JP7041915B2 - Manufacturing method of chemical pulp - Google Patents

Description

The present disclosure relates to a method for producing chemical pulp and a method for cooking a lignocellulosic material.

As a method for producing pulp by chemically treating chemical pulp, that is, a lignocellulosic material, there are an alkaline cooking method and a sulfurous acid cooking method. The alkaline cooking method in the present disclosure includes various methods such as a craft cooking method, a soda cooking method, a sulfite cooking method, and an organosolve cooking method. Further, the sulfurous acid cooking method (sulfurous acid method) in the present disclosure is a general term for various sulfurous acid methods such as an alkaline sulfurous acid method, a neutral sulfurous acid method, an acidic sulfurous acid method, and a heavy sulfurous acid method.
When the lignocellulosic material is steamed to produce pulp, hydroanthraquinones such as dihydroanthraquinone and tetrahydroanthraquinone are used as a cooking aid from the viewpoint of improving the pulp yield and the cooking rate. (For example, Patent Document 1). Further, a polyoxyalkylene alkyl ether carboxylate is known as a deresinating agent for a cooking step (Patent Document 2).

Japanese Unexamined Patent Publication No. 54-82401 Special Publication No. 53-28522

However, in recent years, the carcinogenicity of anthraquinone has been pointed out. For example, the European Food Safety Authority (EFSA) announced in 2012 that anthraquinone could not rule out its carcinogenic potential. In response, the Federal Institute for Risk Assessment (BfR) announced in 2013 that anthraquinones would be excluded from the list of substances approved for use in food packaging paper, and the use of anthraquinones. Is in the direction of refraining from. Further, even if the polyoxyalkylene alkyl ether carboxylate is added, there is a problem that the pulp yield and the pulp quality cannot be sufficiently improved. Furthermore, if the copper value obtained in the cooking process is high, there is a problem that a large amount of bleaching agent (oxygen, chlorine dioxide, chlorine, hypochlorine, hydrogen peroxide, sodium hydroxide, ozone, etc.) is required in the bleaching process. be.

Therefore, instead of the conventional method, there is a demand for a new cooking aid capable of improving the pulp yield and reducing the copper value.

The present disclosure provides a method for producing and cooking a chemical pulp capable of improving the yield and reducing the copper value in at least one of the embodiments.

The present disclosure is, in one embodiment, a method for producing chemical pulp by alkaline cooking or sulfurous acid cooking of a lignocellulosic material, which comprises steaming the lignocellulosic material in a chemical solution containing a radical scavenger. Regarding.

The present disclosure relates to a method for producing chemical pulp, which comprises, in one aspect, cooking the lignocellulosic material in an alkaline solution containing a radical scavenger.

The present disclosure relates to, in one embodiment, a method for alkaline or sulfurous acid cooking of a lignocellulosic material, which comprises steaming the lignocellulosic material in a chemical solution containing a radical scavenger.

According to the present disclosure, it is possible to provide a method for producing and cooking a chemical pulp capable of improving the yield and reducing the copper value in at least one of the embodiments.

Is a block diagram showing an example of a flow of a chemical pulp production system.

The present disclosure is based on the finding that digestion in the presence of a radical scavenger can promote delignin, improve the selection yield and / or reduce the copper value.

The reason why the above effect is obtained by performing cooking in the presence of a radical scavenger is not clear, but it is presumed as follows.
That is, free or fragmented lignin, cellulose, etc. by cooking the lignocellulosic material in the presence of a radical scavenger such as N, N'-di-sec-butyl-1,4-phenylenediamine (PDA). Hydrogen or the radical scavenger itself reacts with the derived radicals. By this reaction, the radical coupling reaction between lignin and the radical coupling reaction between lignin and cellulose can be suppressed. As a result, the repolymerization of lignin can be prevented, and the radical polymerization reaction in the lignocellulosic material can also be prevented. It is considered that these can promote delignin and suppress the lignocellulosication of cellulose, thereby improving the selection yield (pulp yield) as compared with the conventional case. In the present disclosure, the "selection yield (pulp yield)" refers to the dry weight of the pulp (selected pulp) after removing undissolved fibers such as knot meal from the unbleached pulp after cooking, which is used for cooking. It refers to the percentage of the total dry weight of the raw material (lignocellulosic material) that was used. However, the present disclosure is not limited to these mechanisms.

