【作者】 魏入朝；

【导师】 李春义；

【作者基本信息】 中国石油大学 ， 化学工程与技术， 2011， 硕士

【摘要】 低碳烯烃(乙烯、丙烯和丁烯)是重要的石油化工基础原料。目前,其主要来源于以石油为原料的蒸汽裂解和催化裂化工艺。随着石油资源的日趋减少和石油价格的不断攀升,开发非石油基的低碳烯烃生产技术已是大势所趋。甲醇转化制低碳烯烃(MTO)技术和甲醇转化制丙烯(MTP)技术是我国石油化工行业的战略选择,具有巨大的发展潜力。本文以粗孔微球硅胶和硅溶胶作为双硅源,成功合成出了ZSM-5分子筛。随着硅源中硅溶胶比例的增加,分子筛的硅铝比逐渐升高,说明在合成ZSM-5分子筛时,硅溶胶作为硅源的利用率更高。实验发现:不同添加剂对ZSM-5分子筛合成的影响差别很大。NaF使ZSM-5分子筛的晶体形貌发生明显变化,生成了较多的50nm左右厚度薄片的聚集体。KCl和NH4F对ZSM-5分子筛的合成产生强烈的抑制作用。少量NaCl可以减小ZSM-5晶粒尺寸,过量则会增大其尺寸。N-甲基吡咯烷酮和甘油可以促进ZSM-5形成大晶体,其中加入甘油作为添加剂,可以合成出55μm大小的晶体。微米、纳米ZSM-5的MTO反应性能结果表明:常规钠型ZSM-5分子筛基本没有强酸性位,催化甲醇转化为低碳烯烃的活性非常低;低硅铝比的微米H-ZSM-5分子筛和纳米H-ZSM-5分子筛均具有高的MTO反应活性,但低碳烯烃选择性较低;氟硅酸铵改性可以大幅提高纳米HZSM-5分子筛的硅铝比,增大其外比表面积,同时使低碳烯烃选择性得到显著提高。此外,本文合成的一种大晶粒、低钠含量的钠型ZSM-5分子筛,具有较多的强酸性位,不需经过铵交换即可具有很高的MTO反应活性。随分子筛硅铝比的升高,分子筛的酸性下降,低碳烯烃选择性升高。经过铵交换以后,分子筛的钠含量明显下降,酸性有所增强,乙烯选择性升高,丙烯和丁烯选择性下降。磷改性和正硅酸乙酯沉积改性均可以提高ZSM-5分子筛的低碳烯烃选择性,其中磷改性Na-ZSM-5分子筛的丙烯选择性可以升高到44.2%。总之,强酸性位是MTO反应的活性中心,适宜强酸量和大外表面积的ZSM-5分子筛有利于MTO反应。更多还原

【Abstract】 Light olefins(ethylene、propylene and butylene)are very important basic feedstocks of petrochemical industry. Olefins are traditionally produced from petroleum feedstock by steam and catalytic cracking processes. With the decrease of oil resources and the rise in oil prices, it is a trend to develop non-petroleum based technologies to produce olefins. Methanol to olefins (MTO) and methanol to propylene (MTP) processes are the strategy choices of Chinese petrochemical industry and have great potential in development and application.ZSM-5 zeolite was synthesized successfully using silica gel microspheres and silicon sol as double silicon source in this paper. As the proportion of silicon sol in the silicon source increased, the Si/Al ratio of obtained ZSM-5 zeolite increased. Results indicated that the utilization ratio of silicon sol was higher than silica gel microspheres in the synthesis of ZSM-5 zeolite.It was found that effects vary greatly according to different additives on the synthesis of ZSM-5 zeolite. Crystal morphologies were strongly influenced by the addition of NaF and many aggregates made up of sheets with the thickness of 50nm were produced. KCl and NH4F restrained the formation of ZSM-5 zeolite. A small amount of NaCl could decrease the crystal size of ZSM-5 zeolite, while the size increased when excessive NaCl was added. N-Methyl pyrrolidone and glycerol were beneficial to promote the crystal size of ZSM-5 zeolite and ZSM-5 zeolite with crystal size of 55μm was obtained when glycerol was used as additive.Catalytic performances of commercial ZSM-5 zeolite with micro size and nano size for the MTO reaction indicated that there were few strong acid sites for conventional Na-ZSM-5 and its reactivity for MTO reaction was very low. Microsize and nanosized H-ZSM-5 both showed high activity toward MTO reaction, while their selectivities to olefins were very low. Si/Al ratios of nanosized H-ZSM-5 could be enhanced greatly and the external surface areas were also increased by ammonium hexafluorosilicate modification, so the selectivity toward olefins was also increased greatly.Moreover, one type of Na-ZSM-5 with large partical size and low Na content was synthesized in this paper, it possessed lots of strong acid sites. This new type of Na-ZSM-5 exhibited high MTO activity without ammonium exchange. As the Si/Al ratio of Na-ZSM-5 increased, the acidity decreased and the selectivity to olefins increased. After ammonium exchange, the Na content decreased notably and the acidity was strengthened, the ethylene selectivity increased and the selectivity to propylene and butylene both decreased.Selectivity to olefins was increased by phosphorus modification and ethyl orthosilicate deposition modification, the selectivity to propylene was increased to 44.2% by using phosphorus modified Na-ZSM-5 as catalyst.In conclusions: strong acid sites are the active centers to catalyse MTO reaction, ZSM-5 zeolite with the proper amount of strong acid sites and large external specific surface area is beneficial for the MTO reaction.更多还原