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. Two general strategies exist: i direct partial combustion of methane to methanol and ii Fischer—Tropsch -like processes that convert carbon monoxide and hydrogen into hydrocarbons. Strategy ii is followed by diverse methods to convert the hydrogen-carbon monoxide mixtures to liquids. Direct partial combustion has been demonstrated in nature but not replicated commercially.
Technologies reliant on partial combustion have been commercialized mainly in regions where natural gas is inexpensive.
The motivation for GTL is to produce liquid fuels, which are more readily transported than methane. Methane must be cooled below its critical temperature of Because of the associated cryogenic apparatus, LNG tankers are used for transport. Methanol is a conveniently handled combustible liquid, but its energy density is half of that of gasoline.
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. Removing the water yields synthesis gas syngas. Syngas is allowed to react over an iron or cobalt catalyst to produce liquid hydrocarbons, including alcohols. 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 and methanol-to-olefins. In the early s, Mobil developed an alternative procedure in which natural gas is converted to syngas, and then methanol.
The methanol reacts in the presence of a zeolite catalyst to form alkanes. In terms of mechanism, methanol is partially dehydrated to give dimethyl ether :.
The Mobile MTG process is no longer practiced. Methanol can be converted to olefins using zeolite and SAPO-based heterogeneous catalysts. Depending on the catalyst pore size, this process can afford either C2 or C3 products, which are important monomers.
A third gas-to-liquids process builds on the MTG technology by converting natural gas-derived syngas into drop-in gasoline and jet fuel via a thermochemical single-loop process.
This process consists of four fixed bed reactors in series in which a syngas is converted to synthetic fuels. The steps for producing high-octane synthetic gasoline are as follows: . With methane as the predominant target for GTL, much attention has focused on the three enzymes that process methane. These enzymes support the existence of methanotrophs , microorganisms that metabolize methane as their only source of carbon and energy. Aerobic methanotrophs harbor enzymes that oxygenate of methane to methanol.
The relevant enzymes are methane monooxygenases , which are found both in soluble and particulate i. They catalyze the oxygenation according to the following stoichiometry:.
Anaerobic methanotrophs rely on the bioconversion of methane using the enzymes called methyl-coenzyme M reductases.
These organisms effect reverse methanogenesis. Strenuous efforts have been made to elucidate the mechanisms of these methane-converting enzymes, which would enable their catalysis to be replicated in vitro.
Biodiesel can be made from CO 2 using the microbes Moorella thermoacetica and Yarrowia lipolytica. This process is known as biological gas-to-liquids.
Using gas-to-liquids processes, refineries can convert some of their gaseous waste products flare gas into valuable fuel oils , which can be sold as is or blended only with diesel fuel. Gas-to-liquids processes may also be used for the economic extraction of gas deposits in locations where it is not economical to build a pipeline.
This process will be increasingly significant as crude oil resources are depleted. Royal Dutch Shell produces a diesel from natural gas in a factory in Bintulu , Malaysia. New generation of GTL technology is being pursued for the conversion of unconventional, remote and problem gas into valuable liquid fuels. Other mainly U. Another proposed solution to stranded gas involves use of novel FPSO for offshore conversion of gas to liquids such as methanol , diesel , petrol , synthetic crude , and naphtha.
Gas to liquids
GTL using natural gas is more economical when there is wide gap between the prevailing natural gas price and crude oil price on a Barrel of oil equivalent BOE basis. A coefficient of 0.
When natural gas is converted in to GTL, the liquid products are easier to export at cheaper price rather than converting in to LNG and further conversion to liquid products in an importing country.
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Shell GTL Fuel video
Vandewalle, Kevin M. Van Geem, Guy B.
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