A process for the preparation of methyl ethylcyclosiloxanes

Abstract

This invention relates to the technical field of siloxane preparation, and discloses a method for preparing methylethylcyclosiloxane, comprising the following steps: adding high-hydrogen-content silicone oil and ethylene gas under castor catalysis to prepare methylethyl silicone oil, which is then cracked into tetramethyltetraethylcyclotetrasiloxane and pentamethylpentaethylcyclopentasiloxane, thus obtaining methylethylcyclosiloxane. This invention uses the addition of high-hydrogen-content silicone oil and ethylene under castor catalysis to prepare methylethyl silicone oil, which is then cracked into tetramethyltetraethylcyclotetrasiloxane and pentamethylpentaethylcyclopentasiloxane. The preparation process is simpler and cleaner, avoiding the use of highly corrosive raw materials, reducing by-products, and improving the yield and purity of the product.

Description

Technical Field

[0001] This invention relates to the technical field of siloxane preparation, and in particular to a method for preparing methylethylcyclosiloxane. Background Technology

[0002] Organosilicon polymers with polydimethylsiloxane as the main chain structure are ill-suited for the demands of extremely cold weather conditions and specialized fields requiring materials resistant to low temperatures and thermal shock. When the methyl functional groups on the side chains or end groups of a siloxane are partially replaced by ethyl functional groups, methylethyl polysiloxane is obtained. This disrupts the regularity of the dimethylsiloxane structure, lowering the polymer's crystallization temperature and thus enhancing the cold resistance of the organosilicon polymer material. Currently, the main preparation method for methylethyl polysiloxane involves ring-opening polymerization of hexaethylcyclotrisiloxane or triethyltrimethylcyclotrisiloxane. Hexaethylcyclotrisiloxane or triethyltrimethylcyclotrisiloxane is primarily obtained via the Grignard process, which is complex, costly, and highly polluting. Another method, mainly the hydrosilylation method using hydrochlorosilanes, is highly corrosive to equipment; hydrogen chloride can easily corrode and perforate autoclaves, posing a significant risk. Furthermore, this process is complex, involving multiple strong acid steps and producing numerous byproducts.

[0003] For example, Chinese invention patent CN111995754A discloses a method for preparing diethyl silicone oil by reacting methyldichlorosilane with a high-boiling vinyl compound (a waste product from the production of vinyl end caps) via a cracking and rearrangement reaction, followed by hydrolysis. Given that chlorosilanes are highly corrosive to equipment, require high reaction temperatures, and the catalyst, dimethylaniline, is carcinogenic and detrimental to worker health, Chinese invention patent CN114933705A discloses a method for preparing ethyl silicone oil using methyldichlorosilane and ethylene as raw materials, water as a solvent, and chloroplatinic acid as a catalyst. Chinese invention patent CN103450250A discloses a method for preparing methylethyldichlorosilane by hydrosilylation of methyldichlorosilane and ethylene in a high-pressure reactor under chloroplatinic acid catalysis, followed by hydrolysis and cracking under alkaline conditions to obtain a mixture of tetramethyltetraethylcyclotetrasiloxane or trimethyltriethylcyclotrisiloxane. Obviously, chloroplatinic acid loses its activity when dissolved in a large amount of water, and the hydrolysis of methyldichlorosilane yields hydrogen-containing silicone oil, making the proposed method unfeasible, as the yield and purity of the product are low. Summary of the Invention

[0004] To overcome the problems of complex preparation, high pollution, and high risk associated with existing technologies for preparing methylethylcyclosiloxanes, this invention provides a method for preparing methylethylcyclosiloxanes. The method involves adding high-hydrogen-content silicone oil to ethylene under the conditions of a cascade catalyst to prepare methylethyl silicone oil, which is then cracked into tetramethyltetraethylcyclotetrasiloxane and pentamethylpentaethylcyclopentasiloxane. The preparation process is simpler and cleaner.

[0005] The objective of this invention is achieved through the following technical solution: a method for preparing methyl ethyl cyclosiloxane, comprising the following steps: adding high-hydrogen-content silicone oil and ethylene gas under the conditions of a cascade catalyst to prepare methyl ethyl silicone oil, and then cracking it into tetramethyltetraethylcyclotetrasiloxane and pentamethylpentaethylcyclopentasiloxane, thereby obtaining methyl ethyl cyclosiloxane.

