Caroate Delignification II. Enhancement by Halides, 1993 Pulping Conference Proceedings

Due to environmental concerns about chlorinated organics, the pulp and paper industry is being pressured to decrease their application of chlorine-containing compounds in kraft pulp bleaching. A process is described where conventional or extended delignified kraft pulps are further delignified to low kappa numbers by an oxygen stage followed by a caroate stage (OKE*0*). The highly delignified pulps can be brightened by conventional chlorine dioxide treatment or by a high consistency hydrogen peroxide stage.

A halide, preferably chloride, is added to the caroate stage. The chloride accelerates lignin degradation and simultaneously retards cellulose depolymerization. In the process, the chloride is oxidized to chlorine by the peracid. The involvement of chlorine results in an effluent containing 0.5-0.7 kg of adsorbable organic halogens (AOX) per ton of pulp. If the Cl*2* can be replaced by another strong electrophile such as dimethyldioxirane or ozone then ECF or TCF sequences can be projected.

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