EP2334426A1

EP2334426A1 - Integrated method for producing chlorine

Info

Publication number: EP2334426A1
Application number: EP09778753A
Authority: EP
Inventors: Aurel Wolf; Leslaw Mleczko; Oliver Felix-Karl SCHLÜTER; Stephan Schubert
Original assignee: Bayer Technology Services GmbH
Current assignee: Bayer Intellectual Property GmbH
Priority date: 2008-10-09
Filing date: 2009-09-29
Publication date: 2011-06-22
Also published as: DE102008050977A1; CN102176967A; WO2010040459A1; US20110180419A1

Abstract

The invention relates to a method for producing chlorine in three steps, wherein in a first step catalytic oxidation of hydrogen chloride into chlorine is carried out on an uranium oxide catalyst, in a second step the resulting chlorine is separated at least partially, and in a third step electrochemical oxidation of hydrogen chloride into chlorine is carried out.

Description

Integrated process for the production of chlorine

The invention relates to a process for the preparation of chlorine in three Verfahrensschπtten, wherein in a first process step, a catalytic oxidation of hydrogen chloride to chlorine on a uranium oxide catalyst is carried out in a second step, the resulting chlorine at least partially separated and in a third process step, an electrochemical oxidation of Hydrogen chloride to chlorine is carried out.

A reaction of great industrial interest is the process of catalytic hydrogen chloride oxidation with oxygen developed by Deacon in 1868.

Chloroalkane electrolysis has pushed the Deacon process far into the background in the past. Almost the entire production of chlorine was carried out by electrolysis of saline saline solutions.

The o.g. However, the Deacon process is of high economic interest, particularly in view of the world's growing demand for chlorine in view of the less strong demand for caustic soda, which is the major by-product of chloroalkane electrolysis. This development is countered by the process for the production of chlorine by catalytic oxidation of hydrogen chloride, which is decoupled from the sodium hydroxide production. In addition, hydrogen chloride precipitates in large quantities, for example in phosgenation reactions, such as in isocyanate production, as by-product.

The catalytic oxidation of hydrogen chloride to chlorine is an equilibrium reaction. The position of the equilibrium shifts with increasing temperature to the detriment of the desired end product chlorine.

The catalysts currently used for catalytic oxidation of chlorine in the context of processes associated with the above-mentioned. Deacon processes are therefore based on catalyst components which already at low temperatures have a high activity with respect to the conversion of hydrogen chloride to chlorine.

For example, WO 2007/134726 discloses that catalysts based on ruthenium, palladium, platinum, osmium, iridium, silver, copper or rhenium are suitable for this purpose. WO 2007/134726 also discloses that from this first Verfahrensschπtt according to the prior art always still a product stream is obtained, which still contains proportions of hydrogen chloride, water, oxygen, and other secondary constituents, such as carbon dioxide. This results according to WO 2007/134726 in the prior art, the need for further treatment of the product stream, for example by more or less complex processes of adsorption and desorption. WO 2007/134726 therefore discloses that a process comprising a further process step in the sense of an eletrochemical oxidation after vorheπger separation of hydrogen chloride by condensation from the remaining product stream is advantageous. It is disclosed that a purification of the hydrogen chloride is preferred, as contained in the product stream Secondary constituents hereby no longer have a negative influence on the electrochemical oxidation, for example because they no longer occupy the electrolysis cell necessary for the electrochemical oxidation.

WO 2007/134726 does not disclose that a further side effect, which results in particular from the use of catalyst components based on ruthenium, does not occur. This refers to the well-known property of such transition metals as ruthenium is to form complexes with minor constituents of the process gases at elevated temperatures or to be itself converted to a volatile form by oxidation. Such complexes are, for example, those with carbon monoxide, as may also be contained in the process gases in accordance with WO 2007/134726 from the operation of the disclosed process in combination with phosgenation processes. The formation and also the volatility of such compounds are described, for example, by Goodwm et al. in "Reactive metal votalhzation from Ru / Al ₂ O ₃ as a result of ruthenium carbonyl formation" (Appl Catalysis, 1986. 24: 199-209). Herein is also disclosed that such volatilization of ruthenium at temperatures from 100 ⁰ C noticeably occurs.

