Preparation method of nitrogen-doped tungsten carbide / titanium silicalite molecular sieve catalyst

Abstract

The present invention discloses a preparation method of a nitrogen-doped tungsten carbide / titanium silicate molecular sieve catalyst, comprising the following steps: Step (1): Mix raw materials to form a reaction solution, wherein the raw materials include a Ti-MWW molecular sieve precursor containing a structure-directing agent, tungsten isopropoxide, hydrogen peroxide, and an aqueous acid solution; Step (2): Subject the product obtained after the reaction of the reaction solution obtained in Step (1) to high-temperature heat treatment to obtain a nitrogen-doped tungsten carbide / Ti-MWW molecular sieve catalyst. The nitrogen-doped tungsten carbide / titanium silicate molecular sieve catalyst prepared by the present invention can catalyze the in-situ generation of hydrogen peroxide from hydrogen and oxygen, and then react with ethylene to form ethylene glycol. High ethylene glycol selectivity and yield can be obtained at a mild reaction temperature (60 °C), realizing the efficient and green synthesis of ethylene glycol.

Description

Technical Field

[0001] The present invention relates to the fields of zeolite molecular sieves and industrial catalysis, and particularly relates to a preparation method of a nitrogen-doped tungsten carbide / titanium silicate molecular sieve catalyst. Background Art

[0002] Ethylene glycol is the simplest binary alcohol in chemical structure and is mainly used as a raw material in many fields such as polyester fibers, antifreeze, adhesives, unsaturated resins, and polyurethanes. Among them, 87% of ethylene glycol is used in the polyester industry. In recent years, the booming development of the polyester industry has further driven the market demand for ethylene glycol. In addition, ethylene glycol and its derivatives have also been further promoted and applied in new fields such as hydrogen production, fuel cells, and the controllable synthesis of nanomaterials.

[0003] A catalytic system composed of titanium silicate molecular sieve and hydrogen peroxide can achieve the preparation of ethylene glycol under mild reaction conditions (40 - 60 °C) by integrating ethylene epoxidation and ethylene oxide hydration reactions (Journal of Catalysis, 2018, 358:89). Among them, the Ti-MWW molecular sieve with the MWW topological structure has more excellent catalytic performance than other structural titanium silicate molecular sieves. However, hydrogen peroxide is unstable, and the unreacted hydrogen peroxide is prone to ineffective decomposition, resulting in the problems of low effective utilization rate of hydrogen peroxide and low ethylene glycol yield, which limits the industrial application of the above process. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a nitrogen-doped tungsten carbide / titanium silicate molecular sieve catalyst for the preparation of ethylene glycol. This catalyst overcomes the above-mentioned disadvantages in the prior art, catalyzes the reaction of ethylene with hydrogen and oxygen to produce ethylene glycol, and can obtain high ethylene glycol selectivity and yield at a mild reaction temperature (60 °C), realizing the efficient and green synthesis of ethylene glycol.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is a preparation method of a nitrogen-doped tungsten carbide / titanium silicate molecular sieve catalyst, including the following steps:

[0006] Step (1): Mix the raw materials to form a reaction solution, where the raw materials include a Ti-MWW molecular sieve precursor containing a structure-directing agent, tungsten isopropoxide, hydrogen peroxide, and an acid aqueous solution;

[0007] Step (2): Subject the product obtained after the reaction of the reaction solution obtained in step (1) to high-temperature heat treatment to obtain a nitrogen-doped tungsten carbide / Ti-MWW molecular sieve catalyst.

[0008] In one embodiment of the present invention, the Ti-MWW molecular sieve precursor containing a structure-directing agent in step (1) is a Ti-MWW molecular sieve precursor containing hexamethyleneimine or piperidine, wherein the content of the organic structure-directing agent is 5-10 wt.%, and the content of titanium is 3-5 wt.%.

[0009] In one embodiment of the present invention, the concentration of hydrogen peroxide in step (1) is 10-50 wt.%; the aqueous acid solution is one of nitric acid and hydrochloric acid, and the concentration of the acid in the aqueous acid solution is 0.1-6 M.

