RU2413046C1 - Method of bleaching sulphate cellulose - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves treating cellulose with sulphuric acid at the first step after oxygen-alkaline treatment. At the second step, peroxide bleaching is carried out in an alkaline medium in the presence of a stabiliser - magnesium sulphate. The third step involves treating cellulose with chlorine dioxide with its consumption not more than 0.5% for hardwood pulp and with chlorine dioxide consumption of 0.5-0.7% of the weight of absolutely dry cellulose for soft wood pulp. At the fourth step, cellulose is treated with hydrogen peroxide in an alkaline medium.

EFFECT: reduced consumption of chlorine dioxide, reduced corrosion of equipment and high environmental safety of the process.

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Description

The invention relates to the field of pulp production and can be used to produce bleached pulp by "soft" bleaching (from pulp after oxygen-alkaline treatment) without using molecular chlorine and with a significant reduction in the consumption of chlorine dioxide.

A known method of bleaching unbleached pulp, including the alternation of acid and alkaline treatments, characterized in that the pulp after oxygen-alkaline treatment at 1 stage is treated with sulfuric acid with a flow rate of 5% by weight w.s. (pH 2.6-3.0) at a mass concentration of 5-10%, for 30-60 minutes, at 80-90 ° C, at 2 steps, peroxide treatment is carried out with an alkali consumption of 1.0-1.3% of mass of SCC, at 3 steps, the pulp is treated with chlorine dioxide at a flow rate of 1.0-1.6% of the mass of SCC. (RU No. 2266993, CL D21C 9/10, 9/14, 9/16, publ. 2005).

The proposed method differs from the known one in that after oxygen-alkali treatment and washing (pH about 6), the cellulose is treated with sulfuric acid in the first step, hydrogen peroxide is bleached in 2 steps in an alkaline medium in the presence of a stabilizer (magnesium sulfate), in 3 steps cellulose bleach uses chlorine dioxide with a flow rate of 0.3-0.5% (for hardwood pulp) and 0.5-0.7% (for softwood pulp) by weight of the centrifugal pulp, after which the cellulose is treated with hydrogen peroxide with a flow rate of 1.0%, alkali 1.0% by weight at a temperature of 90 ° C.

This difference improves the quality of cellulose due to a significant reduction in the consumption of chlorine dioxide (which reduces the content of organochlorine compounds in finished products by several times) and the use of an environmentally friendly hydrogen peroxide reagent at two stages of bleaching. In addition, a significant reduction in the flow rate and the number of bleaching stages with chlorine dioxide (from three to one) gives significant environmental benefits, since bleaching towers, vacuum filters are one of the sources of gas emissions (chlorine dioxide and chlorine, which is formed during bleaching with this reagent) ventilation from the workshop. On the other hand, the content of chloride ions is reduced, which is especially important for creating a closed water use system, since these ions increase the corrosion of equipment. The environmental benefits of this development will allow in the future, by replacing chlorine dioxide in one step with an environmentally friendly reagent, such as ozone, switch to TCF whitening.

The technical result, which is causally connected with the essential features of the invention, consists in a significant reduction in the consumption of chlorine dioxide due to the introduction of the fourth stage of treatment with hydrogen peroxide, while the emissions of toxic substances into the atmosphere from the equipment are reduced by 3.7 times, and obtaining deciduous whiteness pulp 88.5-90% (breaking length 9.0-9.1 km, tear resistance 61 gs) and softwood pulp 87.4% (breaking length 9.5 km, tearing resistance 62-64 gs), with differences in whiteness They have different contents of pentosans in them, which affects the stage of cellulose acid treatment.

Salient features of the invention: a method for bleaching unbleached pulp, comprising alternating acid and alkaline treatments, characterized in that the pulp after oxygen-alkaline treatment in the first step is treated with sulfuric acid for 60-90 minutes, in the second step, bleaching with hydrogen peroxide is carried out in the presence of magnesium sulfate with a flow rate of 0.35-0.4% by weight cellulose, at the third stage, they reduce the consumption of chlorine dioxide to 0.3-0.7% by weight of SCC, after which the cellulose is treated with hydrogen peroxide at a rate of 1.0% and alkali 1.0% by weight of c. s.ts. at a temperature of 90 ° C.

Example 1. Unbleached hardwood pulp with a hardness of 11.74 units. Kappa, with a viscosity of 759 dm ³ / kg after the BShO, is subjected to treatment with sulfuric acid with a flow rate of 5% by weight of SCC, with a mass concentration of 10% while maintaining the cellulosic suspension at 90 ° C for 60 minutes, then the pulp is separated, washed and treated with hydrogen peroxide at the same mass concentration (with a flow rate of H ₂ O ₂ 2.0% and sodium hydroxide 1.3%, magnesium sulfate 0.35%) at 80 ° C and a duration of 120 minutes, then the cellulose was separated, washed and treated with chlorine dioxide at a temperature of 70 ° C with a flow rate of 0.1% at a concentration of mass, duration and processing similar to the second stage, then the cellulose is washed and subjected to treatment with hydrogen peroxide (with a flow rate of H ₂ O ₂ 1.0% and sodium hydroxide 1.0% by weight of abs. dry cellulose) at a mass concentration of 10%, at 90 ° C and a treatment time of 120 minutes, then dried.

