Influence of pH on the wet oxidation of phenol with copper catalyst

Abstract

This work reports the influence of pH on the catalytic wet oxidation (CWO) of phenol performed with a commercial copperbased catalyst. The results obtained show that pH is a critical parameter able to modify the chemical stability of the catalyst, the significance of the oxidation reaction in the liquid phase, the reaction mechanism and, consequently, the oxidation route of phenol. Experiments have been carried out to study the mentioned aspects. Stirred basket and fixed bed reactors (FBRs) have been employed, at 140°C and at 16 bar of oxygen pressure. Three initial pH values have been used: 6 (the pH of the phenol solution), 3.5 (adjusted by H 2 SO 4 ) and 8 (by addition of Na 2 CO 3 ). Furthermore, some phenol oxidation runs without solid catalyst but with different concentrations of copper in solution have been accomplish at pH o ¼ 3.5. At acid pH, important leaching of copper from the catalyst to the solution was achieved, finding this negligible at pH 8. It was found that the major contribution to the phenol conversion reached at acid pH by using the solid catalyst was due to the catalytic activity of the leached copper. Both oxidation mechanisms at acid and basic conditions have been elucidated to explain the differences in the type and distribution of the intermediates obtained. The catalytic phenol oxidation route found at pH ¼ 8 comprises intermediates less toxic than phenol while at acid pH the cyclic intermediates formed as first oxidation intermediates are far more toxic than phenol.

Catalytic wet peroxide oxidation of phenol over Cu–Ni–Al hydrotalcite

“…5. It was inconsistent with the results obtained by some previous researchers (Liotta et al, 2009;Santos et al, 2002Santos et al, , 2005Zazo et al, 2005) ; temperature: 30°C; pH = 6.5). pressure, and next into maleic acid, and finally into oxalic acid, formic acid and CO 2 (Fig.…”

Treatment of Glyphosate Mother Liquor by Catalytic Wet Oxidation

“…And COD removal ratio decreased slightly, the main reason is that iron ion as homogeneous catalyst in reactions is dissolving out from reaction kettle under acidic conditions of corrosion, improved the conversion rate of COD. In addition, Santos [3] studies showed that the leaching of copper under acidic conditions increased, the formation of homogeneous Cu 2+ led to an increase in COD removal. The pH value has obvious effect on phosphate production ratio.…”

Catalytic behaviour and copper leaching of Cu0.10Zn0.90Al1.90Fe0.10O4spinel for catalytic wet air oxidation of phenol

“…x = 1.90). In this paper, copper was introduced into the ZnFe 0.10 Al 1.90 O 4 catalyst with the aim of extending the working pH range, as the reported copper-based catalysts can be used at both acid and basic solution pH [6]. Because copper ions leaching out from the solid catalyst is an open question in the CWAO reaction, the intention of the present study was to examine the stability of copper species in the Cu 0.10 Zn 0.90 Al 1.90 Fe 0.10 O 4 spinel-type catalyst.…”

“…Different methods for treating these wastewaters have been widely reported [1,2], and particular attention has been devoted to the catalytic wet air oxidation (CWAO) process [3]. Although the development of inexpensive and efficient solid catalysts used in CWAO is of great interest and many supported or unsupported metal oxides such as Fe/C [4], Cu−Zn−Al−O [5], Cu−Cr−Al−O [6] and Mn−Ce−O [7] have been tested, the threat of catalyst deactivation by polymer deposition and leaching of active compounds has emerged as a major drawback.…”