NO854862L - PROCEDURE FOR THE PREPARATION OF ALKALIMETAL BICARBONATE. - Google Patents

Abstract

1. Process for regenerating an organic solution of a water-insoluble nitrogenous organic base from an organic solution of its hydrochloride, in which the organic solution of the base hydrochloride (7) is treated, in the presence of water (13), with an alkaline-earth metal compound (14), to decompose the hydrochloride and form the alkaline-earth metal chloride, characterized in that at least a part of the alkaline-earth metal compound (14) is chosen from the carbonates.

Description

The invention relates to a method for regenerating organic solutions of water-insoluble nitrogenous organic bases, such as for example amines, from organic solutions of hydrochloride of these bases.

There is known a process for the production of sodium bicarbonate according to which an aqueous solution of sodium chloride and an organic solution of a water-insoluble amine are mixed, the resulting mixture is treated with a gas containing carbon dioxide and subjected to decantation to separate an aqueous suspension of sodium bicarbonate, which is collected, and an organic solution of amine hydrochloride

(UK Patent A 1 082 436 (KAISER ALUMINUM & CHEMICAL CORPORATION), page 2, lines 105-125; Central Patents Index, Basic Abstracts Journal, Section E, week T.49, Derwent Publications Ltd., London, abstract 78430T-E : Japanese Patent Application A 72/41 237 (Israel Mining Inds. Inst. Res.&Dev.)).

In the following description, the term "amine method" will refer to this known technique for producing alkali metal bicarbonate.

There is also known a process for producing ammonia by splitting ammonium chloride according to which an aqueous solution of ammonium chloride is mixed with an organic solution of a water-insoluble amine, and an inert gas or carbon dioxide is circulated through the resulting mixture while removing the produced ammonia from this (Central Patent Index, Basic Abstracts Journal, Section E, week E/14, Derwent Publications Ltd., London (Great Britain), abstract 26992E/14; Japanese patent application A 57/034 020 (TOYO SODA MFG K.K.) ).

In the known methods that have just been described, an organic solution of amine hydrochloride is collected as a by-product which it is desirable to process for regeneration of the amine. For this purpose, use is usually made of a method according to which the organic solution of amine hydrochloride is mixed with an aqueous suspension of calcium or magnesium oxide or hydroxide, and an organic solution of the regenerated amine and an aqueous solution of calcium or magnesium chloride which separates is collected separately (British Patent A 1 082 436 (KAISER ALUMINUM & CHEMICAL CORPORATION), page 3, lines 5-9; CentralPatents Index, Basic Abstracts Journal, Section E, weekT.49, Derwent Publications Ltd., London , Abstract 78430T-E: Japanese Patent Application A 72/41 237 (Israel Mining Inds. Inst. Res.&Dev.)J.

In this known method, the application necessitates

of calcium or magnesium oxide or hydroxide for regeneration of the amine a preliminary operation of calcination of calcium or magnesium carbonate; this operation has the disadvantage that it requires expensive calcining furnaces and entails a costly consumption of energy.

The invention is aimed at overcoming this disadvantage by

that a new and economical method is produced for the regeneration of organic solutions of nitrogen-containing organic bases from their hydrochlorides, especially for the regeneration of amines from amine hydrochlorides, as this method no longer involves an expensive calcination of calcium or magnesium carbonate.

Accordingly, the invention relates to a process for regenerating an organic solution of a water-insoluble nitrogenous organic base from an organic solution of its hydrochloride, according to which the organic solution of the base hydrochloride is treated with an alkaline earth metal compound in the presence of water during cleavage of the hydrochloride and formation of the alkaline earth metal chloride; according to the invention, at least a part of the alkaline earth metal compound is selected from among the carbonates.

In the method according to the invention, the nitrogen-containing organic base is, by definition, any water-insoluble nitrogen-containing organic reactant which has a sufficiently basic nature that it reacts with hydrogen chloride to form the base hydrochloride.

In the method according to the invention, the solvent for the organic solution of the nitrogen-containing organic base should be chosen so that it is insoluble in water and aqueous solutions and that it dissolves the base hydrochloride.

The function of the alkaline earth metal compound is to split the base hydrochloride, releasing the base. According to the invention, at least part of said compound is alkaline earth metal carbonate.

The alkaline earth metal carbonate used in the method according to the invention can originate from any metal from group Ila in the periodic table of the elements. Preferably, calcium carbonate, magnesium carbonate or a mixture of calcium carbonate and magnesium carbonate such as dolomite is used. Ground limestone is particularly suitable.

