A new report in SCIENCE evaluates efficiencies and greenhouse gas 
emissions for fuel ethanol (Farrell et al, 27 January 2006, pp 506-508). 
It concludes that there is a net energy yield for ethanol from corn. The 
main correction to a previous study that found negative energy yield was 
the inclusion of the displacement of energy required for coproduct 
production of oil and animal feed. The details of their calculations are 
available separately online.
 
The estimate for net energy yield for ethanol production today is about 
+4.7 megajoules per liter (MK/L), compared to a LHV for ethanol (vapor) of 
21.5 MJ/L (my estimate). Interestingly the "fossil" energy required for 
producing the ethanol is distributed about 5% from petroleum products, 30% 
from natural gas, 40% from coal (largely for generating electricity) and 
4% "other". (Why these don't add up to 100% is not explained; it may be 
because the difference is non-fossil fuel sources, although "other" 
includes nuclear and hydro- electricity generation.)

They do point out that ethanol production from cellulose is much less 
energy dependent, and estimate a net energy yield of about 23 MJ/L. (I do 
not know why this is larger than my estimate of the LHV for ethanol. It 
may be just a matter of data sources for heats of formation, and choice of 
standard states.)

The rather low energy yield of 4.7 MJ/L (only about 22% of the LHV) from 
corn is because the starch that is hydrolyzable to sugars for fermentation 
is such a small fraction of the mass processed. This value suggests that 
ethanol as fuel would be much more expensive than petroleum for the same 
energy yield. Current pronouncements of the economics of ethanol fuel from 
corn usually do not mention the very large subsidies for ethanol 
production.

There currently are no efficient processes for the conversion of cellulose 
to ethanol but if it could be invented the raw materials could be used 
almost in their entirety.

Cellulose conversion by the overall reaction

        C6H10O5 + H2O = 2 C2H5OH + 2 CO2

certainly does not occur spontaneously although it does look exothermic.

40 responses total.

Corn obviously isn't the best source for ethanol, and soybeans 
obviously aren't the best source for biodiesel. Those feedstocks were 
chosen for entirely political reasons. 

I made a mininterpretation of the paper in #0 in the statement those 
percentages "don't add up to 100% is not explained". They shouldn't. What 
those percentages are are the percentage of the energy to produce 1 MJ of 
ethanol required from each of those sources. They add up to 79% or 0.79 MJ 
external energy input to produce 1 MJ equivalent of ethanol. This is why 
the Net Energy produced is 4.7 MJ/L rather than the 21.5 MJ/L LHV of 
ethanol. 

What is a better source for bioethanol than corn, given current 
technology, in terms of net energy yield? Economics is a separate 
question, not addressed in this paper.

Newsprint?  Nonrecyclable plastics?  Old road surfaces?  Old tires?

Ethanol cannot be produced from any of those materials with a positive 
energy efficiency.

I just read in the paper yesterday about a research project at MSU for 
producing ethanol from cellulose (newsprint, if you wish, or any other 
plant material). They were very encouraged a looking forward to 
success....while admitting that they weren't able to do it yet. This is 
one of those "holy grails" of energy research, along with "burning" 
methane directly to methanol, which would revolutionize our energy 
structure.

Here's another similar rosy report: 
http://www.treehugger.com/files/2005/05/genetically_eng.php
No analysis of energy efficiency is given.

And another:
http://www.fiveregionsofthefuture.com/region/entries/EthanolFromWood
No analysis of energy efficiency is given.

And another: 
http://www.esf.edu/newspubs/news/2005/01.18.ethanol.htm 
No analysis of energy efficiency is given.

All of these involve the hydrolysis of cellulose to sugars and then the 
classic fermentation to ethanol, using yeasts or the yeast enzymes 
produced by genetic engineering of bacteria.

The problem is that the hydrolysis of cellulose is more difficult than of 
starch. The route to ethanol from corn is via the hydrolysis of starch.

What makes this especially interesting is that starch and cellulose are 
chemically *almost* alike. Both are polymers of isomers of glucose with 
the empirical formula [C6H10O5]n. The difference is that starch is a 
polymer of a-d(+)glucose and cellulose of b-d(+)glucose, which are 
sterioisomers. Evolution took advantage of the extreme differences in the 
chemical susceptibility of the polymers to hydrolysis to use starches for 
heribvore food and cellulose for supporting plants. All this has been 
known for centuries. If there were any easy way to hydrolyze cellulose it 
would have been done long ago because then all cellulose would be useful 
for food (and viscose rayon would not have been possible). The weird 
symbiotic bacteria of termites can do it, but this has not been translated 
into a sufficiently efficient industrial process.

