WO2013178803A1

WO2013178803A1 - Process and apparatus for the electrolytic synthesis of methanol and/or methane

Info

Publication number: WO2013178803A1
Application number: PCT/EP2013/061303
Authority: WO
Inventors: Oliver Schael; Guido Burmeister
Original assignee: Hettich Holding Gmbh & Co. Ohg
Priority date: 2012-05-31
Filing date: 2013-05-31
Publication date: 2013-12-05
Also published as: DE102013105605A1

Abstract

The invention relates to a process for the electrolytic synthesis of methanol by reduction of carbon dioxide present in an electrolyte in the liquid phase, at the critical point or in the supercritical phase of the electrolyte. The process is characterized in that protons for the reduction of the carbon dioxide are introduced into the electrolyte via a proton-conducting membrane (2). The invention further relates to an apparatus suitable for carrying out the process.

Description

Process and apparatus for the electrolytic synthesis of methanol and / or methane

The invention relates to a method and a device for the electrolytic synthesis of methanol and / or methane by reduction of carbon dioxide contained in an electrolyte in the liquid phase, at the critical point or in the supercritical phase of the electrolyte.

By means of photovoltaic generators, it is now possible to convert sunlight into electricity with high efficiency and, after a relatively short service life, amortizing financial and energy investment. In addition, production capacities for photovoltaic generators have been installed worldwide, enabling the realization of even very large photovoltaic systems. Even with the help of wind turbines is now an implementation of

Wind power into electricity with high efficiency and with a relatively short operating time amortizing financial and energy investment income possible. In addition, worldwide production capacities for wind power converters are now installed, which enable realization of very large wind farms, for example as offshore wind farms.

The importance of the use of hydropower, for example in wave power plants for power generation is gaining in importance. The problem with the use of renewable energy sources is that it mainly takes place decentrally in often poorly developed regions. In order to enable a transport of the energy obtained, the conversion into methanol and / or methane is proposed. For a realization of large projects, especially in sunny or windy but possibly infrastructure poor regions, there is still a need for efficient and cost-effective storage of electricity generated and for a low-loss transport of energy to a remote place of use. Because of their high specific energy content and their relatively easy handling, hydrocarbons are fundamentally ideal fuels. Because of the possibility of methanol either in internal combustion engines or in fuel cells, for example in fuel cells of the SOFC (Solid Oxide Fuel Cell) type or directly in fuel cells of the type

Implementing DMFC (Direct Methanol Fuel Cell) is a particularly favored source of energy for the hydrocarbons methanol. Methane is the main constituent of natural gas and is an important fuel gas. Both products, methanol and methane, are also important raw materials for the chemical industry. From methanol, for example, various chemical products such as plastics, drugs or fuels can be produced.

In an inverse reaction to the running in the DMFC oxidation reaction methanol can also be obtained in principle by reduction electrolytically from water and carbon dioxide (CO ₂ ). If the carbon dioxide is used in aqueous solution, however, only low currents can be achieved in the electrolysis, making it difficult or impossible to use the electrolysis process on a large scale.

From the publication DE 41 26 349 A1, in order to achieve a higher current density for the synthesis of methanol, it is known to carry out an electrolysis of an essentially only CO ₂ electrolyte, this electrolyte being kept in a pressure and temperature range which, in the rich in the critical point of CO ₂ . The electrolysis is thus carried out in a parameter range in which CO ₂ is substantially liquid or in a supercritical phase with a density comparable to the liquid. The high concentration of CO _{2 achieved in this way} makes industrially usable current strengths possible. The electrolyte is accompanied by a conductive substance and a hydrogen-containing substance, for example hydrogen chloride or hydrogen sulfide, in order to provide protons for the reduction of the carbon dioxide on the one hand and to make the electrolyte electrically conductive on the other hand. Methanol formed in the electrolyte and optionally further hydrocarbons are separated in a separator. This separation is complicated, since the methanol formed must be purified, inter alia, by dissociation products of the hydrogen-containing substance used, for example, chlorine-containing or sulfur-containing compounds formed. It is therefore an object of the present invention to provide a method of the type mentioned above or a corresponding device of the aforementioned type, can be synthesized by the methanol and methane electrolytically from carbon dioxide, without an expensive methanol separation and purification is necessary ,

This object is achieved by a device or a method with the respective features of the independent claims.

