METHOD FOR THE REMOVAL AND IMMOBALIZATION OF CARBON DIOXIDE FROM THE ATMOSPHERE AND / OR EXHAUST AIR

Description

[0001] The invention relates to a process for removing and immobilizing carbon dioxide (CO2) from the atmosphere and / or an exhaust gas. CO2 is captured from the air and / or an exhaust gas and converted into solid carbon, which is then permanently stored.

[0002] Carbon dioxide capture and storage (CCS) processes are known to experts for reducing CO2 in the atmosphere. The greenhouse effect has been recognized for about 200 years (J.B. Fourier), and it was discussed at the first World Climate Conference in Geneva in 1979. The removal from the atmosphere and immobilization of greenhouse gases, especially CO2, is also known as sequestration and involves the capture of CO2 from industrial sources and power plants, its transport to a storage site, and, finally, its permanent storage, isolating it from the atmosphere.

[0003] To avoid CO2 emissions, conventional CCS processes capture CO2 and then store the gas. This process involves first removing particles and sulfur compounds from the exhaust gas to be treated. In the next step, the CO2 is separated from the exhaust gas, compressed, transported away if necessary, and stored underground. It is controversial whether this results in permanent binding of CO2 to minerals or whether the gas will be released back into the atmosphere. Furthermore, there is a risk that the underground injection of CO2 under high pressure could lead to earthquakes. Furthermore, mixing with and dissolving CO2 in groundwater could trigger so-called "cold geysers," which would also cause further emissions.

[0004] Another disadvantage of CCS technology is the lack of infrastructure for the necessary transport of CO2. Emission sources such as power plants or cement plants are usually located far from suitable CO2 storage sites, which would require the construction of suitable pipelines.

[0005] In DE 10 2013 112 205 A1, however, it is pointed out that carbon in solid form can be stored long-term and without problems, for example in old coal seams.

[0006] Kamman et al., in "Biochar: A Path to Permanent Carbon Sequestration", Environmental Observation and Climate Impact Research Station Linden, Hessian State Office for the Environment and Geology, Institute of Plant Ecology, Justus Liebig University Giessen, April 2010, pages 1 to 8, DOI 14902790298116661323, discuss the use of biochar in soils.

[0007] DE 10 2007 037 672 A1 describes a process for harmonizing electricity supply / consumption curves through intermediate storage and the inclusion of CO2 utilization. Pure CO2 is extracted from CO2-containing exhaust gases and then temporarily or permanently stored, corresponding to a known CCS process. The splitting of hydrocarbons is not planned, and solid carbon storage does not occur.

[0008] WO 2015 / 044407 A1 describes a process for storing electricity from renewable sources. Pure hydrogen, obtained by electrolysis of water, is reacted with pure CO2 or a CO2 / CO / H2 mixture to produce methane. Methane is temporarily stored and subsequently split into carbon and hydrogen. The carbon is reused to produce CO2 or a CO2 / CO / H2 mixture. CO2 is neither stored nor removed from the atmosphere, as the carbon is fully recycled in the process.

[0009] J. Temple, in "Climate Engineers Get Serious, Scrub CO2 Out of the Air," Technology Review, pages 49 to 52, June 2017, describes the scrubbing of CO2 from the air for plant fertilization. Filters coated with adsorbents are used for separation, which require heating to desorb the CO2, which requires a corresponding amount of energy.

[0010] WO 2014 / 170184 A1 relates to an adsorption device for separating gas, in particular CO 2 , as does WO 2015 / 185434 A1.

[0011] WO 2016 / 005226 A1 is directed to a process for cyclic adsorption or desorption in CCS processes.

[0012] Wurzbacher, JA, in "Development of a temperature-vacuum swing process for CO2 capture from ambient air", 2015, ETH Zurich Research Collection, https: / / doi.org / 10.3929 / ethz-a-010432423, describes a process for the extraction of concentrated CO2 from the atmosphere by adsorption.

[0013] Gebald, C., in "Development of amine-functionalized adsorbent for carbon dioxide capture from atmospheric air", 2014, ETH Zurich Research Collection, https: / / doi.org / 10.3929 / ethza-010171623, discloses the use of aminosilanes as adsorbents used to capture CO 2 from the atmosphere.

[0014] The documents US 9,095,813, US 2015 / 14815661, US 8,119,091, US 8,728,428, US 9,975,100, US 8,871,008, US 9,637,393, US 2017 / 15622883, US 2017 / 15591324, CA 2017051581 are also aimed at the removal of CO 2 from the atmosphere.

[0015] E. Katifu, in "Carbon dioxide absorption using fresh water algae and identifying potential uses of algal biomass", Faculty of Engineering and the Built Environment, University of the Witwatersrand, 2011, Johannesburg, discusses the use of micro-algae to reduce CO2 emissions.

[0016] Documents GB 2 470 452 A, CN 107 058 055 A, and US 2012 / 276616 A deal with the production of biomethane from plant biomass. From the papers MURADOV NZ ET AL: "Green path from fossil-based to hydrogen economy: An overview of carbon-neutral technologies," INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, ELSEVIER, AMSTERDAM, NL, Vol. 33, No. 23, (2008-12-01), pages 6804-6839, DOI: 10.1016 / J.IJHYDENE.2008.08.054; US 2021 / 371277 A; and STEINBERG M ED - KURT EROL ET AL: "Fossil fuel decarbonization technology for mitigating global warming", INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, ELSEVIER, AMSTERDAM, NL, Vol. 24, No. 8, (1999-08-01), pages 771-777, DOI: 10.1016 / S0360-3199(98)00128-1, it is known to split methane into its elements and remove the carbon from the atmosphere in the long term. Finally, the production of synthetic hydrocarbons from carbon dioxide and hydrogen is known from WO 2018 / 112654 A.

[0017] The issue of removing emitted CO2 from the air (carbon dioxide removal, CDR) is gaining importance. It is now considered certain that the climate goal of limiting temperature rise to 1.5°C or 2.0°C cannot be achieved through emissions reduction alone. Rather, a continuous CO2 removal from the atmosphere appears necessary, encompassing 100 GT to 1000 GT of CO2 by the year 2100, according to the IPCC Special Report "Global Warming of 1.5°C" of the Intergovernmental Panel on Climate Change (IPCC), October 2018. Only a few processes exist for capturing the CO2 already released from the atmosphere.

[0018] These can essentially be divided into four groups: i) Combustion of biomass and storage of CO2: BECCS (bioenergy with carbon capture and storage), ii) Removal of CO2 from the ambient air by physical and / or chemical sorption processes, in particular by chemisorption using amines, followed by injection - DACCS (direct air carbon capture and storage), iii) Carbon enrichment in fields by adding biochar, iv) Processes that increase the capacity of soils or water bodies to absorb CO2. For example, crushed minerals are spread over land to assist in the chemical binding of CO2 from the air. Ocean alkalinisation has also been proposed, whereby ground minerals lower the pH of the water and thus promote CO2 storage in the ocean.

