Process and device for separating a mixture or extracting a material.

The invention relates to a process, such as supercritical extrac¬ tion, for separating a mixture or extracting a material, in which at least the following steps are carried out: a) treatment of the mixture or material with an extraction fluid in a treatment vessel, said extraction fluid entraining product from the mixture of material, which results in a laden extraction fluid which is discharged from the treatment vessel, b) separating product from the laden extraction fluid, which results in an extraction fluid depleted of product, c) increasing the density of the depleted extraction fluid of step b) , and return thereof to the treatment vessel.

A process of this type is generally known. In the case of, for exam¬ ple, supercritical extraction, a supercritical fluid, i.e. a fluid such as carbon dioxide, in the supercritical state at a high density in a treatment vessel takes up product from a mixture or material. Then the extraction fluid enriched with product is discharged from the treatment vessel, whereupon the pressure of the fluid is lowered, as a result of which the density (and consequently the dissolving power thereof) de¬ creases, so that product is separated from the extraction fluid. Separa¬ tion of product from the extraction fluid under conditions such as at high pressures of, for example, 300 bars is alternatively possible by lowering the vapour pressure by lowering the temperature. After the sepa¬ ration step, the density (and thus the dissolving power) of the extrac¬ tion fluid depleted of product (i.e. the product is partially or com¬ pletely removed) is increased by compressing said fluid, whereupon the extraction fluid is returned to the treatment vessel in order to take up product. The extraction fluid, which is mostly under high pressure, is conveyed, in so doing, by means of pumps and compressors, very large pressure differentials occurring in the extraction fluid during the en¬ tire process. The drawback of the known process is that great demands are made of -the pumps and compressors required, not least owing to the high operating pressure. Furthermore, the compressors and pumps required are very expen¬ sive and, moreover, have a high energy consumption.

The object of the present invention is to overcome these drawbacks. This is achieved by increasing the density of the depleted extraction fluid by cooling said fluid in step c), and by heating said extraction fluid at a point in space which preferably is situated lower down than the point where the cooling of step c) is performed. If required, propel¬ ling means such as fans can be used to promote the transport of the ex¬ traction fluids.

Cooling and heating the extraction fluid in this manner achieves, on the one hand, the density differences of the extraction fluid, which are required for the extraction process, while, on the other hand, a natural convection is produced which surprisingly accomplishes the transport of the extraction fluid between the various steps. Said natural convection can be ascribed to the density differences and/or temperature differen¬ ces. As a result, pumps and compressors for conveying the extraction fluid between the various steps are superfluous.

Heating of the extraction fluid preferably takes place upstream and/or downstream of the treatment vessel. By heating the extraction fluid upstream of the treatment vessel, the extraction fluid can be brought to a temperature suitable for extraction, while it is possible to reduce, by means of heating downstream of the treatment vessel, the load¬ ing of the extraction fluid. Heating at at least one of these points effects a natural circulation of the extraction fluid.

However, it is also possible for the heating of the extraction fluid to take place in the treatment vessel, preferably at the top . Thus a reflux is advantageously effected in the treatment vessel, as a result of which a separation vessel with additional provisions for the reflux to the treatment vessel is superfluous. Separation vessel and .treatment vessel can then be integrated.

According to the invention, the extraction fluid can advantageously be heated in step b) . Said heating causes a lowering in the density, as a result of which product is separated from the laden extraction fluid. By heating during step b) , the heating required for the transport of the extraction fluid is thus advantageously combined with the separation of product. According to a further advantageous procedure according to the in¬ vention, the extraction fluid, after the cooling of step c), is passed into a buffer and from this buffer is returned to the treatment vessel, the discharge of the buffer being situated lower down than the supply of

the buffer. In such a buffer a pressure is built up by the extraction fluid, as a result of gravity, which promotes the transport to the treat¬ ment vessel. Such a buffer may, for example, comprise an upright cylin¬ drical element such as a tube. According to the invention it is very advantageous if the cooling in step c) and the heating, at a lower point, of the extraction fluid is carried out with the aid of heat exchangers. By means of such heat ex¬ changers the temperature of the extraction fluid and thus the extraction process and the transport of the extraction fluid can readily be control- led.

