I have read with genuine excitement about new technologies for direct air capture of CO2, electrolytic conversion of water to hydrogen and then using the H2 to make ammonia, and using CO2 from direct air capture and combining it through electrolysis to make jet fuel. There are other interesting options, but we can start with these.
These technological advances are truly impressive from a scientific perspective – amazing, really. However, you will need to forgive me for being rather simple-minded as I look at these impressive accomplishments. Being a simple person, I need to look at little things like the energy consumed to achieve the desired result or the budget of energy required to make a “carbon-free” fuel versus the energy produced by that fuel.
The literature on direct air capture is consistently clear that the energy required to segregate and capture 0.042-percent concentrations of CO2 directly from the air is very highly energy intensive. An article from recent years in Nature entitled, “Unrealistic energy and materials requirement for direct air capture in deep mitigation pathways,” indicates that DAC requires more than 90 percent of the energy to capture the CO2 than was generated by burning the organic fuel. To my simple mind this does not make sense when huge point sources are producing 60-70-percent CO2, or Allam cycle power plants might supply 100-percent pure CO2 for storage or reuse.
Thus, a simpleton’s question: Why not use that vast amount of power directly to offset the massive amount of coal, trees and dung being burned globally today instead of using it to capture a minute amount of CO2?
We read that Canadian Prime Minister Justin Trudeau has recently inked a deal with France to build a huge wind farm in Newfoundland to produce electrolytic hydrogen for sale to France. Transporting H2 overseas is very challenging, so the most likely path is to produce ammonia with the H2 and ship it as ammonia to France. The pesky details involved are the huge amounts of power to make and install the wind turbines, electrolyze the H2, make the NH4, ship the NH4 across to France, and pull the H2 back out of the NH4 once in France. The net energy balance is immensely negative.
Thus, a simpleton’s question: Why not use that vast amount of power directly to offset the massive amount of coal, trees, and dung being burned in North America today instead of using it to capture and transfer a small amount of fuel to France?
Now to the very cool promise of taking CO2 from the air to produce net-zero jet fuel. This process also entails DAC for CO2, though point sources might reduce the huge energy deficit a bit. The DAC CO2 is mixed with electrolytic H2 at very high temperatures with a catalyst to produce jet fuel and a range of other petrochemical products. Very simple thermodynamics (excluding all the energy lost to heat and electrical transmission) tell us that the energy consumed in CO2 capture, wind turbine construction, H2 electrolysis, and the petrochemical synthesis process vastly exceeds the energy provided by the jet fuel.
Thus, the simpleton’s questions: How much will that jet fuel cost? And, why not use that vast amount of power directly to offset the massive amount of coal, trees and dung being burned globally today instead of using it to manufacture a tiny percentage of global jet fuel consumption?
I am sure more sophisticated folks can provide a concise, economically viable answer.