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 the 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).

In this video, ultrasonic extraction from hops (humulus lupulus) is demonstrated. With the ultrasonicator UP200Ht caryophyllene and other compounds are extracted.

Ultrasonic Extraction of Hops with UP200Ht with S2614 probe

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 extraction can be combines with common extraction systems, e.g. Soxhlet extraction, Clevenger extraction, supercritical CO2, Ohmic hydrodistillation etc. (Sono-Soxhlet, Sono-Clevenger, Sono-scCO2, ultrasonic Ohmic hydrodistillation).

Ultrasonic Extraction of Essential Oils

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. The bubble implosion generates micro-jets which destroy the lipid glands in the plant cell 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 flavor 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.

Ultrasonic batch process for hydrodistillation pre treatment like herbal extraction

Ultrasonic hydrodistillation

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Ultrasonic system for batch extraction (Click to enlarge!)

Customized ultrasonic setup for extraction

Advantages of Ultrasonic Extraction

  • Fast & efficient extraction
  • Non-thermal, mild process
  • High quality extracts
  • High yield
  • Full aroma spectrum
  • Less raw material
  • Green Extraction

Essential oils can be efficiently extracted by sonication! www.hielscher.com

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!

Ultrasonic Effects

The ultrasonic extraction effects are based on the principle of ultrasonic cavitation. Cavitation in liquids creates high shear forces, liquid streaming and microturbulences, which are purely mechanical effects.

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Sono-Clevenger for the extraction of essential oils. Picture from Pingret et al., 2014.

Clevenger with UP200Ht
Picture: Pingret et al., 2014.

Ultrasonic Extraction Systems

Hielscher’s power ultrasound systems 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’s 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 technial lab and process center to explore the capabilities of Hielscher’s ultrasonic systems!
Our robust ultrasonic systems can be used for batch and inline sonication. A retrofitting of existing production lines can be easily done, too.

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Literature / References

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.

Solvent Extraction

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.

Extraction Solvents

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

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.