Acknowledgments We graciously acknowledge Lt. Larry E. Keister, Neryda Galceran, Lt. Richard H. West, Mike Macau, and Kevin O’Donnell for their laboratory assistance, as well as Dr. Donald K. Atwood, Dr. George R. Harvey, Dr. Peter Ortner, and Dr. John Farrington for their comments. Finally, we thank the officers and crew of t h e NOAA Ships Ferrel and G. B. Kelez and t h e R/V Venture for their sampling assistance. Literature Cited (1) Murtaugh, J. J., Bunch, R. L., J. Water Pollut. Control Fed., 39,
404-9 (1967). (2) Smith, L., Kohler, D. P., Hempel, J. E., Van Lier, J. E., Lipids,
3,301-6 (1968). (3) Kirchmer, C. J., Ph.D. Thesis, The University of Florida, Gainesville, Fla., 1971. (4) Tabak, H. H., Bloomhuff, R. N., Bunch, R. L., in “Development in Industrial Microbiology”, Vol. 13, American Institute of Biological Sciences Publication, Washington, D.C., 1972, pp 296307. (5) Dutka, B. J., Chau, A. S. Y., Coburn, J., Water Res., 8,1047-55 (1974). (6) Martin, W. J., Ravi Sabbiah, M. T., Kittke, B. A., Birk, C. C., Naylor, M. C., Lipids, 8,208-15 (1973). (7) Eyssen, H., Parmentier, G., Compernolle, E., DePauw, G., Piessens-Denef, M., Eur. J . Biochem., 36,411-21 (1973). ( 8 ) Hatcher, P. G., Keister, L. E., McGillivary, P. A., Bull. Enuiron. Contam. Toxicol., 17,491-8 (1977). (9) Goodfellow,R. M., Cardoso, J., Eglinton, G., Dawson, J. P., Best, G. A.,Mar. Pollut. Bull., 8,272-6 (1977).
(IO) Freeland, G. L., Swift, D. J. P., Stubblefield, W. L., Cok,A. E., Am. SOC.Limnol. Oceanogr. Spec. Symp., 2,90-101 (1976). (11) Lee, C., Gagosian, R. B., Farrington, J., Geochim. Cosmochim. Acta, 41,985-92 (1977). (12) Huang, W. Y., Meinschein, W. G., Geochim. Cosmochim. Acta,
40,323-30 (1976). (13) Hatcher, P. G., Keister, L. E., Am. SOC.Limnol. Oceanogr. Spec. Symp., 2,240-8 (1976). (14) West, R. H., Hatcher, P. G., Atwood, D. K., NOAA ERL-MESA Data Report, 1978, in press. (15) Gross, M. G., Geol. SOC.Am. Bull., 83,3163-76 (1972). (16) Pearce, J. B., in ‘‘MarinePollution and Sea Life”,Ruivo, M., Ed., Fishing News (Books) Ltd., Surrey, England, 1972, pp 401-11. (17) Charnell, R. L., Mayer, D. A., NOAA Technical Memo ERL MESA-3,1975,29 pp. (18) Harris, W. H., Am. SOC.Limnol. Oceanogr. Spec. Symp., 2, 102-23 (1976). (19) zloPb dates were obtained by L. Benninger, Yale University, (1977) under a NOAA, MESA Grant (04-4-022-35).The ages were determined after normalization to the organic matter as described by: Benninger, L. K., Ph.D. Thesis, Yale University, New Haven, Conn., 1976. (20) Volumes prior to 1965were supplied by Mr. Harold M. Stanford, NOAA, Marine Ecosystem Analysis Program; all others were obtained from Pararas-Carayannis, G., U S . Army, Corps of Engineers Technical Memo, No. 39,1973, I59 pp. (21) Hatcher, P. G., Berberian, G. A., Cantillo, A,, McGillivary, P. A., Hanson, P., West, R. H., in “Ocean Dumping of Industrial Wastes”, Ketchum, B. H., Kester, D. R., and Park, P. K., Eds., Plenum Press, New York, in press. (22) Nishimura, M., Koyama, T., Geochim. Cosmochim. Acta, 41, 379-86 (1977). Received for reuiew June 19, 1978. Accepted June 6, 1979.
