Supercritical leaching applications

In many situations, ultrasound-assisted leaching is an expeditious, inexpensive, efficient alternative to conventional extraction techniques and, in some cases, even to supercritical fluid and microwave-assisted extraction. A number of applications to both organic and inorganic analytes in a wide variety of samples exist. Most are conducted by hand. As with automatic extractions, applications involving continuous systems are still very scant and hence one possible target for future research. 

Ultrasound-assisted leaching has also been used to extract natural compounds such as vitamins A, D and E from feeds [57], paclitaxel and related taxoids from leaf tissue of Taxus [58], opiates from hair samples [59] and antioxidants from rosemary [60]. Ultrasounds have so far had much more restricted application in this field than in the previous ones, possibly as a result of the technique being at a disadvantage with respect to alternatives such as microwave-assisted extraction [57] or supercritical CO, extraction [60]. 

There has been an increasing amount of interest in the use of supercritical fluids (SCF) for leaching or extracting compounds from solids or liquids in the food and pharmaceutical industries because of the nontoxic nature of the primary SCF—carbon dioxide. In this section we will briefly consider the properties of SCFs that make them interesting for extraction. Then a typical process for SCF extraction will be explored and several applications will be discussed. 

Potentially, these advantages allow for high reaction rates, high rates of transport of substrate over the catalyst, and low leaching of both the catalyst and the IL. Besides, the favorable properties of CO2 in terms of very low toxicology, few environmental hazards, process safety, and low material costs make it especially attractive for green and sustainable synthetic processes. There would appear to be excellent potential for the application of SILP systems with supercritical flow in a variety of different catalytic reactions. 

---