MOF混合基质膜的原位制备及相容性强化

发布时间：2018-03-15 18:23

本文选题：气体分离　切入点：CO_2捕集　出处：《大连理工大学》2017年博士论文　论文类型：学位论文

【摘要】：进入21世纪以来,化石能源在全球范围内的消耗逐年增高,温室气体减排和能源气体净化成为CO_2捕集的两个重要组成部分,其中代表性分离体系为烟道气(CO_2/N_2)和天然气(CO_2/CH_4)。膜分离作为一种节能高效、清洁环保的新型分离技术,应用于CO_2分离有良好前景。混合基质膜由聚合物基体和分散于其中的无机填料共同构成,结合了聚合物膜易加工和无机膜分离性能高的优点,是高性能气体分离膜的重要发展方向。金属有机骨架(MOF)是一种具有规整孔道结构的新型晶体材料,由过渡金属离子与有机配体经共价键或配位键桥接而成。与传统无机填料相比,MOF具有合成条件温和、易功能化等优点,因此,MOF混合基质膜成为当前研究的热点。然而,目前文献报道的MOF混合基质膜多为通过浇铸得到,对具有薄选择层MOF混合基质膜研究较少。此外,MOF混合基质膜还存在相界面易产生缺陷、MOF柔性骨架削弱选择性等问题。本论文基于三种对CO_2具有选择性的MOF(ZIF-7、ZIF-8和Cu-BTC),利用MOF在聚合物溶液中原位合成实现具有薄选择层的MOF混合基质膜的制备,并通过离子液体在MOF中预先负载强化MOF/聚合物界面相容性,从而提高混合基质膜的分离性能。首先,基于非对称膜的传统制备工艺(浸没沉淀相转化法,NIPS),采用直接共混和微波辅助分别制备了具有超薄皮层的ZIF-7/PES和MW-ZIF-7/PES非对称膜,ZIF-7的加入可同时提高膜对H2和CO_2的渗透速率和选择性。MW-ZIF-7/PES膜在经PDMS堵孔后,其H2和CO_2渗透速率高于PES膜,然而选择性下降明显。这是因为NIPS法对铸膜液组成要求较高,该方法用于制备表面无缺陷非对称MOF混合基质膜时,制备窗口较窄。其次,为拓宽MOF在聚合物溶液中的原位合成范围,开发出Cu-BTC前驱体和PES在DMSO中的稳定相容体系,在高温下,铸膜液热致相分离(TIPS)和Cu-BTC合成同时发生,得到非对称的Cu-BTC/PES膜,首次实现了非对称MOF混合基质膜的一步制备。该方法制备的Cu-BTC/PES膜具有典型的非对称结构,由致密的皮层和多孔支撑层构成,制备得到的Cu-BTC/PES膜可通过乙醇与DMSO的置换成功活化。Cu-BTC在膜中的含量可以通过Cu(NO_3)_2的投加量调节,且随Cu(NO_3)_2用量的提高,Cu-BTC/PES膜致密层厚度降低,膜渗透速率得到明显提高。当Cu-BTC含量从7.5 wt%提高到21.0 wt%,膜的H2和CO_2渗透速率提高了接近20倍,CO_2/N_2选择性保持在20左右。进一步通过纤维素醚类聚合物(EC)与Cu(NO_3)_2的络合作用实现了 Cu-BTC/EC混合基质膜的常温原位制备。EC起到降低溶液中前驱体扩散速率、促进Cu-BTC合成的作用。在Cu-BTC含量为26 wt%,Cu-BTC/EC膜气体分离性能最好,其CO_2渗透系数相对于纯EC膜提高了 69%,而CO_2/CH_4选择性仅从10.7下降到9.9。通过考察Cu-BTC/EC膜的热性能、机械性能及不同温度压力下的气体渗透性能,发现在Cu-BTC含量较低时,Cu-BTC/EC界面相容性较好,Cu-BTC可以提高聚合物相的耐CO_2塑化能力。最后,为强化混合基质膜中MOF与聚合物(Pebax)界面相容性,将具有高CO_2选择性和聚合物亲和性的离子液体[bmim][Tf2N]引入到ZIF-8孔道中,制备了 IL@ZIF-8材料及IL@ZIF-8/Pebax膜。IL@ZIF-8的水洗处理可有效限制[bmim][Tf2N]向Pebax基体中扩散。测试了 IL@ZIF-8/Pebax膜的机械性能和气体分离性能,结果表明IL@ZIF-8同时提高了 Pebax膜的机械性能和CO_2分离性能,添加量为15 wt%时,膜的CO_2渗透系数为104.0 Barrer,CO_2/N_2选择性为83.9,CO_2/CH_4选择性为34.8,相对于原膜分别提高了 45%、74%和92%,超过了 2008年Robeson上限。通过膜的SEM和DSC表征及Maxwell传递模型对比,确认了 IL@ZIF-8对Pebax膜机械性能和气体分离性能的增强主要源于离子液体对ZIF-8/Pebax界面相容性的强化。
[Abstract]:Since twenty-first Century, the consumption of fossil energy in the global scope increased year by year, greenhouse gas emission reduction and energy gas purification become the two important parts of CO_2 capture, the representative system for flue gas separation (CO_2/N_2) and natural gas (CO_2/CH_4). The membrane separation as a new energy efficient and clean separation technology the application of CO_2 in environmental protection, has a good prospect. The separation of mixed matrix membranes composed of polymer matrix and inorganic filler dispersed therein, with the advantages of easy processing of polymer membrane and inorganic membrane separation performance is high, high performance is an important development direction of gas separation membrane. The metal organic framework (MOF) is a new type of crystal materials with ordered pore structures, by transition metal ions and organic ligands through covalent bond or coordination bond bridging. Compared with traditional inorganic filler, MOF has mild synthesis conditions and easy functionalization The advantages, therefore, MOF mixed matrix membranes become the focus of current research. However, the current MOF mixed matrix membranes reported in the literature were obtained by casting with thin layer MOF, mixed matrix membrane research. In addition, MOF also has a mixed matrix membrane interface defects, MOF flexible framework and other issues. Selective weakening this thesis is based on three kinds of selectivity to CO_2 MOF (ZIF-7, ZIF-8, and Cu-BTC) in the polymer solution in situ synthesis with a thin layer of the choice of MOF mixed matrix membranes were prepared by the MOF, and the ionic liquid in MOF pre load strengthening MOF/ polymer interface compatibility, so as to improve the separation performance of mixed