Molecular sieve catalyst with directionally passivated outer surface as well as preparation method and application of molecular sieve catalyst

Abstract

The invention discloses a molecular sieve catalyst with a directionally passivated outer surface and a preparation method and application thereof, the preparation method comprises the following steps: S1, selecting one-dimensional straight-through ten-membered ring molecular sieve powder as a raw material, mixing and stirring the raw material and an ammonium chloride solution according to a mass ratio of 1: 10, filtering and separating out a solid, washing, drying and roasting to obtain first molecular sieve powder; s2, forming a passivation layer on the outer surface of the first molecular sieve powder to obtain second molecular sieve powder; and S3, mixing the second molecular sieve powder with pseudo-boehmite or silica sol according to a mass ratio of 8: 2, adding deionized water to form a plastic paste, drying, and roasting to obtain the molecular sieve catalyst with the directionally passivated outer surface. According to the molecular sieve catalyst with the directionally passivated outer surface, provided by the invention, a compact passivation layer is formed on the outer surface of the molecular sieve catalyst, and a proper Bronsted acid site in a pore channel is reserved, so that side reaction caused by an external acid site is shielded.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a molecular sieve catalyst with directional passivation of its outer surface, its preparation method, and its application. Background Technology

[0002] In the utilization of α-olefins, double bond isomerization is a typical fundamental reaction, its importance lying in improving the stability and application value of olefins by controlling the position of the double bond. Light olefins, especially those in the C4–C6 range, occupy an important position in oil refining, coal chemical industry, and synthetic materials industry. 1-Pentene, as a representative terminal olefin, is widely available, but its high reactivity makes it difficult to utilize directly. Therefore, it usually needs to be converted to 2-pentene through a double bond migration reaction. In this process, the selection and control of the catalyst are key to determining the reaction efficiency and selectivity.

[0003] In the existing technology, the shortcomings of catalysts in the isomerization of 1-pentene double bonds are mainly manifested in the following aspects: on the one hand, most of the existing control measures are to weaken the overall acid amount or acid strength, and lack precise shielding of acid sites on the outer surface; on the other hand, the existing modification methods are rough and unstable, the process window of acid washing or steam treatment is narrow, the batch stability is insufficient, and it is easy to damage the molecular sieve skeleton and affect the service life. Summary of the Invention

[0004] This disclosure aims to address the problems existing in the prior art by providing a molecular sieve catalyst with directional passivation of its outer surface, its preparation method, and its application.

[0005] According to a first aspect of this disclosure, a method for preparing a molecular sieve catalyst with directional passivation of its outer surface is provided, comprising the following steps: Step S1: Select one-dimensional straight-through ten-membered ring molecular sieve powder as raw material, mix the raw material with ammonium chloride solution at a mass ratio of 1:10, filter to separate the solid, wash, dry, and calcine to obtain the first molecular sieve powder; Step S2: A passivation layer is formed on the outer surface of the first molecular sieve powder to obtain the second molecular sieve powder; Step S3: Mix the second molecular sieve powder with boehmite or silica sol at a mass ratio of 8:2, add deionized water to form a plastic paste, dry and calcine to obtain a molecular sieve catalyst with directional passivation on the outer surface.

[0006] In one embodiment of this disclosure, step S2 includes placing the first molecular sieve powder in a fixed bed deposition apparatus, introducing nitrogen gas, heating to a predetermined temperature and maintaining the temperature, then introducing hexamethyldisilazane along with nitrogen gas into the fixed bed deposition apparatus to react for a predetermined time, continuing nitrogen purging, and calcining to obtain a second molecular sieve powder with a passivation layer formed on its outer surface.

[0007] In one embodiment of this disclosure, the total feed amount of hexamethyldisilazane in step S2 is 1wt%-3wt% of the mass of the first molecular sieve powder, and the Si loading in the second molecular sieve powder is 1wt%-6wt%.

[0008] In one embodiment of this disclosure, step S2 further includes pre-curing the powder at 300°C after nitrogen purging, followed by calcination in an air atmosphere at 500°C, to form a stable passivation layer on the surface of the first molecular sieve powder.

[0009] In another embodiment of this disclosure, step S2 includes mixing tetraethyl orthosilicate and anhydrous ethanol at a volume ratio of 1:5 to obtain a first solution; adding the first molecular sieve powder from S1 to the first solution to form a slurry with a solid-liquid ratio of 1:10, adjusting the pH to 4.5-5.5, and stirring; after the reaction is completed, filtering, drying, and calcining to obtain a second molecular sieve powder with a passivation layer formed on its outer surface.

[0010] In one embodiment of this disclosure, the raw material in step S1 is a one-dimensional through-hole ten-membered ring molecular sieve powder with a relative crystallinity ≥95% and a Si / Al molar ratio of 50-120.

[0011] In one embodiment of this disclosure, the acid density in the first molecular sieve powder is 0.30 mmol / g to 0.35 mmol / g.

