HEMICELLULASES IN PULP BLEACHING PDF
Hemicellulase-aided bleaching is the first full-scale biotechnical application in the pulp and paper industry which truly exploits the unique specificity and safety of. () reported that the chlorine dosage can be reduced 25% for hemicellulase- assisted chlorine bleaching to obtain the similar bleached pulp. Paice et al. Elemental chlorine, while effective in bleaching pulp and low in both primary classes: hemicellulases (xylanase) and oxidases (laccase).
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This is applied before carrying out the normal mechanical or chemical pulping. It is a primary hfmicellulases of this invention to provide a means to overcome the deleterious effect of Kraft black liquor on enzyme processes for pulp bleaching.
It has previously been found that these enzymes do not work well on the partially washed brownstock bleavhing is typical of commercial Kraft pulp mills. Topics Discussed in This Paper. The present invention relates to processes for treating paper pulp and particularly relates to an improved method for treating paper pulp with hemicellulase enzymes to enhance the bleaching of Kraft pulp.
An example of such a strain is T.
USA – Method for the use of enzymes in bleaching paper pulp – Google Patents
The activity is calculated from an enzyme dilution liberating 4 micromoles of reducing sugar under assay conditions. Modification of xylanase to improve thermophilicity, alkalophilicity and thermostability. US USA en Knots and incompletely cooked chips are removed from nleaching pulp slurry in specialized machines called knotters. For enzyme systems, a high degree of specificity is maintained, with the reaction proceeding 10 6 to 10 12 times faster than the spontaneous, uncatalyzed reaction in aqueous solution.
Xylanase focuses in a band corresponding to an isoelectric point pI of 9.
The pH of unbleached Kraft brownstock taken directly from an operating Kraft mill was adjusted by the addition of sulphuric acid. Hemicellulases are used to modify the structure of xylan and glucomannan in pulp fibers in order to enhance the chemical delignification.
It was found that the relevant pH for the enzyme reaction appears to be the pH at which the pulp equilibrates. The alkali can make the treated pulp yellow and, consequently, hydrogen peroxide is used subsequently to bleach the alkali deinked pulp.
Studies of the extracellular xylanase activity of some thermophilicactinonycetes. Field of blleaching Invention The present invention relates to processes for treating paper pulp and particularly relates to a method for enzyme treatment of paper pulp. What is claimed is: They save production costs and prevents formation of unwanted products during pulp bleaching process.
Hemicellulaes result is not surprising, because black liquor contains many aromatic and sulfide compounds that would be expected to be detrimental to enzyme activity. Conventional way of making paper pulp Bark of wood is removed. Hardwood and softwood Kraft pulp 2. These results are shown in Table 1.
The key challenges are poor and technology obsolete, lacking ability in achieving economy scale and lack of skilled labor http: One enzyme unit liberates one micromole of reducing sugar calculated as xylose per one minute under assay conditions.
Pulp and paper processors worldwide are under intense regulatory pressure to reduce these emissions. Applied Microbiology and Biotechnology. The manufacture of high quality, bright white paper largely depends on removing the lignin from the wood pulp with minimal degradation to the cellulose and bleachjng.
Hemicellulases in the bleaching of chemical pulps.
One of the primary objectives of this invention is to provide an improved way pullp using enzymes as part of the bleaching process to make it practical to reduce AOX discharges without incurring significant capital expenses.
To illustrate the advantage obtained by using the enzyme two common bleaching sequences were also applied. The enzymes added should be from the class of hemicellulose degrading enzymes that have a pH optimum for hydrolysis between 3.
The data show again that, by using the enzyme, considerably less active chlorine is needed to reach the same brightness level than with a no elemental chlorine containing bleaching sequence. The enzymes of T. Any remaining ink is removed during a conventional flotation step.
Process for high consistency oxygen delignification of alkaline treated pulp followed by ozone delignification. The resulting pulp was further bleached chemically using the following sequence under standard conditions: Another objective is to overcome the inhibition of enzyme activity that is observed in the presence of dilute Kraft black liquor. These treatment stages are known as the “brightening” stages because the final product is the desired bright white pulp.
The inventors have found, for example, that the conventional treatment conditions used to obtain a peak brightness boost of 7. The results are shown in FIG. In these studies, unbleached pulp was treated with enzymes before the addition of the bleaching chemicals. Biermann, Handbook of Pulping and Papermaking, This, in turn, leads to a significantly reduced chlorine requirement to bleach pulp.
Role Of Biotechnology In Pulp And Paper Industry
While the well washed samples of brownstock used in our laboratory testing had residual soda levels below 1 Kg per ton, one often finds residual soda levels ten times this high in operating mills. The preferred pH for hemicellilases process isa more preferred range is 6. A number of microorganisms are known to make hemicellulase enzymes.