The present invention relates to an active alcohol filter, an apparatus containing the filter, a method for preparing said active alcohol filter and its use for removing an al cohol from a gas or a gas mixture.

Alcohols such as ethanol are omnipresent in our environment, for instance ethanol is widely used as cleaning and disinfection agent, with concentrations easily reaching 10000 parts per million by volume (ppm). ¹ Furthermore, alcohol concentrations in breath can reach up to 410 ppm after moderate alcohol consumption (0.028 %) in blood). ² Thereby, alcohols can act as interferants for many applications, for instance, gas sensing. Removal of the alcohols is important for accurate and precise meas urements of the target gases.

In contrast to the omnipresence of alcohols even in high concentrations, breath markers, such as acetone, isoprene and ammonia, are contained in significantly low er concentrations. Therefore, the alcohols, which interfere with the breath markers, are to be removed, wherein the breath markers shall be essentially unaffected.

One study showed complete ethanol removal by an active porous Ga ₂ 03 filter oper ated at 800°C for selective methane sensing. ³ However, it can be expected that most organic compounds will be converted at such high temperatures, including target an alytes. Also, this temperature is hardly compatible with portable device integration. Finally, a modular packed bed filter with Au nanoparticles on Fe ₂ 03 support was in vestigated to remove ethanol and CO, for selective propane and methane sensing. ⁴ At an operation temperature of 150-200 °C, both ethanol and CO were completely converted while propane and methane remained unaffected.

List of References

1. Bessonneau, V. & Thomas, O. Assessment of exposure to alcohol vapor from alcohol-based hand rubs. Int. J. Environ. Res. Public Heal. 9, 868-879 (2012). 2. Vukovic, J., Modun, D. & Markovic, D. Comparison of breath and blood alcohol concentrations in a controlled drinking study. Cent. J. Subst. Abus. Alcohol. 3, 1029 (2015).

3. Fleischer, M., Kornely, S., Weh, T., Frank, J. & Meixner, H. Selective gas de tection with high-temperature operated metal oxides using catalytic filters. Sens. Ac tuators B. Chem. 69, 205-210 (2000).

4. Oliaee, S. N., Khodadadi, A., Mortazavi, Y. & Alipour, S. Highly selective Pt/Sn0 ₂ sensor to propane or methane in presence of CO and ethanol, using gold nanoparticles on Fe ₂ 03 catalytic filter. Sens. Actuators B. Chem. 147, 400-405 (2010).

The technical problem underlying the present invention is to provide a filter, its use, and a method for its production, wherein the drawbacks of the prior are avoided and in particular a filter is provided, with which alcohols can be removed from a gas or a gaseous mixture continuously and selectively.

This has been achieved by the active alcohol filter as defined in claim 1 , the appa ratus of claim 13, the method for its production as defined in claim 16 and its use as defined in claim 17. Preferred embodiments are defined in the dependent claims.

According to the present invention, there is provided an active alcohol filter for re moving ethanol from a gas or a gaseous mixture, wherein the active alcohol filter comprises or consists of a catalyst configured to selectively convert alcohols. The alcohols are preferentially converted to non-sensitive species, in particular carbon dioxide and water. The term“non-sensitive species” means that a detector signal obtained from the exposure to such a species is at least 10 times, in particular at least 50 times, for example at least 100 times smaller than the signal obtained from exposure to the target analyte, e.g. the breath marker to be analyzed (at same expo sure concentrations), including alcohols.

Filtration takes place by the catalytic conversion of the alcohol. As mentioned above, alcohols, for example ethanol, are omnipresent in high concentrations. When breath ing air is analyzed regarding the presence of breath marker (compounds that are re lated to disorders of which are otherwise medically relevant), the alcohol adversely affects the detection of the breath markers. According to the present invention, these alcohols can be removed from a gas or gaseous mixtures, i.e. a gas containing at least two compounds, so that the alcohols do not any longer negatively interfere with the detection of the breath markers.

An alcohol is a hydroxylated aliphatic or alicyclic hydrocarbon, in particular with 1 to 6 C-atoms. Examples of alcohols are ethanol, propan-2-ol and propan-1 -ol.

