Titanium-silicon catalyst for catalyzing olefin epoxidation reaction and preparation method of titanium-silicon catalyst

Abstract

The preparation method comprises the following steps: mixing a Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide, tetrabutyl titanate and modified porous carbon, then carrying out a crystallization reaction, collecting insoluble substances, and carrying out calcination treatment, the titanium-silicon catalyst for catalyzing the olefin epoxidation reaction is obtained. According to the invention, a structure-directing agent tetrapropylammonium hydroxide is introduced on the basis of the Ti-Beta molecular sieve, modified porous carbon is also introduced when tetrapropylammonium hydroxide and tetrabutyl titanate are used for treatment, carbon components of the modified porous carbon are removed during high-temperature calcination, and metal components are combined with the molecular sieve in situ, so that pore diameters in a composite structure are richer, and a Ti active center is easier to expose. The titanium-silicon catalyst constructed by the invention has good catalytic activity and selectivity on olefin epoxidation reaction, and also has good reproducibility.

Description

Technical Field

[0001] The present invention relates to the technical field of organic compound catalysts, and in particular to a titanium silicon catalyst for catalyzing olefin epoxidation reaction and a preparation method thereof. Background Art

[0002] Olefin epoxidation is a key method for the industrial synthesis of bulk and fine chemicals. Its resulting epoxides have important applications in the chemical industry, perfumes and fragrances, pharmaceuticals, resins, pesticides, and other fields. For example, 1,2-butylene oxide is commonly used in the synthesis of antioxidants, corrosion inhibitors, and surfactants; 1,2-epoxyhexane can react with a variety of organic compounds to produce chiral compounds; and epichlorohydrin is commonly used in the preparation of rubber.

[0003] For epoxidation reactions, the quality of the catalyst is one of the key factors affecting the reaction efficiency. Titanium silicate molecular sieve, as a type of heterogeneous catalyst, has good catalytic activity for the selective oxidation of olefins and is often used as a catalyst for the selective oxidation of olefins to produce epoxides. Improving the selectivity, stability, and uniformity of silicon titanium catalysts to achieve a longer operating life has become a focus of current research. CN118594605A discloses a titanium silicate molecular sieve catalyst prepared from SiO2, H2O, tetrapropylammonium hydroxide, TiO2, and isopropanol in a molar ratio of 1:15-22:0.25-0.35:0.025-0.035:4.4-4.5, and also adding 5.5%-7.5% modified graphene. This catalyst can reduce the loss of active neutral titanium during the catalytic reaction and improve the catalyst's stability. However, the preparation of modified graphene is cumbersome and expensive. CN11786172A discloses a titanium silicate molecular sieve catalyst, its preparation method, and application. The preparation method comprises hydrolyzing a mixture of a silicon source solution and a titanium source solution to obtain a hydrolyzed solution, followed by a hydrothermal reaction and calcination. This catalyst is used in the catalytic oxidation of 1-hexene, promoting contact between reactants and active sites and accelerating the release of products, with high selectivity and conversion. However, the preparation method requires high-speed stirring at 5500-6000 rpm, which is difficult to control and difficult to control.

[0004] It is necessary to develop simple and feasible titanium-silicon catalysts to prepare efficient and stable ones. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a method for preparing a titanium silicon catalyst for catalyzing olefin epoxidation reaction, comprising: Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide, n-butyl titanate and modified porous carbon are mixed and then crystallized, and insoluble matter is collected and calcined to obtain a titanium silicon catalyst for catalyzing olefin epoxidation reaction.

[0006] Beta zeolites possess a unique three-dimensional cross-pore structure, with the main pores composed of twelve-membered rings and a pore diameter of approximately 0.65 nanometers, resulting in improved hydrothermal and chemical stability. Conventional Ti-Beta zeolites typically contain aluminum during synthesis. The resulting aluminum framework produces B acid sites, which generally reduce the catalytic performance of olefin epoxidation reactions. Some studies have removed the aluminum through acid treatment and used the dealuminized Beta zeolite as a silicon source, introducing a titanium source and a structure-directing agent to prepare Ti-Beta zeolites with multipolar pore sizes. While such Ti-Beta zeolites can mitigate the effects of diffusion limitations to a certain extent, the Ti active centers of the resulting titanium silicalite are still primarily distributed within the zeolite pores. Concentrating the distribution of Ti active centers on the catalyst's outer surface is a more effective approach to addressing diffusion limitations.

