DD290858A5 - INDUSTRIAL PROCESS FOR SEPARATION AND RECOVERY OF CHLORINE - Google Patents

Abstract

The invention relates to a process for removing chlorine from a gaseous mixture comprising chlorine gas and carbon dioxide gas. The process of the present invention comprises adding a solution or suspension containing an alkali metal sulfite and / or an alkaline earth metal sulfite, and washing the gaseous mixture with the solution or suspension, during the pH of the solution or suspension within a range of 1.9 to 6 3, whereby chlorine alone is removed from the gaseous mixture. {Chlorine removal; Chlorine gas / carbon dioxide gas; Chlorine alone removed}

Description

For this 4 pages drawings

Field of application of the invention

The invention relates to a process for the separation and recovery of chlorine from a gaseous mixture containing chlorine, carbon dioxide and non-condensable gas. The invention also relates to a method for removing chlorine from such a gaseous mixture.

More particularly, the invention relates to a process for separating and recovering chlorine from a gaseous mixture containing chlorine, carbon dioxide and noncondensable gas in high concentrations. The invention also relates to a process for recovering chlorine from a gaseous mixture containing chlorine, carbon dioxide and at least 50% by volume of non-condensable gas. Furthermore, the invention also relates to ei.) Process for absorbing and removing chlorine gas contained in carbon dioxide gas, which is formed in the production odor wounding of chlorine.

Characteristic of the known state of the art

A variety of processes have been proposed for the recovery of chlorine from a chlorine-containing gaseous mixture, for example, in the following patent publications:

(1) In U.S. Patent Nr.3,972,691 a process for recovering liquid chlorine from a gaseous mixture is described which 20-90% in volume fraction of chlorine, 10-80 ⁰ ^ '* -' '' imenanteilen carbon dioxide, nitrogen, Oxygen and carbon monoxide. The method comprises compressing the gaseous mixture to 4 to 8 atm, cooling and liquefying the compressed gaseous mixture in a total reflux-type rectification column, and then adjusting the temperature of liquid chlorine accumulated in a bottom portion of the rectification column to evaporate carbon dioxide ru, which is dissolved in the liquid chlorine.

(2) US Pat. No. 2,199,797 states that an organic contaminant contained in a concentration of 1% by mass or lower in chlorine gas can be removed with liquid chlorine by mixing the chlorine gas with liquid chlorine in one Washing column is brought into contact in countercurrent.

! 3) In British Patent No. 938,073, a method of separating a non-condensable impurity having a lower boiling point than chlorine and forming an exclusive mixture with chlorine of gaseous chlorine containing this impurity is described. The method comprises gradually lowering the temperature of the gaseous chlorine and contacting the final gaseous residue countercurrently with liquid chlorine, the temperature of which

the condensation temperature of gaseous chlorine or lower has been lowered in a liquefaction column to liquefy gaseous chlorine, thereby separating chlorine from the low boiling point impurity.

(4) In U.S. Patent No. 3,443,902, there is disclosed a method of compressing chlorine gas obtained by contacting a chlorine gas containing impurities countercurrently with liquid chlorine in a scrubbing column, and the contaminant from then on has been absorbed and removed from the liquid chlorine to thereby liquefy a part of the chlorine gas by its heat exchange with the liquid chlorine in the washing column and then to use the thus liquefied chlorine for the same purpose as the above-mentioned liquid chlorine.

(5) British Patent No. 1,164,069 teaches that a gaseous mixture consisting of noncondensable gas, including nitrogen and chlorine, can be separated into liquid chlorine and the non-condensable gas separated by the gaseous mixture 6 to 10 Atm is compressed, the compressed gaseous mixture is cooled in two stages and then the cooled gaseous mixture further to -12O ⁰ F (-84.4 ⁰ C) to -15O ⁰ F (-101 ⁰ C) is cooled by heat exchange ,

(6) US Pat. No. 2,540,905 describes a process for recovering chlorine in a carbon dioxide-free form. The method comprises absorbing chlorine from a liquefaction residual gas obtained after electrolysis of liquor and containing 5-10% by mass of chlorine together with carbon dioxide, carbon monoxide, hydrogen, nitrogen, oxygen and other gaseous components with a chlorinated solvent, whereupon then carbon dioxide, which has been absorbed at the same time, is caused to evaporate at a temperature higher than the absorption temperature by a method such as heating a lower part of an absorption column.

(7) US Pat. No. 2,765,873 describes a process for recovering chlorine in a form substantially free of non-condensable gas. Wherein the method is effected in that a solvent, a gaseous mixture consisting of 30-50% by mass of chlorine and air, under a pressure from 2.0 to 14.3 atm at a column temperature of above ⁰ C to -22.8 32.2 ⁰ C and a column bottom temperature which is higher by 27.8 ⁰ C to 52.8 ⁰ C than the column temperature above absorbed.

(8) In DE Patent No. 2413358 a method is described for absorbing chlorine alone from a mixture of chlorine and carbon dioxide gas as the hydrochlorite of an alkali metal and / or alkaline earth metal using a multi-stage countercurrent absorption apparatus, wherein an alkali metal hydroxide and / or an alkaline earth metal hydroxide is used and the apparatus is operated while the pH of the liquid side final stage is controlled to about 7.5.

The methods described in publications (1), (2), (3) and (4) are used respectively when chlorine or chlorine and carbon dioxide are contained as one or more condensable components at relatively high concentrations. For the recovery of chlorine from a chlorine-containing gaseous mixture in which the concentration of non-condensable gas is about 50% by volume or even higher, these processes are accompanied with disadvantages due to the excessive presence of non-condensable gas.

In all of these methods, countercurrent contact between the descending liquid chlorine and the ascending crude chlorine gas is employed in a column, although their purposes are liquefaction, washing and distillation, respectively, and therefore differ from each other. If non-condensable components are contained in a rising crude chlorine gas in a high level, it is impossible in this way. Entrainment due to the rising gas and a reduction in the efficiency of the gas-liquid contact due to channeling in the descending liquid or a similar reason to report, whereby it is difficult to achieve their separation to the desired extent. If the amount of the descending liquid is increased in order to maintain the efficiency, both the cooling capacity and the heating capacity of the distillation column increase and, in addition, larger units of larger equipment - such as column main body, condenser and recooler - must be used. This technical solution is therefore not economical. In the case of the method (4), the circulation load of the non-condensable -> ases becomes extremely large and the dew point of the compressed gas decreases. When the compression pressure is low, there is a potential problem that chlorine can not be liquefied in its heat exchange with the scrubbing column. Even if liquefaction is feasible, energy costs increase because of an increased compression ratio of the compressor and an increased circulation load, so that the advantage of this method is lost.

