EPA/600/D-87/229
July 1987
DETERMINATION OF HENRY'S LAW CONSTANTS OF
SELECTED PRIORITY POLLUTANTS
H. Paul Warner
Jesse H. Cohen
John C. Ireland
Wastewater Research Division
Water Engineering Research Laboratory
Cincinnati, Ohio 45268
EPA Project Officer
John C. Ireland
WATER ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OH 45268
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TECHNICAL REPORT DATA
(Pleetr rtod Inttruclloni on iht rtvmt btfort comp' „..„.. •» « i . n ,.
IEPORT NO.
EPA/600/D-87/229
a. "
«. TITLE AND SUBTITLE 6REPQI
DETERMINATION OF HENRY'S LAW CONSTANTS OF SELECTED Ju
PRIORITY POLLUTANTS
6 PER'C
7 AUTHOR'S) 8 PERK
H. Paul Warner. Jesse M. Cohen, and John C. Ireland
9 PERFORMING ORGANIZATION NAME AND ADDRESS 10 PRO!
Same as Item (12)
12 SPONSORING AGENCY NAME AND ADI
Water Engineering Research 1
Office of Research and Devel
U.S. Environmental Protectlc
Cincinnati, OH 45268
11 CON
>RESS .3 TVPI
.aboratory- Cincinnati, OH Publ 1
opnent 14 SP°'
>n Agency
EPA/6
»T DATE
ly 1987
>r.MING ORGANIZATION CODE
)RMINO ORGANIZATION REPORT NO
JRAM CLEMENT NO
TRACT/GRANT NO
E Of REPORT AND PERIOD COVERED
shed Paner
4SORING AGENCV CODE
00/14
IS SUPPLEMENTARY NOTES
Project Officer, John C. Ireland (com 569-7413/FTS 684-7413)
16 ABSTRACT
The Henry's law constants (H) for 41 selected priority pollutants were determined
to characterize these pollutants and provide Information on their fate as they pass
through wastewater treatment systems. All experimental values presented for H are
averages of two or more replicates. Calculated values are based on data from many
ublished sources. Many calculated results correspond closely to the experimental
/alues, several deviate significantly, and no values could be calculated for some
compounds due to Insufficient data.
17
a DESCRIPTORS
KEY WORDS AND DOCUMENT ANALYSIS
b IDENTIFIERS/OPEN END
18 DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
UNCLASSIFIED
20 SECURITY CLASS iTIiu
UNCLASSIFIED
ED TERMS C COSATi 1 irld'Oioup
KtfO'll 21 NO 0' PAGES
pjfr, 33 PRICE
EPA For* 2220-1 (R» 4-77) PWCVIOUI COITION it
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SECTION 1
INTRODUCTION
Millions of people living In this nation are concerned with the effect
their environment has on them. The weight of this concern has produced
legislation which will, it 1s hoped, protect them from the hazards of their
environment. One result of this concern was the Issuance of the Consent
Decree In 1976 which designates specific compounds considered to be poten-
tially toxic to various life forms. This decree and other legislation
require that the U.S. Environmental Protection Agency (USEPA) act to answer
questions concerning the ultimate fate and effect of these materials on
those life forms and to reduce, through effective regulation, the conse-
quences of unregulated dissemination of those compounds which are found to
be toxic.
The responsibility given to the USEPA provokes many questions.
. Of these compounds, are any present In concentrations
sufficient to be toxic?
• If so, what are their origins?
• By what mechanism do they enter the environment?
• What are their*health related effects on various life forms?
• How can they be controlled?
• Where should they be controlled?
A very complex multi-disciplinary effort 1s required to answer these questions.
The USEPA through its Municipal Environmental Research Laboratory
(MERL) in Cincinnati, Ohio, is addressing some of these questions by
characterizing the ability of municipal wastewater treatment systems to
remove pollutants of health concern and by providing information relating
to the fate of these pollutants as they pass through these systems.
Part of this effort involves the determination of Henry's Law constant
(H) for as many of the volatile priority organics as possible. These values
for H will enhance the ability to predict the fate of volatile organ1cs in
wastewater treatment systems.
