Phosphorus modified beta molecular sieve

Abstract

The invention discloses a phosphorus-modified beta molecular sieve, which is characterized in that after being treated at 800 DEG C for 17 hours in a 100% water vapor atmosphere, the molar ratio of silicon oxide / aluminum oxide of a skeleton measured by 29Si MAS NMR is less than or equal to 40, and the ratio of the resonance signal characteristic peak area of chemical shift-17 + / -3 measured by 31P MAS NMR to the resonance signal characteristic peak area of chemical shift-30 + / -5 measured by 31P MAS NMR is greater than or equal to 0.70.

Description

Technical Field

[0001] The present invention relates to the field of molecular sieves, and more particularly to beta molecular sieves. Background Art

[0002] β molecular sieve has a three-dimensional twelve-membered ring channel structure and was first synthesized by Mobil Corporation in the United States in 1967 (US3308069). Due to the unique topological structure and good thermal and hydrothermal stability of β molecular sieve, it exhibits excellent catalytic performance in reactions such as hydrocracking, hydroisomerization, hydrocarbon cracking, and alkylation.

[0003] In catalytic cracking reactions, although many researchers have found that β molecular sieves as additives can optimize the distribution of catalytic cracking reaction products and increase the yield of light olefins and gasoline components, they are easy to dealuminate, resulting in low reaction activity under harsh reaction conditions. At present, the industry usually improves the reaction performance of β molecular sieves by modifying them, among which phosphorus modification is considered to be a very effective means.

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

[0005] CN1179994A proposes a modification method for β molecular sieve, in which the Naβ molecular sieve is exchanged with ammonium ions until the Na2O content on the molecular sieve is less than 0.1% by weight; the ammonium-exchanged β molecular sieve is then treated with acid to remove part of the framework aluminum, so that its silicon-aluminum ratio is greater than 50; the dealuminated β molecular sieve is mixed with phosphoric acid or phosphate and then dried to make the amount of P2O5 on the obtained molecular sieve 2-5% by weight; and finally, it is hydrothermally roasted at 450-650°C for 0.5-4 hours in a water vapor atmosphere. Through this modification method, the β molecular sieve can obtain a higher yield of olefins, especially isoolefins, and a lower coke yield when used in the cracking reaction of hydrocarbons.

[0006] The existing technology usually only focuses on the phosphorus modification method of β molecular sieve when studying the phosphorus modification of β molecular sieve, and there is little research on the calcination conditions after phosphorus modification. Since the template agent remaining in the pores of β molecular sieve can usually only be completely removed by calcining for more than 3 hours under air / water vapor conditions at above 450°C, most researchers assume that the calcination temperature must be above 450°C. Summary of the invention

[0007] After phosphorus modification, β molecular sieves will inevitably have serious dealumination when calcined at a calcination temperature above 450°C. After extensive research, the inventor unexpectedly discovered that when β molecular sieves are calcined at a lower temperature after phosphorus modification, although the template agent is not completely removed, it can better prevent the removal of the framework aluminum of the β molecular sieve, so that the β molecular sieve modified with phosphorus compounds exhibits unique physical and chemical characteristics.

[0008] Therefore, one of the purposes of the invention is to provide a phosphorus-modified β molecular sieve having characteristics different from those of the prior art, and the second purpose is to provide a method for preparing the molecular sieve.

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

[0010] 29 In Si MAS NMR, the chemical shift 104±1 resonance signal characteristic represents the four coordinations of silicon, which are three oxygen bridges connected to silicon and one oxygen bridge connected to aluminum, while the chemical shift 110±1 and 114±1 resonance signal characteristics represent that the four coordinations of silicon are connected to other silicon after oxygen bridges. The area of ​​the characteristic peak of the chemical shift 104±1 resonance signal is defined as A, the area of ​​the characteristic peak of the 110±1 resonance signal is defined as B, and the area of ​​the characteristic peak of the 114±1 resonance signal is defined as C. 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 the present invention, after being treated at 800°C for 17 hours under 100% water vapor atmosphere, has a molar ratio of silicon oxide to aluminum oxide in the framework of ≤40, preferably ≤37.

