Noun
synthesis gas (countable and uncountable, plural synthesis gases)
(petrochemistry) The gas obtained by heating coal and steam; coal gas.
Because the carbon dioxide feed is recovered from ammonia synthesis gas, it contains traces of hydrogen that can mingle with passivation air to form an explosive mixture if allowed to accumulate. Source: Internet
Hydrocarbons other than methane can be used to produce synthesis gas with varying product ratios. Source: Internet