Gas to liquids

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LNG tankers are used to transport methane. Methanier aspher LNGRIVERS.jpg
LNG tankers are used to transport methane.

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. [1] [2]

Contents

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 tankers are used for transport. Methanol is a conveniently handled combustible liquid, but its energy density is half of that of gasoline. [3]

Fischer–Tropsch process

GTL process using the Fischer Tropsch method GTL process.GIF
GTL process using the Fischer Tropsch method

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 (H2) into long chained hydrocarbons. These hydrocarbons are typically liquid or semi-liquid and ideally have the formula (CnH2n+2).

In order to obtain the mixture of CO and H2 required for the Fischer–Tropsch process, methane (main component of natural gas) may be subjected to partial oxidation which yields a raw synthesis gas mixture of mostly carbon dioxide, carbon monoxide, hydrogen gas (and sometimes water and nitrogen). [4] The ratio of carbon monoxide to hydrogen in the raw synthesis gas mixture can be adjusted e.g. using the water gas shift reaction. Removing impurities, particularly nitrogen, carbon dioxide and water, from the raw synthesis gas mixture yields pure synthesis gas (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 (natural gas) in a series of three reactions:

Steam reforming
CH4 + H2O → CO + 3 H2  ΔrH = +206 kJ mol−1
Water shift reaction
CO + H2O → CO2 + H2  ΔrH = -41 kJ mol−1
Synthesis
2 H2 + CO → CH3OH   ΔrH = -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 catalyst to form alkanes. In terms of mechanism, methanol is partially dehydrated to give dimethyl ether:

2 CH3OH → CH3OCH3 + H2O

The mixture of dimethyl ether and methanol is then further dehydrated over a zeolite catalyst such as ZSM-5, 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). [5]

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. [6] [7]

Syngas to gasoline plus process (STG+)

The STG+ Process STG+ Process.jpg
The STG+ Process

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. [8]

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: [9]

  1. Methanol Synthesis: Syngas is fed to Reactor 1, the first of four reactors, which converts most of the syngas (CO and H2) to methanol (CH3OH) when passing through the catalyst bed.
  2. Dimethyl Ether (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 and much of it is converted to DME, which involves a dehydration from methanol to form DME (CH3OCH3).
  3. 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, naphthenes (cycloalkanes) and small amounts of olefins (alkenes), mostly from C6 (number of carbon atoms in the hydrocarbon molecule) to C10.
  4. Gasoline Treatment: The fourth reactor provides transalkylation and hydrogenation treatment to the products coming from Reactor 3. The treatment reduces durene (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.
  5. 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 methanotrophs, 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 monooxygenases, which are found both in soluble and particulate (i.e. membrane-bound) varieties. They catalyze the oxygenation according to the following stoichiometry:

CH4 + O2 + NADPH + H+ → CH3OH + H2O + NAD+

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. [10]

Biodiesel can be made from CO2 using the microbes Moorella thermoacetica and Yarrowia lipolytica. This process is known as biological gas-to-liquids. [11]

Commercial uses

INFRA M100 GTL Plant INFRA M100 GTL Plant.jpg
INFRA M100 GTL Plant

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. The World Bank estimates that over 150 billion cubic metres (5.3×10^12 cu ft) 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, [12] 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, Malaysia. Another Shell GTL facility is the Pearl GTL plant in Qatar, the world's largest GTL facility. [13] [14] SASOL has recently built the Oryx GTL facility in Ras Laffan Industrial City, Qatar and together with Uzbekneftegaz and Petronas builds the Uzbekistan GTL plant. [15] [16] [17] Chevron Corporation, in a joint venture with the Nigerian National Petroleum Corporation is commissioning the Escravos GTL in Nigeria, 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. [18]   

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. [19] [20] 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, [21] Greenway Innovative Energy, [22] Primus Green Energy, [23] Compact GTL, [24] and Petronas. [25] Several of these processes have proven themselves with demonstration flights using their jet fuels. [26] [27]

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. [28]

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 on a Barrel of oil equivalent (BOE) basis. A coefficient of 0.1724 results in full oil parity. [29] 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 and further conversion to liquid products in an importing country. [30] [31]

However, GTL fuels are much more expensive to produce than conventional fuels. [32]

See also

Bibliography

Related Research Articles

<span class="mw-page-title-main">Methanol</span> CH3OH; simplest alcohol

Methanol is an organic chemical compound and the simplest aliphatic alcohol, with the chemical formula CH3OH. It is a light, volatile, colorless and flammable liquid with a distinctive alcoholic odour similar to that of ethanol . Methanol acquired the name wood alcohol because it was once produced chiefly by the destructive distillation of wood. Today, methanol is mainly produced industrially by hydrogenation of carbon monoxide.

