Gas-to-liquid

Gas to liquids (GTL) is a refinery process to convert natural gas or other gaseous hydrocarbons into longer-chain hydrocarbons, such as gasoline or diesel fuel. Methane-rich gases are converted into liquid synthetic fuels either via direct conversion—using non-catalytic processes that convert methane to methanol in one step—or via syngas as an intermediate, such as in the Fischer Tropsch, Mobil and syngas to gasoline plus processes.

The Fischer–Tropsch process starts with partial oxidation of methane (natural gas) to carbon dioxide, carbon monoxide, hydrogen gas and water. The ratio of carbon monoxide to hydrogen is adjusted using the water gas shift reaction, while the excess carbon dioxide is removed with aqueous solutions of alkanolamines (or physical solvents). Removing the water yields synthesis gas (syngas) which is chemically reacted over an iron or cobalt catalyst to produce liquid hydrocarbons and other byproducts. Oxygen is provided from a cryogenic air separation unit.

Methanol is made from methane (natural gas) in a series of three reactions:

The methanol thus formed may be converted to gasoline by the Mobil process.

In the early 1970s, Mobil developed an alternative procedure in which natural gas is converted to syngas, and then methanol. The methanol polymerized over a zeolite catalyst to form alkanes.

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