Chapter 9 - Mass transfer and catalytic reactions

Abstract

In any catalytic system not only chemical reactions per se but mass and heat transfer effects should be considered. Mass and heat transfer effects are present inside the porous catalyst particles as well as at the surrounding fluid films. In addition, heat transfer from and to the catalytic reactor gives an essential contribution to the energy balance. Physical transport processes can play an especially important role in heterogeneous catalysis. Besides film diffusion on the gas/liquid boundary there can also be diffison of the reactants (products) through a boundary layer to (from) the external surface of the solid material and additionally diffusion of them through the porous interior to from the active catalyst sites. Heat and mass transfer processes influence the observed catalytic rates. The core of modeling a two-phase catalytic reactor is the catalyst particle, namely simultaneous reaction and diffusion in the pores of the particle should be accounted for. These effects are completely analogous to reaction-diffusion effects in liquid films appearing in gas-liquid systems. Gas-liquid diffusion can be essential in homogeneous and enzymatic reactions if the catalyst is dissolved in the fluid phase, while one of the reactants has to be first dissolved. The process of simultaneous reaction and diffusion in fluid films and in porous materials is discussed. The chapter provides a summary of different reaction types of gas-liquid reactions, liquid-liquid diffusion with phase transfer catalysis, as well as catalytic two-phase systems It elucidates the impact of mass transfer.