METHOD OF FORMING AN ALUMINOSILICATE-ZEOLITE LAYER ON AN ALUMINIUM-CONTAINING METALLIC SUBSTRATE AND USE OF THE SUBSTRATE OBTAINED THEREBY

Abstract

The invention relates to a method of forming an aluminosilicate zeolite layer on an aluminium-containing metallic substrate composed of metallic aluminium or an aluminium alloy which is introduced into an alkalized aqueous reaction dispersion in which silicon and optionally aluminium are present as network-forming elements, where, irrespective of whether or not aluminium is present in the aqueous reaction dispersion, the molar ratio between the aluminium in the aqueous reaction dispersion and the sum total of the network-forming elements present in the aqueous reaction dispersion is below 0.5, where, when aluminium is not present in the aqueous reaction solution, the deficiency molar ratio is 0, and the alkalized aqueous reaction dispersion containing the aluminium-containing metallic substrate is heated and aluminium is removed from the aluminium-containing metallic substrate for the aluminosilicate zeolite formation process and the layer of an aluminosilicate zeolite is formed on the aluminium-containing metallic substrate by in situ crystallizative application. In the course of this, an aluminium complexing agent with anchoring oxygen atoms is incorporated into the alkalized aqueous reaction dispersion. The invention further relates to the advantageous use of the method product in sorption-based fields of application.

Claims

1. A method of forming an aluminosilicate-zeolite layer on an aluminium-containing metallic substrate of metallic aluminium or an aluminium alloy, which is introduced into an alkalised aqueous reaction dispersion, in which silicon and optionally aluminium are contained as network-forming elements, whereby irrespective of whether aluminium is present in the aqueous reaction dispersion or not, the molar ratio between the aluminium in the reaction dispersion to the total of the network-forming elements contained in the aqueous reaction dispersion is below 0.5, whereby, when aluminium is not present in the aqueous reaction solution, the deficiency molar ratio is 0 and the alkalised aqueous reaction containing the aluminium-containing metallic substrate is heated and aluminium is removed from the aluminium-containing metallic substrate for the aluminosilicate-zeolite formation process and the layer of an aluminosilicate-zeolite is formed on the aluminium-containing metallic substrate by in situ crystallization, characterised in that an aluminium complexing agent with O anchor atoms is incorporated in the alkalised aqueous reaction dispersion.

2. A method as claimed in claim 1, characterised in that the aluminium complexing agent with O anchor atoms constitutes an organic polyacid or its salt in the form of a sodium and/or potassium salt.

3. A method as claimed in claim 2, characterised in that citric acid, tartaric acid, oxalic acid, malonic acid, malic acid and/or maleic acid is used as the organic polyacid or a salt thereof.

4. A method as claimed in claim 1, characterised in an aluminosilicate-zeolite layer is formed on a component, which includes an aluminium-containing metallic layer of aluminium or an aluminium alloy, which has a thickness of more than 0.05 mm.

5. A method as claimed in claim 1, characterised in that, as an additional Al source as well as the aluminium-containing substrate aluminium oxide hydrates, particularly pseudoboehmite and/or sodium aluminate, are used as well as the aluminium contained in the substrate.

6. A method as claimed in claim 1, characterised in that silica, silicates and/or silicic acid esters are used as an Si source.

7. A method as claimed in claim 1, characterised in that potassium hydroxide, basic Na or K salts and/or aluminates are used to produce alkaline conditions in the aqueous reaction dispersion.

8. A method as claimed in claim 1, characterised in that the pH value of the aqueous reaction dispersion is set to more than 9 and/or less than 13.8, when the Al alloy has an Al content of more than 90%.

9. A method as claimed in claim 1, characterised in that the ratio of the surface area of the aluminium-containing substrate to the volume of the aqueous reaction dispersion (in cm.sup.2/cm.sup.3) is set to between 1 and 8.

10. A method as claimed in claim 1, characterised in that those aluminium-rich aluminosilicate-zeolites are formed, in which the Si/Al ratio is less than 10.

11. A method as claimed in claim 1, characterised in that a layer of an aluminium-rich aluminosilicate-zeolite in the form of LTA, FAU, CHA, MOR or GIS is formed on the aluminium-containing substrate.

12. A method as claimed in claim 1, characterised in that the deficiency molar ratio is less than 0.05.

13. A method as claimed in claim 1, characterised in that the aqueous reaction dispersion contains an organic template or organic structure controlling agent, particularly in the form of amines or ammonium salts or crown ethers, is present.

