Separation of glycerol and organic acids in model ethanol stillage by electrodialysis and precipitation

Abstract

Glycerol and organic acids are often by-products of ethanol production by fermentation. The feasibility of separating these compounds from stillage was studied with model solutions of glycerol, lactic acid, and succinic acid. Electrodialysis of the mixture resulted in a lactate flux of 100–150 g m −2 h −1 A −1 and a succinate flux of 30 g m −2 h −1 A −1. Glycerol remained largely in the diluting (feed) stream, but some appeared in the concentrating (product) stream owing to diffusion. Lactic acid was precipitated and crystallized as the zinc salt. The zinc lactate was then acidified to produce the lactic acid. Lactate recoveries were typically 85% or greater. Multiple-stage operation can maximize the yield of glycerol and purity of the organic acids. The glycerol transport rate through the electrodialysis membrane was a function of the feed concentration.