Non-destructive method for determining the residual filtration capacity of an adsorbent filter and associated test bench

Abstract

The invention relates to a non-destructive method for determining the residual holding capacity of a given type of adsorbent filter, the adsorbent filter being capable of adsorbing a target gas, characterised by the fact that the method comprises the following steps: (a) choosing a probe gas and a carrier gas; (b) at given operating temperature, pressure and hygrometry, choosing injection parameters which comprise at least one sudden variation in the concentration of the probe gas in the carrier gas, for a given type of adsorbent filter, referred to as reference filter; (c) injecting the probe gas and the carrier gas into the reference filter according to the injection parameters, and measuring the change in the concentration of probe gas over time, downstream of the reference filter, for different known saturation rates of the reference filter, for an adsorbent filter referred to as the filter under test; (d) injecting, the probe gas and the carrier gas into the filter under test according to the injection parameters and measuring the change in probe gas concentration over time, downstream of the filter under test; (e) comparing the change in the concentration of probe gas for the filter under test and for the reference filter, in order to determine a value of the saturation level of the filter under test; and, (f) deducing the residual holding capacity of the filter under test.

Description

non-destructive method for determining the residual stopping capacity of an adsorbent filter and associated test bench

[0001] The present invention relates to the field of adsorbent filtration, and in particular relates to a non-destructive method for determining the residual stopping capacity of an adsorbent filter, and to a test bench configured to implement said non-destructive method.

[0002] An adsorbent filter is a device based on adsorbent material (activated carbon, zeolite, Metal Organic Framework, etc.) used to purify a fluid (air, water, etc.) of contaminants. For example: activated carbon-based respiratory protection mask filter, activated carbon-based filter, etc.

[0003] As a preamble, certain technical terms will be defined for later use.

[0004] A target gas is a gas or vapor that is to be removed from an airflow, its removal by the adsorbent bed of the adsorbent filter being part of the primary objective of installing an adsorbent filter. For example, this target gas may be an air pollutant or a volatile toxic agent that is removed from the ambient air by adsorption in the carbon bed of a respirator filter in order to protect human breathing.

[0005] A carrier gas is a pure gas or vapor or a mixture of gases or vapors continuously flowing through the adsorbent filter. For example, this carrier gas is often air at atmospheric pressure for air cleaning applications. The carrier gas is not stopped by the adsorbent filter.

[0006] A probe gas is a gas sent punctually to determine the saturation rate of the filter's adsorbent bed. The probe gas is not stopped by the adsorbent filter.

[0007] A parasitic gas is a pure gas or a pure vapor or a mixture of gases or vapors stopped by an adsorbent filter, but which the filter is not intended to stop (for example, vehicle exhaust emissions for a military filter whose purpose is to stop toxic war products).

[0008] The adsorbent bed of an adsorbent filter is a volume of adsorbent material through which a flow of carrier gas (e.g., air) passes, having properties of stopping target gases and parasitic gases (e.g., air pollutants) other than the carrier gas and the probe gas. The constituent materials of the adsorbent bed may, for example, be activated carbons (in the form of grains, beads, powders, pellets, fibers or condensates), zeolites and their zeolitic derivatives ZIFs (from the Anglo-Saxon term "Zeolitic Imidazole Framework"), organometallic networks of the MOFs or IRMOFs type (respectively from the Anglo-Saxon terms "Metal-Organic Framework (MOF)" and "Isoreticular Metal Organic Framework (IRMOF)"), organic crystalline porous solids such as COFs (from the Anglo-Saxon term "Covalent Organic Framework"), alumino-silicates, mesoporous silicas, membranes, sieves and composite filtration / adsorption materials, such as glass fibers,cellulose esters, cellulose fibers, kieselguhr or perlite particles, diatomaceous earth, nylon-polyamide, organic polymer membranes (e.g. polyvinylidene fluoride (PVDF), polyether sulfone (PES)), inorganic membranes (ceramic or stainless steel), resins, etc.,

[0009] The breakthrough curve measurement method (called breakthrough for simplification), illustrated in, is a method for destructively measuring the stopping capacity of a filter, consisting of the continuous injection of a target gas into a carrier gas upstream of the filter (for example, cyclohexane in air) at a constant concentration throughout the experiment. The measurement of the concentration of this target gas downstream of the filter as a function of time shows the progression of saturation of the adsorbent layers of the filter. The experiment continues until the target gas concentration downstream of the filter is equal to the concentration injected upstream of the filter. At the end of this measurement, the filter is inoperative, making the method destructive. For example, the paper entitled "Removal of volatile organic compound by activated carbon fiber" (Das et al., Carbon, volume 42, Issue 14, 2004, p 2949-2962, describes a device allowing breakthrough measurements through an adsorbent bed.

[0010] The breakdown concentration (referred to as "end life" in English) is a target gas concentration value downstream of the filter defined according to toxicological criteria (e.g., toxicological only) or analytical criteria (e.g., detection limit of a detector). The target gas concentration injected in a breakthrough measurement is always higher than this breakdown concentration. For example, the breakdown concentration of a respiratory protection mask filter for a toxic agent such as chlorine (Cl2) is reached when the chlorine concentration downstream of the filter reaches the beginning of the toxicological threshold for chlorine, i.e., 0.5 ppm. The wearer of the respiratory protection mask at this stage risks having the first effects on his health such as moderate irritation in the eyes, tearing, blepharospasm, burning sensation in the nose, throat, sneezing, coughing.

[0011] The effectiveness time corresponds, in a breakthrough measurement, to the duration measured between the start of the injection of the target gas at constant concentration and the time measured to reach the breakdown concentration (example: toxicological threshold of the target gas, detection limit of a detector, etc.) in target gas downstream of the filter.

[0012] The stopping capacity of a filter is defined, for a given temperature, humidity and target gas concentration, as the maximum mass of target gas, retained by the filter, reached during breakdown.

[0013] The residual stopping capacity of a filter is the mass of target gas that can still be retained by an adsorbent filter at a given time, before it has reached its stopping capacity.

[0014] The saturation rate of a filter is the ratio between the quantity of target gas stopped by the filter at a given time and the total stopping capacity of the filter.

[0015] Consequently, since the filter stopping capacity is the sum of the target gas quantity stopped and the residual filter stopping capacity, the saturation rate can be defined as:

[0016]

[0017] Peak concentration is the highest concentration of a given component measured with a continuous analyzer during a specified sampling period. [IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). Online version (2019-) created by S. J. Chalk. ISBN 0-9678550-9-8. https: / / doi.org / 10.1351 / goldbook.].

[0018] In the field of air filtration, the purification of an air flow by an adsorbent filter has many advantages:

[0019] - it is a commonly used, well-known and industrially mastered process;

[0020] - it is a relatively inexpensive process, used in many sectors: worker protection via filter cartridges with activated carbon on respiratory protection masks, military sector for air purification, aeronautics sector for cabin air purification, etc.

[0021] In this respect, a variety of literature specifies its different applications.

[0022] Generally, the stopping function of an adsorbent filter is not specific to a given pollutant. Thus, for example, an adsorbent filter whose function is to stop toxic war products in a military context also stops pollutants, such as vehicle exhaust emissions, which will be called "parasitic gas" (see definition above). These parasitic gases, stopped by the filter, lead to a reduction in the stopping capacity of the adsorbent filter with respect to the target gas(es), even if no exposure to a target gas (in particular toxic gas) has taken place. It is thus possible for an adsorbent filter to lose all stopping efficiency with respect to the target gas(es) due to the parasitic gases.

[0023] One of the current disadvantages of adsorbent filters is that there is no effective non-destructive method to determine the residual stopping capacity of the adsorbent filter.

