Essential Oil Extraction Machine With A Side Passage Of Vapour

water water where Noil stands for the number of moles of the oil in the vapor phase and Nwater the number of moles of water in the vapor phase. It is nearly impossible to calculate the proportions as an essential oil is a multicomponent mixture of variable composition.

The simplest method of essential oil extraction is by means of hydrodistillation, for example, by immersion of the biomass in boiling water. The plant material soaks up water during the boiling process and the oil contained in the oil cells diffuses through the cell walls by means of osmosis. Once the oil has diffused out of the oil cells, it is vaporized and carried away by the stream of steam. The volatility of the oil constituents is not influenced by the rate of vaporization but does depend on the degree of their solubility in water. As a result, the more water-soluble essential components will distil over before the more volatile but less water-soluble ones. The usefulness of hydrodiffusion can be demonstrated by reference to rose oil. It is well known that occasionally some of the essential oil constituents are not present as such in the plant but are artifacts of the extraction process. They can be products of either enzymic splitting or chemical degradation, occurring during the steam distillation, of high-molecular-weight and thus nonvolatile compounds present in the plants. These compounds are often glycosides. The main constituents of rose oil, citronellol, geraniol, and nerol are products of a fermentation that takes place during the water-distillation process.

Hydrolysis of esters to alcohols and acids can occur during steam distillation. This can have serious implications in the case of ester-rich oils and special precautions have to be taken to prevent or at least to limit the extent of ester degradation. The most important examples of this are lavender or lavandin oils rich in linalyl acetate and cardamom oil rich in a-terpinyl acetate. Chamazulene, a blue bicyclic sesquiterpene, present in the steam-distilled oil of German chamo-mile, Chamomilla recutita (L.) Rauschert, flower heads is an artifact resulting from matricin by a complex series of chemical reactions: dehydrogenation, dehydration, and ester hydrolysis. As chamazulene is not a particularly stable compound, the deep blue color of the oil can change to green and even yellow on aging.

The design of a water/steam distillation plant at its simplest, sometimes called "false bottom apparatus," is as follows: a still pot (a mild steel drum or similar vessel) is fitted with a perforated metal plate or grate, fixed above the intended level of the water, and a lid with a goose neck outlet. The lid has to be equipped with a gasket or a water seal to prevent steam leaks. The steam outlet is attached to a condenser, for example, a serpentine placed in a drum containing cold water. An oil collector (Florentine flask) placed at the bottom end of the serpentine separates the oil from the distilled water (Figure 4.9). The whole assembly is fixed on a brick fireplace. A separate water inlet is often provided to compensate for water used up during the process. The biomass is placed inside the still pot above the perforated metal plate and sufficient biomass should be used to completely fill the still pot. The fuel used is firewood. This kind of distillation plant was extensively used at the end of the nineteenth century, mainly for field distillations. A disadvantage of this system was that in some cases excessive heat imparted a burnt smell to the oils. Furthermore, when the water level in the still dropped too much the, plant material could get scorched. Till today there is a necessity to clean the distillation vessel after two cycles with water to avoid burning notes in the essential oil. In any case, the quality of oils obtained in this type of apparatus was very variable and varied with each distillation. A huge improvement to this process was the introduction of steam generated externally. The early steam generators were very large and unwieldy and the distillation plant could no longer be transported in the field. The biomass had now to be transported to the distillation plant, unlike with the original type of distillation plant. Originally, the generator was fuelled with dry,

FIGURE 4.9 Old distillation apparatus modernized by electric heating.

extracted biomass. Today gas or fuel oil is used. The delivery of steam can be carried out in various ways. Most commonly, the steam is led directly into the still through its bottom. Overheating is thus avoided and the biomass is heated rapidly. It also allows regulation of steam quantity and pressure and reduces distillation time and improves oil quality. In another method, the steam is injected in a spiraling motion. This method is more effective as the steam comes into contact with a greater surface of the biomass. The velocity of steam throughput and the duration of the distillation depend on the nature of the biomass. It can vary from 100 kg/h in the case of seed and fruits to 400 kg/h for clary sage. The duration of the distillation can vary from about 20 min for Lavender flowers (Denny, 1995, personal communication) to 700 min for dried Angelica root. The values quoted are for a 4 m3 still pot (Omigbaigi, 2005). Specialists on distillation found as formula that distillation can be stopped when the ratio of oil to water coming from condenser will achieve 1:40. In all cases of hydrodistillation, the distillation water is recovered and reused for steam generation. In a coho-bation, the aqueous phase of the distillate is continuously reintroduced into the still pot. In this method, any essential oil constituents emulsified or dissolved in the water are captured, thus increasing total oil yield. There is one important exception: In the case of rose oil the distillation water is collected and redistilled separately in a second step. The "floral water" contains increased amounts of b-phenylethyl alcohol, up to 15%, whereas its maximum permissible content in rose oil is 3%. The reason for this is its significant solubility in water, ca. 2%.

The distillation of rose oil is an art in itself as not only quality but quantity as well play an important role. It takes two distillation cycles to produce between 200 and 280 g of rose oil. Jean-François Arnodou describes its manufacture as follows (Arnodou, 1991): The still pot is loaded with 400 kg of rose petals and 1600 L of water. The contents are heated until they boil and steam-distilled. Approximately, the quantity of flowers used is then distilled. That action will last about 2-3 h. Specially designed condensers are required in order to obtain a good quality. The condensing system comprises a tubular condenser followed by a second cooler to allow the oil to separate. The oil is collected in Florentine-type oil separators. About 300 L of the oil-saturated still waters are then redistilled in a separate still in order to recover most of the oil contained in them. Both oils are mixed together and constitute the rose oil of commerce. BIOLANDES described in 1991 the whole process, which uses a microprocessor to manage parameters such as pressure and temperature, regulated by servo-controlled pneumatic valves.

