Preparation method of Pt-Pd coating slurry and Pt-Pd coating

Abstract

The invention discloses a preparation method of Pt-Pd coating slurry and a Pt-Pd coating. The coating can inhibit the inner wall of the EDC cracking furnace pipe from coking. The coating effectively isolates catalytic active sites on the metal surface from being in contact with a coking matrix, and the carbon deposition resistance is excellent; a coke layer and H2 generated by reaction can be catalyzed to generate redox reaction, so that the thickness of the coke layer is reduced; the coating is uniform in thickness, has the characteristics of excellent heat transfer performance, high temperature resistance, difficulty in falling off and simplicity in manufacturing, and is suitable for harsh conditions of high-temperature cracking processes such as dichloroethane, ethylene and petrochemical engineering.

Description

Technical Field

[0001] This invention belongs to the field of coking suppression in high-temperature organic pyrolysis units, and relates to a slurry for preparing an anti-coking coating by spraying it onto the metal surface of a pyrolysis device and a method for preparing the coating. Background Technology

[0002] Polyvinyl chloride (PVC) is the world's third-largest produced synthetic polymer plastic. The main PVC production process currently involves the addition of ethylene to dichloroethane (EDC), followed by pyrolysis to produce vinyl dichloroethylene (VCM), which is then further polymerized to produce PVC. Coking in the EDC pyrolysis furnace is a significant factor inhibiting VCM capacity growth and stable operation. The main functions of the EDC pyrolysis furnace are: at 500-600℃, EDC is pyrolyzed to produce VCM using a high-temperature resistant chromium-nickel alloy. At high temperatures, iron and nickel atoms in the alloy migrate to the surface, causing EDC and pyrolysis byproducts to accumulate on the equipment surface. Under further catalysis by metal ions, coke is formed and ultimately deposited on the equipment surface, increasing the furnace's heat transfer coefficient and affecting energy consumption; it also affects the furnace's gas flow rate and feedstock throughput; in more severe cases, coking can clog pipelines, affecting gas flow and leading to a systemic shutdown.

[0003] Currently, there are few reports on anti-coking methods for EDC pyrolysis furnaces. Drawing on anti-coking approaches from other processes, the main methods for inhibiting coking both domestically and internationally include: adding inhibitors to the pyrolysis feedstock, designing and developing furnace tubes with excellent anti-coking properties, and preparing coatings on the inner wall of the furnace tubes. Among these, the inhibitor method requires continuous injection with the feedstock, resulting in high costs; the manufacture of new pyrolysis furnace tubes requires complex smelting processes and manufacturing equipment, and is only suitable for the construction and installation of new pyrolysis furnaces or the retrofitting of in-service pyrolysis furnaces. Preparing an anti-coking coating on the inner wall of the pyrolysis furnace tubes through chemical treatment is not only simple and inexpensive, but also utilizes existing utilities in the pyrolysis furnace area, and allows for repeated coating of in-service furnace tubes without affecting product distribution and yield.

[0004] There are some reports on pyrolysis furnace coatings, such as CN102046846B and CN103857971A, which describe how adding alloying elements to the coating can improve the surface's exfoliation and adhesion properties, but none of them can promote carbon transfer of the generated carbon on the surface. Summary of the Invention

[0005] The purpose of this invention is to provide a low-cost precious metal coating slurry that can effectively inhibit coking in iron-chromium-nickel alloy pyrolysis furnace tubes. The coating prepared by this slurry promotes coke decomposition and resists coking during the coking process. In this reaction system, not only can the peelability of coke in pipes and equipment be increased, but carbon transfer within the system can also be promoted, reducing the thickness of the coke layer.

[0006] To achieve the aforementioned objective, the present invention employs the following technical solution:

[0007] A method for preparing a Pt-Pd coating slurry to inhibit coking in iron-chromium-nickel alloy pyrolysis furnace tubes includes the following steps:

[0008] (1) Prepare an aqueous solution of Pd(NO3)2·2H2O, PtN2O6, and Mn(NO3)3·4H2O, add ethylene glycol and citric acid to it, stir to prepare a gel, dry and calcine;

[0009] (2) The product obtained in step (1) is ground and sieved to obtain powder;

[0010] (3) Mix the powder with aluminum dihydrogen phosphate solution, and then add polyvinyl alcohol to prepare a slurry.

