GB2264112A

GB2264112A - Hydrogen generating composition

Info

Publication number: GB2264112A
Application number: GB9201679A
Authority: GB
Inventors: Peter Morgan
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1992-01-27
Filing date: 1992-01-27
Publication date: 1993-08-18
Anticipated expiration: 2012-01-27
Also published as: GB2264112B; GB9201679D0

Abstract

A hydrogen generating composition contains from 0.001 to 50 percent by weight of calcium and/or lithium and/or an alloy, hydride, salt and/or organometallic of calcium and/or lithium which reacts with water to generate gaseous hydrogen, and from 0 to 10 percent by weight of at least one additive, with the balance, apart from incidental constituents and impurities, being at least one chloride of sodium and/or potassium. Suitable additives are a particle flow enhancer (eg MgSO4 or sodium ferricyanide) a surfactant, an anti-foaming agent, a bubble nucleation material and a ballast material (eg a calcium salt, talc, TiO2 and/or Al2O3). The composition is preferably in pellet form.

Description

HYDROGEN GENERATING COMPOSITION AND METHOD OF PRODUCTION THEREOF This invention relates to a hydrogen generating composition which reacts with water to generate gaseous hydrogen and to a method of producing such a composition in pellet form.

There are many areas of industry in which the production of bubbles of gas in a material during production thereof is necessary. Examples are in the food industry such as in the production of confectionary, in the manufacture of metals in which additives are made to a molten metal for refining or other purposes, in the packaging industry in which plastics material is foamed by the addition of gas producing additives to the liquid material and in the insulation industry where voids are created in an insulating material by gas bubbles. The production of bubbles of gas for these requirements must satisfy various conditions depending upon the particular use and for example in the food industry it is necessary to ensure that the additive producing the gas, and the gas so produced, are non-toxic.

Additionally no residue should be left in the material after the production of the gas bubbles which will be toxic.

There is thus a need for a composition which can produce a gaseous material such as hydrogen in a non-toxic and simple manner.

According to one aspect of the present invention there is provided a composition which reacts with water to generate gaseous hydrogen, containing from 0.001 to 50 percent by weight of calcium and/or lithium and/or an alloy, hydridge, salt and/or organometallic of calcium and/or lithium which reacts with water to generate gaseous hydrogen, and from 0 to 10 percent by weight of at least one additive, with the balance, apart from incidental constituents and impurities being at least one chloride of sodium and! our potassium.

Preferably, the calcium and or lithium and! our alloy, hydridge, salt and/or organometallic of calcium and! our lithium, and the at least one chloride of sodium and! our potassium are present in particulate form in the composition and most preferably are present in compacted particulate form.

Conveniently, the composition contains from 0.001 to 50 percent by weight of calcium hydride, from 0 to 10 percent by weight of at least one additive, with the balance, apart from incidental constituents and impurities, being sodium chloride.

Advantageously the additive is at least one of a particulate material flow enhancer, a surfactant, an anti-foaming agent, a gaseous hydrogen bubble nucleation site material, a ballast material, a porosity enhancing agent, a density reducing agent or a fragmentation enhancing agent.

Preferably the flow enhancer is magnesium sulphate and! our sodium ferrocyanide.

Conveniently the surfactant is sodium dodecyl sulphate andlor a dodecyl benzene sulphonic acid sodium salt.

Advantageously the gaseous hydrogen bubble nucleation site material is a calcium salt, talc, titanium dioxide and! our alumina.

According to another aspect of the present invention there is provided a pellet comprising the composition as hereinbefore described in compacted form.

According to yet another aspect of the present invention there is provided a method of producing a pellet in which a mixture of the composition as hereinbefore described in particulate form is compacted at a load in the range of from 2 to 10 tons per square inch, at a temperature in the range of from 10 to 300C, at a relative humidity of not more than 70 percent, in vacuo or in a gaseous medium, for a time in the range of up to 10 minutes.

Preferably the compaction load is carried out in air at a load of substantially 10 tons per square inch, at a temperature of substantially 200 C, at a humidity of substantially 60 percent and for a time of substantially 2 minutes.

For a better understanding of the present invention, and to show how the same may be carried into effect, various embodiments of the present invention will now be described by way of example.

A composition according to the invention which reacts with water to generate gaseous hydrogen basically contains from 0.001 to 50 percent by weight of calcium andlor lithium andlor an alloy, hydridge, salt andlor organometallic of calcium andlor lithium which reacts with water to generate gaseous hydrogen, and from 0 to 10 percent by weight of at least one additive, with the balance, apart from incidental constituents and impurities, being at least one chloride of sodium andlor potassium.

Preferably the constituents of the composition are present in particulate form and most preferably are present in compacted particulate form.

