JPH0987985A - Bleaching of chemical pulp for paper making - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the use of chlorine dioxide, accordingly suppressing the byproduction of organic chlorine compounds and preventing environmental pollution attributable to bleaching waste water in manufacturing of highly whitened chemical pulp for paper making. SOLUTION: In a process for delignification and bleaching of chemical pulp, cooked chemical pulp is subjected to a chlorine dioxide bleaching in the following condition. The bleaching is carried out while the pH before bleaching, the pH during the initial period of bleaching or the pH during the terminal period of bleaching is kept at 1-3, and subsequently delignification and bleaching are performed in an alkali medium with a peroxide or a combination of a peroxide and oxygen.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the production of chemical pulp for papermaking. More particularly, it relates to improvements in delignification and bleaching of chemical pulp.

[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 (C), hypochlorite (H), and chlorine dioxide (D), for example, C-E-H-D,
Bleaching has been performed by a sequence such as C / D-E-H-D (C / D is a combined bleaching stage of chlorine and chlorine dioxide, E is an alkali extraction stage). However, since these chlorine-based bleaching chemicals by-produce an organic chlorine compound that is harmful to the environment during bleaching, environmental pollution of bleaching wastewater containing this organic chlorine compound poses a problem.

The most effective method for reducing or preventing the by-production of organic chlorine compounds is to reduce the amount of chlorine-based chemicals used or not to use them, and especially to avoid using molecular chlorine in the first stage. Is the most effective method. The pulp produced by this method is called ECF (elementary chlorin-free) pulp, and it is most of this pulp in Europe at present.

As a method for producing ECF pulp, Japanese Patent Publication No.
No. 221482, Japanese Patent Publication No. 4-245988, and Japanese Patent Publication No. 6-207390, it is proposed to use an enzyme such as hemicellulase or xylanase as a method for delignification. However, this method includes
There are problems that the viscosity of the pulp is reduced and the yield is decreased due to the use of the enzyme, and the bleaching cost is increased because the enzyme itself is very expensive.

[0005] As another method that has been drawing attention, methods using ozone have been proposed in Japanese Examined Patent Publication No. 3-40888, Japanese Examined Patent Publication No. 5-163691, and Japanese Examined Publication No. 5-302285. When ozone is used, delignification progresses significantly and the whiteness is considerably improved, but this also has problems such as a decrease in pulp viscosity and a decrease in yield. Furthermore, ozone is also a very expensive chemical, and the use of ozone leads to a significant increase in bleaching costs.

As a method for producing ECF pulp in Europe, after cooking or oxygen bleaching, instead of molecular chlorine, a treatment with chlorine dioxide, which produces extremely less organic chlorine compound as a byproduct than molecular chlorine, is carried out. A general method is alkali extraction or peroxide bleaching, which is a non-chlorine bleaching agent under alkaline conditions, and the subsequent transfer.
However, in order to replace chlorine used in the first stage with chlorine dioxide, the production capacity of the chlorine dioxide generator is required to be 3 to 5 times that of the current one, and a huge amount of investment is required for the expansion.

Generally, when chlorine dioxide treatment is carried out, "Pulp treatment and bleaching" 233-25 edited by the Japan Paper Pulp Technology Association.
According to page 5, the treatment pH is described as follows. The pH of the chlorine dioxide treatment is preferably 5-6. The reaction rate is low in the low pH range, and the reaction rate increases as the pH increases, but the whiteness shows the highest whiteness around pH 6, and the higher the pH, the lower the whiteness. . Also, the pulp viscosity is pH
It reaches a maximum around 5, and it clearly decreases at pH 7 and above. From these things, when actually processing, the initial p
It is common to start the treatment around H7 and finish it near pH 4 (the decrease in pH in this case is due to the action of the acid generated by the reaction). When the peroxide treatment is performed after the chlorine dioxide treatment at the above pH, the effect of the peroxide is often not sufficiently exerted because heavy metals in pulp and water used are not sufficiently removed.

[0008]

DISCLOSURE OF THE INVENTION The object of the present invention is, in the production of high-whiteness chemical pulp for papermaking, when first-stage chlorine dioxide bleaching is carried out and then peroxide bleaching is carried out,
By increasing the effect of peroxides, it is possible to reduce the amount of chlorine dioxide used, thereby suppressing by-products of organic chlorine compounds and preventing environmental pollution due to bleaching wastewater.

