METHOD AND DEVICE FOR THE PRODUCTION OF CARBON MONOXIDE

Description

[0001] The present invention relates to a method and an apparatus for the production of carbon monoxide, see claims 1 and 4.

[0002] Many energy production processes release carbon dioxide. To reduce the climate-damaging effects of carbon dioxide in the atmosphere, it can be converted into other substances. However, this is complicated by the fact that carbon dioxide is stable and relatively unreactive. Furthermore, the carbon in the carbon dioxide molecule is in its highest oxidation state. Therefore, carbon dioxide cannot be further used for energy production through combustion.

[0003] However, carbon dioxide can be reduced to carbon monoxide by supplying energy.

[0004] Carbon monoxide contains carbon in a lower oxidation state than carbon dioxide. Consequently, carbon monoxide can be used for more applications than carbon dioxide. Therefore, converting carbon dioxide to carbon monoxide not only reduces the amount of climate-damaging carbon dioxide, but also yields a valuable chemical raw material.

[0005] For example, carbon monoxide combines with hydrogen to form a synthesis gas containing the elements carbon, oxygen, and hydrogen, which are essential for the production of important organic chemicals. This synthesis gas is therefore suitable for many petrochemical processes, such as the production of synthetic fuels, natural gas, methanol, or formaldehyde. Hydrogen can be obtained relatively easily through various methods. Therefore, the production of carbon monoxide is of particular importance.

[0006] The production of a chemical using energy is also known as " Power-to-X" known because of energy (“ Power ") a chemical (" X ") can be obtained. By using climate-damaging carbon dioxide as a feedstock, this concept can contribute to reducing global warming. Furthermore, fossil fuels can be conserved by producing synthetic fuels from the resulting carbon monoxide. Synthetic fuel can be used to power vehicles in an environmentally friendly way without requiring extensive modifications to the vehicles' designs. For these reasons, the conversion of carbon dioxide to carbon monoxide can contribute to the energy transition, especially if renewable energy is used for this conversion.

[0007] Electrolysis processes are known in the art that can convert carbon dioxide into carbon monoxide with the input of energy. However, these have a low efficiency.

[0008] Processes for obtaining carbon monoxide are known from US 2019 / 127 865 A1 and WO 2012 / 118 065 A1. Furthermore, a process for producing carbon-based secondary energy carriers or basic chemicals by coupling oxyfuel combustion of carbon-based fuels and high-temperature solid electrolyte electrolysis (HT-SOEL) is known from DE 10 2015 226 111 A1.

[0009] Based on this, the present invention aims to overcome at least some of the problems known from the prior art and, in particular, to present a method and a device for producing carbon monoxide with which an improved efficiency can be achieved.

[0010] These tasks are solved using the features of independent method and apparatus claims 1 and 4.

[0011] Further advantageous embodiments of the invention are specified in the dependent claims. The features listed individually in the dependent claims can be combined in a technologically meaningful manner and can define further embodiments of the invention. Furthermore, the features specified in the claims are specified and explained in more detail in the description, which also presents further preferred embodiments of the invention.

[0012] According to the invention, a process for the production of carbon monoxide is presented, see claim 1. The process comprises inter alia: a) Humidifying a carbon dioxide-containing reactant gas with water, b) Feeding the humidified reactant gas from step a) into an electrolysis cell, and c) Electrolyzing the humidified reactant gas fed in according to step b) in the electrolysis cell, so that the carbon monoxide is obtained.

[0013] Carbon monoxide can be produced using the described process. Together with hydrogen, carbon monoxide forms the synthesis gas described in the state of the art. The described process is part of the concept of "Power-to-X". Unlike co-electrolysis, the described process does not aim for the direct production of synthesis gas from carbon monoxide and hydrogen, but primarily for the production of carbon monoxide. While hydrogen can also be produced in the described process, the quantity is lower compared to co-electrolysis.

[0014] In the described process, the carbon monoxide is obtained from carbon dioxide by electrolysis, and according to the invention, by the type of high-temperature electrolysis.

