The Modern Alchemy Of Carbon Dioxide Extraction

R. Guba, Essential Therapeutics Pty Ltd., 100 Dight Street, Collingwood, Vic.

The modern alchemy of carbon dioxide extraction

3066, Australia. E-mail: esstherapeutics@ozemail. com.au

Ron Guba

W

tillation,

and

less

commonly,

e must thank the practi-

Lastly, the remaining plant resi-

tioners of the ancient hermetic art of alchemy for what we know as essential oils today. The famous physician and alchemist Ibn Sina or Avicenna (AD

due or fixed sulphur would be completely burnt or calcined, the ash would be washed with water and the water evaporated, to liberate the water soluble mineral salts or the sal

through solvent extraction (the flower absolutes, generally extracted using the petrochemical, hexane). I would like to consider another form of the preparation of volatile

980–1037) is credited with perfecting the process of steam distillation to produce pure essential oils. This extraction method was only part of the

(which represents the ‘body’ or vehicle of the first two principles). The three ‘principles’ were then joined together to create a finished

sulphur, using the modern alchemy of dense carbon dioxide extraction. Cagniard de la Tour first discovered the phenomenon of a su-

process for creating an alchemical ‘spagyric’ preparation (from the Greek spagyria – spao- to draw out or divide and ageiro – to gather bind or

preparation. In the view of alchemists, ordinary plant tinctures only utilise part of the curative powers of the plant. Spagyric preparation

percritical fluid back in 1822. In 1879 and 1880, the first research was published detailing that various gases under high pressure were found to

join: hence to ‘dissolve and bind’). As in the treatises of the ‘father’ of western alchemy, Paraecelsus (AD 1493–1541), the creation of aspagyric

‘opens’ the plant, and liberates stronger curative powers. As in Homeopathy and other forms of vibrational medicine, spagyric

exhibit excellent solvent qualities for lipophilic compounds (i.e., compounds that dissolve in non-polar solvents such as vegetable oil, etha-

plant remedy was based on the liberation and joining together of the ‘three philosophical principles’ of the plant. First, the volatile sulphur would be

preparations are based on their synergistic and ‘energetic’ effects, instead of simply looking at pharmacologically active components (Junius, 1985).

nol, benzene, etc.). Due to the lack of technology in developing the key high pressure equipment required, supercritical fluid extraction was not commercia-

liberated via steam distillation. This is the essential oil that represents the very ‘soul’ or consciousness of the plant. Sulphur is fiery, radiant and a

In Aromatherapy then, we have an entire therapeutic approach based on the volatile sulphur of the alchemists. We can see where the

lised for over 50 years. Eventually, in the 1980s, a number of supercritical carbon dioxide extraction plants came into operation (Supercritical

masculine or active yang principle. Then, the plant residues would be fermented with yeast to produce ethanol – or grain alcohol. This was

term ‘essential oil’ derived from – ‘essence’ meaning the ‘soul’ or deeper ‘personality’ of the individual plant (and with mercury, we can still go to

Technology Consultants, 2002). A number of gases have been trailed for supercritical extraction, including trifluromethane, ethane,

distilled to create the pure mercury, which represents the principle of life; the vital power or ‘life force’, prana Qi, etc. It represents the feminine or passive Yin principle.

the liquor store and purchase a bottle of ‘spirits’). Traditionally, Aromatherapy has employed the use of essential oils created primarily through steam dis-

dinitrogen monoxide, sulphur hexafluoride and propane. However, carbon dioxide has been accepted as the extraction medium of choice, for the extraction of volatile compounds for

0962-4562/02/$ - See Front Matter
2002 Published by Elsevier Science Ltd

d

120

The International Journal of Aromatherapy 2002

vol d 12 no d 3

flavour, fragrance and therapeutic use, for decaffeinating coffee beans, for extraction of cocoa butter and other vegetable oils and on (Stahl et al., 1988; Phasex Corporation, 2002).

