IndustriaU handling of
FLUORINE
Ralph Landau1 and R. Rosen* THE KELLEX CORPORATION, 233 BROADWAY, S E U YORK, N. Y .
RECEUT del elopmeiits in the industrial handling of fluorine are described. The unusual physical and chemical properties of fluorine, the most reactive of all elements, i n 1886 ( 5 ) , b u t n o are summarized aiid tabulated. Its ph?siological properties and the use of protective large scale use for this gas clothing are discussed. Tables of corrosion data at low and high temperatures are predeveloped. Moreover, pubsented and reviewed; these indicate that nickel, &Ionel,aluminum, and magnesium, l i s h e d i n f o r m a t i o n on its among the metals, are excellent, but that few other materials except metal fluorides in properties and methods of their highest valence state are nonreactive with fluorine. However, inhibited reactions handling is scanty. I n the past few years some comsometimes occur. Piping, valves, instruments, compressors, and other equipment for mercisl applications for fluofluorine must be selected with care for safe and economical handling, particularly at rine have been developed, high pressure. Some successful industrial applications are summarized. Storage of and experience has accumucompressed gas is feasible if properly protected. Safety precautions for the handling of lated in handling it. This this pas are outlined. and some successful methods for disposal of waste fluorine are should be of assistance in reviewed. planning new applications for this element. The presCORROSIVE PROPERTIES OF FLUORINE ent paper gives a brief survey of some of the properties of fluorine and recent developments on handling it in laboratory Tables I1 and 111 give illustrative data on the reactivity of and plant; much of the information is the result of work fluorine mith a number of materials. I n amplification of these done by Hooker Electrochemical Company, The Harshaw data, the folloiving comments are significant: Chemical Company, E. I. du Pont de Semours & Company, Inc., The Johns Hopkins Vniversity, and Columbia University, but by RE.%CTIOS O F FLUORIXE WITH METALS. For corrosion resistand large the paper is w i t t e n on the basis of The Kellex Corpora:tiice to fluorine at low and high temperat,ures, nickel and Monel tion's experience in handling fluorine, both on a laboratory and have excellent properties; aluminum and magnesium are also good. Iron and steel are much poorer, particularly a t high templant scale. peratures (900" F, and above). The resistance of nickel and hIonel is due to the protective nature of the nickel fluoride film, PHYSICAL AUD CI%E\IIC.ALPROPERTIES which is adherent and invisible rather than green and polvdery, as is the case for iron fluoride. Fluorine is the most reactive chemical element, n-ith a potential FLUORIXE FLAMES. Combustion of materials in fluorine USUally gives a flame of white hot intensity, similar to that from an of -2.85 volts (4). At normal temperatures it {rould be exosyacetylene torch. Fluorine under high pressure, xhen sudpected to follow the perfect gas laws with small deviation, and denly released under conditions such that it reacts v i t h adjacent this has been confirmed by one of the authors through measurematerials or water vapor, gives a flame like that of a high-current ments on its f l o characteristics ~ under plant conditions. The gas electrical flare. is colorless in dilute concentrations but has a definite greenish IXHIBITED REACTIOKS.Some of the reaction$ of fluorine are frequently characterized by errat,ic rates. Thus, generally, cast, more yelloiv then the corresponding color of chlorine, in more fluorine reacts vigorously with water, either in the form of n vaconcentrated quantities. I t has a pronounced odor nhich can be por or liquid, to form hydrofluoric acid and oxygen, but unexdetected in concentrations of only a few parts per million, the plained inhibition has frequently been observed, so that quantiodor being different from chlorine and very characteristic and ties of Ivater vapor may accumulate in the presence of fluorine until the reaction is suddenly initiated with explosive violcnce. unpleasant. It can be compared to a relatively strong ozone Some inhibition has been noted in reaction with organic matter, odor, with some evidence of a chlorinelike smell. particularly with fluoiine a t pressures around atmospheric. Its extreme reactivity is shown by the fact that