JPH06220786A - Method for bleaching pulp - Google Patents

Abstract

PURPOSE:To improve pulp bleaching effect by asdding xylanase in a specific mode to pulp obtained from digesting process. CONSTITUTION:The bleaching is carried out by adding to pulp obtained from digesting process xylanase is such a state that 0.01-10wt.% of a salt has been added to a xylanase-diluted solution. By this method, pulp whiteness can be raised while maintaining pulp strength at a given level. This salt is an alkal (alkaline earth) metal salt, and the bleaching solution may also be prepared by adding xylanase to a 0.01-10wt.% aqueous solution of the salt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulp bleaching method for wood resources. More specifically, the present invention aims to reduce chlorine bleaching agents,
In enzyme bleaching, it is a pulp bleaching method that enhances the effect of the enzyme and improves the enzyme bleaching efficiency.

[0002]

BACKGROUND OF THE INVENTION Colored lignin remains in unbleached pulp after digestion. Therefore, in order to use the unbleached pulp for paper products, residual lignin is removed to improve whiteness. Processing (bleaching) is required. For example, in the case of kraft pulp made from wood, chlorine (C), hypochlorite (H), chlorine dioxide (D), caustic soda are generally used except for packaging materials such as bags and adhesive tapes. It is bleached with a bleaching agent such as da (E) and hydrogen peroxide (P) and a bleaching aid to remove lignin which is a cause of coloring of unbleached pulp.

Common bleaching is C-E-H-E-D, C
The chlorine-based multi-stage bleaching sequence is the mainstream, as represented by -EDE-D, C-E-H-P-D, etc., but the bleaching waste liquid contains chlor, which causes significant metal corrosion. Therefore, it is difficult to perform concentrated combustion in the chemical recovery process during cooking and recycle use in the bleaching process. Therefore, the bleaching waste liquid is discharged to the outside of the system such as a river after being subjected to wastewater treatment such as activated sludge and pseudo-precipitation. However, carcinogenic dioxins and toxic organochlorine compounds remain in such wastewater, so preventing environmental pollution by chlorine-based chemicals has become an important issue (C. Rappe, S.Swan
son, et al., Pulp and Paper Canada. 90.T273 (1989)).

From this point of view, the bleaching method using a non-chlorine chemical is drawing attention, and oxygen / alkali bleaching (oxygen bleaching), microbial bleaching, enzyme bleaching, etc., which are carried out between the digesting step and the bleaching step, are being used. Can be mentioned.

In general, in oxygen bleaching, digested pulp is mixed with caustic soda and oxygen, and lignin in the pulp is oxidatively decomposed during passage through a reaction vessel under pressure to be solubilized in alkali. It is a method of performing delignification. In this method, a part of the chlorine (C) stage of the chlorine-based multi-stage bleaching sequence can be replaced by oxygen bleaching, so that chlorine contamination is reduced and the waste liquid does not contain chlorine, so the waste liquid It can be recycled.
7-5202, JP-A-49-7503). However, with only oxygen bleaching, the whiteness is 85%.
Since it is not possible to obtain a high-whiteness pulp of a certain degree, it is the current situation that a large amount of chlorine-based bleaching agents must be used in the sequence after oxygen bleaching.

On the other hand, microbial bleaching is a bleaching treatment by adding lignin-decomposing bacteria to pulp after digestion or pulp after oxygen bleaching, and its purpose is to greatly reduce the chlorine bleaching agent thereafter. However, the microbial treatment has a drawback that it takes time (see Japanese Patent Laid-Open No. 4-240287).

On the other hand, enzyme bleaching is a bleaching treatment by adding a lignin-degrading enzyme such as hemicellulase to pulp after digestion or pulp after oxygen bleaching. For the purpose of significantly reducing the amount (Japanese Patent Application Laid-Open No. 2-264087, Japanese Patent Application Laid-Open No.
(See JP-A-40887). This enzyme bleaching has attracted attention because it requires a short processing time and can be processed by a relatively simple apparatus, and is being put to practical use.

