Gas storage devices

Abstract

The invention relates to a device (10) for dispensing oxygen (30) under pressure. The device comprises a canister (12) filled with activated carbon (14) and oxygen (30) at a pressure of between 4 and 20 barg. when measured at room temperature. The canister is sealed with a valve assembly (18) allowing release of oxygen from the canister on actuation of the valve assembly. To ensure the activated carbon does not react with the oxygen generating carbon monoxide the device further comprises a catalyst (16) that prevents or significantly reduces the presence of carbon monoxide. In a further aspect there is a device (10) for dispensing a gas (30) under pressure which device comprises a canister (12) with a volume of 11 or less filled with activated carbon (14) to adsorb the gas under a pressure of between 4 and 20 barg when measured at room temperature. The canister (12) is sealed with a valve assembly (18) crimped to the canister over a seal allowing release of the gas (30) from the canister on actuation of the valve assembly, wherein the gas is carbon dioxide, oxygen, nitrogen or air, and the canister is a steel canister. In a particularly favoured embodiment the device is filled with carbon dioxide and includes a high volume discharge valve making it useful as a pet behaviour correction device.

Claims

1. A device (10) for dispensing oxygen (30) under pressure comprising a canister (12) filled with at least 40% activated carbon (14), by volume, and oxygen (30) at 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 oxygen from the canister on actuation of the valve assembly, characterised in that the device further comprises a catalyst (16) that prevents or significantly reduces the presence of carbon monoxide.

2. The device as claimed in claim 1, wherein the catalyst is one which converts carbon monoxide to carbon dioxide at ambient temperature.

3. The device as claimed in claim 2, wherein the catalyst comprises manganese dioxide and copper oxide.

4. The device as claimed in claim 3, wherein the catalyst is Hopcalite.

5. The device as claimed in claim 1, wherein the activated carbon is derived from coconut shell or a coal base.

6. The device as claimed in claim 1, wherein the activated carbon has a density of from 0.4-0.5 g cm.sup.3.

7. A kit comprising the device as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An embodiment of the invention is further described hereinafter with reference to the accompanying drawing, in which:

(2) FIG. 1 is a device according to a first aspect of the invention.

DETAILED DESCRIPTION

(3) 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).

(4) 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).

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

(6) The invention is further exemplified by reference to the test data generated in Examples 1 and 2.

Example 1

(7) Effect of Catalyst on Carbon Monoxide Levels

(8) Canisters (12) of various sizes under 1 l 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).

(9) 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.

(10) 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).

(11) 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.

(12) TABLE-US-00002 TABLE 2 Days Carbon Hopcalite after O.sub.2 Carbon Type Weight/g Weight/g 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

(13) 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.

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

Example 2

(15) Effect of Canister Type on Heat Transfer and Device Failure

(16) 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.

(17) 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.

(18) 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 in consequence 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.

(19) The results of the test are given below: Gas Used: carbon dioxide Steel canister size: diameter 65 mm, height 195 mm. Volume=r2h=646 ml Aluminium canister size: diameter 66 mm, height 218 mm. Volume=r2h=745 ml Steel canister at room Temp: 14.5 C. Aluminium canister: at room Temp: 14.5 C. Carbon amount in steel canister: 265 grams Carbon amount in aluminium canister: 282 grams Both canisters were gassed at a pressure of 10 barg Steel canister temperature after pressurising to 10 barg: 18.2 C. Aluminium canister temperature after pressurising to 10 barg: 61 C.

(20) 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.

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

(22) Preferred Activated Carbon Source.

(23) 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.

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

(25) A suitable mesh range is, for example, 3070 or 1220 US mesh with >85 CTC activity and <5% moisture.

(26) An appropriate, though non-limiting, density range is 0.4-0.5 g cm.sup.3.