Device for trapping tritium and carbon-14 in a gaseous mixture

Abstract

The invention relates to a trapping system (12) for one or more compounds present in an initial gaseous mixture, said initial gaseous mixture comprising at least water and carbon dioxide, said system comprising a first cartridge (38) at least partially filled with a porous coordination polymer enabling the trapping of water present in said initial gaseous mixture passing through said first cartridge, the porous coordination polymer having an affinity ratio between water and carbon dioxide of at least 95 / 5.

Description

Title of the invention: Device for trapping tritium and carbon-14 in a gaseous mixture. Field of the invention

[0001] The present invention relates to a system for trapping one or more compounds present in a gaseous mixture comprising at least water and carbon dioxide, and to a method for trapping using this system. The invention also relates to measuring the radioactivity of the trapped water and / or carbon dioxide. The invention further relates to the use of a porous coordination polymer for trapping water present in a gaseous mixture. Technological background

[0002] Nuclear power plant reactors generate and release gaseous effluents comprising radioactive compounds, including tritium or molecules comprising carbon-14. The quantity of radioactive compounds present in these effluents and released into the atmosphere must be measured to verify that it is compatible with the regulatory limit for public exposure.

[0003] For this purpose, a portion of the effluents is taken regularly for a determined period, for example a quarter, and then analyzed, which makes it possible to determine the quantity of radioactive compounds present in the effluents.

[0004] A method currently used to analyze the amount of carbon-14 in samples of gaseous effluents from a nuclear power plant consists of oxidizing all forms of carbon-14 to carbon dioxide using a catalytic furnace and then passing the resulting gas mixture through a molecular sieve cartridge, which may be zeolite-based. This method is easy to use and can be used for long periods of time without requiring special monitoring or maintenance.

[0005] However, this method can be improved because the gaseous mixture from the furnace passing through a molecular sieve cartridge contains a variable proportion of water, which competes with carbon dioxide for trapping by the molecular sieve. Thus, some of the carbon dioxide that should have been trapped could escape from the sieve cartridge (perforation of the sieve) and therefore might not be taken into account when determining the amount of carbon-14 in the sampled portions of the gaseous effluents. The analysis of the gaseous effluents generated by the nuclear power plant is then biased.

[0006] Another known method consists of passing the taken portions of gaseous effluents through a furnace in order to oxidize all the carbon molecules present in the Portions of gaseous effluents are converted into carbon dioxide, and the resulting mixture is then passed through a bubbler system containing a sodium hydroxide solution. The advantage of this method is that carbon-14 capture is almost quantitative. However, this method has several drawbacks. The system can become clogged quite frequently due to sodium hydroxide crystallization and therefore requires close monitoring. Furthermore, when the system becomes clogged, the ability to determine the amount of carbon-14 trapped is lost, and maintenance is necessary. Finally, the sodium hydroxide used in the bubbler is concentrated, a toxic chemical that can pose safety risks to operators.

[0007] Another disadvantage of the two aforementioned methods is that they do not allow the quantity of tritium in the portions taken from the gaseous mixture to be determined in addition to the quantity of carbon dioxide. Description of the invention

[0008] An objective of the invention is to be able to determine the quantity of carbon in a gaseous mixture, and in particular of carbon 14 in nuclear power plant effluents.

[0009] Another objective of the invention is to be able to determine the quantity of water in a gaseous mixture, and in particular of tritium in nuclear power plant effluents.

[0010] Another objective of the invention is to use a system that is simple to use, requires minimal maintenance and avoids the use of toxic products.

[0011] To this end, the invention has as its first object a system for trapping one or more compounds present in an initial gaseous mixture, said initial gaseous mixture comprising at least water and carbon dioxide, said system comprising a first cartridge at least partially filled with a porous coordination polymer enabling the trapping of water present in said initial gaseous mixture passing through said first cartridge, the porous coordination polymer having an affinity ratio between water and carbon dioxide of at least 95 / 5.

[0012] The system thus makes it possible to remove a large part, or even all, of the water present in the initial gas mixture, and this by trapping little or no carbon dioxide.

