Envlron. Scl. Technol. 1882, 16, 857-861
Schmidt, J. W.; Conn, K. Can. Min. J . 1969, 90, 54. Schmidt, J. W.; Conn, K. Can. Min. J . 1971, 92,49. Rolia, E., Division Report MRP/MSL 78-46 (TR); CANMET, Energy, Mines and Resources Canada; 1978. Rolia, E.; Barbeau, F. Talanta 1980, 27, 596. Stamm, H.; Goehring, M.; Feldman, U. 2.Anorg. Allg. Chem. 1942, 250, 266; Chem Abstr. 1943, 37, 3:5329. Fava, A.; Bresadola, S. J. Am. Chem. SOC.1966, 77,5792. Nickless, G., Ed. "Inorganic Sulfur Chemistry";Elsevier: New York, 1968; p 528. Byerley, J. J.; Fouda, S. A.; Rempel, G. L. J. Chem. Soc., Dalton Trans. 1973, 889. Naito, K.; Hayata, H.; Mochizuki, M. J . Inorg. Nucl. Chem. 1975,37, 1453. Cotton, M. L.; Spira, P.; Wheeland, K. G., Noranda Research Centre, Pointe Claire, Quebec, Canada, private communication. Gluud, W. Ber. Dtsch. Chem. Ges. B 1921,54B, 2425. Forward, F. A.; Peters, E.; Majima, H., paper presented at the AIME Annual Meeting, Feb 1964, New York. Naito, K.; Yoshida, M.; Shieh, M.; Okabe, T. Bull. Chem. Soc. Jpn. 1979,43, 1365. Rolia, E. M.Sc. Thesis, Carleton University, Ottawa, Canada, 1981.
Table 111. Effect of Temperature on the Reaction Half-Life for the Oxidation of Thiosulfate (10 mM) at 690 kPa of Oxygen Pressure and for an Initial Hydroxide Concentration of 0.025 M IO6 x rate of oxid of 10w, s,o,,-, temp, "C t,,,, s S-' M s-' 100 124 130 138
2070 432 241 162
0.33 1.60 2.87 4.28
3.33 12.5 17.8 21.6
83.3 kJ mol-'; AS*= -89.6 J mor1 K-l. The rate equation for the oxidation of thiosulfate by molecular oxygen in an autoclave can be written as follows: -d[S,032-]/dt = Iz[S~032-][OH-]1.'(Po,)'.66 (16) From the observed rates, after subtraction of induction periods, the average value of the rate constant k, based on 8'. The range six calculations, was 1.66 X 10-6M-1~1(PoJ-1~es was (1.3-2.0) X lo4, standard deviation was 0.32 X lo*, and the relative standard deviation was 199%. Literature Cited (1) Paine, P. J. M.Eng. Thesis, University of Ottawa, Canada; 1978.
Received for review September 16, 1981. Revised manuscript received June 21, 1982. Accepted July 19, 1982.
A Photoreactor for Investigations of the Degradation of Particle-Bound Polycyclic Aromatic Hydrocarbons under Simulated Atmospheric Conditionst Joan M. Dalsey,' Catherine 0. Lewandowskl, and Mllena i o r i Institute of Environmental Medicine, New York University Medical Center, New York, New York 10016
A fluidized-bed photochemical reactor has been developed for laboratory studies of reactions of particulateadsorbed polycyclic aromatic hydrocarbons (PAH) under simulated atmospheric conditions. The reactor consists of a glass column in which particles are suspended by the flow of air through a fritted disc at the base of the column. A quartz mercury vapor lamp, aligned with the column of suspended particles, is used for irradiation. Although the spectral wavelength distribution of the glass-filtered light is not identical with those of sunlight, it is a reasonably good approximation in the actinic region of the spectrum. The reactor is inexpensive and simple to construct and operate. It is three-dimensional and permits unlimited reaction time. Reaction conditions can be varied. Rate constants determined in the reactor have been shown to be reproducible to within f20% a t the 95% confidence level. Introduction Polycyclic aromatic hydrocarbons (PAH) in industrial and ambient atmospheres have long been of concern as a human health hazard (1). Many of the individual PAH compounds are potent carcinogens while others act as cocarcinogens or tumor promotors in mammalian bioassays. Evidence of tumorigenic potential in humans has come from epidemiologicalstudies of workers exposed to high levels of these compounds (1-4). Presented at the Symposium on Atmospheric Chemistry, 182nd National Meeting of the America1 Chemical Society, August 23-28, 1981, New York; Abstr. PHYS 184. 0013-936X/82/0916-0857$01.25/0
The polycyclic aromatic hydrocarbons are environmentally ubiquitous compounds, which are produced by combustion of fossil fuels and certain industrial processes such as coke production and petroleum refining. Emissions from fossil fuel combustion can vary over several orders of magnitude depending upon the particular fuel and combustion conditions (1,5). Emissions of PAH per BTU from coal or wood burning for residential space heating are several orders of magnitude greater than for gas or oil burning (1,5). Thus, the trend toward increased use of coal and wood in the United States can have a substantial impact on the concentrations on airborne PAH. Although airborne PAHs have been studied for almost 30 years, our knowledge of the chemical lifetimes of these compounds in the atmosphere