Titanium silicon molecular sieve and preparation method thereof

Abstract

The present invention relates to the technical field of molecular sieve preparation, and in particular to a titanium silicate molecular sieve and a preparation method thereof. The method comprises: (1) uniformly mixing a silicon source, an alkaline template, a titanium source and water to obtain a titanium silical sol; (2) adding a silanization agent to the titanium silical sol, and hydrothermally crystallizing and calcining the obtained mixture. The present invention treats the titanium silical sol precursor with a specific silanization agent, so that the prepared titanium silicalite has mesoporous channels with a specific pore size and a large specific surface area and pore volume.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieve preparation, in particular to titanium silicon molecular sieve and a preparation method thereof. Background Art

[0002] Since its initial synthesis by Taramasso et al. in 1983, titanium silicalite (TS-1) has demonstrated numerous advantages in the selective oxidation of hydrocarbons using hydrogen peroxide, including mild reaction conditions, high atom utilization, and an environmentally friendly, pollution-free process. This has revolutionized the heterogeneous selective catalytic oxidation of organics. TS-1 possesses an MFI topological structure, consisting of primary structural units such as silicon-oxygen tetrahedra and titanium-oxygen tetrahedra connected by oxygen bridges to form secondary structural units of five-membered rings, which further form a three-dimensional microporous framework. The MFI molecular sieve possesses a two-dimensional pore structure, with ten-membered rings parallel to the a-axis forming an S-shaped pore with a pore size of 0.51 nm × 0.55 nm, and ten-membered rings parallel to the b-axis forming a linear pore with a pore size of 0.54 nm × 0.56 nm.

[0003] Currently, TS-1 has been successfully applied in industrial production processes such as liquid-phase epoxidation of propylene and ammoximation of cyclohexanone. However, the pore size of TS-1 is approximately 0.55 nm, which may limit the diffusion and mass transfer of large molecular hydrocarbons, thus restricting its application. For different systems, especially reactions involving large molecular hydrocarbons, the preparation of TS-1 with multi-level pores with hollow or even macroporous structures to improve diffusion and mass transfer is a difficult problem that needs to be solved urgently. There are many methods for preparing titanium silicalite molecular sieves, such as the alkaline dissolution method, the hard / soft template method, and the silanization agent support layer method; among them, the silanization agent support layer method is an effective method for preparing titanium silicalite molecular sieves.

[0004] Treatment with silanization reagents can introduce a certain proportion of mesoporous channels into titanium silicate molecular sieves, and titanium silicate molecular sieves have good catalytic oxidation activity. However, the silanization reagents currently used to synthesize titanium silicate molecular sieves are relatively simple, and their catalytic oxidation performance needs to be further improved. Summary of the Invention

[0005] The purpose of the present invention is to improve the catalytic oxidation performance of titanium silicate molecular sieve in the prior art and to provide titanium silicate molecular sieve and a preparation method thereof.

[0006] In order to achieve the above object, the first aspect of the present invention provides a method for preparing titanium silicate molecular sieve, the method comprising:

[0007] (1) uniformly mixing a silicon source, an alkaline template, a titanium source, and water to obtain a titanium silicate sol;

[0008] (2) adding the compound represented by formula (I) to the titanium silicalite, and subjecting the obtained mixture to hydrothermal crystallization and calcination;

[0009]

[0010] wherein i is an integer of 1-10; and R1, R2 and R3 are each independently selected from a C1-C6 alkyl group.

[0011] The second aspect of the present invention provides a titanium silicate molecular sieve prepared according to the method described in the first aspect.

[0012] Through the above technical solution, the present invention uses a specific silanization agent to treat the titanium silicalite precursor, so that the prepared titanium silicalite has specific mesoporous channels and a large specific surface area and pore volume. When the titanium silicalite is used as a catalyst for the oxidation of cyclohexene to prepare cyclohexene oxide, the conversion rate of cyclohexene is as high as 99.1%, and the selectivity of cyclohexene oxide is as high as 98.8%. DETAILED DESCRIPTION

[0013] 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 obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0014] As mentioned above, the first aspect of the present invention provides a method for preparing titanium silicate molecular sieve, the method comprising:

[0015] (1) uniformly mixing a silicon source, an alkaline template, a titanium source, and water to obtain a titanium silicate sol;

[0016] (2) adding the compound represented by formula (I) to the titanium silicalite, and subjecting the obtained mixture to hydrothermal crystallization and calcination;

[0017]

[0018] wherein i is an integer of 1-10; and R1, R2 and R3 are each independently selected from a C1-C6 alkyl group.