[0013] The affinity ratio between water and carbon dioxide may preferably be at least 99 / 1.

[0014] The affinity ratios indicated are determined in particular from an initial gaseous mixture comprising 400 ppm of carbon dioxide and between 0% and 100% water, at ambient temperature and atmospheric pressure. porous coordination polymer

[0015] The porous coordination polymer is a metal-organic network (MOF).

[0016] The coordination polymer comprises metal ions coordinated to organic ligands and preferably forms three-dimensional nanoporous structures. Preferably, the coordination polymer used comprises a single type of metal coordinated to a single type of ligand, the number of ligands per metal depending on the oxidation state of the metal ion and the structure of the ligand, in particular the chemical functions it comprises.

[0017] Thanks to their nanoporous structure, these coordination polymers possess a very high specific surface area.

[0018] Preferably, the coordination polymer has a specific surface area of ​​at least 300 m² / g, and preferably at least 400 m² / g. Alternatively, the specific surface area may be at most 600 m² / g, preferably at most 500 m² / g. The specific surface area of ​​the coordination polymer may, in particular, be determined according to the Brunauer, Emmett and Teller (BET) standard / method.

[0019] The coordination polymer is preferably used in the form of beads.

[0020] The first cartridge can comprise from 200 g to 300 g of porous coordination polymer capable of treating a volume of gas up to 1.5 m3, which means capable of trapping all of the water present in this volume of gas when this volume of gas passes through the cartridge, for humidity levels in this volume of gas ranging from 0% to 100% at ambient temperature.

[0021] The first cartridge may for example have a volume ranging from 450 cm3 to 550 cm3, which is at least partially filled with the porous coordination polymer, preferably in the form of beads, so as to be traversed by the volume of gas described above.

[0022] The first cartridge is preferably elongated in shape, for example cylindrical, and preferably made of stainless steel.

[0023] Preferably, the ligand of the porous coordination polymer comprises at least one chemical function selected from a phosphonate, a squarate, and a carboxylate.

[0024] When the ligand of the porous coordination polymer has at least one phosphonate-type chemical function, said ligand may preferably be a bisphosphonate. The metal ion of the coordination polymer may then be selected from an ion of titanium (Ti), aluminum (Al), iron (Fe), gallium (Ga), indium (In), vanadium (V), manganese (Mn), scandium (Sc), zirconium (Zr), or tin (Sn). Preferably, the metal ion of the coordination polymer may be selected from a titanium ion or an aluminum ion. The coordination polymer porous can preferably be MIL-91 in which the ligand is N,N'-piperazine bisphosphonate, and more preferably MIL-91(Ti) or (Al).

[0025] When the ligand of the porous coordination polymer has at least one squarate-type chemical function, said ligand may preferably be 1,2-Bis(dicyanomethylene)squarate. The metal ion of the coordination polymer may then be chosen from among the transition metals, the alkaline earth metals, and the lanthanides.

[0026] When the ligand of the porous coordination polymer has at least one carboxylate-type chemical function, said ligand may preferably be 1,2,4,5-benzenetetracarboxylate. The metal ion of the coordination polymer may then be selected from among the transition metals, the alkaline earth metals, and the lanthanides. The porous coordination polymer may preferably be MIL-120.

[0027] Thus, the ligand of the porous coordination polymer can be chosen from bisphosphonate, 1,2-Bis(dicyanomethylene)squarate and 1,2,4,5-benzenetetracarboxylate. CO2 capture

[0028] According to one embodiment, the trapping system according to the first object may further comprise a second cartridge positioned downstream of the first cartridge and in fluidic communication with the first cartridge, said second cartridge being at least partially filled with a zeolite and allowing the trapping of carbon dioxide present in an intermediate gaseous mixture corresponding to the initial gaseous mixture free of water after it has passed through the first cartridge.

[0029] The trapping system can thus independently trap water and carbon dioxide. Furthermore, the carbon dioxide trapping, which occurs after the water trapping, is not affected by the presence of water in the gas mixture, since the water has already been trapped by the first cartridge and the intermediate gas mixture is water-free. Therefore, the second cartridge can trap all the carbon dioxide present in the intermediate mixture without the latter being replaced, in the second cartridge, by water molecules, as in prior art devices.

