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Primus Green Energy to support gas-to-liquids research at Princeton University; comparing STG+ to other GTL platforms

Schematic diagram of the Primus STG+ process. Click to enlarge.

Primus Green Energy Inc., developer of a proprietary process to produce gasoline and other fuels from biomass and/or natural gas (earlier post), will provide financial support to engineers at Princeton University for general research on synthetic fuels, which will include assessments of various gas-to-liquids (GTL) technologies—including Primus’ own STG+—for sustainability and economic viability.

STG+ technology converts syngas into drop-in high-octane gasoline and jet fuel with a conversion efficiency of ~35% by mass of syngas into liquid transportation fuels (the highest documented conversion efficiency in the industry) or greater than 70% by mass of natural gas. The fuels produced from the Primus STG+ technology are very low in sulfur and benzene compared to fuels produced from petroleum, and they can be used directly in vehicle engines as a component of standard fuel formulas and transported via the existing fuel delivery infrastructure.

The work at Princeton University will be conducted in the laboratories of Professor Christodoulos Floudas, Ph.D. Floudas is an expert in chemical process systems engineering, with a specific emphasis on process synthesis and design, interaction of process design and control and process operations. His research has garnered him academic and industry-wide recognition, including the 2001 Professional Progress Award from the American Institute of Chemical Engineers (AIChE), the 2006 Computing in Chemical Engineering Award from the CAST Division of AIChE, and the Presidential Young Investigator award from the National Science Foundation. He was elected in 2011 to the National Academy of Engineering.

Primus’ STG+ platform is a next-generation gas-to-liquids technology that has the potential to have a significant impact on process efficiency standards and economic viability in the alternative fuels industry. As part of my research, I will be comparing STG+ to other leading GTL platforms against a variety of metrics, including financial, technical and sustainability.

—Prof. Floudas

Primus Green Energy estimates that the cost of production for its fuels will be competitive with petroleum-based fuels when crude oil is trading at $65 per barrel (oil is currently trading at approximately $95 per barrel). Primus is nearing completion of its demonstration plant, which is expected to reach mechanical completion in Q2 2013, and expects to break ground on its first commercial plant in the first half of 2014.

Primus is also an adviser to the Northeast Woody/Warm-season Biomass Consortium (NEWBio), a group led by Pennsylvania State University that is tasked with developing perennial feedstock production systems and supply chains for biomass feedstocks. NEWBio is supported by a nearly $10 million grant from the U.S. Department of Agriculture.

STG+. STG+ (Syngas To Gasoline +, the plus standing for the multiple end products yielded by the process) essentially improves upon commercial methanol synthesis processes and ExxonMobil’s methanol to gasoline (MTG) process, combining them into a single-loop process that converts syngas directly to gasoline. 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 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.


  • Introduction To Primus’ STG+ Technology

  • Baliban, R. C.; Elia, J. A.; Floudas, C. A. (2013) Biomass to liquid transportation fuels (BTL) systems: process synthesis and global optimization framework. Energy & Environmental Science 6, 267-287 doi: 10.1039/C2EE23369J

  • Richard C. Baliban, Josephine A. Elia, Christodoulos A. Floudas, Barri Gurau, Michael B. Weingarten, and Stephen D. Klotz (2013) Hardwood Biomass to Gasoline, Diesel, and Jet Fuel: 1. Process Synthesis and Global Optimization of a Thermochemical Refinery. Energy & Fuels doi: 10.1021/ef302003f





What does the price of oil need to be to justify the capital expense of building such a system? Which forward thinking US corporation will invest in this? Why not just use the methanol for value added chemicals rather than converting to gasoline and then burning it?


Synthetic fuels could eliminate entire U.S. need for crude oil, create 'new economy'

I don't advocate no petroleum nor creating a "new economy", but not being at the whim of OPEC sure would be nice after more than 40 years.


Synthetic fuels are the wet dream of the people who own the feedstocks (coal and natural gas).  The taxpayers will likely get stiffed on loan guarantees for building it but once a synfuel plant is built, it is going to be a guaranteed consumer of their stuff for the next 50 years as long as there's a marginal operating profit to be made.

These people also say that we have 100 years of natural gas in the ground.  They don't mention that if you triple consumption to make synfuels, that falls to 33 years; if you import another hundred million people from the rest of the world like they want to, it shrinks to 25 years.  25 years of natural gas doesn't sound so good, does it?

Forget synfuels.  Go nuclear-electric, and close the border.

Roger Pham

E-P has many good points.

Since NG has LHV of 50 MJ/kg while gasoline has LHV of 44 MJ/kg, on energy basis, this conversion from NG to gasoline is 70% x 44/50 = 61.7 % efficiency. Add this efficiency loss to the investment costs of the conversion plant and maintenance, etc. and CNG becomes much more appealing economically for big trucks, or PHEV using non-CO2 electricity for cars.

Also, for the sake of lowering GHG emission, closing the border is a good idea, since each American consumes ~10x the energy level (GHG-energy emission) of each citizen of 3rd world countries and eats far more meats that also resulted in a lot of GHG emission (methane from cow's fart!) and farming practice.


