Modified MCM-22 molecular sieve catalyst as well as preparation method and application thereof

Abstract

The invention discloses a modified MCM-22 molecular sieve catalyst and a preparation method and application thereof, the preparation method comprises the following steps: S1, adding MCM-22 molecular sieve raw powder into an alkaline solution, reacting for a preset time, and filtering to obtain a first sample; s2, adding the first sample into an ammonium nitrate solution, mixing and stirring, filtering, and roasting to obtain a second sample; and S3, adding the second sample in the step S2 into a molybdenum ion solution, mixing and stirring, standing for a preset time, filtering, washing, drying and roasting to obtain the modified MCM-22 molecular sieve catalyst. According to the preparation method of the modified MCM-22 molecular sieve catalyst provided by the invention, framework silicon in the molecular sieve is selectively dissolved through the alkaline solution, so that a pore channel of the molecular sieve is expanded, and the proportion of a medium acid site of the molecular sieve is increased through molybdenum modification, so that the diffusion and catalysis requirements of high-carbon olefins are effectively met; the reasonable regulation and control on the isomerization product composition are realized.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a modified MCM-22 molecular sieve catalyst, its preparation method, and its application. Background Technology

[0002] Currently, the olefin isomerization technology widely used in industry mainly targets low-carbon olefins of C4-C7, and its process system generally adopts a gas-phase reaction mode, relying on fixed-bed reactors and medium-to-high temperature operating conditions. However, this technical route faces significant bottlenecks when extended to the isomerization of high-carbon olefins of C16-C18: on the one hand, high-carbon olefins have large molecular weights and high boiling points, and are prone to thermal cracking side reactions under the high-temperature conditions required by traditional gas-phase reactions, leading to a decrease in the yield of the target product and carbon deposition and deactivation; on the other hand, to achieve gas-phase feeding, a large amount of carrier gas is often required, which not only increases energy consumption but also significantly increases the cost of subsequent product separation and recovery, thus restricting the economics and feasibility of the high-carbon olefin isomerization process.

[0003] Furthermore, existing catalytic systems lack the ability to precisely control product selectivity. High-carbon olefin isomerization involves two pathways: skeletal isomerism (changes in branch positions) and double bond isomerism, each with significantly different effects on end-product indicators such as lubrication performance and pour point. However, current technology cannot control the ratio of these two types of isomers as needed, nor does it possess a dynamic response mechanism, making it difficult to adapt to the flexible production requirements of different raw material compositions or product specifications. Summary of the Invention

[0004] This disclosure aims to address the problems existing in the prior art by providing a modified MCM-22 molecular sieve catalyst, its preparation method, and its application.

[0005] According to a first aspect of this disclosure, a method for preparing a modified MCM-22 molecular sieve catalyst is provided, comprising the following steps: Step S1: Add the MCM-22 molecular sieve raw powder to the alkaline solution, react for a predetermined time, and then filter to obtain the first sample; Step S2: Add the first sample from step S1 to the ammonium nitrate solution, mix and stir, filter, and calcine to obtain the second sample; Step S3: Add the second sample from step S2 to the molybdenum ion solution, mix and stir, and let stand for a predetermined time. Then filter, wash, dry, and calcine to obtain the modified MCM-22 molecular sieve catalyst.

[0006] In one embodiment of this disclosure, step S1 further includes adding MCM-22 molecular sieve raw powder to an alkaline solution, ultrasonically treating it and letting it stand for a predetermined time before filtering, washing the filtered solid with water until the pH of the washing solution is neutral, and drying the solid in an oven to obtain a first sample.

[0007] In one embodiment of this disclosure, the solid-liquid ratio of MCM-22 molecular sieve powder to alkaline solution in step S1 is 1:10-1:30.

[0008] In one embodiment of this disclosure, step S2 further includes adding the first sample to an ammonium nitrate solution, mixing and stirring, filtering, washing the filtered solid with water until the pH of the washing solution is neutral, and then calcining the solid to obtain the second sample.

[0009] In one embodiment of this disclosure, the solid-liquid ratio of the first sample to the ammonium nitrate solution in step S2 is 1:70-1:90.

[0010] In one embodiment of this disclosure, step S3 further includes adding ammonium molybdate to deionized water and sonicating it until the ammonium molybdate is completely dissolved to prepare a molybdenum ion solution of 0.1 mol / L-1.5 mol / L.

[0011] In one embodiment of this disclosure, the solid-liquid ratio of the second sample to the molybdenum ion solution in step S3 is 1:10 to 1:40.

[0012] In one embodiment of this disclosure, the concentration of the alkaline solution in step S1 is 0.2 mol / L to 3 mol / L.

[0013] According to a second aspect of this disclosure, a modified MCM-22 molecular sieve catalyst is provided, said modified MCM-22 molecular sieve catalyst being prepared by the above-described preparation method.

[0014] According to a third aspect of this disclosure, an application of a modified MCM-22 molecular sieve catalyst in the liquid-phase isomerization reaction of C16-C18 olefins is provided, wherein the modified MCM-22 molecular sieve catalyst is a modified MCM-22 molecular sieve catalyst prepared according to the above preparation method.