[0007] To this end, the present invention introduces a structure-directing agent, tetrapropylammonium hydroxide, and modified porous carbon during treatment with n-butyl titanate on the basis of Ti-Beta molecular sieve. The carbon component of the modified porous carbon is removed during high-temperature calcination, and the metal component is in situ combined with the molecular sieve, making the pore size in the composite structure richer and making the Ti active center more easily exposed.

[0008] Furthermore, the mass ratio of the Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide, n-butyl titanate and modified porous carbon is 0.8-1.2:12-20:0.1-0.5:0.06-0.1:0.01-0.05; Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide, and n-butyl titanate are mixed for 3 to 6 hours, and then the modified porous carbon is added.

[0009] The use of organic acid metal salts to prepare porous carbon has been widely reported. During the process under high-temperature heat preservation atmosphere, the organic components in the organic acid metal salts form a carbon matrix, and the inorganic components gradually decompose and are reduced by the amorphous carbon at high temperature, thereby forming in-situ etching of the carbon matrix. After the calcination is completed, the inorganic components are removed to obtain a porous carbon material with a high specific surface area, structured pores, and a thin layer structure. The porous carbon material is adsorbed with nickel salt to obtain modified porous carbon, and the structure of the Ti-Beta molecular sieve is optimized and regulated.

[0010] Furthermore, the preparation method of the modified porous carbon includes: calcining the organic acid metal salt under a protective gas atmosphere to obtain porous carbon; The porous carbon, the soluble nickel salt and the solvent are stirred and mixed in a mass ratio of 1:0.05-0.1:20-50 to obtain the modified porous carbon.

[0011] It should be noted that, in the present application, the type of organic acid metal salt does not need to be strictly limited, and illustratively, it can be at least one of a metal citrate, a metal gluconate, a metal gallate, etc.; preferably, sodium citrate or potassium citrate. The type of soluble nickel salt does not need to be strictly limited, and illustratively, it can be at least one of nickel chloride hexahydrate, nickel nitrate hexahydrate, nickel acetate tetrahydrate, etc. The type of solvent for dispersing the porous carbon and dissolving the soluble nickel salt does not need to be strictly limited, and illustratively, it can be at least one of water, ethanol, acetone, isopropyl alcohol, ethylene glycol, dimethyl sulfoxide, etc.

[0012] 1,4,7-Triazacyclononane-1,4,7-triacetic acid (NOTA). The 1,4,7-triazacyclononane in its structure is the core structure of the compound. It is a nine-membered heterocyclic ring containing three nitrogen atoms, which has a certain rigidity and unique spatial conformation. Acetate groups are attached to the nitrogen atoms at positions 1, 4, and 7, respectively. The presence of these acetate groups increases the compound's hydrophilicity and acidity, and provides active sites for reactions such as coordination with metal ions. To further optimize the subsequent calcination process, NOTA is also introduced during the nickel ion adsorption process.

[0013] Furthermore, 1,4,7-triazacyclononane-1,4,7-triacetic acid in an amount of 0.01 to 0.03 of the mass of the porous carbon is added during the stirring and mixing.

[0014] Furthermore, the preparation method of the Ti-Beta molecular sieve comprises: Reflux the Beta molecular sieve in an acid solution to obtain an acid-treated Beta molecular sieve; Acid-treated Beta molecular sieve, water, tetrapropylammonium hydroxide, n-butyl titanate and a mineralizer are mixed to form a reaction system, wherein the molar ratio of silicon dioxide, water, tetrapropylammonium hydroxide, titanium dioxide and the mineralizer in the reaction system is 0.8-1.2:15-25:0.25-0.35:0.025-0.035:0.2-0.6, followed by a crystallization reaction, and the insoluble matter is collected and calcined to obtain a Ti-Beta molecular sieve.

