【作者】 李文；

【导师】 刘云凌；

【作者基本信息】 吉林大学 ， 无机化学， 2024， 博士

【摘要】 小分子的碳氢化合物是重要的化工原料和燃料,其来源十分广泛,可以从石油化工生产中获得,也可以从煤层气和页岩气等一次能源气中获得。这些气态能源物质通常是混合物,包含二氧化碳（CO₂）和氮气（N₂）等不可燃的气态物质,在实际工业生产中需要对这些小分子气体分离纯化后再进行下一步的应用。目前工业上通常利用有机醇胺溶液捕获CO₂,该方法存在能耗高、污染环境和腐蚀设备等问题;对小分子碳氢化合物的分离主要采用低温精馏的技术,具有能耗高,设备占地面积较大,工艺流程复杂等问题。因此,亟需开发基于物理吸附剂的变压吸附（pressure swing adsorption,PSA）技术,实现低能耗,高效率的小分子气体分离。金属有机骨架（Metal?Organic Frameworks,MOFs）材料是一类由金属离子或金属簇与有机配体构成的多孔晶态杂化材料,因其结构可设计和孔道易修饰等特点,可以实现对特定气体分子的选择性吸附,是优异的物理吸附剂材料。在众多MOFs材料中,微孔MOFs与气体分子间更强的相互作用力,展现出对小分子气体优良的分离能力。基于以上考虑,本论文在网格化学策略的指导下,通过调变金属或配体,设计合成了三种不同拓扑学结构的微孔MOFs材料,精确调控孔道环境,实现了对不同小分子气体的高效分离。论文的主要内容分为以下三个部分:（1）MOFs材料在气体吸附与分离领域具有广阔的应用前景,但是大多数MOFs材料的水稳定较差,严重限制了其实际应用。在本部分工作中,依据软硬酸碱（HSAB）理论,设计合成了三个具有高稳定性的微孔MOFs材料（化合物1-3）。该系列化合物均以H₆BHB（4,4’’-benzene-1,3,5-triyl-hexabenzoic acid）配体,通过调变金属簇结构基元实现对骨架电荷的有效调控,成功提升了MOFs材料的比表面积和CO₂吸附能力。化合物1具有由三核In₃O（COO）₆结构基元与H₆BHB配体构筑的阳离子骨架材料,其BET比表面积为301 m²/g;化合物2的阳离子骨架材料由Fe₃O（COO）₆簇与H₆BHB配体构成,由于Fe的相对原子质量低于In,导致骨架密度降低,其BET比表面积增加至446 m²/g;化合物3是由Fe₂Ni O（COO）₆金属簇与H₆BHB配位连接的中性骨架材料,其BET比表面积最高,为808 m²/g。化合物1-3具有优异的化学稳定性和热稳定性,且具有微孔笼状结构和丰富的开放金属位点,在298 K,1 bar的条件下展现出良好的CO₂吸附能力（分别为28.0、51.5和99.6 cm³/g）。IAST计算结果表明,在常温常压条件下,化合物1-3展现出优异的CO₂/N₂选择性（CO₂/N₂=0.15/0.85,分离比分别为35.2、43.2和43.2）和较高的CO₂/CH₄选择性（CO₂/CH₄=0.5/0.5,分离比分别为14.4、11.5和10.1）。穿透实验测试进一步证明这些化合物在CO₂/N₂和CO₂/CH₄分离的高效性。化合物1-3的高稳定性、低吸附焓、易再生以及优异的CO₂/N₂和CO₂/CH₄分离能力,使其在烟道气分离以及天然气纯化领域具有潜在的应用价值。（2）乙炔（C₂H₂）和二氧化碳具有相似的分子大小、形状和沸点,两者在工业上难以分离。因此,开发高效分离C₂H₂/CO₂的物理吸附剂至关重要。在本部分的研究中,基于柱层策略,设计合成了两种具有pcu拓扑结构的MOFs材料（化合物4-5）:利用4-吡唑羧酸配体与Ni²⁺构筑了二维的sql层状结构,以4,4’-联吡啶作为柱支撑配体与该sql层组装形成了具有pcu拓扑的化合物4。化合物4的笼状形孔道中含有丰富的吸附位点,具有较高的C₂H₂吸附能力,可以分离C₂H₂和CO₂（298 K,1 bar条件下,等摩尔C₂H₂/CO₂的选择性为4.5）。为了进一步提升C₂H₂/CO₂的分离效果,以更短的吡嗪作为柱支撑配体与sql层组装,合成了具有相同pcu拓扑结构的化合物5。化合物5通过对孔隙的进一步优化从而显著提升了C₂H₂/CO₂分离能力（298 K,1 bar条件下,等摩尔C₂H₂/CO₂的选择性提升至14.0）。理论计算揭示了化合物4和化合物5之间的主客体相互作用的细微差异是导致它们具有不同的C₂H₂/CO₂分离选择性的原因。化合物5单次穿透实验的C₂H₂吸附量为2.01 mmol/g,远高于化合物4的吸附量（1.16 mmol/g）,连续循环穿透实验表明化合物4-5优异的循环使用性。化合物4-5较低的成本、高效的分离性能、优异的稳定性和良好的循环使用能力使它们具有在工业应用中分离C₂H₂/CO₂的潜力。（3）利用MOFs材料作为物理吸附剂结合PSA技术进行甲醇制烯烃（methanol-to-olefins,MTO）产物分离以及天然气纯化是一种高效节能的方法。与大多数MOFs材料的高成本相比,由生物分子构筑的金属有机骨架（Bio-MOFs）材料具有成本低、毒性小等优点,展现出良好的工业应用的价值。在本部分的研究工作中,利用网格化学策略,分别以甲酸、乙酸和丙酸作为端基配体,合成了一系列以腺嘌呤和Cu²⁺为基元的Bio-MOFs材料（化合物6-8）。实验结果表明,端基配体尺寸的改变对孔道环境产生了细微的影响,从而导致化合物6-8吸附能力和稳定性发生显著变化。其中,化合物6的热稳定性较差,化合物8较低的孔隙率和孔道中乙基的自由旋转抑制了其对轻质烃的分离,化合物7具有最高的比表面积和优异的气体分离能力。在298 K和1 bar下,化合物7的等摩尔C₃H₈/CH₄和C₃H₆/C₂H₄选择性分别为746和10.9。常温常压穿透测试结果表明,化合物7具有良好的分离能力,可以一步分离不同比例的C₂H₄/C₃H₆（50/50,50/20和90/10）混合物,循环使用性好。化合物7利用简单易得的腺嘌呤和乙酸为配体,具有低成本、低毒性和易合成等优势,有利于工业应用。更多还原

【Abstract】 Light hydrocarbon are essential chemical raw materials and fuels,with diverse sources ranging from petrochemical production to primary energy gases like coal bed methane and shale gas.However,these gaseous energy substances typically come as mixtures,often containing non-combustible gases like carbon dioxide（CO₂）and nitrogen（N₂）.Therefore,separating and purifying these mixtures in industrial production becomes necessary before further applications.Currently,the industry commonly utilizes organic alcoholamine solutions for CO₂ capture,but this method faces challenges such as high energy consumption,environmental pollution,and equipment corrosion.On the other hand,the separation of light hydrocarbon primarily relies on low-temperature rectification technology,which