Bleaching stage using xylanase with hydrogen peroxide, peracids, or a combination thereof

Abstract

The present invention discloses methods of bleaching chemical pulp that combine xylanase enzymes with hydrogen peroxide, peracids, or a mixture. The method comprises the steps of carrying out a chemical pulping operation, optionally followed by delignifying the pulp with oxygen, then combining xylanase enzymes with hydrogen peroxide, peracids, or a mixture to bleach the pulp. The method allows the mill to use both xylanase and peracids in a single bleaching tower to decrease the usage of chlorine dioxide and other bleaching chemicals. The pulp bleaching method of the present invention may be performed in a pulp mill as part of a complex pulp bleaching process.

Description

[0001] The invention relates to methods of bleaching pulp. More specifically the invention relates to methods of bleaching pulp using xylanase enzymes with hydrogen peroxide, peracids, or or a combination thereof.[0002] The production of bleached chemical pulp is a major industry around the world. More than 50 million tons of bleached pulp is produced annually. Bleached chemical pulp is the largest component of all types of white paper, including that used in photocopy paper, writing paper, and paper packaging. In addition, bleached chemical pulp is also used to impart strength to less expensive grades of paper, such as newsprint. Bleached chemical pulp has large markets because of its high degree of whiteness and cleanliness, the stability of the whiteness, its high strength, and the ease and uniformity of the printing surface it provides. These attributes are obtained when lignin, which is colored and decreases the interfiber bonding of the cellulose, is almost completely removed ...

AI Technical Summary

Benefits of technology

[0029] The present invention also provides a method of reducing kappa number of a chemical pulp comprising:

[0041] The method of the invention is an improvement over the separate treatments of xylanase and peroxyacids. The method of the invention uses only one bleaching tower rather than two. Surprisingly, the presence of the hydrogen peroxide and peracids do not destroy the activity of the xylanase. The benefit that a mill obtains from the use of peracids with xylanase is greater than the benefit with peracids alone. This enables a mill to run a less costly bleaching operation, or to further decrease the usage of chlorine-containing bleaching chemicals.

Problems solved by technology

While pulping removes most of the lignin in the feedstock material, it is not capable of removing all the lignin without destroying the cellulose fibers of the feedstock.

Alkali-oxygen delignification reduces the amount of lignin in the pulp by 35-50%, but this process is harsh on the pulp and is often accompanied by destruction of some of the cellulose fibers in the pulp if the extent of delignification is greater than 50%.

However, beyond a certain low level of hydrogen peroxide, there is a significant possibility of damaging the fibers.

Unfortunately, it is not practical to make and use manganese peroxidase lignin peroxidase, or laccase at an industrial scale.

However, there is no disclosure in these reports of mixtures comprising hydrogen peroxide and xylanase alone.

Although the interest and mill usage of peracids is increasing, the relatively high cost of the peracids, resulting from the need to combine two or more different chemicals, has limited the use of peracids to this point.

This in turn decreases the chlorinated effluent produced by such processes.

Images