WO2002074886A1

WO2002074886A1 - Refining of crude extracts and mixtures

Info

Publication number: WO2002074886A1
Application number: PCT/GB2002/001332
Authority: WO
Inventors: Peter Frederick Wilde
Original assignee: Naturol Limited
Priority date: 2001-03-20
Filing date: 2002-03-20
Publication date: 2002-09-26
Also published as: GB0106972D0

Abstract

A method of refining a crude extract of a material of natural origin is provided and comprises: a. contacting the crude extract with a first solvent comprising a blend of a first liquefied gas having a first solvating range and a second liquefied gas having a second solvating range so as to form a solution of a first fraction of components of the crude extract in the first solvent; b. separating the solution of step (a) from the crude extract; c. contacting the remainder of the crude extract with a second solvent comprising an at least quantitatively different blend of liquefied gases to that of step (a) so as to form a solution of a second fraction of the components of the crude extract in the second solvent; and d. removing the first and second solvents from the solutions to provide refined first and second fractions of the crude extract. The first liquefied gas is preferably an iodofluorocarbon. The second liquefied gas is preferably an hydrofluorocarbon.

Description

Refining of Crude Extracts and Mixtures

This invention relates to the refining of a crude extract of a material of natural origin, especially by fractionation of the various components therein.

The extraction of fixed oils (that is, natural mixtures of non-volatile vegetable oils) from natural sources such as seeds and nuts has traditionally entailed the crushing of the seeds or nuts and squeezing of the mass so formed to press out the oil. This procedure dates back many thousands of years. Olive oil presses have been found which date back to pre-Christian times.

The remaining cake may then be treated by heating it in water, whereupon some of the remaining oil floats upon the surface of the water and can be skimmed off. This practice has been in use until very recently.

A more modern way of recovering further oil from such cake, however, has employed a variety of powerful solvents. The cake is typically stirred with one of a variety of solvents and the oil rich solution so formed is separated from the spent broken seeds or nuts by filtration. The oil may then be recovered by evaporation of the solvent from the solution.

The production of oleo-resins, which are flavour-rich extracts of plant material such as black pepper corns, chillies and other spices and herbs, has traditionally employed solvents. The crushed herb or spice is stirred with the solvent and the oleo-resin rich solution is concentrated by evaporation of the solvent.

The fragrance industry prepares its starting materials known as "concretes" from fragrant flowers such as jasmine, tuberose and orange blossom in much the same way.

In the case of the petrochemical industry, mineral oil or petroleum rich slurries such as drilling muds are extracted with solvents to remove as much of the oil as possible prior to their disposal (often at sea). This is necessary as the mineral oils contained within these muds are a serious pollution hazard.

For obvious reasons, it has always been assumed that powerful solvents should be used for all the above purposes and indeed this would appear to be self-evident. The more powerful the solvent, the lesser the quantity it is necessary to use to achieve the desired degree of- de-oiling, de-fatting or de-greasing of the material to be subjected to extraction.

The solvents used for these purposes, over many decades, have included halogenated hydrocarbons such as dichloromethane, perchlorethylene etc., aromatic hydrocarbon solvents such as benzene, toluene etc. and aliphatic hydrocarbons such as hexane, pentane and other gasoline fractions. Ketones such as acetone and esters such as ethyl acetate are also used.

However, there are several main difficulties arising out of the use of these solvent materials.

The first problem is that they are (almost without exception) highly toxic to those operators exposed to them (to say nothing of the ultimate "consumers" of the end product) and are polluting to the environment.

A second problem is that several of them are flammable and hence highly hazardous when in use.

A third problem arises from their "powerful" solvent nature.

A fourth problem arises from their relatively high boiling point. Though these solvents are often referred to as "volatile", they are in fact all liquids at room temperature and atmospheric pressure. Their boiling points are typically 50-100 degrees Celsius. Hence, it is necessary to subject the solution of oil in these solvents to elevated temperatures in order to drive off the solvent. Vacuum stripping is also frequently used in attempts to rid the resulting oil, concrete or oleo-resin extract of solvent. These attempts are never completely successful, as residual solvent can always be detected in the oil / extract end product. The degree of contamination of the end product with such solvent residues cannot simply be improved by more heating, to yet higher temperatures and/or under yet harder vacuum, as the quality of the concrete or oleo-resin is severely adversely affected by such treatments. The very chemicals in the concrete, oleo-resin or extract which are of value to the customer are often substantially stripped from the oil before such low solvent residue levels can be reached.

