to form gaseous hydrocarbons. For example, the Fisher assay oil yield for the New Albany shale was approximately 0.052 gallon per pound of organic material, whereas the Colorado shale oil yield was approximately 0.088 gallon per pound of organic material. T h e carbon-hydrogen ratios were approximately 7.85 to 7.20. respectively. T h e lower oil yield with the New Albany material indicates an increased tendency to form residual carbon rather than oil vapor. This tendency of the kerogen to form carbonaceous residue appeared to have a similar effect on the hydrogasification yields. Acknowledgment
Thanks are due to E. J. Pyrcioch, W. G. Bair, H. L. Feldkirchner, S. Volchko, and H. A. Dirksen for their helpful suggestions in operation and design of the equipment. E. J. Pyrcioch, R . E. Cartier, E. C . Higgins, R . J. Hrozencik, J. C . Wolak, LV. Podlecki, R . 0. Buskey, and C. Wuethrich assisted in conducting tests and performing calculations. A. Attari and J. E. Neuzil supervised the analytical work. Thanks are also due to the Indiana Geological Survey for assistance in locating and obtaining the New Albany oil shale used in these studies.
literature Cited
(1) Aarna, A. Ya.. Tr. Tallinsk. Politrkhn. Insf. Ser. -1 1955, No. 63. pp. 65-81. (2) Feldkirchner. H. L.. Linden, H. R.: Di\-ision of Fuel Chernistrv. 143rd Meeting. .4CS. Cincinnati. Ohio. Januarv 1963. (3) jukkola. E. E.. Denilauler. .A. J.. Jensen. H. B.. BLrnet. \V, I . ? Murphy, I V . I . K..Ind. Eric. Cheni. 45, 2711-14 (1953). (4) Linden, H. R.. 48th National Meeting, American Institute of Chemical lingineers, Denver, Colo.. August 26-29, 1962; Preprint 14, 1--52. (5) Mason. D. h4c.A.. Eakin, B. E., Institute of Gas Technology Research Bull. 32 (December 1961). (6) Murphy. \V. I. K.. U. S. Bur. Mines. Laramie, \Vyorning, personal communication. September 1962. (7) Shultz, E. R.. Jr., IND.ENG. CHEM.PROCESS DESIGN DEVELOP. 1, 111-16 (1962). (8) Shultz. E. B.. ,Jr., 48th National Meeting, American Institute of Chemical Engineers, Denver, Colo.. .august 26-29, 1962; preprint 9, 44-57. (9) Shultz, E. B., Jr., Linden, H. R., Ind. Ery. Chem. 51, 573-76 (1959). (10) Van Arnstel. A . P.: Peiroi. RrJner 39, 151-52 (.March 1960). RECEIVED for review May 21. 1964 ACCEPTED December 30. 1964 Division of Fuel Chemistry, 147th Meeting. XCS. Philadelphia, Pa., April 1964. \Vork supported by the Gas Operations Research Committee of the .-4inerican Gas Xsociation as part of the Pr\R (Proinotion-l~d\.ertising-Kesearch)Plan of the association. LVork guided by the Project PB-23b Supervising Committee under the chairmanship of C. F. Mengers.
PRODUCTION OF TETRAFLUOROETHYLENE B Y REACTION OF CARBON WITH CARBON
TETRAFLUORIDE IN AN ELECTRIC ARC R A Y M O N D
F. B A D D O U R A N D
B A R R Y
R .
B R O N F I N '
Department of Chemical Engzneerrng. Massachusetts Institute o t Technolog), Cambridle. M a s s .
A high-intensity carbon arc, into which carbon tetrafluoride was introduced, was operated over the pressure range of 0.1 to 1 .O atm. A cold, small-diameter, quench tube, through which samples were withdrawn for analysis, was inserted into the carbon-fluorine plasma formed b y the arc. At sufficiently high levels of power input, 69 mole of the carbon tetrafluoride feed was converted to tetrafluoroethylene. Additional fluorocarbon gases were observed in small concentrations. Possible reaction sequences yielding the observed quenched product distribution are discussed, treating the existing high-temperature thermochemical data taken from the literature.
