High-temperature alkali-resistant silicone defoamer and preparation method thereof

Abstract

This invention discloses a high-temperature alkali-resistant silicone defoamer and its preparation method, aiming to solve the core defects of existing silicone defoamers, such as silicon-oxygen bond breakage and emulsion demulsification instability, under industrial conditions of high temperature and strong alkali (85–100 °C, pH=10–14). The defoamer is composed of an interpenetrating network (IPN) structure formed in situ during the polymerization of a three-dimensional alkyl polyether-modified polysiloxane and a high-viscosity silicone composition; wherein the main chain of the three-dimensional alkyl polyether-modified polysiloxane is polydimethylsiloxane (PDMS), with C-terminated branches on the side chains. 12 –C 18 Linear or branched saturated alkyl polyethers enhance the alkali-lysis activation energy of Si–O–Si bonds through steric hindrance; the high-viscosity organosilicon composition is selected from one of methyl vinyl silicone oil, phenyl silicone oil, or fluorosilicone oil, with a kinematic viscosity of 10 at 25 °C. 5 -10 6 It has a concentration of mPa·s, is compatible with PDMS, and forms a Si–C covalently bridged interface. Its oil-in-water emulsion has an average particle size D. 50 =0.8–1.2 μm, absolute value of Zeta potential ≥35 mV, applicable pH range 10–14. Tested under harsh conditions such as textile printing and dyeing soaping (95 ℃ / pH=13) and papermaking cooking (100 ℃ / pH=14), the defoaming period reaches 8–10 h, and the defoaming performance retention rate is ≥90% after 24 h.

Description

Technical Field

[0001] This invention relates to the field of fine chemicals and industrial additives, and in particular to a high-temperature alkali-resistant organosilicon defoamer and its preparation method. Background Technology

[0002] In many key stages of industrial production, such as alkaline dyeing and high-temperature soaping in textile printing and dyeing, alkaline cooking and black liquor treatment in papermaking and pulping, alkaline wastewater treatment and high-temperature reaction systems in petrochemicals, and strongly alkaline processes in building materials and fermentation industries, a large amount of foam is generated due to material reactions, agitation, and temperature changes. The presence of this foam brings a series of serious problems: on the one hand, it leads to a significant decrease in production efficiency, as foam occupies the effective volume of the reactor, hinders material mixing and heat and mass transfer, and prolongs the production cycle; on the other hand, it directly affects product quality. For example, in the printing and dyeing industry, foam can cause uneven dyeing and color defects in fabrics, while in the papermaking industry, foam can cause defects such as pinholes and breaks in paper. In addition, foam can also cause abnormal equipment pressure and pipeline blockage, increasing production safety hazards, while also increasing subsequent processing costs and affecting the continuity and stability of production.

[0003] The high temperature conditions in this invention are 85–100 ℃, and the strong alkaline conditions are pH values ​​of 10–14. This defoamer is suitable for harsh working conditions within this range in industries such as textile printing and dyeing, papermaking and pulping, and petrochemicals.

[0004] Traditional silicone defoamers widely used in industry, while possessing some basic defoaming ability due to the low surface tension of polysiloxanes, are prone to molecular structure degradation under harsh conditions such as high temperatures (above 80 ℃) and high alkalinity (pH≥10). This leads to demulsification and stratification in the emulsion system, resulting in a rapid decline in defoaming effect and a significantly shortened foam suppression cycle, failing to meet the practical needs of long-term stable production. Especially in high-end industrial sectors, the requirements for the high-temperature and alkali resistance of defoamers are constantly increasing, and the performance shortcomings of traditional products have become a bottleneck restricting the high-quality development of related industries.

[0005] Meanwhile, existing improved silicone defoamers mostly use simple compounding methods to improve performance, lacking molecular-level structural design, which makes it difficult to achieve a balance between high temperature resistance and alkali resistance. Some products can withstand certain high temperatures, but are prone to failure in strongly alkaline environments; some products have good alkali resistance, but cannot adapt to high temperature conditions, and generally have problems such as low defoaming efficiency, poor foam suppression persistence, and poor compatibility with the system, making it difficult to adapt to complex industrial production scenarios.

