![Methanier aspher LNGRIVERS](https://upload.wikimedia.org/wikipedia/commons/2/20/Methanier_aspher_LNGRIVERS.jpg)
Gas to liquids (GTL) is a
refinery
A refinery is a production facility composed of a group of chemical engineering unit processes and unit operations refining certain materials or converting raw material into products of value.
Types of refineries
Different types of refineries ...
process to convert
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
or other gaseous
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
s into longer-chain hydrocarbons, such as
gasoline
Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organi ...
or
diesel fuel
Diesel fuel , also called diesel oil, is any liquid fuel specifically designed for use in a diesel engine, a type of internal combustion engine in which fuel ignition takes place without a spark as a result of compression of the inlet air and ...
.
Methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
-rich gases are converted into liquid
synthetic fuel
Synthetic fuel or synfuel is a liquid fuel, or sometimes gaseous fuel, obtained from syngas, a mixture of carbon monoxide and hydrogen, in which the syngas was derived from gasification of solid feedstocks such as coal or biomass or by refo ...
s. 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 -82.3 °C in order to be liquified under pressure. Because of the associated cryogenic apparatus,
LNG tanker
An LNG carrier is a tank ship designed for transporting liquefied natural gas (LNG).
History
The first LNG carrier '' Methane Pioneer'' () carrying , classed by Bureau Veritas, left the Calcasieu River on the Louisiana Gulf coast on 25 January ...
s are used for transport. Methanol is a conveniently handled combustible liquid, but its
energy density is half of that of gasoline.
Fischer–Tropsch process
![GTL process](https://upload.wikimedia.org/wikipedia/commons/e/ed/GTL_process.GIF)
A GtL process may be established via the Fischer–Tropsch process which comprises several chemical reactions that convert a mixture of carbon monoxide (CO) and hydrogen (H
2) into long chained hydrocarbons. These hydrocarbons are typically liquid or semi-liquid and ideally have the formula (C
''n''H
2''n''+2).
In order to obtain the mixture of CO and H
2 required for the Fischer–Tropsch process,
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
(main component of natural gas) may be subjected to partial oxidation which yields a raw synthesis gas mixture of mostly
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
,
carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
,
hydrogen gas
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, a ...
(and sometimes water and nitrogen). The ratio of
carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
to hydrogen in the raw synthesis gas mixture can be adjusted e.g. using the
water gas shift reaction
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a s ...
. Removing impurities, particularly nitrogen,
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
and water, from the raw synthesis gas mixture yields pure
synthesis gas
Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principly used for producing ammonia or methanol. Syngas is combustible and can be used ...
(syngas).
The pure syngas is routed into the Fischer–Tropsch process, where the syngas reacts over an iron or cobalt catalyst to produce synthetic hydrocarbons, including alcohols.
Methane to methanol process
Methanol is made from
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
(natural gas) in a series of three reactions:
;
Steam reforming
Steam reforming or steam methane reforming (SMR) is a method for producing syngas (hydrogen and carbon monoxide) by reaction of hydrocarbons with water. Commonly natural gas is the feedstock. The main purpose of this technology is hydrogen product ...
:CH
4 + H
2O → CO + 3 H
2 Δ
rH = +206 kJ mol
−1
;
Water shift reaction
:CO + H
2O → CO
2 + H
2 Δ
rH = -41 kJ mol
−1
;Synthesis
:2 H
2 + CO → CH
3OH Δ
rH = -92 kJ mol
−1
The methanol thus formed may be converted to gasoline by the Mobil process and methanol-to-olefins.
Methanol to gasoline (MTG) and methanol to olefins
In the early 1970s,
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
Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H+. These p ...
catalyst to form
alkanes
In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in whi ...
. In terms of mechanism, methanol is partially
dehydrated
In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...
to give
dimethyl ether
Dimethyl ether (DME; also known as methoxymethane) is the organic compound with the formula CH3OCH3,
(sometimes ambiguously simplified to C2H6O as it is an isomer of ethanol). The simplest ether, it is a colorless gas that is a useful precursor ...
