A biodiesel plant is a type of refinery that produces diesel fuel from organic sources called biomass. These plants use biomass, which may be crops, virgin oils, or waste oils and fats to produce diesel fuel through a process in which alcohols are added to the fats and react with them, creating organic diesel fuel and glycerin, as a by-product. Most biodiesel plants have facilities for testing, preparing, and processing the raw material into fuel, as well as storage and distribution equipment.
Making biodiesel is a matter of separating the glycerin from the fats in the oils in a process called transesterification. The oils are treated with an alcohol, usually methanol, and produce glycerin along with compounds called methyl esters, which make up the biodiesel fuel. The glycerin is a valuable by-product of biodiesel production and is used in many industrial fields such as soap-making, beauty and cosmetic product manufacturing, and the food industry.
Most plants that produce biodiesel fuels can accept more than one type of biomass or oil for fuel production. They will have facilities that test the biomass for production capacity to determine how much fuel may be produced from a given amount of raw material, as well as the precise amount of alcohol needed to produce the desired result. This testing will also reveal any impurities or other chemicals that may be present in the biomass.
A rendering facility may be used to render oils from raw biomass. The facility usually consists of machinery that crushes the biomass and equipment that separates the vegetable oils from the waste and other liquids. The remains are often used in livestock feed products. The oils are then treated to remove as much of the water and free fatty acid as possible, to prevent soap formation in the fuel. A biodiesel plant may have its own rendering facility, though some accept only oils ready for use.
After the waste oils are treated to remove impurities and particulate wastes, a catalyst is mixed with alcohol, and this mixture is combined with the oil. This the main function of a biodiesel plant. The oil and alcohol will react, over a number of hours, forming methyl esters and glycerin. This reaction is often carried out at room temperature, for safety purposes, but each biodiesel plant may perform this step at different temperatures. At higher temperatures, the reaction occurs more quickly.
Once the reaction is complete, the glycerin and the fuel are separated, either by gravity separation or by centrifuge. The fuel that results may be further treated to remove any remaining water, catalysts, or glycerins. These steps make up what is known as the batch process. A biodiesel plant may be designed to use other methods, which allow for continuous production, elimination of the catalyst, or reduced reaction time, but the basic principles of the process remain unchanged.
Biodiesel fuel is made entirely from renewable resources, is low in sulfur and other impurities, and may be used by itself in any diesel engine. It can also be mixed in any proportion desired with petroleum based diesel fuels. Biodiesel blends are designated with the letter "B" and a number indicating the percentage of biodiesel in the blend. B80 biodiesel fuel, therefore, contains 80 percent biodiesel and 20 percent petroleum-based diesel fuel.