Process for the production of chlorine

Holder: Same (7l)

Agent: Bert & de Keravenant, 115, boulevard Haussmann, Paris (8).

(54) Process for the preparation of chlorine from hydrochloric gas.

72) invention of:

33) (32) (31) Convention priority: Patent application filed in the Federal Republic of Germany on December 20, 1969, η. P 19 63 946.4 on behalf of your plaintiff.

Sale of booklets at the IMPRIMERIE NATIONALE, 27, rue de la Convention - PARIS (15^e) ~ 1 =

42575 the invention relates to a process for the preparation of chlorine from hydrochloric gas or gas containing it

New processes for the preparation of. For some time now, chlorine have been gaining in importance because of the increasing chlorine needs of the chemical industry and in particular of the plastics industry. Above all, processes are sought which make it possible to recover chlorine from the hydrochloric gas formed during the chlorination of organic substances or during the flame hydrolysis of silicon halides or halogenated silanes or halogen silanes._sand this in a simple and economical way

It is known to transform hydrochloric gas into chlorine using oxygen in the presence of a catalyst based on potassium chloride and iron chloride._p by passing a mixture of gases at 450° C. through the molten catalyst.

This process makes it possible to transform approximately 60% of the hydrochloric gas into chlorine, but it requires a large expenditure of electrical energy to maintain the catalysts in the liquid state. In addition, the hydrochloric gas must be dried before its decomposition and should not contain_p as much as possible_s foreign gases. But generallyp the hydrochloric gas to be regenerated is humid and diluted by foreign gasesp so that the conversion must be preceded by expensive separation and drying measures.

the object of the invention is therefore to find a process which makes it possible to regenerate chlorine from humid hydrochloric gas and diluted by foreign gases_? as obtained, for example, in the flame hydrolysis of silicon halides or halosilanes to pyrogenic silicon dioxide₃simply and without expensive equipment.

For this purpose_s the present invention relates to a process for the preparation of chlorine from hydrochloric gas or from gas in containers, characterized in that the hydrochloric gas is transformed into an aqueous solution having an HOl content of 20 to 40% by weight₉ preferably $25 — $35 in weight_ÿ and 02s.

then transforms it into chlorine with hydrogen peroxide.

It is surprising that this oxidation reaction in an aqueous medium requires the minimum concentrations of hydrochloric acid indicated when it is desired to obtain good yields.

At concentrations below 20 there is practically no chlorine formation. On the contrary, we observe a stagnation /U 42S/Ô

- 2 2072469 d© consumption of HCl and strong decomposition of hydrogen peroxide. For the oxidation of dissolved hydrochloric gas, aqueous solutions of hydrogen peroxide with a content of up to to use concentrations of hydrogen peroxide which do not bring too great a dilution of the reaction medium by adding water from dissolutions, but which;, on the other hand, do not require too expensive a preconcentration. These concentrations are between 4-0 and 70% HgOg. From an economic point of view, a fraction containing 50% hydrogen peroxide, originating from the known anthraquinone s⁰is shown to be particularly favorable

The hydrochloric gas to be transformed can be made to be absorbed in water until the desired concentration is obtained (for example 25-35 $ by weight). yet absorbs directly into hydrochloric acid of the desired concentration.

According to another advantageous embodiment of the process of the invention, the hydrochloric acid used for the absorption of the hydrochloric gas is maintained at a temperature at most 20° above ambient temperature, generally between 27 and 35° C. The choice of the optimum absorption temperature generally depends on the inert gas content of a gas mixture containing HC1„ If this content is high, it is necessary, to avoid HCl losses at the top of the absorption column, spraying with hydrochloric acid at a temperature which sufficiently lowers the partial pressure of the hydrochloric gas

A considerable advantage of the method of the invention compared to the methods described at the beginning is the fact that the transformation takes place already at room temperature or at a slightly higher temperature, at a sufficient speed, which avoids the application of heat energy. additional participants in the reaction, hydrochloric gas and hydrogen peroxide, can, depending on the embodiment chosen, be mixed at the planned temperature, of the absorbent or at temperatures which correspond to those due to the exothermic reaction in the transformation medium » These latter temperatures are generally situated below 60° G » the release of the chlorine formed during the reaction can be influenced by performing the reaction under pressure