:
:2 CH
3OH → CH
3OCH
3 + H
2O
The mixture of dimethyl ether and methanol is then further dehydrated over a zeolite catalyst such as
ZSM-5
ZSM-5, Zeolite Socony Mobil–5 (framework type MFI from ZSM-5 (five)), is an aluminosilicate zeolite belonging to the pentasil family of zeolites. Its chemical formula is NanAlnSi96–nO192·16H2O (0 , which in practice is polymerized and hydrogenated to give a gasoline with hydrocarbons of five or more carbon atoms making up 80% of the fuel by weight. The Mobil MTG process is practiced from
coal-derived methanol in China by
JAMG. A more modern implementation of MTG is the Topsøe improved gasoline synthesis (TiGAS).
Methanol can be converted to olefins using zeolite and SAPO-based
heterogeneous catalyst
In chemistry, heterogeneous catalysis is catalysis where the phase of catalysts differs from that of the reactants or products. The process contrasts with homogeneous catalysis where the reactants, products and catalyst exist in the same phase. P ...
s. Depending on the catalyst pore size, this process can afford either C2 or C3 products, which are important monomers.
Syngas to gasoline plus process (STG+)
![STG+ Process](https://upload.wikimedia.org/wikipedia/commons/d/d0/STG%2B_Process.jpg)
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.
[LaMonica, Martin]
Natural Gas Tapped as Bridge to Biofuels
''MIT Technology Review'', 27 June 2012. Retrieved: 7 March 2013.
The STG+ process follows four principal steps in one continuous process loop. 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:
[Introduction to Primus' STG+ Technology](_blank)
''Primus Green Energy'', undated. Retrieved: 5 March 2013.
#
Methanol Synthesis: Syngas is fed to Reactor 1, the first of four reactors, which converts most of the syngas (CO and ) to methanol () when passing through the catalyst bed.
#
Dimethyl Ether
Dimethyl ether (DME; also known as methoxymethane) is the organic compound with the formula CH3OCH3,
(sometimes ambiguously simplified to C2H6O as it is an isomer of ethanol). The simplest ether, it is a colorless gas that is a useful precursor ...
(DME) Synthesis: The methanol-rich gas from Reactor 1 is next fed to Reactor 2, the second STG+ reactor. The methanol is exposed to a
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
and much of it is converted to DME, which involves a dehydration from methanol to form DME ().
# Gasoline synthesis: The Reactor 2 product gas is next fed to Reactor 3, the third reactor containing the catalyst for conversion of DME to hydrocarbons including paraffins (
alkanes),
aromatics
Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past groupin ...
, naphthenes (
cycloalkanes) and small amounts of olefins (
alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
s), mostly from (number of carbon atoms in the hydrocarbon molecule) to .
# Gasoline Treatment: The fourth reactor provides
transalkylation
In organic chemistry, transalkylation is a chemical reaction involving the transfer of an alkyl group from one organic compound to another. The reaction is used for the transfer of methyl and ethyl groups between benzene rings. This is of particul ...
and
hydrogenation
Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organ ...
treatment to the products coming from Reactor 3. The treatment reduces
durene
Durene, or 1,2,4,5-tetramethylbenzene, is an organic compound with the formula C6H2(CH3)4. It is a colourless solid with a sweet odor. The compound is classified as an alkylbenzene. It is one of three isomers of tetramethylbenzene, the other t ...
(tetramethylbenzene)/isodurene and trimethylbenzene components that have high freezing points and must be minimized in gasoline. As a result, the synthetic gasoline product has high octane and desirable viscometric properties.
# Separator: Finally, the mixture from Reactor 4 is condensed to obtain gasoline. The non-condensed gas and gasoline are separated in a conventional condenser/separator. Most of the non-condensed gas from the product separator becomes recycled gas and is sent back to the feed stream to Reactor 1, leaving the synthetic gasoline product composed of paraffins, aromatics and naphthenes.
Biological gas-to-liquids (Bio-GTL)
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
methanotroph
Methanotrophs (sometimes called methanophiles) are prokaryotes that metabolize methane as their source of carbon and chemical energy. They are bacteria or archaea, can grow aerobically or anaerobically, and require single-carbon compounds to s ...
s, microorganisms that metabolize methane as their only source of carbon and energy. Aerobic methanotrophs harbor enzymes that oxygenate methane to methanol. The relevant enzymes are
methane monooxygenase
Methane monooxygenase (MMO) is an enzyme capable of oxidizing the C-H bond in methane as well as other alkanes. Methane monooxygenase belongs to the class of oxidoreductase enzymes ().
