In silico COSMO-RS predictive screening of ionic liquids for the dissolution of plastic

Abstract

Plastic waste is currently produced at an alarmingly high rate, nearing 400 Mt per year. The accumulation of plastics in the environment is growing rapidly, yet our knowledge of their persistence is very limited. Efficient and affordable dissolution and chemical upcycling of plastic wastes are also a significant hurdle in the conversion of plastic polymers to value-added chemicals, and finding a suitable solvent is also a major concern. Ionic liquids (ILs) have recently demonstrated their ability to dissolve and convert polyethylene terephthalate (PET) into valuable products. However, identifying an optimal IL from the large number of anion and cation combinations possible is quite challenging. To address this issue, the COSMO-RS (COnductor-like Screening MOdel for Real Solvents) model has emerged as a reliable computational tool that can screen numerous ILs based on the different thermodynamic properties that are needed for polymer dissolution. The current study demonstrates the dissolution behavior of plastic wastes in ILs using the COSMO-RS model. In this study, 99 cations and 95 anions were chosen and combined to form 9405 ILs, which were evaluated by predicting logarithmic activity coefficient (ln(γ)) and excess enthalpies (H^E) of typical plastic wastes (PET, polystyrene, polypropylene, and polyvinylchloride). Based on the COSMO-RS predicted thermodynamic properties (ln(γ) and H^E), anions such as acetate, formate, glycinate, and N-methylcarbamate in combination with the cations like superbase, ammonium, and pyrrolidinium are predicted to be suitable solvents for plastic dissolution. The predicted ln(γ) and H^E results are further validated with the experimental results and the predicted thermodynamic properties and experimental results are in good alignment. An excess enthalpy calculation demonstrated that strong hydrogen bond interactions between the polymer and the IL are vital factors for efficient dissolution to occur, with the anion and the cation of the IL having a similar effect on the process.