[0015] The modified MCM-22 molecular sieve catalyst disclosed herein, its preparation method, and its application involve selectively dissolving the framework silicon in the molecular sieve using an alkaline solution during the preparation process, thereby expanding the pores of the molecular sieve and facilitating the entry of macromolecular reactants. Furthermore, molybdenum modification increases the proportion of moderately acidic sites in the molecular sieve, effectively adapting to the diffusion and catalytic requirements of high-carbon olefins and achieving reasonable control over the composition of isomerization products (the ratio of framework isomers to double bond isomers).

[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 modified MCM-22 molecular sieve catalyst provided in one embodiment of this disclosure; Figure 2 These are NH3-TPD diagrams of the MCM-22 molecular sieve catalyst before and after modification; Figure 3 This is a pore size distribution diagram of the MCM-22 molecular sieve catalyst before modification; Figure 4 This is a pore size distribution diagram of the modified MCM-22 molecular sieve catalyst. 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] Currently, the olefin isomerization technology widely used in industry mainly targets low-carbon olefins of C4-C7, and its process system generally adopts a gas-phase reaction mode, relying on fixed-bed reactors and medium-to-high temperature operating conditions. However, this technical route faces significant bottlenecks when extended to the isomerization of high-carbon olefins of C16-C18: on the one hand, high-carbon olefins have large molecular weights and high boiling points, and are prone to thermal cracking side reactions under the high-temperature conditions required by traditional gas-phase reactions, leading to a decrease in the yield of the target product and carbon deposition and deactivation; on the other hand, to achieve gas-phase feeding, a large amount of carrier gas is often required, which not only increases energy consumption but also significantly increases the cost of subsequent product separation and recovery, thus restricting the economics and feasibility of the high-carbon olefin isomerization process.

[0024] Furthermore, existing catalytic systems lack the ability to precisely control product selectivity. High-carbon olefin isomerization involves two pathways: skeletal isomerism (changes in branch positions) and double bond isomerism, each with significantly different effects on end-product indicators such as lubrication performance and pour point. However, current technology cannot control the ratio of these two types of isomers as needed, nor does it possess a dynamic response mechanism, making it difficult to adapt to the flexible production requirements of different raw material compositions or product specifications.

[0025] This disclosure aims to address the problems existing in the prior art by providing a modified MCM-22 molecular sieve catalyst, 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 modified MCM-22 molecular sieve catalyst, comprising the following steps: Step S1: Add the MCM-22 molecular sieve raw powder to the alkaline solution, react for a predetermined time, and then filter to obtain the first sample; Step S2: Add the first sample from step S1 to the ammonium nitrate solution, mix and stir, filter, and calcine to obtain the second sample; Step S3: Add the second sample from step S2 to the molybdenum ion solution, mix and stir, and let stand for a predetermined time. Then filter, wash, dry, and calcine to obtain the modified MCM-22 molecular sieve catalyst.

[0027] Specifically, the framework of MCM-22 molecular sieve consists of silicon-oxygen tetrahedra (SiO4) and a small amount of aluminum-oxygen tetrahedra (AlO4). -The MCM-22 molecular sieve is composed of a framework where the introduction of aluminum imparts a negative charge, forming Brønsted acid sites (≡Si–OH–Al≡) through proton equilibrium. In step S1, by adding the raw MCM-22 molecular sieve powder to an alkaline solution (such as sodium hydroxide solution), hydroxide ions preferentially attack the electrically neutral Si–O–Si bonds in the framework, while the negatively charged Si–O–Al bonds remain relatively stable. Therefore, silicon atoms are more easily dissolved than aluminum. This selectivity leads to the hydrolysis of some framework silicon, which enters the solution as soluble silicates (such as Na₂SiO₃), while aluminum is relatively enriched in the remaining framework. As desilication proceeds, mesopores are generated in the originally dense microporous structure, and some framework aluminum migrates to the outer surface of the molecular sieve due to local structural reconstruction, forming an aluminum-rich region on the surface. This process not only moderately expands the pore structure of the MCM-22 molecular sieve but also introduces other pores, which is more conducive to the entry of macromolecular reactants.

[0028] Furthermore, since the first sample after alkali treatment contains residual sodium ions introduced by the use of sodium hydroxide, these sodium ions occupy the negative charge equilibrium sites originally generated by the framework aluminum, thereby inhibiting the formation of Brønsted acid sites, leading to a significant decrease in catalyst acidity or even deactivation. Therefore, in order to restore the acid catalytic performance of the catalyst, in step S2, the material needs to be dried and placed in an ammonium nitrate solution for ion exchange. During this process, the ammonium ions in the solution, by virtue of their concentration advantage and electrostatic interaction, displace the sodium ions adsorbed or bound to the molecular sieve channels and framework surface, generating soluble sodium salts that enter the solution, while the ammonium ions occupy the corresponding sites. Subsequently, after drying again and calcining at an appropriate temperature, the ammonium ions are thermally decomposed into ammonia and protons (H2O). + The proton combines with the bridging oxygen in the framework to reform the catalytically active Brønsted acid site (≡Si–OH–Al≡), thereby restoring or even optimizing the activity and selectivity of the catalyst in acid-catalyzed reactions.

