Glycerin

Abstract

Glycerin is a coproduct of fat splitting (hydrolysis), soap making, and transesterification of fats and oils. The history of glycerin and its economic value as an industrial chemical provide an introduction to its importance in our society in recent times. Two distinct types of glycerol are processed, soap lye crude, which contains significant levels of sodium chloride, and sweetwater crude, which has little to no sodium chloride contamination present. Processing glycerol into high‐purity refined grades requires pretreatment steps followed by evaporation to concentrate the glycerol solution into crude glycerin. The removal of sodium chloride requires specialized equipment. Refining crude glycerin into finished USP‐grade glycerin requires distillation equipment, which operates under a high vacuum. The final step of the process is carbon adsorption to remove any colored particles of high molecular weight. Storage of finished and unprocessed glycerin requires special considerations. The effect of processing on glycerin odor and color is critical to final product quality. Processing plants require special considerations in terms of layout, materials of construction, instruments and controls, and piping. Overall considerations in glycerin processing include physical properties, quality and testing, grades and test methods, losses and waste management. A discussion of glycerin usage and future considerations provides reference for the current glycerin industry.