The Distillation of Essential Oils Part 2
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The Distillation of Essential Oils Part 2 in Personal Care magazine July 2012

The Distillation of Essential Oils Part 2 in Personal Care magazine July 2012

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  • I am very interesting in hydro steam distillation. Where I can find more information for process and design equipment. Equipment is more simple than ordinary steam distillation. Best regards,
    Kenan
    cengic.kenan@gmail.com
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  • This is extremely interesting stuff. My team and I are new to distillation. We're distilling frankincense gum/resins. While reading the hydro steam distillation process part, I've had so many clicks in my head. This reading has dotted the I's and crossed the T's in the hand on work we've done. Thanks for sharing it. How can we get in touch with you, Mr. Hunter?
    Mohamed, Dubai
    mohamedali2020 AT hotmail DOT com
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    The Distillation of Essential Oils Part 2 The Distillation of Essential Oils Part 2 Document Transcript

    • Murray Hunter – University Malaysia Perlis ESSENTIAL OILS The distillation of essential oils 2: PART Part two of this three part series on distillation carries on from the basic principles laid out in part one to look at the stages of the general distillation process and outlines the various basic types of distillation.Distillation occurs in a number of definable Stage one Stage two Stage threestages. During the first stage, initial heatingoccurs through the charge where the plantmaterial has been placed. Plant material Linaloolwill not be saturated with moisture and thetemperature differential between the steam Percentage increase of the distillateand the plant material will allow quick Methyl chavicoldissipation of latent heat from the steam tothe plant material. The initial steam,particularly if it is wet will tend to coolthroughout the lower layers of the charge,where some condensation may occur. Thishas to be watched carefully, as too much 1,8 Cineolecondensation may flood the lower parts ofthe charge. Dry superheated steam mayhave the effect of drying out the plantmaterial. Both flooding and drying out ofthe plant material are detrimental toefficient distillation. At this early stagesteam is the only contributor to vapour Eugenolpressure until saturation occurs and thelayering process, discussed above begins. The second stage begins when the Progressive number of constituentsvapour reaches the condenser. At this pointthe oil-to-water ratio will be at its highest. Figure 1: The distinct stages of distillation, and during the second phase, for sweet basil oil.During the second phase the distillationprocess will go through three sub-phases. the change in composition of sweet basil the vat and the plant material surfacesɀ In the early stage, due to some effect oil during distillation.2 area within the charge. The rate of steam from relative volatilities of the various The height of the still will influence this flow per hour is subject to the amount of constituents, the most volatile phenomenon. High stills tend to negate plant material in each charge. Daily constituents will tend to vaporise first this effect because as the more volatile throughput is thus limited by the amount of and carry a higher than proportionate constituents from the bottom layer reach steam that can be generated on an hourly weight in the distillate as compared to the top layer, the less volatile constituents basis at a distillation plant. Steam must the normal oil. It is also reported that from the bottom layer will have already also be adjusted to suit the absorptive oxygenated constituents also have a started distilling over and reaching the capacity of the plant material. This greatly tendency to distil over before upper layers of the charge. varies between different herbs and the hydrocarbons.1 The final stage of distillation occurs condition they are in before distillation.ɀ During the middle stages, the oil will be when the water-to-oil ratio is very high as Steam produced by high pressure distil over in the same proportions as the charge becomes exhausted of oil. It will external boilers is usually very dry and can the normal oil, and no longer be economical to continue with often be superheated. Steam produced byɀ During the third stage, the least volatile the distillation. medium pressure boilers around 3 constituents of the oil will contribute a atmospheres pressure will contain higher than proportionate composition in Steam and pressure moderate moisture content, but will not the distillate. For efficient distillation, i.e., achieving the tend to superheat. Steam produced from maximum amount of oil with the minimum evaporators at atmospheric pressure isThe distinct stages of the second stage quantity of steam, requires the maximum relatively moist. In water-steam distillationdistillation can be seen in Figure 1 showing exposure between the steam flowing into array where steam is produced in the same July 2012 P E R S O N A L C A R E 67
