Method for fixed-point modulation of molecular sieve acid center

Abstract

The invention discloses a method for fixed-point modulation of acidity of a molecular sieve. The method comprises the following steps: (1) dissolving a proper amount of cinnamate in benzene, uniformly stirring, and fully dissolving; (2) impregnating a molecular sieve with the solution obtained in the step (1), and filtering the molecular sieve after impregnation; wherein the pore diameter of the molecular sieve is 0.4 nm to 0.9 nm; (3) purging the molecular sieve filtered out in the step (2) with hot nitrogen, and naturally cooling to room temperature after purging; and (4) cleaning the molecular sieve obtained in the step (3) with deionized water to obtain the acid center modulated molecular sieve. According to the invention, only the acid center at the cross position of the molecular sieve pore channel is modified, the acid center at the straight-through pore channel is not influenced, and the smoothness of the pore channel is not influenced.

Description

Technical Field

[0001] The present invention belongs to the field of molecular sieve materials, and relates to a method for site-specific modulation of acid centers of molecular sieves, specifically a method for site-specific modulation of acid centers at the intersections of mesopores of molecular sieves with pore diameters of 0.4 nm to 0.9 nm. Background Art

[0002] Molecular sieves are solid acid catalytic materials with an ordered pore structure and acidity, and are widely used in various petrochemical production processes. For example, Y-type molecular sieves are used in catalytic cracking processes, ZSM-5 molecular sieves are used in toluene methanol alkylation processes, catalytic dewaxing processes, aromatization processes, etc., and Beta molecular sieves are used in cumene synthesis processes, etc.

[0003] When molecular sieves are applied, it is often necessary to modulate and modify their acidity or pore structure to obtain the most suitable acidity distribution, strength and pore structure for the reaction. For example, in order to eliminate strong acid centers in molecular sieves, means such as hydrothermal treatment, loading oxides of alkali metals or rare earth metals are commonly used; in order to increase the number of medium strong acid centers, phosphorus oxide modification is commonly used; in order to eliminate acid centers on the outer surface of molecular sieve crystals, silanization or organic phosphorus compound modification is commonly used; in order to increase the tortuosity of the pores of molecular sieves, means of loading metal or non-metal oxides are commonly used; in order to reduce the pore mouth size of molecular sieves, silanization methods are commonly used.

[0004] In the pore structure of molecular sieves, there are usually a large number of pore intersections, that is, two pores penetrate each other at a certain angle (such as 90°) and are internally connected, such as ZSM-5 molecular sieves, Beta molecular sieves and Y molecular sieves. The space at the intersection of such pores is open, and acid centers are more concentrated than at non-intersection sites, and often become active areas for side reactions to occur or carbon deposition precursors to be generated. For example, when ZSM-5 molecular sieves catalyze the alkylation reaction of ethylstyrene, the target product p-diethylbenzene is restricted by the pore space in the straight-through pores and generally undergoes side reactions. However, at the pore intersection, the space is open, and p-diethylbenzene can continue to react with ethylene under the action of acid centers to undergo cyclization and condensation reactions to generate carbon deposition precursors. Another example is that in the reaction of the bimolecular condensation of aniline catalyzed by Beta molecular sieves to form diphenylamine, there is enough space and a sufficient number of acid centers at the intersection of two-dimensional pores to catalyze the cyclization and condensation reactions of aniline molecules to generate macromolecules such as tricyclic linear acridine and bicyclic planar quinoline, and diffuse out of the pores, reducing the selectivity of diphenylamine. However, among the existing modification methods for molecular sieves, there is no method that can specifically modulate only the acid centers at the intersections of the pores of molecular sieves. For example, the modification means of loading oxides of alkali metals or rare earth metals is a general modulation means that does not distinguish the positions of acid centers, that is, it can cover the acid centers in both the straight-through pores and the pore intersections of molecular sieves, thus covering the acid centers in the straight-through pores that do not need to be modulated. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a method for site-specific modulation of acid sites at the intersections of molecular sieve pores. This method only modifies the acid sites at the intersections of molecular sieve pores and will not affect the acid sites at the straight-through pores.

[0006] The present invention provides a method for site-specific modulation of acid sites at the intersections of molecular sieve pores, which is applicable to various molecular sieves with pore diameters of 0.4 nm to 0.9 nm. The metal oxide accounts for 0.1% to 10% by weight of the molecular sieve, preferably 1% to 6%.

