In-situ Synthesis And Modification Of ZSM-5 Zeolite And Its Catalytic Activity On Methanol To Propylene Process

Propylene is traditionally produced by petroleum cracking. However, due to the rising price of petroleum caused by its scarce resources, the development of propylene industry is highly restricted. Methanol to propylene (MTP) technology refers to a new method that based on coal /natural gas for producing propylene. With the increasing scale and lower cost of methanol production, MTP is the most promising technology that would substitute the traditional oil route for producing propylene. Thus, MTP has been received intensive study in recent years in both academic and industry fields. One of the key points in methanol to propylene technology is the activity and selectivity of catalyst, which makes the synthesis and post-processing of catalyst an important part.ZSM-5 has the highest propylene selectivity compared with other catalysts in methanol to propylene process. Former researches indicated that the catalyst's catalytic performance is closely related to its physical property. Therefore, the catalytic activity of ZSM-5 in MTP reaction can be enhanced by adjusting its morphology, pore structure and acid property by different synthesis and modification methods. The research of this paper examined the physical properties of in-situ synthesis of ZSM-5 in three different systems—ZSM-5 made by metal elements incorporation, ZSM-5 made from matrix and ZSM-5 made from surfactant. Their catalytic activities in methanol to propylene process were also tested. The main research work and conclusions of the paper are as follows:The first part systematicly examined the effects of Cs,Ca,Mg,Fe,Zn,Ti,Ni bringing on the properties of product ZSM-5 and the metallic element modified ZSM-5 with the best MTP performance was obtained. First, Cs, Ca, Mg, Fe, Zn, Ti, and Ni etc. seven different metal elements were used hydrothermal in-situ synthesis of ZSM-5. Secondly, ZSM-5 zeolites made by different metal elements incorporation were tested by MTP reaction for their catalytic performance. The results showed that: Ca-ZSM-5 had the highest propylene selectivity, which may relate to its more B-acid sites and larger average pore size. Finally, the comparison among in-situ modification method, ion exchange modification method and impregnation modification method were made toward Fe-ZSM-5 system. It showed that catalyst treated by in-situ modification method contained minimal amount of metal elements, then followed by ion exchange modification method. Impregnation modification method loaded most content of metal elements.In the second part, the kaolin in-situ synthesis technology was used in MTP reaction for the first time. Multi-functional ZSM-5 zeolite catalyst with high propylene selectivity was obtained. Firstly, changes of matrix in-situ synthesis of ZSM-5 crystal structure with the reaction time were compared under both static and dynamic reaction conditions. It was found that the crystal phase transformation process under dynamic reaction condition was much faster than that under static reaction condition. This might caused by the speeding up of the mass and heat transfer process from dynamic mixing in dynamic reaction condition. And in the crystallization process, ZSM-5 crystal was first formed and then transformed into MOR crystal with analcime as mid-phase. Then, the effect of matrix bringing on the physical properties was further examined, and the difference between metakaolin and spinel in-situ synthesis of ZSM-5 zeolites was investigated for industry application. The results showed that matrix in-situ synthesis of ZSM-5 had small crystal size. Besides, they exhibited a gradient pore distribution and increased medium BrOnsted acid sites. By conducting MTP reaction, both metakaolin co-synthesis ZSM-5 and spinel co-synthesis ZSM-5 exhibited high selectivity for propylene. Metakaolin co-synthesis ZSM-5 showed better catalytic activity toward MTP reaction which might owning to its unique morphology,pore structure and acid properties.The third part of the paper applied low concentration of surfactant (CTAB) to in-situ synthesis of ZSM-5 for the first time, and systematicly investigated the effects of both the properties and MTP reaction performances of ZSM-5 zeolite made by different CTAB amount. Through the characteristic analysis, it was found that after adding surfactant in the synthesis system, the crystallinity of the product zeolites decreased when compared with that of regular ZSM-5. Besides, smaller crystal size and larger specific surface area were also formed. For the acid property, samples with surfactant accounting for 0.5% and 4.2% mass fraction of total investment has more B acid sites. By conducting methanol to propylene reaction, the product zeolite with surfactant account for 4.2% mass fraction of total investment might greatly enhance propylene yield,strengthen product zeolite stability and resist hydrogen transfer reaction efficiently.