Chemistry | Chemical Analytics | Reaction Monitoring in the Production of Polysterene
Polystyrene can be found in many areas of everyday life
Polystyrene is a widely used, low-cost plastic and highly versatile. Depending on the type of production, a distinction is made between fine-pored extruded polystyrene (XPS) and the more coarse-pored expanded polystyrene (EPS), which characteristically consists of small plastic beads that are fused together. Due to its technical properties such as low weight, stiffness and formability, expanded polystyrene can be used in a variety of applications, for example as a shock-absorbing packaging material or for thermal insulation for buildings.
During the production process of expandable polystyrene beads, continuous monitoring of the polymerization reaction is essential for the Italian chemical manufacturer »Versalis S.p.A« in order to obtain a high-quality product and high yield and to ensure optimal control of the production line. Important parameters that must be controlled during the suspension polymerization of EPS are the measurement of the polymer particles that form and grow during the reaction, as well as the degree of conversion of the styrene monomer into the polymer.
Precise endpoint determination during the polymerization reaction of expandable polystyrene
Continuous monitoring of critical parameters during the production of polystyrene beads
Industrial Production of Polymers
Production of Plastics
Process Analytical Technology (PAT)
Polystyrene is an amorphous, transparent thermoplastic and is produced in two process steps in chain polymerization from the monomer styrene. During these two process steps, the particle size and the progress of the conversion of the styrene monomer must be continuously monitored. The degree of conversion is crucial for determining the end point of the reaction. The conversion reaction of the monomers is very fast. The reaction must therefore be monitored very accurately and in real time.
If the end point of the polymerization is not detected in time, it can happen that the styrene monomers, which develop into pellet-like beads in the course of the reaction, clump together to form a large ball and cause a blockage at the reactor outlet. In the worst case, this large ball causes the blockage of the entire plant.
The current procedure involves manual sampling and estimation of the particle size of these beads in front of a light beam. This procedure requires a great deal of expertise and is difficult to reproduce.
For a more precise and efficient monitoring of these control parameters in the heterogeneous phase, a method is needed that is reproducible, can ensure the monitoring of the relevant parameters continuously and does not require frequent maintenance interventions at the plant. The measuring technology used must not interfere with the fluid dynamics of the reactor, not be susceptible to contamination and must be ATEX Zone 2 IIB T3 compatible.
During the polymerisation the monomer is in a first step mixed with additives. In the second reactor, the conversion process from styrene to polystyrene occurs. During the polymerization process, gas inclusions are formed. With the aid of pentane as a blowing agent and pure steam, the polystyrene granulate expands. The expansion of the gas can be used for further processing of the granulate. The beads expand up to 50 times their own volume. In this final step, the polystyrene granules can be formed into any geometric shape.
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