Gas absorption in reactive slurries: Particle dissolution near gas-liquid interface

Abstract

The rates of gas absorption into reactive slurries constituted by “fine” particles of a sparingly soluble reactant are known to be enhanced when the particle size is smaller than the characteristic diffusional lengths of the reactive species. This study examines the process of particle dissolution and the consequent change in particle size(s) near the gas-liquid interface, in the presence of diffusional gradients, using Higbie's extended theory of mass transfer with chemical (instantaneous) reaction. The effect of changing particle size (including complete dissolution of the particles in this “film” zone) on the mechanism and extent of enhancement in the specific rate of absorption has been assessed using a population balance approach to track the interaction of the dissolution process with the evolving particle size distributions. It has been shown that the rates predicted from the proposed theory differ considerably from those computed using models available in the literature, for particles which are “small” enough. A variety of initial particle size distributions of different spreads have been used to show that for a given mean particle size, wide distributions produce lower enhancements in the specific rate than narrow ones. The specific rate-batch time trajectories for a typical batch slurry reactor have been generated along with the evolution of the particle size distributions in the bulk slurry phase in order to track the solid conversion as a function of batch time. Such conversions computed from theories available in the literature are likely to be gross overestimates in relation to the actual scenario. Some of the reported experimental absorption data have been reinterpreted in the light of the models developed here.