Phosphorus-modified beta molecular sieve

Abstract

The application discloses a phosphorus-modified beta molecular sieve, characterized in that, after being treated under the condition of 800 DEG C, 17 hours and 100% water vapor atmosphere, the beta molecular sieve has the following characteristics: 29 The molar ratio of silica / alumina of the framework measured by Si MAS NMR is ≤40, 31 The ratio of the characteristic peak area of the chemical shift-17±3 resonance signal to the characteristic peak area of the chemical shift-30±5 resonance signal measured by P MAS NMR is ≥0.70.

Description

Technical Field

[0001] This invention relates to the field of molecular sieves, and more specifically to β-molecular sieves. Background Technology

[0002] β-zeolites possess a three-dimensional twelve-membered ring pore structure and were first synthesized by Mobil Corporation in 1967 (US3308069). Due to their unique topological structure and good thermal and hydrothermal stability, β-zeolites exhibit excellent catalytic performance in reactions such as hydrocracking, hydroisomerization, hydrocarbon cracking, and alkylation.

[0003] In catalytic cracking, although many researchers have found that β-zeolites, as additives, can optimize the product distribution and increase the yield of low-carbon olefins and gasoline components, their reactivity is low under harsh reaction conditions due to their tendency to undergo dealumination. Currently, industrially, β-zeolites are typically modified to improve their reactivity, with phosphorus modification considered a very effective method.

[0004] CN103771437A discloses a phosphorus-containing modified Beta molecular sieve, with a phosphorus content of 3-10% by weight (based on P2O5). 27 In Al MAS NMR, the ratio of the resonance peak area at a chemical shift of 40±3 ppm to that at a chemical shift of 54±3 ppm is greater than or equal to 1. In this phosphorus-containing modified Beta molecular sieve, phosphorus is well coordinated with the framework aluminum, which is fully protected, resulting in excellent hydrothermal stability and better product selectivity.

[0005] CN1179994A discloses a method for modifying β-zeolites. This method involves exchanging Naβ-zeolites with ammonium ions to reduce the Na₂O content on the zeolite to less than 0.1 wt%. The ammonium-exchanged β-zeolite is then treated with acid to remove some of the skeletal aluminum, resulting in a silicon-to-aluminum ratio greater than 50. The dealuminized β-zeolite is then mixed uniformly with phosphoric acid or phosphate and dried to achieve a P₂O₅ content of 2–5 wt%. Finally, it is hydrothermally calcined at 450–650 °C for 0.5–4 hours under a steam atmosphere. This modification method allows β-zeolites to achieve higher yields of olefins, especially isomeric olefins, and lower coke yields when used in hydrocarbon cracking reactions.

[0006] Current research on phosphorus modification of β-zeolites typically focuses only on the phosphorus modification methods, with limited attention paid to the calcination conditions after phosphorus modification. Since the template agent remaining in the pores of β-zeolites usually requires calcination at above 450°C under air / steam conditions for at least 3 hours to be completely removed, most researchers assume that the calcination temperature must be above 450°C. Summary of the Invention

[0007] When β-zeolites are modified with phosphorus and then calcined at temperatures above 450°C, severe dealuminization inevitably occurs. Through extensive research, the inventors unexpectedly discovered that when β-zeolites are calcined at lower temperatures after phosphorus modification, although the template agent is not completely removed, the removal of aluminum from the β-zeolite framework is better prevented, resulting in β-zeolites modified with phosphorus compounds exhibiting unique physicochemical characteristics.

[0008] Therefore, one of the purposes of the invention is to provide a phosphorus-modified β-zeolite that differs from the features of existing technologies, and the other purpose is to provide a method for preparing the zeolite.

[0009] To achieve one of the objectives of this invention, the phosphorus-modified β-molecular sieve provided in the first aspect of this invention is characterized in that the molecular sieve is treated at 800°C for 17 hours under a 100% water vapor atmosphere. 29 The molar ratio of silicon oxide to aluminum oxide in the framework, as measured by Si MAS NMR, is ≤40. 31 The ratio of the characteristic peak area of ​​the chemical shift -17±3 resonance signal to the characteristic peak area of ​​the chemical shift -30±5 resonance signal measured by PMAS NMR is ≥0.70.

