Green synthesis method of tetraacetylethylenediamine and catalyst used in green synthesis method

Abstract

The invention discloses a green synthesis method of tetraacetylethylenediamine and a used catalyst, and belongs to the technical field of organic synthesis. According to the synthesis method, a microwave-assisted technology and a recyclable acidic ionic liquid catalyst are creatively combined, ethylenediamine and acetic anhydride are adopted as raw materials, and tetraacetylethylenediamine (TAED) is efficiently synthesized through a two-step continuous acetylation process without intermediate separation. The reaction efficiency is enhanced through the microwave-ionic liquid synergistic effect, and the problems of long reaction time, high energy consumption, catalyst pollution and low product purity in the traditional synthesis process are solved. The product yield can reach 85% or above, the purity can reach 98.0% or above, the activity retention rate is still larger than or equal to 90% after the acidic ionic liquid catalyst is recycled 15 times, no acidic wastewater is discharged, and the method has remarkable economic and environmental benefits and is suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a green synthesis method for tetraacetylethylenediamine and the catalyst used. This method is suitable for the efficient and clean production of tetraacetylethylenediamine (TAED) required by the detergent, textile, and paper industries. Background Technology

[0002] Tetraacetylethylenediamine (TAED) is an important low-temperature bleaching activator. It can synergistically generate highly oxidizing peracetic acid with hydrogen peroxide at 30-50℃, significantly improving bleaching efficiency. It is widely used in detergent, textile printing and dyeing, papermaking and other industrial fields.

[0003] Currently, the industrial synthesis of TAED mainly involves a stepwise acetylation reaction of ethylenediamine and acetic anhydride under the catalysis of a liquid acid (such as sulfuric acid). This process has the following drawbacks: (1) Low reaction efficiency: Traditional processes rely on external heating (such as oil bath or jacket heating), which has low heat transfer efficiency. The reaction takes 6-10 hours to complete and the energy consumption is as high as 800-1000 kWh / t TAED. (2) Serious environmental pollution: Liquid acid catalyst is difficult to recover. For every ton of TAED produced, 5.8-6.5 tons of acidic wastewater (pH≤2) needs to be discharged. It needs to be treated in multiple steps such as neutralization and flocculation to meet the discharge standards, which results in high treatment costs. (3) Low product purity and yield: Liquid acid catalysis has poor selectivity and is prone to over-acetylation or decomposition of raw materials. The purity of TAED is usually below 95% and the yield is only 65-70%. (4) Significant waste of raw materials: In order to promote the complete reaction, the traditional process requires the use of 60-100% excess acetic anhydride (molar ratio of ethylenediamine to acetic anhydride 1:6.0-9.0). Unreacted acetic anhydride needs to be recovered by distillation, which increases energy consumption and process complexity.

