EP2337629A2

EP2337629A2 - Adsorber element and method for producing an adsorber element

Info

Publication number: EP2337629A2
Application number: EP09771470A
Authority: EP
Inventors: Jürgen Sauer; Belal Dawoud; Stefanie Chmielewski; Hendrik Van Heyden; Heike Klaschinsky
Original assignee: Viessmann Werke GmbH and Co KG
Current assignee: Viessmann Werke GmbH and Co KG
Priority date: 2008-10-10
Filing date: 2009-10-02
Publication date: 2011-06-29
Also published as: US20110183835A1; KR20110069119A; CN102176964A; WO2010040335A3; WO2010040335A2; JP2012505071A; DE102008050926A1

Abstract

The invention relates to an adsorber element and to a method for the production thereof, comprising a carrier material (1) on which adsorbent particles (3) are arranged as the adsorber layer using a binding agent (2). According to the invention, the adsorber layer comprises inorganic fibers (4) and the binding agent (2) is designed as a colloid.

Description

Ordsorberelement and method for producing a

adsorber

The invention relates to an adsorber element according to the preamble of patent claim 1 and to a method for producing an adsorbing element according to the preamble of patent claim 15.

An adsorber element of the aforementioned type is used for example in heat pumps on so-called Adsorbentbasis (for example: silica, activated carbon or zeolite [then molecular sieve base]). Such adsorbents (molecular sieves) are usually characterized by the fact that they absorb refrigerant (for example water) in a reversible reaction and release it again when heat is applied. This is due to the pronounced pore structure of this material class, which also includes the zeolites. Heat is dissipated during refrigerant uptake, and heat is needed to release the refrigerant. The heat of reaction of each reaction, refrigerant adsorption (adsorbent gives off heat) or refrigerant desorption (adsorbent absorbs heat) can, as mentioned, be exploited in heat pumps. For this it is necessary that heat can be transported efficiently to or from the adsorbent. Similarly, the adsorbent must be accessible to refrigerant molecules, i. H. its pore structure must not be clogged or blocked.

Adsorbents are generally crystalline solids whose particle size is usually in the range of a few micrometers. Advantageous for use in a heat pump is a good connection of these Adsorbentpartikel to a material of very good thermal conductivity, as it represents, for example, aluminum or copper. As adsorbent particles are generally not The use of adhesion promoters (binder materials), which adhere the particles to one another and to the metal, is necessary. These bonding agents must meet two criteria. They should not hinder the adsorption of refrigerant into the adsorbent and, more generally, should not hinder the function of the heat pump. They should also consist of environmentally friendly and economically enforceable materials.

The heat pump operates under pure refrigerant vapor pressure at different temperatures. Increasing the existing pressure in the heat pump leads by the presence of inert gases to a reduction in performance of the heat pump up to a complete failure. For this reason, the adsorbent layer must not release any gases for a desired service life of 15 years, i. H. in particular, the adhesion promoter (binder material) used must not release any gases.

In order to apply adsorbent layers to metal, according to DE 33 47 700 C2, the use of metal knits (metal wool) for the preparation of zeolite shaped bodies is provided. Zeolite suspensions are poured into metal mesh with a binder and dried, the metal mesh being attached to metal walls, for example, by a heat pump. However, the method is described in DE 44 05 669 Al by the same applicant as insufficient. Thus, the metal mesh with zeolite is released from the metal walls during cyclic stresses.

