Anti-foaming Agent is added to the foam system and diffuses to the gas-liquid interface, making it difficult for the surfactant with foam stabilization to restore the membrane elasticity.
3. Promoting the drainage of liquid film
Anti-foaming agent can promote the drainage of liquid film, thus causing the bubbles to burst. The rate of foam drainage can reflect the stability of the foam. Adding a substance that accelerates the foam drainage can also play a defoaming role.
4. Adding hydrophobic solid particles can cause the bubbles to burst
Certain low-molecular substances that can be fully mixed with the solution can solubilize the bubble surfactant and reduce its effective concentration. Low-molecular substances with this effect, such as alcohols such as octanol, ethanol, and propanol, can not only reduce the surfactant concentration on the surface layer, but also dissolve into the surfactant adsorption layer, reduce the tightness between surfactant molecules, and thus weaken the stability of the foam.
6. Electrolytes break up the double layer of surfactants
For foaming liquids that produce stability by relying on the interaction of the double layer of surfactants in foam, adding ordinary electrolytes can break up the double layer of surfactants to play a defoaming role.
03Classification of Anti-foaming Agents
Commonly used anti-foaming agents can be divided into silicone (resin)
type, surfactant type, paraffin type and mineral oil type according to different ingredients.
1. Silicon (resin) type
Silicone resin defoamer is also called emulsion type defoamer. The method of use is to emulsify and disperse silicone resin in water with emulsifier (surfactant) and then add it to the wastewater. Silicon dioxide fine powder is another silicone defoamer with good defoaming effect.
2. Surfactant type
This type of anti foam is actually an emulsifier, that is, the dispersion effect of surfactant is used to keep the foam-forming substance in a stable emulsified state in water, thereby avoiding the formation of foam.
3. Paraffin type
Parallel defoamer is a defoamer made by emulsifying and dispersing paraffin wax or its derivatives with an emulsifier. Its use is similar to that of the emulsified defoamer of surfactant type.
4. Mineral oil type
Mineral oil is the main defoaming component. In order to improve the effect, metal soap, silicone oil, silica and other substances are sometimes mixed and used together. In addition, in order to make mineral oil easily diffuse to the surface of the foaming liquid, or to make metal soaps and the like evenly dispersed in the mineral oil, various surfactants can sometimes be added.
04 Advantages and disadvantages of different types of defoamers
Mineral oils, amides, lower alcohols, fatty acids and fatty acid esters, phosphates and other organic defoamers were studied and applied earlier and belong to the first generation of anti-foaming agents. They have the advantages of easy raw materials, high environmental performance, and low production costs; the disadvantages are low defoaming efficiency, strong specificity, and harsh conditions of use.
polyether defoamers are the second generation of anti-foaming agents, mainly including linear polyethers, polyethers with alcohol or ammonia as initiators, and end-esterified polyether derivatives. The biggest advantage of polyether defoamers is their strong anti-foaming ability. In addition, some polyether defoamers have excellent properties such as high temperature resistance and 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 foam breaking rate is low.
Silicone defoamers (third generation defoamers) have strong defoaming performance, fast foam breaking ability, low volatility, no toxicity to the environment, no physiological inertness, and a wide range of applications. Therefore, they have broad application prospects and huge market potential, but their antifoaming performance is poor.
Polyether modified polysiloxane defoamers have the advantages of both polyether defoamers and silicone defoamers, and are the development direction of anti-foaming agents. Sometimes they can be reused according to their reverse solubility, but at present, there are few types of such anti-foaming agents, and they are still in the research and development stage, and the production cost is high.
05 Selection of Anti-foaming Agent
The selection of Anti-foaming Agent should meet the following points:
1. Insoluble or poorly soluble in the foaming liquid
In order to break the foam, the Anti-foaming Agent should be concentrated and concentrated on the foam film. For the case of the foaming agent, it should be concentrated and concentrated instantly, and for the case of the foaming agent, it should always be kept in this state. Therefore, the Anti-foaming Agent is in a supersaturated state in the foaming liquid, and only when it is insoluble or poorly soluble can it easily reach a supersaturated state. Insoluble or poorly soluble, it is easy to gather at the gas-liquid interface, easy to concentrate on the foam film, and can play a role at a lower concentration. For the Anti-foaming Agent used in the water system, the molecules of the active ingredients must be strongly hydrophobic and weakly hydrophilic, and the HLB value must be in the range of 1.5-3, so that the effect is best.
