Partial Vapour Pressures and Activity Coefficients of Gb and Gd in Aqueous Solution
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National Defense I♦ Defence nationale
PARTIAL VAPOUR PRESSURES AND ACTIVITY COEFFICIENTS OF GB AND GD IN AQUEOUS SOLUTION
by J.M. Preston Chemical Defence Section Protective Sciences Division and
V. Starrock Canadian Defence Research Fellow attached from Wehrwissenschaftliche Dienststel/e Bw ABC-Schutz, Munster, Germany
DEFENCE RESEARCH ESTABLISHMENT OTTAWA REPORT 893
PCN September 1983 13A Ottawa ABSTRACT
The partial vapour pressures and thus the activity co efficients of GB and GD and water in aqueous solutions of the agents have been measured through the range of mole fractions in which the agent and water are miscible. The technique used was to measure the total vapour pressure over the agent/water mixture and then to solve numerically for the partial vapour pressures with a computer implementation of the Gibbs-Duhem equation. The agent activity coefficients display the hydrophobic nature of the nerve agents at mole fractions less than one half, but are close to unity otherwise.
RESUME
On a mesure les tensions de vapeur partielles et, ainsi, les coefficients d'activite du GB, du GD et de l'eau dans des solutions aqueuses de ces agents dans la plage des fractions molaires pour laquelle l'agent et l'eau sont miscibles. La technique utilisee consistait a mesurer la tension de vapeur totale au-dessus du melange agent/eau, puis de calculer la valeur numerique des tensions de vapeur partielles a l'aide d'une version informatisee de l'equation de Gibbs-Duhem. Les coefficients d'activite traduisent la nature l1ydrophobe des agents neurotoxiques a des fractions molaires de mains de 0,5 mais ils sont voisins de l'unite a des fractions molaires superieures.
ZUSAMMENFASSUNG
Die Partialdruecke, sowie daraus abgeleitet, die Aktivitaetskoeffizienten von GB, GD and H 0 in waesserigen Loesungen dieser Kampfstoffe wurden ueber den gesamten Molenbruch-Bereich,2 in dem diese Kampfstoffe and Wasser sich mischen, bestimmt. Hierbei wurde der sich bei einer gegebenen Temperatur einstellende Gesamt-Dampfdruck ueber den Kampfstoff-Wasser-Mischungen gemessen; mit Hilfe eines Rechnerprogrammes liessen sich bei Zugrundelegung der Gibbs-Duhem'schen Gleichung die entsprechenden Partialdruecke von GB, GD and H 0 ermitteln. Die hydrophoben Eigenschaften der Nervenkampfstoffe kommen bei2 Molenbruechen < 0.5 deutlich
INTRODUCTION
General
When liquid nerve agents are released in the field they come in contact with water, as vapour, liquid, or solid. The purpose of the investigation reported here is to measure the effect of this interaction on the agent vapour pressure. This measurement amounts to a determination of the partial vapour pressures, and therefore the activity coefficients, of GB/water mixtures and GD/water mixtures over the full available range of agent mole fractions.
Our motivation for undertaking this study was to enable more accurate models of agent behaviour in humid field conditions to be constructed. Watts (1), in discussing the paucity of data on nerve agent interaction with water, discusses the two effects which the absorption of water will have on a falling drop of agent: to change the agent vapour pressure and hence its rate of evaporation, and to enlarge the drop and hence its terminal velocity. The evaporation rate of agent on vegetation and soil will similarly be affected by interaction with water.
These measurements of activity coefficients may also be applicable to biochemical studies of G agents in the bloodstream.
Theory of Partial Vapour Pressure and Activity Coefficients
An ideal solution is defined as one in which the cohesive forces between molecules are uniform, regardless of the identities of the molecules (2). The partial pressure of each component above such a solution is proportional to its mole fraction in the solution, i.e., (1) pi = x;: p� where P. is the partial vapour pressure of component i, X� is the mole fractioii of component i in the solution, and P? is the va�our pressure of the pure compound. Equation 1 is a statement of R�oult's Law.