[0030] In this description, the expression "free of water" means that the intermediate gas mixture contains at least 95% less water compared to the initial gas mixture.

[0031] The zeolite is in the form of a microporous skeleton whose pore size can range from 8 Å to 15 Å.

[0032] The zeolite present in the second cartridge makes it possible to trap at least 90% of the carbon dioxide present in the intermediate gas mixture, and preferably at least 99% of the carbon dioxide present in the intermediate gas mixture.

[0033] Zeolite can be used in powder or bead form, preferably in bead form to facilitate the desorption of trapped carbon dioxide.

[0034] Preferably, the zeolite has a specific surface area of ​​at least 300 m² / g and preferably at least 400 m² / g. Furthermore, the specific surface area of ​​the zeolite may be at most 600 m² / g, preferably at most 500 m² / g. The specific surface area of ​​the zeolite may, in particular, be determined according to the BET standard / method.

[0035] The second cartridge B can comprise from 250 g to 350 g of zeolite, and for example 300 g, capable of treating a volume of gas up to 1.5 m3, which means capable of trapping the carbon dioxide present in this volume of gas when this volume of gas passes through the second cartridge, the proportion of carbon dioxide in this volume of gas being able to reach up to 450 ppm if more is to be trapped.

[0036] The second cartridge may for example have a volume ranging from 450 cm3 to 550 cm3 which is at least partially filled with zeolite, preferably in the form of beads, so as to be traversed by the volume of gas described above.

[0037] The zeolite present in the second cartridge is preferably an aminosilicate, preferably 13X aminosilicate. The pore size can then be about 10 Å for beads having a diameter of about 1 to 2 mm.

[0038] Method for trapping water and determining the radioactivity of water

[0039] The invention has as its second object a method of trapping water in an initial gaseous mixture comprising at least water and carbon dioxide by means of the system according to the first object, said method comprising a step SI consisting of passing the initial gaseous mixture through the first cartridge so as to trap the water present in the initial gaseous mixture.

[0040] Given the selectivity of the porous coordination polymer, the process allows for the selective trapping of water present in the initial gas mixture, while the carbon dioxide remains in the gas mixture and is not trapped by the porous coordination polymer. After passing through the first cartridge, the gas mixture is thus free of water and contains the same amount of carbon dioxide as before passing through the first cartridge.

[0041] When the initial mixture contains radioactive water, the process also allows the amount of radioactivity present in the water trapped in the first cartridge to be determined, and includes the following steps: - S2: recover the water trapped by the first cartridge by desorption to obtain a first final mixture, and - S3: determine the amount of radioactivity present in the first final mixture and deduce the amount of radioactive water present in the initial gaseous mixture.

[0042] Step S2 recovers the water trapped in the first cartridge by the porous coordination polymer. Desorption can be achieved, in particular, by heating the first cartridge, notably to a temperature of 120°C for up to 12 hours (h). A first final mixture is then recovered, said first final mixture comprising all the water that had been trapped by the first cartridge during step SL

[0043] In step S3, the amount of radioactivity present in the first final mixture, in particular the radioactivity of the tritium present in the water, is determined conventionally by liquid scintillation. Knowing the initial volume that passed through the first cartridge, it is possible to deduce the amount of radioactive water present in the initial mixture.

[0044] Once the water has been desorbed by heat treatment, the coordination polymer can be reused at least 10 times, and preferably at least 5 times.

[0045] Method for trapping carbon dioxide and determining the radioactivity of carbon dioxide

[0046] The invention has as a third object a method for trapping carbon dioxide in an initial gaseous mixture by means of the system according to the first object when it includes the second zeolite cartridge, said method comprising the following steps: - S4: pass the initial gas mixture through the first cartridge so as to trap the water present in said initial gas mixture and obtain an intermediate gas mixture after passing through the first cartridge, and - S4: pass the intermediate gas mixture through the second cartridge so as to trap the carbon dioxide present in said intermediate gas mixture.