The inventive method for the electrolytic synthesis of methanol and / or methane by reduction of carbon dioxide contained in an electrolyte in the liquid phase, at the critical point or in the supercritical phase of the electrolyte is characterized in that protons for reducing the carbon dioxide by a proton-conducting membrane be introduced into the electrolyte.

By supplying the protons (H ⁺ ) via the proton-conducting membrane, the reaction for the synthesis of methanol (H ₃ COH) is split into two partial reactions. The corresponding partial reactions then proceed at an anode in an anode compartment and at a cathode in a cathode compartment and are represented as follows:

Partial reaction at the anode (anode reaction):

2 H ₂ 0 -> 4 H ⁺ + 4 e ^" + 0 ₂ , and partial reaction at the cathode (cathode reaction):

6 H ⁺ + 6 e ^" + C0 ₂ H ₃ COH + H ₂ 0. The overall result is the following overall reaction:

3 H ₂ + C0 ₂ H ₃ COH + H ₂ 0.

Methane (CH ₄ ) can also be formed as a competing reaction according to the overall reaction: 4H ₂ + C0 ₂ ^ CH ₄ + 2H ₂ 0.

The division into the partial reactions and the associated spatial separation of the partial reactions prevents mixing of the products and educts of the partial reactions at the individual electrodes, ie at the anode and at the cathode. Accordingly, the synthesized methanol can be recovered directly at the cathode without mixing the methanol with the preferably aqueous electrolyte in the anode compartment, e.g. dilute sulfuric or hydrochloric acid. Accordingly, complicated steps for separation of the methanol from the electrolyte in the anode compartment or purification of the methanol can be dispensed with.

In an advantageous embodiment of the method, this is carried out in a reactor vessel, which is subdivided by the proton-conducting membrane into an anode space and a cathode space, wherein a pressure equalization is performed to compensate for differences in pressure of the electrolyte in the anode space and in the cathode space. The pressure compensation is preferably carried out automatically by a connection of the anode compartment and the cathode compartment, this connection being arranged spatially in a region of the anode compartment and the cathode compartment, in which the electrolyte is present in gaseous form. In this way, the proton-conducting membrane is protected from pressure differences that might otherwise occur in view of the relatively high operating pressures in the liquid phase, at the critical point, or in the supercritical phase of the electrolyte.

In a further advantageous embodiment of the method, the carbon dioxide-containing electrolyte is almost pure carbon dioxide. This carbon dioxide-containing electrolyte is the electrolyte in the cathode compartment. When this is nearly pure carbon dioxide, on the one hand, the concentration of carbon dioxide is maximal, which maximizes the reaction rate. On the other hand, methanol is not soluble as a reaction product at the cathode in such an electrolyte and precipitates accordingly. Thus, a complex separation of the methanol and the electrolyte in the cathode space is not required. In the context of the application, almost pure carbon dioxide is to be understood as meaning a carbon dioxide concentration of more than 95% and preferably of more than 99%. In addition to the carbon dioxide, for example, additives may be provided in the electrolyte, which serve to increase the electrical conductivity, in particular paratoluene sulfonic acid. Paratoluene sulphonic acid has The advantage, for example, of adding quaternary ammonium salts as conductivity additive is that acids release protons as conductive positive ions, which not only promotes the electrical conductivity in general, but also specifically with regard to the ions which are directly involved in the chemical reaction.

In a further advantageous embodiment of the method can be present as the electrolyte liquid carbon using ionic or anionic surfactants and optionally suitable emulsifiers in the form of an emulsion. The preparation of an emulsion of the product water and the educt carbon dioxide has the advantage that the current density at the cathode can be increased.

