Abstract:
The present invention relates to a device for the extraction of a compound from a solid material, comprising: (1) a microwave unit; (2) an inner vessel housed and fluidly sealed within an outer vessel, the inner and outer vessels enclosed within the microwave unit, wherein the outer vessel is configured to hold a solvent to be vaporized and the inner vessel is configured to hold the solid material; (3) a condenser for condensing the vaporized solvent and delivering a condensed solvent to the inner vessel; (4) the inner vessel further comprising a solvent outlet configured to deliver the condensed solvent containing an extracted compound back to the outer vessel; and (5) a first stirrer within the outer vessel and a second stirrer within the inner vessel for agitating the solvent within the inner and outer vessels during the extraction process.

Description:
[0001]    This application claims priority to European Patent Application 10 425 097.2 filed Mar. 29, 2010. This and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method for the extraction of compounds from solid material and to a device for carrying out said method. In particular, the present invention is concerned with the extraction by microwaves based on the soxhlet extraction principle. 
       BACKGROUND 
       [0003]    Extraction of solid material is traditionally performed by standard techniques such as a soxhlet extraction. The soxhlet method proceeds by iterative percolation of the sample to be extracted with recondensed vapors of solvent. This method is one of the most used techniques for extraction. Since this process can be quite lengthy, new methods using microwave radiation have been developed. 
         [0004]    A fast extraction is specifically of interest if the amount of a specific compound, for example fat, within solid material, for example within food or other materials, has to be determined. So far, even when using microwave-assisted extraction, a fast extraction still is difficult. 
         [0005]    The prior art methods are therefore limited in terms of efficiency and rapidity. 
         [0006]    In view of the above, there is thus a need to provide an improved microwave-assisted extraction process which overcomes at least some limitations of the known processes. 
       SUMMARY OF THE INVENTION 
       [0007]    Accordingly, this object is achieved by means of the features of the independent claims. The dependent claims develop further the central idea of the invention. 
         [0008]    A first embodiment of the present invention relates to a device suitable for the extraction of a compound from a solid material by microwave irradiation, comprises: (1) a microwave unit; (2) an inner vessel housed and fluidly sealed within an outer vessel, the inner and outer vessels enclosed within the microwave unit, wherein the outer vessel is configured to hold a solvent to be vaporized and the inner vessel is configured to hold the solid material; (3) a condenser comprising an upper portion disposed outside of the microwave unit and a lower portion extending within the microwave unit an coupled to a cover that is configured to fluidly seal the outer vessel, wherein the condenser receives the vaporized solvent and delivers a condensed solvent to the inner vessel for extracting the compound from the solid material; (4) the inner vessel further comprising a solvent outlet configured to deliver the condensed solvent containing an extracted compound back to the outer vessel; and (5) a first stirrer within the outer vessel and a second stirrer within the inner vessel for agitating the solvent within the inner and outer vessels during the extraction process. 
         [0009]    A second embodiment of the present invention relates to a method for the extraction of a compound from a solid material, comprising the steps of: (1) placing the solid material to be extracted in an inner vessel housed within an outer vessel; (2) placing a quantity of a solvent in the outer vessel and the inner vessel, wherein the quantity of solvent in the inner vessel surrounds the solid material; (3) subjecting the outer and inner vessels to microwave irradiation, the microwave irradiation causing at least partial vaporization of the solvent within the outer vessel; (4) condensing the vaporized solvent in a condenser and delivering a condensed solvent to the inner vessel for extracting the compound from the solid material; (5) transferring the solvent in the inner vessel containing the extracted compound to the outer vessel; and (6) agitating the solvent within the inner and outer vessels with first and second stirrers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0010]    The present invention is further described hereinafter with reference to some of its embodiments shown in the accompanying drawings in which: 
           [0011]      FIG. 1  depicts a schematic overview of a device according to the present invention, 
           [0012]      FIG. 2  schematically depicts a part of a device according to the present invention, 
           [0013]      FIG. 3  schematically depicts an inner vessel as used within a preferred embodiment of the present invention, 
           [0014]      FIGS. 4   a  and  4   b  depict a container for the solid material to be extracted, and 
           [0015]      FIG. 5  is a flowchart showing schematically the process steps according to the method of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring to  FIG. 1  the device suitable for carrying out the method of the present invention is schematically shown. However, with reference to  FIG. 1  the general principle underlying the present invention will be explained. It is to be noted that several components of the present invention in  FIG. 1  are omitted for the sake of clarity. 
