Diffusion of quercetin in compressed liquid ethyl acetate and ethanol

Abstract

Supercritical fluids are alternatives to conventional harmful organic compounds. In the case of supercritical fluid extraction, CO2 is the most common solvent and can be advantageously modified with small contents of co-solvents like ethanol and ethyl acetate. The rigorous estimation of the tracer diffusion coefficients (D12) of solutes in supercritical mixtures (CO2 + co-solvent) requires their individual D12 values in pure CO2 and pure co-solvent under the same operating conditions. This essay focuses the diffusivity of quercetin (solute) in two compressed liquid co-solvents (ethanol and ethyl acetate). Quercetin is a natural compound possessing a wide variety of bioactive properties, used as one of the most noticeable dietary antioxidants. The tracer diffusivity measurements are accomplished by the chromatographic peak broadening technique over 303.15–333.15 K and 1–150 bar. The diffusion coefficients lie between 0.414 × 10−5and 0.813 × 10−5 cm2s−1 in ethanol, and between 1.06 × 10−5 and 1.69 × 10−5 cm2s−1 in ethyl acetate. Influence of temperature, pressure and hydrodynamic coordinates is analyzed and discussed based on the most relevant transport theories. Modeling is also carried out with eleven models from the literature and demonstrated the unreliability of predicting equations in opposition to the very good correlations available to fit D12 data. The influence of the accurate estimation of auxiliary properties (like solvent volume and viscosity) upon the calculated tracer diffusivities is also assessed, being possible to detect D12 differences as high as ca. 70 %.