Method for producing chlorine

The present invention relates to a method for producing chlorine by catalytically oxidizing hydrogen chloride.

In a method developed by Deacon in 1868 to catalyze hydrogen chloride (catalytically), oxygen oxidizes hydrogen chloride to chlorine in an exothermic equilibrium reaction. The conversion of hydrogen chloride to chlorine makes it possible to separate the production of chlorine from the production of sodium hydroxide by chlorine-alkali electrolysis. Globally, such separations are attractive because the demand for chlorine is growing faster than the demand for sodium hydroxide. In addition to this, hydrogen chloride is obtained in large quantities as a by-product, for example, in the production of isocyanates (eg, in phosgenation reactions). The hydrogen chloride formed in the production of isocyanates is most used to oxychloride ethylene to 1,2-dichloroethane. In addition, 1,2-dichloroethane is further processed into vinyl chloride, and finally processed into PVC.

Patent Document 1 (EP-A0765838) describes a method for treating a reaction gas generated in the oxidation of hydrogen chloride (this reaction gas contains chlorine, hydrogen, oxygen and water vapor), and this method describes oxidation. The reaction gas leaving the reactor is cooled to the extent that the reaction water and hydrogen chloride are condensed in the state of concentrated hydrochloric acid (concentrated hydrochloric acid). Concentrated hydrochloric acid is then separated from the reaction gas and discharged, and the remaining gas from which substantially all of the water and some of the hydrogen chloride has been removed is dried. The dried reaction gas containing chlorine, oxygen, and hydrogen chloride is pressurized (compressed) to 1-30 bar, and the pressurized reaction gas is cooled and thus mostly liquefied. The non-condensable component of the reaction gas is partially recirculated to the oxidation reactor.

The dried and pressurized reaction gas mixture is liquefied in a so-called chlorine-recovery heat exchange device provided as an expansion cooler to separate chlorine until the residual ratio is as small as about 10 to 20%. .. The main liquid chlorine stream separated in the chlorine-recovery heat exchanger is then dissolved and residual hydrogen chloride, oxygen and inert gas is removed and further purified in the distillation column. The gas taken from the top of the distillation column, which essentially contains hydrogen chloride, chlorine, oxygen and an inert gas, is recirculated to the pressurization step. The gas components that are not condensed in the chlorine-recovery heat exchanger contain chlorine in its residual proportions and are partially liquefied at significantly lower temperatures during the rear-cooling process. Residual off-gas (residual exhaust gas) containing unreacted hydrogen chloride, oxygen, and inert gas is recirculated to the oxidation reactor. Some of the recirculated gas is separated as purge gas and is expelled from the process to prevent the accumulation of impurities.

<patcit num="1"><text>EP-A0765838</text></patcit>

<p> The hydrogen chloride used in the Deacon reaction is often gaseous hydrogen chloride obtained as a by-product in other manufacturing steps (eg, isocyanate production).</p><p> The disadvantage of the prior art (in this prior art, chlorine is separated mainly by condensation from the chlorine-containing product generated from the oxidation of hydrogen chloride) is to remove the chlorine-based product gas. , A very low temperature is required. Moreover, the residual gas stream containing the non-condensable gas component still contains a significant amount of the inert gas, including carbon dioxide. In the recirculation of the oxygen-containing residual gas stream to the hydrogen chloride oxidation reactor, they accumulate at unacceptably high levels. To this end, the purge gas must be separated from this residual gas stream and discharged from the process before the residual gas stream is recirculated to the oxidation of hydrogen chloride. However, this purge stream still contains a significant amount of chlorine, as chlorine can only be separated incompletely by condensation. Therefore, a considerable amount of chlorine is lost in the purge stream.</p><p> The present invention is to provide an improved method for producing chlorine from hydrogen chloride, and in particular a method of alleviating the disadvantages of the prior art.</p>