[0012] In one embodiment of this disclosure, the ratio of the number of external acid sites to the total number of acid sites in the molecular sieve catalyst with directional passivation of the outer surface is ≤0.10.

[0013] According to a second aspect of this disclosure, a molecular sieve catalyst with an externally directionally passivated surface is provided, the molecular sieve catalyst being prepared by the above-described preparation method.

[0014] According to a third aspect of this disclosure, an application of an externally surface-directed passivated molecular sieve catalyst in the isomerization of 1-pentene double bonds is provided, wherein the externally surface-directed passivated molecular sieve catalyst is an externally surface-directed passivated molecular sieve catalyst prepared according to the above-described preparation method.

[0015] The molecular sieve catalyst with directional passivation on the outer surface disclosed herein, its preparation method and application, form a dense passivation layer on the outer surface of the molecular sieve catalyst and retain appropriate Brønsted acid sites in the pores, thereby shielding the side reactions initiated by the external acid sites, ensuring efficient protonation of 1-pentene and migration of 1,2-hydrogen, and achieving a 2-pentene selectivity of ≥90%.

[0016] Other features and advantages of the invention will become clear from the following detailed description of exemplary embodiments of the invention with reference to the accompanying drawings. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the present disclosure and, together with their description, serve to explain the principles of the present disclosure.

[0018] Figure 1 This is a flowchart of a method for preparing a molecular sieve catalyst with directional passivation of the outer surface, provided in one embodiment of this disclosure. Detailed Implementation

[0019] To make the inventive objectives, technical solutions, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with specific embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of this application.

[0020] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an unspecified range.

[0021] In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" include the number itself, and "several" in "one or more" means two or more.

[0022] The foregoing description of this invention is not intended to describe every disclosed embodiment or implementation. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are merely representative and should not be construed as exhaustive.

[0023] In the utilization of α-olefins, double bond isomerization is a typical fundamental reaction, its importance lying in improving the stability and application value of olefins by controlling the position of the double bond. Light olefins, especially those in the C4–C6 range, occupy an important position in oil refining, coal chemical industry, and synthetic materials industry. 1-Pentene, as a representative terminal olefin, is widely available, but its high reactivity makes it difficult to utilize directly. Therefore, it usually needs to be converted to 2-pentene through a double bond migration reaction. In this process, the selection and control of the catalyst are key to determining the reaction efficiency and selectivity.

[0024] In the existing technology, the shortcomings of catalysts in the isomerization of 1-pentene double bonds are mainly manifested in the following aspects: on the one hand, most of the existing control measures are to weaken the overall acid amount or acid strength, and lack precise shielding of acid sites on the outer surface; on the other hand, the existing modification methods are rough and unstable, the process window of acid washing or steam treatment is narrow, the batch stability is insufficient, and it is easy to damage the molecular sieve skeleton and affect the service life.

[0025] This disclosure aims to address the problems existing in the prior art by providing a molecular sieve catalyst with directional passivation of its outer surface, its preparation method, and its application.

[0026] like Figure 1 As shown, according to a first aspect of this disclosure, this disclosure provides a method for preparing a molecular sieve catalyst with directional passivation of its outer surface, comprising the following steps: Step S1: Select one-dimensional straight-through ten-membered ring molecular sieve powder as raw material, mix the raw material with ammonium chloride solution at a mass ratio of 1:10, filter to separate the solid, wash, dry, and calcine to obtain the first molecular sieve powder; Step S2: A passivation layer is formed on the outer surface of the first molecular sieve powder to obtain the second molecular sieve powder; Step S3: Mix the second molecular sieve powder with boehmite or silica sol at a mass ratio of 8:2, add deionized water to form a plastic paste, dry and calcine to obtain a molecular sieve catalyst with directional passivation on the outer surface.

[0027] Specifically, in step S1, one-dimensional through-type ten-membered ring molecular sieve powder with a relative crystallinity ≥95% and a Si / Al molar ratio in the range of 50-120 is selected as raw material. This raw material molecular sieve is mixed with ammonium chloride solution at a mass ratio of 1:10 (accuracy ±0.2) to perform ion exchange on the raw material molecular sieve. The preferred conditions are: maintaining the reaction temperature at 80℃ using a constant temperature water bath, a stirring rate of 300 r / min, a time of 2 hours, and repeating this process 3 times to ensure that the Na content in the raw material molecular sieve after ion exchange is within acceptable limits. + Content ≤0.1wt%, thus avoiding Na + It occupies the cation exchange sites of Al atoms in the molecular sieve framework, providing a basis for subsequent NH4+ cation exchange.4+ This creates conditions for sufficient binding with the Al sites on the backbone; while preventing excessive Na. + The neutralization of acid sites ensures the presence of NH4+ during subsequent roasting. 4+ It can completely decompose and remove the skeletal Al, successfully converting it into catalytically active Brønsted acid sites, while ensuring the acid density of the first molecular sieve powder remains stable within the target range of 0.30 mmol / g-0.35 mmol / g, meeting the requirements of the 1-pentene double bond isomerization reaction for the number and intensity of active sites; furthermore, it can avoid the problems caused by Na. + The problem of uneven acid strength distribution caused by excessive residual acid content is prevented from the effect of insufficient local acid strength on reaction efficiency or the side reactions such as cracking and oligomerization caused by excessive local acid strength. At the same time, it maintains the uniform distribution of active sites in the one-dimensional through ten-membered ring molecular sieve pores, providing a stable microenvironment for the directional diffusion and selective reaction of the subsequent reactant 1-pentene in the pores.

