Method and apparatus for the production of carbon from carbon dioxide, in particular from biomass-derived carbon dioxide

Abstract

A method for the production of carbon from carbon dioxide, in particular from biomass derived carbon dioxide, comprises the steps of: a) reacting zinc oxide with sodium hydroxide to form a solution of sodium tetra hydroxido zincate, especially by dissolving zinc oxide in sodium hydroxide; b) the solution of step a) is used to produce metallic zinc by an alkaline galvanic process in which sodium tetra hydroxide zincate is converted to sodium hydroxide and metallic zinc, wherein, preferably, therewith gained sodium hydroxide is used in step a); c) reducing the carbon dioxide, in particular from biomass derived carbon dioxide, to carbon monoxide with metallic zinc of step b) as reduction agent, wherein, preferably, therewith gained zinc oxide is used in step a), in particular without any treatment; d) reducing the carbon monoxide gained in step c), and optionally any residual carbon dioxide present after step c), with metallic zinc of step b), preferably using a ferrum containing catalyst, to obtain a mixture of solid carbon and zinc oxide, and optionally the ferrum containing catalyste); e) dissolving the zinc oxide in the mixture of step d) by adding sodium hydroxide in order to form a dispersion comprising sodium tetra hydroxido zincate, solid carbon; f) separating the solid carbon, and optionally the ferrum containing catalyst, from the dispersion of step e)

Description

[0001] Method and apparatus for the production of carbon from carbon dioxide, in particular from biomass-derived carbon dioxide

[0002] The invention relates to a method and an apparatus for the production of carbon from carbon dioxide, in particular from biomass derived carbon dioxide.

[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] Hydrogen, for example is alternative energy source of great technological interest. However, hydrogen must be obtained with the help of other energy sources (fossil energy, nuclear energy, or renewable energy) for industrial usability, making it a secondary energy carrier. Thus, hydrogen is not automatically sustainable, but only as sustainable as the primary energies from which the hydrogen is obtained.

[0007] Specifically, so-called biohydrogen is of great interest. Biohydrogen is H2that is produced biologically. For example, dark fermentation uses anaerobic fermentation to produce biohydrogen (H2), methane (CH4) and carbon dioxide (CO2) from biomass, including biological waste. The biohydrogen produced in this process is labeled as green hydrogen. This technology is of great interest since such H2is a rather clean fuel.

[0008] Also, DE 10 2020 116 950 A1 discloses for example a method for splitting hydrogencontaining 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.

[0009] Specifically, a disadvantage of fermentation is that carbon dioxide is released again, which was previously contained in the atmosphere and then absorbed by the organic waste. Given the aim to actively reduce the amount of carbon dioxide in the atmosphere, there is still a need for improved solutions that overcome the aforementioned drawbacks at least partly.

[0010] It is thus the object of the invention to create a process and apparatus pertaining to the technical field initially mentioned, wherewith an overall content of atmospheric carbon dioxide, especially biomass derived carbon dioxide, can be actively reduced on a long term.

[0011] The solution of the invention is specified by the features of claim 1. Specifically, the invention is related to a method for the production of carbon from carbon dioxide, in particular from biomass derived carbon dioxide, comprising the steps of: a) reacting zinc oxide with sodium hydroxide to form a solution of sodium tetra hydroxido zincate, especially by dissolving zinc oxide in sodium hydroxide; b) the solution of step a) is used to produce metallic zinc by an alkaline galvanic process in which sodium tetra hydroxide zincate is converted to sodium hydroxide and metallic zinc, wherein, preferably, therewith gained sodium hydroxide is used in step a) and / or e); c) reducing the carbon dioxide, in particular biomass derived carbon dioxide, to carbon monoxide with metallic zinc of step b) as reduction agent, wherein, preferably, therewith gained zinc oxide is used in step a), in particular without any treatment; d) reducing the carbon monoxide gained in step c), and optionally any residual carbon dioxide present after step c), with metallic zinc of step b), preferably using a ferrum containing catalyst, to obtain a mixture of solid carbon and zinc oxide, and optionally the ferrum containing catalyst; e) dissolving the zinc oxide in the mixture of step d) by adding sodium hydroxide, especially sodium hydroxide gained in step b), in order to form a dispersion comprising sodium tetra hydroxido zincate, solid carbon, and optionally the ferrum containing catalyst; f) separating the solid carbon, and optionally the ferrum containing catalyst, from the dispersion of step e), wherein, preferably, the remaining solution of sodium tetra hydroxido zincate is reused in step b), in particular without any treatment.

