JPH01221586A - Production of bleached pulp - Google Patents

Abstract

PURPOSE: To obtain the subject pulp efficiently by treating a cellulose-containing raw material under heating with a specific cooking liquid, treating the cooked cellulosic raw material with a hot lower fatty acid in a water-containing state and extracting a residual lignin while reducing an environmental pollution. CONSTITUTION: This method for producing a bleached pulp is provided by treating a cellulose-containing raw material with a steam-cooking liquid containing at least one kind of >50 wt.%, preferably 85-98 wt.% water- containing organic acid and at least one kind of <1 wt.%, e.g. 0.05-0.5 wt.% mineral acid under heating. The cooked and broken up cellulosic raw material is treated by a hot and water-containing 1-3C fatty acid or a mixture of these acids until its kappa number becomes <25 and then the residual lignin is extracted.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing pulp. Pulp herein is to be taken to mean common industrial cellulose products of moderately high purity.

This typically includes common industrial cellulose products of somewhat higher purity, especially those used in the manufacture of paper or the manufacture of products from regenerated or chemically modified cellulose.

PRIOR ART AND THEIR PROBLEMS Conventional methods for producing norlp from typical raw materials on an industrially large scale (particularly the sulfide and sulfate processes) have problems due to environmental pollution. The main causes include the need for sulfur compounds in conventional cooking liquors, the use of chlorine-containing bleaches, and the difficulty in disposing or utilizing by-products such as lignin.

DE 34 45 132 discloses a process for the production of pulp based on the use of a cooking liquor having at least acetic acid as a major component (ie containing at least 50% by weight of acetic acid). Hereinafter, this method will be referred to as the "acetic acid dissolution treatment method." In addition to acetic acid, this known cooking liquor also contains small amounts of hydrochloric acid, typically less than 1% by weight. Digestion of cellulose-containing raw materials in acetic acid dissolution processing is typically carried out under elevated temperatures and substantially atmospheric pressure. It is still not optimal in this respect. In addition to the disadvantage of consuming relatively large amounts of acetic acid, this method also requires
There are disadvantages of using sodium hydroxide solution and/or organic solvents for the final washing of the cooked pulp (this process is called "extraction"). Further disadvantages are the relatively large consumption of peroxides acting as bleaching agents in the case of hardwood pulps and the often insufficient brightness in the case of softwood pulps.

Means for Solving the Problems The object of the present invention is to provide the same advantages as the acetic acid solution treatment process in terms of reducing environmental pollution, but with improved cost efficiency. The object of the present invention is to provide methods of the type disclosed. The inventor is
It has been found that the method described in claim 1 not only does not impair environmental protection, but also further reduces environmental pollution and achieves the above object. Further, preferred embodiments of the method of the present invention are as follows.
It has the configuration described in Section 2.

To carry out the cooking step of the process of the invention, known cellulose-containing raw materials such as hardwood, coniferous, annual plants, etc., can be used, which can be produced by conventional methods, e.g. mechanical grinding. Can be done. The cooking liquor can contain formic acid and/or propionic acid instead of or in addition to acetic acid. The content of these fatty acids is
In total, 50% by weight for a cooking liquor consisting of the above-mentioned mixture of fatty acids having 1 to 3 carbon atoms mixed in substantially any relative amount of single or individual fatty acids having 1 to 3 carbon atoms. %, preferably at least 70 weight %, more preferably 85 to 98 weight %.

Instead of or in addition to hydrochloric acid, other mineral acids, preferably cellulose, are typically contained in the cooking liquor in an amount of less than 1%, e.g. Volatile mineral acids that do not oxidize can be used.

Therefore, a typical cooking liquor for carrying out the method of the present invention is:
85-95% by weight of one type of fatty acid having 1 to 3 carbon atoms or a mixture of these fatty acids (calculated as an acid without water), 0.05-0.5% by weight of hydrochloric acid (calculated as anhydride), and the remainder from water. configured.

The cooking temperature is usually between 50° C. and the boiling point of the cooking liquor at the process pressure. At this time, the cooking process is preferably carried out under conditions such that the cooking process does not significantly exceed 300 minutes. This can usually be accomplished at 100-150<0>C. The cooking stage of the process according to the invention can be carried out under substantially atmospheric pressure. Although higher pressures can be implemented, there are generally no advantages that justify the greater expense of the pressurized system required. Generally, cooking is carried out at atmospheric pressure, typically 1.5
It is carried out under pressure not exceeding bar. A particularly preferred cooking temperature is 105-112°C.

The working conditions of the extraction stage of the method of the invention are usually such that the pulp obtained by the extraction process has a kappa value of less than 25.
Usually selected. Kappa values were calculated using the usual method (Merkblatt IV, Germany). / 37
/80), which is generally considered to be a measure of the amount of residual lignin in the pulp.