[0010] 29 In Si MAS NMR, the resonance signal characteristic at chemical shift 104±1 represents the four coordination sites of silicon, with three oxygen bridges connecting silicon and one oxygen bridge connecting aluminum. The resonance signals at chemical shifts 110±1 and 114±1 represent the four coordination sites of silicon, each connected to other silicon atoms via oxygen bridges. Let the area of ​​the characteristic peak at chemical shift 104±1 be defined as A, the area of ​​the characteristic peak at 110±1 be defined as B, and the area of ​​the characteristic peak at 114±1 be defined as C. Then, the formula for calculating the molar ratio I of silicon oxide to aluminum oxide in the framework is I = (A + B + C) / 0.25A. The phosphorus-modified β-molecular sieve of this invention, after treatment at 800℃ for 17 hours in a 100% water vapor atmosphere, has a molar ratio of silicon oxide to aluminum oxide in the framework ≤40, preferably ≤37.

[0011] 31 In pMAS NMR, the chemical shift -17±3 resonance signal represents phosphorus species coordinated with a six-coordinated non-framework aluminum phase; the chemical shift -30±5 resonance signal represents phosphorus species coordinated with a four-coordinated framework aluminum phase and phosphorus species in aluminum phosphate. The phosphorus-modified β-molecular sieve of the present invention, after treatment at 800°C for 17 hours in a 100% water vapor atmosphere, exhibits a characteristic peak area ratio of -17±3 resonance signal to -30±5 resonance signal ≥0.70, preferably ≥0.90.

[0012] To achieve the second objective of this invention, the method for phosphorus-modified β-molecular sieve provided in the second aspect of this invention is characterized by comprising the following steps:

[0013] (1) The β molecular sieve powder undergoes ammonium salt ion exchange to become ammonium form;

[0014] (2) Ammonium-type β-molecular sieves are impregnated with phosphate salts and then dried;

[0015] (3) The β molecular sieve impregnated with phosphorus was calcined at 150-350℃ to obtain a modified β molecular sieve modified with phosphorus-containing compounds.

[0016] More specifically, the method for phosphorus-modified β-zeolite provided by the present invention includes the following steps:

[0017] (1) The β molecular sieve powder undergoes ammonium salt ion exchange to become ammonium type β molecular sieve, so that the Na2O content of the molecular sieve is less than 0.2% by weight.

[0018] (2) The ammonium-type β molecular sieve is impregnated with a phosphorus-containing compound. Preferably, the phosphorus-containing compound is completely dissolved in deionized water. The powder of the ammonium-type β molecular sieve is evenly spread into a thin layer of 1-5 mm. The phosphorus-containing compound solution is evenly dripped into the molecular sieve layer until it is completely wetted. The sieve is dried at 80-120℃ for 12 hours to obtain a phosphorus-impregnated β molecular sieve. The added phosphorus is calculated as phosphorus pentoxide and reaches 5%-10% of the mass of the β molecular sieve.

[0019] (3) The phosphorus-impregnated β molecular sieve is calcined at a temperature of 150-350℃, preferably 200-350℃, to obtain phosphorus-modified β molecular sieve; optionally, the calcination process is carried out at a heating rate of 0.5-10℃ / min to reach the calcination temperature, and then kept at a constant temperature for 3-7 hours.

[0020] In the method provided by this invention, the β-zeolite raw powder can be derived from industrially produced nano-β-zeolite, and can be synthesized using a template agent method or a template-free method. Preferably, it is a sodium-type β-zeolite synthesized using a template agent method. Preferably, the β-zeolite raw powder has an average crystallite size ≤300nm, a molar ratio of silicon oxide to aluminum oxide of 20-40, preferably 20-30, and a half-peak width at 20°-23.5° ≥0.230, preferably ≥0.24, in its XRD pattern.

[0021] The method provided by this invention includes the following specific process for ammonium salt ion exchange: sodium-type β-molecular sieves are exchanged in an ammonium salt solution at 50-90°C. The ammonium salts used can be, for example, one or more of ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium acetate, and ammonium oxalate. The concentration of the ammonium salt aqueous solution is 5-20% by weight, the exchange time is 1-3 hours, the mass ratio of sodium-type β-molecular sieves to ammonium salt solution is 1:5-1:20, the number of exchange cycles is 1-4, and the sodium oxide content of the ammonium-type β-molecular sieves after ammonium salt ion exchange is ≤0.2% by weight.

