Binary diffusion coefficients of α-pinene and β-pinene in supercritical carbon dioxide

α-Pinene and β-pinene are two important structural isomers, which appear as major components of the pine tree essential oil. In this work, their binary diffusion coefficients at infinite dilution in supercritical CO2 were measured at 313.15, 323.15 and 333.15 K and pressures ranging from 12 to 20 MPa using the Capillary Peak Broadening technique. The experimental errors found for α and β isomers are 1.28 and 1.92%, respectively. The dependency on pressure, temperature, free-volume and density of carbon dioxide, and solute molar volume at its normal boiling point is examined, as well as the hydrodynamic behaviour. The applicability of several models is evaluated: Dymond, Funazukuri–Hachisu–Wakao, Funazukuri–Ishiwata–Wakao, Catchpole–King, Liu–Silva–Macedo, He–Yu–Su, and Wilke–Chang, Tyn–Calus, Lusis–Ratcliff, Reddy–Doraiswamy and Scheibel. The 1-parameter correlation of Liu–Silva–Macedo achieves the best representation; the Wilke–Chang and Scheibel equations are the best purely predictive models for α-pinene and β-pinene, respectively.