Preparation method of tri-long-chain alkyl methyl carbonate quaternary ammonium salt

Abstract

The invention discloses a preparation method of tri-long-chain alkyl methyl carbonate quaternary ammonium salt, which comprises the following steps: firstly, adding dimethyl carbonate, a small amount of tri-long-chain alkyl tertiary amine and methanol into a high-pressure reaction kettle, then rapidly increasing the temperature in the reaction kettle to 120-150 DEG C under the protection of nitrogen and stirring, and after the pressure is stable, cooling to room temperature to obtain the tri-long-chain alkyl methyl carbonate quaternary ammonium salt. The feeding of the tri-long-chain alkyl tertiary amine is controlled by a pump according to a certain flow rate, so that the dimethyl carbonate in the reaction kettle is greatly excessive relative to the pumped tri-long-chain alkyl tertiary amine, and the dimethyl carbonate and the tri-long-chain alkyl tertiary amine entering the reaction kettle are rapidly and completely reacted. The conversion rate of the tri-long-chain alkyl tertiary amine reaches 98% or above, and the method has the characteristics of reduction of the use amount of dimethyl carbonate, reduction of the raw material and recycling cost, improvement of the reaction rate, shortening of the reaction time, low free amine content, good product quality and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical synthesis, and particularly relates to a method for preparing a tri-long-chain alkyl methyl carbonate quaternary ammonium salt. Background Art

[0002] Quaternary ammonium salts are currently the most widely used cationic surfactants in industry and have been widely used in various fields such as daily chemicals, textiles, printing and dyeing, construction, plastic processing and oil extraction. The traditional synthesis method is to use toxic substances such as alkyl halides or dimethyl sulfate as quaternizing agents, which often remain in the product due to incomplete quaternization reaction, causing certain harm to the human body and the natural environment. Dimethyl carbonate (DMC) is a widely used basic raw material for organic synthesis. In 1992, it passed the registration of non-toxic chemicals in Europe and was called a green chemical. Because its molecules contain methyl groups and have good reactivity, it can be used as a green and non-toxic quaternizing agent, completely replacing toxic methyl chloride, dimethyl sulfate, etc. for the preparation of quaternary ammonium salts. The synthesized methyl carbonate quaternary ammonium salt has an anion of CH3CO3 - It has a weak acidity and can react with different acids, even those weaker than carbonic acid, to prepare quaternary ammonium salts with various anions. In addition, since methanol and carbon dioxide are by-products of the hydrolysis and electrolysis of methyl carbonate quaternary ammonium salts, high-purity quaternary ammonium bases free of inorganic salts can be prepared through hydrolysis and electrolysis.

[0003] In the 1950s, Werntz et al. (US, 2635100) began to study the quaternization reaction of dimethyl carbonate. However, up to now, most reports have focused on the quaternization reaction of short-chain tertiary amines, the main representatives of which are trimethylamine, triethylamine and tributylamine.

[0004] The Chinese invention patent with the patent number ZL200610048203.3 discloses a method for synthesizing a fatty tertiary amine quaternary ammonium salt derivative. The method comprises placing a long-chain fatty tertiary amine, dimethyl carbonate and a low-carbon alcohol solvent in an autoclave, reacting at a temperature of 130-160°C, maintaining a reaction pressure of 0.5-1.5 MPa, and reacting for 4-10 h to obtain a quaternary ammonium ester, wherein the long-chain fatty tertiary amine is C8-C 18 Single long chain fatty acids or C8-C 18 of double-chain fatty acids.

[0005] The Chinese invention patent application with patent application number 201811371636.1 discloses a method for synthesizing a long-chain alkyl methyl carbonate quaternary ammonium salt, which comprises adding a long-chain alkyl dimethyl tertiary amine (monoalkyl tertiary amine) to dimethyl carbonate, and reacting the mixture at 145-155°C for 2.5-3.5 hours under nitrogen protection; after the obtained material is cooled, the long-chain alkyl methyl carbonate quaternary ammonium salt automatically precipitates from the dimethyl carbonate, and the mixture is obtained by solid-liquid separation, and the unreacted long-chain alkyl dimethyl tertiary amine is dissolved in the dimethyl carbonate.

[0006] In 2010, Geng Tao et al. (Fine Chemicals, 2010, 27 (6), 537-540) reported the quaternization reaction of dimethyl carbonate with long-chain alkyl tertiary amines to synthesize methyl carbonate quaternary ammonium salts. The quaternization rates of monoalkyl tertiary amines with different carbon chain lengths all reached above 98%, while the conversion rates of di-10- and di-18-carbon tertiary amines were lower, at 88.09% and 68.77%, respectively, because their steric hindrance was significantly greater than that of monoalkyl tertiary amines.

