Method for producing a sustainable energy carrier

Abstract

The invention relates to a method for producing a sustainable energy carrier, the method including the following steps: - producing a gas (2) comprising methane (3) and carbon dioxide (4) from organic waste (1) in a fermentation unit (10), - separating the methane (3) and the carbon dioxide (4) from the gas (2) in a separation unit (20), - converting the methane (3) to hydrogen (5) and carbon (6) in a converting unit (30), in particular a pyrolysis unit, - converting the carbon dioxide (4) and the hydrogen (5) to methanol (7) in a methanol synthesis unit (40), wherein the separation unit (20), the converting (30) unit and the methanol synthesis unit (40) are powered, preferably exclusively, by electricity and / or heat produced in a solar power unit (50).

Description

[0001] Method for producing a sustainable energy carrier

[0002] The present invention relates to the field of sustainable energy production, in particular to a method and a plant for producing a sustainable energy carrier using organic waste.

[0003] Since the beginning of the industrial revolution in 1800, atmospheric carbon dioxide has risen from a previously stable 280 ppmv (parts per million by volume) to over 400 ppmv. It is predicted that this increase will continue or even increase if techniques to limit carbon dioxide emissions are not implemented.

[0004] The main objective of the ratified Paris Agreement is to limit the increase in the global average temperature to below 2.0 °C above pre-industrial levels, which requires a reduction in carbon dioxide emissions to zero by 2050. Proposals to limit these emissions include the use of biofuels, solar energy and wind turbines. However, reducing carbon dioxide emissions, i.e. limiting the increase in carbon dioxide levels in the atmosphere, is not sufficient in the long term to correct the imbalance between oxygen and carbon dioxide in the atmosphere caused by the overproduction of carbon dioxide. Rather, it is necessary not only to stop the increase in the carbon dioxide content of the atmosphere in the long term, but to actively reduce it.

[0005] At the same time, the demand for a secure energy supply for industry, transportation and mobility remains high. Although there are many efforts to electrify the mobility sector and use renewable energy sources to provide the electricity needed, most regions of the world lack the infrastructure to get the electricity to where it is needed. Furthermore, electrification in some sectors, such as large parts of aviation and shipping, is not easy due to technological limitations.

[0006] DE 10 2020 116 950 A1 discloses a method for splitting hydrogen-containing gases into molecular hydrogen. The hydrogen-containing gas can be biogas. However, the known method is not carbon neutral, as the biogas is usually produced by fermentation of organic waste and contains carbon dioxide. During fermentation, carbon dioxide is released which was previously contained in the atmosphere and then absorbed by the organic waste. Furthermore, although hydrogen produced by the known method can be used as an energy carrier, the storage and transportation of hydrogen poses significant safety concerns due to its high flammability and the risk of leakage. Therefore, the widespread introduction of hydrogen as an energy carrier faces numerous hurdles.

[0007] Given the aim to actively reduce the amount of carbon dioxide in the atmosphere, there is a need for a green energy source that is not only carbon-neutral, but even carbonnegative.

[0008] The present invention solves this problem by providing a method of producing a sustainable energy carrier, the method comprising the following steps: producing a gas comprising methane and carbon dioxide from organic waste in a fermentation unit,

[0009] - separating methane and carbon dioxide from the gas in a separation unit,

[0010] - converting the methane into hydrogen and carbon in a converting unit, in particular a pyrolysis unit,

[0011] - converting carbon dioxide and hydrogen to methanol in a methanol synthesis unit, wherein the separation unit, the converting unit and the methanol synthesis unit are powered, preferably exclusively, by electricity and / or heat produced in a solar power unit.

[0012] The invention has several advantages. Organic waste that is decomposed by fermentation normally releases methane, a potent greenhouse gas, into the atmosphere. However, the method according to the invention captures and utilizes the methane, thereby preventing the release of methane, which helps to reduce greenhouse gas emissions. Furthermore, the gas containing methane is converted into hydrogen and carbon in a converting unit. By converting methane into hydrogen, the invention avoids the direct emission of methane into the atmosphere, thus helping to reduce the impact on climate change. The carbon dioxide separated from the gas is also not released into the atmosphere. Instead, it is used in the methanol synthesis unit, where it is combined with hydrogen to produce methanol. This method effectively captures and utilizes the carbon dioxide so that it does not contribute to the greenhouse effect. Furthermore, by producing methanol, the methods of the invention provide an energy carrier that can be easily transported around the world and used in most conventional industries. Methanol is not easily flammable, forms a liquid at temperatures below 64.7 °C and is biodegradable.

