We report new information concerning the effect of oxygen concentration and catalyst concentration and identity [MnBr2, CoBr2, ZrBr4, and Mn(OAc)2] on the partial oxidation of p-xylene in dense water from 250 to 380 °C. Water is a more environmentally benign replacement for the acetic acid solvent used commercially. We used a 440 mL Hastelloy batch reactor for all experiments and monitored O2 consumption and product (including COx) formation. Increasing the catalyst concentration at 300 °C significantly increased terephthalic acid yields. MnBr2 was the most active catalyst of those we assessed. Increasing the initial O2 concentration beyond a modest excess did not significantly alter the terephthalic acid yield, but it increased the CO2 yield. Injecting supplemental O2 midreaction, however, did cause the terephthalic acid yield to increase. The highest terephthalic acid yields (>80%) occurred at 300 °C, [p-xylene]0 = 0.02 M, [O2]0 = 0.10 M, [Br] = 0.014 M, and t = 5-15 min. These yields are the highest reported to date from this reaction in high-temperature liquid water. Moreover, under these conditions and t = 15 min, COx yields were below 2% and reaction intermediates were not detected.
All Science Journal Classification (ASJC) codes
- Environmental Chemistry