WO2012034549A2

WO2012034549A2 - Method for producing hydrogen and/or silane

Info

Publication number: WO2012034549A2
Application number: PCT/DE2011/001472
Authority: WO
Inventors: Norbert Rade; Ernst Oepen
Original assignee: Norbert Rade; Ernst Oepen
Priority date: 2010-07-16
Filing date: 2011-07-18
Publication date: 2012-03-22
Also published as: WO2012034549A3; DE112011104220A5

Abstract

In order to improve a method for producing hydrogen by electrolyzing an aqueous electrolyte and/or an electrolyte containing alcohols, an element of main group IV is fed to the electrolyte.

Description

Process for the production of hydrogen and / or silane

[01] The invention relates to a process for the production of hydrogen by electrolysis of an aqueous and / or an alcohol-containing electrolyte. Likewise, the invention relates to a process for the production of silane. [02] For example, it is known from DE 36 12 666 A1 to use nickel-containing anodes for the electrolysis of potassium hydroxide solutions. Also, many other electrolytic processes for producing hydrogen are known in the prior art.

On the other hand, the production of silane is known, for example, by decomposition of magnesium silicide under acidic conditions, by the method of Sundermeyer in a molten salt reaction medium of tetrachlorosilane with a hydrogen donor, and by a Muller-Rochow synthesis. Monosilane can also be prepared, for example, by passing hydrogen or chloromethylene through pure silicon powder. Higher-grade silanes can be prepared, for example, by pyrolysis by means of electrical discharge, as known, for example, from WO 2008/000241 A2 or from DE 694 07 839 T2, in which case even complex purification processes or distillations are necessary.

[04] According to the invention, a method for producing hydrogen by means of electrolysis of an aqueous electrolyte is proposed, which is characterized in that an element of IV. Main group is applied to the electrolyte. [05] Alternatively or cumulatively, a method for producing hydrogen by electrolysis of an electrolyte containing alcohols is proposed, which is also characterized in that the electrolyte is given an element of the fourth main group.

It has been found that the alcohols can of course also be present in diluted form and in particular methanol leads to excellent results. In addition to a high hydrogen yield, in particular the carbons with the Element of the fourth main group react and excreted, so that the surface cycle of carbon, which ultimately includes the climate-damaging carbon dioxide, carbon can be withdrawn, since the excreted substances can be readily disposed of. [07] In this case, for example, silicon in crystalline form, preferably reasonably finely ground silicon, can be introduced into the electrolyte. On the other hand, it is also conceivable that germanium or tin or carbon or lead are similarly advantageous.

[08] In an alternative embodiment, but also in addition thereto, the element of the IV. Main group can also be given in the form of compounds, for example in crystalline form, as an oxide or as part of a molecular chain to the electrolyte. For example, silicon can be applied as silicon oxide or in the form of silanes to the electrolyte.

[09] It has been found that the presence of silicon leads to completely unexpected reactions. Initial analyzes show the production of silanes, whereby the current intensity or the electrical voltage can therefore - as the assumption is - even easily represent higher-order silanes. Possibly. For example, by the presence of other atoms or molecules, the silanes can be modified as desired. With suitable process control, the silanes can be removed, for example by additional temperature control. [10] If the silanes are not removed, they oxidize with the available oxygen to silica. It has not yet been conclusively clarified whether it is possible to split the silica again and thus to use the silicon as a catalyst for hydrogen production. Again, it may be possible to use the electrochemical conditions of the present method for this purpose. Accordingly, a method for producing silane is proposed, which is characterized in that an electrolyte containing silicon or a silicon compound is subjected to electrolysis. It should be emphasized that in the present context, the term "silane" is to be understood in its broadest sense and in particular also includes the derivatives of silanes, such as chlorosilanes, tetramethylsilane, dichloromethylsilanes and all other corresponding compounds. [13] It has proven particularly advantageous to use an alkali or alkaline-earth solution in the form of an electrolyte. In particular, corresponding hydroxides are advantageous.

