Liquid-to-particle mass transfer in fixed bed reactor with cocurrent gas-liquid downflow

Abstract

Mass transfer coefficient ku was measured over a range of flow rates of gas Ug= 0-100 cm s-1 and liquid (Ul=0.05-25 cm -s_1 in a column packed with spheres of three different diameters d=2.8-12.7 mm. The systems used were the dissolution of benzoic acid in water and diffusion-limited oxidation of brass with dichromate ion in sulfuric acid solution. The effect of Ugon kis is not found at all in gas continuous flow, is the greatest in pulse flow and becomes less significant again in dispersed bubble flow. The value of ku increases rapidly around the transition from gas continuous to pulse flow. The enhancement factor ft (=ku in two-phase flow/ ku in single-phase flow) increases from 1.2 to 2 with increasing d in gas continuous flow while it equals the reciprocal of liquid holdup in pulse and dispersed bubble flows. A liquid-film analogy in gas continuous flow and a single-phase analogy in pulse and dispersed bubble flows are proposed and the experimental results are examined in the light of them. © 1976, The Society of Chemical Engineers, Japan. All rights reserved.