(576f) Technoeconomic Analysis of Plastics Recycling Process Via Mechanocatalytic Reactions

Conventional plastic recycling pathways such as pyrolysis and solvolysis involve high energy consumption, use of chemicals or solvents and are capital intensive. Such factors currently make recycling economically not viable [1, 2]. Therefore, creating new depolymerization processes to recycle and reuse plastics is crucial in implementing sustainable practices and reducing negative environmental effects. One promising route is the mechanochemical depolymerization of plastic waste wherein the polymer chain is deconstructed by the application of mechanical energy which then activates the chemical reaction. The mechanocatalytic hydrolysis reactions are performed in ball-mill reactors that are known to have the potential to process polymers in the solid state to valuable plastic monomers in a sustainable and economical way[3, 4]. Coupled with the reactor unit, several purification steps are necessary to purify the resulting output stream exiting the ball-mill reactor. To address this challenge, we provide an end-to-end approach for developing a complete process flowsheet for all the unit operations required to transform model polymer feeds (e.g., PET) in powder form to monomers. The unit operations incorporated in the depolymerization process are reactive crystallization, solid-liquid extraction, distillation, and solid filters [5].

In this talk, we will present the model equations, connecting streams and recycle streams incorporated within the integrated model-based flowsheet. Conventional units such as distillation units and solid filters are integrated with custom-made models developed for the ball-mill reactor and reactive crystallization [4-6]. Results of a comprehensive technoeconomic and energy analysis will be presented for each individual unit, and cost-energy trade-offs will be discussed. Finally, sensitivity analysis [7] studies will be performed with respect to the overall achieved yield of the monomer as well as the total amount of raw materials utilized, to identify process degrees-of-freedom that significantly affect cost and energy metrics.

Citations

[1] I. Vollmer et al., "Beyond Mechanical Recycling: Giving New Life to Plastic Waste," Angew Chem Int Ed Engl, vol. 59, no. 36, pp. 15402-15423, Sep 1 2020, doi: 10.1002/anie.201915651.

[2] R. Meys, F. Frick, S. Westhues, A. Sternberg, J. Klankermayer, and A. Bardow, "Towards a circular economy for plastic packaging wastes – the environmental potential of chemical recycling," Resources, Conservation and Recycling, vol. 162, 2020, doi: 10.1016/j.resconrec.2020.105010.

[3] V. Štrukil, "Highly Efficient Solid‐State Hydrolysis of Waste Polyethylene Terephthalate by Mechanochemical Milling and Vapor‐Assisted Aging," ChemSusChem, vol. 14, no. 1, pp. 330-338, 2021.

[4] J. Lu, S. Borjigin, S. Kumagai, T. Kameda, Y. Saito, and T. Yoshioka, "Practical dechlorination of polyvinyl chloride wastes in NaOH/ethylene glycol using an up-scale ball mill reactor and validation by discrete element method simulations," Waste Management, vol. 99, pp. 31-41, 2019/11/01/ 2019, doi: https://doi.org/10.1016/j.wasman.2019.08.034.

[5] M. A. McDonald et al., "Reactive crystallization: a review," Reaction Chemistry & Engineering, vol. 6, no. 3, pp. 364-400, 2021.

[6] N. Metta, M. Ierapetritou, and R. Ramachandran, "A multiscale DEM-PBM approach for a continuous comilling process using a mechanistically developed breakage kernel," Chemical Engineering Science, vol. 178, pp. 211-221, 2018/03/16/ 2018, doi: https://doi.org/10.1016/j.ces.2017.12.016.

[7] A. Saltelli, M. Ratto, S. Tarantola, and F. Campolongo, "Sensitivity analysis for chemical models," Chemical reviews, vol. 105, no. 7, pp. 2811-2828, 2005.