suffers from drawbacks such as high energy consumption,large equipment footprint,and complex process flows.Hence,there is an urgent need to develop pressure swing adsorption（PSA）technology utilizing physical adsorbents to achieve efficient and energy-saving separation of small molecule gases.Metal-organic frameworks（MOFs）are porous crystalline hybrid materials composed of metal ions or clusters and organic ligands.MOFs offer designable structures and facile pore modifications that enable selective adsorption of specific gas molecules,making them excellent physical adsorbents.Among various MOFs,those with stronger interaction forces between microporous structures and gas molecules exhibit exceptional separation capabilities for small molecular gases.Based on the aforementioned considerations,this thesis focuses on the design and synthesis of three types of distinct microporous MOFs with varying topological structures.The modulation of metals or ligands allows precise regulation of the pore environments,thereby achieving efficient separation of different small molecule gases.This thesis is divided into the following three main parts:（1）MOFs materials have broad prospects for application in the field of gas adsorption and separation.However,most MOFs materials exhibit poor water stability,which significantly limits their practical use.In this study,three robust MOFs materials（compounds 1-3）were designed and synthesized based on the hard-soft acid base（HSAB）theory.These compounds utilize H₆BHB（4,4"-benzene-1,3,5-triyl-hexabenzoic acid）as ligands to effectively modulate the charge of the framework by adjusting the metal cluster structure elements,thereby enhancing the specific surface area and CO₂ adsorption capacity of the MOFs materials.Compound 1 features a cationic framework composed of trinuclear In₃O（COO）₆ and H₆BHB ligand,with a BET specific surface area of 301 m²/g.Compound 2 possesses a cationic framework consisting of Fe₃O（COO）₆ clusters and H₆BHB ligands.Due to the lower relative atomic mass of iron atom compared to indium atom,the framework density decreases,resulting in an increased BET surface area of 446 m²/g.Compound 3 is a neutral framework material coordinated by Fe₂Ni O（COO）₆ clusters with H₆BHB,exhibiting the highest BET specific surface area of 808 m²/g.Compounds 1-3 demonstrate excellent chemical and thermal stability,possessing a microporous cage structure and abundant open metal sites.At 298 K and 1 bar,they exhibit significant CO₂ adsorption capacities（28.0,51.5,and 99.6 cm³/g,respectively）.IAST results show that all three MOFs exhibit high separation selectivity toward CO₂ over N₂（35.2,43.2 and 43.2 for CO₂/N₂=0.15/0.85）and CO₂ over CH₄（14.4,11.5 and 10.1 for CO₂/CH₄=0.5/0.5）at298 K,1 bar.Breakthrough experiments further validate the high efficiency of these compounds in separating CO₂/N₂ and CO₂/CH₄.The exceptional stability,low adsorption enthalpy,ease of regeneration,and excellent CO₂/N₂ and CO₂/CH₄separation capabilities of compounds 1-3 make them promising candidates for applications in flue gas separation and natural gas purification.