FI92844C - Process for the preparation of alkali metal hydroxide, chlorate and hydrogen - Google Patents

Description

92844 5

Process for the preparation of early metal hydroxide, chlorate and hydrogen - Preparation of fractions of alkali metal hydroxide, chlorate and hydrogen

The invention relates to a process for the preparation of an alkali metal hydroxide, chlorate and hydrogen by chlor-alkali electrolysis, in which an alkali metal chloride solution is electrolyzed to form an alkali metal hydroxide, chlorine and hydrogen.

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The problem with the chlor-alkali industry in several countries is the imbalance between the demand for the main metal products of electrolysis, metal hydroxide and chlorine. In the future, it can be seen that this imbalance will be exacerbated by the environmental pressure on the use of chlorine and its downstream products. It follows that other alternatives must be found for the production of alkali metal hydroxides because they cannot be produced sufficiently by conventional chlor-alkali electrolysis.

Other known methods for the preparation of alkali metal hydroxides include e.g. the following processes: - chemical decarbonisation of soda ash with either lime milk or ammonia, - electrolytic decomposition of alkali metal sulphate to al-25 potassium hydroxide and sulfuric acid, electrolytic decomposition of alkali metal chlorate to potassium metal hydroxide and chlorine dioxide.

Chlorate is generally prepared by the electrolytic decomposition of alkali metal chlorides.

None of the known methods is detrimental to current chlor-alkali manufacturers. The most common disadvantages of alternative 2,92844 processes are as follows: the process produces sulfur compounds as a by-product that cannot be used on a large scale; the process is too expensive in terms of raw material and energy costs compared to the market price of the product; process 5 requires large investments and thus becomes unfavorable in terms of cost of capital compared to the market price of the product.

The object of the present invention is to provide a process for the preparation of an alkali metal hydroxide which avoids the above-mentioned disadvantages of the known processes and which can be carried out in chlor-alkali plants, in which the ratio of alkali metal hydroxide to chlorine produced by chlor-alkali electrolysis can be adjusted, and which further produces hydrogen and alkali metal chlorate. which 15 can still be exploited.

The main features of the invention appear from the appended claims.

The invention is based on the realization that at least a part of the alkali metal chloride consumed in the chlor-alkali electrolysis can be prepared by neutralizing or decarbonizing the early metal carbonate with chlorine, whereby alkali metal chlorate is simultaneously formed.

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The term metal in this context means mainly sodium and potassium, in particular sodium.

The reaction products for the neutralization of the early metal carbonate are carbon dioxide, early metal chloride and chlorate.

* · According to a preferred embodiment of the invention, in the neutralization step, the alkali metal carbonate and chlorine are introduced into a reactor containing water or a solution containing alkali metal chloride or alkali metal chlorate and alkali metal chloride. When the alkali metal carbonate is neutralized with chlorine, alkali metal chloride and chlorate are formed. The solution becomes supersaturated with chloride and thus alkali

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3,92844 Thallium chloride can be separated from the solution as crystals. This alkali metal chloride is then used in a conventional manner in electrolysis to form chlorine, early metal hydroxide and hydrogen. Preferably, at least some of the chlorine is returned to the above-mentioned reactor. To prevent the reactor solution from becoming over-penic to chlorate, a side stream is taken out of the reactor for further chlorate treatment.

The crystalline alkali metal chloride obtained from the reactor is preferably dissolved in the solution circuit of the chlor-alkali plant, i.e. in the dilute alkali metal chloride solution leaving the chlor-alkali electrolysis, the solution obtained being preferably close to the saturated chloride concentration. After purification, this solution is returned to chlor-alkali electrolysis.

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According to another preferred embodiment of the invention, in the neutralization step, the early metal carbonate and chlorine are mixed with a dilute alkali metal chloride solution leaving the chlor-alkali electrolysis. When the alkali metal carbonate is neutralized with chlorine, alkali metal chloride and chlorate are formed. From the resulting solution, the alkali metal chlorate is removed or converted to the desired compound in a known manner, and the concentrated alkali metal chloride solution thus obtained is, after purification, returned to chlor-alkali electrolysis to form early metal hydroxide, chlorine and hydrogen. Preferably, at least part of the chlorine obtained is passed to the above-mentioned neutralization step.

The concentration of the alkali metal chloride-30 solution fed to the chlor-alkali electrolysis is preferably close to the saturated chloride concentration.

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The pH of the solution in neutralization is preferably above 3 and in particular between 3 and 11.

The neutralization can be carried out either continuously or batchwise over a wide temperature range, preferably between 20 ° C and 100 ° C. The temperature affects the alkali metal chlorate and chloride concentrations of the solution to be extracted. Neutralization can be performed in one or more steps.

According to the process of the invention, the alkali metal chloride is electrolyzed in a known manner in electrolytic cells to produce alkali metal hydroxide. Electrolysis can be performed in mercury cathode, diaphragm or membrane cells. The time metal hydroxide-10 solution obtained after electrolysis corresponds to the quality of the product obtained by the conventional electrolysis method.