DE 44 05 669 A1 describes a method for coating metals with zeolite suspensions, in which case commercial high-temperature binder materials, such as, for example, "GunGum" from Holst, are used as binder material. This approach has at least three disadvantages: "GunGum" is a water glass based material, an alkali silicate. However, it is known to the person skilled in the art that the water resistance of alkali metal silicates is poor. In a long-term load in which cyclic water condenses on the binder material or the alkali metal silicate and acts heat, there is a hydrolysis of the alkali metal silicate. This is accompanied by a decrease in the strength, an embrittlement of the silicate, so that the binding ability decreases and there may be a degradation of the adsorbent layer. Another problem lies in the alkalinity of alkali metal silicates, since many adsorbents, among them the families of aluminophosphates, called silicoaluminophosphates and silicon-rich zeolites, are attacked or dissolved by alkaline substances. In particular, the molecular sieve (adsorbent) with the name "FAM" from Mitsubishi, which is particularly suitable for use in a heat pump, is attacked by alkaline substances and thus also by "GunGum". The third problem with the use of "GunGum" or other alkali silicates as binding material, finally, are the carbonate impurities commonly found in these materials. These are due to the fact that alkaline substances in contact with air absorb the carbon dioxide present in small amounts in the air and form the corresponding alkali carbonate during this process. In the case of a long-term loading of a layer produced with such a binder, it may then lead to elimination of carbon dioxide from the alkali metal carbonates formed, which increases the pressure within the heat pump and thus leads to a reduction in performance.

When other non-alkali-silicate high temperature binders are used, other problems arise. Thus, for example, the high-temperature binder Sauerfeisenzement type 8 from SeppZeug GmbH contains no alkali metal silicates, but magnesium oxide, magnesium phosphate and zirconium silicate. However, if this material is used as a binder, so massive Shrinkage cracks up. Shrink cracks generally have their cause in the decrease in volume of the solidifying suspension due to the evaporation of liquid, for example, they can often be observed in dried, loamy river banks. The adsorbent layer adheres very instable to aluminum sheet and falls off with slight vibrations immediately. The same problem occurs with the high temperature binder Ceramabond from Kager GmbH. This binder contains as well as the acid rice type 8 no alkali silicates, but especially corundum in fine particle size. Experiments show that adsorbent coatings made with this binder also have numerous shrinkage cracks and immediately peel off the metal at a temperature load (16O ⁰ C).

In principle, the performance and, in particular, the stability of molecular sieve layers can be improved by the use of glass wool nonwovens as likewise described in DE 44 05 669 A1. For this purpose, a glass wool nonwoven is applied directly to metal and then glued to the molecular sieve / binder suspension. A disadvantage of this approach is that such a glass wool nonwoven can be applied only in easily accessible geometries of the metal body.

Other patents and publications are concerned with the preparation of zeolite layers on different substrates, wherein organic adhesion promoters are used, or the zeolite layer grows on a substrate in a tedious process.

Organic adhesion promoters have the inherent disadvantage that outgassing reactions of the organic substances within the heat pump can occur over long periods of time, which then impair the function of the heat pump. This is done against the background that the layers in the cyclic operation of the heat pump temperatures above 150 ⁰ C from are set and organic substances tend to decompose at these temperatures.

According to WO 2002/045847 A2, for example, a zeolite layer which is produced by the use of organic polymer binders is provided.

JP 63291809 A, JP 59213615 A, DE 693 20 195 T2 and DE 103 09 009 Al describe methods by which zeolites grow directly on substrates. For this purpose, for example, alumina substrates (JP 63291809 A), glass (JP 59213615 A), ceramic (DE 103 09 009 Al) or metals or metal alloys such as aluminum or steel (DE 693 20 195 T2) are brought into a reactive synthesis solution in which may result in partial dissolution of the substrates. The dissolved substrate can then be incorporated into nascent zeolite crystals which adhere directly to the as yet unresolved substrate.

With these methods, very well adhering, thin zeolite layers are obtained. The disadvantage is that the manufacturing method can not generally be applied to all substrate materials and is very expensive. Thus, moldings to be coated (the substrates) must be placed in reactors and typically maintained at high pressures and temperatures over a period of several days. Just untreated and reactive aluminum, as it is very advantageous for this production method, but is undesirable in heat pumps, because it can come to so-called hydrogen corrosion over a longer period. In this type of corrosion, water reacts with aluminum to form aluminum hydroxide and / or alumina hydroxide and / or alumina and hydrogen. However, the formation of hydrogen is highly undesirable in a heat pump, since this gas increases the operating pressure of the heat pump. The invention has for its object to improve an adsorber element or a method for producing an adsorber of the type described above.

