A method for catalytic coke cleaning of potassium-based double perovskite oxides

Abstract

The present invention relates to a method for catalytic coke cleaning using potassium-based double perovskite oxides, which includes: preparing a quaternary metal MOFs precursor using potassium salt K, alkaline earth metal nitrate A, rare earth metal nitrate R, and transition metal potassium cyanide T; calcining the obtained quaternary metal MOFs precursor to prepare potassium-based double perovskite oxide AAˊ 1‑x A〞 x B2O6, and the molar ratio of metals in the potassium-based double perovskite oxide is A:Aˊ:A〞:B = 1:(1 - x ): x :2, where 0.01 ≤ x ≤ 0.40; through the catalytic action of the potassium-based double perovskite oxide on the conversion reaction of coke and water vapor, efficient coke cleaning is achieved, and the addition amount of the potassium-based double perovskite oxide is 0.5% - 10.0% of the coke mass. In the process of preparing perovskite oxide according to the present invention, the synthesis temperature is low, energy consumption is saved, and the double perovskite oxide is used in the catalytic conversion reaction of coke and water vapor, and the catalytic conversion of the already formed coke can be realized in-situ.

Description

Technical Field

[0001] The present invention relates to catalytic coke cleaning in the petrochemical field, and specifically to a method for catalytic coke cleaning using potassium-based double perovskite oxides. Background Art

[0002] During the steam cracking process, coke is formed inside the cracking furnace tubes, and this process is called coking. The main reasons for coking are catalytic coking, free radical coking, and polycondensation coking. The formation of coke will cause the cross-sectional area of the ethylene cracking furnace to decrease, the thermal resistance of the furnace tubes to increase, the heat transfer coefficient to decrease, and phenomena such as furnace tube carburization and local overheating to occur, seriously shortening the service life of the furnace tubes and thus affecting the long-term stable operation of ethylene production.

[0003] Currently, there are many methods for removing coke. Mechanical coke cleaning uses a high-pressure water pump to push a coke cleaning ball to reciprocate inside the heating furnace tubes to clean the tubes. This method will generate a large amount of sewage, increasing the treatment cost. High-temperature coke burning removes coke in an air atmosphere. This method requires high energy consumption. Due to the large thickness of the coke, a higher temperature is required, and it may even burn through the furnace tubes. Steam coke cleaning converts coke into carbon oxides in a steam atmosphere. This process does not require shutdown operations and does not affect the normal production of ethylene. Therefore, there is an urgent need to develop an efficient catalytic coke cleaning catalyst.

[0004] Alkali metals are used as catalysts to catalyze coke in a steam environment. However, in the high-temperature cracking process of hydrocarbon vapors, alkali metals are easily lost under the influence of the cracking environment, corroding the furnace tubes, and the use of this catalyst is restricted. Therefore, improving its high-temperature stability is the key.

[0005] It is difficult to remove the coke generated during the ethylene cracking process, and shutdown operations are required, and the coke burning process has high energy consumption. Therefore, in response to the need to remove coke during the ethylene cracking process, the present invention proposes a method for in-situ catalytic coke cleaning using potassium-based double perovskite oxides, which is of great significance for improving the ethylene production cycle. Summary of the Invention

[0006] The object of the present invention is to provide a method for catalytic coke cleaning using potassium-based double perovskite oxides, which is used to solve the problem that it is currently difficult to remove the coke generated during the ethylene cracking process.

[0007] The technical solution adopted by the present invention to solve its technical problems is: This method for catalytic coke cleaning using potassium-based double perovskite oxides includes the following steps:

[0008] Step 1: Prepare a quaternary metal MOF precursor. Dissolve potassium salt K, alkaline earth metal nitrate A, and rare earth metal nitrate R in a certain volume of ethanol solution to obtain solution S1; dissolve transition metal potassium cyanide T in a certain volume of ethanol solution to obtain solution S2; add solution S2 to solution S1, stir evenly, age at room temperature, then perform vacuum filtration and freeze-drying to obtain the quaternary metal MOF precursor.

[0009] Step 2: Calcinate the quaternary metal MOF precursor prepared in Step 1 to prepare a potassium-based double perovskite oxide AAˊ with adjustable morphology, specific surface area, and pore structure 1-x A〞 x B2O6, where A is a rare earth metal element, Aˊ is an alkaline earth metal element, A〞 is a potassium metal element, B is a transition metal element, and the molar ratio of metals in the potassium-based double perovskite oxide is A:Aˊ:A〞:B = 1:(1 - x ) : x : 2, where 0.01 ≤ x ≤ 0.40;

[0010] Step 3: Through the catalytic effect of the potassium-based double perovskite oxide on the reaction of coke and steam conversion, achieve efficient coke cleaning. Add a mixture of the potassium-based double perovskite oxide and coke to a tubular furnace, introduce steam for reaction, and the equilibrium pressure gas is an inert gas. The addition amount of the potassium-based double perovskite oxide is 0.5% - 10.0% of the coke mass, the mass ratio of coke to steam is 1:30 - 1:120, and the coke conversion rate ≥ 99%.

