(354j) Multi-Scale Regionalized Assessment of the Absolute Environmental Potential of Circular Polymers in Europe

The global demand for polymers has been increasing, notably in the plastic packaging sector, representing 31% of the annual plastic consumption in 2019 [1]. The sector heavily depends on fossil feedstock, with most polymers deriving from refinery operations, particularly the business-as-usual (BAU) technology, naphtha steam cracking [2]. Moreover, this industry follows a mostly linear economy model, with only a small fraction of the total plastic waste generated being recycled (19.5% in 2015) [3]. For instance, 95% of the value of plastic packaging is lost after their first use. They have a particularly short life span and generate substantial amounts of waste globally, i.e., 140 million tons (46.7% of the global plastic waste generation) in 2015 [2,3]. The need for a circular economy of polymers has motivated the development and implementation of new recycling technologies to extend the lifetime of materials and decrease the detrimental environmental effects caused by mismanaged plastic waste [4]. Schwarz et al. provided insights into the technology readiness level (TRL) of 12 recycling pathways and their respective carbon footprint [5]. Their results showcase the potential of deploying chemical recycling technologies (i.e., pyrolysis and gasification) for monomer production. They present lower emissions than waste-to-energy alternatives and can compete with mechanical recycling for most polymer types.

Although recycling technologies exist, waste collection and sorting are still challenging steps in the implementation of a circular economy of polymers. Sorting efficiencies and recovery rates depend heavily on polymer type, and pure streams of waste polymers can only be obtained after significant sorting efforts [6]. Additionally, despite the potential of deploying high TRL technologies to produce high-quality secondary materials, only a small fraction of the total European plastic consumption is covered by secondary plastics (5.5%), as shown by Hsu et al. [7]. This indicates that, despite the increasing recycling rates reported by European countries [8], the local polymer economy is still very linear.

Our study aims to quantify, for the first time, the current environmental impact of the polymer economy in European countries by combining process simulation with a regionalized life cycle assessment (LCA) analysis, thereby covering the multi-scale nature of the problem. The study is based on material flows of four main polymers used in plastic packaging, i.e., polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET). The assessment considers the production, consumption and waste management of polymers in EU countries. Furthermore, we compare the country-wise BAU scenarios to an alternative chemical recycling route, which produces secondary polymers from waste in a four-step pathway with three intermediate products (i.e., syngas, methanol, and olefins).

The chemical recycling pathway consists of a methanol-from-waste polymer plant coupled with a methanol-to-olefins unit, which in turn provides olefins as raw materials for the polymerization step to generate secondary polymers that can be re-implemented in the economy. The methanol-from-waste polymer process is simulated in Aspen Plus v12, while the two adjacent units are taken from literature, as they are well implemented in the chemical industry. The simulated methanol production occurs in two steps: first, a mixed-polymers stream reacts with steam in a gasifier to produce syngas, which then converts to methanol in a catalytic reactor. Carbon capture and storage (CCS) is deployed to minimize the process’ CO₂ emissions. Data from the mass and energy balances are used to build the life cycle inventory of methanol-from-polymers.

To quantify the environmental impacts of the country-specific BAU system and the alternative circular model deploying chemical recycling, we perform a LCA for regional systems. This LCA bridges the process and technosphere levels by connecting the foreground data taken from the process model with the background data of the surrounding processes in different EU locations. The assessment is implemented in Brightway2 v2.4.2 using data from Ecoinvent 3.8, following a cradle-to-grave approach. The LCA method employed is based on the absolute environmental sustainability assessment (AESA) framework [9], which relies on the planetary boundaries (PBs) framework developed by Rockström et al. [10] and Steffen et al. [11]. This approach considers sustainability thresholds for different Earth-system processes beyond which technologies can be deemed environmentally unsustainable. For regional systems, the environmental impacts should be calculated according to the resource availability of the specific locations and the PBs adapted to local scales [12]. Thus, we here employ characterization factors described by Bjørn et al. [13], Pierrat et al. [14], and Vea et al. [15] to quantify the impacts of the studied systems on their respective locations. Moreover, we apply different downscaling methods to assess the environmental sustainability levels of the studied systems against regional boundaries defined for freshwater use, biogeochemical flows of nitrogen, and climate change.

Along these lines, our work combines process simulation with regional AESA to provide an overview of the current environmental performance of the BAU scenario of the country-specific polymer economy and the proposed circular solution. Preliminary results showcase that the BAU systems of the European countries transgress at least one of the regional boundaries and, therefore, can be deemed environmentally unsustainable. Moreover, the implementation of the proposed circular alternative can ease reducing the pressure on the studied Earth-system processes and contribute to a greener polymer economy in Europe. On the same note, the world demand for plastics will likely increase over time, accentuating the need for effective waste treatment methods. The proposed process serves as a possible recycling path to polymers that can be incorporated to satisfy both demands simultaneously.

Acknowledgments: This research is a part of the National Center of Competence and Research NCCR Catalysis, funded by the Swiss National Science Foundation.

References

1. Statista, Distribution of plastic consumption worldwide in 2019, by application, (2023), https://www.statista.com/topics/10136/plastic-packaging-industry-worldwide/ [last accessed: 02.04.2023]
2. Ellen MacArthur Foundation, The New Plastics Economy - Rethinking the future of Plastics, (2016)
3. Geyer et al., Production, use, and fate of all plastics ever made, Science Advances, 3(7), (2017)
4. Ellen MacArthur Foundation, Towards the circular economy, (2013)
5. Schwarz et al., Plastic recycling in a circular economy; determining environmental performance through an LCA matrix model approach, Waste Management, 121, 331-342, (2021)
6. Kleinhans et al., Development and application of a predictive modelling approach for household packaging waste flows in sorting facilities, Waste Management, 120, 290-302, (2021)
7. T. Hsu et al., How circular are plastics in the EU?: MFA of plastics in the EU and pathways to circularity, Cleaner Environmental Systems, 2, (2021)
8. Plastics Europe, Plastics – The Facts 2022, (2022)
9. Bjørn et al., A Framework for Development and Communication of Absolute Environmental Sustainability Assessment Method, Journal of Industrial Ecology, 23, 4, (2019)
10. Rockström et al., Planetary Boundaries: Exploring the Safe Operating Space for Humanity, Ecology and Society, 14, 2, (2009)
11. Steffen et al., Planetary boundaries: Guiding human development on a changing planet, Science, 347, 6223, (2015)
12. Ryberg et al., Downscaling the planetary boundaries in absolute environmental sustainability assessments – A review, Journal of Cleaner Production, 276, (2020)
13. Bjørn et al., A planetary boundary-based method for freshwater use in life cycle assessment: Development and application to a tomato production case study, Ecological Indicators, 110, (2020)
14. Pierrat et al., Multicompartment Depletion Factors for Water Consumption on a Global Scale, Environmental Science & Technology, 57, 10, 4318–4331, (2023)
15. B. Vea et al., Spatially differentiated marine eutrophication method for absolute environmental sustainability assessments, Science of the Total Environment, 843, (2022)