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 principally used for producing ammonia or methanol. Syngas is combustible and can be used as a fuel. Historically, it has been used as a replacement for gasoline, when gasoline supply has been limited; for example, wood gas was used to power cars in Europe during WWII.

<span class="mw-page-title-main">Gasification</span> Form of energy conversion

Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (CO2). This is achieved by reacting the feedstock material at high temperatures (typically >700 °C), without combustion, via controlling the amount of oxygen and/or steam present in the reaction. The resulting gas mixture is called syngas (from synthesis gas) or producer gas and is itself a fuel due to the flammability of the H2 and CO of which the gas is largely composed. Power can be derived from the subsequent combustion of the resultant gas, and is considered to be a source of renewable energy if the gasified compounds were obtained from biomass feedstock.

The Fischer–Tropsch process (FT) is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen, known as syngas, into liquid hydrocarbons. These reactions occur in the presence of metal catalysts, typically at temperatures of 150–300 °C (302–572 °F) and pressures of one to several tens of atmospheres. The Fischer–Tropsch process is an important reaction in both coal liquefaction and gas to liquids technology for producing liquid hydrocarbons.

<span class="mw-page-title-main">Steam reforming</span> Method for producing hydrogen and carbon monoxide from hydrocarbon fuels

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 production. The reaction is represented by this equilibrium:

In industrial chemistry, coal gasification is the process of producing syngas—a mixture consisting primarily of carbon monoxide (CO), hydrogen, carbon dioxide, methane, and water vapour —from coal and water, air and/or oxygen.

<span class="mw-page-title-main">Sabatier reaction</span> Methanation process of carbon dioxide with hydrogen

The Sabatier reaction or Sabatier process produces methane and water from a reaction of hydrogen with carbon dioxide at elevated temperatures and pressures in the presence of a nickel catalyst. It was discovered by the French chemists Paul Sabatier and Jean-Baptiste Senderens in 1897. Optionally, ruthenium on alumina makes a more efficient catalyst. It is described by the following exothermic reaction:

<span class="mw-page-title-main">Catalytic reforming</span> Chemical process used in oil refining

Catalytic reforming is a chemical process used to convert petroleum refinery naphthas distilled from crude oil into high-octane liquid products called reformates, which are premium blending stocks for high-octane gasoline. The process converts low-octane linear hydrocarbons (paraffins) into branched alkanes (isoparaffins) and cyclic naphthenes, which are then partially dehydrogenated to produce high-octane aromatic hydrocarbons. The dehydrogenation also produces significant amounts of byproduct hydrogen gas, which is fed into other refinery processes such as hydrocracking. A side reaction is hydrogenolysis, which produces light hydrocarbons of lower value, such as methane, ethane, propane and butanes.

<span class="mw-page-title-main">Methanol economy</span>

The methanol economy is a suggested future economy in which methanol and dimethyl ether replace fossil fuels as a means of energy storage, ground transportation fuel, and raw material for synthetic hydrocarbons and their products. It offers an alternative to the proposed hydrogen economy or ethanol economy, although these concepts are not exclusive. Methanol can be produced from a variety of sources including fossil fuels as well as agricultural products and municipal waste, wood and varied biomass. It can also be made from chemical recycling of carbon dioxide.

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 common process chain is "Coal to Liquid Fuels" (CTL).

<span class="mw-page-title-main">Synthetic fuel</span> Fuel from carbon monoxide and hydrogen

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 reforming of natural gas.