[0024] Historically, due to the lack of a non-destructive device, a measurement of the residual stopping capacity of a filter is sometimes carried out using the breakthrough method (see definition above) after use of this adsorbent filter. A target gas is injected into the carrier gas, upstream of the filter to be tested, to determine the residual stopping capacity of the filter. This injection is carried out at a constant concentration, until the target gas concentration exceeds a certain value downstream of the adsorbent filter. The effectiveness time (see definition above), proportional to a mass of stopped target gas, is then compared to the effectiveness time obtained on another new filter of the same model with the same characteristics, itself proportional to a mass of stopped target gas. This then makes it possible to determine the saturation rate (see definition above) of the adsorbent filter.Many patents and publications use this method (“Removal of volatile organic compound by activated carbon fiber”, Elimination of volatile organic compound by activated carbon fiber, Das et al., Carbon, volume 42, Issue 14, 2004, p 2949-2962).

[0025] This method has many disadvantages:

[0026] - the residual stopping capacity of the filter is only known after its use: if the filter is no longer effective, we learn too late that it needs to be changed;

[0027] - the method is destructive: if the filter was still effective, the residual stopping capacity was destroyed to carry out the test by the breakthrough method;

[0028] - the method is expensive, complex to implement and uses target products that are generally toxic – even if the use of substitute or simulant target gases (“surrogate” in English) allows tests to be carried out while limiting the risks, but which nonetheless remain destructive.

[0029] Alternative destructive methods exist, such as the use of a homothetic or sacrificial filter on the filtration line. This involves bypassing the main filter with a smaller filter – called a "homothetic filter" or "sacrificial filter", through which a smaller flow rate passes than the main filter, and whose saturation rate will remain equivalent to that of the main filter. Rather than performing a destructive breakthrough test on the large filter to measure the residual stopping capacity, the residual stopping capacity is measured on the homothetic filter, again using the breakthrough method. This is described, for example, in the publication of international application WO2009 / 055511A1. This method remains destructive, and has the following drawbacks:

[0030] - we must assume that the homothetic filter allows us to precisely transpose the saturation rate of the main filter, which is never exactly the case;

[0031] - the method remains destructive for the homothetic filter which must therefore be changed for each breakthrough measurement carried out;

[0032] - the method remains expensive and requires regular measurement of the residual efficiency of the homothetic filter.

[0033] A reliable and non-destructive indicator of the saturation rate of an adsorbent filter would be relevant, both from an operational safety and economic point of view.

[0034] Since 1925, several studies have been conducted to determine the residual stopping capacity of an adsorbent filter in a non-destructive manner. The methods considered during these studies were the following, as explained in the document "End of Service Life Indicator (ESLI) for Respirator Cartridges. Part I: Literature Review", 2005, Georges Favas, Australian Government, Department of Defence (available freely on the internet):

[0035] - passive systems:

[0036] - method based on the reaction of the target gas with a reagent (for example, colorimetric reaction): an indicator inside the adsorbent material of the filter makes it possible to highlight that the contaminating product has reached a certain level in the adsorbent material;

[0037] - method based on the reaction of another air product with a reagent, in particular by detecting the presence of water downstream of the filter;

[0038] - method based on the release of an odorous substance when the product to be filtered penetrates up to a certain level into the adsorbent material;

[0039] - active systems:

[0040] - mechanical method, linked to the sensitivity of an element to the presence of the product to be filtered (for example, wax which changes hardness in the presence of the target gas);

[0041] - electrical method, based on the change in impedance of a given material (e.g., polymer) in the presence of the target gas;

[0042] - thermal method: the heat released by adsorption is measured or even melts a material (for example, wax); and

[0043] - active detector (e.g., flame ionization detector (FID)) that detects the presence of the target gas at a given level of the filter's adsorbent material.

[0044] Currently, none of these methods are actually used, except for a few colorimetric methods, which have the major drawback of being specific to a given compound. Thus, partial or total saturation of the adsorbent filter by a parasitic gas, preventing the adsorbent filter from absorbing the target gas, cannot be detected if the colorimetric indicator is not sensitive to this parasitic gas.

[0045] Most of the time, the above methods are ineffective because:

[0046] - too specific to the target gas (e.g., colorimetry);

[0047] - too insensitive (for example, method of releasing an odorous substance, method by certain active detectors);

[0048] - suffering from false positives or false negatives (for example, method linked to a temperature variation);

[0049] - response time too high;

[0050] - biased in their very principle (for example, method by detecting the presence of water: in fact, even if water can pass through an adsorbent filter (end of the filter's effectiveness with respect to water), a long effectiveness with respect to the target gas can persist).

[0051] Therefore, as things stand, only the method of placing a target gas detector downstream of the adsorbent filter is actually used. Downstream of this detector, a second filter can prevent rapid saturation of the first filter. This technique therefore requires the equivalent of two filters, and is specific to the chemical families that the detector is able to analyze.

[0052] The present invention aims to overcome the drawbacks of the prior art.

[0053] The present invention therefore relates to a non-destructive method for determining the residual stopping capacity of an adsorbent filter of a given type, the adsorbent filter being capable of adsorbing a target gas, characterized in that the method comprises the following steps:

[0054] (a) choosing a probe gas and a carrier gas capable of passing through an adsorbent filter of the given type not saturated with target gas without remaining attached thereto, the probe gas having an adsorption isotherm such that at a partial pressure of 0.1 atmospheres in probe gas, the adsorption isotherm has an adsorption capacity of less than 100 µmol of probe gas per gram of adsorbent, the probe gas being intended to be mixed with the carrier gas to be injected into the adsorbent filter of the given type,

[0055] (b) at a given operating temperature, pressure and humidity, choosing parameters for injecting probe gas and carrier gas into an adsorbent filter of the given type, the injection parameters comprising, for the probe gas and the carrier gas, a given duration and a flow rate curve as a function of time, the concentration of the probe gas in the carrier gas comprising at least one sudden variation during the injection duration, each sudden variation of the probe gas concentration in the probe gas injection parameters being characterized by an absolute value of the derivative of the probe gas concentration with respect to time which exceeds 100 ppmv / s,

[0056] for an adsorbent filter of the given type, called the reference filter,

[0057] (c) injecting, at the given operating temperature, pressure and hygrometry, the probe gas and the carrier gas into the reference filter according to the injection parameters of step (b) and measuring the evolution of the probe gas concentration as a function of time downstream of the reference filter for increasing quantities of known target gas material adsorbed by the reference filter, the last of these quantities corresponding to the breakdown of the reference filter, and deducing the stopping capacity m a of the reference filter,

[0058] for an adsorbent filter of the given type whose residual stopping capacity is to be determined, called the filter under test,

[0059] (d) inject, at the given operating temperature, pressure and hygrometry, the probe gas and the carrier gas into the filter under test according to the injection parameters of step (b) and measure the change in the probe gas concentration as a function of time downstream of the filter under test,

[0060] (e) compare the evolution over time of the probe gas concentration for the filter under test and for the reference filter to determine a saturation rate value of the filter under test τ sft , And

[0061] (f) deduce the residual stopping capacity of the filter under test by the following calculation: residual stopping capacity = (1 – τ sft ) * m a .

[0062] Downstream and upstream of the filter refer to the direction of flow of the target, carrier or probe gas through the adsorbent filter. Downstream therefore corresponds to the outlet of the adsorbent filter, upstream to the inlet of the adsorbent filter.

[0063] The operating temperature, pressure and humidity do not need to be controlled, they just need to be measurable and remain the same as in steps (b), (c) and (d).

[0064] Step (c) for the reference filter and step (d) for the filter under test are performed sequentially.

[0065] The probe gas and the carrier gas, unlike the target gas, cannot be permanently fixed on the filter adsorbent.

[0066] At least one of the probe gas and the carrier gas must be detectable downstream of the adsorbent filter: if the probe gas is detectable, the change in its concentration downstream of the adsorbent filter can be directly detected. If the carrier gas is detectable, the change in the probe gas concentration downstream of the adsorbent filter can be deduced from the change in its concentration downstream of the adsorbent filter, knowing the injection parameters.

[0067] The carrier gas will advantageously have a concentration of its components that is stable over time. The injection of probe gas will cause a sudden variation in the concentration of at least one of the compounds of the probe gas and the carrier gas during the injection period.

[0068] The reference filter and the filter under test, of the same type, have the same characteristics and therefore the same stopping capacity. The stopping capacity m a of the reference filter can be expressed as the mass concentration of target gas sent during the duration of a breakdown test multiplied by the flow rate through the filter multiplied by the effectiveness time.

