Study On Relationship Of Structure And Performance Of Catalyst For Side-Chain Alkylation Of Toluene With Methanol

Styrene is an important chemical raw material that is widely used for synthesizing synthetic rubber,resins and plastics,and also it is used in pharmaceuticals,dyes,pesticides and beneficiation.The traditional processes for the synthesis of styrene include the catalytic dehydrogenation of ethylbenzene,oxidative dehydrogenation of ethylbenzene,alkylation of benzene with ethylene and so on.Among these traditional processes,about 90%of styrene in industry is derived from the catalytic dehydrogenation of ethylbenzene.However,The traditional process for the synthesis of styrene has many disadvantages,such as high energy consumption,complex process and so on.Compared with traditional methods,the side chain alkylation of toluene with methanol for producing a mixture of styrene and ethylbenzene has many irreplaceable advantages,such as low energy consumption,simple process,wide material sources and low cost.In the process of producing chemical productions,there is a lot of toluene,which has very low direct utilization rate,the price of methanol is very low and it is easily available.Therefore,it has great potentiality in market application to using excess toluene and cheap and readily available methanol instead of benzene and ethylene to synthesize styrene directly with great potentiality,and this reaction will arouse more widespread attention in the next few years.It is found that the mechanism of the side chain alkylation of toluene with methanol is that the methanol decomposes to form formaldehyde under the effect of the base sites of the catalyst,the formaldehyde is adsorbed on the acid sites,meanwhile,the toluene is also adsorbed on the acid sites,the methyl of toluene is activated under the effect of the base sites,the adsorbed formaldehyde and the methyl react to generate the adsorbed styrene,then the adsorbed styrene desorbs from the acid sites.Therefor,this is a acid-base synergistic catalysis reaction.Based on this mechanism,CsX modified with different amount solution of K₂B₄O₇,K₂B₄O₇ with La?NO₃?₃,Ce?NO₃?₃,Yb?NO₃?₃ and Gd?NO₃?₃,K₂B₄O₇ and K₃PO₄ or K₃PO₄.These catalysts was investigated in the reaction of the side chain alkylation of toluene with methanol.The catalytic performance was characterized by XRD,CO₂-TPD,NH₃-TPD,FTIR,and SEM,and the following conclusion could be drawn:1.Middle base site is the key requirement for side-chain alkylation of toluene with methanol.2.K₂B₄O₇ supported on CsX zeolite could improve the selectivity of styrene from 30%to 95%.3.Loading K₃PO₄ on K₂B₄O₇/CsX could increase the number of the middle base sites and decrease the middle acid sites.4.Loading La?NO₃?₃,Ce?NO₃?₃,Yb?NO₃?₃,Gd?NO₃?₃ on K₂B₄O₇/CsX could not prolong the life of the catalysts,which may be the four rare earth elements could not improve the hydrothermal stability of the zeolite.5.Loading K₃PO₄ on Cs X could improve the selectivity of ethylbenzene to over 80%,and the life of the catalyst could prolong to 320 hours through this method.6.The strong base sites and strong acid sites emerged after reaction.The strong acid sites may react with zeolite and destroy the structure of the zeolite.So,that will reduce the catlytic activity of the catlysts.