Composition of the organic components in polyxometalate (POM) liquors from kraft pulp bleaching

Abstract

Promising results from the selective oxidative delignification of kraft pulp with polyoxometalates (POMs) prompted interest in elucidating the lignin oxidation mechanism. The degradation of lignin model compounds and residual lignin in kraft pulps, upon treatment with POMs was studied and differences in the reaction mechanisms between guaiacyl (G-) and syringyl (S-) units were found. Our studies are aimed at comparing soluble lignin products resulting from POM treatment of softwood and hardwood kraft pulps to further explore the behavior of G/GS units of lignin incorporated in the pulp matrix. Oxidative treatment of unbleached kraft pulps, commercial mixed softwood and laboratory birch, was performed using POM solutions containing the active [SiVW11O40]5anion. The solutions obtained after POM bleaching were extracted with organic solvents of different polarity, after acidification to pH2 and centrifugation/filtration. Only low-molecular weight lignin fragments were dissolved during POM treatment since acidification did not induce lignin precipitation. The extracts were analyzed by NMR spectroscopy and GC-MS. The majority of degradation compounds were carbonyl and carboxyl aromatic compounds indicating extensive oxidation reactions on lignin. These reactions included C[alpha]-C[beta] and alkyl-aryl cleavage.

Citation

Bujanovic, Biljana; Hirth, Kolby C.; Ralph, Sally A.; Reiner, Richard S.; Atalla, Rajai H. 2007. Composition of the organic components in polyxometalate (POM) liquors from kraft pulp bleaching. Proceedings of the 14th International Symposium on Wood Fibre and Pulping Chemistry : 2007 June 25-28, Durban, South Africa. Kloof, South Africa : TAPPSA, 2007: [9] pages.