【作者】 瞿新营；

【导师】 陈欢林； 张林；

【作者基本信息】 浙江大学 ， 生物化工， 2011， 博士

【摘要】 本文首先利用水热合成法制备了两种具有水分子扩散孔道的纳米分子筛,探索在不同界面聚合反应相中添加这种无机纳米颗粒,建立了含纳米无机多孔颗粒的超薄反渗透复合膜制备方法,探明了分子筛杂化膜的成膜机理；将不同分子筛添加到界面聚合单体相中制备聚酰胺杂化膜,并获得了无机分子筛性质对反渗透杂化膜结构及分离性能影响的统一规律；比较不同种类分子筛杂化膜的化学稳定性及对有机物体系的分离性能；在此基础上,根据界面聚合反应机理,采用硅烷偶联剂对分子筛进行改性,获得无机颗粒与聚合物基体相容性良好的均相纳米复合膜。上述研究结果为高性能分子筛杂化膜指出了研究方向,主要结论如下：(1)纳米分子筛的制备。为了避免高温煅烧去模板剂所造成的分子筛聚集,选用与分子筛颗粒表面具有相互作用力的聚乙烯醇与分子筛共混成膜后再进行煅烧。聚乙烯醇经高温煅烧后完全分解,其分解温度较高,可以很好地保持煅烧过程中分子筛颗粒之间的间隔状态,从而缓解煅烧后分子筛强烈团聚的问题。聚乙烯醇浓度为2wt%时可以获得分散良好、粒径在50-70 nm左右的纳米分子筛颗粒。(2)分子筛杂化膜成膜机理研究。在界面聚合反应过程中添加NaA型纳米分子筛制备分子筛／聚酰胺反渗透复合膜。通过比较分子筛添加在水相或者油相中所成膜的结构及分离性能变化规律,探明了含分子筛杂化膜的成膜机理。当分子筛添加在油相,分子筛上的羟基与酰氯基团发生反应,在分子筛周围形成紧密的聚酰胺基质,之后向外围扩散聚合成膜,因此分子筛与聚酰胺膜结合紧密；当分子筛添加在水相时,分子筛沉积在底膜表面,与油相接触后,形成的初生态膜覆盖在分子筛上,分子筛周围存在一定的空隙。因此,分子筛添加在油相利于复合膜分离性能的提高,当油相中分子筛含量为0.1 wt%时,杂化膜的水通量为纯聚酰胺的两倍,同时截留率提高到了98%以上。(3)分子筛种类对膜结构与性能的影响。通过添加不同种类分子筛考察膜结构及分离性能的变化,添加NaA型分子筛后导致膜表面更加粗糙,添加相同大小的MFI型分子筛,特别是Silicalite-1,所制备膜表面则相对较光滑。主要原因是由于不同的分子筛其水合化热焓不同,导致成膜过程中分子筛放热量有较大差异,其中NaA型分子筛放热量大,有助于局部反应加快,使得膜表面结构更粗糙。对于MFI型分子筛,当分子筛中Si/Al比增加,分子筛对膜结构的影响程度变小,添加全硅型Silicalite-1分子筛后,膜形貌较光滑。分离结果表明,影响分子筛填充膜通量的关键因素是分子筛的孔道大小及孔道结构。当分子筛含量为0.1wt%时,杂化膜的水通量大小次序为：NaA<ZSM-5 <Silicalite-1;由于分子筛填充膜的聚酰胺部分交联度均增加,因此杂化膜的截留率均有所增加。其中,Silicalite-1型分子筛杂化膜具有更高的水通量,有望取代NaA型分子筛,成为含分子筛杂化膜的主要研究方向之一(4)分子筛化学稳定性对膜性能的影响。通过调整料液的pH值,考察了NaA型和Silicalite-1型分子筛杂化膜的酸耐受性,结果表明,由于NaA分子筛的耐酸性差,在处理酸性料液时,NaA分子筛晶体结构塌陷,导致膜性能急剧下降,因此不宜使用NaA型分子筛杂化膜,而添加全硅型的分子筛可以提高反渗透膜的耐酸性。对于含氯化钙的料液,纯聚酰胺膜和Silicalite-1分子筛杂化膜的分离性能较稳定,但是NaA型分子筛填充膜的分离性能会明显下降,主要原因是由于分子筛中的Na+与Ca2+发生离子交换导致分子筛结构破坏。(5)改性分子筛在膜内分散性的研究。为了提高分子筛在膜内的分散性,研究了分子筛表面改性对膜结构和性能的影响。采用APTES改性分子筛后,其在正己烷中的分散性得到较好的改善,在成膜过程中,分子筛表面氨基可以参与界面聚合反应,分子筛表面所接枝的有机基团也增加了无机分子筛与有机聚合物基质之间的相容性,因此,所制备的复合膜结构更加均一光滑,分子筛在膜内的分散性更好。膜的通量和截留率均有所增加,并且随着分子筛含量增加,这种变化愈明显。通过本论文的研究,探明了纳米分子筛杂化反渗透复合膜的成膜机理,制备出了分散性良好的杂化膜,获得了分子筛种类对膜结构和性能影响关系,为后续更高性能分子筛杂化膜制备研究奠定了基础。更多还原