[0007] The method for site-specific modulation of molecular sieve acid sites according to the present invention includes the following steps: (1) Dissolve an appropriate amount of cinnamate in benzene, stir evenly, and fully dissolve it; (2) Immerse the molecular sieve with the solution obtained in step (1), and filter the molecular sieve after immersion; wherein, the pore diameter of the molecular sieve is 0.4 nm to 0.9 nm; (3) Purge the molecular sieve filtered in step (2) with hot nitrogen, and naturally cool it to room temperature after purging; (4) Wash the molecular sieve obtained in step (3) with deionized water to obtain a molecular sieve with modulated acid sites.

[0008] Furthermore, the cinnamate can be a soluble salt such as sodium cinnamate or potassium cinnamate. Among them, the mass fraction of cinnamate in the obtained benzene solution is 0.5% - 20%, preferably 1% - 5%.

[0009] Furthermore, the pore diameter of the molecular sieve is 0.4 nm to 0.9 nm, and specifically can be molecular sieves with suitable pore diameters such as Hβ molecular sieve, HZSM-5 molecular sieve or HZSM-11 molecular sieve. Its silica-alumina ratio is 2 to 250, preferably 2 to 220.

[0010] Furthermore, the liquid-solid ratio in step (2) for immersion is 4 to 10 mL / g, preferably 5 to 8 mL / g. The immersion time is generally 1 to 10 hours, preferably 1 to 5 hours.

[0011] Furthermore, the temperature of the hot nitrogen in step (3) is 80°C to 180°C, preferably 85°C to 150°C; the nitrogen volumetric space velocity is 100 h -1 ~3000 h -1 and preferably 200 h -1 ~2000 h -1 ; the purging time is 2 hours to 24 hours, preferably 5 hours to 20 hours.

[0012] Further, the liquid-solid ratio of the washing in step (4) is 4 to 10 mL / g, preferably 5 to 8 mL / g; the washing temperature is from room temperature to 80°C, preferably 40°C to 70°C; the number of washing times is 1 to 10 times, preferably 2 to 6 times.

[0013] Further, step (4) also includes: filtering, drying and calcining the washed molecular sieve to obtain the finished product. Among them, the conditions for the drying are generally: the drying temperature is 60°C to 150°C, preferably 80°C to 120°C, and the drying time is 2 hours to 24 hours, preferably 5 hours to 20 hours. The conditions for the calcination are generally: the calcination temperature is 300°C to 800°C, preferably 400°C to 700°C, and the calcination time is 2 hours to 24 hours, preferably 3 hours to 8 hours; during the calcination, the molecular sieve is purged with an air stream, and the air volume space velocity is generally 100h -1 ~3000h -1 preferably 200h -1 ~2000h -1 .

[0014] In the present invention, first, the cinnamate is dissolved in benzene to form a solution, and then the solution is filled into the pores of the molecular sieve. Then, it is purged with hot nitrogen. At high temperature, the C=C in the cinnamate reacts with benzene to form a macromolecular salt product with two benzene rings. Since the molecular size of this reaction product is larger than the diameter of the straight through pores of the molecular sieve, even if there are acid centers required for the reaction in the straight through pores, it cannot be generated in the straight through pores, and can only be generated at the pore intersections where there is sufficient space and acid centers. The hot nitrogen will also vaporize the excess benzene in the pores and carry it out of the molecular sieve. The unreacted cinnamate remaining in the pores is removed during the water washing, while the macromolecular product generated by the reaction is restricted by the molecular size and cannot be carried out of the pores and continues to remain at the pore intersections. The calcination step fully oxidizes and burns the carbon and hydrogen components in the macromolecular product into carbon dioxide and water vapor and escapes from the molecular sieve, and the remaining metal oxides continue to adhere to the pore intersections of the molecular sieve, playing a role in covering the acid centers and adjusting the size of the pore intersections.

[0015] The method of the present invention only modulates the acid centers at the pore intersections of the molecular sieve, will not affect the acid centers at the straight through pores, nor will it affect the smoothness of the pores. Embodiment

[0016] The technical solutions of the present invention will be described in detail below with reference to the embodiments, but the present invention is not limited to the following embodiments. Example 1

[0017] (1) Dissolve an appropriate amount of potassium cinnamate in benzene, stir evenly until fully dissolved, and prepare a solution with a mass percentage content of 6.5%; use this solution to impregnate 200 g of Hβ zeolite with a silica-alumina ratio of 25 at a liquid-solid ratio of 5 mL / g. After impregnation for 2 hours, filter out the zeolite; (2) Purge the filtered zeolite with hot nitrogen at 110 °C at a space velocity of 800 h -1 for 4 hours, and then naturally cool to room temperature after purging; (3) Wash the zeolite obtained in step (2) with deionized water at a liquid-solid ratio of 6 mL / g. Dry the washed zeolite at 110 °C for 5 hours and calcine it at 550 °C for 5 hours to obtain the modified Hβ zeolite, and this sample is denoted as A.

