Measurement and modelling of tracer diffusivities of gallic acid in liquid ethanol and in supercritical CO2 modified with ethanol

•Measurement of tracer diffusivities (D12) of gallic acid by Taylor-Aris method.•Solvents: compressed liquid ethanol and SC-CO2 modified with 16 wt% ethanol.•Experimental conditions studied: 303.15-333.15 K and 1250 bar.•Diffusive behaviour interpreted in terms of free volume and hydrodynamic theories.•Accurate modelling with DHB, TLSMd and Magalhães et al. correlations.

The tracer diffusion coefficients, D12, of gallic acid in liquid ethanol and in supercritical carbon dioxide (SC-CO2) modified with 16 mol.% ethanol were measured using the chromatographic peak broadening technique of Taylor-Aris. The diffusivity in ethanol ranged 0.485 × 10−5−0.905 × 10−5cm2·s−1 (303.15-333.15 K and 1-100 bar) and in SC-CO2/ethanol 3.256 × 10−5−4.978 × 10−5cm2⋅s−1 (313.15-333.15 K and 150-250 bar). The dependencies of D12 upon temperature, pressure and Stokes-Einstein coordinates were examined in detail. With respect to modelling, lower deviations were achieved in both systems by: four 2-parameter correlations of Magalhães et al. (error 0.9-3.0%;); the 1-parameter TLSMd model (5.8% and 2.9% of error); and the 2-parameter Dymmond-Hilbrand-Batchinski (DHB) expressions (5.7% and 1.6% of error). The Wilke-Chang correlation cannot be applicable, due to consistent overpredictions of 133.0% (gallic acid/ethanol) and 114.0 % (gallic acid/SC-CO2/ethanol).

Graphical abstractDownload high-res image (105KB)Download full-size image