Encyclopedia
Biodiesel refers to a
diesel-equivalent, processed fuel derived from biological sources. Though derived from biological sources, it is a processed
fuel that can be readily used in diesel-engined vehicles, which distinguishes biodiesel from the
straight vegetable oils or
waste vegetable oils used as fuels in some modified diesel vehicles.
In this article's context, biodiesel refers to alkyl esters made from the transesterification of both vegetable oils and/or animal fats. Biodiesel is biodegradable and non-
toxic, and has significantly fewer emissions than
petroleum-based
diesel when burned. Biodiesel functions in current
diesel engines, and can supplement
fossil fuels as the world's primary transport energy source.
Biodiesel can be distributed using today's infrastructure, and its use and production are increasing rapidly. Fuel stations are beginning to make biodiesel available to consumers, and a growing number of transport fleets use it as an additive in their fuel. Biodiesel is generally more expensive to purchase than petroleum diesel but this differential may diminish due to economies of scale, the rising cost of petroleum and government tax subsidies.
Description
Biodiesel is a light to dark yellow liquid. It is practically immiscible with water, has a high boiling point and low vapor pressure. Typical methyl ester biodiesel has a flash point of ~ 150 °C , making it rather non-flammable. Biodiesel has a density of ~ 0.86 g/cm³, less than that of water. Biodiesel uncontaminated with starting material can be regarded as non-toxic.
Biodiesel has a
viscosity similar to
petrodiesel, the industry term for diesel produced from
petroleum. It can be used as an additive in formulations of diesel to increase the lubricity of pure Ultra-Low Sulfur Diesel fuel, although care must be taken to ensure that the biodiesel used does not increase the sulfur content of the mixture above 15 ppm. Much of the world uses a system known as the "B" factor to state the amount of biodiesel in any fuel mix, in contrast to the "BA" or "E" system used for
ethanol mixes. For example, fuel containing 20% biodiesel is labeled B20. Pure biodiesel is referred to as B100.
Technical standards
The common international standard for biodiesel is EN 14214.
There are additional national specifications. ASTM D 6751 is the most common standard referenced in the United States. In Germany, the requirements for biodiesel is fixed in the DIN EN 14214 standard. There are standards for three different varieties of biodiesel, which are made of different oils:
The standards ensure that the following important factors in the fuel production process are satisfied:
Basic industrial tests to determine whether the products conform to the standards typically include
gas chromatography, a test that verifies only the more important of the variables above. More complete tests are more expensive. Fuel meeting the quality standards is very non-toxic, with a toxicity rating of greater than 50 mL/kg.
Applications
Biodiesel can be used in pure form or may be blended with petroleum diesel at any concentration in most modern diesel engines. Biodiesel will degrade natural
rubber gaskets and
hoses in vehicles , although these tend to wear out naturally and most likely will have already been replaced with
Viton which is nonreactive to biodiesel. Biodiesel's higher lubricity index compared to petrodiesel is an advantage and can contribute to longer fuel injector life. Biodiesel is a better solvent than petrodiesel and has been known to break down deposits of residue in the fuel lines of vehicles that have previously been run on petrodiesel. Fuel filters may become clogged with particulates if a quick transition to pure biodiesel is made, as biodiesel “cleans” the engine in the process. It is, therefore, recommended to change the fuel filter within 600-800 miles after first switching to a biodiesel blend.
Usage
In warm climates, pure unblended biodiesel can be poured straight into the tank of any diesel vehicle. Some older diesel engines still have natural rubber parts which will be affected by biodiesel, but in practice these rubber parts should have been replaced long ago. Biodiesel has been noted to be linked to premature injection pump failures. While many vehicles have been using biodiesel for many years without ill effect, the uncanny correlation between several cases of pump failure and biodiesel cannot be dismissed. Pure biodiesel produced 'at home' is in use by thousands of drivers who have not experienced failure, however. The fact remains that biodiesel is a very new subject and will carry some risk until it is fully researched. Biodiesel sold publicly is held to high standards set by the ASTM.
Gelling
The temperature at which pure biodiesel starts to gel varies significantly and depends upon the mix of esters and therefore the feedstock oil used to produce the biodiesel. For example, biodiesel produced from low
erucic acid varieties of canola seed starts to gel at approximately -10 °C. Biodiesel produced from tallow tends to gel at around +16 °C.
