An apparatus and method for the continuous preparation of low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane.

Abstract

This invention relates to an apparatus and method for the continuous preparation of low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane. The method utilizes hexamethylcyclotrisiloxane as a raw material to continuously prepare low-viscosity hydroxyl silicone oil with a viscosity range of 15-40 mPa·s under the action of an organic solvent and a solid catalyst. The specific steps are as follows: the raw material is fed into a mixer and mixed evenly with a capping agent and solvent, then fed into a reactor. The mixture reacts under the action of a solid catalyst. The crude product is collected in a phase separator to separate the oil and water phases. The aqueous phase is returned to the mixer to continue participating in the reaction. The oil phase is sequentially passed through a flash separator and a falling film evaporator to evaporate and separate the residual solvent. The solvent is recovered and reused after passing through a multi-stage condensation system. This invention uses D3, a byproduct of the production of organosilicon DMC in the organosilicon industry, as a raw material to prepare low-viscosity hydroxyl silicone oil. The raw material is inexpensive, readily available, and has a much higher reactivity than DMC.

Description

Technical Field

[0001] This invention belongs to the field of polysiloxane synthesis technology, and in particular to an apparatus and method for the continuous preparation of low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane. Background Technology

[0002] Low-viscosity hydroxyl silicone oil is a hydroxyl-terminated polydimethylsiloxane with a relative molecular mass of 100-1000. It is an important processing aid in the field of silicone rubber and other polymers, primarily used as a structure control agent to prevent silicone rubber from slowly hardening and deteriorating in processing performance during long-term storage. In addition, low-viscosity hydroxyl silicone oil emulsions are also widely used in fiber fabric finishing and can serve as an excellent additive and filler silanizing agent for plastic products. With the continuous expansion of domestic market demand for silicone rubber and plastic products, low-viscosity hydroxyl silicone oil has broad application prospects.

[0003] The widely used method for preparing low-viscosity hydroxyl silicone oil is the "acid anhydride method". This process uses dimethylsiloxane mixed cyclic compound (DMC) as raw material, which undergoes ring-opening polymerization with acetic anhydride under the catalysis of sulfuric acid and phosphoric acid. The crude product is then hydrolyzed and washed to obtain low-viscosity hydroxyl silicone oil. This process is a batch production process with high raw material and auxiliary material prices, low catalytic activity, and low primary conversion rate. In addition, the hydrolysis and washing process of the crude product generates a large amount of acidic wastewater, and the product often contains residual acidic substances and odors, which affect the product's appearance and storage performance.

[0004] Chinese patent ZL 202110473909.9 discloses a process for producing low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane. This process uses a nitrogen-containing organic base as a catalyst. After the reaction, an acidic substance is added as a neutralizing agent. After neutralization, the product remains in the form of salt, resulting in an ammonia odor that affects downstream applications. Furthermore, this patented technology does not include steps for removing water and siloxane rings from the low-viscosity hydroxyl silicone oil, resulting in an effective hydroxyl content (i.e., -Si-OH content) of only 6.5%-8.5%. Summary of the Invention

[0005] The purpose of this invention is to provide an apparatus and method for the continuous preparation of low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane. The low-viscosity hydroxyl silicone oil is prepared using D3 as a raw material, which is inexpensive, readily available, and highly reactive. A hydrophobic modification process using a strong acid cation exchange resin is preferred, which solves the problems of low activity and easy residue in traditional liquid acid-base catalysts, while ensuring the long-term stability and catalytic activity of the hydrophobically modified strong acid cation exchange resin catalyst. A high-efficiency phase separator and a high-efficiency solvent removal device are preferred, enabling continuous operation of the entire apparatus. The overall product yield can reach over 98%, and the solvent reuse rate can reach over 95%. A freeze-drying process is preferred, resulting in a product with a water content of less than 50 ppm, a siloxane cyclic content of 0.01%-1%, and a hydroxyl content of 8%-12%.

[0006] Technical solution of the present invention:

[0007] An apparatus for the continuous preparation of low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane, the apparatus comprising a feeder connected in sequence to a reactor and a phase separator, the top of the phase separator being connected in sequence to a flash separation tank and a falling film evaporator via pipes, the top of the falling film evaporator being connected in sequence to a multi-stage condensation system via pipes, a preheater being provided between the top of the phase separator and the flash separation tank via pipes, the bottom of the falling film evaporator being connected in sequence to a product cooler and a freeze dryer, and the freeze dryer being connected to a product packaging machine.

