[Background and Overview][1][2]

　　In industries such as dyeing, papermaking, fermentation, sugar production, and petroleum distillation, foam often forms on the liquid surface, which is highly detrimental to the production process. It not only disrupts operations but also causes environmental pollution and, in severe cases, may even lead to fires. When this occurs, rapid defoaming is essential. Substances that, when added in small quantities, can quickly eliminate foam are known as defoamers. Also called antifoaming agents, defoamers began to be used industrially in the 1930s. Many industrial fermentation processes rely on defoamers to prevent excessive foaming, including applications in paints, coatings, pulp and paper manufacturing, inks, laundry detergents, fermentation, and the food industry. The United States and Europe constitute the world’s two largest defoamer markets; however, due to environmental constraints, the Asia-Pacific region—led by China and India—is currently experiencing the fastest growth in the defoamer market.

　　Most defoamers are surfactants. For example, when lubricating oil comes into contact with air and is agitated by it, tiny bubbles often form and are difficult to dissipate. This can lead to inadequate lubrication and equipment malfunctions in bearing and gear systems, and may even cause the oil volume to expand, resulting in overflow from the reservoir. In service, the presence of entrained air can dramatically alter power transmission. Fresh oil also tends to foam as it ages. Adding 0.001% to 0.0001% of poorly soluble dimethylsiloxane to the oil can sometimes completely halt foaming; accordingly, this compound is commonly used as a defoamer for turbine oils, gear oils, and similar applications. Defoaming methods generally fall into two main categories: physical and chemical approaches. Physical defoaming involves altering the conditions that give rise to foam while leaving the chemical composition of the foam‑forming solution unchanged. Chemical defoaming, on the other hand, entails introducing chemical agents into the foam to induce a chemical reaction with the foaming agent, thereby achieving defoaming. For instance, when sodium fatty acids serve as the foaming agent, adding acids or calcium–magnesium salts can generate insoluble fatty acids or calcium–magnesium soaps, which neutralize the foaming action and cause the foam to collapse. In industrial practice, ideal defoamers are characterized by low dosage, high efficiency, and rapid defoaming performance. Defoamers can be classified into alcohols, fatty acids and their esters, amides, phosphates, organosilicon compounds, and others.

　　【 Category 】 [ 4]

　　A wide variety of substances can be used as defoamers, including oil-based, solution-based, emulsion-based, powder-form, and composite types. They can be classified into the following major categories:

　　Oils and fats: such as castor oil, linseed oil, mineral oil, animal oil, etc.;

　　Fatty acids, such as stearic acid, oleic acid, palmitic acid, caprylic acid, capric acid, and lauric acid, among others;

　　Esters, such as stearates, phosphates, and sulfates;

　　Alcohols, such as 3-heptanol, 2-ethylhexanol, polyoxyethylene alcohol, and polypropylene glycol;

　　Ethers, such as 3-heptyl solvating agent, nonyl solvating agent–3-heptyl carbitol, and fatty alcohol polyethylene glycol ethers;

　　Amines, such as dipentylamine, stearylamine, and oleylamine, etc.;

　　Amides, such as polyamides, 12-hydroxy stearoyl‑beeswax amide, N,N′‑stearoyl ethylenediamine, fatty acid diamides, and bis(octadecanoyl) piperidine, among others;

　　Metal soaps, such as aluminum stearate, calcium stearate, potassium oleate, and calcium oleate, etc.;

　　Silicone-based compounds, such as dimethicone, silicones, fluorosilicones, and methyl silicone–polyoxyethylene block copolymers, among others;

　　Organic polar compounds, such as polypropylene glycol and its adducts with ethylene oxide, etc.;

　　Epoxides: Ethylene oxide, due to its high water solubility, is not suitable as a defoaming agent; however, the oligomers of propylene oxide can be used as defoamers in protein adhesives.

　　Other categories include ferrous sulfate, bauxite, trifluorotrichloropropane, talc powder, silica and silicate sols, tall oil mixtures, organophosphorus compounds, and acetals, among others.

　　[Characteristics]

　　① Strong defoaming performance with a low dosage.

　　② When added to a foaming system, it does not alter the system’s fundamental properties; that is, it does not react with the defoamed system.

　　③ Low surface tension.

　　④ Exhibits good surface balance.

　　⑤ Excellent heat resistance.