[0015] This takes place in an electrolysis cell. The electrolysis cell has an anode and a cathode, which are separated from each other by at least one electrolyte. In addition to the electrolyte, further layers can be arranged between the anode and the cathode. Preferably, the electrolysis cell is substrate-supported or electrolyte-supported. In a substrate-supported configuration, it is preferred that the cathode is designed as a Ni-YSZ electrode, the electrolyte is formed from YSZ, a barrier layer of CGO is arranged between the electrolyte and the anode, and the anode is formed from LSC. Alternatively, in an electrolyte-supported configuration, it is preferred that the cathode is designed as a Ni-CGO electrode, the electrolyte is formed from YSZ, a barrier layer of CGO is arranged between the electrolyte and the anode, and the anode is formed from LSCF.

[0016] Furthermore, the electrolysis cell preferably has an anode compartment adjacent to the anode. A gas can flow along the anode in the anode compartment. The electrolysis cell also has a cathode compartment adjacent to the cathode. A gas flows along the cathode in the cathode compartment. The anode compartment and / or cathode compartment preferably each have an inlet and an outlet.

[0017] The carbon dioxide used in the described process can originate from any source. In particular, the carbon dioxide can be produced as a byproduct of combustion. The carbon dioxide-containing gas produced during combustion is preferably purified before being fed into the electrolysis cell. Preferably, sulfur compounds, silicon compounds, halogen compounds, and certain hydrocarbons, such as aromatics and polyaromatics, are removed from the gas. The purified gas can then be fed directly to the electrolysis cell. Alternatively, the gas produced during combustion can also be temporarily stored and / or transported in a container (before or after purification) before being fed to a purification process or the electrolysis cell.

[0018] The described process starts with a reactant gas comprising carbon dioxide. The reactant gas can be pure carbon dioxide or can contain other components, in particular carbon monoxide and / or water vapor. Preferably, the reactant gas contains 5 to 15% carbon monoxide. This can, for example, prevent or at least reduce the reoxidation of nickel in the electrolyte. The fact that the described process serves to produce carbon monoxide does not preclude the use of carbon monoxide as a reactant. Thus, when using carbon monoxide as a reactant, the described process can produce further carbon monoxide. The quantity and amount of carbon monoxide can therefore be increased using the described process. The carbon monoxide used as a reactant can be derived from the product gas—at least once the process has started. In this case, a portion of the carbon monoxide obtained is fed back into the process.

[0019] The reactant gas, comprising carbon dioxide, is introduced into the cathode chamber in a gaseous state via the inlet of the cathode chamber, so that the reactant gas flows along the cathode.

[0020] If an electric current is applied between the anode and cathode, the carbon dioxide from the reactant gas is reduced at the cathode according to the following chemical equation: CO₂(g) + 2e⁻ → CO(g) + O₂(g) (1)

[0021] According to this reaction equation, a molecule of gaseous carbon dioxide (CO 2 ) is converted into a molecule of gaseous carbon monoxide (CO) and an oxygen ion (O 2-< ) by gaining two electrons (e -< ).

[0022] The electrolyte is preferentially permeable to oxygen ions (O²⁻), but not to gas molecules such as CO₂, CO, H₂O, or H₂. The oxygen ions (O²⁻) can therefore move from the cathode compartment to the anode compartment. There, the following oxidation reaction can take place: 2 O²⁻ → O₂ (g) + 4e⁻ (2)

[0023] According to this reaction equation, two oxygen ions (O 2-< ) are converted to one molecule of gaseous oxygen (O 2 ), releasing four electrons (e -< ).

[0024] Electrons can be moved from the anode to the cathode via a voltage source. The reaction equations (1) and (2) thus yield the following balance equation for the electrolysis cell: x CO₂ → x CO₂ + ½ x O₂ (3)

[0025] The electrolysis cell can therefore produce carbon monoxide from carbon dioxide with the input of energy. The carbon monoxide is produced at the cathode and can be discharged via an outlet in the cathode compartment. Oxygen is also produced in the anode compartment and can be discharged via the anode compartment outlet. Thus, oxygen can also be produced using the described process. The carbon monoxide and oxygen can therefore be obtained separately.

