Patent ID: 12187527

DETAILED DESCRIPTION

FIG.1illustrates 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, 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).

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 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); ande) 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 2DaysCarbonHopcaliteafter O2Carbon TypeWeight/gWeight/gFilling[CO]/ppmCoconut Shell2200200650Coconut Shell22410200Not DetectedCoal Base1400200150Coal Base14510200Not DetectedCoconut Shell910.12105Coconut Shell920.4210Not DetectedCoconut Shell930.9210Not DetectedCoconut Shell931.8210Not 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.

Example 2

Effect of Canister Type on Heat Transfer and Device Failure

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.

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.

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.

The results of the test are given below:Gas Used: carbon dioxideSteel canister size: diameter 65 mm, height 195 mm. Volume=πr2h=646 mlAluminium canister size: diameter 66 mm, height 218 mm. Volume=πr2h=745 mlSteel canister at room Temp: 14.5° C.Aluminium canister: at room Temp: 14.5° C.Carbon amount in steel canister: 265 gramsCarbon amount in aluminium canister: 282 gramsBoth canisters were gassed at a pressure of 10 bargSteel canister temperature after pressurising to 10 barg: 18.2° C.Aluminium canister temperature after pressurising to 10 barg: 61° C.

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.

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.

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, 30×70 or 12×20 US mesh with >85 CTC activity and <5% moisture.

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