CN110787818B

CN110787818B - Propylene epoxidation catalyst, preparation method and application thereof

Info

Publication number: CN110787818B
Application number: CN201910837541.2A
Authority: CN
Inventors: 苏暐光; 王文鑫; 杨梁锋; 宋旭东; 白永辉; 王焦飞; 于广锁
Original assignee: Ningxia University
Current assignee: Ningxia University
Priority date: 2019-09-05
Filing date: 2019-09-05
Publication date: 2022-04-15
Anticipated expiration: 2039-09-05
Also published as: CN110787818A

Abstract

The invention belongs to the technical field of heterogeneous catalysis, and particularly relates to a propylene epoxidation catalyst, and a preparation method and application thereof, wherein the method comprises the following steps: (1) mixing a copper precursor and a CNT carrier, dissolving in a solvent, and stirring and dispersing to obtain a carrier dispersion liquid; dissolving a precipitant in a solvent, mixing the obtained precipitant solution with the carrier dispersion liquid, and performing precipitation reaction to obtain a CuO/CNT catalyst; (2) the CuO/CNT catalyst is contacted with absolute ethyl alcohol for reaction to prepare CuO after ethanol treatment_xa/CNT catalyst; (3) mixing CuO_xImpregnation of/CNT catalyst in Na₂CO₃In the water solution, the propylene epoxidation catalyst is prepared. The catalyst prepared by the method contains Cu with small particle size⁺The species can be used as an active center of propylene epoxidation reaction, so that the propylene epoxidation activity is obviously improved, the selectivity of propylene oxide is greatly increased, and the generation of propylene oxide is facilitated.

Description

Propylene epoxidation catalyst, preparation method and application thereof

Technical Field

The invention belongs to the technical field of heterogeneous catalysis, and particularly relates to a propylene epoxidation catalyst, and a preparation method and application thereof.

Background

Propylene oxide is also called methyl ethylene oxide or propylene oxide (PO for short), is a third class of propylene derivatives except acrylonitrile and polypropylene, and is also an important basic chemical synthesis raw material in organic chemical production; it can be used to synthesize propylene glycol ether, propylene glycol, polyether polyol, etc. and used to produce emulsifier, non-ionic surfactant, fire retardant, plasticizer, etc.

The industrial production method of Propylene Oxide (PO) mainly comprises the following steps: chlorohydrin processes, co-oxidation processes, and direct oxidation of hydrogen peroxide processes. The chlorohydrin method has the defects of high chlorine consumption, serious equipment corrosion, serious environmental pollution and the like. The co-oxidation method has the defects of long process, large investment, many co-products and the like. The direct hydrogen peroxide oxidation method has great industrialization potential due to the characteristics of low energy consumption and little pollution, but the cost of the hydrogen peroxide is higher.

At present, the direct epoxidation reaction of propylene and oxygen is used in the experimental stage, and the production method is expected to be thick. The main reason is that the oxygen source is wide, the environment is not harmed and clean, and the price is low. The atom utilization of the reactants in the direct epoxidation of propylene with oxygen, which can reach 100%, is considered to be the most ideal and economical process route for producing propylene oxide.

The WangYe discovers halogen-free K⁺Modified CuO_xCatalyst and application in the epoxidation of propylene. Modifier K⁺When not added, the oxidation product is predominantly acrolein; cuo prepared by sol-gel process_xThe catalyst adopts a modifier K⁺After modification, propylene oxide becomes the main reaction product, K⁺Can change the reaction pathway of propylene oxidation (Journal of Catalysis,2006,241(1): 225-. Zhu et al found K prepared by a sol-gel method⁺Modification ofCuO of (2)_x-SiO₂The catalyst is effective for propylene oxygen epoxidation reactions. The catalyst does not need pre-reduction, and the selectivity of Propylene Oxide (PO) can reach 78% under the oxygen-rich condition. The authors believe that the Cu (I) species formed during the reaction are the active center, K, of the oxygen epoxidation of propylene⁺Interaction with Cu species can disperse Cu species, contributing to improved PO selectivity (Journal of Physical Chemistry C,2008,112(20): 7731-.

Su et al have studied Cu/SiO₂Catalyzing propylene oxygen to directly perform epoxidation reaction, and performing N on the catalyst before reaction₂Or H₂Pretreatment, acrolein was found to be the major oxidation product in both cases. The catalyst is modified by different modifiers, and the selectivity of propylene oxide is obviously improved after KAc is added, and the generation rate of the propylene oxide can reach 2.5 mmol-g^-1·h^-1. Researches the catalytic activity of different modifiers on the direct epoxidation reaction of propylene and oxygen, and the obtained epoxidation activity of propylene is ranked as KAc>NaAc>NaCl>KCl. Infrared spectrum shows Cu⁰And Cu⁺Can activate the carbon-carbon double bond in propylene (Journal of Catalysis,2009,268(1): 165-174).

Yang et al conducted propylene epoxidation studies on V modified unsupported Cu catalysts and found that the addition of V increased the dispersion of Cu particles and resulted in Cu particles²⁺To Cu⁺The transformation occurs, and in-situ XRD tests show that part of Cu is in the propylene epoxidation process²⁺Conversion to Cu⁺，H₂TPR indicates that the V species is reduced to a lower valence, VO, during the epoxidation of propylene_xThe formation of species in lower valence state inhibits the reactivity of lattice oxygen and favors the formation of propylene oxide (Journal of Catalysis,2010,276(1): 76-84).

He et al studied Cs⁺Modified CuO_x/SiO₂Propylene epoxidation performance of (1), Cs was found⁺Is CuO_x/SiO₂Most effective modifier in the catalyst, Cs⁺And CuO_xThere is a strong interaction between them. Modifier Cs⁺Acidity of the added catalystThe activity of lattice oxygen is reduced, the reaction proceeds toward the direction favorable for the production of propylene oxide, and the selectivity of propylene oxide is improved (Journal of Catalysis,2013,299(2): 53-66).

In conclusion, some achievements are obtained in the epoxidation reaction of propylene on the Cu-based catalyst at present, and researchers compare different oxidation states of Cu to find that the low-valence state of Cu is more favorable for the generation of propylene oxide. However, in general, the selectivity to propylene oxide over Cu-based catalysts is still relatively low, mainly Cu-based catalysts in O₂In the presence of oxygen, it is readily oxidized to a higher valence state, so it is important to effectively maintain the low valence state of the Cu species. In addition, as the reaction temperature increases, Cu species may grow and accumulate, resulting in a decrease in the epoxidation activity of the Cu-based catalyst.