The filter according to the present invention selectively and catalytically removes al cohols from a gas or a gaseous mixture. That is, other compounds are essentially not affected, wherein essentially unaffected means that less than 50%, in particular less than 30%, for example less than 10 % of these other compounds are reacted. Exam ples of such other compounds are isoprene, ammonia, acetone, formaldehyde, H ₂ , methane, pentane, ethane, N0 ₂ , NO, CO, S0 ₂ , toluene, CS ₂ , COS, CH ₅ N, HCN, and C ₂ H ₆ S.

It has furthermore be found that the filter according to the present invention can con vert alcohols to water and carbon dioxide at lower temperatures than other com pounds are reacted, for example the above mentioned other compounds. For exam ple, the filter according to the present invention converts the alcohols at a tempera ture of about 30°C lower than the temperature at which the other compounds for ex ample acetone, are reacted. Therefore, the feature that the filter according to the present invention selectively removes alcohols is to be understood in the sense that this takes place at the respective temperature at which the filter converts the alcohol but essentially not the other compounds.

The filter comprises or consists of a catalyst, in particular an oxide, in particular a metal oxide. The metal oxide can be a metal oxide containing only one type of metal, so that is it is not a mixed oxide. In particular, the metal present in the metal oxide is an element from group 1 -12 of the periodic table of elements, in particular any ele ment in the d-block on the periodic table of elements (groups 3-12). The groups are defined according to the lUPAC (International Union of Pure and Applied Chemistry).

Examples of metal oxides are: Mn ₃ 04 _, MnO, Mn ₂ 0 ₃ , Fe ₂ 0 ₃ , CuO, Ce0 ₂ , ZnO, Y ₂ 0 ₃ , Al ₂ 0 ₃ (group 13), Zr0 ₂ , V ₂ Os, ln ₂ 0 ₃ (group 13), Ti0 ₂ , Sn0 ₂ (group 14), W0 ₃ , Mo0 ₃ , and Bi ₂ 0 ₃ (group 15). ln particular, ZnO is suitable since it has a high selectivity for ethanol conversion over acetone conversion of 85 % and 5%, respectively.

The catalyst, for example, the oxide, in particular the metal oxide, is noble metal free meaning that the content of any noble metal impurity, in particular at the surface of the filter material, is less than 0.1 wt%, in particular less than 0.05 wt%, in particular less than 0.01 wt%, in particular less than 0.001 wt%.

In a further embodiment, the filter can meet at least one of the following parameters independently:

• Weight of filter material: It can be smaller than about 10 g, in particular smaller than about 5 g, in particular smaller than about 1 g, for example smaller than about 500 mg, for instance about 250 mg, in particular 5 mg to 50 mg. The amount of filter material can depend on the amount of alcohol to be removed so that higher amounts of filter material are used when higher amounts of alcohol are to be removed.

• Filter surface: The specific surface area of the filter can be larger than about 5 m ² /g, for example larger than about 10 m ² /g, like larger than about 30 m ² /g, for ex ample larger than 50 m ² /g. The surface is thereby measured by BET nitrogen ad sorption.

• Temperature: The filter can be operated at a temperature below about 300 °C, for example below about 250 °C, below about 200 °C, below about 150 °C, for ex ample at about 100 °C. The device according to the present invention can be config ured by respective means to provide the temperature.

• Cross-sectional area: The filter can have a cross-sectional area smaller than about 350 mm ² , for example smaller than about 100 mm ² , smaller than about 20 mm ² , for example about 12 mm ² .

• Filter length: The filter can have a length smaller than about 20 cm, smaller than about 10 cm, smaller than about 5 cm, for example smaller than about 3 cm for example about 1 cm.

• The filter is configured to remove an alcohol concentration, in particular etha nol concentration of up to 100 ppm, in particular up to 500 ppm, in particular up to 1000 ppm, in particular up to 5000 ppm, in particular up to 10000 ppm, in particular up to 20000 ppm.

• The maximum alcohol, in particular ethanol, concentration to be removed can be 20000 ppm. That is, the filter is configured to remove this amount of alco hol/ethanol.