[0012] The invention has several advantages. Especially, the process according to the invention has the advantage that the zinc oxide can be used in a circular process, i.e. the zinc oxide can be reused in the process after the carbon has been produced. This means that the zinc oxide is not consumed.

[0013] Therefore, the method according to the invention can be implemented as a circular process wherein the carbon dioxide is the only consumable in the process. Therewith, preferably no other substances are consumed. However, if other products are produced from the carbon in an additional step, it may be necessary to use other substances which are consumed.

[0014] Specifically, once the process has been initiated, it can in principle be maintained without additional raw materials apart from the supply of carbon dioxide and energy, since sodium hydroxide and zinc oxide is recovered. This creates a process that can be used particularly in areas that are difficult to reach. The process can thus be maintained essentially self-sufficiently. This makes the process particularly cost- effective and logistically easy to manage.

[0015] Most preferred, the inventive process is a carbon dioxide negative process. This means in particular that the process is performed such that during the production of the carbon, the process removes more carbon dioxide from the environment, e.g. the atmosphere, than it emits during the production of the product.

[0016] Even if the CO2negative mode of operation is of course preferred, it is possible to run the process in in a carbon dioxide non-negative manner, e.g. in a carbon dioxide neutral manner or in a manner emitting more carbon dioxide during the production of the carbon than the process removes from the environment, especially the atmosphere. This depends in particular on whether the energy source is CO2-neutral or not.

[0017] Furthermore, with the method according to the invention carbon dioxide can be actively removed while at the same time a product suitable for different applications is obtained.

[0018] Especially, carbon dioxide produced in chemical processes, e.g. during fermentation of biomass, is converted to solid carbon instead of being released into the atmosphere. Therefore, the method according to the invention effectively captures the carbon dioxide so that it does not contribute to the greenhouse effect anymore. This helps to improve the carbon dioxide balance of fermentation processes such as e.g. used for the production of biohydrogen.

[0019] Also, the carbon produced is a solid material. As such it can be stored without need for demanding storage means as required for example with gaseous products. Also, with the method according to the invention, it is possible to produce the carbon required for many industrial and agricultural processes and / or products in a cost-effective manner. This is of particular importance since it has not been economically feasible to recycle carbon to date.

[0020] It is particularly advantageous if the carbon obtained 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 carbon as an active carbon dioxide-reducing soil conditioner.

[0021] 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.

[0022] Overall, the inventive process provides for an effective, inexpensive, sustainable and robust process for producing carbon with a low or even a negative carbon footprint. Thanks to the inventive combination of process steps, the process can be implemented without any fossil raw materials and fossil energy sources.

[0023] The inventive process can be carried out particularly advantageously in the sun belt, along the equator, between the northern and southern turn radius, and / or in deserts. In these locations, almost any amount of solar energy, i.e. solar radiation energy that can be harnessed with photovoltaic cells and / or solar thermal energy that can be made available with solar thermal collectors, is available.

[0024] Especially, the energy required for performing the method step(s) according to the invention is electricity and / or thermal heat. The energy required in the form of electricity is in particular produced by a photovoltaic unit and / or a wind power unit, and / or the energy required in the form of heat is in particular produced with solar thermal collectors. However, other forms of energy can be used as well.