7 0
Y UNCONFINED
electric arc. operated a t high power levels,
A-is capable of producing high gas temperatures in the range of 2000' to 1O,00Oo K. It is possible to use the high-intensity electric arc to couple energy into chemical reactants to achieve gas phase chemical syntheses by a high temperature route. This is an especially useful technique if one or both electrodes may be fabricated from one of the reactants. Electric Arc
4 high-intensity electric rent density is sufficiently anode. If two electrodes. connected to a d.c. source. 1
arc is one in which the anode curhigh to cause rapid erosion of the separated by a small distance, are current can be made to flow across
Presmt addrrss. Naval Research Laboratory. \Vashington 25,
n.c. 162
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PROCESS DESIGN A N D DEVELOPMENT
the electrode gap. Initiation of the arc can be effected readily by applying a high-frequency. high-voltage current to ionize the interrupting gas Once this conducting path is established, a stable d.c arc can be sustained. I n the d.c. arc process a large current of electrons leaves the negative cathode and streams, through successive collisions, toward the positive anode. A s the current through the arc is first increased. the anode spot grows without significant increase in the current density. Eventually the entire face is covered, and further increase in the current results in a n increase in the current density. At this point, the energy flux a t the anode surface is so high that radiation and convective cooling does not sufficr to protect the anode, and anode failure occurs; a metal electrode melts. and a graphite electrode vaporizes, creating a large luminous tail-flame of carbon vapor. To sustain an arc during electrode erosion. the anode must be
advanced to maintain a small gap to prevent the arc from being extinguished. The term "high-intensity'' arc is used to describe the anode-consuming arc, with high power inputs. With graphite electrodes the high intensity region corresponds to about 40 amperes per sq. cm. Use of High-Intensity Arc as Chemical Reactor. The high-intensity electric arc can be exploited as a chemical reactor by introducing reactants into the luminous, hightemperature arc region. T h e reactants may be introduced as a solid, liquid, or gas directly into the reaction zone, and/'or be produced as a result of electrode vaporization, so that the electrode material becomes a reactant. T h e luminous reaction zone is a region of intense chemical activity. The significant properties of the high-intensity arc reactor which make it interesting for chemical synthesis are : Extremely high temperatures in the reaction zone, ranging from 2000' to 10,000' K. Very high throughputs because of rapid reaction rates and rapid coupling of energy into reactants. Production of high concentrations of very reactive species, not available at conventional chemical reactor temperatures. Simple, versatile, small-scale equipment requirements. The conversion of methane to acetylene in a high-intensity carbon arc with a yield in excess of 50% has been reported ( 7 ) . Some work in the synthesis of fluorocarbons in a highintensity carbon arc has also been reported ( 4 ) . T h e arc reactor has also been used experimentally to reduce metal oxides to metals of high purity (7). The prospect of commercial utilization of the electric arc for chemical synthesis continues to look favorable, considering the continued low cost of electric power despite rising costs of labor and raw materials. The arc synthesis of fluorocarbons, particularly fluorocarbon monomers, looks especially attractive because of the high cost of these materials. Reaction Sequence in Arc Synthesis. T h e high-intensity arc employed as a chemical reactor is essentially two reactors in series, as diagrammed in Figure 1. First, the production of large concentrations of reactive compounds and free radicals involves the introduction of reactants into the arc. T h e thorough mixing of any externally supplied reactant with the small plasma zone is essential, a n d often difficult to achieve. T h e reactants must reside in the plasma zone long enough for the desired high-temperature species to form. Fortunately, within this high-temperature zone, heating rates and reaction rates are extremely high. Thus, with good mixing and rather short residence times the arc reactor is capable of producing large concentrations of free radicals, in the range of 10 to 100 mole %. If the chemical species produced in the arc are allowed to cool slowly to ambient temperatures along a reversible equilibrium path, the most desired products may not be obtained. Trapping of the high-temperature transient species to promote the reaction sequence to desired products is the function of the quench reactor. One of the problems confronting researchers in the plasma chemistry field is the absence of theoretical or experimental kinetic data at high temperatures. Thus the quenching
Production of
Reactants
+ h i g h - temperature intermediates
,
,
Trapping of precursors lo ----+ Product, y i e l d desired products
Figure 2. Carbon-fluorine system equilibrium calculations a t 1 atm.