A modern distillation plant consists of the biomass container (still pot), a cooling system (condenser), an oil separator, and a high-capacity steam generator. The kettle (still pot) looks like a cylindrical vertical storage tank with steam pipes located at the bottom of the still. Perforated sieve-like plates are often used to separate the plant charge and prevent compaction, thus allowing the steam unimpeded access to the biomass. The outlet for the oil-laden steam is usually incorporated into the design of the usually hemispherical, hinged still pot lid. The steam is then passed through the cooling system, either a plate heat exchanger or a surface heat exchanger, such as a cold-water condenser. The usually liquid condensate is separated into essential oil and distillation water in an appropriate oil separator such as a Florentine flask. The distillation water may, in some cases, be redistilled and any essential oil recovered dried and stored. Figure 4.10 shows a cross section of such a still.

The following illustrations show different parts of an essential oil production plant. Figure 4.11 shows a battery of four production units in the factory. Each still has a capacity of 3000-5000 L. Owing to their large size, the upper half of the stills is on the level as shown while the lower half is situated on the lower level. Figure 4.12 shows open stills and displays the steam/oil vapor outlets on the underside of the lids leading to the cooling units. On the right side of the illustration, one can see the perforated plate used to prevent clumping of the biomass. Several such perforated plates, up to 12, depending on the type of biomass, are used to prevent clumping. Spacers on the central upright control the optimum distance between these plates for improved steam penetration. Figure 4.13 shows the unloading of the still. Unloading is much faster than the loading process where the biomass is compacted either manually or by means of tractor wheel (Figure 4.14). This type of loading is called "open mouth" loading. Figure 4.15 shows the cooling unit. The cold water enters the tank equipped with a coil condenser. The cooling water is recycled so that no water is wasted. The two main types of industrially used condensers

Essential Oil Condenser Design
FIGURE 4.10 Cross section of a hydrodistillation plant.

are the following. The earliest was the coil condenser that consisted of a coiled tube fixed in an open vessel of cold water with cold water entering the tank from the bottom and leaving at the top. The oil-rich steam is passed through the coils of the condenser from the top end. The second type of condenser is the pipe bundle condenser where the steam is passed through several vertical tubes immersed in a cold water tank. The tubes have on the inside walls horizontal protuberances that slow down the rate of the steam flow and thus result in more effective cooling. Figure 4.16 shows the inside of a Florentine flask where the oil is separated from the water. Most essential oils are lighter than water and thus float on top of the water. Some essential oils have a specific gravity >1, for example, they are heavier than water thus collecting at the bottom of the collection vessel. A modified design of the Florentine flask for such oils is shown in Figure 4.17. Figure 4.18 shows oil in the presence of turbid distillation water. The liquid phase is contaminated with biomass matter and the oil has to be filtered. The capacity of the still pot depends on the biomass. Weights vary from 150 to 650 kg/m3. Wilted and dried plants are much lighter than seeds and fruits or dried roots that can be very heavy.

FIGURE 4.11 Battery of four distillation units.
FIGURE 4.12 Open kettle with opening for vapor and oil.

A very special case is the production of the essential oils of Ylang-Ylang from the fresh flowers of Cananga odorata (Lam.) Hook. f. et Thomson forma genuina. The flowers are water distilled, stopped, and restarted again. In this manner, a total of four fractions is obtained. The chemical composition of the first fraction is characterized by a high concentration of p-cresol methylether, methyl benzoate, benzylacetate, linalool, and £-cinnamyl acetate. The second fraction contains less f those volatiles but an increased amount of geraniol, geranyl acetate, and b-caryophyllene. The third fraction contains higher boiling substances such as germacrene-D, (£,£)-a-farnesene, (£,£)-farnesole, benzyl benzoate, (£,£')-farnesyl acetate, and benzyl salicylate. Of course, smaller quantities of the lower boiling

FIGURE 4.13 Unloading a kettle.
Conspiracy
FIGURE 4.14 Loading a kettle and pressing by concreted tractor wheel.

components are also present. This kind of fractionation has been practiced for a long time. At the same time, the whole oil, obtained by a single distillation is available as "Ylang complete." This serves as an example of the importance the duration of the distillation can have on the quality of the oil.

Raw materials occurring in the form of hard grains have to be comminuted, for example, ground up before water distillation. This is carried out in the presence of water, such as in a wet-grinding turbine, and the water is used later during the distillation. The stills themselves are equipped with blade stirrers ensuring thorough mixing and particularly dislodging oil particles or biomass articles sticking to the walls of the still, the consequence of which can be burning and burnt notes. Dry grinding is likely to result in a significant loss of volatiles. Pepper, coriander, cardamom, celery seed, and angelica seed as well as roots, cumin, caraway, and many other seeds and fruit are treated in this manner. The process used in all these cases is called "turbo distillation." The ratio oil/condensate is

Loss Drying Flasks

FIGURE 4.15 Cooling unit.

FIGURE 4.16 Inner part of a Florentine flask.

very low when this method is used and it is for that reason that turbo distillation uses a fractionating column to enrich the volatiles. This also assists in preventing small particles of biomass passing into the condenser and contaminating the oil. As in many other distillation and rectification units, cold traps are installed to capture any very volatile oil constituents that may be present. This water-distillation procedure is also used for gums such as myrrh, olibanum, opopanax, and benzoin.