In a further advantageous embodiment of the method, this is carried out continuously by passing at least the carbon dioxide-containing electrolyte past the proton-conducting membrane. A continuous implementation is industrially particularly useful. However, as an alternative to continuous process control, discontinuous process management (batch operation) is also possible.

A device according to the invention for carrying out the aforementioned method has a pressure-resistant reactor vessel for receiving a carbon dioxide-containing electrolyte in the liquid phase, at the critical point or in the supercritical phase of the electrolyte. The device is characterized in that the reactor vessel of a proton-conducting

Membrane is divided into an anode compartment with an anode for receiving an aqueous electrolyte and a cathode compartment with a cathode for receiving the carbon dioxide-containing electrolyte. This results in the advantages mentioned in connection with the method.

In an advantageous embodiment of the device, the anode contains platinum (Pt) and / or ruthenium (Ru) or stainless steel. The cathode preferably contains magnesium (Mg), copper (Cu), zinc (Zn), aluminum (Al), nickel (Ni), iron (Fe), titanium dioxide (TiO ₂ ) or ruthenium (Ru). Combinations of the mentioned materials are also possible. The materials mentioned are particularly suitable electrode materials with regard to their overvoltage potential. In a further advantageous embodiment of the device, the anode and the cathode are each applied in layers on one side of the membrane, so that a membrane electrode assembly (MEA) is formed. Preferably, the MEA is defined between contact plates with incorporated flow channels for the electrolytes. In this way, a particularly compact construction of the device can be achieved. In addition, the largest possible and lossless power supply to the electrodes via the contact plates is given.

In a further advantageous embodiment of the device, a pressure equalization arrangement is provided to compensate for differences in pressure of the electrolyte in the anode compartment and in the cathode compartment. In this way, the proton-conducting membrane is protected from pressure differences which otherwise could occur in view of the relatively high operating pressures in the liquid phase, at the critical point or in the supercritical phase of the electrolyte.

Preferably, the pressure compensation arrangement is formed by a connection of in the anode compartment and cathode compartment, said connection being spatially arranged in a region of the anode compartment and the cathode compartment, in which the electrolyte is present in gaseous form. In this way, a pressure equalization can be done easily and without complex control technology. By way of example, the connection comprises a pressure compensation line and / or a pressure compensation container which has an inner membrane which allows pressure equalization without material passage. Alternatively, an equal pressure in the anode space and in the cathode space can also be achieved by a corresponding control of inlet and outlet valves which are arranged on the rooms.

Further advantageous embodiments and further developments are given in the respective dependent claims.

The invention is illustrated in more detail below with reference to three figures. The figures show:

Fig. 1 shows a first embodiment of a device for electrolytic

Synthesis of methanol,

Fig. 2 shows a second embodiment of an apparatus for the electrolytic synthesis of methanol and Fig. 3 is a phase diagram of carbon dioxide.

1 shows a schematic overview of a first embodiment of a device for methanol synthesis according to the method of the invention.

The apparatus comprises a pressure-resistant reactor vessel 1, which is subdivided by a proton-conducting membrane 2 into two reaction chambers, an anode chamber 3 and a cathode chamber 4. The anode chamber 3 and the cathode chamber 4 receive an anode- or cathode-side electrolyte during operation of the device , The reactor vessel 1 is made of a stable, in particular friction-resistant material, which is chemically inert to the reaction educts and products used, for example of a stainless steel or of inertly coated materials.

