Granulation process

A process for forming granules (e.g., alpha-HMX containing granules) from at least one particulate material comprises the steps of: (a) selecting particulates (e.g., alpha-HMX particulates) having a particle size distribution; and (b) fluidizing the particulates, whereby particulates agglomerate to form granules. Optionally, the particulates can be coated with one or more second materials, such as energetic materials or fuels. If one or more of the second materials comprise polymerizable monomers, the process can optionally further comprise the step of polymerizing those monomers in situ, either before or after the granule is formed.

 

What is claimed is:

1. A process for forming granules from at least one particulate material, comprising the steps of:

(a) selecting particulates having a particle size distribution; and

(b) fluidizing the particulates, whereby particulates agglomerate to form granules;

wherein the particulates comprise alpha-HMX.

2. The process of claim 1, wherein the particulates impact against a solid surface in step (b).

3. The process of claim 2, wherein particulates continuously impact the solid surface.

4. The process of claim 3, wherein the surface is curved.

5. The process of claim 4, wherein the curved surface is part of a vessel having a circular cross-section.

6. The process of claim 3, wherein a rotating impeller accelerates the particles against the solid surface.

7. The process of claim 1, wherein in step (b) the particulates are circulated around a circular or elliptical path.

8. The process of claim 7, wherein the particulates are circulated in a channel in a vessel.

9. The process of claim 1, wherein the particle size distribution in step (a) is provided by sieving.

10. The process of claim 1, further comprising adding about 0.001-0.5 g of an organic solvent per g of particulates.

11. The process of claim 10, wherein about 0.05-0.1 g of solvent are added per g of particulates.

12. The process of claim 1, wherein the particulates are alpha-HMX particulates having a second material coated thereon.

13. The process of claim 12, wherein the alpha-HMX particulates further comprise a second material sorbed therein.

14. The process of claim 12, wherein the second material is an energetic material.

15. The process of claim 14, wherein the energetic material is selected from the group consisting of beta-HMX, RDX, TNT, ammonium nitrate, and mixtures thereof.

16. The process of claim 12, wherein the second material is a fuel.

17. The process of claim 16, wherein the fuel is selected from the group consisting of aluminum, lithium hydride, lithium aluminum hydride, and mixtures thereof.

18. The process of claim 12, wherein the second material alters the structural properties of the composition as compared to the structural properties of the alpha-HMX particulates in the absence of the second material.

19. The process of claim 18, wherein the second material increases at least one of the durability, density, or structural strength of the composition.

20. The process of claim 12, wherein the second material comprises one or more polymerizable monomers.

21. The process of claim 20, wherein the second material comprises caprolactam.

22. The process of claim 20, wherein the second material comprises adipic acid and hexamethylene diamine.

23. The process of claim 20, further comprising the step of polymerizing the polymerizable monomers in situ.

24. The process of claim 12, wherein the second material is sorbed onto the alpha-HMX particles by a process comprising the steps of:

(a) providing at least one second material;

(b) mixing the second material with a liquid solvent;

(c) contacting the solvent with alpha-HMX particles; and

(d) evaporating the solvent, whereby the second material adsorbs onto the alpha-HMX particles.

25. The process of claim 24, wherein the solvent is an organic solvent.

26. The process of claim 1, wherein the granules formed in step (b) have greater bulk density than the particulates.

27. The process of claim 1, wherein the density of the granule is controlled by selecting the amount of kinetic energy imparted to the particulates in step (b).

28. A process for making an alpha-HMX composition, comprising the steps of:

(a) mixing particulate alpha-HMX and at least one particulate material selected from the group consisting of energetic materials and fuels, thereby forming a particulate mixture;

(b) fluidizing the particulate mixture; and

(c) impacting the particulate mixture against a solid surface, whereby the particulate mixture agglomerate to form granules.

29. The process of claim 28, wherein in step (c) the particulate mixture is circulated around a circular or elliptical path.

30. The process of claim 29, wherein in step (c) the particulate mixture is circulated in a channel in a rotating vessel.

31. The process of claim 28, wherein the article comprises no binder.

32. The process of claim 28, wherein the particulate mixture comprises no more than about 2% by weight graphite.

33. The process of claim 28, wherein the article comprises at least one energetic material selected from the group consisting of beta-HMX, RDX, TNT, and ammonium nitrate.

34. The process of claim 28, wherein the article comprises at least one fuel selected from the group consisting of aluminum, lithium hydride, and lithium aluminum hydride.

35. The process of claim 28, wherein the article comprises about 0.1-20% by weight aluminum.

36. The process of claim 28, wherein the granules contain void spaces, and wherein the process further comprises the step of sorbing at least one second material into the granules.

37. The process of claim 36, wherein the second material is sorbed into the granules by using a vacuum to a gas phase that comprises draw the second material into the granule.

38. The process of claim 36, wherein the second material is sorbed into the granules by:

(d) mixing at least one second material with a liquid solvent;

(e) contacting the solvent with the granules; and

(f) evaporating the solvent, whereby the second material is sorbed into the granules.

39. The process of claim 38, wherein the solvent is an organic solvent.

40. The process of claim 38 wherein the second material of step (d) is an energetic material.

41. The process of claim 39, wherein the energetic material is selected from the group consisting of beta-HMX, RDX, TNT, ammonium nitrate, and mixtures thereof.

42. The process of claim 37, wherein the second material of step (d) is a fuel.

43. The process of claim 41, wherein the fuel is selected from the group consisting of aluminum, lithium hydride, lithium aluminum hydride, and mixtures thereof.

44. A process for forming granules from at least one particulate material, comprising the steps of:

(a) selecting particulates having a particle size distribution and adding to the particulates about 0.001-0.5 g of an organic solvent per g of particulates; and

(b) fluidizing the particulates, whereby particulates agglomerate to form granules.

