JP2000017593A - Production of polysulfide cooking liquor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing polysulfide cooking liquor, capable of improving oxidation selectivity to sodium sulfide according to a lime mud method and capable of increasing the productivity of polysulfide by perceiving a lime mud method in producing polysulfide cooking liquor in which it is possible to be carried out through simple, additional equipment alteration without steep change in a conventional process for recovering KP(kraft process) chemicals. SOLUTION: The method comprises graduating green liquor from a black liquor- recovering process in the cooking process of a kraft process or a polysulfide method into a solution containing sodium sulfide in a low concentration and a solution containing sodium sulfide in a high concentration, causticizing the solution containing sodium sulfide in a low concentration by adding lime formed in a calcining kiln and containing calcium oxide as a principal ingredient, adding the solution containing sodium sulfide in a high concentration to the causticized solution or separating lime mud formed and containing calcium carbonate as a principal ingredient, followed by dispersing lime mud into the solution containing sodium sulfide in a high concentration, and oxidizing sodium sulfide content with oxygen-containing gas in the presence of a transition metal compound to convert the sodium sulfide component into polysulfide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polysulfide cooking liquor, and more particularly to a method for producing pulp by digesting a lignocellulosic substance with a cooking liquor containing sodium sulfide and / or polysulfide. About the method.

[0002]

2. Description of the Related Art Kraft (hereinafter sometimes abbreviated as KP) cooking is a mixed chemical solution of caustic soda and sodium sulfide.
As the main method of producing chemical pulp by digesting wood-based lignocellulosic substances, it is used in most chemical pulp manufacturing plants worldwide. Sodium sulfide (Na-
Polysulfide (Na- (S-) x-Na:
x = 2 to 5), the polysulfide (hereinafter sometimes abbreviated as PS) digestion method has a higher pulp yield than the KP method at the same degree of digestion, and reduces the environmental burden of pulp bleaching wastewater. This method has attracted attention as a method for reducing the residual lignin of bleached pulp, and has been put to practical use in several factories in Japan.

[0003] As a method for producing a cooking liquor of the PS method, (1)
Method for producing PS by adding elemental sulfur to sodium sulfide
(Hagglundt, Svensk Papperstidn. 49 (9): 191 (1946)
), (2) Method of mixing KP white liquor with black liquor and oxidizing with air (Landmark et al., Norsk Skogind. 14 (5): 221 (1961)
), (3) A method of oxidizing sodium sulfide with a manganese oxide-based catalyst (Barker, Tappi 53 (6): 1087 (1970)), (4) A method of oxidizing air with a water-repellent activated carbon catalyst (Smith et al.,
U.S. Pat.No.4,024,229 (1977), Japanese Patent Publication No. 50-40395
), (5) Activated carbon pore diameter and its pore volume ratio, a method of air oxidation with a granular activated carbon catalyst having a limited average particle size and the like (Suzuki et al., JP-A-61-259754), (6) How to air oxidize green or white liquor with lime mud (Dor
ris, US Pat. No. 5,082,526 (1992)) and the like.

In the method (1) for producing PS, since the chemical balance of sodium / sulfur after the addition of sulfur is greatly changed, there are problems of odor, operability due to removal of sulfur in a separate process, corrosion, and complicated equipment. There is no practical use.

In the method (2), the amount of air for oxidation and the concentration of black liquor are not described, but the black liquor is converted into white liquor by 20 to 7 times.
By adding 0%, the PS concentration becomes 1.5 to 2.2 g / l
(S conversion). According to the report of the inventor of (5), Suzuki et al. (Paper Pulp Technology Times 32 (8): 1 (1989)), the effect of improving the pulp yield by PS digestion was 0.8% per timber (S conversion). It is stated that the pulp yield improvement does not clearly exceed 1% without the addition of PS. The PS additive rate 0.8% (S conversion), the general concentration 100 g / l (Na ₂ O equivalent) of active alkaline concentration of white liquor, the active alkali addition rate of 20%, white the amount of PS cooking liquor When the amount is the same as the liquid, the PS concentration is calculated to be 4.0 g / l (S conversion) or more. Therefore, PS concentration 1.5 ~
At 2.2 g / l (S conversion), the PS concentration, which improves the pulp yield, is about half of 4.0 g / l (S conversion), which is not enough for a clear pulp yield improvement effect. In addition, black liquor is a waste liquid obtained by digesting a natural lignocellulosic substance with alkali and contains a large amount of foaming components.Therefore, the method of oxidizing by bubbling with air is extremely vigorous in foaming and has a problem in operability. It has not been converted.