[0007] Chinese invention patent number ZL201510261221.9 discloses a method for preparing tri-long-chain alkylammonium bicarbonates and carbonates. The method uses tri-long-chain alkylamine, dimethyl carbonate, and methanol as raw materials, using carbon dioxide or a mixture of carbon dioxide and nitrogen as a protective gas. The reaction temperature is 110-150°C, the pressure is 0.5-1.5 MPa, and the reaction time is 12 hours to obtain trialkylmethylammonium methyl carbonate. This method specifies a molar ratio of tri-long-chain alkylamine to dimethyl carbonate of 1:4-5. However, the molar ratio of N235 to dimethyl carbonate described in Examples 1 and 2 is 1:5.5, and the molar ratio of N235 to dimethyl carbonate described in Example 3 is 1:5. This patent uses a large amount of dimethyl carbonate, which requires a long reaction time and high energy consumption to recover and reuse the dimethyl carbonate.

[0008] The Chinese invention patent with patent number ZL201710324368.7 discloses a method for preparing methyl tri-long-chain aliphatic ammonium carbonate. The method comprises the following steps: quaternizing a tri-long-chain aliphatic tertiary amine with dimethyl carbonate under the catalysis of bromide to obtain a mixture containing methyl tri-long-chain aliphatic carbonate monomethyl ester quaternary ammonium salt. After the dimethyl carbonate is recovered by vacuum distillation of the mixture, the mixture is placed in an alkaline solution for hydrolysis reaction. The hydrolysis reaction product is separated into oil and water, and the oil phase is methyl tri-long-chain aliphatic ammonium carbonate.

[0009] The above studies have shown that longer tertiary amine carbon chains increase steric hindrance, making it difficult for nitrogen atoms to attack the methyl groups on dimethyl carbonate. In particular, tri-long-chain alkyl tertiary amines are difficult to quaternize, resulting in low conversion rates. Achieving higher conversion rates requires increasing the ratio of dimethyl carbonate to tertiary amine, adding catalysts, increasing the amount of solvent (methanol), extending the reaction time, or raising the reaction temperature. These factors increase energy consumption and raw material costs, and complicate subsequent processing. Summary of the Invention

[0010] The present invention aims to solve the above technical problems existing in the prior art and provides a method for preparing a tri-long-chain alkyl methyl carbonate quaternary ammonium salt.

[0011] The technical solution of the present invention is: a method for preparing a tri-long-chain alkyl methyl carbonate quaternary ammonium salt, which is carried out according to the following steps: Step 1. Add dimethyl carbonate and methanol in a molar ratio of 1:0.5-1.5 to a reactor, and then add a tri-long chain alkyl tertiary amine in an amount of 5-30% by weight of the total tri-long chain alkyl tertiary amine to the reactor; Step 2. Replace the air in the reactor with nitrogen, then fill it with nitrogen to a pressure of 0.1-0.5 MPa. Heat to 120-150°C while stirring. Step 3. After the pressure in the reactor stabilizes, the remaining amount of the methanol solution of the tri-long-chain alkyl tertiary amine is pumped into the reactor at a rate of 5-20 kg / h until the molar ratio of the total amount of the tri-long-chain alkyl tertiary amine entering the reactor to dimethyl carbonate is 1:2-3, and the molar content of the tri-long-chain alkyl tertiary amine in the methanol solution of the tri-long-chain alkyl tertiary amine is 75-90%; starting from the time the remaining amount of the methanol solution of the tri-long-chain alkyl tertiary amine is pumped in, the reaction is continued for 9 hours, and the molar content of the tri-long-chain alkyl tertiary amine in the methanol solution of the tri-long-chain alkyl tertiary amine is 75-90%; Step 4. Cool the reactor naturally to room temperature and discharge the material; Step 5. The material is subjected to reduced pressure distillation to recover dimethyl carbonate and methanol, and the remaining residual liquid is methyl carbonate quaternary ammonium salt.

[0012] Preferably, the long-chain alkyl tertiary amine is trioctyldecyl tertiary amine, trioctyl tertiary amine or triheptyl tertiary amine.

[0013] The preferred preparation method of tri-long chain alkyl methyl carbonate quaternary ammonium salt is carried out according to the following steps: Step 1. Add 45 kg of dimethyl carbonate and 15 kg of methanol to a 500-liter autoclave, and then add 10 kg of triheptylamine to the reactor; Step 2. Replace the air in the reactor with nitrogen, then fill it with nitrogen to a pressure of 0.1 MPa. Heat to 140°C while stirring. Step 3. After the pressure in the reactor stabilized, 45 kg of triheptylamine methanol solution was pumped into the reactor at a rate of 15 kg / h, and then 15 kg of triheptylamine methanol solution was pumped into the reactor at a rate of 7.5 kg / h. The mixture was then allowed to react for a further 4 hours. The triheptylamine methanol solution was prepared by mixing 50 kg of triheptylamine with 10 kg of methanol. Step 4. Cool the reactor naturally to room temperature and discharge the material; Step 5. The material is subjected to reduced pressure distillation to recover dimethyl carbonate and methanol, and the remaining residual liquid is methyl carbonate quaternary ammonium salt.