mechanism is highly complex and not well understood. 'I'here is some suggestion that the composition of the quenching surface may be an important variable (4). Consideration must be given to the proper location of the quenching zone in relation to the plasma zone, which is complicated by the difficulty of temperature determination in the high-temperature reactor, containing a large number of molecular species. Equilibrium Calculations for Carbon-Fluorine System
T h e system studied here was the carbon-fluorine system, using mainly tetrafluoromethane, CFa, as a convenient source of fluorine. Considering the two-step reaction process, it is in the thermal plasma of the arc reactor that temperatures as high as 6000" K. are obtained (6). Using the available thermochemical data for the various known carbon-fluorine species as a function of temperature ( 5 ) and a material balance, a computer program was used to solve for the composition of the system at equilibrium using the technique of free energy minimization (73). Figure 2 shows the results of the computer calculation of the composition of a system with a ratio C / F = 2, as a function of temperature. a t 1 atm. Below the sublimation temperature, T,, which is 4430' K. for this rase, the composition is independent of the C / F ratio, since this is the region where the multicomponent gas phase exists in equilibrium with solid carbon. Referring to the plot, thermodynamic data indicate that difluoroacetylene, C2F2, is stable over the wide temperature range between 2000" .and 4000' K. Above about 4500' K. nearly all species are reduced to atoms It is interesting to note the form of carbon species below the sublimation temperature ; Ca predominates over approximately equal concentrations of C2 and CI. For simplicity, the Cq and higher gaseous carbon agglomerates have been omitted from this plot, since they occur a t least a factor of 10 lower in concentration. T h e concentration of tetrafluoroethylene, ClF,. over the entire region illustrated is in the range of l o p 5 to mole yG% and so does not appear. Other calculations made over the pressure range from 0.1 to 1.0 atm. showed this plot to change only slightlv with pressure. VOL. 4
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INSULATING GASKET HOLLOW GRAPHITE CATHODE I
G R A P ~ ~ TA E~ O D E
NM
SLIDING VACUUM SEAL I\
" I
I
11
..
SAMPLING PROBE
SLIDING ANODE HOLDER
SIGHT GLASS
Figure 3.
Diagram of high-intensity arc reactor
Experimental Apparatus
T o investigate the carbon-fluorine system a t arc temperatures. the arc reactor diagrammed in Figure 3 was constructed. T h e reactor consisted of four electrically insulated sections. T h e central section was a 3-inch diameter cross serving as the reaction chamber, which is electrically floating. .4t one of the four ports was mounted the anode section, which was Cesigned to allow a continuous motor-driven feed of a 1/2-inch-o.d. graphite anode. The anode shown in Figure 3 was centerboreu to allow reactant gas to flow directly into the center of the plasma formed between anode a n d cathode. Runs were also made with a solid graphite rod, with reactant flowing along the outside surface of the anode, and into the hollow cathode pipe. At the opposite port was mounted the 2-inch 0.d. stationary hollow graphite cathode. Provision was made a t the last insulated section for the positioning of a watercooled hypodermic probe of small internal diameter, of the same design as in previous studies (3, 9 ) , a t a variable position down the center of the hollow cathode. A large viewing winbow was mounted in a port normal to the electrode ports to allolv