JP3360694B2 - Delignification bleaching method of chemical pulp for papermaking. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the treatment of chemical pulp for papermaking, and more particularly to an improvement in the delignification and bleaching treatment of chemical pulp.

[0002]

2. Description of the Related Art Bleaching of chemical pulp for papermaking is carried out by a multistage bleaching treatment. Conventionally, chlorine bleaching chemicals have been used as bleaching agents in this multi-stage bleaching.
Specifically, chlorine (C), hypochlorite (H), chlorine dioxide
By the combination of (D), for example, CEHD, C / D-
EHED (C / D is a combined bleaching stage of chlorine and chlorine dioxide,
(E stands for an alkali extraction stage).

[0003] However, these chlorine-based bleaching chemicals produce by-products of organic chlorine compounds that are harmful to the environment during bleaching, and there is a problem of environmental pollution of bleaching wastewater containing these organic chlorine compounds.
Organochlorine compounds are generally analyzed and evaluated by the AOX method, for example, the United States Environment Agency method (EPA METHOD-9020).

[0004] In order to reduce or prevent by-products of organic chlorine compounds, it is most effective to reduce or not use chlorine-based chemicals. As a method of reducing the amount of chlorine-based bleaching chemicals used, an oxygen bleaching method in which oxygen is allowed to act under high temperature and pressure in an alkaline medium at the first stage after the digestion treatment has been developed, and is now widely used. According to this oxygen bleaching method, 40 to 5 of lignin remaining after cooking is removed.
Since 0% is removed, not only can the amount of the subsequent bleaching chemicals be reduced, but also the waste liquid of the oxygen bleaching process can be circulated to the digestion process, so that the chemicals and energy can be recovered, In addition, the load of wastewater treatment can be reduced.

[0005] However, in order to obtain high whiteness even by introducing the oxygen bleaching method, it is necessary to use a considerably large amount of chlorine bleaching chemicals in the subsequent stage, and as a result, a considerable amount of organic chlorine compounds is produced as a by-product. It is inevitable to do.

As an improvement of the oxygen bleaching method, a method of bleaching pulp after digestion using oxygen and peroxide is disclosed in Japanese Patent Application Laid-Open No. Sho 6
It is disclosed in JP-A-2-53497 and JP-A-3-14687. However, as a result of investigations by the present inventors, delignification or high whiteness is not sufficient, and a considerable amount of chlorine-based bleaching chemicals still has to be used.

Further, in Japanese Patent Publication No. 2-15671, oxygen and peroxide, cyclic keto compounds and / or
Alternatively, it is possible to increase the whiteness without deterioration of the pulp by using a cyclic amino compound system. However, this method makes it difficult to recover and reuse expensive cyclic keto compounds and / or cyclic amino compounds. However, the chemical cost is considerably high, which is economically disadvantageous.

Further, as a method of subjecting a chemical pulp after digestion treatment to acid treatment and then bleaching with hydrogen peroxide (Ep), Japanese Patent Application Laid-Open No.
No. 1-102103, JP-A-56-85489 and JP-B-2-17679 have been proposed. These include acid treatment and hydrogen peroxide at 100 ° C. or lower without adding oxygen. It is described that bleaching increases delignification. However, as a result of investigations by the present inventors, any of these methods cannot always provide a sufficient effect in terms of delignification and high whiteness.

In Japanese Patent Application Laid-Open No. 2-264087, oxygen bleaching is followed by xylanase enzyme treatment, followed by chlorine treatment, chlorine dioxide treatment, hypochlorite treatment, peroxide treatment in an alkaline medium, and ozone treatment. A method of performing a nitrogen dioxide treatment has been proposed. However, this method is mainly intended to perform chlorination or chlorine dioxide treatment after xylanase enzyme treatment, and is a method for reducing or eliminating chlorine by xylanase enzyme treatment. According to the contents of the publication, it is possible to perform a peroxide treatment in an alkaline medium after the xylanase enzyme treatment. The material treatment does not provide a sufficient effect on the peroxide treatment itself.

Japanese Patent Application Laid-Open No. 3-27191 proposes a method in which a chelating agent treatment is performed after oxygen bleaching, followed by delignification and bleaching with hydrogen peroxide or hydrogen peroxide and oxygen in an alkaline medium. . This method is a method of performing delignification and bleaching again with hydrogen peroxide or hydrogen peroxide and oxygen after oxygen bleaching, so it is more effective than the above series of delignification and bleaching methods, but the effect is not sufficient. .

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the load of post-stage bleaching in delignification and bleaching of chemical pulp for papermaking by promoting delignification and high whiteness without deterioration of the pulp. To provide an economical means to make this happen. Then, the amount of chlorine-based bleaching chemicals used in the subsequent stage is reduced, the by-products of organic chlorine compounds are suppressed, and environmental pollution due to bleaching wastewater is prevented.