[0019] The BECCS and DACCS processes are based on capturing and sequestering CO2 underground. In the BECCS process, biomass is used as fuel, and biogenic CO2 is removed from the exhaust gas. In the DACCS process, CO2 is extracted from the ambient air using sorption processes, i.e., chemical or physical processes. The gaseous CO2 must then be transported to remote storage facilities and geologically stored.

[0020] In the BECCS, DACCS and CCS processes in general, CO2 is separated and stored as such, although there are known disadvantages due to the compression and storage of gases.

[0021] In the DACCS process, ambient air is forced through adsorption material with the help of fans, whereby CO2 is physically and / or chemically bound to the surface of the adsorption material. After a saturation equilibrium is reached, CO2 is desorbed by heating in a second step, thus regenerating the adsorption material. Typically, such systems use at least two devices that operate in phase shifts, i.e., alternately, with adsorption taking place in one of the devices, while regeneration is carried out in the second. This type of alternation is also known as the swing process. This process is characterized by the need to filter significant amounts of air, which is due to the low concentration of CO2 in the air (approx. 400 ppm).

[0022] Gaseous CO2 is produced, which, for example, must be stored geologically for long-term storage. Therefore, storage in gaseous form is necessary here as well.

[0023] With regard to the CO2 balance, the operation of a DACCS plant also requires the availability of emission-free energy to generate the heat required for desorption, as well as the suitability of geological formations for storing the gaseous CO2.

[0024] Among other options for capturing CO2, landfilling biomass in a green form, for example through composting, is not effective in ensuring the permanent removal of CO2 from the atmosphere, since the decomposition of biomass through aerobic processes leads to the re-formation of CO2. Furthermore, the storage of solid wood in the form of logs, for example, requires the acceptance of long growth periods of the biomass, ranging from several years to decades, in addition to CO2 emissions.

[0025] There is also discussion about pyrolyzing biomass and storing the resulting carbon, also known as biochar, in landfills or using it in agriculture. This can also lead to further CO2 emissions, as carbon can be exposed to the oxidizing effects of atmospheric oxygen. Furthermore, the energy contained in the biomass remains unused in this form. However, biomass consists largely of hydrogen, which, if used for energy, would not produce CO2 emissions. This potential is lost when pyrolyzed biomass is stored in landfills or used in landscapes.

[0026] In addition, the application of pH-altering chemicals such as minerals to land areas or for ocean alkalization may result in as yet unknown environmental effects.

[0027] One object of the invention is to separate CO2 from the atmosphere and / or exhaust gases and reliably prevent re-emission. Furthermore, the amount of energy required for this purpose should be reduced, or at least part of the energy converted in the process should be usable. Disclosure of the invention

[0028] A process for removing and immobilising carbon dioxide from the atmosphere and / or an exhaust gas is proposed, comprising the steps of: a) converting the carbon dioxide from the atmosphere and / or an exhaust gas into biomass by means of photosynthesis, preferably on agricultural land, in particular in a greenhouse, b) carrying out a biogas reaction in which the biomass produced in step a) is converted into biogas containing methane and carbon dioxide, in particular in a biogas reactor, c) separating the methane from the resulting biogas, d) splitting the methane into carbon and hydrogen, the carbon being obtained as a solid, e) collecting the resulting carbon, f) depositing the resulting carbon and g) reacting carbon dioxide from the biogas with the hydrogen obtained in step d) to form a hydrocarbon mixture.

[0029] The process according to the invention comprises three biological or chemical reactions to remove CO2 from the air. These are photosynthesis in step a), the biogas reaction, in particular anaerobic digestion, in step b), and the splitting of methane, in particular pyrolysis of methane, in step d).

[0030] In step a), photosynthesis takes place. Photosynthesis involves the conversion of low-energy starting materials, namely CO2 and water, to substances with higher energy levels under the influence of light. In nature, photosynthesis leads to the formation of biomass and its byproducts, such as organic waste and farmyard manure, for example, in the form of manure and slurry. photosynthesis Photosynthesis promotes the growth of plants and algae in nature. Photosynthesis is also used for the industrial production of biomass in greenhouses or algal bioreactors.

[0031] Step a) of producing biomass can take place in an agricultural process, i.e. on an agricultural land, and / or in a greenhouse.

[0032] Biomass is defined, in particular, as substances and mixtures thereof produced through photosynthesis. These are also referred to as primary biomass. Biomass also includes substances and mixtures thereof that have been created as a result of the use of primary biomass and have retained their biogenic character. Biomass can include, in particular, straw, forest residues, farmyard manure, food waste, and / or municipal waste.

[0033] In industrial applications, it is advantageous to optimize biomass production by adjusting reaction parameters such as the concentration of CO 2 in the ambient air. The efficiency of photosynthesis increases, depending on the plant, with increasing CO 2 concentration. In C 4 plants such as corn, sugar cane or millet, maximum growth, i.e. maximum efficiency of photosynthesis, is already achieved at today's atmospheric conditions with regard to CO 2 concentration. In C 3 plants such as wheat, rye, barley, potatoes, soybeans and trees, growth rates continue to increase with increasing CO 2 concentration. In step a), C 3 plants are preferably used to convert CO 2 via biosynthesis. Maximum efficiency of photosynthesis in C 3 plants is achieved at more than 1000 ppm CO 2.Overall, increasing the CO2 concentration in the ambient air under optimal conditions regarding temperature, irrigation, and nutrient supply, especially nitrogen, can lead to up to 40% higher yields in biomass production, especially in greenhouses. Yields can be further increased by using fast-growing C3 plants. Increased CO2 concentration also increases the growth rate of algae.

[0034] The exhaust gas whose CO2 is potentially converted into biomass in step a) can, for example, be exhaust gas produced by the combustion of fossil fuels in a power plant. The exhaust gas can also be a by-product of an industrial manufacturing process, or it can be a production gas produced during the extraction of fossil fuels such as coal, crude oil, or natural gas. One example of a production gas is mine gas. The largest share of the resulting exhaust gases comes from the production of electricity from fossil fuels.

[0035] Industrial processes are equally important sources of climate-relevant emissions. One example of an industrial manufacturing process is cement production, where CO2 emissions are largely attributable to the calcination process. During the production of iron and steel, as well as the associated auxiliary materials, the production emissions contain CO2. Climate-relevant emissions can also occur in refineries, for example.

