A multi-level pore p-zsm-5 molecular sieve, a preparation method and application thereof

Abstract

The application provides a kind of multi-level hole P-ZSM-5 molecular sieve and its preparation method and application, belong to molecular sieve technical field, using asymmetric quaternary phosphonium base as structure directing agent and phosphorus source one-step method in no alkali metal system guiding synthesis of multi-level hole structure phosphorus-containing ZSM-5 molecular sieve;The application simplifies the pore-forming step in the preparation process of traditional multi-level hole ZSM-5 molecular sieve, and simplifies the steps such as impregnation, grinding, filtration, calcination and hydrothermal aging in the traditional phosphorus modification method;Synthesized in no alkali metal system, avoids a series of steps such as ammonium ion exchange and filtration in the existing alkali metal technology system, and the process is environmentally friendly, with no ammonia-nitrogen wastewater discharge and low energy consumption.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of molecular sieve, in particular to an asymmetric quaternary phosphonium base oriented multi-level pore P-ZSM-5 molecular sieve and a preparation method and application thereof. BACKGROUND

[0002] ZSM-5 molecular sieve is applied to catalytic cracking, aromatization, methanol-to-propylene and biomass conversion and many other catalytic reaction systems due to its unique three-dimensional pore structure, adjustable acidity and excellent shape selectivity. However, in practical application, the conventional ZSM-5 molecular sieve cannot meet the performance requirements of the above catalytic reactions due to its pore structure, acidity and hydrothermal stability. Phosphating of molecular sieve is the most critical technology to improve the hydrothermal stability of ZSM-5 and increase the olefin selectivity of the catalytic reaction, which is successfully applied to alcohol-to-olefin, alkylation of toluene and methanol and catalytic cracking to increase propylene production in industry, and the phosphorus content is usually 1-7wt%.

[0003] Although the phosphating of ZSM-5 molecular sieve effectively improves the hydrothermal stability of the molecular sieve and the olefin selectivity of the product, it still cannot avoid the problem of carbon deposition caused by the coking of carbon precursors in the micropore channel during the reaction, which reduces the service life of the catalyst. Therefore, it is of great significance to construct P-ZSM-5 molecular sieve with multi-level pores, which can improve the hydrothermal stability of the molecular sieve and the olefin selectivity of the product, enhance the mass transfer performance of ZSM-5 channel, make the carbon deposition precursors rapidly diffuse in the channel instead of coking, and thus increase the service life of the catalyst.

[0004] The preparation of conventional multi-level pore P-ZSM-5 mainly focuses on the double-structure directing agent method, which can significantly improve the overall reaction activity, but cannot avoid the problems of complicated process and expensive double-structure directing agent. Therefore, from the requirements of ZSM-5 molecular sieve, it is necessary to meet the high catalytic reaction effect and mass transfer effect, and the process should be simple, and the existing technology is difficult to achieve satisfactory results. SUMMARY

[0005] In view of the problems such as unsatisfactory hydrothermal stability, olefin selectivity and reaction anti-coking ability in the prior art, the present application proposes a single-structure directing agent oriented synthesis of multi-level pore P-ZSM-5 molecular sieve and a preparation method thereof to meet the requirements of mass transfer, hydrothermal stability and olefin selectivity of ZSM-5 molecular sieve catalyst in practical application. The present application uses a specific asymmetric quaternary phosphonium base as a structure directing agent to obtain a phosphorus-containing multi-level pore P-ZSM-5 molecular sieve, which has different physicochemical characteristics from conventional phosphorus-containing multi-level pore P-ZSM-5 molecular sieve, the synthesis process is simple, the utilization efficiency of phosphorus in the molecular sieve is improved, and the hydrothermal stability and catalytic reaction olefin selectivity are improved.

[0006] The technical solution of this invention is as follows:

[0007] A hierarchical porous P-ZSM-5 molecular sieve is synthesized using a structure-directing agent, an asymmetric quaternary phosphonium base. The P-ZSM-5 molecular sieve contains phosphorus within its crystals and has a hierarchical porous MFI structure. Its anhydrous chemical expression is: xSiO2:Al2O3:yP2O5, where x = 50–300 and y = 0.5–30.

