A system and process for continuous production of methyl silicone oil

Abstract

The application provides a continuous production methyl silicone oil system and process, which comprises a mixing and batching tank, a reaction preheater, a fixed bed reactor, a separator and a low boiling point remover connected in sequence; the mixing and batching tank is provided with a stirring device and a plurality of feed inlets for feeding linear siloxane, cyclic siloxane and terminal agent respectively; the fixed bed reactor is internally filled with a catalyst, and a distributor is arranged at the feed inlet for enabling the mixed material to perform ring-opening and condensation polymerization under the action of the catalyst. The application has the beneficial effect that through the series connection design of the fixed bed reactor and the multi-stage separation unit, efficient continuous production from raw material mixing to product refining is realized, the reaction period is greatly shortened, the unit volume productivity is improved, the frequent temperature rising and falling and catalyst loading and unloading operations in batch production are avoided, the energy consumption and labor cost are reduced, and the uniformity and stability of the performance of each batch of products are ensured.

Description

Technical Field

[0001] This invention relates to the field of desulfurization tower technology, specifically to a continuous production system and process for methyl silicone oil. Background Technology

[0002] Methyl silicone oil is a type of linear polysiloxane product with silicon-oxygen bonds as the main chain and methyl groups as side groups. Due to its excellent thermal stability, chemical inertness, electrical insulation, hydrophobicity, and physiological inertness, methyl silicone oil is widely used in numerous fields such as daily chemicals, textiles, electronics, machinery, medicine, and aerospace. In the industrial production of methyl silicone oil, its synthesis typically uses dimethylsiloxane mixed cyclic compounds or octamethylcyclotetrasiloxane as raw materials, which are obtained through ring-opening polymerization under the action of a catalyst.

[0003] Currently, most domestic methyl silicone oil manufacturers still widely use the traditional batch polymerization process. This process typically uses acidic or alkaline substances as catalysts, and the polymerization equilibrium reaction takes place in a reactor. This batch production mode has many inherent drawbacks: low equipment capacity, high production costs, high personnel requirements, and low product yield; firstly, low production efficiency and long production cycles, with single-batch reaction times typically lasting 6 to 10 hours, limiting production capacity; secondly, poor product quality stability, as uneven heat distribution during batch operation makes it difficult to accurately reproduce temperature, pressure, and catalyst activity between batches, resulting in significant fluctuations in key indicators such as product viscosity, molecular weight distribution, and volatile matter content; thirdly, low by-product utilization, and the need to introduce organic solvents in some processes, increasing environmental pollution risks and production costs. These drawbacks make it difficult for batch-produced methyl silicone oil to meet increasingly stringent market demands in terms of both quality and cost.

[0004] To overcome the inherent shortcomings of batch processes, the industry has gradually begun to explore continuous production technologies. Compared with batch methods, continuous production can significantly shorten production cycles, improve batch consistency, reduce energy and material consumption, and achieve cleaner production. However, existing continuous production processes mostly employ tubular reactors or stirred tanks in series, and the catalysts are mostly homogeneous systems, which still present problems such as difficulties in catalyst separation and low reaction conversion rates. Therefore, developing a continuous production system for methyl silicone oil based on a fixed-bed reactor is of significant practical importance for improving the production efficiency, product quality, and technological advancement of methyl silicone oil. Summary of the Invention

[0005] To address the issues that existing continuous production processes often employ tubular reactors or stirred tanks in series, and where catalysts are mostly homogeneous systems, problems such as difficulty in catalyst separation and low reaction conversion rates still exist. This invention provides a continuous production system for methyl silicone oil, comprising a mixing tank, a reaction preheater, a fixed-bed reactor, a separator, and a de-sinking device connected in sequence; the mixing tank is equipped with a stirring device and multiple feed inlets for feeding linear siloxanes, cyclic siloxanes, and terminal agents, respectively; the fixed-bed reactor is filled with a catalyst, and a distributor is provided at the feed inlet for the mixture to undergo ring-opening and condensation polymerization reactions under the action of the catalyst.

[0006] As a preferred embodiment, the amount of catalyst loaded inside the fixed-bed reactor meets the required reaction residence time.

