Kraft pulp bleaching using dimethyldioxirane: stability of the oxidants

Abstract

Dimethyldioxirane (DMD) is a cyclic peroxide made by oxidizing acetone with peroxymonosulfate (PMS) in water buffered at pH 7.5 using sodium bicarbonate. It has been shown that DMD generation can be achieved in situ within a pulp suspension allowing very selective TCF bleaching of kraft pulp. This process involves simultaneous generation of DMD, reaction of PMS and DMD with residual lignin, and spontaneous decomposition of both oxidants. The first part of this work is a kinetics study of the decomposition of PMS and DMD as a function of pH under conditions similar to those for in situ bleaching. The effect of chelation as well as the effect of transition metal ions on decomposition rate was also investigated. DMD is very sensitive to pH and its half-life is very short under alkaline conditions. The presence of any transition metal ion that can be involved in a one-electron transfer is detrimental to DMD stability. However, fast reaction of DMD with pulp almost counteracts the effect of metal ions.Key rvorrls: bleaching, peroxyn~onosulphate, dimethyldioxirane, metal ions, kinetics, decomposition, kraft pulp.RCsumC : Le dimkthyldioxirane (DMD) est un peroxyde cyclique obtenu par oxydation de l'acktone avec le peroxymonosulfate (PMS) en milieu aqueux tamponnC i pH 7,5 i I'aide du bicarbonate de sodium. La synthkse du DMD, lorsque rCalisCe in situ dans une suspension de pate kraft, reprCsente un procCdC de blanchiment sans chlore trks selectif. Au cours de ce prockdC, la synthkse du DMD, l'attaque de la lignine rksiduelle par le DMD et le PMS ainsi que la dCcomposition naturelle de ces deux oxydants se produisent simultanCrnent. Le premikre pnrtie de ce travail consiste en une ttude cinitique de la dCcoinposition du DMD et du PMS en fonction du pH dans des conditions similaires i celle du procCdC de blanchiment in situ. L'effet de la chelation ainsi que la prCsence d'ions mCtalliques ont Cgalement CtC CtudiCs. La dCcomposition du DMD est trks sensible au pH et des demi-vies trks courtes sont observtes en milieu basique. La prCsence de mCtaux de transition pouvant Cchanger un Clectron s'avkre ntfaste j. la stabilitk du DMD mais la vitesse de rkaction du DMD diminue grandement cet effet ntgatif.

Catalysis and Activation of Oxygen and Peroxide Delignification of Chemical Pulps: A Review

“…since other agents require free phenolic hydroxyl groups to act upon. On the same front, Bouchard and coworkers studied the stability of DMD under kraft pulp bleaching conditions (127). This work showed that the decomposition of DMD was accelerated by the presence of transition metals.…”

The Role of Ferulic Acid Removal during Bleaching of Wheat Straw Mechanical Pulp with Peroxygen Reagents

“…Bleached pulps were diluted with water and acidified to about pH 5 by sodium metabisulfite prior to DMD is reported to be a very effective bleaching agent for chemical pulps (Ragauskas 1993;Lee et al 1993). In pulp bleaching, DMD can be added as an isolated form by reacting PMS with acetone in a buffer and then distilling off the DMD as an acetone solution or generated in situ by mixing acetone and buffer with pulp then adding the required amount of PMS (Ragauskas 1993;Lee et al 1994;Bouchard et al 1998). The use of in situ generated DMD in pulp bleaching is probably more efficient and practical due to the low yield and instability of isolated DMD (Ragauskas 1993;Lee et al 1994).…”

“…Given a charge of active oxygen, the amount of added acetone may be an important factor influencing the bleaching efficiency of in situ generated DMD. In the previous reports (Ragauskas 1993; Lee et al 1994;Allison et al 1997;Bouchard et al 1998), a broad range of acetone-to-active oxygen ratio was used in chemical pulp bleaching. A minimum amount of acetone must be applied to allow the formation of an adequate concentration of DMD.…”

Total Chlorine-Free Bleaching ofPopulus deltoidesKraft Pulp by Oxone

“…Current exotic chemicals that are used in various bleaching sequences include peroxyacetic acid [5], peroxyformic 2 International Journal of Carbohydrate Chemistry acid [5], potassium peroxymonosulfate (Oxone) [5,6], potassium peroxymonophosphoric acid [7], and dimethyl dioxiranes [8].…”