<p> The purpose of this is the following process, a) A flow a1 containing hydrogen chloride and a flow a2 containing oxygen are supplied to the oxidation region, and hydrogen chloride is catalytically oxidized to chlorine to produce chlorine, water, oxygen, carbon dioxide, and an inert gas. The process of obtaining the flow a3, including b) Generated gas flow<u style="single">a</u>Steps of cooling 3 and removing water and hydrogen chloride as hydrous hydrochloric acid, leaving a gas stream b containing chlorine, water, oxygen, carbon dioxide and an inert gas, c<u style="single">) Moth</u>Step of drying the stream b) to leave a gas stream c that does not contain water and contains chlorine, oxygen, carbon dioxide and an inert gas, d) A step of liquefying the gas flow c and the chlorine-enriched recirculation flow f1 containing chlorine, oxygen, and carbon dioxide by pressurization and cooling at least partially to obtain a flow d which is at least partially liquefied. , e) Gas / liquid separation of the flow d into a gas flow e1 containing chlorine, oxygen, carbon dioxide, and an inert gas and a liquid flow e2 containing chlorine, oxygen, and carbon dioxide.<u style="single">About</u> f) Supply at least one part of the gas flow e1 to the membrane separation device and separate it by membrane separation, and the chlorine-enriched recirculation flow f1 and the gas flow containing chlorine, oxygen, and carbon dioxide and having a low chlorine content. The step of obtaining f2 and recirculating the chlorine-enriched recirculation flow f1 to step d), g) Including the step of separating the liquid stream e2 into a chlorine stream g1 and a stream g2 containing at least 50 mol% oxygen and carbon dioxide by distillation.<u style="single">as well as</u><u style="single">Step e introduces the pressurized stream d from the top of the column into the column and flows through the column countercurrent to the rising gas phase and thereby dissolves in the chlorine-enriched liquid stream d. The oxygen and the dissolved inert gas are removed from the descending liquid flow d by the ascending gas flow inside the column, and at the same time, the carbon dioxide existing in the ascending gas flow is removed from the descending liquid flow. By dissolving and removing from the gas stream and recirculating part of the liquid stream e2 to the top of the column, and</u> It is achieved by a method of producing chlorine from hydrogen chloride, characterized in that at least a portion of the gas streams e1 and / or f2 is recirculated to the oxidation region of step a).</p>

The supply gas stream a1 containing hydrogen chloride used in step a) is usually an HCl-containing stream, and this HCl-containing stream is usually discharged in the step where hydrogen chloride is formed as a by-product. Obtained as. The above-mentioned steps may be performed, for example. (1) Production of isocyanates from phosgenes and amines, (2) Manufacture of acidic chloride, (3) Manufacture of polycarbonate, (4) Manufacture of vinyl chloride from ethylene dichloride, (5) Chlorination of aromatic compounds, Can be mentioned.

The HCl-containing supply gas stream a1 can contain a second component. It usually contains water-insoluble impurities, which can be either organic or inorganic in nature. Organic impurities are, for example, hydrocarbons or chlorinated hydrocarbons. Typical impurities that may be present in the HCl-containing feed gas stream used in accordance with the present invention are aromatic compounds such as benzene, toluene, xylene, and C.₆-C₁₂-Contains aliphatic compounds. Representative examples of chlorinated hydrocarbons include phosgene, carbon tetrachloride, vinyl chloride, and dichloroethane. Hydrocarbons and chlorinated hydrocarbons can be present in an amount of 20% by volume or less, usually 30000 ppm or less, preferably 10000 ppm or less, and particularly 100-3000 ppm. The inorganic second component that may be present is, for example, carbon monoxide, carbon dioxide, nitrogen and another inert gas, the amount of which is 10% by volume or less, preferably 1% by volume or less.