[14] In particular, the monovalent hydroxides may comprise potassium hydroxide, which, according to experiments by the inventors, leads to a high yield with good controllability of the process. On the other hand, in particular sodium hydroxide, under certain circumstances also in admixture with potassium hydroxide, applicable. Likewise, however, other monovalent hydroxides, such as lithium, rubidium, cesium, and fruium hydroxide, appear to be suitably applicable. Particularly preferably, the use of only potassium hydroxide as the electrolyte, although traces of other electrolytes may be present, so that even the use of 90% potassium hydroxide as the electrolyte brings corresponding advantages.

[15] Cumulative zw. Alternatively, salts can be given to the electrolyte. Saline (sodium chloride) or potassium chloride is particularly suitable for this purpose. By the suitable salts, in particular the temperature coefficient in the electrolysis can be controlled, in which regard, in particular, cooking salt has proved to be an excellently suitable additive.

[16] As an electrode, an electrode containing metals of VI. or VII. Subgroup, be provided.

[17] Preferably, the electrodes consist essentially of nickel, in particular with a purity of more than 95% or more than 99%, so that any other constituents, in particular also other metals, can only be regarded as impurities. Other metals of the platinum and nickel triad of VIII. Subgroup can be used appropriately advantageous, but are generally much more expensive. Likewise, metals of the iron group as well as the light and heavy platinum group can be used. Also, it has been found that chromium and the other metal of the VI. Subgroup can be used as appropriate electrodes. Also in the case of the abovementioned metals, preferably relatively pure metallic structures, if appropriate as joined together, for example sintered single crystals, are used, whereby purities of more than 95% or 99% are also advantageous here. [18] It is understood that essentially the electrode surfaces are important for the electrolysis. In this respect, the electrodes can be constructed relatively complex and, for example, have a correspondingly coated carrier material. Structurally particularly simple, however, is the use of corresponding plates, it has surprisingly been found that even by planar metallic surfaces, in particular with the features described above in terms of purity and resistivity, a sufficient efficiency can be realized. On the other hand, the electrodes can also be made more complex and comprise, for example, a porous material. Likewise, the electrodes may have further catalytically active layers, such as a suitable porous surface coating or the like. Also, the electrode surfaces may include metal alloys or sintered surfaces of a plurality of different of the aforementioned metals.

[19] In the present context, the term "electrolyte" refers to any medium from which hydrogen or silane can be supplied by means of electricity, but in particular an electrolyte according to the invention may be in liquid form and is preferably water in which ions, for example potassium ions and OH groups, are enriched to close the circuit.

Preferably, a housing made of irreversibly crosslinked plastic, preferably made of synthetic resin or polypropylene (PP), is used as the electrolysis tank, so that a sufficient fatigue strength and in particular also tightness can be ensured in relation to the electrolytes used. Such a housing proves to be reliable long-term stability especially with potassium hydroxide or under the selected operating conditions.

[21] The electrolyte and / or the electrodes can be tempered. Depending on the specific requirements, a cooling or heating may be useful, this possibly also can be provided by the chemical or electrochemical processes, In particular, by the appropriate choice of the abandoned ion, for example in the form of the abovementioned hydroxides or salts, in particular by the use of potassium hydroxide and / or common salt, the temperature of the reactions to the existing requirements be adjusted. In particular, the ions can be used in mixtures, for example in the form of both potassium hydroxide and common salt.

[22] Further advantages, objects and characteristics of the present invention will be explained with reference to the following description of the appended drawings. In the drawing show:

Figure 1 is a schematic representation of an electrolysis tank;

Figure 2 is a schematic detail of the electrolysis tank of Figure 1;

Figure 3 is a schematic detail of another electrolysis tank in

Section along the line III-III in Figure 4;

Figure 4 is a section through the electrolysis tank of Figure 3 taken along the line IV-IV in Figure 3;

Figure 5 is a section through the electrolysis tank of Figures 3 and 4 along the

Line V-V in Figure 4; and

FIG. 6 shows a section through the electrolysis container according to FIGS. 3 to 5 along the line

VI-VI in FIG. 5.

The electrolysis tank 10 shown schematically in FIG. 1 (see in particular FIG. 2) is connected to a water reservoir 1 1 via a supply line 12 and is connected to a power source 15 via connection lines 13, 14.

The electrolysis tank 10 is filled with a 5% potassium hydroxide solution 16, provided by the electrolysis and the intake manifold 7 supplied hydrogen and oxygen lead to a corresponding reduction of water in the electrolysis tank 10, which via the supply line 12 from the water reservoir 1 1 is replaced.

