Catalysis and Activation of Oxygen and Peroxide Delignification of Chemical Pulps; A Review, 2000 Pulping / Process & Product Quality Conference Proceedings

M. Suchy, D. S. Argyropoulos--Oxygen and hydrogen peroxide have always been technologically attractive oxidants to the pulp and paper industry, with their significance becoming of increasing importance as environmental regulations become more stringent. The fact that molecular oxygen has a triplet ground state whose direct interaction with singlet-state organic molecules is a spin-forbidden transition, limits its oxidative selectivity. Industrially, it will be extremely beneficial to fix molecular oxygen within organic or inorganic compounds capable of transferring it selectively to an organic substrate such as lignin. Since a variety of research endeavours have already been made to catalyse oxygen delignification and activate peroxide delignification of chemical pulps this paper initially attempts to critically review them. In addition, this effort covers peracids, which can be considered as organic molecules containing active oxygen. Another example of an inorganic molecule containing active oxygen is peroxymonosulfuric acid, which was shown to improve oxygen delignification of kraft pulps. Dioxiranes have also been shown to possess the ability to transfer a single activated oxygen atom onto aromatic and unsaturated substrates. As such, dimethyldioxirane is reviewed for its potential as a novel and selective non-chlorine containing bleaching agent for the production of fully-bleached totally chlorine-free pulp. Another form of activated oxygen may also be present within peroxycarboximidic acid, which is thought to be an intermediate in the interaction of cyanamide with peroxide, proposed as a peroxide activator for the bleaching of sulphite pulps. Finally, our critical review covers the recent scientific and patent literature which contains a number of examples where transition metals have been used as additives in peroxide and oxygen delignifications i.e. tungsten, molybdenum, certain manganese complexes, silicomolybdates and polyoxometalates.