The proton-conducting membrane 2 is advantageously a polymer membrane, such as that marketed by the company DuPont under the trade name "Nation." In operation, both the anode and cathode chambers 3, 4 are pressurized 2 through

To prevent pressure differences between the two chambers 3.4, these are connected to each other via a pressure equalization line 5. The pressure equalization line 5 is preferably arranged in an upper region of the reactor vessel 1 in order to prevent thorough mixing of the electrolytes in the two chambers 3, 4. In order to prevent destruction of the reactor vessel 1 and a risk of such destruction, overpressure valves 6, 7 are provided here in the area of the pressure equalization line 5 and in each case separately at the spaces 3, 4. In the illustrated embodiment, the device for a discontinuous implementation of the method is set up (batch mode). The reaction chambers 3, 4 of the reactor vessel 1 are first filled with the respective electrolyte and then the electrolysis process started. For filling the reaction chambers 3, 4 vent valves 8 are attached to each of the spaces 3.4 in the upper region of the reactor vessel. When the vent valve 8 is open, the anode chamber 3 is first filled with an aqueous electrolyte. For this purpose, a reservoir 34 for the aqueous electrolyte is provided which communicates with the anode chamber 3 via an inlet valve 35. is bound. Subsequently, both vent valves 8 are closed. Carbon dioxide is then introduced from a reservoir 44 as a cathode-side electrolyte via an inlet valve 45 into the cathode chamber 4. As a reservoir 44, for example, a carbon dioxide cylinder with liquefied CO _{2 is} used which has a carbon dioxide lifter. Carbon dioxide can thus be released in its liquid phase. By opening the inlet valve 45, the cathode space 4 is filled with CO ₂ , wherein a pressure equalization takes place via the pressure equalization line 5 to the anode chamber 3.

In both reaction chambers 3, 4, a tempering device 36 and 46 is provided to set a desired temperature for the electrolyte 3, 4. At the end of the filling process, there is an aqueous electrolyte in a liquid phase in the anode compartment 3 and carbon dioxide in the cathode compartment 4 in a likewise liquid, critical or supercritical phase. For the subsequent electrolysis process, the inlet valve 45 is closed.

In the anode chamber 3, an electrode 31, hereinafter also referred to as the anode 31, and in the cathode chamber 4, an electrode 41, hereinafter also referred to as the cathode 41, respectively. Via terminals 32 and 42, the electrodes can be acted upon externally with a voltage. By applying such a voltage, a current flow between the electrodes 31 and 41 and thus the electrolysis process begins. In the two reaction chambers 3 and 4, the flow of electrons within the electrolytes takes place via ionic conduction, whereby only protons, ie positively charged hydrogen ions, pass over from the anode space 3 into the cathode space 4 due to the proton-conducting membrane 2.

At the anode 31, the following anode reaction starts:

2 H ₂ O -> 4ΗΓ + 4 e ^" + O ₂ , and at the cathode 41 the following cathode reaction:

6 KT + 6 e ^" + CO ₂ H ₃ COH + H ₂ O. In summary, a decomposition of the water from the aqueous electrolyte with the release of oxygen gas takes place in the anode chamber 3 and a reduction of the CO ₂ to methanol and water in the cathode chamber 4. The highest possible concentration of C0 ₂ as starting material in the cathode space 4 is obtained when C0 _{2 is} liquid. According to the phase diagram of carbon dioxide, this may for example be temperature-dependent in a pressure range of about 62 bar at 24 degrees Celsius to 72 bar at 30 degrees Celsius. The desired temperature is ensured in the cathode chamber 4 by the tempering 46. The tempering device 46 is preferably designed as a combined heating and cooling device, for example by using a Peltier element. Carbon dioxide has a critical point in its phase diagram at a temperature of 31, 5 degrees Celsius (° C) and a pressure of 74 bar (see also Fig. 3). At this point, liquid CO ₂ becomes a supercritical phase, in which the medium exhibits both gas and liquid properties, fluid properties. Even in the supercritical phase, the carbon dioxide concentration in the cathode chamber 4 is high, so that operation of the device can also take place in this pressure / temperature range.