[0008] This invention also provides a method for preparing the hierarchical porous P-ZSM-5 molecular sieve, comprising the following steps:

[0009] An asymmetric quaternary phosphorus base, a silicon source, an aluminum source, and water are mixed, and the mixture undergoes a hydrothermal crystallization reaction to obtain a hydrothermal crystallization product.

[0010] The hydrothermal crystallization product was dried and calcined to obtain hierarchical porous P-ZSM-5 molecular sieve.

[0011] The asymmetric quaternary phosphonium base is a tributyl asymmetric quaternary phosphonium base, Butyl3R1P. + OH - , where the length of the R-base chain is 1 to 16, and not equal to 4.

[0012] The aluminum source is one or more of alumina, boehmite, aluminum sol, aluminum hydroxide, and aluminum isopropoxide, mixed in any proportion.

[0013] The silicon source is one or more of solid silica gel, silica sol, tetraethyl orthosilicate, and silica in any proportion.

[0014] In the mixture obtained by mixing the asymmetric quaternary phosphonium base, aluminum source, silicon source and water, the molar ratios are Si / Al = 25-150, P / Al = 0.5-30, and H2O / Si = 2-20. According to the above ratios, the anhydrous chemical expression of the final product is: xSiO2:Al2O3:yP2O5, where x = Si / Al*2 = 50-300 and y = P / Al = 0.5-30.

[0015] The hydrothermal crystallization reaction is as follows: the first stage of pre-crystallization is at a temperature of 50–100°C for 12–50 h, and the second stage of crystallization is at a temperature of 150–200°C for 24–72 h.

[0016] The drying temperature is 80–150°C, the calcination temperature is 500–700°C, and the time is 3–24 hours.

[0017] The present invention also provides the application of the hierarchical porous P-ZSM-5 molecular sieve in the methanol-to-propylene reaction system.

[0018] Compared with the prior art, the application provides a multi-level hole P-ZSM-5 molecular sieve synthesized by using an unsymmetrical quaternary phosphonium base as a structure directing agent, which is a multi-level hole P-ZSM-5 molecular sieve with high-efficiency and stable skeleton aluminum of phosphorus species in the molecular sieve crystal, and the phosphorus species is not easy to flow out.

[0019] The application also provides a preparation method of the multi-level hole P-ZSM-5 molecular sieve, which is synthesized by using a single unsymmetrical quaternary phosphonium base in an alkali-free system, the pore-forming step in the preparation process of the traditional multi-level hole ZSM-5 molecular sieve is simplified, and steps such as impregnation, grinding, filtering, calcining and hydrothermal aging in the traditional phosphorus modification method are simplified; the synthesis in the alkali-free system avoids a series of steps such as ammonium ion exchange and filtering in the existing alkali metal technical system, is environmentally friendly, has no ammonia-nitrogen wastewater discharge and low energy consumption; the phosphorus in the multi-level hole P-ZSM-5 synthesized by using the unsymmetrical quaternary phosphonium base directly acts on the four-coordinated aluminum of the skeleton, and the stability of the skeleton aluminum is high. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The XRD spectrum of ZSM-5 prepared for Comparative Example 1;

[0021] Figure 2 The XRD spectrum of P-ZSM-5 (IWI) prepared for Comparative Example 2;

[0022] Figure 3 The XRD spectrum of HPZ-1 prepared for Example 2;

[0023] Figure 4 The pore size distribution graph of HPZ-1 prepared for Example 2;

[0024] Figure 5 The TEM graph of HPZ-1 prepared for Example 2;

[0025] Figure 6 The XRD spectrum of HPZ-2 prepared for Example 3;

[0026] Figure 7 The pore size distribution graph of HPZ-2 prepared for Example 3;

[0027] Figure 8 The TEM graph of HPZ-2 prepared for Example 3;

[0028] Figure 9 The XRD spectrum of HPZ-3 prepared for Example 4;

[0029] Figure 10 The pore size distribution graph of HPZ-3 prepared for Example 4;

[0030] Figure 11 TEM image of HPZ-3 prepared for Example 4;

[0031] Figure 12 SEM image of HPZ-7 prepared for Example 8;

