JP2001192991A - Method of bleaching alkali pulp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of bleaching pulp, capable of effectively removing lignin and color substance in alkali pulp, producing a pulp having high whiteness and high strength absolutely without using chlorine and perfectly preventing the generation of organic chlorine compounds such as chlorinated dioxin and chloroform. SOLUTION: An alkali pulp is treated under acidic condition to reduce the transition metal ion in the pulp, a stabilizer is added to the system while keeping the acidic state to stabilize the reduced transition metal ion, the pulp is bleached by mixing hydrogen peroxide and the bleaching is continued with or without adding oxygen after returning the pulp to an alkaline state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chlorine-free bleaching method for alkaline pulp, and more particularly, to suppressing the self-decomposition of hydrogen peroxide in the bleaching of alkaline pulp with hydrogen peroxide and increasing the efficiency of bleaching. It is about the method. The method of the present invention can effectively remove lignin and coloring substances contained in alkali pulp, and can produce pulp having high whiteness and high strength without using chlorine at all. In addition, the present invention provides a method for bleaching pulp without generating any chlorinated dioxins and organic chlorine compounds such as chloroform.

[0002]

2. Description of the Related Art Conventionally, in alkaline pulp bleaching, oxygen bleaching treatment (hereinafter referred to as O treatment) is first performed, followed by chlorine and chlorine dioxide treatment (hereinafter referred to as (C + D) treatment), and alkali extraction treatment (hereinafter referred to as E treatment). Alternatively, an alkali extraction treatment to which oxygen is added (hereinafter, Eo treatment) or an alkali extraction treatment to which oxygen and hydrogen peroxide are added (hereinafter, Eop treatment), a hypochlorite treatment (hereinafter, H treatment), a chlorine dioxide treatment ( Hereinafter, D treatment) and hydrogen peroxide treatment (hereinafter, P treatment) were performed. Further, a method of washing the pulp by performing an acid treatment (hereinafter referred to as a treatment) or a chelating agent treatment (hereinafter referred to as Q treatment) has been studied, but hardly practically used.

[0003] There are three main roles of acid treatment in alkaline pulp bleaching. That is, washing of metal ions present in the pulp, decomposition of hexenuronic acid (Journal of Pulp and Paper Science (Journal of Pulp and Paper Science)
r Science), Vol. 25, No. 5, pp. 155 (19
1999)), bond cleavage between the benzylic position of lignin and carbohydrate (Journa of Wood Science (Journa)
l of Wood Science), 45 volumes, 3
No. 233 (1999)). It has been known that hydrogen peroxide decomposes in alkaline pulp bleaching. The typical theories are as follows: ionic decomposition mechanism by base catalyst, radical decomposition mechanism by base catalyst, radical decomposition mechanism by transition metal ion, decomposition mechanism by reaction of transition metal ion and perhydroxyanion, transition metal ion Decomposition mechanism of colloidal oxides by surface reaction was observed (Journal of Pulp and Paper Science (Journal of Pulp and Paper)
p and Paper Science), Volume 14,
6, J126 (1988)). The decomposition of hydrogen peroxide implies not only the loss of bleaching capacity but also the formation of new colored structures by decomposition products (SvenskPapperstedni).
ng), Vol. 88, No. 9, page R84 (1985)).

On the other hand, it has been known that the catalytic decomposition reaction of hydrogen peroxide induced by transition metal ions is accelerated particularly by manganese (Paper Engineering Co., Ltd., Vol. 49, No. 4,
21 (1995)). It has also been known that the catalytic decomposition behavior of hydrogen peroxide differs depending on the difference between the oxidation state of manganese and the pH of the reaction solution (Journal of American Chemical Society (J. Am. Ch.
em. Soc. ), 69, 741 (1947),
Svensk paper stained (Svensk Pa
pp. 88, 9, R84 (1985)). Coldette et al. (Journ
al of Pulp and Paper Scie
nce, Vol. 14, No. 6, p. J3 (1989)) discusses in detail the mechanism of stabilization of hydrogen peroxide by sodium silicate, and the order of addition of sodium silicate and sodium hydroxide affects hydrogen peroxide decomposition. That was shown. However, the effect of the oxidation state of manganese was not examined in detail.

