Preparation method of low-methanol long-chain alkyl trimethyl ammonium chloride

Abstract

The invention belongs to the technical field of organic synthesis, and provides a preparation method of low-methanol long-chain alkyl trimethyl ammonium chloride, which comprises the following steps: pumping long-chain fatty amine into a reaction kettle, vacuumizing and dehydrating at negative pressure, dehydrating ethanol by using a molecular sieve, adding ethanol as a solvent, introducing chloromethane into the reaction kettle by using a chloromethane control system, and reacting for 2-4 hours; and adding deionized water, uniformly stirring, and adjusting the hardness of the finished product to obtain a white vanishing cream finished product. A chloromethane flow controller and a chloromethane evaporator are additionally arranged between a chloromethane storage tank and a reaction kettle, so that chloromethane enters the reaction kettle in a complete gaseous state at a constant speed, and meanwhile, a gas distributor is additionally arranged at the bottom of the reaction kettle, so that gaseous chloromethane is better distributed at each corner of the reaction kettle; the chloromethane and the long-chain fatty amine can be fully contacted and react, so that the generation of byproducts can be effectively avoided.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a method for preparing low-methanol long-chain alkyltrimethylammonium chloride. Background Technology

[0002] Aliphatic alkyltrimethylammonium chloride is a cationic surfactant. As a cationic surfactant, it has good emulsifying, wetting, detergency, bactericidal, softening, antistatic and anti-corrosion properties. Long-chain aliphatic alkyltrimethylammonium chloride has good softening and smoothing properties and is widely used in hair conditioners. However, as an additive in hair conditioners, it comes into direct contact with the human body. Long-chain alkyltrimethylammonium chloride contains a certain amount of methanol as a byproduct. Methanol is a harmful substance to humans. Therefore, it is necessary to design a process to prepare long-chain alkyltrimethylammonium chloride with low methanol content.

[0003] In the production of long-chain alkyltrimethylammonium chloride, especially in hair conditioners where the carbon chain length is typically between C16 and C22, solvents are required for the quaternization process to proceed smoothly. Since hair conditioners come into direct contact with the human body, food-grade ethanol is commonly used as the solvent. The ethanol is ultimately added to the conditioner along with the long-chain alkyl quaternary ammonium salt as a conditioning agent. The main factors contributing to methanol generation during the production of long-chain alkyltrimethylammonium chloride are: 1. Even food-grade ethanol inevitably introduces some methanol. 2. Methanol is a byproduct generated from the reaction of chloromethane, a raw material in the production of fatty alkyltrimethylammonium chloride. The methanol content in normally produced long-chain alkyltrimethylammonium chloride often exceeds 100 ppm. However, the lower the methanol content, the lower the irritation to the human body. Some hair conditioner manufacturers require a methanol content below 30 ppm, and some even lower. Currently, the main method used by long-chain alkyltrimethylammonium chloride manufacturers to control methanol is to remove the ethanol solvent at the end of the production process, carrying away the methanol, and then replenish the solvent. The solvent removal process increases energy consumption and production time, and the removed solvent often contains excessive levels of methanol, rendering it unusable. Replenishing the removed solvent is also cumbersome. This invention addresses this by controlling the methanol content before and during the reaction, keeping it below 20 ppm. Summary of the Invention

[0004] In order to control the methanol content in long-chain alkyl trimethyl ammonium chloride to below 20 ppm and meet the application requirements in the daily chemical industry, this invention provides a method for preparing low-methanol long-chain alkyl trimethyl ammonium chloride.

