A process for the synthesis of hexamethyldisilazane

Abstract

The application provides a synthesis process of hexamethyldisilazane. The synthesis process comprises the following steps: adding trimethylchlorosilane into liquid ammonia, then performing high-pressure stirring reaction to obtain a reaction liquid; performing layer separation, and performing rectification on the lower layer of the reaction liquid to obtain hexamethyldisilazane; performing pressure relief on the upper layer of the reaction liquid, and ammonia gas is generated after the liquid ammonia is vaporized, and ammonium chloride solid is precipitated; performing reduced-pressure drying on the ammonium chloride solid, desorbing the ammonia gas adsorbed on the ammonium chloride, and obtaining refined ammonium chloride. The reaction does not need to add any solvent, the reaction rate is adjusted by controlling the dropping speed of trimethylchlorosilane, and the generated by-product ammonium chloride is completely dissolved by controlling the addition amount of liquid ammonia, so that the mass and heat transfer effects of the reaction are ensured, the product conversion rate is improved, the reaction time is shortened, and the product is easy to separate. The method avoids the use of solvent, generates less waste liquid, is green and environmental protection, and is low in cost.

Description

Technical Field

[0001] This invention relates to a synthesis process for hexamethyldisilazane, belonging to the field of organic synthesis. Background Technology

[0002] Hexamethyldisilazane, an important organosilicon reagent, has also rapidly developed in recent years as an indispensable intermediate in antibiotic preparation. It has wide applications in the pharmaceutical, semiconductor, and rubber industries.

[0003] In the pharmaceutical field, hexamethyldisilazane is mainly used for silylation in the synthesis of amikacin, penicillin, cephalosporins, fluorouracil, and various penicillin derivatives. In the semiconductor field, it is used as a binder in photoetching agents to modify the surface of crystal wafers. In the rubber industry, it can be used not only as a raw material for synthesizing silicone rubber but also as a modifier to effectively improve the heat resistance of rubber. In the lithium battery industry, adding hexamethyldisilazane to the electrolyte improves the storage and thermal stability of lithium-ion electrolytes, while also improving the electrochemical and cycle performance of lithium-ion batteries.

[0004] There are three commonly used processes for synthesizing hexamethyldisilazane: ① Reaction of trimethylsilane with ammonia under Pt or Pd catalysis; this method requires high reaction temperatures and strict equipment requirements. ② Reaction of hexamethyldisilazane with concentrated sulfuric acid to form silica ester sulfate, followed by direct ammonia reaction; this method has low yield, and production costs are constantly increasing due to the scarcity of raw material silica ethers. ③ Ammoniation of trimethylchlorosilane and ammonia to produce hexamethyldisilazane; this method has a simple reaction process, requiring only the introduction of ammonia into the reaction solution to obtain the product. However, this method requires the addition of a large amount of solvent, resulting in high separation energy consumption. It also produces ammonium chloride as a byproduct, forming solid agglomerates that easily encapsulate reactants and products, severely hindering mass transfer and product separation, leading to slow reaction conversion and difficulty in improving the conversion rate. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a synthesis process for hexamethyldisilazane. This invention uses trimethylchlorosilane and liquid ammonia as raw materials, and produces hexamethyldisilazane through high-pressure reaction and liquid-phase ammoniation. This invention eliminates the need for any solvents. The reaction rate is adjusted by controlling the dropping rate of trimethylchlorosilane, and the amount of liquid ammonia added is controlled to ensure complete dissolution of the byproduct ammonium chloride, guaranteeing efficient mass and heat transfer, improving product conversion rate, shortening reaction time, and facilitating product separation. This method avoids the use of solvents, generates minimal waste liquid, is environmentally friendly, and has low cost.

[0006] The technical solution of the present invention is as follows:

[0007] A process for synthesizing hexamethyldisilazane includes the following steps:

[0008] (1) Trimethylchlorosilane was added dropwise to liquid ammonia, and then the reaction was carried out under high pressure and stirred to obtain a reaction solution; the layers were separated, and the clear lower layer of the reaction solution was distilled to obtain hexamethyldisilazane;

[0009] (2) After depressurization, the upper clear liquid of the reaction solution is vaporized to obtain ammonia gas, and ammonium chloride solid is precipitated at the same time. The ammonium chloride solid is dried under reduced pressure to desorb the ammonia gas adsorbed on the ammonium chloride and obtain refined ammonium chloride.

