JPH08218290A - Production of non-chlorine-bleaching pulp - Google Patents

Abstract

PURPOSE: To obtain the non-chlorine-bleaching pulp having a high whiteness by digesting broad-leaf tree chips with a polysulfide solution containing an anthraquinone compound, bleaching the digested product with oxygen, treating the product with both an enzyme and a chelating agent, and subsequently bleaching the product with hydrogen peroxide. CONSTITUTION: The method for producing the non-chlorine-bleaching pulp comprises digesting a broad-leaf tree lignocellulose substance with a polysulfide digestion chemical agent solution containing an anthraquinone compound as a digestion auxiliary agent, bleaching the digested non-bleaching pulp having a Kappa value of 16.0-14.0 with oxygen, treating the product having a Kappa value of 9.5-7.0 with both an enzyme and a chelating agent, bleaching the product having a Kappa value of 8.5-6.0 with hydrogen peroxide, and subsequently bleaching the produced pulp having a Kappa value of 7.5-4.5 and a Hunter whiteness of 55-75% with one or more chemical, agents selected from a hypochlorite, chlorine dioxide, hydrogen peroxide and an alkali peroxide. Thus, the highly white pulp having a Hunter whiteness of >=84% is obtained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for oxygen bleaching chemical pulp. More specifically, it relates to a method for producing a chlorine-free bleached pulp in which a lignocellulosic material is made into a pulp having a low kappa number by polysulfide cooking to which an anthraquinone compound is added, and oxygen bleaching, simultaneous treatment of an enzyme and a chelating agent, and hydrogen peroxide bleaching are carried out.

[0002]

In order to use lignocellulosic material as a raw material for paper products, it is necessary to bleach the pulp obtained by cooking. Bleaching pulp decomposes and decomposes lignin and coloring substances adhering to the inside and surface of pulp fibers.
Deterioration or solubilization and removal. Bleaching of chemical pulp usually involves chlorine, hypochlorite, hydrogen peroxide,
A method of stepwise treatment with caustic soda and chlorine dioxide is used.

When the chlorine treatment is C, the alkali treatment is E, the hypochlorite treatment is H, the hydrogen peroxide treatment is P, and the chlorine dioxide treatment is D, C-E-H is a concrete multistage treatment. −
P-D, C-E-H-D-D, C-E-D-E-D and the like. Further, in recent years, an oxygen bleaching method has also been adopted for the purpose of reducing the load of wastewater and reducing the cost of bleaching chemicals, and is installed in the preceding step of the above-mentioned multistage bleaching treatment.

On the other hand, recently, so-called non-chlorine bleaching, which does not use chlorine-based chemicals, has been developed and put into operation in view of regulations and safety of AOX containing dioxin. Non-chlorine bleaching includes TCF that does not use chlorine and chlorine dioxide and other chlorine-based chemicals and ECF that does not use chlorine gas alone.

The most common method of ECF bleaching is to provide a chlorine dioxide stage as the first stage of the multistage bleaching process. As a specific method, D-E-D-E-D, D-E-H-P-
D, D-E-D-P-D, etc. are mentioned. Oxygen bleaching may be performed before these bleaching. More recently, ozone bleaching has been developed and incorporated into the bleaching stages of ECF and TCF. Non-chlorine bleaching methods using these chlorine dioxide and ozone are already known. Although non-chlorine bleaching can be achieved by these methods, bleaching wastewater cannot be recovered by non-chlorine bleaching using chlorine dioxide in the first stage, and ozone bleaching requires high equipment costs. was there.

[0006]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made extensive studies to solve the above-mentioned problems, and as a result, obtained a pulp with a low Kappa number by polysulfide cooking with addition of anthraquinone compound, oxygen bleaching, enzyme and chelate. It was found that non-chlorine bleaching can be achieved by simultaneously treating the agents and bleaching with hydrogen peroxide, and the present invention has been completed based on this finding. It is an object of the present invention to provide a non-chlorine bleaching method which solves the above-mentioned problems in non-chlorine bleaching and enables wastewater recovery at low cost.

