Patent Application
20190291059
Not applicable.
Not applicable
The invention relates to a method for the manufacture of a hydrogen permeable membrane in accordance with the pre-characterising part of the independent method claim and to a starting material for this method and further to a hydrogen permeable membrane.
Hydrogen permeable membranes are layers which have a high selective permeability for hydrogen and are substantially impermeable for other gases. Accordingly such membranes are used to extract hydrogen from gas or fluid mixtures.
Global environmental demands and the short supply of oil reserves have led to huge efforts being made to develop other methods of the production of electrical energy, and also to develop viable alternatives with respect to ecological and economic aspects in the transport field to classic combustion engines which work with petroleum based fuels. Important issues here are the reduction of the emission of environmentally harmful materials such as carbon dioxide for example and energy generation from re-generative sources.
Hydrogen is attributed with a large significance in these developments not only with regard to the production of electrical energy but also in the field of transport. However hydrogen is also needed in many other chemical processes, for example in the manufacture of liquid hydrocarbons using to the Fischer-Tropsch method, in the direct liquefaction of coal or in the oil refinery.
On the other hand there are many processes in which hydrogen occurs, for example in the combustion of oil or gas based materials and in steam reforming or catalytic reforming. However, in this connection the hydrogen occurs together with other gases or combustion gases, for example in combination with carbon dioxide and must therefore be first extracted from the gas mixture first in order that it can be used.
In this connection membranes are known among other things, which are selectively permeable for hydrogen. On the one hand there are metallic membranes which have a high selective permeability for hydrogen. On the other hand ceramic membranes are known, which comprise oxides of the perovskite type, for example BACe1-xMxO3, wherein M designates a doped metal such as Y. These ceramic membranes are ionic conductors and have a high proton conductivity for example. However their electron conductivity is generally not adequate to achieve sufficiently large hydrogen flow rates for industrial applications.
Therefore composite membranes have been proposed which contain not only a proton conducting ceramic component but also a good electron conducting metallic component. Membranes of this kind are also termed Cermet membranes (CERamic METal). Such two-phase hydrogen permeable membranes are described for example in U.S. Pat. No. 6,235,417 or in U.S. Pat. No. 6,235,417. For the manufacture of the membranes U.S. Pat. No. 6,235,417 for example discloses the coating of a suitable ceramic powder with palladium by means of chemical deposition from the vapour phase (CVD chemical vapour deposition) or the wet impregnation of the ceramic powder with a palladium chloride solution and subsequent drying, calcining, pressing and sintering.
Starting from the prior art, it is an object of the invention to propose another method for the manufacture of a hydrogen permeable membrane which includes a proton conducting ceramic material and an electron conducting metallic component. The membrane should possess a high proton and electron conductivity, so that suffident hydrogen flow rates can be achieved. Further, by means of the invention a starting material should be proposed for this method and a corresponding hydrogen permeable membrane.
The subjects of the invention satisfying this object are characterised by the independent claims in the respective category.
In accordance with the invention a method is thus proposed for the manufacture of a hydrogen permeable membrane which includes a proton conducting ceramic material and an electron conducting metallic component. The membrane is deposited on a substrate by means of plasma spraying, wherein a starting material is sprayed onto a surface of the substrate in the form of a process beam, with the starting material being injected into a plasma at a low process pressure, which is 10 000 Pa at the most, said plasma defocussing the process beam and said starting material being melted partly or completely there.
Surprisingly it has been shown that by means of such a plasma spraying method, with which very dense and thin layers can be produced on the substrate, a hydrogen permeable membrane can be produced the proton conductivity and electron conductivity of which is so great that with them considerable flow rates for hydrogen of, for example, more than 10 millilitre per minute and square centimetre can be achieved.
A plasma spraying method is preferably used in which in comparison with conventional plasma spraying methods a very long plasma flame is generated. The spraying distance between an outlet nozzle for the process beam and the substrate then amounts to at least 200 mm and preferably to at least 400 mm. As a result the dwell time of the material in the plasma flame is increased considerably, resulting in a higher energy transfer of plasma to the material, which has a very favourable effect on the formation of a thin and dense layer on the substrate.
The ceramic material is preferably an oxide of the perovskite type because these have proved to be very good proton conductors in practice.
