JPH0453991B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF INDUSTRIAL APPLICATION The present invention relates to a method for bleaching lignocellulosic materials. PRIOR ART In order to use lignocellulosic materials in many applications, it is necessary to bleach the resulting pulp by chemical or mechanical action. Unless kraft pulp is used for applications that do not require whiteness, such as packaging materials, bleaching methods such as chlorine, hypochlorite (Hybo), chlorine dioxide, oxygen, hydrogen peroxide, and caustic soda are usually used. Bleach with bleaching agent and bleaching aid,
It is necessary to remove residual lignin and other substances that cause coloration of unbleached pulp. When bleaching chemical pulp that requires strength, in order to maintain the strength of the pulp fiber itself, avoid one-step static bleaching to minimize the effect on the decomposition of carbohydrates (cellulose, etc.).
Multi-stage bleaching, in which the bleaching agent and bleaching conditions are gently changed, is commonly used. Usually, lignin is first chlorinated to make it soluble, and then the lignin is dissolved and extracted with an alkali. Thereafter, a small amount of remaining lignin is further decomposed and removed using hypochlorite, chlorine dioxide, etc. to obtain a pulp with high whiteness. If C represents chlorine treatment, E represents alkaline treatment, H represents hypochlorous acid treatment, D represents chlorine dioxide treatment, and P represents hydrogen peroxide treatment, this bleaching process (bleaching sequence) is determined by the bleaching agent and/or According to the order of bleaching aids, C-E-H-ED-D, C-E-
It is carried out in multiple bleaching stages such as D-E-D and C-E-H-D-P. However, with the conventional method of using chlorine-based bleaching chemicals, waste combustion recovery methods cannot be used because the bleaching liquid contains chlorine ions, and the waste liquid is treated with coagulation sedimentation and activated sludge. The reality is that there are. In the oxygen bleaching method developed in recent years, the bleaching waste liquid can be recycled as a cleaning solution for the pulp after cooking, and can ultimately be burned and recovered together with the cooking waste liquid [JP-A-47
-5202 Publication (corresponding to U.S. Patent No. 3759783), JP-A-49-7503 Publication (U.S. Patent No. 3843473)
(corresponding to the specification)], many oxygen bleaching plants are currently in operation in the world's major pulp and paper producing countries, including Japan. In the oxygen bleaching method, the pulp after cooking is immersed in an alkaline solution of relatively low concentration, which is then squeezed to increase the pulp concentration, loosened thoroughly, and oxygen is forced into a reactor under heat and pressure to remove the This method oxidizes and decomposes residual lignin, resin, etc. and solubilizes it with alkali to bleach the pulp (The
Bleaching of Pulp, P159-209, Tappi
Press1979). This oxygen bleaching method (O ₂ stages) is combined with the conventional chlorine bleaching method to produce not only fully bleached pulp but also
It is applied to the production of semi-bleached pulp. For example, Japanese Patent Publication No. 47-7202 (corresponding to U.S. Pat. No. 3,652,388) describes the O ₂ -C/D-E bleaching sequence; ) corresponds to C/D(D)-
The bleaching sequence of O ₂ -D-E-D is
No. 47-44441 (corresponding to British Patent No. 1342580) describes a bleaching sequence consisting of O ₂ -(C,DC/D)-O ₂ -E; (corresponding to Japanese Patent No. 992265) proposes a bleaching sequence consisting of O ₂ -D/C-E-D. Paper Trade
Journal/August5, 1968 P49-P53 and Tappi
Vol. 54, No. 11 (1971), pages 1893 to 1898 propose various bleaching sequences using oxygen bleach and chlorine bleach, and these methods have greatly contributed to the reduction of chlorine-based wastewater and environmental protection. The degree of oxidative decomposition reaction in this oxygen stage is mainly proportional to the temperature and oxygen pressure during bleaching, and the higher the temperature and the higher the oxygen pressure, the more convenient the reaction is. However, a drawback of this method is that, although the bleaching effect is improved when the oxidation conditions are strengthened, cellulose etc. partially depolymerize, resulting in a decrease in the mechanical properties of the pulp. In order to compensate for the drawbacks of oxygen bleaching, a protective agent was developed.
