CA1074529A - Process for producing cyanogen chloride (i) - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention provides in a process for pro-ducing cyanogen chloride by reacting hydrogen cyanide with hydrogen chloride or hydrochloric acid and hydrogen peroxide in an aqueous medium in the presence of cupric and ferric ions, the improvement in which the reaction is carried out under super-atmospheric pressure and that cyanogen chloride is recovered separately from oxygen and nitrogen.

Description

The present invention relates to the production of cyanogen chloride.
It is known that hydrogen cyanide and hydrogen chloride can be reacted with hydrogen peroxide in the presence of an aqueous solution of cupric and ferric ions as catalysts to cyanogen chloride (see German Patents Nos. 2 027 957 and 2 131 383).
In the reaction a yield of approximately 90 to 92~, relative to hydrogen cyanide, is obtained. The always slight decomposition of the hydrogen peroxide and the oxidative sapon-ification of the hydrogen cyanide cause a proportion of up to 5~ by weight of both oxygen and carbon dioxide in the cyanogen chloride gas.
In the trimerization of the cyanogen chloride to cyanuric chloride the oxygen content causes an increased consum-ption of active carbon, whereby the continuous production of cyanuric chloride is rendered difficult by the frequent interr-uptions of the operation in order to replace the carbon.
The present invention provides continuous process for producing cyanogen chloride from hydrogen cyanide and hydrogen chloride yielding cyanogen chloride which is essentially free from oxygen.
It has been found that cyanogen chloride can be produced essentially free from oxygen and nitrogen and fully continuously when the reaction of hydrogen cyanide and hydrogen chloride or hydrochloric acid with hydrogen peroxide is carried out in an aqueous medium in the presence of cupric and ferric ions under pressure, whereupon cyanogen chloride is recovered separately from 2 and N2.
Pressures of 1.5 to 16 bars, preferably 2 to 4 bars are suitably applied. It is surprising to find that not only did the application of pressure not inhibit the reaction but it even -- 1 -- ... .
~' 107~SZ9 facilitated the formation of cyanogen chloride although according to the summation formula Cu2+, Fe3+
HCN ~- HCQ + H22 > CQCN + 2H2O - 53 kcal mole This is just the opposite of what would have been expected since at a pressure of 1 bar cyanogen chloride escapes from the re-action solution and thus could influence the equilibrium.
However, when applying pressure it was found that cyanogen chloride completely dissolved in the reaction solution and the rate of reaction and thus the yield were substantially increased.
Moreover, cyanogen chloride could now be separated directly from oxygen, nitrogen and from the major portion of the carbon dioxide.
Because of the great difference of the solubilities under pressure between cyanogen chloride and the oxygen formed in the reaction solution due to the slight decomposition of the hydrogen peroxide it was not possible to draw off the gases unsoluble in the reaction solution, i.e., oxygen, nitrogen and carbon dioxide at the top of the reactox. These gases were freed from cyanogen chloride by means of a pressure wash and removed via a pressure-maintaining valve.
By relaxing the reaction solution cyanogen chloride gas which was virtually free from oxygen was obtained in this manner and after drying and without any further purification the gas could be trimerized to cyanuric chloride.
As mentioned above, the cyanogen chloride obtained according to the invention also is fully continuously produced (see German Patents Nos. 2 027 957 and 2 131 383), i.e., the catalyst solution of cupric and ferric ions is separated during the process and returned to the reaction stage.
In this case, too, the water recycled with the hydrogen peroxide and the hydrochloric acid must be removed together with ~074S'~

the water formed during the reaction. This can be effected by means of the procedures described in the German Patent No.

