Why are fatty acids distilled under vacuum during continuous soapmaking?

In the continuous hydrolyzer process, fatty acids are distilled under vacuum primarily to effect purification.1

By distilling the fatty acids after they have been split from natural fats, manufacturers can remove impurities, ensuring the resulting fatty acid feedstock is clean before it is neutralized with an alkali, such as sodium hydroxide, to produce soap. This purification step is a key advantage of the continuous process, as it allows for more precise control over the final product compared to traditional boiling methods.1