The possibility of further oxidation of ruthenium to the volatile compound is described, for example, by Backmann et al. Acta, 2005 93: 297-304) It is also disclosed herein that in addition to the phases Ru and RuO _2, all the oxides of ruthenium are volatile compounds which are known in the art are formed within minutes at temperatures above 800 ^0C in larger quantities. at temperatures of up to 500 ⁰ C, such as are disclosed in WO 2007/134726, is therefore assumed that the formation of the volatile ruthenium species also occurs, although not in speed, however, in industrial processes in which such processes are operated, operating times of months to years are quite common, so that a noticeable effect can be assumed.

As a result, the catalytic oxidation of hydrogen chloride to chlorine after a short time by the loss of catalyst would not be able to achieve a sufficient level of sales. Furthermore, such complexes can be deposited in the subsequent electrochemical oxidation on the electrode surfaces by reduction of the transition metal contained in them, whereby this Verfahrensschπtt is adversely affected.

According to WO 2007/134726, it is therefore also preferable to carry out the catalytic oxidation isothermally. In any case, the catalytic oxidation should be within the temperatures 18O ⁰ C be carried out to 500 ° C. However, particularly preferred are lower temperatures of

Thus, the method disclosed in WO 2007/134726 is disadvantageous because it can not be operated at higher temperatures without fear of losing the catalyst from the catalytic oxidation of hydrogen chloride to chlorine.

However, since the catalytic oxidation of hydrogen chloride to chlorine is an exothermic reaction, such an increase in temperature is always costly to prevent in terms of process engineering or leads in the event of failure to the need for renewal of the subsequently destroyed catalysts of the catalytic oxidation of hydrogen chloride to chlorine. Moreover, the method of WO 2007/134726 is disadvantageous because it still requires a purification step between the catalytic oxidation and the electrochemical oxidation in order to prevent, for example, a deposit of the electrolysis cell necessary for electrochemical oxidation.

It is known from DE 1 078 100 that salts or oxides of the rare earths, of silver and of uranium can also be used as catalysts for the catalytic oxidation of hydrogen chloride to chlorine. It is further disclosed that at a temperature of 480 ⁰ C, a catalyst comprising uranium oxide, a conversion of 62% of hydrogen chloride to chlorine allows.

The process disclosed in DE 1 078 100 is disadvantageous since it permits a maximum conversion of 62%. This is partly due to the equilibrium position at elevated temperatures. Starting from the prior art, there is still the problem of providing a process which makes it possible to convert hydrogen chloride to chlorine without the limitations of the processes of the prior art Technology regarding the necessary cleaning of the gas stream or to be subjected to lower recoverable sales.

It has now surprisingly been found that a process for preparing chlorine from a reaction mixture A containing at least hydrogen chloride, comprising the steps of a) oxidation of hydrogen chloride with oxygen to chlorine in at least a first reaction zone in the presence of a catalyst containing a product stream P), b) at least partially separating the chlorine contained in the product stream P ₁ from a), obtaining a product stream P ₃ , c) electrochemical oxidation of the hydrogen chloride contained in the product stream P ₃ from b) in a second reaction zone, the product stream P ₃ including water, and optionally also includes chlorine, characterized in that the product stream P ₃ from b) is fed directly to the reaction zone according to c) and that the catalyst according to a) comprises a uranium compound, to be able to achieve this object.

The inventive method is particularly advantageous because it was surprisingly found that the inventive method allows the direct supply of the product stream P ₃ in the electrochemical oxidation of hydrogen chloride to chlorine without a need for further treatment except the separation of chlorine is necessary, so that the reaction mixture fed to step a) of the process may also comprise secondary constituents which need not be separated off in step b) of the process. This is due to the catalyst comprising a uranium compound, which can be operated at higher temperatures, without its catalytic properties are significantly affected and because at these higher temperatures, the Nebenbestandteüe optionally contained in the reaction mixture A can be oxidized.

By-products in the context of the present invention refer to materials comprising carbon and in which the carbon is at least partially present in an oxidation number less than or equal to two.

Examples of Nebenbestandteüe, in whose presence, the inventive method proves to be particularly advantageous therefore halogenated or non-halogenated aromatic hydrocarbons, such as chlorobenzene, o-dichlorobenzene, p-dichlorobenzene, Tπchlorbenzole, the corresponding chlorotoluenes or chloroxylenes, chloroethylbenzene, toluene, or xylene , Such Nebenbestandteüe usually come from Phosgemerverfahren with which the inventive method can thus be operated in an advantageous manner in combination.