To increase the conductivity of the liquid carbon dioxide, a conductivity additive can be added thereto, for example quaternary ammonium salts, but in particular paratoluene sulfonic acid. Paratoluenesulfonic acid has proved to be more suitable as a conductivity additive than quaternary ammonium salts. Paratoluene sulfonic acid has the advantage over quaternary ammonium salts that acids release protons as conductive positive ions, favoring not only the electrical conductivity in general, but also specifically with respect to the ions directly involved in the chemical reaction. When these first protons released by the acid are consumed at the cathode, they are replaced by the electrical termination of the proton-conducting membrane via the acid to the cathode.

When using ionic or anionic surfactants and, if appropriate, suitable emulsifiers, the liquid carbon may also be in the form of an emulsion. The preparation of an emulsion of the product water and the educt carbon dioxide offers the advantage that the current density at the cathode can be increased, since in a smaller space a high conductivity of the aqueous is present in the immediate vicinity of the carbon dioxide as a reaction partner. An increase in the current density generally results in an increase in the yield

As the material for the cathode 41, for example magnesium can be used, which has a low overvoltage potential and thus a high efficiency for the specified reaction. Alternative and usable in combination cathode materials are Cu, Zn, Al, Fe, Ni, TiO ₂ or Ru. In order to provide a high surface area for the cathode reaction at the electrode 41, the cathode material may be used in the form of a granule or colloid. In this case, a carrier material may be provided, to which the (active) electron material is applied. Alternatively, it is also possible for the electrode material in the form of a colloid or granulate to be formed into a carrierless electrode 41 in a sintering process.

15

As (active) electrode material of the anode 31, for example, platinum (Pt), in turn, can be used in colloidal form with the highest possible surface area. Other known materials for this reaction, for example, a platinum-ruthenium (Ru) mixture can be used. Also stainless steel can 0 as a suitable and inexpensive electrode material for the anode

31 are used.

Since both water and methanol are poorly soluble in liquid CO ₂ as reaction products in the cathode compartment 4, the reaction products precipitate and collect at the bottom of the cathode compartment 4 of the reaction container 1. In turn, methanol and water are very well soluble in each other, thus forming a highly concentrated methanol-water mixture according to the reaction stoichiometry with respect to the methanol concentration. This methanol-water mixture can after sufficient operating time of the device

30 opening an outlet valve 52 are discharged from the cathode chamber 4 in a reservoir 53. The methanol-water mixture can advantageously be used after storage and / or transport in just this mixture as the fuel of a DMFC fuel cell, and thus be used for power generation.

35

On the anode side, oxygen gas is formed in the anode chamber 3 at the anode 31. This oxygen gas can already be removed during operation of the device by suitable actuation of the venting valve 8 of the anode compartment 3. are left so as not to increase the pressure in the reactor vessel 1 undesirably. Due to power losses during operation of the device heat is generated at the electrodes, which is absorbed by the respective electrolyte. In order to keep the temperature in the desired range, a tempering device 36 is also provided on the anode side.

Fig. 2 shows another apparatus for carrying out a method for the electrolytic analysis of methanol. Identical reference signs in this figure denote the same or equivalent elements as in the first embodiment of FIG. 1. In contrast to this, the device shown here is not suitable for batch operation but for a continuous implementation of the method.

Again, a reactor vessel 1 is provided which is subdivided by a proton-conducting membrane 2 into two reaction spaces, an anode space 3 and a cathode space 4. In the anode compartment 3, an anode 31 and in the cathode compartment 4, a cathode 41 is arranged as an electrode, wherein each one Anodenbzw. Cathode terminal 32 and 42 are guided for contacting the electrodes 31, 41 to the outside.

