(14) Union Carbide Parma Standard Test Method PSM-1016,
References (1) Habibi, K., Enuiron. Sci. Technol., 7, 223 (1973). (2) McKee, H . C., McMahon, W. A., Jr., J . Air Pollut. Contr. Assn., 10,456 (1960). (3) Ter Haar, G. L., Bayard, M. A., Nature, 232,553 (1971). (4) Lee. R. E.. Patterson. R. K.. Crider. W. L.. Waaman. J., Atmos. Enuiron., 5,225 (1971). (5) Moran, J . B., Manary, 0. J., Fay, R. H., Baldwin, M. J., “DeveloDment of Particulate Emission Control Technioues for I
Spark Ignition Engines,” Final Report to the Environmental Protection Agency by the Dow Chemical Co., Midland, Mich., July 1971. (6) Moran, J . B., Baldwin, M. J., Manary, 0. J., Valenta, J . C., “Effect of Fuel Additives on the Chemical and Physical Characteristics of Particulate Emissions in Automotive Exhaust,” i b i d , June 1972. (7) Robbins, J. A,, Snitz, F. L., Enuiron. S’ci. Technol., 6, 164 (1972). (8) Sampson, R. E , Springer, G. S., ibid., 7 , 5 5 (1973). (9) Smythe, R. J.,“The Application of High Resolution Gas Chromatography and Mass Spectrometry to Analysis of Engine Exhaust Emissions.” PhD Thesis. Universitv of Waterloo, Waterloo, Ont ., 1973. (10) Boyer, K. W., “Analysis of Automobile Exhaust Particulates.” PhD Thesis. Universitv of Illinois. Urbana. Ill.. 1974. (11) Ter Haar, G. L., Lenane,“D. L., Hu, J . N., Brandt, M., J . AirPollut Contr. Assn., 22,39 (1972). (12) Habibi, K., Jacobs, E. S., Kunz, W. G., Jr., Pastell, D. L.,
“Characterization and Control of Gaseous and Particulate Exhaust Emissions from Vehicles,” presented at the Air Pollution Control Association, West Coast Section, Fifth Technical Meeting, San Francisco, Calif., October 1970. (13) Rosen, A. A., Middleton, F. M., Anal. Chem., 27,790 (1955).
“Gas Chromatographic and Ultraviolet Spectrophotometric Determination of Polynuclear Aromatic Compounds in Airborne Particulates,” Union Carbide Corp., 1972. (15) Hoffmann, D., Wynder, E. L., “Chemical Analysis and Carcinogenic Bioassays of Organic Particulate Pollutants,” Chap. 20 in “Air Pollution,” 2nd ed., Edited by A. C. Stem, Academic Press, New York, N.Y., 1968. (16) Karasek, F. W., Res. Develop., 24,40 (Oct. 1973). (17) “Eight Peak Index of Mass Spectra,” 1st ed.., Vols. I and 11, Mass Spectrometry Data Center, AWRE, Aldermaston, Reading, U.K., 1970. (18) Harris, W. E., Habgood, H. W., “Programmed Temperature Gas Chromatography,” p 155, Wiley, New York, N.Y., 1968. (19) Fritsch, A. J., “Gasoline,” Center for Science in the Public Interest, Washington, D.C., April 1972. (20) Shimp, N. F., Leland, H. V., White, W. A., “Distribution of Major, Minor and Trace Constituents in Unconsolidated Sediments from Southern Lake Michigan,” Enuiron. Geol. Notes, Ill. State Geological Survey, Urbana, Ill., No. 32, 1970. Received for reuiex July 26, 1974. Accepted December 20, 1974. This utork was supported by a research grant from Universal Oil Products Co. and by the National Science Foundation R A N N Grant 31605. The mass spectral data processing equipment used at the University of Illinois, School of Chemical Sciences Mass Spectrometv Center, was provided by NIH Grants CA 11388 and GM 16864, from the National Cancer Institute and the National Institute of General Medical Sciences, respectiuely. The electron rnicroscop.y equipment used at the University of Illinois Center for Electron Microscopy was provided in part by N S F Grant GA 123946-32-53-358. T h e automobile engine was donated by the Ford Motor Co. K . W.B. held an Environmental Protection Agency Predoctoral Felloxship in Air Pollution (U910093).
