Division, in operating the pilot kettle and pilot treating facilities.
Literature Cited Aldersley, J. W., Hope, P., Angew. Makromol. Chem., 24, 137-153 (1972). Baekeiand. L. H., (to General Bakelite Co.) U.S. Patent 1 038 475 (1912). Freeman, J. H., Lewis, C. W., J. Am. Chem. SOC.,76, 2080-2087 (1954). Hyman. J. B., Kordzinski, S., Sterr, W. R., Yurcick, P. A,, (to Catain Corp.) British Patent 835 757 (1956). Manasse, O., Ber., 27, 2409-2413 (1894).
Carbon Tetrafluoride
Meier, J. F., Bellott, E. M., Frank, P. P., J. App. Polym. Sci., in press (1976). Meier, J. F. (to Westinghouse Electric Corp.) US. Patent 3 897 589 (1975). National Electrical Manufacturers Association Standards for Laminated Thermosetting Decorative Sheets, L D I (1964). Schrader, P. G., Partansky, A. M. (to Dow Chemical Co.) U.S. Patent 2 620 321 (1951). Zavitsas, A. A., Beanlien, R. D., Leblanc, J. R., J. Polym. Sci., Part A-1, 6, 2541-2559 (1968).
Received for reuiew March 8, 1976 Accepted October 5,1976
+ Carbon in Ionizing Radiation
Billy R. Rodgers'' and Thomas M. Reed Department of Chemical Engineering, University of Florida, Gainesville, Florida 3260 1
The apparent inertness of pure CF4 in ionizing radiation disappears when CF4 is mixed with other substances which can react with fluorine atoms, radicals, and ions produced by radiolysis. Studies of the time dependence of the composition of CF4 C mixtures in ionizing radiation show that both the amounts and maximum size of volatile perfluoroalkanes larger than CF4 increase with exposure in the ionizing radiation of a nuclear reactor. The ratio of material not volatile at 25 OC increases and the ratio of CF4 remaining decreases with exposure.
+
The thermochemical properties of the perfluoroalkanes, C, F'n+2, are such that all members of this homologous series with n > 1 are, in the presence of fluorine, unstable with respect to the first member, CF4, but if solid carbon and FPare present in the equilibrium system the homologues with n > 1 are more stable than CF4 (Reed, 1964). It is essentially impossible to maintain an equilibrium when F2 is reacting with carbon at its usual rapid rate. Thermodynamics has little relevancy to the prediction of the behavior of systems in ionizing radiation. We mention it here simply to point out that in the perfluoroalkanes series, reactions may be effected with ionizing radiation that cannot be done without it. In particular CF4 can be made to yield the higher homologues when it is in contact with solid carbon and is under irradiation with y rays and neutrons in a nuclear reactor (Askew and Reed, 1967). Small amounts (0.1 wt %) of molecules as large as CL0F%2 have been made in this way and obtained in the volatile material produced from CF4 carbon. When CF4 is irradiated alone (in a pure aluminum container) 98 to 99% is recovered unchanged (Askew et al., 1968). The irradiation of mixtures of CF4 with CiF6 containing more than 50 w t % C P F ~produces straight-chain and branched-structured perfluoroalkanes in greater quantity than is produced in systems of CF4 with carbon under the same conditions with respect to ionizing radiation (Askew and Reed, 1972), but the specific species produced and their ratios are essentially the same in both cases.
+
Experimental Section Materials. Perfluoromethane from the Matheson Co., Inc., was found to be chromatographically pure; it was used without further purification. The carbon granules were activated charcoal Nuchar C-190, 30 mesh, from the West Virginia Pulp and Paper Co.
Sample Preparation. Sample tubes 5.5 in. long of f/s-in. 0.d. X 0.025-in. wall aluminum Versatube were prepared, cleaned, and weighed, as previously described (Askew et al., 1968). To ensure uniformity of particles, the charcoal was screened through a Tyler 20-mesh screen with 0.0328-in. openings. Approximately 0.04 g of charcoal was poured into the tubes and weighed. The compounds and the tubes containing the carbon were degassed and dried. Carbon dioxide was removed by passage over Ascarite. Samples of approximately 0.077 g of CF4 were condensed from a vacuum system into the aluminum tubes by cooling in liquid nitrogen. Prior to condensing the sample, the aluminum tubes were baked at 200 "C while being pumped out. The tubes were sealed, while attached to the vacuum system, by Heliarc weld under argon gas. Irradiation. The samples were exposed to nuclear radiation at location C-41 of the Low Intensity Training Reactor at Oak Ridge National Laboratory. The characteristics of the neutron flux a t this location are given in Table I. Analyses. Gas chromatography, as previously described (Askew et al., 1968) was used for quantitative and qualitative determination of the volatile components from the irradiated samples. Material not volatile into a low vacuum system at 20 to 30 O F was not removed from the tubes or analyzed. The results of the analyses are given in Table 11. Results Samples of CF4 C were irradiated for 1 h, 6 h, 1 day, 3 days, 1 week, and 4 weeks, respectively. The 1-h duration
+
Table I
+
' Address correspondence to this author at Oak Ridge National Laboratory,Oak Ridge, Tenn. 37830.
