Envlron. Sci. Technol. 1002, 26, 2017-2022
Hutzinger, 0.;Safe, S.; Zitko, V. The Chemistry of PCBs; CRC Press: Cleveland, OH, 1974; Chapters 1, 2. Erickson, M. D. In Analytical Chemistry of PCBs; Erickson, M. D., Ed.: Ann Arbor Science: Ann Arbor, MI, 1986; Chapter 1. Paasivirta, J.; Mhtykoski, K.; Paukku, R.; Piilola, T.; Vihonen, H.; Siirkka, J.; Granberg, K. Aqua Fenn. 1986, 16, 17-23. Waid, J. S., Ed. PCBs and the Environment; CRC Press: Boca Raton, FL, 1986. Safe, S.; Safe, L.; Mullin, M. In PCBs, Environmental Occurrance and Analysis; Safe, S., Ed.; Springer: Berlin, Germany, 1987; pp 1-13. Voogt, P. de; Brinkman, U. A. Th. In Halogenated Biphenyls, Terphenyls, Naphthalenes, Dibenzodioxins and Related Products; Kimbrough, R. D., Jensen, A. A., Eds.; Elsevier: Amsterdam, The Netherlands, 1989; pp 1-45. Ballschmiter, K.; Zell, M. Fresenius 2. Anal. Chem. 1980, 302,20-31. Alford-Stevens, A. L.; Bellar, T. A.; Eichelberger, J. W.; Budde, W. L. Anal. Chem. 1986,58, 2014-2022. Weaver, G. Environ. Sci. Technol. 1984, 18, 22A-27A. Burruss, R. P. Assessment of the Environmental and Economic Impacts of the Ban on Imports of PCBs; EPA560/6-77-007; U.S. Government Printing Office: Washington, DC, 1977. Andrianov, K. A., Ed.Sovol. New unflammable insulating fluid; ONTI: Moscow, 1938 (in Russian). Andrianov, K. A,, Ed. Sovol and Sovtol; Gosenergoizdat:
Moscow-Leningrad, 1941 (in Russian). Maiophis, I. M., Ed. In Chemistry of Dielectrics; Higher School Publishing House: Moscow, 1970; pp 311-312 (in Russian). Andrianov, K. A.; Skipetrov, V. V., Eds. Synteticheskie 1962; Chapter Zhidkie Dielectric; Gosenergoizdat: MOSCOW, 2 (in Russian). Gulevitch, A.; Kireev, A. I., Eds. Production of Power Capacitors; Higher School Publishing House: Moscow, 1970; pp 65-66 (in English). Shachnovitch, M. I. Elaboration and investigation of new types of synthetical liquids for transformers. Ph.D. Dissertation, Moscow Institute of Oil and Gas Industry, Moscow, 1977; pp 30-31, 34 (in Russian). Mullin, M. D.; Pochini, C. M.; McCrindle, S.; Romkes, M.; Safe, S. H.; Safe, L. M. Environ. Sci. Technol. 1984, 18, 468-476. Duinker, J. C.; Hillebrand, M. T. J. Environ. Sci. Technol. 1983, 17, 449-456. Ballschmiter, K.; Schiifer, W.; Buchert, H. Fresenius 2. Anal. Chem. 1987,326, 253-257. Onuska, F. A.; Terry, K. A. J . High Resolut. Chromatog. Chromatogr. Commun. 1986,9, 671-675. Slivon, L. E.; Gebhart, J. E.; Hayes, T. L.; Alford-Stevens, A. L.; Budde, W. L. Anal. Chem. 1985, 57, 2464-2469.
Received for review January 3,1992. Revised manuscript received May 11, 1992. Accepted May 12, 1992.
