JPH0215671B2 - - 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. Bleaching agents such as chlorine, hypochlorite (hypo), chlorine dioxide, oxygen, hydrogen peroxide, and caustic soda are usually used unless the kraft pulp is used in applications that do not require whiteness, such as packaging materials. and bleaching with a 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 we represent chlorine treatment as (C), alkaline treatment as (E), hypochlorous acid treatment as (H), chlorine dioxide treatment as (D), and hydrogen peroxide treatment as (P), this marking process (sequence) ) are C-E-H-E-D, C-E-, according to the order of bleaching agent and/or bleaching aid used.
It is carried out in multiple bleaching stages such as D-E-D and C-E-H-D-P. However, in the conventional method of using chlorine-based bleaching chemicals, the combustion recovery method cannot be used because the bleaching liquid contains chlorine ions. This is the reality. 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). The degree of this oxidative decomposition reaction 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. Protective agents were developed to compensate for the drawbacks of oxygen bleaching, and were published in Japanese Patent Publication No. 42-2003 (corresponding to U.S. Patent No. 3384535) and Japanese Patent Publication No. 47-4722.
No. 3 (corresponding to U.S. Pat. No. 3,657,065) discloses that inorganic salts such as magnesium carbonate, alkali metal borates, titanium dioxide, silica, alkali metal silicates, alkaline earth metal silicates, etc. 47
-9203 (U.S. Pat. No. 3,652,386) proposes that magnesium complex salts are effective, and JP-A-48-9370 and JP-A-49-
No. 133601 (corresponding to US Pat. No. 3,951,732) shows that triethanolamine salts are 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 a combination of peroxide and oxygen can obtain sufficient whiteness even if the lignocellulosic material is in contact with oxygen for a short time, and when compared at a constant whiteness, compared to the conventional method, it is possible to obtain a sufficient degree of whiteness even if the lignocellulose material is in contact with oxygen for a short time. It is possible to produce pulp with a low degree of polymerization and high viscosity, and the oxygen peroxide bleaching method is more effective at lower oxygen pressures, which has the advantage of not necessarily requiring the pressure-resistant container normally used in oxygen bleaching. There is. 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 reaction promotion effect has no selectivity and significantly accelerates the depolymerization reaction of cellulose, etc. Under the same oxygen pressure, the Katsupar number decreases and the yield decreases. It also has the disadvantage that it also decreases. Therefore, it has been found that in order to maintain the yield, the oxygen pressure must be further reduced, and as a result, the advantage of increased whiteness disappears. (Object of the invention) The present invention was made to solve the above-mentioned drawbacks of the bleaching method in combination with oxygen peroxide. It is to provide. 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) To summarize the present invention, the present invention provides lignocellulosic material in the presence of an alkaline medium,
The present invention relates to a method for bleaching lignocellulosic materials, characterized in that the treatment is carried out in the presence of a peroxide and a cyclic keto compound and/or a cyclic amino compound. Next, the elements constituting the present invention will be explained in detail. Peroxides used in the bleaching system of the present invention include known peroxides such as hydrogen peroxide, sodium peroxide, peracetic acid, t-butyl peroxide, m-chlorobenzoate, cumene hydroperoxide, and tetrahydrofuran hydroperoxide. Oxides can be used.
There are also compounds that react with oxygen in the bleaching system to form peroxides in situ, such as tetrahydrofuran (converted to α-tetrahydrofuran hydroperoxide), cumene (converted to cumene hydroperoxide), and acetaldehyde (converted to cumene hydroperoxide). Chemicals such as (converts to acetic acid) can also be used. The effect of the present invention is exhibited as the ratio of peroxide added per pulp is increased, 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 bleaching system of the present invention, both oxygen and oxygen-enriched air can be used, but oxygen gas can be used if the volume of the reaction vessel, pressurization, and reaction efficiency are taken into consideration. It is preferable to do so. 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. The cyclic keto compounds or cyclic amino compounds used in the bleaching system of the present invention are as follows:
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 bleaching system of the present invention is from 1 to
35% (by weight), preferably about 5 to 20%, and the pulp concentration after mixing with an alkaline medium or peroxide is preferably about 1 to 20%. The bleaching temperature is 70
~160°C, preferably about 80~150°C. The reaction time is 5 to 120 minutes, preferably 20 minutes.
~90 minutes. The reaction pressure is 1 to 10 kg/cm ² , preferably 1 to 5 kg/cm ² . The alkaline media used in the bleaching system of the present invention, such as aqueous alkaline chemicals, include sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, Kraft white liquor, oxidized white liquor, green liquor, oxidized green liquor, and tetraboric acid. sodium, sodium metaborate, etc., and the amount of alkali added per pulp is
It is preferably 0.5 to 3.0% in terms of Na ₂ O. In carrying out the bleaching of the present invention, pulp kept alkaline may be impregnated with a peroxide solution containing a cyclic keto compound or a cyclic amino compound, and then pressurized with oxygen may be applied. A peroxide solution may be added to alkaline-maintained pulp containing the compound, and then pressurized with oxygen; further, oxygen pressurization is applied to alkaline-maintained pulp containing the compound, The peroxide solution may then be added in several portions, and a number of methods can be applied. The lignocellulosic materials to be bleached in the present invention are GP (ground wood pulp), RMP (refined mechanical pulp), TMP (thermomechanical pulp), CGP (chemiground pulp), SCP (semi-chemical pulp), and SP (salmon 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. Although the bleaching method of the present invention can be carried out as a standalone bleaching step, it may also be substituted as part of a conventional bleaching sequence. (Examples of the Invention) Next, the present invention will be described with reference to Examples, but the present invention is not limited thereto in any way. In the examples set forth below, experiments on oxygen bleaching of lignocellulosic materials and measurements of physical properties of the pulp were carried out by the following procedure unless otherwise indicated. (Oxygen bleaching experiment) 200g of softwood pulp (Douglas fir) and hardwood pulp (beech) each (absolutely dry) were placed in a Teflon bag, and the mixture was mixed in proportion to the cut par value (cut par value x
0.1%) Add a predetermined amount of alkali, a predetermined amount of peroxide, a predetermined amount of a cyclic keto compound, and a predetermined amount of a cyclic amino compound, and then add a predetermined amount of water to make the pulp concentration 15%. After stirring thoroughly, Put the pulp into the autoclave. The air in the 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. (Measurement of physical properties of pulp) Regarding the physical properties of pulp, centrifugally dehydrated and washed pulp was processed using a PFI mill to achieve Canadian freeness.
Beating to 600c.c., TAPPI test method T205os−71 (JIS
The measurement was made using a sheet with a weight of 60 g/m ² that was hand-sheeted according to P8209). 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 testing method (JIS P8210) using the following equipment: tearing length JIS P8113, specific bursting JIS P8112, and specific tearing JIS P8116. Examples 1-2 and Comparative Examples 1-2 Examples 1-2 and Comparative Examples 1-2 show experiments using Douglas fir pulp. In Examples 1 and 2, hydrogen peroxide as a peroxide and 9 as a cyclic keto compound were added to softwood Douglas Furkraft pulp with a cut par number of 31.2, respectively.
10-anthraquinone (AQ) (Example 1) and 1,
Oxygen bleaching was carried out by adding 4,4a,9a-tetrahydro-9,10-diketoanthracene (THAQ) (Example 2) together with caustic soda (3.12% based on pulp). In the comparative example, caustic soda was added (for pulp 3.12
%) pulp was bleached using only oxygen (Comparative Example 1) and an example where hydrogen peroxide and caustic soda were added to the same pulp to perform oxygen bleaching (Comparative Example 2). The results are shown in Table 1 below.

