RU2503764C1 - Method of bleaching of bisulfite pulp - Google Patents

Abstract

FIELD: textiles, paper.

SUBSTANCE: method comprises delignification by hydrogen peroxide in an acidic medium in the presence of sodium molybdate catalyst at a flow rate of H₂O₂ 1.0-4.0%, H₂SO₄ 0.5-1.0%, Na₂MoO₄ 0.05-0.5% by weight of absolutely dry pulp, the temperature of 70-98°C for 70-180 minutes, and the concentration of mass of 10%, then alkaline treatment is carried out at a flow rate of NaOH 1.5% by weight of absolutely dry pulp, at a temperature of 60-70°C for 60-90 minutes. Final bleaching is carried out in two stages: the first stage of final bleaching - by sodium chlorite at its flow rate of 0.5-1.5% and the flow rate of hydrochloric acid of 1.0-2.0% by weight of absolutely dry pulp, at a temperature of 60-90°C for 120 -240 minutes; the second stage - by alkaline solution of hydrogen peroxide in the presence of a complexing agent Trilon C at a flow rate of H₂O₂ 1.0-2.5%, NaOH 1.0-2.0%, Na₂SiO₃ 3.0%, Trilon C 0.1-0.5% by weight of absolutely dry pulp, at a temperature of 60-80°C for 120-180 minutes.

EFFECT: increase of whiteness and improvement of mechanical properties of the pulp.

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Description

The invention relates to the pulp and paper industry, and in particular to methods for bleaching bisulfite pulp, and can be used in the production of bleached pulp for the manufacture of paper and cardboard.

A known method of bleaching bisulfite cellulose by sequentially treating the pulp with sodium chlorite in an amount of 1-2% by weight of absolutely dry cellulose, nitric acid at a temperature of 40-55 ° C and a mass concentration of 5-10%, alkali at a temperature of 50-60 ° C, finishes with hypochlorite and chlorine dioxide (see ed. St. No. 1141128, class D21C 9/10, publ. 23.02.85).

The disadvantages of this method are the use of bleaching hypochlorite, the use of which in the bleaching process leads to the formation of toxic and carcinogenic organochlorine compounds, including chloroform, which have a negative impact on the vital activity of living organisms that harm the environment and human health; low mechanical indicators of bleached pulp.

Closest to the proposed method is a method of bleaching bisulfite cellulose, according to which the delignification of cellulose is carried out in two stages by chlorination in an alkaline medium with a consumption of caustic soda 0.5-4.0%, active chlorine 1-10% by weight of absolutely dry cellulose at a temperature 20-80 ° C, mass concentration of 5-15% for 15-150 min, and whitewashing is carried out with sodium hypochlorite at a temperature of 35-50 ° C, mass concentration of 8-12%, duration 90-180 min, hypochlorite consumption (in units of active chlorine) 10-20 kg / t cellulose and water peroxide kind with a flow of H ₂ O ₂ 0,7-1,5%, Na ₂ SiO ₃ 1,5-2,5%, NaOH 0,5-1,0% by weight of absolutely dry fibers at a temperature of 60-80 ° C , the duration of 120-180 minutes and a mass concentration of 8-12% (see ed. certificate No. 990919, class D21C 9/10, publ. 23.01.1983). This method is adopted as a prototype.

The disadvantages of the known method adopted for the prototype are as follows. When chlorinated in an alkaline medium, molecular chlorine interacts with the alkali to form sodium gynochlorite. The use of molecular chlorine and sodium gynochlorite during bleaching leads to pollution of wastewater with toxic chlorinated organic compounds, which also include chloroform, which have a harmful effect on human health and the environment. The high consumption of active chlorine for bleaching contributes to a high concentration of toxic organochlorine compounds in wastewater. The disadvantages of the method include the low mechanical strength and whiteness of the pulp.

Signs of the prototype, which are common with the claimed solution, the delignification of cellulose; the addition of the mass with a chlorine-containing reagent and hydrogen peroxide.

The objective of the invention is to increase environmental friendliness, increase whiteness and improve the mechanical properties of cellulose by eliminating elemental chlorine and reducing the consumption of chlorine-containing reagents.

The problem is solved due to the fact that in the known method of bleaching bisulfite cellulose, including delignification of cellulose and whitening the mass with a chlorine-containing reagent and hydrogen peroxide, delignification is carried out with hydrogen nonoxide in an acidic medium in the presence of a sodium molybdate catalyst at a flow rate of H ₂ O ₂ 1.0-4 , 0%, H ₂ SO ₄ 0.5-1.0%, Na ₂ MoO ₄ 0.05-0.5% by weight of absolutely dry cellulose, at a temperature of 70-98 ° C for 70-180 min and mass concentration 10%, then alkaline treatment is carried out at a NaOH flow rate of 1.5% by weight of absolutely dry cellulose, temperature re 60-70 ° C for 60-90 minutes; whitewashing is carried out in two stages: the first stage of whitewashing - with sodium chlorite at a flow rate of 0.5-1.5% and a flow rate of hydrochloric acid 1.0-2.0% by weight of absolutely dry cellulose, at a temperature of 60-90 ° C for 120 -240 min, the second stage — with an alkaline solution of hydrogen nonoxide in the presence of trilone C comilex former at a flow rate of H ₂ O ₂ 1.0–2.5%, NaOH 1.0–2.0%, Na ₂ SiO ₃ 3.0%, Trilon C 0.1-0.5% by weight of absolutely dry cellulose, at a temperature of 60-80 ° C for 120-180 minutes

