Process for the preparation of low residual chloromethyl ethyl ether

Abstract

This invention relates to the field of chemical technology, and particularly to a method for preparing low-residue chloromethyl ethyl ether, comprising the following steps: loading an adsorption support into an adsorption column, introducing hydrogen chloride gas for adsorption, and obtaining a fixed adsorption support; mixing anhydrous ethanol and paraformaldehyde, stirring until homogeneous, to obtain a reaction stock solution; loading the fixed adsorption support into the bed of a reactor, adding the reaction stock solution to the reactor, starting a circulation pump, and completing the circulation reaction to obtain a reaction product; recovering ethanol from the reaction product by atmospheric pressure distillation, and collecting the fraction by vacuum distillation to obtain chloromethyl ethyl ether. By pre-fixing hydrogen chloride gas onto the adsorption support, the reaction stock solution reacts with the fixed hydrogen chloride as it flows through the bed under the drive of the circulation pump. This provides mild reaction conditions, avoiding the problems of local overconcentration and residue caused by directly introducing hydrogen chloride, and suppressing polychlorination side reactions from the source.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, and in particular to a method for preparing low-residue chloromethyl ethyl ether. Background Technology

[0002] Chloromethyl ethyl ether is a key intermediate in the synthesis of the herbicide acetochlor and occupies a crucial position in the fine chemical industry. As a major pesticide product in my country, acetochlor is widely used for pre-emergence weed control in crops such as soybeans, corn, peanuts, and cotton. Market demand is rigid and continues to grow, placing high demands on the purity and residue control of chloromethyl ethyl ether.

[0003] Currently, the synthesis of chloromethyl ethyl ether mainly employs a process system involving anhydrous ethanol, paraformaldehyde, and hydrogen chloride. This process offers mild reaction conditions and readily available raw materials. However, a large amount of free hydrogen chloride remains in the system during and after the reaction, which easily induces polychlorination side reactions, generating various chlorine-containing impurities and directly reducing the purity of the chloromethyl ethyl ether product.

[0004] To remove free hydrogen chloride, alkaline solutions are typically used to wash the product. However, this process often introduces new problems: on the one hand, washing generates a large amount of organic wastewater, increasing environmental protection and maintenance costs; on the other hand, the water introduced during the washing process can cause chloromethyl ethyl ether to undergo hydrolysis, resulting in loss of the target product and reducing the overall production yield. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing low-residue chloromethyl ethyl ether, which reduces side reactions and lowers the residual chlorine content in the product by immobilizing the hydrogen chloride reaction system.

[0006] To solve the above-mentioned technical problems, the present invention includes the following preparation method: S1. The adsorption support is packed into the adsorption column, and hydrogen chloride gas is introduced for adsorption to obtain the immobilized adsorption support. S2. Mix anhydrous ethanol with paraformaldehyde, heat to 40-60°C, stir until homogeneous, and obtain the reaction stock solution. S3. The immobilized adsorption carrier is loaded into the bed of the reactor, the internal temperature of the reactor is controlled at 40-60℃, the reaction stock solution is added into the reactor, the circulation pump is started, and the reaction product is obtained after the circulation reaction is completed. S4. The reaction product is distilled at atmospheric pressure to recover ethanol. After vacuum distillation, the fraction is collected to obtain chloromethyl ethyl ether.

[0007] Preferably, the adsorbent carrier comprises the following preparation process: S11. Thoroughly mix SBA-15 raw powder, silica sol, and guar powder, add water and stir to adjust, seal and let stand to obtain plastic mud; S12. The plastic clay is processed into a preset shape, air-dried, and then fired to obtain a molded carrier. S13. The calcined molded support is dispersed in anhydrous toluene, and 3-chloropropyltrimethoxysilane is added for silanization treatment to obtain a chloropropylated support. S14. Disperse the chloropropylated support in N,N-dimethylformamide, add imidazole and potassium carbonate, stir and react, filter, wash and dry to obtain the adsorbent support with surface covalently grafted imidazole.

[0008] Preferably, the SBA-15 raw powder, silica sol, and guar gum powder are uniformly mixed in a mass ratio of 100:20 to 40:5 to 10.

