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Dow and NREL Partner on Thermochemical Conversion of Biomass to Ethanol and Other Chemical Building Blocks

Process flow diagram with research barriers for cost-competitive thermochemical ethanol production. Click to enlarge. Source: NREL

The Dow Chemical Company (Dow) and the US Department of Energy’s National Renewable Energy Laboratory (NREL) are jointly developing and evaluating a thermochemical process that will convert biomass to ethanol and other chemical building blocks.

The process will gasify non-food biomass feedstock to produce a synthesis gas, which Dow’s catalyst technology will then convert into a mixture of alcohols—predominantly ethanol—that can be used as transportation fuels or chemical building blocks. The joint evaluation program will focus on improving the mixed alcohol catalyst, as well as demonstrating pilot scale performance and the commercial relevance of an integrated facility.

In 2007, NREL published a report—Thermochemical Ethanol via Indirect Gasification and Mixed Alcohol Synthesis of Lignocellulosic Biomass—that assessed the potential for a gasification/mixed alcohol synthesis process to meet a cost target of $1.07/gallon by 2012. A key finding of that report was the importance of R&D for the synthesis catalysts.

Poor performance could increase MESP [minimum ethanol selling price] by 25% or more. Whether this is due to actual non-target catalyst formulations or due to poor performance in Clean-Up and Conditioning that leads to poor alcohol synthesis catalyst performance, the cost effects are major. The catalyst cost sensitivity range was extremely large, from $2.50/lb to over $2,250/lb. This was done to bracket a variety of potential catalyst systems, not just cobalt moly-sulfide. Exotic metals such as rhodium (Rh) or ruthenium (Ru) can add considerable cost to a catalyst system even at relatively low concentrations. At low catalyst costs, total CO conversion and alcohol selectivity (CO2-free basis) have the largest impact on the overall MESP. The catalyst productivity (g/kg/hr) did not show much impact over the sensitivity range chosen. In reality, all of these catalyst performance indicators are tightly linked. It is unlikely that research could change one without affecting the others.

The thermochemical conversion process for mixed alcohol production has six basic steps:

  • Feedstock handling and preparation.

  • Gasification. NREL considered indirect gasification is considered in its assessment. Heat for the endothermic gasification reactions is supplied by circulating hot synthetic olivine “sand” between the gasifier and the char combustor. Conveyors and hoppers are used to feed the biomass to the low-pressure indirectly-heated entrained flow gasifier. Steam is injected into the gasifier to aid in stabilizing the entrained flow of biomass and sand through the gasifier.

    The biomass chemically converts to a mixture of syngas components (CO, H2, CO2, CH4, etc.), tars, and a solid “char” that is mainly the fixed carbon residual from the biomass plus carbon (coke) deposited on the sand. Cyclones at the exit of the gasifier separate the char and sand from the syngas.

    Air is introduced to the bottom of the reactor and serves as a carrier gas for the fluidized bed plus the oxidant for burning the char and coke. The heat of combustion heats the sand to more than 1,800°F.

  • Gas cleanup and conditioning. This consists of multiple operations: reforming of tars and other hydrocarbons to CO and H2; syngas cooling/quench; and acid gas (CO2 and H2S) removal with subsequent reduction of H2S to sulfur. Tar reforming is envisioned to occur in an isothermal fluidized bed reactor; de-activated reforming catalyst is separated from the effluent syngas and regenerated on-line.

    The hot syngas is cooled through heat exchange with the steam cycle and additional cooling via water scrubbing, which also removes impurities such as particulates and ammonia along with any residual tars. The cooled syngas enters an amine unit to remove the CO2 and H2S. The CO2 is vented to the atmosphere in this design.

  • Alcohol synthesis. The cleaned and conditioned syngas is converted to alcohols in a fixed bed reactor. The mixture of alcohol and unconverted syngas is cooled through heat exchange with the steam cycle and other process streams. The liquid alcohols are separated by condensing them away from the unconverted syngas.

  • Alcohol separation. The alcohol stream from the alcohol synthesis section is depressurized and dehydrated using vapor-phase molecular sieves. The dehydrated alcohol stream is introduced to the main alcohol separation column that splits methanol and ethanol from the higher molecular weight alcohols.

  • Heat and power. A conventional steam cycle produces heat (as steam) for the gasifier and reformer operations and electricity for internal power requirements (with the possibility of exporting excess electricity as a co-product). The steam cycle is integrated with the biomass conversion process.

The alcohol synthesis reactor is the key to the entire process. After researching several decades of work on alcohol synthesis catalysts, NREL selected a modified Fischer-Tropsch catalyst for the process design, specifically a molybdenum-disulfide-based (MoS2) catalyst, originally from Dow/Union Carbide.

The former Dow/UCC catalyst was chosen as the basis because of its relatively high ethanol selectivity and because its product slate is a mixture of linear alcohols (as opposed to the branched alcohols that result from modified methanol catalysts). This particular catalyst uses high surface area MoS2 promoted with alkali metal salts (e.g. potassium carbonate) and cobalt (CoS). These promoters shift the product slate from hydrocarbons to alcohols, and can either be supported on alumina or activated carbon, or be used unsupported.

