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An alternative to petroleum-based
diesel fuel that can be made from renewable resources.
By
C.J. Baker
In
the search for renewable fuel sources that also are environmentally
friendly, biodiesel fuel is frequently mentioned. Because
diesel engines are playing an increasing role in daily transportation,
as well as satisfying the demands of the recreational vehicle
market, biodiesel fuel deserves some investigation. In researching
biodiesel on the Internet, we found a wealth of information
from sources such as the National Biodiesel Board, the American
Biofuels Association, the Canadian Renewable Fuels Association,
and the Alternative Fuels Data Center. As you would expect,
all of these sources promote the use and benefits of biodiesel
fuel, but several also present potential disadvantages. We
will summarize this information to give you a balanced look
at the biodiesel alternative.
The
first question everyone asks is what is biodiesel? The general
description is that biodiesel is a domestically produced,
renewable fuel that can be manufactured from vegetable oils
or recycled restaurant greases. A more technical description
is that biodiesel is a fuel comprised of mono-alkyl esters
of long chain fatty acids derived from vegetable oils or
animal fats that meets the requirements of ASTM D 6751. Biodiesel
is said to be safe, biodegradable, nontoxic and essentially
free of sulfur and aromatics. It is a renewable resource,
based on soybean and other oil crops that are grown anew
each year. There is an excess production of soybeans in this
country, so biodiesel is an economic way to utilize this
surplus while reducing our dependence on foreign oil. Biodiesel
contains no petroleum, but it can be blended in any percentage
with petroleum diesel to create a biodiesel blend. Such blends
are labeled Bxx, where the xx denotes the percentage of biodiesel
in the blend. For example, B20 would be 20 percent biodiesel
and 80 percent petroleum diesel. B100 is pure biodiesel fuel.
According
to the Alternative Fuels Data Center, “The use of biodiesel
has grown dramatically during the last few years. The Energy
Policy Act was amended in 1998 to include biodiesel fuel
use as a way for federal, state, and public utility fleets
to meet requirements for using alternative fuels. That amendment
started the sharp increase in biodiesel users, which include
the U.S. Postal Service and the U.S. Departments of Energy
and Agriculture. Countless school districts, transit authorities,
national parks, public utility companies, and garbage and
recycling companies also use the fuel.” And according
to the American Biofuels Association, with government incentives
comparable to those provided for ethanol, biodiesel sales
could reach about 2 billion gallons per year, or about 8
percent of highway diesel consumption.
This
last point is important because it addresses one of the big
shortcomings
of biodiesel: its cost. The
major disadvantage of biodiesel is high production costs.
Biodiesel is currently about one and a half times more expensive
than petroleum diesel fuel. These costs come from a variety
of sources. First, soybeans, the predominant source of vegetable
oil for biodiesel, are only 20 percent oil. Utilizing recycled
cooking oils produces a more cost efficient yield, but there
isn’t nearly enough recycled cooking oil available to
meet the anticipated demand for biodiesel. Second, it takes
a lot of energy to manufacture the fertilizers for the vegetable
oil crops, and to support the planting, cultivating, fertilizing,
harvesting, transporting, and processing of the crops for
the energy return from the biodiesel fuel. All of the above
is also very labor intensive, as compared to refining petroleum
diesel or producing synthetic diesel (see "Synthetic
Diesel Fuel" elsewhere on this site). And lastly,
although not technically a cost of production, pure biodiesel
delivers only 90 percent of the fuel economy of petroleum
diesel.
Biodiesel
is made from any fat or vegetable oil through a refinery
process called transesterification to produce chemical compounds
known as fatty acid methyl esters. When used as fuel, these
esters are called biodiesel. A by-product of the process
is glycerol, which is used in cosmetics and pharmaceuticals.
Here’s how the process works. First, the oils and fats
are filtered to remove contaminants and water. Then alcohol
(usually methanol) and a catalyst (usually sodium or potassium
hydroxide) are added to the fats and oils. The oil molecules
(triglycerides) are broken down into esters and glycerol,
which are then separated and purified. The resulting biodiesel
contains no sulfur or fossil fuel aromatics. Interestingly,
biodiesel is almost 10 percent oxygen, making it an oxygenated
fuel, which aids combustion in fuel rich circumstances.