Apparatus for Vapor-Phase Adsorption of Polycyclic Organic Matter onto Particulate Surfaces Antonio H. Miguel’ and W. A. Korfmacher* School of Chemical Sciences, University of Illinois, Urbana, 111. 61801
E. L. Wehry and G. Mamantov Department of Chemistry, University of Tennessee, Knoxville, Tenn. 379 16
D. F. S. Natusch“ Department of Chemistry, Colorado State University, Fort Collins, Colo. 80523
The design and operation of a n apparatus for vapor-phase adsorption of polycyclic organic matter (POM) onto the surface of coal fly ash and other solid adsorbents are described. Provision is made for vapor-phase fluorometric analysis of the effluent vapor stream in the adsorption apparatus. Several POMs were adsorbed, at fixed temperatures, on the surface of fly ashes collected with electrostatic precipitators of coalfired power plants. The adsorption of vapor-phase pyrene in the temperature range of 150-265 “C revealed t h a t the adsorption equilibrium capacity of the fly ashes and the equilibration time both decreased linearly with increasing temperature. The results of these measurements indicate that the amount of adsorbed POM can be controlled quite easily by adjusting either the time or temperature of adsorption.
Polycyclic aromatic hydrocarbons and their derivatives, collectively referred t o as “polycyclic organic matter” (POM), Present address, Instituto de Quimica, Universidade Federal do Rio de Janeiro, Ilha do Fundao, Rio de Janeiro, Brazil. Present address, Chemistry Division, HFT-154, National Center for Toxicological Research, Jefferson, Ark. 72079.
can be formed in any combustion process involving carbonaceous fuels (1).Because many types of POM are carcinogenic, and because POM is mobilized in the environment in association with airborne particles derived from fossil-fuel combustion processes, increasing emphasis has been placed upon studies of the health effects of, ultimate fate of, and analytical methods for these compounds. In addition, the difficulty of procuring and manipulating samples from combustion sources (e.g., power plant emissions) has created a need for simpler model systems that can be employed for realistic investigations of the properties and fate of POM adsorbed on particulate matter. A useful model system for POM adsorbed on coal fly ash should accurately simulate real samples t h a t would be obtained from a “real source”, such as a fossil-fueled power plant plume. In that regard, it has been established (2-4) that association of P O M with emitted coal fly ash involves rapid vapor-phase adsorption of the P O M onto the fly ash surface near the stack exit. Therefore, a realistic model system should incorporate the vapor-adsorption process in the samplepreparation step. We describe herein the design and evaluation of a model system that enables vapor-phase adsorption of individual P O M compounds onto any particulate adsorbant.