Furthermore, the methods (1) and (5) are basically determined for chlorine gas having a high concentration. A chlorine-containing gaseous mixture to be treated is compressed and cooled to liquefy chlorine for its separation. However, these methods are intended for the recovery of high purity chlorine. Therefore, an exhaust gas separated from chlorine and composed mainly of non-condensable gas contains chlorine in a high concentration of 5-9% by volume in the method (1) and 10% by volume even in the method (5). The industrial recovery of chlorine creates an atmospheric pollution problem by venting an exhaust gas containing chlorine at such high levels. For a gas to be in a state of being exhausted as exhaust gas, it must be free of chlorine. However, this requires at least one chemical in an immense amount for the removal of chlorine, not to mention equipment and, moreover, it leads to a loss of chlorine. These methods are therefore not economical. In order to reduce the chlorine content in an exhaust gas to such a low level that the chlorine can be neglected, it is necessary to further increase the compression pressure while further lowering the cooling and condensing temperature. This in turn leads to increased energy costs and also to increased cooling costs. Moreover, for safety reasons, it is not advantageous to compress a chlorine-gaseous mixture to a high pressure. In addition, it is not allowed to lower the cooling and condensing temperature to the freezing temperature of carbon dioxide (-56.6 ⁰ C at 5.2 atm.) Or lower in order to avoid clogging of equipment due to the occurrence of dry ice. Such a liquefaction process therefore can not avoid the inclusion of chlorine at a certain concentration in an exhaust gas.

The methods (6) and (7) both use a solvent by which an impurity is absorbed and then desorbed to recover chlorine. Of these, the method (6) involves heating a lower part of an absorbent to cause part of both of the chlorine and the main part of the carbon dioxide absorbed in the solvent to evaporate, so that chlorine gas, which is obtained in an evaporation column, may have a higher purity. It is therefore inevitable that chlorine accompanies an exhaust gas from the upper part of the absorption column.

In particular, when carbon dioxide is contained at a high level, it is necessary to intensify the heating of the lower part of the absorption column accordingly. As a result, the chlorine concentration in the Abfjas increases, and the loss of chlorine and the solvent increases significantly.

The method (7) requires that evaporation be carried out under a particularly high pressure in an evaporation column because chlorine released from a solvent is recovered there by liquefaction. As the solvent absorbs more air than necessary in the absorption column, chlorine of reduced purity is recovered. It is therefore necessary to reduce the amount of the absorption solvent. Due to this requirement, if carbon dioxide and noncondensable gas having a high level are contained, the absorption of chlorine can not be sufficiently performed, and the levels of chlorine and the solvent accompanying the exhaust gas increase abruptly.

In order to lower the chlorine concentration in an exhaust gas by the solvent absorption method, the possibilities include further increasing the amount of a solvent, further lowering the temperature of the solvent, or further increasing the pressure of an absorption column. It is difficult though. To recover chlorine with a high purity, because the absorption of carbon dioxide and non-condensable gas proceeds, whichever method is chosen.

Chlorine is a useful raw material used industrially in egg. em large scale is primarily generated by alkali analysis and is widely used. Gaseous components are formed as by-products in the production of chlorine.

These components are accompanied by chlorine, so due to the toxicity of chlorine they can not be released into the atmosphere without further treatment.

Accordingly, chlorine contained in such a gas is usually removed by its absorption with an alkaline substance. However, when a gas other than chlorine is contained and this other gas is acidic (such as carbon dioxide gas), not only chlorine but also carbon dioxide is absorbed in an alkaline solution. As a consequence, alkali is required in an amount equal to the sum of carbon dioxide and chlorine. In particular, when a gas contains high-level carbon dioxide and trace-level chlorine, there is a disadvantage that a large amount of alkali is required for removing such a trace amount of chlorine. It is therefore desirable to develop a process for the selective absorption and removal of chlorine contained in carbon dioxide.

The method (8) has already been proposed as a method of removing chlorine from a mixture of carbon dioxide gas and chlorine. However, in this method, pH 7.5 is a value much higher than 6.35, which is the first dissociation constant (pKa) of carbonic acid as shown in Fig. 4, and falls within the range where carbon dioxide gas is mixed with an alkali metal hydroxide and / or alkaline earth metal hydroxide reacts to form the corresponding bicarbonate.

In order to absorb chlorine of all of the mixture of carbon dioxide and chlorine in the above range, it is necessary to use an alkali in an equimolar amount as chlorine. As the concentration of chlorine varies, it is difficult to balance the amount of alkali with the amount of chlorine.

In addition, pH 7.5 is close to the dissociation constant of hydrochlorous acid. When the pH becomes lower than the above-mentioned level, hypochlorous acid takes the form of a free acid, so that it starts to tend to decompose. Precise control of the pH is therefore necessary. Even if chlorine is successfully removed, the resulting hydrochloric acid solution has strong oxidative and offensive odor and therefore can not be thrown away as it is. An additional process step is required for its degradation or reduction.

Object of the invention

The object of this invention is to provide a process for separating and recovering chlorine from a gaseous mixture comprising chlorine, carbon dioxide and non-condensable gas, specifically the chlorine to be recovered substantially completely from the gaseous mixture and optionally present Chlorine remaining in the residual gas should be removed so far that the residual gas can be released into the atmosphere.

Explanation of the essence of the invention

The object of the invention is the separation of chlorine from a gaseous mixture which also contains carbon dioxide and other non-condensable gases, wherein in the gas mixture to be treated on the one hand, the concentration of chlorine can be so high that so much chlorine is recovered that an industrial production of chlorine, and on the other hand, the concentration of chlorine may be relatively small, but too high to vent the gas mixture into the free atmosphere, reducing the residual chlorine level to the extent that the resulting residual gas can be released. Furthermore, it should be possible with combined process steps simultaneously generation of chlorine and purification of gas to tolerable residual levels.

According to the invention, the object is achieved according to a first aspect of the invention by a process for separating and recovering chlorine from a gaseous mixture containing chlorine, carbon dioxide and noncondensable gas, the process comprising compressing and cooling the gaseous mixture to thereby obtain the gaseous mixture into a residual gas, which is principally formed by a large part of the non-condensable gas, and a condensate, which is formed mainly of chlorine, to separate, and the introduction of the condensate in a Abtreibkolonne to carbon dioxide and a small part of in Desorb the condensate dissolved nicm condensable gas comprises. According to a second aspect of this invention, there is also provided a process for the separation and recovery of chlorine from a gaseous mixture comprising chlorine, carbon dioxide and non-condensable gas in a separation and recovery system. This method comprises i) compressing the gaseous mixture and then cooling and liquefying it to thereby separate it into a residual gas mainly composed of a large part of the non-condensable gas and a condensate mainly composed of chlorine ii) introducing the condensate alone into a stripping column to carbon dioxide and a small portion of the dissolved in the condensate

desorbing uncondensable gas to thereby separate and recover chlorine; iii) mixing an aborted gas that has flowed out from the top of the stripping column and is formed mainly of chlorine and carbon dioxide with the residual gas of step i), iv) introducing at least a part of the mixed gas in an absorption column using a halogenated hydrocarbon as a solvent, whereby the main part of the remaining chlorine is absorbed to lower the chlorine content, preferably to 1% in volume parts or lower, and one of carbon dioxide and the and separating the solvent having the chlorine absorbed therein into a distillation column to separate chlorine from the halogenated hydrocarbon.