It is very advantageous in this case if, on the one hand, the ex¬ traction fluid and, on the other hand, an auxiliary fluid flow through said heat exchangers, said fluids flowing through the heat exchangers in opposite directions. In this arrangement, the auxiliary fluid can be maintained at essentially atmospheric conditions, which is very advanta¬ geous with respect to the pumps, lines, heating and/or cooling means etc. required for the auxiliary fluid. In this arrangement it is particularly advantageous if the auxiliary fluid is conveyed around a circuit into which the heat exchangers are incorporated. Thus the heat absorbed from the extraction fluid in step c) is utilised for heating the extraction fluid at a lower point in space, which decreases the energy to be sup¬ plied, required for carrying out the process.

Furthermore it is very advantageous, according to the invention, if the temperature of the auxiliary fluid is controlled by heating and/or cooling it. Thus it is possible to control, via the auxiliary fluid, the separation or extraction process in an energetically favourable manner.

According to the invention it is very advantageous if the maximum pressure differential of the extraction fluid is at most five bars, or if the maximum pressure differential (ΔPmax) of the extraction fluid satis- fies the relationship:

ΔPmax ≤ H _c x g X p _c where H _c is the height at which the cooling of step c) takes place, g is the gravitational acceleration, and p _c is the density of the extraction fluid after the cooling of step c) . Such low pressure differentials are, surprisingly, sufficient for conveying the extraction fluid between the various steps, said pressure differentials being maintainable by means of heating and cooling and/or simple propelling means. The maximum pressure differential of the extrac-

tion fluid in this case refers to the maximum pressure differential between two points in the circuit through which the extraction fluid is conveyed.

The stream of extraction fluid flowing through the treatment vessel is easily controllable with valves arranged in the extraction circuit. In this way it can be achieved that neither too much nor too little mixture to be separated or material to be extracted is entrained into the treat¬ ment vessel. If the flow velocity is too high, the mixture components or materials, which should remain in the treatment vessel, will come into the further extraction circuit from the treatment vessel, by which the obtainable purity decreases. If the flow velocity is too low, the effi¬ ciency of the extraction process will be lower.

The invention further relates to a device for applying the process according to the invention. A device of this type comprises: - a treatment vessel in which the extraction fluid takes up product from the mixture or material, separating means to separate from the extraction fluid product taken up therein, which results in an extraction fluid depleted of pro¬ duct, - cooling means for cooling the depleted extraction fluid, and heating means for heating the extraction fluid.

The cooling means in this arrangement are disposed at a point in space which is situated higher up than that of the heating means, and the heating means are preferably disposed just upstream and/or downstream of the treatment vessel and/or therein. Furthermore, it is advantageous, if the separating means comprise heating means.

According to an advantageous embodiment, the invention comprises a buffer which has a supply coming from the cooling means and a discharge passing through the treatment vessel, the discharge being situated lower down than the supply. In such a buffer, for example in the form of a vertically extending tubular part, a pressure is built up, as in a water tower, under the influence of gravity, which promotes the transport of the fluid.

In a device according to the invention, the cooling and heating means preferably comprise at least two heat exchangers, which advantage¬ ously have flow passing through them in opposite directions, on the one hand of the extraction fluid, and on the other hand of an auxiliary fluid which is passed round in an essentially closed circuit. By means of con-

trollable additional cooling and heating means arranged in this circuit, the entire separation process can be controlled via the auxiliary fluid.

The process and device according to the invention can very appropri¬ ately be used for a process to be carried out continuously. The invention is explained below in more detail with reference to a drawing, in which

Figure 1, in diagrammatic representation, shows a first embodiment of a device for the process according to the invention, Figure 2, in diagrammatic representation, shows a second embodiment of a device for the process according to the invention, and

Figure 3. n diagrammatic representation, shows a third embodiment of a device for the process according to the invention. Figure 1 shows a diagrammatic representation of an extraction pro¬ cess and device for separating product mixtures, the required purity of both the final top product and the final bottom product being achieved by recycling a portion of the top product to the treatment vessel. In the process, supply means 1 (comprising a pump and lines) are employed to supply a mixture to the treatment vessel 2 at point 50. Said treatment vessel, in which step a) takes place, comprises a packed column which, via line 3. s supplied with extraction fluid. This extraction fluid takes up product from the mixture in the treatment vessel.

Said laden extraction fluid is then, via lines 4, passed to a heat exchanger 5» where step b) takes place. In the heat exchanger 5. the laden extraction fluid is heated, which causes the density of the extrac- tion fluid to decrease, and at least part of the product taken up therein is separated therefrom via line ^~ 1. Said separated product is split, by means of an overflow device 12, into top product which, via line 43, is passed to a store, and a stream which, via line 44, is returned to the treatment vessel, so that at the top of the treatment vessel, a liquid stream is produced which is in countercurrent with the extraction fluid. The bottom product is passed via line 42 to a store.

