Bleaching of wood pulp

The perhydroxyl ion, OOH , derived from the dissociation of hydrogen peroxide in alkaline solution, is generally considered the active agent in the bleaching of wood pulp using hydrogen peroxide. This ionization may be expressed by the following reversible reaction ... 

A particularly interesting reaction (and one of considerable commercial value in the BOROL process for the in situ bleaching of wood pulp) is the production of dithionite, S204 , from SO2 ... 

Alkaline Extraction Stage of Bleaching of Wood Pulps, TAPPI Monograph Series No. 27, New York, 1964. 

O. Samuelson Suppression of undesirable reactions during oxygen bleaching of wood pulp... 

It is interesting to note that ozone is the subject today of many discussions in relation with environmental concerns. However, this gas remains an important chemical reagent in industrial areas like the sterilization of water or the bleaching of wood pulp [1],... 

Calcium and sodium hypochlorite are both used in the bleaching of wood pulp, primarily as a step in multistage bleaching. The conditions used are a pH of 10-11, temperatures around 100°C for 2-3 hr. Average chlorine use is about 1.5% based on the pulp. 

An electrolytic cell permitting gas-liquid reaction has promise for direct conversion of 02 into 2% H202 in 1 M NaOH, a solution used for bleaching of wood pulp. The cell reactions are... 

The major market for sodium chlorate is for the preparation of the chlorine dioxide used for bleaching of wood pulp (Chap. 15). This market has recently risen by an order of magnitude every 10 years from the demand to replace of part, or all of the chlorine previously used for bleaching [13]. Other smaller uses of sodium chlorate are as a weed killer, for the making of matches and fireworks, and for the tanning of hides. A small market exists for sodium (and potassium) perchlorate, made by electrolysis of sodium chlorate using platinum electrodes (Eq. 8.30). 

Kraft, E. (1969). Bleaching of Wood Pulps. In The Pulping of Wood, 2nd edition, ed. R. G. MacDonald, and J. N. Eranklin. New York McGraw-Hill. 

Lignin, one of the major polymeric constituents of wood, is a highly crosslinked phenolic polymer derived from the free-radical coupling of substituted phenylpropa-noids (Figure 5.9). It reacts with aqueous chlorine to form oxidized and chlorinated species. This is a key reaction in the bleaching of wood pulp by the kraft process... 

Polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), often termed dioxins , consist of 210 different compounds which have similar chemical properties. This class of compounds is persistent, toxic, and bioaccumulative. They are generated as byproducts during incomplete combustion of chlorine containing wastes like municipal solid waste, sewage sludge, and hospital and hazardous wastes. Industrial processes such as bleaching of wood pulp in the manufacture of paper products, can also produce PCDDs and PCDFs [39]. 

Y. Watanabe, K. Yamaguchi and L Morishima Non-Chlorine Bleaching of Wood Pulps Mediated by Heteropolyoxometalates... 487 I. A. Weinstock, J. L. Minor and R. H. Atalla... 

NON-CHLORINE BLEACHING OF WOOD PULPS MEDIATED BY HETEROPOLYOXOMETALATES... 

Pemg YS, Oloman CW, Watson PA, James BR (1994) Catalytic oxygen bleaching of wood pulp with metal porphyrin and phthalocyanine complexes. Tappi J 77 119... 

Oxidative depolymerization of cellulose occurs during the bleaching of wood pulp under alkaline conditions (alkali-oxygen and alkali-peroxide bleaching processes) leading to losses in pulp strength and involve the reactions outlined above. The oxidation at the C-2, -3 or -6 hydrot ls usually is initiated by hydroxyl radicals... 

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