    • ESSENTIAL OILSvessel that the plant material is stored will that the temperature gradient increases, Recently a variation on the operation ofproduce very wet steam. thus increasing the effects of latent heat pressure in steam distillation has been Different steams can be utilised as a exchange and reduces the likelihood of reported a number of times, utilising acontrol mechanism to correct the hydrolysis. However the use of high technique called instantaneous controlledconditions within the still housing the plant pressure distillation is limited by the extent pressure drop (DIC). This is a techniquecharge. that prolonged high temperatures will where the foliage is first exposed to Wet steam is a saturated vapour is damage the composition of the essential saturated steam and then the pressuresuitable for most distillation. In most cases, oil. drastically dropped to a vacuum level ofwet steam from a water bath produces ‘a Inversely, as operating pressure is around 5-50 KPa to provoke auto-richer oil’ with much shorter extraction time reduced, so does the temperature of the vaporisation of the superheated volatilethan other forms of steam.3 This is distillation. This method can be used for compounds through expanding andparticularly the case with plant material the extraction of heat sensitive constituents breaking up the cell walls withthat contains superficial oil glands. that would normally be damaged through instantaneous cooling.4 Experiments haveIncreasing steam rates does not speed up exposure to excess heat. However shown that results can be varied throughdistillation, especially if the process of distillation under reduced pressure has a changing time, pressures and the amounthydro-diffusion is required. As plant number of limitations. Steam under of moisture in the leaves.5material is already saturated with moisture reduced pressure is less dense, so requiresand there is a constant diffusion rate. If more steam to carry out a distillation than Wilting crops beforeherbs contain a lot of moisture, then there under normal atmospheric pressure. The distillationwould be sufficient moisture in the plant condenser system would need to be As the moisture condition of the herb is amaterial to commence hydro-diffusion and almost twice the size of a conventional still factor in the efficient distillation of thedry steam would be the most suitable to or a refrigeration system required in herb, wilting is often carried out to dry theapply. However dry steam has less mass condensing the distillate. The recovery crop before processing. The objective ofthan wet steam and as such reduces the vessel and separator would have to be wilting is to dry the herb enough tolatent heat of steam, thus prolonging the sealed within the closed system, which increase its absorptive surface. Manydistillation period. would lead to design and engineering practitioners believe it is to dry out excess A superheated steam occurs when the difficulties. moisture so that distillation will be shortertemperature of the vapour is higher thanthat of the same saturated vapour at thesame pressure. Superheated steam isindependent of pressure and thereforeadvantageous in a number of situations, asit can be utilised at any temperaturewithout increasing pressure, i.e., canincrease the temperature of distillationwithout having to change the steam flow-rate due to changes in pressure.Superheated steam can be used for dryingout a flooded charge vessel, where there istoo much liquid around the plant material.However superheated steam is notadvisable for general distillation as it woulddry out the plant material, preventing thehydro-diffusion process occurring and is apoor conductor of latent heat – two of theimportant processes needed for efficientdistillation. Superheated steam is mostsuitable for the distillation of glabrous herbmaterial and can increase yieldssubstantially. High boiling oils exert less vapourpressures and require relatively largetemperature gradients to extract themduring distillation. This leads to prolongeddistillation periods. If the constituents arestable under long periods of heat,distillation can be performed underpressures above the atmosphere, whichincreases temperature. This cuts back ondistillation time and saves energy. Asincreasing the still pressure, increasestemperature, the temperature gradient willalso increase between the vapour space inthe still and the plant material. This assistsin the vaporisation of high boiling volatile Figure 2: Mint foliage, cut and laid on the ground for wilting, being picked up by the harvesterconstituents. The advantage of pressure is for distillation at Myrtlefor, Victoria.68 P E R S O N A L C A R E July 2012
