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Is Cellulosic Ethanol All it’s Cracked Up to Be?

Illinois Plant Produces Alternate Fuel

The EPA has long promoted cellulosic ethanol as the future of biofuels, but technical challenges have kept production far below targets. A recent rule change allows RNG, renewable natural gas, to qualify as cellulosic biofuel even though RNG is not cellulosic, but this helps the EPA to appear to be meeting their goals.

RNG growth has been dramatic and is the lowest carbon vehicle fuel available today. Perhaps the EPA should be promoting a Renewable Gas Standard instead of a Renewable Fuel Standard.

In 2013, production of cellulosic ethanol was effectively zero, even though the legislated target volume for for 2013 was 1 billion gallons. In August 2013, EPA reduced the target to 6 million gallons, and again reduced the target retroactively to 810,185 gallons, less than 1 million. By all accounts this represents a complete failure of the cellulosic ethanol program. In July 2014 the EPA revised the cellulosic biofuel rules to allow RNG to be categorized as cellulosic.

The RFS production data tells the story. In 2013, cellulosic biofuel production was nearly zero. In 2014, a small amount of cellulosic ethanol was produced, but all of a sudden there are 17.5 million gallons of renewable CNG and LNG. The appearance of RNG was purely a function of the rule change in July that allowed already existing (unsubsidized) production of renewable CNG/LNG to qualify. The production of cellulosic ethanol is barely half of the already modest target despite extensive federal support.

dodge RINs1

EPA uses five RIN D-codes (D3, D4, D5, D6 and D7) to define biofuels under the RFS. D3 and D7 are for cellulosic biofuels with a GHG reduction requirement of 60%; D6 is for corn ethanol (GHG reduction 20%); D4 is for biomass-based diesel (50% GHG reduction); and D5 is for advanced biofuels, including sugarcane ethanol and biogas (50% GHG reduction).

Ethanol fuels have been subject to a great deal of criticism for both environmental and engineering reasons. Ethanol is traditionally made from sugars fermented into alcohol. The sugars are derived from agricultural crops, predominantly corn in the USA and sugarcane in Brazil, the world’s two largest ethanol producing countries. Since the use of food crops for fuel competes with food production and raises food prices there has been much effort to develop alternative pathways to produce (cellulosic) ethanol from non-food crops such as grasses, wood and waste.

The problem with cellulosic ethanol is that it is quite challenging to break down cellulose because it is the part of a plant that is meant to be tough. Cellulosic ethanol producers have struggled to find energy- and cost-efficient means of accomplishing the task and many have gone bankrupt, such as KiOR recently.

There are significant engineering challenges in using ethanol as well, the biggest being that ethanol is hydroscopic, meaning that it attracts and absorbs water. Water build up can create corrosion in tanks, fuel lines and engines and can create phase separation of the fuel itself causing engine performance issues. Ethanol also breaks down certain types of polymers and rubber sealants, as well as attacking iron, copper and brass and in some circumstances ethanol has been thought to react with fiberglass fuel tanks creating sludge build up.

Older engines can be ruined by the use of ethanol, though modern engines use materials that are resistant to such failures. A properly designed engine can run on pure (neat) ethanol, though attention must be made to manufacturer’s instructions regarding appropriate fuel choice.

Ethanol blends in gasoline up to 10%, known as E10, are approved for general use in the US and are common today, but blending ethanol above 10% is a heated debate. The 10% threshold is known as the “blend wall” and current ethanol production lies right at that level. Ethanol producers and advocates are actively lobbying the government to approve blends of E15 and E85 (15% and 85%). Petroleum interests are actively opposed to increased ethanol blends, for obvious reasons, as they are trying to protect market share for their product.

Consumers, vehicle manufactures, fuel distributors and retailers are caught in the middle. E15 would be marketed for general use and there is a great deal of concern that increased ethanol ratios will create major maintenance problems. As it stands today E10 is not used in boating, is discouraged for use in small engines such as lawn mowers and chain saws, and is not distributed through pipelines due to corrosion issues. Ethanol must be transported separately from gasoline in trucks and blended at the end of the line near the point of distribution.

The vast majority of ethanol produced in the US is made from corn, which is an intensive crop to cultivate, requiring fertilizers, pesticides and heavy equipment, all of which run on fossil fuels. This is why life-cycle greenhouse gas emissions from corn ethanol are only marginally lower than for gasoline. GHG emissions from corn ethanol are higher than that of fossil natural gas. Cellulosic ethanol has low GHG emissions in theory, but since there is hardly any actual commercial production it remains a theory.

Renewable natural gas has clear benefits over ethanol. First, RNG is chemically identical to fossil natural gas and can be blended and used without restriction. No engineering modifications must be made to accommodate RNG.

