【作者】 杨东晓；

【导师】 王志；

【作者基本信息】 天津大学 ， 化学工程， 2009， 博士

【摘要】 固定载体膜因其中的活性载体可以与CO₂发生可逆化学作用,大大促进了CO₂在膜中的传递,因此这类膜具有良好的CO₂分离性能和很大的应用潜力。目前,固定载体膜的传质机理尚未完全探明,对固定载体膜应用过程的研究更是缺乏。本文研究了固定载体膜的促进传递机理,对分离CO₂固定载体膜的应用过程进行了模拟和优化。研究结果对固定载体膜的开发和应用具有重要指导作用。本文以两种含胺基固定载体膜为例,对固定载体膜促进传递过程的一般特征和规律进行了实验验证,为固定载体膜传质机理的研究提供了数据基础。对固定载体膜促进传递过程微观机制进行分析,提出了平衡浓度区理论,进而建立了新的传质数学模型。利用该模型得到固定载体膜内传质阻力的非均匀分布和固定载体膜渗透速率与膜厚度的非线性关系。通过对不同温度条件下实验数据的拟合,得到固定载体膜内CO₂扩散过程和CO₂与载体相互作用的表观活化能,数值均在文献报道范围内。对伊春海博士提出的促进传递模型进行改进,得到了考虑渗透侧压力影响的渗透速率数学模型。利用模型分析的结果表明,在不同的渗透侧压力条件下,组分的渗透速率是不同的,较低的渗透侧压力有利于提高固定载体膜中的渗透速率。据此,本文提出了针对固定载体膜的进料侧加压（压力保持在较低范围）和渗透侧抽真空相结合的压力操作模式。针对天然气脱除CO₂和燃烧尾气捕集CO₂两个重要的分离CO₂过程,分析了并流模型、逆流模型和错流模型的模拟结果,证明错流模型适用于两种过程,而且具有简易的特点。利用错流模型对固定载体膜在两种分离CO₂过程中的应用潜力进行了研究,比较了单级过程和带有循环流二级过程的分离性能。结果表明,对上述两个分离CO₂过程,固定载体膜都比现有商品膜更容易实现分离目标;与单级过程相比,带有循环流二级过程的分离效果显著提高。对带有循环流二级过程的操作压力进行优化,使分离CO₂的成本大大降低,并可与胺吸收法相竞争,说明固定载体膜在燃烧尾气捕集CO₂领域具有良好的应用潜力。本文还对带有循环流二级过程进行了参数分析。结果表明,对于分离因子较大的膜,提高慢气（渗透速率较低的气体组分）渗透速率,可以减少过程所需膜面积;对于分离因子较小的膜,提高分离因子,循环气流量降低,过程所需膜面积减少。采用较高分离因子的膜和较低的操作压力比,可以得到更高CO₂浓度渗透气,有利于对富含CO₂的渗透气的后续处理（例如地下埋存）。更多还原

【Abstract】 Because of the reversible chemical interaction between CO₂ and the carrier, the CO₂ transport in the fixed carrier membrane is facilitated remarkably. Hence, the fixed carrier membrane has excellent separation performance and great application potential. Currently, the mass transport mechanism of the fixed carrier membrane is still not quite clear and the application study of the fixed carrier membrane is needed. In this paper, the mechanism of the facilitated transport of the fixed carrier membrane is further studied. The application process of the fixed carrier membrane is simulated and optimized. The results can offer guidance for the development and application of the fixed carrier membrane.The characteristics of the facilitated transport process of the fixed carrier membrane were investigated experimentally, taking PEI-PVA/PS and PAAm-PAM/PS composite membranes as examples. The experimental data offered foundation for the research of the mechanism of the fixed carrier membrane.The microscopic mechanism of the facilitated transport of the fixed carrier membrane was analyzed, and an equilibrium region theory was proposed according to which novel mathematical model was founded. Analysis was carried out by using the novel model. The nonlinear distribution of the transport resistance and the relationship between the permeance of fixed-carrier membrane and the membrane thickness were obtained. The apparent activation energies for the CO₂ diffusion and collision between the CO₂ molecular and the active site in the fixed-carrier membrane were obtained by fitting the experiment data. The calculation results were in good agreement with the literature.A mathematical model reflecting the effect of the permeate side pressure was derived from the macroscopic model founded by Dr. Yi of our research group. The new model was used to analyze the effect of the permeate side pressure. Results showed that under different permeate pressures, the permeance was different. High permeance could be obtained by increasing the permeate side pressure. Therefore, the operating model of the combination of feed compression and permeate vacuum pumping was suggested. The calculation results of the cocurrent flow model, the countercurrent flow model and the cross flow model were analysed for the processes of the CO₂ removal from the natural gas and the CO₂ capture from the post-combustion gas. The cross-flow model proved simple and suitable for the two processes and was thus used in the analysis in this paper. The application potential of the fixed carrier membrane in the two processes was investigated, and the separation performance of the two stage system with recycle was compared with that of the single stage system. Results showed that the separation target could be achieved more easily by using the fixed carrier membrane than using the current commercial membranes; the separation performance of the two stage system with recycle is much better than that of the single stage system. The operating pressures of the two stage system was optimized and the CO₂ separation cost decreased remarkably. The cost of the optimized two stage system was competitive with the amine absorption method and the application potential of the fixed carrier membrane in the field of the CO₂ capture from the post-combustion gas was verified.Parametric analysis was carried out for the two stage system with recycle. Results indicated that for the membrane with high selectivity the membrane area could be reduced by increasing the slow gas （the gas component with low permeance） permeance. For the membrane with low selectivity, as the selectivity increases the recycle flowrate decreases and membrane area requirement decreases. The permeate gas with higher CO₂ concentration, which is beneficial to the further treatment of the permeate gas rich in CO₂ （for example, geo-sequestration）, can be obtained by adopting membrane with high selectivity and low operating pressure ratio.更多还原