Production process of octamethylcyclotetrasiloxane
The production process of octamethylcyclotetrasiloxane is optimized through composite solid acid catalysts and multi-stage molecular distillation technology, solving the problems of equipment corrosion and environmental pollution in traditional processes, and achieving high-purity and low viscosity product production, suitable for high-end silicone materials.
Patent Information
- Application Number
- CN202510440359.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-09
- Publication Date
- 2025-07-11
AI Technical Summary
In the traditional octamethylcyclotetrasiloxane production process, there are problems such as strong equipment corrosion, serious environmental pollution, low product purity and difficult separation and purification, which are difficult to meet the needs of high-end applications.
The composite solid acid catalyst is composed of molecular sieve and heteropolyate salts, combined with multi-stage molecular distillation and ultrasonic dispersion technology, optimizes the hydrolysis and condensation reaction and separation process, and uses polyether modified silicone deemulsifiers and activated carbon adsorption treatment to achieve efficient separation and purification.
Significantly improve the purity of octamethylcyclotetrasiloxane to more than 99%, reduce product viscosity and moisture content, meet the requirements of high-end silicone materials, and reduce equipment maintenance costs and environmental pollution.
Abstract
Description
Technical Field
[0001] The present invention relates to the field of chemical engineering technology, and in particular to a production process of octamethylcyclotetrasiloxane. Background Art
[0002] Octamethylcyclotetrasiloxane (D4), as an important monomer in the silicone industry, is widely used in the preparation of downstream products such as silicone oil, silicone rubber, and silicone resin. Its purity directly affects the performance of the end products. Traditional D4 production processes mostly adopt the hydrolysis and condensation reaction of dimethyldichlorosilane under acidic conditions, and concentrated sulfuric acid is a commonly used catalyst.
[0003] Due to the inaccurate control of hydrolysis reaction conditions and the insufficient separation and purification technology in traditional D4 production processes, not only the content of D4 in the product is low (usually less than 90%), but also the residual high - cycle bodies (such as D5, D6) generated by side reactions and the incomplete removal of moisture during hydrolysis result in an increase in product viscosity and a large water content. High viscosity will increase the downstream processing difficulty, while residual moisture will cause stability problems of silicone products in high - temperature applications, seriously restricting their applications in fields such as high - end silicone oil and electronic packaging materials.
[0004] At the same time, this method has significant defects: the strong corrosiveness of concentrated sulfuric acid requires strict requirements for reaction equipment, resulting in high equipment maintenance costs; a large amount of waste acid needs to be neutralized after the reaction, causing environmental pollution and resource waste; at the same time, the by - products of side reactions are complex, and the subsequent separation and purification are difficult. The content of D4 in the final product is usually less than 90%, making it difficult to meet the requirements of high - end applications.
[0005] In recent years, solid - acid catalysts have become a research hotspot due to their recyclability and environmental friendliness. For example, molecular sieves and heteropolyacid salt catalysts have been tried in the synthesis of siloxanes, but the problems of low catalytic efficiency and poor stability of their single components have not been solved. In addition, there are problems of uneven mixing and low mass transfer efficiency in the hydrolysis and condensation reaction in traditional processes, resulting in long reaction time and high energy consumption; in the stratification and purification stage, the phase separation effect is often affected by emulsification phenomena, and a large amount of demulsifiers need to be added additionally, increasing the process complexity. In the purification link, the separation efficiency of conventional distillation technology for D4 and low - boiling substances (such as D3) and high - cycle bodies (D5 - D6) is limited. Although multi - stage rectification can improve the purity, the process is long, the energy consumption is high, and high temperature is likely to cause thermal decomposition of the product. Summary of the Invention
[0006] The present invention provides an efficient, environmentally friendly and low - cost D4 production process, aiming to solve the problems of equipment corrosion, environmental pollution, low product purity and large separation and purification difficulty existing in the hydrolysis and condensation reaction catalyzed by concentrated sulfuric acid in the prior art.
