Drug – bio-affecting and body treating compositions – Combustible or chemically reactive to produce a smoke – mist...
Reexamination Certificate
1999-05-18
2002-08-27
Azpuru, Carlos (Department: 1615)
Drug, bio-affecting and body treating compositions
Combustible or chemically reactive to produce a smoke, mist...
C424S405000, C424S601000, C424S682000
Reexamination Certificate
active
06440390
ABSTRACT:
TECHNICAL FIELD
This invention concerns formulations for use in the generation of phosphine. These formulations are particularly suited for the production of phosphine for use in the fumigation of grain and similar particulate commodities stored in bulk, but they are not limited to that purpose.
BACKGROUND TO THE INVENTION
Phosphine (PH
3
) has been a preferred gaseous fumigant for stored grain and similar particulate commodities because any residue of the fumigant will be lost or oxidised to a harmless phosphate when the grain or other commodity is processed to produce a food. Examples of the fumigation of grain with phosphine are found in the specifications of: International patent application No. PCT/AU90/00268 (which is WIPO Publication No. WO 91/00017); U.S. Pat. Nos. 4,059,048, 4,200,657, 4,756,117 and 4,812,291; and Australian patent No.598,646 and its equivalent South African patent No. 86/4806. This list is not exhaustive.
The phosphine used to fumigate a grain silo or other storage may be supplied by cylinders which contain phosphine or (more usually) a mixture of phosphine and carbon dioxide. Alternatively, the phosphine may be supplied by on-site generators in which phosphine is produced by the reaction of water or water vapour with a metal phosphide (typically aluminium phosphide or magnesium phosphide). However, the more traditional technique for disinfecting a grain silo or the like with phosphine involves the use of a probe to position formulations of aluminium phosphide or magnesium phosphide within the grain mass, where moisture in the air circulating through the grain reacts with the phosphide in the formulation to generate phosphine.
A modification of this technique involves the placement of pellets of a metallic phosphide in the head space of a grain silo. The phosphine produced when the phosphide reacts with moisture in the atmosphere above the grain is circulated through the stored grain either by the natural convection currents that are present in the silo or by active recirculation of air from the head space through the grain using recirculation ducts. Examples of this approach are found in the aforementioned specifications of U.S. Pat. Nos. 4,200,657 (to J S Cook) and 4,756,117 (to W. Friemel). Such techniques, however, cannot be guaranteed to supply phosphine to all regions of the bulk stored grain to eradiate weevils and other unwanted grain pests. In addition, when these traditional techniques are used, there is no control over the concentration of phosphine in the grain after the phosphide formulation has been added, and there is no possibility of regulating the phosphine concentration/time regime in the bulk storage to be most effective.
When using phosphine from cylinders which contain this gas (they usually contain 2 per cent phosphine and 98 per cent carbon dioxide), the phosphine should be mixed with air externally of the stored grain and the resultant gas mixture should then be pumped through the grain. This method of disinfestation of the grain should be carried out periodically, or whenever it is perceived that fumigation of the grain is necessary or desirable. Although this approach to the fumigation of grain is regarded as the most efficient, its major disadvantage is the need to guarantee a supply of expensive cylinders of the gas mixture to the treatment site.
There is one significant problem with the use of phosphine. When its concentration in air reaches certain values, the gas mixture is flammable and potentially explosive. The generally accepted maximum safe concentration of phosphine in air at standard temperature and pressure is 1.79 per cent by volume. The paper entitled “The Flammability Limit of Pure Phosphine-Air Mixtures at Atmospheric Pressure”, by A. R. Green et. al., which was published in “Controlled atmosphere and fumigation in grain storages” (Edited by B. E. Ripp et. al.), Elsevier, 1983, pages 433-449, confirms this safe concentration limit and provides further information about the flammability of phosphine.
Other potential problems with the use of phosphine are the toxicity of phosphine to mammals when the phosphine is present in high concentrations, and the exothermic nature of the hydrolysis reaction which produces the phosphine.
Thus the use of on-site phosphine generators, such as the generator described in European Patent Publication No. A-0318040 (the specification of European patent application No. 88119701.6), presents a number of hazards to the user. In addition, with the fumigation regimes now being employed (for example, maintaining low phosphine concentrations for long periods), it is possible that the on-site phosphine generators may be left unattended for a considerable time. This is particularly likely to be the situation when the phosphine generator is used for the fumigation of storages at remote locations. Thus on-site phosphine generators, with their attendant fire or explosion risk, have been unattractive for long term fumigation operations.
It is an objective of the present invention to provide formulations of a reactive phosphide which are inherently safe for storage and/or transportation and which can be added periodically to water, or over which moist air can be passed, so that phosphine is generated in a controlled manner. In achieving this objective, the present invention provides an alternative to the phosphine generation systems (which use either phosphides in powder form positioned within a chamber closed by a membrane which is porous to moisture and phosphine, or the periodic dropping of pellets of phosphide into a water bath) which are described in the specifications of International patent application No. PCT/AU91/00264 (which is WIPO publication No. WO 91/19671) and its equivalent U.S. Pat. No. 5,573,740.
The present invention achieves this objective by mixing together a particulate phosphide and a water-immiscible compound which is inert with respect to the phosphide. The water-immiscible compound may be petroleum jelly or a non-volatile oil (for example, paraffin oil), or a mixture of petroleum jelly and a non-volatile oil. Preferably, however, the water-immiscible compound is a wax which has a melting point in the range of from about 35° C. to about 65° C.
If the water-immiscible compound is petroleum jelly and/or a non volatile oil, the quantity of water-immiscible compound in the formulation must be sufficient to ensure that the formulation is capable of being extruded through an orifice (for example, for feeding into a water bath) at the temperature of use of the formulation.
In some uses of the formulation, moisture-laden warm air will be passed over a sample of such a formulation. Thus a sample of the formulation must slump in a controlled manner (to expose the phosphide particles in the formulation) at its temperature of use. These constraints mean that the particulate phosphide must comprise from about 65 per cent (by weight) to about 85 per cent (by weight) of the formulation, and is preferably in the range of from 70 to 75 per cent (by weight) of the formulation. These phosphide concentrations have also been found to be appropriate when the water-immiscible compound of the formulation is a wax having a melting point in the specified range.
When a formulation in accordance with this invention, having petroleum jelly and/or a non-volatile oil as its water-immiscible compound, is placed in a water bath, or in a moist air flow, the covering of the phosphide particles (which may be pellets) is at least partially dispersed. Water, in liquid or vapour form, then comes into contact with the exposed phosphide, and reacts with it to form phosphine and a hydroxide.
If, however, a sample of the formulation which has a wax as its water-immiscible compound is placed in a water bath or in a flow of moist gas (moist air),
(a) if the formulation sample has exposed phosphide particles at its surface, the water (in liquid or vapour form) comes into contact with the exposed phosphide and reacts with it to form phosphine and a hydroxide; but
(b) if there is no exposed phosphide particle at
Waterford Colin Joseph
Winks Robert Gordon
Azpuru Carlos
Commonwealth Scientific and Industrial Research Organisation
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