Ultrasonic Hydrodistillation of Essential Oils
- The conventional extraction of essential oils is expensive and time-consuming.
- Ultrasonic extraction gives higher yields and superior extract quality.
- Ultrasonic can be carried out as solvent- or water-based extraction method. Alternatively, sonication can be combined with traditional extraction systems to improve efficiency and quality.
Hydrodistillation of Botanical Extracts
Hydrodistillation is a variant of steam distillation. For the hydrodistillation extraction, plant material is soaked for some time in water after which the mixture is heated and volatile materials are carried away in the steam, condensed and separated. It is a common extraction process to separate phytochemical compounds from plant material. Steam distillation is a common technique to isolate essential oils, e.g. for perfumery.
Since many organic compounds tend to decompose at high sustained temperatures, the industry is stepping forward to use alternative mild processing methods, which give better extraction results (superior quality, higher yields). Ultrasonic hydrodistillation is a mild, yet highly efficient extraction technique, which is used to produce high-quality essential oils.
Challenges of Conventional Essential Oil Production
Problems of the traditional extraction techniques such as steam distillation lie in the huge quantities of plant material, which are required to extract essential oils on commercial scale. For 1kg (2 1/4 lb) of lavender essential oil are approx. 200kg (440lb) of fresh lavender flowers required, for 1kg of rose oil are between 2.5 and 5 metric tonnes of rose petals needed and for 1kg of lemon essential oil the raw material consists in approx. 3,000 lemons. Therefore essential oils are very expensive. For rose absolute the price is around 20.000€ (21,000US$) per liter.
To gain advantages regarding profitability and competitiveness, producers of essential oils must implement more efficient and effective extraction methods. The favourable techniques of ultrasonic extraction excels traditional extraction methods by mild extraction conditions, high yields and superior extract quality. Sonication can be performed as solvent-based or solvent-free extraction. Alternatively, ultrasonic probe-type extraction can be combined with common extraction systems, e.g. Soxhlet extraction, Clevenger extraction, supercritical CO2, Ohmic hydrodistillation etc. (Sono-Soxhlet, Sono-Clevenger, Sono-scCO2, ultrasonic Ohmic hydrodistillation).
Advantages of Ultrasonic Extraction and Hydrodistillation
Ultrasound-assisted extraction and hydrodistillation is nowadays an established technique for the production of high-quality essential oils. As non-thermal extraction technique, sonication avoids thermal degradation of heat-sensitive compounds. At the same time, extraction efficiency and essential oil yields are significantly increased. Find the benefits of ultrasonic essential oil production below:
- High extraction efficiency: Extraction using a probe-type ultrasonicator isolates essential oils more efficiently than traditional extraction methods, such as steam distillation or solvent extraction. This is because the sound waves cause cavitation in the liquid, which helps to break down the cell walls of the plant material and release more of the essential oil.
- Shorter extraction time: Ultrasonic extraction can extract essential oils in a much shorter time than traditional extraction methods. This is because the intense sound waves generates by an ultrasonic probe can penetrate the plant material more deeply, disrupt the plant cell with superior efficiency and therefore extract the essential oil more quickly and efficaciously.
- Improved quality of the essential oil: As ultrasonic extraction is a non-thermal treatment, it can produce essential oils with a higher quality than traditional extraction methods. This is because ultrasound waves can extract the essential oil without damaging the delicate aromatic compounds that give the oil its fragrance and therapeutic properties.
- Energy-efficient: Ultrasonic extraction is an energy-efficient method of extraction compared to traditional methods, such as steam distillation, which requires a lot of energy to produce steam.
- Environmentally friendly: Ultrasonication is a clean and environmental-friendly technique of extraction, as it does not require the use of solvents or chemicals, which can be harmful to the environment.
These benefits turn ultrasonic essential oil extraction into a highly efficient and economical technique that offers many advantages over traditional extraction methods.
Working Principle of Ultrasonic Essential Oil Extraction
Ultrasonic extraction has been proven to give higher extraction yields and to reduce the energy consumption. The working principle of ultrasonic extraction is the bubble implosion generated by ultrasonic cavitation. Ultrasonic / acoustic cavitation generates liquid micro-jets which destroy the lipid-containing glands in the plant tissue. Thereby, mass transfer between cell and solvent is improved and the essential oil is released. A major advantage of today’s modern ultrasonic extractors is the precise control over the operating parameters (e.g. ultrasonic intensity, temperature, treatment time, pressure, retention time etc.). Increased yield of essential oils as well as lower thermal degradation, high quality and a good aroma and flavour profile are scientifically proven (Porto et al. 2009; Asfaw et al. 2005).
