A process for the preparation of a cyclosiloxane

Abstract

The application provides a preparation method of cyclosiloxane, which comprises the following steps: uniformly mixing siloxane polymer, non-ionic surfactant and alkaline catalyst, performing cleavage reaction, and performing rectification separation on the reaction product to obtain the corresponding cyclosiloxane, wherein the non-ionic surfactant is at least one of block copolymer of polyethylene glycol and polypropylene glycol, polyethylene glycol, polyethylene glycol monomethyl ether, polyethylene glycol dimethyl ether and fatty alcohol polyoxyethylene ether. According to the application, the whole reaction system exists in liquid form from the beginning to the end, the insoluble siloxane crosslinked polymer is less, the safety of the equipment in the preparation process is ensured, and the convenience of residue discharge is ensured, the solvent can be recycled and applied for multiple times after simple treatment, there is no large odor in the whole reaction process, the stimulation is low, and the yield is high.

Description

Technical Field

[0001] This invention belongs to the field of polysiloxane preparation technology, specifically relating to a method for preparing cyclosiloxanes. Background Technology

[0002] Cyclic oligomers of siloxanes, also known as cyclosiloxanes or cyclosiloxanes, are essential raw materials for the production of many organosilicon products such as silicone oils, silicone rubbers, and silicone resins. Currently, industrially commonly used cyclosiloxanes are monomers or mixtures obtained by polymerizing 3-5 siloxane units. Their preparation typically involves two steps: hydrolysis and reforming (or cracking). Placing polysiloxane mixtures under high temperature and high vacuum conditions, and using strong alkali catalysis, causes the silicon-oxygen bonds to break, reforming the macromolecules into smaller molecules with relatively concentrated polymerization. This process is widely implemented industrially. For example, dimethyldichlorosilane, after hydrolysis, bond-breaking reforming, and distillation, yields a mixture of dimethylcyclosiloxanes (DMC), which is then further separated by distillation to obtain cyclotri-, cyclotetra-, and cyclopentasiloxanes (D3, D4, D5). Similarly, methylvinyldichlorosilane, after hydrolysis, reforming, and distillation, can produce the corresponding cyclotri-, cyclotetra-, and cyclopentasiloxanes (V3, V4, V5).

[0003] In the early 1980s, foreign countries reported solvent-based cracking and reforming technology, which uses low-viscosity, high-boiling-point, and stable solvent oil as a heat carrier added to the cracking reaction system. By reducing the viscosity of the material and improving the mass and heat transfer efficiency, it aims to stabilize the cracking conditions, extend the continuous operation time of the unit, and improve the safety of the unit. Wang Wenjin et al. used n-octadecyl alcohol as a solvent to crack dimethyldichlorosilane hydrolysate to obtain DMC under the catalysis of KOH, and achieved good results, with the highest conversion rate reaching more than 95% (Organosilicon Materials, 2018, 32(3):205~208; Organosilicon Materials, 2020, 34(3):51~54.).

[0004] However, in industrial implementation, the reaction system of n-octadecyl alcohol and polysiloxane will precipitate n-octadecyl alcohol at low temperature. The n-octadecyl alcohol will mix with the cross-linked siloxane polymer produced in the cracking system, which is difficult to separate and produces a large amount of strongly alkaline solid waste or hazardous waste. The treatment is difficult and costly, and it is not easy to remove the residue from the reactor. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing cyclosiloxanes.

[0006] The present invention adopts the following technical solution:

[0007] A method for preparing cyclosiloxanes involves uniformly mixing a siloxane polymer, a nonionic surfactant, and an alkaline catalyst, carrying out a pyrolysis reaction, and separating the reaction products by distillation to obtain the cyclosiloxane of the corresponding single component.

