Experimental and theoretical analysis of the diffusion behavior of chromium(III) acetylacetonate in supercritical CO2

Abstract

The tracer diffusion coefficients, D-12, of solutes in supercritical carbon dioxide (SC-CO2), modified or not with cosolvents, are necessary for industrial and research applications. In this study, the determination and analysis of D-12 values of chromium(III) acetylacetonate in SC-CO2 are presented. The measurements were carried out by the chromatographic impulse response (CIR) method from 308.15 to 333.15 K at pressures from 125 to 250 bar, and yield diffusivities between 0.570 x 10(-4) and 1.529 x 10(-4)cm(2) . s(-1) The experimental trends of D-12 with temperature, pressure, density, and Stokes-Einstein coordinates are also presented. Eleven equations were evaluated for modeling the new data, and the best results were achieved using the semi-empirical correlations of Magalhaes et al. (error of 1.95% and 1.90%), the universal model of Lito et al. (2.01%), and the predictive modified Stokes-Einstein equation (3.16%) and Vaz et al. expression (3.27%). Finally, a comparison between the diffusivities of this work and those reported in the literature for other metal acetylacetonates (Co(acac)(3), Cr(acac)(3), Pd(acac)(2) and Pt(acac)(2)) was accomplished, being possible to conclude that the correct interpretation of the diffusive phenomenon of these systems requires not only the molecular weight but also solute diameter. (C) 2016 Elsevier B.V. All rights reserved.