[0022] In the method provided by this invention, the phosphorus-containing compound can be selected from inorganic phosphorus sources such as phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate, or from one or more organic phosphorus sources that are soluble in water, such as phosphazenes.

[0023] The phosphorus-modified β-molecular sieve provided by this invention better prevents the removal of skeletal aluminum into non-skeletal aluminum than existing technologies, and has excellent hydrothermal stability and product selectivity. It can be applied in catalytic cracking or catalytic pyrolysis reactions as an active component of catalysts or additives. Attached Figure Description

[0024] Figure 1 This is the XRD pattern of sample A from Example 1.

[0025] Figure 2 This is an SEM image of sample A from Example 1.

[0026] Figure 3 This refers to Sample A from Example 1, which underwent hydrothermal treatment at 800°C for 17 hours in a 100% steam atmosphere. 29 Si MASNMR spectrum.

[0027] Figure 4 This refers to Sample A from Example 1, which underwent hydrothermal treatment at 800°C for 17 hours in a 100% steam atmosphere. 31 p MASNMR spectrum.

[0028] Figure 5 This refers to Sample B from Example 2, which underwent hydrothermal treatment at 800°C for 17 hours in a 100% steam atmosphere. 29 Si MASNMR spectrum.

[0029] Figure 6 This refers to Sample B from Example 2, which underwent hydrothermal treatment at 800°C for 17 hours in a 100% steam atmosphere. 31 p MASNMR spectrum.

[0030] Figure 7 This refers to sample C from Example 3 after hydrothermal treatment at 800°C for 17 hours in a 100% steam atmosphere. 29 Si MASNMR spectrum.

[0031] Figure 8 This refers to sample C from Example 3 after hydrothermal treatment at 800°C for 17 hours in a 100% steam atmosphere. 31 p MASNMR spectrum.

[0032] Figure 9 Comparative Example 2 sample DB-D after hydrothermal treatment at 800℃ for 17 hours in a 100% steam atmosphere 29 SiMAS NMR spectrum.

[0033] Figure 10 Comparative Example 2 sample DB-D after hydrothermal treatment at 800℃ for 17 hours in a 100% steam atmosphere 31 PMAS NMR spectrum. Detailed Implementation

[0034] The present invention will be further illustrated by the following examples, but these examples do not limit the scope of the invention.

[0035] In all examples and comparative examples, the phase diagrams obtained by X-ray diffraction (XRD) were determined by Philips Panalytical X'pert under the following conditions: Cu target, Kα radiation, Ni filter, high-energy detector, tube voltage 30 kV, and tube current 40 mA. The contents of P2O5, SiO2, and Al2O3 in the β-zeolite of each sample were determined by X-ray fluorescence spectrometry (see *Analytical Methods in Petrochemical Engineering (RIPP Experimental Methods)*, edited by Yang Cuiding et al., Science Press, 1990).

[0036] Scanning electron microscope (SEM) images were obtained using a Quanta 200F scanning electron microscope from FEI.

[0037] Solid-state NMR results were obtained using a Bruker AVANCE III 600WB NMR spectrometer. After peak fitting of the resonance peak spectra, the area and ratio of each peak were calculated using the integration method.

[0038] Example 1

[0039] β-molecular sieve (Changling Catalyst Branch of Sinopec Catalyst Company, SiO2 / Al2O3 = 22, the same below) was added to a prepared ammonium chloride solution, and washed until the sodium oxide content was less than 0.2% by weight. After filtration and drying, sample A1 was obtained. 132g of sample A1 was weighed and impregnated with an aqueous solution of diammonium hydrogen phosphate (Beijing Yili Fine Chemicals Co., Ltd., 99%), which contained 16g of diammonium hydrogen phosphate and 98g of water, to obtain sample A2. Sample A2 was dried and calcined at 250℃ for 3 hours to obtain sample A.

