JPH11286883A - Production of kraft pulp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for raising the efficiency in producing a pulp such as an improvement in pulp yield. SOLUTION: This method for cooking comprises a previous permeation step for carrying out the permeation of a lignocellulosic substance with an oxidized green liquor containing a polysulfide sulfur prepared by oxidizing a green liquor and a cooking step for further adding a cooking liquor comprising a white liquor or an oxidized white liquor and containing the polysulfide sulfur to the resultant product and cooking the product. At least one kind of compound selected from an anthraquinone-based compound, an anthrahydroquinone-based compound or a precursor thereof is added to the oxidized green liquor used in the previous permeation step.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing kraft pulp including a step of cooking a lignocellulosic material. More particularly, the present invention relates to a method for producing kraft pulp comprising a pre-penetration step and a cooking step in a method for cooking lignocellulosic substances.

[0002]

2. Description of the Related Art Among the methods for producing pulp for papermaking, methods for producing pulp by the kraft method have been established in which a calorific value and an alkali content can be recovered from cooking effluent. In addition, it has become a typical method for producing chemical pulp in major paper pulp countries around the world because of the advantage of not selecting a specific tree species as a raw material.

[0003] In recent years, various improved methods of the Kraft method have been proposed with the aim of improving pulp crystallinity and pulp yield.
One example is a cooking method in which a cooking aid such as a quinone compound is added. It is said that the amount of alkali added can be reduced without reducing the cooking degree, so that damage to the pulp by the alkali can be reduced and the pulp yield can be improved, and it is currently used in many factories. In addition, improvements have been made in cooking methods such as the MCC method for continuous cooking, the super-batch method for batch cooking, and the one-stage polysulfide cooking method with improved cooking liquor.
However, all of these methods increase pulp yield and improve pulp quality, but they cannot reduce the operating load to a large hat, and require large-scale remodeling and additional installation of equipment. There are problems such as becoming.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing kraft pulp for improving the efficiency of pulp production such as improving the pulp yield.

[0005]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above problems, and as a result, have completed the present invention. That is, according to the present invention, a pre-penetration step of permeating a lignocellulosic substance using an oxidized green liquor containing polysulfide sulfur obtained by oxidizing a green liquor, and further adding a white liquor or an oxidized product to the obtained product A cooking method comprising a cooking step in which a cooking liquor containing polysulfide sulfur consisting of white liquor is added and cooked, wherein the oxidized green liquor used in the preliminary permeation step contains an anthraquinone compound, an anthrahydroquinone compound, or a precursor thereof. And a method for producing kraft pulp characterized by adding at least one compound selected from the group consisting of:

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The lignocellulosic material used as a pulp raw material in the present invention includes not only various types of wood but also non-wood such as bagasse, rice straw, kenaf and hemp.

[0007] The concentration of polysulfide sulfur in the oxidized green liquor used in the pre-penetration step is 2 to 20 g / l, preferably 4 to 20 g / l.
１５15 g / l, and the sodium carbonate concentration is 30-1
00 g / l, preferably 40 to 90 g / l. Sodium hydroxide and sodium sulfide may be contained in the oxidized green liquor used in the pre-penetration step, but the sodium hydroxide concentration is 70 g / l or less, preferably 50 g / l.
1 or less. The sodium sulfide concentration is 50 g / l
Or less, preferably 2 to 35 g / l or less.

The quinone compound to be added is anthraquinone, 1,4,4a, 9a-tetrahydro-9,10
One or more selected from anthraquinone, 1,4-dihydro-9,10-dihydroxyanthracene and salts thereof. The amount of the quinone-based compound to be added is 0.02% by weight or more, preferably 0.03% by weight or more per absolutely dry chip. The upper limit is usually 0.1% by weight.

In the pre-permeation step, the permeation temperature is 1
It is 00-160 ° C, preferably 120-140 ° C.
The permeation retention time depends on the type of lignocellulosic substance and the permeation temperature, but is usually 10 to 50 minutes, preferably 20 to
40 minutes. Since the pre-penetration step is a mild condition as described above, an effective action of polysulfide sulfur or a quinone-based compound in the oxidized green liquor to be added can be exhibited. That is, the decomposition of polysulfide sulfur by high temperature is reduced, the effect of protecting the terminal of hemicellulose from oxidation is increased, and the stabilization and terminal lignin action of the terminal of hemicellulose by the quinone compound are promoted. Therefore, in the next cooking step, the pulp yield can be improved and the amount of alkali added can be reduced.

[0010] In the cooking step, a cooking liquor containing polysulfide sulfur consisting of white liquor or oxidized white liquor obtained by oxidizing the white liquor is added to the product obtained in the pre-penetration step, and the cooking is further advanced. The concentration of sodium sulfide in the cooking liquor added to the product from the pre-osmosis step is 10
５０50 g / l, preferably 12-40 g / l. The sodium hydroxide concentration is 40 to 110 g / l, preferably 60 to 100 g / l. The cooking liquor may contain polysulfide sulfur, the polysulfide sulfur concentration of which is 0 to 20 g / l, preferably 0 to 12 g / l.
l.

