Using supercritical fluid chromatography to determine diffusion coefficients of lipids in supercritical CO2

Supercritical fluid chromatography was used for the determination of diffusion coefficients by the Taylor–Aris peak broadening technique. Binary diffusion coefficients of pure lipids, such as fatty acids and their esters, triglycerides and a diglyceride in supercritical carbon dioxide, were determined and the effect of pressure (25.0–36.0 MPa), temperature (40–60°C) and number and position of double bonds on the diffusion coefficient was studied. Addition of a secondary solvent such as ethanol indicated an apparent enhancement in the diffusion coefficient of oleic acid. Diffusivity of oleic acid decreased with pressure and increased with temperature. Increasing the number of double bonds reduced the diffusion coefficient of fatty acids. A shift in the position of double bond from ω-3 to ω-6 resulted in an increase in the diffusion coefficient of linolenic acid. The diffusion coefficient of methyl oleate was higher than that of ethyl oleate, indicating an alkyl effect in the esters of fatty acids. Diffusion coefficients of free fatty acids were lower than those of their esters. Knowledge of transport properties such as diffusion coefficients in supercritical fluids is of great importance to the design of extraction, fractionation and reaction systems involving lipids using these media.