(353b) Economic and Environmental Assessment of Fischer-Tropsch Electro-Diesel from Captured CO2

The transportation sector is responsible for 8.19 Gt of CO₂ emitted in 2019 due to its dependence on fossil fuels and particularly diesel [1]. Under current policies, there is a strong motivation to replace fossil diesel with more sustainable alternatives. Nevertheless, the good properties of diesel and the current compression ignition engines make the transition particularly challenging. As a substitute of fossil diesel, Fisher-Tropsch electro-diesel (FT e-diesel) is thought to be one of the best alternatives with the highest “drop-in” quality, as it shares similar features with its fossil analog [2]. Notably, FT e-diesel could be integrated into the existing infrastructure with the potential to reduce pollutant emissions [2].

Many previous works on FT e-diesel focused on carbon emissions while disregarding impacts beyond global warming. However, burden-shifting has been observed in many emerging technologies when attempting to mitigate climate change; that is, improvements in some environmental categories inevitably worsen others. Notably, carbon capture and utilization [3], low carbon power mixes [4] and biomass synthetic fuel synthesis [5], to mention a few, have been shown to lead to burden-shifting. This narrow scope of current assessments is also found in FT e-diesel studies, which in view of the former examples, raises the question of this collateral damage being present in the production of the synthetic fuel.

In this work, we assess the economic and environmental performance of FT e-diesel to shed light on the potential occurrence of burden-shifting. We consider six different scenarios resulting from the combination of two CO₂ capture technologies (post combustion capture at a coal power plant, COAL, and direct air capture, DAC) and three electricity sources (wind onshore, solar photovoltaic and nuclear). The material and energy flows in the foreground system were extracted from a simulation in Aspen HYSYS v11, and combined with life cycle inventory data of the background system retrieved from an environmental database. The total annualized cost was computed following well-stablished correlations [6], while the life cycle assessment (LCA) was applied following the ISO 14040 standards [7], using SimaPro v9.2 [8] and Ecoinvent v3.8 [9] to carry out the calculations.

The results show that Fischer-Tropsch electro-diesel from captured CO₂ is economically unappealing (400 – 1000 % increase in cost relative to fossil diesel), with DAC CO₂ being more expensive than the COAL scenario, and solar energy-powered H₂ more costly than nuclear and wind. The inclusion of externalities, that is, the monetization of the ReCIPe 2016 endpoint impacts [10], helps close the gap between COAL and DAC, although regardless of the scenario, fossil diesel still holds the lowest cost.

Regarding the LCA analysis, the global warming impact of FT e-diesel, especially in the DAC and nuclear scenario, decreases drastically with respect to fossil diesel (- 3,87 kg CO₂-eq/kg vs. 0.57 kg CO₂-eq/kg, respectively). The wind-DAC scenario also reduces the impact (- 1.94 kg CO₂-eq/kg), while solar-DAC and all the COAL-related scenarios perform worse than fossil diesel. However, although resource scarcity follows the decreasing trend in global warming impact, both human health and ecosystems quality worsen their performance relative to fossil diesel.

Overall, our results, highlighting the occurrence of burden-shifting in FT e-diesel from captured CO₂, reinforce the need to embrace a wide range of impacts in the environmental assessments of fuels to avoid myopic solutions mitigating greenhouse gas emissions at the expense of exacerbating other impacts.

References

[1] European Union. L 282/4. Official Journal of the European Union 19.10.2016. Paris agreement 2016:1–15.

[2] Schemme S, Samsun RC, Peters R, Stolten D. Power-to-fuel as a key to sustainable transport systems – An analysis of diesel fuels produced from CO2 and renewable electricity. Fuel 2017;205:198–221. https://doi.org/10.1016/j.fuel.2017.05.061.

[3] Algunaibet IM, Guillén-Gosálbez G. Life cycle burden-shifting in energy systems designed to minimize greenhouse gas emissions: Novel analytical method and application to the United States. J Clean Prod 2019;229:886–901. https://doi.org/10.1016/J.JCLEPRO.2019.04.276.

[4] Galán-Martín Á, Tulus V, Díaz I, Pozo C, Pérez-Ramírez J, Guillén-Gosálbez G. Sustainability footprints of a renewable carbon transition for the petrochemical sector within planetary boundaries. One Earth 2021;4:565–83. https://doi.org/10.1016/j.oneear.2021.04.001.

[5] Cuéllar-Franca R, García-Gutiérrez P, Dimitriou I, Elder RH, Allen RWK, Azapagic A. Utilising carbon dioxide for transport fuels: The economic and environmental sustainability of different Fischer-Tropsch process designs. Appl Energy 2019;253:113560. https://doi.org/10.1016/j.apenergy.2019.113560.

[6] Turton R, Bailie RC, Whiting WB, Shaeiwitz JA, Bhattacharyya D. Analysis, Synthesis and Design of Chemical Processes. Fourth. Prentice Hall; 2012.

[7] ISO - ISO 14040:2006 - Environmental management — Life cycle assessment — Principles and framework n.d.

[8] Goedkoop M, De Schryver A, Oele M, Durksz S, de Roest D. Introduction to LCA with SimaPro 7. PRé Consult Netherlands 2008.

[9] Wernet G, Bauer C, Steubing B, Reinhard J, Moreno-Ruiz, E., Weidema B. The ecoinvent database version 3 (part I): overview and methodology. Int J Life Cycle Assessment, [Online] 21(9) 2016:1218–1230. http://link.springer.com/10.1007/s11367-016-1087-8 (accessed January 24, 2020).

[10] Weidema BP. Comparing Three Life Cycle Impact Assessment Methods from an Endpoint Perspective. J Ind Ecol 2015;19:20–6. https://doi.org/10.1111/jiec.12162.