It is rare, however, to find even binary solutions which agree well with Raoult's Law. More usually the force of attraction or repulsion between the two components is different from that in neat solutions, thereby increasing or decreasing the partial vapour pressures. The differences are often referred to as deviations from Raoult's Law. For these non-ideal solutions one writes 0 = pi ai pi (2) which serves as a definition of the activity, a., of each component, i. Since the activity is the product of the mole £?action and a value proportional to the deviation from ideality, one also writes (3) 2 where y is called the activity coefficient. Thus the activity coefficient is equal to the partial vapour pressure of a compound divided by the partial vapour pressure which that compound would exhibit in an ideal solution. L o y. = P. / X. P. (4) 1. 1. 1. 1.
Activity coefficients are widely used when considering physical and chemical equilibria (with cognizance of the appropriate standard state).
Reactivity of G-agents
In this work we studied solely the physical interaction between agent and water. The effects of chemical reactions were minimized by selection of observation time and of pH of the added water, which greatly affects rates of hydrolysis (3). The requisite pH range, 4-6, may well be encountered in real situations.
EXPERIMENTAL
Our experimental approach was to measure the total vapour pressure over the agent/water solution, throughout the range of mole fractions, and at various temperatures. The technique used to calculate the partial vapour pressures from these measurements of total vapour pressure will be discussed in the next section.
The apparatus is shown diagramatically in Figure 1. The key element is the magnetic reluctance manometer (hereafter called MRM) (Validyne DP7 Variable Reluctance Differential Pressure Transducer, Validyne Engineering Corporation, Northridge, California, and Pace CD25 Transducer Indicator, Pace Engineering Co., North Hollywood, California). In the centre of this manometer is a thin steel diaphragm which deforms according to the pressure differential across it, while its position is sensed by small electromagnets located synnnetrically on either side. In principle, this manometer can be calibrated and used to measure pressure difference directly. In practice, however, it tended to drift or jump in both zero setting and sensitivity. To overcome this we used a conventional manometer, containing di-octyl phthalate. Once the agent/water solution was in equilibrium with its vapour on one side of the MRM (with the stopcock above that side-arm closed), laboratory air was admitted slowly into the other side and the manifold until the MRM read zero. The pressure above the agent/water solution could then be read directly from the di-octyl phthalate manometer by means of a cathetometer. Since the zero setting of the MRM was adjusted just before each measurement, and verified after each run, this was considered to be a technique free of systematic error. The rotary pump was capable of evacuating the system to less than 2.5 Pa (20 mTorr)*.
* 1 Torr = 133.3 Pa 7.50 Torr = 1 kPa 3
i_ { ( '< ( \ \ '\ ✓ t
l ( ( I I 1,_1_, fl ( Wa:w r-f ...l <{w r->-.....1�<{ (.)Io Or-z 0 ..!.I <{ wa:I Oa...:::--== a: � f- � <{ <{ f 3:CD (/) � <{ ....J CD<{
wa: (.)(.)w -zf wf- ...... ,. w zr-� c,UO w <{::J z - �- � ....J <{ �� ��IL__ Q. C}
Oa. ...J <{ Oa: (.)f-
> a:a. Q<{� f-r- Oa.::J a:
Fig. 1. Apparatus used to measure the total vapour pressure of agent/water mixtures. The water bath surrounding the sample cells, magnetic reluctance manometer, and the connections between them could be removed for freeze-thaw degassing of the samples. 4
The solutions were prepared by weighing typically 250 mg of agent into small vials which could be fitted directly onto the sidearm of the MR.M with greased ground-glass joints. The mass of water required to produce the desired mole fraction was then calculated and added by syringe, after which the solution was reweighed so that the precise mole fraction could be GB which had been distilled within the last year and since then calculated. ° kept at -20 C proved satisfactory, but GD with a similar history had vapour pressures well above the literature values. The GD used in this experiment was synthesized two days before data collection started. Since only one mole fraction was studied each day, aliquots for approximately one week's work were removed from the freezer when required. No stabilizer was used. Distilled water from the DREO still was used. Its pH, measured by pH paper, was 4, so in some experiments trace amounts of ammonium hydroxide were used to raise the pH, as discussed below.
