Method for producing methane

Abstract

A method for producing methane is specified. According to one embodiment, the method comprises providing a metal hydrogen carbonate and hydrogen gas in a reaction volume (1) and reacting the metal hydrogen carbonate with the hydrogen gas in the reaction volume (1) to form products, wherein a first product is methane.

Description

[0001] Description

[0002] METHOD FOR PRODUCING METHANE

[0003] A method for producing methane is speci fied .

[0004] It is an obj ect to provide a simple method for producing methane .

[0005] A method for producing methane is speci fied . Methane has the chemical formula CH4.

[0006] According to at least one embodiment , the method comprises providing a metal hydrogen carbonate and hydrogen gas in a reaction volume . In particular, the metal hydrogen carbonate is an alkali metal hydrogen carbonate . For example , the metal hydrogen carbonate is sodium hydrogen carbonate or potassium hydrogen carbonate . In particular, the reaction volume is located in a packed bed reactor, for example in a moving bed reactor . For example , the metal hydrogen carbonate can be provided in the reaction volume and transported through the reaction volume by gravity in a vertical installation of the packed bed reactor . In this instance , the metal hydrogen carbonate can be transported into the reaction volume and solid products can be transported out of the reaction volume by screw conveyors . Alternatively, the entire transport of the metal hydrogen carbonate and / or solid products in, through, and out of the reaction volume , respectively, can be carried out by means of a solid transport system such as conveyor screws . In this instance , the transport of the metal hydrogen carbonate can be independent of the installation of the packed bad reactor . For example , the hydrogen gas is added directly to the reaction volume from an external hydrogen gas source , in particular in a concentration of 100 % hydrogen gas . For instance , no carbon dioxide is added to the reaction volume from an external source .

[0007] According to at least one embodiment , the method comprises reacting the metal hydrogen carbonate with the hydrogen gas in the reaction volume to form products , wherein a first product is methane . In particular, the metal hydrogen carbonate is reacted with the hydrogen gas according to the following formula : 2 MHCO3+ 4 H2CH4+ M2CO3+ 3 H2O . In other words , two metal hydrogen carbonates and four hydrogen molecules form one methane molecule , one metal carbonate and three water molecules . For example , reacting the metal hydrogen carbonate with the hydrogen gas according to the above formula is an exothermic process . For instance , a standard enthalpy change for the above reaction at 300 ° C is AH° ( T = 300 ° C ) = -41 . 34 kJ / molMHco3.

[0008] According to at least one embodiment , the method for producing methane comprises providing a metal hydrogen carbonate and hydrogen gas in a reaction volume and reacting the metal hydrogen carbonate with the hydrogen gas in the reaction volume to form products , wherein a first product is methane .

[0009] It is an idea of the present application to provide a simple and ef ficient method for producing methane . By reacting the metal hydrogen carbonate with hydrogen gas in one reaction volume , the method for producing methane can advantageously be carried out in a particularly energy-ef ficient way . According to at least one embodiment , reacting the metal hydrogen carbonate comprises calcinating the metal hydrogen carbonate to form carbon dioxide and methani zing the carbon dioxide .

[0010] Here and in the following, calcination is understood to mean a thermal decomposition of a reactant such as the metal hydrogen carbonate . In particular, the metal hydrogen carbonate is reacted by applying a thermal energy . For example , the metal hydrogen carbonate is calcinated according to the following formula : 2 MHCO3 M2CO3 + CO2 + H20. In other words , two metal hydrogen carbonates form one metal carbonate , one carbon dioxide molecule and one water molecule .

[0011] Here and in the following, methanation is understood to mean a conversion of carbon dioxide to methane through hydrogenation . In particular, the carbon dioxide is methani zed according to the following formula : CO2 + 4 H2CH4+ 2 H20. In other words , one carbon dioxide molecule and four hydrogen molecules form one methane molecule and two water molecules . In particular, reacting the carbon dioxide with hydrogen gas is an exothermic process . In other words , thermal energy is released during reacting the carbon dioxide with hydrogen gas .

[0012] In particular, both the calcination reaction and the methanation reaction take place in the reaction volume . In other words , the calcination reaction and the methanation reaction take place in the same reaction volume . For example , the calcination reaction and the methanation reaction take place in the same reaction volume in the same reactor . In other words, the calcination reaction and the methanation reaction are not spatially separated from each other.

[0013] According to at least one embodiment, thermal energy released during methanizing the carbon dioxide is used for calcinating the metal hydrogen carbonate. In particular, the calcination reaction and the methanation reaction are thermally coupled. For example, thermal energy released during methanizing is transferred to the metal hydrogen carbonate for calcination. In other words, a directed transfer of thermal energy to the metal hydrogen carbonate takes place in the reaction volume.

[0014] In particular, the thermal energy is directly transferred from gaseous products produced during the methanation reaction such as methane or water vapor to the metal hydrogen carbonate in the reaction volume. For example, the thermal energy is not transferred via a heat exchanger. For example, the gaseous products produced during the methanation reaction come into direct contact to the metal hydrogen carbonate in the reaction volume. During this direct contact, the thermal energy is transferred. By reacting the metal hydrogen carbonate with hydrogen gas in one reaction volume, the thermal energy released during methanizing the carbon dioxide can advantageously be provided to the metal hydrogen carbonate and thus for the calcination reaction in a simple manner .