[0008]

SUMMARY OF THE INVENTION In view of the above situation, the present inventors have conducted diligent research on enzyme bleaching, and as a result, in enzymatic bleaching, particularly in bleaching with xylanase of hemicellulase, xylanase was converted into pulp. Before adding, salt is added to the xylanase diluted solution in advance, or salt is added in diluted water in advance and dissolved, and then xylanase is added to maintain the pulp strength at a constant level. However, they have found that the whiteness can be made higher than that of ordinary xylanase bleaching, and have completed the present invention.

Therefore, the present invention is a method for further enhancing the effect of xylanase bleaching. By improving the bleaching effect, the amount of xylanase added is reduced and the chlorine-based bleaching agent is reduced thereafter. The purpose of the present invention is to provide a pulp bleaching method which, when combined with oxygen bleaching, also contributes to environmental pollution measures due to a significant reduction in chlorine bleaching agents.

[0010]

DISCLOSURE OF THE INVENTION The present invention is a bleaching method for pulp, which comprises a step of treating the pulp obtained from the cooking step with an enzyme xylanase, in advance of adding xylanase to the pulp. Add salt to the diluent.
This is a pulp bleaching method characterized in that 0.01 to 10% by weight of salt is added in advance, or 0.01 to 10% by weight of salt is added to diluted water in advance and dissolved, and then xylanase is added.

The enzyme xylanase used in the pulp bleaching method of the present invention may be obtained from any microbial source, but preferably it has endo-xylanase activity as a main component and acts on cellulose. It is desirable to use endo-xylanase that does not contain cellulase activity that reduces pulp strength.

The addition rate of xylanase per 100 wt.% Of dry pulp is such that the xylanase activity (EXU) is 600EXU /
g xylanaze stock solution in the range of 0.01 to 1.0% by weight, the reaction time in the range of 30 to 300 minutes, and the reaction temperature in the range of
The temperature is in the range of 40 to 70 ° C., the pulp concentration is in the range of 5 to 15%, and the pH during the reaction is in the range of 5 to 9.

Here, the xylanase stock solution was added in an amount of 0.01-1.
The range of 0% by weight is because the bleaching effect is not exhibited when the amount is less than 0.01% by weight, and the cost is too high when the amount exceeds 1.0% by weight. Is about 0.2% by weight. The reaction time is 3
The reason for setting the range to 0 to 300 minutes is that if the time is less than 30 minutes, the bleaching effect is not exhibited due to the reaction time being too short, and if it exceeds 300 minutes, the capacity of the reaction tank becomes large and the cost of the facility becomes high. . Further, the reason why the reaction temperature is in the range of 40 to 70 ° C is that if the temperature is lower than 40 ° C, the reaction progresses slowly and the reaction time is required to be long, and if the temperature exceeds 70 ° C, the enzyme loses its activity due to being too hot.

Further, the pulp concentration is set in the range of 5 to 15% because if the amount is less than 5%, the probability of the enzyme and the pulp encountering decreases, and the bleaching effect decreases, whereas if it exceeds 15%, the stirring is sufficient. This is because the bleaching effect is reduced because it is not performed.
Furthermore, the reason for setting the pH during the reaction to the range of 5 to 9 is that since the enzyme is a protein, extreme pH causes loss of enzyme activity and coagulation. This is because the effect is not exhibited. In the pulp bleaching method of the present invention, the enzyme needs to be diluted in advance with a xylanase activity (EXU) in the range of 600EXU / g to 0.6EXU / g. This dilution water may be normal industrial water or tap water, but the pH of the dilution water
It is desirable to use near neutral water of 6 to 8.