[0069] According to one embodiment of the invention, the concentration of probe gas downstream of the filter is continuously measured over time with a detector adapted to the probe gas, with the best possible acquisition frequency. It is also possible to measure the carrier gas concentration and to deduce the concentration of probe gas therefrom. For example, if one seeks to measure the residual stopping capacity according to the method of the invention for an adsorbent filter with CO2 as the probe gas and air as the carrier gas, it would be possible to inject a sudden variation of nitrogen into the flow passing through the filter under test and to measure the nitrogen concentration at the outlet of the adsorbent filter in order to deduce, from the change in the nitrogen concentration over time, the change in the CO2 concentration (the CO2 concentration in the air being known) over time and therefore the saturation rate of the filter.Similarly, the CO2 concentration in the air as a carrier gas can be monitored, with the injection of nitrogen serving to create the significant variation in CO2 concentration by dilution. As such, a given compound, such as CO2, of the carrier gas can be considered as a probe gas, as long as the injection of the probe gas, such as nitrogen, creates a significant variation in the concentration of said compound of the carrier gas. As a non-limiting example, the detector used will be a Fourier transform infrared detector or an infrared detector of the dispersive infrared detector type (NDIR). These measurements will be recorded so that they can be used in the following steps ((e)) and (f)). This step has a duration depending on the nature of the probe gas, the sudden variation in probe gas sent into the upstream air flow, the adsorbent, the saturation of the adsorbent, the temperature and the relative humidity.This step can be completed automatically when the time derivative of the probe gas concentration downstream of the filter, taken as an absolute value, is less than 10 ppbv / s.

[0070] According to one embodiment of the invention, the probe gas concentration curve downstream of the filter is mathematically analyzed as a function of time. A numerical quantity subsequently called the “curve signature” is then extracted. This signature can be:

[0071] - when the sudden variation is a concentration peak, the value of the peak concentration of the probe gas measured downstream of the filter during the duration of the experiment (concentration);

[0072] - when the sudden variation is a concentration peak (according to the definitions at the beginning of the document), the width of the gas concentration peak during the duration of the operation (duration);

[0073] - the duration between the start of the injection of probe gas upstream of the filter and the start time of detection of probe gas downstream of the filter (duration);

[0074] - the parameters resulting from a mathematical modeling of the probe gas concentration curve downstream of the filter, with several modeling parameters. For example, we can cite a modeling with five parameters x1, x2, x3, x4 and x5, according to the following equation:

[0075]

[0076] In this equation, y represents the probe gas concentration downstream of the filter, t represents time, and the parameters x1, x2, x3, x4 and x5 are determined by software as being the parameters which make it possible to obtain a theoretical curve according to this equation which is closest to the probe gas concentration curve measured experimentally downstream of the reference filter or the filter under test.

[0077] The evolution of the probe gas concentration curve measured downstream of the reference filter or the filter under test is thus entered in the form of a series of measurements in a software which will model this evolution in the form of a curve according to the equation above, and will automatically calculate the parameters x1, x2, x3, x4 and x5. A classic state-of-the-art algorithm for minimizing the distance between the experimental curve and the theoretical curve makes it possible to numerically adjust the parameters (see experimental curves and approximation curves on the). The use of the parameter x3, for example, then makes it possible to give a specific signature to the probe gas concentration curve over time. As an example, thepresents the experimental data obtained which make it possible to link the parameter x3obtained in to the saturation rate of the filter.A concentration curve signature may consist of one of a parameter or a combination of parameters of the mathematical model which, over the saturation rate range of the reference filter, has a monotonic variation and a derivative as a function of the maximum saturation rate, and the comparison of the concentration curve signature between the filter under test and the reference filter.

[0078] According to one embodiment of the invention, the signature obtained is compared to charts made beforehand with the measurements made in step (c) on the reference filter. These charts must take into account as parameters the hygrometry and the temperature of the probe and carrier gases, as well as the saturation rate of the filter. The shape of the probe gas concentration curve as a function of time downstream of the adsorbent filter is dependent on the saturation rate of the adsorbent filter. Thus, the value of the signature of the probe gas concentration curve as a function of time, downstream of the filter, makes it possible to determine the saturation rate of the adsorbent filter tested, and therefore the residual stopping capacity thereof.

[0079] The invention thus resides in the equivalence made between a probe gas concentration curve as a function of time measured beforehand on a reference filter of a given type, for several saturation rate values, which makes it possible to constitute a reference, in particular by producing charts with the values ​​measured in step (c), and the probe gas concentration curve measured with a non-destructive method on a filter under test of the same type as the reference filter. By same type, we mean the same model of adsorbent filter having the same characteristics.

[0080] According to one embodiment, each sudden variation of the probe gas concentration in the probe gas injection parameters is characterized by an absolute value of the derivative of the probe gas concentration with respect to time which exceeds 100 ppmv / s.

[0081] An abrupt change can, for example, be a peak in the probe gas concentration in the carrier gas, a trough in the probe gas concentration in the carrier gas, or a rising or falling step in the probe gas concentration in the carrier gas.

[0082] By way of example, and without limiting the scope of the patent, a temperature and relative humidity of the carrier gas, air at atmospheric pressure, of 23°C and 40% respectively are measured. A zero CO2 concentration is then injected 2 seconds after the start of the test according to the method of the invention, then a sudden variation in 20ms makes it possible to reach a CO2 concentration of 4000 ppmv, with a concentration plateau for 1 second at 4000 ppmv before returning, in 20ms, to a CO2 concentration in the carrier gas flow which is again zero.

[0083] The probe gas concentration C could also, for example, have a sinusoidal evolution of type C = C0sin(ω * t) with ω = π / T, and a zero value otherwise. As a non-restrictive example, C 0° =4000ppmv and T=1 second.

[0084] The time derivative of the probe gas concentration downstream of the filter will be less significant in absolute value than the derivative upstream of the filter and will depend on the saturation rate of the filter. It is therefore possible, for a sudden variation, to determine the saturation rate of the filter.

[0085] According to one embodiment, the probe gas has an adsorption isotherm such that at a partial pressure of 0.1 atmospheres of probe gas, the adsorption isotherm has an adsorption capacity of less than 100 µmol of probe gas per gram of adsorbent. Similarly, the carrier gas has an adsorption isotherm such that at a partial pressure of 0.1 atmospheres of carrier gas, the adsorption isotherm has an adsorption capacity of less than 100 µmol of carrier gas per gram of adsorbent. The carrier gas and the probe gas are thus not stopped by the adsorbent filter, or in a negligible manner and therefore not measurable by a breakthrough measurement.

[0086] According to one embodiment, the comparison of the evolution of the concentration of the filter under test and the reference filter comprises the search for at least one parameter representative of the sudden variation in the probe gas concentration on the probe gas concentration curve measured downstream of the filter, and the comparison of this parameter representative of the sudden variation in concentration between the filter under test and the reference filter.

[0087] According to one embodiment, the comparison of the evolution of the concentration of the filter under test and the reference filter comprises the calculation of the duration of passage from 95% to 5% of the maximum value of the probe gas concentration downstream of the adsorbent filter obtained after the sudden variation of the probe gas concentration, and the comparison of the value of the duration calculated between the filter under test and the reference filter.

[0088] According to one embodiment, the comparison of the evolution of the concentration of the filter under test and the reference filter comprises the calculation of the time period between the start of the sudden variation of the probe gas in the carrier gas flow and the quantifiable start of the variation in the concentration of probe gas downstream of the filter, and the comparison of the value of the calculated time period between the filter under test and the reference filter.

[0089] According to one embodiment, the comparison of the evolution of the concentration of the filter under test and the reference filter comprises the computer calculation of a mathematical model with several parameters of the probe gas concentration curve measured downstream of the filter, the determination of a signature of the concentration curve constituted by one of a parameter or a combination of parameters of the mathematical model which, over the range of variation of the saturation rate of the reference filter, has a monotonic variation and a maximum derivative as a function of the saturation rate, and the comparison of the signature of the concentration curve between the filter under test and the reference filter.

