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

Abstract

The application discloses a titanium-silicon catalyst for catalyzing an olefin epoxidation reaction and a preparation method thereof, and the preparation method comprises the following steps: mixing Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide, n-butyl titanate and modified porous carbon, and then performing a crystallization reaction; collecting insoluble substances and performing calcination treatment, so as to obtain the titanium-silicon catalyst for catalyzing the olefin epoxidation reaction. In the application, the structure directing agent tetrapropylammonium hydroxide and the n-butyl titanate are introduced on the basis of the Ti-Beta molecular sieve, and the modified porous carbon is further introduced when the n-butyl titanate is treated. The carbon component is removed in high-temperature calcination, the metal component is combined with the molecular sieve in situ, the pore size of the composite structure is more abundant, and the Ti active center is more easily exposed. The titanium-silicon catalyst constructed in the application has good catalytic activity and selectivity for the olefin epoxidation reaction, and has good regeneration.

Description

TECHNICAL FIELD

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

[0002] Olefin epoxidation reaction is one of the important methods for synthesizing bulk and fine chemicals in industry, and the product epoxide has important applications in the fields of chemical industry, perfume and flavor, medicine, resin, pesticide, etc. For example, 1,2-epoxybutane is often used to synthesize antioxidants, corrosion inhibitors, surfactants, etc.; 1,2-epoxyhexane can react with various organic substances to generate compounds with chiral structure; epichlorohydrin is often used to prepare rubber.

[0003] For epoxidation reaction, the quality of the catalyst is one of the key factors affecting the reaction effect. As one of the heterogeneous catalysts, titanium-silicon molecular sieve has good catalytic activity for selective oxidation of olefins, and is often used as a catalyst for preparing epoxide compounds by selective oxidation of olefins. Improving the selectivity, stability and uniformity of the titanium-silicon catalyst to make it have a longer running life has become the focus of current research. CN118594605A discloses a titanium-silicon molecular sieve catalyst prepared from SiO2, H2O, tetrapropylammonium hydroxide, TiO2, isopropyl alcohol according to a molar ratio of 1:15~22:0.25~0.35:0.025~0.035:4.4~4.5, and 5.5%~7.5% modified graphene is also added. This catalyst can reduce the loss of active neutral titanium during catalytic reaction and improve the stability of the catalyst. However, the preparation of modified graphene is complicated and expensive. CN11786172A discloses a titanium-silicon molecular sieve catalyst, a preparation method and application thereof. The preparation method includes mixing a silicon source solution and a titanium source solution to obtain a hydrolysis solution, and then performing hydrothermal reaction and calcination. This catalyst can promote the contact between the reactants and the active sites and speed up the removal of the products, and has high selectivity and conversion rate. However, the preparation method requires high-speed stirring at 5500~6000 rpm, which is difficult to control.

[0004] It is necessary to develop a simple and feasible method for preparing a high-efficiency and stable titanium-silicon catalyst. SUMMARY

[0005] In order to solve the problems existing in the prior art, the present application provides a preparation method of a titanium-silicon catalyst for catalyzing olefin epoxidation reaction, which comprises,

[0006] The Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide, n-butyl titanate and modified porous carbon are mixed and subjected to crystallization reaction, the insoluble substance is collected and calcined to obtain the titanium-silicon catalyst for catalyzing olefin epoxidation reaction.

[0007] Beta molecular sieve has a unique three-dimensional cross-pore structure, the main pore is composed of a twelve-membered ring, the pore size is about 0.65 nanometers, and it has better hydrothermal stability and chemical stability. The synthesis of traditional Ti-Beta molecular sieve usually contains aluminum, and the B acid site generated by the framework aluminum generally reduces the catalytic performance of the olefin epoxidation reaction. Some studies remove aluminum by acid treatment, and use the de-aluminized Beta molecular sieve as a silicon source to introduce a titanium source and a structure directing agent to prepare Ti-Beta molecular sieve with multiple polar pore diameters. Such Ti-Beta molecular sieve can improve the influence of diffusion limitation to a certain extent, but the Ti active center of the obtained titanium silicalite is still mainly distributed in the internal pore of the molecular sieve. Concentrating the distribution of Ti active centers on the outer surface of the catalyst is a more effective method to solve the diffusion limitation.