[0005] The technical solution adopted in this invention is as follows: A method for preparing low-methanol long-chain alkyltrimethylammonium chloride includes the following steps: S1: The long-chain fatty amine is pumped into the reactor and stirred at a rate of 500 r / min. After purging with nitrogen three times, the reactor is heated to 100-120℃ and dehydrated under vacuum for 1-2 hours with a vacuum degree of -0.095~-0.098 MPa, until the moisture content is detected to be less than 0.1%. S2: Ethanol is dehydrated using molecular sieves, and ethanol with a water content of less than 0.1% is added as a solvent to the vacuum-dehydrated reaction vessel. S3: Heat the reactor to 60-70℃ and introduce chloromethane into the reactor through the chloromethane control system. Control the reaction pressure in the reactor at 0.12-0.15Mpa and the reaction temperature at 80-90℃. After the chloromethane is introduced, keep the reactor at this temperature for 1 hour. Take a sample for analysis and check that the free amine content is less than 1.5%. The reaction is then complete. At the same time, detect the methanol content. S4: Add deionized water and stir well to adjust the consistency of the finished product, and obtain the white snow cream.

[0006] Furthermore, the chloromethane control system in step S3 includes a mass flow meter, an evaporator, and a distributor. The chloromethane, after being controlled by the flow meter and evaporated by the evaporator, enters the distributor through a pipeline and is then evenly distributed within the reactor by the distributor.

[0007] Furthermore, the distributor is installed at the bottom of the reactor and is connected to the evaporator through a pipe. The top surface of the distributor is provided with evenly distributed small holes with a diameter of 300-500 μm and a density of 3-5 holes per square centimeter.

[0008] Furthermore, the ethanol contains less than 30 ppm of food-grade ethanol.

[0009] Furthermore, the molar ratio of chloromethane to long-chain fatty amine is 0.97-1:1.

[0010] Furthermore, the amount of ethanol added in step S2 is 24%-26% of the mass of the mixture in the reactor.

[0011] Furthermore, the rate at which chloromethane is introduced in step S3 is 1-2 g / min. Furthermore, the amount of deionized water added in step S4 is 4%-6% of the finished product mass.

[0012] After adopting the above technical solutions, the beneficial effects of the present invention are as follows: By adding a chloromethane flow controller and a chloromethane evaporator between the chloromethane storage tank and the reactor, chloromethane enters the reactor in a uniform, completely gaseous state. At the same time, a gas distributor is added to the bottom of the reactor to better distribute the gaseous chloromethane in all corners of the reactor. Since chloromethane can fully contact and react with long-chain aliphatic amines, the generation of byproducts can be effectively avoided.

[0013] Food-grade ethanol is selected as the solvent, with a methanol content of less than 30 ppm, which can control the methanol content brought in by external raw materials; the moisture content in the food-grade ethanol is controlled to less than 0.1% by molecular sieve, and the moisture in long-chain fatty amines is removed by vacuum dehydration to avoid methanol generated by chloromethane and water during the reaction.

[0014] This technical solution, through the control of raw materials and process engineering, can ensure that the methanol content in the finished product meets the requirements of the daily chemical industry, avoiding the increase in energy consumption and time caused by methanol removal processes such as distillation and solvent removal. Attached Figure Description

[0015] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0016] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0017] Preparation Example

[0018] A method for preparing low-methanol long-chain alkyltrimethylammonium chloride includes the following steps: S1: The long-chain fatty amine is pumped into the reactor and stirred at a rate of 500 r / min. After purging with nitrogen three times, the reactor is heated to 100-120℃ and dehydrated under vacuum for 1-2 hours with a vacuum degree of -0.095~-0.098 MPa, until the moisture content is detected to be less than 0.1%. S2: Dehydrate purchased food-grade ethanol with a methanol content of less than 30ppm using molecular sieves, and control the moisture content to below 0.1%. Ethanol is added as a solvent to the vacuum-dehydrated reaction vessel. S3: Heat the reactor to 60-70℃. Control the flow rate of chloromethane in the chloromethane storage tank using a mass flow meter. After evaporation through an evaporator, the chloromethane is sent to a distributor at the bottom of the reactor. The top surface of the distributor has evenly distributed small holes with a diameter of 300-500μm and a density of 3-5 holes per square centimeter. The chloromethane rises evenly through the distributor and forms bubbles to fully contact and react with the long-chain fatty amine. The reaction pressure in the reactor is controlled at 0.12-0.15Mpa, and the reaction temperature is controlled at 80-90℃. The molar ratio of chloromethane to long-chain fatty amine is 0.97-1:1. The amount of solvent ethanol added is 24%-26% of the mass of the mixture. After the chloromethane is completely introduced, keep the mixture at this temperature for 1 hour. Take a sample for analysis and check that the free amine content is less than 1.5%. The reaction is considered complete. At the same time, the methanol content is also tested. S4: Add 4%-6% of the weight of the finished product in step 3 with deionized water and stir well to adjust the hardness of the finished product, and finally obtain the white snow cream.