Evaporation Rates of Oil Components Zephyr R. Regnier and Brian F. Scott* Water Science Section, Water Quality Research Division, Environment Canada, Ottawa, K1A OE7, Ont., Canada
w Rate constants for the evaporation of n-alkane components of Arctic Diesel 40, a No. 2 fuel oil, were determined by gas chromatography. Using a constant wind speed of 21 km hr-l, the evaporation was studied at a series of temperatures. Arrhenius activation energies were calculated. The rate constants and the initial concentration of t h e alkanes were also utilized t o determine the amounts of the alkanes present a t various time intervals. These results coincided with the evaporation behavior of the total oil. Such constants should aid in determining the oil remaining from spills on ice and on water.
When oil is spilled in a n aqueous environment, it is altered from its original composition by a series of processes which influence its weathering. Processes which contribute t o weathering are evaporation, photochemical and oxidative reactions, dissolution of individual components, and emulsion formation, as well as the action of microorganisms ( I ) . In a system where all these processes are active, interpretation of the d a t a is extremely difficult, compounded by the multitude of components in the oil. Descriptive studies of crude oils, where most of these processes were operative have previously been reported ( 2 ) . Refined oil products have been investigated, usually as a function of certain aspects of weathering (3, 4 ) . The process which causes the greatest initial change in the composition of most oils is evaporation (5, 6).
This work reports the determination of evaporation rate constants of selected oil components. Such constants are known for various one-, two-, and three-component systems. It is, however, desirable to obtain the evaporation rate constants for the components as they occur in a n oil matrix. If a sufficient number of these constants is known, it should be possible t o predict the evaporative loss of oils spilled in the environment. Such values would be applicable to spills on ice and water where the oil lay is more than just a few molecules thick. A number of parameters, such as temperature, wind speed, solar radiation, thickness of oil on the surface, and composition of the oil, govern its rate of the evaporation. Of these, only temperature was varied in our experiments; the others were held constant. Experimental
Materials. The refined oil, Arctic Diesel 40, was obtained from Imperial Oil Ltd. This No. 2 fuel oil is the fraction cut between 150” and 280°C. All experiments were run on the same source batch. Samples of the alkanes, obtained from Chromatographic Specialties (Brockville, Ont.), were of sufficient purity. Evaporation Conditions. An environmental chamber, Miss Delta Model, Delta Design Inc., provided a constant wind speed of 21 k m hr-1 (13 mi hr-I) over the samples and was set to operate at temperatures of 5”, lo”, 20”, and 30°C. In addition, the darkened chamber ensured that incident radiation would not influence the temperature of Volume 9,Number 5, May 1975
469
the oil. To prevent the recirculation of vapors, the exhaust outlet was connected to a water aspirator which removed them a t a rate of 2 liters min-I. Samples of oil (each 12 f 0.7 grams) were weighed into 90-mm diameter Petri dishes and placed in the chamber. The oil thickness was roughly 3 mm. The air movement over the samples produced small wavelets which resulted in a stirring action. Analysis. Duplicate samples were placed in the environmental chamber for each kinetic run. Before each periodic weighing, a 0 . 4 5 ~ 1aliquot was taken from one dish for gas chromatographic analysis. A Perkin-Elmer 900 gas chromatograph was used for the analysis under the conditions shown in Table I. Retention times of individual components were established on an OV-1 as well as an OV-225 SCOT column. The linearity of the amplifier system was checked using n-hexane, and the response for each major component was determined- relative to n-hexane on a weight basis. This was done by ascertaining the area under the peaks by a triangulation method. The precision of this method was confirmed using a Hewlett-Packard 3370B integrator. Samples containing known weights of the original oil and n-hexane were injected into the gas chromatograph. The amount of n-hexane added was similar to the average concentration of the major components in the oil. As shown in Figure 1, a typical chromatogram of the oil is extremely complex. For the purposes of this work, it was assumed that the resolved peaks stand on a continuum of unresolved peaks. For all chromatograms, a continuum was drawn, as illustrated by the dashed line in Figure 1, and the areas of the major components were calculated. These areas were then transformed into weights, relative to n-hexane, and the resulting values were normalized. Since the percentage of n-hexane was known, the percentage of each of the major components could be easily calculated.
