POLYOXOMETALATE-CATALYZED OXYGEN DELIGNIFICATION PROCESS: KINETIC STUDIES, DELIGNIFICATION SEQUENCES AND REUSE OF HPA-5-Mn^II AQUEOUS SOLUTION

Abstract

Kinetic studies on the use of Mn-assisted molybdovanadophosphate polyoxoanion (HPA-5-Mn^II) as catalyst for the aerobic delignification of Eucalyptus globulus kraft pulps were performed. The delignification as measured by the decrease of kappa number corrected to the lignin content in pulp followed pseudo-first-order reaction kinetics with a rate constant of 4.0 × 10⁻³ min⁻¹, while carbon dioxide production followed pseudo-zero-order kinetics with a rate constant of 0.031 g Kg⁻¹ min⁻¹. Aqueous delignification filtrate containing the polyoxometalate (POM) HPA-5-Mn^II could be used in 16 multiple delignification cycles without showing significant changes in the kappa number of the delignified pulps and presenting only slight decreases in their intrinsic viscosity. Delignification sequence including a conventional alkaline-oxygen delignification stage followed by a POM stage generated a kappa number decrease of 76% while intrinsic viscosity had a drop of only 23%.

Keywords:

• Bleaching sequence
• Catalysis
• Kinetics
• Oxygen delignification
• Polyoxometalates
• Selectivity

Acknowledgments

The authors wish to thank University of Aveiro for the financial support of this work and to Grant Culbertson for the English and technical support.