According to a third aspect of this invention, there is also provided a process for the removal of chlorine from a gaseous mixture containing chlorine gas and carbon dioxide gas, for example, from the exhaust gas released in step iv) of the process according to the second aspect of this invention , This method comprises supplying an aqueous solution or suspension containing an alkali metal sulfite and / or an alkaline earth metal sulfite and washing the gaseous mixture with the solution or suspension while the pH of the solution or suspension is within a range of 1.9 to 6.3 is controlled, whereby chlorine alone is removed from the gaseous mixture.

In the first aspect of this invention, a gaseous mixture containing chlorine, carbon dioxide and non-condensable gas is cooled and liquefied to separate the non-condensable gas in advance. After introducing the condensate alone into a stripping column, it is distilled to recover chlorine. The process according to the first aspect of this invention makes it possible to reduce the stress or performance of the stripping column, thereby making it possible to reduce the diameter of the stripping column significantly compared to the stripping column used in US Pat. No. 2,765,873 , The initial costs for the Abtreibkolonne can therefore be reduced. The method according to the first aspect of this invention therefore has a significant value from the industrial point of view. In the second aspect of this invention, a chlorine recovery step using a halogenated hydrocarbon solvent is combined with the process according to the first aspect, whereby the chlorine contained in a gas supplied for the treatment substantially completely as high-purity chlorine can be recovered. The second aspect, therefore, provides a process for the separation and recovery of chlorine, which is very advantageous from an industrial point of view.

The third aspect of this invention allows the removal of chlorine from a gas containing carbon dioxide gas and chlorine. When an exhaust gas produced in the process according to the second aspect and composed of carbon dioxide and non-condensable gas containing chlorine at a concentration of 1% by mass or less is treated by the process according to the third aspect, chlorine may that is contained at such a trace level that it can not be detected by the method according to the second aspect are almost completely removed here. It is therefore possible to complete a plant that is virtually free from the problem of pollution.

As already stated, it is thus apparent that the present invention is extremely valuable from the practical point of view in the industrial production of chlorine.

embodiment

In the following the invention will be explained in more detail by embodiments, reference being also made to the accompanying drawings

 In the drawings show

Fig. 1 is a flow chart showing, as an example, an apparatus for practicing a method in which chlorine is separated and recovered from a gaseous mixture comprising chlorine, carbon dioxide and non-condensable gas by (1) compressing the gaseous mixture and cooling, (2) the resulting gaseous mixture is separated into a residual gas formed mainly of a major part of the non-condensable gas and a condensate mainly composed of chlorine, and then (3) the condensate alone Abtreibkolonne is supplied to desorb carbon dioxide and a smaller proportion of the non-condensable gas dissolved in the condensate;

Fig. 2 is a flow chart showing an apparatus used in a comparative example in which a conventional method according to the method of Fig. 1 has been practiced;

Fig. 3 is a flow chart showing, as an example, a plant for practicing an industrial process for the separation and recovery of chlorine; i) Compressing a gaseous mixture containing 10-60% by volume of chlorine, carbon dioxide and noncondensable gas and subsequent cooling and liquefying thereof, ii) separating it into a residual gas constituted mainly of a large proportion of the non-condensable gas, and a condensate formed mainly of chlorine, iii) introducing the condensate alone into a stripping column, desorbing carbon dioxide and a small proportion of the non-condensable gas dissolved in the condensate to thereby separate and recover chlorine; iv) mixing an aborted gas that has flowed out the upper part of the stripping column and mainly chlorine and carbon dioxide is formed, with the residual gas from stage i), v) introduction n at least a portion of the mixed gas in an absorption column to absorb a large portion of the remaining chlorine with a halogenated hydrocarbon, vi) separating an exhaust gas composed of carbon dioxide and the non-condensable gas and not more than 1% by volume of chlorine vii) introducing the adsorbed chlorine-containing solvent into a distillation column to separate the solvent into a recovered gas mainly composed of chlorine and the halogenated hydrocarbon, viii) returning the solvent, to reuse it as an absorbent in the absorption column, and ix) recycling the recovered gas to the compression stage;

Figure 4: ionic forms of absorbents useful in the practice of the present invention

are at different pH levels in their aqueous solutions; Fig. 5 is a flow chart showing the absorption of chlorine in Example 8; and Fig. 3 is a flow chart of a plant usable in combination for use in practicing the methods according to the first, second and third aspects of this invention is.

Descriptions of preferred embodiments of the invention will now be given.

In each of the three aspects of this invention, the method is applied to a gaseous mixture composed of carbon dioxide and non-condensable gas containing chlorine, or to carbon dioxide containing chlorine. The following gases can be cited as examples of gases to which the method is applicable:

a) a gaseous mixture formed in the step of producing chlorine by oxidation of hydrogen chloride and containing chlorine, carbon dioxide and non-condensable gas;

b) a gaseous mixture obtained by removing chlorine to a certain extent from the gaseous mixture a) and containing a remaining portion of the chlorine together with the carbon dioxide and non-condensable gas, and

c) a mixture containing chlorine gas and carbon dioxide.

Bsi chlorination or phosgenation of organic compounds, a large part of hydrogen chloride is formed as a by-product. Since its amount is much larger than the demand for hydrochloric acid, a large amount of hydrogen chloride has not been used any more and has been disposed of as waste. Substantial costs have thus arisen for its elimination.

Accordingly, it has been desired to develop a method for efficiently removing chlorine from hydrogen chloride, which has been removed as a waste in a large amount as mentioned above, and for industrial production of chlorine.

It has been known for many years to produce chlorine by oxidizing hydrogen chloride. However, no industrial manufacturing process has been completed.

In recent years, it has been found that a chromium oxide catalyst obtained by calcining chromium hydroxide has particularly high activity even at relatively low temperatures, resulting in providing an industrial process for producing chlorine by oxidizing η of hydrogen chloride.

In the process according to the first, second and third aspects of this invention, the gaseous mixture comprising chlorine, carbon dioxide and noncondensable gas and to which the process is applied may be a gaseous mixture formed in such a process as It has recently been developed for the production of chlorine. Namely, this invention is useful as an effective method for the recovery of chlorine or as a method for the removal of chlorine from an exhaust gas in the aforementioned industrial production method of chlorine.

Hereinafter, certain embodiments included in the present invention will be described in detail.

In Figure 1, a compressor 101, a stripping column 102, which may be a conventional column column packed unit, a heat exchanger 103, a separation unit 104, and a distillation or evaporation furnace 105 are shown.

A gaseous mixture, which generally contains 10-60% by volume of chlorine and 40-90% by volume of carbon dioxide and non-condensable gas, is supplied through a conduit 106 and is then compressed to a predetermined pressure by the compressor 101.

As the non-condensable gas, nitrogen, oxygen or carbon monoxide may be cited as examples.

The compressed gaseous mixture is cooled to a predetermined temperature by the heat exchanger 103, wherein a portion of the chlorine is liquefied. The resulting liquid-gas mixture is then fed through a conduit 112 to the separation unit 104, where the mixture is separated into a residual gas consisting mainly of a large proportion of the non-condensable gas and a condensate consisting mainly of chlorine.