FIELD OF THE INVENTION

The invention relates to processes for producing HMX (1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane), processes for producing intermediates that can be used to produce HMX, and compounds and compositions produced by various of these processes.

BACKGROUND OF THE INVENTION

HMX (1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane), also referred to as octogen or cyclotetramethylenetetranitramine, is a highly energetic material that is useful in various explosives and propellants for military and non-military applications. HMX is recognized as one of the most powerful nitramine explosives, and is used as the benchmark for all other explosives.

HMX is known to exist in four different crystal structures or polymorphic forms--alpha, beta, gamma and delta. Of these polymorphs, it was long believed that the beta form was the least sensitive and most stable, and thus the beta polymorph has been the most widely used form of HMX. The alpha and gamma polymorphs have commonly been dismissed as too dangerous for use due to greater sensitivity, and the delta polymorph is so unstable that it is of no commercial significance.

Despite its superior energetic properties, HMX has not been widely used as an explosive due to difficulties in large-scale production and excessive manufacturing costs. The first known process for the manufacture of HMX, the Bachmann process, was developed in the 1940's. The Bachmann process involves nitrolysis of hexamine (also known as hexamethylenetetraamine) with a mixture of nitric acid and a large excess (e.g., 20-fold) of acetic anhydride. HMX is produced as a by-product or contaminant along with a greater amount of another explosive, RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine). The Bachmann process typically provides yields of 80-84%, of which only about 10-40% is HMX, based on the methylene content of the feed. When fully optimized for HMX, the maximum reported yield of HMX per mole of hexamine feed is about 64%. Due to the inefficiencies in the process, and the large amounts of hazardous waste materials produced, it is not appropriate for large-scale industrial production.

Other synthetic routes for making HMX have been proposed, involving various intermediates. One such intermediate that has been used to produce HMX is DAPT (3,7-diacetyl-1,3,5,7-tetraazabicyclo-[3.3.1]-nonane). DAPT is generally made by reaction of wet hexamine and acetic anhydride. One problem common to all methods of manufacturing DAPT is the massive amount of heat generated by the reaction. Because DAPT in solution will decompose rapidly at temperatures ranging from about 20-120.degree. C., depending on pH, it is necessary to remove heat from the reaction mixture and thus keep the temperature low. In effect, the rate of DAPT production is typically limited by the capacity of the reaction apparatus to withdraw heat by means of heat exchangers or the like. Due to the extremely exothermic nature of this reaction, in practice the rate of addition of acetic anhydride to the hexamine has been kept very low, so the rate of heat generation is kept at manageable levels. As a result, the time required to synthesize a given amount of DAPT is quite long, and the cost is relatively high.

One method proposed for dealing with the tremendous amounts of heat generated by the reaction is to mix ice and water with hexamine to create a slurry, and then add acetic anhydride to the slurry. (Lukasavage U.S. Pat. No. 5,246,671.) Suitable temperatures for this reaction slurry are described as ranging from -18.degree. C. up to 120.degree. C.

Another intermediate that can be used in the production of HMX is TAT (1,3,5,7-tetraacetyl-1,3,5,7-tetraazacyclooctane, also known as 1,3,5,7-tetraacetyloctahydro-1,3,5,7-tetrazocine). TAT can be prepared by heating DAPT with acetic anhydride under anhydrous conditions, but the yields from this process have been poor. Another process used to prepare TAT involves reacting DAPT with acetic anhydride, acetyl chloride, and an alkanoic acid salt such as sodium acetate, under anhydrous conditions. (Siele U.S. Pat. No. 3,979,379.) However, this process uses a large excess of acetic anhydride, thus making it relatively expensive. Yet another process that has been used to make TAT involves reacting DAPT with acetic anhydride in the presence of a metal acetate under anhydrous conditions at temperatures of 100-125.degree. C. (Surapaneni U.S. Statutory Invention Registration H50.) However the reaction conditions and yield that have been reported for this process indicate that it is not economical for commercial use.

HMX can be synthesized by nitrolysis of TAT, using nitric acid and dinitrogen pentoxide or phosphorous pentoxide, at temperatures ranging from room temperature up to 40.degree. C. (Lukasavage U.S. Pat. Nos. 5,124,493 and 5,268,469.) This process too, however, has not seen acceptance on a large production scale due to the economics involved.

SOLEX (1-(N)-acetyl-3,5,7-trinitro-cyclotetramethylenetetramine) is another nitramine explosive, which is a byproduct of the nitration of TAT to form HMX. SOLEX is relatively stable, having twice the impact resistance of RDX, is easily isolated, and can be produced using far less nitrating agent than is required for the direct preparation of HMX from TAT.

One process that has been described for the production of SOLEX involves adding TAT to a solution of 98% nitric acid and phosphorus pentoxide at a temperature between 20-45.degree. C. (Lukasavage U.S. Pat. No. 5,120,887.) The purity and product yields from this method are reported to be quantitative. Significantly, however, this method requires an excess of nitrating agent, i.e., 7.5 grams of nitric acid per gram of TAT used, which makes the process relatively expensive. The SOLEX can be converted to HMX by treatment with strong nitric acid.

Beta-HMX has been widely used as an explosive, despite the difficulties and expense involved in its manufacture. One specific form that is sold is referred to as Class 5 beta-HMX (defined as particulate beta-HMX of which 98% by weight will pass a 325 mesh (44 .mu.m) sieve). Class 5 beta-HMX can be sold for a higher price than coarser beta-HMX products, but is also more difficult to make. Usually it is made by first forming larger beta-HMX particles, and then either grinding them in a water slurry or "sand blasting" them against a hard surface, whereby the desired finer beta-HMX particles are produced. This procedure is troublesome and relatively expensive.

Recently it was discovered that alpha-HMX can be produced that exhibits less sensitivity to impact than beta-HMX. (Lukasavage U.S. Pat. No. 5,268,469.) Production of this polymorph at a reasonable cost on a large scale would be advantageous as it would be useful as a substitute for the beta-HMX used in existing explosive formulations.

