FI68681B - FOER FARLBLEKNING AV CELLULOSA - Google Patents

Description

[TSSr ^ l [B1 nil ANNOUNCEMENT 68681

• SvSHP ™ "UTLÄGGNINGSSKRIFT DODO I

ee ^ VC ^ C Patent granted October 10, 1985

Patent ceddolat (51) Kv.lk. * / Lnt.CI. * D 21 C 9/10, 9/16 (21) Patent application - Patentansökning 1321 1 5 (22) Application date - Ansöknlngsdag 01 + .07.79 (23) Starting date - Giltighetsdag 0 ^ .07.79 (41) Has become public - Blivit offentlig 22.03.80

National Board of Patents and Registration / 44 ^ Date of submission and publication. - 28.06.85

Patent and ocean registration 'Ansökan utlagd och utl.skriften publicerad (32) (33) (31) Pyydetty etuoikeus — Begärd priority 21 .09.78

Federal Republic of Germany-Förbunds Repub Iiken Tyskland (DE) P 281 + 1013.1 Proven-Styrkt (71) Degussa Aktiengesellschaft, Weissfrauenstrasse 9, 6000 Frankfurt 1,

Federal Republic of Germany1ta-Förbundsrepubliken Tyskland (DE) (72) Horst Kröger, Darmstadt, Wilhelm Berndt, Frankfurt,

This invention relates to newer steps, at least three steps. The present invention relates to newer steps, at least three steps, to a method for the complete bleaching of cellulose. method for complete bleaching of cellulose.

It is known from DE-0S 23 27 900 and DE-PS 22 19 504 to bleach cellulose using peroxides.

In the process according to DE-PS 22 19 504, which consists of a series of steps P-D-P, considerable corrosion problems can occur.

The present invention relates to a multi-stage process of at least three stages for the complete bleaching of cellulose, which process is characterized in that the cellulose, possibly after pretreatment with magnesium salts and / or organic complexing agents, is bleached with per-compound in the first stage, chlorite in the second stage and chlorite in the third stage. compound.

In the case of celluloses which are difficult to bleach or in order to set the desired degree of polymerization, other known bleaching steps can be added to the previous steps.

68681

Such bleaching steps are described in Ullmann's Enzyklopädie der technischen Chemie, e-edition, 18 Band.s 778 (1967). The implementation of the method according to the invention can be carried out, for example, in bleaching devices as described in the above-mentioned book 18.Band.page 755.

Between the different bleaching steps, washing with water can be carried out in a known manner. However, in a preferred embodiment of the invention, the washing can be omitted between the second and third stages without any detriment to the quality of the product being observed.

The process according to the invention can be used for all known cellulose grades. Such celluloses may be arbitrary softwood or hardwood sulphite celluloses, such as spruce sulphite cellulose or beech sulphite cellulose. Particularly preferably, the process according to the invention can be used to bleach spruce paper and viscose sulphite cellulose or beech sulphite-artificial silk cellulose. However, it can also be used for bleaching all long and short fiber celluloses, such as poplar and birch celluloses.

The pretreatment of the cellulose can be carried out in aqueous solution with a pulp concentrate of 2 to 15% by weight (based on atrocellulose), preferably 3 to 5% by weight. In this case, the temperature may be between 5 and 80 ° C, preferably between 5 and 20 ° C. The duration of the pretreatment may be between 3 and 60 minutes, preferably between 5 and 10 minutes. The concentration of the magnesium salt may be 0.05 to 0.6% by weight, preferably 0.1 to 0.4% by weight (based on Atro cellulose and MgSO 4).

As the magnesium salt, the following can be used: MgSO 4, MgCl 2 * MgiNO ^^ ·

Mg EDTA (ethylenediaminetetraacetic acid) or magnesium salts of polycarboxylic acids. Such polycarboxylic acids are described, for example, in DE-0S 19 04 940. DE-0S 19 04 941 and DE-0S 19 42 556.

The concentration of complexing agent in the pretreatment broth may be 0.005 to 0.6% by weight, preferably 0.1 to 0.3% by weight (based on Atro cellulose). Ethylenediamineacetic acid (EDTA) can be used as the complexing agent. Na 2 DTPA, polycarboxylic acids as described, for example, in DE-0S 19 04 940 DE-0S 19 04 941 or DE-0S 19 42 556.