[0040] The XRD pattern of sample A is shown below. Figure 1 SEM photos can be found Figure 2 .

[0041] The XRD pattern and SEM image of sample A are shown below. Figure 1 and Figure 2 .

[0042] Sample A was subjected to hydrothermal aging at 800℃ for 17 hours in a 100% water vapor atmosphere, and then... 29 Si MAS NMR, 31 Characterized by PMAS NMR.

[0043] 29 The Si MAS NMR spectrum is shown below. Figure 3 The molar ratio of silica to alumina in the framework obtained by peak separation calculation is shown in Table 1.

[0044] 31 The PMAS NMR spectrum is shown below. Figure 4 The ratio of the characteristic peak area of ​​the resonance signal with a chemical shift of -17±3 to that with a chemical shift of -30±5 is shown in Table 2.

[0045] Comparative Example 1

[0046] Add β molecular sieves to the prepared ammonium chloride solution, wash until the sodium oxide content is less than 0.2% by weight, filter and dry; weigh 132g of the obtained sample and impregnate it with an aqueous solution of diammonium hydrogen phosphate (Beijing Yili Fine Chemicals Co., Ltd., 99%), the aqueous solution containing 16g of diammonium hydrogen phosphate and 98g of water. After drying the sample, calcine the obtained sample at 550℃ for 5 hours to obtain sample DB-A.

[0047] Sample DB-A was hydrothermally aged at 800℃ for 17 hours in a 100% water vapor atmosphere, and then subjected to... 29 Si MASNMR, 31 Characterized by PMAS NMR. 29 The molar ratio of silica to alumina in the framework obtained by Si MAS NMR peak separation calculation is shown in Table 1. 31 The ratio of the characteristic peak area of ​​the PMAS NMR chemical shift -17±3 resonance signal to that of the characteristic peak area of ​​the -30±5 resonance signal is shown in Table 2.

[0048] Example 2

[0049] Add β molecular sieves to a prepared ammonium chloride solution, wash until the sodium oxide content is less than 0.2% by weight, filter and dry to obtain sample B1; weigh 105g of the obtained sample B1 and impregnate it with an aqueous solution of phosphoric acid (Beijing Chemical Plant, 85%), the aqueous solution of phosphoric acid containing 14g of phosphoric acid and 85g of water to obtain sample B2; dry sample B2 and calcine at 350℃ for 4 hours to obtain sample B.

[0050] Sample B was hydrothermally aged at 800℃ for 17 hours in a 100% water vapor atmosphere, and then subjected to... 29 Si MASNMR, 31 Characterized by PMAS NMR. 29 The Si MAS NMR spectrum is shown below. Figure 5 The molar ratio of silica to alumina in the framework obtained by peak separation calculation is shown in Table 1. 31 The PMAS NMR spectrum is shown below. Figure 6 The ratio of the characteristic peak area of ​​the resonance signal with a chemical shift of -17±3 to that with a chemical shift of -30±5 is shown in Table 2.

[0051] Example 3

[0052] Add β-molecular sieves to a prepared ammonium chloride solution, wash until the sodium oxide content is less than 0.2% by weight, filter and dry to obtain sample C1; weigh 100g of the obtained sample C1 and impregnate it with an aqueous solution of diammonium hydrogen phosphate (Beijing Yili Fine Chemicals Co., Ltd., 99%), the aqueous solution of diammonium hydrogen phosphate containing 20g of phosphoric acid and 100g of water to obtain sample C2; ​​dry sample C2 and calcine at 300℃ for 4 hours to obtain sample C.

[0053] Sample C was subjected to hydrothermal aging at 800℃ for 17 hours in a 100% water vapor atmosphere, and then used... 29 Si MASNMR, 31 Characterized by PMAS NMR. 29 The Si MAS NMR spectrum is shown below. Figure 7 The molar ratio of silica to alumina in the framework obtained by peak separation calculation is shown in Table 1. 31 The PMAS NMR spectrum is shown below. Figure 8 The ratio of the characteristic peak area of ​​the resonance signal with a chemical shift of -17±3 to that with a chemical shift of -30±5 is shown in Table 2.

