WO2024256532A1 - Device for concentrating vapours of chemical molecules contained in the air - Google Patents

Abstract

A device (DC) for concentrating vapours 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) having: • 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 to one another 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) provided with a sheath (G) made of a material capable of absorbing said vapours, said heating wire (FC) being woven with the rods (TG); • - a cover (CVC) for the receptacle (RCP), said cover having one or more outlet orifices (OSA, OSA1, OSA2, OSA3) radially external with respect to said cage and extending over the peripheral contour (CPH) of said cage.

Description

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

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

The invention relates more particularly to a device for concentrating these vapors in the air.

Previous Art

There are many techniques for detecting vapors of molecules in the air. Whatever the technique used, it is important to sample the air volume properly, i.e. to provide the detector itself with a sample of air containing the vapors in a concentration adapted to the detection limit of the detector. For example, for explosive vapors, the saturation vapor pressure is typically between 10 ^-2 bar and 10 ^-18 bar depending on the nature of the explosive vapors.

For a given detector that 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).

Furthermore, each detector has an optimized design that generally fixes its ability to analyze volumes (or air flow rates) in a given and generally restricted range. Also, air sampling is a means of collecting the vapors of chemical molecules to be detected at the ad hoc location by providing the appropriate volume of air to the detector used at that location.

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 can 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, air sampling before reaching the saturation vapor pressure in the volume to be sampled, for example in a very large volume of air, or the presence of ventilation generating a dilution effect on the vapors or a combination of several of these factors or other factors.

It is therefore understood that, whatever the detection technique used at the detector level, 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).

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

Some concentrators are well suited for very sensitive detectors with very low analysis volumes because they process small sample volumes per unit time. An example is 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 Explosive Vapors." Journal of Chromatography A 1597 (2019/07/19/ 2019): pp. 54-62. This article describes 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 at 200 °C. This type of concentrator is not suitable for addressing large volumes of air.

In contrast, other concentration devices are well suited for very large volume detectors, such as those common in the chemical reprocessing industry. For example, Linker's article, Kevin L. Large-Volume Sampling and Preconcentration 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, such devices are not mobile and therefore cannot be used ad hoc at any location.

Devices for concentrating chemical molecule vapors in air that are capable of both treating large volumes and being mobile (or portable) are rarer or poorly 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 cm ² 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).

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

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

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

For this purpose, 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;
- 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 with respect to said cage and extending over the peripheral contour of said cage.

The invention may include at least one of the following characteristics, taken alone or in combination:

- said rods are in odd number;

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

- the cage has at least one thermocouple;

- 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 internal layer being furthermore made of an electrically insulating material and the radially external layer being furthermore made of a material capable of absorbing said vapors, said heating wire being either wound around all of the rods either 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;

- said plurality of rods of the additional cage is of odd number;

- said rods of the additional cage are distributed at regular intervals around the circumference of said crowns;

- 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;

- the additional cage includes at least one thermocouple;

- 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 internal layer being moreover made of an electrically insulating material and the radially external layer being moreover made of a material capable of absorbing said vapors, said heating wire being either wound around the set of rods is 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;

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

- said rods of said other additional cage are distributed at regular intervals around the circumference of said crowns;

- 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;

- the cumulative surface area of all the sections of the outlet orifices is strictly greater than the surface area of the section of the central air inlet orifice;

- a means of opening/closing the or each air outlet opening of the cover.

Brief description of the figures

Other features and advantages of the invention will become apparent upon reading the detailed description which follows, for the understanding of which reference will be made to the attached drawings and for which:

There is an exploded perspective view of a device for concentrating vapors of chemical molecules in accordance with the invention;

There is a perspective view of various cages used in the device shown in the ;

There is a view of the cages shown on the once assembled and housed in a receptacle of the device shown in the ;

There is a cross-sectional view of a heating wire with an electrically conductive core 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 on the ;

There is a diagram representing, in operation, the passage taken by an air flow within the device shown in the ;

There is a diagram representing a type of fitting between the crown of a cage and the bottom of the receptacle of the device according to the invention to ensure sealing;

There is a diagram representing a type of fitting between the crown of a cage and the cover of the device according to the invention to ensure sealing;

There is a side view of an alternative embodiment of the device according to the invention in which the heating wire is wound around the rods of the cage.

