Device for Removing One or More Undesirable or Dangerous Substances From a Gas or Vapor Mixture and a Gas Mask Comprising Such a Device

The present invention relates to a device for removing one or more undesirable substances or dangerous substances for humans from a gas or a vapor mixture, a gas mask filter, comprising such a device, a gas mask comprising such a filter and a method for warning of the presence of undesirable or dangerous substances.

Filters are used in order to remove dangerous substances from the air. Gas masks provided with filters are for example used for removing many sorts of poisonous components from air to be breathed.

In certain professions it is advisable to wear a gas mask. Furthermore, national laws increasingly require that the gas masks be worn for example in the building profession by painters and fitters who in their daily work in enclosed areas run a relatively large risk of coming into contact with dangerous chemicals. Gas masks are also worn in war situations.

The removal of undesirable or dangerous substances in vapor or gas form is presently, usually carried out in a gas mask filter by means of adsorption of these substances onto a layer of activated carbon. The more dangerous substances are adsorbed, the more the layer of activated carbon is saturated whereby the adsorption capacity of the filter decreases in time. The capacity of a filter is difficult to predict. The rate at which such filters are used up is an uncertain factor, since this is dependent on parameters such as the environmental temperature, the nature and concentration of the contaminants to be adsorbed and the rate and amount of breathing of the gas mask user. In practice the filters are seldom changed at the correct moment, i.e. the moment in time whereby adsorption in (substantially) no longer possible and as a consequence whereby dangerous substances begin to reach the user. When filters are changed too early, this leads to an unnecessary high usage thereof with the accompanying economic disadvantages, whilst changing a filter too late means that the user runs the risk of damage to the health.

It is an object of the present invention to substantially obviate one or more disadvantages of the state of the art, such as the above mentioned disadvantages, and/or to provide an improved use of a gas mask especially by providing an alarm with respect to the saturation level of the filter of a gas mask.

The present invention provides a device for removing one or more undesirable or dangerous substances for the human race from a gas or vapour mixture, said device comprising:

a predetermined amount of adsorbent for adsorbing the substances and an odourant for releasing an odour in order to alarm a person, wherein the odourant is arranged in such a manner that maid odourant is displaceable by the substances (adsorbates), following a predetermined level of saturation of the adsorbent.

Organic vapors and dangerous substances are accordingly removed from the environmental air by means of adsorption into the device. On coming into contact with the vapors/dangerous substances, the odourant is displaced such that the user smells the odourant.

The device is preferably provided with an odourant substrate, whereon the odour is loaded.

Since the odourant is itself loaded onto a substrate, displacement of the odourant by means of adsorption of the dangerous substances onto the substrate at the expense of the odourant is effected, whereby the odourant is actively displaced into the environment by the adsorbates.

The adsorbent for adsorbing the dangerous substances in preferably substantially unloaded in order to provide a good adsorbing capacity.

The density of the odourant substrate can differ from the density of the adsorbent. When the air resistance of the odourant substrate is chosen to be lower than the adsorbent, more air flows through the odourant substrate with respect to the adsorbent, than in comparison with a device wherein the adsorbent and the odourant substrate have the same densities such that the odourant is more rapidly displaced.

In the case wherein the odourant substrate has a greater density than the adsorbent, displacement of the odourant accordingly occurs at a slower rate.

The device according to the present invention can thus be made to meet the requirements of different users taking into consideration the displacement time whereby a certain degree of safety is built into the device.

The adsorbent and/or the odourant substrate are preferably substantially micro and/or macro and/or mesoporous in nature.

A microporous structure yields a good adsorbent capacity at a low relative pressure and displacement of the odourant is facilitated by means of the meso and macro-pores. The adsorbent and/or the odourant substrate is preferably substantially hydrophobic in nature. Accordingly, displacement of the odourant is not brought about by means of water vapor which could lead to a false indication of the consumption of the device.

In order to provide a consistent adsorption and desorption, the adsorbent and/or the odourant substrate are preferably homogenous.

The adsorbent and/or the odourant substrate preferably comprise activated carbon which is a very efficient adsorbent.

The activated carbon is preferably synthetic in order to be as homogenous as possible and the activated carbon is preferably chosen from the group consisting of R1 carbon (Norit), Saratoga carbons.TM. (Blucher) and ELC carbon.TM. (Norit), since these provide good results.

The odourant preferably has a characteristic smell and is substantially harmless to the health.

Furthermore the odourant preferably has a low odour barrier.