0013-936X/79/0913-1229$01,00/0 @ 1979 American Chemical Society
Volume 13, Number 10, October 1979
1229
N2 GAS
-
POM VAPOR
INLET-
EXPANDED
VAPOR
ADSORBENT BED-
GENERATOR
I
Figure 1. Block diagram of vapor adsorption apparatus
,
/
z cm
I ICDIFFUSION
8 A L L 8 SOCK€
z m m BALL JOINT
/
TUBE
EXTENSION
2 CM c (
Figure 2. Diffusion cell (generator)used for generation of vapor-phase POM
Description of Apparatus Figure 1 shows a flow diagram that indicates the three principal component blocks of the apparatus designed for preparation of vapor-adsorbed POM samples. Each of the principal components of the apparatus is described below. Vapor-Phase POM Generator. Figure 2 shows the device employed for generation of POM vapor. It consists of a diffusion cell that delivers a constant quantity of POM vapor into nitrogen gas. Detailed descriptions of its construction and operating characteristics have appeared elsewhere ( 5 ) . The diffusion cell is contained in an insulated box (inside dimensions: 1ft3) constructed from 0.5-in. transite sheet and covered on all outside surfaces with fiberglass insulation. Heating for the insulated box is provided by a 1000-W cone heating coil. The current load requirement for each coil to maintain the desired temperature is sensed by a thermistor coupled to a temperature controller, which is capable of maintaining the contents of the box to within 3 "C of the desired value over a period of at least several days. The temperature of the box can be maintained to within f0.5 "C of the desired value by periodic adjustment of the temperature controller. The box is equipped with an air circulating fan from a gas-chromatograph oven to provide uniform distribution of heat throughout its interior. Nitrogen gas from a cylinder is passed into the diffusion cell, as indicated in Figure 2. The Nz serves two functions. First, it acts as the carrier gas for the POM vapor produced in the diffusion cell and transports it to the adsorption bed. Second, the nitrogen provides a means of expanding the adsorbent bed so as to maximize the rate of mass transfer of POM vapor through the bed during the adsorption process. All gas lines were fabricated from stainless steel tubing. Within the insulated box, the stream of Nz passes through a 13-ft length of steel tubing prior to entering the diffusion cell, in order to allow the gas to reach thermal equilibrium prior to mixing with the POM vapor. POM vapors leaving the diffusion cell are entrained in the nitrogen and swept into the adsorbent bed. Expanded Adsorption Bed. The column containing the expanded bed of adsorbent (shown in Figure 3) was constructed from 8- and 13-mm Pyrex tubing. The main body of the column is held in place by steel clamps which hold Teflon O-ring seal joints. An extra-coarse glass frit is used to hold the 1230
Environmental Science B Technology
Figure 3. Expanded-bedadsorption column; note that the adsorbent bed can be bypassed by altering the settings of the three-way valves
adsorbent bed, which is expanded and agitated by the nitrogen-POM mixture flowing through it. A coarse upper glass frit prevents any entrained adsorbent particles from leaving the column. The three-way Teflon valves (Figure 2) serve to switch the gas mixture flow from the bypass to the adsorption bed (or vice versa). The adsorption bed is contained within a second insulated transite box similar in design to that used for the POM vapor generator. Extension handles on the three-way valves permit switching of the direction of gas mixture flow from outside the insulated box during the course of an adsorption experiment. The ball and socket joints shown in Figure 3 permit easy removal of the main body of the adsorption column. The adsorption bed inlet (Figure 3) is connected to the diffusion cell outlet (Figure 2) by a 13-ft length of stainless steel tubing. It is important to note that, when in operation, the box containing the POM vapor generator must be maintained at a lower temperature than that containing the adsorbent bed, in order to ensure that only adsorption (and not condensation) occurs in the adsorbent column. Heated Fluorescence Cell. In order to monitor the course of adsorption, it is necessary to determine the presence of POM in the gaseous effluent from the adsorption column. The inherently high sensitivity of fluorescence spectrometry, coupled with the intense fluorescence of many POM compounds in the vapor phase (6-IO),makes fluorescence spectroscopy a useful method for this purpose. The design of the heated fluorescence cell used in this work is described elsewhere (7).Vapor leaving the adsorption bed is transported to the cell by a stainless steel transfer line wrapped with heating tape and insulated with asbestos paper. The cell holder is covered by an aluminum block that is fitted with channels containing two 85-W cartridge heaters for temperature control. Temperatures as high as 330 "C can be achieved in the fluorescence cell with only relatively slight temperature increases (5-10 "C) being experienced in the adjacent portions of the fluorescence spectrophotometer. An Aminco-Bowman spectrophotofluorometer, equipped with a 150-W xenon lamp source and 1P28 photomultiplier as detector, was used to obtain fluorescence spectra in the present series of experiments. Experimental