2. The surface tension is lower than that of the foaming liquid
Only when the intermolecular force of the Anti-foaming Agent is small and the surface tension is lower than that of the foaming liquid, can the anti-foaming agent particles be immersed and expanded on the foam 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 foaming solution.
3. A certain degree of affinity with the foaming liquid
Since the defoaming process is actually a competition between the foam collapse speed and the foam generation speed, the Anti-foaming Agent must be able to disperse quickly in the foaming liquid so that it can quickly play a role in a wider range of the foaming liquid. In order to make the Anti-foaming Agent diffuse faster, the active ingredients of the Anti-foaming Agent must have a certain degree of affinity with the foaming liquid. If the active ingredients of the Anti-foaming Agent are too close to the foaming liquid, they will dissolve; if they are too distant, they will be difficult to disperse. Only when the affinity is appropriate, the effect will be good.
4. No chemical reaction with the foaming liquid
When the Anti-foaming Agent reacts with the foaming liquid, on the one hand, the defoaming agent will lose its effect, and on the other hand, harmful substances may be produced, affecting the growth of microorganisms.
5. Low volatility and long action time
First, it is necessary to determine the system in which the Anti-foaming Agent needs to be used, whether it is a water-based system or an oil-based system. For example, in the fermentation industry, oily anti-foaming agents such as polyether-modified silicon or polyether are used. Water-based defoaming agents and silicone defoaming agents are used in the water-based coating industry. Select the defoaming agent, compare the addition amount, and refer to the price to get the most suitable and economical defoaming agent product.
06 Factors affecting the use effect of anti-foaming agent
1. Dispersibility of anti-foaming agent in solution
The dispersion state and surface properties of anti-foaming agent in solution significantly affect other defoaming properties. Anti-foaming agent should have a suitable degree of dispersion and particles with too large or too small particle size will affect their defoaming activity.
2. Compatibility of anti-foaming agent in foam system
When the surfactant is completely dissolved in the aqueous solution, it is usually oriented at 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 accumulated on the foam, and the foam acts as a defoaming agent.
3. Foaming system ambient temperature
The temperature of the foaming liquid will also affect the performance of the defoaming agent. When the temperature of the foaming liquid itself is relatively high, it is recommended that a special high-temperature resistant defoaming agent must be used, because if an ordinary defoaming agent is used, the defoaming effect will definitely be greatly reduced, and the Anti-foaming Agent will directly demulsify the emulsion.
4. Packaging, storage and transportation
The defoaming agent 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 commonly used chemical storage method, make sure to seal it after use to avoid deterioration.
5. Anti-foaming Agent addition ratio
The addition of the original solution and the addition after dilution have some deviations to a certain extent, and the proportions are not equal. Due to the low concentration of surfactants, the diluted Anti-foaming Agent emulsion is extremely unstable and will not be stratified soon. The defoaming performance is relatively poor and is not suitable for long-term storage. It is recommended to use it immediately after dilution. The proportion of adding Anti-foaming Agent needs to be verified by field tests to verify the effect, and it should not be added excessively.
07Amount of Anti-foaming Agent
There are many types of Anti-foaming Agents, and the amount of each type of Anti-foaming Agent is different. Here we introduce the amount of six types of defoaming agents: 1. Alcohol defoamers: When alcohol defoamers are used, the amount is generally within 0.01-0.10%. 2. Grease defoamers: The amount of grease defoamers is between 0.05-2%, and the amount of fatty acid ester defoamers is between 0.002-0.2%. 3. Amide defoamers: Amide defoamers have better effects, and the amount is generally within 0.002-0.005%. 4. Phosphoric acid defoamers: Phosphoric acid defoamers are most commonly used in fibers and lubricating oils, and the amount is between 0.025-0.25%. 5. Glue defoamers: Glue defoamers are mainly used in fiber processing, and the amount is 0.02-2%. 6. Ether defoaming agents: Ether defoaming agents are widely used in papermaking, printing and dyeing, and cleaning, and the addition amount is generally 0.025-0.25%.