The salt added to the enzyme xylanase diluent in the bleaching method of the present invention is a salt composed of an alkali metal or an alkaline earth metal, preferably a salt composed of sodium, potassium, magnesium or calcium. Is desirable. The acid may be any acid, but hydrochloric acid, sulfuric acid, acetic acid, tartaric acid, and succinic acid are preferable. Specifically, sodium chloride, sodium sulfate, sodium acetate, sodium tartrate, sodium succinate, potassium sulfate, potassium acetate, potassium succinate, magnesium chloride, magnesium acetate, alone or a mixture of several selected from salts. It is desirable to use the salts according to.

The salt may be added to the enzyme xylanase diluent, or any method may be used in which the enzyme xylanase is added after the salt is added to the diluted water in advance and dissolved. Although there is no problem, it is preferable to add a salt to the diluted water in advance and dissolve it, and then add xylanase to dilute it. Regarding the addition rate of salt, it is desirable to add 0.01 to 10% by weight to the xylanase diluent. If it is less than 0.01%, the salt concentration is too low to be effective, and if it is more than 10%, the concentration is too high, which is harmful to the enzyme. A particularly preferred range is 0.05 to 5% by weight based on the xylanase diluent.

The present invention is a conventional kraft pulp, modified kraft pulp, alkaline pulp, sulfite pulp,
Can be used alone or as part of a conventional bleaching sequence for bleaching chemical pulps such as, and oxygen bleached pulps of these pulps, and other wood pulps, waste paper pulps and non-wood pulps.

[0018]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the following Examples and Comparative Examples, the bleaching conditions for pulp and the physical properties of the obtained pulp were measured by the following procedures unless otherwise specified. In addition,% shown here indicates% by weight unless otherwise specified.

Enzyme bleaching (O stage) Hardwood unbleached kraft pulp (mixture of domestic hardwood, K
Value 12.8) with oxygen bleaching (caustic soda addition amount: 2% to pulp, pulp concentration: 20%, oxygen pressure: 5 kg / cm
³ , treatment temperature: 100 ℃, treatment time: 40 minutes),
I washed it with water.

Preparation of Enzyme Bleaching Pulp O-stage treated pulp (whiteness 39.7%, K value 8.7) was diluted with tap water to a concentration of 2%, and further with sulfuric acid to a pH of 7.5. After soaking, it was suction-dehydrated. This neutralized pulp had a whiteness of 40.1% and a K value of 8.5.

Enzyme bleaching (Enz stage) Pour the neutralized pulp after O stage treatment into a plastic bag,
As a stock solution of 600EXU / g xylanase, 0.1% was added, and further, a predetermined amount of water was added so that the pulp concentration became 10%, thoroughly mixed by hand-stirring, and immersed in a constant temperature bath at 55 ° C. Hold for 2 hours. Every 30 minutes on the way, stirring was performed by hand, and further, sufficient mixing was performed. After the reaction was completed, the pulp was taken out from the bag, washed with water, and suction-dewatered.

Chlorine bleaching (C-stage) Suction-dehydrated Enz-stage treated pulp was placed in a plastic bag, and a predetermined amount of chlorine water was added (1.5% as effective chlorine based on the weight of absolutely dry pulp), and the pulp concentration was 4%. A predetermined amount of water was added so that the concentration would be 0.5%, and the mixture was thoroughly mixed by stirring by hand, immersed in a constant temperature bath at 60 ° C., and kept for 30 minutes. After the reaction was completed, the pulp was taken out from the bag, washed with water, and suction-dewatered.

Alkali extraction (E stage) Suction-dehydrated C stage treated pulp is put in a plastic bag,
Add a specified amount of alkali (caustic soda) (0.8% based on the weight of the absolutely dry pulp), add a specified amount of water so that the pulp concentration becomes 12.5%, and mix thoroughly by hand stirring. Then, it was immersed in a constant temperature bath at 60 ° C. and kept for 80 minutes. After the reaction was completed, the pulp was taken out from the bag, washed with water, and suction-dewatered.

