Synthesis of anisole by vapor phase methylation of phenol with methanol over catalysts supported on activated alumina

The synthesis of anisole by vapor phase methylation of phenol with methanol over activated alumina (AA) supported catalysts was investigated in a fixed bed reactor. KH2PO4/AA gave the best performance among the eight tested catalysts. The catalyst was prepared by loading KH2PO4 on AA and then calcining at the optimized temperature of 700 °C for 8 h. In the vapor phase reaction, the level of anisole yield (LAY) has a maximum at 400–450 °C when the temperature varied from 300 to 500 °C, which decreased slightly with increasing WHSV and increased distinctly with increasing mole fraction of methanol. On comparing O-methylation and C-methylation of phenol, a low temperature, high WHSV (short residence time), and a low methanol concentration over the KH2PO4/AA catalyst with higher K contents were found to increase anisole selectivity by O-methylation of phenol. The reaction routes to the major products and the catalytic mechanism were suggested, and a ‘K-acid’ bifunctional process may be a critical factor to the formation of anisole.

Graphical AbstractUnder catalysis of KH2PO4/Al2O3, phenol and methanol was activated by K and Al sites respectively. Anisole yield decreased with increasing space velocity, increased with increasing methanol fraction, and appeared a maximum value with increasing temperature.Figure optionsDownload full-size imageDownload as PowerPoint slide