The vial containing the solution was placed on a sidearm, with an empty vial on the other sidearm. Four cycles of cooling the solution in a dry ice-acetone bath with pumping and then warming to room temperature with the stopcock closed were used to degas the sample. On the fourth cycle the MR.M was zeroed, then with the stopcock closed the dry ice-acetone bath was replaced by a water bath in which the MRM, its sidearms, the vials, and the tubing up to the stopcocks was immersed. The reading of the MR.M was then monitored to determine when equilibrium had been reached (usually at least 30 min) and to ensure that hydrolysis was not occuring (if the pressure was found to be falling significantly the run was discarded). When the MR.M indicated a steady value the di-octyl phthalate manometer was used to read the pressure, as discussed above.
° The regulator for the water bath was set to either 25.0 C or 40.0° C. However a thermometer which had been calibrated by the National ° ° Research Council of Canada indicated temperatures of 25.3 C and 39.7 C, which we accepced as authoritative. Measurements were also taken in an ice-water
bath. The use of ° distilled water and distilled-water ice produces a temperature of 0.0 C.
Even if the MR.M had recently been zeroed at room temperature, it did not read zero at other temperatures, presumably due to thermal expansion and contraction in the transducer. The differences were measured under vacuum, with empty vials on both sidearms and both stopcocks
open, and were found to correspond to an artificial° pressure in the left-hand° side of the MR.M of 25 Pa (0.19 Torr) at 39.7 C, 12 Pa (0.09 Torr) at 25.3 C, and for 0.0 ° C 72 Pa (0.54 Torr) in the right-hand side. These corrections were then applied to all readings.
The density of the di-octyl phthalate was determined by weighing degassed samples in picnometers. The mean result was 0.9999 g/mL at ° 22 C.
The data points were collected, at a rate of one mole fraction per day, in a random order, rather than a systematic progression of increasing or decreasing mole fractions. 5
RESULTS AJ.'l'D ANALYSIS
Neat Liquids
The values found with this apparatus for the vapour pressures of the pure compounds are compared with literature values in Table 1. Of the values measured, most agree extremely well with the literature, and the largest discrepancy is 64 Pa (0.48 Torr). This good agreement serves as an indication of the accuracy of this experiment, as discussed further below. The use of distilled rather than de-ionized water may account for the consistently low values for water.
Decomposition of G-agents
There are two common reactions by which GB and GD decompose, and both need to be considered in the analysis of this experiment. The most widely known of these is hydrolysis (3), in which the corresponding acid is formed
The pH of the solution significantly affects the reaction rate; for GB and GD the hydrolytic half-lives are maximized at 160 and 250 h respectively if the pH lies between 4 and 6, at 25 °C. The second decomposition reaction is unimolecular. It is documented primarily in mass-spectral studies (6), but is also known to occur in liquids (7 ,8):
GB: + CH2 =CHCH3
There were three significant experimental observations relating to these reactions. In solutions with agent mole fractions less than 0.92, the vapour pressure over the solution was observed to fall ° typically 3% per hour at 25 C. If distilled water directly from the DREO still (pH=4) had been used, the rate of fall was noticeably faster; 3% per hour was a typical result if traces of ammonium hydroxide had been added to raise the pH of the water to about 7. Secondly, in solutions with very little or no water (agent mole fraction exceeding 0.92), the vapour pressure over the solution rose at about 6% per hour. Thirdly, determinations of the vapour pressure of samples of neat agent agreed well with literature values for GB, but for GD only if the sample was recently synthesized (Table 1 does not reflect values obtained with older GD samples).
