The Ideal Transport Fuel

Hydrogen has been proposed as a transport fuel but it has many problems in its pure form.

• The hydrogen gas molecule is very small and will pass through solid steel when under pressure.   This means that in a compressed gas storage tank you can expect to lose about 1% per day.
• Hydrogen causes steels to become brittle.  This can ultimately lead to brittle fracture of pressurized steel containment vessels.
• Hydrogen has a wide flammability range which makes it more of an explosion hazard than any other fuel. Hydrogen has a flammability range from 4% to 75% as compared to, methane at 2% to 9%.
• Hydrogen has a low energy per unit volume compared with liquid fuels such as methanol, and ethanol.  Hydrogen has a higher heating value of 11.7kJ/L and methane is 36.5kJ/L at 1bar pressure and 25°C.  Methanol’s higher heating value of 18MJ/L is a 1000 times higher than that of hydrogen at ambient conditions.
• It takes a great deal of energy to compress or liquefy it for transport and storage.  It takes approximately 18MJ/kg to compress hydrogen to 400bar, but only 2MJ/kg to compress methane to the same pressure.  To liquefy hydrogen requires dropping the temperature to -253°C (20K), a process of only 7% efficiency.
• Metal hydrides for storage have a high energy requirement to bind the hydrogen into the metals, and then heat to release it again.  The hydrogen needs to be compressed.  The storage is inefficient with only 55-60kg(H₂)/m³ compared with 71kg(H2)/m³ for liquid hydrogen and 100kg of hydrogen contained in one cubic meter of methanol.
• Transport through pipe systems or by truck is very energy intensive.  To transport hydrogen gas at 200bar 200km by diesel truck will consume 38% of the energy delivered, whereas methane at 200bar will consume only 10% of the energy delivered.  Liquid fuels require only a fraction of a percent to deliver.  Piping hydrogen 1000km will consume 9% of the input energy value.
• The generation of hydrogen from other sources is inefficient.  Electrolysis is at best 70% efficient.  Reformation from coal and hydrocarbons is very energy intensive and at best only 60% efficient.
• To generate electricity from hydrogen through a fuel cell is of the order of 50% efficient.

The bond that hydrogen forms is still a good energy source.  So why not join the hydrogen up to carbon atoms on a carbon chain?  Is that not what hydrocarbons in gasoline are?

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