Biofuels. Biofuels have been used since the dawn of human civilization. Not always in a way that we would be proud of today. But, with the exception of such shameful episodes, biofuels played an important positive role in human lives for uncountable generations….
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Biofuels have been
used since the dawn
of human civilization
Not always in a way that we would be proud of today...
But, with the exception of such shameful episodes, biofuels played an
important positive role in human lives for uncountable generations….
Biofuels were used for cooking,...
…for heating human dwellings,
…or for making light.
Oil lamp ( olive oil, or
whale oil )
In the XX-th century simple biofuels like firewood were “running
out of favor” – they were used mostly in leisure activities, e.g.,
for barbecuing, in “family time” at a fireplace, etc.
However, firewood is now
“returning with vengeance”,
as wood pellets.
Single-home heating instal-
lations using firewood in
such form are fully auto-
matic and require little
The wood-pellet industry
in the US is growing fast. Advantages: it’s a non-polluting fuels, does
not add “new” CO2 to the atmosphere (rather, it “recycles” the natural
CO2), and there is much wood available for making pellets.
However, today we most often talk about biofuels as of
potential alternatives to fossil fuels used in transportation.
It’s not a new concept – in the XIX Century many American trains
were running on firewood.
Yet, today we need “bio-alternatives” to liquid petroleum-
based fuels, such as gasoline, diesel, and jet fuel.
A promising alternative to gasoline is bio-ethanol.
Bio-ethanol has been used by humans since ancient
times, but rather for “fueling” people (by drinking
beer, wine, whisky…), not cars. Essentially, almost
all ethanol (CH3CH2OH) ever made by humans was
“bio”, because it was obtained from natural sugars
made by plants, through a fermentation process
involving yeast (single-cell living microorganisms).
Gasoline engines can run on ethanol or ethanol-
gasoline mixtures after a small modification of the
fuel-injection system (up to 15% of ethanol, no
modification is even needed).
The energy content of ethanol is ~2/3 of that of gasoline.
A real “bio-ethanol paradise” is
Brazil. About 50% of their cars
run on ethanol, not on gasoline.
Brazilians make their ethanol from
sugar cane – a plant that grows very
well in their hot climate. The process
is pretty straightforward: the “syrup”
extracted from the canes is fermented
by yeast. The product contains ~15%
of CH3CH2OH. Then, pure ethanol is
extracted from it by distillation.
Unfortunately, sugar cane does not grow well in
the United States…
However, ethanol can also be obtained from starch.
Starch molecules are made up of many sugar mole-
cules, linked into a long “chain”. There are many
starch-producing plants that grow well in the US:
wheat, barley, potato, corn (a.k.a. maize). The latter
is the best “starch-producer” of all of them.
But yeast cannot convert starch to ethanol
directly. Therefore, a two-step process is
Amylose (starch) molecule: 500 or more sugar molecules are linked to
form a long chain:
Another liquid biofuel that currently recieves strong interest
“Normal” diesel fuel consist of hydrocarbon molecules
(general chemical formula: CnH2n+2 ) with n = 12-16.
Almost all fats produced by
plants or animals have the
same general structure:
namely, three “fatty acid
molecules” are attached
to a single glycerol
A single “fatty acid chain”
contains a similar number of carbon atoms as an average
hydrocarbon molecule in diesel fuel.
The viscosity of some vegetable oils is low enough for
using them directly as a fuel for a Diesel engine.
In fact, in the first public demonstration of the
engine – at the Paris World Exhibition in the
year of 1900 – Dr. Rudolf Diesel used peanut
oil as a fuel.
However, the viscosity is still “a bit too high”.
In cold weather, the oil “thickens”, and the
engine cannot be started.
Some ingenious “biodiesel fans” install special
heaters that heat the oil up to about 180 F.
Then they can run, e.g., on leftover oil they
can buy for cents from restaurants.
Dr. Rudolf Diesel
The first engine
However, a better solution is to de-attach the fatty acid
chains from the glycerol molecule. Single chains are
chemically quite similar to the diesel fuel hydrocarbon
chains – except that they are acids, meaning that they
are pretty corrosive substances.
Fortunately, their acidity can be easily neutralized by
combining each chain with a molecule of methyl alcohol
CH3OH, in a process called “esterification”. The physical
properties and the energy content of the “fatty acid methyl
esters” obtained in that way are very similar to those of a
“normal” diesel fuel.
This is how biodiesel is being made at industrial scale –
but the estrification apparatus is so simple that one can
install such a device in a garage. Many such “estrificators”
have been built by OSU student.
Canola, an oil-seed plant that grows well in the US, yields
about 120 gallons of oil par acre.
The ratio value
is usually given as 3 – 4, so it is significantly better than that
of the US-made bioethanol.
“Cellulosic ethanol” – it may be an attractive option for
Sugar in sugar cane, and starch in corn can be thought of
as substances containing “stored solar energy”. In fact,
plants use solar energy in the process of combining atmo-
spheric carbon dioxide (CO2) and water (H2O) to produce
simple sugars (glucose, fructose) in a process known as
photosynthesis. Those molecules can be further converted
into larger sugar molecules (e.g., of sucrose, a.k.a. “table
sugar”). In sugar cane, the process stops at sucrose, which
is “yeast-fermentable”; in corn, the process of adding sugar
molecules continues, yielding large starch molecules, which
have to be broken down by enzymes to make them “yeast-
Yet, most of the solar energy used by plants goes for
Cellulose is the main “scaffolding material” of which plants
make their leaves, stems, branches, trunks….
Interestingly, the basic “building blocs” for making cellulose
are the very same simple sugars that sugar cane converts
into sucrose, and corn into starch. Cellulose molecules,
however, are much larger and sturdier than those of starch.
Cellulose molecules can be broken down into yeast-fermen-
table sugars. Such a process has been pioneered at indus-
trial scale by German firms in the closing years of the XIX
Century. The technology was also used in the US in the
mid-XX century, but it was not financially viable and
therefore the production was discontinued.
In the corn plant, much more photosynthesis products are
converted to cellulose than to starch!
In the existing technology of making corn bioethanol, the
cellulose is simply wasted.
However, if viable technologies of converting cellulose to
sugar were developed, much more bioethanol could be
obtained from the same amount of “biomass”!
Actually, corn wouldn’t even be
needed any longer – there
are other plants that yield much
more cellulose per acre
than corn, and are much less
“demanding” – one such plant
is switchgrass that can be grown
almost everywhere in the US.
Bioethanol will be the topic of one of the “students’
presentation” in this course, and therefore we will
not continue the discussion here.
There are many new exciting developments in the
cellulosic ethanol area – you will learn about them
from that presentation!
On the other hand, there are opinions that converting
plant cellulose to ethanol is not the best way of utilizing
it. It is argued that the amount of usable energy obtained
from cellulose can be much higher if other technologies
are used, not involving fermentation. Please read the
discussion in this article from the renowned SCIENCE