[0047] Since the intermediate gas is water-free, the carbon dioxide can be trapped by the second cartridge without being replaced by water molecules, as in prior art processes. It is thus possible to trap all the carbon dioxide present in the intermediate mixture, which corresponds to all the carbon dioxide present in the initial mixture, since the first cartridge selectively traps water and does not trap carbon dioxide. Carbon dioxide trapping is therefore optimized and reliable, even in a humid environment.

[0048] When the initial mixture contains radioactive carbon dioxide, said process further allows the amount of radioactivity present in the carbon dioxide trapped in the second cartridge to be determined; the process then comprises the steps of: - S5: recovering the carbon dioxide trapped by the second cartridge (B) by desorption to obtain a second final mixture, and - S6: determine the amount of radioactivity present in the second final mixture and deduce the amount of radioactive carbon present in the initial gaseous mixture.

[0049] Step S5 recovers the carbon dioxide trapped in the second cartridge by the zeolite. Desorption can be achieved, in particular, by heat treatment of the second cartridge, for example at a temperature of 400°C. A second final mixture is then recovered, said second final mixture comprising all the carbon dioxide that was trapped by the second cartridge during step S4.

[0050] In step S6, the amount of radioactivity present in the second final mixture, in particular the radioactivity of carbon-14 present in the carbon dioxide, is determined conventionally by liquid scintillation. Specifically, the second mixture is prepared by bubbling desorbed radioactive carbon dioxide through sodium hydroxide, thereby transforming it into carbonate ions. Knowing the initial volume that passed through the first and second cartridges, it is possible to deduce the amount of radioactive carbon dioxide present in the initial mixture.

[0051] Once desorption has been carried out, the zeolite can be reused at least 10 times, and preferably at least 5 times. Use of a porous coordination polymer

[0052] The invention has as its fourth object the use of a porous coordination polymer to selectively trap water present in a gaseous mixture comprising water and carbon dioxide, said porous coordination polymer having an affinity ratio between water and carbon dioxide of at least 95 / 5.

[0053] The affinity ratio between water and carbon dioxide may preferably be at least 99 / 1.

[0054] The affinity ratios indicated are determined in particular from an initial gaseous mixture comprising 400 ppm of carbon dioxide and between 0% and 100% water, at ambient temperature and atmospheric pressure.

[0055] The coordination polymer can be used in a system such as that described in the first object and can also be used in other systems requiring the selective trapping of water with respect to carbon dioxide, water and carbon dioxide being present in a gaseous mixture.

[0056] The characteristics and properties described concerning the porous coordination polymer for the system according to the first object are also valid for use according to the fourth object.

[0057] Unit for sampling gaseous effluents from a nuclear power plant

[0058] The invention has as its fifth object a unit for collecting gaseous effluents from a nuclear power plant, said unit comprising at least one system according to the first object, said unit being supplied with portions of gaseous effluents representing the initial gaseous mixture.

[0059] Such a unit makes it possible to analyze the gaseous effluents that are evacuated from a nuclear power plant, and in particular to quantify the carbon 14 and tritium evacuated.

[0060] For this purpose, portions of gaseous effluents discharged from the nuclear power plant are regularly sampled over a period of time, for example from 1 to 300 times per day for three months. However, the period of time can be of any duration and the sampling frequency can be higher or lower.

[0061] For each sample, the portion of the gas mixture taken passes through a furnace that heats the gas mixture to a temperature of at least 400°C. The hydrogen, including tritium, initially contained in various molecules of the gas mixture, is removed from the furnace as water. Furthermore, the carbon, including carbon-14, initially contained in various molecules of the gas mixture, is removed from the furnace as carbon dioxide.

[0062] The gaseous mixture exiting the furnace and corresponding to the initial gaseous mixture described in the first object, thus comprises at least water and carbon dioxide, a part of the water containing tritium and a part of the carbon dioxide containing carbon 14.

[0063] This initial gaseous mixture then passes through the first cartridge containing the porous coordination polymer and then through the second cartridge containing the zeolite as described for the system according to the first object.

