GB2574120A

GB2574120A - Improvements in gas storage devices

Info

Publication number: GB2574120A
Application number: GB1905840.3A
Authority: GB
Inventors: Michael Barratt Joe; James Sygrove Matthew
Original assignee: Simply Breathe Ltd
Current assignee: Simply Breathe Ltd
Priority date: 2017-03-01
Filing date: 2017-03-01
Publication date: 2019-11-27
Anticipated expiration: 2037-03-01
Also published as: GB2574120B; GB201905840D0

Abstract

The invention relates to a device 10 for dispensing a gas 30 under pressure, comprising a steel canister 12 filled with activated carbon 14 and the gas at a pressure of between 4 and 17 barg, sealed with a valve assembly 18 allowing release of gas from the canister, wherein the gas is carbon dioxide, oxygen or air. In one embodiment the device is filled with carbon dioxide and includes a high-volume discharge valve 20 making 1t useful as a pet behaviour correction device.

Description

IMPROVEMENTS IN GAS STORAGE DEVICES [0001] This invention relates to improvements in gas storage devices and more particularly to devices filed with e.g. oxygen or carbon dioxide. It also relates to an improved method of storing gases, particularly, oxygen, carbon dioxide or air, in a device, and to the storage device perse.

BACKGROUND [0002] Traditionally canisters filled with gasses are either filled with a compressed gas or utilise a propellant, such as HFA-134a, to facilitate discharge. Such systems suffer from a number of disadvantages.

[0003] By way of example, GB2411812 discloses a pet behaviour correction device comprising a canister filled with a pressurised inert condensed gas, in the form of a hydrofluorocarbon (HFC). In use the gas is discharged, towards the head of e.g. a dog, to generate a hissing sound. However, such a device has a number of limitations including: the undesirable nature of HFC’s (environmental damage) giving rise to their legislative phase out, the fact that their liquid nature limits the orientation of use (they don’t function effectively when inverted), and on depressurisation rapid cooling occurs, which can be distressing for pets if activated too close to the animal, and if triggered accidentally, in e.g. a user’s pocket, can give rise to freeze burns.

[0004] Alternative propellants may be used to replace HFC’s but, for example, hydrocarbon gases, such as butane, are highly flammable and also suffer from volatile substance abuse potential. Many of the propellants will also leave residue deposits which in applications such as gas dusters can cause damage to sensitive electronic equipment. A gas duster is a device that is used to clean hard to reach surfaces, such as the grooves and crevices in equipment and electronic or sensitive appliances that can’t be accessed or cleaned using conventional solvents.

[0005] However, because air and its components including oxygen, nitrogen and carbon dioxide are not readily liquefied, only a small quantity of gas can be stored without the need to provide reinforcement for excessively high pressure.

[0006] W02005/054742 discloses a storage container for a gas comprising a sealed vessel containing an amount of activated carbon and a gas which is adsorbed thereon.

[0007] One such gas is oxygen.

[0008] Containers filled with compressed oxygen may be used for a range of applications, such as, for example, therapeutic or sport enhancement purposes.

[0009] The use of activated carbon as a storage means enables greater volumes of gas to be stored in a given volume. For oxygen this is about two to three times that obtained by compression alone, at the same pressure, depending upon the grade of activated carbon.

[0010] Typically the gas is stored at a pressure of from 4-17 barg (measured at room temperature), and the container typically contains at least 40%, by volume, of activated carbon.

[0011] The device may be adapted to receive a mask, mouthpiece and / or nose piece and typically comprises a valve assembly which allows filling and dispensing. It may also contain a filter between the activated carbon and a valve of the valve assembly.

[0012] The device may be connected to the mask, mouthpiece and / or nose piece via a connector, for example tubing, and these components may be sold separately or as a kit of parts.

[0013] Where the device is filled with oxygen at pressures above about 8 barg it is desirable to use a high activity carbon (one having an activity of above 60% CTC (carbon tetrachloride)), although a lower activity carbon may also be used, particularly at lower fill pressures.

[0014] Applicant has determined that devices comprising activated carbon, which are filed with oxygen or air under pressure, contain not insignificant amounts of carbon monoxide (concentrations of over 100 ppmv) as a result of a reaction between the activated carbon and oxygen. Whilst not inherently dangerous at these levels carbon monoxide has a binding affinity for haemoglobin which is 250 times greater than oxygen. In consequence even relatively low levels of carbon monoxide can negate the benefits obtained from breathing pure oxygen. Indeed at concentrations of 200 ppmv carbon monoxide can cause headache and nausea.