[0028] After the exchange process, the solid was separated by vacuum filtration and washed with deionized water until the filtrate was free of Cl. - (The test method is as follows: Take 10 mL of filtrate and add 0.1 mol / L silver nitrate solution. If no white precipitate forms, the filtrate does not contain Cl.) - The powder was then dried at 120°C for 12 hours, and finally calcined in air at 500°C for 4 hours to obtain the first molecular sieve powder. Step S1 allows stable Brønsted acid centers to form inside the first molecular sieve powder, thereby providing active sites for the subsequent migration of the 1-pentene double bond.

[0029] In step S2, the external acid sites are passivated by silane deposition or sol-gel coating. The purpose is to form a dense passivation layer with controllable thickness on the outer surface of the molecular sieve without penetrating the interior of the pores.

[0030] In step S3, preferably, to adapt to industrial fixed-bed applications, the passivated second molecular sieve powder is mixed with boehmite or silica sol with a purity ≥92% and a boehmite content ≥85% at a mass ratio of 8:2. Deionized water is added to adjust the humidity, and the mixture is kneaded for 30 minutes at a speed of 60 r / min using a twin-screw kneader to form a plastic paste with a kneading degree ≥80%. A strip sample is then extruded using a single-screw extruder at an extrusion rate controlled at 5 cm / min to obtain wet strips with a length of 3 mm-5 mm, a strip diameter of 1.3 mm–1.8 mm, and a compressive strength ≥80 N / cm (measured according to GB / T 31590-2015), suitable for use in fixed-bed industrial equipment. The strips are then dried in a 120℃ forced-air drying oven for 12 hours, and then calcined in air at 550℃ for 4 hours to obtain a shaped molecular sieve catalyst with a directional passivated outer surface.

[0031] The passivation process disclosed herein only acts on the outer surface of the molecular sieve catalyst. As verified by X-ray diffraction (XRD), the relative crystallinity retention rate of the passivated molecular sieve catalyst is ≥95%. Furthermore, as verified by nitrogen adsorption-desorption, the pore volume retention rate is ≥90% and the specific surface area retention rate is ≥92%, which can avoid the skeleton damage caused by existing acid treatment / steam treatment.

[0032] The specific methods for nitrogen adsorption-desorption are as follows: Sample preparation: Take the first molecular sieve powder before passivation in step S1, denoted as sample A, and the second molecular sieve powder after passivation in step S2, denoted as sample B. Both are dried at 120℃ for 12 hours and passed through an 80-100 mesh sieve (to eliminate the influence of particle size difference). Weigh 0.15±0.02g (accuracy 0.0001g) of each and place them in a quartz sample tube.

[0033] Desorption and impurity removal: Place the sample tube into the pretreatment station of a fully automated gas adsorption instrument (such as Micromeritics TriStar II3020) at 200℃ and a vacuum degree ≤10. -3 Under constant temperature desorption conditions of Pa for 4 hours, the vacuum level was recorded every 30 minutes to ensure no leakage and to completely remove water molecules, residual ammonium chloride and organic impurities adsorbed on the sample surface.

[0034] Instrumentation and Adsorbate: A liquid nitrogen bath at -196℃ (liquid nitrogen purity ≥99.99%, constant bath surface height) was used as the adsorbate, with high-purity nitrogen gas (purity ≥99.999%, water content ≤1ppm).

[0035] Test parameters: relative pressure (P / P0) range 0.01-0.99, one point is taken every 0.02 in the P / P0=0.01-0.3 range, and one point is taken every 0.05 in the 0.3-0.99 range; the adsorption / desorption equilibrium time at each pressure point is 10min-30min (equilibrium is determined when the rate of change of adsorption is ≤0.01cm³ / g・min), and finally the type IV adsorption-desorption isotherms of samples A and B are collected (matching the mesoporous characteristics of one-dimensional ten-membered ring molecular sieves).

[0036] The calculation methods for pore volume retention rate and specific surface area retention rate are as follows: Specific surface area (S, m² / g): Using the BET model, a linear interval of P / P0 = 0.05-0.3 was selected (linear correlation coefficient R² ≥ 0.999), and substituted into the BET equation:

[0037] (V = adsorption capacity, V) m= Monolayer saturated adsorption capacity, C = Adsorption heat correlation constant), V is obtained by fitting. m Then, the cross-sectional area of ​​nitrogen molecules (0.162 nm²) was used for calculation:

[0038] (m = sample mass, 22414 = volume of 1 mol of gas under standard conditions, cm³ / mol).

