Microwave assisted process intensification and kinetic modelling: Extraction of camptothecin from Nothapodytes nimmoniana plant

Process intensification of natural products extraction is possible through assistance of microwaves, ultrasound, high pressure, enzyme pretreatments and supercritical fluids. In the present paper microwave-assisted process intensification is investigated for the extraction of camptothecin (CPT) from Nothapodytes nimmoniana plant. CPT is an industrial raw material for the production of anticancer agents topotecan and irinotecan and semisynthetic analogs of CPT. Nothapodytes nimmoniana is found wild in India and is a prime source for CPT. Effects of various process factors such as stirring, solid to liquid ratio, microwave power, irradiation time and particle size on extraction kinetics have been studied. The results showed that stirring, microwave power and the temperature had a significant effect on extraction rate and yields of camptothecin. Overall process intensification has been achieved with extraction yield of 0.41% w/w of CPT, an efficiency of about 97% in very short time of just 2 min as against 6 h by classical string extraction method. Scanning electron microscopy (SEM) analysis of the spent plant material was performed to assess the effect of microwaves and found complete cell disruption has happened. This cell disruption and associated enhancement in mass transfer could be the prime reason for the process intensification. An attempt has been made to fit the extraction kinetics data with different kinetic models such as second order rate model, power law model and two site kinetic models. The second order rate model appears to be the best fit to explain the microwave assisted kinetics.