[0010] According to a preferred embodiment of the present invention, in step (1), the reaction between trimethylchlorosilane and liquid ammonia is carried out in a reaction vessel; the volume of liquid ammonia filling the reaction vessel is ≥50% (i.e., the volume of liquid ammonia accounts for ≥50% of the volume of the reaction vessel).

[0011] According to a preferred embodiment of the present invention, in step (1), the mass ratio of trimethylchlorosilane to liquid ammonia is 1:(1-5), preferably 1:1.5.

[0012] According to a preferred embodiment of the present invention, in step (1), the dropping rate is 4 kg / min-10 kg / min. During the dropping process, the reaction inside the reactor is violent, and the dropping rate is controlled to ensure the stability of the reaction temperature and pressure.

[0013] According to a preferred embodiment of the present invention, in step (1), during the addition of trimethylchlorosilane, the temperature of the liquid ammonia system is controlled to be ≤60℃, preferably 30-35℃; the pressure is controlled to be ≥0.5MPa, preferably 0.7-0.8MPa; the addition is carried out under stirring conditions, with a stirring speed of 900-1000r / min.

[0014] According to a preferred embodiment of the present invention, in step (1), the temperature of the high-pressure stirring reaction is ≤60℃, preferably 30-35℃; the time of the high-pressure stirring reaction is 0.5-3h; the pressure of the high-pressure stirring reaction is ≥0.5MPa, preferably 0.7-0.8MPa; and the stirring speed of the high-pressure stirring reaction is 900-1000r / min.

[0015] According to the present invention, in step (1), the reaction solution will separate into layers after standing. The main component of the lower layer is hexamethyldisilazane, and the main component of the upper layer is liquid ammonia.

[0016] According to a preferred embodiment of the present invention, in step (1), the distillation is carried out in a distillation column; the bottom temperature of the distillation column is 125-130°C and the top temperature is 100-105°C; hexamethyldisilazane is obtained at the bottom of the column and hexamethyldisilazane is obtained as a byproduct at the top of the column.

[0017] According to a preferred embodiment of the present invention, in step (2), the pressure relief rate is ≤0.49 MPa / min, preferably 0.05 MPa / min. The ammonium chloride particle size is controlled by controlling the pressure relief rate.

[0018] According to a preferred embodiment of the present invention, in step (2), ammonia gas is dried and then compressed to obtain liquid ammonia for reuse.

[0019] According to a preferred embodiment of the present invention, in step (2), the reduced pressure drying conditions are: temperature controlled at 30-60℃, preferably 50℃; vacuum degree controlled at 0.01-0.09MPa, preferably 0.07MPa.

[0020] According to a preferred embodiment of the present invention, the synthesis process of hexamethyldisilazane includes the following steps:

[0021] The reactor is pre-cooled to ≤30℃. Liquid ammonia is then transferred into the reactor, and the internal pressure is set to 0.7-0.8MPa and the temperature to 30-35℃. Stirring is then started. Trimethylchlorosilane is transferred to a metering tank and then added dropwise into the reactor. During the dropwise addition, the reactor temperature is maintained at 30-35℃ and the pressure at 0.7-0.8MPa. After the dropwise addition is complete, a high-pressure stirring reaction is carried out at a pressure of 0.7-0.8MPa and a temperature of 30-35℃ to obtain a reaction solution. The reaction solution is transferred to a separator, and the pressure in the transfer pipeline and the separator is maintained at 0.7-0.8MPa. The mixture is allowed to stand at room temperature for 0.2-3 hours to separate into layers. The lower clear liquid is transferred to a crude product buffer tank, depressurized, and then transferred to a distillation column for distillation. Hexamethyldisilazane is obtained from the bottom of the column and transferred to a finished product tank. Hexamethyldisilazane is obtained from the top of the column and transferred to a by-product finished product tank.