Table I. Chromatographic Conditions Instrument Perkin-Elmer 900 Mode Dual Column; Detectors: FID Column SCOT 0.02 in. internal diameter X 50 ft (0.50 rnrn X 15.2 rn) OV-1 liquid phase
Injector temperature Detector temperature Initial column temperature Final column temperature Rate of heating Carrier gas Split ratio
250°C 275°C 60°C for 0 min 220°C for 32 rnin
PC/min He at 2 . 3 rnl/min flow rate 10.0-1
The results were found to agree with values obtained using a Hewlett-Packard 3370B integrator, where the appropriate integrator output was factored into area of the peak and area of the continuum. The peak areas were normalized relative to the total area of the chromatogram, and no internal standard was used. The former method, utilizing n-hexane as an internal standard, was used in all subsequent determinations since response factors of the heavier unresolved components might cause difficulties in the subsequent evaporation studies. For the evaporation studies the chromatograms were treated in a manner similar to the original determination of the percentage of major components, but no internal standard was added. After the relative amount of each component was ascertained it was corrected for the concentrating effect of the evaporation, though no correction was needed for change in density since this did not alter significantly with evaporation. During these studies, aliquots of the original sample were injected as a calibration check. Once the percentages of the remaining, individual components of interest were determined as a function of time, the results were subjected to Powell plots, and the order with respect to components was established. The results were then analyzed by standard kinetic procedures. The precision in the determination of any peak area was 4% maximum. This value is compounded when calculating the normalized area to an estimated maximum of 10%.
Results In Figure 2 the evaporation profiles of the refined oil, Arctic Diesel 40, are shown as a function of the remaining oil. Although a smooth curve was obtained a t each temperature, no simple order for the evaporation of the oil could be determined. This might be expected since the oil is a multicomponent system, and each component would contribute to the total order of the evaporation. Only the n-alkanes, identified on the chromatogram shown in Figure 1, were studied in detail. Although they represent only 18% of the oil, as shown in Table 11, it was hoped that their evaporative behavior would reflect that of the total sample. The evaporation rate constants for each n-alkane, first order with respect to that component, are listed in Table 111. A typical plot of the log of concentration of the alkane remaining vs. time is shown in Figure 3. As expected, for a particular alkane, the evaporation rate constant increases with temperature. At a given temperature, the rate constant decreases with increasing molecular weight. Of the 35 constants, only five values appeared to show deviation from these trends. These deviations perhaps arose from accumulation of erroE in the experimental method. The vapor pressure of each individual alkane was calcu-
5
Figure 1. Chromatogram of No. 2 fuel oil, Arctic Diesel 40, with n-hexane added as internal standard Area under dashed line represents continuum, from left to right: (1) n-hexane, ( 2 ) nonane, (3) decane, ( 4 ) undecane, (5) dodecane, (6) tridecane, (7) tetradecane, - ( E ) pentadecane, (9) hexadecane, (10) heptadecane, and ( 1 1) octadecane
470
Environmental Science & Technology
lated from standard equations (7). The ratios of the vapor pressures a t a .given temperature to those at 30°C (V,t " / V , 3 0 ° ) were compared to the corresponding ratios of the evaporation rate constants (kt"/k300) for the various alkanes. These are shown in Table IV. Usually there was a reasonable 1:l correspondence between the vapor pressure ratios and rate constant ratios for the same compound at the temperatures studied. This indicates that the measured rates are functions of the components from which they were derived and not of the total system. Because there was a 1:1 correspondence between the ratios of vapor pressure and of the evaporation rates, only one set of rate constants at one temperature is needed to determine the rates at other temperatures.
