Titanium silicalite molecular sieve as well as preparation method and application thereof

Abstract

The invention relates to a titanium silicalite molecular sieve and a preparation method and application thereof, and the method comprises the following steps: S1, mixing a titanium source, a nitrogen-containing heterocyclic compound and an optional solvent to obtain a synthetic titanium source; s2, mixing a synthetic titanium source, a silicon source and a template agent, and carrying out hydrolysis treatment to obtain a hydrolysis mixture; and S3, carrying out hydrothermal crystallization treatment, drying treatment and roasting treatment on the hydrolysis mixture. The content of non-framework titanium in the titanium silicalite molecular sieve can be effectively reduced, the raw material conversion rate and the target product selectivity of the titanium silicalite molecular sieve in an organic catalytic reaction are improved, and the reaction stability of the titanium silicalite molecular sieve is improved.

Description

Technical Field

[0001] This application relates to the field of inorganic material preparation technology, specifically to a titanium-silicon molecular sieve, its preparation method, and its application. Background Technology

[0002] Titanium-containing heteroatom molecular sieves refer to heteroatom molecular sieves whose framework contains tetracoordinated titanium. Using titanium-containing heteroatom molecular sieves as catalysts for the catalytic oxidation of olefins to prepare epoxides has long been a focus of research due to its mild reaction conditions, high atom utilization, and environmentally friendly, pollution-free process.

[0003] Titanium silicate molecular sieves are a novel type of heteroatom molecular sieve developed since the early 1980s. Currently synthesized varieties include TS-1 with an MFI structure, TS-2 with a MEL structure, MCM-22 with a MWW structure, and TS-48 with a relatively large pore structure. Among them, TS-1 was first developed and synthesized by the Italian company Enichen. It is a novel titanium silicate molecular sieve with excellent catalytic selective oxidation performance, formed by introducing the transition metal element titanium into a molecular sieve framework with a ZSM-5 structure. TS-1 not only possesses the catalytic oxidation activity of titanium but also the shape-selective effect and excellent stability of ZSM-5 molecular sieves. Using this titanium silicate molecular sieve as a catalyst, various types of organic oxidation reactions can be catalyzed, such as the epoxidation of alkenes, partial oxidation of alkanes, oxidation of alcohols, hydroxylation of phenols, and ammoxidation of cyclic ketones.

[0004] In the oxidation of organic matter, TS-1 molecular sieves can utilize low-concentration, pollution-free hydrogen peroxide as an oxidant, avoiding the problems of complex oxidation processes and environmental pollution. It possesses unparalleled advantages over traditional oxidation systems, including energy saving, economy, and environmental friendliness, and exhibits excellent reaction selectivity. As a selective oxidation catalyst for organic matter, titanium-silicon molecular sieves can overcome the drawbacks of traditional catalytic oxidation systems, such as complex reaction processes, harsh conditions, and severe environmental pollution. Therefore, in today's increasingly stringent environmental protection requirements, they have received considerable attention.

[0005] However, the titanium-silicon molecular sieves prepared by existing processes still contain a large amount of non-framework titanium, which prevents them from achieving ideal results in catalytic oxidation reactions. Summary of the Invention

[0006] The purpose of this disclosure is to provide a titanium-silicon molecular sieve, its preparation method and application, which effectively reduces the non-framework titanium content in the titanium-silicon molecular sieve, improves the raw material conversion rate and target product selectivity of the titanium-silicon molecular sieve in organic catalytic reactions, and improves the reaction stability of the titanium-silicon molecular sieve.

[0007] To achieve the above objectives, the first aspect of this disclosure provides a method for preparing titanium-silicon molecular sieves, comprising the following steps:

[0008] S1. Mix the titanium source, the nitrogen-containing heterocyclic compound, and an optional solvent to obtain the synthetic titanium source;

[0009] S2. The synthesized titanium source, silicon source and template agent are mixed and subjected to hydrolysis to obtain a hydrolyzed mixture;

[0010] S3. The hydrolyzed mixture is subjected to hydrothermal crystallization, drying and calcination.

[0011] Optionally, the nitrogen-containing heterocyclic compound is selected from one or more nitrogen-containing heterocyclic compounds having 3 to 12 carbon atoms;

[0012] Preferably, the nitrogen-containing heterocyclic compound is selected from one or more of pyrrole, thiazole, imidazole, pyrazole, pyridine, pyrimidine, quinoline and purine; more preferably, it is selected from one or more of pyridine, pyrimidine and purine.

[0013] Optionally, the titanium source is selected from one or more of inorganic titanium sources and organic titanium sources.

[0014] Optionally, the inorganic titanium source is selected from one or more of titanium tetrafluoride, titanium tetrachloride, titanium tetrabromide, titanium trichloride, and titanium sulfate; the organic titanium source is selected from one or more of tetramethyl titanate, tetraethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate.

[0015] Optionally, the silicon source is selected from at least one of silicone grease, solid silica gel, fumed silica, and silica sol; preferably, it is selected from at least one of silicone grease, solid silica gel, and fumed silica.

[0016] Optionally, the silicone grease is selected from one or more compounds with the structure shown in formula (1):

[0017]

[0018] R a 、R b 、R c and R d Each is independently selected from alkyl groups having 1 to 4 carbon atoms, wherein the alkyl group is branched or straight-chain alkyl; preferably, the R a 、R b 、R c and R d Each of the following is independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl; more preferably, the organosilicon grease is selected from one or more of tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, and dimethyl diethyl silyl ester; even more preferably, it is selected from one or more of tetramethyl silicate, tetraethyl silicate, and dimethyl diethyl silyl ester.

[0019] Optionally, the template agent is selected from one or more of organic quaternary ammonium salts and organic bases;

[0020] Optionally, the organic quaternary ammonium salt is selected from one or more of tetraethylammonium chloride, tetraethylammonium bromide, tetrapropylammonium chloride, tetrapropylammonium bromide, tetrabutylammonium chloride, and tetrabutylammonium bromide;

[0021] Optionally, the organic base is selected from one or more of organic quaternary ammonium bases and organic amines; preferably, the organic quaternary ammonium base is selected from one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide; the organic amine is selected from one or more of ethylamine, n-butylamine, butanediamine, hexamethylenediamine, monoethanolamine, diethanolamine, triethanolamine, theanine, toluidine, and p-phenylenediamine.

