【作者】 刘星生；

【导师】 陈标华； 李英霞；

【作者基本信息】 北京化工大学 ， 化学工程与技术， 2009， 博士

【摘要】 沸石颗粒催化剂在石油化学工业中具有非常广泛的应用,而传统的制备方法中加入粘结剂成型会造成催化剂性能下降和利用率低的问题,因此亟需新的制备方法。本论文以MCM-22沸石为对象,对汽相法原位制备无粘结剂沸石颗粒催化剂进行研究,开发沸石催化剂制备的新途径。首先对无粘结剂MCM-22沸石颗粒催化剂的硅铝胶基质特性进行了系统的研究。研究了在不同的原料、制备方法、pH值和聚乙二醇20000含量的情况下对硅铝胶基质及晶化的影响。实验发现,在不同的硅铝胶基质的原料组合中,选择硅溶胶为硅源,NaAlO₂为铝源和硝酸做酸度调节剂更有利于无粘结剂MCM-22沸石颗粒催化剂的制备;采用干硅铝胶法、湿硅铝胶法和干粉直接混合法制备的三种硅铝胶基质都能制备无粘结剂MCM-22沸石颗粒催化剂;硅铝胶基质在pH值10.0附近硅源和铝源最有利于相互结合成[Si-O-Al^-],使硅铝胶基质有利于晶化成无粘结剂MCM-22沸石颗粒催化剂;通过对硅铝胶基质中添加扩孔剂聚乙二醇20000用量的控制,能有效的调控无粘结剂MCM-22沸石颗粒催化剂孔径分布。考察了汽相法制备无粘结剂MCM-22沸石颗粒催化剂的工艺条件。实验得到以硅溶胶和偏铝酸钠为原料汽相法制备无粘结剂MCM-22沸石颗粒催化剂条件为原料配比SiO₂:（0.02-0.033）Al₂O₃:（0.09-0.12）Na⁺:1.0HMI:（5-30）H₂O,晶化温度150℃,晶化时间168 h。水热合成沸石过程中模板剂的回收利用及碱性废液的处理一直是个难题。对釜底残留液进行检测和分析发现,在汽相法制备无粘结剂MCM-22沸石颗粒催化剂过程中,有一部分模板剂并没有起到结构导向作用,仍保留在釜底残留液中,且化学特性没有变化。对釜底残留液中补充适量水和模板剂后,仍能成功制备无粘结剂MCM-22沸石颗粒催化剂。通过釜底残留液中模板剂和水的重复利用,有效的改善了汽相法制备无粘结剂MCM-22沸石颗粒催化剂中模板剂用量大的不足,减少了废液的排放,为沸石催化剂清洁制备提供了参考。在对无粘结剂MCM-22沸石颗粒催化剂的晶化过程进行表征的基础上,系统研究了无粘结剂MCM-22沸石颗粒催化剂多级孔道体系的形成与晶化机理。实验发现,在晶化前48 h,颗粒孔道仍然由无定形硅铝胶胶粒相互堆积组成,在晶化72 h到168 h之间,颗粒孔道是由MCM-22沸石晶片组成;通过汽相法168 h的晶化,整个由硅铝胶组成的低比表面积,低孔体积和孔道结构单一的颗粒转化成高比表面积,高孔体积和具有多级孔道结构的无粘结剂MCM-22沸石颗粒催化剂;汽相法制备无粘结剂MCM-22沸石颗粒催化剂晶化机理为液相转变机理。对传统方法和汽相法原位制备的MCM-22沸石颗粒催化剂进行了比较和催化性能的研究。汽相法原位制备的MCM-22沸石颗粒催化剂不但不需要加入粘结剂,而且比表面积和平均孔径达分别达到486.82 m²/g和115.85 nm,酸量为1.01×10^-3 mol/g。其比表面积,平均孔径和总酸量都比用传统方法制备的MCM-22沸石颗粒催化剂大;无粘结剂MCM-22沸石颗粒催化剂在苯和丙烯烷基化反应中,随着温度和苯烯比的提高,产物中异丙苯的含量增加,而二异丙苯和三异丙苯的含量下降,改变丙烯空速和反应时间对产物中异丙苯、正丙苯、二异丙苯和三异丙苯的分布没有明显影响;在苯和丙烯烷基化反应中,汽相法原位制备的无粘结剂MCM-22沸石颗粒催化剂对异丙苯选择性要比传统方法制备的MCM-22沸石颗粒催化剂高出约5%,而对二异丙苯的选择性要减少30%,对三异丙苯的选择性更是减少了约60%。更多还原