[0019] In the present invention, C1-C6 alkyl refers to an alkyl group having 1 to 6 carbon atoms, for example, it can be one of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl and n-hexyl.

[0020] In some preferred embodiments of the present invention, i is an integer of 1-5, that is, the number of methylene groups between silicon and alkenyl (-CH2=CH2-) is 1-5, for example, 1, 2, 3, 4 or 5.

[0021] In some preferred embodiments of the present invention, R1, R2 and R3 are each independently selected from methyl, ethyl, n-propyl or isopropyl. In the present invention, R1, R2 and R3 may be the same or different. Preferably, R1, R2 and R3 are the same.

[0022] In the present invention, a specific silanization agent (a compound represented by formula (I)) is added to the titanium silicalite sol. Through the dispersion force between the alkenyl groups in the silanization agent and the attraction between molecules, a multi-level pore titanium silicalite with a specific pore structure can be prepared. When the titanium silicalite is used in the cyclohexene epoxidation reaction, it is beneficial to improve the mass transfer of the product cyclohexene oxide, thereby improving the cyclohexene conversion rate and cyclohexene oxide selectivity.

[0023] According to the present invention, if the amount of the silanization agent (the compound shown in formula (I)) is too high, the crystallization performance of the titanium silical sol will deteriorate and the molecular sieve cannot be obtained; and if the amount of the silanization agent (the compound shown in formula (I)) is too low, the specific surface area of ​​the obtained titanium silicalite molecular sieve will be reduced, affecting mass transfer and further affecting its catalytic oxidation activity; under preferred conditions, in step (1), the silicon source is calculated as SiO2, and the molar ratio of the silicon source to the compound shown in formula (I) is 1: (0.01-0.3), preferably 1: (0.01-0.2); more preferably 1: (0.05-0.2).

[0024] In some preferred embodiments of the present invention, the silicon source is calculated as SiO2, the alkaline template is calculated as N when it contains nitrogen, and as OH when it does not contain nitrogen. - The molar ratio of the silicon source, the alkaline template and water is 1: (0.05-0.4): (5-40); preferably 1: (0.1-0.3): (5-25).

[0025] According to the present invention, under preferred conditions, the silicon source is selected from at least one of methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate, butyl orthosilicate, silica gel, white carbon black and silica sol.

[0026] According to the present invention, under preferred conditions, the alkaline template is selected from at least one of quaternary ammonium bases, aliphatic amines and aliphatic alcohol amines, preferably at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide.

[0027] In some preferred embodiments of the present invention, the silicon source is calculated as SiO2, the titanium source is calculated as TiO2, and the molar ratio of the silicon source to the titanium source is 1:(0.001-0.04), preferably 1:(0.005-0.025), and more preferably 1:(0.01-0.02).

[0028] According to the present invention, under preferred conditions, the titanium source is selected from an organic titanium source and / or an inorganic titanium source; further preferably, the titanium source is selected from at least one of titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate and tetrabutyl titanate.

[0029] In a preferred embodiment of the present invention, step (1) further comprises: mixing a silicon source, an alkaline template, and water, and stirring the mixture at room temperature for a first time for 0.1-2 hours, then adding a titanium source during the stirring process, and stirring the mixture for a second time for 0.5-6 hours to obtain a titanium silicalite. Under preferred conditions, the second stirring time is 0.5-3 hours, more preferably 2-3 hours.

[0030] According to the present invention, under preferred conditions, step (1) further comprises: driving out the alcohol after the mixing; driving out the alcohol can remove the alcohol generated by the hydrolysis of the silicon source and the titanium source. In the present invention, it is preferred to use azeotropic distillation to remove the alcohol generated in the system, and at the same time, replenish the water lost by azeotropic distillation during the driving out of the alcohol to ensure that the ratio of each substance in the titanium silicalite meets the above requirements; preferably, the conditions for driving out the alcohol include: temperature of 30-100°C and time of 2-10h; more preferably: temperature of 40-90°C and time of 4-10h, and further preferably, the conditions for driving out the alcohol include: temperature of 60-70°C and time of 6-8h.