[0029] In step S3, the second sample is added to the molybdenum ion solution and mixed. The purpose is to utilize the abundant Brønsted acid sites on the surface and within the pores of the molecular sieve as anchoring points, allowing molybdate ions or polymerized molybdenum species to be uniformly adsorbed onto the pores and outer surface of the molecular sieve through electrostatic attraction, hydrogen bonding, or acid-base interactions. During subsequent drying and calcination, ammonium molybdate or polymerized molybdenum species decompose to generate molybdenum oxides (MoOx). These molybdenum precursors further undergo condensation reactions with framework oxygen to form Mo–O–Si or Mo–O–Al chemical bonds, directly covering or destroying the original Brønsted acid centers. On the other hand, the loaded MoOx species themselves are relatively weakly acidic, effectively diluting the density of strong acid sites, thus weakening the strength and quantity of strong acids in the molecular sieve, and correspondingly increasing the proportion of moderately strong acids.

[0030] Furthermore, since alkali treatment induces some skeletal aluminum to migrate to the surface to form an aluminum-rich shell, Brønsted acid sites are more concentrated on the outer surface or near the surface. These sites have less steric hindrance and moderate acid strength, which is more conducive to reactions such as double bond migration that only require weak to moderate acidity and rapid desorption. In contrast, skeletal isomerization usually requires stronger acidity and longer reaction time and occurs within confined channels. Therefore, the modified MCM-22 molecular sieve catalyst prepared in this disclosure can achieve reasonable control over the composition of isomerization products (the ratio of skeletal isomers to double bond isomers).

[0031] In one embodiment of this disclosure, step S1 further includes adding MCM-22 molecular sieve raw powder to an alkaline solution, ultrasonically treating it, letting it stand for a predetermined time, filtering it, washing the filtered solid with water until the pH of the washing solution is neutral, and drying the solid in an oven to obtain a first sample.

[0032] Specifically, the introduction of ultrasonic assistance in step S1 can significantly improve the uniformity and efficiency of alkali treatment. The cavitation effect, microjets, and strong disturbances generated by ultrasound in the liquid can accelerate the OH- process. - The diffusion rate of ions promotes silicon dissolution and avoids uneven processing caused by localized over-etching or particle agglomeration. Simultaneously, ultrasonic treatment helps promote the timely removal of silicate ions released during desilication, preventing their localized redeposition. Furthermore, the filtered solid is washed with water until the washing solution reaches a neutral pH, and then dried to thoroughly remove soluble alkaline substances (such as NaOH, Na₂SiO₃, etc.) and reaction byproducts remaining in the molecular sieve channels, surface, and interparticle spaces, preventing them from adversely affecting subsequent reactions.

[0033] In one embodiment of this disclosure, the solid-liquid ratio of MCM-22 molecular sieve powder to alkaline solution in step S1 is 1:10-1:30. If the solid-liquid ratio is too high (i.e., too much solid and too little liquid), the alkaline solution will not be able to fully wet all the molecular sieve particles, leading to an increase in OH- ions in the reaction system. - Uneven ion concentration in certain areas can lead to incomplete desilication of some particles due to insufficient contact with the alkaline solution, while others may experience over-etching due to excessively high local concentrations. Conversely, if the solid-liquid ratio is too low (i.e., too much liquid and too little solid), although the reaction uniformity improves, the OH groups may not be fully etched. - An excess of ions may cause the desilication reaction to be too violent or difficult to control precisely, especially during long-term processing, which can easily lead to framework collapse.

[0034] In another embodiment of this disclosure, step S2 further includes adding the first sample to an ammonium nitrate solution, mixing and stirring, filtering, washing the filtered solid with water until the pH of the washing solution is neutral, and then calcining the solid to obtain the second sample.

[0035] Specifically, because the first sample after alkali treatment contains residual sodium ions introduced by the use of sodium hydroxide, these sodium ions occupy the negative charge equilibrium sites originally generated by the framework aluminum, thereby inhibiting the formation of Brønsted acid sites and causing a significant decrease or even deactivation of the catalyst's acidity. Therefore, in order to restore the catalyst's acid catalytic performance, in step S2, the material needs to be dried and placed in an ammonium nitrate solution for ion exchange, thereby displacing the sodium ions adsorbed or bound to the molecular sieve channels and framework surface, generating soluble sodium salts that enter the solution, while ammonium ions occupy the corresponding positions. In order to thoroughly remove excess ammonium nitrate, sodium salts generated by the reaction, and other soluble ionic impurities physically adsorbed or remaining in the molecular sieve channels and interparticle gaps, in step S2, the filtered solid also needs to be washed with water until the pH of the washing solution is neutral, and then calcined at an appropriate temperature to allow the ammonium ions to decompose into ammonia and protons (H+). + The proton combines with the bridging oxygen in the framework to reform the catalytically active Brønsted acid site (≡Si–OH–Al≡), thereby restoring or even optimizing the activity and selectivity of the catalyst in acid-catalyzed reactions.

[0036] In one embodiment of this disclosure, the solid-liquid ratio of the first sample to the ammonium nitrate solution in step S2 is 1:70-1:90. If the solid-liquid ratio is too high (i.e., too much solid and too little liquid), the concentration of ammonium ions in the ammonium nitrate solution is relatively insufficient, making it difficult to fully contact and effectively replace all the sodium ions in the molecular sieve, resulting in incomplete ion exchange and residual Na+. + It will occupy the negatively charged sites generated by the skeletal aluminum, hindering the formation of Brønsted acid sites during subsequent calcination, thereby significantly reducing the acidity and activity of the catalyst. Conversely, if the solid-liquid ratio is too low (i.e., too much liquid and too little solid), it will result in a large waste of ammonium nitrate reagent, increasing the burden of wastewater treatment and production costs.