The use of hydrogen nonoxide in cellulose delignification in an acidic medium followed by alkaline treatment instead of two-stage chlorination in an alkaline medium and the replacement of sodium hypochlorite with sodium chlorite during cellulose extraction will significantly reduce the formation of chlorinated organic compounds in wastewater.

The completion of cellulose with hydrogen nonoxide in an alkaline medium in the presence of a trilon C complexing agent promotes an increase in the whiteness of cellulose while maintaining its mechanical properties.

Features distinguishing from the prototype: delignification is carried out with hydrogen peroxide in an acidic environment in the presence of a catalyst of sodium molybdate at a flow rate of H ₂ O ₂ 1.0-4.0%, H ₂ SO ₄ 0.5-1.0%, Na ₂ MoO ₄ 0 , 05-0.5% by weight of absolutely dry cellulose, at a temperature of 70-98 ° C for 70-180 minutes and a mass concentration of 10%; then alkaline treatment is carried out at a NaOH flow rate of 1.5% by weight of absolutely dry cellulose, at a temperature of 60-70 ° C for 60-90 minutes; whitewashing is carried out in two stages: the first stage of whitewashing - with sodium chlorite at a flow rate of 0.5-1.5% and a flow rate of hydrochloric acid 1.0-2.0% by weight of absolutely dry cellulose, at a temperature of 60-90 ° C for 120 -240 min, the second stage with an alkaline solution of hydrogen peroxide in the presence of complexing agent Trilon C at a flow rate of H ₂ O ₂ 1.0-2.5%, NaOH 1.0-2.0%, Na ₂ SiO ₃ 3.0%, Trilon C 0.1-0.5% by weight of absolutely dry cellulose, at a temperature of 60-80 ° C for 120-180 minutes

The proposed method for bleaching bisulfite pulp is as follows.

Unbleached bisulfite cellulose is disintegrated in water, squeezed out, placed in a bleaching bath and delignification is carried out. To do this, add the required amount of H ₂ O ₂ , H ₂ SO ₄ , Na ₂ MoO ₄ to the bleaching bath. Delignification with hydrogen peroxide in an acidic medium (PC stage) is carried out at a temperature of 70-98 ° C for 70-180 minutes and a mass concentration of 10%. After the delignification of hydrogen with hydrogen oxide in an acidic environment is completed, the pulp is washed with water and alkaline treatment is carried out at a flow rate of sodium hydroxide (NaOH) of 1.5% by weight of absolutely dry cellulose for 60-90 min at a temperature of 60-70 ° C. After a predetermined time, the pulp is again washed with water and the cellulose is bleached with sodium chlorite in an acidic medium at a temperature of 60-90 ° C for 120-240 minutes. Next, the mass is washed with water and a bleaching solution consisting of hydrogen nonoxide, alkali, sodium silicate and Trilon C complexing agent is introduced into the bleaching bath to carry out peroxide bleaching. Conditions for peroxide bleaching: consumption of Н ₂ О ₂ 1.0-2.5% NaOH 1.0-2.0%, Na ₂ SiO ₃ 3.0%, Trilon С 0.1-0.5% by weight, absolutely dry cellulose, a temperature of 60-80 ° C, a duration of 120-180 minutes and a mass concentration of 10%.

After bleaching with hydrogen nonoxide, the mass is acidified with hydrochloric acid at a rate of 1.0% by weight of absolutely dry cellulose at room temperature for 30-60 minutes.

After each stage of bleaching, the pulp is washed with water until neutral.

Examples of specific performance.

Example 1

Unbleached bisulfite cellulose weighing 40 g of absolutely dry cellulose with a hardness of 125 ppm, 60% whiteness and a breaking length of 10450 m was disintegrated in water, squeezed on a Buchner funnel and placed in a porcelain cup, which was heated in a thermostat to maintain a constant temperature. The mass was heated to a temperature of 70 ° C and a solution was added containing H ₂ O ₂ 1.0%, H ₂ SO ₄ 0.5%, Na ₂ MoO ₄ 0.05% by weight of absolutely dry cellulose. The delignification with hydrogen peroxide in an acidic medium was carried out for 180 minutes. But at the end of the set time, the pulp was washed on a Buchner funnel and placed in a porcelain cup, which was heated in a thermostat. Upon reaching a temperature of 60 ° C, an aqueous solution of sodium hydroxide (NaOH) was poured into the mass, the flow rate of which was 1.5% by weight of absolutely dry cellulose. Alkaline treatment was carried out for 60 minutes. After processing, the pulp was washed and bleached with sodium chlorite at a rate of 0.5% and hydrochloric acid at a rate of 1% of the mass of absolutely dry cellulose at a temperature of 60 ° C for 240 min.

