Preparation method and application of acid-base dual-functional aramid fiber catalyst

Abstract

The present invention discloses a preparation method and application of an acid-base bifunctional aramid fiber catalyst, which belongs to the field of green catalysis technology. The preparation method of the acid-base bifunctional aramid fiber catalyst comprises the following steps: reacting the cleaned aramid fiber with chlorosulfonic acid to obtain an aramid fiber containing a sulfonyl chloride group, and then reacting the above-mentioned fiber with diamine and water respectively to obtain an acid-base bifunctional aramid fiber catalyst containing an amino group and a sulfonic acid group. In the catalytic Knoevenagel condensation reaction, the acid-base bifunctional aramid fiber catalyst exhibits excellent catalytic activity, and has the advantages of short reaction time, high reaction yield, green solvent, and good recycling performance. In addition, the aramid catalyst has high flexibility and can be woven into various shapes, which is convenient for filling an industrial fixed bed and has potential industrial application value.

Description

Technical Field

[0001] The present invention relates to the technical field of green catalysis, and in particular to a preparation method and application of an acid-base dual-functional aramid fiber catalyst. Background Art

[0002] Enzyme catalysis, with its advantages of high efficiency, diversity, specificity, mildness, and tunable catalytic activity, has become a significant area of research in the field of catalysis. Inspired by enzyme catalysis, acid-base bifunctional catalysis has become a new research hotspot in recent years. Because acid-base functional groups can simultaneously activate both electrophiles and nucleophiles, bifunctional acid-base catalysis of C—C bond formation is possible. However, in homogeneous systems, bifunctional acid-base catalysis is relatively uncommon due to the formation of inactive salts during acid-base neutralization. Furthermore, catalyst recycling is a challenge.

[0003] Therefore, immobilization of acid-base functional groups provides a good solution to these problems. In heterogeneous systems, studies on inorganic carrier-immobilized acid-base bifunctional catalysts have been reported one after another, such as ACS Sustainable Chem. Eng. 2016, 4, 8, 4296–4304; Angew. Chem., Int. Ed., 2005, 44, 1826-1830. Chem. Eur. J., 2008, 14, 4017-4027. Chem. Eur. J., 2012, 18,12773-12782. Chem. Commun., 2014, 50, 8507-8510. However, these catalysts still suffer from drawbacks such as cumbersome preparation, easy deactivation, and low selectivity. Polymer-supported catalysts offer advantages such as ease of operation, high selectivity, easy control of the catalytic reaction, environmental friendliness and high efficiency, mild reaction conditions, and easy purification and recyclability of the reaction products, thus holding broad application prospects.

[0004] Aramid fiber, also known as aromatic polyamide fiber, is a chemical synthetic fiber. It has high thermal stability, high modulus, high strength, good heat resistance, low density and chemical resistance, making it often used in the manufacture of composite materials.

[0005] Therefore, it is a problem worthy of research to provide a preparation method and application of an acid-base bifunctional aramid fiber catalyst which has extremely high catalytic efficiency, can meet a variety of complex reaction conditions and has excellent softness and stability. Summary of the Invention

[0006] The present invention aims to provide a method for preparing and applying a bifunctional acid-base aramid fiber catalyst, which exhibits extremely high catalytic efficiency, can meet a variety of complex reaction conditions, and exhibits excellent softness and stability. The prepared bifunctional acid-base aramid fiber catalyst is applied to catalyze the Knoevenagel reaction. This bifunctional acid-base aramid fiber catalyst has advantages such as a simple preparation method, high catalytic activity, and good recyclability, and has considerable industrial application value.

[0007] The object of the present invention is achieved like this:

[0008] A method for preparing an acid-base dual-functional aramid fiber catalyst comprises the following steps:

[0009] Step 1: Aramid fiber cleaning: The aramid fibers are placed in different solvents, refluxed and stirred for a certain period of time, and the pretreated aramid fibers are rinsed and dried to remove organic matter attached to the fiber surface.

[0010] Step 2: Preparation of an acid-base bifunctional aramid fiber catalyst: The pretreated aramid fiber dried in step 1 and the dichloromethane solution of chlorosulfonic acid are mixed and stirred at a certain temperature for a period of time. This step is to graft sulfonyl chloride groups onto the aramid fiber to facilitate the subsequent grafting of sulfonic acid groups and amino groups.