By odour it is meant that: the concentration of a substance in the air is such that 50% of people in the vicinity are able to smell the odour. Accordingly, a good perception of the odour at low concentrations thereof is ensured and the amount of the odourant substrate with respect to the adsorbent can be limited.

The odourant is preferably chemically inert in order to ensure that no chemical reaction takes place, which could possibly negatively affect the functioning of the device or the perception of the odour, and the odourant preferably has a boiling point of 100.degree. C. or less, in order to provide a good displacement.

The odourant is crotonaldehyde, cyclohexane, butylamine, diisopropylamine, ethylidenenorborene, triethylamine, isoamylacetate, diisobutylketone, butylene, butylene cellosolveacetate, ethyl mercaptan, butyl mercaptan, ethylene mercaptan or methylcyclohexane. Preferably, the odourant is cyclohexane, isoamylacetate, butylene, butyl mercaptan, ethyl mercaptan or ethylene mercaptan, and most preferably is isoamylacetate.

Isoamylacetate is most preferred by way of its characteristic smell, low odour barrier and the fact that this is substantially harmless for humans.

The odourant can be loaded onto the substrate in the range of 0.01-0.5, preferably 0.1-0.4 and most preferably 0.2-0.3 grams of odourant per gram substrate in order to enable a good desorption of the odourant.

The odourant substrate is preferably provided with protection means in order to protect and shield odourant substrate from the adsorbent, wherein the protection means preferably comprises a tube of which both ends are open, positioned in the adsorbent, wherein the odourant substrate is arranged with this tube.

Accordingly, the influence of the adsorbent on the odourant substrate and vice versa is minimized. The ratio of the odourant substrate surface area to the surface area of the adsorbent lies in the range of 1:5000, preferably 1:1000, more preferably 1:100 and most preferably about 1:60.

On arranging the odourant substrate surface with respect to the adsorbent, the concentration of odourant in the effluent can be increased or decreased according to the desires of the user.

The odourant substrate which is arranged in the tubes of which both ends are open, can be arranged in a foam-like material, preferably an open foam, in order to provide an easy positioning of the tube within the device and furthermore to yield a good consistent air resistance.

According to another aspect of the present invention, there is provided a gas mask filter, comprising the above mentioned device.

According to another aspect of the present invention there is provided a gas mask, comprising such a gas mask filter.

The present invention furthermore relates to the use of the above device for removing one or more undesirable or dangerous substances for humans from a gas or vapour mixture, and for warning of the saturation level of the adsorbent by means of odour release.

Since there is no effective manner at the moment for warning gas mask users of the level of saturation of the gas mask filter, the gas mask filter according to the present invention solves this problem.

The invention furthermore relates to a device and use of this device, comprising a tube holder with an open end and a substrate loaded with an odourant for use in a gas mask filter and/or a gas mask. The odourant is crotonaldehyde, cyclohexane, butylamine, diisopropylamine, ethylidenenorborene, triethylamine, isoamylacetate, diisobutylketone, butylene, butylene cellosolveacetate, ethyl mercaptan, butyl mercaptan, ethylene mercaptan or methylcyclohexane. Preferably, the odourant is cyclohexane, isoamylacetate, butylene, butyl mercaptan, ethyl mercaptan or ethylene mercaptan, and most preferably is isoamylacetate.

Such a device can be arranged in existing gas masks in order to warn gas mask users of the level of saturation of the gas mask filters.

Other applications of a device according to the present invention include filters and air fresheners, for example bio-bins, toilets and the like.

The present invention will now be described by way of the following specific description, model calculations and experimental results, wherein reference is made to the accompanying figures, wherein:

FIG. 1 shows a side view of a first device according to the present invention;

FIG. 2 shows a side view of a second device according to the present invention;

FIG. 3 shows a sequence wherein the device from FIG. 1 is shown, wherein subsequent levels of saturation are depicted;

FIG. 4 shows a perspective, partially cut away view of a gas mask, comprising the device from FIG. 1;

FIG. 5 schematically shows a second system used by the inventors to research the displaceability of odourants from a device as shown in FIG. 1;

FIGS. 6 to 20 show graphically the manner of displacement of varying odourants by varying adsorbates;

FIG. 21 shows the influence of the air resistance on the displacement of isoamylacetate from Saratoga carbon;

FIG. 22 shows the influence of the positioning of the odourant subtrates in the device;

FIG. 23 shows the influence of the odourant loading on the active carbon;

FIG. 24 shows the influence of the height of the odourant substrates in the device;

FIG. 25 shows the influence of the height of the odourant substrates on the displacement of isoamylacetate from ELC carbon.