[0036] These exhaust gases, which are normally released into the atmosphere, can be captured after they are generated and fed into the proposed process.

[0037] In addition to the carbon oxides already mentioned, industrial exhaust gases usually contain other substances that must be taken into account when treating the exhaust gas. These include methane, hydrogen, water vapor, and the inert gas nitrogen, with the nitrogen content being up to 97% by volume. Other exhaust gas components may include contaminants such as hydrogen sulfide, mercury, and / or heavy metals. These contaminants require pretreatment to achieve prescribed limit values. Oxygen can also be found in the exhaust gas from power plants in concentrations of up to 6% by volume. Exhaust gases produced during the production of natural gas, for example, contain not only methane but also CO2 and nitrogen in significant proportions.

[0038] Preferably, the exhaust gas is cleaned of dust, sulphur-containing compounds and other contaminants such as nitrogen oxides, hydrogen chloride, hydrogen fluoride, mercury, other metals and other organic or inorganic substances before being fed in using conventional, already known methods.

[0039] The exhaust gas supplied to step a) is in particular a mixture comprising CO 2. Furthermore, the exhaust gas may comprise, as further components, at least one inert gas such as nitrogen or argon and, optionally, water vapor.

[0040] The exhaust gas used in step a) preferably originates at least partially from the use of the hydrogen produced in step d) or the biogas formed in step b), in particular the methane. If appropriate, the exhaust gas is desulfurized, cleaned of other impurities, and / or dedusted in a pretreatment. Further preferably, the exhaust gas used in step a) consists exclusively of exhaust gas that is recycled within the process. Even more preferably, the exhaust gas used in step a) originates exclusively from the biogas produced in step b), in particular from the use of the hydrogen produced in step d). Accordingly, the exhaust gas can originate from the biogas directly or indirectly, i.e., after subsequent decomposition of the methane.

[0041] The biogas reaction in step b) particularly comprises an anaerobic digestion reaction. During anaerobic digestion, the biomass is converted into biogas, i.e., a mixture of predominantly methane and carbon dioxide. The biogas produced in step b) preferably contains a total of at least 90 vol.%, more preferably at least 95 vol.%, of methane and CO2, based on the total biogas.

[0042] In particular, the biomass is hydrolyzed under the action of various microorganisms, such as bacteria. During the biogas reaction, the pH is preferably in the range of 6 to 7, more preferably from 6.5 to 7, and especially from 6.6 to 6.7. The temperature during the biogas reaction is preferably constant and more preferably in a range of 25°C to 45°C, more preferably from 30°C to 40°C, in particular from 33°C to 37°C, for example at 35°C. In the biogas reaction, substances such as sugars, amino acids, and / or fats are degraded. Hydrolysis is preferably followed by fermentation or acetylation, forming acids that are subsequently converted into methane and carbon dioxide. The described reaction conditions represent an optimum for methane-forming bacteria.

[0043] The preferred biomass used in step b) is plants, particularly C3 plants, biowaste, farmyard manure such as manure and / or slurry, and / or municipal waste. The biomass produced in step a) can be used directly in step b). Thus, plants produced in step a) can be directly fed into the biogas reaction in step b). Alternatively, the biomass produced in step a) can be at least partially used or converted first, so that it is present in step b) as biowaste, municipal waste, or fertilizer.

[0044] The biogas reaction is preferably carried out in a closed container, also known as a fermenter. Before the biogas reaction is carried out, the biomass can be crushed and, if necessary, sorted. The biomass can be fed continuously to the fermenter. The residence time of the biomass in the fermenter is preferably more than one day. The biogas produced accumulates, in particular, in an upper region of the fermenter above a liquid and solid phase. The biogas preferably contains at least 40 vol.%, more preferably 50 vol.% to 75 vol.%, in particular 62 vol.% to 75 vol.% methane, based on the total biogas. The biogas also contains CO2 and, if necessary, water vapor, hydrogen sulfide, and / or ammonia.

[0045] Controlled fermentation, the biogas reaction, especially in a closed container, offers the advantage of reducing emissions, for example in the form of acids that can contaminate groundwater or methane emissions that are released uncontrolled into the atmosphere and thus contribute to climate change.

[0046] The produced biogas contains CO2, which can be separated in a biogas treatment process, particularly a CO2 separation device, and fed back into photosynthesis. Step c) can therefore also be referred to as biogas processing.

[0047] For example, polyimide hollow fiber membranes can be used to separate carbon dioxide.

[0048] In step g), CO2 from the biogas is converted with hydrogen produced in step d) to form a hydrocarbon mixture.

[0049] Preferably, the CO2 from the biogas, after the separation of methane in step c), is reacted with the hydrogen produced in step d). The hydrocarbon mixture obtained from the reaction of the CO2 with the hydrogen contains, in particular, kerosene, gasoline, and / or waxes.

[0050] To convert the CO2 from the resulting biogas into a hydrocarbon mixture, the CO2 can be fed into a Fischer-Tropsch device.

[0051] As an alternative to a Fischer-Tropsch device, the CO2 can also be converted into methane and water using the hydrogen produced in step d). This can be achieved, for example, in a catalytic Sabatier reaction or a biochemical process using methane-forming microorganisms. Suitable methane-forming microorganisms include, for example, Methanobacterium, Methanospirillium hungatii or Methanosaeta.

[0052] In addition to the conversion of CO2 with the hydrogen obtained in step d) to form a hydrocarbon mixture, a portion of the CO2 from the resulting biogas can be recycled to step a) after the separation of methane in step c). Furthermore, a portion of the CO2 from the resulting biogas can be liquefied after the separation of methane in step c).

[0053] To increase the yield of solid carbon, it is further particularly preferred to introduce at least some of the hydrocarbons obtained in step g) into the methane decomposition reaction in step d). In this case, not only the methane is decomposed into carbon and hydrogen, but also the hydrocarbons contained in the hydrocarbon mixture.

[0054] The separation of the methane in step c) is preferably carried out physically, in particular by means of condensation, adsorption, and / or a membrane process. The separation of the methane from the resulting biogas in step c) is preferably carried out continuously.

[0055] For the separation of methane, pressure swing adsorption, temperature-vacuum adsorption, chemical adsorption, membrane separation, pressure gas scrubbing processes and / or alternating concentration adsorption are used in particular.

[0056] After separation in step c), the material stream of the separated methane preferably contains more than 95 vol.% methane and more preferably not more than 1 vol.% CO 2 .

[0057] In step d), which can also be referred to as pyrolysis, at least a portion of the methane formed in step b) and, if the hydrocarbons obtained in step g) are also recycled to step d), the hydrocarbons are split into the elements hydrogen and carbon. The reactions that take place in step d) can be represented by the following reaction equations: CH 4 → 2H 2 + C CH 3 (CH 2 ) nCH 3 → (n+3)H 2 + (n+2)C

[0058] These reactions are endothermic, meaning that energy must be supplied to the reaction system for the reaction to occur.