Orris roots are also extracted by water distillation. However, in this case, the distillation has to be carried out under conditions of slightly elevated pressure. This is achieved by means of a reflux column filled with Raschig rings. This is important as the desired constituents, the irones, exhibit very high boiling points. It is noteworthy that in this case there is no cooling of the vapors, as not only the irones but also the long-chain hydrocarbons will immediately be transported to the top of the column. Figure 4.19 shows a Florentine flask with the condensed oil/water emerging at a temperature of nearly 98°C. Orris oil or orris butter (note that the term orris "concrete" is incorrect, as the process is not a solvent extraction) is one of the few essential oils that are, at least partly, solid at room temperature. Depending on its trans-anethole content rectified star anise oil is another example of this nature.

Oil heavier than water FIGURE 4.17 Two varieties of Florentine flasks.

Oil lighter than water

Oil heavier than water FIGURE 4.17 Two varieties of Florentine flasks.

Oil lighter than water

Florentine Flask
FIGURE 4.18 (See color insert following page 468.) Oil and muddy water in the Florentine flask.

A relatively new technique that saves time in loading and unloading of the biomass is the "on-site" or "container" distillation. The technique is very simple as the container that is used to pick up the biomass and transport it to the distillery serves itself as the still pot. The first plant crops treated in this way were peppermint and mint, clary sage, lavandin grosso, L. angustifolia, Eucalyptus polybractea, and tea tree. In its simplest form, the mobile still assembly is composed of the following components: A tractor is coupled to an agricultural harvester that cuts the plant material and delivers it directly into the still pot (or vat) via a chute. The still pot (vat) is permanently fixed onto a trailer that is coupled to the harvester. Once the still pot is completely filled, it is towed by the tractor into the factory where it is uncoupled and attached to the steam supply and condenser and

Florentine Flask
FIGURE 4.19 Orris distillation, Florentine flask at nearly 98°C.

distillation commences. Presupposition for a proper working of the container as vat is a perfect insulation. Every loss of steam and heat will guide to worse quality and diminished quantity. Lids will have to be placed properly and fixed by clamps. The tractor and harvester are attached to an empty still pot and the process is repeated. The design, shape, and size of the still pot as well as the type of agricultural harvester depend on the type of plant crop, the size of the plantation, the terrain, and so on. The extracted biomass can be used as mulch or, after drying, as fuel for the steam boiler. The unloading is automated using metal chains running over the tubes with steam valves. This method requires less manpower and thus reduces labor costs. Loading and unloading costs are minimal. It lends itself best to fresh biomass, lavender and lavandin, mallee eucalypts, tea tree, and so on. It may not be as useful for the harvesting and distillation of mint and peppermint as these crops have to be wilted before oil extraction. Figures 4.20 through 4.22 show the harvesting of mallee eucalyptus, containers in processing, and the whole site of container distillation. Figure 4.23 gives a view into the interior of a container.

Another interesting distillation method has been developed by the LBP Freising, Bavaria, Germany. The plant consists of two tubes, each 2 m long and 25 cm in diameter, open at the top. The tubes are attached vertically to a central axis that can be rotated. One tube is connected, hydrauli-cally or mechanically, to the steam generator and on top to a condenser. During the distillation of the contents of the tube, which may take 25-40 min depending on the biomass, the other tube can be loaded. When the distillation of the first tube has been completed the tubes are rotated around the axis and distillation of the second tube commenced. The first distilled tube can now be emptied and reloaded. The only disadvantage of this type of apparatus is the small size. Only 8.5-21 kg of biomass can be treated. This system has been developed for farmers intending to produce small quantities of essential oil. The apparatus is transportable on a truck and will work satisfactorily provided a supply of power is available.

Most commercially utilized essential oil distillation methods, excepting the mobile still on-site methods, suffer from high labor costs. Apart from harvesting the biomass, 3-4 laborers will be required to load and unload the distillation pots, regulating steam pressure and temperature, and so on. The loading and distribution of the biomass in the distillation vessel may not be homogeneous. This will adversely affect the steam flow through the biomass by channeling, for example, the steam passing through less compacted areas and thus not reaching other more compacted areas. This will result in lower oil yields and perhaps even alter the composition of the oil. In times of high energy

FIGURE 4.20 Harvesting blue mallee with distillation container.
FIGURE 4.21 A battery of containers to be distilled, one opened to show the biomass.

costs the need for consequent recovery has to be considered. Given the demand for greater quantities of essential oils, the question is how to achieve it and at the same time improve the quality of the oils. For this, several considerations have to be taken into account. The first is how to process large quantities of biomass in a given time? Manpower has to be decreased as it still is the most important factor affecting costs. The biomass as a whole has to be treated uniformly to ensure higher oil yields and more constant and thus better oil composition. How can energy costs and water requirements be reduced in an ecologically acceptable way? The answer to this was the development of continuous distillation during the last years of the twentieth century. Until then all distillation processes were discontinuous. Stills had to be loaded, the distillation stopped, and stills unloaded. The idea was to develop a process where the steam production was continuous with permanent unchanged parameters. This was achieved by the introduction of an endless screw that fed the plant material slowly into the still pot from the top and removed the exhausted plant material from the bottom at the same speed. The plant material moves against the flow of dry steam entering the still from the bottom. In this fashion, all of the biomass comes into contact with the steam ensuring optimum essential oil extraction.

