Analysis of ternary LLE data on increasing limonene solubility in water using alcohol as cosolvent

The essential oil (EO) quality can be enhanced by increasing the concentration of oxygenated compounds. This can be achieved by extracting terpenes from the oil. As terpenes are insoluble in water, alcohols are often added to increase the solubility. It is important to find a suitable co-solvent to increase the efficiency of terpene extraction using water; this can be indicated by the miscibility (one phase) region in the water–cosolvent–terpene ternary diagram. In this work, three alcohols, i.e., methanol, ethanol and propanol, were selected as the cosolvents. The mutual solubility of water– methanol/ethanol/propanol–limonene is analysed through the phase equilibria generated from literature data and predicted by the Conductor-like Screening Model (COSMO-RS) programme. COSMO-RS was able to generate accurate LLE data at equilibrium based on the reported experimental feed compositions. The extraction efficiency of using an alcohol increased following the order of methanol<ethanol<propanol according to the increment of the respective miscibility region. At equilibrium, the composition of alcohol is higher in the aqueous phase than that in the organic phase, indicating the affinity of alcohol towards water and the suitability of using alcohol as the co-solvent. As observed, in methanol, its small methyl group increased its solubility in water, but reduce the methanol solubility in limonene (terpene), thus reducing also the miscibility region. Propanol was found to be the most suitable alcohol, and this encourages us for further studies to find other green cosolvents.