A magnesium-modified NiAPO-11 molecular sieve catalyst and its application

Abstract

The present invention discloses a magnesium-modified NiAPO-11 molecular sieve catalyst and its application. The catalyst is prepared by the following method: a template, a nickel salt, and a magnesium salt are added to an aqueous solution containing a phosphorus source and an aluminum source, stirred evenly, and a molecular sieve precursor gel is obtained. The resulting product is transferred to a hydrothermal kettle for hydrothermal reaction, and the obtained solid product is washed to neutrality, dried, and calcined to obtain a white solid product. The magnesium-modified NiAPO-11 molecular sieve catalyst provided by the present invention can be used to catalyze the skeletal isomerization reaction of n-butene to produce isobutylene, and has good catalytic activity and isobutylene selectivity.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, in particular to a magnesium-modified NiAPO-11 molecular sieve catalyst and application thereof. Background Art

[0002] Since the beginning of the 21st century, my country's petrochemical and coal chemical industries have experienced rapid development, resulting in the production of large quantities of C4 hydrocarbons as by-products. Currently, C4 hydrocarbons are primarily used as industrial and residential fuel gas. However, due to the low prices of crude oil and raw coal in recent years, burning large amounts of C4 hydrocarbons as fuel gas is uneconomical. Therefore, how to increase the utilization value of C4 hydrocarbons has become a major challenge that companies urgently need to address.

[0003] n-Butene is a key component of C4 hydrocarbon resources. Currently, its primary use is in alkylation with isobutylene to produce trimethylpentane. Due to its high octane number, trimethylpentane is an ideal blending component for clean gasoline. A small amount is also used for disproportionation to produce propylene. Therefore, the current chemical utilization rate of n-butene is very low. Improving this utilization rate would undoubtedly bring significant economic benefits.

[0004] As an important chemical raw material, isobutylene has broad application prospects, particularly in my country's energy, chemical, and materials industries. High-purity isobutylene is primarily used to produce chemical products such as MTBE (methyl tert-butyl ether), ETBE (ethyl tert-butyl ether), MMA (methyl methacrylate), IIR (butyl rubber), PIB (polyisobutylene), and TBA (tert-butyl alcohol). my country's isobutylene supply primarily comes from liquefied petroleum gas (LPG) as a byproduct of domestic refineries, imported LPG, and a mixed C4 fraction from MTO process byproducts. Isobutylene resources are relatively scarce and have a relatively limited source.

[0005] Currently, the main methods for producing isobutylene include isobutane dehydrogenation, sulfuric acid extraction, resin dehydration, and n-butene skeletal isomerization. The first three production processes are complex, corrosive to the reaction equipment, and associated with environmental pollution, resulting in unsatisfactory economic benefits. In contrast, the n-butene skeletal isomerization process requires less equipment, is simple to operate, poses fewer environmental risks, and offers superior catalytic stability, resulting in considerable economic benefits and significant advantages. n-butene skeletal isomerization processes can be categorized by catalyst type, including gamma-alumina and molecular sieve. The gamma-alumina process has high reaction temperatures (generally around 500°C), low isobutylene selectivity (<85%), and low single-pass yields, as well as short catalyst life and instability. The molecular sieve process, on the other hand, offers lower reaction temperatures (around 350°C), higher isobutylene selectivity (>90%), higher single-pass yields, and improved catalyst stability, making it a significant advantage in industrial applications.

[0006] The core of n-butene skeletal isomerization technology lies in catalyst preparation. The n-butene skeletal isomerization reaction occurs at acid sites of moderate strength. The acid strength required for n-butene skeletal isomerization is equivalent to 48-68% sulfuric acid by mass, based on sulfuric acid. A wide range of catalysts meet this requirement. Researchers have conducted extensive research on these catalysts for the n-butene skeletal isomerization reaction. Early catalysts employed were primarily oxide-type catalysts modified with halogens or halide compounds. While halide catalysts exhibit high reactivity for n-butene skeletal isomerization, they are highly corrosive, causing corrosion to the reactor. Furthermore, the halogen in halide catalysts is easily lost, leading to rapid catalyst deactivation. The catalyst regeneration process requires reintroduction of halogen, which is complex, impacts the long-term operation of the equipment, and can cause environmental pollution. To reduce equipment corrosion and environmental pollution, non-halide catalysts have been used for n-butene skeletal isomerization. However, drawbacks such as susceptibility to deactivation and the required high reaction temperatures have limited the development of non-halide catalysts. With the continuous development of molecular sieve catalysts, researchers have begun to apply molecular sieve catalysts to the skeletal isomerization reaction of n-butene. Research results show that compared with traditional oxide-type catalysts, molecular sieve catalysts have the advantages of good selectivity, high catalytic activity, not easy to deactivate, and no environmental pollution.