A log-log plot of the evaporation rate constants vs. the vapor pressures produced a linear relationship (Figure 4). Only those points where the vapor pressure was greater atm) were included. A least squares than 10.13N m-2 fit of the data produced the following equation,
+
log(V,) = 1.25 log(k) 0.160 Accordingly, if the vapor pressure of a component, is known, its rate constant can be calculated. By use of experimental evaporation rate ionstants, Arrhenius evaporation energies were calculated (Table V) . Included in Table V are the energies of evaporation of the rz-alkanes a t 25°C and reported enthalpies of evaporation (8). There is a significant but relatively constant differ-
I
20'
'i
2000
1000
3000
TIME 2000
4000
8000
6000
TIME
,
\>a
,I.
-
-0m - 5 -6
983
-
.. J' 7.'
-
18.27
Table 111. First Order Evaporation Rate Constants of n-Alkane Components of Arctic Diesel 40 Evaporation rate constants, min-1
Component
n-Cs n-Clo n-C1l n G n-CI1 n-C14 n-C1 ~-CX n-Ci7
n-G,
Temperature,
100
50
3.49 x 1.19 x 4.15 x 1.57 X 1.57 x 2.21 x 5.61 X 1.08 X 4.00 x
10-3 10-3
10-4 1010-4
10-5 l.0-6 lo-'
20
30°
Table IV. Vapor Pressures and Evaporation Rate Constants of n-Alkanes Relative to 3OoC VpjO
1.87 x 7.17 x 2.86 x 1.20 x 4.20 x 4.28 x 2.58 x 5.70 x 2.20 x
10-3 10-4 10-4 10-4
10-6
10-5 10-5
3.44 x 1.31 x 5.25 x 2.46 x 1.14 x 5.24 x 3.99 x 4.08 x 4.00 x
10-3 10-3 10-4 10-4
10-4 10-5
10-5 10-5
6.98 x 10-3 2.48 x 10-3 1.28 x 10-3 5.72 x 10-4 2.94 x 10-4 1.14 x 10-4 6.14 x 10-5 1.11 x 10-4
~
n-Alkane
Vp300
n-Clo n-CI1 n-C1* n-C13 n-Cla n-Cls n-C16 n-C1;
0.162 0.142 0.121 0.104 (0.089) (0.077) (0.067) (0.060)
k50
-
k300
0.171 0.167 0.123 0.274 0.075 0.049 0.018 0.036
_
ypiao
kioO
Vp3Qo
k3Oo
vp300
0.240 0.217 0.192 0.169 0.150 0.134 (0.120) (0,110)
0.268 0.289 0.223 0.210 0.143 0.375 0.420 0.513
0.502 0.480 0.453 0.426 0.402 0.381 0.361 (0.347)
_
-
Vp200
.~
k2oo k300
0.493 0.528 0.410 0.435 0.386 0.460 0.650 0.355
Volume 9, Number 5,May 1975 471
Table V. Energy Parameters for Evaporation of n-AI ka nes
Corn pound
Decane U ndecane
Dodecane Trideca ne Tetradecane Pentadecane Hexadecane
Arrhenius activation energy as Enthalpy of determined evaporation at i n this work, 25% (8), kcal/M kcal/M
15.23 15.34 17.73 18.97 22.60 :').68 36.96
12.27 13.46 14.65 15.86 16.99 18.21 19.45
Arrhenius energy of evaporation at 25"C, kcal/M
14.71 14.82 17.21 18.44 22.08 26.16 36.44
ence between the values in the third and fourth columns for the first four compounds. For the last three compounds, the difference increases drastically. Finally, the evaporation rate constants and the initial concentrations of each n-alkane were used to ascertain, on a percentage basis, the amount of the n-alkanes remaining a t definite time intervals. This was then compared with the percentage of the total oil remaining at the same time intervals. The experimental values were in excellent agreement with the calculated results as shown in Figure 2. Discussion Just after an oil spill on water or on ice, the major weathering factor acting on the oil is evaporation. Later, depending on the physical and chemical properties of the oil and on the environmental conditions, other factors become equally or more important. Since residues of oil spills in the form of tar balls have been found to contain small amounts of tridecane and tetradecane, it was decided to study the evaporation of a refined oil containing these and other alkanes in a matrix of oil components. Components with vapor pressures lower than n-octadecane will not evaporate significantly under normal conditions, while those with vapor pressures higher than n-octane would not be expected to persist too long in an open environment (9). Therefore, evaporation of components having vapor pressures between those of n-octane and n-octadecane would be expected to control the short-term aging of the oil. The evaporation rates determined for the alkanes a t the temperatures of interest illustrate trends which would be expected. When we use these to determine the total concentration of the n-alkanes, an excellent correlation between the evaporation of the alkanes and the evaporation of the oil was obtained. Evaporation energies of the n-alkanes in the oil matrix differ significantly from those of the pure compounds.