[0032] Figure 13 Comparison of methanol conversion of HPZ-1 in Example 2 and P-ZSM-5 (IWI) in Comparative Example 2;

[0033] Figure 14 Comparison of product selectivity of HPZ-1 in Example 2 and P-ZSM-5 (IWI) in Comparative Example 2;

[0034] Figure 15 Comparison of methanol conversion of HPZ-1, HPZ-2, HPZ-3 in Example 2-4 and ZSM-5, P-ZSM-5 (IWI) in Comparative Example 1, 2;

[0035] Figure 16 Comparison of propylene selectivity of HPZ-1, HPZ-2, HPZ-3 in Example 2-4 and ZSM-5, P-ZSM-5 (IWI) in Comparative Example 1, 2. DETAILED DESCRIPTION

[0036] In order to further illustrate the present application, the multi-level pore P-ZSM-5 molecular sieve provided by the present application and the preparation method and application thereof are described in detail below in combination with specific examples, but they should not be understood as limiting the scope of protection of the present application.

[0037] In the present application, the asymmetric quaternary phosphonium base has the structure shown in Formula I, wherein the R group chain length is 1 to 16, and is not equal to 4:

[0038]

[0039] The preparation method of the asymmetric quaternary phosphonium base of the present application is not particularly limited, and can be prepared by a method known to those skilled in the art, such as the method disclosed in CN114940690 A, or purchased from the market.

[0040] In the present application, the water used is deionized water.

[0041] Example 1

[0042] The preparation method of the asymmetric quaternary phosphonium base comprises the following steps:

[0043] (1) Take 7.5 mL of tributylphosphine, 7.5 mL of ethanol, and add them to a three-necked flask, stir and heat to 70℃, and heat to reflux for 2h;

[0044] (2) Then 1-bromopropane 6 mL, ethanol 10 mL were mixed and added into the flask, the mixture was stirred and heated to 80℃, and refluxed for 5h;

[0045] (3) The reacted liquid was rotary evaporated at 0.01 MPa and 77℃ for 3h to obtain a white solid sample;

[0046] (4) The white solid sample was taken out and extracted with deionized water, and the upper layer of the residual organic liquid was filtered out, and the lower layer of the aqueous solution was taken out;

[0047] (5) The aqueous solution was added to a chromatography column filled with silica gel and solvent (dichloromethane), and gradient eluted with polar solvents of different polarity (dichloromethane / methanol volume ratio = 50 / 1; 20 / 1; 10 / 1), and thin layer chromatography was used to monitor the eluent until all the substances were separated;

[0048] (6) The target liquid was vacuum dried at 0.025 MPa and 70℃ overnight to obtain a white solid sample, which was the pure asymmetric tributylpropylphosphonium bromide;

[0049] (7) 2g of tributylpropylphosphonium bromide was taken out and ion exchanged using a bipolar membrane electrodialysis device after adding 50 mL of water, and the product in the alkali chamber was an aqueous solution of asymmetric tributylpropylphosphonium hydroxide;

[0050] (8) The water was removed by rotary evaporation at 0.02 MPa and 80℃ to obtain an aqueous solution of asymmetric tributylpropylphosphonium hydroxide with a specified concentration.

[0051] 1-bromopropane in step (2) was replaced by 1-bromomethane or 1-bromooctane or 1-bromohexadecane, and the corresponding asymmetric quaternary phosphonium base tributylmethylphosphonium hydroxide aqueous solution, tributyl octylphosphonium hydroxide aqueous solution, and tributylhexadecylphosphonium hydroxide aqueous solution were prepared according to the method of Example 1.

[0052] Comparative Example 1

[0053] A method for synthesizing ZSM-5 molecular sieve by TPAOH guidance, comprising the following steps:

[0054] (1) 0.0675g of pseudo-boehmite (Macklin, analytical pure, Al2O3 content 70wt%) was taken out and mixed with 3.3g of tetrapropylammonium hydroxide (National Pharmaceutical Group Chemical Reagent Co., Ltd., analytical pure, TPAOH content 25wt%) and placed in the polytetrafluoroethylene liner of the crystallization kettle, and then heated to 140℃ at a heating rate of 2℃ / min and kept for 3h, and then cooled to room temperature to obtain an intermediate product;

[0055] (2) Add 4 g of white carbon black (Shanghai Aldrin Biochemical Co., Ltd., analytical pure, SiO2content 99.7 wt%) and 30 mL of deionized water to the intermediate product, and the mixture has a molar ratio of TPAOH / Si = 0.06, Si / Al = 75, and H2O / Si = 6.5. After stirring uniformly, crystallization is performed at 170°C for 48 h;

[0056] (3) The crystallized product is filtered, dried at 120°C for 12 h, and calcined at 550°C for 3 h to obtain the TPAOH-directed synthesized ZSM-5 molecular sieve.