（2）Acetylene（C₂H₂）and carbon dioxide have similar molecular size,shape,and boiling point,making their industrial separation challenging.Therefore,it is crucial to develop effective physical adsorbents for the efficient separation of C₂H₂/CO₂.In this study,two MOF materials（compounds 4-5）with pcu topology were designed and synthesized by pillar-layered strategy.Compound 4 was created by using a 4-pyrazolecarboxylic acid ligand and Ni²⁺to construct a two-dimensional sql layer structure,and then assembled with 4,4’-bipyridine as a pillar ligand,resulting in the formation of framework with pcu topology.Compound 4 possesses abundant adsorption sites in the cage pore,exhibiting a high adsorption capacity for C₂H₂ and enabling the separation of C₂H₂ and CO₂（the selectivity of equimolar C₂H₂/CO₂ is 4.5at 298 K and 1 bar）.To enhance the C₂H₂/CO₂ separation efficiency further,compound5 with same pcu topology was synthesized using a shorter pyrazine as the pillar ligand.By optimizing the pores,compound 5 significantly improved the C₂H₂/CO₂ separation capacity（the selectivity of equimolar C₂H₂/CO₂ increased to 14.0 at 298 K and 1 bar）.Theoretical calculations revealed that subtle differences in host-guest interactions between compound 4 and compound 5 are responsible for their different C₂H₂/CO₂separation selectivity.In single breakthrough test,compound 5 exhibited an adsorption capacity of 2.01 mmol/g for C₂H₂,which was much higher than compound 4（1.16mmol/g）.Additionally,both compounds 4-5 demonstrated excellent cycling performance in continuous cycling breakthrough tests.Due to their low cost,efficient separation performance,excellent stability,and good recycling ability,compounds 4-5hold great potential for industrial applications in the separation of C₂H₂/CO₂.（3）The utilization of MOFs as physical adsorbents in combination with PSA technology is an efficient and energy-saving method for the separation of methanol to olefins（MTO）product and natural gas purification.While most MOF materials come with a high cost,Bio-MOFs made of biomolecules offer the advantage of being low-cost and low-toxicity alternatives,making them highly valuable for industrial applications.In this study,a series of Bio-MOFs（compounds 6-8）based on adenine and Cu²⁺were synthesized by using formic acid,acetic acid,and propionic acid respectively,as terminal ligands through reticular chemistry strategy.The experimental results indicate that changes in the size of the terminal ligands subtly affect the pore environment,leading to significant variations in the adsorption capacity and stability of compounds 6-8.Among them,compound 6 exhibits poor thermal stability,compound8 has low porosity,and the free rotation of ethyl in the pore hinders its separation of light hydrocarbons.On the other hand,compound 7 exhibits the highest specific surface area and excellent gas separation abilities.At 298 K and 1 bar,compound 7 exhibits selectivity of 746 for C₃H₈/CH₄ separation and 10.9 for C₃H₆/C₂H₄ separation.Breakthrough tests conducted at ambient conditions demonstrate that compound 7exhibits excellent separation performance,allowing for the separation of different proportions of C₂H₄/C₃H₆ mixtures（50/50,50/20,and 90/10）in one-step while also exhibiting good recycling capabilities.Compound 7,which employs easily accessible adenine and acetic acid as ligands,offers the advantages of low cost,low toxicity,and facile synthesis,making it highly suitable for industrial utilization.更多还原