Evaluation of non-ionic surfactants for aqueous two-phase extraction of butyric acid

• Among the non-ionic surfactants tested, Ecosurf™ EH-3 exhibited the highest butyric acid recovery (79.15 %) and partition coefficient (K p = 7.49). • Variations in initial acid concentration and extraction time showed no significant effect on butyric acid recovery or K p . • Ecosurf™ EH-3 achieved the lowest break-even selling price (11.28 USD/kg); however, this remains above current market levels (2–2.5 USD/kg). Economic competitiveness requires process optimization and scale-up. The rising demand for bio-based volatile organic acids (VOAs) like butyric acid is driven by consumer preference for natural products, but recovery from fermentation broth remains inefficient. To address this challenge, this study investigates non-ionic surfactants (NISs) for butyric acid recovery via aqueous two-phase (ATP) extraction, aiming to identify the most suitable NIS and evaluate its economic potential. From seven pre-selected NISs based on properties, four NISs (Makon® NF-12, Ecosurf™ EH-3, Nonidet™ RK-18, Triton™ X-45) were tested at varying initial butyric acid concentrations (10%, 15%, 20%, 25% w/w) and extraction times (1 h, 5 h, 8 h, 24 h). Results show that Ecosurf™ EH-3 performed best, achieving 79.15% recovery and a partition coefficient (K p ) of 7.49. Statistical analysis also revealed that only the surfactant type significantly affected extraction efficiency. Economically, Ecosurf™ EH-3 was the most cost-effective, with the lowest break-even selling price of 11.28 USD/kg over a seven-year payback period, though still above the market price of 2–2.5 USD/kg. Scaling up from 1000 to 20,000 kg/h with high-acid broth (4.30% w/w) could improve market competitiveness, but low-acid broths remain less viable. Improved extraction efficiency and lower surfactant use are essential to reduce costs below 2 USD/kg and enhance commercial potential.