[0064] The invention has as its sixth object a method for determining the quantity of tritium and / or carbon-14 in a portion of gaseous effluents emitted by a nuclear power plant using the sampling unit according to the fifth object, the method comprising - the determination of the quantity of tritium contained in the tritiated water from the initial gaseous mixture, and - the determination of the quantity of carbon-14 contained in the carbon dioxide present from the initial gaseous mixture, the quantity of tritiated water being determined according to the process described in the second object, and the quantity of carbon dioxide 14 being determined according to the process described in the third. Brief description of the Figures

[0065] Other features and advantages of the invention will become apparent from the following description, given solely by way of example and with reference to the accompanying drawings, in which:

[0066] [Fig-1] is a schematic and cross-sectional view of a sampling unit according to an embodiment of the fifth object;

[0067] [Fig.2] is a flowchart representing a process according to an embodiment of the invention;

[0068] [Fig.3a] is a graph representing the isotherm of H2O adsorption by the zeolite 13X;

[0069] [Fig.3b] is a graph representing the CO2 adsorption isotherm by the zeolite 13X in a mixture including water; and

[0070] [Fig.4] is a graph representing the CO2 breakthrough curve. Detailed description of an example of implementation

[0071] A sampling unit 10 shown in [Fig.1] includes a system 12 for trapping one or more compounds present in an initial gaseous mixture comprising at least water and carbon dioxide.

[0072] The sampling unit 10 is fluidly connected to an exhaust stack 14 of a nuclear power plant which evacuates all the gases generated by the nuclear power plant.

[0073] The sampling unit 10 includes a first inlet circuit 16 of a gaseous mixture constituting a portion of the gases evacuated by the chimney 14. This portion of gaseous mixture may, for example, have a volume of 75 cm3.

[0074] The first inlet circuit 16 conventionally includes a filter 18 for retaining solid particles, a needle valve 20, a flow meter 22 and a first diaphragm pump 24. The first inlet circuit 16 thus allows the circulation of the portion of the gas mixture from the chimney 14 to a stabilizing cylinder 26.

[0075] The stabilizer cylinder distributes the portion of the gas mixture between a second intermediate circuit 28 and a third exhaust circuit 30.

[0076] The second intermediate circuit 28 includes a second dosing pump 32 and leads to a furnace through which the portion of gaseous mixture passes.

[0077] Before entering the furnace 34, the portion of the gaseous mixture comprises various molecules containing hydrogen, including a certain proportion of tritium, and carbon, including a certain proportion of carbon-14. During its passage through the furnace, which heats the gas to a temperature of approximately 400°C, the molecules in the portion of the gaseous mixture are transformed by the heat. The hydrogen, including tritium, which is then found in the form of water molecules and carbon, including carbon 14, which is then found in the form of carbon dioxide.

[0078] The gaseous mixture exiting the oven, called the initial gaseous mixture, then passes through a trapping circuit 36 ​​which includes a first cartridge 38 and a second cartridge 40. The first cartridge 38 is filled with a porous coordination polymer such as that described in the first object of the invention and the second cartridge 40 is filled with a zeolite such as that described in the first object of the invention.

[0079] The initial gas mixture then passes through the first cartridge 38, which selectively traps the water. An intermediate gas mixture exiting the first cartridge 38, free of water, then passes through the second cartridge 40, which traps the carbon dioxide. A final gas mixture exiting the second cartridge 40 is then discharged through the exhaust stack 14.

[0080] According to the flowchart illustrated in [Fig. 2], a process 50 for trapping water and carbon dioxide present in nuclear power plant effluents and determining the radioactivity contained in the water and carbon dioxide is described. This process is implemented by the sampling unit 10.

[0081] The process 50 includes a first step SI consisting of passing the initial gas mixture through the first cartridge 38 so as to trap the water present in the initial gas mixture and obtain an intermediate gas mixture after passing through the first cartridge.

[0082] A step S4 is then carried out, this step consisting of passing the intermediate gas mixture into the second cartridge 40 so as to trap the carbon dioxide present in said intermediate gas mixture.

