Karapinka. 0.. Orchin, M., J. Crg.Chem., 28,4187 (1961). Manuel, T. A., J. Org. Chem., 27, 3941 (1962). Orchin, M., Adv. Catal., 18. 1 (1966). Piacenti, F., Pucci, S., Bianchi. M.. Pino, P., J. Am. Chem. Soc., 90, 6847 (1968). Roos, L., Ph.D. Thesis, University of Cincinnati, Cincinnati, Ohio, 1965. Sternberg, H., Wender. I., Orchin, M., lnorg. Syn.. 5, 192 (1957). Ungvary, F., Marko, L., J. Organomet. Chem., 20, 205 (1969).
von Bezard. D. A., Consiglio. G., Pino, P., Chimia. 29,30 (1975).
Received for reuiew March 31,1975 Accepted June 25,1975 Fellowship support to J.F.T. from Standard Oil Co. of Ohio is gratefully acknowledged.
Hopcalite Catalyst for Catalytic Oxidation of Gases and Aerosols James K. Musick' and Frederick W. Wllllams Naval Research Laboratory, Chemical Dynamics Branch, Washington, D.C. 20375
Thirty-six gases and aerosols mixed with air were exposed to hopcaliie catalyst in a laboratory-scale catalytic burner under operatin conditions similar to those used in submarine burners. Various catalyst temperatures in the range 200 to 425 C, including the typical submarine burner temperature (316 f 14OC), were used in the work. The 36 gases and aerosols comprised hydrogen, hydrocarbons, oxygenated compounds, nitrogen compounds, sulfur compounds, a diesel fuel, a lubricating oil, a triaryl phosphate hydraulic fluid, and a paint thinner. The extents to which the different gases and aerosols were oxidized in the burner were measured by various analytical methods. The compounds were classified into two groups: 35 compounds were classified as susceptible to hopcalite-catalyzed decomposition and one was found to be resistant to hopcalitacatalyzed decomposition. This classification is consistent with that used in a previous paper (Musick and Williams, 1974) and the results presented here supplement those presented in that paper.
!
The use of catalytic combustion to purify air containing a wide variety of contaminants a t low concentrations was previously reported (Musick and Williams, 1974). Specific data in the previous paper covered 19 halogenated hydrocarbon contaminants as classified into two groups: those (a) resistant and (b) susceptible to hopcalite-catalyzed decomposition. The basis of the classification was the ratios and amounts of the compounds decomposed when mixed with air and exposed to hopcalite catalyst a t 305 and 315'C in a laboratory-scale catalytic burner. Except for size, the laboratory scale burner duplicated the operating conditions of the 500-cfm catalytic burners used in the air purification systems of nuclear submarines. However, in the experimental work other temperatures in addition to the submarine burner temperature (316 f 14OC) were used to gain additional information. Those compounds which were decomposed in the laboratory-scale burner a t 316 f 14'C, to an extent measurable by a gas chromatograph, were classified as susceptible to hopcalite-catalyzed decomposition. The 1 2 halogenated compounds classified in this group were decomposed to different degrees varying from 1.5% to 100% of their influent concentrations. Those compounds which were decomposed in the burner a t 316 f 14'C to such a slight degree that the amount was not measurable by gas chromatography were classified as resistant to hopcalite-catalyzed decomposition. The seven compounds in the resistant group, however, did decompose slightly. This was shown by detector tube and detector paper analyses which revealed the presence of trace amounts of decomposition products in the burner exhaust. The action of hopcalite catalyst on many air contaminants other than halogenated hydrocarbons has also been investigated using the laboratory-scale burner. This paper summarizes the results of these studies. The substances covered in this paper were chiefly organic compounds con284
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sidered to be representative of the major types of contaminants found in closed spaces such as submarines. The compounds studied included hydrogen, hydrocarbons, oxygenated compounds, nitrogen compounds, sulfur compounds, and mixtures of compounds such as diesel fuel, lubricating oil, triaryl phosphate hydraulic fluid, and paint thinner. Also, aerosols of some of these contaminants are included in this work.
