IL111684A - Process and installation for extracting products of biological origin without solvents using microwave heating - Google Patents

Description

111684/3 mtpa ft i uptttt o sw vnn N ^>« ipnai vbrm Process and installation for extracting products of biological origin without solvents using microwave heating Archimex C.95596 111684/2 1 The invention concerns the field of extracting natural products which are contained in biological matter and notably, but not exclusively, the extraction of such products from plants.

The extraction of natural products from biological matter can be carried out by means of several processes which use one or several extraction solvents or not, depending on the nature of the biological matter used and the nature of the product or products required to be extracted from it. On this subject, it should be noted that the name given to an extract is often a function of the technology used to extract it. Thus^ concretes, restnoids, oteoresins... which are extracts consisting of volatile composites or of non volatile waxy or greasy products are traditionally obtained in the presence of at least one organic solvent. Essential oils, mainly consisting of fragrant volatile composites are themselves generally obtained by distillation with water vapour (hydrodistillation) and/or by mechanical processes.

For example, oilseeds, essential oils of citrus fruit peels, fish oils. .. are traditionally extracted using physical processes such as crushing and/or pressing, without solvents or by hydrodistillation. Apart from the fact that they have low implementation costs, such techniques have the advantage that they allow extraction products to be obtained (and a biological matter after extraction) which are free from solvent residues and which therefore do not have to undergo a subsequent treatment to eliminate these residues.

There are however many products which cannot be extracted from the natural matter which contains them according to such methods and for which extraction techniques using organic solvents have to be used. With these techniques, the product to be extracted diffuses in the solvent and dissolves in it. However, it is then necessary to separate the extracted product from the solvent, so that the concentration of the extract can be guaranteed. Numerous parameters influence the yields of extractions performed with solvents, amongst which can be cited : - the solubility of the extracted product in the chosen solvent, - the diffusion of the extracted product within the solid matrix of the biological matter used.

It is possible to alter the first parameter notably by varying the operating temperature or even the concentration of the solvent used.

Furthermore, it is also possible to alter the second parameter, either before the extraction stage or concomitantly with the extraction stage. For example, the diffusion of an extracted product can be greatly improved by subjecting the biological matter to a pre-treatment which might consist notably of a crushing process, an enzymatic digestion process or even a drying process. The biological matter can also be acted upon during the operation itself, for example by heating it or stirring it. Processes which are also used in the profession include, for example, sound processes consisting of applying ultrasound to the mixture made up of the biological matter and the solvent in order to encourage the extract to diffuse into the solvent. Mechanical waves made up of ultrasound in effect allow cavitation of the biological matter to be generated locally and consequently heat the biological matter up improving the release of the extract.

It has also been proposed previously within the profession that extraction of a product from biological matter can b improved by subjecting the biological matter to microwave radiation. Such electromagnetic waves are in effect absorbed selectively by the media having a high dielectric constant and therefore, for biological matter, mainly by water, in other words, essentially by the vascular and glandular tissues and more especially the vacuoles in the case of plant matter. During such an absorption, the radiation energy is converted into calorific energy which allows the parts of the biological matter absorbing the microwaves to be heated selectively.

The European patent EP 0398798 divulges a technique for extracting products from biological matter assisted by microwaves, including the following steps consisting of : subdividing biological matter (peppennint, lovage, cedar or garlic) having a dispersed component absorbing microwaves (water), putting this 'subdivided matter into a solvent which is transparent or partially transparent to microwaves and which absorbs less microwaves than the dispersed component, such as hexane, ethanol or dichloromethane, exposing the mixture consisting of the subdivided matter and the solvent to microwaves so as to allow the soluble products to be extracted by heating the subdivided matter preferentially to the solvent, separating the residual biological matter from the solvent and, recuperating the extracted product.

Although the technique described in the patent EP 0398798 has the advantage of improving extraction yields, it does not allow the previously cited disadvantages to be overcome which are linked to the presence of the solvent in the obtained extract.

It should be noted that it has also been proposed in the profession that essential oils be extracted from biological matter by microwave radiation without solvents.

The article which appeared in the review "Flavour and Fragrance Journal", vol.4 pp 43-44 under the title "Microwave Oven Extraction of an Essential Oil" effectively describes an extraction technique of the Lippia sidoid essential oil by heating with microwaves, according to which plant samples of 30 to 40 grammes are placed, without any solvents, in a bottle inside a microwave oven and are subjected to microwave radiation for 5 minutes. The bottle used is designed so that the essential oil is entrained by an air flow from the outside.