[0083] The process 50 then includes a step S2 consisting of recovering the water trapped by the first cartridge 38 by desorption to obtain a first final mixture and a step S3 consisting of determining the quantity of radioactivity present in the first final mixture and deducing the quantity of radioactive water present in the initial gaseous mixture.

[0084] Furthermore, the process 50 includes a step S5 consisting of recovering the carbon dioxide trapped by the second cartridge 40 by desorption to obtain a second final mixture and then a step S6 consisting of determining the quantity of radioactivity present in the second final mixture and deducing the quantity of radioactive carbon present in the initial gaseous mixture. EXAMPLE

[0085] In this embodiment, the trapping system is a sampling cabinet used for sampling tritiated water and CO2 containing carbon 14. The sampling cabinet includes, in particular, a sampling unit 10 as previously described.

[0086] In this embodiment example, the porous coordination polymer is a titanium bisphosphonate MIL-91(Ti) in the form of beads. Synthesis of MIL-91(Ti)

[0087] The synthesis of MIL-91(Ti) is carried out in a 30 L glass reactor at ambient pressure. Initially, 500 g of N,N'-piperazine bisphosphonate ligand are added to 12.5 L of water in the reactor. The mixture is then heated to 85 °C and held at this temperature for 15 minutes to solubilize the ligand. 475 g of titanium oxyacetylacetonate and 500 mL of water are then added to the mixture, which is then heated under reflux for 68 h. The mixture is then vacuum-filtered to obtain a crude powder, which is then washed in water at pH 9. The mixture is stirred for 72 h at 90 °C to remove unreacted precursors.

[0088] The mixture is then vacuum-filtered to obtain the MIL-91(Ti) coordination polymer in powder form, which is then dried. Its structure and crystallinity are confirmed by powder X-ray diffraction, and its specific surface area is evaluated by nitrogen adsorption porosimetry. The specific surface area calculated by the BET method is approximately 440 m².g⁻¹. The water adsorption capacity of the material was also evaluated by a water adsorption measurement as described below.

[0089] Once the MIL-91(Ti) coordination polymer has been synthesized in powder form, it is transformed into granules to facilitate its handling and also the measurement of the quantities of H2O trapped by the coordination polymer. Powder shaping#:

[0090] The MIL-91(Ti) coordination polymer is then shaped by wet granulation to form 200 g of beads with a diameter of 2 to 2.5 mm. Wet granulation consists of mixing the previously ground coordination polymer powder with a binder that has been previously dissolved in a solvent, isopropanol in this case. The polyvinyl butyral (PVB) binder is selected, and the optimal PVB content is estimated at 3% by mass. This binder content in isopropanol allows for optimized mechanical properties of the coordination polymer while maintaining the porosity of the beads. Finally, to ensure the mechanical stability of the beads, they are treated at 120 °C for 72 hours under primary vacuum, meaning a vacuum of less than 103 bar.Calcination of the beads ensures the strengthening of the bond between the binder and the coordination polymer, the binder enabling the agglomeration of the coordination polymer particles into beads. To confirm that the adsorption properties are maintained after calcination... After shaping, the specific surface area was again evaluated by nitrogen porosimetry and estimated at approximately 400 m².g⁻¹ (BET method). The mechanical strength of the beads was also studied by compression measurements and determination of the granule fracture force using a Lloyd Instruments CS2 series texture analyzer.

[0091] The evaluation of the adsorption capacities of the materials under dry and wet conditions by measurements of adsorption isotherms and breakthrough curves was carried out.

[0092] Measurements were performed under static conditions with pure substance adsorption isotherms (CO2 and H2O), then with co-adsorption isotherms (CO2 / N2, CO2 / N2 / H2O), and finally under dynamic conditions with breakthrough curves (CO2 / N2, H2O / N2, and CO2 / N2 / H2O) in a single or dual cartridge system. Initially, the pure substance adsorption isotherms (CO2 and H2O) were measured at different temperatures (293, 298, 303, and 313 K). The adsorption isotherms at 298 K were measured using a Micromeritics volumetric sorption apparatus (Triflex). For the other temperatures, the tests were carried out with gravimetric instruments (Rubotherm for CO2 and N2 and DVS Vacuum for H2O).