[0025] Thus, in a further preferred embodiment, the inventive process comprises a further process step of generating the renewable energy, especially with a photovoltaic unit and / or a wind power unit and / or solar thermal collector. Especially, the energy required is generated at the same location, especially in the same plant, where steps a), b), c) d), e) and / or f) take(s) place.

[0026] In particular, the carbon dioxide is biomass-derived carbon dioxide. Likewise, the carbon produced is biomass-derived carbon. Biomass is meant to be matter from recently living organisms, especially plants, algae and / or animals. Specific examples of biomass are wood, wood residues, energy crops, agricultural residues, and / or organic waste from industry and / or households.

[0027] Biomass derived carbon dioxide can be distinguished from fossil-material derived carbon dioxide by the proportion of14C atoms. The same is true for carbon product.

[0028] Specifically, biomass derived carbon dioxide and biomass derived carbon has14C atoms. By the determination of the14C content, it is possible to establish unambiguously whether and in what proportion the carbon dioxide or the carbon obtained is biomass-derived. Specifically, biomass-derived carbon dioxide or carbon differs from non-biobased or fossil material-derived carbon dioxide or carbon by a measurable proportion of the14C carbon isotope.

[0029] The14C isotope present in the atmosphere has a half-life of about 5730 years and is incorporated into living biological organisms. A fresh organic sample contains about 1 ppt (parts per trillion, 10-12) of14C atoms, based on the sum total of all carbon atoms. In dead organisms, the amount of bound radioactive14C atoms decreases according to the decay law, but the decrease is only measurable over long periods. Organic compounds which have been produced from fossil raw materials are not biomass- derived and do not have a measurable14C content.

[0030] The14C content of a sample can be determined analytically. The content can be used to determine the proportion in which the carbon dioxide and / or the carbon is biomasse- derived. Preferably, the14C content and the biomass derived content of the carbon dioxide or the carbon obtained are determined in accordance with ASTM D6866 “Standard Test Methods for Determining the Biobased Content of Solid, Liquid, and Gaseous Samples Using Radiocarbon Analysis”. The proportion of14C carbon atoms in the carbon dioxide and / or the carbon produced preferably is more than 0.1 ppt, especially more than 0.25 ppt, more than 0.5 ppt or more than 0.8 ppt, based on the sum total of all the carbon atoms present in the carbon dioxide and / or the carbon produced.

[0031] In preferred embodiments, the carbon dioxide used in the process and / or the carbon produced is biomass-derived to an extent of at least 10 wt.%, especially to an extent of more than 25 wt.%, to an extent of more than 50 wt.%, to an extent of more than 75 wt.%, to an extent of more than 90 wt.%, to an extent of more than 95 wt.%, to an extent of more than 98 wt.% or to an extent of 100 wt.%, with respect to the total weight of the carbon dioxide used.

[0032] In a further preferred embodiment, the method according to the invention comprises a step of producing carbon dioxide from biomass, especially in a fermentation unit. The fermentation unit may be configured to use bacteria and / or heat to decompose the biomass.

[0033] Thereby, preferably, a gas comprising methane and carbon dioxide is produced from the biomass and the carbon dioxide is separated from the methane in a separation unit.

[0034] If desired, the methane then may be converted into hydrogen and carbon in a converting unit, in particular a pyrolysis unit.

[0035] The sodium tetra hydroxide zincate formed in step a) in particular is meant to be Na2Zn(OH)4.

[0036] In step a), preferably, zinc oxide is dissolved in sodium hydroxide in order to form a concentrated sodium tetra hydroxido zincate solution. The concentrated sodium tetra hydroxido zincate solution then can be used for galvanic zinc wining.

[0037] In step b) metallic zinc is extracted from the sodium tetra hydroxide zincate, especially the sodium tetra hydroxide zincate in the sodium hydroxide solution, by galvanization or galvanic zinc deposition, respectively. Preferably, the separation takes place according to the following reaction equation:

[0038] Anode: 4 OH- - 4 e- O2+ 2 H2O

[0039] Cathode: 2 Zn2++ 4 e- 2 Zn Thereby, besides metallic zinc, oxygen (O2) is released.

