Preparation method and application of solid alkali KF / gamma-Al2O3 catalyst

Abstract

The invention relates to a preparation method and application of a solid alkali KF / gamma-Al2O3 catalyst. The method comprises the following steps: adsorbing KF on a gamma-Al2O3 carrier through an impregnation method, and roasting to obtain the solid alkali KF / gamma-Al2O3 catalyst, the catalyst is used for catalytic synthesis of oxo-bis-(N-methylphthalimide), and the yield is high. The method is simple in process and low in cost, the catalyst can be recycled only by washing and drying, and the catalytic yield is still stabilized at 80% after repeated tests.

Description

Technical Field

[0001] The invention relates to the field of catalytic technology, and in particular to a preparation method using a solid base KF / γ-Al2O3 catalyst and its application in the synthesis of oxybis-(N-methylphthalamide) (BPI). Background Art

[0002] Oxybis-(N-methylphthalamide) (BPI) is a key intermediate for the synthesis of 3,3',4,4'-diphenyl ether dianhydride (ODPA) and is widely used in the manufacture of polymer materials for polyimide (PI). PI is widely used in high-end manufacturing fields such as aerospace, electronics and electrical appliances due to its excellent heat resistance, mechanical properties and chemical stability. A mixed liquid alkali metal system is commonly used in the synthesis of BPI, which has certain limitations. The post-treatment steps include hydrolysis, acidification, recrystallization purification and dehydration, which are not only complicated to operate, but may also affect the purity and color of BPI, and ultimately affect the overall quality of PI materials. In addition, the waste acid and wastewater generated during the post-treatment process is also an environmental issue that cannot be ignored. Therefore, it is particularly important to select a suitable catalytic system to improve the purity of BPI, achieve green and environmentally friendly sustainable development, and ensure the supply of PI materials.

[0003] Solid base KF / γ-Al2O3 catalyst, as an innovative supported heterogeneous catalytic strategy, not only retains the activity of traditional alkali metal systems, but also provides operational convenience. It is gradually becoming an ideal substitute for liquid alkali metal systems in chemical industry production.

[0004] In existing research, patent CN112707879A prepared a solid base KF / Al2O3 catalyst to synthesize BPI. The preparation method of the catalyst includes: first preparing an aqueous solution of KF, mixing Al2O3 with ethanol, dripping the KF aqueous solution under ultrasonic stirring, and obtaining the solid base KF / Al2O3 catalyst after aging, solvent removal, drying and calcination. However, the synthesis path of the catalyst is complicated, and its appearance and active center at different calcination temperatures have not been studied in depth, resulting in a decrease in catalytic activity in the reaction. Two stages are required, and the yields of the two stages are 45.0-55.0% and 30.0-40.0%, respectively. The total yield of the final two stages is 80.0-85.0%. The reaction has to be designed as two stages to overcome the challenge of selectivity, but unfortunately, the yields of the two stages are not ideal, which also shows that the process conditions have not been fully optimized. The lack of fine control of key parameters such as temperature, solvent dosage, catalyst preparation and dosage makes the overall reaction efficiency low and cannot meet the needs of large-scale production. In addition, the reuse and purification of the catalyst may be a challenge. Although the catalyst in the above patent can be regenerated, it needs to be heated and refluxed in ethanol for 8.0 hours, filtered and dried before regeneration, which makes it difficult to maintain the activity of the catalyst continuously, increases production costs and may introduce other impurities, thereby affecting the final quality of the product. In order to improve production efficiency and product quality, it is necessary to control these key parameters more accurately and explore more effective catalyst regeneration methods.

[0005] Therefore, developing a solid base catalyst with simple process, low cost, high yield, stable structure and easy recycling and reuse for application in the synthesis of BPI has significant practical significance and huge economic value. Summary of the invention

[0006] The present invention aims to solve the limitations of the existing solid base KF / Al2O3 catalyst in the selectivity, stability and recycling and reuse of synthesizing BPI, and provides a preparation method and application of a solid base KF / γ-Al2O3 catalyst. The method is to adsorb KF on a γ-Al2O3 carrier by an impregnation method, and obtain a solid base KF / γ-Al2O3 catalyst by roasting. The catalyst exhibits a relatively regular porous structure at this temperature. The process of the present invention is simple, the cost is low, and the yield of BPI is high; when the catalyst is recycled and reused, it only needs to be washed and dried. After repeated tests, the catalytic yield is still stable at 80%.