[0011] Step 3: After taking out the aramid fiber from step 2 with tweezers, immediately place it in an organic amine and stir it at a certain temperature for a period of time; this step can graft amino groups onto the aramid fiber;

[0012] Step 4: Take out the aramid fiber in step 3 and put it into water. Stir it at a certain temperature for a period of time. The water will react with the remaining sulfonyl chloride groups in step 2 to generate sulfonic acid groups. After the reaction is completed, take out the aramid fiber and wash it with distilled water until it is neutral. After drying, an acid-base dual-functional aramid fiber catalyst is obtained.

[0013] In the step 1, the solvents are ethanol and cyclohexane, respectively, and the reaction time is 4-10 h. The aramid fiber is first placed in ethanol and refluxed for 4-10 h, then taken out of ethanol and placed in cyclohexane and refluxed for 4-10 h, and then taken out of cyclohexane and rinsed and dried.

[0014] In step 2, the mass of the pretreated aramid fiber is 50-500 mg, the concentration of chlorosulfonic acid is 0.5-5%, and the mass ratio of the chlorosulfonic acid dichloromethane solution to the pretreated aramid fiber is 1:10-1:50.

[0015] In the step 2, the reaction temperature is -10-25°C, and the reaction time is 5-60 min.

[0016] In the step 3, the organic amine is N,N-dimethyl-1,3-propylenediamine.

[0017] In the step 3, the reaction temperature is 25-80° C., and the reaction time is 2-8 h.

[0018] In step 4, the reaction temperature is 25-100° C., and the reaction time is 10-240 min.

[0019] The invention discloses an application of an acid-base bifunctional aramid fiber catalyst and an application of the acid-base bifunctional aramid fiber catalyst in catalyzing a Knoevenagel reaction.

[0020] The beneficial effects of the present invention are:

[0021] (1) This invention is the first to prepare an acid-base dual-functional aramid fiber catalyst using aramid fiber as a carrier. The catalyst has a simple preparation process, high catalytic activity, low cost, and good recycling performance. It effectively solves the problems of existing acid-base dual-functional catalyst carrier materials with insufficient performance, complex preparation process, unsatisfactory catalytic activity, and loss of catalytic sites.

[0022] (2) The aramid fiber acid-base bifunctional catalyst prepared by the present invention was applied to the Knoevenagel reaction. The catalyst exhibited excellent catalytic activity, with advantages such as short reaction time, high reaction yield, green solvent, and good recycling performance. In addition, the acid-base bifunctional aramid fiber catalyst is highly flexible and can be woven into various shapes, facilitating the filling of industrial fixed beds, thus having potential industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the structural formula diagram of the acid-base dual-functional aramid fiber of the present invention;

[0024] Figure 2 This is an example diagram of the Knoevenagel reaction of the present invention;

[0025] Figure 3 The present invention adopts acid-base dual-functional aramid fiber to catalyze the nuclear magnetic resonance hydrogen spectrum of the Knoevenagel reaction product. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the accompanying drawings and examples.

[0027] Example 1

[0028] The preparation method of the acid-base dual-function aramid fiber catalyst of this embodiment is as follows:

[0029] (1) 2 g of aramid fiber and 50 mL of cyclohexane were added to a 100 mL round-bottom flask and refluxed for 4 h. The aramid fiber was taken out and placed in a 100 mL round-bottom flask containing 50 mL of ethanol and refluxed for 4 h. The pretreated aramid fiber was then rinsed and dried.

[0030] (2) 50 mg of dry pretreated aramid fiber, 0.5 mL of chlorosulfonic acid and 50 mL of dichloromethane were stirred at -10 °C for 10 min; the mechanism is as follows Figure 1 This step is to graft sulfonyl chloride groups on the aramid fiber to facilitate the subsequent grafting of sulfonic acid groups and amino groups; then the fiber is taken out with tweezers and immediately placed in N,N-dimethyl-1,3-propylenediamine and stirred at room temperature for 15 minutes; the mechanism is as follows Figure 1 As shown. Through this step, amino groups can be grafted onto aramid fibers. Finally, the fibers are taken out and placed in water and stirred at room temperature for 4 hours. The water reacts with the remaining sulfonyl chloride groups in the previous step to generate sulfonic acid groups. After the reaction is completed, the fiber catalyst is taken out and washed with distilled water until neutral. After drying, the acid-base dual-functional aramid fiber catalyst AF-NS-0.12 is obtained. The structural formula is shown below. Figure 1 shown.

