Gas to liquids

Gas to liquids

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Gas to liquids is a refinery
Oil refinery
An oil refinery or petroleum refinery is an industrial process plant where crude oil is processed and refined into more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied petroleum gas...

 process to convert natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 or other gaseous hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

s into longer-chain hydrocarbons such as gasoline or diesel fuel. Methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

-rich gases are converted into liquid synthetic fuel
Synthetic fuel
Synthetic fuel or synfuel is a liquid fuel obtained from coal, natural gas, oil shale, or biomass. It may also refer to fuels derived from other solids such as plastics or rubber waste. It may also refer to gaseous fuels produced in a similar way...

s either via direct conversion or via syngas
Syngas
Syngas is the name given to a gas mixture that contains varying amounts of carbon monoxide and hydrogen. Examples of production methods include steam reforming of natural gas or liquid hydrocarbons to produce hydrogen, the gasification of coal, biomass, and in some types of waste-to-energy...

 as an intermediate, for example using the Fischer Tropsch or Mobil
Mobil
Mobil, previously known as the Socony-Vacuum Oil Company, was a major American oil company which merged with Exxon in 1999 to form ExxonMobil. Today Mobil continues as a major brand name within the combined company, as well as still being a gas station sometimes paired with their own store or On...

 processes.

Fischer–Tropsch process


This method starts with partial oxidation of methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 (natural gas) to carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

, hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 and water, the carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 to hydrogen (H2) ratio is adjusted using the water gas shift reaction
Water gas shift reaction
The water-gas shift reaction is a chemical reaction in which carbon monoxide reacts with water vapor to form carbon dioxide and hydrogen:The water-gas shift reaction is an important industrial reaction. It is often used in conjunction with steam reforming of methane or other hydrocarbons, which is...

) and the excess carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 removal by aqueous solutions of alkanolamine (or physical solvents) the water is removed yielding synthesis gas (syngas
Syngas
Syngas is the name given to a gas mixture that contains varying amounts of carbon monoxide and hydrogen. Examples of production methods include steam reforming of natural gas or liquid hydrocarbons to produce hydrogen, the gasification of coal, biomass, and in some types of waste-to-energy...

) that is chemically reacted over an iron or cobalt catalyst to produce liquid hydrocarbons and other byproducts.

Mobil process


An alternative path starts by conversion of the natural gas to syngas, conversion of the syngas to methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...

 which is subsequently polymerized into alkanes over a zeolite
Zeolite
Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that...

 catalyst. It was developed by Mobil
Mobil
Mobil, previously known as the Socony-Vacuum Oil Company, was a major American oil company which merged with Exxon in 1999 to form ExxonMobil. Today Mobil continues as a major brand name within the combined company, as well as still being a gas station sometimes paired with their own store or On...

 in early 1970s.

Methanol is made from methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 (natural gas) in a series of three reactions:
  1. Steam reforming: CH4 + H2O → CO + 3 H2 ΔrH = +206 kJ mol-1
  2. Water shift reaction CO + H2O → CO2 + H2 ΔrH = -41 kJ mol-1
  3. Synthesis 2 H2 + CO → CH3OH ΔrH = -92 kJ mol-1


The methanol thus formed may be converted to gasoline by the Mobil process. First
methanol is dehydrated to give dimethyl ether
Dimethyl ether
Dimethyl ether , also known as methoxymethane, is the organic compound with the formula . The simplest ether, it is a colourless gas that is a useful precursor to other organic compounds and an aerosol propellant. When combusted, DME produces minimal soot and CO, though HC and NOx formation is...

:
2 CH3OH → CH3OCH3 + H2O

This is then further dehydrated
Dehydration reaction
In chemistry and the biological sciences, a dehydration reaction is usually defined as a chemical reaction that involves the loss of water from the reacting molecule. Dehydration reactions are a subset of elimination reactions...

 over a zeolite catalyst, ZSM-5, to give a gasoline with 80% (by weight based on the organics in the product stream) C5+ hydrocarbon products.

ZSM-5 is deactivated by a carbon build-up ("coking") over time in converting methanol to gasoline. The catalyst can be re-activated by burning off the coke in a stream of hot (500 °C (932 °F)) air; however, the number of re-activation cycles is limited.

