DE102006030449A1 - Reversible storage of hydrogen using inorganic as potassium carbonate and/or potassium hydrogen carbonate by supply of the inorganic in aqueous solution in reactor vessel, catalytic treatment of the inorganic and splitting of oxygen - Google Patents

Abstract

In the reversible storage of hydrogen, an inorganic as a potassium carbonate and/or potassium hydrogen carbonate is supplied in an aqueous solution (2) in reactor vessel (1). The inorganic is catalytically treated in the aqueous solution by catalytically activated nickel electrodes contained in the reactor vessel. The catalysts are a ZnO or a ZnO/TiO2. Oxygen is split from carbon dioxide by introducing a current via the electrodes with 2.5 V under simultaneous hydrogenation of the inorganic at the surface of the electrodes to form potassium formate. In the reversible storage of hydrogen, an inorganic as a potassium carbonate and/or potassium hydrogen carbonate is supplied in an aqueous solution (2) in reactor vessel (1). The inorganic is catalytically treated in the aqueous solution by catalytically activated nickel electrodes contained in the reactor vessel. The catalysts are a ZnO or a ZnO/TiO2. Oxygen is split from carbon dioxide by introducing a current via the electrodes with 2.5 V under simultaneous hydrogenation of the inorganic at the surface of the electrodes to form potassium formate. The hydrogenation takes place in the reactor vessel by supplying gaseous hydrogen. The produced inorganic is stored in aqueous solution in the same reactor or in a storage container (20). The potassium formate is converted into formic acid and methanol by further hydrogenation under adding of CO2. In the place of potassium formate, the process produces a different hydrocarbon. The emerging gas flows into a container through a KOH or a K2CO3-solution. The CO2-proportion is removed from the gas and forms K2CO3 and/or K2HCO3 and the remaining hydrogen is removed by a discharge pipe (18). The potassium formate is catalytically dissociated or split in a container with platinum or palladium-catalysts, and the hydrogen (4) is released. The potassium formate or formic acid or mixtures from it is added in aqueous solution. The hydrogen and the inorganic are released during the process and a renewed catalytic treatment and hydrogenation are carried out after discharge of the hydrogen. The released hydrogen is supplied to a fuel cell and/or a hydrogen engine or other device, which releases energy from hydrogen. A membrane from non-conducting, ion-permeable material both sides coated with silver is arranged in the storage. A voltage is measured by connecting the coatings with contacts during the discharging and/or the oxidation of potassium formate to potassium hydrogen carbonate. The membrane is a non porous and is used as wall element inserted into the container for chambers formation. The anode of the Ni-electrode arrangement is assigned in the chamber, and the corresponding cathode and the silver coating are present in another chamber. The coating layer in the other chamber forms the negative pole and the other coating layer in an additional chamber forms the positive pole.

Description

The The invention relates to a method for storing hydrogen under Use of potassium carbonate and / or potassium bicarbonate.

Various methods are used to recover energy and store it in the form of hydrogen. In these processes, the hydrogen is obtained, for example, via electrolysis, photolysis or thermolysis. By way of example, mention may be made of a method by which zinc oxide (ZnO) in solar concentrators as a reactor is thermolytically split into zinc (Zn) and oxygen (O ₂ ) at temperatures above 2000 ° C. on an industrial scale. The zinc is then used to break down water to release hydrogen. It is again oxidized to ZnO and reused in the reactor. Transport of the zinc to the place of energy demand and return of the zinc oxide to the reactor is unprofitable for reasons of weight. Therefore, to distribute the recovered energy, the hydrogen is used directly or the power generated therefrom by means of fuel cells.

Further known methods are in the field of photolysis, in which water by irradiation of sunlight with various catalysts as an acceptor is split into hydrogen and oxygen. The case (previously on a laboratory scale) achieved conversion efficiency of the light is above the from known photovoltaic solar panels.

hydrogen also arises in larger quantities as a waste product in the industry, eg. B. in the chlorine processing and in the refining of crude oil products to fuels and fuel oil.