[0004] To address the aforementioned issues, researchers in this field have attempted to employ solid acid catalysts (such as zeolites and resins) or ultrasound-assisted processes, but these approaches still have limitations: solid acid catalysts have small specific surface areas and unevenly dispersed acidic sites, resulting in TAED yields that only increase to 70-75%; while ultrasound assistance can shorten reaction time to 4-5 hours, it cannot solve the problems of catalyst recovery and wastewater pollution. Therefore, there is an urgent need to develop a new TAED synthesis method that balances efficiency, environmental friendliness, and economy. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a green synthesis method for tetraacetylethylenediamine based on microwave assistance and cyclic acidic ionic liquid catalysis, as well as the catalyst used. This synthesis method solves the technical problems of "long reaction time, high energy consumption, serious pollution, and low product purity" in existing TAED synthesis processes.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A green synthesis method for tetraacetylethylenediamine includes the following process steps: S1: Preparation of acidic ionic liquid catalysts: 1-Methylimidazole and 1,4-butyric acid lactone were added to a reaction vessel in a certain molar ratio. After stirring and reacting, the intermediate 1-sulfonate butyl-3-methylimidazole inner salt was generated. After cooling to room temperature, p-toluenesulfonic acid with an equimolar amount of 1-methylimidazole was added, and the temperature was raised to 80-90℃ and reacted for 3-4 hours. Trace amounts of water were removed by vacuum distillation to obtain 1-sulfonate butyl-3-methylimidazole p-toluenesulfonate ([BSMIM]PTSA), which is the acidic ionic liquid catalyst mentioned above. S2: TAED Synthesis: (1) Diacetylation reaction: Ethylenediamine and the [BSMIM] PTSA catalyst prepared in step S1 are added to a microwave reactor. The microwave device is turned on and the stirring is started. The microwave power is adjusted to 300-500W and the stirring rate is 200-300rpm. The reactor is heated to 70-80℃ and acetic anhydride is added dropwise at a rate of 150-250g / h. During the dropwise addition, the diacetylation reaction is completed to generate diacetylenediamine (DAED). (2) Tetraacetylation reaction: After the acetic anhydride is added, the microwave power is adjusted to 500-600W, and the temperature is raised to 90-100℃ to continue the reaction for 2.0-4.0h, so that DAED is further converted into TAED; S3: Product separation and catalyst recycling: After the reaction is complete, the reaction system is cooled to 40-50℃ and allowed to stand to separate into layers. The upper layer is crude TAED and the lower layer is [BSMIM]PTSA ionic liquid phase. The crude TAED in the upper layer is post-processed to obtain refined TAED. The lower ionic liquid phase is post-processed and recycled.

[0007] In a further technical solution, in step S1, the molar ratio of 1-methylimidazole to 1,4-butyryl lactone is 1:1-1.2, preferably 1:1.1.

[0008] In a further technical solution, the amount of catalyst used in the diacetylation reaction of step S2 is 3.0-9.0% of the mass of ethylenediamine; preferably, the amount of catalyst used is 5.0-8.0% of the mass of ethylenediamine, at which point the TAED yield is ≥85% and the purity is ≥98.5%. The molar ratio of ethylenediamine to acetic anhydride is 1:4.2-5.0.

[0009] In a further technical solution, the matching relationship between microwave power and reaction temperature in step S2 is as follows: 300-500W power is only matched with a temperature of 70-80℃, and 500-600W power is only matched with a temperature of 90-100℃; this matching relationship can make the acetic anhydride decomposition rate ≤2.5% and the TAED selectivity ≥97%.

[0010] A further technical solution is that the post-processing of the upper layer crude TAED in step S3 is as follows: the upper layer crude TAED is washed with water 2-3 times and vacuum dried at 60-70℃ and 0.08-0.09MPa for 2-3 hours to obtain high-quality TAED.

[0011] A further technical solution involves the following post-treatment process for the lower ionic liquid phase in step S3: the lower ionic liquid phase is subjected to vacuum distillation at 110-120℃ and 0.095MPa for 1-1.5 hours to remove moisture and trace impurities before recycling. After the [BSMIM]PTSA ionic liquid is recycled 15 times, the TAED yield remains ≥82.8%, the [BSMIM]PTSA content in the ionic liquid is ≥99.0%, and there is no loss of active components.

[0012] In a further technical solution, the reaction process of 1-methylimidazole and 1,4-butyryl lactone in step S1 in the reactor is as follows: the reaction is stirred at 60-70℃ for 4-5 hours to generate the intermediate 1-sulfonate butyl-3-methylimidazole inner salt.

[0013] The present invention also proposes a catalyst, wherein the catalyst is an acidic ionic liquid catalyst prepared by the method described in step S1 above, namely 1-butyl-3-methylimidazolium sulfonate ([BSMIM]PTSA).

