Low ring body hydrogen-containing silicone oil and preparation method thereof

Abstract

The application discloses a kind of low ring body hydrogen-containing silicone oil and preparation method thereof, belong to the technical field of silicone material.The preparation method includes: preparation gradient acid strength core-shell solid acid catalyst;Siloxane raw materials are mixed, and the raw material mixed solution is obtained by dehydration and deoxidation pretreatment;The catalyst is loaded in fixed bed reactor, and the raw material mixed solution is continuously introduced to carry out ring-opening polymerization reaction;Reaction effluent is continuously sent into thin film evaporator, first remove unreacted monomer, then remove ring body and low boiling point substance, collect the product at the bottom of kettle, i.e.low ring body hydrogen-containing silicone oil.The application designs a kind of gradient acid strength core-shell solid acid catalyst, the core is sulfated zirconium oxide, shell is 2-3nm mesoporous SiO2.Limited effect is used in pore, and the limited ring-opening polymerization of cyclosiloxane is realized in fixed bed reactor, chain back-bite into ring is inhibited from space.Combination continuous thin film evaporation separates product in time, so that ring body content is lower than traditional scheme.

Description

Technical Field

[0001] This invention relates to the field of organosilicon materials technology, and in particular to a low-cyclic hydrogen-containing silicone oil and its preparation method. Background Technology

[0002] Hydrogen-containing silicone oils refer to polysiloxanes containing silicon-hydrogen bonds (Si-H bonds) in their molecular chains. Due to the high reactivity of these Si-H bonds, they can react with compounds containing unsaturated bonds through hydrosilylation reactions, and are widely used in crosslinking agents for silicone rubber, fabric finishing agents, waterproofing agents, and defoamers. With increasingly stringent environmental regulations, especially the EU REACH regulation's restrictions on the content of cyclosiloxanes such as octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecylcyclohexasiloxane (D6) (requiring a minimum of 0.1 wt%), the development of low-cyclic hydrogen-containing silicone oils has become a hot research topic in the industry.

[0003] Currently, there are two main methods for industrially producing hydrogen-containing silicone oil: one is ring-opening polymerization using a mixture of dimethylcyclosiloxane rings and hydrogen-containing end-capping agents as raw materials, under the action of acidic catalysts (such as concentrated sulfuric acid, acidic clay, trifluoromethanesulfonic acid, etc.); the other is polycondensation polymerization using hydroxyl-terminated polydimethylsiloxane and hydrogen-containing end-capping agents as raw materials, under the action of chlorinated phosphazene catalysts. However, both methods have significant shortcomings: the acidic catalytic route, due to the polymerization-depolymerization equilibrium, results in a high cyclic content in the product, usually requiring high-temperature, high-vacuum removal of the rings using a thin-film evaporator, which is energy-intensive and difficult to reduce the total D4-D6 rings to below 100 ppm; while the chlorinated phosphazene catalytic route can achieve a lower cyclic content, it requires the use of nitrogen-containing organic amines as neutralizing agents, and the residual nitrogen can poison the platinum catalyst during subsequent hydrosilylation reactions, reducing the reaction rate.

[0004] To address these issues, researchers have attempted to develop novel catalytic systems. For example, patent CN118791743A discloses a method using trifluoromethanesulfonic acid in combination with a hindered amine as a catalytic system. This method reduces the cyclic content in silicone oil products by preventing the molecular chain "backbiting" of organosilicon trifluoromethanesulfonic acid silanolates from forming cyclic compounds. Patent CN104710618A discloses a continuous process for producing high-hydrogen-content silicone oil using a fixed-bed reactor for telomerization. Other literature reports a method for the continuous preparation of polysiloxanes in a fixed bed using a B2O3-MoO3 / ZrO2 solid superacid catalyst. However, these methods still suffer from problems such as complex catalyst separation, easy destruction of Si-H bonds, and limited cyclic inhibition effects.

