JPH08158284A - Method for delignification bleaching of chemical pulp for papermaking - Google Patents

Abstract

(57) [Summary] [Purpose] In bleaching chemical pulp for papermaking, promote delignification and high whiteness without deterioration of pulp,
(EN) An economical means for producing a high-whiteness chemical pulp and a method for reducing the environmental toxicity of bleaching wastewater by reducing the amount of chlorine-based bleaching chemicals used. [Structure] In the method of delignifying and bleaching chemical pulp, the digested chemical pulp is treated under high temperature and high pressure oxygen, and then a reaction catalyst consisting of an oxygen acid of IV, V and VI elements or its salt and a peroxide Mix oxides, pH
Is subjected to delignification / bleaching treatment at a temperature of 3 or less and 75 to 110 ° C., and then delignification and bleaching are carried out in an alkaline medium with a peroxide, or a peroxide and oxygen.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to an improved method for delignification and bleaching of chemical pulp for papermaking. The invention is particularly suitable for delignification and bleaching of chemical pulp from hardwood and softwood.

[0002]

2. Description of the Related Art Bleaching of chemical pulp for papermaking is carried out by a multistage bleaching process. Conventionally, chlorine-based chemicals have been used as a bleaching agent in this multi-stage bleaching. Specifically, by combining chlorine (abbreviated as C), hypochlorite (H) and chlorine dioxide (D), for example, C-E-
Bleaching has been performed by a sequence such as HD, C / D-E-HD (C / D is a combined bleaching stage of chlorine and chlorine dioxide, and E is an alkali extraction stage).

However, these chlorine-based bleaching chemicals by-produce an organic chlorine compound harmful to the environment during bleaching, and environmental pollution of the bleaching wastewater containing this organic chlorine compound poses a problem.

The most effective method for reducing / preventing by-products of organic chlorine compounds is to reduce the amount of chlorine-based chemicals used or not to use them, and especially to avoid using atomic chlorine in the first stage. Is the most effective method. The pulp produced by this method is called ECF (Elementary Chlorine Free) pulp.

As a method for producing ECF pulp by bleaching cooked pulp with chlorine-free chemicals without first-stage chlorine bleaching, chemical pulp after cooking is acid-treated and then bleached with hydrogen peroxide in an alkaline medium. The method is disclosed in JP-A-51-1
No. 02103 and JP-A-56-85489. It is described in these publications that the acid treatment removes a metal that wastefully decomposes hydrogen peroxide in the subsequent hydrogen peroxide bleaching, thereby increasing delignification and bleaching in the hydrogen peroxide stage. However, this method has a drawback that the bleaching effect is excellent, but the delignification effect is low. Therefore, there is a problem that the bleaching in the latter stage is burdened and the bleaching cost and the wastewater treatment cost increase.

[0006] As a method for improving the disadvantage of hydrogen peroxide bleaching in which delignification is inferior, Japanese Patent Publication No. 17679/1990 discloses that after acid treatment is carried out at a temperature of 60 to 100 ° C, hydrogen peroxide bleaching is carried out under alkaline conditions. Although a technique for carrying out the above has been disclosed, the improvement effect of delignification was insufficient according to the study by the present inventors.

[0007]

The object of the present invention is to utilize a peroxide for pulp bleaching in the production of chemical pulp for papermaking, and more specifically to improve the delignification action of the peroxide. Therefore, it is to provide a economical means for producing a high-whiteness chemical pulp by promoting high delignification without deterioration of the pulp. A second object is to reduce the amount of chlorine-based chemicals used in the production of bleached chemical pulp to suppress the by-production of organic chlorine compounds and reduce the environmental toxicity of bleaching wastewater.

[0008]

Means for Solving the Problems The present inventors have found that when a pulp that has been digested is treated with a peroxide or a combination of peroxide and oxygen and delignified, it is treated with a peroxide under acidic and high temperature conditions. It was found that the delignification effect was remarkably improved by adding a step of adding a catalyst and performing pretreatment, and completed the present invention. According to the present invention, surprisingly, although the delignification effect is remarkably improved, the pulp viscosity is hardly reduced.

In the method of the present invention, first, a digested chemical pulp is subjected to an oxygen bleaching treatment under high temperature and high pressure (hereinafter referred to as "O").
Or sometimes referred to as O stage). The pulp concentration, temperature, time, alkali amount, oxygen amount, and operating pressure in the O stage can be determined according to the conditions generally used for oxygen delignification (bleaching). For example, the pulp concentration is 7 to 30%, preferably 10 to 20%, and the temperature is 6
0 to 130 ° C., preferably 90 to 110 ° C., treatment time is 20 to 150 minutes, preferably 30 to 90 minutes, and alkali amount is 0.5 to 6.0% per absolute dry pulp in terms of caustic soda,
The amount of oxygen is preferably 0.5 to 5.0%, and the operating pressure is 2.5 to 10 kg / cm ² , preferably 3.5 to 8 kg / cm ² . Be implemented.

