【作者】 王磊；

【导师】 杨建华；

【作者基本信息】 大连理工大学 ， 化学工艺， 2022， 博士

【摘要】 相较于精馏、吸收和萃取等分离技术,膜分离具有能耗低、效率高、无二次污染等优点,因此在化工分离界日益受到关注。高分离性能、低成本分离膜是膜材料与技术开发的核心任务。膜材料的结构特性与分离体系的物化性质共同决定膜的分离性能。Linde Type A（LTA）和Faujasite（FAU）沸石膜因其结晶孔道结构规整、机械强度高、热稳定性好和优异的抗污染性与亲水性,在渗透汽化分离方面具有很大优势,尤其适用于含水有机物中水分的脱除。以小孔LTA沸石膜为研究主体,采用新制膜工艺,制备有机物脱水用LTA沸石膜并尝试其工业化放大。鉴于LTA沸石膜在酸性条件下分离性能下降的不足,拟选用后修饰法制备1,2-双（三乙氧基硅基）乙烷（BTESE）/LTA复合膜,提高其耐酸性,拓宽其应用领域。同时,将新工艺拓展至大孔FAU沸石膜的制备,满足较大分子分离体系或高通量分离体系的分离需求。主要研究内容与结论如下:（1）为克服传统水热合成法制备LTA沸石膜合成液利用率低,造成原料浪费和环境污染的问题,提出湿凝胶转化法,在釜底不加任何合成液或水的条件下,制备高性能LTA沸石膜。首先,以5 cm长的大孔α-Al₂O₃为载体,制备LTA沸石膜,考察晶化时间、凝胶中水量、水浸渍过程对于LTA沸石膜生长和分离性能的影响,优化合成条件,制备实验用LTA沸石膜。此膜在75℃下渗透汽化分离90 wt.%乙醇/水溶液,渗透通量为2.56 kg/（m²·h）,分离因子约9000,表明所制LTA沸石膜可高效分离乙醇/水体系。然后,以80 cm长的大孔α-Al₂O₃载体,采用同样制膜工艺,制得工业化尺寸LTA沸石膜。此工业化尺寸LTA沸石膜在75℃下渗透汽化分离90 wt.%乙醇/水溶液,平均渗透通量为1.78±0.06 kg/（m²·h）,平均分离因子为7296±65,表明工业化尺寸LTA沸石膜依然可高效分离乙醇/水体系,并有望工业化应用。对比传统水热合成法与湿凝胶转化法制LTA沸石膜凝胶耗用量,湿凝胶转化法节约凝胶96%,可显著降低制膜成本。（2）针对LTA沸石膜在酸性条件下,易发生脱铝现象,分离性能劣化低下,拟对其表面进行修饰,改善其分离特性。因有机硅BTESE材料具有优异的耐酸性、分子选择透过性以及其与沸石材料间良好的结合力,将其用于缺陷LTA沸石膜的表面修饰,改善LTA沸石膜耐酸性的同时,修饰了LTA沸石膜中晶间缺陷。所制膜在保持良好选择性的条件下,发挥了其潜在的高膜渗透通量。实验采用后修饰法,以缺陷LTA沸石膜为底膜,将有机硅BTESE均匀涂敷于LTA沸石膜表面,通过优化BTESE浓度和涂敷次数,制得BTESE/LTA复合膜。将其应用于75℃下渗透汽化分离酸性（p H=3）90 wt.%乙醇/水溶液时,在4 h的测试中,分离性能始终稳定,其渗透通量为1.91 kg/（m²·h）,分离因子达1013,相比于纯相LTA沸石膜,复合膜的耐酸性得到提升,并表现出较高的分离效率。（3）为满足较大分子分离体系或高通量分离体系的分离需求,采用湿凝胶转化法,制备大孔FAU沸石膜。系统考察晶化时间、小晶种悬浮液浓度、小晶种尺寸和合成凝胶中铝源对于FAU沸石膜生长以及分离性能的影响。比较FAU沸石膜和LTA沸石膜对乙醇、异丙醇、丙二醇单甲醚（PGME）等有机水溶液的脱水效果,发现LTA沸石膜对乙醇、异丙醇等小尺寸分子水溶液的脱水效果佳,而FAU沸石膜则对较大尺寸分子PGME水溶液的脱水效果更佳。将所制FAU沸石膜应用于75℃下渗透汽化分离90 wt.%丙二醇单甲醚（PGME）/水溶液,其渗透通量为5.61 kg/（m²·h）,分离因子高于10000。在此基础上,分别以缺陷FAU沸石膜和致密FAU沸石膜为底膜,由BTESE对其表面进行修饰,制得BTESE/FAU复合膜。比较两种BTESE/FAU复合膜乙醇脱水效果,发现以缺陷FAU沸石膜为底膜所制BTESE/FAU复合膜具有更高的渗透通量和相当的分离因子,表明缺陷底膜与BTESE材料的结合对提高BTESE/FAU复合膜的分离效果具有协同作用。更多还原

