Environ. Sci. Technol. 1989, 23, 328-333
The Disappearance of Fuel Hydrazine Vapors in Fluorocarbon-Film Environmental Chambers. Experimental Observations and Kinetic Modeling Daniel A. Stone" and Floyd I.. Wiseman Air Force Engineering and Services Center, Engineering and Services Laboratory, Environics Division, Tyndall AFB, Florida 32403-6001
Jan E. Kilduff and Steven L. Koontzt National Aeronautics and Space Administration, White Sands Test Facility, Las Cruces, New Mexico 88004
Dennis 0. Davis Department of Chemistry, New Mexico State University, Las Cruces, New Mexico 88003
Fluorocarbon-film environmental chambers, of the type often employed in air pollution studies, have been used to investigate the stability of the fuel hydrazines (hydrazine, methylhydrazine, and 1,l-dimethylhydrazine)with respect to atmospheric oxidation. These studies have shown that the observed disappearance of fuel hydrazine vapors in these chambers is caused by physical loss processes rather than oxidation. Vapor-phase decay is affected by chamber size (surface-to-volume ratio), water content of the matrix gas (air or nitrogen), and previous chamber experiments &e., conditioning). A kinetic model has been developed that incorporates adsorption, permeation, and surface site concentration to fit the observed decay data. Introduction The relative stability and high energy content of hydrazines make them widely used fuels in military and aerospace applications. Hydrazine is used in auxiliary and emergency power generating units, in small attitude control and orbit adjust thrusters on satellites, as a component of a liquid rocket propellant, and as a fuel cell reactant. The methyl derivatives, methylhydrazine (MMH) and 1,l-dimethylhydrazine (UDMH), are used as fuels in bipropellant combinations in satellites and rockets (1). Routine handling and transfer operations often result in liquid or vapor releases that constitute a potential health risk. Hydrazine is classified as an animal carcinogen (1) and a suspect human carcinogen (1). Its low threshold limit value (TLV) of 0.1 ppm (2) reflects its toxicity. MMH and UDMH have similarly low TLVs of 0.2 and 0.5 ppm (2), respectively. Numerous investigators have studied the vapor-phase oxidation and atmospheric chemistry of the hydrazines. These studies have utilized relatively small (0.5-60-L) glass and quartz vessels (3-9) and large (5000-30 000-L) fluorocarbon-film chambers (IO,11). Studies in the smaller vessels showed that oxidation was occurring and was a function of surface composition and surface-to-volume (S/V) ratio. The larger chamber studies were an attempt to simulate atmospheric conditions and emphasized reactions with added atmospheric constituents; however, some experiments were conducted with only hydrazines in air. In these latter experiments, the disappearance of the hydrazines was assumed to be caused by relatively slow autoxidation. The results of the current study indicate that air oxidation occurs only very slowly, if a t all, in the absence of reactive trace chemicals or surfaces. +Present address: NASA/Johnson Space Center, Materials Branch, Houston TX 77058. 328
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Environ. Sci. Technol., Vol. 23, No. 3, 1989
Experimental Section 1. Apparatus. Two chambers were constructed by heat sealing 0.127-mm (5-mil) sheets of FEP-Teflon film together in the form of rectangular boxes. The smaller of the two chambers had dimensions of 0.87 m x 0.66 m x 0.56 m giving a volume of 320 L and a S/V ratio of 8.9 m-l. It was located at the Engineering and Services Laboratory, Air Force Engineering and Services Center, Tyndall Air Force Base, FL. A larger chamber, measuring 2.34 m X 2.34 m X 1.19 m with a volume of 6520 L and a S/V ratio of 3.4 m-l, was constructed similarly and located a t the NASA White Sands Test Facility, Las Cruces, NM. Both chambers were enclosed in an additional container to provide a controlled external environment. The smaller chamber was enclosed in a box made from 3.175-mm (1/8-in.) Plexiglas and the larger chamber was enclosed in 0.254-mm (10-mil) polyethylene film which was supported -5 cm from the Teflon walls. The annular space between the enclosures and the Teflon chamber walls was purged with gases of known composition and humidity to maintain reproducible experimental conditions. High-volume pure air systems were constructed at each location. The smaller chamber employed a compressor, a refrigerated air dryer (Zeks-Therm Model 35NCA) and a catalytic air purifier (Aadco Model 737-15A). This system provided up to 100 L/min of air with less than 1 part-per-billion impurities (ozone, methane, hydrocarbons, carbon monoxide, hydrogen sulfide, sulfur dioxide, or fluorocarbons) at a dewpoint of -60 "C. The larger chamber employed a passive pure air system (Balston Model 75-20 air filter with an air purifier and a series of optional adsorbent cartridges) that provided 330 L/min of pure air at a dewpoint of -40 O C . Each delivery manifold was configured in such a way that liquid nitrogen boiloff could be used in the place of pure air when required. There were also provisions for humidifying the gas stream in the small chamber apparatus. The concentration of molecular species in the chambers was monitored with long-path Fourier transform infrared (FT-IR) spectroscopy. The smaller chamber used a Nicolet Model 160SX spectrometer, and the larger chamber used a Mattson Model Sirius 100 spectrometer. Both spectrometers employed liquid nitrogen cooled mercury cadmium telluride detectors, and spectra were recorded a t 1.0-cm-l resolution. Both chambers employed three-mirror White cell arrangements (12) to give an optical path of 65-75 m in the larger chamber and 36.8 m, including the Pimentel modification (13), for the smaller. 