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.
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: [1]
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 catalysts, [2] and the STG+ process also utilizes commercially available shape-selective catalysts, such as ZSM-5. [3]
According to Primus Green Energy, the STG+ process converts natural gas into 90+-octane gasoline at approximately 5 US gallons per million British thermal units (65 litres per megawatt-hour). [4] The energy content of gasoline is 120,000 to 125,000 British thermal units per US gallon (9.3 to 9.7 kilowatt-hours per litre), making this process about 60% efficient, with a 40% loss of energy.
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.
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 reactors. [5]
Other technologies for syngas to liquid fuels synthesis include the Fischer–Tropsch process 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. [6] Preliminary studies suggest that the STG+ process is more energetically efficient and the highest yielding methanol to gasoline process. [7]
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 and iron catalysts, while methanol to gasoline technologies favor molecular size- and shape-selective zeolites. [8] In terms of product types, Fischer–Tropsch production has been limited to linear paraffins, [8] such as synthetic crude oil, whereas methanol to gasoline processes can produce aromatics, such as xylene and toluene, 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. [9]
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. [10] 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. [1] Other methanol to gasoline processes do not incorporate durene reduction into the core process, and they require the implementation of an additional refining step. [10]
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. [11] 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. [7] 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. [12]
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. [13] 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. [14]
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. [15]
In early 2014, the U.S. Patent and Trademark Office (USPTO) allowed Primus Green Energy’s patent covering its single-loop STG+ technology. [15]
Biofuel is a fuel that is produced over a short time span from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels, such as oil. Since biomass can be used as a fuel directly, some people use the words biomass and biofuel interchangeably. However, the word biofuel is usually reserved for liquid or gaseous fuels used for transportation. The U.S. Energy Information Administration (EIA) follows this naming practice.
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 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.
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 is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen or water gas 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 process was first developed by Franz Fischer and Hans Tropsch at the Kaiser Wilhelm Institute for Coal Research in Mülheim an der Ruhr, Germany, in 1925.
Sasol Limited is an integrated energy and chemical company based in Sandton, South Africa. The company was formed in 1950 in Sasolburg, South Africa and built on processes that were first developed by German chemists and engineers in the early 1900s. Today, Sasol develops and commercialises technologies, including synthetic fuels technologies, and produces different liquid fuels, chemicals and electricity.
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.
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, though these concepts are not exclusive.
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).
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.
Biomass to liquid is a multi-step process of producing synthetic hydrocarbon fuels made from biomass via a thermochemical route.
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 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.
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.
An aviation biofuel or bio-jet-fuel or bio-aviation fuel (BAF) is a biofuel used to power aircraft and is said to be a sustainable aviation fuel (SAF). The International Air Transport Association (IATA) considers it a key element to reducing the carbon footprint within the environmental impact of aviation. Aviation biofuel could help decarbonize medium- and long-haul air travel generating most emissions, and could extend the life of older aircraft types by lowering their carbon footprint.
Ze-gen, Inc. was a renewable energy company developing advanced gasification technology to convert waste into synthesis gas. Founded in 2004, Ze-gen was a venture-backed company based in Boston, Massachusetts.
Chemrec AB (Chemrec) is a Stockholm, Sweden-based company with comprehensive experience of pioneering the development of black liquor gasification (BLG) technology for energy and chemicals recovery at pulp mills.
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.
Chemical looping reforming (CLR) and gasification (CLG) are the operations that involve the use of gaseous carbonaceous feedstock and solid carbonaceous feedstock, respectively, in their conversion to syngas in the chemical looping scheme. The typical gaseous carbonaceous feedstocks used are natural gas and reducing tail gas, while the typical solid carbonaceous feedstocks used are coal and biomass. The feedstocks are partially oxidized to generate syngas using metal oxide oxygen carriers as the oxidant. The reduced metal oxide is then oxidized in the regeneration step using air. The syngas is an important intermediate for generation of such diverse products as electricity, chemicals, hydrogen, and liquid fuels.