[0005] Minobu (Abstracts of the Japan Wood Science Society) uses Mn (I
The difference in catalytic decomposition behavior of hydrogen peroxide between I) and Mn (III, IV) was examined. When DTPA was added to a solution containing Mn (II) and hydrogen peroxide, decomposition of hydrogen peroxide in alkaline It was found that it was hardly recognized. Also, glucose or filter paper and Mn
It has been found that when (III, IV) is reacted under acidic conditions, manganese can be reduced and decomposition of hydrogen peroxide in alkaline conditions can be suppressed. However, based on these findings, a new method that replaces the conventional alkaline pulp bleaching technique has not been found yet.

[0006]

However, when treating alkali pulp with chlorine or chlorine-based chemicals, there is a problem that chlorinated dioxins and organic chlorine compounds such as chloroform are generated and pollute the environment. . Further, even if bleaching is performed by using a treatment, a Q treatment, an Eo treatment, an Eop treatment, and a P treatment in combination without using chlorine or a chlorine-based chemical, the viscosity or strength of the pulp fiber is reduced. There is a problem in that self-decomposition of hydrogen oxide occurs and the amount of added hydrogen peroxide must be increased.

[0007]

As a result of intensive studies, the present inventor has solved the above-mentioned problems. That is, the bleaching method of the present invention is a method of bleaching alkali pulp produced from a lignocellulosic material without using chlorine.First, the pulp is treated under acidic conditions to reduce transition metal ions in the pulp. Adding a stabilizer of a transition metal ion under acidic conditions, followed by mixing with hydrogen peroxide, and finally making the pulp alkaline and adding or not adding oxygen to perform bleaching. It provides a new method of bleaching alkaline pulp from cellulosic materials.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A lignocellulose material is a material in which cellulose and lignin are tightly physically or chemically bonded, and representative examples include wood, bamboo, hemp, straw, bagasse and the like. Examples of the cooking method for producing pulp from the lignocellulosic material include a kraft method, a polysulfide method, a soda method, a neutral or alkaline sulphite method, and a cooking method to which an anthraquinone derivative is added as a cooking catalyst. Pulp produced by these methods is called alkaline pulp.
The alkali pulp used in the present invention is pulp obtained by performing a steaming treatment with an alkaline chemical solution, such as pulp produced by these methods. Acid sulphite pulp is not included in the chemical pulp. In these unbleached pulp, lignin and coloring matter altered by alkali remain. In addition, transition metal ions such as manganese, iron, and copper derived from the lignocellulose material and water are attached. The lignin in these chemical pulp is O
By performing the processing, approximately 50% of the amount is removed. However, the resulting oxygen bleached pulp still contains altered lignin and coloring matter. Transition metals such as manganese, iron, and copper are oxidized and strongly adhere to the pulp.

In the present invention, unbleached pulp or oxygen-bleached pulp is treated under acidic conditions in order to reduce transition metal ions such as manganese in the pulp. The pH of the pulp water mixture is pH 1.2 to 2.5, and the temperature is 40 to 100 ° C.
Is performed for 30 to 120 minutes. As a result, transition metal ions such as manganese are reduced. If the pH of the pulp water mixture is higher than 2.5, transition metal ions such as manganese are not reduced, and if the pH is lower than 1.2, the viscosity or strength of the pulp fiber decreases, which is not preferable.

[0010] Chemicals that can be used for the acid treatment of pulp include inorganic acids and organic acids such as sulfuric acid, hydrochloric acid, nitric acid, nitrous acid, sulfurous acid, acetic acid and oxalic acid. From the viewpoint of recovery of bleaching waste liquid, sulfuric acid is used. Alternatively, it is most preferable to use sulfurous acid. Further, after the acid treatment, a stabilizer is added to the mixture to make the pH of the pulp water mixture acidic and to stabilize reduced transition metal ions such as manganese.

The pH of the pulp water mixture after the acid treatment is adjusted to pH
4 to 6, a chelating agent such as DTPA or EDTA is added as a stabilizer, and an aging period of 1 minute to 10 minutes is set at 20 ° C. If the pH of the pulp water mixture is higher than pH 6, transition metals such as manganese are easily oxidized, and pH 4
If it is smaller, a part of the chelating agent such as DTPA is decomposed, which is not preferable.

After the acidic treatment, the pH of the pulp water mixture may be adjusted to pH 4 to 6 without dewatering and washing the pulp, and a stabilizer may be added. Dewater the pulp,
It can also be washed. However, it is not preferable to make the pH of the pulp water mixture higher than pH 6 using alkaline circulating water for washing. When adding sodium silicate and magnesium sulfate as stabilizers,
A ripening period of 1 minute to 30 minutes at 70 ° C. is provided.