neutrons/cm' Thermal neutrons 3 Mev (by s6Ni to Co) 4 Mev (by Fe t o Mn) Temperature: 120 O F
s
3.46 X 101:3 3.48 X 1 O l 2 1.78 X 10"
Ind. Eng. Chem., Prod. Res. Dev., Vol. 16, No. 1, 1977
87
Table 11. Volatile Material Recovered from Irradiated Samples by Volatizing Into a Low Vacuum System Exposure time, h: Gas recovered, wt %: Product
0
100 100
1 -100
6 90.8
99.45 0.303 0.249
93.16 0.131 3.95 2.41 0.345 Trace
24 85.4 Weight % 84.18 None 8.34 3.18 2.16 0.179 1.29 0.062 0.426 0.216 0.0049 0.0034 0.0784
72 70.2
168 90.0
71.90 0.058 7.68 4.86 2.54 1.34 1.82 1.43 0.12 0.614 4.08 Trace 0.538 0.202 0.149 1.93
63.25 0.554 8.73 8.57 2.79 1.22
1.68 2.56 0.878 0.659 4.27 0.115 0.354 0.254 0.157 2.01 0.034 0.038
Trace -0.053 0.225
0.113 0.0741 0.439 0.0226 0.393 0.402 0.0917
0.112 -
0.160 0.254
Discussion Possible Routes to Products. The 1-day irradiations produced the first appreciable radiolysis products above C jF8 in molecular weight. The CrF6 undergoes radiolysis to produce C {Fxand CdF1O in the following ways. C F 3.
CJFF, C2Fj*--+ C jF8 +
C2Fj*
+ CzFi.
+
n-CeFlo
(1) (2)
The fact that n-C4F10does not appear in the 6-h irradiation period when CJFt; concentration had reached the relatively high value of 4 wt % suggests that process (2) is not very likely due to the great abundance of CF3. consuming most of the C2F;. by process (1).The observation of more C?Fs than n 88
Ind. Eng. Chem., Prod. Res. Dev., Vol. 16, NO. 1, 1977
52.15 Trace 13.09 4.94 4.83 1.07 1.63 2.21
0.674 0.673 6.71 1.07 0.842 0.796 0.906 2.96 0.12 0.076
-
-
produced only C2Fe (0.25 wt 96) and C02 (0.30 wt %), these being the first generation species. The COz appears from oxygen adsorbed on the carbon, or from the aluminum oxide on the walls of the container. By 6 h, the second generation products C:jFa (0.35 wt %), C2F6O (2.41 wt %), and a trace of C:3FaO have appeared. The quantity of Cor! diminishes as the oxygen-containing fluorocarbons increase in quantity. The second generation species n-C4Flo and some of the third generation compounds (which include Cz’s, Ce’s, and Cy’s) begin to appear after 1 day of irradiation. At 3 days the remaining third generation species appear and fourth generation species begin to appear (some Cy’s and (28’s). At 1 week the fourth generation species through the Cg’s appear. At 4 weeks CloF22 appears and all molecules larger than CF4 have increased in amount relative to CF4. The CF4 decreases steadily with increase in exposure duration. In homogeneous gas-phase irradiations of pure perfluoroalkanes (Askew et al., 1968) CF4 is the preponderant product.
672 61.3
0.365
0.184 0.620 0.189 0.572 1.80 1.18 0.156
C4F10 a t 24 h is consistent with the postulate (Askew et al., 1968) of an abundance of CF3. during irradiation of CF4 C2F6 mixtures. C:jF8 appears to be an essential precursor for molecules C4F10and larger. Only when C3F8 has attained a significant concentration (e.g., 2% a t 24 h) do higher molecular weight compounds appear. The three largest products following C3Fa are the same three branched-chain structures that predominated in the studies of CF4 C2F6 mixtures (Askew and Reed, 1968) namely, i-CdF10, i-CsF12, and 2,3-(CF3)2CeF~.Each of these is formed from 2-C:jF7. combining with CFa., CzFs- and with itself, respectively. Furthermore, i-CSF12 is augmented by formation from CF3- CdFy, the latter radical coming from the n-C4Flo present. The formation of 2-C9F7- from C3Fa appears to be a very favored process. The absence of neo-CZF12 [(CF3)4C]indicates that the process C C CCC .+++ CCC (CF3)dC does not occur due to the unlikely formation of the tertiary butyl radical. There are several routes for radical combination that arrive a t the two perfluorohexane isomers, 2-CF:jCsFll and 3CF3C5F11.The fact that the ratios of n-C?Flo, i’C4F10, and n-CZFlo do not increase after 72 h suggests that these molecules provide radical for these Ce isomers:
+
+
+
+
CC.