Yet, this ‘fluid’ also shares the properties of a liquid, with its high density and excellent solvating power. As the pressure is increased, the dissolving power of the supercritical carbon di-

importantly compounds found in essential oils: ethers, esters, terpene hydrocarbons, alcohols, ketones, etc. 2. At higher pressure and tempera-

Carbon dioxide We generally know of carbon dioxide

oxide increases. In Fig. 2, we see the solubility of a variety of aromatic compounds found in essential oils, in carbon dioxide. At pressure levels

ture, triglycerides (vegetable oils and animal fats), wax esters (as in Jojoba oil) and other higher weight non-polar compounds

(CO2 Þ in two forms: solid, dry ice, and as a gas. A liquid form does not exist at normal atmospheric pressure (see Fig. 1).

below the supercritical state, these compounds will only dissolve to a small degree, but as the supercritical state is reached the solubility in-

can be extracted. 3. As in the above two statements, compounds that are predominantly non-polar are best ex-

However, as pressure increases we can create a liquid form of CO2 (liquid CO2 plants often operate at 50–60 bar pressure at around 10 C

creases to quite high levels as the pressure is increased further. The solubility of typical essential oil components in dense carbon di-

tracted in carbon dioxide, which functions as a non-polar solvent. Hence, the presence of polar functional groups will

(1 bar ¼ 1 atm (normal atmospheric pressure) ¼ 10 kPa ¼ 76 mm Hg ¼ approximately 14–15 lb/in:2 pressure). As we take the pressure and

oxide at 40 C is shown in Fig. 3.

temperature beyond the ‘critical point’ (T c and P c ), carbon dioxide becomes supercritical, this being the boundary where the difference between being a gas and a liquid dissolve. Hence, we have an extremely dense ‘fluid’ with the properties of a gas – it diffuses easily throughout the plant material being extracted and it has low viscosity and surface tension.

What can be extracted with carbon dioxide?

1. The compounds that are most easily extractable (up to 300 bar pressure) are lipophilic (‘oil-loving’), compounds that have a high vapour pressure (volatility) and a low molecular weight (up to 400 Da). This includes most

lower the extraction to varying degrees. 4. Not extractable are polar compounds such as sugars, glycosides, amino acids, and lecithins; alkaloids are extracted at varying levels. Hence, carbon dioxide is not suitable for the extraction of all medicinal plants – it is dependent on the solubility of the most active compounds desired. 5. More polar modifying compounds, such as water, can be

Fig. 1 Solid–liquid–gas – supercritical fluid diagram. Pc , critical pressure; Tc , critical termperature. The critical pressure and temperature for carbon dioxide is 73.79 bar and 31.04 C, respectively. The triple point is where the solid, liquid, and gas phase co-exist in equilibrium.

The International Journal of Aromatherapy 2002

12 no d 3 vol d

d 121

Fig. 2 The solubility of naphthalene in carbon dioxide increases greatly as the supercritical state is reached, and with further increase of pressure.

Fig. 3 The solubility of typical essential oil components in dense carbon dioxide at 40 C (Franchomme, 1984).

added to the extraction process to increase the extraction of more polar compounds. This includes the extraction of the alkaloids caffeine from coffee beans and nicotine from tobacco as prime examples (Stahl et al., 1988; Amajuoyi, 2001).

Varieties of carbon dioxide extraction Supercritical CO2 plants generally operate from 80 to 500 bar pressure from 40 to 60 C. This supercritical extraction is of most interest in Aromatherapy and herbal medicine, as

d 122

used to create extracts from aromatic plants and for the extraction of vegetable oils, antioxidant compounds, and other therapeutically active compounds that cannot be extracted via steam distillation. Liquid CO2 extraction is the other major variant. As a prime

The International Journal of Aromatherapy 2002

12 no d 3 vol d

example, the prime flavouring compounds from pelletised Hops for use in beer, are extracted by liquid carbon dioxide as in my hometown, Melbourne, Aus-

of steam, and condense upon cooling. Generally, steam distillation is carried out at a temperature of 100 C, the boiling point of water. At

carbon atoms). The ‘heavier’ the compound, the higher its boiling point and vapour pressure, and hence heavier compounds remain behind in the still.

tralia at the Carlton United Breweries. Supercritical extraction is the basis of the remainder of the manu-

this temperature, in the presence of oxygen, water, and elevated temperature, various changes can occur in the structure of aromatic com-

Depending on the plant and whether active ingredients can pass over with steam, a more complete extract can be of higher therapeutic

script (see Fig. 4). Solubility isotherms of typical essential oil components in dense carbon dioxide.

pounds. Certain compounds are heat sensitive, or thermo labile. In other cases, various proteins present will decompose, creating what

value.

