Explanation of Defoamer Principle and Type Selection


The problem of froth in water treatment has troubled many people, such as foam, surfactant foam, impact foam, peroxide foam, and foam produced by non oxidizing bactericides in circulating water treatment. Therefore, the use of defoamer in water treatment is quite common. This paper introduces the principle and classification of defoamer comprehensively. Category, type selection and dosage!


Defoaming Principle


Defoamer, also known as defoamer, has the following principles:


01 the partial surface tension of foam reduces and the bubble burst.


The origin of this mechanism is to spread higher alcohols or vegetable oils onto the foam. When they are dissolved in foam, the surface tension will be significantly reduced. Because these substances are generally less soluble in water, the decrease in surface tension is confined to the local part of the foam, and the surface tension around the foam is almost unchanged. The reduced surface tension is strongly pulled around, extended, and finally ruptured.


02 Destroying the Elasticity of Membrane and Causing Bubble Breakage


The addition of defoamer to the foam system will diffuse to the gas-liquid interface, making it difficult for the surfactant with stabilizing foam to recover the elasticity of the membrane.


03 Promotes liquid membrane drainage


Defoamer can promote liquid membrane drainage, resulting in bubble burst. The rate of foam drainage can reflect the stability of foam. Adding a substance to accelerate foam drainage can also play a role in defoaming.


04 Addition of hydrophobic solid particles can cause bubble bursting


The hydrophobic solid particles on the surface of bubbles attract the hydrophobic end of surfactants, which makes the hydrophobic particles hydrophilic and enter the water phase, thus playing the role of defoaming.


05 Solubilizing and Foaming-Aiding Surfactants Can Cause Bubble Breakage


Some low molecular substances which can mix well with the solution can make the bubble surfactant solubilized and its effective concentration reduced. The low molecular substances such as octanol, ethanol and propyl alcohol can not only reduce the concentration of surfactants in the surface layer, but also dissolve the surfactant adsorption layer to reduce the intermolecular tightness of the surfactant, thus reducing the stability of the foam.


06 Electrolyte Disintegrates Surfactant Double Layer


With the interaction of double layer of foam surfactants, a stable foaming solution can be formed. The addition of ordinary electrolytes can dissolve the double layer of the surfactant to defoaming.


Classification of defoamers


The commonly used defoamers can be divided into silicon (resin), surfactants, alkanes and mineral oils according to their composition.


01 Silicon (Resins)


Silicone defoamer, also known as emulsion defoamer, is used by emulsifying and dispersing silicone resin in water with emulsifier (surfactant) and then adding it to wastewater. Silica powder is another kind of silicon defoamer with better defoaming effect.


02 surfactants


Such defoamer is actually an emulsifier, that is, by dispersing the surfactant, the foam forming material can be dispersed in the stable emulsion state so as to avoid foaming.


03-chain alkanes


Alkane defoamer is a kind of defoamer made by emulsifying and dispersing alkane wax or its derivatives with emulsifier. Its use is similar to that of surfactant emulsifying defoamer.


04 Mineral Oils


Mineral oil is the main defoaming component. In order to improve the effect, sometimes mixed with metal soap, silicone oil, silicon dioxide and other substances used together. In addition, in order to make mineral oil diffuse easily to the surface of foaming fluid, or to make metal soap disperse evenly in mineral oil, sometimes various surfactants can be added.


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