【作者】 潘艳秋；

【导师】 姚平经； 王世广；

【作者基本信息】 大连理工大学 ， 化学工程， 2008， 博士

【摘要】 炭膜是由含碳物质经高温热解炭化制成的一种新型无机膜。它不仅具有良好的耐高温和耐化学溶剂侵蚀的能力、发达的微米或纳米级孔隙和较高的机械强度，还具有制备成功率高、孔径易控制和清洁程度高等特点，因此在液体和气体分离方面有独到之处。但目前对炭膜的液体分离研究大多还处于实验室阶段，离工业应用有一定的距离。主要原因是对分离过程机理不明确和对污染控制措施不利等。因此研究炭膜液体分离机理和建立机理模型十分必要。在气体分离方面，因炭膜具备诱人的应用前景，故炭膜气体分离技术被认为是本世纪可部分替代现有分离技术的一个重要方法。但目前受膜制备方面的影响，气体分离炭膜还没有在工业上被广泛采用。所以加强膜的制备研究以及从机理上进行气体分离过程的研究来促进膜的制备，更有十分重要的意义。针对以上情况，本文在实验的基础上，从建立液体分离系统的机理模型和气体分离的分子模拟两个部分开展炭膜分离过程的机理研究，主要研究内容如下：以煤粉为原料、以羧甲基纤维素（CMC）为粘结剂制备管状煤基炭膜。以管状煤基炭膜作为支撑体、以聚糠醇作为前驱体材料制备复合气体分离炭膜。为实验研究奠定基础。在煤基炭膜微滤刚性颗粒（以二氧化钛为代表）液体混合物实验的基础上，通过探讨过程机理，建立描述微滤过程通量随时间变化的数学模型，同时确定微滤过程中滤饼层孔隙率的分布、颗粒的沉积粒径分布、饼层阻力及饼层厚度增长变化等。通过与实验数据及其他文献发表模型计算数据的对比，证明所建模型的适用性。在煤基炭膜微滤可变形粒子（以油滴为代表）混合液实验的基础上，分析微滤过程的阻力分布，探讨微滤过程机理，并讨论将以上所建刚性颗粒微滤系统模型应用于本系统的实现措施。在气体渗透实验的基础上，采用单孔狭缝模型和μVT-非平衡分子动力学（μVT-NEMD）方法对炭膜气体分离过程进行分子模拟研究。针对常规单孔狭缝模型模拟过程中化学势和压力计算时由于分子间相互作用的截断而产生的系统误差，本文增加了尾部贡献来进行模型校正，并根据压力和温度对CH₄和CO₂纯组分气体传递过程的影响，确定了L-J参数和通量随时间的变化函数，由此考察CO₂／CH₄混合气体通量和气体与膜孔壁间相互作用势能随孔径的变化趋势，确定分离过程机理。构建合适的膜的孔网络模型和孔径分布函数，采用临界路径分析方法（CPA）对膜孔的内部结构进行研究，并结合单孔狭缝模型模拟得到的CH₄／CO₂混合气体通量变化关系，确定炭膜分离CH₄／CO₂混合气体时的孔径范围，解决气体通量与分离选择性之间矛盾的问题。最后，尝试将孔网络模型的研究结果应用于炭膜分离煤层气过程，设计分离方案并确定各级分离膜的孔径。更多还原

【Abstract】 Carbon membrane, as an important member of the inorganic membrane family, is prepared by pyrolysis of various carbonaceous materials. It possesses advantages of better thermal and chemical stabilities, wear resistance and well-defined stable pore structure. Therefore, carbon membrane relevant researches have gained a worldwide interest in liquid separation and gas separation. On the one hand, the carbon membrane has been experimentally demonstrated to be feasible and effective in separation of liquid mixture. On the other hand, the carbon membrane is recognized to have an attractive prospect in separation of gas mixture to displace current separation technology in this century. However, investigations on carbon membrane separation are in the lab-scale and technology push stage with less reports of industrial application. This is due to the lack of the understanding of carbon membrane separation mechanisms.In this dissertation, a systematic research on carbon membrane separation was proposed and performed including membrane fabrication, separation experiments, mechanism model development of liquid separation and molecular dynamics simulation of gas separation. Specifically,The coal-based tubular carbon membrane and the carbon composite membrane using the former as a support were prepared based on available procedures.Experiments was carried out on microfiltration of liquid mixture using TiO₂ as the representative of rigid particles. A mathematic model describing flux variations with time was developed introducing a variable cake porosity function through a mechanism analysis. Critical diameter, cake resistance, cake porosity and cake height variation with time were successfully obtained. The model predictions show excellent agreements with the experimental data, which confirms the practicability and validity of the model developed.Experiments was conducted on microfiltration of oily wastewater with oil droplet as the representative of deformable particles. Based on the modified Hermia’s model, membrane fouling mechanisms were analyzed and resistance controlling factors of permeate flow were determined. Meanwhile, the implemental approach of the model developed for the rigid particle system to be used for the deformable particle system was discussed.Experiments was performed on permeation of pure CH₄ and CO₂. TheμVT ensemble nonequilibrium molecular dynamics （μVT-NEMD） simulation was then conducted using a slit pore model to investigate the effects of temperature and pressure on permeation of pure CH₄ and CO₂ so as to fix the appropriate Lennard-Jones interaction parameters according to the experimental data. Afterwards, the effects of pore size on the fluxes and wall potential energies of a binary mixture of CH₄ and CO₂ are numerically examined. The results show that the process of gas separation in carbon membrane is affected by various factors. Molecular sieving and selective adsorption are the dominating mechanisms of gas separation.A pore network model and a pore size distribution function were constructed. Using the of critical path analysis （CPA） method, a deep insight into the internal structure of pores was attained. With the binary mixture of CH₄ and CO₂ as a prototype, different pore size ranges of the species to be transported in membrane considering the effects of pore connectivity on gas separation were numerically determined based on the flux variation with pore size stimulated by the slit pore model. The membrane flux and its separation selectivity were compromised. And then, the pore size distribution curve was stimulated, which displays an excellent agreement with the experimental measurement, suggesting that the pore network model constructed can represent the separation process of CH₄ and CO₂ of the carbon membrane. At last, the pore network model constructed was applied to predict the separation process of a ternary system of CH₄/CO₂/H₂, the typical three components in coal-bed methane. Two-stage separation strategy was designed with different pore size range determined in each stage.更多还原