[0009]

[Means for Solving the Problems] The inventors of the present invention have worked economically on a method of delignifying and bleaching pulp to obtain pulp with high whiteness and high quality, and to reduce the amount of chlorine bleaching chemicals used. As a result of diligent study on a method that can significantly reduce the amount of chlorine dioxide, attention has been paid to chlorine dioxide, which is attracting attention as an alternative to molecular chlorine, and when performing peroxide treatment in the bleaching process of chemical pulp using chlorine dioxide, the chlorine dioxide stage It was found that by adjusting the final pH to 1 to 3 or the initial pH to 1 to 3, a pulp with delignification and high whiteness can be obtained very effectively after the peroxide treatment to be performed later. Has been completed.

That is, in the present invention, the chemical pulp that has been digested is subjected to chlorine dioxide treatment such that the final pH is 1 to 3 or the initial pH is 1 to 3, and then in an alkaline medium. The present invention relates to a method for bleaching chemical pulp for papermaking, characterized by performing delignification and bleaching with peroxide, or peroxide and oxygen. INDUSTRIAL APPLICABILITY The present invention is suitable for bleaching of chemical pulp for papermaking, and particularly suitable for delignification and bleaching of kraft pulp derived from hardwood and softwood.

The first feature of the present invention is that the whiteness of the chlorine dioxide bleached pulp treated at pH 1 to 3 is 4 at the final pH.
Compared with the conventional chlorine dioxide bleached pulp which is treated at a moderate level, it shows a lower whiteness, but the whiteness is greatly improved in the subsequent peroxide bleaching. The second feature is that, compared with the case where chlorine dioxide treatment and acid treatment are performed individually, by using both in combination, metal removal can be performed very well, and iron removal, which has been considered difficult to remove in the past, is achieved. It is excellent. Furthermore, since the amount of chlorine dioxide used is smaller than in the general method, when the current process of the first stage chlorine treatment is changed to the ECF process of the first stage chlorine dioxide treatment, the capacity increase of the chlorine dioxide generator is minimized, Alternatively, it is an economically superior method that can be dealt with without enhancement and keeps the investment cost low.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The chlorine dioxide treatment of the present invention under the strongly acidic condition (hereinafter, this treatment may be referred to as AD or AD stage) depends on the state of pulp, for example, a pulp concentration of 1 to 40% by weight. %, Preferably 2 to 30% by weight, more preferably 5 to 20% by weight, temperature is 20 to 110 ° C., preferably 40 to 80 ° C., treatment time is 15 to 300 minutes, preferably 60 to 180 minutes, pH For the final pH
1 to 3, or the initial pH is 1 to 3, or the pH is adjusted to 1 to 3 before adding chlorine dioxide. The final pH 1 to 3 here means that the pH after the lapse of a predetermined treatment time is 1 to 3
The adjustment can be achieved by adjusting the initial pH to 4 to 5 with an acid, depending on the condition of pulp and the amount of chlorine dioxide added. Further, the initial pH means a pH immediately after mixing pulp, chlorine dioxide and an acid, and is a pH before being lowered due to the progress of the reaction.

The amount of chlorine dioxide used in the AD stage varies depending on the amount of lignin contained in the pulp after cooking used,
It is 0.05 to 3.0% by weight, preferably 0.1 to 1.0% by weight, based on the bone-dry pulp. An acid is used to adjust the pH in the AD stage, and as the acid here, either an inorganic acid or an organic acid can be used, and sulfuric acid, nitric acid, formic acid, acetic acid, oxalic acid, and a mixture of these acids are most suitable. Is. Among them, sulfuric acid is most preferably used because it is inexpensive and available and has low corrosiveness. The pulp after the AD stage treatment is separated by a dehydrator and then preferably washed.
The AD treatment of the present invention also includes this dehydration / washing step.