No. 47-4722 (corresponding to U.S. Pat. No. 3,657,065) contains magnesium carbonate, alkali metal borate, titanium dioxide, silica, alkali metal Inorganic salts such as silicates and alkaline earth metal silicates are disclosed in Japanese Patent Publication No. 47-9203 (US Pat. No. 3652386)
JP-A-48-9370 and JP-A-49-133601 (corresponding to US Pat. No. 3,951,732) disclose that magnesium complex salts are effective. Salt has been shown to be effective. Triethanolamine salt is more completely soluble in water than magnesium salt, so it is effective as a protective agent for the depolymerization of cellulose, etc. However, the presence of iron ions in the suspension of bleached pulp causes triethanolamine- It has the drawback of forming an iron ion complex compound and promoting the depolymerization of cellulose etc. due to its catalytic effect, thereby significantly reducing the viscosity of the pulp. A method of adding a cyclic keto compound, that is, a quinone compound in the alkaline oxygen bleaching method of lignocellulosic materials is disclosed in JP-A-51-109303 and JP-A-51-119801 (corresponding to Canadian Patent No. 1088261). ), but the purpose of these inventions is to recover the yield loss caused by oxygen bleaching by adding quinone compounds, and also to synergistically improve the whiteness of pulp. It is not intended for this purpose. The use of peroxide as an oxygen bleaching accelerator in the alkaline oxygen bleaching method for lignocellulosic materials was disclosed in Japanese Patent Publication No. 1983-9204 (U.S. Pat. No. 47-9204).
3694309), U.S. Pat.
1982International Sulfite Pulping Conference
(Toronto Canada) Proposed in Preprint P143-148. This method of using peroxide and oxygen in combination can obtain sufficient whiteness even if the lignocellulose material is in contact with oxygen for a short time, and when compared at a constant whiteness, compared to the conventional method, cellulose etc. It is possible to produce high viscosity pulp with a low degree of depolymerization, and the oxygen peroxide combined bleaching method is more effective at lower oxygen pressures, so it does not necessarily require the pressure-resistant container normally used for oxygen bleaching. There are advantages. However, as a result of a multifaceted study on the bleaching method in combination with oxygen and peroxide, the present inventors found that even at low oxygen pressure, this bleaching method has the same whiteness as the oxygen bleaching method in which the oxygen pressure is increased due to the bleaching acceleration effect of peroxide. However, this low oxygen pressure oxygen peroxide bleaching method (hereinafter referred to as O/P or O/P)
For example, it is difficult to achieve a pulp whiteness of approximately 65% (Hunter value) using only the P stage. In addition, when the oxygen pressure is raised to 10 kg/ ^cm2 or higher, it is possible to improve the whiteness of the pulp after the O/P stage to about 65%, but the depolymerization reaction of cellulose etc. It has been found that it is extremely difficult to suppress the decrease in yield and strength because the decrease in yield and strength is significantly accelerated. (Object of the Invention) The present invention was made in order to take advantage of the above-mentioned advantages of the oxygen peroxide combined bleaching method, while solving its disadvantages. It is to provide law. Still another object is to provide a high-strength bleached pulp, yet another object is to provide a low-pressure bleaching method that does not necessarily require a pressure vessel, and still another object is to provide a bleaching method with a low COD load. Further objects will become apparent from the description below. (Structure of the Invention) The present invention is a method for bleaching a lignocellulosic material, which is characterized in that the lignocellulosic material is treated with chlorine, and then treated with oxygen and peroxide in an alkaline medium, and further comprises performing the above treatment. This is a method for bleaching lignocellulosic materials, characterized in that, after the lignocellulosic material has been washed, a treatment with hypochlorite or a treatment with chlorine dioxide is carried out as a third step. That is, the present invention enables inexpensive production of bleached pulp with high strength by combining a chlorination step (C stage) and a treatment step with oxygen and peroxide (O/P stage) as a bleaching process for lignocellulosic materials. becomes possible. By carrying out the O/P stage in the presence of a cyclic keto compound and/or a cyclic amino compound, the yield can be increased and high-strength bleached pulp can be produced at a lower cost. In addition, in the O/P stage following the C stage, the bleaching reaction is accelerated compared to the treatment step with oxygen only (O stage), so the next treatment step with hypochlorite (H stage),
Alternatively, the whiteness of the pulp supplied to the chlorine dioxide treatment step (stage D) is high. Therefore, the amount of chemicals used in stage H or stage D to obtain pulp with the same degree of bleaching can be reduced, or the bleaching sequence can be shortened. Note that, of course, if a high degree of bleaching of the pulp is not required, only the chlorination step (stage C) and the treatment step with oxygen and peroxide are sufficient. Next, the elements constituting the present invention will be explained in detail. Chlorination Step (C Stage) The C stage may be a treatment using chlorine alone or a combination treatment with chlorine and chlorine dioxide. The addition rate of chlorine is 0.1 to 0.3%, preferably 0.2 to 0.3% per pulp number.