[0031] Example 2

[0032] The preparation method of the acid-base dual-function aramid fiber catalyst of this embodiment is as follows:

[0033] (1) 2 g of aramid fiber and 50 mL of cyclohexane were added to a 100 mL round-bottom flask and refluxed for 4 h. The fiber was then taken out and placed in a 100 mL round-bottom flask containing 50 mL of ethanol and refluxed for 4 h. The pretreated aramid fiber was then rinsed and dried.

[0034] (2) 50 mg of dry pretreated aramid fiber, 0.5 mL of chlorosulfonic acid and 50 mL of dichloromethane were stirred at -10 °C for 10 min; the mechanism is as follows Figure 1 This step is to graft sulfonyl chloride groups on the aramid fiber to facilitate the subsequent grafting of sulfonic acid groups and amino groups; then the fiber is taken out with tweezers and immediately placed in N,N-dimethyl-1,3-propylenediamine and stirred at room temperature for 30 minutes; the mechanism is as follows Figure 1 As shown. Through this step, amino groups can be grafted onto aramid fibers. Finally, the fibers are taken out and placed in water and stirred at room temperature for 4 hours. The water reacts with the remaining sulfonyl chloride groups in the previous step to generate sulfonic acid groups. After the reaction is completed, the fiber catalyst is taken out and washed with distilled water until neutral. After drying, the acid-base dual-functional aramid fiber catalyst AF-NS-0.25 is obtained. The structural formula is shown below. Figure 1 shown.

[0035] Example 3

[0036] The preparation method of the acid-base dual-function aramid fiber catalyst of this embodiment is as follows:

[0037] (1) 2 g of aramid fiber and 50 mL of cyclohexane were added to a 100 mL round-bottom flask and refluxed for 4 h. The fiber was then taken out and placed in a 100 mL round-bottom flask containing 50 mL of ethanol and refluxed for 4 h. The pretreated aramid fiber was then rinsed and dried.

[0038] (2) 50 mg of dry pretreated aramid fiber, 0.5 mL of chlorosulfonic acid and 50 mL of dichloromethane were stirred at -10 °C for 10 min; the mechanism is as follows Figure 1 This step is to graft sulfonyl chloride groups on the aramid fiber to facilitate the subsequent grafting of sulfonic acid groups and amino groups; then the fiber is taken out with tweezers and immediately placed in N,N-dimethyl-1,3-propylenediamine and stirred at room temperature for 60 minutes; the mechanism is as follows Figure 1 As shown. Through this step, amino groups can be grafted onto aramid fibers. Finally, the fibers are taken out and placed in water and stirred at room temperature for 4 hours. The water reacts with the remaining sulfonyl chloride groups in the previous step to generate sulfonic acid groups. After the reaction is completed, the fiber catalyst is taken out and washed with distilled water until neutral. After drying, the acid-base dual-functional aramid fiber catalyst AF-NS-0.53 is obtained. The structural formula is shown below. Figure 1 shown.

[0039] Example 4

[0040] The acid-base dual-functional aramid fiber catalyst prepared in the above embodiment is used to catalyze the Knoevenagel reaction, such as Figure 2 As shown, proceed as follows:

[0041] Benzaldehyde (1 mmol), ethyl cyanoacetate (1.5 mmol), anhydrous ethanol (5 mL) and aramid fiber catalyst (20 mol%) were added to the reaction tube and stirred at 80°C for 15 min. After the reaction was complete, the system was cooled to room temperature. The catalyst was removed and washed three times with anhydrous ethanol. The ethanol phases were combined and dried over anhydrous sodium sulfate. After the solvent was dried, the crude product was purified by silica gel column to obtain the product, such as Figure 3 The experimental results are shown in Tables 1 and 2.