[0011] In step (1) of the present invention, the gel is prepared at a temperature of 80-100℃, preferably 90℃, and the stirring time is 11-13h, preferably 12h.

[0012] In step (1) of the present invention, the roasting temperature is 1100-1300℃, preferably 1200℃, and the roasting time is 1-3h, preferably 2h.

[0013] In step (1) of this invention, the aqueous solution contains Pd(NO3)2 at a concentration of 0.0001-0.045 mol / L, PtN2O6 at a concentration of 0.005 mol / L, Mn(NO3)3·4H2O at a concentration of 0.05 mol / L, ethylene glycol at a concentration of 0.0689-0.125 mol / L, and citric acid at a concentration of 0.0689-0.125 mol / L.

[0014] As a preferred embodiment, the molar ratio of Pt:Pd is 1:9-9:1, the molar concentration of Pt is 0.005 mol / L, the molar concentration of Mn is 0.05 mol / L, and the molar ratio of metal cations to ethylene glycol and citric acid in the solution is (3.5-4.5):(4.5-5.5):(4.5-5.5).

[0015] In step (2) of the present invention, the particle size of the powder is 20-40 μm.

[0016] As a preferred embodiment, the aluminum dihydrogen phosphate aqueous solution of the present invention has a mass fraction of 50%.

[0017] As a preferred embodiment, in step (3) of the present invention, the mass ratio of the powder to the aluminum dihydrogen phosphate solution is 1:100.

[0018] As a preferred embodiment, the slurry of the present invention comprises the following components:

[0019] Powder content: 0.98 wt%;

[0020] A 50% aqueous solution of aluminum dihydrogen phosphate, 97.02 wt%;

[0021] Polyvinyl alcohol 2 wt%.

[0022] A Pt-Pd coating for inhibiting coking in iron-chromium-nickel alloy pyrolysis furnace tubes is prepared by the following steps:

[0023] (a) Spray the slurry onto the pretreated surface;

[0024] (b) After the sprayed sample has dried and cured, heat it to 500-550℃ at a heating rate of 5℃ / min and keep it at that temperature for 1 hour;

[0025] (c) Then heat to 800-850℃ at a heating rate of 10℃ / min and hold for 2 hours to finally obtain the noble metal coating.

[0026] As a preferred embodiment, in step (a) of the present invention, the spraying is carried out using a spray gun with a pressure set to 0.5-0.6 MPa, a nozzle distance of 20-50 cm from the sample, and the spraying is carried out until the surface is uniform.

[0027] Compared with the prior art, the advantages of the present invention are as follows: the coating used in the present invention inhibits coking in the furnace tubes of the pyrolysis furnace, and the resulting coating effectively isolates the catalytically active metal ions on the metal surface from contact with the coking matrix, thereby improving the anti-coking performance; the palladium and platinum metal ions contained in the coking coating can catalyze the already formed coke layer to undergo an oxidation-reduction reaction with H2, thereby reducing the amount of coke accumulation. Detailed Implementation

[0028] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0029] Example 1

[0030] Pd(NO3)2·2H2O, PtN2O6, and Mn(NO3)3·4H2O were dissolved in deionized water, and ethylene glycol and citric acid were added to the aqueous solution. The molar concentration of PtN2O6 was 0.005 mol / L, and the molar concentration of Mn(NO3)3·4H2O was 0.05 mol / L. The molar ratio of Pd(NO3)2·2H2O to PtN2O6 was 1:9, and the molar ratio of metal cations to ethylene glycol and citric acid in the solution was 4:5:5. The solution was heated at 90°C and stirred for about 12 hours to form a gel. The gel was dried in an oven for 12 hours, and then calcined in a muffle furnace at 1200°C for 6 hours to obtain the palladium-platinum material required for coating.

