Determination of Mass Transfer Coefficients on the Obtaining of Caffeine from Tea Stalk by Supercritical Carbon Dioxide With andWithout Ethanol

摘要

This study deals determination of mass transfer coefficients on the obtaining of caffeine from tea stalk wastes by supercritical carbon dioxide extraction. Tea stalk wastes of Turkish tea plants that have no economical value were employed as raw material throughout determination of mass transfer experiments. Mass transfer coefficients were calculated at the caffeine extraction experiments with and without cosolvent. For this purpose, ethanol was pumped to the supercritical carbon dioxide extraction system as a cosolvent. In these experimental studies, extraction procedures were repeated at different temperature by keeping optimum conditions at specified the previous study. Optimized parameters in the caffeine leaching from tea stalks were fixed throughout the study such as pressure of 250 bar, the average particle size of 0.202 mm, flow rate of 10 g/min (5.23 g ethanol/100 g . Correlation was obtained from retention time in order to calculate mass transfer coefficient. Using the correlation, coefficients were calculated in supercritical extraction with and without ethanol at 333 K temperature, , , respectively. Consequently, it has been observed that mass transfer coefficient is increased approximately 2.4 times when ethanol is utilized the amount of 5% besides of 95% . On the other hand, more caffeine can be extracted in a shorter period by means of ethanol pumping as cosolvent.