[0013] In order to make the method according to the invention at least carbon-neutral, the separation unit, the converting unit, e.g. a pyrolysis unit, and the methanol synthesis unit are powered by electricity and / or heat from a solar power unit. By using solar energy, the technology eliminates the need for fossil fuels and reduces the carbon footprint associated with energy consumption in the production process.

[0014] Methanol, which is produced from the combination of carbon dioxide and hydrogen, can potentially serve as a carbon sink. If the methanol is used in applications where it is not immediately combusted, such as in chemical processes or as a feedstock for other materials, it can serve as a form of long-term carbon storage.

[0015] The carbon produced during the conversion of methane to hydrogen is a solid material. While the ultimate use of the carbon can vary, storing or using it in a way that keeps it out of the atmosphere can help sequester carbon and further reduce the net carbon emissions associated with the process. The carbon can be used to make many different products, promoting a circular economy.

[0016] With the method according to the invention, it is possible to produce the carbon required for many industrial products in a cost-effective and climate-neutral manner. This is of particular importance since it has not been economically feasible to recycle carbon to date.

[0017] An effect or action is climate-neutral if it does not increase the amount of carbon dioxide in the atmosphere when implemented. An effect or measure is considered to be climate-positive if it actively contributes to the reduction of carbon dioxide in the Earth's atmosphere, i.e. if it removes more carbon dioxide from the atmosphere than it adds to the atmosphere. It is particularly advantageous if the carbon is incorporated into the soil, especially the seabed, for mid-term or long-term storage and / or used as a soil conditioner. Use as a soil conditioner has the further advantage of returning the carbon to a cycle that promotes the reduction of atmospheric carbon dioxide in the long term. As a soil conditioner, carbon is highly effective in accelerating plant growth. Carbon is therefore advantageously used as a soil conditioner for reforestation of plants that are highly receptive to carbon dioxide. As a soil conditioner, the carbon thus contributes to an improved and overall accelerated uptake of atmospheric carbon dioxide into the plants, i.e. into the organic waste, by accelerating the growth of the plants. From this organic waste, the method according to the invention can in turn be used to produce methanol as a carbon dioxide-neutral or even climate-positive fuel and carbon as an active carbon dioxide-reducing soil conditioner.

[0018] In addition, the carbon may be used to produce and / or incorporate into an industrial product. The industrial product is preferably intended for recycling and / or disposal. More specifically, the industrial product is preferably not incinerated. In this way, the carbon produced is stored in the industrial product, at least in the mid-term, and thus does not pollute the atmosphere.

[0019] This effect increases with the amount of carbon produced. In other words, the method described here reduces the amount of carbon dioxide in the atmosphere the faster the more organic waste is processed.

[0020] The method also allows the effect on the global climate to be well controlled. In particular, the climate impact of the method can be adjusted by the use of the resulting products methanol and carbon accordingly, in particular by adjusting the amount of carbon to be stored in the long term. A particularly high climate positive effect can be achieved by long-term storage of the entire amount of carbon produced, e.g. on the seabed. A high climate impact is also achieved when the carbon is used as a soil conditioner. Processing the carbon into marketable products, such as plastics, is at least possible in a climate-neutral manner.

[0021] In a preferred embodiment of the invention, the method is carried out in a plant comprising the fermentation unit, the converting unit and the methanol synthesis unit, wherein the plant is powered exclusively by renewable energy so that the amount of carbon dioxide in the atmosphere is reduced by the incorporation of CO2into the organic waste and the subsequent incorporation and storage of the carbon produced from the organic waste in the soil. Implementing the method in this way is climatepositive and can therefore make a significant contribution to achieving the goals of the Paris Climate Agreement on time.