【table】

[Table] Examples 3-4 and Comparative Examples 3-4 Examples 3-4 and Comparative Examples 3-4 are Katsupar values
This shows an experiment using Douglas fir pulp of No. 31.2 and changing the bleaching conditions to make the pulp digestibility (Katsupar number) the same after oxygen bleaching. Comparative example 3
is an experiment in which only oxygen bleaching was performed without the addition of hydrogen peroxide, and Comparative Example 4 was an experiment in which 1% hydrogen peroxide was added and the holding temperature was lowered by 10°C than in Comparative Example 3. In Example 3, 0.5% of 9,10-anthraquinone (AQ) was further added and the oxygen pressure was lowered by 3 kg/cm ² than in Comparative Example 4. Instead of AQ, 1, 4,
In this experiment, 0.5% of 4a,9a-tetrahydro-9,10-diketoanthracene (THAQ) was added to lower the oxygen pressure by 3 Kg/cm ² and shorten the holding time by 5 minutes compared to Comparative Example 4. The results are shown in Table 2.

[Table] Examples 5-6 and Comparative Examples 5-6 Examples 5-6 and Comparative Examples 5-6 are Katsupar values
An experiment using hardwood beech pulp of 18.5 is shown. Example 5 uses sodium peroxide as the peroxide and anthrone as the cyclic keto compound, and Example 6 uses sodium peroxide as the peroxide and anthraquinone sodium monosulfonate (AMS) as the cyclic keto compound.
Oxygen bleaching was carried out in the same manner as in Examples 1 and 2, respectively. Comparative Example 5 is an example of only oxygen bleaching, and Comparative Example 6
is an example of oxygen bleaching using soda peroxide. The results are shown in Table 3 below.

[Table] Examples 7 to 8 and Comparative Examples 7 to 8 In Examples 7 to 8 and Comparative Examples 7 to 8, beech pulp (Katsupar number 18.5) was bleached to make the digestibility of the pulp the same after oxygen bleaching. Experiments conducted under different conditions are shown. Comparative Example 7 is an example of only oxygen bleaching, and Comparative Example 8
Added 1% cumene hydroperoxide, lowered the temperature by 10°C from Comparative Example 7, and increased the alkali addition rate to 0.5%.
The experiment in which the amount of anthrone was reduced, Example 7, was further reduced by 1
In addition, the temperature was lowered by 5℃ and the oxygen pressure was lowered by 4Kg/cm ² than in Comparative Example 7.
In addition, the temperature was lowered by 5° C. and the oxygen pressure was lowered by 4 kg/cm ² from Comparative Example 7. The above results are shown in Table 4.

【table】

[Table] (Effects of the invention) As is clear from Tables 1 to 4 above, regardless of the difference between softwood pulp and hardwood pulp, a cyclic keto compound, a cyclic amino compound, and a peroxide were used together in an alkaline medium. In the case of oxygen bleaching, under the same bleaching conditions, the pulp yield can be improved without impairing bleaching properties or pulp strength, and the wastewater load is small. Furthermore, when aiming for the same degree of digestion, there is a great advantage in terms of equipment in that the bleaching temperature, bleaching time, alkali addition rate, and oxygen pressure can be significantly reduced individually or in combination.

Claims (1)

[Claims] 1. A method for bleaching lignocellulosic materials, characterized in that the lignocellulosic materials are treated in the presence of oxygen, peroxide and a cyclic keto compound and/or a cyclic amino compound in the presence of an alkaline medium.