3 68681

The first bleaching step can be carried out with the per compound at a bulk density of 5-10% by weight, preferably 8-12% by weight (based on Atro cellulose) in aqueous solution. As the per compound, an organic or inorganic peroxide such as hydrogen peroxide, sodium peroxide or t-butyl hydroperoxide can be used. In a preferred embodiment, hydrogen peroxide is used. The temperature in the first bleaching step may be between 40 and 95 ° C, preferably between 50 and 75 ° C.

The duration of the first stage can be between 30-240 min. preferably between 60 and 180 min.

The concentration of Per compound may be 0.5 to 5% by weight, preferably 0.8 to 1.2% by weight (based on Atro cellulose and 100% h 2 O 2).

The concentration of alkali, preferably sodium hydroxide, may be 1.5 to 10% by weight, preferably 2.0 to 4.0% by weight (based on Atro cellulose and 100% NaOH).

In the second step, alkali chlorite, preferably sodium chlorite, can be used as the chlorite in the aqueous solution. The bulk density of the second stage may be 5-15% by weight, preferably 8-12% by weight (based on Atro cellulose). The temperature may be 20-80 ° C, preferably 25-60 ° C. The inhibition time of the second phase can be between 30-240 min. preferably between 60-180 min. The concentration of alkali chlorite may be 0.05 to 1.0% by weight, preferably 0.1 to 0.3% by weight (based on Atro cellulose and 100% sodium chloride). The pH in the second step may be 2.5 to 5.0, preferably 3.0 to 4 The pH may be adjusted by adding an organic acid, e.g. formic acid or acetic acid or a mineral acid. In a preferred embodiment, nitric acid (HNO 2) is used.

The third step can be carried out with the per compound in aqueous solution at a bulk density of 5-15% by weight, preferably 8-12% by weight (based on Atro cellulose). As the per compound, inorganic or organic peroxides such as hydrogen peroxide, sodium peroxide or t-butyl hydroperoxide can be used. Preferably, hydrogen peroxide can be used as the per compound. The temperature may be 40 to 95 ° C, preferably 50 to 65 ° C. The duration of the third bleaching stage can be 30-240 min. preferably 60-120 min. The concentration of the per compound, preferably hydrogen peroxide, may be 0.2 to 2.0% by weight, preferably 0.4 to 0.8% by weight (based on Atro cellulose and 4,668,600 100% H 2 O 2) · The time concentration may be 0.5 to 3 .0% by weight, preferably 0.8 to 1.2% by weight (based on Atro cellulose and 100% NaOH). Sodium hydroxide can be preferably used as the alkali.

The process according to the invention has the advantage that the combination and sequence of the bleaching steps: per-compound, chlorite and per-compound and the implementation of the chlorite-bleaching step at pH 3-5 make it possible to keep the amount of chlorite so low that no significant amounts of chlorine enter the effluent system. . This means that the process according to the invention operates almost chlorine-free.

The brightness of the final product has been improved compared to the final products of the known methods, in addition to which the yield can be increased by 2-3%.

Furthermore, the washing between the second and third bleaching steps may be omitted, resulting in improved thermal economy.

The temperature of the second stage can be lowered up to 20 ° C, which causes a considerable reduction in the corrosion problems which may occur, for example, in the process according to DE-PS 22 19 504 in the chlorine dioxide stage (D).

The method according to the invention will now be described in more detail with reference to the following examples.

Example 1

Beech sulphite-artificial silk-cellulose bleached according to the prior art Step 1 = 2.2% Cl2 1 hour 3% mass density 15 ° C wash Step 2 = 3.6% NaOH 3 hours 10% mass density 75 ° C wash Step 3 = 0 , 4% active chlorine 4 hours mass density 10% 40 ° C wash (Ca hypochlorite)

Example 2 Bleaching of beech sulphite-artificial silk-cellulose according to the invention

Step 1 = 1.0% H 2 O 2 3 hours 10% bulk density 75 ° C

3.0% NaOH

5 68681 washing Step 2 0.15% NaClO 2 12 hours 10% mass density 30 ° C 0.4% HNO 3 no washing

Step 3 = 0.4% H 2 O 2 for 2 hours 10% mass density 65 ° C

1.0% NaOH

Results of Example 1 Example 2

Light bleached 92.0 94.6 (Elrepho)

Yield% 93.3 96.6 cellulose% 90.6 90.4 R 19% 94.2 93.8

Viscosity (SKV) 178 214

Both examples show for beech sulphite-artificial silk pulp that the process according to the invention provides better bleaching. A 3.3% higher cellulose yield is obtained with almost unchanged Js cellulose content. Only a slight decrease in the R 19 value indicates that the increase in intake is largely maintained in the mashing alkaline (Maischalkalisierung, continuous mercerization of comminuted alkali cellulose) and viscose production. The higher viscosity indicates that the process is extremely sparing of the fibers.