[0007] As a preferred embodiment, the inlet of the reaction preheater is connected to the outlet of the mixing tank via a feed pump and pipeline, for heating the mixture to the reaction initiation temperature; As a preferred embodiment, the fixed-bed reactor and the separator are provided with a gas phase outlet connected to a condensation recovery system.

[0008] As a preferred embodiment, the dewatering device is provided with a gas phase outlet and a liquid phase outlet, the gas phase outlet being connected to a condensation recovery system and the liquid phase outlet being connected to a product collection system.

[0009] As a preferred embodiment, a separation heater is further provided between the separator and the de-sinking device. The inlet of the separation heater is connected to the liquid phase outlet of the separator through a separation discharge pump and a pipeline, and the outlet of the separation heater is connected to the inlet of the de-sinking device.

[0010] As a preferred embodiment, a pressure regulating valve is provided on the pipeline between the outlet of the fixed-bed reactor and the inlet of the separator.

[0011] As a preferred embodiment, the separator operates at an absolute pressure of 18 kPa; the de-cooling device is heated by heat transfer oil, and the de-cooling temperature is not lower than 270°C; the reaction preheater preheats the mixture to above 100°C, preferably 130 to 150°C.

[0012] This invention also provides a process for continuous production of methyl silicone oil, comprising the following steps: S1. Linear siloxane, cyclic siloxane and end-capping agent are continuously mixed according to a predetermined ratio, wherein the mass percentage of linear siloxane is 10% to 50%, to obtain a mixture. S2. After preheating the mixture to the reaction temperature, it is fed into a fixed-bed reactor, where ring-opening polymerization and condensation polymerization are carried out under the action of a catalyst. The reaction residence time is 5 to 30 minutes, and reaction products containing methyl silicone oil are generated. S3. The reaction product is flash-distilled to remove unreacted monomers and generated water, resulting in a crude liquid product. The crude liquid product is then subjected to de-lowering treatment under vacuum conditions, with the de-lowering rate controlled at ≥5%, to obtain a de-lowered liquid product. The de-lowered liquid product is cooled, filtered, and collected to obtain the methyl silicone oil product.

[0013] As a preferred embodiment, the flash separation is carried out in a flash tank or gas-liquid separation tower, with an operating pressure lower than the reactor pressure and an operating temperature of 150 to 250°C. The de-lowering is performed using a thin-film evaporator or a short-path distiller, with a vacuum degree of -0.05 to -0.09 MPa and an operating temperature of 180 to 280°C; the preheating temperature is 80 to 200°C, the reaction temperature is 120 to 300°C, and the pressure is 0.1 to 2.0 MPa.

[0014] The beneficial effects of this invention are as follows: 1. This invention achieves efficient and continuous production from raw material mixing to product refining through a series design of a fixed-bed reactor and multi-stage separation units. The system uniformly mixes linear siloxanes, cyclic siloxanes, and terminal agents in a mixing tank according to a set ratio. After being heated to 130-150°C by a reaction preheater, the mixture enters the fixed-bed reactor. The distributor at the reactor inlet ensures uniform distribution of the mixture within the catalyst bed, effectively utilizing the catalyst's active sites. This allows the ring-opening and condensation polymerization reactions to be fully completed within a precisely controlled residence time. Compared to traditional batch reactor processes, this significantly shortens the reaction cycle and increases the unit volume capacity. It avoids frequent heating and cooling and catalyst loading and unloading operations in batch production, reducing energy consumption and labor costs while ensuring the uniformity and stability of the performance of each batch of product.