This object is achieved with an adsorbent element of the type mentioned objectively according to the characterizing features of claim 1. Technically solve the characterizing features of claim 14 this task

With the present invention, it is possible to durably and stably coat arbitrarily shaped bodies (in particular metal bodies) with adsorbent particles. Due to the binder materials used, no outgassing during heat pump operation can occur.

According to the invention, in particular metal bodies are coated by the application of a liquid, preferably aqueous suspension and a subsequent drying process. In addition to the liquid phase, the suspension contains adsorbent particles, fibers and a colloidal binder.

Colloids (from Greek kolla "glue" and eidos "form, appearance") are particles or droplets which are finely dispersed in another medium (solid, gas or liquid), the dispersion medium. The single colloid is typically between 1 nanometer and 10 microns in size. If they are mobile (eg in a liquid dispersion medium), colloids usually show Brownian motion.

Both the fibers and the colloidal binder are selected from the class of inorganic, inert or substantially inert materials, so that there can be no chemical reactions and / or outgassing during heat pump operation. For example, colloidal silicon oxides or colloidal aluminum oxides / hydroxides are used as colloidal binders for the bonding of adsorbent particles.

Fibers are used to impart elasticity and strength to the layer and to prevent shrinkage cracks, since such may occur particularly during drying of the suspension.

As the layer is constantly exposed to temperature changes, tensions occur between the various materials present; H. Metal, adhesion promoters, fibers and adsorbent. These substances have different thermal expansion coefficients and therefore undergo different volume and length changes when heated, resulting in the mentioned stresses. In order to achieve a permanent strength of the layer, it follows that the layer must be elastic within limits - it must be able to "breathe". In order to obtain a certain relaxation capacity of the layer with relatively brittle materials such as glass, the particular binder material used is preferably used in fiber form.

The maximum possible bending of a fiber until it breaks is critically dependent on the diameter of the fiber. The thinner a fiber is, the more it can be bent without breaking, and the more elastic a layer as a whole in which these fibers are embedded behaves. Ie. Even with brittle, oxidic materials such as glass, elastically flexible materials can be mass-produced when processed as fibers. For example, a drinking water glass is a brittle, fragile object, whereas glass wool has a very high degree of flexibility. One For example, a single glass wool thread can be wound onto a roll without breaking.

According to the invention, fibers of different sizes can be used with particular advantage. Larger fibers impart stability and elasticity over long distances of the layer, while smaller fibers connect the individual adsorbent particles with each other and with the larger fibers and the substrate over short distances (see also FIG. 1, which schematically shows the structure of such a layer).

The use of fiber materials offers two further advantages. On the one hand, a layer crosslinked by fibers is less prone to failure. If, for example, the layer is detached from the metal at one point due to heavy mechanical stress, it will nevertheless adhere to the substrate surface in its entirety, since other sites may still provide sufficient adhesion.

The second advantage lies in the thermal conductivity of the layer. In addition to adhesion and elasticity, this is crucial for the successful implementation of the overall concept. If fibers with a good thermal conductivity are used, the thermal conductivity of the entire layer is increased.

A colloidal binder is necessary as an adhesive to bond together fibers, adsorbent particles and substrate or metal surface at the molecular level. It has the advantage over common adhesives that it does not have to be organic - commercially available adhesives such as eagle owl, epoxy resin, pattex etc. - consist of organic substances with the mentioned disadvantages - nor that it completely pores the adsorbent or can partially bond. A complete bonding of Adsorbentporen is to be avoided when used in a heat pump, because so the adsorbent is prevented from adding or desorbing refrigerant. One possible disadvantage of the technique shown with the aid of fibers to create a partially elastic layer is the possibly generated preferred orientation of fibers by directed shear forces during the application process. Such preferred orientation can cause shrinkage cracks to occur during the drying process of the suspension. In general, the mechanical reinforcement of the adsorbent layer can only take place in the direction of the longitudinal axis of the fibers. However, since the layer is subjected to anisotropic stresses during thermal stress - in all spatial directions - a statistical distribution of the fibers is preferable. Such a statistical distribution can be achieved largely by spraying the suspension onto the respective substrate, which leads to irregularly acting, weak shearing forces. Fibers can no longer orient themselves in this way. A second way is to add a gas generator which is added to the suspension and which is present in the layer homogeneously distributed during the drying process of the suspension and leads to a statistically distributed orientation of the fibers by gas bubble formation. If gas bubbles escape from the still liquid suspension before drying, these lead to an irregular and statistically distributed turbulence of the suspension, as a result of which the fibers present are distributed irregularly as desired. The gas bubble formation additionally leads to a loosening of the dried layer, forming cavities and channels facilitate the diffusion of water molecules, but complicate on the other hand, the heat transport within the layer.

