WO2021230770A1

WO2021230770A1 - Use of agarose as thickener for manufacturing a catalyst

Info

Publication number: WO2021230770A1
Application number: PCT/RU2021/050118
Authority: WO
Inventors: Игорь Михайлович ТУШКАНОВ; Виктор Викторович КЕДРОВ; Павел Иванович ХАЛЬЗОВ; Владимир Николаевич ЗВЯГИН
Original assignee: Общество с ограниченной ответственностью "Экострим"
Priority date: 2020-05-14
Filing date: 2021-04-30
Publication date: 2021-11-18
Also published as: RU2737698C1

Abstract

The group of inventions relates to a method for manufacturing a catalyst and can be used for oxidising ammonia in nitric acid production and for other oxidation processes in the field of the chemical industry. The technical result to be achieved by the group of inventions is to increase adhesion between a catalytic layer and a substrate. The essence of the group of inventions consists in providing a method for manufacturing a catalyst, the method comprising preparing an aqueous solution of a thickener, adding a platinoid compound to said solution, applying the solution produced to the substrate, drying the substrate and annealing the substrate until a metal catalytic layer is obtained thereon, wherein the method is characterized in that agarose is used as the thickener.

Description

[Installed by ISA in accordance with rule 37.2] USE OF AGAROSE AS THICKENER IN CATALYST MANUFACTURING

The group of inventions relates to a method for manufacturing a catalyst and can be used for the catalytic oxidation of ammonia in the production of nitric acid, as well as for other oxidation processes in the chemical industry.

A known method of manufacturing a catalyst, including the sequential deposition on the substrate of a layer of aluminum oxide, a layer of nickel oxide and a layer of platinum, and the layer of platinum is applied from an aqueous solution of a platinum salt with the addition of a thickener in the form of cellulose ether in an amount of up to 1 wt.% Based on the aqueous salt solution platinum [GB1517122, publication date: 12.07.1978, IPC: B01D53 / 94; B01J23 / 89; B01J35 / 04].

As a prototype, a method for manufacturing a catalyst was chosen, which includes two stages, the first stage includes applying an intermediate layer of aluminum oxide to the surface of the substrate, drying and annealing at a temperature of 500 ° C, and the second stage includes applying a catalytic phase in the form of platinum to the intermediate layer of aluminum oxide , which is carried out from an aqueous solution of platinum salt of the following composition, mass. %: platinum salt - 6.0-6.5; ammonia water (25% concentration) - 2.0-4.0; cellulose-based gel-forming additive - 0.7-0.9; Surfactant - 0.1-0.15; water - the rest, [RU2703560, publication date: 10.21.2019, IPC: B01J 37/025, B01J 23/42, B01 J21 / 04].

A common disadvantage of the known technical solutions, including the prototype, is the low adhesion of the metal catalytic layer to the substrate surface. This is due to the fact that the catalytic layer in the technical solution from document GB151712 is applied from a platinum salt solution containing cellulose ether (up to 1%), or, as described in document RU2703560 (prototype), from a platinum salt solution containing a complex of additives based on cellulose and surfactants (more than 1% in total to ensure the required surface wettability and solution viscosity), as a result of which, when drying such a catalytic layer, a bulk precipitate is formed from cellulose ether and platinum compounds or from a mixture of three components: an organic compound based on cellulose, a surfactant and a platinum compound ... Subsequent annealing of the substrate with a layer containing such a bulk deposit leads to the formation of a loose platinum deposit, which does not adhere poorly to the substrate surface. This drawback leads to the subsequent delamination of the metal catalytic layer, as a result of which, during operation, a part of the noble metal is lost from the catalyst surface, which reduces the total volume of the catalytic layer, reducing the working resource of the catalyst and deteriorating its performance characteristics. At the same time, an attempt to reduce the volumetric content of organic substances in the solution leads to a decrease in the viscosity of the solution, which leads to the production of a catalyst with insufficiently high activity and requires multiple deposition of such a solution on the substrate, significantly increasing the resource intensity of the method. Also, this disadvantage leads to a significant increase in the complexity of the method for manufacturing the catalyst, since to achieve the necessary adhesion properties of the metal catalytic layer to the surface of the substrate, before applying the platinoid solution to the substrate, it is necessary to form an intermediate oxide layer on the substrate.