FIGURE 4.22 Distillation plant with container technique.

The earliest of these methods is known as the "Padova System." It consists of a still pot 6 m high and about 1.6 m in diameter (Arnodou, 1991). Its total volume is about 8 m3. The feeding of the still with the plant biomass as well as its subsequent removal is a continuous process. The plant material is delivered via a feed hopper situated at the top of the still. Before entering the still, it is compressed and cut by a rotating knife to ensure a more uniform size. Finally, a horizontal moving cone regulates the quantity of biomass entering the still. The biomass that enters the still moves in the opposite direction to that of the steam. The steam saturated with essential oil vapors is then passed into the cooling system. The exhausted plant material is simultaneously removed by means of an Archimedes screw. This type of plant was originally designed for the distillation of wine residues. A different system is provided by the distillation chimie fine (DCF) aroma process continuous distillation. Once again the plant material is delivered via a hopper to several interconnected tubes. These tubes are slightly inclined and connected to each other. The biomass is carried slowly through the tubes, by means of a worm screw, in a downward direction. Steam is injected at the end of the last tube and is directed upward in the opposite direction to that of the movement of the plant material. The essential oil-laden steam is deflected near the point of entrance of the biomass, into the condenser. The exhausted plant material is unloaded by another worm screw located near the point of the steam entrance to the system.

Texarome, a big producer of cedarwood oil and related products holds a patent on another continuous distillation system. In contrast to other systems, the biomass is conveyed pneumatically within the system. It is a novel system spiked with new technology of that time. Texan cedarwood oil is produced from the whole tree, branches, roots, and stumps. Cedarwood used in Virginia uses exclusively branches, stumps, saw dust, and other waste for oil production; wood is used mainly for furniture making. The wood is passed through a chipper and then through a hammer mill. The dust is collected by means of a cyclone. Any coarse dust is reground to the desired size. The dust is now carried via a plug feeder to the first contactor where superheated steam in reverse flow exhausts it in a first step and following that in a similar second step at the next contactor. The steam and oil vapors are carried into a condenser. The liquid distillate is then separated in Florentine flasks. This process does all transport entirely by pneumatic means. The recycling of cooling water and the use of the dried plant matter as a fuel contribute to environmental requirements (Arnodou, 1991). In the 1990s, the BIOLANDES Company designed its own system of continuous distillation. The reason for this was BIOLANDES' engagement in the forests of south-western France. Between Bordeaux and Biarritz exists the most important area of pine trees (Pinus pinaster Sol.) supplying the paper industry. Twigs and needles have been burnt or left to rot to assist with reforestation with new trees. These needles contain a fine essential oil very similar to that of the dwarf pine oil (Pinus mugo Turra.). Compared to other needle oils dwarf pine oil is very expensive and greatly appreciated. The oil was produced by a discontinuous distillation but as demand rose, new and improved methods were required. First of all, the collection of the branches had to be improved. A tractor equipped with a crude grinder and a ground wood storage box follows the wood and branch cutters and transports it to the nearby distillation unit where the biomass is exhausted via a continuous distillation process. In contrast to the earlier described methods the BIOLANDES continuous distillation process operates somewhat differently. The plant material is carried by mechanical means from the storage to the fine cutter and via an Archimedes screw to the top of the distillation pot. The plant material is now compressed by another vertical screw and transported into a chamber which is then hermetically closed on its back but opening at the front. Biomass is falling down allowing the countercurrent passage of hot steam through it. The steam is supplied through numerous nozzles. Endless screws at the bottom of the still continuously dispose of the exhausted biomass. Oil-laden steam is channeled from the top of the still into condenser and then the oil separator.

It is well known that clary sage yields an essential oil on hydrodistillation. However, a very important component of this oil, sclareole, is usually recovered in only very small quantity when this method is used, the reason for this being its very high boiling point. Sclareole can be recovered in very high yield and quality by extraction with volatile solvents. Consequently, BIOLANDES has incorporated an extraction step in its system (Figure 4.24). Any waste biomass, whether of extracted or nonextracted material, is used for energy production or, mostly, for composting. The energy recovery management distinguishes this system from all other earlier described processes. In all of the latter,

Distilling Biomass
FIGURE 4.24 Scheme of the BIOLANDES continuous production unit. A: biomass; B: distillation vat; C: condenser; D: Florentine flask; E: extraction unit; F: solvent recovery; G: exhausted biomass.

large amounts of cold water are required to condense the essential oil-laden steam. This results in significant wastage of water as well as in latent energy losses. The BIOLANDES system recovers this latent heat. Hot water from the condenser is carried into an aerodynamic radiator. Air used as the transfer gas takes up the energy of the hot water, cooling it down, so that it can be recycled to the condenser. The hot air is then used to dry about one-third of the biomass waste that is used as an energy source for steam and even electricity production. In other words, this system is energetically self-sufficient. Furthermore, since it is fully automated, it results in constant quality products. A unit comprising two stills of 7.5 m3 capacity can treat per hour 3 ton of pine needles, 1.5 ton of juniper branches, and 0.25 ton of cistus branches (Arnodou, 1991). The advantages are once again short processing time of large amounts of biomass, reduced labor costs, and near complete energy sufficiency. All operations are automated and water consumption is reduced to a minimum. The system can also operate under slight pressure thus improving the recovery of higher boiling oil constituents.