The gas generator must be selected from the group of reactive and / or volatile substances, so that after the drying process of the suspension, no gas is formed which could influence the function of the heat pump. Further advantages and details of the invention are:

1. Firmly adherent layers can be obtained by intimately mixing ground fibers having an average length of about 100 microns and a diameter of 5-12 microns with adsorbent powder and adding an alumina / silica-based colloidal binder. The resulting aqueous suspension is intimately mixed again and then applied to any substrate. After a drying process, these layers adhere to different materials having a hydrophilic surface such as copper, glass, aluminum, porcelain.

2. Firmly adherent layers with increased porosity can be obtained as described in 1. above, when the suspension containing fibers, adsorbent particles and colloidal binder, some hydrogen peroxide and a hydrogen peroxide decomposing catalyst, such as iron (III) chloride is added , Hydrogen peroxide decomposes according to the following equation

H ₂ O ₂ -> H ₂ O + 1/2 O ₂

The resulting oxygen escapes and leads to the drying of the layer to pores, which are about 50 microns in size.

Iron (III) chloride is given here only as an example of a catalyst which decomposes the hydrogen peroxide, there are a large number of further suitable catalysts which can be selected depending on the circumstances. Other examples which may be mentioned are: MnO ₂ , colloidal MnO ₂ , MnCl ₂ , Fe (OH) ₂ , Fe (OH) ₃ , colloidal Fe (OH) ₃ . special In addition, the use of colloidal forms of certain transition metal hydroxides / oxides may be advantageous because they have a high catalytic activity for the decomposition of H ₂ O ₂ , that is to say they have to be added only in very small amounts, and because they have sufficient catalyst particle size can not penetrate into the Adsorbentporen, which could lead to a reduction in performance.

3. Firmly adhering layers with an improved thermal conductivity can be obtained as described under 1, if the fibers used are highly thermally conductive fibers, such as, for example, carbon fibers.

4. Firmly adhering layers with a further improved thermal conductivity can be obtained as described under 1. if carbon nanotubes (or carbon nanotubes) are added in a mass fraction of a few percent and distributed homogeneously in the suspension. Preference is given to using hydrophilized multiwall CNTs (carbon nanotubes).

5. Firmly adhering layers with improved thermal conductivity and with increased porosity can be prepared as under 4. if, in addition to the suspension, some hydrogen peroxide and some iron (III) chloride are added as a decomposition catalyst to the suspension, with iron (III) chloride only one Example of such a decomposition catalyst is (see also point 2).

For the sake of completeness, reference is made to the following prior art:

From DE 10 2006 028 372 Al a heat exchanger is known in which a plurality of fibers with a heat-conducting Adhesive film to be fixed on a wall. According to one embodiment, the individual fibers are coated with a sorbent. An adsorber element or a process in which the adsorber layer is applied in the form of a suspension is not disclosed in this document.

From DE 10 2005 000 022 Al a sorbent molding and a method for its preparation and use is known. The powder used or the granules used are in this solution but not in the form of a layer, but as a so-called heap (mixture of solid particles that are loosely mixed or firmly pressed together or baked) are arranged within a cage.

The adsorber element according to the invention and the method for producing the adsorber element according to the invention will be explained in more detail with reference to some examples.

Examples:

All substrates were carefully cleaned and degreased before coating. Aluminum substrates were degreased with pickling degreasers.

