N-Alkylation of Aniline with Methanol over CrPO4and CrPO4–AlPO4(5–50 wt% AlPO4) Catalysts

The vapor-phase alkylation of aniline with methanol was carried out at atmospheric pressure and different temperatures (573–673 K) and feed rates over CrPO4(CrP) and CrPO4–AlPO4(CrAlP, 5–50 wt% AlPO4) catalysts. Aniline methylation was a pseudo-first-order process with respect to aniline concentration. The effect of surface acidity on aniline alkylation, as measured by pyridine and 2,6-dimethylpyridine adsorption, is discussed. The influence of feed rate (WHSV), time-on-stream and temperature on both activity and product selectivity was also investigated. Alkylation is a sequential reaction process, in which methylation of aniline produces N-methylaniline (NMA), then N,N-dimethylaniline (NNDMA) and subsequently N,N-dimethyltoluidines (NNDMT,p->o-). N-methylation products (NMA+NNDMA) are predominant with a selectivity over 90 mol% in the temperature range 573–673 K. Selectivity to N,N-dimethylaniline is enhanced as reaction temperature and/or contact time increases. N,N-dimethyltoluidines are only present in very small amounts at higher temperatures and/or contact times.