Fast reactions in slurry reactors: catalyst particle size smaller than film thickness: oxidation of aqueous sodium sulphide solutions with activated carbon particles as catalyst at elevated temperatures

Abstract

Catalyst particles, smaller than the diffusion film thickness, in slurry reactors, can enhance the specific rate of absorption substantially over that in the presence of coarser particles, even when the reaction is sufficiently fast to occur in the film in the absence of catalyst particles. This is illustrated with a study of the kinetics of absorption of oxygen in aqueous solutions of sodium sulphide. This study was carried out in stirred contactors with plane interface of 14.5 and 7.5 cm i.d. at temperatures of 80°to 150°C and a total pressure of 1.5 to 9.5 atm, with or without fine activated carbon particles (average particle size 1.7 and 4.33 microns; 0.01 to 2.0% w/w loading) as a catalyst. Some experiments were also conducted with coarse carbon particles (average particle size 85 microns and particle size> 20 µm). Under certain conditions, in the absence of activated carbon, the absorption is accompanied by fast pseudo first order reaction in the film. In a number of cases with fine carbon particles, the specific rate of absorption increased by a factor of 2 to 11 and in some cases this factor was as high as 14. A simple theory has been developed which indicates that, under certain conditions, at higher catalyst loading, the specific rate of absorption will be inversely proportional to the particle size.