[0011] In the digestion step, the digestion temperature is higher than the preliminary osmosis temperature, and a temperature of 130 to 190 ° C, preferably 140 to 180 ° C is used. Generally, the temperature is 10 to 90 ° C., preferably 30 ° C., higher than the pre-permeation temperature.
It is preferable to use a temperature as high as about 70 ° C. The digestion holding time is usually 30 to 90 minutes, preferably 40 to 80 minutes. In the cooking step, the lignocellulosic material is digested by both the cooking liquor newly added in the cooking step and the oxidized green liquor used in the pre-osmosis step, but most of the strong cooking liquor containing the newly added sodium hydroxide. It is pulped by digestion. Moreover, in this case, since the terminal of the hemicellulose is oxidized and protected by the polysulfide sulfur in the pre-penetration step, the cellulose is effectively prevented from disintegrating even when subjected to a strong digestion action by sodium hydroxide, and the pulp yield is improved. Further, when polysulfide sulfur is contained in the cooking liquor, the pulp yield is further improved. Incidentally, polysulfide sulfur referred to in the present specification means sodium polysulfide (Na ₂₎ by the following reaction formula.
It means the sulfur produced from S ₂ ).

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In the present invention, a part of the green liquor is oxidized by bringing it into contact with oxygen or oxygen-containing gas (air, oxygen-enriched air, etc.). The oxidation treatment is performed using a catalyst,
The reaction temperature is 60-100 ° C, preferably 70-90 ° C.
° C, the reaction pressure is 0 to ² kg / cm ² , preferably 0 to 0.
It is performed under the condition of 5 kg / cm ² . As the catalyst, various conventionally known oxidation catalysts can be used, but an activated carbon catalyst is preferably used. This activated carbon catalyst
Various forms such as a granular form, a fibrous form, and a cloth form can be used. Further, as the oxidation treatment apparatus, generally, a catalyst tower filled with a catalyst is used. In the oxidation treatment of this green liquor, the reaction rate (oxidation rate) of sodium sulfide is 4
It is good to keep it in the range of 0 to 95%, preferably 70 to 90%. The green liquor to be oxidized prior to the oxidization,
In order to prevent catalyst performance deterioration due to the deposition of solid suspended solids in green liquor on the catalyst, the entire amount of the solids in green liquor was treated by filtration using a filter medium such as cloth, sand, anthracite, etc. The suspended substances can be substantially removed in advance.

[0013] The step of cooking the lignocellulosic material according to the present invention can be carried out in a batch mode or a continuous mode. When the process is carried out in a batch system, a digester is filled with a lignocellulose substance and an oxidized green liquor, and a pre-penetration step is performed. In the case of carrying out in a continuous mode, a pre-infiltration step is carried out by adding an oxidized green liquor to the lignocellulosic substance moving in the digester when the lignocellulose substance enters the digester, and the downstream side is digested. The cooking process may be performed by adding the liquid.

In the pulp manufacturing method of the present invention, the pulp yield is improved by performing the above two specific steps as described above. This means that the organic content in the solid content of the black liquor is reduced, and the load on the recovery boiler is reduced. Also, the amount of green liquor sent to the causticizing step is reduced. Therefore,
Since the amount of calcium oxide to be used is reduced, the load in the step of calcining and converting the by-produced calcium carbonate into calcium oxide again, that is, downsizing of the firing furnace and reduction of the amount of fuel are realized.

[0015]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In addition, green liquor, white liquor shown below,
The liquid shown below was used as the oxidized green liquor. (Green liquor) The liquid used in the factory was used. Chemical composition Na ₂ S: 31.5 g / l Na ₂ O equivalent Na ₂ CO ₃ : 78.2 g / l Na ₂ O equivalent NaOH: 12.4 g / l Na ₂ O equivalent polysulfur sulfur: 0 g / l (white Liquid) The liquid used in the factory was used. Chemical composition _{Na 2 S: 32.2g / l Na} 2 O in terms _{Na 2 CO 3: 21.1g / l} Na 2 O in terms of NaOH: 78.2g / l Na ₂ O in terms polysulfur field Sulfur: 0 g / l (oxidation Green liquor) The green liquor was prepared by air oxidation using activated carbon as a catalyst. In this case, the oxidation rate is determined by Na ₂ S before and after oxidation.
It was about 70% as determined from the concentration. Chemical composition Na ₂ S: 9.6 g / l Na ₂ O equivalent Na ₂ CO ₃ : 79.0 g / l Na ₂ O equivalent NaOH: 29.5 g / l Na ₂ O equivalent polysulfuric sulfur: 8.2 g / l S conversion