The Carbon Nano Tube (CNT) material has a unique hollow structure, a larger specific surface area and an obvious in-tube confinement effect, is moderate in reducibility, controllable in tube diameter and length-diameter ratio, high in conductivity and good in chemical stability, and becomes a hotspot in various research fields at present. How to prepare small-particle-size and low-valence Cu species by using the carbon nano tube as a carrier and keep the Cu species stable in the reaction process is the key for realizing the propylene epoxidation reaction.

Disclosure of Invention

The invention aims to provide a propylene epoxidation catalyst, a preparation method and application thereof, aiming at the problems of the existing propylene epoxidation catalyst; the propylene epoxidation catalyst prepared by the method contains proper content of small-particle-size Cu⁺The species can be used as an active center of epoxidation reaction, so that the epoxidation activity of propylene is obviously improved, the selectivity of propylene oxide is greatly increased, and the generation of propylene oxide is facilitated.

In order to achieve the above purpose, the invention provides the following technical scheme:

in one aspect of the present invention, there is provided a method for preparing a propylene epoxidation catalyst, comprising the steps of:

(1) preparation of CuO/CNT catalyst by deposition precipitation: mixing a precursor compound of copper and a CNT carrier, dissolving the mixture in a solvent, and stirring and dispersing to obtain a carrier dispersion liquid; dissolving a precipitant in a solvent and mixing the resulting precipitant solution with the carrier dispersion (e.g., and slowly dropping the resulting precipitant solution into the carrier dispersion), to prepare a CuO/CNT catalyst through a precipitation reaction;

(2) anhydrous ethanol heat treatment CuO/CNT catalyst: the CuO/CNT catalyst is contacted with absolute ethyl alcohol for reaction to prepare CuO treated by ethyl alcohol_xa/CNT catalyst; wherein the reaction temperature is 130-160 ℃ (for example, 135 ℃, 140 ℃, 145 ℃, 150 ℃, 155 ℃), preferably 145-155 ℃, and the reaction time is 3-48h (for example, 8h, 11h, 15h, 20h, 25h, 30h, 40h, 45h), preferably 10-20 h;

(3) preparation of Na by wet impregnation method₂CO₃Modified CuO_xCNT catalyst: the resulting CuO_xImpregnation of/CNT catalyst in Na₂CO₃In aqueous solution, the chemical composition of Na is prepared₂CO₃-CuO_xA catalyst for epoxidation of propene with CNT.

According to the preparation method of the propylene epoxidation catalyst provided by the invention, preferably, the Na₂CO₃-CuO_xIn the propylene epoxidation catalyst of the/CNT, the value of x is 0.54-0.68, and CuO_xCu contained in₂The average particle diameter of O is 4 to 9nm (e.g., 5nm, 8nm, 9 nm). For example, x is 0.54, 0.55, 0.57, 0.63, 0.68. The Na is₂CO₃-CuO_xCopper oxide CuO in propylene epoxidation catalyst for/CNT_xComprises CuO and Cu₂And O. Where x may reflect Cu in the copper oxide of the propylene epoxidation catalyst₂Mole fraction n of O_Cu2O. The larger x, the larger n_Cu2OThe smaller; the specific calculation formula is that x is 1/(n)_Cu2O+1). In the propylene epoxidation catalyst, a certain content of Cu is required⁺Species, while small particle size Cu⁺The species can promote the generation of propylene oxide and can be used as an active center of the propylene oxygen epoxidation reaction.

The Carbon Nano Tube (CNT) material has a unique hollow structure, a larger specific surface area, good conductivity and obvious in-tube confinement effect, can effectively disperse Cu species when being used as a catalyst carrier, partially limits the aggregation of the Cu species, and is beneficial to charge transfer between the Cu species and the CNT; in addition, the CNT has certain reducibility and can partially inhibit the Cu species from being oxidized. These factors may contribute to the epoxidation of propylene and the formation of propylene oxide.

According to the preparation method provided by the present invention, in some examples, in the step (1), the CNTs are selected from SWCNTs (single-walled carbon nanotubes) and/or MWCNTs (multi-walled carbon nanotubes), preferably MWCNTs. In some preferred embodiments, the MWCNTs have a tube diameter of 6 to 10nm and a tube length of 0.2 to 10 μm.

In some examples, the precipitating agent is selected from urea, NH₃·H₂One or more of O and an alkali metal carbonate; preferably urea. The alkali metal carbonate may be selected from sodium carbonate and potassium carbonate, for example.

In some examples, the copper precursor compound is selected from one or more of copper nitrate, copper acetate, copper chloride and copper sulfate, preferably copper nitrate and/or copper acetate; for example, Cu (NO)₃)₂·3H₂O。

In some examples, the solvent is selected from one or more of water, ethanol, isopropanol, ethylene glycol, and acetone, preferably water.

In some examples, the concentration of the copper precursor compound solution may be in the range of 0.01mol/L to 0.15mol/L (0.02mol/L, 0.05mol/L, 0.1mol/L, 0.12mol/L) and the concentration of the precipitant solution may be in the range of 0.05mol/L to 0.5mol/L (0.08mol/L, 0.1mol/L, 0.2mol/L, 0.4 mol/L).

In some examples, the amount of the solvent used in step (1) (which refers to the total amount of the solvent used for preparing the copper precursor solution and the precipitant solution) may be 50mL to 300mL (e.g., 80mL, 100mL, 150mL, 200mL, 250mL), and preferably 100mL to 200 mL.

Preferably, in the step (1), the mass percentage of CuO is 2 to 18 wt% (e.g., 3 wt%, 5 wt%, 8 wt%, 10 wt%, 15 wt%), more preferably 6 to 12 wt%, based on 100 wt% of the total mass of the CuO/CNT catalyst; the relation of the dosage of CNT and the precursor of copper as the reaction raw material can be obtained by taking the mass percentage content of CuO in the CuO/CNT catalyst as the calculation standard.

Preferably, the molar ratio of the precipitant to copper in the copper precursor compound is in the range of 3 to 20 (e.g., 5, 7, 10, 15, 18), more preferably 8 to 12.