In the method (3), a white liquor is supplied to a reaction tower and oxidized with an oxygen-containing gas while circulating a catalyst slurry such as manganese dioxide, or the white liquor and an oxygen-containing gas are supplied to a catalyst packed tower. Although a method is presented, according to the examples, it takes 3 hours and a long time to generate PS, so that a large reactor is required, and a step of separating the catalyst and white liquor is required. There is a problem and it has not been put to practical use.

[0007] The method (4) is a method practically used in Japan as the Moxy method, but it is said that there are problems with the life and filtration performance of the activated carbon catalyst used. Although some improvements have been made over method (4), they have been put into practical use in Japan.However, both (4) and (5) have high equipment costs,
There is a problem that the activated carbon catalyst needs to be periodically washed with an acid to re-activate the catalyst.

The prior arts (1) to (5) include sodium /
There are problems such as a large change in the chemical balance of sulfur, a complicated and large apparatus, a long reaction time, and an insufficient PS concentration.

The inventors presume that the method (6) generates PS by some catalytic action of lime mud. However, air oxidation using lime mud alone does not provide sufficient selectivity of the oxidizing action of the catalyst. Instead, according to a report by Dorris, the inventor of (6) (Pulp Paper Can., 95 (10): T394 (1994)),
A method of adding MnO ₂ to lime mud to increase the selectivity of formation has been proposed.

The oxidation reaction in which PS is generated by oxidizing a chemical solution containing sodium sulfide with an oxygen-containing gas is represented by the following reaction formula (a).
However, excessive oxidation should be prevented because excessive oxidization produces sodium thiosulfate that is ineffective for digestion due to the reaction formulas (b) and (c). is important. 4Na ₂ S + O ₂ + 2H ₂ O = 2Na ₂ S ₂ + 4NaOH (a) 2Na ₂ S + 2O ₂ + H ₂ O = Na ₂ S ₂ O 3 + 2NaOH (b) 2Na ₂ S ₂ + 3O ₂ = 2Na ₂ S ₂ O3 (c) In the above equation (a), PS is Na ₂
Although it is shown as S ₂ , actually, Na ₂ Sx (x =
It is considered to be expressed by the chemical formula 2-5). The reaction formulas (b) and (c) show that if the oxidation reaction goes too far, sodium sulfide and PS in the reaction solution are oxidized to sodium thiosulfate.

As an index of the PS formation reaction, the oxidation rate, which is the ratio of the oxidized sodium sulfide after the reaction to the sodium sulfide before the reaction, is as follows: Oxidation rate (%) = amount of oxidized sodium sulfide / amount of sodium sulfide before the reaction × 100 PS generation rate, which is the ratio of the amount of PS generated after the reaction to the amount of sodium sulfide before the reaction, is: PS generation rate (%) = PS generation amount / amount of sodium sulfide before the reaction × 100 PS generation amount after the reaction As the PS selectivity, which is the ratio of oxidized sodium sulfide after the reaction, PS selectivity (%) = PS generation amount / oxidized sodium sulfide amount × 100 is used.

Since sodium thiosulfate is a substance that does not exhibit a pulping action, the production of sodium thiosulfate due to excessive oxidation causes the digestibility to deteriorate. Therefore, it is important to increase the PS generation rate while maintaining a high PS selectivity in the PS generation reaction using an oxygen-containing gas, in order to achieve a sufficient yield improving effect and pulping property in PS digestion. JP-A-8-218291 proposes that in the lime mud method (6), lime mud, a transition metal compound and a quinone compound coexist to increase the PS generation efficiency, but the PS selectivity is increased. Only 56%
It is not enough to reduce the deterioration of digestibility.

[0013]

Accordingly, in the preparation of a PS cooking chemical liquid by the lime mud method, a technique for further improving the PS selectivity in the PS generation reaction is required in order to reduce the deterioration of the digestibility. The present invention aims to solve these problems.

