Why not ammonia, NH3, as liquid fuel?

Discussion in 'Chemistry' started by Billy T, Feb 26, 2007.

  1. billvon Valued Senior Member

    I suspect it will be delivered in the form of methane, since:

    1) we already have methane pipelines
    2) we already burn methane directly in cars and buses
    3) we already have an entire industry that makes natural gas appliances

    Not too many ammonia buses or cars on the road, and not too many ammonia fueled hot water heaters in the US.
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  3. ElectricFetus Sanity going, going, gone Valued Senior Member

    Making methane from hydrogen and carbon dioxide is even more energy wasteful then making ammonia, Energy usage will become a bigger factor then infrastructure change, its why battery electrics have so much drive: they provide greatly improved efficiency with a fair change of infrastructure. Hydrogen provides less efficiency so much so that making it from natural gas is still the primary means of manufacturing, and now your asking that we make hydrogen back into natural gas?
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  5. billvon Valued Senior Member

    The Sabatier Process is CO2 + 4H2 -> CH4 + 2H20. The water can then be reused if desired (say, split back into oxygen and hydrogen.) It is exothermic which means that energy is created.

    Yes. As you mentioned, hydrogen is currently so scarce that it's actually economically feasible to make it from methane. We will need a much more economical source of hydrogen if it is ever to be usable as a fuel source. The only way I know of to create that much hydrogen that cheaply is through thermal dissociation of water, which in turn requires high temperature gas reactors (HTGR's.)
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  7. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    Making five molecules into three usually requires considerable pressure and I think is done at high temperature, which has thermal loses to the environment. Are you sure the real process is does not require net energy for the pumps, and thermal loses (if economical scale and insulation thickness is assumed)?
  8. billvon Valued Senior Member

    It is fairly high temperature, but since the reaction is exothermic, once the reaction starts it will maintain itself (with sufficient insulation of course.) It requires a nickel or ruthenium catalyst to reduce activation energies.

    It's been proposed as a very interesting way to get people back from Mars. The process is:

    1) Unmanned rocket places a return vehicle on Mars. The return vehicle has almost empty tanks; it lands with only a small amount of hydrogen (8 tons.) It has an RTG or reactor to provide electrical power.

    2) The Sabatier process combines the hydrogen and atmospheric carbon dioxide into water and methane: CO2 + 4H2 -> CH4 + 2H20

    3) The methane is stored as fuel.

    4) The water is cracked into H2 and O2.

    5) The oxygen is stored as oxidizer.

    6) The H2 is used to make more methane.

    Via this process you can transform 8 tons of hydrogen into almost 112 tons of fuel and oxidizer, sufficient to get back from Mars.
  9. wlminex Banned Banned

    . . .haven't read all previous posts yet, however . . . the concept(s) of chemically "storing" hydrogen makes sense to me . . . a kind of 'hydrogen-battery', if you will. Has anyone toyed with the idea of dissolving hydrogen (under pressure?) into current hydrocarbon fuels . . . as a 'booster'?

    Last edited: Oct 5, 2011
  10. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    Yes that is very interesting idea. I did a little searching at patent office, google etc. and find that with some catalyst, the temperature can be modest (a few hundred degrees C) so even though the process is only "weakly exothermic" that does not seem to be much of a on going cost (after initial start up heating)

    I saw pressures from one to 1000 atmospheres - As I noted in first post, getting 5 gas molecules to become 3 at any interesting rate will require high pressures. So I still think there will be net energy required (for pressure pumps, especially if the CO2 comes from the very low pressure Mars atmosphere) And of course the only place you find H2 is in stars or cosmic space - From either you will pay one hell of an energy price to get it into high pressure chamber on Mars.

    None the less with time* and sunlight, energy is available and getting almost 18 fold more "get home" fuel & O2 mass than the H2 one takes to Mars is very attractive. - Perhaps infinite mass gain if done where there is ice on Mars as the source of needed H2. Also fact that process can recover O2 to breath from recycled (exhaled) CO2 for space traveler is interesting. That is a lot more attractive than than just chemically binding /absorbing it to keep the CO2 level below the lethal 5%. This might be applied to maned submarines too.

    Thanks for making me aware of this process, which seems to be still being perfected. (Lots of related patents already.)