[0008] Therefore, the application introduces a modified porous carbon when treating the Ti-Beta molecular sieve with the structure directing agent tetrapropylammonium hydroxide and n-butyl titanate, the carbon component is removed in high-temperature calcination, and the metal component is combined with the molecular sieve in situ, so that the pore diameter of the composite structure is more abundant, and the Ti active center is more easily exposed.

[0009] Further, 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;

[0010] The Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide and n-butyl titanate are mixed for 3-6 hours, and then the modified porous carbon is added.

[0011] It has been widely reported that porous carbon is prepared using an organic acid metal salt. In the process of high-temperature holding in an atmosphere, the organic component in the organic acid metal salt forms a carbon matrix, the inorganic component gradually decomposes, and is reduced by amorphous carbon at high temperature, so as to form in-situ etching to the carbon matrix. After the calcination is completed, the inorganic component is removed, and a porous carbon material with a high specific surface area, a structured pore and a thin layer structure can be obtained. The porous carbon material is adsorbed with a nickel salt to obtain modified porous carbon, and the structure of the Ti-Beta molecular sieve is optimized and controlled.

[0012] Further, the preparation method of the modified porous carbon comprises,

[0013] The organic acid metal salt is calcined in a protective atmosphere to obtain the porous carbon;

[0014] 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.

[0015] It should be noted that in the present application, the type of organic acid metal salt is not strictly limited, and can be exemplarily at least one of metal citrate, metal gluconate, metal gallic acid, etc.; preferably sodium citrate or potassium citrate. The type of soluble nickel salt is not strictly limited, and can be exemplarily at least one of nickel chloride hexahydrate, nickel nitrate hexahydrate, nickel acetate tetrahydrate, etc. The type of solvent for dispersing porous carbon and dissolving soluble nickel salt is also not strictly limited, and can be exemplarily at least one of water, ethanol, acetone, isopropanol, ethylene glycol, dimethyl sulfoxide, etc.

[0016] 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA), the 1,4,7-triazacyclononane in the structure of which is the core structure of the compound, is a nine-membered heterocycle containing three nitrogen atoms, has a certain rigidity and unique spatial conformation; the nitrogen atoms at positions 1, 4 and 7 are respectively connected with acetic acid groups, the presence of these acetic acid groups increases the hydrophilicity and acidity of the compound, and provides active sites for coordination with metal ions and the like. In order to better optimize the subsequent calcination process, NOTA is also introduced in the process of adsorbing nickel ions.

[0017] Further, 1,4,7-triazacyclononane-1,4,7-triacetic acid accounts for 0.01-0.03 of the mass of the porous carbon during stirring and mixing.

[0018] Further, the preparation method of the Ti-Beta molecular sieve comprises,

[0019] Beta molecular sieve is treated by refluxing in an acid solution to obtain an acid-treated Beta molecular sieve;

[0020] The acid-treated Beta molecular sieve, water, tetrapropylammonium hydroxide, n-butyl titanate and a mineralizer are mixed to form a reaction system, and the molar ratio of silica, 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, and then a crystallization reaction is performed, the insoluble matter is collected and calcined to obtain the Ti-Beta molecular sieve.

[0021] The above process of refluxing the Beta molecular sieve in an acid solution is a conventional operation in the art, and the acid solution is generally concentrated nitric acid with a concentration of 13 mol / L, and the ratio of the Beta molecular sieve to the acid solution is 1 g:5-15 mL, and the refluxing treatment is carried out at 120-150℃ for 18-36 h, and calcination is further carried out after the refluxing treatment.

[0022] Further, the silicon-aluminum ratio of the Beta molecular sieve is 10-25.

[0023] Further, the mineralizer comprises at least one of sodium acetate, sodium benzoate and sodium citrate.

[0024] Further, the crystallization reaction lasts for 18-72h at a temperature of 140-170℃.

[0025] Further, the calcination lasts for 1-8h at a temperature of 450-750℃.

[0026] The application further provides a titanium-silicon catalyst for catalyzing an olefin epoxidation reaction, which is obtained by the preparation method.

