Preparation Of Bimetallic Modified SBA-15 And Its Benzylation Performance

Diphenyl?m?methane is an important fine chemical used in many fields such as medicine,chemical industry and semiconductor.At present,diphenylmethane is mainly synthesized by benzylation of benzene with benzyl chloride in industry.And the catalyst conventionally used is the liquid acid.However,it does not meet the green chemical standards.The reaction efficiency is low.And there are other problems such as difficulty in recycling,corrosion equipment and poor selectivity of target products.Therefore,studies on novel catalysts for benzyl chloride and benzene have received extensive attention.On the self-made benzylation reaction unit,benzene and benzyl chloride are used to synthesize diphenylmethane.Single metal and double metals modification of SBA-15 molecular sieve are carried out.And single metal M?M is Ce,Zr,Mn,Al,Fe,Sr,Mg?and bimetallic M modified SBA-15molecular sieve catalyst are prepared by impregnation method.The results show that the Fe-SBA-15 molecular sieve has a better benzylation effect,and the Mg/Fe-SBA-15 molecular sieve has the best catalytic effect.The catalysts are characterized by XRD,N₂ adsorption-desorption,NH3-TPD,Py-FTIR and TG-DTA characterization methods.The results show that Fe modification does not destroy the two-dimensional hexagonal mesoporous structure of SBA-15 molecular sieve.The introduction of Fe can improve the surface acid strength and acidity of SBA-15 molecular sieve.The introduction of the alkali metal Mg facilitates the dispersion of Fe₂O₃ on the surface of the catalyst.The acidic centers of Fe and Mg have synergistic effect on the catalyzed benzylation reaction.The prepared Mg/Fe-SBA-15 molecular sieves have similar hexagonal mesoporous structure to Fe-SBA-15 molecular sieves.The optimal preparation conditions of the catalyst are investigated by catalyzing the benzylation of benzene with benzyl chloride as a probe reaction.The results show that the Fe-SBA-15 molecular sieve has better benzylation performance when the Fe loading is 9%?mass fraction?.When the loading of Mg is 3%?mass fraction?,the calcination temperature of the catalyst is550°C,the calcination time is 3h,the immersion temperature is 40°C,and the immersion time is 3h,the catalytic effect of Mg/Fe-SBA-15 molecular sieve is optimal.The optimum conditions for the benzylation of benzyl chloride are investigated by using Mg/Fe-SBA-15 molecular sieve catalyst.The results show that the optimum conditions for the reaction of benzylbenzyl chloride to diphenylmethane are as follows:reaction temperature 60°C,reaction time 15min,n?benzene?/n?benzyl chloride?=4:1,catalyst dosage accounts for 2.5%of the amount of benzyl chloride.Under the optimum process conditions,the conversion of benzyl chloride is 100%and the selectivity of diphenylmethane is 77.7%.Under the optimal preparation and process conditions,the catalyst can still provide a higher conversion of 88%and high selectivity after repeated using for 5 times,which indicates that 3%Mg/Fe-SBA-15 molecular sieve has good stability performance.Under the optimal preparation and process conditions,the catalyst can still provide a higher conversion of 90%and high selectivity after four regenerative catalytic cycles,which indicates that 3%Mg/Fe-SBA-15molecular sieve has good regeneration performance.