[0005] Therefore, developing a method for preparing low-cyclic hydrogen-containing silicone oil that can both suppress cyclic formation at the source and efficiently protect Si-H bonds while being simple and environmentally friendly has significant industrial application value. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a low-cyclic hydrogen-containing silicone oil and its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention first proposes a method for preparing low-cyclic hydrogen-containing silicone oil, comprising the following steps: S1. Prepare a gradient acid strength core-shell solid acid catalyst, wherein the gradient acid strength core-shell solid acid catalyst has a core-shell structure, the core being zirconium oxide sulfate and the outer shell being a silica layer with a mesoporous structure. S2. Mix octamethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane and hexamethyldisiloxane or tetramethyldisiloxane, and pre-treat by dehydration and deoxygenation to obtain raw material mixture; D4 (octamethylcyclotetrasiloxane), D4H (tetramethylcyclotetrasiloxane), and MM (hexamethyldisiloxane, end-capping agent) are physically mixed to form a homogeneous siloxane system. Dehydration eliminates water-induced Si-O bond hydrolysis, hydroxyl groups are end-capped, and deoxygenation prevents Si-H from being oxidized to Si-OH. S3. A core-shell solid acid catalyst with gradient acid strength is loaded into a fixed-bed reactor, and the raw material mixture is continuously fed into the fixed-bed reactor to carry out a ring-opening polymerization reaction. The oxygen atom of a strong acid protonates the cyclosiloxane, opening the ring and forming an active silicon cation. D4 / D4H+H + → Cyclic oxonium ion → Linear active chain; The active end is continuously inserted into the ring body: ; MM (hexamethyldisiloxane) provides Me3Si-O-terminals to terminate chain growth: ; In this process, the strong acid in the core achieves efficient ring opening, while the mesoporous SiO2 in the outer shell inhibits back-biting ring formation, avoids the generation of new D4, D5, and D6 molecules, and suppresses the protonation and decomposition of Si-H. At the same time, due to the shape-selective pores, linear molecules are preferentially diffused out.

[0008] S4. The effluent from the reaction in S3 is continuously fed into a thin-film evaporator to remove unreacted monomers, then remove cyclic compounds and low-boiling substances. The product at the bottom of the vessel is collected to obtain low-cyclic hydrogen-containing silicone oil.

[0009] The catalyst bed can be washed with anhydrous ethanol / toluene at low pressure and low speed. After removing the catalyst, it can be calcined in air or nitrogen atmosphere to activate and regenerate the catalyst at high temperature.

[0010] Preferably, in S1, the mesopore size of the silicon dioxide layer is 2-3 nm.

[0011] Preferably, in S1, the preparation method of the gradient acid strength core-shell solid acid catalyst includes: a. Zirconium oxychloride is dissolved in water, and ammonia is added to adjust the pH to 9-10, resulting in precipitation. The mechanism is as follows: ; After standing for 12-14 hours, the grains grow and the structure becomes more regular. After filtration, the precipitate is washed, dried, and passed through a 40-mesh sieve. It is then calcined at high temperature to dehydrate ZrO(OH)2 and generate ZrO2, forming a porous zirconium oxide carrier with a high specific surface area. b. Impregnate the zirconium oxide support with dilute sulfuric acid for 12-14 hours at a solid-liquid ratio of 1:9-11. After impregnation with dilute sulfuric acid, -OSO3H groups are formed on the surface of ZrO2. After drying and calcination, the sulfated zirconium oxide core is obtained. ; After calcination, superacid sites are formed, which are the catalytic centers for ring-opening polymerization.

[0012] c. Disperse zirconium oxide sulfate in anhydrous ethanol, add template agent and silicon source, carry out hydrolysis reaction, remove template by washing, drying and calcination to obtain gradient acid strength core-shell solid catalyst; The silicon source hydrolyzes under the guidance of a template agent, forming an ordered mesoporous SiO2 shell on the surface of sulfated ZrO2; after calcination, the template is removed, forming 2-3 nm mesoporous channels. .

[0013] Preferably, in S2, the mass ratio of octamethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane, and hexamethyldisiloxane is 85-95:3-10:2-8; the dehydration and deoxygenation pretreatment reduces the moisture content to below 10 ppm and removes dissolved oxygen.

[0014] Preferably, in step S3, the ring-opening polymerization reaction temperature is 80-100℃, the pressure is 0.1-0.3MPa, and the space velocity is 0.5-2.0h. -1 .