In the present disclosure, the "chemical pulp" is a pulp obtained by chemically treating a lignocellulosic material to remove lignin. Examples of the chemical pulp include sulfite pulp, dissolved sulfite pulp, alkaline pulp, kraft pulp, dissolved kraft pulp and the like in one or more embodiments.

As a method for producing chemical pulp, there are an alkaline cooking method or a sulfurous acid cooking method. As an alkaline cooking method, in one or more embodiments, a strong alkaline aqueous solution such as an aqueous solution of sodium hydroxide or a mixed solution of sodium hydroxide and sodium sulfide is used as a cooking solution, for example, a cellulose raw material is used at 140 to 180 ° C. Examples thereof include a method of cooking to obtain pulp. Examples of the alkaline cooking method include various methods such as a craft cooking method, a soda cooking method, a sulfite cooking method, and an organosolve cooking method in one or more embodiments. Further, as the sulfurous acid cooking method, in one or a plurality of embodiments, various sulfurous acid methods such as an alkaline sulfurous acid method, a neutral sulfurous acid method, an acidic sulfurous acid method, and a heavy sulfurous acid method can be mentioned.

In the present disclosure, "melting" means that wood or non-wood lignocellulosic material is treated with chemicals at high temperature and high pressure to dissolve or remove non-fibrous substances such as lignin from the lignocellulosic material to obtain cellulose and the like. Separation of fiber elements. The cooking method in the present disclosure includes an alkaline cooking method or a sulfurous acid cooking method. The cooking can be carried out in one or more embodiments by heating the lignocellulosic material and an alkaline solution (steaming liquid) containing a radical scavenger in a kettle. The "melting" in the present disclosure includes not only cooking under high temperature and high pressure using a cooking pot for fiberization (palping), but also oxygen cooking for delignin (for example, an oxygen cooking apparatus in an oxygen delignin step). It can include cooking) performed in an O ₂ reactor). Examples of the high temperature treatment in the present disclosure include heating to 80 ° C. or higher in one or more embodiments. The digestion in the production method of the present disclosure comprises heating in one or more embodiments so that the temperature of the chemical solution containing the radical scavenger or the alkaline solution is 80 ° C to 200 ° C. Examples of the high-pressure treatment in the present disclosure include pressurizing to 0.2 MPa or more, preferably 0.3 MPa or more, 1.0 MPa or more, or 3.0 MPa or less in one or more embodiments. It is preferably 2.0 MPa or less.

In the present disclosure, the "lignocellulosic material" may be various kinds of wood such as wood chips or non-wood such as straw. Examples of the wood include softwood (N material) chips and hardwood (L material) chips in one or more embodiments. Examples of the coniferous tree include larch, Japanese red pine, and Sugi in one or more embodiments. Hardwoods include, in one or more embodiments, eucalyptus, acacia, and the like. The lignocellulosic material may be a single type of lignocellulosic material or a mixture of two or more types of lignocellulosic material in one or more embodiments. The lignocellulosic material in the present disclosure may include not only the above-mentioned wood chips and the like, but also pulp slurry (for example, unbleached or unbleached pulp and the like) discharged in a cooking pot (cooking step).

In the present disclosure, the "radical scavenger" refers to a compound that binds to or can bind to a radical species generated during cooking, or a compound that can suppress or suppress a polymerization reaction caused by the generated radical species. The radical scavengers of the present disclosure can also be referred to as free radical scavengers in one or more embodiments.

Examples of the radical scavenger include an amine-based radical scavenger, a tetramethylpiperidinoxyl-based radical scavenger, a phenol-based radical scavenger, a quinone-based radical scavenger, and the like in one or more embodiments.

As the amine-based radical trapping agent, in one or more embodiments, N, N'-di-sec-butyl-1,4-phenylenediamine (PDA), N, N'-bis (1,4-dimethylpentyl) )-1,4-Phenylenideamine, N- (1,4-dimethylpentyl) -N'-phenyl-1,4-phenylenediamine, N-phenyl-N'-(1,3-dimethylbutyl) -1, 4-Phenylamine, N-Phenyl-N'-Isopropyl-1,4-Phenylenediamine, N, N'-Di-Phenyl-1,4-Phenylenediamine or N, N'-di-2-naphthyl-1 , 4-Phenylene diamine-based radical trapping agents, N, N-diethylhydroxylamine (DEHA) or N, N-dimethylhydroxylamine and other hydroxylamine-based radical trapping agents, tributylamine, diphenylamine, phenothiazine, or phenyl. -Α-naphthylamine and the like can be mentioned.