[0006] Patent CN120714275A discloses a defoamer that is stably dispersed in liquid detergents. It is composed of a simple mixture of seven components, including silicone grease composition, polyether-modified polyorganosiloxane, and propylene glycol block copolymer. The components are only physically bonded and there is no chemical bond between them. Defoaming and dispersion are achieved by relying on the synergistic effect of the components. This invention is only suitable for conventional mild liquid detergent systems. Under high temperature and strong alkaline conditions, the physically compounded components will easily separate, the emulsion will break down and separate, the Si–O–Si bonds of ordinary polyether-modified polyorganosiloxane will be easily degraded by strong alkali, and the defoaming function will quickly fail.

[0007] With the advancement of green and efficient industrial development trends, the market demand for high-temperature alkali-resistant defoamers is becoming increasingly urgent. Developing a high-temperature alkali-resistant and highly stable organosilicon defoamer has become the key to solving industry pain points and promoting the upgrading of related industries. Summary of the Invention

[0008] The purpose of this invention is to provide a high-temperature alkali-resistant organosilicon defoamer and its preparation method, so as to solve the problems mentioned in the background art.

[0009] The above-mentioned objective of the present invention is achieved through the following technical solution: a high-temperature alkali-resistant organosilicon defoamer, which is composed of an interpenetrating network structure formed in situ during the polymerization reaction of a three-dimensional alkyl polyether modified polyorganosiloxane and a high-viscosity organosilicon composition; The three-dimensional alkyl polyether-modified polyorganosiloxane has a polydimethylsiloxane backbone with branched alkyl polyethers on the sides; wherein the alkyl group is a straight-chain or branched saturated hydrocarbon group with a carbon chain length of C. 12 –C 18 ; The high-viscosity organosilicon composition is one of methyl vinyl silicone oil, phenyl silicone oil, or fluorosilicone oil.

[0010] Three-dimensional alkyl polyether-modified polyorganosiloxanes, with polydimethylsiloxane (PDMS) as the main chain, provide a basis for high-temperature stability and low surface tension; its side-linked C 12 –C 18 Straight-chain or branched alkyl groups shield Si–O–Si bonds through steric hindrance, increasing the alkaline activation energy and significantly inhibiting the breaking of silicon-oxygen bonds under strong alkaline conditions. The high-viscosity organosilicon composition, as a continuous dispersed phase in the interpenetrating network, generates melt shear resistance through viscosity, forcing PDMS chains to entangle on its surface. Meanwhile, 0.1–0.3 mol% vinyl groups undergo free radical copolymerization with the active end groups of PDMS to form a Si–C covalent bridging interface, achieving dual stability through physical interpenetration and chemical bonding.

[0011] Furthermore, the alkyl group in the alkyl polyether modified polyorganosiloxane is one or more of dodecyl, tetradecyl, hexadecyl, octadecyl or isostearyl.

[0012] Furthermore, the mass ratio of the three-dimensional alkyl polyether modified polysiloxane to the high-viscosity organosilicon composition in the interpenetrating network is 4:1.

[0013] Furthermore, the high-viscosity silicone composition is one of methyl vinyl silicone oil, phenyl silicone oil, or fluorosilicone oil, with a kinematic viscosity of 10 at 25°C. 5 -10 6 mPa·s.

[0014] Furthermore, the defoamer is an oil-in-water emulsion with an average particle size D. 50 =0.8–1.2 μm, absolute value of Zeta potential ≥35 mV, applicable pH range 10–14.