[0014] The core technical solution of this invention is "microwave-ionic liquid synergistic catalysis + intermediate-free two-step continuous acetylation", specifically including three modules: acidic ionic liquid preparation, TAED synthesis, and product separation and catalyst recycling. The key innovations and beneficial effects are as follows:

[0015] I. Customized Design of Acidic Ionic Liquid Catalysts

[0016] The preparation process of this invention uses 1-butyl-3-methylimidazolium sulfonate ([BSMIM]PTSA) as a catalyst, whose molecular structure simultaneously contains: (1) Strong acidic site: -SO3H group (pKa≈1.2), which can protonate the carbonyl group of acetic anhydride (enhancing electrophilicity) and efficiently catalyze the acetylation reaction of primary and secondary amino groups; (2) Highly soluble framework: The imidazole ring and butyl sulfonate chain can form strong interactions with ethylenediamine and acetic anhydride, enabling the reaction to proceed homogeneously under organic solvent-free conditions; (3) Easy separation characteristics: The density of [BSMIM]PTSA (1.28 g / cm³) is significantly higher than that of TAED (1.12 g / cm³). After the reaction, it can be quickly separated by static layering, avoiding the complicated recovery process of traditional catalysts.

[0017] The preparation process strictly controls the molar ratio of raw materials and the reaction temperature: 1-methylimidazolium and 1,4-butyryl lactone react in a molar ratio of 1:1.1 to avoid byproducts (such as disubstituted inner salts) caused by excess 1,4-butyryl lactone; the addition of an equimolar amount of p-toluenesulfonic acid ensures complete protonation of the inner salt and increases the acidity site density (the acidity of [BSMIM]PTSA was 2.8 mmol / g by potentiometric titration, which is significantly higher than the 1.5 mmol / g of the traditional ionic liquid [HMIM]HSO4).

[0018] II. Microwave-Ionic Liquid Synergistic Effect

[0019] The preparation process of this invention utilizes the synergistic effect of microwave and ionic liquid to achieve a reaction rate constant of 0.085 min. -1 It is more than 4 times better than a single microwave or single ionic liquid system.

[0020] This invention experimentally verifies that microwaves and [BSMIM]PTSA have a significant synergistic effect, the specific mechanism of which is as follows: (1) Activation effect of microwaves on ionic liquids: The "volume heating" characteristic of microwaves can rapidly polarize [BSMIM]PTSA molecules (increasing polarizability by 25%), promote proton transfer of -SO3H groups, and reduce the reaction rate constant from 0.018 min. -1 (Ionic liquids only, conventional heating) Increased to 0.085 min -1 ; (2) The stabilizing effect of ionic liquids on microwaves: The high polarity of [BSMIM]PTSA can inhibit microwave-induced decomposition of acetic anhydride (the decomposition rate drops from 8.5% (microwave only) to 1.2%), while avoiding carbonization of TAED due to local overheating (the product color changes from pale yellow to pure white). (3) Selective regulation effect: Microwaves can directionally accelerate the secondary amino acetylation reaction (the activation energy is reduced from 85kJ / mol to 52kJ / mol), which increases the conversion efficiency of DAED to TAED by 40%, and reduces the residual TriAED by-product from 10% to below 2.8%.

[0021] III. Two-step continuous acetylation process without intermediate separation

[0022] This invention eliminates the step of "separating DAED intermediates" in traditional processes, and completes two-step acetylation in the same reactor: Step 1 (Diacetylation): Under microwave power of 300-500W and temperature of 70-80℃, ethylenediamine preferentially undergoes primary amino acetylation with acetic anhydride to generate DAED (conversion ≥99%). Low temperature and low power in this stage can prevent premature reaction of the secondary amino group and reduce the formation of TriAED. The relevant reaction formulas are as follows: H2NCH2CH2NH2+ 2(CH3CO)2O → CH3CONHCH2CH2NHCOCH3+ 2CH3COOH; Step 2 (Tetraacetylation): Increase microwave power to 500-600W and temperature to 90-100℃. The secondary amino group of DAED is completely acetylated to TAED under the catalysis of [BSMIM]PTSA. The high temperature and high power at this stage can break the reaction equilibrium and ensure that the acetylation rate of the secondary amino group is ≥98%. The relevant reaction formula is as follows: CH3CONHCH2CH2NHCOCH3+ 2(CH3CO)2O → (CH3CO)2NCH2CH2N(COCH3)2+ 2CH3COOH Process parameter optimization: The molar ratio of ethylenediamine to acetic anhydride is controlled at 1:4.2-5.0, which reduces the amount of acetic anhydride used by 40% compared with the traditional process; by precisely controlling the dropping rate (150-250g / h), excessive acetylation caused by excessively high local acetic anhydride concentration is avoided.