In place of an aqueous solution of sodium hydroxide or an organic solvent, which was previously regarded as an essential component in the extraction step and is disclosed in German Patent Application No. 3,445,132, carbon atoms of 1 to 3 carbon atoms are added.
It was unexpected that such fatty acids could be used successfully. Especially because,
Carbon number 1 to 3, which was also used as the main component of cooking liquor
This is because extraction using these fatty acids has clear advantages.

In the extraction process of the method of the present invention, using an aqueous solution of fatty acids having 1 to 3 carbon atoms,
It is usually possible to achieve a kappa number of less than 25 at a temperature of 105°C, under substantially atmospheric pressure, and with an extraction time typically between 10 and 100 minutes. As in the case of cooking;
Higher working pressures are also possible, but again do not offer any particular advantages for the extraction. The water content of fatty acids having 1 to 3 carbon atoms in the extraction stage is 5% relative to the extract liquid.
~10% by weight.

When hardwoods are used as raw materials, the digested pulp obtained therefrom is preferably extracted according to the invention to a kappa number of 10 or less.

When extracting pre-cooked raw materials according to the invention, it is generally important to carry out the extraction in a dispersed state. For this purpose, the pulp obtained by cooking is preferably fiberized mechanically, preferably in the presence of a liquid phase, using a stirrer, a refiner or the like. As the liquid phase, a fatty acid or a fatty acid mixture having 1 to 3 carbon atoms, which is also used in the previous cooking process or is to be used in the next extraction process, is again preferably used.

After the extraction process, the pulp is usually bleached with ozone according to the method detailed below. Bleaching is preferably carried out using again the C1-C3 fatty acid and/or the medium replacing the fatty acid already used in the previous step. This medium serves as a water entrainer in the recovery of fatty acids by azeotropic distillation, especially esters of 01-C3 fatty acids and C,-C6 alkanols, such as toluene and butyl acetate.

With or without the above bleaching treatment, fatty acids or fatty acid esters can be removed from the resulting pulp without washing with water, if desired.

The acid or ester can be recovered in a relatively environmentally friendly manner.

Cooking and extraction and the subsequent bleaching process can be carried out by countercurrent methods. The fatty acids emerging from the downstream processing stage are then used in the previous processing stage without any special intermediate treatment and are only supplied with the necessary special additives. Particularly preferably, known rotary reactors (ca.
rousel reactor).

Therefore, a numerically preferred embodiment of the process of the invention consists of the following steps: (A) using a C1-C3 fatty acid, especially concentrated acetic acid, containing a small amount of a volatile mineral acid, preferably hydrochloric acid; (B) After fiberization, extraction is carried out using the same concentration of fatty acids as in step (A); (C) Combined bleaching using peroxide or peracetic acid and ozone; bleach trea
and (D) recovering a fatty acid having 1 to 3 carbon atoms using an organic solvent that forms an azeotrope with water.

The process of the present invention can be carried out without substantially any pollutant emissions, since no waste water or pollutant-containing flue gas is generated. Since solid inorganic chemicals are not used in either the cooking or bleaching process, there is no need for water washing, as is the case with conventional processing methods that use large amounts of such inorganic chemicals. The cooking chemicals used, preferably acetic acid and hydrochloric acid, can be recovered by vaporization. Peracetic acid and ozone decompose to acetic acid and oxygen during the bleaching process. When lignin is burned to provide energy, it does not emit sulfite-containing flue gas.

The cooking is preferably carried out in accordance with German Patent Application No. 344
It is carried out continuously or batchwise according to the method described in No. 5132. At the laboratory level, 0.16 to 0.
Batch cooking carried out under reflux using 5 times the amount of 93% acetic acid containing 2% hydrochloric acid is preferred. On an industrial level, countercurrent extraction using, for example, a rotary extractor is preferred, since the consumption of acetic acid is low.

Extraction of the cooked pulp is preferably carried out using a hot aqueous C,-C3 fatty acid solution of the same concentration as that used in cooking. When carrying out countercurrent extraction, as mentioned above, the fatty acids used in the initial cooking are not intermediately distilled,
It can be used as an extractant and then as a second digestion agent.

In this case, it is advantageous to mechanically fiberize the cooked pulp before extraction. In the laboratory, the pulp can be fiberized by beating with a strong stirrer in excess acetic acid, but on an industrial scale it is usually more suitable to use refining equipment.

The bleaching treatment can be selected depending on the type of wood and the Kappa number of the extracted pulp. The use of acetic acid (here converted to peracetic acid) as a medium for bleaching pulp with hydrogen peroxide is described in German patent application no.
It has already been disclosed in No. 2. It has also been found that ozone is a significantly more effective and selective bleaching agent in C1-3 fatty acids or acetic acid than in aqueous media.

