RU2687986C1 - Method of regenerating sodium salts from black liquor solution during production of sulphate cellulose - Google Patents

Abstract

FIELD: pulp industry.

SUBSTANCE: invention relates to the production of cellulose. Task is achieved by neutralization of the solution after separation of organic compounds using sodium hydroxide directed from the step of absorbing an alkaline solution, and after the second evaporation step, potassium hydroxide is added at a ratio of NaOH:KOH 1:4, to obtain an end product of potassium sulphate, wherein the alkaline solution is absorbed by hydrogen sulphide fed from the black liquor acidification step to obtain white liquor with sulphidity of 55–85 %.

EFFECT: achieved technical result of the proposed invention consists in production of an additional product (potassium sulphate) with reduction of corrosive activity of the solution by introduction of sodium hydroxide, while improving the pulping process and the quality of cellulose by increasing sulphidity of white liquor of 55–85 %, thereby diversifying production while maintaining quality of pulping.

1 cl, 3 ex

Description

The invention relates to the production of pulp and can be used for the regeneration of sodium salts from a solution of black liquor in the production of sulphate pulp.

The known method of acid-base processing of black liquor sulphate pulp production / Patent № 2617569, IPC D21C 11/00, publ. 25.04.2017, Kazakov VG, Lukanin P.V., Smirnova O.S. /.

The essence of the method lies in the fact that the sulphate solution obtained after extraction of organic compounds in the form of lignin from black liquor, acidifying the solution with sulfuric acid, is treated with alkali metal salts, for example, KOH to PH≥7 and evaporated with crystallization of salts to 100-500 g of water per 100 g of dry salts, while the mother liquor of the salts after separation of the solid and liquid phases and adjusting the solution, feeding it to the absorption of hydrogen sulfide, is sent to cooking process chips, with a sulfidity of 30%, and the solid product after it is separated I removed from the drying process as a commercial product. The method allows, while maintaining the quality of the final product, to simplify the hardware and technological scheme of the regeneration of alkali from black liquor, to improve the environmental safety of the processing of black liquor, to diversify production.

The disadvantages of the described method include:

- with the introduction to neutralize caustic sodium alkali as a result of evaporation, solid sodium sulfate is obtained, which must be regenerated for further use, having low consumer demand;

- the introduction of KOH does not affect the quality of the final product, but increases the corrosivity of the solution, and the high consumption of expensive reagent and the increase in material flows leads to large capital and operating costs;

- an alkaline solution, which, after adjustment, adds to the cooking of process chips, has a low% sulphidity - 30%, this affects the delignification process and increases the cooking time to a certain degree of penetration.

The technical task is to eliminate these drawbacks, namely, obtaining additional product (potassium sulfate) while reducing the corrosivity of the solution by introducing sodium hydroxide, while improving the cooking process and the quality of cellulose by increasing the sulfidity of white liquor 55-85%, thereby diversifying production while maintaining the quality of pulping.

The task is achieved by the fact that in the method of production of cellulose, including acidification of black liquor with sulfuric acid with the release of organic compounds containing lignin, followed by neutralization of the resulting solution with alkali, evaporation of the solution in two steps with obtaining the solid phase of the finished product, potassium sulfate and alkaline solution, which is absorbed by hydrogen sulfide to produce white liquor, sent for cooking process chips, characterized in that the neutralization of the solution after separation of the organization Sodium compounds are carried out with sodium hydroxide, sent from the alkaline solution absorption stage, and after the second evaporation stage, potassium hydroxide is introduced at a NaOH: KOH ratio of 1: 4, to obtain the finished potassium sulfate product, and the alkaline solution is absorbed with hydrogen sulphide fed from the black liquor acidification step to white liquor with a sulfidity of 55-85%.

The essential difference of the claimed method is the inextricable set of actions set forth in the claims, which allows to achieve a technical result consisting in obtaining an additional product (potassium sulfate) while reducing the corrosivity of the solution by introducing sodium hydroxide, while improving the quality of pulping white liquor sulphidity 55-85%, thereby diversifying production while maintaining the quality of pulping.

The resulting solid precipitate is treated with a solution of potassium hydroxide. As a result of the exchange reaction between sodium sulfate and potassium alkali solution according to the equation:

(Na _m K _n ) SO ₄ + mKOH → K ₂ SO ₄ + mNaOH

two products are formed: solid potassium sulfate and a solution of sodium alkali. When processing solid sediment by converting it with a KOH solution, the resulting sodium alkali after additional adjustments is returned to the process as white liquor for cooking process chips. The solid product is liquid and can be used in the form of potassium sulfate fertilizer.

Examples of the method:

Example 1

The mother solution of lignin after acidification with sulfuric acid and neutralization with sodium hydroxide 122 g / dm ^{3 is} evaporated to a weight ratio of a suspension of 500 g of water per 100 g of dry salts. The sodium sulfate precipitate is filtered and treated in a continuous mode using an auto-dispenser with 50% potassium hydroxide solution, in a ratio of NaOH: KOH 1: 4, from the condition for obtaining a molar fraction of potassium alkali in suspension 60%. Conversion time - 60 minutes. Then the solution is filtered, 82% K ₂ SO ₄ (57% K ₂ O) passes into the precipitate of potassium sulfate. The filtrate, which is a caustic alkali solution, is fed to an absorber, into which hydrogen sulfide enters from the stage of acidification of black liquor with sulfuric acid. The absorption is carried out in 2 steps, the temperature of black liquor is 30 ° C, the concentration of caustic alkali is 45%, as a result of which a solution of white liquor with a sulphidity of 85% is obtained, which is fed to the cooking of process chips.