[0015] A method for preparing the aforementioned high-temperature alkali-resistant organosilicon defoamer includes the following steps: S1. Under nitrogen protection, add octamethylcyclotetrasiloxane (D4) and C-containing compounds to the reactor. 12 –C 18 Alkyl polyether silane coupling agent and catalyst, heated to 120 ℃ for ring-opening polymerization, to generate three-dimensional alkyl polyether modified polyorganosiloxane prepolymer; S2. When the prepolymer viscosity reaches 10 4 -10 5 At mPa·s, a high-viscosity organosilicon composition was added dropwise in situ under stirring for 30–60 min. After the addition was completed, the reaction was continued at the temperature for 2–4 h. S3. Add a capping agent to terminate the reaction, remove low molecular weight compounds, and obtain the crude product; S4. Add hydrophobic silica and emulsifier to the crude product, and homogenize by high-speed shearing at a speed of 7000-9000 r / min for 15-25 min to obtain the finished organosilicon defoamer.

[0016] Furthermore, in step S1, the catalyst is KOH; in step S2, the dropping temperature of the high-viscosity organosilicon composition is 120–130 °C, and the dropping rate is controlled at 0.5–1.2 g / min.

[0017] Furthermore, in step S4, the hydrophobic silica is surface-treated with hexamethyldisilazane, resulting in a specific surface area of ​​200-300 m². 2 / g, with a surface methyl coverage of ≥92%, and the amount of hydrophobic silica added is 6%-10% of the weight of the crude product.

[0018] Hexamethyldisilazane end-capping agent eliminates free Si–OH end groups (content <0.02%), preventing end groups from becoming the starting point for alkali attack; after treatment with hexamethyldisilazane, the methyl coverage of hydrophobic silica is ≥92%, uniformly anchored at the IPN interface, absorbing shear stress and preventing particle migration and aggregation at high temperatures.

[0019] Furthermore, in step S4, the nonionic emulsifier is a mixture of Span-85 and Tween-60 in a mass ratio of 3:1, and the total amount added is 2–5% of the weight of the crude product.

[0020] The Span-85 / Tween-60 (3:1) compound emulsifier was used to construct a bilayer interface with HLB=9.2, ensuring that the absolute value of the Zeta potential of the oil-in-water emulsion was ≥35 mV in the pH range of 10–14, the particle size distribution PDI was <0.21 within 120 h, and there was no demulsification. Attached Figure Description

[0021] Table 1 shows the performance test results of the high-temperature alkali-resistant silicone defoamer under high-temperature and high-alkali conditions. Detailed Implementation

[0022] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

[0023] Example 1 Raw material preparation: Octamethylcyclotetrasiloxane (D4), polyether silane coupling agent containing n-hexadecyl group, catalyst KOH, methyl vinyl silicone oil with a kinematic viscosity of 5 × 10⁻⁶ at 25 °C. 5 mPa·s, hexamethyldisilazane end-capping agent, hydrophobic silica (surface treated with hexamethyldisilazane, specific surface area 250 m² / s). 2 / g, with 95% methyl coverage on the surface), emulsifier (Span-85 and Tween-60 in a mass ratio of 3:1).

[0024] Preparation steps S1: In a reactor under nitrogen protection throughout the process, add octamethylcyclotetrasiloxane (D4), a polyether silane coupling agent containing n-hexadecyl, and catalyst KOH according to the formula. After stirring and mixing evenly, slowly raise the temperature to 120 ℃ to carry out the ring-opening polymerization reaction and continue the reaction until a three-dimensional alkyl polyether modified polyorganosiloxane prepolymer is generated.

[0025] S2: Real-time monitoring of prepolymer viscosity; when the prepolymer viscosity reaches 5×10... 4At mPa·s, the reaction system temperature was maintained at 125 ℃, and high-viscosity methyl vinyl silicone oil was added in situ at a rate of 0.8 g / min under stirring at 300 r / min for 45 min. After the addition was completed, the reaction was continued at 125 ℃ for 3 h. During this process, an interpenetrating network structure of three-dimensional alkyl polyether modified polyorganosiloxane and methyl vinyl silicone oil was formed in situ, wherein the mass ratio of three-dimensional alkyl polyether modified polyorganosiloxane to methyl vinyl silicone oil was 4:1.

[0026] S3: A quantitative end-capping agent is added to the reaction system to terminate the polymerization reaction. Then, low-molecular-weight volatiles in the system are removed by vacuum distillation to obtain a crude product with an interpenetrating network structure.