Why not stop at step 2, and use dimethylether in a diesel engine ?
Works perfectly, doesn't cause soot emissions.


You can sell methanol, DME, gasoline, diesel or jet fuel, whatever the market needs for vehicles that don't have to be modified at all.

Since NG has LHV of 50 MJ/kg while gasoline has LHV of 44 MJ/kg, on energy basis, this conversion from NG to gasoline is 70% x 44/50 = 61.7 % efficiency.
You forget, a substantial amount of carbon is lost in most conversions (at least 20%), and around half the hydrogen.  This cuts the usual energy efficiency to less than 50%.
Why not stop at step 2, and use dimethylether in a diesel engine ?
Why not stop at step 1, and use methanol in a spark-ignition engine?  There are substantial energy losses in the conversion of MeOH to DME; burning the methanol puts that energy into the cylinder, and MeOH allows ultra-turbocharged engines with much lower weight and friction than even diesel engines.

If we need liquid fuels, methanol ought to be one of the top priorities.

Roger Pham


>>>"You forget, a substantial amount of carbon is lost in most conversions (at least 20%), and around half the hydrogen. This cuts the usual energy efficiency to less than 50%."

This substantial amount of carbon and hydrogen loss is accounted for in the 70% efficiency by mass from NG to gasoline. By example, for every 100 gm of NG, only 70 gm of gasoline is obtained. From an energy efficiency standpoint,since NG has higher energy per mass unit than gasoline, another adjustment will be needed to account for the differing energy content per mass unit of NG vs Gasoline. So, 70% x 44/50 = 61.7% efficiency energy wise. How do you come up with 50% efficiency? Perhaps this 50% is previous level of GTL efficiency, which is now raised by Primus to ~62% efficiency.

Kit P

"Go nuclear-electric"

Charging batteries is a lot less practical and more expensive than GTL. GTL is also proven technology to make liquid transportation fuel.

We are no developing High Temperature Modular Gas Cooled Reactors to produce H2 and heat for this process. Oil will need to become scarce for the economics to work. The world will miss cheap OPEC oil.


It would be good to compare oil to gasoline versus natural gas to gasoline. If oil is 70% efficient after refining and hydro cracking, then GTL is 63%, what would the public say?

Lets see, 63% versus 70%, but GTL has no sulfur, no benzene, no imported oil, cleaner air...I like 63%. With OPEC, we have no idea what the price of oil will be tomorrow, but with NG we can get long term contracts.

GTL is also proven technology to make liquid transportation fuel.
Pray tell, how many countries supply their transportation fuel using GTL?  Oh, wait... neither Qatar nor Indonesia?  Not good for your thesis!
We are no[w] developing High Temperature Modular Gas Cooled Reactors to produce H2 and heat for this process.
There are no such reactors being submitted for licensing to the NRC in the USA.  So far as the United States is concerned, neither the reactors nor the dependent fuel cycle exist.  What Twit P. is doing is throwing up a smokescreen of a non-existent nuclear hydrogen cycle to replace the hydrocarbons that electricity is slowly squeezing out of the market.

I'm expecting delivery of a PHEV in weeks if not days.

If oil is 70% efficient after refining and hydro cracking, then GTL is 63%, what would the public say?
45% is pretty good for GTL, and the public should know that.  Burning NG directly costs less than $1/gge, and the public should be encouraged to do it; it takes revenues directly from OPEC.

Roger Pham

Good point, SJC. Come to think of it, GTL at 62% efficiency for superior fuel vs 70% from crude to gasoline is very good, and a lot better than tar sand to gasoline.

However, developing infrastructure for CNG in transportation now that can later accomodate renewable-energy H2 or nuclear H2 would be more economical and lower CO2 emission going toward zero CO2 emission in the long run. The much lower cost of CNG means that the price premium for a CNG car or truck will pay for itself in a few short years. Having CNG dispenser at major gas station would cost less than building a large number of GTL plants that can accommodate America's thirst for liquid fuel. Well, a small number of GTL plants may need to be built to make jet fuels, but the rest of the transportation fleet such as cars, buses, trucks, trains, and ships can run on CNG or LNG. PHEV will take care of the rest of the car fleet.

The day will come when we will have a vast numbers of solar and wind energy collectors and hence a large quantity of excess of renewable energy at certain times or certain seasons that can be used to make H2 to be stored in depleted NG wells or oil wells, or depleted salt mine, etc. from one season to be used for the next season. H2 production will solve the problem of intermittency of solar and wind energy, as well as allowing nuclear plants to run at full capacity all the time to recoup the high construction cost. Adapting the surface transportation fleet to CNG now will make H2 utilization much easier in the future.

Roger Pham

However, to be fair, CNG tank and a PHEV battery pack do take more space out of a vehicle and is heavier than a gasoline tank. Many people (shoppaholics or frequent travelers) want a huge trunk space and would prefer a gasoline vehicle instead of a CNG vehicle or a PHEV with smaller trunk space. So, triple development of GTL plants in parallel with CNG filling at large gas station and PHEV would probably be best. Different strokes for different folks!


A removable CNG tank pack for a dual-fuel vehicle allows a "have your cake and eat it" scenario.

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