Defoamers, also known as antifoaming agents, are ubiquitous in daily life and industrial processes. Beneficial foams appear in fire extinguishers, insulating foam plastics for heat, noise, and shock reduction, and mineral froth flotation. However, in most production scenarios—such as petrochemicals, wastewater treatment, papermaking, printing and dyeing, food manufacturing, and biological fermentation—excessive foam disrupts process control, causes false liquid levels, wastes equipment space, and reduces capacity. Uncontrolled foam can lead to overflows, affecting operations and causing significant economic losses. Thus, controlling harmful foam with defoamers holds immense technical and economic value.
Methods for Foam Elimination
Physical Methods
Physical approaches to foam elimination include installing baffles or meshes, mechanical stirring, electrostatic methods, freezing, heating, steam application, radiation exposure, high-speed centrifugation, pressure changes, high-frequency vibration, instantaneous discharge, and ultrasound (acoustic liquid control). These methods accelerate gas permeation across liquid films and promote drainage, making foam stability factors weaker than decay factors, thus reducing foam quantity. Drawbacks include environmental constraints and slower defoaming rates, while advantages encompass eco-friendliness and high reusability.
Chemical Methods
Chemical foam elimination involves reactions or adding defoamers. Chemical reactions use reagents to react with foaming agents, forming water-insoluble substances that lower surfactant concentrations in liquid films, prompting bubble rupture. However, uncertainties in foaming agent composition and potential harm from insoluble substances to systems and equipment are downsides. The most widespread method across industries is adding antifoaming agents, prized for high bubble-breaking efficiency and ease of use, though selecting suitable, effective defoamers is crucial.
Principles of Defoamers
Defoamers, or antifoaming agents, operate via several mechanisms:
- Local Surface Tension Reduction Leading to Foam Burst
- Sprinkling higher alcohols or vegetable oils on foam dissolves into the liquid, markedly lowering local surface tension. Due to low water solubility, this reduction is localized, with surrounding tension unchanged. The lowered area is pulled and extended outward, ultimately rupturing.
- Disrupting Membrane Elasticity Causing Bubble Burst
- Defoamers diffuse to the gas-liquid interface, preventing foam-stabilizing surfactants from restoring membrane elasticity.
- Promoting Liquid Film Drainage
- Defoamers accelerate drainage, leading to bubble burst. Foam drainage rate reflects stability; substances speeding it up act as defoamers.
- Adding Hydrophobic Solid Particles Inducing Bubble Burst
- Hydrophobic particles on bubble surfaces attract surfactant hydrophobic ends, rendering particles hydrophilic and entering the aqueous phase, thus defoaming.
- Solubilizing Foam-Promoting Surfactants Leading to Bubble Burst
- Low-molecular substances miscible with solutions solubilize bubble surfactants, reducing effective concentrations. Examples like octanol, ethanol, and propanol decrease surface layer surfactant density and loosen molecular packing in adsorption layers, weakening foam stability.
- Electrolytes Disintegrating Surfactant Double Electric Layers
- For foams stabilized by surfactant double electric layers, common electrolytes collapse these layers, achieving defoaming.
Types of Defoamers and Research Advances
Fatty Acid-Based Defoamers
First-generation defoamers comprise mineral oils, fatty acids and esters, fatty alcohols, lower alcohols, and other organics. They are inexpensive, with readily available raw materials and eco-friendly performance, suitable for low-shear liquids with mild foaming. However, they poorly handle dense foams and lack versatility.
Current research on fatty acid-based defoamers focuses on preparing fatty alcohol emulsion defoamers, emulsification, and stability studies. These are extensively used in papermaking processes.
Polyether Defoamers
Polyether defoamers are high-performance water-soluble nonionic surfactants from ethylene oxide (EO) and propylene oxide (PO) ring-opening polymerization. For varied foaming systems, adjusting EO/PO segment lengths, ratios, and molecular weights tunes hydrophilicity/lipophilicity, cloud point, and surface tension. Defoaming occurs above the cloud point, so modifying it adapts to different conditions.
Typically initiated by polyols, polycarboxylic acids, or amines with active hydrogens (O-H or N-H bonds), polymerizing with EO/PO yields polyethers. Glycerol-initiated ones, called glycerol polyethers, are most common.