[0039] Pore ​​volume (V, cm³ / g): Using the BJH model, the total adsorption amount (standard state) at the adsorption isotherm P / P0≈0.99 is taken. After deducting the monolayer adsorption amount, the liquid volume is converted to liquid volume according to the liquid nitrogen density (0.808 g / cm³), which is the total pore volume (the proportion of micropores in one-dimensional ten-membered ring molecular sieve is <5%, no additional correction is required).

[0040] Specific surface area retention rate (RS):

[0041] (S) B = Specific surface area of ​​sample B, S A = Specific surface area of ​​sample A, RS ≥ 92%.

[0042] Pore ​​volume retention rate (R) V ):

[0043] (V) B = Sample B pore volume, V A = Sample A pore volume, required R V ≥90%).

[0044] The passivation layer on the outer surface of the molecular sieve catalyst acts as an inert barrier, covering the outer surface of the molecular sieve crystals and preventing external acid sites from contacting reactants, thus avoiding side reactions. Because the thickness of this passivation layer is controllable and does not penetrate the pores, the Brønsted acid sites inside the molecular sieve catalyst remain active. 1-Pentene is successfully converted to 2-pentene within the pores through protonation, 1,2-hydrogen migration, and deprotonation. It is through this dual mechanism of "directional shielding of external surface acid sites + retention of internal acid sites" that the externally surface-directed passivated molecular sieve catalyst prepared in this disclosure achieves high product selectivity and long-lifetime double bond isomerization catalytic performance.

[0045] In one embodiment of this disclosure, step S2 includes placing the first molecular sieve powder in a fixed bed deposition apparatus, introducing nitrogen gas, heating to a predetermined temperature and maintaining the temperature, then introducing hexamethyldisilazane along with nitrogen gas into the fixed bed deposition apparatus to react for a predetermined time, continuing nitrogen purging, and calcining to obtain a second molecular sieve powder with a passivation layer formed on its outer surface.

[0046] In this embodiment, step S2 employs hexamethyldisilazane (HMDS) vapor deposition for passivation. Preferably, the first molecular sieve powder is placed in a fixed-bed deposition apparatus, nitrogen gas (99.99% purity, water content ≤10ppm) is introduced, and the flow rate is stably controlled at 30mL / min (mass flow meter accuracy ±0.5mL / min). The temperature is raised to 200℃ at a rate of 5℃ / min and held at this temperature for 1 hour to remove adsorbed water from the molecular sieve surface. Subsequently, hexamethyldisilazane (HMDS) is injected using a micro-injection pump. Nitrogen gas was injected at a rate of 0.1-0.3 mL / h to form hexamethyldisilazane (HMDS) vapor, which reacted with the surface of the first molecular sieve powder for 2 hours. After the reaction was completed, the HMDS feed was cut off, and nitrogen was continued to purge for 1 hour to remove unreacted HMDS vapor. After calcination, a stable SiO2 passivation layer was formed. The passivation layer could be observed by transmission electron microscopy (TEM), and the thickness of the passivation layer was found to be 2-5 nm, and the coverage was uniform.

[0047] In one embodiment of this disclosure, the total feed amount of hexamethyldisilazane in step S2 is 1wt%-3wt% of the mass of the first molecular sieve powder, and the Si loading in the second molecular sieve powder is 1wt%-6wt%.

[0048] Specifically, the total feed amount of hexamethyldisilazane (HMDS) needs to be strictly controlled during the deposition process. If the feed amount is too high, excessive SiO2 deposition will occur, which may not only block the one-dimensional through-ten-membered ring pores and cover the active sites at the pore openings, reducing the diffusion efficiency and conversion rate of reactants, but may also weaken the mechanical strength of the catalyst due to an excessively thick surface silicon layer. If the feed amount is too low, an effective passivation layer cannot be formed on the outer surface, and the residual Brønsted strong acid sites will still trigger side reactions, making it difficult to improve the selectivity of 2-pentene. By controlling the feed amount of hexamethyldisilazane, preferably 1wt%-3wt% of the mass of the first molecular sieve powder (error ±0.1wt%), the final Si loading can be controlled within the range of 1wt%–6wt%. This allows for efficient and selective passivation of the acid sites on the outer surface without damaging the pore structure. The Si loading is determined by X-ray fluorescence spectroscopy (XRF), with a repeatability error ≤3%.

[0049] In one embodiment of this disclosure, step S2 further includes pre-curing the powder at 300°C after nitrogen purging, followed by calcination in an air atmosphere at 500°C, to form a stable passivation layer on the surface of the first molecular sieve powder.

[0050] Specifically, pre-curing (2 hours at 300°C) aims to induce the initial hydrolysis and condensation of adsorbed hexamethyldisilazane, forming an oligomeric siloxane network that is firmly anchored to the outer surface of the molecular sieve. This prevents the siloxane from volatilizing, decomposing, or migrating into the pores during subsequent high-temperature treatment, thus avoiding pore blockage and uneven passivation. Subsequent calcination (3 hours at 500°C in air) completely removes the organic groups from the pre-cured layer, transforming it into a dense, chemically inert amorphous SiO2 passivation layer. This layer enhances adhesion through condensation with surface hydroxyl groups, effectively shielding Brønsted acid sites on the outer surface while retaining active centers within the pores. If pre-curing is omitted and calcination is performed directly, it can easily lead to uncontrolled precursor distribution, pore contamination, and poor passivation, making it difficult to achieve the ideal "internal active, external passive" catalytic structure.