[0037] In one embodiment of this disclosure, step S3 further includes adding ammonium molybdate to deionized water and sonicating until the ammonium molybdate is completely dissolved, thus preparing a molybdenum ion solution of 0.1 mol / L-1.5 mol / L. If the molybdenum ion concentration is too high, during the impregnation process, a large number of molybdate ions will rapidly adsorb onto the outer surface of the molecular sieve, exceeding its pore capacity and the number of surface Brønsted acid sites. This leads to excessive aggregation of molybdenum species after drying and calcination, forming large-sized crystal particles. These particles will block the pores of the molecular sieve, hindering reactant diffusion. Conversely, if the molybdenum ion concentration is too low, the loading will be insufficient, failing to form a sufficiently dense active center on the molecular sieve, resulting in low catalytic activity and difficulty in meeting the conversion requirements of industrial reactions.

[0038] In one embodiment of this disclosure, the solid-liquid ratio of the second sample to the molybdenum ion solution in step S3 is 1:10-1:40. If the solid-liquid ratio is too high (i.e., too much solid and too little liquid), the molybdenum ion solution cannot adequately wet all the molecular sieve particles, causing molybdate ions in the solution to be unable to diffuse uniformly into the internal pores of the particles, and instead accumulate locally on the outer surface. During subsequent drying and calcination, these locally high-concentration areas are prone to forming clusters or crystals, which not only block the pores and reduce the specific surface area, but also mask the active acid sites, thereby reducing the conversion rate and catalyst lifetime. Conversely, if the solid-liquid ratio is too low (i.e., too much liquid and too little solid), the actual concentration of molybdenum in the solution is relatively low, resulting in insufficient overall catalyst loading and a higher proportion of strong and weak acids and a lower proportion of medium-strong acids, thus reducing the conversion rate and selectivity.

[0039] In one embodiment of this disclosure, the concentration of the alkaline solution in step S1 is 0.2 mol / L-3 mol / L. If the concentration of the alkaline solution is too low, the pore-expanding effect will be weakened, and the pore size of the catalyst will not be fully expanded. Large molecules will easily enter and cause pore blockage, thereby reducing the conversion rate and catalyst lifetime. If the concentration of the alkaline solution is too high, the pore-expanding effect will be too strong, which will easily lead to the catalyst pores being too large or the framework collapsing, thereby reducing its selectivity and catalyst lifetime.

[0040] According to a second aspect of this disclosure, a modified MCM-22 molecular sieve catalyst is provided, which is prepared by the above-described preparation method.

[0041] According to a third aspect of this disclosure, an application of a modified MCM-22 molecular sieve catalyst in the liquid-phase isomerization reaction of C16-C18 olefins is provided, wherein the modified MCM-22 molecular sieve catalyst is a modified MCM-22 molecular sieve catalyst prepared according to the above preparation method.

[0042] Specifically, the process flow for the liquid-phase isomerization reaction of high-carbon-number olefins is as follows: Step 1: The modified MCM-22 molecular sieve catalyst prepared by the above method is loaded into a fixed bed reactor, and the catalyst bed is filled and fixed with quartz wool and quartz sand on the top and bottom; the temperature is raised to 300℃, and nitrogen gas (flow rate 40mL / min) is introduced for online activation for 12h to remove adsorbed water and impurities on the surface of the molecular sieve. Step 2: Dehydrate and remove oxygen-containing compounds from C16-C18 Fischer-Tropsch oil feedstock to ensure that the water content is <100ppm and the oxygen-containing compound content is <50μg / mL, thereby avoiding impurities from poisoning the acidic sites of the catalyst; Step 3: After calibrating the liquid transfer pump flow rate, heat the reactor to 120℃-180℃, and send the pretreated raw materials into the reactor through the transfer pump. React under normal pressure, and control the raw material mass hourly space velocity (MHSV) at 3h.-1 ; Step 4: Take samples periodically and analyze the product composition using gas chromatography (e.g., equipped with an FID detector). Optimize the ratio of skeletal isomers to double bond isomers by adjusting the reaction temperature (within the range of 120℃-180℃).

[0043] 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.

[0044] Example 1 Purchased MCM-22 raw powder with a silicon-to-aluminum molar ratio of 30 was added to a 1.4 mol / L NaOH solution, with a solid-liquid ratio of 1:18. The solution was ultrasonically treated at 60℃ for 8 hours, followed by standing for 1.5 hours. After filtration, the solution was repeatedly washed with deionized water 3-6 times until the pH of the washing solution was neutral. The molecular sieve was then dried in a 150℃ oven for 5 hours to obtain the first sample. The dried sample was then added to a 1 mol / L ammonium nitrate solution, with a solid-liquid ratio of 1:80. The solution was stirred at 80℃ for 5 hours, and the mixture was exchanged 3 times. After filtration and washing until neutral, the solution was calcined in a muffle furnace at 500℃ for 5 hours to obtain the second sample. Ammonium molybdate was added to deionized water and sonicated until completely dissolved to prepare a 0.8 mol / L molybdenum ion solution. The second sample was added to the molybdenum ion solution with a solid-liquid ratio of 1:22. The mixture was stirred at 70°C for 8 hours, allowed to stand for 1.5 hours, filtered, and washed repeatedly with deionized water 3-6 times until the pH of the washing solution was neutral. The solid was dried at 150°C for 5 hours and then calcined at 500°C for 5 hours to obtain the modified MCM-22 molecular sieve catalyst.