[0022] Optionally, the solvent is selected from one or more of polar protic solvents and aprotic solvents; preferably, the polar protic solvent is selected from one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol; the aprotic solvent is selected from one or more of dichloromethane, dichloroethane, allyl chloride, methylchloropropene, 1-chlorobutane, acetonitrile, N,N-dimethylformamide, toluene, acetone, propylene glycol methyl ether and dimethyl sulfoxide.

[0023] Optionally, in step S1, the molar ratio of titanium source: nitrogen-containing heterocyclic compound: solvent is 1:(0.5-8):(0-1000), preferably 1:(1-4):(20-50).

[0024] Optionally, in step S2, the molar ratio of silicon source: synthetic titanium source: organic base: water is 1:(0.001~0.5):(0.001~0.8):(5~150), preferably 1:(0.01~0.2):(0.01~0.5):(10~50), wherein the silicon source is calculated as SiO2 and the synthetic titanium source is calculated as TiO2.

[0025] Optionally, in step S2, the conditions for the hydrolysis treatment include: first heating to 60-100°C at a first heating rate, and then hydrolyzing at a constant temperature for 0.5-10 hours; preferably, first heating to 70-90°C at a first heating rate, and then hydrolyzing at a constant temperature for 1-5 hours.

[0026] Optionally, the first heating rate is 5 to 30°C / h, preferably 10 to 20°C / h.

[0027] Optionally, in step S3, the conditions for the hydrothermal crystallization treatment include:

[0028] First, the temperature is increased to 100-200°C at a second heating rate, and then crystallized at a constant temperature for 6-120 hours; preferably, the temperature is increased to 140-180°C at a second heating rate, and then crystallized at a constant temperature for 10-100 hours.

[0029] Optionally, the second heating rate is 0.3 to 1.7 °C / min, preferably 0.5 to 1.4 °C / min.

[0030] Optionally, in step S3, the drying conditions include: a drying temperature of 80–120°C and a drying time of 2–30 h; preferably, the drying temperature is 90–110°C and the drying time is 5–10 h.

[0031] Optionally, the calcination conditions include: a calcination temperature of 450–650°C and a calcination time of 1–10 h; preferably, the calcination temperature is 480–620°C and the calcination time is 2–6 h.

[0032] The second aspect of this disclosure provides a titanium-silicon molecular sieve prepared according to the method described in the first aspect of this disclosure.

[0033] This disclosure provides a third aspect regarding the application of the titanium-silicon molecular sieve described in the second aspect of this disclosure in organic catalytic reactions.

[0034] Optionally, the organocatalytic reaction includes the epoxidation of 1-hexene to produce hexane oxide;

[0035] Optionally, the epoxidation of 1-hexene to produce hexane comprises: contacting a catalyst with 1-hexene and hydrogen peroxide to carry out a catalytic oxidation reaction, wherein the catalyst comprises the titanium-silicon molecular sieve;

[0036] Preferably, the conditions for the epoxidation of 1-hexene to produce hexane include: a catalyst to hydrogen peroxide weight ratio of 0.01 to 10:1, preferably 0.02 to 2:1, wherein the weight of the catalyst is based on titanium silicate molecular sieves; and a hydrogen peroxide to 1-hexene molar ratio of 0.5 to 2:1, preferably 1 to 1.2:1.

[0037] Optionally, the reaction temperature is 30–60°C, the reaction pressure is atmospheric pressure, and the reaction time is 1–10 h; preferably, the reaction temperature is 35–50°C, and the reaction time is 2–6 h.

[0038] Through the above technical solution, this disclosure provides a titanium-silicon molecular sieve, its preparation method, and its application in organic catalytic reactions, particularly in the epoxidation of 1-hexene to hexane oxide. This disclosure first involves mixing a titanium source with a nitrogen-containing heterocyclic compound and a solvent to obtain a synthetic titanium source. The nitrogen-containing heterocyclic molecule has a large volume and, as a ligand compound, can form significant steric hindrance, effectively inhibiting the self-polymerization of titanium salts and minimizing the formation of TiO2 from the hydrolysis of the titanium source, thus reducing the generation of non-framework titanium. Furthermore, more titanium is located within the pores of the molecular sieve. Compared with existing technologies, the titanium-containing molecular sieve synthesized in this disclosure exhibits better catalytic oxidation activity and selectivity, as well as better catalytic activity stability. In the epoxidation of 1-hexene to hexane oxide reaction, the titanium-silicon molecular sieve provided by this disclosure can achieve higher feed conversion rates and target product selectivity, and effectively improve the catalytic activity stability of the titanium-silicon molecular sieve in organic catalytic oxidation reactions, ensuring the catalytic effect of the catalyst while allowing for multiple reuses.

[0039] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0040] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0041] Figure 1 The UV-Vis spectra of the molecular sieve products obtained in Example 1, Comparative Example 1, and Comparative Example 2 are shown below.

[0042] Figure 2 The peak fitting result of the ultraviolet-visible (UV-vis) spectrum of the titanium-containing molecular sieve sample synthesized in Example 1 is shown.

[0043] Figure 3 The peak fitting results of the ultraviolet-vis (UV-vis) spectrum of the titanium-containing molecular sieve sample synthesized in Comparative Example 1 are shown.

[0044] Figure 4 The peak fitting results of the ultraviolet-vis (UV-vis) spectrum of the titanium-containing molecular sieve sample synthesized in Comparative Example 2 are shown.

[0045] Figure 5 The XRD patterns are of the molecular sieve products obtained in Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0046] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0047] The first aspect of this disclosure provides a method for preparing titanium-silicon molecular sieves, comprising the following steps:

[0048] S1. Mix the titanium source, the nitrogen-containing heterocyclic compound, and an optional solvent to obtain the synthetic titanium source;

[0049] S2. The synthesized titanium source, silicon source and template agent are mixed and subjected to hydrolysis to obtain a hydrolyzed mixture;

[0050] S3. The hydrolyzed mixture is subjected to hydrothermal crystallization, drying and calcination.