[0015] An aim of the present invention is to ensure that oxygen or air delivered using activated carbon is substantially free of carbon monoxide.

[0016] A second, and independent aspect, is to manage heat affects associated with the filling of canisters with a gas, which aspect is not limited to oxygen. Indeed this second aspect can be a greater problem where the gas is carbon dioxide due to the much greater volumes (as much as 25 times that of compressed carbon dioxide) that can be adsorbed in canisters filled with activated carbon, the adsorption being exothermic.

[0017] Indeed, where the gas is carbon dioxide, W02005/054742 teaches filling the device with solid carbon dioxide or dry ice to counteract any exothermic reaction.

[0018] However, accurately dispensing dry ice proves difficult, and for a 1 I canister, a variation of as little as plus 3 g can give rise to a variance of as much as 1.6 I of carbon dioxide, which can in turn give rise to the over pressurising of the device when it equilibrates to room temperature.

[0019] Alternatively, W02008/064293 teaches a filling methodology, which obviates the need to conduct a stepwise filling process which involves multiple cooling and recharging steps, by placing dry ice in the canister and then crimping a valve assembly to the canister.

[0020] The reason for this methodology is that devices are typically made using aluminium canisters, and a valve assembly is crimped to the canister over a rubber seal. Applicant has determined that due to the high thermal conductivity of aluminium, in small devices (1 I or less) the rapid transfer of heat to the canister can distort the rubber seal causing devices to fail - leak about the crimp - hence the use of the methodology taught in W02008/06429.

[0021] A further and independent aim of the present invention is to find alternative methods to manage heat, or otherwise improve the manufacturing process to ensure simpler and more accurate filling, with reduced device failure, in the manufacture of activated carbon filled devices.

[0022] In contrast to the above, the applicant has determined that, at least for devices of small volume, i.e. a canister with a volume of 1 I or less, by selecting a canister of steel, as opposed to the more conventional aluminium, it is possible to fill the canister using a commercial gasser, in a single or two step process, through the device’s valve assembly at pressures of at least up to 17 barg at room temperature. This obviates the need to either fill a part assembled device and subsequently crimp the valve assembly to the canister or to fill the device in a step wise manner, many times, cooling between each partial fill.

[0023] This has the significant advantages of:

i) Speeding the filling process; and ii) Reducing failures due to either canister failure around the crimp, or the over pressurising of canisters.

[0024] In contrast to the teaching of W02008/064293 the method comprises or consists essentially of gassing a device comprising an activated carbon filled steel canister, in a single or two step process, via its valve assembly.

[0025] The gas is particularly carbon dioxide, but may be oxygen or air.

[0026] The device is preferably one with a canister volume of no more than 1 I.

BRIEF SUMMARY OF THE DISCLOSURE [0027] In accordance with a first aspect of the present inventions there is provided a device for dispensing oxygen under pressure comprising a canister filled with activated carbon and oxygen at a pressure of between 4 and 17 barg, when measured at room temperature, which canister is sealed with a valve assembly allowing release of oxygen from the canister on actuation of the valve assembly, characterised in that the device further comprises a catalyst that prevents or significantly reduces the presence of carbon monoxide.

[0028] Preferred catalysts convert the carbon monoxide to carbon dioxide at ambient temperature.

[0029] A preferred catalyst is Hopcalite which is a mixture of copper and manganese oxides. A variety of compositions are available.

[0030] By way of example only, Hopcalite I is a mixture of 50% MnO, 30% CuO, 15% C02O3, and 5% Ag₂O and Hopcalite II is approximately 3:1 manganese dioxide: copper oxide.

[0031] Preferably the Hopcalite is used at a concentration of greater than 0.4% (w/w).

[0032] Hopcalite comes in a number of forms, and a preferred form is pellets.

[0033] The activated carbon may be any carbon that has been specifically treated to develop an extensive capacity for the adsorption of a gas to be adsorbed.

[0034] Suitable carbons include carbonaceous sources such as, for example, peat, wood, coal, nutshell, petroleum, coke and bone, or synthetic sources, such as, poly(acrylonitrile) or phenol-formaldehyde.

[0035] As disclosed in W02005/054742 (incorporated by reference), numerous methods for activation of carbon exist, and the activation process develops an intricate network of pores of various sizes ranging from macroporous (pore diameters greater than 50 nm) to sub-microporous (pore diameters less than 2 nm). The larger pores are known as transport pores and serve to provide access to the smaller pores in which most of the adsorption of gaseous species takes place.

