Smart Polymer-Assisted Separation of Tocopherol Homologues and Fast Recovery of the Extractant

Due to the strong similarities in their structures and properties, the separation of natural homologues is quite challenging. Current separation methods of these products require large solvent consumption, have low separation efficiency, and result in significant energy expenditure. To address these issues, we have proposed a novel strategy to use ionic liquid polymers (PIL) or polyethyleneimine (PEI) as extractants for the liquid-liquid extraction of α-tocopherol from tocopherol homologues. The PIL was synthesized by RAFT copolymerization of N-isopropylacrylamide and ionic liquid, while the PEI is commercially available. The PIL was thermoresponsive in acetonitrile with upper critical solution temperatures (UCST) varying from 25.7 to 34.8 °C, and the PEI also had a stimuli-responsive property in acetonitrile triggered by CO₂. Both the two polymer extractants showed a good separation efficiency of tocopherol homologues. The distribution coefficient of δ-tocopherol between the extract (PIL as extractant) and raffinate phases (D_δ) and the selectivity coefficient of δ-tocopherol to α-tocopherol (S_δ/α) reached as high as 7.86 and 13.0, respectively, while D_δ (PEI as extractant) was 6.35 and S_δ/α was 6.83. The PIL and PEI could be reused for multiple extraction cycles with a slight change in the tocopherol distribution and selectivity coefficients. The use of stimuli-responsive polymer extractants offers great benefits by reducing the back extraction steps that are normally required. This work demonstrates the potential of smart polymers for use in high performance separation of natural products.