The chlorine used to neutralize the precious metal carbonate is preferably produced by electrolysis. Chlorine decarbonates 15 natural carbonates, again forming alkali metal chloride, alkali metal chlorate and carbon dioxide. The carbon dioxide can be further purified and liquefied in a known manner for further use. The alkali metal chlorate may be derived from the preparation of an alkali metal chlorate or a process which consumes alkali metal chlorate or may be converted to a chloride solution by hydrochloric acid, or may be disposed of or further processed in any other desired manner.

One significant advantage of the invention is that existing but undercapacity chlor-alkali plants can be utilized in the process. According to the invention, by adjusting the amount of alkali metal carbonate, it can be influenced how much of the chlorine produced by the electrolysis remains as a sales product of the process 30. The essential features of the invention are precisely that the ratio of chlorine production to time production of time metal hydroxide can be infinitely adjusted from about 0 to almost 100% by changing the amount of time metal salt fed to the process. The remainder of the alkali metal chloride required for electrolysis is obtained by feeding new alkali metal chloride into the solution circuit.

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Another significant advantage of the invention is that chlorination of carbonate produces chlorate which is easily and economically exploitable. By adjusting the reactor temperature, the chlorate and chlorine-5 content of the resulting solution can be influenced and thus the composition of the solution best suited for the purpose can be obtained.

A third advantage of the invention is the hydrogen formed in the process, which can be used as a raw material in the chemical industry and in an environmentally friendly way in the production of energy as a fuel.

The most significant advantages of the present invention for existing chlor-alkali plants are the following: An inexpensive, even crude, alkali metal carbonate suitable for electrolytic use can be used in the process. The method does not produce harmful sulfur compounds as a by-product. The method can make full use of existing electrolytic cell capacity. The investment required by the method in existing plants is very small compared to alternative processes with the same alkali metal hydroxide production capacity. The method is very flexible when the need to produce chlorine and lye for sale changes. The manufacturing cost of the alkali metal hydroxide implemented by the method is low compared to alternative processes. The process produces chlorate and hydrogen as by-products, which can be economically utilized and the process is thus more economically uniform.

The invention will now be described in more detail with reference to the accompanying drawing, in which Figure 1 is a block diagram showing the principles of alkali metal hydroxide preparation according to the present invention applied to lye, and Figure 2 shows block diagram the principles of another alkali metal hydroxide preparation according to the present invention.

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In Figure 1, the electrolysis is indicated by the reference number 1. Sodium chloride solution is fed to the electrolysis via purification 4. Electrolysis 1 gives the desired sodium hydroxide solution and hydrogen, which can be further processed in a manner known per se. The chlorine gas produced by the electrolysis 1 is fed to the reactor 2, where the chlorine gas can also be taken in by liquefaction 6 and evaporation 7. In the reactor 2, the sodium chloride crystal formed as a reaction product of chlorine and soda is separated off from the reactor solution and dissolved in dilute brine returning from electrolysis 1 at the saturation station 3, to which additional sodium chloride is also introduced if necessary. Saturated brine is passed from impregnation station 3 to brine purification 4, from where to further electrolysis 1. Reactor 2 also generates carbon dioxide CO 2 and sodium 15 chlorate, which are passed to further treatments 5 and 8. Further treatment 5 may be the separation of sodium chlorate from solution or its use as such in other processes.

In Figure 2, sodium chloride solution is fed to electrolysis 1 through purification 4. Electrolysis 1 gives the desired sodium hydroxide solution and hydrogen, which can be further worked up in a manner known per se. Sodium carbonate and the chlorine produced by electrolysis 1 are fed directly to the solution circuit of chlorine-25 potassium electrolysis 1 in reactor 2. Chlorine gas can also be introduced into reactor 2 via liquefaction 6 and evaporation 7. In reactor 2, the chlorate formed in the solution circuit is converted to the desired compound in a known manner at step 9, from which the concentrated brine is passed to purification 4 and further to electrolysis 1. If chlorine is desired, additional sodium chloride is introduced into the solution circuit, for example in step 2.

The functionality of the process has been tested in several laboratory-scale-35 experiments. They have sought to elucidate the effect of temperature, pH, and various concentrations on the reaction. course. According to the results, five or more times five times the amount of chloride is formed relative to chlorate. The final pH is

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7,928,44 depending on the degree of roughness. According to the chlorate / chloride-solubility curve, the temperature and concentrations have a dependence ratio, which determines the composition of the solution to be removed from the reactor.

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Example 1

250 ml of a solution containing 170 g / l of NaCl were taken

NaClO3 400 g / l 10 Na2CO3 50 g / l

temperature <30 ° C

Chlorine gas was passed through this solution until all the sodium carbonate had reacted with the chlorine. The resulting solution was discarded with residual chlorine with stirring. The chlorinated solution and the crystals formed in the chlorination were analyzed. The result was a solution of

NaCl 185.2 g / l NaCl103 406.2 g / l

9.3 g of crystalline salt were obtained, containing 0.42 g of NaClO3 and 8.92 g of NaCl. The final pH was 4.7.