[0051] In another embodiment of this disclosure, step S2 includes mixing tetraethyl orthosilicate and anhydrous ethanol at a volume ratio of 1:5 to obtain a first solution; adding the first molecular sieve powder from S1 to the first solution to form a slurry with a solid-liquid ratio of 1:10, adjusting the pH to 4.5-5.5, and stirring; after the reaction is completed, filtering, drying, and calcining to obtain a second molecular sieve powder with a passivation layer formed on its outer surface.

[0052] In this embodiment, step S2 employs a tetraethyl orthosilicate sol-gel coating method. Preferably, tetraethyl orthosilicate (TEOS, 98% purity) and anhydrous ethanol (99.9% purity) are mixed at a volume ratio of 1:5 and stirred for 10 minutes until completely homogeneous to prepare a first solution, namely a tetraethyl orthosilicate alcohol solution. The first molecular sieve powder is added to the first solution for impregnation, forming a slurry with a solid-liquid ratio of 1:10. The pH is adjusted to 4.5-5.5 with hydrochloric acid or ammonia, and the mixture is stirred in a 30°C constant temperature water bath for 3 hours. After the reaction, the sample is filtered and separated, dried at 120°C for 12 hours, and calcined in air at 500°C for 4 hours to form a uniform and dense SiO2 passivation layer, wherein the Si loading is 3wt%-5wt%, which can be obtained by X-ray fluorescence spectroscopy (XRF).

[0053] In one embodiment of this disclosure, the raw material in step S1 is a one-dimensional through-hole ten-membered ring molecular sieve powder with a relative crystallinity ≥95% and a Si / Al molar ratio of 50-120.

[0054] Specifically, relative crystallinity can be characterized by X-ray diffraction (XRD). Using the standard PDF diffraction card of the corresponding one-dimensional through-hole ten-membered ring molecular sieve as a reference, under test conditions of a scanning range of 5°-50° and a step size of 0.02°, several characteristic diffraction peaks are selected. The ratio of the sum of the intensities of the corresponding peaks in the sample to the sum of the intensities in the standard card is calculated, and then multiplied by 100% to obtain the relative crystallinity (%). Simultaneously, the Si / Al molar ratio of the molecular sieve is determined using X-ray fluorescence spectroscopy (XRF), with the result error controlled within ±2%, ensuring the stability of the molecular sieve acid density and the consistency of its catalytic performance.

[0055] In one embodiment of this disclosure, the acid density in the first molecular sieve powder is 0.30 mmol / g to 0.35 mmol / g.

[0056] Specifically, step S1 results in the formation of stable Brønsted acid centers within the first molecular sieve powder, with an acid density of 0.30–0.35 mmol / g. This acid density range provides sufficient active sites to ensure the effective conversion of the 1-pentene double bond isomerization reaction while avoiding side reactions such as cracking, oligomerization, or carbon deposition caused by excessively dense acid sites, thus significantly improving the selectivity for 2-pentene. If the acid density is too high, local acid center aggregation is likely to occur within the pores. Optimizing the acid density to 0.30–0.35 mmol / g helps to ensure a uniform distribution of acid sites within the pores. Furthermore, this acid level also helps maintain the overall catalytic activity balance after passivation of the outer surface and slows down the carbon deposition rate, extending the catalyst lifetime.

[0057] In one embodiment of this disclosure, the ratio of the number of external acid sites to the total number of acid sites in the molecular sieve catalyst with directional passivation of the outer surface is ≤0.10.

[0058] Specifically, to verify the passivation effect of the external acid sites in the second molecular sieve, this disclosure uses 2,6-di-tert-butylpyridine (2,6-DTBP) adsorption-infrared spectroscopy to characterize the external acid sites, and combines this with pyridine infrared spectroscopy (Py-IR) to determine the total acid sites. The ratio of the two is the external acid ratio. The specific steps are as follows: 2,6-Di-tert-butylpyridine (2,6-DTBP) adsorption-infrared spectroscopy: Sample pretreatment: 100 mg of passivated second molecular sieve powder sample was pressed into a self-supporting sheet with a diameter of 13 mm and placed in an infrared sample cell at 350 °C and a vacuum degree of 10. -3 Desorption at Pa for 2 hours; Adsorption test: The temperature was lowered to 150℃, and 2,6-DTBP vapor (99% purity, partial pressure 1.3 kPa) was introduced for adsorption for 1 hour, followed by adsorption at 150℃ and a vacuum of 10 kPa. -2 Desorption for 30 minutes under Pa conditions; Spectral acquisition: Fourier transform infrared spectroscopy was used for testing. The characteristic peak corresponding to the Brønsted acid site on the outer surface is at 1635 cm⁻¹. -1 The number of external acid sites was calculated using baseline integration.