It is 0.25%. Processing temperature is 10-40℃, preferably
The temperature is 20-30℃. The pulp concentration is 1-10%, preferably 3-5%. Processing time is 30-90 minutes, preferably 45-60 minutes. The pH of the treatment bath is preferably 3.0 or less. ClO ₂ when using chlorine dioxide in the chlorine stage
The substitution rate is 0 to 90%, preferably 5 to 15%, and the method of adding _ClO2 may be either sequential or serial. Oxygen/peroxide treatment step (O/P stage) Peroxides used in the O/P stage of the bleaching system of the present invention include hydrogen peroxide, sodium peroxide, peracetic acid, t
Known peroxides such as -butyl peroxide, m-chlorobenzoate, cumene hydroperoxide, and tetrahydrofuran hydroperoxide can be used. Also, compounds that react with oxygen in the bleaching system to form so-called "in situ" peroxides, such as tetrahydrofuran (converted to α-tetrahydrofuran hydroperoxide), cumene (converted to cumene hydroperoxide), acetaldehyde (converted to cumene hydroperoxide), Chemicals such as (converts to acetic acid) can also be used. The effect of the present invention will be exhibited as the ratio of peroxide added per pulp increases, but it is preferably about 0.1% to 10.0% (in terms of H ₂ O ₂ ) per pulp weight, and more preferably 1.0%. ~5.0%. As the oxygen used in the O/P stage of the bleaching system of the present invention, both oxygen and oxygen-enriched air can be used, but depending on the volume of the reaction vessel, the pressurization,
In consideration of reaction efficiency, it is preferable to use oxygen gas. To maximize the effects of the present invention, high pressure (10
It is more effective to use a low oxygen pressure than to carry out at a pressure of 1 Kg/cm ² or more, preferably 1 Kg/cm ² to 10
Kg/cm ² , more preferably about 1 Kg/cm ² to 5 Kg/cm ² . Therefore, since the reaction can be carried out at relatively low pressure, there is no need for conventional high-pressure oxygen bleaching equipment, and both vertical and horizontal reactors can be used. Alternatively, oxygen may be injected into the mixer where the pulp is mixed with peroxide. Examples of cyclic keto compounds or cyclic amino compounds used as necessary in the O/P stage include:
As the cyclic keto compound, benzoquinone, naphthoquinone, anthraquinone, anthrone, phenanthrenequinone, nuclear substituted products of the above quinone compounds such as alkyl, amino and hydroxy derivatives, hydro derivatives of the above compounds, and tautomers thereof are suitable. and 9,10-diketohydroanthracene or 9,10- selected from the group consisting of unsubstituted and lower alkyl substituted Diels-Alder reaction adducts of naphthoquinone and benzoquinone.
It can be appropriately selected from dioxyhydroanthracene compounds. As a 9,10-diketohydroanthracene compound, 1,4,4a,9a-tetrahydro-9,10
-diketoanthracene, 1,4,4a,5,8a,
9a,10a-Octahydro-9,10-diketoanthracene and 1,4-dioxy-9,10-diketoanthracene are suitable. Examples of 9,10-dioxyhydroanthracene compounds include 1,4-dihydro-9,10-dioxyanthracene, 1,4,
Suitable are 5,8-tetrahydro-9,10-dioxyanthracene, 1,4,5,8,8a,10a-hexahydro-9,10-dioxyanthracene or their sodium salts. Examples of the cyclic amino compound (nitrogen-containing heterocyclic compound) include phenazine, dihydrophenazine, quinoxaline, and alkyl, alkoxy, hydroxy, carboxy, and amino derivatives thereof. The amount of these compounds added per pulp is 0.01
~5% by weight, preferably about 0.02~3.0%. The pulp concentration applied to the O/P stage of the bleaching system of the present invention is 1 to 35% (by weight), preferably about 5 to 20%, and the pulp concentration after mixing with an alkaline medium or peroxide is 1 to 20%. % is preferable. The bleaching temperature is about 70-160°C, preferably about 80-150°C. The reaction time is 5 to 120 minutes, preferably 20 to 90 minutes. The reaction pressure is 1 to 10 Kg/cm ² , preferably 1
~5Kg/ ^cm2 . The alkaline media used in the O/P stage of the bleaching system of the present invention, such as aqueous alkaline chemicals, include sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, ammonia, Kraft process white liquor, oxidized white liquor, green liquor, and oxidized green liquor. liquid, sodium tetraborate, sodium metaborate, etc., and the amount of alkali added per pulp is preferably 0.5 to 3.0% in terms of Na ₂ O. In carrying out the O/P stage bleaching of the present invention, a known O/P stage operating method is adopted, and the O/P stage bleaching method is adopted.
