【作者】 乔智威；

【导师】 周健； Randall Q.Snurr；

【作者基本信息】 华南理工大学 ， 化学工程， 2013， 博士

【摘要】 流体混合物的吸附分离不仅是化工过程中一个重要的单元操作，而且在产品分离、尾气处理、药物提纯、节能减排、海水淡化和环境保护等多个领域中也发挥着重要的作用。借助于计算机分子模拟技术研究混合物在多孔材料内的吸附分离对于从分子水平上理解其内部分离机制具有重要的意义和明显的优势。为了系统地研究各种多孔材料的特性（自由体积、聚合度、官能团、孔径），吸附质的性质（分子大小、粘度、逸度、极性、手性），它们之间的相互作用（范德华力、氢键作用、静电），外界条件（温度、压力、湿度和进料浓度）对吸附分离行为，尤其是吸附量和分离因子的影响，本论文通过密度泛函法（Density functional theory，DFT）、蒙特卡罗方法（Monte Carlo，MC）和分子动力学方法（Molecular Dynamics，MD）结合，并使用Gaussian，Materials Studio，MuSiC，RASPA等多种软件平台进行计算，对多种力场进行比较，以期能够发现适合实际需要的吸附分离材料，并模拟分析出最合适的分离条件以及分离结果，从而满足分离技术应用中的需求。本论文具体研究内容分为以下五个部分：1.采用巨正则蒙特卡罗方法（Grand canonical Monte Carlo，GCMC），研究在不同压力（10-1000kPa）、不同温度（298-338K）以及不同聚合度（100-1000）下，聚乙烯醇（PVA）聚合物膜中水和乙醇共沸物（乙醇质量分数为95.57wt%）的渗透汽化过程。通过计算吸附等温线和分离因子，发现水和乙醇吸附量和分离效率随着温度升高缓慢的下降；随着聚合度升高，二者的吸附量都先上升后下降，而分离因子则相反。我们分析了聚合物膜的自由体积分率和它与吸附分子之间的氢键作用，并用于解释上述现象：当聚合度升高时，自由体积分率变化的趋势与之前讨论吸附量的趋势是相似的，但是极值所对应的聚合度却不同，而氢键作用则被成功地用于解释这一区别。经过深入地讨论发现，吸附量的变化主要是因为自由体积分率和氢键作用从共同作用到竞争作用的变化。研究发现，分离最优的操作条件为温度298K以及压力101.325kPa，在这一条件下，1000聚合度PVA膜对乙醇和水共沸物的分离因子可达到80，这一分离效率足以制备99.96wt%的无水乙醇。2.采用GCMC方法讨论了不同温度、压力及管径下，碳纳米管对H2S/N2混合物(主体相体积比为1:99)的吸附分离选择性。结果表明，随着碳纳米管管径的增大，H2S的吸附选择性先增加后减小；而(11，0)碳纳米管（管径为0.86nm）对H2S的选择性最高。经过对吸附构型和吸附热的分析，我们发现H2S的吸附选择性与管径的关系是由几何效应和能量效应共同决定的。针对(11，0)碳纳米管，讨论了温度和压力对H2S吸附量和选择性的影响。模拟结果表明，随着温度上升，H2S的吸附量和选择性都呈先增加后减小的趋势；随着压力增加，H2S的吸附量和选择性都有所下降。此研究可为含硫气体混合物的吸附分离提供一定的指导。3.并行退火-构型偏倚-巨正则蒙特卡罗（PT-CB-GCMC）和并行摩尔分率-构型偏倚-巨正则蒙特卡罗（PMF-CB-GCMC）方法被用于研究四种烷烃醇在纯手性金属-有机骨架材料（HOIZA-1）中的手性分离机制。由于这类系统中的手性分子紧密结合于窄孔中，传统的GCMC方法不能够满足于此系统的模拟。但是，并行退火和并行摩尔分率的技术手段因为MC移动接受率的改进克服了这一问题。研究中，无限稀释流体吸附焓的分析证明了所使用的两种改进GCMC方法是优于传统GCMC方法的。其模拟结果显示(R,S)-烷烃醇的手性吸附分离原因与手性分子特殊的几何构型以及材料孔道尺寸和形状密切相关的。4. GCMC方法被运用于研究五种不同的金属-有机骨架材料（Metal-organicframework，MOF）中CH4和CO2混合物的吸附分离机制，它们是未改性MIL-53(Al)以及四种胺基基团（-NH2,-(NH2)4,-NHCO,-CH2CONH2）改性的MIL-53(Al)。研究发现，虽然未改性的MIL-53材料有最高的吸附量，但是它并没有最优的分离效率，而-(NH2)4胺基官能团改性MIL-53材料的分离效率达到最优。进一步发现，-NH2和-NHCO功能化材料的分离性能也优于未改性的材料，但-CH2CONH2改性材料的性能却不是非常优异的，它的分离因子和吸附量都低于未改性材料。几何效应和能量效应被用于分析和解释它们分离效率的不同。这一工作揭示了设计新型功能化MOF材料是一种有效地改进CH4和CO2分离效率的方法，同时它也对将来MOF材料的合成和应用有极其重要的推进作用。5.本章工作提出了一种新颖的筛选方法，这一方法对大量MOFs以及它们的功能化材料性能进行重复筛选层层分析。为了解释这一方法，我们分三步详细讨论和分析了不同胺基官能团功能化MOFs材料的CH4和CO2分离性能。第一步，筛选了大量传统的未改性MOFs材料；第二步，筛选了多种多样的胺基官能团；第三步，筛选了不同数目的胺基官能团。模拟结果显示：其中两种材料的分离效率在近150种材料中达到最佳，而且在研究中我们提出了“胺基官能团饱和度”这一概念。这一新颖的筛选方法和胺基官能团饱和度的提出有助于大幅度提升实验合成功能化MOFs材料的经济效率，并缩短开发新型功能化MOFs材料的周期。更多还原