Hypo-bleaching (H-stage) Suction-dehydrated E-stage treated pulp is placed in a plastic bag,
Add a predetermined amount of hypochlorite (sodium hypozincate) (0.6% as effective chlorine per dry pulp weight) and alkali (0.2% caustic soda per dry pulp weight), Further, a predetermined amount of water was added so that the pulp concentration became 13%, and the mixture was thoroughly mixed by hand-stirring, immersed in a constant temperature bath at 75 ° C., and kept for 35 minutes. After the reaction was completed, the pulp was taken out from the bag, washed with water, and suction-dewatered.

Chlorine dioxide bleaching (D-stage) Suction-dehydrated H-stage treated pulp is placed in a plastic bag,
Add a specified amount of chlorine dioxide (0.8% chlorine dioxide based on the dry pulp weight), and then add a specified amount of water so that the pulp concentration becomes 12%, mix thoroughly by hand stirring and mix at 65 ° C. It was immersed in a constant temperature bath and kept for 210 minutes. After the reaction was completed, the pulp was taken out from the bag, washed with water, and suction-dewatered.

Measurement of Physical Properties of Pulp (1) Whiteness Taapi test method T205 os-71 after disintegration of pulp dehydrated by suction
A sheet having a basis weight of 60 g / m ² was prepared according to (JIS P 8209) and measured according to JIS P 8123.

(2) Pulp Viscosity Peel the suction-dehydrated pulp finely by hand, and then tap
i Determined according to test method T230 os-82.

(3) Cleavage length and specific tear strength The pulp dewatered by suction was disintegrated to give 400 ml C.I. with a PFI mill at a pulp concentration of 10%. S. Beat by F (Canadian standard freeness) and weigh 60 g according to JIS P 8209.
/ M ² sheet created, JIS P 8113 and JIS P 8116
Was measured according to.

(4) Discoloration The pulp dehydrated by suction was disintegrated to prepare a sheet having a basis weight of 60 g / m ² , and the sheet was dried with a hot air circulating constant temperature dryer at 105 ° C. for 24 hours.
Time-fading processing was performed, and whiteness was measured according to JIS P 8123.

Example 1 Hardwood unbleached kraft pulp (mixed hardwood domestically produced, K
No. 12.8) was used for bleaching with a sequence of Ens-C-E-H-D. In Example 1, the enzyme stock solution (600EXU / g, Pipezyme HB manufactured by Novo Nordisk Bio-Industry Co., Ltd.) was preliminarily used in the Ens stage to prepare 20 stock solutions.
0.1% sodium chloride in 0 times the amount of diluted water
The enzyme stock solution was added to a solution that was added (relative to the diluent) and sufficiently dissolved to prepare a 200-fold enzyme diluted solution with respect to the stock solution. Then, 0.1% based on the weight of the absolutely dried pulp of this enzyme diluted solution was added to the post-cooking neutralized pulp.

Comparative Example 1 In Comparative Example 1, the enzyme stock solution was preliminarily diluted with 20 times the stock solution in the Ens stage.
The same treatment as in Example 1 was performed, except that the enzyme stock solution was added to the 0-fold amount of diluted water without adding the salt, and a 200-fold enzyme diluted solution was prepared with respect to the stock solution.

Example 2 In Example 2, the enzyme stock solution was preliminarily diluted with 20 times the stock solution in the Ens stage.
0.05% sodium chloride in 0 times the amount of diluted water
The same treatment as in Example 1 was performed, except that the enzyme stock solution was added to a solution that was sufficiently dissolved (to the diluent) and the enzyme diluted solution was prepared 200 times the stock solution.

Example 3 In Example 3, the enzyme stock solution was preliminarily diluted with 20 times the stock solution in the Ens stage.
0.5% sodium chloride in 0 times the amount of diluted water
The same treatment as in Example 1 was performed, except that the enzyme stock solution was added to the solution that was sufficiently dissolved (to the diluent) and the enzyme diluted to 200 times the stock solution was prepared.

