JPH09209285A - Method for producing bleached pulp - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To obtain satisfactory whiteness and Kappa number by hydrolyzing hemicellulose in wood pulp and at the same time performing delignification treatment in a comparatively short time unlike conventional methods. A method for bleaching wood pulp is provided. SOLUTION: A pulp bleaching method is characterized in that a wood pulp is enzymatically treated with an enzyme agent obtained from a medium after basidiomycetes are cultivated and fruit bodies are harvested.

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 which comprises enzymatically treating wood pulp with an enzyme agent obtained from a medium after basidiomycete cultivation and fruit body harvesting.

[0002]

2. Description of the Related Art Since strongly colored lignin remains in wood pulp, the residual lignin is removed to provide whiteness for use in applications requiring high whiteness such as high quality paper. Bleaching is required. Chlorine bleach is used for bleaching at present, but since the bleaching effluent contains chlorine with significant metal corrosion, it is difficult to concentrate in the chemical recovery process, recycle and reuse in the bleaching process, After undergoing wastewater treatment such as activated sludge and coagulation sedimentation, it is discharged outside the system. However, in recent years, organochlorine compounds such as dioxins have been detected in treated wastewater, and since these substances have strong toxicity such as mutagenicity, environmental pollution due to chlorine bleach becomes a major problem. There is. In order to solve this point, it is necessary to develop a bleaching process that reduces the amount of chlorine bleach used as much as possible and reduces the emission of organic chlorine compounds out of the system as much as possible.

Recently, hydrogen peroxide, oxygen and ozone have been used as alternative bleaching agents for chlorine compounds, but these compounds also have various drawbacks. For example, if kraft pulp is subjected to the same degree of delignification as hydrogen peroxide-based compounds, the cellulose fibers will deteriorate beyond an allowable amount,
As a result, the pulp yield is lowered, and the reduction of the clay in the pulp causes the production of paper with weak mechanical properties.

In order to overcome such drawbacks of pulp bleaching, non-contaminating biochemical bleaching methods using enzymes have been developed. For example, Phanerochaete chrysospo, which is a white immortal fungus
There is a pulp bleaching method in which lignin is directly decomposed using rium) (JP-A-3-104993). However, bleaching using such a bacterium has a very slow delignification rate, and at least 3 to 7 days are required to obtain a satisfactory whiteness and Kappa number. On the other hand, there are some reports that xylanase is used for delignification of pulp from the viewpoint that lignin is bound to hemicellulose. For example, JP-A-6-501609 and JP-A-5-50008.
7 and so on. In the former, the Trichoderma reesei (Tri
xylan-degrading enzyme from choderma reesei), and in the latter, Malbranchea cinnammia (Malbranchea cin
namomea), Humicola insolen
s), Bacillus pulmilus, Bacillus stearothermophilus (Bacillus stearother)
mophilus), Salmon Monospora Fusca (Thermonmono
spora fusca) and xylan-degrading enzyme derived from Streptomyces olivochromogenes. In any of the methods, in order to effectively remove lignin in wood pulp, several kinds of enzyme agents are necessary because the range of the optimum temperature or the optimum pH is limited in the enzyme chemical property, or relatively. It may take a long time for enzyme treatment. Further, in order to obtain these enzyme agents, it takes a long time to culture the microorganisms and purify the enzyme agents, which is not economical.

[0005]

DISCLOSURE OF THE INVENTION The present invention uses an enzyme agent obtained from a medium after basidiomycetes are cultivated and fruit bodies are harvested to hydrolyze hemicellulose in wood pulp, and at the same time Disclosed is a method for bleaching wood pulp, which is characterized by obtaining a satisfactory whiteness and Kappa number by performing delignification treatment in a relatively short time, which is not available in the method. Furthermore, with one kind of enzyme agent, the temperature is 10 to 100 ° C
Preferably 30-80 ° C, pH 2-12, preferably p
Provided is a method of bleaching wood pulp without causing deterioration of cellulose fibers in the range of H3 to 9.

[0006]

Means for Solving the Problems As a result of intensive research to solve the problems of the prior art, the present inventor obtained from a medium which is normally discarded after culturing basidiomycete and harvesting fruiting bodies. It was discovered by chance that treating the wood pulp with the above-mentioned enzyme agent allows the pulp to be bleached more effectively in a shorter time as compared with the conventional enzyme treatment method.