Whilst other modern extraction techniques offer only limited capability for scale-up to industrial production, potency to scale up the ultrasonic extraction to industrial level is already proven. For instance, the extraction yield of essential oils from Japanese citrus was increased by 44% compared to the traditional extraction methods (Mason et al. 2011).
Ultrasonic Pretreatment for the Extraction of Essential Oils
For the ultrasonic extraction of essential oil from plant material (e.g. lavandin, sage, citrus etc.), a probe-type sonication system such as the UIP2000hdT can be used for extraction at bench-top, pilot and production scale. The extraction system can be setup as a batch or inline system.
For the ultrasonic batch extraction, a container with a surrounding cold water bath is recommended. The water bath allows to avoid an undesired temperature rise and the resulting degradation. For the lavandin essential oil extraction, lavender flowers are extracted with e.g. 2L of distilled water for an extraction time of 30 min. The ultrasonic amplitude is set to 60%. After the ultrasonic pretreatment, the lavender flower is removed, and conventional steam distillation is performed to extract the essential oil.
For the inline extraction setup, the ultrasonic processor ist equipped with sonotrode and flow cell. For cooling purpose, the flow cell reactor is equipped with a cooling jacket. For the ultrasonic pre-treatment, the macerated plant material is pumped through the reaction chamber where it passes directly through the cavitational zone. A further benefit of the ultrasonic inline extraction is the possibility of pressurizing the reaction chamber to increase the extraction effect.
The ultrasonic pre-treatment before hydrodistillation increases the yield of extracted essential oils and improves the extraction rate – resulting in an overall more efficient procedure.
Advantages of Ultrasonic Extraction and Hydrodistillation
- Fast & efficient extraction
- Non-thermal, mild process
- High quality extracts
- High yield
- Full aroma spectrum
- Less raw material
- Green Extraction
Case Study: Ultrasonic Hydrodistillation of Essential Oil from Satureja khuzistanica
Rasouli et al. (2021) investigated the extraction efficiency for essential oils from the herbal plant Satureja khuzistanica Jamzad comparing traditional hydrodistillation and ultrasonically intensified Clevenger (Sono-Clevenger). They compared both extraction techniques, hydrodistillation and ultrasonic Clevenger, regarding isolation time, yield, and quality of essential oils obtained. The results show that while the obtained essential oils chemical profile and biological properties are both of comparable high quality, the ultrasonic extraction method enhances essential oil isolation yield efficiency by up to 40%. The Scanning electron micrograph (SEM) images of the treated Satureja leaves reveal a more efficient disruption of plant cell walls by ultrasonication. As a result, an enhancement in essential oil extraction by about 40% compared to conventional hydrodistillation methodology was observed.
This study underlines the results of many other reports, in which the ultrasonic pretreatment before the hydrodistillation has been investigated and shown that probe-type ultrasonication enhances both the quality and quantity of the essential oil whilst decreasing extraction time and energy consumption compared to the conventional techniques.
Ultrasonic Extractors for Essential Oil Hydrodistillation
Hielscher power ultrasound extractors are available for bench-top, pilot plant and industrial plant installations. Our ultrasonic processors are precisely controllable and can deliver very high amplitudes (up to 200µm for industrial ultrasonicators, higher amplitudes on request) to generate an intense acoustic field. All our ultrasonic devices, from lab to industrial systems, are built for 24/7 operation under heavy duty conditions.
Hielscher ultrasonic extractors can be tested at bench-top scale for feasibility tests and process optimization. Afterwards, all process results can be linearly scaled to full industrial production. Our long experience in ultrasonic processing enables us to consult and assist our clients from first tests and process optimization to the implementation of an highly efficient industrial operation.
Visit our technical lab and process center to explore the capabilities of Hielscher ultrasonic systems!
Our robust ultrasonic systems can be used for batch and inline sonication. For essential oil production, a synergistic combination can be achieved by installing an ultrasonic probe in a conventional hydrodistillation setup. Retrofitting of existing production lines can be easily done, too.
