An assessment of the suitable operating conditions for the CeO 2/γ-Al 2O 3 catalyzed wet air oxidation of phenol

Abstract

It has been shown that the CeO 2/γ-Al 2O 3 catalyst is a feasible alternative to CeO 2 for the catalytic wet air oxidation (CWAO) of phenol because it remains an effective catalyst and yet is cheaper to prepare. In this study, we found that the optimal cerium content in the CeO 2/γ-Al 2O 3 catalyst was 20 wt.%, regardless of catalyst loading. Furthermore, at 180 °C, with a phenol concentration of 1000 mg l −1, and an O 2 partial pressure of 1.0 MPa or 1.5 MPa, the optimal catalyst loading was 3.0 g l −1. The efficacy of CWAO of phenol improved with O 2 partial pressure, although the effects of O 2 pressure were more significant between 0.5 MPa and 1.5 MPa than between 1.5 MPa and 2.0 MPa. After 2 h of reaction, approximately 100% phenol conversion and 80% total organic carbon (TOC) removal was recorded at 180 °C, 1000 mg l −1 of phenol and 3.0 g l −1 of catalyst. Because these percentages subsequently leveled off, it is suggested that 2 h is a suitable time over which to run the reaction. The efficacy of CWAO of phenol decreased as initial phenol concentration was raised (from 400 to 2500 mg l −1), with the exception of phenol conversion after about 2 h, for which 400 mg l −1 produced the lowest phenol conversion figure. Higher phenol concentrations require both catalyst loading and O 2 partial pressure to be increased to maintain high performance. For example, for 2000 mg l −1 and 2500 mg l −1 phenol, nearly 100% phenol conversion and 90% TOC removal after 4 h of reaction at 180 °C required 4.0 g l −1 of catalyst and 2.0 MPa.