As regards falling vapour pressure, our interpretation is that hydrolysis was occuring. The products of this reaction are involatile 6
TABLE 1
Comparison of Experimental and Literature Vapour Pressures (Pa) of Pure Compounds
0.0 °C 25.3 °C 39.7°C Lit Lit Expt Lit Expt Lit Expt Ref
Water 611 601 (2) 3221 3177 (4) 7259 7195 (2) 4
GB 63 63 (1) 379 428 (2) 5
GD 53 77 (1) 169 204 (1) 5
Each experimental point 1S the mean of the number of determinations given in brackets.
and their existence would decrease the partial vapour pressures of agent and of water by decreasing the mole fractions and decreasing the activity coefficients through association in the liquid phase. Therefore, we took the pressure readings reported here between 30 and 45 min after the final freeze-pump cycle. This time period allowed physical equilibrium to be achieved, as we knew from experiments with water, but minimized the effect of these chemical changes. It was not practical, or particularly meaningful, to measure the pH of agent solutions as concentrated as those used here; instead if the rate of change of vapour pressure was seen to be unacceptably fast the run was discarded and repeated with water which was more alkaline.
Rising vapour pressures were observed with samples of neat GB and GD and in the experiments with GD in which only traces of water were used. (No experiments were done with GB at such high mole fractions.) Under these conditions, unimolecular decomposition appears to be more important than hydrolysis, and the alkene which is produced inflates the pressure readings. Again, taking the reading at the appropriate time minimized the effect of these reactions, as seen by the good agreements in Table 1. Table 2 shows approximate values for the vapour pressures of these alkenes (the values listed are extrapolations from the tabulated boiling points (4) using Trouton's Rule (2) to estimate the heats of vapourization). ° At 25 C they are sufficiently large that small concentrations will have significant effects on experimentally measured vapour pressures.
Finally, we observe that the freeze-pump cycles, using dry ice-acetone baths, would effectively remove propene from GB solutions due to its considerable vapour pressure at the dry ice temperature. Thus the unimolecular decomposition of GB would not interfere significantly with the determination of its vapour pressure with the procedure used here. 3,3-Dimethylbutene, however, would not be significantly pumped away during these cycles since its partial vapour pressure would not be far above the 7
TABLE 2
Vapour Pressures of Alkenes which are Products of the Unimolecular Decompositions of GB and GD
APPROXIMATE AGENT WHICH ALKENE VAPOUR PRESSURE (kPa) AT ° PRODUCES ALKENE -78 C 25° C
Propene 19 1500 GB
3,3-Dimethylbutene 0.1 56 GD
system vacuum. Thus samples of GD, unless newly synthesized or distilled, would be expected to exhibit increased vapour pressures. This also was observed. A correction for this alkene was applied to the GD vapour pressure values reported here. This correction, which was small, was calculated by observing the apparent increase in vapour pressure for each day an aliquot of GD was stored at room temperature, and applying a proportional correction to each experimental value.
Miscibility of G-agent and Water
Water and GB were found to be miscible in all proportions, as reported in the literature (5).
GD, on the other hand, is reported (5) to be soluble only up to about 1 mole/L in water. This corresponds to a mole fraction of GD in water of only 0.02. It was found in this experiment, though, that GD and water are miscible in all mole fractions greater than about 0.32. The lower limit of miscibility was not investigated precisely. It was observed that solutions with mole fractions between 0.2 and 0.32 could sometimes, but not always, be prepared at room temperature (spheres of water in GD could easily be seen when the solution was shaken if there was iillliliscibility). Solutions with these mole fractions separated when cooled in the dry ice-acetone bath. If the mole fraction exceeded 0.32 the separation was not observed.
Calculation of Partial Vapour Pressures
Since these experiments were performed on a binary mixture, the total vapour pressure is given by
(5) 8 where a indicates agent and w water. There are two unknowns in this y and y , and so a further equation is needed to find a solution. equation, a w From considerations (2) of the chemical potential energy in the solution and in the gas phase, it is possible to write the Gibbs-Duhem equation in the form
X d(ln y ) + X d(ln y ) = 0 (6) a a w w Equations 5 and 6 contain the same two unknowns and therefore can be solved to give numerical values for the activity coefficients. The solution is not straightforward, however, because Equation 6 is a differential equation.