[0007] The technical solution of the present invention is: A method for preparing a solid base KF / γ-Al2O3 catalyst, the method comprising the following steps: Potassium fluoride is dissolved in deionized water to form a KF solution, and then a γ-Al2O3 carrier is added thereto, and magnetic stirring is performed at room temperature for 20.0-40.0 minutes, and ultrasonication is performed for 1.0-10.0 minutes; the adsorbed mixture is dried at 80.0-130.0°C for 9.0-11.0 hours, and the dried substance is calcined at a temperature range of 300-500°C for 3.0-5.0 hours to obtain a solid base KF / γ-Al2O3 catalyst; The concentration of KF solution is 0.06 g / mL~0.13 g / mL; 0.2~0.6 g γ-Al2O3 is added to every 1 mL of KF solution; The speed of magnetic stirring is 500~1200r / min.

[0008] The loading amount of KF in the catalyst is 10.0-25.0 wt%.

[0009] The preferred calcination temperature of the solid base KF / γ-Al2O3 catalyst is 300°C.

[0010] The solid base KF / γ-Al2O3 catalyst obtained by the method is used for catalytic synthesis of oxybis-(N-methylphthalimide) (BPI).

[0011] Specifically, the steps include: adding the obtained solid base KF / γ-Al2O3 catalyst and N-methyl-4-nitrophthalimide (4-NPI) to a solvent, heating and refluxing at 150.0-170.0°C and normal pressure for 9.0-11.0 hours to obtain BPI; wherein, 5.0-10.0 mmol of N-methyl-4-nitrophthalimide and 0.10-0.30 g of solid base KF / γ-Al2O3 catalyst are added to every 7-20 g of solvent; The solvent is N,N-dimethylformamide (DMF).

[0012] The optimal conditions for the reaction are: reaction temperature of 150° C. and reaction time of 10 hours.

[0013] The application also includes a catalyst recovery step: the solid base KF / γ-Al2O3 catalyst is filtered and collected after use, the catalyst is washed with deionized water, and after washing, it is immersed in a KF solution for 20.0-40.0 minutes, and dried at 80.0-130.0°C for 9.0-11.0 hours, so as to be used in the next reaction: Wherein, the concentration of the KF solution is 0.06g / mL~0.13g / mL.

[0014] This method is suitable for large-scale production of BPI and meets the requirements of green chemistry and sustainable development.

[0015] The beneficial effects of the present invention are: 1. The present invention prepares a new solid base KF / γ-Al2O3 catalyst for efficient synthesis of BPI, which can achieve a yield of 81.79% with only one feeding operation. During the preparation of the catalyst, the calcination temperature is selected to be 300°C and the calcination time is 4 hours, presenting a relatively regular porous structure, which significantly increases the catalytic effect. In addition, cheap and readily available γ-Al2O3 is used as a carrier, and no additional treatment is required, which reduces the cost of heterogeneous catalysts.

[0016] 2. The present invention conducts an in-depth and systematic study on the preparation process and catalytic performance of the catalyst. Using X-ray diffraction (XRD) technology, it was successfully verified that the solid base KF / γ-Al2O3 catalyst was converted into K3AlF6 during the calcination process, and it was clarified that K3AlF6 is the key active component of the catalytic process. The mesostructure morphology of the catalyst calcined at different temperatures was analyzed by scanning electron microscopy (SEM). The results showed that when calcined at 300°C, the catalyst had a relatively regular morphology and a rich and significant void structure, thereby achieving the highest catalytic activity.