[0007] The technical solution adopted by the present invention is: a production process of octamethylcyclotetrasiloxane, comprising the following steps:
[0008] Step 1: Hydrolyze and condense dimethyldichlorosilane raw material and deionized water in the presence of a composite solid acid catalyst;
[0009] Step 2: Subject the reaction solution to layering treatment to obtain a crude product mixture;
[0010] Step 3: Purify the crude product mixture by multi-stage molecular distillation;
[0011] Among them, in Step 1, the composite solid acid catalyst is composed of molecular sieve and heteropolyacid salt compounded according to a mass ratio of 1:0.3 - 0.8, the reaction temperature is 50 - 80°C, and the reaction pressure is -0.05 to 0.1 MPa.
[0012] As a further improvement of the present invention, the molecular sieve in the composite solid acid catalyst is of the HZSM-5 type, the heteropolyacid salt is cesium phosphotungstate, and its total addition amount is 0.5% - 2.5% of the raw material mass.
[0013] As a further improvement of the present invention, in Step 1, the reaction equipment uses an enamel reaction kettle with an inner wall coated with a polytetrafluoroethylene layer and is equipped with an ultrasonic dispersion device, and the ultrasonic frequency is 20 - 40 kHz.
[0014] As a further improvement of the present invention, the power density of the ultrasonic dispersion device is 50 - 150 W / L, and the ultrasonic action adopts an intermittent mode, with a working cycle of ultrasonic for 10 - 30 s and an interval of 5 - 15 s.
[0015] As a further improvement of the present invention, in Step 1, the molar ratio of dimethyldichlorosilane to deionized water is 1:1.8 - 2.2, the hydrolysis and condensation reaction is carried out under an inert gas atmosphere throughout, and the inert gas flow rate is 0.5 - 2 L / min.
[0016] As a further improvement of the present invention, in Step 1, the condensation reaction is controlled by temperature in two stages: the first stage is maintained at 40 - 60°C for 0.5 - 1.5 hours, and the second stage is heated to 70 - 85°C and maintained for 2 - 4 hours.
[0017] As a further improvement of the present invention, before the layering treatment in Step 2, a demulsifier with a mass fraction of 0.01% - 0.1% is added to the reaction solution, and the demulsifier is a polyether-modified siloxane compound.
[0018] As a further improvement of the present invention, in Step 2, the layering treatment is carried out by centrifugal separation, the centrifugal speed is 3000 - 6000 rpm, the layering temperature is 50 - 70°C, and the layering time is 0.5 - 2 hours.
[0019] As a further improvement of the present invention, the multi-stage molecular distillation in step three includes: the first-stage distillation temperature is 80 - 100 °C, the pressure is 1 - 5 kPa to remove low-boiling substances; the second-stage distillation temperature is 120 - 150 °C, the pressure is 0.1 - 1 kPa to collect the main fraction of D4; the third-stage distillation temperature is 160 - 180 °C, the pressure is ≤0.01 kPa to recover high-ring by-products.
[0020] As a further improvement of the present invention, the main fraction of D4 collected in step three needs to be treated by activated carbon adsorption. The addition amount of activated carbon is 0.1% - 0.5% of the mass of the fraction, the adsorption temperature is 40 - 60 °C, and the adsorption time is 1 - 3 hours.
[0021] Beneficial effects of the present invention: Through the synergistic optimization of the composite solid acid catalyst and the multi-stage molecular distillation technology, the present invention not only significantly improves the purity of D4 to over 99%, but also achieves breakthroughs in low viscosity and low water content of the product. Specifically: (1) The multi-stage molecular distillation accurately removes low-boiling substances (such as D3 and trace moisture), combined with activated carbon adsorption treatment, making the water content of the final product less than 0.05%; (2) High-efficiency separation of high-ring by-products (recovery rate of D5 - D6 > 80%), greatly reducing high-molecular-weight impurities, and the viscosity of the product is reduced by more than 30% compared with the traditional process. Verified by examples, the viscosity of the D4 product can be controlled below 2.5 mPa·s, and the water content ≤0.03%, fully meeting the strict requirements of high-end silicone materials for low viscosity and low water content. Detailed implementation manners
[0022] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer, the present application will be further described in detail below with reference to examples. It should be understood that the examples described here are only used to explain the present application and are not used to limit the present application.