Secondly, RNG is readily producible from non-food resources, particularly waste from landfills, farms, food and sewage. All of the raw materials that have been identified as potential cellulosic ethanol feedstocks could be more easily used as RNG feedstocks. There are many proven pathways for producing RNG, ranging from simple digestion processes up to more complex thermochemical processed suitable for more difficult feedstocks. 10% – 20% of natural gas supplies could be renewable.

While ethanol offers questionable greenhouse gas reductions, RNG is widely regarded as the lowest carbon vehicle fuel available. Data from the Department of Energy’s Alternative Fuels Data Center (shown below) presents the case clearly. Agricultural crops converted into ethanol and biodiesel are barely lower in carbon than gasoline and are higher than fossil natural gas. Landfill CNG has the lowest carbon intensity for both light duty and heavy duty vehicles.

Dodge Rins2 Dodge Rins3Natural gas is the fastest growing vehicle fuel in use today, it is safe and non-toxic with the lowest emissions of criteria pollutants and also the lowest carbon emissions of any fossil fuel. Renewable natural gas takes carbon emissions down to the lowest possible levels and is a universal fuel that can replace coal and petroleum, while ethanol is strictly a blend stock for gasoline that requires substantial engineering upgrades for questionable energy security and environmental outcomes.

It is time to consider a Renewable Gas Standard to replace the failed Renewable Fuel Standard.

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Rick Engebretson's picture
Rick Engebretson on December 16, 2014

As a once upon a time protein Biophysical Chemist, now living among and working with cellulose all the time, I honestly don’t know where some of this “science” comes from.

The big issue for me is 100 year old trees die and a ton of wood ligno-cellulose takes another 30 years to rot under optimal conditions of moisture, termites, fungi, etc. Properly dried and treated, wood ligno-cellulose lasts hundreds of years. Cellulose from other sources are also durable. I suspect these claims come from Biochemists who have enormous vocabularies, but only cursory exposure to physics. People who make pharmaceuticals don’t make energy.

After submitting a requested proposal to mass produce “recycled plastic livestock septic tanks” in 1987 as a cost/performance structure to actually create “biogas” and market plastic garbage, I learned the only way to do honest science is to stay away from politicians. I still don’t know how all those thermal, chemical, huge biogas tanks can be made globally without recycled plastic.

Ed Dodge's picture
Ed Dodge on December 16, 2014

Food to fuel is not a good solution for our energy problems. We need to use fuel to produce food, turning around and burning the food is energetically backwards. And we can’t produce remotely enough ethanol or any biofuels to break the grip of petroleum on transportation, not within orders of magnitude. It does not really matter if ethanol is a few pennies cheaper than gasoline if we can’t produce the quantities we need.

To say that the cellulosic ethanol program is working is wildly off-base, try to find an EPA official who will make that claim. If it was working why did they classify RNG as cellulosic? Why do they keep revising the production targets downwards?

The corn ethanol industry would not exist without generous subsidies and the cellulosic industry has had far more failure than success spending tax dollars. RNG on the other hand has been used for years in transport without subisides at all, check out how many garbage trucks run on landfill gas (and they run better than on diesel).

As for cellulosic ethanol, it is more efficient to take those same feedstocks and make RNG which can be utilized in our existing infrastructure. Ethanol requires all manner of investments and upgrades in engines, distribution and storage systems for little benefit environmentally or economically. Ethanol is just a lousy fuel, which is why the military won’t touch it.

Methane is being produced already in enormous quantities by the Earth’s natural systems, by capturing it and using it we keep it out of the atmosphere and directly replace fossil fuels.

Rick Engebretson's picture
Rick Engebretson on December 16, 2014

Please excuse my odd ball perspectives, but I think the corn ethanol process is doing a terrific job creating food, and providing a very successful fuel additive. The process is certainly not an energy process, as often noted.

Making complex amino acids, nucleic acids, phospolipids, etc. is done by growing yeast from sugar and primary ingredients. Ethanol is a waste product. One energy killer rarely mentioned is ethanol-water is azeotropic; you can’t distill it past about 85% EtOH. And unless I’m wrong, I thought the word was hygroscopic, not hydroscopic. But hydroscopic is OK by me. Certainly the benefit of ethanol combustion oxygenate is demonstrated. Perhaps even fuel efficiency. But I agree entirely, developing ethanol fuel technology from here seems very uncertain.

And I entirely agree, gas is a great future fuel option, from whatever source.

Well, back to my odd-ball cave. Thanks for the post.

