Method of bleaching hardwood sulphate pulp

 

(57) Abstract:

The essence of the invention: method of bleaching hardwood sulphate pulp, including the processing of the original pulp suspension in mineral acid at 70 to 95C and a pH of 1.2 to 2.5, the delignification hydrogen peroxide with the addition of sodium hydroxide and sodium silicate at a flow rate of hydrogen peroxide is 0.5 to 2.5%, of sodium hydroxide 0.5 to 1.2% of sodium silicate 2 - 5% of the mass of absolutely dry pulp at a pH of 9.5 - 10.5 and later washing the mass with water, before delignification hydrogen peroxide pulp suspension pre-treated with an alkaline-based solution of sodium hydroxide when the consumption of 2 - 4% in% NaOH by weight of absolutely dry pulp for 1 , 1 for 2.0 h at pHKon10-11, followed by washing with water until pH 7 - 8. When this process is carried out at a ratio of sodium hydroxide at the stages of pre-treatment and delignification and hydrogen peroxide, respectively, from 1 : 0.5 to 4 0.5 to. As the alkaline solution using sodium hydroxide or a mixture of spent solution from stage delignification hydrogen peroxide; as a mineral acid using sulfuric or hydrochloric acid or a mixture thereof with waste acid in cootes is used to improve ergonomy historical properties of pulp and paper respectively.

There is a method of bleaching wood pulp, comprising processing the mass of acid and subsequent treatment with hydrogen peroxide in alkaline medium [1].

As the acid used aminocarbonyl acid, and conditions of peroxide bleaching: hydrogen peroxide concentration of 1.5-2.0%, NaOH concentration of 1.5-2.0%, temperature 50 to 75aboutC. the Time for bleaching of hydrogen peroxide 35-40 minutes

The closest analogue of the invention is a method of bleaching hardwood sulphate pulp, including the processing of the original pulp suspension in mineral acid at 70-95aboutC and a pH of 1.2 to 2.5, the delignification hydrogen peroxide with the addition of sodium hydroxide and sodium silicate at a flow rate of hydrogen peroxide is 0.5 to 2.5%, sodium hydroxide 0.5 to 1.2% of sodium silicate 2-5% of the mass of absolutely dry pulp at a pH of 9.5-10.5 and later washing the mass with water [2].

As a mineral acid using hydrochloric acid.

The known method does not allow to achieve a high degree of bleaching of hardwood pulp.

New technical result of the proposed method is the achievement of a higher rate of white pulp.

This technical result reached is Uspenie mineral acid at 70-95aboutC and a pH of 1.2 to 2.5, the delignification hydrogen peroxide with the addition of sodium hydroxide and sodium silicate at a flow rate of hydrogen peroxide is 0.5 to 2.5%, of sodium hydroxide 0.5 to 1.2% of sodium silicate 2-5% of the mass of absolutely dry pulp at a pH of 9.5-10.5 and later washing the mass with water, before delignification hydrogen peroxide pulp suspension pre-treated with an alkaline-based solution of sodium hydroxide when the flow rate of 2-4% per unit Paon by weight.with. pulp for 1,2-2,0 h at pHKon10-11, followed by washing with water until pH 7-8, the process is carried out at a ratio of sodium hydroxide at the stages of pre-treatment and delignification and hydrogen peroxide, respectively, from 1: 0.5 to 4 0.5 to. As the mineral acid used fresh sulfuric or fresh hydrochloric acid or their mixtures with waste acid, and as the alkaline solution using sodium hydroxide or a mixture of spent solution from stage delignification hydrogen peroxide. If the mineral acid in the processing phase, use a mixture of fresh acid with waste, the mixture contains, respectively, each component of 1:1.

Carrying out the alkali treatment after the acid. the thus, the invention meets the requirement of novelty.

Alkaline processing hardwood sulphate pulp (aspen+birch) is performed for removal of acidic phenolic components of the residual lignin and acid products of the decomposition of hemicellulose. These acidic products prevent the delignification hydrogen peroxide.

Found that at pH 10 0,5 - peroxide reagent solution of N2ABOUT2stabilized silicate, is more effective for deciduous SFA cellulose. So for alkaline extraction of all acid components deciduous SFA cellulose requires a relatively greater amount of hydroxide PA (not less than 2%).