[0031] The material is ground and sieved to obtain palladium-platinum metal powder. The palladium-platinum metal powder is mixed with a 50% aluminum dihydrogen phosphate solution at a mass ratio of 1:100. Then, 2% PVA is added to the mixture and stirred until a slurry is formed. The slurry is sprayed onto a pre-treated surface. After the sprayed sample dries and cures, the temperature is increased to 500-550℃ at a heating rate of 5℃ / min and held for 1 hour; then increased to 800-850℃ at a heating rate of 10℃ / min and held for 2 hours, finally obtaining a precious metal coating.

[0032] After being coated with this anti-coking precious metal coating, under conditions of 480℃, 1.2MPag, and an EDC residence time of 15s in the tube, and an EDC pyrolysis rate of 55% for 8 hours, the coking amount was 2.40g, and the total methane in the tail gas was 1.06g. This can achieve a 40% reduction in the amount of pyrolyzed coke generated in the EDC (dichloroethane) pyrolysis furnace and a coke conversion rate of 50%.

[0033] Example 2

[0034] Pd(NO3)2·2H2O, PtN2O6, and Mn(NO3)3·4H2O were dissolved in deionized water, and ethylene glycol and citric acid were added to the aqueous solution. The molar concentration of PtN2O6 was 0.005 mol / L, and the molar concentration of Mn(NO3)3·4H2O was 0.05 mol / L; the molar ratio of Pd(NO3)2·2H2O to PtN2O6 was 1:3, and the molar ratio of metal cations to ethylene glycol and citric acid in the solution was 4:5:5. A gel was prepared, which was then dried to produce a palladium-platinum material. The drying process of the prepared mixed solution was as follows: heating at 90℃ and stirring for about 12 h to form a gel. The gel was dried in an oven for 12 h, and then calcined in a muffle furnace at 1200℃ for 6 h to obtain the palladium-platinum material required for coating.

[0035] The material is ground and sieved to obtain palladium-platinum metal powder. The palladium-platinum metal powder is mixed with a 50% aluminum dihydrogen phosphate solution at a mass ratio of 1:100. Then, 2% PVA is added to the mixture and stirred until a slurry is formed. The slurry is sprayed onto a pre-treated surface. After the sprayed sample dries and cures, the temperature is increased to 500-550℃ at a heating rate of 5℃ / min and held for 1 hour; then increased to 800-850℃ at a heating rate of 10℃ / min and held for 2 hours, finally obtaining a precious metal coating.

[0036] After being coated with this anti-coking precious metal coating, under conditions of 480℃, 1.2MPag, 15s residence time in the tube for EDC, and 55% EDC pyrolysis rate, the coking amount was 2.0g and the total methane in the tail gas was 1.6g. This can reduce the amount of pyrolyte produced by the EDC (dichloroethane) pyrolysis furnace by 50% and achieve a coke conversion rate of 60%.

[0037] Example 3

[0038] Pd(NO3)2·2H2O, PtN2O6, and Mn(NO3)3·4H2O were dissolved in deionized water, and ethylene glycol and citric acid were added to the aqueous solution. The molar concentration of PtN2O6 was 0.005 mol / L, and the molar concentration of Mn(NO3)3·4H2O was 0.05 mol / L; the molar ratio of Pd(NO3)2·2H2O to PtN2O6 was 1:1, and the molar ratio of metal cations to ethylene glycol and citric acid in the solution was 4:5:5. A gel was prepared, which was then dried to produce a palladium-platinum material. The drying process of the prepared mixed solution was as follows: heating at 90℃ and stirring for about 12 h to form a gel. The gel was dried in an oven for 12 h, and then calcined in a muffle furnace at 1200℃ for 6 h to obtain the palladium-platinum material required for coating.