[0017] 3. The present invention determines the optimal process conditions for synthesizing BPI, which significantly improves the product yield. The reaction conditions are: 7 mmol of 4-NPI; 25 wt% of KF in the solid base KF / γ-Al2O3 catalyst; 8.485 g of DMF; 150°C of reaction temperature; and 10 hours of reaction time.

[0018] 4. The solid base KF / γ-Al2O3 catalyst of the present invention exhibits excellent recycling performance. When repeated tests are performed, the yield of BPI is stabilized at more than 80%, which significantly improves production efficiency and product quality. It can be directly reused without cumbersome subsequent processing steps. This feature not only greatly reduces production costs, but also significantly reduces environmental pollution, which is highly consistent with the core concept of green chemistry and sustainable development.

[0019] 5. The present invention is simple to prepare and does not require special equipment or instruments.

[0020] Therefore, the present invention not only has important value in academic research, but also has broad application prospects in industrial production, and is expected to promote the progress and sustainable development of BPI synthesis technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 XRD spectra of carrier γ-Al2O3 and KF / γ-Al2O3 at different calcination temperatures obtained in Example 1; Figure 2SEM images of carrier γ-Al2O3 and KF / γ-Al2O3 at different calcination temperatures obtained in Example 1, where: Figure 2 (a) is the SEM image of the carrier γ-Al2O3; Figure 2 (b) is the SEM image of KF / γ-Al2O3 calcined at 300℃; Figure 2 (c) is the SEM image of KF / γ-Al2O3 calcined at 400℃; Figure 2 (d) is the SEM image of KF / γ-Al2O3 calcined at 500℃; Figure 3 This is a performance diagram of the recycling of the solid base KF / γ-Al2O3 catalyst obtained in Example 3. DETAILED DESCRIPTION

[0022] In the experimental scheme of the present invention, a method for synthesizing oxybis-(N-methylphthalimide) (BPI) using a solid base KF / γ-Al2O3 catalyst is provided. The method comprises the following steps: in the presence of the catalyst, subjecting N-methyl-4-nitrophthalimide (4-NPI) to an etherification condensation reaction in an N,N-dimethylformamide (DMF) solvent to generate BPI.

[0023] The chemical equation for generating BPI in the present invention is as follows:

[0024] In order to further optimize the synthesis process of BPI, the present invention systematically studies and optimizes the reaction conditions. Through the single factor test method, the present invention determines the optimal process conditions for synthesizing BPI, including reaction temperature, solvent dosage, catalyst dosage, etc. Under these optimal process conditions, the synthesis yield of BPI is significantly improved to 81.79%, and the BPI yield is stabilized at 80.0% during repeated tests, which is much higher than 63.44% of the traditional mixed liquid alkali metal catalyst.

[0025] In order to specifically demonstrate the embodiments of the present invention, several specific experimental examples are provided below to illustrate how to synthesize oxybis-(N-methylphthalimide) (BPI) using solid base KF / γ-Al2O3 catalyst. These examples are intended to further illustrate the method of the present invention, but should not be regarded as limiting the present invention.

[0026] Embodiment 1: Preparation of Solid Base KF / γ-Al2O3 Catalyst Weigh 0.8 g of potassium fluoride dihydrate (KF·2H2O) and 5.0 g of deionized water into a small beaker to form 5.0 mL of 0.1 g / mL KF aqueous solution. Add 2.0 g of γ-Al2O3 carrier to the solution, stir magnetically at 800 r / min for 30 minutes, and ultrasonicate for 5 minutes until the γ-Al2O3 is evenly mixed. Place the adsorbed mixture in a vacuum drying oven, dry at 110 ° C for 10.0 hours, and calcine at 300 ° C for 4.0 hours to obtain a solid base KF / γ-Al2O3 catalyst.

