Monitoring and investigating reactive extraction of (di-)carboxylic acids using online FTIR - Part I: Characterization of the complex formed between itaconic acid and tri-n-octylamine

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-noctylamine (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. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study successfully applied Fourier Transform Infrared (FTIR) spectroscopy to detect and quantify the acid-extractant complex formed between itaconic acid (IA) and tri-noctylamine (TNOA) in 1-decanol, and the experimental setup enabled online monitoring of the complex concentration and interaction mechanism.