it combines Frequently, reaction ivit'h metals EFFECT OF IMPURITIES. with virtually every material under suitable conditions and with and even some organic material, such as rubber or cloth, may be very limited irhen the materials are clean, but if a spot of grease or rnost materials spontaneously a t room temperature. S o organic other organic material is present, firing may result in the presence material is completely resistant to fluorine except carbon tetraof pure fluorine. To establish the nature of these reactions more fluoride n-hich is the thermodynamically stable end product of the quantitatively, a series of experiments was run, under controlled reaction of fluorine and carbon. Fluorine also reacts with most conditions, with various types of materials. Figure 1 s h o w the layout, and Tables IV and V summarize the results. The experiinorganic materials, except the inert gases and the metal fluorides ments were run under two dLfferent conditions, one with pure in their highest valence state. The reaction n-ith most metals is fluorine, the other n-ith a mixture containing 20% fluorine in nicomparatively s l o ~a t room temperatures, but the reaction is trogen, a t varying pressures (mostly a t 50 pounds). These revigorous at sufficiently elevated temperatures and is usually selfsults indicate that dilute fluorine has substant,ially different properties from those of pure fluorine, and the precautions required sustaining. The extent of the reaction is determined by the in the former case need not be so rigid as in the latter. temperature, time, concentration, and amount of fluorine. Thermodynamic calculations show that the heat of reaction PHYSIOLOGICAL PROPERTIES for reactions in which fluorine participates is much greater than the heat of reaction with chlorine or oxygen. I n comparing This discussion is limited to the exposure 1.0 concentratrd and typical reactions (Table I), the difference in the valence between relatively large amounts of fluorine. The effects of prolonged oxygen and fluorine must be considered; in these rases the heats exposure to small amounts of fluorine or fluoride ion on animal of reaction are presented in two ways. metabolism are being studied by the Medical Department of the Manhattan District. The accepted tolerance level for hydro1 Present address, Scientific Design Company, I n c . , K e w York, S Y. fluoric acid is 3 parts per million, but as yet 110 tolerance level has 2 Present address, Standard Oil Development Company, N e w York, N. Y.
LUORISE was isolated
I
281
282
INDUSTRIAL AND ENGINEERING CHEMISTRY PRESSURE GAUGES
been set for fluorine even though extensive experimentation has been carried out. Theoretically, a blast of fluorine on the exposed skin should result in a thermal burn caused by the heat of reaction of fluorine with the skin and the water in air. This type of burn is similar to t h a t caused by a n oxyacetylene flame and should be treated as any combination chemical and thermal burn. The few burns t'hat have occurred in operations have actually been chemical and closely resembled those due to hydrofluoric acid. After contact with fluorine, there is a latent period varying with the degree of exposure. If t'he exposure is relatively small, several hours may elapse before the patient is conscious of pain or injury. The lesion becomes reddened, then swollen and pale, with a macerated appearance, and is accompanied by severe throbbing pain. Adequate treatment will usually stop the pathological changes a t this stage; if not, necrosis and ulceration will ensue. Because treatment is specific and highly efficient, it should be instituted immediately, even in cases of questionable severity. The skin should be flushed with copious amounts of tepid t a p water. An emergency shower equipped with a quick-acting valve is recommended in cases of widespread exposure. The washing should be continued for a t least 15 minutes and should not be stopped even while contaminated clothing is being removed. If a physician considers t h a t the burn is mild, a waterbase paste containing magnesium hydroxide is then applied. If there is even a slight chance of the burn developing beyond t h e erythema stage, the tissue beneath and around the affected area should be infiltrated with 10% calcium gluconate. This precipitates the fluorine as inert calcium fluoride. The injection of calcium gluconate is surprisingly painless but may be