[0023] The present invention provides a production process of octamethylcyclotetrasiloxane, including the following steps:
[0024] Step one: Hydrolytic condensation reaction is carried out on the dimethyldichlorosilane raw material and deionized water in the presence of a composite solid acid catalyst;
[0025] Step two: The reaction solution is subjected to layering treatment to obtain a crude product mixture;
[0026] Step three: The crude product mixture is purified by multi-stage molecular distillation;
[0027] Among them, in step one, the composite solid acid catalyst is composed of molecular sieve and heteropolyacid salt compounded according to a mass ratio of 1:0.3 - 0.8, the reaction temperature is 50 - 80 °C, and the reaction pressure is -0.05 to 0.1 MPa.
[0028] In the present invention, the molecular sieve in the composite solid acid catalyst is of the HZSM-5 type, and the heteropolyacid salt is cesium phosphotungstate, with a total addition amount of 0.5%-2.5% of the raw material mass. In step one, the reaction equipment uses an enamel reaction kettle with an inner wall coated with a polytetrafluoroethylene layer and is equipped with an ultrasonic dispersion device, with an ultrasonic frequency of 20-40 kHz. The power density of the ultrasonic dispersion device is 50-150 W / L, and the ultrasonic action adopts an intermittent mode, with a working cycle of ultrasonic for 10-30 s and an interval of 5-15 s. In step one, the molar ratio of dimethyldichlorosilane to deionized water is 1:1.8-2.2, and the hydrolysis and condensation reaction is carried out under an inert gas atmosphere throughout, with an inert gas flow rate of 0.5-2 L / min. The condensation reaction in step one is controlled by temperature in two stages: the first stage is maintained at 40-60 °C for 0.5-1.5 hours, and the second stage is heated to 70-85 °C and maintained for 2-4 hours.
[0029] In step two of the present invention, a demulsifier with a mass fraction of 0.01%-0.1% is added to the reaction solution before the layering treatment, and the demulsifier is a polyether-modified siloxane compound. The layering treatment in step two uses centrifugal separation, with a centrifugal speed of 3000-6000 rpm, a layering temperature of 50-70 °C, and a layering time of 0.5-2 hours.
[0030] In step three of the present invention, the multi-stage molecular distillation includes: the first-stage distillation temperature is 80-100 °C, the pressure is 1-5 kPa, to remove low-boiling substances; the second-stage distillation temperature is 120-150 °C, the pressure is 0.1-1 kPa, to collect the main fraction of D4; the third-stage distillation temperature is 160-180 °C, the pressure is ≤0.01 kPa, to recover the high-ring by-products. The main fraction of D4 collected in step three needs to be treated by activated carbon adsorption, with the activated carbon addition amount being 0.1%-0.5% of the fraction mass, the adsorption temperature being 40-60 °C, and the adsorption time being 1-3 hours.
[0031] Example 1:
[0032] Step one: Add 100 kg of dimethyldichlorosilane and deionized water (molar ratio 1:1.8) to an enamel reaction kettle with an inner wall coated with polytetrafluoroethylene, and add a composite solid acid catalyst (mass ratio of HZSM-5 to cesium phosphotungstate 1:0.3, total addition amount being 0.5% of the raw material mass). Pass nitrogen (flow rate 0.5 L / min) to displace air, and turn on the ultrasonic dispersion device (frequency 20 kHz, power density 50 W / L, intermittent mode: ultrasonic for 10 s / interval 15 s). Control the temperature in two stages: the first stage is maintained at 40 °C for 1.5 hours, and the second stage is heated to 70 °C and maintained for 4 hours, with the reaction pressure controlled at -0.05 MPa.
[0033] Step 2: After the reaction is completed, add 0.01% polyether-modified silicone defoamer to the reaction solution, transfer it to a centrifuge (rotation speed 3000 rpm, temperature 50 °C) and separate for 1 hour to obtain a crude product mixture with a D4 content of 93.5%.
[0034] Step 3: Perform three-stage molecular distillation on the crude product: (1) First-stage distillation: temperature 80 °C, pressure 5 kPa, to remove low-boiling substances such as D3 (residual amount 0.5%); (2) Second-stage distillation: temperature 120 °C, pressure 1 kPa, collect the main D4 fraction (purity 98.2%); (3) Third-stage distillation: temperature 160 °C, pressure 0.01 kPa, recover D5-D6 high-ring bodies (recovery rate 82%).
