DE19803001A1 - Bleaching and delignification of pulp by Caroate / Carosche acid and production of the same from Persulfaten / Perschsefelsäure, which is produced electrochemically - Google Patents

Abstract

The invention relates to a method for bleaching and/or delignifying cellulose in which a) a sodium hydroxide solution and a peroxydisulfate solution are first of all produced by electrolysis of a sulphate, b) the peroxydisulphate solution is converted by hydrolysis into a Caro's acid/caroate solution, c) said Caro's acid/caroate solution is left to cool and d) used immediately as a bleaching solution for bleaching and/or delignifying cellulose, the Caro's acid/caroate solution becoming neutralized upon introduction into the bleaching solution.

Description

The present invention relates to a method for bleaching or / and pulp delignification using a Caro's acid / caroate solution.

Traditionally, chlorine has been used in large quantities as a bleach Paper pulp used. However, since chlorinated lignin world toxic polychlorinated aromatic compounds the bleach chlorine has been increasingly tried to be replaced by other bleaching agents. This was initially great success in using chlorine dioxide / chlorate as Bleach achieved. However, there are other efforts also chlorine dioxide / chlorate through other bleaching agents to make a TCF pulp (TCF = Total Chlorine Free) hold.

As bleach came here u. a. Ozone, oxygen and what hydrogen peroxide used to make chlorine-free paper len. However, all of these bleaches have drawbacks such as insufficient delignification, insufficient brightness of the bleached pulp or / and costly or / and manufacturing processes associated with hazards.

As a further bleaching agent for bleaching and delignifying pulp, Caroat / Carosche acid (Peroxomonosulfuric acid, H ₂ SO ₅ ) has also been proposed, in particular for chlorine-free bleaching of fine paper to achieve bleaching levels with a whiteness level of 89 degrees ISO. A disadvantage of using Caroat / Caroscher acid as a bleaching agent, however, is the high effort required to obtain the pure salt as a crystalline product. Furthermore, Caro's acid in its pure form is an extremely corrosive substance, which makes it difficult to store and transport it.

The object of the present invention was therefore a Ver drive to provide with which the advantageous bleaching and Delignification effects of Caro's acid / Caroat used can be while using the pure product Carosic acid / Caroat related difficulties Lich manufacturing costs and risk of corrosion for storage and Transport devices can be avoided.

This object is achieved according to the invention by a method for bleaching and / or delignifying pulp, in particular paper, whereby one

• (a) first by electrolysis of a sulfate sodium hydroxide solution and produces a peroxodisulfate solution,
• (b) the peroxodisulfate solution by hydrolysis in a Carosche Transferred acid / caroate solution,
• (c) this Caro's acid / caroate solution is allowed to cool and
• (d) then immediately as a bleaching solution for bleaching or / and Delignification of pulp, especially paper ver applies, whereby the Caro's acid / Caroat solution at Introduced into the bleaching liquor neutralized.

The method according to the invention enables the use of Caroic acid / Caroat in the form of a solution, which means that with the crystalline pure product of Caro's acid / Caroat ver bound disadvantages can be avoided. These disadvantages are, in particular, the high effort required to do this to obtain pure salt as a crystalline product as well as the Corrosiveness of Caro's acid.

It is essential to the invention that a Carosche Acid / caroate solution in or in the immediate vicinity of a cell fabric or paper mill can be generated so that long Transport routes that separate the water from the solution and formation of the pure product required will. The separation of water and the formation of the pure Product Caro's acid / Caroat before long storage or transport over long distances is necessary because  on the one hand, the pure product itself is more stable and therefore longer is storable as a solution and on the other hand with a wide range Transport routes the water content in the solution transport considerably more difficult and more expensive.

The preparation of a Caro's acid / caroate solution in or in succeed in the immediate vicinity of a pulp or paper mill by first by electrolysis of a sulfate, for example sodium sulfate, potassium sulfate and / or calcium sulfate, sodium hydroxide solution and a peroxodisulfate solution, for example as sodium peroxodisulfate, potassium peroxodisulfate or / and Calcium peroxodisulfate. The peroxodisulfate solution can then by hydrolysis in a Caro's acid / caroate solution be transferred. Danger during this manufacturing process carried out near wood, pulp or paper is the conventional manufacture of caroat Oleum and 70% hydrogen peroxide are very risky because every contact of the raw materials with wood, pulp or paper causes a fire. Because of this, it was So far not possible, Caroic acid / Caroat near a To produce pulp or paper mill.

Another advantage of using electrolysis for manufacturing provision of a peroxodisulfate solution and simultaneous preparation The position of caustic soda can be seen in the fact that in cells Fabric and paper mills often produce cheaper electricity Hydropower and waste sulfate from sulfate pulp is available that can be used cheaply. Prefers is the proportion of waste sulfate from sulfate pulp in the Total amount of sulfate used in step (a) more than 5% by weight, more preferably more than 50% and most preferably more than 90%.