[0059] Preferably, the splitting of the methane and optionally the hydrocarbons in step d) is carried out by means of a pyrolysis process and in particular at a temperature of at least 800°C, more preferably at least 1000°C, in particular more than 1200°C, further preferably more than 1400°C.

[0060] The energy required to carry out the aforementioned reaction is preferably provided in the form of electricity from renewable sources such as wind, biogas, and / or photovoltaics, which cannot currently be taken from the power grid. In particular, no fossil fuel is used for this purpose. Alternatively, a portion of the biogas or the hydrogen produced can be used to provide the energy required for the splitting process.

[0061] The cracking of methane and, if present, hydrocarbons can be carried out by thermopyrolysis, in which the necessary energy is provided by direct or indirect heating. Regarding direct thermal cracking, processes are known in which methane and / or hydrocarbons flow through a column of liquid metal in the form of bubbles, heating up and cracking. Carbon collects on the surface of the metal column, hydrogen escapes and is sent for further processing. A thermal process is also known in which the cracking takes place in a moving bed consisting of carbon granules.

[0062] Furthermore, the splitting of the methane and, if appropriate, the hydrocarbons can be carried out using an arc, with the energy being supplied by electrical discharge in the gas phase. Such a process is known to those skilled in the art as the Kvaerner process. The splitting of the methane and, if appropriate, the hydrocarbons can be carried out accordingly in a plasma hydrogen generator. The plasma is generated, for example, by irradiating electromagnetic waves. The plasma splitting of the methane and, if appropriate, the hydrocarbons takes place at temperatures of up to 2000°C and at a locally high energy density.

[0063] The decomposition of the methane and, optionally, the hydrocarbons can alternatively be carried out in the presence of at least one catalyst at elevated temperature, in particular in a range from 800°C to 1000°C. At least one metal, in particular selected from the group consisting of Fe, Ni, and Cr, and / or activated carbon can be used as the catalyst.

[0064] Pyrolysis produces a gas phase containing hydrogen as a gaseous product and carbon, particularly elemental carbon, as a solid. This reaction splits the energy source methane and, if present, the hydrocarbons into two substances. The hydrogen can be used for energy without any negative impact on the climate, since the combustion of hydrogen with air produces water or water vapor, not a greenhouse gas. If, alternatively, soot were burned to generate the corresponding energy, for example, 3.67 kg of climate-damaging CO2 would be produced when 1 kg of soot was burned.

[0065] The gas phase after pyrolysis preferably comprises hydrogen, an inert gas, methane, and optionally hydrocarbons. The gas phase can be fed at least partially to a separation device, in particular a membrane, producing hydrogen and a residual gas.

[0066] Preferably, step d) is followed by a filter in which the carbon is separated from the hydrogen. The conversion of the methane and, if appropriate, the hydrocarbons into hydrogen and carbon preferably takes place with a yield of approximately 96 to 97%.

[0067] Preferably, after the methane and optionally the hydrocarbons have been split in step d), the hydrogen is separated from the residual gas, i.e. other gaseous components, in particular by means of a membrane process.

[0068] The hydrogen can be used for material or energy purposes and can be fed into a power plant or a transport and distribution system. The residual gas remaining after the hydrogen is separated from the gas phase is preferably fed into the power plant. The power plant preferably includes a gas engine for generating electricity and heat. The heat generated in the power plant can be used, at least in part, to generate cold. The gas phase, i.e., without separation of the hydrogen, can also be fed into the power plant.

[0069] The electricity generated in the power plant is preferably used to operate the reactor for splitting methane and, if necessary, hydrocarbons and / or fed into the public power grid to stabilize the grid. Furthermore, the power plant generates heat and exhaust gases, which can be used to produce the biomass in step a), particularly in a greenhouse.

[0070] In a preferred embodiment, part of the hydrogen is returned to the reactor to split the methane and, if appropriate, the hydrocarbons.

[0071] Preferably, at least a portion of the hydrogen produced during the fission is used as a starting material in the chemical industry, as an energy source for generating electricity and / or heat, with the heat optionally being used at least in part to generate cold, or as a fuel for vehicles. To generate energy, the hydrogen can be mixed with combustion air and burned in a gas turbine. The gas turbine can drive a power generator that generates electricity. The exhaust gases from the combustion can be used via a steam generator to generate process steam.

[0072] It is also conceivable to convert the hydrogen into electrical power using a fuel cell or to use the hydrogen for other purposes, such as refueling hydrogen-powered vehicles or for heating.

[0073] Preferably, at least a portion of the hydrogen produced in step d) or the biogas produced in step b) is used as an energy source for splitting the methane and optionally the hydrocarbons in step d). Preferably, the energy required for the splitting according to step d) is provided at least partially by using the hydrogen produced in step d) and optionally the residual gas and / or generated from renewable sources. Alternatively or additionally, the methane separated in step c) can also be used to generate electricity and / or heat. For example, 30 to 50 vol.% of the biogas produced, in particular in the form of methane and / or hydrogen, can be used to generate electricity and / or heat.

[0074] Preferably, the hydrogen produced in step d) is used at least partly as a starting material for syntheses in the chemical industry, as an energy carrier for the generation of electricity, heat, optionally cold and / or as fuel for vehicles.

[0075] Preferably, after the methane and optionally the hydrocarbons have been split in step d), the hydrogen is separated from the carbon, in particular by filtration. The separated hydrogen is fed to step g) together with the CO2 from the biogas to produce hydrocarbons, in particular methane. This can significantly increase the yield of solid carbon.

[0076] In particular, the carbon obtained as a solid in step d) is not used as an energy source. The carbon is preferably collected, transported to a landfill site, and permanently stored or disposed of. Preferably, the carbon obtained in step d) is completely landfilled. Further preferably, the carbon obtained in step d) is separated from the gas phase containing the hydrogen.

[0077] More preferably, the carbon obtained in step d) is mixed with other components, in particular other solids, before being deposited in step f) in such a way that energetic use is no longer possible, in order to permanently immobilize the carbon and store it particularly securely. Examples of other solids that can be used include sand, clay, gravel, construction rubble, slag, stones, waste, in particular from industrial dismantling, or a combination of several of these materials. Accordingly, the carbon obtained in step d) is preferably immobilized, and permanent immobilization is ensured by mixing the resulting carbon with another solid. The resulting solid mixture, which comprises the resulting carbon with at least one other solid, is stored, in particular, geologically and permanently in a carbon sink, such as a mine.