Although allowing extraction in a much shorter time than the time required to perform extraction operations correctly by hydrodistillation, such a method has the major disadvantage that it requires a large amount of energy to allow extraction which means that the process is not of great economic interest.

All extraction processes of natural products by microwaves described in documentation can only be used on very low volumes of processed biological matter with respect to the power of the microwaves applied. Generally, this power varies from 10 OOCi W to 20 000 W per kilogram of biological matter. The maximum power of microwave emitters on the market, operating at a frequency of 2450 MHz, is 6 kW. Consequently, these processes, in order to be used on an industrial scale, must be adapted to continuous operation, so that a small volume can be punctually placed before a microwave source of reasonable power.

The aim of this invention is to propose an extraction process by microwave of natural products, which does not have the disadvantages of current processes.

In particuJar, one of the objectives of the invention is to provide such a process allowing extraction without solvents and therefore allowing an extract which is free from any solvent residue to be obtained.

Another objective of the invention is to propose such a process which does not require an excessive amount of energy, for a given quantity of biological matter to be processed.

Another objective of the invention is to propose an installation for implementing such a process.

The invention concerns an extraction process by microwaves of at least one natural product from biological matter, the said process consisting of : placing the said biological matter in a chamber, without any solvent, subjecting the said biological matter in the said chamber to microwave radiation so as to cause at least part of the water contained in the said biological matter to evaporate and consequently causing the cellular structures of the said biological matter to break down so as to allow at least part of the said natural product to be released, separating the residual biological matter from the extracted natural product, the said process being characterised in that it includes the following additional steps consisting of : applying, intermittently, a lower pressure inside the said chamber during the said microwave application step, in order to encourage the cellular structures of the said biological matter to break down induced by the application o'f microwaves, heating, during at least the essential part of the said microwave application step, the said chamber in order to compensate for the drop in temperature resulting from the evaporation of the water from the biological matter, the combination of the said steps of microwave application, the application of a reduced pressure inside the chamber and the heating of the chamber allowing hydrodistillation of the said natural product by entraining it in the water vapour from the said biological matter.

Such a process can be favourably used on all natural biological matter, whether of animal, plant or micro-biological origin provided that these have a water content of around at least 30 % . This process might notably be used for extracting essential oils from plants, tissues of animal origin and notably from fish, but also from algae and micro-algae and possibly even micro-organisms. Naturally, this biological matter might, depending on its nature, be subdivided before being introduced into the chamber in order to increase its exposure factor to microwaves.

The process according to the invention allows the product to be extracted to be hydrodistilled, not due to the water introduced from the outside during the process but due to the water contained in the processed biological matter, it should be noted on this subject that, within the scope of this description, this water will he called water of constitution, although it might have been added to the biological matter beforehand, when this was available in a dehydrated form, during a rehumidification step.

The process according to the invention therefore consists of submitting the processed biological matter to microwave radiation, without any extracting solvent, enabling the contents of the cells of this matter to be ejected to the outside. In order to encourage this phenomenon and with the aim of entraining the extracted product azeotropically, the pressure in the chamber is reduced. This pressure reduction allows, on the one hand, the mechanicaJ stresses exerted on the cell walls of the biological matter to be increased and, on the other hand, the volatility of the azeotropic mixture made up of the product to be extracted and water vapour to be increased. According to the invention, concomitantly heating the chamber allows the very rapid temperature drop to be compensated, resulting from the evaporation of the water of constitution under the effect of the pressure reduction in the chamber. Such a temperature drop is in effect likely to conceal the action of the microwaves completely.

The process according to the invention has many advantages.

Other than the fact that it leads to extracts without residual solvents, in addition it allows, with respect to traditional hydrcKiistillation, an extract with an equivalent composition and with ' an equivalent yield to be obtained, in a substantially shorter time. Whilst the time for traditional hydrodistillation is usually counted in hours, the hydrodistillation time under reduced pressure according to the invention is counted in minutes. For some products, it is therefore possible to obtain a given quantity of the extract in a tenth of the time of traditional water vapour distillation.

Furthermore, the process according to the invention consumes much less energy than current microwave assisted extraction processes. For the same quantity of processed biological matter, the energy used within the scope of the invention is also less than that required for hydrodistillation. Within the scope of hydrodistillation, it is effectively necessary to heat the biological matter and the added water, of which the mass can be up to 10 times the mass of the biological matter.