[0022] The step of converting the methane into hydrogen and carbon in the converting unit may comprise heating the methane to a temperature between 750°C and 2100°C. Preferably, methane is converted into hydrogen and carbon by a pyrolysis process. Pyrolysis is a thermal process in which the methane is decomposed at high temperatures in the absence of oxygen. To do this, the methane is heated in a pyrolysis reactor, typically to temperatures above 700°C, preferably between 750°C and 2100°C. The lack of oxygen prevents complete combustion of the methane, so that the methane breaks down into its components:

[0023] CH4^ H2+ C

[0024] Specifically, the methane is converted to hydrogen and elemental carbon (also called active coal or carbon). The hydrogen produced can then be further processed, while the carbon remains as a solid residue.

[0025] To convert the methane to hydrogen and carbon, the methane can be heated in particular in an electric plasma reactor or in a bubble tower reactor filled with a liquid metal catalyst. In the method presented here, it is preferable that the electrical energy be generated exclusively from renewable sources, preferably by a large-scale photovoltaic system. The large-scale photovoltaic system can be part of a hybrid solar power unit that provides not only electrical energy from the large-scale photovoltaic system, but also thermal energy from a solar thermal system. The thermal energy can be used for further processes as part of the method according to the invention.

[0026] Methane conversion or methane cracking in a bubble tower reactor is energetically efficient. Methane can be cracked in a bubble tower reactor in various ways, depending on the specific reaction conditions and the catalysts used. In general, the methane gas in the bubble tower reactor is introduced into a liquid containing a catalyst. In particular, the catalyst may be a liquid metal catalyst, for example, having a melting point between 0 °C and 300 °C. In particular, the liquid metal catalyst may comprise mercury, gallium, indium, bismuth, lead, cadmium and / or tin. The liquid metal may be combined with a solvent to form the liquid metal catalyst. The introduction of methane gas into the liquid creates gas bubbles that rise through the liquid metal catalyst in the reactor, thus increasing the contact surface between the methane and the catalyst. It is preferable to introduce the methane from below into a bath of liquid metal catalyst within the bubble tower reactor.

[0027] As the methane rises through the liquid metal catalyst in the bubble tower reactor, there is intensive contact between the gas bubbles and the liquid phase, which allows the gas bubbles to be absorbed. At the same time, the catalysts in the liquid can catalyze the decomposition of the methane.

[0028] The methane is thus split by the catalytic reaction of the methane in the liquid phase. The reaction preferably takes place at a temperature between 0°C and 300°C. These temperatures can be achieved with comparatively low energy input, which improves the energy efficiency of the method. Ultrasound can also be introduced into the bubble tower reactor to assist the catalytic reaction. The liquid metal catalyst can be recovered from the liquid phase for reuse, improving the economics of the method.

[0029] Alternatively, the methane can also be split by thermocatalytic decomposition. In thermocatalytic decomposition, the methane is heated in the absence of oxygen (pyrolysis) but in the presence of one or more catalysts. The catalysts used reduce the temperature required to break down the methane compared to conventional plasma pyrolysis. Thermocatalytic decomposition therefore saves energy. In addition, the composition of the catalysts can be varied to produce carbon with different properties. This increases the chances of the carbon being reused in industry.

[0030] The carbon produced from the methane conversion can be further processed into various products. For example, carbon is used as a reducing agent in metallurgy, particularly in the production of iron and steel. Carbon reacts with metal oxides and reduces them to metallic metal. Carbon can also be used as a raw material in the chemical industry. It can be used in various syntheses and reactions to produce various chemical compounds. Carbon particles can also be used in the production of electrodes. Carbon can be used as an electrode material in batteries, fuel cells and other electrochemical systems. Carbon can be used as an adsorbent to remove gases or contaminants from gas or liquid streams. Carbon in solid form is commonly used in air and water treatment systems. In some applications, carbon may be used as a lubricant. Graphite, a form of carbon, is used in various industrial applications for its lubricating properties.

[0031] In a further preferred embodiment of the method according to the invention, it is provided that the methanol is further processed to produce plastics, in particular polyethylene and / or polypropylene and derivatives thereof. Plastics can be produced from methanol using, for example, methanol-to-olefins (MTO) technology. MTO is a process that converts methanol into lighter olefins, such as ethylene and propylene. These olefins are then used as feedstocks for the synthesis of various plastics. Plastics that can be produced from methanol include polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC) and / or polystyrene (PS).