Infinite Dilution Activity Coefficients and Henry's Law Coefflclents of Some Priority Water Pollutants Determined by a Relative Gas Chromatographic Method Ginger Tse, Hasan Orbey, and Stanley I . Sandier*
Center for Molecular and Engineering Thermodynamics, Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716
A simple, fast relative measurement method based on gas chromatography developed recently has been used to determine the infinite dilution activity coefficients and Henry's law coefficients in water of some priority pollutants. We show that this simple method can be used to obtain accurate data quite rapidly, which is especially valuable for screening studies. Further, the infinite dilution activity coefficient and Henry's law coefficient data reported here can be useful for directly estimating environmentally important properties such as solubilities in water, multimedia partitioning, and octanol-water partition coefficients. Introduction
To predict bioaccumulation, the distribution of pollutants in the environment, and multimedia partitioning ( I ) , and to design equipment to purify polluted aqueous streams, it is necessary to have information on the fugacity of pollutants in water. For a species which is a liquid as a pure component at the conditions of interest, the fugacity of species i in solution, f i , is fi(TP,xi)= xiyi(TP,xi)fi"(TP) (1) where f i o is the pure component fugacity at the temperature T and pressure P of the solution and y i and x i are its activity coefficient and mole fraction. Since pollutants are generally present at low concentrations, our interest is with activity coefficients at very high dilutions, indeed, in the limit of infinite dilution. 00 13-936X/92/0926-2017$03.00/0
There are two general methods of determining infinite dilution activity coefficients. The first is to extrapolate activity coefficient information obtained in the midcomposition range (typically from vapor-liquid equilibrium data) to high dilutions. This is subject to great inaccuracy and cannot be done for strongly hydrophobic chemicals which have only limited solubility in water, such as the volatile organic pollutants of interest to us. The second class of methods is the direct measurement of infinite dilution behavior; this is what we have used here. Before consideration of the specifics of the measurements we have made, it should be pointed out that infinite dilution activity coefficients are useful in a number of ways. First, if water is relatively insoluble in the pollutant, aqueous solubilities of water contaminants can be estimated from infinite dilution activity coefficients. In liquid-liquid equilibrium the fugacity of each component must be equal in each phase, so we can write for the component i
f?(TP,xi')= fi"(TP,xi")
(2)
Here the f i terms are the fugacities of component i in water-rich phase I and in chemical-rich phase 11, respectively. These fugacities can be rewritten in terms of activity coefficients as xiIyiIfi,pureO
I1 I I f . 0 xi yi &,pure
(3)
where fi,pureo is the pure component reference fugacity of component i a t the system temperature, the yi terms are
0 1992 American Chemical Society
Envlron. Sci. Technol., Vol. 26,
No. 10, 1992 2017
the activity coefficients of i in the two phases, and the xi terms are mole fractions. Recognizing that the pure component fugacities cancel, and assuming that water is essentially insoluble in the chemical phase (so that xiE = yin = l ) , and that the chemical is only sparingly soluble in water (so that y : = y?"), one can write xi = l/yi" (4) The octanol-water partition coefficient is an important parameter which is widely used to characterize chemicals in the environmental literature. Again starting from equality of fugacities of a solute in the water-rich and octanol-rich phases, and following the procedure described above, the octanol-water partition coefficient,KO,,can be written as
ment technique which eliminates many of these problems. We used this technique in this study. While the experimental and theoretical details of this new technique were reported in the elsewhere (2), in this section we briefly review the method and compare it with the direct gas chromatographictechnique for the measurement of infinite dilution activity coefficients. In the conventional approach for the determination of infinite dilution activity coefficients by gas chromatography, the solvent, assumed to be involatile, is supported on an inert solid in a column, and the solute is considered to be at infinite dilution in the solvent as it passes through the column. The thermodynamic relationship between the infinite dilution activity coefficient of the solute i in solvent j and the retention quantities measured in the gas chromatograph can be written as w;RT&z
