Mechanisms of physical and reaction enhancement of mass transfer in a gas inducing stiffed slurry reactor

This study further evaluates four mechanisms for the enhancement of gas-liquid (G-L) mass transfer [Can. J. Chem. Eng. 81 (2003) 632-639]: (1) boundary layer mixing, (2) shuttling, (3) coalescence inhibition, and (4) boundary layer reaction. The present work focuses on G-L mass transfer enhancement in a gas inducing stirred slurry reactor (GIR) in a range of mixing intensities (0.5-30kW m(1)(-3)). Physical enhancement (mechanisms 1-3) and reaction enhancement (mechanism 4) are investigated separately by dynamic gas absorption experiments without reaction and pseudo-steady-state gas absorption experiments with reaction. Two Pd-catalysed reactions are studied: oxidation of glucose (aqueous phase) and hydrogenation of alpha-methyl styrene (AMS) (organic phase). The influence of lyophobic carbon particles, lyophilic silica particles, and of electrolyte on G-L mass transfer is studied. Mechanism 1 is predominant at low mixing intensity, whereas the contribution of mechanism 2 is insignificant. Carbon/silica particles and electrolyte individually increase the volumetric G-L mass transfer coefficient, which is mainly attributed to mechanism 3. Especially a combination of particles and electrolyte strongly increases G-L mass transfer. Mechanism 3 also holds at higher mixing intensity. Mechanism 4 magnifies the impact of mechanisms 1 and 3. The carbon/silica particle lyophobicity strongly influences the interaction with the G-L interface. In aqueous glucose slurry, physical enhancement (mechanisms 1 and 3) and reaction enhancement (mechanism 4) are observed. In organic AMS-cumene slurry, lyophobicity/lyophilicity affects reaction enhancement only. (C) 2003 Elsevier B.V. All rights reserved.