we can assume that no perturbation in the stratification of the sediment and no permeation of water containing ABS into the sediment have occurred since the beginning of the deposition of ABS, the average rate of sedimentation can be calculated from the thickness of ABS-containing layer and the number of years of ABS use. The date of the beginning of the deposition of ABS in Tokyo Bay was estimated to be about 10 years before the time of sampling of the sediment, according to the data on the production of synthetic detergents in Japan and the secular change of ABS in the water of the River Tama, one of the main polluted rivers flowing into Tokyo Bay. The average rate of sedimentation was calculated as 3 cm/year in this point, and one of the examples of the usefulness of ABS as a geological tracer was presented. Though the time range in which ABS can be used is limited to only 10-20 years, such an estimation by a manmade substance is promising to apply in the area where the sedimentation process is very rapid, as in an estuary.
Acknowledgment
The author thanks Takahisa Hanya, Tokyo Metropolitan University, for his kind advice. Literature Cited Abbot, D. C., Analyst, 87,286-93 (1962). Ambe, Y., Hanya, T., Jap. Anal., 21, 252-6 (1972); C.A., 76, 157982~(1972). American Public Health Association, American Water Works Association, Water Pollution Control Federation, “Standard Methods of the Examination of Water and Wastewater,” 296303, 1965. Hill, W. H., Shapiro, M. A., Kobayashi, Y., J. Amer. Water Works Ass., 54,409-16 (1962). Longwell, J., Maniece, W. D., Analyst, 80, 167-71 (1955). Oba, K., Yukagaku, 14,625-9 (1965); C . A . ,64,6910e (1966). Otsuki, A,, Hirayama, M., Hanya, T., Utsumi, S.,Nippon Kagaku Zasshi, 85,335-40 (1964); C.A., 61,4966f (1964).
Received for review July 5, 1972. Accepted March 1, 1973
Permeation of Sulfur Dioxide Through Polymeric Stack Sampling Interfaces Charles E. Rodes,’ , 2 Richard M. Felder, and James K. Ferrell Department of Chemical Engineering, N.C. State University, Raleigh, N.C. 27607 ~~
Preliminary developmental studies on the use of a cylindrical polymeric tube as a permeable interface between a stack and a continuous ambient SO2 monitor have been carried out under controlled laboratory conditions. Isothermal SO2 trans-wall flux measurements were made over a range of concentrations of SO2 in air a t several temperatures, using PTFE Teflon, silicone rubber, and fluorosilicone rubber tubes. The flux varied linearly with the trans-wall concentration gradient in all cases. The activation energies in kcal/g-mol for permeation of SO2 were 7.0 for Teflon, 0.94 for the silicone rubber, and 1.33 for the fluorosilicone rubber. The relaxation times, or times required for the fluxes to reach steady-state values following changes in operating conditions, were on the order of minutes for each material. The results of these preliminary studies indicate that the polymer tube interface is a promising device for stack monitoring. Stack-gas monitoring on a continuous basis has become important in many industrial processes. The Clean Air Act of 1970 specifies that air pollution control implementation plans must include emission standards and requirements for monitoring stationary source emissions. If individual sources are to meet these standards, control equipment will have to be installed; because of the added operating expense of this equipment, optimal performance of this equipment may be essential. A continuous stack To whom correspondence should be addressed. Present address, Environmental Protection Agency. S E R C , Research Triangle Park, N.C. 27711 1 2
monitor can measure and record the efficiency of control devices, and under some circumstances can be integrated into a process control system to monitor product and byproduct losses. A number of factors, such as high particulate loadings, high temperatures, and high humidities, can complicate the process of obtaining and analyzing a representative gas sample from a stack. To minimize the effects of these conditions, an interface between the stack and the gas analyzer must be devised to condition the sampled gas. Research programs on pollutant analyzer systems, especially for ambient SO2 monitoring, have resulted in the development of several commercially available analyzers (see, for example, Stevens et al., 1971); incorporating these analyzers into the sampling system with an interface device is a logical step toward continuous stack monitoring. Stack sampling interface systems have been described by Nacovsky (1967), Thoenes and Guse (1968), Risk and Murray (1964), Rossano and Cooper (1968), and many others. These systems are adequate for short-term applications, but require continuous surveillance when used for longer periods of continuous sampling. Some of the maintenance problems include rapid clogging of particulate filters, fluctuations in gas flow aggravated by multiple streams, flowmeter malfunctions, and malfunctions in the continuous analyzer caused by minute quantities of particulates or an excessive pressure-flow fluctuation in the sample line. The use of a polymeric barrier as a sampling interface between the stack and the analytical system has been proposed to alleviate these problems (O’Keeffe, 1970). The polymeric material might be in a tubular form such that a Volume 7 , Number 6, June 1973