Another example of a Nebenbestandteü, in whose presence, the inventive method proves to be particularly advantageous is carbon monoxide. While in methods e.g. according to the disclosure of WO 2007/134726 it is to be expected that the presence of e.g. Carbon monoxide for the formation of transition metal complexes in the catalytic oxidation of hydrogen chloride to chlorine and thus after a short time to poor conversion of the catalytic oxidation, and subsequently also leads to deficient conversion in the course of electrochemical oxidation by deposition of elemental transition metal on the electrode of the electrochemical oxidation proves Surprisingly, the process of the invention is unimpeachable of such problems, since the catalyst comprising a uranium compound does not tend to form such complexes.

It was thus further surprisingly found that the catalyst used in step a) of the process according to the invention, comprising a uranium compound, in no way, for example in In the sense of volatile compounds with minor constituents, is discharged from the reaction zone of step a) of the inventive method, so that a permanent operation of a erfϊndungsgemäßen method can also be ensured.

Furthermore, it is thus ensured that no metal or transition metal residues can be present in the product stream P ₃ , which can precipitate on the surface of the electrodes of the electrochemical oxidation according to step c) of the inventive method.

Catalysts comprising a uranium compound may or may not comprise a support material according to the present invention. If a catalyst comprising a uranium compound in step a) of the process according to the invention is used, usable carrier materials are those selected from the list containing silicon dioxide, aluminum oxide, titanium dioxide, tin dioxide, zirconium dioxide, ceria, carbon nanotubes or mixtures thereof.

Usually, the proportion of the uranium compound in the catalyst, if it additionally comprises a Trägermateπal, in the range of 0.1 to 90 wt .-%, preferably in the range of 1 to 60 wt .-%, particularly preferably in the range of 1 to 50 wt .-% based on the total mass of uranium compound and Trägermateπal.

The use of catalysts comprising a support material is generally advantageous, in particular to obtain the structured beddings described below. However, the Trägermateπahen according to the above list similar to the catalysts used in the prior art may optionally be found in the product stream P ₁ and / or P ₃ , so that their use against the preferred further development described below may be disadvantageous. In general, the support materials have a better tendency to deposit on the electrodes of step c) of the method according to the invention, so that they are nevertheless usable in a pπnzipiell.

Suitable uranium compounds of the catalyst are uranium oxides, uranium chlorides and / or uranium oxychlorides. Suitable uranium oxides are either UO ₃ , UO ₂ , UO, or uranium oxides of a nichtstöchimoetπschen composition. Preferred uranium oxides of nichtstöchimoetπscher composition are those having a uranium to oxygen ratio according to the formula UO _x of UO ₂ , i to UO. ₅ Particularly preferred are those uranium oxides selected from the list containing U ₃ O ₅ , U ₂ O ₅ , U ₃ O ₇ , U ₃ O ₈ and U ₄ O ₉ . Uranoxychloπde refer in the context of the present invention substances of the general composition UO _x CI _y , where x and y are each natural numbers greater than zero. Thus, uranoxychloπde also not stόchiometnsche compositions containing chlorine, oxygen and uranium. - -

In a preferred further development of the process according to the invention, the catalyst used contains only one carrier of a uranium compound D.h. The catalyst contains only one uranium compound.

The use of such catalysts is particularly advantageous because the use of transition metals and noble metals can be completely dispensed with, and thus the above disadvantages of the prior art processes with respect to the used

Catalysts can be excluded. In addition, interfering influences of Trägermateπalien on the electrochemical oxidation according to step c) may also be excluded in this case. Such disturbing influences are, for example, the at least partial entrainment of these carrier material in the product stream A, which in turn can then precipitate on the surfaces of the electrodes of the electrochemical oxidation according to step c) of the process according to the invention.

Thus, the inventive method can be operated for a long time without a renewal of the catalyst of step a) or the electrodes of step c) is necessary. This is particularly economically advantageous.

The catalyst used can be present as a bed of particles or in the form of moldings.

If the catalyst is present as a bed of particles, it preferably has a structured bed, which is characterized in that the catalyst activity m in the main flow direction of the reaction zone of step a) increases.

This structured bed is particularly advantageous because in the main flow direction of the reaction zone of step a), the same conversions per room unit are achieved. While high reaction rates can already be achieved at the entrance of the reaction zone due to the high concentration of hydrogen chloride and oxygen, they are further maintained against the exit of the reaction zone by the increased catalyst activity. This requires a particularly efficient use of the catalyst.