The results obtained are shown in Table 1.

[Table 1]

Example 4 Hardwood unbleached kraft pulp (mixed hardwood domestically produced, K
No. 12.8) was used for bleaching with a sequence of O-Ens-C-E-H-D. In Example 4, the enzyme stock solution was added to the Ens stage in advance by adding 0.1% (to the diluting solution) of sodium sulfate in 200 times as much diluted water as the stock solution, and the enzyme stock solution was added to a sufficiently dissolved solution. Then, an enzyme diluted solution of 200 times the stock solution was prepared. Then, the enzyme diluted solution was added to the pulp after the O-stage bleaching and neutralization treatment in an amount of 0.1% based on the weight of the absolutely dry pulp.

Example 5 In Example 5, the enzyme stock solution was preliminarily diluted with 20 times the stock solution in the Ens stage.
0.1% sodium acetate in 0 times the amount of diluted water
The same treatment as in Example 4 was performed, except that the enzyme stock solution was added to the solution that was sufficiently dissolved (to the diluent) and the enzyme diluted solution was prepared 200 times the stock solution.

Comparative Example 2 In Comparative Example 2, the enzyme stock solution was preliminarily diluted with 20 times the stock solution in the Ens stage.
The same treatment as in Example 4 was carried out except that the enzyme stock solution was added to the 0-fold amount of the diluted water without adding the salt, and the enzyme diluted solution was prepared 200 times the stock solution.

The results obtained are shown in Table 2.

[Table 2]

Pulp according to the method of the present invention, which has been bleached after adding a salt to xylanase in advance, is almost the same as the normal enzyme xylanase bleaching, although the strengths such as breaking length and specific tear strength are almost the same. It provides high-quality pulp with good fading properties. Therefore, if the whiteness is set to the same level as that of the conventional bleaching method in which no salt is added, the amount of xylanase added and the chlorine-based chemicals thereafter can be reduced.

[0040]

According to the present invention, as compared with the enzyme xylanase bleaching by the conventional method, in the bleaching method of pulp, which comprises a step of treating the pulp obtained from the cooking step with the enzyme xylanase, the xylanase is used. Before adding to the pulp, 0.01 to 10% by weight of salt is added to the xylanase diluting solution in advance, or 0.01 to 10% by weight of salt in diluting water is added in advance.
Since 10% by weight was added and dissolved, xylanase was added, so addition of salt did not become harmful to the enzyme and pulp strength was maintained at a constant level, while xylanase bleaching Also has the effect that the whiteness can be increased, the bleaching effect of the pulp is improved, and the pulp with high whiteness can be produced.

Further, when the whiteness level is the same as that of the enzyme xylanase bleaching by the conventional method, the amount of expensive enzyme xylanase added is reduced without a large change in equipment.
Moreover, it becomes possible to reduce the amount of chlorine-based chemicals thereafter, and it is also useful as a measure against environmental pollution due to wastewater from chlorine-based chemicals.

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[Procedure amendment]

[Submission date] April 26, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction content]

The results obtained are shown in Table 1.

[Table 1]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0038

[Correction method] Change

[Correction content]

The results obtained are shown in Table 2.

[Table 2]

Claims (3)

[Claims] 1. A method for bleaching pulp, which comprises a step of treating the pulp obtained from the digestion step with an enzyme xylanase, in which salt is previously added to the xylanase diluent before the xylanase is added to the pulp. A method for bleaching pulp, characterized in that 0.01 to 10% by weight is added, or 0.01 to 10% by weight of salt is added in advance to the diluted water and dissolved, and then xylanase is added. 2. The method for bleaching pulp according to claim 1, wherein the enzyme xylanase used in the method for bleaching pulp has an endo-type xylanase activity as a main component. 3. The pulp according to claim 1, wherein the salt to be added to the xylanase diluent is a salt consisting of a salt of an alkali metal or an alkaline earth metal, alone or in combination. Bleaching method.