Method for improving activity site of TS-1 molecular sieve in catalyzing ammoximation reaction

Abstract

The present application relates to a kind of method for improving the active site of TS-1 molecular sieve catalytic ammoniooximation reaction, belong to molecular sieve catalysis technical field.The method specifically includes the following steps: (1) with ammonia water as pretreatment agent, TS-1 molecular sieve is mixed with pretreatment agent and is handled for a certain time;(2) ammonia water pretreated TS-1 molecular sieve is dried, and is treated using ozone under ultraviolet light;(3) using HCl gas to the TS-1 molecular sieve is handled under heating condition, i.e. the TS-1 molecular sieve of improved active site is obtained.The method of the present application is directly synthesized TS-1 molecular sieve is improved after active site, and the proportion of molecular sieve skeleton titanium in total titanium species significantly increases.When TS-1 molecular sieve for improving active site using the method of the present application as catalyst carries out cyclohexanone ammoniooximation reaction, relative to TS-1 molecular sieve without improving treatment, catalytic activity and selectivity are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve catalysis technology, specifically involving a method for improving the active sites of the TS-1 molecular sieve catalytic ammonium oximation reaction, thereby improving the activity and selectivity of the TS-1 molecular sieve catalytic ammonium oximation reaction. Background Technology

[0002] The TS-1 type titanium-silicon molecular sieve has an MFI topology. Its framework titanium can activate hydrogen peroxide and catalyze the ammoniation reaction of hydrogen peroxide, ammonia and cyclohexanone. The generated cyclohexanone oxime is an important intermediate for the synthesis of caprolactam and the production of nylon 6.

[0003] In addition to the catalytically active four-coordinate framework titanium, the TS-1 molecular sieve synthesized directly by hydrothermal synthesis usually contains non-framework titanium species such as exoskeleton titanium and anatase titanium dioxide. The presence of non-framework titanium species such as exoskeleton titanium and anatase titanium dioxide leads to a decrease in the content of framework titanium as catalytically active sites and can also cause ineffective side reactions such as hydrogen peroxide decomposition. In the ultraviolet-vis diffuse reflectance (UV-vis) spectrum, the absorption peak of four-coordinate framework titanium is located at 200-210 nm, the absorption peak of exoskeleton titanium species is located at 260-270 nm, and the absorption peak of anatase titanium dioxide is located at 310-340 nm. As described in the literature (AIChE Journal 2021, 67(8), e17261), the proportion of different titanium species in the total titanium species can be calculated by performing peak fitting on the UV-vis spectrum.

[0004] Currently, the main methods for modifying TS-1 molecular sieves to improve their catalytic performance include silanization modification, fluorination modification, acid modification, and alkali modification. Patent CN101602013A discloses a silanization modification method for TS-1. This method involves placing the TS-1 molecular sieve in a nitrogen atmosphere at 50–300°C and then introducing a silanizing agent for modification. The silanizing agent undergoes a condensation reaction with silanols, enhancing the hydrophobicity of TS-1 and thus improving its catalytic performance. In the literature (ACS Catalysis 2011, 1(8), 901-907), ammonium fluoride was used to modify TS-1. Some Si-OH atoms react with fluorine atoms to generate Si-F, thereby reducing the amount of silanols in the catalyst and lowering the hydrophilicity of TS-1. Patent CN1657168A describes acid modification of TS-1 by mixing uncalcined TS-1 powder with an inorganic acid solution and performing modification treatment at room temperature to 200°C. After modification, the number of non-framework titanium species in the TS-1 molecular sieve is reduced, and its activity is significantly improved. Patent CN101850985A discloses an alkali modification method for TS-1. This method involves adding TS-1 to an aqueous solution of a pore-forming agent and an alkali source, and reacting the mixture in a hydrothermal reactor. This modification increases the number of mesopores in the catalyst, reduces mass transfer resistance, exposes active sites, and thus improves catalytic performance. These methods improve catalytic performance by modifying TS-1 molecular sieves through hydrophobic modification, removal of non-framework titanium, or mesoporous modification. Summary of the Invention

