A process for the conversion of lower alkanes
By preparing a mixed catalyst of hydrofluoric acid and metal-modified ZSM-5 molecular sieve with Y-type molecular sieve, the problem of low utilization efficiency of low-carbon alkanes in steam cracking process was solved, achieving efficient conversion of low-carbon alkanes and improving ethylene production yield.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DALIAN INSTITUTE OF CHEMICAL PHYSICS CHINESE ACADEMY OF SCIENCES
- Filing Date
- 2024-11-29
- Publication Date
- 2026-05-29
AI Technical Summary
In existing steam cracking processes, the ethylene yield from naphtha is low, and the utilization efficiency of low-carbon alkanes such as isobutane and n-butane is not high, which limits the economic benefits of ethylene production.
A catalyst was prepared by mixing ZSM-5 molecular sieve modified with hydrofluoric acid and metal with Y-type molecular sieve and then aging it through hydrothermal aging. This catalyst is used for the conversion of low-carbon alkanes, including isobutane and n-pentane, and forms a highly efficient and stable catalyst.
It improves the conversion rate of low-carbon alkanes, especially isobutane, thereby increasing the yield and economic benefits of ethylene production. The catalyst is simple to prepare and the reaction conditions are easy to control.
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Abstract
Description
Technical Field
[0001] This application relates to a method for converting low-carbon alkanes, belonging to the field of chemical engineering. Background Technology
[0002] Ethylene, propylene, and butadiene produced by steam cracking are fundamental raw materials for the petrochemical industry, widely used in the production of synthetic materials such as plastics, rubber, and fibers. Ethylene is the most in-demand basic chemical raw material among these three olefins; 95% of the world's ethylene production is achieved through steam cracking, and China's domestic steam cracking capacity accounts for over 80% of the total ethylene production capacity. Steam cracking to produce ethylene is a non-catalytic thermal processing method, and the ethylene yield is determined by the overall composition of the feedstock. In China, the main feedstock for steam cracking units is naphtha, but the ethylene yield from naphtha cracking is typically only around 30%, far lower than that of ethane (approximately 80%) and propane (approximately 40%). Low-carbon hydrocarbons are an important component of naphtha; pre-converting them to ethane and propane before feeding them into the steam cracking unit can significantly improve the ethylene yield.
[0003] Isobutane can only be used as a fuel, except for its use in the production of alkylated gasoline, while its isomer n-butane shows significant potential in chemical applications. When using light hydrocarbons as feedstock for ethylene production via steam cracking, n-butane offers higher overall economic benefits, with an ethylene yield three times that of isobutane. Summary of the Invention
[0004] According to one aspect of this application, a method for converting low-carbon alkane is provided, characterized in that...
[0005] Includes the following steps:
[0006] In a reactor under a hydrogen atmosphere, a raw material containing low-carbon alkanes is brought into contact with a catalyst and reacted to obtain a product containing small-molecule hydrocarbons.
[0007] The catalyst is obtained through the following steps:
[0008] (1) Mix ZSM-5 molecular sieve with fluorosilicic acid, heat, filter, wash, dry I, calcine I, to obtain substance I;
[0009] (2) Mix substance I with an equal volume of an aqueous solution containing a metal salt, dry II, and calcine II to obtain substance II;
[0010] (3) Mix substance II with Y-type molecular sieve, aluminum source, nitric acid and water, knead, extrude into strips, shape, let stand, dry (III), and calcine (III) to obtain substance III.
[0011] (4) Subject III is aged with water vapor to obtain the catalyst.
[0012] The catalyst has the characteristics of high catalytic activity, good selectivity, and low deactivation.
[0013] The mass ratio of ZSM-5 molecular sieve to fluorosilicic acid is 1:3 to 20.
[0014] The heating temperature is 50–80°C;
[0015] The heating time is 1 to 5 hours;
[0016] The temperature of the drying process I is 30–120°C;
[0017] The drying time for step I is 1 to 12 hours;
[0018] The temperature of the calcination I is 300–600°C;
[0019] The roasting time for the first roasting step is 1 to 12 hours.
[0020] The metal salt is selected from at least one of ferric nitrate, zirconium nitrate, cerium nitrate, or silver nitrate;
[0021] The concentration of the metal salt in the aqueous solution containing the metal salt is 0.1–0.5 wt%.