[0035] Post-treatment: Add 0.1% activated carbon to the main D4 fraction (adsorb at 40 °C for 1 hour), and after filtration, the final D4 purity reaches 99.4% with a total yield of 92%.
[0036] Example 2:
[0037] Step 1: Take 200 kg of dimethyldichlorosilane and deionized water (molar ratio 1:2.0), the mass ratio of the composite catalyst is 1:0.5 (total addition amount 1.5%), the nitrogen flow rate is 1 L / min, and the ultrasonic frequency is 30 kHz (power density 100 W / L, intermittent mode: ultrasound for 20 s / interval 10 s). Control the temperature in two stages: maintain at 50 °C for the first stage for 1 hour, and raise the temperature to 80 °C and maintain for 3 hours in the second stage, and the reaction pressure is 0.05 MPa.
[0038] Step 2: Add 0.05% defoamer and perform centrifugal separation (4500 rpm, 60 °C, 1.5 hours), and the D4 content of the crude product is 96.8%.
[0039] Step 3: (1) First-stage distillation: temperature 90 °C, pressure 3 kPa, D3 residual amount 0.3%; (2) Second-stage distillation: temperature 135 °C, pressure 0.5 kPa, D4 purity 99.1%; (3) Third-stage distillation: temperature 170 °C, pressure 0.008 kPa, D5-D6 recovery rate 87%.
[0040] Post-treatment: 0.3% activated carbon (adsorb at 50 °C for 2 hours), the final D4 purity is 99.7%, and the total yield is 94%.
[0041] Example 3:
[0042] Step 1: 300 kg of dimethyldichlorosilane and deionized water (molar ratio 1:2.2), composite catalyst mass ratio 1:0.8 (total addition amount 2.5%), nitrogen flow rate 2 L / min, ultrasonic frequency 40 kHz (power density 150 W / L, intermittent mode: ultrasound for 30 s / interval 5 s). Two-stage temperature control: the first stage is maintained at 60 °C for 0.5 hours, and the second stage is heated to 85 °C and maintained for 2 hours, reaction pressure 0.1 MPa.
[0043] Step 2: Add 0.1% demulsifier, centrifuge (6000 rpm, 70 °C, 0.5 hours), and the content of crude product D4 is 98.1%.
[0044] Step 3: (1) Primary distillation: temperature 100 °C, pressure 1 kPa, D3 residue 0.1%; (2) Secondary distillation: temperature 150 °C, pressure 0.1 kPa, D4 purity 99.5%; (3) Tertiary distillation: temperature 180 °C, pressure 0.005 kPa, D5-D6 recovery rate 89%.
[0045] Post-treatment: 0.5% activated carbon (adsorption at 60 °C for 3 hours), final D4 purity 99.9%, total yield 96%.
[0046] The data of the above Examples 1-3 are shown in the following table.
[0047] Parameter / Result Example 1 Example 2 Example 3 Catalyst mass ratio 1:0.3 1:0.5 1:0.8 Catalyst addition amount (%) 0.5 1.5 2.5 Reaction temperature (°C) 40→70 50→80 60→85 Ultrasonic power density (W / L) 50 100 150 Centrifugal speed (rpm) 3000 4500 6000 Content of crude product D4 (%) 93.5 96.8 98.1 Final purity of D4 (%) 99.4 99.7 99.9 Residual amount of D3 (%) 0.5 0.3 0.1 Recovery rate of D5-D6 (%) 82 87 89 Total yield (%) 92 94 96
[0048] As can be seen from the above table, (1) the increase in the ratio and addition amount of the catalyst of the present invention (1:0.3 → 1:0.8, 0.5% → 2.5%) significantly improves the content of crude product D4 (93.5% → 98.1%), and the total yield is increased from 92% to 96%; (2) the increase in ultrasonic power density (50 → 150 W / L) and the increase in centrifugal speed (3000 → 6000 rpm) synergistically enhance the mass transfer and separation efficiency, shortening the layering time to 0.5 hours; (3) the combination of tertiary molecular distillation and activated carbon adsorption makes the D4 purity ≥ 99.4%, and the recovery rate of high-ring by-products > 80%, realizing resource recycling.
