NL2022070B1 - METHOD AND APPARATUS FOR DETERMINING THE CONCENTRATION OF A GASEOUS POLLUTION IN A PRODUCT GAS-CONTAINING GAS MIXTURE - Google Patents

Abstract

Method and device for determining the concentration of a gaseous pollutant in a gas mixture containing product gas, by means of an absorber containing an adsorbent for the product gas and the pollutant and comprising inlet means and outlet means and pressure measuring means for the gas mixture, wherein the adsorbent has such properties that an adsorption equilibrium between adsorbed product gas and gas phase product gas is established within a first period of time Atl and an adsorption equilibrium between adsorbed contamination and gas phase contamination is established within a second period of time Atz, the first period of time Atl a predefined value shorter than the second duration Atz.

Description

METHOD AND APPARATUS FOR DETERMINING THE CONCENTRATION OF A GASEOUS POLLUTION IN A PRODUCT GAS-CONTAINING GAS MIXTURE

The invention relates to a method for determining the concentration of a gaseous pollutant in a product gas, for example hydrogen gas, containing gas mixture.

Determining the impurity concentration is of particular importance in the production of hydrogen gas, for example in a steam reformer, where a feed gas containing methane and water vapor is converted into a product gas containing mainly carbon dioxide and hydrogen, after which the product gas is converted into a pressure swing adsoption (PSA) setup is separated into hydrogen gas mixture and tail gas.

The purity of the hydrogen gas mixture produced in a PSA set-up can, for example, be measured in a known manner in a gas chromatograph. A gas chromatograph is relatively expensive, is maintenance-sensitive and has a too high detection limit for very pure gases, and is therefore less suitable for a measurement on location of a PSA setup. For this reason, in the production and separation of hydrogen gas in a PSA arrangement, the PSA arrangement is often set to limit the yield of separated hydrogen gas in order to achieve the highest purity of that hydrogen gas.

It is an object of the invention to provide a method for determining the impurity concentration in a product gas-containing gas mixture, which is applicable during the production of that product gas, without the intervention of an operator.

This object is achieved, and other advantages are attained by a method of the type mentioned in the preamble, which according to the invention is carried out using an adsorbent for the impurity, and comprising selecting an adsorbent for the product gas and the impurity, wherein an adsorption equilibrium between adsorbed product gas and gas phase product gas is established within a first period ht ₂ and an adsorption equilibrium between adsorbed pollution and gas phase contamination is established within a second period ht ₂ , such that the first period hti predefined value is shorter than the second duration ht ₂ .

It is known per se that there are absorbents that absorb (and desorb) some gases more slowly than others. For example, some CMS (carbon molecular sieves} absorbents absorb hydrogen, oxygen, carbon dioxide and water relatively quickly and other gases such as methane, carbon monoxide and nitrogen are much slower. (Although there is a difference between the terms absorbing for a macroscopic process and adsorbing for a process on molecular scale, in this description a connection is sought with the common parlance, according to which an adsorbent material is kept in an absorber, and gas molecules are adsorbed on the adsorbent material.)

According to the invented method, an adsorbent is known to absorb the product gas, for example hydrogen gas, relatively quickly, and to absorb other gases such as methane, carbon monoxide and nitrogen much more slowly.

The degree of loading of an adsorbent with molecules of a (pollutant) gas in a closed vessel is in equilibrium with a pressure P _ads of that gas, which can be expressed as a partial pressure, when that pollutant gas is part of a certain gas mixture. According to the method, the partial pressures of the slowly absorbing gases are suddenly changed. This can be achieved, for example, by a pressure change (resulting in a change of all partial pressures) or by replacing the gas mixture with a new gas mixture of a different composition (resulting in a change of only the partial pressures of the slowly absorbing gases). The rapidly adsorbing gases are almost immediately de-adsorbed to the new equilibrium. After changing the partial pressures (and adjusting the equilibrium of the rapidly adsorbing gases), the vessel with the adsorbent is isolated by closing all connections to the outside world. The slowly adsorbing gases will now also de- or adsorb until a new equilibrium is established. This will cause an increase or decrease in pressure. The concentration of the slowly absorbing gases in a gas mixture can be determined from this pressure increase or decrease.

In an embodiment, wherein the adsorbent is contained in an absorber, the method comprises the steps of (i) contacting the adsorbent with the gas mixture and establishing and ht ₃ for a third time longer than the second time ht ₂ maintaining a predetermined pressure with value P0 in the adsorption vessel, (ii) entering a quantity of the quantity of the same within a fourth time period ht ₄ which is shorter than the second time period ht ₂ and longer than the first time period ht ₂ gas mixture under a predetermined first pressure Pi with a value Pi> Po in the absorber, (iii) closing the absorber and keeping the gas mixture in contact with the adsorbent therein for a fifth period ht ₂ which is at least equal to the second time period ht ₂ , and determining the pressure (P ₂ - ΔΡ ₂ ) in the absorber after the fifth time period hts, and (iv) deriving the concentration of the gaseous form from the determined pressure values Pi, ΔΡι and Po Some contamination in the product gas containing gas mixture.

During the maintenance of the pressure Po in the absorber in the first step (i), an equilibrium is established between the molecules of the pollutant gas that have been adsorbed and the molecules that are in the gas phase by adsorption to or desorption of the adsorbent, depending on of the original loading of the adsorbent with pollutant gas.

After closing the absorber according to step (iii), the pressure in that vessel decreases by a value of ΔΡι, due to the adsorption of molecules of the pollutant gas to the adsorbent. Since the adsorbent is charged with the pollutant gas during the first step (1), an amount of pollutant gas is present in the absorber when the gas mixture is introduced, the pressure of which corresponds to the equilibrium pressure P _ads , so that after the inlet during step (iii) of the gas mixture pollutant gas are adsorbed until the partial pressure of the pollutant gas has decreased to the equilibrium pressure P _ads , the pressure in the vessel decreasing by a value of ΔΡι. From the pressure drop occurring ΔΡι immediately after increasing the pressure in the absorber from a value P _o to the value Pi, the concentration of pollutant molecules (c _imp ) in the gas mixture can be derived directly, as follows c _imp = ΔΡ! / (Pi - Po) (1).

In a practical situation, the values for Pi and P _{o can} be determined by a direct measurement and the values for ΔΡ by a differential pressure measurement.

