S t o r a g e o f fluorine in
PRESSURE CYLINDERS Homer F. Priest and Aristid V. Grosse' W 4 R R E S E A R C H LABORATORIES, COLL.1IBIA LYIVERSITY, \ E W I O R K , 1. \
IS NOVEAIRER 19t1, a Dennis-type fluorine production cell was used in certain work where i t was desirable to have fluorine available a t all times a t each of seteral locations, an impractical situation with a single electrolysis cell. Therefore i t was decided to store the gas a t elevated pressures (150 to 300 pounds per square inch) in proper cylinders. Pressure was developed by condensing t h e outp u t of the fluorine cell in a calibrated glass trap with liquid nitrogen as coolant and heliumas buffer gas; then theliquid
was transferred to a nietal trap by distillation, from which i t was allowed to expand to a 3-liter copper spherical bulb. After set era1 trials 2-liter copper cylinders were built. Later a complete standard trapping and expansion system was built to compress larger quantities of fluorine by means of a bellows type pump in 3-, 5 ,and 12-liter copper and nickel cylinders. A film of fluoride protects these metals from attack by fluorine. Even after a pear of use, such a cylinder shows no sign of corrosion.
F
fact that some metals, particularly copper and nickel, are quite resistant to the corrosive action of elementary fluorine, as shown from their behavior in the electrolytic celi. This was evidently due to a protective film of fluorides. T h e question was whether this film would be a sufficient protection under pressure and for how long. Figure 1 shows the first experimental setup. Its purpose was to trap a known volume of liquid fluorine and t o expand it into a storage vessel. A spherical copper storage vessel having a volume of 2875 cc. was fitted with a copper trap and valve system having a volume of 28 cc. The procedure was as follom: Fluorine, which was generated in a Dennis-type high-temperature electrolysis cell, was passed through a sodium fluoride tube to remove hydrogen fluoride, then through a trap immersed in dry ice followed by one in liquid oxygen, and finally through a coppcr glass seal to a glass trap immersed in liquid nitrogen. To prevent condensation of air in the liquid nitrogen trap, helium was used as a buffer
LUORISE is the most reactive chemical substance known and has for a long time withstood attempts to store it. Since the time of H. Moissan, it was customary t o use i t up as it was produced. A literature search failed to show any description of successful storage of fluorine under pressure similar to other gasesz. One of us became interested in the problem of storing fluorine in 1931 and 1932 when, jointly with P. Kronenberg, the volatile fluorides of uranium ( 2 ) , columbium, and tantalum were prepared for Aston's mass spectrographic study of the isotopic composition of these elements (1). This n-ork, performed in Germany, was intcrrupted by departure to this country. It was resumed in the fall of 1941 when we became seriously interested in various phases of the chemistry of elementary fluorine. The advantages of being able t o use fluorine a t any time, either under pressure or in a vacuum, were obvious and stimulated our work. The starting point of our attempts was the well-established
p
VACUUM
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SPHERE
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FLUORINE CELL
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NANOMETER-
HEL.IUM 1
LIQUID N I T R O G E N TRAP
Figure 1.
* Present address, H o u d r y Process Corporation, I f a r c u s Hook, P a . 2 >Ye are indebted t o Paul Gross, of Duke University, for bringing to our notice, a t t h e time this symposium was presented, i i paper b y H . v. \!-artenberg [ Z a n o r g . Chem., 242, 406, 408 (1939)l on AgF,. Reference is made t o a "fluorine bomb" from the I. G . Farbenindustrie's Leverkusen plant. T h e bonib contained 7 6 % fluorine, 1 7 5 nitrogen. and 8% oxygen. A t the symposium i t was reported t h a t our technical intelligence teams had just brought hack information from German? on fluorine storage i n high pressure cylinders. Gross further informs us t h a t O s t Rasson's "Lehrbuch der chemischen Technologie" (22nd ed., p. 293, AIas Jhnecke Verlagsbuchhandluny, 1941) states t h a t "anhydrous hydrogen fluoride as well as elementary fluorine (h.p., -188' C.) have recently become available in pressure cylinders;" , . Our failure t o notice these references is due t o t h e fact t h a t they occurred only in the body of a paper on another subject.