[0022] The upper clear liquid in the separator is transported to the dryer and depressurized, where the liquid ammonia is vaporized and ammonium chloride solid is precipitated. The ammonia gas is dried in the dryer and transported to the ammonia gas compression system to obtain liquid ammonia for reuse. The ammonium chloride solid is dried under reduced pressure to desorb the ammonia gas adsorbed on the ammonium chloride and obtain refined ammonium chloride.

[0023] According to the present invention, liquid ammonia can be transported by means of high-pressure pumps, pressure differential, etc., with pressure differential transport being preferred. The liquid ammonia storage tank is pressurized by a liquid ammonia vaporizer to achieve the purpose of transporting liquid ammonia. Other materials can be transported by means of high-pressure pumps, pressure differential, etc., with pressure differential transport being preferred.

[0024] The technical features and beneficial effects of this invention are as follows:

[0025] 1. This invention uses trimethylchlorosilane and liquid ammonia as raw materials to produce hexamethyldisilazane through high-pressure reaction and liquid-phase ammoniation. Liquid ammonia serves as both a reactant and a solvent, eliminating the need for additional solvent addition. Due to the high solubility of ammonium chloride in liquid ammonia (37.2 g / 100 g, -20.5 °C), no solvent is required during the reaction. By controlling the amount of liquid ammonia added and the dropping rate of trimethylchlorosilane, the reaction rate can be controlled, ensuring complete dissolution of the byproduct ammonium chloride. This guarantees efficient mass and heat transfer, reduces resistance to mass and heat transfer, improves the stability of reaction temperature and pressure, and enhances product conversion, yield, and purity while shortening reaction time.

[0026] 2. The byproduct ammonium chloride produced by this invention is completely dissolved in liquid ammonia, avoiding the encapsulation and adsorption of the raw material trimethylchlorosilane by solid ammonium chloride, thereby improving the reaction conversion rate, shortening the production time of a single batch, and increasing the production capacity of the equipment.

[0027] 3. This invention does not add any solvent to dissolve ammonium chloride, avoiding the consumption of large amounts of solvent, reducing separation energy consumption, lowering costs, and making it environmentally friendly. The absence of a salt-dissolving agent avoids both the generation of large amounts of waste liquid and the side reaction of hexamethyldisilazane to siloxane conversion. Furthermore, this invention does not produce ammonium chloride solution or wastewater, making it environmentally friendly. The generated ammonia gas is recovered from liquid ammonia using an ammonia compressor, significantly reducing environmental pollution during production and saving raw material liquid ammonia, thus lowering costs. The generated ammonium chloride solid can be fully recovered, achieving full utilization of all substances and maximizing economic benefits. In summary, this invention is environmentally friendly, low-cost, and maximizes economic benefits, making it suitable for industrial applications.

[0028] 4. The post-processing method of this invention can avoid the encapsulation of the product by solid ammonium chloride, making the product easy to separate and obtain a high-purity target product. This post-processing method generates no wastewater and can recover liquid ammonia and ammonium chloride, fully realizing the reuse of materials and maximizing economic benefits.

[0029] 5. The preparation method of the present invention, as a whole, combines a suitable mass ratio of trimethylchlorosilane and liquid ammonia, a suitable dropping rate of trimethylchlorosilane, suitable high-pressure reaction conditions, and a suitable post-processing method to achieve the excellent effect of the present invention. Detailed Implementation

[0030] The present invention will be further described in detail below through specific embodiments. However, these specific embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0031] Unless otherwise specified, the experimental methods involved in the embodiments are existing methods; the reagents, equipment, etc. involved are existing technologies and can be obtained commercially unless otherwise specified.