[0054] Example 4

[0055] Add β molecular sieves to a prepared ammonium chloride solution, wash until the sodium oxide content is less than 0.2% by weight, filter and dry to obtain sample D1; weigh 40g of sample D1 and impregnate it with an aqueous solution of ammonium dihydrogen phosphate (Beijing Yili Fine Chemicals Co., Ltd., 99%), the aqueous solution of ammonium dihydrogen phosphate contains 9g of ammonium dihydrogen phosphate and 30g of water to obtain sample D2; dry sample D2 and calcine at 330℃ for 4 hours to obtain sample D.

[0056] Sample D was hydrothermally aged at 800℃ for 17 hours in a 100% water vapor atmosphere, and then subjected to... 29 Si MASNMR, 31 Characterized by PMAS NMR. 29 The molar ratio of silica to alumina in the framework obtained by Si MAS NMR peak separation calculation is shown in Table 1. 31 The ratio of the characteristic peak area of ​​the PMAS NMR chemical shift -17±3 resonance signal to that of the characteristic peak area of ​​the -30±5 resonance signal is shown in Table 2.

[0057] Comparative Example 2

[0058] Add β molecular sieves to the prepared ammonium chloride solution, wash until the sodium oxide content is less than 0.2% by weight, filter and dry; weigh 40g of the obtained sample and impregnate it with an aqueous solution of ammonium dihydrogen phosphate (Beijing Yili Fine Chemicals Co., Ltd., 99%), the aqueous solution containing 9g of ammonium dihydrogen phosphate and 30g of water. After drying the sample, calcine the obtained sample at 450℃ for 4 hours to obtain sample DB-D.

[0059] After hydrothermal aging at 800℃ for 17 hours in a 100% water vapor atmosphere, sample DB-D was subjected to... 29 Si MASNMR, 31 Characterized by PMAS NMR. 29 The Si MAS NMR spectrum is shown below. Figure 9 , 29 The molar ratio of silica to alumina in the framework obtained by Si MAS NMR peak separation calculation is shown in Table 1. 31 The PMAS NMR spectrum is shown below. Figure 10 , 31 The ratio of the characteristic peak area of ​​the PMAS NMR chemical shift -17±3 resonance signal to that of the characteristic peak area of ​​the -30±5 resonance signal is shown in Table 2.

[0060] Table 1

[0061]

[0062] As can be seen from the data in Table 1, after hydrothermal aging treatment at 800℃ for 17 hours in a 100% water vapor atmosphere, the bulk SiO2 / Al2O3 molar ratio of the phosphorus-modified β-zeolite of the present invention remained essentially unchanged, as measured by fluorescence spectroscopy. 29 The SiO2 / Al2O3 molar ratio of the framework, as measured by SiMAS NMR, decreased significantly, indicating a substantial reduction in framework dealuminization and resulting in higher hydrothermal stability.

[0063] Table 2

[0064]

[0065] Based on the data in Table 1, and as shown in Table 2, the phosphorus-modified β-zeolite of the present invention, compared with the comparative example, removes less skeletal aluminum under hydrothermal conditions, while also exhibiting stronger interaction between phosphorus and the non-skeletal aluminum removed from the zeolite by high temperature.

[0066] Test case

[0067] This embodiment illustrates the effect of the phosphorus-modified β-molecular sieve of the present invention on hydrothermal stability and reaction performance in the catalytic cracking of pure hydrocarbons.

[0068] The samples prepared in Examples 1-4 and Comparative Examples 1-2 were all subjected to aging at 800°C and 100% steam for 17 hours, and then pressed into tablets and sieved to obtain particles of 20-40 mesh. Evaluation was then conducted in a fixed-bed microreactor. The evaluation raw material was n-tetradecane.

[0069] The evaluation conditions were: reaction temperature 550℃, regeneration temperature 600℃, oil feed rate 1.56g, oil feed time 70 seconds, and catalyst content 2g.

[0070] The evaluation results are listed in Table 3.

