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.

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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.




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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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Advantages and disadvantages of different kinds of defoamer
Organic defoamer such as mineral oils, amides, low alcohols, fatty acids, fatty acid esters and phosphate esters has been studied and applied earlier, belonging to the first generation of defoamer, which has the advantages of easy access to raw materials, high environmental performance and low production cost. The disadvantages are low defoaming efficiency, strong specificity and harsh use conditions.


Polyether defoamer is the second generation of defoamer, which mainly includes straight chain polyether, polyether with alcohol or ammonia as the starting agent and polyether derivatives with end group esterification. The biggest advantage of polyether defoamer is its strong anti-foam ability. In addition, some polyether defoamer has excellent properties such as high temperature resistance, strong acid and alkali resistance. The disadvantages are that the use conditions are limited by temperature, the use field is narrow, the defoaming ability is poor, and the bubble breaking rate is low.


Silicone defoamer (the third generation of defoamer) has the advantages of strong defoamer performance, rapid defoamer ability, low volatility, no toxicity to the environment, no physiological inertia, wide range of use, etc., so it has broad application prospects and huge market potential, but the foam suppression performance is poor.


Polyether modified polysiloxane defoamer has the advantages of polyether defoamer and silicone defoamer at the same time, which is the development direction of defoamer. Sometimes it can also be reused according to its reverse solubility, but at present, there are fewer types of such defoamer, which is still in the research and development stage, and the production cost is high.






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Selection of defoamer
The selection of defoamer should meet the following points:


1, insoluble or insoluble in the foaming liquid


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 liquid


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.




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Factors affecting the effect of defoamer use
1. Dispersibility of defoamer in solution


The dispersion state and surface properties of defoamer in solution significantly affect other defoamer properties. The defoamer should have a suitable degree of dispersion and particles that are too large or too small will affect their defoaming activity.


2. Compatibility of defoamer in foam system


When the surfactant is completely dissolved in an aqueous solution, it usually arranges directionally at the gas-liquid interface of the foam to stabilize the foam. When the surfactant is in an insoluble or supersaturated state, the particles disperse in the solution and accumulate on the foam, which acts as a defoamer.


3, foaming system ambient temperature


The temperature of the foaming liquid also affects the performance of the defoamer. When the temperature of the foaming liquid itself is relatively high, it is recommended that special high temperature defoamer must be used, because if ordinary defoamer is used, the defoamer effect will certainly be greatly reduced, and the defoamer will directly break the emulsion.


4. Packaging, storage and transportation


The defoamer is suitable for storage at 5 ~ 35℃, and the shelf life is generally 6 months. Do not place it near a heat source or expose it to sunlight. According to the common chemical storage method, ensure that it is sealed after use to avoid deterioration.


5, the proportion of defoamer added


The addition of the stock solution and the addition after dilution have some deviations to a certain extent, and the proportion is not equal. Due to the low surfactant concentration, diluted defoamer emulsions are extremely unstable, will not stratify quickly and have relatively poor defoamer performance, and are not suitable for long-term storage.


The proportion of defoamer added needs to be verified by field tests, and should not be added excessively.






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The amount 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%.