[0015] Preferably, in step S4, the conditions for removing unreacted monomers are a temperature of 100-120°C and atmospheric pressure; the conditions for removing cyclic compounds and low-boiling substances are a temperature of 150-180°C and a vacuum degree of less than 50 Pa; the unreacted monomers are condensed and recycled back to the raw material mixture in step S2.

[0016] Preferably, in step c, the template agent is one of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, or triblock copolymer F127; the silicon source is one of tetraethyl orthosilicate, methyl orthosilicate, or sodium silicate. The mass ratio of zirconia sulfate core, template agent, and silicon source is 1:0.08-0.12:0.35-0.45.

[0017] The present invention also proposes a low-cyclic hydrogen-containing silicone oil prepared by the aforementioned preparation method, wherein the total content of octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane and dodecylcyclohexasiloxane in the low-cyclic hydrogen-containing silicone oil is less than 100 ppm and the silane-hydrogen bond retention rate is higher than 98%.

[0018] Preferably, the low-cyclic hydrogen-containing silicone oil has a viscosity of 10-5000 mPa·s and a molecular weight distribution index of 1.5-2.0.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. Existing technologies for preparing hydrogen-containing silicone oils generally employ acidic catalysts (such as concentrated sulfuric acid or trifluoromethanesulfonic acid). The polymerization process follows a thermodynamic equilibrium mechanism, meaning that the ring-opening polymerization of cyclosiloxanes and the depolymerization of linear polysiloxanes into rings occur simultaneously and are reversible. When the reaction reaches equilibrium, the system inevitably contains a certain proportion of cyclosiloxanes (typically 8-15%). Even with subsequent removal via high-temperature, high-vacuum thin-film evaporation, it is difficult to reduce the total amount of D4-D6 rings to below 100 ppm, and the energy consumption is extremely high. This invention completely breaks through this technological bottleneck: it innovatively designs a core-shell structured solid acid catalyst with a 2-3 nm mesoporous outer shell, confining the polymerization reaction within a nanoscale confined space. When cyclosiloxane monomers enter mesoporous channels and initiate polymerization at the core strong acid sites, the resulting linear polysiloxane chains grow within the channels. Because the channel diameter (2-3 nm) is much smaller than the conformational space required for "back-biting" and ring formation when the polymer chain extends freely (typically requiring more than 5 nm), the chain ends cannot bend close to the Si-O bonds in the middle of the chain, thus spatially blocking the occurrence of intramolecular cyclization side reactions. This source-based inhibition mechanism, based on spatial confinement effects, results in a naturally extremely low cyclic content in the polymerization product. Combined with subsequent thin-film evaporation, the total D4-D6 content can be easily controlled below 100 ppm, achieving a technological leap from "passive removal" to "active inhibition."

[0020] 2. In existing acidic catalytic processes, although Si-H bonds are relatively stable under alkaline conditions, prolonged exposure to a strong acid environment can still lead to hydrolysis, oxidation, or disproportionation side reactions, resulting in decreased hydrogen content and deteriorated product performance. This invention cleverly solves this problem through catalyst gradient acid strength design and diffusion-controlled polymerization mechanism: First, the catalyst adopts a core-shell structure. The core is a superacidic zirconium sulfate (acid strength H0≈-16), providing highly efficient initiation activity; the outer shell is weakly acidic mesoporous silica, ensuring that the strong acid center is not directly exposed to the reaction body. The Si-H bonds are in contact with a mild acidic environment in the reaction body region, significantly reducing the probability of attack. Second, when the polymerization reaction occurs within the mesoporous channels, the high monomer concentration and rapid polymerization rate within the channels cause the generated polymer chains to rapidly diffuse out of the channels under the drive of the concentration gradient, promptly leaving the catalyst's active center region and avoiding prolonged residence in a strong acid environment. This "fast in, fast out" diffusion control mode shortens the contact time between each polymer molecule and the strong acid center to the minute level, while the contact time in traditional batch reactors can be as long as several hours. With the entire process operated in an anhydrous and oxygen-free environment (moisture content <10ppm, nitrogen protection), this invention achieves a silicon-hydrogen bond retention rate of over 98%, far exceeding existing technologies (typically 85-95%), providing high-quality active groups for subsequent hydrosilylation reactions.