[0093] Adsorption isotherms obtained by gravimetric measurements allowed for the estimation of CO2 / N2 selectivities using the Ideal Adsorbed Solution Theory (IAST). These measurements at different temperatures were also used to estimate the heats of adsorption of CO2 and N2 using the Clausius-Clapeyron method. Subsequently, the adsorption isotherms of CO2 at 303 K were measured after pre-adsorption of H2O at 30% relative humidity on a gravimetric instrument (DVS Vacuum).

[0094] The adsorption isotherms of H2O and CO2 are shown in Figures 3a and 3b respectively.

[0095] The curve in [Fig.3a] shows the amount of water absorbed when humid air is passed through the cartridge, the amount of water absorbed increasing rapidly and then reaching a plateau when the cartridge is saturated with water.

[0096] Figure 3b shows the amount of carbon dioxide absorbed for two different compositions: a first composition consisting solely of carbon dioxide and a second composition consisting of carbon dioxide and 30% moisture. For the first composition, the absorption curve rises until it reaches a plateau, indicating that all the carbon dioxide is trapped. However, in the second mixture, CO2 is not absorbed at all, as its absorption level remains at zero. These curves show that as soon as the mixture contains moisture, CO2 is no longer absorbed. This means that the CO2 passes through the cartridge without being captured because the cartridge has a greater affinity for water than for CO2.

[0097] These isotherms show the good adsorption capacities of MIL-91(Ti) for water as well as the transparency of this material in humid conditions with respect to CO2.

[0098] Furthermore, an adsorption breakthrough curve reflects the evolution of the concentration of a given effluent (CO2 in a CO2 / N2 mixture in the present case) at the outlet of an adsorbent bed, as a function of time.

[0099] Breakthrough curves are essential for the characterization of porous materials, in particular for gas separation.

[0100] The CO2 breakthrough curves of the coordination polymers MIL-91(Ti) and MIL-91(A1) are shown in [Fig. 4], in comparison with that of 13X zeolite, and demonstrate the complete transparency of these coordination polymers to CO2 under the operating conditions compared to zeolite. Indeed, for MIL-91(Ti) and MIL-91(A1), after 350 seconds and 250 seconds respectively, which represent the passage time of the gas mixture containing 400 ppm of CO2 through the first cartridge, all of the injected CO2 exits the cartridge. For zeolite, the CO2 is completely retained in the second cartridge until saturation after 15,000 seconds. Once saturation is reached, the CO2 passing through the cartridge is no longer retained because no more absorption sites are available and therefore exits the cartridge.

[0101] The manufactured coordination polymer is then used in the sampling unit 10. The first and second cartridges are 304L stainless steel cylinders of 1.2 kg and 500 cm3. The first cartridge is filled with 212 g of coordination polymer and the second cartridge is filled with 300 g of zeolite.

[0102] The process for trapping water and carbon dioxide is then implemented using the sampling unit 10 under conditions of 100% humidity. For this purpose, portions of gaseous effluents are sampled every 6.5 minutes over a total period of three months. The volume of each sample is 75 cm³ and the total volume sampled after three months is approximately 1.5 m³ and contains 400 ppm of carbon dioxide in the presence of water.

[0103] Water and carbon dioxide are then quantitatively trapped by the trapping system 12, the water being quantitatively trapped by the first cartridge 38 and the carbon dioxide being quantitatively trapped by the second cartridge 40.

Claims

Demands

1. A trapping system (12) for one or more compounds present in an initial gaseous mixture, said initial gaseous mixture comprising at least water and carbon dioxide, said system comprising a first cartridge (38) at least partially filled with a porous coordination polymer capable of trapping water present in said initial gaseous mixture passing through said first cartridge, the porous coordination polymer having an affinity ratio between water and carbon dioxide of at least 95 / 5.

2. System (12) according to claim 1, wherein the ligand of the porous coordination polymer comprises at least one chemical function selected from a phosphonate, a squarate, and a carboxylate.

