The Study Of Catalysts For Side-chain Alkylation Of Toluene And Methanol To Styrene

Styrene is an important chemical material for elastomer,resin and plastic.The development of catalysts and new technology for the preparation of strene is the key factor to increase market competitiveness in China.Compared with the traditional technologies（the catalytic dehydrogenation of ethylbenzene）,the side-chain alkylation has obvious significant economical advantages in technological procedure and material source.The exploration to efficient catalysts for the side-chain alkylation of toluene with methanol is the hot research topics.The side-chain alkylation of toluene with methanol is acid-base cooperativity.Many researchers have investigated that zeolites were attractive materials for alkylation reactions because their acid–base properties can be easily modified by ionic-exchange or other additives.Meanwhile non-zeolite alkaline porous materials were successfullyused for side-chain alkylation,but the catalytic of these catalysts were still inferior.In this paper,in order to acquire efficiently acid-base synergistic catalysts,different mass fraction of K_PO₄ were supported on CsX,different phosphate salt were loaded on CsX,different potassium salt were burden on CsX and the cause of deactivation for 5wt%K_PO₄/Cs X.These catalysts were used for the side-chain alkylation of toluene with methanol and were characterized by XRD 、 CO₂-TPD 、NH3-TPD、SEM、XPS、FT-IR、TG-MS and so on.These results get conclusions as follows:1.Potassium phosphate supported on ion-exchanged CsX zeolite was prepared by impregnation method.The amount of weak acid decreased with the addition of K_PO₄.On the other hand,however,the strength and amount of middle base sites increased,partucilarly the base sites at 270-300 ℃（CO₂-TPD）.The catalyst activity and selectivity of styrene and ethylbenzene were improved significantly.When K_PO₄ was more than 5wt%,The conversion of methanol and selectivity of styrene and ethylbenzene reached 84.1% and 92.8%.The catalytic activity was decreased slightly with K_PO₄ loading of 10wt%.2.In order to research the role of acid-base sites and phosphate group,K_PO₄,Na₃PO₄,Ca₃（PO₄）2,Mg₃（PO₄）₂ was supported on CsX and applied to the side-chain alkylation of toluene and methanol.The results showed that K_PO₄/CsX,Na3PO₄/CsX increased the strength and amountof middle base sites when Ca3（PO₄）₂/CsX,Mg₃（PO₄）₂/CsX had weak base sites.The results showed that K_PO₄/CsX,Na₃PO₄/CsX catalytic activity and selectivity of styrene and ethylbenzene were improved significantly,Ca3（PO₄）₂/CsX,Mg₃（PO₄）₂/CsX catalytic activity and selectivity of styrene and ethylbenzene were poor.It could concluded that middle base sites were the key factor for the catalytic activity of side-chain alkylation of toluene and methanol.3.K_PO₄,KAC,K₂CO₃,KNO₃,KCl,K₂SO₄ were loading on the CsX.The catalytic results showed that K_PO₄/Cs X,KAC/CsX,K₂CO₃/CsX significantly improved the catalytic activity of the side-chain alkylation,except for KNO₃/CsX,KCl/CsX,K₂SO₄/CsX.Characterization results showed that strong base-weak acid salt can improve the strength and amount of middle base sites and other salt did no obvious change in the base sites.It also proved the key function of middle base sites.4.The 5wt%K_PO₄/CsX catalyst began to deactivate at 6h.The cause of catalyst deactivation was investigated by means of characterization.The results concluded that carbon deposit,structural breakdown and the loss of base-acid active sites were the deactivation reasons.The catalyst after reaction was regenerated by oxidizing roasting.The catalytic activity of side-chain alkylation was recovered to 90%comparing with the fresh catalyst.It can be conclude that carbon depositwas the main cause of catalyst deactivation.