[0008] Preferably, the bottom of the multi-stage condensation system is connected to the feeder via a pipe.

[0009] Preferably, the bottom of the phase separator is connected to the feeder via a pipe.

[0010] Preferably, the feeder is equipped with a precision flow meter and a regulating valve, and the material temperature is 30-60℃;

[0011] The reactor is equipped with a heat exchange jacket on its outer wall;

[0012] The flash separator is equipped with a liquid distributor at the top and densely packed with Pall rings, Raschig rings, Taylor rings and other packing materials in the middle, which are made of corrosion-resistant materials.

[0013] The falling film evaporator is equipped with a liquid distributor at the top and a tube set in the middle, and the material flows downward in a thin film on the inner wall of the tube set;

[0014] A multi-stage condensation system consists of 2 to 5 heat exchangers and a collection tank.

[0015] A method for continuously preparing low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane, the method comprising the following steps:

[0016] S1: The raw material enters the feeder and is mixed evenly with the capping agent and solvent. It then enters the reactor and reacts under the action of a solid catalyst. The crude product is collected in the phase separator to separate the oil and water phases.

[0017] S2: The aqueous phase returns to the batching unit to continue participating in the reaction; the oil phase passes through a flash separator and a falling film evaporator in sequence to evaporate and separate the residual solvent. The solvent is recovered and reused after being processed by a multi-stage condensation system. The product is collected in a storage tank to obtain a crude low-viscosity hydroxyl silicone oil product.

[0018] Preferably, in step S1, the raw material is hexamethylcyclotrisiloxane (referred to as "D3"), with a main component content of 80%~99.99%; the end-capping agent is pure water; the molar ratio of raw material to end-capping agent is 1:(0.5-2); and the solvent is acetone. The reason is that the melting point of raw material D3 is 64℃, which is higher than the reaction temperature, and it is difficult to dissolve in water. Using acetone as a solvent can dissolve D3 and water simultaneously, achieving a homogeneous reaction, which is beneficial to improving the reaction efficiency. In addition, the boiling point of acetone is 56.5℃, which is very different from the boiling point of the effective component in low-viscosity hydroxyl silicone oil, making it very convenient for distillation separation and recovery.

[0019] The solid catalyst is a hydrophobically modified acidic cation exchange resin with a particle size of 1-5 mm.

[0020] The material temperature in the batching unit is 30-60℃.

[0021] The reactor temperature is controlled at 30-60℃ because the raw material hexamethylcyclotrisiloxane has strong reactivity. If the reaction temperature is higher than 60℃, the viscosity of the material will increase sharply and the process will be difficult to control.

[0022] Preferably, the preparation process of the hydrophobically modified acidic cation exchange resin is as follows: a fluorinated silane coupling agent and an alkyl silane coupling agent are mixed and prepared in a molar ratio of 1:(10-100) to form a modifier. Toluene and cyclohexane are used as dispersants. The strong acidic cation exchange resin is soaked in the dispersant with 1%-10% of the modifier for 4h-20h for modification. After filtration, washing, hot nitrogen purging and drying, it is ready for use.

[0023] Preferably, the fluorinated silane coupling agent is one or more selected from trifluoropropyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, and heptadecafluorodecyltrimethoxysilane; the alkylsilane coupling agent is one or more selected from methyltrimethoxy(ethoxy)silane and ethyltrimethoxy(ethoxy)silane. To improve the hydrophobic properties of the strongly acidic cation exchange resin surface, its static adsorbed water weight is reduced to below 5%, preventing hydroxyl silicone oil from adhering to the surface of the strongly acidic cation exchange resin, which would lead to agglomeration and caking of the solid catalyst, thus extending the service life of the solid catalyst to 3-5 years.

[0024] Preferably, in step S2, the material temperature inside the flash separator is 30~80℃, and the vacuum degree is 0.08~0.1MPa;

[0025] The material temperature inside the falling film evaporator is 30~80℃, and the vacuum degree is 0.08~0.10MPa;

[0026] The multi-stage condensation system uses circulating water, 3℃ water, -15℃ chilled brine, liquid ammonia or other heat exchange media, and the collection tank is insulated with a -15℃ chilled brine jacket.