[0015] According to at least one embodiment, the metal hydrogen carbonate is essentially a solid in the reaction volume. In particular, at least 99 %, in particular at least 99.5 %, for example at least 99.9 %, of the metal hydrogen carbonate is present as a solid in the reaction volume. For example, essentially all of the metal hydrogen carbonate, in particular all of the metal hydrogen carbonate , is , within the bounds of process engineering tolerances , present as a solid in the reaction volume . For instance , the metal hydrogen carbonate is not present in the reaction volume in solution . Using a solid metal hydrogen carbonate in the reaction volume can advantageously increase the energy ef ficiency of the calcination reaction as no solvent such as water needs to be heated and / or evaporated . Further, as no solvent such as water enters the gas phase , a water vapor partial pressure in the reaction volume can advantageously not be increased and thus , an equilibrium of the calcination reaction remains on the product side .

[0016] According to at least one embodiment , a temperature in the reaction volume is at most 350 ° C, in particular at most 300 ° C . For example , the temperature is chosen in such a way that , independent of a pressure in the reaction volume , any water that is present in the reaction volume is in gaseous form . Further, the temperature can be chosen in such a way that a sintering of the metal hydrogen carbonate is at least reduced, in particular prevented . A temperature of at most 350 ° C in the reaction volume can advantageously ensure that the metal hydrogen carbonate does not undergo sintering reactions and that the metal hydrogen carbonate is not solved in liquid water but is essentially a solid in the reaction volume .

[0017] According to at least one embodiment , the temperature in the reaction volume is at least 230 ° C, in particular at least 250 ° C . In particular, the methanation reaction starts at a temperature of at least 230 ° C . For example , a temperature of at least 250 ° C results in space velocities of above 9000 GHSV ( gas hourly space velocity) using a catalyst being AI2O3 with 5 wt.-% Ru. A temperature of at least 250 °C, in particular when using a catalyst being AI2O3 with 5 wt.-% Ru, can advantageously have sufficient space velocities for large-scale applications.

[0018] According to at least one embodiment, a gas volume in the reaction volume at most consists of hydrogen gas, water vapor, carbon dioxide, carbon monoxide, methane, and residuals of air. In particular, a gas volume in the reaction volume is free of gases other than hydrogen gas, water vapor, carbon dioxide, carbon monoxide, methane, and residuals of air. For example, carbon dioxide, carbon monoxide, and water vapor are produced during calcinating the metal hydrogen carbonate in the reaction volume. For instance, methane and water vapor are produced during methanizing the carbon dioxide in the reaction volume.

[0019] According to at least one embodiment, reacting the metal hydrogen carbonate is an at least 70 %, in particular an at least 80 %, for example an at least 90 %, an at least 95 %, or an at least 99 %, for instance a 100 %, autothermal process. Here and in the following, an autothermal process is a chemical reaction in which an exothermic reaction and an endothermic reaction take place in parallel in such a way that the overall process is independent of an external input of thermal energy. In particular, the calcination is an endothermic reaction and the methanation is an exothermic reaction. For example, at most 30 %, in particular at most 20 %, for example at most 10 %, at most 5 %, at most 1 % or none of the energy needed for the endothermic reaction is supplemented from an external energy source. By thermally coupling the two reactions in the reaction volume, an at least 70 % autothermal process can advantageously be reali zed .

[0020] According to at least one embodiment , the products comprise gaseous products and solid products . In particular, the gaseous products can be separated from the solid products when the products are removed from the reaction volume . The separation can be achieved by a material separation . For example , the gaseous products comprise methane and water vapor . The gaseous products can be mixed with hydrogen gas , carbon dioxide , and carbon monoxide that are present in the reaction volume prior to , during an / or after reacting the metal hydrogen carbonate with hydrogen gas . In particular, the solid products comprise a metal carbonate . The solid products can be mixed with residues of the metal hydrogen carbonate that was provided in the reaction volume prior to reacting the metal hydrogen carbonate with hydrogen gas .

[0021] According to at least one embodiment , the gaseous products are used for heating the hydrogen gas and / or the metal hydrogen carbonate prior to reacting the metal hydrogen carbonate . In particular, the gaseous products are used for heating the hydrogen gas and / or the metal hydrogen carbonate before entering the reaction volume . In particular, the gaseous products comprise the thermal energy released during methani zing carbon dioxide in the reaction volume . For instance , the thermal energy is trans ferred to the hydrogen gas and / or the metal hydrogen carbonate in at least one heat exchanger . In other words , the hydrogen gas and / or the metal hydrogen carbonate is preheated prior to entering the reaction volume . By using the gaseous products for heating the hydrogen gas and / or the metal hydrogen carbonate , suf ficiently high temperatures of the hydrogen gas to overcome the high activation energy of the methanation reaction in the reaction volume and of the metal hydrogen carbonate to overcome the activation energy of the calcination reaction in the reaction volume can advantageously be reali zed .

