Cecilia Salah


Last Name

Salah

First Name

Cecilia

ORCID

0000-0002-3376-706X

Organisational unit

09655 - Guillén Gosálbez, Gonzalo / Guillén Gosálbez, Gonzalo

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2022 - 20256
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Publications 1 - 6 of 6
  • Assessing the Environmental Potential of Hydrogen from Waste Polyethylene
    Item type: Conference Paper
    Salah, Cecilia; Cobo Gutiérrez, Selene; Guillén Gosálbez, Gonzalo (2022)
    Computer Aided Chemical Engineering ~ 14th International Symposium on Process Systems Engineering
    In 2019, nearly 370 million tonnes of waste plastic were generated, an amount that has been steadily increasing over the years. Here we assess hydrogen production from waste polyethylene in the context of a circular economy of plastics. Based on the gasification of polyethylene waste (wPG), we performed a Life Cycle Assessment (LCA) study following the ReCiPe method. Our results show that the wPG process coupled with carbon capture and storage (CCS) performs very well environmentally relative to other H2 production routes, outperforming steam methane reforming (SMR) with and without CCS and biomass gasification (BG) in the three endpoint impact categories.
  • Polyethylene hydrogenolysis to liquid products over bimetallic catalysts with favorable environmental footprint and economics
    Item type: Journal Article
    Nogueroles Langa, Iris; Ge, Yuzhen; Salah, Cecilia; et al. (2025)
    Nature Communications
    Assessing the sustainability of plastic chemical recycling requires realistic feedstocks and catalysts designed within sustainability-led frameworks (Plastic-to-X). We link catalyst design and systems analysis to study hydrogenolysis of high-density polyethylene (virgin and bottle caps; Mw = 100–200 kDa). We report Ru–Ni alloy nanoparticles (3–4 nm) supported on titania that yield up to 55% liquid C6–C45 products under optimized conditions, whereas monometallic Ru produces virtually no liquids Operando spectroscopy and simulations reveal structure sensitivity: backbone scission follows dehydrogenation and hydrogenation cycles at defective alloy sites formed in situ. Integrating these mechanistic insights with life cycle and techno-economic analyses indicates profitable processing of plastic caps over the optimal catalyst (2.5 wt% Ru, 5 wt% Ni) with substantially lower CO2 emissions even when using green H2. Furthermore, within the Plastic-to-X framework, we identify a minimum average chain length threshold of C11 for product distributions as a critical design metric to reconcile environmental and economic objectives.
  • Environmental Benefits of Circular Ethylene Production from Polymer Waste
    Item type: Journal Article
    Salah, Cecilia; Istrate, Robert; Bjørn, Anders; et al. (2024)
    ACS Sustainable Chemistry & Engineering
    The linear nature of the current plastics economy and increasing demand for polymers poses a pressing global problem. In this work, we explore the environmental and economic performance of a circular alternative for polymer production through chemical plastic recycling following the waste-to-methanol-to-olefins (WMO) route. We assess the life-cycle environmental impacts and techno-economic feasibility of this novel circular production route (CPR) in 2020 and 2050, and compare them to the existing linear production route (LPR), deploying naphtha steam cracking for olefin production, and a mix of landfill and incineration as end-of-life treatment. Our results showcase that CPR could enable significant impact reductions, notably in 2050 assuming a low-carbon electricity mix based on renewables. However, the shift from linear to circular comes with burden-shifting, increasing the impacts relative to LPR on five environmental indicators in 2020 (i.e., terrestrial and freshwater eutrophication, particulate matter formation, acidification, and metal/mineral resources use). From the techno-economic viewpoint, we found that ethylene from waste polymers could become competitive with fossil ethylene when deployed at large scale. Moreover, it is significantly cheaper than its green analogs, which deploy methanol-to-olefins with green methanol from captured CO2 and electrolytic H2, showcasing the potential of implementing high-readiness level technologies to close the loop for polymers.
  • Environmental Sustainability Assessment of Hydrogen from Waste Polymers
    Item type: Journal Article
    Salah, Cecilia; Cobo Gutiérrez, Selene; Pérez-Ramírez, Javier; et al. (2023)
    ACS Sustainable Chemistry & Engineering
    The rising demand for single-use polymers calls for alternative waste treatment pathways to ensure a circular economy. Here, we explore hydrogen production from waste polymer gasification (wPG) to reduce the environmental impacts of plastic incineration and landfilling while generating a valuable product. We assess the carbon footprint of 13 H2 production routes and their environmental sustainability relative to the planetary boundaries (PBs) defined for seven Earth-system processes, covering H2 from waste polymers (wP; polyethylene, polypropylene, and polystyrene), and a set of benchmark technologies including H2 from natural gas, biomass, and water splitting. Our results show that wPG coupled with carbon capture and storage (CCS) could reduce the climate change impact of fossil-based and most electrolytic routes. Moreover, due to the high price of wP, wPG would be more expensive than its fossil- and biomass-based analogs but cheaper than the electrolytic routes. The absolute environmental sustainability assessment (AESA) revealed that all pathways would transgress at least one downscaled PB, yet a portfolio was identified where the current global H2 demand could be met without transgressing any of the studied PBs, which indicates that H2 from plastics could play a role until chemical recycling technologies reach a sufficient maturity level.
  • The role of chemical and solvent-based recycling within a sustainable circular economy for plastics
    Item type: Journal Article
    Klotz, Magdalena; Oberschelp, Christopher; Salah, Cecilia; et al. (2024)
    Science of The Total Environment
    Chemical and solvent-based recycling of plastic waste may help overcome some of the challenges faced by predominantly applied mechanical recycling techniques. This study quantifies the environmental impacts of chemical and solvent-based recycling as a function of varying process parameters and product composition using life cycle assessment. Furthermore, potential benefits and impacts on a system level are determined. To that end, a high-resolution material flow analysis is conducted for the reference system of Switzerland, covering all main plastic types and applications. In a scenario for the year 2040, we employ environmentally beneficial mechanical recycling where possible and convey suitable remaining waste streams to chemical or solvent-based recycling processes. Applying chemical or solvent-based recycling as a complement to maximum mechanical recycling, instead of thermal treatment with energy recovery, may achieve a reduction in the climate change impact of the system ranging from less than 10 % to almost 40 %. For achieving high environmental benefits, proper process choice and configuration are crucial. Dissolution or depolymerization provide higher benefits relative to other chemical recycling processes, but can only treat certain waste streams and require prior sorting into plastic types. Pyrolysis and gasification appeared to only have the ability to achieve substantial benefits over incineration if their output products can substitute high-impact chemicals and provided that efficient heat transfer and recovery is warranted when implemented on a large scale. As industrial-scale plants for chemical or solvent-based plastic recycling are still lacking, the upscaling potential and the environmental benefits achievable in practice are highly uncertain today.
  • Life cycle sustainability assessment of thermo-chemical recycling for future circular plastics
    Item type: Doctoral Thesis
    Salah, Cecilia (2025)
    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.
Publications 1 - 6 of 6