is very limited and based entirely on studies in model systems (6-13). Much of the early work on the degradation of PAH suggested lifetimes of the order of hours (1).More recent work by Korfmacher et al. (14) and by Butler and Crossley (15) indicates that the chemical lifetimes of particle-bound PAH are of the order of days. The degradation rates estimated from the available model studies vary widely (16) because many of the parameters of the model systems have not been well defined, e.g., light intensity, particle surface areas and surface composition, and concentration of PAH per gram of substrate. Many of the studies were done in two-dimensional model systems, i.e., PAH on a thin-layer chromatography plate. The flow-through chamber of Tebbens and coworkers (11-13) more closely approximates an environmental system. However, the flow-through system is relatively complex and has some of the same problems as
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smog chambers in terms of wall losses of particles. In addition, the time of irradiation is limited by the flow rate and dimensions of such a reactor. The reproducibility of the various model systems has not been reported and presumably has not been investigated. Thus, the uncertainties of the rate constants estimated from these studies are not known. In order to gain a better understanding of the reactions of particle-bound PAH and eventually to relate the rates and products of reaction determined in laboratory studies to those in the environment, we have developed a unique fluidized-bed photoreactor for studies of photoreactions under simulated atmospheric conditions. Design Considerations
A photoreactor system was sought in which environmental conditions for reactions of particle-bound PAH could be simulated as closely as possible but which would be reasonably inexpensive and simple to construct and operate. Required features were as follows: (a) The system should be three dimensional, with particles suspended in air or other gases during irradiation. (b) The system should not limit the irradiation time. (c) The light spectrum in the reaction should be as similar to that of sunlight as possible. In addition, it should be possible to determine light intensity in the reactor. (d) I t must be possible to vary system conditions, specifically light intensity, gas composition, temperature, humidity, and particle substrate. (e) Rates of degradation determined by using the reactor should be reproducible. Prototype Photoreactor
A fluidized-bed design was selected as the most likely to meet all of the above criteria. In the initial stages of development a glass chromatography column 39 cm X 2.0 cm i.d. with an extra coarse frit was used as a prototype reactor. A 200-W medium-pressure mercury vapor lamp with a reflector (from Canrad-Hanovia, Inc.) was aligned with the column to irradiate the particles. The reactor and lamp were mounted in a cabinet 38 cm X 46 cm at the base, 70 cm high, to provide protection from ultraviolet wavelengths and to fix the positions of column and lamp. The glass reactor acted as a filter so that particles within the reactor were irradiated only by wavelengths greater than about 300 nm. Particles could be suspended indefinitely through a flow of air or any gas through the frit at the base of the column. Small samples of particles were withdrawn at regular intervals for analysis. A series of experiments were conducted with the prototype reactor to determine optimal gas flows, temperature stability within the column, and the extent of ozone generation and to test the system as a reactor. It was anticipated that about 1-2 g of particles with the 0.05-0.1 monolayer of pyrene would be required to provide sufficient material for analysis of multiple samples. In addition, a relatively large particle size ( 75-250 pm) was selected in these preliminary experiments in order to prevent wall losses. Several different types of particles of densities ranging from 0.65 to 3.3 g/cm3 and diameters in the range of 60-180 pm were tested in the reactor to determine the approximate gas flows required to suspend and circulate the particles to a height of about 10 cm. This "bed" height is close to the length of the lamp (11.4 cm). A t mass loadings of 0.5-2.0 g, air flows of about 10-20 L/min were required. For a large mass of particles (-10 g), it was N
