【作者】 杨启鹏；

【导师】 王修林； 赵学波；

【作者基本信息】 中国海洋大学 ， 环境科学， 2013， 博士

【摘要】 一般认为，H₂是最符合人类可持续发展要求的绿色能源。由于自然界中仅存在极少量的游离态H₂，因此在工业生产中通常采用CH₄裂解法制备H₂，其中H₂与CH₄气体分离是制备高纯H₂的关键工艺技术。目前，一般采用变压吸附法分离H₂与CH₄，但由于选择性较低，难以生产出高纯H₂，同时还存在能耗大、成本高等问题。膜分离技术是有着广泛发展前景的气体分离高新技术，但传统的膜材料都难以满足高纯H₂制备技术的要求。例如聚砜膜、醋酸纤维膜等有机聚合物膜气透性较低，结构稳定性较差。炭分子筛膜等无机膜具有良好的热稳定性，但由于孔道结构很难控制，导致分离选择性较差。因此，在高纯H₂制备工业化生产技术发展中，迫切需要开发新型膜材料。二十世纪末，人们开发出金属有机骨架化合物（MOF），由于其具有结构热稳定性高、孔道结构可控等特点，在包括气体高选择性分离在内的诸多领域展现出广泛而良好的应用前景。目前，国际上关于气体分离MOF膜的研究尚处于起步阶段，即使关于MOF膜制备的文献报道也不多。对于理想的H₂/CH₄分离膜技术，既要具有MOF材料的高选择性和结构热稳定性等特性，又要具有无机膜材料较强的机械强度等特性。因此，本文研究目的是针对CH₄裂解法高纯H₂制备中，H₂和CH₄气体分离的关键工业技术，研制开发同时具有极高选择性、较高结构热稳定性、较大机械强度等特性的新型MOF/多孔氧化铝复合膜。该研究对于扩展MOF膜材料在混合气体中高选择性分离H₂具有实际应用价值，同时对于开发新型MOF材料，也具有重要的理论意义，研究结果主要体现在三个方面：一、新型H₂/CH₄气体分离MOF膜的晶体合成、结构表征及热稳定性。对于理想的H₂/CH₄气体分离MOF功能材料，不仅要求在结构上具有高选择分离性能，具有孔道结构且孔径应介于H₂和CH₄气体分子动力学直径之间，而且要求具有良好的结构热稳定性，在373-473K温度范围内仍能保持稳定的孔道结构。对此，本文选择5种配体，采用反应物浓度0.003-0.05mol/L，溶剂为水、甲醇或DMF，实验温度298-453K，反应周期4-7天等实验条件，共合成出8种新型MOF晶体材料，结果如下：1、应用单晶衍射方法测量表明，配合物1: Cu（ClO4）2.C₁₆H₁₆N₂O₅、2:[C₁₆H₁₈N₂O₅].[ZnCl4]、3:[C₁₆H₁₇N₂O₅]·[ZnCl3]、4:[C₁₆H₁₇N₂O₅]·[ZnCl3]和5:Cu₂（ClO₄）₂（OH）₂·(C₁₆H₁₆N₂O₅)2·2CH₃OH具有零维密实的晶体结构。配合物6:HgI2·C18H₂4N6O4具有一维晶体结构，在C轴方向形成一维孔道，孔径约为0.5nm。配合物7:Co(C₁₀H₈N₂).（CHO2）2为三维密实晶体结构。配合物8:Ni_1.5(C₁₀H₈N₂)_1.5.C₁₂H₂₈O₉P₃.（H₂O）₃具有三维晶体结构，属四方晶系，沿C轴方向形成一维孔道结构，孔径为0.38nm。在八种新型MOF晶体材料中，配合物6和8具有孔道结构，但配合物6孔径为CH₄气体动力学直径1.3倍，只有配合物8的孔径大小正好介于H₂和CH₄气体分子动力学直径之间。2、应用热重分析方法检测表明，在氮气气氛下，配合物8在低于453K时，能够保持结构稳定，具有较强的结构热稳定性。3、配合物8晶体材料对单组分气体吸附实验表明，在压力0-1000mbar，温度303K条件下，由于H₂气体分子与MOF材料间的作用力极弱，导致晶体材料对H₂气体吸附量为零；在温度303K，压力1000mbar下，晶体材料对分子动力学直径小于孔径的CO2吸附量约为2wt%。然而，在273K和303K温度条件下，由于CH₄分子动力学直径大于MOF孔径，CH₄无法进入孔道，导致MOF晶体材料对CH₄的吸附量为零。这说明，配合物8晶体结构对气体分子具有很强的分子筛筛分性能。二、多孔氧化铝膜基底材料制备及H₂/CH₄气透性。对于高选择性H₂/CH₄气体分离的MOF复合膜，理想的无机基底材料不仅要与MOF材料有较强的表面附着力，而且要具有较强的机械强度和良好的气透性，这些主要决定于基底表面性质、厚度及孔径大小。一般而言，镍网、多孔陶瓷片、透气钢片和多孔氧化铝膜等是常用的无机基底材料。应用原位法制备MOF/无机基底材料复合膜，实验结果表明，多孔氧化铝膜为最优基底材料。多孔氧化铝膜厚度为77.4μm，孔径为25nm时，可以同时满足复合膜在气透性和机械强度两方面的要求。其耐压强度大于1Mpa，H₂和CH₄气透率分别为5.607×10-5mol/Pa·m²·s和2.385×10-5mol/Pa·m²·s。三、新型MOF/多孔氧化铝复合膜制备和H₂/CH₄气体分离性能。理想的MOF/多孔氧化铝复合膜在分离性能上应具有H₂/CH₄气体分离性高和结构热稳定性高，在物理性质上应具有厚度可控且均一、耐压强度好和气透性适中等特性，具体结果如下：1、采用平板真空法制备新型MOF/多孔氧化铝复合膜，MOF涂膜液浓度及涂布方式、操作温度及不同镍盐等对复合膜结构都产生不同程度的影响。实验表明，MOF涂膜液浓度在0.2-0.7%之间均可以得到完整复合膜；反应温度由413K升高到433K，复合膜的厚度由450μm降低到200μm；采用Ni（CH₃COO）₂.4H₂O作为镍盐得到复合膜厚度为200μm，但晶体存在纵向堆积。2、综合考虑MOF复合膜质量，选择MOF晶种层厚度是450μm，多孔氧化铝膜厚度77.4μm的MOF/多孔氧化铝复合膜作为气体测试膜。复合膜耐压强度大于1MPa，在温度298K时，单组分H₂和CH₄气体渗透率实验表明，H₂气透率为1.44×10-9mol/Pa·m²·s，并且在压差0.1-0.3MPa间几乎不随压力变化，而CH₄气透率为零，无法透过该复合膜。3、在298-373K温度范围内测试H₂/CH₄混合气体渗透率。实验表明，H₂气透率随温度的升高逐渐降低，CH₄气透率为零，这说明该复合膜对H₂/CH₄混合气体有极高的选择性，可以用来制备高纯H₂。综合上述研究结果，新型MOF/多孔氧化铝复合膜具有良好结构热稳定性、较强的耐压强度及极高的H₂/CH₄气体分离性能，有望在CH₄裂解法高纯H₂制备中得到应用。其中，科学创新点主要是在国际上首次采用平板真空法制备出同时具有较强耐压强度、高结构热稳定性及极高H₂/CH₄选择性的新型MOF/多孔氧化铝复合膜。研究特色主要是得到了MOF/多孔氧化铝复合膜制备技术参数，为MOF/多孔氧化铝复合膜在高纯H₂制备工业化技术开发中，提供了必要的理论指导及技术基础。更多还原

【Abstract】 As a kind of green energy, hydrogen has been considered to meet therequirements of human sustainable development. Generally, hydrogen is produced bydecomposition of methane, because there is only a small amount of hydrogen innature. During productive process, the key technology is how to separate purehydrogen from hydrogen and methane mixtures. At present, because of its lowselectivity, as well as high energy consumption and high cost, it is difficult to separatepure hydrogen from the mixed gases by pressure swing adsorption. In contrast totraditional separation technologies, Membrane-based gas