Christian (9) describes a numerical approach to the simultaneous solution of these equations. A more recent computer program was obtained (10) and modified slightly for our use. The program first performs a non-linear least-squares fit of all the pressure data recorded for a particular binary mixture at one temperature, as a function of mole fraction. This result is differentiated, and the result used, with Equation 5, to calculate the partial vapour pressures. It is assumed that the gases behave ideally. This program had been used by other investigators on various binary mixtures, and was tested by us using data available in the literature (11). It was capable of solving for the partial vapour pressures of the individual components with an accuracy of 1% or better.
Partial Vapour Pressures and Activity Coefficients
The first step in the simultaneous solution of Equations 5 and 6 is the fitting of a polynomial (fifth order was selected) to the experimental values of total pressure over the mixture through the range of mole fractions. The experimental points and the fitted curves are displayed in Figures 2-5. Also plotted in these figures are the partial pressures of the agent and the water as calculated by the program, and the total pressure which the solution would have if it were ideal (Raoult's Law value).
The activity coefficients are easily calculated from the partial vapour pressures. Figures 6-10 give the activity coefficients of both agent and water in all the situations studied. Activity coefficients are plotted only within the range of values studied experimentally, that 1s, not for very small concentrations. The activity coefficient of a pure compound is unity. 9
DISCUSSION
Accuracy of Results
The principal source of measurement error was the magnetic reluctance manometer (MRM). The MRM did not operate as consistently as might have been expected. It has already been explained that it was not used as a source of pressure data but only to indicate zero pressure difference, and that it was zeroed just before each run and the zero verified soon after. Nevertheless, the scatter in Figures 2 to 5 can be accounted for by the lack of reproducibility demonstrated by the MRM. If it is assumed that the total vapour pressure data should lie on some smooth curve, an estimate of the accuracy of the pressure measurements can be obtained. Of the cases studied, the largest root mean square deviation of the experimental° points from the fitted curve is 239 Pa (1.8 Torr) for GD/water at 39.7 C. The fitted curve, therefore, has an accuracy associated with it of 239//fs = 56 Pa (0.42 Torr), since there are 18 data points. This amounts to a percentage error of 1.5% at a mole fraction of 0.5. The deviations are less in the other three cases but so are the pressures, and the percentage errors lie between 0.8% and 1.8%.
The error in the mole fraction arises from two sources, both more important at high agent mole fractions. Agent impurities would not exceed 3%, with a corresponding error in the mole fraction. Weighing the quantity of water added was only significantly in error when only traces of water were used and in these cases the effect on the mole fraction was negligible.
Trials with literature data (10) had shown that the computer program was accurate to about 1% for slowly varying data. This is probably too low an estimate for rapidly changing data, such as that for GB/water at low agent mole fractions at 0° C.
There is only an error of about 0.1% arising from the assumption that the agent vapours, and water vapour, are ideal gases. This can be calculated by estimating the critical temperature and pressure of the agents (12) and, with the corresponding values for water (2), calculating the = = reduced values Tr T/Tc, Pr P/Pc and hence the compressibility factor (12), which is one minus the deviation from ideality. For agents we find 0.999, for water 0.9999. Thus, within the accuracy of the experiment, we can assume ideal gas behaviour.
The RMS sum of these errors is about 2% for pressures and about 3% for mole fractions. However the complexity of the reactions occuring in the system under study suggests that the values of pressure are more uncertain than this. There are two significant reactions for an agent/water mixture, one raising the pressure and the other lowering it. We cannot prove that these reactions were not occuring rapidly and simultaneously, although it seems unlikely based on the good agreement for the vapour pressures of neat agents and the reasoning that unimolecular reactions should be unaffected by the presence of other species. Another point is that the presence of hydrocarbons in the solution will affect the activity coefficient of water, at least. No technique was available to exclude these effects; they could only be minimized by using the purest available agent and 10 allowing the minimum time for reaction consistent with physical equilibrium. We estimate, based on typical observed rates of change of pressure, that these effects amount to additional errors of about 3% in activity coefficients, thus about 5% in total.