Downstream of heat exchanger 5. the extraction fluid stripped of product or depleted of product continues via line 6 to heat exchanger 7• In heat exchanger 7. step c) then takes place. The extraction fluid is cooled here, the density of the extraction fluid increasing. From the heat exchanger ^~ , the cooled extraction fluid is supplied to the buffer 9 via line 8 from above. The extraction fluid collects in said buffer in a manner as in a water tower, as a result of which at the bottom of buffer

S a higher pressure is produced than at the top of the buffer. Said pres¬ sure promotes the discharge of extraction fluid from the buffer ^~ via lines 10 and 3 to the treatment vessel 2. By means of heat exchanger 11, the extraction fluid can be brought to a temperature suitable for the treatment in the treatment vessel 2, by heating (or possibly cooling) the extraction fluid therewith.

According to the invention, the heat exchanger 7» in which the cool¬ ing of step c) takes place, is situated higher up than heat exchanger 5. in which the extraction fluid is heated. (In this context, situated higher up refers to the location with respect of, for example, the ground, i.e. heat exchanger 7 is disposed, for example, 20 metres above ground, and heat exchanger 5. for example, 5 metres lower down, at 1 metres above ground.) By suitable placement of heat exchanger 7 above heat exchanger 5 anά" the action of said heat exchangers, a natural con- vection is effected in the extraction fluid, which is sufficient to over¬ come the resistance of lines, treatment vessel, heat exchangers etc. , so that the extraction fluid, as a result of said natural convection, is conveyed from one step to the next step.

The heat exchangers 5. 7 and 11 have flowing through them, on the one hand, the extraction fluid and, on the other hand, an auxiliary fluid which is pumped over anticlockwise in an essentially closed circuit of lines 20-26 by means of a pump 30. In addition, there are incorporated in the auxiliary-fluid circuit, additional cooling and heating means 31» 32 and 33 (of which 31 cools, 3 heats and 33 cools or heats), by means of which the temperature of the auxiliary fluid can be controlled. By means of the auxiliary fluid and the additional cooling and heating means, the entire process can be controlled in an energetically advantageous manner.

At the highest point in the extraction-fluid circuit a valve 4l can be opened, so that gases accumulated here, such as nitrogen and oxygen, can be discharged. At the lowest point of the circuit, a similar valve 40 is disposed, in order to be able to discharge (insoluble) material en¬ trained by the extraction fluid. Through line 52, inert gas can flow directly from buffer 9 to valve 4l. Moreover, said line 2 ensures that there is a constant pressure differential across heat exchanger 7. so that no backflow takes place in the heat exchanger. This may, in particu¬ lar, be a problem in the case of two-phase flows as in Example 2, yet to be described.

The circuit for the extraction fluid does not require compressors or pumps which, due to the high operating pressure, would be very complex and expensive. As to the pump, additional heating and cooling means in¬ corporated in the auxiliary-fluid circuit, these, owing to the approxi- mately atmospheric conditions prevailing here, can be embodied by rela¬ tively simple and inexpensive means.

Figure 2 shows in diagrammatic form a device and process according to the invention, which mainly differ from those in Figure 1 in that heat exchanger 5 has been replaced by an evaporation vessel 5' with a heating element 55 therein through which the auxiliary fluid flows. The remaining reference numerals are indeed identical. The device and the process ac¬ cording to Figure 2 are, in particular, suitable for obtaining a pure bottom product at discharge 42.

Figure 3 shows in diagrammatic form a device and a process according to the invention, which mainly differ from those in Figure 1 in that heat exchanger 5 has been replaced by two absorption vessels 5 ¹ ' . in which step b) takes place. As in this case the auxiliary fluid does not have to exchange any heat in step b) with the extraction fluid, the circuit of the auxiliary fluid has been modified somewhat. From heat exchanger ^~ , the auxiliary fluid is now, via line 22'', passed directly to pump 30, from pump 30 via line 23' ' to a heating (or possibly cooling) means 32'', and then, via line 24'', to heat exchanger 11, by means of which the extraction fluid is heated. Between heat exchanger 11 and heat exchanger 7, the auxiliary-fluid circuit corresponds to that in Figure 1. In addi- tion, the supply means 1 open into the treatment vessel at the top. In the case of the absorption vessels 5' ' _• valves 60 and 6l and lines 62-65 are arranged in order to pass the extraction fluid optionally either through the one or the other absorption vessel.

