【作者】 郭宇；

【导师】 王金渠； 张雄福；

【作者基本信息】 大连理工大学 ， 化学工艺， 2010， 博士

【摘要】 钯复合膜作为一种重要的透氢膜材料,具有优异的透氢性能、良好的化学和热稳定性,已广泛应用到氢气提纯、分离及催化等各种涉氢领域,成为近年来国内外学者们研究的热点。特别是在苯一步羟基化制备苯酚反应中表现出的特殊性能,使得钯膜的研究更具有学术和开发意义。本论文以钯-陶瓷复合膜制备为基础,通过沸石生长技术对载体表面进行修饰,制备出性能优越的钯-沸石复合膜,并应用于苯羟基化合成苯酚反应。借助于SEM、XRD、TEM、EDX、XPS、EPMA、FT-IR和高温气体渗透测试等表征手段对钯复合膜的形貌结构及透氢性能进行了研究。本课题的研究结果对于钯复合膜制备工艺的改进与创新及钯膜反应器稳定性的提高具有十分重要的意义。具体体现在如下几方面：1.利用化学镀法在管式Al2O3载体表面制备了钯膜。考察了不同温度、时间和载体形貌对钯膜沉积的影响。研究结果表明：温度在303～333 K范围内,钯沉积量随着温度的升高而不断增加；温度过低,化学镀反应较慢；温度过高,化学镀反应过快,导致钯颗粒聚集严重；反应温度为318 K时,钯膜形貌和沉积状况最佳。随着时间的延长,在载体表面钯沉积量增加,反应2 h可获得平整连续的钯膜。载体表面形貌对钯膜影响显著,在孔径为3μm的大孔α-Al2O3管式载体表面很难制备出薄而致密钯膜,必须对大孔载体表面修饰后才能获得较为完整的钯复合膜。2.采用silicalite-1 (Sil-1)和钛硅沸石分子筛(TS-1)层对载体表面进行调控修饰后,通过化学镀方法在其表面制备出连续致密的钯-沸石复合膜。研究发现,Sil-1沸石修饰层的形貌对钯膜性能影响显著,沸石层表面过于光滑,会降低钯膜与载体之间结合力,使得钯膜易脱落。在载体表面调节Sil-1沸石层厚度为2μm,获得的Pd-Sil-1复合膜性能最佳,在773K时,Pd-Sil-1复合膜的H2渗透速率和H2／N2理想选择性分别达到1.2×10-6 mol·m-2·s-1·Pa-1和420。同样,利用上述方法制备出完整的Pd-TS-1复合膜,在773K时,其透氢速率和H2／N2理想选择性分别为3.7×10-7 mol·m-2·s-1Pa-1和310。3.利用“共晶种”法制备了高性能的钯-沸石复合膜(CS-Pd-Sil-1和CS-Pd-TS-1复合膜),其中,钯／沸石“共晶种”可以同时为沸石层的形成和钯膜的沉积提供成核中心。研究了钯复合膜的形成过程,发现钯沿着沸石晶间孔隙从底部晶种层逐渐生长至沸石层表面,钯膜与沸石修饰层相互穿插,有助于提高钯膜的稳定性。控制沸石修饰层微结构和厚度是关键,通过优化调控Sil-1沸石生长过程,从而改善钯膜与Sil-1沸石层之间的嵌入式结构,当沸石晶粒不完全交织生长并形成厚度为2μm的多孔微结构可以获得致密稳定的CS-Pd-Sil-1复合膜；在773K时,其H2渗透速率和H2／N2理想选择性分别达到1.78×10-6 mol·m-2·s-1·Pa-1和1280；在623K连续操作200小时并且进行18次H2和N2的交替操作,在473K进行10次H2和N2转换测试,在773K、20～100 kPa之间进行15次压力循环以及在673-773K范围内进行了15次温度循环,CS-Pd-Sil-1复合膜的透氢性能保持稳定。利用“共晶种”法制备出致密稳定的CS-Pd-TS-1复合膜,在773K时,H2渗透速率和H2／N2理想选择性分别达到5.3×10-7mol·m-2·s-1·Pa-1和450,在673-773K范围内进行了15次温度循环后,钯膜仍然保持稳定。4.利用CS-Pd-Sil-1复合膜反应器进行苯羟基化直接合成苯酚,系统地考察了反应温度和H2／O2进料比对反应性能的影响。研究表明：在423～523 K范围内,随着温度的升高,加氢反应进行的趋势增强,当温度为473K,H2／O2进料比为4.7时,苯的转化率最高为5.1%,苯酚选择性为60.8%。分析了水的生成过程,证明了水主要是由钯膜表面氢和氧之间的反应所产生；研究了CS-Pd-Sil-1复合膜反应器在苯羟基化反应中的稳定性,在473K下,CS-Pd-Sil-1复合膜反应器进行46小时羟基化反应,苯转化率和反应前后钯膜透氢性能保持稳定。更多还原

