Catalytic Performance Of MCM-22 'Family' Zeolites On Benzene Alkylation With Propylene In Liquid Phase

Cumene is an important intermediate in the petrochemical industry for the production of phenol and acetone, which is manufactured exclusively by the alkylation of benzene with propylene. The growth rate of cumene is closely related to that of phenol and is expected to be approximately 5.0% per year worldwide over the next ten years. Process technology for cumene has been moving away from conventional aluminium chloride and phosphoric acid catalyzed Friedel-Crafts alkylation of benzene, toward zeolite-based processes. Additional research will undoubtedly be directed towards identifying improved alkylation catalysts. Alkylation catalysts that produce even lower byproduct concentration at low benzene to propylene levels are likely to be the focus of future research and development efforts. Currently, interests in studying and developing novel efficient zeolite catalysts, which can be operated at relatively low benzene-to-propylene ratios to decrease the operate cost and relatively low temperature to decrease byproduct concentration, are continuously growing.MCM-22"family"zeolites are consists of a series layered microporous materials with a MWW topology, including MCM-22, MCM-49, MCM-56, MCM-36, ITQ-1 and ITQ-2. MCM-22 zeolite shows excellent catalytic performance in benzene alkylation with propylene in liquid phase. However, further work is still required in order to improve the catalytic performance of the catalyst, and to study the influence of catalyst structure, reaction condition, acid properties etc on the catalytic property, and to clarify the nature of active sites for understanding the reaction mechanism. Particularly, a systemic study on the role of MCM-22's external surface acid sites in benzene alkylation with propylene should be carried out. Materials that surpass even MCM-22's superior ability to operate at high propylene concentration could lead to important advance in cumene synthesis. In this work, a series of nano MCM-22"family"zeolites were prepared, including MCM-22, MCM-49 and MCM-36, and the catalytic performance for benzene alkylation with propylene was investigated. The structure and acid properties were modified by various methods. All sample were characterized by means of XRD, N2-adsorption/desorption, NH3-TPD, FTIR and NMR in order to clarify the relationship between the structure, acid-base properties and their catalytic performance. The main results obtained are as follows:1. Catalytic performance of nano MCM-22 and MCM-49 zeolites on benzene alkylation with propylene in liquid phaseNano MCM-22 and MCM-49 zeolites with different Si/Al were prepared and the catalytic performance of benzene alkylation with propylene in liquid phase was investigated. The effects of reaction condition on catalytic performance were studied, such as temperature, pressure, space velocity and feed ratio. The detailed investigation on reaction condition shows that the reaction temperature and the benzene to propylene ratio have considerable effect on the catalytic performance.The acid properties and catalytic performance of nanoMCM-22 and MCM-49 zeolite with different Si/Al were studied. NH3-TPD and FTIR results reveal that both the total acid amounts and B acid amounts decrease with the increment of Si/Al in zeolite, and the acid strength becomes weaker. For benzene alkylation with propylene in liquid phase, Nano MCM-22 and MCM-49 with a Si/Al range from 12.5 to 25 show a similar catalytic activity. The selectivity to total alkylation products (named as IPBs) decreases with the increase of Si/Al, while the selectivity to IPB increases. At a relatively low benzene-to-propylene ratios and reaction temperature, nano-MCM-49 zeolite shows higher catalytic activity and selectivity to IPBs than MCM-22 zeolite, however shows a relatively low selectivity to IPB. TPBr-MCM-49 zeolites, with the acid sites mainly located on their external surface, were prepared with selectively ion-exchange, and the catalytic performance were investigated for the purpose to clarify the nature of active sites for the alkylation of benzene. It is proposed that the main active sites for benzene alkylation with propylene are the protonic sites located in the external surface cups. Combined with the characterization results, we proposed that the appropriate acid property for benzene alkylation with propylene on MWW structure zeolite should be as follows: firstly, there are enough total acid amounts to achieve a completely conversion of propylene; secondly, poses a relatively low acid amounts on 10MR channel and supercage of MWW zeolite to restrain the producing of oligmers; thirdly, provides a bigger external surface area, lower acid density and little strong acid amounts in order to achieve a higher selectivity to IPBs and IPB.2. Structure, acid properties and catalytic performance of modified nano-MCM-49 zeoliteFor the purpose of improving the selectivity to IPB, various methods were tried to modify the structure and acid properties of nano-MCM-49 zeolite. Experimental results show that dealumination, phosphate-load and rearearth-loaded (or ion exchange) are effective methods to modify the acid properties of nano-MCM-49, resulting in a decrease in strong acid amounts. Under an appropriate modification condition, the selectivity to IPB could be increased obviously, as well as the catalytic activity keeps unchanged. Among all these methods, La-MCM-49 zeolite prepared by ion exchange shows the most excellent catalytic performance with an obviously higher selectivity to IPB than MCM-49. Combined with the characterization results, it is proposed that the decrease in strong acid amounts should be benefit to improve the selectivity to IPB.3.Catalytic performance of pillared layered MCM-36 zeolite on benzene alkylation with propylene in liquid phasePillared layered MCM-36 zeolite was synthesized from pure MCM-22 precursor with polymeric silica as pillaring agent. Swelling and pillaring create a new interlayer mesoporous system, thus remarkably increasing the specific surface area and the mesopore surface area of MCM-36, providing a larger amount of structurally accessible acid sites than MCM-22 zeolite synthesized from the same precursor. Characterization results of acidic properties indicated a decrease in the amounts of strong Lewis acidic and Br?nsted acidic, as well as a decrease in the acid strength compared to MCM-22 zeolite.The catalytic performace of MCM-36 is superior to MCM-22 zeolite synthesized from the same precursors, shows higher selectivity to both IPBs and IPB. Results of 200h continuous reaction indicate that MCM-36 shows excellent catalytic stablility.Combined with the characterization results of acidic properties and textural parameters, it is supposed that the increase of the selectivity to IPB in MCM-36 should be mainly due to the decrease of the amounts of strong Br?nsted acid sites, while the improvement of the catalytic activity and selectivity to IPBs can be mainly assigned to the presence of a larger amount of structurally accessible acid sites in this material.