Beyond Phase Equilibria: Selecting Suitable Solvent Systems for Reactive Extraction of Carboxylic Acids

Reactive extraction is an attractive separation technology that can replace energy-intensive water evaporation steps in the industrial production of carboxylic acids. We systematically review the current literature on the extraction of low-value bioproducts and thereby identify the reduced availability of predictive models, limited selectivity, and challenging phase separation as possible bottlenecks in the industrial implementation of reactive extraction. Furthermore, we discuss requirements and strategies for closing the material cycles for batch and continuous processes. With these challenges in mind, we analyze the most widely used extractants (trioctylamine, trioctylphosphine oxide, and tributyl phosphate) in combination with common diluents (e.g., long-chain alcohols and alkanes) in terms of their ability to meet process needs. We illustrate the subordinate role of equilibrium constants in overall process design while emphasizing the potential for flexible reactive extraction systems tailored to process requirements.