Another problem in the prior art involves making durable shaped articles that contain explosive materials. Such articles typically comprise both an explosive substance and a binder, the latter giving the composition the physical characteristics needed to retain the desired shape. However, such binders or other additives dilute the explosive power.

A long-standing need exists for an improved process for making HMX, and improved HMX compositions and articles that exhibit desirable stability, impact sensitivity, and explosive properties. A particular need exists for an improved process for making alpha-HMX that is relatively impact-insensitive.

SUMMARY OF THE INVENTION

One aspect of the invention is a process for making a 3,7-dialkanoyl-1,3,5,7-tetraazabicyclo-[3.3.1]-nonane. The process comprises the steps of:

(a) dissolving hexamine in water, thereby forming a reaction mixture having a temperature of about 0-30.degree. C. (preferably about 10-25.degree. C., most preferably about room temperature (about 22.degree. C.));

(b) cooling the reaction mixture to keep its temperature below about 20.degree. C.; and

(c) adding to the reaction mixture an alkanoic acid anhydride having the formula (RCO).sub.2 O, where R is straight chain or branched alkyl having 1-5 carbon atoms, whereby a product solution comprising a compound having the formula ##STR1##

is produced, and wherein R is as defined above. Preferably in step (b), the reaction mixture is cooled to a temperature between about -30 and 10.degree. C., more preferably between about -15 and 5.degree. C., most preferably at or below about 0.degree. C.

In one preferred embodiment of this process, the alkanoic acid anhydride is acetic anhydride and the product solution comprises DAPT. It is preferred to use about 2.0-2.5 moles of acetic anhydride per mole of hexamine, most preferably about 2.0-2.1 moles of acetic anhydride per mole of hexamine.

One preferred way of cooling the reaction mixture is to use an external cooling jacket through which a heat transfer fluid flows. Another way of cooling the reaction mixture involves the addition of ice (e.g., at least about 0.2 g of ice per g of hexamine). It is preferred to add about 0.2-5.0 grams of ice to the reaction mixture per gram of hexamine (more preferably about 0.2-1.0, most preferably about 0.5), and to use about 0.5-1.5 grams of water in step (a) per gram of hexamine (most preferably about 1.0 gram of water per gram of hexamine).

The ice preferably is present in an amount sufficient to maintain the temperature of the reaction mixture at a temperature between about -30.degree. C. and about 10.degree. C., more preferably in an amount sufficient to maintain the temperature of the reaction mixture at between about -15.degree. C. and about 5.degree. C., most preferably at or below about 0.degree. C. The ice can be used in any of a variety of forms, such as crushed ice, shaved ice, block ice, and mixtures of ice and water.

Optionally, at least some of the ice or other device to provide cooling can be enclosed in a container that prevents physical contact between it and the reaction mixture, but permits heat transfer with the reaction mixture. For example, the container can be a flexible bag made of one or more thermoplastic polymers, or a rigid enclosure made of one or more thermoplastic or thermosetting polymers.

As another option, the ice can be pre-cooled to a temperature below about 0.degree. C. before being added to the reaction mixture, preferably to a temperature below about -10.degree. C., most preferably to below about -30.degree. C.

As alternatives to an external cooling jacket or addition of ice, cooling of the reaction mixture can be provided by cooling coils having a heat transfer fluid flowing therethrough, thermal control rods, and the like.

The product solution in this process will typically comprise some volatile compounds. One method of removing such volatile compounds comprises the further steps of:

(d) heating the solution to at least about 40.degree. C. and contacting the solution with a flow of air that is substantially saturated with water vapor; and

(e) when about 50-80% by weight of the product solution has been evaporated, heating the solution to about 70-150.degree. C. and continuing to contact the solution with a flow of air.

The pH of the product solution preferably is maintained above about 6.5 during steps (d) and (e), more preferably above about 7.0. In a preferred embodiment of these purification steps, the product solution is heated to about 40-45.degree. C. in step (d), and to about 130-140.degree. C. in step (e).

Another way of removing such volatile compounds comprises the additional steps of (d) feeding a liquid stream that comprises the product solution into the upper half of a stripper column; (e) feeding a gas stream having a temperature of at least about 120.degree. C. into the lower half of the stripper column, whereby the gas stream and the liquid stream come into countercurrent contact in the stripper column; (f) withdrawing a stream comprising the compound having the formula (I) from the bottom of the stripper column; and (g) withdrawing a waste stream comprising air and one or more of water vapor, water, formaldehyde, and acetic acid, from the top of the column. In one embodiment, the temperature of the gas stream is about 120-130.degree. C. In other embodiments, the temperature of the gas stream is greater than about 150.degree. C., or even greater than about 200.degree. C. Preferably the gas stream consists essentially of air, and the stripper column comprises packing.

This method of removing the volatile compounds can be considered to provide thermal dissociation of the DAPT salt (e.g., DAPT acetate) that enters the upper part of the stripper column, thereby forming an acid and a base. The stripper column can optionally be operated at reduced (e.g., sub-atmospheric) pressure and temperature.

One particularly preferred embodiment of this process can be used to make DAPT, and comprises the steps of:

(a) dissolving hexamine in water, at a ratio of about 1.0 gram of water per gram of hexamine, at a temperature of about 10-30.degree. C., thereby forming a reaction mixture;

(b) adding ice to the reaction mixture in an amount sufficient to maintain the reaction mixture at or below about 0.degree. C.;

(c) adding about 2.0-2.1 moles of acetic anhydride per mole of hexamine to the reaction mixture, whereby a product solution comprising DAPT and volatile compounds is produced;

(d) feeding a liquid stream that comprises the product solution into the upper half of a stripper column;

(e) feeding a gas stream having a temperature of at least about 120.degree. C. into the lower half of the stripper column, whereby the gas stream and the liquid stream come into countercurrent contact in the stripper column;

(f) withdrawing a stream comprising the compound having the formula (I) from the bottom of the stripper column; and

(g) withdrawing a waste stream comprising air and one or more of water vapor, water, formaldehyde, and acetic acid, from the top of the column.

