Treatment of Combined Bleach Plant Effluents via Wet Oxidation over a Pd−Pt−Ce/Alumina Catalyst

Abstract

Supported Pd−Pt−Ce/alumina catalyst showed promising activity over traditional iron oxide, zinc oxide-type, oxidation catalysts for the treatment of pulp mill effluents. However, hot solution coupled with chlorine ions in the oxidation medium not only requires special process equipment but also often leads to catalyst deactivation due to metal leaching of catalyst. Dissolution of catalyst in the reaction medium also requires a further process step to remove the toxic metal ions from the treated stream. To address these problems, we proposed a combined treatment approach for catalytic oxidation of the bleach plant effluents from a softwood kraft pulp mill. Experimental study indicated metal leaching from catalyst can be significantly reduced even avoid with the combined stream at temperatures ranging from 403 to 443 K and at 1.5 MPa in a slurry reactor. Pd−Pt−Ce/alumina catalyst showed promising activity for wet catalytic oxidation of the combined streams. At 443 K and 1.5 MPa, 65% total organic carbon (TOC) and 99% color were removed after 3 h treatment, while only 10% TOC and 79% color reduction were achieved without catalyst at the same experimental conditions. Another advantage with combined treatment approach is that that cheap ferrous-based alloy may be used as construction material for process equipment. Based on the experimental results, implications for process development are discussed.