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The inhibiting effect of high feed carbon dioxide concentrations (12–33%) on ethene epoxidation and combustion reactions over Ag/Al2O3 catalyst was studied by the flow-circulation method. Kinetic measurements have been carried out under steady-state conditions, at atmospheric pressure and in the temperature range 483–565 K. It has been established that the feed carbon dioxide inhibits considerably both the epoxidation and the combustion of ethene, the effect on the latter being stronger. Therefore, the presence of carbon dioxide in the feed affects the selectivity favourably. The inhibiting effect is described quantitatively by a kinetic model consisting of two rate equations, one for the epoxidation and the other for the combustion reactions. The model is to be used when the carbon dioxide concentration in the reaction mixture is higher than 10% and the temperature is in the range 513–565 K. The model is empirical and it is compared with a mechanistic model derived on the basis of the assumed reaction mechanism. The empirical model fits the experimental results better.

The selective oxidation of ethylene over supported silver catalyst was studied in the presence of 0.2–16% feed water vapour. In addition to silver, alumina and silica, the catalyst also contains Li, Na, K, Mg, Ca, Ba, Mn and Fe additives in trace amounts. Steady-state kinetic measurements were carried out using a glass flow-circulation system at atmospheric pressure and in the temperature range 210–264°C, varying the oxygen-to-ethylene concentration ratio in the feed. The results show that the partial oxidation of ethylene is inhibited by the presence of feed water but the complete oxidation is promoted by it. This result contradicts the results of other workers. The reason for this contradiction is probably the presence of the additives in the studied catalyst. The effect of water is stronger at low feed concentrations (0.2–1.4%), at which the process is carried out in the industrial reactor. This fact could be of great importance for selecting the optimum conditions for the industrial process. The presence of feed water has an unfavourable effect on the selectivity for ethylene oxide, unlike the effect of carbon dioxide in the feed established in previous work over the same catalyst. An explanation of the effect of water vapour on the oxidation of ethylene is proposed on the basis of the assumed reaction mechanism.

A kinetic study of selective ethylene oxidation to ethylene oxide over a silver catalyst has been carried out by the circulation flow method. The silver was promoted by a Ca additive and was supported on alumina. The experiments were conducted under steady state conditions in the temperature interval 210 – 292°C and at atmospheric pressure. As a result of this kinetic study two rate equations, for the partial and for the complete oxidation reactions, are proposed. A reaction scheme is put forward, according to which adsorbed molecular oxygen produces ethylene oxide, whereas the atomic oxygen is responsible for the complete oxidation reaction. The empirical kinetic model corresponds to a Rideal-Eley type of mechanism. Selectivity decreased with temperature increase and with decrease of the oxygen content in the feedstock.

The kinetics esterification of the methacrylic acid (MA) with ethylene oxide (EO), catalysed by polymer-supported ferric chloride, has been studied in a static reactor under quasi-stationary conditions. The temperature interval 50–90°C was investigated and the mole ratio of MA to EO was varied from 2:1 to 1:10. The catalyst amount was varied from 1 to 10 wt.-%. As a result a kinetic model of the reaction is proposed. The model corresponds to a single-site Langmuir-Hinshelwood mechanism. The rate-limiting step is a surface reaction. Optimum conditions for the esterification are 80°C, a mole ratio of MA to EO of 1:1 and 1–3 wt.-% catalyst.

The kinetics of the isomerization of butenes over an industrial CoO MoO3/Al2O3 catalyst for hydrodesulphurization of Diesel fractions has been studied by the flow circulation method. The study was carried out under steady-state conditions at atmospheric pressure and in the temperature range 325–425°C. The selectivity of the catalyst for cis-2-butene is practically the same for both the reduced and the sulphided form, but the activity of the reduced form is greater. The selectivity decreases with increasing temperature, with contact time and with 1-butene concentration in the feed, for both the sulphided and the reduced form. Evidence was obtained that suggests that surface reactions are the rate-determining steps under these reaction conditions. The values of the relative rate constants for the three experimental temperatures of 325, 375 and 425°C were calculated by the Wei-Prater method. These values and those obtained for the activation energies show that cis-2-butene is a kinetic control product, as it is formed faster than trans-2-butene which is a thermodynamic control product.

The kinetics of the complete oxidation of ethylene oxide over a supported silver catalyst in the absence of dichloroethane was studied by the flow circulation method. The temperature range 100–300°C was investigated under steady-state conditions and at atmospheric pressure. The kinetic measurements showed that ethylene oxide oxidation starts at 190°C. Below this temperature, the ethene oxidation over a silver catalyst proceeds according to the parallel reaction scheme. At 300°C and an oxygen: ethylene oxide feed ratio of 1:2 catalytic decomposition of ethylene oxide to ethene and oxygen was observed. A sequential experimental design was applied for the determination of the parameters and the simultaneous discrimination of rival kinetic models. A kinetic model is proposed that describes the rate of uninhibited ethylene oxide oxidation in the temperature range 250–300°C. The model corresponds to a mechanism in which ethylene oxide and oxygen adsorption (dissociative and non-dissociative) are fast steps at equilibrium. The rate-limiting steps are ethylene oxide oxidation to formaldehyde and further to carbon dioxide and water with the participation of both atomic and molecular adsorbed oxygen. These steps are irreversible. The calculated kinetic constants offer the possibility of evaluating tentatively the rate constants of the irreversible steps and the equilibrium constants of the fast reversible steps.

The kinetics of isomerization of butenes over an industrial CoO MoO 3 /Al 2 O 3 catalyst have been studied by the flow-circulation method under steady state conditions, at atmospheric pressure and in the temperature interval 325–425°C. As a result of the study a kinetic model is proposed for the reduced form of the catalyst. The kinetic model is of the Langmuir-Hinshelwood type and corresponds to a single site mechanism. The adsorption and desorption of the three isomers, 1-butene, cis-2-butene and trans-2-butene are fast steps at equilibrium under these experimental conditions. The rate-limiting step is a surface reaction. The kinetic constants of the model provide a possibility to evaluate the rate constants of the surface interactions. The model adequacy for the description of the dependence of selectivity and conversion on temperature, contact time and feed composition is extensively illustrated.

The complete oxidation of ethylene oxide over a supported Ag/A1203 catalyst has been studied independently and separately from ethene oxidation [ 1,2]. During a steady-state kinetic study in the absence of the industrial promoter of selectivity, ethylene dichloride, autooscillations of the catalyst bed temperature were observed. [ 11. This result is interesting as no oscillations during this reaction have been reported in the literature. According to Stoukides and Vayenas [ 3 1, who studied rate oscillations during propylene oxide oxidation over silver, such oscillations will not be observed during the catalytic oxidation of ethylene, propene and ethylene oxide under the same conditions. The aim of the present letter is to describe briefly the conditions and the form of these thermooscillations, which were observed for the first time during the catalytic oxidation of ethylene oxide.