Device for concentrating vapors of chemical molecules contained in the air

Abstract

The invention relates to a device for concentrating (DC) vapors of chemical molecules contained in the air, said device comprising: - a receptacle (RCP) having a central air inlet orifice (OEA); - a cylindrical cage (CG) housed in the receptacle, said cage (CG) comprising: a first ring (PC1) defining a central orifice (OC1) communicating with the central air inlet orifice (OEA) of the receptacle (RCP), a second ring (PC2), a plurality of rods (TG) extending parallel between the first ring (PC1) and the second ring (PC2), said rods being distributed over the circumference of said rings (PC1, PC2), and a heating wire (FC) having a sheath (G) made of a material suitable for absorbing said vapors, said heating wire (FC) being woven with the rods (TG);- a cover (CVC) for the receptacle (RCP), said cover having one or more outlet(s) (OSA, OSA1, OSA2, OSA3) radially external to said cage and extending over the peripheral contour (CPH) of said cage. Figure for the abbreviation: Figure 1;

Description

Title of the invention: Device for concentrating vapors of chemical molecules contained in the air. Technical field of the invention

[0001] The present invention relates to the field of detecting vapors of chemical molecules contained in the air, for example in the field of security (explosive vapors), the environment or industry.

[0002] The invention relates more particularly to a device for concentrating these vapors in the air. Previous Art

[0003] There are many techniques for detecting molecular vapors in the air. Whatever the technique used, it is important to sample the air volume properly, i.e. to provide the detector itself with an air sample containing the vapors in a concentration suitable for the detection limit of the detector. For example, for explosive vapors, the saturated vapor pressure is typically between 102 bar and 10 18 bar depending on the nature of the explosive vapors.

[0004] For a given detector which is intrinsically more or less sensitive depending on the technique it uses, it is therefore possible to vary the detection limits by modifying the sampled quantity containing the vapors of chemical molecules to be detected. Indeed, the lower the concentration of sampled vapors, the more it is necessary to collect a large volume of air so that the detector has enough material to pass above its own detection limits (sensitivity).

[0005] Furthermore, each detector has an optimized design which generally fixes its capacity to analyze volumes (or air flow rates) in a given and generally restricted range. Also, air sampling is a means which makes it possible to collect at the ad hoc location the vapors of chemical molecules to be detected by supplying at this location the adequate volume of air to the detector used.

[0006] At a given temperature, each molecule is intrinsically capable of delivering into the air immediately surrounding it a maximum vapor pressure, i.e. the saturation vapor pressure, which is specific to it. However, in a real situation, the saturation vapor pressure is rarely reached and the actual pressure may even be much lower than the saturation vapor pressure (by one or more orders of magnitude). The causes may be related to the presence of a physical barrier such as one or more packages between the compound (solid or liquid) generating the vapors of chemical molecules to be detected and the location of the air sampling, a sample air flow before reaching the saturated vapor pressure in the volume to be sampled, for example in a very large volume of air, or the presence of ventilation generating a vapor dilution effect or a combination of several of these factors or other factors.

[0007] It is therefore understood that, whatever the detection technique used at the detector, it is of interest to concentrate the vapors of interest in a volume of air compatible with the performance of the detector. Furthermore, doing so with large air flow rates can only significantly reduce the sampling time (speed).

[0008] Several types of devices for concentrating chemical molecule vapors already exist.

[0009] Some concentrators are well suited for very sensitive detectors with very low analysis volumes because they process small sample volumes per unit time. For example, we can cite the article by Giordano, Braden C., Daniel C. Ratchford, Kevin J. Johnson, and Pehr E. Pehrsson. "Silicon Nanowire Arrays for the Preconcentration and Separation of Trace Explosives Vapors." Journal of Chromatography A 1597 (2019 / 07 / 19 / 2019): pp. 54-62. In this article, a device for concentrating chemical molecule vapors suitable for a flow rate of 180 mL / min (3 L / h) based on silicon-based nanowires heated to 200°C is described. This type of concentrator is not suitable for addressing large volumes of air.

[0010] Conversely, other concentration devices are well suited to detectors with very large analysis volumes, for example common in the chemical reprocessing industry. For example, the article by Linker, Kevin L. Large-Volume Sampling and Pre-concentration for Trace Explosives Detection, Sandia National Laboratory, 2004 describes a series of very large volume concentrators with flow rates between 200 and 1160 m3 / h. However, these types of devices are not mobile and therefore cannot be used ad hoc at any location.

