LU85506A1 - PROCESS FOR THE PREPARATION OF AN AQUEOUS SODIUM CHLORIDE SOLUTION AND PROCESS FOR THE MANUFACTURE OF SODIUM BICARBONATE - Google Patents

Description

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Process for the preparation of an aqueous solution of sodium chloride and process for the manufacture of sodium bicarbonate

Case S.83 / 23 'SOLVAY & Cie (Société Anonyme)

The present invention relates to a process for the preparation of an aqueous solution of sodium chloride from an aqueous solution of sodium bicarbonate.

A technique is known for the manufacture of sodium bicarbonate, according to which an aqueous solution of sodium chloride and an organic solution of an amine insoluble in water are mixed, the resulting mixture is treated with a gas containing carbon dioxide, then decanted to separate an aqueous suspension of sodium bicarbonate and an organic amine hydrochloride solution, and treat the aqueous suspension of sodium bicarbonate to separate the solid sodium bicarbonate that '' contains and mother liquor (GB-A-1 082 436 (KAISER ALUMINUM & CHEMICAL CORPORATION), page 2, i line 105 to page 3, line 5; Central Patents Index, Basic Abstracts

15 Journal, Section E, Week T.49, Derwent Publication Ltd., London, abstract 78430T-E: patent application JP-A-7241237 (ISRAEL MINING

i; IND. INST. RES. & DEV.)).

‘In the following description, the expression" amine technique "will designate this known technique for the manufacture of bicarbo-I; 20 sodium nate.

In the amine technique, sodium chloride is usually added to the mother liquor of the crystallization of sodium bicarbonate, to reconstitute the starting aqueous solution of sodium chloride. This practice makes it possible to recover all of the sodium and the carbonate and bicarbonate ions from the mother liquor and thus ensures a maximum rate of use of the sodium used. However, it has so far imposed the use of high purity sodium chloride and in particular prohibits the use of rock salt. Indeed, the presence of impurities in the salt

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Γ- * I "" r- tt \ - i ù -2- îl ü gem and, more specifically, calcium sulphate results in: j precipitating the carbonate and bicarbonate ions from the mother liquor, to 1 l 'state of calcium carbonate and form sodium sulfate b which goes into solution; on the one hand, there is a loss of ions! 5 carbonate and bicarbonate and, on the other hand, a progressive enrichment of the aqueous solution of sodium chloride, in sodium sulfate, which leads to a decrease in the solubility of the chloride | ‘Sodium and parasitic reactions with the amine, detrimental to the proper functioning of the technique for manufacturing sodium bicarbonate.

| The invention aims to provide a process for the preparation of aqueous sodium chloride solutions from aqueous sodium bicarbonate solutions, which is suitable for use! rock salt while avoiding the aforementioned drawbacks.

The invention therefore relates to a process for the preparation of an aqueous solution of sodium chloride from an aqueous solution of sodium bicarbonate, according to which the aqueous solution of sodium bicarbonate is treated with chloride of a cation i; ‘! organic to decompose the sodium bicarbonate, the carbon dioxide which is formed is removed and rock salt is added to the solution! resulting aqueous.

j. In the process according to the invention, the aqueous solution of sodium bicarbonate can for example be mother liquor of the | 'crystallization of sodium bicarbonate as obtained by j; 25 carbonation of aqueous solutions of sodium hydroxide or in the amine technique defined above.

i The organic cation is, by definition, any organic cation i * which, in the chloride state, is capable of reacting with sodium bicarbonate j to form sodium chloride, carbon dioxide. and an organic base. In a preferred embodiment of the invention, the organic cation chloride is selected from those for which said base has a basic character sufficient for it to be able to reconstitute the organic cation chloride by reaction with hydrogen chloride . In this embodiment of the invention, chlorides of nitrogenous organic cations are advantageously selected, and more particularly those derived from water-insoluble organic nitrogenous bases such as, for example, insoluble imines. in water and their derivatives, water insoluble quaternary ammonium salts and water insoluble amines and amine derivatives. Chlorides of organic cations which are especially suitable in the context of the invention are the primary, secondary and tertiary amine hydrochlorides; primary amine hydrochlorides are especially advantageous, especially primary alkyl amine hydrochlorides.

The organic cation chloride is used in an amount sufficient to decompose at least a substantial part of sodium bicarbonate from the sodium bicarbonate solution. It is preferable to use an amount of organic cation chloride at least sufficient to decompose all of the sodium bicarbonate from said solution.

