Bleaching chemical pulps

R. H. Voss, C. E. Luthe, B. 1. Deming, R. M. Berry and L. H. AHen, "Some New Insights into the Origins of Dioxins Formed During Chemical Pulp Bleaching," paper presented at the CPPA Environment Conference 1988, Vancouver, B.C., Canada, Oct. 25—26,1988. 

In all cases, chlorine dioxide is produced at the point of use either from sodium chlorite or sodium chlorate. Production volume can be accurately estimated from total sodium chlorate consumption for chemical pulp bleaching because this use accounts for greater than 95% of all chlorine dioxide production. 

R. G. Hise, "Process Changes to Lower the Eormation of Dioxius During Chemical Pulp Bleaching," Tappi 1991 Bleach Plant Operations Short Course, June 23-28, 1991, pp. 245-258. 

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... 

Kraft Chemical Pulped Bleached Paper Production... 

Chemical pulp bleaching, 22 43-48 Chemical pulp bleach plant, 22 43 Chemical pulping, 22 21-31... 

Chemical pulps bleaching, 21 31-32 standard, 22 64-65 in papermaking, 25 94 Chemical purification, ion exchange in,... 

Figure 4.11 Flocculation and formation effects in a chemically pulped bleached softwood pulp (slightly refined). Fibre suspensions settled for 40 min. Sheets (60 gm 2) photographed in transmitted light, (a) no additives, (b) polyelectrolyte added to induce flocculation. Scale bar = 2 cm.

Chemical pulps bleached using CI2 and CIO2 show very little light-induced yellowing because of their extremely low lignin contents. However, so-called ECF and totally chlorine-free (TCP) pulps contain somewhat more lignin, and are more sensitive to light. Research in this area is in its infancy, and only a few spectroscopic studies have appeared. 

CW Dence. Chemistry of chemical pulp bleaching. In CW Dence, DW Reeve, eds. Pulp Bleaching. Principles and Practice. TAPPI Ppress, Atlanta, pp. 125-160, 1996. 

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