Method and apparatus for the production of one or more of carbon dioxide, carbon monoxide, carbon and hydrogen from a gas

Abstract

A method for the production of one or more of carbon dioxide, carbon monoxide, carbon and hydrogen from a gas comprising carbon dioxide and preferably water, in particular from air, comprising the following steps: in a first step, the gas comprising carbon dioxide is brought into contact with sodium hydroxide, preferably a sodium hydroxide solution, to absorb carbon dioxide and to form sodium carbonate, in particular sodium carbonate with water of crystallization; in a second step, the sodium carbonate is reacted with zinc oxide, in particular with a surplus of zinc oxide, for releasing one or more of carbon dioxide, carbon monoxide and, if water is present, hydrogen. An apparatus for carrying out a method for providing one or more of carbon dioxide, carbon monoxide, carbon and hydrogen from a gas comprising carbon dioxide and preferably water, in particular from atmospheric air, comprising an absorber that is configured for performing the first step and a decomposition unit that is configured for performing the second step.

Description

[0001] Method and apparatus for the production of one or more of carbon dioxide, carbon monoxide, carbon and hydrogen from a gas

[0002] The invention relates to a method and an apparatus for the production of one or more of carbon dioxide, carbon monoxide, carbon and hydrogen from a gas comprising carbon dioxide and preferably water, in particular from air, wherein in a first step, the gas comprising carbon dioxide is brought into contact with sodium hydroxide, preferably a sodium hydroxide solution, to absorb carbon dioxide and to form sodium carbonate, in particular sodium carbonate with water of crystallization.

[0003] As the world continues to face the challenge of climate change, there is growing recognition of the importance of reducing carbon emissions across all sectors of the economy. In response to this challenge, many companies are developing CO2neutral chemical products that do not emit any net carbon dioxide into the atmosphere during their production, use, and disposal.

[0004] CO2neutral chemical products refer to chemicals that are produced using low-carbon or renewable energy sources, and that do not emit any net carbon dioxide during their lifecycle. This means that the carbon emissions associated with their production and use are offset by the removal of an equivalent amount of carbon dioxide from the atmosphere, through activities such as carbon capture and storage or the use of renewable energy sources.

[0005] Further, attempts are being made to produce so-called CO2negative products. CO2negative products refer to products or technologies that actively remove more carbon dioxide from the atmosphere than they emit during their production, use, and disposal. This means that they have a net negative carbon footprint and can help to mitigate the effects of climate change.

[0006] The decentralized provision of all components for the production of alcohols and hydrocarbons plays a key role in all concepts for the extraction of energy sources or the production of energy-intensive raw materials in remote areas. In particular, the provision of a carbon source is often complex, as carbon dioxide-containing waste gas is not available in regions where energy from renewable sources would be available in large quantities and is not needed locally. Such regions are areas with high, regular solar radiation, where photovoltaics and solar thermal energy work with good efficiency. These are found around the equator in the "Earth's sun belt", preferably in deserts or semi-deserts. The only practically unlimited carbon source available is carbon dioxide in the air, which is present in low concentrations and is to be extracted using special processes that are summarized as Direct Air Capture processes (DAC). The majority of known DAC processes are not scalable in the dimensions required to replace fossil fuels or fossil raw materials, or can only be scaled up at great expense. In addition to the provision of the carbon source, water consumption is also a critical factor in arid zones. Processes with high water consumption are therefore ruled out, as are very energy-intensive processes and processes with reactions that would be highly efficient but run very slowly so that the investment costs are high due to the low throughput. The boundary conditions to be fulfilled are a closed cycle of the process, the avoidance of absorbents or membranes with a limited shelf life and an excessive demand for rare precious metals. The process in question takes into account these boundary conditions, which must be fulfilled in order to enable the economical extraction of the components carbon dioxide, carbon monoxide and hydrogen from air using renewable energy sources and to provide synthesis gas in large quantities for any application in remote areas with poor infrastructure.

[0007] While the development of CO2negative products is an important step towards reducing carbon emissions and mitigating the effects of climate change, there are several challenges associated with their production. One of the main challenges is the cost of implementing these technologies, which can be prohibitively expensive and may require significant investment in research and development.

[0008] Another challenge is the scalability of these technologies, as many of the currently known CO2negative products are still in the early stages of development and may not be able to be produced at a large scale. In addition, the energy and resource requirements of producing CO2negative products may offset the benefits of their carbon negativity, especially if renewable energy sources are not used. Thus, there is still a need for improved solutions that overcome the aforementioned drawbacks at least partly.

[0009] It is the object of the invention to create a process and apparatus pertaining to the technical field initially mentioned, wherewith one or more of carbon dioxide, carbon monoxide, carbon and hydrogen from a gas can be produced cost effectively.

[0010] The solution of the invention is specified by the features of claim 1. According to the invention, in a second step, the sodium carbonate is reacted with zinc oxide, in particular with a surplus of zinc oxide, for releasing one or more of carbon dioxide, carbon monoxide and, if water is present, hydrogen.

[0011] According to the invention, the method for the production of one or more of carbon dioxide, carbon monoxide, carbon and hydrogen from a gas comprising carbon dioxide and preferably water, in particular from air, comprising the following steps: a) the gas comprising carbon dioxide and water is brought into contact with sodium hydroxide, preferably a sodium hydroxide solution, to absorb simultaneously carbon dioxide and water to form sodium carbonate, in particular sodium carbonate with water of crystallization, and a water enriched sodium hydroxide solution; b) sodium carbonate crystals from the solution of step a) are separated, preferably by filtration or centrifugation, wherein optionally additional sodium carbonate can be separated by distillation of the sodium hydroxide solution to enhance the cristallisation; c) the sodium carbonate crystals from step b) are reacted with zinc oxide, in particular with a surplus of zinc oxide, for releasing carbon dioxide by the formation of sodium zincate; d) the sodium zincate of step c) is reacted with water to form sodium hydroxide, saturated with sodium tetra hydroxido zincate, and solid zinc oxide, wherein at least a part of the solid zinc oxide is separated; e) the remaining solution of sodium tetra hydroxido zincate in sodium hydroxide is used as absorbent in step a); f) the solution of step d) is used to produce metallic zinc by alkaline galvanic process, in particular by converting sodium tetra hydroxide zincate to sodium hydroxide and metallic zinc, wherein the metallic zinc is used as a reduction agent for one or more of the following processes:

[0012] I. the metallic zinc is used as a reduction agent to reduce carbon dioxide gained in step c) to carbon monoxide, wherein therewith gained zinc oxide is used in step c), in particular without any treatment;

[0013] II. the metallic zinc is used as a reduction agent to reduce carbon monoxide gained in step I to carbon, preferably using a ferrum containing catalyst, wherein carbon and zinc oxide is separated, preferably by solving the zinc oxide in sodium hydroxide in order to form a concentrated sodium tetra hydroxido zincate solution, wherein the concentrated sodium tetra hydroxido zincate solution is used for galvanic zinc wining for the use in step f) and recovery of sodium hydroxide solution, for the use as absorbent in step a);

[0014] III. the metallic zinc is used as a reduction agent to reduce water, preferably water of the water enriched sodium hydroxide solution of step a), to hydrogen, by forming a concentrated sodium tetra hydroxido zincate solution, which is preferably used for galvanic zinc winning and recovery of higher concentrated sodium hydroxide solution for the use in step a).

[0015] Reference is made below to the steps numbered a) to f) and the substeps I to III where necessary.

[0016] According to the invention, zinc oxide is used for the reaction with sodium carbonate. Even if the reaction could in principle be carried out with other substances, there are several advantages the advantage in the use of zinc oxide. Zinc is relatively abundant in the earth's crust, and the production cost of zinc oxide is comparatively low. Due to its widespread use in various commercial applications, zinc oxide is very common and therefore readily available almost everywhere in the world. This means that zinc oxide is readily available and inexpensive to procure. Zinc oxide is generally considered to be non-toxic to humans and the environment, which means that it can be stored and used in the application according to the invention, for example, without special, particularly cost-intensive safety precautions. This means that workers are not exposed to any particular dangers. Further it is even biocompatible, which means that it is generally well-tolerated by living tissues.