[0032] Example 1

[0033] A process for synthesizing hexamethyldisilazane includes the following steps:

[0034] The volume is 1m³ 3 The high-pressure reactor was pre-cooled to ≤30℃. 420 kg of liquid ammonia was transferred into the reactor, and the internal pressure was set to 0.7-0.8 MPa and the temperature to 30-35℃. The reactor was stirred at 960 r / min. 280 kg of trimethylchlorosilane was transferred to a metering tank and gradually added dropwise to the high-pressure reactor via an automatic interlocking device at a dropping rate of 6 kg / min. During the dropping process, the reactor temperature was maintained at 30-35℃ and the pressure at 0.7-0.8 MPa. After the dropping was completed, the reactor was kept at 0.7-0.8 MPa and 30-35℃ with continued stirring for 2 hours to complete the reaction and obtain the reaction solution.

[0035] The reaction liquid is transported to the separator, and the pressure in the transport pipeline and separator is maintained at 0.7-0.8 MPa. It is allowed to stand at room temperature for 0.5 hours to separate into layers. The lower clear liquid is transported to the crude product buffer tank and depressurized. Then it is transported to the distillation column for continuous crude product distillation. The bottom temperature of the distillation column is controlled at 125-130℃ and the top temperature is controlled at 100-105℃. The hexamethyldisilazane at the bottom of the column is transported to the finished product tank, and the hexamethyldisilazane at the top of the column is transported to the by-product finished product tank.

[0036] The upper clear liquid in the separator is transported to the dryer and depressurized at a rate of 0.05 MPa / min. The liquid ammonia is vaporized, and ammonium chloride solid is precipitated. The ammonia gas is dried in the dryer and transported to the ammonia compression system to obtain liquid ammonia for reuse. The ammonium chloride solid is dried under reduced pressure (the temperature in the dryer is gradually increased from room temperature to 50°C, and the vacuum degree is gradually increased from 0 to 0.07 MPa) to desorb the ammonia gas adsorbed on the ammonium chloride, thus obtaining refined ammonium chloride.

[0037] The above-mentioned material conveying methods can be implemented using existing technologies; they can be carried out using high-pressure pumps, pressure differentials, etc.

[0038] Example 2

[0039] A synthesis process for hexamethyldisilazane is the same as in Example 1, except that the amount of liquid ammonia added is 280 kg and the amount of trimethylchlorosilane added is 280 kg; the other steps and conditions are the same as in Example 1.

[0040] Example 3

[0041] A synthesis process for hexamethyldisilazane is the same as in Example 1, except that: the amount of liquid ammonia added is 420 kg, and the amount of trimethylchlorosilane added is 210 kg; other steps and conditions are the same as in Example 1.

[0042] Example 4

[0043] A synthesis process for hexamethyldisilazane is the same as in Example 1, except that the temperature inside the reactor is maintained at 40-45°C; other steps and conditions are the same as in Example 1.

[0044] Example 5

[0045] A synthesis process for hexamethyldisilazane is the same as in Example 1, except that the temperature inside the reactor is maintained at 55-60°C; other steps and conditions are the same as in Example 1.

[0046] Example 6

[0047] A synthesis process for hexamethyldisilazane is the same as in Example 1, except that the pressure inside the reactor is maintained at 0.5-0.6 MPa; other steps and conditions are the same as in Example 1.

[0048] Example 7

[0049] A synthesis process for hexamethyldisilazane is the same as in Example 1, except that the pressure inside the reactor is maintained at 0.9-1 MPa; other steps and conditions are the same as in Example 1.

[0050] Comparative Example 1

[0051] A synthesis process for hexamethyldisilazane is the same as in Example 1, except that: the amount of liquid ammonia added is 70 kg, and the amount of trimethylchlorosilane added is 280 kg; other steps and conditions are the same as in Example 1.

[0052] Comparative Example 2

[0053] A synthesis process for hexamethyldisilazane is the same as in Example 1, except that the dropping rate of trimethylchlorosilane is 28 kg / min; the other steps and conditions are the same as in Example 1.

[0054] Comparative Example 3

[0055] A synthesis process for hexamethyldisilazane is the same as in Example 1, except that the dropping rate of trimethylchlorosilane is 2 kg / min; the other steps and conditions are the same as in Example 1.

