Introduction to Defoamers - Part 1

Foams in coffee (Cited from: https://pixabay.com/zh/photos/coffee-cup-coffee-heartbeat-cup-2317201/)

Cover Photo cited from: https://pixabay.com/zh/photos/beach-coast-sea-sand-wave-ocean-2562563/

As we mentioned in the last article, silicone oil as one of the most important industrial products in today’s global market. Today, we are going to introduce another type of similar products- the defoamers.

Why Foams Are Harmful?

In industrial applications, many procedures of running or artifacts may lead to severe problems due to producing foams. For instance, the lubricants may produce foams when working and the foams will reduce the lubricity of the oil and even lead to worse conditions like damage the components or even cause incidents. In some drive line system, foams could lower the oil pressure and efficiency, which may directly cause the shortage of oil supply and lead to some operation failure. During the process of gas absorption, the produced foams will lower the processing capacity of absorption device and even cause flooding. During the4 fermentation process of antibiotics, glutamate and aginomoto, it is common that produced foams will severely curb the utilization rate of fermentation tanks, what is worse, the foams may even influence the oxygen supply and lower the collection rate of targeted products. Thus, it is evident that to remove the produced foams have utmost important technological and commercial meanings.

The producing of foams of liquid system is not only related to the chemical components and physical properties of itself, but also related to the working conditions and the mixed impurities which include solids, gases and liquids. Some materials whose surfaces are active, like detergents, soaps, starch and protein are easy to produce foams. Liquids will produce foams while being mixed strongly and transmitted when there is air or impurities; the gases which are soluble in the liquids will produce foams whey they are released during being heated or chemical reactions.

The theory of thermodynamics indicates that the foams produced from pure liquids will only exist for a very short period. However, for the impure liquids, there will be stronger trend to produce foams and the foams will be stable and last for a longer time. Usually, gases take most part of foam and the foams are only isolated by slim liquid films. When two foams of different sizes contact, it is due to the small one has a higher inner pressure, it is after some time the air will be transmitted from the small one to the big one and finally they will be merged together to a larger foam. Once the biggest foam is produced, it is due to the reason like relative density is low, the foam will gradually move to the top and leave the liquid. Therefore, when the producing rate of foams is bigger than the breaking rate of foams, the foams will be a huge damage.

Properties of Defoamers

There are many ways to destroy or remove the foams in industry. For example, the well-designed devices and strict operations could reduce the production rate of forms. When we take X-rays to beam, to reduce the pressure rapidly, to put some cold air, to use heated metal wires to contact and to use machine to put the foams out, all of the methods could reduce the damages from foams. However, all of them are not satisfied methods as well, especially for a large number of foams. At the same time, if we put some type of certain material into the foaming system and there are no foams producing with good defoaming effectiveness, we call the material defoamers.

There are many organic compounds which are good in making defoamers, like silicone oil, polyether, alcohol, fatty acid, amidate and metallic soaps. However, among all of the materials, silicone oil and polyether are the ones with the best defoaming performance and they have the widest application ranges as well.

Defoamers usually have stronger targeting and specialty, one type of defoamer may perform well in one foaming system but may be the agent to increase foam producing rate in another system. Therefore, it is to meet different customers’ needs, the sellers of defoamers usually need to develop many different types of defoamers.

The common thought mechanism of defoamers is the defoamer which has lower surface tensile strength enter some parts of bimolecular orientation foam films and then destroy the mechanical balance of the films. However, there are also many other theories on the detailed procedures. Another opinion indicates that the particles of low surface tensile strength are attached on the surface of foam films and then lower the tensile strength of the liquid films at the contact points which lead to make some weak points instead. The surfaces of foams will be broken after the pulling from a stronger tensile force.

Another type of point says there are actually three steps to antifoamers. Firstly, the defoamer particles which have low surface tensile strength penetrate the liquid films of foams, and then the defoamer films extend further to the foam films and become thinner; finally, the defoamer films are broken and the whole foams are broken as well.

It is according to these theories, the compounds which are good for being defoamers had better contain all of the following three conditions:

1.      The material will not be soluble in the liquid which will produce foams basically;

2.      The surface tensile strength of the material must be lower than the foam liquid;

3.      The material must be fast in spreading in the foam liquid.

If we use the defoamers which have high solubility and high dispersivity, the foams will be faster to be broken but the corresponding foam curbing ability will be weaker; if we use the high solubility and low dispersivity ones, the ability to break and curb foams will both be weak; if we use the ones with low solubility and low dispersivity, the curbing ability will be high while the breaking ability will be weaker. Therefore, only the defoamers who have low solubility and high dispersivity could perform well in both curbing and breaking. This is the main direction of making new defoamers and this is why silicone oil is not common being used as defoamers but instead silicone oil will be processed further to lubricants and other forms to increase its dispersivity to the max limitation to reach the goal of excellent foam-breaking and foam-curbing properties.

Summary

In this article, some basis of the defoamers has been introduced. In the next article, we will introduce more on the details of the defoamers.