According to the invention, the peroxodisulfate solution produced by electrolysis is then converted into a Caro's acid / caroate solution by hydrolysis. Such a Caro's acid / caroate solution was found to be relatively stable after cooling. By adding H ₂ O ₂ during hydrolysis, Caro's acid / caroate decay can be further minimized. According to the invention, the Caro's acid / caroate solution obtained is used directly as a bleaching solution for bleaching and / or delignifying pulp, preferably paper. The Caro's acid / caroate solution can, for example, be fed to the bleaching liquor via a direct line or in the form of a bulk transport. According to the invention, it is therefore not necessary to produce Caro's acid / caroate in crystalline form.

When entering the bleaching fleet, the Carosche Neutralized acid / caroate solution according to the invention. The neutra lizing at this time is advantageous because a pH <5 favors the stability of Caro's acid / caroate solution and also in the bleaching fleet the neutralisa that is released tion heat is distributed, causing decomposition of the Caroats / the Caro's acid is further reduced.

As already stated above, it is essential to the invention that the inventive method in or in the immediate vicinity a pulp or paper mill. Another advantage of such an arrangement is that large paper mills usually already have a chlorine alkali electrolysis plant, which after adaptation to the Persulfate electrolysis requirements can be used can. Furthermore, in the kraft pulp process, for example about 5 to 20 kg of sodium sulfate added per ton of paper leads. This sodium sulfate can be fed into the Circulation of the pulp process through the persulfate electro be lysed. That again after the paper bleaching Recovered sulfate is then used for the pulp process used. This way it becomes for the pulp process anyway needed sodium sulfate before feeding into the Pulp process by the bleaching process according to the invention smuggled, recovered from it and has enough  Adequate purity, then for the pulp process to be able to be used.

Another advantage of the method according to the invention is in that it is not necessary to add additional chemi kalien to use, so related problems visible disposal and environmental compatibility ten.

According to the invention, the one produced in the electrolysis is preferred Sodium hydroxide solution to neutralize Caro's acid / Caroat-Lö used in the bleaching liquor.

Furthermore, it is preferred to use a membrane for the electrolysis cell or a diaphragm cell, as in for example in Ullmann, Volume 19, page 216 is described.

The hydrolysis of the peroxodisulfate solution, in which a Carosche Acid / caroate solution is formed is preferred at 50 to 90 ° C and particularly preferably at 60 to 80 ° C for 30 to 60 minutes, preferably 30 to 40 minutes. To the hydro lysis is preferably a 1 to 4 N sulfuric acid. After hydrolysis, the Caro's acid / caroate solution is left which preferably has a pH of <5, to 0 ° C to Cool 50 ° C, preferably to 10 ° C to 30 ° C.

That when bleaching and / or delignifying pulp, especially sulfate formed from paper can be recovered and fed into a sulfate pulp process, for example will. According to the invention, any suitable sulfate for the Electrolysis can be used, sodium sulfate is preferred, Potassium sulfate and / or calcium sulfate used.

With the method according to the invention, pulp, in particular paper with high brightness, can be achieved with a whiteness level of 89 degrees ISO. A preferred bleaching sequence is, for example:

OQP- -XP *,

wherein O is oxygen, Q is a complexing agent, such as EDTA, PH ₂ O ₂ and XP *, the Caro's acid / caroate solution. However, other bleaching sequences can also be used.

The invention is further illustrated by the following examples tert.

example 1 Production of Caro's acid

Daro's acid was removed from a sodium peroxo by hydrolysis prepared disulfate solution. For this, 2 mol / l (4n) NPS (Na triumpersulfate), that is 476 g / l and 0.25 m sulfuric acid (25.5 g / l) with stirring at 70 ° C. The together The solution before and after hydrolysis is shown in Table 1 specified:

Table 1

The yield of H ₂ SO ₅ was 46.9% after 3 hours. After cooling the solution to room temperature, a decrease in the caroate content of only 2.8% was observed in 20 hours (104 g H ₂ SO ₅ / l).

In another experiment, 2 mol / l (4n) NPS, that is 476 g / l, and 2N sulfuric acid (98 g / l) with stirring to 70 ° C tempered. The composition of the solution before and after Hydrolysis is given in Table 2.  

Table 2

The yield of H ₂ SO ₅ was 71.2% after 1 hour. After the solution had cooled to room temperature and partial neutralization to 0.34N H ₂ SO ₄ , the caroate content only decreased relatively by 1.3%.