Materials. Pyrene (Aldrich) was purified by a single vac-
uum sublimation. Other POMs, obtained from commercial sources, were analyzed by fluorescence spectrometry and/or high performance liquid chromatography, and were purified by vacuum sublimation when the analysis indicated the presence of impurities. Liquid chromatography was performed using a methanol-water solvent system and a Partisil P X S 10-ODS column; the chromatograph was assembled from Laboratory Data Control components. A number of different types of particles and several fly ashes derived from both Middle Western bituminous and Western subbituminous U S . coals have been employed in the adsorption apparatus described herein. For the purposes of illustration, however, results are described only for a single fly ash obtained from the State Line, Ill., power plant, burning a 40:60 weight percent mixture of high and low sulfur coals. All samples were dried overnight a t 120 "C prior to use and were size fractionated by sieving using either a sonic sifter (Model L3P, ATM Corporation) or a series of manual sieves in cascade. Adsorption experiments were conducted using either the 45-63-ym or 45-74-pm particle diameter ranges. (The 45-74-ym size range constitutes 46.5% by weight of the above fly ash.) A number of fly ash samples were subjected to exhaustive soxhlet extraction with benzene and methanol prior to use and were shown not to contain detectable amounts of POM both by gas chromatography and ultraviolet absorption spectrometry (11, 12). Operating Procedure. The following stepwise procedure is employed for operation of the vapor adsorption apparatus: (a) Both the transfer lines and fluorescence cell are initially heated to a temperature that is sufficiently high to prevent condensation of the polycyclic organic vapor species flowing through the system (330-350 "C for pyrene). The nitrogen flow rate is normally adjusted to approximately 200 cm3/ min. (b) A sample of fly ash (0.2-3 g) is weighed accurately into the main body of the expanded-bed adsorption tube, which is then assembled into the apparatus shown in Figure 3; the entire assembly is then placed into the second insulated box. (c) With a short section of stainless steel tubing substituting for the diffusion cell in the first insulated box, the adsorbent is degassed for 20 min a t 125 "C by switching the three-way Teflon valve to the position indicated in Figure 3. (d) Upon completion of the d6gassing process, the three-way valves (Figure 3) are switched to the bypass position and the expanded bed is heated t o the adsorption temperature necessary to produce the desired POM concentration on the adsorbent (e.g., 153 "C for pyrene). Then, the generator, containing an accurately weighed quantity of POM in the diffusion tube (Figure 2), is substituted for the short stainless steel tubing section, and the insulated box containing the generator is heated to the necessary temperature (e.g., 142 "C for pyrene) to produce the desired POM vapor concentration in the nitrogen stream. (e) At "zero time", the three-way valves (Figure 3) are switched from "bypass" to the "adsorption" position. The concentration of POM in the exit gas stream immediately decreases as adsorption onto the fly ash takes place. As the fly ash approaches its adsorption capacity, the concentration of POM in the exit stream returns to its initial value (as indicated by fluorescence measurements on the effluent). The three-way valves are then switched back to the bypass position, and the temperatures of both the diffusion cell and adsorption bed are rapidly reduced by blowing room-temperature air over them, in order to prevent further gas-particle interactions. (f) When the POM concentration has attained its equilibrium value in the effluent from the adsorption column, a known volume (usually 1 L) of the gas stream is bubbled
Table 1. Generator and Adsorbent Bed Temperature for Vapor Adsorption of POM and Resulting Concentrations of Adsorbed POM a compd
generator temp, "C
adsorptlon bedo temp, c
85 142 102 103 112 94 171 172 189 203
105 153 114 115 124 104 183 184 199 223
acenaphthene pyrene acridine fluoranthene fluorene phenanthrene phenazine benzo[ a] pyrene anthracene carbazole
concn of adsorbed POM, + g / g b
NQ
270 f loc NQ
80 NQ
210 f 6 2 c NQ
50
300 NQ
a Flow = 200 mL/rnin; adsorption time = 10 h; weight of fly ash = 2 g. NQ = not quantitated. 9 5 % confidence interval based upon five replicate rneasurements.