[0045] Isomerization reaction conditions: reaction temperature 120℃-180℃, atmospheric pressure, mass hourly space velocity (H₂S) of 3 h⁻¹ -1 .

[0046] Experimental results: α-olefin conversion rate 93.6%, double bond isomer selectivity 87.4%, catalyst lifetime 496 h. The above α-olefin conversion rate and double bond isomer selectivity are experimental data from the stable operation period. The catalyst lifetime was determined based on a conversion rate of over 90% and a double bond isomer selectivity of over 80%.

[0047] Example 2 Purchased MCM-22 raw powder with a silicon-to-aluminum molar ratio of 30 was added to a 1.4 mol / L NaOH solution, with a solid-liquid ratio of 1:10. The mixture was ultrasonically treated at 60℃ for 8 hours, followed by standing for 1.5 hours. After filtration, the sample was repeatedly washed with deionized water 3-6 times until the pH of the washing solution was neutral. The molecular sieve was then dried in a 150℃ oven for 5 hours to obtain the first sample. The dried sample was then added to a 1 mol / L ammonium nitrate solution, with a solid-liquid ratio of 1:80. The mixture was stirred at 80℃ for 5 hours, and the reaction was repeated 3 times. After filtration and washing until neutral, the sample was calcined in a muffle furnace at 500℃ for 5 hours to obtain the second sample. Ammonium molybdate was added to deionized water and sonicated until completely dissolved to prepare a 0.8 mol / L molybdenum ion solution. The second sample was added to the molybdenum ion solution with a solid-liquid ratio of 1:22. The mixture was stirred at 70°C for 8 hours, allowed to stand for 1.5 hours, filtered, and washed repeatedly with deionized water 3-6 times until the pH of the washing solution was neutral. The solid was dried at 150°C for 5 hours and then calcined at 500°C for 5 hours to obtain the modified MCM-22 molecular sieve catalyst.

[0048] Isomerization reaction conditions: reaction temperature 120℃-180℃, atmospheric pressure, mass hourly space velocity (H₂S) of 3 h⁻¹ -1 .

[0049] Experimental results: α-olefin conversion rate 92.9%, double bond isomer selectivity 87.5%, catalyst lifetime 368h.

[0050] By comparing the experimental results of Example 1 and this example, it can be seen that reducing the amount of sodium hydroxide solution during the modification process will weaken the pore-expanding effect of the alkali, resulting in insufficient expansion of the catalyst pore size. This makes it easier for macromolecular materials to block the pores when entering the catalyst, thereby reducing both the conversion rate and the catalyst lifetime.

[0051] Example 3 Purchased MCM-22 raw powder with a silicon-to-aluminum molar ratio of 30 was added to a 1.4 mol / L NaOH solution, with a solid-liquid ratio of 1:30. The mixture was ultrasonically treated at 60℃ for 8 hours, followed by standing for 1.5 hours. After filtration, the sample was repeatedly washed with deionized water 3-6 times until the pH of the washing solution was neutral. The molecular sieve was then dried in a 150℃ oven for 5 hours to obtain the first sample. The dried sample was then added to a 1 mol / L ammonium nitrate solution, with a solid-liquid ratio of 1:80. The mixture was stirred at 80℃ for 5 hours, and the reaction was repeated 3 times. After filtration and washing until neutral, the sample was calcined in a muffle furnace at 500℃ for 5 hours to obtain the second sample. Ammonium molybdate was added to deionized water and sonicated until completely dissolved to prepare a 0.8 mol / L molybdenum ion solution. The second sample was added to the molybdenum ion solution with a solid-liquid ratio of 1:22. The mixture was stirred at 70°C for 8 hours, allowed to stand for 1.5 hours, filtered, and washed repeatedly with deionized water 3-6 times until the pH of the washing solution was neutral. The solid was dried at 150°C for 5 hours and then calcined at 500°C for 5 hours to obtain the modified MCM-22 molecular sieve catalyst.

[0052] Isomerization reaction conditions: reaction temperature 120℃-180℃, atmospheric pressure, mass hourly space velocity (H₂S) of 3 h⁻¹ -1 .

[0053] Experimental results: α-olefin conversion rate 93.4%, double bond isomer selectivity 84.7%, catalyst lifetime 312h.

[0054] By comparing the experimental results of Example 1 and this example, it can be seen that increasing the amount of sodium hydroxide solution during the modification process will lead to an excessively strong pore-expanding effect of the alkali, resulting in excessively large or collapsed pores in the catalyst channels, thereby reducing both the conversion rate and the catalyst lifetime.