[0012]

Means for Solving the Problems The present inventors have worked on a method for delignifying and bleaching pulp economically, and in Japanese Patent Application Laid-Open No. 3-64589, the pulp which has been digested is acid-treated. 50 ~ 90 ℃, atmospheric pressure ~ 3Kg
An oxygen bleaching method using peroxide at / cm ² was announced. The present inventors have further studied and obtained pulp with high whiteness and high quality without the need for drastic changes in the commonly used bleaching equipment, and significantly reduced the amount of chlorine-based bleaching chemicals used. As a result of intensive studies on ways to reduce the costs,
The cooked pulp is subjected to ordinary high-temperature and high-pressure oxygen bleaching treatment, followed by xylanase enzyme treatment with a chelating agent, or xylanase enzyme treatment, and then an acid is added to the same system, followed by continuous acid treatment. Alternatively, it has been found that bleaching with peroxide and oxygen can provide a delignified and highly whitened pulp very effectively, thereby completing the present invention.

That is, the present invention provides a chemical pulp that has been digested, subjected to a high-temperature and high-pressure oxygen bleaching treatment, followed by a xylanase enzyme treatment, and then peroxide or peroxide in an alkaline medium. Delignification by oxygen
The present invention relates to a method for bleaching chemical pulp for papermaking, which comprises performing bleaching. INDUSTRIAL APPLICABILITY The present invention is suitable for bleaching chemical pulp for papermaking, and particularly suitable for delignification and bleaching of kraft pulp derived from hardwood and softwood.

In the present invention, the digested chemical pulp is first subjected to a normal high-temperature and high-pressure oxygen bleaching treatment (hereinafter, referred to as a “high-pressure oxygen bleaching treatment”).
This high temperature / high pressure oxygen bleaching is sometimes referred to as O or O stage). The pulp concentration, temperature, time, alkali amount, oxygen amount, and operating pressure in the O-stage treatment are performed in accordance with generally performed conditions. For example, the pulp concentration is 7 ~
30%, preferably 10-20%, temperature 60-130 ° C
Preferably, the treatment time is 90 to 110 ° C, the treatment time is 20 to 150 minutes, preferably 30 to 90 minutes, and the alkali amount is 0.5 to 6.0%, preferably 1.0 to 3.0%, based on NaOH in terms of absolute dry pulp.
0%, the amount of oxygen per oven-dry pulp 0.5 to 5.0%, operating pressure 2.5~10Kg / cm ^2, preferably 3.5~8Kg
/ Cm ² .

The pulp after the O-stage treatment is washed and dehydrated, and then treated with a xylanase enzyme (Q) solution in combination with a chelating agent (K) (hereinafter, this treatment may be referred to as K + Q or K + Q stage) or xylanase After the treatment, the acid is added to the same system, and the continuous acid treatment with an acid solution (hereinafter, referred to as
(This process is sometimes referred to as Q → A or Q → A stage.)
I do.

The K + Q of the present invention depends on the state of the pulp, but for example, the pulp concentration is 1 to 30%, preferably 2 to 1%.
5% at a temperature of 20-95 ° C, preferably 40-80 ° C,
Processing time is 15 minutes to 400 minutes, preferably 30 to 200 minutes.
The treatment is carried out at a pH of 3 to 9, preferably 4 to 8.

The chelating agent used is at least one chelating agent selected from the group consisting of an aminocarboxylate-based chelating agent and an aminoalkylphosphate-based chelating agent represented by Chemical formula 2. Specifically, as aminocarboxylate-based chelating agents, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTP)
A), N-hydroxyethylethylenediamine-N,
N ′, N ″ -triacetic acid (HEDTA), nitrilotriacetic acid (NTA), cyclohexanediaminetetraacetic acid (CyD
TA) and its salts, and aminotrimethylenephosphonic acid (ATM)
P), ethylenediaminetetramethylenephosphonic acid (E
DTMP), diethylenetriaminepentamethylenephosphonic acid (DTPMP), propylenediaminetetramethylenephosphonic acid (PDTMP), dipropylenetriaminepentamethylenephosphonic acid (DPTPMP), and salts thereof, and at least one of them is used. The amount of the chelating agent used varies depending on the amount of heavy metals contained in the pulp and the service water, but is 0.01 per absolutely dry pulp.
To 5.0% by weight, preferably 0.05 to 1.0% by weight.

Embedded image (X ₂ O ₃ PCH ₂ ) ₂ · N · {(CH ₂ ) _m · N · CH ₂ PO ₃ X ₂ » _n
CH ₂ PO ₃ X ₂ wherein X represents hydrogen, ammonium, or an alkali metal, m represents an integer of 2 to 3, and n represents an integer of 0 to 3. ]

As the xylanase to be used, a commercially available xylanase product can be used as it is, and its active concentration is 0.5 to 100 IU, preferably 2.5 to 50 IU per gram of pulp.
Used in the IU range. For example, an active concentration of 5000
IU / g of commercially available xylanase would have a pulp content of 0.0.
It is used in an amount of 1 to 2.0% by weight, preferably 0.05 to 1.0% by weight.

