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

Abstract

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 H 2 and captured CO 2 . 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 H 2 combined with DAC CO 2 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.

The E factor at 30: a passion for pollution prevention

“…311 The production of e-diesel in an electrically driven FT process will substantially reduce its global warming impact but the total environmental impacts of the two processes need to be compared for a complete evaluation (caveat emptor). 312 Replacing energy intensive steam crackers, that use gas-fired furnaces and generate huge amounts of carbon dioxide, by electric cracking of hydrocarbons using renewable electricity is also a possibility. 313 Electrolytic reduction of carbon dioxide can be utilised to produce methanol as a high-energy-density liquid fuel and raw material for commodity chemicals manufacture, in a methanol economy as envisaged by Olah and co-workers.…”

“…311 The production of e-diesel in an electrically driven FT process will substantially reduce its global warming impact but the total environmental impacts of the two processes need to be compared for a complete evaluation (caveat emptor). 312 Replacing energy intensive steam crackers, that use gas-fired furnaces and generate huge amounts of carbon dioxide, by electric cracking of hydrocarbons using renewable electricity is also a possibility. 313…”

Identifying key environmental objectives for integrated process and fuel design

“…Electricity-based fuels (e-fuels), for instance, can reduce GWI substantially compared to fossil fuels if produced from renewable electricity and carbon sources, at the cost of increases in other impact categories, e.g., resource use of minerals and metals. 22,23 In contrast, biomass-based fuels (biofuels), e.g., ethanol, are known to increase agricultural land occupation substantially compared to their fossil-based counterparts. 24 Therefore, a holistic design approach should cover a wide range of impact categories as additional objectives to quantify and avoid potential burden-shiing.…”

Proof of Concept for O2 Removal with Multiple LCCF Membranes Accommodated in the Effluent of a CO2 Plasma Torch

“…10 Thus, for the plasma process to be competitive, the removal of O 2 is necessary to deliver an industrially relevant gas mixture for the production of synthetic fuels, e.g., via the Fischer−Tropsch process. 11 One sensitivity analysis study has shown that gas separation would be the dominant cost factor in a plasmabased CO 2 -to-CO chemical plant. 12 Strategies/technologies that have been proposed to process the outlet mixture of a plasma reactor to produce O 2 -free streams include the use of sacrificial materials such as biochar that consume the produced O 2 , 13 zeolites that selectively remove CO 2 and CO from the gas stream 14 and mixed ionic-electronic conductors (MIECs) as standalone membranes or ion conductors incorporated in electrochemical cells for oxygen removal.…”

“…The outlet gas mixture of plasma-based conversion technology consists typically of CO 2 , CO, and O 2 , which contrasts with the O 2 -free streams produced by electrolysis cells . Thus, for the plasma process to be competitive, the removal of O 2 is necessary to deliver an industrially relevant gas mixture for the production of synthetic fuels, e.g., via the Fischer–Tropsch process . One sensitivity analysis study has shown that gas separation would be the dominant cost factor in a plasma-based CO 2 -to-CO chemical plant .…”