Nanometer buct-10 molecular sieve, and synthesis method and application thereof

Abstract

The application discloses a nano BUCT-10 molecular sieve, a synthesis method thereof and application of the molecular sieve in catalyzing linear olefin skeletal isomerization. The molecular sieve has a magnesium aluminum phosphate framework composition, which can be expressed as Mg x Al y PO4, wherein 0

Description

Technical Field

[0001] This invention belongs to the field of molecular sieves, and particularly relates to a nano-BUCT-10 molecular sieve, its synthesis method and its application in catalytic isomerization of straight-chain olefin skeletons. Background Technology

[0002] Olefins are commercially valuable addition reaction feedstocks in the chemical industry, used to prepare fuels, polymers, oxygen-containing compounds, and various fine chemicals. Among them, isomeric olefins have broad application prospects and high added value, and their efficient preparation technologies have attracted much attention from the industry. Taking isobutylene as an example, the existing mainstream production processes mainly include MTBE etherification, sulfuric acid extraction, isobutane dehydrogenation, adsorption separation, n-butane isomerization, and n-butene skeletal isomerization. Among these, sulfuric acid extraction and adsorption separation have cumbersome processes and poor overall economic efficiency; isobutane dehydrogenation and n-butane isomerization dehydrogenation processes have drawbacks such as high energy consumption and complex equipment processes. In contrast, the n-butene skeletal isomerization process has more prominent advantages: a simplified overall process, less equipment investment, low pollutant emissions and low environmental impact, excellent economic benefits, and efficient utilization of surplus C4 resources, resulting in significantly higher resource utilization.

[0003] Since the 1990s, the application of molecular sieve catalysts in the olefin skeletal isomerization has gradually attracted widespread attention, especially ten-membered ring molecular sieves. This is mainly due to the significant advantages of ten-membered ring molecular sieve catalysts, such as unique pore structure, tunable acid properties, and non-toxicity. Subsequently, researchers at home and abroad have conducted extensive and in-depth research on the application of ten-membered ring molecular sieve catalysts in this reaction. Compared with oxides, these molecular sieve catalysts have lower reaction temperatures, slower catalyst coking and deactivation, and higher selectivity for isobutene. Currently, the molecular sieve catalysts used for the isomerization of n-butene to isobutene mainly include FER-type and AEL-type molecular sieves.

[0004] Patent CN119118152A discloses a molecular sieve, BUCT-10, with a novel topological structure and unique X-ray powder diffraction characteristics. It features one-dimensional ten-membered ring straight channels with oval-shaped pore openings and a characteristic pore size of approximately 4.8 Å × 5.6 Å. It can be synthesized in various systems, including aluminum phosphate (AlPO), aluminum silicate phosphate (SAPO), aluminum metal phosphate (MeAPO), and aluminum silicate phosphate (MeSAPO). Patent CN120004684A discloses a method for isomerization of straight-chain olefin skeletons. Its key feature is that, under isomerization conditions, a catalyst containing BUCT-10 molecular sieve is used to react with straight-chain olefins, achieving the conversion to isomeric olefins rich in methyl branches. This method combines the advantages of high initial selectivity and good catalyst stability of both AEL-type and FER-type molecular sieve catalysts for isomerization of olefins.

[0005] The microscopic morphology of molecular sieves (such as particle size, aspect ratio, exposed crystal planes, etc.) directly determines their catalytic efficiency and service life. Corma et al. used a synergistic effect of piperidine and hexadecylmethylpiperidinium bromide as dual organic structure-directing agents to directly synthesize nano-FER zeolites with dimensions of only 10 - 30 nm along the

[001] direction of the 10-membered ring channels and an external specific surface area exceeding 250 m o at a low temperature of 120 2 / g without post-treatment to construct hierarchical pores; the accessibility of the active sites of this material is increased to more than 55%, and in the reaction of 1-pentene oligomerization to diesel fractions, the conversion rate exceeds 90%, the catalytic life is extended, and the diesel selectivity is higher, which is significantly better than conventional micron-FER zeolites (Angew. Chem. Int. Ed. 2018, 57, 3459 - 3463). Du et al. directly synthesized hierarchical pore FER zeolites with a sea urchin-like morphology, hollow inner cavity and abundant mesopores using L-lysine as an additive. Compared with traditional FER zeolites, this material has a higher specific surface area and pore volume, slightly stronger acidity and more accessible Brønsted acid sites. In the 1-butene skeletal isomerization reaction, due to its shorter diffusion path and stronger anti-coking ability, it shows a higher conversion rate and more remarkable stability than traditional FER (Chem. Eur. J., 2023, 29(62): 1). Rimer et al. prepared fin-like protrusions with adjustable sizes of 25 - 50 nm on the surface of two-dimensional pore FER zeolites by a seed-assisted secondary growth method to obtain fin-like ferrierite; the micropore volume of this material remains unchanged, and the external specific surface area is increased to a maximum of 134 m 2 / g. In the reaction of 1-butene isomerization to isobutene, the catalytic life is increased by 3 times and the isobutene selectivity is increased by 12% (Angew. Chem. Int. Ed.2022, 61, e202113077). Summary of the Invention

[0006] The object of the present invention is to provide a nano-BUCT-10 molecular sieve, its synthesis method and application in the catalytic skeletal isomerization of linear olefins.