         [0017]    The device  1  according to the present invention comprises a microwave unit  2 . 
         [0018]    The microwave unit  2  is preferably a multi-mode laboratory grade microwave unit with a maximum delivered power of 1000 watt variable in 10 watt increments. The microwave unit  2  may be any microwave used commonly in the art. For instance, it may be a Milestone ETHOS microwave oven or a Milestone NEOS microwave oven. 
         [0019]    A first outer vessel  3  is placed in the microwave unit  2 . Into the outer vessel  3  a second inner vessel  4  is placed, which is smaller than the outer vessel in height and diameter. Preferably, the inner vessel  4  is placed onto a support  5  within the outer vessel  3  at a defined distance from the bottom of the outer vessel  3 . 
         [0020]    The outer vessel  3  and the inner vessel  4  preferably are made out of a material which poorly absorbs microwave radiation and does not hinder the propagation of microwaves. Preferably, the outer vessel  3  and the inner vessel  4  are traditional glass beaker-type flat bottom containers. 
         [0021]    The inner vessel  4  additionally comprises an outlet  6  for delivering solvent  8  from the inner vessel  4  into the outer vessel  3 . The outlet  6  preferably is provided within a sidewall of the inner vessel  4 . 
         [0022]    The solid material  7  to be extracted is placed into the inner vessel  4 . The solid material  7  can be placed directly into the inner vessel  4  or, according to a preferred embodiment, the solid material  7  is filled into a container, which in turn is placed into the inner vessel  4 . 
         [0023]    A solvent  8  is filled into the outer vessel  3 . Preferably, only a part of the solvent when starting the extraction process is filled into the outer vessel  3  and the rest of the solvent is filled into the inner vessel  4 . 
         [0024]    A cover  9  is placed on top of the outer vessel  3 . The cover  9  comprises a first opening  10  and the microwave unit  2  on its top comprises a second opening  11 . Through the second opening  11  and the first opening  10  the lower portion of a condenser  12  is inserted. The microwave unit  2  hereby has a large port in the upper part for introducing the reflux adapter of the condenser  12 . The connection between the condenser  12  and the first opening  10  as well as the connection between the cover  9  and the outer vessel  3  is air tight in order to ensure a closed loop, i.e. to avoid that solvent  8  or vapors of solvent  8  are leaving the circulation path between outer vessel  3 , condenser  12  and inner vessel  4 . 
         [0025]    With reference to  FIG. 1  now the circulation of the solvent  8  will be explained. The circulation path in  FIG. 1  is indicated by arrows A, B and C. With the presented circulation path of solvent  8 , a compound is extracted from the solid material  7  within the inner vessel  4 . 
         [0026]    Due to the microwave radiation the solvent  8  within the outer vessel  3  is heated so that fresh solvent not containing the extracted compound is vaporized and as shown by arrow A ascends into the condenser  12 . In the condenser  12  the fresh vaporized solvent is condensed and the condensed fresh solvent as shown by arrow B drops down into the inner vessel  4 . Within the inner vessel  4  then the fresh solvent  8  surrounds the solid material  7  and extracts the compound to be extracted. When the solvent  8  within the inner vessel  4  reaches a predefined level, whereby the level depends on the type and/or position of the outlet  6 , solvent  8  containing the extracted compound as shown by arrow C will be delivered from the inner vessel  4  back into the outer vessel  3 . The circulation then starts again, whereby from the outer vessel  3  only the solvent  8  without extracted compound is vaporized, so that fresh solvent is constantly delivered into the inner vessel  4 . The extracted compound remains within the outer vessel  3 . 
         [0027]      FIG. 2  depicts an enlarged view on the device  1  according to a preferred embodiment of the present invention. 