Supercritical carbon dioxide extraction demonstrates a number of advantages over the traditional methods of obtaining essential oils

are known as artefacts. These can be various types of decomposition products such as hydrogen sulphide, ammonia, acetaldehyde, and others.

and absolutes.

Linalyl acetate will decompose back to linalool and acetic acid in lavender oil; the sesquiterpene lactone, matricin (above 80 C) will decompose to the intensely blue sesquiterpene hy-

Carbon dioxide vs. steam distillation Steam distillation is the oldest and most common method of obtaining essential oils. In fact, we can define an essential oil as the volatile com-

drocarbon, chamazulene in German Chamomile. This is why the very expensive Bulgarian Damask Rose oil does not quite smell like a Rose – it has

pounds that will be removed via steam distillation. Volatile aromatic compounds, with a boiling point of 150–200 C,

been changed to some degree during steam distillation. As well, steam distillation favours only the most volatile compounds,

are selectively separated out from other plant constituents via the heat

starting with monoterpenes (10 carbon atoms) and lastly diterpenes (20

Fig. 4 Diagram of a supercritical carbon doxide extraction plant.

The International Journal of Aromatherapy 2002

12 no d 3 vol d

d 123

Solvent extraction A variety of organic non-polar solvents can be used for extracting lipophilic (oil loving) compounds, such as ethanol (in herbal tinctures, etc.), benzene, and trichloroethylene. In Aromatherapy, we see are the floral absolutes, obtained using the petrochemical solvents hexane and pentane. The traditional fat-extraction method, or enfleurage is hardly used these days, due to the very high labour costs involved. Almost all ‘absolutes’ are produced via hexane/ pentane extraction, as well as a few other novel hydrocarbon solvents (butane, for example). Solvent extraction is generally employed for the finest floral fra-

atmosphere each week (PNP Inc., 2002). Lastly, no matter how efficient the final extraction of hexane is from the finished absolute, some

Carbon dioxide extraction, on the other hand, bypasses the above problems. • CO2 extraction uses relatively low temperature; in the absence of oxygen and water. Hence, no decomposition products or artefacts are formed. The final extract contains what originally was in the plant. • As in hexane solvent extraction, all the heavier, less volatile components will be extracted, without the problem, however, of any solvent residues. At the end of extraction, the pressure is reduced to normal and the CO2 simply evaporates. • CO2 extracts do not require further processing, as hexane extracted concretes do. More highly volatile ‘top notes’ are retained. • CO2 extraction is non-toxic, nonflammable and is environmentally safe without harmful emissions or toxic by-products. In the case of one large manufacturer, Flavex Naturextrakte, natural carbon dioxide is collected from areas of volcanic activity. Hence, no additional CO2 is added to the atmosphere. Supercritical CO2 extraction also has the unique capacity to selectively extract different components. At 80– 100 bar pressure at 40–60 C, supercritical CO2 will extract primarily the volatile aromatic compounds, termed a ‘select’ extract. This is somewhat comparable to a hexane extracted absolute. By increasing the pressure from 200 to 500 bar with a longer extraction cycle, heavier lipophilic components are removed, including waxes,

hexane residues do remain in the final product. The current European Union standards are for less than 10 parts per million solvent

triglycerides (vegetable oils), wax esters (as in Jojoba), carotenoids, etc. These are termed total extracts and are somewhat comparable with a

residues in a finished absolute. This permitted level is small (0.001% or less), nevertheless, from a therapeutic perspective, a solvent-free

hexane extracted concrete.

