Method for pulp whitening

FIELD: pulp-and-paper industry, in particular method for PULP whitening.

SUBSTANCE: craft pulp mass with concentration of 2.5-5.0 % after oxygen-alkaline treatment is treated with potassium permanganate in consumption of 0.01-0.1 % based on dry cellulose at 40-80°C and pH 1.6-3.0 or with sulfuric acid solution in consumption of 1.0-1.5 % at 90°C for 30 min. In steps II and IV cellulose with concentration of 10 % is treated with hydrogen peroxide in consumption of 2 % based on mass of dry cellulose for 120 min at 80-90°C and pH 9.5-10.5 wherein consumption of sodium alkali and sodium silicate is 1.3 % and 2.5 %, respectively. In step III cellulose is treated with potassium permanganate in consumption of 0.01-0.4 % under step I conditions.

EFFECT: reduced consumption of whitening agents.

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The invention relates to the field of pulp and can be used to produce bleached pulp without chlorine-containing reagents (TCF pulp).

The known method TCF-bleaching of cellulose in which the cellulose rigidity 83 permanganate units are subjected to alternating processing oxygen-containing reagents in five stages, with hydrogen peroxide in alkaline medium on I, III and V stages and potassium permanganate in sulphuric solution of II and IV, while the bleaching of pulp with hydrogen peroxide was carried out at 70-100°With consumption of 2% and the concentration of pulp 2-7%, and treatment with potassium permanganate (flow rate of 0.01 to 0.8%) at 18-25°carried to its full absorption (EN 2142529, class D 21 9/16, op. 10.12.1999). The technical result consists in obtaining the white pulp in an environmentally friendly way without the use of chlorine-containing reagents with white pulp 83-85%.

The disadvantage of this method is the high consumption of potassium permanganate, resulting in a reduction of mechanical properties of cellulose.

The present invention is the development of TCF-technologies for the pulp after oxygen-alkali treatment (AAT) using potassium permanganate and hydrogen peroxide to obtain a technical result, which consists in reducing the cost of these reagents.

This technical is such a result is achieved by a method for bleaching pulp, comprising processing unbleached pulp, alternating acid and alkali treatments on the first stage, the pulp after oxygen-alkali treatment with the mass concentration of 2.5-5% is treated with potassium permanganate with a flow rate of 0.01-0.1% of the mass of absolutely dry pulp at a temperature of 40-80°With a pH of 1.6 to 3.0, or a solution of sulfuric acid with its consumption, 1.0 to 1.5% at 90°C for 30 min, II and IV stages of the process of pulp consistency of 10% hydrogen peroxide with a flow rate of 2% from the mass of absolutely dry pulp within 120 min, pH of 9.5 to 10.5 at 80-90°and the cost of caustic soda to 1.3%, and sodium silicate 2.5%, and stage III is carried out by processing cellulose potassium permanganate from 0.01 to 0.4% in the first stage.

The proposed method allows to reduce the consumption of bleaching chemicals.

This is the technical result, which is in causal connection with the essential features of the invention.

The essential features of the invention is the treatment of unbleached pulp in the first stage, after the oxygen-alkali treatment with the mass concentration of 2.5-5% potassium permanganate with a flow rate of 0.01-0.1% of the mass of absolutely dry pulp at a temperature of 40-80°With a pH of 1.6 to 3.0, or a solution of sulfuric acid with its consumption, 1.0 to 1.5% at 90° for 30 min, II and IV stages carried the t treatment of the pulp with a concentration of 10% hydrogen peroxide with consumption of 2% of the mass of absolutely dry pulp within 120 min, pH=9,5-10,5 at 80-90°and with the cost of caustic soda to 1.3%, and sodium silicate 2.5%, and stage III is carried out by processing cellulose potassium permanganate with expenses of 0.01-0.4% in the first stage. The invention is illustrated by the following examples.

Example 1.

Pulp from hardwoods, after the oxygen-alkali treatment rigidity 53,2 permanganate units, viscosity 48,2 JV, white 48.7% and treated with a solution of potassium permanganate in acidic medium with a flow rate of 0.1% of the mass of absolutely dry cellulose (molar ratio of sulfuric acid/potassium permanganate 100:1), the mass concentration of 2.5%at a temperature of 40°, until complete absorption of the potassium permanganate (pH=1,85). On the second and fourth stages of the cellulose is treated with hydrogen peroxide under the conditions: the concentration of mass 10%, temperature 80°, duration 120 min, pH=10,0) and the following expenses: a 2.0% N2O2and 1.3% NaOH, 2.5% Of Na2SiO3. In the third stage, the pulp is treated with a solution of potassium permanganate in similar to the first stage conditions, with a flow rate of KMnO40,4%. After each stage the pulp is washed after the last - dried.