Ed Dodge's picture
Ed Dodge on December 16, 2014

I’ll accept that corn ethanol is a better gasoline additive than MBTE that it replaced and analysis I have seen suggests that the ethanol additive market is market is firmly established and does not need additional subsidies. Ethanol as an additive means sticking to the E10 threshold we are at today and that does nothing to address energy security nor does it make substantive improvements in the environment.

If we want to end our military entaglements in the Middle East we need to fundamentally break the grip of petroleum on transportation markets. A combination of EV’s and natural gas can accomplish this. Biomass resources can contribute effectively to increasing natural gas supplies and lower GHG emissions, but biomass alone in any formulation will never offer the quantities needed to replace petroleum and in that regard I consider ethanol to be a distraction.

It is also worth noting that ethanol is not used at all for aviation, maritime, military or diesel applications, ZERO. And that is because it is a lousy fuel. But gas to liquids produce superior quality diesel and aviation fuels.


Jeffrey Miller's picture
Jeffrey Miller on December 16, 2014

How is the carbon intensity of something like Landfill CNG calculated exactly? I assume the calculation involves a credit for capturing methane which otherwise would have gone into the atmosphere and a debit from the CO2 emissions from then burning the fuel and these two roughly net out.

Could you gives us the quantitative version of this calculation? I’m curious to see how the numbers fall out.

Jeffrey Miller's picture
Jeffrey Miller on December 16, 2014

How exactly is using enormous tracts of prime farmland and huge amounts of fossil fuel resources to grow corn for fuel “doing a terrific job of creating food”? I thought the almost universal consensus was that it did the exact opposite, driving up corn prices and reducing the amount available for food  (with the added benefit of not reducing carbon emissions at all).

Ed Dodge's picture
Ed Dodge on December 16, 2014

I just use the official figures from EPA, DOE, and other reputable agencies. Personally, I share your question about how carbon emissions are calculated across the board in all scenarios. There are a lot of assumptions and murky science applied if you ask me, and you see debate and controversy periodically over specific figures. So that is why I just stick with the official numbers and if the analysis behind those conclusions shifts I will shift accordingly.

Here is the EPA’s webpage on the Landfill gas calculations. They don’t mention anything about including displaced atmospheric methane as part the analysis, just the displacement of fossil natural gas with biomethane for fuel.

Jeffrey Miller's picture
Jeffrey Miller on December 16, 2014


I looked at the EPA calculator you link to and it seems that most of the benefit is from capturing the methane and not allowing it to go into the atmosphere. This effect dominates the avoided CO2 emissions from burning fossil gas by a factor of about 10.






James Thurer's picture
James Thurer on December 16, 2014


Gasoline has an energy content of 114,000 btu / gallon, and currently wholesales for $1.58 / gallon, or $13.86 / mmbtu.  Ethanol has an energy content of 76,000 btu / gallon, and currently wholesales for $1.66 / gallon, or $21.84 / mmbtu.   (

In other words, ethanol is currently 1.58 times more expensive than gasoline on an energy equivalent basis, even though corn and ethanol prices are at historically very low levels. In fact, corn ethanol and cellulosic ethanol have never in history been less expensive than gasoline.

As to your suggestion that the drop in ethanol prices caused the recent sharp drop in oil prices, the net energy yield of corn ethanol production is the energy equivalent of about 300,000 barrels of oil per day, or less than 10% of oil production from fracking in the U.S., and about one third of 1% of global oil consumption.  The impact of corn ethanol production on oil price is insignificant, and is far more than offset by increased food prices.

Finally, as to your claim that cellulosic ethanol is starting to come online, I challenge you to produce a reliable reference stating the cost and eroei of cellulosic ethanol production.

John Miller's picture
John Miller on December 16, 2014

Edward, Cellulosic ethanol continues to be challenged by conversion/production costs and the ability to qualify as an ‘advanced biofuel’ with ‘full lifecycle’ GHG emissions 50% less than the petroleum gasoline (equivalent) fuel displaced.  The reason why cellulosic ethanol struggles to achieve any significant delivered volumes appears to be due to the still huge technology gaps and developments/innovations needed to achieve positive ‘net energy values’ (i.e. production energy/fossil fuels consumption < than finished ethanol fuel heat content).  Will cellulosic ethanol ever overcome these hurdles?  Only time, continuing R&D and (hopefully) future achieved advancements will tell.