As of 2006, there are a very limited number of products that will significantly lower the gel point of straight biodiesel. One such product, Wintron XC30, has been shown to reduce the gel point of pure biodiesel fuels. Wintron XC30 is a blend of
styrene copolymer
esters in a
toluene base. It reduces the tendency of the
viscosity of biodiesel to increase as it is cooled. This is a key step in cold temperature crystallisation. In this way it acts to decrease both the temperature at which the crystals formed become large enough to block the pores of a fuel filter and the lowest temperature at which the fuel will still flow . A number of studies have shown that winter operation is possible with biodiesel blended with other fuel oils including #2 low
sulfur diesel fuel and #1 diesel / kerosene. The exact blend depends on the operating environment: successful operations have run using a 65% LS #2, 30% K #1, and 5 % bio blend. Other areas have run a 70 % Low Sulfur #2, 20 % Kerosene #1, and 10% bio blend or a 80% K#1, and 20 % biodiesel blend. According to the National Biodiesel Board , B20 does not need any treatment in addition to what is already taken with petrodiesel.
Water contamination
Biodiesel is hydrophilic. Some of the water present is residual to processing, and some comes from storage tank
condensation. The presence of water is a problem because:
- Water reduces the heat of combustion of the bulk fuel. This means more smoke, harder starting, less power.
- Water causes corrosion of vital fuel system components: fuel pumps, injector pumps, fuel lines, etc.
- Water freezes to form ice crystals near 0 °C . These crystals provide sites for nucleation and accelerate the gelling of the residual fuel.
- Water accelerates the growth of microbe colonies which can plug up a fuel system. Biodiesel users who have heated fuel tanks therefore face a year-round microbe problem.
Previously, the amount of water contaminating biodiesel has been difficult to measure by taking samples, since water and oil separate. However it is now possible to measure the water content using water in oil sensors.
Availability
Production
- Main article: Biodiesel production
Chemically, transesterified biodiesel comprises a mix of mono-
alkyl esters of long chain
fatty acids. The most common form uses
methanol to produce methyl esters as it is the cheapest alcohol available, though
ethanol can be used to produce an ethyl ester biodiesel and higher alcohols such as isopropanol and butanol have also been used. Using alcohols of higher molecular weights improves the cold flow properties of the resulting ester, at the cost of a less efficient transesterification reaction. A byproduct of the transesterification process is the production of
glycerol. A
lipid transesterification production process is used to convert the base oil to the desired esters. Any Free
fatty acids in the base oil are either converted to soap and removed from the process, or they are esterified using an acidic catalyst. After this processing, unlike
straight vegetable oil, biodiesel has combustion properties very similar to those of petroleum diesel, and can replace it in most current uses.
Biodiesel feedstock
A variety of oils can be used to produce biodiesel. These include:
...
such as
mustard,
palm oil,
hemp,
jatropha, and even
algae show promise ;
Worldwide production of vegetable oil and animal fat is not yet sufficient to replace liquid fossil fuel use. Furthermore, some environmental groups object to the vast amount of
farming and the resulting over-
fertilization,
pesticide use, and land use conversion that would be needed to produce the additional vegetable oil.
Many advocates suggest that waste vegetable oil is the best source of oil to produce biodiesel. However, the available supply is drastically less than the amount of petroleum-based fuel that is burned for transportation and home heating in the world. According to the United States
Environmental Protection Agency , restaurants in the US produce about 300 million US gallons of waste cooking oil annually. Although it is economically profitable to use WVO to produce biodiesel, it is even more profitable to convert WVO into other products such as soap. Hence, most WVO that is not dumped into
landfills is used for these other purposes. Animal fats are similarly limited in supply, and it would not be efficient to raise animals simply for their fat. However, producing biodiesel with animal fat that would have otherwise been discarded could replace a small percentage of petroleum diesel usage.
The estimated transportation fuel and home heating oil used in the United States is about 230 billion US gallons . Waste vegetable oil and animal fats would not be enough to meet this demand. In the United States, estimated production of vegetable oil for all uses is about 24 billion pounds or 3 billion US gallons , and estimated production of animal fat is 12 billion pounds .
Biodiesel feedstock plants utilize
photosynthesis to convert solar energy into chemical energy. The stored chemical energy is released when it is burned, therefore plants can offer a sustainable oil source for biodiesel production. Most of the carbon dioxide emitted when burning biodiesel is simply recycling that which was absorbed during plant growth, so the net production of greenhouse gasses is small and CO
2 zero.