[0021] 3. Traditional hydrogen-containing silicone oil production is mostly carried out using batch reactor processes, which have the following inherent drawbacks: First, the reaction time is long (usually 4-10 hours), and the polymerization products remain at the reaction temperature for a long time, continuously undergoing depolymerization-polymerization equilibrium reactions, resulting in the continuous accumulation of cyclic compounds; second, the catalyst needs to be removed by subsequent neutralization, water washing, or thermal decomposition, generating a large amount of wastewater, waste salt, or amine-containing waste gas; third, there are large batch-to-batch quality fluctuations and low production efficiency. This invention, based on the process intensification concept, systematically integrates fixed-bed continuous polymerization with thin-film evaporation for online separation, constructing a new continuous production paradigm: the material residence time in the fixed-bed reactor is precisely controllable (0.5-2 hours), and the polymerization products immediately enter the thin-film evaporation system after generation, completing separation within minutes, completely avoiding secondary equilibrium reactions at the reaction temperature; the solid catalyst is packed in a fixed bed, eliminating the need for separation steps, and can be reused through online regeneration, with a lifespan exceeding 2000 hours, achieving zero catalyst emissions; unreacted monomers are directly recycled after condensation, achieving a raw material utilization rate of over 95%. This fully continuous process not only produces stable product quality (molecular weight distribution PDI 1.5-2.0, superior to the traditional process of 2.5-3.5), but also generates no wastewater or waste salt, and reduces energy consumption by more than 30%, representing the green and intelligent development direction of hydrogen-containing silicone oil production. Attached Figure Description

[0022] Figure 1 This is a TEM image of the gradient acid strength core-shell solid acid catalyst proposed in this invention. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0024] Example 1: A method for preparing a low-cyclic hydrogen-containing silicone oil, comprising the following steps: S1. Prepare a gradient acid strength core-shell solid acid catalyst, wherein the gradient acid strength core-shell solid acid catalyst has a core-shell structure, the core being zirconium oxide sulfate and the outer shell being a silica layer with a mesoporous structure. S2. Mix octamethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane and hexamethyldisiloxane, and pre-treat by dehydration and deoxygenation to obtain raw material mixture; S3. A core-shell solid acid catalyst with gradient acid strength is loaded into a fixed-bed reactor, and the raw material mixture is continuously fed into the fixed-bed reactor to carry out a ring-opening polymerization reaction. S4. The effluent from the reaction in S3 is continuously fed into a thin-film evaporator to remove unreacted monomers, then remove cyclic compounds and low-boiling substances. The product at the bottom of the vessel is collected to obtain low-cyclic hydrogen-containing silicone oil.

[0025] In S1, the mesopore size of the silicon dioxide layer is 2-3 nm.

[0026] In S1, the preparation method of the gradient acid strength core-shell solid acid catalyst includes: a. Dissolve zirconium oxychloride in water, adjust the pH to 9.5±0.5 with ammonia, precipitate, let stand for 12 hours, filter, wash and dry the precipitate, pass it through a 40-mesh sieve, and calcine to obtain zirconium oxide carrier. b. The zirconia support was impregnated with dilute sulfuric acid for 12 hours at a solid-liquid ratio of 1:10, and then dried and calcined to obtain the sulfated zirconia core; c. Disperse zirconium oxide sulfate in anhydrous ethanol, add template agent and silicon source, carry out hydrolysis reaction, remove template by washing, drying and calcination to obtain gradient acid strength core-shell solid catalyst.

[0027] In S2, the mass ratio of octamethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane, and hexamethyldisiloxane is 85:10:2; the dehydration and deoxygenation pretreatment reduces the moisture content to below 10 ppm and removes dissolved oxygen.

[0028] In step S3, the ring-opening polymerization reaction temperature is 100℃, the pressure is 0.2MPa, and the space velocity is 1.0h. -1 .

[0029] In step S4, the conditions for removing unreacted monomers are a temperature of 120°C and atmospheric pressure; the conditions for removing cyclic compounds and low-boiling substances are a temperature of 160°C and a vacuum degree of less than 50 Pa; the unreacted monomers are condensed and recycled back to the raw material mixture in step S2.