[0059] Pyridine Infrared (Py-IR) Method: Sample pretreatment is the same as the steps described above; Adsorption test: After desorption, the temperature was lowered to 200℃; pyridine vapor (purity 99.5%, partial pressure 2.7 kPa) was introduced for adsorption for 1 hour, and desorption was carried out at 200℃ for 30 minutes; Spectral acquisition: The characteristic peaks corresponding to the total acid sites (Brønsted acid + Lewis acid) are at 1540 cm⁻¹. -1 (Brønsted acid) and 1450cm -1 (Lewis acid), the integration range is 1530cm. -1 -1550cm -1 1440cm -1 -1460cm -1 Calculate the total number of acid sites.

[0060] This disclosure requires an external acid ratio (number of external acid sites / total number of acid sites) ≤ 0.10 (error ± 0.01) because this disclosure has found through experiments that when the external acid ratio > 0.10, the selectivity and stability of 2-pentene decrease significantly.

[0061] According to a second aspect of this disclosure, a molecular sieve catalyst with an externally directionally passivated surface is provided, the molecular sieve catalyst being prepared by the above-described preparation method.

[0062] According to a third aspect of this disclosure, an application of an externally surface-directed passivated molecular sieve catalyst in the isomerization of 1-pentene double bonds is provided, wherein the externally surface-directed passivated molecular sieve catalyst is an externally surface-directed passivated molecular sieve catalyst prepared according to the above-described preparation method.

[0063] Specifically, the process conditions for the 1-pentene double bond isomerization reaction are as follows: a fixed-bed microreactor is used, with a catalyst loading of 2 mL. Pretreatment conditions include baking at 500℃ for 1 hour under a nitrogen atmosphere. The feed is 1-pentene with a purity ≥99%, with a flow rate controlled at 10 mL / min, and the reaction is carried out at 220℃-280℃, 0.1 MPa-0.8 MPa, and a space velocity of 1.0 h⁻¹. -1 -4.0h -1The reaction is carried out under specific conditions, and a small amount of hydrogen (0.1 vol%) can be introduced during the reaction if necessary to reduce carbon buildup. Online gas chromatography analysis shows that under these conditions, the passivated one-dimensional through-ring molecular sieve catalyst can achieve a 2-pentene selectivity of ≥90% and a byproduct of ≤3%, and the catalyst still maintains high stability after continuous operation for more than 100 hours.

[0064] Furthermore, to address the activity decrease caused by a small amount of carbon buildup during catalyst operation, this disclosure also provides a regeneration process to achieve multiple catalyst recycling. When the 1-pentene double bond isomerization reaction process operates for more than 100 hours or its performance deteriorates due to carbon buildup, an air / steam mixture can be used for regeneration. Specifically, a nitrogen stream or air containing 3%-10% oxygen is introduced at 420℃-460℃, while simultaneously introducing 10% (volume fraction) water vapor for regeneration for 1-2 hours. After regeneration, the process is switched to pure nitrogen gas for cooling to the reaction temperature. Tests show that the regenerated catalyst's 2-pentene selectivity can be restored to over 95% of its initial level, and it maintains good performance even after three regenerations.

[0065] The embodiments of the present invention will be described in detail below with reference to the examples. The catalysts used in the following examples are all... Figure 1 The preparation method shown is illustrated, but those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the examples were performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0066] Example 1 A one-dimensional straight-through ten-membered ring molecular sieve with a Si / Al ratio of 90 was subjected to ion exchange three times at 80℃ with 1.0 mol / L ammonium chloride solution for 2 hours each time. After filtration and washing, it was dried at 120℃ and calcined at 500℃ for 4 hours to obtain the first molecular sieve powder. Hexamethyldisilazane (HMDS) vapor deposition was used to treat it at 200℃ under nitrogen for 2 hours, with the amount of HMDS being 2.5 wt% of the molecular sieve mass. After deposition, it was pre-cured at 300℃ for 2 hours and calcined at 500℃ for 3 hours. 2,6-Di-tert-butylpyridine infrared spectroscopy revealed an external acid ratio of 0.08. The passivated molecular sieve was mixed with boehmite in an 8:2 ratio, extruded into strips with a diameter of 1.6 mm, and calcined at 550℃ for 4 hours to obtain catalyst A with a mechanical strength of 85 N / cm.

[0067] Characterization showed that the hexamethyldisilazane (HMDS) vapor deposition method achieved a Si loading of 2.5 wt%, a 2-pentene selectivity of 91%, and a total byproduct amount not exceeding 2.5%. Furthermore, after 120 hours of continuous operation, the activity of catalyst A did not show a significant decrease, demonstrating excellent stability.