CONCLUSIONS
The activity coefficients of both the agent and the water in aqueous solutions of GB and GD have been measured with an accuracy of about 5%. The measurement was made by recording the total vapour pressure over the agent water mixture and then solving numerically for the partial vapour pressures with a computer implementation of the Gibbs-Duhem equation.
For agent mole fractions greater than 0.6, the deviations from ideality (i.e. deviations from Raoult's Law) were found to be small. For GB at 0 °C they are insignificant. A drop of G agent in a humid environment, therefore, will absorb water at a rate which can sensibly be calculated assuming ideal gases and an ideal solution. The drop will absorb water if the partial pressure of water in the atmosphere exceeds the partial vapour pressure in the relevant graph of Figures 2-5. At 25 °C and 50% relative humidity, for example, a GB drop will absorb water until the agent mole fraction falls to about 0.69. After this, since agent will continue to evaporate (as it will unless the atmosphere is heavily contaminated), water will re-evaporate to maintain this mole fraction.
In solutions with agent mole fractions less than 1/2 the hydrophobic nature of the nerve agents is displayed. The deviations from Raoult's Law are large enough that in one case (GB/water at 0 °C) the agent partial vapour pressure at X = 0.05 approaches the vapour pressure of neat GU agent. This case was investigated thoroughly by experimental runs at low GB mole fractions. As seen in Figure 3, the total pressure was well in excess of the vapour pressure of pure water over a significant range of agent mole fractions. The GB activity coefficients are very large (Figure 10), implying high reactivity for agents in such solutions.
The activity coefficient of water lies between 1 and 2.2 for all agent mole fractions less than 0.85 in all cases studied. Only for low concentrations of water is the activity coefficient large. 11
ACKNOWLEDGEMENTS
Several helpful discussions with Dr. J.G. Purdon and Dr. C. Gardner, who provided the computer program, were instrumental in the completion of this work. As well as giving helpful advice, Dr. R.A.B. Bannard completed all the glass blowing to his normal high standard. We are glad to have the opportunity to express our gratitude.
We are also grateful to the Canadian Defence Research Fellowship Program for allowing one of us the opportunity to carry out this work.
REFERENCES
1. Watts P., "Factors Pertinent to the Evaporation of Chemical Warfare Agents, Part l", Chemical Defence Establishment, Technical Paper 286 (1980). UNCLASSIFIED
2. Moore W.J., "Physical Chemistry", Prentice-Hall International Inc (1962) (or other texts).
3. Epstein J., Science, 170, 1396 (1970).
4. "Handbook of Chemistry and Physics", Chemical Rubber Co., Cleveland, Ohio.
5. "Chemical Agent Data Sheets", Edgewood Arsenal Special Report ED-SR-74001 (1974). UNCLASSIFIED
6. McLafferty F.W., "Interpretation of Mass Spectra", University Science Books, Mill Valley, California; 3rd Edition, Section 4.9.
7. Gamrath R.R., Halton R.E., and Weesner W.E., Ind. Eng. Chem., 46, 208 (1954).
8. Eto M., "Organophosphorus Pesticides: Organic and Biological Chemistry", CRC Press, Cleveland, Ohio (1974) p. 100.
9. Christian S.D., J. Phys. Chem., 64, 764 (1960).
10. Gardner C., Defence Research Establishment Ottawa, Private Connnunication.
11. "International Critical Tables", compilied by National Research Council, Washington, D.C., McGraw-Hill (1926).
