[[ Editor’s Note:
This post is taken from “In-flight Propellant Transfer Spaceplane Design and Testing Considerations”, AIAA 95-2955, by Captain Mitchell Burnside Clapp (*), Phillips Laboratory, Kirtland AFB, NM 87117
Hydrogen peroxide is not currently available at 98% concentration in the United States. It may, however, be produced from 70% concentration peroxide, which is a commodity item, by fractional crystallization26. The 70% liquid is chilled to -67 F, which forms a two-phase system consisting of solid hydrogen peroxide and 62% concentration liquid. The solid peroxide occludes a great deal of liquid, so centrifugal separation is required to yield the pure peroxide solid, which is then thawed. The process has several advantages. It is safer than distillation. Impurities tend to remain in the liquid solution rather than the solid precipitate. The 62% liquid may be distilled to 70% for reuse in the system. Most of the concern about 98% H2O2 for rocket applications is anecdotal. John Clark’s book “Ignition — An Informal History of Liquid Rocket Propulsion” devotes an entire chapter to hydrogen peroxide27, and has two problems with it. First, the freezing point is high — about 31.4Ãƒâ€šÃ‚Â°F (-0.4Ãƒâ€šÃ‚Â°C). Anything added to hydrogen peroxide to depress the freezing point made it unstable and potentially explosive. Secondly, the Navy tested a puddle of jet fuel upon which they poured 90% H2O2. The peroxide sank though the fuel, began to decompose in contact with the dirt, formed an oxygen/fuel vapor mixture, and blew up. Spills of this type must, as a result, be avoided.
The second source of concern with peroxide is the Me-163B experience28 and the capture of stocks of 70% H2O2 by the Allies after V-E day. The Me-163B often landed in flames and had a real problem with safety. The oxidant for the Me-163B was 70% H2O2, but it was manufactured by coerced labor with shoddy quality control under wartime conditions. Modern hydrogen peroxide, according to David Andrews29 is a “completely different material”. The Me-163B itself had wooden primary structure. Finally, the real risk was in the fuel — a mixture of nitrous oxide, hydrazine hydrate, methanol, and potassium cuprocyanate. The Me-163A, which used 70% H2O2 as a monopropellant, was much safer.
The overwhelming choice for oxidizer in the aircraft rocket world has been hydrogen peroxide. The AR-2 engine, used in the FJ-4, F-86, and the NF-104, was a 90% H2O2 and JP-5 or JP-4 engine, had a two hour time between overhauls (a number that isn’t even specified for most rockets) and was operated and maintained by ordinary Air Force enlisted servicemen for years18. The Snarler and Screamer engines used in the UK’s Buccaneer fighter also employed 85% H2O2 and kerosene17, and eventually begat the Gamma engine used in the Black Knight and Black Arrow rocket programs.
Hydrogen peroxide in any concentration is an oxidant and as such needs to be treated with respect and care. It is clearly a less powerful oxidant than oxygen, but even so, it has to be handled according to a well-defined set of procedures. The hazards usually manifest themselves in the effect of impurities on the peroxide rather than the effect of the peroxide on the impurities. Notice that this is the reverse of the mechanism of failure with liquid oxygen, where a small impurity tends to burn and cause an evolution of oxygen gas that destroys delicate parts and leads to catastrophic failure. Nevertheless, the failures are equally catastrophic and the standard of cleanliness is the same. Impurities of all kinds, particularly organics, must be absolutely avoided30.
One additional precaution is needed with peroxide — anything that touches it must be passivated beforehand. There are a large number of procedures for passivation, generally involving the washing of the part with high strength nitric acid and then with progressively higher grades of peroxide until final peroxide strength is reached. Not all materials are suitable for peroxide use. Stainless steels, some aluminum alloys, zirconium, glass, and tin can all be treated to class 1 compatibility with 98% H2O2. Class 1 means “suitable for storage tanks and long term continuous exposure” and involves a decomposition rate of 0.4 to 0.1 % per year. Of particular concern is the choice of materials for lubricants and seals. Only fluorinated polymers (such as Teflon, Kel-F, or Viton) appear to be suitable.
An interesting result of the long term compatibility results for hydrogen peroxide is that 98% H2O2 is more stable that 90% H2O2. The reason for this appears to be that the water molecule is very slightly catalytic, being polar31. Also, elevated pressure can suppress decomposition (by reason of Le Chatelier’s principle), but the recommended practice is to vent peroxide storage and transport containers.
