First, the generation of bubbles
When there are surfactants in the liquid, because the surface of the bubble can adsorb surfactant molecules, when these molecules aligned on the surface of the bubble reach a certain concentration, a solid bubble wall film is formed. Surfactant molecules adsorb on the gas-liquid interface to form a liquid film, so that the surface tension decreases, thereby increasing the gas-liquid contact surface, so that bubbles are not easy to merge. Air bubbles, which are much less dense than water, float to the surface of the liquid, and when the rising bubbles pass through the liquid surface, they adsorb the top surfactant molecules on the liquid surface. Therefore, the bubble film of adsorbed surfactant exposed to air is different from the bubble film in solution. It is covered with two layers of surfactant molecules. The adsorbed surfactant has a protective effect on the liquid film, and the hydrophobic group of the second layer of surfactant molecules faces the air, as shown in Figure -1.



Second, the harm of foam




1, the production capacity is greatly limited: such as a variety of biological fermentation (beer production, alcohol manufacturing, pharmaceutical production of major antibiotics...) In various fermenters, reaction tanks and cooking tanks and other equipment, in order to prevent the emergence of foam, to prevent the loss of overflow, the feeding coefficient should be greatly reduced.






2, resulting in the waste of raw materials and products: due to the reason of foam, it can cause useful or valuable raw materials to overflow and loss, the resulting waste is self-evident.






3, prolong the reaction cycle: because the chemical reaction products include gas and liquid, the foam will cause gas retention, prolong the reaction cycle, and unnecessarily consume more power. And if the wine fermentation overreacts due to the presence of foam and becomes stale...






4, affect product quality: dyeing, printing and water-based coating process in the textile industry, due to the retention of bubbles, resulting in stains and defects on the finished cloth; In addition to causing harm to environmental health and workers' health, the foam of the pulp slurry will also appear many holes in the finished paper, resulting in a serious decline in product quality.






5, not conducive to accurate measurement: in the industrial process, due to the existence of foam, interference with the accuracy of the liquid level meter, resulting in measurement errors, due to the existence of foam in the liquid, making the liquid density fluctuate greatly, often can also cause the reaction tank absorption tower distillation tower liquid level virtual high, resulting in the operation out of balance, and even accidents.






6, pollution of the environment, one of the causes of the accident: due to foam overflow, it will inevitably pollute the production environment and its surrounding environment, and some even cause major accidents.






These are far from all the dangers of bubbles, but it is enough to see how serious they are. In short, the existence of bubbles, affecting various sectors of the national economy, all aspects, if not well solved, it is no exaggeration to say that "bubbles" will become our obstacles, become some process "bottleneck". The good news is that there are good ways to deflate bubbles.




3. Defoaming mechanism


Foam elimination, generally using static, heating or pressure reduction methods, but time-consuming, and in a variety of production processes and product use process need to quickly eliminate the foam generated, you must use defoamer. Therefore, it is necessary to understand the mechanism of defoamer.






Theoretically speaking, the purpose of defoaming can be achieved by eliminating the factors that make the foam stable. Because the main factor affecting the stability of the foam is the strength of the liquid film, after the defoamer is added to the working liquid, it becomes a solution, emulsion or dispersion, and adsorbed on the surface of the foam. Because it has a lower surface tension than the foam, the surfactant or foam substance can be attracted to reduce the surface viscosity of the foam liquid film, local thinning and rupture. Therefore, the main cause of foam destruction is the thinning of liquid film drainage and the diffusion of gas in the bubble. At the same time, in order to prevent the regeneration of foam, the surface elasticity should be reduced or eliminated, that is, the use of brittle surface film instead of elastic surface film, resulting in unstable foam.


Fourth, the types and characteristics of defoamer






For defoamer, we hope to have the effect of defoamer and defoamer at the same time, the solubility in water should be small, and it is not easy to be emulsified and solubilized by the working liquid. There are many varieties of defoamer, but according to the category, it can generally be divided into two categories: silicon-containing and silicon-free.




01 Silicon-containing defoamer


Silicon-containing defoamer has the advantages of low surface tension, small solubility, good dispersion, lasting effect and small dosage, that is, it has a strong ability to break bubbles and suppress bubbles. And the chemical properties of the defoamer are not active, non-toxic and pollution-free to the environment. It mainly includes four kinds of silicone oil, silicone oil emulsion, silicone oil solution (silicone oil dissolved in organic solvent), silicone oil and other fillers (such as SiO2, Al2O3).






02 Silicon-free defoamer


According to the different components, there are mainly the following:


(1) Phosphate defoamer: the defoamer effect is better and the application is more common.






(2) alcohols, ethers, fatty acids and their esters, animal and plant oils or mineral oils and polyethylene glycol propylene glycol and other substances: characterized by easy access to raw materials, there is a certain defoaming effect, a small amount is used alone, most of them are used in combination.






(3) Polyether defoamer: adducts of alcohols and epoxide/propane. By controlling the carbon content of alcohol and the ratio of ethylene oxide/propane, its defoaming performance can be controlled. The characteristic of this defoamer is that some high-temperature resistant products can be developed. Because it does not contain silicon, there will be no stain and oil stains on the equipment wall and fabric. Some products not only have the effect of defoaming and defoaming, but also play the role of functional additives such as penetration, washing, slow dyeing and leveling for the textile industry, which is more widely used than silicon-containing defoaming agents.


Points of attention for selecting defoamer:


1, insoluble or insoluble in the foaming liquid


2, the surface tension is lower than the foaming liquid.


3. It has a certain degree of affinity with foaming liquid.


4, no chemical reaction with foaming liquid.


5, small volatility, long action time.