Organic compounds -- part of the class 532-570 series – Organic compounds – Unsubstituted hydrocarbyl chain between the ring and the -c-...
Reexamination Certificate
2001-03-21
2002-02-26
Ford, John M. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Unsubstituted hydrocarbyl chain between the ring and the -c-...
C540S475000
Reexamination Certificate
active
06350871
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved method of crystallizing 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0
5,9
0
3,11
]-dodecane, also known as hexanitrohexaazaisowurtzitane, hereinafter referred to as CL-20. In particular, this method involves crystallization of CL-20 as an epsilon-polymorph.
2. Description of the Related Art
For most existing propellant and weapons systems, the most critical ingredient in terms of propulsive and explosive performance is the oxidizer. CL-20, with its substantial increase in performance output, is an organic oxidizer presenting significant opportunities in terms of energy capabilities for propellants and explosives. For example, the use of CL-20 as the energetic filler in weapons systems may provide increased anti-armor penetration, enhanced missile payload velocity and flight, increased underwater torpedo effectiveness and lethality, and improved gun propellant impetus.
The performance of CL-20 in propellant and weapon systems is highly dependent upon the crystal polymorph of CL-20. CL-20 has several different crystal polymorphs, the most preferred of which is a high density phase known in the art and referred to herein as the &egr;-polymorph (or epsilon-polymorph) of CL-20. The &egr;-polymorph of CL-20 is preferred because of the high energetic performance and relatively low sensitivity attributable to the &egr;-polymorph. However, many conventional CL-20 synthesis techniques produce &agr;-polymorph as the predominant crystal polymorph. The &agr;-polymorph has a much lower density that the &egr;-polymorph. For these reasons, CL-20 synthesized by many conventional techniques must be subjected to re-crystallization in order to increase the concentration of the &egr;-polymorph.
Conventionally, CL-20 has been crystallized using chloroform to precipitate CL-20 from ethyl acetate. Chloroform has been found to produce consistently and reproducibly the desirable &egr;-polymorph of CL-20. However, one disadvantage to using chloroform is that defects are often found in the crystalline structure of &egr;-polymorph CL-20 crystallized with chloroform. Another disadvantage of this conventional technique is that chloroform and ethyl acetate cannot be separated effectively and efficiently by distillation, thus complicating the reuse of these solvents. Because the chloroform cannot be easily reused, a continual discharge of a chlorinated waste stream must be disposed of in an environmentally acceptable manner. As a chlorinated solvent, chloroform may potentially contribute to ozone depletion, thus complicating waste disposal of chloroform and other chlorinated solvents. It is, therefore, advantageous to crystallize CL-20 into the &egr;-polymorph with solvents that can be recycled within the crystallization process without producing a discharge of chlorinated solvents.
A CL-20 crystallization technique that avoids the use of chloroform and other chlorinated solvents and non-solvents is disclosed in U.S. Pat. No. 5,874,574, in which CL-20 is dissolved in a solution containing a CL-20 solvent, such as ethyl acetate, and water to form an aqueous phase and a wet solvent phase. The wet CL-20 solvent phase is then dried by azeotropicly. A low density CL-20 non-solvent is then added to the dry CL-20 solvent phase to cause crystallization of &egr;-polymorph CL-20. The CL-20 crystals are then separated from the non-solvent and the solvent by adding sufficient water to displace the non-solvent and the solvent from the surface of the &egr;-polymorph CL-20 crystals. Although high recoveries of &egr;-polymorph CL-20 are reported in U.S. Pat. No. 5,874,574, it is also disclosed that relatively large quantities of water are needed to separate the nonsolvent and solvent from the CL-20 crystals. In some cases, the quantities of water can require larger separation and recycling equipment, thus increasing the capital expenditures and operating costs of this process.
It would therefore be a significant improvement in the art to provide a method for crystallizing high concentrations of &egr;-polymorph CL-20 having high quality and little defects without relying on chlorinated solvents and non-solvents or large water separation and recycling equipment needed by conventional processes.
SUMMARY OF THE INVENTION
It is, therefore, an object of this invention to overcome a long-felt need in the art by providing a method that produces &egr;-polymorph (epsilon-polymorph) CL-20 possessing excellent quality in high yields, yet which method is environmentally friendly and more economically efficient than known methods.
In accordance with the principles of this invention, the above and other objects are attained by a method in which CL-20 is crystallized from a solution comprising at least one CL-20 organic solvent and a CL-20 non-solvent comprising at least one nitrate ester, in particular poly(glycidyl nitrate) and/or a nitrate ester plasticizer. The nitrate ester is preferably poly(glycidyl nitrate) and/or triethyleneglycol-dinitrate, although other nitrate plasticizers having acceptable volatilities and impact sensitivities can be used. The solution is saturated with CL20, and CL-20 is crystallized from the saturated solution by, for example, adding &egr;-polymorph CL-20 crystalline seeds to the solution and evaporating off the CL-20 solvent. Evaporation is preferably conducted under vacuum or with the aid of a similar technique for removing the solvent vapor, such as blowing a dry gas over the evaporator. The nitrate ester non-solvent and any non-evaporated remnants of the solvent are then separated from the crystalline CL-20 by a suitable solid-liquid separation technique, such as by filtration of the CL-20 crystals. If necessary or desirable, prior to solid-liquid separation the nitrate ester non-solvent can be diluted, and its viscosity lowered, by diluting the slurry of non-solvent and CL-20 with a solvent that is miscible with the non-solvent but in which the CL-20 is insoluble. The CL-20 can then be washed.
Advantageously and unexpectedly, the crystallization of the CL-20 in the nitrate ester non-solvent produces high quality &egr;-polymorph CL-20 crystals that may have few crystal defects and exhibit enhanced energetic performance and lower impact sensitivity compared to CL-20 crystallized by known techniques. Additionally, the solution in which the CL-20 is dissolved and eventually crystallized comprises a mixture of an environmentally acceptable solvent and a non-solvent free of chlorinated compounds and other compounds regulated as Hazardous Air Pollutants (HAPs) under the Clean Air Act. Both the solvent and non-solvent can be recycled for further processing without further treatment or purification.
The CL-20 crystallized by this method is excellent for use in propellant, explosive, and pyrotechnic formulations.
Other objects, aspects, and advantages of this invention will become more apparent to those skilled in the are upon reading the specification and appended claims, which explain the principles of this invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS AND METHODS OF THE INVENTION
Crystallization of CL-20 in accordance with this novel method is performed in a solution comprising at least one CL-20 organic solvent and a CL-20 non-solvent comprising at least one CL-20 nitrate ester that is miscible with the solvent.
As referred to herein, the term “CL-20 solvent” includes solvents that have a relatively high CL-20 solubility of at least 20% weight/volume (g/ml) of CL-20 in the solvent. The CL-20 solvent preferably has a relatively low boiling point to permit evaporation of the CL-20 solvent at temperatures not exceeding 60° C. Solvent evaporation can be, and preferably is, conducted under a vacuum or in the presence of a blowing dry gas or the like to remove the solvent vapor. Ethyl acetate is currently the preferred solvent because of its low boiling point and environmental acceptability compared to chlorinated solvents. Other non-halogenated CL-20 solvents suitable for use i
Hamilton Richard S.
Sanderson Andrew J.
Warner Kirstin F.
Alliant Techsystems Inc.
Ford John M.
Sullivan Law Group
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