[0011] 31 In P MAS NMR, the chemical shift -17±3 resonance signal represents the phosphorus species coordinated with the hexacoordinated non-framework aluminum phase; the chemical shift -30±5 resonance signal represents the phosphorus species coordinated with the tetracoordinated framework aluminum phase and the phosphorus species in aluminum phosphate. After the phosphorus-modified beta molecular sieve of the present invention is treated at 800° C. for 17 hours under 100% water vapor atmosphere, the characteristic peak area ratio of the chemical shift -17±3 resonance signal to the -30±5 resonance signal is ≥0.70, preferably ≥0.90.

[0012] In order to achieve the second object of the present invention, the method for phosphorus-modified beta molecular sieve provided in the second aspect of the present invention is characterized by comprising the following steps:

[0013] (1) The β molecular sieve raw powder is subjected to ammonium salt ion exchange to be an ammonium type;

[0014] (2) the ammonium type β molecular sieve is impregnated with phosphate salt and dried;

[0015] (3) The phosphorus-impregnated β molecular sieve is calcined at 150-350° C. to obtain a modified β molecular sieve modified with a phosphorus-containing compound.

[0016] More specifically, the method for phosphorus-modified beta molecular sieve provided by the present invention comprises the following steps:

[0017] (1) exchanging the original β molecular sieve powder with ammonium salt ions to obtain an 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 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 into the molecular sieve layer until the molecular sieve layer is completely wetted, and the β molecular sieve is dried at 80-120° C. for 12 h to obtain a phosphorus-impregnated β molecular sieve, wherein the added phosphorus is calculated as phosphorus pentoxide to reach 5%-10% of the mass of the β molecular sieve;

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

[0020] In the method provided by the present invention, the raw β molecular sieve powder can be derived from industrially produced nano β molecular sieves, which can be synthesized by a template method or a template-free method, and preferably a sodium type β molecular sieve synthesized by a template method. The raw β molecular sieve powder preferably has an average grain size of ≤300nm, a molar ratio of silicon oxide to aluminum oxide of 20-40, preferably 20-30, and a characteristic peak half-peak width of 20°-23.5° in the XRD spectrum of ≥0.230, preferably ≥0.24.

[0021] In the method provided by the present invention, the more specific process of the ammonium salt ion exchange is as follows: the sodium type β molecular sieve is exchanged in an ammonium salt solution at 50-90° C., the type of ammonium salt used may 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 the sodium type β molecular sieve to the ammonium salt solution is 1:5-1:20, the number of exchanges is 1-4 times, and the ammonium type β molecular sieve after the ammonium salt ion exchange has a sodium oxide content of ≤0.2% by weight.

[0022] In the method provided by the present invention, the phosphorus-containing compound can be selected from inorganic phosphorus sources such as phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, etc., and can also be one or more water-soluble organic phosphorus sources including phosphazene.

[0023] The phosphorus-modified beta molecular sieve provided by the present invention can better prevent the removal of framework aluminum into non-framework aluminum than the prior art, has excellent hydrothermal stability and product selectivity, and can be applied to catalytic cracking or catalytic cracking reactions as an active component of a catalyst or an auxiliary agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the XRD spectrum of sample A in Example 1.

[0025] Figure 2 This is a SEM photograph of sample A in Example 1.

[0026] Figure 3 The sample A of Example 1 was subjected to hydrothermal treatment at 800°C for 17 hours in a 100% steam atmosphere. 29 Si MAS NMR spectrum.

[0027] Figure 4 The sample A of Example 1 was subjected to hydrothermal treatment at 800°C for 17 hours in a 100% steam atmosphere. 31 P MAS NMR spectrum.

[0028] Figure 5 The sample B of Example 2 was subjected to hydrothermal treatment at 800°C for 17 hours in a 100% steam atmosphere. 29 Si MAS NMR spectrum.

[0029] Figure 6 The sample B of Example 2 was subjected to hydrothermal treatment at 800°C for 17 hours in a 100% steam atmosphere. 31 P MAS NMR spectrum.

[0030] Figure 7 The sample C of Example 3 was subjected to hydrothermal treatment at 800°C for 17 hours in a 100% steam atmosphere. 29 Si MAS NMR spectrum.

