DE19920517C1 - Membrane module for removing hydrogen from product gas produced in a reforming reaction in fuel cells of vehicles has separating elements containing an electrically conducting substrate - Google Patents

Abstract

Membrane module comprises one or more separating elements (1) containing a porous substrate (2) which has an active coating (3). The substrate is made of an electrically conducting material and an electrical heating current circuit (4) is provided into which the substrate is looped as Ohmic heat resistor.

Description

The invention relates to a membrane module for selective Separation of a permeate gas from a gas mixture from the remaining the residual gas with one or more separation elements, the one include porous substrate, which with a release active Be layering is provided. Such membrane modules are used in used for example for the selective separation of hydrogen, which is contained in the product gas of a reforming reaction.

An important application is fuel cell vehicles, their Fuel cells are operated with hydrogen, which by ei ne reforming reaction from entrained methanol or a other feed is generated. With the selective water Separation of substances by the membrane module is particularly important prevents the fuel cells from being poisoned by carbon monoxide be tet that contains the reforming reaction in the product gas is.

For selective hydrogen separation have long been mem branches made of different materials, such as ceramics, glasses, buttocks polymers and metals, in use, with metal membranes due to high selectivity and temperature stability in all ding relatively low permeation rates. Specifically can be used for selective hydrogen separation Me tall foils, for example made of palladium or palladium alloy conditions exist. Palladium is already at room temperature and low capable of hydrogen pressures, 600 to 900 times to store its volume of hydrogen. For use as  Pure palladium membrane is not so suitable, because at certain temperatures a β-hybrid phase arises, which can lead to embrittlement and thus to cracking. Mostly the palladium is therefore an alloy partner from groups VIII or IB of the periodic table added. Comes in commercial Lichen hydrogen separation units are mostly rolled foils from the various palladium alloys in a thickness between around 50 µm and 100 µm are used.

To reduce the precious metal content, it is already be knows to use membrane modules of the type mentioned at the beginning, where the active metal alloy is separated by a suitable Coating method such as PVD, CVD, electroless chemical loading layering or electrodeposition, on a porous sub strat is applied. This allows the thicknesses to be relatively small release-active coating of less than 10 µm. The porous Substrate typically consists of a ceramic or glass mass material.

The permeation rate of the active component of the membrane mo duls is typically temperature dependent. To a desired one To achieve a peremation rate, most of them have to be separated tive metals and metal alloys on a material-specific Minimum operating temperature to be brought above the room temperature temperature lies. This is conventionally done e.g. B. by a external heating of the membrane module with the help of an electri heating device or by catalytic combustion a suitable one, preferably used anyway in the system Fuel on or in the membrane module. In addition to the detachable Membrane layer and possibly the associated porous sub Other components of a massi often become strat ven membrane module heated up, which is a relatively high energy consumption and a comparatively long heating-up time Has.

In the older, unpublished German patent application Application No. 198 04 286.8 is a reactor for a catalytic surface  Mix reaction described, in the reaction chamber porous Hollow fibers as membranes for selective permeate gas separation are introduced, which are made of an electrically insulating ceramic or glass material and with a separating active metalli coating. For rapid heating of the separating active metallic coating is an electrical Heating circuit provided in this coating as an ohm the heating resistor is looped in.

The invention is a technical problem of providing a membrane module of the type mentioned that to selectively separate one from a gas mixture separating gas, here called permeate gas, is suitable and release-active coating in the event of a cold start with a relatively high low energy consumption quickly to be effective selective Permeate gas separation heated to suitable operating temperature can be.

The invention solves this problem by providing a Membrane module with the features of claim 1. In this mem branmodul is the porous substrate on which the detachable, d. H. the coating effecting selective permeate gas separation is applied from an electrically conductive material forms and as an ohmic heating resistor in an electrical Heating circuit looped in.

The release-active coating ensures that the appropriate operating temperature the desired separation of the Per meatgases from the supplied gas mixture. During a cold start, it can brought very quickly to the required operating temperature that the electrical heating circuit is activated, d. H. an associated heating voltage is applied to this, so that porous substrate and with it through direct solid-state heat contact the active coating can be heated. The remaining peripheral components of the membrane module can be from this heating largely remain unaffected, which is a re relatively low energy consumption and a short heating up time  to reach the desired operating temperature for the release-active coating enables. Compared to modules with Ab separating elements in which this is the release-active coating load-bearing substrate made of an electrically insulating material stands and the electrically conductive, release-active coating as an ohmic heating resistor in an electrical heating circuit is looped in, enables the use according to the invention an electrically conductive, porous substrate as an ohmic Heating resistance due to the larger volume of a higher one Heating power for heating the thermally conductive connected com plexes of porous substrate and release-active coating.