[0017] From a chemical point of view, other elements could also be used for the process. However, tests have shown that the use of zinc has procedural advantages over the other metals. In principle, iron can also be used for the process, but it forms different oxides that are difficult to handle and can impair the function of the device. Calcium can also be used. However, calcium carbonates also have the disadvantage that they stick to the system and are therefore difficult to handle. Finally, all the experiments carried out have shown that zinc or zinc oxide has particularly favourable properties in the process according to the invention.

[0018] The process according to the invention has the advantage that the zinc oxide can be used in the cycle, i.e. the zinc oxide can be reused in the process after the carbon dioxide has been released. This means that the zinc oxide is not consumed. The process also has the advantage that the product ratios between carbon dioxide, carbon monoxide, carbon and hydrogen can essentially be freely adjusted. In particular, only carbon monoxide can be produced, for example, depending on requirements. In a further variant, only carbon can be produced. In a further variant, twice as much carbon dioxide as carbon monoxide can be produced (in terms of mass or moles). Furthermore, equal amounts of carbon dioxide, carbon monoxide, carbon and hydrogen can be produced (in terms of mass or moles). The person skilled in the art will realise that any number of other examples could be given.

[0019] Thus, a further advantage of the process is that one or more of carbon dioxide, carbon monoxide, carbon and hydrogen can be produced from air in any ratio to each other in a single process.

[0020] In particular, the gas is preferably the only consumable in the process. Therewith, preferably no other substances are consumed. However, if other products are produced from one or more of carbon dioxide, carbon monoxide, carbon and hydrogen, it may be necessary to use other substances which are consumed.

[0021] 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 of one or more of carbon dioxide, carbon monoxide, carbon and hydrogen, the process removes more carbon dioxide from the environment, e.g. the atmosphere, than it emits during the production of the product.

[0022] Even if the CO2negative mode of operation is of course preferred, it is of course 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 one or more of carbon dioxide, carbon monoxide, carbon and hydrogen than the process removes from the environment, especially the atmosphere. This depends in particular on whether the energy source is CO2-neutral or not.

[0023] The inventive process provides for an effective, inexpensive, sustainable and robust process for producing one or more of carbon dioxide, carbon monoxide, carbon and hydrogen 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.

[0024] Also, the inventive process is highly modular. This means that individual process steps can be effected in one and the same place or plant, respectively, or individual process steps can be performed at different places. For example, step a) can for example be performed in regions with high solar radiation. Step c) can be performed at the location, where the one or more of carbon dioxide, carbon monoxide, carbon and hydrogen are used. However, since zinc oxide can be reused in this process (i.e. zinc oxide is not consumed in this process), it is preferred to perform the process steps a) and c) at the same place.

[0025] 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.

[0026] Especially preferred, the energy required for performing the process step(s) in particular 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.

[0027] 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.

[0028] Especially, the energy required is generated at the same location, especially in the same plant, where step a) or b) or both steps, take(s) place.

[0029] The carbon dioxide captured in step a) is at least partly used for producing the carbon dioxide, carbon monoxide and carbon. If water is present in the gas, also hydrogen can be produced. Water is adsorbed by the sodium hydroxide. Water is particularly well adsorbed by solid sodium hydroxide or by a concentrated sodium hydroxide solution.

[0030] The method preferably uses air as a source for the carbon dioxide and, if present, water. The air is preferably atmospheric air or ambient air. The process therewith preferably removes carbon dioxide and, if present, water from the air. In the first step, the gas comprising carbon dioxide is brought into contact with sodium hydroxide, preferably a sodium hydroxide solution, to absorb carbon dioxide and to form sodium carbonate, in particular sodium carbonate with water of crystallization according to the following equation:

[0031] 2 NaOH + CO2+ H2O^ Na2CO3.H2O

[0032] However, the water does not have to occur in exactly this ratio; in variants, more or less water can also be involved.

[0033] In the second step, the sodium carbonate is reacted with zinc oxide, in particular with a surplus of zinc oxide, for releasing one or more of carbon dioxide, carbon monoxide and, if water is present, hydrogen. As the zinc oxide is used in the cycle, it can also be used equimolar or submolar.

[0034] Preferably the gas is air, in particular atmospheric air, and wherein, after step c) zinc oxide and sodium hydroxide is recovered, in particular completely recovered for the reuse in step a), and wherein in particular the water is preferably extracted from the gas, in particular to a large extent.

[0035] Once the process has been initiated, it can in principle be maintained without additional raw materials apart from the supply of air 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.

[0036] The skilled person is aware that exhaust gases and the like can also be used instead of atmospheric air.

[0037] In variants, the recovery of zinc oxide or sodium hydroxide can also be dispensed with, at least in part, so that zinc oxide and / or sodium hydroxide must be continuously added to the process, even if this is not the preferred embodiment.

[0038] In step a) the gas comprising carbon dioxide is preferably brought into contact with concentrated sodium hydroxide solution, in particular with a sodium hydroxide solution comprising at least 10 mol / L sodium hydroxide, preferably between 12 to 19 mol / L sodium hydroxide.

[0039] The use of concentrated sodium hydroxide solution has the advantage that the reaction takes place more quickly and the carbon dioxide can therefore be absorbed more efficiently. The concentrated solution also has a hygroscopic effect, so that water can be adsorbed more efficiently from the gas in the air.

[0040] In variants, the sodium hydroxide solution can also have a concentration of less than 10 mol / L.

[0041] In step a) the sodium carbonate, in particular sodium carbonate with water of crystallization, is preferably precipitated, in particular due to exceeding the solubility. The sodium carbonate typically precipitates as a monohydrate. The sodium carbonate can, for example, be separated by filtration, in particular in a chambered liter press or similar. The sodium carbonate can be stored in this form for any length of time until further use in the process. The advantage of this process lies in the relatively low amount of energy required to separate the sodium carbonate from the solution.

[0042] In variants, the water can also be evaporated or vaporized instead of precipitated. This can be carried out using solar thermal energy or process waste heat, for example.

[0043] Preferably, between step b) and step c) the sodium carbonate comprising water of crystallization is dried, in particular with water recovery. The sodium carbonate is preferably dried when sufficient thermal energy is available (e.g. solar thermal energy or process waste heat). Preferably, the water is recovered and reused in the process step d). The reuse of water can be particularly important in areas with a low water supply and low rainfall. The dried sodium carbonate can also be stored temporarily for as long as required.

[0044] The dried sodium carbonate can also be stored temporarily for as long as required. The sodium carbonate can also be dried only after the moist sodium carbonate has been temporarily stored - this can be useful, for example, if insufficient solar thermal energy or process heat is available during the production of the moist sodium carbonate.

[0045] In some variants, the drying of the sodium carbonate can be omitted. Drying can also take place in the subsequent step c) (see below). It is also not absolutely necessary to recover the water during the drying process.

[0046] For the reaction of sodium carbonate and zinc oxide in step c), the sodium carbonate is preferably melted, in particular together with zinc oxide, wherein preferably a mass ratio between sodium carbonate and zinc oxide is greater than 4:1 , preferably to reduce a viscosity and wherein zinc oxide together with sodium carbonate is added, in particular continuously added to the melt. Carbon dioxide is released in this process step.

[0047] In a first variant, the sodium carbonate can be mixed with the zinc oxide and then heated, which converts the sodium carbonate into a melt. In another variant, the sodium carbonate can be melted and then mixed with zinc oxide. The melt preferably contains an excess of sodium carbonate, in particular greater than 4:1 , to keep the viscosity low.

[0048] Preferably, zinc oxide is fed into the melt from above together with fresh sodium carbonate, releasing carbon dioxide. The sodium zincate product is preferably removed from the bottom of the melt and cooled.

[0049] It may also be possible to omit melting the sodium carbonate. The mixture can also be roasted, in particular at a temperature below the melting point, in order to release the carbon dioxide.

[0050] Preferably, the reaction of sodium carbonate and zinc oxide in step c) takes place at a temperature higher than 600°C, in particular at a temperature between 700°C and 1000°C, more preferably between 800°C and 900°C. It is also preferable to react the sodium carbonate and the zinc oxide at a temperature between 850 and 900°C. Both dried and moist sodium carbonate can be used. It has been shown that an optimum reaction rate in relation to the energy input is achieved in this temperature range.

