A supported Cu beta molecular sieve catalyst for isobutene oligomerization reaction and a preparation method thereof

Abstract

The application provides a Cu-loaded beta molecular sieve catalyst for isobutene oligomerization reaction and a preparation method thereof, and belongs to the technical field of isobutene selective oligomerization reaction. 2‑ The characteristic peak of the Cu-loaded beta molecular sieve catalyst at 1386.6 cm ‑1 belongs to the vibration absorption peak of S=O, the beta molecular sieve is a molecular sieve with a 12-membered ring and a three-site cross-pore system, the N2 adsorption-desorption isotherm of the catalyst with different active component loadings is type IV, and the hysteresis loop is type H1; the specific surface area of the Cu-loaded beta molecular sieve catalyst is 341-472 m 2 / g, the pore size is 2.9-3.81 nm, and the pore volume is 0.32-0.34 ml / g. The Cu-loaded beta molecular sieve catalyst utilizes the characteristics of the Beta molecular sieve, i.e. the molecular sieve framework is highly defective and more active compared to other structural molecular sieves, and through loading of metal Cu and the like, the acidity of the surface of the Beta molecular sieve catalyst is regulated, the isobutene conversion rate is improved, and the selectivity of the polymeric product is improved.

Description

[0001] This application is a divisional application based on parent application number 202310779743.2, entitled "A method for preparing trimer products by highly selective oligomerization of isobutylene", filed on June 29, 2023. Technical Field

[0002] This invention relates to the field of selective oligomerization technology of isobutylene, and more specifically to a Cu-supported β-zeolite catalyst for isobutylene oligomerization and its preparation method. Background Technology

[0003] Mixed C4 olefins are a crucial chemical resource, a byproduct of catalytic cracking and steam cracking, containing abundant usable C4 olefins. Catalytic cracking is a pillar industry in my country's petrochemical sector, thus generating substantial amounts of C4 olefins as a byproduct. Currently, my country's main utilization methods for C4 olefins include: using 1,3-butadiene as a raw material to synthesize novel polymer materials; using n-butene as a raw material to produce polyethylene, methyl ethyl ketone, butadiene, and other products; and using isobutene primarily to produce MTBE, isoprene, and for oligomerization to produce polymers.

[0004] Due to increasingly stringent environmental regulations and the automotive industry's requirements for unleaded gasoline, there is an urgent need to improve gasoline composition. Currently, most isobutylene from C4 olefins is used to synthesize methyl tert-butyl ether (MTBE). However, MTBE is highly soluble in groundwater, thus polluting the environment. As society develops and people demand a better environment, the reduction or even ban of MTBE usage is inevitable. This phenomenon will lead to a large surplus of isobutylene, a raw material for MTBE, which bleaks the prospects of the MTBE industry. Therefore, how to utilize C4 olefin resources more environmentally friendly and efficiently, how to convert MTBE plants to produce other chemical products, and the losses caused by the reduction of MTBE are increasingly attracting attention from academia and oil refining companies.

[0005] Selective oligomerization of isobutylene can separate n-butene from a mixture of C4 molecules. The separated n-butene can provide raw materials for companies that require n-butene to produce methyl ethyl ketone, sec-butyl acetate, n-pentanal, etc. The oligomerization reaction of isobutylene can generate C8, C96, and C164 compounds. 12 C 16 etc., including trimer C 12 Isotridecyl alcohol can be synthesized via carbonyl synthesis, and C12 is also an important raw material for the synthesis of neo-acids, which have significant industrial value. Therefore, improving the selectivity of trimer products in the oligomerization reaction of isobutylene has been a long-standing research topic.

[0006] Chinese patent CN106861731A discloses a method for isobutylene oligomerization. The method involves impregnating ferric sulfate and nickel sulfate onto a composite support containing zinc oxide and alumina using an impregnation method. The final catalyst is then obtained through drying and calcination. The composite support contains 80.0-97.0 wt% zinc oxide and alumina, while the active components are 2.0-12.0 wt% ferric sulfate and 1.0-8.0 wt% nickel sulfate. This catalyst exhibits mild reaction conditions, high selectivity for dimer products and low selectivity for trimer products under high conversion conditions, maintaining good catalyst activity.

