engleski

Modeling of the monolith reactors: the Influence of Intraphase Mass Transfer

The demand for new and better catalytic systems for reduction of NOx has given rise to extensive research in this area1. Present study is the continuation of our previous investigation in catalytic decomposition of NO over powder zeolite-based catalyst2,3. It deals with the use of a monolithic catalyst in the same reaction system. The preparation of the monolithic catalyst, composed of cordierite as an inert carrier and copper containing ZSM-5 zeolite as a catalytic washcoat, is described in details. Reaction of NO decomposition was performed in the temperature range from 573 to 773 K, over the monolith catalyst of various lengths and with various thickness of catalytic layer. The one- (1D) and two-dimensional (2D) heterogeneous models were used for simulation of the monolith reactor with the view to determining the importance of diffusional effects within the washcoat layer. Simulation of the whole monolith was reduced to the analysis of a single channel. Several assumptions were taken into account, such as steady-state, isothermal conditions, ideal flow and negligible pressure drop along the monolith channel. The change in the geometry of the monolith channels with the increase in the thickness of the catalytic washcoat was also considered. Previously proposed Langmuir-Hinshelwood type of the equation rate was used to describe kinetics of the reaction2,3. Physical parameters applied to the models were calculated using several correlations proposed in the literature. Under the conditions employed in this study, better agreement between the experimental results and theoretical prediction was obtained using 2D heterogeneous model. It has been concluded that 2D heterogeneous model can describe essential features of the monolith reactor, especially when the intraphase mass transfer resistance is significant. On the other hand, simple 1D model based on properly evaluated mass transfer coefficients can successfully predict the behaviour of the monolithic reactor only when the catalytic washcoat is very thin, i. e. with the valid assumption that the reaction occurs at the surface of the washcoat. References: 1. J.N. Armor, Chem. Mater., 6 (1994) 730.; 2. V. Tomasic, Z. Gomzi, S. Zrncevic, React.Kinet.Catal. Lett., 64(1) (1998) 89.; 3.V. Tomasic, Z. Gomzi, S. Zrncevic, Appl. Catal. B: Environ., 18(1998) 233.

modeling; monolith reactor; mass transfer

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