TRAITEMENT DE CONDENSATS PROPRES DES EVAPORATEURS PAR OXYDATION CATALYTIQUE

摘要

Foul and clean condensates, produced during the evaporation of black liquor, are mainly composed of water but contain significant concentration of methanol and sulfides. Steam stripping the foul condensate removes most of the odourous species, but the untreated clean condensate contains sufficient reduced sulfur species to prevent its reuse within the pulp mill. In addition, the reduced sulfur species give rise to pungent odours from the effluent treatment system. Chemical oxidants are only partially effective for odour abatement - the products of the oxidation reaction of mercaptant also are odourous. In this paper, the use of catalytically enhanced oxidations is described. Sodium hypochlorite is used in conjunction with a nickel-based catalyst to treat kraft pulp mill clean condensate. The results of this laboratory study demonstrate that the catalyst provides for virtually complete oxidation of the reduced sulfur species to non-odourous sulfonic acids or sulfones. In addition, the COD of condensate is reduced by 10%; for identical chemical additions, no reduction in COD was observed in the absence of the catalyst. It was also observed that there is no hypochlorite present in the treated effluent. This process is suitable for treating clean condensates, and thereby permitting their reuse within the pulp mill.