Feedstock yield efficiency per acre affects the feasibility of ramping up production to the huge industrial levels required to power a signifcant percentage of national or world vehicles. The highest yield feedstock for biodiesel is
algae, which can produce 250 times the amount per acre as soybeans.
Efficiency and economic arguments
According to a study written by Drs. Van Dyne and Raymer for the
Tennessee Valley Authority, the average US farm consumes fuel at the rate of 82
liters per hectare of land to produce one crop. However, average crops of rapeseed produce oil at an average rate of 1,029 L/ha , and high-yield rapeseed fields produce about 1,356 L/ha . The ratio of input to output in these cases is roughly 1:12.5 and 1:16.5. Photosynthesis is known to have an efficiency rate of about 16 % and if the entire mass of a crop is utilized for energy production, the overall efficiency of this chain is known to be about 1 %. This does not compare favorably to
solar cells combined with an electric drive train. Biodiesel out-competes solar cells in cost and ease of deployment. However, these statistics by themselves are not enough to show whether such a change makes economic sense.
Additional factors must be taken into account, such as: the fuel equivalent of the energy required for processing, the yield of fuel from raw oil, the return on cultivating food, and the relative cost of biodiesel versus petrodiesel. A 1998 joint study by the
U.S. Department of Energy and the
U.S. Department of Agriculture traced many of the various costs involved in the production of biodiesel and found that overall, it yields 3.2 units of fuel product energy for every unit of fossil fuel energy consumed. That measure is referred to as the energy yield. A comparison to petroleum diesel, petroleum gasoline and
bioethanol using the USDA numbers can be found at the Minnesota Department of Agriculture website In the comparison petroleum diesel fuel is found to have a 0.843 energy yield, along with 0.805 for petroleum gasoline, and 1.34 for bioethanol. The 1998 study used soybean oil primarily as the base oil to calculate the energy yields. Furthermore, due to the higher energy density of biodiesel, combined with the higher efficiency of the diesel engine, a gallon of biodiesel produces the effective energy of 2.25 gallons of ethanol. Also, higher oil yielding crops could increase the energy yield of biodiesel.
The debate over the energy balance of biodiesel is ongoing, however. Transitioning fully to biofuels could require immense tracts of land if traditional crops are used. The problem is especially severe for nations with large economies, since energy consumption scales with economic output. If using only traditional plants, most such nations do not have sufficient arable land to produce biofuel for the nation's vehicles. Nations with smaller economies and more arable land may be in better situations, although many regions cannot afford to divert land away from food production. For
third world countries, biodiesel sources that use marginal land could make more sense, e.g. honge oil nuts grown along roads or
jatropha grown along rail lines.
More recent studies using a species of
algae with up to 50 % oil content have concluded that only 28,000 km² or 0.3 % of the land area of the US could be utilized to produce enough biodiesel to replace all transportation fuel the country currently utilizes. Furthermore, otherwise unused desert land could be most effective for growing the algae, and the algae could utilize farm waste and excess CO
2 from factories to help speed the growth of the algae.
The direct source of the energy content of biodiesel is solar energy captured by plants during
photosynthesis. The website biodiesel.co.ukdiscusses the positive energy balance of biodiesel:
- When straw was left in the field, biodiesel production was strongly energy positive, yielding 1 GJ biodiesel for every 0.561 GJ of energy input .
- When straw was burned as fuel and oilseed rapemeal was used as a fertilizer, the yield/cost ratio for biodiesel production was even better . In other words, for every unit of energy input to produce biodiesel, the output was 3.71 units .
Biodiesel is becoming of interest to companies interested in commercial scale production as well as the more usual home brew biodiesel user and the user of
straight vegetable oil or waste vegetable oil in diesel engines. Homemade biodiesel processors are many and varied.
The success of biodiesel homebrewing, and micro-economy-of-scale operations, continues to shatter the conventional business myth that large economy-of-scale operations are the most efficient and profitable. It is becoming increasingly apparent that small-scale, localized, low-impact energy keeps more resources and revenue within communities, reduces damage to the environment, and requires less waste management.
Environmental benefits
Environmental benefits in comparison to petroleum based fuels include:
- Biodiesel reduces emissions of carbon monoxide by approximately 50 % and carbon dioxide by 78 % on a net lifecycle basis because the carbon in biodiesel emissions is recycled from carbon that was already in the atmosphere, rather than being new carbon from petroleum that was sequestered in the earth's crust.
- Biodiesel contains fewer aromatic hydrocarbons: benzofluoranthene: 56 % reduction; Benzopyrenes: 71 % reduction.