【Abstract】 Adsorption separation of the fluid mixture is an operating unit of chemical process andhas an important influence on seawater desalination, purification, wastewater treatment,environmental protection etc. The molecular simulation methods (DFT, MC and MD) andGaussian, Materials Studio, MuSiC and RASPA softwares can be employed to studymembrane properties (free volume, degree of polymerization, functional groups), the natureof adsorbate (molecular size, viscosity, fugacity, polarity), the interactions between membraneand adsorbate (van der Waals force, hydrogen bonds, electrostatics), the external conditions(temperature, pressure, humidity, feed concentration) on the adsorption separation behavior.The optimized adsorption loading and separation factor can be found for the actual adsorptionprocess. The thesis includes five parts, as follows.1. Grand canonical Monte Carlo (GCMC) simulation is used to investigate theperformance of poly (vinyl alcohol)(PVA) membrane in separating the azeotropicwater/ethanol mixture (95.57wt%ethanol) over a wide range of pressures (10–1000kPa),temperatures (298–338K) and PVA polymerization degrees (100–1000). By calculating thesorption isotherms and the ethanol-to-water separation factors, we observe that thewater/ethanol adsorption amount and separation factor decline slowly with the increase oftemperature; as the polymerization degree rises, both of adsorption amounts first increase andthen decrease, while the separation factor changes adversely. Concepts such as fractional freevolume (FFV) and hydrogen bonding interactions were analyzed to explain the observation.As the polymerization degree increases, the FFV changing trend is similar to the onementioned in the discussion of adsorption amount, but their inflexions are different. Hydrogenbonding interaction successfully explains this variation. We further deduce that the fact thatthe change of adsorption amount results from a transition from cooperation to competitionbetween FFV and hydrogen bonding interactions. The optimal operating conditions forseparation are298K and101.325kPa. Under this condition, the PVA membrane(polymerization degree1000) has a separation factor of～80for the water/ethanol azeotropicmixture, which means that ethanol can be refined to99.96wt%and anhydrous ethanol ispossible to be obtained by PVAmembrane evaporation.2. Adsorption and separation of1:99(volume ratio) H2S/N2mixture by single wallcarbon nanotubes are studied using the GCMC method at a range of nanotube diameters,pressures and temperatures. It is demonstrated that the selectivity towards H2S increases andthen decreases with increasing nanotube diameter and the selectivity is highest for (11,0) carbon nanotube, which is due to the synergy of geometry effect and energy effect. It is shownthat under different operation conditions, the adsorption isotherm and selectivity can varysignificantly. At100kPa, the amount of adsorbed of H2S in (11,0) carbon nanotube and theselectivity towards H2S firstly increase and then decrease with increasing temperatures.Moreover, at300K, with increasing pressures, the adsorbed amount of H2S and the selectivitytowards H2S decrease. The simulation findings in this work would be helpful for the designand development of sulfur removal processes.3. Parallel tempering and parallel mol-fraction grand canonical Monte Carlo simulationswith configurational bias are used to study the enantioselective adsorption of four alkanols ina homochiral metal-organic framework (MOF), known as HOIZA-1. Conventional GCMCsimulations are not able to converge satisfactorily for this system due to the tight fit of thechiral alkanols in the narrow pores. Parallel tempering and parallel mol-fraction simulationsovercome this problem because of the improvement of acceptance ratios of Monte Carlomoves, the results of infinite dilution enthalpy of adsorption also prove that they are superiorto conventional GCMC. The simulations show that the enantioselective adsorption of thedifferent (R,S)-alkanols is due to the specific geometry of the chiral molecules relative to thepore size and shape.4. GCMC simulations are employed to study the adsorption and separation of carbondioxide/methane gas mixture by five different metal organic frameworks (MOFs) includingthe unmodified MIL-53(Al) and four amine functionalized (-NH2,-(NH2)4,-NHCO,-CH2CONH2) MIL-53(Al) MOFs. It is found that although original MIL53had the bestadsorption amount, its separation efficiency is not very high. The carbon dioxide/methaneseparation factor of-(NH2)4amine functionalized MIL-53is the best in five MOFs. Moreover,the predicted separation performance of-NH2and-NHCO functionalized MIL-53alsosurpass that of the original one. However, the predicted separation performance of-CH2CONH2modified MIL-53is not so good; i.e., both its carbon dioxide/methaneseparation factor and adsorption amount are lower than those of the original one. Thegeometric effect and energetic effect are analyzed to explain the difference of separationefficiency. This work shows that a rational design of functionalized MOF is a feasible way toimprove the carbon dioxide/methane separation efficiency and to provide helpful informationfor future MOF preparation and applications.5. A novel3-step in-silica screening method for a large number of MOFs and theirfunctionalized ones is offered. The improvement of CO2separation capability from theCO2/CH4mixtures using different amine functionalized MOFs are discussed and analyzed carefully. In the first step, plenty of classical types of original MOFs are screened. In thesecond step, the various amine functional groups are screened. In the third step, differentnumbers of amine functional groups are screened. The results show that the separationefficiencies of (NHCOH)4-MIL-53and (NH2CH2CH2NH2)9-Co-MOF-74reach maximum inabout two hundred screened MOFs; amine functional group saturation degree is also proposed.The novel screening method and the concept of functional group saturation degree could beapplied in cost-effective experiments and reduce the period of the development of newfunctionalized materials in future researches.更多还原