[0078] Preferably, the carbon obtained as a solid in step d) is mixed with at least one other solid, in particular sand and / or rock, before being deposited in step f).

[0079] The depositing in step f) preferably extends for at least 30 years, more preferably at least 50 years.

[0080] Carbon is preferably deposited underground, for example, in old mines, particularly potash mines or salt mines. However, carbon is also suitable as backfill material for opencast mines, excavations, gravel, gypsum, or clay pits. To prevent geological damage and to fulfill nature conservation obligations, abandoned mining sites undergo extensive remediation and recultivation measures. The cavities of the underground mines and the pits themselves are filled with mineral material. Suitable materials include construction rubble, slag, stone, waste from industrial dismantling, and other industrial waste of sufficient strength. If carbon were used alone, it would first have to be compressed for backfilling.Mixing the powdered carbon with minerals or waste proves to be advantageous because carbon can penetrate into the porous structure of the minerals and be permanently fixed there.

[0081] The disposal in step f) of the process according to the invention can also be understood as the use of the carbon produced as a solid in the construction industry, in particular road construction, and / or in agriculture.

[0082] The material use of carbon in solid form in industrial products such as electrical cable sheathing, insulation, underground structures, etc., can also be classified as landfilling, as long as it is ensured that the lifetime of the applications extends to at least 30 years, more preferably at least 50 years. In this case, the carbon in solid form is usually mixed into the material used for the products.

[0083] Preferably, disposal includes exclusively geological disposal, in particular underground disposal, for example in mines.

[0084] Preferably, at least steps a) to e) and step g) are carried out in one module. A module is understood to be a spatially coherent unit. Further preferably, hydrocarbons are produced in the module, using CO2 and the residual gas.

[0085] Furthermore, it is preferable to install several modules in different locations.

[0086] Preferably, at least steps a) to e) and g) are carried out in at least two modules, i.e. in at least two spatially connected units, and more preferably, the at least two modules are connected to a central control center.

[0087] Preferably, the resulting carbon is mixed with another solid outside or independently of the modules. The resulting carbon originates from at least one module. The mixing process can be connected to the central control center, particularly via data transmission. Advantages of the invention

[0088] With the described process, the CO2 "extracted" from the atmosphere and / or exhaust gases is removed from the atmosphere. Permanent immobilization of the carbon is possible, thus achieving a purification effect for the atmosphere.

[0089] Compared to the combustion of this carbon, geological storage and corresponding binding of 3.67 kg CO2 equivalent can be achieved when 1 kg of carbon is deposited in landfill.

[0090] The combination of photosynthesis, anaerobic digestion, pyrolysis, and landfilling—steps a), b), d), and f——thus enables the reduction of CO2 in the atmosphere. In contrast to other known processes for separating CO2 from the atmosphere described above, the process according to the invention produces hydrogen and, where appropriate, biogenic CO2, which can be used economically.

[0091] Converting CO2 into carbon in solid form significantly simplifies sequestration, as it immobilizes a solid rather than a gas. Finding a suitable carbon landfill site appears to be many times easier than finding suitable storage capacity for gaseous CO2, as required for conventional CCS processes.

[0092] Furthermore, depositing carbon in solid form eliminates the risks of re-emission. The geological risks associated with injecting gaseous carbon dioxide under high pressure are eliminated.

[0093] The conversion of the CO2 contained in biogas with the hydrogen obtained during the cracking process to hydrocarbons, including methane, has a positive effect on the yield of solid carbon. The amount of carbon can be increased up to twice as much as in a process without introducing hydrocarbons into the cracking process. This consequently increases the desired effect of removing climate-damaging CO2 from the atmosphere.

[0094] Based on the following drawings ( Fig. 1 - 4 ), the list of reference symbols and the patent claims as well as the examples, the invention is described in more detail.

[0095] They show: Figure 1 is a diagram of the method according to the invention in a first embodiment, Figure 2 is a diagram of the method according to the invention in a second embodiment, Figure 3 is a diagram of a linking of several modules for carrying out the method according to the invention and Figure 4 is a section of a module for carrying out several steps of the method according to the invention, Figure 5 is a process diagram of the first method carried out in example 4, Figure 6 is a process diagram of the second method carried out in example 4.

[0096] Figure 1 shows a schematic of the process according to the invention, with solid arrows indicating material flows and dashed arrows indicating energy flows. The circles represent points of contact with the system's environment, and the dashed two-dot line marks the boundaries of the module 14 under consideration.

[0097] In step a), biomass 100 is produced from CO2 102 by photosynthesis. This occurs, for example, through plant growth in a field or, alternatively or additionally, through the cultivation of plants in a greenhouse 1. By carefully selecting the plants, rapid growth of the biomass 100 can be promoted and the suitability for the production of biogas 101 can be optimized.

[0098] To enhance plant growth, the air in greenhouse 1 can be enriched with CO2 102 and heated. The CO2 102 can be supplied to greenhouse 1 separately and / or as part of an exhaust gas 113. The CO2 102 is preferably recycled from further steps of the process, in particular from a processing 3 of biogas 101 produced in the process and as part of the exhaust gas 113 from a combined heat and power (CHP) plant 9.

[0099] In step b) of the process, the biomass 100 is fermented, in particular by an anaerobic bacterial reaction, to produce biogas 101 containing methane 103 and CO2 102. The reaction is carried out continuously in a mixing tank, which constitutes a biogas reactor 2.

[0100] In step c) of the process, the biogas 101 is fed to a processing unit 3, wherein methane 103, in the form of a methane-rich stream, is separated from a stream containing CO 2 102. The CO 2 102, for example the entire CO 2 102-containing stream, can be returned to the greenhouse 1 to enrich the air in the greenhouse 1 with CO 2 102. Alternatively or in addition to the return of the CO 2 102 from the processing unit 3 to the greenhouse 1, at least a portion 102a of the CO 2 102 is passed to a Fischer-Tropsch and / or methanation device 11.

[0101] A further portion 102b of the CO 2 can be fed to a CO 2 liquefaction unit 12, from which liquid CO 2 102c can then be extracted.

[0102] In step d) of the process, the methane 103 from processing 3 is fed to a reactor 4. There, it is heated to a high temperature. In reactor 4, methane 103 is split into its components: carbon as a solid 106 and hydrogen 110. All of the reaction types mentioned, including reactions by pyrolysis, for example, thermopyrolysis, arc pyrolysis, plasma pyrolysis, or catalytic pyrolysis, can be used here.

[0103] The conversion of methane 103 is incomplete, and other hydrocarbons are also produced in small amounts. A product gas mixture 105 is formed at the outlet of reactor 4, containing gaseous methane 103, hydrogen 110, and other hydrocarbons 114, as well as carbon as a solid 106.

