SU478904A1 - The method of regeneration of the spent solution from the delignification of cellulose-containing raw materials, such as wood, chlorine-containing reagents - Google Patents

Description

one

The invention relates to the field of regeneration of chemicals from spent liquors from pulp production, in particular from the production of pulp, involving the use of chlorine-containing compounds as a delignifying reagent.

There is a known method for the regeneration of waste solutions from cellulose delignification with chlorine dioxide, which means that the spent solution is concentrated and discharged, the products obtained by burning are subjected to electrolysis; Chlorine-containing chemicals and alkaline compounds formed during electrolysis are returned to the cooking solution preparation stage.

The known method cannot be used for the regeneration of the spent solution from delignification using the chlorate-peroxide method, since during concentration (evaporation) of these liquors the residual chlorate contained in them and the organic substances that have gone into solution form an explosive mixture.

In order to allow the waste solution to be regenerated from delignification by the chloro-T1 reox method, a method has been proposed, according to which the waste solution is pretreated first with sulfur dioxide and then with calcium salt, taken in an amount of 1.0-1.5%.

The resulting precipitate is separated from the solution, which is neutralized to a pH of 5-6, and one stripped off or uncooked neutralized solution is subjected to processing by known methods.

The method is carried out as follows.

The original spent liquor from the chlorate-peroxide cooking method, containing residual chlorate and other oxychloride compounds, is treated with sulfur dioxide in an amount of 1.0-1.5% of the weight of absolutely dry wood, and then calcium salts, such as calcium chloride in the amount of 1 , 0-1,5% of the weight of absolutely dry wood. The precipitate formed is removed, and sodium hydroxide is added to the clarified solution during its acidic reaction, and in the case of an alkaline reaction, hydrochloric acid. The solutions are introduced in such an amount that the pH of the medium is 5-6.

Next, the neutralized solution is subjected to burning by known methods, for example by wet burning or by evaporation and burning one stripped off of the concentrated liquor. The chlorides formed by the burning of liquor are used to produce sodium chlorate, caustic soda, chlorine and hydrogen by electrolysis of the chloride solution. Hydrochloric acid is obtained from chlorine and hydrogen, and excess hydrogen is used as an additional fuel during the combustion of one stripped off liquor.

The proposed method for the regeneration of chemicals from liquors from the production of cellulose according to the chlorate-peroxide method is carried out according to the scheme shown in the drawing. The liquor from apparatus 1 at a temperature of 70-63 ° C from the chlorate delignification step from apparatus 1, containing the oxidation products of lignin and wood carbohydrates — organic acids, as well as residual chlorate, hydrochloric acid, and the products of chlorate reduction — chlorine dioxide, elemental chlorine, and chloride sodium, is separated from hemicellulose and sent to tank 2, where sulfur dioxide or its aqueous solution is supplied. When adding sulfur dioxide, the following reactions occur, leading to the formation of a liquor

NaClOa + SSOa + SH.O NaCl-f 3HjSO4

2C1O2 + 5SO2 + 6H2O- 2HC1 + 5H2SO4

Cl3 + SO2 + 2H, O 2HCl-fH, SO,

In the result of the reactions, elemental chlorine and oxychloro compounds are converted to chlorides (NaCl and HCl). Lye, containing chlorides, organic acids and acid, is fed to reservoir 3, where sulfuric acid is precipitated by adding calcium salts. In particular, chloride can be used for this purpose. Alcium, which is a waste of soda production. When this happens the reaction

CaCla + H2SO4 CaSO4 + 2HCl

CaSO4 is sent to the dump, and the obtained liquor, containing chlorides, organic acids, residual and newly formed hydrochloric acid, is sent to the collection of 4 liquors, there likewise serves liquor from the second delignification stage from tank 5, containing residual hydrogen peroxide, caustic soda and sodium salts of organic acids.

In the collection of 4 liquors, the liquor and washings from the 1st and the 5th stages of the chlorate-peroxide pulp production method are shifted. When mixing liquors and washings, the following reactions take place between hydrochloric acid from liquors of the 1st stage and caustic soda and sodium salts of organic acids from the liquors of the nth stage: HCl + NaOH - NaCl + HjO

HCl + R-COONa- NaCl + R-COOH

5-hydrochloric acid is added thereto to create a pH in an alkaline reaction or an alkali is added in an acid reaction.