It is particularly preferable when the ceramic material of the perovskite type has the form ABO3, wherein A is selected from the group which consists of barium (Ba), calcium (Ca), magnesium (Mg) and strontium (Sr) and B has the form CexZryM1-x-y whereby x and y are respectively smaller than or equal to 1 and larger than or equal to zero and M is selected from the group which consists of yttrium (Y), ytterbium (Yb), europium (Eu), gadolinium (Gd), indium (In), neodymium (Nd), thulium (Tm), holmium (Ho), rhodium (Rh), samarium (Sm), titanium (Ti) and scandium (Sc). This means the component B of the perovskite like ceramic is preferably either only cerium or only zirconium or a mixture of zirconium and cerium. The latter can be realised for example by a solid solution of BaZrO3 and BaCeO3.
The metallic component is preferably one of the metals: palladium (Pd), vanadium (V), niobium (Nb), tantalum Ta) or zirconium (Zr) or an alloy of at least one of these metals. Tantalum has proved to be of particular value. The electron conductivity of the membrane can be considerably improved by this metallic component. Palladium alloys, especially with gold (Au), copper (Cu) or silver (Ag) or also tantalum alloys have proved to be of particular value.
In order to realise particularly dense layers it has proved advantageous when the process pressure in the plasma spraying method amounts to at least 10 Pa and preferably 50 Pa to 1000 Pa.
The total flow rate of the process gas in plasma spraying is preferably less than 200 SLPM (standard litre per minute) and particularly preferably amounts to 60 to 80 SLPM.
As regards the supply rates of the powdered starting material it has proved favourable in practice when a supply rate is selected of from 10 to 200 g/min, preferably of 40-120 g/min.
The starting material in accordance with the invention for the manufacture of a hydrogen permeable membrane in accordance with the method of the invention contains a proton conducting material and an electron conducting metallic component. This starting material is a powder or a powder mixture, either of which can be deposited on a substrate by means of plasma spraying.
In the same way as has been explained for the method in accordance with the invention the ceramic material of the starting material is an oxide of the perovskite type.
In the starting material, the ceramic material of the perovskite type preferably has the form ABO3, wherein A is selected from the group which consists of barium (Ba), Calcium (Ca), magnesium (Mg) and strontium (Sr) and B has the form CexZryM1-x-y whereby x and y are respectively smaller than or equal to 1 and larger than or equal to zero and M is selected from the group which consists of yttrium (Y), ytterbium (Yb), europium (Eu), gadolinium (Gd), indium (In), neodymium (Nd), thulium (Tm), holmium (Ho), rhodium (Rh), samarium (Sm), titanium (Ti) and scandium (Sc).
In the case of the starting material the metallic component of one of the metals is preferably palladium (Pd), vanadium (V), niobium (Nb), tantalum Ta) or zirconium (Zr) or an alloy of at least one of these metals. This is particularly preferably a palladium alloy, tantalum or a tantalum alloy.
A hydrogen permeable membrane is further proposed by the invention which is manufactured in accordance with a method of the invention or from a starting material in accordance with the invention.
A substrate with a hydrogen permeable membrane in accordance with the invention is further proposed wherein the substrate is in particular plate-like or tubular. The planar plate-like shape of the substrate is characterised in particular by the simple manufacture, whereas the tubular design has the advantage of a particularly large membrane surface relative to the volume enclosed.
Further advantageous measures and preferred designs of the invention result from the dependent claims.
The invention will be explained more closely in the following with the help of the embodiments and with the help of the drawings. In the schematic drawings there is shown, partly in section:
The method in accordance with the invention for the manufacture of a membrane selectively permeable for hydrogen, which includes two phases, namely a proton conducting ceramic material and an electron conducting metallic component, is in particular characterised in that the membrane is generated by means of a plasma spraying process with which a dense microstructure can be produced.
The method in accordance with the invention preferably includes a plasma spraying process of the kind described in WO-A-03/087422 or also in U.S. Pat. No. 5,853,815. This plasma spraying process is a thermal spraying process for the manufacture of a so-called LPPS thin film (LPPS=low pressure plasma spraying).
An LPPS thin film process (LPPS-TF=LPPS thin film) is specially carried out with the plasma spraying apparatus 1 shown in
The plasma spraying apparatus 1 illustrated in
In the case of the LPPS-TF process described here the starting material P is injected into a plasma defocusing the material beam at a low process pressure which is 10 000 Pa at the most and preferably 1000 Pa at the most and is partly or completely melted therein or at least made plastic. For this purpose a plasma is produced with sufficiently high specific enthalpy, so that a very dense and thin layer 11 arises on the substrate. The variations of the structure are substantially influenced and controllable by the coating conditions, in particular by process enthalpy, working pressure in the coating chamber and also the process beam. Thus the process beam 2 has characteristics which are determined by controllable process parameters.
