Knitted net bag and net pile

Abstract

The utility model relates to a knitted net bag, which is used for being inserted into a reactor to convert ammonia into nitric oxide or hydrocyanic acid, the knitted net bag consists of metal wires containing metals selected from Pt, Pd, Rh, Au, Ag, Co, Ni, Ir, Ru, W and alloys thereof, and the knitted net bag is characterized in that at least two nets are connected with each other along the whole circumference in edge areas in a flush manner. The technical result is that by connecting the edge regions of at least two webs during or after the knitting process, the webs are fixed relative to each other, thereby preventing one web from sliding relative to the other. The utility model further relates to a net pile.

Description

Technical Field

[0001] This invention relates to a knitted mesh bag consisting of at least two stacked meshes for converting ammonia into nitrogen oxides or hydrogen cyanide. A pile of meshes having at least one mesh bag is also protected. Background Technology

[0002] Noble metal-catalyzed gaseous reactions, such as the oxidation of ammonia with atmospheric oxygen in nitric acid production (Ostwald process) or the reaction of ammonia with methane in the presence of oxygen to produce hydrogen cyanide (Andrussow process), have long been of considerable industrial significance. These methods have provided large-scale basic chemicals for the chemical industry and fertilizer production (Andreas Jess, Peter Wasserscheid: Chemical Technology; Wiley-VCH Verlag, Weinheim 2013, Chapter 6.4).

[0003] At the heart of these heterogeneous catalytic gas reactions is the noble metal catalyst in a permeable, spatially structured form in which the reaction occurs. For some time now, successful applications have been made in this area using woven (DE4028916C2), braided (DE4300791A1; EP606535A1), or knitted (EP364153B1, DE4206199C1) webs made of fine noble metal wires.

[0004] In this configuration, the catalyst mesh is typically arranged in a flow reactor in a plane perpendicular to the flow direction of the gas mixture. A conical arrangement is also known. Several meshes can be conveniently arranged one after another and combined into a mesh stack.

[0005] The reactant gas or fresh gas (an ammonia-air-oxygen mixture with an ammonia content of 9% to 13% by volume) flows through the grid stack under atmospheric or high pressure, wherein ignition of the gas mixture occurs in the inlet region, and the combustion reaction producing nitric oxide (NO) and water covers the entire reaction zone.

[0006] 4NH3 + 5O2 (air) → 4NO + 6H2O

[0007] Undesirable side reactions include the oxidation of ammonia to nitrogen and nitrous oxide (N₂O). While the former only reduces NO production, the latter is also a potent greenhouse gas.

[0008] 4NH3 + 3O2 (air) → 2N2 + 6H2O

[0009] 4NH3 + 4O2 (air) → 2N2O + 6H2O

[0010] The NO in the outflowing gas mixture then reacts with excess atmospheric oxygen to produce NO2.

[0011] 2NO + O2 → 2NO2

[0012] An undesirable side reaction here is the formation of nitrous oxide:

[0013] 2NO+ 1 / 2O2→2N2O

[0014] NO2 reacts with water during downstream absorption to form nitric acid, for example, in fertilizer production.

[0015] 3NO2 + H2O → 2HNO3 + NO

[0016] Precious metal wires, made of platinum, rhodium, or alloys of these metals with other precious or base metals, are used to produce precious metal meshes. Platinum-rhodium or platinum-palladium-rhodium alloys typically contain 88% to 98% platinum by weight. Platinum is necessary to achieve the highest possible ammonia conversion, while rhodium improves selectivity for NO, thereby reducing nitrous oxide emissions and increasing the mechanical strength of the mesh (GR Maxwell, “Synthetic Nitrogen Products – A Practical Guide to the Products and Processes,” Springer Science + Business Media, Inc. 2005, p. 220). Palladium, in turn, is used to reduce precious metal loss by forming a more stable alloy structure and, depending on current precious metal prices, to reduce precious metal costs by replacing less platinum.

[0017] Several patent publications on the subject of ammonia oxidation have been published. For example, US5266293A describes a woven precious metal fabric in which the precious metal is selected from platinum group metals, gold and silver, and their alloys.

[0018] The previously mentioned DE4206199C1 relates to a method for preparing a noble metal permeable mesh for catalytic oxidation of ammonia. The method uses a noble metal mesh obtained by knitting metal wires, wherein the wires are composed of a platinum-rhodium alloy containing 4 wt% to 12 wt% rhodium or a platinum-palladium-rhodium alloy containing 4 wt% to 12 wt% palladium and rhodium. The diameter of the wires ranges from 50 μm to 120 μm. It can preferably be produced on a plain knitting machine, wherein the pitch (the distance between needles on the plain knitting machine) is between 3.63 mm and 1.81 mm, and the needle length is between 2 mm and 6 mm. Multilayer meshes in a mesh stack can also be advantageously used for the oxidation reaction under consideration (EP680787A1).