[0051] In some variants, the temperature can also be below 600°C.

[0052] Preferably, the reaction of sodium carbonate and zinc oxide in step c) takes place in a rotary kiln. Rotary kilns have proven to be particularly optimal in this process step, as they are particularly good at circulating solids.

[0053] However, the skilled person is also aware of other suitable devices for reacting the sodium carbonate with zinc oxide. In particular, a stirred tank can also be provided.

[0054] In step c) preferably one or more of the following reactions take place: i) carbon dioxide is produced, wherein the sodium carbonate is dried and in particular heated with zinc oxide to a temperature above 850 °C; ii) carbon monoxide is produced, wherein the sodium carbonate is dried and in particular a surplus of metallic zinc is added and preferably heated to a temperature above 900 °C, or carbon monoxide is produced from carbon dioxide by contacting carbon dioxide from i) with liquid or gaseous zinc; iii) carbon dioxide and hydrogen is produced, wherein an equimolar amount of zinc is added in relation of an amount of water present and in particular heated to a temperature below 900 °C; iv) carbon monoxide and hydrogen is produced, wherein a surplus of metallic zinc is added to sodium carbonate and water, in particular to wet sodium carbonate and preferably heated to a temperature above 900 °C; v) carbon is produced by reducing CO2or CO with metallic zinc, in particular with a ferrum catalysator.

[0055] Preferably, the sodium hydroxide and zinc circuit in step f)ll) is separated from the sodium hydroxide and zinc circuit in the absorption circuit in a) in order to avoid the carry-over of iron or carbon.

[0056] These process steps can optionally be carried out in addition to the reaction of sodium carbonate with zinc oxide. The sodium carbonate produced in step a) can thus be fed to a first part of the reaction with zinc oxide in step c), while a second part can be fed to one or more of the above reactions. The result is a process in which one or more of carbon dioxide, carbon monoxide, carbon and hydrogen can be produced variably and in any desired proportions. The process thus becomes particularly dynamic and can be adapted to the current needs (of the market).

[0057] The special common feature of the reactions above is, that each of these reactions can be carried out using zinc or zinc oxide, whereby the zinc or zinc oxide can be recovered in each case after the reaction has taken place.

[0058] Preferably, in step c) a sodium zincate, in particular Na2ZnO2, is obtained in addition to carbon dioxide, wherein in particular the sodium zincate is extracted from the melt.

[0059] The reaction preferably takes place according to the following reaction equation:

[0060] Na2CO3+ ZnO Na2ZnO2+ CO2t However, the skilled person is also aware of other possible reaction pathways.

[0061] Preferably, the reaction of sodium carbonate and zinc oxide is carried out with an excess of zinc oxide. Sodium carbonate is preferably mixed with zinc oxide powder and additional zinc powder is preferably used as a separating agent. However, the zinc powder as the separating agent can be omitted. The sodium carbonate thus dispersed in zinc oxide is preferably melted, e.g. in a rotary kiln, whereby preferably spherical particles of sodium zincate coated with excess zinc oxide are formed. After the subsequent process steps, the excess zinc oxide is separated together with the zincate produced during the decomposition process.

[0062] Preferably, sodium zincate / zinc oxide particles, after optional mechanical separation of zinc oxide dust by sieving, are dissolved in hot water as sodium tetrahydroxidozincate and then preferably kept at temperature for several hours to recover zinc oxide and sodium hydroxide. This recovers zinc oxide for the process step of reacting zinc oxide with sodium carbonate, as well as highly concentrated sodium hydroxide solution for absorbing carbon dioxide and water from the air. To obtain a high concentration of the sodium hydroxide solution, more sodium zincate is preferably added to the water than dissolves (saturated solution with sediment). Solid zinc oxide is preferably separated from the concentrated caustic soda solution, e.g. by filtration in a chamber filter press.

[0063] Preferably, the sodium zincate obtained in step c) is added in water, preferably at a temperature above 80°C, wherewith at least a part of the sodium zincate is hydrolyzed to sodium tetrahydroxidozincate and wherein the tetrahydroxidozincate is at least partially decomposed to sodium hydroxide solution and zinc oxide, wherein preferably solid zinc oxide is separated, in particular precipitated, and wherein in particular an amount of the added water is selected in such a way, that the obtained sodium hydroxide solution has a concentration between 12 mol / L and 19 mol / L in particular for the reuse in step a). More preferably the resulting sodium hydroxide solution has a concentration between 17 and 19 mol / L. After the decomposition, the solution is preferably cooled in order to reduce the solubility of zinc oxide, preferably until the amount of zinc oxide in the solution is below 10 wt.%.

[0064] Preferably the unreacted sodium carbonate is filtered off in this way together with the precipitated zinc oxide, dried and reused in the step, where sodium carbonate is mixed with zinc oxide. The sodium carbonate still dissolved in the sodium hydroxide solution is returned to the absorber and is therefore not lost.

[0065] The temperature of the water can also be below 80 °C. More preferably, the tetrahydroxidozincate is fully decomposed to sodium hydroxide solution and zinc oxide. However, due to the equilibrium reaction, this is usually hardly possible directly.

[0066] Therefore, the zinc oxide is preferably removed during the process in order to shift the equilibrium in the direction of decomposition. This can be done continuously or discontinuously.

[0067] By selecting the amount of water, the sodium hydroxide solution obtained by decomposing the sodium zincate can be used directly in step a) of the process to absorb carbon dioxide from a gas, in particular from the air.

[0068] However, the skilled in the art is also aware of other possible reaction pathways capable to release sodium hydroxide from sodium zincate.

[0069] Preferably the water is obtained by distillation of water of crystallization from the sodium carbonate of step a) and / or obtained by drying the sodium carbonate.

[0070] The water preferably originates from the respective gas in the air or was obtained during the drying of the sodium carbonate. This makes the process largely independent of water sources. In variants, however, the water can also come from other sources.

[0071] Preferably, metallic zinc is extracted from the remaining tetrahydroxidozincate in the sodium hydroxide solution by galvanization. This significantly reduces the zinc content of the sodium hydroxide solution, so that the sodium hydroxide solution subsequently precipitates sodium carbonate without or with very little zinc oxide when used in the absorber, which prevents deposits of zinc oxide in the absorber and increases the capacity of the solution for the capture of CO2. Preferably, the separation takes place according to the following reaction equation:

[0072] Anode: 4 OH- - 4 e- O2+ 2 H2O

[0073] Kathode: 2 Zn2++ 4 e- 2 Zn The energy required for this is preferably 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 (see below).

[0074] However, the galvanic reduction to zinc can also be omitted, in particular in the case where neither carbon monoxide, coal nor hydrogen are produced. This eliminates the need to produce metallic zinc, which is used in the present process exclusively as a reducing agent for the production of one or more of carbon monoxide, carbon and hydrogen. This eliminates the need for galvanisation.

[0075] Preferably, the sodium hydroxide solution remaining after galvanisation is used again in step a). This makes the process largely independent of material suppliers. This can be omitted in some variants of the invention.

[0076] Preferably, the metallic zinc is at least partially reacted in one or more of the following processes: i) metallic zinc is brought in contact with water, in particular with water from air, and reacted to zinc oxide and hydrogen; ii) 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 carbon dioxide, in particular with carbon dioxide of step c), to zinc oxide and carbon monoxide; iii) metallic zinc is reacted with carbon dioxide and / or carbon monoxide in the presence of a catalyst, in particular ferric oxides, to zinc oxide and carbon; iv) metallic zinc is reacted with oxygen to zinc oxide, in particular with oxygen obtained from the galvanic process, wherein the energy released by the reaction is converted into electrical energy or thermal energy.

[0077] Galvanic zinc deposition is particularly advantageous, as the elemental zinc can be used as a reducing agent according to the following reaction equations: Zn + 2 NaOH + 2 H2O Na2Zn(OH)4+ H2$

[0078] With this reaction, zinc is used as a reducing agent to produce hydrogen. Sodium tetrahydroxidozincate, which is a by-product of hydrogen production, can in turn be used in electroplating.

