Controlled manipulation of selectivity between O- versus C-alkylation in methylation of phenol using ZrO2-WO3- SiO2 catalysts

Abstract

Anisole and o-cresol are very important chemicals which could prepared from phenol using different catalytic routes favoring either O- or C-alkylation. In the methylation of phenol with methanol, the selectivity to either anisole or o-cresol could be manipulated using a suitable tailor-made catalyst having a proper balance of acidic and basic sites. In the current work, a series of compositions based on zirconium, tungsten and silicon oxides (xZrO2-yWO3-SiO2) were prepared and employed as catalysts in fixed bed methylation of phenol. In the absence of silica as support, methylation of phenol over 20% WO3-ZrO2 and 40% WO3-ZrO2 favored predominantly C-alkylated product o-cresol. Among various combinations 10% ZrO2-30% WO3-SiO2 gave the best results and selectivity to the desired product anisole. Effect of various parameters affecting selectivity to anisole or o-cresol were studied systematically. The mechanism of formation of different products with reference to catalyst structure and functionality was explored in detail. The process parameters could be optimized to get the desired product. Thus, the proper choice can be made to choose the selectivity of O-versus C-alkylation using a single catalyst. The time on stream study was carried out for 16 h to find that the catalyst was stable and could be regenerated.