[0008] The siloxane polymer has the following structural formula:

[0009]

[0010] In the structural formula, n≥3, m≥3, and R1 and R2 include alkyl functional groups, olefin functional groups, aromatic functional groups, and cyano functional groups;

[0011] The nonionic surfactant is at least one of the following: a block copolymer of polyethylene glycol and polypropylene glycol, polyethylene glycol, polyethylene glycol monomethyl ether, polyethylene glycol dimethyl ether, and fatty alcohol polyoxyethylene ether.

[0012] In some embodiments, preferably, the alkyl functional group is methyl, ethyl, or propyl; the olefin functional group is vinyl or allyl; the aromatic functional group is phenyl, benzyl, or phenethyl; and the cyano functional group is cyanoethyl or cyanopropyl.

[0013] Furthermore, the pyrolysis-reforming reaction proceeds in two steps:

[0014] A preheated system containing an active alkali metal siloxane salt is obtained by mixing a nonionic surfactant, an alkaline catalyst, and / or a siloxane polymer in the same weight proportion as the nonionic surfactant and heating the mixture to its boiling point under high vacuum conditions.

[0015] The remaining siloxane polymer is added dropwise to the preheated system at a certain rate to react, and the mixture is condensed in the gas phase to obtain a cyclic siloxane mixture. The cyclic siloxane mixture is then separated by simple distillation to obtain the corresponding single-component siloxane cyclic compounds. Further, the molecular weight of the block copolymer of polyethylene glycol and polypropylene glycol is 200-2000.

[0016] The molecular weight of the polyethylene glycol is 200 to 2000;

[0017] The molecular weight of the polyethylene glycol monomethyl ether is 300 to 1000;

[0018] The molecular weight of the polyethylene glycol dimethyl ether is 300 to 1000;

[0019] The fatty alcohol polyoxyethylene ether is selected from one or more of the AEO series products, the isomeric tridecyl alcohol polyoxyethylene ether series products, and the Softanol series products.

[0020] Furthermore, the weight ratio of the siloxane polymer, nonionic surfactant, and alkaline catalyst is (1000-30100):(80-120):(0.5-5).

[0021] In some embodiments, preferably, the weight ratio of the siloxane polymer, nonionic surfactant, and alkaline catalyst is 10100:100:1.

[0022] Furthermore, the pyrolysis reaction conditions are: pressure -0.098MPa to -0.103MPa, and temperature 110℃ to 160℃.

[0023] In some embodiments, preferably, the pyrolysis reaction conditions are: pressure -0.1 MPa and temperature 135°C.

[0024] Furthermore, the alkaline catalyst is at least one selected from Na3PO4, K3PO4, NaOH, KOH, and LiOH.

[0025] In some embodiments, preferably, the alkaline catalyst is KOH.

[0026] Furthermore, the yield of the cyclosiloxane is higher than 90%.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) The present invention uses a nonionic surfactant that is compatible with siloxane polymers at low temperatures as a dispersant (solvent). After the two are mixed, the entire reaction exists in liquid form from beginning to end. The cross-linked bodies generated during the pyrolysis process are few and can be continuously dissolved in the dispersant, ensuring that the cross-linked bodies do not affect the reaction process during the preparation process, increasing the single batch processing capacity of siloxane polymers, and the residual liquid after the reaction is easy to be discharged from the reaction vessel, which improves the safety of the equipment. There is no strong odor and low irritation during the entire reaction process.

[0029] (2) In this invention, a nonionic surfactant, an alkaline catalyst and a siloxane polymer of the same weight as the nonionic surfactant are first mixed and heated to the boiling point under high vacuum to obtain a preheated system. The remaining siloxane polymer is gradually added later, which can reduce the initial reaction temperature of the entire reaction system by 10-20°C. This reduces energy consumption during production and significantly reduces the breaking of Si-C bonds in the molecule, thereby reducing the formation of siloxane crosslinked polymers and improving product yield.

[0030] (3) In this invention, there are multiple choices of alkaline catalysts. When KOH and NaOH are selected, the product yield is greater than 90%. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention.