[0009] Preferably, the mass of the 3-chloropropyltrimethoxysilane is 15% to 40% of the mass of the carrier.

[0010] Preferably, the molar amount of the imidazole is 2 to 3 times the molar amount of chloropropyl in the chloropropylated support.

[0011] Preferably, the molar amount of potassium carbonate is 0.5 to 2 times the molar amount of chloropropyl groups in the chloropropylated carrier.

[0012] Preferably, the molar ratio of anhydrous ethanol to formaldehyde units in paraformaldehyde is 2 to 4:1.

[0013] Preferably, the degree of polymerization of the paraformaldehyde is 8 to 20.

[0014] After adopting the above technical solution, the beneficial effects of the present invention are: Hydrogen chloride gas is pre-immobilized on an adsorbent carrier and packed into the reactor bed. The reaction solution, driven by a circulating pump, flows through the bed and reacts with the immobilized hydrogen chloride. The reaction conditions are mild, avoiding the problems of localized overconcentration and residue caused by directly introducing hydrogen chloride, thus suppressing polychlorination side reactions at the source. After the reaction, the product contains almost no free hydrogen chloride, reducing environmental treatment costs. Detailed Implementation

[0015] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments.

[0016] I. Preparation of Adsorption Carrier Mix SBA-15 raw powder, silica sol, and guar gum powder in a mass ratio of 100:20-40:5-10, add water and stir to adjust the mixture, control the moisture content of the mixture to 30% (mass fraction), seal and let stand for 1 hour to allow the moisture to penetrate evenly in the system, and obtain plastic clay.

[0017] SBA-15 raw powder (silicon-to-aluminum ratio ≥500, pore size 6-8nm, BET specific surface area ≥550m²) 2 / g) is a mesoporous molecular sieve used as a basic framework, providing high specific surface area and mesoporous structure. Silica sol (30% solid content) is used as a binder to ensure effective bonding between powders. Guarnan powder (≥99.5% passing through a 120-mesh sieve) is used as a molding aid and pore-forming agent to ensure good plasticity of the clay and increase the porosity of the carrier.

[0018] The plastic clay is extruded into a columnar body with a diameter of 5 mm and a length of 8 mm. It is then placed in a dark and ventilated place to air dry at room temperature for 24 hours, and then calcined in a muffle furnace at 500℃ for 3.5 hours. After natural cooling, the molded carrier is obtained.

[0019] The silica sol is dehydrated at high temperature to form a SiO2 cross-linked network, which firmly bridges the SBA-15 powder through Si-O-Si bonds. The guar powder is decomposed and removed at high temperature, forming micro-interconnected channels inside the particles. This ensures the mechanical strength of the molded carrier while fully preserving the ordered mesoporous structure and high specific surface area of ​​SBA-15.

[0020] The prepared carrier was dispersed in anhydrous toluene at a solid-liquid ratio of 1:5 (g / mL), and 15% to 40% of the carrier mass of 3-chloropropyltrimethoxysilane was added to carry out a silanization reaction. The reaction was refluxed at 80°C for 6 hours, and after filtration, washing and drying, the chloropropylated carrier was obtained.

[0021] The prepared chloropropylated support was dispersed in N,N-dimethylformamide at a solid-liquid ratio of 1:5 (g / mL). Based on the molar amount of chloropropyl groups in the chloropropylated support, 2 to 3 molar amounts of imidazole and 0.5 to 2 molar amounts of potassium carbonate were added. The mixture was refluxed at 100°C for 6 hours. After filtration, washing, and drying, the adsorbent carrier with surface covalently grafted imidazole was obtained.

[0022] Potassium carbonate is used to neutralize the HCl generated in the reaction, preventing the imidazole from being protonated and deactivated, thus shifting the chemical equilibrium to the right and increasing the conversion efficiency of chloropropyl and the imidazole grafting density.

[0023] II. Adsorption on Adsorption Carrier An adsorbent carrier grafted with imidazole was packed into an adsorption column (Φ50×500mm) to a height of 90% of the column length. The top of the adsorption column was connected to a tail gas absorption device, and dry hydrogen chloride gas was introduced from the bottom of the adsorption column. The empty column linear velocity was 0.5cm / s, thus obtaining a fixed adsorbent carrier.

