352
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 39, No. 3
conrunied in the TABLE I. EFFECTS O F zkFTERTREATIKGP E R F L U O R O C A R B O S S early part of the oil fovd ( ~ y c l e . '/o Hydrogen by TreatTenip., Recovery, Pyrolytic Method ( 2 ) Thcse conclusions Phase ment C. m Before After o n d e g r c ' c of Liquid AgFz 240 87 0.11 0 04 fluorination were Liquid CoFs 275 92 0.07 0.03 Vapor CoFs 310 90 0.08 0.02 * bornc out when E t h e a m o u n t of ,!, ('oF3 o r AgF2 5VI necessary to finish -o.ol ; the fluorination (dc- these data, a typical crude wa.3 distilled through a column of tn-o f scribed 1atc.r) n-as or three theoretical plates, and cuts with a 10" boiling rangt' ~vcre determined. taken. The vapor pressure and viscosity were determined on Sinw t hi, hJ-tIroeach of these cuts and then plotted against the boiling point. a 3 gen replacctnmt by These data made it possible to predict the viscosity and vapor fluorinr \vas not pressure of any given blend of distilled perfluorocarhons or to cornplctc in one obtain by distillation a perfluorocarbon +cithany desired viscosity. pass o w r CoF8, I t was not possible to predict the viscosity or vapor pressure of a methods wcrc decrudr, since minor variations in procedure affected thc nature of 100 140 180 220 260 vc~lopcd t o comt h r product to an unknown estent. DISTILLING RANGE ?C./lOmm.Hg) plcxttb the, fluorinat i u n . Any one of Figure 5 . Viscosity and Vapor ACKNOWLEDGMENT Pressure of Fluorocarbons the folloiving three methods n-as found The authors wish to acknowledge the tvork of J. B. Roberts and capahlc. of lowerKilliam Mcnges who designed the reactor and its auxiliary ing the hydrogen content t o less than 0.055. heating apparatus. r o
1. Treating the liquid perfluorocarbon with AgFl a t 240" C.: this method is described in detail in the fourth paper of this series (page 352). 2. Heating the liquid perfluorocarbon with CoF3 a t 275 C. 3. Repassing the perfluorocarbon vapor over CoFs in exactly the manner just described. Table I s h o w the effects of these aftertreatments. The material recovery varied from 87y0 with AgFp at 240" C. to 92% with liquid-phase CoF3a t 275'. I n all cases the hydrogen content was satisfactorily reduced. PHYSICAL PROPERTIES OF PERFLUOROCARBOR S
Figure 5 shon-s the viscosity and vapor pressure of the higher fluorocarbons and their variation with boiling point. T o obtain
LITERATURE CITED
(1) Benner, Benning, Downing, Irwin, Johnson, Linch, Parmelee, and Wirth, IXD.EXG.CHEM..39, 329 ( 1 9 4 7 ) : F o w l e r , Burford, Hamilton, Sweet, Weber, Kasper, and Litant, Ibid., 39, 293 ( 1 9 4 7 ) ; Rosen, -4.C.S meeting, Chicago, 1940. Cady, Grosse, Barber, Burger, and Sheldon, I bid., 39, 290 (1947). (2) Miller, Hunt, Hass, and hIcBee, And. Chem., 19, 140 (1947). PREsn:s.rE:u before the s y l l i p o ~ i u m o n F'luorine Cheiiiistry as pnper 86, Divi>ion of Industrial and Enrineering Chemistry, 110th 3Ieeting of the A ~ r ~ a i r hCIIIENICAL s SOCIETY, Chirago, Ill. T h e work described i n this paper is cox-ered also i n a comprehensire report of work n-itli fluorine and fluorinated cuinpounda undertaken i n connection with the 3 I a n h n t t a n Project. This report is soon to be published :is Volume 1 of Ilivi,ion V I 1 of
t h e M a n h a t t a n Project Technical Series.
(PREPARATION O F CHLOROFLUOROCARBONS)
FUuorinution of petroleum oiUs in liquid phuse with siUver difluoride W. S. Struve, A. F. Benning, F. B. Downing, R. Ti. Lulek, and W. V. Wirth E. I. DU PONT DE NEMOURS & COMPAIVY, IVC., WIL\lIXGTON, DEL.
h 31ETHOD is described for fluorinating petroleum oils in the liquid phase with silver difluoride, using as diluent a fluorocarbon of medium molecular %eight. Yields of 60-70% of theory were obtained. Various properties of the resulting fluorinated product are giFen.
