Determination of Diffusion Coefficients in Supercritical Fluid

This chapter discusses the techniques for determining the diffusion coefficients in Supercritical Fluids. It explains measurement methods, their advantages and disadvantages and the theories of frequent experimental techniques in detail. The Chromatographic Impulse Response (CIR) method is widely used to measure the solubility, retention factor, partial molar volume and diffusion coefficient for gas, liquid and supercritical fluid chromatographies. Lai and Tan have also employed the CIR method with the moment technique to measure the infinite dilution binary diffusion coefficients of ethyl acetate, toluene, phenol and caffeine in supercritical CO_{2 (}SCO₂). The Solid Dissolution technique employs a diffusion cell in which the solid solute compressed into a tablet structure. While Nuclear Magnetic Resonance has long been employed for diffusion study, it became truly practical only after recent developments in hardware, pulse sequences and data analysis. This method is employed to measure the diffusion coefficients over a wide range of temperatures and pressures.