[0007]

According to the present invention, a lignocellulosic material is cooked with a polysulfide cooking chemical containing an anthraquinone compound as a cooking aid, and a kappa number of 1 is obtained.
An unbleached pulp of 6.5 to 14.0 was obtained, and subsequently, a kappa number was adjusted to 9.5 to 7.0 by oxygen bleaching, and then an enzyme and a chelating agent were simultaneously treated to give a kappa number of 7.5 to 4. 5. Obtaining pulp with Hunter whiteness of 55-75%, and then bleaching with Hunter whiteness of 84% or more using one or more chemicals selected from hypochlorite, chlorine dioxide, hydrogen peroxide and alkali. The present invention relates to a method for producing non-chlorine bleached pulp, which is characterized by producing pulp.

The present invention comprises two means. One is a means for promoting delignification in the digestion step to lower the Kappa number, and the other is means for effectively using hydrogen peroxide in the bleaching step to increase the whiteness and lower the Kappa number. The chlorine-free bleaching of the present invention is achieved using these two means.

In order to reduce the load and easily increase the whiteness in the bleaching step, it is important to reduce the Kappa number of the unbleached pulp that enters the bleaching step. Especially in the case of chlorine-free bleaching that does not use chlorine, it is necessary to reduce the Kappa number of unbleached pulp. In the present invention, polysulfide cooking in which an anthraquinone compound is added as a cooking aid is performed as a means for reducing the Kappa number of unbleached pulp.

In the case of producing bleached pulp, the kappa number after cooking is usually 16.5 or more in kraft cooking. This is because if the cooking is advanced to a Kappa number of 16.5 or less, the cooking yield and the pulp viscosity are extremely lowered.

In the present invention, in order to reduce the load of the bleaching step, polysulfide cooking using an anthraquinone compound as a cooking aid is carried out to a kappa number of 16.5 or less. It is known that the polysulfide digestion improves the cooking yield compared to kraft digestion. Further, adding an anthraquinone-based compound as a cooking aid to perform cooking increases the delignification rate and reduces the Kappa number,
It is known to further improve the cooking yield.

In the present invention, both are combined to obtain unbleached pulp having a Kappa number of 16.5 or less. The cooking method and conditions are as follows. Polysulfide cooking can be done in several ways. One method is to add sulfur to the cooking liquor of Kraft cooking. Although this method can also perform polysulfide cooking, it is not so preferable because it has a drawback that the balance of alkali and sulfur in the process is lost.

As a preferred method, there is a method of producing polysulfide by oxidizing sodium sulfide contained in white liquor which is a cooking chemical. As a concrete means of this method, for example, Japanese Patent Publication No.
2100 and the like, and polysulfide cooking can be carried out by these methods.

The polysulfide cooking conditions are as follows: cooking temperature 140 to 200 ° C., preferably 160 to 180 ° C., cooking time 10 to 360 minutes, preferably 20 to 240 minutes, effective alkali addition rate 10 to 25% by weight (Na ₂ O conversion). , To dry chips) It is preferably 12 to 20% by weight (Na ₂ O equivalent, dry chips). The polysulfide addition rate is required to be 0.7% by weight or more (converted to S, to dry chips) in order to effectively exhibit the effect of polysulfide cooking.

The anthraquinone-based compound used as a cooking aid is anthraquinone, 1, 4, 4a, 9a
-Tetrahydro-9.10-anthraquinone, 1.4-
Examples include dihydro-9.10-dihydroxyanthracene and salts thereof. The addition rate of the anthraquinone compound is 0.005 to 0.2% by weight (relative to dry chips), preferably 0.01 to 0.1% by weight (relative to dry chips).

With regard to the cooking conditions for these polysulfide cookings and the addition rate of the anthraquinone compound, suitable conditions can be selected so that the Kappa number after cooking becomes 14.0 to 16.5. Oxygen bleaching is performed after polysulfide cooking, and it is known that the Kappa number after oxygen bleaching is proportional to the Kappa number after cooking. Therefore, if the Kappa number after polysulfide cooking is reduced to 14.0 to 16.5, the Kappa number after oxygen bleaching is also reduced, and the pulp of the present invention having a Kappa number of 7.0 to 9.5 is obtained under ordinary oxygen bleaching conditions. Is obtained.

Oxygen bleaching in this case is generally carried out by a method called medium concentration oxygen bleaching.
-15%, temperature 70-140 ° C, residence time 10-90
Min, pressure atmospheric pressure to 9 kg / cm ² , oxygen addition rate 0.5 to
3.0% by weight (versus dry pulp), alkali addition rate 0.5
-3.0 wt% (vs. dry pulp). When performing a method called high-concentration oxygen bleaching, the pulp concentration is 20 to 4
0%, and other conditions are the same as the above medium concentration.