Such a structuring of the catalyst bed can be effected by different ratios of uranium compound to Trägermateπal or by different dilution of a catalyst with an Inertmateπal. If the catalyst is in the form of a shaped body, moldings of any desired shape are suitable; preference is given to tablets, rings, cylinders, stars, carriage wheels or spheres, particular preference being given to spheres, chambers, cylinders or star strands.

The reaction zone of step a) of the process according to the invention can be operated at temperatures above 350 ⁰ C up to temperatures of 800 ° C. Preferably, it is operated at temperatures of 400 to 600 ⁰ C. In contrast to the methods according to the prior art, as described for example in WO 2007/134726, in this case the upper temperature is not a limit at which the method according to the invention can no longer be carried out adequately, but merely represents a limitation in that that the surprising positive effect of the possibility of oxidation of secondary constituents has already almost completely occurred, so that a further increase in temperature appears economically unfavorable.

The lower temperature limit is particularly advantageous because at this temperature, a large number of the minor constituents in the reaction zone of step a) of the process according to the invention is already oxidized to form further gaseous compounds. In the case of minor constituents comprising only hydrocarbons, such further gaseous compounds are, for example, carbon monoxide and / or carbon dioxide. In the case of minor constituents which comprise chlorine, such further gaseous compounds are, for example, hydrogen chloride and / or chlorine, which in turn are part of the process according to the invention. The process thus has a particularly advantageous effect if the secondary constituents are halogenated, in particular chlorinated hydrocarbons, or carbon monoxide smd.

Further, the catalyst comprising a uranium compound becomes surprisingly more active at these temperatures than at lower temperatures, contrary to e.g. the ruthenium catalysts of the prior art, which tend to be entrained with the product stream Pi with increasing temperature, and thus lose activity in the course of the operation of such processes. This is not the case in the method according to the invention.

The step a) of the inventive method is usually carried out at pressures between 1 and 30 bar. Preferably at pressures of 5 to 10 bar.

These pressures are not essential to the particularly advantageous practicability of the method according to the invention compared to the preferred temperature ranges disclosed above. Rather, the pressures disclosed herein are the areas in which the general embodiment of the inventive method has proven to be economical. However, it is also possible, e.g. by the interconnection of the method according to the invention with other methods in the sense of a process network, lower or higher pressures prove to be advantageous, without thereby the inventive method would lose its particular advantage. Step a) of the process according to the invention can be carried out in one or more reaction zones connected in parallel or in series. In this case, the individual reaction zones can be located in one device or can also be present in divided form in different devices.

The oxygen can be added either completely together with the hydrogen chloride before the first reaction zone or distributed over the various reaction zones. - -

Furthermore, step a) of the process according to the invention can be carried out continuously or discontinuously independently of step b) of the process according to the invention. Preferably, however, step a) of the process according to the invention is carried out continuously.

Devices in which step a) of the process according to the invention can be carried out are, for example, fixed bed, fluidized bed or fluidized bed reactors, as are generally known to the person skilled in the art in their embodiments. Preference is given to fixed bed reactors, since in these the aforementioned structured bed of the catalyst can be achieved in an advantageous manner

In a preferred further development of step a) of the process according to the invention, the heat generated in the reaction zone by the exothermic formation of chlorine from hydrogen chloride from the reaction zone or after the reaction zone is withdrawn from the product stream Pi and for the heating of the reaction mixture A m or before the reaction zone of the step a) used. If appropriate, this can take place together with the at least partial transfer of the product stream Pi from step a) into a liquid phase, as will be described below. Such removal of heat is particularly advantageous because it makes the process more economical.

The separation according to step b) of the process according to the invention is usually carried out according to principles generally known to those skilled in the art for separating chlorine or hydrogen chloride from gas streams. Non-exhaustive examples include the fractionated or unfractionated condensation of at least hydrogen chloride, or the adsorption and subsequent desorption of chlorine or hydrogen chloride.

It is essential that at least portions, preferably over 50 wt .-%, more preferably over 80 wt.% Of the chlorine contained in the product P] containing a product stream P _{2 are} separated, since this in the presence of water in the sense of an equilibrium reaction for the formation of Hydrogen chloride tends, which is well known in the art. Since chlorine is to be formed with the process according to the invention, such formation of hydrogen chloride is disadvantageous.