In a further embodiment, wherein the adsorbent is contained in an absorber, and the absorber is provided with an inlet and an outlet, the method comprises the steps of (i) introducing an amount of the gas mixture under a predetermined first pressure Pi in the absorber and maintaining a first pressure Pi in the absorber for a third period ht ₃ which is longer than the second period ht ₂ , (ii) keeping it for a fourth period Δ1 ₄ shorter than the second period ht ₂ via the intake inlet of a quantity of the gas mixture, and simultaneously through the exhaust outlets of gas mixture, while maintaining the first pressure P ₂ in the absorption vessel, (iii) closing of the absorption vessel and keeping it in contact of the gas mixture with the adsorbent for a fifth time period At _s which is at least equal to the second time period ht ₂ , and determining the pressure (P ₂ - ΔΡ ₂ ) in the absorptive flow after the fifth time period ht ₅ at, (iv) evacuating the absorber creating a second pressure P _o and maintaining the pressure P _o in the absorber for a sixth period ht ₆ longer than the second period ht ₂ , (v) a seventh time period ht ₇ which is shorter than the second time period ht ₂ via the inlet inlet of an amount of the gas mixture and the simultaneous outlet of the gas mixture while maintaining the second pressure _Po in the absorber, (vi) the closing of the inlet and the outlet, followed by determining a pressure (P _o + ΔΡ ₀ ) in the absorber after an eighth period At _s longer than the second period ht ₂ , and (vii) it from the determined pressure values P ₂ , ΔΡι, P _o and ΔΡ ₀ derive the concentration of the gaseous pollutant in the product gas-containing gas mixture.

According to this embodiment, during the first step (i), gas mixture is introduced into the absorber at a first pressure, and the gas mixture is changed during the second step (ii). After closing the absorber, an adsorption equilibrium is established in the third step (iii), the pressure in the absorber decreasing by a value of ΔΡι. Then, during the fourth step (iv), the absorber is evacuated to a pressure _Po and the gas mixture is changed during the fifth step (v), a new adsorption equilibrium is established, the pressure in the absorber increasing by a value ΔΡ ₀ .

After closing the absorber according to step (iii), the pressure in that vessel decreases by a value ΔΡ _ΪΖ due to the adsorption of molecules of the pollutant _gas to the adsorbent, which value is given by

ΔΡ1 = Pimp, l ^- Pads (2), in which P _MPRL the partial pressure of the impurity gas in the gas mixture indicates at the pressure P _2. After closing the absorber according to step (v), the pressure in that vessel increases by a value of ΔΡ ₀ , due to the desorption of molecules of the pollutant gas from the adsorbent, which value is given by

ΔΡο - Pads “Pimp, Ο (3), where Pi _mp , o denotes the partial pressure of the pollutant in the gas mixture at the pressure P _o , so that the sum of the measured pressure drop and pressure rise can be expressed as ΔΡ-1 + ΔΡο = Pimp, 1 “Pimp, 0 (4).

The partial pressure Pi _mp , o can be expressed as Pimp, 0 ⁼ (Po / Pl). Pimp, l (5), so that from (3) the value of the partial pressure P _imp , p can be derived as

Pimp.l = {Pi / (Pi ^_ Po)} · (ΔΡι + ΔΡ ₀ ) (6).

The concentration of contaminant molecules (cp _mp ) in the gas mixture is then given by the ratio of the partial pressure Pi _mp , i and the pressure Pp, as follows:

Cimp = Pimp, i / Pi = (ΔΡρ + ΔΡ ₀ ) / (Pp - Po) (7).

In a practical situation, the values for Pp and P _{o can} be determined by means of a direct measurement and the values for ΔΡρ and ΔΡ ₀ by means of a differential pressure measurement.

When the gas mixture is changed during the second step (ii) and the fifth step (v), measurement errors resulting from jumps in the partial voltage of the product gas and temperature fluctuations in the adsorbent as a result of successively adsorbing and desorbing molecules of the pollutant gas and the product gas are eliminated.

In yet a further embodiment, wherein the adsorbent is contained in an absorber, and wherein the absorber is provided with an inlet and an outlet, the method comprises the steps of (i) introducing an amount of the gas mixture through the inlet and simultaneous discharge of gas mixture via the outlet, establishing and maintaining for a third period ht ₃ which is longer than the second period ht ₂ of a first pressure Pp in the absorption vessel, (ii) closing the inlet and evacuating via the outlet the absorption vessel in such a way that a second pressure P _o with a value P ₀ <Pp is established in the absorption vessel within a fourth period At ₄ which is shorter than the second period bt ₂ , (iii) closing the outlet and isolating the absorber for a fifth period dt ₅ which is at least equal to the second period bt ₂ , and determining the pressure (P _o + ΔΡ ₀ ) in the absorber after the fifth period bt ₅ , and (iv) deriving from the determined pressure values P ₂ , P _o and ΔΡ ₀ the concentration of the gaseous pollutant in the product gas-containing gas mixture.

After closing the absorber according to step (iii), the pressure in that vessel increases by a value of ΔΡ ₀ , due to the desorption of molecules of the pollutant gas to the adsorbent. The adsorbent is charged with the contaminant gas in the first step (i), so that in the step (iii) molecules of the pollutant gas are desorbed, until partial pressure of the pollutant gas has increased to equilibrium pressure P _ads , the pressure in the vessel increasing with a value ΔΡ ₀ . From the occurring pressure jump ΔΡ ₀ immediately after decreasing the pressure in the absorber from a value Pi to the value Po, the concentration of pollutant molecules (c _imp ) in the gas mixture can be deduced directly from equation (7), as follows, as follows c _imp = ΔΡ ₀ / (Pi - Po) (8).

In a practical situation, the values for P ₂ and P _{o can} be determined by a direct measurement and the values for ΔΡ by a differential pressure measurement.

For example, in this last embodiment, prior to step (iii), step (ii) is followed by step (iia), comprising rinsing the absorber (1 after a waiting time Δt _w which is longer than the second period bt _2). ) by introducing the gas mixture via the inlet and simultaneously exiting the gas mixture via the outlet, establishing and maintaining for a period of time At _s shorter than the second period of time bt ₂ of the second pressure P _o in the absorber.

By purging the gas mixture absorber during the step (iia), measurement errors resulting from jumps in the partial voltage of the product gas and temperature fluctuations in the adsorbent due to successively adsorbing and desorbing molecules of the pollutant gas and the product gas are eliminated .

In yet a further embodiment, wherein the adsorbent is contained in an absorber, and the absorber is provided with an inlet and an outlet, the method comprises the steps of (1) introducing an amount of the gas mixture through the inlet and simultaneous discharge of gas mixture through the outlet, establishing and maintaining for a third period ht ₃ which is longer than the second period ht ₂ of a first pressure P _o in the absorption vessel, (ii) closing the outlet and inlet via the inlet of gas mixture into the absorption vessel in such a way that, in the absorption vessel and a second pressure P ₂ having a value Pi> Po is established within a fourth period of time ht _4, which is shorter than the second period of time ht _2, (iii) closing the inlet and isolating the absorber for a fifth period ht ₅ which is at least equal to the second period ht ₂ , and determining the pressure (P ₂ + ΔΡ ₂ ) in the absorption vessel after the fifth period ht ₅ t, and (iv) deriving from the determined pressure values P _o , Pi and ΔΡ ₂ the concentration of the gaseous pollutant in the product gas-containing gas mixture.

