Radio Frequency Enhanced Extraction of an Anti-Cancer Compound from Porous Media

by Izadifar, Mohammad

Abstract (Summary)
Podophyllotoxin is a natural medicine possessing an outstanding anti-tumour activity. It can be extracted from the rhizome of Podophillum peltatum (American Podophyllum). Volumetric heating of a packed bed of particles including solvent during the extraction can eliminate the solvent pre-heating time and provide uniform and quick heating of the bed. RF-assisted extraction has a potential to be a promising extraction alternative over conventional methods. The characterization and assessment of RF-assisted extraction of podophyllotoxin is crucial. Thermal properties including specific heat capacity, thermal conductivity, and thermal diffusivity of a packed bed of P. peltatum with and without ethanol solutions were determined and the associated multiples regression equations were obtained for the purpose of thermal analysis of RF-assisted packed bed extraction process and related modeling investigations.

The dielectric properties of the packed bed of rhizome particles 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 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 those 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.

A RF-transparent batch reactor was made of glass filled Teflon and the extraction kinetics of podophyllotoxin was characterized. The effects of temperature, ethanol volumetric concentration, solid/liquid ratio, RF heating and particle moisture content on the extraction rate and yield of podophyllotoxin were investigated at different extraction conditions. A generalized diffusion mathematical model taking into account three major particle geometries was developed and coupled with genetic algorithm for determination of effective diffusivity and partition coefficient through an inverse simulation approach. The approach was first verified by reported experimental data of andrographolide extraction followed by determining the effective diffusivity and partition coefficient of podophyllotoxin for different conditions. The optimum batch extraction condition was achieved with 30% ethanol-water solution at 53¢XC. A prototype was developed for RF-assisted extraction of podophyllotoxin using two optical and RF-transparent reactors with horizontal and vertical orientations. Applying the optimum conditions obtained from batch experiments, the potential of RF heating for providing a uniform temperature in the packed bed was evaluated. The effect of solvent dielectric loss factor on uniform RF heating was investigated and the chemical effect of NaCl used for increasing dielectric loss factor of the solvent on podophyllotoxin was assessed. The horizontal packed bed demonstrated a large temperature gradient across the thickness of the bed during RF heating; however, a uniform RF heating was achieved when the vertical packed bed reactor was used for RF-assisted extraction of podophyllotoxin. The concentration of 2.5 g NaCl/L of the solvent at the temperature controller set point of 40aC provided a relatively good uniform temperature of 50aC within the bed. Evaluating three flow rates of 130, 160 and 200 ml/min for the solvent of 30% ethanol with 2.5 g NaCl/L indicated that the flow rate of 160 ml/min could provide better temperature overlap of four positions of the bed height.

Bibliographical Information:

Advisor:Oon-Doo Baik; Valérie Orsat; Huqing Guo; Lope J. Tabil; Gap-Soo Chang; Venkatesh Meda

School:University of Saskatchewan

School Location:Canada - Saskatchewan

Source Type:Master's Thesis

Keywords:dielectric properties effective diffusivity modeling packed bed extraction podophyllotoxin solvent thermal radio frequency


Date of Publication:03/09/2009

© 2009 All Rights Reserved.