The Role of Defoamers

Sep 17, 2021

The current theories about foam formation differ between defoaming and defoaming. The function of defoamer is to trap air at the interface. The function of the defoaming agent is to make the tiny air (microbubbles) dispersed in the coating film quickly rise to the surface after the coating process and the coating film are completed. However, it is often impossible to make this distinction clearly in practical applications. Antifoaming agents can also eliminate microfoam to some extent. The defoaming mechanism of defoamers in water-based coatings and inks is discussed below.

In order for a defoamer to show effect, it must meet certain requirements. One of them is that they must be able to disrupt the aforementioned foam stabilization mechanism. For this reason, the defoamer must have a certain degree of incompatibility in the system and be able to migrate to the air interface. Of course, there can be no serious side effects like shrinkage caused by the use of defoamers.
In order to be able to defoam, the defoamer emulsified into tiny droplets in the paint must be combined with the foam-stabilizing surfactant layer and penetrate into the bimolecular film layer of the foam. Next, the defoamer must spread quickly through the cracked surfactant layer. Compared with the previously stabilized interlayer surfactant film, the elasticity of the film at this time has been significantly reduced. Finally, this instability leads to the rupture of the bimolecular film, thereby achieving the effect of defoaming. Therefore, incompatibility, high spreading ability and low surface tension are important properties that every defoamer must have.

Adding fine hydrophobic particles, such as silica, to the defoaming agent will effectively enhance its defoaming ability. Their mechanism of action can be explained as a dehumidification process. The stable surface active agent bimolecular film layer cannot wet the hydrophobic solid particles, resulting in instability of the surface tension in the local area and rupture of the bimolecular film layer.

The stability of the bubble is affected by several factors. One of the factors is that the stable interlayer is very thin, and the liquid in the interlayer cannot be discharged or is discharged slowly. In addition, the electrostatic repulsion between the surfactant ions occupying the interlayer also prevents the bubble from bursting. Another factor contributing to the stability of the bubble is Gibbs' resilience. By stretching the film with surface active substances, this elastic effect will be manifested. In this case, the surface of the double film layer is expanded, resulting in a local decrease in the concentration of the surfactant and an increase in surface tension. The stretched film layer is like a stretchy skin, so that the surface tension reaches the lowest possible level.

Silicone oil defoamers are widely used in the petroleum industry and have become an indispensable and important additive in the production process. Due to the large amount of strong foaming surfactants used in drilling fluids, defoamers are not only indispensable for extracting crude oil, but defoamers must also be used in the post process of crude oil refining. In the crude oil distillation process, silicone oil defoamer is needed. Secondly, the gas removed from the top of the tower or the natural gas from the gas well contains impurities such as H2S and CO2. When ethanolamine or (HOCHMeCH2) 2NH is used as the H2S absorption liquid circulation A large amount of foam will be produced during operation, which will affect the normal production. If silicone oil defoamer is added to the amine solution, high-efficiency continuous operation can be realized.
In the process of separating aromatics (benzene, toluene, xylene, etc.) from crude oil fractions, foams are more or less generated during cracking and hydrogenation reforming reactions. In the hydrocracking process, due to the use of water-diethylene glycol as the solvent, the latter has a strong tendency to foam, and all these processes require the use of defoamers. In addition, in the production of various lubricating oils, due to the addition of oil slick agents, antioxidants, rust inhibitors, solid lubricants and extreme pressure anti-wear agents, they are all surface active substances with varying degrees of It has a foaming effect, so it is necessary to add silicone oil defoamer.