[0011] In the above scheme, the potassium salt K is one of potassium nitrate, potassium chloride, potassium bromide, potassium fluoride, potassium iodide, and potassium chlorate; the alkaline earth metal nitrate A is one of calcium nitrate, magnesium nitrate, barium nitrate, and strontium nitrate; the rare earth metal nitrate R is one of lanthanum nitrate, praseodymium nitrate, neodymium nitrate, and samarium nitrate; the transition metal potassium cyanide T is one of potassium ferrocyanide, potassium cobaltocyanide, and potassium nickel cyanide.

[0012] In the above scheme, in Step 1, the concentration of the rare earth metal nitrate R solution is 2.5 mmol / L - 12.5 mmol / L, the concentration of the alkaline earth metal nitrate A solution is 1.5 mmol / L - 11.3 mmol / L, the concentration of the potassium salt K solution is 0.5 mmol / L - 10.0 mmol / L, and the concentration of the transition metal potassium cyanide T solution is 5.0 mmol / L - 25.0 mmol / L; the mass fraction of ethanol in the solution is 33 wt.% - 67 wt.%, and it ages at room temperature for 6 h - 36 h.

[0013] In the above scheme, the calcination conditions are: in an air atmosphere, the heating rate is 0.5 °C / min - 10 °C / min, the calcination temperature is 500 °C - 700 °C, and the calcination time is 0.5 h - 6 h.

[0014] In the third step of the above solution, the water vapor partial pressure is 1.0×10 4 Pa - 4.0×10 4 Pa, and the mass flow rate of water vapor is 0.025 g / min - 0.267 g / min; the reaction temperature is 700°C - 950°C, and the reaction time is 40 min - 120 min.

[0015] The present invention has the following beneficial effects:

[0016] 1. The present invention utilizes the catalytic effect of potassium-based double perovskite oxides on the reaction of coke with water vapor, introduces metal potassium elements, and at the same time anchors through the lattice structure of the double perovskite to improve the high-temperature stability of its potassium elements, realizing the efficient conversion of coke, solving the bottleneck problems of easy coking and difficult removal in the current ethylene cracking process, and is of great significance for improving the ethylene production cycle.

[0017] 2. In the process of preparing perovskite oxides in the present invention, the synthesis temperature is low, saving energy consumption; the obtained perovskite products have high purity; the morphology, specific surface area and pore structure can be regulated.

[0018] 3. The catalyst regeneration process is simple, has a long service life, and low production cost.

[0019] 4. In view of the characteristics of easy coking in the ethylene production process, the present invention proposes a method of using potassium-based double perovskite oxides for the catalytic conversion reaction of coke with water vapor, which can in-situ realize the catalytic conversion of the generated coke and achieve efficient coke removal. Embodiment

[0020] The following is a further description of the present invention: Example

[0021] Weigh 0.4330 g of La(NO3)3•6H2O, 0.1905 g of Sr(NO3)2•2H2O and 0.0101 g of KNO3 and dissolve them in 80 mL of an ethanol aqueous solution with a mass fraction of 40 wt.%, stir until dissolved to obtain solution S1; weigh 0.6584 g of K3Fe(CN)6•5H2O and dissolve it in 80 mL of an ethanol aqueous solution with a mass fraction of 40 wt.%, stir until dissolved to obtain solution S2. Under rapid stirring, add solution S2 to solution S1, mix the solutions evenly, age them at room temperature for 12 h, then carry out vacuum filtration and freeze drying to prepare a quaternary metal MOFs precursor; put the quaternary metal MOFs precursor into a muffle furnace, introduce air and heat it to 600°C at a rate of 8°C / min, and calcine for 6 h; after the sample is cooled to room temperature, obtain potassium-based double perovskite oxide LaSr 0.9 K 0.1 Fe2O6, and crush it with a ball mill.