[0051] This disclosure provides a method for preparing titanium-silicon molecular sieves. First, a titanium source is mixed with a nitrogen-containing heterocyclic compound and a solvent to obtain a synthetic titanium source. The nitrogen-containing heterocyclic compound has a large molecular weight and, as a ligand compound, can form significant steric hindrance, effectively inhibiting the self-polymerization of titanium salts and minimizing the formation of TiO2 from the hydrolysis of the titanium source, thus reducing the generation of non-framework titanium. Furthermore, more titanium is located within the pores of the molecular sieve. The titanium-containing molecular sieve synthesized in this disclosure exhibits better catalytic oxidation activity and selectivity compared to existing technologies, while also demonstrating better catalytic activity stability. In the epoxidation of 1-hexene to hexane, the titanium-silicon molecular sieve provided by this disclosure can achieve higher feed conversion rates and target product selectivity, and effectively improves the catalytic activity stability of the titanium-silicon molecular sieve in organic catalytic oxidation reactions.

[0052] In this disclosure, "nitrogen-containing heterocyclic compound" refers to a compound that has a cyclic structure and contains nitrogen atoms in the cyclic structure. It may also contain or not contain other types of heteroatoms (such as S, O, etc.). The heterocyclic compound may be a monocyclic compound or a polycyclic compound containing two or more cyclic structures.

[0053] In one embodiment, the nitrogen-containing heterocyclic compound is selected from one or more nitrogen-containing heterocyclic compounds having 3 to 12 carbon atoms.

[0054] In a preferred embodiment, the nitrogen-containing heterocyclic compound is selected from pyrrole. Thiazole imidazole Pyrazole Pyridine Pyrimidine Quinoline and purines benzothiazolium and benzimidazole One or more of the following; preferably one or more selected from pyridine, pyrimidine, and purine. Using the nitrogen-containing heterocyclic compound provided in this embodiment as the ligand compound in the synthesis of titanium source can achieve a better effect of inhibiting the self-polymerization of titanium, further reducing the non-framework titanium content in titanium-silicon molecular sieves, and improving the catalytic performance of titanium-silicon molecular sieves.

[0055] In one embodiment, the titanium source is selected from one or more of inorganic titanium sources and organic titanium sources;

[0056] Optionally, the inorganic titanium source is selected from one or more of titanium tetrafluoride, titanium tetrachloride, titanium tetrabromide, titanium trichloride, and titanium sulfate; the organic titanium source is selected from one or more of tetramethyl titanate, tetraethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate. Preferably, an organic titanium source is used, more preferably tetraethyl titanate. The synthetic titanium source formed by the organic titanium source (especially tetraethyl titanate) and a nitrogen-containing heterocyclic compound provided in this embodiment can prepare titanium-silicon molecular sieves with lower non-framework titanium content.

[0057] In one embodiment, the silicon source is selected from at least one of silicone grease, solid silica gel, fumed silica, and silica sol; preferably, it is selected from at least one of silicone grease, solid silica gel, and fumed silica.

[0058] Optionally, the silicone grease is selected from one or more compounds with the structure shown in formula (1):

[0059]

[0060] R a R b R c and R d Each is independently selected from alkyl groups having 1 to 4 carbon atoms, wherein the alkyl group is branched or straight-chain alkyl; preferably, the R a R b R c and R d Each of the following is independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl; more preferably, the organosilicon grease is selected from one or more of tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, and dimethyl diethyl silyl ester; even more preferably, it is selected from one or more of tetramethyl silicate, tetraethyl silicate, and dimethyl diethyl silyl ester.

[0061] In one embodiment, the template agent is selected from one or more of organic quaternary ammonium salts and organic bases;

[0062] Optionally, the organic quaternary ammonium salt is selected from one or more of tetraethylammonium chloride, tetraethylammonium bromide, tetrapropylammonium chloride, tetrapropylammonium bromide, tetrabutylammonium chloride, and tetrabutylammonium bromide;

[0063] Optionally, the organic base is selected from one or more of organic quaternary ammonium bases and organic amines; preferably, the organic quaternary ammonium base is selected from one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide; and the organic amine is selected from one or more of ethylamine, n-butylamine, butanediamine, hexamethylenediamine, monoethanolamine, diethanolamine, triethanolamine, theanine, toluidine, and p-phenylenediamine.

[0064] In one embodiment, the solvent is selected from one or more of polar protic solvents and aprotic solvents; preferably, the polar protic solvent is selected from one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol; the aprotic solvent is selected from one or more of dichloromethane, dichloroethane, allyl chloride, methylchloropropene, 1-chlorobutane, acetonitrile, N,N-dimethylformamide, toluene, acetone, propylene glycol methyl ether, and dimethyl sulfoxide. The solvent is preferably an aprotic solvent, more preferably dichloromethane. The aprotic solvent provided in this embodiment, particularly dichloromethane, can form titanium-containing precursors with better performance as titanium sources for synthesis with titanium sources and nitrogen-containing heterocyclic compounds, and further improve the framework titanium content of titanium-silicon molecular sieves.

[0065] In one embodiment, in step S1, the molar ratio of titanium source: nitrogen-containing heterocyclic compound: solvent is 1:(0.5-8):(0-1000), preferably 1:(1-4):(20-50). The synthetic titanium source solution obtained according to the preferred molar ratio in this embodiment can prepare titanium-silicon molecular sieves with better catalytic performance.

[0066] In one embodiment, in step S2, the molar ratio of silicon source: synthetic titanium source: organic base: water is 1:(0.001-0.5):(0.001-0.8):(5-150), preferably 1:(0.01-0.2):(0.01-0.5):(10-50), wherein the silicon source is calculated as SiO2 and the synthetic titanium source is calculated as TiO2. The titanium-silicon molecular sieve obtained according to the preferred molar ratio in this embodiment has better catalytic activity and can have higher feed conversion rate and product selectivity in organic catalytic reactions.