         [0028]    According to the present invention, a first stirrer  13  is provided within the outer vessel  3  and a second stirrer  14  is provided within the inner vessel  4 . With these two stirrers  13 ,  14  the solvent  8  within each of the vessels  3 ,  4  is constantly agitated. This results in the effect that fresh solvent  8  within the inner vessel  4  is always present in the vicinity of the solid material  7  to be extracted. Further, the temperature of the solvent  8  in the outer vessel  3  and the inner vessel  4 , respectively, is kept at a homogeneous value. Additionally, by use of the first stirrer  13  within the outer vessel  3 , the vaporization of fresh solvent is supported. 
         [0029]    The first stirrer  13  and the second stirrer  14  can be any conventional type of non microwave absorbing stirrers adapted to constantly agitate the solvent  8  within the vessels. The stirrers can be lying loosely on the bottom of the respective vessel or they can be attached to an appropriate part of the vessel or any other object within the vessel. Preferably, the stirrers are magnetic-type non microwave absorbing stirrers. 
         [0030]    In a preferred embodiment, the first stirrer  13  within the outer vessel  3  is attached to the support  5 . Preferably, the first stirrer  13  is provided within the center of the outer vessel  3 , so that an even agitation of the solvent  8  within the outer vessel  3  is achieved. The support  5  hereby comprises a base plate  5   a  onto which the inner vessel  4  is placed. The base plate  5   a  can partially or completely cover the surface area delimited by a horizontal plane of the outer vessel  3 . The support further comprises a plurality of legs  5   b , so that the base plate  5   a  has a predefined distance from the bottom of the outer vessel  3  and so that a space is provided between the bottom of the outer vessel  3  and the base plate  5   a . The first stirrer  13  is attached to the base plate  5   a  and is moving in the space provided between the base plate  5   a  and the bottom of the outer vessel  3 . 
         [0031]    Likewise, within the inner vessel  4 , a material support can be  15  is provided, onto which the solid material  7  to be extracted is placed and to which the second stirrer  14  is attached in the same manner as the first stirrer  13  to the support  5 . The material support  15  can have the same shape as the support  5  and can partially or completely cover the surface area delimited by a horizontal plane of the inner vessel  4 . 
         [0032]    By attaching the stirrer to the vessel itself or to a support within the vessel, the position of the stirrer can be fixed during the extraction process. Preferably, each stirrer is placed within the center of the respective vessel and kept by appropriate means at this position, so that throughout the whole extraction process an evenly distributed agitation of the solvent  8  within both vessels becomes possible. 
         [0033]    The first stirrer  13  and the second stirrer  14  preferably are magnetic stirrers, which are agitated by a common magnetic motor  40 , provided below the microwave unit  2  or within the bottom of the microwave unit  2 . 
         [0034]    If necessary, within the inner vessel  4  and/or the outer vessel  3 , additional components can be placed to displace the solvent  8 , in case that a necessary height of the solvent  8  within the respective vessel without such additional component would not be reached. 
         [0035]    The cover  9 , the support  5 , the material support  15  and above mentioned additional components preferably are made out of a material which does not absorb microwave radiation. Preferably, these components are made out of glass or microwave transparent polymers like polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE, also known under Teflon®), perfluoroalkoxy (PFA) or any combinations thereof. 
         [0036]    With the present invention (based on the Soxhlet principle), which uses microwave radiation for heating the solvent and a stirrer within each of the vessels, a very fast and effective extraction is achieved, as will be explained in the following. Thereby, the advantages of the present invention will become evident. 
         [0037]    Generally, at the surface of the solid material  7 , an equilibrium is formed between the percentage of compound to be extracted within the solid material  7  and the percentage of compound already dissolved within the solvent  8 . If no fresh solvent is delivered to the surface of the solid material  7 , due to the equilibrium, the extraction process would stop. By constantly providing a flow of fresh solvent  8  to the solid material  7 , the extraction is kept going on. With the present invention by constantly agitating the solvent  8  through the second stirrer  14  within the inner vessel  4 , a continuous flow of fresh solvent  8  around the solid material  7  is achieved, so that the extraction becomes very efficient. 
         [0038]    Further, due to the stirrers within both vessels, the temperatures of the solvent  8  within both vessels is also kept uniform, which assures a fast extraction. 
         [0039]    With the use of microwave radiation, a faster and more uniform heating of the solvent  8  within the outer vessel  3  is achieved, so that the speed of the extraction is further supported. 