After bleaching with sodium chlorite, the pulp is washed until neutral with water and bleached with hydrogen nonoxide under the following conditions: consumption of H ₂ O ₂ 1.0%, NaOH 1.0%, Na ₂ SiO ₃ 3.0%, trilon C 0.1 % by weight of absolutely dry cellulose, temperature 60 ° C, 180 min, mass concentration 10%.

After completion of peroxide bleaching, the mass was washed with water and subjected to acidification, which was carried out with hydrochloric acid. The consumption of hydrochloric acid was 1.0% by weight of absolutely dry cellulose. Acid conditions - room temperature, duration 30-60 minutes. After acidification, the pulp was again washed with water until neutral.

Examples 2-6 are carried out analogously to example 1. The parameters of the stage of delignification with hydrogen peroxide in an acidic medium, stages of completion with sodium chlorite and hydrogen peroxide of bisulfite pulp, as well as indicators of bleached pulp are shown in the table.

The table shows that bleaching bisulfite pulp according to the proposed scheme allows to obtain bleached pulp with a whiteness of 87.0-91.0% while maintaining mechanical properties and with minimal chemical losses.

Thus, the claimed method of bleaching bisulfite cellulose but in comparison with the prototype allows you to:

- increase the whiteness of cellulose;

- to obtain cellulose with high mechanical strength due to the use of hydrogen peroxide for the delignification of cellulose in an acidic medium followed by alkaline treatment instead of two-stage chlorination in an alkaline medium and the replacement of sodium hypochlorite with sodium chlorite with doblex cellulose;

- increase the environmental friendliness of the bleaching process by reducing the consumption of active chlorine on bleaching.

Table Cellulose bleaching conditions according to the scheme Pk - Shch - Kht - P - K and indicators of bleached pulp Bleaching conditions Example Number one 2 3 four 5 6 one 2 3 four 5 6 7 Pc step Consumption,% by weight of absolutely dry cellulose: H ₂ O ₂ one 2 four one 2 four Na ₂ MoO ₄ 0.05 0.2 0.5 0.05 0.2 0.5 H ₂ SO ₄ 0.5 0.75 1,0 0.5 0.75 1,0 Temperature ° C 70 70 70 98 98 98 Duration min 180 180 180 70 70 70 Stage Xt Consumption,% by weight of absolutely dry cellulose: Na ₂ ClO ₂ 0.5 1,0 1,5 0.5 1,0 1,5 Hcl 1.0 1,5 2.0 1,0 1,5 2.0 Temperature ° C 60 60 60 90 90 90 Duration min 240 240 240 120 120 120 Stage P Consumption,% by weight of absolutely dry cellulose: H ₂ O ₂ . 1,0 1,5 2,5 1,0 1,5 2,5 NaOH 1,0 1,5 2.0 1,0 1,5 2.0 Na ₂ SiO ₃ 3.0 3.0 3.0 3.0 3.0 3.0 Trilon C 0.1 0.3 0.5 0.1 0.3 0.5 Temperature ° C 60 60 60 80 80 80 Duration min 180 180 180 120 120 120 Bleached Pulp Yield,% of unbleached pulp 94.2 93.5 92.7 93.1 92.2 90.2 White,% 87.0 87.5 88 89.5 90.0 91.5 The degree of penetration, unit 10 10 8 6 6 four Breaking length, m 8900 8450 8000 8500 8200 7850 Resistance to corrosion, kPa 370 350 340 360 330 310

Claims (1)

A method of bleaching bisulfite cellulose, including delignification of cellulose and weight gain with a chlorine-containing reagent and hydrogen peroxide, characterized in that the delignification is carried out with hydrogen peroxide in an acidic medium in the presence of a sodium molybdate catalyst at a flow rate of H ₂ O ₂ 1.0-4.0%, H ₂ SO ₄ 0.5-1.0%, Na ₂ MoO ₄ 0.05-0.5% by weight of absolutely dry cellulose, at a temperature of 70-98 ° C for 70-180 min and a mass concentration of 10%, then alkaline processing at a flow rate of NaOH of 1.5% by weight of absolutely dry cellulose, at a temperature of 60-70 ° C for 60-90 minutes; whitewashing is carried out in two stages: the first stage of whitewashing - with sodium chlorite at a flow rate of 0.5-1.5% and a flow rate of hydrochloric acid 1.0-2.0% by weight of absolutely dry cellulose, at a temperature of 60-90 ° C for 120 -240 min, the second stage with an alkaline solution of hydrogen peroxide in the presence of complexing agent Trilon C at a flow rate of H ₂ O ₂ 1.0-2.5%, NaOH 1.0-2.0%, Na ₂ SiO ₃ , 3.0% Trilon C 0.1-0.5% by weight of absolutely dry cellulose, at a temperature of 60-80 ° C for 120-180 minutes