Reactive Extraction of Carboxylic Acids in Aqueous Solutions

Reactive extraction of carboxylic acids in aqueous solutions is a tailored liquid–liquid separation process that combines selective chemical reaction and phase transfer to recover valuable acids from dilute streams. It addresses the shortcomings of conventional downstream techniques—such as the high energy demand of distillation and the difficulty of isolating low-concentration solutes from fermentation broths, hydrometallurgical effluents and biomass-derived mixtures. In this method, an organic phase containing a reactive extractant—commonly an amine, phosphine oxide or ionic liquid—forms reversible complexes with the acid, enhancing transfer across the interface. Key parameters include pH control, extractant concentration, choice of organic diluent and temperature, all of which influence distribution coefficients, loading capacity and phase stability. Recent advances feature the use of green solvents, statistical optimisation of operating conditions and the integration of continuous mixer-settler or membrane systems to boost throughput. Applications span the recovery of lactic, succinic, malic, citric and oxalic acids, with growing emphasis on deep eutectic solvents and ionic liquids to improve selectivity and reduce environmental impact. The field is maturing towards scalable, energy-efficient processes that support circular-economy goals in biochemical and metallurgical industries.

Research from Nature Portfolio

Recent studies have harnessed systematic experimental design to enhance reactive extraction of dicarboxylic acids. One investigation optimised the recovery of malic acid from dilute aqueous streams using a system comprising trioctylamine and 1-decanol. Through response surface methodology and a Box–Behnken design, extraction efficiencies exceeded 93 % under optimised conditions of temperature (circa 305 K), extractant composition (approximately 23 % v/v) and initial acid concentration. The work provided a detailed model correlating process variables with equilibrium constants, facilitating scale-up. Importantly, it demonstrated strategies to prevent third-phase formation and maintain robust mass transfer, indicating clear pathways to continuous membrane-based processes for carboxylic acid separation.

Reactive Extraction of Carboxylic Acids in Aqueous Solutions publication trend

The graph below shows the total number of articles in reactive extraction of carboxylic acids in aqueous solutions across all publications each year (not limited to Nature Index journals).

Technical terms

Reactive extraction: Liquid–liquid separation in which a chemical reaction between the target solute and an extractant enhances its transfer into the organic phase.

Carboxylic acid: Organic compound containing one or more –COOH groups, often produced by fermentation or biomass conversion.

Extractant: Organic reagent that selectively binds a solute to form a complex soluble in the organic phase.

Deep eutectic solvent: Mixture of hydrogen-bond donors and acceptors that forms a low-melting liquid, used as an eco-friendly solvent.

Distribution coefficient: Ratio of solute concentration in the organic phase to that in the aqueous phase at equilibrium.

Back-extraction: Release of the solute from the loaded organic phase into a fresh aqueous phase for final recovery.

References

1. Reactive liquid-liquid extraction of lactic acid from microfiltered sweet sorghum silage press juice in an agitated extraction column using a hydrophobic natural deep eutectic solvent as modifier. Journal of Cleaner Production (2024).
2. (Selective) Isolation of acetic acid and lactic acid from heterogeneous fermentation of xylose and glucose. Chemical Engineering Journal Advances (2023).
3. The effect of fermentation broth composition on removal of carboxylic acids by reactive extraction with Cyanex 923. Separation and Purification Technology (2020).
4. Reactive Extraction of Malic Acid using Trioctylamine in 1–Decanol: Equilibrium Studies by Response Surface Methodology Using Box Behnken Optimization Technique. Scientific Reports (2020).