For the manufacture of the hydrogen permeable membrane the layer 11 is produced in such a way that it has a very dense microstructure which will be explained further on.
First of all the method step of the production of the layer 11 by means of LPPS-TF will now be explained more closely.
A powder of suitable composition is selected as starting material P, such as will be described further on. In this connection it is a possibility that the starting material P is present in the form of a single powder, which contains not only the ceramic material but also the metallic component. Another possibility is that of using two different materials in powder form as the starting material, of which one contains the ceramic material and the other contains the metallic component. These two materials can either be injected into the plasma flame simultaneously via two different powder inlets or also one after the other with regards to time.
As has already been mentioned, in the LPPS-TF method the plasma flame is very long due to the adjusted process parameters in comparison with conventional plasma spraying processes. Moreover, the plasma flame is considerably widened. A plasma with a high specific enthalpy is produced, through which a high plasma temperature results. Due to the high enthalpy and the length and/or the size of the plasma flame, a very high energy input into the material particles 21, 21 arises which are thereby, on the one hand, strongly accelerated and, on the other hand, brought to a high temperature, so that they are readily melted and are also still very hot after their deposition on the substrate 10. Since, on the other hand, the plasma flame and thus the process beam 2 is very greatly broadened, the local heat flow into the substrate 10 is slight, so that a thermal damaging of the material is avoided. The broadened plasma flame has the further consequence that usually, with a single sweep of the process beam 2 over the substrate 10, the material particles 21, 22 are deposited in the form of individual splashes (splats), which do not produced any continuous i.e. cohesive layer. By this means very thin layers 11 can be generated. The high kinetic and thermal energy which the material particles receive in their long residence in the plasma flame in comparison to conventional plasma methods, favours the formation of a very dense layer 11, which in particular has few boundary surface cavities between splats lying one on top of the other.
The plasma is produced for example in a plasma torch known per se in the plasma generator 3 with an electrical direct current and by means of a pin cathode and a ring-shaped anode. The energy supplied to the plasma, the effective energy can be determined empirically with relation to the resulting layer structure. The effective energy which is given by the difference between the electrical energy and the heat given off by the cooling, lies, as experience has shown, in the range of 40 to 80 kW for example. In this connection it has proved valuable when the electrical current for the plasma production lies between 1000 and 3000 A, in particular between 1500 and 2600 A.
A value between 10 and 10000 Pa, preferably between 100 and 1000 Pa is selected in the process chamber for the process pressure of the LPPS-TF plasma spraying for the production of the hydrogen-permeable membrane.
The starting material P is injected into the plasma as a powder beam with a feed gas, preferably argon or a helium argon mixture. The flow rate of the feed gas preferably amounts to 5 to 40 SLPM (standard litres per minute), in particular to 10 to 25 SLPM.
The process gas for the production of the plasma is preferably a mixture of inert gases, in particular a mixture of argon Ar, hydrogen H and helium He. In practice the following gas flow rates for the process gas have proved particularly valuable:
Ar flow rate: 30 to 150 SLPM, in particular 50 to 100 SLPM
H2 flow rate: zero to 20 SLPM, in particular 2 to 10 SLPM
He flow rate: zero to 150 SLPM, in particilar 20 to 100 SLPM,
wherein the total flow rate of the process gas is preferably smaller than 200 SLPM and in particular amounts to 60 to 180 SLPM.
The powder supply rate with which the starting material P is supplied, lies between 10 and 200 g/min in particular, preferably between 40 and 120 g/min.
It can be advantageous when the substrate is moved with rotating or swinging movements relative to this cloud during the material application. It is naturally also possible to move the plasma generator 3 relative to the substrate 10.
The spraying distance, i.e. the distance D between the outlet nozzle 7 and the substrate 10 preferably amounts to 200 to 2000 mm and in particular to 400 to 1000 mm.
The hydrogen permeable membrane is built up by means of this plasma spraying—typically by the deposition of a plurality of layers. By this means the densest possible structure and a thin layer is produced.
The total layer thickness of the membrane typically amounts to 30 μm at the most. Values of the layer thickness of 5 μm to 10 μm are preferred.