As the tetramethylpiperidine oxyl-based radical trapping agent, in one or more embodiments, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (H-TEMPO), 2,2,6, 6-Tetramethylpiperidine-1-oxyl, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-cyano-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-Benzoxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-oxo-2,2,6 6-Tetramethylpiperidine-1-oxyl, 4-acetamide-2,2,6,6-tetramethylpiperidine-1-oxyl, or bis- (2,2,6,6-tetramethylpiperidine-1-oxyl) -Examples include TEMPO.

As the phenolic radical trapping agent, in one or more embodiments, 2-methylphenol, 2-ethylphenol, 2-propylphenol, 2-methoxyphenol, 2,4-dimethylphenol, 2,6-dimethylphenol, Examples thereof include 2,6-dimethoxyphenol, 2-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-methylphenol, 4-tertiary butyl catechol and the like.

Examples of the quinone-based radical trapping agent include hydroquinone, benzoquinone, methquinone, ethylhydroquinone, propylhydroquinone, butylhydroquinone, pentylhydroquinone, hexylhydroquinone, tertiary butylhydroquinone, hydroxyhydroquinone, and naphthoquinone in one or more embodiments. Be done.

[Manufacturing method of chemical pulp]
The present disclosure relates to, in one aspect, a method for producing chemical pulp (the production method of the present disclosure). The production method of the present disclosure is, in one embodiment, a method of producing chemical pulp by alkaline cooking or sulfurous acid cooking of a lignocellulosic material, in which the lignocellulosic material is steamed in a chemical solution containing a radical scavenger. including. Further, the production method of the present disclosure relates to a method for producing chemical pulp, which comprises, in one embodiment, steaming in an alkaline solution containing a radical scavenger.

As the chemical solution containing the radical trapping agent, in one or more embodiments, the chemical solution used in the cooking step in the production of chemical pulp such as sulfite pulp, dissolved sulfite pulp, soda pulp, kraft pulp, and dissolved kraft pulp ( Cooked pulp), chemicals used in the oxygen delignin step, and the like.

Examples of the chemical solution containing the radical scavenger include, in one or more embodiments, an alkaline solution containing the radical scavenger.

Examples of the alkaline solution containing the radical scavenger include a cooking solution used for alkaline cooking in one or more embodiments. The chemical solution or alkaline solution (distilled solution) containing the radical trapping agent used in the production method of the present disclosure is, in one or more embodiments, a radical trapping agent, sodium sulfide (Na _2S ), and sodium hydroxide ( It contains NaOH), preferably sodium sulfide and sodium hydroxide as main components, and contains a radical trapping agent as a cooking aid. The sulfurization degree in the chemical solution or alkaline (cooking solution) containing the radical scavenger is 10% to 35%, preferably 27% to 30% in one or more embodiments. The amount of alkali added (active alkali addition rate (AA)) is 5% to 35%, preferably 13% to 30% in one or more embodiments. The degree of sulfurization is represented by (Na ₂ S) / (NaOH + Na ₂ S) × 100. The active alkali is expressed in terms of NaOH ₊ Na 2S.

The chemical solution and alkaline solution containing the radical scavenger used in the production method of the present disclosure are substantially free of organic solvents in one or more embodiments. Substantially not contained in the present disclosure means that, in one or more embodiments, the concentration of the organic solvent in the chemical solution or alkaline solution is 5% by weight or less, 4% by weight or less, 3% by weight or less, and 2% by weight or less. 1, 1% by weight or less, 0.5% by weight or less, approximately 0% by weight, or 0% by weight.

Examples of the alkaline solution containing the radical scavenger include a chemical solution (treatment solution) used in the oxygen delignin step in one or more embodiments. The alkaline solution containing the radical scavenger used in the production method of the present disclosure contains, in one or more embodiments, at least a radical scavenger and an alkaline agent such as sodium hydroxide or potassium hydroxide. The pH of the alkaline solution is 11 or more or 12 or more, or 14 or less or 13.5 or less in one or more embodiments.

