【作者】 李琳；

【导师】 邱介山； 王同华；

【作者基本信息】 大连理工大学 ， 膜科学与技术， 2013， 博士

【摘要】 炭分子筛膜,简称炭膜,是由聚合物膜经高温热解制备而成的一种新型炭基膜材料。因具有优异的气体分离性能,良好的热、化学稳定性,在气体分离领域尤其是小分子气体分离领域具有广阔的应用前景,被誉为“最有希望实现大面积工业化生产的高性能无机气体分离膜”。然而炭膜至今未能实现大规模产业化应用,其原因主要是现有炭膜不仅强度低,而且气体渗透性还无法满足产业化应用的要求。因此,解决现有炭膜的强度和气体渗透性能低下的问题,是实现炭膜大规模产业化应用的关键。为了解决上述制约炭膜产业化的关键问题,本论文从炭膜前驱体结构设计出发,通过研究前驱体由高聚物结构向炭结构的演变过程,热解炭化机理及炭膜孔结构的形成机制,揭示纯炭膜气体渗透能力相对较低的原因。并以此为依据,探讨提高炭膜气体渗透性能的方法与途径。为了解决纯炭膜的机械强度低的问题,以廉价的煤基炭膜为支撑体,制备复合支撑炭膜；通过增加介孔炭中间层改善支撑体膜表面结构,探讨进一步提高支撑炭膜气体渗透性能的方法。取得了如下研究成果：(1)以Kapton型聚酰胺酸为前驱体,研究其热解炭化过程,化学结构在热解过程中的变化规律；探讨了纯炭膜气体渗透性能低的原因。结果表明,聚酰亚胺膜的热解炭化过程包括低温热解和高温炭化,低温热解主要发生亚酰胺化和结构重整,形成交联网络结构,构成炭结构的雏形；高温炭化伴随着剧烈的热分解和热缩聚反应,形成的交联网络结构经脱杂原子基团、环化、芳构化过程形成六角碳环的多环芳烃结构,并进一步稠环化转化成平面网状结构,形成炭微晶。炭微晶的无序堆积构成了炭膜的无序孔道结构(称为“蠕虫”状孔结构)。聚酰亚胺的化学结构对所形成炭膜的微结构和性能具有很大的影响；自由体积大、结构刚性强并含有较多杂原子的聚酰亚胺热解炭化后形成的炭膜结构疏松,有利于气体渗透扩散。然而,纯炭膜的“蠕虫状”孔结构使其孔道蜿蜒曲折、路径长,气体在孔道中渗透扩散时间长、阻力增大,这就是为什么纯炭膜气体渗透通量低的原因。所以,打破纯炭膜“蠕虫状”孔结构,是制备高渗透、高分离选择性炭膜的核心。(2)在前驱体中引入无机纳米粒子制备杂化炭膜是打破纯炭膜“蠕虫状”孔结构重要途径。以纳米沸石分子筛为功能基团制备杂化炭膜,探讨了沸石分子筛的种类、颗粒度、沸石孔道尺度、类型和完整性及制备工艺参数如沸石分子筛的加入量、炭化温度等对所制备杂化炭膜的结构及气体分离性能的影响。结果表明,在前驱体中引入沸石分子筛,其纳米粒子界面和尺度效应及微相分离作用,可以在炭与沸石分子筛的界面产生间隙,形成界面孔隙结构,不仅丰富了炭膜极微孔结构体系,同时打破了纯炭膜的“蠕虫状”孔结构,降低了气体在炭膜孔道中渗透扩散阻力,明显地提高炭膜的气体渗透性能。沸石分子筛的种类、粒度及孔道结构与尺度、制备工艺对所制备杂化炭膜的结构及气体分离性能有很大影响。通过对分子筛的颗粒度、孔道结构与尺度及制备工艺的优化设计,可以实现了对炭膜极微孔结构的重新构建及孔道尺度和分布的调控；从而在保持炭膜较高选择性条件下,大幅度地提高炭膜的气体渗透性能。制备出具有高渗透性、高分离选择性的杂化功能炭膜。在较优化的制备工艺条件下,制备的杂化炭膜对O2/N2选择性达到15.6,O2渗透系数为501Barrer,H2的渗透系数为2280Barrer。(3)支撑炭膜是改善炭膜机械强度最有效的方法。以廉价的煤基板状多孔炭膜为支撑体,聚酰胺酸为分离层制膜液,成功地制备了具有良好气体分离性能的支撑炭膜。通过合成具有介孔结构的聚合物对支撑体表面进行修饰,实现了在较大孔隙结构支撑体上制备具有高渗透性、高分离选择性的支撑炭膜。介孔炭中间层对烟煤支撑体表面进行修饰,有效提高了复合支撑炭膜的气体渗透分离性能,对02/N2的选择性达到11.03,02的通量为0.70mol·m-2·s-1·Pa-1×10-8。通过扩大支撑体的孔隙率,降低中间层的制备成本,提高分离层亲和性等手段能够进一步改善支撑炭膜的性能。更多还原