The HCl-containing feed stream a1 is preferably pre-purified by passing it through a purification bed and adsorbing the hydrocarbons present therein prior to introduction into the oxidation region. The refined bed contains a suitable adsorbent, which is preferably in the form of a lump (body) such as a sphere, extruded product, or pellet. Suitable materials that can be used as adsorbents are, for example, activated carbon, aluminum oxide, titanium oxide, titanium dioxide, iron oxide, zeolites, and molecular sieves. Suitable materials are metals or metal halides such as copper or ruthenium oxide, or halides or mixtures thereof, which are provided on a carrier and the carrier is aluminum oxide, titanium oxide. , Or a heat-resistant inorganic material such as silicon dioxide. Preferred adsorbents are aluminum oxide, activated carbon, and clay minerals.

In the oxidation step a, the hydrogen chloride-containing stream a1 is supplied to the oxidation region together with the oxygen-containing stream a2 and is catalyzed.

In the method using a catalyst, which is also known as the Deacon method, hydrogen chloride is oxidized to chlorine by the principle of exothermic equilibrium reaction using oxygen, and water vapor is also formed at this time. Normal reaction temperatures range from 150 to 500 ° C, and normal reaction pressures range from 1 to 25 bar. It is also advantageous to use oxygen in excess of stoichiometric amounts. For example, it is common to use 2-4 times excess oxygen. It may be advantageous to treat at relatively high pressures and therefore longer residence times than at atmospheric pressures, as there is no concern of diminished selectivity.

Suitable catalysts are, for example, ruthenium oxide, ruthenium chloride, or other ruthenium compounds, which are provided on silicon dioxide, aluminum oxide, titanium dioxide or zirconium dioxide as carriers. Suitable catalysts can be obtained, for example, by applying ruthenium chloride to the carrier and then drying or drying and "calcinating". Suitable catalysts can further include, or instead of, ruthenium compounds, other precious metals such as gold, palladium, platinum, osmium, iridium, silver, copper, or rhenium. Suitable catalysts can also be chromium (III) oxide.

Equally suitable are 0.001-30% by mass gold, 0-3% by mass of one or more alkaline earth metals, 0-3% by mass of one or more of the total mass of the catalyst in each case. It is a catalyst containing an alkali metal of 0 to 10% by mass, one or more rare earth metals, and one or more other metals of 0 to 10% by mass or more in a carrier. Here, the other metal is selected from ruthenium, palladium, platinum, osmium, iridium, silver, copper, and ruthenium.

Such gold-containing supported catalysts have higher activity in the oxidation of hydrogen chloride, especially at temperatures below 250 ° C., than conventional ruthenium-containing catalysts.

A typical reactor in which hydrogen chloride is catalyzed to oxidize is a fixed bed reactor or a fluidized bed reactor. Oxidation of hydrogen chloride can be carried out in a plurality of steps (steps).

Catalytic oxidation of hydrogen chloride should be performed adiabatically, preferably isothermally, or substantially isothermally, in batch (discontinuous), or preferably continuously, as a fluidized or fixed bed method. Can be done. In a fluidized bed reactor, it is preferably carried out at a temperature of 320 to 400 ° C and a pressure of 2 to 8 bar.

In the isothermal or substantially isothermal mode of operation, multiple reactors, i.e. 2-10, preferably 2-6, particularly preferably 2-5, particularly 2-3, are connected in series. And it can also be used in a state where an intermediate cooling is additionally provided. It is possible to add all of the oxygen along with hydrogen chloride before the first reactor, and it is also possible to disperse the addition of oxygen in various reactors. It is also possible to combine such a series arrangement of individual reactors within a single device.

One embodiment includes the use of a structured catalyst bed in which the catalytic activity increases in the flow direction within the fixed bed reactor. The construction of such a catalyst bed is achieved by different impregnations (this impregnation is the impregnation of the catalyst carrier with the active ingredient) or different dilutions (this dilution is the dilution of the catalyst with an inert substance). It is possible. As the inert material, for example, titanium dioxide, zirconium dioxide, or a mixture thereof, a ring-shaped material such as aluminum oxide, steatite, ceramic, glass, graphite, or stainless steel, a cylinder-shaped material, or a spherical material can be used. It is possible. As a preferred use of the molded catalyst, the Inactive substance preferably has similar external dimensions (outer dimensions).

