1. How to eliminate bubbles

1. Physical methods


From the perspective of physics, the methods to eliminate foam mainly include placing baffles or filters, mechanical stirring, static electricity, freezing, heating, steam, radiation, high-speed centrifugation, pressure and decompression, high-frequency vibration, instantaneous discharge and ultrasonic (acoustic) Liquid control), etc., these methods promote the gas permeation rate at both ends of the liquid film and the drainage of the bubble film to varying degrees, so that the stability factor of the foam is smaller than the attenuation factor, and the number of foams is gradually reduced. However, the common shortcomings of these methods are that the use is more restricted by environmental factors, the defoaming rate is not high, etc., and the advantages are environmental protection and high reuse rate.


2. Chemical methods


The methods to eliminate foam from a chemical point of view mainly include chemical reaction methods and methods of adding defoamers. The chemical reaction method refers to the chemical reaction by adding some reagents to the foaming agent to produce water-insoluble substances, thereby reducing the concentration of surfactants in the liquid film and promoting the rupture of the foam, but this method has foaming The composition of the agent is uncertain, and the production of insoluble substances is harmful to the system equipment and other shortcomings. 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 high foam breaking efficiency and convenient use. However, finding a suitable and efficient defoaming agent is the key.


2. The principle of defoamer


Antifoaming agent, also called defoaming agent, has the following principles:


1. The decrease in the local surface tension of the foam leads to the collapse of the foam


The origin of this mechanism is to sprinkle higher alcohol or vegetable oil on the foam. When it dissolves into the foam liquid, it will significantly reduce the surface tension there. Because these substances are generally less soluble in water, the reduction of surface tension is limited to the local area of the foam, and the surface tension around the foam hardly changes. The part with reduced surface tension is intensively pulled around, extended, and finally ruptured.


2. Destroy the elasticity of the membrane and cause the bubble to burst


When the defoamer is added to the foam system, it will diffuse to the gas-liquid interface, making it difficult for the foam-stabilizing surfactant to recover the elasticity of the film.


3. Promote liquid film drainage


The defoaming agent can promote the drainage of the liquid film, which causes the bubble to burst. The rate of foam drainage can reflect the stability of the foam. Adding a substance that accelerates the drainage of the foam can also play a defoaming effect.


4. Adding hydrophobic solid particles can cause bubbles to burst


The hydrophobic solid particles on the surface of the bubbles will attract the hydrophobic end of the surfactant, making the hydrophobic particles hydrophilic and enter the water phase, thereby playing a defoaming effect.


5. Solubilizing and foaming surfactants can cause 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 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 weakening the stability of the foam.


6. Electrolyte breaks down the electric double layer of surfactant


For the interaction of the electric double layer of the surfactant with the foam to produce a stable foaming liquid, the addition of ordinary electrolyte can disintegrate the electric double layer of the surfactant to have a defoaming effect.


Third, the classification of defoamers


Commonly used defoamers can be divided into silicone (resin) type, surfactant type, paraffin type and mineral oil type according to their composition.


1. Silicon (resin) type


Silicone resin defoamer is also called emulsion type defoamer. The method of use is to emulsify and disperse silicone resin with an emulsifier (surfactant) in water and then add it to wastewater. Silica fine powder is another silicon defoamer with better defoaming effect.


2. Surfactants


This type of defoaming agent is actually an emulsifier, that is, using the dispersion of surfactants to maintain a stable emulsified state of the foam-forming substance in the water, thereby avoiding the formation of foam.


3. Paraffinic hydrocarbons


Paraffinic defoamers are defoamers made by emulsifying and dispersing paraffin wax or its derivatives with emulsifiers. Its use is similar to that of surfactant-based emulsified defoamers.


4. Mineral oil


It uses mineral oil as the main defoaming ingredient. In order to improve the effect, sometimes mixed with metal soap, silicone oil, silicon dioxide and other substances used together. In addition, in order to make the mineral oil easily diffuse to the surface of the foaming liquid, or to evenly disperse metal soaps in the mineral oil, various surfactants can sometimes be added.


Fourth, the advantages and disadvantages of different types of defoamers


The research and application of mineral oils, amides, lower alcohols, fatty acids and fatty acid esters, phosphate esters and other organic defoamers are relatively early. They belong to the first generation of defoamers. They have easy-to-obtain raw materials, high environmental performance, and production Advantages such as low cost; disadvantages are low defoaming efficiency, strong specificity, and harsh use conditions.