[0079] Zn + CO2— > ZnO + 00$

[0080] 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 c) of the inventive process. In a specially preferred embodiment carbon monoxide or a mixture of carbon dioxide and carbon monoxide may be produced simultaneously in step c), where the sodium carbonate is reacted with zinc oxide in order to release carbon dioxide, wherein the process is modified by the addition of metallic zinc to the zinc oxide and sodium carbonate.

[0081] Primary set free carbon dioxide will be immediately reduced by metallic zinc to carbon monoxide in an amount corresponding to the added metallic zinc.

[0082] Zn + CO — > ZnO + C

[0083] With this reaction, the carbon monoxide can be further reduced to carbon. Again, zinc oxide as the by-product can be reused in step c) of the inventive process.

[0084] All of the above reactions have the advantage that no substances are consumed, but can be fed back into the process in the cycle. The individual products such as carbon dioxide, carbon monoxide, coal and hydrogen can be produced in different ratios as required.

[0085] In addition, zinc can be used as the central reagent for all of the above reactions, which is inexpensive, non-toxic, readily available and, last but not least, can be recycled after each reaction.

[0086] However, none of the above reactions need to be carried out. In some variants, only carbon dioxide can be produced. Preferably, all gases and water used in the method are extracted from the air, in particular from atmospheric air, and in particular, intermediary gases and water are recycled in the method.

[0087] This results in a process for the production of one or more of carbon dioxide, carbon monoxide, carbon and hydrogen, which is particularly independent of material suppliers. All materials can preferably be recycled and reused in the process.

[0088] The invention further relates to an apparatus for carrying out a method as described above for providing one or more of carbon dioxide, carbon monoxide, carbon and hydrogen from a gas comprising carbon dioxide and preferably water, in particular from atmospheric air. The apparatus comprises an absorber that is configured for performing step a) and a decomposition unit that is configured for performing step c).

[0089] There are several ways to bring the gas into contact with the sodium hydroxide. Basically, a device is provided for conveying the gas, in particular the ambient air, which leads the gas to the sodium hydroxide where the reaction takes place. In a first variation, the gas can be blown into a sodium hydroxide solution, especially below the surface. In a second variant, the sodium hydroxide solution can be circulated in the presence of the gas in order to achieve an efficient conversion to sodium carbonate. In a preferred embodiment, a spraying device is provided which sprays the sodium hydroxide solution in the presence of the gas. Such spray reactors are generally known to the skilled person. These have the advantage that the sodium hydroxide solution has a very large surface area in the spray mist, with which the carbon dioxide can be efficiently absorbed. The skilled person is also aware of other devices with which the carbon dioxide can be extracted from the gas using sodium hydroxide solution.

[0090] The decomposition unit preferably comprises a heating device with which the mixture of zinc oxide and sodium carbonate can be heated to release the carbon dioxide. There are also many possibilities known to the skilled person.

[0091] Particularly preferably, the device comprises an arrangement in which the absorber is arranged above the decomposition unit. This allows the sodium hydroxide solution to be sprayed in the spray reactor in the presence of the gas and collected at the lower end of the spray reactor. The solution, which now contains sodium carbonate, can then be further processed directly, for example by precipitating the sodium carbonate and then reacting it with the zinc oxide, preferably in an oven, to release the carbon dioxide. This arrangement results in a particularly compact system.

[0092] In variants, the absorber can also be arranged next to the decomposition unit. Other arrangements of the apparatus are also known to the skilled person.

[0093] Preferably, the absorber and / or the decomposition unit are designed as a roof-mounted system. This design means that the device can also be installed in populated areas or in industrial areas where particularly high levels of carbon dioxide are produced. In this case, no building land is required for the system.

[0094] The skilled person is aware that the device does not necessarily have to be designed as a roof-mounted system, but can also be installed in other ways. In particular, the system can also be dimensioned so large that a floor area of a building is to be built for a particularly large system,

[0095] Preferably, the absorber and / or the decomposition unit comprises one or more absorber modules and / or decomposition unit modules. This has the advantage that the apparatus can be flexibly adapted to local requirements at low cost.

[0096] The modular structure can also be dispensed with in variants.

[0097] In a particular embodiment, the absorber unit, in particular a module of the absorber unit, can comprise a frame which is encased in order to obtain a cylindrical module which can be stacked permanently high. A top module may be equipped with a spraying device with which the sodium hydroxide solution is sprayed to absorb carbon dioxide from the air. The skilled person is also aware of other ways in which an absorber unit can be constructed in a modular and cost-effective manner. E.g. the sodium hydroxide solution may be sprinkled over filling material, in particular filling bodies, to enhance the contact surface between the air and the sodium hydroxide solution.

[0098] The decomposition unit preferably comprises a rotary kiln. A rotary kiln is a cylindrical furnace-like structure that rotates on its axis. It is commonly used in various industrial processes such as cement production, calcination of minerals, and thermal treatment of materials. Inside the kiln, materials are fed in at one end and gradually move towards the other end as the kiln rotates.

[0099] Rotary kilns are particularly suitable for drying the sodium carbonate and roasting it together with the zinc oxide. The rotary kiln also has the advantage that the process can be carried out continuously. This continuous operation enhances productivity and efficiency in the processes. Rotary kilns can achieve and maintain high temperatures, making them especially preferred for the inventive process. Further, the rotating motion of the kiln ensures uniform heat distribution as well as a good mix throughout the material being processed, resulting in an efficient and therefore economical use of energy.

[0100] The residence time of the materials inside the rotary kiln can be controlled by adjusting the kiln's rotation speed and angle, allowing for precise control over the process parameters, again resulting in an efficient and economical execution of the procedure.

[0101] Rotary kilns have a relatively compact footprint compared to other types of industrial reactors, making them suitable for installation in space-limited industrial facilities, in particular on a roof top.

[0102] Overall, rotary kilns offer numerous advantages in terms of versatility, continuous operation, temperature capability, heat distribution, control over residence time, feed material handling, emissions reduction, and footprint size, making them a preferred choice of the present process.

[0103] However, other suitable decomposition systems are also known to those skilled in the art. For example, shaft kilns are traditional technology used for thermal decomposition. They are vertical kilns where raw materials are fed from the top and move downwards through the kiln. Shaft kilns can operate in various modes such as wet or dry processes.

[0104] Overall, a process for providing synthesis gases from carbon dioxide and water is thus provided, wherein carbon dioxide and water are preferably obtained from the air. The synthesis gases can be used in a known manner to produce various substances, in particular hydrocarbons and / or alcohols, which can be used as energy sources or raw materials. These substances can be produced with a neutral or even negative CO2 balance.

[0105] The method preferably provides a process for the direct production of highly concentrated sodium hydroxide solution as an absorbent in the cycle.

[0106] The water for the synthesis is preferably obtained at least partially, and in a particularly preferred embodiment even or nearly completely, from the air.

[0107] Preferably, regenerative energy (for example photovoltaics, wind energy, solar thermal energy, etc.) is used in the process in part, in particular preferably exclusively.

[0108] Preferably, the electrochemical processes are carried out without membranes. This has the advantage that costs can be reduced, durability improved and maintenance work reduced. The process is therefore also independent of the availability of membranes. Galvanic zinc deposition is favored over water electrolysis.

[0109] The generated gases CO2, O2, CO, H2can be produced in separate (spatially separated) process steps or in defined mixtures for subsequent syntheses. In particular, elemental zinc can be added during the reaction between zinc oxide and sodium carbonate in order to produce carbon monoxide as well as carbon dioxide. The ratio between carbon dioxide and carbon monoxide can be controlled as desired by adding zinc - in extreme cases, only carbon monoxide can be produced. If the mixture of zinc oxide, zinc and sodium carbonate still contains water, hydrogen can be produced in the same process. The process is therefore particularly variable using a small number of inexpensive reagents.

[0110] The separate process steps for producing carbon monoxide and carbon by reduction with elemental zinc and the reduction of water with zinc enable the gases CO2, O2, CO and H2to be produced separately in terms of time and space.