    • ESSENTIAL OILSand more efficient. However this is a Condenser coolingfallacy. For example, with tough leaves like water outleteucalyptus and tea tree, wilting does littleto dry them out or increase their surface Vapour condenserabsorption, so wilting will have no benefitto the distillation process. Moisture in the Vapour outletplant material is actually of benefit to the to condenserdistillation process.6 In fact there are riskswith wilting in that the process may lead to Condenser cooling Still chamber for water inletlosses in oil, not through evaporation, but plant materialthrough chemical reactions like oxidisation, (loaded byresinisation and the formation of glycosides cartridge,and enzymes in the materials. Excessive or directly)drying of moisture can remove necessarymoisture breaking the contact between the Welded wire Separatoroil component and surface of the plant Steam inlet mesh floor flaskmaterial, thus hindering the promotion of from boiler Steam outlethydro-diffusion during the distillationprocess. Which crops require wilting before Still drain valvedistillation generally depends upon theirnatural surface absorption capacity. Non- Figure 3: Diagram of a steam distillation still.absorptive herbs like mint and basil needsome wilting to promote absorption during which need to be comminuted before become part of the boiling mixture anddistillation, as wilting to promote partial distillation, like almond powder and huon resulting mixed vapour.breakdown of the surface cellular structure pine saw dust. As water boils and converts to steam atof the leaf. In this case distillation would In water distillation there are a number the bottom of the vat and rises through thethen commence with a wet steam fraction, of simultaneous processes that act to plant charge, it will come into contact withfollowed by slightly drier steam once extract volatile constituents from plant the plant material. Some oil is exposed onmoisture has permeated into the leaf material that are different from steam the surface of this material will bestructure. Herbs with absorptive surfaces distillation. vaporised by the rising steam as it comeslike lavender do not need to be wilted. In Essential oils contain a number of into contact with the plant surfaces. Thisfact they do not have enough moisture to oxygenated constituents that are relatively steam carrying some volatile vapour willlink the oil glands to the surface via a water soluble in water. This would include rise to the surface and carry over into theinterface, so wet steam fractions are phenols, alcohols and some aldehydes. vapour space above the water until itneeded during distillation. Grass crops like During the early stages of a water reaches the still condenser.lemongrass and citronella contain enough distillation, these compounds would The boiling temperature of water at themoisture within their leaf structure to dissolve in the surrounding water and bottom of the vat in water distillation iscreate a water-oil-surface interface forhydro-diffusion to occur during distillation, Table 1: Some common water soluble aroma chemicals in essential oil.so wilting is not necessary. As moisturecontent is already sufficient in the leaf, dry Slightly soluble Moderately soluble Very solublesteam would be suitable for the distillation (<500 ppm) (501-1999 ppm) (>2000 ppm)process. Aldehyde C11 Calamene Benzlaldehyde Aldehyde C12 (lauric) 1,8-Cineole Benzyl acetateWater distillation Aldehyde C12 MNA Nerol Cinnamic alcoholWater distillation involves distilling plantmaterial totally immersed in water. Amyl cinnamic aldehyde Neryl acetate Citronellyl acetateDepending upon the specific gravity and Amyl salicylate Rose oxide α-Copanenecharge mass in the still, the material will Benzyl salicylate Eugenoleither float or sit totally immersed in the Cedrol Geranialwater. Heat is introduced by direct heating Citronellol Geraniolof the sides of the vat, a steam jacket, a Citronellyl butyrate Limoneneclosed system coil or in some cases aperforated steam coil. Water distillation was Citronellyl formate Linaloolthe only method used before the 20th Eudesmol Mentonecentury. Geranyl formate Myrcene Water distillation is useful for the Limonene (E)-β-ocimenedistillation of flower materials which would Linalyl acetate Phenylethylacetatenormally congeal and form lumpy masses α-Pinene Phenylethylalcoholunder steam distillation, where steamwould not penetrate, like rose petals and Sabineneorange blossoms. This method is also Terpinen-4-oluseful for fruit kernels that would form α-Terpineolglutinous masses under steam distillation Terpinoleneand powdered forms of plant material July 2012 P E R S O N A L C A R E 69
