(325f) Semi-Continuous Fractionation of Bioactive Essential Oils with Supercritical Carbon Dioxide. Experiments, Modeling and Separation of Stereoisomers

In this work we study the fractionation of two essential oils with biocidal activity (Salvia officinalis and Tagetes minuta) with supercritical carbon dioxide in a semi-continuous single stage apparatus, as a green alternative to traditional methods such as solvent extraction and vacuum distillation. Essays were performed at 313 K and 80 bar in order to selectively remove the hydrocarbon monoterpenes and obtain an  oxygenated and sesquiterpene enriched fraction. Succesive extracts were collected during the process and their composition determined by gas chromatography. From these results, the feasibility of a single stage deterpenation process with high purity and recovery of products is discussed. The systems [carbon dioxide + essential oil] are modeled as mixtures of pseudocomponents and their behavior predicted using the group contribution equation of state (GC-EOS). With this thermodynamic model, the fractionation process is simulated using the mathematical background of batch distillation (Rayleigh equation). The correlation between the simulation and the experimental data is improved when a composition-dependent relative volatility is considered instead of only a pressure and temperature-dependent one.

Separation of stereoisomers is also investigated. Although no selectivity is observed between optical isomers (a- and b-thujone in Salvia oil), this is not the case for the stereoisomer Z- and E-ocimenone from Tagetes oil. These components exhibit an important degree of separation, which is an interesting feature considering that the bioactivity of stereoisomers is usually different.