CA1077234A - Process for producing cyanogen chloride (ii) - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention provides a process for producing cyanogen chloride by reacting hydrogen cyanide and hydrogen chloride or hydrochloric acid with hydrogen peroxide in a recycling aqueous catalyst solution containing cupric and ferric ions, the improvement in which the reaction is carried out under elevated pressure, and cyanogen chloride is recovered separately from oxygen and nitrogen, the reaction component hydrogen chloride or hydrochloric acid being at least partially formed directly in the recycling catalyst solution of cupric and ferric ions by reaction of chlorine and hydrogen cyanide.

Description

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The present invention relates to the product 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 produce cyanogen chloride (see German Patents Nos. 2 027 957 and

2 131 383).
In the reaction a yield of approximately 90 to 92%, rel-ative to hydrogen cyanide, is obtained. The always slight decomp-osition of hydrogen peroxide and the oxidative saponification ofthe 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 consumption of active carbon, whereby the continuous production of cyanuric chloride is made difficult by the frequent interrup-tions of the operation in order to replace the carbon.
It has now 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 oxygen and nitrogen, the reaction component hydrogen chloride or hydrochloric acid being partially or entirely directly formed in the recycle catalyst solution of cupric and ferric ions by reaction of chlorine and hydrogen cyanide.
This reaction can be carried out under pressure or without pressure.
According to the present invention therefore there is provided a process for producing cyanogen chloride by reacting hydrogen cyanide and hydrogen chloride or hydrochloric acid with hydrogen peroxide in a recycling aqueous catalyst solution .

10~34 containing cupric and ferric ions, the improvement in which the reaction is carried out under elevated pressure, and cyanogen chloride is recovered separately from oxygen and nitrogen, the reaction component hydrogen chloride or hydrochloric acid being at least partially formed directly in the recycling catalyst solution of cupric and ferric ions by reaction of chlorine and hydrogen cyanide.
The formation of hydrogen chloride or hydrochloric acid is preferred at a point in the circulation at which the recycle medium is virtually free from hydrogen peroxide.
The course of the reaction corresponds to the following formulae I HCN + CQ2 ~ CQCN + HCQ.
II HCQ + HCN + H2O2 > CQCN + 2 H2O
The advantage of the combination of the equations I
and II for carrying out the process lies in that the chlorine is completely converted into cyanogen chloride without obtaining hydrochloric acid which must be separated. Thus, storage space for the hydrochloric acid obtained is superfluous.
The two reactions I and II can be carried out either in a reactor or each reaction can be carried out separately in a separate reactor. As mentioned hereinbefore, pressure is applied for the chlorination of the hydrogen cyanide or the operation is carried out at standard pressure.
Pressures of l.S to 16 bars, preferably 2 to 4 bars are used, if required also for the chlorination of the hydrogen cyanide.
It was surprising to find that not only did the application of pressure not inhibit the course of the reaction in which cyanogen chloride is formed but it even facilitated the formation of cyanogen chloride although according to the summation formula just the opposite would have been expected since : .

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at a pressureoflbar cyanogen chloride escapes from the reaction solution and thus can influence the equilibrium.
Moreover, it could not be predicted that the chlorina-tion reaction according to equation I in the catalyst solution under pressure had no side reactions.
The application of pressure showed that cyanogen chloride dissolved completely in the reaction solution and the rate of reaction of the hydrogen cyanide and thus the yield were substantially increased.
Hydrogen cyanide is used in the usual form, preferably inthe gaseous or in the liquid form. Hydrogen chloride is 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 unless it is not only used for the chlorination of the hydrogen cyanide but is also fed from an external source.
Hydrogen peroxide is used in commercial solutions, for example, as a 25 to 90~ by weight, preferably as a 30 to 50% by weight aqueous hydrogen peroxide.
The technical advance of the process according to the in~ention lies in that hydrogen cyanide is more completely reacted to cyanogen chloride, as compared with the process at standard pressures so that the proportion of hydrogen cyanide in the gas is substantially reduced and the yield of cyanogen chloride is substantially increased.
Moreover the cyanogen chloride obtained is essentially free from oxygen so that the trimerization of the cyanuric chloride can be carried out in a much simpler way than heretofore.
Furthermore, compared with the conventional reaction process by direct chlorination of hydrogen cyanide, there is the additional advantage that the hydrochloric acid obtained in the chlorination can be immediately converted into cyanogen ' ' ' ' ' . ' :