[0032] Key experimental material sources and physicochemical parameters:

[0033] Polyethylene glycol monomethyl ether and polyethylene glycol dimethyl ether were purchased from BASF (China) Co., Ltd.

[0034] Fatty alcohol polyoxyethylene ether (AEO series products) was purchased from Jiangsu Haian Petrochemical Plant, isomeric tridecyl alcohol polyoxyethylene ether series products were purchased from Shanghai Duolun Chemical Co., Ltd., and Softanol series products were purchased from Nippon Shokubai Co., Ltd.

[0035] The No. 200 solvent oil was purchased from Jilin Petrochemical Company of China National Petroleum Corporation.

[0036] High-boiling-point methyl vinyl siloxanes: These are linear polymers derived from the hydrolysis of methyl vinyl dichlorosilane.

[0037] Methyl vinyl siloxane hydrolysate: derived from the cyclic and linear mixture obtained after the hydrolysis of methyl vinyl dichlorosilane, which contains methyl vinyl siloxane cyclic units (3 to 8 siloxane polymer units) and methyl vinyl siloxane linear polymers.

[0038] High-boiling-point methylphenylsiloxanes: These are linear polymers derived from the hydrolysis of methylphenyldichlorosilane.

[0039] High-boiling-point methylpropyl polysiloxanes: These are linear polymers derived from the hydrolysis of methylpropyl dichlorosilane.

[0040] Dimethylsiloxane high-boiling-point derivatives: derived from linear polymers produced during the hydrolysis of dimethyldichlorosilane;

[0041] All other raw materials or structures not specifically described in this invention already exist in the prior art and can be purchased directly from the market.

[0042] Example 1

[0043] This embodiment provides a method for preparing cyclosiloxanes, the specific steps of which are as follows:

[0044] By mass, add 0.5 parts KOH and 100 parts polyethylene glycol monomethyl ether to a 1000 mL three-necked flask, stir, and evacuate the system until the vacuum level is below -0.1 MPa. Then raise the temperature to 110 °C. Add 1500 parts of dimethylsiloxane high-boiling liquid as shown in Formula A1 to the three-necked flask, and collect the distillate. This is the methylcyclosiloxane mixture with a yield of 98.5%.

[0045] The contents of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane were determined by gas chromatography (Gas Chromatography-based Fuli 9790Plus type, column type OV-1, 30m) to be 7.6%, 80.2%, and 8.1%, respectively. The reaction formula is shown in Formula 1, where n≥3.

[0046]

[0047] In this embodiment, the methylcyclosiloxane mixture was separated by distillation to obtain hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane, all with a purity of over 98%.

[0048] Example 2

[0049] This embodiment provides a method for preparing cyclosiloxanes, the specific steps of which are as follows:

[0050] By mass, add 100 parts of polyethylene glycol dimethyl ether, 2.5 parts of LiOH and 100 parts of methyl vinyl siloxane high-boiling material as shown in Formula A2 to a 1000 mL three-necked flask. Stir and evacuate the system until the vacuum level is below -0.098 MPa, then raise the temperature to 125 °C.

[0051] When a small amount of liquid begins to distill from the distillation head, add an additional 2000 parts by mass of the high-boiling methyl vinyl siloxane to the three-necked flask, collect the distillate, which is the methyl vinyl cyclosiloxane mixed ring, and the yield of the distillate is 95.8% (calculated based on the added high-boiling 2100 parts).

[0052] The contents of trimethyltrivinylcyclotrisiloxane, tetramethyltetravinylcyclotetrasiloxane, and pentamethylpentavinylcyclopentasiloxane were determined by gas chromatography to be 5.6%, 67.7%, and 23.8%, respectively, with a purity of over 98%. The reaction formula is shown in Formula 2, where n ≥ 3.

[0053]

[0054] Example 3

[0055] This embodiment provides a method for preparing cyclosiloxanes, the specific steps of which are as follows:

[0056] By mass, add 100 parts of fatty alcohol polyoxyethylene ether (AEO-9), 5 parts of NaOH and 100 parts of methyl vinyl siloxane high-boiling material as shown in Formula A2 to a 1000 mL three-necked flask. Stir and evacuate the system until the vacuum level is below -0.1 MPa, then raise the temperature to 120 °C.

