Side-chain Alkylation Of Toluene And Methanol To Produce Styrene And Ethylbenzene

Styrene is an important unsaturated aromatic monomer,which acts as a basic petrochemical raw material to produce polystyrene,acrylonitrile butadiene styrene and acrylonitrile-styrene copolymer and plays an important role in chemical industry.Compared with conventional ethylbenzene dehydrogenation and styrene-propylene oxide co-production process,side-chain alkylation of toluene and methanol to produce styrene technology has advantages in reaction condition,materials costs,energy consumption,atom utilization and technical economy.In this paper,we studied side-chain alkylation mechanism and catalysts,including reaction conditions optimization and thermaldynamic properties and control step anlysis.Based on experimental research,molecular simulation technology was applied to investigate side-chain alkylation reaction and provide theoretical support for catalysts development.Different alkali metal modified X zeolites and Mg-Al oxide?Layered Double Oxide-LDO?prepared by coprecipitation method were characterized and evaluated.The results reveal that the framework of zeolite catalysts was intact and catalyst base strength increased with the raise of atom number.Though the base strength in LDO is similar to CsX,among the materials only CsX showed side-chain alkylation activity,confirming that this reaction requires certain base strength and appropriate pore structure.CsX series catalysts which ion exchange degree vary from 28.8%to 78.6%were prepared by controlling the solution concentration,exchange time and times.With the increase of Cs exchange degree,base strength of CsX catalysts grew gradually and the zeolite framework kept intact.There was a significantly positive correlation between catalyst performance and Cs exchange degree.Besides,catalysts showed obvious catalytic activity only when Cs exchange degree reached 40%.The value of toluene conversion was 6.5%,total yield of styrene and ethylbenzene was 22.1%and styrene selectivity was 5.7%when Cs exchange reached saturation.Results illustrate that Cs cation located at SII site was active center for side-chain alkylation.In addition,the reaction optimal condition were as follows:T=425?,Space velocity=2.0h^-1,Toluene/methanol ratio?mole?=3.0.CO₂ and CO atmosphere could effectively improve styrene selectivity for inhibiting formaldehyde decomposition.Thermodynamic analysis indicates that high temperature facilitated methanol dehydrogenation and formaldehyde decomposition,but it was not conductive to main reaction.From thermodynamic aspect,formaldehyde decomposition reaction is easier than methanol dehydrogenation and because side-chain alkylation which equilibrium constant is relatively high,so methanol dehydrogenation is the key step for alkylation reaction.However,before reaching thermodynamic equilibrium,the reaction is under dynamic control.The energy barrier of formaldehyde decomposition is much higher than that of methanol dehydrogenation,so the former reaction is harder to carry out than the later one.Therefore,the utilization of formaldehyde is actual control step for side-chain alkylation.Materials Studio software simulation found that reactant co-adsorption had promote effect,which facilitates side-chain alkylation.The adsorption energy and binding energy of co-adsorption were-39.4 kJ/mol and 51.7 kJ/mol,respectively.Meanwhile,the interaction between styrene and catalyst was weaker than reactant adsorption,so product could desorb easily.The results also indicate that side-chain alkylation reaction mechanism was carbanion form methyl of toluene and carbocation from formaldehyde combination.The study provides theoretical support for mechanism and catalyst research of side-chain alkylation of toluene and methanol to produce styrene and ethylbenzene.