【作者】 马晓华；

【导师】 许振良；

【作者基本信息】 华东理工大学 ， 化学工程， 2012， 博士

【摘要】 渗透汽化膜是渗透汽化过程的核心,其化学特性和物理结构在很大程度上决定着渗透汽化过程分离效率的高低。催化与渗透汽化耦合双功能膜具有更优的分离性能和良好的催化性能,仅是将制备渗透汽化膜方法的简单重复很难制备出性能良好的催化膜,必须将制备渗透汽化膜和制备催化剂的各种方法或技术有机地结合起来才能有所创新。本文选用全氟磺酸(PFSA)作为催化剂,采用浸涂法制备具有两层结构的催化与渗透汽化双功能中空纤维膜,将优选出的催化与渗透汽化双功能中空纤维膜用作精馏结构填料,并对其作为反应精馏的结构填料和催化剂生产乙酸乙酯的工艺过程进行了研究。论文研究结果如下：首先,以聚丙烯腈(PAN)为底膜,采用浸涂法制备了壳聚糖-海藻酸钠/聚丙烯腈(CS-SA/PAN)、壳聚糖-三聚磷酸钠/聚丙烯腈(CS-STPP/PAN)和戊二醛(GA)表面交联聚乙烯醇/聚丙烯腈(GA-PVA/PAN)3种单功能渗透汽化平板复合膜。运用FTIR、SEM、EDX、溶胀度、渗透汽化分离乙酸乙酯/水体系等方法表征了3种单功能渗透汽化平板复合膜的结构和性能。实验结果表明：40℃时,对于分离含97wt.%乙酸乙酯的水溶液,三种单功能膜的渗透通量分别为348 g/(m2-h),340 g/(m2-h)和168g/(m2·h),相对应的分离选择性分别为7245,6268和9182；在97wt.%乙酸乙酯的水溶液中,三种单功能膜的溶胀度最大分别可达51.0%,37.4%和23.7%,说明3种膜的稳定性逐次提高。考虑到膜的稳定性和后续乙酸-乙醇酯化反应实验,本文选用GA-PVA/PAN单功能渗透汽化平板膜作为催化与渗透汽化双功能膜的基膜。其次,建立了表面交联反应模型,以CS-STPP/PAN单功能渗透汽化平板复合膜为对象,考察并分析了交联剂浓度和交联反应时间对膜结构和性能的影响。实验结果表明：对于CS-STPP/PAN单功能渗透汽化平板复合膜,表面交联反应15min时,基本达到了表面交联反应的平衡状态,与文献报道相一致；交联率与交联反应时间成指数关系,与交联剂浓度成线性关系；通过控制交联反应时间和交联剂浓度,可以制备出所期望的理想的渗透汽化复合膜。再次,将优选出的GA-PVA/PAN单功能渗透汽化平板复合膜制备成单功能渗透汽化中空纤维复合膜并考察其性能。实验结果表明：4wt.% GA表面交联的PVA/PAN单功能中空纤维复合膜具有较好的性能,渗透汽化分离乙酸乙酯塔顶粗酯(乙酸乙酯87.36wt.%,乙醇3.73wt.%,水8.91wt.%)时,其渗透通量为181 g/(m2·h),相对应的水对乙醇的分离选择性为203,水对乙酸乙酯的分离选择性为3953。再以优选出的4wt.%GA表面交联的PVA/PAN单功能渗透汽化中空纤维复合膜作为底膜,在其表面采用浸涂法涂覆催化剂涂膜液,催化剂涂膜液以PFSA为催化剂、以纳米颗粒(SiO2、TiO2或Al2O3)为支撑体、以PVA为粘结剂,制备了3个体系(纳米SiO2、纳米TiO2或纳米Al2O3)、27种催化与渗透汽化双功能中空纤维复合膜。使用水动态接触角、机械强度、FTIR、SEM、EDX、XRD、TGA、渗透汽化分离乙酸乙酯塔顶粗酯、乙酸-乙醇酯化反应等方法表征了这27种催化与渗透汽化双功能中空纤维复合膜的结构和性能。实验结果表明：PFSA催化剂被成功地涂覆到催化与渗透汽化双功能中空纤维复合膜的外表面,且附着良好,纳米颗粒(SiO2、TiO2或Al2O3)为其提供了大的比表面积；双功能膜具有较好的亲水性能和机械性能；当催化剂涂膜液中含有2wt.% PFSA、3wt.% PVA和8wt.%纳米颗粒(SiO2、TiO2或Al2O3)(分别命名为DMS1、DMT1和DMA1)时,双功能中空纤维复合膜具有较好的分离性能和催化性能,分离乙酸乙酯塔顶粗酯时,渗透通量最高可达179 g/(m2·h),相对应的水对乙醇的分离选择性为95,无乙酸乙酯透过：相较于空白实验,加入双功能膜后,乙酸-乙醇酯化反应的时间显著缩短,100min就能达到空白反应400min时的转化率,约为40.0%(平衡转化率为66.7%,全回流)；双功能膜具有较好的稳定性,乙酸-乙醇脂化反应24h前后的FTIR和SEM基本没有变化。优选出DMS1、DMT1和DMA1三种双功能中空纤维复合膜作为后续研究。随后,以优选的3种催化与渗透汽化双功能中空纤维膜DMS1、DMT1和DMA1作为精馏结构填料,上升蒸汽和下降液体均从双功能中空纤维膜的壳层流动,以异丙醇-水、乙醇-水为分离体系,考察了以双功能膜为结构填料时的精馏性能。实验结果表明：当使用双功能中空纤维膜作为精馏结构填料时,与传统结构填料相比,能在液泛线以上区域操作,传质单元高度显著降低；与文献报道的中空纤维膜作为结构填料相比(上升蒸汽走壳层,下降液体走管层),其有相似的结果；对于异丙醇-水体系,化质单元高度(HTU)可低至9cm,对于乙醇-水体系,HTU可低至3.6cm。证明使用双功能中空纤维膜作为填料是可行的,并为渗透汽化-反应精馏耦合过程提供了实验基础。最后,以优选的3种催化与渗透汽化双功能中空纤维膜DMS1、DMT1和DMA1作为反应精馏结构填料和催化剂,上升蒸汽和下降液体均从双功能中空纤维膜的壳层流动,以乙酸-乙醇酯化反应为体系,考察了反应精镏生产乙酸乙酯的工艺条件。实验结果表明：把催化剂涂敷在中空纤维膜的外面,并将其作为结构填料装填在精馏塔中,在确保良好的精馏性能的同时,中空纤维结构填料外表面的催化薄层和反应混合物可以大面积接触,缩短了扩散距离,确保了反应的高效性和选择性；当乙酸与乙醇摩尔比为4：1,油浴温度为145℃,装填双功能中空纤维膜为40根,回流比为2,双功能中空纤维膜为DMT1时,其反应精馏的操作条件最优,此时乙酸乙酯转化率可达97.3%,基产率可达86.8%。更多还原

【Abstract】 Pervaporation membrane is the core of pervaporation process, the chemical property and physical structure of which determine the pervaporation separation efficiency to a great extent. Difunctional membrane coupling catalysis with pervaporation has good catalytic performance and even better separation performance over pervaporation membrane. Only a simple repetition of the methods of preparation pervaporation membrane is hard to prepare catalytic membrane with good performance. It must combine both preparation methods of membrane and catalyst together to make innovation. In this paper, perfluorosulfonic acid (PFSA) was used as catalyst to prepare difunctional hollow fiber composite membranes with two layers, catalyst layer and separation layer, by dip-coating method. The difunctional hollow fiber composite membranes with remarkable capabilities were chosen and used as packing