In the exemplary embodiment illustrated here, the electrodes 31, 41 with the membrane 2 are combined to form a so-called MEA (Membrane Electrode Assembly). For this purpose, the corresponding electrode material in colloidal form, if appropriate with a carrier substance, for example graphite in likewise colloidal form, is applied to one side of the membrane 2 in each case. This may be done, for example, after slurry in a preferably volatile liquid in a spray or screen printing process. As a result, formed on the respective side of the membrane 2 is a porous, electrically conductive layer of the carrier material with embedded electrode material, which provides a large surface area of the electrochemically active electrode material. Since a current discharge in the lateral direction of the layer leads to high ohmic losses due to the relatively high resistance of the layer in the layer direction, current can also be conducted in a direction perpendicular to the membrane 2, for example by a metal grid placed parallel to the layer. With regard to the preferably catalytically active materials of the electrodes 31 and 41, reference is made to the statements in connection with the first exemplary embodiment. In order to achieve a continuous operation of the device, intermediate containers 37, 47 are provided for the anode or cathode-side electrolyte. Via pumps 39 on the anode side and 49 on the cathode side, an electrolyte flow through the anode or cathode chamber 3, 4 is called forth. On the anode side, this electrolyte flow is in the direction of the reactor vessel 1 by the reference numeral 33 and back to the intermediate vessel 37 by the reference numeral 33 ', on the cathode side is the corresponding electrolyte flow in the cathode compartment with the reference numeral 43 and back from the cathode compartment 4 with the reference numeral 43rd 'marked. In the embodiment of FIG. 2, pumps 39 and 49 are provided both for the flow 33, 43 to the reactor vessel and for the return flow 33 ', 43'. In alternative embodiments, it is conceivable to use only one pump 39, 49 in each of the electrolyte circuits. In the intermediate containers 37, 47, the electrolytes are preferably kept under the same pressure and temperature conditions as used in the reactor vessel 1. Therefore, temperature control devices 36 and 46 are arranged in the intermediate containers 37, 47. In addition, temperature control devices (not shown) for the reactor vessel 1 may be present in this figure. With regard to the electrolytes used, reference is made to the statements on the first exemplary embodiment. During operation of the electrolysis device resulting reaction products, in particular the resulting at the cathode side methanol-water mixture is removed via further pump 49 from the cathode chamber 4 and from the intermediate container 47, which is again utilized that the methanol / water mixture has a low solubility in which liquid carbon dioxide has, which is optionally used with conductive additives, as a cathode side electrolyte. The methanol-water mixture precipitates accordingly and settles in the lower region of the cathode space 3 or of the cathode-side reservoir 47. It is collected in a reservoir 53 for further use.

The oxygen gas accumulating on the anode side in the anode chamber 3 and in the anode-side intermediate container 37 is conducted correspondingly via anode-side pumps 39 into an oxygen reservoir 62. It is noted that depending on the pressure under which the reservoirs 53 and 62 for the reaction products compared to the pressure under which the electrolytes in the reactor vessel 1 and the intermediate containers 37, 47 are, instead of pumps 39, 49 and controlled valves for Draining the reaction products used can be. In order to compensate for the decreasing amounts of electrolyte in the intermediate tanks 37 and 47 during operation, they are connected to storage tanks 34 and 44 for the electrolytes and corresponding pumps 39, 49 or valves - again depending on the pressure conditions.

With the anode chamber 3 and the cathode chamber 4 pressure sensors 38 and 48 are connected, which detect the present in the respective reaction chambers 3, 4 of the reactor vessel 1 pressures during operation. The measured pressures are detected in a process control device, not shown, and used to control the pumps 39 and 49 or the valves used instead. The control takes place in such a way that in the anode chamber 3 and the cathode chamber 4 as much as possible the same operating pressure is present. The pressure set during operation depends in turn on the phase diagram of the electrolyte used on the cathode side, such that operation with liquid C0 ₂ or C0 ₂ in a supercritical phase or C0 ₂ at the critical point is achieved. In order to prevent pressure differences in the anode chamber 3 and the cathode chamber 4, which may occur due to control inaccuracies, for example, damage the membrane 2, pressure equalization lines 5 lead from the reaction chambers 3, 4 of the reactor vessel 1 to a pressure equalization tank 9. The pressure equalization tank 9 has an inner membrane that allows pressure equalization without material passage in a certain pressure range.