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SECTION 2
EXPERIMENTAL PROCEDURES
The apparatus used 1n this study Is that described by Mackay, et al.t
(1) with some modifications. The major modification was an Increase 1n
the liquid depth In the stripping vessel to assure system equilibrium for
all compounds studied. Figure 1 1s a diagram of the apparatus. Nitrogen
from a high pressure cylinder was passed through a two-stage pressure
regulator and rotameter, and then bubbled through water to saturate It and
prevent water evaporation from the stripping vessel. The nitrogen was
then introduced into the bottom of the stripping vessel through a sintered
glass disc. The liquid depth in the stripping vessel was 60 oh with a
liquid volume of 1 liter. The vessel was water-jacketed and maintained at
25° + 0.05°C. The exit gas was vented to a hood for safety and the flow
rate was measured by a soap bubble flow meter.
The general procedure was to prepare a saturated solution of the test
compound by adding a quantity of the compound, sufficient to exceed its
solubility, to distilled deionized water and mixing overnight. A portion
of this solution, the quantity of which was dictated by analytical pro-
cedure, was mixed with the temperature-stabilized deionized water from the
stripping vessel, the volume was adjusted to 1 liter, and the solution was
returned to the vessel for stripping. The resulting test solution varied
from 10 ug/1 to 10 mg/1 of solute, depending on compound solubility and
analytical sensitivity.
Distilled deionized water was used in all experiments. Hydrocarbons
used were of the purest quality available and were used without further
purification. In most cases, the purity was stated as > 99X.
Several of the compounds with stated purities of >99% were significantly
less pure than indicated and some contained impurities of up to SOX. These
impurities complicated the sample analysis, and in a few instances, required
the application of GC/MS analysis for identification of the test compound.
As suggested by Nackay, et al., (1), the system equilibrium should
not be significantly dependent upon gas-flow rates and thus varying the
rate should not significantly affect the experimentally determined value
for H. Confirmation of this can be seen in Figure 2. Varying the stripping
gas flow rate from 50 to 250 cc/min with benzene as the solute produced an
average value for H of 5.6 x 10'3 m3 atm/mol and a standard deviation of
+ 7.28%. The average experimental value compared favorably with the calcu-
Tated value of 5.5 x 10"3 m3 atm/mol. A "standard" flow rate of 100 cc/min
was selected for the remainder of this study. This rate was chosen because
it produced a good bubble pattern in the stripping vessel, and it allowed
adequate time for sampling. Flow rates were checked before, during and
after completion of each run as dictated by elapsed time to assure constancy
of flow.
-------
Ill Exit
To Flow Meter
p
R
(^
Nitrogen
ress
egul,
&
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i
f
Sample
Tap
Lire
itor
Strip
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I "' /7?h "*
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Flow Saturator
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1
0
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o
0
0
0
o
0
0
o
oc
So
000
<3°°
00
OOO
o o
ooo
On
? c
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K
*.
«v
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1 •
Glass
Frit
•
1
-*
Pump
'emperature
Control
Bath
c<
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Figure 1. Stripping apparatus diagram
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r-
X
o 6
«•*
co 4
n
k o
= 3(
•
. - Calculated
• Experimental
i i
) 50 100
•
III
150 200 25
I
Flow, cc/min
Figure 2. Flow rate vs Henry's law constant for
volatilization of benzene
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-5-
To evaluate the reprodudblllty of this system at the selected gas
flow rate of 100 cc/m1n, repetitive runs were made using benzene as the
solute. As can be seen In Table 1, no experimentally significant vari-
ation In the value for H was produced.
TABLE 1. REPRODUCIBILITY OF EXPERIMENTAL PROCEDURE
Run H. m3 atm/mol x IP'3 Correlation Coefficient
1 5.41 0.999
2 5.76 0.999
3 5.34 0.998
4 5.49 0.998
5 5.62 0.999
These results give a mean value for H of 5.52 x 10~3 m3 atm/mol and a
standard deviation of + 3%.
In order to assure that equilibrium within the stripping vessel was
being attained, one of the more volatile compounds, benzene, was run
repetitively'at varying liquid depths. The results 1n Table 2, show no
significant change in tKe experimental value for H was produced with
reductions in liquid depth of up to 50%.
