Method of producing brine for electrolysis

FIELD: chemistry.

SUBSTANCE: present invention can be used for obtaining aqueous saturated solutions of alkali metal halides, which are used in the production of chlorine and alkali from electrolysis. The method of producing aqueous saturated brine of alkali metal halides involves underground dissolving of salt deposits with simultaneous purification of brine in the brine production well. Purification from toxic impurities - calcium and magnesium compounds is done using spent brine of a halide of the corresponding metal as the solvent, obtained from an electrolysis unit with pH 9-12. The brine from the well is then purified from calcium and magnesium compounds.

EFFECT: simplification of the flowchart of the process and allows for cutting on capital and operational costs.

2 cl, 1 tbl, 2 ex

Aqueous solutions of alkali metal halides (brines) are widely used in various industrial processes, for example in the production of halogen and alkali, soda ash, potash fertilizers, edible salts, etc. To clean brines high demands, especially when used in the electrolysis.

The content of compounds of magnesium, calcium, strontium, barium, aluminum, iron, silicon, etc. in the brine entering the electrolysis must be reduced to the level (ppm) or even billions of shares (ppb), especially in the case of membrane electrolysis. The high content of compounds of these metals in the brine for membrane electrolysis leads to lower performance of the process or damage to the membranes. In the case of mercury electrolysis significantly deteriorate the performance of the process and quality of the products. In diaphragm electrolysis harmful impurities influence the operation of the iris.

The present invention concerns a method of obtaining and preparing aqueous solutions of alkali metal halides (brines) for further use in various industrial processes, in particular in the process of electrolysis. The main objective of the invention is the simplification of the technological scheme for obtaining and purifying brine, reducing operational and capital expenditures.

the alley in the description anywhere under the brine is meant an aqueous solution of a halide of an alkali metal, such as sodium chloride, potassium chloride. Under saturated brine refers to an aqueous solution of a halide of an alkali metal rich (or close to saturation) at the corresponding temperature and pressure. Under depleted (undersaturated) brine refers to the brine released from the electrolytic cell (anolyte) and having a concentration of the basic substance in 1.5-2 times lower than in saturated brine.

In the global industrial practice, the most often used process scheme in which a saturated brine receive in wells underground dissolution of salts in water (Table salt. Production and application in the chemical industry. /Arm, Mpele, Idiomelon. - M.: Chemistry, 1989. - 272 S. [1]; Reference to the production of chlorine, caustic soda and major glorproducts. / Limekilns, Miyasaki. - M.: Chemistry, 1976. - 440 S. [2]). Saturated brine then enters the clearing of compounds of calcium and magnesium to a residual level 4-6 ppm and 0.5-1 ppm by deposition of the ions with solutions of soda ash and caustic soda in the clarifiers (settling tanks). In the clarifiers is the deposition of water-insoluble magnesium hydroxide and calcium carbonate due to the gravitational forces. To accelerate deposition is used flocculants. After clarification of brine additionally filtered and fed to a stage in which paravane in a multistage evaporator plant. The obtained solid salt or a salt slurry is used to Considine depleted brine (anolyte). Consistency to the required concentration of the brine is then further processed depending on the purpose of its further use. So, in membrane electrolysis brine undergoes additional treatment from compounds of magnesium and calcium ion-exchange resins to the level concentrations of 2-5 ppb.

Saturated brine in the case of sodium chloride has a concentration of 305±10 g/DM³. After electrolysis of the electrolytic cell goes depleted brine with a concentration of sodium chloride 150-260 g/DM³and subjected to a first vacuum obeshlorivanie (to remove dissolved chlorine), and then chemical obeshlorivanie with reagents reductants. Obesshlamlennyj stream of depleted brine is again sent to Considine evaporated salt, and then passes above the cleaning cycle prior to the electrolysis. This technology may have certain options that do not have a significant impact on the performance and technical-economic indicators.

In the present invention we provide Considine depleted brine (homesharing anolyte) to carry out directly in rassledovavshij wells with simultaneous precipitation of part of the impurities, especially compounds MAGN what I and calcium, through the use of alkaline stream of depleted brine with a pH value equal to 9-12. The flow temperature is in the range of 20-50°C. To this thread added to 0.2-0.3 m³water on one cube depleted brine to make up for losses on electrolysis and maintain the volume of brine-Analitika cycle. Well there is a saturation of depleted brine in the case of sodium chloride concentration of 120-200 g/DM³to the concentration of 305±10 g/DM³and at the same time the deposition part of magnesium ions and calcium due to the reactions:

Saturation occurs faster as the concentration is increased from 120 to 200 g/DM³and not practically from zero, when the solvent is water. When underground donsimoni completely eliminated costly stage of evaporation of salt. By reducing the concentration of compounds of magnesium and calcium in saturated and raised to the surface of the brine decreases the load on the clarifier, which improves its performance and stability. In addition, the proposed method of producing brine has the ecological advantage compared to the standard technology, it reduces the quantity of sludge sod is howling and caustic cleaning (due to deposition in the well), which require special storage locations on the earth's surface or disposed.

