JPH08218291A - Production of polysulfide digestion solution - Google Patents

Abstract

PURPOSE: To efficiently prepare polysulfide digestion solution by oxidative treatment of a chemical solution containing sodium sulfide in the presence of lime mud, a transition metal compound and a quinone compound. CONSTITUTION: The green liquor obtained in the chemical recovery process for the kraft pulp is combined with one or more kinds of foam regulator selected from an anionic or cationic surfactant and black liquor and the resulting sodium sulfide-containing chemical solution is oxidatively treated by feeding an oxygen-containing gas such as heated and moistened air into the solution in the presence of lime mud, 0.01-10wt.% of a manganese oxide and/or its salt on the absolutely dry basis of the lime mud and 0.1-20wt.% of a quinone such as dihydroxyanthracene to give this polysulfide digestion solution efficiently.

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 cooking liquor for producing a pulp by digesting a lignocellulosic material with a cooking liquor containing polysulfide.

[0002]

Background Art Kraft pulp (hereinafter abbreviated as KP) cooking method is a mixed chemical solution of caustic soda and sodium sulfide, which is a mainstream method for producing chemical pulp by cooking a lignocellulosic material mainly composed of wood. It is used in the majority of the chemical pulp manufacturing plants. Sodium sulfide (Na ₂ S)
Changes to the polysulfide of _{(Na 2 S X: x =} 2~
The polysulfide (hereinafter abbreviated as PS) cooking method using 5) has a higher pulp yield than the KP method at the same degree of cooking, and reduces the load on the environment of pulp bleaching wastewater.
It has attracted attention as a method for reducing the residual lignin of unbleached pulp. The PS method has been evaluated for its ability to reduce residual lignin without lowering the pulp yield as compared with the current KP method, and has been put to practical use in several factories in Japan.

[0003] As a method for producing a PS digestion liquid,
(1) A method of adding PS to sodium sulfide to produce PS [Hagglundt, Svensk Papperstidn. 49 (9): 191 (194
6)], (2) Method of mixing black liquor with KP white liquor and oxidizing with air [Landmark et al., Norsk Skogind. 14 (5): 221 (196)
1)], (3) Method of oxidizing sodium sulfide with a manganese oxide-based catalyst [Barker, Tappi 53 (6): 1087 (1970)], (4) Method of air oxidation with a water-repellent activated carbon catalyst [Smith et al. , U.
S. Patent 4,024,229 (1977)], (5) A method of air-oxidizing with a granular activated carbon catalyst in which the pore diameter of activated carbon, the pore volume ratio, and the average particle diameter are limited [Suzuki et al., JP 61-25975
4], (6) A method of air-oxidizing green liquor or white liquor with lime mud [Dorris, US Patent 5,082,526 (1992)] and the like have been proposed.

In the PS production method (1), the chemical balance of sulfur is greatly changed, so a method for removing sulfur is required in a separate step, and there is a problem in operability such as corrosion, and the apparatus is complicated. However, it has not been put to practical use due to problems such as high sulphuration degree and severe odor.

The method (2) does not describe the amount of air for oxidation and the concentration of black liquor, but black liquor is converted to white liquor by 20 to 70%.
PS concentration is 1.5-2.2 g / l as
S has been obtained. By the way, according to the report of the inventors [5] [Paper and Pulp Technology Times 32 (8): 1 (1989)], the effect of improving the pulp yield by PS cooking is 0.8% as per wood.
It was confirmed that the PS yield was improved by more than 1% at the PS addition rate of S, and the effect of PS was confirmed. Assuming that the active alkali concentration of white liquor is 100g / liter as Na ₂ O and the active alkali addition rate is 18%, the PS concentration is 4.4
More than g / liter is required. At the PS concentration of 1.5 to 2.2 g / liter as S mentioned above, PS required for improving pulp yield is
The concentration is less than half of 4.4 g / l as S, which is low in concentration.Black liquor is a waste liquor obtained by alkaline digestion of natural lignocellulosic substances, and it contains a large amount of foaming components, so it is possible to remove it by air. The method of bubbling and oxidizing has not been put into practical use because foaming is extremely violent and there is a problem in operability.