[0011] Devices for concentrating vapors of chemical molecules in air that are capable of both treating large volumes and being mobile (or portable) are rarer or little described. However, we can cite Gillanders, Ross N., James ME Glackin, Janja Filipi, Nikola Kezic, Ifor DW Samuel, and Graham A. Turnbull. "Preconcentration Techniques for Trace Explosive Sensing." Science of The Total Environment 658 (2019 / 03 / 25 / 2019): 650-58. In this article, a device is described with a sampling flow rate of 60 L / min (1 L / h) for a significant concentration. Indeed, the concentration factor for 120 cm2 of absorbent improves the final concentration by a factor of 3 for 10 minutes of sampling. This method is described as specific to the detector used (fluorescence) and the environment to be sampled (bee hives). Summary of the invention

[0012] An objective of the invention is to propose an improved device for concentrating vapors of chemical molecules in the air.

[0013] In particular, an objective of the invention is to propose a device for concentrating vapors of chemical molecules capable of treating large volumes of air with high flow rates.

[0014] In particular also, another objective of the invention is to propose such a device which is portable by a human operator.

[0015] To this end, the invention proposes a device for concentrating vapors of chemical molecules contained in the air, said device comprising: - a receptacle comprising a central air inlet orifice; - a cylindrical cage housed in the receptacle, said cage comprising: a first crown defining a central orifice communicating with the central air inlet orifice of the receptacle, a second crown, a plurality of rods extending parallel between the first crown and the second crown, said rods being distributed over the circumference of said crowns, and a heating wire provided with a sheath either made of the same electrically insulating material, resistant to the temperature level likely to be produced in the heating wire and capable of absorbing said vapors or made of at least two layers made of distinct materials but all resistant to the temperature level likely to be produced in the heating wire, the radially inner layer being furthermore made of an electrically insulating material and the radially outer layer being furthermore made of a material capable of absorbing said vapors,said heating wire being either wound around all of the rods or woven with the rods; - a cover for the receptacle, said cover comprising one or more outlet orifice(s) radially external to said cage and extending over the peripheral contour of said cage.

[0016] The invention may comprise at least one of the following characteristics, taken alone or in combination:

[0017] - said rods are in odd number;

[0018] - said rods are distributed at regular intervals around the circumference of said crowns;

[0019] - the cage comprises at least one thermocouple;

[0020] - the device according to the invention further comprises an additional cylindrical cage housed in the receptacle, said additional cage comprising a first crown defining a central orifice, a second crown defining a central orifice, and a plurality of rods extending parallel between the first crown and the second crown, said rods being distributed over the circumference of said crowns, the central orifices of said crowns of the additional cage having a diameter corresponding to the external diameter of the crowns of said cage, a heating wire provided with a sheath either made of the same electrically insulating material, resistant to the temperature level likely to be produced in the heating wire and capable of absorbing said vapors or made of at least two layers made of distinct materials but all resistant to the temperature level likely to be produced in the heating wire, the radially inner layer being furthermore made of an electrically insulating material and the radially outer layer being furthermore made of a material capable of absorbing said vapors, said heating wire being either wound around all of the rods or woven with the rods of the additional cage,the or each air outlet orifice of the cover being radially external with respect to the additional cage;

[0021] - said plurality of rods of the additional cage is in odd number;

[0022] - said rods of the additional cage are distributed at regular intervals on the cir conference of the said crowns;

[0023] - the sheath of the heating wire of the additional cage is made of a material identical to the sheath of the heating wire of said cage;

[0024] - the additional cage comprises at least one thermocouple;

[0025] - the device according to the invention another additional cylindrical cage housed in the receptacle, said another additional cage comprising a first crown defining a central orifice, a second crown defining a central orifice, and a plurality of rods extending parallel between the first crown and the second crown, said rods being distributed over the circumference of said crowns, the central orifices of said crowns of said another additional cage having a diameter corresponding to the external diameter of the crowns of the additional cage, a heating wire provided with a sheath either made of the same electrically insulating material, resistant to the temperature level likely to be produced in the heating wire and capable of absorbing said vapors or made of at least two layers made of distinct materials but all resistant to the temperature level likely to be produced in the heating wire,the radially inner layer being furthermore made of an electrically insulating material and the radially outer layer being furthermore made of a material capable of absorbing said vapors, said heating wire being either wound around all of the rods or woven with the rods of said one other additional cage, the or each air outlet orifice of the cover being radially external with respect to said one other additional cage;

[0026] - said rods of said other additional cage are in odd number;

[0027] - said rods of said other additional cage are distributed at intervals regular on the circumference of said crowns;

[0028] - the sheath of the heating wire of said other additional cage is made of a material identical on the one hand to that of the sheath of the heating wire of the additional cage and on the other hand to that of the sheath of the heating wire of the cage;