[0015] In the above process, the acid reflux treatment of Beta molecular sieve is a conventional operation in the art. The acid is generally selected as concentrated nitric acid with a concentration of 13 mol / L. The ratio of Beta molecular sieve to acid is 1 g: 5-15 mL. The reflux treatment is continued at 120-150° C. for 18-36 hours. Calcination treatment is also performed after the reflux treatment.

[0016] Furthermore, the silicon-aluminum ratio of the Beta molecular sieve is 10-25.

[0017] Furthermore, the mineralizer includes at least one of sodium acetate, sodium benzoate, and sodium citrate.

[0018] Furthermore, the crystallization reaction is continued at a temperature of 140-170° C. for 18-72 hours.

[0019] Furthermore, the calcination is continued at a temperature of 450-750° C. for 1-8 hours.

[0020] The present invention also provides a titanium silicon catalyst for catalyzing olefin epoxidation reaction, which is obtained by adopting the above preparation method.

[0021] Compared with the prior art, the present invention has the following beneficial effects: The present invention introduces a structure-directing agent, tetrapropylammonium hydroxide, into a Ti-Beta molecular sieve, along with modified porous carbon during the treatment with n-butyl titanate. During high-temperature calcination, the carbon component of the modified porous carbon is removed, and the metal components are in situ bonded to the molecular sieve, resulting in a richer pore size in the composite structure and easier exposure of the Ti active centers. The titanium-silicon catalyst constructed in this invention exhibits excellent catalytic activity and selectivity for olefin epoxidation reactions, as well as good regeneration. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 shows a transmission electron micrograph of porous carbon; Figure 2 shows a scanning electron microscope image of the titanium silicon catalyst prepared in Example 2; Figure 3 The scanning electron microscope image of the titanium silicon catalyst prepared in Comparative Example 3 is shown. DETAILED DESCRIPTION

[0023] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0024] Introduction of some raw materials used in the examples and comparative examples of the present invention: Beta molecular sieve, with a silicon-aluminum ratio of 15, was customized by Shanghai Xinnian Petrochemical Additive Co., Ltd.

[0025] NOTA, CAS number is 56491-86-2.

[0026] The preparation method of porous carbon is: Potassium citrate was placed in a nitrogen atmosphere muffle furnace and heated to 650°C at a heating rate of 3°C / min and kept warm for 2 hours; then naturally cooled, the insoluble matter was immersed in 1.5 mol / L hydrochloric acid, washed with water until the pH of the supernatant was 6.5-7.5, and transferred to a 120°C oven for drying for 12 hours to obtain porous carbon.

[0027] The preparation method of Ti-Beta molecular sieve is: 1 kg of Beta molecular sieve was placed in 10 L of 13 mol / L concentrated nitric acid, refluxed and acid-washed at 140 ° C for 24 h, the insoluble matter was filtered out, washed with water, dried in an 80 ° C oven for 12 h, and then calcined in a 500 ° C muffle furnace for 5 h to obtain acid-treated Beta molecular sieve; Acid-treated Beta molecular sieve, water, tetrapropylammonium hydroxide, n-butyl titanate and sodium acetate are mixed to form a reaction system, in which the molar ratio of silicon dioxide, water, tetrapropylammonium hydroxide, titanium dioxide and sodium acetate is 1:20:0.3:0.03:0.45. The temperature is then raised to 160°C for crystallization reaction for 48 hours, the insoluble matter is collected and washed three times with water, and placed in a 120°C oven to dry for 12 hours; then the mixture is transferred to a muffle furnace at 500°C and air atmosphere and calcined for 6 hours to obtain Ti-Beta molecular sieve.