2 13L 383.
However, it was found to be extremely favourable to remove the water fed in with the components and formed during the reaction from the circulation along with the catalyst sol-ution by way of an ion exchanger. The copper ions and the iron ions are bonded by the ion exchanger and t,he discharged solution is wasted. By this removal the copper and iron ions are recovered but the ammonium chloride formed in the catalyst solution by the oxidative saponification of the hydrogen cyanide is enriched in the recycle solution only up to a certain level since it is not bonded by the ion exchanger and thus is removed along with the waste water.
In a somewhat modified procedure it was found to be advantageous to use as the reaction component a liquid hydrogen cyanide stabilized with phosphoric acid. In this case, the ion exchanger is treated with mineral acids not immediately after charging the catalyst solution to be concentrated but only after a preceding intermediate wash with alkaline reacting substances such as dilute alkali liquors or alkaline reacting salt solutions, as for example, carbonates or acetates.
Commercial cation exchangers are suitable as ion exchangers. Thus, ion exchange resins based on polystyrene or polystyrene divinyl benzene are suitable. Macroporous ion exchangers based on polystryrene with weakly acid exchange-active groups are preferably used.
Upon saturation with the catalyst solution the ion exchanger is washed and the copper and iron ions are separated by means of dilute mineral acid. A 1 to 10% by weight aqueous hydrochloric acid is particularly suitable for this purpose.

The catalyst solution, which then is in a concentrated form, is recycled.

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The higher the concentration of the catalyst solution fed in the more water can be removed per unit time.
Continuous removal and continuous return of the re-generated catalyst solution are preferred in order to keep the optimum catalyst concentration constant.
When carrying out the process it is desirable to keep the pH value between 0.1 and 0.5, preferably between 0.25 and 0.35 during the reaction and to adjust the reaction temperature to 40 - 60C, preferably to approximately 50C.
Some of the heat of reaction is used for maintaining the reaction temperature, but the excess is removed by cooling.
The formation of dicyanogen can be avoided to a great extent by the measures described above. The decomposition of hydrogen peroxide is also kept within narrow limits.
Hydrogen cyanide is used in the usual form, preferably in the gaseous or liquid form. Hydrogen chloride is also used in the gaseous form or as an aqueous solution with 0.5 to 36 by weight of hydrogen chloride, preferably with 8 to 20% by weight of hydrogen chloride. The same also applies to hydrogen peroxide, which is used in commercial solutions, for example, as a 25 to 90~ by weight, preferably as a 30 to 50% by weight hydrogen peroxide.
The reactants must be used in approximately stoichio-metric amounts and, for example, hydrogen cyanide, hydrogen chloride and hydrogen peroxide must each be present in a range from 0.9 to 1.1 moles.
The yield of cyanogen chloride, relative to hydrogen peroxide, is the most favourable at an optimum catalyst concen-tration, which is 0.077 mole per litre for copper and 0.0125 to 0.025 mole per litre for iron. Higher or lower concentrations are possible but do not affect the yield of cyanogen chloride in such a favourable manner. In general, 0.5 to 0.005 mole per 10'~'4SZ~