In the sense of the step c) of the process according to the invention, which is preferably carried out in a liquid phase, it is preferred if the hydrogen chloride present in the product stream P _{1 is} fractionated in step b), ie essentially only the hydrogen chloride and optionally water by condensation from the product stream P _{1 is} separated and this condensate forms the product stream P ₃ , while the übπge chlorine in the sense of a second product stream P _{2 is led} out of the process substantially. The electrochemical oxidation of hydrogen chloride to chlorine according to step c) of the process according to the invention can be carried out by generally known diaphragm processes or by means of an oxygen-consuming cathode.

Possible embodiments of diaphragm methods are described in WO 2007/134726.

In a preferred embodiment of the method according to the invention, step c) of the method is carried out with an oxygen-consuming cathode.

For this purpose, the product stream P ₃ from step b) of the process according to the invention is preferably first converted into a liquid phase. In this preferred embodiment of the method using a Sauerstoffverzehrkathode located in the reaction zone of step c), a first electrode space Ei to which from step b) of the inventive method resulting product stream P ₃ , comprising hydrogen chloride, is fed, and it is m the Reaction zone another electrode space E ₂ , also containing an electrode into which an electrolyte solution comprising dissolved oxygen or a gas comprising oxygen, is introduced, wherein electrode space Ei and electrode space E _{2 are} separated by a membrane and the electrodes via a power supply S electrically conductive connected to each other.

The electrode of the electrode space Ej can be used in the form of a rod, a plate, a net or a woven fabric and may be made of a material selected from the list containing carbon black, graphite or metal. As metals, for example, titanium or titanium alloys or the special metal alloys, which are known to the skilled worker under the name Hastelloy and Incolloy, can be used.

Mateπalen selected from the list containing graphite, titanium, titanium alloy, or the special metal alloys Hastelloy and Incolloy are particularly preferred. The electrode of the electrode space E ₂ may have the same shapes as the electrode of the electrode space E ₁ and may be made of titanium or titanium alloys such as titanium-palladium and may be coated. If the electrode is coated, it is preferably coated with a mixed oxide comprising one or more of the metals ruthenium, iridium and titanium. Particularly preferred is a coating comprising a mixed oxide of ruthenium oxide and titanium oxide or a mixture of ruthenium oxide, iridium oxide and titanium oxide.

The electrode of the electrode space E ₂ may also be made of graphite and other carbon materials such as diamond.

The aforementioned materials of the electrodes of the electrode spaces E] and E ₂ are particularly advantageous because they are particularly resistant to the chemically aggressive substances hydrogen chloride and chlorine. That is, these materials are in contact with the product stream P ₃ do not tend to corrosion, so that the advantage of the method according to the invention is particularly pronounced, since the need for renewal of catalyst and / or electrodes for a long time is not necessary and the entire process can thus be operated for a long time without necessary maintenance. The membrane located between the electrode spaces E ₁ and E _{2 of} the reaction zone of step c) is usually a polymer membrane. Preferred polymer membranes are all polymer membranes, which the person skilled in the art generally knows under the generic term of the cation exchange membrane. Preferred membranes include polymeric perfluorosulfonic acids. The membranes may also comprise reinforcing fabrics of other materials, preferably fluorinated polymers, and more preferably polytetrafluoroethylene.

The thickness of the membrane is usually less than 1 mm. Preferably, the thickness of the membrane is less than 500 microns, more preferably less than 400 microns, most preferably less than 250 microns.

The step c) according to the preferred embodiment is usually operated by applying a current density of 4-7 kA / m ² .

The step c) of the method according to the invention can be carried out at any pressure. However, it is preferably carried out at lower pressure than that of step a) of the process according to the invention. Particularly preferably, step c) is carried out at about ambient pressure (1013 hPa). The step c) of the method according to the invention can likewise be carried out at arbitrary temperatures. However, it is preferably carried out at temperatures from room temperature to 100 ^° C.

The temperatures are particularly advantageous because the energy content of the material stream obtained from step c) of the process is thus reduced, so that this energy is available for the process according to the invention. This energy was preferably recovered in the form of heat according to the previously described preferred further development of step a) of the process and used for heating the reaction mixture A of the bulkhead a) of the process according to the invention.

The invention will be explained below with reference to examples and figures, without thereby restricting them thereto.

