DE102013009230A1 - Process and membrane reactor for the production of chlorine from hydrogen chloride gas - Google Patents

Abstract

An improved process for the electrochemical production of chlorine by electrolysis is described. In an electrochemical membrane reactor (5), an electrode unit (6), which contains a membrane (3) coated with catalyst and gas diffusion layers, is used to convert hydrogen chloride to chlorine. The protons released migrate from the anode (1) to the cathode (2), where they react with oxygen and form water. In this process, both reactants are gaseous, a gap-free electrode arrangement (6) is used, and the membrane (3) is optimally moistened. The apparatus used and the half-cell reactions are described.

Description

Field of application of the invention

The present invention relates to the production of chlorine from hydrogen chloride. The described process takes place in a membrane electrochemical reactor containing a bilateral catalyst coated membrane and gas diffusion layers on both sides of the catalyst coated membrane. Gaseous HCl is fed to one side of the catalyst-coated membrane while oxygen-containing gas is passed through the cell on the other side of the catalyst-coated membrane. The resulting in the reduction of hydrogen chloride gas to chlorine protons migrate through the membrane and react there with oxygen supplied to water.

The invention further relates to an electrode unit designed for carrying out the method and to a membrane reactor equipped therewith.

State of the art

The electrochemical conversion of hydrogen chloride to chlorine: 2HCl → Cl ₂ + H ₂ Equation 1 is a well known reaction and is used for the conversion of hydrogen chloride to chlorine. Since hydrogen chloride as a byproduct in many industrial processes, such. As in the production of isocyanates, arises, it is readily available as a starting material. Often HCl is formed in chlorination reactions in which chlorine is used as starting material, so that one can also speak of a chlorine recycling in the industrial chlorine production according to equation 1.

The electrolysis according to equation 1 starts in most cases from aqueous solutions. The voltage to be applied is quite high at about 1.5V to 2.0V per cell, resulting in low energy efficiency.

There is a great deal of literature on the electrolysis of hydrogen chloride. The largest part relates to aqueous hydrochloric acid solutions, such as in EP 0 785 294 A1 . WO 02/068722 A2 . EP 1 366 213 A2 . US 4,210,501 A and US 2006/249380 A described. There are numerous attempts to eliminate the disadvantages of existing technology. In the DE 197 55 636 A1 describes a method in which gaseous hydrogen chloride is reacted in an electrochemical cell in two stages. The cell is supplied in the first stage (voltages of 1.6 to 1.73 V at current densities of 6 to 10 kA / m ² ) with gaseous hydrogen chloride, but not with oxygen. In this first stage, a low turnover is achieved. Therefore, an expensive second stage (voltages of 1.18 to 1.36 V at current densities of 2.8 to 4.4 kA / m ² ) is needed to increase the conversion. The second stage is equipped with an oxygen-consuming cathode (gas diffusion electrode), which is supplied with aqueous hydrogen chloride solution (see Equation 2). 4HCl + O ₂ → 2Cl ₂ + 2H ₂ O Equation 2

In Journal Electrochem. Soc. Vol. 142, no. 11, November 1995, pages 3619-3625 experiments on the conversion of gaseous hydrogen chloride to chlorine have been described. HCl was directed to the anode of the cell. Liquid water was pumped into the cell on the cathode. The half-cells were separated by a polymeric proton-conducting membrane (Nafion ^®), which was coated with catalysts. Hydrogen chloride is oxidized to chlorine, the protons move through the membrane and hydrogen is generated at the cathode. The catalysts used (cathode / anode) are Pt / Pt, RuO ₂ / SnO ₂ and Pt / RuO _2, with Pt / Pt combinations giving the best results.