[0057] The sample is subjected to XRD characterization, and the XRD spectrum is shown in Figure 1 , which proves that the structure is a ZSM-5 structure.

[0058] Comparative Example 2

[0059] A method for modifying ZSM-5 molecular sieve by a diammonium hydrogen phosphate impregnation method, comprising the following steps:

[0060] (1) 0.17 g of diammonium hydrogen phosphate (National Pharmaceutical Group Chemical Reagent Co., Ltd., analytical pure) and 2 g of deionized water are weighed into a crucible;

[0061] (2) 2 g of ZSM-5 prepared in Comparative Example 1 is added to the diammonium hydrogen phosphate aqueous solution in step (1), and stirred at room temperature for 0.5 h;

[0062] (3) The sample obtained in step (2) is dried in an oven at 140°C for 10 h, and then heated to 550°C at a heating rate of 10°C / min in a muffle furnace for calcination for 6 h to obtain sample P-ZSM-5(IWI).

[0063] The sample is subjected to XRD characterization, and the XRD spectrum is shown in Figure 2 .

[0064] Example 2

[0065] A method for guiding synthesis of hierarchical pore P-ZSM-5 molecular sieve by tributylpropylphosphonium hydroxide, comprising the following steps:

[0066] (1) 0.0675 g of pseudo-boehmite (Mcclin, A2O3 content 70 wt%), 4 g of white carbon black, and 10.5 mL of deionized water are taken according to the molar ratio of Si:Al:H2O:P = 75:1:195:3, and 4.41 g of tributylpropylphosphonium hydroxide aqueous solution (tributylpropylphosphonium hydroxide content 25 wt%) are mixed and stirred uniformly, and then placed in a reaction kettle;

[0067] (2) The reaction kettle is placed in an 80°C oven for pre-crystallization for 24 h, and then transferred to a 170°C oven for crystallization for 24 h;

[0068] (3) The product after crystallization is filtered, dried at 120℃ for 12h, and calcined at 550℃ for 3h to obtain the oriented synthesis of hierarchical pore P-ZSM-5 molecular sieve. The final product has a chemical formula of 75SiO2:Al2O3:3P2O5, and is named as HPZ-1.

[0069] The XRD spectrum of HPZ-1 is shown in Figure 3 , which proves that the structure of the synthesized product is MFI structure; the pore size distribution is shown in Figure 4 , which proves that the structure of the synthesized product is hierarchical pore structure, and the TEM morphology is shown in Figure 5 .

[0070] Example 3

[0071] A method for oriented synthesis of hierarchical pore P-ZSM-5 molecular sieve by tributyl octyl phosphonium hydroxide, the tributyl propyl phosphonium hydroxide aqueous solution in step (1) of example 2 is replaced by tributyl octyl phosphonium hydroxide aqueous solution, the molar ratio of Si, Al, H2O and P in the mixture is unchanged, and the others are the same as example 2. The molecular sieve prepared is named as HPZ-2.

[0072] The XRD spectrum of HPZ-2 is shown in Figure 6 , which proves that the structure of the synthesized product is MFI structure, the pore size distribution is shown in Figure 7 , which proves that the structure of the synthesized product is hierarchical pore structure, and the TEM morphology is shown in Figure 8 .

[0073] Example 4

[0074] A method for oriented synthesis of hierarchical pore P-ZSM-5 molecular sieve by tributyl octyl phosphonium hydroxide, the tributyl propyl phosphonium hydroxide aqueous solution in step (1) of example 2 is replaced by tributyl octyl phosphonium hydroxide aqueous solution, the molar ratio of Si, Al, H2O and P in the mixture is unchanged, and the others are the same as example 2. The molecular sieve prepared is named as HPZ-2.

