PROCESS FOR THE PRODUCTION OF HYDROGEN BY MEANS OF THERMAL ENERGY

Abstract

A process for the production of hydrogen by thermal energy based on a closed metal-chloride material cycle, where in the hydrogen release segment the metal is oxidized with hydrochloric acid at room temperature and in the regeneration segment the metal ions are reduced by heat treatment. This is a closed-cycle technological material flow, carried out by use of thermal energy and enables the production of hydrogen at room temperature on the basis of a solid energy carrier represented by metals. The process includes three main technological segments: an oxidation segment in which oxidation of a hydrogen-releasing metal is performed, a regeneration segment in which metal ions are reduced for metal regeneration, and a gaseous HCl capture segment in which gaseous HCl is dissolved in water. The material cycle is closed; there are no emissions or waste. Only water enters the process while hydrogen and oxygen exit.

Claims

1. A process for the production of hydrogen by means of thermal energy based on a solid energy carrier, characterized by comprising: an oxidation segment (i) including step one (1) of the process, in which, in a hydrogen-release reaction vessel, oxidation of a metal M is carried out with a hydrochloric acid solution at room temperature, resulting in the production of hydrogen gas and a metal-chloride salt solution; a regeneration segment (ii), in which reduction of metal ions is carried out for the regeneration of a metal M, comprising step two (2) which is crystallization in a crystallization unit, step three (3) which is step one of heat treatment in a system for step one of heat treatment, and step five (5) which is step two of heat treatment in the system for step two of heat treatment, and wherein the regeneration of the metal ions in the chloride solution, formed in the oxidation segment (i), is carried out by reducing the oxidation state of the metal ions by heat treatment, in which in step two (2) which is crystallization, liquid water is evaporated causing the crystallization of the metal-chloride salt or the metal chloride hydrate, and then in step three (3), which is step one of heat treatment, a metal chloride salt or metal chloride hydrate is converted into metal oxide, metal oxohydroxide or metal hydroxide species in air, which are then in step five (5) which is step two of heat treatment, in the reduction process, converted to elemental metal, wherein oxygen or reducing agent oxide is formed, and the obtained elemental metal is reintroduced to the oxidation segment (i) of the process; and a segment (iii) of capturing gaseous HCl, in which in step four (4) of the process, in the system for dissolving gaseous HCl in water, the gaseous HCl released in step one of heat treatment of metal chloride is dissolved in water, wherein an aqueous HCl solution is obtained which is led for re-use to the oxidation segment (i) of the process or stored in suitable tanks for re-use in the oxidation segment (i), wherein individual segments of the process can be repeated once or several times.

2. The process according to claim 1, characterized in that a metal M is selected from a group consisting of elemental metals, their mutual alloys, their intermetallic compounds or multi-elemental metals.

3. The process according to claim 1, characterized in that a metal M is selected from a group consisting of elemental metals selected from Fe, Zn, Sn, Al or Mg, mutual alloys of these metals, preferably Zn—Fe alloys, intermetallic compounds of these metals, preferably Fe.sub.3Zn.sub.10, FeZn.sub.7, Fe.sub.5Sn.sub.3, FeSn, and multi-element metals containing a major proportion of said elemental metals.

4. The process according to claim 1, characterized in that a metal M is elemental iron or an iron alloy or an intermetallic metal with iron or a multi-element metal containing a predominant content of iron, the preferred metal M being iron.

5. The process according to claim 1, characterized in that the heat needed in the regeneration segment (ii) of the process in step two (2) which is crystallization and/or step three (3) which is step one of heat treatment, is obtained from conventional sources or renewable sources or a combination thereof, wherein the heat energy obtained from renewable sources is preferably selected from a group consisting of geothermal heat energy, solar heat energy, industrial excess heat or heat obtained from the processes of heat recuperation, or any combination thereof.

6. The process according to claim 5, characterized in that the heat needed in the regeneration segment (ii) of the process in step two (2) which is crystallization and/or step three (3) which is step one of heat treatment, is obtained from renewable sources, the heat energy being preferably selected from a group consisting of geothermal heat energy, solar heat energy, industrial excess heat or heat obtained from the processes of heat recuperation, or any combination thereof.

7. The process according to claim 1, characterized in that step two (2), which is crystallization, comprises an oxidation sub-step (2a) that is carried out in an oxidation subunit, in which metal ions are oxidized by adding oxidants, and a crystallization sub-step (2b) in which a metallic chloride or a metallic chloride hydrate is crystallized.

