Zur Abscheidung von Methyljodid and Silberzeolithen / Investigations on the Fixation of Methyl Iodide by Silver Zeolites

Abstract

Abstract Alkyl iodides especially methyl iodide from the offgas of reactors and of reprocessing plants are difficult to remove. In earlier investigations it was shown that silver zeolites are qualified for a total fixation of methyl iodide, only when these sieves were exhaustively loaded with silver ions. In order to explain why only exhaustively loaded silver zeolites of type X are able to remove methyl iodide completely from the air, the reaction products from the chemisorption reaction were identified. The proportion of the silver ions that had reacted was calculated. Exhaustively loaded Ag-LMS-X pellets heat-treated at 400 °C (water content 0.94% by wt.) react with CH3I to form dimethylether. If the same pellets were gently dried with P2O5 (water content 15% by wt.) dimethylether and methanol were the products. The identification was done by gas chromatography and infrared spectroscopy. The chemisorption reaction can be described in the following way: a) CH3I + HOH+Ag+ →AgI + CH3OH + H+ b) CH3I + CH3OH+Ag+ → AgI + CH3OCH3 + H+ If only small concentrations of methyl-iodide and an excess of water vapour are present only methanol is expected. The experimental results are in good agreement with the assumptions.