The pulp after the O stage treatment is washed and dehydrated, and then treated with an acidic peroxide in the presence of a catalyst (hereinafter, the acidic peroxide treatment in the presence of the catalyst is Ap (cat) or Ap).
(cat) stage).

The acid treatment of the Ap (cat) stage is carried out by adding p
It is carried out by setting H to 3 or less, preferably 1.0 to 2.5. An aqueous solution containing an inorganic acid or an organic acid can be used for the acid treatment, and sulfuric acid, nitric acid, formic acid, acetic acid, oxalic acid,
And an aqueous solution containing a mixture of these acids is preferred. Of these, sulfuric acid is most preferably used because it is inexpensive and can be obtained with low corrosiveness. Particularly, in a plant having a kraft cooking facility, it is convenient to use the waste liquid after the acid treatment as a supplement of chemicals in the kraft cooking.

The Ap (cat) treatment of the present invention depends on the properties of the pulp, but usually the pulp concentration is 1 to 40%, preferably 5
~ 30%, most preferably 10-20%, temperature 75-1
10 ° C., preferably 80-100 ° C., treatment time 30-
It is carried out in 300 minutes, preferably 60 to 180 minutes.

In the present invention, in the Ap (cat) treatment, the pulp is kept at a strong acidity of pH 3 or less and the treatment temperature is set to a high temperature of 75 to 110 ° C., so that delignification or bleaching is performed. The effect rises sharply. pH exceeds 3 or processing temperature is 75-110
When the temperature is out of the range of ℃, the delignification or bleaching effect becomes low, and the viscosity of pulp remarkably decreases.

As the peroxide of the Ap (cat) stage, hydrogen peroxide, an adduct of hydrogen peroxide and inorganic salts, sodium peroxide,
Inorganic and organic peroxides such as persulfates, formic acid and peracetic acid can be used, and hydrogen peroxide is preferably used. The amount of peroxide used is 0.01 to 5%, preferably 0.1 to 3%, per 100% hydrogen peroxide, based on absolutely dry pulp.
Is.

The present invention is characterized in that a reaction catalyst is used in the Ap (cat) stage. As the reaction catalyst used in the Ap (cat) stage, an oxygen acid of IV, V, or VI group element or a salt thereof,
And, a heteropolyacid of a IV, V, or VI group element or a salt thereof is used. As a typical oxygen acid or its salt,
Oxygen acids such as tungsten, molybdenum, vanadium, selenium, and titanium, or their alkali metal salts, salts of alkaline earth metal salts or ammonia salts,
At least one of them is used.

As tungstic acid and its salt, H
₂ WO _{4 and} its soda salts, calcium salts and ammonium salts, and molybdic acid and its salts include H ₂ MoO ₄ , H ₂ Mo ₂ O ₇ , H ₆ Mo ₇ O _{24 and} their soda salts, Examples thereof include calcium salts and ammonium salts. Examples of vanadium acid and its salts include HV
Examples thereof include O ₃ , H ₃ VO ₄ , H ₄ V ₂ O _{7 and} their soda salts, calcium salts and ammonium salts. Examples of selenate and its salts include H ₂ SeO _{4 and} its soda salts, calcium salts and Ammonium salts and the like,
Examples of titanic acid and its salt include H ₂ TiO ₃ and H ₄ Ti.
O ₄ and soda salts, calcium salts and ammonium salts thereof can be mentioned.

As a typical heteropoly acid or a salt thereof, a part or all of protons of tungsten, molybdenum or vanadium heteropoly acid or a heteropoly acid thereof is cation such as alkali metal, alkaline earth metal, rare earth metal or ammonium. The salt of the replaced heteropoly acid may be mentioned.