The oxygen bleaching treatment gave a Kappa number of 7.0 to 9.
After setting to 5, the enzyme and the chelating agent are simultaneously treated and hydrogen peroxide bleaching is performed, but if the Kappa number is 9.5 or more, it becomes difficult to increase the whiteness to a predetermined level by hydrogen peroxide bleaching.
If the Kappa number is 7.0 or less, the pulp viscosity and the yield are lowered, which is not preferable.

Prior to the bleaching with hydrogen peroxide, the enzyme and the chelating agent are simultaneously treated, but the enzyme that can be used is called hemicellulase or cellulase, which is an enzyme that hydrolyzes hemicellulose, and is intended for hardwood pulp. Uses an enzyme mainly composed of xylanase. The chelating agent used is diethylenetriamine pentaacetic acid (DTP
A), organic chelating agents containing nitrogen such as nitrilotriacetic acid (NTA), and chelating agents composed of salts of these polymers such as polyalkylene polyamine polyacetate.

Treatment is carried out with a mixture of these enzymes and a chelating agent. The treatment conditions are pulp concentration of 2 to 20%, treatment temperature of 30 to 80 ° C., treatment time of 30 to 150 minutes, and treatment p.
H4 to 10, the amount of enzyme added is 0.1 for xylanase
-1000 U / g (vs. absolute dry pulp), and the amount of chelating agent added is 0.01-5 wt% (vs. absolute dry pulp). Here, the xylanase activity is 1 μl per minute when 1 ml of 1% xylan (pH about 5) and 1 ml of enzyme are allowed to act at 50 ° C. for 30 minutes.
The activity of producing a reducing sugar corresponding to mol xylose is expressed as 1 U / g.

The kappa number is adjusted to 6.0 to 8.5 by simultaneous treatment of the enzyme and the chelating agent under these conditions, but the reduction of the kappa number in this treatment is mainly due to the effect of delignification by the enzyme. The reduction in Kappa number due to this treatment is 1.
0 to 2.0 is preferable. When it is 1.0 or less, the subsequent hydrogen peroxide bleaching is loaded, and when it is 2.0 or more, the pulp viscosity and the yield are lowered, which is not preferable.

Hydrogen peroxide bleaching is carried out after the simultaneous treatment of the enzyme and the chelating agent. Bleaching conditions for hydrogen peroxide are 0.1 to 3.0% by weight of hydrogen peroxide added (vs. dry pulp), reaction temperature 3
0 to 120 ° C., reaction time 30 to 240 minutes, reaction pH 8 to
13, the pulp concentration is 2 to 20%. Bleaching with hydrogen peroxide under these conditions gives a pulp having a Hunter whiteness of 55 to 75% and a Kappa number of 4.5 to 7.5.

In the present invention, bleaching is then carried out using one or more of hypochlorite, chlorine dioxide, hydrogen peroxide and alkali. When the hypochlorite treatment is H, the chlorine dioxide treatment is D, the hydrogen peroxide treatment is P, and the alkali treatment is E, the treatment methods after hydrogen peroxide bleaching are HPD, DD, and H-.
D, D-E-D, etc. As the bleaching conditions for these bleaching stages, the bleaching conditions for each stage in the ordinary multistage bleaching of chemical pulp can be used as they are. If the pulp obtained after bleaching with hydrogen peroxide obtained in the present invention has a Hunter whiteness of 55 to 75% and a Kappa number of 4.5 to 7.5, these multistage bleaching methods are commonly used bleaching methods, and the object of the present invention is It is possible to obtain a bleached pulp having a Hunter whiteness of 84% or more.

The production of the chlorine-free bleached pulp of the present invention is accomplished by a production process from the series of cooking steps to the bleaching step.

[0025]

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 examples, whiteness is JIS
P8123 (Hunter whiteness method), Kappa number is TAP
PI T336hm-85, pulp viscosity is TAPPI
It was measured by the method of T230om-82.

Example 1 Using domestic hardwood chips, polysulfide cooking to which an anthraquinone compound was added was performed. Cooking conditions are effective alkali addition rate 14% by weight (Na ₂ O conversion, absolute dry chips), cooking temperature 170 ° C., cooking time 45 minutes, polysulfide addition rate 1.0% by weight (S conversion, absolute dry chips), Anthraquinone compound addition rate 0.05% by weight
(Vs. dry chips).

