RU2523118C1 - Bleaching process of hardwood sulphate pulp - Google Patents

Abstract

FIELD: textiles, paper.SUBSTANCE: method comprises the steps of delignification followed by alkaline treatment and final bleaching with sodium chlorite followed by alkaline extraction with use of hydrogen peroxide. Delignification is carried out with hydrogen peroxide in an acidic medium in the presence of catalyst sodium molybdate at a rate of HO1.0-3.0%, HSO0.5-1.5%, NaMoO0.05-0.5% by weight of absolutely dry pulp at a temperature 60-90°C for 90-180 min and the mass concentration of 10%. The alkaline treatment is carried out at a rate of NaOH 1.5% by weight of absolutely dry pulp at a temperature of 60-70°C for 60-90 min. Then, final bleaching is carried out with sodium chlorite at its rate of 0.5-1.5% and the rate of hydrochloric acid of 0.5-1.5% by weight of absolutely dry pulp at a temperature of 60-90°C for 100-180 min. Alkaline bleaching with hydrogen peroxide is carried out in two stages in the presence of stabiliser sodium silicate and complexing agent trilon C. The first stage of bleaching with hydrogen peroxide is carried out at a rate of HO1.0-1.5%, NaOH 1.0-1.5%, NaSiO3.0%, trilon C 0.1-0.5% by weight of absolutely dry pulp at the temperature of 60-80°C for 150-180 min. The second stage - at a rate of HO0.9-1.2%, NaOH 0.9-1.2%, NaSiO3.0%, trilon C 0.1-0.3% by weight of absolutely dry pulp at the same temperature for 100-150 minutes.EFFECT: increase in pulp whiteness while maintaining its mechanical properties, environmental friendliness, efficiency of the bleaching process.1 tbl

Description

The invention relates to the pulp and paper industry and can be used in the production of hardwood bleached bleached pulp for the manufacture of paper and cardboard.

A known method of bleaching hardwood sulfate cellulose, including delignification of cellulose with sodium hypochlorite and whitewash with sodium chlorite in two stages with intermediate alkaline bleaching with hydrogen peroxide. At the first stage of completion, the consumption of sodium chlorite is 1.5-2.5%, at the second stage - 0.4-0.5% of absolutely dry cellulose. Alkaline bleaching with hydrogen peroxide is carried out at a flow rate of 1.0%, sodium hydroxide flow rate - 0.5%, sodium silicate - 3.0% by weight of absolutely dry fiber (see RF patent No. 2347864, class D21C 9/14, 9 / 10, 9/12, published on February 27, 2009).

The disadvantages of this method are the low yield of bleached pulp, which entails a high consumption of the original unbleached pulp for bleaching; insufficiently high pulp whiteness, pollution of wastewater with organochlorine compounds due to the use of sodium hypochlorite during bleaching.

The closest method of the same purpose to the claimed invention in terms of features is a method for bleaching sulphate cellulose, according to which the delignification of cellulose 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 1.0-5.0%, H ₂ SO ₄ 1.0%, Na ₂ MoO ₄ 0.5% by weight of absolutely dry cellulose at a temperature of 75-95 ° C for 120-150 min and a mass concentration of 10%, followed by alkaline treatment at a flow rate of NaOH of 1.5% from mass of absolutely dry cellulose at a temperature of 60-70 ° C for 60-90 min, and whitewashing is carried out with sodium chlorite in two stages with intermediate alkaline extraction in the presence of hydrogen peroxide. At the first stage of completion, the consumption of sodium chlorite is 1.3%, at the second stage - 0.6% of the mass of absolutely dry cellulose. Duration of completion at the first stage of completion - 135 minutes, at the second - 120 minutes. The consumption of hydrochloric acid at both stages is 0.7% of the mass of absolutely dry cellulose, temperature is 90 ° C, and the mass concentration is 10%. Intermediate alkaline extraction is carried out at a flow rate of NaOH 1.5% and H ₂ O ₂ 0.2% by weight of absolutely dry cellulose, at a temperature of 70-75 ° C for 120 minutes (see patent RU No. 2445415, class D21C 9/10 , published on March 20, 2012). This method is adopted as a prototype.

The prototype, which is common with the claimed solution, is the delignification of cellulose with hydrogen peroxide in an acidic medium in the presence of a sodium molybdate catalyst at a flow rate of H ₂ O _{2 of} 1.0-3.0% and a mass concentration of 10%, followed by alkaline treatment at a flow rate of NaOH 1, 5% by weight of absolutely dry cellulose at a temperature of 60-70 ° C for 60-90 minutes; an addition with sodium chlorite followed by alkaline extraction using hydrogen peroxide.

The disadvantage of this method, adopted as a prototype, is not sufficiently high whiteness of cellulose, high consumption of an expensive reagent - sodium chlorite.

The objective of the invention is to increase the whiteness of cellulose while maintaining its mechanical properties, as well as environmental friendliness, efficiency of the bleaching process.