[0040] The energy required for this reaction preferably is generated by photovoltaics. However, the skilled person is aware that other energy sources can also be used. Galvanic zinc deposition is particularly advantageous, as the elemental zinc can be used as a reducing agent.

[0041] Preferably, the sodium hydroxide therewith produced and / or remaining after galvanization is used again in step a) and / or e). This makes the process largely independent of material suppliers. This can be omitted in some variants of the invention.

[0042] Especially preferred, a first part of the sodium hydroxide gained in step b) is used in step a) and a second part of the sodium hydroxide gained in step b) is used in step e).

[0043] In step c) the metallic zinc is reacted with the carbon dioxide, to obtain carbon monoxide.

[0044] Zn + CO2— > ZnO + 00$

[0045] With this reaction, zinc is used as a reducing agent to produce carbon monoxide. Zinc oxide as the by-product can be reused in step a) of the inventive process.

[0046] In step d), the the carbon monoxide obtained in step c) can be further reduced to carbon.

[0047] Zn + CO — > ZnO + C

[0048] Again, metallic zinc is used as a reducing agent to produce solid carbon and zinc oxide as the by-product. Thereby, any residual carbon dioxide present after step c) can be converted to carbon monoxide and carbon as well.

[0049] In particular, step d) is performed with a ferrum containing catalyst, especially a ferrum oxide catalyst. Step d) results in a mixture of solid carbon and zinc oxide, and optionally the ferrum containing catalyst. Especially, the mixture is present in the form of a particulate material, especially a powdery material.

[0050] Especially, in step c) and / or d), the metallic zinc is heated to a temperature of at least 400°C, in particular to a temperature between 600°C and 1'000°C and reacted with the carbon dioxide and / or carbon monoxide. The reaction can e.g. be performed in a rotary tube reactor or and / or a rotary kiln. Rotary tube reactors and rotary kilns have proven to be particularly optimal in this process step, as they are particularly good at circulating solids. However, the skilled person is also aware of other suitable devices.

[0051] Subsequently, in step e), zinc oxide in the mixture of step d) is dissolved by adding sodium hydroxide, especially sodium hydroxide gained in step b). Thereby a dispersion comprising sodium tetra hydroxido zincate, solid carbon, and optionally the ferrum containing catalyst is formed. Especially, the ferrum containing catalyst is a solid material as well.

[0052] In step f), the solid carbon, and optionally the ferrum containing catalyst, is then separated from the dispersion of step e). This can be done by filtration, especially with a filter press. Preferably, the remaining solution of sodium tetra hydroxido zincate is reused in step b), in particular without any treatment.

[0053] If desired, the ferrum containing catalyst may additionally be separated from the carbon, e.g. by treatment with an acid, and optionally be recovered for further use in the method according to the invention.

[0054] However, it is also possible to dispense with the separation of the ferrum containing catalyst. In this case, the the ferrum containing catalyst is a consumable of the method according to the invention. Since a proportion of the ferrum containing catalyst with respect to the carbon usually is small, it will hardly have a negative impact on the properties of the carbon. In particular, ferrum containing catalysts, especially ferrum oxides, are bio-compatible and thus a better usable end product is obtained when compared to methane decomposition. Preferably, after step c), zinc oxide is recovered, in particular completely recovered, for the reuse in step a) and after step f), the remaining solution of sodium tetra hydroxido zincate sodium is reused in step b).

[0055] Especially, steps c) and d) can take place simultaneously or one after the other.

[0056] It is a great advantage that zinc can be used as the central reagent for the above reactions. Zinc is inexpensive, non-toxic, readily available and, last but not least, can be recycled after each reaction. Furthermore, in contrast to other methods based on hydrogen and methane, with the zinc based method according to the invention products free of polycyclic aromatic hydrocarbon (PAH; toxic and carcinogenic substances) are available. This is due to the fact, thanks to the zinc, no hydrogencontaining reagents are required to obtain the carbon product.