[0067] In one embodiment, in step (2), the conditions for the hydrolysis treatment include: first heating to 60-100°C at a first heating rate, and then hydrolyzing at a constant temperature for 0.5-10 hours; preferably, first heating to 70-90°C at a first heating rate, and then hydrolyzing at a constant temperature for 1-5 hours.

[0068] Optionally, the first heating rate is 5 to 30°C / h, preferably 10 to 20°C / h.

[0069] In one embodiment, the conditions for the hydrothermal crystallization treatment in step S3 include:

[0070] First, the temperature is increased to 100-200°C at a second heating rate, and then crystallized at a constant temperature for 6-120 hours; preferably, the temperature is increased to 140-180°C at a second heating rate, and then crystallized at a constant temperature for 10-100 hours.

[0071] Optionally, the second heating rate is 0.3 to 1.7 °C / min, preferably 0.5 to 1.4 °C / min.

[0072] In one embodiment, in step S3, the drying conditions include: a drying temperature of 80–120°C and a drying time of 2–30 h; preferably, the drying temperature is 90–110°C and the drying time is 5–10 h.

[0073] In one embodiment, in step S3, the conditions for the calcination treatment include: a calcination temperature of 450–650°C and a calcination time of 1–10 h; preferably, the calcination temperature is 480–620°C and the calcination time is 2–6 h.

[0074] The titanium-silicon molecular sieve prepared according to the preferred process conditions provided in this disclosure can have better catalytic performance.

[0075] The second aspect of this disclosure provides a titanium-silicon molecular sieve prepared according to the method described in the first aspect of this disclosure.

[0076] In a preferred embodiment, the titanium-silicon molecular sieve has the following UV-Vis characteristics:

[0077] The UV-Vis spectrum of the titanium-silicon molecular sieve exhibits peaks at positions of 210±10 nm, 270±10 nm, and 330±10 nm, respectively; the peak area of ​​the peak at position 210±10 nm in the UV-Vis spectrum of the titanium-silicon molecular sieve is denoted as A. 210 Let A denote the peak area of ​​the spectral peak at position 270±10nm. 270 Let A denote the peak area of ​​the spectral peak at position 330±10nm. 330 The titanium-silicon molecular sieve, as defined in formula (2), has an X1 value that is any value within the range of 60% to 100%.

[0078] X1=(A 210 +A 270 ) / (A 210 +A 270 +A 330 Formula (2) is 100% × 100%.

[0079] The titanium-silicon molecular sieve disclosed herein has a higher titanium content in the framework and a lower titanium content in the non-framework, resulting in better catalytic oxidation activity and selectivity.

[0080] In a preferred embodiment, X1 is any value within the range of 70% to 90%.

[0081] In one embodiment, the molar ratio of silicon to titanium in the titanium-silicon molecular sieve is 1:0.01 to 0.1, more preferably 1:0.015 to 0.06.

[0082] In one specific embodiment, the average particle size of the titanium-silicon molecular sieve particles is 50–400 nm, preferably 100–300 nm; the BET specific surface area is 300–550 m². 2 / g, preferably 350-500m 2 / g; total pore volume is 0.2–0.4 cm³. 3 / g, preferably 0.25~0.35cm 3 / g;

[0083] In one specific embodiment, the titanium-silicon molecular sieve is selected from one or more of the following molecular sieves: MFI structure, MEL structure, MOR structure, BEA structure, MWW structure, IMF structure, CON structure, TUN structure, FAU structure, and EWT structure. Preferably, it is selected from one or more of the following molecular sieves: MFI structure, BEA structure, CON structure, and EWT structure. Different template agents result in different structures of the synthesized titanium-containing molecular sieves. For example, the titanium-containing molecular sieve is MFI type TS-1, and the template agent is one or more combinations of tetrapropylammonium chloride, tetrapropylammonium bromide, tetrapropylammonium hydroxide, and organic amines; the titanium-containing molecular sieve is MEL type TS-2, and the template agent is one or more combinations of tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium hydroxide, and organic amines.

[0084] In this disclosure, the titanium-silicon molecular sieve can be used directly as a catalyst from raw molecular sieve powder, or it can be used after being shaped, such as by pressing into tablets, by rolling to prepare microspheres or small spheres of catalyst, by extrusion to prepare strip catalyst, by spray drying to prepare spherical catalyst, etc. Alternatively, the titanium-silicon molecular sieve can be used without being shaped, and can be added to the reaction of this disclosure simultaneously or sequentially with other catalysts, co-catalysts, and inert matrix supports.

[0085] According to this disclosure, the catalyst containing titanium-silicon molecular sieves preferably contains 20-100% by weight, more preferably 50-100% by weight, and even more preferably 80-100% by weight. In addition to titanium-silicon molecular sieves as the main catalyst, it may also contain binders, co-catalysts, pore expanders, inert matrix supports, etc., all of which are conventionally selected reagents in the art.

[0086] This disclosure provides a third aspect regarding the application of the titanium-silicon molecular sieve described in the second aspect of this disclosure in organic catalytic reactions.

[0087] In a preferred embodiment, the organocatalytic reaction is the epoxidation of 1-hexene to produce hexane oxide.

[0088] Optionally, the epoxidation of 1-hexene to produce hexane comprises: contacting a catalyst with 1-hexene and hydrogen peroxide to carry out a catalytic oxidation reaction, wherein the catalyst comprises the titanium-silicon molecular sieve;

[0089] Preferably, the conditions for the epoxidation of 1-hexene to produce hexane include: a catalyst to hydrogen peroxide weight ratio of 0.01 to 10:1, preferably 0.02 to 2:1, wherein the weight of the catalyst is based on titanium silicate molecular sieve; and a hydrogen peroxide to 1-hexene molar ratio of 0.5 to 2:1, preferably 1 to 1.2:1.

[0090] Optionally, the reaction temperature is 30–60°C, the reaction pressure is atmospheric pressure, and the reaction time is 1–10 h; preferably, the reaction temperature is 35–50°C, and the reaction time is 2–6 h.