[0030] In step c, the template agent is one of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and triblock copolymer F127; the silicon source is one of tetraethyl orthosilicate, methyl orthosilicate, and sodium silicate. The mass ratio of zirconia sulfate core, template agent, and silicon source is 1:0.12:0.35.

[0031] Example 2: A method for preparing a low-cyclic hydrogen-containing silicone oil, comprising the following steps: S1. Prepare a gradient acid strength core-shell solid acid catalyst, wherein the gradient acid strength core-shell solid acid catalyst has a core-shell structure, the core being zirconium oxide sulfate and the outer shell being a silica layer with a mesoporous structure. S2. Mix octamethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane and hexamethyldisiloxane, and pre-treat by dehydration and deoxygenation to obtain raw material mixture; S3. A core-shell solid acid catalyst with gradient acid strength is loaded into a fixed-bed reactor, and the raw material mixture is continuously fed into the fixed-bed reactor to carry out a ring-opening polymerization reaction. S4. The effluent from the reaction in S3 is continuously fed into a thin-film evaporator to remove unreacted monomers, then remove cyclic compounds and low-boiling substances. The product at the bottom of the vessel is collected to obtain low-cyclic hydrogen-containing silicone oil.

[0032] In S1, the mesopore size of the silicon dioxide layer is 2-3 nm.

[0033] In S1, the preparation method of the gradient acid strength core-shell solid acid catalyst includes: a. Dissolve zirconium oxychloride in water, adjust the pH to 9.5±0.5 with ammonia, precipitate, let stand for 12 hours, filter, wash and dry the precipitate, pass it through a 40-mesh sieve, and calcine to obtain zirconium oxide carrier. b. The zirconia support was impregnated with dilute sulfuric acid for 12 hours at a solid-liquid ratio of 1:10, and then dried and calcined to obtain the sulfated zirconia core; c. Disperse zirconium oxide sulfate in anhydrous ethanol, add template agent and silicon source, carry out hydrolysis reaction, remove template by washing, drying and calcination to obtain gradient acid strength core-shell solid catalyst.

[0034] The gradient acid strength core-shell solid acid catalyst was characterized by TEM, and the results are as follows: Figure 1 As shown; Figure 1The central dark region is a zirconium oxide sulfate core (high atomic number, strong scattering), surrounded by a light-colored, uniform outer layer of mesoporous silica. The core and shell are clearly defined, with a particle size of 80-120 nm. The outer shell is uniform and continuous, without independent nucleation, proving the successful construction of a core-shell structure. The porous, flocculent characteristics of the shell are consistent with a 2-3 nm mesoporous structure, and the particle aggregation morphology is also consistent with the typical morphology of the catalyst after drying and calcination, which is completely in line with the design concept of this invention.

[0035] In S2, the mass ratio of octamethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane, and hexamethyldisiloxane is 90:7:5; the dehydration and deoxygenation pretreatment reduces the moisture content to below 10 ppm and removes dissolved oxygen.

[0036] In step S3, the ring-opening polymerization reaction temperature is 100℃, the pressure is 0.2MPa, and the space velocity is 1.0h. -1 .

[0037] In step S4, the conditions for removing unreacted monomers are a temperature of 120°C and atmospheric pressure; the conditions for removing cyclic compounds and low-boiling substances are a temperature of 160°C and a vacuum degree of less than 50 Pa; the unreacted monomers are condensed and recycled back to the raw material mixture in step S2.

[0038] In step c, the template agent is one of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and triblock copolymer F127; the silicon source is one of tetraethyl orthosilicate, methyl orthosilicate, and sodium silicate. The mass ratio of zirconia sulfate core, template agent, and silicon source is 1:0.10:0.40.

[0039] Example 3: A method for preparing a low-cyclic hydrogen-containing silicone oil, comprising the following steps: S1. Prepare a gradient acid strength core-shell solid acid catalyst, wherein the gradient acid strength core-shell solid acid catalyst has a core-shell structure, the core being zirconium oxide sulfate and the outer shell being a silica layer with a mesoporous structure. S2. Mix octamethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane and tetramethyldisiloxane, and pre-treat by dehydration and deoxygenation to obtain raw material mixture; S3. A core-shell solid acid catalyst with gradient acid strength is loaded into a fixed-bed reactor, and the raw material mixture is continuously fed into the fixed-bed reactor to carry out a ring-opening polymerization reaction. S4. The effluent from the reaction in S3 is continuously fed into a thin-film evaporator to remove unreacted monomers, then remove cyclic compounds and low-boiling substances. The product at the bottom of the vessel is collected to obtain low-cyclic hydrogen-containing silicone oil.

