Polycondensation

For many economic sectors, the chemical industry is an indispensable supplier of raw materials. The automotive industry, mechanical engineering, plastics, foodstuff, glass, or building materials industries, for example, are all reliant on substances that are produced by the chemical industry. Plastics or synthetic resins, which are used as the basis for coatings or foams, play by far the most important role. These are employed in a countless number of end products that we use daily. Vacuum technology is crucial for a large part of these applications in the chemical industry.

Application requirements

  • Avoid deposits with special material/coatings or accessories
  • High reliability
  • Exact design of vacuum requirements

How does it work?
Polycondensation is a chain reaction of small molecule compounds, or monomers. The functional groups of the monomers involved generally react by losing water and becoming long-chain molecules, or polymers. Accordingly, only monomers with at least two functional groups can create chains or networks. The product that is formed at the end of the polycondensation depends on the number and types of functional groups of the reacting monomer. During this process, vacuum technology is used in order to prevent unwanted byproducts of polycondensation. In polymer chemistry, polycondensation is one of the most important processes. It is used to produce plastics such as polyethylene terephthalate (PET), polyethylene or polycarbonate in large quantities. Adhesives are also produced with polycondensation as well as brake pads for automobiles.

Vacuum requirements
Vacuum conditions in the medium vacuum range between 1 and 10 mbar are an essential part of the polycondensation process, especially in the production of high-quality plastics. Together with temperature, vacuum technology steers the complete polycondensation process and significantly affects the resulting end-product. Even the smallest fluctuations in pressure during the reaction can lead to damage of the end-product or even render it unusable. The thermal load is reduced by vacuum during the process, especially with temperature-sensitive materials. Without vacuum, the production of certain plastics would not be possible; they would burn.

High-quality plastics such as PET, which the food industry uses to manufacture, among other things, millions of beverage bottles, must fulfill strict quality requirements. Those include a long-life span and low diffusion in order to avoid leakage of carbon dioxide, for example. Vacuum technology guarantees high quality in the production of these plastics.

Product portfolio
In order to generate the necessary vacuum conditions, a multistage combination of Roots and liquid ring pumps are typically utilized. These pumps must be precisely matched to accommodate the special requirements of the specific application. In the production of plastics, products that tend to stick and bake on to things are the order of the day. When configuring a vacuum system, an important task is to ensure that no process components leave deposits in the vacuum pumps. With its extensive product portfolio, Pfeiffer Vacuum offers diverse solutions that can be individually adjusted to suit the requirements of your specific application. The combination of Roots pumps – in normal and gas-cooled versions – with liquid ring pumps has established itself as a reliable solution. Especially with this combination of liquid ring vacuum pump and gas-cooled Roots pump, it contributes significantly to the stability of the process. Besides numerous advantages for the chemical industry, liquid ring vacuum pumps also carry a crucial disadvantage in their use. This is based on their dependence on a liquid, which can lead to the pump not being able to reach the specified pressure or pumping speed in case of contamination or temperature fluctuations. These variations can be compensated by the gas-cooled Roots pump, as this pump principle is self-regulating. This is based largely on the formula: p (pressure) x V (volume) = constant. The ratio between inlet and outlet pressure determines how much cold gas from the heat exchanger is fed into the hot gas inside the pump. In this way, any differential pressure could theoretically be realized. Limiting factors are the size of the heat exchanger and the power of the engine. Both are specifically coordinated for each application.

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