[0029] - the cumulative surface area of ​​all the sections of the outlet orifices is strictly greater than the cross-sectional area of ​​the central air inlet orifice;

[0030] - a means for opening / closing the or each air outlet orifice of the lid. Brief description of the figures

[0031] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which one will refer to the appended drawings and for which:

[0032] [Fig. 1] is an exploded perspective view of a device for concentrating vapors of chemical molecules in accordance with the invention;

[0033] [Fig.2] is a perspective view of various cages used in the device shown in [Fig.l];

[0034] [Fig.3] is a view of the cages shown in [Fig.2] once assembled and housed in a receptacle of the device shown in [Fig.l];

[0035] [Fig.4] is a sectional view of a heating wire provided with a conductive core of electricity surrounded by a sheath capable of absorbing vapors of chemical compounds, according to 3 figures to represent the 3 wires envisaged with each of the different cages represented in [Fig.2];

[0036] [Fig.5] is a diagram showing, in operation, the passage taken by a flow of air within the device shown in [Fig.l];

[0037] [Fig.6] is a diagram showing a type of interlocking between the crown of a cage and the bottom of the receptacle of the device according to the invention to ensure sealing;

[0038] [Fig.7] is a diagram showing a type of interlocking between the crown of a cage and the cover of the device according to the invention to ensure sealing;

[0039] [Fig.8] is a side view of an alternative embodiment of the device according to the invention in which the heating wire is wrapped around the rods of the cage. Detailed description of the invention

[0040] The invention is described with the support of all the appended figures.

[0041] The invention proposes a device for concentrating DC vapors of chemical molecules contained in the air. The DC device comprises an RCP receptacle comprising a central air inlet orifice OEA, a cylindrical cage CG housed in the RCP receptacle and a CVC cover provided with an air outlet.

[0042] The RCP receptacle is advantageously cylindrical. The central OEA air inlet orifice is advantageously circular.

[0043] The cage CG comprises a first crown PCI defining a central orifice OC1 communicating with the central air inlet orifice OEA of the receptacle RCP. The cage CG also comprises a second crown PC2. The cage CG also comprises a plurality of rods TG extending parallel between the first crown PCI and the second crown PC2, said rods TG being distributed over the circumference of the crowns PCI, PC2. Finally, the cage CG comprises a heating wire FC provided with a sheath G capable of absorbing said vapors, said heating wire FC being woven with the rods TG. Advantageously, the number of rods TG is odd. This facilitates the weaving of the heating wire FC. Also advantageously, the rods TG are distributed at regular intervals over the circumference of the crowns PCI, PC2.This ensures a homogeneous weaving of the FC heating wire on the rods and consequently, a certain symmetry conducive, in use, to obtaining isotropic behavior of the air circulation and therefore of the concentration of vapors to be detected.

[0044] The air outlet is for example produced by a plurality of orifices OSAI, OSA2, OS A3 made in the cover CVC, radially external with respect to the cage CG, and distributed over the peripheral contour CPH of the cage CG. The air inlet orifice OEA being central and the orifices OSAI, OSA2, OS A3 being peripheral, the air flow within the receptacle RCP has both an axial and radial movement. This arrangement facilitates the passage of air through the structure formed by the heating wire FC woven with the rods TG. Advantageously, the cumulative surface area of ​​all the sections of the outlet orifices OSA is strictly greater than the surface area of ​​the section of the central air inlet orifice OEA (single). This makes it possible, in use, to reduce the pressure losses.For example, it may be provided that the cumulative surface area of ​​all the sections of the OSA outlet orifices is greater by at least 10%, for example between 10% and 30%, than the surface area of ​​the section of the central air inlet orifice OEA.

[0045] The heating wire FC consists of an electrically conductive wire FCE, for example metallic but which can be made of another electrically conductive material, covered with a sheath G made of at least one material capable of absorbing the vapors of chemical molecules to be concentrated (and which one ultimately seeks to detect). The conductive wire FCE can be a single-strand wire, as shown in [Fig. 4] or multi-strand. The electrically conductive wire FCE, for example visible in [Fig. 4], begins and ends with connection lugs CBE which allow an external connection with an electrical energy source. As can be understood, the sheath G is electrically insulating and capable of withstanding the temperatures (typically in a range from 140°C to 300°C) likely to be imposed by the wire conductor of the heating wire (Joule effect) when an electric current passes through it.