[0014] The present invention first adds dimethyl carbonate, a small amount of tri-long-chain tertiary alkyl amine, and methanol to a high-pressure reactor. Then, under nitrogen protection and stirring, the temperature in the reactor can be rapidly raised to 120-150°C. After the pressure stabilizes, a pump is used to control the feeding of the tri-long-chain tertiary alkyl amine at a certain flow rate, thereby ensuring that the dimethyl carbonate in the reactor is greatly excessive relative to the pumped tri-long-chain tertiary alkyl amine, ensuring that the dimethyl carbonate and the tri-long-chain tertiary alkyl amine entering the reactor react quickly and completely. Compared with the existing technology, the present invention has the following advantages: (1) Shorten the reaction time. From the start of feeding the tri-long chain alkyl tertiary amine by using a pump at a certain flow rate to the end of the reaction, it only takes 9 hours; (2) Reduce the amount of dimethyl carbonate used. The molar ratio of the total amount of tri-long chain alkyl tertiary amine entering the reactor to dimethyl carbonate is only 1:2-3, which reduces the reaction time for dimethyl carbonate recovery and reduces energy consumption; (3) No catalyst is required, which reduces the cost of raw materials and avoids the problems of complicated post-processing caused by the use of catalysts.

[0015] (4) The target product has high yield and purity, the conversion rate of tri-long-chain alkyl tertiary amine is greater than 98%, and the free amine content is low. DETAILED DESCRIPTION

[0016] Implementation 1: A method for preparing a tri-long-chain alkyl methyl carbonate quaternary ammonium salt is carried out according to the following steps: Step 1. Add 45 kg of dimethyl carbonate and 20 kg of anhydrous methanol to a 500-liter autoclave, and then add 10 kg of trioctyldecyl tertiary amine (approximately 16.7% of the total amount of 60 kg) to the reactor. Step 2. Tighten the autoclave, replace the air in the reactor with nitrogen, and then fill it with 0.1 MPa nitrogen as a protective gas. Heat to 150°C while stirring. Step 3. After the pressure in the reactor stabilizes, 45 kg of a methanol solution of trioctyldecylamine was pumped into the reactor at a rate of 15 kg / h for 3 hours before the reaction. 15 kg of a methanol solution of trioctyldecylamine was then pumped into the reactor at a rate of 7.5 kg / h for 2 hours, followed by a further 4 hours of reaction. The methanol solution of trioctyldecylamine was prepared by mixing 50 kg of trioctyldecylamine with 10 kg of methanol. Step 4. Cool the reactor naturally to room temperature and discharge the material; Step 5. The material is subjected to vacuum distillation to recover dimethyl carbonate and methanol. The remaining residue consists of methyl methyl carbonate quaternary ammonium salt and unreacted trioctyldecyl tertiary amine. The methyl methyl carbonate quaternary ammonium salt content in the remaining residue is determined by chromatographic internal standard method. The conversion rate of trioctyldecyl tertiary amine is calculated to be 98.2%. Therefore, the small amount of trioctyldecyl tertiary amine in the remaining residue is negligible, and the remaining residue is methyl methyl carbonate quaternary ammonium salt. Example 2

[0017] A method for preparing a tri-long-chain alkyl methyl carbonate quaternary ammonium salt is carried out according to the following steps: Step 1. Add 45 kg of dimethyl carbonate and 20 kg of anhydrous methanol to a 500-liter autoclave, and then add 10 kg of trioctylamine (approximately 16.7% of the total amount of 60 kg) to the reactor. Step 2. Tighten the autoclave, replace the air in the reactor with nitrogen, and then fill it with 0.1 MPa nitrogen as a protective gas. Heat to 150°C while stirring. Step 3. After the pressure in the reactor stabilized, 45 kg of trioctylamine methanol solution was pumped into the reactor at a rate of 15 kg / h for 3 hours before the reaction. 15 kg of trioctylamine methanol solution was then pumped into the reactor at a rate of 7.5 kg / h for 2 hours, followed by an additional 4 hours of reaction. The trioctylamine methanol solution was prepared by mixing 50 kg of trioctylamine with 10 kg of methanol. Step 4. Cool the reactor naturally to room temperature and discharge the material; Step 5. The material is subjected to vacuum distillation to recover dimethyl carbonate and methanol. The remaining residue consists of methyl carbonate quaternary ammonium salt and unreacted trioctylamine. The methyl carbonate quaternary ammonium salt content in the remaining residue is determined by chromatographic internal standard method. The trioctylamine conversion rate is calculated to be 98.8%, so the small amount of trioctylamine in the remaining residue is negligible. The remaining residue is methyl carbonate quaternary ammonium salt. Example 3