The chemical solution (distilled solution) containing a radical scavenger used in the production method of the present disclosure includes, in one or more embodiments, a sulfurous acid solution containing a radical scavenger or a hydrogen sulfite solution containing a radical scavenger (sodium bisulfite). Solution) and the like.

In one or more embodiments, the amount of the radical scavenger added can be appropriately determined according to the absolute dry weight of the lignocellulosic material as a raw material. The amount of the radical scavenger added is, in one or more embodiments, 0.005% by weight to 5% by weight, preferably 0.01% by weight to 4% by weight, based on the absolute dry weight of the lignocellulosic material. It is more preferably 0.05% by weight to 3% by weight. The amount of the radical scavenger added in the present disclosure includes, in one or more embodiments, the concentration of the radical scavenger in the treatment liquid in which the cooking of the present disclosure is carried out.

The production method of the present disclosure may include, in one or more embodiments, a step of adding a radical scavenger. The location of the radical scavenger is not particularly limited as long as the lignocellulosic material is added so as to be digestible in the chemical solution containing the radical scavenger. In one or more embodiments, the radical scavenger may be added at least one place from the raw material chip supply step prior to the cooking step to the cooking step of alkaline cooking or sulfurous acid cooking of the lignocellulosic material. In one or more embodiments, the radical scavenger may be added to the cooking pot where the cooking is performed, or from the viewpoint of improving the yield, any one of the raw material chip supplying steps of supplying the raw material chips to the cooking pot. It is preferable to add to. Examples of the addition site in the raw material chip supply step include a chip bin (13 in FIG. 1), a steaming vessel (14 in FIG. 1), a metal trap, a chip chute, a high-pressure feeder, and the like in one or more embodiments. It may also be added to the injection circulation line of the cooking liquid (white liquid and black liquid). It may be added to the oxygen cooking apparatus in the delignin step after cooking in the cooking pot. The radical scavenger may be added at once or in divided portions in one or more embodiments.

FIG. 1 shows an example of a flow of a method for producing chemical pulp. The flow of FIG. 1 includes a raw material chip supply step of the lignocellulosic material, a cooking step, and an oxygen delignin step.
(Raw material chip supply process)
The lignocellulosic material chips 11 chipped with a chipper (not shown) are stored in the chip silo 12. The chips stored in the chip silo 12 are selected by a chip screen (not shown) and sent to the chip bin 13, and then the gas phase inside the chips is replaced with water vapor in the steaming vessel 14.
(Creating process)
In the chip having enhanced permeability in the steaming vessel 14, the penetration of the cooking liquid into the chip is promoted by the introduction of the alkaline cooking liquid in the penetration tower 15. After that, in the cooking kettle 16, wood chips, which are pulp materials, and a solution containing sodium hydroxide or the like are mixed and steamed under pressure to mix black liquor in which non-fiber components are dissolved and pulp. The slurry is discharged. Further, the permeation column 15 may be used as a pre-hydrolysis kettle (PHV) column for pre-hydrolysis using an acid in some cases.
(Oxygen delignin process)
The pulp slurry discharged from the cooking pot 16 is washed in the black liquor washing tower 17, passed through the screen 18, the decker 19, and the unbleached high-concentration storage tower 20, and then introduced into the oxygen cooking apparatus 21. In the oxygen cooking apparatus 21, after further deligninization, the mixture is transferred to a bleaching step (not shown).

The heating temperature during cooking is, in one or more embodiments, 80 ° C to 200 ° C, preferably 140 ° C to 180 ° C. The production method of the present disclosure comprises, in one or more embodiments, a cooking step comprising heating the lignocellulosic material in a chemical solution, which is an alkaline solution containing a radical scavenger, at 80 ° C to 200 ° C.

The heating time during cooking is, in one or more embodiments, 30 to 400 minutes, preferably 50 to 300 minutes.

The production method of the present disclosure may include pretreatment of the lignocellulosic material prior to the above-mentioned cooking. Examples of the pretreatment include hydrothermal treatment (pre-hydrolysis treatment) and the like in one or more embodiments. The hydrothermal treatment can be performed in one or more embodiments by treating the chip-shaped lignocellulosic material with hot water or steam.