[0007] In recent years, research on the skeletal isomerization of n-butene has focused on FER molecular sieves. Due to their excellent catalytic stability, they are widely used. However, their industrial application has also exposed significant shortcomings. Due to the irrational distribution of Br and L acids, a large amount of byproducts is produced for a considerable period of time during the early stages of the reaction. However, the skeletal isomerization of n-butene requires relatively mild acidic sites. Therefore, the development of molecular sieve catalysts with superior catalytic performance, resulting in higher catalytic activity and isobutylene selectivity in the skeletal isomerization of n-butene, is an urgent task. Summary of the Invention

[0008] The present invention aims to provide a magnesium-modified NiAPO-11 molecular sieve catalyst based on the deficiencies of existing molecular sieve catalysts for the skeletal isomerization reaction of n-butene exposed during industrial application. Another object of the present invention is to provide applications of the above-mentioned magnesium-modified NiAPO-11 molecular sieve catalyst. The present invention achieves the purpose of adjusting the molecular sieve active sites and improving the n-butene conversion rate and isobutylene selectivity by magnesium modification of the NiAPO-11 molecular sieve.

[0009] The technical solution of the present invention is: a magnesium-modified NiAPO-11 molecular sieve catalyst is prepared by the following method, the specific steps of which are as follows:

[0010] (1) dissolving phosphoric acid in deionized water and stirring uniformly to form a phosphoric acid solution, then adding an aluminum source and stirring uniformly to obtain a mixed solution;

[0011] (2) dissolving the template in the mixed solution obtained in step (1) and stirring evenly;

[0012] (3) adding a nickel source to the mixed solution obtained in step (2), adding a magnesium source after stirring evenly, and stirring for a period of time to obtain a molecular sieve precursor gel;

[0013] (4) The molecular sieve precursor gel obtained in step (3) is transferred to a hydrothermal reactor for hydrothermal crystallization, and the hydrothermal product is then centrifuged, washed, filtered, dried, and calcined to obtain a magnesium-modified NiAPO-11 molecular sieve catalyst, which is referred to as Mg-NiAPO-11.

[0014] Preferably, the aluminum source described in step (1) is one of pseudo-boehmite, sodium aluminate or aluminum isopropoxide; the molar ratio of the aluminum source to phosphoric acid is 1:(1-2) as calculated by Al2O3 / P2O5; and the molar ratio of the aluminum source to deionized water is 1:(50-200) as calculated by Al2O3 / H2O.

[0015] Preferably, the template agent in step (2) is one of di-n-propylamine and diisopropylamine; the molar ratio of the template agent to the aluminum source in step (1) calculated as Al2O3 is (1-3):1.

[0016] Preferably, the nickel source described in step (3) is one of nickel nitrate hexahydrate, nickel chloride or nickel sulfate; the magnesium source is one of magnesium nitrate hexahydrate, magnesium chloride or magnesium sulfate; the molar ratio of the nickel source to the aluminum source in step (1) is (0.01-0.05):1 as calculated by Ni / Al2O3; the molar ratio of the nickel source to the magnesium source is 1:(0.05-0.3) as calculated by Ni / Mg; and the stirring time is 1-4 hours.

[0017] Preferably, the hydrothermal temperature in step (4) is 150-200°C; the hydrothermal time is 24-70h; the drying temperature is 80-110°C; the roasting temperature is 550-600°C, the heating rate is 2-8°C / min, and the roasting time is 4-6h.

[0018] The present invention also provides the use of the aforementioned magnesium-modified NiAPO-11 molecular sieve catalyst in the catalytic skeletal isomerization of n-butene to produce isobutylene. The specific steps are as follows: the magnesium-modified NiAPO-11 molecular sieve catalyst is loaded into the middle of a fixed-bed reactor tube, both ends are filled with quartz wool, nitrogen is first introduced for purging, the temperature is then raised to 350°C to 450°C, and the temperature is maintained for 1 to 2 hours. Then, n-butene and nitrogen are introduced for reaction to produce isobutylene.

[0019] The reaction pressure is preferably normal pressure; the mass ratio of catalyst to quartz wool is (10-100):1; the mass space velocity of raw materials is 2-16h -1 A mixture of n-butene and nitrogen is introduced for reaction; the nitrogen flow rate is 2-10 mL / min; the volume ratio of nitrogen to n-butene is (1-9):1; and the reaction time is 3-12 hours. After the reaction, the exhaust gas composition is detected by FID chromatography.

[0020] The specific surface area of ​​the magnesium-modified NiAPO-11 molecular sieve catalyst prepared by the present invention is 250 to 320 m 2 / g, pore volume is 0.16~0.35cm 3 / g.

