DEGRADATION OF PULP-MILL EFFLUENT BY OXYGEN AND NA-5[PV2MO10O40], A MULTIPURPOSE DELIGNIFICATION AND WET AIR OXIDATION CATALYST

Water-soluble salts of polyoxometalate (POM) anions can be used as (ne t) catalysts for selective, effluent-free oxygen delignification (blea ching) of unbleached kraft wood-pulps. Essential to this process is th e use of the POM anions as catalysts for the wet oxidation of the lign in removed from the pulp fibers. In anaerobic bleaching, a 0.5 M solut ion of alpha-Na-5[PV2Mo10O40] (POMox) is combined with wood pulp and t he mixture heated to 125 degrees C. This treatment dissolves certain o rganic compounds (some lignin and polysaccharide fragments) with a com bined chemical oxygen demand (GOD) of 1500-2000 mg of O-2/L. Before th e solution can be used again for bleaching, the POM anions (POMred) mu st be reoxidized and the dissolved organic compounds removed. Here, a second function of the POM anions is realized. They are used under mil d conditions (150 degrees C, 0.7 MPa of O-2) to catalyze the wet air o xidation of the dissolved organic compounds. After several cycles of a naerobic bleaching and wet oxidation, a steady-state condition in COD (at ca. 550 mg of O-2/L) is achieved.