Detailed description of the invention

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

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

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

The CG cage comprises a first crown PC1 defining a central orifice OC1 communicating with the central air inlet orifice OEA of the RCP receptacle. The CG cage also comprises a second crown PC2. The CG cage also comprises a plurality of rods TG extending parallel between the first crown PC1 and the second crown PC2, said rods TG being distributed over the circumference of the crowns PC1, PC2. Finally, the CG cage 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 PC1, 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.

The air outlet is for example produced by a plurality of orifices OSA1, OSA2, OSA3 made in the CVC cover, radially external relative to the CG cage, and distributed over the peripheral contour CPH of the CG cage. The air inlet orifice OEA being central and the orifices OSA1, OSA2, OSA3 being peripheral, the air flow within the RCP receptacle has both an axial and radial movement. This arrangement facilitates the passage of air through the structure formed by the FC heating wire woven with the TG rods. Advantageously, the cumulative surface area of all the sections of the OSA outlet orifices 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 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.

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 we ultimately seek to detect). The conductive wire FCE can be a single-strand wire, as shown in the or multi-strand. The electrical conductive wire FCE, for example visible on the , begins and ends with CBE connection lugs that allow an external connection with an electrical energy source. As can be understood, the G sheath is electrically insulating and capable of withstanding temperatures (typically in the range of 140°C to 300°C) likely to be imposed by the conductive wire of the heating wire (Joule effect) when an electric current passes through it.

In practice, we can consider a sheath made of the same material with the properties mentioned above. A material that can be used for sheath G is PDMS (polydimethylsiloxane) whose chemical formula is: -(Si(CH ₃ ) ₂ -O) _n . This material can concentrate vapors such as those of 4-NT (4-nitrotoluene), TNT (trinitrotoluene) or DMNB (dimethyldinitrobutane) for example.

Alternatively, it is also possible to envisage a G sheath 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 (this 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 (this may be a PDMS-based material comprising one or more additives, for example of the molecular sieve type such as Carboxen®). The same functionalities are fulfilled, but with two layers with complementary properties.

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 G sheath. 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. Limiting the residual vapors in the material allows rapid reuse of the DC concentration device by considerably reducing the amplitude of the memory effect responsible for a persistent residual of chemical molecules in the material.

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 disk DSQ rotatably mounted on the cover CVC, the disk DSQ comprising openings OV1, OV2, OV3 which may (or may not) be aligned 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 faster temperature rise of the volume of air present in the receptacle).

In a variant, in this case schematized on the , 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 may be associated with a means for opening/closing the orifice OSA of the cover in the form of a cap (not shown) with dimensions adapted to those of the cover. The also represents the air flow FA within the DC concentration device. This air flow is the same in the presence of several outlet ports on the cover, as shown in the .

It may be provided that the cage CG includes 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. The temperature can be monitored 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.

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.

For this purpose, the concentration device may provide an additional cylindrical cage CG1 housed in the receptacle, arranged around said cage CG. In general, the additional cage CG1 is similar to the cage CG, but simply has a larger diameter. More precisely, the additional cage CG1 comprises a first crown PC11 defining a central orifice OC11. The additional cage CG1 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 PC11 and the second crown PC12, said rods being distributed over the circumference of said crowns PC11, PC12. Furthermore, the central orifices OC11, OC12 of the crowns PC11, PC12 of the additional cage CG1 have an internal diameter corresponding to the external diameter of the crowns PC1, PC2 of said cage CG. The additional cage CG1 finally comprises a heating wire FC10 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 CG1. Here too, the or each air outlet orifice OSA, OSA1, OSA2, OSA3 of the CVC cover is radially external relative to the additional cage CG1. 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 CG1 before exiting the receptacle RCP and the concentration device DC.