Referring to the third problem mentioned above and in relation to extraction from fragrant flowers, for example, hexane or "petroleum ether", which are the normal solvents with which fragrant flowers are extracted, are so powerful that they do not simply extract the fragrant oil which is the desired end product for the perfumer. They also extract pigments, waxes, fatty acids, triglycerides, sterols and their esters and any resins that may be present in the flowers. The same is true in the case of extraction of oleo-resins for food use. These powerful solvents also extract many "impurities" which are of no benefit to the food flavorist and in fact dilute the potency of the food flavouring with useless contaminants.

Inevitably, therefore, the use of such powerful solvents produces extracts which are a mixture of a vast range of materials of a wide spread of chemical types. This is rarely desirable and steps are frequently necessary to refine these mixtures in order to render them more suitable for further use. The objectives of such refining treatments are to either dissolve the desired components in another solvent which does not dissolve the unwanted "impurities", or conversely to dissolve the unwanted impurities away, leaving a residue enriched with the desired components.

In the case of perfumed "concretes", for example, the crude extract after preparation with hexane can be milled with strong ethyl alcohol. The alcohol is able to dissolve the fragrant end-product oil (known as absolute) from the mixture, leaving some of the unwanted waxes and other impurities undissolved. Freezing of the alcoholic slurry to minus 10 degrees Celsius can improve matters by precipitating from solution yet more of the impurities. After filtration at low temperature, the alcohol is conventionally removed by evaporation.

In the production of ever more potent oleo-resins and in the preparation of further refined substances from oleo-resins, for example capsaicin from chilli oleo-resin, it is desirable to refine the crude extract thereby enriching the product with the desired "active" ingredient or ingredients.

Steps of refinement and enrichment are particularly important when extracting pharmacologically active materials from plant or other sources. For example, in the case of colchicine-containing extracts derived from Autumn Crocus (or Meadow

Saffron) Colchicum autumnale, hexane or methylene chloride extracts are highly contaminated and a lengthy and expensive refining process is needed. The same can be said to be true of extracts of Artemisia annua, where the active principle (Artemisinine) is the desired end product. Likewise, Tonka beans (Dypterix odorata) yield copious quantities of coumarine, though it is heavily contaminated with impurities when first extracted with powerful solvents such as those described above. In addition, the various Yew trees, of the Taxus genus (species brevifolia, baccata, canadiensis, yunanensis) provide small amounts of the anti-cancer drug Paclitaxel. These minuscule amounts must be refined out of the crude biomass extracts before the pharmacologically active ingredient is of use.

It is also significant that many interesting and potentially useful components of plant tissue are highly thermolabile. Thus, it is desirable to conduct both the original extraction procedure and the subsequent refining at low temperatures to avoid anything but minimal damage to the active ingredient.

Previous reports have shown the benefits of using liquefied gases at room temperature as solvents for the preparation of extracts (US Patent No, 5,512,285, PCT Application No. WO 95/26794, EP Application No. EP0616821A). In addition, WO 01/10527 describes the properties of Iodotrifluoromethane (CF₃I), referred to henceforth as "ITFM", as an excellent solvent for preparing crude extracts from plant and animal biomass and for the degreasing of drilling muds prior to disposal at sea. Other iodofluorocarbons having similar properties are described in US 5,611,210.

Briefly, the desirable properties of ITFM are: 1. It is a very powerful solvent;

2. It has a low boiling point of minus 26 degrees Celsius at atmospheric pressure;

3. It has a modest vapour pressure at room temperature, in the region of 450kPa-600kPa (4.5-6 BarG);

4. It is neither an ozone depleting substance nor classed as a volatile organic compound (VOC);

5. It is not a "greenhouse gas", having a zero global warming potential;

6. It has a short half life when released into the atmosphere;

7. It is not flammable (indeed its major utility today is as a fire extinguisher); and

8. It can be recovered at room temperature (or below) for re-use, leaving a substantially solvent-free extract which has neither been thermally damaged nor vacuum stripped.

