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Study Suggests “Flexible Carbon to Liquid” Fuel Process Could Displace 15-20% of Transportation Fuels in the US

A preliminary analysis of a feedstock-flexible biomass waste/residue thermochemical pathway for liquid fuel production by researchers at Purdue University suggests that such a “flexible carbon to liquid” fuel (FCTL) process could replace 15%-20% of transportation fuels consumed in US and reduce greenhouse gas emissions by more than 50% compared with petroleum-derived gasoline.

At the same time, it could be more environmentally sustainable since few changes would be needed in agricultural and forestry practices, and may be more resilient against external disturbances such as feedstock supply shocks and market demand changes, they say.

This technique is more flexible than conventional methods because we can process a wider range of very different feedstocks and, at the same time, we can generate a wider range of end products—not just gasoline and diesel but ethanol and hydrogen. Or we could generate electricity directly from the gas produced.

—Professor Fu Zhao

In a paper presented on 29 September during the 6th Global Conference on Sustainable Product Development and Life Cycle Engineering in Busan, Korea, Zhao and his colleagues divide the FCTL process into two sub-processes: biomass gasification and FT synthesis.

The FT synthesis subsystem in an FCTL plant is identical to that in a CTL plant and has been well investigated. The main challenges facing the development of FCTL lie in the gasification part.

—Zhao et al. (2008)

Gasifiers fall into three main categories:, based on the means of supporting the feedstock in the reactor vessel; the direction of flow of both the feedstock and oxidant; and the way heat is supplied to the reactor: fixed/moving bed, fluidized bed, and entrained flow. Of the three, the fluidized bed gasifier supports a wide range of feedstock and particle sizes and can be operated under a wide range of conditions.

In their analysis, Zhao and his team selected a fluidized bed gasifier, and noted that plant availability could be further improved by using low rank coal as the backup feedstock.

In addition to concluding that liquids derived from an FCTL process could replace 15-20% of transportation fuel in the US, the study suggests that:

  • The cost of the derived fuels is in the range of $1.50-$2.00/gallon gasoline equivalent—i.e., competitive with other biofuels;

  • Lifecycle water withdrawal and land use of fuels derived from FCTL process are less than other biofuels;

  • A FCTL plant may generate local but intensive water supply and water quality challenges and the development of integrated water management strategies within the plant is critical;

  • A FCTL system is more resilient against external disturbances—e.g. feedstock supply shocks and market demand changes than other biofuel technologies.

The paper calls for the development an integrated process simulation model of a FCTL plant and a complete life cycle assessment in order to achieve a better picture of the economic and environmental performance of such a process.


  • Fu Zhao, Dongyan Mu, P. Suresh Rao, Thomas Seager (2008) Technical, Economic and Environmental Analysis of Flexible Carbon to Liquid Process: A Preliminary Analysis


Henry Gibson

There is no doubt that carbon-to-liquids facilities should be built immediately. The present economic crisis was created by all major nations ignoring and allowing the speculation in crude oil which drained the capital markets, nations and individuals of money. Such facilities could soon eliminate the demand for non-north american oil in the US.

A fraction of the monies spent to bolster world markets could be lent to coal companies to build faclities to use organic wastes as well as natural gas and coal. There should also be a guaranteed price for methanol produced.

The units should, however, produce methanol for long term storage pehaps in massive salt caverns. Methanol can be converted into gasoline or used directly if the US government mandated that a hundred dollars be spent to make all new cars methanol capable. Many race cars burned methanol for many years until ethanol became more politically correct. Methanol can also be converted into DME that can be used as the sole fuel in diesel engines, but it is like propane so it can be used for many propane uses as well. I have not heard of mixtures of propane and DME being used in diesel engines, but it might be a very good and cheap fuel.

Since the worst coal and even oilshale can be used in gassifiers, mine mouth plants can eliminate many transportation costs and use otherwise waste material. If such a plant can be located where oilfields can use the CO2 for better production that would be an advantage. In the future this CO2 may be recovered to make methanol from nuclear produced hydrogen. CO2 can also be recycled directly from the air if nuclear energy is cheap enough. Such a process will use mostly cheap nuclear heat. If the solar energy proponents wish to do the world a favor, they could implement units that use solar heat energy to recapture CO2 from the air. That is mechanical units that do not require lots of water like live plants do, and operate at higher efficiency than the one percent of live plants. ..HG..