Example 2 Bleaching and delignification with KMPS (potassium monopersulfate) and hydrogen peroxide compared to caroate from Example 1

Two Finnish pulp samples were examined:
Sample 5656 contains 68.5% water, a biocidal additive and the kappa value (lignin) is 20.3. Sample 5657 contains 60.9% water, a biocidal additive and the kappa value (lignin) is 12.8. Sample 5657 is already pre-treated with oxygen. It is therefore lighter in color and contains less lignin.

Experiment a)

Pulp sample 5656 (not pre-bleached) was bleached with KMPS. The consistency was 3%. 13% KHSO ₅ atro (29.6 g Curox / 100 g dry cellulose) were used, which corresponds to 10% H ₂ SO ₅ atro. The bleaching effect was visible immediately after the addition.

After 30 minutes of treatment at 60 ° C. and pH 2.5 The sample is sucked off and washed with plenty of water. After careful mem drying at 30 ° C overnight was brightness and weight certainly.

Experiment b)

Pulp sample 5656 (not pre-bleached) became hydrogen bleached peroxide.  

The consistency was 3%. There were 2.9% H ₂ O ₂ atro. In the active oxygen content (corresponds to 1.4% AO atro), this amount is the same as the 10% H ₂ SO ₅ atro (experiment a).

After 30 minutes of treatment at 60 ° C and pH 6, the sample became sucked off and washed with plenty of water. After careful Drying at 30 ° C overnight was brightness and weight certainly.

Experiment c)

Pulp sample 5656 (not pre-bleached) was bleached with a solution of 116.4 g of H ₂ SO ₅ obtained according to Example 1.

The consistency was 3%. 10% H ₂ SO ₅ atro were used. This amount is in the active oxygen content corresponds to 1.4% AO atro.

After 30 minutes of treatment at 60 ° C and pH 1.5 The sample is sucked off and washed with plenty of water. After careful Men drying at 30 ° C overnight became brightness and weight certainly.

Experiment d)

Pulp sample 5657 (not pre-bleached) was geized with KMPS bleaches.

The consistency was 3%. 13.3% KHSO ₅ atro (29.6 g Curox / 100 g dry cellulose) were used, which corresponds to 10% H ₂ SO ₅ atro.

After 30 minutes of treatment at 60 ° C. and pH 2.5 The sample is sucked off and washed with plenty of water. After careful Men drying at 30 ° C overnight became brightness and weight certainly.  

Tries)

Pulp sample 5657 (pre-bleached) became hydrogen peroxide bleached.

The consistency was 3%. There were 2.9% H ₂ O ₂ atro. In the active oxygen content (corresponds to 1.4% AO atro), this amount is the same as the 10% H ₂ SO ₅ atro.

After 30 minutes of treatment at 60 ° C and pH 6, the sample became sucked off and washed with plenty of water. After careful Drying at 30 ° C overnight was brightness and weight certainly.

Experiment f)

Pulp sample 5657 (not pre-bleached) was bleached with a solution of 116.4 g of H ₂ SO ₅ obtained according to Example 1.

The consistency was 3%. 10% H ₂ SO ₅ atro were used. This amount is in the active oxygen content corresponds to 1.4% AO atro.

After 30 minutes of treatment at 60 ° C and pH 1.5 The sample is sucked off and washed with plenty of water. After careful Men drying at 30 ° C overnight became brightness and weight certainly.

Overview of bleaching tests a) to f)

Claims (8)

1. A method for bleaching and / or delignifying pulp, wherein one

• (a) first produced by electrolysis of a sulfate, sodium hydroxide solution and a peroxodisulfate solution,
• (b) converting the peroxodisulfate solution into a Caro's acid / caroate solution by hydrolysis,
• (c) this Caro's acid / caroate solution is allowed to cool and
• (d) then immediately used as a bleaching solution for bleaching and / or delignifying pulp, neutralizing the Caro's acid / caroate solution when it is introduced into the bleaching liquor.

2. The method according to claim 1, characterized, that the sodium hydroxide solution produced in step (a) to Neutralize used in step (d). 3. The method according to claim 1 or 2, characterized, that one for the electrolysis in step (a) Membrane or a diaphragm cell used. 4. The method according to any one of the preceding claims, characterized, that the hydrolysis of the peroxodisulfate solution in step (b) is carried out at 50 ° C to 90 ° C. 5. The method according to any one of the preceding claims, characterized, that the hydrolysis of the peroxodisulfate solution in step (b) is carried out in 1 to 4N sulfuric acid.   6. The method according to any one of the preceding claims, characterized, that the Caro's acid / Caroat solution to 0 ° C to Allow to cool 50 ° C. 7. The method according to any one of the preceding claims, characterized, that when bleaching and / or dilignifying Pulp formed sulfate is recovered. 8. The method according to any one of the preceding claims, characterized, that a sulfate selected from the group consisting of Sodium sulfate, potassium sulfate and / or calcium sulfate ver is applied.