The pulp after the AD stage is later subjected to a peroxide or a delignification / bleaching step using peroxide and oxygen (hereinafter, this peroxide bleaching step is referred to as Ep or Ep).
Step, Eop or Eo bleaching process with peroxide and oxygen
Sometimes referred to as p stages). In this treatment, the pulp is subjected to delignification / bleaching action by peroxide, or peroxide and oxygen in an alkaline medium. When the peroxide and oxygen are used in combination, the peroxide and oxygen act on the pulp substantially at the same time. 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 and can be preferably used because it can be recycled to the digestion step to reduce the replenishment of chemicals in the digestion step. The amount of the alkaline agent used is 0.1 to 6.0% by weight, preferably 0.5, based on the absolute dry pulp in terms of NaOH.
~ 3.0% by weight. 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 markedly reduced. As oxygen in the Eop stage, oxygen gas and air can be used, but oxygen gas is preferred. The amount of oxygen used is preferably 0.1 to 1.0% by weight per bone-dry pulp, and the operating pressure of the Eop stage is preferably atmospheric pressure to 3.5 Kgf / cm ² (gauge pressure).

The peroxides in the Ep or Eop stage include hydrogen peroxide, an adduct of hydrogen peroxide and inorganic salts, sodium peroxide, persulfates, formic acid, peracetic acid and other inorganic and organic acids. A peroxide can be used, and hydrogen peroxide is generally preferably used. The amount of peroxide used is 0.05 to 8.0% by weight, based on 100% hydrogen peroxide, per absolutely dry pulp.
It is preferably 0.2 to 3.0% by weight. If the amount of the peroxide used is less than this, the delignification / bleaching effect is low, and if it is more than this, the efficiency of the peroxide decreases. The order of addition of chemicals to pulp in the Ep stage and Eop stage of the present invention is preferably an alkaline agent and then oxygen, and the peroxide is added after addition of the alkaline agent, immediately before, at the same time as or immediately after oxygen addition. It is preferably carried out. Ep of the present invention
The pulp concentration of the stage and the Eop stage is 7 to 30% by weight, preferably 10 to 20% by weight. The temperature is 40 to 120 ° C, preferably 70 to 100 ° C. Processing time is 15-18
It is 0 minutes, preferably 30 to 120 minutes.

Further, it is preferable to use a magnesium compound in combination in the Ep and Eop stages. 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 or the like can be used, but magnesium sulfate is generally used. The amount of magnesium compound used is 0.005 to 0.7 per absolutely dry pulp as magnesium ion.
It is 5% by weight, preferably 0.01 to 0.3% by weight.
The magnesium compound is preferably added before the addition of the alkaline agent, oxygen and peroxide. That is, it is preferable from the viewpoint of uniform dispersibility of the magnesium compound to add the magnesium compound when the pulp slurry is in the neutral to weakly acidic region.

The bleached pulp obtained by the AD-Ep (or Eop) of the present invention shows a considerably high whiteness as it is, but it is further increased by the full bleaching in which a single-stage or multi-stage bleaching step is continuously added. A pulp showing whiteness can be obtained. In that case, since a high degree of delignification has already been performed up to the Ep stage and the Eop stage, and since it is in a high whiteness state at that stage, as a chemical for subsequent bleaching,
Bleaching with little or no chlorine and hypochlorite is possible. For example, after the O-AD-Ep (or Eop) step, chlorine dioxide (D) and then peroxide bleaching (P) are performed, and O-AD-Ep (or Eop)-is performed.
Full bleaching sequences without chlorine and hypochlorite, such as DP, are possible. In these full bleaching sequences, the current typical sequence is OC /
It is possible to obtain a pulp product having high viscosity and high whiteness equal to or higher than that of D-Eo (combined with oxygen in E stage) -HD. Also,
Since chlorine and hypochlorite are not used, it is possible to bleach with a significantly smaller amount of by-produced organic chlorine compounds than in the existing method.