[0022] The temperature of the drying II process is 30–120°C;
[0023] The drying time for step II is 1–12 hours;
[0024] The temperature of calcination II is 300–600°C;
[0025] The roasting time for the second stage is 1 to 12 hours.
[0026] The aluminum source is selected from at least one of boehmite, aluminum hydroxide, sodium aluminate, aluminum sulfate, and aluminum isopropoxide.
[0027] The mass fraction of the nitric acid is 1-5%;
[0028] The mass ratio of ZSM-5 molecular sieve to aluminum source is 1:4 to 10, and the mass of aluminum source is based on the mass of Al2O3 therein.
[0029] The settling period refers to 12 hours of settling at room temperature.
[0030] The temperature of the drying III process is 30–120°C;
[0031] The drying time for step III is 1–12 hours;
[0032] The temperature of calcination III is 300–600°C;
[0033] The roasting time for the third stage is 1 to 12 hours.
[0034] The steam aging time is 0.1 to 10 hours;
[0035] In the water vapor aging process, the mass ratio of water vapor to substance III is 0.5 to 5:1.
[0036] The reactor is selected from fixed-bed reactors, moving-bed reactors, or fluidized-bed reactors.
[0037] The low-carbon alkane is a C4-C6 isoalkane, selected from at least one of isobutane, n-pentane, isopentane, and 2,3-dimethylbutane;
[0038] The small molecule hydrocarbons are selected from at least one of ethane, propane, and n-butane.
[0039] The mass hourly space velocity (MSV) of the low-carbon alkanes in the feedstock is 0.1–10 h⁻¹. -1 ;
[0040] The molar ratio of hydrogen to low-carbon alkanes in the raw material is 0.2 to 10:1.
[0041] The reaction temperature is 250–500°C;
[0042] The reaction is carried out at a pressure of 0.1–10 MPa.
[0043] The catalyst is pre-reduced with hydrogen.
[0044] The hydrogen pre-reduction process involves a hydrogen volume hourly space velocity (VHSV) of 100–10000 h⁻¹. -1 ;
[0045] The temperature for hydrogen pre-reduction is 200–600°C;
[0046] The hydrogen pre-reduction time is 0.2 to 1000 h.
[0047] The beneficial effects that this application can produce include:
[0048] (1) This application provides a simple and efficient method for preparing a low-carbon hydrocarbon conversion catalyst. The method involves mixing hydrofluoric acid and metal-modified ZSM-5 molecular sieve with Y-type molecular sieve, followed by hydrothermal aging to obtain a low-carbon hydrocarbon conversion catalyst with high catalytic activity and strong stability. The preparation method is simple and the reaction conditions are easy to control.
[0049] (2) This application presents a simple process with easily controllable reaction conditions, providing a convenient and efficient method for preparing a low-carbon hydrocarbon conversion catalyst. This catalyst can effectively catalyze the conversion of isobutane under mild conditions. The catalyst of this invention exhibits excellent reaction performance in the isobutane conversion reaction, including high isobutane conversion rate and high selectivity for high-quality steam cracking feedstocks (ethane, propane, and n-butane), under mild reaction conditions. The operation is simple, and the catalyst is easy to prepare and recyclable. Detailed Implementation
[0050] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.
[0051] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.
[0052] Example 1
[0053] (1) Weigh 30g of ZSM-5 molecular sieve, place it in a 1%wt silicofluoric acid solution, treat it in a laboratory reactor at 50℃ for 2h, then wash it with deionized water, dry it at 120℃ for 12h, and calcine it at 350℃ for 2h.
[0054] (2) The modified ZSM-5 molecular sieve was mixed with an equal volume of ferric nitrate aqueous solution. The concentration of the ferric nitrate aqueous solution was calculated as 0.2% of the mass of iron element in the ZSM-5 molecular sieve. After mixing, the mixture was dried at 120℃ for 12h and calcined at 350℃ for 2h.
[0055] (3) After mixing the molecular sieve obtained in step (2) with an equal mass of Y-type molecular sieve, a certain amount of pseudoboehmite is added, wherein the mass of pseudoboehmite is ZSM-5:Al2O3 = 1:4, and 10g of 1%wt dilute nitric acid is added. The mixture is then kneaded, extruded, and shaped. The shaped sample is dried at 120℃ for 12h and calcined at 450℃ for 2h.