[0042] Table 1 Evaluation of the activity of acid-base bifunctional aramid fiber catalyst in catalyzing the Knoevenagel reaction

[0043]

[0044] Table 2 Evaluation of the Knoevenagel reaction cycle performance of acid-base dual-functional aramid fiber catalyst

[0045]

[0046] Comparison of different catalysts reveals that the Knoevenagel reaction yields were 2% and 3% when using no catalyst or unmodified aramid fiber as a catalyst, respectively, indicating that the fiber support has no catalytic activity. When the catalyst base-acid ratio was 0.12, the reaction yield increased to 40% using AF-NS-0.12 as the catalyst. The reaction yield reached a maximum of 96% when using AF-NS-0.25 as the catalyst, at a base-acid ratio of 0.25. However, increasing the base-acid ratio to 0.53 further decreased the Knoevenagel reaction yield using AF-NS-0.53 to 73%. This demonstrates that the acid-base bifunctional aramid fiber catalyst effectively catalyzes the Knoevenagel reaction, with the catalytic activity reaching its peak at a base-acid ratio of 0.25. Furthermore, under the same conditions, the reaction yield of AF-NS-0.25 did not decrease after three cycles, and even reached 85% after six cycles, as shown in Table 2. This demonstrates the excellent recyclability of the acid-base bifunctional aramid fiber catalyst.

Claims

1. A method for preparing an acid-base dual-functional aramid fiber catalyst, characterized by: The following steps are involved: Step 1: Aramid fiber cleaning: The aramid fiber is placed in different solvents, refluxed and stirred for a certain period of time, and the pretreated aramid fiber is rinsed and dried to remove organic matter attached to the fiber surface; Step 2: Preparation of acid-base dual-functional aramid fiber catalyst: Mix the pretreated aramid fiber dried in step 1 and the dichloromethane solution of chlorosulfonic acid, and stir for a period of time at a certain temperature; Step 2 is to graft sulfonyl chloride groups onto the aramid fiber; Step 3: After taking out the aramid fiber in step 2 with tweezers, immediately put it into organic amine and stir it at a certain temperature for a period of time; through step 3, the amino group is grafted onto the aramid fiber; Step 4: Take out the aramid fiber in step 3 and put it into water, stir it at a certain temperature for a period of time, and react the water with the remaining sulfonyl chloride groups in step 3 to generate sulfonic acid groups. After the reaction is completed, take out the aramid fiber and wash it with distilled water until it is neutral. After drying, an acid-base dual-functional aramid fiber catalyst is obtained.

2. The method for preparing the acid-base dual-functional aramid fiber catalyst according to claim 1, characterized in that: In the step 1, the solvents are ethanol and cyclohexane, respectively, and the reaction time is 4-10 h. The aramid fiber is first placed in ethanol and refluxed for 4-10 h, then taken out of ethanol and placed in cyclohexane and refluxed for 4-10 h, and then taken out of cyclohexane and rinsed and dried.

3. The method for preparing the acid-base dual-functional aramid fiber catalyst according to claim 1, characterized in that: In step 2, the mass of the pretreated aramid fiber is 50-500 mg, the concentration of chlorosulfonic acid is 0.5-5%, and the mass ratio of the chlorosulfonic acid dichloromethane solution to the pretreated aramid fiber is 1:10-1:

50.

4. The method for preparing the acid-base dual-functional aramid fiber according to claim 1, characterized in that: In the step 2, the reaction temperature is -10-25°C, and the reaction time is 5-60 min.

5. The method for preparing the acid-base dual-functional aramid fiber according to claim 1, characterized in that: In the step 3, the organic amine is N,N-dimethyl-1,3-propylenediamine.

6. The method for preparing the acid-base dual-functional aramid fiber according to claim 1, characterized in that: In the step 3, the reaction temperature is 25-80° C., and the reaction time is 2-8 h.

7. The method for preparing the acid-base dual-functional aramid fiber according to claim 1, characterized in that: In step 4, the reaction temperature is 25-100° C., and the reaction time is 10-240 min.

8. Use of the acid-base bifunctional aramid fiber catalyst according to claim 1, wherein the acid-base bifunctional aramid fiber catalyst is used in catalyzing a Knoevenagel reaction.

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