1 shows an embodiment of the process according to the invention in which a reaction mixture (A) containing hydrogen chloride, oxygen and secondary constituents comprising carbon monoxide and chlorobenzene or other partially halogenated aromatics such as dichlorobenzene or the like, having a temperature T ₂ in a first reaction zone (R ₁ ) containing a catalyst (K) from uranium oxide, is introduced after the reaction mixture A in a first Heat exchanger (W |) was heated from a temperature T ₁ to T ₂ > T ₁ . In the reaction zone R ₁ , the reaction mixture is heated to a temperature T ₃ > T ₂ and exits as the first product stream P) containing residues of hydrogen chloride, and chlorine and carbon dioxide in a second heat exchanger (W ₂ ), the first product stream P ₁ to a Temperature T ₄ <T ₃ cooled. The heat obtained in this way is supplied to the first heat exchanger W ₁ by means of a heat transfer fluid connection (L). The first product flow P | is here partially condensed in the second heat exchanger W ₂ , so that a second product stream in the form of a gas stream (P ₂ ) comprising essentially chlorine and carbon dioxide, can be led out of the process. The condensed third product stream (P ₃ ) is then forwarded to a first electrode space (E ₁ ) in a second reaction zone (R ₂ ), the first electrode space E _{1 being} connected to a second electrode space (E ₂ ) via a membrane (M) The electrode spaces E ₁ and E ₂ are each graphite electrodes in bar form (1, 2), which are connected to a power source (S). In the second reaction zone R ₂ , chlorine is formed in the electrode space E ₁ by means of electrochemical oxidation from the remainder of hydrogen chloride in P ₃ , while at the same time oxygen is reduced to water in the second electrode space E ₂ . A fourth product stream P _{4 is obtained} from the electrode space E _{1 of} the second reaction zone R ₂ , which contains only chlorine.

Examples:

Example 1: Preparation of a uranium oxide catalyst on an alumina support

40 g of gamma-Al ₂ O ₃ shaped bodies (BET of 200 m ² / g, from Saint Gobain) were impregnated in a glass beaker with a 10% by weight aqueous solution of uranyl acetate dihydrate (Riedel de Haen) by spraying.

After an exposure time of 1 h, the solid was dried in an air stream at 80 ^° C. for 2 h. The entire experiment was repeated until 12 wt .-% uranium are present on the moldings.

Example 2 Preparation of a catalyst containing only uranium oxide 2 g of a powdered uranium (V / VI) -Oxides (from Strem Chemicals.) Were dried overnight at 150 ⁰ C in a drying oven at ambient pressure and then for 2 h in air at 500 ⁰ C calcined.

EXAMPLE 3 (Comparative Example) Preparation of a Ruthenium Catalyst on an Aluminum Oxide Support 5 g of spherical gamma-Al ₂ O ₃ molding (from Saint-Gobain) with an average diameter of 1.5 mm and a BET surface area of 200 m ² / g were impregnated with a solution of 0.258 g of commercial Rutheniumchloπd-n-hydrate (Riedel de Haen) m 6.5 g H ₂ O analogous to Example 1.

After a contact time of 1 h, the solid was dried in an air stream at 60 ⁰ C for 5 h. Subsequently, the catalyst was calcined at 250 ^° C. for 16 h. The result is a catalyst with the equivalent of 2 wt .-% of ruthenium.

Example 4: Carrying out the step a) of the process with catalyst according to Example 1

25 g of the catalyst from Example 1 were introduced into a Ni fixed bed reactor (diameter 22 mm, length 800 mm) together with 25 g of TiO ₂ Inertmateπal. In this case, a fixed bed of about 150 mm was obtained. The fixed bed was heated by means of an electric heater so that a radial temperature gradient of 400-600 ⁰ C is formed. The fixed bed reactor was flowed through at a pressure of 4 bar with a gas mixture of 100 Nl / h of hydrogen chloride, 100 Nl / h of oxygen and 60 Nl / h of nitrogen.

The product stream was passed over two condensation vessels, so that the water formed and the remaining hydrogen chloride were condensed out, while the chlorine was separated as a gas stream. After an operating time of 6 hours, the condensate formed was measured for the content of aluminum and titanium by means of ICP-OES (Inductively Coupled Plasma - Optical Emission Spectrometry, device: Vaπan Vista-PRO, method according to manufacturer's instructions) and the content of uranium by means of ICP- MS (Inductively Coupled Plasma - Mass Spectrometry, device: HP Agilent 4500, Method according to manufacturer's instructions). From the analysis, the concentrations of aluminum, titanium and uranium in the condensate shown in Table 1 were determined.