During the rinsing of the absorber in the first step (i) while maintaining the relatively low pressure P _o (P ₀ <Pi), the loading of the adsorbent with molecules of the pollutant gas becomes extremely low. As a result, almost all the impurities are adsorbed at the relatively high pressure P _2. This is particularly advantageous when the gas mixture is supplied at a low pressure, for example hydrogen which has been purified using a hydrogen permeable membrane. In that case, little gas needs to be compressed. The low pressure P _o is, for example, 1 bar, the high pressure P ₂ is, for example, 20 bar.

After closing the absorber according to step (iii), the pressure in that vessel decreases by a value of ΔΡ ₂ , due to the adsorption of molecules of the pollutant gas to the adsorbent. Because the adsorbent has been flushed with gas mixture during the first step (1), Pads, the partial pressure of the pollutant gas with which the adsorbent balances, has become equal to the partial pressure of the pollutant gas in the gas mixture at the pressure P _o , so that after the inlets during step (iii) of the gas mixture pollutant gas are adsorbed until the partial pressure of the pollutant gas has decreased to the equilibrium pressure P _ads , the pressure in the vessel decreasing by a value of ΔΡι. From the occurring pressure drop ΔΡι immediately after increasing the pressure in the absorber from a value Po to the value Pi, the concentration of pollutant molecules (ci _mp ) in the gas mixture can be deduced directly from equation (1), as follows c _imp = ΔΡι / (Pi - _Po ) (1).

In a practical situation, the values for Pi and P _{o can} be determined by a direct measurement and the values for ΔΡ by a differential pressure measurement.

For example, in this last embodiment, prior to step (iii), step (ii) is followed by step (iia), comprising rinsing the absorber ₂ after a waiting time Δt _w which is longer than the second duration ht. via the inlet inlets of the gas mixture, and simultaneously through the exhaust outlets of gas mixture under creation and retention for a time period at _s which is shorter than the second period of time ht ₂ of the second pressure P ₂ in the absorption vessel.

By purging the gas mixture absorber during the step (iia), measurement errors resulting from jumps in the partial voltage of the product gas and temperature fluctuations in the adsorbent due to successively adsorbing and desorbing molecules of the pollutant gas and the product gas are eliminated .

In yet a further embodiment, wherein the adsorbent is contained in an absorber, and the absorber is coupled to a first inlet conduit and a second inlet conduit and includes an outlet, the method comprises the steps of (i) passing through the first inlet conduit inlet of an amount of the gas mixture and the simultaneous outlet of the gas mixture through the outlet, establishing and maintaining for a third period ht ₃ which is longer than the second period ht ₂ of a first pressure Pi in the absorber, (ii) closing the first inlet conduit and via the second inlet inlets of a quantity of product gas and simultaneously through the exhaust outlets of gas mixture under creation and retention during a fourth period of time ht _4, which is shorter than the second period of time ht ₂ of the first pressure P ₂ in the absorber, (iii) closing the second inlet pipe and insulating the absorber for a fifth time ht ₅ d ie is at least equal to the second period ht ₂ , and after the fifth period ht ₅ determining the pressure (Pi + ΔΡι) in the absorber, and (iv) it from the determined pressure values Pi and Δ ?! deriving the concentration of the gaseous pollutant in the product gas-containing gas mixture.

According to the latter method, the absorber is successively purged with the gas mixture containing the pollutant gas and with as pure product gas as possible from a storage container provided for this purpose, so that during the determination of the pressure (Pi + ΔΡι) in the absorber by desorption of pollutant molecules, the partial pressure of the pollutant gas in the absorber again increased to that in the gas mixture at the pressure _P2.

The methods described here are particularly suitable for determining impurities in a gas mixture where the product gas is hydrogen gas.

The adsorbent includes, for example, carbon molecular sieve (CMS) material, which contains, for example, pores with a diameter in the range between 0.2 nm and 0.4 nm.

The invention furthermore relates to a device for determining the concentration of a gaseous pollutant in a gas mixture containing product gas, at least comprising an absorption vessel in which an adsorbent for the product gas and the pollution is included and which is provided with inlet means and outlet means and pressure measuring means for the gas mixture. wherein the adsorbent is selected from a group of adsorbents having properties such that an adsorption equilibrium between adsorbed product gas and gas phase product gas is established within a first time period hti and an adsorption equilibrium between adsorbed and gas phase impurity is established within a second duration ht ₂ , wherein the first duration ht _{2 is} a predefined value shorter than the second duration ht ₂ .

In an embodiment of a device according to the invention, in which the absorption vessel is provided with an inlet and an outlet, the inlet is coupled to a first buffer vessel for storing an amount of the gas mixture, and the outlet is coupled to a second buffer vessel for storing gas mixture extracted from the absorber.

In another embodiment of a device according to the invention, the absorber is coupled to a first inlet conduit for inlet of an amount of the gas mixture and to a second inlet conduit for inlet of an amount of pure product gas, and provided with an outlet.

For example, in this latter embodiment, the second inlet conduit is coupled to a first buffer vessel for storing an amount of pure product gas, and the outlet is coupled to a second buffer vessel for storing the gas mixture withdrawn from the absorption vessel.

In a device according to the invention, the pressure measuring means comprise, for example, a pressure differential sensor, which is, for example, directly coupled to the absorber on a first pressure measuring side and coupled to the absorber on a second pressure measuring side via at least one valve.

In an embodiment, the volume of the absorber is less than 0.5 liters, preferably less than 0.1 liters.

Embodiments of the device according to the invention will be described and elucidated hereinbelow on the basis of exemplary embodiments, with reference to the drawings.