8. The process according to claim 7, characterized in that the oxidant used for the oxidation of the metal ions in the chloride solution in oxidation sub-step (2a) is in liquid or gaseous form, wherein hydrogen peroxide is preferably added as the oxidant in liquid form, or oxygen or a gas mixture containing oxygen or air is added as oxidant in gaseous form, and wherein the gaseous oxidant is added by purging the chloride solution with oxygen or a gas mixture containing oxygen, or air, preferably the oxidation of metal ions in the chloride solution is carried out by purging the solution with air.

9. The process according to claim 1, characterized in that the heat released in the reaction between the metal M and the HCl solution in the oxidation segment (i) in step one (1) of the process is recovered in a heat recuperator and the heat thus obtained is fed into the crystallization process to step two (2) of the process and/or to the crystallization sub-step (2b) of the process and/or step three (3) which is step one of heat treatment.

10. The process according to claim 1, characterized in that step three (3) which is step one of heat treatment, is carried out in humid air and at a temperature identical to or lower than 550° C.

11. The process according to any claim 1, characterized in that in the oxidation segment (i) in step one (1) of the process, in a hydrogen-release reaction vessel, oxidation of elemental iron (Fe) is carried out with a hydrochloric acid (HCl) solution at room temperature, resulting in the production of hydrogen gas and a metal chloride solution (FeCl.sub.2(aq)), followed by the regeneration segment (ii) of the process, in which in step two (2), which is crystallization, liquid water is evaporated in the crystallization unit from an FeCl.sub.2 solution, such that ferrous chloride hydrate (FeCl.sub.2.4H.sub.2O.sub.(s)) is crystallized, followed by step three (3), which is step one of heat treatment, in which the resulting (FeCl.sub.2.4H.sub.2O.sub.(s)) is heat-treated at about 550° C. in humid air, resulting in the digestion of chloride and the formation of gaseous HCl and Fe-oxide species, which can be oxides, hydroxides and oxohydroxides, which are then converted into elemental iron in the subsequent step five (5), which is step two of heat treatment, in the reduction process following the metallurgical process in blast furnaces, wherein oxygen and reducing agent oxide are formed, in segment (iii) of capturing gaseous HCl in water, the resulting gaseous HCl is dissolved in water in step four (4) in the system for dissolving the gaseous HCl in water, preferably in a scrubber, wherein hydrochloric acid is formed which is re-used in the reaction with iron in the oxidation segment (i) of a new technological cycle, or the hydrochloric acid is optionally stored in an appropriate storage tank for re-use in a reaction with iron in the oxidation segment (i) of a new technological cycle.

12. The process of claim 11 characterized in that, in the regeneration segment (ii), step two (2), which is crystallization, comprises an oxidation sub-step (2a) and a crystallization sub-step (2b), wherein in the oxidation sub-step (2a), in the oxidation subunit, the Fe.sup.2+ ions of the chloride solution are oxidized to Fe.sup.3+ ions by adding oxidants which may be in liquid or gaseous form and selected from a group consisting of liquid hydrogen peroxide, oxygen gas, an oxygen-containing gas mixture and air, wherein, optionally, in the case of oxidation with oxygen from FeCl.sub.2(aq) in the presence of a sufficient quantity of chloride ions, a reaction takes place, in which FeCl.sub.3(aq) and water are formed, or in the absence of excess chloride ions a reaction takes place, in which FeCl.sub.3(aq) and Fe.sub.2O.sub.3(s) are formed, the resulting product mixture is passed to the crystallization subunit after the oxidation step, where water is evaporated in the crystallization sub-step (2b) to crystallize FeCl.sub.3.6H.sub.2O.sub.(s), followed by step three (3) of the process in which FeCl.sub.3.6H.sub.2O.sub.(s) together with Fe.sub.2O.sub.3 is heat treated at about 500° C. in humid air, which leads to the digestion of chloride and the formation of Fe-oxide and gaseous HCl, and in the subsequent step five (5) of step two of heat treatment Fe-oxide, following a metallurgical process in blast furnaces, is converted back into elemental iron, producing oxygen or reducing agent oxide, the resulting gaseous HCl, in segment (iii) of the process, in step four (4) in the system for dissolving the gaseous HCl in water, preferably in a scrubber, is dissolved in water, wherein hydrochloric acid is formed which is re-used in the reaction with iron in the oxidation segment (i) of a new technological cycle, or the hydrochloric acid is optionally stored in an appropriate storage tank for re-use in a reaction with iron in the oxidation segment (i) of a new technological cycle.