separation technology is ofhigh efficiency and plays an increasingly important role in industrial processes.However, traditional membrane materials are difficult to meet the development of thistechnology. Polymer membranes are prone to be plasticized or swollen, leading to alow efficiency of gas separation. With high thermal stability, inorganic membranes,such as carbon molecular sieve membrane, could maintain stability at hightemperature, however, the uncontrollable pore structure limits its further development.Thus it is urgent and necessary develop a new type of membrane material to separatepure hydrogen during industrial production.In the end of the twentieth century, metal-organic framework （MOF）, which arecrystalline hybrid materials composed of metal ions and organic ligands, have beendeveloped rapidly and used widely, such as gas-sorption properties depend on theirlarge porosity and designability of structures. Till now, there are few studies reportedabout MOF composite membranes, much less than their gas separation properties. Asideal composite membranes to separate hydrogen from mixed gases, it is necessary tocombine the thermal stability and high selectivity of metal organic framework with the mechanical strength characteristics of inorganic materials. This research couldexpand the utilization of MOF/PAAM composite membranes in the field of gasseparation, especially for hydrogen separation. And it could promote the developmentof new MOF materials as well. Results of this research are as follows:1. The synthetic processes and structural characterizations of new metal organicframeworks.As ideal MOF materials to separation H₂and CH₄, it should exhibit highseparation performance with the pore structure, moreover, the pore size is between thetwo molecule diameters of H₂and CH₄. In addition, thermal stability is equallyimportant for them when the temperature ranges from373K to473K. In this research,we synthesized eight compounds using five ligands. The experimental conditionswere as follows: concentration was0.003-0.05mol/L, solvent was H₂O or CH3OH,synthetic temperature was in the range298-453K, reaction time was from four toseven days.1) Compound1to5were proved to be zero dimensional compact structures bysingle crystal diffraction method. Compound6belongs to monoclinic system with onedimensional structure. Along the C axis, compound6forms one dimensional porewith the aperture0.5nm. Compound7is compact structure. Compound8belongs totetragonal system with the one dimensional pore along the C axis. The aperture is0.38nm. Among eight new MOF crystal materials, both compound6and8have porestructures, but the aperture of compound6is1.3times larger than the kinetic diameterof CH₄. Thus only compound8meets the requirement of pore size.2) With nitrogen protected, it is possible to maintain a stable structure below473K by gravitational thermal analysis.3) Gas adsorption behavior of single component gas on compound8wasinvestigated. The result shows that at303K, gas adsorption of H₂is zero with pressurefrom0-1000mbar, because of the weak interaction between the H₂molecule and MOFmaterials, although the H₂molecule can diffuse into the pores. Maximum adsorption capacity of CO2is2wt%. At273K and303K, the gas adsorption of CH₄is zero,because the kinetic diameter of CH₄is larger than the crystal aperture. Thisphenomenon confirms that compound8possesses obvious