The polysulfide cooking liquor used was prepared by air-oxidizing the kraft cooking liquor by the method described in Japanese Patent Publication No. 05-032100. The anthraquinone compound used was a sodium salt of 1,4-dihydro-9,10-dihydroxyanthracene (trade name: SAQ manufactured by Kawasaki Kasei Co., Ltd.). Table 1 shows the Kappa number, pulp viscosity and cooking yield of the unbleached pulp obtained.

The above unbleached pulp was then bleached with oxygen. The bleaching condition is that the alkali addition rate is 1.5% by weight (NaOH
Conversion, dry pulp), reaction temperature 110 ° C, reaction time 6
The pulp density was 0% for 0 minutes. Table 1 shows the Kappa number and pulp viscosity of the pulp obtained by oxygen bleaching.

After bleaching with oxygen, bleaching with hydrogen peroxide was followed by treatment by simultaneously adding an enzyme and a chelating agent. Simultaneous treatment conditions of enzyme and chelating agent are 10 xylanases.
U / g (against dry pulp) and 0.2 wt% of diethylenetriamine pentaacetic acid (DTPA) as a chelating agent were added at the same time to obtain a pulp concentration of 10% and a treatment temperature of 50.
C., the treatment time was 60 minutes, and the treatment pH was 5.0. enzyme,
Table 1 shows the Kappa number and pulp viscosity of the pulp obtained by the simultaneous treatment with the chelating agent.

Then, hydrogen peroxide bleaching was performed. The bleaching conditions are as follows: hydrogen peroxide addition rate 1.0% by weight (versus dry pulp), reaction temperature 80 ° C., reaction time 100 minutes, reaction pH 11.0,
The pulp concentration was 12%. The Kappa whiteness and pulp viscosity of the pulp obtained by bleaching with hydrogen peroxide are shown in Table 1.

Bleaching was then carried out in the HPD bleaching sequence. The sodium hypochlorite bleaching condition is that the sodium hypochlorite addition rate is 0.8% by weight (vs. dry pulp), the reaction temperature is 60 ° C., the reaction time is 120 minutes, and the pulp concentration is 12%. Hydrogen peroxide addition rate 0.15% by weight (vs. dry pulp), reaction temperature 70 ° C, reaction time 11
The chlorine dioxide bleaching conditions were as follows: chlorine dioxide bleaching conditions: chlorine dioxide addition rate: 0.3% by weight (versus dry pulp), reaction temperature: 75 ° C., reaction time: 140 minutes, pulp concentration: 12%. The whiteness, pulp viscosity and yield of the obtained bleached pulp are shown in Table 1.

Example 2 Polysulfide cooking was carried out under the same conditions as in Example 1 except that the same domestic hardwood chips as in Example 1 were used and anthraquinone was used as the anthraquinone compound. Table 1 shows the Kappa number, pulp viscosity and cooking yield of the unbleached pulp obtained.

After oxygen bleaching, the enzyme and the chelating agent were simultaneously treated under the same conditions as in Example 1 except that diethylenetriaminepentaacetic acid (DTPA) was used as the chelating agent.
Table 1 shows the Kappa number, pulp viscosity and cooking yield of the obtained pulp.

Next, the amount of hydrogen peroxide added was 1.2% by weight.
Bleaching with hydrogen peroxide was carried out under the same conditions as in Example 1 except that (to the absolute dry pulp) was used. Table 1 shows the Kappa number and pulp viscosity of the pulp obtained by bleaching.

Then, bleaching was carried out in the D-E-D bleaching sequence. The first chlorine dioxide bleaching condition was a chlorine dioxide addition rate of 0.4% by weight (vs. dry pulp), a reaction temperature of 75 ° C., a reaction time of 120 minutes, and a pulp concentration of 12%, and the alkali treatment condition was a sodium hydroxide addition rate of 0. 0.5% by weight (vs. absolute dry pulp), reaction temperature 70 ° C., reaction time 110 minutes, pulp concentration 12%, and chlorine dioxide bleaching conditions in the final stage were chlorine dioxide addition rate 0.25% by weight (vs. absolute dryness). Pulp, reaction temperature 75 ° C., reaction time 140 minutes, pulp concentration 12%. The whiteness, pulp viscosity and yield of the obtained bleached pulp are shown in Table 1.