[0007] The nano-BUCT-10 molecular sieve of the present invention has a magnesium aluminum phosphate framework composition, which can be expressed as Mg x Al y PO4, where 0 < x < 0.1 and 0.9 < y < 1.0; it has a short rod-like morphology, and the size in the c-axis direction (

[001] direction, parallel to the one-dimensional ten-membered ring pores) is 10 - 500 nm.

[0008] To achieve the above object, the present invention is synthesized by the following steps: 1) Stir the phosphorus source, aluminum source, magnesium source, fluorine source, alkali source, organic template agent and regulator to form an initial mixture; 2) Remove excess water from the initial mixture obtained in step 1) to obtain a dry gel precursor; 3) The dry gel precursor obtained in step 2) is transferred to a closed reaction vessel and heated for crystallization. The crystallized product is filtered, washed and dried to obtain nano BUCT-10 molecular sieve.

[0009] In step 1) of the above synthesis method, the phosphorus source is selected from one or more of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphorus pentoxide, preferably phosphoric acid; the aluminum source is selected from one or more of aluminum isopropoxide, boehmite, aluminum acetate, aluminum nitrate, aluminum sulfate, aluminum hydroxide, aluminum chloride, aluminum oxide, kaolin, and metallic aluminum, preferably aluminum isopropoxide and boehmite; the magnesium source is selected from one or more of magnesium acetate, magnesium nitrate, magnesium sulfate, magnesium chloride, magnesium carbonate, and magnesium oxide, preferably magnesium acetate; the fluorine source is selected from one or more of hydrofluoric acid, ammonium fluoride, and sodium fluoride, preferably hydrofluoric acid; the alkali source is selected from one or more of tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetraethylammonium hydroxide, and tetramethylammonium hydroxide, preferably tetrapropylammonium hydroxide and tetrabutylammonium hydroxide; the organic template agent is selected from one or more of butyltrimethylammonium, propyltrimethylammonium, and hexamethylammonium, preferably butyltrimethylammonium; the regulator is selected from one or more of hexadecyltrimethylammonium, L-lysine, and polyethylene glycol, preferably hexadecyltrimethylammonium and L-lysine.

[0010] In step 1) of the above synthesis method, the molar ratio of phosphorus source (P), aluminum source (Al), magnesium source (Mg), fluorine source (F), alkali source (B), and organic template agent (R) is P: a Al: b Mg: c F: d B: e R, where a = 0.5~1.5, b = 0~1.0, c = 0~2, d = 0~2, e = 0~5; preferably: a = 0.8~1.2, b = 0.01~0.2, c = 0.1~1.0, d = 0.1~1.0, e = 0.01~2.

[0011] In step 1) of the above synthesis method, the weight of the regulator accounts for 3-10% of the total weight of the initial dry mixture.

[0012] Step 1) of the above synthesis method contains water in the initial mixture. The water may come from the reaction raw materials or be added separately.

[0013] In step 2) of the above synthesis method, the water content in the dry gel precursor is 2-10% of the total weight of the dry gel.

[0014] The crystallization temperature in step 3) of the above synthesis method is 80~250 °C, preferably 150~200 °C.

[0015] The crystallization time in step 3) of the above synthesis method is 5 min to 48 h, preferably 1 to 24 h.

[0016] The above-mentioned nano-BUCT-10 molecular sieve is used in the catalytic reaction of linear olefin skeleton isomerization.