[0022] According to at least one embodiment , the solid products are used for preheating the hydrogen gas prior to reacting the metal hydrogen carbonate . In particular, the solid products are used for heating the hydrogen gas before entering the reaction volume . In particular, the solid products comprise the thermal energy released during methani zing carbon dioxide in the reaction volume . For instance , the thermal energy is trans ferred to the hydrogen gas in a heat exchanger . In other words , the hydrogen gas is preheated prior to entering the reaction volume . By using the solid products for heating the hydrogen gas , a suf ficiently high temperature of the hydrogen gas to overcome the high activation energy of the methanation reaction in the reaction volume can advantageously be reali zed .

[0023] According to at least one embodiment , the hydrogen gas passes through a first heat exchanger, a second heat exchanger and a third heat exchanger in this order prior to entering the reaction volume , the metal hydrogen carbonate passes through a fourth heat exchanger prior to entering the reaction volume , the gaseous products pass through the third heat exchanger, the fourth heat exchanger and the first heat exchanger in this order after leaving the reaction volume , and the solid products pass through the second heat exchanger after leaving the reaction volume . In particular, the first heat exchanger and the third heat exchanger are gas / gas heat exchangers , for example plate heat exchangers . In particular, the second heat exchanger and the fourth heat exchanger are gas / solid heat exchangers , for example rotary kilns .

[0024] In particular, the first heat exchanger is a heat exchanger for preheating the hydrogen gas . For example , the hydrogen gas having a first temperature enters the first heat exchanger and is heated by the gaseous products having a ninth temperature in the first heat exchanger to a second temperature . In other words , the first temperature is lower than the second temperature . The gaseous products having the ninth temperature can be cooled in the first exchanger to a tenth temperature . In other words , the ninth temperature is higher than the tenth temperature . For example , the first temperature is at most 30 ° C such as 25 ° C . In other words , the first temperature is a temperature under ambient conditions . For instance , the second temperature is at least 100 ° C such as 115 ° C . For example , the ninth temperature is at least 120 ° C such as 144 ° C . For instance , the tenth temperature is at most 100 ° C such as 89 ° C .

[0025] In particular, the second heat exchanger is a heat exchanger for preheating the hydrogen gas . In the second heat exchanger, the hydrogen gas preheated in the first heat exchanger can be preheated further . For example , the hydrogen gas having the second temperature enters the second heat exchanger and is heated by the solid products having an eleventh temperature in the second heat exchanger to a third temperature . In other words , the second temperature is lower than the third temperature . The solid products can be fed into the second heat exchanger as a particle flow . In particular, the solid products are free of the gaseous products when entering the second heat exchanger . The solid products having the eleventh temperature can be cooled in the second heat exchanger to a twelfth temperature. In other words, the eleventh temperature is higher than the twelfth temperature. For example, the third temperature is at least 230 °C such as 250 °C. For instance, the eleventh temperature is at most 300 °C such as 280 °C. For example, the twelfth temperature is at most 200 °C such as 187 °C.

[0026] In particular, the third heat exchanger is a heat exchanger for preheating the hydrogen gas. In the third exchanger, the hydrogen gas can be preheated to a temperature that is at most 25 %, in particular at most 20 % below the temperature in the reaction volume. For example, the hydrogen gas having the third temperature enters the third heat exchanger and is heated by the gaseous products having a seventh temperature in the third heat exchanger to a fourth temperature. In other words, the third temperature is lower than the fourth temperature. The gaseous products having the seventh temperature can be cooled in the third heat exchanger to an eighth temperature. In other words, the seventh temperature is higher than the eighth temperature. For example, the fourth temperature is at least 250 °C such as 261 °C. For instance, the seventh temperature is at most 300 °C such as 280 °C. For example, the eighth temperature is at most 275 °C such as 264 °C.

[0027] In particular, the fourth heat exchanger is a heat exchanger for preheating the metal hydrogen carbonate. For example, the metal hydrogen carbonate having a fifth temperature enters the fourth heat exchanger and is heated by the gaseous products having the eighth temperature in the fourth heat exchanger to a sixth temperature. In other words, the fifth temperature is lower than the sixth temperature. The solid products can be fed into the fourth heat exchanger as a particle flow . The gaseous products having the eighth temperature can be cooled in the fourth heat exchanger to the ninth temperature . In other words , the eighth temperature is higher than the ninth temperature . For example , the fi fth temperature is at most 30 ° C such as 25 ° C . In other words , the fi fth temperature is a temperature under ambient conditions . For instance , the sixth temperature is a minimum temperature for the metal hydrogen carbonate when entering the reaction volume in order to achieve an autothermal process in the reaction volume . For example , the sixth temperature is at least 80 ° C such as 99 ° C .

[0028] By using four heat exchangers in such a configuration, a heat integration can advantageously be reali zed which results in a complete or nearly complete autothermal process management .

[0029] According to at least one embodiment , the hydrogen gas passes through a first heat exchanger prior to entering the reaction volume and the gaseous products pass through the first heat exchanger after leaving the reaction volume . In particular, the first heat exchanger is a gas / gas heat exchanger, for example a plate heat exchanger . In particular, the first heat exchanger is a heat exchanger for preheating the hydrogen gas .

