Method of bleaching sulphate cellulose

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.

1 tbl, 7 ex

 

The invention relates to the field of pulp and can be used to produce bleached pulp by "soft" bleaching (pulp after oxygen-alkali treatment) without the use of molecular chlorine and the substantial reduction in the consumption of chlorine dioxide.

There is a method of bleaching of unbleached pulp, comprising alternating acid and alkali treatments, characterized in that the pulp after oxygen-alkali treatment on level 1 is treated with sulfuric acid with a flow rate of 5% by weight VSC. (pH of 2.6-3.0) at a concentration of 5-10 weight%, for 30-60 min at 80-90°C, 2-stage peroxide treatment is carried out with alkali consumption of 1.0 to 1.3% by weight VSC., on 3 steps are treatment of pulp with chlorine dioxide at a flow rate of 1.0 to 1.6% by weight VSC. (RU # 2266993, CL D21 9/10, 9/14, 9/16, publ. 2005).

The proposed method differs from the known fact that the pulp after oxygen-alkali treatment and leaching (pH about 6) at the first stage is treated with sulfuric acid, 2 stages are bleaching by hydrogen peroxide in alkaline medium in the presence of the stabilizer (magnesium sulfate), 3-speed for the bleaching of pulp using chlorine dioxide with a flow rate of 0.3-0.5% (hardwood pulp) and of 0.5-0.7% (for softwood pulp) from the mass VSC., after which the pulp is subjected to treatment with hydrogen peroxide is with a flow rate of 1.0%, alkali to 1.0% by weight VSC. at a temperature of 90°C.

This difference improves quality of pulp due to the substantial reduction of the consumption of chlorine dioxide (which reduces several times chlorinated organic compounds in finished products) and the use of environmentally friendly reagent hydrogen peroxide at two levels of bleaching. In addition, a significant reduction in consumption and the number of levels of chlorine dioxide bleaching (three to one) gives significant environmental benefits, as one of the sources of gas emissions (chlorine dioxide and chlorine, which is formed during the bleaching of this reagent) are the bleaching tower, vacuum filters, ventilation of the shop. On the other hand, decreases the chloride-ion content, which is especially important to create a closed system of water use, since these ions increase the corrosion of the equipment. Environmental benefits of such development will allow in the future by replacing the chlorine dioxide on the same stage for environmentally friendly reagent such as ozone, go to TCF-bleaching.

The technical result, which is in causal connection with the essential features of the invention is the substantial reduction in the consumption of chlorine dioxide by introducing a fourth stage of processing hydrogen peroxide, when it is the emission of toxic substances into the atmosphere from equipment decreased 3.7 times, and getting white hardwood pulp and 88.5-90% (breaking length of 9.0-9.1 km, resistance to tearing, 61 HS) and softwood pulp 87,4% (breaking length of 9.5 km, resistance to tearing, 62-64 HS), and differences in whiteness index due to different content of pentosans, which affects the level of processing cellulose acid.

The essential features of the invention: method of bleaching of unbleached pulp, comprising alternating acid and alkali treatments, characterized in that the pulp after oxygen-alkali treatment on the first stage is treated with sulfuric acid for a period of 60-90 min, at the second stage bleaching with hydrogen peroxide is carried out in the presence of magnesium sulfate with a flow rate of 0.35-0.4% by weight VSC. cellulose, on the third level, reduce the consumption of chlorine dioxide of 0.3 to 0.7% by weight VSC., after which the pulp is subjected to treatment with hydrogen peroxide with a flow rate of 1.0% and alkali to 1.0% by weight VSC. at a temperature of 90°C.

Example 1. Unbleached pulp from hardwood rigidity 11,74% Kappa, viscosity 759 DM3/kg after AAT treated with sulfuric acid with a flow rate of 5% by weight VSC., with a mass concentration of 10% while maintaining the pulp slurry at 90°C for 60 minutes, then the pulp mass is separated, washed and treated with hydrogen peroxide at the same concentration mass (with supplies is DAMI N 2About22.0% sodium hydroxide 1,3%, magnesium sulfate 0,35%) at 80°C and a duration of 120 min, and then the pulp is separated, washed and treated with chlorine dioxide at a temperature of 70°C at a rate of 0.1% at a concentration of mass, duration of treatment, similar to the second stage, then the pulp is washed and treated with hydrogen peroxide (expenses N2About21.0% and sodium hydroxide and 1.0% by weight of the abs. dry cellulose) at a concentration of mass 10%at 90°C. and a processing time of 120 min, and then dried.