Show in the drawings

Fig. 1 schematically shows a first embodiment of a device according to the invention for determining the concentration of a gaseous pollutant in a gas mixture containing product gas, FIGS. 2a, 2b, 2c a graphical representation of the pressure as a function of time during various concentrations in a scale shown in FIG. 1 absorber shown,

Fig. 3 schematically shows a second embodiment of a device according to the invention, FIGS. 4a, 4b, 4c graphically depict the pressure as a function of time during various scales in a scale shown in FIG. 3 absorber shown,

Fig. 5 schematically shows a third embodiment of a device according to the invention, FIGS. 6a, 6b, 6c a graphical representation of the pressure as a function of time during a concentration determination in a scale shown in FIG. 5 absorber shown,

Fig. 7 schematically shows a fourth embodiment of a device according to the invention, FIGS. 8a, 8b, 8c a graphical representation of the pressure as a function of time during various concentrations in a scale shown in FIG. 7 absorber shown,

Figs. 9a, 9b, 9c a graphical representation of the pressure as a function of time during different concentrations in a scale shown in FIG. 3 absorber shown,

Fig. 10 schematically shows a fifth embodiment of a device according to the invention, FIGS. 11a, 11b, 11c a graphical representation of the pressure as a function of time during different concentrations in a scale shown in FIG. 10 absorber shown,

Fig. 12 schematically shows a sixth embodiment of a device according to the invention, FIG. 13 schematically shows a seventh embodiment of a device according to the invention, FIG. 14 schematically shows an eighth embodiment of a device according to the invention, FIG. 15 schematically shows a ninth embodiment of a device according to the invention, FIG. 16 schematically shows a tenth embodiment of a device according to the invention,

Fig. 17 is a graphical representation of the pressure as a function of time during a concentration determination in one of those shown in FIGS. 12-16 absorbers shown.

In the figures, corresponding parts are designated with the same reference numerals. Arrows in the figures correspond to the flow direction of gases.

Fig. 1 is a schematic representation of a device 10 for determining the concentration of a gaseous pollutant in a product gas-containing gas mixture, with an absorption vessel 1 in which an adsorbent 2, for example CMS pellets, for a product gas, for example hydrogen gas and the pollutant, for example nitrogen gas, is included and is provided with an opening 3. The opening 3 is connected to an inlet pipe 4 with valve 5 and an outlet pipe 6 with valve 7. The pressure in the absorber 1 can be measured with a pressure sensor 8. The adsorbent 2 is such chosen that an adsorption equilibrium between adsorbed product gas and gas-phase product gas is established within a first period of time Ati and an adsorption equilibrium between adsorbed pollution and gas-phase pollution is established within a second period of time ht ₂ , the first period of time Ati having a defined value is shorter than the second duration bt ₂ .

Example 1

An adsorption vessel 1 of one shown in FIG. 1, device 10 shown has a content of 0.1 l and is almost completely filled with CMS pellets. To find the concentration of nitrogen (the pollutant gas) in a mixture of hydrogen and nitrogen (the sample gas) with a pressure P ₂ = 7 bara ~ 7. 10 ⁵ Pa to be determined with the device 10, in a first step (i), that gas is introduced into the absorption vessel 1 via an inlet pipe 4 with valve 5, which is then evacuated via the outlet pipe 6 with valve 5 closed and valve 7 open (vacuum pumped with a pump or connected to a vacuum buffer) until after a time period ht3 longer than the second time period ht2 defined above, a predetermined pressure Po = 200 mbara (0.2.10 ⁵ Pa) has been set. Then, in a second step (ii), within a fourth period of time ht4 which is shorter than the second period of time ht ₂ and is longer than the above-defined first period of time Ati with valve 5 opened via inlet line 4., an amount of the sample gas under a predetermined first pressure P ₂ having a value Pi> P ₀ in the absorber 1 embedded. Then valve 5 is closed and the sample gas is kept in contact with the adsorbent for a fifth period ht _5, which is at least equal to the second period ht ₂ , the pressure P ₂ in the vessel 1 due to adsorption of contaminant molecules to the adsorbent 2 will drop to a stationary value, with the pressure decreased by a value ΔΡ ₂ = 2 mbara (200 PA). The concentration of impurity molecules (c _imp ) in the gas mixture according to equation (1) above is given by:

c _imp = ΔΡι / (P ₂ - P _o ) (1).

Substitution of the above-mentioned values of ΔΡ ₂ , P ₂ and Po results in c _imp = 0.000294 = 294 ppm. The described method can be briefly characterized as successively increasing the pressure in the absorber 1, enclosing the sample gas and measuring the pressure thereof.

Figs. 2a, 2b, 2c are graphs showing the pressure in the absorber 1 as a function of time for the measurement described in Example 1, the measured values of the pressures P _o and P ₄ being indicated in bara, and the steps ( i) through (iii) are indicated in the time course.

Fig. 2a shows the course of the pressure on a scale from 6,995 to 7,005 bara.

Fig. 2b shows the course of the pressure on a scale from 0.000 to 8.000 bara.

Fig. 2c shows the course of the pressure on a scale from 0.195 to 0.205 bara.

Fig. 3 is a schematic representation of a second device 20 according to the invention, with an absorber 1 having an inlet 3 and an outlet 9 connected to an outlet conduit 6 with valve 7.

Example 2

An adsorption vessel 1 of one shown in FIG. 3, device 20 has a content of 0.1 l, and is almost completely filled with CMS pellets. The pressure in the vessel (P _a ) initially has a value of 3,000 bara. To determine with the device 20 the concentration of nitrogen (the pollutant gas) in a mixture of hydrogen and nitrogen (the sample gas) with a pressure Pi = 7 bara = 7. 10 ⁵ Pa, in a first step (i) a quantity of the sample under the first pressure P let into the absorber 1, and is ht _3, which is longer during a third period of time than the second period of time ht _2, the first pressure P ₄ in the absorber 1 maintained. In a second step (ii), for a fourth period of time At _4, which is shorter than the second period of time ht _2, an amount of the sample gas is introduced into, and while maintaining the first pressure Pi, simultaneously released through the outlet 9. from the absorption vessel 1. in a third step (iii) the absorber vessel is closed, whereby the sample gas during a fifth period of time at _s which is at least equal to the second period of time at ₂ remains in contact with the adsorbent 2, and, after the fifth time period If _{s determines} the pressure (Pi - ΔΡ ₂ ) in the absorber 1, from which a value ΔΡι = 0.002 bara results. In a fourth step (iv), the absorber 1 is evacuated with the creation of a second pressure with a value P _o = 0.200 bara and the pressure P _o in the absorber 1 becomes for a sixth period Atg longer than the second period bt _2. after which in a fifth step (v) for a seventh time period bt ₇ shorter than the second time period At _2, an amount of the sample gas is introduced into the inlet 3 and, while maintaining the second pressure P _o , simultaneously via the outlet 9 is discharged from the absorber 1. In a sixth step (vi), the inlet 3 and the outlet 9 are closed, and after an eighth period bt ₈ which is longer than the second period bt _2, the pressure (P _o + ΔΡ ₀ ) in the absorber 1, from which a value ΔΡ ₀ = 0.002 bara results. The concentration of impurity molecules (c _imp ) in the gas mixture according to equation (7) above is given by:

c _imp = (ΔΡ ₂ + ΔΡ ₀ ) / (Ρ-ι - P _o ) (7)

Substitution of the above-mentioned values of ΔΡ ₂ , ΔΡ ₀ , Pi and Po gives c _imp = 0.00588 = 588 ppm. The described method can be briefly characterized as successively increasing the pressure of the sample gas and keeping it pressurized in the absorption vessel 1, replacing the sample gas, confining the sample gas and measuring the pressure thereof, lowering of the pressure of the sample gas and keeping it pressurized, replacing the sample gas, sealing the absorber and measuring the pressure therein.