    • ESSENTIAL OILSslightly less than the boiling point of water, the plant surface material as possible material from directly coming into contactdue to the mixed liquid of solublised during the distillation. with the heating coils.volatiles and water. Heat applied to the still The effects of hydro-diffusion are much With many materials, part of the oilwill cause the creation of a small bubble of slower in water than other types of dissolves in the water during distillation andsaturated mixed vapour from the liquid distillation. Consequently, especially for forms a milky emulsion, as a number ofphase, where upon formation it rises to the wood materials extensive comminution aromatic constituents are soluble to sometop of the water in the charge. During the must be undertaken so that particles in the degree in water. This loss could range up torise, the bubble’s pressure, temperature charge are fine and as much oil as possible 25% of the essential oil.7 This means thatand proportion of oil to water decreases. is exposed on the surface of the material. the recovery of oil is incomplete and theThe condensing volatiles, mostly being less In water distillation, plant material is recovered oil will be deficient in somedense than water, float to the top of the placed in a sealed vessel or retort that constituents that would be the case withwater and form a film on the surface of the connects directly to a condenser. From the the oil recovered through steam distillation.water in the vessel. This lost oil tends to condenser the distillate runs into a Upon separation in water distillation, theremain on top of the surface and cannot separator. The rate of distillation is water distillate is returned directly to there-vaporise easily due to its higher boiling controlled by the intensity of the fire, the charge vessel to replace the decreasingpoint and the generally cooler temperatures pressure of the vessel or retort and/or the water level due to evaporation. This isat the water surface. Most of the oil rate of introduction of steam. As many called cohobation. Sometimes the waterrecovered in water distillation is the portion woods contain high boiling compounds, distillate is redistilled in another vessel toof the oil that does not condensate through pressure is vital to create high enough extract the volatiles in emulsion. Salt isthis action. temperatures to vaporise the volatile often added to the distillate to reduce the Observation shows that distillation constituents. These constituents may take solubility of water. Whether this process isundertaken with vigorous boiling produces many hours to boil out. Hydro-stills should undertaken depends upon the probability ofbetter and quicker yields than mild boiling. generally be wide to maximise the the constituents being damaged by furtherSome distillers even install small propellers evaporation area. Where particles are fine heat and the economics of re-distillation.intruding into the side of the still to assist such as saw dust and powders some form Another method to recover the dissolvedin agitation. This is most probably effective of mesh or “P” shape pipe arrangement aromatic materials from the water distillatebecause the agitation in the charge tank should exist at the entrance to the is to add a solvent. The mixture is thenprevents oil droplets clinging to the herb condenser to prevent plant material from vigorously shaken to pick up dissolvedsurfaces. It is necessary to generate entry and possible clogging. Heavy charges constituents from the water into theenough steam in the water so that it will and where heat coils are used in the still solvent. These materials are then recoveredcome in contact with as much of the oil on require a perforated grid to prevent plant through vacuum distillation of the solvent Table 2: A comparison between water, water and steam and steam distillation. Water distillation Water and steam distillation Steam distillation Construction Usually simply constructed, Inside vat contains a grill where Utilises an outside steam source based on ancient designs. plant material rests above the water Plant material suitability Finely powdered materials such Can be used for most herb and Most materials, except fine as woods and rhizomes, flowers leaf materials. Material must powders. Good for high boiling that congeal with steam. be packed in a uniform materials. Material must be packed Not suitable for materials that manner to avoid channeling in a uniform manner to contain acidic material which can of steam. avoid channeling of steam. saponify, water soluble or high boiling constituents. Material must be completely covered with water. Hydro-diffusion Excellent Good Steam should be slightly wet to promote diffusion. Superheated or high pressure steam can dry out the plant material and inhibit diffusion. Available Pressure Atmospheric pressure Atmospheric pressure Can be adjusted for both high and reduced pressures. Available Temperature 100˚C, but care must be taken Approximately 100˚C Can be increased or reduced not to burn the plant material according to pressure used. from direct heat on the sides. Hydrolysis Condition Usually a high rate of ester Hydrolysis is usually low, however Slight hydrolysis. hydrolysis. excessive wetting of the plant material through prolonged distillation can promote hydrolysis during later stages of distillation. Rate of distillation and yield Slow rate of distillation. Moderate distillation rate. Fast rate of distillation. Low rates of yield due to Good yields if no channels Good yields if no channels hydrolysis and loss of water occur in charge. Usually good yields. occur in charge. Usually good yields. soluble constituents into the water. High boiling constituents often left undistilled.70 P E R S O N A L C A R E July 2012