[0030] For example , the hydrogen gas having a thirteenth temperature enters the first heat exchanger and is heated by the gaseous products having a seventeenth temperature in the first heat exchanger to a fourteenth temperature . In other words , the thirteenth temperature is lower than the fourteenth temperature . The gaseous products having the seventeenth temperature can be cooled in the first heat exchanger to an eighteenth temperature . In other words , the seventeenth temperature is higher than the eighteenth temperature. For example, the thirteenth temperature is at most 30 °C such as 25 °C. In other words, the thirteenth temperature is a temperature under ambient conditions. For instance, the fourteenth temperature is at least 200 °C such as 250 °C. For example, the seventeenth temperature is at most 300 °C such as 280 °C. For instance, the eighteenth temperature is at most 100 °C such as 80 °C.

[0031] By using only one gas / gas heat exchanger in such a configuration, a simple and efficient heat integration can advantageously be realized which results in a complete or nearly complete autothermal process management.

[0032] According to at least one embodiment, providing the metal hydrogen carbonate comprises providing a mixture of the metal hydrogen carbonate and a catalyst. The catalyst can be configured for catalyzing the methanation reaction. In particular, the metal hydrogen carbonate and the catalyst are mixed prior to providing the mixture in the reaction volume. For example, the catalyst is present in the reaction volume as a solid, for instance in the form of particles. The catalyst can have a specific surface area of between and including 100 m2 / kg and 250 m2 / kg. For example, the catalyst is AI2O3 with 5 wt.-% Ni or AI2O3 with 5 wt.-% Ru. Alternatively, the catalyst can be FesCg with between and including 2 wt.-% and 10 wt.-% Ni, for example with 5 wt.-% Ni . Alternatively, the catalyst can be FesCg with between and including 2 wt.-% and 10 wt.-% Ru, for example with 5 wt.-% Ru.

[0033] According to at least one embodiment, a weight ratio of the metal hydrogen carbonate and the catalyst in the mixture is at least 2:1, in particular at least 1:1, for example at least 1:2. In particular, the weight ratio is chosen in such a way that the catalyst is provided in the same amount as or in excess of the metal hydrogen carbonate. A weight ratio of the metal hydrogen carbonate and the catalyst in the mixture of least 2:1 can advantageously increase the reaction rate of the methanation reaction.

[0034] According to at least one embodiment, a second product is a metal carbonate. In particular, the metal carbonate is essentially a solid, for example present in the form of particles. For example, the catalyst is separated from the metal carbonate after reacting the metal hydrogen carbonate with the hydrogen gas. For instance, the separation can be carried out by means of a cyclone. The cyclone can make use of the different densities of the metal carbonate and the catalyst. Alternatively, the catalyst can be provided in the form of pellets having a larger diameter than the metal carbonate particles. In this instance, a sieve can be used for the separation.

[0035] According to at least one embodiment, the catalyst is separated from the metal carbonate by dissolving the metal carbonate. In particular, the metal carbonate is dissolved in water. For example, the catalyst is insoluble in water. As a result, the metal carbonate and the catalyst can be separated, for example by filtering. Separating the metal carbonate and the catalyst by dissolving the metal carbonate can be advantageous if the metal carbonate is used in solution in subsequent applications such as in an absorbent for carbon dioxide absorption. According to at least one embodiment, the catalyst is separated from the metal carbonate by means of a magnetic field. In particular, the catalyst comprises a magnetizable carrier material such as a ferromagnetic carrier material. For example, the catalyst is FeaCg with between and including 2 wt.-% and 10 wt.-% Ni, for example with 5 wt.-% Ni, or FeaCg with between and including 2 wt.-% and 10 wt.-% Ru, for example with 5 wt.-% Ru. In this instance, the FeaCg is the magnetizable carrier material. For instance, the catalyst and the metal carbonate are separated in the solid phase. In other words, the separation takes place without generating an aqueous phase. Separating the metal carbonate and the catalyst by means of a magnetic field can advantageously be carried out simply and cost-ef f iciently .

[0036] According to at least one embodiment, the metal hydrogen carbonate is produced as follows:

[0037] - contacting an absorbent with a gas stream comprising carbon dioxide, wherein the absorbent comprises a metal carbonate,

[0038] - producing a loaded absorbent, wherein the metal carbonate is at least partially converted to a metal hydrogen carbonate,

[0039] - precipitating at least a portion of the metal hydrogen carbonate from the loaded absorbent, and

[0040] - separating the precipitated metal hydrogen carbonate from the aqueous phase of the loaded absorbent.

[0041] In particular, the method steps of contacting an absorbent with a gas stream comprising carbon dioxide and producing a loaded absorbent are performed simultaneously. For example, the metal carbonate is converted to the metal hydrogen carbonate according to the following formula: M2CO3 + CO2 + H2O 2 MHCO3. For instance, the conversion of the metal carbonate to the metal hydrogen carbonate is an exothermic process . For example , a standard enthalpy change for the above reaction at 25 ° C is AH° ( T = 25 ° C ) = -27 . 3 kJ / molC02 -

[0042] In particular, the gas stream comprising carbon dioxide is air, for example ambient air with a carbon dioxide concentration of at most 10 % or greater than or equal to 100 ppm and less than or equal to 650 ppm . In particular, the precipitated metal hydrogen carbonate comprises at least 90 wt . -% of the metal hydrogen carbonate . In particular, the precipitated metal hydrogen carbonate is separated from the aqueous phase of the loaded absorbent using a centri fuge , a hydrocyclone , a belt filter, or combinations thereof .