The "precipitation method" used in step (1) is well known to those skilled in the art and will not be described herein. For example, a copper precursor and a precipitant are respectively and completely dissolved in a solvent, then a CNT carrier is added to the copper precursor solution and stirred and dispersed, ultrasonic stirring can be performed for 0.5 to 5 hours at room temperature to 50 ℃, and the obtained precipitant solution is slowly added dropwise to the carrier dispersion solution to perform a precipitation reaction. In some examples, the process conditions of the precipitation reaction include: the reaction temperature is 60-120 deg.C (e.g., 70 deg.C, 80 deg.C, 85 deg.C, 90 deg.C, 95 deg.C, 100 deg.C, 110 deg.C), preferably 80-100 deg.C; the reaction time is 5 to 50 hours (e.g., 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, 40 hours, 45 hours), preferably 20 to 28 hours.

In some examples, step (1) further comprises: after the reaction system is cooled to room temperature, the obtained reaction crude product is filtered, washed to be neutral and dried. The washing (the washing agent used in the washing process can be one or more selected from water, ethanol and acetone, and is preferably water) and the filtration are all conventional operations in the field. The process conditions of the drying treatment comprise: vacuum drying and/or drying under normal pressure, preferably vacuum drying; the drying temperature is 50-120 deg.C (e.g., 60 deg.C, 70 deg.C, 85 deg.C, 90 deg.C, 95 deg.C, 100 deg.C, 110 deg.C), preferably 80-100 deg.C, and the drying time is 5-24h (e.g., 10.5h, 11h, 11.5h), preferably 10-12 h.

For example, in the step (1), a precursor compound of copper and a precipitant are dissolved in a solvent to prepare a precursor compound solution of copper and a precipitant solution; then adding a CNT carrier into the copper precursor compound solution, stirring and dispersing to obtain carrier dispersion liquid; slowly dripping the precipitant solution into the carrier dispersion liquid, carrying out precipitation reaction at the temperature of 80-110 ℃ for 20-24h, and cooling to room temperature; and filtering, washing to neutrality and drying the obtained reaction product to obtain the CuO/CNT catalyst.

According to the preparation method provided by the present invention, preferably, in the step (2), the mass ratio of the absolute ethanol to the CuO/CNT catalyst is 30 to 400 (e.g., 40, 60, 80, 100, 150, 300, 350), and more preferably 60 to 200.

After the CuO/CNT catalyst obtained in the step (1) is contacted with absolute ethyl alcohol, ultrasonic stirring can be carried out for 0.5-3h at the room temperature (for example, 25 ℃) to 50 ℃ for dispersion. In the heat treatment using anhydrous ethanol as a solvent, the reaction mixture may be heated to a desired reaction temperature, for example, at a temperature rise rate of 0.5 to 10 ℃/min, preferably 1 to 5 ℃/min. The crude reaction product after the heat treatment of the absolute ethyl alcohol solvent can be subjected to post-treatment. In some examples, step (2) further comprises: after the CuO/CNT catalyst reacts with absolute ethyl alcohol, evaporating a reaction system to dryness, and drying the obtained reaction product; the drying process conditions include: vacuum drying and/or drying under normal pressure, preferably vacuum drying; the drying temperature is 50-120 deg.C (e.g., 60 deg.C, 70 deg.C, 85 deg.C, 90 deg.C, 95 deg.C, 110 deg.C), preferably 80-100 deg.C, and the drying time is 5-24h (e.g., 8h, 11h, 15h, 18h, 20h), preferably 10-12 h.

CuO/CNT catalyst is subjected to anhydrous ethanol heat treatment to obtain CuO_xCuO in/CNT catalyst_xThe mass fraction of (A) is 2-18%, preferably 6-12%; cu in copper oxide₂The mole fraction of O is 30-70%. CuO (copper oxide)_xWhen the/CNT catalyst is used in propylene epoxidation reaction, the selectivity of propylene oxide can be obviously improved. Particularly, when the heat treatment temperature of the absolute ethyl alcohol is 150 ℃, the effect of improving the propylene epoxidation activity of the catalyst is most remarkable.

According to the preparation method provided by the invention, preferably, in the step (3), Na⁺With said CuO_xThe molar ratio of Cu in the/CNT catalyst is 0.1 to 1.2 (e.g., 0.2, 0.4, 0.6, 0.9, 1.0), preferably 0.4 to 0.8.

In some examples, Na₂CO₃The molar concentration of the aqueous solution may be 0.005mol/L to 0.2mol/L (e.g., 0.008mol/L, 0.01mol/L, 0.02mol/L, 0.05mol/L, 0.1mol/L, 0.15mol/L), preferably 0.01mol/L to 0.04 mol/L.

The "wet impregnation method" used in step (3) is well known to those skilled in the art and will not be described herein. In some examples, in step (3), the process conditions of the impregnation include: stirring is carried out at room temperature (e.g., 25 ℃) to 50 ℃ for 0.5 to 6 hours (e.g., 1 hour, 2 hours, 3.5 hours, 4 hours, 4.5 hours), preferably 3 to 5 hours, and then constant temperature is carried out at 50 to 90 ℃ (e.g., 60 ℃, 70 ℃, 80 ℃) for 1 to 10 hours (e.g., 2 hours, 4 hours, 6 hours, 8 hours).

The reaction product after wet impregnation may be subjected to a post-treatment. In some examples, step (3) further comprises: evaporating the reaction system to dryness, and drying the obtained reaction product; the drying process conditions include: vacuum drying and/or drying under normal pressure, preferably vacuum drying; the drying temperature is 50-120 deg.C (e.g., 60 deg.C, 70 deg.C, 85 deg.C, 90 deg.C, 95 deg.C, 110 deg.C), preferably 80-100 deg.C, and the drying time is 5-24h (e.g., 8h, 11h, 15h, 18h, 20h), preferably 10-12 h.

For example, the resulting CuO_xImpregnation of/CNT catalyst in Na₂CO₃Stirring in water solution at room temperature (e.g. 25 deg.C) for 3-5 hr, maintaining at 50-90 deg.C for 1-10 hr, evaporating the reaction system, and vacuum drying the reaction product. Grinding the obtained reaction product to obtain a black chemical composition of Na₂CO₃-CuO_xA catalyst for epoxidation of propene with CNT.

CuO obtained after absolute ethanol treatment_xModified agent Na of/CNT catalyst₂CO₃After modification, when the obtained propylene epoxidation catalyst is used for propylene epoxidation reaction, the selectivity of propylene oxide is further increased.

