Mass transfer characteristics of wire-mesh honeycomb reactors

Abstract

The mass transfer characteristics in honeycombs made of catalyst-deposited metal wire meshes (wire-mesh honeycomb; WMH) were studied to test the prediction that WMH has better flow distribution and a higher rate of interphase mass transfer than the conventional ceramic type of honeycomb module. The WMH module was constructed from alternating layers of flat and corrugated wire-mesh sheets packed within a frame. Wire-mesh sheets were coated with aluminum particles using electrophoretic method. Thermal sintering at 800degreesC and then calcinations at 500degreesC yielded a porous layer of Al/Al2O3 composite particles that were firmly attached on the wire surface. The alumina-protected wire meshes were further deposited with Pt/TiO2 catalyst powder by washcoating method. The oxidation of ethyl acetate was monitored as model reaction. A one-dimensional model was established and the parameters of intrinsic first-order kinetics were regressed from the reaction results obtained in the region controlled by chemical reaction, after which interphase mass transfer coefficients were regressed in other region. Three expressions for the Sherwood number that are typically used for honeycomb, wire-mesh gauze and packed bed reactors were examined to determine the optimal expression for WMHs. The mass transfer coefficient in the WMH was found to be quite different from that in the conventional ceramic honeycomb reactor and much higher than that in the wire-mesh gauze reactor. The best-fit results were obtained with packed-bed expression, Sh = 1.06Re(0.50)Sc(1/3), indicating the mechanism of reaction in the WMH is most similar to that in a packed bed. The optimal Sh expression was then used to predict the behavior of systems with a larger channel size or longer bed; the model predictions showed good agreement with experimental results from real WMH reactors. (C) 2002 Elsevier Science Ltd. All rights reserved.