Liquid biofuels - ethanol, biodiesel, etc.

Feb 13 19:54 UTC 2006

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.

response 2 of 40:

Feb 14 07:38 UTC 2006

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.

response 4 of 40:

Feb 14 18:49 UTC 2006

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.

response 6 of 40:

Feb 14 21:16 UTC 2006

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

response 8 of 40:

Feb 15 07:21 UTC 2006

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.)

response 10 of 40:

Feb 15 20:59 UTC 2006

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.

response 12 of 40:

Apr 27 01:26 UTC 2006

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.

response 14 of 40:

Apr 27 05:24 UTC 2006

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).

response 16 of 40:

Apr 28 16:42 UTC 2006

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

response 18 of 40:

Apr 28 17:57 UTC 2006

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

response 20 of 40:

Apr 28 18:34 UTC 2006

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

response 22 of 40:

Apr 28 18:41 UTC 2006

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

response 24 of 40:

May 12 21:11 UTC 2006

i gotcher corn lobby hangin, collegeboy!