[0040] In S1, the mesopore size of the silicon dioxide layer is 2-3 nm.

[0041] In S1, the preparation method of the gradient acid strength core-shell solid acid catalyst includes: a. Dissolve zirconium oxychloride in water, adjust the pH to 9.5±0.5 with ammonia, precipitate, let stand for 12 hours, filter, wash and dry the precipitate, pass it through a 40-mesh sieve, and calcine to obtain zirconium oxide carrier. b. The zirconia support was impregnated with dilute sulfuric acid for 12 hours at a solid-liquid ratio of 1:10, and then dried and calcined to obtain the sulfated zirconia core; c. Disperse zirconium oxide sulfate in anhydrous ethanol, add template agent and silicon source, carry out hydrolysis reaction, remove template by washing, drying and calcination to obtain gradient acid strength core-shell solid catalyst.

[0042] In S2, the mass ratio of octamethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane, and tetramethyldisiloxane is 95:3:8; the dehydration and deoxygenation pretreatment reduces the moisture content to below 10 ppm and removes dissolved oxygen.

[0043] In step S3, the ring-opening polymerization reaction temperature is 100℃, the pressure is 0.2MPa, and the space velocity is 1.0h. -1 .

[0044] In step S4, the conditions for removing unreacted monomers are a temperature of 120°C and atmospheric pressure; the conditions for removing cyclic compounds and low-boiling substances are a temperature of 160°C and a vacuum degree of less than 50 Pa; the unreacted monomers are condensed and recycled back to the raw material mixture in step S2.

[0045] In step c, the template agent is one of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and triblock copolymer F127; the silicon source is one of tetraethyl orthosilicate, methyl orthosilicate, and sodium silicate. The mass ratio of zirconia sulfate core, template agent, and silicon source is 1:0.08:0.45.

[0046] The following comparison model was also set: Comparative Example 1: Based on Example 2, the difference is that zirconium sulfate was prepared, but without its silica shell coating. That is, zirconium sulfate powder was directly pressed into tablets to obtain a pure solid acid catalyst without shell coating. The rest is the same as in Example 2.

[0047] Comparative Example 2: Concentrated sulfuric acid (98%), which accounts for 1% of the total mass of the raw materials, was used as a catalyst.

[0048] Comparative Example 3: Tetramethylammonium hydroxide silanoate was used as a catalyst at 0.1% of the total mass of the raw materials.

[0049] Comparative Example 4: Based on Example 2, the difference is that the catalyst is pure mesoporous silica supported with sulfuric acid, without the strong acid core of sulfated zirconium oxide, and the rest is the same as Example 2.

[0050] Comparative Example 5: Based on Example 2, the difference is that only atmospheric distillation is performed to remove monomers after the reaction, and high-vacuum thin-film evaporation is not performed to remove cyclizers. The rest is the same as Example 2.

[0051] Comparative Example 6: Based on Example 2, the difference is that the raw material mixture is not subjected to dehydration and deoxygenation pretreatment, the moisture content is >100ppm, and it contains dissolved oxygen. The rest is the same as Example 2.

[0052] Performance testing: The cyclic content was determined according to HG / T 6395-2025 "Determination of Volatile Methylcyclosiloxane Content in Silicone Oil"; the hydrogen content and silane-hydrogen bond retention rate were determined according to HG / T 4804-2015 "Methyl High-Hydrogen Silicone Oil"; the viscosity was determined according to HG / T2363-1992 "Test Method for Kinematic Viscosity of Silicone Oil"; and the appearance, color, and moisture content were determined according to HG / T 4804-2015 "Methyl High-Hydrogen Silicone Oil". The results are shown below: Table 1. Test data for low-cyclic hydrogen-containing silicone oil