2. Materials. Hydrazine and MMH were propellantgrade materials (Olin Chemicals, Inc.) and analyzed according to MIL-P-26536-C and MIL-P-27404-B, respectively. Typical analyses were >98.7% purity and > [GI. If it is true that [Fila >> [GI, then the second-order term, ki([Fil0 [GF,]), can be replaced with the pseudo-first-order term, ki[Filo. For single data set fits, this approximation is sufficient, but the second-order term is necessary in composite fits to explain the conditioning process. For single data sets, two condensed versions of the large model have been used: permeation (results with N = 1in Table 11) and a model involving both adsorption and effusion. Both fit single data sets equally well. Multiple data sets require adsorption using the second-order term, [F,!, - [G-F,], and at least effusion as a second process. This requires four parameters, kl, [FJo, k1, and k,. In some cases, better correspondence is obtained by replacing effusion with permeation; hence replacing the parameter k, with k,*, k,, and kD*. The results for fits of typical sequential runs using the adsorption-effusion model are listed in Table 111. Figure 6 shows plots of the composite fit for the data taken from 14-17 April 1986 (first entry in Table 111). The second-order adsorption-effusion model used to fit the data describes the decay curves quite well. As is evident from the data (Figure 5), and explained by the model (Figure 6), the binding sites become almost 332 Environ. Sci. Technol., Vol. 23, No. 3, 1989
I
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.75
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2
.5
v
w
0
z
m U .25
a
7
14
21
28
TIME ( h r )
i = 2 to N - 1
d[G-Si]/dt = k~*([G-si-,]
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1
Flgure 6. Fit of the secondarder adsorption-effusion model to a typical set of sequential runs of hydrazine decay in dry air in the smaller chamber.
full after the third run in a sequential set of runs. This process is reversible, and the chamber can be slowly deconditioned in dry conditions by letting it sit. In humid conditions, deconditioning is much more rapid. This is evident by the larger values of k-, (the desorption rate constant) for the runs in humid air, and by the fact that flushing the larger chamber with humid air produces trace amounts of hydrazine vapor after a dry air run. As shown in Table 111, kl,k+ and k, all increase substantially with humidity. That k, and k, increase implies that hydrazine has a stronger affinity for wetted surfaces. However, the observed increase in k-l shows that adsorbed hydrazine also desorbs faster from wetted surfaces. This implies that hydrazine is forming a hydrate on the wetted surfaces in preference to adsorbing onto a Teflon surface site. The resulting hydrate can also occupy a surface site, but is more readily desorbed in a process that gives free hydrazine in the vapor phase. The increase in k-l also suggests that deconditioning can be greatly expedited by flushing the chamber with humid air. Using dry air for purging would require several weeks to decondition the chamber. The half-life for deconditioningin dry air is -3 weeks in the smaller chamber; whereas in humid air, the half-life for deconditioning is between 3 and 15 h. Conclusions a n d Significance
Fuel hydrazine vapors disappear from fluorocarbon-film environmental chambers with a half-life that is dependent largely on the surface-to-volume ratio. Added internal surface area in the form of sheets of wall material has little effect on the overall rate of disappearance. The lack of effects caused by the presence or absence of oxygen in the matrix gas and the lack of observable oxidation products force the conclusion that neither surface-catalyzed nor homogeneous chemical oxidation are major factors responsible for the disappearance of the vapor. Physical processes such as adsorption and permeation can qualitatively and quantitatively account for the disappearance
Environ. Sci. Technol. 1989, 23, 333-340
of hydrazine. Atmospheric humidity and previous conditioning experiments play significant roles in altering the fluorocarbon-film surface and thus changing the behavior of hydrazine vapor in this type of chamber. Previous studies of the atmospheric chemistry of fuel hydrazines using fluorocarbon-film environmental chambers have failed to account for these noncatalytic effects and thus overestimated the rate constants for homogeneous oxidation reactions.
Development Office: Tyndall Air Force Base, FL, January 1978. (8) Stone, Daniel A. T h e Autoxidation of Monomethylhydrazine Vapor; ESL-TR-79-10, Air Force Engineering and Services Center: Tyndall Air Force Base, FL, April 1979. (9) Stone, Daniel A. T h e Vapor Phase Autoxidation of Un-
Registry No. Teflon FEP, 25067-11-2;MMH, 60-34-4; UDMH, 57-14-7; hydrazine, 302-01-2; water, 7732-18-5.
