Biodiesel (AQA A Level Chemistry): Revision Note

Biodiesel

Biodiesel production

• Biodiesel is produced from renewable vegetable oils rather than non-renewable petrochemicals

• Natural triglycerides are converted into methyl esters by reaction with methanol

  • This reduces the viscosity of the oil, making it suitable for use as a fuel

• For example, biodiesel can be made from rapeseed oil by a process called transesterification

  • In this reaction, the triglyceride reacts with methanol to form fatty acid methyl esters (FAME) and glycerol

• Both acids and alkalis can be used as catalysts

  • An acid catalyst works by protonating the carbonyl group, increasing its susceptibility to nucleophilic attack

  • An alkaline catalyst (such as NaOH or KOH) works by generating a stronger nucleophile from methanol

• In industry, alkaline catalysts are more commonly used

  • Because the reaction is reversible, an excess of methanol is used to shift the equilibrium to the right and increase the yield

• Under optimal conditions, yields of around 98% can be achieved