U 420/0

20/2407 = 3 reducedo In some cases_B it may be useful to remove chlorine from the aqueous phase using purge gas₉ preferably air_p or combine these two means®

Lu unprocessed hydrochloric acid can₉after cooling to temperature⁸absorption9 be recycled as an agent of⁸absorbe the process can be carried out continuously or discontinuously. In the case of a continuous reaction_s the water introduced can be drawn off with the hydrogen peroxide and the water formed during the reaction in the form of dilute hydrochloric acidp to maintain the expected concentration of hydrochloric acid®. A reduction in the concentration of hydrochloric acid can be avoided by parallel introduction hydrochloric gas®

According to another embodiment of the method of the invention_p the chlorine gas obtained is washed against the current with hydrochloric acid of the intended concentration (for example 25-35% HCl) preferably cooled to 0° which eliminates the small quantities of hydrochloric gas possibly contained in the chlorine gas ®

For the continuous implementation of the process, the operating modes described below have proven to be particularly practical ®

According to a preferred embodiment close to the practice, the hydrochloric gas is first separated from the gases which contain it;, for example a mixture of HC1₉ water vapor and air_p by backwashing, possibly in several stages_p with hydrochloric acid of the concentration provided, then optionally with water, the eluate is eliminated before its transformation with hydrogen peroxide₉ the heat of absorption p the cooled eluate is then passed co-currently with hydrogen peroxide over the fillers of a reaction tower_Bthe chlorine gas formed is drawn off against the current and part of the dilute hydrochloric acid is released, which returns to the absorption stage to eliminate the excess water®

This method allows chlorine to be obtained even from gas mixtures with a very low HCl® content.

Another preferred continuous process is as follows g the hydrogen chloride gas is separated from the gases which contain it by backwashing, possibly in several stages, with hydrochloric acid of the intended concentration / V “t 4 ZU/ZHU7 and possibly with water_B the eluate is boiled until the azeotrope containing approximately 22% of hydrochloric acid is obtained; the hydrochloric gas thus desorbed is passed countercurrently to the hydrochloric acid of the planned concentration and water oxygenated and in the direction of flow of the chlorine formed on the fillers of a reaction tower p a part of the dilute hydrochloric acid formed is recycled to the reaction and the azeotropic hydrochloric acid is separated to eliminate the excess water

This method therefore produces inside the reaction tower both an oxidation of the hydrochloric gas and a concentration of the hydrochloric acid introduced which opposes the effect of dilution due to the water introduced by the water. hydrogen peroxide and the water formed during the reactions * A third possibility of practical implementation of the process consists in passing the hydrochloric gas without prior separation of the diluent gases directly into an aqueous medium and in oxidizing it with hydrogen peroxide_s by obtaining as the product of the reaction a gaseous chlorine diluted by the accompanying gases the process is essentially based on the fact that the hydrochloric gas is passed from the gases which contain it against the current of the acid hydrochloric acid of the planned dilution and hydrogen peroxide and in the direction of the flow of chlorine r

formed on the reaction bodies of a column which serves as a reactor_s the chlorine obtained and the waste gas are washed_s for example in a column with bell trays_s with water_B the hydrochloric acid is recycled to the reactor after cooling to the expected absorption temperature of part of the hydrochloric acid stream₉hydrochloric gas is desorbed until the azeotrope is obtained and > n separates the hydrochloric acid, azeotrope to eliminate the euexees ectu_has

This variant of the process allows a particularly compact layout of the equipment $ it is preferably chosen when gas with a high HCl content is available_ethe yields of gaseous chlorine obtained in the process of the invention are very high and are practically greater than 90%_s calculated against

To carry out the process_B no special devices are needed® For the absorption and the reaction one can

42575 = 5 2072469 implement backwashers of any model_has for example counter-current columns fitted with packing bodies and the like. The desorption of HCl from hydrochloric acid until the azeotropic solution (approx.