[0010] In one embodiment of the present invention, the mass ratio of the Ti-MWW molecular sieve precursor containing a structure-directing agent, tungsten isopropoxide, hydrogen peroxide and the aqueous acid solution in step (1) is 1:0.1:1-5:10-50.

[0011] In one embodiment of the present invention, the reaction conditions in step (2) are to react at 80-140 °C for 0.5-12 hours.

[0012] In one embodiment of the present invention, the high-temperature heat treatment conditions in step (2) are to heat in a hydrogen atmosphere at 600-800 °C for 6-12 hours, and then heat in an air or oxygen atmosphere at 400-600 °C for 2-6 hours.

[0013] The present invention also provides a nitrogen-doped tungsten carbide / titanium-silicon molecular sieve catalyst prepared by the preparation method of the nitrogen-doped tungsten carbide / titanium-silicon molecular sieve catalyst described above.

[0014] In addition, the present invention also provides the application of the described nitrogen-doped tungsten carbide / titanium-silicon molecular sieve catalyst in the preparation of ethylene glycol.

[0015] The present technical solution has the following beneficial effects:

[0016] The nitrogen-doped tungsten carbide / titanium-silicon molecular sieve catalyst provided by the present invention is prepared by mixing and reacting a Ti-MWW molecular sieve precursor containing a structure-directing agent, tungsten isopropoxide, hydrogen peroxide and an aqueous acid solution, and then performing high-temperature heat treatment. In the present invention, under the combined action of the aqueous acid solution and hydrogen peroxide, the structure-directing agent on the Ti-MWW molecular sieve precursor provides a nitrogen source and a carbon source, reacts with tungsten isopropoxide to form a nitrogen-doped tungsten carbide precursor, and then obtains a nitrogen-doped tungsten carbide / titanium-silicon molecular sieve catalyst through high-temperature heat treatment. The nitrogen-doped tungsten carbide / titanium-silicon molecular sieve catalyst can catalyze the in-situ generation of hydrogen peroxide from hydrogen and oxygen, and then react with ethylene to form ethylene glycol. High ethylene glycol selectivity and yield can be obtained at a mild reaction temperature (60 °C), realizing the efficient and green synthesis of ethylene glycol. Description of the Drawings

[0017] Figure 1It is the gas chromatogram of Embodiment 1 of the present invention;

[0018] Figure 2 It is the gas chromatogram of Comparative Example 2 of the present invention. Detailed implementation manners

[0019] The present invention will be further described below in conjunction with the embodiments and the attached Figure 1 and 2 drawings.

[0020] During the process of implementing the present invention, conditions, experimental methods, etc., except for the specifically mentioned content below, are all common knowledge and well-known common sense in the art, and the present invention has no particularly restricted content. All embodiments are operated according to the operation steps of the above technical solutions.

[0021] In the embodiments and comparative examples, the Ti-MWW molecular sieve precursor containing a structure-directing agent was prepared according to the literature method (The Journal of Physical Chemistry B, 2001, 105: 2897).

[0022] Embodiment 1

[0023] (1) A Ti-MWW molecular sieve precursor containing hexamethyleneimine, tungsten isopropoxide, hydrogen peroxide, and an acid aqueous solution are in a weight ratio of 1: 0.1: 3: 20. Among them, the hydrogen peroxide is an aqueous solution of 30 wt.% hydrogen peroxide, and the acid water is 6M nitric acid;

[0024] (2) The reaction solution obtained in step (1) is reacted at 80 °C for 12 hours. After the reaction is completed, the obtained product is subjected to high-temperature heat treatment to obtain a nitrogen-doped tungsten carbide / Ti-MWW molecular sieve catalyst. The high-temperature heat treatment conditions are heating in a hydrogen atmosphere at 600 °C for 12 hours, and then heating in an air atmosphere at 500 °C for 4 hours.