[0027] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for describing Example 1: Figure 1 The XRD spectra of the carrier γ-Al2O3 and KF / γ-Al2O3 at different calcination temperatures in Example 1. According to the XRD standard data, it can be seen that there is no diffraction peak of KF, indicating that KF is well dispersed in the carrier γ-Al2O3. Among them, the characteristic diffraction peaks of the carrier γ-Al2O3 are near 2θ=32.6°, 36.9°, 39.5°, 45.5°, 67.1°, etc.; the characteristic diffraction peaks of K3AlF6 are near 2θ=15.8°, 18.2°, 29.8°, 36.8°, 42.9°, 53.1°, 62.1°, etc. By comparing the spectra of KF / γ-Al2O3 at different calcination temperatures, it is found that the appearance of the characteristic diffraction peak of K3AlF6 has nothing to do with temperature changes, but its intensity is related to temperature. When the calcination temperature is 300 ℃, the characteristic diffraction peak intensity of K3AlF6 is the largest. As the calcination temperature continues to increase, the characteristic diffraction peak intensity of K3AlF6 continues to decrease. This may be because the calcination temperature is too high, which will sinter the active components in the catalyst. K3AlF6 is the active component of the catalyst, and its catalytic activity also decreases.

[0028] Figure 2 The SEM images of the carrier γ-Al2O3 and KF / γ-Al2O3 at different calcination temperatures in Example 1, Figure a is the structural morphology of the carrier γ-Al2O3, Figure b is the structural morphology of KF / γ-Al2O3 at a calcination temperature of 300°C, Figure c is the structural morphology of KF / γ-Al2O3 at a calcination temperature of 400°C, and Figure d is the structural morphology of KF / γ-Al2O3 at a calcination temperature of 500°C. It is found that the surfaces of the carriers γ-Al2O3 and KF / γ-Al2O3 are both uneven, but the latter has clear holes and the surface is also rougher, which may be because KF reacts with γ-Al2O3 at a higher temperature. Moreover, at 300°C, the catalyst is more regular, with many and obvious holes, and the catalyst activity is the highest, but with the increase of calcination temperature, scattered particles appear around the catalyst, the grains are no longer regular, and the catalyst activity gradually decreases.

[0029] Embodiment 2: Synthesis reaction of BPI 7.0 mmol of N-methyl-4-nitrophthalimide (4-NPI), 8.485 g of N,N-dimethylformamide (DMF) and 0.2 g of the solid base KF / γ-Al2O3 catalyst in Example 1 with a KF loading of 25 wt% in the catalyst were added to a three-necked round-bottom flask with a condenser and a magnet, and placed in a constant temperature magnetic stirrer and heated to reflux at 150°C for 10 hours. After the reaction stopped, the catalyst was separated by filtration, and the filtrate was subjected to reduced pressure distillation to remove the solvent. The residue was dissolved with an appropriate amount of water, and then stirred at 55°C for 1 hour to induce BPI precipitation. The precipitate was collected by filtration, and the BPI product was obtained after drying, and the yield was calculated by weighing.

[0030] Embodiment 3: Catalyst recovery and recycling The solid base KF / γ-Al2O3 catalyst used in Example 2 was collected by filtration. The catalyst was washed with an appropriate amount of deionized water to remove reactants and by-products attached to its surface. The washed catalyst was first immersed in 5.0mL of 0.16g / mL KF aqueous solution for 30.0 minutes, and then dried at 110°C for 10 hours to remove moisture and restore its catalytic activity. The dried catalyst can be reused in the next synthesis cycle without additional treatment. The post-treated solid base KF / γ-Al2O3 catalyst was recycled 6 times.

[0031] Figure 3 The figure is a performance diagram of the solid base KF / γ-Al2O3 catalyst obtained in Example 3. It can be seen that after being recycled for 6 times, the performance of the solid base KF / γ-Al2O3 catalyst has no obvious change, and the product yield is still maintained at more than 80%.

[0032] Optimization of the best reaction conditions Embodiment 4-5: The other steps are the same as in Example 2, except that the reaction temperature is changed from 150°C to 160°C and 170°C respectively;

[0033] It can be seen that as the reaction temperature increases, the yield gradually increases. Therefore, the optimal reaction temperature is 150°C.

