Dicarboxylic acids are experiencing an increased interest as intermediate chemical building-blocks within industrial biotechnology. Due to their two terminal carboxylic groups, as well as the high reactivity, they can be efficiently used e.g. for polymerization reactions, or precursors for classical chemical reactions. Due to recent advances within the upstream processing (metabolic engineering of microbial strains, optimization of fermentation conditions) product titers have now reached a level suitable for an industrial implementation. However, due to their high hydrophilicity, presence in a complex fermentation broth, as well as the common exclusion of thermal separation processes, the downstream processing still marks the bottleneck for industrial applications.
In order to overcome this bottleneck, reactive extraction using amines as extractants can serve as a viable tool to ensure a selective and efficient downstream processing . Within this work a complete reactive extraction concept was developed (extraction and re-extraction) using ethyl oleate as biocompatible organic phase, cis,cis-muconic acid as model dicarboxylic acid from fermentation, and different water insoluble amines as extractants. Within this work, different parameters such as the influence of polar modifiers, the pH, and amine concentration were investigated. Based on the results it was possible to determine a best performing system for the reactive extraction. Yields of 94 ± 4.0% and higher were achieved for a system using a tri-amine as extractant and a biocompatible solvent mixture as organic phase. Several experiments were conducted to investigate the underlying mechanism during reactive extraction of the dicarboxylic acid. Reactive extraction was shown to be mainly based on complex formation of undissociated acid and the amine via H-bond. Furthermore, in order to show the applicability for the purification on a process scale, different re-extraction concepts were evaluated. These included the addition of water soluble amines or a pH shift in the re-extraction phase. Based on these results, a complete downstream processing concept for the biocompatible reactive extraction of cis,cis-muconic acid is presented. The results allow for a further development of an in situ downstream processing concept for biocatalytic produced dicarboxylic acids.
 J. Gorden, T. Zeiner, C. Brandenbusch, Fluid Phase Equilibria, 393 (2015) 78-84