[0021] The principle of the present invention for modifying NiAPO-11 molecular sieve catalyst with magnesium is that, on the one hand, magnesium is adjacent to aluminum and phosphorus in the periodic table and has similar chemical properties, making it easier to form a molecular sieve with high crystallinity during the hydrothermal crystallization process. On the other hand, during the crystallization process, the phosphorus oxygen tetrahedron (PO4 + ) and aluminum oxide tetrahedron (AlO4 - ) forms a PO-Al bond. The PO-Al bond is flexible and structurally diverse, making it easier for heteroatoms such as nickel and magnesium to be incorporated into the molecular sieve. The present invention modifies the NiAPO-11 molecular sieve with magnesium to adjust the distribution of acidic sites, making it more conducive to catalyzing the skeletal isomerization reaction of n-butene.

[0022] Beneficial effects:

[0023] The magnesium-modified NiAPO-11 molecular sieve catalyst provided by the present invention can be used to catalyze the skeletal isomerization reaction of n-butene to produce isobutene, and has good catalytic activity and isobutene selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 XRD patterns of Mg-NiAPO-11-3 and NiAPO-11. DETAILED DESCRIPTION

[0025] The present invention is described in more detail with reference to the following examples, which are merely descriptions of the best mode of carrying out the present invention and do not limit the scope of protection of the present invention in any way.

[0026] In addition, unless otherwise specified, the preparation processes in the following examples are conventional means in the prior art in the field, and thus will not be described in detail; the percentages in the following examples are all by mass percentages.

[0027] Example 1

[0028] A method for preparing a magnesium-modified NiAPO-11 molecular sieve catalyst comprises the following steps:

[0029] Step 1. Under magnetic stirring, add 7.92g of phosphoric acid (the phosphoric acid used has an H3PO4 mass content of 85% and the remainder is H2O) to 29.68g of deionized water. After vigorously stirring for 10 minutes, add 4.46g of pseudo-boehmite (the pseudo-boehmite used has an Al2O3 mass content of 78.4%) and continue stirring until uniform. Then, add 3.47g of di-n-propylamine to the mixed solution and continue stirring until uniform. Finally, add 0.30g of nickel nitrate hexahydrate and 0.079g of magnesium nitrate hexahydrate to the mixed solution and stir for 1 hour to obtain a magnesium-modified NiAPO-11 molecular sieve precursor gel, recorded as Mg-NiAPO-11 precursor. (The molar ratio of each raw material is Al2O3:P2O5:di-n-propylamine:Ni:H2O=1:1:1:0.03:50, Mg:Ni=0.3)

[0030] Step 2. The Mg-NiAPO-11 precursor gel was placed in a polytetrafluoroethylene liner, placed in a hydrothermal reactor, and crystallized in an oven at 160°C for 24 hours. After crystallization, the mixture was cooled to room temperature, the mother liquor was removed, and the resulting product was washed until neutral, followed by drying at 80°C for 12 hours. The dried product was then ground into a powder, placed in a muffle furnace, heated to 600°C at a heating rate of 2°C / min, and calcined for 4 hours to obtain a magnesium-modified NiAPO-11 molecular sieve catalyst, designated Mg-NiAPO-11-1.

[0031] Example 2

[0032] A method for preparing a magnesium-modified NiAPO-11 molecular sieve catalyst comprises the following steps:

[0033] Step 1. Add 11.88g of phosphoric acid (the mass content of H3PO4 in the phosphoric acid used is 85% and the rest is H2O) to 121.87g of deionized water under magnetic stirring, stir vigorously for 10 minutes, then add 5.70g of sodium aluminate and continue to stir evenly. Then add 6.95g of diisopropylamine to the mixed solution and continue to stir evenly. Finally, add 0.13g of nickel chloride and 0.0048g of magnesium chloride to the mixed solution respectively, stir for 2h, and obtain a magnesium-modified NiAPO-11 molecular sieve precursor gel, recorded as Mg-NiAPO-11 precursor. (The molar ratio of each raw material is Al2O3:P2O5:diisopropylamine:Ni:H2O=1:1.5:2:0.03:200, Mg:Ni=0.05)

[0034] Step 2. The Mg-NiAPO-11 precursor gel was placed in a polytetrafluoroethylene liner, placed in a hydrothermal reactor, and crystallized in an oven at 150°C for 36 hours. After crystallization, the mixture was cooled to room temperature, the mother liquor was removed, and the resulting product was washed until neutral, followed by drying at 90°C for 12 hours. The dried product was then ground into a powder and calcined in a muffle furnace at a heating rate of 3°C / min to 590°C for 5 hours to obtain a magnesium-modified NiAPO-11 molecular sieve catalyst, designated Mg-NiAPO-11-2.