[0036] The activated carbon may be provided in powdered, granular or pelleted forms and in a variety of sizes, both of which affect the adsorption kinetics. The skilled person will select the appropriate combination depending upon the desired material adsorption performance required.

[0037] Suitable activated carbons for use with oxygen include those of different origins, densities, activities and mesh sizes, as outlined in Example 1 of W02005/054742, the selection being made to maximise adsorption.

[0038] Selecting an activated carbon with a high microporosity (less than 2 nm) and a high surface area (greater than 500 m²/g, and more preferably greater than 1000 m²/g) is clearly desirable. One such material is illustrated in Table 3 of W02005/054742, which disclosure is incorporated by reference and the table is reproduced as Table 1 below:

[0039] Table 1

Designation	. SRD/347/1
Carbon size/mm	2 mm pellets
Bulk Density/g cm’³	0.40
CTC Sorntion/% _ _ _ - -- _x- - --	109
OXYGEN capacity (at 12 bargj	8;64g/100g _;; 34.5 g/litre.
BET Surface Area/m² g’¹	1342
Total Pore Volume/cm³ g’¹	0.850
Micropore Volume/cm³ g'¹	0.777
Narrow Micropore Vol/cm³ g'¹	0.367
Broad Micropore Vol/cm³ g	0.410
MERCURY POROSIMETRY O 1 Total Pore Volume/cm g'	0.881
Mesopore Volume/cm³ g'^!	0.413
Macropore Volume/cm³ g’¹	0.468

NOTE: Nitrogen Total Pore Volume ... 0 - 200 ©width.

Micropore Volume ... 0-20 ©width

Narrow Micro. Vol. ... 0 - 6 ® width

Broad Micro. Vol. ... 6-20 © width

Mercury Total Pore Volume .. 20 - 10⁵ ©width

Mesopore 20 - 500 ® width

Macropore 500 - 10⁵ © width [0040] For devices filled with gases, W02005/054742 teaches that the uptake of e.g.

carbon dioxide may vary with the degree of activation (measured as the ability to adsorb carbon tetrachloride (CTC) vapour). In W02005/054742 this is exemplified with reference to activated carbons with CTC values ranging from 27% CTC to 111% CTC in the pressure range 0-20 barg.

[0041] It is reported that at lower pressures, of under about 8 barg (Fig 2 therein), lower activity carbon can show higher uptake, and it is further taught that the bulk density of the activated carbon appears as one of the most important factors in maximising adsorption. The teaching illustrates bulk densities in the range 0.35-0.55 g/cm³.

[0042] It will be apparent from this teaching that selecting an appropriate activated carbon for a given application is something a skilled person would routinely undertake.

[0043] Having selected an appropriate activated carbon, the canister is filed with the activated carbon, which for most applications is typically by greater than 40%, through 50%, 60%, 70% and greater (by volume). There are however applications where very much smaller volumes of activated carbon may be used.

[0044] Preferably the device is also fitted with a filter, which sits between the activated carbon and the valve of the valve assembly. More preferably the filter is a HEPA filter.

[0045] Where the device is filled with oxygen or air, preferably the device is provided with a mouth and / or nose piece, facemask or the like and a connector, e.g. flexible tubing for connection to the device. An actuator allows for release of the adsorbed gas from the canister via the valve, and optionally a regulator.

[0046] Preferably the device is charged via the valve assembly, care being taken to manage the exothermic nature of the filling process. This can be effectively achieved by using a steel canister with a volume of about 1 I or less.

[0047] In accordance with a second and independent aspect of the present invention there is provided an improved method for charging a device for dispensing a gas under pressure which device comprises a canister filled with activated carbon to adsorb the gas under a pressure of between 4 and 17 barg, when measured at room temperature, which canister is sealed with a valve assembly allowing release of the gas from the canister on actuation of the valve assembly, wherein the gas is carbon dioxide, oxygen or air, the canister comprises steel, and the canister is filed in a single or two step operation, via the valve assembly.

[0048] Preferably the canister has a volume of 1 I or less and includes canisters of, for example, approximately 370 ml, 640 ml and 980 ml.

[0049] Such sized canisters when filled, can typically hold, respectively, approximately 10 I, 20 I and 30 I of oxygen or 40 I, 70 I or 100 I of carbon dioxide [0050] In accordance with a third aspect of the present invention there is provided a device for dispensing a gas under pressure which device comprises a canister filled with activated carbon to adsorb the gas under a pressure of between 4 and 17 barg, when measured at room temperature, which canister is sealed with a valve assembly allowing release of the gas from the canister on actuation of the valve assembly, wherein the gas is carbon dioxide, oxygen or air, and the canister comprises steel.