The various embodiments of the above-described process can be operated safely with much greater throughput than prior processes. This process is especially valuable for producing DAPT. The increased production rate possible with this process significantly reduces the cost of producing DAPT.

A second aspect of the invention is a process for making a 1,3,5,7-tetraalkanoyl-1,3,5,7-tetraazacyclooctane. This process comprises the steps of:

(a) reacting a compound having the formula ##STR2##

wherein R is straight chain or branched alkyl having 1-5 carbon atoms, with an alkanoic acid anhydride having the formula (RCO).sub.2 O, where R is as defined above, or an alkanoic acid halide (such as acetyl chloride) having the formula RC(O)X, where R is as defined above and X is halide, thereby producing a compound having the formula: ##STR3##

wherein R is as defined above; and

(b) reacting the compound having the formula (II) with the alkanoic acid anhydride in the presence of water and a catalytic amount of at least one transition metal oxide, thereby producing a compound having the formula ##STR4##

where R is as defined above.

In a preferred embodiment of this process, each R group is methyl, the alkanoic acid anhydride is acetic anhydride, and the product of step (b) comprises TAT. It is also preferred to use transition metal oxide catalysts selected from the group consisting of copper oxides, iron oxides, and mixtures thereof.

Preferably about 2.0-2.5 moles of alkanoic acid anhydride are used per mole of the compound having the formula (I), more preferably about 2.0-2.2 moles of alkanoic acid anhydride per mole of that compound. It is also preferred to use about 1.0-3.0 moles of water per mole of the compound having the formula (II).

Step (a) preferably is performed at a temperature below about 138.degree. C. Most preferably, step (a) is performed at a temperature of about 110-120.degree. C., and subsequently the temperature is raised to about 130-140.degree. C. for a time sufficient to evaporate residual water, alkanoic acid anhydride, and other volatile compounds.

One specific embodiment of this process makes TAT, and comprises the steps of:

(a) reacting DAPT with acetic anhydride, thereby producing a compound having the formula: ##STR5##

wherein R is methyl; and

(b) reacting the compound having the formula (II) with acetic anhydride in the presence of water and a catalytic amount of at least one transition metal oxide, thereby producing TAT.

Another embodiment is a process for making TAT that comprises the steps of the steps of: (a) reacting DAPT with acetic anhydride; and (b) reacting the product of step (a) with acetic anhydride in the presence of a catalytic amount of at least one transition metal oxide. Preferably the product of step (b) comprises TAT, and the process also includes the step of reacting TAT with nitric acid and either phosphorus pentoxide or dinitrogen pentoxide, thereby forming HMX.

This process requires much less anhydride than prior processes, and therefore is more cost-effective.

A third aspect of the invention relates to a novel intermediate that can be used to make HMX, and a process for making that intermediate.

The novel intermediate is a compound having the formula ##STR6##

wherein R is straight chain or branched alkyl having 1-5 carbon atoms. One such compound is 1-acetyl,5-acetate hexamethylene tetraamine (AAHT).

A process for making such an alkanoyl alkanoate hexamethylene tetraamine comprises the step of:

(a) adding an alkanoic acid anhydride having the formula (RCO).sub.2 O, where R is straight chain or branched alkyl having 1-5 carbon atoms, to a slurry of hexamine and water, the slurry having a temperature between about -78.degree. C. and about 0.degree. C., whereby an alkanoyl alkanoate hexamethylene tetraamine is produced.

In the presently preferred embodiment of this process, R is methyl, the alkanoic acid anhydride is acetic anhydride and the alkanoyl alkanoate hexamethylene tetraamine is AAHT.

In one embodiment, the slurry can further comprise ice. It is preferred that the temperature of the slurry of hexamine, ice, and water is between about -50.degree. C. and about -10.degree. C., most preferably no higher than about -30.degree. C. Preferably about 1.0-2.5 moles of alkanoic acid anhydride are added per mole of hexamine, most preferably about 1.0-2.2 moles of alkanoic acid anhydride per mole of hexamine.

The slurry of hexamine, ice, and water can suitably be formed by dissolving hexamine in water, and subsequently adding ice in an amount sufficient to lower the temperature of the slurry to at least about -10.degree. C. Preferably the ice is added in an amount sufficient to lower the temperature of the slurry to at least about -30.degree. C. Optionally the ice can be pre-cooled to at least about -30.degree. C. prior to being added to the hexamine and water. Preferably the slurry comprises about 1-5 grams of hexamine per gram of ice, most preferably about 3 grams of hexamine per gram of ice.

One specific embodiment is a process for making AAHT that comprises the steps of:

(a) dissolving hexamine in water, thereby forming a hexamine solution;

(b) forming a slurry of hexamine, ice, and water by adding ice that has been pre-cooled to at least about -30.degree. C. to the hexamine solution, the ice being added in an amount sufficient to lower the temperature of the slurry to at least about -10.degree. C.; and

(c) adding acetic anhydride to the slurry of hexamine, ice, and water, whereby AAHT is produced.

Another novel way of preparing an alkanoyl alkanoate hexamethylene tetraamine comprises the steps of:

(a) combining hexamine with water in a ratio of at least six moles of water per mole of hexamine, thereby forming an aqueous mixture comprising hexamine hexahydrate;

(b) cooling the mixture to at least about -10.degree. C.;

(c) adding to the mixture an alkanoic acid anhydride having the formula (RCO).sub.2 O, where R is straight chain or branched alkyl having 1-5 carbon atoms, with the mixture being at a temperature of -10.degree. C. or lower, thereby producing an alkanoyl alkanoate hexamethylene tetraamine.

