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Team from Coskata, GM and Auburn University lays out a case for cellulosic ethanol

22 March 2011

The conversion of biomass to cellulosic ethanol is the most efficient and productive use of biomass to create a high-octane, environmentally friendly transportation fuel, according to a perspective paper published in the Journal of Chemical Technology & Biotechnology. Authors of the paper are Rathin Datta, cellulosic ethanol company Coskata’s chief scientific officer; Mark Maher, executive director, powertrain/vehicle integration, GM Powertrain; Coleman Jones, GM biofuels implementation manager; and Richard Brinker, Dean and Professor of Forestry and Wildlife Sciences, Auburn University.

The paper draws four primary conclusions: the conversion of biomass-to-ethanol has natural efficiencies; ethanol has a history of superior performance; today’s cars are ready for ethanol; and sufficient biomass exists to make an impact.

Natural efficiencies. Biomass feedstocks that are abundantly available in the US and worldwide contain a high quantity of oxygen (approximately 40% or higher). To utilize this biomass most efficiently, the conversion must include the entire feedstock, including the oxygen, the authors argue. Cellulosic ethanol is the alternative transportation fuel which retains most of the oxygen portion of the feedstock.

...based on the fundamentals of photosynthesis and simple laws of thermodynamics, the biomass feedstocks that are and will be readily available are highly oxygenated and are lignocellulosic materials. For liquid fuel or chemical feedstock production from this feedstock, the winning strategy is to produce a product that has proven and widespread use, with the highest yield using the entire feedstock—and that is ethanol.

—Datta et al.

Ethanol’s compatibility with the oxygen in biomass and lower carbon requirements lead ethanol to have a higher yield and more BTUs of output per ton of incoming biomass than “drop in” alternatives such as butanol or hydrocarbons. The theoretical yield for ethanol, they note, is 51%; for n-butanol or iso-butanol, 41%; and for octane C8-hydrocarbon, 29.7%.

Comparison of yields of ethanol vs other reduced products. Source: Datta et al. Click to enlarge.

Conversion pathways. Much R&D has focused primarily on a biochemical pathway or a thermochemical pathway for producing ethanol from biomass, the authors note. The biochemical approach uses enzymes to convert pretreated lignocellulosic biomass materials into sugars, which can then be fermented into ethanol. The thermochemical approach gasifies a biomass feedstock to produce syngas, which is then converted into ethanol by a chemical reaction utilizing chemical catalysis.

Biochemical approaches are hampered by expensive pre-treatment requirements; the inability to ferment lignin (biomass contains 20 to 25% lignin); the complexity of biological conversion of cellulose to glucose; and limited feedstock flexibility.

Thermochemical approaches are hampered by lack of catalyst selectivity; thermodynamic inefficiency caused by combination of the exothermic reactions and need for specific H2:CO ratios; high pressure requirements (>1000 psig) increases the mechanical complexity and capital costs; and sensitivity to impurities.

The authors argue that Coskata’s approach, consisting of gasification, syngas fermentation, and separation, is attractive because of its feedstock flexibility; its ability to use all the feedstock; its low greenhouse gas profile; selective ethanol production; low operating costs; and low capital costs.

Emissions and engine efficiency. The authors note that numerous studies and reports have been made on the reductions of harmful emissions such as carbon monoxide, VOCs (volatile organic compounds), and sulfur oxides form the use of ethanol.

Ethanol’s high octane enables the use of higher compression ratios, particularly in dedicated ethanol vehicles. The high heat of vaporization produces a charge cooling effect, particularly in direct injection engines, that can again allow higher compression ratios. This effect is enhanced by the increased volume of fuel that is required to compensate for the lower energy content of ethanol, they note.

Even when a vehicle is not optimized to take advantage of some of ethanol’s attributes, the higher octane and faster flame propagation speeds for ethanol result in increased energy efficiency (miles per BTU of energy present in the fuel used) for high ethanol blends relative to gasoline.

On average, 2010 model year vehicles deliver a 2% improvement in energy efficiency with E85. There is significant variation within and between manufacturers; for example General Motors products delivered an average 3.19% improvement in energy efficiency. This is typically due to vehicle calibration variation and how well each vehicle can take advantage of the improved properties of E85.

These studies support the expectation that ethanol’s octane values and other attributes will increase combustion efficiency and lead to more efficient power output in high ethanol content blends such as E85. However, improvements beyond those shown are unlikely to be realized in the near future in the commercial world because of the long time it will take to transition from predominantly gasoline to predominantly ethanol as the liquid motor fuel.

—Datta et al.

Impact. The authors cited the recent major studies conducted by the USDA, DOE and major National Laboratories which projected that large and sustainable biomass feedstock supplies are available and going to be available to produce ethanol efficiently in very large quantities of around 340 billion L (90 billion gallons) per year in the US.

The authors also summarized the experience gained over the past 70 years in the south-eastern USA to further support the fact that efficient and sustainable biomass supply can be developed and maintained to support much increased usage.


  • Rathin Datta, Mark A. Maher, Coleman Jones, and Richard W. Brinker (2011) Ethanol – the primary renewable liquid fuel. J. Chemical Technology and Biotechnology 86: 473-480 doi: 10.1002/jctb.2580

March 22, 2011 in Cellulosic ethanol | Permalink | Comments (14) | TrackBack (0)


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It would be more efficient to use rural and urban biowaste to manufacture methanol through plasma arc pyrolysis.