In US 5,580,437 A and US 5,411,641 A , both from Newman and Eames, the data from their above article from J. Electrochem. Soc. The reaction of anhydrous hydrogen chloride to dry chlorine is described (Equations 1 and 2). In this case, an oxygen-consuming cathode is used. However, experimental data were presented only for Equation 1. Equation 2 lacks proof of the proposed concept, experimental data does not exist. The experiments according to equation 1 were carried out in an electrochemical cell with an active area of 1 cm ² . At the anode of the cell gaseous hydrogen chloride is supplied, which is oxidized to chlorine. Protons pass through a cation exchange membrane (Nafion ^® ) to the cathode. There the protons are reduced to hydrogen. Time tensions between 1.1 V and 2.8 V at current densities up to 957 mA / cm ² were measured. However, the actual operability of the oxygen-consuming electrode for Equation 2 is not established in this patent application.

Object of the invention

Despite the improvements described in earlier work, there is still a lack of a process that can meet the requirements for high energy efficiency. Furthermore, a reduction of the cell voltage is desirable. The process should be able to be performed with high gas throughput at high sales. The associated reactor should enable stable long-term operation.

Summary of the invention

The above-mentioned objects are achieved by the method according to claim 1, the associated electrode unit according to claim 8 and the membrane reactor according to claim 14 equipped therewith.

The object of the invention is an improved process for the electrochemical conversion of gaseous hydrogen chloride to chlorine. Surprisingly, it has been found that the electrochemical conversion of hydrogen chloride with oxygen can be carried out at relatively low cell voltages. As already mentioned above, the electrochemical conversion of gaseous hydrogen chloride in a membrane reactor with catalyst-coated membranes in contact with gas diffusion layers as such is known. However, it has been found that the water balance of the membrane must be given special consideration and controlled in order for the cell to behave stably under operating conditions. The investigations presented here prove that surprisingly low cell voltages in the range from 0.6 V to 1.6 V at current densities of up to 5.5 kA / m ² can be achieved with the cell according to the invention and the method according to the invention.

The operating principles of the invention will be described first with the aid of and be explained.

In the functional principle of the process used in the invention is explained. The equations given for the two half-cells 4HCl → 2Cl ₂ + 4H ⁺ + 4e ^- O ₂ + 4H ⁺ + 4e ^- → 2H ₂ O give the overall equation 4HCl + O ₂ → 2Cl ₂ + 2H ₂ O.

On the anode 1 gaseous hydrogen chloride is directed into the cell. On the cathode 2 oxygen-containing gas is supplied. Both electrodes contain a noble metal catalyst, a supported noble metal catalyst or a metal-free catalyst. Test results pertaining to these embodiments are described below. At the anode, hydrogen chloride is oxidized to chlorine, resulting in protons and electrons. Through a cation exchange membrane 3 , here Nafion ^® , the transport of protons from the anode takes place 1 to the cathode 2 , On the cathode side, the protons and electrons are converted to water with oxygen. The electrochemical reactor 5 in total and the gas streams can be heated or cooled as needed. The designated heater or heat exchanger units are as 4 designated. The components 1 to 3 form the electrode unit 6 ,

shows the electrode unit 6 out in a more detailed view (exploded view).

electrode design

The electrode unit 6 The invention consists of a proton-conducting polymer membrane 21 , Which is preferably made of Nafion ^®, the catalytically active membrane coatings 22 (in the examples described below, platinum supported on carbon) and the gas diffusion layers 26 , The gas diffusion layers 26 are themselves multi-layered and always include a microporous layer 23 attached to the catalytically active layer 22 borders. On top of this is an optional intermediate layer 24 applied for further adjustment of the wetting of the electrodes, which in the examples described in more detail below a polytetrafluoroethylene. This is followed by an electron-conducting finishing layer 25 containing the gas diffusion layer 26 limited to the gas space of the half-cell out and which is formed in the examples of a carbon cloth. It is characteristic of the electrode unit according to the invention 6 in that it is constructed in a layered and preferably gap-free manner. The loadings of said components for the anode and cathode side can be symmetrical or asymmetrical. With regard to the central proton-conducting membrane, the electrode unit is constructed symmetrically.

