DD283594A5 - INDUSTRIAL PROCESS FOR SEPARATION AND RECOVERY OF CHLORINE - Google Patents

Abstract

A process for recovering chlorine serves not only as a production process for chlorine, but also as a process for purifying exhaust gas to greatly reduce its chlorine content. A gaseous mixture containing chlorine, carbon dioxide and non-condensable gas is compressed and cooled to separate it 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 fed to a stripping column to desorb carbon dioxide and a small portion of the non-condensable gas dissolved in the condensate. The aborted gas mainly consisting of chlorine and carbon dioxide can be treated further. For this purpose, it is mixed with the residual gas. At least a portion of this mixed gas is fed to an absorption column in which the majority of the remaining chlorine is absorbed to lower the chlorine content. Chlorine can be removed from such a gas mixture or an exhaust gas from the above process by washing it with a solution or suspension containing an alkali metal sulfite and / or an alkaline earth metal sulfite, the p H of the solution or suspension being in the range of 1 9 to 6.3. {Separation of Chlorine and Carbon Dioxide Gas; Gas separation plant; multi-stage gas separation process; gas liquefaction; Exhaust gas purity; Chlorine product purity; Energy costs; Kapazitaetserhoehung}

Description

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Industrial process for the separation and recovery of chlorine

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 gas

shaped mixture containing chlorine, carbon dioxide and non-condensable 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% non-condensable gas in proportions by volume. Furthermore, the invention also relates to a method for absorbing and removing chlorine gas contained in carbon dioxide gas, which is formed in the production or use 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) US Pat. No. 3,972,691 discloses a method of

Recovery of liquid chlorine from a gaseous mixture, which comprises 20-90% in volume percent chlorine, 10-80% in volumes of carbon dioxide, nitrogen, oxygen and carbon monoxide. The process 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 To cause carbon dioxide, 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.

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(3) In British Patent No. 938,073, a method of separating a non-condensable impurity having a boiling point lower than chlorine and forming an exclusive mixture with chlorine of gaseous chlorine containing this impurity is described. The process involves gradually lowering the temperature of the gaseous chlorine and contacting the final gaseous residue countercurrently with liquid chlorine, the temperature of which is related to the | Condensation temperature of gaseous chlorine or never | driger in a liquefaction column to liquefy gaseous chlorine, whereby chlorine is separated 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 chlorine-containing impurity countercurrently with liquid chlorine in a scrubbing column and contaminating it from thereon 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) It is described in British Patent No. 1,164,069 that a gaseous mixture consisting of non-condensable gas, including nitrogen and chlorine, can be separated into liquid chlorine and the non-condensable gas by raising the gaseous mixture to 6 to 10 atm is compressed, the compressed gaseous mixture is cooled in two stages and then the cooled gaseous mixture further to -120 ° F (-84.4 ⁰ C) to -15O ° F (-101 ⁰ C) by heat Aus-

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exchange is cooled.

(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 causing carbon dioxide which has been absorbed at the same time to cause. at a temperature higher than the absorption temperature is evaporated by a method such as heating a lower part of an absorption column.

(7) U.S. Patent No. 2,765,873 describes a process for recovering chlorine in a form substantially free of non-condensable gas. In the process, a solvent is caused to produce a gaseous mixture consisting of 30-50% by mass of chlorine and air, under a pressure of 2.0 to 14.3 Atm, at a column top temperature of -22.8 C to 32 , 2 ° C and a column bottom temperature which is higher by 27.8 ° C to 52.8 ° C than the column top temperature.

(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, one of Alkali metal hydroxide and / or an alkaline earth metal hydroxide use

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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 applied respectively when chlorine or chlorine and carbon dioxide are contained as one or more condensable constituents 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% in J

Volume ratios or even higher, these methods are accompanied by disadvantages, which is 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. In this way, when high-level non-condensables are contained in an ascending crude chlorine gas, entrainment due to the rising gas and reduction in the efficiency of gas-liquid contact due to channeling in the descending liquid or the like are impossible which makes it difficult to achieve their separation to the desired extent.