[0018] Comparative Example 1 Using potassium nitrate as the precursor, impregnate Hβ zeolite with a silica-alumina ratio of 25 by the conventional impregnation method. After impregnation for 2 hours, filter out the zeolite, and dry it at 110 °C for 5 hours and calcine it at 550 °C for 5 hours. This sample is denoted as A1. Example 2

[0019] (1) Dissolve an appropriate amount of potassium cinnamate in benzene, stir evenly until fully dissolved, and prepare a solution with a mass percentage content of 3.5%; use this solution to impregnate 200 g of HZSM-5 zeolite with a silica-alumina ratio of 80 at a liquid-solid ratio of 6 mL / g. After impregnation for 4 hours, filter out the zeolite; (2) Purge the filtered zeolite with hot nitrogen at 110 °C at a space velocity of 1000 h-1 for 5 hours, and then naturally cool to room temperature after purging; (3) Wash the zeolite obtained in step (2) with deionized water at a liquid-solid ratio of 5 mL / g. Dry the washed zeolite at 120 °C for 7 hours and calcine it at 540 °C for 3 hours to obtain the modified HZSM-5 zeolite, and this sample is denoted as B.

[0020] Comparative Example 2 Using potassium nitrate as the precursor, impregnate HZSM-5 zeolite with a silica-alumina ratio of 80 by the conventional impregnation method. After impregnation for 5 hours, filter out the zeolite, and dry it at 110 °C for 7 hours and calcine it at 550 °C for 3 hours. This sample is denoted as B1. Example 3

[0021] (1) Dissolve an appropriate amount of potassium cinnamate in benzene, stir evenly until fully dissolved, and prepare a solution with a mass percentage content of 5%; use this solution to impregnate 200 g of HZSM-11 zeolite with a silica-alumina ratio of 40 at a liquid-solid ratio of 6 mL / g. After impregnation for 3 hours, filter out the zeolite; (2) Purge the filtered zeolite with hot nitrogen at 120 °C at a space velocity of 1000 h-1 for 3 hours, and then naturally cool to room temperature after purging; (3) Wash the molecular sieve obtained in step (2) with deionized water at a liquid-solid ratio of 6 mL / g. Dry the washed molecular sieve at 110 °C for 4 hours and calcine it at 560 °C for 5 hours to obtain the modified HZSM-11 molecular sieve, and this sample is denoted as C.

[0022] Comparative Example 3 Using potassium nitrate as the precursor, impregnate the HZSM-11 molecular sieve with a silica-alumina ratio of 40 by the conventional impregnation method. After impregnation for 5 hours, filter out the molecular sieve, dry it at 110 °C for 7 hours and calcine it at 550 °C for 3 hours, and this sample is denoted as C1. Example 4

[0023] (1) Dissolve an appropriate amount of potassium cinnamate in benzene, stir evenly and dissolve completely to prepare a solution with a mass percentage of 8%. Impregnate 200 g of Hβ molecular sieve with a silica-alumina ratio of 80 with this solution at a liquid-solid ratio of 7 mL / g. After impregnation for 3 hours, filter out the molecular sieve; (2) Purge the filtered molecular sieve with hot nitrogen at 120 °C at a space velocity of 1100 h -1 for 3 hours, and after the purge is completed, cool it naturally to room temperature; (3) Wash the molecular sieve obtained in step (2) with deionized water at a liquid-solid ratio of 8 mL / g. Dry the washed molecular sieve at 110 °C for 3 hours and calcine it at 550 °C for 3 hours to obtain the modified Hβ molecular sieve, and this sample is denoted as D. Example 5

[0024] (1) Dissolve an appropriate amount of potassium cinnamate in benzene, stir evenly and dissolve completely to prepare a solution with a mass percentage of 4.5%. Impregnate 200 g of HZSM-5 molecular sieve with a silica-alumina ratio of 150 with this solution at a liquid-solid ratio of 8 mL / g. After impregnation for 4 hours, filter out the molecular sieve; (2) Purge the filtered molecular sieve with hot nitrogen at 140 °C at a space velocity of 1300 h -1 for 2 hours, and after the purge is completed, cool it naturally to room temperature; (3) Wash the molecular sieve obtained in step (2) with deionized water at a liquid-solid ratio of 5 mL / g. Dry the washed molecular sieve at 110 °C for 3 hours and calcine it at 550 °C for 6 hours to obtain the modified HZSM-5 molecular sieve, and this sample is denoted as E. Example 6