Concentrations in ppm refer to ppm by volume.

It has been advantageously found that with any of the above parameters it is possible to provide a particular useful miniaturization of the device so that a very compact de vice can be obtained, which can be easily held in one hand of a human being. Fur thermore, a good conversion of the alcohol can be achieved providing a good alcohol removal.

In one embodiment, the filter is selected from the group consisting of nanoparticles (having a size of 1 nm to 100 nm), microparticles (having a size larger than 100 nm), non-porous and porous materials, in particular microporous materials (pores size 2 nm and less), mesoporous materials (pore size between 2 and 50 nm) and macroporous materials (pores size 50 nm and larger).

To remove ethanol even at very high concentration at small filter size, the filter mate rial should have a high specific surface area. This can be achieved by small nanopar ticles or by porous materials.

In one embodiment, the filter is combined with a detector for detecting gases. There fore, there is provided an apparatus for gas analysis comprising the above described filter and a detector. The detector is combined with the filter in such a way that the analysis takes place after removal of the alcohol from the gas or the gaseous mix ture.

The detector (also referred to as sensor) that can be generally used in combination with the filter are sensors of resistive type like chemo-resistive metal oxides, ion con ductors, polymers, carbon nanotubes, or graphene; of amperometric type like elec trochemical sensors; of capacitive type; of potentiometric type; of optical type; of thermal type; of thermochemical type; of thermophysical type; of gravimetric type; of biochemical type or any combination thereof.

In one embodiment, the detector can be a metal oxide gas sensor, for example se lected from the group consisting of

• Sn02, in particular doped Sn02 (e.g. 1 mol% Pd-, 6 mol% Si-, 0.15 mol% Pt- or 4.6 mol% Ti-doped);

• WO3, in particular doped WO3 (e.g. 10 mol% Si-, or 10 mol% Cr-doped);

• ZnO, in particular doped ZnO (e.g. 2.5 mol% Ti-doped);

• M0O ₃ , in particular doped M0O ₃ (e.g. 3 wt.% S1O ₂ added);

• ln ₂ 0 ₃ , in particular doped ln ₂ 0 ₃ .

• Ti0 ₂ , in particular doped Ti0 ₂ .

• CuO, in particular doped CuO.

• Cu ₂ 0, in particular doped Cu ₂ 0.

Metal-oxide gas sensors offer a simple application, high miniaturization potential, low power consumption and minimal production costs. The mechanism relies on changes of electrical conductivity by the change in the surrounding atmosphere. Gas detection is related to the reactions between ionosorbed surface oxygen and target analyte gas (receptor function). The equilibrium state of the surface oxygen reaction is shifted by the target analyte (receptor function) changing the sensing material’s resistance (transducer function).

The filter can be configured as a packed bed, coated surface or foam, pressed pellet or membrane. Specifically, the filter can be configured as a packed bed of particles; as a coating of the gas sensing nanoparticles; as a membrane; as a foam structure; or as an overlayer of the gas sensing film. The filter can be arranged as a dead-end configuration, i.e. the sensor is placed in a cavity that is closed by the filter, or in an open-end configuration, i.e. the gas can enter through an inlet (that might comprise the filter) and exit by an outlet, therefore allowing an active flow through the filter. These configurations are very suitable for miniaturizing the device so that a very compact device can be obtained which can be easily held in the hand of a human being.

The filter can be heated at a given temperature and/or irradiated. Thereby, the heat ing and/or irradiation may change the reactivity, selectivity and/or recovery of the fil ter. The heating and/or irradiation may be constant, pulsed or triggered (only at a given time point), for instance after sampling the gas sample.

Further, there is provided a Method for preparing an active alcohol filter, in particular as described above for removing alcohol from a gas or a gaseous mixture by flame spray pyrolysis, comprising the following steps:

(a) preparing a precursor solution of the catalyst;

(b) producing a spray of the precursor solution;

(c) igniting the spray;

(d) collecting particles obtained by igniting the spray by a means for collecting particles; and

(e) removing the catalyst particles from the means for collecting particles in step (d).