[0025] Embodiment 2

[0026] (1) A Ti-MWW molecular sieve precursor containing piperidine, tungsten isopropoxide, hydrogen peroxide, and an acid aqueous solution are in a weight ratio of 1: 0.1: 4: 50. Among them, the hydrogen peroxide is an aqueous solution of 10 wt.% hydrogen peroxide, and the acid water is 0.1M hydrochloric acid;

[0027] (2) The reaction solution obtained in step (1) is reacted at 100 °C for 6 hours. After the reaction is completed, the obtained product is subjected to high-temperature heat treatment to obtain a nitrogen-doped tungsten carbide / Ti-MWW molecular sieve catalyst. The high-temperature heat treatment conditions are heating in a hydrogen atmosphere at 700 °C for 8 hours, and then heating in an air atmosphere at 400 °C for 6 hours.

[0028] Embodiment 3

[0029] (1) Mix the Ti-MWW molecular sieve precursor containing hexamethyleneimine, tungsten isopropoxide, hydrogen peroxide, and aqueous acid solution at a weight ratio of 1:0.1:5:10. Among them, the hydrogen peroxide is an aqueous solution of 50 wt.% hydrogen peroxide, and the aqueous acid is 2M nitric acid;

[0030] (2) React the reaction solution obtained in step (1) at 140 °C for 0.5 hour. After the reaction, the obtained product is subjected to high-temperature heat treatment to obtain a nitrogen-doped tungsten carbide / Ti-MWW molecular sieve catalyst. The high-temperature heat treatment conditions are heating in a hydrogen atmosphere at 800 °C for 6 hours, and then heating in an air atmosphere at 600 °C for 2 hours.

[0031] Example 4

[0032] (1) Mix the Ti-MWW molecular sieve precursor containing piperidine, tungsten isopropoxide, hydrogen peroxide, and aqueous acid solution at a weight ratio of 1:0.1:3:30. Among them, the hydrogen peroxide is an aqueous solution of 40 wt.% hydrogen peroxide, and the aqueous acid is 2M nitric acid;

[0033] (2) React the reaction solution obtained in step (1) at 80 °C for 12 hours. After the reaction, the obtained product is subjected to high-temperature heat treatment to obtain a nitrogen-doped tungsten carbide / Ti-MWW molecular sieve catalyst. The high-temperature heat treatment conditions are heating in a hydrogen atmosphere at 800 °C for 6 hours, and then heating in an air atmosphere at 500 °C for 6 hours.

[0034] Example 5

[0035] (1) Mix the Ti-MWW molecular sieve precursor containing hexamethyleneimine, tungsten isopropoxide, hydrogen peroxide, and aqueous acid solution at a weight ratio of 1:0.1:4:30. Among them, the hydrogen peroxide is an aqueous solution of 30 wt.% hydrogen peroxide, and the aqueous acid is an aqueous solution of 3M nitric acid;

[0036] (2) React the reaction solution obtained in step (1) at 120 °C for 8 hours. After the reaction, the obtained product is subjected to high-temperature heat treatment to obtain a nitrogen-doped tungsten carbide / Ti-MWW molecular sieve catalyst. The high-temperature heat treatment conditions are heating in a hydrogen atmosphere at 700 °C for 12 hours, and then heating in an oxygen atmosphere at 600 °C for 6 hours.

[0037] Comparative Example 1

[0038] (1) Mix the Ti-MWW molecular sieve precursor containing hexamethyleneimine, hydrogen peroxide, and aqueous acid solution at a weight ratio of 1:3:20. Among them, the hydrogen peroxide is an aqueous solution of 30 wt.% hydrogen peroxide, and the aqueous acid is 6M nitric acid;

[0039] (2) React the reaction solution obtained in step (1) at 80 °C for 12 hours. After the reaction is completed, the obtained product is subjected to high-temperature heat treatment to obtain a Ti-MWW molecular sieve catalyst. The high-temperature heat treatment conditions are heating in a hydrogen atmosphere at 600 °C for 12 hours, and then heating in an air atmosphere at 500 °C for 4 hours.

[0040] Comparative Example 2

[0041] (1) A Ti-MWW molecular sieve precursor containing hexamethyleneimine, tungsten isopropoxide, and an aqueous acid solution are in a weight ratio of 1:0.1:20. Among them, the aqueous acid is 6M nitric acid;

[0042] (2) React the reaction solution obtained in step (1) at 80 °C for 12 hours. After the reaction is completed, the obtained product is subjected to high-temperature heat treatment to obtain a catalyst. The high-temperature heat treatment conditions are heating in a hydrogen atmosphere at 600 °C for 12 hours, and then heating in an air atmosphere at 500 °C for 4 hours.

