【作者】 陶玲；

【导师】 尹双凤；

【作者基本信息】 湖南大学 ， 化学工程与技术， 2010， 硕士

【摘要】 随着石油资源日趋枯竭和原油价格居高不下,储量相对丰富的天然气的综合利用越来越受到关注。甲烷经溴甲烷制备高附加值的芳烃是高效利用天然气的有效方式,为芳烃开辟了新的合成路线,对缓解芳烃原料的缺乏具有现实意义。本论文旨在研究溴甲烷制备芳烃的高效催化剂,试图揭示催化剂的构效关系、反应机理和失活机理。本论文首先研究了商业HZSM-5分子筛负载PbO催化剂上的溴甲烷芳构化反应情况。考察了载体、改性组分、焙烧条件、反应条件等因素对催化剂性能的影响。结果表明,HZSM-5分子筛载体优于SiO2、A12O3、ZrO2和HSAPO-34; PbO表现出优于其他金属氧化物的芳构化性能；最佳的PbO负载量和HZSM-5分子筛硅铝比分别为5wt.%和70；450℃焙烧8 h的5wt.%-PbO/HZSM-5催化剂性能最佳；360℃左右的反应温度和较低的溴甲烷空速有利于提高芳烃的选择性。XRD、SEM等表征结果表明,HZSM-5的酸性质对溴甲烷芳构化反应尤其重要；PbO高度分散于HZSM-5分子筛表面,显著减少了催化剂表面的中强酸密度,稍微增加了弱酸和强酸密度,从而促进了溴甲烷的芳构化,芳烃收率达31.6%；反应物在催化剂表面的积碳是导致催化剂失活的主要原因。为了寻求更加高效的HZSM-5催化剂,以廉价的正丁胺为模板剂,采用水热晶化法成功合成了小晶粒HZSM-5分子筛,并在固定床反应装置上评价了其对溴甲烷转化为芳烃反应的催化性能。系统考察了投料硅铝比、母液碱度、氯化钠添加量、晶种、晶化时间等因素对合成产物的收率、物化性质和催化性能的影响,并采用XRD、SEM、NH3-TPD等手段对部分合成的分子筛进行了表征,还关联了催化剂的构效关系。结果表明,当投料中SiO2/Al2O3为70,正丁胺(BTA)/SiO2为0.2847, Na2O/SiO2为0.1237, H2O/SiO2为37.4,NaCl/Al2O3为60,添加自制晶种为5wt.%/SiO2,晶化条件为100℃/24h-170℃/24h时,合成的HZSM-5分子筛结晶完好,晶粒尺寸为0.3μm-0.7/μm,对溴甲烷制备芳烃反应具有更好的催化性能,芳烃收率达44.2%; HZSM-5分子筛的结晶度越高或者晶粒较小,有利于改善其催化性能；而且分子筛表面酸性适中有利于溴甲烷高选择性地转化为芳烃。更多还原

【Abstract】 In view of increasing shortage of petroleum resource and high price of crude oil, the utilization of the relatively abundant natural gas, composed mainly of CH4, has attracted significant attention. The catalytic conversion of natural gas into aromatic hydrocarbons via bromomethane as intermediate is a desirable way to develop effectively natural gas industry and enhance its added-value, which opens up a novel and feasible synthetic route for aromatic hydrocarbon and provides new raw materials for aromatics. This paper try to develope highly efficient catalysts for the conversion of methyl bromide into aromatics, clarify the structure-catalytic efficiency relationship of the catalysts and make a preliminary study on the reaction mechanism and catalysts deactivation mechanism.The catalytic conversion of CH3Br to aromatics was firstly investigated over PbO-modified commercial HZSM-5 catalyst. The effects of supports, modifying components, calcination conditions and reaction conditions on catalytic performance were studied. It was found that HZSM-5 is better than SiO2, A12O3, ZrO2 or HSAPO-34 as support. PbO is superior to the other metal oxides selected to modify HZSM-5, and the most suitable PbO loading and SiO2/Al2O3 ratio are 5wt.% and 70, respectively. The 5wt.%-PbO/HZSM-5 calcined at 450℃for 8 h performs the best. Also, The characterization results indicate that (i) the PbO species is highly dispersed on the HZSM-5 support, which leads to a significant decrease in the density of the surface moderate intensity acidity and a slight increase in the density of the strong and weak intensity acidity of the catalyst, (ii) the role of PbO is to promote hydrocarbon aromatization, and (iii) the acid sites of HZSM-5 are indispensable for CH3Br conversion into aromatics. (iiii) the deactivation of catalyst is due to pore blocking by carbonaceous deposits on the surface of catalysts.In order to obtain more efficient catalyst, H-ZMS-5 zeolite was prepared by hydrothermal crystallization method, using n-butylamine (BTA) as template. The as-prepared materials were evaluated for the conversion of CH3Br into aromatics in the fixed-bed reactor. The effects of batch SiO2/Al2O3 ratio, alkalinity, NaCl/Al2O3 ratio, seed crystals and crystallization time on the yield, physico-chemical properties and catalytic performance of ZSM-5 zeolites were systematically studied. The structure-catalytic efficiency relationships of the catalysts were also clarified by the characterization techniques of XRD、SEM and NH3-TPD. Using the optimum sol (SiO2/Al2O3=70, BTA/SiO2= 0.2847, Na2O/SiO2= 0.1237, H2O/SiO2= 37.4, NaCl/Al2O3= 60, and Seed crystals/SiO2= 5wt.%), and the preferable crystallization conditions of 100℃/24h-170℃/24h, HZSM-5 zeolites with high crystallinity and a small size of 0.3μm-0.7μm were obtained and found to exhibit better activity, selectivity and stability towards the CH3Br conversion into aromatics, the aromatic yield reach up to 44.2%. It can be deduced that higher crystallinity or smaller crystal size will favor the improvement of the catalytic performance of HZSM-5 zeolites. Moreover, efficient conversion of methyl bromide into aromatics can be obtained only when the surface acidity of the HZSM-5 zeolite is moderate.更多还原