Applicants have found that no report of CuO/CNT catalysts as propylene epoxidation catalysts is found. In addition, after the CuO/CNT catalyst is subjected to heat treatment by the absolute ethyl alcohol solvent, a part of CuO is converted into Cu₂O, indicates the presence of Cu⁺And forming species. And, via Na₂CO₃After modification, Cu⁺The content of species is further increased. Small particle size (e.g., 4-9nm) Cu⁺The species is favorable for the generation of propylene oxide and can be used as an active center for the epoxidation reaction of propylene and oxygen.

According to the preparation method provided by the invention, in some examples, the chemical composition of the propylene epoxidation catalyst has a general formula of Na₂CO₃-CuO_x/CNT, wherein CuO, an active component, is present in an amount of 100 wt% based on the total mass of the propylene epoxidation catalyst_xIs 1 to 15 wt% (e.g., 2 wt%, 3 wt%, 8 wt%, 9 wt%, 12 wt%), preferably 5 to 10 wt%; the carrier CNT is present in an amount of 73 to 98.8 wt% (e.g., 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, 98 wt%), and Na as an auxiliary agent₂CO₃Is contained in an amount of 0.2 to 12 wt% (e.g., 0.5 wt%, 0.8 wt%, 1 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%), preferably 1.5 to 5.5 wt%.

In another aspect of the present invention, there is provided a propylene epoxidation catalyst prepared by the above preparation method, wherein the chemical composition of the propylene epoxidation catalyst has a general formula of Na₂CO₃-CuO_x/CNT, wherein CuO, an active component, is present in an amount of 100 wt% based on the total mass of the propylene epoxidation catalyst_xIs 1 to 15 wt% (e.g., 2 wt%, 3 wt%, 8 wt%, 9 wt%, 12 wt%), preferably 5 to 10 wt%; the carrier CNT is present in an amount of 73 to 98.8 wt% (e.g., 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, 98 wt%), and Na as an auxiliary agent₂CO₃Is contained in an amount of 0.2 to 12 wt% (e.g., 0.5 wt%, 0.8 wt%, 1 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%), preferably 1.5 to 5.5 wt%.

In still another aspect of the present invention, there is provided a propylene epoxidation catalyst prepared by the above-mentioned preparation method or the use of the propylene epoxidation catalyst as described above in the epoxidation reaction of propylene with oxygen.

The propylene epoxidation catalyst of the present invention requires pretreatment before application in the epoxidation of propylene and oxygen. The pretreatment process is understood by those skilled in the art, for example, the propylene epoxidation catalyst is placed in a quartz tube reactor and N is passed into the reactor before the reaction₂(40mL/min) and pre-treated at 300 ℃ -500 ℃ for 1-5 h. After the pretreatment process, the temperature in the quartz tube reactor is reduced to the temperature range required by the propylene epoxidation reaction, and then propylene epoxidation is carried outAnd (4) carrying out a reaction.

Propylene and oxygen epoxidation reactions are understood by those skilled in the art. In some examples, the process for the epoxidation of propylene and oxygen comprises:

the activity evaluation of the catalytic epoxidation reaction of propylene was carried out on a fixed bed reactor, and a sample of the catalyst was packed in a quartz tube having an inner diameter of 6mm and a length of 450 mm.

The reaction temperature is 140-: volume ratio C₃H₆:O₂:N₂1:1:8 (total volume flow of inlet gas is 50mL/min), and the mass space velocity is 30000-90000 mL-g^-1·h^-1Preferably 60000mL · g^-1·h^-1. Performing real-time detection by gas chromatograph equipped with dual-channel detector for reaction products, separating propylene from organic products such as acetaldehyde, propylene oxide, propionaldehyde, acetone and acrolein by KB-Wax (50m × 0.32mm × 0.33 μm) capillary chromatographic column, and detecting by FID detector; propylene and CO₂The separation was carried out by Porapak-Q packed column chromatography and detected by TCD detector. C₃H₆The conversion of (a) and the selectivity to product propylene oxide are calculated from the carbon balance method.

For example, the oxidant used for the gas phase epoxidation of propylene may be molecular oxygen and/or air.

For example, the pressure of the propylene gas phase epoxidation reaction is 0.1-0.3MPa, and the reaction temperature is 140-300 ℃.

Compared with the prior art, the technical scheme of the invention has the following beneficial effects:

in the method, the step of heat treatment by the absolute ethyl alcohol solvent is beneficial to Cu in the catalyst⁺Speciation, in turn, increases propylene conversion and propylene oxide selectivity in propylene epoxidation catalysis. XRD characterization shows that after the CuO/CNT catalyst is subjected to heat treatment by using an absolute ethyl alcohol solvent, a part of CuO is converted into Cu₂O, indicates that there is Cu⁺And forming species. Cu⁺The species favors the production of propylene oxide, and the conversion rate of propylene and the selectivity of propylene oxide are obviously higher than those before the treatment.

CuO obtained after absolute ethyl alcohol treatment_xModified agent Na of/CNT catalyst₂CO₃After modification, the conversion rate of propylene and the selectivity of propylene oxide are further increased compared with those before the modification treatment. Through Na₂CO₃After modification of (2), Cu in the resulting catalyst⁺The content of species was further increased, but Na was excessive₂CO₃The treatment will result in Cu⁺The species aggregate to grow. Small particle size Cu⁺The species may be the active site of the epoxidation reaction of propylene with oxygen, favoring the production of propylene oxide. Thus, in propylene epoxidation catalysts, Cu⁺Species content and Cu⁺The species average grain diameter is influenced mutually only when certain Cu is satisfied⁺Species content and small average particle size are ensured at the same time, so that the epoxidation reaction of propylene can be facilitated.

In a preferred embodiment, both the conversion of propylene and the selectivity to propylene oxide are good when the reaction temperature for the epoxidation of propylene is 240 ℃.

Drawings

FIG. 1 is an XRD spectrum of a sample of the propylene epoxidation catalyst obtained in preparation example 1 and comparative example 6 (the samples are designated as Cat 1 and D-Cat 6).

Detailed Description

In order that the technical features and contents of the present invention can be understood in detail, preferred embodiments of the present invention will be described in more detail below. While the preferred embodiments of the present invention have been described in the examples, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein.

