【作者】 蒋海洋；

【导师】 林跃生； 张宝泉；

【作者基本信息】 天津大学 ， 工业催化， 2004， 博士

【摘要】 近年来,分子筛膜越来越受人关注。分子筛膜可用于高温高压等苛刻环境;膜的孔径均一,可提供很高的分离选择性,规则的孔道结构又能保证气体快速扩散。除了可以应用于气体分离外,还能与催化剂一起或单独由分子筛膜本身构成膜反应器,使反应过程与扩散同时进行,从而提高反应的转化率或选择性,也是分子筛膜的一个重要应用方向。MFI型分子筛作为催化剂的甲苯歧化、用甲醇使甲苯烷基化和二甲苯异构化制对二甲苯等反应是分子筛择形催化的重要实例。对位选择性可达90%以上。然而高选择性却以牺牲转化率为代价的(转化率仅为20~30%),大量的原料需要循环使用,造成设备投资的增加和能耗增加。本文以James WeiP[117]P所建立的高对位选择性反应动力学模型为基础,提出了一种新型催化膜反应器的模型,并进行了数学模拟。证实了采用死端模型的改性ZSM-5分子筛催化膜反应器,通过把反应物与产物的分离,降低产物端压力,能在甲苯的转化率接近100%的情况下,对位选择性仍保持在99%以上。并对模型的原料处理能力、转化率以及对位选择性的影响因素进行了讨论,为催化膜反应器的开发提供了理论依据。在分子筛膜制备方面,首先以固体硅胶为硅源制备出70 nm尺度的silicalite-1分子筛,并以其作为晶种,采用无模板剂二次生长法在α-AlB2BOB3B多孔支撑体表面合成出MFI型分子筛膜,发现多层晶粒膜生长机理和两种新的无模板剂二次生长配方,可以制备出不同形貌的单层柱状MFI型分子筛膜。制备多层晶粒膜和单层柱状膜的关键区别是合成液与晶种层接触的充分程度,如果固体胶状物质沉积在晶种层表面,就会阻碍上层晶种层向外生长,而转向各层晶粒共同发展,吸入晶种层的胶体物质充填在晶粒间的空隙,起弥补缺陷的作用。通过MFI型分子筛膜进行了单气体渗透测试,发现即使经过450℃焙烧,采用无模板剂方法制备的分子筛膜仍然无法分离正丁烷/异丁烷。以甲苯歧化为模型反应,用改性HZSM-5分子筛膜组装成催化膜反应器,研究了多种因素对反应过程的影响。实验结果表明,由于膜存在缺陷,大量甲苯原料通过缺陷扩散到渗透端,甲苯转化率只有1%左右。通过MgP2+P离子交换和有机硅的化学液相沉积,无助于弥补缺陷,但可以通过缩小分子筛孔道或覆盖外表面酸中心,将对位选择性提高到90%。对于无缺陷的Mg-HZSM-5分子筛膜甲苯转化率可达31.1%,此时对位选择性为62.5%。更多还原

【Abstract】 Recently, zeolite membranes have attracted considerable interests in bothindustrial and academic sectors. They can be applied to high-temperature andhigh-pressure conditions. Zeolite membranes offer high permeance and excellentseparation properties because of the molecular sieving pore size, uniform pore sizedistribution, and excellent adsorption properties of zeolites. The zeolite membranescan also be used in membrane reactors by taking advantages of both separation andcatalytic properties. On the other hand, the disproportionation of converting toluene top-xylene and benzene is one of the most important processes of shape-selective MFItype zeolite. Although the p-selectivity of the reaction can be more than 90%, thehigh-selectivity is at cost of low conversion (only 20-30%), a great deal of reactantshave to be recycled in the reactor.In this paper, the modeling analysis of toluene disproportionation to p-xylene inan MFI type zeolite membrane reactor was reported. The model calculation revealedthat high p-selectivity (>99%) could be achieved for the situation where touluene wascompletely converted completely by using reactant and product regions. Such analysisprovided guidelines for experimental efforts in development of the MFI type zeolitefor effective formation of p-xylene.In respect of the zeolite membrane preparation, silica gel was selected as thesilica source to synthesize the 70 nm-sized silicalite-1 zeolite seeds. MFI type zeolitemembranes were synthesized by the template-free secondary growth method. Wefound the growth mechanism of multilayer zeolite membranes and two synthesisrecipes by which could grow different morphological single-layer zeolite membranescould be grown. The key of the synthesis of multilayer zeolite membranes was thecontact condition of synthesis sol with the seed layer, if the seeds layers were coveredby the silica gel in the synthesis solution, the upper seeds would not be able to growoutwards to form a single-layer membrane, and the silica gel that was adsorbed intothe seed layers would infill the boundaries of the crystal grains, and repair the gaps.Single gas permeation was adopted to test the MFI type membrane, the results showedthat the membrane made by the template-free secondary growth method could notdistinguish between n-butane and i-butane even after the calcination at 450℃.The catalytic membrane reactor equipped with the modified ZSM-5 zeolitemembrane was evaluated by the disproportionation of toluene. The results showedthat if there were gaps in the membrane, toluene would mainly diffuse to the permeateside through the gaps, and the toluene conversion was reduced to about 1%. Therewas no use for the ion exchange of MgP2+P and for the chemical liquid deposition of Sito plug up the gaps, but the modification method could reduce the pore opening of thezeolite, leading to increasing the p-xylene selectivity up to 90%. The tolueneconversion with no gap Mg-HZSM-5 zeolite membrane made in this paper could beup to 31.1%, where the p-selectivity was 62.5%.更多还原