Method of bleaching pulp

 

(57) Abstract:

The method relates to pulp and can be used to produce bleached pulp without molecular chlorine. Unbleached pulp is treated with a solution of potassium permanganate in acidic medium at pH of 1.2 and 2.1. As the acidic environment of the use of sulfuric acid or acid reactor residues from the production of chlorine dioxide. The potassium permanganate take not more than 1% of the mass of absolutely dry pulp. Stand at room temperature until complete absorption of potassium permanganate pulp mass. The mass is separated from the solution and neutralize. Then subjected to a four-stage bleaching. The first and third stages are in the presence of hydrogen peroxide in an alkaline medium at a temperature of 70-100oWith the consumption of hydrogen peroxide of 1.5-2.0% by weight of absolutely dry pulp. On the second and fourth stage bleached pulp is treated with a solution of chlorine dioxide at a temperature of 50-70oWhen the total chlorine consumption of 1.1-1.3% of the mass of absolutely dry pulp. The method allows to increase the degree of whiteness of the bleached pulp. 2 C.p. f-crystals, 1 table.

The invention relates to the field of pulp and can be IP is b bleaching with the use of potassium permanganate, ozone chlorine dioxide [1]. This sulphate pulp from eucalyptus exposed to potassium permanganate after the preliminary oxygen delignification in the rigidity of cellulose 7-8 Kapp scheme: potassium permanganate, ozone, chlorine dioxide. Consumption of chemicals (in % of the mass of absolutely dry pulp): ozone - 1,2; chlorine dioxide-1,0; potassium permanganate-2-4.

The disadvantage of this method is the high consumption of oxidants (more than 9% of active chlorine at 8 Kapp). In addition, the high cost of oxidants cause significant degradation of the cellulose fibers and the decrease of mechanical properties such as resistance to tearing, which will affect the quality of the paper.

There is a method of bleaching of sulphate pulp, taken as a prototype, including a two-stage processing of cellulose. On the first stage of the treatment is carried out with chlorine dioxide at a concentration of 2-10 mass% to the total absorption of ClO2pulp mass at a temperature of 50-100oC for 30-120 minutes, the consumption of 0,07-0,12% ClO2per unit Kappa, and the second stage bleached pulp concentration mass of 10-12% is treated with hydrogen peroxide at a pH of 9.5 to 10.5 in the presence of the stabilizer at a temperature of 70-100th pulp is separated from the solution and neutralize [2].

The disadvantage of this method is not sufficiently high whiteness within 80,0-85,9% at a concentration of pulp 12-20% (at a temperature of 70-80oC when handling hydrogen peroxide white is 75-80%), while the consumption of the reactants is higher than the proposed method.

The goal of this research is to develop a more effective method for bleaching pulp.

The result is achieved by introducing a stage of treatment with potassium permanganate in acidic medium, the redistribution of the costs of hydrogen peroxide and chlorine dioxide and bleaching of each of these reagents in two stages.

The proposed method differs from the known fact that before bleaching the pulp mass is treated with a solution of potassium permanganate (KMnO4in acidic medium at a pH of 1.2 and 2.1, and instead of the solution of a mineral acid, [1] proposed to use the acid reactor remains (CROS) generated as waste in the production of chlorine dioxide, which leads to significant savings on cost and improves the environmental performance of production in General, as these residues (CROS) fall into the waste water, and this allows to increase the degree of whiteness of the pulp to 85-88% at lower tempera on what best supports the diffusion of bleaching reagents, while the implementation of bleaching in four stages in sequential impact of nucleophilic and electrophilic reagents more efficiently than the degree be between bleaching with chlorine dioxide.

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 pre-processing unbleached pulp at a concentration of mass 2-7% solution of potassium permanganate in acidic medium (pH 1,2-2,1) with a flow rate of KMnO4no more than 1% of the mass of absolutely dry pulp at a molar ratio of acid: potassium permanganate (12,5-100):1, upper limit (100:1) is limited by the size of the degradation of cellulose (the reduction in the degree of polymerization of cellulose), and bottom (12,5: 1) the area of education manganese dioxide (IV), the acid used is sulfuric acid or acid reactor residues from the production of chlorine dioxide (KPO), the extract in solution at a temperature of 15-25oC until complete absorption of KMnO4pulp mass within 30-90 minutes, the separation from the solution, its neutralization and subsequent bleaching of pulp in four stages, with the first and third bleaching stage Pro,5) in the presence of the stabilizer, the treatment is carried out until complete absorption of the hydrogen peroxide at a temperature of 70-100oC for 120-240 minutes, the consumption of H2O2is 0.5 to 2.0% by weight of absolutely dry pulp, and as a stabilizer uses sodium silicate in the amount of 2.0 to 3.7% of the mass of absolutely dry pulp, bleached mass is separated from the solution and neutralize, second and fourth stages of bleaching carried out by treatment of bleached cellulose (concentration of 5-8 weight%) solution of chlorine dioxide (ClO2) until complete absorption of ClO2cellulose at a temperature of 50-70oC for 60-120 minutes, the consumption of ClO2is 1.1-1.3% of the mass of absolutely dry pulp is then bleached mass is separated from the solution and neutralize.