One disadvantage of this solvent, however, is its cost. Solvent husbandry is the key to the economic commercial use of this material as an extraction solvent. It is absolutely vital when using it that no leakage into the atmosphere takes place. However, this can be arranged with adequate equipment design.

ITFM has advantages not possessed by other more conventional solvents and can be used very successfully for the efficient extraction of high yields of crude extracts from a very wide range of starting materials.

ITFM is not highly toxic. Nevertheless, the plant operators are not exposed to it, as the extractions are always carried out in sealed equipment. It is not polluting to the environment since it is neither damaging to the ozone layer, nor will it promote global warming. ITFM is not flammable and is not hazardous when is use. It has a low boiling point (-26 degrees Celsius) and can therefore be removed from extracts without the use of high temperatures and vacuum stripping. Hence, the light, volatile fragrance and flavour notes desired by the perfumer and food flavour technologist are not lost and the products are not cooked.

Hence, ITFM can be said to eliminate three of the four main difficulties of conventional solvents listed above.

The third main difficulty referred to above in respect of extraction with the conventional range of solvents arises from their powerful nature.

Iodofluorocarbons such as ITFM are also powerful solvents. The extracts they produce are extremely crude. The extracts are darkly coloured and often comprise mixtures of a wide range of chemical entities. It has been necessary, therefore, to develop means for refining such mixtures in order to eliminate impurities and enrich the concentrations of the specific ingredients sought.

Thus, the object of the present invention is to provide improved methods for the refinement of crude extracts of natural materials.

Accordingly, the invention provides methods of refining a crude extract of a material of natural origin, the methods being described by the appended claims.

The process principle employed in the present invention is to balance the power of two or more miscible liquefied gas solvents. One must be a very poor or weak solvent and another should be a powerful solvent (preferably an iodofluorocarbon). The ability is exploited of defined mixtures of two or more such solvents to selectively dissolve the specific materials required from a complex crude (mixed) extract, whilst not dissolving those materials that it is desired to reject.

The more powerful liquefied gas solvent is preferably an iodofluorocarbon. The iodofluorocarbon may be selected from 1,1,2,3,3,3-heptafTuoro-l-iodopropane, 1 , 1 , 1 ,2,3 ,3 ,3-heptafluoro-2-iodopropane, fluoroiodomethane,

1 , 1 ,2,2-tetrafluoro- 1 -iodoethane, 1 , 1 ,2,2,3 ,3 ,4,4,4-nonafluoro- 1 -iodobutane, difluorodiiodomethane, undecafluoro-1-iodopentane, tridecafiuoro-1-iodohexane and iodotrifluoromethane. A particular preferred iodofluorocarbon is iodotrifluoromethane.

The weaker liquefied gas solvent may be selected from hydrofluorocarbons, perfluorocarbons and straight chain, branched or cyclo-alkanes selected from those which are gaseous at room temperature and pressure. Hydrofluorocarbons or perfluorocarbons* are preferred, especially those selected from hydrofluoromethanes, hydrofluoroethanes, hydrofluoropropanes and perfluoropropane. Particularly preferred hydrocarbons are fluoromethane, difluoromethane, trifluoromethane, pentafluoroethane, 1,1,1-trifluoroethane, 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane,

1 , 1 , 1 ,2,3 ,3 -hexafluoropropane, 1,1,1 ,2,2,3 -hexafluoropropane,

1,1,1 ,3,3,3-hexafluoropropane and 1,1,1 ,2,2,3,4,5,5,5-decafluoropentane.

Co-solvents may be added to the liquefied gas solvents. These co-solvents may be selected from hydrocarbons, ketones, chlorinated and chlorofluorinated hydrocarbons, ethers, alcohols, dimethylformamide, tetrahydrofuran, dimethyl sulphoxide, carboxilic acids and anhydrides, nitriles, anhydrous liquefied ammonia, liquefied sulphur dioxide, nitric oxide, nitrogen dioxide, nitrous oxide, liquefied hydrogen sulphide, carbon disulphide, nitromethane and nitrobenzene.

