Environ. Sci. Technol. 1985, 19, 280-282
Bouwer, E. J.; Rittman, B.E.; McCarty, P. L. Environ. Sci. Technol. 1981,15, 596-599. Bouwer, E. J.; McCarty, P. L. Appl. Environ. Microbiol. 1983,45, 1286-1294. Parsons, F.; Wood, P. R.; DeMarco, J. J.-Am. Water Works Assoc. 1984, 76, 56-59. Caoile, J. "Field Investigations of Uncontrolled Hazardous Waste Sites", 1983, task report submitted to the Environmental Protection Agency, Contract 68-01-6056. Easley, D. M.; Kleopfer, R. D.; Carasea, A. M. J . Assoc. Off, Anal. Chem. 1981,64,653-656. Longbottom, J. E.; Lichtenberg, J. J. "Methods for Organic Chemical Analysis of Municipal and Industrial Wastewater";
U.S. Environmental Protection Agency: 1982; EPA 600/ 4-82-057, Method 624. (14) Kaufman, D. D. In "Pesticides in Soil and Water"; Guenzi, W. D, Ed.; SSSA Publishers: Madison, WI, 1974; pp 133-202. (15) Stanier, R. Y. J . Bacteriol. 1947, 54, 339-348. (16) Sprague, R. T., Post, Buckely, Schuh and Jernigan, Denver, CO, private communication, 1983. Received for review August 22,1983. Revised manuscript received May 7, 1984. Accepted August 9,1984. Mention of products and manufacturers is for identification only and does not imply endorsement by the US.Environmental Protection Agency.
Gas-Phase Hydrogenolysis of Polychlorobiphenyls Jeffrey A. Manlon, Peter Mulder, and Robert Louw'
Goriaeus Laboratories, The University of Leiden, 2300 RA Leiden, The Netherlands ~
Chloroarenes in an atmosphere of hydrogen are thermally dechlorinated to yield HC1 and benzene as major products between 700 and 925 "C, with residence times of ca. 10 s. Polychlorobiphenyls (PCBs) are both dechlorinated and split into chlorinated benzenes, with splitting about twice as fast as dechlorination. Thermal hydrogenolysis, which occurs via radical mechanisms involving H atoms, may therefore be considered as a useful method for workup of (toxic) chlorinated wastes. Following studies on thermolysis (1-3) and on several free-radicalgas-phase aromatic substitutions-chlorination (4),cyanation (5), nitration (6),and oxidation (7)-we are now engaged in thermal conversions of benzene and derivatives with hydrogen. Within this category, "hydrocracking" of chlorinated arenes deserves special attention. In general, reaction 1 is of potential interest as a method Ar(R)Cl
+ H,
Ar(R)H
+ HC1
(1)
for dechlorination of (highly) chlorinated industrial waste materials etc. Thermolysis of chlorinated benzenes in an excess of H2 (quartz flow reactor, atmospheric pressure, residence time 5-15 s) proceeds smoothly at 750 "C and shows very high degrees of conversion (HC1 formation) at ca. 900 "C (8). Sooting is unimportant even at 900 "C provided that the Hz:arene molar intake ratio is above 10. Aliphatic and olefinic chlorides, in general, react much faster than chlorobenzenes (8). Polychlorobiphenyls (PCBs) have found widespread application, especially as transformer oil, its use and disposal entailing considerable environmental problems. We therefore thought it worth while to examine the behavior of PCB in hydrocracking (eq 1). Our observations, including those on appropriate model compounds reported below, confirm our expectation that PCB can be completely converted into HC1 and non-chlorinated organic products, mainly benzene. Hydrocracking thus constitutes an environmentally clean alternative to incineration. Representative examples with Aroclor 1248 (C1= 48% wt) are outlined in Table I. That conversion of PCB is essentially complete and is illustrated by Figure 1. Dechlorination of chlorobenzene (PhC1) is 297% ; monochlorobiphenyls are seen in minor amounts only, biphenyl comprising ca. 0.7% on the PhCl feed. This biphenyl stems from PhC1-or better, from benzene made therefrom-rather than from PCB (vide infra). Notable conversion occurs at 715 "C (run 1). 280
Environ. Sci. Technol., Vol. 19, No. 3, 1985
Table I. Thermolysis of PCB in Chlorobenzene with Hydrogena 1
T,OC 7,
conversionbof PCBs, % PhC12,C" % PhC18,C % Phz,' % ClPh2,dJ % PhH:PhCl molar ratio
715 8.9 (ca. 10) 4.8 1.2
0.010 0.053 0.059
run no. 2 3 760 8.3 28 8.5 1.5 0.034 0.18 0.19
805 8.3 70 1.5 0.10 0.040 0.13 0.92
4 875 7.6 >99.W 0.2 0 0.60
