Study On Effect Of Methanol Dehydrogenation Catalytic Component On Side-chain Alkylation Of Toluene With Methanol Over CsX Zeolite Composite Catalyst

Styrene is an important polymer monomer.Compared with the conventional ethylbenzene dehydrogenation process,side-chain alkylation of toluene with methanol to produce styrene has great potential advantages.However,the development of excellent catalysts for the side-chain alkylation of toluene with methanol remains an important challenge.Based on the previous work in our laboratory,this study focuses on the adjustment of methanol dehydrogenation components in order to improve the catalytic performance of CsX zeolite-based ternary composite catalyst.Main research contents and results are summarized as follows:Firstly,a series of binary composite catalysts in combination of methanol dehydrogenation components(alkali salts,metal oxides and zeolites)with CsX zeolite were prepared by granulestacking,and the side-chain alkylation of toluene with methanol over these catalysts was studied.Results showed that the ratio of styrene to ethylbenzene of the side-chain alkylation reaction could be significantly improved with the binary catalysts containing alkali salts,metal oxides and zeolites,instead of cesium oxide modified CsX zeolite,as methanol dehydrogenation component.Under the condition of reaction temperature was 430?,toluene and methanol molar ratio was 6:1,and WHSV was 2 h-1,the binary CsX zeolite composite catalysts containing Na2B4O7?CuO/SiO2 and Na-ZSM-5 as methanol dehydrogenation component exhibited 49.1%,77.7%and 61.8%methanol conversion,25.4%,22.4%and 19.1%styrene and ethylbenzene yield,as well as 1.9,0.9 and 0.6 styrene to ethylbenzene ratio,respectively.On this basis,in order to overcome the shortcomings of the binary composite catalysts in the aspects of formaldehyde intermediate decomposition and styrene transfer hydrogenation to ethylbenzene,a series of ternary composite catalysts containing methanol dehydrogenation components(alkali salts,metal oxides and zeolites),CsX zeolite and B/SiO2 were prepared by granule-stacking method.A systematic study on the side-chain alkylation of toluene with methanol over these catalysts was carried out.The effects of cesium ion exchange degree(CsED),component content,composite manners among the components and reaction conditions on the side-chain alkylation were also investigated in detail.Results showed that the introduction of B/SiO2 into the composite catalysts could stabilize the formaldehyde intermediate and increase the ratio of styrene to ethylbenzene as well as the yield of styrene and ethylbenzene.Under the condition of reaction temperature was 430?,toluene and methanol molar ratio was 6:1,and WHSV was 2 h-1,the optimized CsX-CuO/SiO2-B/SiO2 ternary composite which had a CuO/SiO2(Cu 1.9 wt%),B/SiO2(H3BO3 16 wt%)and CsX zeolite(CsED 46.3%)mass ratio of 0.2:0.15:1.0,reached a styrene to ethylbenzene ratio of 3.1 and a styrene and ethylbenzene yield of 31.0%in the side-chain alkylation.Results also showed there was an obvious synergistic effect between CuO/SiO2 component and CsX zeolite in the ternary composite catalyst in the appropriate reaction temperature range.That is,the dehydrogenation of methanol to formaldehyde over CuO/SiO2 could promote the side-chain alkylation of toluene over CsX zeolite.Meanwhile,the conversion of formaldehyde into side-chain alkylation products over CsX zeolite could thermodynamically drove the dehydrogenation of methanol over CuO/SiO2 component in return.Further,a better ternary composite catalyst CsX-(Na2CO3-CuO)-B/SiO2 was prepared by the granule-stacking method which contained Na2CO3-treated CuO,instead of CuO/SiO2,as its methanol dehydrogenation component.Under the condition of reaction temperature was 430?,toluene and methanol molar ratio was 6:1,and WHSV was 2 h-1,the catalyst gave a styrene and ethylbenzene yield of 32.4%and a styrene to ethylbenzene ratio of 4.5 in the side-chain alkylation.Study indicated that the main reason why the treatment of CuO with Na2CO3 could significantly improve the ratio of styrene to ethylbenzene on ternary CsX-(Na2CO3-CuO)B/SiO2 composite catalyst lies in the inhibition of the hydrogenation of styrene to ethylbenzene over the methanol dehydrogenation component.Nevertheless,the CsX-(Na2CO3-CuO)-B/SiO2 catalyst exhibited an accelerated deactivation because of the more serious styrene condensation at higher styrene to ethylbenzene product ratio.To overcome this problem,it is necessary to think about the use of a fluidized bed or a moving bed reactor for the side-chain alkylation in the future study.