[0056] Comparative Example 4

[0057] A synthesis process for hexamethyldisilazane is the same as in Example 1, except that the pressure inside the reactor is maintained at 0.1-0.2 MPa; other steps and conditions are the same as in Example 1.

[0058] Comparative Example 5

[0059] A synthesis process for hexamethyldisilazane is the same as in Example 1, except that the temperature inside the reactor is maintained at 75-80°C; other steps and conditions are the same as in Example 1.

[0060] Comparative Example 6

[0061] A process for synthesizing hexamethyldisilazane includes the following steps:

[0062] The volume is 1m³ 3 The high-pressure reactor was pre-cooled to ≤30℃. 420 kg of liquid ammonia was added to the reactor, setting the pressure inside to 0.7-0.8 MPa and the temperature to 30-35℃. The reactor was stirred at 960 r / min. 280 kg of trimethylchlorosilane was added to a metering tank and gradually dripped into the high-pressure reactor using an automatic interlocking device at a drip rate of 6 kg / min. During the dripping process, the reactor temperature was maintained at 30-35℃ and the pressure at 0.7-0.8 MPa. After the dripping was complete, the reactor was kept at 0.7-0.8 MPa and 30-35℃ with continued stirring for 2 hours to complete the reaction and obtain the reaction liquid. The pressure was released, the liquid ammonia was vaporized, and ammonia gas was recovered, while ammonium chloride solid precipitated. After filtration, the filtrate was sent to a distillation column for distillation. The bottom temperature of the distillation column was controlled at 125-130℃, and the top temperature at 100-105℃. Hexamethyldisilazane was obtained at the bottom of the column.

[0063] Comparative Example 7

[0064] A process for synthesizing hexamethyldisilazane includes the following steps:

[0065] The volume is 1m³ 3 The high-pressure reactor was pre-cooled to ≤30℃. 420 kg of liquid ammonia was transferred into the reactor, and the internal pressure was set to 0.7-0.8 MPa and the temperature to 30-35℃. The reactor was stirred at 960 r / min. 280 kg of trimethylchlorosilane was transferred to a metering tank and gradually added dropwise to the high-pressure reactor via an automatic interlocking device at a dropping rate of 6 kg / min. During the dropping process, the reactor temperature was maintained at 30-35℃ and the pressure at 0.7-0.8 MPa. After the dropping was completed, the reactor was kept at 0.7-0.8 MPa and 30-35℃ with continued stirring for 2 hours to complete the reaction and obtain the reaction solution. Depressurize, vaporize liquid ammonia, recover ammonia gas, and precipitate ammonium chloride solid; add 700 kg of water as a salt solvent under stirring conditions, let stand at room temperature for 30 minutes, separate into layers, take the supernatant, and send it to a distillation column for distillation, control the bottom temperature of the distillation column to 125-130℃ and the top temperature of the column to 100-105℃, and obtain hexamethyldisilazane at the bottom of the column.

[0066] Test case

[0067] The yield and purity data of the target product hexamethyldisilazane in the examples and comparative examples are shown in Table 1 below.

[0068] Table 1

[0069]

[0070]

[0071] As can be seen from the above, the embodiments of the present invention have superior effects compared to the comparative examples. The preparation method of the present invention, as a whole, works together to achieve the superior effects of the present invention; any change in conditions will affect the yield of the obtained product, etc.

Claims

1. A process for synthesizing hexamethyldisilazane, comprising the following steps: (1) Trimethylchlorosilane was added dropwise to liquid ammonia and then subjected to high-pressure stirring to obtain a reaction solution; the reaction solution was separated into layers, and the clear lower layer of the reaction solution was distilled to obtain hexamethyldisilazane; the dropping rate was 4 kg / min-10 kg / min; the mass ratio of trimethylchlorosilane to liquid ammonia was 1:(1-5); the temperature of the high-pressure stirring reaction was ≤60℃; the pressure of the high-pressure stirring reaction was ≥0.5 MPa; (2) After the upper clear liquid of the reaction solution is depressurized, the liquid ammonia is vaporized to obtain ammonia gas, and ammonium chloride solid is precipitated at the same time. The ammonium chloride solid is dried under reduced pressure to desorb the ammonia gas adsorbed on the ammonium chloride to obtain refined ammonium chloride.