If the step is carried out in the presence of a cyclic keto compound or a cyclic amino compound, the pulp maintained alkaline may be impregnated with a peroxide solution containing the cyclic keto compound or cyclic amino compound, and then pressurized with oxygen. Alternatively, a peroxide solution may be added to the alkaline-maintained pulp containing the above-mentioned compound, followed by oxygen pressurization; Oxygen may be pressurized, and then the peroxide solution may be added in several portions, and various methods may be applied. Hypochlorous acid treatment step (H stage) or chlorine dioxide treatment step (D stage) As the hypochlorite used in H stage, its soda salt and calcium salt are used, but soda salt is usually used. used. The concentration of sodium hypochlorite is 1 to 8%, preferably 2 to 5%, based on the pulp, the temperature is 30 to 80°C, preferably 40 to 60°C, and the pulp concentration is 5 to 20%, preferably 10 to 15%. %, time is 30~
180 minutes, preferably 60-120 minutes, PH 8.5-11.0,
Preferably it is between 9 and 10, and caustic soda is added so that the pH can be maintained at the above value. The concentration of chlorine dioxide in stage D is per pulp
0.3-2.0% (as _ClO2 ), preferably 1-1.5%
It is. Processing temperature is 60-90℃, preferably 70-80℃
It is ℃. Processing time is 100-200 minutes, preferably
It is 150-180 minutes. The pH of the treatment bath is 2-6, preferably 3-4. During treatment, sulfuric acid or caustic soda is added to adjust the pH to maintain it at the above value. The lignocellulosic materials to be bleached in the present invention are GP (ground wood pulp), RMP (refiner mechanical pulp), TMP (thermomechanical pulp), CGP (chemiground pulp), SCP (semi-chemical pulp), and SP (monocarbon pulp). phytopulp),
These include KP (kraft pulp), AP (alkali pulp), and waste paper pulp (deinked secondary fiber), and it goes without saying that it is applicable to both wood pulp and non-wood pulp. Next, the present invention will be explained with reference to examples.
The present invention is not limited to this in any way. In the examples set forth below, bleaching experiments of stage C, O/P and H stage of lignocellulosic material and measurements of physical properties of the pulp were carried out by the following procedure unless otherwise indicated. Chlorine bleaching (C stage) experiment Softwood pulp (Douglas fir) 200g (bone dry)
into a polyfluoroethylene bag, add a predetermined amount of chlorine solution or a mixture of chlorine and chlorine dioxide proportional to the Katsupar number (Katsupar number x 0.2%), stir well, and then heat at 25℃ for 1 hour. Made it react. After the reaction was completed, the sample was taken out and centrifugally dehydrated and washed. Oxygen bleaching (O/P stage) experiment 100g of the pulp treated in the previous stage (absolutely dry) was placed in a polyfluoroethylene bag, and a predetermined amount of alkali and a predetermined amount proportional to the Katsupar number (Katsupar number x 0.1%) were added. peroxide and a predetermined amount of a cyclic keto compound or a cyclic amino compound, and further increase the pulp density.
Add the specified amount of water to make it 15%, stir well, and then add 10% water.
The air in the autoclave in which the pulp was put into the rotary autoclave was replaced with oxygen, and then oxygen was introduced under pressure until a predetermined pressure was reached. The autoclave was heated to raise the temperature from 60°C to a predetermined temperature in 30 minutes, and the reaction was carried out at the predetermined temperature for a predetermined time. After the reaction was completed, the sample was taken out and centrifugally dehydrated and washed. Sodium hypochlorite bleaching (H stage) experiment The O/P stage pulp that had been centrifugally dehydrated and washed was placed in a polyfluoroethylene bag, and 1% of caustic soda and a predetermined amount of sodium hypochlorite were added to the pulp. Further, a predetermined amount of water was added so that the pulp concentration was 10%, and after stirring well, the mixture was allowed to react at a temperature of 40°C for 2 hours. After the reaction was completed, the sample was taken out and centrifugally dehydrated and washed. Measurement of the physical properties of pulp For the physical properties of pulp, centrifugally dehydrated and washed pulp was processed using Canadian Freeness in a PFI mill.
