SELECTIVE O-ALKYLATION OF PHENOL WITH METHANOL OVER SULFATES SUPPORTED ON GAMMA-AL2O3

The reaction of phenol with methanol was studied in a fixed-bed reactor system as a potential source for the production of methyl aryl ethers. For this reason, the performance of alumina-supported catalysts impregnated with sulphate salts of metals of the groups VIIB and IIB was studied. The effects of reaction temperature, reaction time, type of metal, metal content, and potassium content on the selectivity of methyl aryl ethers (MAE), as well as the phenol conversion and the yield of MAE, were established. The reaction temperature and the potassium content were found mainly to affect the selectivity of the catalyst, the phenol conversion, and the yield of MAE. Empirical equations were derived which proved to be useful for predicting the performance of a catalyst over a broad range of reaction conditions. A catalyst (K-3(S)) containing only potassium (3 wt%) in the form of potassium sulphate supported on gamma-alumina was found to have the most promising performance compared to those reported in the literature in terms of MAE selectivity and phenol conversion at atmospheric pressure (selectivity of MAE = 98%, phenol conversion = 65 wt%). The catalyst remains stable over a broad range of temperatures (290-330 degrees C). Ks is an inexpensive catalyst, showing major selectivity advantages and product composition (anisole, 92 wt%; o-cresol, 8 wt%) and a low coke production (7 wt%). The presence of potassium sulphate in the catalyst proved to be the controlling factor for the production of MAE and it was found to be the active phase of the catalyst. The MAE selectivity of potassium sulphate catalysts is determined by the potassium content of the catalyst, while its optimum value is achieved, when acid sites of medium strength (+ 1.5 < H-0 less than or equal to + 4.8) with low acidity values (22 x 10(-4) mmol/m(2)) exist on their surface. (C) 1995 Academic Press, Inc.