[0005] The purpose of this invention is to improve the active sites of the TS-1 molecular sieve in the catalytic ammonium oximation reaction by increasing the proportion of framework titanium in the total titanium species without changing the titanium content in the molecular sieve, thereby enhancing the activity and selectivity of the molecular sieve in the catalytic ammonium oximation reaction.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for improving the active sites of the TS-1 molecular sieve catalytic ammonium oxime reaction includes the following steps:

[0008] (1) Using ammonia water as a pretreatment agent, TS-1 molecular sieve is mixed with the pretreatment agent and treated for a certain period of time;

[0009] (2) After the TS-1 molecular sieve pretreated with ammonia water is dried, it is treated with ozone under ultraviolet light.

[0010] (3) The TS-1 molecular sieve was treated with HCl gas under heating conditions to obtain the TS-1 molecular sieve with improved active sites.

[0011] Furthermore, in step (1), the mass concentration of ammonia water is 5-8%, and the mass ratio of ammonia water to TS-1 molecular sieve is 5-10.

[0012] Furthermore, in step (1), the mixing temperature is 50-70°C and the mixing time is 1-3 hours.

[0013] Furthermore, in step (2), the wavelength of the ultraviolet light is 200-300 nm, and the ultraviolet irradiance is 10,000-100,000 milliwatts per square meter.

[0014] Furthermore, in step (2), the ozone volume concentration is 2-5%.

[0015] Furthermore, in step (2), the processing temperature is room temperature to 80°C, and the processing time is 1 to 2 hours.

[0016] Furthermore, in step (3), the heating temperature is 120-200℃ and the processing time is 2-5 hours.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. After improving the active sites of the directly synthesized TS-1 molecular sieve, the proportion of framework titanium (catalytic active sites) in the obtained TS-1 molecular sieve sample is significantly increased, while the proportion of non-framework titanium species (including six-coordinate non-framework titanium and anatase ineffective titanium species outside the framework) is significantly reduced. The activity and selectivity of the molecular sieve in the catalytic ammonium oxime reaction are significantly improved.

[0019] 2. The implementation process of this invention does not use organic amines or fluorides, resulting in minimal environmental pollution. Attached Figure Description

[0020] Figure 1 The UV-vis spectrum of the TS-1 molecular sieve prepared in Comparative Example 1 is shown.

[0021] Figure 2 The UV-vis spectrum of TS-1 molecular sieve after treatment in Comparative Example 2 is shown.

[0022] Figure 3 The UV-vis spectrum of TS-1 molecular sieve after treatment in Comparative Example 3 is shown.

[0023] Figure 4 The UV-vis spectrum of the improved TS-1 molecular sieve in Example 1.

[0024] Figure 5 The UV-vis spectrum of the improved TS-1 molecular sieve in Example 2;

[0025] Figure 6 The UV-vis spectrum of the improved TS-1 molecular sieve in Example 3;

[0026] in, Figure 1-6 In the diagram, the solid line represents the measured UV-vis spectrum, and the dashed line represents the peak fitting results. Detailed Implementation

[0027] The technical solution and effects of the present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0028] Comparative Example 1