[0027] Compared with the prior art, the application has the following beneficial effects:

[0028] The application introduces modified porous carbon when introducing a structure-directing agent tetrapropylammonium hydroxide and n-butyl titanate in the Ti-Beta molecular sieve, the carbon component is removed in high-temperature calcination, the metal component is combined with the molecular sieve in situ, the pore size of the composite structure is more abundant, and the Ti active center is more easily exposed. The titanium-silicon catalyst constructed by the application has good catalytic activity and selectivity for an olefin epoxidation reaction, and has good regeneration. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 A transmission electron microscope image of the porous carbon is shown;

[0030] Figure 2 A scanning electron microscope image of the titanium-silicon catalyst prepared in Example 2 is shown;

[0031] Figure 3 A scanning electron microscope image of the titanium-silicon catalyst prepared in Comparative Example 3 is shown. DETAILED DESCRIPTION

[0032] The endpoints of the ranges and any values disclosed in the present application are not to be understood as limited to the exact values recited as the exact dimensions are not critical to the present application. The ranges recited are intended to cover values approximating these ranges. For numeric values recited as ranges from a lower limit to an upper limit, any numeric value, or integer, within the range is contemplated as a separate embodiment. Numeric values are approximations only and thus any numeric value or integer within the numeric range is contemplated as a separate embodiment.

[0033] Introduction of some raw materials used in the examples and comparative examples of the application:

[0034] Beta molecular sieve, the silicon-aluminum ratio is 15, and is customized by Shanghai Xinnian Petrochemical Additives Co., Ltd.

[0035] NOTA, CAS No. 56491-86-2.

[0036] The preparation method of the porous carbon is that,

[0037] The potassium citrate was heated to 650℃ at a heating rate of 3℃ / min in a muffle furnace under nitrogen atmosphere and kept for 2h; after natural cooling, the insoluble substance was soaked in 1.5mol / L hydrochloric acid, washed with water until the supernatant pH was 6.5-7.5, and transferred to a 120℃ oven for drying for 12h to obtain the porous carbon.

[0038] The preparation method of the Ti-Beta molecular sieve is,

[0039] 1kg of Beta molecular sieve was placed in 10L of 13mol / L concentrated nitric acid and acid washed at 140℃ for 24h, and the insoluble substance was obtained by filtration and washed with water, and dried in an 80℃ oven for 12h and then calcined in a 500℃ muffle furnace for 5h to obtain the acid-treated Beta molecular sieve;

[0040] The acid-treated Beta molecular sieve, water, tetrapropylammonium hydroxide, n-butyl titanate and sodium acetate were mixed to form a reaction system, and the molar ratio of silica, water, tetrapropylammonium hydroxide, titanium dioxide and sodium acetate in the reaction system was 1:20:0.3:0.03:0.45, and then the temperature was raised to 160℃ for crystallization reaction for 48h, the insoluble substance was washed with water three times, and then placed in a 120℃ oven for drying for 12h; and then transferred to a 500℃ muffle furnace in an air atmosphere for calcination for 6h to obtain the Ti-Beta molecular sieve.

[0041] The other raw materials not mentioned are common raw materials, and the above content is only for the purpose of helping to illustrate the present application, and should not be understood as a strict limitation of the present application. Those skilled in the art can directly purchase or prepare the same / similar raw materials. These contents will not be described in detail in the examples.

[0042] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with specific embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0043] Example 1

[0044] A preparation method of a titanium-silicon catalyst for catalyzing olefin epoxidation reaction,

[0045] S1, respectively, 1kg of Ti-Beta molecular sieve, 18kg of water, 0.3kg of tetrapropylammonium hydroxide, 0.08kg of n-butyl titanate and 0.03kg of modified porous carbon;

[0046] S2, the Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide and n-butyl titanate were stirred at 200 rpm for 5 h, then the modified porous carbon was added and stirred for 2 h; then the stirring was stopped and the temperature was raised to 160°C, and crystallization was carried out under static conditions for 36 h, the insoluble matter was collected and washed with water for three times, and was placed in a 120°C oven for drying for 12 h; then it was transferred to a muffle furnace at 500°C in an air atmosphere for calcination for 6 h, to obtain a titanium-silicon catalyst for catalyzing an olefin epoxidation reaction.

[0047] The preparation method of the modified porous carbon is as follows: 1 kg of porous carbon, 0.08 kg of nickel acetate tetrahydrate, and 45 kg of water are stirred at 200 rpm for 3 h, the insoluble matter is collected by filtration and washed with water for three times, and is placed in a 120°C oven for drying for 12 h, to obtain the modified porous carbon.

