Graduate Thesis Or Dissertation
 

Microwave extraction of peppermint oil and comparison to the currentpractice of steam extraction

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/pv63g279f

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  • The increase of diesel fuels and natural gas has increased the energy cost of the mint oil extraction industry in the Willamette Valley. In this study the energy evaluation of a distillation facility in Oregon is considered. Solvent free microwave extraction of peppermint oil is introduced as a new technique to obtain the essential oils. Technology from approximately fifty years ago was the common characteristic of all the farms visited at the beginning of this research. Three sets of data from the Setniker farm were collected; information from all the possible sample points were recorded to then evaluate the energy cost of pound of oil extracted. It was found that on average the energy usage cost is $1.26 per pound of oil obtained; the maximum fraction of oil recovered was reported to be 20% of all the oil available from the plant. Suggestions to improve the current setup without major modifications were done based on the findings of this part of this work. Solvent free microwave extraction has been used as an analytical tool; the advantages and disadvantages on extraction of essential oils, specifically on the peppermint oil extraction, were investigated in the second objective of this work. Dry peppermint hay was placed in a 100 mL distillation flask. Three different power settings were explored, 1120 W, 649W and 518W; the extraction time was the other variable investigated. Four combinations of the power applied to the plant material were also studied, 1120W-649W and 1120-518W, starting at 1.5 minutes and 2 minutes on the higher power setting and varying the lower power level. A Galanz WP700L17-8 (2.45 GHz) microwave was modified to direct the vapors to a condenser and which then allowed the liquids to be collected and then analyzed. The microwave cavity was modified with consideration of all safety precautions. The composition of the oil extracted was analyzed by gas chromatography. With the modest optimization of process performed, roughly three times more oil was extracted compared to the traditional process at an energy cost of approximately 3% lower than the energy cost from the steam distillation facilities. The quality of the oil varies in some of its major components. One example is menthol which was 4% less than the ideal standard for peppermint oil. The microwave extracted material also was high in menthofuran content, 230% higher than the ideal standards created from blending. While in this study this fluctuation was shown to be overshadowed by normal mint crop oil composition variance, further investigation of how this behavior can affect the mint industry is recommended. In general the solvent microwave extraction is more efficient than the steam distillation process. The microwave system was able to extract more essential oils than the steam process and do so in 3.25 minutes of extraction time. In comparison, the steam extraction process requires roughly 1.5 hours. This work offers the foundation for development of a pilot scale microwave system and an associated overall plant operations cost assessment.
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