The use of ozone in acetic acid is suitable for the lignin removal step. In conventional pulp bleaching processes, chlorine is used in the lignin removal step and chlorinated organic compounds are discharged into the effluent from the bleaching plant. For example, pinewood pulp treated with 2% ozone based on the pulp,
Its kappa number is 2 without significantly reducing the degree of polymerization.
It will be lowered from 2.5 to 4.2. If a pulp with a lower kappa number is used as starting material, which is possible by suitable extraction with acetic acid, it is possible to treat with even smaller amounts of ozone. ISO brightness greater than 80% can be obtained for hardwood pulps by subsequent bleaching treatment with 1-2% hydrogen peroxide contained in fatty acids having 1 to 3 carbon atoms, acetic acid or fatty acid esters such as butyl acetate. In contrast, softwood pulps may require a third bleaching step, typically with less than 1.5% ozone. However, if the kappa number after extraction is very low, the third bleaching step can also be omitted in the case of softwood pulps.

It has become clear that a high concentration of oxidizing agent is advantageous both when bleaching with hydrogen peroxide and when bleaching with ozone. In the case of ozone bleaching, it is preferred to carry out with fluffed pulp having a high pulp content of 20-45% by weight, preferably 30-45% by weight. On the other hand, bleaching with hydrogen peroxide can be carried out in a rotary extractor using a high initial concentration of hydrogen peroxide. However, bleaching with ozone at low concentrations (pulp concentration in acetic acid of 5 to 20% by weight) is also possible, for example in a countercurrent process, by creating a gradient in the ozone concentration. When bleaching with hydrogen peroxide, butyl acetate or other acetate esters, which together with hydrogen peroxide also form peracetic acid, can also be used as solvents.

The ozone bleaching temperature may be room temperature, but must not exceed 50°C. It may also be appropriate to lower the temperature by cooling. The preferred temperature for ozone bleaching is 10-30
℃, and the bleaching treatment time is usually 5 to 100 minutes, preferably 30 to 60 minutes. The temperature of bleaching with hydrogen peroxide is 50-100°C, preferably 60-80°C, and the treatment time is 2-6 hours.

Although the concentration of the digested cellulosic raw material in the liquid medium (preferably a fatty acid having 1 to 3 carbon atoms, particularly preferably acetic acid) used in the ozone bleaching treatment in the method of the present invention is not particularly limited, 1-95 for medium
%, preferably 55-75%. The ozone volume in the gas phase at that time is not particularly limited, but is 0.
It is 1 to 10% by volume, preferably 0.5 to 3% by volume.

After bleaching, fatty acids or acetic acid can be removed from the pulp by squeezing and washing with fatty acid ester or butyl acetate and water. Instead of the preferred compound butyl acetate, other organic solvents which form low temperature azeotropes with water can also be used. Butyl acetate can also be conveniently removed from the pulp by superheated steam. Butyl acetate is then used as an entrainer in the purification of fatty acids by distillation.

Example The method of the present invention will be explained below with reference to Examples.

"%" means "% by weight".

Example 1 (A) 666 g of poplar (Populus tremuloides) with 10% hydrated bone (30 x 30 x 7 mm) was mixed with glacial acetic acid 2,
790 g, water 144 g and 37% hydrochloric acid 12 ml and refluxed for 4 hours. Then frit
and washed with hot 93% acetic acid.

Yield: 45.8%;
content): 0.2%; Kappa number: 17.8; D
Pw: 3619; Destruction length: 9390m (Rotten bark 45°5
R) (B) Divide the pulp obtained above into 6 parts and divide each into 9 parts.
Beating was performed using 2 g of 3% acetic acid at 20° C. for 7 minutes with a strong stirrer. It was then filtered with suction through Fri Soto and washed with hot acetic acid.

Kappa number = 7.7 (C-1) The fluffed pulp (concentration 35%) in a refiner was heated to 20
Gas treated at °C (ozone 0.05 g/min, ozone 0
．． 06g/1g of oxygen). The pulp was washed with acetic acid on a frit.

Kappa number: less than 0.5 (C-2) 50 g (absolute dry weight) of the obtained pulp was 93
% acetic acid and 33% hydrogen peroxide 3C1I3 (2% relative to pulp) in a round bottom flask at 70° C. for 6 hours. After filtering with suction and washing with hot acetic acid and water, the pulp had the following characteristics:

DP: 1697. Brightness Near 7.9% ISO Example 2 (A+B) Pine wood (Pinus sylvestris) chips were cooked and heated in the same manner as in Section A of Example 1, except that the treatment time was 6 hours. I washed it with Thereafter, the pulp had the following characteristic values.