[0043] With such a method, metal hydrogen carbonate used in the method for producing methane described herein can be produced as the precipitation product from a carbon dioxide absorption from a gas stream using a metal carbonate solution . By synergistically combining the method for producing methane with the production of the metal hydrogen carbonate via an absorption of carbon dioxide from a gas stream, a highly ef ficient coupling between carbon dioxide absorption and methane synthesis can advantageously be reali zed as both method steps are exothermic processes .

[0044] According to at least one embodiment , a second product is a metal carbonate , and the metal carbonate is used as the metal carbonate in the absorbent . By using the metal hydrogen carbonate produced in the absorption to produce methane and by using the metal carbonate produced during producing methane in the absorption, a highly ef ficient cycle can advantageously be reali zed . Advantageous embodiments and developments of the method for producing methane will become apparent from the exemplary embodiments described below in conj unction with the figures .

[0045] In the figures :

[0046] Figures 1 to 5 and 8 each shows a method for producing methane according to di f ferent exemplary embodiments ,

[0047] Figure 6 shows the methane yield as a function of the temperature in the reaction volume , and

[0048] Figure 7 shows the average dwell time of hydrogen gas in the reaction volume for complete conversion to methane as a function of the temperature in the reaction volume .

[0049] In the exemplary embodiments and figures , similar or similarly acting constituent parts are provided with the same reference signs . The elements illustrated in the figures and their si ze relationships among one another should not be regarded as true to scale . Rather, individual elements may be represented with an exaggerated si ze for the sake of better representability and / or for the sake of better understanding .

[0050] Figure 1 shows an exemplary embodiment of a method for producing methane . A metal hydrogen carbonate (MHCO3 ) is provided as a solid in a reaction volume 1 , for example in a packed bed reactor such as a moving bed reactor . The reaction volume 1 can be operated with a continuous transport of the solid metal hydrogen carbonate . In the exemplary embodiment of figure 1 , the reaction volume 1 is shown in a vertical installation and the transport of the metal hydrogen carbonate through the reaction volume 1 can be carried out by gravity . The transport of the metal hydrogen carbonate in the reaction volume 1 and a transport of solid products out of the reaction volume 1 can also be carried out by screw conveyors . Alternatively, the entire transport of the metal hydrogen carbonate and / or solid products in, through, and out of the reaction volume 1 , respectively, can be carried out by means of a solid transport system such as conveyor screws .

[0051] The solid metal hydrogen carbonate is reacted in the reaction volume 1 with hydrogen gas (H2) according to the following formula : 2 MHCO3+ 4 H2CH4+ M2CO3+ 3 H20. The reaction produces a metal carbonate (M2CO3) in solid form and methane ( CH4) and water (H20) in gaseous form . In particular, the metal hydrogen carbonate is calcinated in the reaction volume 1 to form carbon dioxide ( C02) according to the following formula : 2 MHCO3M2CO3+ C02+ H20. The carbon dioxide formed during calcinating the metal hydrogen carbonate is methani zed in the reaction volume 1 according to the following formula : C02+ 4 H2CH4+ 2 H20.

[0052] The temperature in the reaction volume 1 is at most 350 ° C, for example at most 300 ° C . The calcination reaction and the methanation reaction are thermally coupled in the reaction volume 1 in such a way that thermal energy released during the methanation reaction is used for the calcination reaction . This results in an at least 70 % autothermal process in the reaction volume 1 .

[0053] During reacting the metal hydrogen carbonate with hydrogen gas , gaseous products and solid products are formed . The gaseous products comprise methane and water vapor produced in the methanation reaction . Further, the gaseous products can be mixed with hydrogen gas present in the reaction volume 1 for reacting with the metal hydrogen carbonate and carbon dioxide and carbon monoxide produced in the calcination reaction. The solid products comprise a metal carbonate produced in the calcination reaction. Further, the solid products can be mixed with residues of the metal hydrogen carbonate that was provided in the reaction volume 1 for reacting with hydrogen gas. When the products are removed from the reaction volume 1, the gaseous products can be separated from the solid products, for example by a material separation .

[0054] The metal hydrogen carbonate can be mixed with a catalyst for catalyzing the methanation reaction prior to entering the reaction volume 1. In particular, the weight ratio of the metal hydrogen carbonate and the catalyst in the mixture is at least 2:1, for example at least 1:1, for instance at least 1:2. The mixture of the metal hydrogen carbonate and the catalyst can then be provided in the reaction volume 1. The catalyst is provided in solid form, in particular in the form of pellets or particles. For example, the catalyst is AI2O3 with 5 wt.-% Ni, AI2O3 with 5 wt.-% Ru, FesCg with between and including 2 wt.-% and 10 wt.-% Ni, for example with 5 wt.-% Ni, or Fe3O4with between and including 2 wt.-% and 10 wt.-% Ru, for example with 5 wt.-% Ru.

[0055] After the solid products leave the reaction volume 1, the catalyst is separated from the solid products. Due to the different densities of the solid products, in particular the metal carbonate, and the catalyst, a cyclone can be used for the separation. Alternatively, the solid mixture of the solid products, in particular the metal carbonate, and the catalyst can be dissolved, for example in water. In this instance, the solid products, in particular the metal carbonate, are dissolved and trans ferred into the aqueous phase and the solid, non-soluble catalyst material is recovered . Alternatively, the solid products , in particular the metal carbonate , and the catalyst can be separated by a magnetic field . In this case , the catalyst comprises a magneti zable carrier material such as ferromagnetic FeaCy .