The condensate is supplied through a line 107 to an upper part of the stripping column 102, and as it descends through the column, the condensate is contacted with chlorine vapor boiled up through the evaporation furnace 105. As a result, carbon dioxide and non-condensable gas dissolved in the condensate are caused to be vaporized, so that the condensate accumulates as high-purity liquid chlorine in the bottom part of the stripping column and thereafter withdrawn as a chlorine product through a pipe 111 can.

When a gaseous mixture comprising chlorine, carbon dioxide and noncondensing gas is compressed and then introduced into a stripping column as it is to carry out liquefaction and distillation there, the stripping column must have a larger diameter as long as one usual surface speed is used.

However, if the non-condensable gas is separated therefrom and the condensate is introduced alone into a stripping column, as is the case with the present invention, it is possible to carry out stripping in a small diameter column of only about 30% of that which is used in the abovementioned Abtreibkolonne perform.

Carbon dioxide and non-condensable gas, which has been driven off the condensate, are allowed to flow out of the stripping column at its obor end, passing through a conduit 109 and then connecting to the residual gas supplied from the separation plant through a conduit 108 , After that they are discharged as exhaust from the system.

In order to recover as much chlorine as possible from the gaseous mixture, it is desirable that the compression pressure of the compressor is set as high as possible and the cooling temperature of the heat exchanger is set as low as possible. However, from a safety point of view, it is not recommended to increase the compression pressure for a chlorine-containing gas indiscriminately and uncritically. In addition, there is a further limitation of the type that the cooling temperature for the liquefaction of a mixture containing carbon dioxide should be higher than the melting point of carbon dioxide (-56.6 ⁰ C at a CO ₂ partial pressure of 5.2 atm) , Accordingly, the cooling temperature is limited so that clogging or sealing of equipment parts due to formation of dry ice is prevented. The Komr. Rcess compression at the compressor and the cooling and liquefaction temperature at the heat exchanger should be in the appropriate manner

Be determined with regard to economic factors, eg. B. in view of the energy required by the compressor, the Kühlleistuno the heat exchanger, the heating power to the distillation vessel or the Verdamp '. gas and the cost of removing exhaust gas, these above factors must be considered simultaneously.

In general, it is preferable to set the compression pressure of the gaseous mixture to 3 to 15 kg / cm ^{2 G} and the cooling and liquefying temperature at -1O ⁰ C to -5o ⁰ C and the stripper at a pressure of 3 to 15kg / cm ² Overpressure and a Bodenentempera'.ur from 20 to 45 ⁰ C to operate.

The purity of the chlorine obtained by such operation is usually 99% by volume or more.

FIG. 3 shows a compressor 301, a cooler 302, a condenser 303, a gas / liquid separation unit 304, a stripping column 305, a distillation vessel or evaporator furnace 306, an absorption column 307, a heat exchanger 308, a pressure reducing valve 309, a distillation column 310 , a condenser 311, a gas / liquid separation unit 312, a distillation vessel or evaporator furnace 313, a condenser 314, and pumps 315 and 316. It should be noted, by the way, that each of the columns 305, 307 and 310 can be generally a packed or a tray column.

A gaseous mixture 317 comprising chlorine, carbon dioxide and non-condensable gas is mixed with a gas 326 recovered from the gas-liquid separator 312, and is then compressed to a predetermined compression pressure by the compressor 301.

In diooe manner, a gaseous mixture containing chlorine in a range of 10-60% by volume can be treated. As gaseous mixtures with such a chlorine content in the. Formation of chlorine by oxidation of hydrogen chloride in the presence of a specific chromium oxide catalyst, these gaseous mixtures can be treated by this seduction.

Than that not. Condensable gas In the gaseous mixture, for example, nitrogen, oxygen, carbon monoxide and / or the like may be mentioned.

The Comorsssionsdruck can be 3 to 15 kg / cm ² pressure, with 5 to 12 kg / cm ² pressure are preferred. The gaseous mixture is cooled by the cooler 302, followed by liquefaction by the condenser 303. At least two thirds of the chlorine contained in the gaseous mixture are liquefied here.

The cooling and liquefying temperature may range from - rich 1O ⁰ C to -BO ⁰ C, with -20 ° C being preferred to -4o C ^0.

After the resulting gas-liquid mixture has been separated by the separation unit 304 into a Restgai, 319, which is mainly formed of a major portion of the non-condensable gas, and a condensate 318, which consists mainly of chlorine, the latter is the Abtreibkolonne 305 supplied.

The stripping column 305 may be operated at 3 to 15 kg / cm ³ gauge, preferably 5 to 12 kg / cm ² .

The condensate, which has been supplied to the upper part of the column, falls down through the column. During this movement, carbon dioxide and noncondensable gas dissolved in the condensate evaporate from the condensate, namely, by rising steam, which is mainly chlorine, boiled up through the evaporator furnace 306 at a bottom temperature of 20 to 45X , Therefore, the condensate accumulates as liquid chlorine in the bottom of the column and is obtained as chlorine product 321. The carbon dioxide and the non-condensable gas which have been evaporated from the condensate, together with chlorine, are discharged as an aborted gas 320 from the upper part of the stripping column 305 and are mixed with the residual gas 319. At least a portion of the mixed gas is supplied to the absorption column 307. It is preferable to operate the absorption column under the same pressure as the stripping column because the effect of absorption increases as the pressure of the absorption column increases, provided that the temperature of the absorption solvent is constant.

Of a gas 323 introduced into the absorption column 307, all of the chlorine and portions of the carbon dioxide and non-condensable gas are ultimately absorbed in a solvent 330 falling from the top of the column. The gas 323 is therefore released from the system as an exhaust 324 composed of carbon dioxide and non-condensable gas and containing not more than 1% by volume of Chloi. The solvent used in the above process is a halogenated hydrocarbon such as carbon tetrachloride or chloroform. The solvent may be used in an amount of 2 to 100 times, preferably 3 to 30 times, by weight of the gas introduced into the absorption column. A solvent 325 in which chlorine, carbon dioxide and non-condensable gas absorb. 1 is withdrawn from the bottom and is supplied to the heat exchanger 308 by the pump 315. After the solvent has been preheated by the heat exchanger 308, it is fed to the distillation column 310.

The distillation column 310 may be at a pressure of 0.1 to 15 kg / cm ^{2 G,} preferably, be operated 1 to 10kg / cm ² pressure.

The solvent introduced into the distillation column 310 is boiled through the evaporator furnace, condensed by the condenser, and distilled by reflux or reflux 327 to the distillation column so that the absorbed gases are forced to evaporate to produce a recovered gas mainly composed of chlorine. separate.