[0025] (1) Dissolve an appropriate amount of potassium cinnamate in benzene, stir evenly and dissolve completely to prepare a solution with a mass percentage of 5.5%. Impregnate 200 g of HZSM-11 molecular sieve with a silica-alumina ratio of 120 with this solution at a liquid-solid ratio of 6.5 mL / g. After impregnation for 4 hours, filter out the molecular sieve; (2) Purge the filtered molecular sieve with hot nitrogen at 120 °C at a space velocity of 1400 h -1Purge with an airspeed of 4 hours and then naturally cool to room temperature after purging is completed; (3) Wash the zeolite obtained in step (2) with deionized water at a liquid-solid ratio of 8 mL / g, dry the washed zeolite at 120 °C for 3 hours and calcine it at 540 °C for 6 hours to obtain the modified HZSM-11 zeolite. This sample is denoted as F. Example 7

[0026] Take the samples of the above examples and comparative examples and conduct organic matter adsorption measurements using an Intelligent Gravimetric Analyser (IGA-002). Measure the m-xylene adsorption capacity of the modified Hβ zeolite and the cyclohexane adsorption capacity of the modified HZSM-5 and HZSM-11 zeolites. Before the measurement, first conduct impurity removal treatment on the zeolite to remove moisture and residual template agents and other impurities. The impurity removal treatment is to heat the sample to be tested from room temperature to 300 °C at a rate of 5 °C / minute under a vacuum state, and then lower it back to room temperature after its mass becomes constant, and then start the measurement of the m-xylene or cyclohexane adsorption capacity. Pass the m-xylene or cyclohexane vapor into the sample chamber after impurity removal. After the sample is completely adsorbed and saturated (i.e., the weight is constant), record the weight difference. The adsorption capacities of each sample are shown in Table 1.

[0027] Table 1 Sample m-Xylene / Cyclohexane Adsorption Capacity g / 100g A 24.45 A1 13.22 B 15.11 B1 6.23 C 16.35 C1 8.45 D 22.80 E 14.01 F 15.11 As can be seen from the results in Table 1, compared with the conventionally modified zeolites, the zeolites treated by the modification means of the present technical solution have more unobstructed pores because only the pore intersections of the zeolites are directionally modified, and still have a relatively high m-xylene or cyclohexane adsorption capacity.

Claims

1. A method for modulating the acid sites of a molecular sieve at a fixed point, characterized in that, it comprises the following steps: (1) Dissolve an appropriate amount of cinnamate in benzene, stir evenly, and fully dissolve; (2) Impregnate the molecular sieve with the solution obtained in step (1), and filter the molecular sieve after impregnation; wherein, the pore diameter of the molecular sieve is 0.4 nm to 0.9 nm; (3) Purge the molecular sieve filtered out in step (2) with hot nitrogen, and naturally cool it to room temperature after purging; (4) Wash the molecular sieve obtained in step (3) with deionized water to obtain a molecular sieve with modulated acid sites.

2. The method according to claim 1, characterized in that, the cinnamate is selected from sodium cinnamate and / or potassium cinnamate.

3. The method according to claim 1 or 2, characterized in that, the mass fraction of cinnamate in the obtained benzene solution is 0.5% - 20%, preferably 1% - 5%.

4. The method according to claim 1, characterized in that, the molecular sieve is selected from one or more of Hβ molecular sieve, HZSM-5 molecular sieve and HZSM-11 molecular sieve, and the silica-alumina ratio of the molecular sieve is 2 to 250.

5. The method according to claim 1, characterized in that, the liquid-solid ratio for impregnation in step (2) is 4 to 10 mL / g.

6. The method according to claim 1 or 5, characterized in that, the impregnation time in step (2) is 1 to 10 hours.

7. The method according to claim 1, characterized in that, the temperature of the hot nitrogen in step (3) is 80°C to 180°C.

8. The method according to claim 7, characterized in that, The volumetric space velocity of the hot nitrogen purge is 100 h -1 ~3000 h -1 , preferably 200 h -1 ~2000 h -1 ; the purge time is 2 hours to 24 hours, preferably 5 hours to 20 hours.

9. The method according to claim 1, characterized in that, the liquid-solid ratio for washing in step (4) is 4 to 10 mL / g.

10. The method according to claim 1, characterized in that, step (4) further includes: filtering, drying and calcining the washed molecular sieve to obtain a finished product.

11. The method according to claim 10, characterized in that, wherein, the drying conditions in step (4) are: the drying temperature is 60°C to 150°C, and the drying time is 2 hours to 24 hours; the calcining conditions are: the calcining temperature is 300°C to 800°C, and the calcining time is 2 hours to 24 hours.