[0043] All examples and comparative examples are applied to the reaction of ethylene with hydrogen and oxygen to produce ethylene glycol: First, add 0.2 g of the catalyst into a reaction tube with an inner diameter of 8 mm and heat it to 60 °C; then, introduce a mixed gas of ethylene, hydrogen, and oxygen into the reaction tube. Among them, the molar ratio of ethylene, hydrogen, and oxygen is 1:1:1, and the total flow rate is 240 mL / min; finally, the reactants and products are analyzed using on-line gas chromatography (Agilent 8890B, DB-Wax capillary column 30 m × 0.25 mm × 0.25 μm).

[0044] The compositions of the catalysts in the examples and comparative examples are shown in Table 1.

[0045] The reaction results of the catalysts in the examples and comparative examples for the reaction of ethylene with hydrogen and oxygen to produce ethylene glycol are shown in Table 2.

[0046] Figure 1 and Figure 2 are the gas chromatograms of Example 1 and Comparative Example 2 respectively. Ethylene glycol is the only product of Example 1, while Comparative Example 2 mainly has the by-product ethylene oxide.

[0047] Table 1

[0048]

[0049]

[0050] Table 2

[0051]

[0052] Compared with Comparative Examples 1 and 2, in Examples 1-5, the nitrogen-doped tungsten carbide / Ti-MWW molecular sieve catalyst prepared by the present invention was used to catalyze the reaction of ethylene with hydrogen and oxygen to produce ethylene glycol, and high ethylene glycol selectivity and yield could be obtained at a mild reaction temperature (60 °C), realizing the efficient and green synthesis of ethylene glycol.

[0053] The above specific embodiments are only used to explain the present invention, rather than limiting the present invention. Any changes and substitutions made to the present invention without creative labor within the scope of the concept and claims of the present invention fall within the protection scope of the present invention patent.

Claims

1. A preparation method of a nitrogen-doped tungsten carbide / titanium silicalite molecular sieve catalyst, characterized in that, It includes the following steps: Step (1): Mix the raw materials to form a reaction solution. The raw materials include a Ti-MWW zeolite precursor containing a structure-directing agent, tungsten isopropoxide, hydrogen peroxide, and an aqueous acid solution. The structure-directing agent is hexamethyleneimine or piperidine; Step (2): After the reaction of the reaction solution obtained in step (1) is completed, the product is subjected to high-temperature heat treatment to obtain a nitrogen-doped tungsten carbide / Ti-MWW zeolite catalyst. In the Ti-MWW zeolite precursor containing a structure-directing agent in step (1), the content of the structure-directing agent is 5-10 wt.%, and the content of titanium is 3-5 wt.%.

2. The preparation method according to claim 1, characterized in that, The concentration of hydrogen peroxide in step (1) is 10-50 wt.%; the aqueous acid solution is one of nitric acid and hydrochloric acid, and the concentration of the acid in the aqueous acid solution is 0.1-6 M.

3. The preparation method according to claim 1, wherein, The mass ratio of the Ti-MWW zeolite precursor containing a structure-directing agent, tungsten isopropoxide, hydrogen peroxide, and the aqueous acid solution in step (1) is 1:0.1:1-5:10-50.

4. The preparation method according to claim 1, wherein, The reaction conditions in step (2) are to react at 80-140 °C for 0.5-12 hours.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The high-temperature heat treatment conditions in step (2) are to heat in a hydrogen atmosphere at 600-800 °C for 6-12 hours, and then heat in an air or oxygen atmosphere at 400-600 °C for 2-6 hours.

6. The preparation method according to any one of claims 1 to 4, characterized in that, 7. A nitrogen-doped tungsten carbide / titanium silicate zeolite catalyst obtained by the preparation method according to any one of claims 1-6.

8. Use of the nitrogen-doped tungsten carbide / titanium silicate zeolite catalyst according to claim 7 in the preparation of ethylene glycol. ​

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