A device or process according to Figure 3 is suitable, for example, for removing contaminants or impurities from process streams. In this case, contaminants or impurities are removed in an absorption vessel, by means, for example, of a silica gel bed and/or activated-carbon bed, from the extraction fluid which, in the treatment vessel, has been laden with contaminants or impurities from the process stream supplied via supply means 1. If an absorption bed is saturated, it is possible to switch over, by means of valves 60 and 61, to the absorption bed in the other absorption vessel, it then being possible to replace or clean the first absorption bed or vessel.

EXAMPLE 1

A device according to Figure 1 can be used, for example, to separate a volatile component from a mixture of less volatile components, carbon dioxide being used as the extraction fluid. An example of this is the separation of alkane mixtures, which is commonly encountered in the (petro)chemical industry. A treatment vessel (extraction column) 2 is supplied, via supply means 1, with a feed stream containing mixture, which consists of 25 of tetradecane (molecular weight 198) , 25- of hexadecane (molecular weight 226) and ^~ >0% of heavier components. The conditions during separation of tetradecane from this mixture are:

Extraction fluid:

Treatment vessel 2:

Line 6:

Buffer 9

Position heat exchanger 11 z _n = 0 m (ground level) Position heat exchanger ^~ z ₅ = 20 m (above ground) Position heat exchanger ^~ z _? = 25 m (above ground)

In this case, the pressure differential (ΔP) available for transport of the extraction fluid can be calculated via:

ΔP = g (p ₉ - p ₂ )(z ₅ ~ Z-i) ⁺ g (P ₉ ~ Pό) (z ₇ - z ₅ ) = 9-81 (325 x 20) + 9-81 (727 x 5) = 0.994 x 10 ⁵ Pa where g is the gravitational acceleration. The purities which can be achieved by this process can be calculated via standard methods. The relative solubility of tetradecane with respect to hexadecane in the extraction fluid is 1.37 under the given conditions. This means that the amount of tetradecane dissolved in the fluid phase is 1.37 times that of hexadecane. If, via overflow device 12 and line 44, nineteen times as much is recycled to the treatment vessel 2 as is dis¬ charged via line 43 as the top product, the following compositions, ex¬ pressed in per cent by weight, can be calculated:

The top stream through line 43 contains 20.8% of the mixture sup¬ plied via line 50 to the treatment vessel. The composition of the top product which is discharged via line 43, after removal of the carbon dioxide from this top product, is: Tetradecane: 99.0%

Hexadecane: 1.0% The bottom stream through line 42 contains 79.2% of the mixture entering the treatment vessel through line 50. The composition of the bottom product which is discharged via line 42, after removal of the carbon dioxide from this bottom product, is:

Tetradecane: 5-6%

Hexadecane: 31-3%

Heavier Alkanes: 63-1%

The composition of the extraction fluid discharged via line 6 to the buffer is:

Tetradecane: 0.42% Hexadecane: 0.0016% (16 ppm)

Carbon dioxide: 99-58%. The liquid stream which flows downwards in the column and is dis- charged via line 42, contains 40% of carbon dioxide in dissolved form. The stream which flows downwards in the heat exchanger 5. contains 18% of carbon dioxide in dissolved form. The required weight of carbon dioxide is ^~ times the weight of the mixture supplied via supply means 1 as the feed. The separation requires 35 equilibrium stages, of which 23 are disposed above the point 50, where the mixture supplied as a feed enters the treatment vessel, and 12 are disposed below the point 50. Based on the fact that an equilibrium stage on average requires 0 cm of packings, this means that the total packed height of the column is 17-5 ^~ -- The separation method described above is particularly advantageous for creat- ing a pure top stream.

EXAMPLE 2

A device according to Figure 2 can be used to remove contaminants from streams; in this case, specific requirements such as high purity can be imposed upon the bottom product, in particular. Examples include the removal of solvents from polymers or the purification of large product streams which contain small amounts of contaminants. An example of the purification of large product streams is the removal of 0.1% (1,000 ppm)