13. The process according to claim 11, characterized in that the heat supplied to the regeneration segment (ii) of the process in step two (2) which is crystallization and/or crystallization sub-step (2b) which is crystallization and step three (3) which is step one of heat treatment, is obtained from conventional sources or renewable sources, the supplied heat energy being preferably selected from renewable sources and selected from a group consisting of geothermal heat energy, solar heat energy, industrial excess heat or heat obtained from the processes of heat recuperation, or any combination thereof.

14. Process according to claim 1, characterized in that only water enters the process while hydrogen and oxygen exit, and the amount of metal and chloride ions remains unchanged, and that the process produces the same number of moles of hydrogen as the moles of metal used, preferably iron.

15. Process according to claim 1, characterized in that the hydrogen formed in the oxidation segment (i) is immediately, without intermediate storage, converted into heat or electricity.

Description

[0022] The process according to the invention will be described in the following and presented in the drawings, in which:

[0023] FIG. 1: A general scheme of the process according to the invention represents a cyclic technological process of hydrogen production based on a reaction of a metal and HCl with steps: step one 1 which is the oxidation of a metal M with a hydrochloric acid solution, step two 2 which is crystallization, step three 3 which is step one of heat treatment (low-temperature heat treatment), step four 4 which is the dissolution of gaseous HCl, step five 5 which is step two of heat treatment (high-temperature heat treatment).

[0024] FIG. 2: A scheme of the process according to the invention represents a material flow and a cyclic technological process of hydrogen production based on a reaction of iron and HCl with an example of a three-step treatment of a FeCl.sub.2 solution in the regeneration segment ii of the process: step two 2 which is crystallization, step three 3 which is low temperature heat treatment of FeCl.sub.2.4H.sub.2O, and step five 5 which is high-temperature heat conversion of Fe-oxide species to elementary iron (g denotes gas, l denotes liquid, s denotes solid matter and aq denotes aqueous solution).

[0025] FIG. 3: A scheme of the process according to the invention represents a material flow and a cyclic technological process of hydrogen production based on a reaction of iron and HCl with an example of a four-step treatment of a FeCl.sub.2 solution in the regeneration segment ii of the process: oxidation sub-step 2a which is oxidation of FeCl.sub.2 to FeCl.sub.2, crystallization sub-step 2b which is crystallization, step three 3 which is low-temperature heat treatment of FeCl.sub.3.6H.sub.2O, and step five 5 which is high-temperature heat conversion of Fe-oxide species to elementary iron.

[0026] Wherever they appear in this text, the designations denote: g denotes gas, l denotes liquid, s denotes solid matter and aq denotes aqueous solution.

[0027] The cyclic technological process according to the invention is a multi-step process comprising the following steps: step one 1, in which hydrogen is released in a hydrogen-release reaction vessel, step two 2 which is crystallization in a crystallization unit, step three 3 which is step one of heat treatment (low-temperature heat treatment), step four 4 which is the dissolution of gaseous HCl in a system for dissolving gaseous HCl in water, and step five 5 which is step two of heat treatment (high-temperature treatment, metallurgical process). The crystallization unit may, if necessary, be divided into an oxidation subunit in which oxidation sub-step 2a takes place, and a crystallization subunit, in which crystallization sub-step 2b is carried out, depending on the chemical properties of the metal chloride.

[0028] In the oxidation segment i in step one 1, a chemical reaction takes place in the hydrogen-release reaction vessel, in which hydrogen is formed at room temperature. The chemical reaction occurs between the HCl solution and a metal M following the reaction:

M.sub.(s)+xHCl.sub.(g).fwdarw.MCl.sub.x(aq)+x/2H.sub.2(g)

[0029] To reach a good yield of the process according to the invention, it is important that this reaction is thermodynamically spontaneous, which means that the free Gibbs energy decreases during the reaction. Thus, no additional energy is required for the reaction to take place and the reaction can proceed at room temperature. The reaction releases heat which can be recovered in the heat recuperator and fed to the processes requiring heat, in particular to the crystallization process in step two 2 and to step one of the heat treatment in step three 3. The reactions relevant to this technological process have already been described and also thermodynamically evaluated, but never used in the cyclic material flow which is the subject of this patent protection.

[0030] The term metal M, referred to hereinbefore and hereinafter, represents elemental metals, their alloys, their intermetallic compounds or multi-elemental metals.

[0031] Preferably, the process uses a metal M selected from the group consisting of elemental metals selected from Fe, Zn, Sn, Al or Mg, mutual alloys of these metals, preferably Zn—Fe alloys, intermetallic compounds of these metals, preferably Fe.sub.3Zn.sub.10, FeZn.sub.7, Fe.sub.5Sn.sub.3, FeSn, and multi-element metals containing a major proportion of said elemental metals.

