Abstract
Sulphonic ion-exchange resins are very hygroscopic and readily adsorb water. As a result, the catalytic activity of this type of ion-exchange resin decreases substantially when water contaminates the reaction medium. The influence of water on the gas-phase decomposition of methyl tert.-butyl ether (MTBE) at 50.5°C catalysed by the macroporous ion-exchange resin Amberlyst 15 was studied. The results show that the addition of small amounts of water causes a very strong decrease in decomposition rate of MTBE. A set of Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic models are proposed. The statistical discrimination between them permits the selection of two models whose only difference lies in the adsorption model of MTBE: on two active centres with or without dissociation. The values of the parameters of these models (overall kinetic constant, kK IK M; MTBE adsorption constant, K E; and water adsorption constant, K W) obtained from the fit of data coincide, within the limits of experimental error, with those obtained from the fit of each of the curves r E vs. P E corresponding to different amounts of water in the feed. It is concluded that water reduces the rate of the MTBE decomposition reaction by occupying active centres in a competitive way with the ether. Finally, the values for K W in the literature agree fairly well with those determined in this work.
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