Example 1 After removing the irregularly shaped chips and ducts from the domestic hardwood chips used in the factory, air-drying them, storing them in a polyethylene bag, taking out a part thereof, and accurately weighing 400 g equivalent in absolute dry weight, This was placed in a 4 liter pressure cooker. Then 394
ml of the oxidized green liquor, 366 ml of water, and 0.03% by weight of the quinone compound to the chip were added, and the lid was closed. The quinone compound used was sodium salt of 1,4-dihydro-9,10-dihydroxyanthracene (trade name: SAQ manufactured by Kawasaki Kagaku Kogyo Co., Ltd.). Next, heating was disclosed with an electric heater, and the temperature was raised to 130 ° C. 25 minutes after the temperature reached 100 ° C., and the temperature was maintained for 30 minutes to perform preliminary infiltration. After cooling the kettle and returning the pressure inside the kettle to atmospheric pressure, 3
45 ml of the white liquor and 455 ml of water were added. The heating was opened again, the temperature was raised to 173 ° C. 35 minutes after the temperature reached 130 ° C., and the temperature was maintained for 43 minutes to perform digestion. After the gas in the kettle was evacuated and the internal pressure was returned to atmospheric pressure, the entire contents were taken out, water was added, and the mixture was stirred and washed with water to completely remove cooking waste liquid adhering to the pulp after digestion. Next, use a flat screen (slit width 0.2
mm), the pulp and the undigested fraction were separated and dried, and the weight of each was weighed to determine the pulp yield. In addition, using a part of the pulp, the kappa number, which is an index of the degree of cooking, was measured.
The amount of the oxidized green liquor in the preliminary osmosis, the amount of the white liquor in the digestion, and the water were adjusted so that the weight ratio of the liquid / chip was about 4.0.

Comparative Example 1 In Example 1, 573 ml of white liquor and 9
87 ml of water was added, and the temperature was kept at 130 ° C. and the additional addition of white liquor was omitted.
After 0 minute, the temperature was raised to 173 ° C.
An experiment was conducted in the same manner as in Example 1 except that the amount was kept for a minute.

The following experimental results were obtained from the experiments of the above-mentioned Examples and Comparative Examples.

[0019]

[Table 1]

The contents of the items shown in Table 1 are as follows. (Pulp yield) The pulp yield of the comparative example was shown as a relative ratio when the pulp yield was 100. In this case, the pulp yield is the ratio of air-dried pulp weight to absolutely dry wood chip weight. (Kappa number of pulp) This is a value obtained by expressing the index of the degree of digestion by the residual lignin ratio in the pulp, and TAPPIT-236.
hm-85. (Effective alkali addition rate) It is shown as a relative ratio when the effective alkali addition rate of the comparative example is 100. In this case, the effective alkali addition rate is the amount of alkali (Kg) added per ton of air-dried pulp in terms of Na ₂ O. (Recovery boiler load) The organic content per ton of air-dried pulp was shown as a relative ratio when the comparative example was set to 100. (Causticizing load) The amount (Kg) of Na ₂ CO ₃ per ton of causticized air-dried pulp was shown as a relative ratio when the comparative example was set to 100.

As can be seen from the experimental results shown in Table 1,
By combining a pre-penetration step using an oxidized green liquor and a quinone-based compound with a digestion step in which a white liquor or an oxidized white liquor is added to the obtained product and digested, an improvement in pulp yield is achieved. Also, the use of such a two-stage process significantly reduces the operating load of the causticizing step of causticizing the green liquor to obtain a white liquor, which means that Ca in the context of the causticizing step is reduced. The operation load of the baking process of ₂ CO ₃ is also remarkably reduced, which means that the economic efficiency in pulp production is greatly improved. In addition, the organic matter in the cooking effluent also decreases,
The load on the recovery boiler that performs black liquor combustion is also reduced.

[0022]

According to the present invention, the pulp yield can be improved as compared with the conventional kraft pulp production method.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Yoshihiro Oguchi 2-1-1, Tsurumichuo, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Inside Chiyoda Chemical Works, Ltd. (72) Eiji Watanabe Chuji-Tsurumi-chu, Tsurumi-ku, Yokohama, Kanagawa Chiyoda Kako Construction Co., Ltd. (72) Inventor Ryuichi Inaba 2-1-1, Tsurumi Chuo, Tsurumi-ku, Yokohama, Kanagawa Prefecture

Claims (1)

[Claims] 1. A pre-penetration step in which a lignocellulosic substance is infiltrated with an oxidized green liquor containing polysulfide sulfur obtained by oxidizing a green liquor, and the obtained product is further treated with white liquor or oxidized white liquor. A cooking method comprising a cooking step in which a cooking liquor containing polysulfide sulfur is added and cooked, wherein the oxidized green liquor used in the preliminary permeation step is selected from an anthraquinone-based compound, an anthrahydroquinone-based compound, or a precursor thereof. A method for producing kraft pulp, further comprising adding at least one compound.