What is Biodiesel?
By Rick Da Tech
Biodiesel is a clean-burning sustainable diesel fuel substitute made from vegetable oil and animal fats. The oil used to make biodiesel comes from the farm, not from oil wells. Since plants produce biodiesel by absorbing carbon dioxide from the air, it is a carbon-neutral fuel.
Diesel engines today only remotely resemble the engine that Rudolf Diesel designed. His engine was initially designed to run on coal dust. Moreover, for the first few decades, they could run on just about anything that would burn. Even as late as the 1970's, automotive diesel engines were extremely tolerant when it comes to the fuel they could use. Today's diesel engines are much more efficient and cleaner than the early versions, partly because they run on a narrowly defined diesel fuel. It allows the engine manufactures to tune the fuel system for improved efficiency. Biodiesel and Diesel fuel are very similar in their physical and chemical characteristics. They are similar enough that modern diesel engines can run on biodiesel.
You can blend Biodiesel with diesel fuel at any ratio. You find biodiesel blends like B20, which is 20% biodiesel and 80% diesel, at truck stops and gas stations. Blending biodiesel with diesel fuel results in a fuel that burns cleaner than diesel alone. Everyone has seen those black clouds, or soot, pouring from the exhaust of a diesel truck when it is under load. However, when we blend biodiesel with diesel, the soot is reduced, and dirty diesels can become clean diesels.
We make biodiesel from vegetable oil; biodiesel is NOT vegetable oil. We can add vegetable oil to diesel as a diesel fuel extender, but only for a few tanks. Blending vegetable oil with diesel over the long run damages the engine and shortens its usable life. Vegetable oil is thicker or more viscous than diesel and does not burn efficiently in a fuel system designed for diesel fuel. So, we chemically alter vegetable oil into biodiesel using a process called transesterification.
Vegetable oil is three long chains of hydrocarbons (carbon and hydrogen atoms) glued to an alcohol molecule called glycerin. The chemical process swaps out the glycerin molecule with three methanol molecules. Since the reaction is reversible, we use an excess of methanol to drive the reaction in the direction of methyl esters (biodiesel). Transesterification needs a strong base as a catalyst to get the reaction going. The glycerin separates from the biodiesel with the help of gravity.
Glycerin is a high-value product used in the medical and food industries. It has numerous uses from sweeteners to fillers and lubricants. Unfortunately, homebrewers make a glycerin that is not pure and not worth much.
The industrial name for biodiesel made from methanol is FAME which stands for Fatty Acid Methyl Esters. Ethanol also works for making biodiesel and is called FAEE for Fatty Acid Ethyl Esters. In the United States, methanol is less expensive and is the primary alcohol used to make biodiesel. In some other countries, ethanol is the primary alcohol used to make biodiesel.
The US Government commissioned Clean Cities to revise the NREL biodiesel use and handling guide. It contains lots of information on biodiesel as it pertains to those who want to use it. The guide goes into detail about what biodiesel is and the differences between biodiesel and other fuels. It covers how to use biodiesel, how it affects your engine as well as the best way to store biodiesel.