　　⑥ It exhibits excellent diffusivity and permeability, with a relatively high spreading coefficient.

　　⑦ Chemically stable with excellent oxidation resistance.

　　⑧ Excellent gas solubility and permeability.

　　⑨ It has low solubility in foaming solutions.

　　⑩ It exhibits no physiological activity and has a high safety profile; when used in the food, cosmetic, and pharmaceutical industries, it shall comply with the relevant regulations.

　　[Defoaming Principle]

　　Foam is a dispersed system in which gas is dispersed within a liquid; the gas constitutes the dispersed phase, while the liquid serves as the dispersing medium. Stability arises because the gas is insoluble in the surfactant. Once bubbles form, intermolecular interactions within the foaming system cause hydrophilic and hydrophobic groups to adsorb onto the bubble wall, arranging themselves in an orderly fashion: the hydrophilic groups face the aqueous phase, and the hydrophobic groups face the interior of the bubble, thereby creating an elastic film at the bubble–liquid interface that exhibits strong stability and resists rupture under normal conditions. At the same time, foam is a thermodynamically unstable system; under the influence of gravity, it continuously undergoes processes such as drainage of the liquid film, evaporation, and rupture, as well as liquid redistribution and permeation between adjacent bubble films. The mechanisms underlying defoaming can be broadly categorized into two main aspects: (1) defoaming agent molecules, which readily spread and adsorb, displace the surfactant molecules, forming a film of reduced mechanical strength; and (2) during the spreading process, defoaming agent molecules carry away portions of the solution from the neighboring surface layer, thinning the bubble’s liquid film, reducing its stability, and making it more susceptible to breakdown.

　　From the above, we can see that for a defoamer to be effective, it must first penetrate the bilayer of the foam film; this penetration capability is quantified by the penetration coefficient E. Once the defoamer has penetrated, it must disperse rapidly, and this dispersing ability is characterized by the dispersion coefficient S.

　　In the equation: γF denotes the surface tension of the foaming medium; γDF denotes the surface tension of the defoamer; and γD denotes the interfacial tension between the foaming medium and the defoamer. When E > 0, the defoamer can penetrate into the foam; when E < 0, the defoamer cannot penetrate the foam; when S > 0, the defoamer can spread on the liquid film surface; when S < 0, the defoamer cannot spread on the liquid film surface. Therefore, the defoamer exhibits defoaming activity only when both E > 0 and S > 0.

　　[Application]

　　1. Application in the Delayed Coking Process

　　Delayed coking is a thermal processing technology in which refineries subject heavy residual oil to deep conversion, thereby increasing the yield of light products. During delayed coking, hydrocarbon vapors generated by high‑temperature cracking within the coke drum escape from the partially cracked coker feed—high‑viscosity, resinous material—forming a thick foam layer that entrains substantial amounts of coke fines. As the coke bed in the drum grows, these fines and unreacted heavy oil are carried upward with the coker off‑gas through the overhead gas‑oil line to the fractionation column, leading to coking in the fractionator and potentially causing blockages in the radiant‑section feed filter, the bottom‑circulation filter, and the feed pump, as well as coking in the furnace tubes—severely jeopardizing the safe operation of the unit. The coke fines carried into the fractionator are further processed and end up in the coker gasoline and diesel streams, posing risks to downstream hydrotreating and other downstream processes. To mitigate these adverse effects, both domestically and internationally, it has become common practice to inject defoaming agents into the upper section of the coke drum. These defoamers exhibit strong defoaming performance, reducing the height of the foam layer, thereby minimizing the carryover of coke fines and extending the operating cycle of the coking unit.

