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During industrial production, numerous harmful foams are generated, necessitating the addition of defoamers. There are many types of defoamers, including silicone defoamers, polyether defoamers, fatty alcohol defoamers, and high-carbon alcohol defoamers. Defamers are widely used to eliminate harmful foams produced in the manufacturing processes of industries such as papermaking, water treatment, textile sizing, food fermentation, biopharmaceuticals, coatings, petrochemicals, and industrial cleaning.
1. Natural Oil-based Defoamer & antifoam (e.g., soybean oil, corn oil)
Advantages: These defoamers & antifoams are readily available, cost-effective, and easy to use.
Disadvantages: If stored improperly, they may deteriorate, leading to increased acid value.
2. High-Carbon Alcohol Defoamer & Antifoam
High-carbon alcohols are linear molecules with strong hydrophobicity and weak hydrophilicity. In the early 1970s, Soviet researchers conducted experiments in aqueous solutions of anionic, cationic, and nonionic surfactants, proposing that the defoaming effect of alcohols correlates with their solubility and diffusion rate in foaming liquids. C7–C9 alcohols are the most effective defoamers. High-carbon alcohols (C12–C22) can be formulated into aqueous emulsions with particle sizes of 4–9 μm and concentrations of 20–50% using suitable emulsifiers, serving as defoamers in aqueous systems. Certain esters, such as benzyl oleate and benzyl laurate, also function as defoamers in penicillin fermentation, with the latter additionally serving as a precursor.
3. Polyether Defoamer & Antifoam
There are numerous types of polyether defoamers, primarily including the following:
a. GP-type defoamers, synthesized via addition polymerization using glycerol as the starting material and either propylene oxide or a mixture of ethylene oxide and propylene oxide, exhibit poor hydrophilicity and low solubility in foaming media. Therefore, they are suitable for use in dilute fermentation broths. Polyether defoamers exhibit superior foam suppression over foam elimination capabilities. They are suitable for addition to the base medium to inhibit foam generation throughout the entire fermentation process.
b. Polyglycol chains terminated with polyoxyethylene glycidyl ethylene oxide (PEGOEG) are produced by further adding ethylene oxide to the polypropylene glycol chain ends. These compounds feature hydrophilic groups at the chain ends. With ethylene oxide addition levels of 10%, 20%, ..., 50%, these defoamers exhibit enhanced hydrophilicity, spreading readily in foaming media with strong defoaming capability. However, their higher solubility results in shorter-lasting defoaming activity, making them more effective in viscous fermentation broths.
c. Novel polyether defoamers feature hydrophobic stearate ester end-capping at the chain ends, forming block copolymers with hydrophobic chains at both ends separated by a hydrophilic chain. This molecular structure readily aggregates in a flat conformation at the gas-liquid interface, endowing such polyether defoamers with strong surface activity and high defoaming efficiency.
4. Silicone-Based Defoamer & Antifoam
The most commonly used is polydimethylsiloxane defoamer, also known as dimethicone oil. This type of defoamer has low surface energy and low surface tension, with low solubility in water and general oils yet high activity. The main chain of polydimethylsiloxane defoamers consists of siloxane bonds, forming nonpolar molecules. They exhibit poor affinity for the polar solvent water and minimal affinity for common oils. Polydimethylsiloxane defoamers are low in volatility, chemically inert, relatively stable, and have low toxicity. Pure polydimethylsiloxane cannot readily function as a defoamer without dispersion treatment. This is likely due to its high interfacial tension with water and low spreading coefficient, making dispersion in foaming media difficult. Therefore, it is produced by mixing silicone oil with SiO₂ aerosol to form a composite. Specifically, hydrophobic-treated SiO₂ aerosol is blended into dimethyl silicone oil and processed at specific temperatures and durations.
Organosilicon defoamers are mechanically emulsified from silicone grease, emulsifiers, water repellents, thickeners, and appropriate amounts of water. They feature low surface tension, high surface activity, strong defoaming power, low dosage requirements, and cost-effectiveness. Silicone defoamers are immiscible with water and most organic substances, yet they effectively eliminate bubbles in various bubble-forming media. They exhibit excellent thermal stability, functioning reliably across a broad temperature range of 5°C to 150°C. Their chemical stability is also notable, as they resist reactions with other substances. When properly formulated, they can be used in acidic, alkaline, or saline solutions without compromising product quality. Silicone defoamers also exhibit physiological inertness (LD50 250g/kg rat), making them suitable for food and pharmaceutical applications. They function as both foam inhibitors and bubble breakers across all bubble systems, falling under the broad-spectrum defoamer category. They are widely used for defoaming in detergent production, papermaking, pulp processing, sugar refining, electroplating, fertilizer manufacturing, chemical additives, and wastewater treatment. In the petroleum industry, silicone defoamers are extensively used for natural gas desulfurization and accelerating oil-gas separation. They also control or suppress foaming in installations such as ethylene glycol drying, aromatic hydrocarbon extraction, asphalt processing, and lubricant dewaxing. In the textile industry, it is used for defoaming in dyeing, scouring, and sizing processes. In the chemical industry, it is employed for defoaming in the synthesis of resins, latex, coatings, and inks. In the food industry, it is utilized for defoaming in various concentration, fermentation, and distillation processes. Silicone grease can be applied to pot walls, outlets, or coated onto metal mesh for defoaming. Silicone grease can be formulated into a solution for defoaming in oil-phase systems. When blended with low-viscosity silicone oil to form an aqueous emulsion, it serves as a defoaming agent for diverse water-phase systems.
5. Polyether-modified Silicone Defoamer & Antifoam
Polyether-modified silicone defoamer combines the advantages of both polyether and organic silicone defoamers. It is non-toxic, harmless to microbial strains, requires minimal dosage, and offers high cost-effectiveness.