When the amount of the descending liquid is increased from the viewpoint of maintaining the efficiency, both the cooling performance and the heating efficiency of the distillation tower increase and, in addition, larger units of larger equipment such as the co-ion main body, condenser and recooler are used

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become. This technical solution is therefore not economical. In the case of the method (4), the circulation load of the non-condensable gas 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% in volatiles in the method (1) and 10% in volume parts 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, this leads to a loss of chlorine. These methods are therefore not economical. To the chlorine content in

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To reduce an exhaust gas to such a low level that the chlorine can be neglected, it is indispensable to further increase the compression pressure while further lowering the cooling and condensing temperature. This in turn leads to increased energy |

energy costs and also to increased cooling costs. Moreover, it is not advantageous for reasons of safety of the systems to compress a chlorine-containing 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 ° C at 5.2 atm.) Or lower, to prevent 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.

"Processes (6) and (7) both use a solvent by which an impurity is absorbed and then desorbed to recover chlorine, of which method (6) involves heating a lower part of an absorption tower to cause That a part of both the chlorine and the main part of the carbon dioxide absorbed in the solvent evaporates, so that chlorine gas obtained in an evaporation column can have a higher purity, it is therefore inevitable that chlorine is an exhaust gas Especially 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 exhaust gas and the loss of chlorine and the solvent increase rises significantly.

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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. However, it is difficult to recover chlorine having a high purity because the absorption of carbon dioxide and non-condensable gas proceeds, whichever method is chosen.

Chlorine is a useful raw material that is industrially produced on a large scale, primarily by alkali analysis, and is widely needed. 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 s, absorption with an alkaline substance. If, however, another gas is present except chlorine, and that other gas is acidic. ^

is (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 alone from the mixture of carbon dioxide and chlorine in the above range, it is necessary to use an alkali just 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.

Additionally, pH 7.5 is close to the dissociation constant of hydrochlorous acid. When the pH is low,

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ger than the level indicated above decreases. Chloric acid in the form of a free acid, so that it begins to prone to decomposition. 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 discarded 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, with combined process steps to simultaneously produce chlorine and purification of exhaust gas

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be possible up 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 condensate dissolved non-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 desorb carbon dioxide and a small portion of the non-condensable gas dissolved in the condensate to thereby separate and recover chlorine; iii) mixing an aborted gas coming from the top of the stripping column has flowed out and is formed mainly of chlorine and carbon dioxide, with the residual gas of step i), iv) introducing at least a portion of the mixed gas into an absorption column, wherein

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a halogenated hydrocarbon is used as a solvent, whereby the main part of the remaining chlorine is absorbed to lower the chlorine content, preferably to 1% by volume or lower, and an off-gas consisting of carbon dioxide and the non-condensable gas is released from the system and v) introducing 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 maintaining 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.

In the first aspect of this invention, a gaseous mixture containing chlorine, carbon dioxide and non-condensable gas is cooled and liquefied to pre-separate the non-condensable gas. After introducing the condensate alone into a stripper column, it is distilled to recover chlorine. The method 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 compare the diameter of the stripping column significantly. to the stripping column used in U.S. Patent No. 2,766,573. The initial costs for

the Abtreibkolonne can therefore be lowered. 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 consisting of carbon dioxide and non-condensable gas and containing chlorine at a concentration of 1% in parts by mass less is treated by the process according to the third aspect, chlorine that is included in such a trace level that it can not be removed 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, somic shows that the present invention is extremely valuable from the practical standpoint 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:

Figure 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 and cooling the gaseous mixture (2) the resulting gaseous mixture is separated into a residual gas mainly composed of a major part of the non-condensable gas and a condensate mainly composed of chlorine, and then (3) the condensate is fed to a stripping column alone is to desorb carbon dioxide and a minor portion 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;

Figure 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% in volumes

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Containing chlorine, carbon dioxide and non-condensable gas, and then cooling and liquefying the same, ii) separating it into a residual gas mainly composed of a large proportion of the non-condensable gas and a condensate mainly composed of chlorine, iii) Introducing the condensate alone into a stripping column to desorb carbon dioxide and a small portion of the non-condensable gas dissolved in the condensate to thereby separate and recover chlorine; iv) mixing an aborted gas coming from the upper part of the stripping column v. introduction of at least a portion of the mixed gas into an absorption column to absorb a large portion of the remaining chlorine with a halogenated hydrocarbon, vi) separation of a stream of chlorine and carbon dioxide Exhaust gas consisting of carbon dioxide and not condensed vii) introducing the adsorbed chlorine-containing solvent into a distillation column to convert the solvent into a recovered gas mainly composed of chlorine, wherein the gas is composed of not more than 1% by volume of chlorine and vaporizing the exhaust gas from the system; and separating 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, at