[0027] Preferably, the drying and purification process of the crude low-viscosity hydroxyl silicone oil product collected from the bottom of the falling film evaporator is as follows: the product is cooled to 20-40°C by a product cooler, and then further cooled to -40°C to -20°C in a freeze dryer to freeze and crystallize the water and siloxane rings in the low-viscosity silicone oil. The solids are then removed by screening in the freeze dryer. The prepared low-viscosity hydroxyl silicone oil product has a viscosity range of 10-40 mPa·s, a hydroxyl content of 8%-12%, a water content of 1-100 ppm, and a siloxane ring content of 0.01%-1%.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. Low-viscosity hydroxyl silicone oil is prepared by using D3, a byproduct of the production of organosilicon DMC in the organosilicon industry, as a raw material. The raw material is inexpensive, readily available, and has a much higher reactivity than DMC.

[0030] 2. A hydrophobic modification process for strongly acidic cation exchange resin was optimized, which not only has high catalytic activity but also strong water resistance. It can maintain stability and catalytic activity in water for a long time, solving the problems of low activity and easy residue of traditional liquid acid and alkali catalysts. The product yield can reach over 98%.

[0031] 3. A high-efficiency phase separator is selected. The crude polymer product is pre-separated by the phase separator, and some of the solvent can be directly reused, which greatly reduces the processing volume of the subsequent solvent removal process and also effectively reduces the loss caused by the extraction of volatile solvents through the vacuum pipeline. The solvent reuse rate can reach more than 95%.

[0032] 4. The flash separator and falling film evaporator are used as high-efficiency solvent removal equipment. The ultra-low pressure flash evaporation and falling film evaporation process enables the low-boiling-point solvent in the crude product to be rapidly vaporized and separated. This avoids the hydroxyl polycondensation and viscosity increase caused by the low viscosity hydroxyl silicone oil being in a high temperature and high vacuum environment for a long time. It also enables the whole unit to operate continuously, greatly improving production efficiency. The product viscosity, hydroxyl content and other technical indicators are significantly better than the "acid anhydride method" process.

[0033] 5. A freeze-drying process using low-viscosity hydroxyl silicone oil is employed. This method leverages the principle that the crystallization temperature of hydroxyl-terminated polysiloxanes in the crude low-viscosity hydroxyl silicone oil is much lower than that of water and siloxane rings. Freeze-drying effectively removes water and siloxane rings from the product, avoiding the volatilization or loss of short-chain hydroxyl-terminated polysiloxane components with gas flow that occurs in vacuum distillation. It also avoids the problems of excessively high viscosity and reduced hydroxyl content caused by intermolecular dehydration and condensation of hydroxyl-terminated polysiloxanes under vacuum heating conditions. The resulting product has a water content of less than 50 ppm and a siloxane ring content of less than 1%. Attached Figure Description

[0034] Figure 1 This invention relates to an apparatus for the continuous preparation of low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane.

[0035] Figure 2 Example 2: Catalyst breakage, caking, and other undesirable phenomena.

[0036] In the diagram: 1. Feeder; 2. Reactor; 3. Solid catalyst; 4. Phase separator; 5. Flash separator; 6. Falling film evaporator; 7. Multi-stage condensation system; 8. Preheater; 9. Product cooler; 10. Freeze dryer; 11. Product packaging machine. Detailed Implementation

[0037] To enable those skilled in the art to better understand the technical solutions of the present invention, the applicant will now provide a more detailed description of the present invention in conjunction with the embodiments and accompanying drawings.

[0038] Example 1

[0039] An apparatus for the continuous preparation of low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane is provided. The apparatus includes a feeder 1, which is connected in sequence to a reactor 2 and a phase separator 4. The top of the phase separator 4 is connected in sequence to a flash separation tank 5 and a falling film evaporator 6 via pipes. The top of the falling film evaporator 6 is connected in sequence to a multi-stage condensation system 7 via pipes. A preheater 8 is provided between the top of the phase separator 4 and the flash separation tank 5 via pipes. The bottom of the falling film evaporator 6 is connected in sequence to a product cooler 9 and a freeze dryer 10. The freeze dryer 10 is connected to a product packaging machine 11.