【Abstract】 Zeolite catalysts are widely applied in petrochemical industries. Synthetic zeolites and related molecular sieves are generally produced as powders of relatively loosely bonded zeolite. The binder is indispensable in order to produce particles catalyst of optimal dimension and form and having a high mechanical resistance. In such particles catalyst, the fact that the zeolite is diluted with a material that in most instances is inert in the process reduces the effective surface area of the product. Moreover, negative effects, such as blocking of the micropores and active sites by the binder, are pronounced when zeolite powders are prepared by adding an inorganic binder. Therefore, some novel alternative technologies are desired. Self-bonded MCM-22 particles catalyst were in-situ prepared using vapor-phase transport method in this dissertation. And, properties of self-bonded zeolite MCM-22 particles catalyst were investigated by alkylation of benzene and propylene.The characters of the aluminosilicate gel were firstly studied. It was found that self-bonded zeolite MCM-22 particles catalyst could be obtained by dry gel, hydrated gel, and dry powder method when the aluminosilicate gels were prepared using colloidal silica as silica sources, sodium aluminate as aluminum sources. Colloidal silica and sodium aluminate could be dissolved more easily and facilitate preparation self-bonded zeolite MCM-22 particles catalyst when the pH value of the aluminosilicate gel was 10.0. By adding polyethylene glycol to the aluminosilicate gel, the pore size distributions of zeolite particles catalyst could be adjusted.Based on the experimental results of in-situ preparation self-bonded zeolite MCM-22 particles catalyst, the suitable conditions are as follows: the ratio of material is SiO₂:（0.02-0.033）Al₂O₃:（0.09-0.12）Na⁺:1.0HMI: （5-30）H₂O, crystallization temperature 150℃and crystallization periods 168 h. The surplus liquid, chemical properties of which have not change after preparation self-bonded zeolite MCM-22 particles catalyst by the vapor-phase transport method, still contained only hexamethyleneimine and H₂O. Re-adding of hexamethyleneimine and deionized water, the surplus liquid could be reused. It could effectively improve the vapor-phase transport method’s disadvantage of a large quantity of waste water and made the vapor-phase transport method become a cleaner process.The as-synthesized products obtained at different crystallization periods were carefully characterized and the crystallization process of self-bonded zeolite MCM-22 particles catalyst was discussed. It was found that the as-synthesized products were amorphous at 48 h and the amorphous phase disappeared at 72 h. The zeolite particles catalyst, prepared by aluminosilicate gel, had been transformed into hierarchical self-bonded zeolite MCM-22 particles catalyst after 168 h of crystallization. The crystallization proceeded via solution phase nucleation mechanism.Compared with the conventional method, the zeolite MCM-22 particles catalyst prepared by the new method, for which the total acid sites, the specific surface area and the average pore diameter reached 1.01×10^-3 mol/g, 486.82 m²/g and 115.85 nm respectively avoided binder accession. The distributions of products were discussed at different reaction conditions in in alkylation of benzene and propylene reaction. In the experiments, self-bonded zeolite MCM-22 particles catalyst possessed excellent reaction stability. The selectivity of cumene increased with increasing the reaction temperature and benzene/propylene ratio, the change of space velocity and reaction time had little influence on the selectivity of products. Self-bonded zeolite MCM-22 particles catalyst were more conducive to the purpose product in alkylation of benzene and propylene reaction. The selectivity of cumene could be improved about 5%. The selectivity of diisopropylbenzene and triisopropylbenzene Gould be reduced about 30% and 60%, respectively.更多还原