In the process according to the invention, the organic cation chloride is generally used in the form of an organic solution, so that at the end of the reaction between sodium bicarbonate and the chloride organic cation, a dilute aqueous solution of sodium chloride and an organic solution containing the above-mentioned organic base resulting from the said reaction are collected separately. The choice of the nature and the quantity of organic solvent to be used is therefore conditioned by the need for it to form, with said base, an organic solution insoluble in aqueous solutions of sodium chloride. The separation between the aqueous sodium chloride solution and the organic solution of the base can then be carried out by any suitable means, generally decantation by gravity or centrifugation.

The treatment of the aqueous sodium bicarbonate solution with the organic cation chloride can be carried out in any suitable chemical reactor, designed to ensure regular evacuation of the carbon dioxide formed. The evacuation of carbon dioxide as it is formed, and adjusted so as to permanently maintain a partial pressure of carbon dioxide sufficiently low in the reactor, to promote the decomposition reaction of the bicarbonate sodium by chloride - organic cation. The selection of the optimum partial pressure of carbon dioxide in the reactor depends on various factors, in particular the temperature in the reactor, the concentration of the aqueous sodium bicarbonate solution and the organic cation chloride used. The temperature is generally produced in the reactor at least 15 ° C and a partial pressure 10 of carbon dioxide less than 3 bars. Temperatures of at least 40 ° C and partial pressures of carbon dioxide not exceeding 0.9 bar are preferred, temperatures between 30 and 90 ° C and partial pressures of carbon dioxide, between 1 and 0, 3 bar being especially advantageous.

Any suitable known means can be used to evacuate the carbon dioxide from the reactor and achieve therein the desired partial pressure of carbon dioxide. One suitable means is to bubble an inert gas into the reaction mixture, for example nitrogen or argon. Alternatively, the reactor may also be subjected to controlled vacuum.

The means used to add the rock salt to the aqueous solution resulting from the treatment of the sodium bicarbonate solution with the organic cation chloride is not critical.

It is possible, for example, for this purpose, to use a continuously operating dissolver, supplied in a controlled manner with solid rock salt i * I and with said aqueous solution. Examples of dissolvers used | 'sands in the implementation of the method according to the invention are; 'described in patent FR-Â-2,471 35G (SOLVAY & Cie).

i According to a particularly advantageous embodiment of the method according to the invention, for adding rock salt to the solution | aqueous resulting from the treatment of the solution of sodium bicarbonate with the chloride of organic cation, one makes percoier i said solution through an underground deposit of rock salt; a | for this purpose, two pipes are pressed into the gem • t -5- salt deposit, in the vicinity of one another (usually a tubular pipe and an annular coaxial pipe), the aqueous solution is injected under pressure into the one of the lines and an aqueous solution of sodium chloride is drawn off through the other line (Dale W. KAUFMANN "Sodium Chloride", American Chemical Society Monograph Sériés, 1960, Reinhold Publishing Corporation, Chapman & Hall, Ltd., London, pages 142 to 185).

The aqueous solutions of sodium chloride obtained by the process according to the invention can be used in any industry requiring the use of concentrated, generally saturated aqueous solutions of sodium chloride, and especially in the technique of manufacturing soda with ammonia, in the amine technique defined above and in the electrolysis techniques for the production of chlorine and aqueous solutions of sodium hydroxide.

The method according to the invention finds an interesting application in the amine technique defined above, for simultaneously regenerating therein the aqueous sodium chloride solution and the organic amine solution. The invention therefore also relates to a process for the manufacture of sodium bicarbonate, in which an aqueous solution of sodium chloride is mixed with an organic solution of a water-insoluble amine, the resulting mixture is treated with a gas containing carbon dioxide to form an aqueous suspension of sodium bicarbonate and an organic solution of amine hydrochloride, the aqueous suspension of sodium bicarbonate is treated to separate the solid sodium bicarbonate it contains and a water mother water is treated with at least part of the organic amine hydrochloride solution, the carbon dioxide formed is removed and a dilute aqueous solution of sodium chloride and an organic amine solution are collected separately , rock salt is added to the dilute sodium chloride solution and the resulting concentrated aqueous sodium chloride solution and the organic amine solution are recycled to the above mixture you.

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Special features and details of the invention will emerge from the following description of the single figure of the appended drawing, which represents the general diagram of an installation for the manufacture of sodium bicarbonate by the amine technique described above, which incorporates a preferred embodiment of the method according to the invention.