[0040] Preferably, the bottom of the multi-stage condensation system 7 is connected to the feeder 1 via a pipe.

[0041] Preferably, the bottom of the phase separator 4 is connected to the feeder 1 via a pipe.

[0042] Preferably, the feeder 1 is equipped with a precision flow meter and a regulating valve, and the material temperature is 30-60℃;

[0043] The outer wall of reactor 2 is equipped with a heat exchange jacket;

[0044] The flash separator 5 is equipped with a liquid distributor at the top and densely packed with Pall rings, Raschig rings, Taylor rings and other packing materials in the middle, which are made of corrosion-resistant materials.

[0045] The falling film evaporator 6 is equipped with a liquid distributor at the top and a tube set in the middle, and the material flows downward in a thin film on the inner wall of the tube set;

[0046] The multi-stage condensation system 7 consists of 4 heat exchangers and a collection tank.

[0047] A method for continuously preparing low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane, the method comprising the following steps:

[0048] S1: The raw material enters the feeder 1 and is mixed evenly with the end-capping agent and solvent. It then enters the reactor 2 and reacts under the action of the solid catalyst 3. The crude product is collected in the phase separator 4 to separate the oil and water phases.

[0049] S2: The aqueous phase returns to the feeder 1 to continue participating in the reaction; the oil phase passes through the flash separator 5 and the falling film evaporator 6 in sequence to evaporate and separate the residual solvent. The solvent is recovered and reused after being processed by the multi-stage condensation system 7. The product is collected in the storage tank to obtain a crude low-viscosity hydroxyl silicone oil product.

[0050] Example 2

[0051] Using the apparatus and method of Example 1, Amberlyst 15 type strong acid cation exchange resin without hydrophobic modification was used as the catalyst, acetone as the solvent, the mass ratio of D3 to solvent was 1:1, and the molar ratio of D3 to water was 1:1. The reaction was carried out at 50°C for 30 min (reactor 2). The product was then desolventized at 50°C and a vacuum of 0.099 MPa (flash separation tank 5, falling film evaporator 6). The product viscosity was 48 mPa·s, and the hydroxyl content was 4.42%. After 30 days of continuous operation, the apparatus exhibited adverse phenomena such as catalyst breakage and caking. Figure 2 The device could no longer operate.

[0052] Example 3

[0053] Using the apparatus and method of Example 1, Amberlyst 16 WET type wet strong acid cation exchange resin without hydrophobic modification was used as the catalyst, acetone as the solvent, the mass ratio of D3 to solvent was 1:1, and the molar ratio of D3 to water was 1:1. The reaction was carried out at 50°C for 30 min (reactor 2). The product was desolventized at 50°C and a vacuum of 0.099 MPa (flash separation tank 5, falling film evaporator 6). The product viscosity was 34 mPa·s, and the hydroxyl content was 5.84%. After 30 days of continuous operation, adverse phenomena such as catalyst agglomeration occurred, and the effective throughput of reactor 2 decreased to 60% of the initial operation level.

[0054] Example 4

[0055] Using the apparatus and method of Example 1, a modifier was prepared by mixing tridecafluorooctyltrimethoxysilane, trifluoropropyltrimethoxysilane, and methyltrimethoxysilane in a molar ratio of 1:1:50. 10% of the modifier was added to a toluene dispersant and then soaked in Amberlyst 15 type strong acid cation exchange resin for 20 hours. After washing three times with toluene, the resin was purged with hot nitrogen and dried for later use. Using the above-mentioned hydrophobically modified strong acid cation exchange resin as a catalyst and acetone as a solvent, the mass ratio of D3 to solvent was 1:0.75, and the molar ratio of D3 to water was 1:1. The reaction was carried out at 50℃ for 30 min (reactor 2). The product was then desolventized at 60℃ and a vacuum of 0.099 MPa (flash separator 5, falling film evaporator 6), and then freeze-dried at -5℃. The product viscosity was 32.7 mPa·s, the hydroxyl content was 7.88%, the water content was 98 ppm, and the siloxane cyclic content was 8.474%. The reason for this was that the temperature of freeze dryer 10 was too high, the crystallization effect of siloxane cyclics was limited, and the cyclic removal effect was not obvious.