2. The synthesis process of hexamethyldisilazane according to claim 1, characterized in that, In step (1), the reaction between trimethylchlorosilane and liquid ammonia is carried out in a reaction vessel; the volume of liquid ammonia in the reaction vessel is ≥50%.

3. The synthesis process of hexamethyldisilazane according to claim 1, characterized in that, In step (1), the mass ratio of trimethylchlorosilane to liquid ammonia is 1:1.

5.

4. The synthesis process of hexamethyldisilazane according to claim 1, characterized in that, In step (1), during the addition of trimethylchlorosilane, the temperature of the liquid ammonia system is controlled to be ≤60℃; the pressure is controlled to be ≥0.5MPa; the addition is carried out under stirring conditions, with a stirring speed of 900-1000 r / min.

5. The synthesis process of hexamethyldisilazane according to claim 4, characterized in that, In step (1), during the addition of trimethylchlorosilane, the temperature of the liquid ammonia system is controlled at 30-35℃ and the pressure is controlled at 0.7-0.8MPa.

6. The synthesis process of hexamethyldisilazane according to claim 1, characterized in that, In step (1), the temperature of the high-pressure stirring reaction is 30-35℃; the time of the high-pressure stirring reaction is 0.5-3h; the pressure of the high-pressure stirring reaction is 0.7-0.8Mpa; and the stirring speed of the high-pressure stirring reaction is 900-1000 r / min.

7. The synthesis process of hexamethyldisilazane according to claim 1, characterized in that, In step (1), distillation is carried out in a distillation column; the bottom temperature of the distillation column is 125-130℃ and the top temperature is 100-105℃; hexamethyldisilazane is obtained at the bottom of the column and hexamethyldisilazane is obtained as a byproduct at the top of the column.

8. The synthesis process of hexamethyldisilazane according to claim 1, characterized in that, In step (2), the depressurization rate is ≤0.49 MPa / min.

9. The synthesis process of hexamethyldisilazane according to claim 8, characterized in that, The pressure relief rate is 0.05 MPa / min.

10. The synthesis process of hexamethyldisilazane according to claim 1, characterized in that, In step (2), ammonia is dried and then compressed to obtain liquid ammonia for reuse; the vacuum drying conditions are: temperature controlled at 30-60℃; vacuum degree controlled at 0.01-0.09MPa.

11. The synthesis process of hexamethyldisilazane according to claim 1, characterized in that, The synthesis process of hexamethyldisilazane includes the following steps: pre-cooling the reactor to ≤30℃, transferring liquid ammonia into the reactor, setting the pressure inside the reactor to 0.7-0.8MPa and the temperature to 30-35℃, and starting stirring; transferring trimethylchlorosilane into a metering tank, and then adding it dropwise into the reactor; during the dropwise addition, maintaining the reactor temperature at 30-35℃ and the pressure at 0.7-0.8MPa; after the dropwise addition is completed, conducting a high-pressure stirring reaction at a pressure of 0.7-0.8MPa and a temperature of 30-35℃ to obtain a reaction solution; transferring the reaction solution into a separator, maintaining the pressure of the conveying pipeline and the separator at 0.7-0.8MPa, allowing it to stand at room temperature for 0.2-3 hours, allowing it to separate into layers, transferring the lower clear liquid to a crude product buffer tank, depressurizing it, and then transferring it to a distillation column for rectification, obtaining hexamethyldisilazane at the bottom of the column and transferring it to a finished product tank, and obtaining hexamethyldisilazane at the top of the column and transferring it to a by-product finished product tank; The upper clear liquid in the separator is transported to the dryer and depressurized, where the liquid ammonia is vaporized and ammonium chloride solid is precipitated. The ammonia gas is dried in the dryer and transported to the ammonia gas compression system to obtain liquid ammonia for reuse. The ammonium chloride solid is dried under reduced pressure to desorb the ammonia gas adsorbed on the ammonium chloride and obtain refined ammonium chloride.

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