Foam problems in water treatment troubled a lot of people, debugging the initial foam, surfactant foam, impact foam, peroxide foam, circulating water treatment by adding non-oxidizing biocides generated by the foam and so on, so the use of antifoam in water treatment is relatively common, this article comprehensively introduces the principle of antifoam agent, classification, selection and dosage!
Foam elimination methods
1. Physical methods
Methods of eliminating foam from a physical point of view mainly include placing baffles or screens, mechanical agitation, electrostatics, refrigeration, heating, steam, ray irradiation, high-speed centrifugation, pressurization and decompression, high-frequency vibration, instantaneous discharge and ultrasonic waves (acoustic liquid control), etc. All of these methods promote the rate of gas permeation through the two ends of the liquid film and the drainage of the bubble film to different degrees, making the stabilizing factor of the foam less than the attenuating factor and thus the number of bubbles gradually decreases. However, the common disadvantage of these methods is that the use of environmental factors by the strong constraints, defoaming rate is not high, but the advantages of environmental protection, high reuse rate.
2. Chemical methods
Methods of eliminating foam from the chemical point of view mainly include the chemical reaction method and the method of adding defoamer.
Chemical reaction method refers to the chemical reaction with the foaming agent by adding some reagents to generate insoluble substances, thereby reducing the concentration of surfactant in the liquid film, prompting the rupture of the foam, but this method exists in the foaming agent composition is not certain, the generation of insoluble substances on the system equipment to produce hazards and other shortcomings. Nowadays, the most widely used defoaming method in various industries is the method of adding defoamer, the biggest advantage of this method lies in the high efficiency of bubble breaking, easy to use and other advantages, but finding a suitable and efficient defoamer is the key.
Principle of defoamer
Defoamers, also known as defoamers, are based on the following principles:
1. Foam localized surface tension reduction leads to foam bursting
The origin of this mechanism is the sprinkling of higher alcohols or vegetable oils on the foam, which, when dissolved in the foam solution, significantly reduces the surface tension at that location. Because these substances are generally less soluble in water, the reduction in surface tension is limited to the localized area of the foam, while the surface tension around the foam remains virtually unchanged. The part with reduced surface tension is strongly pulled and extended in all directions and finally ruptures.
2、Destroy the membrane elasticity and lead to bubble bursting
The defoamer added to the foam system will diffuse to the gas-liquid interface, making it difficult for the surfactant, which has a foam stabilizing effect, to undergo the ability to restore film elasticity.
3. Promote fluid membrane drainage
Antifoam agent can promote the liquid film discharge, thus leading to bubble bursting, the rate of foam discharge can reflect the stability of the foam, add a substance to accelerate the foam discharge, can also play a role in defoaming.
4, adding hydrophobic solid particles can lead to bubble bursting
Hydrophobic solid particles on the bubble surface attract the hydrophobic end of the surfactant, causing the hydrophobic particles to become hydrophilic and enter the aqueous phase, thus acting as an antifoam.
5, solubilizing anti-foaming surfactants can lead to bubble bursting
Certain low molecular substances that can be fully mixed with the solution can make the bubble surfactant be solubilized, so that its effective concentration is reduced. This effect of low molecular substances such as octanol, ethanol, propanol and other alcohols, not only can reduce the surfactant concentration of the surface layer, but also dissolve into the surfactant adsorption layer, reducing the degree of compactness between surfactant molecules, thus weakening the stability of the bubble.
6. Electrolyte disintegration of surfactant bilayers
In the case of a foaming liquid that is stabilized by the interaction of the surfactant bilayer of the foam, the addition of a common electrolyte can disintegrate the surfactant bilayer to produce an antifoaming effect.
Classification of defoamers
Commonly used defoamers can be divided into silicon (resin), surfactants, alkane hydrocarbons and mineral oils according to the different components.
1、Silicon（Resin）type
Silicone resin antifoam agent is also known as emulsion-type antifoam agent, the use of silicone resin with emulsifier (surfactant) emulsification dispersed in water and then added to the wastewater. Silicon dioxide fine powder is another silicone antifoam agent with better defoaming effect.
2、Surfactants
This type of antifoam agent is actually an emulsifier, i.e., using the dispersing effect of surfactants to keep the foam-forming substances dispersed in the water in a stable emulsified state, thus avoiding the generation of foam.
3. Chain alkanes
Chain alkane antifoam agent is an antifoam agent made by emulsifying and dispersing chain alkane waxes or their derivatives with an emulsifier, and its use is similar to that of the emulsifying antifoam agent of surfactant class.
4. Mineral oils
Mineral oil is the main antifoaming ingredient. In order to improve the effect, it is sometimes mixed with metal soap, silicone oil, silicon dioxide and other substances and 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, etc. uniformly dispersed in the mineral oil, sometimes can be injected with a variety of surfactants.
Advantages and disadvantages of different types of defoamers
Mineral oils, amides, lower alcohols, fatty acids and fatty acid esters, phosphate esters and other organic antifoam agent research and application of early, belonging to the first generation of antifoam agent, which has the advantages of easy to obtain raw materials, high environmental performance, low production costs, etc.; the disadvantage of defoamer efficiency, specialization, the use of harsh conditions.