[0051] The device is preferably filed with oxygen or carbon dioxide.

[0052] Preferably the canister has a volume of 1 I or less and includes canisters of, for example, 370 ml, 640 ml and 980 ml..

[0053] A preferred device filled with carbon dioxide is a pet behaviour correction device, which device comprises a high volume discharge valve.

[0054] The high volume discharge valve has a stem with an orifice diameter of at least 0.3 mm, more preferably at least 0.4 mm, and as much as about 0.6 mm.

[0055] Another preferred device filled with carbon dioxide is a gas duster device and it comprises a tube connectable to the valve assembly to allow the gas to be directed, on discharge, to a target surface.

[0056] Preferably the canister is filled to at least 85%, more preferably at least 90%, and most preferably at least 95% by volume, with activated carbon. Were the device to be filled with dry ice sufficient space would have to be left for the dry ice such that it would not be possible to maximise the efficient filling.

[0057] Where the gas is oxygen or air the device may be provided together with one or more of a mask, mouthpiece and / or nose piece and a connector, for example tubing and these components may be sold separately or as a kit of parts.

[0058] The device or kit may be provided together with instructions for use.

[0059] In a further embodiment the device may comprise a regulator and / or a counter or other means for determining usage. The counter may be integral with the device or may communicate usage to a device carried or worn by the user, such as, for example, a smart phone or wearable device, for example, a Fit Bit®. This enables the user or a third party to monitor the effect of taking oxygen on performance and recovery.

BRIEF DESCRIPTION OF THE DRAWINGS [0060] An embodiment of the invention is further described hereinafter with reference to the accompanying drawing, in which:

Fig 1 is a device according to a first aspect of the invention.

DETAILED DESCRIPTION [0061] Fig 1 illustrates a device (10) according to a first aspect of the invention. It comprises a canister (12), preferably steel, filled with activated carbon (14) and a catalyst (16) which is sealed with a valve assembly (18) comprising a valve (20) and an actuator (22). A filter (24) prevents activated carbon clogging the valve stem (26).

[0062] The device is, according to a second aspect of the invention, filled with a gas (30), for example, oxygen, which is adsorbed into the activated carbon, and which can be subsequently released from the device by operation of the actuator (22).

[0063] To fill the device (10) gas (30) is forced into the canister (12), via valve (20), under pressure using a proprietary gasser.

[0064] The invention is further exemplified by reference to the test data generated in Examples 1 and 2.

Example 1

Effect of catalyst on carbon monoxide levels [0065] Canisters (12) of various sizes under 1 I were assembled as set out below:

a) A pellet or two of Hopcalite (16) were added to an empty (steel) canister (12) such that the net concentration of Hopcalite was above, about, 0.5 % w/w;

b) the canister (12) was filled with granular activated carbon (14), preferably using vibration to maximise the packing;

c) a filter (24) was fitted to the valve stem (26) of a valve assembly (18), and the protected valve stem (24,26) was inserted into the activated carbon (14);

d) the valve assembly (18) was crimped to the canister (12); and

e) the device (10) was gassed with a proprietary gasser using oxygen (30).

[0066] On analysis, post filling, it was noted that a small quantity of carbon monoxide appeared to form from the interaction of the oxygen, at high pressure, with the highly activated carbon surface. Tests showed that after storage for 1 month, at room temperature, the carbon monoxide concentration in the gas discharged from the device was approximately 300 ppmv, and could be as high as 600 ppmv.

[0067] This concentration, whilst not a direct hazard to health, was grossly undesirable in a product of this type, and so the Applicant undertook some further tests to see if the problem could be alleviated through the addition of a catalyst (e.g. Hopcalite).

[0068] The activated carbon precursor type was varied, as shown in Table 2, as was the amount of Hopcalite, and the amount of carbon monoxide was determined approximately 200 days post filing.

Table 2

Carbon Type	Carbon Weight/g	Hopcalite Weight/g	Days after O₂ Filling	[CO]/ppm
Coconut Shell	220	0	200	650
Coconut Shell	224	10	200	Not Detected
Coal Base	140	0	200	150
Coal Base	145	10	200	Not Detected
Coconut Shell	91	0.1	210	5
Coconut Shell	92	0.4	210	Not Detected
Coconut Shell	93	0.9	210	Not Detected
Coconut Shell	93	1.8	210	Not Detected

[0069] As can be seen from Table 2, the addition of Hopcalite considerably diminished the carbon monoxide concentration, and the data indicated that a concentration of >0.4 % is sufficiently effective to ensure a nil concentration of carbon monoxide.