Yield: 50.0%; Kappa number: 22.5; Burst length: 10
150m (Rotten bark 30, beating time 8 minutes); Rupture area: 63. 3rr1'; Tear strength: 65.2cN; DP
:3420 (C-1) A bleaching treatment with 2% ozone was then carried out according to Section C-1 of Example 1 to give the following values.

Yield: 45.8%; Kappa number: 4.2. Burst length: 919
0 m (Rotten bark 26); Burst area: 53.2 mm; Tear strength: 61.6 cN (C-2) Pulp pre-bleached with ozone was treated with 1% peroxide in 93% acetic acid at a pulp concentration of 12%. 70 by hydrogen
Bleached at ℃ for 6 hours.

Yield: 45.5%; Kappa number: less than 1.5; Whiteness: 4
0% ISO, bursting length: 8930m (rokibark 27);
Rupture area: 57.1 rri'; Tear strength: 58.8 cN (C-3) Then bleached again according to Example 1, Section C-1 using 0.6% ozone.

Yield: 45.096; Brightness: 62% ISO; Burst length:
9440m (rokibark 30); rupture area: 56.6n
i'; Tear strength: 56.3 cN Example 3 50 g of the pulp obtained according to Example 2 was
%, and then mechanically crushed. The fiberized pulp was placed in a flask and treated with 1-3.3% ozone (0.05 g/min of ozone, 0.06 g of ozone/1 Ω of oxygen). After treatment for 10-40 minutes, the pulp was washed with acetic acid and water.

Ozone (pulp 1.0 1.9 2.7 3.
% of 3) Kappa number 11.8 5.3 2.7 1
．． 3DPW3250 2990 2180 1660 Paper properties Low wood bark ('SR) 21 23 26
29 Breaking length (m) 7060 7380 82
50 8230 rupture area (Go) 51.2 55
゜0 56.3 57.5 Tear strength (cN) 7
B, 8 77.6 69.8 67J (or more)

Claims (12)

[Claims] (1) Process cellulose-containing raw materials under heating using a cooking liquor that contains at least one hydrous organic acid as a main component and at least one mineral acid in an amount of less than 1% by weight based on the cooking liquor. Then, the digested cellulosic raw material is obtained, and the cellulosic raw material in a loose state is treated with hot hydrous C_1-C_3 fatty acids or a mixture of these acids until the kappa number is less than 25, and the remaining lignin is removed. A method for producing pulp from a cellulose-containing raw material, characterized by extraction. (2) The method according to claim 1, wherein the cellulose-containing raw material is obtained from a coniferous tree or a hardwood, and when the raw material is obtained from a hardwood, the extraction is performed until the kappa number is less than 10. (3) Acetic acid or C_1- containing acetic acid as the main component
3. Process according to claim 1 or 2, in which a C_3 fatty acid mixture is used as fatty acid for cooking and extraction. (4) The method according to any one of claims 1 to 3, wherein the cellulosic raw material obtained by cooking is mechanically pulverized in the presence of a liquid medium before extraction. (5) The method according to any one of claims 1 to 4, wherein the obtained cellulosic raw material is bleached with ozone and/or peroxide before or after the extraction. (6) C_1-C cellulosic raw materials in bleaching treatment
_3 When dispersed in fatty acids and using peroxide,
6. The method according to claim 5, wherein at least a part of the C_1-C_3 fatty acids is replaced by an ester of acetic acid and an alkanol having a carbon number of C_1-C_6. (7) The method according to any one of claims 1 to 6, wherein the C_1-C_3 fatty acid or acetic acid contains less than 50% by weight of water. (8) The method according to any one of claims 1 to 7, wherein a multi-step bleaching process is carried out using the same or different bleaching agents in each step. (9) bleaching is carried out with ozone in a proportion of 0.1 to 10% in the gas phase, and bleaching of cooked cellulosic raw material in a liquid medium with a concentration of 1 to 95% by weight relative to the liquid medium; The method according to any one of claims 5 to 8, wherein the method is subjected to treatment. (10) The method according to any one of claims 1 to 9, wherein the bleaching treatment with peroxide is carried out at a high temperature of 50 to 100°C, and the bleaching treatment with ozone is carried out at a temperature of 50°C or lower. (11) The method according to any one of claims 1 to 10, wherein the mixture of C_1-C_3 fatty acids or acetic acid used is recovered by extraction or azeotropic distillation in the presence of an entrainer of water. (12) Claim 1 in which a mineral acid is added to the C_1-C_3 fatty acid used for extraction, and then the fatty acid is used as a cooking liquor.
12. The method according to any one of 11 to 11.