[0104] To operate reactor 4, energy such as electrical power 104a from renewable sources, particularly wind energy and photovoltaics, is preferably used. Electrical power 104 can be generated alternatively or additionally in the cogeneration plant 9.

[0105] The reactor 4 is followed by a filter 5 in which the solid 106 is separated from a gas phase 109 containing hydrogen 110.

[0106] At least a portion 109a of the gas phase 109 can, if necessary, be temporarily stored and fed into the integrated CHP plant 9 as fuel. Furthermore, the electrical power 104 generated in the CHP plant can be fed into the public power grid to stabilize the grid.

[0107] Alternatively, the hydrogen 110 can be separated from the residual gas 112 present in the gas phase 109 in an H2 separation device 8, for example, an alternating pressure adsorption system or by means of membranes. For this purpose, at least a portion 109b of the gas phase 109 is fed to the membrane 8. Part of the hydrogen 110a can be returned to the reactor 4, and another portion can be further utilized as product 110b. For this purpose, the hydrogen further utilized as product 110b can first be fed to an H2 commissioning unit 10 and, for example, compressed and filled into gas cylinders or introduced into a pipeline for further transport.

[0108] According to the invention, at least a portion 109c of the gas phase 109 or, alternatively, of the hydrogen 110c is fed to the Fischer-Tropsch and / or methanation device 11. Here, the hydrogen from the gas phase 109 or the hydrogen 110 together with CO2 102 originating from the processing 3 can be converted into a hydrocarbon mixture 114. The hydrocarbon mixture 114 preferably contains kerosene, gasoline, waxes, and mixtures thereof.

[0109] As an alternative to the Fischer-Tropsch device 11 mentioned here, any other process for producing hydrocarbons known to those skilled in the art can also be used, for example, a catalytic Sabatier reaction or a biochemical process using methane-forming microorganisms. Longer-chain hydrocarbons, such as kerosene, gasoline, and / or waxes, or even methane or shorter-chain hydrocarbons such as ethane, propane, or butane, as well as mixtures thereof, can be produced in the Fischer-Tropsch and / or methanation device 11 or in the alternatively used process.

[0110] The residual gas 112 used after separation from the gas phase 109 and serving as a fuel or propellant can, if necessary, be temporarily stored and fed to the cogeneration plant 9. As an alternative to an external power source, the electrical power 104 generated in the cogeneration plant 9 can be used to split the methane 103 in the reactor 4. Furthermore, the exhaust gases 113 generated in the cogeneration plant 9, in particular with the heat 115 generated there, are preferably fed to the greenhouse 1.

[0111] The Figure 1 The process described can be locally combined into a module 14. A module 14 can serve for the local supply of electricity 104, hydrogen 110 and heat 115 as well as the production of hydrocarbons 114.

[0112] Figure 2 shows an alternative embodiment of the method according to the invention, which differs from that in Figure 1shown embodiment in particular by the introduction of the hydrocarbons and / or methane produced in the Fischer-Tropsch and / or methanation device 11 into the reactor 4.

[0113] By introducing at least a portion 114a of the hydrocarbons and / or methane produced in the Fischer-Tropsch and / or methanation device into the reactor 4, the yield of solid carbon 106 can be significantly increased.

[0114] In this case, not only is the methane 103 converted into carbon 106 and hydrogen 110 in the reactor, but also the hydrocarbons and / or methane 114a introduced into the reactor, which were obtained in the Fischer-Tropsch reaction, are split into solid carbon 106 and hydrogen 110. The reaction carried out is the same as above for Figure 1 for the splitting of methane.

[0115] To convert the CO2 into hydrocarbons 114, 114a in the Fischer-Tropsch and / or methanation device, in addition to the portion 109c of the hydrogen-containing gas phase 109, a portion 110a of the hydrogen separated in the H2 separation device 8 is also introduced into the Fischer-Tropsch and / or methanation device 11. As an alternative to the embodiment shown here, it is also possible to introduce only the portion 109c of the hydrogen-containing gas phase 109 or only the hydrogen 110a into the Fischer-Tropsch and / or methanation device 11.

[0116] It is also possible, as shown here, to remove a portion of the hydrocarbons and / or methane 114 obtained in the Fischer-Tropsch and / or methanation device 11 as product and introduce only a portion 114a into the reactor 4. However, in order to obtain the maximum yield of solid carbon 106, it is preferred to introduce all of the hydrocarbons and / or methane produced in the Fischer-Tropsch and / or methanation device 11 into the reactor 4.

[0117] Figure 3 shows a diagram of a connection between several modules 14, where the solid arrows indicate material flows and the dotted arrows indicate data flows. The modules 14 have an internal, i.e., local, transport and distribution system for the distribution of hydrogen 110.

[0118] The modules 14 are interconnected via data technology, enabling optimized operation with regard to factors such as product portfolio, capacity utilization, or distribution. The optimization of the control of the modules 14 is carried out from a control center 13, where data is centrally collected, stored, and processed. The control center 13 and the modules 14 communicate with each other via a data network such as the internet.

[0119] The carbon accumulating in the modules 14 as solid 106 is processed in a central mixing device 6, which is also connected to the control center 13, with further solids 107, also referred to as fillers, such as sand or bulk material, to form a solid mixture 108. The solid mixture 108 can then be geologically and permanently stored in a carbon sink 7, such as an old mine. The carbon as solid 106 can also be used in other applications in which it is permanently immobilized, so that it can be considered an equivalent for the CO2 removed from the air. Alternatively, the carbon can also be mixed into materials used to manufacture sheaths for electrical cables, insulation, soundproofing materials, or to seal underground structures.

[0120] Figure 4shows a section of a module 14 in air purification mode. The balance boundary 15 corresponds to Example 3 below. Biomass 100 is fed to the biogas reactor 2, which also receives electrical power 104 and heat 115 from the CHP plant 9. The biogas 101 extracted from the biogas reactor 2 is separated in the processing unit 3 into (bio)methane 103 and gaseous CO2 102. The methane 103 is in turn converted in the reactor 4 into a product mixture 105, i.e., a carbon-gas mixture, with carbon being removed as a solid 106, for example, as soot, in the filter 5.

[0121] At least a portion 102a of the gaseous CO2 is fed to a Fischer-Tropsch and / or methanation device 11 for producing hydrocarbons and / or methane. A portion 114a of the hydrocarbons is fed to reactor 4 for decomposition into solid carbon 106 and hydrogen 110. After separation from the residual gas obtained in the reactor, at least a portion 110a of the hydrogen is fed to the Fischer-Tropsch and / or methanation device 11.

[0122] If not all of the hydrocarbons 114a produced in the Fischer-Tropsch and / or methanation device 11 are introduced into the reactor 4, a portion of the hydrocarbons 114 can be removed as product.

