Synthesis,Characterization And Catalytic Performance Of MCM-41Zeolite Containing Aluminophosphate Building Units

A series of MCM-41,SAPO-5and MCM-41zeolite containing aluminophosphate building units were synthesized by hydrothermal and microwave radiation methods and characterized by XRD,BET,IR,SEM,TEM,27Al and31P NMR,TG-DTA and NH3-TPD techniques. The catalytic cracking of1,3,5-triiso-propylbenzene were carried out over the zeolites.(1) The best synthesis conditions of MCM-41zeolite containing aluminophosphate building units by hydrothermal method in laboratory are [SiO2+1/2Al2O3]/AlPO4=4.5,crystalline temperature120℃and crystalline time48h.The best synthesis conditions of MCM-41zeolite containing aluminophosphate building units by microwave radiation method in laboratory are CTAB/Al(OC3H7)3=0.633,subsection crystalline pressure1.2,1.5,1.8MPa and crystalline power75%.(2) The result of N2adsorption-desorption isotherm showed that the MCM-41zeolite had symmetrical aperture of2.8nm and the MCM-41zeolite containing aluminophosphate building units had both micropore and mesopore structure. The average mesopore size is2.5nm and micropore size is0.58nm.(3) The SEM photos shows that the crystal grain of SAlP zeolite agglomerated,small grain grew over big grain.,the grain patterns are globular shape or spheroidicity.The crystalloid of MCM-41zeolites is homogeneous and their dimension is nearly10μm.(4) The TEM photos shows that the aperture section of MCM-41zeolite is same as dactylogram and aperture is bigger than2nm, which is similar to2.8nm of N2adsorption-desorption result. The MCM-41zeolite containing aluminophosphate building units has dense aperture and inhomogeneous dimension, which validates that MCM-41zeolite containing aluminophosphate building units has micro-mesopore structure.(5) The TG-DTA result demonstrated that the framework of MCM-41zeolite collapsed at780℃, while that of MCM-41zeolite containing aluminophosphate building units collapsed at900℃, so the MCM-41zeolite containing aluminophosphate building units had better heat stability.(6) Cracking convertion of1,3,5-triisopropylbenzene over the HMCM-41zeolite is60.1%, and the convertion declines with the increase of Si/Al ratio of the zeolite. The selectivity of benzene, m-diisopropylbenzene and p-diisopropylbenzene increases with the increase of Si/Al ratio of the zeolite. The1,3,5-triisopropylbenzene has been converted above87.2%over the MCM-41zeolite containing aluminophosphate building units with [SiO2+1/2Al2O3]/AlPO4of1-6. The selectivity of benzene and m-diisopropylbenzene increases and the selectivity of p-diisopropylbenzene decreases gradually with the decrease of [SiO2+1/2Al2O3]/AlPO4ratio of the zeolite.(7) Catalytic activities of cracking of1,3,5-triisopropyl-benzene over HSAPO-5,HMCM-41,SAlP and mechanical mixture zeolites indicate that the SAlP zeolite possesses the highest activity,and the selectivity of all production are high. The convertion of1,3,5-triisopropyl-benzene over HMCM-41was60.1%,the selectivity of benzene, m-diisopropylbenzene and p-diisopropylbenzene is not high. HSAPO-5had the lowest convertion14.8%, and the produc only had benzene and m-diisopropylbenzene. The mechanical mixture zeolite APCM shows an activity of57.4%,between the MCM-41and SAPO-5. The SAlP zeolite has a mico-mesopore structure, which is different from MCM-41, SAPO-5and mechanical mixture zeolite, and its catalytic cracking performance is superior to SAPO-5zeolite, HMCM-41zeolite and mechanical mixture zeolites.