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以EMT为晶种外延生长制备NaY沸石膜及其渗透蒸发性能研究

发布时间:2018-03-18 20:43

  本文选题:EMT沸石 切入点:二次生长法 出处:《太原理工大学》2015年硕士论文 论文类型:学位论文


【摘要】:NaY沸石膜具有独特的三维十二元环孔道体系,孔径尺寸为0.74nm,有利于大分子物质的分离,骨架中高的铝含量以及笼穴周围高度分散的钠离子,,使其具有较强的亲水性和极性,对亲水性和极性强的分子具有较优的分离选择性。碳酸二甲酯(DMC)的合成一般以甲醇(MeOH)为原料,反应后常会存在两者的共沸物,不易分离;采用酯交换法合成碳酸二苯酯(DPC)过程中,由于受到热力学平衡的限制,反应平衡转化率低,同样存在DMC和MeOH共沸的问题,及时将产物MeOH进行有效地分离能够提高反应的转化率。MeOH分子动力学直径为0.38nm,DMC具有与丙酮和甲基叔丁基醚相似的结构,其动力学直径与两者接近(丙酮为0.47nm,甲基叔丁基醚为0.63nm),MeOH分子尺寸小于DMC,且亲水性和极性高于DMC。NaY沸石膜作为亲水性膜材料能够优先吸附MeOH,对醇的选择性较好,同时NaY沸石膜分离MeOH/DMC的混合物能够克服有机膜易溶胀的缺点,稳定性好。 本论文考察了合成条件(晶种及晶种层、二次生长液组成)对NaY沸石膜微结构的影响,以EMT沸石为晶种,α-A12O3为载体,采用二次生长法制备了致密且连续的NaY沸石膜。通过X-射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)等分析测试手段对EMT沸石晶种、晶种层及NaY沸石膜进行了一系列的表征,并对沸石膜进行了渗透分离性能的检测,结果表明: 1、采用偏铝酸钠为铝源在无模板剂及低温条件下合成EMT型沸石,晶粒呈现六方形貌,晶粒大小约为20-30nm左右。以无水乙醇作为分散介质,晶种液浓度为0.1%,晶种担载量为1.0mL,晶种能够完全覆盖载体,制备均匀完备的晶种层,在此晶种层上,经二次生长可制备连续致密的NaY沸石膜,膜层厚度约12μm。 2、二次生长液物质的量组成n SiO2: n Al2O3: n Na2O: n H2O=10:1:14:840,在室温下搅拌陈化24h,于100℃下晶化6h制备的NaY沸石膜交联程度较高,沸石膜连续致密,且没有杂晶的出现。 3、NaY沸石膜在50℃条件下渗透分离MeOH/DMC(50wt%)体系,随渗透时间的延长沸石膜保持良好的稳定性,总渗透通量为0.110-0.120Kg/(m2·h),分离因子约为18;随着原料液中甲醇浓度(20-80wt%)的增大,总渗透通量(0.115-0.137Kg/(m2·h))增加,分离因子(34.2-5)降低;随着原料液温度(30-80℃)的升高,总渗透通量(0.09-0.179Kg/(m2·h))增大,分离因子降低(20.9-3)。
[Abstract]:The NaY zeolite membrane has a unique three-dimensional 12 element annular pore system with a pore size of 0.74 nm, which is favorable to the separation of macromolecules. The high aluminum content in the framework and the highly dispersed sodium ions around the cage cavity make the membrane have strong hydrophilicity and polarity. The dimethyl carbonate (DMC) was synthesized with methanol MeOH as raw material. After the reaction, azeotropic compounds were often found, which were not easy to be separated. In the process of synthesis of diphenyl carbonate by transesterification, due to the limitation of thermodynamic equilibrium, the equilibrium conversion of the reaction is low, so there is also the problem of azeotropic reaction of DMC and MeOH. The effective separation of the product MeOH in time can improve the conversion. MeOH molecular dynamics diameter of 0.38 nm DMC has a structure similar to acetone and methyl tert-#china_person0# ether. Its kinetic diameter is close to that of both (acetone is 0.47 nm, methyl tert-#china_person0# is 0.63 nm) and the molecular size of MeOH is smaller than that of DMC, and the hydrophilicity and polarity are higher than that of DMC.NaY zeolite membrane as hydrophilic membrane material, MeOH can be preferentially adsorbed, and the selectivity of alcohol is better. At the same time, NaY zeolite membrane separation of MeOH/DMC mixture can overcome the disadvantages of easy swelling of organic membranes and good stability. In this paper, the effects of synthesis conditions (seed and seed layer, composition of secondary growth liquid) on the microstructure of NaY zeolite membrane were investigated. EMT zeolite was used as seed and 伪 -A12O3 as carrier. Compact and continuous NaY zeolite membranes were prepared by secondary growth method. The seed, seed layer and NaY zeolite membrane of EMT zeolites were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The permeation performance of zeolite membrane was tested. The results showed that: 1. 1. EMT zeolites were synthesized by using sodium metaluminate as aluminum source at low temperature and without template. The grain size is about 20-30nm, and the crystal size is about 20-30nm. Anhydrous ethanol is used as the dispersing medium. The seed liquid concentration is 0.1 and the seed load is 1.0 mL. The seed can cover the carrier completely and prepare a uniform and complete seed layer. On this layer, continuous and compact NaY zeolite membrane can be prepared by secondary growth. The thickness of the film is about 12 渭 m. (2) the composition of n Sio _ 2: n Al _ 2O _ 3: n Na _ 2O: n Na _ 2O: n H _ 2O 10: 10: 1 14: 840, agitated at room temperature for 24 h, and crystallized at 100 鈩

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