grances, as the process creates less ‘re-arrangement’ of compounds than steam distillation (hence truer to the fragrance of the original flower) and will also extract heavier lipophilic components. Although this is valuable for the perfume and flavour industry (and hexane extraction is also the dominant method for the extraction of commercial vegetable oils), we find problems with the use of solvent extracted absolutes in Aromatherapy. Firstly, hexane, being simply high-vapour-pressure petrol, is very volatile, flammable and explosive. Numerous hexane extraction plants have exploded and burned over the past 50 years, often with the loss of multiple lives (PNP Inc., 2002). It has also been suggested that prolonged exposure to hexane amongst workers in extraction plants leads to a variety of illnesses (Franchomme, 1984). A severe environmental problem exists with the inevitable loss of hexane to the atmosphere during manufacturing and processing. Even a state-of-the-art, medium sized soybean oil producing plant is estimated to leak approximately 88,000 kg of hexane into the

extract for topical application, certainly for ingestion, would be preferred.

Disadvantages of carbon dioxide extraction • The first limitation is that of cost. As compared to the set-up costs of a

d 124

bush still, CO2 extraction plants are very expensive, in the range of millions of US dollars. This is a major reason why there are but a handful of CO2 plants in operation. This, however, does not translate to extraordinary prices for the extracts. Some extracts are comparable in cost to a corresponding, high quality essential oil. Other extracts, depending on yield and other factors, are significantly more expensive. • Pesticide residues. As compared to the amount of pesticide residues in spices that can be extracted by conventional liquid solvent extraction, carbon dioxide extraction has been demonstrated to concentrate from seven to 53 times more pesticide residues in the final extract. This can be addressed, of course, by only extracting plant material from certified organic growing practices, or shown to be pesticide-free by analysis. Varying different parameters of the extraction process will also reduce the extraction of pesticides (Amajuoyi, 2001).

Carbon dioxide extracts for therapeutic use The major market for CO2 extracts is their application in flavours and fragrances. Additionally, there are a number of extracts available that have definite applications in herbal and aromatic medicine. A selected list of such extracts includes: Calendula, German Chamomile, Frankincense, Ginger, Kava Kava, Marjoram, Melissa, and Rosemary; primarily vegetable oil extracts of Borage, Evening Primrose, Neem, Rose Hip, and Sea Buckthorn. Let us consider three extracts with outstanding therapeutic properties. Calendula CO2 total extract (Calendula officinalis) contains the active triterpene monools, diols, and

The International Journal of Aromatherapy 2002

12 no d 3 vol d

Table 1

Anti-inflammatory activity of Calendula officinalis extracts in reducing croton oil-induced oedema of mouse ear (Della Loggia et al., 1990a,b)

Substances

Dose (lg per ear)

Milligrams of crude druga

Inhibition of edema (%)

Hydro alcoholic extract

300 600 1200

1.04 2.08 4.16

9.3 12 20

Carbon dioxide extract

75 150 300

1.79 3.58 7.16

14.5 30.6 44

600 1200

14.3 28.6

58.7 70.7

30 120

– –

37.3 73.3

Indomethacin a

Milligrams of dried calendula flowers.

their esters, with the faradiol monoesters being the most important (about 20% of the total extract). Such compounds could not be extracted by steam distillation; they

substantially altered during steam distillation. The dark blue colour of German Chamomile is due to the sesquiterpene hydrocarbon, chamazulene, which is formed from the

apy, are extrapolated from the use of the whole rhizome. However, the essential oil lacks the active, less volatile pungent phenyl propanoid compounds.

are found in low concentration in both hydro alcoholic (tinctures) and vegetable oil extracts (infused oils).

decomposition of the sesquiterpene lactone, matricin during distillation. The CO2 extract of German Chamomile maintains the matricin content.