[0015] 2. This invention achieves gradient decompression and high-temperature stripping through a separator and a stripper, which sequentially separates and removes unreacted cyclic siloxanes, low-boiling-point substances, and small-molecule byproducts. The separation heater reheats the material before it enters the stripper, ensuring that the high-boiling-point components are fully evaporated in the stripper, ultimately obtaining a high-quality methyl silicone oil product. Attached Figure Description

[0016] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 This is a schematic diagram of the structure of the present invention; The following are labels in the diagram: 1. Mixing tank, 2. Feed pump, 3. Reactor preheater, 4. Fixed bed reactor, 5. Separator, 6. Separator discharge pump, 7. Separator heater, 8. De-sinker. Detailed Implementation

[0017] To illustrate the features of the present invention, the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] Example 1: Please see Figure 1 This invention provides a continuous production system for methyl silicone oil, comprising a mixing tank 1, a feed pump 2, a reaction preheater 3, a fixed-bed reactor 4, a separator 5, a separation discharge pump 6, a separation heater 7, and a descaling device 8 connected sequentially along the material flow direction.

[0019] The mixing tank 1 is a vertical mixing tank with an effective volume of 2 cubic meters. It is equipped with a frame-type agitator with a stirring speed of 60 rpm. The top of the tank has three inlets for feeding the linear siloxane, cyclic siloxane, and terminal agent, respectively. Each inlet is equipped with a mass flow meter to precisely control the feeding ratio of each component. In this embodiment, the linear siloxane is fed at 5 kg / h, the cyclic siloxane at 20 kg / h, and the terminal agent MM at 1 kg / h.

[0020] The outlet of the mixing tank 1 is connected to the inlet of the feed pump 2 via a pipeline. The feed pump 2 is a gear pump, pressurized to 0.4 MPa. The outlet of the feed pump 2 is connected to the inlet of the reaction preheater 3 via a pipeline. The reaction preheater 3 is a shell-and-tube heat exchanger with a heat exchange area of ​​8 square meters, heated by thermal oil, and used to preheat the mixture to 135 degrees Celsius.

[0021] The outlet of the preheater 3 is connected to the inlet at the top of the fixed-bed reactor 4 via a pipeline. The fixed-bed reactor 4 is a vertical cylindrical vessel with an inner diameter of 0.8 meters and a height of 4 meters. It is filled with a solid acid catalyst at a volume of 1.5 cubic meters, meeting the required reaction residence time. An annular distributor is installed at the reactor inlet, with 12 evenly spaced 6-mm diameter outlet holes to ensure uniform distribution of the mixture, facilitating ring-opening and condensation polymerization reactions under the action of the catalyst. A pressure regulating valve is installed on the outlet pipeline of reactor 4 to control the operating pressure within the reactor.

[0022] The discharge port of the fixed-bed reactor 4 is connected to the inlet in the middle of the separator 5 via a pipeline. After processing for approximately 30 minutes, the material enters the separator 5. The separator 5 is a vertical gas-liquid separator with an inner diameter of 0.6 meters and a height of 1.8 meters. It operates at an absolute pressure of 18 kPa and is equipped with a wire mesh demister inside. The top of the separator 5 has a gas phase discharge port connected to a condensation recovery system for recovering unreacted light components such as cyclic siloxanes. The bottom of the separator 5 has a liquid phase discharge port.

[0023] The liquid phase outlet of separator 5 is connected to the inlet of separation discharge pump 6 via a pipeline. Separation discharge pump 6 is a gear pump with a flow rate of 1.0 cubic meters per hour and a head of 30 meters. The outlet of separation discharge pump 6 is connected to the inlet of separation heater 7 via a pipeline. Separation heater 7 is a shell-and-tube heat exchanger with a heat exchange area of ​​6 square meters, heated by thermal oil, and used to further heat the separated liquid phase material.

[0024] The outlet of the separator heater 7 is connected to the inlet in the middle of the descaling unit 8 via a pipe. The descaling unit 8 is a vertical thin-film evaporator with an inner diameter of 0.5 meters and a height of 2.5 meters. It is heated by heat transfer oil, and the descaling temperature is set to 280 degrees Celsius. The top of the descaling unit 8 has a gas phase outlet connected to a condensation recovery system for removing low-boiling substances. The bottom of the descaling unit 8 has a liquid phase outlet connected to a product collection system for collecting the finished methyl silicone oil. The product viscosity is measured to be approximately 85 cp, and the reaction yield is approximately 90%.

[0025] This system achieves continuous polymerization through a fixed-bed reactor, combined with two-stage purification by a separator and a deionizer, enabling stable production of high-quality methyl silicone oil with low volatile content, significantly improving production efficiency compared to batch processes.

