Method of bleaching pulp

 

(57) Abstract:

The method relates to the field of pulp and can be used to produce bleached pulp without the use of molecular chlorine and chlorine dioxide. Cellulose rigidity 83 permanganate units are subjected to alternating processing oxygen-containing reagents in five stages. Hydrogen peroxide in alkaline medium on I, III and V stages and potassium permanganate in sulphuric solution of II and IV. The bleaching of sulphate pulp with hydrogen peroxide is carried out at 70-100°C with its consumption of 2% and the concentration of pulp 2-7%. Treatment with potassium permanganate lead to its consumption of 0.01 to 0.8% at 18-25°C until its complete absorption. 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%. table 1.

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

There is a method of bleaching unbleached pulp with the use of potassium permanganate, ozone, and chlorine dioxide with and the leach Conf., Vancouver is., June 15,1994: Pousters. - Monreal, 1994, - c 141 - 145.- Kojim Transformer-Coupled Amplifier. Cjorine free bleaching og KR wich permanganatea] .

There is a method of bleaching, involving pre-treatment with potassium permanganate solution for 30 to 90 minutes, in an acidic medium at a pH of 1.2 to 2.1 and when the molar ratio of acid : permanganate (50-100):1 with a flow rate of KMnO40.1 to 4% by weight of absolutely dry pulp and sequential processing of chlorine dioxide and hydrogen peroxide (RU patent N 2129179, class D 21 C 9/16 published 20.04.1999).

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

There is a method of bleaching of unbleached pulp, taken as the closest analogue involving pre-treatment of unbleached pulp with a solution of potassium permanganate in acidic medium at a pH of 1.2 and 2.1, when the molar ratio of acid : permanganate ( 12,5-100):1 and the concentration of the mass of 2-7% (as acid can be used sulfuric acid contained in the acid reactor residues of chlorine dioxide production) and consumption KMnO4no more than 1% of the mass of absolutely dry pulp, which was kept in the solution at a temperature of 15-25oC until complete absorption of the potassium permanganate Zell in an alkaline medium with a flow rate of the last 1.5-2% of the mass of absolutely dry pulp and the use of the stabilizer when the value of pH = 10-10.5, Dr. chlorine dioxide with a flow rate of 1.1-1.3% of the mass of absolutely dry pulp. After each stage bleached mass is separated from the solution and neutralize (RU patent N 2128261, class D 21 C 9/16, published. 27.03.1999). The disadvantage of this method is the use of chlorine - containing reagent chlorine dioxide, the production of which is connected with environmentally unsafe sulfur dioxide, waste management, and the formation of chlorinated organic compounds in the bleaching process. Modern requirements to the bleaching provides for the elimination of this process, any chlorine-containing reagents [müller L. N. Trends in technology of bleaching// Pulp, paper, cardboard,- 1997 - N 3-4, - n-24 ].

The present invention is the development of TCF-technologies for the pulp without using chlorine-containing reagents.

The result is achieved through the use of alternating alkaline and acid treatment under specified modes, at 1 stage the pulp with a concentration of 10-20 mass% process H2O2; in an alkaline environment (pH of 9.5 to 10.5) at 70-100oC for 120-180 min, at a flow rate H2O22% of the mass of absolutely dry pulp, II and IV stages cellulose concentration mass 2-7% is treated with a solution of KMnO

The proposed method differs from the known fact that you do not need a thorough washing of the pulp after sulphate cooking from residual alkalinity, since the first stage is used bleaching agent is hydrogen peroxide in an alkaline environment. Holding stable peroxide bleaching of sulphate pulp in the first stage, possibly due to a significant reduction in the degree of delignification of the pulp, for example, at a flow rate of hydrogen peroxide 2% degree of delignification is about 50%, and the selectivity of the reagent is more pronounced in comparison with the oxygen-alkali treatment.

Subsequent treatment with potassium permanganate is carried out under the conditions specified in the [Method of bleaching cellulose/ Fedorov, E. I., Smolev L. L., Demin C. A., E. Kulkova Century; RU patent N 2123261, class D 21 C 9/16, op. 27/03/1999], after which the pulp is again treated with hydrogen peroxide under conditions identical to the first stage of bleaching. For reduction of consumption of hydrogen peroxide can be applied oxidative bucking (soda treatment wash).

The consumption of potassium permanganate in the next stage of bleaching depends on the stiffness of cellulose and is 0.01 to 0.2%, after che is includes sequential processing of pulp with hydrogen peroxide and permanganate treatment in an acidic medium according to the scheme: P-Gr-P-Gr-P, where PM - permanganate in an acidic environment. Considered the scheme provides for the replacement of potassium permanganate to other oxygen-containing substances, such as ozone, which extends the TCF technology.

