**4. New "green" extraction methods**

### **4.1 Microwave-assisted extraction**

Since 1986, microwave energy has been widely used in chemistry laboratories. Researchers have studied the potential of this unconventional energy source for synthetic, analytical, and processing applications. Currently, there are over 3000 articles documenting the use of dielectric heating in synthesis and over 1000 articles documenting its use in extraction.

Microwave-assisted extraction is a revolutionary technology that has garnered a lot of interest. It has a distinctive friction-based heating mechanism. It is inexpensive, and performs well under atmospheric conditions.

Microwave-assisted extraction achieves higher extraction yields, shorter extraction times, and improved selectivity as compared to traditional extraction techniques. This process is also less complicated and expensive than supercritical fluid extraction. However, it usually requires for more organic solvent, which makes it less environmentally friendly [26].

Recent methods of microwave-assisted extraction include microwave-assisted vacuum hydrodistillation, compressed air distillation, and microwave-assisted accelerated steam distillation [27].

### *4.1.1 Dielectric heating and fundamentals of microwave extraction*

Microwave irradiation utilizes a specific electromagnetic field frequency, similar to activated photochemical reactions. The frequency range is vast, extending from 300 MHz to 300 GHz, but only certain frequencies are authorized for industrial, scientific, and medical use. These include frequencies of 0.915 and 2.45 GHz. The magnetron, found in domestic and laboratory microwave furnaces, is a typical microwave generator for such frequencies. Industrial magnetrons can reach powers of several tens of kilowatts, while laboratory devices generally have powers of less than 1 kW. Solid-state generators have recently been introduced, which narrow the microwave generator's emission band, allowing the user to vary the system's frequency within the range of authorized industrial, scientific, and medical frequencies. This variation can play a crucial role in chemical synthesis, particularly with regard to selectivity and efficiency. However, solid-state generators operating at 2.45 GHz typically have a power rating of 100 W, which is also frequently used in medical applications [28].

Microwave-assisted extraction (MAE) is a process that removes solutes from a solid matrix into a solvent. The process involves complex phenomena such as heat transfer electromagnetic transfer, mass transfer, and momentum transfer [29].