Beaten to 600 c.c., TAPPI test method T205os−71
The measurement was made using a sheet with a weight of 60 g/m ² that was hand-sheeted in accordance with (JISP8209). In addition, each test method was performed according to the following method. Whiteness JIS P8123 The following measurements were carried out in accordance with the paper pulp strength test method (JIS P8210) using the following equipment: tearing length JIS P8113, specific bursting JIS P8112, and specific tearing JIS P8116. Bleaching wastewater load Chemical oxygen consumption (COD) of pulp bleaching wastewater
It was measured according to JIS K 0102-1974 using as an index. Examples 1 to 3 and Comparative Examples 1 and 2 In Examples 1 to 3, Douglas fir pulp, a softwood material with a cut par value of 31.2, was treated with chlorine, and then hydrogen peroxide was added as a peroxide with caustic soda (pulp 3.12).
%) to perform oxygen bleaching, followed by chlorine dioxide bleaching. In Examples 2 and 3, 9,
10-anthraquinone (AQ) (Example 2) and 1,
Oxygen bleaching was performed by adding 4,4a,9a-tetrahydro-9,10-diketoanthracene (THAQ) (Example 3), followed by chlorine dioxide bleaching. Comparative Example 1 is an example in which a pulp prepared by adding caustic soda to a chlorinated pulp (3.12% based on the pulp) was bleached using only oxygen, and then chlorine dioxide bleaching was performed. Comparative Example 2 is an example in which the bleaching conditions in the O/P stage and the addition rate in the D stage were increased in order to match the final whiteness to Examples 1 to 3. The results are shown in Table 1 below. (In addition, the additive compound in the table indicates the type of cyclic keto compound or cyclic amino compound. The same applies hereinafter.

[Table] Examples 4 to 6 and Comparative Examples 3 and 4 Examples 4 to 6 are C stage and O/P stage are Examples 1 to 6.
This is an example in which bleaching was performed under the same conditions as in case 3, followed by hypochlorous acid bleaching. Comparative Examples 3 and 4 are examples in which the C stage and O/P stage were bleached under the same conditions as in Comparative Examples 1 and 2, and then hypochlorous acid bleaching was performed. The pulp used was Douglas fir pulp, a softwood material with a cut par value of 31.2. The results are shown in Table 2.

【table】

[Table] (Effect of the invention) As is clear from the results of Tables 1 and 2 above, regardless of the difference in C-O/P-D and C-O/P-H sequences, C-O-D Or C-O-H
Compared to the C-O/P-D or C-O/P-H sequence, when pulp is bleached using the C-O/P-D or C-O/P-H sequence, the PN value of the pulp after C-O/P is lower and the whiteness is higher. Even if the amount of chlorine dioxide added in the D stage or the amount of hypo added in the H stage is small, the final whiteness can be made the same, and therefore the chemical cost can be reduced.
Furthermore, by reducing the amount of chlorine dioxide added in the D stage or the amount of hypo added in the H stage, bleaching becomes gentler in the D or H stage, suppressing the disintegration of cellulose and hemicellulose, and improving the strength of the pulp, especially the ratio. Pulp with high tear strength can be obtained. In addition, by using H ₂ O ₂ in the O stage, O
The O/P stage plays three roles: alkali extraction of the chlorinated pulp, delignification with oxygen, and whitening of the pulp with H ₂ O ₂ , so the white stage is usually 84-85% (Hunter value). The five stages of bleaching required to obtain this can be reduced to three stages. Therefore, it is possible to reduce power costs and energy. Moreover, when a cyclic keto compound or a cyclic amino compound is used in combination in the O/P stage, the above effects become even more remarkable.

Claims (1)

Claims: 1. A method for bleaching lignocellulosic material, characterized in that the lignocellulosic material is treated with chlorine and then with oxygen and peroxide in an alkaline medium. 2. A method for bleaching lignocellulosic material, characterized in that the lignocellulosic material is treated with chlorine, then treated with oxygen and peroxide in an alkaline medium, and then further treated with hypochlorite. 3. A method for bleaching lignocellulosic material, characterized in that the lignocellulosic material is treated with chlorine, then treated with oxygen and peroxide in an alkaline medium, and then further treated with chlorine dioxide.