[0007] Chinese patent application CN113145162A discloses a method for preparing a ZSM-5 molecular sieve catalyst, wherein the metal M is selected from at least one of alkaline earth metals, Zn, Fe, Co, Ni, and rare earth metals; the surface of the Si / M / ZSM-5 molecular sieve is rich in silicon, the molar ratio of SiO2 / Al2O3 in the molecular sieve framework is 10–60, and the molar ratio of SiO2 / Al2O3 on the molecular sieve surface is 70–180; the microporous specific surface area of ​​the ZSM molecular sieve is 200–300 m² / g. 2 ·g -1 The micropore volume is 0.88-1.15 mL·g. -1 The Si / M / ZSM-5 molecular sieve has tunable pores and a silicon-rich surface, which can further improve the selectivity of isobutylene dimerization while maintaining a high isobutylene conversion rate.

[0008] However, in existing literature on the catalytic oligomerization of isobutylene, the selectivity of dimer isobutylene is far greater than that of trimer isobutylene due to defects in the preparation process and structure of conventional catalysts. Therefore, developing a catalyst to improve the conversion rate of isobutylene and the selectivity of trimer is an urgent problem to be solved. Summary of the Invention

[0009] To address the aforementioned problems, this invention provides a Cu-supported β-zeolite catalyst for isobutylene oligomerization and its preparation method. The Cu-supported β-zeolite catalyst utilizes the highly defective and more reactive molecular sieve framework of Beta zeolites compared to other molecular sieve structures. By supporting metals such as Cu, the acidity of the Beta zeolite catalyst surface is controlled, thereby improving isobutylene conversion and the selectivity of polymer products.

[0010] This invention provides a Cu-supported β-zeolite catalyst for isobutylene oligomerization, wherein SO4 is formed in the Cu-supported β-zeolite catalyst. 2- Chelated ligands, the Cu-supported β-zeolite catalyst at 1386.6 cm⁻¹ -1The characteristic peak at the location belongs to the vibrational absorption peak of S=O. The β molecular sieve is a system with a twelve-membered ring and a three-dimensional cross-channel. The N2 adsorption-desorption isotherm of the catalyst with different active component loadings is type IV, and the hysteresis loop is type H1.

[0011] The specific surface area of ​​the Cu-supported β-zeolite catalyst is 341-472 m². 2 / g, pore size is 2.9-3.81 nm, pore volume is 0.32-0.34 ml / g.

[0012] Furthermore, the Cu-supported β-zeolite catalyst has a Cu loading of 2-8 wt%.

[0013] More preferably, the Cu-supported β-zeolite catalyst has a Cu loading of 4-6 wt%.

[0014] The present invention also provides a method for preparing the aforementioned Cu-supported β-zeolite catalyst, the method comprising the following steps:

[0015] Step 1: Calcine the β-molecular sieve at 400-600℃ for 2-6 hours to remove the template agent from the β-molecular sieve;

[0016] Step 2: Acid washing: Prepare a 0.5-2 mol / L sulfuric acid solution, pour the calcined β molecular sieve into the sulfuric acid solution, and wash it for 2-6 hours under magnetic stirring;

[0017] Step 3: Drying and calcination: After soaking, rinse the β molecular sieve with deionized water, then put it into a drying oven and dry it at 100-150℃ for 2-6 hours; then put the acid-washed β molecular sieve into a muffle furnace and calcinate it at 400-600℃ for 2-6 hours.

[0018] Step 4: Impregnation: Take CuSO4•5H2O and put it into a round-bottom flask. Add distilled water dropwise and mix thoroughly to dissolve and obtain an impregnation solution. Add the calcined β molecular sieve from Step 3 to the impregnation solution, mix evenly, and then impregnate by rotary evaporation for 2-6 hours.

[0019] Step 5: Drying and calcination: The β molecular sieve obtained in step 4 is placed in a drying oven and dried at 100-150℃ for 2-6 hours, and then placed in a muffle furnace for calcination at 400-600℃ for 2-6 hours to obtain Cu-supported β molecular sieve catalyst.

[0020] In step 2 of this invention, the purpose of acid washing of the β-zeolite is to remove the L-acid at the Si-OH sites on the surface of the zeolite, thus removing SO42-. 2-The functional group chelate ligands exhibit Brønsted acidity on the surface of molecular sieves, thereby intensifying the polymerization reaction and improving the selectivity of trimer products.