[0024] When the adsorbent is exposed to an HCl gas environment, the basic nitrogen atom on the imidazole ring captures the protons of HCl, generating imidazole-onium chloride ion pairs, thus achieving chemical immobilization of HCl, which is not easily spontaneously desorbed at room temperature.

[0025] III. Cyclic Reaction Anhydrous ethanol was mixed with paraformaldehyde (n) with a degree of polymerization (n) of 8–20, wherein the molar ratio of formaldehyde units to anhydrous ethanol in the paraformaldehyde was 1:2–4. The mixture was heated to 40–60°C and stirred until homogeneous to obtain the stock solution. An immobilized adsorbent carrier containing adsorbed hydrogen chloride gas was packed into the bed of a reactor, and the internal temperature of the reactor was controlled at 40–60°C. The stock solution was added to the reactor, and a circulation pump was started to initiate the cyclic reaction. The system composition was monitored in real time using an FT-NIR fiber optic probe. The disappearance or stabilization of the formaldehyde characteristic peak was used as the criterion for reaction termination, yielding the reaction product.

[0026] The reaction stock solution flows continuously under the action of the circulating pump, repeatedly flowing through the bed to react. HCl is gradually consumed, avoiding the problems of local overconcentration and residue caused by directly introducing HCl. It inhibits polychlorination side reactions from the source. After the reaction is completed, the product contains almost no free hydrogen chloride, reducing the cost of environmental treatment.

[0027] IV. Separation and Purification The reaction product was discharged, and the adsorbent carrier was collected. The reaction product was heated to 80°C and distilled under normal pressure. The distillate was collected to obtain ethanol. Anhydrous sodium sulfate and other solid drying agents were added to the distillate, stirred evenly, and filtered to remove the drying agent, yielding crude anhydrous chloromethyl ethyl ether. The crude chloromethyl ethyl ether was subjected to vacuum distillation, controlling the vacuum degree at 30 kPa and the heating temperature at 65°C, to obtain the chloromethyl ethyl ether product.

[0028] The collected adsorption carrier was soaked in anhydrous ethanol to remove residual organic matter on the surface, dried, and then packed into an adsorption column to re-adsorb HCl.

[0029] Preparation of Adsorbent A This embodiment provides a method for preparing an adsorbent support, including the following steps: 1. Mix SBA-15 raw powder, silica sol, and guar gum powder in a mass ratio of 20:4:1, add water and stir to adjust the mixture, control the moisture content of the mixture to 30%, seal and let it stand for 1 hour to obtain plastic mud. 2. The plastic clay is extruded into columnar bodies with a diameter of 5mm and a length of 8mm. It is then placed in a dark and ventilated place to air dry at room temperature for 24 hours. After that, it is calcined in a muffle furnace at 500℃ for 3.5 hours and then naturally cooled to obtain the molded carrier. 3. The molding carrier was dispersed in anhydrous toluene at a solid-liquid ratio of 1:5. 3-Chloropropyltrimethoxysilane at 15% of the mass of the molding carrier was added to carry out a silanization reaction. The reaction was refluxed at 80°C for 6 hours. After filtration, washing and drying, the chloropropylated carrier was obtained. 4. Disperse the chloropropylated support in N,N-dimethylformamide at a solid-liquid ratio of 1:5. Based on the molar amount of chloropropyl groups in the chloropropylated support, add 2 molar amounts of imidazole and 0.5 molar amounts of potassium carbonate. Reflux at 100°C for 6 hours. After filtration, washing, and drying, obtain adsorbent A with surface covalently grafted imidazole.