Finally, it should be noted that the residual biological matter obtained from the process is in a dry form, since the water of constitution it contained was used to entrain the extracted product and that the process does not require any external water to be used. Consequently, this residual matter can be easily attacked thermally and can therefore be subsequently recycled as a fuel.

Preferentially, the said step of the process according to the invention, consisting of intermittently applying a reduced pressure, consists of submitting the inside of the said chamber to depressurising cycles.

According to a variation of the invention, the said separation step of the residual biological matter from the extract consists of : - cooling the water vapour containing the said extracted natural product, - decanting the liquid mixture resulting from such a cooling process and, - separating the said extracted natural product from the water resulting from such a decanting process.

Although another advantage of the process is that it produces much less residual water compared to traditional hydrodistillation processes, at least a part of the said water resulting from the said decanting step is advantageously injected into the chamber so as to perform hydrodistillation of the natural product remaining in the said residue of the biological matter.

Furthermore, the said heating step is preferentially performed at a temperature lower than lOO'C. It should be noted than the process can be performed advantageously at a temperature lower than 75 'c so as to allow products having a tendency to degenerate under the effect of heat to be extracted.

The microwaves used for the said microwave radiation step advantageously have an frequency of at least 300 MHz. Tt should be noted however that in many countries, the use of frequencies is very strictly controlled and that, for example, in France only frequencies of 915 MHz and 2450 MHz are allowed for industrial microwave generating equipment.

Furthermore, the said microwave radiation step will be preferentially performed so that a power from around 100 W to approximately 10 000 W per kilogram of product processed is applied.

According to an implementation variation of the process, the said microwave radiation step is performed whilst mechanically stirring the biological matter. Such a stirring operation allows the exposure factor of the biological matter to the microwaves to be increased.

The invention also relates to an installation for implementing such a process and is characterised in that it includes : - a chamber fitted with microwave generating means inside the said chamber and having a double thermostated wall; - heating means allowing the temperature of the said double thermostated wall to be regulated; - means allowing the pressure within the said chamber to be reduced; - means for recuperating the extract at the outlet of the said chamber.

Preferentially, the said means for recuperating the extract include means for cooling the water vapour containing the extract.

Also, the said installation preferably has means of operating the said means allowing the pressure with the chamber to be reduced cyclically.

Advantageously, the said chamber is fitted with stirring means.

Finally, and also advantageously, the said installation includes means allowing the residual water obtained from the extract recuperating means to be re-channelled into the said chamber.

The invention, as well as its advantages, will be easily understood with the aid of the description followed by operating examples of this with reference to the diagrams, in which : - figure 1 shows a diagrammatical view of an installation according to the invention; - figure 2 shows the evolution of the pressure of the chamber and the temperature of the biological matter, within the scope of a first implementation example of the process according to the invention with the diagrammatical installation of figure 1 , for extracting peppermint essential oil; - figure 3 shows the evolution of the yield of peppermint essential oil obtained using the first implementation example of the process; - figure 4 explains the evolution of the pressure of the chamber and the temperature of the biological matter, within the scope of a comparative example for extracting peppfermint essential oil.; - figure 5 shows the evolution of the yield of peppermint essential oil obtained using the comparative example; - figure 6 shows the evolution of the pressure of the chamber and the temperature of the biological matter, within the scope of a second implementation example of the process according to the invention for extracting medicinal sage essential oil; - figure 7 shows the evolution of the yield of medicinal sage essential oil obtained using the second implementation example of the process according to the invention.

With reference to figure 1 , an installation for extracting natural products from biological matter is represented diagrammatically. Such an installation includes a chamber 1 fitted with means 2 allowing microwaves to be generated within the volume it delimits. In accordance with legal provisions, these means 2 enable microwaves with a frequency of 2450 MHz to be emitted. (It should be noted that it would also be possible to use a microwave generator with a frequency of 915 MHz, since this other frequency is also allowed in France).

The chamber 1 , is also fitted in its lower part with stirring means 9, consisting of a three blade turbine, allowing the biological matter to be stirred whilst it is inside the chamber 1 , whilst it is subjected to the action of the microwaves. Such stirring allows the exposure of the biological matter to the microwaves to be increased and prevents some zones of the biological matter being insufficiently irradiated so that the extraction operation is completed correctly.