[0017] The modifier-modified nano-BUCT-10 molecular sieve catalyst provided by this invention has a higher straight-chain olefin conversion rate and better catalytic stability than the unmodified BUCT-10 molecular sieve catalyst. Attached Figure Description

[0018] Figure 1 The XRD patterns are of the nano molecular sieve N-BUCT-10 in Example 1 and the molecular sieve BUCT-10 in Comparative Example 1. Figure 2 SEM images of the nano molecular sieve N-BUCT-10 in Example 1 and the molecular sieve BUCT-10 in Comparative Example 1; Figure 3 The N2 adsorption-desorption curves of the nano molecular sieve N-BUCT-10 in Example 1 and the molecular sieve BUCT-10 in Comparative Example 1 are shown. Figure 4 The NH3 temperature-programmed desorption curves of the nano molecular sieve N-BUCT-10 in Example 1 and the molecular sieve BUCT-10 in Comparative Example 1 are shown. Figure 5 The following graphs show the catalytic performance of the nano molecular sieve N-BUCT-10 in Example 1 and the molecular sieve BUCT-10 in Comparative Example 1 in the reaction of 1-butene skeletal isomerization to isobutene as a function of running time: (a) 1-butene conversion, (b) isobutene selectivity, and (c) isobutene yield. Detailed Implementation

[0019] The present invention will be described in more detail below with reference to the embodiments. These embodiments are merely descriptions of the best mode of implementation of the present invention and do not limit the scope of protection of the present invention in any way.

[0020] Example 1 Weigh 0.569 g of an 85 wt% phosphoric acid aqueous solution, and add 1.785 g of 25 wt% tetrapropylammonium hydroxide, 0.085 g of butyltrimethylammonium chloride, 0.273 g of 40 wt% hydrofluoric acid, 0.025 g of magnesium acetate tetrahydrate, 1.120 g of aluminum isopropoxide, and 0.120 g of L-lysine to the solution. Stir to obtain an initial mixture. Heat the mixture on a 110 °C heating plate to remove excess moisture, obtaining a dry gel precursor with a water content of 5% of the total weight. Transfer the dry gel precursor to a sealed reaction vessel and crystallize it in an oven at 180 °C for 4 h. After crystallization, wash, filter, and dry the product to obtain a white solid powder, which is the nano-BUCT-10 molecular sieve, denoted as N-BUCT-10.

[0021] The N-BUCT-10 molecular sieve samples were subjected to crystal phase analysis using a Bruker D8 FOCUS X-ray diffractometer (XRD). During testing, the samples were ground and compacted in a sample cell. Testing was conducted using Cu target Kα radiation (λ = 1.5418 Å) as the light source, with a tube voltage of 40 kV and a tube current of 40 mA. The scanning range was 2θ = 3°–53°, with a step scan interval of 0.01°. The sample morphology was characterized using an S-4700 field emission scanning electron microscope (SEM) at an operating voltage of 20 kV. Before testing, the samples were uniformly dispersed on a conductive adhesive surface and sputtered with gold to improve conductivity. The resulting nano-BUCT-10 molecular sieve samples were calcined in a box muffle furnace at 550 °C for 6 h in air to remove the template agent. After calcination, the specific surface area and pore structure of the samples were analyzed using a Konta Autosorb-iQ3 physical adsorption analyzer, with N2 as the adsorbent gas and a test temperature of 77 K. Before testing, the samples were degassed at 300 °C to ensure thorough drying. NH3-TPD was performed using a DAS-7000 instrument to characterize the acidity of the samples. Before testing, the samples were activated at 300 °C for 30 min in a 99.99% N2 atmosphere; subsequently, they were adsorbed at 100 °C for 60 min in a 3% NH3 / Ar mixed atmosphere. After adsorption, N2 was purged for 15 min to remove physically adsorbed ammonia molecules, followed by a programmed temperature desorption test under N2 protection, with a heating range of 100–750 °C and a heating rate of 10 °C / min. The XRD, SEM, N2 physical adsorption, and NH3-TPD characterization results are as follows: Figure 1 , 2 As shown in Figures 3 and 4.

[0022] Example 2 Weigh 0.569 g of an 85 wt% phosphoric acid aqueous solution, and add 1.785 g of 25 wt% tetrapropylammonium hydroxide, 0.085 g of butyltrimethylammonium chloride, 0.273 g of 40 wt% hydrofluoric acid, 0.025 g of magnesium acetate tetrahydrate, 1.120 g of aluminum isopropoxide, and 0.100 g of hexadecyltrimethylammonium bromide. Stir to obtain an initial mixture. Heat the mixture on a 110 °C heating plate to remove excess moisture, obtaining a dry gel precursor with a water content of 5% of the total weight. Transfer the dry gel precursor to a sealed reaction vessel and crystallize in an oven at 180 °C for 4 h. After crystallization, wash, filter, and dry the product to obtain a white solid powder, which is the nano-BUCT-10 molecular sieve.