[0006] Compared to existing technologies, this invention does not use hydrochlorosilanes as reactants or chloroplatinic acid as catalysts. Instead, it uses high-hydrogen-content silicone oil and ethylene gas in a caster catalyst environment for an addition reaction to produce methylethyl silicone oil, which is then cracked to obtain methylethylcyclosiloxane. The entire reaction process is simpler, avoids the use of highly corrosive raw materials, and can directly crack to obtain tetramethyltetraethylcyclotetrasiloxane and pentamethylpentaethylcyclopentasiloxane. The yield and purity of the cracking products are high, and the number of byproducts is low.

[0007] Preferably, the hydrogen content in the high-hydrogen silicone oil is 1 to 1.62%.

[0008] Preferably, the amount of the cassette catalyst added is 0.08 to 0.12% of the mass of the high-hydrogen-content silicone oil.

[0009] Preferably, the addition is performed by introducing ethylene gas into a nitrogen atmosphere to a pressure of 1-8 atm.

[0010] Preferably, the addition reaction conditions are heating to 80-90°C and reacting for 4-12 hours.

[0011] Preferably, an organic solvent is added during the addition process. This organic solvent is free of carboxyl, hydroxyl, sulfur, phosphorus, and nitrogen groups. The organic solvent is octamethylcyclotetrasiloxane or toluene, more preferably octamethylcyclotetrasiloxane.

[0012] The addition of octamethylcyclotetrasiloxane not only reduces the viscosity of the system, thereby accelerating the reaction rate and shortening the reaction time, but also increases the overall yield of the cracking reaction.

[0013] Preferably, the pyrolysis is performed by mixing methyl ethyl silicone oil and sulfonic acid resin and then subjecting the mixture to vacuum pyrolysis.

[0014] Preferably, the amount of sulfonic acid resin added is greater than 5% of the mass of methyl ethyl silicone oil.

[0015] Sulfonic acid resin acts as a catalyst to accelerate the reaction. It can be a perfluorosulfonic acid resin or a conventional sulfonic acid resin (fluorine-free), and more preferably a perfluorosulfonic acid resin.

[0016] Preferably, the temperature of the vacuum pyrolysis is 105–115°C.

[0017] Preferably, the pressure of the depressurization pyrolysis is an absolute pressure of 800-1200 Pa.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) Methyl ethyl silicone oil is prepared by adding high-hydrogen silicone oil to ethylene under the conditions of a cascade catalyst, and then cracked into tetramethyltetraethylcyclotetrasiloxane and pentamethylpentaethylcyclopentasiloxane. The preparation process is simpler and cleaner, avoiding the use of highly corrosive raw materials, reducing by-products, and improving the yield and purity of the product.

[0020] (2) During the addition reaction, the hydrogen content of the high hydrogen content silicone oil, the pressure of ethylene gas and the reaction parameters will affect the ratio of methyl and ethyl in the methyl ethyl silicone oil, which will in turn affect the composition of the cracking products and the yield and purity of the products. Therefore, the parameters in this invention are mutually coordinated and mutually influential, and can obtain tetramethyltetraethylcyclotetrasiloxane and pentamethylpentaethylcyclopentasiloxane with high yield and high purity. Detailed Implementation

[0021] The technical solution of the present invention is illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto:

[0022] A method for preparing a methylethylcyclosiloxane includes the following steps:

[0023] A high-hydrogen-content silicone oil (with a hydrogen content of 1–1.62%) and ethylene gas are added under the condition of a cassette catalyst, wherein the amount of cassette catalyst added accounts for 0.08–0.12% of the mass of the high-hydrogen-content silicone oil. Ethylene gas is introduced under a nitrogen atmosphere to a pressure of 1–8 atm, and the temperature is raised to 80–90°C for 4–12 h to prepare methyl ethyl silicone oil. An organic solvent may also be added during this addition reaction. The organic solvent is a solvent that does not contain carboxyl, hydroxyl, sulfur, phosphorus, or nitrogen.