[0021] Further, in step 4, after stirring evenly, the round-bottom flask is fixed on the rotary evaporator, the rotation speed is set to 100 RPM and the temperature is 20℃, and it is rotated for 2 hours; then the rotation speed is set to 150 RPM and the temperature is 90℃, and it is rotary evaporated for 2 hours.

[0022] In step 4 of this invention, the introduction of copper sulfate greatly enhances the acidity of the β molecular sieve, forming Cu-O bonds or Si-O-Cu bonds on the structure of the molecular sieve. The higher the asymmetric stretching motion of the S=O bonds, the higher the acidity of the β molecular sieve catalyst.

[0023] In step 5 of this invention, after drying and heating CuSO4·5H2O at 100-150℃, the four water molecules in the crystal are removed, forming CuSO4·H2O. After further calcination at 400-600℃ (the temperature initially rises to 200℃ and eventually to 400-600℃), CuSO4·xH2O is formed, where x is between 0 and 1. The removal of H2O creates an empty orbital in the 3d orbital of Cu, which can accept a lone pair of electrons; this is the formation process of a Lewis acid. Simultaneously, under the influence of Cu ions, the H2O molecule dissociates into H+. + This is the process of Bronze acid formation. After high-temperature calcination, copper sulfate decomposes on the molecular sieve to form B acid. The introduction of ketone sulfate increases the acidity of the catalyst. The inductive effect of the S=O double bond on Cu ions makes copper sulfate more acidic, which in turn lengthens the polymerization chain and makes it easier to form trimer products.

[0024] The beneficial effects of this invention are as follows:

[0025] (1) The surface of the β-zeolite catalyst has a large amount of L-acid and Brønsted acid, mainly Brønsted acid. Strong acid leaching can effectively remove the L-acid from the surface of the β-zeolite, and SO42- 2- The functional group exists in the form of chelate ligands;

[0026] The introduction of copper sulfate significantly enhances the acidity of the catalyst. Higher asymmetric stretching motion of the S=O bond and the inductive effect of the S=O double bond on Cu ions result in higher acidity of the β-zeolite catalyst. SO42- is generated during the acid leaching process. 2- The combined effect of chelate ligand formation and dehydroxylation on the catalyst surface contributes to Cu 2+ The formation of [a specific type of structure] provides an active center for the isobutylene oligomerization reaction.

[0027] (2) By loading copper sulfate onto β molecular sieve, Cu-O bonds or Si-O-Cu bonds will be formed on the structure of the molecular sieve. The bond length of Cu-O bond is longer than that of Si-O bond, which can also be seen from infrared and BET characterization. Loading Cu will cause the pore size of the molecular sieve to increase. The sites with these bonds represent Brønsted acid sites. Brønsted acid is strong and has strong adsorption. The dimer adsorbed on the molecular sieve is not easy to desorb and continue to polymerize to form trimer. This shows the improved selectivity of trimer products. Attached Figure Description

[0028] Figure 1 The images show the FT-IR characterization of the β-zeolite before and after acid washing in Example 4.

[0029] Figure 2 X-ray diffraction (XRD) characterization for this invention.

[0030] Figure 3 The N2 adsorption-desorption isotherms are for catalysts supported on different active components according to the present invention. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] This invention provides a Cu-supported β-zeolite catalyst for isobutylene oligomerization, in which SO4 is formed. 2- Chelate ligand with a specific surface area of ​​472 m² 2 / g, pore size of 3.81nm, pore volume of 0.32ml / g; Cu-supported β-zeolite catalyst with a Cu loading of 2%.

[0034] The preparation method is as follows:

[0035] Step 1: Take 10 g of β molecular sieve (silicon-to-aluminum ratio of 25, purchased from Nankai University Catalyst Co., Ltd.) and calcine it in a muffle furnace at 400℃ for 2 h to remove the template agent in the β molecular sieve;

[0036] Step 2: Acid washing: Prepare a 0.5 mol / L sulfuric acid solution, take 20 ml of sulfuric acid solution in a beaker, add 10 g of calcined β molecular sieve, and wash for 2 hours with magnetic stirring;

[0037] Step 3: Drying and calcination: After soaking, rinse the β molecular sieve from step 2 with deionized water, and then put it into a drying oven to dry at 100℃ for 2 hours; then put the acid-washed and dried β molecular sieve into a muffle furnace and calcinate at 400℃ for 2 hours.

