A method for CO2-neutral commercial production of magnesium with later-stage recovery of hydrogen and / or synthetic fuels.

Abstract

The present invention relates to a method for the CO2-neutral commercial recovery of metallic magnesium from seawater, wherein the recovered magnesium is further processed for use as a metallurgical raw material and can also be used as a starting material for the CO2-neutral recovery of hydrogen, and the CO2 recovered or released throughout the method is dissolved and bound to seawater.

Description

Technical Field

[0001] The present invention relates to a commercial method for the CO2-neutral recovery of metallic magnesium from seawater.

[0002] This method is modular and consists of the verification of known technical processes. The individual modules (methods) are not CO2-neutral and are based on conventional methods that are already technically used. CO2 neutrality is achieved by the order according to the present invention of the individual modules. By the preferred selection of the individual method steps, the overall method has a footprint ranging from completely CO2-neutral to CO2-negative.

[0003] The obtained magnesium can be further processed as a raw material for metallurgy. It can also be used as a starting material for the CO2-neutral recovery of hydrogen. The commercial method disclosed herein also offers the possibility of producing synthetic fuels, and the obtained hydrogen is used as a raw material. In contrast to known commercial methods for producing green hydrogen or synthetic fuels, the method according to the present invention does not involve complex electrolysis processes and is very efficient in terms of energy and cost.

[0004] Seawater can absorb a very large amount of CO2. The absorption capacity increases as the temperature decreases and the sea depth increases. Also, according to Henry's law, it is proportional to the partial pressure of CO2 in the atmosphere above the water. Even at room temperature and atmospheric pressure, the technical literature assumes about 2 grams of dissolved CO2 per liter of water, as described in "Carbon Dioxide in Water and Seawater: The Solubility of a Non-Ideal Gas" Marine Chemistry 2 (1974) 203-215. This value also agrees with the results of the inventors' own measurements.

[0005] The previously unpublished German patent application publication No. 102022108490.6 describes a method for recovering Mg(OH)2 particles from seawater. This method generates a large amount of alkaline wastewater, which can be introduced into the sea.

[0006] U.S. Patent No. 2,167,120, "Process of calcining finely divided calcium carbonate," describes, as an example, the calcination of calcium carbonate into calcium oxide. Calcium carbonate compressed into pellets was heated using an airflow at 1100°C to 1200°C for 20 minutes, and then separated from impurities by sieving.

[0007] European Patent No. 0196176, "Energy conserving limestone calcining system," describes calcination from 900°C in which the work is performed in a vacuum, thereby minimizing heat loss.

[0008] According to the literature "Physicochemical characteristics of fired clay-limestone mixes," Cement and Concrete Research 30,7-11(2000), it is known that complete firing is possible even at 800°C.

[0009] German Patent No. 2637504, "Slaking lime," describes the subsequent production of calcium hydroxide. In this case, calcium oxide is introduced into four times its volume of water while vigorously stirring for about four minutes.

[0010] German Patent Application Publication No. 2232355, "Activated Magnesia Production," describes the calcination of magnesium hydroxide precipitated from seawater. To produce such activated magnesium hydroxide, magnesium hydroxide is precipitated from seawater or brine using lime milk, washed with NaCl to a chloride content of less than 0.7% by weight, and spray-dried. The dried, finely particulated magnesium hydroxide powder is then calcined with Mg(OH)2 in a parallel flow of 40 m³ at an exhaust gas temperature of 440-450°C. 3 Activated MgO is produced by firing it in an indirectly heated rotary kiln while passing unheated, undried air at a rate of / h·kg through it.

[0011] U.S. Patent Document No. 2437815, "Process of Magnesium Production," describes the carbothermal production of metallic magnesium. To achieve the reduction of magnesium oxide with carbon, a temperature above the boiling point of magnesium is required to remove the gaseous magnesium from the reaction equilibrium. A mixture of magnesium oxide and coal is heated to approximately 2000°C in an air-excluded furnace. Since the reverse reaction of carbon monoxide with magnesium to magnesium oxide is dominant below 1850°C, the gas phase is rapidly cooled to approximately 200°C using natural gas, and thus the magnesium vapor is condensed.

[0012] U.S. Patent No. 0400309, "Carbothermal reduction reactor system, components thereof, and methods of using the same," demonstrates that magnesium can be produced by this method even at 1500°C using a vacuum system.

