Platinum catalysed wet oxidation of phenol in a stirred slurry reactor - The role of oxygen and phenol loads on reaction pathways

The catalytic wet oxidation of phenol was studied in a slurry phase continuous stirred tank reactor (CSTR) using platinum on graphite support as a catalyst. The investigation was carried out in the temperature range 120-180degreesC and at total pressure of 1.8 MPa. while the phenol feed concentration was varied between 5 and 70 mol/m(3), and oxygen partial pressures between 0.01 and 0.8 MPa. It was found that both the oxygen load and the stoichiometric oxygen excess determine the extent of oxygen coverage on the platinum surface, which influences the reaction pathways and selectivity to CO2 and H2O. A fully oxidised platinum surface resulted into catalyst deactivation (over-oxidation), which favoured the formation of p-benzoquinone and polymeric products. Whereas free platinum surface was vulnerable to poisoning by carbonaceous compounds, a fully reduced platinum surface favoured the formation of acetic and succinic acids which are difficult to oxidise. A reaction scheme for platinum catalysed phenol oxidation in liquid phase is proposed. (C) 2003 Elsevier Science B.V. All rights reserved.