Dielectric properties of a packed bed of the rhizome of P. Peltatum with an ethanol/water solution for radio frequency-assisted extraction of podophyllotoxin

The dielectric properties of a packed bed of the rhizome particles of Podophyllum peltatum and an ethanol/water solution were measured from 10 to 30 MHz using a precision LCR meter and a liquid test fixture. The effects of temperature, particle moisture content, volumetric concentration of ethanol and bed porosity on the dielectric constant, dielectric loss factor and power penetration depth were investigated. The dielectric constant of ethanol decreased with temperature but the effect of frequency was not significant. The dielectric constant of packed beds with 100% and 70% ethanol increased with the moisture content. For a packed bed with 30% ethanol, the dielectric constant was not significantly affected by particle moisture content. Frequency and temperature had no significant effect on the dielectric constant of the packed bed. The dielectric loss factor significantly increased with the particle moisture content for the beds with 100% and 70% ethanol but not with 30% ethanol. The dielectric loss factor was proportional to temperature directly and to frequency inversely. With 30% ethanol (and therefore 70% water) the dielectric loss factor of the bed dramatically increased compared to 70% and 100% ethanol. Porosity had a significant effect on the dielectric constant but not on the dielectric loss factor. The power penetration depth of a packed bed with 100% ethanol was significantly larger than that of the packed bed with 30% and 70% ethanol. Empirical regression equations were developed for simulation and design of an RF-assisted packed bed extraction of podophyllotoxin.