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What is biodiesel

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 engine vehicles, which distinguishes biodiesel from the straight vegetable oils (SVO) or waste vegetable oils (WVO) 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 is a possible candidate to replace fossil fuels as the world's primary transport energy source.

Biodiesel can be distributed using today's infrastructure, and its use and production is 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 can be made at home for much cheaper than either. This differential may diminish due to economies of scale, the rising cost of petroleum and government tax subsidies.


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 ~ 0.8, 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 petrodiesel (ULSD) fuel. 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 bioalcohol 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. The standard ASTM D 6751, which is the most common standard referenced in the United States. In Germany, the requirements for biodiesels are fixed in the DIN EN 14214 standard. There are standards for three different varieties of biodiesel, which are made of different oils:

   * RME (rapeseed methyl ester, according to DIN E 51606)
   * PME (vegetable methyl ester, purely vegetable products, according to DIN E 51606)
   * FME (fat methyl ester, vegetable and animal products, according to DIN V 51606)

The standards ensure that the following important factors in the fuel production process are satisfied:

   * Complete reaction.
   * Removal of glycerin.
   * Removal of catalyst.
   * Removal of alcohol.
   * Absence of free fatty acids.

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 testings are more expensive. Fuel meeting the quality standards is very non-toxic, with a toxicity rating (LD50) of greater than 50 mL/kg.


Biodiesel can be used in pure form (B100) or may be blended with petroleum diesel at any concentration in most modern engines. Biodiesel does have a disadvantage of degrading certain types of rubber gaskets and hoses in vehicles (mostly found in vehicles manufactured before 1992). 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 petroleum. Fuel filters may become clogged with particulates if a quick transition to pure biodiesel is made, but biodiesel cleans the engine in the process. It is therefore recommended, to change the fuel filter 800 miles after switching to biodiesel.

In a study at a U.S. military base[citation needed], a biodiesel blend was used as a replacement for heating oil at housing on the base. Due to the good solvating ability of biodiesel, residues that had been present in fuel tanks for decades were dissolved. The particulate component of the residues caused repeated clogging of fuel strainers, requiring repeated replacement, cleaning, and in some cases installation of higher capacity filters. Due to the relatively smaller surface area and service life of fuel tanks in motor vehicles and mobile equipment, filter clogging is less prevalent but still a factor to be considered.


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 (FFAs) in the base oil are either converted to soap and removed from the process, or they are esterified (yielding more biodiesel) 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. Small scale Biodiesel processorsand detailed Books about making biodiesel & processors are now available for personal and small commercial organizations.

Biodiesel Feedstock
A variety of oils can be used to produce biodiesel. These include:

* Virgin oil feedstock; rapeseed and soybean oils are most commonly used, though other crops such as mustard, palm oil, hemp, jatropha, and even algae show promise (see List of vegetable oils for a more complete list);
* Waste vegetable oil (WVO);
* Animal fats including tallow, lard, yellow grease and as a byproduct from the production of Omega-3 fatty acids from fish oil.

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 (EPA), restaurants in the US produce about 300 million US gallons (1,000,000 m) 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 230,000 million US gallons (0.87 km) (Briggs, 2004). 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 23,600 million pounds (10,700,000 t) or 3,000 million US gallons (11,000,000 m)), and estimated production of animal fat is 11,638 million pounds (5,279,000 t). (Van Gerpen, 2004)

For a truly renewable source of oil, crops or other similar cultivatable sources would have to be considered. Plants utilize photosynthesis to convert solar energy into chemical energy. It is this chemical energy that biodiesel stores and is released when it is burned. Therefore plants can offer a sustainable oil source for biodiesel production. Different plants produce usable oil at different rates. Some studies have shown the following (rough) levels of annual production:

                       US Gallons/acre   Litres/hectare
Soybean        40                         375
Rapeseed       110                       1,000
Mustard          140                       1,300
Jatropha         175                       1,590
Palm Oil         650                        5,800

Environmental benefits

Environmental benefits in comparison to petroleum based fuels include:

* Biodiesel reduces emissions of carbon monoxide (CO) 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. (Sheehan, 1998)
* Biodiesel contains fewer aromatic hydrocarbons: benzofluoranthene: 56 % reduction; Benzopyrenes: 71 % reduction.
* It also eliminates sulfur emissions (SO2), because biodiesel does not contain sulfur.
* Biodiesel reduces by as much as 65 % the emission of particulates, small particles of solid combustion products. This reduces cancer risks by up to 94 % according to testing sponsored by the Department of Energy.[citation needed]
* Biodiesel does produce more NOx emissions than petrodiesel, but these emissions can be reduced through the use of catalytic converters. The increase in NOx emissions may also be due to the higher cetane rating of biodiesel. Properly designed and tuned engines may eliminate this increase.
* Biodiesel has higher cetane rating than petrodiesel, and therefore ignites more rapidly when injected into the engine. It also has the highest energy content of any alternative fuel in its pure form (B100).
* Biodiesel is biodegradable and non-toxic - tests sponsored by the United States Department of Agriculture confirm biodiesel is less toxic than table salt and biodegrades as quickly as sugar.[citation needed]
* In the United States, biodiesel is the only alternative fuel to have successfully completed the Health Effects Testing requirements (Tier I and Tier II) of the Clean Air Act (1990).

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 (>150 °C) is significantly higher than that of petroleum diesel (64 °C) or gasoline (−45 °C). 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 (B100) 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 % (B2) have been shown to restore lubricity. Many municipalities have started using 5 % biodiesel (B5) in snow-removal equipment and other systems.

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 (3 m) 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" (highest prize) 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." [7]

During the 1920s diesel engine manufacturers altered their engines to utilize the lower viscosity of the fossil fuel (petrodiesel) 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.

The revival of biodiesel production started with farm co-operatives in the 1980s in Austria, but in 1991 the first industrial-scale plant opened in Aschach, also in Austria, with a capacity in excess of 10,000 m per year. 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 (known locally as diester) 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 (public transportation). Renault, Peugeot, and other manufacturers have certified truck engines for use with up to this partial biodiesel. Experiments with 50 % biodiesel are underway.