Measurement of static dielectric constants of supercritical fluid solvents and cosolvents: Carbon dioxide and argon, carbon dioxide, and methanol at 323 K and pressures to 25 MPa

A new apparatus for the measurement of dielectric constants of high pressure gases has been constructed. The apparatus consists of a recirculating visual flow cell and a concentric cylinder dielectric constant flow cell. Measurement of the dielectric constant is made by a unique counter-oscillator circuit, in which the capacitance is determined by relaxation of a unijunction transistor oscillator circuit and counted by a crystal oscillator. Dielectric constants are reported for supercritical mixtures of carbon dioxide + argon and carbon dioxide + methanol at a temperature of 322.9 K and pressures to 25 MPa. The dielectric constant shows a sharp increase near the critical pressure. Dielectric constants were linear with densities calculated by the Suzuki equation-of-state. The dielectric constant for the methanol-carbon dioxide system was found to be less than a mole fraction average of the pure component dielectric constants.