14. A method as claimed in claim 1, characterised in that in the case of colloidal Si and/or Al sources, fluoride salts or hydrofluoric acid are added for their mineralisation.

15. A method as claimed in claim 1, characterised in that the aqueous reaction dispersion is heated to a temperature of 50 to 200 C.

16. A method as claimed in claim 1, characterised in that in order to accelerate the crystal formation in the formation of the aluminium-rich aluminosilicate-zeolite layer, crystal nuclei or an aged gel are added.

17. (canceled)

18. A method for heterogeneous catalysis in one of the following processes, separation and cleaning in sorption heat pumps, in conjunction with immobilised catalysts and in micro-reaction technology wherein the aluminosilicate-zeolite formed in claim 1 is employed.

19. A method as claimed in claim 1, characterised in an aluminosilicate-zeolite layer is formed on a component, which includes an aluminium-containing metallic layer of aluminium or an aluminium alloy, which has a thickness of more than 0.2 mm.

20. A method as claimed in claim 1, characterised in that those aluminium-rich aluminosilicate-zeolites are formed, in which the Si/Al ratio is less than 6.

21. A method as claimed in claim 1, characterised in that the deficiency molar ratio is less than 0.02.

Description

EXAMPLE 1

[0040] A reaction mixture of composition 1.65 Na.sub.2O:1.0 SiO.sub.2:0.5 trisodium citronate:140 H.sub.2O with sodium metasilicate as the silicon source is produced. For component solution 1, a 25% NaOH solution with the required citric acid and half of the water is stirred into it at 600 rpm for 1 h. For component solution 2, the silicon source (98%) is stirred with the remainder of the water, also at 600 rpm for 1 h. Component solution 2 is then added to component solution 1 and the mixture stirred at 800 rpm for 2 h.

[0041] 120 ml PTFE containers were used for the synthesis. Aluminium specimens (with nucleation crystals) are placed in the containers and covered with the reaction solution. The containers are then closed and placed in a preheated oven for 36 h at 95 C.

[0042] After the synthesis, the containers are cooled with water (5-10 min). The coated aluminium specimens are removed and thoroughly washed with water. The specimens are then dried at 75 C.

[0043] Analysis: Zeolite X in the layer formed on the aluminium specimens.

EXAMPLE 2

[0044] A reaction mixture of composition 0.9 Na.sub.2O:1.0 SiO.sub.2:0.5 disodium tartrates:140 H.sub.2O was produced with sodium metasilicate as the silicon source in a manner corresponding to Example 1.

[0045] 120 ml PTFE containers were used for the synthesis. Aluminium specimens (with or without nucleation crystals) are placed in the containers and covered with the reaction solution. The containers are then closed and placed in a preheated oven at 70 C. for 70 h.

[0046] After the synthesis, the containers are cooled with water (5-10 min). The coated aluminium specimens are removed and thoroughly washed with water. The specimens are then dried at 75 C.

[0047] Analysis: Zeolite Y in the layer formed on the aluminium specimens.

[0048] The following figures are to provide a contribution to further understanding of the present invention.

[0049] FIG. 1: shows dissolution of aluminium in the NaOH solution without additives at pH 12.5 with the formation of disadvantageous gibbsite

[0050] FIG. 2: shows aluminium dissolution in the NaOH solution with Na tartrate (complexing agent in accordance with the invention) at pH 12.5. No formation of gibbsite is indicated

[0051] FIG. 3: XRD measurement (x-ray powder diffractometry) on sediment from the reaction of metallic aluminium in 0.9 Na.sub.2O:140 H.sub.2O:x complexing agent (TEothA=triethanolamine, bis-tris=bis-(2-hydroxy-ethyl)-amino-tris(hydroxymethyl)-methane. It may be clearly be seen in FIG. 3 that without complexing agents or with a lower concentration of amine complexing agents undesired gibbsite is produced. With polyacid complexes or a significant excess of triethanolamine pseudoboehmite is produced, which is a common Al source in zeolite synthesis.

[0052] FIG. 4: this relates to XRD measurements on the products of the dissolution of metallic aluminium in alkaline solution at low tartrate concentration. Only pseudoboehmite is formed. The solution corresponds to a zeolite synthesis solution in accordance with the invention but without the required Si source (0.9 Na.sub.2O:0.5 disodium tartrate:140 H.sub.2O)

[0053] FIG. 5: this shows Al NMR spectra of the Al complexes of polyacids a) maleic acid, b) malic acid and c) citric acid.