Chlorine-free pulp bleaching

Chemical pulp bleaching has undergone significant process changes since around 1990. Until that time, nearly every chemical pulp mill that had used bleaching had incorporated elemental chlorine (Clj) into some of its processes. Because of environmental and health concerns about dioxins, U.S. pulp mills now use elemental chlorine free (ECF) and total chlorine free (TCF) bleaching technologies. The most common types of ECF and TCF are shown in Table 21.5. The difference... 

The EPA passed its "Cluster Rule that requires kraft and soda pulp mills to utilize elemental chlorine-free (ECF) bleaching and all sulfite mills to use ECF or totally chlorine-free (TCF) bleaching. 

Nelson, P., Elemental Chlorine Free (ECF) and Totally Chlorine Free (TCF) Bleaching of Pulps, in Environmentally Friendly Technologies for the Pulp and Paper Industry, R. A. Young and M. Akhtar (Eds.), John Wiley Sons, New York, 1998. 

In all cases in modern pulp bleaching, elemental chlorine is excluded and only chlorine dioxide is applied to yield elemental chlorine-free pulps (ECF pulps). If any chlorine-containing compound is avoided totally chlorine-free pulps (TCF pulps) are achieved. Concerning the bleaching, Kraft pulp mills have been converted predominantly to elemental chlorine-free (ECF) bleaching. Totally chlorine-free (TCF) bleaching is the method of choice for sulphite mills. Therefore, the extent of TCF bleaching remains at around 5% of the pulp production. 

Elementary chlorine-free (ECF)-bleached unrefined softwood pulp obtained from a mill in southern Finland was grotmd in a Supermass colloider " to produce fines. The Bauer-McNett analysis of the fines showed that 92% of the fines passed through the 200 mesh. The consistency of the produced fines-PCC composite was in the range of 0.085-0.1%. Calcium hydroxide was mixed to obtain 2 1 PCC nanofibrils and carbonised to crystallise PCCs with colloidal, rhombohedral, and scalenohedral morphologies. 

Caro s acid is effective ia delignifying wood pulp (qv) made by chlorine-free bleaching sequences. When conditions are carefully controlled, the mechanical properties of the final paper (qv) are not impaired. These processes were developed ia the 1980s and commercialized ia the 1990s (68). 

Domtar Inc., Chlorine-Free Bleaching of Kraft Pulp Feasibility Study, Ontario Ministry of the Environment, and Environment Canada, June 1993. 

ECF [Elemental chlorine free] A generic term for pulp-bleaching processes which use chlorine dioxide and other oxidants in place of elemental chlorine. See also TCF. 

Murata, S. Kondo, R. Sakai, K. Kashino, Y. Nishida, T. Takahra, Y. Chlorine free bleaching process of Kraft pulp using treatment with the fungus IZU-154. Tappi J. 1992, 75, 91-94. 

Today, the pulp and paper industry operates with two main pulping processes and three bleaching processes. The latter are the chlorine bleaching process, the elementary chlorine-free (ECF) process, and the totally chlorine-free (TCF) process they are compared in Table 6.4. 

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