EP1791624A1

EP1791624A1 - Device for gas separation and method for producing one such device

Info

Publication number: EP1791624A1
Application number: EP05774386A
Authority: EP
Inventors: Wilhelm A. Meulenberg; Ralf Hansch; Hans Peter Buchkremer; Detlev STÖVER
Original assignee: Forschungszentrum Juelich GmbH
Current assignee: Forschungszentrum Juelich GmbH
Priority date: 2004-09-24
Filing date: 2005-08-13
Publication date: 2007-06-06
Also published as: JP2008514387A; US8016924B2; CA2581419A1; AU2005287770B2; WO2006032230A1; DE102004046310A1; AU2005287770A1; US20090193975A1; CN101031352A

Abstract

The invention relates to a method for producing a device for gas separation, said device comprising a layer system wherein a functional layer consisting of Ti02 and/or Zr02 having an average pore diameter of less than 1 nm is applied to at least one side of a carrier layer that is porous throughout. Said carrier layer is preferably between 100 µm and 1 mm thick and comprises continuous pores with an average pore diameter in the µm range. The functional layer which is applied directly or by means of at least one intermediate layer comprises continuous pores with an average pore diameter of less than 1 nm, especially less than 0.8 nm. The functional layer can advantageously be embodied as a graduated layer. The invention is especially characterised by the symmetrical structure of the device, in which functional layers are applied to both sides of the carrier layer, optionally by means of respectively at least one intermediate layer.

Description

Device for gas separation and method for producing such a device

The invention relates to a device for gas separation, particularly for the separation of N _2/0 _2, CO ₂ / H ₂ and N ₂ / CO mixtures Gasmi¬ _2. Furthermore, the invention relates to a method for producing such a device.

State of the art

A separation of media, in particular of gases, is possible in principle with membranes. A distinction is made between so-called mesoporous membranes, ie those with pore diameters between 2 and 50 nm, and microporous membranes which have pores with a pore diameter of less than 2 nm.

In mesoporous membranes, gas transport occurs via Knudsen diffusion, which depends on the adsorption properties of the membrane material. For such membranes, the separation factor for gas mixtures is usually low.

For the separation and / or separation of individual gases from gas mixtures, the use of microporous membranes, eg. As silica membranes, known from the literature. The separation of the gases is based on the principle of molecular sieving, whereby a first gas from the gas mixture can pass through the membrane, but not another because of the larger kinetic molecular diameter. The driving force for the separation process is the pressure difference between the two gas spaces. The most important characteristics of gas separation membranes are their permeability and separation factors. These properties give the separation performance and the membrane requirements for a separation task.

A flow J (unit: kg m ^"2 s ^{' 1} ) sets in at steady-state conditions under the driving force of a partial pressure difference for a particle through a membrane piece with the area A. The permeability P of a membrane is normalized as a gas flow per membrane area, time and partial pressure difference for the permeating gas indicated (unit: Nm ³ (STP) m ^"2 h ^{" 1} bar ^"1 , STP: O ⁰ C, 101325 Pa, 22.414 1 Molvolu¬ men).

The separation efficiency of a membrane material is indicated by the separation factor α. The separation factor for a gas pair is defined as the ratio of the gas permeabilities P. It depends on the temperature, the feed pressure and the pressure difference across the membrane as well as the pore diameter and the pore distribution. Separation factors are approximately not dependent on the membrane thickness. Exceptions are membranes with very thin separation layers (<0.1 μm) compared to isotropic films (100 μm).

Gas permeation separates gas streams into streams of different components. As established industrial applications, it has the separation of hydrogen from the process gas, the nitrogen / oxygen separation from air and the recovery of organic vapors such as, for example, gasoline vapors from gas / air mixtures.

Also promising is the use of gas permeation with inorganic membranes. There are both microporous membranes, such as multilayer silica membranes (amorphous SiO ₂ ), zeolite membranes or carbon membranes, as well as metal membranes (eg PdAg alloy) or perovskite membranes as mixed-conducting dense membranes. Their fields of application are versatile and different. They have in common their applicability under difficult process conditions, such as, for example, high temperature and / or high pressure.

The typical applications of gas permeation with inorganic membranes are, in particular, the necessary purification of gas streams with regard to subsequent process steps (eg risk of catalyst poisoning), the shift of the reaction equilibrium by selective separation of products or by-products and the concentration of product streams to reduce the energy requirement subsequent finishing steps.

