Study On Enhancement Of Gas-Liquid Mass Transfer By Catalyst Particles In Slurry Reaction System

The intensification of chemical engineering process is one of the important developments that go beyond traditional chemical engineering. Frequently the absorption rate of sparingly soluble gas reactant to liquid phase limits the reaction rate. While the adsorption rate can be significantly enhanced by the presence of fine catalyst particles. This paper intends to study the enhancement effect and mechanism of catalyst particles to gas-liquid mass transfer in reaction system.The experiments of isobutene hydration reaction and isobutene solubility in mixed solvents of water and tertiary butyl alcohol were carried out in a stirred autoclave reactor. The volume of reactor is 1dm3. The reaction rates catalyzed by various catalyst particle size and various catalyst solid contents were studied at 350K and 0.74MPa. Isobutene solubility in water-alcohol mixtures has been correlated with alcohol concentration and temperature for alcohol concentrations up to 2.0 kmol/m3 and temperature range from 335.15K to 358.15K at pressure of 0.74MPa.The gas-liquid mass transfer coefficient of isobutene and isobutene hydration kinetics parameters were obtained by using the model of reaction process, experimental data and multi-parameter estimation procedures. It was found that the volumetric mass transfer coefficient increase with decreasing size of catalyst particles and it is a positive effect for the catalyst loading on gas-liquid mass transfer at low solid content and the effect of smaller size particle is more notable than that of larger size particle.The enhancement mechanism of gas-liquid mass transfer by heterogeneous chemical reaction near interface has been proposed. By analyzing the enhancement mechanism an unsteady-state three-dimensional model was developed based on film-penetration theory. The composite grid technique has been used to solve the model equations. The composite grid is consisted of simpler component grids chosen suitably to describe a particular subdomain and overlapping where they meet. The different component grids and coordinate systems are chosen to cover the diffusion field on which the PDF can be solved using a finite difference scheme.With mechanism model the effect of particle size, first order reaction rate constant, distance of particle to gas-liquid interface and residence time of particle neargas-liquid interface on the mass transfer enhancement have been discussed. The single particle simulations calculated results show that the enhancement factor increases with decreasing distance of particle to gas-liquid interface or increasing particle size in the same distance to interface, the particle position parameter is more importance than particle diameter and the adsorption capability of particle is major influence factor when reaction rate is little. Two particles simulation show that the presence of other particles in the vicinity of the particle considered may affect its influence on the gas absorption, and the influence is not additive relation of two single particle in the similar position. Taking all particles into account the investigated and integral region was chosen arbitrarily. It was found that the viscosity has more influence on enhancement factor in higher solid content than in lower solid content when the apparent viscosity of slurry was considered. The model calculation results described reasonably well the experimental data of isobutene hydration reaction catalyzed by resin particles.