[0053] Data Analysis: The total cyclic content in Examples 1-3 was 75 ppm, 68 ppm, and 82 ppm, respectively, all below 100 ppm, while the comparative examples were all above 1200 ppm, with Comparative Example 5 even reaching 1980 ppm. This significant difference demonstrates the key innovation of the technical solution of this invention. First, the mesoporous silica shell (pore size 2-3 nm) of the gradient acid strength core-shell catalyst provides a spatial confinement effect: when cyclosiloxane monomers polymerize within the channels, linear chain growth is limited by the nanopores, and the chain ends cannot bend back to attack the Si-O bonds in the middle of the molecule, thereby suppressing the side reaction of intramolecular cyclization to form D4-D6 from the source. Comparative Example 1 (without shell) and Comparative Example 4 (without strong acid core) had cyclic contents as high as 1520 ppm and 1270 ppm, respectively, due to lack of confinement and insufficient activity, confirming the necessity of the core-shell structure. Second, the coupled process of continuous fixed-bed polymerization and thin-film evaporation for online separation enhances process control: the polymerization product immediately enters the evaporation system after generation, avoiding secondary equilibrium cyclization caused by prolonged residence at the reaction temperature. Comparative Example 5, although using the same catalyst, did not undergo high-vacuum decyclization, and the cyclic content was close to 2000 ppm. This indicates that although the confinement effect can suppress the formation, trace amounts of cyclic compounds still exist in the product and need to be completely removed by thin-film evaporation. Only through the synergy of both methods can the optimal effect be achieved. Comparative Examples 2 (concentrated sulfuric acid) and 3 (tetramethylammonium hydroxide) are conventional homogeneous catalysts. Due to the polymerization-depolymerization equilibrium, the cyclic content was 1480 ppm and 1390 ppm, respectively, which cannot compare with the source suppression of this invention.

[0054] The Si-H bond retention rates of Examples 1-3 were 98.2%, 98.4%, and 98.1%, respectively, significantly higher than those of Comparative Examples 2 (78.5%), 3 (92.3%), and 6 (72.1%). The catalyst of this invention employs a core-shell structure, with the core being a strong acid, zirconium sulfate (providing high activity), and the outer shell being weakly acidic mesoporous silica. This prevents the strong acid centers from being directly exposed to the reaction substrate, allowing the Si-H bonds to contact a mild acidic environment in the reaction zone, greatly reducing the probability of attack. Simultaneously, the high monomer concentration and rapid polymerization rate within the pores allow the polymer chains to quickly diffuse out of the pores, shortening the contact time with the strong acid centers (on the order of minutes). Comparative Example 1 (without an outer shell) suffered from direct exposure to the strong acid, resulting in a retention rate of only 85.2%; Comparative Example 2 (concentrated sulfuric acid), being a homogeneous strong acid system with a long contact time, had a retention rate of only 78.5%. Furthermore, strict anhydrous and oxygen-free pretreatment (moisture content <10 ppm) protected the Si-H bonds from hydrolysis and oxidation. Comparative Example 6 (raw material moisture > 100 ppm) had a retention rate of only 72.1% and the product was turbid, proving that moisture is the key factor in the destruction of Si-H. Although Comparative Example 3 (alkali catalysis) had a relatively high retention rate of 92.3%, alkali catalysis still attacked Si-H, and the high cyclic content resulted in poor overall performance.

[0055] The products from Examples 1-3 were all colorless and transparent, with a color intensity of 10-15 and a moisture content of <10 ppm. In contrast, Comparative Examples 1 (slightly turbid, color intensity 50), 2 (slightly yellow, color intensity 80), 3 (turbid, color intensity 40), and 6 (turbid, color intensity 60) all showed deterioration in appearance. The solid catalyst of this invention requires no neutralization washing, avoiding acid and alkali residues and wastewater generation. The fixed-bed continuous flow reactor achieves steady-state production, with precise controllable material residence time and a narrow molecular weight distribution (stable viscosity). Thin-film evaporation promptly separates unreacted monomers and cyclic compounds, preventing thermal degradation and discoloration. Comparative Example 2 generated wastewater during washing and neutralization, and its product was slightly yellow. Comparative Example 3's thermal decomposition produced trimethylamine gas and may leave residual nitrides leading to subsequent platinum catalyst poisoning, both demonstrating the shortcomings of traditional processes. This invention's process generates no wastewater, and the catalyst can be regenerated online, representing a green and efficient production paradigm.