chloride and the separation of the hydrochloric acid is dispensed with.
Likewise, in the process according to the invention the removal of the water along with the catalyst solution from the recycle solution with the aid of cation exchangers is particularly favourable as in copending application No.~ 6~, filed on even date herewith. The recovery of the catalyst solution described therein, even that for special cases, can be used for the process of the present invention.
Thus it has been 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 solution by way of an ion exchanger. ~he copper ions and the iron ions are bonded by the ion exchanger and the 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 polystyrene with weakly acid exchange-active s~- - . - .
`''.'' ~ ' ' -' , ~077Z34 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.
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 regenerated 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 temperatures 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 dicyanogén can be avoided to a great ~;
extent by the measures described above. The decomposition of hydrogen peroxide is also kept within narrow limits.
The present invention will be further described -~
by way of the following Examples in conjunction with the accompan-ying drawings in which;
Fig. 1 is a schematic of a continuous process according to one embodiment of the present invention in a single reactor and Fig. 2 is a schematic of a continuous process according to another embodiment of the present invention in two reactors.
Example 1 In the pilot-plant apparatus shown in Figure 1, 45 litres of an aqueous solution of 13.0 g of CuCQ2~2H2O per litre -~: :
. ~ . , ::
~ .

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and 6.7 g of FeCQ3 6H20 per litre are recycled by way of reactor I, its upper portion II, relaxation tank III and washer VI.
1.6 kg of hydrogen cyanide, which is stabilized with a 0.1% by weight orthophosphoric acid, are added per hour in the liquid form through pipe 1. This solution is fed into the reactor I through pipe 8 and pump 8a. 2.0 kg of chlorine gas per hour are added through pipe 3 and half the amount of hydrogen cyanide is thus reacted to cyanogen chloride and hydrogen chloride.
Because of the cyanogen chloride gas formed a pressure of approximately 3 bars is built up in the reactor I with the upper portion II and the pressure wash V. The reactor I
is blocked bythe pressure valve 5a. At a pressure lower than

3 bars the cyanogen chloride goes into solution up to 5% by weight.
The cyanogen-chloride-containing catalyst solution is passed through the pipe 6 into the relaxation tank III and its pressure is reduced by means of the valve 6a.
The solution with approximately 1 to 2% by weight of cyanogen chloride then is returned to the reactor I through pipe 7, washer VI, pipe 8 by pump 8a. By adding 2.22 kg of a 50% by weight of hydrogen peroxide per hour, added in an excess of 10% above the equivalent amount through pipe 2, the hydrochloric acid formed in the reactor II by chlorination is reacted in reactor I with the other half of the amount of hydrogen cyanide to form cyanogen chloride.
Thus, in the continuous operation the entire hydrogen cyanide and the hydrochloric acid formed during the chlorination are continuously consumed in the catalyst-containing recycle solution by the reaction to cyanogen chloride and the pH value in the recycling solution is steadily maintained at 0.25 to 0.35.
The gas mixture (2~ N2, CO2) formed by the slight decomposition of the hydrogen peroxide and by the oxidative 1077Z3~