[0056] (4) The catalyst obtained above was subjected to steam treatment at 600℃, with the steam content to catalyst mass ratio being 1:1 to obtain catalyst 1. # .
[0057] Example 2
[0058] (1) Weigh 30g of ZSM-5 molecular sieve, place it in a 2% wt silicic acid solution, treat it in a laboratory reactor at 60℃ for 2h, then wash it with deionized water, dry it at 120℃ for 12h, and calcine it at 350℃ for 2h.
[0059] (2) The modified ZSM-5 molecular sieve was mixed with an equal volume of cerium nitrate aqueous solution. The concentration of the cerium nitrate aqueous solution was calculated as 0.2% of the mass of iron in the ZSM-5 molecular sieve. After mixing, the mixture was dried at 120°C for 12 hours and calcined at 350°C for 2 hours.
[0060] (3) After mixing the molecular sieve obtained in step (2) with a certain mass of Y-type molecular sieve (mass ratio ZSM-5:Y = 2:1), a certain amount of pseudoboehmite is added, wherein the mass ratio of pseudoboehmite is ZSM-5:Al2O3 = 1:4, and 10g of 1%wt dilute nitric acid and 5g of deionized water are added. The mixture is then kneaded, extruded, and shaped. The shaped sample is dried at 120℃ for 12h and calcined at 450℃ for 2h. (4) The catalyst obtained above is treated with steam at 600℃ for 2h, and the steam content is 1:1 with the mass ratio of the catalyst to obtain catalyst 2. # .
[0061] Example 3
[0062] (1) Weigh 30g of ZSM-5 molecular sieve, place it in a 3%wt silicofluoric acid solution, treat it in a laboratory reactor at 65℃ for 2h, then wash it with deionized water, dry it at 120℃ for 12h, and calcine it at 400℃ for 2h.
[0063] (2) The modified ZSM-5 molecular sieve was mixed with an equal volume of cerium nitrate aqueous solution. The concentration of the cerium nitrate aqueous solution was calculated as 0.2% of the mass of iron in the ZSM-5 molecular sieve. After mixing, the mixture was dried at 120°C for 12 hours and calcined at 350°C for 2 hours.
[0064] (3) After mixing the molecular sieve obtained in step (2) with a certain mass of Y-type molecular sieve (mass ratio ZSM-5:Y = 2:1), a certain amount of pseudoboehmite is added, wherein the mass ratio of pseudoboehmite is ZSM-5:Al2O3 = 1:6, and 10g of 1%wt dilute nitric acid and 5g of deionized water are added. The mixture is then kneaded, extruded, and shaped. The shaped sample is dried at 120℃ for 12h and calcined at 450℃ for 2h. (4) The catalyst obtained above is treated with steam at 600℃ for 2h, and the steam content is 2:1 to obtain catalyst 3. # .
[0065] Example 4
[0066] (1) Weigh 30g of ZSM-5 molecular sieve, place it in a 4%wt silicofluoric acid solution, treat it in a laboratory reactor at 65℃ for 2h, then wash it with deionized water, dry it at 120℃ for 12h, and calcine it at 400℃ for 2h.
[0067] (2) The modified ZSM-5 molecular sieve was mixed with an equal volume of zirconium nitrate aqueous solution. The concentration of the zirconium nitrate aqueous solution was calculated as 0.2% of the mass percentage of zirconium element in ZSM-5 molecular sieve. After mixing, the mixture was dried at 120℃ for 12h and calcined at 350℃ for 2h.
[0068] (3) After mixing the molecular sieve obtained in step (2) with a certain mass of Y-type molecular sieve (mass ratio ZSM-5:Y = 3:1), a certain amount of pseudoboehmite is added, wherein the mass ratio of pseudoboehmite is ZSM-5:Al2O3 = 1:6, and 10g of 1%wt dilute nitric acid and 5g of deionized water are mixed, kneaded, extruded and shaped. The shaped sample is dried at 120℃ for 12h and calcined at 450℃ for 2h. (4) The catalyst obtained above is treated with steam at 600℃ for 2h, and the steam content to catalyst mass ratio is 2:1 to obtain catalyst 4. # .
[0069] Example 5
[0070] (1) Weigh 30g of ZSM-5 molecular sieve, place it in a 5% wt silicic acid solution, treat it in a laboratory reactor at 70℃ for 2h, then wash it with deionized water, dry it at 120℃ for 12h, and calcine it at 450℃ for 2h.