Services Center: Tyndall Air Force Base, FL, April 1980. (10) Pitts, J. N., Jr.; Tuazon, E. C.; Carter, W. P. L.; Winer, A. M.; Harris, G. W.; Atkinson, R.; Graham, R. A. Atmospheric
symmetrical Dimethylhydrazine and 50-Percent Unsymmetrical Dimethylhydrazine 50-Percent Hydrazine Mixtures; ESL-TR-80-21, Air Force Engineering and
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Chemistry of Hydrazines: Gas Phase Kinetics and Mechanistic Studies; ESL-TR-80-39,Air Force Engineering
Literature Cited Schmidt, Eckart W. Hydrazine and I t s Derivatives; Wiley-Interscience: New York, 1984.
and Services Center: Tyndall Air Force Base, FL, August 1980. (11) Tuazon, E. C.; Carter, W. P. L.; Brown, R. V.; Atkinson, R.; Winer, A. M.; Pitts, J. N., Jr. Atmospheric Reaction Mechanisms of Amine Fuels; ESL-TR-82-17, Air Force Engineering and Services Center: Tyndall Air Force Base, FL, March 1982. (12) White, J. L. J . Opt. Soc. Am. 1942, 32, 285-288. (13) Horn, D.; Pimentel, G. C. Appl. Opt. 1971,10,1892-1898. (14) Fersht, A. R.; Jencks, W. P. J. Am. Chem. SOC.1970,92, 5432-5442. (15) Johnston, Harold S. Gas Phase Reaction Rate Theory; Ronald Press: New York, 1969; pp 329-332.
Hazards of Chemical Rockets and Propellants. Volume ZII Liquid Propellants; Hannum, John A. E., Ed.; Chemical Propulsion Information Agency, CPIA Publication 394, The Johns Hopkins University, Applied Physics Laboratory: Laurel, MD, September 1984. Bowen, E. J.; Birley, A. W. Trans. Faraday SOC.1951,47, 580-583. Winning, W. I. H. J . Chem. SOC.1954, 926-931. Moody, K. N. P b D . Dissertation, The University of Leeds, Leeds, England, 1985. Vernot, E. H.; MacEwen, J. D.; Geiger, D. L.; Haun, C. C. A m . Ind. Hyg. Assoc. J. 1967,28, 343-347. Stone, Daniel A. T h e Autoxidation of Hydrazine Vapor; CEEDO-TR-78-17, Civil and Environmental Engineering
Received for review February 12,1988. Accepted October 3,1988.
Acidic Deposition and Cistern Drinking Water Supplies Harvey Olem"
Olem Associates, 1000 Connecticut Avenue, N.W., Suite 202, Washington, D.C. 20036 Paul M. Berthouex
Department of Civil and Environmental Engineering, University of Wisconsin, Madison, Wisconsin
rn The water quality characteristics, including the trace elements Cd, Cu, Pb, and Zn, in rainwater cistern supplies representing an area receiving acidic deposition were compared to cistern water chemistry in a control area that does not receive a significant input of acidic deposition. Mean volume-weighted pH for bulk deposition was two pH units higher and SO4 was 50% lower in the control region. Rainwater was neutralized upon contact with cistern masonry in both regions, as indicated by a 1.5-unit increase in pH and an increase in calcium and alkalinity. While there seemed to be a clear difference in water quality for the two study regions, any difference in trace metals was marginal. Metal concentrations were below current drinking water limits in all but a few samples. Cistern water that remained in the home plumbing system overnight exceeded the proposed drinking water standard of 5 pg/L for lead in 18 homes in the region receiving acidic deposition and 10 homes in the control region. No relation between metal concentrations and roofing material, plumbing materials, or water stability indices could be found. ~~
Introduction
Very little information is currently available on the relationship between acidic deposition and drinking water supplies. McDonald (I) reviewed the direct and indirect effects of acidic deposition on human health and suggested 0013-936X/89/0923-0333$0 1.50/0
that users of small, private, rural water supplies sustain the greatest health risk because many of these waters are corrosive to plumbing systems and operators of these systems do not usually monitor water quality. It was mentioned, however, that no conclusive evidence exists linking acidic deposition to increased leaching of contaminants from drinking water systems. Several studies have documented elevated concentrations of Cd, Cu, Pb, Zn, and other constituents in shallow wells, springs, surface water supplies, and rainwater cisterns (2-11). Review articles on the subject have suggested that these results implicate acidic deposition (12-15), but no study to date has rigorously evaluated the relationship between acidic deposition and drinking water degradation because of the difficulty in determining whether acidic deposition leads to the increased levels of contaminants. Cisterns have received more attention than other individual water systems because these supplies receive rainwater directly. Water does not come in contact with soils and rocks that can alter its characteristics. Young and Sharpe (2)found that tap water remaining in the pipes of cistern systems overnight exceeded the current drinking water limit for P b in 9 of the 40 systems sampled. The leaching of contaminants from the plumbing system was attributed to acidic deposition, although there was no estimate of how much leaching would occur if rainfall had not been acidic. Other investigators (5, 6) also found
0 1989 American Chemical Society
Environ. Sci. Technol., Vol. 23, No. 3, 1989
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