[0048] Example 2

[0049] A preparation method of a titanium-silicon catalyst for catalyzing an olefin epoxidation reaction,

[0050] S1, 1 kg of Ti-Beta molecular sieve, 18 kg of water, 0.3 kg of tetrapropylammonium hydroxide, 0.08 kg of n-butyl titanate and 0.03 kg of modified porous carbon were weighed respectively;

[0051] S2, the Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide and n-butyl titanate were stirred at 200 rpm for 5 h, then the modified porous carbon was added and stirred for 2 h; then the stirring was stopped and the temperature was raised to 160°C, and crystallization was carried out under static conditions for 36 h, the insoluble matter was collected and washed with water for three times, and was placed in a 120°C oven for drying for 12 h; then it was transferred to a muffle furnace at 500°C in an air atmosphere for calcination for 6 h, to obtain a titanium-silicon catalyst for catalyzing an olefin epoxidation reaction.

[0052] The preparation method of the modified porous carbon is as follows: 1 kg of porous carbon, 0.08 kg of nickel acetate tetrahydrate, 0.02 kg of NOTA and 45 kg of water are stirred at 200 rpm for 3 h, the insoluble matter is collected by filtration and washed with water for three times, and is placed in a 120°C oven for drying for 12 h, to obtain the modified porous carbon.

[0053] Comparative Example 1

[0054] Compared with Example 1, the difference is that the modified porous carbon is replaced by porous carbon.

[0055] Comparative Example 2

[0056] 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 h, the insoluble matter is collected by filtration and washed with water for three times, and is placed in a 120°C oven for drying for 12 h, to obtain the modified porous carbon.

[0057] Comparative Example 3

[0058] A method for preparing a titanium-silicon catalyst for catalyzing an olefin epoxidation reaction,

[0059] S1, 1 kg of Ti-Beta zeolite, 18 kg of water, 0.3 kg of tetrapropylammonium hydroxide and 0.08 kg of n-butyl titanate were weighed respectively;

[0060] S2, the Ti-Beta zeolite, water, tetrapropylammonium hydroxide and n-butyl titanate were stirred at 200 rpm for 5 h; then the stirring was stopped and the temperature was raised to 160°C, and the crystallization was carried out under static conditions for 36 h, the insoluble matter was collected and washed with water for three times, and was placed in a 120°C oven for drying for 12 h; then it was transferred to a muffle furnace at 500°C in an air atmosphere for calcination for 6 h, to obtain a titanium-silicon catalyst for catalyzing an olefin epoxidation reaction.

[0061] Test Example

[0062] The structure of the prepared porous carbon was observed by transmission electron microscopy, as shown in FIG. 1, it can be seen that the prepared porous carbon has a rich pore structure, and has a thin layer structure similar to graphene. Figure 1

[0063] The micro-morphology of the titanium-silicon catalysts prepared in Example 2 and Comparative Example 3 was observed by scanning electron microscopy. From FIG. 2 and FIG. 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 crystal size. This is because Ti-Beta zeolite as the matrix of the catalyst, the structure directing agent tetrapropylammonium hydroxide also acts as an alkaline medium, during the stirring and static crystallization, the dissolution and recrystallization of the Ti-Beta zeolite framework occur simultaneously, the introduction of modified porous carbon affects the balance during the dissolution and recrystallization process, and in the subsequent calcination, the carbon component is removed, the metal component is combined with the zeolite in situ, and these combined effects make the pore size of the composite structure more abundant, thereby changing the structure of the titanium-silicon catalyst. In addition, it also shows that the introduction of porous carbon and the removal of porous carbon at high temperature do not affect the structure of the titanium-silicon catalyst. Figure 2 Figure 3 The specific surface area of the catalysts prepared in the examples and comparative examples was analyzed by a specific surface and pore size analyzer, and the specific surface area was calculated by the Brunauer-Emmett-Teller (BET) method, and the results are shown in Table 1.

[0064] Table 1 Specific surface area test results

[0065] Table 1 Specific surface area test results

[0066]

[0067] ​​From the test results of Table 1, it can be seen that the specific surface area of the examples is higher than that of the comparative examples. Among them, the specific surface area of Comparative Example 1 is larger than that of Comparative Example 3, and the porous carbon is added during stirring and static crystallization, and the porous carbon is removed during calcination, so that the overall porosity is increased. The specific surface area of Example 1 and Comparative Example 2 is further increased by modifying the porous carbon with nickel salt and NOTA, respectively, because of the interaction of nickel with the molecular sieve matrix and the pore expansion caused by the decomposition of NOTA. The catalyst of Example 2 has the highest specific surface area, which is due to the chelation of NOTA to nickel, which makes the decomposition of the modified porous carbon introduce more abundant pore structure.