         [0040]    Due to the fast heating, the constant flow of fresh solvent and the homogeneous temperature, the present invention enables a very fast and effective extraction. 
         [0041]    The solvent  8  is heated either directly or indirectly by microwave radiation  16  schematically indicated in  FIG. 2 . A solvent which is heated directly by microwaves can be any solvent selected from polar solvents such as water, methanol, ethanol etc. Alternatively, a non-polar solvent selected from hexane, cyclohexane, limonene etc. can be used. More specifically, the solvent can be any one of the following solvents, whereby in the following listing the solvents are listed from high to low polarity: ethylene glycol, ethanol, DMSO, 2-propanol, formic acid, methanol, nitrobenzene, 1-butanol, 2-butanol, 1,2-dichlorobenzene, NMP, Acetic acid, DMF, 1,2-dichloroethane, water, chlorobenzene, chloroform, acetonitrile, ethyl acetate, tetrahydrofuran, dichloromethane, toluene, hexane or a combination thereof. 
         [0042]    In case of non-polar solvents additionally a heating component  17  is provided within the outer vessel  3 , which can be heated by microwave radiation  16  and thereby heats the solvent  8  into which it is placed. As heating component  17  for example a plate lying at the bottom of the outer vessel  3  can be used. Alternatively, several heating particles of any shape can be used and placed within the solvent  8  within the outer vessel  3 . 
         [0043]    The heating component  17  preferably is made of a compound capable of absorbing microwaves. Such compound is typically a polytetrafluoroethylene/graphite or PTFE/carbon compound. Such material is for example known under the trade name of Weflon™. The use of such a compound allows diffusion of heat created by the microwaves to the surrounding solvent  8 . 
         [0044]    As already described with reference to  FIG. 1 , an outlet  6  is provided within the sidewall of the inner vessel  4 , which allows solvent  8  to be delivered from the inner vessel  4  to the outer vessel  3 . The outlet hereby in a first embodiment as shown in  FIG. 1  can be provided as access flow valve, so that as soon as the height of the solvent  8  within the inner vessel  4  reaches the height of the outlet  6 , solvent  8  constantly flows or drops from the inner vessel  4  into the outer vessel  3 . 
         [0045]    In a preferred embodiment as shown in  FIG. 2  and  FIG. 3 , the outlet is a siphon  20 . The shape and functionality of the siphon will be explained in detail with reference to  FIG. 3 . 
         [0046]    The siphon has a functionality and shape of a conventional well known siphon and therefore is only briefly explained. As depicted in  FIG. 3 , siphon  20  has a first opening  21 , which is integrated into the sidewall  4   a  of the inner vessel  4 . From the first opening  21  a first longitudinal portion  22  extends along the sidewall  4   a  of the inner vessel  4 , leads into a curve  23  and further into a second longitudinal portion  24  extending parallel to the first longitudinal portion  22 . The second opening  25  is provided at the end of the second longitudinal portion  24 . 
         [0047]    Indicated in  FIG. 3  are also the first height  30 , at which the solid material  7  is placed within the inner vessel  4 , and the second height  31  indication the maximum vertical extension of the solid material  7  within the inner vessel  4 . 
         [0048]    As soon as the solvent  8  reaches the height of the curve  23  of the siphon  20 , a large amount of solvent  8  is emptied from the inner vessel  4  and delivered to the outer vessel  3 . Solvent  8  flows from the inner vessel  4  through the siphon  20  to the outer vessel  3  until the height of the solvent  8  within the inner vessel  4  reaches the first opening  21  of the siphon. Then the flow of solvent  8  stops until the height again reaches the height of the curve  23  of the siphon. 
         [0049]    In order to provide an effective extraction of the compound from the solid material  7 , the first opening  21  of the siphon  20  is provided below the solid material  7 , i.e. below the first height  30 . Further, the height of the curve  23  is above the second height  31 , i.e. above the solid material  7 . In order to achieve this geometrical relationship, either a specific vessel with a corresponding siphon can be chosen and/or the height of the support  5  can be adapted accordingly. 