[0018] That is, as heteropoly acid or salt thereof _{tungsten, H 3 (PW 12 O 4} 0), H 3 (AsW 12
O ₄₀ ), H ₄ (SiW ₁₂ O ₄₀ ), H ₄ (TiW ₁₂ O ₄₀ ),
H ₅ (CoW ₁₂ O ₄₀ ), H ₅ (FeW ₁₂ O ₄₀ ), H ₅ (B
_{W 12 O 40), H 3} (VW 12 O 40), H 6 (BeW 9 O 31)
H ₆ (TeW ₆ O ₂₄ ), H ₅ (IW ₆ O ₂₄ ), H ₄ (NiW ₆
O ₂₄ H ₆ ), H ₃ (GaW ₆ O ₂₄ H ₆ ), H ₆ (P ₂ W
₁₆ O ₆₂ ), H ₆ (As ₂ W ₁₈ O ₆₂ ), H ₇ (PW
₁₁ O ₃₃ ), and cation exchangers such as soda, potassium, calcium, cerium or ammonium of these heteropolyacids.

[0019] heteropoly acid or salt thereof _{molybdenum, H 3 (PMo 12 O 40} ), H 3 (AsMo 12 O 40),
H ₄ (SiMo ₁₂ O ₄₀ ), H ₄ (GeMo ₁₂ O ₄₀ ), H ₄
(TiMo ₁₂ O ₄₀ ), H ₈ (CeMo ₁₂ O ₄₂ ), H ₈ (T
hMo ₁₂ O ₄₂ ), H ₇ (AsMo ₁₁ O ₃₉ ), H ₇ (PMo
₁₁ O ₃₉ ), H ₈ (GeMo ₁₁ O ₃₉ ), H ₆ (MnMo ₉ O
₃₂ ), H ₆ (NiMo ₉ O ₃₂ ), H ₆ (TeMo ₆ O ₂₄ ),
_{H 5 (IMo 6 O 24)} , H 3 (CoMo 6 O 24 H 6), H
_{3 (CrMo 6 O 24 H 6} ), H 3 (FeMo 6 O 24 H 6), H
₃ (GaMo ₆ O ₂₄ H ₆ ), H ₄ (NiMo ₆ O ₂₄ H ₆ ), H
_{6 (P 2 Mo 18 O 62} ), H 6 (As 2 Mo 18 0 62), and, soda these heteropoly acids, potassium, calcium, include Seryuumu or cation exchanger, such as ammonium.

As vanadium heteropolyacid or salts thereof, H ₄ (PW ₁₁ VO ₄₀ ), H ₄ (PMo ₁₁ VO ₄₀ ),
H ₅ (PMo ₁₀ V ₂ O ₄₀ ) and cation exchangers such as soda, potassium, calcium, cerium or ammonium of these heteropoly acids can be mentioned.

The amount of the reaction catalyst used varies depending on the delignification conditions of the pulp, but it is 0.001 per bone-dry pulp.
˜1%, preferably 0.005-0.5%. As the method of adding the acid, the reaction catalyst and the peroxide to the pulp, each of them may be sequentially mixed with the pulp, or the acid, the peroxide and the reaction catalyst may be previously mixed and then mixed with the pulp.

The reaction catalyst in the Ap (cat) stage of the present invention is
The peroxide promotes the reaction of decomposing or modifying the lignin or pigment contained in the pulp under acidic conditions, and exerts the action of improving the delignification or bleaching effect in the subsequent treatment with peroxide in an alkaline medium.

The pulp after the Ap (cat) treatment is separated by a dehydrator and then preferably washed. Ap of the present invention
The (cat) treatment also includes this dehydration and washing step. The separated Ap (cat) treatment liquid is reused in the Ap (cat) treatment step,
It can be used for washing the pulp after the cooking step or after the O-stage treatment, and can be recycled to the cooking chemical recovery step.

The pulp after the Ap (cat) stage is subsequently subjected to a delignification / bleaching step using peroxide or a peroxide and pressurized oxygen. (Hereafter, this peroxide bleaching step
E or p or Ep stage, peroxide bleaching process with pressurized oxygen
Or sometimes referred to as Eop stage).

In the Ep stage or Eop stage treatment, pulp is subjected to delignification / bleaching action in an alkaline medium with peroxide, or peroxide and pressurized oxygen. In the case of peroxide bleaching with the use of pressurized oxygen, oxygen and peroxide act on the pulp substantially simultaneously.

As the alkaline agent in the Ep or Eop stage, caustic soda, caustic potash, lime, soda ash, etc. can be used. Among them, caustic soda is inexpensive and can be suitably used because it can be recycled to the cooking chemical recovery step to reduce the amount of chemical replenishment in the cooking step. The amount of the alkaline agent used is 0.1 to 6.0%, preferably 0.5 to 3.0%, based on the dry pulp, in terms of caustic soda.
If the amount of the alkaline agent used is less than this, the delignification / bleaching effect is reduced, and if it is more than this, the viscosity of the pulp is significantly reduced.