Any shape of the molding catalyst is suitable, but pellets, rings, cylinders, stars, wheels with spokes, or spheres are preferable, and ring-shaped, cylinder-shaped, or star-shaped extrusion moldings are preferable. Especially preferable.

Suitable homogeneous catalysts are, in particular, ruthenium compounds or copper compounds provided on the carrier material, and these can also be doped, with a more doped ruthenium catalyst being preferred. Suitable carrier materials are, for example, silicon dioxide, graphite, titanium dioxide (titanium dioxide has a rutile or anatase structure), zirconium dioxide, aluminum oxide, or mixtures thereof, preferably titanium dioxide, zirconium dioxide, aluminum oxide. Or a mixture thereof, particularly preferably gamma- or alpha-aluminum oxide or a mixture thereof.

The supported copper or ruthenium catalyst is obtained, for example, as follows. That is, the carrier material is CuCl.₂Or RuCl₃And, if desired, it can be obtained by impregnating with an aqueous solution of an accelerator for doping (additive addition) (this accelerator is preferably in the form of chloride). Molding of the catalyst can be performed after impregnation of the carrier material, but is preferably performed before impregnation.

Suitable accelerators for doping are alkali metals such as lithium, sodium, potassium, rubidium, and cerium, preferably lithium, sodium, and potassium, particularly preferably potassium and magnesium, calcium, strontium, and barium. Alkaline earth metals such as, preferably magnesium and calcium, particularly preferably magnesium, scandium, ittrium, lanthanum, and rare earth metals such as cerium, placeodium, and neodymium, preferably scandium, ittrium, lanthanum, and cerium, particularly preferably. Is a lantern and cerium or a mixture thereof.

The molding can then be dried and calcinated if desired, which calcination is at a temperature of 100-500 ° C, preferably 100-400 ° C, eg nitrogen, argon, or air. It can be done in an atmosphere. The molding is preferably first dried at 100-200 ° C and then "calcinated" at 200-400 ° C.

The conversion rate of hydrogen chloride in a single pass can be limited to 15-90%, preferably 40-85%, particularly preferably 50-80%. Unreacted hydrogen chloride can be partially or wholly recirculated to catalytic oxidation of hydrogen chloride after its separation. The ratio of hydrogen chloride to oxygen at the inlet of the reactor is usually 1: 1 to 20: 1, preferably 2: 1 to 8: 1, and particularly preferably 2: 1 to 5: 1.

In step b), which can also be referred to as a cooling and absorption step, the product stream a3 (produced gas stream a3) is cooled and water and hydrogen chloride are separated from the product stream a3 as hydrous hydrochloric acid. Contact with a cooling medium, usually water or diluted hydrochloric acid, cools the hot product stream a3. This cooling takes place in a suitable phase contact device, such as a packed column or tray column, jet scrubber or spray tower, and usually some of the hydrogen chloride is absorbed into the cooling medium. The product stream thus cooled is then contacted with the absorption medium. A suitable absorption medium is water or diluted hydrochloric acid that is not saturated with hydrogen chloride. It is preferable to use water as an absorption medium. The absorption temperature is usually 0 to 150 ° C, preferably 30 to 100 ° C, and the absorption pressure is usually 0.5 to 20 bar, preferably 1 to 10 bar. The resulting hydrochloric acid (hydrochloric acid) can be used as a cooling medium for cooling the product stream a3.

The gas stream b off the cooling and absorption regions also includes chlorine, water, oxygen, carbon dioxide, and usually the inert gas (mainly nitrogen). Further, the gas stream b can contain a predetermined amount of hydrogen chloride. In the next drying step c), it is also possible to bring the gas stream b into contact with a suitable desiccant to remove the remaining trace amount of water (moisture). Suitable desiccants are, for example, concentrated sulfuric acid, molecular sieves, or hygroscopic adsorbents. Substantially water is subsidized, and a gas stream c containing chlorine, oxygen, carbon dioxide and, in some cases, an inert gas is obtained.

