Enhancement Of Gas-liquid Mass Transfer Research Articles

Solid effects on gas-liquid mass transfer in three-phase slurry catalytic hydrogenation of adiponitrile over raney nickel

Many three-phase catalytic reactions are limited by gas-liquid mass transfer. Previous works have found the transfer rate to be increased by the presence of fine catalyst particles. Most of the studies concerned active carbon particles in aqueous media. This paper intends to point out and to explain this effect in the case of catalytic hydrogenation of adiponitrile over Raney nickel particles. The experiments based on pressure variation due to the hydrogen absorption in a stirred batch reactor point out clearly an increase of k 1a at an optimum catalyst loading. This positive effect is reduced at high stirring speed and turns back to a small negative effect when using inert particles. The enhancement of gas-liquid mass transfer by particles is maximum when a layer of water is physisorbed at the catalyst surface. The water located at the solid surface could induce a better adhesion of the particles to the bubble. The total gas-liquid mass transfer could be enhanced when using particles with high hydrogen adsorption capability, by a “shuttle” or a “bridge” effect. The solid particles act as hydrogen carriers. These assumptions have been further supported by original experiments involving the same equipment and measurements with a simultaneous reaction. A model which takes into account particles adhesion at the interface has been set up and is in good agreement with the experiments.

Enhancement of gas-liquid mass transfer in a modified reversed flow jet loop reactor with three-phase system

Experiments were being performed to obtain the overall volumetric mass transfer coefficient, K L a in the modified gas-liquid-solid reversed flow jet loop reactor. Effect of solid particles on K L a has been studied and the results were compared with those in the other types of reactors reported in the literature

Enhancement of gas-liquid mass transfer using oscillatory flow in a baffled tube

We report experimental data on the effect of oscillatory flow in baffled tubes on the mass transfer of oxygen into water. Gas bubbles are sparged into a vertical tube and the kinetics of the liquid oxygen concentration followed. Fluid oscillation in the absence of internal baffles has little effect on the measured k La values; however, if both the baffles and oscillations are present, an up to sixfold increase in k La is reported. Trends in the mass transfer measurements are consistent with the fluid mechanics observed within the tube, and power density calculations suggest that the system is more energy-efficient than gas-sparged stirred tanks.

Enhancement of gas-liquid mass transfer by a dispersed second liquid phae

From experiments in a stirred cell contactor with flat gas-liquid interface, it is shown that the rate of mass transfer of oxygen into an aqueous solution can be enhanced by the presence of small amounts (0.5–1 vol%) of a dispersed organic phase (e.g. hexadecane, decane, decanol or cyclohexane), provided that the droplet diameter is in the order of or smaller than the film thickness (D/kL) and the solubility of oxygen in the organic phase is larger than in water. A simple model is proposed that predicts the experimentally observed enhancement factors with reasonable accuracy.