Esterification of edible oils
Thread Content
I have been working on the ethylation of edible corn oil recently, and then concentrating the fatty acids using molecular distillation. Procedure: The oil was preheated, then a sodium hydroxide-ethanol solution (anhydrous) was added. After a 2-hour reaction, the mixture was taken out directly and no separation occurred; however, when water was added, the solution turned milky white or light yellow, appearing to be emulsified. What is going on? Other papers mention that layering occurs immediately after the reaction, followed by washing with a salt solution. Why does it separate into layers as soon as it’s taken out, and why doesn’t the liquid emulsify? When the reaction time is up, should an acid solution be added to neutralize the base, turning the solution acidic before separating the layers and then adding water? Will adding water directly cause saponification? Is the oil phase after normal stratification in the same state as oil? Generally, is the volume of the oil phase after esterification very different from the volume of the crude oil? Is it still more or less the same? What is the difference between esterification and saponification?
The oil was preheated, then a sodium hydroxide-ethanol solution (anhydrous) was added; the reaction proceeded for 2 hours. After removing the mixture directly, no separation occurred, but upon adding water the solution turned milky white or light yellow, appearing homogeneous as if it had been emulsified – and indeed it had been emulsified. Esters will emulsify or even saponify in an alkaline environment. Emulsification does not occur without adding water; when water is added, the unreacted sodium hydroxide in the material turns into a solution, allowing the ester to undergo hydrolysis and thus leading to emulsification.
What you’re doing is similar to the transesterification process used in industry to produce first-generation biodiesel, except that biodiesel is usually produced using methanol and potassium hydroxide. Sodium hydroxide has a much lower catalytic efficiency compared to potassium hydroxide; the temperature needs to be kept at 60 degrees. A clear separation into layers should occur – with glycerin along with a small amount of soap in the lower layer, and ethyl fatty acids in the upper layer.
Yours has probably been saponified; it’s unclear what the preheating temperature was – if it’s too low, saponification easily occurs.