The problem is solved due to the fact that in the known method of bleaching hardwood sulfate pulp, which includes the stage of delignification with hydrogen peroxide in an acidic medium in the presence of a catalyst of sodium molybdate at a flow rate of H ₂ O _{2 of} 1.0-3.0% and a mass concentration of 10%, followed by by alkaline treatment at a NaOH flow rate of 1.5% by weight of absolutely dry cellulose at a temperature of 60-70 ° C for 60-90 min and finished with sodium chlorite, followed by alkaline extraction using hydrogen peroxide, according to the invention, cellulose delignification oxide is conducted at a hydrogen flow rate of H ₂ SO ₄ 0,5-1,5%, Na ₂ MoO ₄ 0.05-0.5% by weight of oven-dry pulp at a temperature of 60-90 ° C for 90-180 minutes, and whitewashing is carried out with sodium chlorite at a flow rate of 0.5-1.5% and hydrochloric acid flow rate of 0.5-1.5% by weight of absolutely dry cellulose at a temperature of 60-90 ° C for 100-180 minutes, followed by alkaline bleaching with peroxide hydrogen in the presence of a sodium silicate stabilizer and Trilon C complexing agent in two stages, while the first stage of bleaching with hydrogen peroxide is carried out at a flow rate of H ₂ O ₂ 1.0-1.5%, NaOH 1.0-1.5%, Na ₂ Si O ₃ 3.0%, Trilon C 0.1-0.5% by weight of absolutely dry cellulose, at a temperature of 60-80 ° C for 150-180 min, and the second stage at a flow rate of H ₂ O ₂ 0.9- 1.2%, NaOH 0.9-1.2%, Na ₂ SiO ₃ 3.0%, Trilon C 0.1-0.3% by weight of absolutely dry cellulose at the same temperatures for 100-150 minutes

Signs that distinguish from the prototype: delignification with hydrogen peroxide is carried out at a flow rate of H ₂ SO _{4 of} 0.5-1.5%, Na ₂ MoO _{4 of} 0.05-0.5% by weight of absolutely dry cellulose at a temperature of 60-90 ° C within 90-180 minutes; whitewash with sodium chlorite is carried out in one step at a flow rate of 0.5-1.5% and a flow rate of hydrochloric acid of 0.5-1.5% by weight of absolutely dry cellulose at a temperature of 60-90 ° C for 100-180 minutes; after bleaching with sodium chlorite, alkaline bleaching is carried out with hydrogen peroxide in two steps in the presence of a sodium silicate stabilizer and Trilon C complexing agent; The first stage of bleaching with hydrogen peroxide is carried out at a flow rate of H ₂ O ₂ 1.0-1.5%, NaOH 1.0-1.5%, 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 150-180 min; the second stage is carried out at a flow rate of H ₂ O ₂ 0.9-1.2%, NaOH 0.9-1.2%, Na ₂ SiO ₃ 3.0%, Trilon C 0.1-0.3% by weight absolutely dry pulp at the same temperatures for 100-150 minutes

Hydrogen peroxide in an alkaline environment has an effective effect on the destruction of the chromic groups of lignin, without affecting cellulose. The presence of sodium silicate and the complexing agent of Trilon C helps to stabilize hydrogen peroxide, i.e. increase the efficiency of its use for bleaching pulp. This leads to an increase in the brightness of cellulose while maintaining its mechanical properties.

The proposed method for bleaching hardwood sulfate pulp is as follows.

Unbleached hardwood sulfate pulp is disintegrated in water, squeezed out, placed in a bleaching bath and delignified. 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 60-90 ° C for 90-180 minutes and a mass concentration of 10%. After the delignification with hydrogen peroxide in an acidic medium 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 whitened with sodium chlorite in an acidic medium, followed by bleaching with hydrogen peroxide in two steps.

When bleached with sodium chlorite (stage Xt), its consumption is 0.5-1.5%, the consumption of hydrochloric acid is 0.5-1.5% by weight of absolutely dry cellulose, the concentration of the mass is 10%, the duration is 100-180 minutes, the temperature is 60 -90 ° C.

The first stage of bleaching with hydrogen peroxide (stage P ₁ ) is carried out at a flow rate of H ₂ O ₂ 1.0-1.5%, NaOH 1.0-1.5%, 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 150-180 min, and the second stage (stage P ₂ ) - at a flow rate of H ₂ O _{2 of} 0.9-1.2%, NaOH 0 , 9-1.2%, Na ₂ SiO ₃ 3.0%, Trilon C 0.1-0.3% by weight of absolutely dry cellulose, at the same temperature for 100-150 minutes.

