聚酰亚胺中空纤维膜的制备及其气体分离特性

发布时间：2018-03-07 04:21

本文选题：聚酰亚胺　切入点：中空纤维膜　出处：《东华大学》2017年硕士论文　论文类型：学位论文

【摘要】：温室效应及能源问题已经引起全球广泛关注,烟道气中二氧化碳(CO_2)的控制排放、天然气及生物沼气中CO_2的分离等都是亟待解决的混合气体分离问题。中空纤维分离膜具有能耗低、环境友好、填充密度高等突出优点,对于能源利用和环境治理都有举足轻重的作用,已成为最有效的混合气体分离方法之一。膜材料是膜技术的核心,聚酰亚胺(polyimide,PI)具有优良的机械性能、热性能和渗透性能,在众多膜材料中脱颖而出,有望在气体分离膜领域得到广泛应用。为此,本论文在具有分离特性聚酰亚胺的合成、中空纤维膜的纺丝成形及表面涂层等方面开展研究工作,主要内容包括:通过分子结构设计引入较大自由体积和促进CO_2传质的官能团,分别改善PI的渗透性和选择性。本文以六氟二酐(6FDA)为二酐单体,4,4'-二氨基二苯醚(ODA)、2,2-双[4-(4-氨基苯氧基)苯基]丙烷(BAPP)、2,2-双[4-(4-氨基苯氧基)苯基]六氟丙烷(HFBAPP)、4,4'-双(4-氨基苯氧基)二苯砜(BAPS)为二胺单体在溶剂N-甲基-2-吡咯烷酮(NMP)中合成不同结构的聚酰亚胺,制备的聚酰亚胺薄膜在常规有机溶剂中具有极好的溶解性能,具有较好的力学强度,密度在1.388~1.427 g/cm3之间,自由体积分率在0.144~0.162之间,玻璃化转变温度在257oC~304oC之间,接触角在53°~93°之间。其中6FDA-HFBAPP型聚酰亚胺溶解性能最好、自由体积分率最大为0.162、接触角最大为93°、玻璃化转变温度最低为257oC,是制备中空纤维气体分离膜的理想材料。以合成的6FDA-HFBAPP型聚酰胺酸溶液为纺丝液,采用干-湿法及后处理工艺制备了具有致密皮层和多孔支撑层的中空纤维膜,研究了纺丝液的性质、内外凝固浴组成、内凝固浴流速、空气层高度对中空纤维膜结构和性能的影响。结果表明,该体系适合采用两步法纺丝,当外凝固浴为纯水、内凝固组成为VH2OVNMP?=10/90、内凝固流速与纺丝液流速之比在0.4~0.6之间、空气层高度为6 cm时,制备的中空纤维膜的性能最佳,CO_2渗透速率为89 GPU,CH4的渗透速率为75 GPU。为改善所制备的中空纤维膜的分离特性,以制备的聚酰亚胺中空膜为底膜,用PDMS涂层液对底膜进行浸渍涂覆以封堵在干湿法成型过程中致密层产生的缺陷,制备了中空纤维复合膜。结果表明,当涂层质量浓度为5%时,涂覆的效果最佳,经涂覆后CO_2的渗透速率为42 GPU,CH4的渗透速率为7.8 GPU,分离系数为5.4。并采用Henis复合阻力模型分析了复合膜的分离机理。
[Abstract]:Greenhouse Effect and energy issues have attracted worldwide attention. The separation of CO_2 from natural gas and biogas is an urgent problem to be solved. The hollow fiber separation membrane has the advantages of low energy consumption, friendly environment, high filling density and so on. Membrane material is the core of membrane technology, and polyimide polyimide (PII) has excellent mechanical, thermal and permeable properties. It is expected to be widely used in the field of gas separation membrane. In this paper, the synthesis of polyimide with separation characteristics, spinning of hollow fiber membrane and surface coating are studied. The main contents include the introduction of large free volume and the promotion of CO_2 mass transfer through the design of molecular structure. The permeability and selectivity of Pi were improved respectively. In this paper, hexafluorodianhydride 6FDAA was used as the monomer of dianhydride 4H 4N -diaminodiphenyl ether (ODAO) 2H 2- BAPPX 2N, BAPPU 2H 2- Bis (4-N 4-Aminophenoxy) phenyl] Hexafluoropropane (HFBAPPU) 4N, Bis 4N, Bis 4N, benzylamino aminophenylamino. Polyimide with different structures was synthesized in the solvent N-methyl-2-pyrrolidone (NMPP) using oxy) diphenyl sulfone (BAPS) as a diamine monomer. The prepared polyimide films have excellent solubility and good mechanical strength in conventional organic solvents. The density is between 1.388g / cm ~ 3 and 1.427 g / cm ~ 3, the free volume integral ratio is 0.144 ~ 0.162, and the glass transition temperature is between 257oC ~ 304oC. The contact angle is between 53 掳and 93 掳. The solubility of 6FDA-HFBAPP polyimide is the best. The maximum free volume integral ratio is 0.162, the contact angle is 93 掳, the glass transition temperature is the lowest 257oC, which is the ideal material for the preparation of hollow fiber gas separation membrane. The synthesized 6FDA-HFBAPP polyamide acid solution is used as spinning solution. Hollow fiber membranes with dense cortex and porous supporting layer were prepared by dry-wet process and post-treatment process. The properties of spinning solution, composition of internal and external coagulation bath, flow rate of internal coagulation bath were studied. Effects of air layer height on the structure and properties of hollow fiber membrane. The results show that the system is suitable for two-step spinning when the external coagulation bath is pure water and the internal solidification composition is VH _ 2O VNMP? 10 / 90, when the ratio of internal solidification velocity to spinning fluid velocity is between 0.4 and 0.6, and the height of air layer is 6 cm, the best permeation rate of CO _ 2 is 89GPUU _ (CH4) and the permeation rate of the prepared hollow fiber membrane is 75GPU. in order to improve the separation characteristics of the prepared hollow fiber membrane, The hollow fiber composite membrane was prepared by impregnating the polyimide hollow membrane with PDMS coating liquid to seal the defects of the dense layer in the process of dry-wet molding. The results showed that the coating concentration was 5. After coating, the permeation rate of CO_2 was 7.8 GPA and the separation coefficient was 5.4. The separation mechanism of the composite membrane was analyzed by using the Henis composite resistance model.
【学位授予单位】：东华大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ051.893

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