Catalyst system and method for the catalytic combustion of ammonia to form nitrogen oxides in a medium-pressure system

Patent metadata

Field	Value
Publication number	US-12378115-B2
Application number	US-202017309891-A
Country	US
Kind code	B2
Filing date	Jan 9, 2020
Priority date	Jan 14, 2019
Publication date	Aug 5, 2025
Grant date	Aug 5, 2025

Abstract

Known catalyst systems for the catalytic combustion of ammonia to form nitrogen oxides consist of a plurality of single- or multilayer catalyst gauzes warp-knitted, weft-knitted or woven from platinum-based noble metal wire, which, when arranged one behind the other in a fresh gas flow direction, form a front group of gauze layers and at least one downstream group of gauze layers arranged after the front group. To provide from this starting point a catalyst system for use in a medium-pressure plant for ammonia oxidation, with which a high service life and a high yield of the main product NO can be achieved, it is proposed that the front group comprises a gauze layer or a plurality of gauze layers made of a first, rhodium-rich noble metal wire, wherein the gauze layer or one of the gauze layers made of the rhodium-rich noble metal wire is a front gauze layer facing the fresh gas, and that the downstream group comprises gauze layers made of a second, rhodium-poor noble metal wire, wherein the rhodium content in the rhodium-rich noble metal wire is at least 7 wt. % and no more than 9 wt. % and is at least 1 percentage point higher than the rhodium content in the rhodium-poor noble metal wire.

First claim

The invention claimed is:

1. A catalyst system for the catalytic combustion of ammonia to form nitrogen oxides in a medium-pressure plant, having a plurality of single- or multilayer catalyst gauzes warp-knitted, weft-knitted or woven from platinum-based noble metal wire, which, when arranged in a fresh gas flow direction, form a front group of gauze layers and at least one downstream group of gauze layers arranged after the front group, characterized in that the front group comprises at least one gauze layer made of a first, rhodium-rich noble metal wire, wherein the at least one gauze layer made of the rhodium-rich noble metal wire is a front gauze layer facing the fresh gas, and in that the downstream group comprises gauze layers made of a second, rhodium-poor noble metal wire, wherein the rhodium-rich noble metal wire contains at least 7 wt. % and no more than 9 wt. % rhodium, and wherein the rhodium-poor noble metal wire contains 4 to 6 wt. % rhodium, and wherein each of the rhodium-rich noble metal wire and the rhodium-poor noble metal wire consist of platinum and rhodium.

2. The catalyst system of claim 1 , wherein the rhodium-rich noble metal wire contains 7.8 to 8.2 wt. % rhodium and the rhodium-poor noble metal wire contains 4.8 to 5.2 wt. % rhodium.

3. The catalyst system of claim 1 , wherein the front group of the gauze layers has a proportion by weight of less than 30% of all the catalyst gauzes in a catalyst pack.

4. The catalyst system of claim 1 , wherein the front group comprises no more than three gauze layers.

5. The catalyst system of claim 1 , wherein the front group of gauze layers is formed by a frontmost gauze layer.

6. The catalyst system of claim 5 , wherein the frontmost gauze layer lies on the gauze layers of the downstream group.

7. The catalyst system of claim 1 , wherein the catalyst gauzes arranged in the fresh gas flow direction form a catalyst pack composed of a front assembly with three catalyst gauzes having a first average grammage, and a downstream assembly of catalyst gauze layers arranged behind the front assembly having a second average grammage.

8. The catalyst system of claim 7 , wherein the average grammage of the front assembly has a weight reduction ranging from 1.5% to 29% relative to the second average grammage, the first average grammage is in the range of 410 to 530 g/m 2 , and the second average grammage is in the range of 540 to 790 g/m 2 .

9. The catalyst system of claim 7 , wherein the catalyst gauzes of the front assembly consist of a warp-knitted fabric with a first warp-knit pattern and a first mesh size, or of a woven fabric with a first weave pattern and a first mesh size, or of a weft-knitted fabric with a first weft-knit pattern and a first mesh size, and the catalyst gauzes of the downstream assembly consist of a warp-knitted fabric with a second warp-knit pattern and a second mesh size, or of a woven fabric with a second weave pattern and a second mesh size, or of a weft-knitted fabric with a second weft-knit pattern and a second mesh size, wherein the first mesh size is greater than the second mesh size.

10. The catalyst system of claim 7 , wherein an individual grammage of the catalyst gauze layers of the front assembly is constant or increases in the fresh gas flow direction.

11. The catalyst system of claim 1 , wherein the front group of the gauze layers has a proportion by weight of less than 25% of all the catalyst gauzes in a catalyst pack.

12. The catalyst system of claim 1 , wherein the front group of the gauze layers has a proportion by weight of less than 20% of all the catalyst gauzes in a catalyst pack.

13. The catalyst system of claim 8 , wherein the weight reduction is no more than 25%, the first average grammage is in the range of 415 to 510 g/m 2 , and the second average grammage is in the range of 575 to 710 g/m 2 .

14. The catalyst system of claim 7 , wherein the catalyst system further comprises one or more getter gauzes downstream of the catalyst pack.

15. The catalyst system of claim 14 , wherein the one or more getter gauzes are composed of Pd82.5Pt15Rh2.5.

16. The catalyst system of claim 3 , wherein the catalyst system further comprises one or more getter gauzes downstream of the catalyst pack.

17. The catalyst system of claim 16 , wherein the one or more getter gauzes are composed of Pd82.5Pt15Rh2.5.

Assignees

• Heraeus Deutschland Gmbh & Co Kg

Inventors

• Boll Willi
• Maier Dirk

Classifications

• B01J35/58

  Fabrics or filaments · CPC title

• B01J35/19 Primary

  Catalysts containing parts with different compositions · CPC title

• D10B2403/0242

  enhancing chemical properties · CPC title

• D10B2101/20

  Metallic fibres · CPC title

• D04B21/20

  specially adapted for knitting articles of particular configuration · CPC title