The peroxides in the Ep stage or Eop stage include hydrogen peroxide, an adduct of hydrogen peroxide and inorganic salts, inorganic and organic substances such as sodium peroxide, persulfates, formic acid and peracetic acid. A peroxide can be used, and hydrogen peroxide is generally preferably used. The amount of the peroxide used is, based on 100% hydrogen peroxide, 0.05 to 8%, and preferably 0.2 to 3.0%, based on the absolutely dry pulp. If the amount of peroxide used is less than this, the delignification / bleaching effect is low, and if it is more than this, the efficiency of peroxide is reduced.

As the pressurized oxygen in the Eop stage, oxygen gas and air can be used, but oxygen gas is preferred. The amount of oxygen used in the Eop stage is 0.1 to 1.0% per bone-dry pulp.
Is preferred, and the operating pressure is preferably atmospheric pressure to 3.5 kg / cm ² .

The addition of chemicals to pulp in the Ep stage and Eop stage of the present invention is preferably carried out in the order of adding oxygen next to the alkaline agent. The peroxide is preferably added after the addition of the alkaline agent and immediately before, at the same time as or immediately after the addition of oxygen. The pulp concentration of the Ep stage and the Eop stage of the present invention is preferably 7 to 30%, more preferably 10 to 20%. The temperature is preferably 40 to 120 ° C, 70 to 95 ° C
Is more preferable. The treatment time is preferably 15 to 150 minutes, more preferably 30 to 120 minutes.

Further, in the Ep stage or Eop stage, it is preferable to use a magnesium compound. By using the magnesium compound, the delignification / bleaching action of the peroxide is increased, and the decrease in the viscosity of the pulp is reduced.

As the magnesium compound, magnesium sulfate, magnesium hydroxide, magnesium oxide, magnesium carbonate, magnesium nitrate and the like can be used, and magnesium sulfate is preferably used. The amount of magnesium compound used is preferably 0.005 to 0.75%, and 0.01 to 0.3%, as the magnesium ion, based on the absolutely dry pulp.
Is more preferable. The addition of the magnesium compound is preferably done prior to the addition of the alkaline agent, oxygen and peroxide.

According to the method of the present invention, both delignification and whiteness are significantly improved. The mechanism is not clear,
By treating pulp with a strongly acidic aqueous solution to dissolve and remove metals that are harmful to alkaline peroxide bleaching in the next step, the action of peroxide and reaction catalyst promotes decomposition of residual lignin in pulp. It is believed that this is due to the synergistic effect that the further decomposed lignin is more effectively hydrolyzed under strongly acidic conditions. As a result, the whiteness improvement and delignification in the alkaline peroxide bleaching in the next stage are further improved, and the whiteness and delignification are equal to or superior to those obtained by the method using a chlorine-based chemical.

In carrying out the present invention, the high temperature and high pressure oxygen bleaching equipment and the medium and low pressure oxygen bleaching equipment which are currently widespread can be used as they are, so that a large additional investment in equipment is not required.

The bleached pulp obtained by the method of the present invention has a considerably high whiteness as it is, but it is possible to obtain a pulp having a higher whiteness by performing full bleaching in which several bleaching steps are continuously added. it can. In that case, since the bleached pulp obtained by the method of the present invention is already highly delignified and has a considerably high whiteness, it is a full bleach without any chlorine bleaching agent in the subsequent bleaching step. Can be bleached. Full bleaching is possible industrially without using at least molecular chlorine and hypochlorite, and even if chlorine bleach is used, it is only necessary to use a small amount of chlorine dioxide, which is a small byproduct of organic chlorine compounds. .

For example, O-Ap (cat) -Ep (or Eo
p) step, followed by chlorine dioxide (D) and then peroxide bleaching (P), O-Ap (cat) -Ep (or Eop) -D
Full bleaching sequences without chlorine and hypochlorite, such as -P, are possible. In this full bleaching sequence, the current typical full bleaching sequence, OC
/ D-Eo (combined medium and low pressure oxygen in the E stage) -A pulp product having high viscosity and high whiteness equivalent to or higher than that of HD can be obtained. Further, since chlorine and hypochlorite are not used, bleaching with a significantly smaller amount of AOX produced can be performed as compared with the existing method.

O-Ap (cat) -Ep (or Eop) -D-
The chlorine dioxide stage (D) conditions in the P sequence are the normal D stage conditions. For example, pulp concentration 7 to 30
%, Temperature 40 to 90 ° C., time 60 to 240 minutes, chlorine dioxide usage 0.1 to 2.0%.