[0028] All other raw materials not mentioned are commonly available. The above description is provided solely to illustrate the present invention and should not be construed as a strict limitation of the present invention. Those skilled in the art can purchase or prepare similar or similar raw materials commercially. These details will not be further detailed in the examples.

[0029] The following will be combined with specific embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] Example 1 A method for preparing a titanium silicon catalyst for catalyzing olefin epoxidation reaction, S1. Weigh 1 kg Ti-Beta molecular sieve, 18 kg water, 0.3 kg tetrapropylammonium hydroxide, 0.08 kg n-butyl titanate, and 0.03 kg modified porous carbon respectively; S2. Stir Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide and n-butyl titanate at 200 rpm for 5 hours, then add modified porous carbon and continue stirring for 2 hours; then stop stirring and raise the temperature to 160°C, crystallize under static conditions for 36 hours, collect insoluble matter, wash three times with water, and place in a 120°C oven to dry for 12 hours; then transfer to a muffle furnace at 500°C and air atmosphere and calcine for 6 hours to obtain a titanium silicon catalyst for catalyzing olefin epoxidation reaction.

[0031] The modified porous carbon was prepared by stirring 1 kg of porous carbon, 0.08 kg of nickel acetate tetrahydrate, and 45 kg of water at 200 rpm for 3 h, collecting the insoluble matter by filtration and washing it three times with water, and drying it in an oven at 120 ° C for 12 h to obtain the modified porous carbon.

[0032] Example 2 A method for preparing a titanium silicon catalyst for catalyzing olefin epoxidation reaction, S1. Weigh 1 kg Ti-Beta molecular sieve, 18 kg water, 0.3 kg tetrapropylammonium hydroxide, 0.08 kg n-butyl titanate, and 0.03 kg modified porous carbon respectively; S2. Stir Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide and n-butyl titanate at 200 rpm for 5 hours, then add modified porous carbon and continue stirring for 2 hours; then stop stirring and raise the temperature to 160°C, crystallize under static conditions for 36 hours, collect insoluble matter, wash three times with water, and place in a 120°C oven to dry for 12 hours; then transfer to a muffle furnace at 500°C and air atmosphere and calcine for 6 hours to obtain a titanium silicon catalyst for catalyzing olefin epoxidation reaction.

[0033] The modified porous carbon was prepared by stirring 1 kg of porous carbon, 0.08 kg of nickel acetate tetrahydrate, 0.02 kg of NOTA, and 45 kg of water at 200 rpm for 3 h, collecting the insoluble matter by filtration and washing it three times with water, and drying it in an oven at 120 ° C for 12 h to obtain the modified porous carbon.

[0034] Comparative Example 1 Compared with Example 1, the difference is that porous carbon is used instead of modified porous carbon.

[0035] Comparative Example 2 Compared with Example 1, the difference is that the preparation method of the modified porous carbon is as follows: 1 kg of porous carbon, 0.02 kg of NOTA, and 45 kg of water are stirred at 200 rpm for 3 hours, the insoluble matter is collected by filtration and washed three times with water, and then placed in an oven at 120°C for 12 hours to obtain the modified porous carbon.

[0036] Comparative Example 3 A method for preparing a titanium silicon catalyst for catalyzing olefin epoxidation reaction, S1. Weigh 1 kg Ti-Beta molecular sieve, 18 kg water, 0.3 kg tetrapropylammonium hydroxide, and 0.08 kg n-butyl titanate respectively; S2. Stir Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide and n-butyl titanate at 200 rpm for 5 hours; then stop stirring and raise the temperature to 160°C, crystallize under static conditions for 36 hours, collect insoluble matter, wash three times with water, and place in a 120°C oven to dry for 12 hours; then transfer to a muffle furnace at 500°C and air atmosphere and calcine for 6 hours to obtain a titanium silicon catalyst for catalyzing olefin epoxidation reaction.

[0037] Test Case The structure of the prepared porous carbon was observed using transmission electron microscopy. Figure 1 As shown, it can be seen that the prepared porous carbon has a rich pore structure and a thin layer structure similar to graphene.