[0039] The material is ground and sieved to obtain palladium-platinum metal powder. The palladium-platinum metal powder is mixed with a 50% aluminum dihydrogen phosphate solution at a mass ratio of 1:100. Then, 2% PVA is added to the mixture and stirred until a slurry is formed. The slurry is sprayed onto a pre-treated surface. After the sprayed sample dries and cures, the temperature is increased to 500-550℃ at a heating rate of 5℃ / min and held for 1 hour; then increased to 800-850℃ at a heating rate of 10℃ / min and held for 2 hours, finally obtaining a precious metal coating.

[0040] After being coated with this anti-coking precious metal coating, under conditions of 480℃, 1.2MPag, and an EDC residence time of 15s in the tube, and an EDC pyrolysis rate of 55% for 8 hours, the coking amount was 1.60g, and the total methane in the tail gas was 2.24g. This can achieve a 60% reduction in the amount of pyrolyte produced by the EDC (dichloroethane) pyrolysis furnace and a coke conversion rate of 70%.

[0041] Example 4

[0042] Pd(NO3)2·2H2O, PtN2O6, and Mn(NO3)3·4H2O were dissolved in deionized water, and ethylene glycol and citric acid were added to the aqueous solution. The molar concentration of PtN2O6 was 0.005 mol / L, and the molar concentration of Mn(NO3)3·4H2O was 0.05 mol / L; the molar ratio of Pd(NO3)2·2H2O to PtN2O6 was 3:1, and the molar ratio of metal cations to ethylene glycol and citric acid in the solution was 4:5:5. A gel was prepared, which was then dried to produce a palladium-platinum material. The drying process of the prepared mixed solution was as follows: heating at 90°C and stirring for about 12 hours to form a gel. The gel was dried in an oven for 12 hours, and then calcined in a muffle furnace at 1200°C for 6 hours to obtain the palladium-platinum material required for coating.

[0043] The material is ground and sieved to obtain palladium-platinum metal powder. The palladium-platinum metal powder is mixed with a 50% aluminum dihydrogen phosphate solution at a mass ratio of 1:100. Then, 2% PVA is added to the mixture and stirred until a slurry is formed. The slurry is sprayed onto a pre-treated surface. After the sprayed sample dries and cures, the temperature is increased to 500-550℃ at a heating rate of 5℃ / min and held for 1 hour; then increased to 800-850℃ at a heating rate of 10℃ / min and held for 2 hours, finally obtaining a precious metal coating.

[0044] After being coated with this anti-coking precious metal coating, under conditions of 480℃, 1.2MPag, and an EDC residence time of 15s in the tube, and an EDC pyrolysis rate of 55% for 8 hours, the coking amount was 1.40g, and the total methane in the tail gas was 2.25g. This can achieve a 65% reduction in the amount of pyrolyzed coke generated in the EDC (dichloroethane) pyrolysis furnace and a coke conversion rate of 65%.

[0045] Example 5

[0046] Pd(NO3)2·2H2O, PtN2O6, and Mn(NO3)3·4H2O were dissolved in deionized water, and ethylene glycol and citric acid were added to the aqueous solution. The molar concentration of PtN2O6 was 0.005 mol / L, and the molar concentration of Mn(NO3)3·4H2O was 0.05 mol / L. The molar ratio of Pd(NO3)2·2H2O to PtN2O6 was 9:1, and the molar ratio of metal cations to ethylene glycol and citric acid in the solution was 4:5:5. A gel was prepared, which was then dried to produce a palladium-platinum material. The drying process of the prepared mixed solution was as follows: heating at 90°C and stirring for about 12 hours to form a gel. The gel was dried in an oven for 12 hours, and then calcined in a muffle furnace at 1200°C for 6 hours to obtain the palladium-platinum material required for coating.

[0047] The material is ground and sieved to obtain palladium-platinum metal powder. The palladium-platinum metal powder is mixed with a 50% aluminum dihydrogen phosphate solution at a mass ratio of 1:100. Then, 2% PVA is added to the mixture and stirred until a slurry is formed. The slurry is sprayed onto a pre-treated surface. After the sprayed sample dries and cures, the temperature is increased to 500-550℃ at a heating rate of 5℃ / min and held for 1 hour; then increased to 800-850℃ at a heating rate of 10℃ / min and held for 2 hours, finally obtaining a precious metal coating.