[0090] According to one embodiment, the carrier gas is at least one gas among:

[0091] air, oxygen (O2), hydrogen (H2), nitrogen (N2), argon (Ar), helium (He), the aforementioned pure gas mixtures used as standard gases during calibration, over- or under-oxygenated gas mixtures such as those used for deep diving (examples: Trimix®, heliair, heliox, surox, nitrox, triox or helitrox), medical gases (examples: nitrous oxide, equimolar mixtures of oxygen - nitrous oxide (MEOPA), nitric oxide (NO)), respiratory function testing gases (EFR), respiratory mixtures such as helium / oxygen and other gas mixtures used for the treatment of certain types of deafness (MEDI OD 93, MEDI OD 95, these two mixtures being marketed in particular by the company Linde Healthcare).

[0092] According to one embodiment, the temperature and relative humidity of the carrier gas must be measured, without the need for them to be controlled and the flow rate of the carrier gas must be measured and controlled according to a defined setpoint. By way of example, and without limiting the scope of this patent: air injected at a flow rate of 20L / min through the filter under test, the measured temperature and humidity of which are respectively 23°C and 60% relative humidity, at atmospheric pressure.

[0093] According to one embodiment, the probe gas is at least one gas among:

[0094] carbon dioxide (CO2), nitrous oxide (N20), an alkane such as methane, ethane, propane, isopropane, butane, pentane, or hexane, propylene, isobutene, an ether such as methoxymethane, compounds of the halogenated gas family including halogenoalkanes such as chloromethane (CH3Cl), bromobutane, hydrofluorocarbons (HFCs), chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrobromofluorocarbons (HBFCs), bromofluorocarbons (BFCs).

[0095] The probe gas is different from the target gases of the adsorbent filter in question. The probe gas is chosen so as not to be stopped by the adsorbent material, which only slows down the passage of the probe gas compared to the carrier gas (e.g., air). For example, CO2 with a purity greater than 99%, injected from a compressed CO2 cylinder expanded to 2 bars via a pressure gauge, is a suitable choice for activated carbon adsorbent filters.

[0096] By "chosen not to be stopped", a person skilled in the art will understand that the probe gas must have an adsorption isotherm such that at a partial pressure of 0.1 atmospheres of probe gas, the adsorption isotherm must have an adsorption capacity of less than 100 µmol of probe gas per gram of adsorbent. For example, a MOF-type adsorbent, specifically developed to stop CO2 (e.g. in the document “Dynamics of CO2adsorption on Amine Adsorbents. 1. Impact of Heat Effects”, Bollini et al., Ind. Eng. Chem. Res. 2012, 51, 46, 15145–15152, or “Processing and performance of MOF (Metal Organic Framework)-loaded PAN nanofibrous membrane for CO2adsorption”, Wahiduzzaman et al., Journal of Materials Engineering and Performance, volume 25, pages 1276–1283, 2016) which then becomes a target gas, cannot have CO2 as a probe gas and the choice of the person skilled in the art will have to turn to other probe gases. By way of non-limiting example, the following probe gases are good candidates for most adsorbents: carbon dioxide (CO2), nitrous oxide (N20), an alkane such as methane, ethane, propane, iso-propane, butane, pentane, or hexane, propylene, iso-butene, an ether such as methoxymethane, compounds of the halogenated gas family including halogenoalkanes such as chloro-methane (CH3Cl), bromobutane, hydrofluorocarbons (HFCs), chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrobromofluorocarbons (HBFCs), bromofluorocarbons (BFCs).

[0097] According to one embodiment, steps (d) to (f) are carried out punctually, repeatedly or periodically.

[0098] A single measurement is the determination of the filter saturation rate from a single series of steps (d) to (f).

[0099] Repeated measurements can be made, for example, every minute for 5 minutes, as long as the absolute value of the time derivative of the probe gas concentration downstream of the adsorbent filter has returned to a value below 10 ppbv / s after each point measurement. This allows the filter saturation rate measurements to be averaged, and a more accurate assessment of the instantaneous filter saturation can be obtained.

[0100] Periodic measurements, whether carried out via a single (one-off) measurement or several close (repeated) measurements, can be made, for example, every day, in order to precisely monitor the evolution of the filter saturation over time.

[0101] The invention also relates to a test bench comprising:

[0102] - a flow regulator whose inlet is configured to be connected to a carrier gas source and whose outlet is configured to be connected to the gas inlet of an adsorbent filter;

[0103] - a temperature indicator, a pressure indicator and a humidity indicator connected to the flow regulator input;

[0104] - a probe gas injector whose inlet is configured to be connected to a probe gas source and whose outlet is connected to the output of the flow regulator;

[0105] - a probe gas detector configured to be connected to the gas outlet of the adsorbent filter; and

[0106] - a control and signal processing module connected to the probe gas detector, the flow regulator, the temperature, pressure and humidity indicators, the probe gas injector, the probe gas detector and the signal processing module of said test bench being configured to carry out the method of determining residual capacity as defined above.

[0107] The temperature indicator, pressure indicator and hygrometry indicator can, for example, be sensors or regulators (thermometer, manometer for example for temperature and pressure). The measurement of hygrometry is important because this hygrometry has an impact on the gas concentration curve probe downstream of the filter as a function of time. The charts produced take this into account.

[0108] Thus, the flow regulator makes it possible to maintain the flow of a carrier gas stream at a constant flow rate through the material constituting the adsorbent filter; the temperature and humidity indicators (for example, sensors or regulators) make it possible to know the humidity level and the temperature of the system at the time of the measurement; the probe gas injector makes it possible to inject, upstream of the gas inlet of the adsorbent filter, a probe gas into the carrier gas stream with rapid concentration variations (greater than 100 ppmv / s); the probe gas detector makes it possible to measure the probe gas concentration curve as a function of time downstream of the gas outlet of the adsorbent filter; and the signal processing module makes it possible to analyze the measured probe gas concentration curve and to determine the residual capacity of the adsorbent filter as a function of said analysis.

[0109] According to one embodiment, the probe gas detector is at least one of: an infrared (IR) detector such as a simple IR detector, a Fourier transform IR detector or a non-dispersive IR detector, a mass spectrometer, a photoacoustic detector, a katharometer and an electrochemical sensor.

[0110] The probe gas detector must have a low response time compared to the duration of the measured sudden variation (case of the injection of a sudden probe gas signal or case of the rising or falling edge type step), typically at least 10 acquisitions during the duration of the sudden variation so as to be able to measure the probe gas concentration downstream of the adsorbent filter over time (so-called continuous measurement). This differentiates the present device from a breakthrough measurement device, because the response time of the detector must be significantly shorter in the case of the present invention, for example at least 1 Hz.

[0111] According to one embodiment, the probe gas injector is a valve controlled by an electronic control module capable of opening and closing in less than 50 ms, for example, a solenoid valve controlled by a computer, a pneumatic valve, an electromagnetically controlled valve, an injection loop, associated with a flow limiter, itself connected to a pressure reducer, itself connected to a bottle of compressed probe gas. Thus, the control of the valve connected to the probe gas source allows the generation of a sudden variation of probe gas in the carrier gas flow. This differentiates the present device from a breakthrough measurement device, because the response time of this valve must be significantly shorter in the case of the present invention, to open and close in a few milliseconds.

[0112] According to one embodiment, the probe gas injector is a flow regulator controlled by an electronic control module, the flow regulator having a valve capable of opening and closing in less than 50 ms. Thus, the control of the flow regulator connected to the probe gas source allows the generation of a sudden variation in the probe gas concentration in the carrier gas flow.

[0113] According to one embodiment, the probe gas injector is a gas syringe.

[0114] Unlike the prior art, the probe gas according to the invention is chosen so as not to be stopped by the adsorbent material of the filter. As such, the invention is therefore non-destructive and different from a breakthrough method: the method used does not reduce the stopping capacity of the tested filter. In addition, the probe gas injection times are very short (of the order of a few seconds) compared to the effectiveness times of the adsorbent filter with respect to a target gas (of the order of a few hours). There is therefore a difference in nature (non-destructive) and parameters (times, test means, nature of the gas) between this method and a breakthrough measurement.