The pulp after the xylanase treatment is separated from the xylanase solution by a dehydrator and then preferably washed. The xylanase treatment of the present invention also includes the dehydration and washing steps. The separated xylanase solution can be reused in the same treatment step and / or used for washing pulp after the digestion step and after the O-stage treatment, and in some cases, can be recycled to the digestion step.

In the K + Q treatment, a chelating agent may be used, followed by a xylanase enzyme treatment (K → Q), or a xylanase enzyme treatment followed by a chelating agent treatment (Q → K). A washing operation may be inserted between the chelating agent treatment and the xylanase enzyme treatment. The processing conditions are the same as those of the K + Q stage. Note that K + Q processing and K
The effects of the → Q and Q → K treatments are almost the same, and K + Q is preferred from the viewpoint of reducing the number of steps and time.

The Q → A treatment of the present invention depends on the state of the pulp, but for example, the pulp concentration is 1 to 30%, preferably 2 to 30%.
~ 15%, most preferably 3 ~ 10%, temperature 30 ~ 95
C., preferably at 40-80.degree. The treatment time is 15 minutes to 400 minutes, preferably 30 to 200 minutes for the xylanase enzyme treatment, and the subsequent acid treatment is performed for 5 to 120 minutes, preferably 15 to 60 minutes. In the xylanase enzyme treatment, the pH is set at pH 3 to 9, preferably 4 to 8, and the subsequent acid treatment is carried out at pH 1 to 5, preferably pH 1.5 to 3, by adding an acid to the same system after the xylanase enzyme treatment. .

The pulp after the Q → A treatment is separated from the acid solution by a dehydrator and then preferably subjected to washing. The Q → A treatment of the present invention also includes this dehydration and washing step. The separated acid solution can be reused for the acid treatment step and / or used for washing the pulp after the cooking step and after the O treatment,
In some cases, it can be recycled to the cooking process.

As the xylanase to be used, a commercially available xylanase product can be used as it is, and its active concentration is 0.5 to 100 IU, preferably 2.5 to 50 IU per gram of pulp.
Used in the IU range. For example, an active concentration of 5000
IU / g of commercially available xylanase would have a pulp content of 0.0.
It is used in an amount of 1 to 2.0% by weight, preferably 0.05 to 1.0% by weight.

The acid used for adjusting the pH to 1 to 5 may be any of an inorganic acid and an organic acid. In particular, an inorganic acid is preferable, and sulfuric acid, nitric acid, sulfurous acid, nitrous acid, and a mixture of these acids are used. Is done. Among them, sulfuric acid and sulfurous acid can be suitably used because they are not only available at low cost but also have low corrosiveness. Especially when kraft cooking is taking place,
This results in the advantage that the acid solution after acid treatment can be used as a replenisher for chemicals in kraft cooking.

In the Q → A treatment, washing may be performed after the xylanase enzyme treatment, followed by acid treatment. Alternatively, an acid treatment may be performed, followed by washing, further neutralization, and then a xylanase enzyme treatment (A → Q). The processing conditions are Q →
The processing is performed under the same processing conditions except that the stage A is reversed. The effects of the Q → A treatment and the A → Q treatment are almost the same, and Q → A is preferred from the viewpoint of reducing the steps and time.

The pulp after K + Q stage or after Q → A stage is
Subsequently, the mixture is subjected to a delignification / bleaching step using peroxide or peroxide and low-pressure oxygen (hereinafter, this peroxide bleaching step is referred to as Ep or Ep stage, and the peroxide-combined low-pressure oxygen bleaching step is referred to as Eop or Eop). Sometimes referred to as a step). In this treatment, the pulp is subjected to delignification and bleaching action of peroxide or peroxide and low pressure oxygen in an alkaline medium. In the case of a combination of peroxide and low pressure oxygen, both act on the pulp simultaneously.

As the alkaline agent in the Ep stage or the Eop stage, caustic soda, caustic potash, lime, soda ash and the like can be used. Among them, caustic soda is inexpensive,
Recycling to the cooking step can reduce the replenishment amount of chemicals in the cooking step, so that it can be suitably used. The amount of the alkaline agent used is 0.1 in terms of NaOH per absolutely dry pulp.
-6.0 wt% is preferable, and 0.5-3.0 wt% is more preferable. If the amount of the alkaline agent is smaller than this, the delignification / bleaching effect is reduced, and if it is larger than this, the viscosity of the pulp is significantly reduced.

As oxygen in the Eop stage, oxygen gas and air can be used, but oxygen gas is preferable. The amount of oxygen used is 0.1 to 2.0% by weight, preferably 0.2 to 1.0% by weight, based on the dry pulp, and the processing operation pressure in the Eop stage is atmospheric pressure to 3.5 kg / kg. cm ² is preferred. As the peroxide, hydrogen peroxide, an adduct of hydrogen peroxide with inorganic salts, inorganic and organic peroxides such as sodium peroxide, formic acid, and peracetic acid can be used, and hydrogen peroxide is generally preferred. Used for The amount of the peroxide to be used is preferably 0.05 to 8.0% by weight, more preferably 0.2 to 3.0% by weight, based on 100% hydrogen peroxide, based on the absolutely dry pulp. If the amount of peroxide is less than this, the delignification / bleaching effect is low, and if it is more than this, the efficiency of peroxide decreases.