So that the material particles 21, 22 readily melt in the process beam 2 and receive a high thermal and kinetic energy, in order to produce the layer 11 with the dense structure, the starting material in powder form P is advantageously very fine grained. The size distribution of the powder particles in the starting material P is determined by means of a laser scattering method. It is advantageously the case for this size distribution that a substantial part of it lies substantially in the range between 1 and 80, preferably between 5 μm and 45 μm.
Various methods can be used for the manufacture of the powder particles: for example spray drying or a combination of melting and subsequent crushing and/or grinding of the solidified melt.
The starting material P is preferably present in the form of a mixture (blend). This powder mixture contains a proton-conducting ceramic material and the metallic component. The ceramic material is preferably an oxide of the perovskite type and has the form ABO3. In this connection A designates an element which is selected from the group which consists of barium (Ba), calcium (Ca), magnesium (Mg) and strontium (Sr). B has the form CexZryM1-x-y whereby x and y are respectively smaller than or equal to 1 and larger than or equal to zero and M is selected from the group which includes yttrium (Y), ytterbium (Yb), europium (Eu), gadolinium (Gd), indium (In), neodymium (Nd), thulium (Tm), holmium (Ho), rhodium (Rh), samarium (Sm), titanium (Ti) and scandium (Sc). In this connection x and y can also take on the value zero, wherein however x and y do not both have the value zero at the same time. I.e. the element B can either contain both of the elements Ce and Zr or only one of the two elements Ce and Zr. The added element M is preferably contained in B in a proportion of 0.4 at most, i.e. 1−x−y is smaller or equal to 0.4.
A crucial aspect under which the specific composition of the ceramic components is selected is a very good, or very high proton conductivity. The ceramic components can, for example have the following compositions:
In addition to the ion conductivity, especially the proton conductivity, the ceramic components should also exhibit mechanical strength or stability, in order to then serve as a framework in particular which supports the membrane and prevents a creeping of the material.
The electron conducting metallic component is a preferred embodiment of a palladium (Pd) alloy and especially a palladium-gold alloy, a palladium-copper alloy or a palladium-silver alloy. Pd alloys have a good selective permeability for hydrogen in atomic form and, moreover, have a very good electronic conductivity. Further preferred materials for the metallic components are vanadium (V), niobium (Nb), tantalum (Ta), zirconium (Zr) or an alloy which contains at least one of these metals. Tantalum or a tantalum alloy are further particularly preferred as a metallic component.
In addition to the electron conductivity, the object of the metallic components is further to give the membrane ductility and a good permeability for atomic or ionic hydrogen.
The choice of suitable partners for the ceramic material on the one hand and the metallic components on the other hand, takes place having regard to the thermal characteristics of the two partners. Since hydrogen permeable membranes are often used at operating temperatures of 650° C. to 900° C., the thermal characteristics should suit each other in such a way that a reciprocal disintegration does not result, for example through extremely differing thermal expansions.
The hydrogen permeable membrane should further also be chemically stable in the long term, especially in reducing environments, for example in environments which contain CO2, H2O, CO or sulphur—to name only a few examples.
Depending on the application case a further aspect in the selection of suitable ceramic and metallic components is that the membranes also have to be chemically stable in cyclically changing, reducing and oxidising atmospheres.
It will be understood that a plurality of different ceramic materials and/or a plurality of different electron conducting metallic components can also be used for the manufacture of the hydrogen permeable membrane.
The proton conducting ceramic material and the electron conducting metallic components are used as a starting material P for the plasma spraying. A possibility exists in making available the ceramic material and the metallic components in the form of a powder mixture (blend), which can be processed in the plasma spraying process. As already mentioned, in this connection the size distribution of the particles in the powder for the LPPS-TF process should be such that a large part of it lies substantially in the range between 1 μm and 80 μm. Methods known per se, such as spray drying for example, are suitable for the manufacture of the starting material in powder form.
If, as a ceramic component, one is selected in which both cerium and also zirconium are contained in the component B of the compound ABO3, then this ceramic component can be manufactured by a solid solution of BaZrO3 and BaCeO3, which is then further doped with one of the elements M.
For the manufacture of a starting material P, which contains both the ceramic component and also the metallic component, it is also possible to coat the ceramic material in powder form with the metallic component (cladding), so that the individual ceramic particles or agglomerates thereof are wholly or partially provided with a metallic layer.
It is naturally also possible to introduce the ceramic material and the metallic components into the LPPS-TF process separately from one another and/or one after the other.
