Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: AnkitaA on 14/06/2019 11:26:12
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Mridul asks:
"Could sodium be modified in any way so that it could used as fuel?"
Can you help?
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Any flammable substance can be used as a fuel in principle. Sodium has some disadvantages, though. It takes a lot of energy just to produce it (elemental sodium is highly-reactive and does not occur in nature). Its reactivity to moisture would also make it dangerous to work with. I'm pretty sure its energy density is less than that of hydrocarbon fuels as well.
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In addition to the safety and efficiency concerns pointed out by Kryptid, I will comment on a few points:
• Good fuels are not just for storing and releasing energy. That energy has to be able to do work (son). For conventional fuels in combustion engines, this work is in the form of PV work (change in pressure and volume), which means that during combustion, they release hot gases, which then push the pistons, and move the vehicle forward. Sodium produces a lot of heat (thermal energy) when reacting with oxygen, but does not produce any gas (in fact it consumes gas), so it would be rather inefficient at performing PV work--most, if not all, energy would just go to heat (this heat could be used to expand another gas, which could do PV work, as in a heat engine, but I don't imagine that would be more effective than an internal combustion engine.
Another way for sodium to perform work would be to use it in an electochemical cell, have it produce an electromotive force, and use that to perform work. This could well be significantly more efficient than an internal combustion engine. I believe there is actually a significant amount of work being done on sodium-oxygen, sodium-air, and sodium sulfur batteries (though I don't know if there are any plans for putting these in cars or planes...) It is somewhat controversial whether the electron sources in batteries count as "fuel" but this is only a semantic argument.
• One could also imagine reacting sodium with water to produce heat and hydrogen, which would then be combined with oxygen to make hot water vapors which could drive a combustion-type engine, but there are many safety and logistical issues with this approach. Sodium metal is a solid (though it melts at only about 100 °C), so it would be difficult to transfer it from storage tanks to fuel tanks, and from there into whatever engine could use it (liquid fuels are very convenient). Also, the violence of the reaction with water could be a very significant safety hazard, and the caustic (and boiling hot) sodium hydroxide solution would be very corrosive, placing severe limitations on the materials that could be used for constructing the engine (as well as have a high cost for disposal). When combined with the requirements for robustness to thermal shock, I think there would be very few suitable materials indeed.
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There have been several projects that used molten sodium as a coolant in fast-breeder nuclear reactors.
- There were numerous problems with sodium leaking and sodium fires.
- Handling large volumes of liquid sodium is just too much trouble!
See, for example: https://en.wikipedia.org/wiki/Monju_Nuclear_Power_Plant#1995_sodium_leak_and_fire
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"Could sodium be modified in any way so that it could used as fuel?"
As soon as we find sodium mines or trees that grow it.
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Sodium metal is a solid (though it melts at only about 100 °C), so it would be difficult to transfer it from storage tanks to fuel tanks, and from there into whatever engine could use it
Like coal, for instance.
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It's good that they had a handy alkaline lake to dispose of the wartime sodium.
Now that lake is just a little more alkaline...
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Sodium metal is a solid (though it melts at only about 100 °C), so it would be difficult to transfer it from storage tanks to fuel tanks, and from there into whatever engine could use it
Like coal, for instance.
Oh, so I take it your automobile and your plane both run on coal?
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Sodium metal is a solid (though it melts at only about 100 °C), so it would be difficult to transfer it from storage tanks to fuel tanks, and from there into whatever engine could use it
Like coal, for instance.
Oh, so I take it your automobile and your plane both run on coal?
It did if you lived in South Africa.
https://en.wikipedia.org/wiki/Sasol#History
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Samuel Henson's Aerial Steam Carriage almost certainly flew before the Wright Brothers, adn there are plenty of traction engines and road rollers still running on coal. All that electric propulsion has done for us is to reduce the overall efficiency of the system by burning coal hundreds of miles away from where we need the power.
It is possible to run turbine engines on a slurry of powdered coal, with pretty much the same energy density as AVTUR.
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All that electric propulsion has done for us is to reduce the overall efficiency of the system by burning coal hundreds of miles away from where we need the power.
Well...
https://en.wikipedia.org/wiki/Cogeneration
However, there's little or nothing to be said for sodium as a fuel except for some unusual process.
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If being a solid is a problem, you could use NaK instead of pure sodium. It's a liquid at room temperature.
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Indeed, NaK is awesome stuff (in the biblical sense), and so fun to make... 8)
But I think this thread has gotten a little off topic... ;D
I think there are many good reasons given in previous posts as to why sodium does not have what it takes to make a good fuel.