It is desirable that the alkaline earth metal carbonate is used

in painted form. Its particle size is not decisive. In practice, it is desirable that it be used in the form of particles whose mean diameter does not exceed 25 mm, preferably 10 mm. The choice of powders whose diameter does not exceed 1 mm is particularly advantageous.

By choosing at least a part of the alkaline earth metal compound from among the carbonates, the method according to the invention saves an operation with calcination of these carbonates. All else being equal, the savings are proportionally higher

the higher the relative amount of alkaline earth metal carbonate. In practice, it is desirable that the alkaline earth metal compound should consist of alkaline earth metal carbonate in a ratio of at least 50% of its weight, preferably in a ratio of more than 75% of its weight; the rest can then consist of, for example, alkaline earth metal oxide or hydroxide.

According to a particular embodiment of the invention, it is preferred that all alkaline earth metal compounds used are in the form of carbonate. This embodiment of the invention thus provides the further advantage that it is made possible to completely abolish a plant for the calcination of alkaline earth metal carbonate. In this embodiment of the invention, the alkaline earth metal carbonate may, if appropriate, be in excess in relation to the stoichiometric amount corresponding to the amount of hydrochloride of the base to be regenerated.

The choice of the optimum temperature for carrying out the process depends on various parameters, in particular on the nitrogen-containing organic base, the alkaline earth metal carbonate selected and its particle size. As a general rule, it is desirable that it is above 50°C, and it is appropriate that it does not exceed a value above which the nitrogen-containing organic base is unstable and one runs the risk of it dissociating. Temperatures of between 50 and 230°C are recommended, especially in the case where the nitrogenous organic base is an amine; temperatures of between 10 and 200°C, and more particularly between 80 and 180°C, are preferred, especially in the case of primary alkylamines.

In the method according to the invention, an amount of water sufficient to dissolve all the formed alkaline earth metal chloride should be used. It has been found desirable to use an excess of water so that the resulting aqueous solution contains at most 4 moles of alkaline earth metal chloride per kg; concentrations of less than 2 mol/kg are preferred.

At the end of the treatment of the organic solution of amine hydrochloride with the alkaline earth metal compound, an organic phase and an aqueous phase are collected which are not miscible, the organic phase containing the regenerated organic base and the aqueous phase containing the alkaline earth metal chloride. The separation of the two phases can be carried out in any known suitable manner, such as separation by gravity or centrifugation. The method described in French patent application 83/07 22 6 (SOLVAY&CO) can be used.

The method according to the invention generally finds application when it comes to the nitrogen-containing organic bases which are water-insoluble and which can bind hydrogen chloride while forming the base hydrochloride, for example water-insoluble imines and their derivatives, water-insoluble quaternary ammonium salts and water- insoluble amines and amine derivatives. It finds application without distinction when it comes to primary, secondary or tertiary amines and with advantage primary alkylamines which contain more than 7 carbon atoms in their molecule, for example between 10 and 30 carbon atoms.

The method according to the invention finds a particularly advantageous application in the regeneration of organic solutions of amines from their hydrochloride, in the production of sodium bicarbonate by the amine method described earlier.

Accordingly, the invention also relates to a method for producing alkali metal bicarbonate according to which alkali metal chloride in the presence of water is treated with a gas containing carbon dioxide and an organic solution of a water-insoluble nitrogenous organic base, an aqueous suspension of alkali metal bicarbonate and an organic solution of the hydrochloride of the nitrogenous organic base is collected, the aqueous suspension is treated, extracting from it the alkali metal bicarbonate which it contains, and. the organic solution of the nitrogen-containing organic base is regenerated from the organic solution of hydrochloride by means of the method according to the invention.

In the method for producing alkali metal bicarbonate according to the invention, advantageous use is made of a water-insoluble primary amine, more particularly a primary alkylamine, as the nitrogen-containing organic base. Preferred primary alkylamines are those containing more than 7 carbon atoms in their molecule.

In an advantageous embodiment of the method

for the production of alkali metal bicarbonate according to the invention, carbon dioxide formed during the reaction of the alkaline earth metal carbonate with the organic solution of hydrochloride of the nitrogenous organic base is recycled together with the gas.

The method for producing alkali metal bicarbonate according to the invention is advantageously used in the production of sodium bicarbonate from sodium chloride.

The invention therefore relates to sodium carbonate obtained

by calcination of sodium bicarbonate produced using the method according to the invention.