In the Ep stage and the Eop stage of the present invention, the order of adding chemicals to the pulp is preferably an alkali agent and oxygen in this order. It is preferred to be performed in.

The pulp concentration of the Ep stage and the Eop stage of the present invention is preferably from 7 to 30%, more preferably from 10 to 20%. The temperature is preferably from 40 to 120 ° C, more preferably from 70 to 95 ° C. The treatment time is preferably from 15 to 150 minutes, more preferably from 30 to 120 minutes.

Further, the inventors unexpectedly found that Q
→ We found that pulp pretreated with acid by using a mixture of sulfuric acid and sulfurous acid in the acid treatment in the A stage was very effectively delignified and bleached by low-pressure oxygen bleaching using a subsequent peroxide. . In this case, the ratio of both in the mixture of sulfuric acid and sulfurous acid is 0.02 as sulfuric acid / sulfuric acid (weight ratio).
1-2 are preferable, 0.02-1 are more preferable, and 0.1 is preferable.
Most preferably, it is from 0.5 to 0.5. PH of solution in acid treatment
And other treatment conditions, the method of operating the acid solution after the treatment, and the like are the same as the above-described acid treatment conditions.

Further, in the Ep stage and the Eop stage, it is preferable to use a magnesium compound. . The use of the magnesium compound increases the delignification bleaching action of the peroxide and reduces the decrease in the viscosity of the pulp.
As the magnesium compound, magnesium sulfate, magnesium hydroxide, magnesium oxide, magnesium carbonate, magnesium nitrate and the like can be used, but magnesium sulfate is generally used. The amount of the magnesium compound used is preferably 0.005 to 0.75% by weight, preferably 0.01 to 0.3% by weight in terms of the amount of magnesium ions based on the absolutely dry pulp.
% By weight is more preferred. Preferably, the addition of the magnesium compound is made prior to the addition of the alkaline agent, oxygen and peroxide. That is, pulp slurry
When is in a neutral to weakly acidic range, it is preferable to add a magnesium compound from the viewpoint of uniform dispersibility of the magnesium compound.

In the present invention, O- (K + Q) -Ep (or E
op), the bleached pulp obtained by O- (Q → A) -Ep (or Eop) has a considerably high whiteness as it is, but further bleaching with the continuous addition of multiple bleaching steps results in further bleaching. Pulp having high whiteness can be obtained. In this case, since a high delignification has already been achieved in the Ep stage and the Eop stage, and in a high whiteness state, bleaching using little or no chlorine and hypochlorite is performed as the subsequent bleaching. It is possible.

For example, O- (K + Q) -Ep (or E
op), O- (Q → A) -Ep (or Eop) step, chlorine dioxide bleaching (D), then peroxide bleaching (P)
O- (K + Q) -Ep (or Eop) -D-
Full bleaching without chlorine and hypochlorite, such as P, O- (Q → A) -Ep (or Eop) -DP
Kens is possible. In these full bleaching sequences, the current typical full bleaching sequence, OC
/ D-Eo (combined use of low pressure oxygen in stage E) -HD and pulp products with high viscosity and high whiteness equal to or higher than H-D. Further, since chlorine and hypochlorite are not used, Bleaching with significantly less AOX production compared to current methods is possible.

The chlorine dioxide bleaching (D) stage in the present invention is carried out under ordinary D stage conditions. For example, the pulp concentration is 7 to 30%, the temperature is 40 to 90 ° C, the time is 1 to 4 hours, and the amount of chlorine dioxide used per pulp is 0.1 to 2.0% by weight.

The subsequent peroxide bleaching (P) stage is carried out under normal peroxide bleaching conditions. That is, the pulp concentration is 7 to 30% and the temperature is 40 to
The reaction is performed at 100 ° C. for a time in the range of 1 to 4 hours. Examples of the alkaline agent include caustic soda, caustic potash, lime, soda ash and the like, and caustic soda is generally used. The amount of the alkali agent used is in the range of 0.1 to 2% by weight as caustic soda per pulp. Examples of the peroxide include hydrogen peroxide, adducts of hydrogen peroxide with inorganic salts, and inorganic and organic peroxides such as sodium peroxide, formic acid, and peracetic acid. Hydrogen is used, and the amount of peroxide used is in the range of 0.1 to 3.0% by weight per absolutely dry pulp in terms of 100% hydrogen peroxide.

A feature of the present invention is to perform effective delignification bleaching in the O- (K + Q) -Ep (or Eop) or O- (Q → A) -Ep (or Eop) process.
In that case, xylanase enzyme treatment (Q treatment) is included (K +
The effects of (Q) and (Q → A) are considered as follows.

