Hydrophobic eutectic mixtures as volatile fatty acid extractants

Adriaan van den Bruinhorst (Corresponding author), Sanne Raes, Sausan Atika Maesara, Maaike C. Kroon, A. Catarina C. Esteves, Jan Meuldijk (Corresponding author)

Research output: Contribution to journalArticleAcademicpeer-review

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Organic waste streams can be converted into volatile fatty acids (VFAs) via fermentation. VFAs can be used as intermediates in the synthesis of added-value chemicals. In this work, hydrophobic eutectic mixtures were designed for the liquid-liquid extraction of VFAs from dilute aqueous solutions. The eutectic behaviour was screened for over 100 combinations of 16 hydrophobic components that were selected based on a set of predetermined criteria. Mixtures of dihexylthiourea and trioctylphosphine oxide (TOPO) showed the best extraction performance and were stable over a wide pH range. The extraction efficiency increased with increasing hydrophobicity of the VFAs, and only undissociated acids were extracted. Upon increasing the TOPO content of the eutectic mixture, the extraction performance could be improved, confirming the tuneable nature of eutectic solvents. However, the extraction performance was less than that for solutions of TOPO in hydrophobic solvents, even though mole fractions of TOPO were higher in the eutectic mixtures. It was hypothesized that the intermolecular VFA–TOPO interactions required for extraction are suppressed by the inter-component interactions in the eutectic mixture. The inter-component interactions are responsible for the negative deviation from ideality of the melting temperature depressions that extend the liquid window of the mixtures towards the extraction temperature. Hence, the design of novel hydrophobic extractants based on eutectic mixtures was demonstrated. Their performance might be improved by selecting counterparts that interfere less with the interactions required for VFA extraction.

Original languageEnglish
Pages (from-to)147-157
Number of pages11
JournalSeparation and Purification Technology
Publication statusPublished - 1 Jun 2019


  • Deep eutectic solvents
  • Designer solvents
  • Eutectic mixtures
  • Liquid–liquid extraction
  • Volatile fatty acid recovery

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