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[Display omitted] • Identifying limiting factors of reactive extraction and back-extraction with online FTIR spectroscopy. • Evaluation of reaction equilibria and reaction kinetics using FTIR spectroscopy. • Investigation on the strength of the acid-extractant complexes. • Optimized amine selection for reactive extraction and back-extraction. • Optimizing downstream concept for (di–)carboxylic acids through mechanistic understanding of complex formation. The downstream processing of biocatalytically produced (di–)carboxylic acids still is a challenging task. One innovative approach, demonstrating industrial applicability, applies an initial reactive extraction (RE) using hydrophobic amine extractants into an organic solvent, followed by a subsequent back-extraction (BE) using water soluble amine extractants into a (fresh) aqueous solution. Although showing promising results in terms of yield and selectivity, state-of-the-art amine extractant selection is only based on trial-and-error screening approaches. Thus, to enable an optimized process design and thereby optimized downstream processing, a deeper understanding of RE and BE on a molecular level is crucial. Within this work, we successfully applied an experimental setup incorporating online Fourier Transform Infrared (FTIR) spectroscopy to elucidate influencing factors on RE and BE as well as to provide a guideline for an optimized selection of amine extractants. Investigations on the kinetics of complex formation between itaconic acid (IA) and tri- n -octylamine (TNOA) in 1-decanol revealed the reaction order to be zero in TNOA, indicating that mass transfer is the rate limiting step in RE. Reaction equilibrium investigations revealed that for all IA - amine extractants combinations in 1-decanol reaction equilibrium was almost completely on the product (complex) side. The strength of the acid-extractant complexes was evaluated using FTIR experiments, providing a novel approach / methodology to efficiently select an optimal combination of amine extractants for RE and BE. Applying the novel online FTIR spectroscopy setup allowed to monitor a complete process sequence of RE and BE of IA with selected amine extractants, validating the proposed guidelines for an optimized selection of amine extractants. The results of this work will facilitate the definition of appropriate RE and BE systems for biocatalytically produced (di–)carboxylic acids. [ABSTRACT FROM AUTHOR]

[Display omitted] • Online monitoring of reactive extraction of (di-)carboxylic acids. • Simultaneous time-dependent measurements in aqueous and organic phase. • Time-dependent concentration and reaction profiles using FTIR spectroscopy. • Identification of complex stoichiometry using FTIR spectroscopy. • Optimizing reactive extraction by mechanistic understanding of complex formation. Reactive extraction (RE) using amine extractants in an organic solvent has been proven a promising downstream strategy for (di–)carboxylic acids of biocatalytic origin. Available analytical techniques allow for observation of the acid depletion in the aqueous phase and thus an indirect link to the course of the RE as well as concentration of the complex. In order to further optimize RE performance in these systems, a direct information on the complex concentration as well as its stoichiometry (amine extractant to (di–)carboxylic acid ratio in the complex) in the organic phase is crucial. Within this work, we successfully applied Fourier Transform Infrared (FTIR) spectroscopy for the detection and quantification of the acid-extractant complex formed between itaconic acid (IA) and tri-n-octylamine (TNOA) in 1-decanol. A newly developed experimental setup incorporating FTIR spectroscopy and a systematic procedure for the characterization of the acid-extractant complex allow clarifying the structure of the acid-extractant complex. Our investigations revealed the complex formation between IA and TNOA to be based on the ion-pair mechanism whereas the stoichiometry was identified to be 2:1 (TNOA:IA) when TNOA is available in excess. Applying the experimental setup enables online monitoring of the IA concentration simultaneously in both phases during extraction of IA using 1-decanol as organic extraction phase. The mechanistic understanding of the complex formation on a molecular basis gained from the results of this study as well as the possibility to online monitor RE enables the optimization of RE as downstream strategy for (di–)carboxylic acids. [ABSTRACT FROM AUTHOR]