[0035] Example 3

[0036] A method for preparing a magnesium-modified NiAPO-11 molecular sieve catalyst comprises the following steps:

[0037] Step 1. Add 7.92g of phosphoric acid (the mass content of H3PO4 in the phosphoric acid used is 85% and the rest is H2O) to 60.68g of deionized water under magnetic stirring, stir vigorously for 10 minutes, then add 14.04g of aluminum isopropoxide and continue to stir evenly. Then add 10.43g of di-n-propylamine to the mixed solution and continue to stir evenly. Finally, add 0.10g of nickel sulfate hexahydrate and 0.022g of magnesium sulfate hexahydrate to the mixed solution respectively, stir for 3h, and obtain a magnesium-modified NiAPO-11 molecular sieve precursor gel, recorded as Mg-NiAPO-11 precursor. (The molar ratio of each raw material is Al2O3:P2O5:di-n-propylamine:Ni:H2O=1:1:3:0.01:100, Mg:Ni=0.25)

[0038] Step 2. The Mg-NiAPO-11 precursor gel was placed in a polytetrafluoroethylene liner, placed in a hydrothermal reactor, and crystallized in an oven at 160°C for 36 hours. After crystallization, the mixture was cooled to room temperature, the mother liquor was removed, and the resulting product was washed until neutral, followed by drying at 100°C for 12 hours. The dried product was then ground into a powder and calcined in a muffle furnace at a heating rate of 4°C / min to 580°C for 6 hours to obtain a magnesium-modified NiAPO-11 molecular sieve catalyst, designated Mg-NiAPO-11-3.

[0039] Example 4

[0040] A method for preparing a magnesium-modified NiAPO-11 molecular sieve catalyst comprises the following steps:

[0041] Step 1. Under magnetic stirring, add 15.84g of phosphoric acid (the phosphoric acid used has an H3PO4 mass content of 85% and the remainder is H2O) to 43.92g of deionized water. After vigorously stirring for 10 minutes, add 4.46g of pseudo-boehmite (the pseudo-boehmite used has an Al2O3 mass content of 78.4%) and continue stirring until uniform. Then, add 3.47g of di-n-propylamine to the mixed solution and continue stirring until uniform. Finally, add 0.30g of nickel nitrate hexahydrate and 0.021g of magnesium nitrate hexahydrate to the mixed solution and stir for 4 hours to obtain a magnesium-modified NiAPO-11 molecular sieve precursor gel, recorded as Mg-NiAPO-11 precursor. (The molar ratio of each raw material is Al2O3:P2O5:di-n-propylamine:Ni:H2O=1:2:1:0.03:75, Mg:Ni=0.08)

[0042] Step 2. The Mg-NiAPO-11 precursor gel was placed in a polytetrafluoroethylene liner, placed in a hydrothermal reactor, and crystallized in an oven at 170°C for 36 hours. After crystallization, the mixture was cooled to room temperature, the mother liquor was removed, and the resulting product was washed until neutral, followed by drying at 110°C for 12 hours. The dried product was then ground into a powder and calcined in a muffle furnace at a heating rate of 5°C / min to 570°C for 6 hours to obtain a magnesium-modified NiAPO-11 molecular sieve catalyst, designated Mg-NiAPO-11-4.

[0043] Example 5

[0044] A method for preparing a magnesium-modified NiAPO-11 molecular sieve catalyst comprises the following steps:

[0045] Step 1. Under magnetic stirring, add 7.92g of phosphoric acid (the phosphoric acid used has an H3PO4 content of 85% by mass, the remainder being H2O) to 75.98g of deionized water. After vigorous stirring for 10 minutes, add 4.46g of pseudo-boehmite (the pseudo-boehmite used has an Al2O3 content of 78.4% by mass) and continue stirring until uniform. Subsequently, add 3.47g of di-n-propylamine to the mixed solution and continue stirring until uniform. Finally, add 0.50g of nickel nitrate hexahydrate and 0.040g of magnesium nitrate hexahydrate to the mixed solution and stir for 1 hour to obtain a magnesium-modified NiAPO-11 molecular sieve precursor gel, recorded as Mg-NiAPO-11 precursor. (The molar ratio of each raw material is Al2O3:P2O5:di-n-propylamine:Ni:H2O=1:1:1:0.05:125, Mg:Ni=0.09)

[0046] Step 2. The Mg-NiAPO-11 precursor gel was placed in a polytetrafluoroethylene liner, placed in a hydrothermal autoclave, and crystallized in an oven at 180°C for 36 hours. After crystallization, the mixture was cooled to room temperature, the mother liquor was removed, and the resulting product was washed until neutral, then dried at 100°C for 12 hours. The dried product was then ground into a powder, placed in a muffle furnace, heated to 570°C at a heating rate of 5°C / min, and calcined for 6 hours to obtain a magnesium-modified NiAPO-11 molecular sieve catalyst, designated Mg-NiAPO-11-5.