In accordance with this invention, the chamber 1 is connected on the one hand to means 5 allowing its internal pressure to be reduced and, on the other hand to means 6 of recuperating the extracted natural product due to the action of the microwaves on the biological matter. The means 5 allowing the pressure in the chamber to be reduced can consist of any device traditionally used for the effect of creating a partial vacuum inside the chamber, such as, for example, a pump or glass filter pump. Within the scope of this example, the means 6 for recuperating the extracted product include a pipe U fitted in the upper part of the chamber 1 , around which cooling means 7 are fitted formed by a coil in which cooling fluid circulates.

The pipe 11 allows the vapours resulting from the action of the microwaves to be recuperated and in which is the essential oil. Due to the cooling means 7 these water vapours are condensed. A decanter 12 is fitted to the outlet of the pipe 1 1 to recuperate these condensed vapours and to separate the essential oil. The remaining residual water, after decanting, is advantageously re-channelled, through a pipe 10, into the chamber 1 where it is recycled to complete the extraction.

In order to allow the inside of the chamber 1 to be reheated to compensate for the reduction in temperature resulting from the decrease in the pressure created by the vacuum pump 5, the chamber 1 has a double thermostated wall 4 connected to the heating means 4.

The installation described above has been used to implement the extraction process by microwaves of this invention in order to extract essential oils of peppermint (example 1) and medicinal sage (example 3).

Example 1 One kilogramme of peppermint (Mentha piperita L. , Hungarian variety) with 15 % of dry matter was placed inside the chamber L The heating means 4 were adjusted so that the thermostated wall 3 induced a temperature of approximately 70 "C inside the chamber 1 and the stirring means 9 were used at a speed of 40 revolutions per minute.

The power emined by the microwave generating means 2 is 1 150 W and the retlected power varies benveen 170 W and 220 \V. During the extraction operation, which lasted 15 minutes, the power effectively absorbed was therefore 930 to 908 W.

During the extraction, the pump 5 was used so as to reduce the pressure to 250 mb. This reduction in pressure was carried out after 5 minutes, 10 minutes and 13 minutes.

Furthermore, the temperature of the cooling medium circulating in the coil 7 was fixed at 5 C so as to cause the vapours resulting from the action of the microwaves on the peppermint and containing the essential oil to condense.

The evolution of the temperature of the mint in the chamber and the pressure inside the chamber is given in figure 2. Under the action of the microwaves, the temperature of the product goes quickly from the ambient temperature to approximately 15 ' C. As soon as the inside of the chamber is subjected to a partial vacuum (250 mb) due to the pump 5 , the temperature drops. This drop in temperature is quickly compensated for by the hearing device of the chamber so that the action of the microwaves is not concealed.

With reference to figure 3, after 15 minutes of extraction and 3 depressurising cycles, 1.52 ml of essential oil were recuperated (giving a yield of 1.01 ml for lOOg of dry matter).

Hydrodistiilation of the peppermint residue resulting from such an extraction operation by microwave only allowed less than 50 mg of essential oil to be obtained. The process according to the invention therefore allows an essential oil yield close to the exhaustion of the biological matter to be obtained.

The comparison of the chromatographic profiles during the gas phase of two essential oils ob ained by the extraction process according to the invention and by traditional hydrodistiilation did not show any major composition difference.

Example 2 The same quantity of peppermint as in example 1 was processed by using the same operating conditions as in example 1 but by making the pump 5 operate continuously so that the pressure in the chamber 1 was fixed at 250 mb throughout the whole extraction operation.

The evolution of the temperature of the mint and the pressure in the chamber is given in figure 4.

With reference to figure 5, the yield of essential oil was only 0.2 ml for 100 g, being 5 times less than in example 1. 1 150 mg of essential oil were recuperated in the mint residue after the extraction operation. These results show the importance of me intermittent nature which must be given, according to the invention, to the reduction in pressure inside the chamber.

Example 3 Five hundred grammes of medicinal sage (Salvia officinalis L.,) with 25% of dry matter were placed inside the chamber 1. The heating means 4 were adjusted so that the thermostated wall 3 induced a temperature of approximately 70 °C inside the chamber 1 and the stirring means 9 were switched on at a speed of 40 revolutions per minute.

