(161f) Optimized Designs and Techno-Economic Evaluation for Solvent-Based Separation of Multi-Layer Plastic Films

Multilayer plastics used in food packaging incorporate several layers of polymers to achieve unique food-preserving properties that increase their shelf-life and facilitate food transport [1]. The production of multilayer plastics generates large amounts of plastic waste known as post industrial waste (PIW) that cannot be mechanically recycled [2,3]. Recently, the solvent-targeted recovery and precipitation (STRAP) process was developed to enable the separation and recycling of the constituent polymers of multilayer plastic films [4]. Preliminary techno-economic analysis and life-cycle assessments of conceptual models suggest that STRAP recycling may be both economically competitive and more environmentally favorable compared to virgin production of multilayer plastic films from petroleum [5,6]. However, existing configuration models for the STRAP recycling process have not yet been optimized for solvent usage and recovery, have yet to consider potential mass transfer limitations of scale-up, and their potential economic and environmental sustainability have yet to be compared against other end-of-life disposal methods.

Currently, three STRAP approaches exist: antisolvent-assisted precipitation (STRAP-A) [4], low-temperature precipitation (STRAP-B) [5], and a mixed approach that uses either antisolvent-assisted or low temperature precipitation (STRAP-C) for the separation of a wider range of multilayer plastics [5]. The STRAP-A process results in greater capital and utility expenditures due to the need to recover the antisolvent from the solvent using distillation columns. Although STRAP-B avoids the need for an antisolvent, some plastic layers cannot be precipitated by only reducing temperature and may require a specialized antisolvent. Therefore, there is a need to optimize STRAP configurations by balancing the use and degree of purification of antisolvents and by introducing heat integration strategies to minimize utility consumption. The main assumption driving uncertainty in the potential financial and environmental sustainability of the STRAP process is solvent requirement. Existing models of the STRAP process, implementing a consecutive train of single-stage dissolution and precipitation tanks, may be subject to mixing issues at scale-up that need to be compensated by higher solvent recirculation [7]. Although assumptions on solubilities are based on lab-scale experimental data and rigorous molecular dynamic and statistical mechanical simulations (e.g., COSMO-RS), rigorous mass transfer modeling is required to assess the implications of scale-up and whether alternative configurations that maximize concentration gradients would be required.

In this work, we present a design framework (implemented in BioSTEAM, an open-source process simulation library in Python) to optimize designs that balance solvent separation and purity in order to minimize environmental impact and maximize profitability. The framework implements a new configuration that maximizes concentration gradients for dissolution using fixed-bed columns under pseudo steady-state operation [8]. Mass transfer modeling for dissolution and precipitation of multilayer plastics are performed to assess the performance of this new configuration against conventional dissolution tanks. The proposed configuration also implements industry-relevant methods for utility savings, including a heat exchanger network and multi-effect evaporation for the separation of solvents using BioSTEAM [9,10]. The optimization framework developed in this study may be leveraged in future studies to compare the potential sustainability of STRAP configurations against other end-of-life disposal methods such as incineration, landfilling, and other solvent-based recycling processes.

(1) Kaiser, K.; Schmid, M.; Schlummer, M. Recycling of Polymer-Based Multilayer Packaging: A Review. Recycling 2017, 3 (1), 1.

(2) Billiet, S.; Trenor, S. R. 100th Anniversary of Macromolecular Science Viewpoint: Needs for Plastics Packaging Circularity. ACS Macro Lett. 2020, 9 (9), 1376–1390. https://doi.org/10.1021/acsmacrolett.0c00437.

(3) Niaounakis, M. Recycling of Flexible Plastic Packaging; William Andrew, 2019.

(4) Walker, T. W.; Frelka, N.; Shen, Z.; Chew, A. K.; Banick, J.; Grey, S.; Kim, M. S.; Dumesic, J. A.; Van Lehn, R. C.; Huber, G. W. Recycling of Multilayer Plastic Packaging Materials by Solvent-Targeted Recovery and Precipitation. Sci. Adv. 2020, 6 (47), eaba7599. https://doi.org/10.1126/sciadv.aba7599.

(5) Sánchez‐Rivera, K. L.; Zhou, P.; Kim, M. S.; González Chávez, L. D.; Grey, S.; Nelson, K.; Wang, S.; Hermans, I.; Zavala, V. M.; Van Lehn, R. C.; Huber, G. W. Reducing Antisolvent Use in the STRAP Process by Enabling a Temperature‐Controlled Polymer Dissolution and Precipitation for the Recycling of Multilayer Plastic Films. ChemSusChem 2021, 14 (19), 4317–4329. https://doi.org/10.1002/cssc.202101128.

(6) Munguía-López, A. del C.; Göreke, D.; Sánchez-Rivera, K. L.; Aguirre-Villegas, H. A.; Avraamidou, S.; Huber, G. W.; Zavala, V. M. Quantifying the Environmental Benefits of a Solvent-Based Separation Process for Multilayer Plastic Films. Green Chem. 2023, 25 (4), 1611–1625. https://doi.org/10.1039/D2GC04262B.

(7) Hörmann, T.; Suzzi, D.; Khinast, J. G. Mixing and Dissolution Processes of Pharmaceutical Bulk Materials in Stirred Tanks: Experimental and Numerical Investigations. Ind. Eng. Chem. Res. 2011, 50 (21), 12011–12025. https://doi.org/10.1021/ie2002523.

(8) Gabelman, A. Gabelman Process Solutions, LLC. Adsorption Basics Part 1. American Institute of Chemical Engineers (AIChE), Chemical Engineering Progress (CEP), Back to Basics, 48-53, 2017.

(9) Cortes-Peña, Y.; Kumar, D.; Singh, V.; Guest, J. S. BioSTEAM: A Fast and Flexible Platform for the Design, Simulation, and Techno-Economic Analysis of Biorefineries under Uncertainty. ACS Sustainable Chem. Eng. 2020, 8 (8), 3302–3310. https://doi.org/10.1021/acssuschemeng.9b07040.

(10)Cortés-Peña, Y. Thermosteam: BioSTEAM’s Premier Thermodynamic Engine. JOSS 2020, 5 (56), 2814. https://doi.org/10.21105/joss.02814.