Comparative Example 1 Kraft cooking was performed using the same domestic hardwood chips as in Example 1. The cooking conditions are as follows: effective alkali addition rate 14.5% by weight (Na ₂ O conversion, anti-drying chips), cooking temperature 170
C., the cooking time was 45 minutes.

The above-mentioned unbleached pulp was sequentially subjected to oxygen bleaching, simultaneous treatment with enzyme and chelating agent, hydrogen peroxide bleaching and then bleaching in the HPD sequence under the same conditions as in Example 1.
Table 1 shows the Kappa number, whiteness, pulp viscosity and yield of pulp obtained by cooking and bleaching stages.

Comparative Example 2 Same as Comparative Example 1 except that the same domestic hardwood chips as in Example 1 were used and the effective alkali addition rate was changed to 17% by weight (Na ₂ O conversion, absolutely dry chips) under cooking conditions. Kraft cooking was carried out under the conditions.

The unbleached pulp was sequentially bleached with oxygen under the same conditions as in Example 1, simultaneously treated with an enzyme and a chelating agent, bleached with hydrogen peroxide and then bleached with the HPD sequence.
Table 1 shows the Kappa number, whiteness, pulp viscosity and yield of pulp obtained by cooking and bleaching stages.

Comparative Example 3 Using the same domestic hardwood chips as in Example 1, Example 1
Under the same conditions as above, polysulfide cooking with addition of anthraquinone compound was carried out, followed by oxygen bleaching. After oxygen bleaching, a chelating agent was treated prior to hydrogen peroxide bleaching.
The treating conditions were 0.2% by weight of diethylenetriamine pentaacetic acid (DTPA) as a chelating agent (versus dry pulp), pulp concentration of 10%, treating temperature of 60 ° C., treating time of 60 minutes, and treating pH of 6.0. Example 1 after simultaneous treatment with chelating agent
Hydrogen peroxide bleaching was carried out under the same conditions as above, followed by bleaching with an HPD sequence. Table 1 shows the Kappa number, whiteness, pulp viscosity and yield of the pulp obtained in the cooking and bleaching stages.

Comparative Example 4 Using the same domestic hardwood chips as in Example 1, Example 1
Under the same conditions as above, polysulfide cooking with addition of anthraquinone compound was carried out, followed by oxygen bleaching. After the oxygen bleaching, the enzyme treatment was performed prior to the hydrogen peroxide bleaching. The treatment conditions were that xylanase as an enzyme was added at 10 U / g (vs. dry pulp), the pulp concentration was 10%, the treatment temperature was 50 ° C., the treatment time was 60 minutes, and the treatment pH was 5.0. After the enzyme treatment, bleaching with hydrogen peroxide was carried out under the same conditions as in Example 1, followed by bleaching with the HPD sequence. Table 1 shows the kappa number, whiteness, pulp viscosity and yield of pulp obtained by cooking and bleaching stages.
Shown in

[0042]

[Table 1]

Examples 1 and 2 in Table 1 and Comparative Examples 1, 2, 3 and
From the comparison of 4, when a pulp having a low Kappa number was obtained by polysulfide cooking to which the anthraquinone compound of the present invention was added, and oxygen bleaching, simultaneous treatment of enzyme and chelating agent and hydrogen peroxide bleaching were performed, yield and pulp quality were improved. It can be seen that non-chlorine bleaching can be performed without lowering, resulting in a high brightness pulp.

[0044]

EFFECTS OF THE INVENTION By using the non-chlorine bleaching method of the present invention, bleaching can be performed with less equipment cost as compared with the conventional non-chlorine bleaching method, and wastewater of the first and second stages of bleaching can be recovered. There is an advantage that you can.

Claims (1)

[Claims] 1. A hardwood lignocellulosic material is digested with a polysulfide cooking chemical containing an anthraquinone compound as an auxiliary agent to obtain unbleached pulp having a Kappa number of 16.0 to 14.0, followed by oxygen bleaching. To 9.5
To 7.0, then simultaneously treat the enzyme and chelating agent to a Kappa number of 8.5 to 6.0, and bleach with hydrogen peroxide to give a Kappa number of 7.5 to 4.5 and Hunter whiteness. Obtaining 55-75% pulp, then hypochlorite,
1 selected from chlorine dioxide, hydrogen peroxide, and alkali
A method for producing a chlorine-free bleached pulp, which comprises producing a bleached pulp having a Hunter whiteness of 84% or more using the above chemicals.