[0057] When a small amount of liquid begins to distill from the distillation head, add an additional 1000 parts of high-boiling methyl vinyl siloxane to the three-necked flask and collect the distillate, which is the methyl vinyl cyclosiloxane mixed ring. The yield of the distillate is 96.1% (based on the 1100 parts of high-boiling methyl vinyl siloxane added).

[0058] The contents of trimethyltrivinylcyclotrisiloxane, tetramethyltetravinylcyclotetrasiloxane, and pentamethylpentavinylcyclopentasiloxane were determined by gas chromatography to be 7.3%, 77.8%, and 9.3%, respectively, with a purity of over 98%. The reaction formula is shown in Formula 2.

[0059] Example 4

[0060] This embodiment provides a method for preparing cyclosiloxanes, the specific steps of which are as follows:

[0061] By mass, add 100 parts of fatty alcohol polyoxyethylene ether (AEO-9), 1 part of KOH and 100 parts of methylphenylsiloxane high-boiling material of formula A3 to a 1000 mL three-necked flask. Stir and evacuate the system until the vacuum degree of the reaction system is lower than -0.098 MPa, then raise the temperature to 160 °C.

[0062] When a small amount of liquid begins to distill from the distillation head, add an additional 2000 parts of high-boiling methyl vinyl siloxane to the three-necked flask and collect the distillate, which is a mixed cyclic methyl phenyl cyclosiloxane. The yield of the distillate is 98.1% (based on the addition of 2100 parts of high-boiling methyl vinyl siloxane).

[0063] The contents of trimethyltriphenylcyclotrisiloxane, tetramethyltetraphenylcyclotetrasiloxane, and pentamethylpentaphenylcyclopentasiloxane were determined by gas chromatography to be 16%, 69.5%, and 12%, respectively, with a purity of over 95%. The reaction formula is shown in Formula 3, where n ≥ 3.

[0064]

[0065] Example 5

[0066] This embodiment provides a method for preparing cyclosiloxanes, the specific steps of which are as follows:

[0067] By mass, add 100 parts of fatty alcohol polyoxyethylene ether (AEO-9), 1 part of KOH and 100 parts of high-boiling-point A4 methylpropyl polysiloxane to a 1000 mL three-necked flask. Stir and evacuate the system until the vacuum level is below -0.098 MPa, then raise the temperature to 140 °C.

[0068] When a small amount of liquid begins to distill from the distillation head, add an additional 2000 parts by mass of methylpropyl polysiloxane high-boiling-point substance to the three-necked flask, collect the distillate, which is the methylpropyl siloxane mixed ring, and the yield of the distillate is 97.8% (calculated based on the added 2100 parts of high-boiling-point substance).

[0069] The contents of trimethyltripropylcyclotrisiloxane, tetramethyltetrapropylcyclotetrasiloxane, and pentamethylpentapropylcyclopentasiloxane were determined by gas chromatography to be 8.3%, 62.5%, and 26%, respectively, with a purity of over 95%. The reaction formula is shown in Formula 4, where n ≥ 3.

[0070]

[0071] Example 6

[0072] This embodiment provides a method for preparing cyclosiloxanes, the raw materials and steps of which are basically the same as those in Example 2, except that the high-boiling-point methylvinylsiloxane as shown in Formula A2 is replaced with the hydrolysate obtained from the hydrolysis of methylvinyldichlorosilane. The cyclosiloxane content in the hydrolysate is approximately 50-70%, of which the proportion of cyclosiloxane units ≥5 is approximately 35%.

[0073] By mass, add 100 parts of polyAEO-9, 0.5 parts of NaOH and 100 parts of hydrolyzed methyl vinyl dichlorosilane to a 1000 mL three-necked flask. Stir and evacuate the system until the vacuum level is below -0.10 MPa, then raise the temperature to 118 °C.