[0024] Methyl ethyl silicone oil and sulfonic acid resin are mixed and subjected to reduced pressure pyrolysis under conditions of absolute pressure of 800-1200 Pa and temperature of 105-115 °C. The amount of sulfonic acid resin added is greater than 5% of the mass of methyl ethyl silicone oil. The pyrolysis yields tetramethyltetraethylcyclotetrasiloxane and pentamethylpentaethylcyclopentasiloxane, which together form methyl ethylcyclosiloxane.

[0025] Example 1

[0026] 50 kg of high-hydrogen silicone oil (hydrogen content 1.50%) was added to a stainless steel autoclave, and nitrogen was used to purge until the oxygen content was less than 1%. Ethylene was introduced, and the pressure was increased to 1 atm. 0.05 kg of cassiterite catalyst (Pt content 3000 ppm) was added. The mixture was heated to 80°C and reacted for 12 h. Residual gases were removed, yielding 71.7 kg of crude methylethyl silicone oil. Residual hydroxyl hydrogen was undetectable.

[0027] 71.7 kg of crude methyl ethyl silicone oil was added to a pyrolysis reactor, along with 7 kg of repeatedly washed sulfonic acid resin. The mixture was subjected to reduced pressure pyrolysis at 110°C and 1000 Pa to obtain the pyrolysis products, which were then purified by distillation. The composition of the pyrolysis products was 54% tetramethyltetraethylcyclotetrasiloxane, 40% pentamethylpentaethylcyclopentasiloxane, 1% hexamethyldisiloxane, and 5% heptamethylethyltrisiloxane.

[0028] Example 2

[0029] 50 kg of high-hydrogen silicone oil (hydrogen content 1.50%) and 17 kg of octamethylcyclotetrasiloxane were added to a stainless steel autoclave, and the oxygen content was purged with nitrogen until it was less than 1%. Ethylene was introduced, and the pressure was increased to 1 atm. 0.05 kg of castor catalyst (Pt content 3000 ppm) was added. The reaction was carried out at 80°C for 6 hours. Residual gases were removed, and low-boiling substances and octamethylcyclotetrasiloxane were distilled off to obtain 68 kg of crude methylethyl silicone oil. Residual hydroxyl hydrogen was undetectable.

[0030] 58 kg of crude methyl ethyl silicone oil was added to a pyrolysis reactor, along with 7 kg of repeatedly washed sulfonic acid resin. The reactor was subjected to reduced pressure pyrolysis at 110°C and an absolute pressure of 1000 Pa to obtain the pyrolysis product, which was then purified by distillation. The composition of the pyrolysis product was 56% tetramethyltetraethylcyclotetrasiloxane, 42% pentamethylpentaethylcyclopentasiloxane, and 4% heptamethylethyltrisiloxane.

[0031] Example 3

[0032] 50 kg of high-hydrogen silicone oil (hydrogen content 1.50%) and 17 kg of toluene were added to a stainless steel autoclave, and the oxygen content was purged with nitrogen until it was less than 1%. Ethylene was introduced, and the pressure was increased to 1 atm. 0.05 kg of cassiterite catalyst (Pt content 3000 ppm) was added. The mixture was heated to 80 °C and reacted for 6 h. Residual gases were removed, and low-boiling-point substances and toluene were distilled off to obtain 68 kg of crude methyl ethyl silicone oil. Residual hydrogen silane was undetectable.

[0033] 68 kg of crude methyl ethyl silicone oil was added to a pyrolysis reactor, along with 7 kg of repeatedly washed sulfonic acid resin. The mixture was subjected to reduced pressure pyrolysis at 110°C and 1000 Pa to obtain the pyrolysis products, which were then purified by distillation. The composition of the pyrolysis products was 54% tetramethyltetraethylcyclotetrasiloxane, 40% pentamethylpentaethylcyclopentasiloxane, 5% heptamethylethyltrisiloxane, and 1% hexamethyldisiloxane.