The use of agarose as a thickener for an aqueous solution of a platinoid compound in the manufacture of a catalyst.

A method for preparing a catalyst includes preparing an aqueous solution of a thickener, adding a platinoid compound to this solution, applying the resulting solution to a substrate, drying the substrate, and annealing the substrate until a metallic catalytic layer is obtained thereon. In contrast to the prototype, agarose is used as a thickener.

An aqueous solution of a platinoid compound for obtaining a catalytic layer on a support during the manufacture of a catalyst contains a thickener. Unlike the prototype, agarose is used as a thickener, and the components of the solution are in the following ratio, wt. %: platinoid 0.3-3.0; agarose 0.02-0.20; water; rest.

The catalyst is a supported metal catalytic layer for the oxidation of ammonia or hydrocarbon gases. The substrate is the carrier of the catalytic layer and can be made in the form of nets, plates with holes or foil made of heat-resistant corrosion-resistant metal alloys such as Fechral, Nichrome, Hastelloy, etc. The choice of heat-resistant and corrosion-resistant metal alloys as a substrate material is also due to their ability to on them at high temperatures in air or in oxygen to form protective oxide layers on their surface.

Any platinum group metal with catalytic activity can be used as the platinoid, preferably platinum, palladium, rhodium, or mixtures thereof presented in the form of their water-soluble compounds. Examples of water-soluble compounds of platinum group metals are simple or complex compounds of the cationic or anionic type: palladium nitrate and chloride, rhodium chloride and nitrate, tetramine platinum (II) chloride Pt (NH3) 4Cl2, tetraminepalladium chloride Pd (NH3) 4Cl2, platinum chloride hydrochloric acid H2P (III) ammonium (NH4) 3 [RhCl6], ammonium hexachloroplatinate (IV) (NH4) 2 [PtCl6], aminonitrite metal complexes (NH4) 2Me (NO2) 4, where Pd or Pt can be represented as Me, (NH4 ) 3Rh (NO2) 6, cationic complexes of platinum group metals with organic ligans, etc. The above examples of water-soluble compounds of platinum group metals do not exhaust the list of compounds that can be used in the invention.

The concentration of platinoid in aqueous solution is from 0.3 to 3.0 wt. %. (in terms of metal content), which provides high catalytic properties of the metal layer deposited on the substrate while maintaining a low resource consumption of manufacturing such a catalyst. The amount of metal deposited from an aqueous solution with a platinoid concentration of less than 0.3 wt. %, has a small accessible surface, as a result of which, to obtain sufficient catalytic activity, multiple repetitions of the process of applying such a solution to the substrate will be required. The lower the concentration of the metal in the solution and the lower the concentration of the thickener, the more the multiplicity of repetition of the deposition operation increases to obtain the required catalyst activity. On the other hand, the use of an aqueous solution with a platinoid concentration of more than 3.0 wt. % significantly increases the resource intensity of the catalyst, practically without increasing its catalytic activity. Preferably, the concentration of the platinoid in the aqueous solution can range from 1 to 2.5 wt. %.

Agarose in the form of powder or granules is used as a thickener. The use of agarose provides the required viscosity of an aqueous solution of platinoid when its concentration in solution is an order of magnitude lower than when using other thickeners. This makes it possible to uniformly keep the required volume of an aqueous solution of platinoid on the surface of the substrate with a minimum content of the organic phase in it. Thus, the viscosity of a 1% aqueous solution of agarose is 10-15 cP, which approximately corresponds to the viscosity of a 50% aqueous solution of sucrose. Thus, the use of agarose as a thickener for aqueous solutions containing platinoid makes it possible to reduce the content of organic matter in them by an order of magnitude, which is the cause of low adhesion between the catalytic layer and the substrate after its annealing. Agarose is a linear polysaccharide isolated from a natural mixture of polysaccharides, such as agar-agar, in which the agarose content can reach 80 wt. %. Due to its high agarose content, this mixture has an almost agarose-like ability to form viscous aqueous solutions at very low levels. On this basis, agar-agar can be used as a thickening agent for the aqueous solution.