Special features and details of the invention will be apparent from the following description of the only figure in the accompanying drawing, which shows the general overview plan of a plant for the production of sodium bicarbonate using a special embodiment of the method for the production of sodium bicarbonate according to the invention.

The plant shown in the figure includes a crystallization chamber 1, which is continuously fed with a mainly saturated aqueous solution of sodium chloride or an aqueous slurry of sodium chloride 2, an organic solution of primary amine 3, insoluble in the aqueous solution of sodium chloride, and a gas containing carbon dioxide 4. The organic solution of primary amine can, for example, be a solution containing 50% by weight of primary alkylamine in xylene, such as, for example, what is known under the name PRIMENE JMT (Rohm&Haas), which contains 18-24 carbon atoms

in its molecule. The gas 4 is preferably a carbon dioxide

rich gas containing at least 60% by weight carbon dioxide.

In crystallization chamber 1, sodium bicarbonate crystallizes, and the amine is converted to amine hydrochloride.

A liquid 5 consisting of a mixture of sodium bicarbonate crystals, a crystallization mother solution and an organic solution of amine hydrochloride is drawn from the crystallization chamber 1. This liquid 5 is transferred to a sedimentation tank 6, where the organic solution of amine hydrochloride 7 is separated by gravity from an aqueous slurry 8. The latter is led to a dewatering or filtering device 9, where the solid sodium bicarbonate 10 and the mother solution 11 are collected separately. The latter is recycled to the crystallization chamber 1 after sodium chloride has been added to it.

The solid sodium bicarbonate 10 may be fed to a calcining furnace, not shown, forming sodium bicarbonate.

The organic solution of amine hydrochloride 7 is treated

according to the method according to the invention during regeneration of the organic solution of amine. For this purpose, the organic solution of amine hydrochloride 7 is introduced

in a reaction chamber 16 which is also supplied with water 13 and ground limestone 14. A temperature of approx. 13 0°C

in the chamber 16, and water, limestone and the organic solution are subjected to stirring in this. The amine hydrochloride reacts with calcium carbonate during the regeneration of the amine, which goes into organic solution, and the formation of carbon dioxide and calcium chloride, which goes into aqueous solution. The chamber 16 is kept under pressure to limit boiling of the organic and aqueous solution it contains.

From the reaction chamber 16 it is taken out on the one hand

formed carbon dioxide 17, which is recycled with the gas stream 4,

and on the other hand, a liquid mixture 18 comprising the organic solution of the regenerated amine and the aqueous solution of calcium chloride. This mixture 18 is transferred to

a sedimentation tank 19, where the separation between the organic and aqueous phase in the mixture 18 takes place. In this way, on the one hand, the organic solution of amine 3 is collected, which is recycled to the crystallization chamber 1, and on the other hand, an aqueous residual liquid 20 containing dissolved calcium chloride is collected.

In the method that has just been described with reference to the drawing, the amount of limestone 14 used can be regulated so that it corresponds to an amount of calcium carbonate in a small excess in relation to the stoichiometric amount required for the decomposition of all the amine hydrochloride that is introduced into chamber 16 via the organic solution 7. The amount of water 13 must be sufficient to dissolve all the calcium chloride that is formed in the chamber 16. The amount of water 13 that is used is preferably regulated so that the residual liquid 20 contains less than 2 mol of calcium chloride per kg^

In the reaction chamber 16, the amine regeneration reaction may be incomplete; the organic solution of amine 3 then contains a residue of amine hydrochloride which circulates back and forth in the plant.

The examples of use that follow refer to tests on the regeneration of organic solutions of amines from their hydrochlorides using the method according to the invention. In these experiments, an organic solution of a water-soluble amine hydrochloride was treated with an aqueous suspension of calcium carbonate under various operating conditions, and the efficiency of amine regeneration from the amine hydrochloride was measured.

The amine used was the primary alkylamine PRIMENE JMT (Rohm&Haas), which contains 18-24 carbon atoms in its molecule. An aliphatic organic solvent known under the name SHELLSOL K (Shell) was used as solvent for the organic solution. The water that was entrained with the carbon dioxide was condensed and recycled.

In the examples, the regeneration yield expresses the amount of amine formed during the process, their unit amount of amine hydrochloride in the organic starting solution.

Example 1

An organic solution containing 0.064 mol amine and 1.272 mol amine hydrochloride per kg was used. 700 g of this organic solution was mixed with 350 g of water and 50 g of limestone with an average particle diameter of less than 0.1 mm and containing 96.5% by weight of calcium carbonate.