Figs. 4a, 4b, 4c are graphs showing the pressure in the absorber 1 as a function of time for the measurement described under example 2, the measured values of the pressures P _o and Pi being indicated in bara, and the steps (i ) through (vi) are indicated in the time course.

Fig. 4a shows the course of the pressure on a scale from 6,995 to 7,005 bara.

Fig. 4b shows the course of the pressure on a scale from 0.000 to 8.000 bara.

Fig. 4c shows the course of the pressure on a scale from 0.195 to 0.205 bara.

Fig. 5 is a schematic representation of a third device 30 according to the invention, with an absorption vessel 1 provided with an inlet 3, which is connected via a inlet pipe 4 with valve 5 to a main pipe 17, in which a control valve 15 is included, and an outlet 9, which is connected to an outlet line 6 with valve 7, and which is connected via a pumping line 18 with valve 16 to a pump or a vacuum buffer (not shown). The vessel 1 is further provided with a sensor line 11 in which a valve 12 and a differential pressure sensor 13 are included. The device 30 is particularly suitable for carrying out a concentration determination, in which in a first step (i) an amount of the sample gas is introduced into the absorption vessel 1 via the inlet 3 and sample gas is simultaneously discharged via the outlet 9, thereby producing and maintaining during a third period of time ht _3, which is longer than the second period of time ht ₂ of a first pressure P ₂ in the absorption vessel 1. in a second step (ii), the inlet 3 is closed and the absorber 1 via the outlet 9 at closed valve 7 and an open valve 16 evacuated in the pumping line 18, a second pressure P _o with a value P ₀ <Pi is established in the absorption vessel 1 within a fourth period ht ₄ which is shorter than the second period ht ₂ . In a third step (iii) the outlet 9 is closed by closing the valve 16, and the absorber 1 is insulated for a fifth period ht _5, which is at least equal to the second period ht ₂ , after which after a fifth period ht ₅ the pressure (P _o + ΔΡ ₀ ) in the absorber 1 is measured. The concentration of contaminant molecules (c _imp ) in the sample gas is given by:

c _imp = ΔΡ ₀ / (P ₂ - Po) (8).

The described method can be briefly characterized as successively using the absorber 1 at a first pressure P _a , rinsing the absorber with sample gas at a pressure Pi, where Pi> P _a , decreasing the pressure in the absorber to a pressure _Po , isolating the absorber 1 and measuring the pressure therein.

Figs. 6a, 6b, 6c are graphs showing the pressure in the absorber 1 as a function of time for a simulation of a measurement described above using a device 30, where the simulated values of the pressures P _o and Pi in bara and steps (i) to (iii) are indicated in the time course.

Fig. 6a shows the course of the pressure on a scale from 6,995 to 7,005 bara.

Fig. 6b shows the course of the pressure on a scale from 0.000 to 8.000 bara.

Fig. 6c shows the course of the pressure on a scale from 0.195 to 0.205 bara.

Fig. 7 is a schematic representation of a fourth device 40 according to the invention, in which the absorption vessel 1 is provided with an inlet 3 and an outlet 9, the inlet 3 being coupled via a inlet pipe 4 with a valve 5 therein to a first buffer vessel 21 for storing an amount of the sample gas, and the outlet 9 is coupled via a conduit 18 with a valve 16 therein to a second buffer vessel 22 with a diversion line 28 containing a valve 26 for storing and discharging gas mixture extracted from the absorption vessel 1 . The device 40 is particularly suitable for carrying out a concentration determination, in which in a first step (i) an amount of the sample gas is introduced into the absorption vessel 1 via the inlet 3 and sample gas is simultaneously discharged via the outlet 9, while producing and maintaining during a third period of time ht _3, which is longer than the second period of time ht ₂ of a first pressure P ₂ in the absorption vessel 1. in a second step (ii), the inlet 3 is closed and the absorber 1 via the outlet 9 at closed valves 6 and 7 and an opened valve 16 evacuated in a pump line 18, whereby a second pressure P _o with a value Po <Pi is established in the absorption vessel 1 within a fourth period At <which is shorter than the second period ht ₂ . The step (ii) is followed by a step (iia), wherein after a waiting time Δt _w which is longer than the second duration ht _2, the absorber (1) is purged by inlet of the gas mixture via the inlet (3) and simultaneously discharging gas mixture through the outlet (9) with formation and maintenance for a duration At _s shorter than the second duration At ₂ of the second pressure P _o in the absorber (1). In a third step (iii) the inlet 3 and the outlet 9 are closed by closing the valves 5 and 16, respectively, and the absorber 1 is insulated for a fifth period At ₅ which is at least equal to the second period ht ₂ , after which the pressure (P _o + ΔΡ ₀ ) in the absorber 1 is measured. The concentration of contaminant molecules (ci _mp ) in the sample gas according to equation (8) above is given by:

c _imp = ΔΡ ₀ / (P ₂ - Po) (8).

The described method can be briefly characterized as successively using the absorber 1 at a pressure P _a , rinsing the absorber with sample gas at a pressure P ₂ , where Pi> P _a , decreasing the pressure in the absorber to a pressure _Po , replacing the sample gas at a pressure _Po and isolating the absorber 1 and measuring the pressure therein. The figure further shows a pumping line 28 with valve 26 for evacuating the second vessel 22. The device 40 offers the advantage that a determination of the concentration of contaminant molecules can be carried out very quickly if, prior to the replacement of the sample gas in the absorption vessel. 1 at the pressure P _o, the pressure in the first buffer vessel 21 is set at such a value (higher than P _o ), and the pressure in the second buffer tank 22 is set at such a value (lower than P _o ) that when simultaneously opening the valves 5 and 16 for a short time, the gas in the absorption vessel 1 is replaced, after which the pressure in each of the three vessels 21, 1, 22 is the value P _o . The first buffer vessel 21 has a volume V _{b / 2} i / such that the product V _b , ₂₁ x (Pi - P _o ) is always greater than the product V _a , ix for all values of P ₂ occurring in the intended specific conditions. P _o , where V _{a / 1 is} the volume of the absorber 1.