The proton-conducting membrane 21 is required to transport the protons produced at the anode to the cathode side so that they can react there with the supplied oxygen to form water. The conductivity of the membrane depends essentially on the degree of humidification. This moistening can take place on the one hand by the water produced in situ and on the other hand by supplying water-moistened gases. In the process presented here, this is of particular importance since only gaseous starting materials are used.

With the help of microporous layers 23 different properties or functions of the gas diffusion layers can be adjusted. In general, the gas diffusion layer has the task to ensure a good electrical contacting of the catalytically active layer with the flow distributor field and to allow the mass transport of the reactants over the active surface of the reactor and the removal of substances from the active surface. Another important task of the gas diffusion layer is to prevent the reactor from an unwanted "flooding" so that the reactor is filled with water, and to prevent the opposite effect, the drying out of the reactor. This property can be adjusted by the additional microporous layer. In this case, the wetting property, ie the hydrophobicity or hydrophilicity, of the entire gas diffusion layer with water through the microporous layer 23 affected. By varying the composition and loading of the microporous layer, water wetting angles in a range of 100 ° to 150 ° can be set in a defined manner.

By means of this structure of the electrode layers, it is possible to set the water balance of the reactor, which is important for the process presented here, in a controlled manner. This has not been recognized in the prior art.

Water balance concept

The achievable performance of the electrochemical reactor depends strongly on the water content of the membrane. The productivity of chlorine is given by the set current density by Faraday's law. However, high current densities can only be achieved with well-moistened membranes. However, moistening, as described above, must not lead to flooding or drying out of the electrodes.

An essential aspect of the invention is therefore to specifically moisten the cathode gas, which consists of oxygen or an oxygen-containing gas, and to introduce it into the membrane in a moistened state. According to the invention, the optimum humidification is ensured by adjusting the temperature of the membrane in the electrode unit and additionally the temperature of the supplied cathode gas as a function of the current density. The humidification of the cathode gas can be done in a gas humidifier. The temperature can be used to set the degree of humidification. In addition, according to equation 2, water is formed in situ. This rate of water production is current-density dependent and, at higher current densities, results in increased membrane temperatures and membrane dehydration unless additional moistening measures are taken. This effect must be balanced by the incoming cathode gas flow. With regard to this water management, the temperature control of the electrolysis process is of crucial importance.

It is preferred to operate the membrane reactor at a constant temperature. This means that the membrane contained therein is kept at a constant temperature.

It is further preferred that the degree of humidification of the cathode gas is at 70 to 100% water vapor saturation. Furthermore, it is preferred that the moistening is controlled so that the mass flow of water is at least 0.1 kg / (h.Nm ³ ), preferably 0.2 kg / (h.Nm ³ ) and up to 0.6 kg / (h · Nm ³ ) (unit: "kilogram per hour and standard cubic meter").

In a particularly preferred embodiment, therefore, all the membrane reactor supplied substances, in particular oxygen, hydrogen chloride and water, are supplied in gaseous form. The gaseous supply of Water is preferably carried out as described above by the cathode gas, namely the oxygen or the oxygen-containing gas, are moistened with water. The cathode gas then contains water in the gaseous form.

Furthermore, it is preferred that the working temperature of the membrane reactor and thus also the temperature at the membrane itself is 20 to 80 ° C. This temperature range is given by the membranes available today, would be desirable proton-conducting membrane materials that are long-term stable even at 200 ° C.

The working pressure within the two electrode chambers should be set to 1 to 3 bar.

The method further preferably operates at current densities of up to 10 kA / m ² and more preferably in the range of 4 to 6 kA / m ² . These current densities are preferably obtained at cell voltages below 2.5V. The process according to the invention can be used on an industrial scale. Sales at medium to high volume flows allow this. In preferred embodiments, both cathode and anode gases with flow rates of 0.2 and preferably up to 25 Nm ³ / (h · m ² ) are passed through the membrane reactor (unit: "standard cubic meter per hour and square meter" (electrode area)).