preceded b y procaine infiltration. The immediate cessation of pain and the pathological changes following the calcium gluconate therapy are strikingly favorable. Fluorine burns of the eye require copious and prolonged irrigation with tepid tap water by using an upturned faucet or immersing the head in a basin of water. Following this, the eye should be irrigated with 3T0boric acid solution. Subsequent treatment should be directed by a n ophthalmologist, and consists of the application of pontocaine for the relief of pain, mydriatics, and the removal of any necrotic tissues in the cornea. Under no circumstances should ointments be applied either to the skin or eye. The inhalation of flood concentrations of fluorine would probably cause asphyxia by a mechanism due to laryngeal and bronchiole spasm and later by bronchiole Obstruction and pulmonary
Group
I
I1 111
I 1' V
Reaction F? 4- ? S a 1 = 2 N a F I1 Clt 2 X a I = 2SaCl 12 Fa S i = KiFt Clt S i = SiClt 02 2Si = 2SiO -C-HFt = -C-FIIF -C-H 4- HCI -c=c- +CltF2==-C-C1 -CF-CF-c=cCI? = -CCl--CCI-C-CFz = 2CF-C-CClz = ZCCIHz0 (gas) F2 = 2 H F ;OJ 4F2 = CFI 4HF CHc
Reactant -240,000:Fz - 105,000/ Clt -283,00O/Ft - 135,000ICl -210,000:oz - 184,000 'Fz - 4P,OOO/CIz -193,00O/Fz
++
+ ++ +
++
+
++ + +
+
- 60,00O/CIr - 162,00O/Fz - 29,00O/Cl*
+ + 2COz + 4H20 2CH4 + 402 2H + F Z = 2 H F (gas) 4H + = 2Hz0 (gas)
I
+ 5Fz = 2CF4 + 2 H F + 5 0 1 = 4COz + 2Hz0
i
p
VI
AH,B T 1- 1.b AIole
CzHz
2CzHz
VI11
- 181,00O/Fz
- 722,00O/CH< - 173,000/01 - 345,00O/CH1 -600,00O/Fz or HI 970,000/0~
0 2
VI1
- 126,00O/Fz
485,00O/Hl - 183,20O/Fz -916,00O/C~Hz -216,400/01 -541,00O/CnHn
Values calculated from thermal d a t a of Bichowaky and Rossini ( 1 ) except items under 111. which are from Bockemueller (3).
Vol. 39, No. 3
0 10 800
0 TO 100
I
THROTTLING VALVE FOR TUBE TESTIYG
FLUORINE
20% FLUORINE SO% NITROGEN
Figure 1.
S c h e m a t i c Flow D i a g r a m for R e s i s t a n c e of RIaterials to Fluorine
edema. The bronchiole obstruction would be due to mucous membrane swelling and the secretion of tenacious mucous. Exposure to high concentration of fluorine would also be accompanied by gastrointestinal symptoms and irritation of the eyes, throat, and skin; but these symptoms xvould be secondary in importance to the lung damage, and survival of the patient would depend on adequate oxygenation of the blood. Treatment of a patient suffering from lung damage is probably of little benefit as far as the final outcome is concerned. As protection against accidental blasts of fluorine, several liundred types of rubber- and plastic-coated fabrics have been tested. Hon-ever, all of these materials immediately burned when exposed to fluorine, as a result of the fluorination of organic compounds, especially the petroleum greases incorporated to facilitate the n-orking or calendering of the finished product. Fireproof neoprene on a fiber glass base, originally developed by The B. F. Goodrich Company for aircraft hangar curtains, has been the only material proving satisfactory against blasts of fluorine (8 liters a t 40 pounds per square inch gage a t zero distance). Somewhat similar materials made by other companies failed under similar conditions. The satisfactory material has been designated by The B. F. Goodrich Compnny a s ECC-11128-14000 (misc.) fabric. ;ill types of cemented sean~sburned briskly on contact with blasts of fluorine except one developed by B. F. Goodrich Company. This cement consisted of the original coating material used in the ECC-11-128-44000 fabric, and for best results the seaming phould be done before the curing of the final product. COKVEYING
PIPIXGA T ATMOSPHERIC PRESSURE. Fluorine is generated at substantially atmospheric pressure and is safely handled in iron pipes a t that pressure. Where any possible contamination 11-ith organic material or water vapor exists, pure fluorine at atmospheric pressure can burn steel equipment, and the burning dl continue as long as the supply of fluorine continues. If the pipe wall thickness is adequate (Le., standard or extra strong pipe), the material weight and surface area are large enough to eliminate spontaneous combustion except in very unusual cases. When fluorine emerges into the wet atmosphere-e.g., through a leaking pipe flange-it reacts with condensed water and forms sparks and flashes which are readily visible at a considerable distance, although the pipe flange itself undergoes no reaction.