[0046] In practice, one can consider a sheath made of the same material having the properties mentioned above. A material that can be used for sheath G is PDMS (polydimethylsiloxane) whose crude chemical formula is: -(Si(CH3)2-O)n. This material makes it possible to concentrate vapors such as those of 4-NT (4-nitrotoluene), TNT (trinitrotoluene) or DMNB (dimethyldinitrobutane) for example.

[0047] Alternatively, it is also possible to envisage a sheath G with a structure made of at least two successive layers with a radially internal electrically insulating layer capable of withstanding the temperatures likely to be imposed on it but not necessarily capable of absorbing the vapors of chemical molecules (it may for example be PDMS), and a radially external layer also capable of withstanding the temperatures likely to be imposed on it but also capable of absorbing the vapors of chemical molecules of interest, without necessarily being electrically insulating (it may be a PDMS-based material comprising one or more additives, for example of the molecular sieve type such as Carboxen®). The same functions are fulfilled, but with two layers with complementary properties.

[0048] The FC heating wire can release the trapped molecules by passing an electric current through the conductive wire located at the core (Joule effect). This causes the rapid release of the vapors trapped in the sheath G. The decreasing temperature gradient from the core to the outside of the heating wire thus created in the absorbent material promotes the release of vapors to the outside by greatly limiting the residual vapors in the material. The limitation of the residual vapors in the material allows rapid reuse of the DC concentration device by considerably reducing the amplitude of T memory effect responsible for a persistent residual of the chemical molecules in the material.

[0049] Advantageously, the concentration device DC comprises a means for opening / closing the orifices of the cover. This opening / closing means may be in the form of a disc DSQ rotatably mounted on the cover CVC, the disc DSQ comprising openings OV1, OV2, OV3 which may (or may not) be placed in correspondence with the orifices of the cover CVC. It is thus possible to leave the orifices OA1, OA2, OA3 open (for example during the absorption of the vapors of chemical molecules in the sheath provided for this purpose in the air flow circulating in the concentration device) or to close them (for example, to ensure a more rapid rise in temperature of the volume of air present in the receptacle).

[0050] In a variant, in this case shown diagrammatically in [Fig. 5], the CVC cover comprises a single air outlet orifice OSA radially external with respect to said cage CG and extending over the peripheral contour CPH of the cover, preferably over the entire peripheral contour. Such a CVC cover can be associated with a means for opening / closing the OSA orifice of the cover in the form of a cap (not shown) with dimensions adapted to those of the cover. [Fig. 5] also represents the air flow FA within the DC concentration device. This air flow is the same in the presence of several outlet orifices on the cover, as shown in [Fig. 1].

[0051] It may be provided that the cage CG comprises at least one thermocouple TC. This thermocouple TC is advantageously placed in the outer part of the sheath G to measure the temperature at the level of the sheath G. Monitoring of the temperature may be carried out with one or more processor(s) looping back with the electrical power supply of the heating wire FC to ensure precise control of the temperature at the level of the sheath G and more generally in the concentration device DC.

[0052] In order to increase the performance or expand the capacities of the DC concentration device, the exchange surface between the sheath and the air within the (given) volume of the RCP receptacle can be increased.

[0053] For this purpose, the concentration device may provide an additional cylindrical cage CGI housed in the receptacle, arranged around said cage CG. Generally, the additional cage CGI is similar to the cage CG, but simply has a larger diameter. More precisely, the additional cage CGI comprises a first crown PCI 1 defining a central orifice OC11. The additional cage CGI also comprises a second crown PC12 defining a central orifice OC12. The additional cage also comprises a plurality of rods TG10 extending parallel between the first crown PCI 1 and the second crown PC12, said rods being distributed over the circumference of said crowns PCI 1, PC12. Furthermore, the central orifices OC11, OC12 of the crowns PC11, PC12 of the additional cage CGI have an internal diameter corresponding to the external diameter of the crowns PCI, PC2 of said cage CG.The additional cage CGI finally comprises a heating wire FC 10 provided with a sheath G10 made of a material capable of absorbing said vapors, said heating wire FC10 being woven with the rods TG10 of the additional cage CGI. Here too, the or each air outlet orifice OSA, OSAI, OSA2, OS A3 of the cover CVC is radially external with respect to the additional cage CGI. This ensures, for example during a step aimed at concentrating vapors of chemical compounds within the concentration device DC, that the air entering through the air inlet orifice OEA of the receptacle RCP circulates inside the cage CG, but also radially to be able to reach the heating wire FC10 of said additional cage CGI before leaving the receptacle RCP and the concentration device DC.

[0054] The additional CGI cage may also include at least one thermocouple TC, advantageously placed in the outer part of the G10 sheath of the FC1O heating wire to measure the temperature at the level of the G10 sheath.