[0115] To better illustrate the object of the present invention, a preferred embodiment will be described below, by way of illustration and not limitation, with reference to the appended drawings.

[0116] On these drawings:

[0117] -is a functional diagram of a test bench according to the present invention;

[0118] -is a flowchart representing a method for determining residual capacity according to the present invention;

[0119] -is a graph representing experimental and modeled curves of CO2 concentration downstream of an adsorbent filter as a function of time for different saturation rates of the adsorbent filter;

[0120] -is a graph representing the evolution of a modeling parameter of the experimental curves of theen as a function of the saturation rate of the adsorbent filter;

[0121] -is a graph illustrating the evolution of the probe gas concentration downstream of the filter with the injection of a sudden variation in the probe gas concentration upstream of the filter for a first example of probe gas;

[0122] -is a graph illustrating the evolution of the probe gas concentration downstream of the filter with the injection of a sudden variation in the probe gas concentration upstream of the filter for a second example of probe gas;

[0123] -is a graph illustrating the evolution of the probe gas concentration downstream of the filter with the injection of a rising edge type step;

[0124] - is a graph illustrating the evolution of the probe gas concentration downstream of the filter with the injection of a falling front type step;

[0125] -is an illustration of a classic breakthrough curve showing the evolution of the saturation rate of the adsorbent filter; and

[0126] -is an exemplary diagram illustrating the method according to the invention.

[0127] Referring to the, it can be seen that there is shown a test bench 1 according to the present invention configured to determine the residual stopping capacity of an adsorbent filter 2.

[0128] The adsorbent filter 2 comprises a gas inlet 2a, a gas outlet 2b and an adsorbent material 2c disposed between the gas inlet 2a and the gas outlet 2b.

[0129] The adsorbent filter 2 may, for example, be a respiratory protection mask filter or a filter for purifying the air from a pollutant in a vehicle.

[0130] Said adsorbent materials make it possible to purify a gas passing through them, such as air, with respect to one or more target gas products.

[0131] The test bench 1 comprises a flow regulator 3 whose inlet is fluidically connected to a carrier gas source 4 and whose outlet is fluidically connected to the gas inlet 2a of the adsorbent filter 2.

[0132] The carrier gas contained in the carrier gas source 4 is at least one of:

[0133] air, oxygen (O2), hydrogen (H2), nitrogen (N2), argon (Ar), helium (He), the aforementioned pure gas mixtures used as standard gases during calibration, over- or under-oxygenated gas mixtures such as those used for deep diving (examples: Trimix®, heliair, heliox, surox, nitrox, triox or helitrox), medical gases (examples: nitrous oxide, equimolar mixtures of oxygen - nitrous oxide (MEOPA), nitric oxide (NO)), respiratory function testing gases (EFR), breathing mixtures such as helium / oxygen and other gas mixtures used for the treatment of certain types of deafness (MEDI OD 93, MEDI OD 95).

[0134] The test bench 1 further comprises a temperature indicator (e.g., sensor or regulator) 5, a humidity indicator (e.g., sensor or regulator) 6 and a pressure indicator 6a fluidically connected to the inlet of the flow regulator 3.

[0135] The flow regulator 3, and the temperature 5 and hygrometry 6 and pressure 6a indicators thus allow the flow of a flow-regulated carrier gas stream through the adsorbent material 2c of the adsorbent filter 2, knowing the temperature and hygrometry of the measurement.

[0136] The test bench 1 further comprises a probe gas injector 7 whose inlet is fluidically connected to a probe gas source 8 of the gas cylinder type via a pressure gauge 9 and a pressure reducer 10 and whose outlet is fluidically connected to the outlet of the flow regulator 3.

[0137] The probe gas injector 7 thus allows the creation, upstream of the gas inlet 2a of the adsorbent filter 2, of a sudden variation in the probe gas concentration of a predefined duration in the carrier gas flow. The sudden variation can for example be a peak in the probe gas concentration in the carrier gas, a trough in the probe gas concentration in the carrier gas or even an upward or downward step in the probe gas concentration in the carrier gas.

[0138] The probe gas contained in the probe gas source 8 is chosen not to be stopped by the adsorbent material of the filter. By "chosen not to be stopped", those skilled in the art will understand that the probe gas must have an adsorption isotherm such that at a partial pressure of 0.1 atmospheres of probe gas, the adsorption isotherm must have an adsorption capacity of less than 100 µmol of probe gas per gram of adsorbent.

[0139] The probe gas injector 7 consists in this case of a solenoid valve 7a controlled by a computer 7b. It should be noted that the probe gas injector 7 could also be any type of valve controlled by an electronic control module (for example a computer-controlled solenoid valve, a pneumatic valve or an injection loop), without departing from the scope of the present invention. The control of the solenoid valve 7a by the computer 7b allows the generation of a sudden variation in the concentration of probe gas in the carrier gas flow. The valve is capable of opening and closing in 50 ms to generate sudden variations in the concentration of the probe gas in the carrier gas.

[0140] The test bench 1 further comprises a probe gas detector 11 fluidically connected to the gas outlet 2b of the adsorbent filter 2.

[0141] The probe gas detector 11 thus allows the measurement of the probe gas concentration curve as a function of time downstream of the gas outlet 2b of the adsorbent filter 2.

[0142] An additional hygrometry indicator (e.g., sensor or regulator) 12 is preferably also fluidically connected to the gas outlet 2b of the adsorbent filter 2.

[0143] The probe gas detector 11 is a low response time infrared detector (e.g., a CO2 infrared detector in the case of a CO2 type probe gas), but could also be any other detector suitable for detecting the probe fluid, such as any type of infrared detectors (e.g., simple IR detectors, Fourier transform IR detectors or non-dispersive IR detectors), a mass spectrometer, a photoacoustic detector, a katharometer or an electrochemical sensor, without departing from the scope of the present invention.

[0144] The test bench 1 further comprises a signal processing module 13 connected to the probe gas detector 11. The signal processing module 13 allows the analysis of the probe gas concentration curve measured by the probe gas detector 11 and the determination of the residual capacity of the adsorbent filter 2 based on said analysis. It should be noted that the signal processing module 13 could also be connected to the computer 7b, without departing from the scope of the present invention.

[0145] Referring to the, it can be seen that there is shown a flowchart representing steps in the method for determining the residual capacity of the adsorbent filter 2 using the test bench 1.

[0146] The non-destructive method for determining the residual stopping capacity of an adsorbent filter of a given type, the adsorbent filter being capable of adsorbing a target gas, comprises the following steps:

[0147] (a) choosing a probe gas and a carrier gas capable of passing through an adsorbent filter of the given type not saturated with target gas without remaining fixed there, the probe gas being intended to be mixed with the carrier gas to be injected into the adsorbent filter of the given type,

[0148] (b) at a given operating temperature, pressure and hygrometry, choosing parameters for injecting probe gas and carrier gas into an adsorbent filter of the given type, the injection parameters comprising, for the probe gas and the carrier gas, a given duration and a flow rate curve as a function of time, the concentration of the probe gas in the carrier gas comprising at least one sudden variation during the injection duration,

[0149] for an adsorbent filter of the given type, called the reference filter,

[0150] (c) injecting, at the given operating temperature, pressure and hygrometry, the probe gas and the carrier gas into the reference filter according to the injection parameters of step (b) and measuring the evolution of the probe gas concentration as a function of time downstream of the reference filter for increasing quantities of known target gas material adsorbed by the reference filter, the last of these quantities corresponding to the breakdown of the reference filter, and deducing the stopping capacity m a of the reference filter,,

[0151] for an adsorbent filter of the given type whose residual stopping capacity is to be determined, called the filter under test,

[0152] (d) inject, at the given operating temperature, pressure and hygrometry, the probe gas and the carrier gas into the filter under test according to the injection parameters of step (b) and measure the change in the probe gas concentration as a function of time downstream of the filter under test,

[0153] (e) compare the evolution over time of the probe gas concentration for the filter under test and for the reference filter to determine a saturation rate value of the filter under test τ sft , And

[0154] (f) deduce the residual stopping capacity of the filter under test by the following calculation: residual stopping capacity = (1 - τ sft )*m a .