All Process of energy production from regenerative energies in the Solar, tidal and wind energy sectors do not provide a comparably continuous available Energy source, as it is the fossil energy or nuclear power. Only through the use of a buffer, such as Hydrogen, as energy storage will be a continuous availability the energy obtained reaches as electrical or thermal Energy can be used if necessary.

Of the decisive disadvantage of gaseous Hydrogen is in its low density. This already leads at low volumes to huge volumes (1 liter of gaseous hydrogen weighs 0.089958 at 0 ° C). Increased Density is in pressure tanks (far over 500 bar) or by liquefaction reached. The one for it However, the necessary amount of technical and energy leads only to unsatisfactory Results. For example, must be more fluid Hydrogen resistant chilled and under pressure to avoid evaporation (boiling point -252.8 ° C). Which in turn only with increased Expenditure of energy can be made. This circumstance leads to the above example of hydrogen as a waste product of chemical industry and oil refineries due to the poor handling of storage to unused, controlled flaring of precious hydrogen.

Hydrogen can be chemically bound or stored in higher density, eg. B. in metal hydrides such. As MgH ₂ , AlH ₂ , LiH or CaH ₂ . Depending on the metal hydride, this requires alternately increased pressures, cooling and high temperatures above 200 ° C for loading and unloading. Handling eg in alanates (AlH ₂ ) is only possible with smaller, technically complex, hydrogen-tight, pressure-resistant "tanks." These must be equipped with devices for heating and cooling as well as capillary inlets and outlets for the hydrogen gas to the nanometer-sized Al aggregates As a result, the "packaging weight" increases enormously and makes the storage and transport of large quantities of hydrogen unprofitable.

The state of the art does not lack effective technologies for converting the energy from hydrogen into electricity. For example, reference may be made to the following patents and patent applications: DE 101 18 744 B4 . DE 103 24 200 A1 . DE 103 24 201 A1 . DE 103 92 493 T5 . DE 696 22 742 T2 ,

From JESSOP, Philip, G., et. al .: Homogeneous Hydrogenation of Carbon Dioxide. In: Chemical Reviews, Vol. 95, no. 2, 1995, pp. 259-272; P. 263, para. B, a conversion process of carbon dioxide (CO ₂ ) to carbon monoxide (CO) using Group 8 catalysts, namely Pd and Ru, in aqueous solution is known.

Out KUDO, K., et. al .: Kinetic Study on the Synthesis of Alkali Formats from Carbon Dioxide and Hydrogen Catalyzed by Palladium (II) Chlorides in an Aqueous Alkali Solution. In: Nihon Kagaku Kaishi, 1977, no. 3, pp. 302-309; P. 307, Equations I to V, Abst., Is a transposition procedure of carbon dioxide using a catalyst of palladium (II) Chlorides in aqueous solution known.

From INOUE, Y., et. al .: Catalytic Fixation of Carbon Dioxide to Formic Acid by Transition-Metal Complex under mild Conditions. In: Chemistry Letters, 1976, p. 863, 864; As a whole, a conversion process of CO ₂ to CO using a TI chloride magnesium system (TiCl ₄ -Mg) in aqueous solution is known. Again, Group 8 catalysts are used. None of the three aforementioned articles are concerned with the storage of hydrogen according to the present invention ing invention. Furthermore, it has been shown that the catalysts used for large series applications in self-sufficient reactors are cost-intensive and polluting.

From the US 4,160,816 It is known for storing electrical energy to use in an electrochemical cell CO ₂ gas in combination with water for the production of formic acid as an electrochemical storage medium. For this purpose, a catalyst is used and constantly supplied CO ₂ .

From JP 06-0 93 485 A, a reduction process for CO ₂ gas is known in which various catalysts, such as Pt catalysts, are used.

From JP 06-1 58 374 A a method for the production of formic acid from CO ₂ for the storage of energy using light is known.

A similar method using light to reduce CO ₂ dioxides is known from JP 05-311476 A.