[0032] Particularly preferably, in the process according to the invention, elemental iron (Fe) or an iron alloy or an intermetallic metal with iron or a multi-element metal containing a predominant iron content is used as the metal M. Elemental iron is particularly preferred.

[0033] The metal ions from the chloride solution, which is the product of the reaction between a metal and HCl in step one 1, must be regenerated into elemental metal for a complete material flow. The first step is the crystallization of metal chloride, which represents step two 2 of the process according to the invention. This process is carried out in an industrial crystallizer, where water is evaporated, which causes the crystallization of a metal chloride (e.g. MCl.sub.x) or a metal chloride hydrate (e.g. MCl.sub.x.yH.sub.2O). The process of oxidation of metal ions can be included in this technological segment of the process before the step of water evaporation in order to adapt the processes in subsequent heat treatment processes. In such a case, step two 2 of the process consists of two sub-steps, namely oxidation sub-step 2a, in which the oxidation process of metal ions takes place, and crystallization sub-step 2b, in which the crystallization process (water evaporation) takes place. The oxidation of metal ions in oxidation sub-step 2a can be carried out by an addition of oxidants, which can be in liquid or gaseous form. An oxidant in liquid form is e.g. hydrogen peroxide H.sub.2O.sub.2. Oxidation with an oxidant in gaseous form is carried out by purging a chloride solution with a gas, which may be, for example, oxygen or a gas mixture containing oxygen, or even air. The oxidation product is then taken to crystallization pre-step 2b, where water is evaporated to crystallize a metal chloride (with a higher oxidation state) or a hydrate of this metal chloride.

[0034] The crystallized metal chloride or its hydrate is heat-treated in a first low-temperature heat treatment step, which is step three 3. This treatment takes place in humid air and in most cases does not exceed a temperature of 550° C. At this stage of processing, chloride species are converted into oxide ones, which are suitable for further metallurgical processing in step five 5 of the process according to known processes and in devices or systems for obtaining metals from ores or minerals. The presence of humid air is important for the fact that during the fusion of chloride species, gaseous HCl is formed as much as possible, which is very soluble in water, instead of gaseous Cl.sub.2. In step four 4 of the process, gaseous HCl is led to a system for dissolving in water (scrubber), where the HCl acid is formed, which is again needed in a new material cycle to react with a metal.

[0035] According to one embodiment of the present invention, the material cycle can be set out in a generalized form in steps: [0036] (1) Hydrogen release: M.sub.(s)+xHCl.sub.(aq).fwdarw.MCl.sub.x(aq)+x/2H.sub.2(g) [0037] (2) Crystallization: MCl.sub.x(aq).fwdarw.MCl.sub.x.yH.sub.2O.sub.(s)+H.sub.2O(g) [0038] (3) Step one of heat treatment: MCl.sub.x.yH.sub.2O.sub.(s)+H.sub.2O.sub.(g).fwdarw.M-oxide species+HCl.sub.(g) [0039] (4) Regeneration of HCl acid: HCl.sub.(g)+H.sub.2O.fwdarw.HCl.sub.(aq) [0040] (5) Step two of heat treatment: M-oxide species (+reducing agent).fwdarw.elemental M+oxygen (or a reducing agent oxide)

[0041] According to a further embodiment of the invention, the crystallization step, which is step two 2 of the process, can take place in two sub-steps, where the oxidation of metal ions takes place in the first oxidation sub-step 2a, followed by the crystallization sub-step 2b of crystallization. The oxidation of metal ions can be carried out by adding liquid oxidants, such as hydrogen peroxide H.sub.2O.sub.2, or by purging a gas, which can be, for example, oxygen, a gas mixture containing oxygen, or even air.

[0042] In the material cycle, the amount of metal and chloride ions remains unchanged, as these components are not consumed, but only circulate through the technological cycle. For these components, the material cycle is closed. Only water enters the cycle while oxygen and hydrogen exit it.

EXAMPLES

[0043] The following are two examples of the processes according to the invention, in which hydrogen is released during the reaction of iron with an HCl solution. Examples of two variants of such a process according to the invention are shown in FIGS. 2 and 3. In both cases, hydrogen is released in the reaction vessel during the reaction between Fe and the HCl solution, which can be described by the equation:

Fe.sub.(s)+2HCl.sub.(aq).fwdarw.FeCl.sub.2(aq)+H.sub.2.