Experimental Section The total number of substances studied was 36, comprising 32 chemical entities and 4 mixtures of compounds. Three of the 36 (two mixtures and one compound) were used as aerosols. Influent concentrations of the aerosols and mixtures were 20 to 150 mg/m3. All pure compounds except hydrogen had influent concentrations in the range 3 to 500 ppm. Hydrogen was used at a concentration of 1%. In all studies catalyst bed dimensions, space velocity, and other operating conditions were the same as those used in the previous work (Musick and Williams, 1974). Two catalytic burners were used in these studies. The first burner was a 28-in. length of 1.5-in. i.d. stainless steel tubing mounted vertically and containing a preheater in the lower section and a reactor (catalyst bed) in the upper section. Except for size, this burner duplicated the operating conditions of a 500-cfm burner used in nuclear submarines. Experience with this burner led to the design of an improved burner which is similar to the first burner in size and operating conditions. The improved burner has been described elsewhere (Musick et al., 1972). However, the wide variety of substances studied required the use of several different methods of analysis, and their widely varying resistances to catalytic decomposition led to the use of several different catalyst temperatures. Further, little information in regard to the combustion products and to catalyst poisoning was obtained. The results obtained were the percentages of
Table I. Compounds Which Are Resistant to Hopcalite-Catalyzed Decomposition Percent decomposed at various catalyst temp ("C) Compound
Formula
Vapor concn in inlet air, ppm
Analytical method
315"
425
1. Sulfur hexafluoride SF, 460-500 GCC 0 Ob Standard burner temperature. At 425"C, the appearance of about 1ppm acid in the burner exhaust indicated decomposition of a trace amount of SFe. No acid was detected in the exhaust gas at 315°C. Analyses made with gas chromatograph. a
Table 11. Compounds Which Are Susceptible to Hopcalite-Catalyzed Decomposition
Compound"
Vapor concn in inlet a i r , ppm
Formula
Percent decomposed at various catalyst temperatures Pc) Analytical method
200
260
300
315"
350
Acetone . . .n CH3COCH3 80-9 5 ... . . . 100 . . . ... Ammonia 50-450 ... . . . 100 . . . "3 90-100 ... Benzene . . . . . . 100 . . . C6H6 Carbitol 7-8 79 82 ... . . . 100 C6H1403 looe Carbon monoxide 50-200 co . . . 100 . . . . . . 30-35 6. Cyclohexane ... ... ... ... 91 75-130f 7. Diesel fuel ... ... ... ... ... 90 8. 2,2-Dime thy lbutane 40 30-35 84 ... 98 ... sH14 9. Dioctyl phthalate 40-1 OOf . .. 100 ... ...... C24H3804 (aerosol) 10. Ethane 80-100 ... 6 ... 12 C2H6 11. Ethylene glycol 3 CHZOHCHZOH 100 ... . . . . . . 12. Hydrazine 5-8 ... . . . . . . 100 . . . N2H4 13. Hydrogen 18 ... ... . . . 100 . . . HZ 14. Methane 100-130 ... . . . 5-8 . . . . . . CH4 100 CHSOH 95 15. Methanol 98 ... ...... 16. Monoethanolamine 19 HOCH2CHzNH2 ... ... ... 20 ... CH3NHNH2 17. Monomethyl hydrazine 100-180 ... ... 100' ... 18. Morpholine 50 C,H,NO ... . . . . . . 100 . . . 19. Navy No. 2190 lube 100-1 50f ... ... 100 . . . . . . oil (aerosol) 20. +Decane 15-20 89 98 ... ... 96 ClOHZZ 21. n-Hexane 50-190 ... . . . . . . 100 . . . C6H14 22. Nitrogen dioxide 100-150 ... ... ... 1 ... NO2 23. +Octane 45-60 . . . n . . . . . . 100 . . . C8H18 24. 1-0ctene 20-30 83 89 ... ... 94 C8H16 25. Ortho cresol 20 C6HdOHCH3 83 99 ... . . . 100 26. Paint thinner 45-60f ... ... . . . . . . 100 . . . 27. Propane 80-100 ... ... ... 95 ... C3H8 28. 2-Propanol CH3CHOHCH3 200-240 ... ... . . . 100 . . . 29. 1,2-Propylene glycol 5 100 ... ... . . . . . . C3H606NZ dinitrate 30. Pyridine 40 ... ... ... 17 ... 31. t- Butylbenzene 20-25 86 96 ... ... 96 32. Tetrahydromethylcyclo50-1 50 ... ... ... 90 ... pentadiene dimer 33. Thiophene 40-70 ... ... ... 50 ... 34. Triaryl phosphate 20-50f ... . . . 100 . . . . . . (aerosol) 35. 1,2,4-Trimethylbenzene 20-25 98 55 ... . . . 100 a Four of the substances are mixtures of compounds. Analyses made with gas chromatograph. Analyses made with detector tubes. Amount of compound oxidized determined by measuring COz produced. Infrared analyzer used. e Hopcalite catalyst will decompose CO at room temperature if protected from water vapor (Miller and Piatt, 1960). f Unit of concentration is mg/m3. g Unit of concentration is percent. h Hydrogen was analyzed with a thermal conauctivity detector. ' Amount of compound oxidized determined by measuring the amount of N 2 0 produced. Gas chromatograph used. Monomethyl hydrazine is 100% decomposed in air at 315°C before being exposed to catalyst. Nitrogen dioxide analyzed by chemiluminescence analyzer. Exhaust analyses showed that 15 ppm NO2 was converted t o NO in the burner. The ratio of partial pressures for the reaction, 2 N 0 + 0252N02, at equilibrium is PNOJPNO = 0.9 at 315°C and PNO~/PNO = 800 at 204°C (Leighton, 1961). The measured value for the burner exhaust was PNO~/PNO = 7. This is the equilibrium value for a temperature between 315 and 204°C. This result could have been due to rapid cooling of the gas samples before analysis, thus freezing the composition of the gas at that temperature (some temperature between 315 and 204°C). Standard burner temperature. No data. 1. 2. 3. 4. 5.