in distillation, and the operation conditions of reactive distillation produce ethyl acetate were optimized when using difunctional hollow fiber as packing and catalyst. The conclusions were as follows:Firstly, three kinds of single-function pervaporation plate composite membranes, chitosan-sodium alginate/polyacrylonitrile (CS-SA/PAN), chitosan-sodium tripolyphosphate/polyacrylonitrile (CS-STPP/PAN) and glutaraldehyde-poly(vinyl alcohol)/polyacrylonitrile (GA-PVA/PAN), were prepared by dip-coating method using PAN ultra filtration membranes as support membranes, and were characterized by FTIR, SEM, EDX, swelling and dehydration ethyl acetate/water solution through pervaporation process. The results showed that the permeation fluxes of them were 348 g/(m2·h),340 g/(m2·h) and 168 g/(m2·h), and the corresponding separation factors were 7245,6268 and 9182, respectively, when dehydrating 97wt.% ethyl acetate aqueous solution at 40℃. The swelling degree, which represented the stabilization of membrane, could reach 51.0%, 37.4% and 23.7% in 97wt.% ethyl acetate aqueous solution, respectively. Considering the stabilization of membrane and the acetic acid-ethanol esterification reaction, GA-PVA/PAN single-function pervaporation plate composite membrane was chosen for further study since CS could dissolve in dilute acetic acid solution.Secondly, a surface-crosslinking reaction model was established to predict the impact of crosslinking agent concentration and surface-crosslinking reaction time on the morphology and the structure of membrane, and CS-STPP/PAN single-function pervaporation plate composite membrane was used to verify this model. The results showed that the surface-crosslinking reaction between CS and STPP on CS-STPP/PAN single-function pervaporation plate composite membrane reached the equilibrium state when reacted 15 min, agreeing well with the corresponding report of literature. The crosslinking ratio had an exponential relationship with surface-crosslinking reaction time and a linear relationship with crosslinking agent concentration. The expected ideal pervaporation composite membrane could be prepared through controlling crosslinking agent concentration and surface-crosslinking reaction time.Then, GA-PVA/PAN single-function pervaporation plate composite membrane was prepared as single-function pervaporation hollow fiber composite membrane and their capabilities were characterized. The results showed that 4 wt.% GA surface crosslinked PVA/PAN hollow fiber composite membrane had good capabilities with permeation flux 181 g/(m2 h), the corresponding separation factors of water to ethanol 203 and water to ethyl acetate 3953 when dehydrating top coarse ester (ethyl acetate 87.36wt.%, ethanol 3.73wt.% and water 8.91 wt.%) through pervaporation process. And then three series (nano SiO2, nano TiO2 or nano Al2O3),27 kinds of difunctional hollow fiber composite membranes with catalysis and pervaporation capabilities were prepared by dip-coating catalytic solution on 4 wt.