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The problem of foam in water treatment has troubled many people. In the early stage of commissioning, foam, surfactant foam, impact foam, peroxide foam, and non oxidation bactericidal foam generated in the treatment of circulating water, so the use of defoamer in water treatment is quite common. This article comprehensively introduces the principle, classification, type selection and dosage of defoamer.
Defoaming principle
Defoamer, also known as defoamer, has the following principles:
01, the local surface tension of foam decreases, resulting in the burst of foam.
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 part with reduced surface tension is strongly pulled around, extended and finally cracked.
02. Bubble burst due to membrane elasticity failure
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. Promote 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. Adding hydrophobic solid particles can cause bubble collapse
The hydrophobic solid particles on the surface of the bubble will attract the hydrophobic end of the surfactant, making the hydrophobic particles produce hydrophilicity and enter the water phase, thus playing the role of defoaming.
05. Solubilizing and foaming aid surfactants can cause bubble collapse
Some low molecular substances which can be fully mixed with the solution can solubilize the bubble surfactant and reduce its effective concentration. 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 disintegration of 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.
Defoamer classification
The commonly used defoamers can be divided into silicon (resin), surfactant, alkane and mineral oil according to different components.
01. Silicon (resin)
Silicone defoamer is also called emulsion defoamer. The method of use is to emulsify and disperse silicone resin with emulsifier (surfactant) in water and then add it to wastewater. Silica powder is another kind of defoamer with good 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. Alkanes
Alkane defoamer is a defoamer made by emulsifying alkane wax or its derivatives with emulsifier. Its application is similar to emulsified defoamer of surfactant.
04. Mineral oil
Mineral oil is the main defoaming component. In order to improve the effect, sometimes mixed with metal soap, silicone oil, silica and other substances. In addition, in order to make mineral oil easily diffuse to the surface of foaming solution, or to make metal soap evenly disperse in mineral oil, various surfactants can be added sometimes.
Selection of defoamer
The selection of defoamer should conform to the following points:
01. Insoluble or insoluble in foaming solution
To dissolve the foam, defoamer should be concentrated and concentrated on the bubble film. In the case of foam breaker, it should be concentrated and concentrated in an instant, and in the case of foam suppression, it should always be kept in this state. Therefore, the defoamer is supersaturated in the foaming solution, and only insoluble or insoluble can it easily reach supersaturated state. Insoluble or insoluble, it is easy to gather at the gas-liquid interface, it is easy to concentrate on the bubble membrane, and it can play a role at a lower concentration. The antifoam used in water system, the molecule of active component, must be strong hydrophobic and weak hydrophilic, the HLB value is in the range of 1.5-3, the best effect is.
02. The surface tension is lower than the foaming liquid
Only when the force between defoamers is small and the surface tension is lower than that of the foaming solution, the defoamer particles can be immersed and expanded on the bubble membrane. It should be noted that the surface tension of foaming solution is not the surface tension of solution, but the surface tension of foaming solution.
03. It has a certain degree of affinity with foaming solution
Since the defoaming process is actually the competition between the rate of bubble collapse and the rate of foam formation, defoamers must be dispersed rapidly in the foaming solution so as to play a role in the wider range of foaming liquid. In order to make the defoamer diffuse quickly, the active components of defoamer must have a certain degree of affinity with the foaming solution. The active components of defoamer are too close to the foaming solution, which will dissolve; too sparse and difficult to disperse. Only when intimacy is appropriate, the effect will be good.
04. No chemical reaction with foaming liquid
When defoamer reacts with foaming liquid, on the one hand, defoamer will lose its function, on the other hand, it may produce harmful substances, which will affect the growth of microorganisms.
05. Low volatility, long acting time
First of all, it is necessary to determine the system that needs to use defoamer, which is water-based system or oil-based system. Such as fermentation industry, it is necessary to use oily defoamers, such as polyether modified silicon or polyether. The water-based coating industry needs water-based defoamer, silicone defoamer. Choose defoamer, compare the amount of addition, at the reference price, we can get the most suitable and economic defoamer products.
Defoamer dosage
There are many kinds of defoamers. Different types of defoamers require different amounts of additives. Here are six types of defoamers:
1. Alcohol defoamer: when alcohol defoamer is used, the dosage is generally within 0.01-0.10%.
2. Oil defoamer: the amount of oil defoamer is 0.05-2%, and the amount of fatty acid ester defoamer is 0.002-0.2%.
3. Amides defoamer: the effect of amides defoamer is better, and the addition amount is generally within 0.002-0.005%.
4. Phosphoric acid defoamer: phosphoric acid defoamer is most commonly used in fiber and lubricating oil, with the addition of 0.025-0.25%.
5. Amines defoamer: amines defoamer is mainly used in fiber processing, with the addition amount of 0.02-2%.
6. Ether defoamer: ether defoamer is widely used in paper printing, dyeing and cleaning, with the addition of 0.025-0.25%.
Source: Water World subscription
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