- Biodiesel can reduce by as much as 20 % the direct emission of particulates, small particles of solid combustion products, on vehicles with particulate filters, compared with low-sulfur diesel. Particulate emissions as the result of production are reduced by around 50 %, compared with fossil-sourced diesel. .
- Biodiesel produces between 10 % and 25 % more nitrogen oxide NOx tailpipe-emissions than petrodiesel. As biodiesel has a low sulphur content, NOx emissions can be reduced through the use of catalytic converters to less than the NOx emissions from conventional diesel engines. Nonetheless, the NOx tailpipe emissions of biodiesel after the use of a calalytic converter will remain greater than the equivalent emissions from petrodiesel. As biodiesel contains no nitrogen, the increase in NOx emissions may be due to the higher cetane rating of biodiesel and higher oxygen content, which allows it to convert nitrogen from the atmosphere into NOx more rapidly. Debate continues over NOx emissions. In February 2006 a Navy biodiesel expert claimed NOx emissions in practice were actually lower than baseline. Further research is needed.
- Biodiesel has higher cetane rating than petrodiesel, and therefore ignites more rapidly when injected into the engine.
- Biodiesel is biodegradable and non-toxic - the U.S. Department of Energy confirms that biodiesel is less toxic than table salt and biodegrades as quickly as sugar.
- In the United States, biodiesel is the only alternative fuel to have successfully completed the Health Effects Testing requirements of the Clean Air Act .
Since biodiesel is more often used in a blend with petroleum diesel, there are fewer formal studies about the effects on pure biodiesel in unmodified engines and vehicles in day-to-day use. Fuel meeting the standards and engine parts that can withstand the greater solvent properties of biodiesel is expected to--and in reported cases does--run without any additional problems than the use of petroleum diesel.
- The flash point of biodiesel is significantly higher than that of petroleum diesel or gasoline . The gel point of biodiesel varies depending on the proportion of different types of esters contained. However, most biodiesel, including that made from soybean oil, has a somewhat higher gel and cloud point than petroleum diesel. In practice this often requires the heating of storage tanks, especially in cooler climates.
- Pure biodiesel can be used in any petroleum diesel engine, though it is more commonly used in lower concentrations. Some areas have mandated ultra-low sulfur petrodiesel, which reduces the natural viscosity and lubricity of the fuel due to the removal of sulfur and certain other materials. Additives are required to make ULSD properly flow in engines, making biodiesel one popular alternative. Ranges as low as 2 % have been shown to restore lubricity. Many municipalities have started using 5 % biodiesel in snow-removal equipment and other systems.
Environmental concerns
Where the oil is grown is of increasing concern to environmentalists, one of the worries being that countries will deforest areas to grow oil producing plants. This has already occurred in the Philippines and Indonesia, and both of these countries plan to increase their biodiesel production levels which will deforest tens of millions of acres .
The Union of Concerned Scientists writes:
"When it comes to buying a new car, gasoline-powered models are better than diesels on toxic soot and smog-forming emissions. The downside to current diesels is that they produce 10 to 20 times more toxic particulates than their gasoline counterparts, more than can be made up for with the use of biodiesel. Diesels fare even worse when it comes to smog-forming nitrogen oxide emissions, with greater than 20 times the emissions of a comparable gasoline vehicle."
Historical background
Transesterification of a vegetable oil was conducted as early as 1853, by scientists E. Duffy and J. Patrick, many years before the first
diesel engine became functional.
Rudolf Diesel's prime model, a single 10 ft iron cylinder with a flywheel at its base, ran on its own power for the first time in
Augsburg,
Germany on August 10, 1893. In remembrance of this event, August 10 has been declared
International Biodiesel Day. Diesel later demonstrated his
engine and received the "Grand Prix" at the
World Fair in
Paris,
France in 1900. This engine stood as an example of Diesel's vision because it was powered by
peanut oil—a
biofuel, though not strictly biodiesel, since it was not transesterified. He believed that the utilization of a biomass fuel was the real future of his engine. In a 1912 speech, Rudolf Diesel said "the use of vegetable oils for engine fuels may seem insignificant today, but such oils may become, in the course of time, as important as petroleum and the coal-tar products of the present time."
During the 1920s diesel engine manufacturers altered their engines to utilize the lower
viscosity of the
fossil fuel rather than vegetable oil, a
biomass fuel. The petroleum industries were able to make inroads in fuel markets because their fuel was much cheaper to produce than the
biomass alternatives. The result was, for many years, a near elimination of the biomass fuel production infrastructure. Only recently have environmental impact concerns and a decreasing cost differential made biomass fuels such as biodiesel a growing alternative.