< sources of raw materials >

Multi-walled carbon nanotubes (MWCNTs), a Chinese academy of sciences, organic chemistry, Inc., with a mass fraction of 95% or more;

Cu(NO₃)₂·3H₂o, Xuzhou tianhong chemical Co., Ltd, analytically pure;

urea, chemical reagents of national drug group, ltd, analytically pure;

absolute ethyl alcohol, Tianjin, Daimao chemical reagent factory, analytically pure;

Na₂CO₃shanghai Guanuo chemical science and technology, Inc., analytically pure;

NaCl, Shanghai Guanuo chemical science and technology, pure by analysis;

propylene, Xian vitrification instrument Co., Ltd, the mass fraction is more than or equal to 99.5 percent;

oxygen, Yinchuan Qinhong gas, etc., the mass fraction is more than or equal to 99.999 percent;

nitrogen, Yinchuan Qinhong gas, etc. with the mass fraction more than or equal to 99.999 percent.

< test methods >

(1) An XRD spectrogram: the copper target K α radiation was used as a radiation source using a Bruker D8 Advance X-ray diffractometer in germany. The test voltage is 40KV, the current is 40mA, the angle scanning range is 3-80 degrees, the frequency scanning is 6 degrees/min, and the step length is 0.02 degree.

(2)Cu₂Calculation of average particle diameter of O: estimation of Cu by XRD spectra according to the Scherrer equation₂Average particle size of O. Calculating the formula: d is K lambda/(beta cos theta), D represents Cu₂Average particle diameter of O, K is Scherrer constant 0.89, lambda is X-ray wavelength, 0.154056nm, beta is Cu₂The full width at half maximum of the diffraction peak of the O (111) crystal face is in radian unit, and theta is Cu₂The diffraction angle of the O (111) plane was 36.4 degrees, unit angle.

Catalyst preparation example 1:

(1) preparation of CuO/MWCNTs catalyst by deposition precipitation method

2g of MWCNTs and 0.6g of Cu (NO) were weighed₃)₂·3H₂O, adding 50mL of deionized water into the mixture, stirring the mixture in a beaker at 25 ℃ for 30min to completely dissolve the mixture, and performing ultrasonic treatment for 30min to obtain a carrier dispersion liquid; then, 10mL of an aqueous solution containing 1.66g of urea was added dropwise to the obtained carrier dispersion, and the resulting suspension in the beaker was transferred to a round-bottom flask; and then transferring the round-bottom flask into an oil bath, carrying out precipitation reaction at 90 ℃ for 24h, stopping heating, cooling the reaction solution in the flask to room temperature of 25 ℃, washing with deionized water, filtering for 4 times until the reaction solution is neutral, and drying in vacuum at 80 ℃ for 12h to obtain the CuO/MWCNTs catalyst with the mass of 2.2g and the mass fraction of CuO of 9%, and collecting for later use.

(2) CuO/MWCNTs catalyst for anhydrous ethanol heat treatment

Weighing 0.5g of the CuO/MWCNTs catalyst prepared in the step (1) into a beaker, adding 60mL of absolute ethyl alcohol into the beaker, and stirring for 30min at 25 ℃ for dispersing; transferring the suspension obtained in the beaker into a hydrothermal kettle with polytetrafluoroethylene as an inner lining, heating to 150 ℃ at the heating rate of 1 ℃/min, and keeping for 12 hours for reaction; cooling the reaction solution in the reaction kettle to room temperature, evaporating to dryness in a constant-temperature water bath at 80 ℃, and vacuum drying the evaporated product at 80 ℃ for 12h to prepare CuO treated by ethanol_xMWCNTs catalyst (labeled CuO)_x/MWCNTs-CH₃CH₂OH)0.5g, among others, of CuO_x9% by mass of the copper oxide (CuO)_x) Middle Cu₂The molar percentage of O is 45%. And collecting the sample for later use.

(3) Preparation of Na by wet impregnation method₂CO₃Modified CuO_xMWCNTs catalyst

CuO prepared in the step (2)_xMWCNTs catalyst (labeled CuO)_x/MWCNTs-CH₃CH₂OH) sample 0.5g was poured into 10mL of Na₂CO₃In aqueous solution (Na)₂CO₃The molar concentration of the aqueous solution is 0.02mol/L, Na₂CO₃The mass of (1) is 0.021g), stirring for 3h at room temperature and 25 ℃; na (Na)⁺With CuO_xThe molar ratio of Cu in the MWCNTs catalyst is 0.7. Then evaporating the reaction solution to dryness in a constant-temperature water bath at 80 ℃, and vacuum-drying the evaporated product at 80 ℃ for 12h to obtain a chemical composition Na₂CO₃-CuO_xA propylene epoxidation catalyst of MWCNTs, sample labeled Cat 1.

Chemical composition of Na₂CO₃-CuO_xIn the catalyst of MWCNTs, x is 0.57 and CuO_xCu contained in₂The average particle diameter of O was 5 nm.

The active component CuO is calculated by taking the total mass of the propylene epoxidation catalyst as 100 weight percent_xIs 8.7% (wherein, Cu in the copper oxide₂75% by mol of O), content of MWCNTs as a carrier87.1 percent of the additive Na₂CO₃The content of (B) was 4.2%.

Catalyst preparation example 2:

production procedure of propylene epoxidation catalyst referring to production example 1, except that in the anhydrous ethanol hydrothermal treatment of step (2), the reaction temperature was changed from 150 ℃ to 130 ℃. To obtain a chemical composition of Na₂CO₃-CuO_xA propylene epoxidation catalyst of MWCNTs, sample labeled Cat 2.

Chemical composition of Na₂CO₃-CuO_xIn the catalyst of MWCNTs, x is 0.68, and CuO_xCu contained in₂The average particle diameter of O was 4.5 nm.

The active component CuO is calculated by taking the total mass of the propylene epoxidation catalyst as 100 weight percent_xContent of (2) 8.7% (wherein, Cu in copper oxide₂The mol percentage content of O is 47%), the content of carrier MWCNTs is 87.1%, and auxiliary agent Na₂CO₃The content of (B) was 4.2%.

Catalyst preparation example 3:

production procedure of propylene epoxidation catalyst referring to production example 1, except that in the anhydrous ethanol hydrothermal treatment of step (2), the reaction temperature was changed from 150 ℃ to 160 ℃. To obtain a chemical composition of Na₂CO₃-CuO_xA propylene epoxidation catalyst of MWCNTs, sample labeled Cat 3.

Chemical composition of Na₂CO₃-CuO_xIn the catalyst of MWCNTs, x is 0.54 and CuO_xCu contained in₂The average particle diameter of O was 8 nm.

The active component CuO is calculated by taking the total mass of the propylene epoxidation catalyst as 100 weight percent_xContent of (2) 8.7% (wherein, Cu in copper oxide₂85 percent of O in mol percent), 87.1 percent of carrier MWCNTs in mol percent, and Na as an auxiliary agent₂CO₃The content of (B) was 4.2%.