[0068] Example 2 A one-dimensional straight-through ten-membered ring molecular sieve with a Si / Al ratio of 90 was subjected to ion exchange three times at 80°C for 2 hours each time using a 1.0 mol / L ammonium chloride solution. After filtration and washing, the sieve was dried at 120°C and calcined at 500°C for 4 hours to obtain the first molecular sieve powder. The surface of the molecular sieve was passivated using the tetraethyl orthosilicate (TEOS) sol-gel method. Tetraethyl orthosilicate (TEOS, 98% purity) and anhydrous ethanol (99.9% purity) were mixed at a volume ratio... After mixing in a 1:5 ratio, the mixture was stirred for 10 minutes until completely homogeneous to prepare a tetraethyl orthosilicate alcohol solution. The first molecular sieve powder was added to the first solution for impregnation, forming a slurry with a solid-liquid ratio of 1:10. The pH was adjusted to 4.5-5.5 with hydrochloric acid or ammonia, and the mixture was stirred in a 30°C constant temperature water bath for 3 hours. After the reaction, the sample was filtered and separated, dried at 120°C for 12 hours, and calcined in air at 500°C for 4 hours to form a uniform and dense SiO2 passivation layer. After deposition, the layer was pre-cured at 300°C for 2 hours and calcined at 500°C for 3 hours. Infrared spectroscopy of 2,6-di-tert-butylpyridine showed an external acid ratio of 0.07. The passivated molecular sieve was mixed with boehmite in an 8:2 ratio, extruded into strips with a diameter of 1.6 mm, and calcined at 550°C for 4 hours to obtain catalyst B.

[0069] Characterization showed that the external acid ratio of catalyst B obtained by controlling the Si loading at 3 wt% using the tetraethyl orthosilicate (TEOS) sol-gel method was 0.07. Reaction performance analysis revealed that the 2-pentene selectivity of the catalyst passivated by the TEOS method was 89%.

[0070] Example 3 The catalyst from Example 1, after running for 120 hours, was regenerated by introducing nitrogen gas containing 5% oxygen (50 mL / min) and 10% water vapor at 450°C for 2 hours, followed by nitrogen cooling. The results showed that the external acid ratio of the regenerated catalyst remained at 0.08. A second reaction test showed that the 2-pentene selectivity recovered to 90%, with a performance recovery rate of 96%. After three regeneration cycles, the catalyst maintained good activity and selectivity, indicating excellent regeneration stability.

[0071] Example 4 A series of catalyst samples with different external acid ratios were prepared by adjusting the amount of hexamethyldisilazane (HMDS), namely 0.25, 0.15, 0.08, and 0.05. All samples with different external acid ratios were extruded into strips (1.6 mm diameter) according to the method in Example 1 to ensure that the external acid ratio was the only variable. Their 1-pentene isomerization performance was tested under uniform reaction conditions, and the experimental results are shown in Table 1.

[0072] Table 1

[0073] As shown in Table 1, the conversion rate of 1-pentene remained stable at 89.5%-91.0%. This is because the external acid ratio only affects the external surface side reactions and does not destroy the active centers inside the pores, thus the conversion rate fluctuates little. When the external acid ratio is >0.10 (0.25, 0.15), the increase in external acid sites triggers cracking (generating small molecules) and oligomerization (generating large molecules) side reactions, leading to a sharp drop in 2-pentene selectivity (<82%) and byproducts >5%. When the external acid ratio is ≤0.10 (0.08, 0.05), the external acid sites are effectively shielded, the side reactions are greatly suppressed, the 2-pentene selectivity is ≥92%, and the byproducts are ≤2.4%.

[0074] The results showed that when the external acid ratio was ≤0.10, the selectivity of 2-pentene was higher than 88%, and the byproducts were less than 3%; while when the external acid ratio was >0.10, the selectivity and stability decreased significantly.

[0075] Comparative Example 1 One-dimensional straight-through ten-membered ring molecular sieve powder with a Si / Al ratio of 70 was selected and subjected to ion exchange three times at 80℃ with 1.0 mol / L ammonium chloride solution for 2 hours each time. After filtration and washing, it was dried at 120℃ and calcined at 500℃ for 4 hours to obtain catalyst C. Catalyst C was mixed with boehmite at a mass ratio of 8:2, and deionized water was added to adjust the humidity to form a plastic paste. The paste was extruded into strips with a diameter of 1.6 mm, dried at 120℃ for 12 hours, calcined at 550℃ for 4 hours, and then sieved to obtain 40-60 mesh particles. These particles were then packed into a fixed-bed reactor and reacted at a temperature of 250℃, a pressure of 0.3 MPa, and a space velocity of 2.0 h⁻¹. -1 The reaction was carried out under the condition that the 1-pentene feed purity was 99%.

[0076] The results showed that the selectivity of 2-pentene was 78% in the initial stage, and the total amount of byproducts reached 8%. After 50 hours of operation, the catalyst activity decreased significantly, and the selectivity of 2-pentene dropped to below 70%, requiring regeneration.

