A Life Cycle Assessment of a Direct Air Capture System Coupled with Fischer-Tropsch Process for Transportation Fuel Production Under Three Electricity Generation Scenarios

Greenhouse gas emissions, specifically carbon dioxide emissions, cause global warming and climate change. There are methods to reduce the amount of carbon dioxide in the atmosphere by capturing and utilizing the carbon dioxide. One method is the direct capture of carbon to produce fuels such as transportation fuels. However, to determine if the system is environmentally friendly, it is required to perform a life cycle assessment. This paper presents a life cycle assessment of an integrated system for transportation fuel production using direct air capture. This system absorbs carbon dioxide at first and then converts it into syngas using water electrolysis and reverse water-gas shift reaction. Subsequently, Fischer-Tropsch Synthesis takes place to produce fuel from the syngas. Environmental impacts are evaluated under three scenarios: using Iran’s electricity grid, future electricity grids, and clean (100% renewable) electricity. Using Iran’s electricity grid, the impacts of the system are 4.6 gCO2 eq./gCO2 captured; the most polluting part of the integrated system is the electricity for hydrogen production used in the Fischer-Tropsch and RWGS. Therefore, the electricity emission factor is identified as the most important factor in determining the integrated system with low environmental effects. In the second scenario, the system has an impact of 0.8 gCO2 eq./gCO2 captured. The environmental impacts of clean electricity are reduced to 0.72 gCO2 eq./gCO2 captured. The results show that the emission factor of the electricity has a significant impact. Therefore, this system can be used only where electricity is generated partly from renewable resources.