As indicated above, preferably the alkanoic acid anhydride is acetic anhydride and the alkanoyl alkanoate hexamethylene tetraamine is AAHT. It is also preferred that the aqueous mixture is at or below about -30.degree. C. in step (b), most preferably by addition of ice pre-cooled to a temperature below about -30.degree. C. This process can suitably use about 2.0-2.5 moles of alkanoic acid anhydride per mole of hexamine, most preferably about 2.0-2.2 moles of alkanoic acid anhydride per mole of hexamine. Optionally, the anhydride can be pre-cooled to at least about -30.degree. C. prior to its addition.

One specific embodiment of this second way of making AAHT comprises the steps of:

(a) combining hexamine with water in a ratio of at least six moles of water per mole of hexamine, thereby forming an aqueous mixture;

(b) cooling the mixture to at least about -10.degree. C., thereby forming hexamine hexahydrate; and

(c) adding to the mixture acetic anhydride that has been pre-cooled to at least about -30.degree. C. prior to its addition, whereby the temperature of the mixture is kept at -10.degree. C. or lower, thereby producing AAHT.

A fourth aspect of the invention relates to dialkanoyl,dialkanoate-1,3,5,7-tetraazacyclooctane compounds, wherein the alkanoyl groups each have 2-6 carbon atoms and the alkanoate groups each have 3-8 carbon atoms. For example, such compounds can have the formula ##STR7##

wherein R is straight chain or branched alkyl having 1-5 carbon atoms. Alternatively, two R groups can be linked as part of a bidentate polymeric moiety. In one preferred compound in this class, R is methyl.

This aspect of the invention also relates to a process for making such a 1,3,5,7-tetraalkanoyl-1,3,5,7-tetraazacyclooctane compound, comprising the steps of:

(a) reacting a compound having the formula ##STR8##

wherein R is straight chain or branched alkyl having 1-5 carbon atoms, with an alkanoic acid anhydride having the formula (RCO).sub.2 O, where R is straight chain or branched alkyl having 1-5 carbon atoms, at a temperature greater than about 50.degree. C., thereby forming a compound having the formula ##STR9##

wherein R is as defined above; and

(b) contacting the compound having the formula (V) with water in the presence of a catalytic amount of at least one transition metal oxide, thereby producing a compound having the formula ##STR10##

wherein R is as defined above. As before, preferably the alkanoic acid anhydride is acetic anhydride, and the product of step (b) comprises TAT.

Preferably the reaction of step (a) takes place at a temperature of at least about 100.degree. C., most preferably at about 110-120.degree. C. The presently preferred transition metal oxide catalysts are copper oxides, iron oxides, or mixtures thereof. It is also preferred to use about 2-4 moles of alkanoic acid anhydride per mole of compound having the formula (IV).

One specific embodiment of this process comprises the steps of: (a) reacting AAHT with acetic anhydride at a temperature greater than about 50.degree. C.; and (b) contacting the product of step (a) with water in the presence of a catalytic amount of at least one transition metal oxide.

Another embodiment comprises the steps of: (a) reacting AAHT with acetic anhydride at a temperature greater than about 100.degree. C., thereby forming the diester derivative of AAHT; and (b) reacting the diester with water in the presence of a catalytic amount of at least one transition metal oxide, thereby producing TAT.

Although one desirable use of this process is to make the diester (i.e., a dialkanoyl, dialkanoate-1,3,5,7-tetraazacyclooctane) for use in making TAT or an analog thereof, it is also possible to stop the process at the point at which the diester has been formed and recover it.

Among the advantages of this process is that the reaction can be carried out at much lower temperatures than those required for making TAT from DAPT. The reduction in temperature increases the yield as well as the safety of the process.

A fifth aspect of the invention is a process for making a 1-(N)-alkanoyl-3,5,7-trinitro-cyclotetramethylenetetramine compound. This process comprises the steps of:

(a) combining a compound having the formula ##STR11##

wherein R is straight chain or branched alkyl having 1-5 carbon atoms, with nitric acid at a temperature between about 15-50.degree. C., thereby producing a reaction mixture; and

(b) adding phosphorus pentoxide to the reaction mixture, whereby a compound having the formula ##STR12##

is formed, wherein R is as defined above.

As stated above, preferably each R group is methyl, and thus the product is SOLEX. The temperature in step (a) preferably is between about 20-40.degree. C., most preferably about 20-30.degree. C. It is also preferred that the weight ratio of nitric acid to the compound having the formula (III) is between about 0.5:1 to about 5:1, most preferably about 1.5:1. (Preferred weight ratios are given for the embodiment where R is methyl. The preferred weight ratio would change if R was changed.) Preferably the weight ratio of phosphorus pentoxide to the compound having the formula (III) is no greater than about 1:1, more preferably no greater than about 0.75:1, most preferably no greater than about 0.5:1.

The rate of reaction can be controlled by controlling the rate of addition of phosphorus pentoxide to the reaction mixture, or (less desirably) by applying external cooling to the reaction mixture. In either method, control can be in response to measurements of the temperature of the reaction mixture. The extent of the nitration of the compound having the formula (III) can be controlled by using a molar excess of that compound. The extent of the excess of compound (III) limits the extent of the conversion.

One specific embodiment of this process produces SOLEX and comprises the steps of:

(a) combining TAT with nitric acid at a temperature between about 10-15.degree. C., thereby producing a reaction mixture; and

(b) adding phosphorus pentoxide to the reaction mixture at a controlled rate, whereby SOLEX is formed.

This process requires much less phosphorus pentoxide than prior methods of making SOLEX. This aspect of the invention takes advantage of the fact that SOLEX is relatively stable, (having twice the impact resistance of RDX), is easily isolated, and can be produced using a far smaller amount of nitrating agent than is required for the direct preparation of HMX from TAT. Further, SOLEX can be readily converted into alpha-HMX, as described below.