[0055] Example 4 Purchased MCM-22 raw powder with a silicon-to-aluminum molar ratio of 30 was added to a 0.2 mol / L NaOH solution, with a solid-liquid ratio of 1:18. The solution was ultrasonically treated at 60℃ for 8 hours, followed by standing for 1.5 hours. After filtration, the solution was repeatedly washed with deionized water 3-6 times until the pH of the washing solution was neutral. The molecular sieve was then dried in a 150℃ oven for 5 hours to obtain the first sample. The dried sample was then added to a 1 mol / L ammonium nitrate solution, with a solid-liquid ratio of 1:80. The solution was stirred at 80℃ for 5 hours, and the mixture was exchanged 3 times. After filtration and washing until neutral, the solution was calcined in a muffle furnace at 500℃ for 5 hours to obtain the second sample. Ammonium molybdate was added to deionized water and sonicated until completely dissolved to prepare a 0.8 mol / L molybdenum ion solution. The second sample was added to the molybdenum ion solution with a solid-liquid ratio of 1:22. The mixture was stirred at 70°C for 8 hours, allowed to stand for 1.5 hours, filtered, and washed repeatedly with deionized water 3-6 times until the pH of the washing solution was neutral. The solid was dried at 150°C for 5 hours and then calcined at 500°C for 5 hours to obtain the modified MCM-22 molecular sieve catalyst.

[0056] Isomerization reaction conditions: reaction temperature 120℃-180℃, atmospheric pressure, mass hourly space velocity (H₂S) of 3 h⁻¹ -1 .

[0057] Experimental results: α-olefin conversion rate 92.6%, double bond isomer selectivity 87.4%, catalyst lifetime 352h.

[0058] By comparing the experimental results of Example 1 and this example, it can be seen that the concentration of sodium hydroxide in the alkaline solution is too low during the modification process, which will lead to a weakening of the alkaline pore-expanding effect, resulting in insufficient expansion of the catalyst pore size. This makes it easy for large molecular materials to cause pore blockage when entering the catalyst, thereby reducing both the conversion rate and the catalyst lifetime.

[0059] Example 5 Purchased MCM-22 raw powder with a silicon-to-aluminum molar ratio of 30 was added to a 3 mol / L NaOH solution, with a solid-liquid ratio of 1:18. The mixture was ultrasonically treated at 60℃ for 8 hours, followed by standing for 1.5 hours. After filtration, the sample was repeatedly washed with deionized water 3-6 times until the pH of the washing solution was neutral. The molecular sieve was then dried in a 150℃ oven for 5 hours to obtain the first sample. The dried sample was then added to a 1 mol / L ammonium nitrate solution, with a solid-liquid ratio of 1:80. The mixture was stirred at 80℃ for 5 hours, and the reaction was repeated 3 times. After filtration and washing until neutral, the sample was calcined in a muffle furnace at 500℃ for 5 hours to obtain the second sample. Ammonium molybdate was added to deionized water and sonicated until completely dissolved to prepare a 0.8 mol / L molybdenum ion solution. The second sample was added to the molybdenum ion solution with a solid-liquid ratio of 1:22. The mixture was stirred at 70°C for 8 hours, allowed to stand for 1.5 hours, filtered, and washed repeatedly with deionized water 3-6 times until the pH of the washing solution was neutral. The solid was dried at 150°C for 5 hours and then calcined at 500°C for 5 hours to obtain the modified MCM-22 molecular sieve catalyst.

[0060] Isomerization reaction conditions: reaction temperature 120℃-180℃, atmospheric pressure, mass hourly space velocity (H₂S) of 3 h⁻¹ -1 .

[0061] Experimental results: α-olefin conversion rate 93.2%, double bond isomer selectivity 83.9%, catalyst lifetime 284h.

[0062] By comparing the experimental results of Example 1 and this example, it can be seen that if the concentration of sodium hydroxide in the alkaline solution is too high during the modification process, the alkaline pore-expanding effect will be too strong, resulting in the catalyst pores being too large or collapsing, thereby reducing both the conversion rate and the catalyst lifetime.

[0063] Example 6 Purchased MCM-22 raw powder with a silicon-to-aluminum molar ratio of 30 was added to a 1.4 mol / L NaOH solution, with a solid-liquid ratio of 1:18. The mixture was ultrasonically treated at 60℃ for 8 hours, followed by standing for 1.5 hours. After filtration, the sample was repeatedly washed with deionized water 3-6 times until the pH of the washing solution was neutral. The molecular sieve was then dried in a 150℃ oven for 5 hours to obtain the first sample. The dried sample was then added to a 1 mol / L ammonium nitrate solution, with a solid-liquid ratio of 1:80. The mixture was stirred at 80℃ for 5 hours, and the reaction was repeated 3 times. After filtration and washing until neutral, the sample was calcined in a muffle furnace at 500℃ for 5 hours to obtain the second sample. Ammonium molybdate was added to deionized water and sonicated until completely dissolved to prepare a 0.8 mol / L molybdenum ion solution. The second sample was added to the molybdenum ion solution with a solid-liquid ratio of 1:10. The mixture was stirred at 70°C for 8 hours, allowed to stand for 1.5 hours, filtered, and washed repeatedly with deionized water 3-6 times until the pH of the washing solution was neutral. The solid was dried at 150°C for 5 hours and then calcined at 500°C for 5 hours to obtain the modified MCM-22 molecular sieve catalyst.

[0064] Isomerization reaction conditions: reaction temperature 120℃-180℃, atmospheric pressure, mass hourly space velocity (H₂S) of 3 h⁻¹ -1 .

[0065] Experimental results: α-olefin conversion rate 92.1%, double bond isomer selectivity 82.4%, catalyst lifetime 488h.

