The Study On The Textural Design And The Properties Control Of Zeolite Catalysts For Alkylation Of Benzene And Propylene

Zeolite MCM-22 had been used as the catalyst for alkylation of benzene and propylene.The dissertation used the cyber-simulation technology to study the action of benzene and propylene in the zeolite MCM-22,βand ZSM-5 with different textural,providing the theories of benzene alkylation with propylene on zeolites.Then the technology of catalyst design engineering to optimize the configuration of the MCM-22 zeolite catalyst from micromechanism to macromechanism,improving the performance of the catalyst.Moreover,the BP neural network model had been established to predict the reaction results according to the catalyst properties and reaction condition.The diffusion and adsorption behaviors of benzene and propylene in the zeolite MCM-22,βand ZSM-5 had been studied by Molecular Dynamics(MD) and Grand Canonical Monte Carlo(GCMC) simulations. The diffusion coefficients of benzene and propylene in the MFI,MWW and BEA zeolites were calculated by simulating the mean-square displacements(MSD).The competitive adsorption was taken place when benzene and propylene adsorbed on zeolites.In the alkylation reaction, because of the large channels inβ,cumene molecule could diffuse quickly;the cumene and propylene could react and create multipropylbenzene not easily,so the selectivity of cumene was higher than MCM-22 and ZSM-5.MCM-22 has supercages which sizes are larger than the 12MR channels ofβ,but the locations of the 10MR windows in the supercages are perpendicular to the direction of the motion,which could hinder the alkylation reaction to occur.So,for MCM-22,the alkylation happened on the cavities at the top and bottom surface,which had the advantages to improve the catalytic performance for the benzene alkylation with propylene.The sizes of channels in ZSM-5 were smaller than the others which were the disadvantages for alkylation.We used the auxiliary chemicals—glycerin under hydrothermal conditions to obtain the MCM-22 zeolite with various morphologies, including the specific areas and the platelets size.The alkylation of benzene with propylene under liquid-phase reaction conditions catalyzed by the prepared MCM-22 zeolites was also carried out to investigate the catalytic performances of the modified zeolites.A conceivable formation mechanism and the reason of catalytic performance improvement in the presence of glycerin as an auxiliary chemical had been suggested that adding appropriate amount of glycerin when MCM-22 synthesis,not only could increase the solubility of hydrophobes and improve the crystallinity, but also could increase the difficulty of forming T-O-T bonding.During calcinations,glycerin molecules enhanced the hindrance of two double-layers and led them to form T-O-T uneasily,and make the platelets thinner and smaller.On these zeolites,cumene could not be further alkylated to form di-isopropylbenzene or tri- iso- propylbenzene easily and the selectivity of cumene could be improved about 5%.The catalyst macroscopical properties were controlled through molding progresss.The influences on the textural properties and catalytic performance were studied by adding different amount of SB powder, HNO₃,PEG20000 and water.The results showed that in the molding progress,adding the suitable amount auxiliary materials could adjust the properties of catalyst,including the surface areas,pore size and acidity. So the properties and alkylation reaction-diffusion were matching each other,which could improve the performance of catalyst.Taking the selectivity of cumene as the objective variable,the optimum technology was followed:15%SB powder:20%HNO3:10%PEG20000:90%H2O. Base on the optimization of microscopical and macroscopical configuration,the conversion of propylene was improve about 2%,and the selectivity of cumene was improved about 3%.Because the alkylation process was very complex and the model of mechanism was established difficultly,The BP neural network was used to predict the results of benzene alkylation with propylene.The average relative deviations of determination showed a good correlation between estimated and experimental data sets.There were high correlations between experimental and estimated data curves,which were another proof that the high performance of ANN for estimation of the product distributions of alkylation reaction.Moreover,the network could be applied to direct the catalysis design,confirming the optimized configurations and reaction conditions and improving the efficiency of experiments on catalysis research.