For example, metal oxide nanoparticles can be synthesized with a known flame spray pyrolysis (FSP) reactor. Therefore, FSP precursor solutions known in the art were prepared as exemplified in Table 1. The precursor is a metal compound con verter in the FSP method to the metal oxide. As solvent, organic, combustible sol vents can be used, like xylene, 2-propanol, 2-ethylhexanoic acid, and acetonitrile. The precursor solution can be supplied through the FSP nozzle at a rate of for exam ple about 5 mL/min and dispersed by for example about 5 L/min oxygen flow (for ex ample at 1.6 bar back-pressure) into fine droplets (i.e. a spray). The spray can be ignited for example by a ring-shaped methane pilot flame (for example at 1.2 L/min CH ₄ and 3.2 L/min O2). Generated particles can be collected for example at 50 cm height above burner (HAB) on a water-cooled glass-fiber filter (GF6 Albet- Flahnemuehle, 257 mm diameter) using a vacuum pump Seco SV 1025 C, Busch, Switzerland). Product nanoparticles can be removed from the filter and sieved to re move any filter residues. Annealing can be conducted for example at about 300 °C for about 5 h using an oven (Carbolite Gero, 30-3000 °C).

Table 1. Precursor composition. The molarity indicated corresponds to the total metal content.

The active alcohol filter can be used for selectively removing alcohols from a gas or a gas mixture. The filter can be operated at a temperature of about 300 °C or less.

In particular, the filter can be used to remove alcohols continuously from air. Fur thermore, the filter according to the present invention can be used to remove unde- sired alcohols, for example ethanol, from gas mixtures containing target analytes, which shall be analyzed, for example breath markers, like acetone, isoprene and ammonia. The high concentration of omnipresent ethanol interferes with the analysis of the target analytes making their analysis difficult. The filter selectively removes the alcohols from the gas to be analyzed so that the analysis of the target analytes is not any longer interfered by the alcohol.

The present invention is further described by the following figures and examples. It is to be noted that the figures and the examples are only intended for illustrating the invention but not to restrict the invention thereto.

Figure 1 shows the concentration of ethanol, acetone, isoprene and ammonia in various sources.

Figure 2 shows the filter according to the present invention used together with a sensor.

Figure 3 shows the filter in a possible configuration according to the present in vention for continuously removing ethanol.

Figure 4 shows the conversion of ethanol in the concentration range of 0.2 to 100 ppm over 18 mg of a ZnO catalyst at 230 °C having a specific surface area of 55 m ² /g

Figure 5 shows the filter performance for elevated concentrations of ethanol and lower concentrations of acetone.

Figure 6 shows various concentrations of ethanol and acetone with and without filter.

Figure 7 shows ethanol conversion at different temperatures for different filters.

Figure 8 shows the temperature profile for 5 ppm acetone and ethanol over a

ZnO filter.

Figure 9 shows the difference between doped and undoped (noble metal free) catalysts.

Materials and Methods:

Metal oxide nanoparticles were synthesized with a flame spray pyrolysis (FSP) reac tor. Therefore, FSP precursor solutions were prepared according to Table 1 above. The liquid precursor solution was supplied through the FSP nozzle at a rate of 5 mL/min and dispersed by 5 L/min oxygen flow (1.6 bar back-pressure) into fine drop lets. The spray was ignited by a ring-shaped methane pilot flame (1.2 L/min CH ₄ and 3.2 L/min O2). Particles were collected at 50 cm height above burner (HAB) on a wa ter-cooled glass-fiber filter (GF6 Albet-Hahnemuehle, 257 mm diameter) using a vac uum pump (Seco SV 1025 C, Busch, Switzerland). Product nanoparticles were re moved from the filter and sieved to remove any filter residues. Annealing was con ducted at 300 °C for 5 h using an oven (Carbolite Gero, 30-3000 °C).

The specific surface area (SSA) was determined using nitrogen adsorption at 77 K (Micrometries II Plus). Samples were degassed with N ₂ at 150 °C for 1 h prior to the measurements.