【Abstract】 Carbon molecular sieving membrane, referred to carbon membrane, is a novel carbon-based membrane material prepared by pyrolysis of polymer membrane. Carbon membrane has a great application potential in the gas separation field, especially the small molecular gas separation, and is pronounced "the most promising large-area industrial production of inorganic membrane with high gas separation performance" due to the excellent gas separation performance, good thermal and chemical stability. However, the carbon membrane has not been achieved large-scaled industrial application so far, because of its poor mechanical strength and low gas permeability.In order to solve these issues, the current thesis began with the design for the structure of the polymer precursor, the evolvement from polymer to carbon and the forming mechanism of the porous structure in carbon membrane have been studied, and the reason of low gas permeability in pure carbon membrane has been discussed. On this basis, the method of enhancing the gas permeability of carbon membrane was proposed. To increase the mechanical strength of pure carbon membrane, the supported carbon membranes have been prepared with the inexpensive coal-based carbon plate as support. The porous structure of the support surface was modified by loading of a mesoporous carbon middle layer; and an improved gas permeability of the supported carbon membrane was achieved thereafter.The results are listed as belows:(1) The chemical changing of Kapton typed polyamic acid, which was applied as the precursor of carbon membrane, during the pyrolysis process was studied. The reason of low permeability was discussed. The results show that the carbonization process includes two steps1. Low-temperature pyrolysis, and2. High-temperature carbonization:imidization and structure reform forming the cross-linking net structure, which is the prototype of carbon structure, occurred during the low-temperature pyrolysis process; accompanied by the severe thermal decomposition and thermal polycondensation reactions, the forming cross-linking structure transformed to the polycyclic strcuture with hexagonal carbon ring through removal of hetero atom group, cyclization and aromatization, further formed into the planar carbon net and constructed the carbon micro-crystals, which accumulated to the disordered porous structure of the carbon membrane ("worm"-like pore structure), occurred at the second step. The chemical structure of polyimide has a great effect on the micro structure and performance of the related carbon membrane. The carbon membrane with loose structure, beneficial to the gas molecular diffusion, was produced by the pyrolysis of the polyimide with larger free-volume, higher rigidity and more hetero-atoms. However, the gas permeation routes in the carbon membrane is long and winding due to the "worms"-like pore structure, which is the reason of the low gas permeability in the pure carbon membrane. Therefore, breaking the wormlike porous structure should be the key issue for the preparation the carbon membrane with both high gas permeability and high selectivity.(2) It is a promising method about introduction of inorganic nano-particles into the carbon matrix to break the "worms"-like porous structure of pure carbon membrane. The hybridized carbon membrane was prepared by embedding the nano-zeolites into carbon matrix. The effects of the properties of zeolites, such as type, granularity, channel structure on the gas separation performance were discussed; and the preparation parameters such as involving the content of zeolites and carbonization temperature on the structure and gas separation performance of hybridized carbon membrane were also studied. Results show that the gas molecular diffusion resistance was reduced and the gas separation performance was enhanced in the zeolite/carbon hybrid membrane by breaking the"worms"-like pore structure of carbon membrane in according to the interfacial gaps between carbon matrix and zeolite was diversified the pore system. The property of zeolites and the parameters in membrane preparation affected on the structure and gas separation performance of the zeolite/carbon hybrid membrane greatly, meaning the restructure of ultramicropore and the modification of the porous structure of carbon membrane could be achieved. And the carbon membrane with both high gas permeability and high selectivity could be fabricated with the O2/N2selectivity of15.6, O2and H2permeability of501Barrer and2280Barrer, respectively.(3) Supporting carbon membranes on porous substrates is most effective way to improve their mechanism strength. Using the inexpensive bituminous coal-based carbon plate as support and Kapton as the precursor, the supported carbon membrane with high gas separation performance was produced. The gas permeation rate and selectivity were further improved by modifying the surface of support with a mesoporous middle layer. In this supported composite carbon membrane, O2/N2selectivity of11.03and O2permeation rate of0.70mol·m-2·s-1·Pa-1×10-8. Moreover, the gas separation performance of the low cost supported carbon membrane could be improved by enlarging the porosity of support and improving the affinity of separation layer also.更多还原