Explosive and thermic compositions or charges – Processes of making
Reexamination Certificate
2000-02-02
2003-02-04
Carone, Michael J. (Department: 3641)
Explosive and thermic compositions or charges
Processes of making
C149S046000
Reexamination Certificate
active
06514361
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a water-in-oil emulsion explosive and a method of preparing same. More particularly, the present invention relates to a PIBSA-based explosive emulsion and a more efficient and economical method of preparing same.
2. Description of the Related Art
Water-in-oil emulsion explosives are well-known in the art, See, for example, U.S. Pat. Nos. 4,356,044; 4,322,258; 4,141,767; 3,447,978 and 3,161,551. Emulsion explosives are found to have certain advantages over conventional aqueous slurry explosives, which have a continuous aqueous phase, as described in U.S. Pat. No. 4,141,767.
An inherent problem with emulsion explosives, however, is their relative instability, due to the act that they comprise a thermodynamically unstable dispersion of supercooled solution or melt droplets in an oil-continuous phase. If the emulsion remains stable these supercooled droplets are prevented from crystallizing or solidifying into a lower energy state. If the emulsion weakens or becomes unstable, however, then crystallization or solidification of the droplets results, and the explosive generally loses at least some of its sensitivity to detonation and becomes too viscous to handle for certain blasting applications. Moreover, it is common to add solid components to emulsion explosives, such as glass microspheres for density reduction and prills or particles of oxidizer salt such as porous prilled ammonium nitrate (AN) for increased energy. These solid components, however, tend to destabilize emulsions.
Emulsion explosives commonly are used as a repumpable explosive, i.e., an explosive that is formulated at a remote facility, loaded or pumped into a bulk container and then transported in the container to a blasting site where it then is “repumped” from the container into a borehole. Alternatively, the explosive may be delivered (repumped) into a centrally located storage tank fro which it will be further repumped into a vehicle for transportation to a blasting site and then again repumped into the borehole. Thus the emulsion explosive must remain stable event after being subjected to repeated handling or searing action, which normally also tends to destabilize an emulsion. Additionally, the emulsion's viscosity must remain low enough to allow for repumping at reasonable pressures and at the low ambient temperatures that may be experienced during colder months. Repeated handling or hearing action also tends to increase the emulsion's viscosity.
Since a density control agent is required in many instances to reduce the density of an explosive and thereby increase its sensitivity to a required level for detonation, and since hollow microspheres are a preferred form of density control, it is important that the emulsion remain stable and have a low viscosity even when containing solid density control agents.
Proposals have been made to improve the stability of water-in-oil emulsion explosives by employing particular surfactants which function to a high level of efficiency in the harsh environment of an oxidizer salt solution. A particularly effective and useful surfactant has been the reaction product of a hydrocarbyl-substituted succinic acid or anhydride and an amine, e.g., a PIBSA (polyisobutenyl succinic anhydride) based emulsifier.
For example, U.S. Pat. No. 4,708,753 discloses water-in-oil emulsions containing as the emulsifier a salt derived from a hydrocarbyl-substituted carboxylic acid or anhydride, or ester or amide derivative thereof, and an amine.
U.S. Pat. No. 4,615,751 discloses the use of an unspecified polybutenyl succinic anhydride derivative (with a tradename of EXPERSE 60) as a water-resisting agent in emulsions containing prills but not as an emulsifier. European Patent Application No. 0 155 800 discloses alkanolamine derivatives of polyisobutenyl succinic anhydride as emulsifiers. See also U.S. Pat. Nos. 4,822,433; 4,919,179 also describes a PIBSA-based surfactant for use in explosive emulsions.
U.S. Pat. No. 4,710,248 discloses water-in-oil emulsion explosives containing as an emulsifier underivatized polyisobutenyl succinic anhydride or polyisobutenyl succinic acid.
U.S. Pat. No. 4,357,184 discloses water-in-oil emulsions containing graft block or branched polymer emulsifiers. One type of block copolymer which is taught contains polyisobutenyl succinic anhydride as the hydrophobic block and polyethylene glycol or polyethylenimine as the hydrophillic block.
Conventional polyisobutenyl succinic anhydride emulsifier chemistry requires that the emulsifier be formed in a 2-step chemical reaction comprising the hydrolysis of polyisobutenyl succinic anhydride, followed by the amination of the hydrolyzed product. The reactions can be burdensome, and add to the cost of using polyisobutenyl succinic anhydride based emulsifiers.
It is therefore an object of the present invention to provide a method of preparing an explosive emulsion which uses a PIBSA-based emulsifier which is more economical, yet still provides the advantages.
These and other objects of the present invention will become apparent to the skilled artisan upon a review of the following description and the claims appended hereto.
SUMMARY OF THE INVENTION
The “in-situ” process of the present invention does away with the conventional amination reaction needed to form a PIBSA-based emulsifier, and forms the emulsifier species during the emulsification process. Reaction times for preparing a water-in-oil emulsion, such as an explosive emulsion, are thereby greatly reduced and the only required materials are the hydrocarbyl-substituted anhydride, preferably polyisobutenyl succinic anhydride; a hydroxy amine, preferably diethylethanol amine; an oxidizer salt solution such as an ammonium nitrate solution; and a continuous phase oil (e.g., pale oil).
The process of the present invention comprises preparing a water-in-oil emulsion, which is comprised of a continuous oil phase and a discontinuous aqueous phase. The process comprises first preparing an oil phase containing a hydrocarbyl-substituted anhydride. An aqueous phase containing an hydroxy amine is then prepared. The two phases are then sufficiently mixed to create a water-in-oil emulsion, with the anhydride and amine reacting at the interface of the two phases. The reaction of the anhydride and amine at the interface creates an emulsifier product which stabilizes the water-in-oil emulsion. In a preferred embodiment, the hydrocarbyl-substituted anhydride is a polyisobutenyl succinic anhydride, and the hydroxy amine is diethylethanol amine. The method is particularly useful for preparing an explosive emulsion, wherein the aqueous phase comprises an oxidizer salt, preferably ammonium nitrate.
The resulting water-in-oil emulsion prepared comprises a continuous oil phase containing a hydrocarbyl-substituted anhydride, a discontinuous aqueous phase containing a hydroxy amine, preferably an N-(hydroxyl substituted hydrocarbyl)amine, whereby the anhydride and amine form a reaction product at the interface of the continuous and discontinuous phases. This reaction product is an emulsifier product which stabilizes the water-in-oil emulsion. The anhydride is preferably polyisobutenyl succinic anhydride, and the amine is preferably diethylethanol amine. It is also preferred to prepare explosive emulsions, whereby an oxidizer salt such as ammonium nitrate is contained in the discontinuous aqueous phase.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The water-in-oil emulsion of the present invention comprises a continuous oil phase containing a hydrocarbyl-substituted anhydride, as well as a discontinuous aqueous phase containing an hydroxy amine, e.g., an N-(hydroxyl substituted hydrocarbyl)amine. Mixing of the two phases creates a stable water-in-oil emulsion as the anhydride and amine form a reaction product at the interface of the continuous and discontinuous phases.
The hydrocarbyl-substituted anhydrides, e.g., PIBSA, can be prepared by any of several known procedures which are described in the f
Baker Aileen J.
Burns Doane Swecker & Mathis L.L.P.
Carone Michael J.
Nelson Brothers, Inc.
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