I feel like the headlines always try to pretend you're getting energy out of the CO₂ rather than putting energy into a hydrocarbon energy storage chemical.
Question of course is economics of converting some (hopefully clean-ish) energy into stored hydrocarbon chemical bond energy and then combusting it in a vehicle vs. just digging up hydrocarbons and combusting them.
It's also a nice thing to do when the spot price of energy goes negative or extremely low when there's tons of surplus renewable energy.
I also heard one example assuming a future with nuclear fusion being cheap and you put a nuclear fusion plant at larger airports to produce jet fuel on-site.
From the article:
> When air was bubbled through potassium hydroxide dissolved in ethylene glycol and the CO2-loaded solution subsequently hydrogenated in the presence of H2 and a metal catalyst, complete conversion to methanol was observed at 140 °C.
Even with catalyst, organic reactions have an awful efficiency. In many of them the reactives produce not only what you want but also other molecules. In this case it's hard to imagine, because methane is very small and all side products I imagine like COH2 can probably be converted to methane inside a hot recipient full of H2.
Anyway, even if you lose no CO2 as side products, the reaction may lose a lot of energy as heat. Photosynthesis has many intermediate steps that help the conversion to be more efficient (and also because photosynthesis builds a bigger molecule that is harder).
If you consider a hybrid PV-CSP plant, the H2 step can be done at 20% from air. CO2 capture is under 10%.
So you'd need to show that the ethylene step is under 5% efficient when you also had an available free low quality steam input (or high quality at 50% sunlight-efficiency).
> One hectare of sugar cane yields 4,000 litres of ethanol per year (without any additional energy input, because the bagasse produced exceeds the amount needed to distill the final product). This, however, does not include the energy used in tilling, transportation, and so on. Thus, the solar energy-to-ethanol conversion efficiency is 0.13%.
but I'm still pessimistic about the efficiency of the new method.
Fertilizers don't contain carbon. Plants need nitrogen, potassium and phosphorus, which they can't easily get from their surroundings, so we provide these via fertilizers. They get their own carbon out of the CO2 in the air.
We do need hydrogen to make fertilizers, and currently the cheapest way to make hydrogen is to start with methane, CH4. But this is just a matter of convenience.
The disadvantage is that there's a high energy cost involved in stripping oxygen off carbon dioxide and replacing it with hydrogen (it is storing energy in C-H and C-C bonds). As the cheap easy-to-extract oil is mostly gone at this point, however, these costs are approaching parity.
The real necessary use cases of hydrocarbon fuels are for rockets and jet airplanes, as battery energy density is just too low. Long-distance oceanic shipping is another area where hydrocarbon fuels might be necessary, although there are some other options (wind/solar/iron redox).
Yeah, and nuclear, which is deployed at huge scale in seafaring vessels in the Navy. Merchant nuclear propulsion had an early start and is likely to see a revival imho.
I'd love to see it, but I'm a bit pessimistic about the political viability of a significant revival of civilian nuclear ships.
A commercial nuclear-powered cargo ship would have to be refueled on the same time scale as a commercial MOX or LEU reactor, likely raising costs quite a bit over any other fuel. Plus, what harbor would allow commercial nuclear reactors, given the costs of catastrophic failure, without ridiculously expensive levels of security and safeguards?
That said, one interesting approach is to use ocean-faring nuclear-powered tugs that basically stay out in international water and hand off massive container barges to little fossil fueled short-haul ones that can take it in to port where people are afraid of nuclear fission but don't care about air pollution or climate change.
As for refueling, it's true that submarines don't need to refuel for 30 years. But there's a lot more room on a container ship, so you can make a big core and run it at less than full power. This way you can get it to only need refueling every 5 years or so with low-enriched uranium. Not bad.
Nuclear tugs: https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1559-3584....
These ports already handle tens of thousands of tons of explosives - the blast in Beirut wa over 1 Kt of TNR equivalent, and all that ammonium nitrate arrived on a single ship. It was basically a small nuclear detonation.
KSA can 10M bbl per day for 40 more years at $20...
This isn't even a closed cycle. It uses up potassium hydroxide.
Electrolyzing water into hydrogen and oxygen is more promising, if you like that sort of thing. Once you have hydrogen, you can make hydrocarbons, if you want to. That's good to have as a technology for when we use up all the natural hydrocarbons and still want to make plastics. As an energy storage system, it sucks.
> "When air was bubbled through potassium hydroxide dissolved in ethylene glycol and the CO2-loaded solution subsequently hydrogenated in the presence of H2 and a metal catalyst, complete conversion to methanol was observed at 140 °C. Moreover, regeneration of the hydroxide base occurred at mild temperatures of 100-140 °C. Notably, a fraction of the base was deactivated in an unwanted side reaction. Currently, the researchers are aiming to minimize the side reactions to efficiently recycle the potassium hydroxide."
Having to use large volumes of ethylene glycol might be an issue, however. There's a whole literature on this particular reaction, for example, as of 2019:
https://www.frontiersin.org/articles/10.3389/fenrg.2019.0008...
> "The methanol production from direct CO2 (using pure sources of CO2 and H2) has several advantages over the conventional process—it results in significantly less byproducts, and requires less energy in product purification (Marlin et al., 2018). However, the methanol production cost via direct CO2 hydrogenation is 2–2.5 times higher than the cost of conventional process (Atsonics et al., 2015)."
You see you could cover enough desert in Nevada with enough solar panels to provide 100% of the current electricity use of the United States. But you couldn't transmit it over the current grid to the rest of the country and it would "turn off" every night. So stupid right? Except maybe you are using that energy to create natural gas and you're shipping natural gas around through pipelines to standard gas electric power plants.
The math works, and the BLM has enough land (caveat the endangered tortoises) and so it is a "technically possible" solution to carbon neutral energy (you're taking CO2 out of the air and then returning it when you burn the natural gas).
This also works with fission power plants as the source of energy, and really shines with fusion power plants (fewer externalized issues like waste management).
The headline should be: "Fuel components from air synthesized into liquid fuel using energy from some other energy source"
I think there’s an opportunity to formalise an excess energy marketplace, established with an inefficient process to get the ball rolling. From there, market forces can dictate winners.
Combine that with Solar storage and geo-thermal storage using that and maybe we will continue to have enough movable energy to have long distance travel that isn't wind driven.
Thw whole advantage of nuclear over renewables is it's reliability for powering critical infrastructure
If you are producing fuels, they can be stored, reliability doesn't matter - only cost.
https://en.wikipedia.org/wiki/Gas_to_liquids
they say
https://en.wikipedia.org/wiki/Pearl_GTL
in Qatar makes about 95 million barrels of liquid a year at $40 a barrel.