【作者】 孔春龙；

【导师】 王金渠；

【作者基本信息】 大连理工大学 ， 化学工艺， 2008， 博士

【摘要】 膜分离作为一种新型的分离技术,由于其能耗低、设备简单、分离时物料无相变、选择透过性好等优点,近年来得到广泛的研究。Silicalite-1沸石分子筛其孔径在0.55 nm左右,与工业上多种重要物质分子动力学直径相近,具有更高的化学、物理稳定性和更强的疏水特性。因此,将Silicalite-1沸石分子筛制成膜,会在膜分离、渗透蒸发及膜反应器等方面有着巨大的潜在应用。开展Silicalite-1沸石分子筛及其复合膜的制备和应用研究具有重要的意义。本文首先采用原位水热法考察Silicalite-1沸石分子筛的制备条件,合成出不同粒径的Silicalite-1沸石分子筛,并得出Silicalite-1沸石分子筛膜的合成配方,然后在此基础上对传统的沸石分子筛膜的制备方法进行改进。采用打磨修饰法,真空引入晶种法和无模板剂法在α-Al₂O₃载体管上合成Silicalite-1沸石分子筛膜,并对合成方法进行优化,制备了性能良好的沸石分子筛膜;采用两步变温法合成Silicalite-1沸石分子筛膜,显著地缩短了成膜时间,合成出质量较好的Silicalite-1沸石分子筛膜;考虑单一膜材料的缺陷,设计制备复合膜兼具两种膜材料的优点,合成了Silicalite-1/炭、Silicalite-1/TiO₂及Silicalite-1/Pd复合膜。将合成的Silicalite-1膜分别应用在渗透蒸发分离乙醇/水混合物和膜催化乙苯脱氢制苯乙烯体系中,得到了较好的乙醇/水分离效果和较高的乙苯转化率。实验主要结论如下:（1）分别考察模板剂四丙基溴化铵（TPABr）和四丙基氢氧化铵（TPAOH）、合成液的碱度、晶化温度、晶化时间及搅拌等因素对Silicalite-1沸石分子筛制备的影响,合成的晶粒尺寸范围为0.1～4μm,且结晶度较高,粒径分布窄;采用TPABr为模板剂时,合成液经历形成凝胶及凝胶分解过程,而TPAOH为模板剂时不经历此过程;高温焙烧Silicalite-1沸石分子筛时,其失重区间主要包括吸附水的脱附、孔道中有机铵的分解、平衡沸石分子筛骨架中负电荷的TPA⁺的分解。（2）分别采用打磨修饰法、二次生长法及无模板剂法在α-Al₂O₃载体管上制备Silicalite-1沸石分子筛膜。研究结果表明:载体打磨前的水热合成时间和砂纸粗细对合成膜的质量影响较大,打磨修饰法能有效地降低沸石分子筛膜的有效厚度,提高膜的质量。室温下,膜对H₂的渗透率达到1.2×10^-6mol/（m²·s·Pa）,H₂/n-C₄H₁₀及H₂/SF₆的理想分离系数分别达到30和84以上;探讨了真空引入晶种法合成Silicalite-1沸石分子筛膜的影响因素,晶种大小与载体孔径相当,压力为0.06～0.07 Mpa时可获得均匀分散、连续的晶种层,合成的膜室温下H₂的渗透率为3.25×10^-7mol/（m²·s·Pa）,H₂/N₂及H₂/SF₆的理想分离系数分别达到4.1和133.2;采用无模板剂法制备Silicalite-1沸石分子筛膜,对晶化时间、水硅比和晶化次数等因素进行了考察,优化结果为:晶化时间5～8 h,水硅比30～45,晶化一次。室温下,膜对H₂的渗透率为1.72×10^-7mol/（m²·s·Pa）,H₂/N₂和H₂/SF₆的理想分离系数分别为2.76和18.5。（3）采用两步变温法在α-Al₂O₃和多孔不锈钢管载体上合成Silicalite-1沸石分子筛膜。实验结果表明:在TPABr的合成体系中,晶化温度为403 K,沸石分子筛成核期为24～36 h,晶化温度升高到443 K后,生长需要12～24 h。膜在不同温度下进行单组分气体渗透实验,H₂的渗透率变化不大,H₂/N₂和H₂/n-C₄H₁₀的理想分离系数下降,H₂/SF₆的理想选择性在423 K时具有最小值。膜在室温下H₂的渗透率为12.25×10^-7mol/（m²·s·Pa）,H₂/n-C₄H₁₀的理想分离系数达到46,合成的膜70%对H₂/n-C₄H₁₀理想分离系数达到25以上,膜的重现性较好。（4）制备出连续的Silicalite-1/炭、Silicalite-1/TiO₂及Silicalite-1/Pd复合膜。实验结果表明:①沸石分子筛粒径、含量（wt%）,前驱体PAA含量（wt%）及前驱体膜等对Silicalite-1/炭复合膜的性能影响很大。采用真空提拉法制备的Silicalite-1/炭复合膜厚约2μm,室温下对O₂的透过率达到158×10^-10mol/（m²·s·Pa）,O₂/N₂的理想分离系数相对炭分子筛膜变化不大;②在α-Al₂O₃载体管表面制备Silicalite-1/TiO₂复合膜,考察Silicalite-1沸石分子筛晶粒大小、含量（wt%）,浸渍次数及H₂O/SiO₂等影响因素,得到适宜的合成条件为:分子筛含量约8%,粒径为900～1000 nm,浸渍6～8次,H₂O/SiO₂约120。室温下,膜对H₂的渗透率达到10×10^-7mol/（m²·s·Pa）,n-C₄H₁₀/i-C₄H₁₀,H₂/SF₆的理想分离系数分别为7.8和206.3;③在多孔不锈钢载体上制备了Silicalite-1/Pd复合膜,Pd膜层厚度不到2μm。773 K时,复合膜对H₂的渗透率达到1.2×10^-6mol/（m²·s·Pa）,H₂/N₂理想分离系数达到150以上,且H₂的渗透率随镀膜次数的增加降低较少,故可以通过镀膜次数来控制合成的复合膜的选择性。（5）初步研究Silicalite-1沸石分子筛膜在5%（wt%）的乙醇/水体系中渗透汽化性能,发现料液温度、进料流速、H₂O/SiO₂及载体等因素对膜的渗透蒸发性能有较大影响。研究结果表明:提高进料流速乙醇/水的分离系数增大,通量提高不明显;提高料液温度,渗透通量增大;当H₂O/SiO₂为50～100时,乙醇/水分离系数为33左右,渗透通量达到0.62 kg/（m²·h）;多孔不锈钢支撑的Silicalite-1沸石分子筛膜对乙醇/水体系分离系数达到36.2,渗透通量达到1.25 kg/（m²·h）。（6）将Silicalite-1沸石分子筛膜应用于乙苯脱氢反应中,分别考察吹扫气速、水烃比、反应温度及乙苯进料空速等因素对膜反应器性能的影响,并与固定床反应器进行了对比。实验结果表明:吹扫气速增大,膜反应器中乙苯转化率提高;提高水烃比,乙苯转化率在两种反应器中均降低;提高反应温度,两种反应器中的乙苯转化率均增加;提高进料空速,乙苯的转化率在两种反应器中均降低;膜催化乙苯脱氢反应是通过膜将反应产物中的小分子H₂连续的移出反应区,使反应的速率提高,从而提高乙苯的转化率。固定水烃比为2.0,进料空速为0.5,吹扫气速与进料摩尔比为2,在反应温度为883～913K时,膜反应器中乙苯的转化率比固定床反应器中的转化率提高6～8%,苯乙烯的选择性提高1～3%。在不同操作条件下连续运行300 h左右,膜反应器的稳定性较好。更多还原

