Process of transesterification

The physical properties of the primary chemical products of transesterification indicate that the boiling points and melting points of the fatty acids, methyl esters, mono, di and triglycerides increase as the number of carbon atoms in the carbon chain increase, but decrease with increases in the number of double bonds. The melting points increase in the order of tri, di and monoglycerides due to the polarity of the molecules and hydrogen bonding. After transesterification of triglycerides, the products are a mixture of esters, glycerol, alcohol, catalyst and tri-, di- and monoglycerides. Obtaining pure esters isnot easy, since there are impurities in the esters, such as di- and monoglycerides. The monoglycerides cause turbidity (crystals) in the mixture of esters. This problem is very obvious, especially for transesterification of animal fats such as beef tallow. The impurities raise the cloud and pour points. On the other hand, there is a large proportion of saturated fatty acid esters in beef tallow esters (almost 50% w/w). This portion makes the cloud and pour points higher than that of vegetable oil esters. However, the saturated components have other value-added applications in foods, detergents and cosmetics. The co-product, glycerol, needs to be recovered because of its value as an industrial chemical such as CP glycerol, USP glycerol and dynamite glycerol. Glycerol is separated by gravitational settling or centrifuging. A small amount of water, generated in the reaction, may cause soap formation during transesterification which needs to be taken care of.