[0038] Step 4: Impregnation: Accurately weigh 20 ml H2O and 0.828 g CuSO4·5H2O, and add them to a round-bottom flask at the same time. Mix and dissolve them thoroughly to obtain the impregnation solution. Weigh 10 g of the calcined β molecular sieve and slowly add it to the above impregnation solution. Stir for 5 min.

[0039] After stirring evenly, fix the round-bottom flask on the rotary evaporator, set the speed to 100 RPM and the temperature to 20℃, and rotate for 2 hours; then set the speed to 150 RPM and the temperature to 90℃, and rotary evaporate for 2 hours.

[0040] Step 5: The impregnated molecular sieve is placed in a drying oven and dried at 100°C for 2 hours, and then placed in a muffle furnace and calcined at 400°C for 2 hours to obtain a Cu / β molecular sieve catalyst with a Cu loading of 2%.

[0041] Example 2

[0042] This invention provides a Cu-supported β-zeolite catalyst for isobutylene oligomerization, in which SO4 is formed. 2- Chelate ligand with a specific surface area of ​​452 m² 2 / g, pore size of 3.64nm, pore volume of 0.32ml / g; Cu-supported β-zeolite catalyst with a Cu loading of 4%.

[0043] The preparation method is as follows:

[0044] Step 1: Take 10 g of β molecular sieve (silicon-to-aluminum ratio of 25, purchased from Nankai University Catalyst Co., Ltd.) and calcine it in a muffle furnace at 500℃ for 3 h to remove the template agent in the β molecular sieve;

[0045] Step 2: Acid washing: Prepare a 0.5 mol / L sulfuric acid solution, take 20 ml of sulfuric acid solution in a beaker, add 10 g of calcined β molecular sieve, and soak for 3 hours under magnetic stirring;

[0046] Step 3: Drying and calcination: After soaking, rinse the β molecular sieve from step 2 with deionized water, and then put it into a drying oven to dry at 120°C for 3 hours; then put the acid-washed and dried β molecular sieve into a muffle furnace and calcinate it at 500°C for 3 hours.

[0047] Step 4: Impregnation: Accurately weigh 20 ml H2O and 1.749 g CuSO4·5H2O, and add them to a round-bottom flask at the same time. Mix and dissolve them thoroughly to obtain the impregnation solution. Weigh 10 g of the calcined β molecular sieve and slowly add it to the above solution. Stir for 5 min.

[0048] After stirring evenly, fix the round-bottom flask on the rotary evaporator, set the speed to 100 RPM and the temperature to 20℃, and rotate for 2 hours; then set the speed to 150 RPM and the temperature to 90℃, and rotary evaporate for 2 hours.

[0049] Step 5: The impregnated molecular sieve is placed in a drying oven and dried at 120°C for 3 hours, and then placed in a muffle furnace and calcined at 500°C for 3 hours to obtain a Cu / β molecular sieve catalyst with a Cu loading of 4%.

[0050] Example 3

[0051] This invention provides a Cu-supported β-zeolite catalyst for isobutylene oligomerization, in which SO4 is formed. 2- Chelate ligand with a specific surface area of ​​362 m² 2 / g, pore size of 2.97nm, pore volume of 0.33ml / g; Cu-supported β-zeolite catalyst with a Cu loading of 6%.

[0052] The preparation method is as follows:

[0053] Step 1: Take 10 g of β molecular sieve (silicon-to-aluminum ratio of 25, purchased from Nankai University Catalyst Co., Ltd.) and calcine it in a muffle furnace at 550℃ for 3 h to remove the template agent in the β molecular sieve;

[0054] Step 2: Acid washing: Prepare a 0.5 mol / L sulfuric acid solution, take 20 ml of sulfuric acid solution in a beaker, add 10 g of calcined β molecular sieve, and soak for 3 hours under magnetic stirring;

[0055] Step 3: Drying and calcination: After soaking, rinse the β molecular sieve from step 2 with deionized water, and then put it into a drying oven to dry at 120°C for 3 hours; then put the acid-washed and dried β molecular sieve into a muffle furnace and calcinate at 550°C for 3 hours.

