Chlorine dioxide bleaching selectivity

M Ragnar. On the importance of the structural composition of pulp for the selectivity of ozone and chlorine dioxide bleaching. Nordic Pulp Pap Res J 16 72-79, 2001. 

Chlorine dioxide, prepared from sodium chlorate by reduction, reacts quite selectively with lignin and is therefore widely used for pulp bleaching. At slightly acidic conditions (pH 4-5) chlorine dioxide can be reduced to chloride ions ... 

Molecular chlorine, CI2, is an ideal chemical for delignification as it is cost-efficient and has reasonable selectivity, well capable of removing 75-90% of the residual lignin in a single stage. However its undesirable effects - waste water with chlorides that is corrosive, and a tiny by-product of chlorinated organic compounds -means that molecular chlorine has been abandoned entirely in some countries and where it is still used this is often in conjunction with chlorine dioxide (D) whose environmental footprint is some 2.6 times smaller. Today, more than 75% of pulps are bleached without any molecular chlorine. These are described as elemental chlorine-free (ECF). Only c. 6% of bleached pulps are total chlorine-free (TCF),... 

In comparison to chlorine (see the next section. Chlorine Bleaching Chemistry), chlorine dioxide has a much higher selectivity in its reactions with lignin, and in analogy to model experiments, oxidation is the major mode of reaction. This has been demonstrated by bleaching experiments of kraft pulp in which the prebleaching was... 

The selection of a decontamination agent is dependent on several factors—and as you might guess cost is one of these. For routine microbiological work in a BSC, alcohols are frequently used to avoid the corrosive nature of bleach. However, some organisms may only be killed by bleach and so it may be utilized. Bleach is also frequently used to decontaminate ordinary laboratory countertops, since it is cheap and can be made quickly and easily. Chlorine dioxide is more expensive, but its broad effectiveness and the introduction of wipes, foams, and sachets have made it more accessible. 

Chlorine is an very effective, selective and inexpensive bleaching agent, but the brightening of the pulp is not sufficient. Therefore, as a third step, the brightening was effected by chlorine dioxide, which is extremely effective and selective in brightening, but is also expensive. 

Chlorination (C) with chlorine, an effective, selective and inexpensive bleaching agent that reacts very fast vidth lignin. For environmental reasons during the last ten years chlorine is being substituted by chlorine dioxide, ozone and/or oxygen all over the world. In Europe substitution is already 100%. In this particular case bleached pulp is called Elementary Chlorine Free - ECF . 

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