Observation of Isotope Effect in Supercritical Fluid and Its Application to Isotope Separation Processes

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Applicability of supercritical carbon dioxide (SF-CO_2) was experimentally studied as an alternative for organic compound as mobile phases of chromatographic isotope separation. Lithium isotope separation was performed by a displacement chromatography with LiCl in methanol diluted by SFCO_2 in a breakthrough manner at 313 K and 10 MPa. As a stationary phase, commercially available cryptand (2s, 2, 1) polymer was employed to form a complex with LiCl and packed in a stainless steel column. Low solubility of LiCl in SF-CO_2 was dramatically improved by the addition of methanol ; the mixture of LiCl, methanol and SF-CO_2 formed a single phase and worked as a mobile phase under the given condition. LiCl was absorbed in a step wise at the front boundary, and, the equilibrium separation factor was evaluated to be 1.025. Use of SF-CO_2 enhanced effective capacity of the complexation of LiCl with cryptand polymer.