In step d), the gas stream b or c and the chlorine-enriched recirculation stream f1 (this recirculation stream f1 contains chlorine, oxygen, and carbon dioxide, and is obtained by membrane separation described below). Is at least partially liquefied by pressurization and cooling. Usually the two streams are combined and One-step pressurization or multi-step pressurization to 5 to 50 bar, and simultaneous cooling to the 0--70 ° C range by one-step cooling or multi-step cooling. This stream can be pressurized and cooled separately, in which case a single liquefied stream d or multiple liquefied streams d liquefied separately can result.

In the next gas / liquid separation step e), the flow d is the gas flow e1 (this gas flow e1 contains chlorine, oxygen, carbon dioxide and optionally an inert gas) and the liquid flow e2 (this liquid flow e2). Is separated into chlorine, oxygen, and carbon dioxide). This process is also referred to as "flash". Phase separation can be performed by separating the gas phase from the liquid phase in a single container. In a preferred embodiment, the gas / liquid separation is performed as follows. That is, a pressurized stream d was introduced from the top of the column into the column, and a portion of the chlorinated liquid phase that flowed back against the rising gas phase through the column and left the bottom of the column was removed from the top of the column. This is done back to, which achieves a partial cycle. Preferably, 0-80% by weight of the chlorine-enriched liquid stream taken out at the bottom of the column is circulated, i.e., preferably returned to the column at the top. The carbon dioxide present in the ascending gas stream is dissolved and removed from the gas stream and later distilled to successfully separate it from chlorine (along with residual oxygen). This results in a gas stream e1 with a low carbon dioxide content and partial recirculation in the oxidized region. Thus, as a purge stream, the side stream separated from the stream e1 or f1 (this side stream is recirculated to the oxidation region to prevent the accumulation of carbon dioxide and is discharged from the process). It is kept at a relatively small amount, which also limits the loss of chlorine from the purge stream.

Strictly speaking, steps d) and g), i.e. gas / liquid separation and distillation of the liquid phase e2 to provide a pure chlorine stream g1, can also be performed together in a single column. However, it is preferred to first perform gas / liquid separation in the first column and then recover chlorine by distilling the liquid phase in another column. This results in good overall separation and a high purity chlorine stream g1.

The separated gas stream e1 is typically 1-40 mol% chlorine, 1-80 mol% oxygen, 1-80 mol% nitrogen, 0-30 mol% carbon dioxide, and 0-20 mol%. It contains other components such as noble gas, carbon monoxide and hydrogen chloride.

The liquid stream e2 is typically 80-100 mol% chlorine, 0-5 mol% oxygen, 0-30 mol% carbon dioxide, and 0-30 mol% another component, such as noble gas, monoxide. Contains carbon and hydrogen chloride.

In step f), at least one portion of the gas stream e1 is supplied to the membrane separator (unit) and fractionated by membrane separation, chlorine-enriched stream f1 and gas stream f2 (this gas stream f2 is chlorine). It has a low content and contains chlorine, oxygen, and carbon dioxide.) In one embodiment, the entire gas stream e1 is supplied to the membrane separation device. In another embodiment, only part of the gas stream e1 is fed to the membrane separation device and another part is directly recirculated to the oxidation region (step a)). The proportion of these sidestreams can be varied. Therefore, if the latter (membrane separator) ages and the flow through the membrane decreases, it can increase the sidestream of flow e1 (which is directly recirculated to the oxidized region). it can.

The temperature of the gas stream e1 is usually &lt;10 ° C, preferably &lt;-5 ° C, particularly preferably &lt;-20 ° C. The pressure on the retention side (holding side) of the membrane separation device is usually 5 to 50 bar, preferably 15 to 35 bar. Membrane separation can also take advantage of the fact that "the pressurized (compressed) gas stream e1 separated by gas / liquid separation is under high pressure". The pressure on the permeate side of the membrane separation device is usually 1 to 15 bar, preferably 1 to 10 bar, particularly preferably 1 to 5 bar.

