syngas to gasoline plus
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Syngas to gasoline plus (STG+) is a thermochemical 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 ...
, 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 or gasified biomass into drop-in fuels, such as gasoline, diesel fuel or jet fuel, and organic solvents.


Process chemistry

This process follows four principal steps in one continuous integrated loop, comprising four fixed bed reactors in a series in which a syngas is converted to synthetic fuels. The steps for producing high-octane synthetic gasoline are as follows:Introduction to STG+ Technology
''Primus Green Energy'', February 2013. Retrieved: 5 March 2013.
* Methanol Synthesis: Syngas is fed to Reactor 1, the first of four reactors, which converts most of the syngas to methanol when passing through the catalyst bed. *: CO + 2 H2 → *
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. *: 2 CH3OH → CH3OCH3 + H2O * 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), typically with the carbon number ranging from 6 to 10. * 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/ isodurene ( tetramethylbenzenes) and
trimethylbenzene The trimethylbenzenes constitute a group of substances of aromatic hydrocarbons, which structure consists of a benzene ring with three methyl groups (–CH3) as a substituent. Through their different arrangement, they form three structural iso ...
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.


Catalysts

The STG+ process uses standard catalysts similar to those used in other gas to liquids technologies, specifically in methanol to gasoline processes. Methanol to gasoline processes favor molecular size- and shape-selective
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 ...
catalysts, and the STG+ process also utilizes commercially available shape-selective catalysts, such as ZSM-5.


Process efficiency

According to Primus Green Energy, the STG+ process converts natural gas into 90+-octane gasoline at approximately . The energy content of gasoline is , making this process about 60% efficient, with a 40% loss of energy.


Gasification

As is the case with other gas to liquids processes, STG+ utilizes syngas produced via other technologies as a feedstock. This syngas can be produced through several commercially available technologies and from a wide variety of feedstocks, including natural gas, biomass and
municipal solid waste Municipal solid waste (MSW), commonly known as trash or garbage in the United States and rubbish in Britain, is a waste type consisting of everyday items that are discarded by the public. "Garbage" can also refer specifically to food waste ...
. Natural gas and other methane-rich gases, including those produced from municipal waste, are converted into syngas through methane reforming technologies such as steam methane reforming and auto-thermal reforming. Biomass gasification technologies are less established, though several systems being developed utilize fixed bed or
fluidized bed A fluidized bed is a physical phenomenon that occurs when a solid particulate substance (usually present in a holding vessel) is under the right conditions so that it behaves like a fluid. The usual way to achieve a fluidize bed is to pump pressur ...
reactors.


Comparison to other GTL technologies

Other technologies for syngas to liquid fuels synthesis include the
Fischer–Tropsch process The Fischer–Tropsch process 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 temperatu ...
and the methanol to gasoline processes. Research conducted at Princeton University indicates that methanol to gasoline processes are consistently more cost-effective, both in capital cost and overall cost, than the Fischer–Tropsch process at small, medium and large scales.Richard C. Baliban, Josephine A. Elia, Vern Weekman, and Christodoulos A. Floudas "Process Synthesis of Hybrid Coal, Biomass, and Natural Gas to Liquids via Fischer–Tropsch Synthesis, ZSM-5 Catalytic Conversion, Methanol Syntehsis, Methanol-to-Gasoline, and Methanol-to-Olefins/Distillate Technologies" in Computers & Chemical Engineering, 2012, Elsevier. Preliminary studies suggest that the STG+ process is more energetically efficient and the highest yielding methanol to gasoline process.Comparison of STG+ With Other GTL Technologies
''Primus Green Energy'', April 2013. Retrieved: 29 April 2013.