[0023] IV. Green Separation and Catalyst Recycling

[0024] After the reaction is complete, the density difference between [BSMIM]PTSA and TAED (difference of 0.16 g / cm³) can be used to achieve stratification by allowing the mixture to stand at 40-50℃ for 30 minutes. (1) Upper layer crude TAED: After washing with water 2-3 times (to remove residual acetic acid and trace amounts of ionic liquid) and vacuum drying (60-70℃, 0.08-0.09MPa), the purity can reach 98.0%-99.5%; (2) Lower ionic liquid phase: Distilled under reduced pressure at 110-120℃ and 0.095MPa for 1-1.5h to remove water (water content reduced to below 0.2%) and trace impurities (such as methyl acetate). It still maintains high activity after being recycled 15 times (TAED yield ≥82.8%). Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0026] Example 1: Preparation of acidic ionic liquid [BSMIM]PTSA

[0027] (1) Add 0.1 mol 1-methylimidazole (8.2 g) and 0.11 mol 1,4-butyryl lactone (15.2 g) to a 250 mL three-necked flask, and install a stirrer and a reflux condenser. (2) The reaction was stirred in a constant temperature water bath at 65℃ for 4.5 h to generate 1-sulfonate butyl-3-methylimidazolium salt; (3) Cool to room temperature (25°C), slowly add 0.1 mol p-toluenesulfonic acid (17.2 g), heat to 85°C and stir for 3.5 h; (4) After the reaction was completed, the system was transferred to a rotary evaporator and distilled under reduced pressure at 80℃ and 0.09MPa for 2 hours to remove trace amounts of water (water content was reduced to 0.15%), and a pale yellow viscous liquid [BSMIM] PTSA was obtained (yield 38.5g, acidity 2.8mmol / g).

[0028] Example 2: Synthesis and Separation of TAED

[0029] (1) Add 60g of ethylenediamine (1.0mol) and 3g of [BSMIM] PTSA (5% of the mass of ethylenediamine) to a 500mL microwave reactor, seal the reactor, and purge with nitrogen three times (to remove air and prevent oxidation of ethylenediamine). (2) Turn on the microwave device and stir, set the microwave power to 400W and the stirring speed to 250rpm, and raise the temperature of the reactor to 75℃ through programmed heating; (3) 440 g of acetic anhydride (4.31 mol, ethylenediamine to acetic anhydride molar ratio 1:4.31) was added dropwise at a rate of 200 g / h through a constant pressure dropping funnel. The dropwise addition process lasted for 2.2 h. After the dropwise addition was completed, the microwave power was adjusted to 550 W and the temperature was raised to 95 °C to continue the reaction for 2.0 h. During this period, samples were taken every 30 min to determine the TAED content (using HPLC method). The reaction was stopped when the TAED content was ≥98%. (5) After the reaction is complete, turn off the microwave device, cool the reaction system to 45°C, and let it stand for 30 minutes. The system is divided into two layers: the upper layer is a white viscous crude TAED product, and the lower layer is a pale yellow [BSMIM] PTSA phase. (6) Transfer the upper crude product to a beaker, add 100 mL of water, stir for 30 min and let stand to separate the layers. Discard the lower aqueous phase (containing acetic acid and trace amounts of ionic liquid), and repeat the water washing 3 times. (7) The washed crude TAED was placed in a vacuum drying oven and dried at 65℃ and 0.085MPa for 3.0h to obtain 193.8g of white crystalline TAED, with a yield of 85.0% and a purity of 98.5% (HPLC detection: TAED peak area accounted for 98.5%, TriAED accounted for 0.8%, and DAED accounted for 0.7%). (8) The lower ionic liquid phase was transferred to a distillation flask and distilled under reduced pressure at 115°C and 0.095 MPa for 1.5 h to obtain 2.95 g of [BSMIM] PTSA (recovery rate 98.3%), which was directly used for the next batch of reaction.