[0032] A subsidiary aspect of the invention relates to a plant for producing a sustainable energy carrier, the plant comprising:

[0033] - a fermentation unit for producing a gas from methane and carbon dioxide from organic waste,

[0034] - a separation unit for separating the methane and carbon dioxide from the gas,

[0035] - a converting unit, in particular a pyrolysis unit, for converting the methane into hydrogen and carbon, the pyrolysis unit preferably comprising a bubble tower reactor filled with a liquid metal catalyst, and

[0036] - a methanol synthesis unit for converting carbon dioxide and hydrogen into methanol wherein the separation unit, the converting unit and the methanol synthesis unit are preferably powered exclusively by energy from renewable energy sources, in particular with electricity and / or heat generated in a solar power unit. The advantages and possible further developments explained in connection with the method described above also apply analogously to the plant described here.

[0037] Other advantageous embodiments and combinations of features come out from the detailed description below and the entirety of the claims. The drawing used to explain the embodiment shows a flow diagram of the inventive process for producing a sustainable energy carrier, especially methanol, and carbon from organic waste.

[0038] The basic idea of the invention is to use the biological process of photosynthesis within plants to capture carbon dioxide 4 from the Earth’s atmosphere. This biological process is done permanently by all plants. However, there are some plants, in particular fast growing plants that absorb more carbon dioxide 4 than other plants. It is therefore preferred, that the organic waste 1 comes from such fast growing plants and that the method described herein also provides for measures that assist the plants in their carbon capture abilities.

[0039] The method thus uses the organic waste 1 that includes atmospheric carbon dioxide 4 and produces an energy carrier that is thus at least carbon neutral and moreover also provides for the option to be climate-positive, i.e. the method reduces the content of carbon dioxide 4 in the atmosphere actively.

[0040] According to the inventive method, organic waste 1 is fed to a fermentation unit 10. The fermentation unit 10 may use bacteria and / or heat to decompose the organic waste 1 . The organic waste 1 is thus separated into a gas, so called biogas 2, which contains methane 3 and carbon dioxide 4, and fermentation residues. The fermentation residues may be discharged as or optionally further processed to produce organic fertilizer. The fertilizer may then be used to assist reforestation of plants. The plants then capture carbon dioxide 4 from the atmosphere again, thus providing a carbon dioxide reduction cycle.

[0041] In a further step of the inventive method, the biogas 2 is then conveyed to a separation unit 20, wherein the biogas 2 is separated to carbon dioxide 4 and methane 3. The carbon dioxide 4 may also be processed in a purification unit 25 to produce clean or pure carbon dioxide 4. The purification unit 25 may be incorporated in the separation unit 20. Separation of the carbon dioxide 4 from the biogas 2 may be performed by various processes. In absorption processes, the gas mixture is brought into contact with a liquid solvent that selectively absorbs carbon dioxide 4. Common solvents include amines or other chemical solutions. The absorbed carbon dioxide 4 is then separated from the solvent. In an adsorption processes, the carbon dioxide 4 is adsorbed by solid adsorbents, such as activated carbon or zeolites, which attract and hold carbon dioxide molecules. The adsorbent material is then regenerated to release the captured carbon dioxide 4.

[0042] Another process for separation carbon dioxide 4 from biogas 2 is Pressure Swing Adsorption (PSA). In PSA, the gas mixture is passed through a bed of adsorbent material at high pressure. Carbon dioxide 4 is selectively adsorbed, and when the bed is saturated, the pressure is reduced to release the captured carbon dioxide 4. Membrane technologies use semi-permeable membranes to selectively allow carbon dioxide 4 to pass through while excluding other gases.

[0043] Depending on the desired purity level, further purification steps may be employed. This may include additional absorption or separation processes to remove remaining impurities. The further purification steps are preferably performed in a separate purification unit 25.

[0044] The purified carbon dioxide 4 may be compressed to the required pressure for transportation. Compression increases the density of carbon dioxide 4, making it more manageable for transport.

