HK40020607B - Improvements in gas storage devices - Google Patents

Description

This invention relates to improvements in gas storage devices and more particularly to devices filed with oxygen. It also relates to an improved method of storing, oxygenin a device, and to the storage device per se.

BACKGROUND

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.

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 (and potentially harmful) 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.

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.

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.

WO2005/054742 discloses a storage container for a gas comprising a sealed vessel containing an amount of activated carbon and a gas which is adsorbed thereon.

One such gas is oxygen.

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

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.

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. However, some canisters can withstand pressures of 20 barg.

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.

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.

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.

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.

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

WO2005/054742 teaches filling the device with oxygen but fails to recognise that the oxygen reacts with the activated carbon.

US 5038768 discloses an apparatus comprising layers of filter and chemical parts through which air containing carbon monoxide with or without carbon dioxide, hydrocarbons and nitrogen oxides passes and is scrubbed for inhalation by a user.

US2013/211158 discloses activated carbon materials and methods of producing and using activated carbon materials.

BRIEF SUMMARY OF THE DISCLOSURE

In accordance with a first aspect of the present inventions there is provided a device (10) for dispensing oxygen (30) which is stored under pressure comprises a canister (12) filled with at least 40% activated carbon (14), by vol, and oxygen (30) which is adsorbed by the activated carbon and stored at a pressure of between 4 and 20 barg, when measured at room temperature, which canister is sealed with a valve assembly (18) allowing release of oxygen from the canister on actuation of the valve assembly, characterised in that the device further comprises a catalyst (16) which converts carbon monoxide to carbon dioxide at ambient temperature to prevents or significantly reduce the presence of carbon monoxide.

Preferred include Hopcalite, which is a mixture of copper and manganese oxides. A variety of compositions are available including Applicants proprietary formulation SB100^™.

By way of example only, Hopcalite I is a mixture of 50% MnO, 30% CuO, 15% Co₂O₃, and 5% Ag₂O and "Hopcalite II" is approximately 3:1 manganese dioxide: copper oxide.

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

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

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.

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.

As disclosed in WO2005/054742 (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.

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.

Suitable activated carbons for use with oxygen include those of different origins, densities, activities and mesh sizes, as outlined in Example 1 of WO2005/054742 , the selection being made to maximise adsorption. A preferred form is Applicants proprietary activated carbons SBC^™.

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 WO2005/054742 , which disclosure is incorporated by reference and the table is reproduced as Table 1 below: Table 1

Designation	SRD/347/1
Carbon size/mm	2 mm pellets
0.40
CTC Sorption/%	109
"OXYGEN capacity (at 12 barg)	8.64g/100g
34.5 g/litre
1342
0.850
0.777
0.367
0.410
MERCURY POROSIMETRY
0.881
0.413
0.468

NOTE:	Nitrogen Total Pore Volume		...	0 - 200	Mercury Total Pore Volume ..		width
Micropore Volume	...	0 - 20	20 - 500	width
Narrow Micro. Vol .	...	0 - 6	width	Macropore "	width
Broad Micro. Vol.	...	6 - 20	width

For devices filled with gases, WO2005/054742 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 WO2005/054742 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.

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.

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.

Having selected an appropriate activated carbon, the canister is filled 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.

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.

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.

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.

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.

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

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.

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.

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

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

An embodiment of the invention is further described hereinafter with reference to the accompanying drawing, in which: Fig 1 is a device according to the invention.

DETAILED DESCRIPTION

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).

The device is 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).

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

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

Canisters (12) of various sizes under 1 I were assembled as set out below:

1. 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;
2. b) the canister (12) was filled with granular activated carbon (14), preferably using vibration to maximise the packing;
3. 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);
4. d) the valve assembly (18) was crimped to the canister (12); and
5. e) the device (10) was gassed with a proprietary gasser using oxygen (30).

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.

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).

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		[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

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.

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

Preferred activated carbon source.

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.

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

A suitable mesh range is, for example, 30 x 70 or 12 x 20 US mesh with >85 % CTC activity and <5 % moisture.

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

Claims (8)

1. A device (10) for dispensing oxygen (30) which can be stored under pressure comprising a canister (12) filled with at least 40% activated carbon (14), by vol, and being able to be filled with oxygen (30) which can be adsorbed by the activated carbon and stored at a pressure of between 4 and 20 barg, when measured at room temperature, which canister is sealed with a valve assembly (18) allowing release of oxygen from the canister on actuation of the valve assembly, characterised in that the device further comprises a catalyst (16) which converts carbon monoxide to carbon dioxide at ambient temperature to prevent or significantly reduce the presence of carbon monoxide.
2. A device as claimed in claim 1 wherein the catalyst comprises manganese dioxide and copper oxide.
3. A device as claimed in claim 2 wherein the catalyst is Hopcalite.
4. A device as claimed in any of the preceding claims wherein the activated carbon is derived from coconut shell or a coal base.
5. A device as claimed in any of the preceding claims wherein the activated carbon has a density of from 0.4 - 0.5 g cm^-3.
6. A kit comprising a device as claimed in any of claims 1-5 together with a mask, mouthpiece and/ or nose piece.
7. A kit as claimed in claim 6 further comprising a connector.
8. A device as claimed in any of claims 1-5further comprising a regulator and / or counter for monitoring gas usage from the device.