[0111] Due to the stable intermediate products, these can be stored for any length of time with little effort in order to enable flexible process management depending on the changing availability of energy (renewable energy sources) and water: Sodium carbonate, sodium zincate, zinc oxide, zinc, water, caustic soda can be easily stored for any length of time. Complex intermediate storage of gases under pressure can be reduced to a minimum. Gases for subsequent syntheses of alcohols or hydrocarbons are preferably produced directly as required using the process described, which largely eliminates the need to store gases.

[0112] Sodium and zinc are preferably in a closed cycle so that there is no need to replenish these elements once the process has been initiated.

[0113] Waste heat that cannot be utilised further, which can be generated in the individual processes, is preferably used to heat the absorption solution and the absorber.

[0114] Other advantageous embodiments and combinations of features come out from the detailed description below and the entirety of the claims.

[0115] The drawings used to explain the embodiments show:

[0116] Fig. 1a a diagrammatic representation of the overall reaction steps of the process;

[0117] Fig. 1b a diagrammatic representation of the reaction steps relating to the carbon dioxide path;

[0118] Fig. 1c a diagrammatic representation of the reaction steps relating to the carbon monoxide path;

[0119] Fig. 1d a diagrammatic representation of the reaction steps relating to the carbon path;

[0120] Fig. 1e a diagrammatic representation of the reaction steps relating to the hydrogen path; and

[0121] Fig. 2 a schematic representation of an exemplary device for carrying out the process.

[0122] In the figures, the same components are given the same reference symbols.

[0123] Figure 1 shows a reaction diagram in which the individual reaction steps for the production of carbon dioxide, carbon monoxide, coal, hydrogen and oxygen are illustrated. The process begins with step 1: water and carbon dioxide from the air are absorbed in a sodium hydroxide solution. The sodium hydroxide solution has a concentration of 40 - 50 wt.% and is preheated with process waste heat. The sodium hydroxide solution is distributed over tower packings to increase the contact surface with the air. The carbon dioxide is reacted with the sodium hydroxide solution to form sodium carbonate. The absorption solution is circulated in order to continuously increase the concentration of sodium carbonate and also to absorb more and more water.

[0124] In the present case, absorption can also be obtained by means of a spray reactor in which the sodium hydroxide solution is sprayed vertically at the top via a spray device, while the air is channeled through the spray reactor from bottom to top in counter flow. Spraying the sodium hydroxide solution creates a particularly large surface area over which the carbon dioxide can be absorbed by forming sodium carbonate and the water. In an alternative variant, the sodium carbonate is formed within a sodium hydroxide solution by blowing air into the sodium hydroxide solution. This first step, which is represented by step 1, is a DAC (direct air capture) process; such processes are known in and of themselves. The sodium carbonate is formed according to the following reaction equation:

[0125] 2 NaOH + CO2Na2CO3.H2O

[0126] In a preferred embodiment, the preferred concentration of the caustic soda solution is 17-19 mol / l at the feed from the plant section 7 and from the plant section 2; due to water absorption from the air and the precipitation of sodium carbonate, the concentration of the caustic soda solution in the absorber drops to 12-15 mol / l in accordance with the invention. It can be seen that the sodium hydroxide solution or the sodium hydroxide from step 7 is therefore added to the absorption step of step 1 in order to keep the concentration high. The sodium hydroxide, as well as the other substances apart from the carbon dioxide and the water, which is obtained from the air, are used in the cycle, i.e. treated and reused in the process. It is clear that the process must initially be started by adding sodium hydroxide (as well as zinc oxide, see step 4 below).

[0127] After the absorption step, an aqueous solution with sodium carbonate and unused sodium hydroxide is present. In step 2, the solution comprising sodium carbonate and unused sodium hydroxide is fed into a crystallisation vessel and heated with process heat. The evaporating or vaporising water is preferably collected from the gas phase and condensed for further use.

[0128] In this process, sodium carbonate monohydrate (Na2CO3H2O) precipitates. The precipitate is separated, e.g. by filtration in a chamber filter press or similar. The sodium carbonate monohydrate can be stored, for example to bridge time periods in which too little energy is available for further process steps.

[0129] The remaining solution, which is depleted in sodium carbonate and water, is preferably fed back to step 1 , the absorption step. Alternatively, a partial stream of the remaining solution can be mixed with metallic zinc for hydrogen recovery (see step 8 below).

[0130] If sufficient thermal energy is available (solar thermal energy or process waste heat), the sodium carbonate can be dried in step 3. The water of crystallization and / or the residual moisture is also recovered here and reused in subsequent steps (see below). The anhydrous sodium carbonate can also be stored so that it can be processed at a later stage. This step can also be skipped if necessary.

[0131] In the next step 4, the dried sodium carbonate from step 3 or directly the moist sodium carbonate from step 2 (see below) is mixed with zinc oxide in order to release carbon dioxide at a temperature of 800°C to 900°C. There are basically two ways of doing this. In a first variant, the sodium carbonate is reacted as a melt with the zinc oxide to release carbon dioxide. In a second variant, the sodium carbonate is roasted together with zinc oxide, in particular in a rotary kiln, to release the carbon dioxide. In this step, sodium zincate is formed according to the following reaction equation:

[0132] Na2CO3+ ZnO Na2ZnO2+ CO2t

[0133] In the process, a mixture of 2-5 parts fine zinc oxide powder and one part coarsegrained sodium carbonate is preferably added to the top of a rotary kiln. The furnace is preferably heated to approx. 900°C with constant rotation, causing the sodium carbonate to melt. Due to the rotation, the melting particles turn into spheres which are coated with zinc oxide. Zinc oxide dissolves inside the balls, while carbon dioxide is released. The product of the roasting process leaves the rotary kiln preferably as particles consisting of sodium zincate Na2ZnO2coated with zinc oxide. In addition, there is preferably further excess zinc oxide powder in the furnace, which acts as a separating agent to prevent molten sodium carbonate from sticking to the rotary kiln. In the furnace, scrapers or similar mechanical devices also ensure that no deposits occur. The mixture of balls and powder is preferably sieved in a first step, and the powder is preferably fed back into the roasting process with new sodium carbonate. Preferably, the larger fused particles are processed in the subsequent step 5 (see below).

[0134] The carbon dioxide can be utilised directly or reduced to carbon monoxide or carbon in further reaction steps with metallic zinc (see below).

[0135] In step 5, the sodium zincate is dissolved in hot water according to the following reaction equation:

[0136] Na2ZnO2+ 2 H2O Na2Zn(OH)4

[0137] Sodium tetrahydroxidozincate is formed by hydrolysis.

[0138] The spheres consisting of sodium zincate and zinc oxide are dissolved in hot water, whereby the spheres disintegrate, zincate hydrolyses and goes into solution as sodium tetrahydroxidozincate, zinc oxide also dissolves partly but instantly separates again due to supersaturation. The solution is supported by mechanical devices such as agitators or in drums. The entire suspension of sodium hydroxide solution with dissolved sodium tetrahydroxidozincate and solid zinc oxide is then fed to the subsequent step 6.

[0139] In step 6, the supersaturated solution is kept just below the boiling temperature for a few hours, during which time most of the sodium tetrahydroxidozincate decomposes to form caustic soda and zinc oxide powder:

[0140] Na2Zn(OH)4ZnO + 2 NaOH

[0141] The conversion to zinc oxide can be further increased by slow cooling to room temperature. With or without a cooling phase, depending on whether there is a higher requirement for zinc oxide or whether a higher content of sodium tetrahydroxidozincate is preferred for subsequent galvanic zinc deposition, the zinc oxide is separated by filtration, preferably in a chamber filter press, or by centrifugation in a continuous centrifuge. Sodium carbonate not converted in the roasting process precipitates here partly together with the zinc oxide. After drying with water recovery, the zinc oxide obtained in this way is used again in the roasting process in step 4. The concentration of the caustic soda produced during the hydrolysis of sodium zincate is 10-20mol / l, preferably 17-19mol / l, the caustic soda is saturated with sodium tetrahydroxidozincate, the absolute zinc concentration in the caustic soda is adjusted via the temperature during the equilibrium adjustment prior to the separation of the ZnO.