The total chlorine input in the known bleaching process according to Example 1 was, based on cellulose, 2.6%, in the process according to the invention 0.06%.

Example 3

Bleaching of spruce sulfite cellulose according to the prior art

Step 1 4% C12 1 hour 3% bulk density 15 ° C

washing

Step 2 3.5% NaOH 1 hour 10% mass density 70 ° C

washing Step 3 1.0% active

chlorine for 3 hours at 10% bulk density at 40 ° C

washing Step 4 1.0% active

chlorine for 3 hours at 10% bulk density at 40 ° C

6 68681

Example 4

Bleaching of spruce sulphite cellulose (for paper) according to the invention Step 1 1.5% H2 ^ 2 1 hour 10% pulp density 70 ° C

3.0% NaOH

washing

Step 2 0.4% NaClO 2 for 3 hours 10% mass density 50 ° C

0.5% HNO does not wash

Step 3 1.0% H2O2 3 hours 10% bulk density 60 ° C

washing

Score

Example 3 The brightness of Example 4 (invention) bleached 90.3 90.7 Yield% 92.5 93.1 With slightly higher brightness and slightly better yield, the chlorine content of the effluent by the process of the invention is reduced from 6% to 0.16% based on the cellulose charged.

Example 5

Bleaching of spruce sulphite cellulose according to the invention Pre-treatment step

0.3% MgSO 4 min 10% mass density 15 ° C

thickening to 10% mass density

Step 1 1.3% H 2 O 2 H 2% mass density 70 ° C

3.0% NaOH

washing

Step 2 0.4% NaClO 2 for 3 hours 10% mass density 30 ° C

Step 3 1.0% H2O2

1.5% NaOH for 3 hours 10% bulk density 60 ° C

The bleached pulp reached 91.0 brightness. By pretreatment with MgSO 4, the step 1 peroxide charge could be reduced to 1.3% H 2 O 2.

Claims (9)

68681 A multi-stage process of at least three stages for bleaching cellulose, characterized in that the cellulose, optionally after pretreatment with magnesium salts and / or organic complexing agents, is first treated with per-compound, second with chlorite and third with per-compound bleached. Process according to Claim 1, characterized in that other known bleaching steps are combined. Process according to Claims 1 and 2, characterized in that it is washed with water between the bleaching steps. Method according to Claims 1 to 3, characterized in that the washing is not carried out between steps 2 and 3. Process according to Claims 1 to 4, characterized in that the pretreatment takes place. at a bulk density of 2 to 15%, preferably 3 to 5% at a temperature of 5 to 80 ° C, preferably 5 to 20 ° C in a time of 5 to 60 min. preferably 5-10 min at a Mg salt content of 0.05 to 0.6% Mg, preferably 0.1 to 0.4% resp, a complexing agent content of 0.05 to 0.6%, preferably 0.1 to 0.3 *. Process according to Claims 1 to 5, characterized in that the first step is carried out as follows, using hydrogen peroxide as the per-compound: mass density 5 to 20%, preferably. 8 to 12% temperature 40 to 95 ° C, preferably 50 'to 75 ° C time 30 to 240 min. preferably 60 to 180 min H 2 O 2 0.5 to 5%, preferably 0.8 to 1.2% NaOH 1.5 to 10% preferably 2.0 to 4.0%. Process according to Claims 1 to 6, characterized in that the second step is carried out as follows, using sodium chlorite as chlorite: mass density 5 to 15%, preferably 8 to 12% temperature 20 to 80 ° C, preferably 25 to 60 ° C 8 68681 time 30 - 240 min. preferably 60 to 180 min. sodium chlorite 0.05 to 1.0, preferably 0.1 to 0.3 pH start, 2.5 to 5.0, preferably 3.5 to 4 Process according to Claims 1 to 7, characterized in that the third step is carried out as follows, using hydrogen peroxide as the per compound: mass density 5 to 15%, preferably 8 to 12%, temperature 40 to 95 ° C, preferably 50 to 65 ° C time 30 to 240 min, preferably 60 to 120 min H 2 O 2 0.2 to 2.0% preferably (} 4 to 0.8% NaOH 0.5 to 3.0% preferably 0.8 to 1.2%. 9 68681