[0066] By comparing the experimental results of Example 1 with those of this example, it can be seen that increasing the solid-liquid ratio of the second sample to the molybdenum ion solution during the modification process, i.e., relatively reducing the amount of molybdenum ion solution, will result in a higher proportion of strong acid and weak acid and a lower proportion of medium-strong acid, thereby reducing the conversion rate and selectivity.

[0067] Example 7 Purchased MCM-22 raw powder with a silicon-to-aluminum molar ratio of 30 was added to a 1.4 mol / L NaOH solution, with a solid-liquid ratio of 1:18. The mixture was ultrasonically treated at 60℃ for 8 hours, followed by standing for 1.5 hours. After filtration, the sample was repeatedly washed with deionized water 3-6 times until the pH of the washing solution was neutral. The molecular sieve was then dried in a 150℃ oven for 5 hours to obtain the first sample. The dried sample was then added to a 1 mol / L ammonium nitrate solution, with a solid-liquid ratio of 1:80. The mixture was stirred at 80℃ for 5 hours, and the reaction was repeated 3 times. After filtration and washing until neutral, the sample was calcined in a muffle furnace at 500℃ for 5 hours to obtain the second sample. Ammonium molybdate was added to deionized water and sonicated until completely dissolved to prepare a 0.8 mol / L molybdenum ion solution. The second sample was added to the molybdenum ion solution with a solid-liquid ratio of 1:40. The mixture was stirred at 70°C for 8 hours, allowed to stand for 1.5 hours, filtered, and washed repeatedly with deionized water 3-6 times until the pH of the washing solution was neutral. The solid was dried at 150°C for 5 hours and then calcined at 500°C for 5 hours to obtain the modified MCM-22 molecular sieve catalyst.

[0068] Isomerization reaction conditions: reaction temperature 120℃-180℃, atmospheric pressure, mass hourly space velocity (H₂S) of 3 h⁻¹ -1 .

[0069] Experimental results: α-olefin conversion rate 91.5%, double bond isomer selectivity 86.8%, catalyst lifetime 346h.

[0070] By comparing the experimental results of Example 1 and this example, it can be seen that reducing the solid-liquid ratio of the second sample to the molybdenum ion solution during the modification process, i.e., relatively increasing the amount of molybdenum ion solution, will cause some catalyst pores to become blocked and the acid strength to be greatly weakened, thereby reducing the conversion rate and catalyst life.

[0071] Example 8 Purchased MCM-22 raw powder with a silicon-to-aluminum molar ratio of 30 was added to a 1.4 mol / L NaOH solution, with a solid-liquid ratio of 1:18. The mixture was ultrasonically treated at 60℃ for 8 hours, followed by standing for 1.5 hours. After filtration, the sample was repeatedly washed with deionized water 3-6 times until the pH of the washing solution was neutral. The molecular sieve was then dried in a 150℃ oven for 5 hours to obtain the first sample. The dried sample was then added to a 1 mol / L ammonium nitrate solution, with a solid-liquid ratio of 1:80. The mixture was stirred at 80℃ for 5 hours, and the reaction was repeated 3 times. After filtration and washing until neutral, the sample was calcined in a muffle furnace at 500℃ for 5 hours to obtain the second sample. Ammonium molybdate was added to deionized water and sonicated until completely dissolved to prepare a 0.1 mol / L molybdenum ion solution. The second sample was added to the molybdenum ion solution with a solid-liquid ratio of 1:22. The mixture was stirred at 70°C for 8 hours, allowed to stand for 1.5 hours, filtered, and washed repeatedly with deionized water 3-6 times until the pH of the washing solution was neutral. The solid was dried at 150°C for 5 hours and then calcined at 500°C for 5 hours to obtain the modified MCM-22 molecular sieve catalyst.

[0072] Isomerization reaction conditions: reaction temperature 120℃-180℃, atmospheric pressure, mass hourly space velocity (H₂S) of 3 h⁻¹ -1 .

[0073] Experimental results: α-olefin conversion rate 92.4%, double bond isomer selectivity 82.7%, catalyst lifetime 474 h.

[0074] By comparing the experimental results of Example 1 and this example, it can be seen that the low concentration of molybdenum ion solution during the modification process leads to a higher proportion of strong and weak acids and a lower proportion of medium-strong acids, thereby reducing the conversion rate and selectivity.

[0075] Example 9 Purchased MCM-22 raw powder with a silicon-to-aluminum molar ratio of 30 was added to a 1.4 mol / L NaOH solution, with a solid-liquid ratio of 1:18. The mixture was ultrasonically treated at 60℃ for 8 hours, followed by standing for 1.5 hours. After filtration, the sample was repeatedly washed with deionized water 3-6 times until the pH of the washing solution was neutral. The molecular sieve was then dried in a 150℃ oven for 5 hours to obtain the first sample. The dried sample was then added to a 1 mol / L ammonium nitrate solution, with a solid-liquid ratio of 1:80. The mixture was stirred at 80℃ for 5 hours, and the reaction was repeated 3 times. After filtration and washing until neutral, the sample was calcined in a muffle furnace at 500℃ for 5 hours to obtain the second sample. Ammonium molybdate was added to deionized water and sonicated until completely dissolved to prepare a 1.5 mol / L molybdenum ion solution. The second sample was added to the molybdenum ion solution with a solid-liquid ratio of 1:22. The mixture was stirred at 70°C for 8 hours, allowed to stand for 1.5 hours, filtered, and washed repeatedly with deionized water 3-6 times until the pH of the washing solution was neutral. The solid was dried at 150°C for 5 hours and then calcined at 500°C for 5 hours to obtain the modified MCM-22 molecular sieve catalyst.

