Nanofiltration coupled with vapor permeation-assisted esterification as an effective purification step for fermentation-derived succinic acid

An integrated membrane process that consists of nanofiltration (NF) and vapor permeation (VP) was employed as a series of purification process for fermentation-derived succinic acid. Separation performance of a ceramic NF membrane was examined for both model solutions and fermentation broth. Rejection of organic acids was investigated for model solutions as a function of feed pressure, feed concentration, and pH. For fermentation broth, the NF showed its usefulness for protein and color removal rather than separation among organic acids. The esterification reactions of succinic acid with ethanol were initially investigated using model solutions. The yield of diethyl succinate (DES) was the function of initial reactant ratio whilst the operating temperature played an important role in productivity. Realistic purification was performed with NF-treated fermentation broth using Actinobacillus succinogenes ATTC 55618 as the succinic acid producer. The yield and volumetric productivity of DES strongly depended on the dehydration rate. Experimental results showed that most succinic acid was converted into DES at the end of the VP-assisted esterification reaction. After fractionation and hydrolysis, a high purity of succinic acid was obtained.