[0091] In one specific embodiment, between reactions, the method further includes adding a solvent to the system, the solvent being a conventional organic solvent, such as acetonitrile, methanol, ethanol, etc.; preferably, the molar ratio of the organic solvent to 1-hexene is 10 to 100:1, more preferably 20 to 50:1.

[0092] The present disclosure is further described in detail below through examples. All raw materials used in the examples are commercially available.

[0093] The UV-Vis diffuse reflectance (UV-vis) spectra of the solid samples synthesized in the examples were measured using a Cary 300 UV spectrophotometer manufactured by Agilent Technologies. The test conditions were: room temperature, normal pressure, and the samples were tested after being compressed into pellets. The scanning range was 190–800 nm.

[0094] The chemical composition of the molecular sieve was determined by XRF analysis.

[0095] The specific surface area of ​​the molecular sieve was measured by nitrogen low-temperature adsorption-desorption method, and the micropore specific surface area was calculated by BET method; the pore volume and pore distribution were determined according to the method described in RIPP 151-90 in "Analytical Methods for Petrochemical Industry" (published by Science Press in September 1990, first edition) compiled by Yang Cuiding et al.

[0096] Unless otherwise specified, all raw materials used in the examples and comparative examples are analytical grade reagents.

[0097] Example 1

[0098] Using pyrrole as a ligand compound, it was mixed uniformly with tetraethyl titanate and dichloromethane to obtain a titanium-containing precursor solution. The molar ratio of tetraethyl titanate, pyrrole, and dichloromethane was 1:3:50. This titanium precursor solution was used as the source for synthesizing titanium. The source for synthesizing titanium and tetraethyl silicate were mixed, and then mixed with an aqueous solution of tetrapropylammonium hydroxide. The molar ratio of silicon source: source for synthesizing titanium: template agent: water was 1:0.04:0.2:30. The temperature was increased by stirring under programmed temperature to obtain a hydrolysate of silicon and titanium. The programmed temperature conditions were: starting from 30°C, the temperature was increased by 10°C every hour until the temperature reached 80°C and hydrolysis was completed for 1 hour. The resulting mixture was hydrothermally crystallized in a reactor. The hydrothermal crystallization conditions were as follows: the temperature was programmed to rise from room temperature to 175°C at a rate of 1°C / min, and then crystallized at a constant temperature under autogenous pressure at 175°C for 75 hours. After crystallization, the solid product was recovered, dried, and calcined to obtain titanium-containing molecular sieves. The drying conditions were drying at 110°C for 5 hours and calcination conditions were calcination at 570°C for 3 hours in an air atmosphere.

[0099] Examples 2-12

[0100] The preparation method described in Example 1 differs from that in Example 1 in that the molecular sieve is prepared according to the types and proportions of raw materials listed in Table 1.

[0101] Example 13

[0102] Using pyrrole as a ligand compound, it was mixed uniformly with tetraethyl titanate and dichloromethane to obtain a titanium-containing precursor solution. The molar ratio of tetraethyl titanate, pyrrole, and dichloromethane was 1:3:50. This titanium precursor solution was used as the source for synthesizing titanium. The source for synthesizing titanium and tetraethyl silicate were mixed, and then mixed with an aqueous solution of tetrapropylammonium hydroxide. The molar ratio of silicon source: source for synthesizing titanium: template agent: water was 1:0.04:0.2:30. The temperature was increased by stirring under programmed temperature to obtain a hydrolysate of silicon and titanium. The programmed temperature conditions were: starting the hydrolysis at 30°C, increasing the temperature by 30°C every hour until the temperature reached 100°C and hydrolysis was completed in 0.5 hours. The resulting mixture was hydrothermally crystallized in a reactor under the following conditions: temperature was increased from room temperature to 130°C at a rate of 0.3°C / min, and crystallized at 130°C under autogenous pressure for 72 hours. After crystallization, the solid product was recovered, dried, and calcined to obtain titanium-containing molecular sieves. The drying conditions were 110°C for 2 hours and the calcination conditions were 650°C for 1 hour in an air atmosphere.

[0103] Comparative Example 14

[0104] Using pyrrole as a ligand compound, it was mixed uniformly with tetraethyl titanate and dichloromethane to obtain a titanium-containing precursor solution. The molar ratio of tetraethyl titanate, pyrrole, and dichloromethane was 1:3:50. This titanium precursor solution was used as the source for synthesizing titanium. The source for synthesizing titanium and tetraethyl silicate were mixed, and then mixed with an aqueous solution of tetrapropylammonium hydroxide. The molar ratio of silicon source: source for synthesizing titanium: template agent: water was 1:0.04:0.2:30. The temperature was programmed and stirred to obtain a hydrolysate of silicon and titanium. The temperature programmed conditions were: starting from 30°C, the temperature was increased by 3°C every 1 hour until the temperature reached 50°C and hydrolysis was completed in 0.3 hours. The resulting mixture was hydrothermally crystallized in a reactor. The hydrothermal crystallization conditions were as follows: the temperature was programmed to rise from room temperature to 90°C at a rate of 3°C / min, and then crystallized at a constant temperature under autogenous pressure at 90°C for 5 hours. After crystallization, the solid product was recovered, dried, and calcined to obtain titanium-containing molecular sieves. The drying conditions were 110°C for 2 hours and calcination conditions were 500°C for 3 hours in an air atmosphere.

[0105] Comparative Example 1

[0106] Using tetrabutyl titanate as the titanium source and tetraethyl silicate as the silicon source, the silicon source and titanium source were mixed and then mixed with an aqueous solution of tetrapropylammonium hydroxide. The ratio of silicon source: titanium source: template agent: water was 1:0.04:0.2:30 (the same ratio as in Example 1). The mixture was heated and stirred to obtain a hydrolysate of silicon and titanium. The remaining steps and process conditions were the same as in Example 1.