　　2. Applications in the Paper Industry

　　Foam control is a persistent challenge in the papermaking industry. During alkaline pulping, raw materials containing natural substances such as fatty acids and resin acids react with added chemical reagents like sodium hydroxide and sodium sulfide to form soap‑like compounds and alkali lignin—both of which are foam‑generating agents. In addition, the stabilizing effect of high‑molecular‑weight cellulose and other polymers, coupled with air entrainment during pulp flow, agitation, and mixing, gives rise to abundant, stable foam. This foam poses significant difficulties for downstream processes such as washing, conveying, and bleaching, ultimately compromising the quality of pulp washing and bleaching. In the paper‑making process, naturally occurring and artificially added foaming surfactants and synthetic polymers carried over from the pulping stage generate substantial foam, leading to surface defects such as spots or translucent areas and even causing paper breaks. During coating, foam in the coating formulation can result in uncoated blemishes—commonly referred to as “fish eyes”—thereby adversely affecting the paper’s printability and smoothness. Consequently, defoaming is an essential operation at every stage—pulping, papermaking, and coating. Research has led to the development of a defoaming composition for papermaking, comprising dimethyl silicone oil, trimethylchlorosilane, ethyl vinyl ether, sodium dodecyl sulfate, lysine, and calcium chloride. The resulting defoamer exhibits excellent defoaming performance, effectively and rapidly eliminating foam generated by the interaction of inorganic and organic components within the papermaking system.

　　3. Applications in the Textile Industry

　　During textile processing, fabrics come into contact with a variety of dyes and auxiliaries. These auxiliaries—particularly surfactants such as wetting agents, detergents, penetrants, antistatic agents, and leveling agents—reduce the surface tension of the sizing solution, thereby significantly enhancing its spreading on fabric surfaces and its penetration into warp yarns. However, when a low‑surface‑tension sizing solution is subjected to mechanical vibration, it readily forms foam. The presence of foam reduces the effective contact area between the liquid and the fabric, leading to uneven processing and severely compromising production efficiency and product quality. In all stages of textile dyeing and finishing, foaming poses a persistent challenge during scouring, bleaching, dyeing, and finishing operations. Foaming can prevent thorough impregnation of fibers or fabrics, diminishing treatment effectiveness, prolonging processing times, and even causing defects such as staining. Defoamers are especially critical in dyeing processes: for polyester fabrics undergoing high‑temperature jet dyeing, achieving uniform coloration requires rapid, high‑speed machine operation. If foam is present in the dye bath, the fabric may exhibit color spots, streaks, and uneven shade, seriously affecting product quality. Yet under high temperature and pressure, conventional siloxane‑based defoamers often precipitate as thin films, leaving blemishes on the dyed material. Consequently, higher demands are placed on the water dispersibility of organosilicone defoamers; standard polyether‑silicone oils typically fail to meet these requirements. Block copolymers offer a viable solution, as their components dissolve in cold water but remain insoluble in hot water, enabling effective defoaming. A high‑concentration, high‑temperature‑and‑strong‑alkali‑resistant defoamer, YAT722, has been developed and tested in the printing and dyeing industry. Trials have demonstrated that YAT722 exhibits excellent resistance to high temperatures (130°C) and strong alkalis, delivering superior defoaming and foam‑suppressing performance while also boasting outstanding self‑emulsification, shear stability, and non‑oil‑floating characteristics—making it particularly well suited for high‑temperature overflow dyeing in the textile sector. Another product, XIAMETER@AFE‑0800 defoamer, features a dilute formulation ideally suited for use in high‑temperature, high‑pressure, and high‑shear conditions such as fabric jet dyeing and scouring. This defoamer maintains excellent stability above 130°C and under extremely high shear forces, simultaneously providing both defoaming and foam‑suppressing effects.

　　4. Defoamers in Monosodium Glutamate Production

　　Glutamic acid is the amino acid produced in the largest quantities worldwide. The fermentation process for producing monosodium glutamate (MSG), which is derived from glutamic acid, is an aerobic fermentation that generates substantial foam. This foam can reduce yield, inhibit microbial respiration, and lower the strain’s acid‑production rate. Antifoaming agents represent the most economical and straightforward means of controlling foam. In MSG production, common antifoaming agents include vegetable‑oil‑based, polyether‑based, and silicone‑based formulations; however, vegetable‑oil‑based antifoamers are seldom used due to poor storage stability, susceptibility to spoilage, and a tendency to exhibit elevated acid values. At present, polyether‑ and silicone‑based antifoamers are widely employed in MSG fermentation, and they have been the subject of extensive research.

　　5. Defoamers in Sugar Production

　　China is one of the earliest countries in the world to produce sugar, employing a concentration‑crystallization process. Defoamers are commonly used industrial additives in sugar production, with the main types including polyglycerol fatty acid esters, sucrose fatty acid esters, polyether‑based defoamers, and organosilicone defoamers. Among these, polyglycerol fatty acid ester–based (N‑type) defoamers exhibit excellent defoaming and foam‑suppressing performance during boiling, significantly reduce the surface tension of the syrup, accelerate the settling of sugar crystals, and enhance syrup filtration. Consequently, polyglycerol fatty acid ester defoamers are currently the most widely used defoamers in the sugar industry.