Thus, the increase in white hardwood sulphate pulp resulting from the introduction of the scheme bleaching after acid treatment and alkali treatment followed peroxide delignification due to the removal of fragments of acid degradation of lignin and carbohydrates, which include significant amounts of highly acidic (RK>9) phenolic structures capable of binding sodium hydroxide, as well as the degradation products polysaccharide complex that can interact with peroxide vodorazdelny effect is particularly noticeable when the consumption of sodium hydroxide (2-4% Paon) in stage peroxide delignification, so for hardwood pulp optimal regime is the following sequence: acid treatment, alkaline treatment - peroxide delignification. The best results in the bleaching of hardwood sulphate pulp is achieved when the ratio Paon ratio of the alkali treatment and peroxide delignification of 1:0.5 to 4 0.5 to.

The growth of white in the proposed method is 2-8% of the white pulp of the prototype. The ratio of consumption Paon is due on the one hand the regime peroxide delignification (optimal pH value), and on the other side - threshold symptoms positive effect of increased whiteness. When the flow Paon on stage alkaline processing less than 2% increase in whiteness from the introduction of this suspension is less than 2%, and at a rate less than 1% Paon - effect is absent.

Thus, the proposed method satisfies the requirement of "inventive step".

P R I m e R 1 (the proposed method). Method of bleaching hardwood sulphate pulp is as follows. A portion of 4.0 g of absolutely dry hardwood pulp with whiteness 26%, disintegrate in water, wring out, transferred into a flask and treated with hydrochloric acid,2, and pHKon1,4. Then the mass is washed with water. After this, the pulp suspension is treated with an alkaline solution at 80aboutC for 2 hours and the consumption Paon is 2% of A. with. pulp and pHKon11,0. After the treatment the pulp is washed with water on a glass filter and delignification hydrogen peroxide at a rate of 2.5% N2ABOUT2, 1,0% Paon, 5% liquid glass at 95aboutC and pHbeg/pHKon9,5, duration of 3 hours the ratio of the number Paon on stage to be the number Paon used at the stage of delignification is 1:0,5.

After bleaching, the pulp is washed reached white 76%.

Subsequent dabelko l2allows you to achieve white 89,8%.

Indicators of quality bleached pulp are shown in table.

P R I m e R s 2-6 carried out analogously to example 1. Operation parameters of the method, as well as indicators of quality bleached pulp are shown in table.

From the table it is seen that the proposed method can improve the whiteness of the pulp. Comparative experiments on the proposed method and the method prototype carried out under comparable conditions using the same source listerellosis suspension of mineral acid at 70 - 95oC and a pH of 1.2 to 2.5, the delignification hydrogen peroxide with the addition of sodium hydroxide and sodium silicate at a flow rate of hydrogen peroxide is 0.5 to 2.5%, of sodium hydroxide 0.5 to 1.2% of sodium silicate 2 - 5% of the mass of absolutely dry pulp at a pH of 9.5 - 10.5 and later washing the mass with water, characterized in that before delignification hydrogen peroxide pulp suspension pre-treated with an alkaline-based solution of sodium hydroxide in its consumption of 2% to 4% in% NaOH by weight of absolutely dry pulp for 1,1 - 2,0 h at pHKon10 - 11, followed by washing with water until pH 7 - 8, while the process is conducted at a ratio of sodium hydroxide at the stages of pre-treatment and delignification and hydrogen peroxide, respectively, 1 : 0,5 - 4 : 0,5.

2. The method according to p. 1, characterized in that the alkaline solution using sodium hydroxide or a mixture of spent solution from stage delignification hydrogen peroxide.

3. The method according to p. 1, characterized in that the mineral acid using sulfuric or hydrochloric acid.

4. The method according to PP.1 and 3, characterized in that use fresh mineral acid or a mixture thereof with waste acid in the ratio of the

 

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2 tbl, 18 ex

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1 tbl, 9 ex

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1 tbl, 17 ex

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EFFECT: increased whiteness and strength characteristics of cellulose and improved environmental safety of bleaching process.

2 cl, 1 tbl

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2 tbl, 11 ex

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42 cl, 2 dwg, 1 ex

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7 cl, 2 dwg

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1 tbl, 6 ex

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1 tbl, 9 ex

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1 tbl, 17 ex

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2 tbl, 11 ex

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2 cl, 1 tbl

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2 cl, 17 ex, 16 tbl

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EFFECT: improved strength of wood pulp and reduction of energy consumed for grinding.

12 cl, 1 dwg, 1 ex

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