【Abstract】 Palladium membranes have drawn increasing attention in recent years due to their good properties, such as good mechanical stability, thermal stability and only permeable to hydrogen. Therefore, as one kind of membrane reactors, Pd membranes have wide applications in hydrogenation, dehydrogenation, H2 separation and purification and some hydrogen related reactions. Especially, the unique property of Pd membrane was illustrated in the direct hydroxylation of benzene to phenol, which made the research of Pd membrane more significant in academic and industry.In this paper, based on the preparation of Pd-ceramic composite membrane, thin dense Pd-silicalite-1 and Pd-TS-1 composite membranes were successfully prepared using conventional electroless plating on macroporousα-Al2O3 substrate. Moreover, in order to increase the stability of Pd membrane and simply the preseeding process of Pd on support in the conventional electroless plating, a novel "co-seedng"method was developed to prepare thin dense composite membranes of excellent stability on macroporousα-Al2O3 supports, and applied in direct synthesis of phenol from benzene. The morphology and hydrogen permeability of the modified support and Pd composite membrane were characterized by means of SEM, XRD, TEM, EDX, XPS, EPMA, FT-IR and high temperature permeation tests. The results will bring on important significance at the side of improving preparation method and increasing the stability of Pd membrane reactor.The thesis mainly includes several aspects as follows:1. Pd-Al2O3 composite membrane was prepared using electroless plating. Some factors on preparation of Pd membrane such as plating time, temperature and support morphology were studied. It indiated that the deposition amount of Pd increased with increasing temperature during 303-333K. The ideal Pd membrane could be obtained at 318K, higher or lower than that temperature would affect the Pd deposition. The reaction performed slower at lower temperature; the higher temperature accelerated reaction, but the Pd particles would congregate seriously. In addition, the longer time for electroless plating favored the deposition of Pd membrane, the uniform and continous Pd membrane could be obtained by elecroless plated for 2 hours. Moreover, the morphology of support played important role in preparation of Pd membrane, it was difficult obtain dense and thin Pd membrane on macroporous support with pore size of 3μm except for modification of the support. 2. In order to improve the topology of macroporousα-Al2O3 supports, silicalite-1(Sil-1) and TS-1 zeolite were adopted, then, dense Pd-zeolite composite membranes were deposited using convenitional electroless plating. It indicated that the morphology of zeolite layer plays important role in performance of Pd membranes. The Sil-1 zeolite layer with smoother surface was bad for preparing Pd membrane, which led to decrease the adhesion between Pd layer and modified support. The Sil-1 layer with thickness of 2μm obtained by hydrothermal synthesis favored the preparation of dense Pd membrane. The H2 permeance and H2/N2 ideal selectivity for the Pd-Sil-1 composite membrane at 773 K were 1.2×10-6 mol·m-2·s-1·Pa-1 and 420, respectively. In addition, continous Pd-TS-1 composite membrane was obtained using above method. The H2 permeance and H2/N2 ideal selectivity for Pd-TS-1 composite membrane could be up to 3.7×10-7 mol·m-2·s-1·Pa-1 and 310, respectively.3. CS-Pd-silicalite-1(CS-Pd-Sil-1) and CS-Pd-TS-1 composite membranes prepared by "co-seeding" method had good H2 permeability and excellent stability. Herein, the Pd/zeolite"co-seeds" were served as seed roles both for growth of zeolite silicalite-1 layer on the support and for Pd membrane deposition. The deposition process of Pd membrane was studied; it indicated that the Pd growth starts from the zeolite seed layer, filling the inter-zeolite pores before forming a Pd film on the surface of the zeolite layer; the Pd layer anchored in the zeolite layer, which was good for increasing the Pd membrane stability. The micro structure and thickness of zeolite layer were the key roles. Adjusting the growth of Sil-1 zeolite, the ideal CS-Pd-Sil-1 composite membrane could be prepared on the silicalite layer with thickness of 2μm. The H2 permeance and H2/N2 ideal selectivity for the CS-Pd-Sil-1 composite membrane were 1.78 x10-6 mol·m-2·s-1·Pa-1 and 1280 at 773 K, respectively. The CS-Pd-silicalite-1 composite membrane was stable over a period of 200 h under hydrogen permeation and 18 gas-exchanging cycles between H2 and N2 at 623K and over 15 pressure cycles between 100 kPa and 20 kPa at 773K. Moreover,15 temperature cycles between 673K-773K and 10 gas-exchanging cycles between H2 and N2 at 473K didn’t impair the hydrogen permeation flux. In the same way, the CS-Pd-TS-1 composite membrane with good stability was prepared. The H2 permeance and H2/N2 ideal selectivity for the CS-Pd-TS-1 composite membrane were 5.3x10-7 mol·m-2·s-1·Pa-1 and 450 at 773 K, respectively. Moreover, the hydrogen permeability was stable after 15 temperature cycles between 673～773 K.4. Direct hydroxylation of benzene to phenol was performed in the CS-Pd-silicalite-1 composite membrane reactor at temperature from 423 to 523K. The H2/O2 ratio and reaction temperature were investigated. The degree of hydrogenation of benzene was remarkable at higher temperature or higher H2/O2 ratio, which affected phenol yield. Both H2 conversion and water generation rate increased with decreasing H2/O2 ratio.An appropriate H2/O2 ratio of 4.7 was optimized, in which the benzene conversion was 5.06%, correspondingly the phenol selectivity was 60.81%. Moreover, the formation process of water was analyzed based on the relationship between the water generation rate and H2 conversion, it indicated that the water was formed on the surface of Pd membrane mainly from H2 reacted with O2. In addition, the CS-Pd-Sil-1 membrane kept stable for 46 h operation in the reaction at 473K.更多还原