[0068] The liquid phase epoxidation reaction 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 2h. After the reaction was completed, the reaction tube was taken out and cooled to 25°C in an ice water bath, and the catalyst was separated by centrifugation. The oxidation product of cyclohexene was analyzed by gas chromatography; the residual amount of H2O2 was determined by titration with Ce(SO4)2 aqueous solution. The catalytic performance of the catalysts of the examples and comparative examples is shown in Table 2.

[0069] Table 2 Catalytic performance

[0070]

[0071] From the test results of Table 2, it can be seen that the titanium-silicon catalysts of the examples of the present application have high raw material conversion rate and product selectivity, which is due to the removal of carbon components during high-temperature calcination, the in-situ combination of metal components with molecular sieve, and the more abundant pore size in the composite structure, which makes the Ti active center more easily exposed.

[0072] The titanium-silicon catalysts of the examples of the present application were also repeatedly subjected to 1-butene catalytic tests for 10 times. After each test, the catalyst was collected and placed in 10 times the mass of deionized water for 10 min of shaking and washing to remove the chemicals adsorbed on the surface of the catalyst, and then the washed catalyst was separated by filtration and dried to constant weight in a 50°C drying oven for the next test. The results are shown in Table 3.

[0073] Table 3 Performance of the 10th catalysis

[0074]

[0075] From the test results of Table 3, it can be seen that the catalysts of the examples of the present application have good catalytic stability.

[0076] 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.

[0077] 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 process for the preparation of a titanium-silicon catalyst for the catalytic epoxidation of olefins, characterized in that, The application relates to a titanium-silicon catalyst for catalyzing an olefin epoxidation reaction. The preparation method of the modified porous carbon comprises the following steps: The organic acid metal salt is calcined under a protective atmosphere to obtain the porous carbon. The porous carbon, the soluble nickel salt and the solvent are mixed in a mass ratio of 1:0.05-0.1:20-50 to obtain the modified porous carbon. The mass ratio of the Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide, n-butyl titanate and the modified porous carbon is 0.8-1.2:12-20:0.1-0.5:0.06-0.1:0.01-0.

05.

2. The method for preparing a titanium silicon catalyst for catalyzing an olefin epoxidation reaction according to claim 1, characterized by, The Ti-Beta molecular sieve, water, tetrapropylammonium hydroxide and n-butyl titanate are mixed for 3-6 hours, and then the modified porous carbon is added. The 1,4,7-triazacyclononane-1,4,7-triacetic acid accounts for 0.01-0.03 of the mass of the porous carbon.

3. The method for preparing a titanium silicon catalyst for catalyzing an olefin epoxidation reaction according to claim 1, characterized by, The preparation method of the Ti-Beta molecular sieve comprises the following steps:

4. The method for preparing a titanium silicon catalyst for catalyzing an olefin epoxidation reaction according to claim 1, characterized by, The Beta molecular sieve is treated by refluxing in an acid solution to obtain an acid-treated Beta molecular sieve. The acid-treated Beta molecular sieve, water, tetrapropylammonium hydroxide, n-butyl titanate and a mineralizer are mixed to form a reaction system, and the molar ratio of silica, 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, and then a crystallization reaction is performed, and the insoluble substance is calcined to obtain the Ti-Beta molecular sieve. The silicon-aluminum ratio of the Beta molecular sieve is 10-25.

5. The method for preparing a titanium silicon catalyst for catalyzing an olefin epoxidation reaction according to claim 4, characterized by, The mineralizer comprises at least one of sodium acetate, sodium benzoate and sodium citrate.

6. The method for preparing a titanium silicon catalyst for catalyzing an olefin epoxidation reaction according to claim 4, characterized by, The crystallization reaction is performed at a temperature of 140-170 DEG C for 18-72 hours.

7. The method for preparing a titanium silicon catalyst for catalyzing an olefin epoxidation reaction according to claim 1 or 4, characterized in that, The calcination is performed at a temperature of 450-750 DEG C for 1-8 hours.

8. The method for preparing a titanium silicon catalyst for catalyzing an olefin epoxidation reaction according to claim 1 or 4, characterized in that, The preparation method is obtained by any one of claims 1-8.

9. A titanium-silicon catalyst for catalyzing an olefin epoxidation reaction, characterized by, ​

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