The present invention is based on the above findings and is characterized in that wood pulp is enzymatically treated with an enzyme agent obtained from a medium after basidiomycetes are grown and fruit bodies are harvested. Regarding the method.

In the present invention, the origin of the enzyme preparation is Enokitake (Fla
mmulina velutipes), Loxophyllum ulum
arium), oyster mushroom (Pleurotus ostreatns), nameko (Pho
llota nameko), shiitake mushroom (Lentinus edodes), and maitake mushroom (Grifola frondosa).
It relates to the described method of bleaching wood pulp.

The present invention relates to a method for bleaching wood pulp according to claim 1 or 2, wherein the enzyme treatment is carried out within a pH range of 2-12.

Normally, the wood pulp bleaching process is an oxygen treatment
Chlorine dioxide treatment → caustic soda treatment → chlorine dioxide treatment → caustic soda treatment → chlorine dioxide treatment are carried out in a 6-step process. In the present invention, by replacing at least one of these steps with an enzyme treatment step, the problems of oxygen treatment, chlorine dioxide treatment, and caustic soda treatment are alleviated, and at least one treatment step is performed.
This brings the effect of being able to omit more steps.

Enzyme agents used in the present invention include enokitake (Flammulina velutipes) and lycophyllum (Lyophyllus).
m ulumarium), oyster mushroom (Pleurotus ostreatns), nameko (Phollota nameko), shiitake mushroom (Lentinus edodes),
There is an enzyme preparation obtained from a medium after cultivating Maitake (Grifola frondosa) and harvesting fruiting bodies, but the enzyme preparation is not limited thereto. These enzyme agents are complex enzymes such as polysaccharide degrading enzymes, proteases and lipases. Although it contains a large amount of cellulase as a polysaccharide-degrading enzyme, it also contains amylase, xylanase, glucanase, and the like in a considerable amount in good balance.

The polysaccharide-degrading activity of the enzyme agents (eg, Pleurotus cornucopiae enzyme) that can be used in the present invention is shown in Table 1. This enzyme preparation contains a lot of cellulase,
Most of them have a relatively high xylan activity. The optimum pH of this enzyme at 30 ° C. is 5 for cellulase and 6 for xylanase. Furthermore, regarding enzyme stability,
Cellulase has a pH of 5 to 7 and xylanase has a pH of 6 to 9, and it is possible to maintain an activity of 70% or more even after treatment at 30 ° C. for 24 hours. More specifically, xylanase can maintain an activity of 40% or more even if it is treated at pH 10 to 12 at 30 ° C. for 24 hours.
This indicates that xylanase is an alkali-resistant enzyme, and if treated at a pH of 7 to 12, cellulase activity can be suppressed and xylanase activity can be expressed at a higher level. On the contrary, if the treatment is carried out on the acidic side, both activities can be efficiently expressed, and the pulp fiber length can be adjusted.

Table 1 Polysaccharide-degrading enzyme activity (unit) ──────────────────── Substrate 5% Pleurotus cornucopiae enzyme preparation ────────── ────────── CMC 5.25 Avicel 0.24 Starch 3.00 Xylan 3.63 Pakiman 1.75 PNPG 0.08 ──────────────── ──── Protein amount 9.20 (mg / ml) ──────────────────── (Note) Enzyme activity is 40 ° C for 1 minute with each substrate and enzyme agent The amount of enzyme that produces a reducing sugar corresponding to 1 μmol of glucose was set to 1 unit.

According to the present invention, hemicellulose in wood pulp can be hydrolyzed, and at the same time, delignification treatment can be performed in a relatively short time, which is not possible by the conventional method, to obtain a satisfactory whiteness and Kappa number. Further, the wood pulp can be bleached while adjusting the cellulose fiber length in the pulp within the range of pH 2 to 12. Hereinafter, the present invention will be described in detail with reference to examples, but the invention is not limited thereto.