[0013] Metallic magnesium is processed in large quantities in metallurgy. However, under certain conditions, magnesium reacts with water vapor to form Mg(OH)2, releasing hydrogen. The transformation of elemental magnesium is disclosed in the publication "Comparative reactivity of industrial metal powders with water for hydrogen production," International Journal of Hydrogen Energy 40, 1026-1036 (2015). Hydrogen is produced from magnesium powder and water in a reactor system at 200°C and a positive pressure of 2–20 bar. This made it possible to obtain up to 0.92 liters (0.041 mol, 0.082 g) of hydrogen per gram of magnesium.

[0014] A long-known technical method for producing synthetic fuels is the Fischer-Tropsch process. This process proceeds from CO or CO2 and hydrogen and provides a mixture of long-chain and short-chain hydrocarbons that can be used, among other things, as fuel for conventional internal combustion engines.

[0015] As described in German Patent No. 293787, "Method for producing hydrocarbons and derivatives thereof," hydrocarbons can be synthesized from a gas mixture of hydrogen and carbon monoxide at a pressure of 120 bar and a reaction temperature of 360-420°C using the Fischer-Tropsch process with a suitable catalyst, such as cobalt oxide.

[0016] Based on the prior art presented above, the object of the present invention is to identify a method for obtaining metallic magnesium in a CO2-neutral manner. This magnesium can then be used, among other things, to produce green hydrogen, from which synthetic fuels can also be produced in a CO2-neutral manner.

[0017] In the method described in German Patent Application Publication No. 102022108490.6, in the first step, seawater is mixed with Ca(OH)2 until a saturation point is reached. This results in a very high pH, ​​causing all the CO2 dissolved in the seawater to precipitate as a solid and be filtered off as CaCO3. CaCO3 is a commercially available product sold in large quantities worldwide.

[0018] In the subsequent process, MgCl2 dissolved in seawater is extracted from the residual seawater using a special nozzle. ++ It precipitates as Mg(OH)2. For each gram of Mg(OH)2, approximately 1 liter of wastewater is generated, which has a pH of about 10 and contains almost no CO2.

[0019] If this alkaline wastewater were sent directly back into the sea, a much larger volume of ocean water would then restore its pH balance.

[0020] However, measurements show that this alkaline wastewater can absorb a relatively large amount of CO2 (about 2-2.5 grams of CO2 per liter) even at room temperature and atmospheric pressure. This is achieved by introducing CO2 that dissolves in water into the water. At the same time, the alkaline wastewater is neutralized by this process.

[0021] If this method is carried out at atmospheric pressure, equilibrium is instantaneously established, and the CO2 dissolved in the water will not escape again. This assumption relies on the fact that the partial pressure of CO2 in the atmosphere does not decrease and the ocean temperature remains below the introduction temperature. Since seawater is naturally slightly alkaline, it is further ensured that the dissolved CO2 remains in the neutralized wastewater. If the neutralized water is introduced into the ocean at a certain depth, the lower temperature and higher pressure that spreads there further ensure that the dissolved CO2 remains.

[0022] When the amount of CO2 released to obtain Ca(OH)2 from CaCO3 required to produce 1 gram of Mg(OH)2 is compared with the CO2 absorption capacity of 1 liter of wastewater released per gram of Mg(OH)2, it can be seen that this absorption capacity is far from being exhausted. Calculations consistent with data from the technical literature show that all the CO2 released in subsequent processes by which metallic Mg is ultimately obtained can be further introduced into this wastewater until its neutralization.

Prior Art Documents

Patent Documents

[0023]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Non-Patent Documents

[0024]

Non-Patent Document 1

Non-Patent Document 2

[0025] The steps in the method according to the present invention can be described in terms simplified by the following reaction equation. 1. CaCO3 → CaO + CO2 2. CaO + H2O → Ca(OH)2 3.Ca(OH)2+MgCl2→ Mg(OH)2+CaCl2 4. Mg(OH)2 → MgO + H2O 5. MgO + C → Mg + CO / CO2

[0026] According to the method of the present invention, in order to achieve CO2 neutrality of the entire method, all method steps must be carried out in one location. In particular, for method steps 1 and 5, the reactor is constructed such that all emitted CO2 is captured in a shell surrounding it. The same applies to the waste gas released during the combustion of carbon-containing primary energy carriers necessary to achieve the corresponding temperature. The entire amount of CO2 thus emitted is collected in a central chamber and added in a specially constructed mixer to the wastewater generated during the recovery of Mg(OH)2 by step 3 (Figure 4).