Figs. 8a, 8b, 8c are graphs showing the pressure in the absorber 1 as a function of time for a simulation of a measurement described above using a device 40, with the simulated values of the pressures P _o and P ₂ in bara are indicated, and steps (i) to (iii) are indicated in the time course.

Fig. 8a shows the course of the pressure on a scale from 6,995 to 7,005 bara.

Fig. 8b shows the course of the pressure on a scale from 0.000 to 8.000 bara.

Fig. 8c shows the course of the pressure on a scale from 0.195 to 0.205 bara.

Figs. 9a, 9b, 9c are graphs showing the pressure in the absorber 1 as a function of time for a simulation of a further embodiment of a concentration determination using a device shown in FIG. 3 shows device 20, wherein the simulated values of the pressures P0 and P1 are indicated in bara, and wherein steps (i) to (iii) are indicated in the time course. According to this embodiment, an amount of a sample gas in a first step (i) is introduced into the absorber 1 through the inlet 3 and is simultaneously released through the outlet 9, establishing and maintaining for a third period of time ht ₃ longer than the second period of time ht ₂ of a first pressure _PO in the absorber 1, after which in a second step (ii) the outlet 9 is closed with the aid of valve 7 and sample gas is introduced into the absorber 1 via the inlet 3 via the inlet 3. such that in the absorber a second pressure Pi with a value Pi> Po is produced within a fourth period At4 which is shorter than the second period dt ₂ . Then, in a third step (iii), the inlet 3 is closed by means of valve 5, and the absorber 1 is insulated for a fifth period ht _5, which is at least equal to the second period ht ₂ , and after the fifth period ht the pressure (P ₂ - ΔΡ ₂ ) measured in the absorber. The concentration of impurity molecules (c _imp ) in the sample gas according to equation (1) above is given by:

c _imp = ΔΡ ₂ / (Pi - P _o ) (1). The described process can be briefly characterized as successively using the absorber 1 at a pressure P _a , rinsing the absorber with sample gas at a pressure P _o , where P ₀ <P _a , increasing the pressure in the absorption vessel to a pressure P _2, and the isolation of the absorption vessel 1, and the measurement of the pressure therein.

Fig. 9a shows the course of the pressure on a scale from 6,995 to 7,005 bara.

Fig. 9b shows the course of the pressure on a scale from 0.000 to 8.000 bara.

Fig. 9c shows the course of the pressure on a scale from 0.195 to 0.205 bara.

Fig. 10 is a schematic representation of a fifth device 50 according to the invention, wherein the absorption vessel 1 is provided with an inlet 3 and an outlet 9, wherein the inlet 3 is coupled via a inlet pipe 4 with a valve 5 therein to a first buffer vessel 21 with supply line 24 and valve 25 for storing an amount of the sample gas, and the outlet 9 via a line 18 with a valve 16 therein is coupled to a second buffer tank 22 for storing gas mixture extracted from the absorption tank 1. The first buffer vessel 21 has a volume V _b , ₂ i / · which is greater than the volume V _{a <1} of the absorption vessel 1. The device 50 is particularly suitable for carrying out a concentration determination, wherein in a first step ( i) an amount of the sample gas is introduced into the absorption vessel 1 via the inlet 3 and sample gas is simultaneously released via the outlet 9, establishing and maintaining for a third period At ₃ which is longer than the second period ht ₂ of a first pressure P _o in the absorber 1. In a second step (ii), the outlet 9 is closed and sample gas is introduced into the absorber 1 via the inlet 3 with valve 5 open, whereby in the absorber 1 a second pressure Pp with a value Pp> P ₀ is established within a fourth duration ht ₄ that is shorter than the second duration ht ₂ . The step (ii) is followed by a step (iia), wherein after a waiting time At _w longer than the second duration At _2, the absorber 1 is purged by introducing the gas mixture via the inlet 3 and simultaneously via the outlet 9 outlets of gas mixture under formation and maintenance for a period of time At _s shorter than the second period of time At ₂ of the second pressure Pp in the absorption vessel 1. In a third step (iii) the inlet 3 and the outlet 9 are closed by closing the valves 5 and 16, respectively, and the absorber 1 is isolated for a fifth period At ₅ which is at least equal to the second period ht ₂ , after which the pressure (Pp - ΔΡρ) in the absorber 1 is measured. The concentration of contaminant molecules (cp _mp ) in the sample gas according to equation (1) above is given by:

Cp _mp = ΔΡρ / (Pp - Po) (1).

The described process can be briefly characterized as successively using the absorber 1 at a pressure P _a , rinsing the absorber with sample gas at a pressure P _o , where P ₀ <P _a , increasing the pressure in the absorber to a pressure Pp, replacing the sample gas at a pressure Pp and isolating the absorber 1 and measuring the pressure therein. The device 50 offers the advantage that a determination of the concentration of contamination molecules can be carried out very quickly if, prior to the replacement of the sample gas in the absorption vessel 1 at the pressure Pp, the pressure in the first buffer vessel 21 is at such a value (higher than Pp), and the pressure in the second buffer vessel 22 is set to a value (lower than PJ) that when the valves 5 and 16 are simultaneously opened for a short time, the gas in the absorption vessel 1 is replaced, after which the pressure in each of the three vessels 21, 1, 22 the value Pi is. The figure further shows a pumping line 28 with valve 26 for evacuating the second vessel 22.

Figs. 11a, 11b, 11c are graphs showing the pressure in the absorber 1 as a function of time for a simulation of the above-described embodiment of a concentration determination using a method shown in FIG. 10 shows device 50, wherein the simulated values of the pressures P _o and?! are indicated in bara, and wherein steps (i) to (iii) are indicated in the time course.

Fig. 11a shows the course of the pressure on a scale from 6,995 to 7,005 bara.

Fig. 11b shows the course of the pressure on a scale from 0.000 to 8.000 bara.

Fig. 11c shows the course of the pressure on a scale from 0.195 to 0.205 bara.

Figs. 12, 13, 14, 15, 16 are schematic representations of a sixth 60, seventh 70, eighth 80, ninth 90 and tenth device 100 according to the invention, respectively, the absorption vessel 1 being coupled to a first inlet conduit 4 for inlet of a amount of the gas mixture, from a second inlet conduit 14 for introducing an amount of pure product gas, and from an outlet 9. The devices 60, 70, 80, 90, 100 are particularly suitable for carrying out a concentration determination, in which a first step (i) through the first inlet line 4 an amount of the gas mixture is let in and simultaneously the gas mixture is let out through the outlet 9, establishing and maintaining for a third period ht ₃ which is longer than the second period ht ₂ of a first pressure Pi in the absorber 1, in a second step (ii) the first inlet pipe 4 is closed and an amount of product gas is introduced via the second inlet pipe and simultaneously n gas mixture is discharged via the outlet 9 under the creation and maintenance for a fourth period At ₄ which is shorter than the second period ht ₂ of the first pressure P ₂ in the absorption vessel 1, after which in a third step (iii) the second inlet pipe 14 is closed and the absorber 1 is isolated for a fifth period At ₅ which is at least equal to the second period ht ₂ , after which the pressure (P ₂ + ΔΡ ₂ ) in the absorber 1 is determined after a fifth period ht ₅ ,, and from the determined pressures P ₂ and ΔΡ ₂ the concentration of the gaseous pollutant in the product gas-containing gas mixture can be derived as follows.

