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

This study further evaluates four mechanisms for the enhancement of gas-liq. (G-L) mass transfer (2003): (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 (0.5-30 kW ml-3). Phys. enhancement (mechanisms 1-3) and reaction enhancement (mechanism 4) are investigated sep. by dynamic gas absorption expts. without reaction and pseudo-steady-state gas absorption expts. with reaction. Two Pd-catalyzed reactions are studied: oxidn. of glucose (aq. phase) and hydrogenation of a-Me styrene (AMS) (org. 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 coeff., which is mainly attributed to mechanism 3. Esp. 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 aq. glucose slurry, phys. enhancement (mechanisms 1 and 3) and reaction enhancement (mechanism 4) are obsd. In org. AMS-cumene slurry, lyophobicity/lyophilicity affects reaction enhancement only. [on SciFinder (R)

Modeling the effect of particle-to-bubble adhesion on mass transport and reaction rate in a stirred slurry reactor : influence of catalyst support

The adhesion of catalyst particles to the gas–liquid interface significantly influences the rate of reaction in a three-phase gas-inducing stirred slurry reactor. For the Pd-catalyzed glucose oxidation reaction at mass transport-limited conditions, the experimental reaction rate is higher for lyophobic 3% Pd/C catalyst than for lyophilic 3% Pd/SiO2 catalyst. This is attributed to a higher particle-to-bubble adhesion (PBA) of the Pd/C catalyst. The interfacial catalyst concentration is quantified by a PBA equilibrium parameter in a PBA isotherm. The classical resistances-in-series GLS model cannot describe the overall reaction rate. An additional gas-to-solid GS model is presented with a gas-to-solid mass transfer coefficient to describe the increased rate of reaction by the catalyst particles adhered to the gas–liquid interface. The PBA equilibrium parameter and the gas-to-solid mass transfer coefficient during reaction are estimated as a function of mixing intensity, oxygen partial pressure, and catalyst concentration. The combined GLS–GS model adequately describes the experimentally observed reaction rates