[0056] The method for producing methane of the exemplary embodiment of figure 2 corresponds essentially to the method for producing methane of the exemplary embodiment shown in figure 1 . In addition, figure 2 shows the integration of four heat exchangers 21 , 22 , 23 , 24 . The four heat exchangers 21 , 22 , 23 , 24 can be used to reali ze a completely autothermal process . The temperatures T1 to T12 are temperatures for the hydrogen gas , the metal hydrogen carbonate , the gaseous products , or the solid products at the respective process stages as shown in figure 2 .

[0057] The hydrogen gas passes through the first heat exchanger 21 , the second heat exchanger 22 and the third exchanger 23 in this order prior to entering the reaction volume 1 . The metal hydrogen carbonate passes through the fourth heat exchanger 24 prior to entering the reaction volume 1 . The gaseous products pass through the third heat exchanger 23 , the fourth heat exchanger 24 , and the first heat exchanger 21 in this order after leaving the reaction volume 1 . The solid products pass through the second heat exchanger 22 after leaving the reaction volume 1 .

[0058] The first heat exchanger 21 is a gas / gas heat exchanger . The first heat exchanger 21 is configured for preheating the hydrogen gas by using the thermal energy carried by the gaseous products . The hydrogen gas enters the first heat exchanger 21 from an external hydrogen gas source with a first temperature T1 and is heated to a second temperature T2 . The gaseous products enter the first heat exchanger 21 after leaving the fourth heat exchanger 24 with a ninth temperature T9 and are cooled to a tenth temperature T10 .

[0059] The second heat exchanger 22 is a solid / gas heat exchanger . The second heat exchanger 22 is configured for preheating the hydrogen gas by using the thermal energy carried by the solid products . The hydrogen gas preheated in the first heat exchanger 21 is a further heated in the second heat exchanger 22 . The hydrogen gas enters the second heat exchanger 22 after leaving the first heat exchanger 21 with the second temperature T2 and is heated to a third temperature T3 . The solid products enter the second heat exchanger 22 directly after leaving the reaction volume 1 with an eleventh temperature Ti l and are cooled to a twel fth temperature T12 .

[0060] The third heat exchanger 23 is a gas gas / gas heat exchanger . The third heat exchanger 23 is configured for preheating the hydrogen gas by using the thermal energy carried by the gaseous products . The hydrogen gas preheated in the first heat exchanger 21 and the second heat exchanger 22 is further heated in the third heat exchanger changer 23 . The hydrogen gas enters the third heat exchanger 3 after leaving the second heat exchanger 22 with the third temperature T3 and is heated to a fourth temperature T4 . In particular, the hydrogen gas is heated in the third heat exchanger 23 to a fourth temperature T4 that is at most 25 % , in particular at most 20 % below the temperature in the reaction volume 1 . The gaseous products enter the third heat exchanger directly after leaving the reaction volume 1 with a seventh temperature T7 and are cooled to an eighth temperature T8 . The fourth heat exchanger 24 is a gas / solid heat exchanger . The fourth heat exchanger 24 is configured for preheating the metal hydrogen carbonate by using the thermal energy carried by the gaseous products . The metal hydrogen carbonate is heated in the fourth heat exchanger 24 to a minimum temperature for the metal hydrogen carbonate when entering the reaction volume 1 in order to achieve an autothermal process in the reaction volume 1 . The metal hydrogen carbonate enters the fourth heat exchanger 24 with a fi fth temperature T5 and is heated to a sixth temperature T 6 . The gaseous products enter the fourth heat exchanger 24 after leaving the third heat exchanger 23 with the eighth temperature T8 and are cooled to the ninth temperature T9 .

[0061] Table 1 shows temperatures T1 to T12 that enable an autothermal process management for the process design shown in figure 2 .

[0062] Table 1

[0063] The method for producing methane of the exemplary embodiment of figure 3 corresponds essentially to the method for producing methane of the exemplary embodiment shown in figure 2 . Figure 3 shows a large-scale technical setup . The metal hydrogen carbonate is provided in a solid silo 3 and fed into the fourth heat exchanger 24 via a flap valve 4 . The fourth heat exchanger 24 is an indirectly heated rotary kiln 26 for gas / solid heat trans fer . The metal hydrogen carbonate then enters the first reaction volume 1 located in a moving bed reactor through a flap valve 4 that is connected to a head part 5 of the moving bed reactor . The head part 5 serves as an inlet for the metal hydrogen carbonate and the hydrogen gas . The hydrogen gas that is provided from an external hydrogen gas source is fed through the first heat exchanger 21 , the second heat exchanger 22 and the third heat exchanger 23 prior to entering the reaction volume 1 . The first heat exchanger 21 and the third heat exchanger 23 are plate heat exchangers 25 for a gas / gas heat trans fer . The second heat exchanger 22 is a directly heated rotary kiln 26 for solid / gas heat trans fer .