[0018] A method for preparing a tri-long-chain alkyl methyl carbonate quaternary ammonium salt is carried out according to the following steps: Step 1. Add 45 kg of dimethyl carbonate and 15 kg of anhydrous methanol to a 500-liter autoclave, and then add 10 kg of triheptylamine (approximately 16.7% of the total amount of 60 kg) to the reactor. Step 2. Tighten the autoclave, replace the air in the reactor with nitrogen, and then fill it with 0.1 MPa nitrogen as a protective gas. Heat to 140°C while stirring. Step 3. After the pressure in the reactor stabilized, three hours before the reaction, 45 kg of triheptylamine methanol solution was pumped into the reactor at a rate of 15 kg / h. Over a further two hours, 15 kg of trioctylamine methanol solution was pumped into the reactor at a rate of 7.5 kg / h. The reaction was then continued for an additional four hours. The triheptylamine methanol solution was prepared by mixing 50 kg of triheptylamine with 10 kg of methanol. Step 4. Cool the reactor naturally to room temperature and discharge the material; Step 5. The material is subjected to reduced pressure distillation to recover dimethyl carbonate and methanol, leaving a residual liquid consisting of methyl carbonate quaternary ammonium salt and unreacted triheptylamine. The methyl carbonate quaternary ammonium salt content in the residual liquid is determined using a chromatographic internal standard method. Calculated conversion of triheptylamine is 98.9%, indicating that the small amount of triheptylamine in the residual liquid is negligible. The residual liquid is methyl carbonate quaternary ammonium salt.

Claims

1. A method for preparing a tri-long chain alkyl methyl carbonate quaternary ammonium salt, characterized in that Follow these steps: Step 1. Add dimethyl carbonate and methanol in a molar ratio of 1:0.5-1.5 to a reactor, and then add a tri-long chain alkyl tertiary amine in an amount of 5-30% by weight of the total tri-long chain alkyl tertiary amine to the reactor; Step 2. Replace the air in the reactor with nitrogen, then fill it with nitrogen to a pressure of 0.1-0.5 MPa. Heat to 120-150°C while stirring. Step 3. After the pressure in the reactor stabilizes, the remaining tri-long-chain alkyl tertiary amine methanol solution is pumped into the reactor at a flow rate of 5-20 kg / h until the molar ratio of the total amount of tri-long-chain alkyl tertiary amine to dimethyl carbonate in the reactor is 1:2-3, and the molar content of the tri-long-chain alkyl tertiary amine in the methanol solution is 75-90%; the reaction is carried out for 9 hours from the start of pumping the remaining tri-long-chain alkyl tertiary amine methanol solution. Step 4. Cool the reactor naturally to room temperature and discharge the material; Step 5. The material is subjected to reduced pressure distillation to recover dimethyl carbonate and methanol, and the remaining residual liquid is methyl carbonate quaternary ammonium salt.

2. The method for preparing a tri-long-chain alkyl methyl carbonate quaternary ammonium salt according to claim 1, wherein: The long-chain alkyl tertiary amine is trioctyldecyl tertiary amine, trioctyl tertiary amine or triheptyl tertiary amine.

3. The preparation method of tri-long chain alkyl methyl carbonate quaternary ammonium salt according to claim 2, wherein Follow these steps: Step 1. Add 45 kg of dimethyl carbonate and 15 kg of methanol to a 500-liter autoclave, and then add 10 kg of triheptylamine to the reactor; Step 2. Replace the air in the reactor with nitrogen, then fill it with nitrogen to a pressure of 0.1 MPa. Heat to 140°C while stirring. Step 3. After the pressure in the reactor stabilized, 45 kg of triheptylamine methanol solution was pumped into the reactor at a rate of 15 kg / h, and then 15 kg of triheptylamine methanol solution was pumped into the reactor at a rate of 7.5 kg / h. The mixture was then allowed to react for a further 4 hours. The triheptylamine methanol solution was prepared by mixing 50 kg of triheptylamine with 10 kg of methanol. Step 4. Cool the reactor naturally to room temperature and discharge the material; Step 5. The material is subjected to reduced pressure distillation to recover dimethyl carbonate and methanol, and the remaining residual liquid is methyl carbonate quaternary ammonium salt.