[0027] S4: Add compound emulsifier at 3% of the weight of crude product, then add hydrophobic silica at 8% of the weight of crude product. Place the mixture in a high-speed shear homogenizer and shear homogenize at 8000 r / min for 20 min to obtain the finished high-temperature alkali-resistant organosilicon defoamer.

[0028] Example 2 Raw material preparation: Octamethylcyclotetrasiloxane (D4), polyether silane coupling agent containing n-octadecyl and isostearyl groups in a 1:1 mass ratio, KOH catalyst, phenyl silicone oil with a kinematic viscosity of 1×10⁻⁶ at 25 °C. 5 mPa·s, hexamethyldisilazane end-capping agent, hydrophobic silica (surface treated with hexamethyldisilazane, specific surface area 200 m² / s). 2 / g, surface methyl coverage 92%), emulsifier (Span-85 and Tween-60 in a mass ratio of 3:1).

[0029] Preparation steps S1: Add octamethylcyclotetrasiloxane (D4), mixed alkyl polyether silane coupling agent, and KOH to a nitrogen-protected reactor. After stirring evenly, heat to 120 °C to carry out ring-opening polymerization to prepare a three-dimensional alkyl polyether modified polyorganosiloxane prepolymer.

[0030] S2: When the prepolymer viscosity reaches 1×10 4 When the system temperature was adjusted to 120 °C, phenyl silicone oil was added dropwise at a rate of 0.5 g / min under stirring at 300 r / min for 60 min. The mass ratio of the three-dimensional alkyl polyether modified polyorganosiloxane to phenyl silicone oil was 4:1. After the addition was completed, the reaction was maintained at 120 °C for 4 h.

[0031] S3: Add a capping agent to terminate the reaction, remove low molecular weight substances under reduced pressure, and obtain the crude product.

[0032] S4: Add 2% of the compound emulsifier and 6% of the hydrophobic silica by weight of the crude product, and shear homogenize at 7000 r / min for 15 min to obtain the finished high-temperature alkali-resistant organosilicon defoamer.

[0033] Example 3 Raw material preparation: Octamethylcyclotetrasiloxane (D4), polyether silane coupling agent containing n-dodecyl and n-tetradecyl in a mass ratio of 2:1, catalyst KOH, fluorosilicone oil with a kinematic viscosity of 1×10⁻⁶ at 25 °C. 6 mPa·s, hexamethyldisilazane end-capping agent, hydrophobic silica (surface treated with hexamethyldisilazane, specific surface area 300 m² / s). 2 / g, surface methyl coverage 98%), emulsifier (Span-85 and Tween-60 in a mass ratio of 3:1).

[0034] Preparation steps S1: Under nitrogen protection, D4, mixed alkyl polyether silane coupling agent, and KOH are added to the reactor, and the temperature is raised to 120℃ for ring-opening polymerization to prepare a three-dimensional alkyl polyether modified polyorganosiloxane prepolymer.

[0035] S2: The viscosity of the prepolymer needs to reach 1×10⁻⁶ 5 At mPa·s, the system temperature was raised to 130 ℃, and fluorosilicone oil was added dropwise at a rate of 1.2 g / min under stirring at 300 r / min for 30 min. The mass ratio of three-dimensional alkyl polyether modified polyorganosiloxane to fluorosilicone oil was 4:1. After the addition was completed, the reaction was maintained at 130 ℃ for 2 h.

[0036] S3: Add a capping agent to terminate the reaction, remove low molecular weight substances, and obtain the crude product.

[0037] S4: Add compound emulsifier at 5% of the weight of crude product and hydrophobic silica (10% of the weight of crude product), and shear homogenize at 9000 r / min for 25 min to obtain the finished high-temperature alkali-resistant organosilicon defoamer.