         [0050]    The siphon principle has the effect that predominantly the fresh solvent  8  being condensed by the condenser  12  and flowing down from the condenser  12  into the inner vessel  4  comes into contact with the solid material  7 . Since due to the siphon  20  a major part of the solvent  8  comprising already extracted compound is removed from the inner vessel  4 , the percentage of extracted compound within the solvent  8  in the inner vessel  4  is kept at a low value so that the fast and effective extraction is further supported. 
         [0051]    With reference to  FIGS. 4   a  and  4   b  now further details of preparing the solid material  7  will be explained. 
         [0052]    Preferably the solid material  7  is placed into a container  18 , as shown in  FIG. 4   a . The container  18  as shown in  FIG. 4   b  is sealed along a sealing line  19 . The material support preferably comprises corresponding openings or recesses to receive a container  18  therein. The openings or recesses hereby can have a size large enough to allow the container  18  to be inserted but small enough to fixedly keep the container  18  therein through the extraction process. 
         [0053]    Now with reference to  FIG. 5  the steps of the method will be explained in more detail. 
         [0054]    The process starts in step S 0 . In step S 1  the solid material  7  to be extracted is weighed, placed in container  18 , which is then sealed, and in step S 2  is placed into the inner vessel  4  together with a part of the solvent  8 . In step S 3  the inner vessel and the solvent  8  are placed into the outer vessel  3 . 
         [0055]    In step S 4  the microwave irradiation is started. In step S 5  at least a part of the solvent within the outer vessel is caused to evaporate and to condense in step S 6  within the condenser  12 . In step S 7  the condensed solvent  8  is delivered to the inner vessel  4  to surround and immerse the solid material  7 , which preferably is contained within the sealed container  18 . In step S 8  solvent  8  is delivered from the inner vessel  4  to the outer vessel  3  via the outlet  6 , which preferably is a siphon  20 . The steps S 5  to S 8  are repeated until the complete compound is extracted from the solid material  7 . 
         [0056]    According to step S 9 , the solvent  8  within both vessels is constantly agitated, i.e. the solvent  8  is agitated during the steps S 5  to S 8 . 
         [0057]    After the extraction is complete, the microwave irradiation in step S 10  is stopped. 
         [0058]    In step S 11  after a drying process the remaining solid material  7  is again weighed. By the difference in weight before and after extraction the amount of extracted compound can be determined. 
         [0059]    The process ends in step S 12 . 
         [0060]    The fact that the extracted compound is determined by said difference in weight has the advantage, that a plurality of different probes can be extracted at the same time, since the purity of the extracted compound is not important. According to the present invention preferably four probes are extracted at one time, but also larger number of probes up to 20 probes or more can be extracted. 
         [0061]    Preferably, according to the present invention the extraction takes places at a constant temperature between 60° C. and 76° C. according to the boiling temperature of the solvent  8  and using a radiation power between 300 W and 1000 W, preferably of 400 W. The extraction duration is less than 20 minutes, preferably about 15 minutes. 
       EXAMPLE I 
       [0062]    The following is a detailed example with respect to the method of the present invention for extracting fat from food. 
         [0063]    An amount of 1 to 2 gram of food is loaded into the container  18 . Preferably as outer vessel  3  a flask with a volume of 2000 milliliters is used and as inner vessel  4  a flask with a volume of 600 milliliters is used. The complete volume of the solvent is 500 milliliters and the recycle volume using the siphon is 300 milliliters. The radiation power is set at 400 watt. The extraction using four containers  18  each comprising an amount of 1-2 gram of solid material is performed for 15 minutes. This duration is sufficient to completely extract the compound, for example fat, from the solid material. 
         [0064]    Solid materials such as bakery products, sausage products, fried foods, cheese, milk, or the like can be used. 
         [0065]    The advantages provided by the extraction device and process according to the present invention are numerous. 
         [0066]    According to the present invention by using microwave radiation, a very fast and uniform heating of the solvent is reached. By further providing a stirrer in each of the vessels, the temperature within the solvent is homogeneously kept. Further, it is ensured that fresh solvent is always in contact with the solid material. 
         [0067]    In a preferred embodiment a siphon is used to deliver solvent from the inner vessel to the outer vessel. Thereby it is ensured that when the inner vessel is refilled, the solid material comes in contact with only fresh solvent, so that the extraction process can be further accelerated.