The method (3) is a method of supplying white liquor to a reaction tower and oxidizing it with an oxygen-containing gas while circulating a catalyst slurry such as manganese dioxide, or supplying white liquor and an oxygen-containing gas to a catalyst packed tower. A method is presented. However, according to the examples, since PS production requires a long time of 3 hours, there is a problem that a large reactor is required and a step of separating the catalyst and the white liquor is required. It has not been converted.

The method (4) is a method that has been put to practical use in Japan as the Moxy method, but it is said that there are problems in the life and filtration performance of the activated carbon catalyst used, and the method (5) is Although it has been put to practical use in Japan with some improvements over the method of (4), both (4) and (5) have high equipment costs,
There is a problem that it is necessary to periodically wash the activated carbon catalyst with an acid to reactivate the catalyst.

The inventor estimates that the method (6) produces PS by some catalytic action of lime mud, but the air oxidation of lime mud alone has sufficient selectivity for the catalytic action of lime mud. But not the inventor's report of (6) [Pulp
Paper Can., 95 (10): T394 (1994)] proposes a method of adding MnO ₂ to lime mud in order to increase the selectivity of PS formation.

Summarizing the above conventional techniques, the chemical balance of sulfur is disturbed, the apparatus is complicated, the reaction takes a long time, large equipment is required, and the PS concentration is insufficient. However, there is a problem that the selectivity of PS generation is poor.

[0010]

DISCLOSURE OF THE INVENTION The present inventors pay attention to the lime mud method, which has the possibility of being put to practical use with a simple additional equipment change, without making a large change to the equipment of the current chemical recovery process. And worked on solving the problem. When lime mud was added to green liquor or white liquor and air-oxidized, it was not always possible to obtain sufficient PS to improve the pulp yield depending on the experimental conditions. This is considered to be due to changes in the particle size, shape, specific surface area, impurities, etc. of the lime mud. Further, in this method, the PS production efficiency was increased by using the transition metal compound as a catalyst, but it was still at a practically insufficient level. Therefore, in order to put the lime mud method into practical use, there is a need for a technique for dramatically increasing the PS concentration and for producing PS in a reproducible and more stable form, and the present invention addresses this problem. And

[0011]

In order to solve the above problems, the present invention adopts the following configurations. (1) A method for producing a polysulfide cooking chemical which comprises oxidizing a sodium sulfide-containing chemical with an oxygen-containing gas in the presence of a lime mud, a transition metal compound, and a quinone compound. (2) The above (1), wherein the proportion of the quinone compound is 0.1 to 20% by weight based on the absolutely dried lime mud.
The method for producing a polysulfide cooking liquor according to item 1. (3) The transition metal compound is an oxide of manganese and / or a salt thereof, and the addition rate to the absolutely dried lime mud is
The method for producing a polysulfide cooking liquor according to (1) or (2) above, wherein the content is 0.01 to 10% by weight. (4) The method for producing a polysulfide cooking chemical solution according to any one of (1) to (3), wherein the sodium sulfide-containing chemical solution contains a bubble control agent. (5) The bubble control agent is one or more selected from anionic surfactants, cationic surfactants, and black liquor (cooking waste liquor generated in the pulp cooking step). A method for producing a polysulfide cooking chemical.

The sodium sulfide-containing chemical liquid used in the present invention is
Various aqueous solutions containing sodium sulfide, such as green liquor, white liquor, and weak liquor produced in the KP chemical recovery process, are targeted. In any case, similar effects can be obtained by selecting the optimum conditions. .

Since the temperature of the green liquor and white liquor handled in the KP chemical recovery step is generally 70 to 110 ° C., heating and cooling are not required in the present invention. The reaction time in the present invention is the concentration of sodium sulfide in the sodium sulfide-containing chemical solution,
Depending on the processing conditions such as the addition amount of lime mud, transition metal compound, quinone compound, etc., air supply amount, etc.
And the residence time of the green liquor in the causticizer is typically 60
It is suitable to apply this residence time to the reaction time as it is ~ 180 minutes.

