Carbon capture and utilization (CCU) plays a key role in reducing greenhouse gas emissions and reaching carbon neutrality goals. This study assesses the environmental impacts of producing carbon nanotubes (CNTs) via molten salt CO2 capture and electrochemical transformation (MSCC-ET) and Catalytic Chemical Vapor Deposition (CCVD), both using CO2 as feedstock. We screened and selected technologies using a parameter-based method and conducted process modeling and an ex-ante Life Cycle Assessment (LCA) to move beyond lab-scale evaluations and included the purification steps. The MSCC-ET approach showed advantages in reducing impacts related to climate change, energy, and ozone depletion impacts, specifically suggesting lower CO2 emissions. However, traditional CCVD outperformed MSCC-ET in several other impact categories. Key contributors to the environmental impacts of MSCC-ET were found in high material use in electrolysis, purification, and electricity consumption, modeled using the Belgium grid. Moreover, including the carbon capture unit in the assessment could provide a complete view of the environmental impacts regarding CCU. For every 100 tons of MWCNTs produced, a monoethanolamine (MEA)-based carbon capture unit integrated into the MSCC-ET system could roughly reduce 716.5 tons CO2-eq. Additionally, electricity consumption was found to constitute a significant portion of the environmental impacts. Therefore, a sensitivity analysis was conducted, revealing that changes in the electricity source, catalyst used, and CO2 source significantly influenced the environmental performance of both technologies. Furthermore, we summarize practical insights from this study to guide the effective application of ex-ante LCA for carbon nanomaterials. The paper concludes with actionable recommendations for early-stage technology developers on optimizing energy use, improving material efficiency, and integrating recycling to enhance sustainability. In addition, we provide recommendations for LCA practitioners on incorporating dynamic systems to transition from lab-scale to industrial contexts, thereby bridging the gap between research and practical implementation.@en

Two electrolysis technologies fed with renewable energy sources are promising for the production of CO₂-free hydrogen and enabling the transition to a hydrogen society: Alkaline Electrolyte (AE) and Polymer Electrolyte Membrane (PEM). However, limited information exists on the potential environmental impacts of these promising sustainable innovations when operating on a large-scale. To fill this gap, the performance of AE and PEM systems is compared, using ex-ante Life Cycle Assessment (LCA), technology analysis and exploratory scenarios for which a refined methodology has been developed to study the effects of implementing large-scale sustainable hydrogen production systems. Ex-ante LCA allows modelling the environmental impacts of hydrogen production, exploratory scenario analysis allows modelling possible upscaling effects at potential future states of hydrogen production and use in vehicles in the Netherlands in 2050. A bridging tool for mapping the technological field has been created enabling the combination of quantitative LCAs with qualitative scenarios. This tool also enables diversity for exploring multiple sets of visions. The main results from the paper show, with an exception for the “ozone depletion” impact category, (1) that large-scale AE and PEM systems have similar environmental impacts with variations lower than 7% in all impact categories, (2) that the contribution of the electrolyser is limited to 10% of all impact categories results, and (3) that the origin of the electricity is the largest contributor to the environmental impact contributing to more than 90% in all impact categories, even when renewable energy sources are used. It is concluded that the methodology was applied successfully and provides a solid basis for an ex-ante assessment framework that can be applied to emerging technological systems.

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Three-dimensional (3D) printing and geo-polymers are two environmentally oriented innovations in concrete manufacturing. The 3D printing of concrete components aims to reduce raw material consumption and waste generation. Geo-polymer is being developed to replace ordinary Portland cement and reduce the carbon footprint of the binder in the concrete. The environmental performance of the combined use of the two innovations is evaluated through an ex-ante life cycle assessment (LCA). First, an attributional LCA was implemented, using data collected from the manufacturer to identify the hotspots for environmental improvements. Then, scaled-up scenarios were built in collaboration with the company stakeholder. These scenarios were compared with the existing production system to understand the potential advantages/disadvantages of the innovative system and to identify the potential directions for improvement. The results indicate that 3D printing can potentially lead to waste reduction. However, depending on its recipe, geo-polymer likely has higher environmental impacts than ordinary concrete. The ex-ante LCA suggests that after step-by-step improvements in the production and transportation of raw materials, 3D printing geo-polymer concrete is able to reduce the carbon footprint of concrete components, while it does still perform worse on impact categories, such as depletion of abiotic resources and stratospheric ozone depletion. We found that the most effective way to lower the environmental impacts of 3D concrete is to reduce silicate in the recipe of the geo-polymer. This approach is, however, challenging to realize by the company due to the locked-in effect of the previous innovation investment. The case study shows that to support technological innovation ex-ante LCA has to be implemented as early as possible in innovation to allow for maintaining technical flexibility and improving on the identified hotspots.

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