[0014]

In order to solve the above-mentioned problems, the present invention relates to (1) a method in which a green liquor obtained from a black liquor recovery step in a Kraft process or a polysulfide process is subjected to a sodium sulfide-containing solution and a high sodium sulfide-containing solution. The low sodium sulfide-containing solution is added to the causticizing solution obtained by adding a lime mainly composed of calcium oxide generated in a calcining kiln, and the high sulfuric acid-containing solution is added in the presence of a transition metal compound. A method for producing a polysulfide digester, comprising oxidizing sodium sulfide using an oxygen-containing gas to convert it into polysulfide.

(2) Kraft method or polysulfide method digestion step The green liquor in the black liquor recovery step is fractionated into a low sodium sulfide-containing liquid and a high sodium sulfide-containing liquid, and the low sodium sulfide-containing liquid is oxidized by a calcining kiln. Causticizing by adding calcium-based lime, clarifying the caustic liquor to produce a Kraft cooking digestion liquid, mixing the lime mud separated in the clarifying step with the high sodium sulfide-containing liquid, and transitioning A method for producing a polysulfide cooking chemical liquid, comprising oxidizing sodium sulfide using an oxygen-containing gas in the presence of a metal compound to convert it to polysulfide.

(3) The method for producing a polysulfide digester according to (1) or (2), wherein the low sodium sulfide-containing liquid has a molar ratio of sodium sulfide to sodium carbonate of 0.05 or less.

(4) Before the sodium sulfide is oxidized with the oxygen-containing gas, the sodium sulfide-containing liquid has a sodium sulfide concentration of 5 to 5.
(1) The method for producing a polysulfide digestion liquid according to (1) or (2), wherein the transition metal abundance with respect to the sodium sulfide-containing liquid is 0.001 to 1 g / 100 ml.

(5) The method according to (1) or (2), wherein the transition metal compound is a manganese oxide or sulfide.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The chemical solution containing sodium sulfide used in the present invention is mainly a green liquor or a white liquor produced in a KP chemical recovery process. The green liquor is obtained by dissolving a smelt residue of a recovery boiler in water, and its main components are sodium carbonate and sodium sulfide. White liquor is obtained by treating green liquor in a causticizing step and converting sodium carbonate in the green liquor to caustic soda.

The causticizing step is a step of causticizing sodium carbonate in the green liquor to convert it into caustic soda and converting the green liquor to white liquor. This causticizing step is carried out by adding calcium oxide to the green liquor, dispersing it as calcium hydroxide fine particles, and reacting sodium carbonate with this calcium hydroxide to convert it into caustic soda. Lime mud (fine-particle calcium carbonate) by-produced in the causticizing process is separated from white liquor by solid-liquid separation, calcined in the calcining process, and then circulated as calcium oxide to the causticizing process.

In the conventional lime mud method, as shown in FIG. 3, a part of the causticizing step of converting green liquor to white liquor is used as an oxidation reaction site. Therefore, the chemical solution containing sodium sulfide and the lime mud to be oxidized exist in the same system after the calcium oxide is added to the green liquor.

A feature of the present invention is that when oxidizing a chemical solution containing sodium sulfide with an oxygen-containing gas, a lime mud obtained by causticizing a low sodium sulfide-containing solution having a molar ratio of sodium carbonate to sodium sulfide of 0.05 or less is obtained. Is to use.
In the conventional lime mud method (molar ratio of sodium sulfide to sodium carbonate: 0.24), the PS selectivity was in the 60% range, but the use of the lime mud according to the present invention improved the PS selectivity by 10 points or more. It is improved to 70% level.

The method for producing a low sodium sulfide-containing liquid having a molar ratio of sodium sulfide to sodium carbonate of 0.05 or less is not particularly limited. Known methods include, for example,
There is a method of crystallizing and separating sodium carbonate from green liquor by utilizing the difference in solubility between sodium carbonate and sodium sulfide (1997 ASKK Symposium B1-2). In this method,
The high sodium sulfide-containing liquid obtained in the process has a higher sodium sulfide content than the original green liquor, and can generate a high concentration of PS after oxidation. Are suitable. For example, the chemical composition of the green liquor before fractionation was changed to sodium carbonate 105 g / L (Na ₂ O
Conversion), 25 g / L of sodium sulfide (in terms of Na ₂ O), 90% of sodium carbonate was fractionated into a low sodium sulfide-containing liquid, and the molar ratio of sodium sulfide to sodium carbonate in the low sodium sulfide-containing liquid was 0.05. Then, the molar ratio of sodium sulfide to sodium carbonate in the high sodium sulfide-containing liquid is 1.93.