Fractionation (separation) to obtain a chlorine-enriched sidestream and a chlorine-rich sidestream can be performed by any of the following means, that is, it has chlorine permeation selectivity. This can be done either with a membrane (ie, a membrane that allows chlorine to penetrate more easily than other gas components), or with a membrane that allows other gases than chlorine, especially nitrogen and oxygen, to penetrate more easily. Can be done. In multi-step membrane separation, it is possible to combine multiple different membranes (including the binding of two types of membranes). The first type of membrane is described, for example, in US5538535, and the latter type is described, for example, in WO2001 / 02290.

The separation active layer of the membrane can include a polymer or an inorganic material such as carbon or ceramic material. In the method of the present invention, it is particularly preferable to use the following membranes, that is, a chlorine-enriched stream is obtained as a penetrant and a stream with a reduced amount of chlorine (deplete) is a residue (retainer). ) Is preferably used. The separation active layer of such a membrane usually comprises a polymer. Preferred polymers have a low degree of crystallization or a glass transition temperature thereof that is lower than the operating temperature of the membrane separator. Block copolymers having at least one phase having the above-mentioned properties are also suitable.

Examples of suitable polymers are silicone rubber, preferably polydimethylsiloxane (PDMS), particularly preferably crosslinked PDMS. Pre-fluorinated polymers and copolymers thereof are also suitable, and polyolefin copolymers such as ethylene-propylene-dienter polymer (EPD) and ethylene-propylene copolymer (EPM) are also suitable. They have sufficient stability against chlorine. The separation active layer can be a dense layer or a micropore layer.

Usually, the separation active layer is applied to a single-layer-or multi-layer carrier structure (carrier) that is stable to chlorine, or placed in the pores of a porous carrier. Such carriers can include stable polymers such as polytetrafluoroethane (PTFE) or polyvinylidene fluoride (PVDF), or inorganic materials such as metals, glass, carbon or ceramics.

This membrane is typically used in a pressure-tight (pressure-free) housing that can separate the holding space from the permeation space under the required pressure conditions. For the shape of the membrane, the membrane has flat geometry (geometry), tubular geometry, multi-channel geometry, capillary tubular geometry to allow the availability of a suitable pressure housing that allows separation of the retaining and penetrating sides. , Or it is possible to have a curved geometry. It is also possible to combine multiple of these elements in one housing to form a module.

The resulting chlorine-enriched stream f1 typically contains 5-50 mol%, preferably 15-30 mol% chlorine. The low chlorine content stream f2, however, usually still contains 0.1-5 mol%, preferably 0.1-3 mol%, particularly preferably 0.1-1 mol% chlorine.

The chlorine r-rich stream f1 is recirculated as a circulating stream in the cooling and pressurizing steps d).

The low chlorine content stream f2 can be discharged from this step as an exhaust gas stream (off-gas stream), or at least partially recirculated to the oxidation region (step a). The low chlorine content stream f2 can be recirculated to the oxidized region only in whole or in part, and in the latter case, another side stream is discharged from this step as a purge stream.

The liquid stream e2 obtained by gas / liquid separation is then separated by distillation to give the chlorine stream g1 and the stream g2 (where the stream g2 essentially contains oxygen and carbon dioxide). Distillation is typically carried out in a distillation column at a temperature range of -50 ° C to + 90 ° C and a pressure in the range of 4 to 40 bar, where the distillation column is, for example, a theoretical plate of 5 to 30 stages. Has (theoretical plate). The chlorine flow g1 thus obtained usually has a chlorine content of 95 to 100 mol%. At least 50 mol% of these two components are present in the stream g2, which essentially contains oxygen and carbon dioxide, and the stream g2 is discharged from this process as an exhaust stream.

Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 schematically illustrates an embodiment of the method of the present invention.

