transesterificatie

Transesterificatie, or transesterification, is a chemical reaction in which an ester reacts with an alcohol to form a different ester and a different alcohol. The process involves exchange of the alkoxy group of an ester with that of another alcohol, typically proceeding under acidic, basic, or enzymatic catalysis.

In practical terms, transesterification is widely used to convert fats and oils (triglycerides) into usable esters. When a triglyceride reacts with an alcohol such as methanol or ethanol, fatty acid esters are produced (fatty acid methyl esters or fatty acid ethyl esters) and glycerol is released as a by-product. The overall reaction can be written simplistically as triglyceride plus three equivalents of alcohol yields three esters plus glycerol. The reaction is reversible, so conditions are chosen to shift the equilibrium toward ester formation, for example by using excess alcohol or removing the by-product glycerol.

Catalysis can be achieved by bases (e.g., NaOH, KOH), acids (e.g., sulfuric acid), or immobilized enzymes (lipases). Base-catalyzed transesterification is fast and common for low free-fatty-acid feeds but can cause soap formation with high acidity; acid catalysis tolerates higher free fatty acids but is slower. Enzymatic routes operate under milder conditions and can tolerate feedstock impurities, though they may be slower and more expensive.

Applications include biodiesel production, where fatty acid methyl esters are the principal product, as well as specialty esters in chemical synthesis and polymer modification. Feedstocks typically include vegetable oils, animal fats, and waste oils, after pretreatment to remove water and impurities.