Research into the use of trans-esterified sunflower oil and refining it to diesel fuel standard was initiated in South Africa in 1979. By 1983 the process to produce fuel quality engine-tested bio-diesel was completed and published internationally . An Austrian Company, Gaskoks, obtained the technology from the South African Agricultural Engineers, put up the first pilot plant for bio-diesel in November 1987 and the erection of the first industrial bio-diesel plant on 12 April 1989, with a capacity of 30 000 tons of rapeseed per annum. Throughout the 1990s, plants were opened in many European countries, including the
Czech Republic,
France,
Germany,
Sweden. At the same time, nations in other parts of world also saw local production of biodiesel starting up and by 1998, the Austrian Biofuels Institute identified 21 countries with commercial biodiesel projects.
In the 1990s,
France launched the local production of biodiesel fuel obtained by the transesterification of
rapeseed oil. It is mixed to the proportion of 5 % into regular
diesel fuel, and to the proportion of 30 % into the diesel fuel used by some captive fleets .
Renault,
Peugeot, and other manufacturers have certified truck engines for use with up to this partial biodiesel. Experiments with 50 % biodiesel are underway.
In September of 2005 Minnesota became the first state to require that all diesel fuel sold in that state contain part biodiesel. The Minnesota law requires at least 2% biodiesel in all diesel fuel sold.
Current research
There is ongoing research into finding more suitable crops and improving oil yield. Using the current yields, vast amounts of land and fresh water would be needed to produce enough oil to completely replace fossil fuel usage. It would require twice the land area of the US to be devoted to soybean production, or two-thirds to be devoted to rapeseed production, to meet current US heating and transportation needs.
Specially bred mustard varieties can produce reasonably high oil yields, and have the added benefit that the meal leftover after the oil has been pressed out can act as an effective and biodegradable
pesticide.
Algaculture
From 1978 to 1996, the
U.S. National Renewable Energy Laboratory experimented with using
algae as a biodiesel source in the "Aquatic Species Program". A recent paper from Michael Briggs at the
UNH Biodiesel Group, offers estimates for the realistic replacement of all vehicular fuel with biodiesel by utilizing algae that has a greater than 50 % natural oil content, which he suggests can be grown on algae ponds at wastewater treatment plants. On 2006-5-11. Aquaflow Bionomic Corporation from
Marlborough, New Zealand announced it had produced its first sample of bio-diesel fuel made from algae found in sewage ponds. Unlike previous attempts, the algae was naturally grown in pond discharge from the Marlborough District Council's sewage treatment works.
The production of
algae to harvest oil for biodiesel has not been undertaken on a commercial scale, but working feasibility studies have been conducted to arrive at the above yield estimate. In addition to a high yield, this solution does not compete with agriculture for food, requiring neither farmland nor fresh water.
Independent results have shown that Green Fuel Technologies, a Cambridge, MA company founded by Isaac Berzin, has been successful in growing algae on flue gas emissions from power plant smokestacks. Using a patented algae bioreactor, GreenFuel utilizes microalgae and a process of photomodulation to reduce emissions: 40 % less
carbon dioxide and 86 % less
nitrous oxide. The company is testing their method at the
MIT cogeneration facility and at an undisclosed 1000-megawatt power facility in the southwestern U.S. Currently GreenFuel is not producing biodiesel from this system as that requires an algal strain with a much higher lipid content than what they are using, but they have a vested interest in successful biodiesel production from algae and are researching it's possibilities.
This oil-rich
algae can then be extracted from the system and processed into biodiesel, and the dried remainder further reprocessed to create ethanol.
See also
References
- A look back at the U.S. Department of Energy Aquatic Species program: Biodiesel from Algae, July 1998, J. Sheehan, et. al. NREL , PDF file].
- An Overview of Biodiesel and Petroleum Diesel Lifecycles, May 1998, Sheehan, et. al. NREL
- Business Management for Biodiesel Producers, January 2004, Jon Von Gerpen, Iowa State University under contract with the National Renewable Energy Laboratory
- , June 2000, I.R. Richards
- Life Cycle Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus, 1998, Sheehan, et. al. NREL
- , August 2004, Michael Briggs, UNH Retrieved December 6, 2004
- , January 11, 2006, Mark Clayton, Christian Science Monitor
Notes
External links