From the EP 0 111 870 B1 For example, a method and apparatus for reducing, in particular, methanation of carbon dioxide, in which a light source is also used in the reduction process, is known.

Similar reduction methods using a light source are also known from US Pat. Nos. 4,609,451 and 4,523,981, which also indicate a hydrogen storage method. The reduced CO ₂ products are pressed by means of a pump in a storage device. Furthermore, from the US 4,240,882 a CO ₂ photoreduction method using light is known.

Also, to use the thermal energy by direct combustion of hydrogen solutions are known. For example, ^BMW® is experimenting with the ^{idea of} injecting hydrogen into an internal combustion engine instead of a fuel cell and favoring it for the future.

The diverse existing hydrogen technologies for energy and energy use show the need for a meaningful hydrogen transport and storage medium. Exemplary Fossil energy (here mainly benzene) is revealed the benefits of liquid Hydrocarbons in terms of handling and energy content.

in the Range of lower hydrocarbons, with the lowest possible carbon and as possible high hydrogen content, are primarily methanol and formic acid at. However, according to the current state of the art to their Production from hydrogen and carbon dioxide, or carbon monoxide at high pressures (> 50 bar) and high Temperatures (> 280 ° C) also high technical and energetic effort necessary only in the large industrial scale worthwhile can be. In DE-PS 28 51 225 a method by means of electro-chemical Production of formic acid proposed. However, this procedure does not offer any use for storing hydrogen present. Further, she uses as the gas to be introduced carbon dioxide. And for its production, compaction and handling additional Expenses must be operated and observed.

Of the Invention has for its object to provide a method with in a simple and energetically economical way hydrogen in higher density can be stored, and this can also be realized on a smaller scale should be. Furthermore, the handling of the liquid storage or Storage material and its starting materials are easy and environmentally friendly.

The Task solves the invention by the in the independent claims 1 and 2 specified methods for storing hydrogen.

advantageous Further developments of the method are in the dependent claims in Detail specified.

at The realization according to claim 1 can be of different types of catalysts of known type are used. It can be bulk catalysts or to be used as built-in block catalysts, in the reactor vessel are included. The reactor vessel can also be the reservoir be yourself. In the case of the method according to claim 2, the reactor vessel may also reservoir be. Is appropriate it, however, when spent potassium formate after recovery the stored hydrogen are returned to the circuit, that the solution from a storage container is removed and the reactor vessel is supplied to the desired Way by the method used to store hydrogen.

Surprisingly, it has been shown that 2 percent by weight of hydrogen can certainly be stored with the mentioned methods. Due to the high efficiency, the specified method can be used, in particular, to store hydrogen without a pressure vessel and to release it again in a recovery process. Also suitable is the direct use in egg a fuel cell. Furthermore, the extracted hydrogen can also be used for operating hydrogen-powered engines. Since the catalytic decomposition and cleavage of the potassium formate in the fuel cell or in a reactor in turn potassium bicarbonate or potassium carbonate is recovered as starting materials, a reuse in a cycle is possible. The starting materials are therefore continuously used for hydrogen storage. The advantages are obvious.

The Invention is described below with reference to the drawings Figures explained in addition.

In show the drawings:

1 a basic structure for implementing a method as indicated in claim 1,

2 a schematic representation of a non-stationary treatment according to the example 1 .

3 a reactor vessel operating according to the method of claim 2,

4 the construction of a container for storing hydrogen in conjunction with an electrode assembly for loading and unloading and

5 The container according to 4 in the unloading process.

The total inventive sequence is based on 1 explained below.