Known methods of production brines halides of alkali metals by erosion of underground salt deposits using undersaturated brines (U.S. Patent No. 3407004; 3366419; 3355212 [3-5]. However, none of these patents is not any clearance from compounds of alkali-earth metals or other polyvalent metals.

In U.S. patent No. 3606466 [6] the claimed method of obtaining saturated sodium chloride brine, providing clear from ions of magnesium and calcium in rassledovavshij well. In the well water is pumped together with reagents for purification. Reagents, solutions of soda ash and caustic soda are served in abundance, so that in the purified brine contains about 0.1-1.0 kg/m³soda ash and 0.05-0.5 kg/m³caustic soda. These values of excess soda and alkali correspond to ground cleaning mode. To improve the deposition process provides for the supply of coagulants.

The obvious disadvantage of this method compared with the present invention is the use as solvent of water and not undersaturated brine. Well performance will be reduced because of the increased time of saturation compared with when the solvent is used obedneny the brine from the installation of electrolysis. When the injection of water into the well requires a higher pressure in the discharge line due to the large hydraulic differences between water and saturated brine. Download depleted brine these differences are significantly reduced and consequently reducing the pressure on the injection of solvent into the well. The use of stoichiometric amounts (excess) of the precipitating reagents causes rapid local formation of large amounts of rainfall, which increases the risk of zalamovanie downhole pipes and reducing the area of dissolution in the well. In our proposed method, the risk of zalamovanie wells is minimal as the substance precipitators are in moderate quantities in the depleted brine with pH 9-12.

The above problems are partially solved by the invention presented in the international application WO 97/06105, A1 [7]. Here in the beginning to get saturated brine in one way or another, including underground dissolution of deposits in the borehole, and then cleanse it from impurities ions of calcium and magnesium through the processing solutions of soda ash and caustic soda in another well. The main disadvantage of this method is the necessity of using two wells, namely the well to dissolve the salt and get saturated brine and well cleaned from ions of calcium and magnesium. This PR which leads to a substantial increase in capital and operating costs of the desalter brine.

The present invention is illustrated by the following examples:

Example 1 (solvent water)

In the well water is pumped with a flow rate of 36 m³/h at a pressure of 3.5 MPa. The content of ions of calcium and magnesium is 0.028 g/DM³and 0.009 g/DM³respectively. The importance of hydrogen ion exponent pH is 6.5. From the well is extracted saturated brine in the number of 34.9 m³/h with a concentration of sodium chloride 310 g/DM³and the content of calcium ions and magnesium, g/DM³: 2.7 and 0.54. The value of pH, the pH of a saturated brine is 7. Then the brine is fed to the purification of compounds of calcium and magnesium and electrolysis.

Example 2 (solvent analyte - depleted brine from the installation electrolysis)

In the well served depleted brine with a flow rate of 33 m³/h at a pressure of 2.5 MPa. The concentration of sodium chloride in the brine is 162 g/DM³.

The content of ions of calcium and magnesium is 0.03 g/DM³and 0.01 g/DM³respectively. The importance of hydrogen ion exponent pH is 11. From the well is extracted saturated brine in the amount of 32 m³/h with a concentration of sodium chloride 310 g/DM³and the content of calcium ions and magnesium, g/DM³: 1.76 and 0.18. The importance of hydrogen ion exponent pH of a saturated brine is 9.4. Then the brine is fed to the purification of compounds of calcium, the magnesium and electrolysis.

The effectiveness of the method of obtaining the solution presented in this invention, is also confirmed by data obtained during operation rassledovavshij wells. It is established that the content of compounds of calcium and magnesium in a saturated brine, extracted from rassledovavshij wells, significantly reduced (table).

1. The method of obtaining water saturated R is Solow halides of alkali metals to electrolysis, including underground dissolution of salt deposits with simultaneous cleaning of the brine in rassledovavshij the borehole, wherein the cleaning part of the impurities of calcium and magnesium is carried out by using as solvent depleted brine of suitable metal halide obtained from the installation of electrolysis, with the value of the hydrogen ion exponent pH of 9-12, and then brine from rassledovavshij wells is directed to the removal of calcium and magnesium.

2. The method according to claim 1, where the alkali metal halide is sodium chloride, potassium chloride.