[0031] Figure 8 The sample C of Example 3 was subjected to hydrothermal treatment at 800°C for 17 hours in a 100% steam atmosphere. 31 P MAS NMR spectrum.

[0032] Fig. 9 The sample DB-D of comparative example 2 was subjected to hydrothermal treatment at 800°C for 17 hours in a 100% steam atmosphere. 29 SiMAS NMR spectrum.

[0033] Fig.10 The sample DB-D of comparative example 2 was subjected to hydrothermal treatment at 800°C for 17 hours in a 100% steam atmosphere. 31 PMAS NMR spectrum. DETAILED DESCRIPTION

[0034] The present invention will be further described below by way of examples, but the contents of the present invention are not limited thereto.

[0035] In each embodiment and comparative example, the X-ray diffraction (XRD) crystal phase diagram was obtained by Philips Panalytical X'pert, and the test conditions were: Cu target, Kα radiation, Ni filter, super energy detector, tube voltage 30KV, tube current 40mA. The P2O5, SiO2, and Al2O3 contents in each sample of β molecular sieve were determined by X-ray fluorescence method (see "Petrochemical Analysis Method (RIPP Experimental Method)", edited by Yang Cuiding et al., Science Press, published in 1990).

[0036] The scanning electron microscope (SEM) images were obtained by a FEI Quanta 200F scanning electron microscope.

[0037] The solid-state NMR results were obtained by using Bruker's AVANCE III 600WB NMR spectrometer. The resonance peak spectrum was fitted and the peak areas and ratios were calculated using the integration method.

[0038] Example 1

[0039] Add β molecular sieve (SiO2 / Al2O3=22, the same below) from Changling Catalyst Branch of Sinopec Catalyst Company into the prepared ammonium chloride solution, exchange and wash until the sodium oxide content is less than 0.2% by weight, filter and dry to obtain sample A1; weigh 132 g of the obtained sample A1 and add diammonium hydrogen phosphate (Beijing Yili Fine Chemicals Co., Ltd., 99%) aqueous solution by immersion, the diammonium hydrogen phosphate aqueous solution contains 16 g of diammonium hydrogen phosphate and 98 g of water, to obtain sample A2; dry sample A2 and calcine at 250°C for 3 hours to obtain sample A.

[0040] The XRD spectrum of sample A is shown in Figure 1 , SEM photos see Figure 2 .

[0041] The XRD spectrum and SEM images of sample A are shown in Figure 1 and Figure 2 .

[0042] After sample A was hydrothermally aged at 800°C for 17 hours in a 100% steam atmosphere, 29 Si MAS NMR, 31 The results were characterized by P MAS NMR.

[0043] 29 Si MAS NMR spectrum is shown in Figure 3 The molar ratio of silicon oxide to aluminum oxide in the skeleton obtained by peak separation calculation is shown in Table 1;

[0044] 31 P MAS NMR spectrum is shown in Figure 4 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 is shown in Table 2.

[0045] Comparative Example 1

[0046] Add the β molecular sieve into the prepared ammonium chloride solution, exchange and wash until the sodium oxide content is less than 0.2% by weight, filter and dry; weigh 132g of the obtained sample and add diammonium hydrogen phosphate (Beijing Yili Fine Chemicals Co., Ltd., 99%) aqueous solution by immersion, the aqueous solution contains 16g diammonium hydrogen phosphate and 98g water, after the sample is dried, the obtained sample is calcined at 550°C for 5 hours to obtain sample DB-A.

[0047] After sample DB-A was hydrothermally aged at 800℃ for 17 hours in a 100% water vapor atmosphere, 29 Si MASNMR, 31 The results were characterized by P MAS NMR. 29 The molar ratio of silicon oxide to aluminum oxide in the skeleton obtained by peak separation calculation of Si MAS NMR is shown in Table 1. 31 The ratio of the characteristic peak area of ​​the P MAS NMR chemical shift -17±3 resonance signal to the characteristic peak area of ​​the -30±5 resonance signal is shown in Table 2.