    *Scrap anything left of the "man to Mars" expenses as US is broke - can not afford it, but plan for sending the unmanned "return vessel" / "Fuel & O2 maker" later, if US ever recovers economically even a couple of decades before men go. (Those men will no doubt speak Chinese, but perhaps the US can sell the technology to them.)
    Last edited by a moderator: Oct 6, 2011
  11. ElectricFetus Sanity going, going, gone Valued Senior Member

    Don't be silly: 4 hydrogen molecules had to be manufacture first from water, your losing energy manufacturing methane and water byproduct, where do you think that heat product comes from, fairy farts?

    No thermal cracking can be down with any kind of high temperature heat sources like solar thermal. There is of course electrolysis which not include the efficiencies of making electricity can get up to 75% efficiency. Lithium ion batteries though generally achieve charge discharged cycle efficiency beyond 90% by the way.
  12. Believe Happy medium Valued Senior Member

    Seems like alot of wasted effort. You take the Hydrogen from H20 first, then use it to make ammonia to then remove it from the ammonia to use as fuel later? Why not just use the H2 straight off the water in the first place? You would waste much less energy then.
  13. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    Storing it how if not used as it is produced?

    If it is used as it is produced, why bother to produce it? - Just use the electricity running the H2 production.
  14. billvon Valued Senior Member

    From the chemical energy contained in the hydrogen. Since it is only slightly exothermic, not much energy is lost.

    The trick is to use the minimal amount of energy possible to generate and transport the fuel. Pure hydrogen is much easier to make - but how to transport it? You can compress it which uses a lot of energy, since its atomic weight is so low. You can liquefy it which uses a truly obscene amount of energy.

    You can convert it to ammonia, which is much easier to transport - but then you have to convert it back to a usable fuel on the other end. (NH3 is burnable directly but it is hard to do it cleanly due to NOx production.) You can convert it to methane which is also easier to transport, and we already have distribution and storage systems in place - and we already have both fuel cells and production vehicles that will run on it.

    Yes, but the temperatures required (over 2000C!) mean you need a high concentrating power solar thermal system (i.e. we're talking a large array of accurate, individually steered mirrors - not panels.) HTGR's are a much more compact way to do it.

  15. Believe Happy medium Valued Senior Member

    Exactly! Ammonia would be even worse off because you do this first, then make ammonia out of it.

    In otherwords you use large amounts of energy to get H2 out of H20 and you also use large amounts of energy break up nitrogen. Then, after you liquify it, you have to use more energy to re-break it to make hydrogen. Yes it takes alot of energy to compress and cool hydrogen, but I doubt it's more then all that added up. It is a also a ready to use fuel requiring no more work once it gets to where its going. With the ammonia you have to have extra systems set up and a way to get energy to break it up to get the H2 back out.
    Last edited: Oct 6, 2011
  16. wlminex Banned Banned

    . . . jug of ammonia? . . . perhaps you mean a jug of ammonium hydroxide . . . ammonia is a gas . . . ammoniim hydroxide is a liquid.
  17. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    It is hard to understand how you can be wrong about every thing in one post, but perhaps you did not understand the point of using ammonia to easily and economically store H2.
    No, the ammonia is made where the H2 is produced so no need to store H2 and then later make NH3 from it. The whole point of making H2 into Ammonia is to avoid storing the H2. And yes there is less electric power needed if the electrolysis is done at higher temperature (which of course with water means higher pressure). In fact you will need both the higher pressure and higher temperature to make NH3 from N2 and H2, quite the opposite of what you are speaking of below:
    You have zero understanding of how NH3 is made. The N2 is not separately broken up to 2N, nor is the H2 cooled, as making NH3 is done at high temperature and pressure. It is true that splitting H2O to get H2 is energy intensive but as I noted above, cheaper thermal energy (which you will need in the NH3 production anyway) can be used to reduce the amount of electrical energy required in H2 production. Here is how NH3 is made:

    "... In 1909 Fritz Haber established the conditions under which nitrogen, N2(g), and hydrogen, H2(g), would combine using
    • medium temperature (~500 C)
    • very high pressure (~250 atmospheres, ~25,500 kPa)
    • a catalyst (a porous iron catalyst prepared by reducing magnetite, Fe3O4). Osmium is a much better catalyst for the reaction but is very expensive.

