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!



Defoaming principle


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




(1) The reduction of local surface tension of the foam leads to 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 bubble collapse



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 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, 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.






Selection of defoamer




The selection of defoamer should meet the following points:






(1) Insoluble or insoluble in the foaming solution






In order to burst the foam, the defoamer should be concentrated and concentrated on the bubble film. For the case of defoaming agent, it should be concentrated and concentrated in an instant, and for the case of defoaming agent, it should always be maintained in this state. Therefore, the defoamer is supersaturated in the foaming solution, and only insoluble or insoluble is easy to achieve supersaturation. Insoluble or insoluble, it is easy to gather at the gas-liquid interface, it is easy to concentrate on the bubble film, and it can play a role at a lower concentration. For the defoamer used in water systems, the molecules of the active ingredients must be strong hydrophobic and weak hydrophilic, and the HLB value should be in the range of 1.5-3 for the best effect.




(2) The surface tension is lower than the foaming solution




Only when the intermolecular force of the defoamer is small and the surface tension is lower than that of the foaming solution, the defoamer particles can be immersed and expanded on the foam film. It is worth noting that the surface tension of the foaming solution is not the surface tension of the solution, but the surface tension of the foaming solution.




(3) It has a certain degree of affinity with foaming liquid



Since the defoaming process is actually a competition between the speed of foam collapse and the speed of foam formation, the defoaming agent must be able to disperse quickly in the foaming solution in order to quickly play a wider range of roles in the foaming solution. In order to make the defoamer diffusion faster, the active ingredient of the defoamer must have a certain degree of affinity with the foaming solution. The active ingredient of defoamer is too close to the foaming solution and will dissolve. Too sparse and difficult to disperse. The effectiveness is good only when the intimacy is right.




(4) No chemical reaction with foaming liquid




The defoamer reacts with the foaming solution, on the one hand, the defoamer will lose its effect, on the other hand, harmful substances may be produced, affecting the growth of microorganisms.




(5) Small volatility, long action time



First of all, it is necessary to determine the system that needs to use defoamer, whether it is a water-based system or an oil-based system. If the fermentation industry, it is necessary to use oil-based defoamer, such as polyether modified silicon or polyether. Water-based coating industry must use water-based defoamer, silicone defoamer. Select the defoamer, compare the added amount, and get the most suitable and economical defoamer product at the reference price.




Dosage of defoamer


There are many types of defoamer, and the amount of addition required for different types of defoamer is different. Here we introduce the amount of six types of defoamer:





1. Alcohol defoamer: When alcohol defoamer is used, the dosage is generally within 0.01-0.10%.




2. Oil defoamer: the addition amount of oil defoamer is between 0.05-2%, and the addition amount of fatty acid ester defoamer is between 0.002-0.2%.





3, amide defoamer: amide defoamer effect is better, the amount of addition is generally within 0.002-0.005%.




4, phosphoic acid defoamer: phosphoic acid defoamer is most commonly used in fibers and lubricating oil, the amount of addition is between 0.025-0.25%.



5, amine defoamer: amine defoamer is mainly used in fiber processing, the addition amount is 0.02-2%.



6. Ether defoamer: ether defoamer is used more in paper printing and dyeing and cleaning, and the addition amount is generally 0.025-0.25%.