O-Ap (cat) -Ep (or Eop) -D-
The peroxide bleaching (P) stage in the P sequence is performed under normal peroxide bleaching conditions. That is, the pulp concentration is 7 to 30% and the temperature is 4 in the alkaline medium.
The temperature is 0 to 100 ° C. and the time is 60 to 240 minutes.
Examples of the alkaline agent include caustic soda, caustic potash, lime, soda ash and the like, but caustic soda is preferably used, and the caustic soda is used in an amount of 0.1 to 2%.

Examples of peroxides include hydrogen peroxide, adducts of hydrogen peroxide and inorganic salts, and inorganic and organic peroxides such as sodium peroxide, formic acid, peracetic acid, and the like. Hydrogen peroxide is used as the amount of peroxide, and the amount of peroxide used is 100% of hydrogen peroxide, and the amount of peroxide used is 0.00 per 100% dry pulp.
It is performed in the range of 01 to 3.0%.

O-Ap (cat) -Ep (or Eo of the present invention
In carrying out p), high temperature and high pressure oxygen bleaching (O) equipment, chlorine bleaching equipment and medium and low pressure oxygen bleaching (Eo) equipment which are currently popular, and conventional equipment such as acid, catalyst and peroxide supply lines are used. No need for major equipment changes. The materials of these auxiliary equipments are SUS316 or SUS316 commonly used in chemical plants.
L and the like are preferably used. Therefore, it can be implemented without requiring a large capital investment.

Also, O-Ap (cat) -Ep (or Eop)
-When performing full bleaching with DP, etc., the existing D-stage bleaching device, P-stage or E-stage device can be used as is for the subsequent D-stage and P-stage, and additional capital investment is required. It can be carried out without.

In the case of the conventional peroxide bleaching, both the whiteness improving effect and the delignification power are inferior to the method using a chlorine bleaching agent, but the method of the present invention has the whiteness and delignification. It is a method that gives the same or superior results as the method using chlorine bleach. Conventionally, a large amount of chlorine bleach such as atomic chlorine has been used for full bleaching, but according to the present invention, a pulp (TCF pulp) containing no chlorine bleach is economical. It is possible to economically produce pulp (ECF pulp) using only a very small amount of chlorine dioxide without using molecular chlorine even if chlorine bleach is used. It is possible.

[0042]

EXAMPLES The present invention will be described in detail with reference to examples. The amount of each chemical used is shown by weight% per bone dry pulp, and the amount of hydrogen peroxide used is 100% hydrogen peroxide equivalent. The pulp used for bleaching was L pulp (crafter whiteness 46.2%, bleached with oxygen after kraft cooking).
It has a K value of 7.4 and a viscosity of 24.2 cp). A series of analytical evaluations was performed by the following method.

Whiteness: JIS-P8123 (Hunter whiteness method) K value: TAPPI K value method Viscosity: J. TAPPI No. 44 method AOX: EPA METHOD 9020 method, Mitsubishi Kasei Co., Ltd. TSX- 10 type used, evaluated by the amount of organic chlorine per ton of bleached pulp.

## EQU1 ## De-lignin ratio (%) = [1-((K value after bleaching) /
(K value before bleaching))] x 100

Example 1 (O-Ap (cat) -Eop) Ap (cat) (acid + peroxide + catalyst) After kraft cooking, an aqueous sulfuric acid solution was added to L pulp subjected to oxygen bleaching, and Na ₂ was added. MoO ₄ was added in the order of 0.05% and H ₂ O ₂ was added in the order of 0.5%, and the mixture was treated for 60 minutes under the conditions of pulp concentration of 10%, pH of 2.0 and temperature of 75 ° C. After the treatment, dilute with water to a pulp concentration of 2.5%, then pulp concentration 22%
After dehydration, the pH was adjusted to about 7 and the pulp concentration was 20% with a dilute aqueous solution of sodium hydroxide.

Eop (peroxide combined with oxygen bleaching) The pulp obtained as described above was mixed with MgSO ₄ at 0.2.
5%, caustic soda 1.2%, H ₂ O ₂ 0.5%, pulp concentration 10%, oxygen 90% at temperature 90 ° C.
After adding and pressurizing to ² kg / cm ² , the pressure was reduced to atmospheric pressure over 90 minutes while maintaining the temperature. After the reaction was completed, it was diluted with cold water to a pulp concentration of 2.5% and then dehydrated to a pulp concentration of 20% to obtain a bleached pulp.

Examples 2 to 4 (O-Ap (cat) -Eop) The temperature at Ap (cat) was 85 ° C, 95 ° C or 110 ° C.
Ap (cat) and then Eop treatment were carried out in the same manner as in Example 1 except that the conditions were changed to ° C.

