Mónia A. R. MARTINS1,2, Sérgio M. VILAS-BOAS1,2,3, João A. P. COUTINHO3, Olga FERREIRA1,2, Simão P. PINHO1,2
1Centro de Investigação de Montanha (CIMO), Instituto Politécnico de Bragança, Campus de Santa Apolónia, 5300-253 Bragança, Portugal
2Laboratório para a Sustentabilidade e Tecnologia em Regiões de Montanha, Instituto Politécnico de Bragança, Campus de Santa Apolónia, 5300-253 Bragança, Portugal
3CICECO – Aveiro Institute of Materials, University of Aveiro, 3810-193 Aveiro, Portugal
Essential oils are mixtures of volatile compounds isolated from animal and plants, mainly composed of terpenes. Per year, 100 000 tons of volatile essential oils, with a value of about 1 billion US$, are produced worldwide for the food, flavor and fragrance industries.
Terpenes and their oxygenated derivatives, terpenoids, have been used since Egyptian civilization and their importance in both nature and human applications is enormous. To be applied in food, perfumery, medicines, and cosmetics, pure terpenes must be extracted from natural sources. However, despite their abundance, they are usually present in low concentrations, so they tend to be expensive or even uneconomic to exploit. On the other side, when in high concentrations, terpenes and terpenoids mixtures can present undesirable properties, and then the deterpenation is imperative.
To produce compounds from natural materials, or for the deterpenation, the extraction of terpenes is of the utmost importance, being an area regarding eagerly for new technological developments. One way forward are ionic liquids (ILs), widely proposed as entrainers in the separation processes due to their thermal and chemical stability, and high-performance extraction abilities. The combination of these two classes of compounds is promising, not only to study the extraction, isolation, and purification of terpenes from essential oils, but also for their recovery from biorefineries effluents. ILs have seldom been used for the separation of terpenes and terpenoids, compounds gaining accrued relevance due to the emergence of biorefineries and for which several separation issues are far from being solved.
To exploit fully the ILs potential in the extraction and separation processes of terpenes, and to avoid a large number of experimental liquid−liquid extractions, screening methods to evaluate the best solvents are needed. The relevant information for the engineering design of extraction process is selectivity, calculated from the measurements of activity coefficients at infinite dilution.
This work combines an experimental and a quantum chemical modeling approach based on COSMO-RS, for the selection of ionic liquids to be used in the extraction and separation of terpenes. The magnitude of the interactions of selected terpenes or terpenoids, with structurally different ILs, was measured through gas–liquid chromatography. Selectivities, capacities, and solvent performance indices were calculated through the activity coefficients at infinite dilution.
The results show that ILs have potential to isolate the main components present in important essential oils. It is also shown that COSMO-RS is a useful predictive tool for the screening of ILs to find suitable candidates as entrainers in many separation problems, including those with terpenes.