    • ESSENTIAL OILSwhich results in a secondary essential oil.8Some common water soluble aromachemicals in essential oils are listed inTable 1. Another method that will contribute tominimising oil loss due to oil solubility inwater during the separation phase is tocontrol the outgoing distillate temperaturefrom the condenser. Where oils are lessdense than water, there will be an optimaltemperature range where oil particles willfreely float to the top of the distillate uponcondensation. Some literature ondistillation practices misses the point aboutthe effect of condensation temperatures onoil yields.9 Based on private work,10 thehigher the temperature of the outgoingdistillate, the freer will be the oil particlesto float to the top. For example, tea tree oildroplets will float to the top of the waterdistillate twice as fast at 60°C than at40°C. The upper temperature limit will berestricted by the potential loss of lowboiling volatiles during condensation. Thishas implications on the design of the Figure 4: The condenser, with the end manifold removed to expose the internal cooling pipes,specific condenser for specific crops and at the author’s property in Perlis, Malaysia.set range limits upon the temperature thatdistillation can take place, to achieve a water distillation. Water and steam steam distillation facilities are designed andspecific outgoing distillate temperature distillation has another advantage over built with the correct steam ratings, theyrange. steam distillation as there are fewer are much more economical to run than decomposed products during the process water and water and steam distillationWater and steam distillation due to less chance of plant material drying systems. A comparison between water,Water and steam distillation involves the out. However water and steam distillation water and steam and steam distillation isstoring of the plant material above a water will take a lot longer. Water and steam shown in Table 2. below.bath situated in the bottom of the charge distillation can produce very good resultsvessel and heating the water either through under reduced pressure. The condenser systemdirect fire, a steam jacket or a closed or Water and steam distillation is much A condenser in an essential oil distillationopen steam coil. Water and steam cheaper to set up than steam distillation system is a heat exchange or dissipatingdistillation produces saturated wet steam at facilities and lends itself to portable stills device. The condenser must not only coolthe prevailing vessel pressure, which is that can be transported from place to the condensate vapour into a liquid, butusually atmospheric pressure. Within this place. also cool the condensate to theconfiguration, unlike water distillation, only temperature range where the oil willsteam comes in contact with the plant Steam distillation separate spontaneously from the water.material. Steam distillation employs an external The usual array for a condenser system Water and steam distillation is not very steam generation system, external to the is a tube or set of tubes running through asuitable for fine materials as steam will find charge vessel. This configuration provides sealed water reservoir to cool the pipes. Ita path of least resistance tending to create much more control (depending upon the is immediately attached to the top of thechannels. This means that steam will not boiler capacity) than water and steam charge vessel to collect all vapour exitingflow through the whole mass of plant distillation. This is because in steam the vessel. The design of the condensermaterial and an incomplete distillation will distillation the wetness fraction, must ensure that the vapour flow istake place. If the plant material is loosely temperature and pressure can be turbulent inside the tubes to prevent highpacked, the same effect will happen, as manipulated according to needs and velocity vapour freely flowing through thethe material will offer no resistance to the conditions. However, it is a misconception condenser and maximise exposure to thesteam. that greater steam volumes and increased cooler walls. A baffle is usually installed at Water and steam distillation may take a pressures have positive effects on the the beginning of the condenser to disrupt along period of time to reach operating process in all cases. As mentioned straight steam flow for this purpose. Failuretemperature as the plant material needs to previously, dry and superheated steam has to achieve