[0038] Comparative Example The types and ratios of raw materials, emulsifiers and their amounts, shear parameters, and testing methods used in the comparative example were all the same as in Example 1. The only difference was that in step S2, the viscosity of the prepolymer did not reach 10. 4 -10 5 Instead of adding it in situ at mPa·s, the pre-synthesized PDMS-C was added. 16 The prepolymer and methyl vinyl silicone oil were mechanically mixed at room temperature for 30 min, and the remaining steps were the same as in Example 1.

[0039] Raw material preparation: Ordinary polydimethylsiloxane (kinematic viscosity 5×10⁻⁶ at 25℃)4 mPa·s), methyl vinyl silicone oil (kinematic viscosity 5×10 at 25 ℃) 5 mPa·s), the mass ratio of the two is 4:1; untreated ordinary silica (specific surface area 250 m²) 2 / g); Emulsifier: Span-85 and Tween-60 in a mass ratio of 3:1; Dispersant.

[0040] Preparation steps: Ordinary polydimethylsiloxane and methyl vinyl silicone oil were stirred and mixed at room temperature for 30 min to obtain a simple compounded organosilicon base material. Ordinary silica and dispersant were added to the above base material, and the mixture was physically dispersed by high-speed stirring at room temperature for 1 hour. Add 3% of the compound emulsifier by weight of the base material, and homogenize by shearing at 8000 r / min for 20 min to obtain a conventional compound silicone defoamer. Table 1 All performance indicators were tested under simulated high-temperature and high-alkali conditions (85-100℃, pH=11-14) in textile printing and dyeing, papermaking and pulping, and petrochemical industries. The initial defoaming rate was determined using the graduated cylinder shaking method, and the time it took for the foam to completely disappear after adding a quantitative amount of defoamer was recorded. The foam suppression period was determined using the bubbling method, and the duration during which the foam did not significantly re-expand under continuous bubbling was recorded. The 24-hour high-temperature alkali resistance stability was determined by placing the defoamer at a constant temperature for 24 hours under these conditions, observing the appearance of the emulsion, testing the defoaming performance after standing, and calculating the retention rate with the initial performance. The average particle size D50 and the absolute value of the Zeta potential were measured at room temperature using a laser particle size analyzer and a potential analyzer, respectively. The former reads the particle size value corresponding to 50% of the cumulative volume, and the latter reads the absolute value of the Zeta potential. The pH range was determined by adding the defoamer to alkaline aqueous solutions of different pH values ​​and observing the pH range in which the emulsion did not break down and separate.

[0041] As shown in Table 1, performance tests were conducted on the in-situ polymerized interpenetrating network (IPN) defoamers of the three examples and the conventional physically compounded IPN defoamers of the comparative example under simulated high-temperature and high-alkali conditions of 85-100 ℃ and pH=11-14. Examples 1-3 showed an initial defoaming rate of 3-5 s and a foam suppression period of 8-10 h; the comparative example showed an initial defoaming rate of 12-20 s and a foam suppression period of only 0.5-1 h, with defoaming efficiency and persistence significantly lower than the examples. Examples 1-3, after standing for 24 h under high-temperature and high-alkali conditions, showed no demulsification or stratification, maintaining over 90% of their defoaming performance, with a particle size change rate ≤5% and a Zeta potential absolute value change rate ≤3%; the comparative example showed demulsification and stratification after 1 h, complete defoaming performance failure after 2 h, a sudden increase in particle size and a Zeta potential approaching 0 mV after 1 h, indicating rapid system instability.

[0042] Examples 1-3 have an average particle size D50 of 0.8-1.2 μm, an absolute Zeta potential of 35-45 mV, and a pH range of 10-14, making them suitable for high-temperature and high-alkali industrial conditions. The comparative example has an average particle size of 2.5 μm, an absolute Zeta potential of 20 mV, and a pH range of only 7-9, making it extremely unsuitable for high-temperature and high-alkali conditions.

[0043] Performance differences among examples: Example 3 has the best defoaming performance retention rate (98%) and initial defoaming speed; Example 1 has the best particle size and potential stability and balanced foam suppression cycle; Example 2 meets the core performance indicators and has outstanding high temperature resistance. All three can be adapted to high temperature and high alkali conditions and can be flexibly selected according to the needs of industrial scenarios.