[0064] The reaction of the metal hydrogen carbonate with the hydrogen gas takes place in the reaction volume 1 . The solid products , in particular the metal carbonate , leave the reaction volume 1 through the bottom part 6 of the moving bed reactor . The bottom part 6 serves as an outlet for the solid products and the gaseous products .

[0065] The solid products are fed through a flap valve 4 into the second heat exchanger 22 . Afterwards , the solid products enter a solid silo 3 through a further flap valve 4 .

[0066] The gaseous products leave the reaction volume through the bottom part 6 of the moving bed reactor and are then fed through the third heat exchanger 23 , the fourth heat exchanger 24 , and the first heat exchanger 21 . The method for producing methane of the exemplary embodiment of figure 4 corresponds essentially to the method for producing methane of the exemplary embodiment shown in figure 2 . In contrast , figure 4 shows the integration of only the first heat exchanger 21 . The first heat exchangers 21 can be used to reali ze a completely autothermal process . The temperatures T13 to T18 are temperatures for the hydrogen gas , the metal hydrogen carbonate , the gaseous products , or the solid products at the respective process stages as shown in figure 4 .

[0067] The hydrogen gas passes through the first heat exchanger 21 prior to entering the reaction volume 1 . The metal hydrogen carbonate enters the reaction volume 1 without passing through a heat exchanger . The gaseous products pass through the first heat exchanger 21 after leaving the reaction volume 1 . The solid products leave the reaction volume 1 without passing through a heat exchanger .

[0068] The first heat exchanger 21 is a gas / gas heat exchanger . The first heat exchanger 21 is configured for preheating the hydrogen gas by using the thermal energy carried by the gaseous products . The hydrogen gas enters the first heat exchanger 21 from an external hydrogen gas source with a thirteenth temperature T13 and is heated to a fourteenth temperature T14 . The gaseous products enter the first heat exchanger 21 after leaving the reaction volume 1 with a seventeenth temperature T17 and are cooled to an eighteenth temperature T18 .

[0069] Table 2 shows temperatures T13 to T18 that enable an autothermal process management for the process design shown in figure 4 . Table 2

[0070] Figure 5 shows an experimental setup of a method for producing methane according to an exemplary embodiment . The experimental setup was used to demonstrate the direct conversion of a metal hydrogen carbonate with hydrogen gas to methane in a reaction volume 1 . In this experimental setup, the reaction volume 1 is located in a discontinuous packed bed reactor that can be uni formly tempered within an oven box 11 . The temperature in the reaction volume 1 and in the oven box 11 can be monitored with temperature sensors 10 . Hydrogen gas as well as carrier gases such as nitrogen gas and argon gas are added to the reaction volume 1 from gas tanks 7 via valves 8 and mass flow controllers 9 . The resulting gaseous products are detected using analyzers 12 for carbon dioxide , methane , and carbon monoxide , respectively, before leaving the experimental setup as exhaust gases 13 .

[0071] With the experimental setup shown in figure 5 , FeaCg with 3 wt . -% to 10 wt . -% Ni was tested as a catalyst comprising a magneti zable carrier material . Using 2 g of a catalyst being FeaCg with 3 wt . -% Ni , a signi ficant catalytic activity was observed starting from a temperature of 340 ° C and methane yields of up to 50 % and a space velocity of 3000 h-1were achieved at 375 ° C . This result proves the general suitability of catalysts comprising a magneti zable carrier material for the method for producing methane described herein . Figure 6 shows the resulting methane yield YCH4 in % for the catalytic conversion of potassium hydrogen carbonate with hydrogen gas as a function of the temperature T in ° C in the reaction volume 1 according to the following formula : 2 KHCO3 + 4 H2CH4+ K2CO3 + 3 H20. The data was obtained using the experimental setup as described in conj unction with figure 5 . Figure 6 shows that at 310 ° C, the methane yield is almost 100 % .

[0072] Figure 7 shows the average dwell time of hydrogen gas in the reaction volume 1 as a function of the temperature T in ° C in the reaction volume 1 to achieve a complete conversion of carbon dioxide to methane . The data was obtained using the experimental setup as described in conj unction with figure 5 .

[0073] The reaction volume 1 contained 1 g of potassium hydrogen carbonate and 5 g of a catalyst being A12O2with 5 % Ru . The speci fic surface area of the catalyst is within a range of 100-250 m2 / g . It can be seen that the methanation reaction starts at a temperature in the reaction volume 1 of 230 ° C . As the temperature increases , the required average dwell time decreases logarithmically . Starting from a temperature of 250 ° C, space velocities of more than 9000 GHSV ( gas hourly space velocity) result . These are suf ficient for large-scale applications .

[0074] Figure 8 shows method steps for producing the metal hydrogen carbonate that is calcinated in the reaction volume 1 . In the method step Al , an absorbent comprising at least a metal carbonate is contacted with a gas stream comprising carbon dioxide . The metal carbonate in the absorbent can be the metal carbonate produced in the reaction volume 1 during the calcination of the metal hydrogen carbonate . In the method step A2 which can take place simultaneously to the method step Al , the metal carbonate of the absorbent is partially converted into the metal hydrogen carbonate . This produces a loaded absorbent . Subsequently, in the method step A3 , at least a portion of the metal hydrogen carbonate is precipitated from the loaded absorbent . In the method step A4 , the precipitated metal hydrogen carbonate is separated from the aqueous phase of the loaded absorbent . The precipitated metal hydrogen carbonate can then be provided in the reaction volume 1 .

