What is transesterification in biodiesel production?

Transesterification is the chemical reaction that converts vegetable oils or animal fats into biodiesel (fatty acid methyl esters, FAME). The process involves: reacting triglycerides (oil/fat) with short-chain alcohol (usually methanol) in the presence of a catalyst (typically sodium or potassium hydroxide) to produce glycerol and fatty acid esters (biodiesel). The reaction proceeds in three steps as triglycerides are converted to diglycerides, then monoglycerides, and finally glycerol plus three FAME molecules. Typical conditions: 60C temperature, 6:1 methanol to oil molar ratio, 1% catalyst by weight, and 1-hour reaction time. After reaction, glycerol is separated by gravity/centrifugation, and biodiesel is washed and dried. Product must meet quality standards (ASTM D6751, EN 14214). Feedstocks include soybean, canola, palm oil, and waste cooking oil.