[0071] (2) The modified ZSM-5 molecular sieve was mixed with an equal volume of ferric nitrate aqueous solution. The concentration of the ferric nitrate aqueous solution was calculated as 0.2% of the mass of iron element in the ZSM-5 molecular sieve. After mixing, the mixture was dried at 120℃ for 12h and calcined at 350℃ for 2h.
[0072] (3) After mixing the molecular sieve obtained in step (2) with a certain mass of Y-type molecular sieve (mass ratio ZSM-5:Y = 4:1), a certain amount of pseudoboehmite is added, wherein the mass ratio of pseudoboehmite is ZSM-5:Al2O3 = 1:8, and 10g of 1%wt dilute nitric acid and 5g of deionized water are mixed, kneaded, extruded and shaped. The shaped sample is dried at 120℃ for 12h and calcined at 450℃ for 2h. (4) The catalyst obtained above is treated with steam at 600℃ for 2h, and the steam content to catalyst mass ratio is 4:1 to obtain catalyst 5. # .
[0073] Example 6
[0074] (1) Weigh 30g of ZSM-5 molecular sieve, place it in a 6%wt silicofluoric acid solution, treat it in a laboratory reactor at 75℃ for 2h, then wash it with deionized water, dry it at 120℃ for 12h, and calcine it at 450℃ for 2h.
[0075] (2) The modified ZSM-5 molecular sieve was mixed with an equal volume of ferric nitrate aqueous solution. The concentration of the ferric nitrate aqueous solution was calculated as 0.2% of the mass of iron element in the ZSM-5 molecular sieve. After mixing, the mixture was dried at 120℃ for 12h and calcined at 350℃ for 2h.
[0076] (3) After mixing the molecular sieve obtained in step (2) with a certain mass of Y-type molecular sieve (mass ratio ZSM-5:Y = 4:1), a certain amount of pseudoboehmite is added, wherein the mass ratio of pseudoboehmite is ZSM-5:Al2O3 = 1:8, and 10g of 1%wt dilute nitric acid and 10g of deionized water are added. The mixture is then kneaded, extruded, and shaped. The shaped sample is dried at 120℃ for 12h and calcined at 450℃ for 2h. (4) The catalyst obtained above is treated with steam at 600℃ for 3h. The ratio of steam usage to catalyst mass is 6:1. # .
[0077] Example 7
[0078] (1) Weigh 30g of ZSM-5 molecular sieve, place it in a 7%wt silicofluoric acid solution, treat it in a laboratory reactor at 80℃ for 2h, then wash it with deionized water, dry it at 120℃ for 12h, and calcine it at 450℃ for 2h.
[0079] (2) The modified ZSM-5 molecular sieve was mixed with an equal volume of ferric nitrate aqueous solution. The concentration of the ferric nitrate aqueous solution was calculated as 0.2% of the mass of iron element in the ZSM-5 molecular sieve. After mixing, the mixture was dried at 120℃ for 12h and calcined at 350℃ for 2h.
[0080] (3) After mixing the molecular sieve obtained in step (2) with a certain mass of Y-type molecular sieve (mass ratio ZSM-5:Y = 5:1), a certain amount of pseudoboehmite is added, wherein the mass ratio of pseudoboehmite is ZSM-5:Al2O3 = 1:3, and 10g of 1%wt dilute nitric acid and 10g of deionized water are mixed, kneaded, extruded and shaped. The shaped sample is dried at 120℃ for 12h and calcined at 450℃ for 2h. (4) The catalyst obtained above is treated with steam at 600℃ for 3h, and the steam content to catalyst mass ratio is 5:1 to obtain catalyst 7. # .
[0081] Example 8 Comparative Example
[0082] Using unmodified ZSM-5 molecular sieve as a comparative example, catalyst 8 was obtained. # .
[0083] Example 9: Evaluation of the catalyst's isobutane conversion activity
[0084] The low-carbon alkane used in the catalyst evaluation was isobutane. The isobutane conversion catalytic performance of catalysts 1# to 7# prepared in Examples 1-7 and the comparative catalysts was evaluated using a fixed-bed reaction.