Cimp ⁼ Pimp, l / Pi ⁼ ΔΡ1 / Ρ1 (9).

Figs. 12 and 13 show simple embodiments of a device 60, 70 according to the invention, wherein the inlet 3 of the absorber 1 is coupled to an inlet pipe 4 with valve 5 for a product gas-containing gas mixture, an inlet pipe 14 with valve 19 for very pure product gas, and an outlet 9. In the in FIG. Device 70 shown, a differential pressure gauge 13 is connected on one side via a valve 12 to the top, and on the other side directly to the bottom of the absorber 1. By closing valve 12 only during the pressure rise from the pressure Pi to the pressure (P ₂ + ΔΡ ₂ ), the differential pressure ΔΡ ₂ can be accurately measured without exposing the differential pressure sensor to excessive differential pressures. The use of the differential pressure gauge 13 in this way makes the device 70 particularly suitable for determining low concentrations.

Fig. 14 shows a device 80 with a buffer vessel 21 with supply line 24 and valve 25 for the supply and storage of high-purity product gas at a pressure P ₂₁ . The buffer vessel 21 has a volume V ₂ i, which is greater than the volume V ₂ of the absorber 1, satisfying the relationship (P ₂ i - Pi) x V ₂ i> Pi x Vi. When the valve 19 in the pipe 14 between the buffer tank 21 and the absorber 1 and the valve 7 in the exhaust pipe 6 of the absorber 1 is opened, the pressure in the exhaust pipe 6 being kept at a value Pi, the pressure in the buffer tank 21 drop to a value Pi. An amount (Ρ ₂ ι-Ρ ₂ ) x V ₂₂ of gas escapes from V ₂₁ , which amount of gas must be more than sufficient to replace the amount of the gas in vessel 1 (Pi x Vi). The device 80 is particularly suitable for performing concentration determinations in situations where very pure product gas is available at a pressure higher than the pressure Pi of the gas mixture.

Fig. 15 shows a device 90 with a first buffer vessel 21 with supply line 24 and valve 25 for the supply and storage of high-purity product gas, and a second buffer vessel 22 with a discharge line 28 containing a valve 26 for storing and discharging the absorption vessel 1 extracted gas mixture. The device is designed for the storage of pure product gas in the first buffer vessel 21 at a pressure which is higher than the target pressure P ₂ at which the absorption vessel 1 is purged during the first step ii.

Fig. 16 shows a device 100 substantially similar to that device 90 of FIG. 15, with the proviso that the first buffer tank 21 of device 100 is greater than the second buffer tank 22. As a result, this apparatus is particularly suitable for concentration determinations when the pure product gas at a low pressure higher than P ₂ is available.

Fig. 17 is a graph showing the pressure in absorber 1 as a function of time on a scale from 6,995 to 7,005 bara for a simulation of a concentration determination using one in one of FIGS. 12-16, devices 60, 70, 80, 90, 100, wherein steps (i) through (iii) are indicated in the time course.

Claims (18)