A solvent 328 having a chlorine concentration not higher than 5000 ppm by mass, preferably not higher than 500 ppm by mass, is withdrawn through the bottom of the column and is then passed to the heat exchanger 308. After heat has been removed from the solvent through the heat exchanger 308, a fresh solvent feed 329 is added to replace any losses incurred. The solvent is then cooled by the condenser 314 and then returned to the absorption column 307. Although the absorption ability of the absorption column increases when the temperature is low at the inlet of the absorption column, it is impossible to keep the temperature below the melting point of the solvent (z. B. -22.6 ⁰ C in the case of carbon tetrachloride [carbon tetrachloride]) to lower. It is desirable to lower the temperature of the condenser of the distillation column to such an extent that the solvent does not evaporate and does not splash around. However, an unduly low temperature causes liquefaction of chlorine, so that more chlorine accompanies the solvent and lowers the absorption capacity of the circulating solvent in the absorption tower. Such an unduly low temperature is therefore not advantageous.

-7- 290 358

It is therefore necessary to determine the optimum conditions for the temperature of the solvent at the inlet of the absorption column and the temperature of the condenser of the distillation column in suitable catfish, taking into account the facts given above. Preferably, the temperature of the solvent at the inlet of the absorption column may range from -2O ⁰ C to ⁰ C and the temperature of the condenser of the distillation column may range from -2O ⁰ C to -1O ⁰ C.

Next, a description will be given of the process for removing chlorine from a gaseous mixture containing chlorine gas and carbon dioxide gas, and this method comprises supplying an aqueous solution or suspension containing an alkali metal sulfite and / or an alkaline earth metal sulfite or an alkali metal sulfite and / or a Containing alkaline earth metal sulfite together with an alkali metal hydroxide and / or an alkaline earth metal hydroxide in a ratio of not more than twice the molar ratio of the alkali metal sulfite and / or alkaline earth metal sulfite, and washing the gaseous mixture with the solution or suspension while maintaining the pH of the solution or Suspension is controlled within a range of 1.9 to 6.3, whereby chlorine is removed from the gaseous mixture.

Examples of the alkali metal hydroxide useful in the practice of the method described above include the hydroxides of alkali metals such as lithium, sodium and potassium, while, for example, alkaline earth metal hydroxides may be hydroxides of magnesium, calcium, barium and the like.

On the other hand, the metal in the form of sulfite may be an alkaline earth metal such as magnesium, calcium or barium ssin. However, an alkali metal having a high solubility in water is preferred.

When an alkali metal sulfite and / or an alkaline earth metal sulfite is used together with an alkali metal hydroxide and / or an alkaline earth metal hydroxide in the above-described process, it is essential that the hydroxide be used in a ratio not larger than twice the molar ratio of the sulfite is used.

Since this method also requires an alkali for the neutralization of chlorine, a sulfite for the reduction of chlorine, at least one equivalent of a reducing sulfite per two equivalents of alkali necessary for the neutralization is required.

When the ratio of the alkali exceeds twice the molar ratio of the sulfite, the reducing sulfite becomes scarce and chlorine can not be absorbed even if the pH is kept within the range of 1.9 to 6.3.

When the ratio of the alkali is not more than twice the molar ratio of the sulfite, the sulfite acts as a substituent for the hydroxide. Furthermore, the larger the sulfite, the more bisulfite ions are present in the absorbent solution. The pH control is so facilitated, which is due to their buffering effect.

Accordingly, the washing solution may be one containing neither alkali metal hydroxide nor alkaline earth metal hydroxide. Chlorine in an exhaust gas may be absorbed by an aqueous solution or suspension of an alkali metal and / or an alkaline earth metal sulfite alone.

The pH range suitable for the chlorine absorption reaction is 1.9 to 6.3. A pH higher than 6.3 converts carbon dioxide gas into bicarbonate ions, as shown in Fig. 4, so that the alkali is consumed. More alkali is therefore consumed to make the process uneconomical.

When the pH becomes lower than 1.9, free sulfurous acid is formed and decomposed to tend to make sulfur dioxide gas more likely to occur. Such a low pH is accordingly not advantageous.

This pH control of the aqueous solution within the range of 1.9 to 6.3 can be achieved by adjusting the amount of the alkali metal sulfite and / or alkaline earth metal sulfite to be added such as the amount of the alkali metal hydroxide and / or the alkali metal hydroxide Alkaline earth metal hydroxide to be added is adjusted in a ratio of not more than twice the molar ratio of the sulfite.

In this case, the hydrox.'d and the sulfite may each be added in a solid form or as an aqueous solution, the latter being preferred. They can be brought together as a single solution. It goes without saying that they can also be added as separate aqueous solutions.

The concentration of each aqueous solution may preferably be in a range such that in the case of an alkali metal salt or alkaline earth metal salt, the starting materials and the resulting salt and sulfate are dissolved. However, the operation is also feasible even if they are added each in the form of a slurry.

When operating in a homogeneous system at a concentration near the solubility of the salt, the reaction temperature should be determined so as to take account of solubility in parallel. Since the solubilities of alkali metal and alkaline earth metal sulfites and chlorides are all not too temperature dependent, the use of a higher temperature can not provide any significant effect in increasing their concentrations.

The reaction rate between chlorine and a sulfite increases as the temperature becomes higher. A reaction temperature of 0 ° C to 7O ⁰ C is however preferred in view of the potential problems of corrosion and deterioration or destruction of the material of the reactor.

Considering the nature of the reaction, the gas can be absorbed by bubbling it in a stirred tank or by treating it in a wash column.

Although the number of stages varies depending on the tolerable level of chlorine in the treated gas, it is not necessary to increase the number of stages too much because the reaction or absorption rate is high.

The embodiment of the invention described above will be described below with reference to FIG.

A gaseous mixture 401 containing carbon dioxide gas and chlorine gas, which may also contain nitrogen, oxygen and the like in some cases, is introduced into the lower portion of an absorption column 407, whereby the gaseous mixture 401 is washed with a washing liquid 402 from an upper portion the column is returned. Washing liquid 402 is an aqueous solution or suspension containing, as described above, an alkali metal sulfite and / or alkaline earth metal sulfite or an alkali metal sulfite and / or alkaline earth metal sulfite together with an alkali metal hydroxide and / or alkaline earth metal hydroxide and has a pH within the range of 1, 9 to 6.3 is kept controlled.

The scrubbing liquid is diluted with water to a desired concentration and circulated while controlling its pH and maintaining its Sf ration rate constant by means of an overflow 404.

After the treatment, an exhaust gas 406, from which chlorine gas alone with the scrubbing liquid has been removed, is discharged from the system.

The methods according to the first to third aspects of the present invention, when combined in practice, form an important part of an industrial production process of chlorine.

Namely, it is possible to perform a combined method by combining the methods according to the first, second and third aspects of the invention as shown in FIG. The combined process allows highly efficient recovery of chlorine from a gaseous mixture composed of carbon dioxide and noncondensable gas containing chlorine, and also almost complete removal of chlorine from an exhaust gas to be discharged from the system, so that the Pollution problem can be solved.

In the following, the combined method will be described with reference to FIG.