The additional cage CG1 may also include at least one thermocouple TC, advantageously placed in the outer part of the G10 sheath of the FC10 heating wire to measure the temperature at the level of the G10 sheath.

In order to facilitate the positioning of the cage CG inside the additional cage CG1, the concentration device DC advantageously comprises complementary cooperation means L1, T1 respectively placed on the first crown PC11 of the additional cage CG1 and on the first crown PC1 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 PC1 of the cage CG and an opening T1 of corresponding shape on the internal periphery of the first crown PC11 of the additional cage CG1.

It can be provided that the heating wire FC10 of the additional cage CG1 is, in particular for the sheath, made of a material identical to the heating wire FC of said cage. This is particularly of 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, FC10 of identical diameter for the two cages CG, CG1 implies a larger exchange surface between the sheath and the ambient air for the heating wire FC10 of the additional cage CG1, because this additional cage CG1 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.

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.

However, and as a variant, it is possible to envisage having a G10 sheath of the FC10 heating wire of the additional cage CG1 made of a different material from the G sheath of the FC heating wire of the CG1 cage. In this case, it is then possible to absorb vapours of different chemical compounds present in the air and therefore ultimately to concentrate different vapour molecules. As an example, it is possible to envisage for the G sheath of the FC heating wire of the CG1 cage PDMS and for the G1 sheath of the FC10 heating wire of the CG10 cage, PDMS incorporating carbon. The carbon can be a material in the form of a molecular sieve (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 chemical molecule vapours to be trapped. Typically, these vapours are in a size range corresponding to those of the n alkanes C2 to C5. The Carboxen® product line is an example of this type of product.

The DC concentration device may also provide yet another additional cylindrical cage CG2 housed in the RCP receptacle. 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 other additional cage CG2 have an internal diameter corresponding to the external diameter of the crowns PC11, PC12 of the additional cage CG1. 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, OSA1, OSA2, OSA3 of the CVC cover is radially external relative 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 receptacle RCP 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 exiting the receptacle RCP and the concentration device DC.

Said other 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.

In order to facilitate the positioning of the additional cage CG1 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 PC11 of said additional cage CG1 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 PC11 of the additional cage CG1 and an opening T2 of corresponding shape on the internal periphery of the first crown PC21 of said another additional cage CG2.

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 heating wire FC10 of the additional cage CG1 and on the other hand to that of the sheath G of the heating wire FC of the cage CG. 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, CG1.

Of course, it is possible to envisage, on the contrary, that the material forming the G20 sheath is different not only from the material forming the G sheath of the FC heating wire, but also from the material forming the G10 sheath of the FC10 heating wire of the additional CG1 cage. It then becomes possible to concentrate vapors from three different chemical families at the same time with the DC concentration device.

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 vapors of another family of chemical compounds.

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, CG1, 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 the which shows such a variant of realization for the CG cage.

In addition, when several cages are envisaged, it can be provided that they 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.

The seal between the bottom of the RCP receptacle and the crowns of each cage CG, CG1, CG2 ( ) on the one hand as well as the sealing between the CVC cover and these same crowns ( ) on the other hand, are advantageously produced 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. On the , this double wave is formed by a bead BPC1 made in the lower crown PC1 of the cage CG1 (in this case) which fits tightly into a corresponding hollow CFRCP made in the bottom FRCP of the receptacle RCP. On the , this double wave is formed by a BPC2 bead made in the upper PC2 crown of the CG1 cage (in this case) which is inserted into a CCVC hollow made in the CVC cover. This design avoids the use of gaskets to ensure this sealing. The BPC1 and FRCP beads can be seen in Figures 2 and 3, respectively.

The free volume of the receptacle, i.e. its total volume minus 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 perform the analysis. For example, consider an explosive detector with an analysis flow rate of 0.1 liters per minute for an analysis time of one minute and a detection limit of 1 ppbv (10 ^-9 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 in 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.