A method for determining the concentration of a gaseous impurity in a product gas-containing gas mixture, using an adsorbent for the impurity, comprising selecting an adsorbent (2) for the product gas and the impurity, wherein an adsorption equilibrium between adsorbed product gas and gas phase product gas is established within a first period of time hti and an adsorption equilibrium between adsorbed pollution and gas phase pollution is established within a second period of time ht ₂ , such that the second period of time ht _{2 is} a predefined value longer than the first duration Ati. A method according to claim 1, wherein the adsorbent (2) is contained in an absorber (1), comprising the steps of (i) contacting the adsorbent (2) with the gas mixture and establishing and during a third time period ht ₃ which is longer than the second time period ht ₂ maintaining a predetermined pressure with value P _o in the absorber (2), (ii) it within a fourth time period At /, which is shorter than the second time period At ₂ and longer than inlets, the first time period Ati for a quantity of the gas mixture under a predetermined initial pressure P ₂ having a value Ρ _3> Ρο in the absorber (1), (iii) closing of the absorption vessel (1) and the keeping the gas mixture in contact with the adsorbent (2) therein for a fifth period At ₅ which is at least equal to the second period At ₂ , and determining the pressure (P ₂ - ΔΡ ₂ ) after the fifth period At _s the absorber (1), and (iv) it from the determined pressures P ₂ , ΔΡ ₂ and P _o directing the concentration of the gaseous pollutant into the product gas-containing gas mixture. The method of claim 1, wherein the adsorbent (2) is contained in an absorber (1), and wherein the absorber (1) includes an inlet (3) and an outlet (9), comprising the steps of (i ) admitting a quantity of the gas mixture under a predetermined initial pressure Pi in the absorber (1), and during a third period of time ht _3, which is longer than the second period of time ht ₂ maintain a first pressure P ₂ in the absorber ( 1), (ii) for a fourth period of time ht ₄ which is shorter than the second period of time ht _2, inputting an amount of the gas mixture via the inlet (3) and simultaneously exiting the gas mixture via the outlet (9) while maintaining the first pressure P ₂ in the absorber (1) (iii) closing of the absorption vessel (1) and therein into contact holding of the gas mixture with the adsorbent (2) during a fifth period of time at ₅ which is at least equal to the second period ht ₂ , and determining after the fifth period ht ₅ the pressure (P ₂ - ΔΡ ₂ ) in the absorber (1), (iv) evacuating the absorber (1) with the creation of a second pressure P _o and it for a sixth period ht ₆ which is longer than the second period At ₂ maintaining the pressure P _o in the absorber (1), (v) it for a seventh period of time At? which is shorter than the second period of time ht ₂ inputting an amount of the gas mixture via the inlet (3) and simultaneously exiting the gas mixture via the outlet (9) while maintaining the second pressure _Po in the absorber (1), ( vi) closing the inlet (3) and the outlet (9), followed by after a eighth period ht ₈ which is longer than the second period ht ₂ determining a pressure (P _o + ΔΡ ₀ ) in the absorber ( 1), and (vii) _deriving from the determined pressure values Ρ _1Λ ΔΡ ₂ , P _o and ΔΡ ₀ the concentration of the gaseous pollutant in the product gas-containing gas mixture. The method of claim 1, wherein the adsorbent (2) is contained in an absorber (1), and wherein the absorber (1) includes an inlet (3) and an outlet (9), comprising the steps of (i ) introducing an amount of the gas mixture via the inlet (3) and simultaneously exiting the gas mixture via the outlet (9) with the establishment and maintenance for a third period of time bt ₃ which is longer than the second period of time At ₂ of a first pressure P ₂ in the absorber (1), (ii) closing the inlet (3) and evacuating the absorber (1) via the outlet (9) in such a way that in the absorber (1) a second pressure P _o with a value P ₀ <Pi is established within a fourth period of time Ata which is shorter than the second period of time bt ₂ , (iii) closing the outlet (9) and insulating the absorber (1) for a fifth period of time bt ₅ which is at least equal to the second period bt ₂ , and determining the dru after the fifth period bt ₅ k (P _o + ΔΡ ₀ ) in the absorber (1), and (iv) deriving the concentration of the gaseous pollutant in the product gas-containing gas mixture from the determined pressure values P ₂ , P _o and ΔΡ ₀ . The method of claim 4, wherein, prior to step (iii), the step (ii) is followed by a step (iia), comprising rinsing the water after a waiting time Δt _w which is longer than the second duration bt _2. absorber (1) by introducing the gas mixture via the inlet (3) and simultaneously exiting the gas mixture via the outlet (9), establishing and maintaining for a period of time At _s shorter than the second period of time bt ₂ of the second pressure P _o in the absorber (1) The method of claim 1, wherein the adsorbent (2) is contained in an absorber (1), and wherein the absorber (1) includes an inlet (3) and an outlet (9), comprising the steps of (i ) introducing an amount of the gas mixture via the inlet (3) and simultaneously exiting the gas mixture via the outlet (9), with the establishment and maintenance for a third period ht ₃ which is longer than the second period ht ₂ of a first pressure P _o in the absorber (1), (ii) closing the outlet (9) and introducing gas mixture through the inlet (3) into the absorber (1) in such a way that a second pressure is applied in the absorber (1) P ₂ having a value Pi> Po is established within a fourth period of time ht _4, which is shorter than the second period of time ht _2, (iii) closing the inlet (3) and the isolation of the absorber (1) during a fifth duration ht ₅ which is at least equal to the second duration ht ₂ , and determining after the fifth duration ht ₅ of the pressure (P ₂ - ΔΡ ₂ ) in the absorber (1), and (iv) deriving the concentration of the gaseous pollutant in the product gas-containing gas mixture from the determined pressure values P _o , P ₄ and ΔΡ ₄ . 7. A method as claimed in claim 6, wherein, prior to the step (iii), the step (ii) is followed by a step (iia), comprising, after a waiting period At which _w is longer than the second period of time ht of the coils ₂ absorber (1) by inlet of the gas mixture via the inlet (3) and simultaneous outlet of the gas mixture via the outlet (9) with the creation and maintenance for a period of time At _s shorter than the second period of time ht ₂ of the second pressure P ₂ in the absorber (1) The method of claim 1, wherein the adsorbent (2) is contained in an absorber (1), and wherein the absorber (1) is coupled to a first inlet conduit (4), a second inlet conduit (14) and includes a outlet (9), comprising the steps of (i) admitting an amount of the gas mixture via the first inlet conduit (4) and simultaneously exiting the gas mixture via the outlet (9) while establishing and maintaining for a third period of time hts that are longer than the second period of time ht ₂ of a first pressure P ₂ in the absorber (1), (ii) the closing of the first inlet pipe (4) and via the second inlet conduit (14) inlets of a quantity of product gas and simultaneously via the outlet (9) outlets of gas mixture under creation and retention during a fourth time period at _4, which is shorter than the second period of time ht ₂ of the first pressure P ₂ in the absorber (1), (iii) closing the second inlet conduit ( 14) and isolating it absorber (1) for a fifth period ht ₅ which is at least equal to the second period ht ₂ , and determining the pressure (P ₂ + ΔΡ ₂ ) in the absorber (1) after the fifth period At _s , and (iv ) deriving from the determined pressure values P ₂ and ΔΡ ₂ the concentration of the gaseous pollutant in the product gas-containing gas mixture. The method of any preceding claim, wherein the product gas is hydrogen gas. The method of any preceding claim, wherein the adsorbent comprises carbon molecular sieve (CMS) material. A method according to any preceding claim, wherein the carbon molecular sieve (CMS) material contains pores with a diameter in the range between 0.2 nm and 0.4 nm. Device (10, 20, 30, 40, 50, 60, 70, 80, 90, 100) for determining the concentration of a gaseous pollutant in a product gas-containing gas mixture, at least comprising an absorber (1) containing an adsorbent (2) is included for the product gas and the impurity and is provided with inlet and outlet means and pressure measuring means for the gas mixture, characterized in that the adsorbent (2) is selected from a group of adsorbents having properties such that an adsorption equilibrium between adsorbed product gas and gas phase product gas is established within a first period of time Ati and an adsorption equilibrium between adsorbed pollution and gas phase pollution is established within a second period of time At ₂ , wherein the first period of time Ati is a predefined value shorter than the second period of time ht ₂ . The device (40, 50) of claim 12, wherein the absorber (1) includes an inlet (3) and an outlet (9), the inlet (3) being coupled to a first buffer vessel for storing a amount of the gas mixture, and the outlet (9) is coupled to a second buffer vessel for storing gas mixture withdrawn from the absorption vessel (1). The device (60, 70, 80, 90, 100) according to claim 12, wherein the absorber (1) is coupled to a first inlet conduit (4) for introducing an amount of the gas mixture and to a second inlet conduit (14) for introducing a quantity of pure product gas, and is provided with an outlet (9). The device (90, 100) of claim 14, wherein the second inlet conduit (14) is coupled to a first buffer vessel for storing an amount of pure product gas, and the outlet (9) is coupled to a second buffer vessel for storing gas mixture withdrawn from the absorption vessel (1). The device (30) according to any one of claims 12-15, wherein the pressure measuring means comprise a differential pressure sensor (13). Device (30) according to claim 16, characterized in that the differential pressure sensor (13) is directly coupled to the absorber (1) on a first pressure measuring side and is coupled to the second pressure measuring side via at least one valve (12). absorber (1). 18. Device (10, 20, 30, 40, 50, 60, 70, 80, 90, 100) according to any one of claims 12-17, wherein the volume of the absorber (1) is less than 0.5 liters, at is preferably less than 0.1 liters.