Pyrethrin exraction from pyrethrum flowers using carbon dioxide

Extractions of pyrethrins from ground pyrethrum flowers, using supercritical carbon dioxide as the solvent, were carried out in a semi-batch pilot plant (extraction volume: 200 ml). Extracts were very similar to those obtained by hexane Soxhlet extraction, except that the ratio of pyrethrins I to pyrethrins II was lower (1.58 instead of 1.79), and less pigments were present. At 40 °C, the amount of crude pyrethrum extract was found to be independent of pressure above 100 bar. Pyrethrin content in the crude extract was shown to be higher at 20 °C than at 40 °C and decreased with decrease in pressure. Effect of particle size was investigated and the biggest particles yielded a lower quantity of extract and contained less pyrethrin. Extract obtained from small particles, at 40 °C, contained more undesired product. We also established that the seed part of the whole flower contained more crude extract and pyrethrins than the flower part. Pre-treatment, by preliminary SC-CO2 washing of unground flowers, improved the quality of SC-CO2 extract, because a part of the undesired waxes was eliminated by this pre-treatment.