[0074] When a small amount of liquid begins to distill from the distillation head, add an additional 20,000 parts by mass of the hydrolysate of methyl vinyl dichlorosilane to the three-necked flask, collect the distillate, which is the methyl vinyl cyclosiloxane mixed ring, and the yield of the distillate is 99.1% (calculated based on the addition of 20,100 parts of high-boiling substances).

[0075] The contents of trimethyltrivinylcyclotrisiloxane, tetramethyltetravinylcyclotetrasiloxane, and pentamethylpentavinylcyclopentasiloxane in the distillate were determined by gas chromatography to be 4.5%, 85.8%, and 9.7%, respectively. After fractional distillation, the purity of each component was above 98%, and the reaction formula is shown in Equation 5, where m≥3 and n≥3.

[0076] The reaction formula is as follows:

[0077]

[0078] Actual research revealed that when the pyrolysis feedstock is hydrolyzed chlorosilane, the throughput significantly increases. This is because the feedstock contains approximately 50% tetracyclic compounds, which can be directly distilled into the collection bottle without further pyrolysis after entering the pyrolysis reactor. Secondly, the crude hydrolysate does not undergo a high-temperature distillation step, reducing the high-temperature residence time of the polysiloxanes, decreasing the probability of Si-C bond breakage, lowering the crosslinking rate, and increasing the yield. Furthermore, the basicity and energy barrier required for the reforming of macrocyclic siloxanes (m≥4) into small-ring siloxanes (2≤m≤4) are lower than those for linear siloxanes.

[0079] Example 7

[0080] This embodiment provides a method for preparing cyclosiloxanes, which uses the reforming and cracking of methyl vinyl polysiloxane as shown in Formula A2 to prepare trimethyltrivinylcyclotrisiloxane (hereinafter referred to as cyclotri), tetramethyltetravinylcyclotetrasiloxane (hereinafter referred to as cyclotetra), and pentamethylpentavinylcyclopentasiloxane (hereinafter referred to as cyclopenta). The steps are basically the same as in Example 1. The specific parameters such as nonionic surfactant, alkaline catalyst, and reaction temperature are shown in Table 1 below:

[0081] Table 1. Raw materials and reaction temperatures in the experimental examples.

[0082]

[0083]

[0084] The content of the products obtained in the above experimental examples was determined by gas chromatography normalization. The yield of the mixture products (calculated based on the total amount of the preheated system and the additionally added methyl vinyl polysiloxane) and the proportion of each compound are shown in Table 2 below:

[0085] Table 2. Yields and proportions of each compound in the mixtures from the experimental examples.

[0086]

[0087] Comparative Example 1

[0088] This comparative example provides a method for preparing a mixed cyclic siloxane, the raw materials and steps of which are basically the same as those in Example 1, except that: sodium dodecyl sulfonate, an anionic surfactant, is added to polyethylene glycol monomethyl ether for modification, replacing the unmodified polyethylene glycol monomethyl ether.

[0089] Since dodecylbenzenesulfonic acid is a solid powder and is not suitable as a solvent, it was modified by adding it to a nonionic solvent. The results showed that the product yield or reaction efficiency did not change significantly after modification.

[0090] Comparative Example 2

[0091] This comparative example provides a method for preparing a mixed cyclic siloxane, the raw materials and steps of which are basically the same as those in Example 2, except that: anionic surfactant quaternary ammonium salt is added to polyethylene glycol dimethyl ether for modification, in order to replace unmodified polyethylene glycol dimethyl ether.

[0092] Since quaternary ammonium salts are solid powders and not suitable for use as solvents, they were modified by adding them to nonionic solvents. The results showed that the product yield or reaction efficiency did not change significantly after modification.

