Extraction of Natural Products Using Near-Critical Solvents

This study describes a technology for extracting natural products with compressed gaseous solvents or liquified gases. The principle advantage of these techniques is that they leave the products uncontaminated. The term "near-critical" is used because the temperature at which the extraction operations are carried out is close to the critical temperature of the solvent. Commercial applications are mainly in the food, beverage and perfumery industries where carbon dioxide is usually used due to its health and safety characteristics. Uses include extraction of hop essences from hops, extraction of essences from herbs and spices, and decaffeination of tea and coffee. Consumer resistance to the use of synthetic organic solvents in food processing and the banning of other solvents due to their effect on the ozone layer mean that the use of near-critical CO2 is increasing and will continue to increase. This book describes in detail the near-critical extraction processes in use today in a practical way with reference to background theory and relevant market trends. Other ways in which solutions in near-critical solvents are useful, for example as reaction and recrystallization media, are also described.