[0027] The Mg obtained in step 5 can be used to produce green hydrogen according to the following formula. 6. Mg + 2H2O → Mg(OH)2 + H2

[0028] The hydrogen recovery described above can also be carried out in a decentralized manner at locations other than Mg production. Based on the above formula, mobile, decentralized hydrogen generators can be envisioned that can be operated in other industrial sites, buildings, or even vehicles. Since the Mg(OH)2 produced by this method is commercially available, it can be sold as is.

[0029] The method according to the present invention also offers the possibility of obtaining synthetic fuel in a CO2-neutral manner. The starting materials in this case are CaCO3, seawater, and, for example, coal. The method, known as the Fischer-Tropsch process, proceeds according to the following formula. 7. (2n+1)H2+nCO → C n H 2n+2 +nH2O

[0030] In this case, water vapor is introduced into the reaction gas produced in step 5 without prior separation of CO. The CO2 neutrality in this step is due to the fact that the CO2 released in step 5 is not introduced into the wastewater but is bound to the resulting fuel. When the fuel is then burned, it releases exactly the amount of CO2 produced in step 5 that was not introduced into the wastewater. Therefore, the wastewater absorbs exactly the amount of CO2 that the fuel releases into the air elsewhere.

[0031] Alternatively, the hydrogen obtained in step 6 can be reacted with CO2 from the air in another location, and the CO2 from step 5 can be introduced into the wastewater. The hydrogen from step 6 is CO2 neutral, and the amount of CO2 released when the fuel burns is taken from the air, so the fuel is also CO2 neutral in this case. Therefore, the method according to the present invention consists of known method steps, which are not CO2 neutral in themselves, but become CO2 neutral only when the released CO2 is neutralized in the wastewater produced by this method. The steps must be carried out in a specific order so that this can occur. The reaction equations above are shown in a simplified form and illustrate this order. From them, it can be seen that CO2 is released in step 1 (equation 1) and step 5 (equation 5). This is then neutralized in the wastewater produced in method step 3 (equation 3).

[0032] The formula is presented again below with a brief explanation.

[0033] 1. CaCO3 → CaO + CO2 High-temperature combustion of limestone to form quicklime. Limestone (CaCO3) is decomposed to form quicklime (CaO) and CO2. The resulting exhaust gas containing CO2 is captured and neutralized in alkaline wastewater from process 3, rather than being sent through the roof.

[0034] 2. CaO + H2O → Ca(OH)2 The quenching of quicklime to form calcium hydroxide (Ca(OH)2). When quicklime comes into contact with water, calcium hydroxide is produced and heat is released. In the method according to the present invention, quicklime can also be added directly to seawater.

[0035] 3.Ca(OH)2+MgCl2→ Mg(OH)2+CaCl2 Precipitation of magnesium-containing particles from seawater. Ca(OH)2 (calcium hydroxide) is added to seawater in an amount below its solubility limit, thereby raising its pH to 12. This alkaline seawater, thus prepared, reacts with magnesium chloride dissolved in the second stream of seawater at the nozzle outlet. Magnesium hydroxide precipitates, producing alkaline seawater with a pH of 10, and the CO2 produced in this manner is neutralized.

[0036] 4. Mg(OH)2 → MgO + H2O Combustion of magnesium hydroxide to form magnesium oxide. When Mg(OH)2 from step 3 is heated, it is converted to magnesium oxide (MgO) and releases water vapor, which can be condensed and used in further processes.

[0037] 5. MgO + C → Mg + CO / CO2 Thermal reduction of magnesium oxide to form magnesium (carbothermal process). Magnesium oxide is heated very vigorously in the presence of carbon. This produces magnesium vapor and carbon monoxide. The magnesium vapor condenses to form metallic magnesium, and the carbon monoxide can be converted to CO2. The CO2 is captured and neutralized in alkaline wastewater from step 3.

[0038] 6. Mg + 2H2O → Mg(OH)2 + H2 Oxidation of magnesium by water vapor (water splitting method). When magnesium powder is heated in the presence of water vapor, the magnesium powder reacts to form magnesium hydroxide and hydrogen.