In a reaction vessel 1 K ₂ CO ₃ and / or preferably KHCO _{3 is} in aqueous solution 2 with H ₂ O together with a porous layered catalyst 3 ZnO or ZnO / TiO ₂ . With both catalysts 3 good results were achieved. The solution 2 and the catalyst 3 become from hydrogen 4 flows through in gas form, which consists of a nozzle or a diffuser 5 exit and in the solution 2 goes up. The gas 4 at the beginning of the reaction consists only of hydrogen 9 coming from the supply line 6 in the gas-mixing room 7 forms a small storage reservoir, and by slight pressure the solution 2 above the nozzle or diffuser 5 holds. When flowing through the hydrogen 9 through the solution 2 he meets the surface of the catalyst 3 which is able to summate the solution in the solution KHCO ₃ to KCOOH and H ₂ O with the hydrogen. After the reaction on the catalyst is now additionally potassium formate in the solution 2 That's the solution 2 ' becomes. This process can continue until everything is in solution 2 ' K ₂ CO ₃ and / or KHCO _{3 is converted} to KCOOH and H ₂ O.

In a further stage of the process can be formed with continuation of the process by further hydrogenating the formate formic acid HCOOH and methanol H ₃ COH. This must be the solution 2 ' CO _{2 are} supplied. This can be done by adding CO ₂ 10 z. B. via the supply line 8th in the mixing room 4 or via a nozzle or a diffuser 5 respectively. CO ₂ can also be taken directly from the ambient air 11 over the surface 12 the solution 2 ' be supplied. The latter always takes place to a limited extent due to the high affinity of KOH for CO ₂ with free contact with the ambient air.

After reaching the desired concentration of hydrocarbons in the solution 2 ' can the solution 2 ' via wire 28 in a storage container 13 be derived. Depending on the intended use for transport or further storage via the drain cock 14 filled into additional containers or, if necessary, for direct use over the line 15 the reaction vessel 16 be supplied. In the reaction vessel 16 becomes the solution 2 ' via a known catalyst 17 , eg Pd, to effect the dehydrogenation of potassium formate into hydrogen and KHCO ₃ and K ₂ CO _3, respectively. The hydrogen bubbles out of the solution and can at the outlet cock 18 be removed. The formation of K ₂ CO ₃ or KHCO ₃ depends on the respective greater proportion of KOH or CO ₂ or H ₂ CO ₃ in the solution. Both substances are present in the solution unless KOH or CO ₂ are saturated. The solution 2 ' is again in the composition of the solution after dehydrogenation of the hydrocarbon 2 and can about the process 19 in the reservoir 20 be directed.

In the case of the use of formic acid or methanol is formed in the reaction vessel 16 In addition to hydrogen also CO ₂ , therefore, the gas 4 ' not at the outlet tap 18 but must be through a KOH or K ₂ CO ₃ solution 21 in the container 29 be led, which removes the gas from the CO ₂ content, while K ₂ CO ₃ or KHCO ₃ forms. The remaining hydrogen 9 in this case is via the outlet tap 23 taken. With conversion of the KOH or K ₂ CO ₃ stock in the solution 21 the composition changes to that of solution 2 , Thus, the solution about the process 22 in the reservoir 20 be directed.

A return of the over the drain cock 14 removed and dehydrated solution can via a filler neck 24 in the reservoir 20 occur.

A return of the over drain cock 14 removed for storage and the non-spent solution can via a filler neck 25 in the reaction vessel 16 be entered.

For the re-storage of hydrogen 9 can the solution 2 from the reservoir 20 over the line 26 in the reaction vessel 1 be directed.

For cleaning or maintenance purposes, the solution 2 from the reaction vessel 1 and from the reservoir 20 over the drain cock 27 out of the device, and over the filler neck 24 be returned to the device.

The overall sequence according to the invention is not necessarily coupled to each other in a localized manner but can, as in FIG 2 shown as a schematic diagram, done completely decoupled. The transport route 31 between the two storage containers 13 and 33 as well as the transport route 32 between the two storage containers 34 and 20 are to be considered from the point of view of a change of location. The reservoir 33 and 34 are additionally required.