[0047] Example 6

[0048] A method for preparing a magnesium-modified NiAPO-11 molecular sieve catalyst comprises the following steps:

[0049] Step 1. Under magnetic stirring, add 7.92g of phosphoric acid (the phosphoric acid used has an H3PO4 content of 85% by mass, the remainder being H2O) to 60.68g of deionized water. After vigorous stirring for 10 minutes, add 2.98g of pseudo-boehmite (the pseudo-boehmite used has an Al2O3 content of 78.4% by mass) and continue stirring until uniform. Subsequently, add 4.64g of di-n-propylamine to the mixed solution and continue stirring until uniform. Finally, add 0.20g of nickel nitrate hexahydrate and 0.018g of magnesium nitrate hexahydrate to the mixed solution and stir for 1 hour to obtain a magnesium-modified NiAPO-11 molecular sieve precursor gel, recorded as Mg-NiAPO-11 precursor. (The molar ratio of each raw material is Al2O3:P2O5:di-n-propylamine:Ni:H2O=1:1.5:2:0.03:150, Mg:Ni=0.1)

[0050] Step 2. The Mg-NiAPO-11 precursor gel was placed in a polytetrafluoroethylene liner, placed in a hydrothermal reactor, and crystallized in an oven at 200°C for 36 hours. After crystallization, the mixture was cooled to room temperature, the mother liquor was removed, and the resulting product was washed until neutral, followed by drying at 90°C for 12 hours. The dried product was then ground into a powder, placed in a muffle furnace, heated to 560°C at a heating rate of 6°C / min, and calcined for 6 hours to obtain a magnesium-modified NiAPO-11 molecular sieve catalyst, designated Mg-NiAPO-11-6.

[0051] Example 7

[0052] A method for preparing a magnesium-modified NiAPO-11 molecular sieve catalyst comprises the following steps:

[0053] Step 1. Under magnetic stirring, add 7.92g of phosphoric acid (the phosphoric acid used has an H3PO4 content of 85% by mass, the remainder being H2O) to 103.75g of deionized water. After vigorously stirring for 10 minutes, add 4.46g of pseudo-boehmite (the pseudo-boehmite used has an Al2O3 content of 78.4% by mass) and continue stirring until uniform. Subsequently, add 3.47g of di-n-propylamine to the mixed solution and continue stirring until uniform. Finally, add 0.25g of nickel nitrate hexahydrate and 0.044g of magnesium nitrate hexahydrate to the mixed solution and stir for 1 hour to obtain a magnesium-modified NiAPO-11 molecular sieve precursor gel, recorded as Mg-NiAPO-11 precursor. (The molar ratio of each raw material is Al2O3:P2O5:di-n-propylamine:Ni:H2O=1:1:1:0.025:170, Mg:Ni=0.2)

[0054] Step 2. The Mg-NiAPO-11 precursor gel was placed in a polytetrafluoroethylene liner, placed in a hydrothermal reactor, and crystallized in an oven at 190°C for 48 hours. After crystallization, the mixture was cooled to room temperature, the mother liquor was removed, and the resulting product was washed until neutral, followed by drying at 80°C for 12 hours. The dried product was then ground into a powder and calcined in a muffle furnace at a heating rate of 7°C / min to 550°C for 6 hours to obtain a magnesium-modified NiAPO-11 molecular sieve catalyst, designated Mg-NiAPO-11-7.

[0055] Example 8

[0056] A method for preparing a magnesium-modified NiAPO-11 molecular sieve catalyst comprises the following steps:

[0057] Step 1. Under magnetic stirring, add 7.92g of phosphoric acid (the phosphoric acid used has an H3PO4 content of 85% by mass, the remainder being H2O) to 116.10g of deionized water. After vigorously stirring for 10 minutes, add 4.46g of pseudo-boehmite (the pseudo-boehmite used has an Al2O3 content of 78.4% by mass) and continue stirring until uniform. Subsequently, add 3.47g of di-n-propylamine to the mixed solution and continue stirring until uniform. Finally, add 0.40g of nickel nitrate hexahydrate and 0.053g of magnesium nitrate hexahydrate to the mixed solution and stir for 1 hour to obtain a magnesium-modified NiAPO-11 molecular sieve precursor gel, recorded as Mg-NiAPO-11 precursor. (The molar ratio of each raw material is Al2O3:P2O5:di-n-propylamine:Ni:H2O=1:1:1:0.04:190, Mg:Ni=0.15)

[0058] Step 2. The Mg-NiAPO-11 precursor gel was placed in a polytetrafluoroethylene liner, placed in a hydrothermal reactor, and crystallized in an oven at 190°C for 70 hours. After crystallization, the mixture was cooled to room temperature, the mother liquor was removed, and the resulting product was washed until neutral, then dried at 110°C for 12 hours. The dried product was then ground into a powder and calcined in a muffle furnace at a heating rate of 8°C / min to 600°C for 6 hours to obtain a magnesium-modified NiAPO-11 molecular sieve catalyst, designated Mg-NiAPO-11-8.