[0056] 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 preparing a low-cyclic hydrogen-containing silicone oil, characterized in that, Includes the following steps: S1. Prepare a gradient acid strength core-shell solid acid catalyst, wherein the gradient acid strength core-shell solid acid catalyst has a core-shell structure, the core being zirconium oxide sulfate and the outer shell being a silica layer with a mesoporous structure. S2. Mix octamethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane and hexamethyldisiloxane or tetramethyldisiloxane, and pre-treat by dehydration and deoxygenation to obtain raw material mixture; S3. A core-shell solid acid catalyst with gradient acid strength is loaded into a fixed-bed reactor, and the raw material mixture is continuously fed into the fixed-bed reactor to carry out a ring-opening polymerization reaction. S4. The effluent from the reaction in S3 is continuously fed into a thin-film evaporator to remove unreacted monomers, then remove cyclic compounds and low-boiling substances. The product at the bottom of the vessel is collected to obtain low-cyclic hydrogen-containing silicone oil.

2. The method for preparing a low-cyclic hydrogen-containing silicone oil according to claim 1, characterized in that, In S1, the mesopore size of the silicon dioxide layer is 2-3 nm.

3. The method for preparing a low-cyclic hydrogen-containing silicone oil according to claim 1, characterized in that, In S1, the preparation method of the gradient acid strength core-shell solid acid catalyst includes: a. Dissolve zirconium oxychloride in water, add ammonia to adjust the pH to 9-10, precipitate, let stand for 12-14 hours, filter, wash and dry the precipitate, pass it through a 40-mesh sieve, and calcine to obtain zirconium oxide carrier. b. The zirconium oxide support is impregnated with dilute sulfuric acid for 12-14 hours with a solid-liquid ratio of 1:9-11, and then dried and calcined to obtain the sulfated zirconium oxide core; c. Disperse zirconium oxide sulfate in anhydrous ethanol, add template agent and silicon source, carry out hydrolysis reaction, remove template by washing, drying and calcination to obtain gradient acid strength core-shell solid catalyst.

4. The method for preparing a low-cyclic hydrogen-containing silicone oil according to claim 1, characterized in that, In S2, the mass ratio of octamethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane, and hexamethyldisiloxane is 85-95:3-10:2-8; the dehydration and deoxygenation pretreatment reduces the moisture content to below 10 ppm and removes dissolved oxygen.

5. The method for preparing a low-cyclic hydrogen-containing silicone oil according to claim 1, characterized in that, In step S3, the ring-opening polymerization reaction temperature is 80-100℃, the pressure is 0.1-0.3MPa, and the space velocity is 0.5-2.0h. -1 .

6. The method for preparing a low-cyclic hydrogen-containing silicone oil according to claim 1, characterized in that, In step S4, the conditions for removing unreacted monomers are a temperature of 100-120°C and atmospheric pressure; the conditions for removing cyclic compounds and low-boiling substances are a temperature of 150-180°C and a vacuum degree of less than 50 Pa; the unreacted monomers are condensed and recycled back to the raw material mixture in step S2.

7. The method for preparing a low-cyclic hydrogen-containing silicone oil according to claim 3, characterized in that, In step c, the template agent is one of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, or triblock copolymer F127; the silicon source is one of tetraethyl orthosilicate, methyl orthosilicate, or sodium silicate. The mass ratio of zirconia sulfate core, template agent, and silicon source is 1:0.08-0.12:0.35-0.

45.

8. A low-cyclic hydrogen-containing silicone oil prepared by the method according to any one of claims 1-6, characterized in that, The total content of octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane and dodecylcyclohexasiloxane in the low-cyclic hydrogen-containing silicone oil is less than 100 ppm, and the silane-hydrogen bond retention rate is higher than 98%.

9. The low-cyclic hydrogen-containing silicone oil according to claim 9, characterized in that, The viscosity of the low-cyclic hydrogen-containing silicone oil is 10-5000 mPa·s, and the molecular weight distribution index is 1.5-2.0.

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