The most preferred composition contains from 0.001 to 50 percent by weight of calcium hydride, from 0 to 10 percent by weight of at least one additive and the balance apart from incidental constituents or impurities, being sodium chloride. As an alternative lithium hydride such as lithium tri tert butoxy aluminohydride can be used in place of all or part of the calcium hydride.

Thus the reactive material is the calcium of lithium material which reacts vigorously with water producing large bubbles of hydrogen. The chloride of sodium andlor potassium such as the preferred sodium chloride is used as a non-toxic soluble host and ballast material. It is preferably dry mixed in powder form with the calcium andlor lithium material such as calcium hydride and compacted by pressure into solid pellets. When such pellets are introduced into contact with water the reactive material such as the calcium hydride rapidly reacts as the host or ballast material such as the sodium chloride starts to dissolve. The reaction products interact with the sodium chloride solution that is generated, partially to passivate the calcium hydride surface.

The passivated material is then ejected as a cloud of fine grain precipitate which provides a cloud of independent nucleation sites for bubble growth. Bubble size control may be effected by varying the ratio of sodium chloride to calcium hydride in the pellet with the smallest bubbles resulting from pellets where this ratio is large.

Such a composition is non-toxic and leaves no toxic residues. This is particularly important for use in industries such as the food or confectionary industry. Various grades of sodium chloride can be used ranging from relatively impure rock salt or sea salt to table grade salt which may contain additives to promote easy flowing such as magnesium sulphate and sodium ferrocyanide. With the preferred composition of the present invention which basically utilises calcium hydride and sodium chloride with or without additives, the residual chemicals from use of this composition in pellet form in water will be a solution of brine, calcium hydroxide precipitate and hydrogen gas which has left the pellet body as small bubbles. There is no toxic waste or other chemicals to dispose of. Although the composition, and pellets having such composition, can be used in fresh or relatively pure water they can also be used in salt or saline water of any degree of salinity.

As previously described a particulate material flow enhancer can form all or part of an additive in the composition as also may a surfactant, an anti-foaming agent, a gaseous hydrogen bubble nucleation site material, a ballast material, a porosity enhancing agent, a density reducing agent or a fragmentation enhancing agent. If necessary a coating can be applied to a pellet produced from the composition of the present invention to delay the bubble forming reaction of the reactive material with water.

This can be advantageous as it allows all the gas to be liberated at a specific depth in water which can be of benefit in the process utilising such a composition.

A surfactant may be added to the composition up to a maximum of 10 percent by weight to alter the distribution of bubble sizes generated in the reaction with water. Such surfactants are preferably solid and may be sodium dodecyl sulphate and/or a dodecyl benzene sulphonic acid sodium salt or may even be present in the composition in liquid form. Such surfactants may have the effect or dissolving the bubble nuclei thereby reducing their size and number and hence changing the bubble size and bubble density per unit volume of water.

The anti-foaming agent additive may be Dow Corning Antifoam MSA (Trade Mark) Compound operable to reduce the bubble size.

The gaseous hydrogen bubble nucleation site material additive may be a calcium salt, talc, titanium dioxide and! our alumina. Such additives can be added to the composition to increase the number of bubbles nucleation sites and thereby increase the bubble density per unit volume of water.

In the composition of the present invention, in pellet form, the at least one chloride of sodium and/or potassium operates as a ballast material and as a coating material which is soluble in water so as initially to enable the composition in pellet form to sink to a desired depth in water and to dissolve so permitting the reactive material to react with the water and generate gaseous hydrogen bubbles. Additional ballast material may be added as part of the additive to the composition to change the rate of descent of a pellet produced therefrom through water.

The density of a pellet produced from the composition of the present application may be altered or the porosity thereof varied by including air or gas in the composition mix or by not excluding the latter. This again will have the effect of altering the rate of descent of a pellet produced from the composition in water. The density may be reduced by addition of solid or liquid material or foams and a fragmentation enhancing agent may form an additive in the composition such as to induce lines of weakness in the pellet produced therefrom or to enhance bubble evolution. Such material promotes breakup of a pellet produced from the composition in water producing a more even distribution of bubbles.

According to another aspect of the present invention the composition is compacted into the form of a pellet. Preferably such compaction is carried out at a load in the range of from 2 to 10 tons per square inch, at a temperature in the range of from 10 to 300C, at a relative humidity of not more than 70 percent, and preferably of less than 1 percent, in vacuo or in a gaseous medium, for a time of up to 10 minutes. Pellets can be formed from the composition of the present invention by compaction in air at a load of substantially 10 tons per square inch, at a temperature of substantially 200 C, at a humidity of substantially 60 percent and for a time of substantially 2 minutes.

The pellet pressing conditions can be selected to alter the strength of the pellet. For example a relatively strong pellet may be desirable for some uses as it is more resistant to damage during delivery to the reaction point and during storage. In other words it can stand higher loadings before it breaks up.