[0059] Comparative Example

[0060] A method for preparing a non-magnesium-modified NiAPO-11 molecular sieve catalyst comprises the following steps:

[0061] Step 1. Add 7.92g of phosphoric acid (the mass content of H3PO4 in the phosphoric acid used is 85% and the rest is H2O) to 60.68g of deionized water under magnetic stirring. After vigorously stirring for 10 minutes, add 14.04g of aluminum isopropoxide and continue to stir evenly. Then add 10.43g of di-n-propylamine to the mixed solution and continue to stir evenly. Finally, add 0.10g of nickel sulfate hexahydrate to the mixed solution and stir for 3 hours to obtain a NiAPO-11 molecular sieve precursor gel, which is recorded as NiAPO-11 precursor. (The molar ratio of each raw material is Al2O3:P2O5:di-n-propylamine:H2O=1:1:3:0.01:100)

[0062] Step 2. The NiAPO-11 precursor gel was placed in a polytetrafluoroethylene liner, placed in a hydrothermal autoclave, and crystallized in an oven at 160°C for 36 hours. After crystallization, the mixture was cooled to room temperature, the mother liquor was removed, and the resulting product was washed until neutral, then dried at 100°C for 12 hours. The dried product was then ground into a powder and calcined in a muffle furnace at a heating rate of 4°C / min to 580°C for 6 hours to obtain a magnesium-modified NiAPO-11 molecular sieve catalyst, designated as NiAPO-11.

[0063] The Mg-NiAPO-11 prepared in the above example and the NiAPO-11 prepared in the comparative example were subjected to XRD test and N2 adsorption-desorption test, respectively, and the results are as follows:

[0064] Figure 1 The XRD patterns of Mg-NiAPO-11-3 and NiAPO-11 are shown in Figure 2. Figure 1It can be seen that both catalysts exhibit characteristic diffraction peaks of the AEL topological structure at 2θ, indicating that the NiAPO-11 molecular sieve has been successfully prepared. In addition, the diffraction peaks of NiAPO-11- and magnesium-modified Mg-NiAPO-11-3 are compared, and the peak shapes are consistent, indicating that the introduction of magnesium does not affect the crystal phase of the NiAPO-11 molecular sieve and the crystallinity is good. In addition, no diffraction peaks of other oxides appear in the peak of Mg-NiAPO-11-3, indicating that the magnesium element has successfully entered the framework of the molecular sieve and is evenly dispersed.

[0065] The specific surface area and pore structure of Mg-NiAPO-11 and NiAPO-11 are shown in Table 1 below:

[0066] Table 1 Specific surface area and pore structure of catalysts

[0067]

[0068] Table 1 shows that magnesium modification of NiAPO-11 significantly increases both the catalyst's specific surface area and average pore size. This increased surface area helps provide more active sites for the reaction, enhancing catalytic activity. The larger pore size of the molecular sieve facilitates the passage of gas molecules and intermediates during the reaction, reducing the formation of heavy byproducts and carbon deposits. Therefore, the data in Table 1 demonstrate that magnesium modification of NiAPO-11 significantly improves the catalyst's catalytic performance.

[0069] The catalyst prepared in the above example was used to catalyze the skeletal isomerization reaction of n-butene to produce isobutene in a fixed bed reactor under normal pressure, specifically as follows:

[0070] Application Example 1

[0071] Mg-NiAPO-11-1 catalyst and high-temperature resistant quartz wool with a mass ratio of 10:1 were added to the middle of the fixed bed reactor, and nitrogen was introduced at a flow rate of 2 mL / min. The temperature was raised to 360 ° C. The catalyst was first activated under nitrogen atmosphere for 1 h, and then the raw material mass space velocity was 2 h at normal pressure. -1 n-Butene and nitrogen were introduced at a volume ratio of 1:4. After 3 hours of reaction, the instantaneous n-Butene conversion was 59.4%, the instantaneous isobutylene selectivity was 69.9%, and the instantaneous isobutylene yield was 41.5%.

[0072] Application Example 2

[0073] Mg-NiAPO-11-2 catalyst and high-temperature resistant quartz wool with a mass ratio of 20:1 were added to the middle of the fixed bed reactor, and nitrogen was introduced at a flow rate of 3 mL / min. The temperature was raised to 390 ° C. The catalyst was first activated under nitrogen atmosphere for 1 h, and then the raw material mass space velocity was 4 h at normal pressure.-1 n-Butene and nitrogen were introduced at a volume ratio of 1:3. After 5 hours of reaction, the instantaneous n-Butene conversion was 60.1%, the instantaneous isobutylene selectivity was 70.5%, and the instantaneous isobutylene yield was 42.4%.