You could drop the 'L' step and just make gas. Since that would be mainly hydrogen and carbon monoxide it would have to go through another stage to make methane, still simpler and less water demanding than Fischer Tropsch. Blend the mainly-methane gas with natgas then compress it in 200 bar tanks for automotive use after minor vehicle modifications. That's a lot of fuel cells and clunky batteries no longer needed.

I doubt CO2 capture and storage will never happen outside of subsidised experiments therefore the main feedstocks should should be biowaste. Carbon taxes should apply to the coal percentage and not to the bio percentage.

Paul F. Dietz

methanol for long term storage pehaps in massive salt caverns.

The solubility of sodium chloride in methanol is about 14mg/g. So, the methanol would likely end up damaging the cavity and being contaminated with salt.

Kum Dollison

Start off with a unit at every landfill in the U.S. Surround it with four miles square of switchgrass. You're well on your way.


It makes no sense whatsoever to make carbon-to-liquids plants as long as we burn natural gas for electricity.  If we are gasifying carbon, we should use it to make electricity and use the natural gas as CNG fuel.  This skips the costly and inefficient Fischer-Tropsch synthesis step.

You can call this the Pickens-EP plan.

black ice


BTL plant can be absolutely energy self sufficient; the electricity is generated from steam rising from the cooling water in the FT reactor. This recoups some of the thermal energy that evolves in the exothermic Fischer-Tropsch synthesis reaction.
The FT step is actually very efficient. Getting clean and conditioned gas is where the major efficiency loses occur.
Fluidized bed is definitely not the best option as it needs oxygen (needs electricity to make).
An ideal plant is one that uses no oxygen, works at atmospheric pressure (no compressors), generates all needed electricity, has only liquids/waxes as the product (no gaseous hydrocarbons).

Andrey levin

EP is right.

Currently dry biomass wastes in US (mostly waste from forestry and lumber industry) are co-combusted in coal-fired power plants to generate electricity. Saved NG is excellent fuel for fleet vehicles: buses, delivery vans, and alike. For many years city I live in has their vehicle fleet fueled by CNG. It is clean, cheap, and as additional bonus engines burning NG last twice longer between overhauls.

However, the main point of biofuels in US is to get reliable and inexpensive domestic liquid transportation fuel. Wet biomass and excess corn are good for this.

Kit P

E-P is less wrong than usual

“It makes no sense whatsoever to make carbon-to-liquids plants as long as we burn natural gas for electricity.”

There is nothing wrong with E-P’s logic but again his conclusion is incorrect because of his documented ignorance of energy supply in the US. We import much more expensive oil than cheaper LNG.

The US has become a net importer of LNG and CNG. The reason is that natural gas is the easiest and fastest new source of electricity. Last year NG out grew wind by a 15:1 ratio. While demand for NG to make electricity is increasing, industrial demand is decreasing as jobs that depend on cheap energy leave the US.

The value of use carbon in decreasing environmental and economic order:

1. Organic fertilizer (especially with excess nutrients)
2. liquid transportation fuel
3. electricity generation
4. natural gas
5. process heating

Excess biomass and poor quality coal is a source of pollution. It goes to the landfill, is burned in place, or rots in place producing ghg and contaminates surface water.

Clearly we can create a variety of jobs designing, building, and operating facilities to concert biomass to liquid fuels. When the quantity of carbon for process heating of a biofuels plant exceeds cogeneration of electricity is a good option.

Here is a company that has been around a long time doing just this:
Energy Products of Idaho:

Roger Pham

BTL and CTL will work, but more expensive and more polluting than CNG. Commercial vehicles frequently used can save on operating cost with a CNG conversion, saving liquid petroleum for private autos.

Biomass can be used to make electricity, saving NG for the commercial vehicle fleets. Why pay more and put up with more pollution and complexity and higher up-front investment?

We import much more expensive oil than cheaper LNG.
This is irrelevant to the claims made above.

The question is whether biomass can displace more petroleum if used for generating liquid fuels or electricity. The comment above does not address this question.

Kit P

Not only can we make electricity, we do make electricity with biomass.

This is a post about an analysis about BTL and CTL. And yes we can do lots of things. However, what most of us do is use petroleum to fuel our POVs. If we want to reduce petroleum to fuel our POVs, the most direct way is a direct fuel replacement.

