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Effectiveness enhancement and reactant depletion in a partially wetted catalyst
Author(s) -
Harold M. P.,
Ng Ka M.
Publication year - 1987
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690330905
Subject(s) - wetting , isothermal process , catalysis , chemistry , pellet , reaction rate , kinetics , thermodynamics , chemical engineering , materials science , organic chemistry , composite material , physics , quantum mechanics , engineering
Abstract A one‐dimensional model is developed to describe reaction between a nonvolatile liquid reactant and a dissolved gas reactant in an isothermal catalytic pellet partially wetted by a flowing liquid film. The kinetics are assumed to be first order and zero order with respect to the dissolved gas and liquid reactant, respectively. The model applies to cases in which there are negligible intraparticle gradients in the direction normal to the wetted surface. A modification of the overall transport coefficients enables the model to approximate cases in which these gradients are important, for both washcoated and uniformly impregnated catalysts. The analytical solutions enable an efficient examination of the interplay between the reaction and several mass transport processes. Conditions are determined for which the catalyst effectiveness is maximized at an intermediate wetting efficiency. It is shown that the maximum is a result of two counteracting processes. As the wetting efficiency is decreased from unity the effectiveness increases if the supply of the gas reactant is more effective on the nonwetted than the wetted part; i.e., effectiveness enhancement. However, if the wetting efficiency is sufficiently reduced, the excess liquid reactant depletes within the pellet, resulting in a decreased effectiveness. A criterion is derived that predicts the minimal activity necessary to initiate depletion of the liquid reactant for a given wetting efficiency. This is useful for determining the conditions for which the common literature assumption of an excess liquid reactant is violated. The model shows good agreement with published data in which the overall rate exhibits a maximum for an intermediate liquid flow rate.