[0056] Step 4: Impregnation: Accurately weigh 20 ml H2O and 2.778 g CuSO4·5H2O, and add them to a round-bottom flask at the same time. Mix and dissolve them thoroughly to obtain the impregnation solution. Weigh 10 g of the calcined β molecular sieve and slowly add it to the above solution. Stir for 5 min.

[0057] After stirring evenly, fix the round-bottom flask on the rotary evaporator, set the speed to 100 RPM and the temperature to 20℃, and rotate for 2 hours; then set the speed to 150 RPM and the temperature to 90℃, and rotary evaporate for 2 hours.

[0058] Step 5: The impregnated molecular sieve is placed in a drying oven and dried at 120°C for 3 hours, and then placed in a muffle furnace and calcined at 550°C for 3 hours to obtain a Cu / β molecular sieve catalyst with a Cu loading of 6%.

[0059] Example 4

[0060] This invention provides a Cu-supported β-zeolite catalyst for isobutylene oligomerization, in which SO4 is formed. 2- Chelate ligand with a specific surface area of ​​341 m² 2 / g, pore size of 2.90nm, pore volume of 0.34ml / g; Cu-supported β-zeolite catalyst with a Cu loading of 8%.

[0061] The preparation method is as follows:

[0062] Step 1: Take 10 g of β molecular sieve (silicon-to-aluminum ratio of 25, purchased from Nankai University Catalyst Co., Ltd.) and calcine it in a muffle furnace at 600℃ for 6 h to remove the template agent in the β molecular sieve;

[0063] Step 2: Acid washing: Prepare a 0.5 mol / L sulfuric acid solution, take 20 ml of sulfuric acid solution in a beaker, add 10 g of calcined β molecular sieve, and soak for 6 h under magnetic stirring;

[0064] Step 3: Drying and calcination: After soaking, rinse the β molecular sieve from step 2 with deionized water, and then put it into a drying oven to dry at 150°C for 6 hours; then put the acid-washed and dried β molecular sieve into a muffle furnace and calcinate it at 600°C for 6 hours.

[0065] Step 4: Impregnation: Accurately weigh 20 ml H2O and 3.937 g CuSO4·5H2O, and add them to a round-bottom flask at the same time. Mix and dissolve them thoroughly to obtain the impregnation solution. Weigh 10 g of the calcined β molecular sieve and slowly add it to the above solution. Stir for 5 min.

[0066] After stirring evenly, fix the round-bottom flask on the rotary evaporator, set the speed to 100 RPM and the temperature to 20℃, and rotate for 6 hours; then set the speed to 150 RPM and the temperature to 90℃, and rotary evaporate for 6 hours.

[0067] Step 5: The impregnated molecular sieve is placed in a drying oven and dried at 150°C for 6 hours, and then placed in a muffle furnace and calcined at 600°C for 6 hours to obtain a Cu / β molecular sieve catalyst with a Cu loading of 8%.

[0068] Comparative Example

[0069] The β-molecular sieve is obtained by immersion in sulfuric acid solution, followed by drying and calcination. The preparation method is as follows:

[0070] Step 1: Take 10 g of β molecular sieve (silicon-to-aluminum ratio of 25, purchased from Nankai University Catalyst Co., Ltd.) and calcine it in a muffle furnace at 550℃ for 3 h to remove the template agent in the β molecular sieve;

[0071] Step 2: Acid washing: Prepare a 0.5 mol / L sulfuric acid solution, take 20 ml of sulfuric acid solution in a beaker, add 10 g of calcined β molecular sieve, add a magnetic stir bar, stir and soak for 2 hours;

[0072] Step 3: Drying and calcination: After soaking, rinse the β molecular sieve from step 2 with deionized water, and then put it into a drying oven to dry at 120°C for 3 hours; then put the acid-washed and dried β molecular sieve into a muffle furnace to calcine at 550°C for 3 hours.