That is, although the Q treatment itself has a considerable delignification effect, when the peroxide treatment is performed next (Q-Ep (or Eop)), the effect of the peroxide at the subsequent stage can be obtained only by the Q treatment. It is rather bad and cannot perform effective Ep (or Eop) processing. Here, when the Q treatment is combined with the chelating agent treatment (K treatment) or the acid treatment (A treatment) and then subjected to peroxide treatment, ((K + Q) -Ep
(Or Eop), (Q → A) -Ep (or Eo
p)), the effect of the peroxide is remarkably improved, and effective delignification bleaching can be performed.

First, the (K + Q) action of the present invention is to remove lignin with xylanase to some extent while removing heavy metals having peroxide decomposition activity from pulp with a chelating agent. That is, in the pulp after the (K + Q) treatment, the presence of heavy metals is considerably reduced, so that unnecessary decomposition of peroxide is reduced, the amount of peroxide involved in bleaching is retained, and the pulp is deoxidized by enzymes. Since lignin is progressing, peroxides and oxygen are in a state where they easily react effectively. It is considered that the peroxide and oxygen effectively act on the pulp by the effect, delignification and whiteness are efficiently advanced, and high-quality pulp is obtained.

Next, the action of (Q → A) of the present invention is (K +
It is considered that, as in the treatment Q), heavy metals having peroxide decomposition activity are removed from the pulp, delignification proceeds, and lignin is easily decomposed. That is, delignification is first performed by Q treatment, and then heavy metal is hardly present by A treatment, so that unnecessary decomposition of peroxide in the subsequent stage is reduced, and the amount of peroxide involved in bleaching is maintained. Is done. In addition, despite the fact that the progress of delignification is not recognized in the acid treatment itself, there is an effect that delignification and bleaching further progress in peroxide bleaching and peroxide combined oxygen bleaching after the acid treatment. The delignification / bleaching effect becomes more remarkable in peroxide combined oxygen bleaching. The above shows that the acid treatment has an effect of changing lignin so as to be easily subjected to decomposition by oxygen and peroxide.
It is considered that by these effects of the (Q → A) treatment, delignification and high whiteness proceed efficiently, and high-quality pulp can be obtained.

The O- (K + Q) -Ep (or Eo) of the present invention
In carrying out p) and O- (Q → A) -Ep (or Eop), a chelating agent, a xylanase enzyme and a high-pressure high-pressure oxygen bleaching (O) facility and a low-pressure medium-temperature oxygen bleaching (Eo) facility, which are currently widely used, are used. Or xylanase enzyme, acid supply line and (K + Q) tank (or tower) or (Q → A)
Conventional equipment such as a processing tank (or tower), a supply line for peroxides and other auxiliaries, and a dehydration / washing equipment can be added, and no major equipment change is required. As the material of these additional facilities, a material generally used in a chemical plant, for example, SUS316 or SUS316L is suitably used. Therefore, the present invention can be implemented without requiring a large capital investment.

In the present invention, O- (K + Q) -Ep (or Eop) -DP, O- (Q → A) -Ep (or Eo)
Even when performing full bleaching such as p) -DP, the subsequent stages D and P can be carried out using the current D stage bleaching apparatus, E or P stage apparatus as they are, and no capital investment is required. Can be implemented.

[0043]

Next, the present invention will be described in detail with reference to examples. The amount of each chemical used is indicated by weight% per absolutely dry pulp,
The amount of H ₂ O ₂ used is 100% H ₂ O ₂ equivalent. The pulp used was L wood unbleached pulp after kraft digestion, and the following three types of pulp were used for each example: A, B, and C. The analysis and evaluation were performed according to the following methods.

◎ Pulp type * A; Hunter-whiteness 32.7%,
Kappa number 17.6, viscosity 36.1 cp Used in Examples 1-4 and Comparative examples 1-6 * B: Hunter-whiteness 34.2%, Kappa number 15.4, viscosity 3
3.4cp Used in Examples 5-7 and Comparative Examples 7-8 * C: Hunter-whiteness 27.5%, Kappa value 20.9, viscosity 3
8.5 cp Used in Examples 8 to 11 and Comparative Example 9 Analysis analysis * Whiteness: JIS-P8123 (Hunter whiteness method) * Kappa value: TAPPI-standard method T236 * Viscosity: TAPPI No. 44 method * AOX: EPA METHOD 9020 method, using TSX-10 model of Mitsubishi Kasei Corporation

Example 1 Delamination bleaching of O- (K + Q) → Eop was performed on unbleached pulp A of L material after kraft digestion under the following conditions. [O- (K + Q) -Eop] O (oxygen bleaching) (1) Pulp concentration 10.5%, temperature 106 ° C, time 60 minutes, Na
OH 1.55%, O ₂ 2.0%, reaction pressure Initial 7kg / cm ² → End
4 kg / cm ² (2) After the completion of the reaction, the pressure was released, the pulp concentration was diluted with cold water to 2.5%, and then dewatered to 20%. Repeat this operation twice,
Move to next stage (K + Q) process.