observation of the arc. All metal parts of the arc reactor !yere water-cooled. Power was fed through the electrodes from series-operated motor-generators supplying u p to 25 k w . d.c. T o promote mixing of the cold reactant gas with the plasma formed across the electrode gap, a magnetic field of approximately 200 gauss was imposed along the electrode central axis, causing rapid rotation of the arc. Cas samples Lvere taken through the water-cooled probe, estimated to have a quenching rate of about lo6 ' K. per second ( 9 , 7 7 ) , a n d were analyzed by on-line gas chromatography. Results
quenched gas product a t high-power levels. Figure 4 is a plot of the data collected with the sampling probe located 1 to 2 inches back from the face of the cathode. The highest conversions, it can be seen, were obtained a t the highest power levels for both CF, feed rates. A power input of 25 kw. corresponds to a carbon vaporization rate from the anode of about 15 grams per minute: which consumes the '#/2-inch-o.d. graphite anode a t a rate of about 3('4 inch per minute. With this power level and a CF, feed rate of 50 cc. per second (S.T.P.), carbon-to-fluorine ratios of approximately 2 result in the homogeneous gas phase region. Figure 5 shows the results of a series of runs conducted a t 0.5 a t m . ; again the same effect is noted. High yields of C2F4, u p to 57 mole % a t this pressure, were obtained a t high power input levels. 4 further increase in yield was obtained in the series of runs a t 0.1 a t m . , shown in Figure 6. U p to 69 mole 70 was obtained at 17 kw. Throughout the series of runs the variation in CFI reactant feed rate has small effect on the CfF4 yield. Figure 5. for example, shows within the scatter of the data that the yield of CsF, is independent of CF, feed rate. Some typical product distributions are shown in Table I. Discussion of Results. An interpretation of the product distributions observed in the quenched gas samples requires a postulation of the quench path in going from plasma species to stable products. Postulations of the reaction sequences must be considered as only tentative because the thermodynamic d a t a for the prediction of the equilibrium plasma composition have not been substantiated a t elevated temperatures, and kinetic data for the fluorocarbon system in quenching from plasma temperatures are nonexistent in the literature. PLASMA COMPOSITION. The temperature in a high-intensity carbon arc has been determined to range from 6000' K. near the anode, corresponding to superheated vapor, to 3000' to 4000' K.in the tail-flame of high-velocity carbon vapor (6, 70). I n Figure 2: it can be seen that, a t around 6000' K., only atomic fluorine and carbon exist in q u a n i t y . However. below the sublimation temperature, 4430' K.. the following species predominate: F, C2F2, and various forms of gaseous carbon. Lower concentrations of CF, are also observed in the vicinity of 3000' K.. and small amounts of C F in the vicinity of 4000' K. POSTULATED MECHANISM OF C2FZ FORMATION.Neither difluoroacetylene, CnF2. nor free fluorine, F2, was observed in
The results of a series of runs a t atmospheric pressure, varying the CF, reactant feed rate and input power levels, showed that it was possible to obtain up to 40 mole yo C2F4 in the
50
b
/
40
s20c
t
I
w
l
e
201
-I
I
5 Figure 4.
164
IO
15 20 P O W E R (kw.)
25
Product yield at 1 atmosphere
I&EC PROCESS D E S I G N A N D DEVELOPMENT
0.4cdsec.
OL I
0
2 5 c c . I sec.
0
Figure
I
5
CF4 FEED RATE (ccIsecJ0.4 A 10.0 0 25.0 1 I I 1 20 25 IO 15 POWER INPUT (kw.)
5. Product yield at 0.5 atmosphere
. Typical Product Distributions (Mole
Table I.