[0034] Example 4

[0035] 50 kg of high-hydrogen silicone oil (hydrogen content 1.50%) and 17 kg of toluene were added to a stainless steel autoclave, and the oxygen content was purged with nitrogen until it was less than 1%. Ethylene was introduced, and the pressure was increased to 3 atm. 0.05 kg of cassiterite catalyst (Pt content 3000 ppm) was added. The mixture was heated to 80 °C and reacted for 6 h. Residual gases were removed, and low-boiling substances and toluene were distilled off to obtain 68 kg of crude methyl ethyl silicone oil. Residual hydrogen silane was undetectable.

[0036] 68 kg of crude methyl ethyl silicone oil was added to a pyrolysis reactor, along with 7 kg of repeatedly washed sulfonic acid resin. The mixture was subjected to reduced pressure pyrolysis at 110°C and 1000 Pa to obtain the pyrolysis products, which were then purified by distillation. The composition of the pyrolysis products was 54% tetramethyltetraethylcyclotetrasiloxane, 40% pentamethylpentaethylcyclopentasiloxane, 5% heptamethylethyltrisiloxane, and 1% hexamethyldisiloxane.

[0037] Example 5

[0038] 50 kg of high-hydrogen-content silicone oil (hydrogen content 1.50%) was added to a stainless steel autoclave, and nitrogen was used to purge until the oxygen content was less than 1%. Ethylene was introduced, and the pressure was increased to 8 atm. 0.05 kg of cassiterite catalyst (Pt content 3000 ppm) was added. The mixture was heated to 80°C and reacted for 5 hours. Residual gases were removed, yielding 71.7 kg of crude methylethyl silicone oil. Residual hydroxyl hydrogen was undetectable.

[0039] 71.7 kg of crude methyl ethyl silicone oil was added to a pyrolysis reactor, along with 7 kg of repeatedly washed sulfonic acid resin. The mixture was subjected to reduced pressure pyrolysis at 110°C and 1000 Pa to obtain the pyrolysis products, which were then purified by distillation. The composition of the pyrolysis products was 54% tetramethyltetraethylcyclotetrasiloxane, 40% pentamethylpentaethylcyclopentasiloxane, 1% hexamethyldisiloxane, and 5% heptamethylethyltrisiloxane.

[0040] Table 1

[0041]

[0042] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A process for the preparation of methyl ethylcyclosiloxane, characterized in that, The method comprises the following steps: adding high hydrogen content silicone oil and ethylene gas under the condition of a Karstedt catalyst to prepare methyl ethyl silicone oil, wherein the hydrogen content of the high hydrogen content silicone oil is 1-1.62%; mixing the methyl ethyl silicone oil and a sulfonic acid resin, and then performing vacuum cracking to obtain tetramethyl tetraethyl cyclotetrasiloxane and pentamethyl pentaehtyl cyclopentasiloxane, i.e. methyl ethyl cyclotetrasiloxane.

2. The method for preparing methylethylcyclosiloxane according to claim 1, characterized in that, The hydrogen content of the high hydrogen content silicone oil is 1.50%.

3. The method for preparing methylethylcyclosiloxane as described in claim 1, characterized in that, The addition amount of the Karstedt catalyst is 0.08-0.12% of the mass of the high hydrogen content silicone oil.

4. The method for preparing methylethylcyclosiloxane according to claim 1, characterized in that, The addition is performed by introducing ethylene gas to a pressure of 1-8 atm under a nitrogen atmosphere.

5. The process for preparing methyl ethylcyclosiloxane according to any one of claims 1 to 4, characterized in that, The reaction condition of the addition is heating to 80-90 DEG C for 4-12 h.

6. The method for preparing methylethylcyclosiloxane according to claim 5, characterized in that, An organic solvent is added during the addition, and the organic solvent is a solvent free of carboxyl, hydroxyl, sulfur, phosphorus and nitrogen.

7. The method for preparing methylethylcyclosiloxane according to claim 1, characterized in that, The addition amount of the sulfonic acid resin is greater than 5% of the mass of the methyl ethyl silicone oil.

8. The method for preparing methylethylcyclosiloxane according to claim 1, characterized in that, The temperature of the vacuum cracking is 105-115 DEG C.

9. The method for preparing methylethylcyclosiloxane as described in claim 1 or 8, characterized in that, The pressure of the vacuum cracking is 800-1200 Pa of absolute pressure.

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