【Abstract】 Due to benefits of efficient use of energy and equipment,maneuverability,free phase inversion and excellent permeability etc.,membrane separation is widely investigated in recent years.The pore size（0.55 nm）of silicalite-1 zeolite is similar to the size of many important industrial materials.Moreover,silicalite-1 zeolite has better chemical and physical stability and stronger hydrophobic property.If the silicalite-1 zeolite membranes can be prepared,they will have potential applications in membrane separation,pervaporation and catalytic membrane reactors due to its unique properties.In a word,it is very significant to research the preparation and application of silicalite-1 zeolite and its composite membranes.Herein,the silicalite-1 zeolite particle preparation is firstly investigated using in situ hydrothermal synthesis.Silicalite-1 zeolite particles with different sizes are obtained and the recipe of the membrane preparation is found.Based on the research of conventional hydrothermal synthesis,the method of membrane synthesis is improved.First,A novel embellishing method,vacuum seeding and template-free method are used for preparation silicalite-1 zeolite membranes on tubularα-Al₂O₃ support.And the methods for membrane preparation are optimized,good performance of silicalite-1 zeolite membranes are prepared. Secondly,A two-stage varying-temperature in situ synthesis is developed for silicalite-1 zeolite membrane synthesis.A continues and dense membrane with a high quality is formed. Moreover,the synthesis time is shortened.Thirdly,the preparation of composite membrane is constructed,considering the intrinsic defects of a single membrane.The composite membrane may have both benefits of the two membranes.Integrated and continues silicalite-1/carbon, silicalite-1/TiO₂,silicalite-1/Pd composite membranes are prepared.Lastly,the as-prepared silicalite-1 membranes are applied to pervaporation for ethanol/water mixture and catalytic membrane reactor for the dehydrogenation of ethylbenzene to styrene.Moreover,a good separation performance for ethanol/water mixture and high ethylbenzene conversion in membrane reactor are obtained.The main results achieved are as follows:（1）The influencing factors of TPABr and TPAOH as template,alkalinity content, crystallization time,crystallization temperature and stirring time on the preparation of silicalite-1 zeolite particles were investigated respectively.The results indicated that silicalite-1 zeolite crystals size within the range of 0.1～4μm were prepared.Moreover,the crystallization degree of the as-prepared zeolite is high and the size distribution is narrow. Using TPABr as template,synthesis solution experiences the gel formation and decomposing process.But using TPAOH as template does not experience the process.Lose weight of silicalite-1 zeolite is composed of three processes during calcination process:desorption of water,decomposing of organic ammonium in zeolite pores and decomposing of TPA⁺.