litre of recycle solution are applicable for both copper and for iron.
The reaction is carried out in reaction tubes used for the production of cyanogen chloride. However, in their upper portions said reaction tubes are provided with an outlet valve for the waste gas.
The advance in the art of the process according to the invention lies in that hydrogen cyanide is more completely react-ed to cyanogen chloride, as compared with the process at atmos-pheric pressure, whereby the proportion of hydrogen cyanide inthe gas is substantially reduced and the yield of cyanogen chloride is substantially increased.
Moreover, a cyanogen chloride which is essentially free from oxygen is obtained so that the trimerization to cyanuric chloride can be carried out in a much simpler way than heretofore.
The present invention will be further illustrated by way of the following Examples and in conjunction with the accompanying drawing in which:
Fig. 1 is a schematic of the process according to one embodiment of the present invention.
Example 1 In the continuously operating apparatus shown in Figure 1, 40 litres of a solution of 13.0 g of CuCQ2 . 2H2O per litre and 3.35 g FeCQ3 . 6H2O per litre is recycled via a reactor 1, a relaxation tank II, washer III, dealcoholization tank IV
and pressure wash V.
1.6 kg of gaseous hydrogen cyanide per hour are fed through pipe 1 into the reaction solution in pipe 10. This re-action solution is fed into the reactor I by pump lOa. 4.301 kg of a 50% by weight aqueous hydrogen peroxide, i.e., an excess of 10% above the stoichiometric amount, per hour are fed into the reactor I through pipe 3 and 21.6 kg of a 10% by weight aqueous 1~'79t~Z9 hydrochloric acid per hour through pipe 2 by means of pumps 3a and 2a respectively.
In a continuous operation the pH of the reaction solution is kept precisely between 0.25 and 0.35 by controlling the addition of hydrochloric acid. Because of the cyanogen chloride being released a pressure of up to 4 bars builds up in the reactor I and in the pressure wash V. This pressure is main-tained constant by the pressure-mainkaining valve 6a at the top of the pressure wash V. The oxygen set free by decomposition of the hydrogen peroxide and the gases carbon dioxide and nitrogen formed by oxidative saponification and secondary reactions accumulate at the top of the reactor I.
The reaction temperature is kept at approximately 50C.
The cyanogen chloride dissolved in the catalyst solution under the built-up pressure passes into the relaxation tank II
through pipe 7 and relaxation valve 7a. In tank 7 the concentra-tion of the solution decreases from approximately 5% by weight to approximately 1 to 2% by weight of cyanogen chloride so that at a circulation of approximately 100 litres per hour approximately 3.5 kg of cyanogen chloride i5 free.
A portion of the catalyst solution obtained at the bottom of the relaxation tank II passes through pipe 9 and valve 9a into the dealcoholization column IV, where it is deprived of cyanogen chloride, hydrocyanic acid and carbon dioxide at 100C.
40 litres of catalyst solution are treated in this manner per hour. 16 litres thereof are conveyed by pump 12a per hour through pipe 12 to the pressure wash V, where the gas mixture accumulated at the top of the reactor I flows in through pipe 5.
This gas mixture is then freed from cyanogen chloride by washing, relaxed through the pipe 6 and the pressure-maintaining valve 6a and discharged.
The wash solution returns to the reactor I through pipe 10~4SZ9 13 and the pump 13a.
The gas escaping from the dealcoholization colume IV
contains, in addition to cyanogen chloride and carbon dioxide, a portion of hydrogen cyanide which was not reacted in the reactor I. In the washer III said unreacted hydrogen cyanide is washed out of the gas mixture with catalyst solution at reduced pressure obtained through pipe 8.
By way of the pipe 17 the washed gas is combined with the gas flowing out of the pipe 18 and passes to the tri-merization via a drying tower (not shown). From the washer III,where the hydrogen cyanide is added, and through pipe 10 the wash solution returns to the reactor I by means of pump 10a together with the solution from the pressure wash V, which is pumped by the pump 13a.
The removal of 25 litres of waste water per hour is brought about with dealcoholized catalyst solution by way of the pipe 14 and the valve 14a (selectively by way of the valve 4a or 4b) to the ion exchanger units VI.
The cupric and ferric ions are retained therein while the ammonium-chloride-containing waste water is discharged into the sewer. The cupric and ferric ions are separated by means of a 10% by weight hydrochloric acid alternately passing through the ion exchange columns saturated with metal ions.
The fresh catalyst solution formed is returned to the reactor I through pipe 15 and the pump 15a in order to maintain the ion concentration.
The average yield of cyanogen chloride, relative to hydrogen cyanide, is 96.2% of the theoretical yield. The cyano-gen chloride contained 0.1 to 0.3% by weight of dicyanogen, 0.5%
by weight of hydrogen cyanide and less than 0.5~ by weight of C2 + N2.
Oxygen can no longer be detected therein by gas chromatography.