those conditions would result inbe heated up with only saturated steam. the effect of drying out plant material, some vapour failing to condensate. WithinThis may cause early condensation and which potentially halts distillation through the condenser system the flows of vapourwetting of the plant material. the stopping of hydro-diffusion process. and cooling water should be in opposite Due to the limits on pressure that can Faster steam flow rates do not necessary directions at the maximum possible speed.be built up in the charge vessel, water and mean quicker recovery times. Fabricated The condenser must be sensitive enough tosteam distillation will have only a limited steam boilers cost much more to run than react on the vapour flow very quickly. Theeffect on extracting high boiling materials water baths and may lead to high required number of tubes and length of thefrom plant materials. However there is less distillation costs, especially if they require condenser depends on the rate of distillateopportunity for hydrolysis to occur than with petrochemical feed stocks. However if flow, the pressure, the temperature of the July 2012 P E R S O N A L C A R E 71
    • ESSENTIAL OILScooling water and the desired exit microscopic oil droplets. Temperature plays Distillate in-flow from stilltemperature range of the distillate. (water-oil mixture) a crucial role in separation, where it should The condenser must remove the be moderately warm to increase theequivalent amount of heat that is needed relative specific gravity differential of the oilto vaporise the distillate, plus the additional Oil and water. Raised temperature of the outletamount of heat to reach the optimal distillate water will allow the small oildistillate temperature range of the particles to rise to the top of the separatorcondensate distillate exiting the condenser. quicker in a similar manner to theThe rate of which heat would be removed condenser exit temperature range wherefrom the distillate can be represented by Water there will be an optimal separator water Internal outletthe following equation: baffle temperature range to promote oil-water Q = UA∆t ∆ separation.11 Where Q = the heat removed by unit During distillation, the more volatile of time constituents tend to vaporise quicker and U = a constant determined by the less volatile constituents vaporise later operating conditions (condensing and in the distillation. This leads to an oil that cooling made up of a number of will vary in constituents during the factors) usually a constant is used. distillation period. By changing separation A = the area available for heat flasks at particular points during a single removal distillation, oils of different constituent ∆t = the temperature difference profiles can be collected. This is important between the vapour and the cooling Figure 5: Schematic view of a hydro-diffusion in ylang ylang and lavender distillation, medium. distillation system. where different oils profiles will have different uses and values to particularU is made up of a number of factors possible separate the oil from the distillate customers. Many distillers also use thisincluding the flow rates of cooling water water. As distillate water volume is much principal to collect specific fractions duringand vapours, the material that the greater than oil, it is important that water the distillation, which can later be blendedcondenser is constructed, and usually a can be removed continuously. Oil and together to create a whole oil that meetsconstant is used due to the difficulty to water separates according to specific with certain specific specifications, such ascalculate. The value of U increases as gravity forming two layers. Lighter than a standard.these factors increase. Thus according to water oils will float to the top and heavier The water distillate will always bethe equation, the surface area can be as than water oils will sink to the bottom. This saturated in oil and directly dumping itlarge or small as desired, as long as the must be considered in separator design for would lead to a loss in yield. For thisother factors compensate. However the water removal. reason some distillers (water and water andoverall capacity of the distillation system If the specific gravity of oil and water is steam distillation) will channel the waterwill have great bearing on the condenser very close, the two components will not distillate back into the still vessel for re-area. Condenser sizes will also vary in size separate immediately. Distillate flowing into distillation in what is called cohobation,according to the temperature of available the separator must therefore not disturb mentioned previously. For this purpose thecooling water on site, thus condensers in the surface area and flow into the body of separator must be placed higher than thetemperate and tropical areas will reflect the water to prevent surface turbulence. still vessel proper so distillate water in thethis