12. Perry J.H., ed., "Chemical Engineer's Handbook" McGraw-Hill (1950). 12
25 ++ 3 GB ...... 25.3° C ...... 20 ...... - ...... 0 ca t:. �c.. }?q ...... - v,,, ...... w o 8 ...... w 2 1.,q 15 a: a: /,f,, ...... ::J ::J ...... Cl) Cl) Cl) ...... Cl) w w ...... c..a: a:c...... 10 1
5
GB
0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1 AGENT MOLE FRACTION
° Fig. 2. Pressures above a GB/water mixture at 25.3 C. The experimental values are of total pressure and the curve is the best-fit fifth order polynomial. The curves labe Ued "GB" and "Water" are the partial vapour pressures of these compounds� calculated as described in the text. If the GB/water solution were ideal� the total pressure uiould be given by Raoult 's Law. 13
800 6 GB 0° C 700 5 - 600 ta ---... a.. ---... 4 t: ...... w w 500 a: ---... ::::> ::::> en I?.t ...... 3 en 400 ollt w w ' .w ...... _ a: a: s l.q ...... a.. 300 ...... 2 ...... 200 1 100 GB .9 1 0 .1 .2 .3 .4 .5 .6 .7 .8 AGENT MOLE FRACTION
° Fig. 3. Pressures above a GB/water mixture at 0.0 C� plotted similarly to Figure 2. 14
GD 35 39.7° C 4 30 - 25 -cc t, a.. � 3 w a: w 20 ::J a: Cl) :::> Immiscible Cl)w Cl) a: Cl)w 2 15 a.. a:a.. � 10 �o 1 "+ '-1-,"c.S' 5 <�"� GD
0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1 AGENT MOLE FRACTION
Fig. 4. Pressures above a GD/water mixture at 39.7 ° C, plotted similarly to Figure 2. 15
' " GD " 25.3° C 2 " � 15 '+ '- -"- -
GD '-
0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1 AGENT MOLE FRACTION
Fig. 5. Pressures above a GD/water mixture at 25. 3 ° C, plotted similarly to Figur2 2. 16
WATER MOLE FRACTION 1.0 .9 .8 .7 .6 .5 .4 .3 .2 .1 O 1.0 1.0
.9 .9 25.3° C / WATER .8 " / .8 " / a: ' w .7 ' .7 I- ID <( ' (!) 3: .6 LL LL .6 0 0 / >- >- I- I- .5 X .5 > > / GB " I- I- / (.) (.) .4 " .4 <( <( / " / " .3 .3 / " / .2 / " .2 / "' .1 / " .1 /
0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 GB MOLE FRACTION
Fig. 6. Activities of GB and Water at 25.3° C. The values have been cal culated from the data presented in Figure 2 by the method described in the test. The dotted lines indicate the activities these com pounds would exhibit if they formed an ideal solution. 17
WATER MOLE FRACTION 1.0 .9 .8 .7 .6 .5 .4 .3 .2 .1 0
1.2 0° C
1.1
1.0 1.0 , 'WATER .9 ' .9 ' ' .8 ' .8 0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 GB MOLE FRACTION ° Fig. ?. Activities of GB and Water at 0.0 C. The values have been calculated from the data presented in Figure 3, and plotted as in Figure 6. If the mol-e fraction of uJater exceeds 0. 5, its activity exceeds the activity of pure uJater. 18 WATER MOLE FRACTION 1.0 .9 .8 .7 .6 .5 .4 .3 .2 .1 0 1.0 1.0 1/ 39.7° C .9 / .9 / .8 .8 /Go / .7 / .7 Cl I- u. < .6 0 .6 >- u. I- 0 Immiscible- .5 > >- .5 I- I- u > < I- .4 u .4 / < � .3 ' .3 � WATER .2 .2 .1 .1 0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 GD MOLE FRACTION ° Fig. 8. Activities of GD and water at 39.7 C. The values have been calculated from the data presented in Figure 4� and plotted as in Figure 6. GD and water are immiscible for agent mole fractions less than about 0.32� except for a small range near zero which was not studied in this experiment. 19 WATER MOLE FRACTION 1.0 .9 .8 .7 .6 .5 .4 .3 .2 .1 0 1.0 1.0 .9 .9 25.3° C .8 /GD .8 a: .7 .7 I- Cl <( C, .6 .6 LL LL 0 0 Immiscible-. >- >- .5 I- I- .5 > > / I- I- (.) (.) .4 / .4 <( <( / .3 .3 .2 ' .2 " WATER .1 .1 0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 GD MOLE FRACTION Fig. 9. Activities of GD and hlater at 25.3° C. The values have been calculated from the data presented in Figure 4, and plotted as in Figure 6. 