（2）Defect-freeα-Al₂O₃-supported silicalite-1 zeolite membranes were successfully prepared by a novel embellishing method,secondary synthesis and template-free method respectively.①Hydrothermal synthesis time before polishing and type of sand paper are two important factors for membrane preparation using the novel embellishing method.The method can effectively improve the quality of as-prepared membrane.At room temperature, the H₂ permeance is 1.2×10^-6mol/（m²·s·Pa）,and the idea selectivities of H₂/n-C₄H₁₀and H₂/SF₆ are 30 and 84 respectively.②The influencing factors of vacuum seeding method were investigated.A homodisperse and continues seed layer was prepared by the method. Herein,the optimized condition is that the size of seed is similar to support pores and pressure is 0.06～0.07 MPa.The gas permeation tests indicate that,at room temperature,the permeance of H2 is 3.25×10^-7mol/（m²·s·Pa）,and idea selectivities of H₂/N₂ and H₂/SF₆ are 4.1 and 133.2 respectively,exhibiting a good separation performance.③The influencing factors of template-free method were investigated.The optimized synthesis condition is that synthesis time is 5～8 h,ratio of silica/water is 30～45 and crystallization one times.At room temperature,the permeance of H₂ of as-prepared membrane is 1.72×10^-7mol/（m²·s·Pa）,the idea selectivities of H₂/N₂ and H₂/SF₆ are 2.76 and 18.5 respectively.（3）Silicalite-1 zeolite membranes were successfully prepared onα-Al₂O₃ and stainless steel supports by the developed two-stage varying-temperature synthesis.The results showed that the zeolite nuclei completely formed at 403 K for 24～36 h,the compact membrane formed by the nuclei regrown at 443 K for 12～24 h and the total synthesis time greatly decreased.Single gas permeation tests at different temperatures indicated that H₂ permeance changed slightly,idea selectivities of H₂/N₂ and H₂/SF₆ decreased,and H₂/SF₆ had a least value.At room temperature,H₂ permeance is 12.25×10^-7mol/（m²·s·Pa）,and the idea selectivity of H₂/n-C₄H₁₀is 46.Moreover,the yield of membranes with perm-selectivity of H₂/n-C₄H₁₀are larger than 25 as a quality criterion reached to 70%of all preparations.The results showed that permeability and reproducibility of the membrane are good.（4）Continues silicalite-1/carbon,silicalite-1/TiO₂,silicalite-1/Pd composite membranes are prepared.①The zeolite size and content（wt%）,PAA content（wt%）and precursor membrane preparation were main influencing factors on permeability of the as-prepared membranes.The compact and continues silicalite-1/carbon composite membrane was prepared by a vacuum slip-casting method and the thickness of the membrane is about 2μm. At room temperature,the permeance of oxygen is 158×10^-10mol/（m²·s·Pa）without decreasing the idea selectivity of O₂/N₂.