[0070] Gassing of the canisters with oxygen was undertaken using a commercial gasser operated, typically, at 10 barg.

Example 2

Effect of canister type on heat transfer and device failure [0071] When a conventional canister of aluminium construction was gassed with carbon dioxide, the temperature, due to the exothermic adsorption of carbon dioxide on activated carbon, was noted to rise by 46.5 °C. This rapid temperature rise caused the seal (usually rubber) between the canister and valve assembly to deform, causing leakage and premature depressurisation of the device.

[0072] In consequence, and in order to avoid over-heating and the risk of over pressurising, it was necessary to introduce the gas in a stepwise manner, allowing the device to cool between steps.

[0073] However, when a similar-sized steel canister was gassed with carbon dioxide it was noted that the temperature rise of the canister was only 3.7 °C, and inconsequence the applicant was able to fill the device in a single step procedure, without the risk of stressing the rubber seal or over pressurising the container.

[0074] The results of the test are given below:

[0075] Gas Used: carbon dioxide [0076] Steel canister size: diameter 65 mm, height 195 mm. Volume = nr2h = 646 ml [0077] Aluminium canister size: diameter 66 mm, height 218 mm. Volume = nr2h = 745 ml [0078] Steel canister at room Temp: 14.5 °C [0079] Aluminium canister: at room Temp: 14.5 °C [0080] Carbon amount in steel canister: 265 grams [0081] Carbon amount in aluminium canister: 282 grams [0082] Both canisters were gassed at a pressure of 10 barg [0083] Steel canister temperature after pressurising to 10 barg: 18.2 °C [0084] Aluminium canister temperature after pressurising to 10 barg: 61 °C [0085] Heat management is an important consideration in this process because too much heat generation can result in device failure due to deformation of the, typically, rubber seal provided between the canister and valve assembly, where the two components are crimped together.

[0086] Previously this has been addressed by using either solid carbon dioxide or a filling process requiring multiple, gassing steps under pressure, followed by cooling.

Preferred activated carbon source.

[0087] Whilst any of these forms and derivations of activated carbon may be suitable for oxygen storage applications, it is preferred to use granular activated carbon derived from coconut shell, also known as an HDS activated carbon, since this provides excellent physical properties with low ash and is a sustainable material with environmentally friendly credentials.

[0088] The precise granulometry should be such as to give the maximum weight filling in the canister without causing difficulties in handling.

[0089] A suitable mesh range is 12 x 20 US mesh with >85 % CTC activity and <5 % moisture.

[0090] An appropriate, though non-limiting, density range is 0.4 - 0.5 g cm^-3.

Claims

1. An improved method for charging a device (10) for dispensing a gas (30) under pressure which device comprises a canister (12) filled with activated carbon (14) to adsorb the gas under a pressure of between 4 and 17 barg, when measured at room temperature, which canister is sealed with a valve assembly (18) allowing release of the gas from the canister on actuation of the valve assembly, wherein the gas (30) is carbon dioxide, oxygen or air, the canister comprises steel, and the canister is filed in a single or two step operation, via the valve assembly.

2. A method as claimed in claim 1 further comprising the step of using vibration to maximise the packing of the activated carbon.

3. A device (10) for dispensing a gas (30) under pressure which device comprises a canister (12) filled with activated carbon (14) to adsorb the gas under a pressure of between 4 and 17 barg, when measured at room temperature, which canister is sealed with a valve assembly (18) allowing release of the gas from the canister on actuation of the valve assembly, wherein the gas (30) is carbon dioxide, oxygen or air, and the canister comprises steel.

4. A device as claimed in claim 3 where the gas is oxygen.

5. A device as claimed in claim 3 wherein the gas is carbon dioxide.

6. A device as claimed in claim 5 which is a pet behaviour correction device and comprises a high volume discharge valve.

7. A device as claimed in claim 6 wherein the high volume discharge valve has a stem with an orifice diameter of at least 0.3 mm.

8. A device as claimed in claim 5 which is a gas duster device and comprises a tube connectable to the valve assembly to allow the gas to be directed, on discharge, to a target surface.

9. A device as claimed in claim 8 in which the canister is filled to at least 85%, more preferably at least 90%, by volume with activated carbon.

10. A device as claimed in any of claims 3-9 wherein the canister has a volume of 11 or less.

11. A kit comprising a device as claimed in any of claims 13-10 together with a mask, mouthpiece and/ or nose piece.

12. A kit as claimed in claim 11 further comprising a connector.

13. A device as claimed in any of claims 13-10 further comprising a regulator and / or counter for monitoring gas usage from the device.