Removal of (Brominated) flame retardants in the dissolution recycling of polystyrene

End-use plastic applications can contain potentially harmful additives such as brominated flame retardants (FRs) that complicate their recycling process. Therefore, effective removal of such substances becomes essential to widen the applicability of the recycling process and increase the quality of the recyclate. To that end, this work proposes a combination of filtration and adsorption as purification technique in the dissolution recycling of polystyrene (PS). Five FRs were selected (i.e., HBCD, TBBPA, DBDPE, TPHP, and PolyFR) with two different solvents (i.e., n-butyl acetate and cyclohexene). Based on their solubility, determined both experimentally and through COSMO-RS modeling, the removal of the FRs was investigated by either filtration or adsorption. Results indicate a near complete removal of undissolved FRs via filtration (i.e., > 99 wt%), while for the dissolved FRs an optimal removal efficiency of 80 to 99 wt% is obtained via adsorption on different types of activated carbon. No significant changes are observed when comparing mixtures without PS to those with 5 wt% PS. However, the strong effect of solvent choice is highlighted, where cyclohexene outperforms n-butyl acetate with differences in removal efficiency as high as 50 wt%. Furthermore, the use of computational modeling tools such as Gaussian16 and COSMO-RS is demonstrated to gain insight into the physicochemical properties of the FRs, which can optimize the purification system, including solvent choice. Finally, applying the proposed treatment process to real-world plastic WEEE samples further proves the effectiveness of the purification, marking a significant step forward in the dissolution recycling of plastics. • New strategy to purify flame retardants (FRs) in the dissolution recycling of PS. • Computational modeling (COSMO-RS) to characterize the solubility behavior of FRs. • Combining filtration and adsorption to remove both undissolved and dissolved FRs. • Achieved removal efficiency of over 99% in filtration and 80%–99% in adsorption. • Successfully applied proposed purification process to real plastic waste samples.