PiUot plant preparution of
POLYCHLOROPOLYFLUOROHEPTANE J. H . Babcock, W. S. Beanblossom, and B. H. Wojcik HOOKER ELECTROCHE\IICAL CO\IPANY, NIAG-IRA F A L L S , Iv. Y.
A SIJIPEIFIEI) and improved method for the production of a highly fluorinated polychloropolyfluoroheptene, suitable for conversion to a satisfactory product by treatment with AgFl or CoF,, has been developed through the pilot plant stage. A proposed flow diagram for commercial production is established.
Figure 1.
chlorine was dissolved, with little if any reaction taking place. K h e n the reaction finally started it mas so energetic and evolved so much heat that it was impossible to maintain the temperature below 35' C. This led to small explosions or burning with the deposition of carbon, which interfered with subsequent chlorination because of poor light distribution. This induction period was probably due to dissolved oxygen in the heptane; it was overcome by bubbling carbon dioxide through the liquid before the start of chlorination in order to displace the oxygen. However, even when this was done, small explosions occurred occasionally, and it proved desirable t o dilute the chlorine with carbon dioxide during the first 8 or 10 hours of the 144 hours needed to complete the chlorination. Later it was learned that, the carbon dioxide could be replaced Lvith anhydrous hydrogen chloride, a by-product of the reaction. During the early stages of this reaction the rate of chlorination was governed by the rate a t which heat could be removed in order to maintain the desired temperature. Horvever, as chlorination progressed, the reaction became sluggish and less efficient in the utilization of chlorine. This sluggishness first began to be apparent a t a specific gravity
C7HZCI, Characteristics 0 -
1.800
I
N T H E pilot plant development of this process, the basic principles of which were discussed in a previous paper', several problems were encountered. Previous viorkl had shown that, nheptane could be chlorinated to an average of 12 atoms of chlorine per mole (83-84y0 Cl?) by passing chlorine into liquid
1.600
heptane illuminated by a strong light:
+ Cl? light ---+ C7H4C112 + HC1 SbCl CiHIF&16 + HCI C,H4Clla + HF CrH4FeCld + SbFs CiHd?loCl? + Sb salts C7Hii
--f
1.400
I I
LEGEND
. 1.200
(2)
0 PR I
(31
4
T h e t,emperature was kept below 35' C. until the gravity reached approximately 1.0; after that it was allowed to rise slowly t o 110" C. a t the end of the chlorination. which was considered complete a t a gravity of 1.830 at, 20' C. Figure 1 s h o w per cent chlorine plotted against specific gravity and atoms of chlorine per mole of chloroheptane. However, when the chlorination of heptane was attempted in a 12-liter flask under conditione considered suitable for plant production, an induction period \vas encountered during ahich 1
2
(1)
'
I 314
-
,800
1
.600 20
Figure 2.
MaBee, E. T . , and associates, unpublished work.
N O R M A L R U N , A T M O S P H E R I C PRESSURE P R 2 ABNORMAL R U N , *' P R 7 NORMAL RUN, 35 P.S.I.
60
CHLORINATION TIME (HOURS)
100
140
ieo
I 220
Effect of Variables on Rate of Chlorination
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1947
315
WATER
Figure 4. Degree of Fluorination Plotted against dmount of .4ntimony Pentachloride Used a
of approximately 1.500 (6 atoms of chlorine per mole) and, by the time 0 atoms of chlorine had been introduced, it -ivas very pronounced, although it xas possible t o continue t o a point where 12 atoms of hydrogen had been replaced. .Ittempts to utilize material of lo-iver chlorine coiittbnt, which could be made without undue difficulties, were unsuccessful, and ways of improving the chlorination were sought. Higher temperatures were tried, but, those appreciably above 110' C. led to carboncarbon fission, with the resultant formittion of hexachloroethane and other undesirable compounds of low molecular weight. Upon conversion to the highly fluorinated derivatives these produced lov- boiling compounds which were unsatisfactory for the intended use. Various cat,alysts were also tried, including ferric chloride, antimony trichloride, iodine, benzoyl peroxide, pelargonj-1 peroxide, and antimony pentafluoride, hut none of these had any appreciable effect on either the degree of chlorinat,ion, the speed of reaction, or chlorine efficiencj-.
RUB0ER
RING
I
Figure 3.