The lime mud referred to in the present invention is a calcium compound produced in the cooking chemical recovery step. Most typically, it is calcium sludge as a residue obtained by separating white liquor after causticizing green liquor in the chemical recovery step of the KP method, or one obtained by firing it. The amount of lime mud used is the weight of absolutely dry lime mud with respect to the chemical solution containing sodium sulfide.
It is in the range of 50 to 500 g / liter. Generally, the concentration of lime mud in the causticizing tank in the craft method chemical recovery process is 100 to 125.
Since it is g / liter, the operating conditions in the ordinary KP cooking chemical recovery process are sufficient. The particle size of lime mud is 1 to 15 μm, which is used in the usual KP cooking chemical recovery process.
Those having a specific surface area of 1 to 10 m ² / g are sufficient. However, the smaller the particle size and the larger the specific surface area, the greater the catalytic action of lime mud and the faster the reaction, but the more likely it is to cause an excessive oxidation reaction, and the worse the sedimentation of lime mud. There is a problem.

As will be described later, considering the simplification of the device, it is considered more rational to target the green liquor. The lime mud used in this case is calcium oxide calcined at 800 ° C. or higher. It is suitable to use lime mud mainly composed of, and when targeting white liquor, it is suitable to use unbaked lime mud that has been causticized.

Oxides or sulfides can be used as the transition metal compound used in the present invention. The metal is a single substance or a mixture selected from manganese, nickel, cobalt, chromium, copper and iron. Among them, an oxide of manganese is preferable because it has the most excellent oxidation catalytic ability. A typical example of manganese oxide is manganese dioxide, but other manganese compounds include Ca.
MnO ₃ , CaMn ₂ O ₅ , CaMn ₃ O ₇ and Ca ₂ Mn
It is also possible to use a calcium salt such as O ₄ . Addition rate of transition metal compound is 0.01-10 per dry lime mud
% By weight, preferably 0.01 to 1% by weight. If it is too small, PS is not sufficiently produced, and if it is too large, the oxidation reaction proceeds excessively, and PS is oxidized and becomes small. 0.5% by weight
The degree is the most suitable.

An oxygen-containing gas is used for oxidizing the sodium sulfide-containing chemical liquid used in the present invention. Air is sufficient as the oxygen-containing gas, but pure oxygen can also be used, and PSA oxygen having an oxygen concentration lower than that of pure oxygen can also be used. If high-concentration oxygen such as pure oxygen or PSA oxygen is used, it is possible to reduce the amount used as compared with low-concentration oxygen such as air. By using a higher concentration of oxygen, the oxygen partial pressure in the chemical solution increases and the solubility of oxygen in the chemical solution increases, so that the oxidation efficiency increases and the PS concentration increases. It is necessary to select a condition that prevents the PS from being further oxidized. However, it is also possible to oxidize with pressurized oxygen or pressurized PSA oxygen in a pipeline reactor, because the use of high concentration oxygen requires a small volume of gas to be supplied. In order to control an excessive oxidation reaction, 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 of PSA oxygen.

When air is used as the oxygen-containing gas, the supply amount of air varies depending on the treatment conditions such as the concentration of sodium sulfide in the sodium sulfide-containing chemical solution and the treatment time, but the G / L ratio is in the range of 1 to 500. Suitable, pure oxygen gas or P
When using SA oxygen, the range of 0.1 to 50 is suitable. Here, the G / L ratio is the ratio of the standard state conversion volume (liter) of gas to the volume (liter) of the sodium sulfide-containing chemical liquid.

The oxidation reaction in which PS is produced by oxidizing a sodium sulfide-containing chemical solution with an oxygen-containing gas is as shown in the following reaction formula (a), but if the oxidation is excessive, the reactions (b) and (c) will occur. Since the formula produces sodium thiosulfate which is ineffective in cooking, excessive oxidation should be prevented and proper control of oxidation 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 O ₃ (c) In the above formula (a), PS is N because it simplifies the reaction formula.
Although shown as a ₂ S ₂ , in reality, as described above, Na ₂ S _x (
x = 2 to 5) It is thought that it should be represented by the chemical formula. The reaction formulas of (b) and (c) show that when the oxidation reaction goes too far, sodium sulfide and PS in the reaction solution are oxidized to sodium thiosulfate.