[0045] The methane 3 separated from the biogas 2 in the separation unit 20 is then converted into hydrogen 5 in a converting unit 20. However, the methane 3 may previously used to produce syngas, which then is converted to hydrogen 5. Conversion of methane 3 or syngas to hydrogen 5 requires energy 8, in particular heat for a pyrolysis process. The pyrolysis process may be a Kvaerner process. The heat may be provided by plasma that may be generated by electric energy 8 produced in a solar power unit 50. The solar power unit 50 will be discussed later in this application.

[0046] Alternatively, the methane 3 may be converted into hydrogen 5 by conveying the methane 3 through a liquid metal in a bubble tower reactor containing a liquid metal catalyst, in particular liquid tin. The bubble tower reactor introduces a gas (or gases) into a liquid through a system that generates bubbles. This can be achieved using spargers, porous plates, or other means to disperse the gas throughout the liquid. The formation of bubbles increases the contact surface area between the gas and liquid phases. This enhanced interface promotes efficient mass transfer, allowing the reactants to come into close proximity and interact.

[0047] By converting the methane 3 in the converting unit 30, hydrogen 3 and pure carbon are produced. Usually, about 3 kg of carbon-6 and about 1 kg of hydrogen 5 are produced from 4 kg of methane.

[0048] The pure carbon may also be called active coal or carbon-6. Carbon 6 is a sought-after raw material for various products in various industries. For example, carbon 6 is a crucial reinforcing agent in tire manufacturing. It improves the strength, wear resistance, and overall durability of rubber compounds used in tires. About 3 kg of carbon 6 are needed for the production a single tire. In plastic products, carbon 6 is added to enhance their strength, conductivity, and UV resistance. It is commonly used in the production of pipes, cables, and other plastic products. Carbon 6 is also used in coatings for applications such as automotive finishes, industrial coatings, and paints. It improves the coating's durability and UV resistance. Last, but not least, carbon 6 may be used as a conductive additive in the electrodes of lithium-ion batteries, contributing to the battery's performance.

[0049] The inventive method is advantageous not because carbon 6 is produced in an environmental friendly manner, but especially because it provides an transportable energy carrier by further processing the hydrogen 5 converted from the methane 3 and the carbon dioxide 5 separated from the biogas 2. Both, the hydrogen 5 and the carbon dioxide 4 are fed to a methanol synthesis unit 40 and combined therein to produce methanol 7. The methanol 7 is carbon-neutral as the method uses renewable energy sources exclusively and further called “aFuel”, because it is a fuel containing atmospheric carbon dioxide 4.

[0050] The methanol synthesis unit 40 may incorporated a Fischer-Tropsch synthesis for converting hydrogen 5 and carbon dioxide 4 into methanol 7. The main chemical reaction for methanol synthesis is the hydrogenation of carbon dioxide 4: catalyst, commonly based on tin, copper, zinc, and / or aluminum oxides, may catalyze this reaction. The reaction typically takes place in a fixed-bed reactor containing the methanol synthesis catalyst. The reaction is exothermic, and the temperature and pressure are carefully controlled to optimize methanol production while avoiding undesirable by-products. Heat exchangers are used to manage and control the temperature within the reactor.

[0051] An essential aspect of the inventive method is the powering of all the processes, in particular the endothermic reactions, mainly or more preferably purely, by renewable energy 8. The energy 8 may in particular generated in a solar power unit 50. The solar power unit 50 preferably is a hybrid solar power unit 50, meaning that the solar power unit 50 includes a photovoltaic unit generating electric energy from solar radiation and a solar thermic unit generating heat form solar radiation. The energy 8, in particular the electric energy and / or the thermic energy, may be transferred to the fermentation unit 10, the separation unit 20, the purification unit 25, the converting unit 40 and / or the methanol synthesis unit 40. Moreover, heat produced in the methanol synthesis unit 40 may also be used to control the temperature in the fermentation unit 10. The heat generated in the solar thermal unit 50 may also be used to produce electric energy by driving a turbine connected to an electric generator.