[0031] According to the present invention, under preferred conditions, step (1) further comprises: adding the compound represented by formula (I) to the titanium silical sol and performing a third stirring for 0.1-24 hours, preferably the third stirring time is 0.5-10 hours, more preferably 2-4 hours.

[0032] According to the present invention, under preferred conditions, in step (2), the conditions for the hydrothermal crystallization include: heating the mixture to 50-200°C within 0.1-3h, and then performing hydrothermal crystallization at 50-200°C for 10-100h; preferably, performing hydrothermal crystallization at a temperature of 100-200°C for 20-80h; further preferably, the heating time is 0.3-0.6h; more preferably, the conditions for the hydrothermal crystallization include: a temperature of 150-180°C and a time of 20-60h.

[0033] The present invention has no particular limitation on the pressure of hydrothermal crystallization, which may be the autogenous pressure of the crystallization system.

[0034] According to the present invention, under preferred conditions, the method further comprises: washing, filtering, and drying the product obtained by hydrothermal crystallization; wherein the washing, filtering, and drying processes are known to those skilled in the art. For example, the washing temperature can be 20-50°C, the washing solvent can be water, and the amount of the washing solvent used is 1-20 times the mass of the crystallized product; the drying conditions can be: temperature 40-150°C, and drying time 0.5-24 hours.

[0035] In some preferred embodiments of the present invention, the calcination conditions include: a temperature of 400-800° C. and a time of 1-15 h; preferably a temperature of 500-600° C. and a time of 4-8 h.

[0036] The second aspect of the present invention provides a titanium silicate molecular sieve prepared according to the method described in the first aspect.

[0037] According to the present invention, under preferred conditions, the specific surface area of ​​the titanium silicate molecular sieve is greater than 620m 2 / g, micropore volume is 0.2-0.25cm 3 / g, and the mesopore volume is 0.4-0.8cm 3 / g, mesopore diameter 35-45nm.

[0038] In the present invention, the form of the catalyst can be selected according to the reaction requirements. For example, powdered titanium silicate can be directly added to the reaction system as a catalyst, or it can be loaded on a carrier to form a granular catalyst.

[0039] According to a particularly preferred embodiment of the present invention, the method for preparing titanium silicate molecular sieve comprises:

[0040] (1) mixing a silicon source, an alkaline template, and water in a molar ratio of 1:(0.1-0.3):(5-25), stirring for a first time at room temperature for 0.1-2 hours, then adding a titanium source during the stirring process, and stirring for a second time for 2-3 hours to obtain a mixed system; wherein the molar ratio of the silicon source to the titanium source is 1:(0.005-0.025);

[0041] Then, the mixed system is subjected to alcohol removal to obtain titanium silicalite; the alcohol removal temperature is 60-70° C. and the time is 6-8 hours;

[0042] (2) adding the compound represented by formula (I) to the titanium silicalite sol and performing a third stirring for 2-4 hours, and performing hydrothermal crystallization and calcination on the obtained mixture; wherein the molar ratio of the silicon source to the compound represented by formula (I) is 1:(0.01-0.2), and the crystallization conditions are: heating the mixture to 150-180°C within 0.3-0.6 hours, and then performing hydrothermal crystallization at 150-180°C for 20-60 hours;

[0043]

[0044] wherein i is an integer from 1 to 5; R1, R2 and R3 are the same; and R1, R2 and R3 are selected from methyl, ethyl, n-propyl or isopropyl.

[0045] The present invention will be described in detail below through examples. In the following examples, room temperature refers to 25±5°C.

[0046] The specific surface areas were obtained by measuring the static N2 adsorption-desorption curves of the samples at liquid nitrogen temperature (77.4 K) using a Micromeritics ASAP2405J static nitrogen adsorption instrument and then performing BET fitting on the adsorption curves.

[0047] The pore volume was determined according to the method described in RIPP 151-90 in Analytical Methods in Petrochemical Engineering compiled by Yang Cuiding et al. (Science Press, first edition, published in September 1990);

[0048] The pore size distribution was calculated according to the BJH formula.

[0049] In the following examples, the chemical structural formulas of the silanization reagents used are shown in Table 1.

