Defoamer knowledge introduction
The foam problem in water treatment has plagued many people. The initial foam, surfactant foam, impact foam, peroxidized foam, foam produced by the addition of non-oxidizing fungicides in circulating water treatment, etc., so the water treatment is eliminated. The use of foaming agents is relatively common. This article fully introduces the principle, classification, selection and dosage of antifoaming agents!
Antifoaming agent, also known as antifoaming agent, has the following principles:
01, the local surface tension of the foam is reduced, causing the foam to burst
The origin of this mechanism is to sprinkle higher alcohol or vegetable oil on the foam. When it is dissolved into the foam liquid, it will significantly reduce the surface tension there. Because these substances are generally less soluble in water, the reduction in surface tension is limited to the local area of the foam, and the surface tension around the foam is almost unchanged. The part with reduced surface tension is strongly pulled, extended around, and finally ruptured.
02, destroy the elasticity of the membrane and cause the bubble to burst
When defoamer is added to the foam system, it will diffuse to the gas-liquid interface, making it difficult for the surfactant with foam stabilizing effect to recover the elasticity of the membrane.
03. Promote liquid membrane drainage
The antifoaming agent can promote the liquid film to drain, which causes the bubbles to burst. The foam draining rate can reflect the stability of the foam. Adding a substance that accelerates the foam draining can also play a defoaming role.
04, the addition of 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, making the hydrophobic particles hydrophilic and enter the water phase, thereby playing the role of defoaming.
05, solubilizing and foaming surfactants 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 between the surfactant molecules Degree, thereby reducing the stability of the foam.
06. Electrolyte disintegration surfactant double layer
For the foaming liquid that interacts with the electric double layer of the surfactant to produce a stable foaming liquid, the electric double layer of the surfactant can be disintegrated by adding a common electrolyte for defoaming.
Commonly used defoamers can be divided into silicon (resin), surfactants, paraffins and mineral oils according to different components.
01. Silicone (resin)
Silicone defoamer is also known as emulsion defoamer. The method of use is to emulsify and disperse silicone resin emulsifier (surfactant) in water and then add it to wastewater. Silica fine powder is another kind of defoamer with good defoaming effect.
Such defoamers are actually emulsifiers, that is, the dispersion of surfactants is used to keep foam-forming substances dispersed in water in a stable emulsified state, thereby avoiding the formation of foam.
Paraffin-type defoamers are defoamers made by emulsifying and dispersing paraffin wax or its derivatives. Its use is similar to surfactant-type defoamers.
04, mineral oil
With mineral oil as the main defoaming ingredient. In order to improve the effect, metal soap, silicone oil, silica and other substances are sometimes used together. In addition, in order to easily diffuse the mineral oil to the surface of the foaming liquid, or to uniformly disperse the metal soap and the like in the mineral oil, various surfactants may sometimes be added.
Selection of defoamer
The selection of defoamers should meet the following points:
01. Insoluble or insoluble in foaming liquid
To break the foam, the defoamer should be concentrated and concentrated on the bubble film. In the case of foam breakers, 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 in a supersaturated state in the foaming liquid, and it is easy to reach the supersaturated state only if it is insoluble or insoluble. Insoluble or insoluble, it is easy to accumulate at the gas-liquid interface, it is easy to concentrate on the bubble film, and it can play a role at a lower concentration. The defoamer used in the water system, the molecule of the active ingredient, must be strong hydrophobic and weak hydrophilic, and the HLB value is in the range of 1.5-3 for the best effect.
02. The surface tension is lower than the foaming liquid
Only when the defoamer has a small intermolecular force and the surface tension is lower than the foaming liquid, can the defoamer particles be immersed and expanded on the bubble film. It is worth noting that the surface tension of the foaming liquid is not the surface tension of the solution, but the surface tension of the bubble assisting solution.
03. Have a certain degree of affinity with the foaming liquid
Since the defoaming process is actually a competition between the rate of foam collapse and the rate of foam generation, the defoamer must be able to quickly disperse in the foaming liquid in order to quickly play a role in a wider range of foaming liquid. For the defoamer to diffuse faster, the active ingredients of the defoamer must have a certain degree of affinity with the foaming liquid. The defoamer active ingredient is too close to the foaming liquid and will dissolve; it is too sparse and difficult to disperse. Effectiveness will be good only if you are close and comfortable.
04. No chemical reaction with foaming liquid
The antifoaming agent reacts with the foaming liquid. On the one hand, the antifoaming agent loses its function. On the other hand, it may produce harmful substances and affect the growth of microorganisms.
05. Low volatility and long action time
First of all, it is necessary to determine whether the system requiring the defoamer is an aqueous system or an oily system. Such as fermentation industry, it is necessary to use oily defoamers, such as polyether modified silicon or polyether. The water-based paint industry requires water-based defoamers and silicone defoamers. Select the defoamer, compare the amount of addition, and at the reference price, you can get the most suitable and economical defoamer product.
There are many types of antifoaming agents. The amount of addition required for different types of antifoaming agents is different. Below we introduce the amount of six types of antifoaming agents for you:
1. Alcohol defoamer: When alcohol defoamer is used, the dosage is generally within 0.01-0.10%.
2. Oil and fat defoamer: The addition amount of oil and fat defoamer is between 0.05-2%, and the addition amount of fatty acid ester defoamer is between 0.002 and 0.2%.
3. Amide defoamer: The effect of amide defoamer is relatively good, and the addition amount is generally within 0.002-0.005%.
4. Phosphoric acid defoamer: Phosphoric acid defoamer is most commonly used in fibers and lubricating oils, with an addition amount of 0.025-0.25%.
5. Amine defoaming agent: Amine defoaming agent is mainly used in fiber processing, and the added amount is 0.02-2%.
6. Ether defoamers: Ether defoamers are used more frequently in papermaking, printing, dyeing and cleaning. The added amount is generally 0.025-0.25%.