% GA surface crosslinked PVA/PAN single-function hollow fiber composite membrane. The catalytic solution consisted of PFSA (used as catalyst), PVA (used as adhesion), and nano SiO2, nano TiO2 or nano Al2O3 (used as support). Their structures and performances were characterized through the water contact angle, mechanical strength, FTIR, SEM, EDX, XRD, TGA, dehydrating top coarse ester by pervaporation process and acetic acid-ethanol esterification reaction. The results showed that PFSA was successfully coated and adhered well by PVA on the outer surface of difunctional hollow fiber composite membrane, and nano SiO2, nano TiO2 or nano Al2O3 supplied a large amount of specific surface area for PFSA. The difunctional hollow fiber composite membranes had good hydrophilic and mechanical properties, and had remarkable separation performance and catalytic activity when the catalytic solution consisted of 2wt.% PFSA, 3wt.% PVA, and 8wt.% nano SiO2, nano TiO2 or nano Al2O3 (named as DMS1, DMT1 and DMA1, respectively). The permeation flux could reach 179 g/(m2 h), the corresponding separation factor of water to ethanol was 95 with no ethyl acetate permeating. Comparing with blank, the acetic acid-ethanol esterificatoin reaction time was shortened greatly when added difunctional hollow fiber composite membrane in the reaction feed solution as catalyst. The conversion at the reaction time 100min could reach that of 400min in blank, as high as 40.0%(the equilibrium conversion is 66.7%, total reflux). The FTIR and SEM had little change when acetic acid-ethanol esterification of 24h, indicating that the difunctional hollow fiber composite membrane had good stabilization. DMS1, DMT1 and DMA1 were chose for further study.Consequently, the optimized DMS1, DMT1 and DMA1 three kinds of difunctional hollow fiber composite membranes were used as structured packings in distillation. Both of vapor and liquid flowed on the shell side of the difunctional hollow fiber composite membranes. The distillation capabilities were characterized by isopropanol-water and ethanol-water systems. The results showed that, comparing with traditional structured packing, difunctional hollow fiber composite membrane structured packing could be operated successfully above the flooding limits and significantly reduced the height of transfer unit (HTU); ant it had the similar performances (despite both of vapor and liquid flowed on the shell side of the membrane) with the hollow fiber distillation reported in literatures (both liquid and vapor had their own channels). The HTU was only 9.0 cm for isopropanol-water system and 3.6 cm for ethanol-water system, representing higher separation efficiency. The results showed that it was feasible to use difunctional hollow fiber composite membrane as packing, and thus provided experiment basis for reactive distillation and pervaporation coupling process.Finally, the operation conditions of reactive distillation produce ethyl acetate were optimized using difunctional hollow fiber composite membrane as packing and catalyst as above. The results showed that the difunctional hollow fiber as distillation packing ensured good distillation characteristics, meanwhile, a large contact area between catalytic film and reaction mixture, combined with the short diffusion length, ensured a high overall efficiency and selectivity of the reaction. The optimal operating conditions were mole ratio of acetic acid to ethanol of 4, reboiler oil temperature of 145℃, fiber numbers of 40, reflux ratio of 2 and fiber types of nano TiO2 embedded difunctional hollow fiber membrane (named as DMT1). Meanwhile, the conversion of esterification could reach 97.3%, and the yield of ethyl acetate could reach 86.8%.更多还原