Brian Rodgers here. This short article was sent in to me by one of my
newsletter readers. We say,"Think global, act local." I am getting my
readers to think biofuels.
Combustion
Our civilization relies on combustion. This has been the situation
for the past several hundred thousand years, since people were in
small groups of hunter-gatherers that used fire. Today there are
sophisticated technologies to burn diverse types of substances that
contain carbon with hydrogen.
At one level combustion is analogous to the chemistry of living
things. The process of respiration is a form of combustion under
complex regulation by enzymes to keep it from getting too feverish.
If the reaction happens too fast then the energy released will destroy
cells. Both combustion and respiration follow this idealized general
reaction:
(CH2O)n + O2 → CO2 + H2O + energy , where (CH2O)n is a carbohydrate
as a model compound. A material must be heated to initiate
combustion. In respiration, enzymes lower the energy barrier to start
the reaction. The problem is that this is an idealized reaction.
Under most normal conditions, there are hundreds of other substances
produced by incomplete combustion. Many of these chemicals are toxic
and/or carcinogenic.
One of the first chemicals directly linked to lung cancer was
benzo-α-pyrene (BP). Chimney sweeps in London had a high rate of lung
cancer and generally died in their 40's. BP was implicated in these
lung cancer cases with animal tests in the early 1900's. BP is
produced by combustion of coal, wood, petroleum and other organic
materials (like tobacco). BP belongs to a class of organic chemicals
called polycyclic aromatic hydrocarbons, or, PAHs. PAHs are common in
many materials, including coal (anthracene), petroleum diesel
(napthalene), and smokes from incomplete combustion. Certain PAHs
are found in exhaust from vehicles. For instance, coronene (10 carbon
ring) in air is directly related to the internal combustion engines
operating in an area, but is not present in the fuel.
Wood smoke typically contains more than 200 substances. Some of
these substances are PAHs. Another set of chemicals are phenols and
cresols, both of which are highly toxic. Then there are the dioxins
and furans. One of the most toxic substances known to us is
2,3,7,8-tetracholoro-p-dibenzodioxin (TCDD). TCDD is the famous
contaminant in "Agent Orange" of Vietnam fame. TCDD is a trace
contaminant from the synthesis of 2,4,5-T. However, TCDD is also
produced in combustion; and, can be found in wood stove chimneys, in
automobile tailpipes, and on barbecued meat surfaces. Matter of fact,
if you really want to make both your and your neighbor's soil toxic,
just throw some PVC or plastic bags and table salt into the wood
stove, and turn the damper way down. TCDD causes miscarriages and
birth defects in laboratory animals, and causes a liver disorder in
people (porphyria cutanea tarda) at high doses. The type of wood
being burned in a community can be "finger-printed" by the profile of
substances in the smoke.
Wood burning is an important air pollution issue. Albuquerque and
Bernalillo County are required to curtail wood burning when there are
atmospheric inversions that trap the smoke near the ground and people.
However, wood burning is not regulated per se, instead it's the
amount of carbon monoxide produced during incomplete combustion that
is. Population size also has an influence. For instance, Las Vegas
with a population of about 16,000 and heavy wood smoke in the winter
is considered too small in population to regulate to reduce health
effects. However, EPA has forced certain areas with larger
populations to curtail wood smoke production because of health
effects. This is solved with the placement of catalytic converters on
chimneys of wood burning stoves. Diesel motors do not fall under
regulation for air pollution by EPA. This is largely from lobbying by
the transportation industry which has successfully argued that air
pollution controls on diesels will be burdensome on the industry.
However, diesel motors produce high levels of PAHs, particulalry when
they produce black smoke. Numerous studies have shown that exhaust
from diesels is toxic to animals, and is carcinogenic. Whether this
holds for biodiesel is another question because the chemistry of the
fuel may be different from that of petroleum diesel.
Crude oil contains high levels of PAHs. Crude oil is passed through
catalytic "crackers" that crack PAH rings to form long chain
hydrocarbons. The process does not destroy all the PAHs. The cracked
oil is then distilled, where various "cuts" are taken for different
fuel and product types. The highest boiling-point temperature
substances, and first to condense at the bottom of a distillation
column (first cut) are fuel and lubricant oils, like those used in
motor oils, home heating, and ships. The next fraction taken is
diesel oils, followed by gasoline, and then "jet fuel" at the top.
Various very small molecules, principally methane and ethane, are
burned off at flares (smokestacks with a flame coming out of the top)
in a refinery as waste from distillation. Consequently, diesel is a
complex mixture of various products from the cracking that happen to
condense at a certain temperature in the distillation tower.
Similarly, there is generally little straight chain octane in
gasoline, however, gasoline is measured on how it performs like octane
when combusted. Substances in the fuels are toxic. For instance,
gasoline contains benzene, which is heavily regulated in manufacturing
industry because it causes leukemia. However, you breathe it every
time you go to a service station, along with a diversity of other
chemicals.
Does biodiesel create the same air pollution that petroleum diesel
does? Given that the chemistry of the fuels are different, you would
expect differences in the exhaust. However, I'm unaware (ignorant?)
of any studies that have addressed this question. Another important
question is whether biodiesel has as toxic of constituents as
petrodiesel does. Both questions bear on the societal decision for
future adoption of biodiesel and its acceptance as a widely used fuel.
A more fundamental question is whether our society can function
without combustion? Are there alternatives to burning for energy
production? Nuclear fission and potential fusion energy sources are
not combustion, but produce high levels of radioactive wastes.
Photovoltaic and wind power may be able to fill some of the role of
fossil fuels, but then batteries to store electrical energy become a
limiting factor and are polluting in their own right from manufacture
and disposal.
Whoever invents a combustion-independent form of convenient,
transportable and efficient energy production will be a
multi-billionaire! Good luck, let me know when you make your first
billion!
Kenneth P. Bentson, Ph.D.
Associate Professor of Natural Resources Management
New Mexico Highlands University
(505) 454-3501
[EMAIL PROTECTED]
_______________________________________________
Biofuel mailing list
Biofuel@sustainablelists.org
http://sustainablelists.org/mailman/listinfo/biofuel_sustainablelists.org
Biofuel at Journey to Forever:
http://journeytoforever.org/biofuel.html
Search the combined Biofuel and Biofuels-biz list archives (50,000 messages):
http://www.mail-archive.com/biofuel@sustainablelists.org/
