The catalytic dehydration of alcohols.

  • O. Olaofe

Student thesis: Doctoral ThesisPhD


The vapour phase dehydration of ethanol, isopropanol and n-butanol over zeolites 13X, 4-A and ZNa and the synthetic cation exchange resin Dowex 50-X-8 has been studied in a continuous stirred gas solid reactor covering a wide range of experimental conditions. Both principal products, ether and olefin were produced. The kinetic data, procured, have been satisfactorily correlated both with the empirical, power function and the Hougen-Watson type of rate, expressions. For the former type of correlation, reaction orders, activation energies and pre-exponential factors for both simultaneous reactions were established for each zeolite and each alcohol. The kinetic data on the dehydration of alcohol over the synthetic cation exchange resin were also satisfactorily correlated by power function rate equations. But the activation energies and pre-exponential factors obtained were markedly different from those for zeolites because of the effect of the adsorption process. Qualitative and statistical considerations were used to discriminate among different Hougen-Watson models. The rate expression based on surface reaction controlling was found to satisfactorily fit the kinetic data. The kinetic and adsorption parameters in the Hougen-Watson rate expression have been satisfactorily correlated as functions of reaction temperature. The activity and selectivity of the zeolites have been systematically investigated. The activity pattern was explained in terms of surface area, pore size and acidic and basic strength. The. importance of geometrical shape on selectivity was clearly demonstrated. The synthetic cation exchange resin was found to be suitable for the exclusive production of di-ethyl ether from the dehydration of ethanol. However both di-iso- propyl ether and propene were formed from the dehydration of isopropanol under the reaction conditions studied. The sequences of the reactivity and activation energy of the alcohols were, explained in terms of an inductive effect and a positively charged intermediate complex. The order of reactivity of alcohols for all the catalysts used was 2- C3>C4>C2 Activation energies and. pre-exponential factors were satisfactorily correlated with an empirical relationship called the 'compensation effect,' Molecular shape selectivity, that is selectivity of the same catalyst between two molecules of different shapes, was assessed. Product distribution from the dehydration of n-butanol was investigated to gain insight of the reaction mechanism. The formation of 2-alkenes (cis-2-butene and trans-2-butene) in the absence of isomerization reactions during the catalytic dehydration of n-butanol over zeolites is unambiguous evidence in favor of a positively charged intermediate, indicating that the reaction proceeds via a El type of mechanism. Experimental data also showed the preferential formation of cis-2-butene over that of trans-2-butene. Fixed bed reactor behavior was simulated using one and two dimensional pseudo-homogeneous isothermal models to test the adequacy of the rate expressions established for the dehydration of isopropanol over zeolite 13X. Experimental conversion data were gathered from a packed tubular reactor. The experimental data agreed fairly well with the predictions of the models.
Date of Award1982
Original languageEnglish
Awarding Institution
  • University of Bath

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