[0056] Example 5

[0057] Using the apparatus and method of Example 1, a modifier was prepared by mixing tridecafluorooctyltrimethoxysilane, trifluoropropyltrimethoxysilane, and methyltrimethoxysilane in a molar ratio of 1:1:50. 10% of the modifier was added to a toluene dispersant and then soaked in Amberlyst 15 type strong acid cation exchange resin for 20 hours. After washing three times with toluene, the resin was purged with hot nitrogen and dried for later use. Using the above hydrophobically modified strong acid cation exchange resin as a catalyst and acetone as a solvent, the mass ratio of D3 to solvent was 1:0.75, and the molar ratio of D3 to water was 1:1. The reaction was carried out at 50°C for 30 minutes (reactor 2). The product was then desolventized at 60°C and a vacuum of 0.099 MPa (flash separation tank 5, falling film evaporator 6), and then freeze-dried at -30°C. The product viscosity was 35.3 mPa·s, the hydroxyl content was 8.24%, the water content was 32 ppm, and the siloxane cyclic content was 0.108%. The excessively high temperature and vacuum in the solvent removal process of the flash separator 5 and falling film evaporator 6 caused some short-chain siloxane droplets to be carried out with the gas-liquid entrainment in the vacuum pipeline, while some short-chain siloxanes underwent dehydration and condensation, resulting in an increase in silicone oil viscosity and a decrease in hydroxyl content.

[0058] Example 6

[0059] Using the apparatus and method of Example 1, a modifier was prepared by mixing tridecafluorooctyltrimethoxysilane, trifluoropropyltrimethoxysilane, and methyltrimethoxysilane in a molar ratio of 1:1:50. 10% of the modifier was added to a toluene dispersant and then soaked in Amberlyst 15 type strong acid cation exchange resin for 20 hours. After washing three times with toluene, the resin was purged with hot nitrogen and dried for later use. Using the aforementioned hydrophobically modified strong acid cation exchange resin as a catalyst and acetone as a solvent, the mass ratio of D3 to solvent was 1:0.75, and the molar ratio of D3 to water was 1:1. The reaction was carried out at 50℃ for 30 min (reactor 2). The product underwent solvent removal at 50℃ and a vacuum of 0.099 MPa (flash separator (5) and falling film evaporator (6)). After freeze-drying at -30℃, the product viscosity was 26.7 mPa·s, the hydroxyl content was 9.87%, the water content was 31 ppm, and the siloxane cyclic content was 0.114%. The excessively high temperature in the solvent removal process of flash separator 5 and falling film evaporator 6 caused some short-chain siloxane droplets to be carried out with the vacuum pipeline, resulting in an increase in the content of long-chain siloxanes, which in turn increased the product viscosity and decreased the silanol content.

[0060] Example 7

[0061] Using the apparatus and method of Example 1, a modifier was prepared by mixing tridecafluorooctyltrimethoxysilane, trifluoropropyltrimethoxysilane, and methyltrimethoxysilane in a molar ratio of 1:1:50. 10% of the modifier was added to a toluene dispersant and then soaked in Amberlyst 15 type strong acid cation exchange resin for 20 hours. After washing three times with toluene, the resin was purged with hot nitrogen and dried for later use. Using the above hydrophobically modified strong acid cation exchange resin as a catalyst and acetone as a solvent, the mass ratio of D3 to solvent was 1:0.75, and the molar ratio of D3 to water was 1:1. The reaction was carried out at 50°C for 30 minutes (reactor 2). The product was then desolventized at 50°C and a vacuum of 0.092 MPa (flash separation tank 5, falling film evaporator 6), and then freeze-dried at -30°C. The product viscosity was 18.2 mPa·s, the hydroxyl content was 11.47%, the water content was 38 ppm, and the siloxane cyclic content was 0.092%. The product viscosity, hydroxyl content, water content, and siloxane cyclic content all meet expectations.

