How Does Biodiesel Work to Produce Energy?
Diesel fuel manufactured from plant or animal oils is called biodiesel. Like other forms of biofuel, biodiesel is an indirect use of solar energy captured by plants through photosynthesis. Plant oils are converted to biodiesel through a simple chemical process.
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Features
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During photosynthesis, plant cells use solar energy to drive synthesis of simple sugars, which are used for energy or become the building blocks or precursors for other compounds. Animals like pigs or humans store excess energy for later use by using it to synthesize glycogen (a type of carbohydrate polymer made of sugars) and triglycerides (fats). While plants rely primarily on carbohydrate polymers like starch for energy storage, some plants use triglycerides for energy storage in their seeds. Plants whose seeds are especially rich in vegetable oils include rapeseed (canola), soybeans and sunflowers.
Function
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Once extracted from an oilseed crop, vegetable oils are converted to biodiesel through a process called transesterifcation. The oil is first filtered and heated to remove water and other contaminants; next, sodium hydroxide mixed with methanol is added to the oil. The ensuing reaction yields glycerol and mono-alkyl esters or biodiesel; the two products separate into two layers as the glycerol sinks, making the biodiesel easier to collect.
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Effects
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Burning biodiesel in an engine is a combustion reaction; oxygen from the atmosphere combines with carbons and hydrogens to form water and carbon dioxide. Breaking bonds always requires energy, while forming new bonds releases energy. The energy released by forming the bonds in the carbon dioxide and water molecules is greater than the energy required to break the bonds in the biodiesel molecules, so this reaction releases energy in much the same way that burning gasoline releases energy.
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References
- Photo Credit agrocultural14 image by Artur Blaszak from Fotolia.com
