Life cycle sustainability assessment of thermo-chemical recycling for future circular plastics
EMBARGOED UNTIL 2027-12-11
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Date
2025
Publication Type
Doctoral Thesis
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EMBARGOED UNTIL 2027-12-11
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Abstract
The global plastics crisis is driven by an increasing polymer demand in a mostly linear system, marked by low recycling rates and widespread waste mismanagement. This high-emitting, fossil-based sector is responsible for substantial greenhouse gas (GHG) emissions globally. Therefore, tackling the plastics problem requires sustainable solutions that address the problem both at the production and end-of-life levels, among which chemical recycling has emerged as a promising way forward.
The present thesis aims to evaluate the environmental and economic potential of chemical recycling technologies in a current and prospective circular economy for plastics. It uses process systems engineering (PSE) tools to model the implementation of these technologies within the plastics value chain at a system level as a means to mitigate the environmental burdens of conventional production pathways. Therefore, this thesis recurrently uses process simulation, techno-economic analysis (TEA), and life cycle assessment (LCA) to conclude on the environmental and economic viability of these technologies within a circular economy. Four studies are hereby presented, progressively increasing the level of carbon circularity within the chemical sector.
A first study aimed to assess the economic and environmental potential of producing H₂ from plastics through gasification. Two routes involving plastics-to-H₂ were simulated in Aspen Plus and compared to 11 alternative production routes, including fossil, biobased, and electrolytic H₂. From the economic viewpoint, we found that plastics-to-H₂ is not competitive with fossil routes, but is cheaper than most electrolytic alternatives. The environmental assessment linked LCA with the planetary boundaries (PBs) framework to quantify the environmental footprint of the 13 assessed H₂ production routes. We found that, although no technology alone could meet the global H₂ demand within the downscaled PBs, environmentally sustainable production can be achieved by deploying an optimized portfolio of H₂ technologies.
Next, we assess the conversion of plastic waste to hydrocarbons as a means to give a second life to the carbon content within plastic materials. Thus, we bridge process simulation, TEA, and LCA with experimental catalyst design to assess the economic and environmental performance of high-density polyethylene hydrogenolysis over a RuNi bimetallic catalyst in a Plastic-to-X concept. We find that the conversion of plastic waste to hydrocarbons can yield GHG emission reductions compared to conventional fuel production and reach competitive costs for certain product distributions—achieved by changing the bimetallic composition in the catalyst. Results of this study highlight the relevance of coupling experimental innovation with PSE tools to help establish targets for future catalyst development.
Circular solutions are, however, preferred in the scope of plastic waste management, as they allow the carbon content to stay within the plastics loop, thus reducing fossil dependence and GHG emissions linked to production and end-of-life operations. Therefore, we next deploy high-readiness level technologies to convert waste low-density polyethylene to methanol and subsequently to ethylene in a circular system. We perform TEA and prospective LCA to determine the techno-economic and environmental potential of this circular production route (CPR) compared to the conventional, mostly linear route in 2020 and 2050. We found that CPR could enable significant impact reductions, notably in 2050, assuming a low-carbon electricity mix based on renewables. However, burden-shifting to other impact categories occurs in the shift from linear to circular. Nevertheless, this solution could significantly support the development of a sustainable circular plastics economy, namely, as ethylene obtained in the CPR is significantly cheaper than its green analogs.
Finally, in the last chapter of this thesis, we combined material flow analysis with LCA and externalities monetization to quantify the true cost of plastics in 14 selected European countries. We found that consuming plastics in the current, mainly linear fossil economy comes with hidden costs two to three times higher than their market price, with externalities being mainly driven by plastics’ impacts on global warming and resource scarcity. Deploying chemical recycling technologies that enable monomer recovery can substantially lower these impacts, decreasing fossil dependence and significantly reducing the external cost of plastics. Therefore, we performed a prospective LCA to quantify the cumulative emissions and external cost savings that can be achieved by progressively implementing chemical recycling in the 14 selected countries until 2050. We found that a faster implementation yields substantial cost savings in the range of trillions of euros while avoiding GHG emissions.
Overall, this doctoral thesis provides a comprehensive understanding of the environmental and economic potential of deploying chemical recycling to close the carbon loop for plastics. The results discussed here provide a scientific basis and valuable insights to support policymakers, industries, and researchers in shaping a sustainable circular economy for future plastics.
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Examiner: Guillén Gosálbez, Gonzalo
Examiner : Pérez Fortes, Mar
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ETH Zurich
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Subject
Chemical recycling; Plastics recycling; Life cycle assessment; Techno-economic assessment; Prospective life cycle assessment; Material flow analysis; Externalities; Circular economy; Process simulation
Organisational unit
09655 - Guillén Gosálbez, Gonzalo / Guillén Gosálbez, Gonzalo
Notes
Funding
180544 - NCCR Catalysis (phase I) (SNF)