Glycerolysis of fats and methyl esters — Status, review and critique

Abstract

With the possible exception of catalytic hydrogenation, perhaps no unit operation within the realm of oleochemistry is as thoroughly complex as that of glycerolysis. Among the misconceptions and half-truths that prevail concerning the glycerolysis of fats are the notions that it involves a strictly random distribution of acyl groups among all of the available hydroxyl groups, that the solubility of glycerol in the fat at the reaction temperature determines the yield of monoglyceride that may be obtained, that the advantageous effects of the Law of Mass Action can be realized only when the reaction media is in ultimate homogeneity, in other words, complete mutual solubility, and, more importantly, that there is an equivalence of emulsification properties for the chief products of glycerolysis, i.e., the α-and β-monoglycerides, in both food and industrial emulsification. Numerous examples from international literature establish the limitations which prevail in temperature, agitation and use of excess of glycerol in batch glycerolysis reactions, but the practical limits for glycerolysis undersuperemulsification conditions remain to be established. The disadvantages of glycerolysis in homogeneous solvents still are insufficient to justify the use of those that are available, but the use of both pressure and gaseous catalysts such as carbon dioxide appear to offer the greatest hope for improvement in yields. Substantial energy savings may dictate the choice of methyl ester glycerolysis processing for future plants, especially those in the international sphere. Pros and cons of monoglyceride analytical methodology are evaluated.