Pulping and bleaching

Various technologies and chemicals are used to manufacture pulp, but most pulp manufacturing systems contain the process sequence shown in Table 21.4. Overall, most of the pollutant releases associated with pulp and paper mills occur at the pulping and bleaching stages where the majority of chemical inputs occur. 

The major sources of pollutant releases in pulp and paper manufacture occur at the pulping and bleaching stages, respectively. As such, nonintegrated mills (i.e., those mills without pulping facilities on site) are not significant environmental concerns when compared to integrated mills or pulp mills. 

NCASI Technical Workshop, Effects of Alternative Pulping and Bleaching Processes on Production and Biotreatability of Chlorinated Organics, NCASI Special Report 94-01, February 1994. 

Wet formed sheets of groundwood, holocellulose pulp and bleached kraft pulp were cold pressed for one minute at a 0.1 MPa and hot pressed between two press wires at 150°C for one minute at... 

Acetosolv A wood pulping and bleaching process which uses hydrogen peroxide and acetic acid. See Organosolv. 

MILOX [Milieu oxidative] A wood-pulping and bleaching process. Wood chips are treated with hydrogen peroxide and formic acid in a three-stage process. Developed by the Finnish Pulp and Paper Research Institute (KCL) and Kemira. Piloted at Oulu, Finland in 1991. 

The surface character of fibres influences their affinity towards various chemical additives by, for example, their adsorption properties and also in their tendency to flocculate. Cellulosic fibres, because of the presence of acidic groups which are introduced during chemical pulping and bleaching, are mildly anionic. These acidic groups may be carboxylic (COOH) or in some cases sulfonic acid (S03H) and they are able to dissociate to leave a net negative... 

Table 1 Types of Pollutants Generated During Chemical (Kraft) Pulping and Bleaching Steps...

Table 2 Low-Molecular-Weight Organic Compounds Found in the Spent Liquors from Pulping and Bleaching Processes... 

Raman spectra obtained from pulp samples 4 to 13 are shown in Figures 2 to 4. For these samples, pulping and bleaching processes produced changes in the 850 to 1850 cm-1 spectral region. The features in these spectra are typical of lignocellulosic materials (authors unpublished work). 

The important parameters in bleaching wood pulp are the concentration (consistency) of pulp and bleaching chemicals, the reaction temperature and duration (residence time), the mixing of pulp and chemical, and the pH at which the reactions are carried out. Initial temperatures and concentrations are usually selected based upon experience with a particular pulps needs. Control is achieved by carefully balancing all these various factors to optimize bleaching with a minimum expenditure of chemical. 

As with pulping and bleaching, biotechnology too could have a considerable impact on the production of chemicals from wood and other forms of plant biomass. The effects of biotechnology probably will be noticed first in areas of enzymatic hydrolysis of polysaccharides and fermentation technology. 

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