The following is a controversial method for essential oil extraction by comparison with classical hydrodistillation methods. In this method, the steam enters the distillation chamber from the top passes through the biomass in the still pot (e.g., the distillation chamber) and percolates into the condenser located below it. Separation of the oil from the aqueous phase occurs in a battery of Florentine flasks. It is claimed that this method is very gentle and thus suitable for the treatment of sensitive plants. The biomass is held in the still chamber (e.g., still pot) on a grid that allows easy disposal of the spent plant matter at the completion of the distillation. The whole apparatus is relatively small, distillation times are reduced, and there is less chance of the oil being overheated. It appears that this method is fairly costly and thus likely to be used only for very high-priced biomass.

Recently, microwave-assisted hydrodistillation methods have been developed, so far mainly in the laboratory or only for small-scale projects. Glass vessels filled with biomass, mainly herbs and fruits or seeds, are heated by microwave power. By controlling the temperature at the center of the vessel, dry heat conditions are established at about 100°C. As the plant material contains enough water, the volatiles are evaporated together with the steam solely generated by the microwave heat and can be collected in a suitably designed condenser/cooling system. In this case, changes in the composition of the oil will be less pronounced than in oil obtained by conventional hydrodistillation. This method has attracted interest owing to the mild heat to which the plant matter is exposed. Kosar reported improvements in the quality of microwave extracted fennel oil due to increases in the yields of its oxygenated components (Kosar et al., 2007).

Very different products can result from the dry distillation of plant matter. ISO Standard 9235 specifies in Section 3.1.4 that products of dry distillation, for example, "... obtained by distillation without added water or steam" are in fact essential oils (ISO/DIS 9235.2, 1997, p. 2). Dry distillation involves heating in the absence of aerial oxygen, normally in a closed vessel, preventing combustion. The plant material is thus decomposed to new chemical substances. Birch tar from the wood exsudate of Betula pendula Roth. and cade oil from the wood of Juniperus oxycedrus L. are manufactured in this way. Both oils contain phenols, some of which are recognized carcinogens. For this reason, the production of these two oils is no longer of any commercial importance, though very highly rectified and almost phenol-free cade oils do exist.

Some essential oils require rectification. This involves redistillation of the crude oil in order to remove certain undesirable impurities, such as very small amounts of constituents of very low volatility, carried over during the steam or water distillation (such as high-molecular-weight phenols, leaf wax components, etc.) as well as small amounts of very volatile compounds exhibiting an undesirable odor, and thus affecting the top note of the oils, such as sulfur compounds (dimethyl sulfide present in crude peppermint oil), isovaleric aldehyde (present in E. globulus oil), and certain nitrogenous compounds (low-boiling amines, etc.). In some cases, rectification can also be used to enrich the essential oil in a particular component such as 1,8-cineole in low-grade eucalyptus oil. Rectification is usually carried out by redistillation under vacuum to avoid overheating and thus partial decomposition of the oil's constituents. It can also be carried out by steaming. Commonly rectified oils include eucalyptus, clove, mint, turpentine, peppermint, and patchouli. In the case of patchouli and clove oils, rectification improves their, often unacceptably, dark color.

Fractionation of essential oils on a commercial scale is carried out in order to isolate fractions containing a particular compound in very major proportions and occasionally even individual essential oil constituents in a pure state. In order to achieve the required separation, fractionations are conducted under reduced pressure (e.g., under vacuum) to prevent thermal decomposition of the oil constituents, using efficient fractionating columns. A number of different types of fractionating columns are known but the one most commonly used in laboratory stills or small commercial stills is a glass or stainless steel column filled with Raschig rings. Raschig rings are short, narrow diameter, rings made of glass, or any other chemically inert material. Examples of compounds produced on a commercial scale are citral (a mixture of geranial and neral) from Litsea cubeba, 1,8-cineole from eucalyptus oil (mainly Eucalyptus polybractea and other cineole-rich species) as well as from Cinnamomum camphora oil, eugenol from clove leaf oil, a-pinene from turpentine, citronellal from citronella oil, linalool from Ho-oil, geraniol from palmarosa oil, and so on. A small-scale high vacuum plant used for citral production is shown in Figure 4.25. The reflux ratio, for example, the amount of distillate collected and the amount of distillate returned to the still, controls equilibrium conditions of the vapors near the top of the fractionation column, which are essential for good separation of the oil constituents.

FIGURE 4.25 High vacuum rectification plant in small scale. The distillation assembly is composed of a distillation vessel (1) of glass, placed in an electric heating collar (2). The vessel is surmounted by a jacketed fractionation column (3), packed with glass spirals or Raschig rings, of such a height as to achieve maximum efficiency (e.g., have the maximum number of theoretical plates capable of being achieved for this type of apparatus). The reflux ratio is automatically regulated by a device (4), which also includes the head condenser (5), a glass tube leads the product to another condenser (6), from there to the both receivers (7). The vacuum pump unit is placed on the right (8).

FIGURE 4.25 High vacuum rectification plant in small scale. The distillation assembly is composed of a distillation vessel (1) of glass, placed in an electric heating collar (2). The vessel is surmounted by a jacketed fractionation column (3), packed with glass spirals or Raschig rings, of such a height as to achieve maximum efficiency (e.g., have the maximum number of theoretical plates capable of being achieved for this type of apparatus). The reflux ratio is automatically regulated by a device (4), which also includes the head condenser (5), a glass tube leads the product to another condenser (6), from there to the both receivers (7). The vacuum pump unit is placed on the right (8).