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

The essential features of the invention:

method of bleaching pulp, comprising the treatment of pulp with a concentration of 10-20 mass% hydrogen peroxide in alkaline medium (pH= 9.5 to 10.5) in the presence of a stabilizer (sodium silicate) and maintaining the pulp slurry at 70-100oC for 120-180 min (the flow rate of the hydrogen peroxide is 2.0%, sodium silicate 2.0 to 3% caustic soda - to 1.3-1.5%), separation from the solution, the neutralization and subsequent treatment of the pulp with a solution of potassium permanganate in acidic medium with the consumption of permanganate of 0.01 to 0.8% by weight of absolutely dry pulp at a molar ratio of acid : potassium permanganate (25-100):1, at t=18-25oC until its total absorption, at a concentration of mass 2-7%, the separation and washing of the masses again with hydrogen peroxide under the conditions and costs discussed above, and then permanganate treatment are already at small R the LCA is similar to the 1st and 3rd stages, the consumption of hydrogen peroxide at this stage depends on the stiffness of cellulose, 1-2% of the mass of absolutely dry pulp. Bleached mass separated and thoroughly washed.

Example 1 (the prototype).

Unbleached pulp from hardwoods, rigidity 95 permanganate units, with a viscosity of 28 SDR is subjected to preliminary treatment with potassium permanganate in sulfuric acid medium with a flow rate of 0.8% by weight of absolutely dry cellulose (molar ratio of sulfuric acid/potassium permanganate 100:1), the concentration of the suspension 5% at room temperature for 45 minutes (pH= 1.4). Then the pulp is thoroughly washed and sequentially treated with hydrogen peroxide and chlorine dioxide under the conditions : the concentration of masses 7 and 10%, a temperature of 70 and 80oC, duration, 120 and 180 minutes, respectively. Bleaching was carried out in four stages, with the following charges: 2nd stage - 1,5% H2O2, 1% NaOH, 3.5% Of Na2SiO34th - 0,5% H2ABOUT2, 0,8% NaOH, 2% Na2SiO3on the 3rd and 5th of 0.6 and 0.7% ClO2respectively. After each stage the pulp is washed after the last - dried.

The white pulp was 85.1%, viscosity 8 SDR, yield 93%.

Example 2.

Nosidney processing at a concentration of mass 10%, temperature 80oC for 120 min, costs 2% H2O2from the mass of absolutely dry pulp, 1,3% NaOH, 2% Na2SiO3pH = 10,8. In the second stage is conducted permanganate treatment with the consumption of KMnO40.4%, and a molar ratio of the potassium permanganate/sulfuric acid 1:100, at a concentration of mass of 2.5%, pH = 1,1. After washing, the pulp is subjected to peroxide treatment under conditions identical to the first stage of bleaching, and then thoroughly washed pulp mass, it is treated with potassium permanganate at a flow rate of 0.2% in conditions similar to the second stage. After washing, the pulp is again treated with hydrogen peroxide under conditions identical to stages of peroxide bleaching (first and third), washed and dried.

White 83.5% of the output 96,0%, the viscosity of 8.1 SDR.

Example 3.

Unbleached pulp is treated according to example 2, with the consumption of potassium permanganate in the second stage of 0.8%. Other conditions similar to example 2.

White cellulose 85%, a viscosity of 8.0 SDR output 92,0%.

Example 4.

Unbleached pulp is treated according to example 2, when the consumption of potassium permanganate on the second of 0.4% and 0.1% in the fourth stage, respectively, when the molar ratio of the potassium permanganate/with the CLASS="ptx2">

Example 5.

Unbleached pulp is treated according to example 2, when the consumption of potassium permanganate on the second of 0.4% and 0.2% in the fourth stages, respectively, when the molar ratio of the potassium permanganate/sulfuric acid 1:50. Other conditions similar to example 2.

White 81,4, the viscosity of 9.3 SDR, exit 95%

Example 6.

Unbleached pulp hardness 83 permanganate units were treated with potassium permanganate at a concentration of mass 2.5% sulfuric acid solution at a molar ratio of the potassium permanganate/sulfuric acid 1:100 (pH = 1,55) at a flow rate of 0.1% of the mass of absolutely dry pulp, room temperature until complete absorption of potassium permanganate. On the second and fourth stages were performed peroxide treatment under identical to example 2 conditions (the total consumption of H2O24%). On the third and fifth stages of the cellulose was treated with potassium permanganate under the same conditions as in the first stage, at a cost of 0.2 and 0.01%, respectively.

White 72-3%, viscosity 7,54 SDR, yield 92%.

Example 7,

Unbleached pulp hardness 83 permanganate units was treated according to example 6, using 0.4% of potassium permanganate under otherwise identical conditions.

White 77.2 percent, a viscosity of 7.4 SDR example 6 with the use of 0.8% potassium permanganate under otherwise identical conditions.

White with 77.7%, a viscosity of 7.1 SDR, yield 90%.

Method of bleaching pulp, comprising processing unbleached pulp by alternating alkaline and acid treatment under specified modes, with stage I to cellulose with a mass concentration of 10 - 20% process H2O2in an alkaline environment (pH of 9.5 to 10.5) at 70 - 100oC for 120 - 180 min at a flow rate H2O22% of the mass of absolutely dry pulp, II and IV stages of pulp with a consistency of 2 to 7% of treated solution KMPO4in an acidic medium with a flow rate of KMPO40.01 to 0.8% in the 18 - 25oC until complete absorption of reagents KMPO4III and V stage is carried out at conditions and costs stage I, given the initial stiffness of the cellulose.

 

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