The installation shown in the figure comprises a crystallization chamber 1 which is supplied, continuously, with a substantially saturated aqueous solution of sodium chloride 2, an organic solution of primary amine 3 insoluble in the aqueous solution of chloride of sodium and a gas containing carbon dioxide. The organic solution of primary amine can for example be a solution at 50% by weight of primary alkylamine in xylene. The gas 4 is preferably an enriched gas, containing 15 60 to 80% by weight of carbon dioxide, obtained for example by mixing in adequate proportions a lime gas with a residual gas from the calcination of sodium bicarbonate into monocarbonate sodium. The amount of gas used must be sufficient to convert a substantial part of the sodium chloride of solution 2 to sodium bicarbonate. As a variant, the treatment in the crystallization chamber 1 can be preceded by a partial carbonation of the mixture by means of a gas poor in carbon dioxide, such as a lime kiln gas.

. Is withdrawn from the crystallization chamber 1, a liquid 5 consisting of a mixture of aqueous solution and organic solution and containing crystals of sodium bicarbonate in suspension.

This liquid 5 is transferred to a settling chamber 6, where an organic solution of anine hydrochloride 7 and an aqueous slurry 8 of sodium bicarbonate crystals are separated by gravity. The latter is sent to a wringing or filtration device 9, where solid sodium bicarbonate 10 and mother liquor 11 are collected separately.

According to the invention, the organic solution of primary amine hydrochloride 7 is divided into two fractions 12 and 12, a fraction 12 and the mother liquor 11 are introduced into a reaction chamber 14 and

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-7- subject them to vigorous stirring to generate a reaction between sodium bicarbonate and the amine hydrochloride, leading to the formation of sodium chloride which passes into aqueous solution, of primary amine which passes into organic solution and carbon dioxide. The size of fraction 12 is sufficient to decompose all of the sodium bicarbonate in the mother liquor.

To promote the reaction between sodium bicarbonate and the amine hydrochloride, the reaction chamber 14 is heated, for example to a temperature of the order of 60 ° C., and the carbon dioxide which is removed therefrom forms therein, by means of a vacuum pump 15. The carbon dioxide 28 withdrawn from the reaction chamber 14 by the pump 15 is advantageously discharged into the crystallization chamber 1.

A liquid 16 15 is drawn from the reaction chamber 14 formed by a mixture of a dilute aqueous solution of sodium chloride and an organic solution of amine; this liquid 16 is sent to a decantation chamber 17 from which the dilute aqueous sodium chloride solution 18 and the organic amine solution 19 are collected separately.

20 The dilute aqueous solution of sodium chloride 18 is then introduced into a rock salt deposit 20, from which an equivalent flow rate of a saturated aqueous solution of sodium chloride 21 is withdrawn, which is combined with a stream 2 of sodium chloride. sodium of. - 25 --------- The organic amine solution 19 collected from the settling chamber 17 can be completely combined with the starting organic amine solution 3 and introduced with it into the crystallization 1.

Alternatively, the organic amine solution 19 collected from the settling chamber 17, or part 22 thereof, can be combined with fraction 13 of the organic solution of amine hydrochloride.

Fraction 13 of the organic amine hydrochloride solution (optionally mixed with the organic amine solution 22) is then treated in a manner known per se in the amine art, to regenerate the amine. For this purpose, it is sent to a reaction chamber 23, where it is subjected to stirring with an aqueous suspension of calcium hydroxide 24, and the resulting reaction mixture 25 is sent to a decantation chamber 26 from which separately collects an aqueous solution of calcium chloride 27 and an organic solution of amine 3 which is recycled to the crystallizer 1.

The advantage of the invention appears from the description of the examples which follow.

10 Example 1

The following were introduced into a reaction chamber: - 315 g of an aqueous solution of sodium bicarbonate, and - 700 g of an organic solution of primary alkylamine hydrochloride comprising from 18 to 24 carbon atoms, in a solvent 15 aromatic organic known under the brand SHELLSOL AB (SHELL).

The aqueous sodium bicarbonate solution had the following weight composition:

NaHC03: 20.0 g / kg

NaCl: 173.9 g / kg The organic solution contained, per kg, 1.115 mole of amine hydrochloride and 0.246 mole of the corresponding amine.

In the reaction chamber, the two solutions were stirred by a mechanical stirrer and crossed by an ascending stream - of nitrogen at a flow rate of 8 l / h; the temperature in the reaction chamber 25 was kept constantly at 40 ° C.

After 90 minutes of reaction, 98.7% of the initial weight of sodium bicarbonate had been converted to NaCl. After 135 minutes of reaction, the reaction chamber was drained and the organic phase and the aqueous phase were collected separately. The aqueous phase collected was found to be an aqueous solution of sodium chloride free of sodium bicarbonate; the organic phase collected contained, per kg, 0.356 mole of amine and 1.014 mole of amine hydrochloride.