TABLE 2. EFFECT OF LIQUID DEPTH ON H
Liquid Depth, cm H, m3 atm/mol x 10'3
60 5.50
50 5.73
40 5.69
30 5.85
Since system equilibrium was achieved with benzene at these depths, it
was assumed that equilibrium would be achieved in systems with less
volatile compounds.
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-6-
Samples for analysis were taken froa the stripping vessel with a
glass syringe through a sample tap positioned at a depth of approximately
20 on from the liquid surface. The sampling frequency varied from minutes
to hours, depending upon the volatilization rate of the specific compound.
Varying the sampling depth during stripping did not result In variation 1n
concentration which confirmed that adequate nixing was accomplished by
the bubbles in the stripping vessel. U-V spectroscopy and two gas chroma-
tography techniques; purge and trap, and solvent extraction, were employed
for analysis of the samples.
A few of the compounds 1n this study were light-sensitive and the
stripping vessel was covered during the test. Some of the compounds were
readily adsorbed on the glass surface of the stripping vessel. To minimize
this effect, the stripping vessel surface was saturated with the compound,
i.e., the adsorption sites were saturated by exposing them to .the test
compound repeatedly prior to each run.
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-7-
SECTION 3
DISCUSSION AND RESULTS
Even a casual Inspection of the organic* on the list of priority
pollutants will show that many of the low molecular weight chlorinated
hydrocarbons are volatile compounds. It follows fron this that loss of
these compounds from solution can be an Important route of removal from
the aqueous flow, but this also Indicates that the potential exists for
contamination of the air around a wastewater treatment plant. Treatment
plants offer ample opportunity for volatilization from processes such as
the flows in the collection system, aerated grit chambers, settlers and
most especially from aeration basins where the driving force for desorp-
tion from solution is provided by the air or oxygen aeration. Thus, it
is not surprising that volatilization from water bodies to the atmosphere
is generally recognized as a significant pathway for transfer of organics
from one environmental medium to another.
The volatilization process from an aqueous solution is generally
accepted as consisting of diffusion of the solute from the bulk of the
water to the interface, followed by transfer across the interface and
finally diffusion from the interface to the bulk of the air phase.
There have been many attempts in the literature to develop mathe-
matical models which would predict the rate of volatilization of a
compound from aqueous solution. Most models incorporate parameters such
as Henry's Law constant, gas and liquid phase mass transfer coefficients
and, more recently, models nave incorporated coefficients which account
for other parameters that affect the volatilization rate such as adsorp-
tion on solids and rate of blodegradation.
An important coefficient in virtually all of the models is Henry's
Law constant (H). This constant is an expression of the distribution of
a volatile solute at equilibrium between the liquid and vapor phases.
Unfortunately for many of the comompounds of environmental interest, the
value for H is not available. When the necessary information on aqueous
solubility and vapor pressure is available, H can be calculated. However,
published vapor pressure and solubility data are, in many cases, question-
able, and in some cases, either erroneous or non-existent. Another
method for obtaining H was required to overcome this inability to obtain
or calculate a value for H from the literature.
Mackay, et al., (1) described an apparatus for the determination of
Henry's Law constants for hydrophobic compounds with an accuracy of about
5%. This device was employed in this study to provide values of H for
as many of the volatile priority pollutants as possible. The method
involves measurement of the compound concentration in only the liquid
phase while being stripped isothermally from solution at a"known gas
flow rate. H can readily be calculated from a plot of the natural log
of the concentration vs. time which should be linear with a slope of
-(HG/VRT). Thus
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-8-
H B slope x VRT
G
where
H ° Henry's Law constant, m3 atm/mol
V = Volume of test solution, m3
R » Gas constant, m3 atm/mol °K
T = Temperature, °K
G - Gas flow rate, m3/m1n
Henry's law constant was determined for 41 compounds. The results of
these tests are presented in Table 3. All experimental values for H
reported In the table are averages of 2 or more replicates. Calculated
values for H were based on data from many published sources (1-11), and
can be calculated by
H =
VP x MW
where
H = Henry's law constant, m3 atm/mol
VP = Vapor pressure of solute, atm
MW = Molecular weight of solute, g/mol
S = Solubility of solute, g/m3
In all cases, except during the first few minutes when it is believed
that high solute concentrations overloaded the analytical detectors,
resultant curves were linear, with correlation coefficients (r) normally
greater than 0.980; see Figures 3 and 4. In all but two of the compounds
studied a precision corresponding to a standard deviation of approximately
6% was achieved.