Comparative Example 1 (O-Ap-Eop) Bleaching was carried out in the same manner as in Example 1 except that Na ₂ MoO ₄ was not added in the Ap (cat) stage of Example 1.

Comparative Examples 2 to 3 (O-Ap (cat) -Eop) Bleaching was carried out in the same manner as in Example 1 except that the temperature of the Ap (cat) stage of Example 1 was 40 ° C or 60 ° C. .

The results of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 1.
Shown in

[Table 1] Ap (cat) condition Eop after pulp analysis Evaluation temperature pH Whiteness K value Viscosity (cP) Example 1 75 2.0 73.7 4.0 (46%) 21.4 2 85 2.0 75.2 3.2 (57%) 20.1 3 95 2.0 76.5 2.1 (72%) 19.6 4 110 2.0 78.3 1.1 (85%) 18.7 Comparative Example 1 75 2.0 71.3 6.6 (11%) 13.1 2 40 2.0 68.1 5.8 (22%) 22.4 3 60 2.0 69.7 5.4 (27%) 21.7 Note ) The (%) after the K value represents the delignification rate.

Example 5 (O-Ap (cat) -Ep) The temperature in Ap (cat) of Example 1 was changed to 80 ° C., and the treatment was carried out at atmospheric pressure without using oxygen in the Eop stage. Otherwise, the same bleaching operation as in Example 1 was performed.

Examples 6 to 7 (O-Ap (cat) -Ep) The temperature at Ap (cat) of Example 5 was 95 ° C or 11 ° C.
Ap (cat) was the same as in Example 5 except that the condition was changed to 0 ° C.
Then, Ep treatment was performed.

Comparative Example 4 (O-Ap-Ep) Bleaching was carried out in the same manner as in Example 5 except that Na ₂ MoO ₄ was not added in the Ap (cat) stage of Example 5.

Comparative Examples 5 to 6 (O-Ap (cat) -Ep) Bleaching was carried out in the same manner as in Example 5 except that the temperature of the Ap (cat) stage in Example 5 was changed to 40 ° C or 70 ° C. .

The results of Examples 5 to 7 and Comparative Examples 4 to 6 are shown in Table 2.
Shown in

[Table 2] Pulp analysis after Ap (cat) condition Ep Temperature pH Whiteness K value Viscosity (cP) Example 5 80 2.0 70.2 4.5 (45%) 22.1 6 95 2.0 74.1 2.9 (61%) 20.6 7 110 2.0 75.7 1.9 (74%) 19.6 Comparative Example 4 80 2.0 68.7 6.9 (7%) 13.3 5 40 2.0 66.7 6.0 (19%) 22.8 6 70 2.0 68.2 5.7 (23%) 22.1 Note) (%) after the K price is It represents the rate of delignification.

Examples 8 to 10 (O-Ap (cat) -Eop) The reaction catalyst of the Ap (cat) stage of Example 1 was Na ₂ WO ₄ 0.05.
%, The temperature was 90 ° C., and the treatment pH was 1.0, 2.0, or 3.0, and the same bleaching as in Example 1 was performed.

Comparative Examples 7 to 8 (O-Ap (cat) -Eop) The same bleaching as in Example 8 except that the treatment pH of the Ap (cat) stage of Example 8 was 5.0 or 6.0. went.

The results of Examples 8 to 10 and Comparative Examples 7 to 8 are shown in Table 3.

[Table 3] Ap (cat) conditions Pulp analysis after Eop Analysis temperature pH Whiteness K value Viscosity (cP) Example 8 90 1.0 76.1 2.2 (70%) 19.7 9 90 2.0 75.9 2.5 (66%) 19.8 10 90 3.0 74.5 3.3 (55%) 20.6 Comparative Example 7 90 5.0 65.3 5.5 (26%) 21.6 8 90 6.0 62.5 6.1 (18%) 22.1 Note) (%) after the K value represents the delignification rate.

Examples 11 to 13 (O-Ap (cat) -Ep) The reaction catalyst of the Ap (cat) stage of Example 5 was Na ₂ WO ₄ 0.05.
%, The temperature was 90 ° C., and the treatment pH was 1.0, 2.0 or 3.0, and the same bleaching as in Example 5 was performed.

Comparative Examples 9 to 10 (O-Ap (cat) -Ep) The treatment pH of the Ap (cat) stage of Example 11 was adjusted to 5.0 or 6.0.
Bleaching was performed in the same manner as in Example 11 except that

Table 4 shows the results of Examples 11 to 13 and Comparative Examples 9 to 10.