545
carrier gas could be passed through the inside of the tube, while the outside tube surface would be exposed to the stack. The resulting pollutant concentration gradient would then lead to permeation of the pollutant through the tube wall into the carrier gas. The advantages of this approach are that a high dilution factor could be obtained with only a moderate carrier-gas flow rate; the use of a dry carrier gas should result in a very low dew point, even if some water vapor diffused through the tube wall; particulate buildup of the type characteristic of ordinary flow-through filtration would be eliminated since transport of the pollutant would be entirely diffusive, and the proper arrangement of the polymer tube could automatically provide a response proportional to the area-averaged pollutant concentration in the stack. With these considerations in mind a developmental program on the use of polymeric interfaces for the stack sampling of SO2 has been undertaken. Several phases of this program will be devoted to the determination of the effects of particulate deposition and water vapor permeation on the device performance and the operating characteristics of the device under actual process stack conditions. The first phase of the program, reported in this paper, concerns the measurement of SO2 permeabilities of tubular sampling devices under controlled laboratory conditions. The specific objectives of the study were to find a polymeric material permeable to SO2 which could withstand typical stack temperatures and would be likely to resist particulate deposition and water permeation, to observe whether measurable fluxes of SO2 through the tube wall could be achieved for typical stack concentrations, to determine how easily these fluxes could be correlated with the stack concentrations, and to measure the time required for the system to respond to changes in the stack concentration. To exclude interfering effects. the simulated stack gas consisted only of SO2 in air.
Experimental A schematic diagram of the experimental system is shown in Figure 1. All lines and fittings except those otherwise identified were stainless steel. To expose the outside surface of a measured length of polymer tubing to simulated stack temperatures and SO2 concentrations, a glass chamber was constructed by clamping 6-in. square stainless steel end plates with Teflon gaskets to the ends of a 3-in. i.d. Pyrex glass pipe 24 in. long. The end plates were drilled and tapped to accept a thermocouple bulkhead fitting, a 0.125-in. tube fitting, and a 0.375-in. tube fitting in each plate. The 0.375-in. fittings were drilled internally to allow a length of 0.375in. tubing to pass through the end plates to fittings inside the chamber. A l/&in. diameter stainless steel support rod was inserted inside the polymer tube to be tested and the tube was connected a t either end to the internal fittings. The chamber assembly was then placed inside a thermostatically controlled oven, adjustable to a maximum temperature of 250°C. A mixture of 5200 ppm SO2 in air and a dilution stream containing less than 0.1 ppm SO2 in air were fed from cylinders through rotameters and into a tee to make up the simulated stack gas. The combined stream passed through an access port on the oven, a 0.125-in. chamber end plate fitting, the chamber on the outside of the polymer tube, the opposite 0.125-in. fitting, and out of the oven to a hood. The carrier gas into which the SO2 permeated consisted of room air pumped through an activated charcoal scrubber and a rotameter by a carbon vane pump. The purified air entered the oven and passed through a 0.375-in. fit546
Environmental Science & Technology
Figure 1.
Diagram of apparatus
ting, the inside of the polymer tube, the opposite 0.375-in. fitting, and out of the oven to a flame photometric detector, which measured the total sulfur concentration in the stream. A 7-in. strip chart recorder permitted continuous monitoring of the detector signal. Two thermocouples passed through the 0.125-in. chamber end plate fittings, and measured the temperature at two points near the outside surface of the polymer tube. The temperature of the carrier gas stream was monitored a t the inlet of the chamber and a t the inlet of the photometric detector. A manometer measured any pressure difference that might exist between the gases on the inside and outside of the polymer tube. The flame photometric detector was calibrated using gravimetrically calibrated permeation tubes, as described by Stevens et al. (1969). A log-linear amplifier permitted measurements by the detector to the nearest 0.005 ppm in the most sensitive range (