3. System (12) according to claim 1 or 2, wherein the ligand of the porous coordination polymer is selected from bisphosphonate, 1,2-Bis(dicyanomethylene) squarate and 1,2,4,5-benzenetetracarboxylate.

4. System (12) according to any one of the preceding claims, wherein the porous coordination polymer is MIL-91.

5. System (12) according to claim 4, wherein the metal may be titanium or aluminium.

6. System (12) according to any one of the preceding claims, wherein the specific surface area of ​​the porous coordination polymer is at least 300 m2 / g.

7. System (12) according to any one of the preceding claims, further comprising a second cartridge (40) positioned downstream of the first cartridge (38) and in fluidic communication with the first cartridge (38), said second cartridge (40) being at least partially filled with a zeolite and enabling the trapping of carbon dioxide present in an intermediate gas mixture corresponding to the initial water-free gas mixture after it has passed through the first cartridge (38).

8. System (12) according to claim 7, wherein the zeolite makes it possible to trap at least 90% of the carbon dioxide present in the intermediate gas mixture.

9. System (12) according to claim 7 or 8, wherein the zeolite is an aminosilicate.

10. A method (50) for trapping water in an initial gas mixture comprising at least water and carbon dioxide by means of the system (12) according to any one of claims 1 to 9, said method (50) comprising a step SI consisting of passing the initial gas mixture through the first cartridge (38) so as to trap the water present in the initial gas mixture.

11. A method (50) according to claim 10 wherein the water present in the initial mixture comprises radioactive water, said method (50) further enabling the determination of the quantity of radioactivity present in the water trapped in the first cartridge (38) and further comprising the steps of: - S2: recovering the water trapped by the first cartridge (38) by desorption to obtain a first final mixture, and - S3: determining the quantity of radioactivity present in the first final mixture and deducing therefrom the quantity of radioactive water present in the initial gaseous mixture.

12. A method (50) for trapping carbon dioxide in an initial gas mixture by means of the system (12) according to any one of claims 1 to 9, said method comprising the following steps: - S1: passing the initial gas mixture through the first cartridge (38) so as to trap the water present in said initial gas mixture and obtain an intermediate gas mixture after passing through the first cartridge, and - S4: passing the intermediate gas mixture through the second cartridge (40) so as to trap the carbon dioxide present in said intermediate gas mixture.

13. A method (50) according to claim 12, wherein the carbon dioxide present in the initial mixture comprises radioactive carbon, said method further enabling the determination of the amount of radioactivity present in the carbon dioxide trapped in the second cartridge (40), and further comprising the steps of: - S5: recovering the carbon dioxide trapped by the second cartridge (40) by desorption to obtain a second final mixture, and - S6: determine the amount of radioactivity present in the second final mixture and deduce the amount of radioactive carbon present in the initial gaseous mixture.

14. Use of a porous coordination polymer for selectively trapping water present in a gaseous mixture comprising water and carbon dioxide, said porous coordination polymer having an affinity ratio between water and carbon dioxide of at least 95 / 5.

15. Use according to claim 14, wherein the porous coordination polymer is MIL-91 associated with aluminum or titanium.

16. A gaseous effluent sampling unit (10) from a nuclear power plant, said unit comprising at least one system according to any one of claims 1 to 9, said unit (10) being supplied with portions of gaseous effluent representing the initial gaseous mixture.

17. Sampling unit (10) according to claim 16, wherein the portions of gaseous effluents comprise tritiated water and / or carbon dioxide 14.

18. A method (50) for determining the quantity of tritium and / or carbon 14 in a portion of gaseous effluents emitted by a nuclear power plant using the sampling unit according to claim 16 or 17, the method comprising - the determination of the quantity of tritium included in the tritiated water from the initial gas mixture, and - the determination of the quantity of carbon 14 included in the carbon dioxide from the initial gas mixture, the quantity of tritiated water being determined according to the method (50) of claim 10, and the quantity of carbon dioxide 14 being determined according to the method (50) of claim 12.

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