To the aqueous sodium chloride solution collected, rock salt was added until saturated with sodium chloride.

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Example 2

The test of Example 1 was repeated, reproducing the same working conditions, except for the temperature, which was set at 60 ° C. It only took 60 minutes of reaction for all of the sodium bicarbonate to be converted to sodium chloride.

Example 3

The aqueous and organic solutions used in the test of Example 1 were mixed in a reaction chamber. The reaction chamber was kept constantly at the temperature of 50 ° C. and was created there. a vacuum of 0.1 bar, by means of a vacuum pump. After 60 minutes of reaction, the reaction chamber was drained and the organic phase and the aqueous phase were collected separately. The aqueous phase collected was found to be an aqueous solution of sodium chloride, free of sodium bicarbonate; it was saturated with sodium chloride by addition of rock salt.

The organic phase collected contained, per kg, 0.358 mole of amine and 1.015 mole of amine hydrochloride.

20 Example 4

Using the reaction chamber of the test of Example 3, there were introduced: - 642 g of an aqueous solution of sodium bicarbonate, and - 168 g of an organic solution of primary alkylamine hydrochloride comprising from 18 to 24 carbon atoms, in the aforementioned organic aromatic solvent SHELLSOL AB.

The aqueous sodium bicarbonate solution had the following composition:

NaHC03: 18.6 g / kg 30 NaCl: 170 g / kg

The organic solution contained, per kg, 1.090 mole of amine hydrochloride and 0.258 mole of the corresponding amine.

The temperature in the reaction chamber was set at 80 ° C and the vacuum at 0.4 bar.

I * * i (t, ii -10- 5 d After 60 minutes of reaction, the reaction chamber i 5 was drained and the organic phase and the aqueous phase were collected separately. The collected aqueous phase is found to be an aqueous solution of sodium chloride, free from sodium bicarbonate; it is then saturated with sodium chloride by adding to it rock salt.

? The organic phase collected contained, per kg, 1.214 mole ·! amine and 0.211 mole of amine hydrochloride.

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Claims (10)

1. Process for the preparation of an aqueous solution of sodium chloride from an aqueous solution of sodium bicarbonate * -, characterized in that the aqueous solution of sodium bicarbonate is treated with chloride of organic cation, to decompose the sodium bicarbonate, the carbon dioxide which forms is removed and rock salt is added to the resulting aqueous solution. 2. Method according to claim 1, characterized in that an organic cation chloride is selected, insoluble in aqueous solutions of sodium chloride. 3. Method according to claim 1 or 2, characterized in that an organic cation chloride is selected which can be obtained by reaction of an organic base with hydrogen chloride. 15 4 - Process according to claim 3, characterized in that the organic cation chloride is selected from the chlorides of nitrogenous organic cations. 5. Method according to claim 4, characterized in that the organic cation chloride is selected from the hydrochlorides of primary amines. 6. Method according to any one of claims 1 to 5, characterized in that the organic cation chloride is used in the form of an organic solution insoluble in water. 7. Method according to any one of claims 1 to 6, characterized in that the aqueous sodium bicarbonate solution and the organic cation chloride are treated at a temperature of at least 15 ° C and under partial pressure carbon dioxide less than 3 bars. 8. Method according to claim 7, characterized in that the aqueous sodium bicarbonate solution and the organic cation chloride are treated at a temperature between 30 and 90 ° C and wi # -12- under partial pressure d carbon dioxide between 0.3 and 1 bar. 9. Method according to any one of claims 1 to 8, characterized in that, in order to dissolve the rock salt in the aqueous solution resulting from the treatment of the sodium bicarbonate solution with the organic cation chloride, said percolate is made to percolate resulting solution in a rock salt deposit. 10. Process for the manufacture of sodium bicarbonate, according to which an aqueous solution of sodium chloride and an organic solution of an amine insoluble in water are mixed, the resulting mixture is treated with a gas containing carbon dioxide to form an aqueous suspension of sodium bicarbonate and an organic solution of amine hydrochloride, and the aqueous suspension of sodium bicarbonate is treated to separate the solid sodium bicarbonate * it contains and a mother liquor, characterized in that the mother liquor is treated with at least part of the organic solution of amine hydrochloride, the carbon dioxide formed is removed and a dilute aqueous solution of sodium chloride and an organic solution of amine are collected separately, rock salt 20. the dilute sodium chloride solution and the concentrated aqueous sodium chloride solution and the organic amine solution are recycled to the above mixture. / / / ./) / ^ ίφ </ Κί & LW / / / / Ί / '