[0029] Weigh the components according to the required molar ratio for synthesizing TS-1 molecular sieve (tetrapropylammonium hydroxide: tetraethyl orthosilicate: tetrabutyl titanate: isopropanol: H₂O = 0.24:1:0.025:0.57:22) and add them sequentially to a beaker. Stir for 2 hours, then heat to 70-75℃ with stirring to remove the alcohol. Transfer the resulting precursor mixture to a crystallization vessel and crystallize at 175℃ for 72 hours. After crystallization, separate and collect the solid, dry it, and calcine it at 500-600℃ to obtain TS-1 molecular sieve. Compositional analysis of the sample showed that the mass fraction of titanium in the sample was 1.92% (based on elemental titanium). The titanium species distribution of the TS-1 sample was characterized by ultraviolet-visible diffuse reflectance (UV-vis) spectroscopy. Peak fitting revealed that the absorption peak of framework titanium species (catalytically active sites) was located around 205 nm, the absorption peak of six-coordinated non-framework titanium was located around 270 nm, and the absorption peak of anatase non-framework titanium was located around 333 nm. Figure 1 As shown, the TS-1 molecular sieve directly synthesized according to this comparative example has a framework titanium species content of 44.6% suitable as active sites for catalytic ammonium oxime reactions.

[0030] The TS-1 molecular sieves used as raw materials to be treated or improved in other comparative examples and embodiments of the present invention are all prepared according to the method described in this comparative example.

[0031] The catalytic performance of the obtained molecular sieve in the ammoniation reaction of cyclohexanone was evaluated. The reaction conditions were as follows: 0.1 g of TS-1 molecular sieve as catalyst, 6.0 g of cyclohexanone, 18 g of tert-butanol, 8.0 g of hydrogen peroxide (27.3% by mass), and 13.9 g of ammonia. The specific process was as follows: the solvent, reactants, and TS-1 molecular sieve as catalyst were added sequentially to a flask, and the reaction was carried out at 75°C for 2 hours under stirring. The results after the reaction were as follows: cyclohexanone conversion rate 52.7%, cyclohexanone oxime selectivity 88.9%, and cyclohexanone oxime yield 46.9%.

[0032] Comparative Example 2

[0033] 10 g of TS-1 molecular sieve (prepared according to the method described in Comparative Example 1) was weighed, and 80 g of 7.0% (mass fraction) ammonia water was weighed. The TS-1 molecular sieve was added to the ammonia water, and the mixture was heated to 60°C and stirred for 2 hours. The solid molecular sieve was separated, collected, and dried. The sample was placed in a tube furnace, heated to 160°C, and further treated with HCl gas for 4 hours to obtain the treated TS-1 molecular sieve. Compositional analysis of the sample showed that the mass fraction of titanium in the sample was 1.93% (based on elemental titanium). The distribution of titanium species in the TS-1 sample was characterized by ultraviolet-visible diffuse reflectance (UV-vis) spectroscopy. Peak fitting showed that the absorption peak of framework titanium species (catalytically active sites) was located near 205 nm, the absorption peak of six-coordinate non-framework titanium was located near 270 nm, and the absorption peak of anatase non-framework titanium was located near 333 nm. Figure 2 As shown, the TS-1 molecular sieve directly synthesized according to this comparative example has a framework titanium species content of 43.1% suitable as active sites for catalytic ammonium oxime reactions.

[0034] The catalytic performance of the product for the ammoniation reaction was evaluated by the ammoniation reaction of cyclohexanone. The reaction conditions were the same as those of Comparative Example 1. The results were: cyclohexanone conversion rate 55.3%, cyclohexanone oxime selectivity 86.3%, and cyclohexanone oxime yield 47.7%.

[0035] Comparative Example 3

[0036] 10 g of TS-1 molecular sieve (prepared according to the method described in Comparative Example 1) was weighed, and 80 g of 7.0% (mass fraction) ammonia water was weighed. The TS-1 molecular sieve was added to the ammonia water, and the mixture was heated to 60°C and stirred for 2 hours. The solid molecular sieve was separated and collected, dried, and then heated to 50°C. Under ultraviolet light irradiation at a wavelength of 254 nm and an irradiance of 55000 mW / m², ozone gas with a volume concentration of 4% was introduced for 1.5 hours to obtain the treated TS-1 molecular sieve. Compositional analysis of the sample showed that the mass fraction of titanium in the sample was 1.90% (based on elemental titanium). The distribution of titanium species in the TS-1 sample was characterized by ultraviolet-visible diffuse reflectance (UV-vis) spectroscopy. Peak fitting showed that the absorption peak of framework titanium species (catalytically active sites) was located near 206 nm, the absorption peak of six-coordinate non-framework titanium was located near 270 nm, and the absorption peak of anatase non-framework titanium was located near 333 nm. Figure 3 As shown, the TS-1 molecular sieve directly synthesized according to this comparative example has a framework titanium species content of 47.4% suitable as active sites for catalytic ammonium oxime reactions.