of methylnaphthalene (molecular weight 142) from 99«9% of octadecane (molecular weight 255) with the aid of carbon dioxide. The purity re¬ quired is achieved by working up the carbon dioxide in a three-phase system, as illustrated in evaporation vessel 5' of Figure 2. In this case the procedure takes place below the critical temperature and pressure and is thus not supercritical. In the three-phase system, the middle phase 71 is continuously fed with liquid carbon dioxide, enriched with product, from the treatment vessel 2. The carbon dioxide is evaporated by means of heating coil 55. so that a gaseous top phase 7 is produced. Because the gaseous carbon dioxide has a much smaller density, it will be able to contain considerably less product taken up (extracted) than the liquid carbon dioxide, as a result of which a pure gaseous top phase is obtain¬ ed. Owing to the evaporation of the carbon dioxide, the middle phase will become supersaturated with extraction product, as a result of which it condenses from the solution and forms a heavier bottom phase 70. Bottom phase 70 contains a relatively small amount of carbon dioxide, so that a pure extraction product is obtained. The conditions at which this sepa¬ ration is carried out are:

Extraction fluid: carbon dioxide with average pressure 60 bar

Treatment vessel 2: temperature T ₂ = 22°C density extraction fluid P ₂ = 753 kg/m ³

Line 6: temperature T ₆ = 22°C density extraction fluid p ₆ = 209 kg/m3

Buffer 9 temperature T ₉ = 0°C density extraction fluid P ₉ = 9^9 kg/m ³

Position heat exchanger 11 z _n = 0 m (ground level) Position heat exchanger ^~ z ₅ = 20 m (above ground)

Position heat exchanger ^~ z ₇ = 25 m (above ground)

In this case, the pressure differential available for transport of the extraction fluid can be calculated via: ΔP = g (p ₉ - p ₂ )(z ₅ - z _n ) + g (p ₉ - p ₆ ) (z ₇ - z ₅ ) = 9-81 (196 x 20) + 9.81 (740 x 5) = 0.747 x l0 ⁵ Pa where g is the gravitational acceleration.

The required purity of the end product is such, that the recir¬ culated carbon dioxide in the evaporation vessel ^{~ '} is worked up by a three-phase system, so that the carbon dioxide supplied at the bottom of the treatment vessel 2 does not contaminate the purified octadecane. The relative solubility of methylnaphthalene, compared to octadecane, in the extraction fluid under these conditions is 1.7. This means that the amount of methylnaphthalene dissolved in the extraction fluid is 1.7 times that of octadecane. If, via overflow device 12, a reflux of 300 to the topside of the treatment vessel 2 is accomplished, the following compositions, expressed in per cent by weight, can be calculated:

The top stream through line 43 contains 0.5% of the product stream entering the treatment vessel 2 via line 50. The top product which is discharged via line 43 and is present as the bottom-most phase in the evaporation vessel, after removal of the carbon dioxide from this top product has the composition:

Methylnaphthalene: 10% Octadecane: 90% The liquid carbon dioxide which, as the middle phase 71» is present in evaporation vessel 5' . has the composition: Methylnaphthalene: 0. 7%

Octadecane: 3•0% Carbon dioxide: 96.43% The gaseous carbon dioxide which, as the top phase 72, is present in evaporation vessel 5' and is discharged via line 6, has the composition: Methylnaphthalene: 3.8 ppm

Octadecane: 4.9 ppm

Carbon dioxide: 99-99913% The bottom stream through line 42 contains 99-5% of the product stream supplied to treatment vessel 2 through line 50. The composition of the bottom product which is discharged via line 42, after removal of the carbon dioxide from this bottom product is:

Methylnaphthalene: 5 PP ^m

Octadecane: 99-9995%.

The bottom product thus obtained is very pure. The required weight of carbon dioxide is 30 times the weight of the feed supplied via the supply means 1. The liquid stream which moves downwards in the treatment vessel and is discharged via lines 42 and 43, contains 50% of carbon dioxide in dissolved form. The separation requires 29 equilibrium stages,

of which 10 should be placed above the feed point 50 and 19 below the feed point 50. Here it was assumed that an equilibrium stage on average requires 50 cm of packings, which amounts to a total packing height of 14.5 m. This separation is very advantageous for obtaining a pure bottom stream.