[0050] Table 1

[0051]

[0052] Example 1

[0053] (1) Methyl orthosilicate, tetrapropylammonium hydroxide, and water were stirred for a first time at room temperature for 0.5 h, and tetraethyl titanate was added during the stirring process and stirred for a second time for 2.5 h to obtain a mixed system; wherein, methyl orthosilicate was calculated as SiO2, tetrapropylammonium hydroxide was calculated as N, and tetraethyl titanate was calculated as TiO2, and the molar ratio of methyl orthosilicate, tetrapropylammonium hydroxide, water, and tetraethyl titanate was 1:0.1:20:0.015;

[0054] Then, the mixed system was subjected to alcoholization at 70°C for 7 hours to obtain titanium silicalite;

[0055] (2) adding compound 1 (structural formula shown in Table 1) to the titanium silicate sol, and stirring for a third time at room temperature for 3 hours to obtain a mixture, wherein the molar ratio of compound (1) to tetramethyl silicate is 0.15:1;

[0056] (3) heating the mixture to 170°C for 0.5 h and performing hydrothermal crystallization at 170°C for 48 h to obtain a crystallized product; the crystallized product was sequentially rinsed with water, filtered, and dried at 120°C for 2 h;

[0057] The dried product was calcined at 550°C for 6 h to obtain titanium silicate molecular sieve.

[0058] Examples 2-9

[0059] Titanium silicate molecular sieve was prepared according to the method of Example 1. The proportions and synthesis conditions are shown in Table 2. The physical properties of the prepared titanium silicate molecular sieve are shown in Table 3.

[0060] Comparative Example 1

[0061] Titanium silicate molecular sieve was prepared according to the method for preparing titanium silicate micro-mesoporous molecular sieve composite material disclosed in "Zeolites, 1992, Vol. 12, pp. 943-950". The specific method is as follows:

[0062] Mix 22.5g of tetraethyl silicate, 7.0g of tetrapropylammonium hydroxide, and 59.8g of deionized water and hydrolyze at 60°C for 1.0h. Then, slowly add 1.1g of tetrabutyl titanate and 5.0g of isopropyl alcohol to the solution while stirring vigorously. Stir the mixture at 75°C for 3h to obtain a clear, transparent colloid. This colloid is then transferred to a sealed stainless steel reactor and crystallized at 170°C for 72h to obtain conventional TS-1 molecular sieve.

[0063] Comparative Examples 2-9

[0064] Titanium silicate molecular sieve was prepared according to the method of Example 1. Its components and synthesis conditions are shown in Table 2. The physical properties of the prepared molecular sieve are shown in Table 3.

[0065] Table 2

[0066]

[0067]

[0068] Note: 1- molar ratio; 2- molar ratio; 3- molar ratio

[0069] Test Case

[0070] This test example illustrates the reaction effects of the samples prepared in the examples and comparative examples provided herein for the epoxidation of cyclohexene to produce epoxycyclohexane and epoxycyclohexane. The reagents used in this test example were all commercially available chemically pure reagents. The concentrations of the various substances after the reaction were quantitatively analyzed using gas chromatography. A 6890 gas chromatograph manufactured by Agilent was used; the analytical column used was an FFAP column. Component concentrations were quantified using the external standard method. First, the peak area of ​​each component was measured, and the component concentrations were obtained using a standard working curve to calculate the various indices.

[0071] The cyclohexene conversion and cyclohexene oxide selectivity in the test example were calculated according to the following formulas:

[0072] Cyclohexene conversion rate % = (1-moles of cyclohexene remaining after reaction / moles of cyclohexene added before reaction) × 100%

[0073] Epoxycyclohexane selectivity % = moles of cyclohexane after reaction / (moles of cyclohexene added before reaction - moles of cyclohexene remaining after reaction) × 100%

[0074] The molecular sieves prepared in Examples 1-9 and Comparative Examples 1-9 were respectively added to a three-necked flask reaction vessel containing cyclohexene and methanol, wherein the molar ratio of the molecular sieve, cyclohexene, and methanol was 1:20:100. After the temperature stabilized to the set value, hydrogen peroxide (concentration 30 wt%) was added, and the molar ratio of cyclohexene and hydrogen peroxide (calculated as H2O2) was 1:3. The reaction was then carried out at a temperature of 80°C and a pressure of 0.1 MPa (atmospheric pressure) for 6 h. The catalyst was removed by filtration and samples were taken for chromatographic analysis. The reaction results are shown in Table 3.

