MODELING OF SUBCRITICAL WATER EXTRACTION PROCESS OF MEDICINAL PLANTS

In this study، the extraction of Zataria multiflora Boiss essential oil with subcritical water was investigated. The most and the most important part of Z. multiflora essential oil was thymol. One two-phase mathematical model was employed for simulating of extraction yield at different operating conditions in packed bed. Three important mass transfer steps consist of diffusion of solutes through particles، convection of solutes through a layer of stagnant fluid outside particles and elution of solute by the flowing bulk of fluid were considered. The unsteady state mass balance of the solute in solid and subcritical water phases led to two partial differential equations that were solved numerically using a linear equilibrium relationship. This model consists of three parameters mass transfer coefficient، axial dispersion coefficient and effective diffusivity. The last parameter was selected to be the model tuning parameter and the others were estimated by existed experimental correlations. The effective diffusivity and mean relative error of data for flow rates 1، 2 and 4 ml/min were 5×10-12 m2/s، 0. 073، 0. 180 and 0. 294 respectively.