Catalyst preparation example 4:

production procedure of propylene epoxidation catalyst referring to production example 1, except that Na in step (3)₂CO₃In the modification, Na⁺With CuO_xThe molar ratio of Cu in the MWCNTs catalyst is 0.4. To obtain a chemical composition of Na₂CO₃-CuO_xA propylene epoxidation catalyst of MWCNTs, sample labeled Cat 4.

Chemical composition of Na₂CO₃-CuO_xIn the catalyst of MWCNTs, x is 0.63 and CuO_xCu contained in₂The average particle diameter of O was 4.8 nm.

Based on the total mass of the propylene epoxidation catalyst, an active component CuO_xContent of (C) 8.8% (wherein, Cu in copper oxide₂The mol percentage content of O is 59 percent), the content of carrier MWCNTs is 88.2 percent, and auxiliary agent Na₂CO₃The content of (B) is 3.0%.

Catalyst preparation example 5:

production procedure of propylene epoxidation catalyst referring to production example 1, except that Na in step (3)₂CO₃In the modification, Na⁺With CuO_xThe molar ratio of Cu in the MWCNTs catalyst is 1.2. To obtain a chemical composition of Na₂CO₃-CuO_xA propylene epoxidation catalyst of MWCNTs, sample labeled Cat 5.

Chemical composition of Na₂CO₃-CuO_xIn the catalyst of MWCNTs, x is 0.55 and CuO_xCu contained in₂The average particle diameter of O was 9 nm.

Based on the total mass of the propylene epoxidation catalyst, an active component CuO_xContent of (C) 8.4% (wherein, Cu in copper oxide₂The mol percentage content of O is 82 percent), the content of carrier MWCNTs is 84.9 percent, and auxiliary agent Na₂CO₃The content of (B) was 6.7%.

Catalyst comparative example 1:

production procedure of propylene epoxidation catalyst referring to production example 1, except that the CuO/MWCNTs catalyst obtained in step (1) was not subjected to the anhydrous ethanol solvent heat treatment, but was directly subjected to Na in step (3)₂CO₃And (5) modification treatment. To obtain a chemical composition of Na₂CO₃-CuO_xPropylene epoxidation catalyst of MWCNTsReagent, sample label D-Cat 1.

Chemical composition of Na₂CO₃-CuO_xIn the catalyst of MWCNTs, x is 0.77 and CuO_xCu contained in₂The average particle diameter of O was 4 nm.

Based on the total mass of the propylene epoxidation catalyst, an active component CuO_xContent of (2) 8.7% (wherein, Cu in copper oxide₂The mol percentage content of O is 30 percent), the content of carrier MWCNTs is 87.1 percent, and auxiliary agent Na₂CO₃The content of (B) was 4.2%.

Catalyst comparative example 2:

preparation procedure of a propylene epoxidation catalyst referring to preparation example 1, except that in step (2), anhydrous ethanol was replaced with acetone for solvothermal treatment, a sample of the catalyst prepared in this procedure was designated CuO/MWCNTs-CH₃COCH₃. Then carrying out modification treatment in the step (3) to obtain a chemical composition Na₂CO₃-CuO_xThe propylene epoxidation catalyst of MWCNTs, sample label D-Cat 2.

Chemical composition of Na₂CO₃-CuO_xIn the catalyst of MWCNTs, x is 0.73 and CuO_xCu contained in₂The average particle diameter of O was 10 nm.

Based on the total mass of the propylene epoxidation catalyst, an active component CuO_xContent of (2) 8.7% (wherein, Cu in copper oxide₂The mol percentage content of O is 37 percent), the content of carrier MWCNTs is 87.1 percent, and the auxiliary agent Na₂CO₃The content of (B) was 4.2%.

Catalyst comparative example 3:

preparation procedure of a propylene epoxidation catalyst referring to preparation example 1, except that in step (2), anhydrous ethanol was replaced with water to conduct solvothermal treatment, a sample of the catalyst prepared in this step was designated CuO/MWCNTs-H₂And O. Then carrying out modification treatment in the step (3) to obtain a chemical composition Na₂CO₃-CuO_xThe propylene epoxidation catalyst of MWCNTs, sample label D-Cat 3.

Chemical composition of Na₂CO₃-CuO_xIn the catalyst of MWCNTs, x is 0.71 and CuO_xCu contained in₂The average particle diameter of O was 9.5 nm.

Based on the total mass of the propylene epoxidation catalyst, an active component CuO_xContent of (2) 8.7% (wherein, Cu in copper oxide₂The mol percentage content of O is 41 percent), the content of carrier MWCNTs is 87.1 percent, and auxiliary agent Na₂CO₃The content of (B) was 4.2%.

Catalyst comparative example 4:

production procedure of propylene epoxidation catalyst referring to production example 1, except that in the anhydrous ethanol solvothermal treatment in step (2), the reaction temperature was changed from 150 ℃ to 120 ℃, and then the modification treatment in step (3) was carried out to obtain a catalyst having a chemical composition of Na₂CO₃-CuO_xThe propylene epoxidation catalyst of MWCNTs, sample label D-Cat 4.

Chemical composition of Na₂CO₃-CuO_xIn the catalyst of MWCNTs, x is 0.72 and CuO_xCu contained in₂The average particle diameter of O was 4.3 nm.

The active component CuO is calculated by taking the total mass of the propylene epoxidation catalyst as 100 weight percent_xContent of (2) 8.7% (wherein, Cu in copper oxide₂39 percent of O in mol percent), 87.1 percent of carrier MWCNTs in mol percent, and Na as an auxiliary agent₂CO₃The content of (B) was 4.2%.

Catalyst comparative example 5:

production procedure of propylene epoxidation catalyst referring to production example 1, except that in the anhydrous ethanol solvothermal treatment in step (2), the reaction temperature was changed from 150 ℃ to 180 ℃, and then the modification treatment in step (3) was carried out to obtain a catalyst having a chemical composition of Na₂CO₃-CuO_xThe propylene epoxidation catalyst of MWCNTs, sample labeled D-Cat 5.

Chemical composition of Na₂CO₃-CuO_xIn the catalyst of MWCNTs, x is 0.51 and CuO_xCu contained in₂The average particle diameter of O was 12 nm.

