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 8C, 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 8C than at 40 8C 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 8C, 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. # 2002 Elsevier Science B.V. All rights reserved.