　　6. Defoamers in Amylase Production

　　Alpha‑amylase (α‑1,4‑gluco‑glucosidase) is widely distributed in animals, plants, and microorganisms and is an important starch‑hydrolyzing enzyme. Domestic researchers have investigated antifoaming agents used in the fermentation of BAA mesophilic α‑amylase; these include the specialized fermentation antifoam LB‑625, the silicone‑based antifoam KY‑2118, and the polyether antifoam PPE. The fermentation of BAA mesophilic α‑amylase involves substantial aeration, particularly during the microbial growth phase and the product‑synthesis phase, when foam formation becomes especially severe. Such foam can lead to overflow, contamination by unwanted microorganisms, and reduced filling ratios, among other adverse effects. The specialized fermentation antifoam LB‑625 is an imported product. Experimental results demonstrate that this imported formulation can completely eliminate all foam within just a few seconds, offering rapid defoaming, long‑lasting foam suppression, no adverse effects on the microorganisms, low dosage requirements, high temperature resistance, virtually no residue, and minimal impact on membrane fouling. The silicone‑based antifoam KY‑2118 is a commonly used domestic antifoam. It boasts high surface activity, low surface tension, low application rates, strong defoaming performance, and low cost. Moreover, it is immiscible with water and most organic substances, effectively suppressing foam across a wide range of bubble‑containing media. Its excellent chemical stability enables it to both break and inhibit foam in various systems, making it a broad‑spectrum antifoam. However, KY‑2118 performs less well in mildly acidic fermentations and may to some extent inhibit hyphal development. The polyether antifoam PPE—also known as “Pao Di”—is distinguished by its strong foam‑inhibiting capability. Although its overall defoaming efficiency falls short of that of silicone‑based antifoams, its foam‑inhibiting power surpasses theirs. A significant drawback, though, is its relatively low foam‑breaking rate: when large amounts of foam are generated, it cannot swiftly and effectively suppress them.

　　7. Antifoaming Agents in Winemaking

　　China is one of the earliest countries to have developed winemaking, with brewing techniques invented as far back as 2,000 years ago. Scholars have investigated the adverse factors arising during fermentation and found that vigorous stirring and bubbling generate substantial foam, which adversely affects wine processing in several ways—such as causing “liquid loss” and reducing filling volumes. These drawbacks further compromise both the yield and quality of the final product. Antifoaming agents represent the simplest and most cost-effective means of controlling foam. Domestic researchers have evaluated various antifoaming additives used in winemaking; their findings indicate that plant oils, lauric acid, sorbitan monostearate, myristic acid, and oleic acid, when employed as fermentation antifoams, require large dosages and deliver unsatisfactory performance. In contrast, organosilicone antifoams based on polydimethylsiloxane prove highly effective in food fermentations, increasing fermentation capacity and boosting yields. With the aid of such antifoams, the headspace of the fermentation vessel can remain sealed throughout the process, thereby minimizing oxidation of the fermenting liquid and enhancing the wine’s clarity. Reduced oxidation also helps maintain excellent physical and chemical stability, even under conditions where some proteins may denature, resulting in a noticeably clearer wine. Moreover, these antifoams lower yeast‑cell adhesion to the vessel walls, easing subsequent cleaning operations.

　　[Production Process]

　　The synthesis of polyether-modified silicone defoamer is as follows: a condensation method is employed, in which hydrogen‑containing silicone oil and polyether are grafted together under the action of a catalyst.

　　In a four-necked flask equipped with a stirrer, condenser, thermometer, and a hydrogen‑gas outlet, the hydrogenated silicone oil, polyether, solvent, and catalyst are added in the prescribed proportions. The stirrer is then activated, and the mixture is slowly heated to a specified temperature, at which point hydrogen gas evolves, producing bubbles. When the conversion reaches a predetermined level, the reaction mixture is cooled, and an alkali is added to neutralize the system. Following filtration under reduced pressure and vacuum distillation to remove residual catalyst and solvent, the polyether‑modified polysiloxane copolymer is obtained.