Achieved effect - obtaining a solution of white liquor with a sulphidity of 85%. Production of potassium sulfate 57% in K ₂ O, which meets the high requirements for potassium sulfate as a fertilizer. Thus, in addition to the implementation of a closed system for the processing of black liquor, the diversification of production with the receipt of additional commercial products is also carried out.

Example 2

The mother solution of lignin after acidification with sulfuric acid and neutralization with sodium hydroxide 183 g / dm ^{3 is} evaporated to a weight ratio of a suspension of 300 g of water per 100 g of dry salts, then the solution is filtered and the solid precipitate of sodium sulfate is treated in a continuous mode using an autosampler (50%) a solution of potassium hydroxide, in a ratio of NaOH: KOH 1: 4 of the conditions for obtaining a molar fraction of potassium alkali in suspension 60%. Conversion time - 43 minutes. Then the solution is filtered. 82% K ₂ SO ₄ (54% K ₂ O) goes into the precipitate of potassium sulfate. The filtrate, which is a caustic alkali solution, is fed to an absorber, into which hydrogen sulfide enters from the stage of acidification of black liquor with sulfuric acid. Absorption is carried out in 1 stage, the temperature of black liquor is 10 ° C, the concentration of caustic alkali is 45%, as a result of which a solution of white liquor with a sulfide content of 80% is obtained, which is used for cooking process chips.

Achieved effect - Preparation of a solution of white liquor with a sulfide content of 80%. Production of potassium sulfate 54% in K ₂ O, which meets the requirements for potassium sulfate as a high-quality fertilizer.

This reduces the time of conversion and increases the filtration performance in comparison with the conditions of example 1. The number of absorber stages is also reduced.

Example 3

The mother solution of lignin after acidification with sulfuric acid and neutralization with sodium hydroxide 146 g / dm ^{3 is} evaporated to a weight ratio of the suspension 500 g of water per 100 g of dry salts, then the solution is filtered, and the solid residue of sodium sulfate is treated in a continuous mode using an autosampler with a 50% solution potassium hydroxide, in a ratio of NaOH: KOH 1: 4 of the conditions for obtaining a molar fraction of potassium alkali in suspension 43%. Conversion time - 60 minutes. Then the solution is filtered, 79% of K ₂ SO ₄ (55% K ₂ O) passes into the precipitate of potassium sulfate. The filtrate, which is a caustic alkali solution, is fed to an absorber, into which hydrogen sulfide enters from the stage of acidification of black liquor with sulfuric acid. The absorption is carried out in 2 steps, the concentration of caustic alkali is 40%, as a result of which a solution of white liquor with a sulfide content of 55% is obtained, which is fed to the cooking of process chips.

Achieved effect - obtaining a solution of white liquor with a sulfidity of 55%. Production of potassium sulfate (55%) in K ₂ O, which meets the requirements for potassium sulfate as a fertilizer. A further decrease in the molar fraction of potassium alkali in the suspension leads to a significant decrease in the yield of potassium sulfate at K ₂ O and ceases to meet the requirements for potassium sulfate as a fertilizer.

Thus, a set of actions allows to increase the sulfidity of white liquor, which is a positive characteristic of the sulphate pulp cooking process, as it reduces the cooking time to a certain degree of penetration, facilitates the delignification process, as well as the yield of cellulose, and also allows the cycle to be closed and the production is diversified. The implementation of the proposed method allows you to:

- regenerate sodium alkali by transferring sodium sulphate to a solid precipitate followed by treatment with a solution of potassium sulphate.

At the same time, sodium chloride alkali and additionally fertilizing potassium sulfate are obtained. Such a diversification of the technological process will significantly reduce the cost of producing pulp.

- the technological process of evaporation is carried out without entering into it a corrosive additive in the solution in the form of potassium alkali, which allows the manufacture of evaporators from ordinary carbon steel;

- the regeneration of sodium alkali is carried out in the hydrochemical process at low capital and energy costs. In the proposed process, there is no need for soda recovery boilers, where the process of obtaining sodium alkali is associated with obtaining molten alkali and subsequent technological processes to obtain green liquor from it, processing it using rotary kilns and entering lime into the process. In addition, these technological redistribution of energy-intensive, characterized by high capital investments and environmental hazards of production.

Claims (1)

The method of regeneration of sodium salts from a solution of black liquor in the production of sulphate pulp, including acidification of black liquor with sulfuric acid with the release of organic compounds containing lignin, followed by neutralization of the resulting solution with alkali, evaporation of the solution in two steps to obtain a solid phase of the finished product, potassium sulfate and alkali solution, which is absorbed by hydrogen sulfide to produce white liquor, directed to the cooking of technological chips, characterized in that the neutralization of After extraction of organic compounds, sodium hydroxide is sent from the alkaline solution absorption stage, and after the second evaporation stage, potassium hydroxide is introduced at a NaOH: KOH ratio of 1: 4, to obtain the finished potassium sulfate product, and the alkaline solution is absorbed by hydrogen sulfide supplied from the acidification stage black liquor to produce white liquor with a sulfidity of 55-85%.