%)
Power input = 20 to 25 kw. CF, feed rate = 25 to 50 cc. /sec. (S.T.P.) Gas analysis via gas chromatography
CFa CeF4 C?FG C8F6
1 Atm.
0.5 Atm.
0.1 ,4tm
54-64
40-48
40-30 2 4
2
28--38 69-60 1 2
57-50 I
the product gas, as would be expected, since they are highly reactive. Difluoroacetylene is reported to have been synthesized a t very low pressures, under carefully controlled conditions, and is reported to be highly unstable (8). T h e observation of high concentrations of C2F4 in the quenched gas may be explained as a result of the following reactions, occurring within the probe. Values of AH are taken from (.5) :
CBFz
+ 2F
2CFr
+
+
C2F4
CaF4
+ 2C(s)
2C2Fn-t C2F4
AH = -118 kcal.,/g.mole
(1)
AH = -90 kcal./g.mole
(2)
AH = -49.1 kcal./g.mole
(3)
Reaction 1 requires a two-fluorine-to-one-difluoroacetylene stoichiometry which is satisfied at about 4000' K., a temperature within the two-phase, heterogeneous region of equilibrium composition, as can be seen by referring to Figure 2. The equilibrium ratio of free fluorine to difluoroacetylene rapidly decreases with decreasing temperatures. In these studies the tip of the quench probe was probably in a heterogeneous region, since the CFI feed rate has such a small effect on product composition. In the heterogeneous region, but not in the homogeneous region, the equilibrium composition is unaffected by changes in the C;'F ratio. The small variations in product yield as a function of CF4 feed rate which can be noted in Figures 4, 5, and 6 may be the result of inexact or nonreproducible positioning of the probe tip in the plasma core. which is subject to high radial temperature gradients. However, a very high feed rate of cold reactant gas would chill the plasma, producing lower temperatures at the entrance of the quench probe. Cooler plasma temperatures would yield lower concentrations of precursors to C2Fa. Perhaps this effect is beginning to be noted a t the 50 cc. per second feed rate shown in Figure 4 . Assuming that the other gases present, mainly CI, C2. and Ca. condense on the walls of the quenching tube as
80
I
1
I
I
solid carbon. about 95 mole 7" C2F4 could be expected. Considerable deposits of carbon were observed on the interior walls of the quench tube after a few seconds of arc operation. Reaction 2: the dimerization of the CF, radical, can contribute about 5 mole % to C4F4 formation if quenching occurs from a lower temperature region, 2000' to 4000'. Reaction 3, the dimerization of difluoroacetylene to form C2F4 and solid carbon, can yield 95 mole To C2F4. again, if quenching occurs from lower temperatures, in the 2500' to 3500' range. The high heat of reaction for all of these reactions requires the presence of a third body to proceed. The cold quench walls serve this function. VARIATION IN QUENCH PROBELOCATION.T h e formation of tetrafluoroethylene, CzF4, via Reaction 1 would be suppressed at lower temperatures, while C2F4 formation via Reactions 2 and 3 would be enhanced a t lower temperatures. Figure 7 shows the product gas composition as a function of quench probe location. As the tip of the sampling probe was withdrawn from the cathode face into successively cooler regions the CzF4 yield decreased. This would suggest the predominance of Reaction 1 in C2F4 formation A slight increase in C3Fe is noted in the sampling of cooled regions. POSTULATED MECHANISM O F CF4 FORMATION. The large concentrations of C F I observed in the product gas cannot be totally attributed to unreacted feed appearing in the sampling tube. I n some preliminary studies using hexafluoroethane, CzFs, and cyclic octafluorobutylene, C4F8, as feed to the highintensity carbon arc, about the same ratios of C2F4 to CF4 were observed as with CF4 feed. Thi: is in agreement with the results of Dennison ( 4 ) ,who used inorganic fluorides, in addition to CF4 feed, and obtained close to the same ratios of CeF4 to CFI in the quenched gas. Severtheless, some bypassing is evident, especially if reactor geometry and run conditions are not correct, and preliminary studies showed about 5 mole C~FP,unreacted, using it as feed; and about 20 mole yo cyclic C4Fs unreacted, using it as feed. Further refinement in experimental design could probably reduce these values. Formation of CF4 may be the result of direct free-fluorine attack of -gaseous carbon, and/or the fluorination of the existing C F and CF2 radicals. C2F4 YIELDWITH H I G H E RPOWERIUPUT. The INCREASISG increasing yield of tetrafluoroethylene with increasing power
7,
I
I
I
I
1
4
5
OPERATING CONDITIONS I ATM. PRESSURE 2 5 kw.POWER INPUT 5 0 c r / s a c . CFq F E E D
-
1 0
I
I
0
Figure 6.