20 5.5 4.5 () 0 5 4 r () <( 0 C') er: LO w C\I r r 4.5 3.5 <( <( 3: CD w CJ r <( z CD ...... 3: 4 3 CD CJ CJ LL z 0 r CD z CJ 3.5 2.5 w LL () 0 LL r LL z w w 0 () () 3 2 >- LL r LLw > 0 r () () 2.5 <( >-r 1.5 > r () 2 1 1.5 .1 .2 .3 .4 .5 .6 .7 .8 .9 1 AGENT MOLE FRACTION Fig. 10. Activity coefficients of GB in GB/water mixtuy,es at 25. 3 ° C (left hand scale) and at 0° C (right hand scale). Figures 6 and 7 display the corr'esponding activities. No data on very small mole fractions was obtained in this experiment. 21 1.3 ° 1.2 .__Immiscible ___.. 39.7 C 0 (!) LL 0 1.1 zI- w 1 (.) 0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1 u:: wLL 0 (.) >- 1.3 I- > �Immiscible� i= 1.2 (.) <( 25.3° C 1.1 1 0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1 AGENT MOLE FRACTION Fig. 11. Activity coefficients of GD in GD/LJateP mixtures at 39.?° C and at ° 25.3 C. Figures 8 and 9 display the corresponding activities. DMC A NON-CONTROLLGED GOODS 23 PRECEDING PAGE BLANK UNCLASSIFIED Security Classification - DOCUMENT CONTROL DATA R & D \Security class1f1cat1on of title, body of abstract and indexing annotation must be entered when the overall document 1s classified) 1 ORIGIN/\TING ACTIVITY 2a. D CLASS Defence Research Establishment Ottawa 09ct1s§fEb IFICATION Department of National Defence 2b. GROUP Ottawa. Ontario KlA OZ4 3. DOCUMENT TITLE Partial Vapour Pressures and Activity Coefficients of GB and GD in Aqueous Solution 4. DESCRIPTIVE NOTES (Type of report and 111clusive dates) Report 5 AUTHOR(S) (Last name, first nar7e, middle inrtral) Preston, Jonathan M. and Starrock, Volker 6. DUl;UMENT DATE 7a. TOTAL I. OF PAGES 7b. NO. OF REFS September 1983 21 I 12 �1a. 1\10 PROJECT OR GRAf\l 9a. ORIGINATOR'S DOCUMENT NUMBER IS) 13A DREO REPORT 893 Sb. CONfRACT NO. 9b. OTHER DOCUMENT NO ISi (Any othP1 numbers that may be ass1q1wd this document) ,__ , ,r-· 1n. lo_. 1 ,-;u i ION ST ATC MEr\JT Distribution is l!nlimited I 1 12. 'oUPl'Ll �fNTARY WJTES Sl'ONSORING ACTIVITY 13. ABSTRACT The partial vapour pressures and thus the activity coefficients of GB and GD and water in aqueous solutions of the agents have been measured through the range of mole fractions in which the agent and water are miscible. The technique used was to measure the total vapour pressure over the agent/ water mixture and then to solve numerically for the partial vapour pressures with a computer implementation of the Gibbs-Duhem equation. The agent activity coefficients display the hydrophobic nature of the nerve agents at mole fractions less than one half, but are close to unity otherwise. DSIS 24 UNCLA S STFJEU Security Classification KEY WORDS Nerve agents G-agents activity coefficients partial vapour pressures vapour pressures decomposition water aqueous solution INSTRUCTIONS 1. ORIGINATING ACTIVITY· Enter the name and address of the 9b. OTHER DOCUMENT NUMBER(S): If the document has been organization issuing the document. assigned any other document numbers (either by the originator or by the sponsor), also enter this number Is). 2a. DOCUMENT SECURITY CLASSIFICATION: Enter the overall security classification of the document including special warning 10. DISTRIBUTION STATEMENT: Enter any limitations on terms whenever applicable. further dissemination of the document, other than those imposed by security classification, using standard statements such as: 2b. GROUP: Enter security reclassification group number. 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