Membrane systems often have a modular design and can therefore be adapted variably to different problems. Fer¬ ner can be driven in a simple manner different throughputs. They do without moving parts and are usually relatively lightweight and compact.

Usually, however, high product purities with membrane processes can generally only be achieved with comparatively high outlay, since, for example, high selection rates are achieved only with dense membranes. Also from Betrieb¬ point forth the membrane process u. a. due to the limited thermal and chemical stability of the membrane materials to relatively narrow pH, temperature and humidity ranges.

The Fraunhofer Institute for Ceramic Technologies and Sintered Materials (IKTS), for example, discloses ceramics with a certain adjusted porosity, which are produced by the sintering of tightly fractionated particles.

This results in open, permeable pore volumes of 30-60% by volume and narrow pore size distributions with center of gravity in the micrometer or nanometer range.

Ceramic filtration membranes for liquid filtration and gas separation are produced by, in part, multiple applications of thin layers each of finer porosity on a coarsely porous substrate. Such membranes are also called asymmetric membranes. Typical substrates are tubes or multi-channel elements. In the case of disks as substrates, the so-called flat membranes are obtained.

The advantage of ceramic membranes over polymer filters is their utilization of the high thermal and chemical resistance of the ceramic.

Also known from the Fraunhofer Institute for Ceramic Technolo- gies and Sintered Materials (IKTS) are polymer membranes with layer thicknesses adjustable between 1 and 5 μm, which are produced by coating the substrate with a specially prepared silicon-organic precursor and subsequent polymer pyrolysis. Depending on the type and the molecular structure of the polymer used, various porosities and pore sizes are obtained. A precursor system gives, for example, a pore diameter of about 1.5 nm with a low distribution and BET surface areas of up to 600 m ² / g. The pyrolysis of other polymer classes leads, depending on the molecular structure and the thermolysis conditions. different pore diameters between 4 and 20 nm with a narrow pore size distribution. After Pyro- lyse is a covering, crack-free and highly porous silicon carbide schichite on the substrate surface. This is used as filter-sensitive separation layer in membrane filtration process use. There are currently over 40 different approaches for the gas-phase separation of technically relevant gases from a fossil-fueled power plant, of which, however, hitherto only the chemical separation technology, ie the absorption into amine solutions in model power plants, has been used.

In the separation via correspondingly set pore sizes, polymer membranes are currently being developed for the separation in the low temperature range. Exist for applications at higher temperatures up to 500 ⁰ C, for example, water-serstoffpermeable AgPd membranes and amorphous microporous silica membranes. Furthermore, dense ionic, mixed or proton conductors are also under discussion.

Disadvantageously, the chemical processes generally have a high loss of efficiency, while the polymer membranes are limited to applications at low temperatures. The maximum Einsätzgrenze for expensive AgPd membranes and silica membranes is about 500 ⁰ C. The disadvantage react these membranes also sensitive to water.

Task and solution

The object of the invention is to provide a device with which a gas separation of technically relevant gases, such as, for example, H ₂ , N ₂ , O ₂ or CO ₂ from a gas mixture, is possible, especially at higher temperatures. Furthermore, it is the object of the invention to provide a method for producing such a device. The objects of the invention are achieved by a device with all the features according to the main claim, and by methods with the entirety of features according to the independent claims. Advantageous embodiments of the method and the device can be found in the respective dependent claims.

Subject of the invention

In the context of the invention, it has been found that a thin membrane comprising a metallic and / or ceramic support layer and an oxide functional layer disposed thereon has an effective separation factor for the separation of gases.

The carrier layer advantageously effects the mechanical stability of the membrane. In particular, it can be made of a steel, for. B. 316 L stainless steel and / or a ceramic. The thickness of the carrier layer is dependent on the separation protolem, and may vary between 100 μm and 1 mm. The thickness of the carrier layer influences the degree of permeation, and should therefore be configured in principle as thin as possible, in particular smaller than 1 mm. However, in order to fulfill their function as a carrier layer, layer thicknesses of at least 100 μm, better 200 μm are desirable. In this case, metallic carrier layers generally have a better stability than ceramic layers with a comparable layer thickness.