In the selective extraction of different fractions from a crude extract, it may be desirable to use multiple blends of liquefied gases which vary not only in their quantitative composition but also in the chemical nature of their component liquefied gases.

The term "liquefied gas" as used herein means a compound which is normally gaseous at room temperature and pressure and which has been condensed to a liquid, preferably a sub-critical liquid, by application of pressure and/or reduction of temperature.

The poor solvents that have been found to be most valuable for the purposes of the invention are hydrofluorocarbons, especially HFC 134a (1,1,1,2 - tetrafluoroethane).

This latter material, like ITFM, has a boiling point of -26 degrees Celsius. Though there are many materials available with poor powers of dissolution, using HFC 134a allows the continued use of very low temperatures when evaporating the solvents and thereby the preservation in full measure of the precious highly volatile and thermo-labile components in the solutions. This characteristic allows the production of high quality extracts, components of which are either lost (by evaporation) or destroyed (by high temperatures) using more traditional procedures.

Though it is irrelevant by what means the crude extracts are obtained, it is preferred to begin the refining process using extracts which have themselves been prepared using an iodofluorocarbon such as ITFM as the extracting solvent and which, therefore, have not been damaged by high temperatures in their preparation.

The invention will now be described in more detail by way of example only.

EXAMPLE 1

500 grams of a commercial Jasmine concrete (originally extracted with hexane) was obtained from Coimbatore in India. It was blended with 500 grams of a good grade of cellulose powder, in a Kenwood Chef dough bowl. It required only about 15 minutes for the solid concrete to spread itself evenly over the cellulose powder. The result was a bright yellow, slightly greasy powder which could be easily handled.

This powder was introduced into a stainless steel tube capable of tolerating lOOOkPa (10 BarG) internal pressure, referred to henceforth as an "extractor", which was about 20cm (8 inches) in diameter and 61cm (two feet) high and furnished with both "inlet" and "outlet" closeable valves at the top. The tube had a wide opening closeable port and lid, which provided a seal and through which materials such as powders could be introduced into and emptied out of the extractor. The bottom outlet of the extractor tube was furnished with a fine mesh filter and a closeable valve.

After filling with powder, the lid of the extractor was replaced and the air was withdrawn from it via one of the top valves using a simple vacuum pump. The inlet valve at the top of the extractor was connected to a source of liquefied HFC 134a and this material was admitted to the tube. After a few minutes, it became possible to withdraw HFC 134a from the bottom outlet of the extractor. A pale yellow HFC134a-based solution was collected in a pre-weighed evaporator comprising a similar stainless steel pressure vessel fitted with two top closeable valves (one to admit liquid solution, the other being an outlet valve to allow for the passage of solvent vapour - see below). Air had also previously been removed from this vessel. Provided the evaporator was kept cooler than the extractor, which itself should be cooler than the reservoir of HFC 134a, no trouble or difficulty was experienced in quickly collecting 10kg of HFC134a-based solution.

The extractor and contents may be shaken or agitated by inversion, if this is thought to be desirable, although it is preferred to work on "fixed beds" of solids during extraction, relying on the plug flow of solvent through the bed for efficient extraction.

Once the 10 kg amount of solution had been collected, the flow of HFC 134a into the extractor was discontinued and the remaining liquid contents of the extractor were drained into the evaporator. The solvent was evaporated from the solution in the evaporator by placing an identical empty "solvent reservoir" bottle, previously evacuated of air, in a freezer and connecting the second evaporator top valve to it. The solvent (HFC 134a) vapour soon passed from the evaporator to the cold solvent reservoir, where it condensed into liquid form ready for re-use. It was considered to be desirable, at this point, to "dry" all the solvent from the jasmine concrete-coated cellulose powder (the powder being soaked with solvent) concurrently, though this may be considered to be unnecessary.

At this point, when all the solvent had been recovered to reservoir bottles, it was desirable to open the evaporator and assess the yield of the first "refined fraction" of the crude extract by weighing or by another analytical means. HFC 134a alone is a poor solvent and hence it is frequently found that littler or no material has been removed from the contents of the extractor at this stage. In this event, it is possible to replace the reservoir of HFC 134a with another one containing a mixture of 10% ITFM and 90% HFC 134a (w/w) and repeat the operation. Using this solvent blend, it is frequently found that a substantial amount (indeed, in the case of jasmine concrete, a substantial, percentage of the original concrete) of material is to be found in the evaporator. The nature of this fraction is usually a pale yellow coloured, mobile, clear and highly fragrant oil.