[0123] If not all of the CO 2 is fed to the Fischer-Tropsch and / or methanation device 11, the remaining CO 2 can be fed to a CO 2 liquefaction device 12 and removed therefrom as liquid CO 2 102c.

[0124] Water 111 produced in the Fischer-Tropsch and / or methanation reaction is condensed and removed from the device.

[0125] The gas phase 109 separated in the filter 5 is passed through the H2 separation device 8, where hydrogen 110 is available. The remaining residual gas 112 is used for energy in the cogeneration plant 9, whereby electrical current 104 within the module 14 is used to liquefy the CO2 102, electrical current 104 and heat 115 are used in the biogas reactor 2, and electrical current 104 is used to split the methane 103 in the reactor 4. Examples Example 1: Removal of CO2 from the air with cultivation of corn

[0126] To quantify CO2 emissions, a subsystem of a module is balanced, which includes a reactor, a filter and an H2 separation device for hydrogen separation, as well as a CHP plant. It is further assumed that no external energy is supplied, i.e., from outside the system, which would result in the streams 104a being set in Figure 1 equals 0.

[0127] Depending on the composition of the biomass used, the methane mixture, i.e., the biogas produced, is nominally already burdened with varying levels of CO2 emissions from the upstream process steps, particularly the production of the biomass. In this example, maize is considered the biomass used. The following emissions from the production of the maize are already attributable to the methane mixture formed from maize: Table 1: Occurrence Equivalents CO2 emissions Cultivation 17.7 g CO 2 eq. / MJ Processing (fermentation in step b)) 4.3 g CO 2 eq. / MJ Processing of biogas 4.5 g CO 2 eq. / MJ In total 26.5 g CO 2 eq. / MJ

[0128] The balanced subsystem is operated in such a way that 60 wt.% of the methane produced from the corn is converted stoichiometrically to hydrogen and carbon. The remaining 40 wt.% of the methane is used to produce electricity, which is used in Figure 1 with the designation 104 of the CHP plant 9.

[0129] The following calculation is based on a consumption of 100 kg of methane.

[0130] The CHP plant generates electricity with an efficiency of 36%. CO2 emissions from the generated electricity are attributed as follows: 40 kg CH 4 x 36 % × 50 MJ / kg × 26 , 5 g CO 2 eq . / MJ = 19 , 08 kg CO 2 eq .

[0131] When methane is split, two products are carbon in solid form and hydrogen. Using 60 kg of methane, with the following equivalent CO2 emissions, produces 45 kg of carbon and 15 kg of hydrogen: 60 kg × 50 MJ / kg × 26 , 5 g CO 2 eq . / MJ = 79 , 5 kg CO 2 eq .

[0132] The resulting solid carbon is permanently bound because it is deposited in a landfill. This solid carbon is of biogenic origin, so a credit for non-emissions is taken into account, as these emissions, which would have occurred, for example, if the solid carbon had been burned, are not released into the atmosphere. 1 kg of bound solid carbon corresponds to a credit of 3.67 kg CO2 equivalent (eq.). For 45 kg of solid carbon to be deposited here, a credit of 165.15 kg CO2 eq. is therefore generated.

[0133] The 15 kg of hydrogen produced, which, taking into account the calorific value of hydrogen of 120 MJ / kg H 2 , corresponds to a usable energy of 1800 MJ (15 kg x 120 MJ / kg H 2 = 1800 MJ), is allocated 79.5 kg CO 2 eq. (44.1 g CO 2 eq. / MJ H 2 ) from electricity generation in the CHP plant and approximately 1 g CO 2 eq. / MJ from the transport and handling of the solid carbon during permanent storage. The greenhouse gas quota for hydrogen is then 54.1 g CO 2 eq. / MJ H 2 .

[0134] As stated above, the credit from the storage of solid carbon is -165.15 kg CO 2 eq. per 100 kg methane (-91.75 g CO 2 eq. / MJ H 2 ). If this credit is taken into account when balancing the hydrogen produced, the CO 2 balance for the hydrogen produced is -46.65 g CO 2 eq. / MJ H 2 (-46.65 = 44.1 + 1.00 - 91.75). Example 2: Removal of CO2 from the atmosphere using manure

[0135] If liquid manure is used instead of maize to produce methane in the biogas reactor, the hydrogen is attributed a CO 2 emission of - 212.48 g CO 2 eq. / MJ H 2 without taking into account the credit for the stored solid carbon and of - 304.23 g CO 2 eq. / MJ H 2 with taking into account the credit for the landfilling of the solid carbon. Example 3: Comparison of the inventive method with known OAC methods

[0136] For the comparison of the method according to the invention, which can also be referred to as an air purification method, with the DAC (direct air capture) method, the following conditions are defined.

[0137] For both processes, the removal of 1 t CO2 from the ambient air is considered.

[0138] Based on S. Deutz, A. Bardow "Supplementary material: Life-cycle assessment for industrial direct air capture process based on temperature-vacuum swing adsorption", Nature Energy, 6, pages 203 to 213 (2021), it is assumed that approximately 0.7 kWh per kg of CO2 removed from the air is required for mechanical work such as operating fans and pumps and an additional 3.3 kWh of heat.

[0139] When using heat pumps, 1.3 kWh of electrical power is required as heat replacement, resulting in a total energy requirement plus liquefaction of 4.11 or 2.11 kWh / kg CO2.

[0140] Regarding the air purification method according to the invention, which is accordingly described in Figure 3As shown, the energy balance takes into account the production of biogas from biomass in the biogas reactor 2, the separation of the biogas into CO 2 and methane by means of membranes in the processing 3, the splitting of methane by means of electricity generated within the process in the reactor 4, whereby the electricity was generated by means of the CHP plant 9, the separation of the solid carbon in the filter 5, which was recorded using CO 2 equivalents, the separation of the hydrogen via the H 2 separation device 8 and the liquefaction of CO 2 in the CO 2 liquefaction plant 12.

[0141] The removal of 1 t of CO2 from the air using the state-of-the-art DAC process requires 2.11 MWh of electrical power, while the removal using the air purification process removes 1 t of CO2 in the form of 157 kg of carbon and 423 kg of CO2 as gas, whereby the energy required for the described process steps is obtained exclusively from biogas and an additional 5 kg of hydrogen and 1.1 MWh of heat are produced, with temperatures of up to 500°C being available. Example 4: Increasing carbon yield by CO 2 methanation

[0142] The system used in this example comprises a biogas upgrading unit 3, a decomposition reactor 4, a carbon filter 5, a H2 separation device 8, and a methanation reactor 11. In contrast to the previous examples, electricity from renewable sources (RE) is used as the energy source. For simplification, it is also assumed that RE has no greenhouse gas emissions. The proportion of methane in the biogas is 58 vol.%. The yields of the reactions correspond to the stoichiometry. The process scheme is shown in the Figure 5 shown.