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useful in the practice of the present invention, at various pH levels in their aqueous solutions;

Figure 5 is a flow chart showing the absorption of chlorine in Example 8, and

Figure 6 is a flow diagram of a plant which may be used in combination for use in practicing the methods of the first, second and third aspects of this invention.

The following are descriptions of preferred embodiments of the invention.

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 residual proportion of the chlorine together with the carbon dioxide and non-condensable gas, and

c) a mixture containing chlorine gas and carbon dioxide.

In 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.

More recently, it has been found that a chromium oxide catalyst obtained by calcining chromium hydroxide has particularly high activity even at relatively low temperatures, leading to the provision of an industrial process for producing chlorine by oxidizing hydrogen chloride.

In the method 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 method is applied may be a gaseous mixture formed in such a method 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.

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Hereinafter, certain methods embraced by the present invention will be described in detail.

FIG. 1 shows a compressor 101, a stripping column 10 2, which may be a conventional tray column or a packed column, a heat exchanger 103, a separation plant 104 and a distillation vessel or evaporation furnace 105.

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

As the non-condensable gas, nitrogen, oxygen or carbon monoxide may be exemplified.

The compressed gaseous mixture is cooled to a predetermined temperature by the heat exchanger 103, whereby 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 fed through a conduit 107 to an upper portion of the stripping column 102, and as it descends through the column, the condensate is contacted with chlorine vapor which is boiled by the evaporation fin 105. As a result, it causes carbon dioxide

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and non-condensable gas dissolved in the condensate are evaporated so that the condensate can accumulate as high-purity liquid chlorine in the bottom part of the stripping column and thereafter withdrawn as a chlorine product through a pipe 111.

When a gaseous mixture comprising chlorine, carbon dioxide and non-condensable 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 a common surface velocity 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 noncondensing gas, which have been driven off the condensate, are allowed to flow out of the stripping column at its upper end, passing through a line 1Q9 and then connecting with the residual gas supplied from the separation plant through a line 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 the point of view of safety, it is not recommended.

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lenswert to increase the compression pressure for a chlorine-containing gas indiscriminately and without criticism. In addition, there is another limitation such that the cooling temperature for the liquefaction of a mixture containing carbon dioxide should be higher than the melting point of carbon dioxide (-56.6C at a COj 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 compression pressure at the compressor and the cooling and liquefaction temperature at the heat exchanger should be suitably determined in view of economic factors, e.g. in view of the energy required by the compressor, the cooling capacity at the heat exchanger, the heating capacity of the distillation vessel or the evaporation furnace and the cost of the removal of exhaust gas, these above factors must be considered simultaneously.

In general, it is preferable to the compression pressure

2 of the gaseous mixture to 3 to 15 kg / cm overpressure and the cooling and liquefaction temperature to -10 C to -50 C set and the Abtreibkolonne at a pressure of 3 to 15 kg / cm overpressure and a bottom temperature of 20 to 45 ° 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 condenser 302, a condenser 303, a gas / liquid separation unit 304, a stripping column 305, a distillation vessel or evaporator 306, an absorption column 307, a heat exchanger 308, a pressure reducing valve 309

Distillation column 310, a condenser 311, a gas / liquid separation plant 312, a distillation vessel or evaporator 313, a condenser 314 and pumps 315 and 316 shown. 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 32 6 recovered from the gas-liquid separator 312, and then compressed to a predetermined compression pressure by the compressor 301.

In this way, a gaseous mixture containing chlorine in a range of 10-60% by volume can be treated. Since gaseous mixtures having such a chlorine content are also formed in the generation of chlorine by oxidation of hydrogen chloride in the presence of a specific chromium oxide catalyst, these gaseous mixtures can be treated by this method.

As the non-condensable gas in the gaseous mixture, there may be mentioned, for example, nitrogen, oxygen, carbon monoxide and / or the like.

