Investigation of thermodynamic and mass transfer properties in supercritical fluid extraction

ABSTRACT Supercritical fluids are effective solvents due to their liquid-like densities and solvation power, and gas-like viscosities and diffusivities. Separation processes based on supercritical fluids are used widely as alternative processes to conventional separation processes, since the solvation power of supercritical fluids vary with temperature and pressure. In supercritical separation processes, carbon dioxide is the most preferred supercritical fluid, because it is nonflammable, nontoxic, readily available and inexpensive, and has a low critical temperature and a moderate critical pressure. In applications regarding the supercritical fluid extraction, reliable solubility and mass transfer models that will allow the determination of optimum operating conditions are needed. This is especially important in the feasibility study of the related process. Although the solubility determination methods are available in literature, the mass transfer studies are still limited. In this work, the essential oils were extracted from lavender flowers obtained from Aydın region using supercritical CO2. In the first stage, the vapor-liquid equilibria and solubility data of a-pinene, limonene, fenchone and camphor, which are the major components of lavender flower essential oil, were taken in supercritical carbon dioxide as a function of pressure and temperature using the static method. Experiments were carried out in the temperature range of 313-333K and in the pressure range of 6-13 MPa. Experimental results were correlated by the Peng-Robinson equation of state using conventional mixing rules with one interaction parameter. In the second stage, the essential oils were extracted from lavender flowers. In the experiments, the effects of solvent flow rate, temperature, pressure and particle size on the extraction rate were investigated. The mass transfer behaviour of extraction process was based on the Simplified Shrinking-Core mass transfer model using the data of process. From the experimental data, it was found that the effective parameter during the extraction was the solubility. The intraparticle diffusion coefficient (effective diffusivity, De=1.2 10"11) was used as the only adjustable parameter in the model solution. Keywords : Supercritical fluid extraction, Solubility, Phase behaviour, Modelling, Peng-Robinson equation of state