For catalytic measurements, calibrated gas standards for acetone (10 ppm in syn thetic air, Pan Gas), isoprene (500 ppm in synthetic air, Pan Gas) and ethanol (10 and 500 ppm in synthetic air, Pan Gas) were used. Synthetic air (Pan Gas, CnHm & NOx <0.1 ppm) was used as a diluent. In addition, synthetic air was connected to a water bubbler to add humidity in the desired amount. The total flow rate was 200 mL/min at 50 % relative humidity (RH), if not stated otherwise. To prevent condensa tion and analyte adsorption, the tubing was made from inert Teflon and heated to 60 °C.

The catalytic reactor unit consisted of a quartz glass reactor with inner diameter of 4 mm. The powder was fixed in a packed bed configuration inside the reactor using quartz wool. For consistency, all catalyst powders were used at an amount corre sponding to 1 m ² surface area as determined according to the Brunauer-Emmett- Teller theory (BET using nitrogen adsorption). The glass reactor was placed inside an oven (Nabertherm, P320) and connected to the gas mixing system through Teflon tubing.

Reaction products were analyzed using a bench-top proton transfer reaction time-of- flight mass spectrometer (PTR-TOF-MS 1000, lONICON, Austria). The drift voltage, temperature and pressure were set to 600 V, 60 °C and 2.3 mbar respectively. H30+ ions were used as primary ions. Breath was collected with a breath sampler that consists of an inlet with disposable mouthpiece and an open-ended tube to capture and store end-tidal breath. After 10 s of exhalation into the sampler, collected breath was either led through the filter or through a bypass and was then analyzed with the PTR-TOF-MS. Breath was investi gated both, for sober conditions and after moderate alcohol consumption. For the latter the subjet was given 0.3 L of beer to drink (with 4.8 % alcohol content) and asked to rinse his mouth with water. For each experiment, at least two consecutive pulses were analyzed with and without filter. The alcohol concentration in blood was approximated using a commercial alcohol breath tester (Drager 3820).

Results

Fig. 1 shows the concentration of ethanol in sober breath (endogenous), after alcohol consumption (exogenous) and in the background (from cleaning and disinfection). The ethanol concentration is compared with the concentration of the breath markers acetone, isoprene and ammonia. As can be taken from this comparison, ethanol is omnipresent in high concentrations which can negatively interfere with the analysis of breath markers.

In Fig. 2, there is shown how the filter 1 according to the present invention converts ethanol (circles) to carbon dioxide and water. In contrast, the breath marker acetone (squares) and isoprene (triangles) passes the filter 1 unhindered, i.e. they are essen tially not converted to carbon dioxide and water. In Fig. 2, the filter 1 is contained in a housing 2 which is connected to the sensor 3, which is contained in a housing 4, by a connection means 5 which in the case of the apparatus of Fig. 2 is an opening be tween the two housings 2 and 4.

Fig. 3 shows the filter 1 according to the present invention for removing/converting alcohol continuously. The filter 1 is contained in the housing 2 with a first and a sec ond opening 6, 7. The filter 1 is located in a passage 8 from the first opening 6 to the second opening 7 so that a gas mixture containing the alcohol introduced in the first opening 6 can flow through the housing 2 passing the filter 1 and leaving the housing 2 through the second opening 7. The passage of the gas mixture is indicated in Fig. 3 by arrows. By such a configuration, the alcohol is continuously converted to carbon dioxide and water so that as a result the alcohol is continuously removed from the gas mixture. Further, for activating the filter, means for heating 9 and/or means for irradiating 10 can be provided.

Fig. 4 shows the conversion of ethanol concentrations ranging from 0.1 to 100 ppm by 18 mg of a ZnO catalyst operated at 230 °C. The specific surface area of the cata lyst was 55 m ² /g. The total flow rate was 0.2 L/min at 50 % relative humidity (RFI). Ethanol is continuously removed over the whole concentration range. The error bar represents three independent measurements.

Fig. 5 is a representation of the filter performance for elevated concentrations of eth anol (square) and lower concentrations of acetone (triangles). The formation of acet aldehyde is shown (circles). Errors are calculated from three independent measures. ZnO catalysts show the desired catalytic behavior, which includes the conversion of intermediately formed acetaldehyde. It is known that acetaldehyde is formed during ethanol oxidation as first intermediate byproduct. Because acetaldehyde is not an inactive analyte for sensors, e.g. Sn0 ₂ sensors, this compound is undesired. By us ing the filters according to the present invention, in particular ZnO, the formed acetal dehyde is further reacted.