As schematically indicated in
As already mentioned, very dense layers can be produced using the method in accordance with the invention.
In order to increase the proportion of the contact surface even more it can be advantageous to sinter the layer 11 or the membrane after its manufacture, advantageously at 800° C. to 1200° C. In this way a subsequent compaction and elimination of faults can be achieved.
The substrate 10 (see-
In the operating state the gas mixture (arrow GF in
The high selective permeability for hydrogen is due to the high proton conductivity of the ceramic material and to the hydrogen diffusion, which is made possible by the metallic component. At a layer thickness S of 5 μm to 20 μm for example, through flow rates for the hydrogen of at least 10 millilitres per minute and square centimetre can be achieved using the hydrogen permeable membrane in accordance with the invention.
In comparison with one phase structures, which only comprise a proton conducting oxide of perovskite type, the proton conductivity of the two-phase structure is considerably higher, which results from the electronic conductivity of the metallic phase.
An embodiment of a hydrogen permeable membrane in accordance with the invention is shown in
It is, for example, also possible to arrange a plurality of such tubular substrates 10, which are each provided with a hydrogen permeable membrane, in a process chamber, which are then filled with the gas mixture GF and put under pressure. The extracted hydrogen can then be led away through the inside of the tubular substrate.
It is further possible to intentionally modify the surface of the layer 11 in a manner known per se, in order to achieve a catalytic action.
In the manufacture of the layer 11 by means of a LPPS-TF method, the specific enthalpy of the plasma is adjusted in dependence on the process pressure.
In a first example the process pressure amounts to 1.5 mbar (150 Pa), an argon/helium mixture is used as plasma gas. The current for the production of the plasma amounts to 1900-2600 A. The gas flow takes place in the ultrasonic range at a speed of 2800-3300 m/s (Mach number 1.5-3). The plasma temperature amounts to 8 000 K to 10 000 K. The specific enthalpy is measured on the axis of the plasma flame at a distance of 400 mm to 1000 mm from the outlet nozzle 7 of the plasma spraying apparatus 1. This corresponds to a typical spraying distance, in which the substrate 10 to be sprayed is located. The specific enthalpy of the plasma amounts to 10 000 to 15 000 kJ/kg. The local heat flow is comparatively slight at 4 MW/m2. The plasma characteristics on the axis are essentially constant in the range of 300 to 1000 mm distance from the outlet nozzle 7.
In a second example the process pressure amounts to 100 mbar (10 000 Pa), an argon/helium mixture is used as a plasma gas. The current for the production of the plasma amounts to 1500-2600 A. The gas flow is largely below the speed of sound at a speed of 200-800 m/s (Mach number 0.4-0.8). The plasma temperature amounts to 2 000 K to 4000 K. The specific enthalpy is measured on the axis of the plasma flame at a distance of 300 mm to 400 mm from the outlet nozzle 7 of the plasma spraying apparatus 1. This corresponds to a typical spraying distance, in which the substrate 10 to be sprayed is located. The specific enthalpy of the plasma amounts to 3 000 to 4 000 kJ/kg. The local heat flow is still slight at 5-16 MW/m2. The plasma characteristics along the axis are not constant: they fall from a maximum to a minimum between 300 mm and 400 mm.
In a third example the process pressure amounts to 1.5 mbar (150 Pa), an argon/hydrogen mixture is used as a plasma gas. The current for the production of the plasma amounts to 1500 A. The gas flow is located in the supersonic range at a speed of 3000 m/s (Mach number 2 to 3). The plasma temperature amounts to 8000 K. The specific enthalpy is measured on the axis of the plasma flame at a distance of 300 mm to 1000 mm from the outlet nozzle 7 of the plasma apparatus 1. This corresponds to a typical spraying distance in which the substrate to be coated 10 is located. The specific enthalpy of the plasma amounts to 15 000 kJ/kg. The local heat flow is comparatively slight at 5 MW/m2. The plasma characteristics in the range of 300 mm to 1000 mm distance from the outlet nozzle 7 are essentially constant.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07114428.1 | Aug 2007 | EP | regional |
The instant application is a continuation of U.S. non-provisional application Ser. No. 12/191,842 filed Aug. 14, 2008, which application claims priority under 35 U.S.C. § 119 of European Patent Application No. 07114428.1 filed on Aug. 16, 2007. The entire disclosures of each of these applications is herein expressly incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12191842 | Aug 2008 | US |
| Child | 16437819 | US |