[0055] In order to facilitate the positioning of the cage CG inside the additional cage CGI, the concentration device DC advantageously comprises complementary cooperation means L1, T1 respectively placed on the first crown PCI 1 of the additional cage CGI and on the first crown PCI of said cage CG at a given location on their respective circumferences. Typically, and as shown in the attached figures, a tab L1 may be provided on the external periphery of the first crown PCI of the cage CG and an opening T1 of corresponding shape on the internal periphery of the first crown PCI 1 of the additional cage CGI.

[0056] It may be provided that the heating wire FC 10 of the additional cage CGI is, in particular for the sheath, made of a material identical to the heating wire FC of said cage. This is of particular interest when seeking to increase the concentration rate of vapors of a given chemical compound in the air and / or increase the processing speed for a given concentration. Furthermore, a heating wire FC, FC 10 of identical diameter for the two cages CG, CGI implies a larger exchange surface between the sheath and the ambient air for the heating wire FC10 of the additional cage CGI, because this additional cage CGI has a larger diameter. This increased exchange surface makes it possible to add a second level of trapping with respect to vapors not trapped by the sheath G of the heating wire FC of the cage CG.

[0057] It should be noted that depending on the availability of materials, the external diameter of the FC10 heating wire may vary, as well as its internal composition, particularly for its sheath, the important thing being that this does not significantly change the final characteristics such as electrical insulation, trapping capacities, or even weight.

[0058] However, and as a variant, it is possible to envisage having a sheath G10 of the heating wire FC 10 of the additional cage CGI made of a different material from the sheath G of the heating wire FC of the cage CGI. In this case, it is then possible to absorb vapors of different chemical compounds present in the air and therefore ultimately to concentrate different vapor molecules. For example, it is possible to envisage for the sheath G of the heating wire FC of the cage CGI PDMS and for the sheath G1 of the heating wire FC10 of the cage CG10, PDMS incorporating carbon. The carbon can be a material in the form of a molecular sieve (derived from the pyrolysis of polymers). With a molecular sieve, it is possible to vary the size of the pores and therefore to target different types of vapors of chemical molecules to be trapped. Typically, these vapors are in a range of sizes corresponding to those of C2 to C5 alkanes. The Carboxen® product range is an example of this type of product.

[0059] The concentration device DC may also provide yet another additional cylindrical cage CG2 housed in the receptacle RCP. This other additional cage CG2 comprises a first crown PC21 defining a central orifice OC21. This other additional cage CG20 also comprises a second crown PC22 defining a central orifice OC22 and a plurality of rods TG20 extending parallel between the first crown PC21 and the second crown PC22, said rods being distributed over the circumference of said crowns PC21, PC22. Furthermore, the central orifices OC21, OC22 of the crowns PC21, PC22 of said another additional cage CG2 have an internal diameter corresponding to the external diameter of the crowns PCI 1, PC12 of the additional cage CGI.This other additional cage CG2 finally comprises a heating wire FC20 provided with a sheath G20 made of a material capable of absorbing said vapors, said heating wire FC20 being woven with the rods TG20 of said another additional cage CG2. Here too, the or each air outlet orifice OSA, OSAI, OSA2, OSA3 of the CVC cover is radially external with respect to said another additional cage CG2. This ensures, for example during a step aimed at concentrating vapors of chemical compounds within the concentration device DC, that the air entering through the air inlet orifice OEA of the RCP receptacle circulates inside the cage CG, but also radially to be able to reach the heating wire FC20 of said at least one other additional cage CG20 before leaving the RCP receptacle and the concentration device DC.

[0060] Said another additional cage CG2 may also include at least one thermocouple TC20, advantageously placed in the outer part of the sheath G20 of the heating wire FC20 to measure the temperature at the level of the sheath G20.

[0061] In order to facilitate the positioning of the additional cage CGI inside said another additional cage CG2, the concentration device DC advantageously comprises complementary cooperation means L2, T2. More precisely, the complementary cooperation means L2, T2 are respectively placed on the first crown PC21 of said another additional cage CG2 and on the first crown PCI 1 of said additional cage CGI at a given location on their respective circumferences. Typically, and as shown in the attached figures, a tab L2 may be provided on the external periphery of the first crown PCI 1 of the additional cage CGI and an opening T2 of corresponding shape on the internal periphery of the first crown PC21 of said another additional cage CG2.