As in the above-described embodiments, a gaseous mixture consisting of carbon dioxide and a non-condensable gas containing chlorine is supplied through a pipe 531 to a compressor 501 where it is compressed to a predetermined pressure. The gaseous mixture is cooled by a radiator 502 to a predetermined temperature and then liquefied by a condenser 503, so that a portion of the chlorine is liquefied. The resulting gas-liquid mixture is supplied to a separator 504 where it is separated into a residual gas consisting mainly of a large portion of the non-condensable gas and a condensate mainly composed of chlorine.

The condensate is fed to an upper part of a stripping column 505. As the condensate falls or moves down the column 505, it is contacted with chlorine chloride which is boiled up through a still or flash oven 506 so that carbon dioxide and non-condensable gas dissolved in the condensate become the bottoms Evaporators are brought. Chlorine accumulates in the bottom of the stripping column as high purity liquid chlorine and is then withdrawn through a line 511 as the product chlorine. The purity of the chlorine obtained by this operation is usually 99% by volume or higher.

The carbon dioxide and the non-condensable gas which have been evaporated from the condensate are discharged from the upper part of the stripping column and then through a pipe 509, and combine with the residual gas supplied from the separator through a pipe 508.

At least a portion of the mixed gas thus combined is supplied to an absorption column 512. Of the mixed gas introduced into the absorption column, almost all of the chlorine and parts of the carbon dioxide and the non-condensable gas are absorbed in a solvent 513 falling down from the upper part of the column.

Accordingly, the mixed gas can be converted into an exhaust gas 514 composed of carbon dioxide and non-condensable gas and containing not more than 1% by volume of chlorine.

A solvent 515, in which chlorine, carbon dioxide and non-corrosive gas are absorbed, is withdrawn from the bottom and supplied to a heat exchanger 517 through a pump 516. After the solvent has been preheated by the heat exchanger 517, it is fed to a distillation column 518.

The solvent introduced into the distillation column 518 is boiled through a distillation vessel or evaporation furnace 519, condensed by a condenser 533, and distilled by reflux or reflux 520 to the distillation column so that the absorbed gases are forced to evaporate to separate a recovered gas mainly composed of chlorine.

A solvent 521 having a chlorine concentration not higher than 5000 ppm by mass, preferably not higher than 500 ppm by mass, is withdrawn through the bottom of the column and then supplied to the heat exchanger 517 by a pump 522. After heat has been removed from the solvent through the heat exchanger 517, a fresh solvent feed 523 is added to replace any losses incurred. The solvent is then cooled by a condenser 524 and then returned to the absorption column 512.

An exhaust gas 514 consisting of carbon dioxide and noncondensable gas and containing not more than 1% by volume of chlorine is introduced into a lower part of an absorption column 525 where the exhaust gas 514 is washed with a scrubbing liquid 526 coming from an upper part the column is returned. The washing liquid is an aqueous solution or suspension containing, as described above, an alkali metal sulfite and / or alkaline earth metal sulfite and / or an alkaline earth metal sulfite together with an alkali metal hydroxide and / or an alkaline earth metal hydroxide and having a pH within the range of 1 , 9 to 6.3 is held. The washing liquid is diluted with water to a desired concentration and is returned again while its pH is controlled and its flow rate

is kept constant by means of an overflow 527.

After the treatment, an exhaust gas 528, from which chlorine gas alone with the scrubbing liquid has been removed, is discharged from the system.

The washing liquid is prepared from water 530 and an aqueous solution of sodium sulfite.

Examples

The invention will be described in more detail by the following examples.

Example i

An apparatus according to the flow diagram of FIG. 1 was provided.

The specifications of the stripping column, the heat exchanger and the separation plant were as follows: stripper: Material: SUS 316L Dimensions of the column: 50 mm in cross section x 1000 mm high Dimension of the packed part: 50 mm cross section x 385 mm high Packed in material: "Sulzer Labopack"

(Trademark: Product of Sumitomo Heavy Industries, Ltd.)

Evaporation furnace section: electrical Heat exchanger: Material: SUS316L Heat transfer area: 1.5 m ² Separation plant: Material: SUS316L Capacity: 3.51

A gaseous mixture consisting of 50% by volume η of chlorine, 15% by volume of carbon dioxide, 10% by volume of nitrogen and 25% by volume of oxygen was compressed by the compressor to 7 kg / cm ² gauge and then at a flow rate of 1.050kgmol / h was allowed to flow through the heat exchanger, the gaseous mixture was cooled to -24 ⁰ C. After the gaseous mixture had been cooled by the heat exchanger, it was supplied to the separator so as to be separated into a gas and a liquid. Only the liquid alone was dropped down through the stripping column. The amount of power supplied to the electric heater was controlled in such a manner that the evaporator furnace portion of the stripping column was maintained at 25 ° C by the electric heater. Liquid chlorine was continuously withdrawn to keep the level of liquid chlorine in the evaporator furnace constant.

When the equipment reached a steady state, the temperature of the upper part of the stripping column was -8 ° C, the temperature of the distillation vessel or evaporation furnace was 25 ° C, and the pressure at the upper part was 7.0 kg / cm ² gauge. At this time, chlorine was obtained from the bottom of the stripping column at a rate of 0.30 kg mol / hr and decreased and its purity was 99.2% by volume.

Example 2

Using the equipment used in Example 1, a gaseous mixture consisting of 39% by volume of chlorine, 13% by volume of carbon dioxide, 9% by volume of nitrogen and 39% by volume of oxygen was set to 10 kg / cm ² pressure was compressed by the compressor and was then allowed to flow through the heat exchanger at a flow rate of 1.050 kg mol / h, the gaseous mixture was cooled to -4O ⁰ C. After the gaseous mixture had been cooled by the heat exchanger, it was supplied to the separator so as to be separated into a gas and a liquid. Only the liquid alone was dropped by the stripping column. The amount of power which was supplied to the electric heater was controlled in such a manner that the evaporator furnace part of the stripping column was maintained by the electric heater at 37 ⁰ C. Liquid chlorine was continuously withdrawn to keep the level of liquid chlorine in the still or evaporation furnace constant.

When the plant reached a steady state, the temperature of the upper part of the stripping column was -12 ⁰ C. the temperature of the evaporator furnace was 37 ⁰ C and the pressure at the top was 10 kg / cm ² pressure. At this time, chlorine was obtained and taken off from the bottom of the stripping column at a rate of 0.35 kg mol / hr, and its purity was 99.2% by volume.

Example 3

Using the equipment used in Example 1, a gaseous mixture consisting of 10% by volume of chlorine, 17% by volume of carbon dioxide, 30% by volume of nitrogen and 43% by volume of oxygen was compressed by the compressor to 12kg / cm ² gauge and was then flowed through the heat exchanger at a flow rate of 1.050 kg mol / hr, with the gaseous mixture cooled to -40 ° C. After the gaseous mixture had been cooled by the heat exchanger, it was supplied to the separator so as to be separated into a gas and a liquid. Only the liquid was dropped down through the stripping column. The amount of power which was supplied to the electric heater was controlled in such a catfish that the evaporator furnace part of the stripping column was maintained by the electric heater at 45 ⁰ C. Liquid chlorine was withdrawn continuously to keep the level of liquid chlorine in the still or evaporator furnace constant.