The concentration of agarose in an aqueous solution of platinoid is from 0.02 to 0.2 wt. %. When the concentration of agarose is below 0.02 wt. % aqueous solution of platinoid has a low viscosity, as a result of which too little platinum metal solution is retained on the surface of the support, which leads to the production of a catalyst with insufficiently high activity and requires multiple deposition of such a solution on the support or an increase in the concentration of platinoid in solution, which together significantly increases the resource intensity of the method ...

When the concentration of agarose is above 0.2 wt. % aqueous solution of platinoid turns out to be too viscous, which leads to the capture of a large volume of solution by the substrate and its uneven distribution on the surface of the substrate. In addition, an increase in the amount of organic matter in solution leads to a weakening of the adhesion of the supported platinum group metal to the substrate. These factors complicate the use of high viscosity platinoid solutions. Preferably, the concentration of agarose in an aqueous solution of platinoid may range from 0.025 to 0.1 wt. %, which gives the optimal ratio between the thickener and platinoid concentrations in the working solution.

Additionally, an aqueous solution of platinoid may contain surfactants to increase the wettability of the substrate, as well as other components that improve the performance of the solution.

The application of an aqueous solution of platinoid to the substrate is carried out by wetting the surface of the substrate and can be performed by spraying an aqueous solution of platinoid over the surface of the substrate or by immersing the substrate in a container with an aqueous solution of platinoid. The latter method makes it possible to obtain a more uniform catalytic layer over the entire surface of the substrate.

The substrate is dried in order to remove water from the volume of solution captured by the substrate and to obtain on the substrate a solid dry precipitate, which is a mixture of the used platinoid compound and the organic phase. Drying of the substrate can be carried out in an oven at a temperature of 80 ° C to 140 ° C for 0.5-2 hours. In a preferred embodiment, drying of the substrate is performed at 110 ° C for 1 hour. The final operation of the method is annealing the dried substrate at an elevated temperature in air for the time required to complete the following processes:

- thermal decomposition of the used platinum group compounds (for example, tetramine platinum (II) chloride Pt (NH3) 4Cl2) with the formation of a catalytically active platinum group metal;

- oxidation (combustion) of organic substances contained in the solution, with the formation of gaseous products (CO, CO2, H2O, etc.); this process can be accelerated by the appearing metallic phase of the platinoid, which transforms this process into catalytic combustion;

- recovery of used compounds of platinoids (for example, platinum-hydrochloric acid, palladium chloride, etc.) by the products of combustion of organic substances.

In this case, annealing can be carried out at temperatures of 500-600 ° C for 0.5-1.5 hours, most preferably 1 hour.

In addition, the method for preparing the catalyst before the step of applying the obtained solution to the support may include the step of oxidizing the support to form an intermediate oxide layer thereon. The oxide layer can be obtained by depositing a solution containing a metal oxide on a metal surface, by chemical vapor deposition of a metal oxide, or the oxide layer can be obtained by preliminary heat treatment of a substrate in air or oxygen. When obtaining an oxide layer by impregnating a support with a suspension containing a metal oxide, agarose can also be used as a thickener for the suspension, and its content in such a solution can be from 0.025 to 0.2 wt. % .. When the oxide layer is obtained by preliminary thermal treatment of the substrate in air or in another gaseous oxygen-containing environment, it is preferable that the metal base is made of heat-resistant and corrosion-resistant metal alloys, such as Fechral, Nichrome, Hastelloy, etc. It should be noted that at high temperature By processing a metal substrate in a gaseous oxygen-containing environment, in addition to the formation of an oxide layer on the surface of the substrate, it is also degreased as a result of the combustion of surface organic matter.