[0073] from Figure 1 As can be seen from this, the wavenumber is 1091.3 cm⁻¹. -1 and 1226.6cm -1 The characteristic peak at 1638.2 cm⁻¹ is the absorption peak of the β-zeolite framework. -1 The characteristic peak at 3434.4 cm⁻¹ represents the vibrational absorption peak of Si-O or Al-O in the β-zeolite framework. -1 The characteristic peak at 1386.6 cm⁻¹ represents the vibrational absorption peak of -OH or OH groups on the surface of the β-zeolite. The β-zeolite after acid washing exhibits this absorption at 1386.6 cm⁻¹. -1 The characteristic peak at this location belongs to the vibrational absorption peak of S=O, indicating that sulfuric acid immersion will have a certain impact on the framework structure of β molecular sieve.

[0074] from Figure 2 As can be seen, the prepared catalyst exhibits characteristic diffraction peaks belonging to BETA molecular sieves at 2θ=7.8° and 22.4°, indicating that the catalyst is a BETA molecular sieve. No other obvious characteristic diffraction peaks appear in the figure, indicating that the active metal component is uniformly loaded, well-dispersed, and without metal clusters. After the addition of the active component, the intensities of the two characteristic diffraction peaks of the BETA molecular sieve decreased, indicating that the addition of the active component affects the lattice strength of the BETA molecular sieve.

[0075] from Figure 3As can be seen, the N2 adsorption-desorption isotherms of catalysts with different active component loadings are of type IV, and the hysteresis loop is of type H1, indicating that the catalysts have an ordered mesoporous structure.

[0076] Table 1 Pore structure parameters of catalysts with different active component loadings

[0077]

[0078] As shown in Table 1, the pore structure parameters of catalysts supported on different active components change with increasing active component loading; the specific surface area and pore size gradually decrease, while the pore volume gradually increases. This indicates that no metal clusters are formed on the catalyst surface, suggesting good dispersion of the supported active components.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. The application of a Cu-supported β-zeolite catalyst in the oligomerization reaction of isobutylene, characterized in that, SO4 is formed in the Cu-supported β-zeolite catalyst. 2- Chelated ligands, the Cu-supported β-zeolite catalyst at 1386.6 cm⁻¹ -1 The characteristic peak at the location belongs to the vibrational absorption peak of S=O. The β molecular sieve is a system with a twelve-membered ring and a three-dimensional cross-channel. The N2 adsorption-desorption isotherm of the catalyst with different active component loadings is type IV, and the hysteresis loop is type H1. The specific surface area of ​​the Cu-supported β-zeolite catalyst is 341-472 m². 2 / g, pore size of 2.9-3.81 nm, pore volume of 0.32-0.34 ml / g; The preparation method of the Cu-supported β-zeolite catalyst includes the following steps: Step 1: Calcine the β-molecular sieve at 400-600℃ for 2-6 hours to remove the template agent from the β-molecular sieve; Step 2: Acid washing: Prepare a 0.5-2 mol / L sulfuric acid solution, pour the calcined β molecular sieve into the sulfuric acid solution, and wash it for 2-6 hours under magnetic stirring; Step 3: Drying and calcination: After soaking, rinse the β molecular sieve with deionized water, then put it into a drying oven and dry it at 100-150℃ for 2-6 hours; then put the acid-washed β molecular sieve into a muffle furnace and calcinate it at 400-600℃ for 2-6 hours. Step 4: Impregnation: Take CuSO4•5H2O and put it into a round-bottom flask. Add distilled water dropwise and mix thoroughly to dissolve and obtain an impregnation solution. Add the calcined β molecular sieve from Step 3 to the impregnation solution, mix evenly, and then impregnate by rotary evaporation for 2-6 hours. Step 5: Drying and calcination: The β molecular sieve obtained in step 4 is placed in a drying oven and dried at 100-150℃ for 2-6 hours, and then placed in a muffle furnace for calcination at 400-600℃ for 2-6 hours to obtain Cu-supported β molecular sieve catalyst.

2. The application according to claim 1, characterized in that, The Cu loading is 2-8 wt%.

3. The application according to claim 1 or 2, characterized in that, The Cu loading is 4-6 wt%.

4. The application according to claim 3, characterized in that, In step 4, after stirring evenly, the round-bottom flask is fixed on a rotary evaporator, the rotation speed is set to 100 RPM and the temperature is 20℃, and the evaporation time is 2 hours; then the rotation speed is set to 150 RPM and the temperature is 90℃, and the evaporation time is 2 hours.

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