DE1940290C - Process for the separation of hydrogen chloride from a gaseous mixture of the same with cyanogen chloride - Google Patents

Description

a) the gaseous mixture within an absorption zone in a countercurrent process contacted an aqueous liquid stream, in this stream essentially the all hydrogen chloride is absorbed from the mixture.

b) entfeint ^ls a gas stream from the absorption zone overhead which mainly consists of Chlorcyandampf.

c) from the aqueous effluent from the absorption zone. which essentially contains chlorinated water off, within an expulsion zone.: · .; Countercurrently drives off the remaining cyanogen chloride with a chlorine-containing gas stream,

d) the HCl-containing substances flowing out of the expulsion zone The bottom stream heated to remove dissolved chlorine, whereupon the bottom stream was stripped off as practically pure hydrochloric acid will,

characterized in that the gaseous mixture is inside the absorption zone at a temperature of 15 to 25 ° C and a contact time of 0.3 ois about 3 seconds with the countercurrent aqueous liquid Electricity contacted.

35

The present invention relates to a process for the separation of hydrogen chloride from a ^; a gaseous mixture of the same with cyanogen chloride, which 25 to 75 mole percent and cyanogen chloride 75 to Mol percent of hydrogen chloride contains which one

a) the gaseous mixture within an absorption zone contacted in a countercurrent process with an aqueous liquid stream, in which stream substantially all Hydrogen chloride is absorbed from the mixture,

b) removed from the absorption zone overhead a gas stream, which mainly consists of cyanogen chloride vapor consists,

c) from the aqueous effluent from the absorption zone, which essentially contains hydrogen chloride, drives off the remaining cyanogen chloride within a stripping zone in countercurrent with a chlorine-containing gas stream,

d) the HCl-containing bottom stream flowing out of the stripping zone is heated to remove dissolved chlorine to remove, whereupon the bottom is drawn off as practically pure hydrochloric acid.

Cyanogen chloride is a valuable intermediate product for the production of cyanochloride, from which by further Implementation pharmaceuticals, herbicides, dyes, optical brighteners and synthetic resins are manufactured can be.

The production of cyanogen chloride from hydrogen cyanide and chlorine is carried out according to the following equation:

HCN + Cl, CNC! _T HCl

The reaction is either; n aqueous medium. z. In U.S. Pat. No. 3,147,273. Or in the gas phase, e.g. B. according to Chem. Abstr .. 15, p. 2593 (19211. carried out.

The hydrogen chloride formed in the reaction is usually absorbed in water, so that as A by-product of the process, an aqueous hydrochloric acid, is used for economic reasons ingestrebi. those for the absorption of the hydrogen chloride to measure the amount of water used so that a Aqueous hydrochloric acid with 20 to 30 percent by weight of hydrogen chloride is produced. The previously known processes of this type have essentially two disadvantages. These are that as a result the hydrolysis sensitivity of the cyanogen chloride increased yield losses must be accepted ui. J that as a result of the high concentration of hydrogen chloride in the aqueous phase makes the complete separation of hydrogen chloride and cyanogen chloride more difficult so that the cyanogen chloride obtained still contains small amounts of hydrogen chloride. Besides that Hydrogen chloride catalyzes the trimerization of cyanogen chloride to cyanuric chloride.

The hydrolysis and polymerization of cyanuric chloride in the presence of hydrogen chloride is the subject the studies by A. B. van C 1 e a r e and H. E. M i 11 ο n, on the Canadian Journal of Research, Vol. 25, Sec. B, pp. 430-439 (1947). Relate the findings of these authors only on the basic behavior of cyanogen chloride in the presence of hydrogen chloride and Water and cannot solve the problem on which the present invention is based can be used.

The object to be achieved by the present invention is to provide a method of the above mentioned type to provide a complete separation of hydrogen chloride from mixtures of hydrogen chloride and cyanogen chloride to obtain a strong, aqueous hydrochloric acid and as far as possible Avoidance of losses through hydrolysis enables.

