screening and analytical measuring devices[2].The interest in using such devices relies on the maximization of fluxes byincreasing transfer areas. Also, the characteristic times for transverse diffusion andconduction are faster. The surface reaction effects are then favoured, and a catalyticporous coating is frequently attached to the wall of the microchannel, providing alarger total solid surface area, where heterogeneous reactions can take place.Although thin layers are typically found, it is possible in general to consider internalmass transfer limitations[3]. Then, the physical picture involves transport of reactantsin a fully developed channel flow by convection and axial diffusion and by radialdiffusion towards the washcoat. Inside the catalyst layer, further diffusion through theporous media occurs, together with reaction at the active sites.When diffusionallimitations inside the washcoat are not negligible, the interaction between transport inthe channel and reaction-diffusion processes in the porous layer determines theperformance of the microchannel reactor. The same problem is relevant in thecontext of processes with catalytic monoliths[4] and hollow-fiber membranereactors[5], e.g.. Efficient modelling techniques have already been developed forsurface wall catalysed reactions with no internal mass transfer resistance[6].In this contribution, a rigorous scaling analysis[7,8] of the general coupledproblem of transport in a microchannel with reaction-diffusion processes occurring atthe washcoat is presented. This results in order-of-magnitude criteria for commonmodeling assumptions, such as: negligible transverse gradients, reduction to the146