[0057] Also, all of the above reactions have the advantage that, apart from carbon dioxide, and optionally the ferrum containing catalyst, no substances need to be consumed, but can be fed back into the process in the cycle.

[0058] Therefore, preferably, the method according to the invention is performed such that carbon dioxide, and optionally the ferrum containing catalyst, is / are the only consumable in the process.

[0059] Most preferred, the method is performed as a circular process.

[0060] Another aspect of the present invention is related to an apparatus for carrying out a method according to the invention for providing carbon from carbon dioxide, especially from biomass-derived carbon dioxide, comprising a galvanic deposition unit that is configured for performing step b), a reducing unit that is configured for performing steps c) and / or d), a dissolving unit that is configured for performing step e) and a separating unit that is configured for performing step f). The separation unit in particular is a filter unit, especially a filter press.

[0061] Furthermore, a reaction unit may be present that is configured for performing step a). However, dissolving zinc oxide in sodium hydroxide may be performed in the galvanic deposition unit as well.

[0062] Additionally, the apparatus according to the invention preferably comprises a feeding system, especially comprising conduits and / or pumps, that is configured to feed back the sodium hydroxide and / or the zinc oxide obtained as by-products of steps b) and / or c) to the unit(s) where steps a) and / or e) takes place, especially the reaction unit, the galvanic deposition unit and / or the dissolving unit, and / or the feeding system is configured to feed back the sodium tetra hydroxido zincate of step f) to the unit where step b) takes place, especially the galvanic deposition unit.

[0063] Other advantageous embodiments and combinations of features come out from the detailed description below and the entirety of the claims.

[0064] The drawings used to explain the embodiments show:

[0065] Fig. 1 a diagrammatic representation of the overall reaction steps of the process.

[0066] In the figures, the same components are given the same reference symbols.

[0067] Figure 1 shows a reaction diagram in which the individual reaction steps for the production of carbon are illustrated.

[0068] The process starts with step 1 : Zinc oxide is dissolved in sodium hydroxide to form a concentrated solution of sodium tetra hydroxido zincate (Na2Zn(OH)4).

[0069] In step 2, the solution of step 1 is used to produce metallic zinc by an alkaline galvanic process. Specifically, metallic zinc is extracted from the sodium tetra hydroxide zincate solution by galvanic zinc deposition. The energy required for this reaction for example is generated by photovoltaics. The separation takes place according to the following reaction equation:

[0070] Anode: 4 OH- - 4 e- O2+ 2 H2O

[0071] Cathode: 2 Zn2++ 4 e- 2 Zn

[0072] Besides the metallic zinc, oxygen (O2) is released.

[0073] The sodium hydroxide (NaOH) therewith produced and / or remaining after galvanization is fed back and reused in step 1 and in step 5 (see below). In step 3, the metallic zinc obtained in step 2 is reacted with carbon dioxide, to obtain carbon monoxide.

[0074] Zn + CO2— > ZnO + 00$

[0075] Thereby, the metallic zinc is for example heated to a temperature between 900°C and 1’000°C and reacted with the carbon dioxide. With this reaction, zinc is used as a reducing agent to produce carbon monoxide.

[0076] The carbon dioxide used in step 3 for example is biomass-derived carbon dioxide that has been obtained in a fermentation reaction from biomass, such as e.g. wood, wood residues, energy crops, agricultural residues, and / or organic waste from industry and / or households.