[0155] Step (d) of the method for determining residual capacity is carried out as follows for the filter under test: the regulation S1 in flow rate, at given operating temperature, pressure and hygrometry, using the flow regulator 3 and the temperature 5, pressure 6a and hygrometry 6 indicators, of a flow of carrier gas coming from the carrier gas source 4; the injection S2, using the probe gas injector 7 from the probe gas source 8, of a sudden variation in the concentration of probe gas in the flow of carrier gas; the flow S3 of the regulated carrier gas flow carrying the sudden variation 14 of probe gas through the adsorbent material 2c of the adsorbent filter 2, the probe gas front thus advancing into the layers of the adsorbent material 2c; the measurement S4, by the probe gas detector 11, of the probe gas concentration curve 15 as a function of time downstream of the gas outlet 2b of the adsorbent filter 2.

[0156] The method continues in steps (e) and (f) with the analysis S5 of the probe gas concentration curve 15 measured using the signal processing module 13 and the determination of the residual capacity of the adsorbent filter 2 as a function of said analysis, the signal processing module 13 making it possible to model the probe gas concentration curve 15 measured so as to return to the indicators of the saturation rate of the adsorbent filter 2.

[0157] Thus, the method according to the invention makes it possible to precisely and reliably measure the saturation of the adsorbent material 2c of the adsorbent filter 2 so as to determine the residual capacity of the adsorbent filter 2 in a non-destructive and non-specific manner.

[0158] The analysis S5 of the probe gas concentration curve 15 comprises the search for a sudden variation, in the example shown a concentration peak 16 on the probe gas concentration curve 15, and the determination of the residual capacity of the adsorbent filter 2 comprises the comparison of the values ​​of the parameters representative of the concentration peak 16 found with an existing database of peak values ​​(or existing charts) so as to determine the residual capacity of the adsorbent filter 2.

[0159] The shape of the probe gas concentration curve 15 being dependent on the saturation rate of the adsorbent filter 2, the value of the concentration peak 16 found on the probe gas concentration curve 15 thus makes it possible to determine the saturation rate of the adsorbent filter 2 tested, and thus the residual stopping capacity thereof.

[0160] The analysis S5 of the probe gas concentration curve 15 may, alternatively or additionally, comprise calculating the decay time of the concentration peak 16 found. The decay time is defined as the time elapsed to go from a probe gas concentration of 95% to 5% of the maximum value of the measured concentration peak. The determination of the residual capacity of the adsorbent filter 2 may, furthermore, comprise comparing the calculated concentration decay value to an existing database, carried out via step (c) of the present method, of decay values ​​(or existing charts) so as to more accurately determine the residual capacity of the adsorbent filter 2.

[0161] The analysis S5 of the probe gas concentration curve 15 may alternatively or additionally comprise calculating the time period between the start of the abrupt change in probe gas concentration 14 in the carrier gas stream and the quantifiable start of the growth of the concentration peak 16 found, and determining the residual capacity of the adsorbent filter 2 may further comprise comparing the calculated time period value to an existing database of time period values ​​(or existing charts) so as to more accurately determine the residual stopping capacity of the adsorbent filter 2.

[0162] The analysis S5 of the probe gas concentration curve 15 may, alternatively or additionally, comprise modeling the measured probe gas concentration curve by calculating modeling parameters, and determining the residual capacity of the adsorbent filter 2 may further comprise comparing said calculated modeling parameters to an existing database or a theoretical model.

[0163] The concentration of the probe gas injected into the carrier gas flow is constant for the predefined duration of the sudden variation of probe gas 14. Thus, a zero concentration of probe gas 14 is injected, for example 2 seconds after the start of the test, then a sudden variation, for example in 20 ms, makes it possible to reach a concentration of probe gas 14 of 4000 ppmv, with a concentration plateau, for example for 1 second, at 4000 ppmv before returning, for example again in 20 ms, to a concentration of probe gas 14 in the carrier gas flow that is again zero. The concentration of probe gas is zero throughout the duration of the test, except between two limits defining the sudden variation of probe gas 14. Between these two limits (t = 0 and t = T), the concentration of probe gas 14 is non-zero and constant. The duration of the sudden variation (T) is thus defined as the duration during which the concentration of probe gas 14 sent is equal to C = C0.

[0164] It should be noted that the concentration of the probe gas injected into the carrier gas flow could also be variable during the predefined duration of the sudden variation of probe gas 14, without departing from the scope of the present invention. The probe gas concentration C could also, for example, have a sinusoidal evolution of type C = C0sin(ω * t) with ω = π / T, and a zero value otherwise.

[0165] Several successive measurements of the residual stopping capacity can be carried out in order to determine more reliably and precisely the residual capacity of the adsorbent filter 2 from test to test.

[0166] A single measurement is the determination of the filter saturation rate from a single series of steps (d) to (f).

[0167] Repeated measurements can be made, for example, every minute for 5 minutes, as long as the absolute value of the time derivative of the gas concentration probe 14 downstream of the adsorbent filter has returned to a value below 10 ppbv / s after each point measurement. This allows the filter saturation rate measurements to be averaged, and a more accurate assessment of the instantaneous filter saturation to be obtained.

[0168] Referring to the, it can be seen that there are shown, as an example, experimental curves and modeled curves of the CO2 concentration as a function of time downstream of the adsorbent filter 2, for different saturation rates of the adsorbent filter 2 (namely, 0%, 10%, 19%, 32%, 48%, 65% and 100%).

[0169] In these experiments, as an example, the probe gas injector 7 generated sudden variations in the CO2 concentration in the carrier gas flow, for a duration of one second, from a CO2 cylinder (50 bar) and expanded to 0.6 bar relative in an air flow at 20 L.min -1 , 23°C and 40%RH (relative humidity), atmospheric pressure, through an activated carbon bed of a respiratory protection mask filter as an adsorbent filter 2.

[0170] The probe gas detector 11 (here a low response time infrared CO2 detector) recorded, every 500 ms, downstream of the adsorbent filter 2 the concentration of the probe gas (CO2) as a function of time.

[0171] The different experimental curves obtained vary according to the saturation of the adsorbent filter 2. When the sudden variation in probe gas concentration, here, a peak, is carried out on a bed with a low saturation rate, the height of the probe gas concentration peak downstream of the filter is lower than when the measurement is made on the same adsorbent material with a higher saturation rate.

[0172] The different curves represent the evolution of the peak of the probe gas concentration curve with the increase in the saturation rate of the activated carbon bed in sorbed target agent (here physisorbed but which can be a chemisorbed target agent) for seven experimental tests (i.e., for a saturation rate, respectively, of 0%, 10%, 19%, 32%, 48%, 65% and 100%).

[0173] The dotted line curves each represent an average of the experimental values ​​of downstream concentrations resulting from the passage of the sudden CO2 signal through an activated carbon bed as a function of time in a carrier air flow at 20 L.min -1 , 40%RH and 23°C, each dotted line curve corresponding to the percentage of the saturation rate indicated near its concentration peak.

[0174] The solid line curves represent the mathematical modeling of the experimental curves.

[0175] The experimental curves obtained are modeled by the following equation (1):

[0176]

[0177] where exp denotes the exponential function, erfc denotes the complementary error function, y denotes the concentration, t denotes the time, and x1 to x5 correspond to the five parameters of the equation which are determined by mathematical calculation software to find an equation curve according to the above equation which most closely matches the curve found experimentally by a distance minimization method, for example by the so-called least squares method.

[0178] In practice, we inject the experimental measurements into a mathematical calculation software with the above equation that we seek to model, the calculation software will calculate the values ​​of the parameters x1 to x5 which give a theoretical curve according to the above equation closest to the experimental values.

[0179] Some parameters of the equation allowing the fine modeling of the concentration peak measured downstream of adsorbent filter 2 are dependent on the saturation rate of adsorbent filter 2. Thus, the more saturated adsorbent filter 2 is, the higher the CO2 concentration peak downstream of adsorbent filter 2. In addition, the more saturated adsorbent filter 2 is, the faster the concentration decrease after the peak. Finally, the time between the generation of the sudden signal and the increase in concentration downstream of the filter is shorter as adsorbent filter 2 is saturated.