As can, be seen in Table 3, many of the calculated results correspond
closely to the experimental values, however, several deviate significantly
from these values and for some of the compounds, no values could be
calculated due to insufficient data. Some deviation between experimental
and calculated values for H can be attributed to the use of the only
available data at temperatures different from the selected system tempera-
ture. Other deviations are due to incorrect solubility and vapor pressure
information. Literature values can vary over three orders of magnitude for
some compounds. Some of the deviation can be attributed to experimental
error, however, questionable published data and confidence in the experi-
mental method dictates that H values determined experimentally are preferred
over calculated values.
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to
0)
to
a
c
*
c
o
+3
(0
0)
u
c
o
o
14
12
10
8
6
4
2h
T = 298° K
V = 9.8x
G = 1.0x 10-4m3/min
r = 0.985
to
0 10 20 30 40 50 60 70 80 90 100
Time, minutes
Figure 3. Typical plot for volatilization of
trichloroethylene
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-0.5r
T = 298° K
V = 9.8x 10-«m3
G = 1.0x 10-4mVmin
r = 0.999
0 10 20 30 40 50 60 70 80 90 100
Time, minutes
Figure 4. Typical plot for volatilization of benzene
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TABLE 3. SUMMATION OF DATA FOR HENRY'S LAW CONSTANT
Compound
Acenaphthene
Benzene
Carbon tetrachloride
Chlorobenzene
1,2,4-Triclilorobenzene
Hexachlorobenzene
1,2-Dichloroethane
1,1,1-Trfchloroethane
Hexachloroethane
1,1-Dichloroethane
thloroforni
l,2-D1chlorobenzene
l,3-D1chlorobenzene
1,4-Dkhlorobenzene
1,7-DichloroethyJene
1,2-trans-Dlchloroethylene
1,2-Dichloropropane
1,3-D1chloropropy1ene
Ethylbenzene
Methylene chloride
Bromoform
Vapor T
Pressure, jfP'
atm.x 10"J °K
Solubility Temp.
1 o
g/mj °K
3.93(1) 298
125(3) 298
149(4) 298
15. 5(-
0.383(1
- —
113*(4
168M-4
1 298
5 298
-
298
298
1780(10) 298
800(2) 298
472(1
30(7
0.006(6
' 298
•
i
) 298
8300(6) 298
5497*(4) 298
50(5) 295
308(4
260(<
1.97(4
1) 298
>) 298
1) 298
2.48(6) 298
- -
-
778(4) 298
263(4
65,8(4
32.9(5
12.5(3
599*(4
7.37(4
287
298
293
) 298
298
) 298
5500(4
9600(4
145(4
123(4
79(4
5000(6
6300(2
2700(4
2700(5
293
298
298
) 298
) 298
) 293
) 293
293
298
206(11) 298
16700 4
31 30* (5
298
298
Molecular
Weight
g/mol
154.2
78.1
153.8
112.6
181.5
284.8
99.0
133.4
236.7
99.0
119.2
147.0
147.0
147.0
97.0
96.9
113.0
111.0
106.2
84.9
252.8
H,. m3 atm/mol x 10"3
Calculated Experimental
5.48
28.6
3.70
2.32
1.35
4.08
5.54
3.23
2.00
2.96
15.1
4.05
2.75
1.35
6.44
3.04
0.595
0.241
5.55
30.2
3.93
1.42
1.70
1.10
4.92
9.85
5.45
3.39
1.94
2.63
2.72
15,0
5.32
2.82
3.55
6.44
3.19
0.532
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TABLE 3. (cont'd) SUMMATION OF DATA FOR HENRY'S LAW CONSTANT
Vapor
Pressure,
atm.x 10"J
833*{4)
65.8(5)
0.197
0.107
0.374
•• ^
«• »
•• ••
5
4
6)
*• M
25.8*(4)
37.4(6)
97.8(6)
- -
- -
Temp.