Commercial uses


Two companies, SASOL
Sasol
Sasol Ltd. is a South African company involved in mining, energy, chemicals and synfuels. In particular, they produce petrol and diesel profitably from coal and natural gas using Fischer-Tropsch process...

 and Shell, have technology proven to work on a commercial scale. PetroSA (Pty) Ltd, in South Africa, completed semi-commercial demostrations of gas-to-liquids used by the company in 2011. Using gas-to-liquids processes, refineries can convert some of their gaseous waste products (flare gas) into valuable fuel oil
Fuel oil
Fuel oil is a fraction obtained from petroleum distillation, either as a distillate or a residue. Broadly speaking, fuel oil is any liquid petroleum product that is burned in a furnace or boiler for the generation of heat or used in an engine for the generation of power, except oils having a flash...

s, which can be sold as is or blended only with diesel fuel. It 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
Peak oil
Peak oil is the point in time when the maximum rate of global petroleum extraction is reached, after which the rate of production enters terminal decline. This concept is based on the observed production rates of individual oil wells, projected reserves and the combined production rate of a field...

. Royal Dutch Shell
Royal Dutch Shell
Royal Dutch Shell plc , commonly known as Shell, is a global oil and gas company headquartered in The Hague, Netherlands and with its registered office in London, United Kingdom. It is the fifth-largest company in the world according to a composite measure by Forbes magazine and one of the six...

 produces a diesel from natural gas in a factory in Bintulu
Bintulu
Bintulu is a coastal town, and the capital of Bintulu District in the Bintulu Division of Sarawak, Malaysia. It is about 650 kilometers from Kuching and about 215 kilometers from either Sibu or Miri....

, Malaysia. Another Shell GTL facility is the Pearl GTL
Pearl GTL
Pearl GTL is a gas to liquids project based in Ras Laffan, Qatar. It will convert natural gas into liquid petroleum products. When constructed, it will be the largest GTL plant in the world.-Technical features:...

 plant in Qatar, the world's largest GTL facility. SASOL has recently built 34kb/d Oryx GTL
Oryx GTL
ORYX GTL is a synthetic fuel plant based in Ras Laffan Industrial City, Qatar, that is owned by Qatar Petroleum and Sasol . It uses gas to liquids technology for converting natural gas into liquid petroleum products. The capacity of Oryx GTL is of oil. When commissioned, it was the world's first...

 facility in Ras Laffan Industrial City
Ras Laffan Industrial City
Ras Laffan Industrial City is an industrial hub located north of Doha, Qatar. It is administrated by Qatar Petroleum.Ras Laffan Industrial City is the Qatar's main site for production of liquefied natural gas and gas-to-liquid...

, Qatar.

On 12 October 2009, a Qatar Airways
Qatar Airways
Qatar Airways Company Q.C.S.C. , operating as Qatar Airways, is the flag carrier of Qatar. Headquartered in the Qatar Airways Tower in Doha, it operates a hub-and-spoke network, linking over 100 international destinations from its base in Doha, using a fleet of over 100 aircraft...

 Airbus A340-600 conducted the world's first commercial passenger flight using a mixture of kerosene and synthetic GTL fuel in its flight from London's Gatwick Airport to Doha.

One other proposed solution is to use a novel FPSO
Floating Production Storage and Offloading
A floating production, storage and offloading unit is a floating vessel used by the offshore industry for the processing of hydrocarbons and for storage of oil. A FPSO vessel is designed to receive hydrocarbons produced from nearby platforms or subsea template, process them, and store oil until it...

 for offshore conversion of gas to liquids (methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...

, diesel, petrol, syn-crude, and naphtha
Naphtha
Naphtha normally refers to a number of different flammable liquid mixtures of hydrocarbons, i.e., a component of natural gas condensate or a distillation product from petroleum, coal tar or peat boiling in a certain range and containing certain hydrocarbons. It is a broad term covering among the...

).

Brazilian oil company Petrobras
Petrobras
Petróleo Brasileiro or Petrobras is a semi-public Brazilian multinational energy corporation headquartered in Rio de Janeiro, Brazil. It is the largest company in Latin America by market capitalization and revenue, and the largest company headquartered in the Southern Hemisphere by market...

 has ordered two small experimental GTL production facilities intended to be posted at offshore oil fields too distant or deep to justify gas pipelines to onshore GTL plant.

The World Bank
World Bank
The World Bank is an international financial institution that provides loans to developing countries for capital programmes.The World Bank's official goal is the reduction of poverty...

estimates that over 150 billion cubic metres of natural gas are flared or vented annually, an amount worth approximately 30.6 billion dollars, equivalent to 25 percent of the United States’ gas consumption or 30% of the European Union’s gas consumption per year, a resource that could be useful using GTL.

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