molecular sievingproperties.2. Preparing PAAM and testing gas transmittance of hydrogen and methane.For high selective MOF composite membrane to separate H₂and CH₄, idealinorganic substrate materials are required to have strong surface adhesion with theMOF materials, strong mechanical strength and good gas permeability, all of whichare decided by the aperture and thickness of substrate. In general, nickel net, porousceramics sheet, breathable stainless steel sheet and PAAM are used as substratematerials for preparing composite membrane. The MOF composite membrane wereprepared by “in suit” method in this work. The result shows that the ideal inorganicsubstrate materials is PAAM. With the thicknesses of77.4and pore of25nm, thestrong mechanical strength and gas permeability meet the requirements. The gastransmission rates of H₂and CH₄are5.60710-5mol/Pa·m2·s and2.38510-5mol/Pa·m2·srespectively.3. Preparing MOF/PAAM composite membranes and measuring gastransmittance of hydrogen and methane.The ideal MOF/PAAM composite membranes should have the followingperformance: high gas separation efficiency, high thermal stability, uniform thickness,high compressive strength and high gas permeability. The results are shown in details:1) The quality of new MOF/PAAM composite membrane which is prepared bytablet vacuum method is influenced by many factors, for example the concentration ofcoating solution, operating temperature and different nickel salt. This experimentshows that the best concentration of coating solution is0.2-0.7percentage. When thetemperature raises from413K to433K, the thickness of composite membranedecreases from450μm to200μm. Gap appears among the crystal particles when thetemperature is453K. The thickness of the composite membrane is200μm using Ni（CH3COO）2.4H₂O as nickel source,however, crystal packing appears through thecross-section of composite membrane.2) Considering the quality of composite membrane, we choose one compositemembrane to test gas permeability. This composite membrane is consisted of twoparts, one is the MOF membrane with thickness of450μm, another is PAAM withthickness of77.4μm. The compressive strength of this composite membrane is greaterthan10barrer. The gas transmission rates of H₂is1.44×10-9mol/Pa·m²·s at298K andalmost keeps as constant with pressure under0.1-0.3Mpa. At the same condition, CH₄can not penetrate through this composite membrane, so the gas transmission rates ofCH₄is zero.3) In range of298-373K, gas transmission rates of H₂decrease with theincreasing temperature. This MOF/PAAM composite membrane shows highselectivity of H₂and CH₄,for example at298K, the gas transmission rates of H₂is1.38×10^-9mol/Pa·m²·s, but the gas transmission rate of CH₄is zero.Based on this research, the MOF/PAAM composite membrane is expected to beapplied in the production of high purity H₂through decomposition of CH₄, because ofits high thermal stability and high compressive strength, especially high gasseparation efficiency. The scientific innovation in this research is that we prepared thefirst new MOF/PAAM composite membrane by tablet vacuum method in the world.The main research feather is that we obtain the preparation technology parameters ofMOF/PPA, such as thickness, temperature, and so on. It will provide necessarytheoretical and technical foundation of MOF/PPAM in production of high pure H₂industrial technology developments.更多还原