[0077] Specifically, the reduction with gaseous zinc proceeds smoothly at normal pressure. The higher the temperature, the faster the conversion takes place. In a preferred design, a rotary tube reactor is used, half of which is charged with carbon dioxide and half with liquid zinc. The lower half of the tubular reactor is heated with a jacket heater so that gas temperatures of preferably 900-950°C are generated in the lower third of the reactor (boiling point zinc 907°C). The actual reaction with the deposition of zinc oxide only takes place in the quarter below half of the tubular reactor. The upper part of the tubular reactor is cooled so that liquid zinc dominates in the center section. Packings with a large surface area are preferably introduced in the center section, which facilitates the condensation of liquid zinc. In order to achieve complete deposition of the zinc, the upper section must be cooled down to approx. 100°C. The metallic zinc accumulates on the surfaces and must be melted at regular intervals by heating the entire reactor. No gas is transported through the reactor during the melting process. In the lowest quarter, the reaction product zinc oxide is separated from the liquid zinc by evaporation. Zinc oxide as the by-product of step 3 is continuously transported downwards and ejected into a gas-tight container, where it cools down or from where it is immediately fed hot into step 1.In step 4, the carbon monoxide obtained in step 3 as well as any remaining carbon dioxide from step 3 is further reduced to carbon with the metallic zinc as a reducing agent and a ferrum oxide catalyst (optional). Zn + CO — > ZnO + C

[0078] Specifically, the conversion of carbon dioxide / carbon monoxide to solid carbon is preferably carried out in the gas phase by reduction with zinc using catalysts, in particular iron oxide. In a preferred embodiment, metallic zinc is heated in liquid form to a temperature of 900-1000°C in the center of a rotary kiln closed at the top, so that reactive zinc vapor is produced. At the same level, carbon dioxide / / carbon monoxide with fine iron oxide particles is blown in upwards. Carbon dioxide is converted to zinc oxide and carbon monoxide. The carbon monoxide reacts with iron oxide in the presence of zinc vapor as a reducing agent to form elemental carbon. This reaction takes place in the gas phase above the inlet on the iron oxide catalyst particles. The iron oxide particles fall onto the tube wall together with the resulting zinc oxide and the carbon formed, where they are transported downwards. Excess metallic zinc is evaporated from the lower part of the tube and returns to the top as a gas. The completeness of the reaction is achieved by the fact that only gas is pumped into the reaction chamber, but there is no possibility for any gaseous product to leave the reaction chamber. Only solids are discharged, i.e. gases remain in the reaction chamber until they are completely converted to solids. To elevate the pressure in the kiln is a possibility to enhance the speed of the reaction.

[0079] Step 4 results in a solid mixture of carbon, zinc oxide, and the ferrum containing catalyst. Especially, the mixture is present in the form of a powdery material.

[0080] In step 5, the zinc oxide in the mixture of step 4 is dissolved by adding sodium hydroxide gained in step 2. Thereby a dispersion comprising sodium tetra hydroxido zincate, solid carbon, and the solid ferrum containing catalyst is formed.

[0081] Then, the solid carbon and the solid ferrum containing catalyst are separated from the dispersion of step 5 with a press filter and the remaining solution of sodium tetra hydroxido zincate is reused in step 2.

[0082] In step 6, the ferrum containing catalyst may be separated from the carbon, e.g. by treatment with an acid, and optionally be recovered for further use in the method according to the invention. The solid carbon obtained in step 6 can for example be stored for further use and / or incorporated into soil.

[0083] In summary, it is to be noted that according to the invention, a method is provided in which a large number of substances can be provided from any source containing carbon dioxide, in particular biomass or atmospheric air, with particularly few reagents, whereby essentially all reagents can be used in the cycle.