March 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
283
particularly under pressure. Commercial large scale experience to date has not involved the extensive piping of fluorine at pressures above 30 Pressure Time of pounds per square inch gage and the use of Monel Temp., of F, Exposure, F. B t m . Abs. Days pipe for this service has beeii very satisfactory. STEEL Present evidence is that Monel piping can be used 167 .itni. 33 20 safely at even higher pressures. Arnico iron Initial 930 Atm. 11" The statements concerning the advantage of Initial 167 Atm. 1 25 6 S 4 E 1010 Final 0.1 welded piping for atmospheric pres-w r e are even Low silicon iron more pertinent for pressure operation. Here only 0 5 187 (0.004'% Si) 1 392 High silicon iron metal gaskets are satisfactory for flanges, and 0.5 324 392 (0.79% Si) screTTed fittings are much more prone t o leak. SICKEL ASD A L L O T S Plastic gaskets (e.g., Teflon) may be used, but 140 0.03 0 5 Probably high 2 Nickel foil 4 125 .itm No evidence of corhfonel weld preferably not at high pressure since contamination rosion or embritwith dirt may result in firing. tlenient S o noticeable at10 250 5b ... Monel tubing \'.ALVES AT A4TUOSPHERICPRESSURE. Valves are tack .4tm 0,006'' Wt. gain .. 930 Nickel sheet the most difficult problem in the indust'rial hanWt. gain Atm. 0.10 1290 dling of fluorine as a result both of leakage around After cleaning ,. 930 .$tin 0.02 hfonel sheet (max.al the stuffing box and of seat leakage when the 1290 Atm. 0 2'1 After cleaning valve is closed. To avoid leakage across the .4LT.\IIUC\I stuffing box, packless valves are preferable. One fi 309 Atni. 0 41 Foil Initial attack IS of the ferr suitable for the industrial handling of higher 0.040 930 Atni. , . Max. of several Sheet fluorine is the Merotest diaphragm packless valve 1110 Atm. 0.06'1 ;\fax. of several which has a copper diaphragm. It can be used C O P P E RA Y D .-\LLOIS with fluorine, if the seat is changed to one made 2 140 0.03 0 6 Probably high Foil of Teflon or its equivalent. Another satisfactory Wool 200-250 Atm Caught fire .. type of packless valve for this service is a 930 Atnl 0 2" Sheet .. 1290 Atm. 3. bellows-sealed valve manufact ured by the Crane 2 140 0 03 Brass (70-30) sheet 1.3 Probably high 2 140 0 03 Bronze Probably high 0.8 Company. A variety of other industrial valves Cu-Ni (80-20) 2 0.03 1 0 140 Probably high have been employed at lo~vpressfires for dilute gas ~ f . 4 ~ s ~.\LLos.'. s l r ~ (Reaere Sheet) with some success; they were all packed with h l A (1 2 9 M n ) 0 03 0 7 2 140 special corrosion-resistant materials such as Teflon. FS-1.4 (3% A I , 1% Zn. 0 2a7, >In) Seat leakage in valves handling low pressure 2 140 0.03 1.5 J-1H ( 6 % AI. 0 7 % fluorine can be substantially overcome by suit0.03 1 4 Zn, 0 2% >In) 2 .140 able design in which Teflon or ita equivalent is the c' H K O X I r11 seating material, with Monel or nickel as the Plate (003-in. on 1 802 Atrn ... N o visible sign of mating element. This design produces a much S.4E 1020) attack tighter seat than an all-metal valve. Metala Penetration in inches per month. b Pounds per square inch gage. seated valves with Rlonel or aluminum bronze seat-and-disk combinations httve also been used. For no type valve, however, is it safe t o assume t h a t the seat will remain tight indefinit,elv, " , and Experience has shovm that welded construction is preferable to it is recommended, Tvithout exception, that double valving be either flanged or screwed piping a t any pressure, since inleakage provided a t all points \\-here tightness is an important conor contamination which may result in fire may occur with the latter. Where joints are necessary for repairs or other operating purposes, a flanged joint is preferable, but' the gaskets must be limited to metals, such as soft copper or aluminum rings, or inert TABLE 111. EFFECT OF FLUORIXE OK SOSXETALLIC MATERIALS" the I o n plastic rings-e.g., Teflon (tetrafluoroethy1ene)-for COSDITIOXS RESULTS pressures. For dilute gases (below 