The electrode unit according to the invention which is particularly suitable for carrying out the method is an electrode unit constructed in layers, preferably a gap-free layer electrode unit.

The electrode unit according to the invention for a membrane reactor for carrying out the newly developed method is distinguished by a membrane of a proton-conducting polymer material which has supported or unsupported catalytically active coatings on both sides and gas diffusion layers arranged thereon. The gas diffusion layers in turn comprise the microporous layers facing the catalytically active layers. Further layers can follow the microporous layers within the gas diffusion layers, with at least one additional layer being provided to the microporous layer, which closes the structure to the gas space of the respective half cell. In preferred embodiments, the microporous layer within the gas diffusion layer is followed by an intermediate layer, for example of PTFE, to assist in the adjustment of the wettability of the gas diffusion layer. The final layer is preferably made of carbon cloth, which is designed to be gas permeable and additionally with carbon, may be loaded Nafion ^® and other additives.

Preferably, therefore, the layers: membrane, catalytic active coating, microporous layer of the gas diffusion layer and complementary layers of the gas diffusion layer on both sides of the membrane are arranged without gaps on each other. To improve the contacts between the layers, they can be connected by pressing.

In particularly preferred embodiments, the gas diffusion layers include a carbon fabric coated with PTFE and carbon, the carbon / PTFE loading being 2 to 8 mg / cm ² .

The microporous layer of the gas diffusion layers of the electrode unit is preferably made of a finely divided carbon such. B. from carbon blacks, CNT or other electron-conducting support materials. In this case, the microporosity can be adjusted by the particle size distribution of the carrier materials.

The catalytically active coatings of the membrane of the electrode unit preferably contain supported or unsupported noble metals, more preferably platinum (Pt), ruthenium (Ru), rhodium (Rh) or iridium (Ir), supported or unsupported metal compounds such as preferably rhodium sulfide, tin oxide, titanium oxide, ruthenium oxide or organometallic compounds, or they contain metal-free catalysts, such as. As carbon or polymer composite compounds. The catalytically active coatings may also contain mixtures of the aforementioned ingredients. It is particularly preferred if the loading of the catalytically active coatings with the catalytically active substance is 0.1 to 5 mg / m ² .

Further preferably, in addition, a proton-conducting compound such. B. Nafion ^{® be present} in the catalytically active coating, and with degrees of loading of 0.2 to 5 mg / m ² .

In the examples it is provided for the catalytically active layer that at least one noble metal is supported on an electron-conducting material, platinum on a carbon material is particularly preferred. As a proton-conducting compound, which is additionally present in the catalytic coating, ^{Nafion® is} selected there.

In the gas diffusion layers, it is particularly preferred if a carbon cloth is coated in a first step with PTFE and in a second step with a microporous layer of a mixture of electron-conducting carbon and PTFE. The coating of the carbon cloth should be 10 to 60% by weight PTFE of the mixture of PTFE and carbon (finely divided) and / or other electron-conducting support materials based on the total weight of the coated cloth. The carbon-PTFE loading of the outer layer, that is to say in particular of the carbon cloth, preferably ranges from 2 to 8 mg / cm ² .

EXAMPLE PART

In the following the invention will be explained in more detail by means of examples and investigations, reference being made to the attached drawings and diagrams. The examples are merely illustrative of the invention and are not intended to be limiting. The person skilled in the art will be able to find further examples on the basis of the general description given above and his specialist knowledge.

