1. Field of the Invention
This invention relates to the production of high explosive materials. More particularly, the invention relates to the removal of excess acidity from crude unrecrystallized nitramines and other explosive materials.
2. State of the Art
Conventional methods of producing nitramine explosive materials typically result in the occlusion of acids in the crude crystals. For some nitramines, the acid must be largely removed to permit the materials to meet government specifications for use in explosives and propellants. The crude unrecrystallized material may contain occluded acidity which is 10 to 50 times the allowable specified acidity.
The procedure presently used for removing the excess occluded acidity comprises dissolving the crude material in an appropriate solvent and recrystallizing the nitramine, whereby most of the acidity remains in the solvent phase. However, this process is very slow and expensive. Moreover, the mean particle size and the particle size distribution may vary widely from batch to batch.
Typically, the recrystallized material must be further ground to a small particle size before use. For example, the high explosive cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX) is graded for differing uses according to the particle size. Class 1 RDX has a relatively large particle size:
______________________________________ U.S. Standard Sieve No. Percent Passing ______________________________________ 20 98 +/- 2 50 90 +/- 10 100 60 +/- 30 200 25 +/- 20 ______________________________________
A finely ground RDX, in which 97+ percent passes a No. 325 sieve, is designated Class 5 RDX.
A present grinding method using a fluid energy mill requires a moisture content less than about 0.1 percent. Thus, the wet recrystallized nitramine(s) must be first dried. Such drying at a relatively low temperature is a slow and energy intensive process.
Thus, starting with a crude slurry of crystallized RDX, the conventional steps required to produce Class 5 RDX ready for compounding into an explosive end product include:
1. dissolution in acetone at 135 degrees F.; PA1 2. recrystallization by adding water and distilling the acetone at 86 degrees F.; PA1 3. settling and decantation of the liquor; PA1 4. adding water and distilling the remaining acetone; PA1 5. dewatering of the slurry to recover RDX; PA1 6. water-washing of recovered RDX.
The entire process is tedious and excessively consumptive of both time and energy.
Similar time consuming steps are used in the production of other explosive materials such as cyclotetramethylenetetranitramine (HMX), coproduced mixtures of RDX and HMX known as CPX, and other explosive materials, to achieve the desired low-acidity products.
There remains the need for a method which will rapidly and inexpensively remove the occluded and surface acidity of explosive materials to a low level. The need exists for a method which achieves the desired particle size reduction as well as acidity removal.