BIODIESELBy Syuanne Lee

What is Biodiesel?

• Biodiesel is an alternative diesel fuel. • It is made from renewable resources such as

vegetable oils and animal fats. • Being made from renewable resources, it has a

carbon neutral footprint. • Vegetable oil is too thick to flow through modern

diesel engines without causing damage, so we can lower it’s viscosity through a process called transesterification.

Differences in Structures

• A typical molecule of biodiesel looks like the structure below. Mostly it is a long chain of carbon atoms, with hydrogen atoms attached, and at one end is what we call an ester functional group (shown in blue).

• Diesel engines can burn biodiesel fuel with no modifications (except for replacing some rubber tubing that may soften with biodiesel). This is possible because biodiesel is chemically very similar to regular diesel, shown below. Notice that regular diesel also has the long chain of carbon and hydrogen atoms, but doesn’t have the ester group present in biodiesel.

• Vegetable oil also has the long rows of carbon and hydrogen atoms, but is about three times larger than normal diesel molecules. It also has ester function.

• That larger size of vegetable oil means that in cold weather it gels, making it hard to use in an engine. Converting it into biodiesel makes it a smaller molecule, closer to the size of regular diesel, so that it has to get colder than vegetable oil before it starts to gel.

Transesterification

• Transesterification is the chemical process which replaces one type of alcohol for another in an ester. • An ester is made by combining an alcohol with an acid.

Chemical Conversion of Vegetable Oil to Biodiesel• Vegetable oil, like biodiesel, belongs to a category of compounds

called esters. • This chemical reaction requires using methanol (shown in green),

which causes the red bonds in the structure below to break. • This breaks off the blue section, like a backbone on the molecule,

which becomes glycerol. • The red bonds that did go to the glycerol backbone are placed with

bonds to methoxy groups, shown in green in the final structure, that came from the methanol

Additional Steps in Making Biodiesel• The first step is to remove any traces of water in the vegetable

oil. This is to prevent soap formation as shown below.

• If soap is made, it complicates the steps after the transesterification reaction (separation of the biodiesel from leftover methanol, the NaOH or KOH catalyst, and the glycerol by-product).

Green Chemistry• Less Hazardous Chemical Syntheses: Wherever practicable,

synthetic routes should be designed to use and make substances that have little or no toxicity to human health and the environment. Biodiesel is made from cooking oils and alcohol, so if you spill it on the ground, it will quickly degrade into natural organic residues. Biodiesel is as toxic as table salt, and safe to handle. Mechanics who use biodiesel notice that their hands don’t crack and dry out the way they do with diesel fuel. Many people use biodiesel in marine environments to protect wildlife and hatcheries.

• Use of Renewable Feedstock: A raw material (or feedstock) should be renewable if technically and economically practicable. Natural, renewable resources such as vegetable oils and recycled restaurant greases can be chemically transformed into clean-burning biodiesel fuels. As its name implies, biodiesel is like diesel fuel except that it’s organically produced. Biodiesel can be made from many oils and fats such as soy, canola, tallow, mustard, and restaurant greases.

• Real-time Analysis for Pollution Prevention: Analytical methods need to be improved so that monitoring of each step can be performed during the manufacturing process to detect and control formation of hazardous substances. There is no use of sulfur in the making of biodiesel, so biodiesel won’t contribute to sulfur dioxide emissions or poison exhaust catalyst. This is unlike some diesel fuels which contain sulphur but does not use it, hence releasing it as sulphur dioxide or trioxide. The by product of biodiesel is also just glycerol, which is not a hazardous substance. After production, the emission of gases are also reduced as stated below.

Differences Between Carbon Dioxide Emitted by Biodiesel

and Diesel

Myth• Biodiesel releases less carbon dioxide

compared to diesel

• Amount of carbon dioxide released by diesel and biodiesel are similar

Truth

Biodiesel• Releases carbon dioxide

which plants extracted a short period of time ago

• This is done by the natural carbon cycle

• No net increase in the percentage of carbon dioxide in the atmosphere

Diesel

• Carbon dioxide emitted is actually those which was sequestered from the environment million years ago

• Result in a cumulative net increase of carbon dioxide

Net Increase in Carbon Dioxide causes

• Global warming (caused by greenhouse effect)• Polar ice caps melt• Ice caps are fresh water• desalinate the ocean- make it less salty• Species which cannot adapt (no evolution) will

extinct• Disrupt the food chain- unbalanced ecosystem

Sulfur Dioxide from Diesel causes

• Acid Rain acidifies the lake, stream and soil• Corrosion of buildings and monuments• Reduces visibility because of soot

Problems brought by Biodiesel

• Certain biodiesel gels easily under cold temperature

• Deforestation for plantation • Degrades rubber in old cars• Synthetic rubbers that are resistant

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