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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 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.

A byproduct of the transesterification process is the production of glycerol. For every 1 tonne of biodiesel that is manufactured, 100kg of glycerol are produced. Originally, there was a valuable market for the glycerol, which assisted the economics of the process as a whole. However, with the increase in global biodiesel production, the market price for this crude glycerol (containing 20% water and catalyst residues) has crashed. Research is being conducted globally to use this glycerol as a chemical building block. One initiative in the UK is The Glycerol Challenge.

Usually this crude glycerol has to be purified, typically by performing vacuum distillation. This is rather energy intensive. The refined glycerol (98%+ purity) can then be utilised directly, or converted into other products. The following announcements were made in 2007: A joint venture of Ashland Inc. and Cargill announced plans to make propylene glycol in Europe from glycerol and Dow Chemical announced similar plans for North America . Dow also plans to build a plant in China to make epichlorhydrin from glycerol. Epichlorhydrin is a raw material for epoxy resins.

Yields of common crops

* Algae yields are projected based on the sustainable average yields of the NREL's aquatic species program.

- Note: Chinese tallow (Triadica Sebifera, or Sapium sebiferum) is also known as the "Popcorn Tree" or Florida Aspen.
Source: Chinese tallow data, Mississippi State University
Source: Used with permission from the The Global Petroleum Club

Typical oil extraction from 100 kg. of oil seeds

Source: Petroleum Club (with permission)
The energy content of biodiesel is about 90 percent that of petroleum diesel.

Environmental benefits

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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 in the atmosphere, rather than the carbon introduced from petroleum that was sequestered in the earth's crust. However, it does produce more NOx emissions than standard diesel fuel. (Sheehan, 1998)
• Biodiesel contains fewer aromatic hydrocarbons: benzofluoranthene: 56% reduction; Benzopyrenes: 71% reduction.
• Biodiesel can reduce by as much as 20% the direct (tailpipe) emission of particulates, small particles of solid combustion products, on vehicles with particulate filters, compared with low-sulfur (<50 ppm) diesel. Particulate emissions as the result of production are reduced by around 50%, compared with fossil-sourced diesel. (Beer et al, 2004).
• Biodiesel has a higher cetane rating than petrodiesel, which can improve performance and clean up emissions compared to crude petrodiesel (with cetane lower than 40).
• 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. (See Biodiesel handling and use guidelines)
• 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.

Environmental concerns

The locations where oil-producing plants are grown is of increasing concern to environmentalists, one of the prime worries being that countries will clear cut large areas of tropical forest in order to grow such lucrative crops, in particular, oil palm. This has already occurred in the Philippines and Indonesia; both countries plan to increase their biodiesel production levels significantly, which will lead to the deforestation of tens of millions of acres if these plans materialize. Loss of habitat on such a scale could endanger numerous species of plants and animals. A particular concern which has received considerable attention is the threat to the already-shrinking populations of orangutans on the Indonesian islands of Borneo and Sumatra, which face possible extinction.

The oils for biodiesel, and biodiesel itself, produced in Asia, South America and Africa are far cheaper than those produced in Europe and North America. Most biodiesel is therefor not a local, carbon neutral product. Biodiesel requires a large investment of energy before it arrives at petrol pumps. Coupled with the deforestation, and monoculture farming techniques used to grow crops, biodiesel represents a serious threat to the environment. Forests contain large quantities of carbon which are released when they are burnt to make space for farming. Forests also trap carbon in humus and soil, something that farming biodiesel crops does not do. Clearing forests is a cause of global warming and desertification. These problems will be exacerbated as biodiesel becomes more popular unless stringent laws are introduced and enforced to control biodiesel production. Biodiesel produced from clear cut forest land offers no environmental advantage over petroleum diesel.

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.

These estimates, however, are based on 2005 model year diesels in the U.S., prior to the introduction of ultra-low sulfur diesel (ULSD) and tightened emissions standards that apply in several U.S. states from January 1, 2007. The introduction of ULSD allows for the use of newer technologies to substantially reduce particulate and other toxic emissions; the European Union has had lower sulfur requirements than the U.S. for several years and as a result NOx emissions are only 2-3 times higher than for gasoline engines (Dieselnet, 2006).

Biodiesel is estimated to produce between 10% and 25% more nitrogen oxide NO_x tailpipe-emissions than petrodiesel. As biodiesel has a low sulfur content, NO_x emissions can be reduced through the use of catalytic converters to less than the NO_x emissions from conventional diesel engines. Nonetheless, the NO_x tailpipe emissions of biodiesel after the use of a catalytic converter will remain greater than the equivalent emissions from petrodiesel. As biodiesel contains no nitrogen, the increase in NO_x 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 NO_x more rapidly. Debate continues over NO_x emissions. In February 2006 a Navy biodiesel expert claimed NO_x emissions in practice were actually lower than baseline. Further research is needed.

Recent advances in the use of cerium-oxide, however, hold the potential to nearly eliminate NOx emissions from both petrodiesel and biodiesel, and diesel fuel additives based on cerium oxide can improve fuel consumption by 11% in unmodified diesel engines.

A look at some of the problems with the pursuit of biodiesel can be found at Biofuelwatch.

1. chemweek's Business Daily, Tuesday May 8, 2007
2. http://www.dow.com/propyleneglycol/news/20070315b.htm, accessed June 25, 2007
3. http://epoxy.dow.com/epoxy/news/2007/20070326b.htm, accessed June 25, 2007
4. Helen Buckland, Ed Matthew (ed.) (19 September 2005). "The Oil for Ape Scandal: How palm oil is threatening the orang-utan" (PDF (458 Kb)). Summary. Friends of the Earth Trust. Retrieved 2007-01-02. {{cite journal}}: |author= has generic name (help); Cite journal requires |journal= (help)
5. "Should I buy a new gasoline hybrid vehicle or a new diesel vehicle and run it on biodiesel?". Clean Vehicles, Biodiesel FAQ. Union of Concerned Scientists. 28 September 2005. Retrieved 2007-01-02.
6. Catherine Foster (27 April 2007). "New catalyst helps eliminate NOx from diesel exhaust" (HTML). Argonne National Laboratory. Retrieved 2007-05-05.