Market glycerol polyethers include GP, GPE, and GPES types.
- Polyoxypropylene Glycerol Polyether (GP Type): From glycerol and polyoxypropylene, used in yeast, streptomycin, papermaking, and biopesticide production.
- Polyoxypropylene Polyoxyethylene Glycerol Ether (GPE Type): Grafts EO segments onto GP ends for better solubility and strong defoaming, common in antibiotic fermentation.
- Polyoxypropylene Polyoxyethylene Glycerol Polyether Ester (GPES Type): Esterifies GPE ends with stearic acid, reducing hydrophilicity, improving tension, and enhancing defoaming. Features non-toxicity, ease of use, dispersibility, high-temperature/strong-alkali resistance, chemical stability, and adjustable cloud point. Drawback: low burst rate for sudden massive foams, requiring continuous addition.
Research on polyether defoamers centers on modifications: reacting active groups with hydroxyls, e.g., esterification with lauric/stearic acids for GPES, or condensation with dimethyldiethoxysilane/methyltriethoxysilane for derivatives.
Organosilicone Defoamers
Silicone oil, mainly polydimethylsiloxane (PDMS) with surface tension as low as 20 mN/m, is key in organosilicone defoamers. Lower than water or typical oils, they suit aqueous and oily systems. Features: low solubility, high activity, strong stability, non-toxicity; widely used in papermaking, petrochemicals, fermentation, and wastewater.
Due to strong hydrophobicity and poor dispersion, silicone alone is ineffective. It’s compounded with hydrophobic silica, emulsifiers, and deionized water into emulsion-type defoamers. These rapidly lower tension, achieving strong defoaming at low doses.
While excelling in defoaming, suppression is weaker, and emulsification is challenging compared to other oils. Incomplete emulsification causes demulsification and layering, impairing performance. Emulsifier selection is critical for quality.
Chinese research focuses on: suitable emulsifiers/thickeners for stable storage; compounded organosilicone defoamers for various industries, temperatures, and pH.
Recent advances include Evonik’s 2023 launch of a defoamer blending silicone and bio-based materials, enhancing eco-friendliness and efficacy. Trends emphasize silicone-based adoption for superior performance and bio-based demands for sustainability.
Polyether-Modified Organosilicone Defoamers
Polyether-modified silicones are polyether-siloxane copolymers grafting hydrophilic polyether segments onto hydrophobic silicone chains.
They combine polyether advantages (high-temperature/strong-alkali resistance, strong suppression) with silicone (non-toxic, low-volatility, non-polluting, strong bursting).
Polyether enhances silicone hydrophilicity for better dispersion in aqueous systems. Inherited adjustable cloud point via EO/PO ratios suits varied temperatures. Hydrophobic polysiloxane enables rapid spreading/penetration for quick bursting.
Amphiphilic structure forms self-emulsifying micelles: polyether outward, polysiloxane inward, ensuring uniform dispersion and optimal defoaming/suppression. Adjusting segment ratios tailors to water- or oil-soluble systems.
Classified by bonding: Si-O-C and Si-C types.
- Si-O-C Type: Acid-catalyzed condensation of polysiloxane with hydroxyl-terminated polyether. Si-O-C bonds hydrolyze easily in water, poor stability, short shelf life.
- Si-C Type: Platinum-catalyzed addition of Si-H polysiloxane with unsaturated polyether. Strong water resistance, no hydrolysis, high-temperature/acid-alkali tolerance; stores over 2 years sealed.
Research focuses on synthesis (optimizing polyether structure, catalyst type/dosage, temperature, time, feeding) for tailored products; and compounding with emulsifiers/thickeners/dispersants for stability.
A 2024 Nature study advanced intelligent foaming/defoaming agents, analyzing temperature, salt, and oil resistance for enhanced performance in harsh conditions. Market trends show growing bio-based and silicone hybrids, with Evonik’s innovations leading sustainability efforts.
For more on related surfactants, visit Surfactants. Questions? Contact us. In conclusion, defoamers and antifoaming agents remain vital for industrial efficiency, with ongoing research driving greener, more effective solutions.
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