Influence of reaction products on the selective oxidation of ethene

Abstract

The kinetics of the selective oxidation of ethene in air over an industrial silver on a-alumina catalyst were studied. Special attention was paid to the influence of the reaction products on the reaction rates of epoxidation and complete combustion. Kinetic data were obtained in two different types of internal recycle reactor and in a cooled tubular reactor, and were fitted separately to several reaction rate expressions based on different kinetic models. A Langmuir-Hinshelwood mechanism, in which adsorbed ethene reacts with adsorbed molecular oxygen, was chosen as the best kinetic model. The reaction products compete for adsorption on the active sites and reduce the rates of both reactions. Carbon dioxide enhances the selectivity towards ethene oxide, whereas water has almost no influence on the selectivity. The fitting of the three individual data sets obtained in the three reactors results in accurate, but different, reaction rate expressions, whereas the fitting of the three data sets simultaneously results in less accurate reaction rate expressions. The systematic deviations found may be explained, to some extent, by differences in the operating regimes in each reactor. The main reason for the deviations is probably the different catalyst activities in the three reactors caused by poisoning. The effect of the addition of products to the feed on the behaviour of the cooled tubular reactor can be described reasonably well by a mathematical model in which the kinetic equations obtained in the laboratory reactors are incorporated. The results of these simulations are sensitive to the kinetics used.

Oxidation of ethene in a wall-cooled packed-bed reactor

“…More information on the activation procedure is given in Schouten et al (1994). checked for a uniform activity of the catalyst over the length of the tube by repacking the catalyst bed.…”

“…To find causes of such inconsistencies the present authors set up a thorough experimental and theoretical programme. Accurate and well defined experiments have been performed in which kinetic parameters [see Borman and Westerterp (1994) and Schouten et al (1994)] and heat transport parameters [see Borkink and Westerterp (1992b) and ] are determined separately_ In this publication the separately determined parameters are used for the modelling of the reactor. Experiments performed in a pilot plant with one, single reactor tube are critically compared with the results of model calculations so that the reliability of different models can be evaluated.…”

“…The combustion of ethene oxide, reaction 3, was found to be negligible under our operating conditions. To determine the kinetics, data from an internal recycle reactor have been used completed with data at low product concentrations from a cooled tubular reactor using a differential interpretation method [see Schouten et al (1994)]. …”

Ethylene epoxidation over supported silver catalysts – influence of catalyst pretreatment on conversion and selectivity

“…Optimal DCE levels for stable catalyst performance are reported to be in the range 1–2 ppm . It has also been reported that the selectivity can be improved by blocking sites responsible for total oxidation via addition of CO 2 to the reactor . The selectivity is improved through reactions of the dissociatively adsorbed oxygen and carbon dioxide forming carbonate species …”

Real‐time optimization of a tubular reactor with distributed feed

“…The epoxidation of ethylene produces ethylene oxide, which is an important industrial chemical in the production of ethylene glycol and other chemicals. 21 The reaction scheme is generally considered to be given by the following parallel network 13,15 :…”