[0019] EP364153B1 describes a knitted precious metal mesh for ammonia oxidation. Its stitch width is 10 to 30 stitches per inch. Using a circular knitting machine, a stitch width of 19 stitches per inch is obtained. However, for testing in so-called high-pressure systems, a mesh with a stitch width of 10 to 12 stitches per inch is used.

[0020] WO2004096702A2 proposes an ammonia oxidation method in which the different chemical compositions of the precious metal mesh within the mesh stack are intended to result in lower nitrous oxide yields. In this case, among other things, a mesh stack is used where the mesh facing the fresh gas has a platinum alloy that is more rhodium-rich than the mesh facing the exhaust gas.

[0021] The plain knitting machine (DE4206199C1) is preferably used for knitting precious metal mesh. The plain knitting machine preferably has a front needle bed and a back needle bed, in which the latch needle is installed. Depending on the machine's programming, the latch needle passes through different positions. Therefore, the programming specifies the structure of the knitted fabric. A special feature of the plain knitting machine compared to other fabric forming machines is that it can independently and synchronously form knitted fabrics (single-bed fabrics) on the front and back needle beds.

[0022] Alternatively, for example, a double-layered web can be knitted on a plain knitting machine, where the web layers are joined to each other only at one or both edges. In the case of joined edges, the resulting web can be folded. A single-layered web, twice the size, is then obtained during the knitting process (EP3795728A1). In the case of a double-layered web where both edges are joined, a flexible tube can be formed (EP3680015A1). These must be cut open so that larger web layers can subsequently be formed.

[0023] When knitted webs are transported or inserted into the reactor body for ammonia reaction, the individual webs tend to slide relative to each other. In this case, simple handling of the webs is no longer possible, as they must be aligned relative to each other again. Therefore, it is necessary to specify an appropriate solution that can prevent this drawback. Utility Model Content

[0024] These and other objectives, which are obvious to those skilled in the art from the prior art, are achieved by a knitted mesh bag for insertion into a reactor to convert ammonia into nitrogen oxides or hydrogen cyanide, the knitted mesh bag being composed of metal wires comprising metals selected from Pt, Pd, Rh, Au, Ag, Co, Ni, Ir, Ru, W and alloys thereof, characterized in that at least two meshes are flush with each other along the entire circumference in the edge region.

[0025] Advantageously, the nets are connected to each other by hammer welding, binding, knitting, gluing, and sewing.

[0026] Advantageously, the mesh in the knitted mesh bag has a different metal composition.

[0027] Advantageously, a knitted mesh bag contains two to six meshes joined at the edges.

[0028] Advantageously, the nets in the knitted net bag have different basis weights, measured in g / cm³. 2 .

[0029] Advantageously, the diameter of the metal wire is 60 μm to 150 μm.

[0030] Advantageously, the diameter of the net is 1m to 6.5m.

[0031] These and other objectives, which are obvious to those skilled in the art from the prior art, are achieved by a mesh stack characterized in that the mesh stack has a knitted mesh bag according to the present invention. Attached Figure Description

[0032] Figure 1 The design of the ammonia oxidation flow reactor is shown;

[0033] Figure 2 A side view of a plain knitting machine used for producing webs is shown; and

[0034] Figure 3 The diagram shows three knitted meshes connected to each other by hammer welding at the edge area. Detailed Implementation

[0035] A knitted web package for insertion into a reactor to convert ammonia into nitrogen oxides or hydrogen cyanide is provided, comprising metal wires containing metals selected from Pt, Pd, Rh, Au, Ag, Co, Ni, Ir, Ru, W, and alloys thereof, wherein at least two webs are flush-connected to each other along the entire circumference at their edge regions, providing a very simple solution for achieving the stated purpose. By connecting the edge regions of at least two webs during or after knitting, the webs are secured relative to each other, thus preventing one web from slipping relative to another. Therefore, the webs can be more easily packaged and thus more easily transferred to the corresponding reactor without major reorientation. The webs can also be secured by an additional metal wire in the middle to prevent slippage. This is particularly advantageous for large webs. However, in a preferred embodiment, the connection between the webs occurs only at the edge regions of the webs, and not anywhere in the center. However, the entire edge of the web is interconnected, not just one or two edges (…). Figure 3 ).