[0022] Weigh 0.20 g of coke and 0.01 g of LaSr 0.9 K 0.1 Fe2O6 and put them into a mortar, grind and mix them until uniform, then add them to a fixed-bed tubular furnace reactor for reaction. Under an inert atmosphere, the temperature is programmed to rise to 900 °C, the mass flow rate of the introduced steam is 0.182 g / min, the reaction time is 100 min, and the solid after the reaction (including LaSr 0.9 K 0.1 Fe2O6 and the unreacted coke) is 0.0115 g, and the conversion rate of coke is 99.25%. Example

[0023] Weigh 0.4330 g of La(NO3)3•6H2O, 0.1693 g of Sr(NO3)2•2H2O and 0.0202 g of KNO3, dissolve them in 80 mL of an ethanol aqueous solution with a mass fraction of 50 wt.%, stir until dissolved to obtain solution S1; weigh 0.6584 g of K3Fe(CN)6•5H2O and dissolve it in 80 mL of an ethanol aqueous solution with a mass fraction of 50 wt.%, stir until dissolved to obtain solution S2. Under rapid stirring, add solution S2 to solution S1, mix the solutions evenly, age them at room temperature for 12 h, then perform vacuum filtration and freeze-drying to prepare a quaternary metal MOFs precursor; put the quaternary metal MOFs precursor into a muffle furnace, heat it to 600 °C at a rate of 6 °C / min under air flow, and calcine for 6 h; after the sample is cooled to room temperature, potassium-based double perovskite oxide LaSr 0.8 K 0.2 Fe2O6 is obtained and pulverized with a ball mill.

[0024] Weigh 0.20 g of ethylene cracking furnace coke and 0.01 g of LaSr 0.8 K 0.2 Fe2O6 and put them into a mortar, grind and mix them until uniform, then add them to a fixed-bed tubular furnace reactor for reaction. Under an inert atmosphere, the temperature is programmed to rise to 900 °C, the mass flow rate of the introduced steam is 0.182 g / min, the reaction time is 100 min, and the solid after the reaction (including LaSr 0.8 K 0.2 Fe2O6 and the unreacted coke) is 0.0110 g, and the conversion rate of coke is 99.5%. Example

[0025] Weigh 0.4330 g of La(NO3)3•6H2O, 0.1481 g of Sr(NO3)2•2H2O and 0.0303 g of KNO3, dissolve them in 80 mL of an ethanol aqueous solution with a mass fraction of 50 wt.%, stir until dissolved to obtain solution S1; weigh 0.6584 g of K3Fe(CN)6•5H2O, dissolve it in 80 mL of an ethanol aqueous solution with a mass fraction of 50 wt.%, stir until dissolved to obtain solution S2. Under rapid stirring, add solution S2 to solution S1, mix the solution evenly, age it at room temperature for 12 h, then perform vacuum filtration and freeze-dry to prepare a quaternary metal MOFs precursor; put the quaternary metal MOFs precursor into a muffle furnace, heat it to 600 °C at a rate of 4 °C / min while introducing air, and calcine for 6 h; after the sample is cooled to room temperature, potassium-based double perovskite oxide LaSr 0.7 K 0.3 Fe2O6 is obtained and pulverized using a ball mill.

[0026] Weigh 0.20 g of ethylene cracking furnace coke and 0.01 g of LaSr 0.7 K 0.3 Fe2O6, put them into a mortar, grind and mix until uniform, then add them to a fixed-bed tubular furnace reactor for reaction. Under an inert atmosphere, the temperature is programmed to rise to 900 °C, the mass flow rate of the introduced steam is 0.182 g / min, the reaction time is 100 min, and the solid after the reaction (including LaSr 0.7 K 0.3 Fe2O6 and the unreacted coke) is 0.0116 g, and the coke conversion rate is 99.2%. Example

[0027] Weigh 0.3031 g of La(NO3)3•6H2O, 0.1481 g of Sr(NO3)2•2H2O and 0.0303 g of KNO3, dissolve them in 80 mL of an ethanol aqueous solution with a mass fraction of 40 wt.%, stir until dissolved to obtain solution S1; weigh 0.6646 g of K3Co(CN)6, dissolve it in 80 mL of an ethanol aqueous solution with a mass fraction of 40 wt.%, stir until dissolved to obtain solution S2. Under rapid stirring, add solution S2 to solution S1, mix the solution evenly, age it at room temperature for 12 h, then perform vacuum filtration and freeze-dry to prepare a quaternary metal MOFs precursor; put the quaternary metal MOFs precursor into a muffle furnace, heat it to 600 °C at a rate of 4 °C / min while introducing air, and calcine for 6 h; after the sample is cooled to room temperature, potassium-based double perovskite oxide LaSr 0.7 K 0.3 Co2O6 is obtained and pulverized using a ball mill.