The chlorine dioxide (D) stage condition in the present invention is a normal D stage condition. For example, the pulp concentration is 7 to 30% by weight, the temperature is 40 to 90 ° C, and the time is 1 to 4
The time and the amount of chlorine dioxide used are in the range of 0.1 to 2.0% by weight. The subsequent peroxide (P) stage is performed under normal P stage conditions. That is, the pulp concentration is 7 to 30% by weight and the temperature is 40 to 1 in the alkaline medium.
The temperature is 00 ° C. and the time is 1 to 4 hours. Examples of the alkaline agent include caustic soda, caustic potash, lime, soda ash, etc. Generally, caustic soda is used, and the caustic soda is used in an amount of 0.1 to 2.0% by weight. Further, as the peroxide, hydrogen peroxide, an adduct of hydrogen peroxide and inorganic salts, sodium peroxide,
Inorganic and organic peroxides such as performic acid and peracetic acid can be mentioned, but hydrogen peroxide is generally used, and the amount of peroxide used is 100% hydrogen peroxide equivalent per absolute dry pulp. It is carried out in the range of 0.1 to 3.0% by weight.

[0019]

EXAMPLES The present invention will be described in detail with reference to examples. The amount of each chemical used is indicated by weight% per bone dry pulp, and the amount of peroxide used is 100% hydrogen peroxide conversion. The pulp used is L-material pulp which has been subjected to oxygen bleaching after kraft cooking. The analysis method was as follows. -Pulp: Whiteness 46.2%, K value: 7.4, 2
4.2cP ・ Analytical evaluation: Whiteness ・ ・ JIS-P8123 (Hunter whiteness method) K value ・ ・ TAPPI K value method Viscosity ・ J. TAPPI No. Method 44 Metal content-ICP method AOX-EPA METHOD 9020 method (using Mitsubishi Kasei Co., Ltd. TSX-10 type)

Example 1 Regarding L material pulp subjected to oxygen bleaching after Kraft cooking,
Delignification bleaching with AD-Ep was performed according to the following conditions. (AD-Ep) AD (chlorine dioxide treatment under strongly acidic conditions) 1) ClO ₂ amount: 0.2%, pulp concentration: 12%, treatment time: 2 hours, treatment temperature: 70 ° C., pH: pH after bleaching treatment The treatment was carried out under the condition that sulfuric acid was added so that 2) After the treatment, it was diluted with water to a pulp concentration of 2.5% and then dehydrated to a pulp concentration of 22%. Further, the pH was adjusted to 6 to 8 with a dilute NaOH aqueous solution, the pulp concentration was set to 20%, and the process was moved to the next Ep stage. Ep (peroxide bleaching) 1) H ₂ O ₂ amount: 1.0%, NaOH amount: 1.2%, M
gSO ₄ amount: 0.25% Pulp concentration: 10%, processing time: 90 minutes, processing temperature: 9
The treatment was carried out under the condition of 0 ° C. 2) After the reaction, dilute the pulp to 2.5% with water,
Then, the pulp concentration was dehydrated to 20% and the bleaching operation was completed.

Example 2 The same bleaching as in Example 1 was carried out except that the pH of the AD stage of Example 1 before the chlorine dioxide treatment was adjusted to 2. (AD-
Ep) Example 3 Bleaching was performed in the same manner as in Example 1 except that the pH before the addition of chlorine dioxide in the AD stage of Example 1 was adjusted to 2. (AD-
Ep)

Comparative Example 1 The same bleaching as in Example 1 was carried out except that the pH of the AD stage of Example 1 after chlorine dioxide treatment was adjusted to 4 in advance. (D-Ep) Comparative Example 2 The same bleaching as in Example 1 was carried out except that the pH of the AD stage of Example 1 after chlorine dioxide treatment was adjusted to 6 in advance. (D-Ep) Comparative Example 3 The same bleaching as in Example 1 was carried out except that the pH of the AD stage of Example 1 after chlorine dioxide treatment was adjusted to 9 in advance. (D-Ep)

The results of Examples 1 to 3 and Comparative Examples 1 to 3 are the first.
It is shown in the table.

[Table 1] Table 1 AD stage pH Whiteness (%) K value Viscosity (cP) ────────────────────────────── ─────── Example 1 After treatment 2 78.2 3.8 22.5 2 Before treatment 2 79.0 3.7 22.8 3 Before addition of D 2 79.1 3.7 22.5 Comparison Example 1 After treatment 4 74.0 4.5 22.5 2 After treatment 6 73.7 4.6 22.2 3 After treatment 9 69.8 4.9 22.0 ─────────── ────────────────────────── As described above, by performing the treatment under the conditions of the method of the present invention, it is possible to significantly improve the whiteness. The progress of delignification was observed.