Since sodium thiosulfate is a substance which does not show a cooking action, it is necessary to prevent it from being produced as much as possible in the production of PS cooking liquor. In other words, in the PS production reaction using the oxygen-containing gas, it is necessary that sodium sulfide be produced in PS with the highest possible concentration and sodium thiosulfate be kept in the lowest possible concentration. As these indexes, the PS production rate which is the ratio of the amount of PS produced after the reaction and the sodium sulfide before the reaction, and the PS selectivity which is the ratio of the production amount of the PS after the reaction and the oxidized sodium sulfide after the reaction Is used, the larger these values are, the more PS production rate is 30% or more.
The selectivity is preferably 40% or more.

The quinone compound used in the present invention is a cyclic keto compound, and examples thereof include benzoquinone, naphthoquinone, anthraquinone, anthrone, phenanthrenequinone and derivatives thereof. Derivatives include these hydrides as well as oxy, amino, alkyl and alkoxy derivatives. Among the above, anthraquinone and its derivatives are particularly preferable, and specifically, anthraquinone, 2-methylanthraquinone, 2-
Ethylanthraquinone, 2,6-dimethylanthraquinone, 2,7-dimethylanthraquinone, 2-aminoanthraquinone, 1-methoxyanthraquinone, anthrahydroquinone, 9,10-dihydroxyanthracene,
1,4-dihydro-9,10-dihydroxyanthracene and the like can be mentioned.

In the present invention, the quinone compound may be used in an amount of 0.01% by weight to 1% by weight based on absolute dry lime mud. However, even if the quinone compound is in a large amount, it acts as a cooking aid in the PS method digestion as it is, so there is no economical waste.

In the present invention, the liquid and the gas are reacted on the surface of the solid, so that it is desirable that the oxygen-containing gas maintain bubbles of an appropriate size during the reaction. In addition, it is also desired to quickly defoam the liquid after handling it in terms of handling the liquid. It is preferable to use a cell regulator which adjusts the cells to easily undergo such a "gas / liquid" reaction, if necessary. Examples of the cell regulator include anionic surfactants, nonionic surfactants, and black. A liquid (a cooking waste liquid generated from a pulp cooking process) or the like can be used. If the control of bubbles is good, the amount of transition metal compound or quinone compound used can be reduced.

As the anionic surfactant, carboxylic acid type, sulfuric acid ester type, sulfonic acid type and phosphoric acid ester type can be used. Specific examples thereof include Na salts of higher fatty acids, Na salts of sulfuric acid esters of higher alcohols, Na alkylbenzene sulfonates, and phosphoric acid ester salts of higher alcohol ethylene oxide adducts. The surfactant is added in the range of about 0.0001 to 0.1% by weight with respect to the sodium sulfide-containing chemical liquid.

As the nonionic type, polyethylene glycol type or polyhydric alcohol type can be used. Specifically, as the polyethylene glycol type, higher alcohol ethylene oxide adduct, alkylphenol ethylene oxide adduct, fatty acid ethylene oxide adduct, polyhydric alcohol fatty acid ester ethylene oxide adduct, higher alkylamine ethylene oxide adduct, fatty acid amide Examples thereof include ethylene oxide addition products, ethylene oxide addition products of fats and oils, and polypropylene glycol ethylene oxide addition products. Examples of the polyhydric alcohol type include glycerol fatty acid ester, pentaerythritol fatty acid ester, sorbitol and sorbitan fatty acid ester, sucrose fatty acid ester, polyhydric alcohol alkyl ether, and alkanolamine fatty acid amide.

Black liquor (a cooking waste liquor produced in the cooking step) also has an appropriate surface-active effect, and black liquor can be used as a substitute for the surfactant. The solid content of black liquor is in the range of 0.01 to 2.5% by weight, preferably 0.01 to 1% by weight, based on the absolute dry lime mud.

[0027]

[Function] The inventors of the present invention analyzed and examined the catalytic action of lime mud on PS, including the results of subsequent experiments. As a result, pure lime mud itself does not have a direct catalytic action on PS. , And made an inference that it is a medium that provides a place of reaction. That is, the sodium sulfide aqueous solution, the oxygen gas, and the oxidation catalyst for PS are temporarily trapped at the solid interface of the lime mud, the oxidation reaction of sodium sulfide progresses to PS, and the desorption process is repeated. I presume.