The chlorine obtained during the reaction can be treated by known means.

The invention makes it possible to obtain the following advantages over the state of the art, g

a) wet hydrochloric gases can be used;

h) almost quantitative yields of chlorine compared to the hydrogen peroxide used $

c) unnecessary use of catalysts g

d) transformation without supply of heat energy g

e) realization in known devices®

The invention will be better understood from the accompanying examples and drawings representing embodiments of the invention.₉ drawings in which g

- Figure 1 .represents a process diagram for obtaining chlorine from gaseous mixtures with a low HC1 content₉ according to example 1 g

-figure 2 represents a diagram of a variant® of the process which provides for a concentration of the hydrochloric acid® in reaction j, in accordance with example 2 and

- Figure 3 shows a process diagram for obtaining chlorine from gas mixtures with a high HClj content, in accordance with example 3®

Example 1

A gas mixture composed of

695 ÎTm^/h of air - corresponding to 896 kg/h air 196 Nm^/h HCl (=20_p7 % by vol) - corresponding to 320 kg/h-HCl and 46 Nin^/h HgO - corresponding to 37 kg/h is introduced according to figure 1 into a column with filling 1 of 500 mm 0 and 2 m filling height (35 mm fiaschig rings of 0)® The column is sprayed with 10 nr/h of a 28% hydrochloric acid (11,400 kg/h) at an inlet temperature of

30° G® Hydrochloric acid absorbs most of the gas

425/5 hydrochloric acid and leaves the absorption column at about 45⁰ C and at a concentration of about 30%_e the rest of the hydrochloric gas contained in the gas mixture is eliminated in a column with bell plates 2_s'rise following₉ which is supplied with approximately 50 l/h of water_p the hydrochloric acid which flows out being mixed with the hydrochloric acid of the main absorption during the exothermic absorption, 18 kg/h of water vapor is eliminated with the air; the hydrochloric acid at about 30 % leaving the

W column 1 (11,790 kg/h) is cooled in condenser 3 to about 30° 0 and fed to the head of reaction column 4 having approximately the same dimensions as column 1. this column 210 kg per hour of an aqueous solution of hydrogen peroxide at approximately 50 $><, II is formed 203 kg per hour of

Clg which are then washed with hydrochloric acid at 28 / to. 0° C in column 5_r the hydrochloric gas being thus reduced to a content of 2 g/kg of chlorine. of 0^4 atm absolute at most in columns 4 and 5® the gaseous chlorine is liquefied in a known way

At the foot of column 4? the flowing hydrochloric acid (11,793 kg/h) at a temperature of 50° C. and at a concentration of about 28% by weight is fed by a pump 7 to the cooler 8₉ is cooled to 30° C and brought back to the tower the tower to remove excess water ©n removes from the cycle 393 kg of hydrochloric acid per hour_P containing approximately 110 kg HCl® the yields are calculated as follows s transformation of HCl s

Hydrochloric gas introduced in the form of hydrochloric acid s 320 kg/h g. Theoretical chlorine output g 312 kg/h §

Chlorine obtained g 203 kg/h_s corresponding to a yield of around 65%

Transformation of Η2θ2^g

Introduced HgOg (100 g 105 kg/h °

Calculated output in chlorine g 219 kg/hg

Chlorine yield g approx. 93%_has

In all, therefore, approximately 65% ​​of the chlorine gas is transformed into chlorine._e while the yield relative to the

425/5 »

HgOg implementation is 93%.

Example 2

Separating from a gaseous mixture of 1,252 Nm^/h of air - corresponding to 1,615 kg/h of air =

313 nm³/h HCl (=20% by volume) = corresponding to

510 kg/h HCl hydrogen chloride gas as described in example 1 by absorption in columns 1 and 2 (see figure 2). the 35% hydrochloric acid thus obtained (3,140 kg/h) is fed to a desorption column 3 and 510 kg per hour of hydrochloric gas are eliminated by boiling, the hydrochloric acid is reduced to a concentration of 22% (azeotrope) and 3150 kg/h of the azeotrope were distributed as follows: s 2630 kg/h flow from the bottom of the desorption column 3 towards the absorption column 1. To extract the excess water, 520 kg/h are eliminated.

the isolated hydrochloric gas (510 kg/h) is fed to a column packed with filler bodies serving as a reactor.