[0026] It is preferred that the anode compartment be purged with a purge gas. Suitable purge gases include, for example, air, oxygen (O₂), and / or nitrogen (N₂). The purge gas allows the oxygen formed at the anode to be carried away from the anode. The partial pressure of oxygen at the anode can thus be reduced. This lowers the voltage required between the anode and cathode for electrolysis, thereby saving energy.

[0027] The purge gas can therefore increase efficiency. The purge gas is preferably heated to a temperature in the range of 800 to 900 °C before being introduced into the anode compartment. This prevents thermal stresses within the electrolysis cell.

[0028] The electrolysis is carried out using carbon dioxide as the reactant, which is supplied to the electrolysis cell in gaseous form. This is done according to the described procedure in step b), so that the electrolysis can be carried out according to step c). The electrolysis takes place according to the invention at a temperature of 800 to 900 °C. For this purpose, the reactant gas is heated to this temperature in step b). During the electrolysis according to step c), the temperature is maintained in the range of 800 to 900 °C.

[0029] It has been found that the efficiency of electrolysis can be increased by humidifying the reactant gas before electrolysis, and especially before heating. Furthermore, it has been determined that humidification can purify the reactant gas. Depending on the source of the carbon dioxide, the reactant gas may contain impurities that can be at least partially removed by humidification.

[0030] In the described process, the reactant gas is therefore humidified in step a). Reactant gas refers to the gas present before humidification, which always includes carbon dioxide. Humidification transforms the reactant gas into "humidified reactant gas," which contains a higher proportion of water compared to the "reactant gas." Humidification takes place before heating for electrolysis, so the humidified reactant gas is heated.

[0031] The humidified reactant gas is fed to the electrolysis cell, in particular by introducing it into the cathode compartment. During the electrolysis then carried out according to step c), an increased efficiency can be achieved. This can be explained by the water content in the humidified reactant gas. Thus, at the cathode, the water in the reactant gas can be reduced according to the following chemical equation: H₂O(g) + 2e⁻ → H₂(g) + O²⁻ (4)

[0032] According to this reaction equation, a water vapor molecule (H 2 O) is converted into a molecule of gaseous hydrogen (H 2 ) and an oxygen ion (O 2-< ) by absorbing two electrons (e -< ).

[0033] Furthermore, the water content in the reactant gas can react with carbon monoxide to form carbon dioxide and hydrogen according to the following reaction equation:

[0034] This reaction, also known as the "reversible water-gas shift," is an equilibrium reaction, meaning that carbon dioxide and hydrogen can react to form carbon monoxide and water. During electrolysis, carbon dioxide (CO₂) is reduced to carbon monoxide according to reaction equation (1), and water vapor (H₂O) is reduced to hydrogen (H₂) according to reaction equation (4). This alters the proportions in reaction equation (5), disrupting the chemical equilibrium. This can lead to the formation of water vapor (H₂O) and carbon monoxide (CO) from hydrogen (H₂) and carbon dioxide (CO₂). Electrolysis with humidified reactant gas is therefore particularly efficient because the hydrogen produced during electrolysis can further support the conversion of carbon dioxide to carbon monoxide.

[0035] Due to reaction equation (5), the product gas may contain a proportion of gaseous carbon dioxide and / or a proportion of water vapor. It is preferred that the product gas, after exiting the cathode compartment outlet, is separated into carbon monoxide on the one hand and all other substances on the other.

[0036] The remaining substances can primarily be carbon dioxide and / or water. The separated carbon dioxide and / or water can be fed back into the electrolysis process.