Another way of making such a 1-(N)-alkanoyl-3,5,7-trinitro-cyclotetramethylenetetramine compound comprises the steps:

(a) combining nitric acid and phosphorus pentoxide, thereby producing a reaction mixture; and

(b) adding to the reaction mixture a compound having the formula ##STR13##

wherein R is straight chain or branched alkyl having 1-5 carbon atoms; wherein the reaction mixture is kept at temperature no greater than about 68.degree. C.; and whereby a compound having the formula ##STR14##

is formed, wherein R is as defined above.

In one preferred embodiment of this process, each R group is methyl, and thus the compound having the formula (VI) is SOLEX. Preferably the weight ratio of nitric acid to phosphorus pentoxide in step (a) is from about 2:1 to about 4:1, more preferably about 3:1. The weight ratio of nitric acid to the compound having formula (III) preferably is from about 1.5:1 to about 3.0:1, and the weight ratio of phosphorus pentoxide to the compound having formula (III) preferably is from about 0.5:1 to about 0.75:1.

It is also preferred that the temperature of the reaction mixture in step (a) is about 0-30.degree. C., and that the temperature of the reaction mixture is allowed to rise no higher than about 40-68.degree. C., more preferably no higher than about 45-55.degree. C.

Another embodiment is a process for nitrating TAT comprising the steps of (a) combining TAT and nitric acid to form a reaction mixture having a temperature of about 15-50.degree. C.; and (b) adding P.sub.2 O.sub.5 to the reaction mixture. The product of step (b) can comprise HMX, SOLEX, or a mixture thereof. The product preferably has a melting point of about 260-281.degree. C., more preferably about 270-281.degree. C. The extent of the nitration, i.e., whether the conversion stops at SOLEX, or produces a mixture of SOLEX and HMX, or pure HMX, can be controlled by using a molar excess of TAT.

A sixth aspect of the invention is a process for making HMX. One embodiment of the invention produces alpha-HMX, and, comprises the steps of:

(a) combining phosphorus pentoxide and nitric acid at a temperature of about 0-25.degree. C., forming a reaction mixture; and

(b) adding a compound having the formula ##STR15##

wherein R is straight chain or branched alkyl having 1-5 carbon atoms, to the reaction mixture, whereby a product comprising alpha-HMX is produced. This reaction is preferably a solid-state nitration reaction, i.e. the SOLEX reacts while still a solid rather than being dissolved in the nitric acid. In one preferred embodiment of this process, the compound having the formula (VI) is SOLEX.

Preferably the temperature in step (a) is about 10-20.degree. C., most preferably about 15.degree. C. It is also preferred that the nitric acid has a concentration of at least about 98% by weight.

The HMX produced by this process is at least 99% by weight alpha-HMX, often essentially 100% alpha-HMX. Further, the yield of alpha-HMX is typically at least 99%.

One specific embodiment of this process for making alpha-HMX comprises the steps of:

(a) adding phosphorus pentoxide to nitric acid at a temperature of about 0-25.degree. C., forming a reaction mixture; and

(b) adding SOLEX to the reaction mixture, whereby a solid-state nitration reaction produces alpha-HMX.

The invention also relates to the alpha-HMX product made by the above-described process. This product is extremely pure alpha-HMX, e.g., essentially no RDX or beta-HMX contamination. For example, the product can be 99 weight % or more alpha-HMX. In a preferred embodiment, the product comprises less than 0.01% by weight RDX, more preferably no RDX whatsoever. The majority by weight (i.e., greater than 50% by weight) of the alpha-HMX particles produced by this process have the form of long fibers. A majority by weight of these alpha-HMX fibers have an aspect ratio (length:diameter) of at least about 50:1, sometimes as great as at least about 100:1 or even 1,000:1.

The alpha-HMX can be made into long fibers by dissolving the alpha-HMX in boiling aqueous solution (e.g., in pure water), and then cooling the solution below the boiling point. These steps form fibrous alpha-HMX. In one embodiment, the majority by weight of the alpha-HMX produced upon cooling is fibers having an aspect ratio (length:diameter) of at least about 50:1, more preferably at least about 100:1, most preferably at least about 1,000:1. In particular, the product of these steps will typically be a mass comprising a plurality of such fibers. This material can be pressed or otherwise shaped into useful articles.

In one embodiment, the product is an equilibrium mixture, as described above, of alpha-HMX HMX (making up by far the majority of the product) and SOLEX (making up a very small percentage, usually much less than 1% of the product).

Preparing alpha-HMX by the synthetic route that goes through SOLEX helps control the polymorphic form of the product, permitting the manufacture of pure (or very nearly pure) alpha-HMX at essentially quantitative yield.

Another way of making an HMX composition comprises the steps of:

(a) combining a compound having the formula ##STR16##

wherein R is straight chain or branched alkyl having 1-5 carbon atoms, with nitric acid, thereby forming a reaction mixture; and

(b) adding phosphorus pentoxide to the reaction mixture, whereby a product that comprises HMX is produced. The compound (VI) preferably is dissolved in nitric acid and the reaction takes place in solution. The HMX produced in this way can be converted easily to beta-HMX HMX by contacting it with an organic solvent, e.g., heated acetone. This provides a less expensive method of manufacturing beta-HMX than the conventional direct synthesis methods.

In one preferred embodiment of this method, the compound having the formula (VI) is SOLEX. In another embodiment, the product of step (b) comprises an equilibrium mixture of alpha-HMX and SOLEX. The melting point of the product of step (b) preferably is at least about 277.degree. C. (All melting points given herein are as determined by capillary methodology.)

When the R group is methyl (i.e., the group pendant from the N is acetyl) it is preferred that the weight ratio of nitric acid to SOLEX in step (a) is from about 1.5 to about 3.0, more preferably about 1.8. It is also preferred that the weight ratio of phosphorus pentoxide to the compound having the formula (VI) is from about 0.25 to about 2.0, more preferably about 0.7-0.8. The product made by the above-described process comprises HMX. Without being bound by theory, the HMX made by this particular process may be a form of alpha-HMX, or it may be a different polymorphic form of HMX. As long as the product's melting point is at least about 277.degree. C., it can easily be converted to highly pure beta-HMX by contacting the product with a hot organic solvent (e.g., acetone at a temperature of 40-100.degree. C., preferably about 56.degree. C.).

