The goal of this research was to evaluate several technologies developed at the National Aeronautics and Space Administration (NASA) Kennedy Space Center (KSC) as a means for the demilitarization of several different munitions commodities. This project sought to develop a system for safe demilitarization of munitions that allow for recycling or reuse of individual components and an environmentally safe wastestream for those components that cannot be reused. The project evaluated the feasibility of three novel technologies developed at NASA’s Kennedy Space Center for the degradation of hexachloroethane, chloroacetophone, trinitrotoluene (TNT), and propellant AF-M315E. The technologies are Zero Valent Magnesium (ZVMg), visible light photocatalysis, and an innovative use of ion exchange resins. The guiding principle of the project was to minimize complexity and operational hazards.
In all, three separate and novel methods were assessed to determine their possible efficacy to demilitarize munitions including TNT, HCE, CN, and AF-M315E.
- Zero valent magnesium (ZVMg) was tested with trinitrotoluene (TNT) in an attempt to determine if a magnesium-based reaction is capable of chemically reducing the TNT to a non-hazardous byproduct. Unfortunately, it appears that the ZVMg is adsorbing the TNT rather than degrading it. While it is possible that degradation may be occurring on the surface of the metal, once it has been adsorbed, this conclusion cannot be supported at this time due to the lack of any observable daughter products. One possibility is that TNT may undergo sequential degradation while it is absorbed to surface of the ZVMg, in which case daughter products would not be observed. However, further testing is necessary to validate this supposition, although literature indicates TNT should be degraded by ZVMg.
- Ion exchange resins were tested to determine if the nitrates (oxidizer portion) of the AF-M315E explosive propellant could be easily removed, allowing for the remaining propellant to be considered “demilitarized”. Two commercial strong base anion (SBA) resins (Purolite A520E and ResinTech SIR-100-HP) were procured for this study. Static and flow-through testing showed that these resins could successfully remove the nitrates from a dilute AF-M315E solution. The flow-through testing also showed that a single batch of resin could be used and regenerated several times and still retain the ability to remove nitrate. Further testing should focus on upscaling the present flow-through system to allow for concurrent nitrate removal and resin regeneration. The ability to use these resins to allow for the long-term and safe storage of the AF-M315E until it was needed, at which point it would be reconstituted, is also proposed for further study.
- Visible light responsive (VLR) photocatalysis in conjunction with Ag-doped TiO2 catalyst was tested for its ability to degrade hexachloroethane, HCE, (smoke generating munition) and 2-chloroacetophenone, CN, (riot control munition). Testing was performed in a static manner using 40-mL vials for both munitions components. Testing of the HCE showed near complete degradation (within 4 hours) as well identifying perchloroethylene, PCE, as a likely daughter product. Also, experimental evidence showed the production of chloride ions which would suggest that complete degradation to HCl and CO2 may be occurring. Testing of the VLR photocatalysis for degrading CN was more difficult as the vial studies used crystals of the CN to produce gaseous CN within the headspace within the vials. As such, degradation of the CN itself was not observed since it was constantly replenished by sublimation of the neat material, however an increase in the degradation byproducts was seen (within 4 hours). Two daughter products, acetophenone and benzaldehyde, were identified during the study, both of which could be re-used in other markets.
Processing rate: Tests 1 and 3 were both fully successful so they can be used to calculate the processing rate. Test 1 used a flow rate of 77 ml/min and test 3 was about half, 38.8 ml/min. Accounting for the 1:500 dilution of AF-M315E in water before processing, this corresponds to a maximum processing rate of 9 ml/hr of pure AF-M315E using a resin bed of 154 ml, containing 153 g. Using a simple linear scaling of 100 to get to 1 l/hr, the bed would be 15 liters. Theoretically, the 154 ml bed should have been able to process 12.4 ml of pure AF-M315E, but in these tests only the equivalent of 5 ml of pure propellant was processed before breakthrough. Further optimization should lead to faster processing rates and/or smaller bed volumes. If implemented in a continuous as described in section 7.2, then the time of regeneration is actually the slow step. In these tests, AF-M315E processing took 30 – 60 minutes while bed regeneration took 120 minutes.
Safety: No safety issues occurred or would be anticipated in future work. Before starting laboratory work for this project, the proposed process went through a full safety review.
The following tasks are proposed to further advance this technology.
- Design and build a scaled up system with multiple beds for continuous processing of AF-M315E and ion exchange resin bed regeneration. Within this task, optimization of the AF-M315E processing rate and the bed regeneration time would be performed.
- Evaluate stability of chloride containing daughter products.
- Attempt to reconstitute the propellant by exchanging chloride for nitrate. Then, the water must be removed from reconstituted propellant. The reconstituted propellant would need to be evaluated by the Air Force Research Lab that makes it to determine if it has the same performance as the fresh material.