[0074] Application Example 3

[0075] Mg-NiAPO-11-3 catalyst and high-temperature resistant quartz wool with a mass ratio of 30:1 were added to the middle of the fixed bed reactor, and nitrogen was purged at a flow rate of 4 mL / min. The temperature was raised to 370 ° C. The catalyst was first activated under nitrogen atmosphere for 2 h, and then activated at a mass space velocity of 6 h under normal pressure. -1 n-Butene and nitrogen were introduced at a volume ratio of 1:1. After 6 hours of reaction, the instantaneous n-Butene conversion was 68.4%, the instantaneous isobutylene selectivity was 74.3%, and the instantaneous isobutylene yield was 50.8%.

[0076] Application Example 4

[0077] Mg-NiAPO-11-4 catalyst and high-temperature resistant quartz wool with a mass ratio of 40:1 were added to the middle of the fixed bed reactor, and nitrogen was introduced at a flow rate of 5 mL / min. The temperature was raised to 400 ° C. The catalyst was first activated under nitrogen atmosphere for 1 h, and then activated at a mass space velocity of 8 h under normal pressure. -1 n-Butene and nitrogen were introduced at a volume ratio of 1:6. After 7 hours of reaction, the instantaneous n-Butene conversion was 64.6%, the instantaneous isobutylene selectivity was 65.5%, and the instantaneous isobutylene yield was 42.3%.

[0078] Application Example 5

[0079] Mg-NiAPO-11-5 catalyst and high-temperature resistant quartz wool with a mass ratio of 50:1 were added to the middle of the fixed bed reactor, and nitrogen was introduced at a flow rate of 6 mL / min. The temperature was raised to 360 ° C. The catalyst was first activated under nitrogen atmosphere for 2 h, and then the raw material mass space velocity was 10 h at normal pressure. -1 n-Butene and nitrogen were introduced at a volume ratio of 1:7. After 8 hours of reaction, the instantaneous n-Butene conversion was 63.1%, the instantaneous isobutylene selectivity was 66.5%, and the instantaneous isobutylene yield was 41.3%.

[0080] Application Example 6

[0081] Mg-NiAPO-11-6 catalyst and high-temperature resistant quartz wool with a mass ratio of 80:1 were added to the middle of the fixed bed reactor, and nitrogen was purged at a flow rate of 8 mL / min. The temperature was raised to 350 ° C. The catalyst was first activated under nitrogen atmosphere for 1 h, and then the raw material mass space velocity was 14 h at normal pressure. -1n-Butene and nitrogen were introduced at a volume ratio of 1:8. After 9 hours of reaction, the instantaneous n-Butene conversion was 62.6%, the instantaneous isobutylene selectivity was 65.5%, and the instantaneous isobutylene yield was 41.0%.

[0082] Application Example 7

[0083] Mg-NiAPO-11-7 catalyst and high-temperature resistant quartz wool with a mass ratio of 90:1 were added to the middle of the fixed bed reactor, and nitrogen was introduced at a flow rate of 9 mL / min. The temperature was raised to 380 ° C. The catalyst was first activated under nitrogen atmosphere for 1 h, and then the raw material mass space velocity was 16 h at normal pressure. -1 n-Butene and nitrogen were introduced at a volume ratio of 1:9. After 10 hours of reaction, the instantaneous n-Butene conversion was 62.5%, the instantaneous isobutylene selectivity was 65.4%, and the instantaneous isobutylene yield was 40.9%.

[0084] Application Example 8

[0085] Mg-NiAPO-11-8 catalyst and high-temperature resistant quartz wool with a mass ratio of 100:1 were added to the middle of the fixed bed reactor, and nitrogen was purged at a flow rate of 10 mL / min. The temperature was raised to 450 ° C. The catalyst was first activated under nitrogen atmosphere for 2 h, and then the raw material mass space velocity was 15 h at normal pressure. -1 n-Butene and nitrogen were introduced at a volume ratio of 1:9. After 12 hours of reaction, the instantaneous n-Butene conversion was 62.5%, the instantaneous isobutylene selectivity was 66.5%, and the instantaneous isobutylene yield was 41.6%.