<span class="mw-page-title-main">Biomass to liquid</span>

Biomass to liquid is a multi-step process of producing synthetic hydrocarbon fuels made from biomass via a thermochemical route.

<span class="mw-page-title-main">Bergius process</span>

The Bergius process is a method of production of liquid hydrocarbons for use as synthetic fuel by hydrogenation of high-volatile bituminous coal at high temperature and pressure. It was first developed by Friedrich Bergius in 1913. In 1931 Bergius was awarded the Nobel Prize in Chemistry for his development of high-pressure chemistry.

A methane reformer is a device based on steam reforming, autothermal reforming or partial oxidation and is a type of chemical synthesis which can produce pure hydrogen gas from methane using a catalyst. There are multiple types of reformers in development but the most common in industry are autothermal reforming (ATR) and steam methane reforming (SMR). Most methods work by exposing methane to a catalyst at high temperature and pressure.

Second-generation biofuels, also known as advanced biofuels, are fuels that can be manufactured from various types of non-food biomass. Biomass in this context means plant materials and animal waste used especially as a source of fuel.

Reactive flash volatilization (RFV) is a chemical process that rapidly converts nonvolatile solids and liquids to volatile compounds by thermal decomposition for integration with catalytic chemistries.

<span class="mw-page-title-main">Electrofuel</span> Carbon-neutral drop-in replacement fuel

Electrofuels, also known as e-fuels, a class of synthetic fuels, are a type of drop-in replacement fuel. They are manufactured using captured carbon dioxide or carbon monoxide, together with hydrogen obtained from water split by sustainable electricity sources such as wind, solar and nuclear power.

Syngas to gasoline plus (STG+) is a thermochemical process to convert natural gas, other gaseous hydrocarbons or gasified biomass into drop-in fuels, such as gasoline, diesel fuel or jet fuel, and organic solvents.

Worldwide commercial synthetic fuels plant capacity is over 240,000 barrels per day (38,000 m3/d), including indirect conversion Fischer–Tropsch plants in South Africa, Qatar, and Malaysia, and a Mobil process plant in New Zealand.

E-diesel is a synthetic diesel fuel created by Audi for use in automobiles. Currently, e-diesel is created by an Audi research facility in partnership with a company named Sunfire. The fuel is created from carbon dioxide, water, and electricity with a process powered by renewable energy sources to create a liquid energy carrier called blue crude which is then refined to generate e-diesel. E-diesel is considered to be a carbon-neutral fuel as it does not extract new carbon and the energy sources to drive the process are from carbon-neutral sources. As of April 2015, an Audi A8 driven by Federal Minister of Education and Research in Germany is using the e-diesel fuel.