There are two forms of MMO: the well-studied soluble form (s ...
s, which are found both in soluble and particulate (i.e. membrane-bound) varieties. They catalyze the oxygenation according to the following stoichiometry:
:CH
4 + O
2 + NADPH + H
+ → CH
3OH + H
2O + NAD
+
Anaerobic methanotrophs rely on the bioconversion of methane using the enzymes called
methyl-coenzyme M reductase
In enzymology, coenzyme-B sulfoethylthiotransferase, also known as methyl-coenzyme M reductase (MCR) or most systematically as 2-(methylthio)ethanesulfonate:N-(7-thioheptanoyl)-3-O-phosphothreonine S-(2-sulfoethyl)thiotransferase is an enzyme tha ...
s. 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
Biodiesel is a form of diesel fuel derived from plants or animals and consisting of long-chain fatty acid esters. It is typically made by chemically reacting lipids such as animal fat ( tallow), soybean oil, or some other vegetable oil ...
can be made from using the microbes
Moorella thermoacetica and
Yarrowia lipolytica
''Yarrowia'' is a fungal genus in the family Dipodascaceae. For a while the genus was monotypic, containing the single species ''Yarrowia lipolytica'', a yeast that can use unusual carbon sources, such as hydrocarbons. This has made it of interes ...
. This process is known as biological gas-to-liquids.
Commercial uses
![INFRA M100 GTL Plant](https://upload.wikimedia.org/wikipedia/commons/9/91/INFRA_M100_GTL_Plant.jpg)
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
Diesel fuel , also called diesel oil, is any liquid fuel specifically designed for use in a diesel engine, a type of internal combustion engine in which fuel ignition takes place without a spark as a result of compression of the inlet air and ...
. The
World Bank
The World Bank is an international financial institution that provides loans and grants to the governments of low- and middle-income countries for the purpose of pursuing capital projects. The World Bank is the collective name for the Inte ...
estimates that over of natural gas are
flared or vented annually, an amount worth approximately $30.6 billion, equivalent to 25% of the United States' gas consumption or 30% of the European Union's annual gas consumption, a resource that could be useful using GTL. 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
Bintulu is a coastal town on the island of Borneo in the central region of Sarawak, Malaysia. Bintulu is located 610 kilometres (380 mi) northeast of Kuching, 216 kilometres (134 mi) northeast of Sibu, and 200 kilometres (120 mi) ...
,
Malaysia
Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...
. Another Shell GTL facility is the
Pearl GTL
The Pearl GTL is a gas to liquids (GTL) plant based in Ras Laffan, Qatar. It converts natural gas into liquid petroleum products. It is the largest GTL plant in the world.
The first commercial shipment from the Pearl GTL was made on 13 June ...
plant in
Qatar
Qatar (, ; ar, قطر, Qaṭar ; local vernacular pronunciation: ), officially the State of Qatar,) is a country in Western Asia. It occupies the Qatar Peninsula on the northeastern coast of the Arabian Peninsula in the Middle East; it ...
, the world's largest GTL facility. SASOL has recently built the
Oryx GTL facility in
Ras Laffan Industrial City
Ras Laffan Industrial City ( ar, راس لفان, Ra’s Lafān) is an industrial hub located north of Doha, Qatar. It is administrated by QatarEnergy.
Ras Laffan Industrial City is Qatar's main site for production of liquefied natural gas and ...
, Qatar and together with
Uzbekneftegaz
The national holding company Uzbekneftegaz ( uz, "Oʻzbekneftegaz" MXK, russian: НХК "Узбекнефтегаз") is a state-owned holding company of Uzbekistan's oil and gas industry.
History
Uzbekneftegaz was established on May 3, 1992. In ...
and
Petronas builds the
Uzbekistan GTL Uzbekistan GTL (Oltin Yo'l GTL) is a gas-to-liquids (GTL) plant in the Qashqadaryo Region, Uzbekistan.
History
Construction of a GTL plant in Uzbekistan was discussed between Uzbekneftegaz and Abu Dhabi's International Petroleum Investment Company ...
plant.
[
][
][
] Chevron Corporation, in a joint venture with the
Nigerian National Petroleum Corporation
NNPC Limited is a for profit oil company in Nigeria. Formerly a government-owned corporation, it was transformed from a corporation to a limited liability company in July 2022. NNPC Limited is the only entity licensed to operate in the country ...
is commissioning the
Escravos GTL in
Nigeria
Nigeria ( ), , ig, Naìjíríyà, yo, Nàìjíríà, pcm, Naijá , ff, Naajeeriya, kcg, Naijeriya officially the Federal Republic of Nigeria, is a country in West Africa. It is situated between the Sahel to the north and the Gulf o ...