[Cooking method]
The present disclosure relates, in one aspect, to a method of alkaline or sulfurous acid cooking of a lignocellulosic material (the cooking method of the present disclosure). The cooking method of the present disclosure comprises, in one embodiment, steaming the lignocellulosic material in a chemical solution containing a radical scavenger. The cooking can be carried out in the same manner as the production method of the present disclosure.

[Cooking aid]
The present disclosure relates, in one aspect, to a cooking aid for producing chemical pulp, which contains a radical scavenger. Examples of the radical scavenger include the above.

The present disclosure may relate to one or more embodiments below;
[1] A method for producing chemical pulp by alkaline or sulfurous acid cooking of a lignocellulosic material.
A production method comprising cooking a lignocellulosic material in a chemical solution containing a radical scavenger.
[2] A method for producing chemical pulp, which comprises cooking a lignocellulosic material in an alkaline solution containing a radical scavenger.
[3] The production method according to [1] or [2], wherein the cooking method comprises heating the chemical solution containing the radical scavenger or the alkaline solution so that the temperature becomes 80 ° C. to 200 ° C.
[4] The production method according to [1] or [2], wherein the cooking temperature is 80 ° C to 200 ° C.
[5] The cooking comprises heating the lignocellulosic material in an alkaline solution containing a radical scavenger and sodium sulfide and / or sodium hydroxide at 80 ° C to 200 ° C [1] to [4]. ] The manufacturing method according to any one of.
[6] A method of alkaline or sulfurous acid cooking of a lignocellulosic material.
A cooking method comprising cooking the lignocellulosic material in a chemical solution containing a radical scavenger.
[7] The cooking method according to [6], wherein the chemical solution is an alkaline solution containing a radical scavenger.

Hereinafter, the present disclosure will be further described with reference to Examples and Comparative Examples. However, this disclosure is not construed as being limited to the following examples.

[Drug]
H-TEMPO (Hydroxy-TEMPO): 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl PDA: N, N'-di-sec-butyl-1,4-phenylenediamine DEHA: N , N-diethylhydroxylamine

[Example 1]
15 g (absolute dry weight) of Japanese red pine chips was packed in a 100 ml metal container. Then, the red pine chips were digested under the following conditions using the cooking solution to which the radical scavenger shown in Table 1 below was added.
Specifically, a liquid ratio of a kraft pulp cooking solution prepared from sodium hydroxide and sodium sulfide and having a sulfurization degree of 29% and an active alkali of 22% (ratio of the cooking liquid weight to the absolute dry weight of the chip: liquid / liquid / After the addition in chip) 4, a radical scavenger was added, and then the mixture was steamed at 170 ° C. for 2 hours. The selected unbleached pulp was measured for selection yield and kappa value according to the following method. The results are shown in Table 1 below. The amount of the radical scavenger added is% by weight of the radical scavenger with respect to the absolute dry weight of the chip.
Further, as a blank (BL), the same treatment and measurement were carried out without adding a radical scavenger. The results are shown in Table 1.
<Cooking conditions>
Equipment: Pressure-resistant container, nitrogen substitution Heating conditions: 170 ° C, 1.4 MPa, 2 hours White liquid (melting liquid): Alkali addition amount 22%, sulfide degree 29%, liquid ratio 4 (W / W)
Radical scavenger: H-TEMPO, PDA or DEHA 1% by weight

[Selection yield]
The obtained unbleached pulp was placed in a cloth bag, thoroughly washed with tap water, and then the undissolved fibers were removed by a flat screen (manufactured by Kumagai Riki Kogyo), and the pulp obtained by dehydration was used as selected pulp. ..
The absolute dry weight of the chips before cooking and the absolute dry weight of the selected pulp were measured, respectively, and the number obtained by dividing the latter by the former was expressed in% by weight to obtain the selected yield.

[Kappa price]
The kappa value of the selected pulp was measured by the method of JIS P 8211.

As shown in Table 1, in Examples 1-1 to 1-3 to which the radical scavenger was added, the copper value was low and the selection yield was high as compared with the blank. That is, both the selected yield and the kappa value could be improved with any of the radical scavengers.