After the second stage of completion, hydrogen peroxide is used to acidify the mass 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 hardwood sulfate pulp weighing 40 g of absolutely dry cellulose having the following characteristics - hardness 94 bp, whiteness 46% and breaking length 9500 m, was disintegrated in water, squeezed on a Buchner funnel and placed in a porcelain cup, which was heated in a thermostat for maintaining a constant temperature. The mass was heated to a temperature of 60 ° 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. 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 treatment, the pulp was washed and whitewashed with sodium chlorite with a flow rate of 0.5% and a flow rate of hydrochloric acid of 0.5% by weight of absolutely dry cellulose at a temperature of 60 ° C, and a mass concentration of 10%. Next, the mass was washed and bleached with hydrogen peroxide in two stages under the following conditions: at the first stage, the consumption of H ₂ O ₂ 1.0%, NaOH 1.0%, Na ₂ SiO ₃ 3.0%, Trilon C 0.1% of mass of absolutely dry cellulose, temperature 60-80 ° C, duration 150-180 min, at the second stage - consumption H ₂ O ₂ 0.9%, NaOH 0.9%, Na ₂ SiO ₃ 3.0%, Trilon C 0 , 1% by weight of absolutely dry cellulose, at the same temperature for 100-150 minutes.

After completion of the second stage of bleaching with hydrogen peroxide, 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 finishing with sodium chlorite and hydrogen peroxide of hardwood sulfate pulp, as well as indicators of bleached pulp are shown in the table.

Table Cellulose bleaching conditions according to the Pk-Shch-Kht-P ₁ -P ₂ -K scheme 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 3 one 2 3 Na ₂ MoO ₄ 0.05 0.2 0.5 0.05 0.2 0.5 H ₂ SO ₄ 0.5 1,0 1,5 0.5 1,0 1,5 Temperature ° C 60 60 60 90 90 90 Duration min 180 180 180 90 90 90 Stage Xt Consumption,% by weight of absolutely dry cellulose: NaClO ₂ 0.5 0.5 0.5 1,5 1,5 1,5 Hcl 0.5 1,0 1,5 0.5 1,0 1,5 Temperature ° C 90 90 90 60 60 60 Duration min one hundred one hundred one hundred 180 180 180 Stage P ₁ Consumption,% by weight of absolutely dry cellulose: H ₂ O ₂ 1,0 1,0 1,0 1,5 1,5 1,5

one 2 3 four 5 6 7 NaOH 1,0 1,0 1,0 1,5 1,5 1,5 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 150 150 150 180 180 180 Stage P ₂ Consumption,% by weight of absolutely dry cellulose: H ₂ O ₂ 0.9 0.9 0.9 1,2 1,2 1,2 NaOH 0.9 0.9 0.9 1,2 1,2 1,2 Na ₂ SiO ₃ 3.0 3.0 3.0 3.0 3.0 3.0 Trilon C 0.1 0.2 0.3 0.1 0.2 0.3 Temperature ° C 60 60 60 80 80 80 Duration min one hundred one hundred one hundred 150 150 150 Bleached pulp Yield,% of unbleached pulp 92.9 92.6 91.9 92.5 91.7 91.3 White,% 88.0 88.5 88.5 89.5 90.0 90.0 The degree of penetration, units 12 12 10 8 6 6 Breaking length, m 8550 8500 8400 8450 8400 8400 Bursting Resistance, kPa 330 310 310 290 290 280 Flexural strength at multiple bends, h.p. 570 570 560 560 550 550

From the data of the table it can be seen that bleaching of hardwood sulfate 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.

This method of bleaching hardwood sulfate cellulose compared with the prototype allows to increase the whiteness of cellulose, reduce chemical losses of cellulose during bleaching, reduce bleaching costs and reduce the environmental burden by alkaline bleaching of cellulose in two stages with hydrogen peroxide in the presence of sodium silicate and trilon C instead of the stages of oxidative alkali and the second stage of bleaching with sodium chlorite.

Claims (1)

The method of bleaching hardwood sulfate pulp, including the stage of delignification with hydrogen peroxide in an acidic medium in the presence of a catalyst of sodium molybdate at a flow rate of H ₂ O _{2 of} 1.0-3.0% and a mass concentration of 10%, followed by alkaline treatment at a flow rate of NaOH of 1.5% from mass of absolutely dry cellulose at a temperature of 60-70 ° C for 60-90 min and finishing with sodium chlorite followed by alkaline extraction using hydrogen peroxide, characterized in that the delignification of cellulose with hydrogen peroxide is carried out at a flow rate of H ₂ SO _{4 of} 0.5-1 , 5%, Na ₂ MoO ₄ 0.05- 0.5% by weight of absolutely dry cellulose at a temperature of 60-90 ° C for 90-180 minutes, and the whitewash is carried out with sodium chlorite at a flow rate of 0.5-1.5% and a flow rate of hydrochloric acid 0.5-1.5 % by weight of absolutely dry cellulose at a temperature of 60-90 ° C for 100-180 min, followed by alkaline bleaching with hydrogen peroxide in the presence of a sodium silicate stabilizer and Trilon C complexing agent in two steps, while the first stage of hydrogen peroxide bleaching is carried out at a flow rate of H ₂ O ₂ 1.0-1.5%, NaOH 1.0-1.5%, 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 150-180 minutes, and the second stage at a flow rate of H ₂ O ₂ 0.9-1.2%, NaOH 0.9-1.2%, Na ₂ SiO ₃ 3.0% Trilon C 0.1-0.3% by weight of absolutely dry cellulose at the same temperatures for 100-150 minutes