Ionic conductivity of alkali-metal salts in sub- and supercritical carbon dioxide plus methanol mixtures

Ionic conductivity of lithium, sodium, and potassium perfluoroacetate salts and lithium acetate in sub- and supercritical carbon dioxide + methanol mixtures is reported as a function of CO2 pressure and temperature. Although the mole fraction of salts was low (10(-4)-10(-2)), the ionic conductivity was large ( similar to 10(-7) -10(-8) S cm(-1)) compared with pure CO2 (below measurement capabilities) and CO2 + methanol ( similar to 10(-7) - 10(-8) S cm(-1)). In the sub-critical two-phase region, the ionic conductivity in the CO2-rich phase increased with pressure, but the conductivity decreased in the supercritical region with CO2 pressure. Solvent viscosity and ion diffusivity in the single-phase region predominantly influence conductivity, whereas it is affected by salt solubility in the two-phase region. (C) 2001 Published by Elsevier Science B.V.