472
Environmental Science 8, Technology
This could arise from several factors or combinations of factors. Interactions between the components of the oil precludes these components from behaving as they might in an ideal solution. A simple high-boiling mixed system was found (10) not to obey simple kinetics whereas single components in isolation obeyed zero order kinetics. Increased viscosity of the mixed oil as the evaporation proceeds may also be a factor in modifying the kinetic parameters of evaporation. The rate of evaporation of any component from a mixture is related (among other factors) to the rate of transportation by stirring or diffusion to the surface. As the more yolatile components evaporate, the mixture becomes more viscous and diffusion processes have progressively more influence on rates of evaporation. Evaporation of the higher boiling components is thus retarded relative to the lower boiling fractions, and relative to their behavior in isolation. Accordingly, care must be exercised if the Arrhenius activation energies determined in this work are used as an aid in estimating the extent of evaporation from an oil spill. Once the oil ceases to flow (because of temperature or weathering factors), the values can no longer be applied since diffusion rates in the bulk oil will predominate. Where the oil is still fluid, these values should be applicable to the evaporation of oil components from spills on ice or water, provided the thickness of the oil is more than just a few molecules. Acknowledgments We thank E . Nagy, S. Ramamoorthy, and D. Carlisle for helpful discussions. Literature Cited (1) U.S.Dept. of the Interior, Federal Water Pollution Control Administration, Water Pollut. Contr. Res. Ser. 15080DJ05/70, 1970. (2) Freegarde, M . , Hatchard, C. G., Parker, C. A., Lab. Pract., 20,35 (1971). (3) Blokker, P. C., Proc. 4th Int. Harbour Conf., p 911, Antwerp, Belgium, 1964. (4) Information Canada, Report of the Task Force-Operation Oil (Cleanup of the Arrow oil spill in Chedabucto Bay) to the Minister of Transport, Vol. 11, T22-2470/2, 1970. (5) Smith, C. L., MacIntyre, W . G., Proc. Joint Conf. on Prevention cnd Control of Oil Spills, p 119, Am. Petrol. Inst., Washington, D.C., 1971. (6) Mackay, D., Matsuga, R. S., Can. J . Chem. Eng., 51, 434 (1973). (7) American Petroleum Institute, Division of Refining, Technical Data Book, Chap. 5, Petroleum Refining, 1970. (8) Morawetz, E.,J. Chern. Therrnodynam., 4, 139 (1972). (9) Kinney, P . J . , Button, D. K., Schell, D . M., Proc. Joint Conf. on Prevention and Control of Oil Spills, p 333, Am. Petrol. Inst., Washington, D.C., 1969. (10) Wall, L. A,, Flynn, J. H., Straus, S., J . Phys. Chem., 74, 3237 (1970).
Received for r e ~ ~ i e lNovember c 5, 1973. Accepted December 13, 1974.