References

  1. ↑ Höök, Mikael; Fantazzini, Dean; Angelantoni, André; Snowden, Simon (2013). "Hydrocarbon liquefaction: viability as a peak oil mitigation strategy". Philosophical Transactions of the Royal Society A. 372 (2006): 20120319. Bibcode:2013RSPTA.37220319H. doi: 10.1098/rsta.2012.0319 . PMID   24298075 . Retrieved 2009-06-03.
  2. ↑ Kaneko, Takao; Derbyshire, Frank; Makino, Eiichiro; Gray, David; Tamura, Masaaki (2001). "Coal Liquefaction". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a07_197. ISBN   978-3-527-30673-2.
  3. ↑ "Alternative Fuels Data Center: Fuel Properties Comparison".
  4. ↑ "Gas POX - Natural Gas Partial Oxidation". Air Liquide. 2016-03-18. Retrieved 2021-02-18.
  5. ↑ Olsbye, U.; Svelle, S.; Bjorgen, M.; Beato, P.; Janssens, T. V. W.; Joensen, F.; Bordiga, S.; Lillerud, K. P. (2012). "Conversion of Methanol to Hydrocarbons: How Zeolite Cavity and Pore Size Controls Product Selectivity". Angew. Chem. Int. Ed. 51 (24): 5810–5831. doi:10.1002/anie.201103657. hdl: 2318/122770 . PMID   22511469. S2CID   26585752.
  6. ↑ Tian, P.; Wei, Y.; Ye, M.; Liu, Z. (2015). "Methanol to Olefins (MTO): From Fundamentals to Commercialization". ACS Catal. 5 (3): 1922–1938. doi: 10.1021/acscatal.5b00007 .
  7. ↑ Ismaël Amghizar; Laurien A. Vandewalle; Kevin M. Van Geem; Guy B. Marin (2017). "New Trends in Olefin Production". Engineering. 3 (2): 171–178. doi: 10.1016/J.ENG.2017.02.006 .
  8. ↑ LaMonica, Martin. Natural Gas Tapped as Bridge to Biofuels MIT Technology Review, 27 June 2012. Retrieved: 7 March 2013.
  9. ↑ Introduction to Primus' STG+ Technology Primus Green Energy, undated. Retrieved: 5 March 2013.
  10. ↑ Lawton, T. J.; Rosenzweig, A. C. (2016). "Biocatalysts for methane conversion: big progress on breaking a small substrate". Curr. Opin. Chem. Biol. 35: 142–149. doi:10.1016/j.cbpa.2016.10.001. PMC   5161620 . PMID   27768948.
  11. ↑ Microbes paired for biological gas-to-liquids (Bio-GTL) process
  12. ↑ World Bank, GGFR Partners Unlock Value of Wasted Gas", World Bank 14 December 2009. Retrieved 17 March 2010.
  13. ↑ "Pearl Gas-to-Liquids Plant, Ras Laffan, Qatar" . Retrieved 2009-06-22.
  14. ↑ Gold, Russell (4 April 2012). "Shell Weighs Natural Gas-to-Diesel Processing Facility for Louisiana". Wall Street Journal. Retrieved 2012-05-05.
  15. ↑ "Petronas signs Uzbek GTL pact" . Upstream Online . NHST Media Group. 2009-04-08. Retrieved 2009-07-18.
  16. ↑ "Malaysia's Petronas in Uzbekistan oil-production deal". Reuters . 2009-05-14. Retrieved 2009-07-18.
  17. ↑ "Contract let for GTL plant in Uzbekistan" . Oil & Gas Journal . PennWell Corporation. 2010-03-08. Retrieved 2010-03-14.
  18. ↑ Wood, D.A.; et al. (November 2021). "A review of an industry offering several routes for monetizing natural gas". Journal of Natural Gas Science and Engineering. 9: 196–209. doi:10.1016/j.jngse.2012.07.001.
  19. ↑ "Smaller-scale and modular technologies drive GTL industry forward".
  20. ↑ Popov, Dmitry. "Unlocking the value of stranded and remote offshore gas assets".
  21. ↑ Chetwynd, Gareth (20 January 2012). "Petrobras puts gas flares out of fashion with GTL" (PDF). CompactGTL.
  22. ↑ "Greenway Technologies Inc. Marks Milestone, Completes First Commercial G-Reformer®" (Press release). 7 March 2018.
  23. ↑ "Primus Green Energy Demonstration Plant Operating Results Confirm Compelling Performance and Economics According to Independent Engineers' Report". Primus Green Energy. November 7, 2013. Archived from the original on 2015-09-24.
  24. ↑ Fairley, Peter (15 March 2010). "Turning Gas Flares into Fuel". MIT Technology Review.
  25. ↑ "UPDATE 2-Malaysia's Petronas in Uzbekistan oil-production deal". Reuters. 14 May 2008.
  26. ↑ "Qatar Airways Makes GTL History".
  27. ↑ "A380 makes test flight on alternative fuel". Reuters. February 2008.
  28. ↑ "Innovative Engineering in Energy Technologies". Bpp-Tech. Retrieved 2014-04-12.
  29. ↑ Hecht, Andrew (6 January 2020). "Crude Oil vs Natural Gas". The Balance.
  30. ↑ "Turkmenistan gas-to-liquids refinery ships first synthetic gasoline to Afghanistan" . Retrieved 25 December 2019.
  31. ↑ "Uzbekistan borrows $2.3 billion for gas-to-liquids plant project" . Retrieved 25 December 2019.
  32. ↑ Qatar Airways Flies Plane With New Fuel, The Wall Street Journal, Wednesday, October 14, 2009, p.B2
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