For the electrically conductive, porous substrate, be use any of the known materials for this. In a Further development of the invention according to claim 2 is a Sin for this term metal, a conductive ceramic or a titanium oxide modification tion, d. H. a suitable composition of titanium oxides or one made of titanium oxides with possible minority components composite material, provided.

The membrane module can be a plate stack with one or more plate-shaped partition elements can be constructed, which from a verse on one or both sides with the release-active coating hen, porous substrate plate are formed. In another advantageous implementation includes the membrane module according to An saying 3 a channel bundle structure from a monolithic porö sen substrate body, in which a plurality of channels are introduced, by which at least one for guiding the gas mixture and the rest gases and the other for guiding the permeate gas NEN, with fewer channels than permeate gas routing are required for the gas mixture / residual gas guidance. The or the Channels that carry the gas mixture and the residual gas point to them the active coating.

Another embodiment of this membrane module with channel bundle structure is specified in claim 4. The monolithic substrate body here has a cylindrical shape, and the channels  stretch in the longitudinal direction in the porous substrate cylinder. The or the channels that carry the gas mixture and the residual gas hen on a first end face of the substrate cylinder connection openings in a local he Most connecting element are provided. On the opposite There is a second end face of the substrate cylinder closing element, the connection openings for both the Gasge mix and the residual gas carrying part of the channels as well as for the has the part of the channels carrying permeate gas. The feed and In this way, all gas flows are discharged at the end. It is understood that the porous substrate cylinder on its order catch gas-tight by a corresponding housing cylinder is closed. An advantageous channel configuration for this Channel bundle structure with a cylindrical porous substrate body specified in claim 5. A central channel acts as one the channel carrying the permeate gas, while several surrounding it Channels bil the channels leading the gas mixture and the residual gas the.

In a further advantageous embodiment of the membrane module with a channel bundle in a monolithic substrate body according to claim 6 in the or the channels that the gas mixture and lead the residual gas, a catalyst material for catalysis introduced a desired chemical reaction, e.g. B. as Pel letfill. This allows the membrane module to be considered a chemical Reactor to carry out the chemical reaction in question act, such as for the catalytic reforming of Methanol or another hydrocarbon derivative or one Hydrocarbon to produce a hydrogen-rich Gas mixture, from which the hydrogen is then used directly as permeate gas is separated from the reaction space.

In a development of the invention according to claim 7, the is from release-active coating galvanically or by a CVD process or by electroless chemical plating on the porous Substrate applied. For the galvanic deposition of the ab release-active coating can be advantageous the fact  take advantage of the fact that the porous substrate itself is electrically conductive is what the plating process compared to other coating ting processes, such as sputter coating, are comparatively simple makes possible.

Advantageous embodiments of the invention are in the drawing are shown and are described below. Here demonstrate:

Fig. 1 is a schematic perspective view of a plate-shaped membrane module separating element with a porous, electrically conductive and heatable and one-sided actively coated substrate plate and

Fig. 2 is a schematic, perspective, exploded view of a membrane module with a monolithic, porous and electrically conductive and heatable substrate cylinder with an inserted channel bundle.

Fig. 1 shows schematically a plate-shaped separating element 1 , which is made of a rectangular, porous substrate plate 2 , which is provided on one side with a hydrogen-separating Be coating 3 . The latter makes it possible to selectively separate the hydrogen from a pending hydrogen-containing gas mixture on the outside by essentially absorbing only the hydrogen from the separating-active coating 3 from the gas mixture and passing through it into the porous substrate plate 2 . From there, the selectively separated hydrogen z. B. leads abge via a hydrogen discharge channel and are supplied for an intended use. A corresponding membrane module includes, as is known per se to the person skilled in the art, one or more such plate-shaped separating elements 1 lying one above the other in a plate stack structure. Suitable connection structures are provided on one or more sides of the plate stack in order to supply the hydrogen-containing gas mixture or a feed mixture for producing the same to the membrane module and to remove the hydrogen on the one hand and the residual gas remaining after the separation of the hydrogen from the gas mixture on the other hand.

Characteristically, the porous substrate plate 2 consists of an electrically conductive material, e.g. B. a Sinterme tallmaterial or an electrically conductive ceramic, such as SiC, or a suitable composition based on titanium oxides. The substrate material is chosen so that the substrate plate 2 has a sufficiently high electrical resistance, so that when voltage is applied, the voltage drop across the substrate plate 2 is sufficient to develop a desired amount of heat in it, which is necessary for rapid heating of the separating element 1 during a cold start. In other words, the porous, electrically conductive substrate plate 2 forms an ohmic heating resistor, to which a corresponding heating current circuit 4 is assigned.