[0075] The XRD spectrum of HPZ-2 is shown in Figure 9 , which proves that the structure of the synthesized product is MFI structure, the pore size distribution is shown in Figure 10 , which proves that the structure of the synthesized product is hierarchical pore structure, and the TEM morphology is shown in Figure 11 .

[0076] Example 5

[0077] A method for oriented synthesis of hierarchical pore P-ZSM-5 molecular sieve by tributyl octyl phosphonium hydroxide, the tributyl propyl phosphonium hydroxide aqueous solution in step (1) of example 2 is replaced by tributyl octyl phosphonium hydroxide aqueous solution, the molar ratio of Si, Al, H2O and P in the mixture is unchanged, and the others are the same as example 2. The molecular sieve prepared is named as HPZ-2.

[0078] Example 6

[0079] A method for synthesizing hierarchical P-ZSM-5 zeolite using tributylhexadecylphosphonium hydroxide as a directing agent, the hierarchical P-ZSM-5 is prepared according to the method of Example 4, except that the feeding amount of Si / Al is 75, and the prepared hierarchical MFI structure zeolite is named HPZ-6.

[0080] Example 7

[0081] A method for synthesizing hierarchical P-ZSM-5 zeolite using tributylhexadecylphosphonium hydroxide as a directing agent, the hierarchical P-ZSM-5 is prepared according to the method of Example 4, except that the feeding amount of Si / Al is 75, and the prepared hierarchical MFI structure zeolite is named HPZ-6.

[0082] Example 8

[0083] A method for synthesizing hierarchical P-ZSM-5 zeolite using tributylhexadecylphosphonium hydroxide as a directing agent, the hierarchical P-ZSM-5 is prepared according to the method of Example 4, except that the feeding amount of Si / Al is 75, and the prepared hierarchical MFI structure zeolite is named HPZ-6. Figure 12 It can be seen that the typical MFI morphology.

[0084] Example 9

[0085] A method for synthesizing hierarchical P-ZSM-5 zeolite using tributylhexadecylphosphonium hydroxide as a directing agent, the hierarchical P-ZSM-5 is prepared according to the method of Example 4, except that the feeding amount of Si / Al is 75, and the prepared hierarchical MFI structure zeolite is named HPZ-6.

[0086] Example 10

[0087] A method for synthesizing hierarchical P-ZSM-5 zeolite using tributylhexadecylphosphonium hydroxide as a directing agent, the hierarchical P-ZSM-5 is prepared according to the method of Example 4, except that the feeding amount of Si / Al is 75, and the prepared hierarchical MFI structure zeolite is named HPZ-6.

[0088] Example 11

[0089] A method for synthesizing hierarchical P-ZSM-5 zeolite using tributylhexadecylphosphonium hydroxide as a directing agent, the hierarchical P-ZSM-5 is prepared according to the method of Example 4, except that the feeding amount of Si / Al is 75, and the prepared hierarchical MFI structure zeolite is named HPZ-6.

[0090] Example 12

[0091] A method for synthesizing hierarchical P-ZSM-5 zeolite using tributylmethylphosphonium hydroxide as directing agent, the hierarchical P-ZSM-5 was prepared according to the method of Example 8, except that the silicon source white carbon black was replaced by tetraethyl orthosilicate, the pre-crystallization condition was 50℃ for 24h, the crystallization condition was 150℃ for 72h, and the calcination condition was 600℃ for 8h, to obtain a hierarchical zeolite with MFI structure, named HPZ-11.

[0092] Example 13

[0093] A method for synthesizing hierarchical P-ZSM-5 zeolite using tributylmethylphosphonium hydroxide as directing agent, the hierarchical P-ZSM-5 was prepared according to the method of Example 8, except that the calcination condition was 650℃ for 12h, to obtain a hierarchical zeolite with MFI structure, named HPZ-12.