[0019] Example 1

[0020] Preparation of 70% cetyltrimethylammonium chloride - corresponding market product 1631-70 350g of hexadecyl dimethyl tertiary amine (market designation: 1631-70) was added to the reactor. Stirring was started, and nitrogen was used for three purgings. The temperature was raised to 100℃, and vacuum dehydration was performed for 2 hours, with a moisture content of 500ppm. Then, 148g of food-grade ethanol (moisture content 900ppm) after molecular sieve drying was pumped into the reactor. The reactor temperature was set to 60℃, and the chloromethane evaporator was turned on and heated to 70℃. Chloromethane was introduced, with a flow rate set to 2g / min. The gaseous chloromethane from the evaporator was introduced into the reactor through a gas distributor. The reaction was exothermic, and the reactor temperature was controlled at 80-90℃ using cooling water. After all 64.5g of chloromethane was added, the mixture was kept at 80℃ for 1 hour. After the holding time, 29.5g of water was added, and the mixture was stirred thoroughly before discharging to obtain a white snow cream sample at room temperature.

[0021] Example 2

[0022] Add 350g of octadecyl dimethyl tertiary amine (market designation: 1831-70) to the reactor, start stirring and purge with nitrogen three times. Heat to 120℃, vacuum dehydrate for 1 hour, and check the moisture content to be 700ppm. Then, draw 148g of food-grade ethanol (moisture content 800ppm) after molecular sieve drying into the reactor. Set the reactor temperature to 70℃, turn on the chloromethane evaporator and control the evaporator temperature to 80℃, and start introducing chloromethane. Set the chloromethane flow rate to 1.5g / min. The gaseous chloromethane from the evaporator is introduced into the reactor through a gas distributor. The reaction is exothermic. Control the reactor temperature at 80-90℃ using cooling water. After all 58.5g of chloromethane has been added, maintain the temperature at 90℃ for 1 hour. After the maintenance is complete, add 27g of water, stir evenly, and discharge to obtain a white snow cream sample at room temperature.

[0023] Comparative Example 1

[0024] Add 350g of hexadecyl dimethyl tertiary amine (market designation: 1631-70) to the reactor. Then, pump 148g of untreated food-grade ethanol (approximately 5% moisture content) into the reactor. Set the reactor temperature to 60℃. Turn on the chloromethane evaporator and control its temperature to 70℃. Set the chloromethane flow rate to 2g / min. The gaseous chloromethane from the evaporator is introduced into the reactor through a gas distributor. The reaction is exothermic, and the reactor temperature is controlled at 80-90℃ using cooling water. After all 64.5g of chloromethane has been added, maintain the temperature at 80℃ for 1 hour. After this time, add 29.5g of water, stir well, and discharge to obtain a white snow cream sample at room temperature.

[0025] Comparative Example 2

[0026] Add 350g of octadecyl dimethyl tertiary amine (market designation: 1831-70) to the reactor, start stirring and purge with nitrogen three times, raise the temperature to 120℃, vacuum dehydrate for 1 hour, and check the moisture content to be 800ppm. Then, draw 175g of food-grade ethanol (moisture content 700ppm) dried with molecular sieves into the reactor, set the reactor temperature to 70℃, open the chloromethane valve, and directly introduce chloromethane into the reactor for reaction. The chloromethane introduction process is an exothermic reaction, and the reactor temperature is controlled at 80-90℃ by cooling water. After all 58.5g of chloromethane has been added, keep at 90℃ for 1 hour, stir evenly, and discharge to obtain a white, hard solid sample at room temperature.

