Pulp-Bleaching Studies

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

Sagfors and Starck [14] used gel permeation chromatography to study calcium lignosulphate of high molecular weight in acid and alkaline kraft pulp bleaching effluents. 

Geraldes and de Pinho [37] modeled NF permeate using a prepared salt solution to evaluate the feasibility of ED for the removal of chloride ions. The modeled permeates contained chloride ions from 1650 to 2250 mg/L depending on the water recovery. In that study, the quality requirements for the washing waters for pulp bleaching were 350 mg/L of NaCl and 30 PtCo units of color. The NF followed by ED met these requirements and the evaluated costs were 0.65 per m at 80% water recovery. Rapp et al. [131] reported the electrical power consumption of ED to be 0.97 kW h/kg chloride removed. 

The case study presented here deals with a pulp and paper production process. The plant produces Bleached Eucalyptus Kraft Pulp, using the ECF process (Elemental Chlorine Free). The Kraft pulping process is performed in two different phases, which influence the final pulp quality the cooking process of wood chips (eucalyptus globules) followed by the pulp bleaching. The cooking process is the phase that most contributes to the preservation of the main pulp characteristics, which, in turn, will ensure high quality paper. 

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. 

It has generally been studied as an alternative to hydrogen peroxide or peracetic acid in chemical pulp bleaching. 

Dioxins are unintended by-products of natural events and human-made processes such as manufacturing, incineration, paper and pulp bleaching, and exhaust emissions. Immunotoxic effects of dioxins have been studied primarily with respect to 2,3,7,8-t c t r a c 111 o r o dib e n / o -/ - d i o x i n (TCDD), the most toxic congener of dioxins and an important immunotoxicant (Vos Moore, 1974). 

Production of rMnP firom P. pastoris for pulp bleaching experiments was previously conducted at pH 6 [4]. A medium pH of 4.5 resulted in very low rMnP concentrations, although the wtMnP is commonly produced in P. chrysosporium cultures at this pH. This observation was also surprising in that Gu et al. [3] found that rMnP purified from P. pastoris cultures shares similar characteristics with the wtMnP and is active at pH 4.5 and relatively stable from pH 3.0 to 6.0. Further experiments on the effect of pH on rMnP were thereby conducted in this study to determine why rMnP is not observed in low pH yeast cultures, although white-rot fiingi typically produce wtMnP at low pH, and the purified P. pastoris rMnP appears to be as stable as the wtMnP at low pH. 

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