(5) yi- =
Here xi0 and xiw are mole fractions of the solute in the octanol-rich and water-rich phases, respectively, and the y are the activity coefficients of the chemical in these phases. In eq 5, the octanol-water partition coefficient is expressed in terms of mole fractions. It is customary to express this parameter in terms of a ratio of molar concentrations in the environmental literature. Noting that the water-rich phase is essentially pure water, and that the octanol-rich phase is 0.725 mol fraction octanol and 0.275 mol fraction water, and assuming that there is no volume change on mixing, it can easily be shown that multiplying KO,in eq 5 by 0.151 we get KO,,the octanol-water partition coefficient in terms of molar concentrations. In most cases a pollutant will be present in very small concentrations, so the y terms in eq 5 can be replaced with their infinite dilution counterparts. It should be noted that among different chemicals KO, varies by 7 orders of magnitude, yiwvaries by 9 orders of magnitude, and yy at infinite dilution, which is a bit more complicated since the octanol-rich phase contains significant amounts of water, varies by less than 2 orders of magnitude (1). Therefore, the value of KO,is strongly dependent on yiw at infinite dilution. Finally, the mole fraction based Henry's law constant is useful in designing stripping and other purification processes. The Henry's law constant Hiof solute i at ambient pressures, considering that solute mole fraction is very low, is
H,(T) = yi"Pi'"P(T)
(6)
where PyP is the vapor pressure of the solute at temperature T . This Henry's constant has units of pressure per mole fraction; its relation to the Henry's constant based is Hi= M J I i / 1 0 6 ,where M, on molar concentration, Hi, is molecular weight of solvent (water), and the concentration unit is cubic meters per mole. The infinite dilution activity coefficients reported here, consequently, can also be used for estimating aqueous solubilities and Henry's law constants, and for the estimation of octanol-water partition coefficients. Relative Measurements o f Infinite Dilution Activity Coefficients and Henry's Law Coefficients by Gas Chromatography
There are a number of experimental difficulties which makes the absolute measurement of thermodynamic properties by gas chromatography difficult to implement and inaccurate, especially when the solvent is volatile, which is the case with water here. However, Orbey and Sandler (2)have recently introduced a relative measure2018
Environ. Sci. Technol., Vol. 26, No. 10, 1992
M;f#)i"Pi"(Av>
(7)
where w; is the weight of the solvent in the column, R is the gas constant, T i s the column temperature, $iand 4; are the gas-phase fugacity coefficients of the solute in the column at T and P, and when it is pure at its saturation pressure Pi"at T , and z is the compressibility of the gas phase in the column. Here AV is the specific retention volume, which can be expressed in terms of the experimentally measured quantities as F(Pexit
AV =
- P ~ ~ 0 ' ) ( 2 7 3 . 1 5 ) ( J-) (tref) t wj(760)T ,
(8)
In this equation F is the flow rate of the carrier gas, Pexit is the pressure measured at the exit of the column (in millimeters of mercury), J is a constant which accounts for the pressure gradient over the column and is a function of the inlet and exit column pressures, and T , is the ambient temperature (kelvin) at which carrier gas flow rate is measured. Finally, t - trefis the net retention time of a chemical, trefis the retention time of an inert substance which does not interact with water in the column, and t is the measured total retention time of the solute. In absolute activity coefficient determinations where the specific retention volume is needed, it is important to accurately measure the carrier gas flow rate, F, the column pressures at the inlet and at the exit, and the amount of the solvent in the column. In the case of a volatile solvent such as water, this is a special problem since the amount of the solvent in the column, wi, changes continuously due to stripping by the carrier gas. The new relative technique (2), on the other hand, eliminates the need for measurement of all the terms in specific retention volume given by