Biodiesel can be made from waste cooking oil through transesterification, which removes glycerin molecules from triglycerides. It is a cheaper and greener option than fossil fuel diesel, and can be made at home with lye and alcohol. Safety protocols must be followed.
Creating biodiesel from waste cooking oil is a technique for generating fuel for diesel engines from leftover grease. It is popular as a way to avoid paying for commercially sold diesel fuel. Biodiesel from cooking oil requires no special modifications to a diesel engine and can be produced from waste oil found in cooking grease traps, which can often be obtained for free at restaurants.
Biodiesel, technically known as fatty acid methyl esters (FAMEs), is derived from fuel fatty acids known as triglycerides that come from plants or animals. In raw cooking oil, triglycerides consist of three fatty acid molecules attached to a single glycerin molecule. The process of generating biodiesel from cooking oil involves the chemical removal of the glycerin molecules, leaving only the fatty acids. From start to finish, this procedure is called transesterification.
The properties of traditional diesel fuel and cooking oil biodiesel are very similar, including high viscosity and flash point. This means it won’t clog fuel systems and is relatively difficult to ignite, making it safer to transport. Proponents say biodiesel also tends to burn cleaner than fossil fuel diesel, making it a greener option.
Home brewing of biodiesel from residual fat can save more than 75% in cost per unit of fuel over prices at the pump. There are up-front costs associated with setting up the home system to process oil into biodiesel, but the reduced ongoing costs generally make up for the short-term shortfall. There are a variety of recipes that take advantage of different ingredients that can vary due to availability and preference.
Most experts recommend starting to make very small batches of biodiesel from cooking oil, typically 0.25 gallons (1 liter) at a time or less. Chemicals required for the process include methyl or ethyl alcohol and lye, which acts as the catalyst that breaks apart the glycerin molecules. Used oil generally must be pre-treated before applying these chemicals to remove any water and free fatty acids (FFA) that have built up, which can prevent transesterification. Pretreatment typically involves oil titration, which is a test that determines the amount of lye that will be needed to separate the FFAs.
In very basic terms, appropriate proportions of lye and alcohol are mixed together and then added to the oil supply. A chemical reaction occurs, and after a settling period, the usable biodiesel can be decanted, washed, dried, and used. There is leftover glycerin and FFA, effectively soap. Lye and the types of alcohol used in transesterification can be dangerous if mishandled, and it’s important to adhere to proper safety protocols to ensure the process remains safe.
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