[0142] Caustic soda used in this process usually contains sodium carbonate too, which does not harm any of the further steps. Sodium carbonate saturated caustic soda is the absorbent, the substrate for the electrodeposition as well as the substrate for the hydrogen production by adding zinc metal to the water enriched absorbent. Even if the concentration could be reduced by cooled crystallization there is no need to do so in order to succeed in doing the inventive cycle process.

[0143] The remaining concentrated sodium hydroxide solution, which is saturated with sodium tetrahydroxidozincate, is used in step 7 for the electrodeposition of metallic zinc. This is done according to the following redox equations:

[0144] Anode: 4 OH- - 4 e- O2+ 2 H2O

[0145] Cathode: 2 Zn2++ 4 e- 2 Zn

[0146] In addition to the metallic zinc, oxygen is also produced. As there are no requirements for the structure or form of the zinc deposit at the cathode, because the zinc formed is then completely broken down or melted off by reactions, the solution from system step 6 can be used directly without further additives. The higher the temperature, the easier it is for oxygen to develop at the anode, which is why a working temperature just below the boiling point is preferred.

[0147] In order to achieve the greatest possible deposition of the dissolved zinc, three- dimensional electrodes in the form of fills, wire meshes, three-dimensional structures etc. are preferably used. The cathode material can consist of zinc itself or any other conductive material with a higher melting point than zinc, preferably steel or stainless steel. The zinc-loaded electrodes are either used directly in the process e. g. by reacting them with water loaded sodium hydroxide absorbent from the absorber to produce hydrogen or, preferably, the zinc obtained (melting point 419.5°C) is extracted from the cathodes by melting it off.

[0148] The caustic soda solution remaining after the galvanic zinc deposition is highly concentrated and low in zinc and is used again as an absorption solution in step 1. Due to the high concentration, this increases the rate of absorption of water from the atmosphere. This is achieved by lowering the vapor pressure above the absorption solution.

[0149] The oxygen can in turn be used to generate electrical or thermal energy by oxidizing metallic zinc - the metallic zinc and the oxygen are therefore an energy storage that can be used for night-time operation, for example.

[0150] In a preferred embodiment, the anodes for the galvanic zinc deposition are separated in open bottom pipes that separate ascending oxygen, which is produced at the anode, to prevent mixture of oxygen with hydrogen that evolves as a side product during galvanisation. The bath for galvanisation is a closed unit where hydrogen is collected. In this way hydrogen is no loss of energy but a useful reagent or product.

[0151] The metallic zinc can be used for one or more of the reduction reactions described below:

[0152] - At least part of the metallic zinc can be used in step 10 to reduce carbon dioxide to carbon monoxide according to the following reaction equation in a separate plant section:

[0153] Zn + CO2— > ZnO + 00$

[0154] The resulting zinc oxide is in turn used in step 4 to release carbon dioxide from sodium carbonate. 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 is continuously transported downwards and ejected into a gas-tight container, where it cools down or from where it is immediately fed hot into plant step 4.

[0155] - At least a portion of the metallic zinc can be used in step 9 to reduce carbon monoxide (and / or carbon dioxide, not shown) to carbon according to the following reaction equation:

[0156] Zn + CO — > ZnO + C

[0157] The direct conversion of carbon dioxide 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 with fine iron oxide particles is blown in upwards. In a first step, zinc oxide and carbon monoxide are produced. The carbon monoxide reacts further 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. The resulting mixture of zinc oxide, carbon and iron oxide is worked up by dissolving it in caustic soda, whereby zinc oxide is dissolved and iron oxide and carbon are separated as solids. The separation of iron oxide and carbon is based on density - light carbon floats in water while iron oxide sinks. Iron oxide residues adhering to the carbon can be dissolved with acid if they interfere with the use of the carbon products. Alternatively, simple closed reactors can also be used in batch operation, where zinc and carbon dioxide with iron oxide particles are also introduced in the center of the reactor, the solid products simply sediment at the bottom of the reactor and are removed after a defined running time. It is also possible to feed this plant with mixtures of carbon dioxide and carbon monoxide or preferably only with carbon monoxide (which was produced in plant section 8). This variant has the advantage that only half the amount of zinc oxide is produced in this process step, which facilitates the processing of the resulting solids mixture. The zinc dust produced in plant section 8 is pure zinc oxide which does not require any processing, while the zinc oxide produced in this step 9 must be separated from iron oxide and carbon.

[0158] - At least part of the metallic zinc can be used in step 8 to reduce water to hydrogen according to the following reaction equation:

[0159] Zn + 2 NaOH + 2 H2O Na2Zn(OH)4+ H2$ The reaction of sodium hydroxide solution with zinc is a well-known process. Zinc powder, particles, plates, cathodes, etc. are placed in sodium hydroxide solution and gaseous hydrogen is spontaneously released. The special feature of this design is that the reaction is carried out with absorption solution, whereby water absorbed from the atmosphere is directly reacted with zinc, dehydrating the sodium hydroxide solution. The product is gaseous hydrogen. The second product is sodium tetrahydroxidozincate, which is dissolved in the dehydrated sodium hydroxide solution. If the process is carried out with larger quantities of metallic zinc, sodium tetrahydroxidozincate decomposes to form zinc oxide and caustic soda. The same reaction occurs in plant section 6, so in a complete plant the resulting solution can be fed into the cycle in step 6 if more zinc oxide is required or fed directly into the galvanic zinc deposition in step 7 to produce metallic zinc again as quickly as possible.

[0160] In a special preferred embodiment, hydrogen evolution and electroplating are carried out at different times in the same reactor. If no current is applied, the zinc coating of the cathodes dissolves and hydrogen is released. The flow direction goes from the crystallization plant section 2 into a tank that temporarily stores the sodium tetrahydroxidozincate / NaOH solution. Once a large proportion of the zinc has been used up, the flow direction is changed so that the solution from the intermediate tank passes via the electroplating system into the absorber 1 , current is applied so that zinc is deposited again and oxygen is released.

[0161] The sodium hydroxide solution required for this can be obtained from step 2 (sodium carbonate depleted absorption solution). Water that was previously absorbed from the air in the absorber is consumed in the process. The resulting sodium tetrahydroxidozincate in sodium hydroxide solution can be fed to step 6 for decomposition of the sodium tetrahydroxidozincate to zinc oxide and sodium hydroxide or directly to the galvanic zinc deposition in step 7.

[0162] It can be seen from steps 8 - 10 above that the metallic zinc can be used in different ways, whereby various products can be produced from carbon dioxide or water. The special feature of this process is that the resulting by-products (in particular zinc oxide and sodium tetrahydroxidozincate) can be reused in steps 4 and 7 respectively. It is also noteworthy that the products carbon dioxide, carbon monoxide, carbon and hydrogen can be produced in any ratio to each other, which means that the process can be adapted particularly easily to current market requirements.

[0163] Even though all steps 8 - 10 are optional, it should be noted that step 8 (reduction of water to hydrogen) is feasible but not preferred due to the great effort involved, in particular due to the need for platinum group metals and membranes.

[0164] However, hydrogen is required to produce alcohols or hydrocarbons from carbon monoxide. This in turn requires water. Water is absorbed from the atmosphere in concentrated sodium hydroxide solution together with carbon dioxide. Some of this water precipitates as water of crystallization in sodium carbonate crystals and is recovered as condensate during the drying process in step 3. If a highly concentrated sodium hydroxide solution is used, the result is predominantly sodium carbonate monohydrate. This means that one mole of water per mole of sodium hydroxide can be obtained from the drying process in step 3. Further water can be distilled directly from the absorption solution of step 2. Preferably, sodium carbonate is precipitated in step 2 by heating the absorption solution with waste heat or solar heat. In this step, the absorption solution is at its warmest and water removal favors and completes the precipitation of sodium carbonate. Therefore, it is preferred to recover water through distillation from the absorption solution during precipitation.