matrix membranes at first, the asymmetric membrane based on the traditional preparation process (immersion precipitation phase inversion method, NIPS), microwave assisted by direct blending were prepared with thin cortex ZIF-7/PES and MW-ZIF-7/PES on That film, the addition of ZIF-7 can also improve the permeation rate and selectivity of.MW-ZIF-7/PES membrane of H2 and CO_2 in the PDMS H2 and the plug hole, the permeation rate of CO_2 is higher than that of PES film, but the selectivity decreased. This is because the NIPS method requires high casting solution, the method for preparation of surface defects asymmetric MOF mixed matrix membrane, preparation of the window is narrow. Secondly, to broaden the scope of in situ synthesis of MOF in polymer solution, developed the Cu-BTC precursor and PES DMSO in the stable compatible system under high temperature, casting solution of thermally induced phase separation (TIPS) and Cu-BTC synthesis occurred at the same time, Cu-BTC/PES the asymmetric membrane, for the first time to achieve a step of preparing asymmetric MOF mixed matrix membrane. The method of the Cu-BTC/PES film prepared with the asymmetric structure, composed of dense cortex and a porous support layer, the Cu-BTC/PES film prepared by ethanol With the DMSO content in the film is the successful replacement of activated.Cu-BTC Cu (NO_3) by adjusting the dosage of _2, and Cu (NO_3) _2 with the increased amount of dense Cu-BTC/PES film thickness decreased, the membrane permeation rate was improved obviously. When the content of Cu-BTC increased from 7.5 wt% to 21 wt%, increased to 20 times the penetration rate of membrane H2 and CO_2, CO_2/N_2 selectivity remained at around 20. The cellulose ether polymer (EC) and Cu (NO_3) _2 complexation achieved Cu-BTC/EC mixed matrix membranes at room temperature in situ preparation of.EC precursor solution to reduce the diffusion rate, promote Cu-BTC synthesis. The content of Cu-BTC is 26 wt%, the separation performance of Cu-BTC/EC membrane gas permeability coefficient CO_2 the best, relative to the pure EC film is increased by 69%, while the selectivity of CO_2/CH_4 only decreased from 10.7 to 9.9. by thermal performance investigation of Cu-BTC/EC films, the mechanical properties of different temperature and pressure The gas permeability, found in Cu-BTC is low, Cu-BTC/EC interface has good compatibility, Cu-BTC can improve the resistance of CO_2 phase polymer plasticizing capacity. Finally, in order to strengthen the MOF and polymer in mixed matrix membrane (Pebax) interface compatibility, high CO_2 selectivity and affinity polymer ionic liquid into [bmim][Tf2N] the channel of ZIF-8, IL@ZIF-8 and IL@ZIF-8/Pebax membrane materials.IL@ZIF-8 were prepared by washing treatment can effectively limit the [bmim][Tf2N] to the Pebax matrix diffusion. The mechanical properties and gas separation performance of IL@ZIF-8/Pebax membrane were tested, the results show that IL@ZIF-8 improves the mechanical properties of Pebax membrane and CO_2 separation performance, when adding 15 wt% film CO_2 the permeability coefficient is 104 Barrer, the CO_2/N_2 selectivity was 83.9, the selectivity of CO_2/CH_4 was 34.8, compared with the original film were increased by 45%, 74% and 92%, more than 2008 Robes On upper limit. Through the comparison of SEM and DSC characterization and Maxwell transfer model, it is confirmed that the enhancement of IL@ZIF-8 on mechanical properties and gas separation performance of Pebax film is mainly due to the enhancement of ionic liquid's compatibility to ZIF-8/Pebax interface.

【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ051.893

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