Measurements of infinite dilution binary diffusion coefficient and partial molar volume of piperine in supercritical carbon dioxide

Piperine is one of key components of peppers, and supercritical fluid extraction has been applied to isolate such heat-sensitive natural substances. The diffusion coefficient (D₁₂) of piperine in supercritical (sc) carbon dioxide is essential for the process design, but no data are available in the literature. In the present study the infinite dilution binary diffusion coefficient (D₁₂) of piperine in scCO₂ was measured at temperatures from 308.2 K to 343.2 K and at pressures from 12 MPa to 30 MPa by the chromatographic impulse response method, and those in methanol, ethanol, 1-propanol and 1-butanol were measured at atmospheric pressure and at temperatures from 303.2 K to 343.2 K by the Taylor dispersion method. The hydrodynamic equation, D₁₂/T =αη^β, T is the temperature and η is the CO₂ and alcohol viscosity, was found to well represent all of the D₁₂ values measured in both scCO₂ and atmospheric liquid alcohols, with a single set of two constants α = 3.655 × 10^–15 kg^-βm^β+2s^β-1K^-1 and β = -0.9145 with the average absolute relative deviation of 4.41 % and maximum deviation of 14.0 % with 72 measurement conditions. Partial molar volumes(PMV) of piperine determined from the retention factors were negative and decreased substantially closer to the CO₂ critical point, as observed for various solutes in scCO₂ reported in the literature. To evaluate the accuracy of the determined PMV values new reliable models and reliable solubility data are needed to describe the PMV values, especially near the critical region.