[0049] In summary, the production process of octamethylcyclotetrasiloxane of the present invention, with its characteristics of high efficiency, environmental protection and low cost, provides a new solution for the industrial production of octamethylcyclotetrasiloxane, and has broad market application prospects and profound social significance.
[0050] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A production process of octamethylcyclotetrasiloxane, characterized in that, It includes the following steps: Step 1: Carry out a hydrolysis and condensation reaction on the dimethyldichlorosilane raw material and deionized water in the presence of a composite solid acid catalyst; Step 2: Subject the reaction solution to a layering treatment to obtain a crude product mixture; Step 3: Purify the crude product mixture by multi-stage molecular distillation; Among them, in Step 1, the composite solid acid catalyst is composed of a molecular sieve and a heteropolyacid salt compounded at a mass ratio of 1:0.3 - 0.8, the reaction temperature is 50 - 80 °C, and the reaction pressure is -0.05 to 0.1 MPa.
2. The production process of octamethylcyclotetrasiloxane according to claim 1, wherein, In the composite solid acid catalyst, the molecular sieve is of the HZSM-5 type, the heteropolyacid salt is cesium phosphotungstate, and its total addition amount is 0.5% - 2.5% of the raw material mass.
3. The production process of octamethylcyclotetrasiloxane according to claim 1, characterized in that, In Step 1, the reaction equipment uses an enamel reaction kettle with a polytetrafluoroethylene layer coated on the inner wall and is equipped with an ultrasonic dispersion device, and the ultrasonic frequency is 20 - 40 kHz.
4. The production process of octamethylcyclotetrasiloxane according to claim 3, characterized in that, The power density of the ultrasonic dispersion device is 50 - 150 W / L, and the ultrasonic action adopts an intermittent mode, with a working cycle of ultrasonic for 10 - 30 s and an interval of 5 - 15 s.
5. The production process of octamethylcyclotetrasiloxane according to claim 1, characterized in that, In Step 1, the molar ratio of dimethyldichlorosilane to deionized water is 1:1.8 - 2.2, and the hydrolysis and condensation reaction is carried out throughout in an inert gas atmosphere, and the inert gas flow rate is 0.5 - 2 L / min.
6. The production process of octamethylcyclotetrasiloxane according to claim 1, characterized in that, In Step 1, the condensation reaction is controlled by temperature in two stages: the first stage is maintained at 40 - 60 °C for 0.5 - 1.5 hours, and the second stage is heated to 70 - 85 °C and maintained for 2 - 4 hours.
7. The production process of octamethylcyclotetrasiloxane according to claim 1, characterized in that, Before the layering treatment in Step 2, a demulsifier with a mass fraction of 0.01% - 0.1% is added to the reaction solution, and the demulsifier is a polyether-modified siloxane compound.
8. The production process of octamethylcyclotetrasiloxane according to claim 1, characterized in that, In Step 2, the layering treatment is carried out by centrifugal separation, the centrifugal speed is 3000 - 6000 rpm, the layering temperature is 50 - 70 °C, and the layering time is 0.5 - 2 hours.
9. The production process of octamethylcyclotetrasiloxane according to claim 1, characterized in that, The multi-stage molecular distillation in Step 3 includes: the first-stage distillation temperature is 80 - 100 °C, the pressure is 1 - 5 kPa, and the low-boiling substances are removed; the second-stage distillation temperature is 120 - 150 °C, the pressure is 0.1 - 1 kPa, and the D4 main fraction is collected; the third-stage distillation temperature is 160 - 180 °C, the pressure is ≤0.01 kPa, and the high-ring body by-products are recovered.
10. The production process of octamethylcyclotetrasiloxane according to claim 9, characterized in that, The D4 main fraction collected in Step 3 needs to be treated by activated carbon adsorption. The addition amount of activated carbon is 0.1% - 0.5% of the fraction mass, the adsorption temperature is 40 - 60 °C, and the adsorption time is 1 - 3 hours.