Abstract
In previous work by the authors, aspects of the surface chemistry connected with methyl chloride synthesis over an η-alumina catalyst have been examined. This communication considers a role for Group 1 metal salts to modify the catalytic performance of the well characterised η-alumina catalyst. Firstly, based on a previously postulated mechanism for the reaction of methanol on η-alumina, a mechanism for methyl chloride synthesis over the η-alumina catalyst is proposed. Secondly, the validity of the new mechanism is tested by observing how the (i) type and (ii) loading of the Group 1 metal salt may perturb methyl chloride selectivity. The outcomes of these measurements are rationalised with reference to the postulated mechanism. Overall, this study represents an example of how a proposed reaction mechanism has been used to inform and guide a catalyst development strategy for a large-scale industrial process.
Highlights
Methyl chloride is an important industrial product with a global capacity of ca. 900 ktonne
In order to improve the understanding of why a doped h-alumina catalyst should convey favourable catalytic performance when applied to synthesis, we examined aspects of synthesis-related surface chemistry over an un-doped commercial grade h-alumina catalyst.[8]
Linearity for both methyl chloride and dimethyl ether production is maintained over this temperature range and yields apparent activation energies of 88.3 (Æ0.9) and 94.8 (Æ1.1) kJ molÀ1 respectively, with the error representing the standard deviation from three replicate runs
Summary
Methyl chloride is an important industrial product with a global capacity of ca. 900 ktonne. It is a valuable starting material in the production of higher chlorinated products, silicones, and methyl cellulose. It has applications as a methylating agent.[1,2,3] One method for the large scale manufacture of methyl chloride is performed via the hydrochlorination of methanol over a solid acid catalyst at elevated temperatures, eqn (1). Selectivity to methyl chloride is reduced by the reaction shown in eqn (2), where the alcohol is converted to dimethyl ether. The reactions shown in eqn (1) and (2) are both reversible, so at any given feed composition and temperature there is an equilibrium product composition. A catalyst that has received considerable application is g-alumina.[4,5] Hydrochlorinations using a ZnCl2/Al2O3 catalyst show selectivity to CH3Cl.[6]
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