The interesting thing is before electricity and POVs, we had city gas (producer gas , syn gas) for street and home lighting and horse.

I will award 1,000,000 carbon offset to the first genius that can explain dive a POV and use electricity.

Reality Czech

You still failed to resolve the question at issue. You also lapsed into incoherence in your last sentence.

Kit P

What issue is unresolved?


Hopefully the good that will come out of the credit disaster will be the end of the greenhouse gas stupidity.

Let's just make the best energy systems that produce the most energy for the least cost and preserve fossil fuel supplies. Skip the faith based initatives to save the earth from carbon and the EU scams to tax energy with carbon taxes.

Quoth the troll:

E-P’s ... conclusion is incorrect because of his documented ignorance of energy supply in the US.
Says the guy who can't seem to cite a figure.

The USA uses approximately 25 and a half quadrillion BTU of motor gasoline and distillate per year; about 72% of the distillate is used for diesel fuel, so the total used for ground transport fuel is about 24 quads.  The USA also uses about 23 trillion cubic feet (about 24 quads) of natural gas per year.  The electric-only sector uses about 6 quads of that, or almost exactly 25% of the energy of all the motor fuel.

Replacing 6 quads of natural gas with gasified biomass at 90% hot-gas efficiency requires 6.7 quads of biomass, or about 410 million dry tons @ 17.4 GJ/ton.  That same biomass turned into ethanol at 100 gallons/ton via a gasification process would yield 3.2 quads of motor fuel.  Using biomass to displace NG for use as CNG yields twice as much useful energy as BTL; if we could put our hands on a billion tons/year of biomass, we could displace enough NG to displace over 60% of motor fuel.

We import much more expensive oil than cheaper LNG.
Thank you for completely missing the point.  Domestic or imported, the NG and biomass are best used in the least-lossy systems.  BTL is one of the lossiest options.

On top of that, carbon isn't a fertilizer.  Processes which avoid destroying soil carbon (e.g. no-till) are at least as important as composting.


First link should be

Kit P

What is the name of this planet you live on E-P? Magic wand world!
E-P is proposing that the 99.7% of NG currently producing electricity be shifted to the 0.3% for currently used for NG transportation. So E-P do you think that there might be some infrastructure issues?
E-P has no clue to the amount of engineering that goes into a power plant. Assuming that permits are hand, engineering done, equipment purchased, let's build some generating stations. Biomass plants are limited to about 50 MWe at time and it takes longer to construct than CCGT that can be built 1000 MWe at time.
Currently, 15,754 MWe of NG is under construction and 868 MWe of non-wind renewable energy are under construction. E-P plan is like trying to empty a lake with a bucket in a rain storm. I saw E-P on the way home. He was hauling hay bails in economy car. I sure that E-P car got better millage, however, my pickup would be better suited for hauling hay bails.

I look forward to the day that we can build new wind, biomass, and nukes to reduce and turn back NG demand for electricity. Until that time, NG for transportation will not be a good choice.

“On top of that, carbon isn't a fertilizer.”
Organic fertilizer has a carbon/nitrogen ration of 10/1 compared to 20/1 for plants and animals.

Reality Czech
Currently, 15,754 MWe of NG is under construction and 868 MWe of non-wind renewable energy are under construction.
This still fails to resolve the question at issue. The question was about energy, your reply is about power. They are not the same.

You make the distinction when it suits you, so this cannot be an accident.

Kit P

Actually, Reality Czech if you want to make a distinction the correct word to be using in a thermodynamic sense is work. To transport a bale of hay over some distance would result in doing some unit of work. One way of doing this that does not rely on a magic wand, is using an ICE that develops a certain amount of power. Typically, the energy to produce the power comes from liquid transportation fuel.

When considering energy conversion systems, a distinction must be made for the kind of work being done, the equipment converting energy to work, and the source of the energy.

Purdue is built on bluff overlooking vast fields of biomass. I was a student at Purdue on October 17, 1973, when OPEC imposed the oil embargo against the West and first used oil as a political weapon. Concurrently, there was a shortage of NG and propane to dry grain, so corn was rotting on the ground. The energy to produce fertilizer and diesel for tractors was going to waste.

Now the Purdue engineering and ag students are looking down the bluff to see if the is an opportunity to produce transportation fuel. Their conclusion is that there is a large opportunity to produce transportation fuel but first they develop a better model and LCA to determine if it is a sustainable model.