This methanol can then be converted into high octane gasoline using the MTG process. The carbon neutral gasoline can then be mixed in with regular petroleum derived gasoline up to any percentage.

Plasma arc pyrolysis of rural and urban biowaste can also be used to manufacture carbon neutral diesel fuel and jet fuel.

The case is compelling and the facts are what they are...but there is this little problem called fossil fuel. There is a fossil fuel production & distribution complex, developed & perfected over many decades...there is not a biofuel production & distribution complex that can even dream of rivaling fossil fuel at this time. So biofuel producers are essentially hijacking the fossil fuel distribution system (which I'm in full support of) but how it happens (big government carrots / sticks or no government at all) is the dilemma.

    ...there is not a biofuel production & distribution complex

It turned out to be possible here in Brazil. It´s not high tech or even new tech. I'm quite sure you'll find a way, if you wish.

Of course we can do this, but U.S. business comes down to profit maximization and not what is good for the country.

CelsoS is correct. Brazil successfully demonstrates the efficacy of biomass derived ethanol. As we see from this study there are sufficient domestic waste resources to produce up to 90B gallons annually. All the while creating JOBS for North Americans - at a lower per gallon cost than foreign oil.

The oil industry has its shills in place to whine about corn subsidies. Let's ask big oil - is it better for domestic workers to have the jobs and to keep the dollars at home -- or send them overseas to hostile nations?

Coskata continues to lead in the field of cellulosic biofuels and we congratulate them on their fortitude.

Don't conflate sugars and cellulose. The US cannot begin to grow enough sugar crops to ferment into ethanol to make a dent in its fuel needs, and growing corn for that purpose is a hugely inefficient use of land and water. The only useful feedstock is cellulose.

That combination of ethanol and PHEVs and EREVs together solve the problem. The VOLT and her coming sisters, needs less than 10% of the gasoline that a equivalent ICE does. Ethanol is already producing and satisfying almost 15% of the demand for liquid fuels today.

In combination they essentially eliminate the need for the wasteful oxidation of fossil liquid hydrocarbons in Ground Transport. The ICE after forty year of effort has been cleansed to the point it is no longer a polluter of toxic gases. Fossil hydrocarbons sufficient for a Millenia or two or more exist, when the wasteful use as a fuel is essentially eliminated.

Problem Solved. Q.E.D.

Resistance to Energy Independence revolves around two camps:

Globalists - who had hoped to resolve world issues via the manufactured "eco-tastrophy" called global warming. Independence of any sort is anathema to these centralists hoping to dominate control of energy and resources.

Big Oil - mammoth international corps with everything to lose if common men generate their own energy from domestic biomass and waste feedstocks. Who hates to see an addict rehabilitated? Drug dealers.

But there is hope for the misbegotten. They can invest their windfall profits in clean energy and domestic JOBS today. Do they have the vision?

Ethanol should be pretty good in high compression atkinson cycle range extenders.

I guess theroetically you should get an even better yield of methanol than ethanol due to the lower chains

If you gasify and synthesize you can make what you want. Methane, methanol, ethanol, gasoline, kerosene, diesel all have their synthesis efficiencies. The way I look at it, the farther up you go the less efficient it becomes. If it takes 5 therms of natural gas to make one gallon of synthetic diesel, we might as well run our trucks on natural gas or DME, it is more efficient.

This methanol can then be converted into high octane gasoline using the MTG process.
The MTG process loses quite a bit of energy to produce a motor fuel of inferior octane rating. Just use it as M85.
It turned out to be possible here in Brazil.
Brazil produces ethanol from sugars in cane juice. It burns the cellulose (bagasse) for process heat, not to power vehicles.

The limited amount of biomass makes its efficient use crucial. No process yielding hydrocarbons is anything close to good enough.

I read that the octane rating of the MTG product was reasonable.
Octane Number, RON 92
It should not matter as much when blended with 85% high octane methanol

I also read that the conversion from methanol to synthetic gasoline has good conversion efficiency.

"The hydrocarbons produced contain 95% of
the energy in the methanol feedstock"

Methanol's RON is 109, MON 89 (R+N/2 = 99). Not only can it be used as an octane-booster for lower-octane (thus cheaper and less energy-intensive) petroleum fractions, it has a relatively low critical temperature and a very high heat of evaporation, making it very attractive for both ultrasupercharged DISI use and supercritical fluid injection with regenerative fuel pre-heating a la Transonic Combustion.

If you need more methanol than biomass can provide, it is much more efficient to turn CH4 into MeOH than gasoline. On top of this, it doesn't form an azeotrope with water as ethanol does. Methanol is the better motor fuel, almost period.

When they state that 95% of the energy is in the hydrocarbons, that may be a bit misleading. It shows that over 80% becomes synthetic gasoline and the rest is other hydrocarbons.

Methanol is a good fuel for internal combustion and fuel cells. It is easy to make and a combination of natural gas and then additional biomass can get us there. It can also be converted into DME at the truck stop for big rigs.

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