金属改性SAPO-34分子筛对MTO反应性能的影响研究

发布时间：2018-04-15 11:02

本文选题：MTO + SAPO-34　；参考：《中国矿业大学》2017年硕士论文

【摘要】：近几年来,随着石油资源的持续短缺以及可持续发展战略的要求,非石油资源合成低碳烯烃的技术路线迅速发展;使用以煤或天然气合成的甲醇为原料,生产低碳烯烃的化工工艺技术(简称MTO)受到人们的广泛关注。而SAPO-34分子筛在MTO反应中展现出了优异的催化性能,这主要是由于其适宜的酸性、较小的孔道以及高温下的水热稳定性。本文使用水热晶化法以三乙胺为模板剂合成不同硅铝比的SAPO-34分子筛,使用XRD,SEM,FT-IR,BET,TPD等进行表征,并在固定床反应器上测试所合成的SAPO-34分子筛的MTO反应性能。考察了在SAPO-34分子筛的MTO反应中,添加少量的苯、甲苯、环己烷、环己烯、环戊烷等对催化剂寿命及产品选择性的影响;并使用不同浓度的硝酸铝水溶液或硝酸铝乙醇溶液对SAPO-34分子筛进行浸渍法改性,探索铝改性对MTO反应性能的影响以及使用不同溶剂改性时对SAPO-34分子筛的影响。在原料甲醇中添加5%的苯、甲苯、环己烷、环己烯或环戊烷会影响SAPO-34分子筛的MTO反应性能,导致催化剂寿命缩短。其中,环己烷对催化剂寿命的影响程度最大,甲苯的影响程度最小,苯、环己烯和环戊烷则居中。烃类的添加对不同硅铝比的SAPO-34分子筛寿命的影响也不同,硅铝比越高,催化剂寿命变化越大;这主要是因为C5+和C6+作为碳池物种对甲醇的转化起着重要的作用,而烃类的加入会加速碳池的形成,并容易形成积碳,导致催化剂的失活,而酸含量越高形成积碳的速率越快。使用硝酸铝水溶液改性后,SAPO-34分子筛的酸强度没有发生变化,酸浓度变化较大;其中弱酸的变化较小,中强酸(B酸)随着硝酸铝浓度的升高而明显降低。改性后的分子筛B酸含量降低,但催化剂寿命却随之缩短;主要是因为改性后的分子筛虽然B酸含量减少,但是铝的引入导致L酸含量的增加以及孔道的减小,从而导致催化剂寿命的缩短。而使用硝酸铝乙醇溶液改性时,催化剂寿命的变化则较小,主要是因为其酸量的变化较小。
[Abstract]:In recent years, with the continuous shortage of petroleum resources and the requirement of sustainable development strategy, the technical route of synthesizing low carbon olefins from non-petroleum resources has developed rapidly; methanol synthesized from coal or natural gas is used as raw material.The chemical technology of producing low-carbon olefin (MTO) has been paid more and more attention.However, SAPO-34 molecular sieve showed excellent catalytic performance in MTO reaction, which was mainly due to its suitable acidity, small pore channels and hydrothermal stability at high temperature.In this paper, SAPO-34 molecular sieves with different Si / Al ratios were synthesized by hydrothermal crystallization with triethylamine as the template. The MTO reaction properties of the synthesized SAPO-34 zeolites were tested in a fixed bed reactor.The effects of a small amount of benzene, toluene, cyclohexane, cyclohexene and cyclopentane on the catalyst life and product selectivity in the MTO reaction of SAPO-34 molecular sieve were investigated.The SAPO-34 molecular sieve was modified with different concentration of aluminum nitrate solution or ethanol solution. The effect of aluminum modification on MTO reaction performance and the effect of different solvent modification on SAPO-34 molecular sieve were explored.The addition of 5% benzene, toluene, cyclohexane, cyclohexene or cyclopentane into methanol will affect the MTO reaction performance of SAPO-34 molecular sieve and shorten the catalyst life.Among them, the influence of cyclohexane on catalyst life is the largest, toluene is the least, benzene, cyclohexene and cyclopentane are in the middle.The effect of hydrocarbon addition on the lifetime of SAPO-34 zeolites with different ratio of Si to Al is also different. The higher the ratio of Si to Al, the greater the change of catalyst life, which is mainly due to the important role of C5 and C6 as carbon pool species in methanol conversion.The addition of hydrocarbons accelerates the formation of carbon ponds and easily leads to the deactivation of catalysts, and the higher the acid content is, the faster the rate of carbon deposition is.The acid strength of SAPO-34 molecular sieve modified with aluminum nitrate aqueous solution did not change, and the acid concentration of SAPO-34 molecular sieve changed greatly, among which the change of weak acid was small, and that of moderate and strong acid B acid decreased obviously with the increase of aluminum nitrate concentration.The modified molecular sieve has lower B acid content, but shorter catalyst life, which is mainly due to the increase of L acid content and the decrease of pore channel due to the decrease of B acid content in the modified molecular sieve, but the introduction of aluminum leads to the increase of L acid content and the decrease of pore channel.As a result, the catalyst life is shortened.However, the change of catalyst life is smaller when modified with aluminum nitrate ethanol solution, mainly because of the small change of acid content.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TQ221.211

【参考文献】