Molybdo-vanado-phosphate heteropolyanion catalyzed pulp ozonation in acetone/water solution. Part 1. Effect of process variables

The effect of solvent and catalyst concentration, pH and ionic strength on ozone bleaching of commercial eucalypt kraft pulp in acetone-water solution in the presence of Keggin-type heteropolyanion [PMo7V5O40]8− (HPA-5) has been examined and compared with conventional (solvent/catalyst free) ozonation systems. The solvent content and medium acidity were found to be the principal factors affecting ozonation efficiency. Increase in acetone concentration from 6% to 60% (w/w) led to gain in pulp brightness by 20.6% and delignification degree by 28.4%. Within the operative pH 1-2 range required for ozonation, the increase in pulp brightness by 7.6% and delignification degree by 18.1% was observed with acidity change from pH 1 to 2. The HPA-5 concentration of 1 mM was found to be optimal for effective pulp ozonation in acetone solution. The role of the Donnan effect was examined. Increase in ionic strength (cation concentration) up to 0.25 M caused significant bleaching improvement.