Continuing to repeat this procedure with ever-increasing increments of ITFM concentration in HFC 134a sequentially allows the removal of all the fragrant oil without, at least initially, any of the attendant waxes present in the concrete. The waxes themselves can be subsequently removed by increasing the ITFM content of the eluting solvent to 50% (w/w) or more.

EXAMPLE 2

Dried, ground, crustacean shells (from cooked (boiled) prawns) were placed into a 500 ml capacity glass extraction column. They were extensively extracted over several hours with ITFM. Upon evaporation of the ITFM, a dark red coloured oily extract was produced.

Such an extract can be refined in two ways.

a. The extract was collected and placed in a 200 ml PET extractor bottle and triturated with portions of solvents comprising an increasing concentration of ITFM in HFC 134a. As the extracts always have a specific gravity lower than that of the solvents, they float on the surface of the solution in the extractor.

Shaking of the extractor and contents and then allowing the contents to settle with the extractor in an inverted orientation produced two phases. The lower phase (the solution) was easily withdrawn into an evaporator and the solvent was recovered leaving an oil in the evaporator. The weight of the oil was assessed, as was its colour. Initially, when the extract was triturated with 100% HFC134a, virtually no colour went into solution in the HFC 134a and only a very small quantity of pale pink oil was harvested. As the concentration of ITFM was increased incrementally more pale oil was removed from the extract. At a concentration of 30% w/w ITFM in HFC 134a, a strongly coloured solution resulted which, on evaporation, was found to contain substantially all of the astaxanthin initially present in the crude extract.

b. A second procedure for refining extracts may be illustrated as follows:

A similar extract of cooked (boiled) crustacean carapace - crabs in this case - was prepared by extracting the dried ground shells with ITFM. The solution of darkly coloured red extract in ITFM was not dried in this case.

To the solution of extract in the extractor was added incremental quantities of HFC 134a. Initially, little change was observed. Upon the concentration of HFC 134a in ITFM reaching 40-50% w/w, a red flocculent precipitate was observed to form, leaving a pale pink clear supernatant.

At this point, the solution was filtered out of the extractor, leaving a filter cake which was initially dried and then taken up in a small quantity of ITFM. This solution was dried whereupon the dark red fraction of the original extract could be harvested. It was found to be rich in astaxanthin.

EXAMPLE 3

One kilogram of tuberose flowers (Polyanthes tuberosa) was thoroughly extracted with ITFM and the solvent was removed by evaporation at room temperature. 30 grams of the crude extract was prepared. To this extract was added 150 grams of alumina. The mixture was stirred to produce a more or less evenly coated powder which was free flowing. This powder was introduced into a glass column some 50 cm long and 5 cm in diameter and which was able to tolerate pressures of up to lOOOkPa (10 BarG). Reservoirs of solvents were attached to the top of this glass column via a pair of pumps normally used for HPLC extraction. One pump was attached to a reservoir of HFC 134a and the other was attached to a reservoir of ITFM. The tubing was arranged such that the solvent streams leaving the pumps could be mixed before they entered the top of the column. A pressure gauge was provided downstream of the pumps in order to measure the head space pressure in the column.

To the bottom outlet of the column was attached, via a screw thread provided on the column, a PTFE block, drilled to accept a screw threaded stainless steel tube (5 mm outer diameter). To the bottom of this tube was attached, via Swagelock compression fittings, an aerosol valve providing a filtered, openable seal and retained in place using a proprietary yoke and screw band clamp. Using this device, it was a simple matter to harvest liquid (solution) from the bottom of the column into a PET 200 ml capacity bottle which was also furnished with a similar aerosol valve seal. By this means, fractions of solution (eluate) were harvested from the bottom outlet of the column.

The reservoir of HFC 134a was the first to be opened. Immediately, the glass column filled with HFC 134a, initially as a gas and eventually as a liquid. As the pressure in the column became equal to the vapour pressure of the liquid HFC 134a in the reservoir, the flow of liquid into the column ceased. An air pocket at the top of the column (head-space) ensured that the column did not fill completely (hydraulically).