[0165] Another way to obtain water from the absorption solution is to carry out a classic alkaline electrolysis to obtain hydrogen with the absorber solution. The disadvantage of classic electrolysis compared to hydrogen production with zinc is that hydrogen and oxygen are produced simultaneously and in close proximity. As a result, membranes or at least diaphragms are required to prevent the formation of explosive mixtures from oxygen and hydrogen gas and to prevent oxygen from entering the hydrogen product stream. In the preferred zinc process according to the invention, oxygen is formed during electrodeposition at the anode, whereas hydrogen is only formed during the reaction of metallic zinc with caustic soda, which is completely separated in terms of time and space. This process can therefore be carried out in simple, even very large reactors on an industrial scale and without membranes. At the same time, oxygen-free hydrogen is guaranteed, which offers optimal conditions for further syntheses of hydrocarbons and alcohols without further purification steps. Nevertheless, alkaline electrolysis is also a viable option for obtaining hydrogen directly from the absorption solution, not least because it is a proven standard process.

[0166] In this process, there are therefore several ways to utilize the water from the air, which is bound in the sodium hydroxide solution in the absorber. The distillation of the water of crystallization of sodium carbonate and the distillation of water from the absorption solution in the crystallization vessel provide liquid water which can be used, for example, to dissolve sodium zincate. The other two routes directly supply hydrogen gas, which can be used for the subsequent synthesis of alcohols or hydrocarbons. All in all, even in desert locations, a sufficient water supply for the entire process is made possible solely by absorbing the humidity in the caustic soda. However, if water is available at the site at low cost and in sufficient quantities (e.g. rainwater), the utilization of these external sources as a partial or sole water supply can lead to energy savings and thus cost savings at some sites. In addition to the costs, the effects of water extraction on the surrounding area must also be examined in order to avoid collateral damage.

[0167] In a further variant, carbon dioxide can be released in step 4 in a combined process and simultaneously reduced to carbon monoxide (not shown in step 4). A mixture of zinc oxide and metallic zinc is used for this purpose. A portion of the metallic zinc can come from the sodium hydroxide solution obtained from step 7. In addition to the reaction equation above, in which sodium carbonate is reacted with zinc oxide to form sodium zincate and carbon dioxide, the carbon dioxide is further reacted with the metallic zinc to form carbon monoxide and zinc oxide:

[0168] Zn + CO2— > ZnO + 00$

[0169] The resulting zinc oxide can in turn be reacted with sodium carbonate to form sodium zincate and carbon dioxide.

[0170] The whole process can take place in the same reactor so that carbon dioxide and carbon monoxide can be produced at the same time. The ratio between carbon monoxide and carbon dioxide can be controlled by the amount of metallic zinc added during the roasting process or in the melt. If metallic zinc is used in excess, almost complete conversion to carbon monoxide is possible in a single step.

[0171] In this case, the system is operated in such a way that the gas phase has a temperature above 900°C, preferably 900-1000°C. Zinc is gaseous at these temperatures and reacts particularly efficiently with the gaseous CO2 released. Zinc oxide is produced as dust and is bound by the addition of fresh sodium carbonate. Zinc contained in the product gas is separated by cooling and returned to the process.

[0172] In a further preferred embodiment of the process, the moist sodium carbonate from step 2 is used directly in step 4. The moist sodium carbonate is mixed with metallic zinc and zinc oxide and subjected to the roasting process. The drying process in step 3 is thus omitted or only partially carried out, so that the sodium carbonate is not completely dried. In other variants, additional water can also be added in order to influence the product ratios. According to the following reaction equation, zinc forms hydrogen with water in the gas phase of the rotary kiln, whereby zinc oxide powder precipitates:

[0173] Zn + H2O — > ZnO + H2T

[0174] In this way, the composition of the released gas is defined via the ratio of sodium carbonate to water to zinc to provide an optimum composition of the synthesis gas for subsequent reactions. Zinc oxide is always kept in excess. Mixtures of H2and CO in any ratio are directly accessible via this process variant and thus form a classic synthesis gas. Mixtures that also contain CO2are possible by adding smaller amounts of metallic zinc. If water is used in excess, drying of the gas may be necessary due to incomplete conversion and depending on the intended use of the synthesis gas. Anyway using zinc as reductant instead of classic reduction with hydrogen gas reduces the need for drying massively.

[0175] In practice, the process is carried out in a rotary kiln; the solids sodium carbonate, zinc oxide and zincate are preferably fed downwards in counter flow to the resulting product gas. The continuous charging of the furnace with zinc and sodium carbonate takes place approximately in the middle, whereby the zinc vapor is drawn upwards with the carbon dioxide produced in the lower half, reacting to form carbon monoxide and depositing zinc oxide along the way. This zinc oxide is transported downwards in the rotary tube and mixed with the added sodium carbonate and transported further downwards together, while it slowly converts to sodium zincate with the release of carbon dioxide. If the ratio of sodium carbonate to metallic zinc is at least equimolar, any excess zinc oxide can be added to optimize transport and prevent sticking, caking etc. without affecting the product gas. The product gas is carbon monoxide or the mixture of carbon monoxide and carbon dioxide, or the mixture of carbon monoxide and hydrogen when using wet sodium carbonate, or carbon monoxide and carbon dioxide and hydrogen when using wet sodium carbonate and less metallic zinc than would be required for all reduction processes together. The product gas is extracted at the top of the rotary kiln. When carrying out the process with metallic zinc, it must be taken into account that zinc is very mobile in the gas phase; cooling and separating devices for zinc must be provided at the furnace outlet. The optimum furnace temperatures in the lower part are 900°C, while slightly higher temperatures of 950- 1000°C lead to good conversion in the upper part. Alternatively, conversion is possible in a fixed furnace that is loaded and unloaded continuously or discontinuously.

[0176] The addition of further alkali or alkaline earth carbonates to lower the melting point and thus reduce the viscosity of the melt is possible. In particular, the use of potassium carbonate and / or lithium carbonate. These variants are not favored for cost reasons, although the technical feasibility is clearly stated at this point. In special cases, e.g. for salt mixtures produced by processing brine from freshwater extraction to an absorption solution and therefore naturally containing elements that lower the melting point, this variant may be considered. As a rule, the addition of elements that lower the melting point is not necessary because it is almost unavoidable that the added elements occur in the entire circuit in all parts of the system, especially in the absorber where large quantities are required.

[0177] Figures 1b to 1e below show parts of the overall reaction scheme, each focusing on the production of one substance and the reaction steps not relevant to this process b.

[0178] Figure 1b shows a diagrammatic representation of the reaction steps relating to the carbon dioxide path. Steps 1 to 6 are sufficient for the production of carbon dioxide. In particular, galvanic zinc deposition can be dispensed with in this process. In the following process paths of carbon monoxide and carbon, zinc is oxidised to zinc oxide, which can be fed back into the process in step 4 and thus remains in the cycle.

[0179] Figure 1c shows a diagrammatic representation of the reaction steps relating to the carbon monoxide path. In addition to removing carbon dioxide, the carbon dioxide must be reduced to carbon monoxide using zinc as a reducing agent, which is produced galvanically in step 7. The reduction takes place in step 10, which means that steps 8 and 9 can be omitted.

[0180] Figure 1d shows a diagrammatic representation of the reaction steps relating to the carbon path. In order to further reduce the carbon monoxide to carbon, metallic zinc from step 7 is used together with an iron catalyst in step 9. This means that only step 8 is omitted.

[0181] Figure 1e shows a diagrammatic representation of the reaction steps relating to the hydrogen path. Water from step 2 is reduced using zinc as reducing agent. The resulting sodium tetra hydroxido zincate can be fed back into the process in step 7 and thus remains in the cycle. In the hydrogen path, the roasting process of step 4 still produces CO2, which can be further processed, e.g. for the production of methane or methanol by catalytic reaction with the produced hydrogen.

[0182] Figure 2 shows a schematic representation of a roof-top arrangement of such a system. The system 101 is arranged on the roof of a high-rise building 100. The system comprises a modular absorber unit - this comprises three absorber modules 102 in the present case. In the absorber unit, carbon dioxide and water are absorbed from the ambient air with a sodium hydroxide solution, thus forming an absorption solution containing sodium carbonate. The absorber unit is arranged on a crystallization unit 103 so that the absorption solution can be fed directly to the crystallization unit 103 by means of gravity. The sodium carbonate is precipitated from the absorption solution in the crystallization unit 103. In addition to the crystallization unit 103, a rotary kiln 104 is also shown schematically, in which the sodium carbonate is heated with zinc oxide in order to release carbon dioxide. The system 101 further comprises solar thermal or photovoltaic elements 105 for the energy supply of the system 101 . 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 the air with particularly few reagents, whereby all reagents can be used in the cycle and the consumables are obtained exclusively from the air.