207,) clean Butyl or Seoprene gaskets can be used, provided the surface of contact with gas is comparatively small and the joint is not broken frequently. hlost rubber$, except Butyl, lose their physical strength quickly conversion t o AIFi on exposure t o fluorine, so t h a t i t is desirable t o replace the rubber CaF2 cement, baked dry (with XaZSiOa) 400' F., approx. N o apparent attack gasket each time the joint is made up. A copper-jacketed asbestos Carbon. amorDhous 212' F. Iuo visible effect Carbon, graphite 212' F. Einbrittlement gasket may also be employed for dilute gases. Glyptal 77' F. So burning, if baked dry Screwed piping is unsatisfactory, but if it must be used, pipe Rubber (various) Various Erratic; inay or may not h a r k d to some~. ex- i l r n ., a r. r ..~...~ dope should be used sparingly and not applied to any parts of tent in all cases, with increasing brittleness, crackthe thread t h a t may be exposed subsequently to fluorine. Speing, surface hardening cial pipe dopes of reduced reactivity, such as a paste of calcium Transite Various Resistant, i f clean 5 % HSOa (?OF) and 100'7,, 1 atin., 4 fluoride in completely fluorinated oil, may be used advantage95% Hi301 (9$-98Y0) hr. K O noticeable change 100'70,1 atni., Little attack: may get warm 1007, H2SC); ously for this purpose. The use of welded pipe, even in the case 100' F. if iiripurities are present of Monel, has been shown t o be substantially as flexible as that of 95% HzSOa loo%, 1 atm., Rapid temp. rise; some er100' F., 1 hr. plosions as temp. rises screwed or flanged piping, since a good welder can cut the pipe 8570 HsPOI loo%, 1 atm., apart and n-eld it together again in a short time. 100'F.. 0.1 br. K O temp. rise PIPISGAT PRESSURES ABOVE 5 POGXDS PER SQUARE INCH These d a t a a n d those of Table I1 are very approximate, and probably do GAGE. I n view of the fact that Monel or nickel pipe is much more not give more than a n orientation on the properties of fluorine. All the systems are thermodynamically unstable, but protective films usually account resistant to ignition by fluorine than is steel, the use of hlonel or for the low actual corrosion rates. nickel for piping is preferable for the handling of pure fluorine, TABLE
O F FLUORISE ON 11. EFFECT
VARIOUS bfETALS Corrosion Rate, JIg./Sq. Ft./ Day Remarks
I
~
284
INDUSTRIAL AND ENGINEERING CHEMISTRY
sideration. In this category are included valves separating fluorine equipment from the atmosphere or from adjacent equipment which does not handle fluorine. In some cases pressuring of the space betneen the two valves with some inert gas, such as dry air, may be required to provide the necessary freedom from inleakage where even traces of fluorine may spoil a reaction or ruin a catalyst. VALVES AT PRESSURE ABOVE 5 P O C K D S PEE SQUARE I \ C I l GAGE. The bellows-sealed valves mentioned in the pi eceding section can be used a t pressures up to 100 pounds in siies of 1 inch and above. .4t present no satisfactory packless valve for higher pressures is known. Up to 400 pounds, Hoke None1 needle valves, packed with Teflon or its equivalent, have been successful. T h e Kerotest 440-A Chlorine Institute valve, packed with Teflon or its equivalent, has been employed succes.fully for use on cylinders containing fluorine under pressure. With fluorine under high pressure, nonmetallic seats or disks are not safe, and the problem of seat leakage is much more acute. Here, too, the desirability of double valving must be emphasized. As recommended in the section on piping, valves should be welded into the line or silver-soldered in small equipment. Flared connections are satisfactory for laboratory installations. Experience has shown that soft solder is not practical for fluorine service. Important instruments for fluorine hanINSTRLMENTATION. dling include flow recorders and controllers, pressure recorders and controllers, pressure reliefs, and temperature indieaton. T h e development of satisfactory instruments is limited by the reactivity of the gas n ith them.