[0094] The methanol-to-propylene catalytic performance of the molecular sieve HPZ-1 prepared in Example 2 and the molecular sieve P-ZSM-5(IWI) prepared in Comparative Example 2 as catalysts was tested:

[0095] The reaction was carried out at a methanol feed flow rate of 4.2uL / min, 0.2g catalyst, a reaction space velocity of 1h -1 , and a reaction temperature of 480℃, and the conversion rate comparison is shown in Figure 13 The stability(210h) of HPZ-1 synthesized using tributylpropyl quaternary phosphonium base as directing agent was higher than that of P-ZSM-5(IWI)(100h) modified by impregnation method, and the product selectivity comparison is shown in Figure 14 The results showed that the propylene selectivity(≈57%) of HPZ-1 synthesized using tributylpropyl quaternary phosphonium base as directing agent was higher than that of P-ZSM-5(IWI)(≈37.7%).

[0096] The methanol-to-propylene catalytic performance of the molecular sieves HPZ-1, HPZ-2, and HPZ-3 prepared in Examples 2-4 and the molecular sieves ZSM-5 and P-ZSM-5(IWI) prepared in Comparative Examples 1 and 2 as catalysts was tested:

[0097] The reaction was carried out at a methanol feed flow rate of 13.1uL / min, 0.1g catalyst, a reaction space velocity of 6h -1 , and a reaction temperature of 480℃, and the reaction stability is shown in Figure 15 , and the propylene selectivity comparison is shown in Figure 16The results show that the stability of HPZ-1 synthesized using tributylpropylphosphonium hydroxide as a directing agent is the highest (45 h), higher than that of P-ZSM-5 (IWI) modified by impregnation (8 h), and the propylene selectivity (≈58%) is higher than that of the P-ZSM-5 (IWI) molecular sieve modified by impregnation (≈38%), and the total olefin selectivity (≈80%) is also higher than that of the P-ZSM-5 (IWI) modified by impregnation (≈67%).

[0098] The above merely describes the preferred embodiments of the present application, and is not intended to limit the present application in any form. It should be noted that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A hierarchical-pore P-ZSM-5 molecular sieve, characterized in that, The asymmetric quaternary phosphonium base is used as a structure directing agent for synthesis, has a hierarchical pore MFI structure, contains phosphorus in the crystal, and has a non-aqueous chemical expression of xSiO2:Al2O3:yP2O5, wherein x=50-300, y=0.5-30. The asymmetric quaternary phosphonium base is a tributyl asymmetric quaternary phosphonium base Butyl3R1P + OH - wherein R is a chain length of 1 to 16, and is not equal to 4.

2. The method of making a hierarchical pore P-ZSM-5 molecular sieve of claim 1, characterized by, The method comprises the following steps: The asymmetric quaternary phosphonium base, a silicon source, an aluminum source and water are mixed, and the mixture is subjected to a hydrothermal crystallization reaction to obtain a hydrothermal crystallization product; The hydrothermal crystallization product is dried and calcined to obtain the hierarchical pore P-ZSM-5 molecular sieve; The mixture obtained by mixing the asymmetric quaternary phosphonium base, the aluminum source, the silicon source and water has a molar ratio of Si / Al=25-150, P / Al=0.5-30 and H2O / Si=2-20.

3. The method of making a hierarchical pore P-ZSM-5 molecular sieve of claim 2, wherein, The aluminum source is one or more of alumina, pseudo-boehmite, aluminum sol, aluminum hydroxide and aluminum isopropyl alcohol in any proportion.

4. The method of making a hierarchical pore P-ZSM-5 molecular sieve of claim 2, wherein, The silicon source is one or more of solid silica gel, silica sol, tetraethyl orthosilicate and white carbon black in any proportion.

5. The method of making a hierarchical pore P-ZSM-5 molecular sieve of claim 2, wherein, The hydrothermal crystallization reaction is specifically as follows: the first-stage pre-crystallization temperature is 50-100 DEG C, and the time is 12-50 h; and the second-stage crystallization temperature is 150-200 DEG C, and the time is 24-72 h.

6. The method of making a hierarchical porous P-ZSM-5 molecular sieve of claim 2, wherein, The calcination temperature is 500-700 DEG C, and the time is 3-24 h.

7. The hierarchical pore P-ZSM-5 molecular sieve of claim 1 is applied to a methanol-to-olefin reaction system.

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