In the illustrated embodiment of FIG. 2, the anode compartment 3 and the cathode compartment 4 are shown as open spaces in which the corresponding electrolytes can move freely. In an advantageous embodiment of the device, provision may be made for the electrolytes to be forced along the electrodes 31, 41 along flow channels of so-called flow fields (flow fields). Different configurations of the flow fields, for example meandering or harp-shaped, are possible. Relative to one another, rectified or counter-directed or crosswise directed currents can be provided on the anode and cathode sides. In such an embodiment, a metal plate, in which the flow channels of the flow field are incorporated, serve as a current collector for the electrodes 31, 41. The reactor vessel 1 is in this case formed by two such metallic contact plates with an interposed membrane or membrane-electrode unit (MEA), wherein the two metal plates serve as anode and cathode connections 32, 42 and are electrically insulated from one another by the interposed membrane 2 - are lier. In a development of the device, a plurality of such arrangements (cells) can be stacked on top of one another, wherein the contact plates in the interior of the stack are then provided with flow channels on both sides and two adjacent cells are simultaneously assigned as so-called bipolar plates.

In both illustrated embodiments can be provided to supply the electrolysis current continuously. However, a pulsed power supply may be used in which the current between two values, one smaller than the other, may be zero or even negative (reversed). The pulsed power supply may on average be associated with more effective implementation and higher efficiency. A brief operation of the arrangement with a reversed power supply is used for catalyst purification and / or regeneration. In addition, the build-up barrier can be broken. Also, a higher efficiency is achieved. The operation with reversed power supply can be done regularly or as needed. In the latter case, it may be provided to carry out a cleaning step by reversing polarity when, during operation, the values of electrolysis current and voltage indicate sinking effectiveness, for example when an increasing voltage is required to achieve a specific, predetermined current flow. For the detection of the rising voltage limit values of the voltage itself or its rate of change (time derivative) can be defined. FIG. 3 shows a phase diagram for carbon dioxide. Here is the

Pressure in bar above the temperature in ° C applied. A phase boundary in the form of a solid gas 71 marks the transition from the solid to the gaseous state of aggregation up to a triple point 72. With further increasing pressures and temperatures, a phase boundary solid-liquid 73 characterizes the transition from the solid to the liquid state of matter and a phase boundary liquid-gaseous 74 Transition from the liquid to the gaseous state. At a so-called critical point 75, the phase boundary liquid-gaseous 74 passes into a phase boundary supercritical-gaseous 76, which indicates the transition from the supercritical to the gaseous state of matter. Of the phase boundaries 73, 74 and 76, a reaction region 77 is limited. In this reaction region 77 is the electrolyte carbon dioxide in the range according to the invention to convert it to methanol. As already mentioned, the method according to the invention and the device according to the invention can be used for the production of methanol and / or methane as energy sources and / or crude products of the chemical industry, for example by producing the mentioned products where a lot of regenerative energy from sun, wind or tides can be won.

LIST OF REFERENCE NUMBERS

1 reactor vessel

2 membrane

3 anode compartment

4 cathode compartment

5 pressure compensation line

6, 7 pressure relief valve

8 bleed valve

9 pressure equalization tank

31 anode

32 anode connection

33 electrolyte flow

33 'electrolyte flow

34 storage tank

35 inlet valve

36 temperature control

37 intermediate container

38 pressure sensor

39 pump

41 cathode

42 cathode connection

43 electrolyte flow

43 'electrolyte flow

44 reservoir

45 inlet valve

46 temperature control

47 intermediate container

48 pressure sensor

49 pump

51 methanol stream

52 exhaust valve

53 reservoir

Sauerstoffgasstror

reservoir Phase boundary fixed-gaseous triple point

Phase boundary solid-liquid

Phase boundary liquid-gas Critical point

Phase boundary supercritical-gaseous reaction range

Claims

claims

Process for the electrolytic synthesis of methanol and / or methane by reduction of carbon dioxide contained in an electrolyte in the liquid phase, at the critical point or in the supercritical phase of the electrolyte, characterized in that protons for reducing the carbon dioxide by a proton-conducting membrane

(2) are introduced into the electrolyte.