[0143] First, the biogas is separated into methane 103 and CO2 102c in the biogas upgrading unit 3. The carbon dioxide 102c is fed to the methanation reactor 11, where it is converted into methane 114a with hydrogen 110a, which is obtained in the H2 separation device 8. The methane 114a produced in the methanation reactor 11, together with the methane 103 from device 3, is fed to the cracking reactor 4, where it is converted into solid carbon 106 and gaseous hydrogen 110. Carbon is separated in the filter 5, and hydrogen is purified in device 8 and split into two streams. A first stream 110a is returned to the methanation reactor, and a second stream 110b is compressed and sold as a product.

[0144] The mass balance of the process is shown in Table 2.

[0145] Alternatively, the conversion of the CO 2 contained in the biogas in the methanation process can be omitted. This is exemplified in Figure 6 In this case, CO2 is emitted into the atmosphere as a gas or liquefied and sequestered. The mass balance of the process is shown in Table 3.

[0146] By partially recycling the hydrogen in the process according to Figure 5 The yield of solid carbon is increased by about 70%. The yield of hydrogen, due to the methanation reaction, is correspondingly reduced. Table 2: Current No. Mass flow [kg / h] CH4 [kg / h] CO2 [kg / h] H 2 [kg / h] C [kg / h] H 2 O [kg / h] 101 332 112 220 - - - 102c 220 - 220 - - - 103 112 112 - - - - 114a 80 80 - - - - 103a 192 192 - - - - 105 192 - - 48 144 - 106 144 - - - 144 - 109 48 - - 48 - - 110 48 - - 48 - - 110a 40 - - 40 - - 110b 8 - - 8 - - 111 180 - - - - 180 Table 3 Current No. Mass flow [kg / h] CH4 [kg / h] CO2 [kg / h] H 2 [kg / h] C [kg / h] H 2 O [kg / h] 101 332 112 220 - - - 102c 220 - 220 - - - 103 112 112 - - - - 114a - - - - - - 103a 112 112 - - - - 105 112 - - 28 84 - 106 84 - - - 84 - 109 28 - - 28 - - 110 28 - - 28 - - 110a - - - - - - 110b 28 - - 28 - - 111 - - - - - - List of reference symbols

[0147] 1Greenhouse 2Biogas reactor 3Biogas processing 4Reactor 5Filter 6Mixing device 7Carbon sink 8H 2 separation device 9Combined heat and power plant 10H 2 commissioning 11Fischer-Tropsch and / or methanation device 12CO 2 liquefaction 13Control center 14Module 15Balance limit 100Biomass 101Biogas 102, 102a, 102bCO 2 102cLiquid CO 2 103Methane 103aMethane-hydrocarbon mixture 104Electric current 104aExternal energy 105Product mixture 106Carbon as solid 107Other solid 108Solid mixture 109, 109a, 109b, 109cGas phase 110, 110a, 110b, 110chydrogen 111water 112residual gas 113exhaust gas 114, 114a, 114bhydrocarbon mixture 115heat

Claims

1. Method for removing and immobilizing carbon dioxide (102) from the atmosphere and / or an exhaust gas (113), comprising the steps: a) Converting the carbon dioxide (102) from the atmosphere and / or an exhaust gas (113) into biomass (100) by means of photosynthesis, preferably on agricultural land, in particular in a greenhouse (1), b) carrying out a biogas reaction in which the biomass (100) produced in step a) is converted into biogas (101) containing methane (103) and carbon dioxide (102), in particular in a biogas reactor (2), c) separating the methane (103) from the biogas (101) obtained, d) splitting the methane (103) into carbon (106) and hydrogen (110), wherein the carbon (106) is obtained as a solid, e) collecting the carbon (106) obtained, f) depositing the carbon (106) obtained, and g) reacting carbon dioxide (102) from the biogas with the hydrogen (110) obtained in step d) to form a hydrocarbon mixture (114).

2. Method according to claim 1, characterized in that the carbon dioxide (102) from the biogas (101) obtained after separation of methane (103) according to step c) is returned to step a).

3. Method according to at least one of the preceding claims, characterized in that at least part of the hydrocarbon mixture (114) obtained in step g) is introduced into step d) and split into carbon (106) and hydrogen (110).

4. Method according to at least one of the preceding claims, characterized in that the biogas (101) produced in step b) contains at least 40 vol.-% methane (103).

5. Method according to at least one of the preceding claims, characterized in that the biogas reaction comprises an anaerobic fermentation reaction.

6. Method according to at least one of the preceding claims, characterized in that the separation of the methane (103) in step c) is carried out physically, in particular by means of condensation, adsorption and / or a membrane process.

7. Method according to at least one of the preceding claims, characterized in that the splitting of the methane (103) in step d) is carried out by means of a pyrolysis process and, in particular, at a temperature of at least 800°C.

8. Method according to at least one of the preceding claims, characterized in that the hydrogen (110) is separated from the carbon (106) after the methane (103) has been split in step d), in particular by filtration.

9. Method according to at least one of the preceding claims, characterized in that after splitting the methane (103) in step d), the hydrogen (110) is separated from a residual gas (112), in particular by means of a membrane process (8).

10. Method according to at least one of the preceding claims, characterized in that the hydrogen (110) produced in step d) is used at least partially as a starting material for syntheses in the chemical industry, as an energy carrier for the generation of electrical power (104) and / or heat (115) and / or as a fuel for vehicles.

11. Method according to claim 10, characterized in that energy required for the splitting according to step d) is provided at least in part by using the hydrogen (110) produced in step d) and, if applicable, the residual gas (112), and / or is generated from renewable sources.

12. Method according to at least one of the preceding claims, characterized in that, after splitting the methane (103) in step d), residual gas (112) separated from the hydrogen (110) and / or the hydrogen (110) obtained in step d) and / or gas phase obtained in step d) are fed to a power plant before the hydrogen is separated off, and the exhaust gas (113) used in step a) originates at least in part from the power plant.

13. Method according to at least one of the preceding claims, characterized in that at least steps a) to e) and, if applicable, step g) are carried out in a module (14).

14. Method according to claim 13, characterized in that at least the steps a) to e) and, if applicable, step g) are carried out in at least two modules (14), and the at least two modules (14) are connected to a central control center (13).

15. Method according to at least one of the preceding claims, characterized in that the carbon (106) obtained as a solid in step d) is mixed with at least one further solid (107), in particular sand and / or rock, before being deposited according to step f).