[0085]
[0086] The reactor has an inner diameter of 9 mm and a catalyst loading of 2 mL. After reduction with hydrogen, the catalyst is reacted with a feedstock containing isobutane and hydrogen. The products were analyzed online using an Agilent 7890A chromatograph. Catalyst activity was evaluated based on indicators such as isobutane conversion and selectivity for high-quality cracked feedstock. The calculation methods for each indicator are as follows:
[0087] Isobutane 进 The mass flow rate (kg / h) of isobutane at the reactor inlet; isobutane 出 and (ethane + propane + n-butane) 出 The values represent the mass flow rates (kg / h) of isobutane and high-quality pyrolysis feed at the reactor outlet, respectively. Table 1 shows the catalysts and catalyst pretreatment conditions, reaction conditions, and isobutane reactivity of the catalysts in Examples 1–8.
[0088] Table 1. Pretreatment conditions, reaction conditions, and catalyst activity of Examples 1-8
[0089]
[0090] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.
Claims
1. A method for converting low-carbon alkane, characterized in that, Includes the following steps: In a reactor under a hydrogen atmosphere, a raw material containing low-carbon alkanes is brought into contact with a catalyst and reacted to obtain a product containing small-molecule hydrocarbons. The catalyst is obtained through the following steps: (1) Mix ZSM-5 molecular sieve with fluorosilicic acid, heat, filter, wash, dry I, calcine I, to obtain substance I; (2) Mix substance I with an equal volume of an aqueous solution containing a metal salt, dry II, and calcine II to obtain substance II; (3) Mix substance II with Y-type molecular sieve, aluminum source, nitric acid and water, knead, extrude into strips, shape, let stand, dry (III), and calcine (III) to obtain substance III. (4) Subject III is aged with water vapor to obtain the catalyst.
2. The method according to claim 1, characterized in that, The mass ratio of ZSM-5 molecular sieve to fluorosilicic acid is 1:3 to 20. The heating temperature is 50–80°C; The heating time is 1 to 5 hours; The drying temperature I is 30–120°C. The drying time for step I is 1 to 12 hours; The temperature of the calcination I is 300–600°C; The roasting time for the first roasting step is 1 to 12 hours.
3. The method according to claim 1, characterized in that, The metal salt is selected from at least one of ferric nitrate, zirconium nitrate, cerium nitrate, or silver nitrate; The concentration of the metal salt in the aqueous solution containing the metal salt is 0.1–0.5 wt%. The temperature of the drying II process is 30–120°C; The drying time for step II is 1–12 hours; The temperature of calcination II is 300–600°C; The roasting time for the second stage is 1 to 12 hours.
4. The method according to claim 1, characterized in that, The aluminum source is selected from at least one of boehmite, aluminum hydroxide, sodium aluminate, aluminum sulfate, and aluminum isopropoxide. The mass fraction of the nitric acid is 1-5%; The mass ratio of ZSM-5 molecular sieve to aluminum source is 1:4 to 10, and the mass of aluminum source is based on the mass of Al2O3 therein. The temperature of the drying III process is 30–120°C; The drying time for step III is 1–12 hours; The temperature of calcination III is 300–600°C; The roasting time for the third stage is 1 to 12 hours.
5. The method according to claim 1, characterized in that, The steam aging time is 0.1 to 10 hours; In the water vapor aging process, the mass ratio of water vapor to substance III is 0.5 to 5:
1.
6. The method according to claim 1, characterized in that, The reactor is selected from fixed-bed reactors, moving-bed reactors, or fluidized-bed reactors.
7. The method according to claim 1, characterized in that, The low-carbon alkane is a C4-C6 isoalkane, selected from at least one of isobutane, n-pentane, isopentane, and 2,3-dimethylbutane; The small molecule hydrocarbons are selected from at least one of ethane, propane, and n-butane.
8. The method according to claim 1, characterized in that, The mass hourly space velocity (MSV) of the low-carbon alkanes in the feedstock is 0.1–10 h⁻¹. -1 ; The molar ratio of hydrogen to low-carbon alkanes in the raw material is 0.2 to 10:
1.
9. The method according to claim 1, characterized in that, The reaction temperature is 250–500°C; The reaction is carried out at a pressure of 0.1–10 MPa.
10. The method according to claim 1, characterized in that, The catalyst is pre-reduced with hydrogen. The hydrogen pre-reduction process involves a hydrogen volume hourly space velocity (VHSV) of 100–10000 h⁻¹. -1 ; The temperature for hydrogen pre-reduction is 200–600°C; The hydrogen pre-reduction time is 0.2 to 1000 h.