, which uses Sasol technology. PetroSA, South Africa's national oil company, owns and operates a 22,000 barrels/day (capacity) GTL plant in Mossel Bay, using Sasol GTL technology.
Aspirational and emerging ventures
New generation of GTL technology is being pursued for the conversion of unconventional, remote and problem gas into valuable liquid fuels.
GTL plants based on innovative Fischer–Tropsch catalysts have been built by
INFRA Technology. Other mainly U.S. companies include Velocys, ENVIA Energy, Waste Management, NRG Energy, ThyssenKrupp Industrial Solutions, Liberty GTL,
Petrobras, Greenway Innovative Energy, Primus Green Energy, Compact GTL, and Petronas. Several of these processes have proven themselves with demonstration flights using their jet fuels.
Another proposed solution to stranded gas involves use of novel
FPSO
A floating production storage and offloading (FPSO) unit is a floating vessel used by the offshore oil and gas industry for the production and processing of hydrocarbons, and for the storage of oil. An FPSO vessel is designed to receive h ...
for offshore conversion of gas to liquids such as
methanol,
diesel
Diesel may refer to:
* Diesel engine, an internal combustion engine where ignition is caused by compression
* Diesel fuel, a liquid fuel used in diesel engines
* Diesel locomotive, a railway locomotive in which the prime mover is a diesel engin ...
,
petrol
Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic c ...
,
synthetic crude, and
naphtha
Naphtha ( or ) is a flammable liquid hydrocarbon mixture.
Mixtures labelled ''naphtha'' have been produced from natural gas condensates, petroleum distillates, and the distillation of coal tar and peat. In different industries and regions ' ...
.
Economics of GTL
GTL using natural gas is more economical when there is wide gap between the prevailing natural gas price and crude
oil price
The price of oil, or the oil price, generally refers to the spot price of a barrel () of benchmark crude oil—a reference price for buyers and sellers of crude oil such as West Texas Intermediate (WTI), Brent Crude, Dubai Crude, OPEC Ref ...
on a
Barrel of oil equivalent
The barrel of oil equivalent (BOE) is a unit of energy based on the approximate energy released by burning one barrel (, or ) of crude oil. The BOE is used by oil and gas companies in their financial statements as a way of combining oil and nat ...
(BOE) basis. A coefficient of 0.1724 results in full
oil parity. GTL is a mechanism to bring down the diesel/gasoline/crude oil international prices at par with the natural gas price in an expanding global natural gas production at cheaper than crude oil price. When natural gas is converted in to GTL, the liquid products are easier to export at cheaper price rather than converting in to
LNG
Liquefied natural gas (LNG) is natural gas (predominantly methane, CH4, with some mixture of ethane, C2H6) that has been cooled down to liquid form for ease and safety of non-pressurized storage or transport. It takes up about 1/600th the volu ...
and further conversion to liquid products in an importing country.
However, GTL fuels are much more expensive to produce than conventional fuels.
[Qatar Airways Flies Plane With New Fuel, The Wall Street Journal, Wednesday, October 14, 2009, p.B2]
See also
*
Biomass to liquid
Biomass to liquid (BtL or BMtL) is a multi-step process of producing synthetic hydrocarbon fuels made from biomass via a thermochemical route.
Main processes
According to a study done by the U.S. Department of Agriculture and the Department of En ...
*
Carbon-neutral fuel
Carbon-neutral fuel is fuel which produces no net-greenhouse gas emissions or carbon footprint. In practice, this usually means fuels that are made using carbon dioxide (CO2) as a feedstock. Proposed carbon-neutral fuels can broadly be grouped ...
*
Coal to liquid
Coal liquefaction is a process of converting coal into liquid hydrocarbons: liquid fuels and petrochemicals. This process is often known as "Coal to X" or "Carbon to X", where X can be many different hydrocarbon-based products. However, the most ...
Bibliography
* Boogaard, P. J., Carrillo, J. C., Roberts, L. G., & Whale, G. F. (2017
Toxicological and ecotoxicological properties of gas-to-liquid (GTL) products 1. Mammalian toxicology. Critical reviews in toxicology, 47(2), 121-144.
References
{{Reflist
Natural gas technology
Synthetic fuel technologies
Industrial gases