This object is achieved by the fact that the gaseous mixture within the absorption zone at a temperature of 15 to 25 ° C and a contact time of 0.3 to about 3 seconds contacted with the countercurrent, aqueous, liquid stream.

In this way, hydrogen chloride can effectively be used as a highly concentrated aqueous solution of cyanogen chloride are separated off, while at the same time the loss by hydrolysis of this product is less than 1%. Furthermore, the inventive method for separating off hydrogen chloride in the form of a aqueous solution in concentrations of up to 25 to 30% without significant loss of cyanogen chloride by hydrolysis when the reaction of hydrogen cyanide and chlorine in the gas phase is performed.

The drawing shows a flow diagram of the formation of the reaction mixture of cyanogen chloride and hydrogen chloride and the subsequent separation of the same, with successive absorption and expulsion operations

Iions can be used according to a preferred embodiment of the present invention.

According to a preferred embodiment of the present invention, a hydrogen cyanide gas stream II in the cyanogen chloride reactor 13 is contacted with a chlorine gas stream 12. The anhydrous gaseous mixture is suitably reacted in the reactor 13. The gaseous effluent 14, which was thus produced by reacting the anhydrous reactants, preferably contains from about 25 to about 75 mol percent cyanogen chloride as the main product, from about 25 to about 75 mol percent hydrogen chloride as a by-product and up to about 50 mol percent of the unreacted chlorine. The hydrogen cyanide is the limiting reactant, the practically stoichiometric conversion. However, there are systems in which gaseous mixtures which lie outside the ranges given above are produced; for example, the amount of hydrogen chloride can range up to about 90 mole percent. However, these ranges are not considered critical provided that the contact time and temperature conditions set out below are maintained.

According to the invention, the mixture thus produced, which contains anhydrous hydrogen chloride, is separated by contacting the gaseous stream 14 within an absorber column 16 in countercurrent with a water stream 15. The absorber can be any of the usual types. z. 3. a flooded, unpacked column or an absorber with falling film, tray column with flooded trays, tubes or cascade designs.

The column should of course be made of acid-resistant material such as glass, tantalum, polytetrafluoroethylene (e.g. Teflon), chemically practically impermeable or inert graphite materials that are in Liquids are practically impermeable under pressure, made of corrosion-resistant compounds, such as are used in the manufacture of chemical process equipment such as a phenolic resin-graphite combination, and the like.

The current through the Ab ^ rl ^ f 16 is regulated so that a gas-liquid contact time of about 0.3 until about 3.0 seconds is obtained. Occasionally the absorber is externally cooled in order to control the temperature of the solution of hydrogen chloride and thereby the loss by hydrolysis to keep it low. In this way, the internal temperature of the absorber is kept around room temperature, around 15 to 25 C. If the temperature is so regulated, the losses due to hydrolysis are about 0.14 to 0.21% of the cyanogen chloride product obtained (cf. Example 10 below}.

The overflowing at the top of the absorber 17 consists of a gaseous stream which essentially contains cyanogen chloride (in concentrations of at least about 95%) and possibly some chlorine vapor as an impurity. This stream can, if desired, be used directly to produce cyanuric chloride by a suitable trimerization reaction.

The aqueous solution 18 from the absorber tower 16 contains hydrochloric acid, which is generally a Concentration of about 10 to 30%. It can also contain small amounts of cyanogen chloride.

for example from about 5 to KV ¹ ", preferably from about 1 to 5" n. corresponding to the temperature that is present inside the absorber.

The absorption solution then becomes countercurrent

with an exhaust gas 19 in a separator 21 contacted. Suitable gas can be air and / or chlorine gas, which removes the remaining cyanogen chloride from the drives out aqueous solution. An exhaust gas containing cyanogen chloride is removed at the top at 22 and can be used in

ίο the cyanogen chloride reactor 13 are returned for further use as a reactant. At the same time, a concentrated salt sump 23 is obtained which contains mainly pure aqueous hydrochloric acid. If an anhydrous gaseous mixture such as the exhaust gas 14 is separated in this way, it has been found that it is possible i-, ι. win hydrochloric acid solutions as sump 23, which have concentrations of about 10 to about 30 " .