Chlorinator
Figure 5 . Refractive Index of F1 u o r o c h 1 o r o h e p t a n e Plotted against Chlorine Content
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 39, No. 3
allowed to rise about 30" C. per day. After 40 hours a pressure of 35 pounds per square inch was applied by partially closing the valve in the exit line. After 72 hours the specific gravity had reached 1.732 (approximately 9.5 atoms of Cld, and heat had to be applied t o maintain a temperature of 90" C. Chlorination LEGEND ' Fas continued to a gravity of 1.837, Is' USE OF Sb SALTS xvhich was reached a t the end of 120 _ - - - - 2''USE _ OF SALTS - -JRDUSE OF SALTS hours, the final temperature being 115' C. -THEORETICAL REPLACEThe finished product had a chlorine conWENT OF CL BY HF tent of 83.6%. ORETICAL H F * GI2 ADDED The n-heptane used in this investiga0 DISTILLATION STARTED 12 C1 INTRODUCED TO REPLACE tion was high grade material (99.5+ 7 ; ~ 20 40 60 eo IO0 I20 140 160 180 obtained from Westvaco Chlorine ProdI I I I I I ucts Corporation. Later, when it. tieFigure 6. Effect of Chlorination and Hydrogen Fluoride Efficit,nc*.i o i l Catalyst Activitycame evident that the necessary amount would not be available from this source, rb-heI)tirne from petroleum x a s investigated. A 987; grade ~ I I ll'hen chlorination was attempted in a 150-gallon unit, it \>:\, tained from Pliillips Petroleum Company proved siLtidactory, found that the 144 hours necessary to complete a run in thc. but the 95TGgrade, although usable, was less desirable. laboratory xere extended to 200 hours under normal conditions, Several improvements over the original proposed process ~ w r e and in one case it was impossible to reach the desired degree of also made during this investigation in the fluorination stcps. chlorinatiun (S3-S4Y0 C1,) even though the reaction continued Since the nature of the product obtained in step 2 had a profound for 240 hours. It n-as therefore apparent that some improveinfluence on the subsequent steps, affecting not only the over-all ment n-ould have to be made if this process xas t o be pracyield but also the consumpt,ion of such critical materials as SbFj tical. Chlorination under a pressure of 35-40 pounds per square and .SgF2 or CoFa, a real effort was made to replace as much inch, nhich had been used on other processes, \ m s tried and chlorine as possible Kith fluorine from hydrogen fluoride. Thereproved highly successful: it reduced the chlorination time to fore, the effect of the rate of hydrogen fluoride addit,ion, the 120 hours under normal conditions and to 168 hours under amount of antimony pentachloridc used, variations in tempcraabnornial conditions. Sornial conditions riLfer to a continuous ture and pressure, and the re-use of the antimony salts were chlorination from start to finish; abnormal conditions are those carefully studied. where, for some reason, the chlorination had to be interrupted. \Then attempts were made to use a chloroheptane containing After such an interruption, especially if it occurred after the chloonly 78p0 chlorine, it as noted that polymerization occurred rination had become sluggish, the reaction was difficult to start lyhich gave rise to undesirable tars and residues. It n w thought again and proceeded at a don-er rate than that prior to such interthat this might be due to the large amount of antimony pentaruption. Figure 2 illustrates the progress of typical runs under chloride present and that it might be reduced by a sloiv addition varying conditions. The curves representing abnormal condiof this salt during t,he course of the reaction, rather than b y adtlitions have been extended a short distance as dotted lines hefore tion of the clntire amount a t the start, of the reaction. This slow and after the interruption took place, t o s h o a this break. These addition, by providing for the presence of fresh antimony pentacurves show that chlorination did not proceed at an equal rate in chloride throughout the reaction, might also lead to a higher all runs. This n-as due to unequal addition of chlorine during degree of fluorination. This was tried, but no particular differthe early stages of the runs, the rate being dependent on the ence could be noted in either the amount of polymerization or cooling capacity. However, after the rate of cooling was no the degree of fluorination, regardless of the chlorine content of longer the limiting factor, the rate of chlorine addition was apthe chloroheptane used-that is, 78 to 8370. proximately the same for all runs; the effect of pressure can best be judged by comparing the time necessary to complete the chlorination after attaining a specific gravity of 1.600. The sluggishness following an interruption in chlorination was probably due to dissipation of any existing free radicals during the stoppage and a break of the chain mechanism upon which this reaction is believed t o depend. The 150-gallon unit used in this investigation is shown in Figure 3. n-Heptane (260 pounds) was charged into this enamel vessel provided with a brine-filled cooling jacket, two glass light wells each carrying a 1200-watt Gviarc lamp, chlorine and hydrogen chloride inlet line, thermometer well, brine-cooled rcRus condenser, and other accessories. Anhydrous hydrogen chloride xvas bubbled through a t a rate of approximately 15 pounds per hour for 10 minutes n i t h the temperature a t 20" C. An equal amount of chlorine was then admit,ted, being mixed with the hydrogen chloride outside the reactor and entering the heptane through the same inlet. The rate of addition was dependI ent on the ability to keep the temperature below 35' C. by use of the cooling jacket. Chlorination started immediately and % BY V O L U M E 0: CHARGE 1 , 1 proceeded smoothly. At the end of 16 hours the hydrogen 50 20 30 40 chloride was shut off and chlorination continued at a n increased F i g u r e 7. Rectification of Step-2 3Iaterial rate of approximately 35 pounds per hour, the temperature being
T-,l--.i --
-- I
1
March 1947 WATER I
-
c
3" C O L U M N
HF
t-g
EXIT
I
I
1
I
THERMOMETER WELL RECEIVER
L
NICKEL
311
INDUSTRIAL AND ENGINEERING CHEMISTRY
REACTOR
Figure 8.
