导　　师： 李忠;林跃生

学科专业： 081701

授予学位： 博士

作　　者： ;

机构地区： 华南理工大学

摘　　要： 随着人类社会现代化进程的加快,化石能源的大量消耗致使温室气体CO/_2的排放量与日俱增,导致的全球气候变暖问题引起了国际社会严重关注,已成为二十一世纪人类社会面临的最为迫切需要解决的重大问题之一。膜分离技术将是从各类工业排气中捕获CO/_2最为有效的技术之一。在膜分离技术中,发展新型的膜材料将成为技术的关键。本文主要研究一种新型的金属有机骨架MOF-5膜以及其对CO/_2气体的渗透分离性能。论文工作主要涉及合成金属有机骨架材料MOF-5晶体,制备MOF-5晶体膜以及孔隙结构表征,测定CO/_2在MOF-5颗粒的吸附热力学和动力学,测量若干单组份、CO/_2混合气体在MOF-5晶体膜中渗透扩散行为和分离因子,属于化学工程和膜科学的研究领域,具有科学研究价值和实际意义。 本文研究了MOF-5晶体合成的反应条件对MOF-5晶体的表面形貌、晶体结构和孔隙结构等物理化学性能的影响。利用SEM、XRD和N/_2吸附//脱附等温线对所制备的MOF-5晶体进行表征分析。研究结果表明:以二甲基甲酰胺为溶剂,将Zn2+//对苯二酸摩尔配比为2.7的合成液中置于130°C下反应4小时可得到小颗粒/(40-60μm/)和高比表面积/( S Langmuir=2500m2//g/)的MOF-5晶体。 本文研究了CO/_2在MOF-5晶体颗粒上的吸附相平衡和动力学。采用重量法测定了CO/_2吸附等温线和动力学曲线,估算出CO/_2气体在MOF-5上的扩散系数、等量吸附热和吸附活化能。结果表明:常压下,MOF-5晶体颗粒对CO/_2的吸附容量很大,明显高于相同条件下在活性炭和13X分子筛的吸附量;CO/_2在MOF-5晶体颗粒上的扩散系数约在10-8cm2//s范围内,明显高于CO/_2在13X分子筛中的扩散系数。该结果首次揭示了CO/_2在MOFs材料上具有很好的吸附扩散行为,是本文重要的新意之处。 本文提出采用二次生长法在α-Al2O3支撑体上制备MOF-5晶体膜,研究了晶体涂布方式、悬浮液以及二次长膜中各类工艺条件对MOF-5晶体膜生长的影响。研究结果表明:采用浸润式短时间连续多次涂布的方法有助于获得覆盖度高且厚度适中的MOF-5晶种层;在二次长膜过程中,添加EDIA可以有效减弱BDC对MOF-5晶种的溶解作用,有助于获得连续致密生长的MOF-5晶膜层;通过对工艺条件的优化,获得制备MOF-5晶体膜新工艺,研制出晶体颗粒2-3μm和膜厚6-7μm的超薄型MOF-5晶膜层。这是目前所报道的晶体颗粒最小且膜厚最薄的MOF-5晶体膜,这是本文重要的创新之处。 本文研究了定量表征和鉴别MOF-5膜缺陷程度的方法,提出采用2-二环己膦基-2'-/(N,N-二甲胺/)-联苯/(DCPDMA/)分子定量表征和鉴别MOF-5膜的缺陷或完整程度。研究表明:本文所制备的MOF-5膜对DCPDMA分子的渗透汽化通量很小,其缺陷孔约分布在8 < p MOF- 5膜<14.5?的范畴。此方法为MOFs类膜缺陷孔的表征提供了技术参考,是本文重要的新意之处。 本文研究单组分气体分子在MOF-5晶体膜上的渗透扩散行为,研究结果表明:轻分子气体H/_2, He, CO, N/_2和CO/_2在MOF-5膜上渗透行为符合Knudsen扩散规律;而SF6分子在MOF-5膜上渗透行为属于活化扩散过程;采用微孔渗透扩散模型估算出CO/_2在MOF-5晶体上的渗透系数与实验测量值很接近,验证了CO/_2在MOF-5膜上的扩散符合努森扩散机理。 本文首次研究了MOF-5膜对混合气CO/_2//H/_2和CO/_2//N/_2组分的分离性能。研究了温度、混合气组分以及渗透压力对混合气分离因子的影响。结果表明:在298-373K的温度范围内,MOF-5膜对CO/_2//H/_2混合气体的渗透分离因子随温度的升高而增加,随CO/_2含量的增加而增加,随填充压力的增加而略有降低;MOF-5膜对CO/_2//N/_2混合气体的渗透分离因子随温度的升高而降低,随CO/_2组分含量和渗透压力的增加而增加,在298K、345kPa和CO/_2含量为88/%时,其分离因子可高达64。这些研究成果也是本文的重要新意之处。 With the quickening process of social modernization, massive consumption of fossil fuels causes increasing CO/_2 emissions. CO/_2 leads to global warming more and more serious. Global warming has become one of the major and urgent issues to solve for international community in the 21st century. Membrane separation technology will be one of the most effective technologies to capture CO/_2 emissions from industrial sources. In the membrane separation technology, the development of new membrane materials will be the key point. This dissertation is mainly concerned with study on a novel metal-organic framework /(MOF-5/) membrane and its permseparation performance for CO/_2. This research mainly involves synthesis of the MOF-5 crystals, preparation and pore structure characterization of the MOF-5 membrane, determination of CO/_2 adsorption thermodynamics and kinetics on the MOF-5 particles, and measurement of the permeation behaviors and separation factors of several single component gases and CO/_2 gas mixture through the MOF-5 membranes. This study belongs to the fields of chemical engineering and membrane science and has scientific research value and practical significance. The effects of synthesis condition for the MOF-5 crystals on its physical properties including the morphology, crystal structure and porous texture were investigated. SEM, XRD and N/_2 adsorption//desorption were used to characterize the MOF-5 crystals. The results showed that MOF-5 crystals whose partical sizes ranged from 40 to 60μm and surface area was up to 2500m2//g were obtained under the following conditions: synthesis temperature of 130°C, reaction time of 4 hours, the Zn2+//BDC molar ratio of 2.7 and N, N-dimethylformamide as the solvent. Adsorption equilibrium and kinetics of CO/_2 on the MOF-5 