The carrier layer itself is designed to be porous throughout and has pores in the μm range on average. The determination of these average pore diameters can be carried out in particular by SEM (scanning electron microscopy) or with smaller pore diameters via TEM (transmission electron microscopy). The pores are markedly larger than those of the adjoining func- tion layer. The carrier layer should be used for mechanical stabilization. care, but if possible, avoid any flow resistance.

On at least one side of the carrier layer of the device according to the invention, a functional layer is arranged which has an average pore diameter as a function of the separation problem to be solved of less than 1 nm, in particular less than 0.8 nm and particularly preferably Partly less than 0.5 nm. The functional layer causes the actual separation of the gas molecules. Theoretically, the average pore diameter should be between those of the gas molecules to be separated. However, it has been shown that even slightly larger pore diameters lead to a very good degree of separation.

The functional layer comprises in particular TiO ₂ or ZrO ₂ and can be made particularly thin. advantageous

Layer thickness are in the range of a few to a few hundred nm. The embodiment depends on the separation problem and the separation performance to be achieved. The selectivity (separation factor α) increases regularly with decreasing pore diameter of the functional layer. On the other hand, the flow (permeation) is significantly reduced by very small pores, in particular in connection with τnd_t a larger layer thickness of the functional layer. The separation .alpha. Always involves a balance between selectivity and permeation and is adapted by the person skilled in the art to the separation sample to be dissolved.

For reasons of better adhesion, an intermediate layer optionally arranged between the T_εrä- gerschicht and functional layer has been found to be advantageous. As a rule, this intermediate layer comprises oxide systems, in particular ceramics. Advantageous materials for the intermediate layer are, for example, TiO ₂ , ZrO ₂ or Al ₂ O ₃ . The intermediate layer is likewise porous throughout. The average pore diameter of the intermediate layer is advantageously between that of the carrier layer and that of the functional layer, in particular between 2 and 100 nm. The intermediate layer advantageously has a layer thickness in the range between 100 nm and 50 μm.

In a particular embodiment of the invention, a functional layer, optionally with an intermediate layer, is disposed on both sides of the carrier layer. The symmetrical arrangement is to be selected in particular when the individual layers are made very thin, since then the bilateral, symmetrical arrangement advantageously leads to an additional stability of the separation device. In addition, the symmetrical structure minimizes distortion during the sintering process.

In a further advantageous embodiment of the invention, the functional layer, if appropriate together with an intermediate layer, is present as a graded layer. The properties of the abovementioned intermediate layer are then present in particular at the boundary layer carrier layer / graded layer, while the properties of the abovementioned functional layer are present in particular on the free surface of the layer system. This means that the average pore diameter from the carrier layer to the free surface gas / functional layer decreases in principle continuously or else in a stepped manner.

In the context of the invention, however, it is also conceivable to arrange a layer with coarser pores on the outer functional layer with a very small pore diameter for stability reasons. To produce the apparatus according to the invention for gas separation, a porous ke¬ ramische or metallic foil, with a layer thickness zwi¬ rule 200- 500 microns thickness is provided as the support layer first. A CerMet is also conceivable as a carrier layer. The porosities are in the μm range. One or more ceramic intermediate layers having pores in the range from 2 to 100 nm are applied thereon, for example, on one side or on both sides. The two-sided coating with the intermediate layer is particularly useful if a delay of a very thin designed carrier layer during the heat treatment is to be prevented ver¬. The functional layer required for the actual gas separation can advantageously be applied by means of a sol-gel method. However, CVD (chemical vapor deposition) or PVD (physical vapor deposition) are also suitable as application techniques. In the case of the sol-gel process, the setting of the porosity in the functional layer is achieved by means of a sol composition, pyrolyzing condition, that is to say the burnout of the organic components, and the sintering conditions.

The devices according to the invention for gas separation (membranes) regularly have high permeability, high selectivity and good stability under conditions of use. They are thus particularly suitable for the gas separation of technically relevant gases such as N ₂ , O ₂ , CO ₂ , H ₂ , He and CH ₄ from gas mixtures.