[0048] Example 2

[0049] Add the β molecular sieve into the prepared ammonium chloride solution, exchange and 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 add it into a phosphoric acid (Beijing Chemical Plant, 85%) aqueous solution by immersion, the phosphoric acid aqueous solution contains 14g phosphoric acid and 85g water, to obtain sample B2; dry sample B2 and calcine at 350°C for 4 hours to obtain sample B.

[0050] After sample B was hydrothermally aged at 800°C for 17 hours in a 100% steam atmosphere, 29 Si MASNMR, 31 The results were characterized by P MAS NMR. 29 Si MAS NMR spectrum is shown in Figure 5 The molar ratio of silicon oxide to aluminum oxide in the skeleton obtained by peak separation calculation is shown in Table 1. 31 P MAS NMR spectrum is shown in Figure 6 The ratio of the characteristic peak area of ​​the chemical shift -17±3 resonance signal to the characteristic peak area of ​​the -30±5 resonance signal is shown in Table 2.

[0051] Example 3

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

[0053] After sample C was hydrothermally aged at 800°C for 17 hours in a 100% steam atmosphere, 29 Si MASNMR, 31 The results were characterized by P MAS NMR. 29 Si MAS NMR spectrum is shown in Figure 7 The molar ratio of silicon oxide to aluminum oxide in the skeleton obtained by peak separation calculation is shown in Table 1. 31 P MAS NMR spectrum is shown in Figure 8 The ratio of the characteristic peak area of ​​the chemical shift -17±3 resonance signal to the characteristic peak area of ​​the -30±5 resonance signal is shown in Table 2.

[0054] Example 4

[0055] Add β molecular sieve into the prepared ammonium chloride solution, exchange and wash until the sodium oxide content is less than 0.2% by weight, filter and dry to obtain sample D1; weigh 40g of the obtained sample D1 and add diammonium phosphate (Beijing Yili Fine Chemicals Co., Ltd., 99%) aqueous solution by immersion, the diammonium phosphate aqueous solution contains 9g diammonium phosphate and 30g water, to obtain sample D2; dry sample D2 and calcine at 330°C for 4 hours to obtain sample D.

[0056] After sample D was hydrothermally aged at 800°C for 17 hours in a 100% steam atmosphere, 29 Si MASNMR, 31 The results were characterized by P MAS NMR. 29 The molar ratio of silicon oxide to aluminum oxide in the skeleton obtained by peak separation calculation of Si MAS NMR is shown in Table 1. 31 The ratio of the characteristic peak area of ​​the P MAS NMR chemical shift -17±3 resonance signal to the characteristic peak area of ​​the -30±5 resonance signal is shown in Table 2.

[0057] Comparative Example 2

[0058] Add the β molecular sieve into the prepared ammonium chloride solution, exchange and wash until the sodium oxide content is less than 0.2% by weight, filter and dry; weigh 40g of the obtained sample and add diammonium phosphate (Beijing Yili Fine Chemicals Co., Ltd., 99%) aqueous solution by immersion, the aqueous solution contains 9g diammonium phosphate and 30g water, and after the sample is dried, the obtained sample is calcined at 450°C for 4 hours to obtain sample DB-D.

[0059] After hydrothermal aging at 800℃ for 17 hours in a 100% steam atmosphere, the samples DB-D 29 Si MASNMR, 31 The results were characterized by P MAS NMR. 29 Si MAS NMR spectrum is shown in Fig. 9 , 29 The molar ratio of silicon oxide to aluminum oxide in the skeleton obtained by peak separation calculation of Si MAS NMR is shown in Table 1. 31 P MAS NMR spectrum is shown in Fig.10 , 31 The ratio of the characteristic peak area of ​​the P MAS NMR chemical shift -17±3 resonance signal to the characteristic peak area of ​​the -30±5 resonance signal is shown in Table 2.

[0060] Table 1

[0061]

[0062] From the data in Table 1, it can be seen that after the phosphorus-modified β molecular sieve of the present invention is subjected to hydrothermal aging treatment at 800°C / 17 hours in a 100% water vapor atmosphere, although the bulk SiO2 / Al2O3 molar ratio measured by fluorescence method remains basically unchanged, 29 The SiO2 / Al2O3 molar ratio of the framework measured by SiMAS NMR decreased significantly, indicating that the framework dealumination was significantly reduced, resulting in higher hydrothermal stability.