An example of the flow will be described below with reference to FIG. First, the green liquor is fractionated into a low sodium sulfide-containing liquid GL and a high sodium sulfide-containing liquid GH by a known method. Calcium oxide is added to the low sodium sulfide-containing liquid GL, and a causticization reaction is performed to obtain a lime mud used in the present invention. The above sodium sulfide-containing solution is added to the caustic solution in which lime mud is dispersed.
GH is added, and sodium sulfide is oxidized using an oxygen-containing gas in the presence of a transition metal compound to obtain a polysulfide digestion liquor.

A flow as shown in FIG. 2 is also possible. The green liquor is fractionated into a low sulfur sulfide-containing liquid GL and a high sulfur sulfide-containing liquid GH. Calcium oxide is added to the low sodium sulfide-containing liquid GL and a causticization reaction is performed to obtain a lime mud used in the present invention. Clarification of caustic liquor, Kraft cooking chemicals W
(GL), the lime mud separated in the clarification step is mixed with the high sodium sulfide-containing liquid GH, and the sodium sulfide component is oxidized with an oxygen-containing gas in the presence of a transition metal compound to polysulfide. Obtain cooking liquor P (GH). MCC, EMC
C, Lo-Solids, in the digestion method in which the addition of the cooking liquor such as ITC, P (GH) as an additive chemical liquid at the beginning of the cooking,
The W (GL) is suitably used as an additive chemical in a countercurrent cooking zone. In a 2-vessel type digestion system having an infiltration tower, it is advantageous to use the P (GH) as an additive chemical in the infiltration tower in terms of the effect of PS digestion. Also, W (GL) can be used as an alkali in the oxygen delignification step.If it does not substantially contain sodium sulfide, the alkali extraction step in the KP bleaching step, the alkaline step such as the hydrogen peroxide step, etc. It is also possible to use as an alkali.

The reaction time in the present invention varies depending on the processing conditions such as the sodium sulfide concentration of the chemical solution containing sodium sulfide, the amount of lime mud, the addition of transition metal oxides, quinone compounds and the like, and the supply amount of oxygen-containing gas. It is.

The concentration of sodium sulfide in the chemical liquid containing sodium sulfide is 1 to 40 g / l (in terms of S), and the concentration of the cooking chemical used in ordinary KP cooking is 5 to 20 g / l (in terms of S). There is no need for special concentration and dilution. However, when the sodium sulfide concentration is low, it is necessary to relax other reaction conditions, and when the concentration is high, it is necessary to strengthen the treatment conditions.

The oxide or sulfide of manganese which is a transition metal compound used in the present invention has an excellent oxidation catalytic activity. These addition rates are 0.001 per chemical solution containing sodium sulfide.
~ 1 g / 100ml, more preferably 0.001 ~ 0.1g / 100
Although it is in the range of ml, when the amount is too small, the oxidation rate is low and the PS selectivity is low. If the amount is too large, the oxidation reaction proceeds excessively, and the generated PS is oxidized to lower the PS selectivity. Manganese oxides include MnO, MnO ₂ , Mn ₂ O ₃ ,
Mn ₃ O ₄ and Mn ₂ O ₇ can be mentioned, and M is particularly preferable.
nO ₂ . Further, a sulfide generated by adding a water-soluble salt of manganese to a chemical solution containing sodium sulfide can also be used. Further, for the purpose of improving the PS selectivity, another transition metal compound such as nickel can be mixed and used with the manganese compound.

An oxygen-containing gas is used for the oxidation of the chemical solution containing sodium sulfide used in the present invention. As the oxygen-containing gas, air is sufficient, but it is also possible to use pure oxygen or high-concentration oxygen such as PSA (Pressure Swing Adsorption) oxygen having a lower oxygen concentration than pure oxygen. The use of high-concentration oxygen increases the oxygen partial pressure in the chemical solution and increases the solubility of oxygen in the chemical solution, thereby improving the oxidation efficiency. It is necessary to select conditions that do not oxidize. However, since the use of high-concentration oxygen requires a small volume of gas to be supplied, it is possible to oxidize with pressurized pure oxygen or pressurized high-concentration oxygen in a pipeline reactor. It is also effective to use a low-concentration oxygen-containing gas having a lower oxygen concentration than air, for example, air diluted with a purge gas from a PSA oxygen production process, for the purpose of controlling an excessive oxidation reaction.