When manganese dioxide is used as a catalyst, it may react with lime under strong alkali in the causticizing step to form manganites, and CaO may act as a catalyst carrier. Conceivable. In addition, the quinone compound is reduced by reducing sodium sulfide to a hydroquinone type, the sodium sulfide is oxidized to produce PS, and the hydroquinone type quinone compound is oxidized by an oxygen-containing gas to become a quinone type and circulates in the system. Therefore, it is presumed that it acts like a redox catalyst.

[0029]

EXAMPLES In order to explain the present invention in more detail, examples will be described below. However, these examples do not limit the present invention in any way. In the embodiment of the present invention,
The following evaluation items were used for evaluation. <Evaluation items> PS concentration: P generated relative to the amount of chemical solution containing sodium sulfide
S concentration (g / liter as S) PS production rate: described in "Equation 1" below PS selectivity: described in "Equation 2" below

[0030]

[Equation 1]

[Equation 2]

Example 1 Green liquor (Na ₂ CO ₃ 90 g / liter as Na ₂ O, Na ₂ S 25 g / liter) was prepared by placing a 1-liter plastic container on a 90 ° C. hot bath and heating it to 90 ° C. in advance. Liter as Na
₂ O) 600 cc was added, and the following A and B were also added, and 0.5 liters of air preheated and humidified to 90 ° C from the bottom of the container was added.
It was supplied at a flow rate of / min (converted to standard state), and an oxidation reaction was performed for 1 hour. (The total supply of gas corresponds to 50 in G / L ratio). A: 60 g of previously dried lime mud (corresponding to 100 g / liter of a chemical solution containing sodium sulfide) was thoroughly mixed with 0.3 g of MnO ₂ (corresponding to 0.5% by weight based on absolute lime mud), and then 2 at 1000 ° C. Time-calcined lime mud B: 1,4-dihydro-9,10-as a quinone compound
Dihydroxyanthracene 0.018g (equal to 0.03% by weight per absolute dry lime mud) 4cm in diameter during addition of each chemical and air supply
The four-bladed stirrer at 1000 rpm is used to stir,
The temperature was maintained at 90 ° C. Table 1 shows the PS concentration of the chemical solution after the reaction and other evaluations.

<Example 2> to <Example 6> and <Comparative Example 1> to <Comparative Example 2> P was the same as Example 1 except that the conditions shown in Table 1 were changed.
S was produced.

[0033]

[Table 1]

[0034]

As can be seen from the examples, it is understood that the present invention is an extremely advantageous method because it is superior to the prior art in the following points. Stable high concentration PS can be obtained regardless of the conditions of lime mud. The lime mud used is a material produced from the chemical process of ordinary KP digestion and does not require major equipment changes. Quinone coexisting with lime mud functions as a cooking catalyst in polysulfide cooking. By using a quinone compound and a transition metal compound in combination with lime mud, a synergistic effect that cannot be achieved by individual catalysts can be obtained. Since the present invention can use the existing white liquor clarifier, which is a conventional lime mud separation process, new equipment for catalyst separation is not required. Since the causticization of green liquor and the oxidation reaction of sodium sulfide to PS can be performed simultaneously, it is not necessary to set the PS production time in particular.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kaoru Yamagami 2-3-2 Higashishinozaki, Edogawa-ku, Tokyo Honshu Paper Co., Ltd.

Claims (5)

[Claims] 1. A method for producing a polysulfide cooking chemical which comprises oxidizing a sodium sulfide-containing chemical with an oxygen-containing gas in the presence of a lime mud, a transition metal compound and a quinone compound. 2. The method for producing a polysulfide cooking liquor according to claim 1, wherein the proportion of the quinone compound is 0.1 to 20% by weight based on the absolutely dried lime mud. 3. The transition metal compound is an oxide of manganese and / or
Or a salt thereof, and the addition rate to the absolutely dried lime mud is 0.01 to 10% by weight, the method for producing a polysulfide cooking liquor according to claim 1 or 2. 4. The method for producing a polysulfide cooking chemical solution according to claim 1, wherein the chemical solution containing sodium sulfide contains a bubble control agent. 5. The foam control agent is one or more selected from anionic surfactants, cationic surfactants, and black liquor (a cooking waste liquor generated from a pulp cooking process). A method for producing the described polysulfide cooking chemical liquid.