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Example 2 In the same apparatus as in Example 1, 40 litres of a solution of CuCQ2 . 2H2O per litre and 6.7 g of FeCQ3 . 6H2O
per litre are recycled, as described in Example 1.
1.6 kg of liquid hydrogen cyanide, which is stabilized with 0.1% by weight of H3PO4, are fed per hour to the reactor I
through pipe 1, pipe 10 and pump lOa. The hydrogen cyanide is fed together with the reaction solution into the pipe 10.
Through pipe 3, 4.3 kg of a 50% by weight aqueous hydrogen peroxide, i.e., a 10% excess above the stoichiometric amount are fed into the reactor I and through pipe 2, 27.0 kg of an 8% by weight aqueous hydrochloric acid are fed into the reactor I by the pumps 2a and 3a. The pH value is controlled by a pH electrode and kept in the range pH 0.25 to 0.35 by correspondingly adding the hydrochloric acid.
The course of the reaction is the same as that in Example 1. However, in this case the amount of waste watér to be removed has increased to approximately 30 litres correspond-ing to the increased dilution of the hydrochloric acid.
The removal is carried out as in Example 1. However, the phosphoric acid adhering to the ion exchanger is washed out with a 0.5% by weight solution of caustic soda before the copper and iron ions are washed out and recycled to the reactor I.
The yield is approximately 96% of the theoretical yield.
The degree of purity is the same as that in Example 1.
The process according to the invention is also applicable to the production of cyanogen bromide.

Claims (12)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for producing cyanogen chloride by reacting hydrogen cyanide with hydrogen chloride or hydrochloric acid and hydrogen peroxide in an aqueous medium in the presence of cupric and ferric ions, the improvement in which the reaction is carried out at a pH between 0.1 and 0.5 under super-atmospheric pressure of 1.5 to 16 bars and that cyanogen chloride is recovered separately from oxygen and nitrogen.

2. In a continuous process for producing cyanogen chloride by reacting hydrogen cyanide and hydrogen chloride or hydrochloric acid and hydrogen peroxide in an aqueous medium in the presence of cupric and ferric ions, the improvement in which the reaction is carried out in a reactor at a pressure of 1.5 to 16 bars and at a pH between 0.1 and 0.5 and the reaction solu-tion is recycled, the pressure of the reaction solution is re-laxed to separate the dissolved cyanogen chloride, a portion of the relaxed reaction solution is dealcoholized and used for a pressure wash of O2, N2, Cl2 and cyanogen chloride containing gas obtained during the reaction and the remaining portion of the relaxed reaction solution is used for washing the hydrogen cyanide-containing cyanogen chloride escaping during the dealco-holization.

3. A process according to claim 1 or 2 in which the reaction is carried out under pressure of from 2 to 4 bars.

4. A process according to claim 1 or 2 in which the reaction is carried out with the reactants present in an amount from 0.9 to 1.1 moles.

5. A process according to claim 1 or 2 in which the reaction is carried out at pH values between 0.25 and 0.35.

6. A process according to claim 1 or 2 in which the reaction is carried out at a temperature from 40 to 60°C.

7. A process according to claim 1, in which the reaction of hydrogen cyanide with hydrogen chloride or hydro-chloric acid and hydrogen peroxide is carried out in the presence of 0.077 mole of cupric ions per litre and 0.0125 to 0.025 mole of ferric ions per litre.

8. A process as claimed in claim 1 which is continuous and in which the catalyst solution of cupric and ferric ions is separated and recycled for further reaction; the water formed during the reaction and the water fed in with the reactants being removed from the recycled catalyst solution.

9. A process as claimed in claim 8, in which the cupric and ferric ions are removed from the recycled solution by means of a cation exchanger which denuded solution is then passed to waste and the catalyst solution regenerated by treat-ment of the exchanger with a mineral acid which is then passed to the reaction.

10. A process as claimed in claim 9, in which the mineral acid is hydrochloric acid.

11. A process according to claim 8, 9 or 10, in which macroporous ion exchangers based on polystyrene with weakly acid exchange-active groups are used as cation exchangers.

12. A process according to claim 8, 9 or 10, in which the catalyst solution contains phosphoric acid and the cation exchanger is treated with mineral acid subsequent to a pre-treatment therewith of alkaline reacting substances.