eq 8 except the net retention time. This is because, as explained below, we measure the relative ratio of infinite dilution activity coefficients of two solutes in the solvent rather than the absolute values. Since both solutes are subject to the same pressure gradient and the carier gas flow rate, and both are in contact with the same amount of solvent simultaneously, all these terms cancel when we look at the ratio. Indeed this is what makes the new technique simpler and more accurate than absolute gas chromatography. When very small amounts of two solutes A and B are injected into a gas chromatograph simultaneously and are completely separated by the column, the ratio of their infinite dilution activity coefficients is, from eq 7 with
where PAsand PBB are the saturation pressures of species A and B at the column temperature, B A 2 and B B 2 are the second virial coefficients between the solutes and the carrier gas, uA1,"and uB1,"are the partial molar liquid volumes of the solutes at infinite dilution, P and T are column pressure and temperature, R is the gas constant, BAAand B B B are the pure component second virial coefficients, UJ and uB' are the pure liquid molar volumes, and CYBA is the ratio of net retention times aBA
=
tnet,B/tnet,A
(11)
The detailed development of eqs 9-11 has been given elsewhere (2). It should be pointed out that in deriving eq 10 we have used the virial equation of state truncated after the second virial coefficient to obtain the solute fugacity coefficients. When the column pressure is kept low enough (see next section) so that gas-phase nonidealities are negligible, the arguments in the exponential terms of eq 10 vanish, and eq 9 can be approximated by TA"/YB"
= ( P B ~ / P A ~ ) ~ B A (12)
Thus, if the infinite dilution activity coefficient of one solute in water is known, the activity coefficient at infinite dilution of the other solute can easily be determined from retention time data and the vapor pressures for both substances. Further, even if the vapor pressure of a substance is not known, we can still obtain its Henry's law coefficient from
HA = y A r n P A S= y B m P B S a B A
(13)
Experimental Section The equipment used in our measurements was essentially the same as reported in our previous work (2). Briefly, the solvent (water) was coated uniformly on inert solid support (Chromosorb GHP, 80/ 100 mesh) packed into a 5-m, l/s-in. stainless steel column by applying suction to one end of the column and dipping the other end into a water container. About 3-4 g of water was loaded this way, and depending on the carrier gas flow rate and the column temperature and head pressure, this was enough to run the GC for 4-8 h. As water is stripped from the column, the absolute values of the retention times get smaller. However, as we have shown in ref 2, the ratio of net retention times remains the same. In fact, while the exact amount of water on the column, carrier gas flow rate, and head pressure all effect the absolute values of retention volumes, they have no effect on the relative retention time ratios, as was verified in the previous study (2). Only when the column is almost dry so that the water phase does not act as a bulk phase (and interfacial adsorption at the liquid-gas interface may play a significant role), do we find that the ratios of infinite dilution activity coefficients are no longer reproducible. This situation is easily recognizable in the laboratory. Accurate measurements of carrier gas flow rates and column inlet and exit pressures were not made since they are not necessary in the technique we have used here. However, in a typical run the head pressure was less than 2 bar (gauge) and helium carrier gas flow rate was -40
cm3/min. In order to determine the retention times of the chemicals, -0.1-pL mixtures were injected into the gas chromatographs, The chromatographs used were Hewlett-Packard Models 5890A and 5730A, both equipped with flame ionization detectors (FID). Such FIDs do not respond to water which is continually stripped from the column during the measurements; it allows accurate detection of the pollutant peaks. Normally very sharp and symmetric peaks were obtained. All chemicals were supplied by Aldrich, with the exception of 1,l-dichloroethane, which came from American Tokyo Kasei, Inc., and all were used without purification. The experiments were carried out over the temperature range of 293.15-313.15 K; the accuracy of temperature readings was -0.1 K, and n-butane was used to