[0062] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for the continuous preparation of low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane, characterized in that, The apparatus used in the method includes a feeder (1), which is connected in sequence to a reactor (2) and a phase separator (4). The top of the phase separator (4) is connected in sequence to a flash separation tank (5) and a falling film evaporator (6) via a pipe. The top of the falling film evaporator (6) is connected in sequence to a multi-stage condensation system (7) via a pipe. A preheater (8) is provided between the top of the phase separator (4) and the flash separation tank (5) via a pipe. The bottom of the falling film evaporator (6) is connected in sequence to a product cooler (9) and a freeze dryer (10). The freeze dryer (10) is connected to a product packaging machine (11). The method includes the following steps: S1: The raw material enters the feeder (1) and is mixed evenly with the end-capping agent and solvent. It then enters the reactor (2) and reacts under the action of the solid catalyst (3). The crude product is collected in the phase separator (4) to separate the oil and water phases. S2: The aqueous phase returns to the feeder (1) to continue participating in the reaction; the oil phase passes through the flash separator (5) and falling film evaporator (6) in sequence to evaporate and separate the residual solvent. The solvent is recovered and reused after being processed by the multi-stage condensation system (7). The product is collected in the storage tank to obtain the crude product of low viscosity hydroxyl silicone oil. The solid catalyst (3) is a hydrophobically modified acidic cation exchange resin; The preparation process of the hydrophobically modified acidic cation exchange resin is as follows: a fluorinated silane coupling agent and an alkyl silane coupling agent are mixed and prepared in a molar ratio of 1:(10-100) to form a modifier. Toluene and cyclohexane are used as dispersants. The strong acidic cation exchange resin is soaked in the dispersant with 1%-10% of the modifier for 4-20 hours for modification. After filtration, washing, hot nitrogen purging and drying, it is ready for use.

2. The method for continuous preparation of low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane according to claim 1, characterized in that, The bottom of the multi-stage condensation system (7) is connected to the feeder (1) via a pipe.

3. The method for continuous preparation of low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane according to claim 1, characterized in that, The bottom of the phase separator (4) is connected to the feeder (1) via a pipe.

4. The method for continuous preparation of low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane according to claim 1, characterized in that, The feeder (1) is equipped with a precision flow meter and a regulating valve; The outer wall of reactor (2) is equipped with a heat exchange jacket; The flash separator (5) is equipped with a liquid distributor at the top and densely packed with Pall rings, Raschig rings, Taylor rings or other packing materials in the middle. The falling film evaporator (6) is equipped with a liquid distributor at the top and tubes in the middle; The multi-stage condensation system (7) consists of 2 to 5 heat exchangers and a collection tank.

5. The method for continuous preparation of low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane according to claim 1, characterized in that, In step S1, the raw material is hexamethylcyclotrisiloxane, with a main component content of 80%~99.99%; the end-capping agent is pure water; and the molar ratio of the raw material to the end-capping agent is 1:(0.5-2). The solvent is acetone; The solid catalyst (3) has a particle size of 1-5 mm; The material temperature of the batching device (1) is 30-60℃; the temperature of the reactor (2) is controlled at 30-60℃.

6. The method for continuous preparation of low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane according to claim 1, wherein the fluorinated silane coupling agent is one or more selected from trifluoropropyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, heptadecafluorodecyltrimethoxysilane, etc.; and the alkylsilane coupling agent is one or more selected from methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane.

7. The method for continuous preparation of low-viscosity hydroxyl silicone oil using hexamethylcyclotrisiloxane according to claim 1, characterized in that, In step S2, the material temperature in the flash separator (5) is 30~80℃ and the vacuum degree is 0.08~0.1MPa; The material temperature inside the falling film evaporator (6) is 30~80℃, and the vacuum degree is 0.08~0.10MPa; The multi-stage condensation system (7) uses circulating water, 3℃ water, -15℃ chilled brine, liquid ammonia or other heat exchange media, and the collection tank is insulated with a -15℃ chilled brine jacket.

8. The method for continuous preparation of low-viscosity hydroxyl silicone oil from hexamethylcyclotrisiloxane according to claim 1, characterized in that, The drying and purification process of the crude low-viscosity hydroxyl silicone oil product collected from the bottom of the falling film evaporator (6) is as follows: it is cooled to 20-40℃ by the product cooler (9), and then further cooled to -40℃~-20℃ in the freeze dryer (10) to freeze and crystallize the water and siloxane rings in the low-viscosity silicone oil. The solids are removed by screen in the freeze dryer. The prepared low-viscosity hydroxyl silicone oil product has a viscosity range of 10~40mPa·s, a hydroxyl content of 8%~12%, a water content of 1-100ppm, and a siloxane ring content of 0.01%-1%.

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