[0015]

Example 1 Unbleached softwood kraft pulp with a Kappa number of 14 was bleached. Enzymatic treatment was carried out as a pretreatment, and then a normal pulp bleaching treatment was carried out to obtain a bleached pulp by performing a six-stage process of oxygen treatment → chlorine dioxide treatment → caustic soda treatment → chlorine dioxide treatment → caustic soda treatment → chlorine dioxide treatment. At the same time, bleaching treatment was performed by a three-step process of chlorine dioxide treatment → caustic soda treatment → chlorine dioxide treatment, and the respective Kappa numbers were compared. Enzyme treatment is 40 ° C, 3 hours, pH
2, 4, 6, 8, 12 phosphate buffers, pulp concentration 1
Performed at 0%, 500 units / ml xylanase activity. Table 2 shows the Kappa number after the enzyme treatment at each pH performed as pretreatment, and Table 3 shows the Kappa number depending on the difference in the number of steps after the enzyme treatment. Almost no difference in Kappa number at each pH in the enzyme pretreatment was observed, and no difference in Kappa number due to the difference in the number of process steps thereafter was also observed. As a result, the bleaching step could be omitted in two steps, and the pretreatment with the enzyme was judged to be beneficial.

Table 2 Kappa number after enzyme treatment ──────────────────────────────── pH 2 4 6 8 12 ─ ─────────────────────────────── After enzyme treatment 8.3 8.4 8.0 8.1 8.1 Without enzyme addition (comparison) 13.9 13.8 13.9 13.7 13.8 ────────────────────────────────

Table 3 Kappa number due to difference in the number of process steps after enzyme treatment ───────────────────────────────── pH 2 4 6 8 12 ──────────────────────────────── After 6-step process 5.3 5.4 5.2 4.2 4.8 3-step process After 5.4 5.5 5.0 4.1 5.0 ─────────────────────────────────

[0018]

Example 2 Unbleached hardwood kraft pulp with a Kappa number of 10 was bleached. Enzymatic treatment was carried out as a pretreatment, and then a normal pulp bleaching treatment was carried out to obtain a bleached pulp by performing a six-stage process of oxygen treatment → chlorine dioxide treatment → caustic soda treatment → chlorine dioxide treatment → caustic soda treatment → chlorine dioxide treatment. At the same time, bleaching treatment was performed by a three-step process of chlorine dioxide treatment → caustic soda treatment → chlorine dioxide treatment, and the respective Kappa numbers were compared. Enzyme treatment is 40 ° C, 3 hours, pH
2, 4, 6, 8, 12 phosphate buffers, pulp concentration 1
Performed at 0%, 500 units / ml xylanase activity. Table 4 shows the Kappa number after the enzyme treatment at each pH performed as pretreatment, and Table 5 shows the Kappa number depending on the difference in the number of process steps after the enzyme treatment. Almost no difference in Kappa number at each pH in the enzyme pretreatment was observed, and no difference in Kappa number due to the difference in the number of process steps thereafter was also observed. As a result, the bleaching step could be omitted in two steps, and the pretreatment with the enzyme was judged to be beneficial.

Table 2 Kappa number after enzyme treatment ─────────────────────────────── pH 2 4 6 8 12 ── ───────────────────────────── After enzyme treatment 7.3 6.8 6.6 6.3 6.4 No enzyme addition (comparison) 10.0 10.1 9.9 9.8 9.8 ── ─────────────────────────────

Table 3 Kappa number due to difference in the number of process steps after enzyme treatment ───────────────────────────────── pH 2 4 6 8 12 ──────────────────────────────── After 6-step process 4.4 4.4 4.2 3.2 3.7 3-step process After 4.4 4.5 4.0 3.1 3.8 ────────────────────────────────

[0021]

EFFECTS OF THE INVENTION According to the present invention, hemicellulose in wood pulp is hydrolyzed, and at the same time, delignification treatment is carried out in a comparatively short time, which is not possible by the conventional method, to obtain satisfactory whiteness and Kappa number. . Furthermore, pH 2-12
Within the range, the wood pulp can be bleached while the cellulose fiber length in the pulp is adjusted.

Claims (3)

[Claims] 1. A method of bleaching pulp, which comprises enzymatically treating wood pulp with an enzyme agent obtained from a medium after basidiomycetes are cultivated and fruit bodies are harvested. 2. The origin of the enzyme preparation is Enokitake (Flammulina).
velutipes), Lyophyllum ulumarium,
Pleurotus ostreatns, oyster mushroom (Phollota na)
meko), Shiitake mushroom (Lentinus edodes), Maitake mushroom (Grifo)
The method for bleaching wood pulp according to claim 1, which is a kind selected from la frondosa). 3. The method for bleaching wood pulp according to claim 1, wherein the enzymatic treatment is carried out within a pH range of 2 to 12.