[0062] It can be envisaged that the sheath G20 of the heating wire FC20 of said other additional cage CG2 is made of a material identical on the one hand to that of the sheath G10 of the FC 10 heating wire of the additional cage CGI and on the other hand, to that of the sheath G of the FC heating wire of the CG cage. In this case, this makes it possible to increase the exchange surface of the material absorbing the vapors of chemical compounds present in the air, in this case at the level of the most radially external cage CG2 and which locally sees a lower concentration of these vapors due to the absorption carried out at the level of the two most internal cages CG, CGI.

[0063] Of course, it is possible to envisage, on the contrary, that the material forming the sheath G20 is different not only from the material forming the sheath G of the heating wire FC, but also from the material forming the sheath G10 of the heating wire FC10 of the additional cage CGI. It then becomes possible to concentrate vapors from three different chemical families at the same time with the concentration device DC.

[0064] It is also possible, if desired, to provide that one of the sheaths G, G10, G20 is made of a material different from the material forming the other two sheaths. In this case, it is then possible to concentrate vapors of two different chemical compounds while increasing, for example, the concentration rate of the vapors of another family of chemical compounds.

[0065] Furthermore, throughout the preceding description, we have presented embodiments for which the heating wire FC, FC10, FC20 is woven with the rods of the associated cage CG, CGI, CG2. Alternatively, it may be provided that the heating wire FC, FC10, FC20 is wound around said rods. When several cages are envisaged, the heating wire may be wound around the rods for a single cage, only certain cages or all the cages. Reference may be made to [Fig.8] which shows such an alternative embodiment for the cage CG.

[0066] Furthermore, when several cages are envisaged, it can be provided that these are secured to each other at their respective crowns. The cages are then in the form of a block, which facilitates the installation of the cages since only one installation is then necessary. It can also be provided that this block is fixable to the bottom of the receptacle and secure the cover to the block, the cover then advantageously providing a handle to facilitate the extraction of the block from its receptacle.

[0067] The seal between the bottom of the RCP receptacle and the crowns of each cage CG, CGI, CG2 ([Fig.6]) on the one hand, as well as the seal between the CVC cover and these same crowns ([Fig.7]) on the other hand, are advantageously achieved by machining a double wave in the mass which allows the assembly of the two parts to ensure sufficient sealing for the proper functioning of the device. In [Fig.6], this double wave is formed by a bead BPC1 made in the lower PCI crown of the CGI cage (in this case) which is inserted in a sealed manner into a corresponding hollow CFRCP made in the FRCP bottom of the RCP receptacle. In [Fig.7], this double wave is formed by a BPC2 bead made in the upper PC2 crown of the CGI cage (in this case) which is inserted into a CCVC hollow made in the CVC cover. This design avoids the use of seals to ensure this seal. The BPC1 and FRCP beads can be seen in Figures 2 and 3, respectively.

[0068] The free volume of the receptacle, that is to say its total volume less the volume of the cage housed therein or, as the case may be, of all the cages housed therein, must be as small as possible while remaining close to the volume required by the detector used downstream of the concentration device to carry out the analysis. For example, consider an explosive detector having an analysis flow rate of 0.1 liters per minute for an analysis time of one minute and a detection limit of 1 ppbv (109 v / v). It can then be associated with a DC concentration device according to the invention sampling 100 liters of air containing 0.01 ppbv of explosive vapors which will be trapped and then released into a smaller volume of the receptacle of 0.1 liters. In this case, the resulting concentration will be 1000, or three orders of magnitude.This gain will allow the detector to have, after the DC concentration device operation according to the invention, a concentration of 10 ppbv, i.e. 10 times above the detection limit of the detector, whereas it would have been impossible to carry out this detection without a concentration device, the concentration being in fact a hundred times lower than the native detection limit of the detector. Reality leads to lower values ​​of the concentration level due to the trapping efficiencies specific to each “chemical molecule - cage equipped with its heating wire with its sheath” pair or the properties of the vapors of the chemical molecules studied.

[0069] It will be noted that several detection technologies are compatible with the DC concentration device according to the invention. It is possible to cite, without this being limiting, mass spectrometry, Raman spectrometry or infrared spectrometry, gas chromatographies associated with sensitive detectors (electron capture detector, mass spectrometry, etc.), portable vapor detectors. In particular, in the case of gas chromatography, it is entirely possible to use standard means such as SPME (for "Solid Phase Micro Extraction" according to the English terminology) to sample the vapors, directly in the hot concentration device at the end of the heating cycle of the concentration device. Presentation of experimental tests

[0070] Tests were carried out with air containing DMNB vapors, which is an official marker for commercial explosive compositions. Prior to the tests, the DMNB vapors were diluted to a value of the order of 0.7 ppbv, i.e., a concentration nearly 2000 times lower than the vapor pressure saturating of this molecule at room temperature. These diluted vapors were drawn through the concentration device described in this patent application, with the air outlets open, at a flow rate of 150 L / min (9,000 L / h) for 10 minutes at 20°C, which represents a sampled gas volume of 1.5 m3 (at 0.7 ppbv in DMNB). Three concentric cages were used, each comprising a heating wire with a PDMS sheath. The total and cumulative length of the heating wire is 17 m and each heating wire has an external diameter of 2.1 mm.

