EFFECT OF H2O2 CATALYZED BY MOLYBDATE ON THE REDUCTION OF DISSOVLED AND COLLOIDAL BLEACHING PROCESS OF ONP

At present, the process of alkaline peroxide hydrogen is widely used in the bleaching of waste paper pulp. The stronger alkaline condition has been regarded as one of the main reasons for higher DCS (dissolved and colloidal substance) content in the bleached pulp. In this article, The molybdate has been applied to catalyze peroxide hydrogen at weak acid condition (pH 5) to bleach ONP (old newsprint pulp) which purpose is to test the possibility of reducing DCS (dissolved and colloidal substance) generation, while the whiteness, viscosity, yield and yellowing number were examined to investigate the quality of bleached pulp compared with conventional process of alkaline peroxide hydrogen. The results shows that the whiteness of ONP bleached by peroxide hydrogen catalyzed with molybdate is a little lower (47.8% ISO) than the results from alkaline peroxide hydrogen (49.3% ISO), but some advantage have been found on the viscosity, yield and yellowing number. The results concerning with the analysis of DCS shows that alkaline condition has strong effect on the generation of DCS, but peroxide hydrogen dosage does not have so much effect. For the results of weak acid bleaching catalyzed by molybdates, much lower content of DCS has been found. UV analysis shows that similar content is found in the liquor of alkaline and weak acid catalyzed bleaching process. In order to get more understanding, MTBE was used to extract the DCS solution into hydrophobic and hydrophilic part. Most of the DCS are hydrophilic substance that means the polysaccharide has been degraded during the process of bleaching, especially under the alkaline condition. After further investigations, weak acid peroxide hydrogen catalyzed by molybdates is expected to be an alternative bleaching process for ONP aiming to reduce the releasing of DCS.