As far as landfill gas or biogas qualifying as an advanced biofuel, this one appears to be another example of the EPA possibly putting political influence over sound science and engineering.  Based on my past research natural gas motor fuels (CNG/LNG) are the 3rd most successful alternative to petroleum gasoline.  However, the natural gas motor fuel comes from well/hydraulic fracturing production, not landfill biogas.  How the EPA rationalizes that landfill biogas qualifies as an advanced biofuel appears to be another example (Re. my past analysis of sugarcane advanced biofuels) of the EPA doing less than a reasonably accurate analysis of certifying another ‘less-than-advanced’ biofuel.  In the case of landfill biogas it can definitely and readily displace natural gas heating fuels used in convective heaters, boilers and power plants, but not very likely petroleum motor fuels.  The problem begins with raw biogas, 50-70% methane and 30-50% carbon dioxide.  To be used as a motor fuel it must be purified by removing the carbon dioxide, which is normally vented into the atmosphere, followed by compression/liquefaction and transported into natural gas fueling infrastructures.  The economic probability of this process-supply chain actually occurring is highly questionable.

A better justification for landfill biogas is that it does reduce natural gas emissions from landfills and does displace natural gas and possibly heating oil fuels.  Applying this to the ‘Renewable Fuel Standards’ appears to be another distortion of this regulation and its primary purpose: displacing and reducing the consumption and associated emissions of ‘petroleum motor fuels’; directly. 

Ed Dodge's picture
Ed Dodge on December 16, 2014


Landfill biogas is being used every day commercially for vehicle fuel. Garbage trucks run on it routinely, the waste management industry totally embraces it and it has been very successful and expanding in use, with no subsidies. So there are real commercial fleet miles driven every day on landfill biogas.

BioCNG is a company that specializes in cleaning up landfill biogas for vehicular use. Interestingly enough, the standards are lower for CNG than pipelines so it is both easier and more profitable to sell landfill gas for transport. The equipment package is surprisingly small and unsophisticated.

T. Boone Pickens’ retail LNG company, Clean Energy Fuels, sells a bioLNG product at commercial volumes and most of it is coming from landfills, though not all.

Rick Engebretson's picture
Rick Engebretson on December 16, 2014

When the Indianapolis 500 and other car race tracks quit using ethanol, I’ll agree “it is a lousy fuel.” However, we can agree current biofuels are not “sustainable fuels.”

Ed Dodge's picture
Ed Dodge on December 16, 2014

You know what they have to do to the engines after the race?

Completely flush them out and eliminate all the ethanol so it does not corrode the engines overnight. Same reason they don’t put ethanol in pipelines or use it in the military. 

Ethanol is a lousy fuel.

John Miller's picture
John Miller on December 16, 2014

Edward, do you know what are the fuel specifications for the BioCNG heavy duty vehicle motor fuels?  Their website is a bit vague.  Important properties begin with Btu/CuFt.  If their processing unit can’t meet normal pipeline spec’s (1,000 Btu/CF minimum) that means they must probably operate totally independent to existing vehicle fueling infrastructures.  That makes this technology a niche market only for a limited number of company vehicles.  Since I suspect the heat content is 70-80% of pipeline spec’s, heavy duty truck VMT per refueling is proportionally less than Commercially available CNG.

Also do you have any estimates of current BioCNG production-consumption volume levels?  It sounds like it could be greater than current hydrogen/fuel cells, but only a very small fraction of EV’s (equivalent fuel Btu basis).

Ed Dodge's picture
Ed Dodge on December 16, 2014

I don’t have good data for current production for RNG vehicle fuels. My new article I just finished is a discussion of resource potential for RNG and it is substantial, certainly a few TCF per year in the USA.

Any methane source is upgradeable to pipeline standards, landfill gas is perhaps the dirtiest source compared to digesters, but it is being done routinely. 

RNG  is used for heat, transport, and power, so use gets divided across all sectors. 

Regulations vary for pipeline injection of RNG, but they are being streamlined and many states have regs in place. At the end of the day RNG is pure methane. A lot of what is being sold is being drawn from pipelines after being injected elsewhere with credits following the transaction.

As for BioCNG specifically, they are just one company and there a number of players in the market. Not sure why their standards are slightly different, just something someone told me at a conference. But they do operate standalone facilities.

Rick Engebretson's picture
Rick Engebretson on December 17, 2014

Sean, there seems to be some very interesting advanced biofuel research taking place within the Indianapolis 500 racing group. Please do your own research. But as I read it, after 40 years using methanol fuel, various methanol/ethanol blends were tried, all using Honda engines.

What is interesting to me is this “biofuel blend” research includes what would be derived from pyrolysis of cellulose, instead of pure ethanol derived from (enzymatic) fermentation of glucose from cellulose. And Honda developing engines accordingly. This is not trivial R&D as many big talkers would declare.

This would be consistent with other cellulose pyrolytic process stream efforts, like “CoolPlanet” you mention. My sense is that working with poly-glucose cellulose is going to be much harder than working with poly-glucose (water soluble corn) starch.

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