Extraction solvent
Solvent extraction method is used to extract non-volatile essential oils [44]. The plant materials are placed in a fresh solvent and is removed non-volatile essential oils of plants. The solvent becomes more enriched with the oil compounds of plants until extraction is complete, followed by filtration. Finally, the filtrate is concentrated by solvent evaporation and a thick residue called ”concentrate” is prepared. then the concentrate mixed with alcohol to extract the oil compounds. The alcohol absorbs oil compounds. Followed distillation of alcohol at low temperatures, the concentrated compound is obtained, which is known as the ”absolute” and used in perfumery. Solvents used in this method should have a low boiling point, be free of odors and impurities, and should also be inert to oil compositions [4, 45, 46]. Different solvents are used in this method such as: acetone, hexane, petroleum ether, methanol, or ethanol [47, 48, 49].
The most important advantage of this method is the appropriate and low temperature (50 oC). Solvent extraction method has disadvantages such as solvent toxicity in some cases, high solvent consumption, flammability of solvents and the most important factor is the solvent remaining in the final product [22]. Sara Lago [50] is reported improved concentration of citrus essential oil by solvent extraction with acetate ionic liquids. The results showed a great performance of these acetate-based ionic liquids. Extraction essential oil of dried sage (Salvia officinalis) using ethanol–water mixtures have been studied by Nicola E.Durling [51]. This gave an extract including 6.9% rosmarinic acid (55% recovery), 10.6% carnosic compounds (75% recovery) and 7.3% essential oil (42% recovery).