Introduction to biodiesel
Biodiesel is not a new fuel in North America. In fact, biodiesel
activities date back to the late 70's and early 80's. Since the
oil embargo of 1973 by the Organization of Petroleum Exporting Countries
(OPEC), a significant amount of research on biodiesel and other
domestically produced fuel has been conducted by various universities,
government agencies, and research organizations. The general conclusion
is that biodiesel is a technically acceptable blending stock for
conventional petroleum diesel. The cost of using biodiesel is quite
economical when compared to the total cost to use other alternative
fuels.
Energy Policy Act (EPACT) regulations require certain fleets to
purchase alternative fueled vehicles and to consume alternative
fuels. Now fleets can receive one vehicle compliance credit for
each 450 gallons of biodiesel consumed in medium and heavy duty
diesel vehicles. This EPACT rule as well as concern over the health
impacts of diesel fuel exhaust, and proposed regulations has spurred
the recent activities to commercialize biodiesel in North America.
A new partial excise tax exemption approved in October 2004 will
also spur consumer acceptance.
What is biodiesel?
Biodiesel is defined as the mono alkyl esters of long chain fatty
acids derived from renewable lipid sources. Biodiesel is typically
produced through the reaction of a vegetable oil or animal fat with
methanol in the presence of a catalyst to yield glycerin and biodiesel
(chemically called methyl esters). Biodiesel is registered with
the US Environmental Protection Agency as a pure fuel or as a fuel
additive and is a legal fuel for commerce. Biodiesel is an alternative
fuel which is typically blended with petroleum diesel for use in
compression ignition (diesel) engines. Its physical and chemical
properties as it relates to operation of diesel engines are similar
to petroleum based diesel fuel.
Biodiesel Attributes
Emissions Reductions
The use of biodiesel in a conventional diesel engine results in
substantial reduction of unburned hydrocarbons, carbon monoxide,
and particulate matter. Emissions of nitrogen oxides are either
slightly reduced or slightly increased depending on the duty cycle
and testing methods. Particulate emissions from conventional diesel
engines can be divided into three components. Each component is
present in varying degrees depending on fuel properties, engine
design and operating parameters. Also, the use of biodiesel reduces
CO2 in the atmosphere, since growing soybeans consumes nearly four
times as much CO2 as the amount of CO2 produced from biodiesel exhaust.
Lubricity
With the lubricity of conventional diesel fuel being scrutinized
due to processing changes required to reduce the sulfur and aromatic
content of diesel fuel, biodiesel use can be demonstrated to be
a benefit. Lubricity test utilizing both the High Frequency Reciprocating
Rig (HFRR) and the Ball On Cylinder Lubricity Evaluator (BOCLE)
have demonstrated the lubricity advantage of biodiesel.
Tests have also been conducted on Jet A-1 fuel. These test results
from a leading independent research institute concluded that biodiesel
shows significant lubricity improvement compared to diesel fuel.
Biodegradability
Biodiesel also has desirable degradation attributes. Studies at
the University of Idaho have been conducted to determine the biodegradation
of biodiesel in an aqueous solution. Biodiesel was compared to diesel
fuel and dextrose. Biodiesel samples degraded more rapidly than
the dextrose control and were 95 percent degraded at the end of
28 days. The diesel fuel was approximately 40 percent degraded after
28 days.
Another study conducted at the University of Idaho tested the "Biodegradability
of Biodiesel in the Aquatic Environment" by the CO2 evolution
method and gas chromatography (GC), comparing the results with regular
diesel. According to the University of Idaho's report, under aerobic
conditions and nutrient supply (N, P), microorganisms will metabolize
a substance to two final products, CO2 and water. Therefore, CO2
is presumed to be the prevalent indicator of organic substance breakdown.
If the substrate is the only carbon source, the amount of CO2 evolved
will be proportional to the carbons consumed by microorganisms from
the test substrate. Thus, the percentage of CO2 evolution is proportional
to the percentage of substrate degradation.
The maximum percent CO2 evolution from several samples of biodiesel
produced were between 85.54-88.49 percent in 28 days, the same as
that of dextrose, indicating there is no difference in their biodegradability.
Yet, the CO2 evolution from the diesel flasks was only 26.24 percent.
It should also be noted that biodiesel blends accelerate the biodegradability
of No. 2 diesel. For example a 20% biodiesel blend degrades twice
as fast as No. 2 diesel. This illustrates that biodiesel use has
demonstrated biodegradability benefits at levels lower than 100%.
Toxicity
Impacts on human health represent a significant criteria as to
the suitability of a fuel for commercial applications. Health effects
can be measure in terms of fuel toxicity to the human body as well
as health impacts due to exhaust emissions. Tests conducted by Wil
Research Laboratories, Inc. investigated the acute oral toxicity
of pure biodiesel fuel as well as a 20% blend of biodiesel with
No. 2 diesel (B20) in a single-dose study on rats. the LD50 of pure
biodiesel, as well as B20, was found to be greater than 5000 mg/kg,
although hair loss was noted on one sample in the B20 group. The
acute dermal toxicity of neat biodiesel was evaluated in a single
dose study involving rabbits. The LD50 of biodiesel was found to
be greater than 2000 mg/kg and the 2000 mg/kg dose level was found
to be a No Observable Effect Level (NOEL) for systemic toxicity.
Acute aquatic toxicity tests with Daphnia Magna have also been
conducted. Table salt (NaCl), diesel and biodiesel were compared
to each other. The LC50 count (the concentration where 50 percent
of the Daphnia Magna have died and 50 percent were still alive)
for table salt was 3.7 parts per million (ppm). Fifty percent of
the Daphnia Magna were dead at 1.43 ppm for diesel fuel. The LC50
number varied for biodiesel from 23 ppm to 332 ppm. There biodiesel
is less toxic than diesel fuel.
Considerations for biodiesel use
Infrastructure
In general, the standard storage and handling procedures used for
petroleum diesel should be used for biodiesel. The fuel should be
stored in a clean, dry, dark environment. Temperature extremes should
be avoided. Acceptable storage tank materials include mild steel,
stainless steel, fluorinated polyethylene, and fluorinated polypropylene.
Biodiesel has a solvent effect which releases the deposits accumulated
on tank walls and pipes, which previously have been used for diesel.
These deposits can be expected to clog filters initially and precautions
should be taken to allow for this.
Materials Compatibility
Biodiesel over time will soften and degrade certain types of elastomers
and natural rubber compounds. Precautions are needed when using
high percent blends to ensure that the existing fueling system,
primarily fuel hoses and fuel pump seals, does not contain elastomer
compounds incompatible with biodiesel. Manufacturers recommend that
natural or butyl rubbers not be allowed to come in contact with
neat biodiesel. Biodiesel will lead to degradation of these materials.
If a vehicle's fuel system does contain these materials, replacement
with biodiesel compatible elastomers such as Viton B is recommended.
The recent switch to low sulfur diesel fuel has caused most OEMs
to switch to components suitable for use with biodiesel, but users
should contact their OEM for specific information.
Cold Flow Properties
As with any diesel fuel, cold flow properties are important. A
20% blend of biodiesel will increase the cold flow properties (cold
filter plugging point, cloud point, pour point) of petrodiesel approximately
1 to 3 degrees Celsius. Thus far, no precautions have been needed
for fueling with 20% blends. The solutions for this potential issue
are much the same as that with low-sulfur #2 diesel (i.e., blending
with No. 1 diesel, utilization of fuel heaters and storage of the
vehicle in or near a building). Biodiesel appears to be unaffected
by conventional pour point depressants.
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