in size. The separator must also be large enough separator can be fed back into the still Using a condenser system with the so that drained water does not carry away through gravity.wrong capacity for the distillation systemwill have a number of operational Steam inletconsequences. A too efficient condensersystem will deliver the distillate at atemperature below the optimum range,which could lead to cool air outside being Downward steam flowsucked into the system. This outside coolerair in the condenser tubes could createexpansion and contraction of vapours in Plant materialthe condenser leading to splattering and Side opens so thatintermittent distillate outflow. This could cartridge with plantalso occur if the cooling water is too cold. material can slide in Grated baseIf the condenser is too small for the and out of stilldistillation system, then the still must beoperated with lower steam rates, which Condenser arraywould lengthen distillation times and openup the possibility of hydrolysis to occurwithin the vessel. Water and oil collectorThe separator systemBefore leaving the subject of distillation inthis chapter, some words about the Collector vesselseparator system must be mentioned. Thefunction of the separator is to as quickly as Figure 6: Oil separator design used in Perlis, Malaysia.72 P E R S O N A L C A R E July 2012
    • ESSENTIAL OILSHydro-diffusion material near the bottom may also lead to 6 Guenther E.The Essential Oils, Volume One:distillation hydrolysis and lead to lesser yields. History – Origin in Plants, Introduction – Analysis,Hydro-diffusion distillation is a variation on However, hydro-diffusion distillation appears Malabar, Florida, Robert E. Krieger Publishingsteam distillation where steam is popular within the aromatherapy industry in Company, P 110, 1948. .introduced on the top of the vessel and Europe. PC 7 Fleisher A. Water-soluble fractions of thecondenses through the plant material in essential oils, Perfumer & Flavorist 1991;the still, where the distillate is collected ɀ The final article in September will 16 (3): 37-41.and condensed under the plant material conclude with a brief discussion about 8 Bouzid N, Toulgouate K, Villarem G, Gaset A.which rests on a grill or perforated tray. applying these principles. Analyse quantitative des fractions d’huileThrough steam travelling down the still, essentielle pouvant co-exister lorsthere is more time for the volatiles and References d’hydrodistillation de plants aromatiques,fatty acids floating on the plant material. 1 Johannes AK, Scheffer JC, Svendsen AB. Rivista Ital Eppos 1997; 79: 15-25.In the case of wood and seeds that have Comparison of Isolation Procedures for Essential 9 Boland DJ, Brophy JJ, House APN. Eucalyptusmany high boiling compounds, which are Oils, Z. Lebensm. Unters. Forsch, Vol. 168, Leaf Oils: Use, Chemistry, Distillation anddifficult to vaporize in an ordinary still, this 1979, pp. 106-111. Marketing 1991; Melbourne, Inkata Press, P .system may be effective. This would be 2 Private communication with Mr. Jon Bonnardeaux 191.valuable when fatty acids contribute to the of Western Australia Department of Agriculture, 10 Unpublished private work on tea tree distillationflavour of a material and it is desirable in early 1990s. at Batu 9, Berseri, Perlis, Malaysia duringthe oil. Thus, hydro-diffusion distillation 3 Denny EFK. Field Distillation for Herbaceous Oils, 2004/5.may return an oil more representative of Lilydale, Tasmania, Denny McKenzie & 11 Hughes AD, (1952), Improvements in the Fieldthe plant’s natural profile.12 Associates, P 81, 1990. . Distillation of Peppermint Oil, Corvallis, It is reported that hydro-diffusion 4 Kristiawan M, Sobolik V, Al-Haddad M, Allaf K. Engineering Experimental Station Bulletin No. 31distillation gives quicker distillations with Effect of pressure drop on the isolation of 1952; Oregon State College, 1-64.lower steam consumption than cananga oil using controlled pressure drop 12 Legast E, Peyron L. Hydrodiffusion Industrialconventional steam distillation.13 However process, Chemical Engineering and Processing Technology to Produce Essential Oils bythis process is governed by the physical 2008; 47 (1): 66-75. Steam, in Proceedings of the 11th Internationallaws that govern any other type of 5 Rezzoug SA, Boutekedjiret C, Allaf K. Congress of Essential Oils, Fragrancesdistillation and the fact that the steam Optimization of operating conditions of rosemary and Flavors Vol. 2 1989; New Dehli, India,travels downwards while cooling may affect essential oil extraction by a fast controlled 69-73.the transfer of latent heat and thus pressure drop using response surface 13 Hall R, Klemme D, Nienhaus J. The H&R Book:increase, rather than decrease distillation methodology, Journal of Food Engineering 2005; Guide to Fragrance Ingredients Vol. 4 1985time. The tendency to saturate the plant 71 (1): 9-17. London, Johnson Publications, P 13. 0 . July 2012 P E R S O N A L C A R E 73