【作者】 张俊梅；

【导师】 周明；

【作者基本信息】 天津大学 ， 化学工程， 2005， 博士

【摘要】 化工过程强化是传统化工发展的重要方向之一。难溶气体参与的气液反应过程中,气液传质是反应过程的主要阻力。催化剂微粒能增强气液传质,提高反应速率。本文就催化剂微粒对气液传质的增强作用做了实验和理论研究。在容积为1L的搅拌釜中,对树脂颗粒催化作用下的异丁烯水合反应及异丁烯在水-叔丁醇混合溶剂中的溶解度进行了实验研究。在0.74MPa、75℃实验条件下,考察了不同粒径颗粒催化剂及不同催化剂固含率作用下的水合反应速率。在70～90℃、0.60～0.74MPa条件下,得到了异丁烯溶解度与温度及叔丁醇摩尔浓度的关联式。利用全混釜浆料反应过程模型、异丁烯水合反应实验数据、参数估计程序,求解出异丁烯水合反应动力学方程参数及异丁烯在液相中的容积传质系数。通过比较不同粒径及不同固含率催化剂作用下的容积传质系数,得到结论为:小粒径颗粒对气液传质有增强作用,粒径越小增强作用越明显;在一定的催化剂固含率范围内,传质系数随固含率的增加而增加,且粒径较小时固含率的增强效果较大。本文提出液膜中催化剂微粒对气液传质的反应增强机理,在分析增强机理的基础上,应用膜-渗透理论,建立了非稳态三维模型。在模型求解中,采用复合网格方法,将整个偏微分方程积分区域分成若干个由单元网格覆盖的子区域,不同子区域选择不同的坐标系和单元网格,组成复合网格的单元网格在它们相遇处重叠。将复合网格形成步骤及算法和有限差分法结合求解此非稳态三维模型。反应增强机理模型考虑了微粒到气液界面的距离、微粒在气液界面停留时间、粒径、化学反应速率等因素及多颗粒对气液传质的影响。单颗粒模拟计算结果表明,微粒距离气液界面越远,微粒对气液传质的增强越小;当微粒与气液界面距离相同时,粒径增大,增强因子增大;当微粒表面的反应速率较小时,微粒表面的吸附性对气液传质起主要增强作用。多颗粒模拟计算结果表明,液膜中多颗粒对界面气液传质有相互影响的作用。在计算催化剂颗粒增强气液传质宏观增强因子的过程中,假设催化剂颗粒呈现初基六方阵分布。若考虑浆料表观粘度的影响,当固含率较大时,浆料粘度的增长降低了颗粒对气液传质的增强效果。模型计算结果和异丁烯水合反应中的实验结果基本吻合。更多还原

【Abstract】 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.更多还原