The total Ginger CO2 extract contains from 25 to 33% of these pungent actives – gingerols, shogaols, and zingerone. Therefore Ginger

As compared to a typical infused oil, the concentration of ‘actives’ in the CO2 extract is approximately 180 times greater. Calendula CO2 is an

It has a fine, characteristic chamomile odour, yellow–green in colour. As well, the extract of choice is derived from the a-bisabolol type Ger-

CO2 extract is therapeutically more active than the essential oil, making it more suitable for treating nausea, travel sickness, muscular pain,

excellent anti-inflammatory and healing extract. It is suited for conditions such as acne, eczema, allergic dermatitis and the healing of burns,

man Chamomile; a-bisabolol having demonstrated anti-inflammatory and wound healing activity (Jakovlev and von Schlichtegroll, 1969).

cramping, arthritis, etc., as outlined in both Eastern and Western herbal medicine (Flavex Naturextrakte, 2002).

wounds, and ulcers. It is also quite non-toxic and non-sensitising; up to a 10% concentration can be applied even on young infant (Quirin and Gerard, 1999).

In terms of anti-inflammatory power, there is research demonstrating that matricin has significantly stronger (10 times more active) antiinflammatory properties than cham-

In summary, we can see that essential oils have progressed beyond the stills of the ancient alchemists. Although traditional steam distilled oils will remain the most popular and

One study demonstrated the superior anti-inflammatory activity of Calendula CO2 extract versus a hydro alcoholic tincture. As well, the CO2

azulene. Hence, in the treatment of inflammatory disorders – dermatitis, oral mucositis, and the like — the

accessible plant extracts used in Aromatherapy, we can see some definite advantages in a variety of carbon dioxide extracts. As the interest

extract was as active in reducing inflammation as the potent anti-inflammatory drug, indomethacin (see Table 1).

CO2 extract stands superior (Della Loggia et al., 1990a,b). Most of the therapeutic applications of steam distilled Ginger

in Aromatherapy and botanical medicine continues to increase, we can look forward to adding more of these products of ‘modern alchemy’

German Chamomile (Matricaria recutita) yields an essential oil that is

(Zingiber officinale) essential oil listed in numerous books on Aromather-

to our working collection of health serving extracts.

The International Journal of Aromatherapy 2002

12 no d 3 vol d

d 125

Acknowledgments With thanks to Flavex Naturetrakte of Rehlingen, Germany for their assistance (www.flavex.com).

References Amajuoyi, I.K. (2001). Behavior and elimination of pesticide residues during supercritical carbon dioxide extraction of essential oils of spice plants and analysis of pesticides in high-lipid-content plant extracts. Doctoral thesis Technische Universit€at M€ unchen. Della Loggia, R. et al. (1990a). Topical anti-inflammatory activity of Calendula officinalis extracts. Planta Med. 56: 658. Della Loggia, R. et al. (1990b). Evaluation of the anti-

inflammatory activity of chamomile preparations. Planta Med. 56: 657–658. Flavex Naturextrakte (2002). Specification – ginger–ginger

Fluids 2000. Available from: . Producers Natural Processing Inc. (2002). Edible oil

CO2 total extract. Available from: . Franchomme, P. (1984). Guarantees on the Plant International

extraction: severe limitations of hexane (solvent extraction) 1999. Available from: .

Phytomedical Foundation. Belv eze -du-Raz es. Jakovlev, J. and von Schlichtegroll, A. (1969). On the inflammation

Quirin, K. and Gerard, D. (1999). New aspects on calendula CO2 extract as a cosmetic ingredient. Cosmetics and Toiletries, 112(4):

inhibitory effect of ())-abisabolol, an essential component of chamomilla oil. Arzneimettelforschung, 19(4): 615–

55–58. Stahl, E. et al. (1988). Dense gases for extraction and refining 11. Springer, Berlin.

616. Junius, M. (1985). Practical handbook of plant alchemy, Inner Traditions Ltd, New York. Phasex Corporation (2002).

Supercritical Technology Consultants (2002). About Supercritical Fluid Technology 2000. Available from:
Introduction

d 126

to

Supercritical

htm>.

The International Journal of Aromatherapy 2002

12 no d 3 vol d