[0180] For each experimental curve of the, five sudden one-second variations in CO2 concentration, with an acquisition time of 130 seconds, were injected into the carrier air flow. During the first injection, a system equilibration takes place, the first curve is slightly higher than the following ones. In order to avoid a dispersion of the results, this first curve was discarded because it indicates the equilibration of the adsorbent system. The average of the four following sudden signals was then taken. It is this experimental average curve (in dotted line on the) which was then mathematically modeled (in solid line on the).

[0181] It was found that the most reliable parameter for measuring the saturation rate of adsorbent filter 2 is the parameter x3. Indeed, it is the parameter which presents the greatest variation over the range of saturation rates of the adsorbent filter, therefore having the greatest derivative with respect to the saturation rate, and which has a monotonic evolution with respect to the saturation rate. However, other parameters or combinations of parameters (for example, peak height, x1, etc.) also make it possible to go back to the saturation rate of adsorbent filter 2, provided that they satisfy the two aforementioned criteria.

[0182] If we refer to the, we can see that it represents the evolution of the modeling parameter x3 as a function of the saturation rate of the adsorbent filter 2, the parameter x3 being derived from Math. 2 during the approximation by the least squares method obtained in, and we can see its monotony and its significant evolution as a function of the saturation rate.

[0183] By controlling the poisoning of the adsorbent filter 2 by filling the porosity of the adsorbent material with a target or parasitic gas, charts can be created based on the saturation rate of the adsorbent filter 2.

[0184] By carrying out the experiment described in (i.e., five sudden successive injections of CO2) as the porosity of the adsorbent material is filled with a target gas, it is possible to obtain the curve representing, on, the decrease in the parameter x3 (parameter linked to the decrease in concentration of the probe gas concentration peak) as a function of the saturation rate of the adsorbent filter 2.

[0185] It should be noted that the parameter x3 obtained by modeling increases as a function of the mass of activated carbon in the adsorbent filter 2, while the maximum of the concentration peak decreases as a function of the mass of activated carbon in the adsorbent filter 2.

[0186] The experiment just described was carried out with poisoning of the porosity of the adsorbent filter 2 by a physisorbed vapor (reversible surface phenomenon). However, the same approach was also carried out with a chemisorbed vapor (irreversibly fixed to the surface) for a similar result, which demonstrates that the method according to the invention is universal and suitable for any type of gas stopped by an adsorbent material.

[0187] By implementing regular tests on adsorbent filters using the method of the invention, this allows:

[0188] - to avoid systematic changing of the adsorbent filters in place without knowing whether or not they are still usable;

[0189] - to test adsorbent filters and know their initial filtration capacities;

[0190] - to limit the size of the filters, thanks to more precise monitoring of their saturation, and thus to save energy, a smaller adsorbent filter having a smaller pressure drop;

[0191] - to replace adsorbent filters that are defective, prematurely saturated, for example, by exhaust residues; and

[0192] Figures 5a and 5b illustrate the injection of a sudden probe gas signal upstream of the filter (dashed line) and the evolution of the probe gas concentration downstream of the filter, illustrating an example of characteristic times for CO2 injected at 2 bars, on a respiratory protection mask filter, the carrier gas being air at 20 L / min and the hygrometry at 80% stabilized, illustrating an example of characteristic times for methyl chloride injected via a gas syringe (100 mL at atmospheric pressure), on a respiratory protection mask filter, the carrier gas being air at 30 L.min -1 and 50% humidity.

[0193] Figures 6a and 6b illustrate respectively the injection of a rising front of probe gas upstream of the filter, and the evolution of the probe gas concentration downstream of the filter, and the injection of a falling front of probe gas upstream of the filter, and the evolution of the probe gas concentration downstream of the filter.

[0194] These examples illustrate the innovative nature of the invention, by the choice of the probe gas which is not stopped by the adsorbent material of the adsorbent filter, and of which the evolution of the concentration downstream of the filter is used on the basis of a sudden variation in concentration upstream of the filter.

[0195] Describes a classic breakthrough curve. The target product is injected into the adsorbent filter at a constant concentration C0. A target concentration C is defined cthat we do not want to exceed at the outlet of the adsorbent filter. The breakdown corresponds to obtaining the concentration C of target gas downstream of the filter equal to C c The efficiency time of the adsorbent filter corresponds to the time elapsed between the start of injection of the target gas upstream of the filter and the obtaining of C=C c downstream of the filter.

[0196] As an example, the preliminary creation of the charts, corresponding to step (c) of the process described above, is described in, and is carried out in the following way.

[0197] For several values ​​of the saturation rate of the adsorbent filter, here the reference filter, a sudden variation of probe gas is sent, here a peak in concentration of the probe gas in the carrier gas.

[0198] In step c1, the concentration peak is generated by the probe gas reservoir, and sent to the adsorbent filter in step c2. It can be seen that in steps c1 to c6, the filter is unsaturated (0%). In steps c3 and c4, the probe gas peak passes through the adsorbent filter, then in step c5 the probe gas concentration downstream of the adsorbent filter is measured to obtain the curve of the probe gas concentration in the carrier gas as a function of time illustrated in step c6, corresponding to the filter in the state completely unsaturated with target gas.

[0199] The steps are then repeated with different saturation states of the adsorbent filter (50% in step c7, 100% in step c8) to obtain the curves of the evolution of the probe gas concentration in the carrier gas as a function of time illustrated in step c8.

[0200] These curves can then be used to determine the saturation state of a filter under test with steps (d) to (f) of the method of the invention.

[0201] Table 1 below explains the protocol followed and illustrates the differences between the invention and a conventional breakthrough bench, with 5 injections of CO2 probe gas for the sudden variation in probe gas concentration downstream of the reference filter for the process according to the invention:

[0202] Test stepsTest device according to the inventionConventional drilled bench1. Generation of 5 injections of CO2 probe gas on an adsorbent filter in the initial state, for a flow rate of 20L / min in carrier gas (air at atmospheric pressure, 23°C, 70% relative humidity). Injection of 4000 ppmv of CO2 for 1 second.X2. Filling of the filter with target gas, cyclohexane, up to 10% of the t eff *X2bis. Generation of 5 CO2 probe gas injections on this adsorbent filter for this saturation rate of 10%X3. Filling of the filter with target gas up to 19% of the t eff*X3bis. Generation of 5 CO2 probe gas injections on this adsorbent filter for this saturation rate of 19%X4. Filling the filter with target gas up to 32% of the t eff *X4bis. Generation of 5 CO2 probe gas injections on this adsorbent filter for this saturation rate of 32%X5. Filling the filter with target gas up to 48% of the t eff *X5bis. Generation of 5 CO2 probe gas injections on this adsorbent filter for this saturation rate of 48%X6. Filling the filter with target gas up to 65% of the t eff *X6bis. Generation of 5 CO2 probe gas injections on this adsorbent filter for this saturation rate of 65%X7. Filling the filter with agent up to t eff * and determination of the quantity of target gas material injected to obtain this breakdown.X7bis: Generation of 5 CO2 probe gas injections on this breakdown adsorbent filter, i.e. a saturation rate of 100%.X*t eff= filter efficiency time measured previously under the same test conditions (temperature, humidity, flow rate and target gas concentration)

[0203] This chart allows us to highlight an evolution of the CO2 probe gas concentration peaks downstream of the filter, as its saturation increases (see). Equation (1) allows us to mathematically approximate the curve, using a classic algorithm for minimizing the distance between the experimental curve and the theoretical curve. The parameter x3 is thus measured for different saturation levels of the adsorbent filter (see). The different measured values ​​of x3 for different saturation rates are then linked by an affine approximation in order to establish a bijective function between the value of x3 thus determined and the saturation rate of the filter.

[0204] This chart is specific to this adsorbent filter model, this hygrometry (70% relative humidity) and this temperature (23°C). Other charts must be produced for other adsorbent filter models, hygrometry, temperature.