...
...
...
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contaminants in air which were oxidized :*y passing the air through the laboratory-scale burner a t particular temperatures. The analytical devices used, gas chromatographs, detector tubes, and detector paper, were described in the previous work (Musick and Williams, 1974). In addition, a Liston-Becker Model 15A nondispersive infrared analyzer was used for the carbon dioxide analyses. A continuous record of the output of this instrument was made by means of a recording potentiometer. Hydrogen analyses were made by a thermal conductivity detector with concentrations being recorded graphically as peak heights. Nitrogen dioxide (NO:!) and nitric oxide (NO) were analyzed by an NO-NO, chemiluminescence monitor manufactured by Aero-Chem Research Laboratories, Inc. The operating principle of this instrument was measurement of the light produced by the chemiluminescent reaction of ozone with nitric oxide. Nitrogen dioxide was analyzed by first converting it to nitric oxide. Nitrous oxide (N20) was analyzed by gas chromatography. However, it was necessary to use a concentrating procedure because of the low ratios of nitrous oxide present and the limited sensitivity of the gas chromatograph to nitrous oxide detection. This was done by passing a relatively large measured volume of the gas to be analyzed through a sample loop containing silica gel. The loop was immersed in a Dry Ice-acetone bath and a t the low temperature of the bath the silica gel adsorbed the nitrous oxide. The nitrous oxide was then driven from the silica into the gas chromatograph by immersing the loop in a hot water bath. Aerosols were produced by means of an aerosol generator (Thompson, 1956) and the mass median diameter and number diameter of the aerosols produced were determined by a light-scattering method (Knudson and White, 1945). Analysis of the aerosol was accomplished by diverting a measured volume of the aerosol through previously weighed Gelman type A fiber glass filters. A second analytical filter was used in series with the first to show that no particulate matter passed through the first filter. In many instances the ratio of a compound decomposed was measured, not by a decrease in the concentration of the compound itself as it passed through the burner, but by an increase in the concentration of a product of its combustion. Thus, the degree of decomposition of many of the organic compounds was measured by the amount of carbon dioxide (CO2) produced. This method gave a good measure of the amount of the compound which was oxidized to completion, Further, in view of the highly turbulent gas flow, high temperature, and large excess of oxygen present it seems reasonable to assume that combustion in the burner was complete and no partially oxidized products such as carbon monoxide (CO) survived to reach the burner exhaust. This has been shown to be the case for n-hexane
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(Carhart, 1968). If this assumption is true, then analysis of the CO:! produced provides an accurate measure of the amount of a compound decomposed in the burner. On the other hand, the only exhaust product measurement made for two of the nitrogen compounds (monoethanolamine and pyridine) was the amount of nitrous oxide (NzO) produced. In these two instances, the measured percentages of the influent compounds decomposed should be considered minimums rather than the actual percentages decomposed. This is true because portions of these compounds may have been oxidized to produce nitrogen dioxide (NO:!) or elemental nitrogen and escaped detection. In addition the instability of NzO above 3OOOC would contribute to low decomposition values. Except for these two compounds, the measured percentages represent the percentages of the influent contaminants which were actually decomposed in the burner.
Results The results of the work are presented in Tables I and I1 where the influent concentrations, analytical method used, and percentages of decomposition for each substance studied are tabulated. On the same basis of classification as used for the halogenated hydrocarbons (Musick and Williams, 1974), only one of the 36 substances tested was found to be in the resistant group. This was sulfur hexafluoride, a very resistant compound, which showed only a trace of decomposition at a catalyst temperature of 425OC. The 35 substances classified as susceptible to hopcalitecatalyzed decomposition were decomposed to the extent of 5-10096 at a temperature of 3OOOC. Acknowledgment The authors are indebted to J. G. Christian and J. E. Johnson for doing much of the experimental work. The work was funded by the Naval Ship Systems Command, United States Navy. Literature Cited Carhart. H. W., “Habitable Atmospheres for Undersea Craft,” Society of Automotive Engineers Transactions, Paper No. 670534, Aug 1968. Knudson, H. W.. White, L., “Development of Smoke Penetration Meters.” Report of NRL Progress, pp 26-42, Sept 14, 1945. Lelghton, P. A,, “Photochemistry of Air Pollution,” p 184, Academic Press, New York, N.Y., 1961. Miller, R. R., Piatt, V. R., Ed., “The Present Status of Chemical Research in Atmosphere Purification and Control on Nuclear-Powered Submarines,” Chapter 7, pp 56-57, Naval Research Laboratory Report 5465 (Apr 21, 1960). Musick. J. K.. Thomas. F. S., Johnson, J. E., I d . €nu. Chern., Process Des. Dev., 11, 350 (1972). Musick, J. K., Williams, F. W., Ind. Eng. Chern., Prod. Res. Dev., 13, 175 (1974). Thompson, J. K.,Report of NRL Progress, pp 14-17, July 1956.
Received for review April 17,1975 Accepted August 27,1975