In the drawings show:

Functional principle for the reaction of gaseous hydrogen chloride with gaseous oxygen in an electrochemical reactor;

schematically illustrated structure of the electrode layer for the membrane reactor;

Maximum mass flow of water vapor in the cathode gas as a function of the temperature at a cathode gas volume flow of 750 NmL / min .;

Maximum water production rate at different current densities;

Temperature and cell voltage at set constant current densities;

Sketch of a laboratory cyclone cell for half-cell measurements in exploded view;

Flow chart for material flow and sequence of half cell experiments;

Polarization curves for HCl oxidation at different temperatures;

Polarization curves for HCl oxidation at various HCl concentrations;

Polarization curves for HCl oxidation with various unsupported and noble metal-free catalysts;

Polarization curves for HCl oxidation with carbon supported platinum catalysts;

Polarization curves for HCl oxidation and oxygen reduction with carbon-supported platinum catalysts;

Sketch for the construction of the electrochemical reactor in exploded view;

Flow chart for the electrolysis of hydrogen chloride using the in represented reactor;

Current-voltage characteristic for the hydrogen chloride electrolysis process.

and have already been described above to illustrate the principles of the invention. to refer to the water balance of the membrane. There now follows the more detailed description of the invention based on experiments and preliminary tests with various structures.

To characterize the in In this process, two series of experiments were carried out in two different experimental setups. In the first series of experiments half-cell experiments were carried out, while in the second series experiments were carried out in a complete electrochemical reactor. The first series of experiments provides, among other things, kinetic data and insights into the effect of the catalyst. The second series of experiments demonstrates the technical feasibility of the new process and the performance achievable with the cell.

Half-cell experiments

For half-cell experiments, the in illustrated cyclone cell 100 used. Such a cell has already been described in the literature ( J. Appl. Electrochem. 29 (1999) 919-926 ). The cell had an active surface of 2 cm ² . In the cell 100 was a polymeric electrolyte membrane 40 , which was equipped on one side with noble metal catalyst (supported or unsupported) or with a metal-free catalyst. On it is a gas diffusion layer 50 , The gas diffusion layer 50 consisted of PTFE-treated carbon fiber fabric, wherein the wettability was adjusted by the additional layer of carbon / PTFE. An electron-conducting carrier 80 made of titanium, carbon-polymer composite or stainless steel was in electrical contact with the gas diffusion layer 50 , In the workspace of the half cell 10 made of polymethylmethacrylate or polycarbonate, e.g. As Makrolon ^{® was} manufactured, gases (oxygen, HCl) can be initiated. In the counter electrode space 20 also made of polymethyl methacrylate or polycarbonate, became a counter electrode 90 used in platinum. The reference electrode space 30 was electrolytically through a capillary with the counter electrode space 20 connected. The capillary was 2 mm from the non-conductive support 70 removed, which of PTFE or polycarbonate, z. B. Makrolon ^® was prepared. There were seals 60 , which were stable to the materials used up to 70 ° C and the pressures used, used between the individual components. For this purpose only (per) fluorinated polymers such as Teflon ^®, ETFE or Viton ^® are. For temperature control, PTFE-coated temperature sensors were connected to the input 110 and exit 120 the counter electrode space and at the entrance 130 and exit 140 of the working electrode space 10 used.

For the following examples, the experimental device was after used. The pilot plant 200 consisted of several mass flow controllers 201 with which the gas flow through the reactor could be adjusted. The liquid electrolyte in the counter electrode space 20 the cyclone cell 206 was perchloric acid (HClO ₄ ), which by means of a peristaltic pump 202 was promoted. The liquid electrolyte was placed in a jacketed vessel 203 by a thermostat 208 was heated, heated. The cyclone cell was heated to the desired temperature to heat the reactant gases 206 in a convection oven 207 with integrated temperature controller 205 built-in. Temperatures of up to 200 ° C can be reached. The temperatures in the entrance and exit of the cyclone cell 206 were through thermocouples 204 measured. The were used in the shown cyclone cell 100 ,

EXAMPLES

In the following examples, results are shown demonstrating improvements in hydrogen chloride oxidation.