Within the electrolysis tank 10 are seven electrodes 17, which are formed as plates and are arranged parallel to each other. One of the two outer plates 17 is connected to the positive pole 18 of the battery 15, which in this embodiment, a voltage of about 12 V connected, while the other of the two outer plates 17 is connected to the negative terminal 19.

The remaining plates 17 are arranged substantially equidistantly between the two outer plates 17. [27] In this way, a voltage gradient of each forms between the plates 17, so that in each case approximately 2 V voltage applied between the respective opposite electrode surfaces,

[28] It is also possible to arrange only correspondingly 6 electrodes without significant impairment. At higher output voltages, for example at about 24 V, on the other hand, much more electrodes are recommended, in which case the area of the electrodes can be reduced if necessary. On the other hand, lower output voltages, for example in the region around 6 V, in which a smaller number of electrodes may be useful. It is understood in the present context that the voltages do not necessarily have to reach exactly these values, [29] In this embodiment, the electrodes are made of nickel with the DIN designation LC-Ni99 (Ni 201).

[30] At a sufficient distance above the liquid level 20, a first filter stage 21 is provided, so that forms a free space below the filter stage 21, which can be used as a foam space 22. In a second filter stage 23, any electrolyte residues, in particular potassium hydroxide components, which are possibly entrained by the electrolytically generated hydrogen or oxygen, can be trapped. In a moisture absorber 24 finest water droplets can be intercepted, so that only gases get into the engine 1. In this way, moreover, losses of electrolyte are largely avoided, with any potassium hydroxide components can be rinsed back through the water when it is replaced via the supply line 12. This way, losses of electrolytes can be minimized

[31] The electrolysis tank 50 shown in Figures 3 to 6 can be used instead of the electrolysis tank 10 of Figures 1 and 2, by the outer Electrodes 52 and 54 of a further three electrodes 56 comprehensive electrode package of parallel nickel plates made of nickel with the DIN designation LC-Ni99 (Ni 201) via terminals 58 to the power source 15 (Figure 1) and gas outlets 60 to the intake manifold 7 (FIG 1) are connected. [32] The electrolysis tank 50 is double-walled, wherein the inner wall 62 encloses an electrolysis space in which the electrodes 52, 54, 56 are arranged. The outer wall 64 encloses on the one hand a water supply 66 and on the other hand a moisture separation chamber 68. Water supply 66 and moisture separation chamber 68 are separated from each other by a wall 70 which has two passages 72 through which water and electrolyte can be transferred from the moisture separation chamber 68 into the water reservoir 66 , In this case, water can be refilled via a refill opening 74, which is closed with a closure 76. Any electrolyte deposited in the moisture separation space 68 is backwashed by replenishment into the water reservoir 66. Potassium hydroxide can be topped up via separate refill openings 78 (merely exemplified), which are each likewise closed by closures 80 (merely numbered as an example).

In addition, water can flow from the water reservoir 66 to the electrodes 52, 54, 56 via equalization openings 82. The flow direction minimizes the loss of electrolyte. For this reason, the compensation openings 82 are also formed relatively small. Alternatively or additionally, refluxes to electrolytes can be minimized by membranes or similar measures. Likewise, each gap between the electrodes 52, 54 56 only a compensation opening 82 is provided, which are also mutually arranged so that short circuits can be avoided as possible. [34] Above the electrolyte, a foam space 84 is also formed in this exemplary embodiment, in which, in particular, oxygen and hydrogen can be temporarily stored and, if appropriate, also mixed with oxyhydrogen gas. In the inner wall gas outlet openings 86 are arranged (numbered example), which extend into the foam space 84, wherein the constriction caused thereby serves as a retaining means for the foam - and in particular for the electrolyte which forms the foam. The gas outlet openings 86 open into the Moisture deposition space 68, in which residual electrolyte can be deposited. Likewise, moisture can separate there and the lane, hydrogen, oxygen and possibly also water molecules mix intimately before they leave the electrolysis tank 50 via the gas outlets 60. [35] In order to implement the invention, in this embodiment, an aqueous slurry of silicon powder is also added to the electrolyte. In a concrete reaction, this may be 200 ml of such a slurry at 300 ml of electrolyte, with approximately 200 g of Si introduced into this slurry. Likewise, cooking salt is also abandoned, and if necessary, the potassium hydroxide can optionally be dispensed with in an alternative reaction.