FIG. 26 shows a side view of a third device according to the present inveention; and

FIG. 27 schematically shows a first system used by the inventors in order to research the displaceability of odourants.

A device 1 (FIG. 1) consists of a layer of adsorbent 2, a tube 4 provided with an open end arranged in the layer 2, in which tube 4 a substrate 6 loaded with an odourant, the so called odourant substrate, is arranged.

Dimensions and characteristics of the device 1 are as follows:

A second device 8 (FIG. 2) according to the present invention consists of a first layer of adsorbing carbon 10, three tubes 12, 14, 16 with open ends, which tubes are arranged in varying positions in the layer 10, and in which tubes activated coal layers 17, 19, 19 are arranged, wherein the layers of activated carbon are loaded with differing odourants.

A third device 50 (FIG. 26) according to the present invention, consists of a first layer of adsorbing carbon 52 and a layer of carbon 54 loaded with an odourant, which layer in arranged directly in the first layer 52.

This embodiment (50) provides an economic advantage with respect to the first two embodiments, since in this case, the odourant substrate is not arranged in a tube.

FIG. 3 shows how the layer of adsorbent 2 becomes saturated in time as depicted by 3, 3iv and 3v until the mass displacement zone has reached the front side of the odourant substrate at which moment, the displacement process starts. At this point in time, odour can be released and detected.

A gas mask 20 (FIG. 4) according to the present invention, comprises eye glasses 22, a replaceable filter 24, a nose cap 28, and an air outlet 30. A device according to the present invention as shown in FIG. 1 is arranged in the filter 24.

A computer model was developed by the inventors, in order to investigate the displaceability of different odourants from activated carbon by means of different adsorbates.

The computer model calculates the loading of odourant on the activated carbon before exposure to the adsorbate (begin situation) and also calculates the loading of the odourant on the activated carbon when this is in equilibrium with a known concentration of adsorbate (end situation).

The level of loading in both situations, (begin, end) was calculated with the aid of a model in the form of a Pascal program. With this model it was determined whether the amount of odourant per gram activated carbon by "certain smelling" was lower than the amount of odourant per gram activated carbon by the not smelling situation. This was determined to be a necessary provision for the release of the odourant at the moment that the carbon loaded with the odourant comes into contact with the adsorbate. The calculations for not smelling (start situation) were made with the aid of the Dubinin adsorption isotherm comparison, and that for the certain smelling (end situation) was made with the aid of the IAS toth comparison.

At the start situation the odourant substrate loading was calculated when the concentration of contamination in the air was zero and wherein the concentration of the odourant was under the odour barrier.

At the end situation, the calculation was carried out when the concentration of contaminant in the atmosphere reached the MAC level and wherein the concentration of odourant in the atmosphere was above the odour barrier.

By MAC value it is meant the maximum acceptable concentration of a gas, vapour, fuse of a substance in the air at a work place during an 8 hour working day.

The loading of varying odourants on activated Saratoga carbon from the Blucher company, when these were exposed to differing concentrations of benzene are shown below in table 1.

The MAC value of benzene is 30 mg/m.sup.3.

A positive difference between the begin situation and the end situation shows that the odourant was displaced by benzene.

The computer model was also used in order to investigate varying activated carbons loaded with isoamylacetate (IAA) with respect to the displacement thereof by benzene under differing circumstances. The activated carbons used were Saratoga carbon from the Blucher company, ELC carbon from the Norit company, R1-carbon from the Norit company. The results are shown in table 2.

Experimental:

Research into the displacement of an odourant from a layer of activated carbon.

The displacement experiments were carried out in the system 100 (FIG. 27) wherein the reference numerals refer to the following elements:

101=mass flow controller 200 ml/min (HI-TEC)

102=bubble vessel with adsorbent

103=mass flow controller 40000 ml/min (HI-TEC)

104=bubble vessel with distilled water

105=needle valve

106=relative humidity meter (VAISALA)

107=mixing vessel

108=filter box

109=sample vessel with clean carbon

110=sample vessel with odour adsorbed onto the carbon

111=infrared spectrophotometer MIRAN 80 (WILKS)

112=recorder (Kipp & Zonen)

113=flow meter (ROTA)

114=filter box

By arranging the optimum wave lengths of the substances to be adsorbed and the odourant in the infrared spectrophotometer, it was possible to simultaneously determine the concentration of odourant and adsorbent in the effluent. For experiments wherein under dry conditions the displacement of the odourant by the adsorbate was measured, the arrangement was adjusted by leaving out components 4, 5 and C. The amount of carbon in vessel 10 was roughly 0.25 grams (0.5 cm bed height), in these experiments, the carbon loaded with odourant in vessel 11 was roughly 0.30 grams (0.5 cm bed height). This configuration differs from the system shown in FIG. 5, since the odour alarm is placed behind the adsorption bed. In the system according to FIG. 5, the break through of the adsorbate is determined by the part of the carbon bed arranged parallel to the tube.