determine treP Each chemical was first injected separately into the gas chromatograph to determine approximate retention times for identification. Next, chemicals were injected in groups together with the chosen standard chemical whose aqueous infinite dilution activity coefficient was known. At least eight measurements were done for each chemical at each temperature. The reference n-butane gas was injected about every 4 h to check the value of treP Note that from eq 12 it is only the residence times, not the peak areas, which are of interest. Results and Discussion A total of 17 chemicals selected from the EPA list of priority water pollutants were studied at 20, 30, 35, and 40 "C. This temperature range was selected since we are particularly interested in solubilities and octanol-water partition coefficients at ambient temperatures. We chose to study only solutes more volatile than water. The results of the measurements are reported in Table I. To convert the infinite dilution activity coefficient ratios obtained using eq 12 to absolute values, chloroform was used as the standard. The reasons for this selection were that we had measured the infinite dilution activity coefficient of chloroform in water directly earlier (3),using an absolute static cell in the temperature range of interest, and that its retention time is comparable to that of the chemicals considered here. This approximate match of retention times is desirable in order €or the measurements to be relatively quick and more accurate. When necessary, to interpolate the previously measured infinite dilution activity coefficient values of chloroform to the temperatures here, we used the two-constant relation In [7(!!')= ] HeX/RT+ C (14) where Hexis the partial molar excess enthalpy of chloroform in water at infinite dilution, which we took to be independent of temperature, and C is an integration constant. Consequently, from a plot of the natural logarithm of the infiiite dilution activity coefficienb versus reciprocal temperature, the chloroform activity coefficient at any temperature is obtained. The values of infinite dilution activity coefficients for chloroform in water obtained this way and used as reference values are given in Table I. We also report in Table I the net retention time ratios measured in this work, the vapor pressures used in calculating the activity coefficients at infinite dilution from eq 12, and derived error estimates. In calculating these error estimates, the possible errors in the measurements of the vapor pressure, temperature, net retention time ratio, and the infinite dilution activity coefficient of chloroform were used in a first-order Taylor series expansion to compute the total absolute error. The estimated error in the activity coefficients for the chemicals with relatively short retention times, such as Envlron. Scl. Technol., Vol. 26, No. 10, 1992
2019
Table I. Infinite Dilution Activity Coefficients and Henry's Law Coefficients of Volatile Organic Chemicals in Water vapor pressure, bar
T, 'C
net retentn time ratio
error in 7-
V by UNIFAC
H, m3atm mol-'
Chloroform f20 818n(3) f21 835n(3) f30 847"(3) f21 850n(3)
911 817 775 736
Bromodichloromethane* f130 f130 f130
213 196 181
0.0016 0.0026 0.0040
9 8 8
0.0004 0.0007 0.0012
11302 9536 8792 8126
0.0204 0.0337 0.0382 0.0452
other H
(ref)
0.20997 0.32315 0.39578 0.48093
20 30 35 40
0.085552 0.13444 0.20444
20 30 40
1.96 1.91 1.87
1025 1050 1070
0.0054268 0.0098120 0.016993
20 30 40
7.29 6.76 6.33
4340 4068 3800
0.12138 0.18898 0.23282 0.28458
20 30 35 40
0.154 0.146 0.16 0.165
9190 9779 8999 8706
Carbon tetrachloride f930 12200 (3) f1000 13100 (3) flOOO f860 13100 (3)
0.023239 0.038773 0.062319
20 30 40
3.72 3.61 3.46
1990 1928 1896
Chlorodibrornomethane* f250 f240 f240
21 20 19
0.0008 0.0014 0.0022
0.046529 0.077278 0.098136 0.12349
20 30 35 40
4.37 4.35 4.34 4.31
846 803 787 768
Dibromomethane f85 868 (3) f81 f87 801 (3) f76
9 9 9 9
0.0007 0.0011 0.0014 0.0017
0.24440 0.37242 0.54986
20 30 40
0.672 0.701 0.731
1046 1034 1017
838 753 680
0.0046 0.0070 0.0102
0.082722
20
3.21
647
704
0.0010
0.13321 0.16673
30 35
3.32 3.35
610 600
630 597
0.0015 0.0018
0.20693
40
3.37
587
1,2-Dichloroethane f54 585 (3) 626 (5) 151 *56 597 (3) 604 (5) 149
567
0.0022
1,l-Dichloroethylene f270 f270 f270
28 26 24
0.0229 0.0337 0.0475
0.0207(8) 0.0316(8) 0.0467(8)
29 28 26
0.0032 0.0049 0.0073
0.0030(8) 0.0048(8) 0.0074(8)
29
0.0079
0.0073(8) 0.0078 (3) 0.0116(8) 0.0127(3) 0.0181(8) 0.0193(3)
Bromoform f510 f480 f440
