Conversion of iron and water to iron oxide and hydrogen using acetic acid (acetate) and associated reactor

Abstract

The present invention describes a process for producing hydrogen and magnetite from water and iron in the presence of an iron(II) salt catalyst. Furthermore, the process describes the use of the iron obtained as an indirect hydrogen storage medium.

Description

[0001] The present invention relates to a process for producing hydrogen and magnetite from water and iron, wherein the water reacts with the iron in the presence of a catalyst. The iron used can be obtained beforehand, for example, by reducing the resulting magnetite or other compounds.

[0002] Hydrogen is considered the energy source of the future. It is a versatile and easily transportable energy source. Hydrogen is produced, among other things, through water electrolysis. The energy required for this process is very high, and storage is energy-intensive. For better storage, hydrogen is cooled to -253°C under very high pressure. This has the advantage of liquefying the gas, allowing it to be transported in a more compact manner. However, this compression process requires a lot of energy.

[0003] The steam iron reaction for producing hydrogen has been known for over 100 years and was used industrially until the early 1970s. The steam iron reaction is typically operated at temperatures around 500 °C at atmospheric pressure. Water is evaporated for this process, and the reaction therefore also takes place in the gas phase. As a result, energy efficiency is low due to the necessary water evaporation, and the reaction, or rather, the process, requires high safety standards due to the gas phase.

[0004] Furthermore, it is well known that it is possible to produce hydrogen using iron and an acid. However, this requires one equivalent of iron and two equivalents of acids for each equivalent of hydrogen produced. Because this is a very uneconomical method for producing hydrogen and produces stoichiometric waste, this process is not typically used outside of the laboratory scale.

[0005] Due to the problems and disadvantages of the current technology described above, as well as the problems associated with fossil fuels and climate change, there is a great need for a new process that provides a safe, energy-efficient method for producing hydrogen from iron. Furthermore, there is also a need for a practical energy storage system to transport hydrogen easily and efficiently in the future.

[0006] Surprisingly, it has been shown that hydrogen can be extracted from liquid water using iron in combination with an iron(II) salt catalyst. The use of liquid water minimizes safety risks and requires less energy to evaporate the water. Furthermore, the extracted hydrogen can be used for iron reduction, and the recovered iron can be reused in a subsequent process to generate hydrogen. The process thus offers a new possibility for long-term indirect hydrogen storage using extracted iron. This allows hydrogen to be transported and stored more energy-efficiently and safely.

[0007] In a first embodiment, the object underlying the present invention is therefore achieved by producing hydrogen and magnetite from water and iron, wherein the water is brought into contact with the iron as a liquid in the presence of at least one catalyst, characterized in that a) the at least one catalyst is an iron(II) salt, in particular iron(II) acetate; (b) the process is carried out at a temperature of 60 to 250 °C, and c) the process is carried out at a pressure at which the water is predominantly present as a liquid.

[0008] According to the invention, iron and water are brought into contact in the presence of an iron(II) catalyst, in particular iron(II) acetate, at a temperature of 90-190°C. Furthermore, the pressure in the process is selected according to the invention such that the water is predominantly present as a liquid. According to the invention, this means that above the liquid phase in a reactor in which the reaction takes place, a gas phase which also contains water in vapor form can be present. According to the invention, however, the iron only reacts with the water in the liquid phase. According to the invention, it is also irrelevant which component is initially introduced and which is added. Iron and water react with one another in an aqueous solution, iron being oxidized to iron oxide or magnetite. Hydrogen is formed. According to the invention, predominantly as a liquid preferably means that the water makes up at least 85% by weight, in particular at least 90% by weight.-% and in particular at least 95 wt.% in the liquid phase based on the total amount of water.

[0009] The process according to the invention thus provides a new, energy-efficient way to produce hydrogen. The hydrogen can then be collected and used directly as a raw material or as an energy carrier. In a preferred embodiment, the resulting magnetite can be reacted with hydrogen again in a subsequent process, which in turn produces iron. The iron serves as an indirect energy carrier for the hydrogen, as it can be used repeatedly to produce hydrogen using the process according to the invention.

[0010] This aspect solves the problem of having to cool hydrogen to -253 °C before storing it as a liquid. Furthermore, all risks associated with transporting liquid hydrogen are eliminated.