Epoxidation with propeneThe total mass of the catalyst is 100 wt%, and the active component is CuO_xContent of (2) 8.7% (wherein, Cu in copper oxide₂96 percent of O in mol percent), 87.1 percent of carrier MWCNTs in mol percent, and Na as an auxiliary agent₂CO₃The content of (B) was 4.2%.

Catalyst comparative example 6:

production procedure of propylene epoxidation catalyst referring to production example 1, except that in the modification of the modifier in step (3), Na is added₂CO₃The aqueous solution was replaced with aqueous NaCl. Finally obtaining NaCl-CuO with chemical composition_xThe propylene epoxidation catalyst of MWCNTs, sample label D-Cat 6.

The chemical composition is NaCl-CuO_xIn the catalyst of MWCNTs, x is 0.56 and CuO_xCu contained in₂The average particle diameter of O was 15 nm.

Based on the total mass of the propylene epoxidation catalyst, an active component CuO_xContent of (2) 8.7% (wherein, Cu in copper oxide₂The mol percentage content of O is 78%), the content of carrier MWCNTs is 86.9%, and the content of auxiliary agent NaCl is 4.4%.

The detection results of the catalyst samples obtained in the respective preparation examples and comparative examples are as follows:

1. FIG. 1 is an XRD spectrum of a sample of the catalyst (samples are designated Cat 1 and D-Cat 6) obtained in preparation example 1 and comparative example 6. As can be seen from fig. 1, the characteristic diffraction peaks at 2 θ equal to 26 ° and 43.1 ° for each sample correspond to the (002) and (100) crystal planes of MWCNTs, respectively.

The Cat 1 sample has diffraction peaks of CuO at 2 theta equal to 35.4 degrees and 38.6 degrees, and the diffraction peaks respectively correspond to (002) and (111) crystal faces of the CuO; in addition, the sample showed Cu at 2 θ equal to 36.4 °, 42.3 °, 61.3 °₂Diffraction peaks of O corresponding to Cu₂And (111), (200) and (220) crystal planes of O. Illustrating the heat treatment with the absolute ethanol solvent and Na₂CO₃After modification, a large part of CuO species in CuO/MWCNTs is converted into Cu₂O。

When NaCl modifier is used, the diffraction peak of CuO in the catalyst sample (D-Cat 6) is obviously weakened, and Cu₂The O diffraction peak is obviously enhanced, which shows that a large part of CuO is coveredReduction to Cu₂O but Cu₂The peak shape of the O diffraction peak is sharp, the half-peak width is narrow, and Cu is shown₂The particle size of O is large.

Evaluation of propylene epoxidation activity of catalyst sample:

evaluation of propylene epoxidation activity of the catalyst samples was carried out on a fixed bed reactor, and each of the propylene epoxidation catalyst samples prepared in the above preparation examples and comparative examples was packed in a quartz tube having an inner diameter of 6mm and a length of 450 mm.

0.05g of the propylene epoxidation catalyst prepared in each of the above preparation examples and comparative examples was placed in a quartz tube reactor, and N was introduced before the reaction₂(40mL/min) and pre-treating for 1h at 300 ℃, then cooling to the reaction temperature of 140 ℃, and introducing reaction raw material gas to carry out propylene epoxidation reaction.

The reaction temperature of propylene epoxidation is 140 ℃ and 300 ℃, the reaction pressure is 0.1-0.3MPa, and the volume ratio of the components of the reaction gas is C₃H₆:O₂:N₂The mass space velocity is 60000mL g for mixed gas with the ratio of 1:1:8 (total volume flow of inlet gas is 50mL/min)^-1·h^-1. Performing real-time detection on the reaction products by a gas chromatograph equipped with a dual-channel detector, separating propylene from organic products such as acetaldehyde, propylene oxide, propionaldehyde, acetone and acrolein by a KB-Wax (50m × 0.32mm × 0.33 μm) capillary chromatographic column, and detecting by an FID detector; propylene and CO₂The separation was carried out by Porapak-Q packed column chromatography and detected by TCD detector. C₃H₆The conversion of (a) and the selectivity to product propylene oxide are calculated from the carbon balance method.

C₃H₆The conversion of (2) is the number of moles of propylene decreased before and after the reaction/the number of moles of propylene before the reaction × 100%.

The selectivity for propylene oxide is defined as the moles of propylene oxide formed per mole of propylene reduced before and after the reaction × 100%.

The results of the tests performed on each catalyst sample for propylene epoxidation are shown in table 1:

TABLE 1 comparative results of propylene epoxidation activity of catalyst samples

Table 1 shows the comparative results of the propylene epoxidation activities of the propylene epoxidation catalyst samples obtained in the respective preparation examples and comparative examples. As can be seen from the table, the solvent heat treatment and Na treatment were carried out with anhydrous ethanol at 160 ℃ of 130-₂CO₃When the modified catalyst samples (Cat 1 to Cat5) were used in the propylene epoxidation test, the conversion of propylene and the selectivity to Propylene Oxide (PO) were significantly higher than the catalyst samples (D-Cat 1 to D-Cat5) obtained in each comparative example. Further, the data of the examples show that the optimum solvothermal temperature is 150 ℃ and Na⁺The optimum molar ratio to Cu was 0.7(Cat 1).

When the absolute ethyl alcohol solvent thermal temperature is 120 ℃ (D-Cat 4), Cu is generated due to lower temperature⁺The species content is low, which is not beneficial to epoxidation reaction; when the ethanol solvothermal temperature was 180 ℃ (D-Cat5), although Cu⁺Species content increased, but Cu⁺The particle size of the species becomes large, which is also not beneficial to the generation of propylene oxide; and then Na is removed₂CO₃The D-Cat 6 sample and the D-Cat5 sample obtained after the aqueous solution was replaced with the NaCl aqueous solution were similar in case. When the catalyst sample obtained after the treatment of water (D-Cat 3) and acetone (D-Cat 2) in the step (2) is used for the test of propylene epoxidation, compared with the catalyst (Cat 1) subjected to the solvent heat treatment of absolute ethyl alcohol at 150 ℃, the propylene epoxidation activity is obviously reduced, the selectivity of propylene oxide is reduced to below 20 percent from 30 percent, and the conversion rate of propylene is also reduced mainly because Cu is subjected to the heat treatment of water and acetone⁺The content of species is low, so when the CuO/MWCNTs are subjected to solvent heat treatment, absolute ethyl alcohol is preferred.