When air is used as the oxygen-containing gas,
The supply amount of air per sodium sulfide-containing chemical solution varies depending on processing conditions such as sodium sulfide concentration and oxidation time of the sodium sulfide-containing chemical solution, but a range of 1 to 500 Nl / l is appropriate, and pure oxygen gas or high-concentration oxygen gas is used. 0.1 to 50N when using
An l / l range is appropriate.

The present inventors have studied the differences between lime mud mainly composed of calcium carbonate produced in a normal causticizing step and lime mud used in the present invention. As a result, differences in particle diameter, specific surface area and X-ray diffraction pattern were found. Was not found. The difference in catalytic performance in the oxidation reaction is estimated to be the difference in the state of the transition metal compound used as a catalyst in the lime mud particles.

[0032]

The present invention will be described below with reference to examples and comparative examples, but these examples do not limit the present invention in any way. In this example, the following evaluation items were used for evaluation. <Evaluation items> PS concentration: PS concentration with respect to the amount of the sodium sulfide-containing chemical solution Oxidation rate (%) = amount of oxidized sodium sulfide / amount of sodium sulfide before reaction x 100 Amount of PS generated after reaction and sodium sulfide before reaction PS selectivity (%) = PS generation rate / oxidized sodium sulfide quantity x 100 All are calculated in S conversion

Example 1 A chemical solution (252 g of Na ₂ CO ₃ (in terms of Na ₂ O)) of an aqueous sodium carbonate solution containing no sodium sulfide heated to 90 ° C. was placed in a stainless steel container heated and kept warm by a rubber heater. 2.0 L was added, and further, 259 g of lime mud which had been dried in advance was sufficiently mixed with 1.2 g of MnO ₂ (equivalent to 0.05 g / 100 ml per sodium sulfide-containing chemical solution immediately before oxidation), and then baked at 1200 ° C. for 2 hours. Lime was added, the temperature was maintained at 95 ° C., and a 4 cm diameter 4-blade stirrer was stirred at 500 RPM for 1 hour to carry out a causticization reaction. Next, Na ₂ S (60 g (Na ₂ O equivalent)) and hot water were added to adjust the volume of the chemical solution to 2.4 L, and then air was supplied from the bottom of the container at a flow rate of 1.0 L / min (standard state equivalent). Then, four blades having a diameter of 4 cm were stirred at 500 RPM to perform an oxidation reaction until the G / L ratio reached 12.5.

Example 2 and Comparative Examples 1 and 2 As shown in Table 1, PS was produced in the same manner as in Example 1, except that the molar ratio of sodium sulfide to sodium carbonate during causticization was changed. In any case, the amount of sodium carbonate before causticization is
252 g (in terms of Na ₂ O) The volume of the chemical solution immediately before oxidation was 2.4 L, and the amount of sodium sulfide was adjusted to be 60 g (in terms of Na ₂ O) in combination with the amount of sodium sulfide present in the chemical solution before causticization.

Example 3 A chemical solution (252 g of Na ₂ CO ₃ (in terms of Na ₂ O), which is an aqueous sodium carbonate solution containing no sodium sulfide and heated to 90 ° C., was placed in a stainless steel container heated and kept warm by a rubber heater. 2.0 L was added, and further, 259 g of lime mud which had been dried in advance was sufficiently mixed with 1.2 g of MnO ₂ (equivalent to 0.05 g / 100 ml per sodium sulfide-containing chemical solution immediately before oxidation), and then baked at 1200 ° C. for 2 hours. Lime was added, the temperature was maintained at 95 ° C., and a 4 cm diameter 4-blade stirrer was stirred at 500 RPM for 1 hour to carry out a causticization reaction. Next, the produced lime mud was separated by filtration with a 5 type C quantitative filter paper specified in JIS P 3801, and the solid content concentration was 75%.
Concentrated. The lime mud obtained here was dispersed in an aqueous solution of Na ₂ S (60 g (in terms of Na ₂ O)), heated to 90 ° C. to make the volume of the chemical solution 2.4 L, and then transferred to the stainless steel container. Air was supplied from the bottom of the vessel at a flow rate of 1.0 L / min (converted to the standard state), and four blades having a diameter of 4 cm were stirred at 500 RPM to perform an oxidation reaction until the G / L ratio reached 12.5. .