The compression pressure may be from 3 to 15 kg / cm 2 gauge with 5 to 12 kg / cm gauge being preferred The gaseous mixture is cooled by the cooler 302 followed by liquefaction through the condenser 303. At least two thirds of that contained in the gaseous mixture Chlorine is liquefied here.

The Xühlungs- and Varflüssigungs-cemperacur can of

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Range from -10 ° C to -50 ° C, with -2O ° C to -4O ° C are preferred.

After the resulting gas-liquid mixture has been separated by the separation unit 304 into a residual gas 319 mainly composed of a major portion of the non-condensable gas and a condensate 318 mainly composed of chlorine, the latter becomes the stripping column 305 supplied.

The stripping column 305 may be at 3 to 15 kg / cm gauge,

preferably 5 to 12 kg / cm, operated.

The condensate, which has been supplied to the upper part of the column, falls down through the column. During this movement, carbon dioxide and non-condensable gas dissolved in the condensate are evaporated from the condensate by rising steam mainly composed of chlorine, which is boiled up through the evaporator furnace 306 at a bottom temperature of 20 to 45 ° C , 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 are discharged together with chlorine 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, almost all of the chlorine and portions of the carbon dioxide and non-condensable gas are absorbed in a solvent 330 falling from the top of the column. The gas 32 3 is des- _(released half out of the system as a waste gas 324 which is composed of carbon dioxide and non-condensable gas and not more than 1% containing in Voluraenanteilen chloride The solvent used in the above process is a halogenated hydrocarbon. 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 are absorbed, is withdrawn from the bottom and is supplied by the pump 315 to the heat exchanger 3Ο8. After the solvent is preheated by the heat exchanger 308, it is fed to the distillation column 310.

The distillation column 310 may be at a pressure of

2 0.1 to 15 kg / cm overpressure, preferably 1 to 10 kg / cm overpressure, operated.

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.

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A solvent 328 having a chlorine concentration not higher than 50,000 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 308. After heat has been removed from the solvent by the heat exchanger 308, a fresh solvent feed 3 29 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 capacity of the absorption column becomes larger as the temperature at the inlet of the absorption column becomes lower, it is impossible to lower the temperature below the melting point of the solvent (e.g., -22.6 ° C in the case of carbon tetrachloride). 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.

It is therefore necessary to appropriately 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, taking into account the facts given above. Preferably, the temperature of the solvent at the inlet of the absorption column may range from -20 ° C to 0 ° C, and the temperature of the condenser of the distillation column may be

range from -20 ° C to -1O ° 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 not greater 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. 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

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essential that the hydroxide be used in a ratio that is not greater than twice the molar ratio of the sulfite used.

Since this method requires an alkali for the neutralization of chlorine and also 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 with 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. It is therefore consumed more alkali to the

Make procedures 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 hydroxide 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

233 5

- 28 -

be that the solubility is pulled in parallel at the same time. 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. However, a reaction temperature of ⁰ ° C to 70 ^° C is 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 a lower part of an absorption column 407, whereby the gaseous mixture 401 with a

Washing liquid 402 is washed, which is returned from an upper part of the column. 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 washing liquid is diluted with water to a desired concentration and circulated while controlling its pH and keeping its flow 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 non-condensable 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.

V fJ Ο ζ O rl _ 30 - ^ ~ ^J · ⁷ - ^v

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 vapor which is boiled up through a still or flash oven 506 so that carbon dioxide and non-condensable gas dissolved in the condensate are vaporized become. 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% in volume fractions 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.

η ο λ ζ · λ Λ _31- - »^ ο *>? w

At least a portion of the mixed gas thus combined is supplied to an absorption column 512. From the in

the mixed gas introduced into the absorption column

ι absorbed almost all of the chlorine and parts of the carbon dioxide and the non-condensable gas in a solvent 513, which falls from the upper part of the column down. 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-condensable 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 5.18.