[0037] The catalytic performance of the product for the ammoniation reaction was evaluated by the ammoniation reaction of cyclohexanone. The reaction conditions were the same as those of Comparative Example 1. The results were: cyclohexanone conversion rate 57.6%, cyclohexanone oxime selectivity 89.1%, and cyclohexanone oxime yield 51.3%.

[0038] Example 1

[0039] 10 g of TS-1 molecular sieve (prepared according to the method described in Comparative Example 1) was weighed, and 80 g of 7.0% (mass fraction) ammonia water was weighed. The TS-1 molecular sieve was added to the ammonia water, and the mixture was heated to 60°C and stirred for 2 hours. The solid molecular sieve was separated and collected, dried, and then heated to 50°C. It was then irradiated with ultraviolet light at a wavelength of 254 nm and an irradiance of 55,000 mW / m², and treated with 4% ozone gas by volume for 1.5 hours. The sample was then placed in a tube furnace, heated to 160°C, and further treated with HCl gas for 4 hours to obtain the TS-1 molecular sieve with improved active sites. Compositional analysis of the sample showed that the mass fraction of titanium in the sample was 1.91% (based on elemental titanium). The titanium species distribution of the TS-1 sample was characterized by UV-Vis diffuse reflectance spectroscopy. Peak fitting revealed that the absorption peak of framework titanium species (catalytically active sites) was located around 202 nm, the absorption peak of six-coordinate non-framework titanium was located around 270 nm, and the absorption peak of anatase non-framework titanium was located around 332 nm. Figure 4 As shown. The TS-1 molecular sieve directly synthesized according to this embodiment has a framework titanium species content of 80.0% suitable as active sites for catalytic ammonium oxime reactions.

[0040] The catalytic performance of the product for the ammoniation reaction was evaluated by the ammoniation reaction of cyclohexanone. The reaction conditions were the same as those of Comparative Example 1. The results were: cyclohexanone conversion rate 93.5%, cyclohexanone oxime selectivity 99.3%, and cyclohexanone oxime yield 92.8%.

[0041] Example 2

[0042] 10 g of TS-1 molecular sieve (prepared according to the method described in Comparative Example 1) was weighed, and 100 g of 5.0% (mass fraction) ammonia water was weighed. The TS-1 molecular sieve was added to the ammonia water, and the mixture was heated to 70°C and stirred for 1 hour. The solid molecular sieve was separated and collected, dried, and then heated to 80°C. It was then irradiated with ultraviolet light at a wavelength of 200 nm and an irradiance of 10,000 mW / m², and treated with 5% ozone gas by volume for 1 hour. The sample was then placed in a tube furnace, heated to 200°C, and further treated with HCl gas for 2 hours to obtain the TS-1 molecular sieve with improved active sites. Compositional analysis of the sample showed that the mass fraction of titanium in the sample was 1.94% (based on elemental titanium). The titanium species distribution of the TS-1 sample was characterized by UV-Vis diffuse reflectance spectroscopy. Peak fitting revealed that the absorption peak of framework titanium species (catalytically active sites) was located around 201 nm, the absorption peak of six-coordinate non-framework titanium was located around 270 nm, and the absorption peak of anatase non-framework titanium was located around 332 nm. Figure 5 As shown, the TS-1 molecular sieve directly synthesized according to this embodiment has a framework titanium species content of 73.1% suitable for catalyzing ammonium oxime reactions.

