Principle,classification,selection and dosage of defoamer

Principle, classification, selection and dosage of defoamer

2023-08-30 16:26:08
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The foam problem in water treatment has troubled many people, debuting the initial foam, surfactant foam, impact foam, peroxide foam, circulating water treatment with non-oxidizing fungicide generated foam, etc., so the use of defoamer in water treatment is more common, this article comprehensively introduces the principle, classification, selection and dosage of defoamer!
Methods of foam elimination
1.Physical methods
From a physical point of view, the methods to eliminate foam mainly include the placement of baffles or filters, mechanical agitation, static electricity, freezing, heating, steam, radiation irradiation, high-speed centrifugation, pressure and pressure reduction, high-frequency vibration, instantaneous discharge and ultrasonic (acoustic liquid control), etc. All these methods promote the gas transmission rate at both ends of the liquid film and the liquid discharge of the bubble film to different degrees. The stability factor of the foam is less than the attenuation factor, and the number of bubbles is gradually reduced. However, the common disadvantage of these methods is that the use of environmental factors is strong, the defoaming rate is not high, and the advantages are environmental protection and high reuse rate.
2.Chemical methods
The methods of removing foam from the chemical point of view mainly include chemical reaction method and the method of adding defoamer.
The chemical reaction method refers to the chemical reaction between the foaming agent and the foaming agent by adding some reagents to produce a substance that is insoluble in water, thereby reducing the concentration of surfactant in the liquid film and promoting the rupture of the foam, but this method has shortcomings such as the uncertainty of the composition of the foaming agent and the harm to the system equipment caused by insoluble substances. Nowadays, the most widely used defoaming method in all walks of life is the method of adding defoaming agent. The biggest advantage of this method is that it has high defoaming efficiency and easy to use, but finding a suitable and efficient defoaming agent is the key.
Principles of defoamer
Defoamer, also known as defoamer, has the following principles:
1. The local surface tension of the foam is reduced, resulting in the collapse of the foam
The origin of this mechanism is that high alcohols or vegetable oils are sprinkled on the foam, and when they dissolve into the foam solution, the surface tension there is significantly reduced. Because these substances are generally less soluble to water, the reduction in surface tension is limited to local areas of the foam, while the surface tension around the foam hardly changes. The portion with reduced surface tension is strongly pulled around, extended, and finally ruptured.
2.Damage the membrane elasticity and cause the bubble to burst
When the defoamer is added to the foam system, it diffuses to the gas-liquid interface, which makes it difficult for the surfactant with foam stabilization function to restore the elasticity of the membrane.
3.Promote liquid membrane drainage
The defoamer can promote the liquid film to drain, which leads to the bubble bursting. The rate of the foam drain can reflect the stability of the foam. The addition of a substance that accelerates the foam drain can also play the role of defoaming.
4.Adding hydrophobic solid particles can cause bubbles to burst
The hydrophobic solid particles on the surface of the bubble will attract the hydrophobic end of the surfactant, so that the hydrophobic particles produce hydrophilicity and enter the water phase, thus playing the role of defoamization.
5.Solubilizing foaming surfactant can cause bubbles to burst
Some low molecular substances that can be fully mixed with the solution can make the bubble surfactant solubilized and reduce its effective concentration. Low molecular substances with this effect, such as octanol, ethanol, propanol and other alcohols, can not only reduce the surfactant concentration of the surface layer, but also dissolve into the surfactant adsorption layer, reducing the tightness of the surfactant molecules, thus weakening the stability of the foam.
6.Electrolyte disintegrates the surfactant double electric layer
For the interaction of the two electric layers of the surfactant with the help of foam to produce a stable foaming solution, the addition of ordinary electrolytes can disintegrate the double electric layer of the surfactant to act as a defoamer.
Classification of defoamer
Commonly used defoamer can be divided into silicon (resin), surfactants, alkanes and mineral oils according to different components.
1.silicon (resin) class
Silicone defoamer, also known as emulsion type defoamer, is used by emulsifying and dispersing silicone resin with emulsifier (surfactant) in water and adding it to wastewater. Silica powder is another kind of silicon defoamer with good defoaming effect.
2.Surfactants
This kind of defoamer is actually an emulsifier, that is, the dispersion of surfactant is used to make the foam-forming substance maintain a stable emulsion state in the water to disperse, so as to avoid the formation of foam.
3.Alkanes
Paraffin defoamer is a defoamer made by emulsifying paraffin wax or its derivatives with emulsifying agent. Its use is similar to that of emulsifying surfactant defoamer.
4.Mineral oil
Mineral oil is the main defoaming component. In order to improve the effect, sometimes mixed metal soap, silicone oil, silica and other substances are used together. In addition, in order to make the mineral oil easily spread to the surface of the foaming liquid, or to make the metal soap and other evenly dispersed in the mineral oil, sometimes a variety of surfactants can be added.

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