On the other hand in some uses a less cohesive pellet is preferable since it breaks up more rapidly in water.

Pellets preferably are stored in hermetically sealed containers with a low permeability to water vapour prior to use.

The composition mixture can be made up in any convenient way for compaction. For example relatively large pieces of the reactive material such as calcium hydride may be buried within a mass of relatively small particle size sodium chloride prior to compaction. When the pellet is introduced into water the sodium chloride starts to dissolve and the length of time for reaction delay can be selected by selecting the thickness of the sodium chloride layer. Further sodium chloride can be applied as a surface covering in any convenient manner to a pellet such as by spraying or the pellet can be coating with a non-aqueous solvent. As part of the additive other water soluble materials that do not interact with the reactive material may be included in the composition to allow the reaction delay to be further modified by selection materials with different rates of dissolution in water.

Various Examples were made up and tested as follows: Example 1 A pellet of calcium hydride and sodium chloride powder dry mixed in the ratio 1 to 100 parts by weight, in which the calcium hydride particles were of 4 mesh size was made up by compaction at substantially 10 tons per square inch for two minutes in air at a temperature of 200C and 60 percent relative humidity in a 13 millimetre diameter cylindrical press tool. The resulting pellet was dropped into a test tank containing tap water in which it sank rapidly and generated a persistent shower of sub-millimetre bubbles.A pellet made up under the same conditions containing calcium hydride and polytetrafluoroethylene in the same ratio of 1 to 100 percent by weight and with the polytetrafluoroethylene being present in particle size of 675,us, not according to the invention, when dropped into a test tank containing tap water generated only a few large bubbles for about 1 minute.

Example 2 A pellet according to the invention of the same composition and conipaction conditions as described in Example 1 was prepared and when dropped into a test tank containing artificial sea water (British Standard 3900) sank rapidly and generated a persistent shower of sub-millimetre bubbles.

Example 3 A pellet having a composition according to the present invention as described in Examples 1 and 2 and having been prepared in the same manner as described in Examples 1 and 2 was dropped into a test tank containing artificial sea water in which it sank rapidly and after 30 seconds began to produce a shower of sub-millimetre bubbles which persisted for at least 5 minutes.

Claims

1. A composition which reacts with water to generate gaseous hydrogen, containing from 0.01 to 50 percent by weight of calcium andlor lithium and! our an alloy, hydride, salt andlor organometallic of calcium andlor lithium which reacts with water to generate gaseous hydrogen, and from 0 to 10 percent by weight of at least one additive, with the balance, apart from incidental constituents and impurities, being at least one chloride of sodium and/or potassium.

2. A composition according to claim 1, in which the calcium and! our lithium andlor alloy, hydride, salt andlor organometallic of calcium and/or lithium and the at least one chloride of sodium and/or potassium are present in particulate form.

3. A composition according to claim 2, in which the calcium andlor lithium andlor alloy, hydride, salt andlor organometallic of calcium and/or lithium, and the at least one chloride of sodium and/or pbtassium are present in compacted particulate form.

4. A composition according to any one of claims 1 to 3 containing from 0.001 to 50 percent by weight of calcium hydride, from 0 to 10 percent by weight of at least one additive, with the balance, apart from incidental constituents and impurities, being sodium chloride.

5. A composition according to any one of claims 1 to 4, in which the additive is at least one of a particulate material flow enhancer, a surfactant, an anti-foaming agent, a gaseous hydrogen bubble nucleation site material, a ballast material, a porosity enhancing agent, a density reducing agent, or a fragmentation enhancing agent.

6. A composition according to claim 5, in which the flow enhancer is magnesium sulphate and! our sodium ferrocyanide.

7. A composition according to claim 5, in which the surfactant is sodium dodecyl sulphate and! our a dodecyl benzene sulphonic acid sodium salt.

8. A composition according to claim 5, in which the gaseous hydrogen bubble nucleation site material is a calcium salt, talc, titanium dioxide and/or alumina.

9. A composition which reacts with water to produce gaseous hydrogen, substantially as hereinbefore described.

10. A pellet comprising the composition of any one of claims 1 to 9, in compacted form.

11. A method of producing a pellet in which a mixture of the composition according to any one of claims 1 to 9, in particulate form is compacted at a load in the range of from 2 to 10 tons per square inch, at a temperature in the range of from 10 to 300 C, at a relative humidity of not more than 70 percent, in vacuo or in a gaseous medium, for a time of up to 10 minutes.

12. A method according to claim 11 in which the compaction is carried out in air at a load of substantially 10 tons per square inch, at a temperature of substantially 200 C, at a humidity of substantially 60 percent and for a time of substantially 2 minutes.