[0093] Comparative Example 3

[0094] This comparative example provides a method for preparing a mixed cyclic siloxane, the raw materials and steps of which are basically the same as those in Examples 1-5, except that: polyethylene glycol monomethyl ether in Example 1, polyethylene glycol dimethyl ether in Example 2, and fatty alcohol polyoxyethylene ether in Examples 3-5 are successively replaced with No. 200 solvent oil.

[0095] The results showed that the cracking reaction was only initiated when the siloxane polymer was a high-boiling dimethylsiloxane, and the product yield or reaction efficiency did not change significantly. However, the cracking reaction was hardly initiated for siloxane polymers containing other functional groups such as vinyl, phenyl, and propyl groups. This indicates that its applicability is not widespread and it only works on specific siloxane polymers.

[0096] Comparative Example 4

[0097] This comparative example provides a method for preparing a mixed cyclic siloxane, the raw materials and steps of which are basically the same as those in Example 2, except that octadecyl alcohol is used instead of polyethylene glycol dimethyl ether.

[0098] The results showed that the reaction efficiency did not change significantly, and the product yield was 93%, which was lower than that of Example 2. In addition, due to the high freezing point of octadecyl alcohol, it was necessary to preheat and melt it during production. The mixture of siloxane crosslinked polymer and octadecyl alcohol produced in the later stage of the cracking reaction was prone to solidification in the reactor, making it difficult to discharge, and the mixture was difficult to separate and reuse.

[0099] Comparative Example 5

[0100] This comparative example provides a method for preparing a siloxane mixed ring, the raw materials and steps of which are basically the same as those in Example 1, except that: polyethylene glycol monomethyl ether with a molecular weight between 300 and 1000 is replaced with polyethylene glycol monomethyl ether with a molecular weight between 200 and 250 and between 1200 and 1400 respectively.

[0101] The results showed that: low molecular weight nonionic surfactants have relatively low boiling points, and under high temperature and vacuum conditions in the later stages, they will evaporate into the product, affecting product quality, reducing the amount of recycling, and affecting secondary reuse; while nonionic surfactants with excessively high molecular weight have high freezing points, making subsequent reuse in production difficult.

[0102] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a cyclosiloxane, characterized in that, The siloxane polymer, nonionic surfactant, and alkaline catalyst are mixed evenly and subjected to a cracking and reforming reaction. The reaction products are then separated by simple distillation to obtain the corresponding cyclosiloxane. The siloxane polymer has the following structural formula: 、 ； In the structural formula, n≥3, m≥3, and R1 and R2 include alkyl functional groups, olefin functional groups, aromatic functional groups, and cyano functional groups; The nonionic surfactant is fatty alcohol polyoxyethylene ether AEO-11; The alkaline catalyst is NaOH; The siloxane polymer is derived from a linear polymer produced during the hydrolysis of chlorosilanes; The pyrolysis reaction proceeds in two steps: A preheated system is obtained by mixing a nonionic surfactant, an alkaline catalyst, and a siloxane polymer in the same weight proportion as the nonionic surfactant and heating the mixture to its boiling point under high vacuum conditions. The remaining siloxane polymer is gradually added to the preheating system to react, and the gas phase is condensed to obtain a cyclosiloxane mixture. The cyclosiloxane mixture is then separated by simple distillation to obtain the cyclosiloxane of the corresponding single component.

2. The method according to claim 1, characterized in that, The weight ratio of the siloxane polymer, nonionic surfactant, and alkaline catalyst is (1000~20100):(80~120):(0.5~5).

3. The method according to claim 2, characterized in that, The weight ratio of the siloxane polymer, nonionic surfactant, and alkaline catalyst is 20100:100:

1.

4. The method according to claim 1, characterized in that, The pyrolysis reaction conditions are: pressure -0.098MPa to -0.103MPa, and temperature 110℃ to 160℃.

5. The method according to claim 4, characterized in that, The pyrolysis reaction conditions are: pressure -0.1 MPa and temperature 135 °C.

6. The method according to claim 5, characterized in that, The yield of the cyclosiloxane is higher than 90%.

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