(247a) Reactive Extraction of (Di-)Carboxylic Acids from Fermentation Broth -Online FTIR for Characterization and Process Control-

Renewable alternatives to fossil-based feedstocks, such as (di-)carboxylic acids from biocatalytic origin, have increasingly been part of academic and industrial research within the last decades. Especially for hydrophilic products (such as (di-)carboxylic acids) present in a complex fermentation broth, design of an efficient downstream concept is crucial, and marks a remaining challenge in the development of biocatalytic production processes. One promising alternative, traditionally considered for the purification of (di-)carboxylic acids, is the reactive extraction (RE). During RE the (di‑)carboxylic acid and a suitable extractant (commonly amine or phosphorus-based extractants) form an acid-extractant complex, which is then selectively extracted into an organic extraction phase. Several aspects within the RE of (di-)carboxylic acids such as (1) the type of (di‑)carboxylic acid suitable for RE, (2) the type of (amine / phosphorus-based) extractant to be used in RE, and (3) the type of organic solvent have already been studied. These investigations commonly aim at optimizing RE parameters such as extraction efficiency or distribution coefficients. However, standard analytics, such as high performance liquid chromatography (HPLC), applied are not suitable to quantify or characterize the complex in the organic phase, only the depletion of the acid from the aqueous phase.

However, direct information of the complex (stoichiometry, concentration) and complex formation is crucial for an optimization of RE performance, especially taking continuous purification concepts and control strategies into account.

Within this work we developed an experimental setup using online Fourier Transform Infrared (FTIR) spectroscopy for the identification and characterization of the acid-extractant complex in both phases of the RE-system. Applying FTIR spectroscopy as qualitative and quantitative online monitoring tool for RE, the aforementioned challenges were addressed by: (1) Identifying the interactions involved in the complex formation, (2) proposing initial approaches to directly quantify the acid-extractant complex via FTIR spectroscopy, (3) characterizing the stoichiometry of the acid-extractant complex systematically, and (4) allowing for continuous online monitoring of all components during RE experiments using an experimental setup developed for this purpose.

Using FTIR spectroscopy as online monitoring tool, phase and reaction equilibria during RE as well as reaction kinetics of complex formation become accessible, demonstrating the potential of applying FTIR spectroscopy for RE investigations.

The methodical approach proposed in this work allows for a deeper mechanistic understanding of the complex formation as basis of RE using amine extractants and thus, enables a further optimization of RE as downstream concept for biocatalytically produced (di‑)carboxylic acids.