[0107] Comparative Example 2

[0108] Using tetrabutyl titanate as the titanium source and tetraethyl silicate as the silicon source, the silicon source and titanium source were mixed and then mixed with an aqueous solution of tetrapropylammonium hydroxide. The ratio of silicon source: titanium source: template agent: water was 1:0.1:0.6:50 (the same ratio as in Example 2). The mixture was heated and stirred to obtain a hydrolysate of silicon and titanium. The remaining steps and process conditions were the same as in Example 2.

[0109] Comparative Example 3

[0110] This comparative example follows the preparation method in Example 1, except that the pyrrole ligand is replaced with N,N-dimethylamide, while the rest of the process is the same as in Example 1, to prepare titanium silicate molecular sieves.

[0111] Table 1

[0112]

[0113]

[0114] The values ​​of X1 (framework titanium content), non-framework titanium content, silicon-titanium molar ratio, and molecular sieve structural characteristic parameters, calculated from the UV-Vis spectra of the molecular sieves prepared according to the above examples, comparative examples, and comparative examples, are listed in Table 2 below.

[0115] Table 2

[0116]

[0117] The XRD patterns of the titanium-silicon molecular sieves prepared in Example 1 and Comparative Examples 1-2 are as follows: Figure 5 As shown in the figure, the titanium-silicon molecular sieves prepared in Example 1 and Comparative Examples 1-2 have an MFI structure.

[0118] The ultraviolet-visible (UV-vis) spectra of the titanium-silicon molecular sieves obtained in Example 1 and Comparative Examples 1-2 are shown below. Figure 1 As shown by curves A, B, and C, from Figure 1 It can be seen that curves B and C have obvious peaks at 330 nm, while the peak of curve A of the titanium-silicon molecular sieve obtained in Example 1 is the least obvious at 330 nm. That is, the content of anatase titanium species in the titanium-silicon molecular sieve prepared in Example 1 is less than that in the titanium-silicon molecular sieves of Comparative Examples 1 and 2.

[0119] Furthermore, peak fitting was performed on curves A to C of the ultraviolet-visible (UV-vis) spectra of the titanium-silicon molecular sieves obtained in Example 1 and Comparative Examples 1-2, and the results are as follows: Figures 2-4 As shown, comparing the three figures reveals that... Figure 2In the peak fitting results of the titanium-silicon molecular sieve of Example 1 shown, the peak area at 330 nm is the smallest, while the peak areas at 210 nm (skeleton-coordinated titanium species) and 270 nm (skeleton-coordinated titanium species) are larger, indicating that the titanium-silicon molecular sieve prepared by the method provided in this disclosure in Example 1 has a higher skeleton titanium content.

[0120] Based on the data in Table 2 above, we can see that:

[0121] Compared with Comparative Examples 1-3, the titanium-silicon molecular sieves in Examples 1-13, which use nitrogen-containing heterocyclic compounds as ligand compounds in the method provided by this disclosure, have a higher content of framework titanium. This shows that the use of nitrogen-containing compounds as ligand compounds in the synthesis of titanium source in this disclosure can effectively inhibit the self-polymerization of titanium salts, thereby minimizing the TiO2 generated by the self-polymerization of titanium source hydrolysis and reducing the generation of non-framework titanium.

[0122] Comparing Example 1 with Example 11, it can be seen that Example 1 uses the specific nitrogen-containing heterocyclic compound provided in this disclosure, and the titanium-silicon molecular sieve prepared in Example 1 has a higher content of framework titanium.

[0123] Comparing Example 1 with Examples 5, 6 and 8, where pyridine, pyrimidine and purine were used as ligand compounds respectively, further inhibited the formation of non-framework titanium and had a better effect on increasing the content of framework titanium;

[0124] Comparing Examples 9-10 with Example 12, the titanium-silicon molecular sieves prepared according to the raw material ratio provided in this disclosure in Examples 9-10 have a higher skeletal titanium content; comparing Example 1 with Examples 9-10, it can be seen that the titanium-silicon molecular sieve prepared according to the optimized raw material molar ratio provided in this disclosure in Example 1 has a higher skeletal titanium content.

[0125] Comparative Example 14 was compared with Example 13, which synthesized titanium-silicon molecular sieves according to the preparation conditions provided in this disclosure. The titanium-silicon molecular sieve obtained in Example 13 had a higher content of framework titanium. Comparative Example 13 was compared with Example 1, which prepared titanium-silicon molecular sieves according to the optimized process conditions provided in this disclosure. The titanium-silicon molecular sieve prepared in Example 1 had a higher content of framework titanium.

[0126] Test Example 1

[0127] This test example is used to illustrate the catalytic oxidation effect of the titanium-silicon molecular sieves prepared in the above examples, comparative examples and comparative examples in the reaction of 1-hexene epoxidation to epoxide.

[0128] The specific evaluation methods include: (1) First reaction experiment: The titanium-silicon molecular sieve, 1-hexene, and 30% (mass fraction) hydrogen peroxide aqueous solution prepared in the examples, comparative examples and comparative examples are put into a round bottom flask, wherein the mass ratio of titanium-containing molecular sieve to hydrogen peroxide (pure substance) is 0.3:1, the molar ratio of hydrogen peroxide (pure substance) to 1-hexene is 1.5:1, methanol is used as solvent, and the molar ratio of methanol to 1-hexene is 20:1. The above mixture is reacted in a water bath at 40°C for 8 hours. After the reaction is completed, samples are taken for analysis.

[0129] (2) Repeated reaction experiment: The titanium silicon molecular sieve was reused in the same way as the first reaction experiment. A total of 10 repeated experiments were conducted, and the product obtained in the 10th experiment was sampled and analyzed.

[0130] The reaction products were analyzed by gas chromatography, and the results were quantified using the external standard method. The chromatographic conditions were as follows: Agilent-6890 chromatograph, HP-5 capillary column, injection volume 0.5 μL, injection port temperature 280℃. Column temperature was maintained at 100℃ for 2 min, then increased to 250℃ at a rate of 15℃ / min and held for 15 min. An FID detector was used, with a detector temperature of 280℃.

[0131] The hydrogen peroxide content was measured by indirect titration with sodium thiosulfate, and the hydrogen peroxide was measured as hydrogen peroxide.