The mixture was subjected to stirring for 155 minutes,

the temperature being kept at 118°C and the absolute pressure at 1.5 bar.

At the end of the treatment, an organic phase was collected which weighed 671.6 g and which contained 1.226 mol of amine and 0.160 mol of amine hydrochloride per kg. The efficiency of the regeneration of amine from the amine hydrochloride in the organic starting solution was thus equal to 87.5 mol%.

Example 2

An organic solution containing 0.068 mol amine and 1.265 mol amine hydrochloride per kg was used. 1050 g of this organic solution was mixed with 600 g of water and 75 g of limestone with an average particle diameter of less than 0.1 mm and containing 96.5% by weight of calcium carbonate.

The mixture was subjected to mixing for 60 minutes, the temperature being maintained at about 132.5°C and the absolute pressure at 2.8 bar.

At the end of the treatment, an organic phase is collected which weighs 1,004.4 g and which contains 1.318 mol of amine and 0.092 mol of amine hydrochloride per kg. The regeneration efficiency was thus equal to 94.5 mol%.

Example 3

The experiment according to example 4 was continued so that the mixing time was 90 minutes. The organic phase collected at the end of the experiment weighed 1,002.6 g and contained 1.365 mol of amine and 0.044 mol of amine hydrochloride per kg. In this experiment, the efficiency of the regeneration of the amine from the amine hydrochloride in the organic starting solution was thus equal to 98 mol%.

Example 4

The crystallization chamber (1) was supplied with 86 l/hour of

an aqueous sodium chloride solution (2) and 178 l/h of an organic solution of a primary amine (3). The salt solution (2) contained 250 g NaCl/kg, and the organic solution of primary amine (3) contained 50% by weight of the organic solvent "SHELLSOL K" and 50% by weight of a mixture of the primary alkylamine "PRIMENE JMT" and the hydrochloride of said amine; the proportion of the amine hydrochloride in the mixture was 15% by weight.

The chamber (1) was also supplied with a gas containing 95% by weight carbon dioxide under an absolute pressure of 3.5 bar. In chambers (1), the reaction mixture was introduced into a first chamber space which had a temperature of 60°C, and then added to a second chamber space which had a temperature of 35°C. Both chambers had dimensions such that the average residence time of the reaction mixture in each chamber was approx. 25 minutes.

The following products were recovered:

9.4 kg/hour of solid sodium bicarbonate (10),

91.6 kg/hour of a mother liquor (11),

74.8 kg/hour of an organic phase (7).

The mother liquor (11) had the following composition:

NaCl: 185 g/kg

NaHCO 3 : 20 g/kg

H20 : 795 g/kg

The organic phase (7) was a mixture of amine and amine hydrochloride in the organic solvent; the proportion of amine hydrochloride in the mixture was 89% by weight. The organic phase was treated in the reaction chamber (16) with 23.4 kg/hour of an aqueous slurry of calcium carbonate, which slurry contained 256 g/kg of calcium carbonate. In the reaction chamber (16) the temperature and the absolute pressure were kept at 128°C and 3.1 bar respectively. The chamber (16) had such dimensions that the average residence time of the reaction mixture in the chamber was approx. 90 minutes.

In the organic phase which was withdrawn from the reaction chamber (16), the proportion of the amine hydrochloride was 11.2% by weight.

Claims (3)

1. Process for the production of alkali metal bicarbonate according to which alkali metal chloride (2) in the presence of water is treated with a gas containing carbon dioxide (4) and an organic solution of a water-insoluble nitrogenous organic base (3), an aqueous suspension of alkali metal bicarbonate (8) and an organic solution of the hydrochloride of the nitrogenous organic base (7) are collected, the aqueous suspension (8) is treated to extract from it the solid alkali metal bicarbonate (10) which it contains, and the organic solution of the hydrochloride of the organic base (7) is reacted with an alkaline earth metal compound (14) in the presence of water (13) while regenerating the organic solution of the nitrogen-containing organic base (3) and releasing an aqueous liquid (20) containing the dissolved alkaline earth metal chloride, characterized in that at least part of the alkaline earth metal compound (14) is selected from the carbonates. 2. Method according to claim 1, characterized in that carbon dioxide (17) released during the reaction between the organic solution of the base hydrochloride (7) and the alkaline earth metal carbonate (14) is recycled with the above-mentioned gas (4). 3. Method according to claim 1 or 2, characterized in that the nitrogen-containing organic base (3) is selected from among water-insoluble primary alkylamines.