[Example 2]
The test was carried out in the same manner as in Example 1 except that 35 g (absolute dry weight) of Japanese red pine chips was used and the cooking treatment was carried out in a 300 ml metal pressure-resistant container under the following cooking conditions. The results are shown in Table 2 below.
<Cooking conditions>
Equipment: Pressure-resistant container, no nitrogen substitution (atmosphere)
Heating conditions: 165 ° C, 1.6 MPa, 2 hours White liquid (distilled liquid): Alkaline addition amount 22%, sulfurization degree 29%, liquid ratio 4 (W / W)
Radical scavenger: H-TEMPO 0.1 or 0.5% by weight

As shown in Table 2, in Examples 2-1 and 2-2 to which H-TEMPO was added, the selection yield was improved as compared with the blank at any concentration.

[Example 3]
The test was carried out in the same manner as in Example 1 using 18 g (absolute dry weight) of Japanese red pine chips and 0.05% by weight or 0.01% by weight PDA as a radical scavenger. The results are shown in Table 3 below.
<Cooking conditions>
Equipment: Pressure-resistant container, nitrogen substitution Heating conditions: 170 ° C, 1.4 MPa, 2 hours White liquid (melting liquid): Alkali addition amount 22%, sulfide degree 29%, liquid ratio 4 (W / W)
Radical scavenger: PDA 0.01 or 0.05% by weight

As shown in Table 3, Examples 3-1 and 3-2 to which the PDA was added had a lower copper value as compared with the blank at any concentration.

[Example 4]
The test was carried out in the same manner as in Example 1 except that 40 g (absolute dry weight) of acacia chips was used and the cooking treatment was carried out in a 300 ml metal pressure-resistant container under the following cooking conditions. The results are shown in Table 4 below.
<Cooking conditions>
Equipment: Pressure-resistant container, no nitrogen substitution (atmosphere)
Heating conditions: 165 ° C, 1.6 MPa, 2 hours White liquor (distilled liquor): Alkaline addition amount 16%, sulfurization degree 29%, liquid ratio 4 (W / W)
Radical scavenger: H-TEMPO 0.1% by weight

As shown in Table 4, in Example 4 steamed in a chemical solution containing H-TEMPO, the kappa value of the obtained chemical pulp was lower and the selection yield was higher than that of the blank. That is, even when the lignocellulosic material is a broad-leaved tree (L material), the selection yield and the copper value are obtained by steaming in a chemical solution containing a radical scavenger, as in the case of a softwood (N material). I was able to improve both.

Claims (6)

A method for producing chemical pulp by alkaline or sulfurous acid cooking of a lignocellulosic material.
Includes cooking the lignocellulosic material in a chemical containing a radical scavenger.
The radical scavenger is 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (H-TEMPO), N, N'-di-sec-butyl-1,4-phenylenediamine (PDA). ), And at least one selected from the group consisting of N, N-diethylhydroxylamine (DEHA) . The lignocellulose material comprises cooking in an alkaline solution containing a radical scavenger, wherein the radical scavenger is 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (H-). TEMPO), N, N'-di-sec-butyl-1,4-phenylenediamine (PDA), and N, N-diethylhydroxylamine (DEHA), which is at least one selected from the group consisting of chemistry. How to make pulp. The production method according to claim 1 or 2, wherein the cooking method comprises heating the chemical solution containing the radical scavenger or the alkaline solution so that the temperature becomes 80 ° C. to 200 ° C. The cooking comprises heating the lignocellulosic material at 80 ° C. to 200 ° C. in an alkaline solution containing a radical scavenger and sodium sulfide and / or sodium hydroxide, according to any one of claims 1 to 3. The manufacturing method described in. A method of alkaline or sulfurous acid cooking of a lignocellulosic material.
It comprises evaporating the lignocellulosic material in a chemical solution containing a radical scavenger.
The radical scavenger is 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (H-TEMPO), N, N'-di-sec-butyl-1,4-phenylenediamine (PDA). ), And at least one selected from the group consisting of N, N-diethylhydroxylamine (DEHA), a cooking method. The cooking method according to claim 5, wherein the chemical solution is an alkaline solution containing a radical scavenger.

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