Last week the US government announced that it believes it has successfully breached the fuel tank on a dead satellite, effectively destroying the toxic fuel stored on board: 1000 pounds of hydrazine. Hydrazine is a simple nitrogen compound, two NH2 groups joined by a NN single bond. How does such a simple compound power a rocket?
Hydrazine is a hypergolic propellant – one that ignites as soon as it comes into contact with an oxidant (something that will react with it to effectively strip away some electrons from the reactant and force the molecule to bond differently, the changes in the bonds between atoms are what release the energy). Hypergolic is apparently a term coined by the German rocket program from hyper (very) + ergon (Greek for work) + ol (from oleum, the Latin for oil). Hydrazine is that, a liquid (if not particularly oily one) that can be used to push satellites around in orbit – to do work.
Hydrazine is a solid in the satellite’s tanks, and once thawed can be catalytically and rapidly decomposed. Almost any metal will do, though iridium is the usual choice. The reactions produce lots of very hot gases, which you can direct through a thruster:
3 N2H4 → 4 NH3 + N2
N2H4 → N2 + 2 H2
NH3 + N2H4 → 3 N2 + 8 H2
A little thermochemistry can quickly tell you just how much energy you might produce from 1000 pounds of hydrazine. The overall reaction is:
5 N2H4 → 5 N2 + 10 H2
which releases 50,000 Joules of energy per mole of hydrazine. A mole of hydrazine weighs about 32 grams, so you get enough energy to make a cold cup of coffee hot from just over an ounce of hydrazine (do NOT try this at home!). If all the hydrazine in that satellite went up at once, it would release about 8 billion Joules (enough to keep the average US citizen in energy for more than a week).
Along with the growing interest in Fuel Cell powered cars comes the need for higher production methods of Hydrogen, both in bulk form and in-car conversions (for fuels such as methanol and ethanol to be converted to hydrogen on board). Previous methods of converting Ethanol to hydrogen was by means of high-temperature steam reformation (at temperatures in excess of 600° C) to produce Hydrogen gas and CO.
This journal describes a special method of low-temperature dehydrogenation of ethanol over special Raney catalyst with Cu added to it. The first step produces one mole each of hydrogen gas and acetaldehyde (per mole of ethanol). This is followed by the decarbonylation of acetaldehyde to form methanol and CO. The whole reaction undergoes a water-gas shift to net one mole each of Methane and Carbon dioxide and two moles of Hydrogen.
Compared to high temperature reformation methods, which produces 6 moles of hydrogen per mole of ethanol, this reaction doesn’t seem as fuel efficient, though the authors were confident, that with an internal combustion engine on-board that uses the methane produced as fuel, the total output energy would be equal.
