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Primus Green Energy’s STG+ patent for liquid fuel synthesis from syngas approved

Primus Green Energy Inc., an alternative fuel company that converts natural gas and other feedstocks directly into drop-in transportation fuels and solvents (earlier post), announced that its patent application covering its STG+ liquid fuel synthesis technology has been allowed by the US Patent and Trademark Office (USPTO). STG+ produces high-quality, cost-effective, drop-in liquid transportation fuels directly from syngas derived from natural gas and other carbon-rich feedstocks in a single-loop process.

STG+ essentially improves upon commercial methanol synthesis processes and ExxonMobil’s methanol-to-gasoline (MTG) process, combining them into an integrated, optimized system that efficiently converts syngas directly to fuels. In addition to the gasoline product, the STG+ process can also produce jet fuel, diesel and high-value chemicals by changing the catalysts and operating conditions. The company, which is currently producing synthetic gasoline at its demonstration plant (earlier post), plans to build several more reactors in parallel to the current production train for other fuel products.

Primus says that STG+ represents a cost breakthrough for the GTL industry, as it demonstrates compelling economics at scales of less than 6,000 barrels per day. The patented process is simpler and more efficient than existing GTL technologies as it transforms syngas to liquid fuels with only one condensation step and also recycles untransformed gases.

These efficiencies result in a high-yield process—STG+ can convert one MMBtu of natural gas into more than five gallons of 90+-octane, drop-in gasoline. Another metric cited by the company is the ability of STG+ to convert 35% by mass of the syngas into final product.

The Primus STG+ process follows four principal steps in one continuous process loop using four fixed bed reactors in series.
  • Reactor 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.

  • Reactor 2 (Dimethyl Ether 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 dimethyl ether (DME), which involves a dehydration from methanol to form DME (CH3OCH3).

  • Reactor 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-C10.

  • Reactor 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 (TMB) 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 recycle gas and is sent back to the feed stream to Reactor 1, leaving the synthetic gasoline product comprising paraffins, aromatics and naphthenes.

Click to enlarge.

STG+ is a new, proprietary thermochemical GTL process that fundamentally transforms the efficiency and economics of liquid fuel synthesis technologies. The allowance of this patent application validates the novelty of the technology we have developed and proven at scale in our research facilities and commercial demonstration plant here in Hillsborough. Further, it greatly strengthens our intellectual property portfolio, an important step as we look toward construction of our first commercial GTL plant.

—Robert Johnsen, CEO of Primus Green Energy

In October 2013, Primus successfully commissioned its 100,000 gallon-per-year natural gas-to-gasoline demonstration plant. (Earlier post.) A recently concluded independent engineers report found that both catalyst performance and STG+ system economics exceeded expectations during demonstration plant operation. The company is now working toward construction of its first commercial plant, which is expected to produce 27.8 million gallons per year of drop-in gasoline from natural gas. The company expects to break ground on the plant in 2014.

Final issuance of the patent covering the STG+ technology is expected in March 2014.

Primus Green Energy is backed by IC Green Energy, Ltd., the renewable energy arm of publicly traded Israel Corp.




Here we go folks, like I said synthetic gasoline made from natural gas at 60% efficiency. Oh, but power plants only get an average of 40%, much too inefficient.


The next wave: thermal and catalytic technologies

But the next wave is coming.

With exotic-sounding costs as low as $1.15-$2.18 per gallon. That is, low enough for fuels at scale with a solid RPI for investors. Several of them drop in to existing refinery infrastructure.


As an Engineer, it has never made sense to me to try to convert masses of vehicles to gaseous operation. It intrinsically, seems simpler and easier, to merely convert gaseous hydrocarbons to liquid fuels. Providing that the energy cost of doing so is not prohibitive, and that the process scales.

This may be the process technology that accomplishes the qualifications.


like I said synthetic gasoline made from natural gas at 60% efficiency

Where did you get the 60%? This article only cites "the ability of STG+ to convert 35% by mass of the syngas into final product" and it is not clear what they mean by final product: Is it just the gasoline they consider a product or are the paraffins, aromatics and naphthenes also recoverable products?

Furthermore, there's no mention of energy inputs here. What are the ERoEIs of this process?


Im interested to buy synthetic gasoline if they open that in my area.


"These efficiencies result in a high-yield process—STG+ can convert one MMBtu of natural gas into more than five gallons of 90+-octane"

Since gasoline is about 120,000 Btus times FIVE, that is 600,000 Btus after you start with one million...60%. They say MORE than five gallons. Total, the French energy company has done methane to DME at 70%, so greater than 60% to gasoline is certainly possible

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