Silicone defoamers: improve slurry performance or bring risks?

For many years, in order to achieve sustainable development, the paper industry has made many efforts to reduce energy, water and chemical consumption, and the use of silicone defoamers is one of them. Organic silicon defoamers have high efficiency and can greatly improve the sustainable development indicators of pulp and paper enterprises.

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Organosilicon is a kind of high molecular polymer material, in which polysiloxane mainly composed of silicon-oxygen bond is used as a skeleton. The structure is shown in FIG. 2. It represents the infinite possibilities of polymers. Changes in the length of the chain, the three-dimensional structure, and the type of organic groups connected to the silicon atom can affect the properties of the silicone.

The silicone oil used in the defoamer is a polymer with high hydrophobicity and extremely low surface tension. Once polydimethylsiloxane (PDMS, a type of silicone) is combined with hydrophobic particles (such as precipitated or fumed silica), a more effective defoamer is formed. The process is shown in Figure 3.

Organic silicon defoamers have been used in the pulping process since the 1980s, solving the problem of low efficiency of traditional organic defoamers. The silicone defoamer can adapt to the pH environment and high temperature conditions, replacing the original defoamer at that time almost overnight. Organic silicon has a simple structure and is easy to use, which has also laid the foundation for most paper mills to develop high-end defoamers.

Although silicone defoamers have many innovative advantages, they also inevitably cause problems, such as the risk of precipitation, residual pollution, emulsification, and scaling.

Sedimentation risk

Because silicone is hydrophobic, it has a high affinity for any hydrophobic surface. The high pH and high temperature of the liquid can promote the condensation of the residual activity of the organic silicon compound, and promote the formation of gels to form precipitates.

Analytical studies have shown that the formation of precipitation is caused by a variety of factors, including the chemical composition of silicone defoamers. Sedimentation is a concern for all pulp mills, as the generation of precipitation during the pulping process will increase the cleaning cost of the pulping line.

The risk of precipitation formation depends on the composition of the defoamer, the quality of the reagents, the dosage and the method of use. Therefore, pulp and paper companies can reduce the risk of precipitation from the following aspects:

First, reduce the amount of defoamer appropriately. It is very important to use an effective defoamer, but excessive use will cause precipitation. Therefore, the dosage of the defoamer should be controlled during the pulping process, and it should not be used too much.

Second, choose an antifoaming agent with few residual substances, and ensure that the remaining substances of this antifoaming agent cannot continue to chemically react with the alkaline environment, thereby significantly reducing the amount of precipitation.

Third, using the correct formulation, the defoamer compound is emulsified so that it can be dispersed in the foamed black liquor.

Drainage problem

In addition to reducing sedimentation, drainage is also critical for defoamers. The strong drainage means that the pulp mill can clean the pulping black liquor with less water and quickly drain the water, which helps to improve the drying efficiency of the pulp in the later stage. This is not only conducive to foam control, but also significantly improves the effectiveness of pulp washing and the sustainability of production, which is also an important reason for selecting silicone defoamers.

Therefore, although the silicone defoamer has the risk of causing precipitation, etc., through effective use, it can reduce pulp energy, water and chemical consumption. For the paper industry, it is still a sustainable and efficient Defoaming technology.


Post time: Dec-12-2019