What is a defoamer?
Defoamer is a wide variety of industrial application auxiliaries, which are widely used in various fields of the national economy. However, there are many different and ever-changing occasions for solving the problem of defoaming. In order to solve the problem of defoaming in many systems, various types of defoaming and dosage forms are needed. According to the raw material source and raw material structure of the antifoaming agent, it can be divided into the following three categories:
1. Natural product-based products, commonly known as vegetable oils and mineral oils, and complexes. Due to the large number of sources and low prices, many varieties are still in use today;
2. Polyether-based defoamers based on petrochemical products, commonly known as polyoxyethylene, polyoxypropylene polymers or block copolymers of both, due to the development of the petrochemical industry, since the 1960s a large type of defoamer;
3. Silicone defoamer with polysiloxane as main raw material is widely used in various fields because of its excellent surface properties.
For the particularity of the PVC production industry, defoamers have excellent application performance at all stages of the PVC production process.
Application of antifoaming agent in the process of preparing dispersion
The first stage of PVC production is mainly the preparation of dispersing agents, which must be formulated when using HPMC and PVa as suspending agents. The mixture is stirred during the preparation, so the solution often foams. Causes the spillage of these foams and the loss of dispersants. It is also impossible to observe the height of the liquid level, and the defoaming can be used to eliminate the above foam. The block polyether antifoaming agent can be well dispersed in a suspension system with HPMC and PVa as dispersing agents, does not damage the stability of the system, and has good defoaming and antifoaming properties.
Application of defoamer in polymerization process
In the polymerization reaction, since the polymerization system uses HPMC and PVa as dispersants, these dispersants have a certain surface tension. Foaming also occurs as the agitation in the polymerization vessel proceeds, and these foams may be referred to as "wet bubbles." The "wet foam" is generated above the liquid level of the reaction system, causing VCM gas phase polymerization to cause the inner wall of the kettle above the liquid level to form a sticking kettle, and the adhesive material is dropped into the kettle, so that the black and yellow spots of the resin are increased. Affect the quality of the resin product. In the kettle type with a reflux condenser, in order to increase the cooling effect, a large amount of VCM gas phase passes through the liquid layer to the condenser in the middle of the reaction, and then condenses into a liquid state by the condenser, and returns to the reaction system. During this process, the VCM vapor phase volatilizes, producing a large amount of foam. This process often occurs during periods of intense reaction, and these bubbles can be called "dry bubbles." The "dry foam" and "wet foam" produced in the reaction system need to be eliminated by using an antifoaming agent. Since the suspension reaction solution is an unstable system, it is reasonable to choose the type of defoamer. It will have a greater impact on the entire reaction process. In addition, the method of adding antifoaming agent should also be seriously considered. Generally, it should be added by continuous dropping after 2 hours from the start of the reaction, and the defoaming agent should be properly diluted. Because a high concentration defoaming agent is added to the reaction system, it is possible to locally destroy the suspension system in the reaction vessel, resulting in coarse particles, which affect the product quality of the resin. The use of defoamers is a good choice, the product has excellent dilution stability, and the defoaming speed is fast, and the suspension has good compatibility.
Application of defoamer in discharging
After the end of the polymerization reaction, the treated slurry is discharged to the discharged sludge, and the unreacted VCM is discharged. When the unreacted gas is discharged, a large amount of foam is generated in the discharge tank, and these foams are discharged along with the unreacted gas, which often causes problems such as blockage of pipes and waste of materials, and the use of an antifoaming agent can eliminate these foams. The defoaming agent used in this process is generally added at the same time as the terminator. The selected defoamer should have a wide pH range, good defoaming performance and optimum antifoam performance, because for most SMEs, the recovered VCM monomer is not recycled by the stripper and is recycled. The defoaming agent is no longer added during the VCM monomer process, and the recovery process takes a considerable period of time. Therefore, the antifoaming performance of the defoaming agent directly affects the speed and time of recovering the VCM monomer. Defoamers are used in this stage of production. It exhibits good defoaming performance and antifoaming performance, and can effectively eliminate and inhibit the generation of foam throughout the recycling process.
Application of defoamer in stripper operation
For companies that use a stripper for VCM monomer recovery, the stripping of the slurry VCM is carried out at the end of the reaction. Since it is generally carried out in a stripping column, the slurry flows from the top of the column to the bottom of the column, and the steam is sufficiently heat-exchanged from the bottom of the column to the slurry. In the process, the slurry on each layer of the column produces foam. . These foams will seriously hinder the volatilization of the slurry VCM and increase the power to remove the VCM. The long time of the foam remaining on the tower wall will also produce "black and yellow particles", which will affect the product quality. In order to eliminate the generation of foam during the stripping operation. An antifoaming agent is required. The defoaming agent should be properly diluted and uniformly added to the stripping equipment. Because of the addition of the high concentration defoaming agent, it is possible to excessively adsorb the PVC particles, affecting the recovery and post-treatment of the VCM monomer. Therefore, the antifoaming agent is diluted and continuously added dropwise. It can eliminate a lot of foam generated during stripping, increase the recovery speed and speed up the recycling process. The excellent performance of the defoamer has been recognized by users.
Application of Defoamer in the Production of PVC Paste Resin
In addition to the ordinary powdery PVC resin produced by the suspension method. Another large variety is PVC paste resin, which is mainly used in synthetic leather and latex products. The use of defoamers should not affect the product quality and post-processing properties of the resin. Defoamers are specially used in the production of paste resins.
The above is the application of defoamer in PVC production.
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