Carbon Dioxide Mitigation Using Renewable Power: Life Is All about Priorities!

The discovery and development of efficient technologies that enable the use of CO₂ as a starting material for chemical synthesis (at scale) is probably one of the biggest scientific challenges of our time. But a key question is if the cure will not be worse than the disease? Renewable energy, specifically renewable power, is generally assumed to be the energy source for CO2 utilization. Various options are available for using renewable power for mitigation of CO2 emissions, including electroreduction of CO2 to hydrocarbons, electrolysis of water to hydrogen, and power for battery electric vehicles. Thermodynamic and practical arguments can be used to rank the effectiveness of renewable power for CO2 mitigation for these options, using a case study as an example. Renewable power used to reduce water to hydrogen, which is then used to convert CO2 into liquid fuels, is only one-fourth as effective at mitigating CO2 emissions compared to use of the renewable power directly. The direct electroreduction of CO2 to liquid fuels, even if achieved with 100% thermal efficiency, is only one-third as effective at mitigating CO2 compared to using electricity directly.

Also the economic feasibility of the electrochemical reduction of CO₂ to ethylene is assessed and compared to electrified steam cracking. It is demonstrated that from a Capital expenditure and Operational expenditure point of view the electrochemical production of ethylene from CO₂ is not feasible under the current market conditions. Even in the case that the renewable electricity price would be zero, the feasibility is hampered by the state-of-the-art catalyst performance (selectivity) and the cost of the electrochemical reactor. Turning the installation on and off, if this would be even practically possible, is not interesting because our study shows that because of the high Capital expenditure, the payback time of the process would become unacceptably high. Finally, because of the high electricity requirement, this Carbon Capture and Utilization process has a lower CO₂ avoidance potential than the substitution of gray electricity by green electricity. This means that today the available green electricity would best be used to close coal and gas based power plants instead of powering the electrochemical conversion of CO₂ to ethylene. Electrified steam cracking on the other hand is economically interesting but the key question is to reduce the SCOPE 3 emissions.