If chlorine is used as the exhaust gas 19 and small amounts of ChIo 'are contained in the sump 23, it may be desirable to recover this chlorine and use it for further separation of cyanogen chloride dissolved in the sump or for further recycling.

settlement with hydrocyanic acid. In such cases the sump is passed into a boiling vessel 24 . from which a chlorine gas stream 25 is removed overhead and is added to stream 19. The sump 26 made of hydrochloric acid, further purified in this way, can then be used for storage and for further use.

The following examples serve to provide a more detailed explanation without, however, restricting it. they describe some embodiments of the invention Process for the separation of hydrogen chloride from gaseous mixtures of the same with cyanogen chloride.

Examples 1 to IU Separation of HCl mixtures under CNCl Use of unpacked Spray absorption columns

Equimolar gaseous mixtures of cyanogen chloride and hydrogen chloride were on the way.

as will be described below, with the reaction flow rates and operating parameters changed as in the following Table is given. Separate cyanogen chloride and chlorine were used for the experimental tests hydrogen streams mixed and the different Subjected to absorption and expulsion operations as shown in the drawing.

The cyanogen chloride charge was prepared by placing liquid cyanogen chloride in a water bath heated to boiling at a constant temperature and the amount flowing off was determined with a rotameter. The flow rate of the hydrogen chloride gas stream was controlled in a similar manner. The gas flows in question were flooded into a.

unpacked absorption coionne through a built-in glass sprayer in countercurrent to a Introduced water stream, the column was surrounded by chilled water, which in a The refrigeration cycle is pumped around and through acetone dryers ice has been cooled.

The sump of the absorber, which contained approximately 3 to 12% cyanogen chloride, was then placed in a 1.8 m high, given column filled with packing, and that

Cyanogen chloride was made from this by propellant gas that was released on The bottom of the column was discharged, aborted. In these experiments, air was used as the propellant gas, the column being charged with air at a rate equal to was only slightly below the plutation capacity.

Gases of the absorber passing over at the top were analyzed by gas chromatography. Samples of the The bottom of the absorber were also extracted with chloroform for the content of cyanogen chloride analyzed. The concentrations of the hydrochloric acid solutions, which were taken from the bottom of the column were determined by titration according to the standard method with sodium hydroxide, with Phcnolphthalcin was used as an indicator. The analyzes of the various experiments are in the Table I given.

It can be seen from the results of Example 1. that. if you have a 15% hydrochloric acid solution from the Separator wins, a hydrolysis loss of only 0.2% is observed. If the reaction parameters are set so that one 20% acid solution (Example 2) wins, so vary the corresponding losses due to hydrolysis of 0.75 to 1.1%. However, if the surface of the Reduced absorption column (Examples 3 to 10). whereby the contact time is also reduced, see above is the loss by hydrolysis, compared with that Loss, which is given in example 2. also decreased.

Similarly, it has been observed that the build-up of hydrolysis can be reduced considerably by lowering the jacket temperature of the absorber to temperatures of 5 to 10 ° C, thereby lowering the absorber temperature to the preferred range of about 15 to 25 ° C. In this connection it should be noted that the hydrolysis loss in Example 9, in which the absorber jacket temperature was maintained at 15 ° C, varied from 0.45 to 0.77%, whereas the hydrolysis loss in Example 10, with the absorber jacket temperature at temperatures from 5 to 10 ⁰ C was maintained (the internal absorber temperature was determined to be 15 ° C), was not more than 0.21%.

