Fossil fuels (natural gas, coal, oil) are non-sustainable and non-renewable resources that our current society has become heavily dependent on. Petroleum (literally rock oil) is the source of gasoline and diesel gas, two common fuels that keep our automobiles running. Prices of these petroleum based fuel are rising due to their high demand and scarcity. In addition, the burning of these fuels increase society’s ecological footprint and add to the green house effect, which underlies global warming. This lesson demonstrates to students the sustainability of a renewable resource, biodiesel.
Biodiesel is a fuel made from vegetable oil through a reaction called transesterification. Transesterification is a reaction between an ester and an alcohol in which the -O-R group of the ester and the -O-R' group of the alcohol trade places.
The ester group in triglyceride will exchange places with the alcohol group in methanol or ethanol* to form biodiesel. Biodiesel is a methyl or ethyl ester (depending on whether methanol or ethanol is used) of a long chain fatty acid hydrolyzed from triglyceride.
The chemical composition of diesel is about 75% saturated hydrocarbons (primarily paraffins including n, iso, and cycloparaffins), and 25% aromatic hydrocarbons (including naphthalenes and alkylbenzenes). The average chemical formula for common diesel fuel is C12H23, ranging from approx. C10H20 to C15H28. The heat of combustion of diesel = 10,700 cal/g.