Special description part

The subject matter of the invention will be explained in more detail below with reference to an exemplary embodiment without the subject of the invention being limited thereby. On a pre-sintered at 900 ° C / l, porous, Folienge¬ cast steel substrate made of a 316 L stainless steel (d = 200-300 microns, particle size less than 5 microns) is by wet powder spraying or screen printing on both sides a TiO ₂ intermediate layer (d = 20-30 μm, grain size 200 nm). After a

Sintering at 950 ° C / l hour in vacuo, the functional layer of TiO ₂ or alternatively ZrO _{2 is} applied. In this case, a sol gel from an organic precursor z. For example, titanium propylate, zirconium propylate and acetylacetone and an α-type carboxylic acid used which is applied by spin coating or a dipping process. Following this, the pyrolysis takes place (eg. As at 600 ° C / l hour) of the organic components of the sol and the final sintering of the sample at temperatures up to 1000 ⁰ C.

Table of some kinetic diameters of gases:

CH ₄ 0, 38 nm

N ₂ 0, 364 nm

O ₂ 0, 346 nm

CO ₂ 0, 33 nm

H ₂ 0, 289 nm

He 0, 26 nm

Claims

Pat ent claims

1. A device for gas separation comprising a layer system, characterized by

- A continuous open-porous, mechanically stable Trä¬ gerschicht having an average porosity in the micron range, and

a TiO ₂ and / or ZrO ₂ comprising at least one side of the carrier layer and comprising a continuous porous functional layer which has an average polymer diameter of less than 1 nm.

2. Device according to the preceding claim 1, with two arranged on both sides of the carrier layer Funktionsa¬ len layers.

3. Device according to one of the preceding claims 1 to 2, wherein the carrier layer has a thickness between 100 microns and 1 mm, in particular has a thickness of 200 microns to 500 microns.

4. Device according to one of the preceding claims 1 or 3, wherein between the carrier layer and wenigs¬ least one functional layer, an intermediate layer is arranged.

5. Device according to the preceding claim 4 with an intermediate layer comprising Al ₂ O ₃ , TiO ₂ and / or ZrO ₂ .

6. Device according to one of the preceding claims 4 to 5, wherein the intermediate layer has a thickness between 100 nm and 100 microns, in particular has a thickness of 20 to 50 microns.

7. Device according to one of the preceding claims 1 to 6, wherein the functional layer has an average pore diameter of less than 0.8 nm, in particular less than 0.5 nm.

8. Device according to one of the preceding claims 1 to 7, wherein the functional layer is formed as a graded layer.

9. Device according to the preceding claim 8, wherein the average pore diameter of the functional layer varies continuously and / or stepwise.

10. Device according to one of the preceding claims 8 to 9, wherein the average pore diameter decreases from the carrier layer in the direction of the free surface functional layer / gas.

11. A method for producing a device for gas separation comprising a layer system in which a functional porous layer of TiO ₂ and / or ZrO ₂ having an average pore diameter of less than 1 nm is applied to a continuous porous support layer on at least one side of the support layer is applied.

12. The method according to the preceding claim 11, wherein on both sides of the carrier layer, a functional layer of TiO ₂ and / or ZrO ₂ having an average Po¬ rendurchmesser of less than 1 nm is applied.

13. The method according to any one of the preceding claims 11 to 12, wherein a carrier layer having a thickness between 100 .mu.m and 1 mm, in particular a thickness of 200 .mu.m to 500 .mu.m is used.

14. The method according to any one of the preceding claims 11 to

13, in which an intermediate layer is arranged between the carrier layer and at least one functional layer.

15. The method according to any one of the preceding claims 11 to

14, in which an intermediate layer comprising Al ₂ O ₃ , TiO ₂ and / or ZrO _{2 is} arranged.

16. The method according to any one of the preceding claims 11 to

15, in which an intermediate layer with a thickness between 100 nm and 100 .mu.m, in particular with a thickness of

20 to 50 microns is arranged.

17. The method according to any one of the preceding claims 11 to

16, in which a functional layer an average pore diameter of less than 0.8 nm, in particular less than 0.5 nm is applied.

18. The method according to any one of the preceding claims 11 to

17, in which the functional layer is applied as a graded layer.

19. The method according to the preceding claim 18, wherein the average pore diameter of the functional

Layer is varied continuously and / or stepped.

20. The method according to any one of the preceding claims 11 to 19, wherein the average pore diameter from the support layer in the direction of the free surface funk¬ tionale layer / gas is designed decreasing.

21. The method according to any one of the preceding claims 11 to 20, wherein a functional layer and / or a Zwi¬ rule layer is aufge¬ introduced by means of a sol-gel method.