Absolute environmental sustainability assessment of renewable dimethyl ether fuelled heavy-duty trucks.

In recent years, liquid fuels from renewable carbon that can replace fossil ones with minimal infrastructure changes have attracted increasing interest in decarbonising the heavy-duty long-haul sector. Here we focus on dimethyl ether (DME), a promising alternative to diesel due to its high cetane number, oxygen content, and more efficient and cleaner propulsion that results in low particulate matter and sulphur oxide emissions. Going well beyond previous studies that quantified the environmental impact of DME, often in terms of global warming, here we evaluate DME use in heavy-duty trucks in the context of seven planetary boundaries, all essential for maintaining the Earth's stability. Focusing on several scenarios differing in the feedstock origin, we find that routes based on fossil carbon, either in the form of coal, natural gas, or captured CO2 from fossil plants, would increase the greenhouse gas emissions relative to the business-as-usual. Only scenarios based on renewable carbon could reduce the impacts on climate change, while hydrogen from biomass gasification coupled with carbon capture and storage (CCS) and DME from biomass gasification with CCS could enable an environmentally sustainable operation within all the planetary boundaries. Overall, our work opens up new avenues for the environmental assessment of fuels considering the finite capacity of the Earth system to guide research and policy-making more sensibly.

Economic and Environmental Barriers of CO2-Based Fischer-Tropsch Electro-Diesel.

Electro-fuels are seen as a promising alternative to curb carbon emissions in the transport sector due to their appealing properties, similar to those of their fossil counterparts, allowing them to use current infrastructure and state-of-the-art automotive technologies. However, their broad implications beyond climate change remain unclear as previous studies mainly focused on analyzing their carbon footprint. To fill this gap, here, we evaluated the environmental and economic impact of Fischer-Tropsch electro-diesel (FT e-diesel) synthesized from electrolytic H2 and captured CO2. We consider various power (wind, solar, nuclear, or the current mix) and carbon sources (capture from the air (DAC) or a coal power plant) while covering a range of impacts on human health, ecosystems, and resources. Applying process simulation and life cycle assessment (LCA), we found that producing e-diesel from wind and nuclear H2 combined with DAC CO2 could reduce the carbon footprint relative to fossil diesel, leading to burden-shifting in human health and ecosystems. Also, it would incur prohibitive costs, even when considering externalities (i.e., indirect costs of environmental impacts). Overall, this work highlights the need to embrace environmental impacts beyond climate change in the analysis of alternative fuels and raises concerns about the environmental appeal of electro-fuels.

Navigating within the Safe Operating Space with Carbon Capture On-Board.

Despite the global pandemic that recently affected human and cargo transportation, the emissions of the maritime sector are projected to keep growing steadily. The International Maritime Organization focused on boosting the fleets' efficiency to improve their environmental performance, while more sustainable fuels are currently under investigation. Here, we assess the economic, technical, and environmental feasibility of an interim solution for low-carbon shipping using state-of-the-art CO2 capture technology, namely, chemical absorption, on-board cargo ships. We compute the carbon footprint of this alternative and perform an absolute sustainability study based on seven planetary boundaries. Our results show that the capture on-board scenario can achieve 94% efficiency on the net CO2 emissions at 85 $/tCO2 while substantially reducing impacts on core planetary boundaries (relative to the business as usual) and outperforming a direct air capture scenario in global warming and all planetary boundaries, except for the nitrogen flow. Hence, capture on-board seems an appealing solution to decarbonize shipping in the short term while alternative carbon-free fuels and related infrastructure are developed and deployed.