The
resultant biodiesel fuel has some very beneficial properties.
It is of a higher lubricity than petroleum diesel, which
can extend fuel pump life. If has a flash point of 300º F.
(as compared to only 125º F. for petroleum diesel) which
makes it very safe to handle. In fact, such a high flash
point means that biodiesel is officially classified as non-flammable,
allowing it to be shipped without a hazardous material classification.
Biodiesel also has very low volatility. Of course, a high
flash point and low volatility makes it more difficult to
ignite at low temperatures in a cold engine, but this is
a moot point because biodiesel is much thicker than petroleum
diesel. Its low temperature pour point and cloud point make
biodiesel undesirable in cold climates. Biodiesel is biodegradable,
which is good news for the environment if it is spilled.
Pure biodiesel will degrade in as little as 30 days. The
downside is that pure biodiesel also has a relatively short
storage life, but biodiesel blends with less than 20 percent
biodiesel can remain relatively stable for 6 months or more.
Biodiesel
is good in terms of most emissions, too. Proponents claim
that biodiesel results in substantial reductions of unburned
hydrocarbons, carbon monoxide, and particulate matter compared
to petroleum diesel in a conventional diesel engine. Unfortunately,
the term “conventional diesel” is not clarified
as whether testing was done with a “modern” diesel
or an older design (see "Diesel
Evolution" elsewhere on this site). Because biodiesel
contains virtually no sulfur (even less than ULSD), it produces
no sulfur oxides or sulfates that contribute to acid rain.
Emissions of nitrogen oxides do increase relative to the
percentage of biodiesel blended with petroleum diesel, but
some biodiesels are better than others are in this regard.
One
note of caution: soybean oil is not the same as biodiesel
fuel and it should not be used as a diesel fuel. Raw soybean
oil does not meet biodiesel fuel specifications, nor is it
legal to use as fuel.
A
common complaint about diesel engines is the odor of the
exhaust. In this regard, biodiesel is different from petroleum
diesel. Biodiesel (B100) exhaust is said to have an odor
similar to french fries. Different biodiesel blends presumably
have a proportionate mix or aromas. We’ll leave it to
you as to whether this is a benefit.
Our
final consideration is the compatibility of biodiesel fuel
with typical automotive diesel engines. Biodiesel is reportedly
usable in any diesel engine with little or no modification
to the engine or fuel system. Blends of up to 20 percent
biodiesel mixed with petroleum diesel can be used in nearly
all automotive diesel applications without modification or
concern. Biodiesel fuel can damage rubber hoses and rubber
seals. It is always best to check with the manufacturer of
your vehicle before using biodiesel, and in any case, it
is wise to check hoses and seals after six month’s use
of biodiesel. The higher the percentage of biodiesel in the
blend, the more important such checks become. Biodiesel has
a solvent effect that may release deposits accumulated in
the fuel system of the vehicle. These deposits then collect
in the fuel filter, which can clog. Clogging occurs most
often when biodiesel is first used after a period of operation
on petroleum diesel. Filters should be changed after the
first several hours of biodiesel use. After that, clogging
is less likely to be a problem, but frequent fuel filter
checks are a good idea.
Biodiesel
is available at some retail outlets, although such outlets
are far from common. For the location of biodiesel outlets,
check the National Biodiesel Board Web site at www.biodiesel.org and
click on “Buying Biodiesel”.
Biodiesel
is not likely to ever fully replace petroleum diesel, but
biodiesel blends can reduce our dependence on foreign oil
while simultaneously reducing the grease and used vegetable
oil dumped in landfills. It can also create a market for
America’s soybean surplus. The goal of the biodiesel
industry is not to replace petroleum diesel, but to extend
its usefulness. It’s nice to know that if push comes
to shove, we can make our own diesel fuel from our excess
and waste.
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