[0052] Reference signs

[0053] 1 organic waste

[0054] 2 biogas

[0055] 3 methane 4 carbon dioxide

[0056] 5 hydrogen

[0057] 6 carbon

[0058] 7 methanol

[0059] 8 energy 9 organic fertilizer

[0060] 10 fermentation unit

[0061] 20 separation unit

[0062] 25 purification unit

[0063] 30 converting unit 40 methanol synthesis unit

[0064] 50 solar power unit

Claims

Claims1 . A method for producing a sustainable energy carrier, the method including the following steps:- producing a gas (2) comprising methane (3) and carbon dioxide (4) from organic waste (1) in a fermentation unit (10),- separating the methane (3) and the carbon dioxide (4) from the gas (2) in a separation unit (20),- converting the methane (3) to hydrogen (5) and carbon (6) in a converting unit (30), in particular a pyrolysis unit,- converting the carbon dioxide (4) and the hydrogen (5) to methanol (7) in a methanol synthesis unit (40), wherein the separation unit (20), the converting unit (30) and the methanol synthesis unit (40) are powered, preferably exclusively, by electricity and / or heat produced in a solar power unit (50).

2. The method according to claim 1 characterized in that the carbon (6) is introduced into the soil, in particular the seabed, for mid-term or long-term storage and / or used as a soil conditioner (9).

3. The method according to claim 1 or 2 characterized in that the carbon (6) is used to produce and / or incorporated into an industrial product, the industrial product being designed in particular for recycling and / or disposal, in particular the industrial product not being incinerated.

4. The method according to any of the preceding claims characterized in thatthe method is carried out in a plant comprising the fermentation unit (10), the converting unit (30) and the methanol synthesis unit (40), wherein the plant is powered exclusively by renewable energy (8) such that the amount of carbon dioxide (4) in the atmosphere is reduced via the uptake of carbon dioxide (4) in the organic waste (1) and the subsequent incorporation and storage of the carbon (6) produced from the organic waste (1) in the soil or industrial product.

5. The method according to any of the preceding claims characterized in that the step of converting the methane (3) to hydrogen (5) and carbon (6) in the converting unit (30) comprising heating the methane (3) to a temperature of between 750°C and 2100°C6. The method according to claim 5 characterized in that the methane (3) is heated in an electric plasma reactor or in a bubble tower reactor filled with a liquid metal catalyst.

7. The method according to claim 6 characterized in that the methane (3) is fed from below into a bath of liquid metal catalyst inside the bubble tower reactor.

8. The method according to any of the preceding claims characterized by producing fermentation residues by fermenting the organic waste (1) in the fermentation unit (10) and further processing the fermentation residues to produce an organic fertilizer (9).

9. The method according to any of the preceding claims characterized in that the solar power unit (50) is a hybrid power plant comprising a photovoltaic unit and a solar thermal unit, the photovoltaic unit providing an electric peak power of at least 1 .0 GW, in particular at least 1 .3 GW, in particular at least 1 .5 GW, the method comprising:producing steam by heating a liquid fluid, in particular water, in the solar thermal unit, and- using the steam for heating the fermentation unit (10) and / or the converting unit (30), in particular the pyrolysis unit, directly and / or for producing electric power by driving a turbine connected to an electric generator.

10. The method according to claim 9 characterized by storing energy (8) provided by the solar power unit (50), in particular the solar thermal unit, in a thermal energy storage.11 . The method according to any of the preceding claims characterized in that the methanol (7) is further processed to produce plastics, in particular polyethylene and / or polypropylene and their derivatives.

12. A plant for producing a producing a sustainable energy carrier, the plant comprising:- a fermentation unit (10) for producing a gas (2) comprising methane (3) and carbon dioxide (4) from organic waste (1),- a separation unit (20) for separating the methane (4) and the carbon dioxide (4) from the gas (2),- a converting unit (30), in particular a pyrolysis unit, for converting the methane (3) to hydrogen (5) and carbon (6), the pyrolysis unit preferably comprising a bubble tower reactor filled with a liquid metal catalyst and- a methanol synthesis unit (40) for converting the carbon dioxide (4) and the hydrogen (5) to methanol (7) wherein the separation unit (20), the converting unit (30) and the methanol synthesis unit (40) are powered, preferably exclusively, by energy (8) fromrenewable energy sources, in particular by electricity and / or heat produced in a solar power unit (50).

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