Hydrofluorination Reactor
Varying the reaction temperature from 40-160" C. had little effect on the degree of fluorination. At the higher temperatures yields were slightly lower, probably because of losses through the exit system, and some difficulty due to sublimation of antimony pentachloride was also encountered. The use of superatmospheric pressures, up to 1600 pounds per square inch, shoxed a slight improvement, but this line of attack was abandoned in favor of other improvements. I n the original experiments carried out a t Purdue Cniversity, 30-40Yc of antimony pentachloride based on the weight of chloroheptane had been used, and a product obtained containing from 30 to 53% of chlorine and 25 to 28% of fluorine, which corresponds to a n average composition of C,H4F6Cls. By varying the amount of antimony pentachloride used from 20 t o 150% in a series of experiments in which other variables were kept constant, it was shown that the use of larger amounts of antimony pentachloride led to a higher degree of fluorination. The maximum input of fluorine, corresponding to 7 atoms per mole of heptane (45% residual chlorinej %-as obtained n-hen equal weights of antimony pentachloride and chloroheptane were employed (Figure 4 and Table I, -4 and B ) . During the course of this investigation it n-as noted that a definite relation existed between the refractive index and the chlorine content of t'he chlorofluoroheptanes; based on a number of actual analyses, a curve was dra\m shom-ing this relation (Figure 5 ) . This curve proved accurate to within 1% of the actual chlorine content of a sample and was used thereafter as a quick means of determining the approximate degree of fluorination. Since i t had been shown that a large amount of antimony pentachloride was desirable, it was necessary to find some way of re-using it, if possible. -it first antimony pentachloride appeared t o act merely as a catalyst, but later we felt that it actually reacted with the hydrogen fluoride t o form a pentavalent antimony
fluorochloride, n-hich in turn acted as the fluorinating agent. In SO doing, it was reduced to the inactive trivalent state, and attempts to re-use it Tere unsuccessful. We found, however, that, if these salts were reoxidixcd to the pentavalent form by treatment with chlorine, they were reactivated and could be used repeatedly (Table I C). The exact estent to which these salt's could be re-used was not ascertained, but they were shown to be active after the fdth reuse. However, it was necessary to add about 10% of fresh antimony pentachloride with each reuse in order t o make up the losses entailed by separation of organic product. During the study it was noted that the spent salts,after activation with chlorine were more active fluorinating agents than fresh antimony pentachloride (Figure 6). Thus it seemed logical to suppose that these salts might be kept a t a high degree of activity if chlorine viere added simultaneously with hydrogen fluoride during the fluorination process. The simultaneous introduction of chlorine and hydrogen fluoride presented serious mechanical difficulties, but intermittent introduction proved highly successful (Figure 6 and Table I D ) . This observation concerning the unusual activity of the reactivated salts resembling antimony pentafluoride in some respects also led to another improvement. Step 3 of the original Purdue process consisted of treating step-2 material with antimony pentafluoride under conditions which provided for the removal of the more highly fluorinated material from the reaction zone by distillation; consequently it seemed possible that a similar effect might be obtained by distilling the step-2 product from the reaction mixture. Results obtained when this was done are shown in Figure 6 and Table I D. This gave a product containing 2426% residual chlorine, which corresponds to a n average composition of C,H4F0.bC12.S. Work done a t Purdue had shown that a polychloropolyfluoroheptane having a boiling range of 70-130' C. and a n average composition of C,H4FlU.6C11.6 could be converted t o a satisfactory product by treatment with AgF2. A rectification curve (Figure 7), obtained on distilling a sample of the step-2 material, showed that 46% distilled within this range. It n'as also shown that, the material boiling above 130" C. could be recycled without difficulty. It was t,hus possible to eliminate entirely step 3 of the original process. As additional information vias accumulated on the nature of the improved step-2 material, the presence of unsaturates in the
TABLE I. EXPERIMEST.4L DATAFOR R E A C T ~ O 2"N purpose Reaction Conditions of HF, of Temp., SbCls, Expt.b theory C. % bywt. 20 A 200 85-100 40 A 200 92-100 100 A 215 90-100 150 A 210 70-87
Clr
Reaction Product Sp. gr. Yield,
63 55 45 46
1.758 1.739 1.733 1.729
1.4981 1.4710 1.4374 1.4420
80 84 81 69
% ' a t 20' C.
