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How to Choose Defoamer for Papermaking and Pulping
Mar 06, 2024Papermaking and pulping defoaming agent is a new type of papermaking and pulping silicone-specific defoaming agent that is composed of special silicone polyether as the main material and good dispersion additives. Its characteristics are high temperature resistance and strong alkali resistance, and it can quickly diffuse bubbles and eliminate foam under high temperature and strong alkali conditions.
Defoaming agent selection method
1. The defoaming agent is insoluble or difficult to dissolve in the foaming liquid.
In order to burst the foam, the defoaming agent should be concentrated on the bubble film. In the case of foam breakers, it should be concentrated in an instant, and in the case of foam suppressors, it should always be maintained in this state. Therefore, the defoaming agent is in a supersaturated state in the foaming liquid. Only insoluble or poorly soluble defoaming agents can easily reach the supersaturated state. Only when it is insoluble or difficult to dissolve can it easily gather at the air-liquid interface, be easily concentrated on the bubble membrane, and function at a lower concentration. For defoaming agents used in water systems, the molecules of the active ingredients must be strongly hydrophobic and weakly hydrophilic, with an HLB value in the range of 1.5–3 to be effective.
2. The surface tension is lower than that of the foaming liquid.
Only when the intermolecular force of the defoaming agent is small and the surface tension is lower than that of the foaming liquid can the defoaming agent particles be able to immerse and expand on the bubble film. It is worth noting that the surface tension of the foaming liquid is not the surface tension of the solution, but the surface tension of the foaming solution.
3. It has a certain degree of affinity with the foaming liquid.
Since the defoaming process is actually a competition between foam collapse speed and foam generation speed, the defoaming agent must be quickly dispersed in the foaming liquid in order to quickly play a role in a wider range of the foaming liquid. To make the defoaming agent diffuse quickly, the active ingredient of the defoaming agent must have a certain degree of affinity with the foaming liquid. If the active ingredient of the defoaming agent is too close to the foaming liquid, it will dissolve; if it is too sparse, it will be difficult to disperse. Only when the distance is appropriate can the effect be good.
The papermaking process is divided into three main processes: pulping, papermaking, and coating. Since the pulping process requires the use of various cooking aids, such as anthraquinone, alkali sulfide, and sodium hydroxide, the washing process requires the use of washing aids (conducive to the separation between cooking waste liquid and plant fiber), such as nonylphenol polyoxyethylene ether (10–12) and sodium alkyl benzene sulfonate, plus pectin, lignin, and other substances present in the plant itself, thus causing a lot of foam to appear during vacuum washing or pressure washing.
If these foams are not eliminated, the operating efficiency of the pulp washer will be greatly reduced. In order to solve this problem, pulp mills must use defoaming agents.
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