Example 4 Regarding L-material pulp subjected to oxygen bleaching after Kraft cooking,
AD processing was performed according to the following conditions. (AD) AD (chlorine dioxide treatment under strongly acidic conditions) 1) ClO ₂ amount: 0.2%, pulp concentration: 12%, treatment time: 2 hours, treatment temperature: 70 ° C., pH: pH 2 before addition of chlorine dioxide The treatment was carried out under the condition of adjustment. 2) After the treatment, it was diluted with water to a pulp concentration of 2.5% and then dehydrated to a pulp concentration of 22%. Further, the pH was adjusted to 6 to 8 with a dilute NaOH aqueous solution, the pulp concentration was adjusted to 20%, and the treatment operation was completed.

Comparative Example 4 Bleaching was carried out in the same manner as in Example 4 except that chlorine dioxide in the AD stage of Example 4 was not added. (A) Comparative Example 5 The same bleaching as in Example 4 was performed, except that the pH before the addition of chlorine dioxide in the AD stage of Example 4 was adjusted to 4. (D) Comparative Example 6 The same bleaching as in Example 4 was carried out except that the pH before the addition of chlorine dioxide in the AD stage of Example 4 was adjusted to 6. (D) Comparative Example 7 The same bleaching as in Example 4 was carried out except that the pH before the addition of chlorine dioxide in the AD stage of Example 4 was adjusted to 9. (D)

The bleaching results of Example 4 and Comparative Examples 4 to 7 are secondarily obtained.
It is shown in the table.

[Table 2] Table 2 AD stage pH Whiteness (%) K value Viscosity (cP) ────────────────────────────── Example 4 (AD) 2 51.9 5.4 23.0 Comparative Example 4 (A) 2 51.0 6.2 23.2 5 (D) 4 53.5 5.4 23.2 6 (D) 6 53.9 5.8 23.4 7 (D) 9 52.3 6.0 23.0 ─────────────────── ───────────────── As described above, comparing the effects of chlorine dioxide treatment alone, it was treated at pH 4 and 6 as compared with AD treatment under the conditions of the present invention. Shows higher whiteness, and delignification has pH
It was similar to that of the treatment of No. 4. However, Example 1
~ 3, as shown in Comparative Examples 1-3, the whiteness after Ep, K
The value of the method of the present invention was remarkably excellent.

Table 3 shows the amounts of heavy metals in the pulp after treated in Example 4 and Comparative Examples 4 and 6.

[Table 3] Table 3 Heavy metal content (mg / kg pulp) AD stage pH Fe Mn Cu ─────────────────────────────── Example 4 (AD) 2 8.2 3.0 3.0 Comparative Example 4 (A) 2 26.5 6.2 1.4 6 (D) 6 48.9 15.4 11.2 ──────────────────────────────────── As mentioned above, AD processing is A processing And shows much better metal removal than the D treatment.

Example 5 Regarding L material pulp subjected to oxygen bleaching after Kraft cooking,
Delignification bleaching by AD-Eop was performed according to the following conditions, and then chlorine dioxide bleaching and then peroxide bleaching were performed on the obtained pulp. (AD-Eop-D
-P) AD (chlorine dioxide treatment under strongly acidic conditions) 1) ClO ₂ amount: 0.3%, pulp concentration: 12%, treatment time: 2 hours, treatment temperature: 70 ° C, pH: pH 2 before addition of chlorine dioxide Was adjusted (sulfuric acid was used for the adjustment). 2) After the treatment, it was diluted with water to a pulp concentration of 2.5% and then dehydrated to a pulp concentration of 22%. Further, the pH was adjusted to 6 to 8 with a dilute NaOH aqueous solution, the pulp concentration was set to 20%, and the process was moved to the next Eop stage. Eop (peroxide + oxygen bleaching) 1) H ₂ O ₂ amount: 1.0%, NaOH amount: 1.2%, M
gSO ₄ amount: 0.25% O ₂ amount: 0.5%, reaction pressure: initial ² kgf / cm ² (gauge pressure) → final stage 0 kgf / cm ² (gauge pressure) pulp concentration: 10%, treatment time: 90 minutes , Processing temperature: 9
The treatment was carried out under the condition of 0 ° C. 2) After the reaction, dilute the pulp to 2.5% with water,
Then, the pulp was dehydrated to a pulp concentration of 20%, and the process was transferred to the next stage, D stage. D (Chlorine dioxide bleaching) 1) Treatment was carried out under the conditions of ClO ₂ amount: 0.2%, pulp concentration: 12%, treatment time: 2 hours, treatment temperature: 70 ° C. 2) After the reaction, dilute the pulp to 2.5% with water,
Then, the pulp was dehydrated to a pulp concentration of 20%, and the process was transferred to the next stage, P stage. P (peroxide bleaching) 1) H ₂ O ₂ amount: 0.2%, NaOH amount: 0.3%, pulp concentration: 15%, treatment time: 120 minutes, treatment temperature: 7
The treatment was carried out under the condition of 0 ° C. 2) After the reaction, dilute the pulp to 2.5% with water,
Then, it was dehydrated to a pulp concentration of 20% and the bleaching operation was completed.