K + Q (Xylanase treatment with chelating agent) (1) Pulp concentration 5.0%, temperature 55 ° C, time 90 minutes, sulfuric acid P
Adjusted to H5.5 DTPA 0.2%, commercially available xylan-sedimentase enzyme with an active concentration of 5000 IU / g 0.25% (2) After completion of the treatment, dilute to a pulp concentration of 2.5% with water,
Dehydrated to a concentration of just over 20%. Next, the process proceeds to the next Eop stage.

Eop (oxygen bleaching with peroxide) (1) Pulp concentration 10.5%, temperature 90 ° C, time 90 minutes, MgS
_{O 4 0.25%, 1.55% NaOH} , H 2 O 2 0.5%, O 2 0.
5%, reaction pressure Initial 2 kg / cm ² → Final 0 kg / cm ² , MgSO ₄
Is added before adding NaOH. (2) After the reaction, dilute the pulp to 2.5% with cold water and then dehydrate to 20% to complete the bleaching operation.

Example 2 Bleaching was carried out in the same manner as in Example 1 except that oxygen (O ₂ ) was not used in the Eop stage of Example 1. [O- (K + Q)-
Ep]

Example 3 O and Eop bleaching were performed in the same manner as in Example 1 except that the following (Q → A) processing was performed instead of the (K + Q) processing. [O- (Q
→ A) -Eop] (Q → A) treatment (1) Q treatment Pulp concentration 5.0%, temperature 55 ° C, time 90 minutes, PH5 with sulfuric acid.
5. Commercially available xylan-sedimentase enzyme with an active concentration of 5000 IU / g 0.25% (2) A treatment After the Q treatment, sulfuric acid was added to the same system, adjusted to PH2.0, adjusted to PH2.0, and treated at a temperature of 50 to 55 ° C. Minute treatment (3) After the treatment, dilute to 2.5% pulp concentration with water.
Dehydrated to a concentration of just over 20%. Next, the mixture was neutralized with an aqueous NaOH solution, and the process moved to the next Eop stage. (If not neutralized after acid treatment, Eo
If an excess amount of alkali equivalent to neutralization is used in the p-stage, E
The delignification bleaching effect of the op stage is the same. )

Example 4 Bleaching was carried out in the same manner as in Example 3 except that oxygen (O ₂ ) was not used in the Eop stage of Example 3. [O- (Q → A)-
Ep]

Comparative Example 1 O and Eop bleaching was performed in the same manner as in Example 1 except that a neutral water treatment was performed instead of the (K + Q) treatment. [O-Water treatment-
Eop]

Comparative Example 2 O and Ep bleaching was performed in the same manner as in Example 2 except that a neutral water treatment was performed instead of the (K + Q) treatment. [O-water treatment-E
p]

Comparative Example 3 O / Eop bleaching was carried out in the same manner as in Example 1 except that instead of the (K + Q) treatment, only the xylanase enzyme was used without the chelating agent DTPA. [O-Q processing-Eop]

Comparative Example 4 O / Ep bleaching was carried out in the same manner as in Example 2 except that instead of the (K + Q) treatment, the treatment was carried out only with the xylanase enzyme except for the chelating agent DTPA. [OQ processing-Ep]

[0055] In Comparative Example 5 Eop, not mix H ₂ O _2, other using only O ₂ was subjected to the same bleaching as in Example 1. [O- (K
+ Q) Treatment-Eo]

[0056] In Comparative Example 6 Eop, not mix H ₂ O _2, other using only O ₂ was subjected to the same bleaching as in Example 3. [O- (Q
→ A) Treatment-Eo] Table 1 shows the results of Examples 1 to 4 and Comparative Examples 1 to 6.

[0057]

Table 1 Hunter-whiteness Kappa value Viscosity (cP) Example 1 63.2 6.1 24.2 Example 2 60.2 6.4 25.7 Example 3 67.4 5.7 24.0 Example 4 64.2 6.1 25.0 Comparative Example 1 55.0 9.4 24.5 Comparative Example 2 53.4 9.8 25.6 Comparative Example 3 56.0 6.6 24.5 Comparative Example 4 54.6 6.8 25.8 Comparative Example 5 58.0 6.6 25.0 Comparative Example 6 58.2 6.2 25.8 (Control: unbleached pulp) 32.7 17.6 36.1 Example 5 L-wood unbleached pulp B after kraft digestion was subjected to delignification bleaching with O- (Q → K) -Eop according to the following conditions. [O- (Q → K) -Eop] O (oxygen bleaching) (1) Pulp concentration 10.5%, temperature 106 ° C, time 60 minutes, Na
OH 1.55%, O ₂ 2.0%, reaction pressure Initial 7kg / cm ² → End
4 kg / cm ² (2) After the completion of the reaction, the pressure was released, the pulp concentration was diluted with cold water to 2.5%, and then dewatered to 20%. Repeat this operation twice,
Move to next stage (Q → K) process.