1,l-Dichloroethane All0 1100 (3),1080 (5)
flOO *loo
0.0028(8) 0.0047(8) 0.0060(8) 0.0076(8)
0.0234(8) 0.0384(8) 0.0486 (8) 0.0611(8)
0.0043(8) 0.0069(8) 0.0106(8)
0.66188 0.95743 1.3452
20 30 40
0.137 0.146 0.157
1894 1930 1936
0.21767 0.33305 0.49347
20 30 40
0.300 0.304 0.305
819 803 807
0.36247
20
0.394
1202
0.53974
30
0.416
1202
f130
1310 (3)
28
0.0118
0.77911
40
0.422
1243
1130
1370 (3)
26
0.0177
0.47656
20
1.47
245
Dichloromethane *25 251 (3)
261
0.0021
0.71003
30
1.60
238
124
236
0.0031
0.85639 1.0254
35 40
1.62 1.65
242 242
f27 f24
226 216
0.0037 0.0045
0.0017(8) 0.0021(3) 0.0026(8) 0.0032(3) 0.0032(8) 0.0039(8)
0.054095 0.087914 0.13789
20 30 40
1.52 1.53 1.54
2089 2006 1925
1910 1694 1512
0.0021 0.0032 0.0048
0.0022(3) 0.0035(3) 0.0050(3)
cis-1,2-Dichl~roethylene~ A118 856 (3) f116 884 (3) f116 866 (3) trans-1,2-Dichloroethylene 1200 (3) f130
Environ. Sci. Technol., Vol. 26, No. 10, 1992
250 (3)
1,2-Dichloropropane f240 2340 (3) f230 2310 (3) f220 2090 (3)
l,l,-dichloroethylene, is generally greater since the uncertainty in the retention time measurement, 0.02 min, is 2020
other y (ref)
7-
then more important. Of course the retention times may be increased by decreasing the flow rate of the carrier gas
Table I (Continued)
H,
other H (ref)
7918 6749 6251 5802
0.0017 0.0028 0.0036 0.0046
0.0020 (3) 0.0032 (3)
1,1,2,2-Tetrachloroethane 3758 *480 3850 (3) 3726 f410 2970 (3) 3197 f440 3460 (5) 3100 f390 3570 (3)
11982 10156 9381 8684
0.0003 0.0005 0.0006 0.0009
0.0004 (3) 0.0006 (3)
l,l,l-Trichloroethane 5880 (3) f690
2525
0.0126
5480 (3)
2227
0.0200
6210 (5) 5410 (3)
2096 1977
0.0235 0.0281
0.0133 (8) 0.0139 (3) 0.0211 (8) 0.0200 (3) 0.0264 (8) 0.0327 (8) 0.0301 (3)
error in
other y (ref)
vapor pressure, bar
T, "C
net retentn time ratio
0.012 010 0.021 173 0.027 654 0.035 753
20 30 35 40
1.85 1.75 1.68 1.62
1,1,1,2-Tetrachloroethane 7730 f760 9280 (3) 7282 f720 8530 (3) 7216 f790 7057 f690 8830 (3)
0.004 401 0 0.008 482 2 0.011 536 0.015 490
20 30 35 40
10.4 9.71 9.09 8.51
0.13149
20
0.249
5245
0.205 19
30
0.247
5324
f700
0.252 99 0.309 41
35 40
0.26 0.265
5097 4986
A700 f650
0.023689
20
4.71
0.040 118 0.065 390
30 40
0.077 544
7-
7-
7-by UNIFAC
m3 atm mol-'
2879
0.0007
4.57 4.39
1,1,2-Trichloroethane 1540 A150 1520 (3) 1500 (5) 1472 f140 1424 1140
2505 2195
0.0011 0.0017
20
0.450
4922
Trichloroethylene f500 5410 (3)
17
0.0070
0.123 49
30
0.434
5034
1520
5180 (3)
17
0.0114
0.190 28
40
0.432
4973
f510
5580 (3)
16
0.0173
Interpolated.
Vapor pressure estimated; all other vapor pressures from DIPPR.
and/or increasing the column length. However, there is a lower limit on carrier gas flow rate for stable GC operation. It is apparent from eq 12 that the accuracy of pure component vapor pressure data is important in the determination of y values. In this work, most vapor pressures were obtained from the Design Institute for Physical Property Data (DIPPR) compilation on the Scientific and Technical International Network (STN). However, for those chemicals indicated with an asterisk in Table I, vapor pressure data were not available. In this case we report their Henry's law constants (for which vapor pressures are not needed), and infiite dilution activity coeffcienta based on vapor pressures estimated using the two reference fluid method described by Reid et al. (4) with propane and octane as the reference fluids. The necessary critical properties of these compounds were estimated by the Ambrose group contribution technique. The vapor pressures calculated in this manner are given in the table. The retention time of cis-1,2-dichloroethyleneis almost exactly the same as for chloroform. Therefore, we have used 1,Pdichloroethane as the standard, but only for this chemical. The experimentally determined activity coefficient of 1,Zdichloroethane obtained earlier (with chloroform as the reference) was used. Consequently, we have a larger error bound for cis-1,2-dichloroethylene. Also reported in Table I are measured aqueous infinite dilution information for some of these same chemicals reported in previous investigations (3, 5 ) and estimates using the UNIFAC group contribution method (6, 7). (Note that the UNIFAC parameters were not available for some group-group interactions. In this case they have been set to zero.) Given that activity coefficients at infiite dilution have been difficult to measure, essentially re-
0.0055 (3)
0.0012 (3)
0.0007 (3) 0.0008 (8)
0.0071 (8) 0.0076 (3) 0.0123 (8) 0.0116 (3) 0.0203 (8) 0.0193 (3)
1,2-Dichloroethane used as reference.