[0075] Table 3

[0076]

[0077] Note: *Cyclohexene oxide is the selectivity of cyclohexene oxide.

[0078] As can be seen from Table 3, when the titanium silicalite prepared in the embodiment of the present invention is used for cyclohexene oxidation reaction, the cyclohexene conversion rate is as high as 99.1%, and the selectivity of cyclohexene oxide is as high as 98.8%, which has high catalytic activity.

[0079] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for preparing titanium silicon molecular sieve, characterized in that: The method comprises: (1) uniformly mixing a silicon source, an alkaline template, a titanium source and water to obtain a titanium silicate sol; (2) adding the compound represented by formula (I) to the titanium silicalite sol, and subjecting the obtained mixture to hydrothermal crystallization and calcination; Formula (I) wherein i is an integer from 1 to 10; R1, R2, and R3 are each independently selected from a C1-C6 alkyl group; The specific surface area of ​​the titanium silicate molecular sieve prepared by the method is greater than 620m 2 / g, micropore volume is 0.2-0.25cm 3 / g, and the mesopore volume is 0.4-0.8cm 3 / g, mesopore diameter 35-45nm.

2. The method according to claim 1, wherein i is an integer from 1 to 5.

3. The method according to claim 1, wherein R1, R2 and R3 are each independently selected from methyl, ethyl, n-propyl or isopropyl.

4. The method according to any one of claims 1 to 3, wherein: The silicon source is calculated as SiO2, and the molar ratio of the silicon source to the compound represented by formula (I) is 1:(0.01-0.3).

5. The method according to claim 4, wherein The silicon source is calculated as SiO2, and the molar ratio of the silicon source to the compound represented by formula (I) is 1:(0.01-0.2).

6. The method according to any one of claims 1 to 3, wherein: The silicon source is calculated as SiO2, the alkaline template is calculated as N when it contains nitrogen, and as OH when it does not contain nitrogen. - The molar ratio of the silicon source, the alkaline template and water is 1: (0.05-0.4): (5-40).

7. The method according to claim 6, wherein: The silicon source is calculated as SiO2, the alkaline template is calculated as N when it contains nitrogen, and as OH when it does not contain nitrogen. - The molar ratio of the silicon source, the alkaline template and water is 1: (0.1-0.3): (5-25).

8. The method according to any one of claims 1 to 3, wherein: The silicon source is calculated as SiO2, the titanium source is calculated as TiO2, and the molar ratio of the silicon source to the titanium source is 1:(0.001-0.04).

9. The method according to claim 8, wherein The silicon source is calculated as SiO2, the titanium source is calculated as TiO2, and the molar ratio of the silicon source to the titanium source is 1:(0.005-0.025).

10. The method according to any one of claims 1 to 3, wherein: The silicon source is selected from at least one of methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate, butyl orthosilicate, silica gel, white carbon black and silica sol.

11. The method according to any one of claims 1 to 3, wherein: The alkaline template is selected from at least one of quaternary ammonium base, aliphatic amine and aliphatic alcohol amine.

12. The method according to claim 11, wherein The alkaline template agent is selected from at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide.

13. The method according to any one of claims 1 to 3, wherein: The titanium source is selected from an organic titanium source and / or an inorganic titanium source.

14. The method according to claim 13, wherein The titanium source is selected from at least one of titanium tetrachloride, titanium sulfate, titanium nitrate, tetraethyl titanate, tetrapropyl titanate and tetrabutyl titanate.

15. The method according to any one of claims 1 to 3, wherein: Step (1) also includes removing alcohol after the mixing.

16. The method according to claim 15, wherein The conditions for driving out the alcohol include: temperature of 30-100° C. and time of 2-10 h.

17. The method according to claim 16, wherein The conditions for driving out the alcohol include: temperature of 40-90° C. and time of 4-10 h.

18. The method according to any one of claims 1 to 3, wherein: The calcination conditions include: temperature of 400-800° C. and time of 1-15 hours.

19. A titanium silicate molecular sieve prepared according to the method according to any one of claims 1 to 18.

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