[0011] According to the invention, magnetite is a mineral from the mineral class of oxides and hydroxides, which is the most stable compound between iron and oxygen. Its exact chemical name is iron(II,III) oxide. Other iron oxides can also be formed in the process according to the invention. In the process according to the invention, iron(II) oxide is initially formed, which immediately decomposes to form magnetite. This decomposition also produces elemental iron, which in turn reacts with the aid of the iron(II) salt catalyst, in particular iron(II) acetate, to form iron oxide and hydrogen.

[0012] A key advantage of the process according to the invention is the use of liquid water, as this requires much less energy than a steam-gas phase reaction. To ensure this, the pressure must be selected so that it is below the vapor pressure of the water. The average person skilled in the art will know which pressure is appropriate for carrying out the process with liquid water. For example, a process according to the invention that is carried out at a temperature of 100 °C requires a pressure of at least approximately 1013 hPa or 1 bar, whereas a process according to the invention that is carried out at 160 °C, for example, requires a pressure of at least approximately 6200 hPa or 6.2 bar. Other vapor pressures corresponding to the process according to the invention can be found in the prior art.

[0013] A catalyst according to the present invention reduces the reaction enthalpy required for the reaction of water with iron, thereby also increasing the reaction rate. The catalyst is not consumed and can be used multiple times. According to the invention, the catalyst comprises an iron(II) salt, in particular iron(II) acetate. In a further preferred embodiment, other iron(II) salts would be possible, such as, for example, iron chloride, iron sulfate, iron nitrate and / or iron phosphate. Other possible iron salts are familiar to the person skilled in the art and can also be used in the process according to the invention. An important aspect of the catalyst according to the invention is that the turnover number of the catalyst remains unchanged after at least 10, preferably 15, most preferably 20 processes according to the invention, and thus the conversion of iron and water remains unchanged for the same reaction time.Surprisingly, the catalyst tests have shown that iron(III) salts cannot be applied to the process according to the invention and no reaction takes place.

[0014] In the process according to the invention, the reaction temperature also depends on the catalyst used. In a preferred embodiment, the temperature is selected from 90°C to 190°C, since the decomposition temperature of iron(II) acetate is 190°C. In a further preferred embodiment, other catalysts can thus also enable higher temperatures for the process according to the invention. The process temperature is determined by the decomposition temperature of the iron catalyst used. In the process according to the invention, a temperature is thus selected between 60°C and 250°C, but preferably a temperature of 80°C to 200°C, and most preferably a temperature of 90°C to 190°C.

[0015] Additionally, it is possible to carry out the process according to the invention at a temperature below the critical point of water. Thus, in a preferred embodiment, a temperature is selected between 0 °C and 374 °C. Furthermore, in further preferred embodiments, temperatures of 100 °C to 350 °C, 150 °C to 320 °C, or 200 °C to 300 °C are possible, as long as the pressure is selected such that the water is predominantly present as a liquid.

[0016] In a preferred embodiment, the catalyst in the process according to the invention is used in an amount of 1-100 mol%, preferably 5-100 mol%. The amount of catalyst relates to the limiting reactant or reagent in the process. This can be the amount of iron or the amount of water, as required. According to the invention, mol% is understood to mean the ratio of limiting reagent to catalyst; thus, 1 mol of catalyst and 100 mol of limiting reagent results in a catalyst amount or loading of 1 mol%. The limiting reagent is thus understood to mean the reactants used in the process according to the invention, whereby the terms reagent and reactant are interchangeable in this context.

[0017] Furthermore, the process according to the invention allows for adjusting the pressure depending on the temperature. In a preferred embodiment of the process, the pressure can be up to 221 bar, 30 bar, or 15 bar. The person skilled in the art will know which pressure is appropriate to remain below the vapor pressure of the water.

[0018] Thus, in a preferred embodiment, the process according to the invention can be carried out at a higher pressure and temperature, in particular at a pressure below 221 bar and at a temperature of up to 374 °C below the critical point at which water remains liquid.

[0019] In a further preferred embodiment of the process according to the invention, the process may include a further step d) for separating the magnetite and hydrogen from the reaction solution at the end of the reaction. Furthermore, in a preferred embodiment, it is possible for the magnetite and the catalyst to be separated from each other so that the catalyst can be further used in a process according to the present invention. The separation of magnetite and catalyst can be achieved, for example, using a magnet and / or a filter.