saponification of the hydrogen cyanide accumulates in the upper portion II of the reactor I, and is passed through pipe 5 to the pressure wash V, where it is washed until it is free from cyanogen chloride, whereupon it is discharged through the pressure-maintaining valve 5a. The solution required for the pressure wash is removed from the relaxation tank III through pipe 10 and valve lOa, is dealcoholized in the dealcoholization column IV and then fed to the pressure wash V through pipe 11 and pump lla. From the pressure wash V the solution is returned to the reactor I through pipe 13 by pump 13a.
The water fed with the hydrogen peroxide into the recycle solution as well as water being formed during the reaction is drawn off below the chlorine-gas inlet pipe 3 and is passed into dealcoholization tank VII through the pipe 9 and the relaxa-tion valve 9a.
The catalyst solution removed at this point contains only approximately 0.4% by weight of hydrogen chloride and no longer any hydrogen peroxide.
After the dealcoholization in tank VII, this catalyst solution passes through pipe 15 and the valve 4a or 4b into ion exchanger VIII, where it is freed from cupric and ferric ions and passed through pipe 16 to waste. The loaded exchange column is regenerated by adding a 10% by weight aqueous solution of hydrochloric acid through pipe 4 after the column had been washed with a 0.5% by weight aqueous solution of caustic soda in order to separate the phosphoric acid prior to recovering the copper and iron ions.
The catalyst solution thus freshly produced is recycled through pipe 17 by pump 17a as well as through pipe 8 to be recycled.
The gas emerging from IV through pipe 12 and from VII

through the pipe 14 contains primarily the hydrogen cyanide not ~077Z3~
reactedinthe reactOr I, in addition to cyanogen chloride. The unreacted hydrogen cyanide is washed in VI, by way of pipe 18, and returned to the reactor I through pipe 8 by pump 8a.
Example 2 In the pilot-plant apparatus shown in Figure 2, 65 litres of an aqueous solution of 13.0 g of CuCQ2 2H2O per litre and 6.7 g of FeCQ3 6H2O per litre are recycled by way of the oxidation reactor I, relaxation tank III, chlorination reactor II, relaxation tank IV and back to the reactor I.
Through pipe 1, 0.8 kg of hydrogen cyanide, stabilized with 0.1% by weight of H3PO4 are added per hour in the liquid form. This solution is chlorinated to cyanogen chlorine in the reactor II by adding 2.0 kg of chlorine per hour through pipe 4.
In the reactor II blocked by the pressure-maintaining valve lla a pressure of approximately 3 bars is built up by the cyanogen chloride formed. At a pressure below 3 bars the cyanogen chloride goes into solution up to 5% by weight. When the pressure is exceeded, then the solution passes into the relaxation tank IV, where cyanogen chloride is set free except for 1 to 2%
by weight. The solution with reduced pressure passes into the oxidation reactor I through line 12 by the pump 12a after 0.8 kg of hydrogen cyanide had been added to it per hour through pipe 2.
2.22 kg of a 50% hydrogen peroxide, 10% excess, are added per hour through pipe 3 and in its presence the hydrochloric acid (1.08 kg of HCQ) formed in the chlorination reactor II is also reacted with hydrogen cyanide to cyanogen chloride. In the reactor I, too, a pressure of approximately 3 bars is built up by the gases being formed. This pressure is kept constant by the pressure-maintaining valve 6a. The cyanogen chloride dissolved under pressure is freed by reducing the pressure of the catalyst solution passing into the relaxation tank III by the relaxation valve 7a. It is passed through the pipe 21 after 11)77~34 drying, to the trimerization together with the cyanogen chloride from the relaxation tank IV and combined in the pipe 22.
The solution, which had its pressure reduced in tank III is passed through the pipe 8 to the washer VII, where the waste gas from the dealcoholization columns V and VIII is washed until it is free from hydrogen cyanide.
The wash solution passes into the chlorination reactor II through pipe 10 by pump lOa.
From the relaxation tank IV acid catalyst solution is passed through pipe 13 and valve 13a into the dealcoholization tank V and then through pipe 14 by pump 14a to the pressure wash VI, where the gas mixture (~,N2,CO2) discharged through valve 6a is washed until it is free from cyanogen chloride. The wash solution passes into the reactor I through pipe 15 by pump 15a.
The waste water to be removed which has a content of hydrochloric acid of 0.3 to 0.4% by weight is drawn off through pipe 9 and valve 9a, dealcoholized in VIII and freed from Cu +
and Fe + ions through pipe 16 and valve 5a or 5b.
Since phosphoric acid is to be separated, in addition to copper and iron ions, with the ion exchanger and since the phosphoric acid adheres to the ion exchanger, this phosphoric acid is first washed with a 0.5% by weight aqueous solution of caustic soda before the copper and iron ions are washed and returned.
The waste water is then discharged through pipe 23 into the sewer (2 litres per hour).
Commercial cation exchangers can be used as ion exchangers. Thus, for example, ion exchange resins based on polystyrene or polystyrene-divinyl-benzene are suitable.
Macroporous iron exchangers based on~polystyrene with weakly acid exchange-reactive groups are preferably used.
Apart from alkali liquors, alkaline reacting salt _ g _ ., ~

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solutions, as for example, alkali carbonates or acetates, are suitable for separating the phosphoric acid.