through a single collection flask containing benzene a t room temperature. A collection period of 5 min is usually used. Any POM that may have adsorbed on the walls of the bubbler tube is dissolved from the bubbler with fresh benzene, which is then added to the collection flask. The quantity of collected POM is then determined by solution fluorescence spectrometry, in order to calibrate the vapor-phase concentration of POM as monitored by the flow-through fluorescence cell. POM collection efficiencies attainable with one collection flask were shown to exceed 96%, as determined by connecting two additional collection flasks in series with the first and determining the total POM content in all three flasks (11). (g) After the diffusion cell and adsorbent bed have cooled to room temperature, the adsorbent column should be tapped several times to dislodge any adsorbent particles entrapped in the upper glass frit. The main body of the reactor is then removed and weighed to determine the quantity of the fly ash lost (this is usually less than 1%). (h) Finally, a portion of the adsorbent is extracted with 20 mL of benzene in a microsoxhlet apparatus for 24 h. The concentration of POM extracted is then determined by room-temperature solution fluorescence or ultraviolet absorption spectrophotometry.
Results and Discussion The performance of the vapor adsorption apparatus has been evaluated for adsorption of a number of polycyclic aromatic hydrocarbons and nitrogen heterocycles. These compounds, and the temperatures employed in the generator and adsorption bed sections of the apparatus for each, are listed, together with representative concentrations achieved for the test fly ash, in Table I. The generator temperature for each compound was chosen to be 5-10 "C lower than the melting point of the solid compound ( 5 ) .The adsorption bed temperature was chosen to be only 5-10 "C above the melting point of the compound, in order to obtain relatively high levels of adsorbed POM. For all listed compounds except anthracene and fluorene, it was possible to remove the adsorbed POM by soxhlet extraction without detectable chemical change (as indicated by comparisons of UV adsorption and fluorescence spectra and liquid chromatograms of the extracts with those of standard solutions of the pure compounds prepared in the same solvents). In the case of anthracene and fluorene, however, adsorption onto the test fly ash resulted in about 10 and 30% oxidation to 9,lO-anthraquinone and 9-fluorenone, respectively. ForVolume 13,Number 10,October 1979
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4 ‘
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’
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L
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200 -
-‘2
i
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-
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.-
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Figure 4. Variation of equilibrium capacity and approximate time re-
quired for equilibration as a function of adsorbent bed temperature, for pyrene vapor-adsorbed on Illinois State Line fly ash (0.2 g sample; specific surface area = 1.40 m21g) mation of these products was detected, and the extent of conversion from products to reactants was determined, by both UV absorption spectrometry and high performance liquid chromatography (LC) using a UV absorption detector; authentic samples of 9,10-anthraquinone and 9-fluorenone were used as retention-volume standards for LC. These reactions took place in the dark during the adsorption step and were primarily a function of the fly ash adsorbent, since they did not take place during sorption onto activated alumina or for the pure compounds in solution. Detailed studies of photochemical and nonphotochemical oxidation of adsorbed POM are described elsewhere (12). The stability of adsorbed POM against vaporization losses was examined extensively for pyrene by storing samples in the dark in sealed vials for periods up to 27 days prior to extraction and determination of the adsorbed pyrene. The amounts of pyrene extractable from fresh and aged samples were found to be indistinguishable a t the 95% confidence level. The equilibrium capacity of fly ash for pyrene adsorption and the approximate time required to achieve adsorption to this capacity were determined as a function of adsorption bed temperature. The results of these measurements, which are illustrated in Figure 4,are in good qualitative agreement with theoretical predictions of vapor phase adsorption of POM onto fly ash ( 2 ) ,and signify that the amount of adsorbed POM can be controlled quite easily by adjusting either the time or temperature of adsorption. Furthermore, the nature of the adsorbed POM is, apparently, closely reminiscent of that encountered in real systems. The surface area of the adsorbant has a pronounced effect on its equilibrium capacity. It was observed that the equilibrium capacity for adsorption of pyrene on fly ash a t a fixed temperature (150 O C ) increased in an approximately linear manner with increasing specific surface area (11).
