DEHYDROGENATION OF ETHYLBENZENE IN THE PRESENCE OF IRON OXIDE CATALYSTS PROMOTED BY POTASSIUM, CERIUM AND MOLYBDENUM: KINETIC MODELLING
Authors:   Kazan National Research Technological University, BOCHKOV M.A. , ULITIN N.V. , TERESHCHENKO K.A. , SHIYAN D.A. , ANDREEV A.P. , KAZANSKAYA M.G. , TUNTSEVA S.N. , PUCHKOVA T.L. ,   Kazan National Research Technological University, BOCHKOVA O.D. ,   Kazan Federal University, MULLAKHMETOV A.A. , KHARLAMPIDI KH.E. ,   Kazan National Research Technological University
Published: November 2024

The present work is devoted to assessing the effect of the chemical composition of iron oxide catalysts promoted with potassium, cerium and molybdenum on their activity, quantified as ethylbenzene conversion, and selectivity of ethylbenzene dehydrogenation and interpreting the results obtained using kinetic modeling. The concentrations of the components of the reaction mixture, the conversion of ethylbenzene and selectivity of the ethylbenzene dehydrogenation were experimentally determined in the presence of synthesized iron oxide catalysts. A kinetic model of the process has been developed in the form of a system of differential equations that describes changes of the reaction system components concentration according to the mass action law. The experimental concentrations of the reaction mixture components, the ethylbenzene conversion and selectivity were described by the kinetic model by the use in the model of the following type of dependencies of the reaction rate coefficients on temperature: k i = k i0 T n i exp⁡(- B i T m i ) , where ki0, Bi, ni, mi are coefficients independent of temperature; T is the process temperature, K. As a result of kinetic modeling, the following patterns were established. The rate of the forward reaction of ethylbenzene dehydrogenation C6H5-C2H5 ⇆ C6H5-C2H3 + H2 is much greater than the rate of the reverse reaction, so chemical equilibrium in the ethylbenzene dehydrogenation reaction is not achieved. The effect of the reverse reaction on the kinetics of the ethylbenzene dehydrogenation process is minimal. The rate of the direct reaction of ethylbenzene dehydrogenation C6H5-C2H5 ⇆ C6H5-C2H3 + H2 is much higher than the rates of the reactions C6H5-C2H5 → C6H6 + C2H4 and C6H5-C2H5 + H2 →C6H5-CH3 + CH4. In this regard, the conversion of ethylbenzene is determined by the rate coefficient of the forward reaction in the reversible reaction of ethylbenzene dehydrogenation C6H5-C2H5 ⇆ C6H5-C2H3 + H2. The selectivity is determined by the ratio of the rate (or the ratio of the rate coefficient) of the direct reaction of ethylbenzene dehydrogenation C6H5-C2H5 ⇆ C6H5-C2H3 + H2 to the sum of the rates (or the sum of rate coefficient) of the direct reaction of ethylbenzene dehydrogenation and the dealkylation reaction of ethylbenzene C6H5-C2H5 ⇆ C6H6 + C2H4. It has been shown that an increase of the ethylbenzene conversion can be achieved, first of all, by promoting the iron oxide catalyst with the potassium compound. Pre-exponential factors and activation energies for all iron oxide catalysts promoted with the potassium compound do not change when cerium or molybdenum compounds are introduced into the catalyst, that is, in the process under consideration, the contribution of cerium and molybdenum compounds to the chemical properties of the iron oxide catalyst is insignificant.