【Abstract】 Compared with distillation,absorption,extraction and other separation methods,membrane separation technology shows the advantages of low energy consumption,high efficiency and no secondary pollution,attracting growing attentions to both scientific and industrial communities.High separation performance,high stability and low cost are required for development of membrane materials and technology.The separation performance of membrane is jointly determined by the structural properties of membrane materials and physicochemical properties of separation system.LTA and FAU zeolite membranes have regular pore structure,high mechanical strength,good thermal stability,excellent anti-pollution performance and hydrophilicity,which make them be ideal membrane materials for pervaporation technology,especially suitable for the removal of water in organic mixture.In this paper,LTA zeolite membrane with small pore size as a main model system was investigated,attemting to build a new route for synthesis of high performance LTA zeolite membrane for organic dehydration.At the same time,industrial scale-up preparation of LTA zeolite membrane by the new route was carried out.Considering the degradation of separation performance of LTA zeolite membrane under acid condition,a post modification method was developed to prepare bis（triethoxysilyl）ethane（BTESE）/LTA composite membrane to effectively enhance the acid stability,so as to broaden its application field.Finally,FAU zeolite membrane with large pore size was prepared using new synthesis method to meet the separation requirement of large molecular size or high flux system.The main contents and achievements are as follows:（1）In order to overcome the problems of low utilization rate of synthesis solution,waste of raw materials and environmental pollution caused by traditional hydrothermal synthesis of LTA zeolite membrane,wet gel conversion was used to prepare LTA zeolite membrane without adding any synthesis solution or water in the bottom of the autoclave.Firstly,the 5 cmα-Al₂O₃tube was selected as the support to prepare LTA zeolite membrane.The effects of crystallization time,water content in the gel and water dipping treatment on the growth and separation performance of LTA zeolite membranes were investigated in detail.Under optimal condition,the synthesized LTA zeolite membrane showed excellent permeation flux of 2.56 kg/（m²·h）with prominent separation factor of near 9000 for the dehydration of 90 wt.%ethanol/water mixture at 75℃by pervaporation,indicating the LTA zeolite membrane can effectively separate ethanol/water system.Based on the wet gel conversion synthesis of 5 cm LTA zeolite membrane,industrial scale LTA zeolite membrane was prepared on the 80 cmα-Al₂O₃support by this route.It was found that the as-synthesized LTA zeolite membranes showed high permeation flux of 1.78±0.06 kg/（m²·h）with excellent selectivity of 7296±65 for dehydration of 90 wt.%ethanol/water mixture at 75℃by pervaporation.The results showed that industrial scale LTA zeolite membrane can still efficiently separate ethanol/water system,and is expected to be applied in industry.Furthermore,the gel weight for membrane growth using wet gel conversion and traditional hydrothermal synthesis method was compared.The result showed that gel weight was saved by more than 96%and the cost of membrane preparation can be significantly reduced by wet gel conversion.（2）The dealuminization easily occurs on LTA zeolite membrane in acid condition,resulting in the decrease of separation performance.In order to improve the separation characteristics of LTA zeolite membrane,the surface modification was proposed.Organosilica BTESE shows high acid resistance,excellent molecular permselectivity and good binding force with zeolite material.If it is used for surface modification of defective LTA zeolite membrane,the acid resistance of LTA zeolite membrane is improved while the intergranular defects of LTA zeolite membrane are modified.The obtained membrane can maintain good selectivity and the potential high permeation flux is also developed.Defective LTA zeolite membrane was selected as the pristine membrane,and the organosilica BTESE layer was coated on the surface of LTA zeolite membrane by post-modification method.By optimizing the coating cycle and concentration of BTESE sol,BTESE/LTA composite membrane can be prepared.The composite membrane was applied for the separation of acidic（p H=3）90 wt.%ethanol/water mixture at 75℃by pervaporization.During the stability test of 4 h,the separation performance remained stable,and the permeation flux was 1.91 kg/（m²·h）with separation factor of 1013.Compared with pure LTA zeolite membrane,the acid resistance of the composite membrane was enhanced and the separation efficiency was high.（3）The wet gel conversion approach was extended to prepare high performance FAU zeolite membrane with large pore size in order to meet the separation requirement of large molecular size or high flux system.The effects of crystallization time,small seeds concentration,small seeds size and aluminum source in the synthesis gel on the growth and separation performance of the FAU zeolite membranes were investigated in detail.The dehydration performances of FAU zeolite membrane and LTA zeolite membrane for ethanol,isopropyl alcohol and propylene glycol monomethyl ether（PGME）were compared.It was found that LTA zeolite membrane was more advantageous for the separation of small molecules such as ethanol and isopropanol solutions,while FAU zeolite membrane was more advantageous for the separation of large molecules PGME solution.FAU zeolite membrane synthesized under optimal condition exhibited a permeation flux of 5.61 kg/（m²·h）and separation factor>10000for the separation of 90 wt.%PGME/water mixture at 75℃by pervaporation.On this basis,defect FAU zeolite membrane and dense FAU zeolite membrane were used as the pristine membranes respectively,and their surfaces were modified by BTESE to prepare BTESE/FAU composite membranes.It was found that the BTESE/FAU composite membrane prepared by using defective FAU zeolite membrane as pristine membrane showed higher permeation flux and equivalent separation factor,indicating that the combination of defective pristine membrane and BTESE material had synergistic effect on improving the separation performance of BTESE/FAU composite membrane更多还原