【作者】 邓慧；

【导师】 张雄福；

【作者基本信息】 大连理工大学 ， 化学工艺， 2011， 硕士

【摘要】 由于钯复合膜具备独特的透氢能力,在氢气分离纯化及催化领域得到越来越多的关注和应用,尤其在苯一步羟基化制备苯酚中表现出良好的催化效果。载体对钯膜制备及其性能有重要影响,且在载体外表面制备钯复合膜易产生污染和刮蹭等问题,对钯复合膜的气体渗透及催化性能的影响很大。本论文分别采用大孔陶瓷管和中空纤维陶瓷管作为载体制备钯复合膜。使用改进化学镀方法优化“共晶种”法所制备钯复合膜结构与气体渗透性能,在中空纤维陶瓷管内表面使用传统制备方法制备钯基复合膜,利用SEM、TEM和气体渗透测试等分析手段表征所制备钯复合膜的形貌结构及气体分离能力。构建具有类似“微通道”特征结构的钯膜反应器,优化苯羟基化反应条件,并对苯制苯酚反应机理进行了一定的研究。1.使用“共晶种”法在孔径2μm的大孔陶瓷管外表面制备了钯-纯硅复合膜。考察提拉晶种时间,水热晶化温度对沸石修饰层的影响：在提拉时间小于20s,423K晶化温度的合成条件下获得纯硅沸石层形貌最佳。通过旋转法和负压法对传统化学镀方法进行改进,获得钯复合膜常温下氮气渗透通量有所下降,旋转和外负压法消除反应生成气泡对膜致密性影响。内负压法增强了钯膜层与沸石层之间的穿插交织,促进了“钯腿”的形成。以上方法制备所得钯膜在高温下气体分离性能相对较差。因此,在大孔陶瓷管外表面不易制备出高性能的钯-纯硅复合膜。2.使用传统化学镀方式,优化制备条件成功在中空纤维陶瓷管内表面制备出厚约2μm的钯基复合膜并具备良好的高温气体渗透、分离能力和稳定性。在773K、0.1MPa下,H2的渗透通量为0.16mol·m-2·s-1, H2/N2理想选择性为493。在473K下经过10次N2/H2转化循环和773K下膜两侧压差在20kPa/150kPa连续交替变化20次后气体渗透通量保持稳定,该钯基复合膜具有良好的抗氢脆和抗压力波动能力。四次高温循环后该钯基复合膜的H2/N2理想选择性从493降至418,热稳定性略有下降。3.利用在中空纤维陶瓷管内表面所制备钯基复合膜,构建具有类似“微通道”特征的钯膜反应器,进行了苯羟基化反应,显示了良好催化活性。在473K下,H2/O2比为3.5时,反应效果最佳：苯转化率和苯酚产率达到最高,分别为16.95%和14.51%,苯酚选择性为85.58%。苯制苯酚反应累计运行9天后,钯基复合膜未出现明显缺陷,氮气渗透通量从8.14×10-4mol·m-2·s-1略微上升至8.60×10-4mol·m-2·s-1,该钯膜具有良好的反应稳定性。更多还原

【Abstract】 Palladium composite membranes have attained more and more application in hydrogen separation、purification and catalytic hydrogen-related reactions due to their unique selectivity of H2, especially in hydroxylation of benzene to phenol. Properties of supports greatly affect preparation and qualities of Pd composite membranes. Palladium composite membranes deposited on outer face of tubular substrates are prone to get polluted and scraped, which easily reduce their gas permeable and catalytic capabilities.In this paper, porous ceramic tubular substrates with large pore size and ceramic hollow fibers were chosen as supports to deposit Pd composite membranes. Two modified electroless plating methods were used to optimize the structure and gas permeability of Pd-Sil-1 composite membranes prepared by "co-seeding" method. Pd-based membranes were deposited on inner face of ceramic hollow fibers by conventional electroless plating. The morphology, structure, gas permeability and selectivity of as-synthesized Pd composite membranes were characterized by means of SEM、TEM and gas permeation tests. A novel Pd membrane reactor with "micro-channel" characteristic was designed and applied in one-step hydroxylation of benzene to phenol. The reaction conditions were optimized and the reaction mechanism was investigated. The main contents and results are as follows:1. Pd-Sil-1 composite membranes were prepared on macroporous ceramic supports with average pore size of 2μm by "co-seeding" method. Different dip-coating time, crystallization temperature were investigated to optimize the growth of Sil-1 membranes. The results showed that the best Sil-1 membranes for subsequent deposition of Pd membranes were achieved under the dip-coating time of less than 20s and the crystallization temperature of 423K. Rotating electroless plating and vacuum-assisted electroless plating were used to improve the performance Pd composite membranes. N2 flux at room temperature of Pd-Sil-1 composite membranes prepared by modified methods were improved. Rotation of supports and vacuum outside the supports could eliminate bubbles generated by redox reaction. Vacuum inside the supports could enhance the adhesion between Sil-1 layer and Pd layer, and encourage the generation of "Pd-legs". All Pd composite membranes prepared by methods mentioned above had poor gas selectivity at high temperature wich indicated that it was hard to prepare good Pd-Sil-1 membranes on macroporous ceramic supports. 2. Palladium-based membranes with a thickness of 2μm were deposited successfully on the inner face of ceramic hollow fibers by conventional electroless plating with 3 times of sensitization/activation at 318K, which had good gas permeability and stability. The hydrogen flux was 0.16 mol·m-2·s-1 at 773K, 0.1MPa and H2/N2 ideal selectivity was 493.10 gas-exchanging cycles between N2 and H2 at 473K and 20 pressure-exchanging cycles between 150kPa and 50kPa at 773K didn’t impair its gas permeation flux. After four temperature changing cycles, the H2/N2 ideal selectivity decreased from 493 to 418, which indicated that the thermal stability of the Pd membrane dropped slightly.3. A palladium membrane reactor with "micro-channel" characteristic was constructed and used in direct hydroxylation of benzene to phenol, which was assembled with the palladium membrane deposited on inner face of ceramic hollow fiber. The highest benzene conversion and phenol yield were obtained when H2/O2 feed ratio was 3.5, which were 16.95% and 14.51%, respectively. After 9 days of reactions, the N2 flux of palladium-based membrane slightly increased from 8.14×10-4mol·m-2·s-1 to 8.60×10-4mol·m-2·s-1, and no defect was observed from SEM images, which meant the membrane had good stability in the hydroxylation of benzene to phenol.更多还原