[0044] Overall conclusion: The products in Examples 1-3 are suitable for the harsh high-temperature and high-alkali conditions of industries such as textile printing and dyeing, and papermaking and pulping. The comparative examples, due to defects in process, raw material selection, and physicochemical properties, exhibited short-term instability and failure under high-temperature and high-alkali conditions, and therefore have no practical industrial application value. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A high-temperature alkali-resistant organosilicon defoamer, characterized in that, It consists of an interpenetrating network structure formed in situ during the polymerization process of a three-dimensional alkyl polyether modified polyorganosiloxane and a high-viscosity organosilicon composition; The three-dimensional alkyl polyether-modified polyorganosiloxane backbone is a polydimethylsiloxane, with pendant branched alkyl polyethers; wherein the alkyl groups are linear or branched saturated hydrocarbon groups, with a carbon chain length of C 12 –C 18 ; The high-viscosity organosilicon composition is one of methyl vinyl silicone oil, phenyl silicone oil, or fluorosilicone oil.

2. The organosilicon defoamer according to claim 1, characterized in that, The alkyl group in the alkyl polyether modified polyorganosiloxane is one or more of dodecyl, tetradecyl, hexadecyl, octadecyl or isostearyl.

3. The organosilicon defoamer according to claim 1, characterized in that, The mass ratio of the three-dimensional alkyl polyether modified polysiloxane to the high-viscosity organosilicon composition in the interpenetrating network is 4:

1.

4. The organosilicon defoamer according to claim 1, characterized in that, The high viscosity silicone composition is one of a methyl vinyl silicone oil, a phenyl silicone oil, or a fluorosilicone oil, and has a kinematic viscosity of 10 5 - 10 6 mPa-s at 25°C.

5. The organosilicon defoamer according to claim 1, characterized in that, The defoaming agent is an oil-in-water emulsion with an average particle size D 50 = 0.8 - 1.2 pm, Zeta potential absolute value > 35 mV, pH range of applicability 10 - 14.

6. A method for preparing the high-temperature alkali-resistant organosilicon defoamer according to claim 1, characterized in that, Includes the following steps: S1. Under the protection of nitrogen, octamethylcyclotetrasiloxane (D4), C 12 –C 18 alkyl polyether silane coupling agent, catalyst, and heated to 120°C to open the ring and polymerize to form a three-dimensional alkyl polyether modified polyorganosiloxane prepolymer; S2. When the prepolymer viscosity reaches 10 4 - 10 5 mPa-s, the high viscosity silicone composition is added dropwise in situ under stirring, the dropwise addition time is 30-60 min, and the reaction is continued for 2-4 h after the dropwise addition is completed. S3. Add a capping agent to terminate the reaction, remove low molecular weight compounds, and obtain the crude product; S4. Add hydrophobic silica and emulsifier to the crude product, and homogenize by high-speed shearing at a speed of 7000-9000 r / min for 15-25 min to obtain the finished organosilicon defoamer.

7. The preparation method according to claim 6, characterized in that, In step S1, the catalyst is KOH; in step S2, the dropping temperature of the high-viscosity organosilicon composition is 120–130 °C, and the dropping rate is controlled at 0.5–1.2 g / min.

8. The preparation method according to claim 6, characterized in that, In step S4, the hydrophobic silica is surface-treated with hexamethyldisilazane, resulting in a specific surface area of ​​200-300 m². 2 / g, with a surface methyl coverage of ≥92%, and the amount of hydrophobic silica added is 6%-10% of the weight of the crude product.

9. The preparation method according to claim 6, characterized in that, In step S4, the nonionic emulsifier is a mixture of Span-85 and Tween-60 in a mass ratio of 3:1, and the total amount added is 2-5% of the weight of the crude product.

10. The preparation method according to claim 6, characterized in that, In step S4, the capping agent is hexamethyldisilazane, and the amount of capping agent added is 0.5%-1.0% of the total weight of the system.

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