The table below gives you an indication of the approximate processing capacity of our ultrasonicators:
|Batch Volume||Flow Rate||Recommended Devices||1 to 500mL||10 to 200mL/min||UP100H|
|10 to 2000mL||20 to 400mL/min||UP200Ht, UP400St|
|0.1 to 20L||0.2 to 4L/min||UIP2000hdT|
|10 to 100L||2 to 10L/min||UIP4000hdT|
|15 to 150L||3 to 15L/min||UIP6000hdT|
|n.a.||10 to 100L/min||UIP16000|
|n.a.||larger||cluster of UIP16000|
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Literature / References
- Rasouli, Seyed Reza; Nejad, Ebrahimi Samad; Rezadoost, Hassan (2021): Simultaneous ultrasound-assisted hydrodistillation of essential oil from aerial parts of the Satureja khuzistanica Jamzad and its antibacterial activity. Journal Of Medicinal Plants, Vol. 20, no. 80; 2021. 47–59.
- Dent, M.; Dragović-Uzelac, V; Elez Garofulić, I.; Bosiljkov, T.; Ježek, D.; Brnčić, M. (2015): Comparison of Conventional and Ultrasound-assisted Extraction Techniques on Mass Fraction of Phenolic Compounds from Sage (Salvia officinalis L.). Chem. Biochem. Eng. Q., 29 (3), 2015. 475–484.
- Djenni, Z.; Pingret, D.; Mason, T.J.; Chemat, F. (2013): Sono–Soxhlet: In Situ Ultrasound-Assisted Extraction of Food Products. Food Anal. Methods 6, 2013. 1229-1233.
- Li, Y.; Fabiano-Tixier, A.-S.; Chemat, F. (2014): Essential Oils as Reagents in Green Chemistry, SpringerBriefs in Green Chemistry for Sustainability, 2014. p.9-20.
- Petigny, L.; Périno-Issartier, S.; Wajsman, J.; Chemat, F. (2013): Batch and Continuous Ultrasound Assisted Extraction of Boldo Leaves (Peumus boldus Mol.). Int. J. Mol. Sci. 2013, 14, 5750-5764.
- Pingret, D.; Fabiano-Tixier, A.-S.; Chemat, F. (2014): An Improved Ultrasound Clevenger for Extraction of Essential Oils. Food Anal. Methods 7, 2014. 9–12.
- Sicaire, Anne-Gaëlle; Vian, Maryline Abert; Fine, Frédéric; Carré, Patrick; Tostain, Sylvain; Chemat, Farid (2016): Ultrasound induced green solvent extraction of oil from oleaginous seeds. Ultrasonics Sonochemistry (2016), Vol. 31. 319-329.
- Yoswathana, N.; Eshiaghi, M.N.; Jaturapornpanich, K. (2012): Enhancement of Essential Oil from Agarwood by Subcritical Water Extraction and Pretreatments on Hydrodistillation. International Journal of Chemical, Molecular, Nuclear, Materials and Metallurgical Engineering Vol:6, No:5, 2012. 453-459.
Facts Worth Knowing
Successfully Extracted by Ultrasonics
The following plant material and plant tissues are proven that ultrasonic extraction attains improved extraction results. The ultrasonic extraction gives higher yields, high quality extracts with a complete compound / aroma profile and full flavour spectrum.
Herbs & leaves: spearmint, mint, stevia, cannabis, hops, basil, thyme, pepper, oregano, sage, fennel, parsley, eucalyptus, olive, green tea, black tea, boldo, tobacco, peppermint, marjoram, etc.
Flowers (attars): Rose, lavender, ylang-ylang, jasmine, patchouli, tuberose, mimosa, etc.
Fruits: orange, citrus, lemon, raspberry, tomato, apple, blueberry, bilberries, mandarin, grapes, olive, jujube, etc.
Spices: saffron, coriander, ginger, laurel, nutmeg, cinnamon, turmeric, vanilla, clove, nutmeg, mace etc.
Wood & bark: agarwood, oak, sandalwood, cedarwood, pine, cinnamon bark, etc.
The botanical extracts contain the full spectrum of active compounds and phytochemicals so that the essential oil contains lipids, terpenes and terpenoids, phenols, alkaloids, flavonoids, carbonylic compounds, antioxidants, vitamins, pigments, enzymes, etc.