The hazards of dealing with high purity hydrogen peroxide fall into four categories: detonation and explosion, uncontrolled decomposition, fire, and personnel injury.
Concentrated vapors will irritate the nasal passages and eyes. Vapors, mists, and liquid will irritate skin. Ingested peroxide will decompose internally, leading to severe distention of the stomach and internal burns. The corrective action is to flush with water. Do not ingest. The vapor pressure is only 1/9 that of water, which helps prevent harmful exposure to hazardous vapor levels.
Hydrogen peroxide is not flammable, but will react with combustible materials with the evolution of enough heat to initiate and support combustion. Removing the air does not help, because the peroxide generates its own oxygen on decomposition. Fight peroxide fires with water. Chemical extinguishers will catalyze further decomposition.
98% H2O2 is not classified as impact or shock sensitive. Numerous tests have been unable to sustain detonation waves in liquid peroxide solutions. Vapor phase concentrations of over 26% peroxide are considered “explosive” in the sense that the release of energy in the vapor phase upon decomposition is rapid enough to produce effects normally associated with explosions. For 98% H2O2 the limit32 is 212Ãƒâ€šÃ‚Â° F. Invariably, peroxide vapor hazards are preceded by a slow buildup of temperature and pressure in the tanks. The corrective action is to monitor temperature and pressure buildups, vent the tanks, do not permit elevated temperatures and avoid impurities.
98% H2O2 can be, and indeed has been, a safe and effective rocket propellant PROVIDED THE RIGHT DESIGN, MANUFACTURE, AND OPERATIONS PROCEDURES ARE FOLLOWED . The entire system must be composed of peroxide compatible materials, preferably class 1. The system must be designed and operated in such a way as to prevent contamination with reactive materials (no garden hose purges, no greasy handprints on the refueling nozzle, etc.). Keep the number of mechanical joints to a minimum. Vent ball valves upstream. Avoid threaded connections. Design the system to amply sustain the maximum operating pressure. Avoid liquid traps in propellant lines. The purge system must not require disconnecting any system joints. All components must be reliable, compatible with peroxide, and properly cleaned and passivated. Following these procedures can assure the user of first-time safety and success33.
Using hydrogen peroxide as a rocket oxidant can offer significant benefits provided it can be handled and used safely. This is a paramount issue for modern rocket designers, and the exothermic nature of 98% H2O2 causes some legitimate concerns. The solution to these concerns is not in new technology, but in proper design, manufacture and operations procedures — in short, the answer is discipline.
17 Andrews, D., and Sunley, H., “The Gamma Rocket Engines for Black Knight,” Journal of the British Interplanetary Society, Vol. 43, No. 7, London, UK, July 1990
18 Drenning, F., “Rocketdyne AR Engines,” BC72-21, March 1972
26 Bloom, R., and Brunsvold, N., “Anhydrous Hydrogen Peroxide as a Propellant,” Chemical Engineering Progress, Vol. 53, No., 11, November 1957
27 Clark, J., Ignition — An Informal History of Liquid Rocket Propulsion, Chapter 5, John Wiley & Sons, 1971
28 Ziegler, M., Flugzeug Messerschmitt Me-163 Komet, Podzun-Pallas Verlag, 6360 Friedberg 3, Germany, 1977
29 Andrews, D., “Advantages of Hydrogen Peroxide as a Rocket Oxidant,” Journal of the British Interplanetary Society, Vol. 43, No. 7, London, UK, July 1990
30 Mackenzie, J., “Hydrogen Peroxide Without Accidents,” Chemical Engineering, June 1990
31 Roth, E. M., and Shanley, E. S., “Stability of pure hydrogen peroxide, ” Ind. Eng. Chem, 45, 2343-9, 1953
32 Satterfield, C. N., Feakes, F., and Sekler, N., “Ignition Limits of Hydrogen Peroxide Vapor,” J. Chem. Eng. Data, Vol. 4, No. 131, 1959
33 Constantine, M., Hydrogen Peroxide Handbook, Technical Report AFRPL-TR-67-144, Air Force Rocket Propulsion Laboratory, Edwards AFB, CA, Jul 1967