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Extraction kinetics of polyphenols and flavonoids from plant material and their separation and concentration by nanofiltration were investigated. The kinetics experiments were carried out with Cotinus coggygria. The influence of the extraction solvent on the extraction rate was defined. Four different extraction solvents or mixtures were applied -methanol, azeotropic ethanol, 50/50 ethanol/water mixture, and pure water. The optimum extraction rate of flavonoids and polyphenols was achieved by using 50 % ethanol as a solvent for extraction. This solvent mixture was used for generating extracts for the nanofiltration experiments. Organic solvent nanofiltration membranes from DuraMem TM series with different pore sizes (200, 300 500 and 900 Da) were tested in dead-end and cross-flow filtration systems. Flux and rejection data were obtained for every membrane type. Very good separation and respectively concentration of the extracted useful compounds was achieved (rejection for polyphenols and flavonoids is 91 and 93 %, respectively). During a feed/extract concentration experiment, the constant polyphenols and flavonoids rejection was measured. The results suggest that the nanofiltration technology could be combined successfully with solid-liquid extraction for natural sourced valuable compounds enrichment.

The current work is concerned with obtaining a new empirical model for the time-variable effective diffusion coefficient (D eff ) by extraction from plant materials. It has been applied for describing a solid liquid extraction from Cotinus coggygria and compared with experimentally obtained extraction kinetics. The experiments have been performed by changing the liquid−solid ratio (ξ = 0.01, 0.02, and 0.03 m 3 kg −1 ), temperature (20, 40, and 50 °C), and extraction solvents (water, 50% ethanol in water, and 70% ethanol in water). A nonlinear seven-parametric model for D eff is obtained in order to represent the influence of those parameters on the extraction process and D eff , respectively. The parameters of the model are obtained by a nonlinear regression of D eff values calculated using the method of regular regime. All experimental conditions have been taken into consideration. A very good coincidence between experimental and empirically obtained data has been found. This is a proof for the ability of the function to describe an extraction process. It can be used to estimate and control the process.

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