Examples of extracted molecules: monoterpenes and monoterpeneoids, sesquiterpenes, limonene, carvone, a-pinene, limonene, 1,8-cineole, cis-ocimene, trans-ocimene, 3-octanone, beta-carotene, α-pinene, camphor, camphene, β-pinene, myrcene, para-cymene, limonene, γ-terpinene, linalool, myrtenol, myrtenal, carvone.
Essential oils show antioxidant and antimicrobial effects, which makes them besides their aroma and flavour a beneficial ingredient for food and medical products, too.
Essential oils, e.g. from lavender, peppermint, and eucalyptus, are mostly produced by steam distillation. Raw plant material such as flowers, leaves, wood, bark, roots, seeds, and peels are extracted by water distillation whilst soaked and boiled with water in a distillation apparatus.
For hydrodistillation, two forms are differentiated: water distillation and steam distillation.
For the isolation of essential oils by water distillation, the plant material is placed in water to be boiled. For steam distillation, steam is injected into/through the plant material. Due to the influence of hot water and steam, the essential oil is released from the lipid glands in the plant tissue. The evaporating water steam carries the oil out of the plant material. Afterwards, the steam is condensed in a condenser by indirect cooling with water. From the condenser, the distilled extract (essential oil) flows into a separator, where the oil separates automatically from the distillate water.
Due to efficiency, most essential oils, e.g. for the perfume and fragrance industry, are produced by solvent extraction, using volatile solvents, e.g. hexane, di-methylene-chloride, or petroleum ether. The main advantages of solvent extraction over distillation is that an uniform temperature (approx. 50°C) can be maintained during the process. Since higher temperatures result in the degradation of essential oil compounds, solvent-extracted oils are characterized by a higher completeness of their volatile compounds and a more natural odor.
Supercritical CO2 is proven to be an excellent organic solvent, too and is therefore another alternative method for the extraction of aromatic oils from botanicals.
Traditional organic solvents for extraction include benzene, toluene, hexane, dimethyl ether, petroleum ether, di-methylene-chloride, ethyl acetate, acetone, or ethanol.
Ethanol is used to extract fragrant compounds from dry plant materials, as well as from impure oils or concretes that have been produced firstly by organic solvent extraction, expression, or enfluerage. Ethanol extracts from dry materials are known as tinctures. Tinctures are not to be confused with ethanol washes, which are carried out to purify oils and concretes to obtain absolutes.
When water is used as extraction fluid, the process is called a solvent-free extraction.
Essential oils are produced by extraction from plant material. As raw material various kind of plant parts can be used, e.g. flowers (e.g. rose, jasmine, carnation, clove, mimosa, rosemary, lavander), leaves (e.g. mint, Ocimum spp., lemongrass, jamrosa), leaves and stems (e.g. geranium, patchouli, petitgrain, verbena, cinnamon), bark (e.g. cinnamon, cassia, canella), wood (e.g. cedar, sandal, pine), roots (e.g. angelica, sassafras, vetiver, saussurea, valerian), seeds (e.g fennel, coriander, caraway, dill, nutmeg), fruits (bergamot, orange, lemon, juniper), rhizomes (e.g. ginger, calamus, curcuma, orris) and gums or oleoresin exudations (e.g. balsam of Peru, Myroxylon balsamum, storax, myrrh, benzoin).
Concrete and Absolute
Concrete is the term for the semi-solid mass which is obtained by solvent extraction of fresh plant material. The fresh plant material is mostly extracted using nonpolar solvents such benzene, toluene, hexane, petroleum ether. After the extraction process, the solvent is evaporated, so that a semi-solid residue of essential oils, waxes, resins and other lipophilic (hydrophobic) phytochemicals are obtained. This is the so-called concrete.
To obtain an absolute from concrete, the concrete must be treated with a strong alcohol in which certain constituents can be dissolved.
Ultrasonic Production of Nanoemulsions
The interest in using nanoemulsions as delivery systems for lipophilic food ingredients, as carrier for active compounds in pharmaceuticals and cosmetics is significantly growing due to their high optical clarity, good physical stability, and ability to increase bioavailability. Ultrasonic emulsification prepares stable micro- and nano-emulsions which guarantee best results in the final product.
Click here to learn more about ultrasonic emulsification!