[0020] Furthermore, in a preferred embodiment of the invention, it is possible to separate the magnetite from the catalyst by washing with a solvent. Suitable solvents are known to those skilled in the art. These are selected depending on the catalyst species. Preferred solvents are polar organic solvents and / or water. Most preferred solvents for separating the catalyst are, for example, 1,4-dioxane, dichloromethane, ethyl acetate, and / or respective mixtures.

[0021] In a further preferred embodiment, additional catalyst species can be added to the process according to the invention to increase or decrease the reaction rate or the reaction enthalpy. Preferred catalysts that can be added are metal oxides, for example, titanium oxide, magnesium oxide, and / or zinc oxide. Other transition metals or metal oxides can also be used.

[0022] Particularly preferably, the process is a continuous process in which iron and water are continuously introduced into a container, by means of which hydrogen and magnetite are obtained.

[0023] In the present invention, the reaction is carried out in the liquid phase of water at 90–190 °C and above the vapor pressure of water, without the presence of oxygen. Advantages include smaller, simpler, more compact designs, lower energy loss / higher energy efficiency (lower temperatures and no water evaporation), no passivation of the iron surface, and higher and faster conversions. The reaction is particularly preferably carried out in a closed vessel so that heat energy and pressure can be maintained while reactants are added and products can be removed. The removal or separation takes place as described in the above paragraphs.

[0024] Furthermore, in a preferred embodiment, the separated magnetite can be reduced again in a subsequent process in order to use the resulting iron as an indirect hydrogen source.

[0025] The process according to the invention can also be used to store renewable energies, for example, to convert excess wind or solar energy into hydrogen and thus store it. Preferably, however, storage is provided using magnetite or iron produced by the process. The energy is converted into hydrogen, for example, by electrolysis, and used to reduce the magnetite or other iron compounds. The resulting iron can thus be converted back into hydrogen and magnetite in a process according to the invention. The resulting iron can thus be regarded as an indirect hydrogen or energy storage medium. The process according to the invention is carried out in the absence of oxygen, since the use of oxygen leads to degeneration of the catalyst.The catalyst is converted to iron(III) acetate with oxygen, which means it can no longer be used in the process.

[0026] Fig. 1 shows schematically a closed device in which the method according to the invention is carried out.

Claims

[1] Process for the production of hydrogen and magnetite from water and iron, wherein the water is brought into contact with the iron as a liquid in the presence of at least one catalyst, characterized by , that a) the at least one catalyst is an iron(II) salt, in particular iron(II) acetate; (b) the process is carried out at a temperature of 60 to 250 °C, and c) the process is carried out at a pressure at which the water is predominantly present as a liquid. [2] Method according to claim 1, characterized by that the catalyst is used in an amount of 1 - 100 mol%, preferably 5 - 100 mol%, based on the limiting reagent. [3] Method according to at least one of claims 1 to 2, characterized bythat the process is carried out at a higher pressure and corresponding temperature, especially at a pressure below 221 bar and at a temperature of up to 373 °C, so that the water remains liquid. [4] Method according to at least one of claims 1 to 3, characterized by that it also includes the following step: d) Separation of magnetite and hydrogen from the reaction solution at the end of the reaction. [5] Method according to at least one of claims 1 to 4, characterized by that the magnetite and the catalyst are separated from each other so that the catalyst can be reused in a process according to at least one of claims 1 to 4. [6] Method according to claim 5, characterized by that the separation of magnetite and the catalyst is carried out using a magnet, leaching and / or filtering. [7] Method according to at least one of claims 1 to 6, characterized bythat at least one further catalyst selected from a metal oxide, in particular titanium oxide, is used. [8] Method according to claim 1, characterized by that the process is carried out as catalyst in step a) with a catalyst selected from iron(II) chloride, iron(II) sulfate, iron(II) nitrate, iron(II) phosphate. [9] Method according to at least one of claims 1 to 8, characterized by that the process is carried out at a temperature of 90 - 190 °C. [10] Method according to at least one of claims 1 to 9, characterized by that the iron extracted is used as an indirect hydrogen storage medium.

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