Apart from employing fractional distillation, with or without the application of a vacuum, some essential oil constituents are also obtained on a commercial scale by freezing out from the essential oil, followed by centrifugation at below freezing point of the desired product. Examples are menthol from Mentha species (this is usually further purified by recrystallization from a suitable solvent, trans-anethole from anise oil, star anise oil, and particularly fennel seed oil and 1,8-cineole from cineole-rich eucalyptus oils.

Most essential oils are complex mixtures of terpenic and sesquiterpenic hydrocarbons, and their oxygenated terpenoid and sesquiterpenoid derivatives (alcohols, aldehydes, ketones, esters, and occasionally carboxylic acids), as well as aromatic (benzenoid) compounds such as phenols, phenolic ethers, and aromatic esters. So-called "terpene-less" and "sesquiterpene-less essential oils are commonly used in the flavor industry. Many terpenes are bitter in taste and many, particularly the terpenic hydrocarbons, are poorly soluble or even completely insoluble in water-ethanol mixtures. Since the hydrocarbons rarely contribute anything of importance to their flavoring properties, their removal is a commercial necessity. They are removed by the so-called "washing process," a method used mostly for the treatment of citrus oils. This process takes advantage of the different polarities of individual essential oil constituents. The essential oil is added to a carefully selected solvent (usually a water-ethanol solution) and the mixture partitioned by prolonged stirring. This removes some of the more polar oil constituents into the water-ethanol phase (e.g., the solvent phase). Since a single partitioning step is not sufficient to effect complete separation, the whole process has to be repeated several times. The water-ethanol fractions are combined and the solvent removed. The residue contains now very much reduced amounts of hydrocarbons but has been greatly enriched in the desired polar oxygenated flavor constituents, aldehydes such as octanal, nonanal, decanal, hexenal, geranial, and neral; alcohols such as nerol, geraniol, and terpinen-4-ol; oxides such as 1,8-cineole and 1,4-cineole; as well as esters and sometimes carboxylic acids. Apart from water-ethanol mixtures, hexane or light petroleum fractions (sometimes called "petroleum ether") have sometimes also been added as they will enhance the separation process. However, these are highly flammable liquids and care has to be taken in their use.

"Folded" or "concentrated" oils are citrus oils from which some of the undesirable components (usually limonene) have been removed by high vacuum distillation. In order to avoid thermal degradation of the oil, temperatures have to be kept as low as possible. Occasionally, a solvent is used as a "towing" agent to keep the temperature low.

Another, more complex, method for the concentration of citrus oils is a chromatographic separation using packed columns. This method allows a complete elimination of the unwanted hydrocarbons. This method, invented by Erich Ziegler, uses columns packed with either silica or aluminum oxide. The oil is introduced onto the column and the hydrocarbons eluted by means of a suitable nonpolar solvent of very low boiling point. The desirable polar citrus oil components are then washed out using a polar solvent (Ziegler, 1982).

Yet another valuable flavor product of citrus fruits is the "essence oil." The favored method for the transport of citrus juice is in the form of a frozen juice concentrate. The fruit juice is partly dehydrated by distilling off under vacuum the greater part of the water and frozen. Distilling off the water results in significant losses of the desirable volatiles responsible for the aroma of the fruit. These volatiles are captured in several cold traps and constitute the "aqueous essence" or "essence oil" that has the typical fruity and fresh fragrance, but slightly less aldehydic than that of the oil. This oil is used to enhance the flavor of the reconstituted juice obtained by thawing and dilution with water of the frozen concentrate.

Producing essential oils today is, from a marketing point of view, a complex matter. As in the field of other finished products, the requirements of the buyer or producer of the consumer product must be fulfilled. The evaluation of commercial aspects of essential oil production is not an easy task and requires careful consideration. There is no sense in producing oils in oversupply. Areas of short supply, depending on climatic or political circumstances should be identified and acted upon. As in other industries global trends are an important tool and should continually be monitored.

For example, which are the essential oils that cannot be replaced by synthetic substitutes such as patchouli oil or blue chamomile oils? A solution to this problem can lie in the breeding of suitable plants. For example, a producer of a new kind "pastis," the traditional aperitif of France, wants to introduce a new flavor with a rosy note in the fennel component of the flavor. This will require the study and identification of oil constituents with "rosy" notes and help biologists to create new botanical varieties by genetic crossing, for example, by genetic manipulation, of suitable target plant species. Any new lines will first be tested in the laboratory and then in field trials. Test distillations will be carried out and the chemical composition of the oils determined. Agronomists and farmers will be involved in all agricultural aspects of the projects: soil research and harvesting techniques. Variability of all physicochemical aspects of the new strains will be evaluated. At this point, the new types of essential oils will be presented to the client. If the client is satisfied with the quality of the oils, the first larger plantations shall be established and consumer market research will be initiated. If everything has gone to plan, that is all technical problems have been successfully resolved and the finished product has met with the approval of the consumers, large-scale production can begin. This example describes the current way of satisfying customer demands.