[0038] The microstructure of the titanium silicon catalysts prepared in Example 2 and Comparative Example 3 was observed using a scanning electron microscope. Figure 2 and Figure 3 It can be seen that the titanium silicon catalyst prepared in Example 2 is composed of nanocrystals with a particle size of about 50 nm, while the titanium silicon catalyst prepared in Comparative Example 3 has a smaller grain size. This is because the Ti-Beta molecular sieve serves as the matrix of the catalyst, and the structure-directing agent tetrapropylammonium hydroxide also serves as an alkaline medium. During the stirring and static crystallization process, the dissolution and recrystallization of the Ti-Beta molecular sieve skeleton occur simultaneously. The introduction of modified porous carbon affects the balance in the dissolution and recrystallization process, and the carbon component is removed in the subsequent calcination. The metal component is combined with the molecular sieve in situ. These combined effects make the pore size in the composite structure richer, thereby changing the structure of the titanium silicon catalyst. In addition, it is also shown that the introduction of porous carbon and the removal of porous carbon at high temperature will not affect the structure of the titanium silicon catalyst.

[0039] The specific surface areas of the catalysts prepared in the examples and comparative examples were analyzed using a specific surface and pore size analyzer, and the specific surface areas were calculated using the Brunauer-Emmett-Teller (BET) method. The results are shown in Table 1.

[0040] Table 1 Specific surface area test results

[0041] As can be seen from the test results in Table 1, the embodiment has a higher specific surface area than the comparative example. Among them, the specific surface area of ​​Comparative Example 1 is larger than that of Comparative Example 3. Porous carbon is added during stirring and static crystallization, and the porous carbon is removed during the calcination process, so that the overall pore size is increased. Example 1 and Comparative Example 2 modify porous carbon with nickel salt and NOTA, respectively, and the specific surface area is further increased. This is because nickel interacts with the molecular sieve matrix and NOTA decomposes and expands the pores. The catalyst of Example 2 has the highest specific surface area. Thanks to the chelating effect of NOTA on nickel, the decomposition of the modified porous carbon introduces a richer pore structure.

[0042] The liquid-phase epoxidation of cyclohexene was carried out in a sealed glass reaction tube. Specifically, 50 mg of catalyst, 10 mmol of 1-butene, and 10 mmol of H₂O₂ were added to the reaction tube and stirred at 60°C for 2 hours. After the reaction was completed, the reaction tube was removed and cooled to 25°C in an ice-water bath, and the catalyst was separated by centrifugation. The cyclohexene oxidation products were analyzed by gas chromatography; the residual H₂O₂ content was determined using titration with Ce(SO₄)₂ aqueous solution. The catalytic performance of the catalysts of the Examples and Comparative Examples is shown in Table 2.

[0043] Table 2 Catalytic performance

[0044] From the test results in Table 2, it can be seen that the titanium silicon catalyst of the embodiment of the present invention has a high raw material conversion rate and product selectivity. This is due to the removal of the carbon component of the modified porous carbon during high-temperature calcination, and the in-situ combination of the metal component and the molecular sieve, which makes the pore size in the composite structure richer and makes the Ti active center more easily exposed.

[0045] The titanium-silicon catalyst of the present invention was also subjected to 10 repeated 1-butene catalytic tests. After each test, the catalyst was collected and washed with 10 times its mass of deionized water for 10 minutes of oscillation to remove chemical substances adsorbed on the catalyst surface. The clean catalyst was then filtered and separated to obtain a clean catalyst. The clean catalyst was then dried in a 50°C drying oven to constant weight before the next test. The results are shown in Table 3.

[0046] Table 3 Performance of the 10th catalysis

[0047] It can be seen from the test results in Table 3 that the catalysts of the embodiments of the present invention have good catalytic stability.

