The composition of natural gas varies with the locality of the gas wells from which it was produced. After removing the water, carbon dioxide and any hydrogen sulfide (H2S) – if any is contained in the gas supply – all natural gas remains a mixture of largely methane, with some ethane, sometimes a little butane, propane, pentane and other hydrocarbons, and perhaps a smaller proportion of nitrogen – and occasionally still some CO2.
When liquefied, the constituents in the supply gas are generally the same as those in LNG, unless removed during the liquefaction process (see the example shown in Table 1, below).
When expressed as Mole Percent, the composition of the LNG is described as the percentage of molecules of a given component in the mixture divided by the total number of moles in the mixture. A mole is the amount of a substance that contains as many elementary entities as there are atoms in 0.012kg of carbon-12.
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