Bleaching of commercial pulps with H2O2 catalyzed by heteropolyacids

Several studies have taken place in order to find an alternative bleaching process which replaces the chlorinated compounds with environmentally frien dly agents as well as recycles the effluents, instead of discharging them. In this study we employed hydrogen peroxide and Keggin-type heteropolyacids for the selective removal of lignin from the pulp. We used heteropolyacids containing W, Mo and Mo/V, in aqueous solution, to bleach different commer cial pulps with hydrogen peroxide. Kraft pulp, water, heteropolyacid (5 mmo l l(-1)) and H2O2 (1% why) were combined to obtain a final pulp consistency of 3%. The mixture was heated in a glass reactor to 60, 80 or 100 degrees C for 2 or 4 h. The best experiment furnished a pulp with a Kappa number of 3.2 and a viscosity of 17.1 cP, using H3PMo12O40 and 1% H2O2 (w/w) at 60 d egrees C for 4 h. (C) 1998 Published by Elsevier Science Ltd. All rights re served.