Example 1:

The membrane-electrode assembly used consisted of a pretreated ^Nafion® 117 polymer electrolyte membrane, the catalyst layers and the gas diffusion coating. The gas diffusion layer consisted of a carbon fiber fabric coated with 20% by weight of PTFE. This was then provided with a microporous PTFE carbon layer. The loading of this coating was 4.5 mg / cm ² . Subsequently, the gas diffusion layer was pressed and sintered. The catalyst layer consisted of carbon-supported platinum and Nafion ^®. The catalyst charge consisted of a mixture of 0.5 mg / cm ² Pt / C and 2.0 mg / cm ² Nafion ^®. After applying the catalyst layer to the membrane, it was hot-pressed. The coating was applied as a suspension in a wet spray process, as is well known to those skilled in the art. A volume flow of 500 NmL / min of gaseous HCl was conveyed through the workspace of the cyclone cell, while perchloric acid was delivered at 300 NmL / min through the cyclone cell's counter electrode space. The initial temperature was 25 ° C and polarization curves were measured potentiostatically in the voltage range of 0.8 V to 1.05 V against an Ag / AgCl reference electrode with saturated KCl. The temperature was 25 ° C, 40 ° C, 50 ° C and 60 ° C. The results are in to see. It can be seen that even at temperatures of 40 ° C technically interesting current densities can be observed, as they are reported in earlier work only at 70 ° C. At 60 ° C they are already clearly exceeded.

Example 2:

A membrane-electrode assembly as in Example 1 was used. A flow of gaseous HCl at a flow rate of 500 NmL / min was fed to the cyclone cell. Perchloric acid was supplied at a flow rate of 300 NmL / min. The temperature was set at 60 ° C and polarization curves were measured potentiostatically in a voltage range of 0.8V to 1.05V against an Ag / AgCl reference electrode with saturated KCl. The volumetric HCl concentration was adjusted to values of 100%, 80%, 60%, 40% and 20%. This was achieved by admixing nitrogen. The results are in shown. It can be seen that technically significant current densities of 4 kA / m ^{2 can be achieved} up to 8 kA / cm ² and that at input concentrations of 40 vol .-% to 100 vol .-% HCl at the temperatures mentioned.

Example 3:

A membrane electrode assembly (MEA) as in Example 1 was used. The catalytic coating consisted of a noble metal, e.g. As platinum, unsupported or supported on carbon, Nafion ^® and carbon with Nafion ^® . For the unsupported platinum-MEA a loading of 5.0 mg / cm ² Pt and 1.0 mg / cm ² Nafion ^® was chosen. For the unsupported carbon MEA a loading of 0.8 mg / ^cm2 carbon and 0.7 mg / cm ² Nafion ^® was used. For the carbon-supported MEA, a platinum loading of 0.5 mg / cm ^{2 was} used. The Nafion ^® -load ² was changed to 0.5, 1.0 and 2.0 mg / cm. The catalyst coated membranes were hot pressed. A gas flow rate of 500 NmL / min was fed to the cyclone cell while the perchloric acid was metered in at a flow of 300 NmL / min. The temperature was set at 60 ° C and polarization curves were measured potentiostatically in a voltage range of 0.8V to 1.05V against an Ag / AgCl reference electrode with saturated KCl. The HCl concentration was 100%. The results for the unsupported catalysts are in shown. The results of the supported catalysts can be found in , It can be seen that even with unsupported catalysts such current densities can be achieved as with supported catalysts. However, the precious metal load was up to 10 times higher.

Example 4:

Both MEA used correspond to those in Example 1. The catalyst layer consisted of a precious metal, here platinum supported on carbon and Nafion ^®. For the Pt / C supported MEA for the oxygen reduction, the loading was 0.5 mg / cm ² Pt at a Nafion ^® -load of 0.5 mg / cm ^2. The MEA for the oxidation of hydrogen chloride had a loading of 0.5 mg / cm ² Pt and Nafion ^® -load of 2.0 mg / cm ^2. Gaseous HCl was fed into the cyclone cell at a flow rate of 500 NmL / min and perchloric acid was delivered at 300 NmL / min. The temperature was adjusted to 60 ° C. Polarization curves were measured potentiostatically against an Ag / AgCl reference electrode with saturated KCl. The concentration of the gases HCl and O ₂ was 100%. How to get in can see, the potential difference of the two half-cell reactions at a current density of 4 kA / m ^{2 is} about 0.9 V and at a current density of 3 kA / m ² only 0.75 V.