Hire some termites or cows.

Cows can't digest cellulose either. Look at their pies. 

The microbes in them digest a lot of the cellulose for them.

I looked into it, and I stand corrected. However I found a lot of
misinformation or missing information on web sites. Starches, which cows
digest even more readily than cellulose, was not mentioned on any site I
looked at. One said digestion of cellulose produced amino acids. The
digestion of cellulose is by anaerobic bacteria, and also produces methane.
That is pretty potent digestion. 

In any case, no way has yet been found to do it outside a cow (or termite) 
economically with high energy efficiency. (It is well known that cows 
don't know how to do it either.)

I once translated an article about adding sawdust to cow feed, and also to
human bread.  It rose better and turned a nice brown and was lower in calories
and higher in fiber.  I wonder if it also generated methane.  I think the
sawmills were behind this research.

Methane is produced in the anaerobic bacterial digestion of carbohydrates.

I'd say that the use of sawdust is as an essentially chemically inert 
filler that modifies the physical properties of the recipe.

I recall an example of the inefficiency of the cow. I once visited a cave 
into which a stream flowed and cows liked to shelter in the large entrance 
on hot days. They of course added a lot of undigested cellulosic material 
to the stream. As one progressed into the cave the water got up to chest 
high and one disturbed the bottom sediments, where the cow excrement 
continued to ferment, releasing bubbles of methane. At the time we were 
using carbide lights (with open flames) and could reach ahead and ignite 
those methane bubbles with most entertaining flashes of flame.

Thinking further about alternative liquid fuels from cellulose - there is 
no reason to think only of ethanol, even though technology for producing 
ethanol from sugars for beverages is an established technology. For energy 
*any* liquid fuel product would be desirable and perhaps ethanol is not 
the most economic product. Here is a site for a course that described 
current industrial fermentation processes and their products.

http://www.limab.ugent.be/ind_fermentations.htm

It seems to me that while Bush is seeming to push the niche energy 
alternatives of photocells and hydrogen, the problem of large scale 
production of a non-fossil liquid fuel is not receiving the attention it 
deserves. The conversion of cellulose to a liquid fuel holds the promise 
of a future secure liquid fuel industry just as important as fusion power 
promises electric energy independence. Cellulose conversion technology 
should receive at least the same or greater investment as fusion research 
has received.

Currently cellulose conversion is being supported by small projects at a 
number of institutions, but there is not yet a mandate to move this work 
to the forefront of national alternative energy policy.

Tonight at the gas station in Ida, Michigan (there is only one) I found
soydiesel for $2.99/gal. Regular diesel was $2.92/gal.

Bush made a speach about alternative fuels a few days ago and talked
about sugarcane being grown in Hawaii and then turned into ethanol.
Which was interesting because I read a few months ago about sugarcane
and pineapple industries moving out of Hawaii and over to India.

OOPS!  FUCKIN FREE MARKET!!!

I heard Bush's speech. He had a bit in his script on cellulosic ethanol, 
but it was clear he didn't know what he was reading. Nevertheless, someone 
put it into his script, which is a slightly encouraging sign. He did not 
put forward any suggestion to significantly expand research in 
cellulose-derived liquid fuels, still apparently thinking we can drill our 
way out of the "oil peak".

He did mention the very large subsidies in research and production that 
ethanol from corn receives (which doesn't much support the production of 
ethanol as fuel - what few admit is that if the ethanol were produced 
using energy *only* from the ethanol produced itself - the industry would 
disappear).

Lately the energy seems to be coming from coal and natural gas.

I can see ethanol being viable if they can come up with a good source
for the energy needed to produce it.  If that energy is, itself, coming
from renewable sources, it might make sense.  If it's just a round-about
way to convert natural gas into a vehicle fuel it's kind of pointless.

Is this a good analogy?
Oil=stocks of 1929
Energy infrastructures=Banks of 1929

No, because the Great Depression did not cause us to go about looking 
for alternatives to money.

Where did I say "money"?
What are you talking about?