The white pulp is 84,51%, the viscosity of 25.6 JV, yield 93%.

Example 2.

The pulp was processed similarly to example 1, with the consumption of potassium permanganate in 1 stage of 0.01%.

White pulp which leaves 81,0%, the viscosity of 27.2 JV, yield 94%.

Example 3.

Cellulose treated with a solution of potassium permanganate in acidic medium at stage 1 with a flow rate of 0.1% of the mass of absolutely dry cellulose (molar ratio of sulfuric acid/potassium permanganate 100:1), the mass concentration of 2.5%at a temperature of 40°, until complete absorption of the potassium permanganate (pH=1,85), and the second stage with hydrogen peroxide under the conditions and costs similar to the second stage of example 1.

The white pulp is 71.6%, yield 98%.

Example 4.

The pulp was processed similarly to example 4, when the temperature at stage 1 treatment with potassium permanganate 80°C.

The white pulp is 75.2 per cent, the yield of 94.5%.

Example 5.

The pulp was processed similarly to example 4, when the mass concentration of 5%.

The white pulp is 69,8%, the yield of 98.2%.

Example 6.

The pulp was processed similarly to example 4, when the temperature at stage 1 treatment with potassium permanganate 80°C.

The white pulp is 71.6%, yield 98%.

Example 7.

Cellulose treated filtrates obtained after the first stage treatment with potassium permanganate example 1 at a temperature of 90° within 30 min, in the second stage are processed by a hydrogen peroxide - similarly to example 1.

The white pulp is 77,3%, the viscosity of 37.5 JV, Vyhod%.

Example 8.

Cellulose treated with sulfuric acid (flow rate of 1.5%) and at a temperature of 90° within 30 min, in the second stage are processed by hydrogen peroxide also similarly to example 1.

The white pulp is 75,0%, viscosity 36,9 JV, yield 98%.

Example 9.

Cellulose treated filtrates obtained after the first stage treatment with potassium permanganate example 1 at a temperature of 90° within 30 min, in the second stage are processed by hydrogen peroxide also similarly to example 1 and again repeat the processing filtrates permanganate treatment and hydrogen peroxide.

The white pulp is 80,3%, viscosity 35,7 SP, output 95,8%.

0,4
Table
Method of bleaching cellulose
No.stage 1stage 2stage 3stage 4Indicators cellulose
KMnO4, %Costs, %:H2About2, NaOH, Na2SiO3KMnO4, %Costs, %: H2About2, NaOH, Na2SiO3White, %Viscosity, SPOutput %
1.0,12,0; 1,3; 2,52,0; 1,3; 2,584,525,6093,0
2.0,012,0; 1,3; 2,50,42,0; 1,3; 2,581,027,294,0
3.0,12,0; 1,3; 2,5--71,6-98
4.0,12,0; 1,3; 2,5--to 75.2-94,5
5.0,12,0; 1,3; 2,569,8-of 98.2
6.the filtrate2,0; 1,3; 2,5--77,3to 38.398
7.H2SO42,0; 1,3; 2,5--75,0-of 97.8
8.the filtrate2,0; 1,3; 2,5the filtrate2,0; 1,3; 2,580,335,795,8

Method of bleaching pulp, comprising processing unbleached pulp alternating acid and alkali treatments, at the first stage, the pulp after oxygen-alkali treatment with the mass concentration of 2.5-5%is treated with potassium permanganate with a flow rate of 0.01-0.1% of the mass of absolutely dry pulp at a temperature of 40-80° With a pH of 1.6 to 3.0, or a solution of sulfuric acid with its consumption, 1.0 to 1.5% at 90°C for 30 min, II and IV stages of the process of pulp concentration of 10% hydrogen peroxide with consumption of 2% of the mass of absolutely dry pulp within 120 min pH of 9.5 to 10.5 at 80-90°and with the cost of caustic soda 1.3% and sodium silicate 2.5%, and stage III is carried out by treatment of cellulose with permanganate potassium with a flow rate of 0.01-0.4% in the first stage.



 

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EFFECT: improved quality of product, reduced average degree of polymerization, and increased reactivity thereof.

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