[0028] Weigh 0.20 g of ethylene cracking furnace coke and 0.01 g of LaSr0.7 K 0.3 The Co₂O₆ was placed in a mortar and ground and mixed until uniform, then added to a fixed-bed tubular furnace reactor for reaction. Under an inert atmosphere, the temperature was programmed to rise to 900 °C, steam was introduced with a mass flow rate of 0.182 g / min, the reaction time was 100 min, and the solid after the reaction (including LaSr 0.7 K 0.3 Co₂O₆ and unreacted coke) was 0.0108 g, and the coke conversion rate was 99.6%. Example

[0029] 0.4350 g of Pr(NO₃)₃•6H₂O, 0.1693 g of Sr(NO₃)₂•2H₂O and 0.0202 g of KNO₃ were weighed and dissolved in 80 mL of an ethanol aqueous solution with a mass fraction of 50 wt.%, and stirred until dissolved to obtain solution S1; 0.6646 g of K₂Co(CN)₆ was weighed and dissolved in 80 mL of an ethanol aqueous solution with a mass fraction of 50 wt.%, and stirred until dissolved to obtain solution S2. Solution S2 was added to solution S1 under rapid stirring, the solutions were mixed evenly, aged at room temperature for 12 h, then subjected to vacuum filtration and freeze-drying to prepare a quaternary metal MOFs precursor; the quaternary metal MOFs precursor was placed in a muffle furnace, and air was introduced and heated to 600 °C at 4 °C / min and calcined for 6 h; after the sample was cooled to room temperature, potassium-based double perovskite oxide PrSr 0.8 K 0.2 Co₂O₆ was obtained and crushed with a ball mill.

[0030] 0.20 g of ethylene cracking furnace coke and 0.01 g of PrSr 0.8 K 0.2 Co₂O₆ were placed in a mortar and ground and mixed until uniform, then added to a fixed-bed tubular furnace reactor for reaction. Under an inert atmosphere, the temperature was programmed to rise to 900 °C, steam was introduced with a mass flow rate of 0.182 g / min, the reaction time was 90 min, and the solid after the reaction (including PrSr 0.8 K 0.2 Co₂O₆ and unreacted coke) was 0.0104 g, and the coke conversion rate was 99.8%.

[0031] Double perovskite-type (A₂B₂O₆) oxides have good chemical stability and low cost. The activity of the catalyst can be regulated by changing the types of metals at the A and B sites. Double perovskite oxides have flexible composition and diverse lattice configurations, which can bring rich active sites and electronic structures on the surface of perovskite oxides, providing the possibility for regulating their catalytic active sites.

Claims

1. A method for catalytic coke cleaning of potassium-based double perovskite oxides, characterized in that Including the following steps: Step 1: Prepare a quaternary metal MOF precursor. Dissolve potassium salt K, alkaline earth metal nitrate A, and rare earth metal nitrate R in a certain volume of ethanol solution to obtain solution S1; dissolve transition metal potassium cyanide T in a certain volume of ethanol solution to obtain solution S2; add solution S2 to solution S1, stir evenly, age at room temperature for 6h - 36h, and then obtain the quaternary metal MOF precursor through vacuum filtration and freeze drying. Step 2: Bake the quaternary metal MOFs precursor obtained in Step 1. The baking conditions are as follows: in an air atmosphere, the heating rate is 0.5 °C / min - 10 °C / min, the baking temperature is 500 °C - 700 °C, and the baking time is 0.5 h - 6 h; prepare potassium-based double perovskite oxide AAˊ with adjustable morphology, specific surface area and pore structure 1-x A〞 x B2O6, where A is a rare earth metal element, Aˊ is an alkaline earth metal element, A〞 is a potassium metal element, B is a transition metal element, and the molar ratio of metals in the potassium-based double perovskite oxide is A: Aˊ: A〞:B = 1: (1 - x ) : x : 2, where 0.01 ≤ x ≤ 0.40; Step 3: Achieve efficient coke cleaning through the catalytic effect of potassium-based double perovskite oxides on the reaction of coke with steam. Add the mixture of potassium-based double perovskite oxides and coke to a tubular furnace, introduce steam for reaction, and the equilibrium pressure gas is an inert gas. The addition amount of potassium-based double perovskite oxides is 0.5% - 10.0% of the mass of coke, the mass ratio of coke to steam is 1:30 - 1:120, and the coke conversion rate ≥ 99%.

2. The method for catalytic coke cleaning by potassium-based double perovskite oxide according to claim 1, wherein: The potassium salt K is one of potassium nitrate, potassium chloride, potassium bromide, potassium fluoride, potassium iodide, and potassium chlorate; the alkaline earth metal nitrate A is one of calcium nitrate, magnesium nitrate, barium nitrate, and strontium nitrate; the rare earth metal nitrate R is one of lanthanum nitrate, praseodymium nitrate, neodymium nitrate, and samarium nitrate; the transition metal potassium cyanide T is one of potassium ferrocyanide, potassium cobaltocyanide, and potassium nickel cyanide.

3. The method for catalytic coke cleaning of potassium-based double perovskite oxide according to claim 2, characterized in that: In the third step described above, the water vapor partial pressure is 1.0×10 4 Pa - 4.0×10 4 Pa, the mass flow rate of water vapor is 0.025 g / min - 0.267 g / min; the reaction temperature is 700°C - 950°C, and the reaction time is 40 min - 120 min.