Running out of oil has prompted us to change our energy source. This is 
a lot different from managing the same energy source, which would be a 
better analogy fit with the great depression.

You think we're going to stop using oil overnight?  Our entire civilization
relies on it too heavily.

I know what you're getting at, but just because both peak oil and stock 
market bubbles create economic depressions....I don't see why an 
analogy can be made.

The analogy points to the fact that the energy market is unregulated.  The
oil companies are steamrolling over consumers.  The fight just to be a
customer has already started.

Here, check this tidbit out..

Russia feels threatened by European Union moves to curtail its role in
Europe's energy markets and has no choice but to seek other buyers, President
Vladimir Putin said.
http://sg.news.yahoo.com/060427/1/40ede.html

Brazil's sugarcane-based ethanol production is apparently several times 
more energy-efficient than the way we produce it from corn in the U.S., 
partly because they use stalks and other waste materials to provide the 
heat for the process.  (U.S. plants use coal or natural gas.)  The 
downside is the acreage needed is considerably higher. 
 
I think it's likely we won't see any major steps forward in ethanol 
production efficiency until we can pry the corn lobby's fingers off it. 

i gotcher corn lobby hangin, collegeboy!

We should build more nuke plants and run electric scooters.

/combs out the poo-corn and sticks it in a scootertank

I read an interesting assessment of the fossil carbon emitted in  the course
of generating electricity via nuclear power. It is abouit 1/3 to 1/2 of that
generated by coal-fired power plants. The fossil carbon arises from fuels used
in mining and processing uranium ore. 

I've heard the net energy balance of nuclear power is not very good when
you take into account construction, mining, refining, etc. and the
relatively short working life of a nuclear plant.  I haven't seen any
numbers personally, though.  It's certainly never lived up to the old
"too cheap to meter" claims.

What is the life of a nuclear plant?

It is determined by the NRC licensing span, which is a political decision.
It is 40 years under current rules, but it could be extended. See
http://ideas.repec.org/p/wpa/wuwpio/9512002.html

I think there are US Navy reactors that have been operating longer than 
that.

I don't think NRC licensing of civilian reactors applies to the military. 
Nothing much in the way of regulation applies to the military....

True, but maybe the more we build nuclear reactors, the longer they will
be usable. Previous designs are no longer licensed because they are
dangerous. Newer ones are not as dangerous.

Originally the target was 30 years, but as rcurl points out, it's been
extended.  Incidents like the corrosion pit at the FirstEnergy plant in
Ohio make me question the wisdom of this a little, though.

That corrosion was discovered in time. All devices become increasingly 
liable to some kind of faults and obsolescence as their use continues, and 
the history is that early on faults are fixed until eventually fixing the 
increasing number of faults appears to be uneconomic compared to 
rebuilding, or obsolescence compared to new designs becomes serious. This 
is true of everything from our computers and cars to nuclear power plants. 
What is a little surprising is having a specific regulation on the allowed 
lifetime, rather than considering it as a problem of changing economics 
and safety over time. Are there any similar regulations for any other 
devices?

While the nuclear plant near Monroe was being built, I went on an SAE tour
there.  At the time, they told me the design life was 20 years.

That's the *design* life, but what should happen in real life? The "design
life" of the Mars Rovers Spirit and Opportunity was three (3) months: they
are still cooking at 29 months. The "design life" is sort of a "we would be
very disappointed if it doesn't last at least as long as" time, not the time
to desire failure. 

The difference is if Spirit breaks, no one dies.  There are portions of 
a nuclear plant that are difficult or impossible to inspect adequately.  
The corrosion at the FirstEnergy plant was found in time, but just 
barely, and it was found by *accident*. 
 
The situation is kind of analogous to some highly stressed aircraft 
parts, such as helicopter rotor blades. They usually have a specified 
lifespan, after which they're discarded and replaced. The lifespan is 
usually calculated based on how quickly fatigue cracks are assumed to 
grow in the part.  The idea is that there's no way to really adequately 
inspect those parts in a way that will detect an impending failure, and 
any failure is catastrophic, so the only safe course is to replace them 
regularly. 
 

I should add that one way around this problem is to try to find designs 
that are inherently safe.  One example is a pebble-bed reactor, which 
is designed in such a way that it can never melt down, even if there's 
a total coolant loss. 

- Backtalk version 1.3.30 - Copyright 1996-2006, Jan Wolter and Steve Weiss