In any of these embodiments of the process, when the nitration reaction has proceeded to the desired extent, the reaction can be stopped by cooling the reaction mixture (e.g., by adding ice). Optionally, a process of making HMX as described above can further comprise the following back-end steps:

(c) filtering the product of step (b), whereby alpha-HMX is retained by a filter and an impurity-containing filtrate is collected;

(d) treating the filtrate with a source of ammonium ions to adjust its pH to about 4.0-5.0;

(e) evaporating water from the filtrate; and

(f) cooling the filtrate sufficiently to crystallize ammonium nitrate crystals.

These additional steps produce a highly pure ammonium nitrate byproduct, which can be sold for use in fertilizer or the like. Thus, these additional steps enhance the economics of the process by reducing the amount of waste material that must be disposed of and creating a valuable byproduct. In these steps, preferably the pH of the filtrate is adjusted to about 4.7 and the source of ammonium ions is ammonia.

Alternatively, instead of performing steps (c)-(f) after filtration to remove the solid product, the remaining nitric acid can be concentrated for recycle.

A seventh aspect of the invention relates to compositions and articles that comprise HMX, as well as processes for making them.

One such composition comprises HMX particles (e.g., alpha-HMX particles) and at least one second material coated thereon and/or sorbed into voids in the particles. The term "second material" is used herein to refer generically to materials other than alpha-HMX which can be combined with alpha-HMX to form mixtures, granules, and/or shaped articles. Preferably, a majority by weight of the alpha-HMX particles are in the form of fibers, which may be porous (i.e., contain some void spaces). Typically a majority by weight of the alpha-HMX fibers have an aspect ratio (length:diameter) of at least about 50:1, often as great as about 1,000:1 or even higher.

A variety of second materials can be used in the invention, including mixtures of two, three, or more different second materials. One suitable example of a second material is an energetic material, such as beta-HMX, RDX, TNT, ammonium nitrate, or a mixture thereof. Another suitable example of a second material is a fuel, such as aluminum, lithium hydride, lithium aluminum hydride, or a mixture thereof. As another example, a first set of particles can have coated and/or sorbed thereon one component of a binary explosive, and a second set of particles can have coated and/or sorbed thereon the other component of the binary explosive (e.g., material comprising nitro moieties and glycerin). When the two sets of particles are combined, a binary explosive composition can be formed.

Yet another suitable example of a second material is one that alters the structural properties of the composition as compared to the structural properties of the alpha-HMX particles in the absence of the second material. For instance, the second material can be one that increases the durability, density, or structural strength of the composition, such as carbon fibers or silicone molding resins. Another suitable example of a second material is one or more polymerizable monomers, such as caprolactam, or a mixture of adipic acid and hexamethylene diamine. It is possible to polymerize such monomers in situ after they are coated onto the alpha-HMX, thereby providing additional strength or other desirable properties. By coating a HMX particle with such monomers, forming a plurality of such articles into a granule or article, and then polymerizing the monomers in situ, an HMX-containing granule or article can be formed that also comprises a polymeric "cage" or framework.

It is also possible to use multiple layers of coatings comprising second materials. For instance, the composition can comprise a plurality of layers coated on the alpha-HMX particles, each layer comprising at least one second material. The second material can be the same in each of the plurality of coated layers. Alternatively, at least two of the plurality of coated layers comprise different second materials, or each coated layer can comprise a different second material.

This aspect of the invention also relates to durable alpha-HMX containing articles, comprising a plurality of particles, the particles comprising alpha-HMX coated with at least one second material. A "durable article" in this context is one that will retain is shape under normal handling.

In such an article, the plurality of coated alpha-HMX particles can optionally comprise (a) a first group of alpha-HMX particles coated with a second material, and (b) a second group of alpha-HMX particles coated with a different second material. For example, the different second materials could be ones that can be combined to firm a binary explosive. Then when the two groups (a) and (b) are combined, the overall composition is explosive.

The article can suitably be formed by pressing the plurality of coated particles into a shape, or by granulating a plurality of such particles, using techniques described below. The article can further comprise a coating of a second material on the exterior of the article, or even a plurality of coatings of one or more second materials on its exterior. As outlined above, the second material can be the same in each of the plurality of coatings, can be different in at least two of the coatings, or can be different in each coating.

In one particular embodiment, the article further comprises a coating on the exterior of the article. This coating comprises alpha-HMX particles that have been coated with a second material. Alternatively, the article can comprise a plurality of coatings, each of which comprises alpha-HMX particles that have been coated with a second material.

The article can also comprise a second material that has been sorbed into the article, or onto an alpha-HMX particle. A process for sorbing a second material onto alpha-HMX particles, comprises the steps of:

(a) providing at least one second material;

(b) mixing the second material with a liquid solvent;

(c) contacting the solvent with alpha-HMX particles; and

(d) evaporating the solvent, whereby the second material sorbs onto and/or into the alpha-HMX particles.

The second material can initially be in a variety of forms (e.g., solid particulates, liquid, or gas).

In one embodiment, the solvent of step (b) is an organic solvent, such as acetone, cyclohexane, gamma butyrolactone, or a mixture of one or more of these. This process can further comprise the step of forming a granule that itself comprises a plurality of the alpha-HMX particles having the second material coated on the particles. The granules and articles formed as described above are highly stable, for example holding their structural integrity in boiling water or acetone.

The combination of materials involved in this aspect of the invention can achieve a higher level of energy per unit volume, thus making the composition highly desirable for use as an explosive or propellant. Depending on what secondary materials are used, the composition can also have its energetic properties per unit volume increased, or its structural strength, density, or durability increased. These enhancements are especially useful for making various explosive, propellant, and pyrophoric devices (e.g., shaped charges).