XRD characterization can find that the Na is added after the heat treatment of the absolute ethyl alcohol solvent₂CO₃Can synergistically promote Cu²⁺Reduction to Cu⁺Species, but excessive solvothermal temperature or Na₂CO₃Too large a content results in the aggregation of Cu species, such that Cu⁺The particle size of the species is increased, which is not beneficial to the epoxidation reaction of propylene. Therefore, by controlling the processes of the step (2) and the step (3), the proper content of Cu is realized⁺Speciation and control of small particle size Cu⁺Species are key factors in increasing propylene conversion and propylene oxide selectivity.

Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A preparation method of a propylene epoxidation catalyst is characterized by comprising the following steps:

(1) preparation of CuO/CNT catalyst by deposition precipitation: mixing a precursor compound of copper and a CNT carrier, dissolving the mixture in a solvent, and stirring and dispersing to obtain a carrier dispersion liquid; dissolving a precipitant in a solvent, mixing the obtained precipitant solution with the carrier dispersion liquid, and performing precipitation reaction to obtain a CuO/CNT catalyst;

(2) anhydrous ethanol heat treatment CuO/CNT catalyst: the CuO/CNT catalyst is contacted with absolute ethyl alcohol for reaction to prepare CuO treated by ethyl alcohol_xa/CNT catalyst; wherein the reaction temperature is 130-160 ℃, and the reaction time is 3-48 h;

(3) preparation of Na by wet impregnation method₂CO₃Modified CuO_xCNT catalyst: the resulting CuO_xImpregnation of/CNT catalyst in Na₂CO₃In aqueous solution, the chemical composition of Na is prepared₂CO₃-CuO_xA CNT-based propylene epoxidation catalyst; na (Na)⁺With said CuO_xThe mol ratio of Cu ions in the/CNT catalyst is 0.1-1.2;

the Na is₂CO₃-CuO_xIn the propylene epoxidation catalyst of the/CNT, the value of x is 0.54-0.68, and CuO_xCu contained in₂O has an average particle diameter of 4-9nm。

2. The method as claimed in claim 1, wherein the reaction temperature in step (2) is 145-155 ℃ and the reaction time is 10-20 h.

3. The production method according to claim 1, wherein, in the step (1),

the CNTs are selected from SWCNTs and/or MWCNTs;

the precipitant is selected from urea and NH₃·H₂One or more of O and an alkali metal carbonate; and/or

The precursor compound of copper is selected from one or more of copper nitrate, copper acetate, copper chloride and copper sulfate; and/or

The solvent is selected from one or more of water, ethanol, isopropanol, ethylene glycol and acetone.

4. The production method according to claim 3, wherein, in the step (1),

the precursor compound of the copper is copper nitrate and/or copper acetate; and/or

The solvent is water.

5. The method according to claim 1, wherein in the step (1), the CuO is contained in an amount of 2 to 18 wt% based on 100 wt% of the total mass of the CuO/CNT catalyst;

the molar ratio of the precipitant to copper in the copper precursor compound is 3-20.

6. The method according to claim 5, wherein in the step (1), the CuO is contained in an amount of 6 to 12 wt% based on 100 wt% of the total mass of the CuO/CNT catalyst;

the molar ratio of the precipitant to the copper in the copper precursor compound is 8-12.

7. The method according to claim 1, wherein in step (1), the process conditions of the precipitation reaction include: the reaction temperature is 60-120 ℃; the reaction time is 5-50 h;

the step (1) further comprises: cooling the reaction system to room temperature, filtering, washing to neutrality and drying the obtained reaction crude product; the process conditions of the drying treatment comprise: vacuum drying and/or normal pressure drying; the drying temperature is 50-120 ℃, and the drying time is 5-24 h.

8. The method according to claim 7, wherein in the step (1), the process conditions of the precipitation reaction include: the reaction temperature is 80-100 ℃; the reaction time is 20-28 h;

the process conditions of the drying treatment comprise: vacuum drying; the drying temperature is 80-100 deg.C, and the drying time is 10-12 h.

9. The preparation method according to claim 1, wherein the mass ratio of the absolute ethanol to the CuO/CNT catalyst in the step (2) is 30 to 400.

10. The preparation method according to claim 9, wherein the mass ratio of the absolute ethanol to the CuO/CNT catalyst in the step (2) is 60 to 200.

11. The method of claim 1, wherein step (2) further comprises: evaporating the reaction system to dryness, and drying the obtained reaction product; the drying process conditions include: vacuum drying and/or normal pressure drying; the drying temperature is 50-120 ℃, and the drying time is 5-24 h.

12. The method of claim 11, wherein the drying process conditions include: vacuum drying; the drying temperature is 80-100 deg.C, and the drying time is 10-12 h.

13. The method according to claim 1, wherein in the step (3), Na is added⁺With said CuO_xThe molar ratio of Cu ions in the/CNT catalyst is 0.4-0.8.

14. The method according to claim 1, wherein in the step (3), the impregnation process conditions include: stirring at room temperature to 50 deg.C for 0.5-6h, and keeping the temperature at 50-90 deg.C for 1-10 h;

the step (3) further comprises the following steps: evaporating the reaction system to dryness, and drying the obtained reaction product; the drying process conditions include: vacuum drying and/or normal pressure drying; the drying temperature is 50-120 ℃, and the drying time is 5-24 h.

15. The method according to claim 14, wherein in the step (3), the drying process conditions include: vacuum drying; the drying temperature is 80-100 deg.C, and the drying time is 10-12 h.

16. The propylene epoxidation catalyst obtained by the production method according to any one of claims 1 to 15, wherein the chemical composition of the propylene epoxidation catalyst has a general formula of Na₂CO₃-CuO_x/CNT, wherein the active component CuO is based on the total mass of the propylene epoxidation catalyst_xThe content of (A) is 1-15 wt%; the content of the carrier CNT is 73-98.8 wt%, and the auxiliary agent Na₂CO₃The content of (B) is 0.2-12 wt%.

17. The propylene epoxidation catalyst of claim 16, wherein said propylene epoxidation catalyst has a chemical composition of the general formula Na₂CO₃-CuO_x/CNT, wherein the active component CuO is based on the total mass of the propylene epoxidation catalyst_xThe content of (A) is 5-10 wt%, and the auxiliary agent Na₂CO₃The content of (B) is 1.5-5.5 wt%.

18. Use of a propylene epoxidation catalyst prepared by the preparation process according to any one of claims 1 to 15 or the propylene epoxidation catalyst according to any one of claims 16 to 17 in the epoxidation of propylene with oxygen.