A
T T E V P T S were made to find improved methods of preparing a substantially perfluorinated hydrocarbon oil, since the vapor-phase reaction of hydrocarbon oils with elemental fluorine in the presence of a silver-plated copper catalyst gave only 1525 yo of viscous perfluorinated hydrocarbons boiling in the range 137-220" C. at 10 mm. ( 1 ) . Attention was directed to the liquid-phase reaction of hydrocarbon oils with active fluorine carriers such as cobalt trifluoride
arid silver difluoride. The reaction of cobalt trifluoride n-ith oils is vigorous, sometimes occurring with explosive violence. I t was found, however, that if either the cobalt trifluoride or the hydrocartion oil was diluted with a medium-molecular-wight iiuorocnrtion, fluorination proceeded smoothly to give a yield of 3050"( fluorocarbon, based on the conversion of CH, to CF,. The use of the less vigorous silver difluoride as a fluorinating agent gave even less breakdown of t'hc hydrocarbon during fluorination, and yields as high as 80% were obtained. The following reactions arc involved:
+ Fz *2 1 g F + Clz + Fs +2AgFg + 4AgFz +-CFz- + 4AgF + 2 H F
2AgCl
2.4gF
-CHZ-
(1) ( 2)
(3)
March 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
%DISTILLED Figure 1. Comparison of Boiling Ranges of Starting Hydrocarbons and Fluorinated Product
Only small amounts of breakdown products tvere recovered, and it is believed that the products obtained were of the same carbon chain length as the original hydrocarbons. The procedure consisted in adding the hydrocarbon oil slowly to a mixture of the medium-molecular-weight fluorocarbon, called the "solvent", and silver difluoride a t 180" C. After being hea1cd a t 240' C. for 12 hours, the reaction mass was cooled and thv Huorocarbon mixture extracted v i t h trifluorotrichloroethane. The C?Cl,F, \yas stripped off, and the fluorocarbons were separated by fractionation under 10 mm. pressure, The fraction boiling a t 137-220" C. a t 10 mm. ITas collected. SILVER DIFLUORIDE
The silver difluoride was prepared by reacting silver chloride with elemental fluorine ( 3 ) ,as described in the third paper of this wries (page 3501, or by regeneration of spent carrier rvith fluorinc (finally at 220-240" C.1 t o obtain a silver difluoride content of 95C, or better. The reaction began a t room temperature with the evolution of heat. I n the case of the preparation from silver as chloride, it Iva- necessary t o keep the temperature below SO" long as possible t o avoid partial fusion of a lowmelting ternary mixture of silver chloride, silver fluoride, and silver difluoride. Excessive temperatures a t the end of the activation of the carrier XTith fluorine also had to be avoided since the extremely vigorous reaction of silver difluoride with various metals employed in construction of equipment was likely t o be initiated to give ( I .
353
silver and metal fluorides. Small scale laboratory experiments showed that a mixture of 307,. iron powder in silver difluoride would fire as low as 90' C. with enough vigor t o melt out the bottom of a Parr bomb in which the mixture had been heated. A small horizontal iron reactor with r a l l s 'I4 inch thick, in which 20 pounds of spent silver fluoride were being regenerated with fluorine a t 200" C., n-as heated with several Bunsen burners. A highly exothermic reaction occurred on the side \There the burners were placed which caused part of the reactor to melt. Previous t o this burnout, the reactor had been used under seemingl? idcntical conditions for about thirty charges of silver difluoride with no trouble. The silver difluoride r a s analyzed by reaction with a n excess of silver iodide to form silver fluoride and iodine. The silver fluoride and the excess silver iodide formed a low melting eutectic (2,9),which acted as a liquid reaction medium. This reaction mass \vas dissolved in acidulated po ide solution, and the iodine was titrated with sodium To obtain the desired degree of fluorination of the hydrocarbon a t 220-240" C., it was necessary to use about :t 257, excess of silver difluoride. The spent carrier then had a silver difluoride content of 20-30%, showing that approximately the theoretical amount of fluorine vias taken up in the react'ion n-ith hydrocarbon oils. FLUOKOCIRBON SOLVENT