[0071] After 10 minutes of sampling the diluted DMNB vapors in the device, the air outlet orifices are closed.

[0072] Then, the device is positioned in an oven at 200°C with heating to this same temperature of the heating wire by a current passage.

[0073] When the temperature of 200°C is reached everywhere, in these tests after 4 minutes, a reference SPME fiber (57300-U, SUPELCO), previously activated according to the manufacturer's recommendations, is positioned for 3 minutes in the OEA orifice. During the 3 minutes the SPME passively captures the concentrated vapors released in the free volume of 368 cm3 of the device according to the invention.

[0074] The SPME is then analyzed by an AGILENT gas chromatograph equipped with an electron capture detector. The average area values ​​obtained for the tests carried out is 2,299,388 AU (arbitrary units), which represents a signal-to-noise ratio of more than 200.

[0075] The tests were carried out systematically after a blank run under the same conditions but without DMNB in ​​order to verify the absence of memory effect of the device between each test. The value of the blanks is approximately 10,000 AU (arbitrary units) each time. This value is deduced from the results presented.

[0076] End of presentation of experimental tests.

[0077] The use of the concentration device according to the invention comprises three main stages.

[0078] In a first step, the DC device is connected, with the air outlets open, at room temperature to a device for suctioning the vapors to be collected. Typically, such a suction device provides an air flow of approximately 150 liters per minute for a duration chosen by the user ranging from a few seconds to several hours depending on the concentration requirements.

[0079] In a second step, the DC device is placed, with the air outlets closed, in an oven allowing the temperature to be raised, for example to around 200°C in order to maintain its external walls at this temperature and at the same time to provide the current necessary to heat the wire heated to this same temperature. This allows the molecules previously collected in the sheath of the heating wire to be released into the free volume of the DC device. Heating is carried out in a few minutes. This is when the concentrated vapor analyzer or collector (e.g. SPME) is positioned above the DC device to analyze after aspiration or collect the concentrated vapors.

[0080] In a final step, the invention is either maintained at a hot temperature with a flow of clean air to evacuate the last vapors or cooled naturally or by a flow of clean ambient air (for example with a flow of approximately 150 L / min), with the air outlet orifices open.

Claims

Claims

1. Device (DC) for concentrating vapors of chemical molecules contained in the air, said device comprising: - a receptacle (RCP) comprising a central air inlet orifice (OEA); - a cylindrical cage (CG) housed in the receptacle, said cage (CG) comprising: a first crown (PCI) defining a central orifice (OC1) communicating with the central air inlet orifice (OEA) of the receptacle (RCP), a second crown (PC2), a plurality of rods (TG) extending parallel between the first crown (PCI) and the second crown (PC2), said rods being distributed over the circumference of said crowns (PCI, PC2), and a heating wire (FC) provided with a sheath (G) made of the same electrically insulating material,resistant to the temperature level likely to be produced in the heating wire and capable of absorbing said vapors is made of at least two layers made of separate materials but all resistant to the temperature level likely to be produced in the heating wire, the radially inner layer being furthermore made of an electrically insulating material and the radially outer layer being furthermore made of a material capable of absorbing said vapors, said heating wire (FC) being either wound around all of the rods (TG) or woven with the rods (TG); - a cover (CVC) for the receptacle (RCP), said cover comprising one or more outlet orifice(s) (OSA, OSAI, OSA2, OSA3) radially external to said cage and extending over the peripheral contour (CPH) of said cage.,

2. Device for concentrating (DC) the vapors of chemical molecules contained in the air according to claim 1, in which said rods (TG) are in odd number.

3. Device for concentrating (DC) the vapors of chemical molecules contained in the air according to one of the preceding claims, in which said rods (TG) are distributed at regular intervals around the circumference of said crowns (PCI, PC2).

4. Device for concentrating (DC) the vapors of chemical molecules contained in the air according to the preceding claim, in which the cage (CG) has at least one thermocouple (TC).

