3 ms·

>Unlike solar cells or battery cells, I don't really see much chance for 'learning rates' and technology improvement to drastically drive down the cost of green

by scythe 2y ago

>Unlike solar cells or battery cells, I don't really see much chance for 'learning rates' and technology improvement to drastically drive down the cost of green ammonia. Falling electrolyser costs are nice, but they're only a portion of the process plant CAPEX, and the cost of the green electricity dominates the economics over the process plant CAPEX anyway. You could get electrolysers for free and still be unable to make cheap green ammonia. So for green ammonia to get adopted, a strong 'carbon price' needs to be in place, and I think that same strong carbon price would make biodiesel competitive. There is a ton of research going into improving the efficiency of the H2 > NH3 conversion, and there are at least two startups (Tsubame in Japan and a new one I don't remember). There's no rule that says you can't beat Haber. Compared to methanol, ammonia is currently more expensive but vastly more scalable in the long run; once you reach the biofuel "ceiling" (roughly corresponding to the availability of farming and forestry byproducts) you're stuck making it via carbon capture, which has its own efficiency problems.

kragen 2y ago
By "efficiency" do you mean energy consumption or hydrogen consumption?
- scythe 2y ago
  Energy consumption. I am pretty sure that the hydrogen utilization in most ammonia production is very high. In theory the energy required to produce ammonia is negative (Hf < 0) but at standard pressure its formation is thermodynamically unfavorable (Gf = Hf + TdeltaS > 0). But the bigger issue is the very high activation energy barrier for ammonia synthesis, which results in a lot of energy being used to make ammonia at very high pressure and temperature. Right now there are two competing approaches to reducing the cost of ammonia production. Tsubame is using a new ruthenium-based catalyst that lowers the reaction temperature (and therefore, also the pressure). The other method is by electrocatalysis. I don't know for sure that this is what NitroVolt is doing but their name certainly suggests it.
  - kragen 2y ago
    Thank you! Presumably if you had some way of rapidly removing the ammonia produced from the reaction, like maybe a high-temperature highly polar solvent that reacted reversibly with the ammonia, but didn't dissolve much hydrogen or nitrogen, you could get by with a lower equilibrium amount of ammonia and thus much lower pressure. Anhydrous phosphoric acid seems like a potential candidate? But that's obvious enough that people probably tried it a century ago.

by scythe 2y ago

kragen 2y ago

By "efficiency" do you mean energy consumption or hydrogen consumption?

scythe 2y ago
Energy consumption. I am pretty sure that the hydrogen utilization in most ammonia production is very high. In theory the energy required to produce ammonia is negative (Hf < 0) but at standard pressure its formation is thermodynamically unfavorable (Gf = Hf + TdeltaS > 0). But the bigger issue is the very high activation energy barrier for ammonia synthesis, which results in a lot of energy being used to make ammonia at very high pressure and temperature. Right now there are two competing approaches to reducing the cost of ammonia production. Tsubame is using a new ruthenium-based catalyst that lowers the reaction temperature (and therefore, also the pressure). The other method is by electrocatalysis. I don't know for sure that this is what NitroVolt is doing but their name certainly suggests it.
- kragen 2y ago
  Thank you! Presumably if you had some way of rapidly removing the ammonia produced from the reaction, like maybe a high-temperature highly polar solvent that reacted reversibly with the ammonia, but didn't dissolve much hydrogen or nitrogen, you could get by with a lower equilibrium amount of ammonia and thus much lower pressure. Anhydrous phosphoric acid seems like a potential candidate? But that's obvious enough that people probably tried it a century ago.