5
I I 15 IO POWER INPUT (kw.)
20
I 20
Product yield at 0.1 atmosphere
25
0
2
I
DISTANCE
Figure 7. location
3
FROM CATHODE FACE (inches)
Product yield vs. quench probe
VOL. 4
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input was observed in each series of runs (Figures 4, 5. and 6). Two effects result from increased power input. First, the temperature of the plasma, particularly in the anode-fall area, increases because of increased numbers of collisions of highenergy electrons with the carbon atoms being vaporized from the anode. The increased current raises the plasma temperature along the arc length also, because of increased ohmic heating, but this is a secondary effect. .4second effect of the increase in power input is the creation of additional gas turbulence, resulting from increased vaporization of the anode and increased enthalpy input to the species in the anode-fall area. Thus the possibility of unreacted CF, channeling by the carbon-rich plasma without reacting is minimized. Further, the increased turbulence promotes more frequent collisions by transients to generate the desired precursors to final products. INCREASING CnF4 YIELD WITH DECREASING PRESSURE.A marked increase in CZF4 concentration, from about 40 mole yoa t 1.0 atm. to 69 mole z t 0.1 a t m . . is observed as the reactor pressure is decreased. I n the patent of Dennison, Edlin, and Whipple ( 4 ) a similarly high yield of C2F4 is reported a t this low pressure. At lower pressures, the diffusion and mixing processes, between cold entering reactant gas a n d the high-velocity carbon plasma, are more efficient. T h e decrease in gas pressure also improves the stability of the carbon arc burning in the annulus formed by the anode rod and the hollow graphite cathode pipe. spreads the tail-flame evenly over the reaction zone, a n d minimizes possible stagnation of the arc column a t one location on the cathode. REACTIOK KINETICS. T h e assumption of thermodynamic equilibrium in the plasma has been made to serve as a basis for prediction of product gas composition. However, it has been observed that the reaction kinetics and mixing kinetics for achieving chemical equilibrium in the arc are somewhat limiting, as evidenced by the appearance of some unreacted feed in the quenched sample gas. Perhaps this limitation decreases as pressure is decreased. A reaction sequence to produce the observed concentrations of C 3 F smay be a nonequilibrium mechanism: combination of C2F2. favored a t equilibrium in the plasma, directly with entering CF4:
CZ2
+ CFI
+
C3Fs
(4)
Reaction 4 would be favored a t lower temperatures, where the C2F2 concentration increases. The results in Figure 7 are in agreement with this postulation, since the concentration of C8Fs in the quench probe is observed to increase slightly as the probe is placed into cooled regions of the plasma. Studies using the carbon-hydrogen system ( 7 ) indicate that equilibrium is probably not attained within the plasma. since acetylene yields of 26 mole yo were obtained using hydrogen feed to the high-intensity carbon arc while 52 mole yGwas obtained, a t the same C,” ratio: using methane feed. I n general. then, there will probably be some variation in product composition as the feed gas is changed. Using the postulated quench reaction of Equation 1. the 95 mole % C2Fd in the product quenched from a n equilibrium carbon-fluorine system a t 4000’ K.. predicted using the postulated quench Reaction 1. was not observed. Perhaps the tip of the quench probe should be placed closer to the arc to attain higher temperatures where C 2 F I precursors are in higher concentration. Attempts to place the probe within the arc column resulted in probe failure caused by the arc’s striking directly to the metal probe. Before going further into the development of quench reaction sequences, a reconsideration of the carbon-fluorine thermo166
