Convert m³ of natural gas to btu's

[Knight]

jim wrote:
Please explain how to convert m3 of natural gas to btu's. Thanks.

Natural gas is mostly Methane (around 92%), with a variety of other contaminants, including ethane, propane, butane and pentane.

From the Handbook of Chemistry & Physics. Chemical Rubber Co. Press LLC, 2001. Under "Heat of Combustion."

Methane (CH4) has an energy content of 890.8 kJ/mol.

One molecule of Methane would be 1 carbon atom and four hydrogen atoms. Carbon has an amu of 12.01 g/mol, and hydrogen has an amu of 1.008 g/mol, so methanes molar weight is:

(1 * 12.01) + (4 * 1.008) = 16.042 g/mol

Finally, looking up methanes density we get 0.717 kg/m³, so:

One cubic meter of Methane weighs 0.717 kg/m³ * 1000 g/kg = 717 grams.

717 grams / 16.042 grams/mol = 44.9 moles of Methane per cubic meter.

44.8 moles * 890.8 kJ/mol = 39,997 kJ, or 40 mJ.

Now, to get to the answer:

There are 1.054 kJ/BTU, so:

39,997 kJ / 1.054 kJ/btu = 37,948 BTU.

So, One cubic meter of natural gas is approximately 37,948 BTU.