[0036] For example, precious metal meshes are preferably used for ammonia oxidation. This is well known to those skilled in the art. Generally, in this case, the precious metals include gold, silver, and platinum (Ru, Rh, Pd, Os, Ir, Pt). The mesh of this invention preferably contains platinum and rhodium. Alloys of these two metals have proven advantageous. For example, one or more precious metal alloy wires containing platinum and rhodium are used to produce precious metal meshes for ammonia oxidation, wherein preferably the alloy contains 80% to 98% by weight of platinum and 2% to 20% by weight of rhodium, more preferably 90% to 98% by weight of platinum and 2% to 10% by weight of rhodium. More preferably, the alloy is selected from PtRh5, PtRh8, PtRh10, PtRh5Pd5, PtRh3, PtRh2, PtRh3.5Pd21.5, and PtRh3.5Pd80. In this case, the numbers in the formula represent the corresponding weight percentage of the component preceding the number. If there is no number after a precious metal element, then the proportion of that precious metal represents the rest of the composition.

[0037] Preferably, during the knitting process, at least two nets are joined together by corresponding knitting actions at the edges of the nets. This possibility is known to those skilled in the art from the prior art. However, the joining of the nets can also preferably be done after knitting. Here, in addition to possible manual knitting actions, other methods known to those skilled in the art can also be used to secure the nets together. For example, these are hammer welding (https: / / application.wiley-vch.de / books / sample / 3527719601_c01.pdf; page 29), binding, gluing, or knitting and sewing as described above.

[0038] It is advantageous to knit two webs simultaneously on the front and back needle beds of a plain knitting machine (DE4206199C1). Figure 2 If the mesh bag has two or more mesh layers, it is preferable to form the bag after knitting the mesh and fix it to the edge using the methods described above. The edge is preferably fixed by a hammer welding process.

[0039] The mesh packs are advantageously combined into larger mesh stacks. Thus, precious metal meshes used in reactors for example, ammonia oxidation, are typically arranged one on top of another in so-called mesh stacks (Optimizing catalyst pack design for ammonia oxidation in Nitrogen & Methanol No. 239, May–June 1999, p. 51ff.; Gierej et al., Investigation of the degradation mechanism of catalytic wires during oxidation of ammonia process, Applied Surface Science 388 (2016), p. 670ff.). Preferably, there are 3 to 35, more preferably 7 to 30, and most preferably 8 to 20 precious metal meshes in a packaged state in the mesh stack. In addition, there are other auxiliary meshes, such as separation meshes and getter meshes (see explanation below; Figure 1 ).

[0040] The meshes within the mesh bundle can be identical. Furthermore, it has proven advantageous if individual precious metal meshes have a certain structure within the mesh bundle or pile, where appropriate. It is advantageous to use precious metal meshes of different compositions in different orders along the gas flow direction. For example, for high-pressure systems, it has proven advantageous if the mesh facing the fresh gas has a higher rhodium content than the mesh facing the exhaust gas. Particularly preferred is that the mesh facing the fresh gas has an alloy, for example, PtRh8, while the mesh facing the exhaust gas has a composition, for example, PtRh5. Therefore, it may be meaningful to use mesh bundles or piles rich in 10% to 50%, preferably 30% to 40%, of rhodium, and that they have 90% to 50%, preferably 70% to 60%, of low rhodium content. It is also preferable to place six precious metal meshes with lower rhodium alloys and up to six meshes, preferably two to four with higher rhodium alloys, in the mesh pile. More preferably, four meshes with higher rhodium content and four meshes with lower rhodium content are installed.

[0041] It has been shown that it is advantageous to install a mesh containing a certain amount of palladium behind the aforementioned precious metal mesh in the mesh bundle along the airflow. In this case, an alloy of Pt and Rh with an additional Pd fraction (e.g., US5656567) is preferred. Besides the lower mesh cost (Pt / Rh is replaced by Pd), the advantages of this mesh bundle or pile configuration are lower N2O emissions and less Pt loss. It has been shown that the Pd content in the Pt / Rh mesh here is preferably 20% to 90% by weight, more preferably 50% to 85% by weight, and most preferably 75% to 83% by weight. Meshes having the following compositions—PtRh1-10Pd20-90, more preferably PtRh2-7Pd40-85, and most preferably PtRh3-5Pd50-85—have proven particularly effective. Preferably, 2 to 10 of these meshes are used in the mesh bundle or pile, more preferably 3 to 8, and most preferably 4 to 6. In general, according to the present invention, it appears to be a very particularly preferred configuration if there are two to six, preferably up to four, meshes (PtRh mesh and PtRhPd mesh) connected at the edges in a package.