[0026] Example 2: This embodiment provides a continuous process for producing methyl silicone oil, specifically including the following steps: S1. Mixing Ingredients Linear siloxanes, cyclic siloxanes, and end-capping agents are continuously added to a mixing tank according to a predetermined ratio. In this embodiment, the linear siloxane (viscosity 50 cst) is fed at a flow rate of 300 kg / h, the cyclic siloxane (D4, purity ≥99.5%) is fed at a flow rate of 600 kg / h, and the end-capping agent (hexamethyldisiloxane, MM) is fed at a flow rate of 100 kg / h. The linear siloxane accounts for 30% of the total material by mass. The mixing tank is equipped with a frame-type stirrer (rotation speed 60 rpm), and the three materials are thoroughly mixed evenly in the tank to form a mixture.

[0027] S2. Preheating and polymerization reaction The mixture is drawn from the mixing tank by a feed pump (gear pump, flow rate 1.0 m³ / h), pressurized to 1.2 MPa, and then sent to the reaction preheater. The reaction preheater is a shell-and-tube heat exchanger, heated by thermal oil, to preheat the mixture to 135°C. The preheated material enters from the top of the fixed-bed reactor, a vertical cylindrical container with an inner diameter of 0.8 m and a height of 4.5 m, filled with a solid acid catalyst (acidic cation exchange resin, 1.8 m³). The material flows from top to bottom through the catalyst bed in the reactor. Under the action of the catalyst's active centers, cyclic siloxanes undergo ring-opening polymerization, and linear siloxanes undergo condensation polymerization with cyclic siloxanes. The reaction temperature is controlled at 135°C, the pressure is maintained at 1.2 MPa, and the reaction residence time is 15 minutes. After the reaction is complete, a crude product containing methyl silicone oil is obtained and discharged from the bottom outlet of the reactor.

[0028] S3. Flash separation and de-lowering treatment The crude product, after being depressurized to 0.3 MPa by a pressure regulating valve, enters a flash tank for flash separation. The flash tank is a vertical gas-liquid separator, operating at an absolute pressure of 18 kPa (lower than the reactor pressure) and an operating temperature of 180 degrees Celsius. Inside the flash tank, unreacted cyclic siloxane monomers and the water generated during the reaction are vaporized and discharged from the top gas outlet. After being collected by a condensation recovery system, the vapor is returned to the mixing and batching process for reuse. The liquid crude product, after the removal of light components, is discharged from the bottom of the flash tank and enters the de-oxidation treatment process.

[0029] The low molecular weight removal process utilizes a thin-film evaporator. A vacuum system maintains the evaporator at a vacuum level of -0.09 MPa (10 kPa absolute pressure), and heat transfer oil heating keeps the evaporator's inner wall temperature at 280 degrees Celsius. The crude liquid product forms a uniform liquid film on the evaporator's inner wall and flows downwards. Low molecular weight components (including unreacted oligomers, cyclic compounds, and a small amount of water) are evaporated and removed under high temperature and high vacuum conditions. The removal rate is controlled at 6% (i.e., the mass of removed low molecular weight components accounts for 6% of the mass of the feed crude liquid product). The removed low molecular weight components are discharged from the vapor outlet at the top of the evaporator and are recovered after condensation.

[0030] The degraded liquid product is discharged from the bottom of the thin film evaporator, cooled to 40 degrees Celsius by a shell-and-tube cooler (cooling water inlet 32 ​​degrees Celsius, outlet 38 degrees Celsius), and then filtered through a bag filter (filtration accuracy 5 microns) to remove residual catalyst powder and mechanical impurities, finally collecting the methyl silicone oil product.

[0031] Testing revealed that the methyl silicone oil product obtained in this embodiment was colorless and transparent, with a viscosity of 95 centipoise (25 degrees Celsius), a volatile content of 0.8% (mass fraction), an acid value of 0.01 mg KOH / g, and a product yield of 88% (based on total siloxane feed). This process achieves continuous production of methyl silicone oil with high reaction efficiency and stable product quality.