Maintaining the pressure in the column at less than lOOOkPa (10 BarG) the pump providing HFC134a was started. Shortly afterwards, a 150 ml sample of the HFC134a solution, which had by now formed as a pool at the bottom of the column, was harvested. The solvent was removed by evaporation and recovered for re-use. The quantity and nature of the solute form the evaporated solution were measured gravimetrically and by smell, respectively.

The pump providing ITFM was started when no more solute could be harvested from the column and its contents. The pumps were programmed so that a flow of mixed solvents was provided which had a smoothly increasing concentration of ITFM and, of course, a correspondingly reducing concentration of HFC 134a.

Approximately 150 ml samples of solution were harvested regularly from the bottom of the column throughout the duration of this experiment. The samples were harvested into tared PET evaporator bottles. In every case, the precise quantities of solution and dried solute were measured and the colour, nature and aromatic properties were assessed. The progressive yield of solute versus the initial charge of crude extract was noted as a percentage figure. The increment of solute percent per ml of solution was compared with the total solution volume passing out of the column.

Using this device and principle it was possible to fractionate the crude tuberose extract into three major fractions:

1. a clear, light yellow, highly mobile and highly aromatic oil extracted early in the experiment when the concentration of HFC 134a was greater than 80%. This fraction accounted for 40% of the weight of the original crude extract;

2. a bright yellow, translucent, viscous and less aromatic oil extracted when the concentration of the HFC 134a in ITFM was less than 70% and more than 30%. This fraction comprised 10% of the weight of the original crude extract; and

3. a cream coloured, almost non-aromatic, waxy and solid material which comprised some 50% of the weight of the original extract. This material eluted only when the concentration of ITFM in the eluting solution exceeded 70% (i.e. when the concentration of HFC134a was less than 30%).

Iodofluorocarbons such as ITFM are very powerful solvents whereas hydrofluorocarbons such as HFC134a (1,1,1,2 - tetrafluoroethane) are poor, weak (or non-) solvents for many substances in crude mixtures. Mixtures of the two types of solvents may be prepared which enable crude extracts containing a considerable variety of chemical entities to be fractionated. The process allows for the refining of such crude extracts into enriched fractions containing only, or predominantly, those ingredients which are of interest. Those fractions containing ingredients which are of no, or little, interest may then be discarded. The desired fractions can be procured substantially free of solvent residues, without the necessity of applying high temperatures and/or high vacuum stripping techniques to them.

Materials of natural origin, for the purposes of the present invention, may include partially processed materials such as, for example, industrial waste, refuse or drilling muds to the extent that they comprise materials of natural origin.

Claims

1. A method of refining a crude extract of a material of natural origin, the method comprising:

a. contacting the crude extract with a first solvent comprising a blend of a first liquefied gas having a first solvating range and a second liquefied gas having a second solvating range narrower than the first solvating range so as to form a solution of a first fraction of components of the crude extract in the first solvent; b. separating the solution of step (a) from the crude extract;

c. contacting the remainder of the crude extract with a second solvent comprising an at least quantitatively different blend of liquefied gases to that of step (a) so as to form a solution of a second fraction of components of the crude extract in the second solvent; and d. removing the first and second solvents from the solutions to provide refined first and second fractions of the crude extract.

2. A method according to claim 1 wherein the blends comprise from 0.001% to 99.99% of the first liquefied gas in the second liquefied gas.

3. A method according to claim 2 wherein the blends comprise from 0.1% to 90% of the first liquefied gas in the second liquefied gas.

4. A method according to claim 3 wherein the blends comprise from 1% to 80% of the first liquefied gas in the second liquefied gas.

5. A method according to any preceding claim wherein at least one of the blends of first and second liquefied gases is produced in situ during the solution-forming step.

6. A method according to any preceding claim wherein the different blends are produced by dispensing, into a region of contact with the crude extract, a continuously increasing amount of one of the first and second liquefied gases and a continuously decreasing amount of the other of the first and second liquefied gases.