For heating the porous substrate plate 2 , a heating voltage from a voltage source 5 is applied to it through the heating circuit 4 , as a result of which a heating current I flows through the heating circuit 4 and thus through the porous substrate plate 2 , which is preferably contacted with the heating circuit 4 on two opposite narrow sides . This results in the generation of Joule heat in the porous substrate plate 2, as a result of which it heats up itself, but also the hydrogen-separating-active coating 3 which is directly connected to it by solid-state contact. Since not only the porous substrate plate 2 as compared with the wasserstoffabtrennaktiven coating 3 a large Ohm ULTRASONIC Heizwiderstandsvolumen provides and other than this direct heating of the Abtrennelementes 1, depending on application case additional other components of the membrane module need not necessarily be mitbeheizt to the same degree, is achieved that the one or more separating elements 1 of the membrane module and thus in particular the hydrogen-separating active coating 3 can be heated to the operating temperature desired for an effective hydrogen separating function with a relatively low energy consumption and short heating-up time.

Fig. 2 shows a membrane module with tube bundle structure for selective separation of z. B. hydrogen. This membrane module includes a porous substrate cylinder 6 made of an electrically conductive material, which is closed radially on the outside by a gas-tight cylinder jacket housing 7 and which has a hollow channel bundle in its interior. The porous substrate cylinder 6 corresponds in its function to the porous substrate plate 2 of FIG. 1 and can consist of one of the electrically conductive materials mentioned there, that is to say, for example, of a sin termetal, a conductive ceramic or a titanium oxide modification. The hollow channel bundle includes several, parallel offset through the substrate cylinder 6 in the cylinder longitudinal direction extending hollow channels, of which a hollow channel 8 in the center of the substrate cylinder and several other channels 9 in the cylinder circumferential direction are evenly spaced from each other around the central channel 8 .

The end of the substrate cylinder 6 is completed with an end plate 10 , 11 , as indicated in the exploded view by arrows P, the end plates 10 , 11 forming connection elements by having suitable connection openings. Specifically, the configuration of the connection openings is selected so that the central hollow channel 8 forms a permeate gas channel through which the selectively separated hydrogen can be drawn off, while the other channels surrounding it form 9 gas mixture channels, in which the gas mixture is led, which contains hydrogen to be separated, and from which the residual gas remaining after the hydrogen separation is withdrawn again. For this purpose, in the one, supply-side end plate 10 to connection openings 12 a only for the gas mixture channels 9 are introduced, while the other, discharge-side end plate 11 has both a central connection opening 13 for the permeate gas to be discharged and surrounding connection openings 12 b, through which the residual gas is discharged becomes.

The gas mixture channels 9 and the gas mixture channels 9 remaining therefrom after successive water separation along the flow path are provided on their inner wall with egg ner hydrogen-active coating 14 corresponding to the hydrogen-active coating 3 of FIG. 1. The attachment of these hydrogen-separating, metallic, e.g. B. made of palladium or a palladium alloy coating 14 is preferably carried out by a suitable galvanic African process, wherein the fact can be used that the porous substrate cylinder 6 is electrically conductive. A coating of the inner wall of the central permeate gas channel 8 can, for. B. can be prevented by covering the same during plating. Alternatively, other coating methods can also be used, such as CVD or electroless chemical plating.

The separated by the membrane module, withdrawn from the central Per meat gas channel 8 hydrogen can then be used for intended use z. B. be supplied as fuel to a fuel cell system. The hydrogen-depleted residual gas, also referred to as raffinate gas, can also be used for further use, depending on the application. B. as fuel gas a catalytic burner for heating a compo nent of a fuel cell system in a fuel cell vehicle.

The electrically conductive, porous substrate cylinder 6 is looped in again as an ohmic heating resistor in an electric heating circuit 15 with associated heating voltage source 16 . Here, as shown, the connecting lines can be contacted with the end plates 10 , 11 , which also consist of an electrically conductive material and are electrically conductively connected to the porous substrate cylinder 6 , for. B. by soldering. In the cold operating state, the porous sub strat cylinder 6 can be heated by applying a heating voltage according to the example of FIG. 1 by the Joule heat developed in it, which also the hydrogen-separating active coating 14 in the gas mixture channels 9 also quickly on them to meet an effective Hydrogen separation function brings necessary operating temperature. In this example too, this direct heating means that no further membrane module components need to be heated, which reduces the heating energy consumption and keeps the heating up time short.