Advantageously, the oxidation of the substrate is performed by thermal treatment of the substrate in air at a temperature of 800 ° C to 1000 ° C for 10-16 hours. In a preferred embodiment, the pre-heat treatment of the substrate is carried out at a temperature of 900 ° C for 12 hours. As a result of this operation, the porosity and specific surface area of the substrate increase, thereby improving the adhesion of the catalytic layer to the substrate surface.

The technical problem to be solved by the group of inventions is the need to improve the operational characteristics of the catalyst.

The group of inventions is characterized by a set of essential features previously unknown from the prior art, characterized in that agarose is used as a thickener for an aqueous solution of platinoid, which, in comparison with other gel-forming substances (thickeners), with its relatively low content in an aqueous solution, gives it a higher viscosity. As a result, when the substrate is annealed, the thickener particles are completely destroyed without the formation of a residue that prevents the adhesion of the metal catalytic layer on the substrate surface. This circumstance plays a decisive role in achieving both the main technical result, which consists in increasing the adhesion between the metal catalytic layer and the substrate, and in achieving an additional technical result, which consists in increasing the service life of the catalyst, thereby improving its operational characteristics.

The technical result to be achieved by the group of inventions is to increase the adhesion between the metal catalytic layer and the substrate.

An additional technical result to be achieved by the group of inventions is to increase the working resource of the catalyst by using agarose as a thickener for an aqueous solution of platinoid.

An additional technical result, to which the group of inventions is directed, is to simplify the method for manufacturing a catalyst by obtaining a catalytically active metal phase on the surface of the substrate in a one-stage process of applying the resulting solution to the substrate.

To illustrate the possibility of implementation and a more complete understanding of the essence of the group of inventions, an embodiment is presented below, which can be changed or supplemented in any way, while the present group of inventions is by no means limited to the presented embodiment.

The group of inventions is implemented as follows.

The preparation of working solutions of platinoids was carried out in two stages. At the first stage, an aqueous agarose solution was obtained by introducing a weighed amount of agarose powder into a given volume of water heated to 80–95 ° C. A magnetic stirrer was used to accelerate the dissolution of the powder. At the second stage, a weighed portion of a water-soluble compound of the platinum group metal was introduced into an agarose solution cooled to room temperature. In some applications, the working solutions contain surfactants. The compositions of the resulting solutions are shown in Table 1.

As substrates, we used plates, wires, and meshes made of Fechrali of Kh23Yu5T composition.

Metal substrates were subjected to preliminary heat treatment at a temperature of 900 ° C for 12 hours in air to obtain an oxide layer with a thickness of at least 1 μm, after which they were coated by immersion with prepared aqueous solutions of platinoid and dried at a temperature of 110 ° C for 1 hour, followed by annealing. at 550 ° C for 1 hour.

The catalytic metal layer obtained by the above method was tested to determine its adhesion strength.

Test 1.

We took substrates in the form of plates made of fechral brand X23Yu5T with dimensions of 150x100x2 mm, tests were carried out using the X-shaped notch method in accordance with GOST 32702.2-2014 as follows.

On the dry surface of the substrate with the applied catalytic layer with a single-edged cutting tool with a blade thickness of 0.43 mm and an edge sharpening angle of 25 °, X-shaped notches were made to the surface of the metal plate, the length of the notches was 55 mm. The angle of intersection of the incisions was 40 °. Then they took an adhesive tape with an adhesive strength of 3 N / cm, a width of 60 mm and a length of 75 mm, and its center was placed on the center of the X-shaped notch, smoothed along sharp corners, pressing it tightly against the coating, and then after 5 minutes it was removed by holding by the free end and smoothly tearing off in 0.5-1.0 s at various angles together with the exfoliated areas of the coating. After that, the appearance of the surface of the cuts of the catalytic coating under good illumination was visually examined using an MBI-2 microscope, on the basis of which the adhesive strength of the applied catalytic coating was evaluated in points.

