Enhancing natural product extraction and mass transfer using selective microwave heating

Abstract

This study uses a combination of empirical observations and an analysis of mass transfer behaviour to yield new insights into the mechanism of microwave assisted extraction. Enhancements in extraction rate and yield were observed experimentally compared with conventional extraction at temperatures in excess of 50°C, however at lower temperatures there was no observable difference between the two processes. A step-change in extract yield between microwave and conventional processes was shown to be caused by selective heating. A temperature gradient of the order of 1 o C is sufficient to reduce the water chemical potential within the cell structure, which changes the osmotic potential such that internal cell pressures can increase to the point where disruption occurs. This paper demonstrates the need to operate microwave extraction processes at a temperature that enables selective heating, and a newly-proposed mass transfer phenomenon that could have wider positive implications for extraction and leaching processes.2

Effect of microwave power on drying kinetics, structure, color, and antioxidant activities of corncob

“…For this reason, microwave‐dried products are associated with a severe reduction in the hardness of drying products. Similar lowering of the textural attributes with MWD was observed for microwave‐dried durian chips, longan fruit, and blueberry fruits (Apinyavisit, Nathakaranakule, Soponronnarit, & Mittal, ; Lee et al, ; Paengkanya, Soponronnarit, & Nathakaranakule, ; Zielinska & Michalska, ). Paengkanya et al () attributed the decrease in hardness and increase in fracturability of durian chips with MWD to the formation of porous structure and a high percentage of void area fraction at high microwave power.…”

Evaluation of Microwave Intensified Vanadium Bearing-High Carbonaceous Shale Acid Extraction Process

“…With 10 wt % CaF 2 added for 60.0 min, the microwave heating significantly promoted the V leaching rate to about 15% higher than that in CH, while, with 0.04 wt % CaF 2 used for 240.0 min, the microwave heating significantly promoted the V leaching rate to about 17% higher than that in CH. As the references reported [20], the activation energy as well as chemical reaction difficulty could be reduced with CaF 2 added. Thus, the leaching system of carbonaceous shale required for MH was also confirmed.…”

“…As the references reported [20], the activation energy as well as chemical reaction difficulty could be reduced with CaF2 added. Thus, the leaching system of carbonaceous shale required for MH was also confirmed.…”

“…Meanwhile, the V leaching efficiency was improved by only 10% under the optimized condition, for which it was not so significant in high-cost terms. Another problem was the explanation about how this consequence was realized was not convincing enough, and the interrelation in it was also not figured out [19][20][21][22].…”

Microwave pyrolysis of biomass within a liquid medium

“…The energy requirements are evidently higher compared to utilising n-hexane (~2 kJ/g), which is to be somewhat expected given that water absorbs microwave energy as well as biomass. As the temperature of water increases the dielectric loss factor decreases [22], and Lee et al [23] have demonstrated that selective heating of biomass can take place within water during microwave heating at temperatures above 50°C due to this phenomenon. The water temperature reached 100°C during the pyrolysis process as there was evidence of water boiling, so it is likely that selective heating did indeed take place and that enough microwave energy was absorbed by the biomass to allow the centre of the particle to reach temperatures sufficient to induce pyrolysis.…”