An eighth aspect of the invention is a process for making beta-HMX. This can be accomplished by a process that comprises the steps of:

(a) combining a compound having the formula ##STR17##

wherein R is straight chain or branched alkyl having 1-5 carbon atoms, with nitric acid, thereby forming a reaction mixture;

(b) adding phosphorus pentoxide to the reaction mixture, whereby a product that comprises HMX is produced;

(c) contacting the so-produced HMX with a solvent; and

(d) evaporating the solvent, whereby beta-HMX crystals are formed.

This aspect of the invention allows the manufacture of beta-HMX by conversion of a different form of HMX (e.g., alpha-HMX). The HMX used as the starting material preferably is made by a process comprising the steps of:

(a) combining a compound having the formula ##STR18##

wherein R is straight chain or branched alkyl having 1-5 carbon atoms, with nitric acid, thereby forming a reaction mixture; and

(b) adding phosphorus pentoxide to the reaction mixture, whereby a product that comprises HMX is produced. The compound (VI) preferably is dissolved in nitric acid and the reaction takes place in solution. The melting point of the product of step (b) preferably is at least about 277.degree. C.

The conversion process comprises the steps of:

(a) contacting the so-produced HMX with a solvent;

(b) evaporating the solvent, whereby beta-HMX crystals are formed.

In one embodiment, the HMX is dissolved or suspended in the solvent in step (a). In a specific embodiment of the process, the solvent is an organic solvent, such as acetone, cyclohexane, gamma butyrolactone, or a mixture of one or more of these.

Optionally, seed crystals of beta-HMX can be added to the solvent to facilitate crystallization. However, seed crystals are generally not required. If seed crystals are used, they can be provided, for example, by including no more than about 1% by weight (preferably no more than about 0.1%) beta-HMX in the HMX of step (a). If a small amount of beta-HMX byproduct is present in the starting HMX composition, it can serve this purpose. Alternatively, the beta-HMX crystals can provided by adding them to the solvent from an external source.

In one preferred embodiment of the process, the solvent is evaporated by spray drying. This spray drying can suitably take place at a temperature of less than about 56.degree. C., preferably at about 50.degree. C. This process can produced Class 5 beta-HMX, or even finer particles.

A ninth aspect of the invention is a process for forming alpha-HMX containing granules from at least one particulate material, comprising the steps of:

(a) selecting particulates having a particle size distribution; and

(b) fluidizing the particulates, whereby particulates agglomerate to form granules.

In one embodiment, this process involves accelerating the fluidized particulates against a solid surface, and more preferably, continuously impacting such particulates against a surface, most preferably a curved surface. Vessels having circular cross-sections are well suited for performing this operation. A rotating impeller, or alternatively a gas stream, can suitably be used to accelerate the particles.

Although this process is especially well-suited for producing granules from alpha-HMX particles made as described above, it is not limited to use with that particular material. This process can be used with a variety of particulate materials, such as drugs and pharmaceutical excipients.

In one preferred embodiment, the fluidized particulates are impacted against a solid surface, for example by being circulated around a circular or elliptical path. Preferably, the particulates are circulated in a channel in a vessel, whereby the motion creates centrifugal force that impacts the particulates against the solid surface of the channel, whereby a granule is formed that tumbles as it continues to circulate around the channel.

The particle size distribution in step (a) can be any desired range, including taking particulate alpha-HMX and using it as-is. Alternatively, a particle size distribution can be cut from the initial material, for example by sieving.

Optionally, a small amount of an organic solvent (e.g., about 0.001-0.5 g of organic solvent per g of alpha-HMX or other particulate material, more preferably about 0.05-0.1 g of solvent per g of particulates) can be added to the particulates. This small amount of solvent helps fluidize the particles, and facilitates formation of a granule, but does not dissolve a large percentage of the alpha-HMX, which could cause the eventual formation of a different polymorph.

Fluidization of the particles can be achieved, for example, by placing them in high velocity gas streams (e.g., "sand-blasting"). The density of the resulting granules can be controlled by selecting the amount of kinetic energy imparted to the particles in step (b). In other words, the greater the velocity of the gas steam(s) in which the particles are fluidized, the denser the resulting granules will be.

Optionally, the alpha-HMX particulates can be coated and/or impregnated with one or more second materials, as described above, such as energetic materials or fuels. If one or more of the second materials comprise polymerizable monomers, the process can optionally further comprise the step of polymerizing those monomers in situ, either before or after the granule is formed.

In one particular embodiment, a second material is sorbed onto the alpha-HMX particles by a process comprising the steps of:

(a) providing at least one second material;

(b) mixing the second material with a liquid solvent;

(c) contacting the solvent with alpha-HMX particles; and

(d) evaporating the solvent, whereby the second material adsorbs onto the alpha-HMX particles.

This aspect of the invention also relates to a durable article that consists essentially of alpha-HMX and at least one second material. In other words, this article need not comprise any binder; the properties of the alpha-HMX particles allow them to be formed into a durable article in a mixture with the second material, without requiring the inclusion of a material with adhesive properties. Optionally, such an article can comprise no more than about 2% by weight graphite, to facilitate manufacturing the article.

The second materials included in such an article can be varied, as described above. One particularly useful second material in this aspect of the invention is aluminum in particulate form. One particular embodiment of the invention is an article as described above that comprises about 0.1-20% by weight aluminum. One especially useful embodiment is a durable article that consists of alpha-HMX and about 0.1-20% by weight aluminum.

This aspect of the invention also relates to a process for making an alpha-HMX composition, comprising the steps of:

(a) mixing particulate alpha-HMX and at least one particulate material selected from the group consisting of energetic materials and fuels, thereby forming a particulate mixture;

(b) fluidizing the particulate mixture; and

(c) impacting the particula