Fig. 6 shows ethanol and acetone concentrations measured in human breath before and after consumption of 0.3 L beer (4.5 vol% alcohol content). ZnO particles (55 m ² /g, 18 mg of catalyst used) were used as filter and operated at 230 °C. Before al cohol consumption and without filter, both acetone and ethanol are clearly detected by the filter. After alcohol ingestion, the ethanol content rises up to 80 ppm and is detected by the sensor without filter. Using an active ZnO filter completely removes the ethanol interference while acetone is remains unaffected. Please note that the slight change in acetone levels with and without filter lies within the variability of two consecutive breath pulses.

Fig. 7 shows the conversion of ethanol using CuO (squares), ZnO (circles) and Ce0 ₂ particles (triangles), respectively. The specific surface area of the particles were 75 m ² /g (CuO), 55 m ² /g (ZnO) and 140 m ² /g Ce0 ₂ ). The tested mass was chosen such that the total surface area corresponds to 1 m ² , i.e. 13 mg of CuO, 18 mg of ZnO and 7 mg of Ce0 ₂ particles. The total flow was 0.2 L/min at 50% RH. The filter was then heated to the depicted temperatures at a heating rate of 10 °C/min where 1 ppm eth- anol was added (at a constant temperature). Afterwards, the filter was heated to the next higher temperature (as indicated by the symbols). Conversion of ethanol starts at about 100 °C and is fully converted below 200 °C for all tested materials.

Fig 8 shows the continuous conversion of 5 ppm ethanol (dotted) and acetone (solid), as well as the formation of acetaldehyde (dashed), by ZnO particles (18 mg, 55 m ² /g). During the experiment, the filter is continuously exposed to the analytes and heated to 280 °C at a heating rate of 100 °C/min. The conversion of acetone starts at 215 °C, reaching full conversion at 250 °C. In contrast, ethanol starts to convert at already 190 °C and reaches almost full conversion at the onset of acetone conver sion. Thus, ethanol interference can be removed selectively, while target analytes such as acetone are hardly affected. Also, acetaldehyde is a known intermediate product during ethanol conversion, and a possible interferant for the detector. The filter, however, also converts acetaldehyde, as it’s measured concentration after the filter is negligible.

The performance difference between doped and undoped (noble metal free) cata lysts are shown in Fig. 9. Fig 9a shows the conversion of ethanol (squares), isoprene (circles) and acetone (triangles) on Ce0 ₂ catalyst. Fig. 9b represents the analyte conversion of Au-doped (1 mol%) Ce0 _2.

The catalytic activity of the pure Ce0 ₂ catalyst is shown in Figure 9a. Ethanol (squares) is converted starting at 110 °C and is fully oxidized at 190 °C. This temper ature is lower compared to previous literature, where less than 30 % of ethanol was oxidized at 190 °C. Also isoprene (circles) is oxidized, remarkably already at around 10 °C lower temperatures. Most importantly, the oxidation of acetone (triangles) starts not before 160 °C. As a result, there is a temperature gap between acetone and ethanol conversion that can be exploited for selective ethanol oxidation, as indi cated by the red arrow. That is, ethanol conversion takes place at lower temperatures than acetone conversion so that the filter selectively converts ethanol at these lower temperatures.

Significantly different behavior is observed for Au-doped Ce0 ₂ (Figure 9b). In fact, the onset of oxidation starts even below 100 °C for acetone and isoprene and almost full oxidation is achieved for all analytes at 160 °C. Gold catalysts are known for their high reactivity already at room temperature. However, no ethanol selectivity is achieved, crucial for effective filters. Therefore, pure Ce0 ₂ is better suited for this application. Further experiments with Pd-doped Sn0 ₂ and Au-doped Fe ₂ 03 support these findings that noble metals are highly reactive but unsuitable for selective etha- nol removal. Hence, the filter according to the present invention essentially contains no or only low amounts of noble metals.