(456a) A Fast Computational Framework for the Design of Sustainable Solvent-Based Plastic Recycling Processes

Multilayer plastic films are widely used in packaging due to their unique protection properties. These materials can protect products from myriad external factors (e.g., water, oxygen, and light) because they combine various layers of different polymers to leverage their individual functional properties. However, the multi-layer design hinders the ability to mechanically recycle films (Rudolph et al., 2020; Ügdüler et al., 2021). Solvent-based recycling processes have emerged as a promising alternative for recycling multilayer films. One such approach is the Solvent-Targeted Recovery and Precipitation (STRAP^TM) process, which uses sequential solvent washes to selectively dissolve and separate the constituent polymers of multilayer plastic films (Walker et al., 2020). This process dissolves one target polymer in each step; therefore, each selected solvent must have a high solubility for the target component and a low solubility for the rest of the components. For the precipitation step (separation of the dissolved polymer from the solvent), previous studies have reported that temperature-driven precipitation is preferred because it can lower costs and environmental impacts (Sánchez‐Rivera et al., 2021; Munguía-López et al., 2023; Ãœgdüler et al., 2020). Molecular-scale models can help predict temperature-dependent polymer solubilities and screen vast arrays of solvent alternatives (Zhou et al., 2021).

Recently, a joint computational and experimental framework demonstrated the accuracy of these solubility predictions and developed a database for common polymers and several solvents (Zhou et al., 2023). Techno-economic analysis (TEA) and life cycle assessment (LCA) of different STRAP^TM process variations have reported significant differences in the economic and environmental impacts due to changes in solvent selection and separation sequence of the polymer layers (Sánchez-Rivera et al., 2023; Yu et al., 2023). Modern packaging commonly uses complex multilayer films composed of tens to hundreds of individual layers, which can result in a combinatorial explosion in possible separation sequences (Wagner, 2016). Therefore, there is a need for a general framework for solvent-based recycling approaches that can integrate all the process design elements and consider all the feasible scenarios for any design of multilayer plastic film.

In this work, we propose a fast and general computational framework that integrates molecular-scale models, process modeling, TEA, and LCA to provide insights into the sustainable design of solvent-based separation processes. We also aim to identify multilayer film designs that are easier to recycle or have lower impacts. The proposed framework can determine the economic and environmental benefits of different process design scenarios, including all feasible separation sequences, solvents that enable temperature-driven precipitation, and process operating conditions.

Our framework uses a series of computational steps that are summarized as follows. First, it generates all possible separation sequences, which depend on the number of polymers of the given multilayer film. Then, it selects solvent candidates for each sequence using the reported database (Zhou et al., 2023). This step reduces the number of potential sequences to only the feasible sequences based on polymer solubility (this will vary with different film designs). After this, the process simulation and TEA are performed using the open-source software BioSTEAM (Cortes-Pena et al., 2020). For the LCA, we use the open-source software openLCA (Ciroth et al., 2020), the Environmental Footprint and AGRIBALYSE databases, and the Environmental footprint impact assessment method (Colomb et al., 2015; Fazio et al., 2018). Finally, the economic and environmental outputs of all feasible scenarios are stored. The framework can be used to quickly identify the feasibility of recycling different designs of multilayer films or complex multicomponent plastic waste using solvent-based processes. We demonstrate the use of the framework in diverse case studies of industrial interest.

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