[0030] Preparation of adsorbent carrier B This embodiment provides a method for preparing an adsorbent support, including the following steps: 1. Mix SBA-15 raw powder, silica sol, and guar gum powder in a mass ratio of 50:15:4, add water and stir to adjust the mixture, control the moisture content of the mixture to 30%, seal and let it stand for 1 hour to obtain plastic mud. 2. The plastic clay is extruded into columnar bodies with a diameter of 5mm and a length of 8mm. It is then placed in a dark and ventilated place to air dry at room temperature for 24 hours. After that, it is calcined in a muffle furnace at 500℃ for 3.5 hours and then naturally cooled to obtain the molded carrier. 3. The molding carrier was dispersed in anhydrous toluene at a solid-liquid ratio of 1:5. 3-Chloropropyltrimethoxysilane at 30% of the mass of the molding carrier was added to carry out a silanization reaction. The reaction was refluxed at 80°C for 6 hours. After filtration, washing and drying, the chloropropylated carrier was obtained. 4. Disperse the chloropropylated support in N,N-dimethylformamide at a solid-liquid ratio of 1:5. Based on the molar amount of chloropropyl groups in the chloropropylated support, add 2.5 molar amounts of imidazole and 1 molar amount of potassium carbonate. Reflux at 100°C for 6 hours. After filtration, washing, and drying, obtain adsorbent B with surface covalently grafted imidazole.

[0031] Preparation of adsorbent support C This embodiment provides a method for preparing an adsorbent support, including the following steps: 1. Mix SBA-15 raw powder, silica sol, and guar gum powder in a mass ratio of 10:4:1, add water and stir to adjust the mixture, control the moisture content of the mixture to 30%, seal and let it stand for 1 hour to obtain plastic mud. 2. The plastic clay is extruded into columnar bodies with a diameter of 5mm and a length of 8mm. It is then placed in a dark and ventilated place to air dry at room temperature for 24 hours. After that, it is calcined in a muffle furnace at 500℃ for 3.5 hours and then naturally cooled to obtain the molded carrier. 3. The molding carrier was dispersed in anhydrous toluene at a solid-liquid ratio of 1:5. 40% of the mass of the molding carrier was added to carry out the silanization reaction. The reaction was refluxed at 80°C for 6 hours. After filtration, washing and drying, the chloropropylated carrier was obtained. 4. The chloropropylated support was dispersed in N,N-dimethylformamide at a solid-liquid ratio of 1:5. Based on the molar amount of chloropropyl groups in the chloropropylated support, 3 times the molar amount of imidazole and 2 times the molar amount of potassium carbonate were added. The mixture was refluxed at 100°C for 6 hours. After filtration, washing and drying, the adsorbent C with surface covalently grafted imidazole was obtained.

[0032] Example 1 This embodiment provides a method for preparing low-residue chloromethyl ethyl ether, including the following steps: 1. 500g of adsorbent carrier A was packed into an adsorption column. Hydrogen chloride gas was introduced from the bottom of the adsorption column. When the HCl concentration at the outlet reached 5% of that at the inlet, the introduction was stopped and the column was purged with nitrogen to obtain an immobilized adsorbent carrier. The adsorption capacity of hydrogen chloride was measured to be 0.65 mmol / g carrier. 2. Mix 1 mol of paraformaldehyde (CH2O)8 with 16 mol of anhydrous ethanol, heat to 40°C, and stir until homogeneous to obtain the reaction stock solution; 3. The immobilized adsorbent carrier containing adsorbed hydrogen chloride gas is packed into the reactor bed, and the internal temperature of the reactor is controlled at 40℃. The reaction stock solution is added to the reactor, the circulation pump is started, and the reaction is circulated. The system components are monitored in real time using an FT-NIR fiber optic probe. The stability of the formaldehyde characteristic peak is used as the criterion for reaction termination, and the reaction product solution is obtained. 4. The reaction product was distilled at atmospheric pressure to recover ethanol. After vacuum distillation, the fraction was collected to obtain 28.7g of chloromethyl ethyl ether, with a yield of 93.4%.