Polyether defoamers are second-generation defoamers, which mainly include straight-chain polyethers, polyethers starting from alcohol or ammonia, and end-group esterified polyether derivatives. The biggest advantage of polyether defoamers is that they have strong anti-foaming ability. In addition, some polyether defoamers have excellent properties such as high temperature resistance, strong acid and strong alkali resistance; the disadvantage is that the use conditions are limited by temperature and the field of use Narrow, poor defoaming ability, low foam breaking rate, etc.


Silicone defoamers (third-generation defoamers) have the advantages of strong defoaming performance, rapid foam breaking ability, low volatility, non-toxic to the environment, no physiological inertia, and wide range of use, so they have a wide range of advantages Its application prospects and huge market potential, but its foam suppression performance is poor.


Polyether modified polysiloxane defoamers have the advantages of polyether defoamers and silicone defoamers, and are the development direction of defoamers. Sometimes it can be reused according to its inverse solubility, but at present there are fewer types of such defoamers and they are still in the research and development stage, and the production cost is relatively high.


5. Selection of defoamer


The selection of defoamer must meet the following points:


1. Insoluble or insoluble in foaming liquid


In order to burst the foam, the defoamer should be concentrated and concentrated on the foam 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 supersaturated in the foaming liquid, and only insoluble or insoluble can it easily reach the supersaturated state. Insoluble or poorly soluble, it is easy to gather at the gas-liquid interface, and it is easy to concentrate on the bubble film, and it can play a role at a lower concentration. For defoamers used in water systems, the molecules of the active ingredients must be strong hydrophobic and weakly hydrophilic, with an HLB value in the range of 1.5-3 for the best effect.


2. The surface tension is lower than the foaming liquid


Only when the defoaming agent has a small intermolecular force and the surface tension is lower than that of the foaming liquid, the defoaming agent particles can 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. There is 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 defoamer must be quickly dispersed in the foaming liquid in order to quickly play a role in a wider range of the foaming liquid. To make the defoamer diffuse faster, the active ingredient of the defoamer must have a certain degree of affinity with the foaming liquid. The active ingredient of the defoamer is too close to the foaming liquid and will dissolve; too thin and difficult to disperse. The effectiveness will be good only if the close relationship is appropriate.


4. No chemical reaction with foaming liquid


The defoamer reacts with the foaming liquid. On the one hand, the defoamer will lose its effect, and on the other hand, it may produce harmful substances that affect the growth of microorganisms.


5. Low volatility and long action time


First of all, determine whether the system that needs to use the defoamer is an aqueous system or an oily system. Such as the fermentation industry, it is necessary to use oily defoamers, such as polyether modified silicon or polyether. Water-based paint industry needs water-based defoamer, silicone defoamer. Choose the defoamer, compare the addition amount, and get the most suitable and economical defoamer product based on the reference price.


6. Factors that affect the effect of defoamer


1. Dispersibility of defoamer in solution


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


2. Compatibility of defoamer in foam system


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


3. Ambient temperature of the foaming system


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 to use a special high-temperature resistant defoamer, because if you use ordinary defoamers, the defoaming effect will definitely be greatly reduced, and the defoamer will directly demulsify 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 commonly used chemical storage methods, ensure that it is sealed after use to avoid deterioration.


5. Addition ratio of defoamer


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 surfactant concentration, the diluted defoamer emulsion is extremely unstable and will not be stratified soon. The defoaming performance is relatively poor, and it is not suitable for long-term storage. It is recommended to use it immediately after dilution.


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


7. Dosage of defoamer


There are many types of defoamers, and different types of defoamers require different addition amounts. Below we will introduce the addition amount of six types of defoamers:


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


2. Grease 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 defoaming agent: The effect of amide defoaming agent is better, and the addition amount is generally within 0.002-0.005%.


4. Phosphoric acid defoamers: Phosphoric acid defoamers are most commonly used in fiber and lubricating oil, and the addition amount is between 0.025 and 0.25%.


5. Amine defoamers: Amine defoamers are mainly used in fiber processing, and the addition amount is 0.02-2%.


6. Ether defoaming agent: Ether defoaming agent is more used in papermaking, printing, dyeing and cleaning, and the addition amount is generally 0.025 to 0.25%.