CCCC .- CCCC d 3-CF:jCsFil C CCC CCCCC
c
“t
-
CCC.+
cc.
CCCCC
CCCCC *H CCCCC
-
2-CF3CsFll
C. C.
2-CF3CnFll
(3) (4)
(5)
~ - C F ~ C ~ F ~ I(6)
The 2-CF:IC5F11isomer can also be formed from combination of l-C:IFi.and 2-C:jFi. which accounts for the greater quantity of this isomer. The n-C6F14appears in greater quantity than its isomers a t a given time because it is formed from combination of 1-C:3F7.one generation ahead of the isomers, which require C4's and Cj's as precursors. The C7Fl6 isomers attain quantities of approximately the same magnitude as the CfiF14isomers a t the same time. This leads to the conclusion that they are formed predominantly from Cd's and Cs's also. In decreasing order of amounts, they may be formed as follows:
- - - -I ccc
ccc
2,4-(CF3)2C5F10
ccc.
cc.
cc"c
cccc cccc *
cccc
3,3-(CF3)2CjFlo
I
\ - -J - ccc'
CCCCC C
cccc CCCCC
cccc
%-
CCCCC
cccc.
3-CF3C6F13
cc.
cc. CCCCC ----t 3-(C2F~)CsFll
cccc
ccc
However, it can be argued that these C$16 isomers are derived entirely from the two branched CSF14 isomers as precursors by processes involving the plentiful CF3. radical; viz.
-
Literature Cited
C.
ccccc
ccccc
This latter scheme is attractive because the C7 isomer formed in largest amount is derived from 2-(CF3)CsFll which is the c g isomer produced in largest amount. The yield of n-C.iF16 is very low because it must be formed only from radicals with one F removed from a CF3 group. This is apparently an improbable process analogous to the low probability for the formation of l-C3F7-which is manifested in the predominance of the branched Cq, Cj, and (36's shown above. Nonvolatile Material. In these experiments a fraction of the CF4 was converted to nonvolatile material or to material so strongly adsorbed by the carbon phase that it is nonvolatile. Table I1 shows that up to 40% nonvolatile product was produced. The irradiation of CF4 alone and of CF4 with c2F6 produced no nonvolatile products a t exposures up to the longest times (4 weeks) experienced in these experiments (Reed et al., 1965; Askew and Reed, 1972). C3Fa and larger perfluoroalkanes when irradiated for 4 weeks in the LITR are converted to 30-50 wt % nonvolatile solid (Reed et al. 1965). It is known (Kuriakose and Margrave, 1962) that fluorine is found in the solid phase when fluorine (F2) is reacted with carbon (as graphite) at temperatures between 315 and 530 "C, and only above 600 "C does the graphite lose weight to the gas phase. This weight loss is mostly the volatilization of CF4 as a product of the reaction. From these observations we may assume that fluorine atoms, radicals or molecules produced from perfluoroalkanes in ionizing radiation will be taken up by the carbon phase. In all probability this absorbed fluorine ultimately produces fluorocarbons from the atoms of the solid carbon phase. The data show that the average value of the ratio of C atoms to F atoms combined in the volatile perfluoroalkanes increase with exposure. This means at least that fluorine is being selectively removed from the volatile fraction of the fluorocarbons.
3,3-(CF3)2CsFlo
Askew, W . C., Reed, T.M., Nucl. Sci. Eng., 29, 143 (1967). Askew, W. C., Reed, T. M., Mailen, J. C., Radiat. Res., 33, 282 (1968). Askew, W. C . , Reed, T. M.. Ing. Eng. Chem., Prod. Res. Dev., 11, 447 (1972). Kuriakose, A. K., Margrave, J. L., J. Phys. Chem., 69, 2772 (1962). Reed. T. M., "Physical Chemistry of Fluorocarbons", in Vol. V of "Fluorine Chemistry", J. H. Simons, Ed., Academic Press, New York. N.Y., 1964. Reed, T.M., Mailen, J. C., Askew, W. C., TID 22421, 1965.
Received for revieu March 9, 1976 Accepted October 23, 1976
Ind. Eng. Chem., Prod. Res. Dev., Vol. 16, No. 1, 1977
89