5. Device for concentrating (DC) the vapors of chemical molecules contained in the air according to one of the preceding claims, comprising an additional cylindrical cage (CGI) housed in the receptacle, said additional cage comprising: a first crown (PCI 1) defining a central orifice (OC11), a second crown (PC12) defining a central orifice (OC12), and a plurality of rods (TG10) extending parallel between the first crown (PC11) and the second crown (PC12), said rods being distributed over the circumference of said crowns (PC11, PC12), the central orifices (OC11, OC12) of said crowns (PC11, PC12) of the additional cage (CGI) having a diameter corresponding to the external diameter of the crowns (PCI, PC2) of said cage (CG), a heating wire (FC 10) provided with a sheath (G 10) is made of the same electrically insulating material,resistant to the temperature level likely to be produced in the heating wire and capable of absorbing said vapors or made of at least two layers made of distinct materials but all resistant to the temperature level likely to be produced in the heating wire, the radially inner layer being furthermore made of an electrically insulating material and the radially outer layer being furthermore made of a material capable of absorbing said vapors, said heating wire (FC 10) being either wound around all of the rods (TG10) or woven with the rods (TG10) of the additional cage (CGI), the or each air outlet orifice (OSA, OSAI, OSA2, OSA3) of the cover (CVC) being radially external with respect to the additional cage (CGI).,

6. Device for concentrating (DC) the vapors of chemical molecules contained in the air according to claim 5, in which said plurality of rods (TG10) of the additional cage (CGI) is in odd number.

7. Device for concentrating (DC) the vapors of chemical molecules contained in the air according to one of claims 5 or 6, in which said rods (TG10) of the additional cage (CGI) are distributed at regular intervals on the circumference of said crowns (PC11, PC12).

8. Device (DC) for concentrating vapors of chemical molecules contained in the air according to one of claims 5 to 7, in which the sheath (G 10) of the heating wire (FC 10) of the additional cage (CGI) is made of a material identical to the sheath (G) of the heating wire (FC) of said cage (CG).

9. Device (DC) for concentrating vapors of chemical molecules contained in the air according to one of claims 5 to 8, in which the additional cage (CGI) comprises at least one thermocouple (TC10).

10. Device (DC) for concentrating vapors of chemical molecules contained in the air according to one of claims 5 to 9, comprising another additional cylindrical cage (CG2) housed in the receptacle, said another additional cage comprising: a first crown (PC21) defining a central orifice (OC21), a second crown (PC22) defining a central orifice (OC22), and a plurality of rods (TG20) extending parallel between the first crown (PC21) and the second crown (PC22), said rods being distributed over the circumference of said crowns, the central orifices (OC21, OC22) of said crowns (PC21, PC22) of said another additional cage (CG2) having a diameter corresponding to the external diameter of the crowns (PC11, PC12) of the additional cage (CGI), a heating wire (FC20) provided with a sheath (G20) is made of the same electrically insulating material,resistant to the temperature level likely to be produced in the heating wire and capable of absorbing said vapors is made of at least two layers made of distinct materials but all resistant to the temperature level likely to be produced in the heating wire, the radially inner layer being furthermore made of an electrically insulating material and the radially outer layer being furthermore made of a material capable of absorbing said vapors, said heating wire (FC20) being either wound around all of the rods (TG20) or woven with the rods (TG20) of said one other additional cage (CG2), the or each air outlet orifice (OSA, OSAI, OSA2, OSA3) of the cover (CVC) being radially external with respect to said one other additional cage (CG2).,

11. Device for concentrating (DC) the vapors of chemical molecules contained in the air according to claim 10, in which said rods (TG20) of said another additional cage (CG2) are in odd number.

12. Device for concentrating (DC) the vapors of chemical molecules contained in the air according to one of claims 10 or 11, in which said rods (TG20) of said other additional cage (CG2) are distributed at regular intervals on the circumference of said crowns (PC21, PC22).

13. Device for concentrating (DC) the vapors of chemical molecules contained in the air according to one of claims 10 to 12, in which the sheath (G20) of the heating wire (FC20) of said other additional cage (CG2) is made of a material identical on the one hand to that of the sheath (G 10) of the heating wire (FC 10) of the additional cage (CGI) and on the other hand to that of the sheath (G) of the heating wire (FC) of the cage (CG).

14. Device for concentrating (DC) vapors of chemical molecules contained in the air according to one of the preceding claims, in which the cumulative surface area of ​​all the sections of the outlet orifices (OSA) is strictly greater than the surface area of ​​the section of the central air inlet orifice (OEA).

15. Device for concentrating (DC) vapors of chemical molecules contained in the air according to one of the preceding claims, further comprising means (DSQ) for opening / closing the (OSA) or each (OSAI, OSA2, OSA3) air outlet orifice of the cover.

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