Oakmoss (Evernia prunastri L. Ach.), along with other tree mosses, is among the most voluminous botanicals which are solvent extracted for use in perfumes. These extracts are manufactured with heavy labor costs. Large quantities of solvent have to be circulated and evaporated. This requires high energy costs. Therefore, there is a place for a quicker continuous automated process.
Traditional Batch Extraction Processes
Despite the fact that each company has a special method of oakmoss extraction, the basis is similar every where. The extraction units are generally separated in two parts: (I) lichen preparation; and (II) solvent extraction linked to solvent evaporation. The moisture content of the stored lichen is around 12%. Before solvent extraction, the lichen is humidified. It can he sprayed with hot water and kept wet overnight as fermentation takes place. The temperature tends to increase and can reach 40°C to 50°C in the heart of the bulk. Today, there is a tendency to simply sprinkle oakmoss lichen with water at room temperature. This prevents dust production in the workshop where the material is left to stand for two or three hours. Moreover, such a moistening restores a permeability to the cell walls which makes the solvent extraction easier. Extraction is still mostly done with benzene affording concretes in the 4-5% yields. The replacement of benzene by hexane results in lower yields (between 1.5 and 3%). Extraction with ethyl alcohol allows the yields to rise to 15%. However, in common industrial practice, this solvent is not used alone but in conjunction with benzene or hexane. Extraction temperature varies from 40°C to the solvent boiling point. The total duration for traditional solvent extraction often exceeds 12 hours.
Industrial Continuous Extraction Processes
Preliminary experiments, performed with a laboratory apparatus, have shown that the product obtained in continuous extraction conditions directly from the dry oakmoss lacks the features of the classical oakmoss concretes.