Study On The Preparation Of MCM-22 Zeolite With Piperidine Template And Benzene Alkylation

With characteristic of suitable acid centers,suitable pore structures for the diffusion of reactants and target products and strong stability,MCM-22 molecular sieves which consist of two-dimensional sine and twelve-membered ring supercavity is excellent catalyst for benzene alkylation.Ethylbenzene is an important chemical,and it is mainly used for the production of styrene,and then for the production of polystyrene resin,acrylonitrile-butadiene-styrene terpolymer（ABS）and ion exchange resins etc.The templating agent used to prepare MCM-22 in commercial is highly toxic hexamethyleneimine（HMI）,which greatly limits the production and application of MCM-22.Therefore,selecting low toxicity,easy-to-using templating agent to prepare MCM-22 is of great significance for promoting application of MCM-22.In this study,a low-toxic piperidine（PI）was used as a template to synthesize MCM-22with good crystal by optimizing relevant factors effecting the preparation.The PI-MCM-22prepared with PI as template is applied to benzene alkylation,its catalytic performance is compared with those of the HMI-MCM-22 prepared with HMI as template and commercial IN-MCM-22,and the influence of the MCM-22 properties on its catalytic performance was investigated.In addition,in order to decrease the diffusion resistance of the reactants and products in the molecular sieve pores and improve the catalytic performance of it,a hierarchical MCM-22 was obtained by the post-treatment of the as-prepared MCM-22.The results of the study indicate that when using PI as template in the preparation of MCM-22 molecular sieves,all changes in the order of addition of solution,molar ratio of Na/SiO₂,and the crystallization time could Influence the crystallization process.The ZSM-5,ZSM-35 and mixed crystals of several molecular sieves are generated under inappropriate conditions.The ultrasound treatment promoted the growth of the molecular sieve crystals;MCM-22 molecular sieves can be obtained by using both dynamic and static crystallization methods.Although the dynamic crystallization method could shorten the crystallization time,its stability is poor than that of the static crystallization method.The optimal process conditions for preparing MCM-22 are as follows,static crystallization synthesis,72h,150°C and ultrasonic under 50°C for 30min.Compared to HMI-MCM-22 and IN-MCM-22,PI-MCM-22 exhibited excellent catalytic performance for the alkylation of benzene with ethylene.At the similar ethylene conversion,the selectivity of the target product ethylbenzene over PI-MCM-22 is highest,which attribute to its appropriate acidity and high ratio of mesopore to micropore.The results of the hierarchical MCM-22 preparation by post-treatment showed that the increasing of NaOH concentration and the treatment time could increase the ratio of mesopore to micropore,reduce the crystallinity of the MCM-22 and eroded/broken the grain morphology of it.The 0.2mol/L NaOH and 30min are appropriate conditions to prepare hierarchical MCM-22 for benzene alkylation.A ZSM-11 with micro-mesoporous structure can be prepared by in-situ growth method using ionic liquid LQ as a template.