This paper (Paper 360 News) pulping process, in order to obtain white pulp, wood chips will undergo cooking, washing and bleaching process (Figure 1), but in this series of fiber treatment process, consume a lot of water, and also produce a lot of bubbles, so choose the appropriate defoamer is very critical.           
For many years, in order to achieve sustainable development, the paper industry has made a lot of efforts in reducing energy, water and chemical consumption, among which the use of silicone defoamer is one of them. The use efficiency of organosilicon defoamer is high, which can greatly improve the sustainable development index of pulp and paper enterprises.           
Organosilicon is a kind of polymer material, in which polysiloxane is mainly composed of silicon oxygen bond as the skeleton, and its structure is shown in Figure 2. It represents the infinite possibility of polymer. The chain length, three-dimensional structure and the type of organic group connected with silicon atom can affect the properties of silicone.           
Silicone oil used in defoamer is a kind of polymer with high hydrophobicity and very low surface tension. Once polydimethylsiloxane (PDMS, one of organosilicon) is combined with hydrophobic particles (such as precipitated or gasified silica), a more effective defoamer will be formed, and the action flow is shown in Figure 3.           
Sedimentation risk           
Because silicone has hydrophobicity, it has high affinity with any hydrophobic surface. High pH value and high temperature can promote the condensation of residual activity of organosilicon compounds, and promote the formation of gelatin and precipitate.           
The results show that the formation of precipitation is caused by many factors, including the chemical composition of organosilicon defoamer. Sedimentation is a concern of all pulp mills, because the production of sedimentation in the pulping process will increase the cleaning cost of the pulping production line.           
The risk of precipitation formation depends on the composition, quality, dosage and method of use of the antifoam. Therefore, pulp and paper enterprises can reduce the precipitation risk from the following aspects:           
First, reduce the dosage of defoamer properly. It is very important to use effective defoamer, but excessive use will lead to precipitation. Therefore, the dosage of defoamer should be controlled in the pulping process, and should not be used too much.           
Secondly, choose a defoamer with less residual substances, and ensure that the residual substances of the defoamer can not continue to react with the alkaline environment, so as to significantly reduce the precipitation.           
Thirdly, the defoamer compound is emulsified with the correct formula so that it can be dispersed in the foaming black liquor.           
Drainage problem           
In addition to reducing sedimentation, drainage capacity is also critical for defoamers. Strong drainability means that the pulp mill can use less water to clean the black liquor and quickly discharge the water, which is helpful 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 and sustainability of the washing process, which is also an important reason for choosing silicone defoamer.           
Therefore, although organosilicon defoamer has the risk of precipitation, it can reduce the energy, water and chemical consumption through effective use. For paper industry, it is still a sustainable and efficient defoaming technology.