    This process produces an ammonia, NH3(g), yield of approximately 10-20%.
    The Haber synthesis was developed into an industrial process by Carl Bosch.
    The reaction between nitrogen gas and hydrogen gas to produce ammonia gas is anexothermic equilibrium reaction, releasing 92.4kJ/mol of energy at 298K (25 C).

    N2(g) nitrogen + 3H2(g) hydrogen --->heat, pressure, catalyst --->2NH3(g) ammonia with H = -92.4 kJ mol-1

    By Le Chetalier's Principle:
    • increasing the pressure causes the equilibrium position to move to the right resulting in a higher yeild of ammonia since there are more gas molecules on the left hand side of the equation (4 in total) than there are on the right hand side of the equation (2). ..."

    Quote from: http://www.ausetute.com.au/haberpro.html

    The last paragraph explains why I have twice told you that The Sabatier Process is CO2 + 4H2 -> CH4 + 2H20.
    and the above Haber process must be done at high pressure to get any economically significant yields because there are less product molecules than reacting molecules.
    Last edited by a moderator: Oct 7, 2011
  18. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    Ammonia is a liquid, even at room temperature, at quite modest pressures. Many thousands of steel tanks holding liquid NH3 are found on larger farms all over the world.
  19. Walter L. Wagner Cosmic Truth Seeker Valued Senior Member

    Hey, that's what I said in my post #200 (though I did not mention that when it is pressurized it turns to a liquid-- I thought that was obvious, but maybe not). Good to see you're an old farmhand too. Reminds me of my tractor-driving days!
  20. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    Yes, I spent year of my early life on farm so far up in the hills of (West?) Virginia that I did not go to any school that year, but we were too poor to use Ammonia - only had sheep and horse shit for fertilizer.* (One of my jobs was to collect it - not a bad one if it has had a few dry days in the sun.)

    "Tractor"? What is that?** I rode on top of the triangular shaped "harrow" (big spikes on bottom side) to give it more weight breaking up dirt clods and kept my balance while steering the horse pulling us. (A grown man doing that was too much weight for the horse to pull.)

    * and at least a dozen or so crows. For why & how I used crows with extreme satisfaction for fertilizer. See http://www.sciforums.com/showpost.php?p=2341632&postcount=9

    ** I heard back then that they use something called "gasoline" but did not know what it was either.
    Last edited by a moderator: Oct 7, 2011
  21. wlminex Banned Banned

    . . .me too . . . old farm boy . . . maybe we need to start an 'old farts' forum?
  22. wellwisher Banned Banned

    Amonina could work as a fuel, but there are some practical problems. For one thing unlike gasoline, ammonia will absorb water. This could cause a performance loss, unless you add dehydration devices, at added cost, all along the supply chain and into each car.

    Burning ammonia will also create NOX, which, in conjunction with water, will make nitric acid. This is nasty on steel and aluminum. You would need to make many engine parts out of stainless steel, with is inert to nitric acid. Or you could use ceramic engine parts. The nitric acid would help keep the stainless steel or ceramic cylinders clean of gunk.
  23. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    Most advocates of NH3 for use in cars don't want to burn it as fuel, but extract H2 from it for fuel cells. NH3 is just a better storage system for H2 (Best I know of by far.) Also NH3 can be distributed by tank trucks like gasoline is, no need to make new, expensive, H2 pipelines.

    Not only can it be held without a cryogenic insulated tank on hot summer day, but each gallon / liter has more hydrogen in it than the same volume of liquid H2, which would need to bee very very cold - much colder than for example liquid nitrogen which you may have freeze rubber balls so they shatter when dropped instead of bounce.

    PS You point about NH3 absorbing H2O is true, but less of a problem than the fact ETOH (alcohol) absorbs more and more rapidly but has functioned just fine as a fuel for many cars in Brazil for 35+ years. Some H2O in the fuel is a benefit - Pure fuel burns hotter and is harder on the IC engine and makes the exhaust heat thrown away greater - more energy lost.

    The steam is expanding and pushing on the piston too. IC engines make more heat than they can use - Some steam in the combustion gas is like internal cooling but unlike the external water cooling, you get force on the piston with this "internal cooling."

    H2O injection was used in WWII fighters to get more power when in deep trouble but of course too much H2O in the fuel is bad and can cause serious corrosion problems in simple steel fuel tanks etc.
    Last edited by a moderator: Oct 11, 2011

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