[0077] Comparative Example 2 Molecular sieves with different topologies were compared under the same conditions. ZSM-5, a three-dimensional ten-membered ring cross-channel molecular sieve, has a high conversion rate (approximately 95%), but severe side reactions, with C1–C3 small hydrocarbon byproducts exceeding 12% and 2-pentene selectivity less than 70%. SAPO-34, an eight-membered ring small-pore molecular sieve, exhibits significant diffusion restriction, resulting in a conversion rate of less than 60%, with products mainly consisting of cracked small molecules. SAPO-11, a one-dimensional ten-membered ring molecular sieve, has relatively weak acidity, achieving a conversion rate of approximately 75% and 2-pentene selectivity less than 82%. ZSM-23, also a one-dimensional ten-membered ring molecular sieve, has a low acid density, maintaining selectivity only at 80–85%.

[0078] By comparing catalyst A from Example 1, catalyst B from Example 2, and catalyst C from Comparative Example 1, it can be seen that the 2-pentene selectivity of catalysts A and B is significantly higher than that of catalyst C, and side reactions are significantly suppressed. Furthermore, through Comparative Example 2, it can be concluded that the one-dimensional through-hole ten-membered ring molecular sieve used in this disclosure, combined with the external surface directional passivation technology, effectively shields external acid sites without damaging the framework structure, and the external acid ratio is stably controlled at ≤0.10, thereby achieving comprehensive performance of high conversion rate, high selectivity, low by-products, and long lifetime.

[0079] The molecular sieve catalyst with directional passivation on the outer surface disclosed herein, its preparation method and application, form a dense passivation layer on the outer surface of the molecular sieve catalyst and retain appropriate Brønsted acid sites in the pores, thereby shielding the side reactions initiated by the external acid sites, ensuring efficient protonation of 1-pentene and migration of 1,2-hydrogen, and achieving a 2-pentene selectivity of ≥90%.

[0080] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein. The scope of the invention is defined by the appended claims.

Claims

1. A method for preparing a molecular sieve catalyst with directional passivation of its outer surface, characterized in that, Includes the following steps: Step S1: Select one-dimensional straight-through ten-membered ring molecular sieve powder as raw material, mix the raw material with ammonium chloride solution at a mass ratio of 1:10, filter to separate the solid, wash, dry, and calcine to obtain the first molecular sieve powder; Step S2: A passivation layer is formed on the outer surface of the first molecular sieve powder to obtain the second molecular sieve powder; Step S3: Mix the second molecular sieve powder with boehmite or silica sol at a mass ratio of 8:2, add deionized water to form a plastic paste, dry and calcine to obtain a molecular sieve catalyst with directional passivation on the outer surface.

2. The preparation method according to claim 1, characterized in that, Step S2 includes placing the first molecular sieve powder in a fixed bed deposition apparatus, introducing nitrogen gas, heating to a predetermined temperature and maintaining the temperature, then introducing hexamethyldisilazane along with nitrogen gas into the fixed bed deposition apparatus to react for a predetermined time, continuing nitrogen purging, and calcining to obtain a second molecular sieve powder with a passivation layer formed on its outer surface.

3. The preparation method according to claim 2, characterized in that, In step S2, the total feed amount of hexamethyldisilazane is 1wt%-3wt% of the mass of the first molecular sieve powder, and the loading amount of Si in the second molecular sieve powder is 1wt%-6wt%.

4. The preparation method according to claim 2, characterized in that, Step S2 further includes pre-curing the powder at 300°C after nitrogen purging, and then calcining it in an air atmosphere at 500°C to form a stable passivation layer on the surface of the first molecular sieve powder.

5. The preparation method according to claim 1, characterized in that, Step S2 includes mixing tetraethyl orthosilicate and anhydrous ethanol at a volume ratio of 1:5 to obtain a first solution; adding the first molecular sieve powder from S1 to the first solution to form a slurry with a solid-liquid ratio of 1:10, adjusting the pH to 4.5-5.5, and stirring; after the reaction is completed, filtering, drying, and calcining to obtain a second molecular sieve powder with a passivation layer formed on its outer surface.

6. The preparation method according to claim 1, characterized in that, The raw material mentioned in step S1 is a one-dimensional through-hole ten-membered ring molecular sieve powder with a relative crystallinity of ≥95% and a Si / Al molar ratio of 50-120.

7. The preparation method according to claim 1, characterized in that, The acid density in the first molecular sieve powder is 0.30 mmol / g-0.35 mmol / g.

8. The preparation method according to claim 1, characterized in that, The ratio of the number of external acid sites to the total number of acid sites in the molecular sieve catalyst with directional passivation on the outer surface is ≤0.

10.

9. A molecular sieve catalyst with directional passivation of its outer surface, characterized in that, The molecular sieve catalyst with directional passivation on its outer surface is prepared by any one of the preparation methods in claims 1-8.

10. The application of a molecular sieve catalyst with directional passivation of its outer surface in the isomerization of 1-pentene double bonds, characterized in that, The molecular sieve catalyst with directional passivation of the outer surface is a molecular sieve catalyst with directional passivation of the outer surface prepared according to any one of the preparation methods in claims 1-8.

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