[0076] Isomerization reaction conditions: reaction temperature 120℃-180℃, atmospheric pressure, mass hourly space velocity (H₂S) of 3 h⁻¹ -1 .

[0077] Experimental results: α-olefin conversion rate 91.3%, double bond isomer selectivity 87.0%, catalyst lifetime 328h.

[0078] By comparing the experimental results of Example 1 and this example, it can be seen that the high concentration of molybdenum ion solution during the modification process will cause some catalyst pores to become blocked and the acid strength to be greatly reduced, thereby reducing the conversion rate and catalyst life.

[0079] Comparative Example 1 Unmodified MCM-22 molecular sieve catalyst.

[0080] Isomerization reaction conditions: reaction temperature 120℃-180℃, atmospheric pressure, mass hourly space velocity (H₂S) of 3 h⁻¹ -1 .

[0081] Experimental results: α-olefin conversion rate 90.5%, double bond isomer selectivity 81.9%, catalyst lifetime 155h.

[0082] from Figure 2 The NH3-TPD spectrum of the unmodified MCM-22 molecular sieve catalyst shows that weak acid sites are around 240℃ and strong acid sites are around 450℃, indicating that the acid content distribution before modification is mainly strong and weak acid. Figure 2The NH3-TPD spectrum of the modified MCM-22 molecular sieve catalyst shows that the acid content distribution is mainly concentrated around 280℃ and 380℃. This indicates that after modification, the acid strength of strong acids in the MCM-22 molecular sieve catalyst is weakened, while the acid strength of weak acids is enhanced, resulting in a suitable acid strength distribution for the isomerization reaction.

[0083] Figure 3 The image shows the pore size distribution of the MCM-22 molecular sieve catalyst before modification. The pore sizes are mainly concentrated in the 0.5nm-0.8nm range, indicating relatively small pore sizes. After modification, as shown... Figure 4 As shown, a large number of pores between 2nm and 5nm appeared, indicating that the pore-expanding effect of the modified material disclosed in this paper is significant.

[0084] The modified MCM-22 molecular sieve catalyst disclosed herein, its preparation method, and its application involve selectively dissolving the framework silicon in the molecular sieve using an alkaline solution during the preparation process, thereby expanding the pores of the molecular sieve and facilitating the entry of macromolecular reactants. Furthermore, molybdenum modification increases the proportion of moderately acidic sites in the molecular sieve, effectively adapting to the diffusion and catalytic requirements of high-carbon olefins and achieving reasonable control over the composition of isomerization products (the ratio of framework isomers to double bond isomers).

[0085] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, and are not 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 modified MCM-22 molecular sieve catalyst, characterized in that, Includes the following steps: Step S1: Add the MCM-22 molecular sieve raw powder to the alkaline solution, react for a predetermined time, and then filter to obtain the first sample; Step S2: Add the first sample from step S1 to the ammonium nitrate solution, mix and stir, filter, and calcine to obtain the second sample; Step S3: Add the second sample from step S2 to the molybdenum ion solution, mix and stir, and let stand for a predetermined time. Then filter, wash, dry, and calcine to obtain the modified MCM-22 molecular sieve catalyst.

2. The preparation method according to claim 1, characterized in that, Step S1 also includes adding MCM-22 molecular sieve raw powder to an alkaline solution, ultrasonicating and letting it stand for a predetermined time before filtering, washing the filtered solid with water until the pH of the washing solution is neutral, and drying the solid in an oven to obtain the first sample.

3. The preparation method according to claim 2, characterized in that, In step S1, the solid-liquid ratio of MCM-22 molecular sieve raw powder to alkaline solution is 1:10-1:

30.

4. The preparation method according to claim 1, characterized in that, Step S2 also includes adding the first sample to an ammonium nitrate solution, mixing and stirring, filtering, washing the filtered solid with water until the pH of the washing solution is neutral, and then calcining the solid to obtain the second sample.

5. The preparation method according to claim 1, characterized in that, In step S2, the solid-liquid ratio of the first sample to the ammonium nitrate solution is 1:70-1:

90.

6. The preparation method according to claim 1, characterized in that, Step S3 also includes adding ammonium molybdate to deionized water and sonicating it until the ammonium molybdate is completely dissolved to prepare a molybdenum ion solution of 0.1 mol / L-1.5 mol / L.

7. The preparation method according to claim 6, characterized in that, In step S3, the solid-liquid ratio of the second sample to the molybdenum ion solution is 1:10-1:

40.

8. The preparation method according to claim 2, characterized in that, The concentration of the alkaline solution in step S1 is 0.2 mol / L-3 mol / L.

9. A modified MCM-22 molecular sieve catalyst, characterized in that, The modified MCM-22 molecular sieve catalyst is prepared according to any one of the preparation methods in claims 1-8.

10. The application of a modified MCM-22 molecular sieve catalyst in the liquid-phase isomerization reaction of C16-C18 olefins, characterized in that, The modified MCM-22 molecular sieve catalyst is a modified MCM-22 molecular sieve catalyst prepared according to any one of the preparation methods in claims 1-8.

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