Modification Of Hierarchical Porous Hβ Zeolites And Its Catalytic Performance For Acylation

The Friedel-Crafts acylation is one of the most important methods for the production of aromatic ketones,which are important chemical intermediates of fine chemicals,pharmaceuticals and pesticides.At present,Friedel-Crafts acylation mainly uses metal halides(Al Cl3,BF3)or protonic acid(HCl,H2SO4)as catalysts.These traditional catalysts have the hazards of corrosion defects,producing a large number of toxic waste,difficulties to recycle,and difficulties to control,which finally pollute the environment.Among many solid acid catalysts,metal oxides,cationic resins,solid heteropoly acids and solid superacid can replace traditional liquid acid catalysts,but zeolites have the best catalytic performance in Friedel-Crafts acylation reaction.β zeolites are microporous molecular sieves with twelve-membered ring channels.They have been extensively studied for their pore sizes similar to the equivalent diameters of reactants and products in acylation reactions.However,the narrow pore sizes of β zeolites make it difficult to diffuse reactants and products,and the catalysts are easy to block and coke,which has a negative impact on the expanded application of β zeolites in acylation reaction.The preparation of hierarchical porous zeolites is one of the methods to solve the above problems.Hierarchical porous zeolites have excellent properties of both microporous and mesoporous structures,which show higher stability and better carbon deposition resistance because of their relatively short diffusion path.In recent years,alkali desilication has attracted wide attention because of its simplicity and low cost.However,the acylation of anisole with Acetic Anhydride Catalyzed by Hierarchical porous β zeolites has not been reported.Hierarchical porous β zeolites,hierarchical porous β zeolites modified by Cr and hierarchical porous β zeolites modified by HPW were prepared on the basis of previous studies and a large number of references.XRD,BET,NH3-TPD,SEM,TEM and FTIR were used to characterize the prepared catalysts.The crystal structure,pore structure,specific surface area,acidity,acidity,acidity and surface morphology of the catalyst were analyzed and investigated to determine the conversion and selectivity of acylation reaction.The results showed that alkali treatment did not change the crystal structure of zeolites,and the zeolites after alkali treatment had a larger mesoporous structure,which improved the mass transfer effect.The acylation reaction of anisole with acetic anhydride was used as a probe to test the catalytic effect of alkali-treated β zeolites.The alkali treatment of 0.2 mol/L Na OH solution on acylation reaction was the best.Hierarchical porous β zeolites modified by Cr were still BEA crystal structure and hierarchical porous structures with micro-porous structure,but the acid content was adjusted.The total acidity of hierarchical porous β zeolites modified by 5wt.% Cr increased from 906.55 umol/g to 1075.7 umol/g.The hierarchical porous β zeolites modified by HPW were also hierarchical porous catalysts with BEA crystal structure too,but the amount of B acid increased from 0.35 mmol/g to 0.75 mmol/g,showing good catalytic effect.The acylation reaction of anisole with acetic anhydride was used as a probe in the autoclave reactor to explore the reaction effect of catalyst.When the hierarchical porous β zeolites were loaded with chromium,the optimum reaction conditions were as follows: chromium loading 5wt.%,reaction temperature 120℃,reactant ratio 1.5:1,10% catalyst,reaction time 2h.At this time,acetic anhydride conversion was 93.0%,the selectivity was 97.5%.Under the conditions of HPW loading 10%,reaction temperature120℃,catalyst dosage 5% and molar ratio of reactants 1.5,the acylation effect of hierarchical porous β zeolites were the best.The optimum conversion of acetic anhydride was 97.2% and the selectivity was 98.3%.The catalysts showed good activity.