[0132] The following indicators of the titanium-containing molecular sieve evaluation reaction were mainly examined in each embodiment, comparative example, and comparative example:

[0133] 1-Hexene conversion rate (%) = number of moles of 1-hexene consumed in the reaction / number of moles of 1-hexene in the feedstock before the reaction × 100%;

[0134] Selectivity of hexane oxide (%) = number of moles of hexane oxide in the product / number of moles of olefins consumed in the formation of main and by-products × 100%;

[0135] Effective utilization rate of hydrogen peroxide (%) = number of moles of hydrogen peroxide consumed in the formation of organic matter in the product / (number of moles of hydrogen peroxide in the raw material before reaction - number of moles of hydrogen peroxide in the product after reaction) × 100%.

[0136] The test results are listed in Table 3 below.

[0137] Table 3

[0138]

[0139] Based on the data in Table 3 above, it can be seen that:

[0140] Compared with Comparative Examples 1-3, the titanium-silicon molecular sieves prepared in Examples 1-13 using the method provided in this disclosure (using nitrogen-containing heterocyclic compounds as ligand compounds) showed better catalytic performance in the epoxidation of 1-hexene to hexane. For example, in the first and tenth reactions, they showed higher 1-hexene conversion, hexane selectivity, and hydrogen peroxide utilization. Furthermore, the stability of the titanium-silicon molecular sieves after repeated reactions was higher.

[0141] Comparing Example 1 with Example 11, it can be seen that Example 1 uses the specific nitrogen-containing heterocyclic compound provided in this disclosure. The titanium-silicon molecular sieve prepared in Example 1 has higher 1-hexene conversion, hexane selectivity, hydrogen peroxide utilization rate and better catalytic stability for repeated use in the first and tenth reactions.

[0142] Comparing Examples 9-10 with Example 12, the titanium-silicon molecular sieves prepared in Examples 9-10 according to the raw material ratios provided in this disclosure exhibit better catalytic performance and higher catalytic stability in the epoxidation of 1-hexene to hexane oxide reaction. Comparing Example 1 with Examples 9-10, it is evident that the titanium-silicon molecular sieve prepared in Example 1 according to the optimized raw material molar ratios provided in this disclosure exhibits higher 1-hexene conversion, hexane oxide selectivity, and hydrogen peroxide utilization rate in both the first and tenth reactions, demonstrating better catalytic activity.

[0143] Comparing Example 1 with Examples 5, 6 and 8, in which pyridine, pyrimidine and purine were used as ligand compounds respectively, the titanium-silicon molecular sieves prepared in Examples 5, 6 and 8 showed better catalytic effects in the first and tenth reactions.

[0144] Comparing Example 1 with Example 13, Example 1 prepared titanium-silicon molecular sieves according to the optimized process conditions provided in this disclosure. The titanium-silicon molecular sieves prepared in Example 1 have better catalytic effects in the epoxidation of 1-hexene to epoxide.

[0145] Test Examples 2-4

[0146] Test Examples 2-4 illustrate the catalytic performance of titanium-silicon molecular sieves under different reaction conditions. Specifically, they employ a reaction method similar to that in Test Example 1, except that the reaction conditions are adjusted (each reaction is carried out in a single run):

[0147] Test Example 2: Titanium silicate molecular sieve, 1-hexene, and 30% (mass fraction) hydrogen peroxide solution were added to a round-bottom flask. The mass ratio of titanium silicate molecular sieve to hydrogen peroxide (pure substance) was 10:1, and the molar ratio of hydrogen peroxide (pure substance) to 1-hexene was 1.5:1. Methanol was used as the solvent, and the molar ratio of methanol to 1-hexene was 80:1. The mixture was reacted in a water bath at 40°C for 8 hours. After the reaction was completed, samples were taken for analysis.

[0148] Test Example 3: Titanium silicate molecular sieve, 1-hexene, and 30% (mass fraction) hydrogen peroxide solution were added to a round-bottom flask. The mass ratio of titanium silicate molecular sieve to hydrogen peroxide (pure substance) was 0.3:1, and the molar ratio of hydrogen peroxide (pure substance) to 1-hexene was 1.5:1. Methanol was used as the solvent, and the molar ratio of methanol to 1-hexene was 20:1. The mixture was reacted at 30°C and 1 MPa for 0.5 h. The rest of the process was the same as in Test Example 1. After the reaction was completed, samples were taken for analysis.

[0149] Test Example 4: Titanium silicate molecular sieve, 1-hexene, and 30% (mass fraction) hydrogen peroxide solution were added to a round-bottom flask. The mass ratio of titanium silicate molecular sieve to hydrogen peroxide (pure substance) was 0.005:1, and the molar ratio of hydrogen peroxide (pure substance) to 1-hexene was 3:1. Methanol was used as the solvent, and the molar ratio of methanol to 1-hexene was 120:1. The mixture was reacted at 20°C and 2 MPa for 12 hours. The rest of the process was the same as in Test Example 1. After the reaction was completed, samples were taken for analysis.

[0150] The catalysts used in the reaction and the corresponding test results are listed in Table 4 below.

[0151] Table 4

[0152]

[0153] According to the data in Table 4 above:

[0154] Compared with Test Example 4, Test Examples 2-3 were carried out in accordance with the range of raw material addition ratios or reaction conditions provided in this disclosure. Under the same conditions of using titanium-silicon molecular sieves, Test Examples 2-3 showed higher 1-hexene conversion, 1-hexene selectivity, and hydrogen peroxide utilization rate in the reaction of 1-hexene epoxidation to hexane.

[0155] Compared with Test Example 1 (data for Test Example 1 is from Table 3), Test Examples 2-3, under the same conditions of using titanium silicate molecular sieves, showed that Test Example 1, with optimized raw material addition ratio or reaction conditions, achieved higher 1-hexene conversion, hexane selectivity, and hydrogen peroxide utilization rate.