Although fluorination of hydrocarbons with silver difluoride began below 100 ' C., reasonably complete fluorination required temperatures above 200" C. Therefore it \\-a3 necessary t o use a fluorocarbon solvent n-ith a reflux boiling point above 200" C. The solvent had a boiling range of 180' C. a t 760 mm. to 137' at 10 mm., and was obtained either as a by-product from the vaporphase fluorination of petroleum oils v i t h elemental fluorine or by the vapor-phase reaction of kermene fractions, of approximate over cobalt trifluoride, as described in molecular formula C1&H34, the third papcr of this series (pagc 350). Either 5 parts of solvent or 15-20 parts of solvent per part of hydrocarbon oil proved satisfactory, but intermediate amounts \Yere unsatisfactory because they gave a pasty mixture with the silver difluoride which Jyas difficult to agitate. With 5 parts of solvent the reaction mixture appeared t o be a dry, free-flowing powder; with 20 parts i t appeared to be a thick slurry. The solvent recovery was 9599%. I t was assumed that most of the losses of solvent were mechanical and were not due t o chemical breakdown of the solvent by AgF2. HYDROCARBON FEE11 STOCKS
I
t I
VENT
A study was made of variou. hydrocarbon oils to determine lvhich one would be commercially available and would yield the optimum amount of fluorocarbons in the boiling range 137-220" C. a t 10 mm. It was found that highly naphthenic oils gave the best yields while highly aromatic oils gave considerably poorer yields, as is shown by the following experimental results with using oils of increasing aromaticity:
MI
- - -- - -
-!Irnb I
THERMOCOUPLE
Starting Oil
Crude I-ield ai Fluorocarbon before Distn., c/o
Highly naphthenic oil from Coastal 200 crude Aromatic ext. of Coastal
88
r l_l _ r~ -2nn _ _p_. "e
Ext. of aromatic fraction (more highly aromatic)
49
42
'TRAP I
Figure 2.
Liquid-Phase Reactor
-4commercial product which, by Raterinan analysis, contained 37, aromatic rings, 36y0 naphthenic rings, and 61% paraffinic chains, and had a boiling range of 220-289' C. a t 10 mm. pressure, gave a 65y0 distilled yield of fluorinated product n ith :t
354
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
viscosity of 23-26 centipoises a t 210" F. By fluorination of a 0 4 0 % distillation foreshot of this oil, a product was obtained with a viscosity of 17-19 centipoises a t 210" F. In general, the boiling range of the fluorinated product was approximately 3040 O C. lower at 10 mm. than that of the starting hydrocarbon oil (Figure 1).
Vol. 39, No. 3
into the reactor at a rate of 0.7 kg. per hour, raising the teniperature as necessary when a "flame test" showed that all of t h e fluorine was not being absorbed. Finally when 240" C. was reached, an excess of fluorine was passed through for 4 hours. .4fter cooling to 150" C., the carrier \vas ready for another cycle. LIQUID-PHASE FLUORISATED PRODUCTS
EXTRACTION O F PRODUCT FRO\I SPENT CARRIER
Fluorocarbons of high molecular weight have only limited solubility in the usual organic solvents, such as benzene, alcohol, acetone, or carbon tetrachloride. However, chlorofluorocarbons proved to be excellent solvents to extract the fluorocarbon mass from the spent fluorine carrier. Of the chlorofluorocarbons commercially available in sufficient quantity, 1,1,2-trifluoro-1,2,2trichloroethane, CCLFCCIFt, had a favorable boiling point (47.6" C.) for easy removal from the extract and so was adopted. OPERATING DETAILS
The complete cycle of activation of the fluorine carrier and reaction of the carrier with the hydrocarbon oil could be carried out in one vessel. In larger scale experiments a 12-gallon horizontal steel reactor with an oil jacket and scraping agitation was used as shown in Figure 2. The reactor contained 56.8 kg. (125 pounds) of silver difluoride. 