It should 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 Anglo-Saxon 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

Tests were carried out with air containing DMNB vapours, which is an official marker of commercial explosive compositions. Prior to the tests, the DMNB vapours were diluted to a value of around 0.7 ppbv, i.e. a concentration nearly 2000 times lower than the saturation vapour pressure of this molecule at room temperature. These diluted vapours were drawn through the concentration device described in this patent application, with the air outlets open, at a flow rate of 150 L/min (9000 L/h) for 10 minutes at 20°C, which represents a volume of gas sampled 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 cumulative length of heating wire is 17m and each heating wire has an outer diameter of 2.1mm.

After 10 minutes of sampling diluted DMNB vapors in the device, the air outlet ports are closed.

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

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.

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.

The tests were systematically carried out after a blank carried out 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.

End of presentation of experimental tests.

The use of the concentration device according to the invention involves three main stages.

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 about 150 liters per minute for a duration chosen by the user ranging from a few seconds to several hours depending on the concentration needs.

In a second step, the DC device is placed, with the air outlets closed, in an oven to raise the temperature, 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 heating wire at 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. It is at this time that the analyzer or the concentrated vapor collector (e.g. SPME) is positioned above the DC device to analyze after aspiration or collect the concentrated vapors.

In a final step, the invention is either kept at a warm 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 ports open.

Claims (15)

Device for concentrating (DC) 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 (PC1) 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 (PC1) and the second crown (PC2), said rods being distributed over the circumference of said crowns (PC1, PC2), and
a heating wire (FC) provided with a sheath (G) 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 (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, OSA1, OSA2, OSA3) radially external with respect to said cage and extending over the peripheral contour (CPH) of said cage. Device for concentrating (DC) the vapors of chemical molecules contained in the air according to claim 1, in which said rods (TG) are of odd number. 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 on the circumference of said crowns (PC1, PC2). Device for concentrating (DC) the vapors of chemical molecules contained in the air according to the preceding claim, in which the cage (CG) comprises at least one thermocouple (TC). 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 (CG1) housed in the receptacle, said additional cage comprising:
a first crown (PC11) 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 (CG1) having a diameter corresponding to the external diameter of the crowns (PC1, PC2) of said cage (CG),
a heating wire (FC10) provided with a sheath (G10) 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 (FC10) being either wound around all of the rods (TG10) or woven with the rods (TG10) of the additional cage (CG1),
the or each air outlet orifice (OSA, OSA1, OSA2, OSA3) of the cover (CVC) being radially external with respect to the additional cage (CG1). 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 (CG1) is of odd number. 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 (CG1) are distributed at regular intervals on the circumference of said crowns (PC11, PC12). Device (DC) for concentrating vapors of chemical molecules contained in the air according to one of claims 5 to 7, in which the sheath (G10) of the heating wire (FC10) of the additional cage (CG1) is made of a material identical to the sheath (G) of the heating wire (FC) of said cage (CG). 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 (CG1) comprises at least one thermocouple (TC10). 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 other 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 other additional cage (CG2) having a diameter corresponding to the external diameter of the crowns (PC11, PC12) of the additional cage (CG1),
a heating wire (FC20) provided with a sheath (G20) 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 (FC20) being either wound around all of the rods (TG20) or woven with the rods (TG20) of said another additional cage (CG2),
the or each air outlet orifice (OSA, OSA1, OSA2, OSA3) of the cover (CVC) being radially external with respect to said other additional cage (CG2). Device for concentrating (DC) the vapors of chemical molecules contained in the air according to claim 10, in which said rods (TG20) of said other additional cage (CG2) are in odd number. 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). 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 (G10) of the heating wire (FC10) of the additional cage (CG1) and on the other hand to that of the sheath (G) of the heating wire (FC) of the cage (CG). 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). Device for concentrating (DC) vapors of chemical molecules contained in the air according to one of the preceding claims, further comprising a means (DSQ) for opening/closing the (OSA) or each (OSA1, OSA2, OSA3) air outlet orifice of the cover.