White 83,9%, output 96,3%.

Example 2. Unbleached pulp from hardwoods after AAT rigidity 11,74% Kappa, viscosity 759 DM3/kg was processed similarly to example 1 at a flow rate of chlorine dioxide of 0.3% by weight VSC. White 86,5%, viscosity 657 DM3/kg, yield 96%.

Example 3. Unbleached pulp from hardwoods after AAT rigidity 11,74% Kappa, viscosity 759 DM3/kg was processed similarly to example 1 at a flow rate of chlorine dioxide of 0.5% by weight VSC. White 88,5%, the viscosity of 675 DM3/kg, the yield of 96.1 per cent.

Example 4. Unbleached pulp from hardwoods after AAT rigidity 11,74% Kappa, viscosity 759 DM3/kg was processed analogously to example 1 with the duration of treatment with hydrogen peroxide in the second stage 180 min and the flow rate of chlorine dioxide of 0.5% of the t mass VSC. White 90,0%, yield 96%.

Example 5. Unbleached pulp from coniferous breeds rigidity of 10.75% Kappa, viscosity 700 DM3/kg after AAT treated with sulfuric acid with a flow rate of 5% by weight VSC., with a mass concentration of 10% while maintaining the pulp slurry at 90°C for 90 minutes, then the pulp mass is separated, washed and treated with hydrogen peroxide at the same concentration mass (expenses N2About22,50% sodium hydroxide and 1.6%, magnesium sulfate 0.4%) at 80°C and a duration of 120 min, and then the pulp is 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 of treatment, similar to the second stage, then the pulp is washed and treated with hydrogen peroxide (expenses N2About21.0% and sodium hydroxide and 1.0% by weight of the abs. dry cellulose) at a concentration of mass 10%at 90°C and the duration of treatment 120 min dried. White 85,5%, viscosity 562 DM3/kg, the yield of 96.2%.

Example 6. Unbleached pulp from coniferous after AAT rigidity of 10.75 Kappa, viscosity 700 DM3/kg was processed analogously to example 5 with a flow rate of chlorine dioxide for 3-stage bleaching of 0.6% by weight VSC. White 86.4 per cent, output 96,0%.

Example 7. Unbleached pulp from coniferous after AAT rigidity of 10.75 Kappa, viscosity 70 DM 3/kg was processed analogously to example 5 with a flow rate of chlorine dioxide for 3-stage bleaching of 0.7% by weight VSC. White 87.5%, viscosity 642 DM3/kg, the output 96,0%.

Table 1
№ p/pstage 1stage 2stage 3stage 4Indicators cellulose
Acid consumption %τ min T°CCm %The consumption of H2O2,%The consumption of NaOH, %Consumption lO2, %The consumption of H2O2, %The consumption of NaOH, %White, %Viscosity, DM3/kgBreaking length, kmResistance to tearing, HS
Hardwood pulp
1.560/9052,0 1,30,11,01,083,9---
2.560/9052,01,30,31,01,086,56579,861
3.560/9052,01,30,51,01,088,56759,160
4.560/9052,01,30,51,01,090,0
Coniferous pulp
5.590/9052,51,60,51,01,085,55629,5-
6.590/9052,51,60,61,01,086,4---
7.590/9052,51,60,71,01,087,56428,165

Method of bleaching of unbleached pulp, including the alternation of acid is based and alkali treatments, characterized in that the pulp after oxygen-alkali treatment on the first stage is treated with sulfuric acid in the second stage peroxide bleaching in alkaline medium is carried out in the presence of the stabilizer is magnesium sulfate, the third step is conducted by treating the pulp with chlorine dioxide in its consumption not more than 0.5% for hardwood pulp and at a flow rate of chlorine dioxide of 0.5-0.7% of the mass of absolutely dry pulp for softwood pulp, at the fourth stage the pulp is subjected to treatment with hydrogen peroxide in alkaline medium.



 

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