[0039] 7. (2n+1)H2+nCO → C n H 2n+2 +nH2O Synthesis of hydrocarbons from hydrogen and carbon monoxide (Fischer-Tropsch process). Under specific conditions, hydrogen from step 6 and carbon monoxide from step 5 react to form hydrocarbons, which can be used, for example, as synthetic fuels.

[0040] The resulting Mg(OH)2 can be returned to the process and used for further magnesium production, which can then be sold in addition to hydrogen. The background is as follows:

[0041] In step 6, 1 mole of Mg, or 24 g of magnesium (molar mass of Mg: 24 g / mol), produces 1 mole of H2, or 2 g of hydrogen (molar mass of H2: 2 g / mol). Therefore, the mass of hydrogen obtained is only about 1 / 12 of the mass of magnesium used. Assuming that the current world market price of Mg is about 3000 euros / ton and the current world market price of hydrogen is about 6000 euros / ton, then 6000 euros worth of hydrogen can be obtained from magnesium worth 36,000 euros. If Mg(OH)2 is sent back to the method and passes through the cycle once, the method becomes very profitable as hydrogen is obtained in addition to magnesium, virtually free of charge. JPEG2026518266000001.jpg43101

[0042] Hydrogen is obtained in the first pass according to Figure (number 1), and magnesium, which can be sold, is not produced until the second pass (number 2). The method then starts again from the beginning with seawater and lime. The present invention will be described in more detail with reference to the drawings and examples. [Brief explanation of the drawing]

[0043] [Modes for carrying out the invention]

[0044] Example 1: Figure 1 schematically shows the method according to the present invention for obtaining metallic magnesium.

[0045] In the first step, a saturated Ca(OH)2 solution (Solution 1) is produced from seawater (SW) and Ca(OH)2. The 1.7 g / liter of Ca(OH)2 required for this was previously obtained by burning CaCO3 to form CaO, which was converted to Ca(OH)2 upon contact with seawater (SW). A considerable amount of energy in the form of heat is released in this method.

[0046] A mixture of salts containing a large amount of Ca(CO)3 precipitates. This can be purified and sold commercially.

[0047] According to the "Informationsblatt CO2-Faktoren" [Fact Sheet on CO2 Factors] published by the German Federal Office for Economic Export Control, 0.89 tons of CO2 are released for every 1 tons of Ca(OH)2 obtained. Therefore, 1.7 × 0.89 = 1.513 g of CO2 are released in the production of the 1.7 g / liter Ca(OH)2 described above. Next, solution 1 is reacted with unused seawater (SW) in a 2:1 ratio, and approximately 1 g / liter of Mg(OH)2 precipitates. The resulting Mg(OH)2 particles are separated by filtration. In this way, 3 liters of suspension are obtained, and 2 × 1.513 g of CO2, i.e., 3.026 g of CO2, were released during its preparation. Therefore, 3.026 grams of CO2 were released for 3 grams of Mg(OH)2 present in the suspension. The aqueous phase produced after the Mg(OH)2 has been filtered out originally has a pH of approximately 10. Next, when the pH drops to a neutral pH of 7 due to the dissolution of CO2, the inventors' own measurements showed that approximately 2 to 2.5 grams of CO2 per liter dissolve in it at room temperature and atmospheric pressure.

[0048] In a subsequent step, the Mg(OH)2 particles thus obtained are burned by heating to approximately 600°C to form MgO particles. The MgO is then mixed with coal dust and reacted at approximately 1800°C. A gas mixture containing Mg and CO in the gas phase is produced. Magnesium is separated from the CO gas by condensation. Instead of the coal dust described above, carbon from any other source can be used. For example, biomass or products from a combustion plant can be used.

[0049] According to the list of emission factors published by the German Federal Environment Agency, natural gas emits 0.055 tCO2 / GJ and coal emits 0.095 tCO2 / GJ. Based on this data, to generate the amount of heat required for the method described above, 0.14 g of CO2 is released from natural gas or 0.24 g of CO2 is released from coal for every 1 gram of Mg(OH)2 used. Furthermore, 0.754 g of CO2 is released per 1 gram of Mg(OH)2 during the reaction of MgO obtained from Mg(OH)2 with coal.

[0050] All CO2 generated during the method shown in Figure 1 is captured and mixed with the alkaline wastewater produced during the precipitation of Mg(OH)2.