[0183] List of reference signs

[0184] 1-10 method steps

[0185] 100 building

[0186] 101 system 102 absorber modules

[0187] 103 crystallization unit

[0188] 104 rotary kiln

[0189] 105 solar thermal or photovoltaic elements

Claims

Claims1. Method for the production of one or more of carbon dioxide, carbon monoxide, carbon and hydrogen from a gas comprising carbon dioxide and preferably water, in particular from air, comprising the following steps: a) the gas comprising carbon dioxide and water is brought into contact with sodium hydroxide, preferably a sodium hydroxide solution, to absorb simultaneously carbon dioxide and water to form sodium carbonate, in particular sodium carbonate with water of crystallization, and a water enriched sodium hydroxide solution; b) sodium carbonate crystals from the solution of step a) are separated, preferably by filtration or centrifugation, wherein optionally additional sodium carbonate can be separated by distillation of the sodium hydroxide solution to enhance the cristallisation; c) the sodium carbonate crystals from step b) are reacted with zinc oxide, in particular with a surplus of zinc oxide, for releasing carbon dioxide by the formation of sodium zincate; d) the sodium zincate of step c) is reacted with water to form sodium hydroxide, saturated with sodium tetra hydroxido zincate, and solid zinc oxide, wherein at least a part of the solid zinc oxide is separated; e) the remaining solution of sodium tetra hydroxido zincate in sodium hydroxide is used as absorbent in step a); f) the solution of step d) is used to produce metallic zinc by alkaline galvanic process, in particular by converting sodium tetra hydroxide zincate to sodium hydroxide and metallic zinc, wherein the metallic zinc is used as a reduction agent for one or more of the following processes:I. the metallic zinc is used as a reduction agent to reduce carbon dioxide gained in step c) to carbon monoxide, wherein therewith gained zinc oxide is used in step c), in particular without any treatment;II. the metallic zinc is used as a reduction agent to reduce carbon monoxide gained in step I to carbon, preferably using a ferrum containing catalyst, wherein carbon and zinc oxide is separated, preferably by solving the zinc oxide in sodium hydroxide in order to form a concentrated sodium tetra hydroxido zincate solution, wherein the concentrated sodium tetra hydroxido zincate solution is used for galvanic zinc winning for the use in step f) and recovery of sodium hydroxide solution, for the use as absorbent in step a);III. the metallic zinc is used as a reduction agent to reduce water, preferably water of the water enriched sodium hydroxide solution of step a), to hydrogen, by forming a concentrated sodium tetra hydroxido zincate solution, which is preferably used for galvanic zinc winning and recovery of higher concentrated sodium hydroxide solution for the use in step a).

2. Method according to claim 1 , wherein the gas is air, in particular atmospheric air, and wherein, after step c) zinc oxide and sodium hydroxide is recovered, in particular completely recovered for the reuse in step a), and wherein in particular the water is extracted from the gas, preferably to a large extent.

3. Method according to claim 2, wherein the gas is the only consumable in the process.

4. Method according to any of preceding claims, whereby in step a) the gas comprising carbon dioxide is brought into contact with concentrated sodium hydroxide solution, in particular with a sodium hydroxide solution comprising at least 10 mol / L sodium hydroxide, preferably between 12 to 19 mol / L sodium hydroxide.

5. Method according to any of preceding claims, whereby in step a) the sodium carbonate, in particular sodium carbonate with water of crystallization, is precipitated, in particular due to exceeding the solubility.

6. Method according to any of preceding claims, whereby between step a) and step c) the sodium carbonate comprising water of crystallization is dried, in particular with water recovery.

7. Method according to any of preceding claims, wherein for the reaction of sodium carbonate and zinc oxide in step c), the sodium carbonate is melted, in particular together with zinc oxide, wherein preferably a mass ratio between sodium carbonate and zinc oxide is greater than 4:1, preferably to reduce a viscosity and wherein zinc oxide together with sodium carbonate is added, in particular continuously added to the melt.

8. Method according to any of preceding claims, wherein the reaction of sodium carbonate and zinc oxide in step c) takes place at a temperature higher than 600°C, in particular at a temperature between 700°C and 1000°C, more preferably between 800°C and 900°C.

9. Method according to any of preceding claims, wherein the reaction of sodium carbonate and zinc oxide in step c) takes place in a rotary kiln.

10. Method according to any of preceding claims, wherein in step c) one or more of the following reactions take place: i) carbon dioxide is produced, wherein the sodium carbonate is dried and in particular heated with zinc oxide to a temperature above 850 °C; ii) carbon monoxide is produced, wherein the sodium carbonate is dried and in particular a surplus of metallic zinc is added and preferably heated to a temperature above 900 °C, or carbon monoxide is produced from carbon dioxide by contacting carbon dioxide from i) with liquid or gaseous zinc; iii) carbon dioxide and hydrogen is produced, wherein an equimolar amount of zinc is added in relation of an amount of water present and in particular heated to a temperature below 900 °C;iv) carbon monoxide and hydrogen is produced, wherein a surplus of metallic zinc is added to sodium carbonate and water, in particular to wet sodium carbonate and preferably heated to a temperature above 900 °C v) carbon is produced by reducing CO2or CO with metallic zinc, in particular with a ferrum oxide catalysator.

11. Method according to any of preceding claims, wherein, in step c) a sodium zincate, in particular Na2ZnO2, is obtained in addition to carbon dioxide, wherein in particular the sodium zincate is extracted from the melt.

12. Method according to claim 11, wherein the sodium zincate obtained in step c) is added in water, preferably at a temperature above 80°C, wherewith at least a part of the sodium zincate is hydrolyzed to sodium tetrahydroxidozincate and wherein the tetrahydroxidozincate is at least partially decomposed to sodium hydroxide solution and zinc oxide, wherein preferably solid zinc oxide is separated, in particular precipitated, and wherein in particular an amount of the added water is selected in such a way, that the obtained sodium hydroxide solution has a concentration between 12 mol / L and 19 mol / L in particular for the reuse in step a).

13. Method according to claim 12, wherein the water is obtained by distillation of water of crystallization from the sodium carbonate of step a) and / or obtained by drying the sodium carbonate.

14. Method according to claim 12 or 13, wherein metallic zinc is extracted from the remaining tetrahydroxidozincate in the sodium hydroxide solution by galvanization.

15. Method according to claim 14, wherein the sodium hydroxide solution remaining after galvanization is used again in step a).

16. Method according to one of claims 14 or 15, wherein the metallic zinc is at least partially reacted in one or more of the following processes: i) metallic zinc is brought in contact with water, in particular with water from air, and reacted to zinc oxide and hydrogen;ii) 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 carbon dioxide, in particular with carbon dioxide of step c), to zinc oxide and carbon monoxide; iii) metallic zinc is reacted with carbon dioxide and / or carbon monoxide in the presence of a catalyst, in particular ferric oxides, to zinc oxide and carbon; iv) metallic zinc is reacted with oxygen to zinc oxide, in particular with oxygen obtained from the galvanic process of claim 6, wherein the energy released by the reaction is converted into electrical energy or thermal energy.

17. Method according to any of preceding claims, wherein all gases and water used in the method are extracted from the air, in particular from atmospheric air, and in particular intermediary gases and water are recycled in the method.

18. Apparatus for carrying out a method according to any one of claims 1 to 17, for providing one or more of carbon dioxide, carbon monoxide, carbon and hydrogen from a gas comprising carbon dioxide and preferably water, in particular from atmospheric air, comprising an absorber that is configured for performing step a) and a decomposition unit that is configured for performing step c).

19. Apparatus according to claim 18, wherein the absorber and / or the decomposition unit are designed as a roof-mounted system.

20. Apparatus according to claim 18 or 19, wherein the absorber and / or the decomposition unit comprising one or more absorber modules and / or decomposition unit modules.

21. Apparatus according to claim 19 or 20, wherein the decomposition unit comprises a rotary kiln.

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