Next, hydrogen peroxide is mixed with the pulp water mixture. The pH of the pulp mixture is preferably pH 4-6.
The treatment so far, that is, the acid treatment and the stabilization treatment at pH 4 to 6 are referred to as A treatment. Next, an alkali agent was added, the pulp mixture was made alkaline, and oxygen was added,
Alternatively, pulp bleaching is performed without adding oxygen. The process of adding oxygen to perform pulp bleaching is referred to as Eop treatment, and the process of performing pulp bleaching without adding oxygen is referred to as Ep treatment. As the alkaline agent used in the present invention, sodium hydroxide,
Potassium hydroxide, sodium carbonate, potassium carbonate, sodium sulfite and the like.

For the Eop processing and the Ep processing, ordinary conditions can be selected. That is, the sodium hydroxide addition rate is 0.5% to 2.0%, the temperature is 60 ° C to 120 ° C, and the hydrogen peroxide addition rate is 0.5% to 3.0%. After the treatment, hydrogen peroxide remains in the pulp water mixture, and the pulp bleaching effect is significantly improved. (AEop) treatment <combination of the above stabilization treatment and treatment for performing pulp bleaching by adding oxygen> or (AEp) treatment <combination of the above stabilization treatment and treatment for performing pulp bleaching without addition of oxygen Treatment>, and then bleaching by hypochlorite treatment (H treatment).

(AEop) -H processing or (AEop)
After bleaching by p) -H treatment, bleaching by chlorine dioxide treatment (D treatment) can also be performed. (AEo
After bleaching by p) -HD treatment or (AEp) -HD treatment, bleaching by hydrogen peroxide treatment (P treatment) can also be performed. (AEop) processing,
Alternatively, before performing bleaching by (AEp) processing, H processing or D processing can be added. In particular, D- (AE
op) processing has proven to be an effective means.

In the present invention, various embodiments are possible. (AEop) or (AEp), which is the final step of the bleaching process described in claim 1 of the present invention.
After the treatment, the following bleaching step can be added. Specifically, (AEop) -H processing,
(AEp) -H treatment, (AEop) -HD treatment, (A
Ep) -H-D treatment, (AEop) -H-D-P treatment,
Alternatively, in addition to the (AEp) -HDP treatment, (AEo)
p) -D treatment, (AEp) -D treatment, (AEop) -D
-P treatment, (AEp) -DP treatment, (AEop) -D
-ED processing, (AEp) -DED processing, (AEo
p) -D-Eo-D treatment, (AEp) -D-Eo-D treatment, (AEop) -DPD treatment, (AEp) -D-
PD processing, (AEop) -D-Ep-D processing, (AE
p) -D-Ep-D processing, (AEop) -DHD processing, or (AEp) -DHD processing.
After the bleaching by the (AEop) treatment or the (AEp) treatment, a small amount of the coloring substance still remains in the pulp. Transition metal ions such as manganese are oxidized and adhere to the pulp. Then, as a method not using a chlorine-based bleaching chemical, after the bleaching by the (AEop) treatment or the (AEp) treatment, the A treatment can be performed again.

Next, specific examples are shown, and the bleaching results are shown.

Example 1 As raw material pulp, pulp obtained by oxygen bleaching softwood kraft pulp was used. As a result of analysis, the kappa number of this pulp was 12.1, the pulp viscosity was 22.9, and 54.2 p.
pm of manganese. This pulp was taken in a dry weight of 100 kg, and 900 kg of water and sulfuric acid were added thereto to prepare 1000 liter of a pulp water mixed solution having a pH of 2.5. This was heated to 70 ° C. and allowed to stand for 30 minutes. While maintaining the pH as it is, stirring the pulp water mixture,
An aqueous solution containing 0.5 kg of DTPA as dry weight
The mixture was added at 0 ° C., mixed, and allowed to stand for 1 minute to stabilize. The solution color changed to a slightly lighter color. Subsequently, an aqueous solution containing 2 kg of hydrogen peroxide was mixed with stirring to start bleaching. Further, while stirring, an aqueous solution containing 1 kg of sodium hydroxide was added to make the pH of the pulp water mixture alkaline, oxygen was introduced into the reaction system at a pressure of 0.35 MPa, and the mixture was heated to 90 ° C and heated to 120 ° C. Continued bleaching for minutes. The amount of hydrogen peroxide remaining in the pulp water mixture was determined, and the bleaching was stopped when the residual level showed 9.2%. The pulp was washed and dried, and the pulp brightness and pulp viscosity were measured to be 60.1% and 19.4 centipoise, respectively.