Natural gas is very good fuel (better as a feedstock for plastics and ammonia) for stationary applications. NG is not a good transportation fuel. If you went to school in a California cesspool where you burn lots of NG to make electricity burning biomass to make electricity may be a better option for air quality reasons.

If that does not answer your question Reality Czech, ask again but try to be more specific.

Reality Czech

I am asking you to address the specifics raised above, and also several questions left begging.

  • Does carbon-to-liquids displace more petroleum than alternative methods? You implied that it can, and have made no response to the substance of the rebuttal.

  • Are the figures related to the 6 quads of NG used for electric generation correct or not?

  • How much energy is the new 15.8 GW of NG turbines expected to generate? How much for the 868 MW of non-wind RE generation?

15.8 GW of peaking generators running 5% of the time generates less total energy than 868 MW of base-load generators running 95% of the time, so specifics are important.

black ice

@BTL is one of the lossiest options

EP, biomass is a lossy option no matter how you use it. For example, it will take 100 to 1000 times more biomass btu's to bring a cup of water to boil than with a clean NG stove. It is simply very inconvenient to use - collection, transport, handling - all of this is difficult, hard to automatize. That's why it is not used when cheap fossils are available.
But that's the challenge! The fact that it is lying around rotting, nobody needs it! However, with a little bit of imagination you can devise some simple but clever schemes to convert it into a water-clear highly flammable liquid with a nice kerosene like odor that can be sold to everybody!
As a chemist, I find these types of things rather fascinating!


Questions raised here are interesting. Even a cursory review of CTL/BTL issues indicates the huge variable cost of biomass transport. This Purdue study suggests a flexible method of addressing related issues by building reactors capable of handling multiple feedstocks.

While theoretical conversion of 6.7 Quads biomass to replace 6.0 Quads NG for electric generation appears efficient - it does not consider the significant costs of moving that biomass to generating facilities.

The FCTL appears to be dynamic in both feedstock inputs and diversity of outputs: "not just gasoline and diesel but ethanol and hydrogen. Or we could generate electricity directly from the gas produced."

Attaching a gas turbine to these reactors for off-grid or local area grid service is an interesting option. As Professor Zhao concludes - the concept deserves detailed modeling and further investigation.

Kit P

The only thing left begging is Reality Czech’s logic. There is an elephant in the room that E-P and Reality Czech chose to ignore.

“LCG, October 16, 2008--The ceremonial groundbreaking occurred yesterday for the Gulf LNG Clean Energy project located southeast of Pascagoula on the Pascagoula Bayou Casotte Ship Channel. When completed, the liquefied natural gas (LNG) terminal will enable 150 tankers per year to deliver natural gas from Africa. The project is scheduled for completion in late 2011 and is estimated to cost $1.1 billion.”

Shifting one imported transportation fuel to another imported transportation fuel results in no net improvement.

For many years we had a huge surplus of cheap NG and many programs promoted NG as a transportation fuel with the following result:

6,874 - electricity generation
0,026 - NGV

My point in presenting the number this way is to illustrate the choices for using NG. While my personal choice would be to use NG as transportation fuel and use biomass and nukes for electricity, that is not the reality of the last 10 years. It does not matter how well engineered you product is if American consumers will not accept it. So E-P and Reality Czech how do you like your NGV?

Now for more reality:

15,754 – new NG electricity generation
00,868 – new non-wind renewable energy electricity generation

Hopefully, new non-wind renewable energy electricity generation will have a high capacity factor while new NG electricity generation a low capacity factor. However, to be specific, Reality Czech seems to think non-mandated NG power plants are being built to collect dust and LNG terminals $1.1 billion to lose money.

Roger Pham

>>"Shifting one imported transportation fuel to another imported transportation fuel results in no net improvement."

Since NG cost a lot less per thermal unit than diesel fuel, even importing NG is a big improvement. Furthermore, the US NG reserve is a lot larger than the US petroleum reserve, meaning real energy security.

It is not realistic to expect the private autos to be converted to NG in large numbers, however, the commercial fleet like trucks and buses will find NG to be real economical, and the cost of conversion can be recuperated in less than a year, from saving in fuel cost, given the high rate of usage of these commercial vehicles.

Kit P


Earth first! We can drill the other planets later. Drilling for oil and NG in the US is a very good way to reduce imports.

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