quiring a differentiation of experimental data, the agreement among the experimental values from different sources is quite good. Of the 17 compounds studied, we found previous measurements for 13. For nine of these the agreement with our measurements is excellent, agreeing with our data to within the limits of estimated uncertainties. For trichloroethylene and l,l,l-trichloroethane, the agreement can be regarded as good to fair given that the absolute values of the infinite dilution activity coefficients are so large that the differences are less meaningful. Only for carbon tetrachloride and 1,1,1,2tetrachloroethane is there some disagreement between the data obtained here and that reported by Wright et al. (3) using a static cell method. However, these compounds exhibit the largest infinite dilution activity coefficient values of the compounds measured. As can be seen from the table, the UNIFAC method can give estimates of the proper order of magnitude of the infinite dilution activity coefficients for some of the paraffinic compounds, but it is not accurate for the brominated compounds (for which reliable parameters are not available) and for the olefinic compounds. While the method of measurement of infinite dilution activity coefficients we have developed is simple and rapid, and does not even require pure components, we have encountered complications with some pollutants we attempted to study. In the cases of hexachlorocyclopentadiene and hexachloro-l,&butadiene, their retention times when injected together with the chloroform standard differed significantly from that found when the chemicals were injected individually. We presume these chemicals reacted with chloroform. In such situations one may have to consider other choices for the internal standard. In the case of 1,3-dichloropropylene, we could only obtain an Environ. Sci. Technoi., Voi. 26, No. 10, 1992 2021
Environ. Sci. Technol. 1992, 26, 2022-2027
approximately equimolar mixture of its two isomers. While the two isomers separated well in the chromatograph column, indicating a difference in their infinite dilution activity coefficients, their values could not be computed since we could not determine which retention time corresponded to which isomer. Conclusions A relative measurement technique has been used to determine the infinite dilution activity coefficients and Henry's law coefficients in water of some priority pollutants. This relative gas chromatographic method is not only accurate, but equally important, it is easy to implement and experimentally very quick. The infinite dilution activity coefficient and Henry's law coefficient data reported here can be used directly for estimating environmentally important properties such as solubilities in water, multimedia partitioning, and octanol-water partition coefficients. Such data are also useful for the further development of group contribution and other prediction methods for infinite dilution activity coefficients. Registry No. (E)-ClCH=CHCl, 156-60-5;ClZCH2,75-09-2; ClCHZCHClCH,, 78-87-5; C13CCHzC1, 630-20-6; ClZCHCHClz, 79-34-5; C13CCH3, 71-55-6; Cl&HCH&l, 79-00-5; CIzC=CHCl, 79-01-6.
Literature Cited Mackay, D. Multimedia Environmental Models; Lewis: Chelsea, MI, 1991. Orbey, H.; Sandler, S. I. Ind. Eng. Chem. Res. 1991, 30, 2006-201 1. Wright, D. A.; Sandler, S. 1.; DeVoll, D. Environ. Sci. Technol., in press. Reid, R. C.; Prausnitz, J. M.; Poling, B. E. The Properties of Gases and Liquids, 4th ed.; McGraw-Hill: New York, 1987. Barr, R. S.; Newsham, D. M. T. Fluid Phase Equil. 1987, 35, 189-205. Fredenslund, Aa.; Gmehling, J.; Rasmussen, P. VaporLiquid Equilibria Using UNIFAC;Elsevier: Amsterdam, 1977. Hansen, H. K.; Rasmussen, P.; Fredenslund, Aa.; Schiller, M.; Gmehling, J. Ind. Eng. Chem. Res. 1991,30,2352-2355 (and earlier papers in the series). Gossett, J. M. Environ. Sci. Technol. 1987, 21, 202-208.