Polyether antifoam agent is the second generation of antifoam agent, mainly including straight chain polyether, alcohol or ammonia as the initiator of the polyether, end group esterification of polyether derivatives of three. The biggest advantage of polyether antifoam agent is that it has strong anti-foaming ability, besides, some polyether antifoam agents have excellent performance such as high temperature resistance, resistance to strong acid and alkali, etc.; the disadvantage is that the conditions of use are limited by the temperature, the field of use is narrow, the anti-foaming ability is poor, and the rate of breaking the bubble is low.
Organosilicon antifoam agent (the third generation of antifoam agent) has the advantages of strong defoaming performance, fast foam breaking ability, low volatility, non-toxic to the environment, non-physiological inertia, wide range of advantages, and so on, so it has a broad application prospects and huge market potential, but the foam inhibition performance is poor.
Polyether modified polysiloxane antifoam agent has the advantages of both polyether antifoam agent and organosilicon antifoam agent, which is the development direction of antifoam agent. Sometimes it can also be reused according to its reverse solubility, but at present the types of such defoamers are fewer, still in the research and development stage, and the cost of production is higher.
Selection of defoamer
The choice of defoamer should comply with the following points:
1、Insoluble or insoluble in foaming solution
To break the foam, the antifoam agent should be concentrated and centralized on the foam film. For the case of foam-breaking agent, it should be concentrated and centralized in an instant, and for the case of foam suppression it should be kept in this state frequently. So the antifoam agent is supersaturated in the foaming liquid, only insoluble or insoluble is easy to reach the supersaturated state. Insoluble or insoluble, it is easy to gather in the gas-liquid interface, it is easy to concentrate in the bubble film, in order to play a role in the lower concentration. Antifoam agent for the water system, the molecules of the active ingredient must be strong hydrophobic and weak hydrophilic, HLB value in the range of 1.5-3, the role of the best.
2、Surface tension is lower than foaming liquid
Only when the intermolecular force of antifoam agent is small and the surface tension is lower than that of the foaming solution, the antifoam agent particles can be immersed and expanded on the bubble 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 anti-foaming solution.
3, and foaming liquid has a certain degree of affinity
As the defoaming process is actually a foam collapse rate and foam generation rate of competition, so the defoamer must be able to quickly dispersed in the foaming liquid, in order to quickly play a role in a wider range of foaming liquid. To make the defoamer diffusion faster, defoamer active ingredient must have a certain degree of affinity with the foaming liquid. Antifoam agent active ingredients and foaming liquid too pro, will dissolve; too sparse and difficult to disperse. Only if the affinity is appropriate, the effectiveness will be good.
4、No chemical reaction with foaming liquid.
If the defoamer reacts with the foaming liquid, on the one hand, the defoamer will lose its effect, on the other hand, it may produce harmful substances and affect the growth of microorganisms.
5、Small volatility, long effect time
First of all, to determine the need to use antifoam agent system, is aqueous system or oily system. Such as fermentation industry, we need to use oily defoamer, such as polyether modified silicone or polyether class. Water-based coating industry should use water-based defoamer, silicone defoamer. Select the defoamer, compare the amount of additive, in reference to the price, can come up with the most applicable and economical defoamer products.
Factors affecting the use of defoamer effect
1、Dispersibility of defoamer in solution
The dispersion state and surface properties of defoamer in solution significantly affect other defoaming properties. Defoamer should have a suitable degree of dispersion and particle size is too large or too small particles will affect their antifoaming activity.
2、Compatibility of defoamer in foam system
When the surfactant is completely dissolved in the aqueous solution, it is usually oriented to arrange on the gas-liquid interface of the foam to stabilize the foam. When the surfactant is in an insoluble state or supersaturated state, the particles are dispersed in the solution and accumulate on the foam, and the foam acts as an antifoam agent.
3、The ambient temperature of foaming system
The temperature of the foaming liquid will also affect 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 defoaming effect will certainly be greatly reduced, and the defoamer will directly break the emulsion.
4、Packaging, storage and transportation
Defoamer is suitable for storage at 5 to 35°C. Shelf life is generally 6 months. Do not place it near heat sources or expose it to sunlight. According to the common chemical storage methods, make sure it is sealed after use to avoid deterioration.
5、Add proportion of defoamer
The addition of the original liquid and the diluted addition have some deviation to a certain extent, and the ratio is not equal. Due to the low concentration of surfactant, the diluted defoamer emulsion is extremely unstable, and soon will not be stratified defoaming performance is relatively poor, not suitable for long-term storage is recommended to use immediately after dilution.
Add the proportion of defoamer need to verify the effect through the field test, should not be over-added.
Dosage of defoamer
There are many types of defoamers, different types of defoamers require different amounts of additives, below we introduce you to six types of defoamers additive amount:
1、Alcohol defoamer: when alcohol defoamer is used, the dosage is generally within 0.01-0.10%.
2, grease antifoam agent: grease antifoam agent additive amount between 0.05-2%, fatty acid ester antifoam agent additive amount is between 0.002-0.2%.
3, amide antifoam agent: amide antifoam agent effect is better, the amount of addition is generally within 0.002-0.005%.
4, phosphate acid antifoam agent: phosphate acid antifoam agent is most commonly used in fiber and lubricating oil, the amount added is 0.025-0.25%.
5, amine antifoam agent: amine antifoam agent is mainly used in fiber processing, add 0.02-2%.
6, ether antifoam agent: ether antifoam agent in paper, printing and dyeing, net wash used more, the amount added is generally 0.025-0.25%.
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