biodiesel production is the process of producing the biofuel, biodiesel, through the chemical reactions transesterification and esterification. this involves vegetable or animal fats and oils being reacted with short-chain alcohols (typically methanol or ethanol). == process steps == the major steps required to synthesize biodiesel are as follows: === feedstock pretreatment === common feedstock used in biodiesel production include yellow grease (recycled vegetable oil), "virgin" vegetable oil, and tallow. recycled oil is processed to remove impurities from cooking, storage, and handling, such as dirt, charred food, and water. virgin oils are refined, but not to a food-grade level. degumming to remove phospholipids and other plant matter is common, though refinement processes vary. regardless of the feedstock, water is removed as its presence during base-catalyzed transesterification causes the triglycerides to hydrolyze, giving salts of the fatty acids (soaps) instead of producing biodiesel. ==== determination and treatment of free fatty acids ==== a sample of the cleaned feedstock oil is titrated with a standardized base solution in order to determine the concentration of free fatty acids (carboxylic acids) present in the vegetable oil sample. these acids are then either esterified into biodiesel, esterified into glycerides, or removed, typically through neutralization. === reactions === base-catalyzed transesterification reacts lipids (fats and oils) with alcohol (typically methanol or ethanol) to produce biodiesel and an impure coproduct, glycerol. if the feedstock oil is used or has a high acid content, acid-catalyzed esterification can be used to react fatty acids with alcohol to produce biodiesel. other methods, such as fixed-bed reactors, supercritical reactors, and ultrasonic reactors, forgo or decrease the use of chemical catalysts. === product purification === products of the reaction include not only biodiesel, but also byproducts, soap, glycerol, excess alcohol, and trace amounts of water. all of these byproducts must be removed to meet the standards, but the order of removal is process-dependent. the density of glycerol is greater than that of biodiesel, and this property difference is exploited to separate the bulk of the glycerol coproduct. residual methanol is typically recove
Biodiesel