[0034] Embodiment 6-8: The other steps are the same as in Example 2, except that the amount of solvent used is changed from 8.485 g to 4.245 g, 12.728 g, and 16.970 g, respectively;

[0035] It can be seen that when the solvent dosage is 8.285 g, the reaction is smooth and the yield is the highest.

[0036] Embodiment 9-11: The other steps are the same as those in Example 2, except that the loading amount of KF in the solid base KF / γ-Al2O3 catalyst is changed from 25wt% to 10wt%, 15wt%, and 20wt% respectively;

[0037] It can be seen that when the KF loading in the catalyst is 20-25wt%, the effect of the KF loading in the catalyst on the yield is not too great, but when it is less than 20wt%, the reaction yield drops significantly. This may be due to the insufficient KF loading in the catalyst, which cannot provide enough active sites for the reactants, resulting in a reduced contact opportunity between the reactants and the catalyst, and a limited reaction rate. It may also lead to insufficient alkalinity in the reaction system and inadequate reaction. Therefore, a solid base KF / γ-Al2O3 catalyst was selected, in which the KF loading was 25wt%.

[0038] According to the experimental results, the optimal synthesis conditions were determined, namely, reaction temperature of 150°C, solvent dosage of 8.485 g, and KF loading of 25 wt% in the solid base KF / γ-Al2O3 catalyst.

[0039] These examples demonstrate the practicability and effectiveness of the present invention, and achieve efficient synthesis of BPI by optimizing the preparation and use conditions of the catalyst. At the same time, the recovery and recycling of the catalyst further demonstrate the potential value of the present invention in industrial applications.

[0040] Matters not covered by the present invention are known technologies.

Claims

1. A method for preparing a solid base KF / γ-Al2O3 catalyst, characterized in that the method comprises the following steps: Potassium fluoride is dissolved in deionized water to form a KF solution, and then a γ-Al2O3 carrier is added thereto, and magnetic stirring is performed at room temperature for 20.0 to 40.0 minutes, and ultrasonication is performed for 1.0 to 10.0 minutes; the adsorbed mixture is dried and calcined at 300 to 500° C. for 3.0 to 5.0 hours to obtain a solid base KF / γ-Al2O3 catalyst; in, The concentration of KF solution is 0.06g / mL~0.13g / mL; 0.2~0.6g γ-Al2O3 is added to every 1mL of KF solution.

2. The method for preparing the solid base KF / γ-Al2O3 catalyst as claimed in claim 1, characterized in that the speed of magnetic stirring is 500~1200r / min.

3. The method for preparing the solid base KF / γ-Al2O3 catalyst as claimed in claim 1, characterized in that the loading amount of KF in the catalyst is 10.0-25.0wt%.

4. The method for preparing a solid base KF / γ-Al2O3 catalyst as claimed in claim 1, characterized in that the mixture is dried at 80.0-130.0°C for 9.0-11.0 hours.

5. Use of the solid base KF / γ-Al2O3 catalyst obtained by the method of claim 1, characterized in that it is used for catalytic synthesis of oxybis-(N-methylphthalimide) (BPI).

6. The use according to claim 5, characterized in that it comprises the following steps: adding the obtained solid base KF / γ-Al2O3 catalyst and N-methyl-4-nitrophthalimide (4-NPI) to a solvent, heating and refluxing at 150.0-170.0°C and normal pressure for 9.0-11.0 hours to obtain BPI; in, For every 7-20 g of solvent, add 5.0-10.0 mmol of N-methyl-4-nitrophthalimide and 0.10-0.30 g of solid base KF / γ-Al2O3 catalyst; The solvent is N,N-dimethylformamide (DMF).

7. The use according to claim 6, characterized in that the reaction temperature is 150°C and the reaction time is 10 hours.

8. The use according to claim 6, characterized in that it also includes a catalyst recovery step: the solid base KF / γ-Al2O3 catalyst is filtered and collected after use, the catalyst is washed with deionized water, and after washing, it is immersed in a KF solution for 20.0-40.0 minutes, and dried at 80.0-130.0°C for 9.0-11.0 hours; in, The concentration of the KF solution is 0.06 g / mL to 0.13 g / mL.

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