The resistance of the membrane depends on the degree of humidification. Nafion ^® can be moistened with liquid water (in the case of a half-cell supplied with liquid acid) or with water vapor (in the case of a gas-supplied reactor). The estimated power loss for a Nafion ^® 117 membrane at current densities of 3 to 4 kA / m ² are shown in Table 1 below. The potential difference between the electrodes plus the voltage losses in the water-equilibrated membrane provide a total reactor voltage of 0.92 V at 4 kA / m ² and approximately 0.79 V at 3 kA / m ² each at a temperature of 60 ° C. This clearly shows that hydrogen chloride electrolysis can be operated at voltages below 1V. Table 1 current density 3 kA / m ² 4 kA / m ² temperature Liquid water Steam Liquid water Steam 50 ° C 0.052 V 0.071V 0.069V 0.095V 60 ° C 0.042V 0.058V 0.056V 0.078 v 70 ° C 0.034V 0.048V 0.046V 0.063V

Measurements in a complete electrochemical reactor

For the following investigations the in illustrated electrochemical reactor 300 used. The reactor 300 had an active area of 30 cm ² and contained a catalyst-coated membrane 301 , The catalyst was used supported or unsupported used. The electrodes were in contact with gas diffusion layers 302 made of carbon fiber cloth coated with PTFE and carbon. For uniform distribution of the gas flows, a flow distributor field was used. This flow distributor field 303 was manufactured from an electron-conducting and corrosion-resistant material such as graphite, carbon-polymer composite material, metals or metal alloys. As chemically stable seals 305 with respect to the handled materials in the reactor PTFE, ETFE or Viton ^® were used. All components were made by end plates 304 fixed.

In the following examples, some results are shown, which were achieved with this reactor in the hydrogen chloride electrolysis.

In the following, the in illustrated experimental plant 400 used. It consists of several mass flow controllers 401 to adjust the volume flows of the gases. To heat the gas streams was heated hoses 402 and for the reactor 403 used electric heating cartridges. The maximum adjustable temperature is 200 ° C. For temperature control, the reactor temperature is measured with the temperature sensor 404 measured. Pressure sensors are used to record the pressures 405 used at cathode and anode output. The humidification of the cathode gas was carried out with a gas washing bottle 406 ,

Example 5:

An MEA was used as in Example 1. The catalyst loading for the anode and the cathode was a mixture of respectively 1.0 mg / cm ² Pt and 0.5 mg / cm ² Nafion ^®. After application of the catalyst layer, hot pressing was carried out. The layers were applied by a wet spraying process. Gaseous hydrogen chloride and also gaseous oxygen were metered into the reactor, each with a volume flow of 500 NmL / min. The initial temperature was room temperature. The current density was increased in steps of 0.1 kA / m ² per 5 minutes. The results obtained are in to see. It is obvious that high current densities can be achieved with simultaneously low voltages (eg 0.95 V at 4 kA / m ² ).

Such high current densities with simultaneously low voltages (0.95 V at 4 kA / m ² , as described above) have so far not been achieved in the prior art for cells which work with two gas diffusion electrodes. A significant improvement in the effectiveness of hydrogen chloride electrolysis could be achieved.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0785294 A1 [0005]
• WO 02/068722 A2 [0005]
• EP 1366213 A2 [0005]
• US 4210501 A [0005]
• US 2006/249380 A [0005]
• DE 19755636 A1 [0005]
• US 5580437 A [0007]
• US 5411641 A [0007]

Cited non-patent literature

• Journal Electrochem. Soc. Vol. 142, no. 11, November 1995, pages 3619 to 3625 [0006]
• J. Appl. Electrochem. 29 (1999) 919-926 [0055]