[Table 4] Pulp analysis after Ap (cat) condition Ep Temperature pH Whiteness K value Viscosity (cP) Example 11 90 1.0 73.7 3.1 (58%) 20.4 12 90 2.0 73.4 3.4 (54%) 20.9 13 90 3.0 72.1 3.7 (50%) 21.3 Comparative Example 9 90 5.0 63.7 5.8 (22%) 21.9 10 90 6.0 60.1 6.3 (15%) 22.3 Note) (%) after the K value represents the delignification rate.

As described above, in order to obtain a sufficient delignification rate and whiteness in the present invention, it is necessary to satisfy both the temperature and pH conditions of the Ap (cat) stage, and either one is not appropriate. If it is not possible to obtain sufficient delignification or bleaching effect.

Examples 14 to 16 (O-Ap (cat) -Eop) Instead of the catalyst Na ₂ MoO ₄ of the Ap (cat) stage of Example 1,
Bleaching was carried out in the same manner as in Example 1 except that Na ₂ TiO ₄ , Na ₂ SeO ₄ or NaVO ₃ was used and the temperature was 90 ° C.

Examples 17-19 (O-Ap (cat) -Eop) Instead of the catalyst Na ₂ MoO ₄ of the Ap (cat) stage of Example 1,
Na ₃ (PW ₁₂ O ₄₀ ), Na ₃ (PMo ₁₂ O ₄₀ ), or N
Bleaching was performed in the same manner as in Example 1 except that a ₄ (PW ₁₁ VO ₄₀ ) was used and the temperature was 90 ° C. Examples 14-19
The results are shown in Table 5.

[0064]

[Table 5] Pulp analysis evaluation catalyst after Ap (cat) condition Eop Whiteness K value Viscosity (cP) Example 14 Na ₂ TiO ₄ 75.9 2.3 (69%) 20.3 15 Na ₂ SeO ₄ 75.6 2.5 (66%) 20.6 16 NaVO ₃ 76.4 2.8 (62%) 19.9 17 Na ₃ (PW ₁₂ O ₄₀ ) 76.7 2.6 (65%) 19.7 18 Na ₃ (PMo ₁₂ O ₄₀ ) 76.3 2.7 (64%) 19.8 19 Na ₄ (PW ₁₁ VO ₄₀ ) 76.6 2.7 (64%) 19.8 Note) (%) after the K value represents the delignification rate.

Example 20 (O-Ap (cat) -Eop-D-
P) Regarding L pulp that has been subjected to oxygen bleaching after craft cooking,
O-Ap (cat) -Eop was delignified according to the following conditions, and then the obtained pulp was bleached with chlorine dioxide (D) and then with hydrogen peroxide.

Ap (cat) (acid + peroxide + catalyst) After Kraft cooking, a sulfuric acid aqueous solution was added to L pulp subjected to oxygen bleaching to add 0.05% Na ₂ WO ₄ and H ₂ O ₂ . 0.
5% added, pulp concentration 10%, pH 2.0, temperature 90
It processed for 60 minutes on condition (degreeC). After the treatment, it was diluted with water to a pulp concentration of 2.5%, dehydrated to a pulp concentration of 22%, and diluted with a caustic soda solution to a pH of about 7 and a pulp concentration of 20%.
Adjusted to%.

Eop (oxygen bleaching with peroxide) The pulp obtained as described above was added with MgSO _{4 in an amount} of 0.6.
%, Caustic soda 1.2%, H ₂ O ₂ 1.0%,
After adding 0.5% oxygen at a pulp concentration of 10% and a temperature of 90 ° C. and pressurizing to ² kg / cm ² , keep the same conditions and
The pressure was reduced to atmospheric pressure over 0 minutes. After the treatment, dilute with cold water to a pulp concentration of 2.5%, and then add a pulp concentration of 2%.
It was dehydrated to 0%.

D (Chlorine dioxide bleaching) Chlorine dioxide was added to the pulp obtained as described above at 0.3%.
%, And the pulp concentration was 13% and the temperature was 70 ° C. for 120 minutes. After treatment, cold water gives a pulp concentration of 2.5%
And then dehydrated to a pulp concentration of 20%.

P (hydrogen peroxide bleaching) 0.2% caustic soda was added to the pulp obtained as described above.
5% and 0.2% of H ₂ O ₂ were added, and the pulp was treated at a pulp concentration of 15% and a temperature of 70 ° C. for 120 minutes. After the treatment, dilute the pulp concentration to 2.5% with cold water, and then add the pulp concentration to 20%.
The bleached pulp was obtained by dehydration to 100%.