(Q → K) treatment (1) Q treatment Pulp concentration 5.0%, temperature 55 ° C, time 90 minutes, PH5.
5 Commercially available xylan-sedimentase enzyme with an activity concentration of 5000 IU / g 0.1% (2) K treatment After Q treatment, add 0.35% of chelating agent EDTA
Adjusted to 5.5 After that, treat at a temperature of 50 to 55 ° C for 30 minutes. (3) After the treatment, dilute to 2.5% pulp concentration with water.
Dehydrated to a concentration of just over 20%. Next, the process proceeds to the next Eop stage.

Eop (oxygen bleaching with peroxide) (1) Pulp concentration 10.5%, temperature 90 ° C, time 90 minutes, MgS
O ₄ 0.4%, NaOH 1.9%, H ₂ O ₂ 1.0%, O ₂ 0.5
%, Reaction pressure 2 kg / cm ^{2 at} initial stage → 0 kg / cm ^{2 at} final stage (2) After completion of the reaction, dilute the pulp concentration to 2.5% with cold water, then dehydrate to 20% and complete the bleaching operation.

Example 6 O and Eop bleaching were performed in the same manner as in Example 5 except that the following (A → Q) processing was performed instead of the (Q → K) processing. [O- (A
→ Q) -Eop] (A → Q) treatment (1) A treatment Pulp concentration 5.0%, adjusted to PH2 with sulfuric acid, temperature 55 ℃, time
After treatment for 40 minutes, dilute the pulp to 2.5% with water and dehydrate to a little over 20%. Then neutralize with NaOH aqueous solution and proceed to Q treatment. (2) Q treatment Pulp concentration 5.0%, temperature 55 ° C, time 90 minutes, PH5 with sulfuric acid.
5 Commercially available xylan-seed enzyme with an active concentration of 5000 IU / g 0.1% (3) After completion of the treatment, after diluting to 2.5% pulp concentration with water,
Dehydrated to a concentration of just over 20%. Next, the process proceeds to the next Eop stage.

Example 7 In the treatment A, an acid mixture of sulfuric acid and sulfurous acid (weight ratio = 0.2)
(A '), and bleaching was carried out in the same manner as in Example 6 except that a PH2 acid treatment was carried out at 55 ° C for 40 minutes. [O- (A '→ Q) -Eo
p] Comparative Example 7 In the Eop step, bleaching was performed in the same manner as that of Example 5 except that MgSO ₄ was not used. [O- (Q → K) -Eop:
Without Mg]

Comparative Example 8 In the Eop step, bleaching was carried out in the same manner as in Example 6, except that MgSO ₄ was not used. [O- (A → Q) -Eop:
No Mg] Table 2 shows the results of Examples 5 to 7 and Comparative Examples 7 and 8.

[0063]

Table 2 Hunter-whiteness Kappa value Viscosity (cP) Example 5 70.0 5.9 24.1 Example 6 72.0 5.7 23.8 Example 7 73.5 5.5 23.0 Comparative Example 7 66.5 6.4 24.2 Comparative Example 8 67.8 6.4 23.5 (Control: unbleached pulp) 34.2 15.4 33.4

Example 8 Delamination bleaching of O- (K + Q) -Eop was carried out for unbleached pulp C after kraft digestion under the following conditions, and the pulp obtained was bleached with chlorine dioxide (D), and then bleached. Hydrogen peroxide bleaching was performed. [O- (K +
Q) -Eop-DP] O (oxygen bleaching) (1) Pulp concentration 10.5%, temperature 106 ° C, time 60 minutes, Na
OH 1.55% O ₂ 2.0%, reaction pressure 7kg / cm ^{2 at the} beginning → 4kg / cm ^{2 at the} end (2) After completion of the reaction, depressurize and dilute to 2.5% pulp concentration with cold water, then dehydrate to 20%. Repeat this operation twice,
Move to (K + Q) process.

(K + Q) treatment (1) Pulp concentration 5.0%, temperature 55 ° C, time 90 minutes, P with sulfuric acid
Adjusted to H5.5 0.5% EDTMP, 0.5% active xylanase enzyme with an active concentration of 5000IU / g (2) After completion of the treatment, after diluting to 2.5% pulp concentration with water,
Dehydrated to a concentration of just over 20%. Next, the process proceeds to the next Eop stage.

Eop (oxygen bleaching with peroxide) (1) Pulp concentration 10.5%, temperature 90 ° C., time 90 minutes, MgS
O ₄ 0.6%, NaOH 2.25%, H ₂ O ₂ 2.0%, O ₂₀ .
5%, reaction pressure 2 kg / cm ^{2 at the} beginning → 0 kg / cm ² at the end (2) After completion of the reaction, dilute the pulp concentration to 2.5% with cold water.
Next, the operation of dehydrating to 20% was repeated twice, and the process shifted to the next stage D bleaching.

