Esterification and interesterification

A versatile and large group of fatty acid esters are prepared from monohydroxy alcohols (C₁ to C₂₂ members), glycols (ethylene and propylene glycols and others), etherglycols (many polyoxyethylene glycols), triols (glycerol and others), tetraols (pentaerythritol and others), polyglycerols, carbohydrate materials (sorbitol, sorbitan, sucrose and others). The two most important direct esterifications of fatty acids are those done with monohydroxy alcohols (methanol, butanol, etc.) and glycerol itself. Esterifications of these materials are carried out with or without the use of catalysts. For edible ester products, the choice of catalyst is determined by (a) rate of reaction promotion permitted by the use of the catalyst; (b) color of product obtained; (c) ease of removal of catalyst; (d) toxicity of catalyst, and perhaps; (e) other factors including promotion of acrolein formation from glycerol, loss by volatilization at high temperatures, inactivation above certain threshold temperatures, and catalyst corrosivity on the materials of construction of the esterifier. In certain instances the last factor may indeed be the paramount one in a particular catalyst choice for a direct esterification. Industrial production of methyl esters is principally by a process of interesterification called methanolysis. Polyols require conditions for complete esterification that are vigorous and severe. The two most important interesterification methods used in the fatty acid industry are the methanolysis of fats and oils for the production of methyl esters and the glycerolysis of fats and oils for the production of three kinds of so-called “monoglycerides”, namely the 40%, 60% and 90% monoglycerides.