Examples 12 and 13

Separation of HCl / CNCl mixtures under
Application of a direct introduction into an absorber column packed with fillers

Mixtures of hydrogen chloride / cyanogen chloride gas

is were made in the manner as in Examples 1 to 11 but a packed absorption column was used (packed with glass filler), and taking the gaseous mixture through a glass tube instead of before Spray apparatus described was distributed. The absorber surrounded by a jacket was through an ethylcnglycol-water mixture, which has the internal absorber temperature between about 15 and 25 ° C held, and in this way the crust by hydrolysis,

as observed after the separation, stabilized

It is particularly noteworthy that in Example 12 a pressure of only 0.49 to 0.78% was determined by hydrolysis, although the HCl solution obtained from the vessel had a concentration of 26.8 to 27.3%. The successive Absorption-Dcsorptions-measures, which also regulate the contact times and the temperatures in the absorption zone allow precise control of hydrolysis loss during the separation significantly below 1% of the cyanogen chloride that is present in the original mixture.

Separation of gaseous CNCl HCI mixtures Examples I to 13

Delivery HO Shell temperature Column height Duration of the attempt game fast
Mole minute 11 ι V 1-
Gun wedge CNCI and IKI cm'I hours ml minute Ambient temperature 37 2 I. 0.049 10.2 22 to 23 C. the same 40 2 2 0.0904 13.2 the same 20th 2 3 0.0904 13.2 the same 10 to 15 1.5 4th 0.0904 13.2 the same 15 to 25 1.0 5 0.0904 13.2 the same 20th 1.0 6th 0.0904 13.2 the same 20th 1.0 7th 0.0904 13.2 the same 15th 1.0 8th 0.113 13.2 15 C 15th 1.0 9 0.113 13.2 5 to 10 C. 15th 1.0 10 0.113 13.2 (Absorber temperature 15 to 20 C) OC 15th 1 11th 0.154 13.2 (Absorber temperature 18 to 32 ° C) -5 to 10 C 15th 1.5 12th 0.154 13Y (Absorber 18 to 23 ° C) -5 to iac 15th 2.0 13th 0.154 13.2 (Absorber 15 to 25 C)

* | Inner diameter - 2.5 cm

Overhead example analyscii % CNCI 1 99.5 2 99.5 3 99.5 4th 99.5 S. 95 6th 95 7th 95 K 95 9 95 K) 95 Π 95 12th 96 13th 95

(Absorber) _% HCI

less than 0.5%

less than 0.5%

less than 0.5%

less than 0.5%

(5% air)

(5% air)

(5% air)

(1% HCl. 5% air)

(5% Cl ₂ , inside)

(5% Cl ₂ , Γ / ο HCI)

(5% Cl _2. 1% HCl)

4%

5%

Absorption sump

N / A

N / A

N / A

3.6

3.6

3.9 to 4.0

11.6
11.5

Abortion swamp

% HCI

14 to 15 20 to 21 20 to 22 20 to 20.3 19.4 to 20.9 20.8 to 21.5 20 to 22.7 22.4 to 23.9 24 to 24.9 23 to 24.6 27.6 to 28.1 26.8 to 27.3 26.1 to 27.2

0.003 to 0.010
0.05 to 0.08
0.02 to 0.05
0.025 to 0.040
0.016 to 0.042
0.012 to 0.034
0.022 to 0.075
0.054 to 0.098
0.04 to 0.07
0.014 to 0.018
0.079 to 0.333
0.049 to 0.077
0.023 to 0.073

Hydrolysis loss

0.07 to 0.20 0.75 to 1.1 0.20 to 0.75 0.32 to 0.52 0.22 to 0.58 0.19 to 0.43 0.30 to 0.98 0.65 to 1.10 0.45 to 0.77 0.14 to 0.21 0.77 to 3.2 0.49 to 0.78 0.23 to 0.73

For this purpose L sheet drawings

309 63

Claims (1)

Claim: Process for the separation of hydrogen chloride from a gaseous mixture of the same with Cyanogen chloride, which contains 25 to 75 mol percent cyanogen chloride and 75 to 25 mol percent hydrogen chloride. with which one