Biodiesel

Bio-diesel is produced from vegetable oils and fats through a simple chemical process. Except for lipids from recuperated oils (e.g. used frying fat), most of the bio-diesel is produced from either soy (USA) or rapeseed (Europe). Bio-diesel consists mainly of methyl esters of C16-C18 fatty acids (FAME, "Fatty Acid Methyl Ester). There are a number of production schemes, but the basic principles are always the same. The oil fraction (triglycerides) are extracted from the oilseeds, and then treated in the presence of methanol with alkalines. A chemical trans-esterification occurs by which glycerol is released and FAMES's are formed.

Synthesis of methylesters out of a triglyceride

After the reaction, the reaction mixture can be physical separated in an oily bio-diesel phase, and a watery phase that contains the salts and glycerol. The excess of methanol is recovered by distillation. The obtained bio-diesel fraction is a slightly yellow low-viscosity liquid, comparable with normal diesel oil. The production scheme is depicted in fig. 6. The mass balance is favourable since 1 kg of oil reacts with approximately 0,1 kg methanol, producing 1 kg of bio-diesel and 0,1 kg glycerol. The co-product glycerol is a relative expensive base chemical that is used in various applications in the cosmetic and chemical industry. Biotechnological alternatives for the current chemical production process are under development.

Bio-diesel (37-41MJ/kg) has an energy content comparable to ordinary diesel fuel (36-45 MJ/kg), and can be mixed with normal diesel fuel, usually up to a percentage of 5 %. In France a mixture of 30 % bio-diesel is used in the so called "Villes Diester", where a considerable share of vehicles runs on this "Diester". The application of bio-diesel does not require any adaptation of the diesel engine. Quite to the contrary, the addition of bio-diesel is highly appreciated because of its good lubrication of the motor. In France one in two diesel cars already runs with 2 % bio-diesel added, without even knowing it as it is not indicated at the pump. Pure bio-diesel can also be used, mainly in Germany and Austria. A small engine adaptation is then however required. Problems can occur during cold winters when using pure bio-diesel, because of crystallization at low temperatures.

In its environmental characteristics, bio-diesel compares very favourable to normal diesel. Bio diesel contains almost no sulphur, contrary to normal diesel that has a maximum sulphur content of 350 ppm in Europe. The presence of oxygen in bio-diesel considerably improves the combustion resulting in a strongly reduced emission of soot (- 30 %), hydrocarbons (-93 %), CO (-50 %) and aromatics. Biodiesel can be used in any diesel engine with no need for modifications, in fact diesel engines run better and last longer with biodiesel:

• Biodiesel fuel burns up to 75% cleaner than conventional diesel fuel made from fossil fuels
• Biodiesel substantially reduces unburned hydrocarbons, carbon monoxide and particulate matter in exhaust fumes
• Sulphur dioxide emissions are eliminated (biodiesel contains no sulphur)
• Biodiesel is plant-based and adds no CO2 to the atmosphere
• The ozone-forming potential of biodiesel emissions is nearly 50% less than conventional diesel fuel
• Nitrous oxide (NOx) emissions may increase or decrease but can be reduced to well below conventional diesel fuel levels by adjusting engine timing
• Biodiesel exhaust is not offensive and doesn't cause eye irritation (it smells like French fries!)
• Biodiesel is environmentally friendly: it is renewable, "more biodegradable than sugar and less toxic than table salt" (US National Biodiesel Board)
• Biodiesel can be used in any diesel engine
• Fuel economy is the same as conventional diesel fuel
• Biodiesel is a much better lubricant than conventional diesel fuel and extends engine life -- a German truck won an entry in the Guinness Book of Records by travelling more than 1.25 million km (780,000 miles) on biodiesel with its original engine
• Biodiesel has a high cetane rating, which improves engine performance: 20% biodiesel added to conventional diesel fuel improves the cetane rating 3 points, making it a Premium fuel
• Biodiesel can be mixed with ordinary diesel fuel in any proportion -- even a small amount of biodiesel means cleaner emissions and better engine lubrication: 1% biodiesel will increase lubricity by 65%

The European production of bio-diesel increases strongly and has exceeded 2 million ton in 2004, mainly produced in Germany, France and Italy. Especially Germany has shown impressive growth. Presently methanol is exclusively used to produce biodiesel. Methanol is produced out of natural gas and is cheaper than ethanol. It is possible to use bio-ethanol instead, obtaining fatty acid ethyl esters, completely obtained from renewable resources. In the future our car may thus run on an interesting chemical combination of sugar beets and rapeseed. The future can also bring other possibilities such as so called oxydiesel, a mixture of normal diesel and bio-ethanol, with considerably improved combustion characteristics, thanks to the presence of oxygen in bio-ethanol.

More information on biofuels in Europe via the Biofuels Technology Platform