[0051] Taking all these CO2 emissions into account and offsetting them by the amount of CO2 that can be absorbed (dissolved) in the alkaline wastewater produced to obtain 1 gram of Mg, we obtain the following description:

[0052] According to the list of emission factors published by the German Federal Environment Agency, when the required amount of heat is generated using natural gas, -0.04g of CO2 is released per gram of Mg, whereas when the same amount of heat is obtained from coal, it is + / -0.00g of CO2 per gram of Mg. Therefore, in both cases, this method is CO2 neutral.

[0053] The conditions underlying the above calculations describe the worst-case scenario. The overall CO2 footprint of the method can be further improved if the following aspects are optimized.

[0054] 1. Fuel: For example, if natural gas is used instead of coal to supply the heat required by the method, according to the list of emission factors published by the German Federal Environment Agency, only 0.055 tons of CO2 are released per 1 GJ of heat obtained, instead of 0.095 tons of CO2, i.e., slightly more than half. In so-called solar furnaces, it is also possible to obtain the required heat from solar thermal energy. This reduces the emissions required to obtain the heat to virtually zero. In this case, the CO2 footprint is improved to -0.120g of CO2 released per gram of Mg.

[0055] 2. Heat Recovery (Figure 4): The majority of the thermal energy is needed to obtain metallic Mg from MgO. The waste heat generated from this process can be used, for example, to operate a kiln to produce CaO from CaCO3. The waste heat from this process can also be used to convert Mg(OH)2 to MgO. The waste heat generated in this process will probably be sufficient to dry the Mg(OH)2. The waste heat can also be used to generate steam, which can then supply the electrical energy required for this process. If waste heat is recovered from individual process steps, approximately -0.08 grams of CO2 per gram of Mg is released using natural gas as fuel, and approximately -0.06 grams per gram of Mg is released using coal as fuel. In either case, the CO2 footprint is negative, meaning that more CO2 is attached to this process than is generated when this process is carried out.

[0056] 3. Carbon sources: When carbon obtained from renewable resources, such as biomass, rather than fossil fuels, is used in the manner described, the CO2 footprint can be greatly improved.

[0057] Example 2: Figure 2 shows the method in Figure 1, in which the obtained Mg is brought into contact with water vapor in a further step. Hydrogen and Mg(OH)2 are produced. As explained above, the method for obtaining the required Mg from Figure 1 is CO2 neutral. Since no further CO2 is released once hydrogen is obtained, the method in Figure 2 is also CO2 neutral.

[0058] Example 3: Figure 3 schematically shows how hydrogen obtained by the method of Example 2 is converted into fuel by the Fischer-Tropsch process.

[0059] Unlike the method in Example 2, the CO produced during the reaction of Mg and carbon is not removed from the mixture but is directly introduced into the steam. This produces Mg(OH)2 separated as a solid and a gas mixture containing CO and H2. This is converted into fuel by the Fischer-Tropsch process. The CO2 released during this process is initially bound to the fuel. It is released when the fuel burns. The amount of CO2 subsequently released is not added to the wastewater as in Examples 1 and 2, so this wastewater can absorb an equal amount of CO2 from the atmosphere. Therefore, the fuel obtained in this way is also CO2 neutral.

[0060] The direct CO2 footprint of this method can be further improved if CO2 from other sources, such as the atmosphere, is used in the synthesis described. In such cases, the CO2 from the preceding method step is then added to the wastewater.

Claims

1. CO2 from metallic magnesium in seawater ２ A method for neutral recovery, Until the saturation point is reached, a certain amount of seawater is converted to Ca(OH) ２ The process of mixing with, CO2 dissolved in the seawater ２ It is precipitated as a solid, and this is CaCO3 ３ The process of filtering, MgCl dissolved in the seawater ２ From Mg(OH) ２ Mg ＋＋ A process to precipitate, A process to obtain alkaline wastewater having a pH of 10, CO released in a preceding or subsequent process step to obtain magnesium ２ A process of capturing or generating, The above CO ２ introducing step into the alkaline wastewater, wherein the CO ２ dissolves in the wastewater, the wastewater is neutralized, and the introduced CO ２ remains bound in the wastewater, and a step; The dissolved CO ２ In order to secure this, the process involves transferring the wastewater that is currently being neutralized to a particularly deep-sea area, Methods that include...

2. The magnesium obtained above is mixed with water and used as an energy carrier, Mg(OH) ２ and obtain hydrogen The method according to claim 1, characterized in that

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