RU2755186C1 - Method for producing caustic soda - Google Patents

Abstract

FIELD: chemical industry.

SUBSTANCE: invention relates to the technology of production of inorganic substances, in particular, the chemical production of caustic soda (NaOH) as a result of the conversion of sodium sulfate. The method for producing caustic soda with the participation of burnt lime and sodium bicarbonate includes mixing solid components in accordance with a stoichiometric ratio of 1:1 and a step-by-step water supply in portions of 10% of the mass of the solid mixture while stirring for 5-7 minutes at a temperature of 35-40°C. New portions of water are added until a pulp containing 60-70% liquid is obtained. The phases are separated by centrifugation and the cake is washed to obtain an alkali solution of 600 g/dm³.

EFFECT: utilization of the by-product accumulated in metallurgical industries, sodium sulfate is ensured and a reduction in energy consumption for dehydration of alkaline solutions is achieved.

1 cl, 1 ex

Description

The invention relates to a technology for the production of inorganic substances, in particular the chemical production of caustic soda (NaOH) as a result of the conversion of sodium sulfate.

Known methods for producing caustic soda (NaOH) by electrochemical and chemical methods.

The electrochemical method is based on the electrolysis of aqueous solutions of sodium chloride with a dissociation reaction [Yakimenko L.M. Production of chlorine, caustic soda and inorganic chlorine products M .: Chemistry, 1974, - 600s, (from 193-270)]:

When direct current is passed through a system using indifferent electrodes: the negatively polarized cathode interacts with a depolarizer, which can be attributed to hydrogen ions (H *). Depolarization of the cathode by hydrogen ions leads to the formation of atomic and molecular hydrogen:

In turn, the chlorine ion acts as a depolarizer at the positively polarized anode. After the discharge, atomic and, then, molecular chlorine (gas) is formed:

As a result, the aqueous solution accumulates alkali - NaOH - the target product. After steaming off the water, dry caustic soda is obtained.

The disadvantages of this method include:

- obtaining gaseous products: hydrogen and chlorine, which must be separated and disposed of;

- low concentration of alkali in the spent electrolyte (up to 120 g / dm ³ ) and, accordingly, significant costs for water steaming;

- high energy consumption.

Known ferritic method for the production of alkali, based on sintering soda ash with iron oxide (Fe ₂ O ₃ ) to obtain sodium ferrite [Shokin IN, Krasheninnikov SA. Soda technology M.: Chemistry 1975. - 288 s, (p. 205-244)]:

An important property of the resulting compound is the possibility of its decomposition in water:

After decomposition, a precipitate of iron oxide is obtained, which is returned for sintering, and a sodium hydroxide solution, which is sent for dehydration. The disadvantage of this method is the significant costs of Na ₂ CO ₃ , characterized by high cost.

Closest to the claimed method is the production of alkali [NS. Akhmetov. Inorganic chemistry. M .: Higher school, 1975, p. 591-592], according to which the interaction of soda ash (Na2C03) with slaked lime is carried out according to the scheme:

The process is called causticization. The main disadvantage is the use of soda ash and significant energy consumption for dehydration of the alkaline solution.

The purpose of the claimed is to reduce the total cost of obtaining an alkaline brine with a NaOH content of up to 600 g / dm ³ using the conversion reaction of sodium sulfate accumulated in metallurgical technologies for processing sulfide raw materials.

This goal is achieved by the fact that the method for producing caustic soda is realized with the participation of burnt lime, and sodium bicarbonate (NaHCO ₃ ) is used as a causticizing reagent, when solid components are mixed in accordance with a stoichiometric ratio of 1: 1 (56 g CaO and 84 g NaHCO ₃ ) and a stepwise supply of water (10% of the mass of the solid mixture) for 5-7 minutes at a temperature of 35-40 ° C with the addition of a new portion of water until a slurry containing 60-70% liquid is obtained, followed by filtration and washing of the cake to obtain a solution alkali containing 600 g / dm ³ NaOH.

For the formation of sodium bicarbonate, it is assumed the use of sodium sulfate. The chemistry of the process of formation of sodium bicarbonate (conversion of sodium sulfate) [Te-Pan-Go, Soda production., M. - L., GNTIHL, 1948, 424 p.]:

In this system, a sparingly soluble compound is NaHCO ₃ (9.6 g of salt dissolves in 100 g of water in water at 20 ° C). Taking into account the complex salt background of solutions, the value of the solubility of NaHCO ₃ decreases to 2.5-3 g per 100 g of water. After separation of the NaHCO ₃ precipitate from the solution, it goes to causticization:

As a result of reaction (10), up to 600 g / dm ³ NaOH accumulates in the solution. This solution is sent for dehydration to obtain dry (fused) NaOH, as well as calcium carbonate precipitate, which is fed for roasting to regenerate lime (CaO) and carbon dioxide involved in carbonization.

During causticization, solid calcined lime and sodium bicarbonate are mixed with the supply of water in small portions (10% of the solid mass) with active stirring, ensuring the operating temperature of the process is 35-40 ° C. After 5-7 minutes of twisting, add the specified amount of water again. The operation is repeated 5-6 times, resulting in a pulp containing 60-70% liquid. The phases are separated by centrifugation.

Example

When mixing 1000 g of burnt lime containing 90% CaO and a precipitate of NaHCO ₃ in an amount of 1580 g (sodium bicarbonate content is 85%), 642 g of alkali and 1647.8 g (including solid impurities) of calcium carbonate were obtained. After leaching in water, a solution was obtained containing 620 g / dm ³ NaOH. The total extraction of alkali from the theoretically possible was 96.1%.

The leaching cake is mainly represented by calcium carbonate returned for drying and thermal decomposition (roasting) to produce carbon dioxide, which is used in the treatment of ammonium sulfate solutions to obtain NaHCO ₃ .

The achieved technical result from the implementation of this method is as follows:

- utilization of a by-product accumulated in metallurgical production - sodium sulfate;

- sodium bicarbonate is effectively used to obtain a product - caustic soda;

- it is possible to turnover the middlings of the main causticization reaction - calcium carbonate - with the production of calcium oxide and carbon dioxide, which are returned, respectively, for causticization (calcium oxide) and the production of bicarbonate (СО ₂ );

- there is a decrease in energy consumption during dehydration of alkaline solutions containing a greater amount of alkali in comparison with the prototype.

Claims (1)

A method of producing caustic soda with the participation of burnt lime, characterized in that sodium bicarbonate is used as a reagent for causticizing calcium oxide, with mixing of solid components in accordance with a stoichiometric ratio of 1: 1 and a stepwise supply of water in portions of 10% by weight of the solid mixture with stirring the systems for 5-7 minutes at a temperature of 35-40 ° C with the addition of a new portion of water to obtain a slurry containing 60-70% liquid, separate the phases by centrifugation and wash the cake to obtain an alkali solution of 600 g / dm ³ .