Fischer–Tropsch process

The primary difference between the Fischer–Tropsch process and methanol to gasoline processes such as STG+ are the catalysts used, product types and economics. Generally, the Fischer–Tropsch process favors unselective
cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...
and
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
catalysts, while methanol to gasoline technologies favor molecular size- and shape-selective zeolites.Eduardo Falabella Sousa-Aguiar, Fabio Bellot Noronha, and Arnaldo Faro, Jr. "The Main Catalytic Challenges in GTL (Gas-to-Liquids) Processes" in Catalysis Science & Technology, 2011, RSC. In terms of product types, Fischer–Tropsch production has been limited to linear paraffins, such as synthetic crude oil, whereas methanol to gasoline processes can produce aromatics, such as
xylene In organic chemistry, xylene or xylol (; IUPAC name: dimethylbenzene) are any of three organic compounds with the formula . They are derived from the substitution of two hydrogen atoms with methyl groups in a benzene ring; which hydrogens are s ...
and
toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) a ...
, and naphthenes and iso-paraffins, such as drop-in gasoline and jet fuel. The main product of the Fischer–Tropsch process, synthetic crude oil, requires additional refining to produce fuel products such as diesel fuel or gasoline. This refining typically adds additional costs, causing some industry leaders to label the economics of commercial-scale Fischer–Tropsch processes as challenging.Broder, John M. and Clifford Krauss
A Big, and Risky, Energy Bet
''The New York Times'', 17 December 2012. Retrieved: 15 April 2013.


Methanol to gasoline

The STG+ technology offers several differentiators that distinguish it from other methanol to gasoline processes. These differences include product flexibility, durene reduction, environmental footprint and capital cost. Traditional methanol to gasoline technologies produce diesel, gasoline or liquefied petroleum gas.Methanol to Gasoline (MTG) Production of Clean Gasoline from Coal
''ExxonMobil'', December 2009. Retrieved: 30 April 2013.
STG+ produces gasoline, diesel, jet fuel and aromatics, depending on the catalysts used. The STG+ technology also incorporates durene reduction into its core process, meaning that the entire fuel production process requires only two steps: syngas production and gas to liquids synthesis. Other methanol to gasoline processes do not incorporate durene reduction into the core process, and they require the implementation of an additional refining step. Due to the additional number of reactors, traditional methanol to gasoline processes include inefficiencies such as the additional cost and energy loss of condensing and evaporating the methanol prior to feeding it to the durene reduction unit. These inefficiencies can lead to a greater capital cost and environmental footprint than methanol to gasoline processes that use fewer reactors, such as STG+. The STG+ process eliminates multiple condensation and evaporation, and the process converts syngas to liquid transportation fuels directly without producing intermediate liquids. This eliminates the need for storage of two products, including pressure storage for liquefied petroleum gas and storage of liquid methanol. Simplifying a gas to liquids process by combining multiple steps into fewer reactors leads to increased yield and efficiency, enabling less expensive facilities that are more easily scaled.Richard C. Baliban, Josephine A. Elia, and Christodoulos A. Floudas "Novel Natural Gas to Liquids Processes: Process Synthesis and Global Optimization Strategies" in American Institute of Chemical Engineers Journal, 2013, AIChE.


Commercialization

The STG+ technology is currently operating at pre-commercial scale in Hillsborough, New Jersey at a plant owned by alternative fuels company Primus Green Energy. The plant produces approximately 100,000 gallons of high-quality, drop-in gasoline per year directly from natural gas. Further, the company announced the findings of an independent engineer’s report prepared by E3 Consulting, which found that STG+ system and catalyst performance exceeded expectations during plant operation. The pre-commercial demonstration plant has also achieved 720 hours of continuous operation. Primus Green Energy has announced plans to break ground on its first commercial STG+ plant in the second half of 2014, and the company has announced that this plant is expected to produce approximately 27.8 million gallons of fuel annually. In early 2014, the U.S. Patent and Trademark Office (USPTO) allowed Primus Green Energy’s patent covering its single-loop STG+ technology.


See also

*
Alternative fuel Alternative fuel, known as non-conventional and advanced fuels, are any materials or substances that can be used as fuels, other than conventional fuels like; ''fossil fuels'' (petroleum (oil), coal, and natural gas), as well as nuclear materi ...
*
Biogasoline Biogasoline or biopetrol (British English) is a type of gasoline produced from biomass such as algae. Like traditionally produced gasoline, it is made up of hydrocarbons with 6 (hexane) to 12 (dodecane) carbon atoms per molecule and can be used i ...
*
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 ...
*
Fischer–Tropsch process The Fischer–Tropsch process 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 temperatu ...
*
Gas to liquids 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 ...


References

{{reflist, 2 Synthetic fuel technologies Gas technologies