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 cork ratio not higher than 5,000 ppm by mass, preferably not higher than 500 ppm by mass, is withdrawn through the bottom of the column and is then supplied to the heat exchanger 517 by a pump 522. After heat has been removed from the solvent by the heat exchanger 517, a fresh solvent

ο 9 "* λ α Λ

feed 523 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% in Vbluroenanteilen chlorine, is introduced into a lower part of an absorption column 52 5, in which the exhaust gas 514 is washed with a washing liquid 526, which from an upper Part of the column is recycled. 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 maintained. 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 52 8, from which chlorine gas alone with the washing 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 1

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:

Stripping column: Material: Dimensions of the column:

Dimensions of the packed part:

Packed material:

Verdampfungsofentei1:

Heat exchanger: Material: Heat transfer surface:

Separator: Material: Capacity:

SUS316L 50 mm in cross-section χ 1000 mm high

50 mm cross-section χ 385 mm high

"Sulzer Labopack" (trademark, product of Sumitomo Heavy Industries, Ltd.)

Electric heater, 1.0 kW max.

SUS316L 1.5m

SUS316L 3.5 1

A gaseous mixture consisting of 50% Volurrenanteilen chlorine, 15% by volume of carbon dioxide, 10% in Volurrenanteilen Nitrogen ur.d 25% in Voluroenanteilen oxygen, 'was. By the compressor

2 compressed to 7 kg / cm gauge and then through the heat exchanger at a flow rate of 1.050 kg mol / h

- 34 - 2 33 5 94

allowed to flow, wherein the gaseous mixture was cooled to -24 ° C. After the gaseous mixture was 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-gauge. At this time, chlorine was obtained and taken off the bottom of the stripping column at a rate of 0.30 kg mol / hr, and its purity was 99.2% in volume.

Example 2

Using the apparatus that had been used in Example 1 was a gaseous mixture consisting of 39% in Volmrenanteilen chlorine, 13% in Vclurrenanteilen carbon dioxide, 9% by volume of nitrogen and 39 · i consisted in Voluirenanteilen oxygen at 10 kg / cm pressure compressed by the compressor and then with a Strcmungsrate of 1.050 kgmol / hr through the heat exchanger is allowed to flow, wherein the gaseous mixture was cooled to -40 ⁰ C.

After the gaseous mixture had been cooled by the heat exchanger, it became the separator

283;> ί.

fed so that it was separated into a gas and a liquid. Only the liquid alone was dropped by 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 37 ° C by the electric heater. Liquid chlorine was continuously withdrawn to keep the level of liquid chlorine in the still or evaporation furnace constant.

When the equipment reached a steady state, the temperature of the upper part of the stripping column was -12 ° C, the temperature of the evaporator furnace was 3 7 ° C and the pressure at the upper part was 10 kg / cm gauge. 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 fed through the compressor to 12 kg / cm Pressurized and was then at a flow rate of 1.050 kg mol / h through the heat exchanger

allowed to flow, wherein the gaseous mixture was cooled to -40 C.

After the gaseous mixture had been cooled by the heat exchanger, it was fed to the separation plant so that it ur.d. a liquid was separated. Only the liquid was dropped down through the stripping column. The amount

The power supplied to the electric heater was controlled in such a manner that the evaporator furnace portion of the stripping column was maintained at 45 ° C by the electric heater. Liquid chlorine was continuously withdrawn to keep the level of liquid chlorine in the still or 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 evaporator furnace was 45 ° C, and the pressure at the top was 12 kg / cm gauge. 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 exchanger 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 compressed to 7 kg / cm gauge by a compressor 201 and then subjected to a stoichiometric reaction. 0.24 kg mol / h fed to the bottom of Abtreibkolonne 202. The Auslaßgastsmperatur was controlled at -24 ° C by a heat exchanger 203. The amount of power supplied to the electric heater.

2 33 5 9 4

was controlled in such a manner that the evaporator furnace portion of the stripping 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 equipment reached a steady state, the temperature at the gas outlet of the heat exchanger was 203-24 ° C, the temperature of the evaporation furnace 205 was 18.4 ° C, and the pressure at the top was 7 kg / cm gauge. 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 is clear that the treating capacity of a gaseous mixture by a method in which a condensate alone is subjected to stripping as in Example 1 is at least about 4 times that of the conventional method of Comparative Example 1.