Global demand for essential oils is on the increase. This also generates some serious problems for which immediate solutions may not easily be found. The first problem is the higher demand for certain essential oils by some of the world's very major producers of cosmetics. They sometimes contract oil quantities that can be of the order of 70% of world production. This will not only raise the price but also restrict consumer access to certain products. From this arises another problem. Our market is to some extent a market of copycats. How can one formulate the fragrance of a competitor's product without having access to the particular essential oil used by him, particularly as this oil may have other functions than just being a fragrance, such as, for example, certain physiological effects on both the body as well as the mind? Lavender oil from L. angustifolia is a calming agent as well as possessing anti-inflammatory activity. No similar or equivalent natural essential oil capable of replacing it is known. Another problem affecting the large global players is ensuring the continuing availability of raw material of the required quality needed to satisfy market demand. This is clearly an almost impossible demand as nobody can assure that climatic conditions required for optimum growth of a particular essential oil crop will remain unchanged. Another problem may be the farmer himself. Sometimes it may be financially more worthwhile for the farmer to cultivate other than essential oil plant crops. All these factors may have some detrimental effects on the availability of essential oils. Man's responsibility for the continued health of the environment may also be one of the reasons for the disappearance of an essential oil from the market. Sandalwood (species of Santalum, but mainly Indian Santalum album) requires in some cases up to 100 years to regenerate to a point where they are large enough to be harvested. This and their uses in religious ceremonies have resulted in significant shortages of Indian oil. Owing to the large monetary value of Indian sandalwood oil, indiscriminate cutting of the wood has just about entirely eliminated it from native forests in Timor (Indonesia). Sandalwood oils of other origins are available, Santalum spicatum from western Australia, and Santalum austrocaledonicum from New Caledonia and Vanuatu. However, their wood oils differ somewhat in odor as well as in chemical composition from genuine Indian oils.

Some essential oils are disappearing from the market owing to the hazardous components they contain and are, therefore, banned from most applications in cosmetics and detergents. These oil components, all of which are labeled as being carcinogenic, include safrole, asarone, methyleugenol, and elemicin. Plant diseases are another reason for essential oil shortages as they, too, can be affected by a multitude of diseases, some cancerous, which can completely destroy the total crop. For example, French lavender is known to suffer from a condition whereby a particular protein causes a decrease in the growth of the lavender plants. This process could only be slowed down by cultivation at higher altitudes. In the middle of the twentieth century lavender has been cultivated in the Rhone valley at an altitude of 120 m. Today lavender is growing only at altitudes around 800 m. The growing shoots of lavender plants are attacked by various pests, in particular the larvae of

Cecidomye (Thomasissiana lavandula) which, if unchecked, will defoliate the plants and kill them. Some microorganisms such as Mycoplasma and a fungus Armillaria mellex can cause serious damage to plantations. At the present time, the use of herbicides and pesticides is an unavoidable necessity. Wild-growing plants are equally prone to attack by insect pests and plant diseases.

The progression from wild-growing plants to essential oil production is an environmental problem. In some developing countries, damage to the natural balance can be traced back to overexploitation of wild-growing plants. Some of these plants are protected worldwide and their collection, processing, and illegal trading are punishable by law. In some Asian countries, such as in Vietnam, collection from the wild is state controlled and limited to quantities of biomass accruing from natural regeneration.

The state of technical development of the production in the developing countries is very variable and depends largely on the geographical zone they are located in. Areas of particular relevance are Asia, Africa, South America, and eastern Europe. As a rule, the poorer the country, the more traditional and less technologically sophisticated equipment is used. Generally, standards of the distillation apparatus are those of the 1980s. At that time, the distillation equipment was provided and installed by foreign aid programs with European and American know-how. Most of these units are still in existence and, owing to repairs and improvements by local people, in good working order. Occasionally, primitive equipment has been locally developed, particularly when the state did not provide any financial assistance. Initially, all mastery and expertise of distillation techniques came from Europe, mainly from France. Later on, that knowledge was acquired and transferred to their countries by local people who had studied in Europe. They are no longer dependent on foreign know-how and able to produce oils of constant quality. Conventional hydrodistillation is still the main essential oil extraction method used, one exception being hydrodiffusion often used in Central America, mainly Guatemala and El Salvador, and Brazil in South America. The construction of the equipment is carried out in the country itself and makes the producer independent from higher-priced imports. Steam is generated by oil-burning generators only in the vicinity of cities. In country areas, wood or dried spent biomass is used. As in all other essential oil-producing countries, the distillation plants are close to the cultivation areas. Wild-growing plants are collected, provided the infrastructure exists for their transport to the distillation plant. For certain specific products permanent fixed distillation plants are used. A forward leap in the technology will be only possible if sufficient investment funds became available in the future. Essential oil quantities produced in those countries are not small and important specialities such as citral-rich ginger oil from Ecuador play a role on the world market. It should be a compulsory requirement that developing countries treat their wild-growing plant resources with the utmost care. Harvesting has to be controlled to avoid their disappearance from the natural environment and quantities taken adjusted to the ability of the environment to spontaneously regenerate. On the other hand, cultivation will have to be handled with equal care. The avoidance of monoculture will prevent leaching the soil of its nutrients and guard the environment from possible insect propagation. Balanced agricultural practices will lead to a healthy environment and superior quality plants for the production of essential oils.

The following are some pertinent remarks on the now prevailing views of "green culture" and "organically" grown plants for essential oil production. It is unjustified to suggest that such products are of better quality or greater activity. Comparisons of chemical analyses of "bio-oils," for example, oils from "organically" grown plants, and commercially produced oils show absolutely no differences, qualitative or quantitative, between them. While the concept of pesticide- and fertilizer-free agriculture is desirable and should be supported, the huge worldwide consumption of essential oils could never be satisfied by bio-oils.

