Biodiesel Basics
NC Future Fuels is a biodiesel producer. Biodiesel is an alternative fuel made from a variety of base materials, or feedstocks, such as soy bean oil, waste vegetable oil, animal lard (tallow), or in our case, trap grease. Biodiesel is compatible with most engines designed to run on petroleum diesel. Gasoline engines can not run on biodiesel, or petroleum diesel.
Most biodiesel is made either from virgin crops or waste vegetable oil. Waste vegetable oil is typically used deep fryer oil and is called “yellow grease”. Yellow grease is fairly clean and nice. We will be making our fuel from trap grease which is called “brown grease”.
Restaurants are required by law to maintain a grease trap on their outgoing sewer line to remove fats, oils, and grease from the waste water supply. These traps are often pumped on a regular schedule by law and can range in size from a few gallons to thousands of gallons in capacity.
Trap grease is very very nasty stuff – anything that might go down the sewer drain can end up in trap grease, including fecal matter. As such, it is considered a hazardous waste by the EPA. We will be doing most of our testing with “bad” yellow grease to simulate trap grease, or pasteurized trap grease to remove pathogens.
The important difference between yellow and brown grease boils down to what form the fat molecules are in. Yellow grease contains fat molecules which are primarily triglycerides. Triglycerides are long fat chains that are stuck together. When a triglyceride is broken apart, such as through hydrolysis (addition of water), the fat chains break away to form Free Fatty Acid (FFA) chains.
Yellow grease contains very low FFA content, typically less than 5%. Brown grease contains very high FFA content, typically >50% and sometimes approaching 100%. The traditional method of creating biodiesel requires the fats to be in the form of triglycerides. Extra FFAs in the oil will cause the creation of excess glycerin or soap as a byproduct. Therefore most biodiesel refiners desire their oil to have very low FFA content, and will not pay for oil with >4% FFA.
We are using a different method which requires the fats to be in FFA form instead, to take advantage of our already high percent FFA content.