[0042] In terms of weight per unit area, different designs of precious metal mesh in a bag or stack are also significant. Advantageously, the mesh in a bag / stack has different weights per unit area, expressed in g / cm³. 2 For example, in high-pressure applications, if the weight per unit area of ​​the mesh facing the fresh gas (g / cm²) 2 The higher unit area weight of the precious metal mesh compared to the exhaust gas side mesh has proven advantageous. In this case, the state of the precious metal mesh can preferably correspond to the state just mentioned. In this case, the ratio of the unit area weight of the first precious metal mesh facing the fresh gas to the unit area weight of the last precious metal mesh facing the exhaust gas is 3:1, preferably 2.5:1, and very preferably 1.5:1. A greater installation weight is provided in the region of increased Pt removal, particularly in the first third of the mesh bundle or stack, which extends the running time with good NO selectivity. In the region of lower Pt removal, i.e., in the latter half of the mesh bundle or stack, less precious metal is bonded (due to the lower unit area weight), which overall reduces the amount of expensive precious metal bonded, thereby helping to reduce the investment cost of the mesh bundle / stack.

[0043] The wire mesh used here has a certain thickness. First, it cannot be too thin, otherwise it will easily break; second, it should not be too thick, otherwise the surface area to amount of the precious metal will be too unfavorable for the catalytic reaction. It has been shown that it is advantageous for the wire mesh to have a thickness of >60 μm and <150 μm, more preferably 70 μm to 110 μm, and most preferably 70 μm to 90 μm.

[0044] The mesh used in the flow reactor has dimensions corresponding to the reactor. The mesh is advantageously circular. Alternatively, the mesh can also be square. Preferably, it is quadrilateral or octagonal, and particularly preferably square. If the mesh is circular, its diameter is from 1 m to 6.5 m, preferably from 1.7 m to 5.6 m, and most preferably from 2.6 m to 5.3 m. If the quadrilateral or octagonal mesh is the focal point, then the diagonals are also located within the aforementioned framework.

[0045] One or more precious metal meshes may consist of monofilaments. However, one or more meshes may also be composed of wires consisting of several individual wires. The wires of a precious metal mesh may, for example, be constructed as sheathed wires and consist of a core and one or more sheathed wires arranged radially symmetrically over another. In this regard, refer to the statement in EP3900826A1.

[0046] Alternatively, the wires of one or more precious metal meshes may consist of twisted monofilaments. If it is advantageous for the wires to consist of twisted monofilaments, the twisted monofilaments comprise an array of n interwoven monofilaments, where n is an integer of 2 ≤ n ≤ 8. In this regard, refer to the statement in EP3523024A1.

[0047] As described above, precious metal mesh is used in a mesh stack in a flow reactor. A flow reactor is a reactor that ensures the reaction gas passes through a mesh stack installed therein. In this case, one or more precious metal meshes are preferably followed by a getter mesh and optionally a separator mesh. The mesh stack preferably consists essentially only of a connected precious metal catalyst mesh on the inlet side (fresh gas side = the front half of the mesh stack in the gas flow direction), and optionally a getter mesh on the outlet side (exhaust gas side = the rear half of the mesh stack in the gas flow direction), and optionally a separator mesh may be installed between the precious metal mesh and / or the getter mesh.

[0048] The mesh whose catalytic activity is used for the reaction of ammonia and oxygen is called a precious metal mesh. A getter mesh is a mesh incorporated into the reaction gas stream on the outlet side of the catalyst mesh to capture volatile platinum oxide for recovery by forming an alloy with, for example, palladium in the getter mesh, thus minimizing platinum loss. Volatile rhodium can also be captured in this manner in a certain proportion and then recovered. The separation mesh is preferably made of, for example, high-temperature stabilized steel, and is installed between the precious metal meshes or packings to prevent the precious metal meshes from sintering together.

[0049] The getter mesh is composed, for example, of an alloy containing 90 to 98 wt% palladium and 2 to 10 wt% nickel. Other compositions have been proposed (e.g., EP216493A1). Upon request, a support mesh, so-called a separation mesh, made of high-temperature stable steel, can be installed in or below the catalytic noble metal mesh stack or the getter mesh stack to increase the long-term stability of the entire mesh stack.