In its design, NREL is targeting a much higher ethanol distribution (70.66 wt%) than found in pervious work (Dow, 34.5%; SRI, 446.12%), enabled by the almost complete recycle of methanol within the NREL process. In the alcohol purification section downstream, virtually all methanol is recovered via distillation and recycled back to mix with the compressed syngas. This is done in order to increase the production of ethanol and higher alcohols.




I believe that this is a good way to synthesize fuel. Whether you make methane, methanol, ethanol, gasoline, kerosene or diesel, gasification is a way to turn biomass into fuel that is proven and can be scaled and replicated across the U.S.


Biomass to X is indeed picking up speed and advocates.

These articles never say enough about timetables to suit me. I hope they intend to report status before 2012:

"to meet a cost target of $1.07/gallon by 2012."

But this looks like a good approach:

"In the alcohol purification section downstream, virtually all methanol is recovered via distillation and recycled back to mix with the compressed syngas. This is done in order to increase the production of ethanol and higher alcohols."

This may draw howls from the fans of methanol and butanol but we will be better off sticking to ethanol now rather than wavering, starting, stopping, and flitting to one alcohol scheme or another.

John McDonnell

Will the char material be available for sale? If so, dependent upon analysis, we may have a potential use for a significant amount. Please contact me at: jmcdonnell@chartertn.net

Thank you.


Great cost target - if, after taxes & margin requirements the retail price is 100% more at the gas station, that is still manageable. Americans seem comfortable paying $2.00-2.50 a gallon.



Gas may remain 2x to 3x above the comfort zone you mentionned for an extended period of time, as fossil sources rarefy.

It is doubtful that alternative fuels will be much cheaper, unless consumption is drastically reduced. Major reductions in worldwide consumption level may take many years. Many of the 700-800 million ICE vehicles are going to be around for 20+ years.

Henry Gibson

Implementing a biomass to liquid process is better than putting the biomass into a landfill, but it might be better to enrich the soil with it. Biomass was once the major fuel of the US and England. England was mostly deforested by the need for fuel for the industrial revolution. There is not enough biomass to make a significant contribution to the energy needs of transportation. Plug-in-hybrid cars are the eventual solution along with Nuclear Reactors. Even lead-acid batteries are suitable for electric cars. Computer controlled charging can give longer life. Firefly's new grids may make lead-acid batteries even longer lived. ..HG..

BG Automotive Group

A fundamental change in our driving habits is now required.

The Automobile Industry is going to be in the same position as the Airline Industry in the next few months. Unless we get away from gas combustion vehicles, including Hybrids, the automobile industry (as we know it) will die.We need to make drastic moves. America needs to move to ELECTRIC. The vehicles are not as fast, not always as fun to drive, but the move will save Americans money (Billions) and help bring change to our automotive companies. Let's "Be Green"!!!!!!!!!!!! BG Automotive Group Ltd. has a car that will travel 80-100 miles per charge for $15,995. Finally a car that most Americans can afford. Did you know that 80% of all drivers, drive less than 50 miles per day? This new car will cost an equivalent of $0.20-0.25 cents/gallon (depending on electricity rates in your area). Why send $700 Billion per year to OPEC (now buying up U.S. companies) when we can use this money for our schools, health care, social security for all Americans, etc, etc, etc. We can make the difference if WE change.


I agree. Only, synthesizing methane from syngas (CO+H2) might not be very useful for transportation fuels.

I see one major issue with using molybdenum sulfide (MoS2) catalysts. The fuels produced still need to meet the EPA specs for S and N. The use of MoS2 catalysts may lead to higher concentrations of S in the fuel.

"Many of the 700-800 million ICE vehicles are going to be around for 20+ years."

I understand China has a 10-year vehicle age limit law. It is really a costly sop. Rapid fuel price increases will lead to much quicker scrappage rates.


"There is not enough biomass to make a significant contribution to the energy needs of transportation."

I personally consider 30 percent to be a significant contribution.


There are several biomass to methane plants that are operating well. Pickens has the plan for NG cars and we can make the methane from biomass...no problem. Delivery by pipeline beat refineries and tanker trucks and you can refuel in your garage at home. This is something I have talked about for years and it will come true soon.


@ Andy

There is enough biomass to make a significant contribution (>30%). Please see the following (Billion Ton) report.




If even part of those billion tons of biomass can make it from plants located close to the source to where it can be used it would help. There are biofuels plants being built in Colorado and Georgia. The plant in Georgia uses pine tree waste from lumber and paper industries. As long as you have a steady stream of feedstock to keep the plant running, it can pay itself back. The seems to be a ready and willing market for their biofuel products at good prices.

Paul F. Dietz

Is biomass-derived syngas really going to be cheaper than syngas derived from coal? Remember, coal can be converted to syngas in situ, allowing otherwise unmineable coal (for example, at great depth, or on continental shelves) to be exploited.

Reality Czech
Pickens has the plan for NG cars and we can make the methane from biomass...no problem.
I doubt that biomass can produce as much methane as is now produced from fossil sources.

I never said biomass could produce as much methane as from fossil sources. I said that we could make methane from biomass and use it in NG cars.


Paul, my comments were based on that research. You must have missed that I was quoting another poster. I think we both agree that 30 percent is significant particularly when our current fleet is so inefficient.

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