The main difference between propane and butane gas is their chemical structure. Although they are both composed of carbon and hydrogen chains, the number of carbons and hydrogens in each differ slightly. Propane, for instance, is composed of a three-carbon chain with eight hydrogens. Butane, on the other hand, has a four-carbon chain with ten hydrogens, which is only one carbon and two hydrogens more than propane.
Ethane is most efficiently separated from methane by liquefying it at cryogenic temperatures. Various refrigeration strategies exist: the most economical process presently in wide use employs a turboexpander, and can recover more than 90% of the ethane in natural gas.
Natural gas, when discharged into the environment is a greenhouse gas whereas propane is not classified as such. Propane is not toxic or damaging and will not harm the environment if it is released into the atmosphere, which is why it is not labeled as a greenhouse gas.