°JL
298
293
293
298
298
•
4»
298
298
298
_
-
Solubility
g/m3
1100(4)
2(5)
0.805 5}
2000(6)
67000(6)
3.93(5)
1.98(5)
150(4)
535(9)
1100 4)
0.2 6
0.186 6)
1.85(8)
0.056(6}
0.275(6)
0.012(5)
1.75(8)
Temp.
°K
298
293
298
298
298
298
298
298
298
298
293
298
298
298
298
298
298
Molecular
Weight
g/tnol
163.8
137.4
168.8
260.8
272.7
123.1
198.1
94.1
152.2
116.2
165.8
92.1
131.5
364.9
380.9
409.8
373.4
389.3
328.4
413.9
H. m3 atm/mol x 10"3
Calculated Experimental
104
25.7
36.2
0.023
—
28.5
6.44
11.7
• M
- -
2.12
58.3
0.783
10.3
16.4
0.024
0.0014
0.0013
0.114
0.117
28.7
5.93
11.7
0.496
0,058
0.048
1.48
0.032
8.37
4.89
Compound
firomodlchloromethane
Trlchlorof1uoromethane
•01 bromochl oromethane
Hexachlorobutadlene
Hexachlorocyclopentadlene
Nitrobenzene
4,6-Olnltro-o-cresol
Phenol
Acenaphthylene
Fluorene
Tetrachloroethylene
Toluene
Trlchloroethylene
Aldrln
Dleldrln
Chlordane
Heptachlor
Heptachlor epoxlde
Arochlor 1254
Toxaphene
( } Reference designation. * Data Interpolated between two data points.
- Data unavailable.
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-13-
REFERENCES
1. Mackay, 0., Shlu.N. Y. and Sutherland, R. P.,
"Determination of Air-Hater Henry's Law Constant for Hydrophobia
Pollutants." Environ. Scl. & Tech.. JL3, 333 (March 1979).
2. DilHng, W. L., "Interphase Transfer Processes. II. Evaporation
Rates of Chloro Methanes, Ethanes, Ethylenes, Propanes, and
Propylenes from Dilute Aqueous Solutions. Comparison with
Theoretical Predictions." Environ. Sc1. & Tech.. 11, 405 (April 1977).
3. Zwollnski, B. J., and Uilholt, R. C., "Handbook of Vapor Pressures
and Heats of Vaporization of Hydrocarbons and Related Compounds,"
API, 44-TRC Publications in Science and Engineering, 1971.
4. Verschueren, K., "Handbook of Environmental Data on Organic Chemicals,"
Van Nostrand Reinhold Company, 1977.
5. Water-Related Environmental Fate of 129 Priority Pollutants. A
Literature Search by Versar, Inc., for USEPA Office of Water Planning
and Standards. Contract No. 68-01-3852. January-February 1979.
Draft copies.
6. ISHOW Data Base, University of Minnesota, Duluth. April 1979.
7. Spencer, W. F., and Fanner, W. J., "Assessment of the Vapor Behavior
of Toxic Organic Chemicals," Contribution of Federal Research, SEA,
USDA and the University of California, Riverside, California.
8. Weil, L., Dure, G., and Quentin, K. E.,
Z. Wasser - Abwasser Forsch, 7(6). 169-185 (1974).
9. Strier, M., "Treatabllity of Organic Priority Pollutants," Part C.
USEPA Office of quality Review, June 1978. Unpublished Manuscript.
10. McAuliffe, C.. Jour. Phys. Chen., 70, 1267 (1966).
11. Identification of Organic Compounds In Effluents from Industrial
Sources. USEPA Report, PB-241 641/OBA.
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ACKNOWLEDGEMENTS
This project could not have been completed without the able assistance
of Thomas A. Pressley, Mho, through GC/NS, verified some of our analytical
results.
Special thanks are also due to Michael Jelus for his cooperation which
enabled a timely completion of the sample analyses.
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