[0033] Example 2 This embodiment provides a method for preparing low-residue chloromethyl ethyl ether, including the following steps: 1. 500g of adsorbent carrier B was packed into an adsorption column. Hydrogen chloride gas was introduced from the bottom of the adsorption column. When the HCl concentration at the outlet reached 5% of that at the inlet, the introduction was stopped and the column was purged with nitrogen to obtain an immobilized adsorbent carrier. The adsorption capacity of hydrogen chloride was measured to be 1.32 mmol / g carrier. 2. Add 1 mol of paraformaldehyde (CH2O) 10 Mix with 30 mol of anhydrous ethanol, heat to 50°C, stir until homogeneous, and obtain the original reaction solution; 3. The immobilized adsorbent carrier containing adsorbed hydrogen chloride gas is packed into the reactor bed, and the internal temperature of the reactor is controlled at 50℃. The reaction stock solution is added to the reactor, the circulation pump is started, and the reaction is circulated. The system components are monitored in real time using an FT-NIR fiber optic probe. The stability of the formaldehyde characteristic peak is used as the criterion for reaction termination, and the reaction product solution is obtained. 4. The reaction product was distilled at atmospheric pressure to recover ethanol. After vacuum distillation, the fraction was collected to obtain 59.6 g of chloromethyl ethyl ether, with a yield of 95.6%.

[0034] Example 3 This embodiment provides a method for preparing low-residue chloromethyl ethyl ether, including the following steps: 1. 500g of adsorption carrier C was packed into an adsorption column. Hydrogen chloride gas was introduced from the bottom of the adsorption column. When the HCl concentration at the outlet reached 5% of that at the inlet, the introduction was stopped and the column was purged with nitrogen to obtain an immobilized adsorption carrier. The adsorption capacity of hydrogen chloride was measured to be 1.93 mmol / g carrier. 2. Add 1 mol of paraformaldehyde (CH2O) 20 Mix with 80 mol of anhydrous ethanol, heat to 60°C, stir until homogeneous, and obtain the original reaction solution; 3. The immobilized adsorbent carrier containing adsorbed hydrogen chloride gas is packed into the reactor bed, and the internal temperature of the reactor is controlled at 60℃. The reaction stock solution is added to the reactor, the circulation pump is started, and the reaction is circulated. The system components are monitored in real time using an FT-NIR fiber optic probe. The stability of the formaldehyde characteristic peak is used as the criterion for reaction termination, and the reaction product solution is obtained. 4. The reaction product was distilled at atmospheric pressure to recover ethanol. After vacuum distillation, the fraction was collected to obtain 87.82 g of chloromethyl ethyl ether, with a yield of 96.3%.

[0035] Compare with Example 1 This embodiment provides a method for preparing low-residue chloromethyl ethyl ether, including the following steps: 1. 500g of adsorbent carrier B was packed into an adsorption column. Hydrogen chloride gas was introduced from the bottom of the adsorption column. When the HCl concentration at the outlet reached 5% of that at the inlet, the introduction was stopped and the column was purged with nitrogen to obtain an immobilized adsorbent carrier. The adsorption capacity of hydrogen chloride was measured to be 1.32 mmol / g carrier. 2. Mix 1 mol of paraformaldehyde (CH2O)8 with 16 mol of anhydrous ethanol, heat to 40°C, and stir until homogeneous to obtain the reaction stock solution; 3. The immobilized adsorbent carrier containing adsorbed hydrogen chloride gas is packed into the reactor bed, and the internal temperature of the reactor is controlled at 40℃. The reaction stock solution is added to the reactor, the circulation pump is started, and the reaction is circulated. The system components are monitored in real time using an FT-NIR fiber optic probe. The stability of the formaldehyde characteristic peak is used as the criterion for reaction termination, and the reaction product solution is obtained. 4. The reaction product was distilled at atmospheric pressure to recover ethanol. After vacuum distillation, the fraction was collected to obtain 58.6 g of chloromethyl ethyl ether, with a yield of 94%.

[0036] Compare with Example 2 This embodiment provides a method for preparing low-residue chloromethyl ethyl ether, including the following steps: 1. 500g of adsorption carrier C was packed into an adsorption column. Hydrogen chloride gas was introduced from the bottom of the adsorption column. When the HCl concentration at the outlet reached 5% of that at the inlet, the introduction was stopped and the column was purged with nitrogen to obtain an immobilized adsorption carrier. The adsorption capacity of hydrogen chloride was measured to be 1.93 mmol / g carrier. 2. Mix 1 mol of paraformaldehyde (CH2O)8 with 16 mol of anhydrous ethanol, heat to 40°C, and stir until homogeneous to obtain the reaction stock solution; 3. The immobilized adsorbent carrier containing adsorbed hydrogen chloride gas is packed into the reactor bed, and the internal temperature of the reactor is controlled at 40℃. The reaction stock solution is added to the reactor, the circulation pump is started, and the reaction is circulated. The system components are monitored in real time using an FT-NIR fiber optic probe. The stability of the formaldehyde characteristic peak is used as the criterion for reaction termination, and the reaction product solution is obtained. 4. The reaction product was distilled at atmospheric pressure to recover ethanol. After vacuum distillation, the fraction was collected to obtain 89.3g of chloromethyl ethyl ether, with a yield of 94.5%.