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Finally, it should be noted that the residence time of a POM in the flow-through fluorescence cell is quite small, because the compounds are entrained in a flowing stream of nitrogen; in addition, the fluorescence source (150-W xenon lamp) is not exceedingly bright. Thus, appreciable photodecomposition of POM in the vapor-phase fluorescence monitor appears improbable. Indeed, comparisons of fluorescence emission spectra of vapor-phase POM (measured in the flow-through cell) with those of benzene solutions of the same compounds failed to indicate that POMs were undergoing photogradation in the vapor-phase cell (Le., no significant differences in the vapor- and solution-phase fluorescence spectra were noted).
Environmental Science & Technology
Conclusions The adsorption apparatus described herein has been employed extensively for preparation of particulate material that provides an effective model for studies of airborne particulate extraction characteristics and of the chemical and photochemical transformations of POM adsorbed on coal fly ash (3, 12,13).The apparatus has proved most satisfactory in all cases and is strongly recommended for use in the preparation of well-defined model systems. Acknowledgments The authors express their thanks to Dr. J. Q. Chambers, University of Tennessee, for use of a liquid chromatograph; Dr. L. R. Faulkner, University of Illinois, for helpful discussions pertaining to vapor-phase fluorescence measurements; and Dr. D. R. Taylor, Colorado State University, for assistance in manuscript preparation.
L i t e r a t u r e Cited (1) Committee on Biologic Effects of Atmospheric Pollutants, “Particulate Polycyclic Organic Matter”, National Academy of Sciences, Washington, D.C., 1972. ( 2 ) Natusch, D. F. S., Tomkins, B. A,, in “Carcinogenesis-A Comprehensive Survey”, Vol. 3, Jones, P. W., Freudenthal, R. I., Eds., Raven Press, New York, 1978, pp 145-54. (3) Natusch, D. F. S., Korfmacher, W.A,, Miguel, A. H., Schure, M. R., in Proceedings of the Symposium on Process Measurements for Environmental Assessment, Atlanta, Ga., Feb 1978. (4) Natusch, D. F. S., Enuiron. Health Perspect., 22,79-90 (1978). (5) Miguel, A. H., Natusch, D. F. S.,Anal. Chem., 47, 1705-7 (1975). (6) Burchfield, H. P., Wheeler, R. J., Bernos, J. B., Anal. Chem., 43, 1976-81 (1971). ( 7 ) Freed, D. J., Faulkner, L. R., Anal. Chem., 44,1194-8 (1972). (8) Robinson, J. W., Goodbread, J. P., Anal. Chim. Acta, 66,239-44 (1973). (9) Mulik, J., Cooke, M., Guyer, M. F., Semeniuk, G. M., Sawicki, E., Anal. Lett., 8, 511-24 (1975). (10) Cooney, R. P., Winefordner, J. D., Anal. Chem., 49, 1057-60 (1977). (11) Miguel, A. H., Ph.D. Dissertation, University of Illinois, Urbana, 1976. (12) Korfmacher, W. A,, Natusch, D. F. S., Taylor, D. R., Mamantov, G., Wehry, E. L., Science, in press. 113) Tomkins. B. A,, Ph.D. Dissertation, University of Illinois, Urbana, 1978.
Received for review November 20, 1978. Accepted June 13, 1979. The research described herein was supported in part by Grants R8039.50030 from the C S . Environmental Protection Agency, Duluth, Minn., EE-77-S-02-4347from the U.S. Department of Energy, and NSF ENV 74-24276from the U.S.National Science Foundation and by Contract N o . RP-332-1 from the Electric Power Research Institute.