All of the adsorbent layers shown in examples a) to e) adhere firmly to the aluminum sheets used and do not detach from the sheets even under thermal stress. For the first review of the strength achieved in each case, the coated sheets were subjected to several thermal shocks. They were brought in an oven to about 160 ⁰ C and immediately placed in a bucket filled with ice water. Thereafter, the procedure was repeated up to three times. In further experiments, the layers were brought to 2O ⁰ C with the aid of a special test structure to 120 ⁰ C and after 10 minutes. When heating was dry air and when cooling humid air flowed over the samples. After 15,000 cycles of this type, the samples had no stability problems.

The average layer thickness of the created layers is about 350 to 450 micrometers.

The adsorbent content in all the layers shown in the examples including the comparative examples is 70% (by mass) based on fully hydrated adsorbent.

a) Preparation of a firmly adhering molecular sieve layer on aluminum sheet using FAM molecular sieve from Mitsubishi: Nine grams of the hydrated FAM molecular sieve were coated with 2.5 g of ground carbon fibers with a diameter of ~ 7 microns (= μm) and an average length of about 100 microns intimately blurred. 4g deionized water was added. After addition of 4.3 g of aqueous, colloidal, alumina-coated silica having a solids content of 30% (wt.%), The pasty mixture was homogenized by trituration. The resulting suspension was spread on aluminum sheet. The suspension was dried at room temperature. The dried layer was annealed at 150 ^° C. in an oven for 6 to 12 minutes.

b) Preparation of a firmly adhering molecular sieve layer on aluminum sheet using molecular sieve DDZ-70 from UOP: The procedure was as described under a). Instead of FAM molecular sieve from Mitsubishi, the molecular sieve DDZ-70 from UOP was used.

c) Preparation of a firmly adhering molecular sieve layer using molecular sieve FAM from Mitsubishi and glass fibers on aluminum sheet: The process was carried out as described under a). However, instead of carbon fibers ground glass fibers with a diameter of 6 micrometers and a length of about 100 micrometers were used.

d) Preparation of a firmly adhering molecular sieve layer using molecular sieve FAM from Mitsubishi and carbon fibers with an increased porosity on aluminum sheet: The procedure was as described under a), with the difference that before application to aluminum sheet enough hydrogen peroxide and molar iron (III ) chloride solution, so that the finished layer has a sufficient porosity and that after admixing of hydrogen peroxide, the suspension was elapsed within 10 minutes.

e) Preparation of a firmly adhering molecular sieve layer using molecular sieve FAM from Mitsubishi and carbon fibers and carbon nanotubes on aluminum sheet: The preparation of these layers was carried out as described under a), but 0.4 g of a carbon nanotube (CNT) was used instead of 0.4 g of water. containing aqueous solution added. For this, the CNTs were hydrophilized.

f) Preparation of a firmly adhering molecular sieve layer using Mitsubishi's FAM molecular sieve on the substrates glass, copper and porcelain: The procedure was as under a), but the following substrates were coated: standard slides for microscopy, copper sheet and porcelain. The coatings adhere firmly to the respective substrates and can only be removed under strong mechanical action (for example with a chisel). They do not detach from the substrates even under thermal shock load. Thus, the layers shown could be brought to copper sheet to 160 ⁰ C and then dipped in ice water, without it came to a visible change in the layers. With glass and porcelain substrates, this treatment sometimes caused jumping of these ceramic objects. However, the molecular sieve layer remained adhered to the fragments.

g) Comparative example, using molecular sieve DDZ-70 from UOP and high temperature binder sour rice cement no. 8 from SeppZeug GmbH. 4.25g molecular sieve DDZ-70 and 1.83g sour rice cement powder and 5ml deionized water were intimately mixed and 4.4g of this mixture was spread on a 50cm ² degreased aluminum plate. This layer results in numerous, clearly visible shrinkage cracks in the layer.

h) Comparative example, use of molecular sieve FAM from Mitsubishi and high-temperature binder sour rice cement no. 8 from SeppZeug GmbH. The procedure was as in g), but instead of the molecular sieve DDZ-70, the molecular sieve FAM was used. There are also numerous, clearly visible shrinkage cracks in the layer.

