Diffusion coefficients of zirconium (IV) acetylacetonate: Measurements and correlation in both pressurized liquid and supercritical fluid

Abstract

Limited data exist on the diffusion coefficient of a solute in both pressurized and supercritical fluids, despite its crucial role as an essential transport property. In this study, we present the first-ever determined diffusion coefficients of zirconium acetylacetonate (Zr(acac)4) in two distinct fluids: pressurized ethanol and supercritical carbon dioxide. Using the Taylor dispersion method, we measured the diffusion coefficients in pressurized ethanol at temperatures between 298.15 and 333.15 K, reaching pressures up to 30.00 MPa. In supercritical carbon dioxide, we employed the chromatographic impulse response (CIR) method, conducting the experiments at temperatures from 308.15 to 343.15 K and pressures up to 35.00 MPa. Remarkably, predissolving Zr(acac)4 in supercritical carbon dioxide and injecting it into the diffusion column enabled the accurate determination of diffusion coefficients in supercritical carbon dioxide, which were approximately an order of magnitude higher than those in pressurized ethanol. Our investigation revealed diffusion activation energies, ranging from 26.7 to 10.2 kJ mol−1 at pressures between 10.00 and 30.00 MPa in supercritical carbon dioxide and from 20.4 to 19.6 kJ mol−1 at pressures between 20.00 and 30.00 MPa in pressurized ethanol. All diffusion data, in both liquid and supercritical states, can be effectively correlated using the equation Sc = ∑n=03(Cnηn) with 2 parameters and 4 adjustable coefficients. This correlation demonstrates high accuracy, with an average absolute relative deviation (AARD) of 3.7 % over a wide fluid viscosity range of 21.0 to 1305.0 μPa s. Additionally, it is observed that all diffusion data can also be well-fitted with the equation D12/T = αηβ with 2 parameters and 2 adjustable coefficients, achieving an AARD of 3.5 %.