Table 1: Content of metal in the condensate according to Example 4

Metal concentration [mg / 1]

Aluminum 1.6

Titanium 7,9

Uranium <0.001

It can be seen that the support materials, which already have a markedly reduced tendency to form volatile compounds compared with the prior art catalysts, since these are already concentrated at least a factor of 1,000 higher in the condensate than the uranium compounds. From this follows both the advantageous over the prior art operation of the method according to the invention, as well as in particular the advantageousness of its preferred embodiments. Example 5: Carrying out the step a) of the process with catalyst according to Example 2

0.2 g of the catalyst obtained according to Example 2 were ground and introduced as a mixture with 1 g of silica sand (100-200 microns) in a quartz reaction tube (diameter of 10 mm).

The quartz reaction tube was heated to 600 ⁰ C and subsequently operated at this temperature. A gas mixture of 80 ml / min of hydrogen chloride and 80 ml / min of oxygen was passed through the quartz reaction tube.

After an operating time of 140 h, the product gas stream formed was passed through a condensation trap for several hours, so that the resulting H ₂ O and unreacted hydrogen chloride were condensed out. The condensate was analyzed analogously to Example 3 for the content of uranium. There was a concentration of uranium of 0.044 mg / 1 in the condensate.

Example 6 (Comparative Example): Performance of Step a) of the Process with Catalyst According to Example 3

A quartz reaction tube was charged analogously to Example 5 with 0.2 g of the catalyst from Example 3 and diluted with quartz sand. The quartz reaction tube was heated to 540 ° C and subsequently operated at this temperature.

A gas mixture similar to that in Example 5 was passed through the quartz reaction tube. After a Betπebszeit of 37 h, the product stream formed was passed through a condensation trap for several hours, so that the resulting H ₂ O and unreacted hydrogen chloride were condensed out. The condensate was investigated analogously to Example 4 on the content of ruthenium and aluminum.

Table 2: Content of metal in the condensate according to Example 6

Metal concentration [mg / l]

Aluminum 1.5

Ruthenium 3.0

It can be seen from this that the concentration of ruthenium in the product stream already exceeds the uranium by a factor of about 68 after a service time of 37 h, compared to example 5 with reduced temperature. The amount of aluminum contained is comparable to that of Example 4. This is the particular advantage of the method according to the invention and in particular according to the preferred development very clear, since now no longer with a deposition of ruthenium in step c) of the method must be expected.

Claims

claims:

1. A process for the preparation of chlorine from a reaction mixture A, which contains at least hydrogen chloride, comprising the steps a) oxidation of hydrogen chloride with oxygen to chlorine in at least a first reaction zone in the presence of a catalyst containing a product stream P ,, b) at least partially separating the chlorine contained in a) in the product stream Pi, sustaining a product stream P _3, c in) electrochemical oxidation of the hydrogen chloride comprised of b) in the product stream P ₃ in a second reaction zone, wherein the product stream P ₃ and water, and optionally includes chlorine, characterized in that the product stream P ₃ from b) is fed directly to the reaction zone according to c) and that the catalyst according to a) comprises a uranium compound.

2. The method according to claim 1, characterized in that the catalyst comprises a Trägermateπal.

3. The method according to claim 2, characterized in that the Trägermateπal is also a uranium compound.

4. The method according to one of vorheπgen claims, characterized in that the uranium compounds are uranium oxides, Uranchloπde and / or Uranoxychloπde.

5. The method according to claim 4, characterized in that the uranium oxides are either UO ₃ , UO ₂ , or UO, or uranium oxides are a mchtstöchimoetπschen composition.

6. The method according to claim 5, characterized in that the uranium oxides nichtstöchimoetπscher composition those with a uranium to oxygen ratio according to the formula UO _x of UO ₂ , i to UO ₅ are.

7. The method according to any one of the preceding claims, characterized in that the step a) at temperatures above 350 ⁰ C up to temperatures of 800 ⁰ C is operated.

8. The method according to one of vorheπgen claims, characterized in that in step b) a fractional condensation is obtained maintaining the product flow P _{3 is} carried out, from which a product stream P ₂ comprising substantially chlorine is separated.

9. The method according to claim 8, characterized in that the product stream Pi withdrawn heat for heating the reaction mixture A in or before the reaction zone of step a) is used.

10. The method according to one of vorheπgen claims, characterized in that Schπtt c) is performed with an oxygen-consuming cathode.