【Abstract】 Up to now, thin-film nanocomposite (TFN) RO membranes have large potential for improving desalination. In particular, the addition of zeolite nanocrystals (A type) into polyamide has proven to be an effective method to tune the properties of polymer membranes. Therefore, in our study, zeolite-polyamide thin film nanocomposite (TFN) reverse osmosis membranes are fabricated by interfacial polymerization of amine and acid chloride monomers in the presence of zeolite nanocrystals.The NaA and MFI type zeolite nanopaticle were successfully prepared. The membrane formation mechanism was proposed, and effect of zeolite crystal structure of zeolites on membrane structure and transport properties was also investigated. Then, the chemical stability and application of TFN membrane was studied. Also the improved dispersion of inorganic nanoparticles in the polyamide matrix was successfully obtained.Firstly, a simple method for synthesis zeolite nanoparticles was proposed. Just one kind of water soluble polymer PVA was used to blending with the zeolite colloidal nanocrystals, as a temporary barrier to isolate as-synthesized nanocrystals during template removal, without chemical reaction, the dicomposed temperature of PVA was about 520℃, and the proper concentration of PVA solution was 2 wt%. This method would promote the industrially application of zeolite nanocrystals, also there was no report about this in the literature.Then, the effects of introducing the NaA zeolite nanocrystals via the aqueous phase or the organic phase on the membrane morphology, surface properties and desalination performance were investigated. When zeolite was added into the aqueous phase, zeolite was covered by the incipient layer of polyamide membrane at the beginning of polymerization, and then polyamide layer would be extended to the support membrane following slow polymerization. And at the bottom layer, there were macrovoids between the polyamide and zeolite because the zeolite surface adsorbed too much water to occur polymerization reaction. For TFN membrane with zeolite in organic phase, the polyamide layer was first formed on the surface as dense core, and then extended from the zeolite surface to other zone, which is as claimed as literature. In addition, NaA in organic phase will be hydrated and release heat when the organic phase contact with aqueous phase, higher reaction temperature may increase MPD diffusivity through incipient membrane, and the NaA zeolite will be enclosed in polyamide very well and the aggregate pores were eliminated by the cross-linked groups. Both the flux and salt rejection increased clearly with the increase of the zeolite loading in organic phase. Therefore, the zeolite should be added in the organic phase.In order to investigate the effect of zeolite properties such as zeolite particle and zeolite type on membrane structure and transport properties, TFN membranes were synthesized through adding NaA zeolite and MFI type zeolite with different Si/Al ratios. The hydration enthalpy and water diffusion coefficient of MFI zeolite were calculated. The surface structure of TFN membrane was relative to the hydration enthalpy of zeolite, and surface of TFN membrane became relative smoother when Silicalite-1 zeolite was used, which has lower hydration enthalpy. The flux of the TFN membrane was determined by the pore diameter and pore structure. The increased order of flux was:Silicalte-1>ZSM-5>NaA, which is the same as the order of water diffusion coefficient. The cross-linked degree of TFN membrane incresead at the order:NaA>ZSM-5>Silicalite-1, and the salt rejection of the TFN membranes were higher than that of the polyamide membrane. For the Silicalite-1 type zeolte loaded reverse osmosis membrane, the flux increased obove 60 L/m2.h with only a little sacrifice of rejection, which was 3-times of the flux for polyamide membrane.The MFI type zeolite was firstly introduced to the TFN membrane, not only the flux of the membrane increased, but also the other properties was enhanced, such as acid-resistance, ion exchange properties, chlorine resistance and separation performance for the organic matter. In our study, the acetic acid was used to detect the acid-resistance of TFN membrane. After immersed in the acid solution, the structure of NaA zeolite was completely destroyed, and the polyamide/NaA membrane showed that flux increased while salt rejection decreased. However, the separation performance of the polyamide and polyamide/Silicalite-1 membranes was steady. Then, the TFN membranes were used to treat the NaCl and CaCl2 mixed solution. Ion exchange would occurre in NaA zeolite, but not in Silicalite-1 zeolite, thus the TFN membrane loaded with Silicalite-1 zeolite showed steady separation performance. So, it has large potential to enhance the chemical stability by adding Silicalite-1 zeolite, and the membrane could be widely applied.As mentioned above, as the zeolite nanoparticle should be added in the organic phase, producing a better organic-inorganic desalination membrane has become quite a challenge, because inorganic materials were hard to well disperse within thin polymer membrane films. Therefore, surface modification of zeolite with silane coupling agents had been proposed to improve the dispersibility of zeolite and interfacial strength in order to enhance the separation performance. The dispersibility of zeolite in the organic phase was improved obviously and subsequently the separation performance of the TFN also was enhanced.In conclusion, TFN membrane loaded with Silicalite-1 zeolite was found with higher separation performace, the flux of the membrane has a three-times increase, at the same time, the salt rejection also increased. In addition, the chemical stability of the membrane was largely improved. The novel membrane has large potential for industrial application.更多还原