This is the first in a series of 8 chemistry labs on the fundamentals of biodiesel.
In this lab we will learn about “The Molecules of the Biodiesel Reaction”.
Written procedures and background information for all 8 labs is provided on the biodiesel
education website.
Molecules are a group of atoms bonded together to make the smallest unit of a substance.
Molecules bond with other molecules in a chemical reaction to make a new substance.
An example most everyone is familiar with is H2O.
Here 2 hydrogen atoms combine with an oxygen atom to form water.
In this laboratory exercise we will learn and construct modules of the biodiesel reaction.
For this you will need molecule model building kits or other items that can be used to build
the models.
Toothpicks and gumdrops work good for this exercise and different colors of gumdrops can
be used to designate different atoms.
So what is biodiesel?
Biodiesel is a renewable fuel made from vegetable oils or animal fats used to run diesel engines.
Vegetable oils or animal fats must be converted into biodiesel by reacting them with an alcohol
in the presence of a catalyst.
This process is referred to as transesterification.
Biodiesel is made when a natural oil or fat molecule, or known in chemistry as a triglyceride
molecule, reacts with 3 molecules of an alcohol, usually methanol or ethanol, to produce 3
molecules of biodiesel and one molecule of glycerol.
In chemical terms, biodiesel is called “methyl esters” when made with methanol or “ethyl
esters” when made with ethanol.
The structure of a molecule can be depicted using a chemical formula, a 2-dimensional
structural chart, or a 3-dimensional model.
In reality, all molecules are 3-dimensional, so we will be creating 3-dimensional models.
After reading the description and looking at the models of each molecule, we will construct
a model of that molecule using the molecule building kit, or gumdrops and toothpicks.
The first model we will construct is a model of a methanol molecule.
Methanol is the most commonly used alcohol in biodiesel production and is the simplest
alcohol with the formula CH3OH.
It’s helpful to look at the structural chart when constructing a 3-D ball-and-stick model.
Methanol is widely used as an antifreeze in windshield washer fluid and as a high octane
fuel in racing engines.
Ethanol can also be used to make biodiesel and is the second molecule model we will construct.
It is a straight-chain hydrocarbon with a molecular formula C2H5OH.
This type of alcohol is also called grain alcohol and is found in all alcoholic drinks.
It can also be blended with gasoline as an octane booster and fuel extender for all gas-powered
cars and trucks.
The next molecule model we will construct is Glycerol.
Vegetable-based glycerol has the molecular formula C3H8O3 and forms the backbone of triglycerides,
or the fat and vegetable oil molecule.
Glycerol, also called glycerin, is a substance found in almost all cosmetics, in many pharmaceuticals,
in personal care products like shampoos, lotions, and toothpaste, and in a lot of food items.
Glycerol is a byproduct of biodiesel production.
The next molecule models we will construct are fatty acids.
Fatty acids are part of triglycerides - (fats and oils).
In nature, they are made up of a chain consisting of an even number of carbon atoms from 4
to 28.
Fatty acids have a carboxyl group (COOH) at one end.
It is this end that combines with the hydrogen/oxygen group on the glycerol molecule to form triglycerides
Oils and fats are called “triglycerides” and are large and heavy molecules that are
made up of three fatty acids connected to a glycerol backbone.
Using 3 fatty acids and a glycerol molecule, construct a triglyceride molecule.
Esters are a class of compounds derived from the reaction of an acid and an alcohol.
For example, the reaction of fatty acids and methanol produce methyl esters, or biodiesel.
The molecular formula for a methyl ester is RCO2CH3, where R represents a fatty acid.
Using 3 methanol molecules and 1 triglyceride molecule, construct 3 methyl ester molecules.
Each methyl ester molecule may be different, depending upon the fatty acid used to make it.
You should have one glycerol molecule left over.
Thank you for watching the “Molecules of the Biodiesel Reaction” lab on the fundamentals
of biodiesel.
Please go to the biodiesel education website for a complete written transcript of this
lab exercise.