Example 4 and Comparative Examples 3 and 4 As shown in Table 2, PS was produced in the same manner as in Example 3 except that the molar ratio of sodium sulfide to sodium carbonate during the causticization was changed. The amount of sodium carbonate during causticization was 25
It is 2 g (in terms of Na ₂ O). The oxidation rate and PS selectivity shown in Table 2 take into account the amount of sodium sulfide in the chemical solution accompanying the lime mud after filtration.

Tables 1 and 2 show the PS concentration of the chemical solution immediately after the end of the oxidation reaction and other evaluations.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

The advantages of the present invention as compared with the above-mentioned known prior art are as follows. (1) Lime mud and a single transition metal oxide and / or transition metal sulfide are allowed to coexist in a sodium sulfide-containing chemical solution,
In the method of oxidizing with an oxygen-containing gas to obtain a polysulfide digestion chemical solution, by using a lime mud obtained by causticizing a chemical solution having a molar ratio of sodium sulfide to sodium carbonate of 0.05 or less, PS selectivity is improved, It is possible to prepare a PS cooking chemical liquid with less deterioration in digestibility. (2) Manganese and nickel used here are not expensive noble metal oxidation catalysts. In addition, their addition rates are as small as 0.001 to 0.1 g / 100 ml per sodium sulfide-containing chemical solution, and they are reused by circulating the cooking chemical recovery process together with lime mud. Since it is a catalyst in principle, it is economical because it is not consumed in the reaction and only a small amount of loss needs to be replenished.

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[Procedure amendment]

[Submission date] September 1, 1998 (1998.9.1)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Added

[Correction contents]

[Brief description of the drawings]

FIG. 1 is a flowchart showing an embodiment of the present invention.

FIG. 2 is a flowchart showing another embodiment of the present invention.

FIG. 3 is a flowchart of a conventional method for producing a polysulfide cooking chemical liquid.

Claims (8)

[Claims] 1. A green liquor obtained from a black liquor recovery step of a kraft method or a polysulfide method digestion step is fractionated into a low sodium sulfide-containing liquid and a high sodium sulfide-containing liquid, and the low sodium sulfide-containing liquid is subjected to a firing kiln. The high sodium sulfide-containing solution is added to the caustic solution causticized by adding the generated calcium oxide-based lime, and the sodium sulfide component is oxidized using an oxygen-containing gas in the presence of a transition metal compound to form polysulfide. A method for producing a polysulfide cooking chemical liquid, comprising: 2. The method according to claim 1, wherein the low sodium sulfide-containing liquid has a molar ratio of sodium sulfide to sodium carbonate of 0.05 or less. 3. The sodium sulfide-containing liquid before the sodium sulfide is oxidized using an oxygen-containing gas has a sodium sulfide concentration of 5 to 20 g / g.
The method for producing a polysulfide cooking chemical solution according to claim 1, wherein the transition metal abundance to the sodium sulfide-containing liquid is 0.001 to 1 g / 100 ml. 4. The method according to claim 1, wherein the transition metal compound is an oxide or sulfide of manganese. 5. A green liquor obtained from a black liquor recovery step of a kraft method or a polysulfide method digestion step is fractionated into a low sodium sulfide-containing liquid and a high sodium sulfide-containing liquid, and the low sodium sulfide-containing liquid is produced in a calcining kiln. Causticized by adding lime mainly composed of calcium oxide, clarifying the caustic solution to produce a Kraft cooking digestion liquid, and mixing the lime mud separated in the clarifying step with the high sodium sulfide-containing liquid. A method for producing a polysulfide cooking chemical liquid, comprising oxidizing sodium sulfide using an oxygen-containing gas in the presence of a transition metal compound to convert it to polysulfide. 6. The method for producing a polysulfide cooking chemical liquid according to claim 5, wherein the low sodium sulfide-containing liquid has a molar ratio of sodium sulfide to sodium carbonate of 0.05 or less. 7. A sodium sulfide-containing liquid before oxidizing sodium sulfide with an oxygen-containing gas has a sodium sulfide concentration of 5 to 20 g / g.
The method for producing a polysulfide cooking chemical solution according to claim 5, wherein the transition metal abundance with respect to the sodium sulfide-containing liquid is 0.001 to 1 g / 100 ml. 8. The method according to claim 5, wherein the transition metal compound is a manganese oxide or sulfide.