[0037] Humidification according to step a) is carried out with water. Thus, water vapor is not simply added to the reactant gas. This would be energetically disadvantageous because a considerable amount of energy would be required to evaporate water. In this respect, in particular, the described process differs from co-electrolysis. The humidified reactant gas contains a water content. Various methods can be used to humidify the reactant gas. For example, the reactant gas can be passed through a humidifier in a supply line to the cathode compartment.

[0038] According to the invention, the reactant gas is passed through the water in step a).

[0039] It has been found that, in the described process, passing the reactant gas through water is particularly efficient. "Passing through" in this context means that the reactant gas is introduced into the water, comes into direct contact with the water, and is then collected. It is therefore insufficient for the reactant gas to simply pass through a pipe surrounded by water, thus preventing direct contact between the reactant gas and the water. Preferably, the reactant gas is passed through the water in the form of bubbles. For example, the reactant gas can be introduced into the water from a multitude of nozzle openings below the water surface. The reactant gas then rises in the water as bubbles. Subsequently, after exiting the liquid water, the reactant gas can be collected and conveyed via a hose or pipe, or conveyed directly through a hose or pipe.The humidified reactant gas can be compressed with a pump, but this is not necessary.

[0040] According to one aspect not supported by the invention, the water in step a) is at a temperature in the range of 18 to 25 °C.

[0041] The specified temperature range corresponds to normal room temperature. An increase in efficiency can already be achieved if the carbon dioxide in step a) is passed through water at this temperature. Accordingly, no heating of the water is required, nor is any energy needed to heat the water.

[0042] When using water with a temperature in the range of 18 to 25 °C, a carbon dioxide humidity level of 3 to 5% can be achieved.

[0043] For example, if a mixture of 90% gaseous carbon dioxide and 10% gaseous carbon monoxide is used as the reactant gas and humidified with water at 18 to 25 °C in step a), a humidified reactant gas containing 87.3% gaseous carbon dioxide, 9.7% gaseous carbon monoxide, and 3.0% water vapor can be obtained. This can then be added to the electrolysis. The product gas obtained at the cathode can contain less than 1% hydrogen in this case. This can be explained by the shift in the equilibrium from reaction equation (5).

[0044] According to a preferred embodiment of the method, the water in step a) is at a temperature in the range of 25 to 40°C.

[0045] In this embodiment, the water is heated above room temperature.

[0046] Using heated water can increase the humidity level of the carbon dioxide. For example, a carbon dioxide humidity level of 5% can be achieved at a water temperature of 33 °C.

[0047] For example, if a mixture of 90% gaseous carbon dioxide and 10% gaseous carbon monoxide is used as the reactant gas and humidified with 33°C warm water in step a), a humidified reactant gas containing 85.5% gaseous carbon dioxide, 9.5% gaseous carbon monoxide, and 5.0% water vapor can be obtained, which can then be added to the electrolysis. The product gas obtained at the cathode can also contain less than 1% hydrogen in this case. This can again be explained by a shift in the equilibrium from reaction equation (5).

[0048] Various methods can be used to heat the water. For example, a heater, an immersion heater and / or a heat exchanger can be used.

[0049] The water used for step a) is heated according to the invention by heat from a product of the electrolysis from step c).

[0050] The heat generated by the products of electrolysis can be recovered and utilized. Potential products include those produced at both the cathode and the anode. At the cathode, this includes carbon monoxide, which is produced using the described process. Hydrogen can also be formed at the cathode. Oxygen is formed at the anode. The products of electrolysis can possess usable thermal energy, particularly due to the pre-heating of the reactant gas. This also applies to components in the reactant gas that leave the cathode compartment without participating in a chemical reaction. If these components were also pre-heated, their thermal energy can be recovered after electrolysis to heat the water used in step a). The products may also be heated due to the chemical reactions themselves.

[0051] The heat from the electrolysis products can be used in various ways to heat the water for step a). For example, a stream of product gas can be passed through a tube within the water. To transfer heat over the greatest possible length of the tube, it is preferably spiral-shaped.