As a result of the above operations, the mixture of liquors and wash water at pH 5-6 will contain sodium chloride (NaCl), free organic acids (R-COOH), a small amount of sodium salts of organic acids (R-COONa).

Organic acids from the liquor prepared in this way are disposed of by any known method (isolation of individual organic acids, biochemical processing, etc.), or they come together with lye for combustion in unit 6, improving the heat balance of the process. Burning can be carried out by chains.

The liquor is subjected to "wet incineration according to the 10th Zimmermann method with the supply of oxygen and high pressure. When “wet burning, all organic acids are burned. The resulting solution contains sodium chloride and a small amount of 15% sodium carbonate. PacTiBOp is purified from impurities (calcium ions, magnesium, SO4, CO2) in the purification apparatus 7 using conventional methods. Then the purified solution is used for electrolysis to obtain sodium chlorate, sodium hydroxide, chlorine and hydrogen in electrolyzers 8. Hydrochloric acid is obtained from chlorine and hydrogen by a known method.

Or liquor is evaporated and burned in a furnace (fluidized bed or any other unit 6. 5 Organic liquor is used as a source of heat. Excess hydrogen is used as an additional fuel. If necessary, heat is compensated for the missing heat by burning mazut, natural gas 0, etc.

After the liquor is burned, the mineral residue is dissolved as in the first case. The solution is purified from impurities in the purification apparatus 7 and transferred to electrolysis 5 electrolytic cells 8, producing sodium chlorate, caustic soda, chlorine and hydrogen using conventional methods.

Example. 100 g of aspen shavings (in terms of absolutely dry) are treated with 0 300 ml of a solution of NaClOs and HC1 with a ratio of 1; 1.7 (for chlorine). The amount of chemicals in the solution of NaCIOs is 23.8 g and HC1 13.9 g.

After delignification, liquor was collected.

96.5% of the originally specified amount. At the same time the consumption of fresh water per 100 g

wood was 137 ml. Total received

liquor and wash water, 430 ml.

Spent from the 1st stage of processing wood liquor contains, g: 0NaClOs0,6

HC10.35

SUG0.025

Cla0,007

NaCl13,1

5R-COOH1,315

(in terms of

on vinegar

acid).

0 Organic content - 35 g (excluding the formation of volatile products). Treatment of liquor with sulfur dioxide. Below is the amount of SO2. The total consumption of 1.145 g spent on the reaction with 5 other components, g:

SOs € NaClOs1,08

with SJ0.059

with CH0.0062

When this is received, g:

H2SO41.74

NaCl0.33

HC10.021

Sulfuric acid binding. The consumption of CaCl2 for H2SO4 binding was 1.94 g. 2.4 g of CaSO4 were obtained.

Received NaOH in the form of salts of organic acids 1.1 g, in terms of Na. Binding of 1.64 g of HC1 requires 1.032 g of sodium taken from the salts of organic acids. All the alkali requirement to neutralize HC1 is covered by the salts of organic acids, which came with the liquor from the P-th stage of delignification.

The solution obtained after the displacement of the caustic sulphates, which arrived with a liquor from the P-th stage of delignification, contains, g:

NaCl15,1

HC11.5

R-COOH2,0

(in terms of

UNHCR) R-COONa0.05

(in terms of CHsCOONa).

Lye can be further regenerated in two ways:

a) Wet burning with getting, g: NaCl15,0

NaaCOs0,1

Sodium chloride can be used for electrolysis by conventional methods to produce sodium chlorate, sodium hydroxide, chlorine, and hydrogen. From chlorine and hydrogen, an acid is obtained in a manner known per se.

b) The evaporation and burning in the furnace of the fluidized bed with the subsequent production of the same products as in the case of wet burning.

Thus, all oxychloride compounds and chlorine are converted to sodium chloride. The regeneration system is closed. Losses of chemicals can be compensated by table salt.

Subject invention

The method of regeneration of the spent solution from the delignification of cellulosic raw materials, such as wood, with chlorine-containing reagents by burning the spent solution and electrolysis of the products obtained by burning, characterized in that, in order to allow the waste solution to be regenerated from the delignification using the chlorate-peroxide method, the spent solution is pretreated first with sulfur dioxide and then calcium salt, taken in the amount of 1.0-1.5% by weight of absolutely dry wood s,

the resulting precipitate is separated from the solution, which is neutralized to pH, and one stripped off or the non-evaporated neutralized solution is subjected to processing by known methods.

CaCi.