[0063] Table 2

[0064]

[0065] Combined with the data in Table 1, it can be seen from the data in Table 2 that the phosphorus-modified β molecular sieve of the present invention removes less framework aluminum under hydrothermal conditions compared with the comparative example, and the interaction between phosphorus and the non-framework aluminum removed by high temperature in the molecular sieve is also stronger.

[0066] Test Case

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

[0068] The samples prepared in the above examples 1-4 and comparative examples 1-2 were aged at 800°C and 100% steam for 17 hours, and then pressed and sieved to obtain particles of 20-40 mesh, and evaluated in a fixed bed microreactor. The raw material for evaluation was n-tetradecane.

[0069] The evaluation conditions are reaction temperature of 550°C, regeneration temperature of 600°C, oil feed amount of 1.56g, oil feed time of 70 seconds, and catalyst storage of 2g.

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

[0071] Table 3

[0072] Sample No. 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] It can be seen from the data in Table 3 that, compared with the comparative example samples, the phosphorus-modified β molecular sieve samples of the present invention improve the cracking ability of hydrocarbons with a higher conversion rate while increasing the cracking reaction depth, and have better reaction activity and a higher yield of light olefins, mainly ethylene and propylene.

Claims

1. A phosphorus-modified beta molecular sieve, characterized in that: After being treated at 800°C for 17 hours in a 100% steam atmosphere, 29 The molar ratio of silicon oxide to aluminum oxide in the framework measured by Si MAS NMR is ≤ 40. 31 The ratio of the characteristic peak area of ​​the resonance signal with a chemical shift of -17±3 to that of the resonance signal with a chemical shift of -30±5 measured by P MAS NMR is ≥0.

70.

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

3. The phosphorus-modified beta molecular sieve according to claim 1, characterized in that: The average grain size is ≤300nm, the molar ratio of silicon dioxide to aluminum oxide is 20-40, and the half-peak width of the characteristic peak at 20°-23.5° in the XRD spectrum is ≥0.

24.

4. The phosphorus-modified beta molecular sieve according to claim 1, characterized in that: The preparation method of β molecular sieve can be derived from either organic template synthesis or organic template-free synthesis system.

5. The method for preparing the phosphorus-modified beta molecular sieve according to claim 1, characterized in that: The following steps are involved: (1) The β molecular sieve raw powder is subjected to ammonium salt ion exchange to be an ammonium type; (2) the ammonium type β molecular sieve is impregnated with phosphate salt and dried; (3) The phosphorus-impregnated β molecular sieve is calcined at 150-350° C. to obtain a modified β molecular sieve modified with a phosphorus-containing compound.

6. The preparation method according to claim 5, characterized in that: The raw β molecular sieve powder is a sodium-type β molecular sieve which is washed with water to a pH value of 7-8 after synthesis.

7. The preparation method according to claim 5, characterized in that: The process of ammonium salt ion exchange of β molecular sieve is as follows: the sodium type β molecular sieve raw material is exchanged in an ammonium salt solution at 50-90°C for 1-3 hours, the mass ratio of the molecular sieve to the ammonium salt solution is 1:5-1:20, the number of exchanges is 1-4 times, and the exchanged β molecular sieve is obtained, and the sodium oxide content is ≤0.2% by weight.

8. The preparation method according to claim 5, 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 ammonium salt aqueous solution is 5-20% by weight.

9. The preparation method according to claim 5, characterized in that: The process of phosphorus impregnation modification of β molecular sieve 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 until the molecular sieve layer is completely wetted, and dried at 80-120°C for 12 hours to obtain the phosphorus-impregnated β molecular sieve.

10. The preparation method according to claim 9, characterized in that: The phosphorus-containing compound is selected from phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or from water-soluble organic phosphorus, such as phosphazene.

11. The preparation method according to claim 9, characterized in that: After the phosphorus impregnation modification, the mass of the phosphorus oxide reaches 5%-10% of the total mass of the molecular sieve.

12. The preparation method according to claim 5, characterized in that: The calcination is carried out at a heating rate of 0.5-10° C. / min and maintained at a set temperature for 3-7 hours.

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