[0050] As a result of this arrangement, if the mesh stack is installed in a flow reactor with the fresh gas side as the inlet and the exhaust gas side as the outlet, the mesh stack can be used in such a way that the reactant gases react only on the precious metal mesh, and the sublimated platinum is subsequently deposited again on the getter mesh. This deposition can be further improved if the getter mesh also has 16 to 20 pins / inch. Therefore, when using a mesh stack with one or more precious metal meshes to oxidize ammonia, it is preferable to have one or more, preferably two to four, meshes downstream for depositing volatile platinum or rhodium.

[0051] One or more net bags according to the present invention, having nets connected at the edges, can be inserted relatively easily into this type of net stack without the nets sliding relative to each other, making them difficult to insert into the reactor. Similarly, there is no risk of incorrect installation sequence. Furthermore, installation can be completed more quickly. Another significant advantage is that the nets no longer easily slip out of the edge area of ​​the reactor due to pressure. Therefore, the present invention also relates to a net stack having at least one knitted net bag according to the present invention.

[0052] Figure 1 Taking catalytic ammonia oxidation (Ostwald process) as an example, a reactor with an internally installed mesh stack is schematically shown, the function of which is described below:

[0053] In the reaction zone (2) of the flow reactor (1), a mesh stack (3) is arranged in a plane perpendicular to the flow direction. The mesh stack consists of several catalyst meshes (4) arranged sequentially on the inlet side and a downstream separation and getter mesh (5). The mesh stack maintains its position by locking.

[0054] The reaction gas (an ammonia-air-oxygen mixture with an ammonia content of 9% to 13% by volume) (6) flows through the grid stack (3) at atmospheric or high pressure, wherein the ignition of the gas mixture occurs in the inlet area and the combustion reaction that produces nitric oxide (NO) and water (i.e., product (7)) covers the entire reaction zone (2).

[0055] exist Figure 2 In this type of knitting machine, there is a front needle bed (8) and a back needle bed (9), in which latch needles (10) are installed. The latch needles pass through different positions according to the machine's programming. Therefore, the structure of the knitted fabric is predetermined by the programming. A special feature of the knitting machine compared to other knitting machines is that it can form knitted fabrics (single-bed fabrics) simultaneously and independently of each other on the front and back needle beds. In addition, spaced-out knitted fabrics (double-bed fabrics) can be formed, in which the yarn alternately forms stitches or double knits (EP1358010 B2). The knitted fabric is knitted downwards between the two needle beds to complete the knitted product (11). This is achieved by continuously binding off (Abketten) individual stitches at the binding position and binding edge (12).

[0056] Figure 3 The diagram shows a mesh stack according to the present invention. Reference numeral (13) indicates the edge of the mesh stack, where the individual meshes are welded together. Region (14) refers to the reaction zone of the mesh stack.

[0057] List of reference numerals :

[0058] 1. Flow reactor,

[0059] 2. Reaction zone,

[0060] 3. Mesh stack,

[0061] 4. Catalyst mesh,

[0062] 5. Getter net,

[0063] 6. Reaction gases,

[0064] 7. Products

[0065] 8. Front needle bed,

[0066] 9. Rear needle bed,

[0067] 10. Tongue acupuncture

[0068] 11. Knitted products,

[0069] 12. Finish the edges.

[0070] 13. The edge of the mesh stack,

[0071] 14. Reaction zone of the mesh reactor.

Claims

1. A knitted mesh bag for insertion into a reactor to convert ammonia into nitrogen oxides or hydrogen cyanide, the knitted mesh bag being composed of metal wires. Its features are, At least two nets are connected to each other flush along the entire circumference in the edge region.

2. The knitted mesh bag according to claim 1, Its features are, The meshes are connected to each other by hammer welding, binding, knitting, gluing, and sewing.

3. The knitted mesh bag according to claim 1 or 2, Its features are, The mesh in the knitted mesh bag has a different metal composition.

4. The knitted mesh bag according to claim 1 or 2, Its features are, A knitted mesh bag contains two to six meshes joined at the edges.

5. The knitted mesh bag according to claim 1 or 2, Its features are, The meshes in the knitted mesh bags have different basis weights, measured in g / cm³. 2 .

6. The knitted mesh bag according to claim 1 or 2, Its features are, The diameter of the metal wire is 60µm to 150µm.

7. The knitted mesh bag according to claim 1 or 2, Its features are, The diameter of the net is between 1m and 6.5m.

8. A mesh stack, characterized in that, The mesh stack has at least one knitted mesh bag according to any one of claims 1 to 7.

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