[0084] List of reference signs

[0085] 1-6 method steps

Claims

Claims1. Method for the production of carbon from carbon dioxide, in particular from biomass derived carbon dioxide, comprising the steps of: a) reacting zinc oxide with sodium hydroxide to form a solution of sodium tetra hydroxido zincate, especially by dissolving zinc oxide in sodium hydroxide; b) the solution of step a) is used to produce metallic zinc by an alkaline galvanic process in which sodium tetra hydroxide zincate is converted to sodium hydroxide and metallic zinc, wherein, preferably, therewith gained sodium hydroxide is used in step a) and / or e); c) reducing the carbon dioxide, in particular biomass derived carbon dioxide, to carbon monoxide with metallic zinc of step b) as reduction agent, wherein, preferably, therewith gained zinc oxide is used in step a), in particular without any treatment; d) reducing the carbon monoxide gained in step c), and optionally any residual carbon dioxide present after step c), with metallic zinc of step b), preferably using a ferrum containing catalyst, to obtain a mixture of solid carbon and zinc oxide, and optionally the ferrum containing catalyst; e) dissolving the zinc oxide in the mixture of step d) by adding sodium hydroxide, especially sodium hydroxide gained in step b), in order to form a dispersion comprising sodium tetra hydroxido zincate, solid carbon, and optionally the ferrum containing catalyst; f) separating the solid carbon, and optionally the ferrum containing catalyst, from the dispersion of step e), wherein, preferably, the remaining solution of sodium tetra hydroxido zincate is reused in step b), in particular without any treatment.

2. Method according to claim 1 , wherein the carbon dioxide is biomass derived carbon dioxide.

3. Method according to any of preceding claims, further comprising a step of producing carbon dioxide from biomass, especially in a fermentation unit.

4. Method according to claim 3, whereby a gas comprising methane and carbon dioxide is produced from the biomass and the carbon dioxide is separated from the methane in a separation unit.

5. Method according to claim 4, whereby the methane is converted into hydrogen and carbon in a converting unit, in particular a pyrolysis unit.

6. Method according to any of preceding claims, wherein in step a), zinc oxide is dissolved in sodium hydroxide in order to form a concentrated sodium tetra hydroxido zincate solution.

7. Method according to any of preceding claims, wherein, after step b) sodium hydroxide is recovered, in particular completely recovered, for the reuse in step a) and / or e).

8. Method according to any of preceding claims, wherein in step c) the metallic zinc is heated to a temperature of at least 400°C, in particular to a temperature between 600°C and 1’000°C, and reacted with the carbon dioxide obtain the zinc oxide and the carbon monoxide.

9. Method according to any of preceding claims, wherein step d) is performed with a ferrum containing catalyst, especially a ferrum oxide catalyst.

10. Method according to any of preceding claims, wherein, after step c), zinc oxide is recovered, in particular completely recovered, for the reuse in step a) and after step f), the remaining solution of sodium tetra hydroxido zincate sodium is reused in step b).

11. Method according to any of preceding claims, wherein a first part of the sodium hydroxide gained in step b) is used in step a) and a second part of the sodium hydroxide gained in step b) is used in step e).

12. Method according to any of preceding claims, wherein the method is performed such that carbon dioxide, and optionally the ferrum containing catalyst, is / are the only consumable(s) in the process.

13. Method according to any of preceding claims, wherein the method is performed as a circular process.

14. Method according to any of preceding claims, wherein all energy for performing the steps is electricity and / or thermal heat, whereby the energy required in the form of electricity is produced by a photovoltaic unit and / or a wind power unit, and / or the energy required in the form of heat is produced with solar thermal collectors.

15. Method according to any of preceding claims comprising a further process step of generating energy with a photovoltaic unit and / or a wind power unit and / or solar thermal collector.

16. Apparatus for carrying out a method according to any one of claims 1 to 15, for providing carbon from carbon dioxide, especially from biomass-derived carbon dioxide, comprising a galvanic deposition unit that is configured for performing step b), a reducing unit that is configured for performing steps c) and / or d), a dissolving unit that is configured for performing step e) and a separating unit that is configured for performing step f), and optionally a reaction unit that is configured for performing step a).

17. Apparatus according to claim 16 further comprising a feeding system, especially comprising conduits and / or pumps, that is configured to feed back the sodium hydroxide and / or the zinc oxide obtained as by-products of steps b) and / or c) to the unit(s) where step a) and / or e) takes place and / or the feeding system is configured to feed back the sodium tetra hydroxido zincate of step f) to the unit where step b) takes place.

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