Separation Of Tocopherol Homologues Using Amino-Based Polymer Extractants

Due to the strong similarities in their structures and properties, the separation of natural homologues is quite challenging. Tocopherols, natural products of significant commercial value, include four homologues:α-, β-, γ- and δ-tocopherol. As the relative biological activities of the homologues in increasing order are δ-<γ-<β-< a-tocopherol, the isolation of a-tocopherol is of great interest.The efficiency and selectivity of using organic solvents for such separations is quite poor. This project investigated improving such separations using a novel approach of polymer-mediated extractions. Various poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) samples having different molecular weights were prepared in combination of acetonitrile (ACN) to be evaluated as an extractant. Compared with pure ACN, adding PDMAEMA significantly improved the distribution and selectivity coefficients of the tocopherols. The distribution coefficient of 8-tocopherol was 4.4 times higher than when using ACN alone, and the corresponding selectivity coefficient of δ- to α-tocopherol was 1.6 times higher.Branched polyethylenimine (PEI) was also evaluated to mediate the extraction. The effects of cosolvent type, molecular weight and concentration of PEI were studied. High distribution and selectivity coefficients of the tocopherols were obtained with PEI-ACN as the extractant. The distribution coefficient of δ-tocopherol was 7.05 at the mole ratio of amine groups on PEI to ACN equaling 0.485, and the corresponding selectivity coefficient of δ- to α-tocopherol was 5.92. Moreover, CO2 was found to have a strong stimuli-responsive ability for PEI and could be employed to facilitate the recovery of tocopherols from the extract phase. Using CO2 bubbling, the number of hexane extractions required to recover>90% tocopherols was reduced to 3 times from its theoretical value of 12 times. The extract phase after recovering tocopherols could release CO2 and be used again as the extractant by N2 bubbling and heating. Only a 10% decrease in the distribution coefficients was observed after three recovery cycles, and the selectivity coefficients remained relatively constant.Another approach investigated for the separation of a-tocopherol from its homologues was adsorption using silica supported PEI as an adsorbent. High adsorption efficiencies and separation factors of tocopherols were obtained. The adsorption efficiency of 8-tocopherol was 96.1% at the ratio of the mass of adsorbent to the volume of tocopherol homologues solution equaling 0.4g/mL, and the separation factor of δ- and α-tocopherol reached 12.1. Tocopherols were effectively desorbed in ACN or ethanol.