Radio frequency-assisted extraction of podophyllotoxin: Prototyping of packed bed extraction reactors and experimental observations

Radio frequency (RF) heating was used for uniform and noncontact heating of a packed bed of rhizome of Podophyllum peltatum while an ethanol/water solution was continuously flowing through the bed during solvent extraction of podophyllotoxin. RF-assisted packed bed extraction was carried out at 27.12 MHz for five solvent flow rates and three levels of dielectric loss factor of ethanol/water solution provided by three fractions of sodium chloride in the solvent. The performances of RF heating on horizontally and vertically oriented packed bed reactor were assessed. RF heating provided a very small temperature gradient across the height of the vertically oriented packed bed with a thickness of 10 cm at the stationary state of the bed; however, the temperature gradient across the horizontally oriented packed bed was significant. A sodium chloride concentration of 2.5 g/L in the solvent at a flow rate of 160 ml/min provided a relatively uniform temperature of 50 °C across the height of the bed during the extraction process. The constant rate and falling rate period of extraction took place within 2 and 8 min, respectively.