For determination of the influence of humid air on the displacement of isoamylacetate by toluene, the arrangement as shown in FIG. 5 was used. The relative humidity by these experiments was equal to 80%. With the aid of the mass flow controller the concentration of toluene was arranged. By arranging the wave lengths of isoamylacetate, toluene and water vapour in the infrared spectrophotometer, it was possible to determine the concentrations of all three substances simultaneously in the effluent.

The conditions of these experiments are shown below in table 3, wherein the results in FIGS. 6 to 20 are shown.

Table 4 provides a summary of eight of the values measured during these experiments:

Further experiments were carried out in the system 30 (FIG. 5), see below.

A stream of air saturated with toluene (stream A) was guided through a mixing vessel 32 by means of pressure air stream B with the correct relative humidity. The mixing vessel 32 was used in order to obtain a good mixing. Subsequently, the air containing the toluene was guided, not simultaneously, through two devices 34, 36, equipped with two odourant substrates 35, 37 respectively, whereafter the effluent was analyzed in a Miran 80 infrared spectrometer 38 and the results were recorded in recorder 40.

The system 30 further consisted of a security filter 42, rotameters 44 and valves 45 in order to guide the stream in the correct direction.

The devices 34 and 36 were firstly conditioned for 20 minutes. A clean air stream was guided through the devices. During this conditioning, the gas stream behind the devices was measured to detect for the presence of any odourant. If the odourant was detected, there was a question of desorption and the experiment was stopped. Following conditioning, a gas stream with dangerous substances was guided through the devices, in order to carry out the following experiments:

Devices 34 and 36 were arranged as follows:

Odourant substrate device 34:

0.07 g Saratoga carbon with a diameter of 6 mm, a height of 5 mm and loaded with 0.1724 gram IAA per gram Saratoga carbon.

Odourant substrate device 36:

0.040 g Saratoga carbon loaded with 0.1724 g/g IAA with a diameter of 6 mm, a height of 5 mm in 45 PPI reticulated foam.

Adsorbent in devices 34 and 36

Norit R1 carbon having a diameter of 50 mm and a height of 10 mm

Experimental conditions:

Temperature=25.degree. C.

Relative humidity=0%

Air with toluene stream per minute=7.5 L/min

Concentration toluene in the system (stream A+B)=2800 mg/m.sup.3

Unless otherwise reported, the odourant substrate was arranged on the underside of the layer of adsorbent.

The results are shown in FIG. 21.

The influence of the depth of the odourant substrate in the device on the displacement of isoamylacetate and the breakthrough of toluene was measured. The experiment was carried out in a system as shown in FIG. 5. The depth of the odourant substrate S in the device, is the distance from the surface of the adsorbent to the surface of the odourant substrate (see FIG. 1).

The device was arranged as follows:

The results are shown in FIG. 22.

Differing amounts of IAA per unit weight were loaded onto the ELC carbon and displacement was carried out by means of toluene in the system as shown in FIG. 5.

The results of this are shown in FIG. 23.

With this experiment the object was to research whether the height of the device influenced the moment of displacement of the odourant with respect to the adsorbates travelling through the device.

The odourant Substrate with a loading of 0.23 35 g/g IAA was placed at the end of the device and ELC carbon was used as the odourant carrier.

The experiment was carried out in the system as shown in FIG. 5, wherein two differing bed heights (B) of 1 and 2 cm respectively adsorbent were chosen, as shown in FIG. 1 for the devices 34, 36 respectively. The results of this are shown in FIG. 24.

This experiment was carried out to research whether the height of the odourant substrate influenced the moment in time that the odourant was released and the concentration at which it was released. ELC carbon was used as carrier for the odourant and the odourant substrate was arranged at the bottom of the device. The results of this experiment are shown in FIG. 25.

The results of this experiment are shown in FIG. 25.

The requested rights are in no way limited by the above shown and described embodiments of the present invention, rather the requested rights are determined in the first instance by the following claims, the scope of which caters for many possible variations.