Biodiesel Production Technology
It is clear an economy based on the use of fossil fuels is not sustainable in the long term. It is equally clear fossil fuels cannot be left behind before suitable alternatives are found. Biodiesel fuels--synthesized fuels made from organic, renewable sources--are on their way to becoming viable substitutes for liquid fossil fuels, as they do not use non-renewable resources and do not increase atmospheric levels of carbon dioxide. Besides, they can be made from domestically produced raw materials, offering the possibility of reducing oil imports.
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Composition
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Biodiesel is comprised of mono-alkyl esters of long-chain fatty acids derived from vegetable oils or animal fats. The oils and fats used as raw materials are highly combustible, making them tempting sources of energy. However, their high viscosity and the impurities that lead to formation of gums and carbon deposits when they are burned make them unsuitable in their original form. The three processes commonly used in the production of biodiesel aim to reduce the viscosity of those, while increasing the octane rating and eliminating the impurities.
Pyrolisis
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Pyrolisis--that is, thermal decomposition under high temperatures--is one of the most basic technologies for the production of biodiesels. The original, high-viscosity triglycerides transform into low-viscosity combustibles with a high octane number. However, biodiesel produced by pyrolisis alone is unacceptable for many applications in terms of ash and carbon residues. The process of production also leads to a removal of oxygen that negates some of the environmental benefits usually associated with biodiesels.
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Microemulsion
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The problem posed by the high viscosity of vegetable oils can also be reduced by means of microemulsions, or solutions made of alcohols, such as methanol or ethanol. The microscopic droplets of oil are suspended in clear or translucent, stable low-viscosity solutions. However, laboratory tests for motors operating on fuels created by microemulsion show carbon deposits, injector needle sticking and an increase in the viscosity of the lubricating oil. Because of the limitations of this method of production and those of pyrolisis, transesterification is usually preferred.
Transesterification
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Glycerol, a highly viscous liquid, is a central component in the structure of many lipids found in animal and vegetable oils. The transesterification process inserts an alcohol like methanol, ethanol, propanol or butanol into the molecular structure of those oils, allowing for the extraction of the glycerol that settles down at the bottom of the vessel. The process requires several hours, but the reaction is accelerated with the application of small amounts of sulphuric acid. For example, a mix of soybean oil and butanol in the presence of one percent sulphuric acid takes three hours to transform into biodiesel when heated to 117 degrees Celsius.
Concerns
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Although reduced carbon emissions are among the rationales for the use of biofuels, some of the industrial and agricultural processes required for the production of biodiesels can actually use more fossil fuels and emit more carbon dioxide than what they save. For example, because of the energy cost of the nitrogen fertilizers used during the cultivation of soybeans, soybean biodiesel production winds up requiring 27 percent more fossil energy than in the biofuel produced. There are also ethical concerns related to the use of food crops for fuel production, as there is an estimated 3.7 billion malnourished people in the world. Both concerns, however, are ameliorated by the use of alternate inputs, like agricultural waste or used oil from the restaurant industry.
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References
- Photo Credit bio-deisel fuel image by John Keith from Fotolia.com