ng
%
B
168 238
75-90 65-90
100 100
46
1.721 1.720
1.4405 1.4330
66
44
C
238 167 230 205
70-80 65-85 50-80 6.5-70
100
45 48 60 44
1.716 1.723 1.750 1.728
1.4345 1,4470 1.4895 1,4360
68 91
D
110 181
100
...
...
187 340
...
55 46 26
D-T
40-60 40-70 70-2OOC 40-60 40-50 55-18OC
10
...
?jl 60
R
c-1 c-2 C-r
...
...
., ..
, ,
24
1:iQz
...
1:jO4
72
k0
.... .. 1:iiio ii.6 .... . . ....
1.3660
Si.5
a Chloroheptane used came from a single pilot plant batch, conrained 83.4% Clt and had a specific gravity of 1.832 a t 20' C. b A , exGeriments carried o u t t o show effect of varying quantity of SbClrnickel reactor. B . reaction performed in aluminum reactor'. C, expenments in aluminum reactor t o determine possibility of re-using spent salte without reactivation: C-1 first re-use, C-2 second re-use, C-r spent salts reactivated with chlorine. D , reaction performed in nickel reactor: salta reactivated with C h before addin,g second increment of HF. D-r, spent salts from D re-used, reactivated w t h Clr before any H F was passed through batch ,and also after first portion of H F had been added. e Distillation temperature.
318
INDUSTRIAL AND ENGINEERING CHEMISTRY ct.2 .
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Vol. 39, No. 3 VENT-
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Figure 9.
I
1
t
Flow- Sheet for 100-Gallon-per-Day Plant
thc spent salts. A h h y d r o u shydrogen fluoride (31 pour~cfh'l w m mixture was established, and it became apparent that the ~"111closer t o c ~ F I ~ F ~ than ~ ,t~ o Pc ,~H~~ .F ~ ~ ~ , ~ l-l1is c ~ , , ~ , then passed through the reaction mixture in 17 hour^ \\-ith the position C. The residual chlorine content of the temperature at 4Or7!" v a s also an improverllent since it meant that less .\gF? or CoFt ss,sc,at the end of this period. ~ ~ h l ~ ~ , . i ~ ~ ~ llaloheptane would be required in thc following step. then passed through the mixture for about 5 hours a t a rate of 2 per hour. This was folloxed by a second treatment with The final procedure for the fluorination of p ~ ~ y c ~ l ~ o r o ] l e p t a npounds c 23 pounds of hydrogen fluoride, which reduced the chlorine t o follows (Figure 8) : 4BC,. The product was then distilled from the rractor up to a teniperature of 200" c. and, after washing and drying, gave a Polychloroheptane (60 pounds) and antimony pentachloride vield of 87.0f'> of a polychloropolgfluoroheptene havlng an aver(6 pounds) )yere added to approximately 54 pounds of spent antiage composition of C;iHpFg.Xl?.5. Upon fractionation this gave many salts contained in & 10-ga]]on nicliel vessel provided --ith an 2-3% Of low boiling material, 45yc of product' suitahle for treatoil jacket, inlet line for chlorine and hydrogen fluoride, a paddlement with iigFa or C;oFz, and 52% of material f o r recycling. type agitator, thermometer, and a Lvater-cooled reflux condenser backed by a brine condenser. After the temperature had been Figure 0 is a proposed f l o diagram ~ for a plant c a p a i k of makraised to 50-TOo c., chlorine \Tas passed through the mixture ing 100 gallons (1500 pounds) of material per day. The c h b at the rate of 3 pounds per hour for 5 hours in order to reoxidiae
March 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
rination, carried out in vessels connected in series of three, would have several advantages-for example, (a)more efficient utilization of chlorine, ( b ) automatic provision for a supply of mixed chlorine-hydrogen chloride gas needed in the early stages of the chlorination, and (c) elimination of the need for brine cooling on two thirds of the vessels. 4CKNOWLEDGMENT
The authors express their thanks to Raphael Rosen of the Office of Scientific Research and Devclopnrc,nt and to the Manhattan
319