[0030] Example 3: Catalyst Cyclic Performance Test

[0031] The [BSMIM] PTSA recovered in Example 2 was reused following the steps in Example 2, and the TAED yield and purity were recorded for each cycle:

[0032] The results showed that after 15 cycles of [BSMIM]PTSA, the TAED yield was still ≥85.8% and the purity was ≥98.2%, meeting the requirements for industrial production. After 20 cycles, the yield decreased slightly, but the activity could be restored by adding 5% fresh catalyst.

[0033] Example 4: Parameter Range Verification Experiment

[0034] To verify the rationality of the catalyst dosage range (3.0-9.0%) in the technical solution, other conditions were kept constant (60g ethylenediamine, 440g acetic anhydride, microwave power 400-550W, reaction time 3h), while the catalyst dosage was varied:

[0035] Conclusion: When the catalyst dosage is 3.0-9.0%, the TAED yield is ≥85% and the purity is ≥98%, which meets the purpose of the invention; the preferred dosage is 5.0-8.0%, at which point the yield and cost-effectiveness are balanced.

[0036] Example 5: Verification of Technical Effect

[0037] To demonstrate the technical advantages of this invention, the following comparative experiment was conducted (experimental conditions: 60g ethylenediamine, 440g acetic anhydride, 5g catalyst, 3h reaction time):

[0038] The results show that the present invention is significantly superior to the existing process in terms of yield, purity, energy consumption, and environmental friendliness, and the catalyst can be recycled, which meets the needs of green chemical development.

[0039] In summary, the present invention has the following significant beneficial effects: (1) Efficiency and energy consumption advantages: The synergistic effect of microwave-ionic liquid shortens the reaction time from 6-10h to 2-4h, reduces energy consumption by more than 30% (from 800kWh / t to 560kWh / t), and increases production efficiency by 2-3 times; at the same time, microwave heating is uniform, which can reduce side reactions caused by local overheating and improve reaction selectivity.

[0040] (2) Environmental and economic advantages: Acidic ionic liquids can be recycled more than 15 times, with no acidic wastewater discharge (only a small amount of washing wastewater is generated, which can be neutralized and reused), reducing the cost of waste treatment by 80%; acetic anhydride usage is reduced by 40%, and raw material costs are reduced by 25%; the entire reaction process does not require organic solvents, the catalyst can be recycled, reducing the discharge of waste, which is in line with the development concept of green chemistry.

[0041] (3) Product quality advantages: The reaction selectivity is improved, and the purity of TAED is increased from below 95% to above 98.0%, which can meet the purity requirements of high-end detergents (such as detergents for baby clothes); (4) Advantages of process feasibility: The two-step continuous process without intermediate separation reduces equipment investment by 30%; the catalyst and product are separated by static layering, which is simple to operate and suitable for large-scale industrial production; the one-step synthesis of TAED simplifies the process flow; by optimizing the reaction temperature, microwave power and raw material ratio, the amount of acetic anhydride is controlled at a molar ratio of 1:4.2-5.0, which reduces the consumption of acetic anhydride and improves the utilization rate of raw materials compared with the traditional process (1:6.0-9.0); (5) Catalyst innovation: The acidic ionic liquid [BSMIM]PTSA synthesized in-house is used as the catalyst. This catalyst has both acidic sites and good solubility. It can efficiently catalyze the acetylation reaction and dissolve the reaction raw materials without the need for additional organic solvents. Moreover, the catalyst and the product are easy to separate into layers and can be recycled, which solves the problems of environmental pollution and difficulty in recycling of traditional liquid acid catalysts.