[0048] After 10 times of catalytic experiments, the catalyst is also placed in 10 times of mass of deionized water to shake and clean for 10 minutes to remove the chemical substances adsorbed on the surface of the catalyst, and then the cleaned catalyst is separated by filtration. The cleaned catalyst is dried in a 50°C drying box until the weight is constant, and then is placed in a 500°C muffle furnace for calcination for 6 hours for regeneration. The results show that the catalytic performance of the regenerated catalyst of the example is more than 98% of the original catalyst performance. These results show that the titanium-silicon catalyst constructed by the present application has good catalytic activity and selectivity for olefin epoxidation reaction, and also has good regeneration.

[0049] Finally, it should be noted that: the above only for the preferred embodiments of the present application, and not for limiting the present application, although the foregoing embodiments of the present application are described in detail, for those skilled in the art, it still can be modified, or part of the technical features of the equivalent replacement, within the spirit and principles of the present application, any modification, equivalent replacement, improvement, etc., should be included in the scope of protection of the present application.

Claims

1. A method for preparing a titanium silicon catalyst for catalyzing olefin epoxidation, characterized in that: include, Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide, n-butyl titanate and modified porous carbon are mixed and then crystallized, and insoluble matter is collected and calcined to obtain a titanium silicon catalyst for catalyzing olefin epoxidation reaction.

2. The method for preparing a titanium-silicon catalyst for catalyzing olefin epoxidation according to claim 1, wherein: The mass ratio of the Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide, n-butyl titanate and modified porous carbon is 0.8-1.2:12-20:0.1-0.5:0.06-0.1:0.01-0.05; Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide, and n-butyl titanate are mixed for 3 to 6 hours, and then the modified porous carbon is added.

3. The method for preparing a titanium-silicon catalyst for catalyzing olefin epoxidation according to claim 1, wherein: The preparation method of the modified porous carbon comprises: calcining the organic acid metal salt under a protective gas atmosphere to obtain porous carbon; The porous carbon, the soluble nickel salt and the solvent are stirred and mixed in a mass ratio of 1:0.05-0.1:20-50 to obtain modified porous carbon.

4. The method for preparing a titanium-silicon catalyst for catalyzing olefin epoxidation according to claim 1, wherein: During the stirring and mixing, 1,4,7-triazacyclononane-1,4,7-triacetic acid in an amount of 0.01 to 0.03 of the mass of the porous carbon is added.

5. The method for preparing a titanium-silicon catalyst for catalyzing olefin epoxidation according to claim 1, characterized in that: The preparation method of the Ti-Beta molecular sieve comprises: Reflux-treating the Beta molecular sieve in an acid solution to obtain an acid-treated Beta molecular sieve; Acid-treated Beta molecular sieve, water, tetrapropylammonium hydroxide, n-butyl titanate and a mineralizer are mixed to form a reaction system, wherein the molar ratio of silicon dioxide, water, tetrapropylammonium hydroxide, titanium dioxide and the mineralizer in the reaction system is 0.8-1.2:15-25:0.25-0.35:0.025-0.035:0.2-0.6, followed by a crystallization reaction, and the insoluble matter is collected and calcined to obtain a Ti-Beta molecular sieve.

6. The method for preparing a titanium-silicon catalyst for catalyzing olefin epoxidation according to claim 5, characterized in that: The silicon-aluminum ratio of the Beta molecular sieve is 10-25.

7. The method for preparing a titanium-silicon catalyst for catalyzing olefin epoxidation according to claim 5, characterized in that: The mineralizer includes at least one of sodium acetate, sodium benzoate, and sodium citrate.

8. The method for preparing a titanium silicon catalyst for catalyzing olefin epoxidation according to claim 1 or 5, characterized in that: The crystallization reaction is continued at a temperature of 140-170° C. for 18-72 hours.

9. The method for preparing a titanium silicon catalyst for catalyzing olefin epoxidation according to any one of claims 1, 3 or 5, characterized in that: The calcination is continued at a temperature of 450-750° C. for 1-8 hours.

10. A titanium silicon catalyst for catalyzing olefin epoxidation, characterized in that: The method is described in any one of claims 1 to 9.

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