②The silicalite-1/TiO₂ composite membrane was prepared by pre-seeding silicalite-1/TiO₂ layer onα-Al₂O₃ support.The silicalite-1 zeolite size and content （wt%）,dip-coating times and H₂O/SiO₂ were main influencing factors on the composite membrane preparation.The optimized condition is that zeolite content is 8%（wt%）,zeolite size is 900～1000 nm（similar to support pore size）,dip-coating times is 6～8 and H₂O/SiO₂ ratio is 120.At room temperature,the permeance of H₂ is 10×10^-7mol/（m²·s·Pa）,and the idea selectivities of n-C₄H₁₀/i-C₄H₁₀and H₂/SF₆ are 7.8 and 206.3 respectively.③The slicalite-1/Pd composite membrane was successfully prepared on porous stainless steel support.Moreover,the thickness of Pd membrane was less than 2μm.At 773 K,the permeance of H₂ is 1.2×10^-6mol/（m²·s·Pa）,the idea selectivity of H₂/N₂ is larger than 150. And the permeance of the H₂ decreased slightly with increasing Pd-plated times.So the selectivity of the composite membrane can be controlled by Pd-plated times.⑤Silicalite-1 zeolite membranes were applied in the pervaporation separation of 5% （wt%）ethanol/water mixture.The influencing factors of feed temperature,feed flow rate, H₂O/SiO₂ and support on pervaporation performance of the membrane were investigated.The results showed that the selectivity of ethanol/water increased without decreasing the flux by increasing the feed flow rate.The flux of the membrane increased by increasing feed temperature.The selectivity and flux of ethanol/water were about 33 and 0.62 kg/（m²·h）when the ratio of H₂O/SiO₂ was 50～100.Moreover,the selectivity and flux of ethanol/water for stainless-steel-supported silicalite-1 zeolite membrane were about 36.2 and 1.25 kg/（m²·h）.⑥The dehydrogenation of ethylbenzene to styrene was applied in silicalite-1 zeolite membrane reactor.The influencing factors of sweep gas flow rate,ratio of water/ethylbenzene, reaction temperature and ethylbenzene feed speed（SV）were investigated.The results indicated that the conversion in membrane reactor was increased with increasing sweep gas flow rate,the conversion in both reactors was decreased with increasing the ratio of water/ethylbenzene and ethylbenzene feed speed and the conversion in both reactors was increased with increasing the reaction temperature.The benefit of the membrane reactor is due to instantaneous removal of H₂ from the reaction zone.The water/ethylbenzene ratio of 2, SV of 0.5,about 6～8%higher conversion for the membrane reactor than the fixed-bed reactor above 600℃without decreasing the styrene selectivity was obtained.The stability of membrane reactor is good for about 300 h operations at different conditions,which indicated that it is a valuable work for further investigation.更多还原