DE102006025683A1 - Method of applying catalytically active material, directly to heat exchanger internal surfaces without use of a carrier layer uses streamless deposition (ELP) or chemical gas phase deposition (CVD) - Google Patents

Abstract

Method of applying catalytically active material, especially 10 and 11 group elements (VIIIA, 1B) to heat exchanger internal surfaces. The material is applied directly to the heat exchanger surfaces without use of a carrier layer by streamless deposition (ELP) or chemical gas phase deposition (CVD). Before deposition the heat exchanger internal surfaces can be roughened by chemical acid treatment and/or oxidation.

Description

The The invention relates to a method for the application of catalytic active material, in particular elements of the 10th and 11th group (VIIIA, IB), on the inner surfaces of heat exchangers.

When Reactors to carry Endo- or exothermic reactions on an industrial scale can be recuperative working heat exchangers be used. The substances to be transposed through channels of these Directed recuperators, these channels act as reaction spaces. On the other side of the walls forming the reaction spaces flows a medium with suitable heat capacity, through which the heat of reaction added or removed becomes. Reactors of this type are thus in reaction chambers and Subdivided heat transport spaces. Often located in a reactor several reaction spaces, which through heat transport spaces from each other are separated and flowed through by the substances to be reacted in parallel.

inadequate heat dissipation in exothermic reactions and insufficient heat in endothermic reactions result in a heterogeneous temperature distribution within the reaction spaces. If the reactions are supported catalytically, already small temperature differences lead to considerable Shifts in reaction rates and change the selectivity performance. It is therefore possible a uniform temperature distribution desirable. In this way, the reactions can be controlled and the formation of by-products are suppressed. Already an increase in selectivity The response in the range of a few tenths of a percent is usually associated with significant economic benefits in industrial processes.

reactors (e.g., for heterogeneous catalytic gas phase reactions), which are based on the principle of the plate heat exchanger are built today are manufactured with very small plate intervals, one as possible high power density (catalytic effective area based on the reactor volume) too receive. The catalytically active material (for example palladium or silver) is applied to the sides of the plates containing the Facing reaction chambers are. Order for to provide a homogeneous temperature profile perpendicular to the plates and the heat transfer To improve from and to the plates, so-called fins can additionally be incorporated into the reaction spaces become. These fins are common as well coated with a catalytically active material and thereby enlarge the chemically active surface in the reaction chambers.

According to the prior art, a porous layer of an oxide ceramic material (eg Al ₂ O ₃ ) as a later carrier substance for the catalytically active materials is applied to the inner surfaces of plate heat exchangers by immersion (wet impregnation) and fixed by various treatments. This support layer can fulfill a variety of tasks, such as the enlargement of the surfaces to be coated. After the carrier layer has been applied, the actual coating with the catalytic active materials is carried out by conventional impregnation or impregnation methods. A weak point of this method is the often limited adhesion of the oxide ceramic support layer on the heat exchanger surface, which often leads to delamination associated with a loss of catalytic activity and significant operational problems due to the blockage of the narrow heat exchanger channels by chipped fragments. In addition, it is very difficult to achieve a homogeneous layer thickness distribution of the carrier layer during the immersion in the narrow heat exchanger channels.

Of the The present invention is therefore based on the object, a method of the above type so that a controlled Coating the inner surfaces of heat exchangers with catalytically active materials in an economical way and without the disadvantages of the prior art allows.

These Task is inventively characterized solved, that without the application of a carrier layer, the catalytic active materials by electroless plating (ELP) or chemical Gas phase deposition (CVD) applied directly to the heat exchanger surfaces become.

The The above-mentioned coating methods are normally used around layers of material on an outer surface of a Object (substrate) to produce. For this purpose, the to be coated substrate surface in contact with liquid solutions (ELP) or with a gas atmosphere (CVD), in which contain the materials to be deposited are. A prerequisite for the production of homogeneous layers is the homogeneous composition of these solutions (ELP) or the gas atmosphere (CVD) over the entire substrate surface to be coated.

Electroless plating (ELP) deposits materials on the surface of a substrate due to an autocatalytic reaction. For this purpose, the substrate to be coated upper surface in a first step by the application of metal particles whose sizes are in the nanometer range activated. Subsequently, the substrate surface is brought into contact with a solution in which the ions of the materials to be deposited are dissolved. By addition of a reducing agent (eg hydrazine (N ₂ H ₄ )), the dissolved ions are reduced at the previously activated substrate surface, whereby a layer grows under suitable coating conditions (substrate activation, composition and temperature of the solution, exposure time). The geometry of the object does not affect the thickness and quality of the deposited layer when coated by ELP. Decisive for the layer structure are primarily the composition of the solution containing the ions, which is in contact with the substrate surface, as well as the activation of the substrate surface. By making sure that this composition is the same throughout the solution and the activation is homogeneous throughout the substrate surface to be coated, the metal is deposited evenly on irregularly shaped objects, along edges, and even in cavities.

A provides further technique for applying layers of material to surfaces chemical vapor deposition (CVD). by sublimation or evaporation in the gas phase transferred compounds, which for the needed the layer Materials contain (precursor), with a carrier gas over the hot surface to be coated (substrate surface) passed. The temperature of the substrate surface is chosen so that under the prevailing conditions decomposition of the precursors at the substrate surface takes place and the metallic elements are deposited on the surface.

According to the invention, it is proposed that fluid media, in the course of the chosen coating process in contact with the inner surfaces to be coated heat exchanger need to be brought and from which substances are deposited on these surfaces (solutions), passed through the heat exchanger channels become. By a suitable combination of flow rate and deposition rate, be in all places of the inner surfaces to be coated heat exchanger nearly same deposition conditions generated.

to execution the method according to the invention is preferably a CVD technique applied, as in a non-prepublished patent application described under the file number 10309359.1 at the German Patent and Trademark Office and the disclosure of which is hereby incorporated by reference the disclosure of the present patent application included becomes. With this technique it is possible to evenly coat large surfaces, if they are not flat. The control of the deposition is predominantly by the amount of an organic solubilizer that is on the to be coated substrate surface is applied in a pretreatment step.

Around to increase the adhesion of the catalytically active materials sees the inventive method before that the inner surfaces the heat exchanger pretreated. Preferably, this pretreatment is carried out by chemical roughening (acid treatment) and / or oxidation.

The proposed method is preferred according to the invention for coating the inner surfaces of aluminum plate heat exchangers used with catalytically active materials.

Claims (4)

Method for applying catalytically active material, in particular elements of groups 10 and 11 (VIIIA, IB), to the inner surfaces of heat exchangers, characterized in that, without the application of a carrier layer, the catalytically active materials are formed by electroless plating (ELP) or chemical vapor deposition (CVD) applied directly to the heat exchanger surfaces. Method according to claim 1, characterized in that that fluid media out of which the coating materials on the surfaces depart, in the course of the chosen The deposition process thereby in contact with the inner to be coated surfaces of the plate heat exchanger be brought that they are passed through the channels of the heat exchanger. Method according to one of claims 1 or 2, characterized that the inner surfaces to be coated before the actual coating by chemical roughening (acid treatment) and / or oxidation pretreated. Use of the method according to the invention for coating the inner surfaces made of aluminum plate heat exchangers with catalytic active materials.