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Splitting Water For Fuel While Removing CO2 From the Air (arstechnica.com)
An anonymous reader quotes a report from Ars Technica: A new study led by the University of California, Santa Cruz's Greg Rau highlights another tool for our CO2 removal toolbox: splitting seawater to produce hydrogen gas for fuel while capturing CO2 with ocean chemistry. In electrolysis, a device powered by electricity is used to split H2O, producing hydrogen gas. Several chemical modifications to this process have been proposed that can also grab CO2 from the atmosphere. Like the idea of using biofuels, this represents a "win-win" by producing an energy resource while capturing CO2, bringing the cost down. [T]he gist is that atmospheric CO2 goes into the ocean as bicarbonate -- which won't acidify the water or harm ecosystems. So if you power the electrolysis process with renewable energy, you can turn solar/wind/hydroelectric energy into hydrogen fuel while also removing CO2 from the air.
The new study focuses on a basic estimate of the cost and maximum potential of this technique. First, the researchers worked out its efficiency of CO2 capture -- about 0.3 tons captured per gigajoule of electricity input, including the losses from quarrying and crushing rock. That's around 10 times greater than biofuel schemes, but it depends on the assumption that there is demand for all the hydrogen fuel you make. The hydrogen can be used by vehicles, and there's the possibility of using hydrogen as a type of storage for the electric grid -- using excess power to make hydrogen that can run a power plant when needed. So it's not too farfetched that demand could rise to meet supply. The researchers' back-of-the-envelope estimate puts the cost of this system at between $3 and $161 per ton of captured CO2, depending on which type of renewable energy powers it. The study has been published in the journal Nature Climate Change.
The new study focuses on a basic estimate of the cost and maximum potential of this technique. First, the researchers worked out its efficiency of CO2 capture -- about 0.3 tons captured per gigajoule of electricity input, including the losses from quarrying and crushing rock. That's around 10 times greater than biofuel schemes, but it depends on the assumption that there is demand for all the hydrogen fuel you make. The hydrogen can be used by vehicles, and there's the possibility of using hydrogen as a type of storage for the electric grid -- using excess power to make hydrogen that can run a power plant when needed. So it's not too farfetched that demand could rise to meet supply. The researchers' back-of-the-envelope estimate puts the cost of this system at between $3 and $161 per ton of captured CO2, depending on which type of renewable energy powers it. The study has been published in the journal Nature Climate Change.
From the sub-heading of TFA:
"Technique could be practical enough to scale."
The real "Libtards" are the Libertarians!
In order to avoid 2C of warming by 2100, we need to have negative annual CO2 emissions by 2050. That's on the most optimistic trajectories, too. More pessimistic ones say we've already locked in 2C of warming, and negative emissions by 2050 are required to avoid 4C of warming by 2100.
In other words, moving to electric cars by itself is not going to produce the negative CO2 emissions that we need. This sort of technology, in conjunction with electrics cars, could.
To possibly produce jet fuel from sea water on aircraft carriers while underway. In addition to obtaining hydrogen and oxygen from electrolysis of sea water you also liberate some of the carbon dioxide that's dissolved in solution as part of that sea water. The combination of hydrogen, oxygen and carbon dioxide can, with sufficient energy input, most likely from the nuclear reactors that power the ship, be converted to a mixture of carbon monoxide, hydrogen and some carbon dioxide in a mixture known as SynGas or "synthesis gas". From there it can be converted via the Fischer Tropsch Process into heavier hydrocarbons and eventually into a mixture of longer chain hydrocarbons approximating JP-5 jet fuel.
Why aren't we already doing this on land you might ask? Well, in a word, because it's expensive in both industrial plant and equipment and also from an energy input perspective. Much more expensive than simply pumping crude oil out of the ground and refining it. However, that matters less on a ship underway at sea, away from land supplies, and with nuclear energy to spare where cost is less of a factor than ease of supply, which is militarily advantageous.
For example, one method uses special membrane filters to separate the hydrogen and hydroxide ions produced during electrolysis. Adding the hydroxide to water allows it to take up CO2 from the air, turning it into bicarbonate. If the hydrogen ions weren't separated, they'd push the chemical equilibrium away from bicarbonate and toward dissolved CO2. But when powdered carbonate rock is added, it can react with the dissolved (atmospheric) CO2 to produce a bunch of happy, stable bicarbonate. Combined, these reactions allow people to tune the hydrogen production and carbonate formation.
The CO2 is not being dissolved into the water to form carbonic acid, it is being added to hydroxide ions produced by electrolysis to form soluble alkaline bicarbonates.
I wish I'd known this was publishable. I wrote up a report on this years ago while working for the Navy... they actually funded someone to try this out, I think.
Short version: it's expensive. Slightly longer version: chlorine is a problem. If you think you're electrochemically evolving hydrogen gas strait from sea water, you're probably just going to kill a lot of people instead. Catalysts are the answer. Bonus detail: the ocean (for a few reasons) concentrates carbon. There's a lot of carbon in there, and the core of this idea is very good.
Palm oil production uses a lot of land though. This typically means deforestation. As most of the world's arable land is already used up, I'd prefer it if electricity and fuel production could be compact facilities that don't use up land that's needed for farming and indigenous animals' habitat.
When you bind the dissolved carbonic acid to hydroxides produced by electrolysis it neutralizes the acid.
Because then you might learn why the range is so large (spoiler: cheap input energy = cheap captured CO2; expensive energy = expensive captured CO2).
Unfortunately, plants grown in elevated-co2 environments are considerably less nutritious. Lots of energy-rich carbohydrates produced from all that CO2, but "not enough calories" isn't exactly a problem with most of the worlds diet.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
And hydrogen isn't even a fuel source - it's a fuel store. It takes more energy to produce hydrogen than the hydrogen itself provides when used. It might be useful for getting around transmission loss over long distances, but it's definitely not a source itself and should not be treated as such in energy policy.