Supercritical CO2 extraction of Eucalyptus leaves oil and comparison with Soxhlet extraction and hydro-distillation methods

Oils were extracted from the leaves of Eucalyptus loxophleba ssp. lissophloia, also known as oil Mallee, using a laboratory scale supercritical fluid extraction (SFE) system using CO2. The effect of temperature (40-80 °C), pressure (10-50 MPa) and extraction time (30-150 min) on the oil yield was investigated using a central composite design method to determine the significance and interactions of these parameters. The results showed that pressure had the most significant enhancing effect on the oil yield, while temperature and time showed a lesser impact. There was also pronounced interaction between temperature and pressure and their combined effect on the yield was such that the oil yield increased with increasing temperature at high pressures but decreased at low pressures. For comparison, the Eucalyptus leaves were also extracted with Soxhlet extraction, using two different solvents, and hydro-distillation methods. In the Soxhlet extraction, the solvent type had a more significant effect on the oil yield than the extraction time. Overall, the Soxhlet extraction produced the highest oil yield while hydro-distillation the lowest among the three methods. The SFE yield was up to 4.78%, comparable in magnitude to that of the hexane Soxhlet extraction of 7.9%. The chemical compositions of the extracted oils were analysed using a gas chromatography-mass spectrometer (GC-MS). The dominant component identified in the Eucalyptus oil was 1,8-cineole. The chemical compositions of the extracts were quite different for the three extraction methods. The oil extracted by hydro-distillation contained only volatile compounds while the oil from the SFE and Soxhlet contained both volatile and higher molecular weight compounds. The effect of the addition of ethanol as a modifier at concentrations from 5 w% to 15 w% on the supercritical fluid extraction of Eucalyptus leaves oil was also investigated. The ethanol addition was shown to increase the efficiency of oil extraction from Eucalyptus leaves and the oil yield increased with increasing ethanol concentrations.