Whiteness 83.9%, yield 96.3%.

Example 2. Unbleached cellulose from hardwood after KShCH hardness of 11.74 units. Kappa, with a viscosity of 759 dm ³ / kg, is subjected to processing analogously to example 1 at a flow rate of chlorine dioxide of 0.3% by weight of cent.sc. Whiteness 86.5%, viscosity 657 dm ³ / kg, yield 96%.

Example 3. Unbleached cellulose from hardwood after KShCH hardness of 11.74 units. Kappa, with a viscosity of 759 dm ³ / kg, is subjected to processing analogously to example 1 at a flow rate of chlorine dioxide of 0.5% by weight of cent.sc. White 88.5%, viscosity 675 dm ³ / kg, yield 96.1%.

Example 4. Unbleached cellulose from hardwood after KShCH hardness of 11.74 units. Kappa, with a viscosity of 759 dm ³ / kg, is subjected to processing analogously to example 1 with a duration of treatment with hydrogen peroxide in the second stage of 180 minutes and a flow rate of chlorine dioxide of 0.5% by weight of cent.sc. Whiteness 90.0%, yield 96%.

Example 5. Unbleached softwood pulp with a hardness of 10.75 units Kappa, with a viscosity of 700 dm ³ / kg after the ash treatment, is subjected to treatment with sulfuric acid with a flow rate of 5% by weight of SCC, with a mass concentration of 10% while maintaining the cellulosic suspension at 90 ° C for 90 minutes, then the pulp is separated, washed and treated with hydrogen peroxide at the same mass concentration (at a flow rate of H ₂ O _{2 of} 2.50% and sodium hydroxide 1.6%, magnesium sulfate 0.4%) at 80 ° C and a duration of 120 minutes, then the cellulose was separated, washed and treated with chlorine dioxide at a temperature of 70 ° C with a flow rate of 0.3% at a concentration of mass, duration and processing similar to the second stage, then the cellulose is washed and subjected to treatment with hydrogen peroxide (with a flow rate of H ₂ O ₂ 1.0% and sodium hydroxide 1.0% by weight of abs. dry cellulose) at a mass concentration of 10%, at 90 ° C and a treatment time of 120 minutes is dried. White 85.5%, viscosity 562 dm ³ / kg, yield 96.2%.

Example 6. Unbleached pulp from coniferous breeds after KShCH hardness of 10.75 Kappa, a viscosity of 700 dm ³ / kg is subjected to processing as in example 5 with a flow rate of chlorine dioxide at 3 stages of bleaching 0.6% by weight of b.c. Whiteness 86.4%, yield 96.0%.

Example 7. Unbleached pulp from coniferous breeds after BWW with a hardness of 10.75 Kappa, a viscosity of 700 dm ³ / kg, is subjected to processing as in Example 5 with a consumption of chlorine dioxide in 3 stages of bleaching 0.7% by weight of high-strength batch. Whiteness 87.5%, viscosity 642 dm ³ / kg, yield 96.0%.

Table 1 No. p / p 1 stage 2 stage 3 step 4 step Pulp performance Acid consumption,% τ min / T ° C Cm, % The consumption of N ₂ O ₂ ,% NaOH consumption,% ClO ₂ consumption,% Consumption of H ₂ O ₂ ,% NaOH consumption,% White,% Viscosity dm ³ / kg Breaking length, km Tear resistance, gf Hardwood pulp one. 5 60/90 5 2.0 1.3 0.1 1,0 1,0 83.9 - - - 2. 5 60/90 5 2.0 1.3 0.3 1,0 1,0 86.5 657 9.8 61 3. 5 60/90 5 2.0 1.3 0.5 1,0 1,0 88.5 675 9.1 60 four. 5 60/90 5 2.0 1.3 0.5 1,0 1,0 90.0 Softwood pulp 5. 5 90/90 5 2.5 1,6 0.5 1,0 1,0 85.5 562 9.5 - 6. 5 90/90 5 2.5 1,6 0.6 1,0 1,0 86.4 - - - 7. 5 90/90 5 2.5 1,6 0.7 1,0 1,0 87.5 642 8.1 65

Claims (1)

A method of bleaching unbleached cellulose, comprising alternating acid and alkaline treatments, characterized in that the cellulose after oxygen-alkaline treatment in the first stage is treated with sulfuric acid, in the second stage, peroxide bleaching in an alkaline medium is carried out in the presence of a stabilizer - magnesium sulfate, the third stage is carried out by processing cellulose with chlorine dioxide at its consumption of not more than 0.5% for hardwood pulp and with a consumption of chlorine dioxide of 0.5-0.7% by weight of absolutely dry cellulose for softwood pulp, per quarter of the second stage, the cellulose is subjected to treatment with hydrogen peroxide in an alkaline environment.