[0042] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A green synthesis method for tetraacetylethylenediamine, characterized in that, The process includes the following steps: S1: Preparation of acidic ionic liquid catalysts: 1-Methylimidazole and 1,4-butyric acid lactone were added to a reaction vessel in a certain molar ratio. After stirring and reacting, the intermediate 1-sulfonate butyl-3-methylimidazole inner salt was generated. After cooling to room temperature, an equimolar amount of p-toluenesulfonic acid was added, and the reaction was carried out at a certain temperature. The trace amount of water was removed by vacuum distillation to obtain 1-sulfonate butyl-3-methylimidazole p-toluenesulfonate, denoted as [BSMIM]PTSA, which is the acidic ionic liquid catalyst. S2: TAED Synthesis: (1) Diacetylation reaction: Ethylenediamine and the acidic ionic liquid catalyst prepared in step S1 are added to a microwave reactor, and acetic anhydride is added dropwise under certain microwave process and temperature conditions. During the dropwise addition, the diacetylation reaction is completed to generate diacetylenediamine. (2) Tetraacetylation reaction: After the acetic anhydride is added, the microwave process and temperature conditions are adjusted to continue the reaction, so that diacetylethylenediamine is further converted into tetraacetylethylenediamine; S3: Product separation and catalyst recycling: After the reaction is complete, the reaction system is cooled to 40-50℃ and allowed to stand to separate into layers. The upper layer is crude TAED and the lower layer is [BSMIM]PTSA ionic liquid phase. The crude TAED in the upper layer is post-processed to obtain refined TAED. The lower ionic liquid phase is post-processed and recycled.

2. The green synthesis method of tetraacetylethylenediamine according to claim 1, characterized in that, In step S1, the molar ratio of 1-methylimidazole to 1,4-butyryl lactone is 1:1-1.

2. After adding p-toluenesulfonic acid, the reaction temperature is 80-90℃ and the reaction time is 3-4h.

3. The green synthesis method of tetraacetylethylenediamine according to claim 1, characterized in that, In step S2, the amount of catalyst used in the diacetylation reaction is 3.0-9.0% of the mass of ethylenediamine, preferably 5.0-8.0%; the molar ratio of ethylenediamine to acetic anhydride is 1:4.2-5.

0.

4. The green synthesis method of tetraacetylethylenediamine according to claim 1, characterized in that, In the diacetylation reaction of step S2, the microwave device and stirrer are turned on, the microwave power is adjusted to 300-500W and the stirring speed is 200-300rpm, the reaction vessel is heated to 70-80℃, and acetic anhydride is added dropwise at a rate of 150-250g / h to carry out the reaction.

5. The green synthesis method of tetraacetylethylenediamine according to claim 1, characterized in that, In step S2, after the acetic anhydride is added, the microwave power is adjusted to 500-600W and the temperature is raised to 90-100℃ to continue the reaction for 2.0-4.0h.

6. The green synthesis method of tetraacetylethylenediamine according to claim 1, characterized in that, The post-processing of the upper layer crude TAED in step S3 is as follows: wash the upper layer crude TAED with water 2-3 times, and vacuum dry it at 60-70℃ and 0.08-0.09MPa for 2-3 hours to obtain high-quality TAED.

7. The green synthesis method of tetraacetylethylenediamine according to claim 1, characterized in that, The post-treatment process of the lower ionic liquid phase in step S3 is as follows: the lower ionic liquid phase is distilled under reduced pressure at 110-120℃ and 0.095MPa for 1-1.5h to remove moisture and trace impurities, and then recycled.

8. The green synthesis method of tetraacetylethylenediamine according to claim 1, characterized in that, The reaction process of 1-methylimidazole and 1,4-butyryl lactone in step S1 in the reactor is as follows: stir the reaction at 60-70℃ for 4-5 hours to generate the intermediate 1-sulfonate butyl-3-methylimidazole inner salt.

9. A catalyst, characterized in that, The catalyst is an acidic ionic liquid catalyst prepared by the preparation method described in step S1 of claim 1.

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