Comparative Example 2

Using a plant 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. However, it was impossible to operate the plant in a steady state because the temperatures of the gas at the inlet and outlet of the heat exchanger varied and were unstable. It is understood that the operation becomes unfeasible when the treatment 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. As the compression pressure of

Compressor was set to 7 kg / cm overpressure 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 condensed in the gaseous mixture. The condensate was fed to the upper part of the stripping column. The stripping column was operated

their pressure at the top was controlled to 7 kg / cm overpressure and their bottom temperature to 25.4 ° C to give liquid chlorine containing 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 cooled to -15 ⁰ C and used as an absorbent solvent. The absorption column was operated so that the upper pressure was maintained at 7 kg / cm gauge. The composition of an exhaust gas from the top of the absorption column was 4 7 ppm in volume percent chlorine, 19.7% in volume percent carbon dioxide, 80.1 percent in volume percent nitrogen plus oxygen, 0.2 percent in volume percent carbon tetrachloride.

_39- ^ 83 5>

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 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 by mass. The recovery rate of chlorine was 99.99%.

Example 5

The plant used in Example 4 was fed with a gaseous mixture consisting of 25% by volume of chlorine, 11% by volume of carbon dioxide and 64% by volume of nitrogen plus oxygen. As the

Compression to 9 kg / cm pressure and the cooling and condensing temperature were set to -3 7 ⁰ C, 20% of the gaseous mixture, namely 71 % of the chlorine in the gaseous mixture condensed.

Next, the condensate was fed alone to the stripping column. The stripping column was operated by controlling its superatmospheric pressure to 9 kg / cm 2 O and its bottom temperature to 28.9 ° C., to obtain liquid chlorine containing 96.3% chlorine, where the gas existed at the inlet of the Absorption column 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 by weight that was 4.1 times the feed to the absorption column - -

7 S3 5 9 4

cooled to -17 ° C and used as an absorbing solvent. The absorption column was operated

2 that their upper pressure was maintained at 9 kg / cm overpressure.

The composition of a. 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 an upper pressure of 3.5 kg / sec overpressure, a condenser temperature of 2 ° C and a bottom temperature of 132.9 ° 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 by mass. The recovery rate for chlorine was 9.99%.

Example 6 j]

In a flask charged with 1 liter of an aqueous solution of sodium sulfite in a mass fraction of 10% 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. The pH dropped as the blowing continued. As the pH dropped to 6 and lower, some of the gas began to flow through. When the pH reached 4, the feeding of a 10% aqueous solution of sodium sulfite at a rate of 15.7 cm / min

_41-treat to keep the pH at 4.

L Π j 5 9 - *

In the above state, the gas flowed through, without causing absorption in the solution, to flow through a trap of N / 2 solution of potassium iodide and then another trap of N / 2 solution of caustic soda. Those solutions were titrated with N / 10 sodium thiosulfate while an aqueous solution of starch was used as an indicator, with the levels of chlorine in the traps being 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 absorbed in the N / 2 solution of potassium iodide and the carbonic acid absorbed in the N / 2 solution of caustic soda were respectively titrated with N / 10 NaOH and N / 10 HCl, respectively. where methyl orange was used as an indicator. As a result, it was confirmed that the blown carbon dioxide gas 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 S, 6% by mass of sodium sulfide and 1.4% by mass of caustic soda. Similarly, 1 i / min of carbon dioxide gas and 100 cc / 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 g 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

analyzed in Example 6. As a result, it was confirmed that the chlorine level was not higher than 1 ppm in volume parts and the carbon dioxide completely flowed through.

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 1000 ppm by volume of chlorine gas was withdrawn at a rate of 500 Nm / hr from a lower portion of Absorption column 407 introduced. The absorption column had a diameter of 0.3 m and was packed with 1-inch Raschig rings to a height of 2.2 .T. ₁ The gaseous mixture 401 was washed with a washing or absorbing liquid 402, which was recirculated at 10 m / h from the top of the column. In the column, the pH was kept at 4.0 with about 94.5 kg / h of an aqueous solution 403 containing 10% in parts by mass of sodium sulfite, while water 405 was added at a rate of 278 kg / h. At the same time, the liquid level was kept constant by means of an overflow line 404. Sin treated gas 406 flowing out of the column through an upper part thereof was collected. As a result of its absorption and analysis with M / 10 aqueous solution of potassium iodide, 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 Figure 6.