[0027] Test case

[0028] The methanol content was determined using the headspace gas phase method.

[0029] Free amines were tested using acid-base titration.

[0030] The test results are recorded in the table below:

[0031] According to the test results, the difference between Example 1 and Comparative Example 1 lies in the water content of hexadecyl dimethyl tertiary amine. After vacuum dehydration, the methanol produced in the reaction with chloromethane in Example 1 is significantly reduced. The difference between Example 2 and Comparative Example 2 lies in the way chloromethane is introduced. By controlling the flow rate and using a method of first evaporation and then distribution via a distributor, chloromethane can fully react with octadecyl dimethyl tertiary amine to produce the finished product. Byproducts such as methanol are significantly reduced, and the product does not need to undergo secondary methanol removal treatment, which can directly meet the needs of high-end flower care products.

[0032] As can be seen from the comparison between the examples and the comparative examples, reducing the water content in the raw materials and solvents during the reaction process, as well as reducing the rate of chloromethane introduction and changing the introduction method, can promote the forward reaction and avoid the generation of byproducts such as methanol.

Claims

1. A process for the preparation of low-methanol long-chain alkyltrimethylammonium chloride characterized in that, The method comprises the following steps: S1: long-chain fatty amine is extracted into a reaction kettle, stirred at a speed of 500 r / min, replaced by nitrogen three times, the reaction kettle is heated to 100-120℃, and vacuum dewatering is performed under negative pressure for 1-2 h, the vacuum degree is-0.095~-0.098 Mpa, and the water content is detected to be less than 0.1%; S2: ethanol is dewatered by using molecular sieves, and ethanol with a water content of less than 0.1% is added into the reaction kettle after vacuum dewatering as a solvent; S3: the reaction kettle is heated to 60-70℃, and chloromethane is introduced into the reaction kettle through a chloromethane control system, the reaction kettle reaction pressure is controlled at 0.12-0.15 Mpa, the reaction temperature is controlled at 80-90℃, after the chloromethane is introduced, the reaction is preserved for 1 h, sampling analysis is performed to check that the free amine content is less than 1.5%, the reaction is ended, and the methanol content is detected; S4: deionized water is added and stirred uniformly, the hardness of the finished product is adjusted, and a white snow cream finished product is obtained.

2. A process for the preparation of low methanol long chain alkyl trimethyl ammonium chloride as claimed in claim 1, wherein, The chloromethane control system in the step S3 comprises a mass flow meter, an evaporator and a distributor, chloromethane and the evaporated chloromethane after passing through the flow meter to control the flow and the evaporator enter the distributor through a pipeline, and are uniformly distributed in the reaction kettle through the distributor.

3. A process for the preparation of low methanol long chain alkyl trimethyl ammonium chloride as claimed in claim 2, wherein, The distributor is installed at the inner bottom of the reaction kettle, the distributor is connected with the evaporator through a pipeline, the top surface of the distributor is provided with uniformly distributed small holes, the diameter of the small holes is 300-500 μm, and the density of the small holes is 3-5 per square centimeter.

4. A process for the preparation of low methanol long chain alkyl trimethyl ammonium chloride as claimed in claim 1, wherein, The methanol content in the ethanol is less than 30 ppm.

5. A process for the preparation of low methanol long chain alkyl trimethyl ammonium chloride as claimed in claim 1, wherein, The molar ratio of the chloromethane to the long-chain fatty amine is 0.97-1:

1.

6. A process for the preparation of low methanol long chain alkyl trimethyl ammonium chloride as claimed in claim 1, wherein, The ethanol addition amount in the step S2 is 24%-26% of the mass of the mixture in the reaction kettle.

7. A process for the preparation of low methanol long chain alkyl trimethyl ammonium chloride as claimed in claim 1, wherein, The introduction speed of the chloromethane in the step S3 is 1-2 g / min.

8. A process for the preparation of low methanol long chain alkyl trimethyl ammonium chloride as claimed in claim 1, wherein, The addition amount of the deionized water in the step S4 is 4%-6% of the mass of the finished product.

Images