[0071] Table 3

[0072] Sample number A DB-A B C D DB-D Conversion rate (%) 71.06 66.03 71.56 71.65 71.28 70.27 Product yield, wt.% Liquefied gas 36.69 27.52 32.13 31.10 33.96 29.09 gasoline 28.82 33.95 34.07 35.12 30.10 36.62 Product distribution, wt.% ethylene 1.60 1.03 1.59 1.53 1.57 1.22 propylene 11.41 9.17 11.44 10.60 11.07 9.54 Total butene 10.10 6.63 6.33 7.45 7.46 7.02

[0073] As can be seen from the data in Table 3, compared with the comparative sample, the phosphorus-modified β-zeolite sample of the present invention has a higher conversion rate while improving the hydrocarbon cracking ability, and increases the cracking reaction depth. It has better reactivity and higher yield of low carbon olefins, mainly ethylene and propylene.

Claims

1. A phosphorus-modified β-molecular sieve, characterized in that, After being treated at 800℃ for 17 hours in a 100% water vapor atmosphere, 29 The molar ratio of silicon oxide to aluminum oxide in the framework, as measured by Si MAS NMR, is ≤40. 31 The ratio of the characteristic peak area of ​​the chemical shift -17±3 resonance signal to the characteristic peak area of ​​the chemical shift -30±5 resonance signal measured by PMAS NMR is ≥0.70; the phosphorus-modified β molecular sieve is prepared by a method including the following steps: (1) the β molecular sieve powder is subjected to ammonium salt ion exchange to exchange into ammonium type β molecular sieve; (2) the ammonium type β molecular sieve is subjected to phosphate salt impregnation treatment and dried; (3) the β molecular sieve impregnated with phosphorus is calcined at 150-350℃ to obtain phosphorus-modified β molecular sieve.

2. The phosphorus-modified β-molecular sieve according to claim 1, characterized in that, Phosphorus content is 5-20% by weight.

3. The phosphorus-modified β-molecular sieve according to claim 1, characterized in that, Average grain size ≤300nm, molar ratio of silicon dioxide to aluminum oxide 20-40, and full width at half maximum (FWHM) of the characteristic peaks at 20°-23.5° in the XRD pattern ≥0.

24.

4. The phosphorus-modified β-molecular sieve according to claim 1, characterized in that, The β-molecular sieve raw powder is a sodium-type β-molecular sieve that has been synthesized and washed with water until the pH value is 7-8.

5. The phosphorus-modified β-molecular sieve according to claim 1, characterized in that, The process of ammonium salt ion exchange for β molecular sieve raw powder is as follows: sodium-type β molecular sieve raw material is exchanged in ammonium salt solution at 50-90℃ for 1-3 hours. The mass ratio of molecular sieve to ammonium salt solution is 1:5-1:20, and the number of exchange times is 1-4 times to obtain ammonium-type β molecular sieve with sodium oxide content ≤0.2% by weight.

6. The phosphorus-modified β-molecular sieve according to claim 1, characterized in that, The ammonium salt is one or more of ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium acetate, and ammonium oxalate, and the concentration of the aqueous solution of the ammonium salt is 5-20% by weight.

7. The phosphorus-modified β-molecular sieve according to claim 1, characterized in that, The process of impregnating ammonium-type β-molecular sieve with phosphate salts is as follows: the phosphorus-containing compound is completely dissolved in deionized water, the ammonium-type β-molecular sieve powder is evenly spread into a thin layer of 1-5 mm, the phosphorus-containing compound solution is evenly dripped in until the molecular sieve layer is completely wetted, and dried at 80-120℃ for 12 h to obtain the β-molecular sieve impregnated with phosphorus.

8. The phosphorus-modified β-molecular sieve according to claim 7, characterized in that, The phosphorus-containing compound is selected from phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

9. The phosphorus-modified β-molecular sieve according to claim 7, characterized in that, The phosphorus-containing compound is selected from water-soluble organic phosphorus compounds.

10. The phosphorus-modified β-molecular sieve according to claim 9, characterized in that, The organophosphorus compound is a phosphazene.

11. The phosphorus-modified β-molecular sieve according to claim 7, characterized in that, The phosphorus oxide content of the β molecular sieve after impregnation with phosphorus reaches 5%-10% of the total mass of the molecular sieve.

12. The phosphorus-modified β-molecular sieve according to claim 1, characterized in that, The calcination is carried out at a heating rate of 0.5-10℃ / min and held at a set temperature for 3-7 hours.

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