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difficult to maintain a uniform motion, i.e., sudden discontinuities ("bumping") would occur. Temperature should have little or no effect on the rates of degradation if the rate-determining step is photochemical. However, since the rates of degradation of PAH have not been sufficiently investigated to establish such independence, a constant temperature was desired within the reactor. As the lamp emits some infrared radiation, a potential existed for increased temperature with increased reaction time. With the lamp at a distance of 12.8 cm from the reactor (center of lamp to center of reactor) and air flowing (14 L/min) through the system, the temperature was monitored in the reactor and in the cabinet for a period of 5 h. A thermocouple was placed in the lower portion of the reactor, Le., the particle bed region. Temperature in the reactor varied by no more than 2-3 "C over a period of more than 4 h. The temperature within the cabinet also increased by several degrees during this period. Subsequent work with the prototype reactor and the reactor used in the later stages of this investigation confirmed these observations, i.e., temperature variations under operating conditions were with f 2 "C. Ozone generation with the reactor was investigated and found to be minimal. A standard iodometric method for the determination of oxidizing substances was employed (27). Ozone liberates iodine when absorbed in a solution of potassium iodide buffered at pH 6.8 f 0.2. The liberated iodine is determined spectrophotometrically by measuring the absorption of triiodide ion at 352 nm. O3 3KI H 2 0 K13 2KOH O2 (1) So that the reactor could be tested under optimal conditions for the generation of ozone, the lamp was placed only 8.5 cm from the reactor, and a fraction of the air passing through the reactor was passed through a buffered 1% KI solution (pH 6.7) in a midget impinger. The flow rate in the impinger was 1.3 L/min; the temperature was 25 "C. The ozone concentration in the air from the reactor was 0.025 ppm, close to the limit of detection (-0.01 ppm) for the method. Laboratory air was sampled at a location 6 f t from the reactor since a faint odor of ozone was noted. The concentration of ozone at this point was found to be 0.05 ppm. The results of experiments with pyrene on glass beads demonstrated the usefulness of the fluidized-bed photoreactor for studies of the degradation of PAH. The degradation followed an apparent firsborder kinetic rate law, and reproducible kinetic data could be obtained.
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Developed Photoreactor
On the basis of the design considerations and the results of experiments with the prototype reactor, the photoreactor shown in Figure 1was developed. The components of this reactor may be purchased from Kontes Glass Company, Vineland, NJ, and with the exception of the thermocouple probe, are not "special design" items. The body of the reactor consists of a Chromaflex extender (column) (K-422440-2525)that is 250 mm long, 25 mm i.d., with adapters at the top and base. A water-jacketed column (K-422430-2525) is also available. The special order adapter shown in Figure 1is used at the base, and a straight adapter (K-422360-0025)is used at the top. The latter could be used at the base as well. A thermocouple in the probe of the thermocouple adapter is used to monitor temperature. Coarse or extra coarse porosity fritted discs, 27 mm 0.d. (K-952050-0025) at the base and top of the reactor are sealed in place with O-rings (wrapped in Teflon tape). The inner O-ring (26 mm in diameter) placed on top of the disc at the base holds the disc in place
e&tdF,ir
disc and O-ring -Probe
Table I. Comparison of Irradiance in the Photoreactor to Solar Irradiance
with Thermocouple
light intensity, W/m2 calcd photoreactor 296.7 nm 296.7-366.0 nm 366-578 nm (visible) solar irradiance 290-365 nm 370-600 nm ambient data, Nassau County, NY Jan 1979 May 1979
Purified Air
Lamp and Reflector
Figure 1. Schematic representation of the developed photoreactor.
while the outer O-ring (31 mm in diameter) seals the glass column and adapter, making an airtight seal. At the top of the column, a 31-mm O-ring seals the column and the adapter. Clamps (K-675050-035)holds the reactor together and help seal the fritted discs in place. Since the discs are not sealed to the glass column, air flows through the entire disc, and particles do not accumulate at the edges. In addition, the reactor can be readily cleaned. A staticmaster ionizing unit (Model 2U 500) from Nuclear Products Company was used to eliminate static charges on the particles produced by friction. Although there was no difference in the rates of reaction with or without the charge neutralizer, without the neutralizer the reactor had to be tapped regularly to dislodge particles clinging to the walls and probe. A flow meter is placed in line between the gas supply and the reactor to prevent any possible contamination of the flow meter. Gases (