[0052] Preferably, only the products from the cathode or only the products from the anode are conveyed through the conduit, thus preventing any mixing of these products. It is also possible to provide separate conduits for the products from the anode and for the products from the cathode. This also prevents mixing.

[0053] Alternatively, the heat from the products, or a portion thereof, can be transferred to a heat transfer medium via a heat exchanger. This heat transfer medium can then be directed to a further heat exchanger, where it transfers its heat to the water used in step a). Preferably, only the products from the cathode or only the products from the anode are passed through the heat exchanger, thus preventing any mixing of these products. It is also possible to provide separate heat exchangers and / or separate branches of a common heat exchanger for the products from the anode and the products from the cathode, respectively.

[0054] According to a further preferred embodiment of the method, step a) is carried out such that after step a) the water content of the moistened reactant gas is 2 to 6%.

[0055] The water content of the humidified reactant gas after step a) can be adjusted by various means. For example, if carbon dioxide is passed through the water as bubbles, more water can be absorbed at a higher water temperature, a higher carbon dioxide temperature, a lower carbon dioxide flow rate, a smaller bubble size, and / or a greater distance to the water surface. By changing these and / or other parameters, the water content of the humidified reactant gas can be adjusted. The parameters for a specific desired water content can be determined experimentally.

[0056] The yield of carbon monoxide is higher the lower the water content of the humidified reactant gas. The efficiency increases with the water content of the humidified reactant gas up to a water content of approximately 20%. It has been found that a water content of 2 to 6% in the humidified reactant gas represents a good compromise between these two aspects.

[0057] As a further aspect of the invention, a device for the production of carbon monoxide is presented, see claim 4. The device comprises, among other things: an electrolysis cell with an anode and a cathode separated by an electrolyte, as well as a cathode compartment adjacent to the cathode, and a lead to the cathode compartment which includes a humidifier.

[0058] The described special advantages and design features of the method are applicable and transferable to the device, and vice versa. The described method is preferably carried out with the described device. The described device is preferably designed and configured for carrying out the described method. Via the supply line with the

[0059] A reactant gas containing carbon dioxide is humidified in a humidifier (step a) of the described process) and fed to the electrolysis cell (step b)). Electrolysis can then be carried out in the electrolysis cell (step c)). For this purpose, the electrolysis cell preferably has a current and voltage source by means of which a current can be applied between the cathode and anode. The electrolysis cell is preferably designed as a high-temperature electrolysis cell.

[0060] In the cathode compartment, a gas can flow along the cathode. Furthermore, the electrolysis cell preferably has an anode compartment adjacent to the anode. In the anode compartment, a gas can flow along the anode. The anode compartment and / or cathode compartment preferably each have an inlet and an outlet. The electrolysis cell preferably also has a supply line to the cathode compartment through which a purge gas can be introduced into the anode compartment.

[0061] The device further includes a heating device for heating water inside the humidifier by means of a product of electrolysis taking place in the electrolysis cell.

[0062] The heating device preferably comprises a line through which products of electrolysis can be passed through the water used for step a). Alternatively, the heating device can also include the heat exchangers described above.

[0063] The invention and its technical context are explained in more detail below with reference to the figures. It should be noted that the invention is not limited by the embodiments shown, but only by the subject matter of the claims defined below.

[0064] The same reference symbols denote the same objects, so that explanations from other figures can be used as a supplement if necessary. They show: Fig. 1: a flowchart of a method according to the invention, and Fig. 2: a device according to the invention.

[0065] Fig. 1 This shows a flowchart of a process for the production of carbon monoxide. The process is described using the reference numerals from Fig. 2 described. The procedure includes: a) Humidifying a carbon dioxide-containing reactant gas with water, b) Feeding the humidified reactant gas from step a) into an electrolysis cell 1, and c) Electrolyzing the humidified reactant gas fed in according to step b) in the electrolysis cell 1, so that the carbon monoxide is obtained.