5.4 kg. (12 pounds) of fluorocarbon solvent were added, and the mass was heated to 175" C. Then 1.06 kg. (21/8 pounds) of hydrocarbon oil were pumped into the reactor by means of a metering pump a t 175-190" C. over a 2-3 hour period. Most of the fluorination took place during this addition, as judged by the evolution of hydrogen fluoride. The charge p a s heated a t 240' C. for 12 hours under refluv to complete the reaction. The cooled reaction mass was extracted ne11 with C,CI,F,, the washes being blown from the spent carrier mass through a screened blow leg t o a hot-water-heated atill. The C2C13Fawas distilled off and returned t o a reservoir for re-use. The fluorocarbon solvent was recovered by fractionation through a ten-plate column, and the product boiling a t 137-250" C. (10 mm.) was collected; about 2.45 kg. (5.4 pounds) were obtained. After the product has been completely washed from the reactor with CzClsF3,the reactor was heated to 50-60" C. under slight vacuum t o remove residual C&laF3. Then fluorine was passed
The fluorocarbon mixture a1 obtained was a colorless liquid R-hich, when cold, had the consistency of molasses and was cloudy as a result, of suspended solid fluorocarbons. The solid dissolved a t 50" C. to give a clear liquid. The viscosity varies much more with temperature than is the case with hydrocarbons. For a typical fluorocarbon sample the viscosities are compared t o those of the starting hydrocarbons as follow: HYDROCARBON FLEORITATED PRODVCT Centistokes a t 100" F. Ceiitirtokes a t 210' F. Viscosity index
41.9 5.54
4-65.5
536 9.05
-.674
The fluorinated product decomposed slowly on heating, as shown by the drop in boiling point when a sample was refluxed under 10 mm. pressure a t still temperatures of about 300"C. The product had a density of 2.0 grams per cc. at 20" C. (68" F.) and 1.85 grams a t 210" F. The index of refraction was 1.33-1.35. ACKNOWLEDGMEVT
The authors wish to acknovledge the work done by D. X. Klein in developing the analysis for silver difluoride and to thank F. B. Stilmsr for helpful discussion. LITERATURE CITED
(1) Cady, Grosse, Barber, Burger, and Sheldon, IKD. ENG.CHEM.,39, 290 (1947). (2) Hayek, E., .lfonntsh , 68, 29 (1936). (3) Ruf? a n d Giese. 2. anorg. allgem. Chem., 219, 144 (1934). PRESESTED before the S g m p x i u m on Fluorine Cheniistry as p'iper 87, Division of I n d w t r i s l and Engineering Chemistry, 110th ZIeerina of t h e AMERICASC H E M I C ASOCIETY, L Chicago, Ill. T h e work described i n t h i s paper is corered also in a comprehensive report of work with fluorine and fluorinated compounds undertaken in connection with the Manhattan Project. This report is soon to be published as Volume I of Division TI1 of the Manhattan Projecc Technical Series.
SYNTHESIS OF TETRAFLUOROETHYLENE Pyrolysis of monochlorodifluoromethane J. D. Park', A. F. Benning, F. B. Downing, J. F. Laucius, and R. C. McHarness E. I. DU PONT D E NENOURS & COMPANY, INC., WILMINGTON, DEL.
A
LIPHATIC fluorine compounds have generally been synthesized by utilization of the following types of reaction for introducing fluorine atoms into aliphatic molecules: (a) direct fluorination of saturated or unsaturated compounds with elemental fluorine, ( b ) addition of hydrogen fluoride to olefins and acetylenes, (c) esterification of alcohols n i t h hydrogen fluoride, and ( d ) interaction of organic halides or polyhalides with inorganic fluorides. However, these methods have limited applicability in the preparation of highly fluorinated aliphatic compounds ( 4 ) . This paper reports the synthesis of highly fluorinated organic compounds whereby a fluorochloro aliphatic compound such as monochlorodifluoromethane (CHCIFn) is subjected to heat until 1
Present addresa, University of Colorado, Boulder, Colo.
a noncatalytic pyrolysis takes place and results in the formation of various aliphatic fluorine compounds. One of these compounds is tetrafliioroethylene, a reactive gas obtained in excellent yields when the pyrolysis is carried out under controlled conditions. As a preparative method for tetrafluoroethglene, this pyrolysis is superior to any of the methods previously described in the literature ( 6 , 9, 1 2 ) . This paper also describes the preparation of an unusual homologous series of compounds starting from II(CFd&I t o H(CF2)IdCl with boiling points ranging from -10" t o +228" C. It is of interest t o note that no evidence of isomeric branched-chain compounds was found in the pyrolysis mixture. A number of cyclic perfluorinated compounds, CIFE ( S ) , CIFP,ClFb ( I ) , CjF,,
.