[0205] By way of example, the method of the invention is illustrated in the context of measuring the saturation rate of an adsorbent filter for a respiratory protection mask:

[0206] 1 / Choice of carrier gas: air at atmospheric pressure, passing through the adsorbent filter at 20L / min, with a measured temperature of 20°C and a measured relative humidity of 40%.

[0207] 2 / Choice of probe gas: CO2, 99.9% purity

[0208] 3 / Injection of CO2 according to the curve in

[0209] 4 / Measurement of the CO2 concentration at a frequency of 2Hz, using a Fourier transform infrared sensor and recording of said values ​​for 130s from the start of CO2 injection upstream of the filter

[0210] 5 / Approximation of the CO2 concentration measured downstream of the filter using equation 1, and use of a classic algorithm for minimizing the distance between the experimental curve and the theoretical curve to obtain the value of x3.

[0211] 6 / Comparison of the value of x3 to an abacus table produced on a reference filter prior to the test, looking at the abacus produced on this model of adsorbent filter, this temperature (23°C) and this hygrometry (40%): obtaining the value of the saturation rate from the abacus curve giving the saturation rate as a function of the value of x3.

[0212] At the end of these steps, the saturation rate of the filter is known, without the saturation rate of the filter under test having been increased. The filter therefore remains usable.

[0213] It is understood that the particular embodiment which has just been described has been given for informational purposes and is not limiting, and that modifications may be made without departing from the present invention.

Claims

– A non-destructive method for determining the residual stopping capacity of an adsorbent filter of a given type, the adsorbent filter being capable of adsorbing a target gas, characterized in that the method comprises the following steps: (a) selecting a probe gas and a carrier gas capable of passing through an adsorbent filter of the given type unsaturated with target gas without becoming bound thereto, the probe gas having an adsorption isotherm such that at a partial pressure of 0.1 atmospheres in probe gas, the adsorption isotherm has an adsorption capacity of less than 100 µmol of probe gas per gram of adsorbent, the probe gas being intended to be mixed with the carrier gas for injection into the adsorbent filter of the given type, (b) at given operating temperature, pressure, and humidity, selecting injection parameters for probe gas and carrier gas into an adsorbent filter of the given type, the injection parameters comprising, for the probe gas and the carrier gas,a given duration and flow rate curve, the probe gas concentration in the carrier gas having at least one abrupt change during the injection time, each abrupt change in the probe gas concentration in the probe gas injection parameters being characterized by an absolute value of the derivative of the probe gas concentration with respect to time that exceeds 100 ppmv / s, for an adsorbent filter of the given type, called the reference filter, (c) inject, at given operating temperature, pressure and humidity, the probe gas and the carrier gas into the reference filter according to the injection parameters of step (b) and measure the evolution of the probe gas concentration as a function of time downstream of the reference filter for increasing amounts of known target gas adsorbed by the reference filter, the last of these amounts corresponding to the breakdown of the reference filter, and deduce the stopping capacity m,a of the reference filter, for an adsorbent filter of the given type whose residual stopping capacity is to be determined, called the filter under test, (d) inject, at the given operating temperature, pressure, and humidity, the probe gas and the carrier gas into the filter under test according to the injection parameters of step (b) and measure the evolution of the probe gas concentration as a function of time downstream of the filter under test, (e) compare the evolution as a function of time of the probe gas concentration for the filter under test and for the reference filter to determine a saturation rate value of the filter under test τ sft , and (f) deduce the residual stopping capacity of the filter under test by the following calculation: residual stopping capacity = (1 - τ sft )*m a . – A method according to claim 1, characterized in that the carrier gas has an adsorption isotherm such that at a partial pressure of 0.1 atmosphere in carrier gas, the adsorption isotherm has an adsorption capacity of less than 100 µmol of carrier gas per gram of adsorbent. – A method according to one of claims 1 and 2, characterized in that the comparison of the evolution of the concentration of the filter under test and the reference filter includes the search for at least one parameter representative of the abrupt variation of the probe gas concentration on the probe gas concentration curve measured downstream of the filter, and the comparison of this parameter representative of the abrupt variation of concentration between the filter under test and the reference filter. – A method according to one of claims 1 and 2, characterized in that the comparison of the evolution of the concentration of the filter under test and the reference filter includes the calculation of the time taken to pass from 95% to 5% of the maximum concentration value of the probe gas downstream of the adsorbent filter obtained after the abrupt change in the probe gas concentration, and the comparison of the calculated time value between the filter under test and the reference filter. – A method according to any one of claims 1 and 2, characterized in that the comparison of the evolution of the concentration of the filter under test and the reference filter includes the calculation of the time period between the start of the abrupt variation of the probe gas in the carrier gas flow and the quantifiable start of the concentration variation (16) in probe gas downstream of the filter, and the comparison of the value of the calculated time period between the filter under test and the reference filter. – A method according to any one of claims 1 and 2, characterized in that the comparison of the evolution of the concentration of the filter under test and the reference filter includes the computer calculation of a mathematical model with several parameters of the concentration curve of the probe gas measured downstream of the filter, the determination of a signature of the concentration curve consisting of one of a parameter or a combination of parameters of the mathematical model which, over the saturation rate range of the reference filter, has a monotonic variation and a maximum derivative as a function of the saturation rate, and the comparison of the signature of the concentration curve between the filter under test and the reference filter. – A method according to any one of claims 1 to 6, characterized in that the carrier gas is at least one of the following: air, dioxygen (O2), dihydrogen (H2), dinitrogen (N2), argon (Ar), helium (He), the aforementioned pure gas mixtures used as calibration gases, over- or under-oxygenated gas mixtures such as those used for deep diving (examples: trimix, heliair, heliox, surox, nitrox, triox or helitrox), medical gases (examples: nitrous oxide, equimolar mixtures of oxygen - nitrous oxide (MEOPA), nitric oxide (NO)), respiratory function testing (RFT) gases, respiratory mixtures such as helium / oxygen and other gas mixtures used for the treatment of certain types of deafness (MEDI OD 93, MEDI OD 95). – A method according to any one of claims 1 to 7, characterized in that the probe gas is at least one gas among: carbon dioxide (CO2), nitrous oxide (N20), an alkane such as methane, ethane, propane, isopropane, butane, pentane, or hexane, propylene, isobutene, an ether such as methoxymethane, compounds of the halogenated gas family including haloalkanes such as chloromethane (CH3Cl), bromobutane, hydrofluorocarbons (HFCs), chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrobromofluorocarbons (HBFCs), bromofluorocarbons (BFCs). – A method according to any one of claims 1 to 8, characterized in that steps (d) to (f) are carried out in a punctual, repeated or periodic manner. – Test bench (1) comprising: - a flow regulator (3) whose inlet is configured to be connected to a carrier gas source (4) and whose output is configured to be connected to the gas inlet (2a) of an adsorbent filter (2); - a temperature indicator (5), a humidity indicator (6) and a pressure indicator (6a) connected to the inlet of the flow regulator (3); - a probe gas injector (7) whose inlet is configured to be connected to a probe gas source (8) and whose output is connected to the outlet of the flow regulator (3); - a probe gas detector (11) configured to be connected to the gas outlet (2b) of the adsorbent filter (2);and- a control and signal processing module (13) connected to the gas probe detector (11), the flow regulator (3), the temperature (5), humidity (6) and pressure (6a) indicators, the gas probe injector (7), the gas probe detector (11) and the signal processing module (13) of said test bench (1) being configured to carry out the residual capacity determination process according to any one of claims 1 to 9.; – Test bench (1) according to claim 10, characterized in that the gas detector probe (11) is at least one of: an infrared (IR) detector such as a simple IR detector, a Fourier transform IR detector or a non-dispersive IR detector, a mass spectrometer, a photoacoustic detector, a catharometer and an electrochemical sensor. – Test bench (1) according to any one of claims 10 and 11, characterized in that the probe gas injector (7) is one of a valve (7a) controlled by an electronic control module (7b) capable of opening and closing in less than 50 ms, a flow regulator controlled by an electronic control module, the flow regulator having a valve capable of opening and closing in less than 50 ms, and a gas syringe.

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