Another possible procedure for the range of the reaction vessel is described below with reference to 3 explains:
In a reaction vessel 51 K ₂ CO ₃ and / or preferably KHCO _{3 is} in aqueous solution 2 with H ₂ O. There are at least two electrodes in the container 53 and 54 used. Whereby electrode 53 the cathode (-) forms and electrode 54 the anode (+). The cathode 53 and the anode according to the invention consist of nickel (Ni) or an alloy of this metal. Experiments carried out and comparative investigations with Sn and Pb electrodes have shown that with Ni electrodes, based on the introduced power, an optimal solution conversion efficiency 2 to solution 2 ' which can be between 92% and 95%. The cathode 53 is formed with the largest possible, porous surface around the solution 2 To provide the largest possible contact surface and a gentle rinsing with solution 2 to allow. In the middle of the cathode 53 is located above the anode 54 a continuous "vent" that causes the beading at the anode 54 resulting gas allowed without hindrance, the solution 2 is easily circulated and mixed.

The implementation of solution 2 in solution 2 ' , which consists of KCOOH, or KCOOH in aqueous solution, is done by applying a voltage to the electrodes 53 and 54 , It is important to make sure that at the cathode 53 no formation of hydrogen gas takes place. This is given in the voltage range of about 1.6 V to 3 V, preferably 1.8 V to 2.2 V. At higher voltages, the evolution of hydrogen gas begins at the cathode, which is in direct competition with the formation of formate. A reaction of the solution 2 in solution 2 ' is characterized and easy to recognize that at the anode 54 Oxygen forms as a gas but bubbles at the cathode 53 no formation of hydrogen gas takes place.

With additional supply of CO ₂ via the supply line 55 and the diffuser 56 into the solution 2 or solution 2 ' In addition to the formation of KCOOH, the formation of HCOOH and in slight traces of higher hydrocarbons takes place. The ratios of the quantity can be influenced by temperature change, with the formation of HCOOH preferably taking place in regions around 0 ° C. and below.

In the 4 and 5 is another example of a reaction vessel 61 shown, in which three chambers are contained by membrane division of non-porous material. In the reaction vessel 61 there are two ion-conductive, closed, non-porous membranes (eg made of Celtec or Nafion) 62 and 63 , creating three chambers 64 . 65 and 66 given are. The membrane 63 is on both sides with a conductive silver coating 67 and 68 provided, which is applied for example by vapor deposition or sputtering. The silver coatings are each with contacts 69 and 70 Mistake. In the chambers 64 and 65 There are two electrodes 71 . 72 made of nickel, which for example directly on the membrane 62 as a coating (vapor-deposited or sputtered) can be applied. The chamber 64 is with aqueous KOH, KHCO ₃ or NaOH solution 73 filled. The chamber 65 whereas, with aqueous KHCO ₃ solution 74 filled. The chamber 66 is with air 75 or gaseous O ₂ or an oxygen donating (eg H ₂ O ₂ ) or filled with another oxidizing liquid.

In the following, the loading process (saving) will be based on the 4 and the discharge process (energy release) on the basis of 5 described.

loading procedure

By applying a voltage of approx. 1.6 V to 1.9 V to the Ni electrodes 71 and 72 where electrode 71 as + pole (anode) and electrode 72 when - pole (cathode) is used, forms at the electrode (anode) 71 gaseous, from the solution 73 bubbles bubbling O ₂ , with the reference numeral 76 is specified. Same time at the electrode (cathode) 72 KHCO ₃ reduced to KCOOH.

This process is not the electrolysis of water but the reduction of CO ₂ . Since these two processes in Konkur If there is a problem with each other, the voltage must be kept below the value at which the electrolysis of H ₂ O begins. The undesirable process of electrolysis can be recognized by the fact that gaseous H ₂ begins to form at the cathode, which then bubbles out.

The loading process can also take place without being in the chamber 66 oxygen 75 is gaseous or is present in an oxidizing liquid.

The chamber 66 but can also be used to absorb the oxygen released during loading and store it until unloading.

unloading

As long as in the liquid 74 in chamber 65 dissolved KCOOH and in chamber 66 oxygen 75 gaseous or present in an oxidizing liquid may be present at the contacts 69 (Anode) as -Pol and 70 (Cathode) as + pole, current are taken off. Here, the KCOOH in the liquid 74 in chamber 65 again oxidized to KHCO ₃ . The membrane 63 with your silver coating 67 and 68 forms a fuel cell in this process.