Claims (15)

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

1. In a continuous process for producing cyanogen chloride by reacting hydrogen cyanide and hydrogen chloride or hydrochloric acid with hydrogen peroxide in a recycling aqueous catalyst solution containing cupric and ferric ions, the improve-ment in which the reaction is carried out under an elevated pres-sure of 1.5 to 16 bars and cyanogen chloride is recovered separ-ately from oxygen and nitrogen, the reaction component hydrogen chloride or hydrochloric acid being at least partially formed directly in the recycling catalyst solution of cupric and ferric ions by reaction of chlorine and hydrogen cyanide.

2. A process as claimed in claim 1 in which the reac-tion of the chlorine and hydrogen cyanide is effected at elevated pressure.

3. A process according to claim 2 in which the elevated pressure is from 1.5 to 16 bars.

4. A process according to claim 1 or 2, in which the elevated pressure is from 2 to 4 bars.

5. A process as claimed in claim 1 or 2 in which the pH value is between 0.1 and 0.5.

6. A process as claimed in claim 1 or 2 in which the pH value is between 0.25 and 0.55.

7. A process as claimed in claim 1 or 2 in which the temperature is from 40 to 60°C.

8. A process according to claim 1 comprising recircu-lating the reaction solution, releasing the pressure on the reaction solution to reduce the solubility of the dissolved cyanogen chloride and enable the cyanogen chloride to be separated from the aqueous reaction solution, stripping a portion of the thus-pressure-released reaction solution to remove cyanogen chloride therefrom, and sending said stripper portion to a pressure washer, maintaining the pressure in the pressure washer by the oxygen, nitrogen, carbon dioxide and cyanogen chloride-containing gases formed in the reaction, and employing a portion of the pressure-released reaction solution for washing the cyano-gen chloride gas volatilized during the stripping to remove hydrogen cyanide therefrom.

9. A process as claimed in claim 1 in which the recycling catalyst solution is contacted with a cation exchanger to remove the cupric and ferric ions therefrom, the denuded solu-tion is passed to waste and the catalyst solution regenerated by contacting the loaded ion exchanger with a mineral acid.

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

11. A process according to the claim 9 or 10 in which the cation exchanger is a macroporous ion exchanger based on poly-styrene with weakly acid exchanger-active groups.

12. A process according to claim 9 or 10 in which the catalyst solution contains phosphoric acid, the treatment of the cation exchanger with mineral acid being carried out after a pretreatment of the exchanger with alkaline reacting substances.

13. A continuous process for producing cyanogen chloride by the oxidation of hydrogen cyanide and hydrogen chloride or hydrochloric acid with hydrogen peroxide in a recirculating aqueous catalyst solution containing cupric and ferric ions, the hydrogen chloride being produced in the recirculating solution by the chlorination of hydrogen cyanide, and water passing into the recirculating solution being discharged while recovering the cupric and ferric ions, the oxidation and the chlorination each being carried out in a reactor at a pressure of 1.5 to 16 bars such that chlorine and hydrogen peroxide are unable to react with each other in the recirculating reaction solution, the pressure of the reaction solution being relaxed after both the oxidation and chlorination for the separation of the cyanogen chloride, a portion of the relaxed recirculating chlorinated solution being dealcoholized and passed for a pressure wash of oxygen, nitrogen oxide, carbon dioxide and cyanogen chloride containing gas obtained during the reaction and the remaining portion of the relaxed recirculating solution being used for washing the hydrogen cyanide containing cyanogen chloride escaping during the dealco-holization.

14. A process as claimed in claim 14 in which the oxidation and chlorination are carried out jointly.

15. A process as claimed in claim 14 in which the oxidation and chlorination are carried out separately.