Received for review February 26, 1992. Revised manuscript received May 26,1992. Accepted June 15,1992. This research was supported, i n part, by Grant CTS-89914299 from the US. National Science Foundation to the University of Delaware and funds from the University of Delaware Undergraduate Honors Program for the support of G.T.
Sensitized Photolysis of Polychlorobiphenyls in Alkaline 2-Propanol: Dechlorination of Aroclor 1254 in Soil Samples by Solar Radiationt Jalal Hawarl,* Attlla Demeter,t and Rejean Samson
Environmental Engineering Group, Biotechnology Research Institute, NRCC, 6 100 Royalmount Avenue, MontrQal,QuQbec,Canada, H4P 2R2 Photodechlorination of Aroclor 1254 (1000 mg/L) in an alkaline 2-propanol solution at X = 254 nm proceeded with a high quantum yield (a = 35.0) as determined by C1release. The Aroclor was completely dechlorinated in 30 min and gave predominantly biphenyl (BP). After 20 h of solar irradiation, only partial dechlorination (25%) was observed, and no BP was formed. In the presence of phenothiazine (PT) sensitizer ( 5 mM) the Aroclor was completely dechlorinated to BP in 1h at 350 nm (a = 2.33) and in 4 h by exposure to sunlight. Under the same conditions, Aroclor 1254 extracts of contaminated soil (730 mg/L) were dechlorinated in 2 h at 350 nm (a = 0.28) and in 20 h on exposure to sunlight. The photoreaction was completely quenched by oxygen and nitrobenzene (0.1 M). Moreover the Aroclor was thermally (ca. 80 "C) dechlorinated to BP using di-tert-butyl peroxide. A free-radical chain reaction was suggested in which the aryl radical anion, Ar'--Cl, was a key intermediate in the dechlorination process. Introduction The unique thermal and chemical stability that makes polychlorobiphenyls (PCBs), e.g., Aroclor 1254,industrially useful has also made them a threat to the environment. They are resistant toward solar photodegradation and microbial biodegradation and therefore tend to persit inNRCC Publication No. 34398. Present address: Central Research Institute for Chemistry of Hungarian Academy of Sciences, P.O.Box 17, H-1525 Budapest, Hungary. +
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definitely. A common and deceptive practice to prevent PCBs from reaching our ecosystem is to dispose of them in landfills; however, this has proved to be potentially dangerous and costly. For example, in a recent accident (Saint-Basile-le-Grand, QuBbec, Canada, on August 23, 1988) 1500 barrels of PCB-laden oil caught fire in a warehouse sending clouds of toxic smoke into the atmosphere, forcing the evacuation of more than 3000 people and costing several millions of dollars to clean up the site and several hectors of surrounding contaminated soil. Presently, incineration is the most widely used technology for the destruction of PCBs, but incineration often leads to the formation of more toxic oxygenated derivatives (e.g., polychlorinated benzofurans and dioxins) if not carefully controlled. Intensive chemical (1, Z ) , photochemical (3-5),and joint physicochemical-microbial dechlorination processes (6, 7)have been reported on the dechlorination of PCBs. Solar photodegradation is one of the most natural and most economical degradation routes for environmental pollution. Unfortunately, most PCB congeners do not absorb strongly above 300 nm, and their direct photolysis often proceeds with very low quantum efficiency (8, 9). Sensitizers and other additives such as amines (10, II), borohydrides (12),alkaline alcohols (131, and hydroquinones (14) have been used to enhance photodechlorination. One striking example has been reported by Nishiwaki in which photodechlorination of Kanechlor, KC-300, a t 298 nm in an alkaline 2-propanol solution proceeds with high quantum yield (a = 36) (13). One drawback of this reaction is its inability to proceed with the same efficiency at longer wavelengths, particularly if
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0 1992 American Chemical Society