The plant was fed with a gaseous mixture consisting of 33.9 % by volume of chlorine, 12.9% by volume of carbon dioxide and 43.2 ' .

- 43 - 2 33 ύ 9

% in volume percent nitrogen plus oxygen. When the compression pressure of the compressor was set at 7 kg / cm gauge and the condenser cooling and condensing temperature was set at -24 ° C., 27.3% of the gaseous mixture, 67.5% of the chlorine in the gaseous mixture, was condensed , Only the condensate was fed to the upper part of the stripping column. The stripping column was operated by setting its upper pressure to 7 kg / cm gauge and its bottom temperature to 25.4 ° C to obtain liquid chlorine containing 99.5% chlorine.

A distilled gas from the top of the stripping column contained 18.6% in volume percent chlorine, 17.1% in voien proportions carbon dioxide, and 64.3% in volume percent nitrogen plus oxygen.

Carbon tetrachloride in an amount by 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 top was kept at 7 kg / cm overpressure. The composition of an exhaust gas from the upper part of the absorption column was 47 ppm in volume percent chlorine, 19.7 percent in volume percent carbon dioxide, 80.1 percent in voien proportions nitrogen plus oxygen, 0.2 percent in volume percent carbon tetrachloride.

 Carbon tetrachloride with chlorine absorbed in it was transferred by the pump from the bottom to the distillation column. The distillation column was operated at a pressure at the top of 1.3 kg / cm 2 gauge, a condenser temperature of -15 ° C and a temperature of 105.6 ° C. The composition of a gas coming from the upper part of the distillation column

_ 44 - ^

9 4-

was 89.4% in chlorite proportions, 7.3% in volumes of carbon dioxide, 3.3% in volumes of nitrogen plus oxygen, and 500 ppm in portions of carbon tetrachloride. The chlorine concentration in the solvent was 5 ppm by mass. The recovery rate of chlorine was 99.99%.

A gaseous mixture discharged from the top of the absorption column consisting of 47 ppm by volume of chlorine, 19.7% by volume of carbon dioxide, 80.1% by volume of nitrogen plus oxygen and 0.2% by volume of carbon tetrachloride was used the waste gas scrubbing column is introduced to remove chlorine. The gaseous mixture was introduced from the bottom while the recirculating absorption liquid was dropped from the upper part. As a result, the chlorine was absorbed in the gaseous mixture.

When the absorption liquid, an aqueous solution containing 10% by mass of sodium sulfite, was allowed to flow down, its pH was controlled 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 mole in volume parts.

Claims (5)

- 45 -. <. ο j claim , Method for separating and recovering chlorine from a gaseous mixture comprising chlorine, carbon dioxide and non-condensable gas / in a separation and recovery system, characterized in that it comprises i) compressing the gaseous mixture and then cooling and liquefying it to thereby form it into a residual gas mainly composed of a large proportion of the non-condensable gas and a condensate mainly composed of chlorine, and ii) introducing the condensate alone into a stripping column to desorb carbon dioxide and a small portion of the non-condensable gas dissolved in the condensate to thereby separate and recover chlorine. 2. The method according to claim 1, characterized in that iii) an expelled gas; which has emanated from the upper part of the stripping column of stage ii) and is formed mainly of chlorine and carbon dioxide, mixed with the residual gas of stage i) (iv) introducing at least a portion of the mixed gas into an absorption column which uses a halogenated hydrocarbon as a solvent and in which a large proportion of the remaining chlorine is absorbed to lower the chlorine content and an exhaust gas which is in the consisting essentially of carbon dioxide and the non-condensable gas, separated and discharged from the system, and v) the solvent having the chlorine absorbed therein is introduced into a distillation column to convert the solvent into a recovered gas mainly composed of recovered chlorine, and to separate the halogenated hydrocarbon. 3. The method according to claim 2,
characterized in that vi) the halogenated hydrocarbon separated in step v) is used as an absorbent for the absorption column in step iv) and the recovered gas is returned to the compression step in step i). 4. The method according to claim 2 or 3, characterized in that the chlorine concentration of the gaseous mixture is 10 to 60 parts by volume in%. 5. The method according to claim 2 or 3, characterized in that the chlorine concentration of the exhaust gas, which is released from the system is not higher than 1 volume fraction in%. U- seeds