Quantification of p-Cymene and Heptane in a Solvent-Based Green Process of Polystyrene Recycling

Abstract

The development of an economically viable technology for recycling polystyrene (PS) is of crucial importance. Most postconsumer PS feedstocks cannot be handled by mechanical recycling due to severe contamination. A solvent-based process was developed by Polystyvert and uses p-cymene as a solvent to solubilize PS and heptane as an antisolvent to precipitate it. This leads to the production of recycled PS resin of high purity. However, the optimization of this process requires the knowledge of p-cymene, heptane, and PS concentrations at different stages, where the samples of interest can be a viscoelastic paste or a solid (pellets). Here, we present an infrared spectroscopy (IR) method that can rapidly quantify the content of these samples at the plant level. Partial least squares statistical modeling on the first derivative IR spectra allowed the simultaneous quantification of the components with a limit of quantification of 0.5% and 1% for p-cymene and heptane. To illustrate the usefulness of this method, samples from a pilot PS-recycling plant were tested to improve the washing efficiency of the process.

Recyclability of Post-Consumer Polystyrene at Pilot Scale: Comparison of Mechanical and Solvent-Based Recycling Approaches

“…Then, the smaller insoluble particles are removed using a 100 µm pore filter, followed by centrifugation, yielding a purified solution thereafter. In the next step, the PS is precipitated by adding heptane, the non-solvent, at its boiling point temperature (i.e., 98 °C at 1 atm) [ 16 ]. This step permits the recovery of the PS but also removes the soluble contaminants including colorants, oil/greases, and halogenated flame retardants such as hexabromocyclododecane (HBCD).…”