District, U. S. Army Corps of Engineers, who helped in the guidance of this investigation and whose financial support) made it possible. The authors also wish to thank E. T. McBec. and associates a t Purdue University for mauy helpful suggestions. before t h e Symposium on Fluorine C h e m i s t r y its p a p e r 7 4 , Division of I n d u s t r i a l a n d Engineering C h e m i s t r y , 110th Meeting of AJIEHICN CHKMIC.AL SOCIETY, Chicago, Ill. T h e work described in this paper is coiered also in a comprehensive report of work with fluorine and fluorinated compounds undertaken in connection a i t h the hIanliattan Project. This report is soon t o be published as Volume I of Division V I 1 of the 1 I a n h a t t a n Project Technical Series. PnEqENTED
PILOT PLANT SYNTHESES Perfluoro-n-heptane, perfluorotlimeth~lc~clolmexane, and high boiling fluorocarbon oils W.B. Burford 111, R . D. Fowler. J. 31. Hamilton. Jr.*. H. C. -Anderson?.C. E. Weber3, and R . G. Sweet4 T H E J O H N S HOPItIhS U N I V E R S I T Y , B i L T I \ I O R E . \ID.
THE design, construction, and operation of a pilot plant for the production of perfluorocarbons b?;the CoFt process is described in detail. The process consists of passing \aporized hydrocarbon oyer CoF3 poi+der at suitable teinperatures, after which the resulting CoF, is regenerated with elenientary fluorine. The reactors, fluorine cells, disposal system, and recovery systems are described i n detail, and t?-pical operating characteristics are outlined. A flow sheet shows schematically the interconnection of the various units. A brief description is included of the ventilation system for the plant, operating personnel required to r u n it, and normal output. Physical properties of some typical perfluorocarbons produced by the unit are included.
H E S it became evident that perfluorocarbons could be made readily by the CoFz process developed by Fowler and co-workers (3) or by the direct fluorination proces? of Grosse, Cady, and co-workers ( I ) , the demand for experiniental scale production became very great. A pilot plant K : L ~therefore set up a t ,Johns Hopkiris to produce materials ranging in hoiling point from that of perfluoro-n-butane (ahout - 2 " C.) to that of an oil boiling over 350" C. Development of pilot plant scale equipment ~va; undertaken before the laboratory inrestigntion ivaq conipletetl. and thiq fact, together n-ith the novelty of the CoF3 process. deiiianded design on the basis of very limited infornration. mthesis of perfluorocarbons is a tn-o-step cyclic procpss:
+
~ C O F ? F? +2CoF3 -CH2-
+ 4CoF3 --+ -CFZ-
+ 2HF + 4CoF2
I n addition to substitution of hydrogen in -CH2-CoF3 will also add fluorine to multiple bonds:
CaH6 $- 18CoFa ---+ GFi2 1 Present ton, Del. 2 Present * Present 6 Present
(1)
(2)
groups, the
+ 6HF + 18CoFz
address, E. I . d u P o u t de S e m o u r s & Company, Inc., Wilmingaddress, Socony-Vacuum Oil Company, Paulshoro, N. J. address, General Electric Company, Schenectady, N. Y . address, Linde Air Products. Tonawanda. X. Y .
T o adapt such a two-step cycle to a continuous operation, the time periods for each step of the cycle must be approxim:ttely q u a l . Since the heat evolution governs the feed rate of fluorine in the first cycle and of hydrocarbons in the second, and since it has been shown (3)that the heats of reaction of the two step- :ire about equttl, it should be possihle t o carry out each step in a h o u t the same length of time. In practice this vvas verified. B further requirement for continuous routine opcrntion n-a.: that the necessary inert gas sweeps (which followed earh htep, for the purpose of removing excess fluorine in step OIIP and hytlrogen fluoride and product, in step tvio) fit into a vmrkatil~tinir srhedd e . The sn-eeping period could also be utilized for tenipernture adjustment, since each step was carried out under tlifferent temperature conditions. .I sn-eeping time equal to 11:df the time required for either step \\-as found suitahle, -inre it permitted easy siniulta~ieous temperat,ure adjustment. Generally two hours were needed for each step, n.ith n one-hour pei,iod of sr\-eeping folloiving each step. It was therefore nossible to