7. A method according to any preceding claim wherein the crude extract is prepared by contacting the material of natural origin with a solvent comprising the first liquefied gas, separating the solution thereby formed from the material of natural origin and removing the solvent from the solution to leave the crude extract.

8. A method according to any preceding claim wherein the first liquefied gas comprises an iodofluorocarbon.

9. A method according to claim 8 wherein the iodofluorocarbon is selected from 1 , 1 ,2,3,3 ,3-heptafluoro- 1-iodopropane, 1,1,1 ,2,3,3,3-heptafluoro-2-iodopropane, fluoroiodomethane, 1 , 1 ,2,2-tetrafluoro- 1 -iodoethane, 1,1 ,2,2,3 ,3 ,4,4,4-nonafluoro- 1 -iodobutane, difluorodiiodomethane, undecafluoro-1-iodopentane, tridecafluoro-1-iodohexane and iodotrifluoromethane.

10. A method according to claim 9 wherein the iodofluorocarbon is iodotrifluoromethane .

11. A method according to any preceding claim wherein the second liquefied gas is selected from hydrofluorocarbons, perfluorocarbons and straight chain, branched or cyclo-alkanes selected from those which are gaseous at room temperature and pressure.

12. A method according to claim 11 wherein the second liquefied gas is a hydrofluorocarbon or perflourocarbon selected from hydrofluoromethanes, hydrofluoroethanes, hydrofluoropropanes and perfluoropropane.

13. A method according to claim 12 wherein the hydrofluorocarbon is selected from fluoromethane, difluoromethane, trifluoromethane, pentafluoroethane, 1,1,1 -trifluoroethane, 1,1,1 ,2-tetrafluoroethane, 1 , 1 ,2,2-tetrafluoroethane, 1,1,1 ,2,3 ,3 -hexafluoropropane, 1,1,1 ,2,2,3 -hexafluoropropane, 1,1, 1,3, 3, 3 -hexafluoropropane and 1,1,1,2,2,3,4,5,5,5-decafluoropentane.

14. A method according to claim 13 wherein the hydrofluorocarbon is 1,1,1 ,2-tetrafluoroethane .

15. A method according to any preceding claim wherein at least one of the solvents contains an additional co-solvent.

16. A method according to claim 15 wherein the additional co-solvent is selected from hydrocarbons, ketones, chlorinated and chlorofluorinated hydrocarbons, ethers, alcohols, dimethylformamide, tetrahydrofuran, dimethyl sulphoxide, carboxilic acids and anhydrides, nitriles, anhydrous liquefied ammonia, liquefied sulphur dioxide, nitric oxide, nitrogen dioxide, nitrous oxide, liquefied hydrogen sulphide, carbon disulphide, nitromethane and nitrobenzene.

17. Use of a solvent comprising a blend of a first liquefied gas having a first solvating range and a second liquefied gas having a second solvating range narrower than the first solvating range for the refinement of a crude extract of a material of natural origin.

18. A method of refining a crude extract of a material of natural origin, the method comprising: a. contacting the crude extract with a solvent comprising a blend of a first liquefied gas having a first solvating range and a second liquefied gas having a second solvating range narrower than the first solvating range so as to form a solution of a fraction of components of the crude extract in the solvent;

b. separating the solution of step (a) from the crude extract; c. removing the solvent from the solution to provide a refined fraction of the crude extract.

19. A method or use according to any preceding claim wherein the material of natural origin comprises plant material.

20. A method of selectively recovering certain extracts from a source material comprising: contacting the source material with a first liquefied gas to form a crude extract dissolved in said first liquefied gas, and adding incremental amounts of one or more second liquefied gases to the crude extract dissolved in said first liquefied gas to cause at least some of the components in the crude extract to separate from the solvent mixture, and collecting those separated components.

21. The method of claim 20 wherein additional amounts of one or more second liquefied gases are added to the solvent mixture containing the crude extract components remaining therein so as to cause additional components in the crude extract to separate from the solvent mixture, and collecting those separated components.

22. The method of claim 21 wherein additional amounts of one or more second liquefied gases are added to the solvent mixture containing the remaining crude extract components so as to cause further additional components in the crude extract to separate from the solvent mixture, and collecting those separated components, until only the desired dissolved extract remains in the solvent mixture, and recovering that desired dissolved extract.