[0066] Fig. 2 shows a device 12 for the production of carbon monoxide, in particular according to the method from Fig. 1 The device 12 comprises an electrolysis cell 1 with an anode 2 and a cathode 3, which are separated from each other by an electrolyte 10. The electrolysis cell 1 further comprises an anode chamber 4 adjacent to the anode 2, in which a gas can flow along the anode 2. The electrolysis cell 1 also comprises a cathode chamber 5 adjacent to the cathode 3, in which a gas can flow along the cathode 3. The anode chamber 4 has an inlet 6 and an outlet 7. The cathode chamber 5 has an inlet 8 and an outlet 9. A supply line 13 with a humidifier 11 is connected to the inlet 8 of the cathode chamber 5. A discharge line 14 is connected to the outlet 9 of the cathode chamber 5. The derivative 14 comprises a heating device 15 for heating the humidifier 11 by means of a product of electrolysis taking place in the electrolysis cell 1.A dotted line indicates that heat can be transferred from the heating device 15 to the humidifier 11.

[0067] A carbon dioxide-containing reactant gas can be introduced into the cathode chamber 5 via the supply line 13 (step b) of the process described above. Fig. 1 The reactant gas is humidified using humidifier 11 (step a)). Electrolysis is carried out in electrolysis cell 1 (step c)).

[0068] In this process, the carbon dioxide from the moistened reactant gas is reduced to carbon monoxide at the cathode 3. At the anode 2, the oxygen ions formed during electrolysis can react to form oxygen. A purge gas can be introduced into the inlet 6 of the anode chamber 4 and discharged from the outlet 7 of the anode chamber 4 together with the oxygen thus produced. In the illustrated embodiment, the purge gas is nitrogen. Alternatively, however, oxygen can also be used as the purge gas.

[0069] The reactant gas can be humidified in step a) by passing it through water within the humidifier 11. Preferably, the water content of the humidified reactant gas is 2 to 6%. The water within the humidifier 11 is heated via the heating device 15 by product gas taken from the cathode chamber 5, preferably to 25 to 40°C.

[0070] Using the described method and the described device 12, carbon monoxide can be produced by CO₂ electrolysis with a particularly high efficiency. This is achieved by humidifying the carbon dioxide-containing reactant gas before electrolysis. Reference symbol list

[0071] 1 Electrolysis cell 2 Anode 3 Cathode 4 Anode compartment 5 Cathode compartment 6 Anode compartment inlet 7 Anode compartment outlet 8 Cathode compartment inlet 9 Cathode compartment outlet 10 Electrolyte 11 Humidifier 12 Device 13 Lead to cathode compartment 14 Cathode compartment outlet 15 Heating device

Claims

1. Process for producing carbon monoxide, comprising: a) humidifying a reactant gas comprising carbon dioxide with liquid water, wherein the reactant gas is passed through the liquid water, b) supplying the humidified reactant gas from step a) to an electrolysis cell (1) and c) electrolyzing the humidified reactant gas supplied according to step (b) in the electrolysis cell (1) to obtain carbon monoxide; wherein the liquid water used for step a) is heated using heat from a product of the electrolysis from step c) and wherein the electrolysis cell (1) is a high-temperature electrolysis cell and wherein the electrolyzing in step c) is performed at a temperature of 800°C to 900°C.

2. Process according to Claim 1, wherein the water in step a) has a temperature in the range from 25°C to 40°C.

3. Apparatus (12) for producing carbon monoxide, comprising: - a high-temperature electrolysis cell (1) having an anode (2) and a cathode (3) separated from one another by at least an electrolyte (10) and a cathode space (5) adjacent to the cathode (3), - a feed conduit (13) to the cathode space (5) which comprises a humidifier (11) configured such that a reactant gas is passed through liquid water present in it for humidification and - a heating means (15) for heating liquid water within the humidifier (11) using a product of an electrolysis proceeding in the high-temperature electrolysis cell (1) in the manner of the high-temperature electrolysis at 800°C to 900°C, wherein heat is passed from the heating means (15) to the humidifier (11).