EXAMPLE 3

A device according to Figure 3 is suitable for removing small amounts of contaminants from streams. Relevant examples include the remo- val of solvents from polymers, the removal of nicotine from tobacco, the removal of impurities from process streams or the purification of efflu¬ ent streams. The extraction fluid at the top of the treatment vessel 2 is laden with impurity removed from the feed material which has been sup¬ plied to the treatment vessel 2 via supply means 1. The extraction fluid is then purified by passing it via one or more absorption vessels 5''. An absorption vessel 5'' may, for example, contain a bed of silica gel or activated carbon. The choice of bed will depend on the product to be removed. By arranging one or more absorption vessels it is possible, when one absorption bed is saturated with impurity to be removed, to put into service another absorption vessel, whereupon the saturated bed can be cleaned or replaced. As a result, the process can be applied continuous¬ ly. An example of purification of a contaminated stream is the removal of the toxic components phenol, m-cresol and p-chlorophenol from a water stream. The impurities are absorbed on a carbon bed. If the components phenol, m-cresol and p-chlorophenol are all dissolved in the effluent in an amount of 100 ppm, said components can be removed from the water under the' following (supercritical) conditions: Extraction fluid: carbon dioxide with average pressure Treatment vessel 2: temperature density extraction fluid Line 6: temperature density extraction fluid Buffer 9 temperature density extraction fluid

Position heat exchanger 11 z _u = 0 m (ground level) Position heat exchanger ^~ z ₅ = 10 m (above ground) Position heat exchanger ^~ z ₇ = 15 m (above ground)

The pressure differential available for transport of the extraction fluid can be calculated via:

ΔP = g (p ₉ - p ₂ )(z ₅ " z _u ) + g (p ₉ - p ₆ ) (z ₇ - z ₅ ) = 9-81 (237 x 20) + 9.81 (237 x 5) = 0.3^9 x 10 ⁵ Pa where g is the gravitational acceleration. For phenol, m-cresol and chlorophenol, respectively, the fraction of a substance in the supercritical fluid phase with respect to the fraction of a substance in the liquid phase is 1.27, 2.20 and 3-^7. respectively. With the aid of these values, the phase equilibria can be calculated. If the stream of extractant is assumed to be equal to the amount of feed and there are seven equilibrium stages in the treatment vessel 2, the compo¬ sitions of the various streams, expressed in per cent by weight can be calculated as follows:

The carbon dioxide at the top of the treatment vessel 2, which is passed to an absorption vessel 5'' via line 4, has the composition: Phenol: 95.4 ppm m-Cresol: 99.8 ppm p-Chlorophenol: 100 ppm Water: 400 ppm

Carbon dioxide: 99-93% The carbon dioxide which, downstream of the absorption vessel 5' ' . is discharged via line 6 to the buffer 9 has the composition:

Phenol: 0.0 ppm m-Cresol: 0.0 ppm p-Chlorophenol: 0.0 ppm Water: 400 ppm

Carbon dioxide: 99-96% The composition of the bottom product which is discharged from the extraction vessel 2 via line 42 is:

Phenol: 4.6 ppm m-Cresol: 0.2 ppm p-Chlorophenol: 0.0 ppm Water: 99-99952%

The water obtained has undergone considerable purification. Based on the fact that an equilibrium stage to be used with water requires an average packing height of 100 cm, the total packing height in the treat¬ ment vessel is ^~ 7 m. The process described for this purpose is particular- ly advantageous for removing small amounts of impurities from process streams.

As can be seen from the figures and examples, a process and device according to the invention does not require any expensive pumps and com¬ pressors in the circuit of the highly pressurised extraction fluid. In- stead of by means of pumps and compressors, according to the invention the extraction fluid is conveyed by heating it at one point and cooling it at a higher point. Said heating and cooling is effected by means of an auxiliary circuit, through which an auxiliary fluid circulates which is maintained under essentially atmospheric conditions. The pump 30 incor- porated in this auxiliary circuit can be relatively simple and thus inex¬ pensive, owing to the atmospheric conditions. The energy to be supplied to the auxiliary fluid is in such an amount, that less energy is consumed in the case of a process or device according to the invention than in the case of processes or devices known hitherto. The energy saving is more than 50%.

It should be noted that many variations and modifications are con¬ ceivable in the case of the present invention, without moving outside the scope of the invention. The following are conceivable, for example:

Fans are used, for example, to promote the transport of extraction fluid. It is even conceivable for said fans to provide for the transport entirely, so that it is no longer necessary for the cool¬ ing to take place at a higher point than the heating. Separation of product may alternatively, instead of by lowering the density, also be effected by, for example, cooling the extraction fluid immediately downstream of the treatment vessel, as a result of which the vapour pressure decreases, or by means of absorption ves¬ sels (as in Example 3)-

The extraction fluid need not be conveyed around in a circuit, but may alternatively, for example, be supplied to the treatment vessel from a store, and after cooling may, for example, be discharged to another store.

The process and device according to the invention can also be ap¬ plied to separation processes other than supercritical extraction, for example the extraction as expounded in Example 2.