Aqueous two-phase (polyethylene glycol + sodium sulfate) system for caffeine extraction: Equilibrium diagrams and partitioning study

• Binodal curves of PEG (400, 4000 and 6000) + Na2SO4 ATPS were determined.
• Tie-lines were experimentally determined for aqueous (PEG 400 + Na2SO4) system.
• Influence of caffeine on LLE of aqueous (PEG 400 + Na2SO4) system was investigated.
• Partitioning of caffeine in aqueous (PEG 400 + Na2SO4) system was investigated.
• Caffeine partition showed to be dependent on temperature and TLL.

Environmental friendly methods for liquid–liquid extraction have been taken into account due to critical conditions and ecotoxicological effects potentially produced by organic solvents applied in traditional methods. Liquid–liquid extraction using aqueous two phase systems (ATPSs) presents advantages when compared to traditional liquid–liquid extraction. (Polyethylene glycol (PEG) + sodium sulfate + water) ATPS was applied to study partition of caffeine. Binodal curves for ATPSs composed of PEG of different molecular weights (400 g · mol−1, 4000 g · mol−1 and 6000 g · mol−1) sodium sulfate + water were determined by cloud point method at three different temperatures (293.15, 313.15 and 333.15) K. Liquid–liquid equilibrium (LLE) data (tie-lines, slope of the tie-line and tie-lines length) were obtained applying a gravimetric method proposed by Merchuck and co-workers at the same temperatures for aqueous (PEG 400 + sodium sulfate) and aqueous (PEG 400 + sodium sulfate + caffeine) systems. Reliability of the experimental tie-line (TL) data was evaluated using the equations reported by Othmer–Tobias and satisfactory linearity was obtained. Concerning to aqueous (PEG + sodium sulfate) system, the results pointed out that the higher PEG molecular weight the largest is the heterogeneous region. Moreover, temperature showed not to be relevant on binodal curves behavior, but it influenced on tie-line slopes. Partitioning of caffeine in aqueous (PEG 400 + sodium sulfate) system was investigated at different temperatures and tie-lines lengths (TLLs). It was shown that the partitioning was depended on the temperature and TLL and at all conditions studied the salting out effect displayed higher influence leading caffeine partition preferentially into the PEG rich (top) phase.

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