l&EC P R O C E S S DESIGN A N D DEVELOPMENT
dynamics may be advisable. T h e techniques of extrapolation of experimental data and the estimation of bond energies and bond distances in the high temperature range may not give thermodynamic values of sufficient accuracy to make meaningful predictions. A possibly serious shortcoming of the analysis is the lack of consideration of species such as C?F, C3F. etc., the hydrogen analogs of which, CsH, C3H. etc., are thought to be very important in the carbon-hydrogen system in the 3000’ to 5000’ K.range (7, 2, 72). Conclusions
T h e production of u p to 69 mole of tetrafluoroethylene. C 2 F 4 ,from tetrafluoromethane, CF,, fed to a high-intensity carbon arc. is postulated as a two-step mechanism. ARCREACTION CF4
+ C (gas)
+
+ 2F
C2Fr
QUENCH REACTIOX C2F2 f 2F -+ C2F4 T h e production of C I F 4 is favored a t lower pressures, bvhich may enhance the very important processes of mixing entering reactant with the carbon plasma, to bring the concentration of C2Fa closer to the approximated 95 mole 7Gpredicted from current equilibrium data and a postulated reaction sequence. Acknowledgment
T h e Avco Corp. provided the funds for the equipment used in these experiments. B. R . Bronfin held a National Science Foundation Fellowship while engaged in this research. Allied Chemical Corp., the Linde Co., and E.I. d u Pont d e Nemours & Co., Inc., contributed some chemicals to the program. literature Cited
(1) Baddour, R. F.. Blanchet, J. L., IND.ENG. CHEM.PROCESS DESIGN DEVELOP. 3, 258-66 (1964). (2) Bauer, S. H.. Duff, R. E., “Equilibrium Composition of the C/H System at Elevated Temperatures,” Los Alamos Scientific Laboratory Rept. LA-2556, Chemistry, TID-4500. 16th ed., Office of Technical Services, U. S. Dept. of Commerce, LVashington 25, D. C. 13) \ , Bronfin. B. R.. “Fluorocarbon Svnthesis in a Hieh-Intensitv Electric Arc.” Sc.D. thesis, Massachusetts Institure of Technology, Cambridge, Mass., June 1963. (4) Dennison. J. T., Edlin, F. E., LVhipple, G. H., U. S. Patent 2,852,574 (Sept. 16, 1958). (5) Dow Chemical Co.. Midland, Mich., “JANAF Interim Tables of Thermochemical Data,” December 1960. (6) Finklenberg. LV., Maecker, H., “Elektrische Bogen und Thermisches Plasma,” in “Handbuch der Physik,” S. Flugge, ed., Vol. X X I I , “Gasentladungen 11,” Springer-Verlag, Berlin: 1956. (7) Gibson, J. 0.. LVeidman, R.. “Chemical Synthesis via the High-Intensity Arc Process.” 49th National Meeting, A.I.Ch.E., New Orleans, March 11, 1963. (8) Middleton, 1%’.J., U. S.Patent 2,831,835 (April 22, 1958). (9) Plooster, M. N.. Reed; T. B., J . Chem. Phys. 31, 66-72 (1959). (10) Sheer, C., et ai., “Investigation of the High Intensity Arc Technique for Materials Testing,” Wright .4ir Develop. Center, LVADC Tech. Rept. 58-142 (November 1958). (11) Skrivan, J. F., Freeman, M. P., A.Z.Ch.E. J . 8, 450-4 (1 962). (12) Slysh, R. S., Kinney, C. R . , J . Phys. Chem. 6 5 , 1074 (1961). (13) Lt‘arga, J., “Conversion Procedure for Solving the Thermochemical Calculation Problem,” Avco Corp., Tech. Rept. RADTM-62-78 (1962). \
,
RECEIVED for review .May 28, 1964 ACCEPTED September 18; 1964 Meeting of Electrochemical Society, Pittsburgh, Pa., April 17. 1963.
