Heat transfer modeling of radio frequency assisted packed bed extraction of an anticancer agent (podophyllotoxin)

Podophyllotoxin is considered as an outstanding anti-tumor agent against lung cancer which is commercially extracted by the percolation of warm ethanol through packed beds of dried rhizomes of Podophyllum emodi or Podophyllum peltatum. Radio frequency (RF) heating can be used for uniform heating of the packed bed during the extraction. Based on local volume averaging (LVA) and local thermal equilibrium (LTE), a mathematical model with variable properties was developed for transient heat transfer during RF-assisted packed bed extraction of podophyllotoxin. The validity of LVA and LTE was assessed by evaluating the length scale, time scale, and convective constraint. A control function was included in the model to take into account the effect of a temperature controller functioning during the actual RF-assisted packed bed extraction. For a vertical packed bed reactor subjected to RF heating, two governing equations associated with the packed bed and the solvent phase at the top of the bed were numerically solved using implicit-finite difference and Gauss–Seidel methods. The simulation results had a good agreement with the experimental data. Heat transfer simulation was performed for different flow rates of ethanol/water solution with different dielectric properties during the RF-assisted packed bed extraction process.