[36] First, a normal electrolytic reaction takes place with the production of gaseous hydrogen and oxygen. After about 30 minutes suddenly, after a current 3A has flowed at 12 V, a very violent reaction sets in and a great deal of hydrogen is produced. Following this, the reaction ebbs a little and can be maintained for hours without applying a voltage only when water is replenished.

[37] In concrete experiments, the reaction was terminated by short-circuiting the electrodes.

[38] In this case, it is assumed that silanes, in particular also higher-value silanes, are produced in the electrolyte and, after a certain period of time, the electrical energy is used essentially catalytically essentially or in high proportions. Silanes are relatively unstable, unlike alkanes. The low silanes, especially with one to four silicon atoms, are very volatile and can self-ignite in the air, explode and spontaneously burn to silica and water.

[39] The reactivity decreases with increasing chain length. In water, silanes usually decompose to silicic acids and hydrogen at a pH above 7.

[40] Derivatives of silanes are formed by the replacement of hydrogen atoms by oxygen.

[41] By oxidation under the action of oxygen, for example from water, follows:

[42] In order to avoid the constant need for new silicon, it seems advantageous to separate silicon and oxygen, so that the silicon acts as a catalyst. The silicon first absorbs the water, it produces silane, which oxidizes with oxygen and releases hydrogen again. The separation of oxygen and silicon may release energy, which in turn catalytically maintains the processes described above.

[43] Insofar it is understood that - according to the law of mass action - that silicon atomic or in metallic form, can be provided as silicon oxide, silane or otherwise. It is also possible, for example, to withdraw or otherwise use silanes, if hydrogen and silicon are then added to the process accordingly.

Claims

claims:

1 . Process for the production of hydrogen by electrolysis of an aqueous electrolyte and / or an electrolyte containing alcohols, characterized in that the electrolyte is an element of IV. Main group is abandoned.

2. hydrogen production method according to claim 1, characterized in that the electrolyte Si (silicon) is abandoned.

3. hydrogen production process according to any one of the preceding claims, characterized in that the element of the IV. Main group is the electrolyte in chemically pure form, preferably with a degree of purity above 90%, abandoned.

4. A process for the production of silane, in particular with the aid of one of the hydrogen generating method according to any one of the preceding claims, characterized in that a silicon or silicon compound containing electrolyte is subjected to an electrolysis.

5. Hydrogen and / or silane production process according to one of the preceding claims, characterized by monovalent hydroxides as electrolyte for the electrolysis.

6. Hydrogen and / or silane production process according to claim 5, characterized in that the monovalent hydroxides comprise potassium hydroxide.

7. hydrogen and / or silane production method according to claim 5 or 6, characterized in that as monovalent hydroxide to more than 90% potassium hydroxide is used.

8. hydrogen and / or silane production method according to any one of the preceding claims, characterized by at least one electrode, the metals of VI. or VII. subgroup contains.

9. Hydrogen and / or silane production method according to claim 8, characterized in that the one electrode has at least one active surface with a carbon content below 0.15%.

10. Hydrogen and / or silane production process according to claim 9, characterized in that the carbon content is less than 0.025%.

The hydrogen and / or silane production method according to any one of claims 8 to 10, characterized in that said one electrode has a resistivity below 0.090 Wmm ² m ^-1 , preferably below 0.086 Wmm ² m ^-1 .

12. hydrogen and / or silane production method according to any one of claims 8 to 1 1, characterized in that both as an anode and as a cathode electrodes with metals of VI. or VII. subgroup.

13. hydrogen and / or silane production method according to claim 12, characterized in that an electrode is used both as an anode and as a cathode.

14. Hydrogen and / or silane production process according to one of claims 8 to 13, characterized in that the one electrode consists essentially of nickel, preferably with a purity of more than 95%.

15. Hydrogen and / or silane production method according to one of the preceding claims, characterized in that the electrolysis container comprises a housing made of irreversibly crosslinked plastic, preferably made of synthetic resin or polypropylene (PP).

16. Hydrogen and / or silane production method according to one of the preceding claims, characterized by a temperature control of the electrolyte and / or the electrodes.