[0086] Comparative Application Examples

[0087] NiAPO-11 catalyst and high-temperature resistant quartz wool with a mass ratio of 30:1 were added to the middle of the fixed bed reactor, and nitrogen was introduced at a flow rate of 4 mL / min. The temperature was raised to 370 ° C. The catalyst was first activated under nitrogen atmosphere for 1 h, and then the raw material mass space velocity was 6 h at normal pressure. -1 n-Butene and nitrogen were introduced at a volume ratio of 1:1. After 6 hours of reaction, the instantaneous conversion of n-Butene was 59.6%, the instantaneous selectivity for isobutylene was 62.8%, and the instantaneous yield of isobutylene was 37.4%.

[0088] The experimental results of the above application examples are summarized in Table 2.

[0089] Table 2 Comparison of experimental results of application examples

[0090]

[0091]

[0092] (Note: [1] Yang Jiabao, Hui Yu, Qin Yucai, et al. Effect of Lewis acid centers in FER molecular sieves on catalytic conversion of isobutylene [J]. Journal of Fuel Chemistry and Technology, 2021, 49(9): 1326-1335.)

[0093] As shown in Table 2, the NiAPO-11 molecular sieve prepared in the present invention exhibits significant improvements in catalytic activity and isobutylene selectivity compared to FER molecular sieves reported in the literature. Furthermore, magnesium modification of the NiAPO-11 molecular sieve significantly enhances catalyst performance. Compared to the comparative application examples, the isobutylene yield in Application Example 3 increased from 37.4% to 50.8%, primarily due to an increase in n-butene conversion from 59.6% to 68.4% and an increase in isobutylene selectivity from 62.8% to 74.3%. The magnesium modification significantly enhanced catalyst activity, while the acidity adjustment reduced byproducts. Furthermore, a comparison with other application examples reveals that the nickel-to-aluminum ratio, magnesium content, hydrothermal temperature and time during molecular sieve preparation, and reaction temperature during catalyst evaluation all influence the catalyst's catalytic performance.

[0094] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

Claims

1. Application of magnesium-modified NiAPO-11 molecular sieve catalyst in catalyzing the skeletal isomerization of n-butene to produce isobutene, characterized in that: The preparation method of the magnesium-modified NiAPO-11 molecular sieve catalyst is as follows: (1) dissolving phosphoric acid in deionized water and stirring uniformly to form a phosphoric acid solution, then adding an aluminum source and stirring uniformly to obtain a mixed solution; (2) dissolving the template in the mixed solution obtained in step (1) and stirring evenly; (3) adding a nickel source to the mixed solution obtained in step (2), adding a magnesium source after stirring evenly, and stirring for a period of time to obtain a molecular sieve precursor gel; (4) transferring the molecular sieve precursor gel obtained in step (3) to a hydrothermal reactor for hydrothermal crystallization, and then centrifugally washing, filtering, drying, and calcining the hydrothermal product to obtain a magnesium-modified NiAPO-11 molecular sieve catalyst, which is referred to as Mg-NiAPO-11; The aluminum source described in step (1) is one of pseudo-boehmite, sodium metaaluminate or aluminum isopropoxide; the molar ratio of the aluminum source to phosphoric acid is 1:(1-2) calculated as Al2O3 / P2O5; the molar ratio of the aluminum source to deionized water is 1:(50-200) calculated as Al2O3 / H2O; The template agent in step (2) is one of di-n-propylamine and diisopropylamine; the molar ratio of the template agent to the aluminum source in step (1) calculated as Al2O3 is (1-3):1; The nickel source described in step (3) is one of nickel nitrate hexahydrate, nickel chloride or nickel sulfate; the magnesium source is one of magnesium nitrate hexahydrate, magnesium chloride or magnesium sulfate; the molar ratio of the nickel source to the aluminum source in step (1) is (0.01-0.05):1 as calculated by Ni / Al2O3; the molar ratio of the nickel source to the magnesium source is 1:(0.05-0.3) as calculated by Ni / Mg; the stirring time is 1-4 hours; The application is to load a magnesium-modified NiAPO-11 molecular sieve catalyst into the middle of a fixed-bed reactor tube, fill both ends with quartz wool, first introduce nitrogen for purging, then raise the temperature to 350° C. to 450° C., maintain the temperature for 1 to 2 hours, and then introduce n-butene and nitrogen for reaction to obtain isobutylene; The mass ratio of catalyst to quartz wool is (10-100):1; the space velocity is 2-16h according to the mass of raw materials. -1 A mixture of n-butene and nitrogen is introduced for reaction; the nitrogen flow rate is 2-10 mL / min; the volume ratio of nitrogen to n-butene is (1-9):1; and the reaction time is 3-12 h.

2. The use according to claim 1, characterized in that: The hydrothermal temperature in step (4) is 150-200° C.; the hydrothermal time is 24-70 hours; the drying temperature is 80-110° C.; the calcination temperature is 550-600° C., the heating rate is 2-8° C. / min, and the calcination time is 4-6 hours.

Images