[0048] After being coated with this anti-coking precious metal coating, under conditions of 480℃, 1.2MPag, and an EDC residence time of 15s in the tube, and an EDC pyrolysis rate of 55% for 8 hours, the coking amount was 1.28g, and the total methane in the tail gas was 2.17g. This can achieve a 68% reduction in the amount of pyrolyzed coke generated in the EDC (dichloroethane) pyrolysis furnace; and a coke conversion rate of 60%.

[0049] Comparative Example

[0050] The small-scale device without the anti-coking metal coating was operated at 480℃ and 1.2 MPa for 8 hours with EDC residence time of 15 s in the tube and an EDC cracking rate of 55%. The coking amount was 4 g and the methane product in the cracking products was 0 g.

Claims

1. A method for preparing a Pt-Pd coating slurry, comprising the following steps: (1) Prepare an aqueous solution of Pd(NO3)2·2H2O, PtN2O6, and Mn(NO3)3·4H2O, add ethylene glycol and citric acid to it, stir to prepare a gel, dry and calcine; (2) The product obtained in step (1) is ground and sieved to obtain powder; (3) Mix the powder with aluminum dihydrogen phosphate solution, and then add polyvinyl alcohol to prepare a slurry.

2. The method according to claim 1, characterized in that, In step (1), the gel is prepared at a temperature of 80-100℃, preferably 90℃, and the stirring time is 11-13h, preferably 12h.

3. The method according to claim 1 or 2, characterized in that, In step (1), the roasting temperature is 1100-1300℃, preferably 1200℃, and the roasting time is 1-3h, preferably 2h.

4. The method according to any one of claims 1-3, characterized in that, In step (1), the aqueous solution contains Pd(NO3)2 at a concentration of 0.0001-0.045 mol / L, PtN2O6 at a concentration of 0.005 mol / L, Mn(NO3)3·4H2O at a concentration of 0.05 mol / L, ethylene glycol at a concentration of 0.0689-0.125 mol / L, and citric acid at a concentration of 0.0689-0.125 mol / L.

5. The method according to any one of claims 1-4, characterized in that, The molar ratio of Pt to Pd is 1:9-9:1, with a molar concentration of Pt of 0.005 mol / L and a molar concentration of Mn of 0.05 mol / L. The molar ratio of the metal cation to ethylene glycol and citric acid in the solution is (3.5-4.5):(4.5-5.5):(4.5-5.5).

6. The method according to any one of claims 1-5, characterized in that, In step (2), the particle size of the powder is 20-40 μm.

7. The method according to any one of claims 1-6, characterized in that, The mass fraction of the aluminum dihydrogen phosphate aqueous solution is 50%; and / or, in step (3), the mass ratio of the powder to the aluminum dihydrogen phosphate solution is 1:

100.

8. The method according to any one of claims 1-7, characterized in that, The slurry comprises the following components: Powder content: 0.98 wt%; A 50% aqueous solution of aluminum dihydrogen phosphate, 97.02 wt%; Polyvinyl alcohol 2 wt%.

9. A Pt-Pd coating for inhibiting coking in iron-chromium-nickel alloy pyrolysis furnace tubes, the preparation method of which includes the following steps: (a) Spraying the slurry according to any one of claims 1-8 onto the pretreated surface; (b) After the sprayed sample has dried and cured, heat it to 500-550℃ at a heating rate of 5℃ / min and keep it at that temperature for 1 hour; (c) Then heat to 800-850℃ at a heating rate of 10℃ / min and hold for 2 hours to finally obtain the noble metal coating.

10. The coating according to claim 9, characterized in that, In step (a), the spraying is done with a spray gun, the pressure is set to 0.5-0.6 MPa, the distance between the nozzle and the sample is 20-50 cm, and the spraying is done until the surface is uniform.