[0037] In Examples 1-3, the yields were 93.4%, 95.6%, and 96.3%, respectively. This indicates that moderately increasing the temperature and the amount of paraformaldehyde and ethanol can more effectively drive the reaction equilibrium and significantly improve the yield. Comparative Examples 1-2 compare different adsorbents under fixed conditions. Under the same reaction conditions, the yields were 94.0% and 94.5%, respectively, indicating that the adsorption capacity of the carrier can improve the product yield within a certain range. In the preparation of low-residual chloromethyl ethyl ether, after the HCl adsorption capacity of the carrier meets the basic requirements, the synergistic optimization of reaction temperature and substrate concentration is more effective in overcoming the yield bottleneck than simply increasing the adsorption capacity of the carrier.

Claims

1. A method for preparing low-residue chloromethyl ethyl ether, characterized in that, The preparation methods include the following: S1. The adsorption support with surface covalently grafted imidazole is packed into the adsorption column, and hydrogen chloride gas is introduced for adsorption to obtain the immobilized adsorption support. S2. Anhydrous ethanol and paraformaldehyde are mixed, heated to 40-60°C, and stirred until homogeneous to obtain the reaction stock solution; S3. The immobilized adsorption carrier is loaded into the bed of the reactor, the internal temperature of the reactor is controlled at 40-60℃, the reaction stock solution is added into the reactor, the circulation pump is started, and the reaction product is obtained after the circulation reaction is completed. S4. The reaction product is distilled at atmospheric pressure to recover ethanol. After vacuum distillation, the fraction is collected to obtain chloromethyl ethyl ether.

2. The method for preparing low-residue chloromethyl ethyl ether according to claim 1, characterized in that, The adsorbent carrier is prepared using the following process: S11. Thoroughly mix SBA-15 raw powder, silica sol, and guar powder, add water and stir to adjust, seal and let stand to obtain plastic mud; S12. The plastic clay is processed into a preset shape, air-dried, and then fired to obtain a molded carrier. S13. The calcined molded support is dispersed in anhydrous toluene, and 3-chloropropyltrimethoxysilane is added for silanization treatment to obtain a chloropropylated support. S14. Disperse the chloropropylated support in N,N-dimethylformamide, add imidazole and potassium carbonate, stir and react, filter, wash and dry to obtain the adsorbent support with surface covalently grafted imidazole.

3. The method for preparing low-residue chloromethyl ethyl ether according to claim 2, characterized in that: The SBA-15 raw powder, silica sol, and guar gum powder are mixed uniformly at a mass ratio of 100:20-40:5-10.

4. The method for preparing low-residue chloromethyl ethyl ether according to claim 2, characterized in that: The mass of the 3-chloropropyltrimethoxysilane is 15% to 40% of the mass of the carrier.

5. The method for preparing low-residue chloromethyl ethyl ether according to claim 2, characterized in that: The molar amount of imidazole is 2 to 3 times the molar amount of chloropropyl in the chloropropylated carrier.

6. The method for preparing low-residue chloromethyl ethyl ether according to claim 2, characterized in that: The molar amount of potassium carbonate is 0.5 to 2 times the molar amount of chloropropyl in the chloropropylated support.

7. The method for preparing low-residue chloromethyl ethyl ether according to claim 1, characterized in that: The molar ratio of anhydrous ethanol to formaldehyde units in paraformaldehyde is 2 to 4:

1.

8. The method for preparing low-residue chloromethyl ethyl ether according to claim 1, characterized in that: The degree of polymerization of the paraformaldehyde is 8 to 20.