[0075] The features and exemplary embodiments described in connection with the figures can be combined with each other according to further exemplary embodiments , even i f not all combinations are explicitly described . Furthermore , the exemplary embodiments described in connection with the figures may have alternative or additional features as described in the general part .

[0076] The invention is not restricted to the exemplary embodiments by the description on the basis of said exemplary embodiments . Rather, the invention encompasses any new feature and also any combination of features , which in particular comprises any combination of features in the patent claims and any combination of features in the exemplary embodiments , even i f this feature or this combination itsel f is not explicitly speci fied in the patent claims or exemplary embodiments .

[0077] This patent application claims the priority of German patent application DE 10 2024 111 355 . 3 , the disclosure content of which is hereby incorporated by reference . References

[0078] I reaction volume

[0079] 21 first heat exchanger

[0080] 22 second heat exchanger

[0081] 23 third heat exchanger

[0082] 24 fourth heat exchanger

[0083] 25 plate heat exchanger

[0084] 26 rotary kiln

[0085] 3 solid silo

[0086] 4 flap valve

[0087] 5 head part

[0088] 6 bottom part

[0089] 7 gas tank

[0090] 8 valve

[0091] 9 mass flow controller

[0092] 10 temperature sensor

[0093] I I oven box

[0094] 12 analyzer

[0095] 13 exhaust gas

[0096] Al method step

[0097] A2 method step

[0098] A3 method step

[0099] A4 method step

Claims

Patent claims1 . A method for producing methane comprising- providing a metal hydrogen carbonate and hydrogen gas in a reaction volume ( 1 ) ,- reacting the metal hydrogen carbonate with the hydrogen gas in the reaction volume ( 1 ) to form products , wherein a first product is methane , wherein the products comprise gaseous products and solid products , wherein the gaseous products are used for heating the hydrogen gas and / or the metal hydrogen carbonate prior to reacting the metal hydrogen carbonate , and / or wherein the solid products are used for preheating the hydrogen gas prior to reacting the metal hydrogen carbonate .2 . The method according to the preceding claim, wherein reacting the metal hydrogen carbonate comprises- calcinating the metal hydrogen carbonate to form carbon dioxide , and- methani zing the carbon dioxide .3 . The method according to the preceding claim, wherein thermal energy released during methani zing the carbon dioxide is used for calcinating the metal hydrogen carbonate .4 . The method according to at least one of the preceding claims , wherein the metal hydrogen carbonate is essentially a solid in the reaction volume ( 1 ) .5 . The method according to at least one of the preceding claims ,wherein a temperature in the reaction volume (1) is at most350 °C.

6. The method according to at least one of the preceding claims , wherein a gas volume in the reaction volume (1) at most consists of hydrogen gas, water vapor, carbon dioxide, carbon monoxide, methane, and residuals of air.

7. The method according to at least one of the preceding claims , wherein reacting the metal hydrogen carbonate is an at least 70 % autothermal process.

8. The method according to at least one of the preceding claims , wherein the hydrogen gas passes through a first heat exchanger (21) , a second heat exchanger (22) , and a third heat exchanger (23) in this order prior to entering the reaction volume (1) , wherein the metal hydrogen carbonate passes through a fourth heat exchanger (24) prior to entering the reaction volume (1) , wherein the gaseous products pass through the third heat exchanger (23) , the fourth heat exchanger (24) , and the first heat exchanger (21) in this order after leaving the reaction volume ( 1 ) , and wherein the solid products pass through the second heat exchanger (22) after leaving the reaction volume (1) .

9. The method according to at least one of the preceding claims ,wherein the hydrogen gas passes through a first heat exchanger (21) prior to entering the reaction volume (1) , and wherein the gaseous products pass through the first heat exchanger (21) after leaving the reaction volume (1) .

10. The method according to at least one of the preceding claims , wherein providing the metal hydrogen carbonate comprises providing a mixture of the metal hydrogen carbonate and a catalyst .

11. The method according to the preceding claim, wherein a weight ratio of the metal hydrogen carbonate and the catalyst in the mixture is at least 2:1.

12. The method according to at least one of the claims 10 or 11, wherein a second product is a metal carbonate, and wherein the catalyst is separated from the metal carbonate by dissolving the metal carbonate.

13. The method according to at least one of the claims 10 or 11, wherein a second product is a metal carbonate, and wherein the catalyst is separated from the metal carbonate by means of a magnetic field.

14. The method according to at least one of the preceding claims , wherein the metal hydrogen carbonate is produced as follows: - contacting an absorbent with a gas stream comprising carbon dioxide, wherein the absorbent comprises a metal carbonate,- producing a loaded absorbent , wherein the metal carbonate is at least partially converted to a metal hydrogen carbonate ,- precipitating at least a portion of the metal hydrogen carbonate from the loaded absorbent , and- separating the precipitated metal hydrogen carbonate from the aqueous phase of the loaded absorbent .15 . The method according to the preceding claim, wherein a second product is a metal carbonate , and wherein the metal carbonate is used as the metal carbonate in the absorbent .

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