[0044] The reaction produces the same number of moles of hydrogen as the moles of iron used. The reaction is thermodynamically spontaneous and proceeds entirely at room temperature. The reaction releases heat which can be recovered in the heat recuperator and fed to the processes requiring heat. The reaction also produces an FeCl.sub.2 solution, which must be converted back to HCl and elemental iron in further technological steps.

Example 1

[0045] In the variant of the process according to the invention shown in FIG. 2, in step two 2, which is crystallization, the water from FeCl.sub.2 is evaporated. The ferrous chloride hydrate FeCl.sub.2.4H.sub.2O.sub.(s) crystallizes. Various heat sources can be used for water evaporation, but it makes economic sense to use renewable sources, such as geothermal or solar heat or excess industrial heat. In a further step three 3 of the process, FeCl.sub.2.4H.sub.2O.sub.(s) is heat treated at about 550° C. in humid air, leading to the digestion of chloride, the formation of Fe-oxide species, which can be oxides, hydroxides and oxohydroxides, and the gaseous HCl. In the case of complete oxidation, the following reaction takes place:

2FeCl.sub.2+2H.sub.2O+½O.sub.2.fwdarw.Fe.sub.2O.sub.3+4HCl.

[0046] Then, in the next step five 5 of the process, the Fe-oxide species are converted back to elemental iron in the blast furnaces following a metallurgical process, and the conversion produces oxygen or a reducing agent oxide (e.g. H.sub.2O or CO.sub.2). The resulting gaseous HCl is dissolved in water in step four 4 of the process in commercial scrubbers to re-form HCl acid, which is fed to the oxidation segment i to be reused for reaction with iron, or can be stored in appropriate re-use tanks for use in a reaction with iron in a new technological cycle.

Example 2

[0047] In the variant of the process according to the invention shown in FIG. 3, step two 2, crystallization, is divided into two sub-steps 2a and 2b, which take place in two subunits. In the first oxidation sub-step 2a, Fe.sup.2+ ions of the chloride solution are oxidized to Fe.sup.3+ ions in the oxidation subunit. This can be achieved by adding oxidants, such as hydrogen peroxide H.sub.2O.sub.2, or by purging a gas, which can be, for example, oxygen, a gas mixture containing oxygen, or even air. In the case of oxidation with oxygen in the presence of a sufficient quantity of chloride ions, the following reaction takes place:

12FeCl.sub.2(aq)+3O.sub.2(g)+12HCl.sub.(aq).fwdarw.12FeCl.sub.3(aq)+6H.sub.2O

[0048] and in the absence of excess chloride ions

6FeCl.sub.2(aq)+3O.sub.2(g).fwdarw.2FeCl.sub.3(aq)+2Fe.sub.2O.sub.3(s).

[0049] Fe.sub.2O.sub.3 precipitates as early as this phase. After oxidation, the whole product is taken to the second crystallization sub-step 2b, where water is evaporated in the second crystallization subunit to crystallize FeCl.sub.3.6H.sub.2O.sub.(s), too. In a further step three 3 of the process, FeCl.sub.3.6H.sub.2O.sub.(s) (together with Fe.sub.2O.sub.3) is heat treated at about 500° C. in humid air, leading to the digestion of chloride, the formation of Fe-oxide and the gaseous HCl according to the equation 2FeCl.sub.3.6H.sub.2O.fwdarw.Fe.sub.2O.sub.3+6HCl+8H.sub.2O. In the next step five 5 of the process, the Fe-oxide is converted back to elemental iron following a metallurgical process in blast furnaces. The HCl is dissolved in water in step four 4 of the process in commercial scrubbers to re-form HCl acid, which can be stored and re-used in a reaction with iron in a new technological cycle.

[0050] The present invention is not obvious in relation to prior art and is innovative as it introduces, into the technological cycle of hydrogen production by means of thermal energy, processes which have not been described so far: [0051] release of hydrogen based on a reaction that takes place at room temperature, [0052] new material flow chemistry based on oxidation-reduction conversion of metal chlorides, and [0053] use of thermal energy to drive chemical processes in the material cycle to produce hydrogen.

[0054] The present invention is useful in enabling environmentally sustainable, carbon-free hydrogen production. As an energy source, it allows the use of sustainable heat sources such as geothermal heat or solar heat, as well as the use of excess industrial heat. The material cycle is closed, there are no emissions or waste. Only water enters the process while hydrogen and oxygen exit it, so such production of hydrogen is environmentally neutral from the point of view of raw material consumption.

LITERATURE

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