When the plant reached a steady state was the temperature of the upper part of the stripper -8 ° C, the temperature of the distillation vessel or evaporator furnace was 45 ⁰ C and the pressure at the top was 12 kg / cm ² pressure. At this time, chlorine was withdrawn and withdrawn from the bottom of the stripping column at a rate of 0.04 kg mol / hr, and its purity was 99.2% by volume.

Comparative Example 1

According to the flow chart shown in Fig. 2, an operation was carried out using the stripping column and the heat exchangers used in Example 1. It should be noted that the stripping column was modified so that a gaseous mixture was introduced from the bottom rather than the top. A gaseous mixture consisting of 50% by volume of chlorine, 15% by volume of carbon dioxide, 10% by volume of nitrogen, and 25% by volume of oxygen was changed to 7 kg / cm ² by a compressor 201

Overpressure compressed and then fed to the bottom of Abtreibkolonne 202 at a flow rate of 0.24 kg mol / h. The outlet gas temperature was controlled at -24 ° C by a heat exchanger 203. The amount of power supplied to the electric heater was controlled in such a manner that the evaporator furnace portion of the agitating column was maintained at 18 ° C by the electric heater. Liquid chlorine was continuously withdrawn to keep the level of liquid chlorine in the still or evaporation furnace 205 constant.

When the plant reached a steady state, the temperature was at the gas outlet of the heat exchanger 203 -24 ⁰ C, the temperature of the evaporation furnace 205 was 18.4 ⁰ C and the pressure at the top was 7 kg / cm ² pressure. At this time, chlorine was obtained and withdrawn from the bottom of the stripping column at a rate of 0.09 kg mol / hr, and its purity was 99.0 vol.%. It will be understood that the treating capacity of a gaseous mixture by a process in which a condensate alone is subjected to stripping as in Example 1 is at least about 4 times that of the conventional one; Method of Comparative Example 1 is.

/ Comparison sheet 2

(Using an arsenic used in Comparative Example 1, a similar test was conducted except that the feed rate of the gas to the bottom of the stripping column was changed to 0.60 kg mol / hr, but it was impossible to operate the plant in a steady state because the temperatures of the gas at the inlet and the outlet of the heat exchanger varied and were unstable It is understandable that the operation becomes unfeasible when the treating capacity is increased in the conventional method.

Example 4

An installation according to the flow chart of FIG. 3 was provided.

A gaseous mixture consisting of 38.9% by volume of chlorine, 12.9% by volume of carbon dioxide and 48.2% by volume of nitrogen plus oxygen was fed to the plant. When the compression pressure of the compressor to 7 kg cm ^{2 G} and the cooling and liquefying temperature of the condenser was adjusted to -24 ^0C /, 27.3% of the gaseous mixture, namely 07,5% of the chlorine were condensed in the gaseous mixture , The condensate was fed to the upper part of the stripping column. The stripping column was operated by applying pressure on top.

7 kg / cm ² pressure and their soil temperature were controlled to 25.4 ⁰ C, whereby liquid chlorine was obtained, which contained 99.5% chlorine.

A distilled gas from the top of the stripper column contained 18.6% in volume percent chlorine, 17.1% in volume percent carbon dioxide, and 64.3 percent in volume percent nitrogen plus oxygen. Carbon tetrachloride (carbon tetrachloride) in an amount by weight of 3.6 times the feed gas to the absorption column

was used to -15 ⁰ C and GEK nit as an absorbent solvent. The absorption column was operated so that the upper pressure was maintained at 7 kg / cm ² gauge. The composition of an exhaust gas from the top of the absorption column was 47 ppm in volume percent chlorine, 19.7 percent in volume percent carbon dioxide, 80.1 percent in volume percent nitrogen plus oxygen, 0.2 percent in volume percent carbon tetrachloride.

Carbon tetrachloride with chlorine absorbed in it was passed through the pump from the bottom to the distillation column. The distillation column was operated at an upper pressure of 1.3 kg / cm ² gauge, at a condenser temperature of -15 ° C and at a bottom temperature of 105.6 ° C. The composition of a gas recovered from the top of the distillation column was 89.4% in volume percent chlorine, 7.3 percent in volume percent carbon dioxide, 3.3 percent in volume percent nitrogen plus oxygen, and 500 ppm in volume percent carbon tetrachloride. The chlorine concentration in the solvent was 5 ppm in parts by mass. The recovery rate of chlorine was 99.99%.

Example 5

In the plant used in Example 4, a gaseous mixture consisting of 25% by volume of chlorine, 11% by volume of carbon dioxide and 64% by volume of nitrogen plus oxygen was charged. When the compression pressure to 9 Kg cm ^{2 G} and the cooling and liquefying temperature at -37 ⁰ C were set /, 20% of the gaseous mixture, namely 71% of the chlorine condensed in the gaseous mixture.

Next, the condensate was fed alone to the stripping column. The stripping column was operated by controlling its upper pressure to 9kg / cm ² gauge and its bottom temperature to 28.9 ° C to yield liquid chlorine containing 96.3% chlorine. Here, the gas at the inlet of the absorption column consisted of 9.9% by volume of chlorine, 12.9% by volume of carbon dioxide and 77.2% by volume of nitrogen plus oxygen. Carbon tetrachloride in an amount which was 4.1 times by weight the feed gas to the absorption column was cooled to -17 ⁰ C and used as an absorbent solvent. The absorption column was operated so that its upper pressure was maintained at 9 kg / cm ² gauge. The composition of an exhaust gas from the top of the absorption column was 16 ppm in volume percent chlorine, 12.4 percent in volume percent carbon dioxide, 87.4 percent in volume percent nitrogen plus oxygen, 0.2 percent in volume percent carbon tetrachloride. On the other hand, the absorption solvent was supplied by the pump from the bottom of the absorption column to the distillation column. The distillation column was operated at a top pressure of 3.5 kg / cm ^{2 G,} a condenser temperature of 2 ° C and a bottom temperature of 132.9 ⁰ C. The composition of a gas distilled from the top of the distillation column was 75.7% in volume percent chlorine, 15.8 percent in volume percent carbon dioxide, 8.5 percent in volume percent nitrogen plus oxygen, and 480 ppm in volume percent carbon tetrachloride. The chlorine concentration in the solvent was 36 ppm in parts by mass. The recovery rate for chlorine was 99.99%.

Example 6

In a flask charged with 1 liter of a 10% by weight aqueous solution of sodium sulfite and equipped with an overflow pipe opening at its lower end, a mixture of 1 liter / min of carbon dioxide gas and 100 ml / min of chlorine gas was bubbled while pH fluctuations were recorded. Initially, the blown gas was completely absorbed. Dor pH dropped as the bubbles continued. As the pH at 6 and

Lower, a portion of the gas began to flow through. When the pH had reached 4, the feeding was of a 10% aqueous solution of NatriumsulfH at a rate of ³ 15,7cm / min started to maintain the pH at the 4th

In the above state, the gas flowed through without causing absorption in the solution to pass through a trap

of an N / 2 solution of potassium iodide and then through another trap with an N / 2 solution of caustic soda.

