A Recovery Process for Spent Polyurethane-Based Propellants

Abstract

The valuable inorganic components-energetics and fuel-of solid propellants are successfully separated and recovered by using swelling and ultrasound. In this study, the inert polyurethane-based propellant is first comminuted in various solvents as swelling media, and an appropriate solvent is then selected. Subsequently an ultrasound induced cavitational reaction for interfacial treatment is performed with the use of a mild oxidant. Through the process, the polymer binders are partially degraded and the propellant network is destroyed, enabling inorganic and metallic constituents to be released and separated.To meet military need, solid composite propellants have been extensively developed and manufactured in the past. Following the end of the cold war, these large quantities of propellants from the demilitarization of missiles brought about the urgency of safe propellant disposal. While noted for their high energy release arid explosion, the spent propellants become hazardous wastes and need to be disposed with caution. In compliance to the Resources Conservation and Recovery Act (RCRA) and EPA regulations, the conventional and primary disposal method of spent propellant-open-pit burning-is no longer legal. These stringent environmental regulations and uprising pollution concerns have prompted the study of the recovery process for spent propellants.To recover the useful inorganic components from the spent propellant, the most common methods of breaking the polyurethane backbone macro-structure under vigorous conditions, such as thermal and hydrolytic cleavage, are not applicable. Currently, several techniques are actively being pursued by different groups. These include: aqueous maceration and extraction of propellant by Thiokol, cryogenic washout by General Atomic, and ammonia extraction at supercritical or near-supercritical conditions by Hercules. In addition to these, alternative methods leading to a mild recovery process are being sought.

Staged Process for Composite Propellants: Recovery of Energetic and Metallic Fuel

“…The experiments for the optimal conditions of the ultrasonication are presented elsewhere (Shiu et al, 1995). Through this process, the polyurethane fragments were further degraded and became soluble in the solvent; the insoluble metallic fuel was precipitated and collected at the bottom of the reactor.…”