Example 2: 100 g of Na 2 CO 3 were dissolved in 1 liter of water. The pH of the resulting solution was 10.2. This solution was chlorinated until Na 2 CO 3 was consumed. The result was a solution containing 83.9 g of NaCl, 25.5 g of NaClO3 and 5.5 g of active chlorine. The final pH was 6.2.

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Claims (14)

92844 1. A process for the preparation of alkali metal hydroxide, chlorate and hydrogen by chlor-alkali electrolysis, in which an alkali metal chloride solution is electrolyzed to form alkali metal hydroxide, chlorine and hydrogen, characterized in that at least part of the alkali metal chloride consumed as chloroal alkali electrolysis is Process according to Claim 1, characterized in that the neutralization is carried out by adding alkali metal carbonate to water or to a solution containing alkali metal chloride or alkali metal chloride and chlorate to which chlorine gas is introduced, the alkali metal chloride crystals formed being separated from the solution and removed from chloroal alkali electrolysis. to an alkali metal chloride solution, which is then returned to chlor-alkali electrolysis after purification. 3. A patent according to claim 2, which is described in Figure 20 for the neutralization of chlorate-chloride solutions in neutralization. Process according to Claim 2, characterized in that part of the chlorate-chloride solution formed in the neutralization is reused in the neutralization. 4. A compound according to claims 1 or 2, which comprises the addition of a minimum of the neutralization of the chlorinated chloride process for the production of alkali metal chlorides or a process for the production of alkali metal chlorides or chlorides. 5. A patent according to claim 1, which provides for the neutralization of the genome without the use of chloral alkali electrolysis, the use of alkali metal chlorides, color chlorine inks, and the presence of alkaline earth salts. Process according to Claim 1 or 2, characterized in that at least part of the chlorate chloride solution formed in the neutralization is passed to an alkali metal chlorate production or process which consumes the alkali metal chlorate or converts it into a chloride solution or discards it. Process according to Claim 1, characterized in that the neutralization is carried out by adding an alkali metal carbonate to a dilute alkali metal chloride solution leaving the chlor-alkali electrolysis to which chlorine gas is introduced, and the concentrated alkali metal chloride solution thus obtained is returned to the chlor-alkali electrolysis. . Process according to Claim 5, characterized in that the alkali metal chlorate which is returned to the chlor-alkali electrolysis solution is converted into the desired compound in a known manner. 6. A patent according to claim 5, which refers to the use of alkali metal chlorides in the form of an account for 92844 chlor-alkali electrolysis for a self-contained process. 7. A preferred embodiment of the present invention, which comprises the concentration of chloral alkali electrolysis in a chlorine-alkaline electrolytic process. Process according to one of the preceding claims, characterized in that the concentration of the alkali metal chloride solution fed to the chlor-alkali electrolysis is close to the saturated chloride concentration. 8. The first step is to use a patent, the pH of which is equal to the pH of the neutralization solution. Process according to one of the preceding claims, characterized in that the pH of the solution in the neutralization is greater than 3. 9. An embodiment of a patent according to the invention, which comprises the neutralization of a container or a sleeve. Process according to one of the preceding claims, characterized in that the neutralization is carried out in one of 15 or more stages continuously or batchwise. 10. A preferred embodiment of the invention, wherein the temperature is neutralized to between 20 ° C and 100 ° C. 20 Process according to one of the preceding claims, characterized in that the neutralization temperature is between 20 ° C and 100 ° C. 20 11. A method according to the invention, which comprises electrolysis of an alkali metal chloride solution, including a quaternary cathode, a diaphragm or a memory. 25 Process according to one of the preceding claims, characterized in that the electrolysis of the alkali metal chloride solution is carried out in a mercury cathode, diaphragm or membrane cell. 25 12. An embodiment of the invention provides a patent for the electrolyzing of alkali metal chlorides and the neutralization of alkali metal carbonates. 30 Process according to one of the preceding claims, characterized in that at least part of the chlorine obtained from the electrolysis of the alkali metal chloride solution is passed to neutralize the alkali metal carbonate. 30 Process according to Claim 12, characterized in that the chlorine gas is purified, liquefied and evaporated separately for neutralization. Process according to Claim 12, characterized in that the chlorine gas is passed directly to the neutralization of the alkali metal carbonate without purification. 10 92844 1. Fertilizers for the production of alkaiimetalhydroxide, chlorates and derivatives of chloral alkali electrolyte, color and alkali metal chloride electrolysis for the preparation of alkai-5 metal hydroxides, chlorine and derivatives, for the production of atoms kalielektrolysen framställs genom neutralisering av alkali -metallkarbonat med chlor. 10 2. A method according to claim 1, which provides for the neutralization of the genome by the addition of an alkali metal chloride or an alkali metal chloride and an alkali metal chloride and a color of the alkali metal, 15 In addition to the chlor-alkali electrolysis process, an alkali metal chloride solution is used, which is then followed by the addition of chlor-alkali electrolysis. 13. A patent according to claim 12, which comprises the use of chlorine, a condenser and a spatula for neutralization. 35 14. A patent according to claim 12, which can be used to directly purify and neutralize alkali metal carbonates.