What is the chemical composition of biodiesel and green diesel? How do they differ from each other?
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Diesel fuel is a fraction from the destillation of crude oil and consists of alkanes, cycloalkanes and aromatic hydrocarbons. In Europe, the properties of this mixture are defined in DIN EN 590.
This includes a certain density range, a minimum cetane number (CN) of 51, a maximum content of 8 mass-% for PAHs, a maximum sulfur content of 50 mg/kg. After distillation at tempertures up to 360 °C, the residue may not be larger than 5 vol-%. Note that diesel fuel may contain up to 7 vol-% biodiesel.
Biodiesel mostly is FAME, fatty acid methyl ester, produced by transesterification of triglycerides from biomass (vegetable oil).
Green diesel, also known as renewable diesel, is a fuel derived from biomass that does not contain monoalkyl esters of fatty acids. This can be achieved by catalytic hydrodeoxygenation (hydrotreatment) of triglycerides or fatty acids and typically involves a cracking step too, leading to an alkane mixture.