Those solutions were titrated with N / 10 sodium thiosulfate while using an aqueous solution of starch as an indicator

in which cases the chlorine levels in the cases were determined by titration. It was found that the concentration of

Chlorine in the exhaust gas was not higher than 1 ppm by volume. In addition, carbonic acid, which was absoi in the N / 2 solution of potassium iodide, and the carbonic acid, which in the N / 2 Solution of caustic soda was absorbed, respectively titrated with N / 10 NaOH and N / 10 HCl, respectively, with methyl orange

was used as an indicator. As a result, it was confirmed that the carbon dioxide gas blown through was not completely absorbed and was allowed to flow through the piston to some extent.

Example 7

A similar reactor as in Example 6 was charged with an aqueous solution containing 8.6% by weight of sodium sulfite and 1.4% by weight caustic soda. Similarly, 1 '/ min of carbon dioxide gas and 100 cm / min of chlorine gas were mixed and allowed to flow. When the pH reached 4, feeding of an aqueous solution having the same composition as the feed solution was started at a rate of 12.1 ml / min to maintain the pH at 4. A gas flowing through the piston in the above state was analyzed by a similar method as in Example 6. As a result, it was confirmed that the chlorine level was not higher than 1 ppm in volume parts and carbon dioxide completely permeated.

Example 8

In accordance with the flow chart shown in Fig. 5, a gaseous mixture 401 containing 30% by volume of carbon dioxide gas, 70% by volume of nitrogen plus oxygen and 10OOppm by volume of chlorine gas was introduced at a rate of 50ONmVh from a lower portion of the absorption column 407 , The absorption column had a diameter of 0.8m and was packed with 1 inch Raschig rings to a height of 2.2m. The gaseous mixture 401 was washed with a washing or absorbing liquid 402, which was allowed to recirculate at 10mVh from the top of the column. In the column, the pH was maintained at 4.0 with about 94.5 kg / hr of 403 aqueous solution containing 10% by mass sodium sulfite while water 405 was added at a rate of 278 kg / hr. At the same time, the liquid level was kept constant by means of an overflow line 404. A treated gas 406 flowing out of the column through an upper part thereof was collected. As a result of its absorption and analysis with N / 10 aqueous solution of hydrochloric acid, it was found that the chlorine level was 1 ppm in parts by volume or lower.

Example 9 The flow diagram of a plant used in the present example is shown in FIG. The plant was fed a gaseous mixture consisting of 38.9% by volume of chlorine, 12.9% by volume Carbon dioxide and 48.2% in volume percent nitrogen plus oxygen. As the compression pressure the compressor

was set to 7 g / cm ² pressure and the cooling and condensing temperature of the condenser to -24 ⁰ C, 27.3% of the gaseous mixture, namely 67.5% of the chlorine in the gaseous mixture condensed. Only that

Condensate was fed to the top of the stripping column. The Abtreibkolonne was operated by their upper pressure

to 7 kg / cm ² pressure and their bottom temperature to 25.4 ⁰ C were adjusted, whereby liquid chlorine was obtained, which contained 99.5% chlorine.

A distilled gas from the top of the stripping column contained 18.6% in volume percent chlorine, 17.1% in Volumes of carbon dioxide and 64.3% in volume percent nitrogen plus oxygen. Carbon tetrachloride in an amount of the weight of 3.6 times the feed gas to the absorption column was

cooled to -15 ° C and used as an absorption solvent. The absorption column was operated so that its pressure

at the upper part to 7 kg / cm ² pressure was maintained. The composition of an exhaust gas from the upper part of

Absorption column was 47 ppm in volume percent chlorine, 19.7% in volume percent carbon dioxide, 80.1% in Volume proportions nitrogen plus oxygen, 0.2% in volume terms carbon tetrachloride. Carbon tetrachloride with chlorine absorbed in it was pumped from the bottom to the distillation column

converted. The distillation column was operated at a pressure of above 1.3 kg / cm ² gauge, a condenser temperature of -15 ° C and a bottom temperature of 105.6 ° C. The composition of a gas coming from the upper part of the

Was recovered 89.4% in volume percent chlorine, 7.3% in volume percent carbon dioxide,

3.3% in volume percent nitrogen plus oxygen and 500 ppm in volume percent carbon tetrachloride. The

Chlorine concentration in the solvent was 5 ppm in parts by mass. The recovery rate of chlorine was 99.99%. A gaseous mixture that was blown off the top of the absorption column and from 47 ppm in Volume proportions chlorine, 19.7% in volume percent carbon dioxide, 80.1% in volume percent nitrogen plus oxygen and 0.2%

consisted in Vol'imenanteilen carbon tetrachloride was introduced into the exhaust gas scrubbing column to remove chlorine. The gaseous mixture was introduced from the bottom, while the recirculating absorption liquid from the upper

Part was dropped down. As a result, the chlorine was absorbed in the gaseous mixture. As the absorption liquid, an aqueous solution containing 10% in mass proportions of sodium sulfite flow down

was left, her pH was adjusted to 4.2. The absorption liquid was contacted with the gaseous mixture to absorb chlorine.

The chlorine concentration in the gas released from the upper part was not higher than 1 ppm by volume.

Claims (3)

A process for the removal of chlorine from a gaseous mixture comprising chlorine gas and carbon dioxide gas, characterized in that it comprises supplying an aqueous solution or suspension containing an alkali metal sulfite and / or an alkaline earth metal sulfite, and washing the gaseous mixture with the solution or Suspension, while maintaining the pH of the solution or suspension controlled within a range of 1.9 to 6.3, whereby chlorine alone is removed from the gaseous mixture. 2. The method according to claim 1, characterized in that the aqueous solution or suspension contains an alkali metal hydroxide and / or an alkaline earth metal hydroxide in a ratio which is not greater than twice in the molar ratio of the alkali metal sulfite and / or alkaline earth metal sulfite. 3. The method according to claim 2, characterized in that the gaseous mixture is an exhaust gas from a process which i) Compressing a gas containing carbon dioxide, non-condensable gas and 10 to 60 Volumenanteiie in% chlorine, and subsequent cooling and liquefying to separate it into a residual gas mainly composed of a large proportion of the non-condensable gas and a condensate mainly composed of chlorine, ii) introducing the condensate alone into a stripping column, to carbon dioxide and desorbing a small portion of the non-condensable gas dissolved in the condensate to thereby separate and recover chlorine; iii) mixing an aborted gas which has flowed out from the upper part of the stripping column and formed mainly of chlorine and carbon dioxide with the residual gas from step i), iv) introducing at least part of the mixed gas into one An absorption column in which a halogenated hydrocarbon is used as a solvent, whereby a large portion of the remaining chlorine is absorbed to lower the chlorine content to 1 volume% or less, and the exhaust gas consisting of carbon dioxide and the non-condensable gas, and v) introducing the solvent having the chlorine absorbed therein into a distillation column to separate chlorine from the halogenated hydrocarbon.