The unloading process can also take place without getting into chamber 64 liquid 73 located.

Claims (13)

A method of reversibly storing hydrogen using potassium carbonate (K ₂ CO ₃ ) and / or potassium bicarbonate (K ₂ HCO ₃ ), comprising the following steps: a) introducing potassium carbonate and / or potassium bicarbonate into a reactor vessel and adding water (H ₂ O b) catalytic treatment of potassium carbonate and / or potassium hydrogencarbonate in aqueous solution in the reactor vessel, using as the catalyst a ZnO or a ZnO / TiO ₂ catalyst, c) simultaneously hydrogenating the potassium carbonate and / or the potassium bicarbonate at the surface a catalyst in the reactor vessel by feeding hydrogen (H ₂ ) in gaseous form to potassium formate (KCOOH) in aqueous solution; d) storing the generated potassium formate in aqueous solution in the same reactor or in a reservoir. Process for the reversible storage of hydrogen using potassium carbonate (K ₂ CO ₃ ) and / or potassium hydrogen carbonate (K ₂ HCO ₃ ) with the following process steps: a) Potassium carbonate and / or potassium bicarbonate are present in an aqueous solution. b) Catalytic treatment of potassium carbonate and potassium bicarbonate in aqueous solution by means of catalytically activated nickel (Ni) electrodes or nickel contained in the reactor vessel, in which the aqueous solution is introduced. c) Cleavage of oxygen from the carbon dioxide by passing a current across the electrodes at a low voltage with simultaneous hydrogenation of the potassium carbonate and / or the potassium bicarbonate at the surface of the electrodes to potassium formate. d) storing the potassium formate produced in aqueous solution in the same reactor or in a reservoir. Method according to claim 2, characterized in that that the voltage of the applied direct current to a value between 1.2V and 3V, preferably limited to 2.5V. A method according to claim 1 or 2, characterized in that the potassium formate is converted by further hydrogenation in formic acid and methanol with addition of CO ₂ . Method according to claim 1 or 2, characterized that instead of potassium formate through the process another hydrocarbon on same way is generated. A method according to claim 1 or 2, characterized in that the escaping gas flows through a KOH or K ₂ CO ₃ solution into a container, wherein the gas from the CO ₂ content is withdrawn and K ₂ CO ₃ or K ₂ HCO ₃ forms and the remaining hydrogen is removed via an outlet tap. Method according to claim 1 or 2, characterized that the potassium formate in a container with at least one catalyst catalytically decomposed or split, thereby releasing the hydrogen becomes. Method according to claim 7, characterized in that that PT or PD catalysts are used for the dissociation, potassium formate or formic acid or mixtures thereof in aqueous solution becomes. Method according to claim 1 or 2, characterized that in the process hydrogen and potassium bicarbonate or Potassium carbonate are released and after release of the hydrogen carried out a renewed catalytic treatment and hydrogenation becomes. Method according to one of the preceding claims, characterized characterized in that the released hydrogen of a fuel cell and / or a hydrogen engine or other hydrogen energy releasing device is supplied. Method according to claim 1 or 2, characterized in that at least one further membrane of non-conductive, ionendurchlässigem Material provided with silver coatings applied on both sides is, from which layers over connected contacts during discharge or during oxidation tapped from potassium formate to potassium bicarbonate a voltage becomes. Method according to claim 11, characterized in that that the membrane is a non-porous membrane is and used as a wall element for chamber formation in the container is. Method according to claim 11 or 12, characterized that another non-porous Membrane used as a wall element for chamber formation in the container is and that in the first chamber, the anode of the Ni electrode assembly is used and in the second chamber, the corresponding cathode and which are a silver coating of the further membrane, wherein the associated terminal forms the negative pole and in the third chamber, the second layer of silver coating the membrane is the positive pole of the voltage source thus formed forms.