The results of tests by the X-shaped notch method are presented in Table 2. On their basis, it can be concluded that, in comparison with the catalytic layer made according to the prototype, where cellulose is used as a thickener of an aqueous solution of platinoid, the catalytic layer obtained from an aqueous solution of platinoid with the addition of agarose, it has a higher adhesion to the metal surface.

Test 2.

The test was carried out by bending around a cylindrical rod in a type 2 device in accordance with GOST R 52740-2007.

We took a substrate in the form of a wire made of Fechral brand X23Yu5T with a diameter of 2 mm and processed in accordance with the above method. The obtained substrates with a deposited metal layer in accordance with GOST R 52740-2007 were bent in a type 2 device using steel cylindrical rods of various diameters: 2, 3, 4, 5, 6, 8, 10, 12, 16, 20, 25 and 32 mm with accuracy ± 0.1 mm. Immediately after removing the wire from the type 2 device, the coating at the point of the wire bend was examined under good illumination using an MBI-2 microscope to detect the formed cracks and / or peeling of the coating from the surface.

As a result of tests by the method of bending around a cylindrical rod, it was found that for a wire with a thickness of 2 mm, processed according to the above method, when it is bent around a rod with the smallest diameter equal to 2 mm, the coating remains intact, without cracking and peeling, while as for the same wire made according to the prototype, where cellulose is used as a thickener, uneven partial delamination of the coating is characteristic when the diameters of the cylindrical rod are 2 mm and 3 mm. These tests indicate an increased adhesion strength of the catalytic layer obtained from an aqueous solution of platinoid containing agarose as a thickener.

Table 1. It illustrates aqueous solutions of platinoid for the formation of a catalytic bed on a support in the manufacture of a catalyst.

Solution components	Solution No.
Solution components	1	2	3	4
water-soluble platinum group metal compound	tetramineplatinum (II) chloride Pt (NH3) 4Cl2		palladium chloride	rhodium aminonitrile
platinum group metal, wt. %	1.00	1.50	2.20	3.00
agarose, mass. %	0.025	0.10	0.15	0.20
water	rest

Table 2. It illustrates the results of the X-notch test on the substrate.

Tape separation angle, °	Solution No.
	1	2	3	4	by prototype
	Score
thirty	0	0	0	0	3
45	0	0	0	0	3
60	0	0	0	0	4

Table 3. It illustrates the results of tests by the method of bending a workpiece around a cylindrical bar.

Rod diameter, mm	Solution No.
	1	2	3	4	by prototype
	The presence of traces of destruction
32	-	-	-	-	-
25	-	-	-	-	-
16	-	-	-	-	-
12	-	-	-	-	-
ten	-	-	-	-	-
eight	-	-	-	-	+
6	-	-	-	-	+
5	-	-	-	-	+
4	-	-	-	-	+
3	-	-	-	-	+
2	-	-	-	-	+

The group of inventions can be made from known materials using known means, which indicates its compliance with the criterion of patentability "industrial applicability".

Patent Literature

Patent GB1517122

Patent RU2703560

Claims

The use of agarose as a thickener for an aqueous solution of a platinoid compound in the manufacture of a catalyst.
A method for manufacturing a catalyst, comprising preparing an aqueous solution of a thickener, adding a platinoid compound to this solution, applying the resulting solution to a support, drying the support, and annealing the support to obtain a metal catalytic layer on it, characterized in that agarose is used as a thickener.
The method according to claim 2, characterized in that a mesh of heat-resistant and corrosion-resistant metal alloys is used as the substrate.
The method according to claim 2, characterized in that before the step of applying the obtained solution to the substrate, the substrate is additionally oxidized by means of its heat treatment.
The method according to claim 2, characterized in that the application of an aqueous solution of platinoid and a thickener to the substrate is performed by immersing it in a container with an aqueous solution of platinoid and thickener.
An aqueous solution of a platinoid compound for obtaining a catalytic layer on a support in the manufacture of a catalyst, containing a thickener, characterized in that agarose is used as a thickener, and the components of the solution are in the following ratio, wt. %: platinoid 0.3-3.0; agarose 0.02-0.20; water; rest