SYNTHESIS OF DIMETHYL ETHER (DME) FROM METHANOL OVER SOLID-ACID CATALYSTS

The catalytic conversion of methanol to dimethyl ether (DME) has been studied over a series of solid-acid catalysts, such as gamma-Al2O3, H- ZSM-5, amorphous silica-alumina, as well as titania modified zirconia. All the catalysts are active and selective for DME formation. The app arent activation energy for DME formation over gamma-Al2O3 is ca. 25 k cal/mol, a value that increases to ca. 37 kcal/mol upon the addition o f 23 Torr of H2O to the reagent. The rate of methanol dehydration decr eases with increasing acidity (silica content) over the amorphous sili ca-alumina catalysts. Although H-ZSM-5 with Si/AL = 25 is the most act ive among the catalysts tested, the DME selectivity is only 20% at 280 degrees C, a typical temperature used in the syngas-to-methanol proce ss. An amorphous silica-alumina catalyst with 20 wt.-% silica content (SIRAL20) exhibits the best catalytic performance of those tested at 2 80 degrees C.