Example 1 (the prototype)

Unbleached sulphate pulp from hardwoods, rigidity 75 permanganate units, white 35%, degree of polymerization 1080 treated with chlorine dioxide at a flow rate of 1.3% (by weight of absolutely dry pulp) at a concentration of mass of 7% and a temperature of 70oC. After 2 h treatment the pulp is thoroughly washed until neutral and hold the second stage, treating the hydrogen peroxide with a flow rate of 1.5% (by weight absolutely shortrate suspension of cellulose 10%, duration 3 hours, the temperature 80oC. After the treatment the pulp is washed with water and dried. White pulp 73,0%, SP = 890, the yield of 98.5% (table, p. 1).

Example 2 (prototype)

Unbleached sulphate cellulose process of example 1 chlorine dioxide with a flow rate of 1.6% ClO2from the mass of absolutely dry pulp. The second stage processing is carried out with hydrogen peroxide at a rate of 2.5%. Other conditions are the same as in example 1. White pulp 75,9%, SP = 880, exit to 98.5% (table, p. 2).

Example 3

Unbleached sulphate 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 a suspension of cellulose 5%, room temperature within 45 minutes (pHk= 1,4). Then the pulp is thoroughly washed and sequentially treated with hydrogen peroxide and chlorine dioxide under the conditions specified in example 1. Redistribution of consumption of hydrogen peroxide and chlorine dioxide provides better diffusion of bleaching agents, bleaching is carried out in four mortar is ertai level of 0.5% H2O2, 0,8% NaOH, 2% Na2SiO3on the third and fifth stages of 0.6 and 0.7% ClO2respectively. After each stage the pulp is washed after the last - dried. The white pulp was 85.1%, SP = 780, yield 93% (table, p. 3).

Example 4

Unbleached sulphate pulp is subjected to preliminary treatment with potassium permanganate in sulfuric acid medium with a flow rate of 0.8% KMnO4from the mass of absolutely dry pulp at a molar ratio of sulfuric acid/potassium permanganate 50: 1, mode and cost of reagents analogous to example 2 (RNA = 1,8). The white pulp is 86,0%, SP = 815, the yield of 93% (table, p. 4).

Example 5

Unbleached sulphate pulp is subjected to preliminary treatment with potassium permanganate according to example 2, pHk = 1,2 (used sulfuric acid contained in the acid reactor residues of chlorine dioxide production-KPO). The molar ratio of sulfuric acid/potassium permanganate 100:1. Then the pulp is separated from the solution and washed with water until neutral and subjected to a four-speed processing reagents in example 2. The white pulp of 88.3%, SP = 770, the yield of 93.5% (table, p. 5).

Example 6

Unbleached sulphate pulp is subjected to processing the reagents in the examples is from the solution and washed with water until neutral. Post-treatment bleaching reagents is carried out according to example 2. White pulp 86,0%, SP = 780, the yield of 92.5% (table, p. 6).

Example 7

Unbleached sulphate pulp hardness 95 permanganate units subjected to preliminary treatment with potassium permanganate with a flow rate of 0.4% by weight of absolutely dry pulp at a molar ratio of sulfuric acid/potassium permanganate, equal to 12: 1. Then the pulp is thoroughly washed and processed bleaching reagents in example 2. White pulp 83%, SP = 800, yield 97% (table, p. 7).

Example 8

Unbleached sulphate pulp hardness 95 permanganate units subjected to preliminary treatment with potassium permanganate in sulfuric acid medium with a flow rate of 2% KMnO4from the mass of absolutely dry pulp (the ratio of sulfuric acid/potassium permanganate 100:1) in example 1, pHk = 1,3. Then the pulp is separated from the solution and washed with water until neutral. The washed pulp is subjected to treatment with hydrogen peroxide with a flow rate of 1.5% of the mass of absolutely dry pulp and the treatment with chlorine dioxide (total flow rate is 1.1%) with intermediate step be. Modes of ongoing hotblock correspond to example 1. After the treatment the pulp is AI.

1. Igt. Pulp Bleach. Conf., Vancouver, June 15, 1994: Pousters.-Monreal, 1994. -C. 141-145.- Kojim Transformer-Coupled Amplifier. Cjorine free bleaching of KR wich permanganatea.

2. RF patent N 2075566. Method of bleaching of sulphate pulp. Publ. BI N 8.

1. Method of bleaching pulp, comprising the step of processing the pulp with a solution of chlorine dioxide and hydrogen peroxide in the presence of the stabilizer at a pH of 9.5 - 10.5 to full absorption of reagents, Department of bleached pulp from the solution and its neutralization, wherein the unbleached pulp is pretreated with a solution of potassium permanganate in acidic medium at a pH of 1.2 and 2.1, which uses sulfuric acid or acid reactor residues from the production of chlorine dioxide from the consumption of potassium permanganate is not more than 1% of the mass of absolutely dry pulp, soak in the solution at a temperature of 15 - 25oC until complete absorption of potassium permanganate pulp mass, and after separation of the mass from the solution and subjected to neutralize its four-stage bleaching, and the first and the third stage is carried out by treatment with a solution of hydrogen peroxide in an alkaline medium at a temperature of 70 - 100oC at a flow rate of hydrogen peroxide of 1.5 - 2.0% by weight of absolutely dry pulp, and the second and fourth stages bleached Celera 1,1 - 1.3% of the mass of absolutely dry pulp.

2. The method according to p. 1, characterized in that when the molar ratio (12.5 to 100):1, respectively.

3. The method according to p. 1, characterized in that the treatment with potassium permanganate lead at a concentration of weight 2 - 7% for 30 - 90 minutes

 

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