Hydrogen chloride flow I and flow II (flow II contains industrial standard oxygen) are supplied to the hydrogen chloride oxidation region, which is the main reactor configured as a fluidized bed reactor. Includes 1 and a post-reactor 2 configured as a fixed bed reactor. The produced gas mixture IIb leaving the post-reactor 2 essentially contains chlorine, water vapor, oxygen, hydrogen chloride, and carbon dioxide. This produced gas mixture IIb is contacted with cooled dilute hydrochloric acid V in a phase contact device 3 (eg, a packed column, jet scrubber, or spray tower) to give a flow XVI. Flow XVI has a higher concentration of hydrochloric acid (HCl content 20-35% by weight). The exhaust stream IV, which still contains HCl, is contacted with the water VI in the absorption column 4, eg, in a packed column or tray column. This gives diluted hydrochloric acid (HCl concentration is 1-15% by mass) V, which is cooled and transported into the phase contact device 3 as a cooling medium. Flow VII off the hydrogen chloride absorption column 4 essentially contains chlorine, oxygen and carbon dioxide, and still contains trace water. In order to remove trace amounts of water (remaining), this stream is concentrated in the tray column or filling column 5.₂SO₄Is contacted with. The resulting, substantially water-free stream VIII is then pressurized to a pressure of 15-35 bar, and in pressurization and cooling step 6, about -20 ° C--50. Cooled to a temperature of ° C. The pressurizing and cooling step 6 includes a multi-step (step) pressurizer provided with intermediate cooling (coolant: water), and a heat exchanger (brine cooling) is provided next to the pressurizer. As a result, most of the chlorine is liquefied. The resulting partially liquefied flow IX is fed to the phase separation device 7. The phase separation device 7 is preferably formed as a packed column, in which case a stream 9 is supplied from the top of the column and a portion of the chlorine-enriched liquid phase taken out from the bottom of the column is recirculated. That is, it is re-supplied to the top of the column. The separated gas phase X essentially contains chlorine, oxygen, and carbon dioxide. This flow X is fed to the membrane separation device 9 and fractionated into a chlorine-enriched stream XI (chlorine-enriched stream XI essentially contains oxygen and carbon dioxide) and stream XV (flow XV is It has a low chlorine content and mainly contains oxygen and a predetermined amount of carbon dioxide). The chlorine-enriched stream XI is recirculated upstream of pressurization and cooling step 6. The purge stream XVII is separated from the stream XV and drained from this step. However, the main part of the flow XV is recirculated to the main reactor 1. The liquid chlorine stream XII off the bottom of the phase separator still contains carbon dioxide and oxygen, and this liquid chlorine stream XII is fed to the distillation column 8. The distillation column 8 is configured, for example, as a tray column with 10 to 20 theoretical stages and is operated in a temperature range of -50 ° C to + 90 ° C and a pressure range of 4 to 40 bar. This results in a pure chlorine stream XIII with a chlorine content of&gt; 95% as the bottom withdrawal stream and an exhaust stream XIV. The effluent XIV is carbon dioxide and oxygen, and a very small amount of chlorine (typically &lt;

FIG. 2 schematically illustrates another embodiment of the method of the invention.

Unlike the process shown in FIG. 1, the sidestream XXI is separated from the gas phase X obtained using gas / liquid separation and recirculated directly to the main reactor 1. Another side stream XX is fed to the membrane separation device 9 and the low chlorine content stream is discharged from the process as purge stream XVII.

FIG. 3 schematically illustrates another embodiment of the method of the invention.

Unlike the process shown in FIG. 2, the first side stream XVII of the flow XVIII, which has a low chlorine content and is obtained by membrane separation, is discharged from the process as a purge flow, and the second side Flow XIX is recirculated to main reactor 1.

<figref num="1">It is a figure which showed typically the Example of the method of this invention.</figref><figref num="2">It is a figure which showed the other embodiment of the method of this invention schematically.</figref><figref num="3">It is a figure which showed the other embodiment of the method of this invention schematicly.</figref>

Code description

1 Main reactor 2 Post-reactor 3-phase contact device 4 Absorption column 5 Fill column 6 Pressurization and cooling process 7 phase separator 8 Distillation column 9 Membrane separation device