[0023] Example 3 Weigh 0.569 g of an 85 wt% phosphoric acid aqueous solution, and add 1.785 g of 25 wt% tetrapropylammonium hydroxide, 0.085 g of butyltrimethylammonium chloride, 0.273 g of 40 wt% hydrofluoric acid, 0.025 g of magnesium acetate tetrahydrate, 1.120 g of aluminum isopropoxide, and 0.220 g of polyethylene glycol 4000. Stir to obtain an initial mixture. Heat the mixture on a 110 °C heating plate to remove excess moisture, obtaining a dry gel precursor with a water content of 5% of the total weight. Transfer the dry gel precursor to a sealed reaction vessel and crystallize in an oven at 180 °C for 4 h. After crystallization, wash, filter, and dry the product to obtain a white solid powder, which is the nano-BUCT-10 molecular sieve.

[0024] Example 4 Weigh 0.569 g of an 85 wt% phosphoric acid aqueous solution, and add 1.785 g of 25 wt% tetrapropylammonium hydroxide, 0.085 g of butyltrimethylammonium chloride, 0.273 g of 40 wt% hydrofluoric acid, 0.025 g of magnesium acetate tetrahydrate, 1.120 g of aluminum isopropoxide, and 0.090 g of hexadecyltrimethylammonium chloride. Stir to obtain an initial mixture. Heat the mixture on a 110 °C heating plate to remove excess water, obtaining a dry gel precursor with a water content of 5% of the total weight. Transfer the dry gel precursor to a sealed reaction vessel and crystallize in an oven at 180 °C for 4 h. After crystallization, wash, filter, and dry the product to obtain a white solid powder, which is the nano-BUCT-10 molecular sieve.

[0025] Example 5 The N-BUCT-10 raw powder sample obtained in Example 1 was heated to 550 °C in a box-type high-temperature muffle furnace to remove the template agent at a heating rate of 10 °C / min. Subsequently, molecular sieves were prepared into catalyst particles of 20–40 mesh, and 0.1 g of catalyst was packed into a high-temperature fixed-bed quartz tube. Nitrogen gas was introduced (flow rate 50 mL / min), and the temperature was increased to 500 °C at a heating rate of 10 °C / min to activate the catalyst. After activation for 1 h, the temperature was lowered to the reaction temperature of 400 °C, and the reaction mixture (1-butene / nitrogen molar ratio 1:1) was switched to a reaction weight hourly space velocity (WHSV) of 8 g. g -1 h -1 Five minutes after the reaction started, the first product sample was collected as the initial reaction data point. Subsequently, the system automatically sampled the product every 1 hour and introduced it into an online gas chromatograph equipped with a flame ionization detector (FID) for analysis. Product analysis was performed using a Shimadzu GC-2014 gas chromatograph equipped with a flame ionization detector (FID) and a capillary column of KB-Al₂O₃ / Na₂SO₄ (50 m × 0.53 mm × 15 μm). The results are as follows: Figure 5 As shown.

[0026] Comparative Example 1 0.569 g of an 85 wt% phosphoric acid aqueous solution was weighed, and 1.785 g of 25 wt% tetrapropylammonium hydroxide, 0.085 g of butyltrimethylammonium chloride, 0.273 g of 40 wt% hydrofluoric acid, 0.025 g of magnesium acetate tetrahydrate, and 1.120 g of aluminum isopropoxide were added to it. The mixture was stirred to obtain an initial mixture. The mixture was heated on a 110 °C hot plate to remove excess water, resulting in a dry gel precursor with a water content of 5% of the total weight. The dry gel precursor was transferred to a sealed reaction vessel and crystallized in an oven at 180 °C for 4 h. After crystallization, the product was washed, filtered, and dried to obtain a white solid powder, which is the BUCT-10 molecular sieve. It was characterized using the XRD, SEM, N2 physical adsorption, and NH3 temperature-programmed desorption methods described in Example 1. The results are as follows: Figure 1 As shown in figures 2, 3, and 4. Comparative Example 2 Using the method of Example 5, the catalytic performance of BUCT-10 molecular sieve from Comparative Example 1 was evaluated after calcination for 1-butene skeletal isomerization. The results are as follows: Figure 5 As shown.

[0027] Figure 1The XRD patterns of N-BUCT-10 and BUCT-10 are shown. It can be seen that the diffraction characteristic peaks of the catalyst sample are consistent with the standard spectrum of BUCT-10 molecular sieve, indicating that the introduction of the modifier did not change the crystal structure of BUCT-10 molecular sieve, and the sample has good crystallinity.

[0028] Figure 2 SEM images of N-BUCT-10 and BUCT-10 are shown. It can be observed that the introduction of the regulator significantly affects the crystal size of the molecular sieve. The crystals of N-BUCT-10 become shorter along the c-axis, decreasing from 1500-2000 nm to 10-500 nm.

