Mass Transfer through a Dense, Polymeric, Catalytic Membrane Layer with Dispersed Catalyst

Abstract

The mass-transfer rates, which enter the catalyst membrane layer, accompanied by first-order, irreversible reactions, were investigated. Depending on the catalyst particle size, heterogeneous and pseudo-homogeneous models were developed to describe the mass transport through the catalytic membrane layer. It was assumed that the chemical reaction occurs inside the catalyst particles. Using a simple physical model for the distribution of the catalyst particles in the membrane layer and for the mass transport into it, explicit mathematical equations were developed for the prediction of the mass-transfer rates, as a function of the physical and chemical parameters. Besides the reaction rate, the mass-transfer rate is strongly influenced by the membrane properties, such as the size of the catalyst particles, the catalyst phase holdup, the distance of the first catalyst particle from the membrane interface, in the case of the heterogeneous model, as well as the diffusion coefficients in the membrane phase and in the catalyst particles, the membrane thickness, etc. By decreasing the particle size and the distance of the first particle from the membrane interface, the mass-transfer rate can be significantly improved. On the other hand, the low diffusion coefficient in the catalytic particles, which is very often the case, can strongly lower the mass-transfer rate, as well as the effect of the chemical reaction on it. The pseudo-homogeneous model was recommended for fine (submicrometer-sized) catalyst particles, whereas the heterogeneous model is recommended for larger particles (approximately several micrometers in size). The simple, mathematical equations that were developed can be applied very easily for the prediction of the mass-transfer rate in the case of a catalytic membrane layer for both models that have been investigated.