[0032] The above embodiments and accompanying drawings are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. The present invention has been described in detail with reference to preferred embodiments. Those skilled in the art should understand that any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the present invention do not depart from the spirit of the present invention and should also fall within the protection scope of the claims of the present invention. Other related technical structures not disclosed in detail in the present invention are existing technologies in the art.

Claims

1. A continuous production system for methyl silicone oil, characterized in that: It includes a mixing tank (1), a reaction preheater (3), a fixed-bed reactor (4), a separator (5), and a de-sinking device (8) connected in sequence: The mixing tank (1) is equipped with a stirring device and multiple feed ports, which are used for feeding linear siloxanes, cyclic siloxanes and terminal agents, respectively. The fixed-bed reactor (4) is filled with a catalyst and has a distributor at the feed inlet to enable the mixture to undergo ring-opening and condensation polymerization reactions under the action of the catalyst.

2. The continuous production system for methyl silicone oil according to claim 1, characterized in that: The amount of catalyst loaded inside the fixed-bed reactor (4) meets the reaction residence time.

3. The continuous production system for methyl silicone oil according to claim 1, characterized in that: The feed inlet of the reaction preheater (3) is connected to the discharge outlet of the mixing tank (1) via a feed pump (2) and a pipeline, and is used to heat the mixture to the reaction start temperature.

4. The continuous production system for methyl silicone oil according to claim 1, characterized in that: The fixed-bed reactor (4) and the separator (5) are equipped with gas phase outlets connected to a condensation recovery system.

5. The continuous production system for methyl silicone oil according to claim 1, characterized in that: The de-sinking device (8) is provided with a gas phase outlet and a liquid phase outlet. The gas phase outlet is connected to a condensation recovery system, and the liquid phase outlet is connected to a product collection system.

6. The continuous production system for methyl silicone oil according to claim 1, characterized in that: A separation heater (7) is also provided between the separator (5) and the depressor (8). The inlet of the separation heater (7) is connected to the liquid phase outlet of the separator (5) through a separation discharge pump (6) and a pipeline. The outlet of the separation heater (7) is connected to the inlet of the depressor (8).

7. The continuous production system for methyl silicone oil according to claim 1, characterized in that: A pressure regulating valve is provided on the pipeline between the outlet of the fixed bed reactor (4) and the inlet of the separator (5).

8. The continuous production system for methyl silicone oil according to claim 1, characterized in that: The operating pressure of the separator (5) is absolute pressure 18 kPa; the de-cooling device (8) is heated by heat transfer oil and the de-cooling temperature is not lower than 270°C; the reaction preheater (3) preheats the mixture to above 100°C, preferably 130 to 150°C.

9. A process for continuous production of methyl silicone oil, characterized in that: Includes the following steps: S1. Linear siloxane, cyclic siloxane and end-capping agent are continuously mixed according to a predetermined ratio, wherein the mass percentage of linear siloxane is 10% to 50%, to obtain a mixture. S2. After preheating the mixture to the reaction temperature, it is fed into a fixed-bed reactor, where ring-opening polymerization and condensation polymerization are carried out under the action of a catalyst. The reaction residence time is 5 to 30 minutes, and reaction products containing methyl silicone oil are generated. S3. The reaction product is flash-distilled to remove unreacted monomers and generated water, resulting in a crude liquid product. The crude liquid product is then subjected to de-lowering treatment under vacuum conditions, with the de-lowering rate controlled at ≥5%, to obtain a de-lowered liquid product. The de-lowered liquid product is cooled, filtered, and collected to obtain the methyl silicone oil product.

10. The process according to claim 9, characterized in that, The flash separation is carried out in a flash tank or gas-liquid separation tower, with an operating pressure lower than the reactor pressure and an operating temperature of 150 to 250°C. The de-lowering is carried out using a thin-film evaporator or a short-path distiller, with a vacuum degree of -0.05 to -0.09 MPa and an operating temperature of 180 to 280°C; the preheating temperature is 80 to 200°C, the reaction temperature is 120 to 300°C, and the pressure is 0.1 to 2.0 MPa.

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