particles were studied. The adsorption isotherms and kinetic curves of CO/_2 measured by using gravimetric method, and the diffusivity coefficients, isosteric adsorption heat and adsorption activation energy of CO/_2 on the MOF-5 particles were estimated. The results showed that the amount adsorbed of CO/_2 on the MOF-5 crystals was up to 2.10 mmol//g at ambient temperature and 1 atm, which was obviously higher than the amount adsorbed of CO/_2 in activated carbon and 13X zeolite; The diffusivity coefficient of CO/_2 within the MOF-5 was about 10-8 cm2//s, which was much higher than that within the 13X zeolite. It suggested that the MOF-5 has an excellent adsorption and transportation properties for CO/_2. This is one of new points in this work. The secondary seeded growth method to fabricate MOF-5 membrane onα-Al2O3 substrate was proposed. The effects of fabrication conditions, including coating matter, suspension preparation and secondary growth, on the growth of the MOF-5 membrane were studied. The results showed that a perfect MOF-5 seeds layer of support can be gained by using three-subsequent dip-coating method with short time contacting with suspension; In the process of secondary growth, the addition of EDIA can efficiently prevent seed crystals from dissolving and simultaneously make the MOF-5 crystal membrane grow well. A novel technology for MOF-5 membrane is obtained after a series of experimental conditions were optimized, and thus an ultra thin MOF-5 membrane with the particle size of 2-3μm and the thickness of 6-7μm was successfully fabricated. This is one of the important innovations in this work. A characterization method for distinguishing quality of the MOF-5 membranes was studied. The organic molecule of 2 - Dicyclohexylphosphino - 2' - /(N,N-dimethylamino/) biphenyl /(DCPDMA/) was used to characterize quantificationally the quality of MOF-5 membranes with the help of pervaporation experiments. The results showed that the pervaporation flux of DCPDMA was very low through the MOF-5 membrane, which indicated the defects distribution of the MOF-5 membrane was in the range of 8 < p MOF? 5 membrane<14.5?. This characterization method provides a technical reference for the detection of the MOF-5 membrane defects, which is a new point of this work. Permeance diffusion behaviors of single component gas through the MOF-5 membrane were investigated. The results showed that the gas permeation diffusion of H/_2, He, CO, N/_2 and CO/_2 was found to be governed by Knudsen diffusion whereas the diffusion of larger molecule SF6 exhibited activated diffusion in the MOF-5 membrane. The permeability of CO/_2 through the MOF-5 membrane estimated by using micropore diffusion model was close to the measured value. This verified that the diffusion behavior of CO/_2 through the MOF-5 membrane was controlled by Knudsen diffusion mechanism. Separation selectivity of CO/_2//H/_2 or CO/_2//N/_2 mixtures through the MOF-5 membrane was studied. Effects of temperature, mixture composition and feed pressure on the separation factor were discussed. The results showed that the separation factor of the MOF-5 membrane for CO/_2//H/_2 mixture was increased with temperature and the composition of CO/_2 and decreased with feed pressure. For CO/_2//N/_2 mixture, the separation factor of the MOF-5 membrane was decreased with temperature and increased with the composition of CO/_2. The separation factor of the MOF-5 membrane for CO/_2//N/_2 mixture was up to 64 at 298K and 345kPa, with a CO/_2 composition of 88/%.

关 键 词： 金属有机骨架 晶体膜 扩散 渗透汽化 气体渗透 混合气分离

分 类 号： [TQ028.8]

领　　域： [化学工程]