This column is sprinkled with 25 m^/h of 28% hydrochloric acid (28,500 kg/h) at an inlet temperature of approximately 30° 0. At the head of the column, one feeds by approximately 400 kg of an aqueous solution of HgOg at 50% per hour. 384 kg per hour of chlorine are drawn off at the top of the column.

hydrochloric acid_B diluted with the water from the reaction and the water contained in the hydrogen peroxide solution (30,063 kg/h)_Sflows at the bottom of reaction column 4. It is pumped to cooler 6 where it is cooled to 30° 0 before being recycled to the top of the column.

About 563 kg per hour of hydrochloric acid at 28 fa are drawn off from the cisuit of acid to remove the excess water.

This is led to the desorption mentioned above &lt;=above_p ra&lt;= led to the concentration of the azeotrope and 520 kg/h of hydrochloric acid at 22 containing 115 kg/h of hydrochloric acid are brought out. the desorbed hydrogen chloride gas (43 kg/h) is returned to the process.

the chlorine drawn off at the head of the column is then washed (as in example 1) in the washer 5 with a 28% hydrochloric acid solution cooled to 0° C. in the refrigerator 7 to be freed from the rest of the gas hydrochloric acid and steam, the liquid flowing from the scrubber 5 is recycled and combined with that which leaves the reactor 4.

“-tZ. J! U

Residual content after washing g &lt;^l_s5 g HgO/kg Cl₂4 2 g HCl/kg Cl₂ the system operates under a pressure of 0_ε4 absolute atm obtained -by the compressor 8_S

The yields are as follows g

Transformation of HCl g

Hydrochloric gas introduced s 510 kg/h % Calculated chlorine yield s 497 kg/h; Chlorine obtained g 384 kg/h_P corresponding to a yield of 77_g5 % approx®

Transformation of î^Og^s^Η2θ2 ^θθ implementation g 200 kg/h ° calculated chlorine yield g 417 kg/h₉Got chlorine? about 92%„ the chlorine yield_s calculated from the hydrochloric gas used, is therefore about 77₉5 %_p calculated according to the hydrogen peroxide implemented approximately 92%®

Example 3

<img file="FR2072469A5_D0001.tif" />

hydrochloric acid at 32% (58,000 kg/h) at 30° C® In addition, 499 kg/h of a solution of hydrogen peroxide are added to the top of the column

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of air 51 kg/h HgO kg of θ ^2^con1^{::in year}1' small residues of HCl® In a column with bell trays 2 then mounted and sprayed with 221 kg/h of water₉ the rest of the hydrochloric gas is removed and brought back to the main column® the hydrochloric acid flows from column 1 at a temperature of about 43° C and is brought back, after cooling to 30° C in the condenser column 1®

998 kg per hour of 32% hydrochloric acid are drawn off from the acid circuit and returned to desorption 3 by boiling at 22%_B which releases 128 kg/h of hydrochloric gas which is recycled to the process®

To remove excess water,₉ 871 kg/h of 22% hydrochloric acid containing about 192 kg HCl® is drawn off, the yields are as follows g

425/5 « 9 «

Conversion of HQ1 g Hydrochloric gas used s 932 kg/hg Calculated chlorine yield g 907 kg/h °

Chlorine obtained g 713 kg/h₉ corresponding to a yield of 79% j

Transformation of g ^2θ2 ^θθⁱⁿ oh^epound § 350 kg/hg

Calculated chlorine yield g 730 kg/hg Chlorine yield g approx. 97_s5 7°·

In all p about 79 7° of the hydrochloric gas used is transformed into chlorine_s while the yield with respect to HgOg is 97p5 7°°

Of course, the invention is not limited to the embodiments described and represented above, from which other shapes and other embodiments can be provided, without departing from the framework of the invention. invention.

42575

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