[0043] The catalytic performance of the product for the ammoniation reaction was evaluated by the ammoniation reaction of cyclohexanone. The reaction conditions were the same as those of Comparative Example 1. The results were: cyclohexanone conversion rate 88.2%, cyclohexanone oxime selectivity 97.8%, and cyclohexanone oxime yield 86.3%.

[0044] Example 3

[0045] 10 g of TS-1 molecular sieve (prepared according to the method described in Comparative Example 1) was weighed, and 50 g of 8.0% (mass fraction) ammonia water was weighed. The TS-1 molecular sieve was added to the ammonia water, and the mixture was heated to 50°C and stirred for 3 hours. The solid molecular sieve was separated and collected, dried, and kept at room temperature. It was then irradiated with ultraviolet light at a wavelength of 300 nm and an irradiance of 100,000 mW / m², and treated with 2% ozone gas by volume for 2 hours. The sample was then placed in a tube furnace, heated to 120°C, and further treated with HCl gas for 5 hours to obtain the TS-1 molecular sieve with improved active sites. Compositional analysis of the sample showed that the mass fraction of titanium in the sample was 1.93% (based on elemental titanium). The titanium species distribution of the TS-1 sample was characterized by UV-Vis diffuse reflectance spectroscopy. Peak fitting revealed that the absorption peak of framework titanium species (catalytically active sites) was located around 201 nm, the absorption peak of six-coordinate non-framework titanium was located around 270 nm, and the absorption peak of anatase non-framework titanium was located around 329 nm. Figure 6 As shown, the TS-1 molecular sieve directly synthesized according to this embodiment has a framework titanium species content of 70.7% suitable as active sites for catalytic ammonium oxime reactions.

[0046] The catalytic performance of the product for the ammoniation reaction was evaluated by the ammoniation reaction of cyclohexanone. The reaction conditions were the same as those of Comparative Example 1. The results were: cyclohexanone conversion rate 86.7%, cyclohexanone oxime selectivity 98.7%, and cyclohexanone oxime yield 85.6%.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for improving the active sites of the TS-1 molecular sieve catalytic ammonium oxime reaction, characterized in that, This method, without changing the titanium content in the molecular sieve, increases the proportion of framework titanium in the total titanium species of the TS-1 molecular sieve, thereby improving the active sites of the TS-1 molecular sieve in the catalytic ammonium oximation reaction and enhancing the activity and selectivity of the molecular sieve in the catalytic ammonium oximation reaction. The specific steps include: (1) Using ammonia water as a pretreatment agent, TS-1 molecular sieve is mixed with the pretreatment agent and treated for a certain period of time; (2) After the TS-1 molecular sieve pretreated with ammonia water is dried, it is treated with ozone under ultraviolet light; (3) The TS-1 molecular sieve was treated with HCl gas under heating conditions to obtain the TS-1 molecular sieve with improved active sites. In step (2), the wavelength of the ultraviolet light is 200-300 nm, and the ultraviolet irradiance is 10,000-100,000 milliwatts per square meter; In step (2), the ozone volume concentration is 2-5%; In step (2), the processing temperature is room temperature to 80°C, and the processing time is 1 to 2 hours.

2. The method for improving the active sites of the TS-1 molecular sieve catalytic ammonium oxime reaction according to claim 1, characterized in that, In step (1), the mass concentration of ammonia water is 5-8%, and the mass ratio of ammonia water to TS-1 molecular sieve is 5-10.

3. The method for improving the active sites of the TS-1 molecular sieve catalytic ammonium oxime reaction according to claim 1, characterized in that, In step (1), the mixing temperature is 50-70°C and the mixing time is 1-3 hours.

4. The method for improving the active sites of the TS-1 molecular sieve catalytic ammonium oxime reaction according to claim 1, characterized in that, In step (3), the heating temperature is 120-200℃ and the processing time is 2-5 hours.

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