【作者】 卢素敏；

【导师】 马友光；

【作者基本信息】 天津大学 ， 化学工程， 2008， 博士

【摘要】 在气体吸收体系中加入活性分散相粒子是传质过程强化的一个重要手段,本文详细研究了三种不同分散相微粒(反应性固体颗粒、吸附性固体颗粒及分散液滴)对气体吸收过程的增强作用,并分别采用两种模型,即宏观模型及微观颗粒模型,对气液传质机理进行描述。宏观模型立足于整个吸收体系,综合考虑各种影响因素,所得到的颗粒对吸收的增强效应是基于全部颗粒影响的一个宏观效果。根据宏观模型,可以从总体上讨论各种影响因素对吸收的影响。微观模型则基于单个颗粒,考查每一个颗粒对浓度场、速度场的影响,考查颗粒之间的相互作用以及颗粒的屏蔽作用,可以从微观角度探求颗粒强化机理。两种模型即可相互检验,又相互补充,存在着密切的联系。由于颗粒间存在着强烈的相互作用,某一时刻颗粒的吸收强化应该是若干颗粒共同作用的宏观效果,如果仅将各单个颗粒对吸收的影响进行叠加,必然造成很大的误差,而宏观模型则可以克服这一不足,从总体角度对微粒的影响进行探索。对于反应性固体颗粒,所提出的模型考虑了颗粒直径分布及溶解效应的影响。当颗粒溶解度较大、反应速率常数较大时,颗粒粒径分布会对吸收产生很大影响。同时当颗粒溶解度较大、反应速率常数较大时,颗粒的溶解效应对传质的影响不能忽略,若不考虑颗粒溶解效应(即恒颗粒模型)所预测的增强因子将会高于实验值。通过不同疏水性能的固体颗粒对气体的增强作用实验以及分子筛疏水改性实验证实了对气体吸收具有强化作用的颗粒应当具备两个方面性质,即一定的疏水性和对溶质选择吸附性,并基于这一认识,建立了吸附性固体颗粒强化吸收模型,模型不仅探讨了各种不同的影响因素,而且合理解释了增强因子随分散固体颗粒浓度增加而渐进地逼近一恒定值的现象。针对液液分散体系强化吸收的特点,作者认为造成液液分散体系初始吸收速率下降的原因主要是界面污染,据此提出了“有效扩散系数”的概念;同时针对乳液形成机理,认为在每一个液滴周围存在着一层表面活性剂吸附膜层,此膜层阻隔了液液之间的传质速率,使传质阻力增加。利用搅拌槽反应器对CO2在不同的分散体系中的吸收进行了实验,并对所提出的模型进行了验证。实验结果与模型预测值能够很好地吻合,表明了模型的合理性。更多还原

【Abstract】 Mass transfer enhancement by introducing a third dispersed phase into gas absorption systems is an important intensification method. The effect of three kinds of dispersed particles with different properties, including reactive solid particles, adsorptive solid particles and dispersed liquid drops, on the enhancement of gas absorption was studied respectively. Two models (macroscopic and microcosmic models) were developed to interpret the mechanism of mass transfer in this paper.Based on the whole gas absorption system, various influence factors were taken into account in the macroscopic model in which the enhancement of gas absorption obtained by the dispersed particles is an overall effect of all particles. The macroscopic model considers the comprehensive effects of whole system and accordingly could be applied conveniently. Differently, the microcosmic model investigates the influence of each single particle on concentration field and velocity field, particle interactions and shielding effect of the first particles, and hence the micro mechanism of mass transfer enhancement by particles can be understanded clearly. The two models are mutually complementary and confirmed, and closely relative each other. Due to the strong interaction among particles, only a simple superposition of the effects of single particles will lead to large errors, however this disadvantage is overcome in macroscopic model considering the effect of dispersed particles entirely and systematically, the enhancement of gas absorption at a certain time should be a macroscopic result from the combined action of many particles.For reactive particles, a model was presented to describe the influence of the size distribution of particles and dissolving effect on enhancement factor. It was shown that the dissolution and the initial size distribution of particles are of key importance to the gas absorption when the particles could be dissolved easily or a fast reaction occurs. The enhancement factor would be considerably overpredicted if the particle dissolution effects are ignored.According to the experimental results of the modification of zeolite and the absorption enhancement by solid particles with different hydrophobicities, it could be found that the particles with an enhancement effect on the gas absorption rate should have two properties, i.e. hydrophobicity and a high adsorption capacity for the solute. A novel mass transfer model was developed and various effect factors were discussed, the phenomena that the enhancement factors increased quickly with solid concentration initially and then gradually reached a constant value were explained reasonably by the present model.In terms of the characteristics of liquid-liquid dispersed system, the initial decrease of gas absorption rate was considered as a result of interfacial contamination, and the concept of “effective diffusion coefficient”was proposed. According to the formation mechanism of emulsion, an adsorptive film by emulsifiers exists around each particle, and obstructs the diffusion of the solute between the two liquids, consequently leading to added resistance of mass transfer.The absorption of CO2 into different dispersed systems was investigated experimentally in a thermostatic reactor, and the models presented in this paper were validated. The calculated results agreed well with the experimental data, indicating the rationality of the models.更多还原