Finally, some remarks as to the concept of honesty are attached to the production of natural essential oils. During the last 30 years or so, adulteration of essential oils could be found every day. During the early days, cheap fatty oils (e.g., peanut oil) were used to cut essential oils. Such adulterations were easily revealed by means of placing a drop of the oil on filter paper and allowing it to evaporate (Karg, 1981). While an unadulterated essential oil will evaporate completely or at worst leave only a trace of nonvolatile residue, a greasy patch indicates the presence of a fatty adulterant. As synthetic components of essential oils became available around the turn of the twentieth century some lavender and lavandin oils have been adulterated by the addition of synthetic linalool and linalyl acetate to the stills before commencing the distillation of the plant material. With the advent of improved analytical methods, such as GC and GC/MS, techniques of adulterating essential oil were also refined. Lavender oil can again serve as an example. Oils distilled from mixtures of lavender and lavandin flowers mimicked the properties of genuine good-quality lavender oils. However, with the introduction of chiral GC techniques, such adulterations were easily identified and the genuineness of the oils guaranteed. This also allowed the verification of the enantiomeric distribution of monoterpenes, monoterpenoid alcohols, and esters present in essential oils. Nuclear magnetic resonance (NMR) is probably one of the best, but also one of the most expensive, methods available for the authentication of naturalness and will be cost effective only with large batch quantities or in the case of very expensive oils. In the future, two-dimensional GC (GC/GC) will provide the next step for the control of naturalness of essential oils.

Another important aspect is the correct botanical source of the essential oil. This can perhaps best be discussed with reference to eucalyptus oil of the 1,8-cineole type. Originally, before commercial eucalyptus oil production commenced in Australia, eucalyptus oil was distilled mainly from E. globulus Labill. trees introduced into Europe [mainly Portugal and Spain (ISO Standard 770)]. It should be noted that this species exists in several subspecies: E. globulus subsp. bicostata (Maiden, Blakely, & J. Simm.) Kirkpatr., E. globulus Labill. subsp. globulus., E. globulus subsp. pseudoglobulus (Naudin ex Maiden) Kirkpatr., and E. globulus subsp. maidenii (F. Muell.) Kirkpatr. It has been shown that the European oils were in fact mixed oils of some of these subspecies and of their hybrids (report by H. H. G. McKern of ISO/TC 54 meeting held in Portugal in 1966). The European Pharmacopoeia Monograph 0390 defines eucalyptus oil as the oil obtained from E. globulus Labill., Eucalyptus fruticetorum F. von Mueller Syn. Eucalyptuspolybractea R. T. Baker (this is the correct botanical name), Eucalyptus smithii R. T. Baker, and other species of Eucalyptus rich in 1,8-cineole. The Council of Europe's book Plants in cosmetics, Vol. 1, page 127 confuses the matter even further. It entitles the monograph as E. globulus Labill. et al. species, for example, includes any number of unnamed Eucalyptus species. The Pharmacopoeia of the Peoples Republic of China (English Version, Vol. 1) 1997 goes even further defining eucalyptus oil as the oil obtained from E. globulus Labill. and Cinnamomum camphora as well as from other plants of those two families. ISO Standard 3065—Oil of Australian eucalyptus, 80-85% cineole content, simply mentions that the oil is distilled from the appropriate species. The foregoing passage simply shows that Eucalyptus oil does not necessarily have to be distilled from a single species of Eucalyptus, for example, E. globulus, although suggesting that it is admissible to include 1,8-cineole-rich Cinnamomum oils is incorrect and unrealistic. This kind of problem is not unusual or unique. For example, the so-called English lavender oil, considered by many to derive from L. angustifolia, is really, in the majority of cases, the hybrid lavandin (Denny, 1995, personal communication).

Another pertinent point is how much twig and leaf material can be used in juniper berry oil? In Indonesia, it is common practice to space individual layers of patchouli leaves in the distillation vessel with twigs of the gurjun tree. Gurjun balsam present in the twigs contains an essential oil that contaminates the patchouli oil. Can this be considered to constitute an adulteration or simply a tool required for the production of the oil?

4.1.16 Concluding Remarks

As mentioned at the beginning, essential oils do have a future. In spite of regulatory limitations, dangerous substance regulations, and dermatological concerns as well as problems with pricing the world production of essentials oil will increase. Essential oils are used in a very large variety of fields. They are an integral constituent of fragrances used in perfumes and cosmetics of all kinds, skin softeners to shower gels and body lotions, and even to "aromatherapy horse care massage oils." They are widely used in the ever-expanding areas of aromatherapy or, better, aromachology. Very large quantities of natural essential oils are used by the food and flavor industries for the flavoring of smallgoods, fast foods, ice creams, beverages, both alcoholic as well as nonalcoholic soft drinks, and so on. Their medicinal properties have been known for many years and even centuries. Some possess antibacterial or antifungal activity while others may assist with the digestion of food. However, as they are multi-component mixtures of somewhat variable composition, the medicinal use of whole oils has contracted somewhat, the reason being that single essential oil constituents were easier to test for effectiveness and eventual side effects. Despite all that, the use of essential oils is still "number one" on the natural healing scene. With rising health care and medicine costs, self-medication is on the increase and with it a corresponding increase in the consumption of essential oils. Parallel to this, the increase in various esoteric movements is giving rise to further demands for pure natural essential oils.

In the field of agriculture, attempts are being made at the identification of ecologically more friendly natural biocides, including essential oils, to replace synthetic pesticides and herbicides. Essential oils are also used to improve the appetite of farm animals, leading to more rapid increases in body weight as well as to improved digestion.

Finally, some very cheap essential oils or oil components such as limonene, 1,8-cineole, and the pinenes are useful as industrial solvents while phellandrene-rich eucalyptus oil fractions are marketed as industrial perfumes for detergents and the like.

In conclusion, a "golden future" can be predicted for that useful natural product: the "Essential Oil"!

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