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LIQUID OXYGEN TRAP
TRAP
First Apparatus for Testing Storage of Fluorine under Pressure
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INDUSTRIAL AND ENGINEERING CHEMISTRY
280
TRAP IMMERSED IN L i a u i o O X Y G E N
I N O P E N TUBE
Figure 2.
NITROGEN
Setup Using Copper Trap for Condensing Fluorine
gas. Thc glass trap was calibrated at 5, 10, arid 13 nil., and previous calculations had shown t h a t 8 nil. (8.0 grams1 of liquid fluorine would produce a pressure of 2 atmospheres i n thr spherical copper vessel. Accordingly, in the first run 11 nil. of liquid fluorine were collected in the glass trap. The liquid fluorine was a dark orange-yellow color and was slightly cloudy. The glass trap was disconnected from the generator and connected t o the spherical copper vessel and trap system, all of which had been evacuated. The valve was then opened, the copper trap imniersed in liquid nitrogen, and the glass trap allowed t o 'ivarm up, during which time all of the fluorine transferred to tlie copper trap. The copper systrni was then disconnected from the glass, placed in a box a s protection in case of reaction, and allowed t o warm u p to room tcmperature. The first experiment was not encouraging. There was rapid reaction with the wills of the storage sphere which became hot while held in tlie hands. Internal examination of the sphere showed that its i ~ a l l swere not pure copper hut coated n-ith some white metal, probably soft solder which reacted Irith the fluorine. Hoirevcr, success came when a fresh, clean copper sphere was used. Two cylinders were then made of copper tubing, 18 inches long and about 2 inches in diameter, with spheric21 heads and fitted Tvith a Kerotest-diaphragm packless valve, having a n inner diaphragm of copper and a copper sest. The fluorine generator was run for 2 hours and the fluorinc. condensed directly in a copper trap, using the apparatus ahown in Figure 2. The helium buffer system as previously described was also used in this condensation, and from previous s t u d i e of cell efficiencies i t would appear t h a t 12 ml. (13.3 grams) of liquid fluorine should have condensed in this operation. This copper trap was then connected t o the fluorine cylinder, the liquid fluorine alloived t o evaporate, the cylinder valve closed, and the t r a p removed. T h e calculated pressure in the cylinder as about 13 atmospheres, but no gage was included in this prelirninai up to determine the actual pressure. The gas under storage was analyzed by gently shaking a satnplc from time t o time in a mercury buret and thus ahsorhing all the fluorine. T h e residual gas was analyzed in 1-r graph. The best storage samples contained over R3vc fluorine, the residual gas being mainly helium. There !vas no evidence of any reaction of the fluorine with the walls of the storage cylinders, and by the end of December 1941 we \vere convinced t h a t fluorine could be successfully stored a t room temperature under moderate pressures. Shortly after, larger nickel cylinders of 3-, 5-, and 12-liter capacity were built on the same pattern, and larger amounts of fluorine were stored u p t o pressures of 20 atmospheres. On opening these cylinders, after a year of use, no corrosion
Vol. 39, No. 3 was noticed. The inside of the copper or nickel cylinders w r e covered with a thin uniform film of copper or, r e s p e c t i v c > l y , nickel f 1 u o r i d e s, \v h i c h evidcntl!- acted as protective coatings. The valves xvere also opc'rating after weeks of scrvicc and shoivctl no signs of failure. At ti later date, a special bcl1on.stype pump \\-as built to pump fiuorine a t fairly low pressures up t o a few atmospheres. I t ivas used successfully to compress the gas into cylinders.
ACK\OK LEDGXlENT
Acknon-ledgment is due R. L. Fox and A . help in our oarlv euperiments.
S.Iienyon
for their
LITER i T L r R E C I T E D
(1) .%ston,E'. IT., S u t u r e . 128, 7 2 5 (1931); 130,130 (1932). ( 2 ) Grossc, .A. V., 2 . a n o r 0 . Chejn., 204, 1 3 - 1 4 (1'382). before the Symposiuin on Fluorine Chemistry as gaiier 3 5 , Division of Industrial and Engineering Chemistry, 110th AIpeting of the A M E R I L A YC H E X I C ~SocIt;rr, L Chicago, Ill. PRzsnrED
COURTESY HOOKER ELECTROCHEMICAL COMPANY
Kneader for Polyperfluorovinyl Chloride Lubricant Stabilization