Comparative Example 8 Using the same oxygen bleached pulp as in Example 5 as the current bleaching method, the C / D (effective chlorine substitution ratio by D: 10) was used according to the conditions generally practiced. %)-Eo
-HD full bleaching was performed. C / D: 2.0%, Eo: NaOH amount 1.0%, O ₂ amount 0.5%, H: 1.0%, D: 0.15% (C / D-E
o-H-D)

The results of Example 5 and Comparative Example 8 are shown in Table 4. In addition, Table 4 shows the amount of organic halogen compound (AOX) generated by bleaching in Example 5 and the amount of AOX generated by bleaching in Comparative Example 8.

[Table 4] Table 4 Whiteness (%) Viscosity (cP) AOX amount (Kg / Pt) ──────────────────────────── ───────── Example 5 87.9 13.9 0.26 Comparative Example 8 86.0 10.6 3.30 ────────────────── ────────────────────

[0031]

According to the AD-Ep (Eop) bleaching of the present invention, delignification can be efficiently carried out without a significant decrease in viscosity, and a pulp having a remarkably high whiteness is obtained. Can be obtained. As a result, the amount of chlorine-based chemicals used in the second-stage bleaching can be significantly reduced, and byproducts of organic chlorine compounds in the bleaching process can be significantly reduced, which contributes to the prevention of environmental pollution due to bleaching wastewater. Further, in carrying out the present invention, since the high temperature and high pressure oxygen bleaching equipment and the medium and low pressure oxygen bleaching equipment which are currently popular can be used as they are, a large additional capital investment is not required.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akiyo Shimada 6-1-1, Shinjuku, Katsushika-ku, Tokyo Mitsubishi Gas Chemical Co., Ltd. Tokyo Research Laboratory

Claims (5)

[Claims] 1. A method of delignifying and bleaching a chemical pulp, wherein when chlorine dioxide bleaching is performed on a digested chemical pulp, chlorine dioxide bleaching is performed at an initial pH of bleaching of 1 to 3, and then in an alkaline medium. A method for bleaching chemical pulp for papermaking, comprising delignification and bleaching with peroxide, or peroxide and oxygen. 2. A method of delignifying and bleaching a chemical pulp, wherein when chlorine dioxide bleaching is performed on the digested chemical pulp, chlorine dioxide bleaching is performed at a final pH of bleaching of 1 to 3, and then in an alkaline medium. A method for bleaching chemical pulp for papermaking, comprising delignification and bleaching with peroxide, or peroxide and oxygen. 3. A method of delignifying and bleaching a chemical pulp, wherein when chlorine dioxide bleaching is performed on a digested chemical pulp, the pH before bleaching is adjusted to 1 to 3, chlorine dioxide bleaching is carried out, and then in an alkaline medium. With peroxide,
Alternatively, a method for bleaching chemical pulp for papermaking, which comprises performing delignification and bleaching with peroxide and oxygen. 4. The peroxide according to claim 1, wherein the peroxide is hydrogen peroxide.
The method for bleaching a chemical pulp for papermaking according to a few items. 5. The method for bleaching chemical pulp for papermaking according to claim 1, wherein chemical pulp subjected to high temperature and high pressure oxygen bleaching after cooking is used.