i) Comparative example, using molecular sieve DDZ-70 from UOP and high-temperature binder Ceramabond 569 from Kager Industrietechnik GmbH. This binder is a paste. In order to achieve a binder content of 30% in the layer to be created, the solids content of the binder was determined by weighing before and after the setting process. He was determined to 83%. To prepare a layer, 4.25 g of molecular sieve DDZ-70 were moistened with about 1 g of water and intimately mixed with 2.19 g of Ceramabond 569 in a mortar. 4.4 g of this mixture were applied to an area of approximately 50 cm ^{2 of} aluminum. brought sheet metal. After drying numerous shrinkage cracks can be seen, after a slight vibration, the layer falls partially from the sheet.

Comparative example, use of molecular sieve FAM from Mitsubishi and high temperature binder Ceramabond 569 from Kager Industrietechnik GmbH. The procedure was as in Example h). Shrinkage cracks are in contrast to Example i) recognizable only with a magnifying glass, but the layer is only marginally more stable than the one created in Example i), and drops after a slight shock.

LIST OF REFERENCE NUMBERS

1 carrier material

2 binder material

3 adsorbent particles

4 inorganic fibers

4.1 "long" fibers (about 100 microns in length)

4.2 "short" fibers (less than 10 microns in length)

Claims

claims

1. Adsorberelement, comprising a carrier material (1) on which with a binder material (2) Adsorbentpartikel (3) are arranged as adsorber sierberschicht, characterized in that the adsorbent layer applied as a suspension contains inorganic fibers (4) and the binder material (2) is colloidally formed.

2. Adsorberelement according to claim 1, characterized in that the colloidal binder material (2) is formed from an inorganic, inert material.

3. adsorber element according to claim 1 or 2, characterized in that the colloidal binder material (2) optionally consists of silica, alumina or aluminum hydroxide.

4. adsorber element according to one of claims 1 to 3, characterized in that as adsorbent particles (3) optionally zeolite, silica gel, alumina or activated carbon is used.

5. adsorber element according to one of claims 1 to 4, characterized in that the adsorber has a thickness of 300 to 500 microns.

6. adsorber element according to one of claims 1 to 5, characterized in that the adsorber has a mass fraction of Adsorbentpar- particles (3) of more than 50%, preferably 70%, more preferably 80% to 85%.

7. adsorber element according to one of claims 1 to 6, characterized in that the adsorbent layer applied as a suspension contains a gas generator.

8. Adsorberelement according to claim 7, characterized in that the gas generator is optionally formed from a reactive and / or volatile substance.

9. Adsorberelement one of claims 1 to 8, characterized in that the fibers (4) are formed of an inert material.

10. Adsorberelement according to any one of claims 1 to 9, characterized in that, for example, that the fibers (4) are of different lengths.

11. Adsorberelement one of claims 1 to 10, characterized in that the fibers (4) have a length of 80 to 120 micrometers.

12. Adsorberelement one of claims 1 to 11, characterized in that the fibers (4) have a diameter of up to 12 micrometers.

13. Adsorbereiement according to one of claims 1 to 12, characterized in that the fibers (4) have good thermal conductivity, preferably as carbon or glass fibers or carbon nanotubes are formed.

14. adsorber element according to one of claims 1 to 13, characterized in that the carrier material (1) made of metal, in particular aluminum, is formed.

15. A process for producing an adsorber element, wherein adsorbent particles (3) are applied as adsorber layer to a carrier material (1) with a binder material (2), characterized in that the adsorber layer is to be dried as a suspension of the colloidally formed binder material (2). , the adsorbent particles (3) and inorganic fibers (4) are applied to the carrier material (1).

16. The method according to claim 15, characterized in that the suspension on the carrier material (1) optionally sprayed on, painted on or applied by dipping.

17. The method according to claim 15 or 16, characterized in that the suspension of hydrogen peroxide and a hydrogen peroxide decomposing catalyst is added.

18. The method according to any one of claims 15 to 17, dadur ch marked zei chne t, that are added to the suspension in homogeneous distribution and in a mass fraction of a few percent carbon nanotubes.