Claims (14)

Process for the production of chlorine from hydrogen chloride gas in an electrochemical membrane reactor ( 5 . 300 . 403 ) with an electrode unit ( 6 ) containing a catalyst-coated membrane ( 3 . 21 . 301 ) and gas diffusion layers ( 26 . 302 ) and separates two half cells, wherein in the first half cell to the electrode unit hydrogen chloride gas is supplied from a first membrane side and converted by means of electrical energy into chlorine gas and wherein the resulting protons diffuse through the membrane into the second half cell and react there with oxygen to water , characterized in that the cathode gas, which consists of oxygen or an oxygen-containing gas, is moistened and in the humidified state to the membrane ( 3 . 21 . 302 ), wherein the temperature of the membrane in the electrode unit ( 6 ) and optionally additionally the temperature of the supplied cathode gas is adjusted as a function of the current density. A method according to claim 1, characterized in that the degree of humidification of the cathode gas at 20 to 100%, preferably 70 to 100% water vapor saturation and that the humidification is controlled accordingly. A method according to claim 1 or 2, characterized in that all the membrane reactor ( 5 . 300 . 403 ), in particular O ₂ , HCl and H ₂ O, are supplied in gaseous form. Method according to one of claims 1 to 3, characterized in that the working temperature is 20 ° C to 80 ° C. Method according to one of claims 1 to 4, characterized in that the working pressure is set within the half-cells to 1 to 5 bar. Method according to one of claims 1 to 5, characterized in that the method at current densities up to 10 kA / m ² , preferably from 4 to 6 kA / m ² , at cell voltages below 2 volts is performed. Method according to one of claims 1 to 6, characterized in that cathode and anode gas with volumetric flows of 0.2 and preferably up to 25 Nm ³ / h · m ^{2 are passed} through the membrane reactor. Electrode unit ( 6 ) for a membrane reactor ( 5 . 300 . 403 ) for carrying out the method according to one of claims 1 to 7, characterized by a membrane ( 3 . 21 . 302 ) of a proton-conducting polymer material, supported or unsupported catalytically active coatings ( 22 ) on both sides of the membrane and gas diffusion layers ( 26 ), the catalytically active layers ( 22 ) facing microporous layers ( 23 ). Electrode unit ( 6 ) according to claim 8, characterized in that the layers: membrane ( 21 ), catalytically active coating ( 22 ), microporous layer ( 23 ) of the gas diffusion layer ( 26 ) and supplementary layer (s) ( 24 . 25 ) of the gas diffusion layer ( 26 ) are arranged without gaps on each other. Electrode unit ( 6 ) according to claim 8 or 9, characterized in that the microporous layer ( 23 ) of the gas diffusion layer ( 26 ) consists of carbon or contains at least 50 wt .-% carbon and optionally additional constituents for adjusting the wettability, in particular PTFE. Electrode unit ( 6 ) according to one of claims 8 to 10, characterized in that at least one of the gas diffusion layers ( 26 ) a carbon fabric ( 25 ), which is used to form the further layers ( 23 . 24 ) including the porous layer ( 23 ) is coated with PTFE, carbon and / or other electron-conductive substrates, wherein the carbon / PTFE / substrate loading is 2 to 8 mg / cm ² . Electrode unit ( 6 ) according to one of claims 8 to 11, characterized in that the catalytically active coatings ( 22 ) supported and unsupported precious metals and metal compounds, metal-free catalysts or mixtures thereof, preferably with loadings of 0.1 to 5.0 mg / cm ² . Electrode unit ( 6 ) according to one of claims 8 to 12, characterized in that at least one of the catalytically active coatings ( 22 ) contains a polymeric proton-conducting compound in an amount of 0.2 to 5.0 mg / cm ² . Membrane reactor ( 5 . 300 . 403 ) for carrying out the method according to one of claims 1 to 7, comprising an electrode unit ( 6 ) according to any one of claims 8 to 13.

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