Example 21 (O-Ap (cat) -Ep-D-
P) The same bleaching operation as in Example 20 was carried out except that the Eop stage of Example 20 was treated under normal pressure without using oxygen.

Comparative Example 11 (O-C / D-Eo-HD) The current bleaching method is generally carried out using the same oxygen-bleached pulp as in Examples 20 and 21. According to the conditions, post-stage bleaching of C / D-Eo-HD was performed.

C / D (Chlorine / Chlorine dioxide bleaching) An aqueous solution of chlorine and chlorine dioxide was added to an L bleached pulp that had been bleached with oxygen after kraft cooking (effective chlorine substitution rate by D: 10%).
Added 2.0% of available chlorine, pulp concentration 4%, temperature 4
It processed for 60 minutes on condition of 0 degreeC. After the treatment, it was diluted with water to a pulp concentration of 2.5%, dehydrated to a pulp concentration of 22%, and diluted with a dilute caustic soda solution to a pH of about 7 and a pulp concentration of 2%.
Adjusted to 0%.

Eo (oxygen bleaching) MgSO ₄ was added to the pulp obtained as described above at 0.6
%, Caustic soda 1.2%, pulp concentration 10%,
After adding 0.5% oxygen at a temperature of 90 ° C. and pressurizing to ² kg / cm ² , the pressure was reduced to atmospheric pressure over 90 minutes while maintaining the same conditions. After the treatment, the pulp concentration is 2.5 with cold water.
% And then dehydrated to a pulp consistency of 20%.

H (Hypochlorous acid bleaching) Hypochlorous acid was added to the pulp obtained as described above at an effective chlorine content of 1.0%, and treated for 120 minutes at a pulp concentration of 10% and a temperature of 45 ° C. did. After the treatment, it was diluted with cold water to a pulp concentration of 2.5% and then dehydrated to a pulp concentration of 20%.

D (Chlorine dioxide bleaching) Chlorine dioxide was added to the pulp obtained as described above in 0.2%.
%, And the pulp was treated at a pulp concentration of 13% and a temperature of 70 ° C. for 180 minutes. After treatment, cold water gives a pulp concentration of 2.5%
And then dewatered to a pulp concentration of 20% to obtain a bleached pulp.

Table 6 shows the analytical results of the bleached pulps obtained in Examples 20 to 21 and Comparative Example 11 and the measurement results of the amount of organic chlorine compounds (AOX) contained in the total bleaching wastewater per ton of bleached pulp.

[0077]

[Table 6] Bleaching pulp analysis evaluation Bleaching wastewater analysis evaluation Whiteness Viscosity (cP) AOX (kg / pt) Example 20 88.7 13.4 0.16 21 87.1 14.2 0.17 Comparative Example 11 87 .2 10.6 3.40

[0078]

According to the bleaching method of the present invention, a remarkably high delignification can be achieved and a pulp having a remarkably high whiteness can be obtained without a large decrease in viscosity. Furthermore, when full bleaching is performed, the amount of chlorine-based chemicals used in the subsequent bleaching process can be significantly reduced, and as a result, by-products of organic chlorine compounds can be significantly reduced, greatly reducing environmental pollution from bleaching wastewater. Is industrially possible.

Claims (5)

[Claims] 1. A method of delignifying and bleaching a chemical pulp, wherein the digested chemical pulp is subjected to (1) oxygen treatment under high temperature and high pressure, (2) oxygen acid of group IV, V and VI elements or The reaction catalyst consisting of the salt and the peroxide are mixed and treated at a pH of 3 or less and at a temperature of 75 to 110 ° C., and (3) a step of treating with a peroxide in an alkaline medium. A method for delignifying and bleaching chemical pulp for papermaking, which comprises: 2. In the step (2), the reaction catalyst is IV.V.
The method for bleaching delignification of chemical pulp for papermaking according to claim 1, which is a heteropolyacid of Group VI element or a salt thereof. 3. The process for removing chemical pulp for papermaking according to claim 1, wherein in the step (2), the reaction catalyst is at least one selected from oxygen acids of tungsten, molybdenum, vanadium, selenium or titanium or salts thereof. Lignin bleaching method. 4. The method for delignifying and bleaching chemical pulp for papermaking according to claim 2, wherein the reaction catalyst is at least one selected from heteropolyacids containing tungsten, molybdenum or vanadium as a polyatom or salts thereof. 5. The method for bleaching delignification of chemical pulp for papermaking according to claim 1, wherein the step (3) is carried out in the presence of oxygen.