[0156] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0157] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0158] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for preparing titanium-silicon molecular sieves, characterized in that, Includes the following steps: S1. Mix the titanium source, the nitrogen-containing heterocyclic compound, and an optional solvent to obtain the synthetic titanium source; S2. The synthesized titanium source, silicon source and template agent are mixed and subjected to hydrolysis to obtain a hydrolyzed mixture; S3. The hydrolyzed mixture is subjected to hydrothermal crystallization, drying and calcination.

2. The method according to claim 1, characterized in that, The nitrogen-containing heterocyclic compound is selected from one or more nitrogen-containing heterocyclic compounds having 3 to 12 carbon atoms; Preferably, the nitrogen-containing heterocyclic compound is selected from one or more of pyrrole, thiazole, imidazole, pyrazole, pyridine, pyrimidine, quinoline and purine; more preferably, it is selected from one or more of pyridine, pyrimidine and purine.

3. The method according to claim 1, characterized in that, The titanium source is selected from one or more of inorganic titanium sources and organic titanium sources. Optionally, the inorganic titanium source is selected from one or more of titanium tetrafluoride, titanium tetrachloride, titanium tetrabromide, titanium trichloride, and titanium sulfate; the organic titanium source is selected from one or more of tetramethyl titanate, tetraethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate.

4. The method according to claim 1, characterized in that, The silicon source is selected from at least one of silicone grease, solid silica gel, fumed silica, and silica sol; preferably, it is selected from at least one of silicone grease, solid silica gel, and fumed silica. Optionally, the silicone grease is selected from one or more compounds with the structure shown in formula (1): R a R b R c and R d Each is independently selected from alkyl groups having 1 to 4 carbon atoms, wherein the alkyl group is branched or straight-chain alkyl; preferably, the R a R b R c and R d Each of the following is independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl; more preferably, the organosilicon grease is selected from one or more of tetramethyl silicate, tetraethyl silicate, tetrabutyl silicate, and dimethyl diethyl silyl ester; even more preferably, it is selected from one or more of tetramethyl silicate, tetraethyl silicate, and dimethyl diethyl silyl ester.

5. The method according to claim 1, characterized in that, The template agent is selected from one or more of organic quaternary ammonium salts and organic bases; Optionally, the organic quaternary ammonium salt is selected from one or more of tetraethylammonium chloride, tetraethylammonium bromide, tetrapropylammonium chloride, tetrapropylammonium bromide, tetrabutylammonium chloride, and tetrabutylammonium bromide; Optionally, the organic base is selected from one or more of organic quaternary ammonium bases and organic amines; preferably, the organic quaternary ammonium base is selected from one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide; the organic amine is selected from one or more of ethylamine, n-butylamine, butanediamine, hexamethylenediamine, monoethanolamine, diethanolamine, triethanolamine, theanine, toluidine, and p-phenylenediamine. Optionally, the solvent is selected from one or more of polar protic solvents and aprotic solvents; preferably, the polar protic solvent is selected from one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol; the aprotic solvent is selected from one or more of dichloromethane, dichloroethane, allyl chloride, methylchloropropene, 1-chlorobutane, acetonitrile, N,N-dimethylformamide, toluene, acetone, propylene glycol methyl ether and dimethyl sulfoxide.

6. The method according to claim 1, characterized in that, In step S1, the molar ratio of titanium source: nitrogen-containing heterocyclic compound: solvent is 1:(0.5-8):(0-1000), preferably 1:(1-4):(20-50).

7. The method according to claim 1, characterized in that, In step S2, the molar ratio of silicon source: synthetic titanium source: organic base: water is 1:(0.001~0.5):(0.001~0.8):(5~150), preferably 1:(0.01~0.2):(0.01~0.5):(10~50), wherein the silicon source is calculated as SiO2 and the synthetic titanium source is calculated as TiO2.

8. The method according to claim 1, characterized in that, In step S2, the conditions for the hydrolysis treatment include: first heating to 60-100°C at a first heating rate, and then hydrolyzing at a constant temperature for 0.5-10 hours; preferably, first heating to 70-90°C at a first heating rate, and then hydrolyzing at a constant temperature for 1-5 hours. Optionally, the first heating rate is 5 to 30°C / h, preferably 10 to 20°C / h.

9. The method according to claim 1, characterized in that, In step S3, the conditions for the hydrothermal crystallization treatment include: First, the temperature is increased to 100-200°C at a second heating rate, and then crystallized at a constant temperature for 6-120 hours; preferably, the temperature is increased to 140-180°C at a second heating rate, and then crystallized at a constant temperature for 10-100 hours. Optionally, the second heating rate is 0.3 to 1.7 °C / min, preferably 0.5 to 1.4 °C / min.

10. The method according to claim 1, characterized in that, In step S3, the drying conditions include: a drying temperature of 80–120°C and a drying time of 2–30 h; preferably, the drying temperature is 90–110°C and the drying time is 5–10 h. Optionally, the calcination conditions include: a calcination temperature of 450–650°C and a calcination time of 1–10 h; preferably, the calcination temperature is 480–620°C and the calcination time is 2–6 h.

11. The titanium-silicon molecular sieve prepared by the method according to any one of claims 1 to 10.

12. The application of the titanium-silicon molecular sieve as described in claim 11 in organic catalytic reactions.

13. The application according to claim 12, characterized in that, The aforementioned organocatalytic reaction includes the epoxidation of 1-hexene to produce hexane oxide; Optionally, the epoxidation of 1-hexene to produce hexane comprises: contacting a catalyst with 1-hexene and hydrogen peroxide to carry out a catalytic oxidation reaction, wherein the catalyst comprises the titanium-silicon molecular sieve; Preferably, the conditions for the epoxidation of 1-hexene to produce hexane include: a catalyst to hydrogen peroxide weight ratio of 0.01 to 10:1, preferably 0.02 to 2:1, wherein the weight of the catalyst is based on titanium silicate molecular sieves; and a hydrogen peroxide to 1-hexene molar ratio of 0.5 to 2:1, preferably 1 to 1.2:

1. Optionally, the reaction temperature is 30–60°C, the reaction pressure is atmospheric pressure, and the reaction time is 1–10 h; preferably, the reaction temperature is 35–50°C, and the reaction time is 2–6 h.

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