The power emitted by the microwave generating means 2 is 1000 W and the reflected power varies between 150 W and 200 W. During the extraction operation, which lasted 10 minutes, the power effectively absorbed was therefore 800 to 850 W.

During extraction, the pump 5 was switched on so as to reduce the pressure to 250 mb. This reduction in pressure was carried out after 3.5 minutes and 7 minutes.

Furthermore, the temperature of the cooling medium circulating in the coil 7 was fixed at 5 °C so as to cause the vapours resulting from the action of the microwaves on the sage and containing the essential oil to condense.

The development of the temperature of the sage in the chamber and the pressure inside the chamber is given in figure 6.

With reference to figure 7, after 10 minutes of extraction and 2 depressurising cycles, 3.06 ml of essential oil were recuperated (giving a yield of 2.55 ml for lOOg of dry matter).

The theoretical yield by traditional hydrodistillation of the same quantity of sage is 2.77 ml for l OOg which shows that using the process according to the invention allowed more than 90% of the essential oil of the treated medicinal sage to be recuperated.

The aim of the operating examples of the invention described here is not . to undermine it. In particular, it might be envisaged that the microwaves are made to act for a longer or a shorter time, or to use different frequencies of microwaves or to separate the extract from the vapour according to a technique other than that described without straying from the scope of the invention.

Claims (13)

111684/2 14 CLAI MS

1. . Extraction process by microwaves of at least one natural product from a biological matter, the said process including steps consisting of : placing Lhe.said biological matter in a chamber, without any solvent, subjecting the said biological matter in the said chamber to microwave radiation , in order to cause at least a part of the water contained in the said biological matter to evaporate and consequently to cause the cellular structures of the said biological matter to break down, so as to allow at least a part of the said natural produce to be released, separating the residual biological matter from the extracted natural product, the said process being characterised in that it includes additional steps consisting of : applying, intermittently, a lower pressure inside the said chamber during the said microwave application stage, in order to encourage the cellular structures of the said biological matter to break down induced by the application of microwaves, heating,, during at least the essential pan of the said microwave application process, the said chamber in order to compensate for the drop in temperature resulting from the evaporation of the water from the biological matter, the combination of the said steps of microwave application , the application of a reduced pressure inside the chamber and the heating of the chamber allowing hydrodistilladon of the said natural product by entraining it in the water vapour from the said biological matter.

2. Process according to claim 1 characterised in that the said application step of a reduced pressure consists of subjecting the inside of the said chamber to depressurising cycles.

3. Process according to claims 1 and 2 characterised in that the said separation step of the residual biological matter from the extract consists of : - cooling the water vapour containing the said extracted natural product, - decanting the liquid mixture resulting from such a cooling operation and, - separating the said extracted natural product and the water resulting from such a decanting operation.

4. Process according to claim 3 characterised in that at least part of the said water resulting from the said decanting step is injected into the chamber so as to carry out hydrodistillation of the natural product remaining in the said biological matter residue.

5. Process according to one of the claims 1 to 4 characterised in that the said heating step uses a temperature less than 100"C.

6. Process according to one of the claims 1 to 5 characterised in that the microwaves used during the said microwave radiation step have a frequency of at least 300 MHz.

7. Process according to one of the claims 1 to 6 characterised in that the said microwave radiatio step is carried out so that a power between approximately 100 W and approximately 10 000 W per kilogram of treated product is applied.

8. Process according to one of the claims 1 to 7 characterised in that the said microwave radiation step is performed whilst the said biological matter is stirred mechanically.

9. Installation for implementing the process according to one of the claims 1 to 8 characterised in that it includes : - a the said chamber and having a double thermostated wall^; - heating means allowing the temperature of the said double thermostated wall ^to be regulated; - means allowing the pressure to be reduced*^ inside the said chamber; - means for recuperating the extract (fi^ t the outlet of the said chamber.

10. Installation according to claim 9 characterised in that the said extract recuperating means include cooling means φφ.

11. Installation according to claim 9 or 10 characterised in that it has means (8) for operating the said means fallowi g the pressure in the chamber to be reduced cyclically.

12. Installation according to one of the claims 9 to 11 characterised in that the said chamber is fitted with stirring means

13. Installation according to one of the claims 9 to 12 characterised in that it includes means (Φθ^ allowing the residual water obtained in the means for recuperating the extract to be re-channelled into the said chamber (i . for tho AppH anM CS. MOLD CQia-ANrtRTNBS