[0029] Figure 3 The images show the N2 adsorption-desorption isotherms for N-BUCT-10 and BUCT-10. Both samples exhibit typical Type I isotherms, consistent with common adsorption characteristics of the microporous structure of aluminum phosphate molecular sieves. The specific surface area and pore volume of the modified molecular sieve catalysts are both increased.

[0030] Figure 4 The NH3-TPD curves for N-BUCT-10 and BUCT-10 are shown. The results indicate that the desorption peak around 200 °C corresponds to the weak acid center of the catalyst, while the desorption peak around 400 °C corresponds to the strong acid center of the catalyst. Comparison of peak areas shows that the acid properties of the two molecular sieves are similar.

[0031] Figure 5 The graph shows the catalytic performance of N-BUCT-10 and BUCT-10 for the 1-butene skeletal isomerization to isobutene as a function of operating time. The graph shows that the initial activity and catalytic stability of the modified catalyst are significantly improved compared to the unmodified catalyst. The initial conversion of 1-butene increases from 58.70% to 65.41%, and the isobutene yield increases from 31.75% to 35.88% at TOS = 7 h.

Claims

1. A nano-BUCT-10 molecular sieve, characterized in that: The molecular sieve has a magnesium aluminum phosphate framework composition, which can be expressed as Mg x Al y PO4, where 0 < x < 0.1 and 0.9 < y < 1.0; the molecular sieve has a short rod-like morphology, and the size in the c-axis direction ([001] direction, parallel to the one-dimensional ten-membered ring pore channel) is 10 - 500 nm.

2. The synthesis method of nano-BUCT-10 molecular sieve according to claim 1, the specific steps are as follows: 1) Stir the phosphorus source, aluminum source, magnesium source, fluorine source, alkali source, organic template agent and regulator to form an initial mixture; 2) Remove excess water from the initial mixture obtained in step 1) to obtain a dry gel precursor; 3) The dry gel precursor obtained in step 2) is transferred to a closed reaction vessel and heated for crystallization. The crystallized product is filtered, washed and dried to obtain nano BUCT-10 molecular sieve.

3. As described in step 1) of claim 2, characterized in that The phosphorus source is selected from one or more of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphorus pentoxide, preferably phosphoric acid; the aluminum source is selected from one or more of aluminum isopropoxide, boehmite, aluminum acetate, aluminum nitrate, aluminum sulfate, aluminum hydroxide, aluminum chloride, aluminum oxide, kaolin, and metallic aluminum, preferably aluminum isopropoxide or boehmite; the magnesium source is selected from one or more of magnesium acetate, magnesium nitrate, magnesium sulfate, magnesium chloride, magnesium carbonate, and magnesium oxide, preferably magnesium acetate; the fluorine source is selected from one or more of hydrofluoric acid, ammonium fluoride, and sodium fluoride, preferably hydrofluoric acid; the alkali source is selected from one or more of tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetraethylammonium hydroxide, and tetramethylammonium hydroxide, preferably tetrapropylammonium hydroxide or tetrabutylammonium hydroxide; the organic template agent is selected from one or more of butyltrimethylammonium, propyltrimethylammonium, and hexamethylammonium, preferably butyltrimethylammonium; the regulator is selected from one or more of hexadecyltrimethylammonium, L-lysine, and polyethylene glycol, preferably hexadecyltrimethylammonium or L-lysine.

4. According to step 1) of claim 2, the molar ratio of phosphorus source (P), aluminum source (Al), magnesium source (Mg), fluorine source (F), alkali source (B), and organic template agent (R) is P: a Al: b Mg: c F: d B: e R, where a = 0.5~1.5, b = 0~1.0, c = 0~2, d = 0~2, e = 0~5; preferably: a = 0.8~1.2, b = 0.01~0.2, c = 0.1~1.0, d = 0.1~1.0, e = 0.01~2.

5. As described in step 1) of claim 2, the weight of the regulator accounts for 3 to 10% of the total weight of the initial dry mixture.

6. As described in step 1) of claim 2, characterized in that The initial mixture contains water, which may come from the reaction raw materials or be added separately.

7. As described in step 2) of claim 2, characterized in that The water content in the dry adhesive precursor is 2-10% of the total weight of the dry adhesive.

8. As described in step 3) of claim 2, characterized in that... The crystallization temperature is 80~250 °C, preferably 150~200 °C.

9. As described in step 3) of claim 2, characterized in that... The crystallization time is 5 min to 48 h, preferably 1 to 24 h.

10. The application of the nano-BUCT-10 molecular sieve according to claims 1-9 in the catalytic reaction of linear olefin skeleton isomerization.

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