Examples 2 to 5 The bleaching was carried out in the same manner as in Example 1 under the conditions shown in Table 1. Softwood oxygen bleached kraft pulp containing 22.9 ppm of manganese was used as a raw pulp.

Examples 6 to 11 The bleaching was carried out in the same manner as in Example 1 under the conditions shown in Table 1. Hardwood polysulfide quinone pulp was used as a raw material pulp. As a comparative example, a condition different from the condition of Example 1 will be described. As a conventional example, a known close one is shown.

(AEop) -A processing or (AEop)
p) After the -A processing, Eop processing or Ep is performed. (AEop)-(AEop) processing, (AEop)-(A
Bleaching by Ep) treatment, (AEp)-(AEop) treatment, or (AEp)-(AEp) treatment produces pulp with high whiteness and high strength without producing chlorinated dioxins and organic chlorine compounds. We were able to. Table 1 shows the results.

[0021]

[Table 1] The whiteness of the bleached pulp in the table is ISO2469, 247
0, 3688. The residual levels of hydrogen peroxide in the table were determined as follows. Sample (100mL)
4N sulfuric acid (5mL) and 10% potassium iodide (5m
L) was added in order, and a 3% ammonium molybdate solution (2 to 3 drops) was added. Then, titration was performed using 0.1 N sodium thiosulfate until the sample solution became colorless. Immediately before the end point, 1 mL of 0.5% starch was added as an indicator. The weight (g) of hydrogen peroxide obtained in this way was R, the weight (g) of hydrogen peroxide initially mixed was A, and the residual degree was R 度 A × 100 (%).

[0022]

According to the present invention, lignin and coloring substances contained in pulp can be effectively removed, and pulp having high whiteness and high strength can be produced without using chlorine. Bleached pulp can be produced without producing chlorinated dioxins. Further, the amount of chlorinated dioxins and the amount of organic chlorine compounds such as chloroform can be significantly reduced, and bleached pulp can be produced.
Furthermore, bleached pulp can be produced without producing any organochlorine compound.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Ni Yonghiro 1-1-1 Tennodai, Tsukuba, Ibaraki Pref. FA13

Claims (7)

[Claims] An alkaline pulp produced from a lignocellulosic material is first treated under acidic conditions to reduce transition metal ions in the pulp, and then a stabilizer is added under acidic conditions, Chlorine characterized by stabilizing reduced transition metal ions, followed by mixing with hydrogen peroxide for bleaching, and then returning the pulp to alkalinity and continuing bleaching with or without the addition of oxygen. Bleaching method of alkaline pulp without using. 2. The method for bleaching alkaline pulp according to claim 1, wherein the pulp is treated under acidic conditions of pH 1.2 to 2.5 at a temperature of 40 to 100 ° C. to reduce transition metal ions in the pulp. 3. A chelating agent such as DTPA or EDTA as a stabilizer for a transition metal ion at a pH of 4 to 6,
The method of claim 1 or 2, wherein sodium silicate and / or magnesium sulfate are added to stabilize the transition metal ion at a temperature of 20 to 70 ° C. 4. The bleaching method according to claim 1, wherein the pulp is returned to alkaline and oxygen is added, or before and after the bleaching is continued without adding oxygen. A bleaching method in which one or more of bleaching with an acid salt, bleaching with chlorine dioxide, and bleaching with hydrogen peroxide are performed. 5. The bleaching method according to claim 1, further comprising bleaching with hypochlorite.
A bleaching method in which bleaching with chlorine dioxide and bleaching with hydrogen peroxide are sequentially performed. 6. The bleaching method according to any one of claims 1 to 3, followed by bleaching with chlorine dioxide, alkali extraction, alkali extraction with addition of oxygen, bleaching treatment with hydrogen peroxide, or hypochlorous acid. A method of sequentially performing bleaching with salt and bleaching with chlorine dioxide 7. An alkali pulp produced from a lignocellulosic material is first treated under acidic conditions to reduce transition metal ions in the pulp, and then a stabilizer is added under acidic conditions. Stabilize the reduced transition metal ions, then mix with hydrogen peroxide to perform bleaching, return the pulp to alkalinity and continue bleaching with or without oxygen, and after a certain time, again Treating the pulp under acidic conditions to reduce the transition metal ions in the pulp, then adding a stabilizer while still under acidic conditions,
Chlorine characterized by stabilizing reduced transition metal ions, followed by mixing with hydrogen peroxide for bleaching, and then returning the pulp to alkalinity and continuing bleaching with or without the addition of oxygen. Bleaching method of alkaline pulp without using.