Process according to claim 1, carried out in a reactor vessel (1) subdivided by the proton-conducting membrane (2) into an anode space (3) and a cathode space (4), wherein a pressure equalization is made to differentiate the pressure of the electrolyte in the anode space

(3) and in the cathode compartment (4) to compensate.

A method according to claim 2, wherein the pressure equalization is carried out automatically by a connection of the anode compartment (3) and the cathode compartment (4), said connection being arranged spatially in a region of the anode compartment (3) and the cathode compartment (4) the electrolyte is in gaseous form.

Method according to one of claims 1 to 3, wherein the carbon dioxide-containing electrolyte is almost pure carbon dioxide.

The method of claim 4, wherein paratoluene sulfonic acid is added to the nearly pure carbon dioxide.

Method according to one of claims 1 to 5, wherein liquid ion is present in an emulsion using ionic or anionic surfactants and suitable emulsifiers.

Method according to one of claims 1 to 6, wherein the carbon dioxide-containing electrolyte is located on one side of the proton-conducting membrane (2) and an aqueous electrolyte on the other side of the membrane (2).

8. The method of claim 7, wherein the aqueous electrolyte is a dilute acid, in particular hydrochloric or sulfuric acid.

The method of claim 8, wherein the carbon dioxide-containing electrolyte is in contact with a cathode (41) and the aqueous electrolyte is in contact with an anode (31).

10. The method according to any one of claims 1 to 9, characterized in that the anode (31) Pt and / or Ru or stainless steel and the cathode (41) Mg, Cu, Zn, Al, Ni, Fe, Ti0 ₂ or Ru ,

1 1. Method according to one of claims 1 to 10, which is carried out continuously by at least the carbon dioxide-containing electrolyte is guided past the proton-conducting membrane (2).

12. The method according to any one of claims 1 to 1 1, characterized in that a discontinuous and continuous process control is made possible.

13. Apparatus for carrying out a method according to one of claims 1 to 12 with a pressure-resistant reactor vessel (1) for receiving a carbon dioxide-containing electrolyte in the liquid phase, at the critical point or in the supercritical phase of the electrolyte, characterized in that the reactor vessel (1) is divided by a proton-conducting membrane (2) into an anode space (3) with an anode (31) for receiving an aqueous electrolyte and a cathode space (4) with a cathode (41) for receiving the carbon dioxide-containing electrolyte.

14. The apparatus of claim 13, wherein a pressure equalization arrangement is provided to compensate for differences in pressure of the electrolyte in the anode compartment (3) and in the cathode compartment (4).

15. The apparatus of claim 14, wherein the pressure equalization arrangement is formed by a connection in the anode chamber (3) and cathode chamber (4), said compound being arranged spatially in a region of the anode chamber (3) and the cathode chamber (4) the electrolyte is present in gaseous form.

16. The apparatus of claim 15, wherein the connection comprises a pressure equalization line (5).

17. The apparatus of claim 15 or 16, wherein the compound a

Includes surge tank (9) having an inner membrane, which allows a pressure equalization without material passage.

18. Device according to one of claims 13 to 17, wherein the anode (31) contains Pt and / or Ru or stainless steel.

19. Device according to one of claims 13 to 18, wherein the cathode (41) contains Mg, Cu, Zn, Al, Ni, Fe, Ti0 ₂ or Ru.

20. Device according to one of claims 13 to 19, wherein the anode (31) and the cathode (41) in each case on one side of the membrane (2) is applied in layers, so that a membrane electrode assembly is formed.

21. Device according to claim 20, in which the membrane-electrode unit is fixed between contact plates with incorporated flow channels for the electrolyte.