Comparison of conventional and microwave-assisted distillation of essential oil from Pogostemon cablin leaves: Analysis and modelling of heat and mass transfer

Leaves of Pogostemon cablin were subjected to microwave-assisted hydrodistillation (MAHD) and solvent-free microwave extraction (SFME), respectively. A comparison was made between MAHD and SFME with the conventional hydrodistillation (HD) method in terms of effectiveness in the extraction of essential oil (EO). The microwave-assisted extraction methods offer important advantages over conventional alternatives, viz. shorter extraction times (66 min for MAHD and 45 min for SFME vs. 417 min for HD); almost equal yields (2.177% for MAHD and 2.374% for SFME vs. 2.622% for HD); lower relative electric consumption (1.509 kWh/g EO for MAHD and 0.417 kWh/g EO for SFME vs. 13.821 kWh/g EO for HD); and lower relative amounts of CO₂ emissions (1.207 kg CO₂/g EO for MAHD and 0.334 kg CO₂/g EO for SFME vs. 11.056 kg CO₂/g EO for HD). A mathematical model based on heat and mass transfer fundamentals is applied to correlate the experimental data. Higher yield results from higher extraction rates by microwaves and could be due to a synergy of two transfer phenomena: heat and mass acting in the same way. The results of this study suggest that MAHD and SFME can be termed as green technologies because of their less energy requirements per gram of essential oil extraction.