N-ALKYLATION OF ANILINE WITH METHANOL OVER ALPO4-AL2O3 CATALYSTS

Amorphous AlPO4-Al2O3 (5-25 wt% Al2O3, APAl-A) systems were selective catalysts for the N-alkylation of aniline with methanol. The methylati on reaction (that was carried out in a continuous down-flow reactor op erating at atmospheric pressure, 523 K and aniline feed rates over 3 x 10(-6) mol s(-1)) is a pseudo-first order process with respect to ani line concentration, taking place through consecutive formation of N-me thyl and NN-dimethylanilines. Also, there is always more N-methylanili ne (NMA) than N,N-dimethylaniline (NNDMA). Increasing reaction tempera ture enhances the selectivity of NNDMA. AlPO4 and Al2O3 are slightly a ctive, but AlPO4-Al2O3 catalysts exhibit significantly higher activity (an order of magnitude more active) and, besides, there is a slight i ncrease in activity on increasing Al2O3 loading up to 15 wt%, thereby showing that APAl-A catalysts are suitable for selective obtaining N-a lkylation products. The effect of surface acidity on aniline alkylatio n activity is discussed. Strong acid sites are not required for the N- methylation of aniline, whereas, weak to moderate acid sites seem to b e responsible for this reaction. Furthermore, there is no catalyst dea ctivation by coke deposition, whereas, the addition of pyridine or 2,6 -dimethylpyridine deactivate the catalyst. (C) 1998 Elsevier Science B .V.