In a preferred implementation, the gas mixture channels 9 with a catalyst material z. B. in the form of a pellet bed, which catalyzes a desired chemical reaction, such as a hydrogen-generating reforming reaction, in which methane or another hydrocarbon derivative or a carbon hydrogen z. B. is reformed with steam. Suitable catalyst materials for such purposes are known to the person skilled in the art and do not require any further explanation here. In this realization, the membrane module then forms a reforming reactor with an integrated hydrogen separation stage which, under the action of the catalyst material, forms a hydrogen-rich mixture in the gas mixture channels 9 in the gas mixture channels 9 , of which the hydrogen is selectively processed by the separation-active coating 14 in the material of the porous substrate cylinder 6 and from there into the permeate gas channel 9 , from where it can be withdrawn who can. In this embodiment of the invention, the reforming reaction space formed by the gas mixture channels 9 can then be heated directly by the heating circuit 15 and in this way quickly brought to an operating temperature that is higher than room temperature and kept there. If the reforming reaction is endothermic, the heating current in the heating circuit 15 during the reforming operation can be maintained so far that the heating heat formed by the porous substrate 6 covers the heat demand of the reforming reaction. Alternatively, it is of course possible to use the membrane module as a separate hydrogen separation stage which is connected downstream of a reforming reactor, the product gas of which is introduced as a hydrogen-containing gas mixture into the membrane module.

It goes without saying that, as an alternative to the use of the middle channel 8 shown as a permeate gas channel and the other channels 9 giving it as gas mixture channels, any other division of the channels 8 , 9 into permeate gas channels on the one hand and gas mixture channels on the other hand can be provided. For this purpose, only a corresponding configuration of the connection openings, in particular of the supply-side end plate 10, must be selected, ie, connection openings are introduced into the end plate 10 on the drive side only for those channels which are intended to function as gas mixture channels. A suitable downstream connection configuration on the discharge-side end plate 11 then ensures separate removal of the permeate gas on the one hand and the residual gas on the other hand. So z. B. an approximately half term division of all channels into permeate gas channels and gas mixture channels may be provided, preferably in an alternating arrangement in which a channel of one type is largely surrounded only by channels of the other type.

The examples shown illustrate that the invention Membrane module through the use of an electrically conductive Material for the porous substrate, which the separation-active Be stratification carries quickly and with little energy consumption from cal operating state for effective permeate gas separation required operating temperature can be heated, which is why porous substrate as an ohmic heating resistor in an associated Heating circuit is looped in. Preferred areas of application of the membrane module according to the invention are selective Hydrogen separation for both stationary and mobile burning cell systems as well as for other areas of chemical and electronic industry. It is also suitable membrane module according to the invention, of course, also for selective ven separation of another contained in a gas mixture Permeate gas, then the active coating on it is to be chosen in a suitable manner, as the skilled worker per se knows.

Claims (7)

1. Membrane module for the selective separation of a permeate gas from a gas mixture from the remaining residual gas, in particular for the selective separation of hydrogen contained in the product gas of a reforming reaction, with one or more separation elements ( 1 ) which contain a porous substrate ( 2 ) which has a release-active coating device ( 3 ) is provided, characterized in that

• a) the porous substrate ( 2 ) is formed from an electrically conductive material and
• b) an electrical heating circuit ( 4 ) is provided, into which the porous substrate is looped in as an ohmic heating resistor.

2. membrane module according to claim 1, characterized in that the substrate material is a sintered metal, a conductive ceramic or is a titanium oxide modification. 3. Membrane module according to claim 1 or 2, characterized in that it has a channel bundle structure with a plurality of channels ( 8 , 9 ) spaced apart from one another in the porous substrate formed by a monolithic substrate body ( 6 ) and of which a first part ( 9 ) on the channel wall from separating coating ( 14 ) and for guiding the gas mixture and the residual gas and the rest of the second part ( 8 ) is used to guide the permeate gas. 4. Membrane module according to claim 3, characterized in that the substrate body ( 6 ) is of cylindrical shape and the channels ( 8 , 9 ) in the longitudinal direction of the substrate cylinder and he stretch on a first end face of the substrate cylinder with a first connection element ( 10 ) one or more connection openings ( 12 ) only for the first part ( 9 ) of the channels and on the second, the first opposite end face of the substrate cylinder, a second connection element ( 11 ) with a plurality of connection openings ( 12 a, 13 ) for the first and the second part ( 8 , 9 ) of the channels is provided. 5. Membrane module according to claim 4, characterized in that the second part of the channels from a single, in the longitudinal center region of the substrate cylinder ( 6 ) arranged permeate gas channel ( 8 ) and the first part of the channels from several, distributed in the circumferential direction around the permeate gas channel arranged channels ( 9 ). 6. Membrane module according to one of claims 3 to 5, characterized in that the first part ( 9 ) of the channels contains a catalyst material for Kata lysierung a chemical reaction in which a feed to be fed into a gas mixture containing the permeate gas is reacted. 7. Membrane module according to one of claims 1 to 6, characterized in that the release-active coating ( 3 ) by galvanic deposition, a CVD process or electroless chemical plating is applied to an associated surface of the porous substrate ( 2 ).