D (Bleaching with chlorine dioxide) (1) Pulp concentration 13%, temperature 70 ° C., time 120 minutes, ClO ₂
0.55% (2) After completion of the reaction, dilute the pulp concentration to 2.5% with cold water and then dehydrate to 20%. This operation is repeated twice, and the process proceeds to the next stage P bleaching.

P (Hydrogen peroxide bleaching) (1) Pulp concentration 15%, temperature 70 ° C, time 120 minutes, NaO
H 0.25%, H ₂ O ₂ 0.2% (2) After completion of the reaction, dilute the pulp concentration to 2.5% with cold water, and then dehydrate to 20% to complete the bleaching operation.

Example 9 Bleaching similar to Example 8, except that DTPMP-0.5% was used in place of the chelating agent EDTMP in the (K + Q) treatment of Example 8 and that oxygen (O ₂ ) was not used in the Eop stage. Was done. [O- (K + Q) -Ep-DP]

Example 10 Bleaching was carried out in the same manner as in Example 8 except that the following (Q → A) treatment was performed instead of the (K + Q) treatment. [O- (Q → A) -Eo
p-DP] (Q → A) treatment (1) Q treatment Pulp concentration 5.0%, temperature 55 ° C, time 90 minutes, PH5 with sulfuric acid.
5 Commercially available xylan-sezyme enzyme with an active concentration of 5000 IU / g 0.5% (2) A treatment After sulfuric acid was added to the same system after Q treatment, adjusted to PH2.0, adjusted to PH2.0, and then treated at a temperature of 50 to 55 ° C for 30 minutes. (3) After the treatment, after diluting to a pulp concentration of 2.5% with water,
Dehydrated to a concentration of just over 20%. Next, the mixture was neutralized with an aqueous NaOH solution, and the process moved to the next Eop stage.

Example 11 Bleaching was performed in the same manner as in Example 10 except that oxygen (O ₂ ) was not used in the Eop stage of Example 10. [O- (Q →
A) -Ep-DP]

Comparative Example 9 As the current bleaching method, the unbleached pulp C after the kraft digestion was subjected to the O bleaching of Example 8, and then the C / D (effective chlorine by D Subsequent bleaching was performed with a substitution rate of 10%)-Eo-HD. [O → C
/ D → Eo → H → D] Table 3 shows the results of Examples 8 to 11 and Comparative Example 9. Table 3 shows the amount of the organic chlorine compound (AOX) measured by combining the waste liquids in the D stage and the P stage after the bleaching.

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Table 3 Hunter-Whiteness Viscosity (cP) AOX (kg / pt) Example 8 86.6 15.5 0.31 Example 9 85.5 15.8 0.36 Example 10 88.2 0 0.28 Example 11 87.0 14.3 0.32 Comparative Example 9 85.5 10.9 2.05 (Control: unbleached pulp) 27.5 38.5 −

[0074]

According to the present invention, extremely high delignification can be performed without a significant decrease in viscosity.
In addition, pulp with extremely high whiteness can be obtained.
As a result, the amount of chlorine-based chemical used in the subsequent bleaching can be significantly reduced. In particular, bleaching without any chlorine and hypochlorite in the subsequent bleaching is also possible. Therefore, by-products of the organic chlorine compound can be significantly reduced, and the environmental pollution of the bleaching wastewater can be significantly reduced. In carrying out the method of the present invention, high-temperature / high-pressure oxygen bleaching equipment and medium-low-pressure oxygen bleaching equipment that are currently in widespread use can be used as they are, without requiring a large additional capital investment.

Continuation of the front page (56) References JP-A-6-207390 (JP, A) JP-A-6-116889 (JP, A) JP-A-2-264087 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) D21C 9/10-9/16

Claims (4)

(57) [Claims] 1. The digested chemical pulp is subjected to a high-temperature and high-pressure oxygen bleaching treatment, followed by a xylanase enzyme treatment, and an acid treatment by adding an acid, followed by a peroxide treatment in an alkaline medium. A method for bleaching chemical pulp for papermaking, comprising performing delignification and bleaching with a substance or a peroxide and oxygen. 2. The digested chemical pulp is subjected to high-temperature and high-pressure oxygen bleaching treatment, followed by acid treatment, washing, neutralization, xylanase enzyme treatment, and alkalinization. A method for bleaching chemical pulp for papermaking, comprising performing delignification and bleaching with a peroxide or a peroxide and oxygen in a medium. 3. The digested chemical pulp is subjected to a high-temperature and high-pressure oxygen bleaching treatment, followed by an acid treatment or a xylanase enzyme treatment combined with a chelating agent treatment. A method for bleaching chemical pulp for papermaking, wherein delignification and bleaching are performed with a magnesium compound or a peroxide, oxygen and a magnesium compound. 4. The method for bleaching chemical pulp for papermaking according to claim 1, wherein in the acid treatment, the acid treatment is performed with a mixed solution of sulfuric acid and sulfurous acid.