Clean brass Clean c o w e r Clean stainless steel 1,'d-h oil-co\.ered brass (1/1~-in. wall) '/s-in. oil-covered copper a/:-in. oil-covered stainless steel (:/ls-in. wall) a
P*'o reaction
S o data N o data No data
S o data Sc darn S o darn
X o data 1-cdat:i
Heated t o red heat,, no burning B u r ne d as long a s gas flowed Heated t o red heat, no burning
N o data
S o datn
So d a t a '
B u r n ed aR long as gas flowed Heated t o red heat, no burning
50
S(t
S o data
So d a t a
S o reaction S o reaction
1-o
data
re:i(~tion
N o d a t a available for $//s-inch orifice
Vol. 39, No. 3
desirable; two controllers have been used successfully in throttling from 30 pounds per square inch gage to a steady level of 1 pound. For pressures below 30 pounds, where plastic seats can be used safely, this double control system may not be necessary but it is desirable in case of extreme precision requirements. Temperature measurements are best made with completely enclosed thermowells; thermocouple elements cannot be depended upon when in direct contact with fluorine. COMPRESSION
The compression of pure fluorine with ordinary compressors is extremely difficult, because the normal lubricants needed react with fluorine. In the case of mechanical compressors luhricated with fluorinated oils, experience so far is not sufficient to establish the commercial applicability of such equipment. It is evident, however, that considerable difficulties result and that leaking around the piston may be serious. The use of bellows-type pumps has not been satisfactory, because the flexing of the bellows in fluorine under pressure results in intergranular corrosion or in rupture, with serious leaks. ;1 compressor of the diaphragm type in which a metal diaphragm of comparatively small stroke is employed has been successfully built by the Wrilson Pulsafeeder Company and the Hooker Electrochemical Company for compresPing fluorine to about 40 pounds. In this way there is a complete absence of cont,act between lubricated parts and the fluorine under pressure. Difficulties due to leakage around the inlet and exhaust valves are to be expected with the metal-seated valves used, but this is not serious since pumping efficiency is not the most important variable. Centrifugal equipment, properly pealed at the shaft with resistant rings such as graphite or Teflon, has functioned on pure fluorine a t pressures near atmospheric. Considerable development work is still necessary t o achieve means for mechanical compression of fluorine to higher pressures; but except for very large installations, compression to 30 or 40 pounds per square inch gage (using the diaphragm pump) is adequate, and for reasons of safety it is desirable that this pressure should not be exceeded. For compression of fluorine above thin level, the only known means vhich is reliable involves the condensation of the fluorine by cooling with liquid nitrogen, folloivcd by vaporization to the desired pressure. Vacuum pumps, lubricated Tyith completely fluorinated oil, can be used directly on dilute fluorine gas, and laboratory pumps, such as the conventional Cenco or its equivalent, have been employed for this purpose. Larger pumps (up to 100 cubic feet per minute) handling dilute gas have been constructed for plant use by the F. J. Stokes hlnchine Company and the Reach-Russ Company. STORAGE
I n the case of flow recorders and controllers and prebsure recorders and controllers, blind multipliers or transmitters with bellows construction, either welded or silver-soldered, and employing a buffer zone containing a n inert gas such as air, have been used successfully. They are manufactured by the Moore Company and the Taylor Instrument Companies, among others. These transmitters or multipliers can be used with any normal type of instrument for recording, indicating, or controlling. For simple pressure measurement all-welded Bourdon-type gages are practical. 'There has been no satisfactory experience x i t h pressure relief valves for fluorine because of the seat leakage. For this reason motor- and air-operated valves are difficult to maintain tight against pure fluorine because insufficient torque is available for :seating. For operations on fluorine under pressure, it has been found that control is best exercised in staqes by using several valves in series with suitable alarms and by-passes. If the pressure difference is too great, additional stages of throttling may be
111 conjunction ivitli the pressuring of fluorine, it is frequently necessary that storage facilities be provided to furnish gas for intermittent uses or to remote locations not easily reached by a piping system. The storage of fluorine can present a great hazard, particularly if large quantities are involved. Experience has shown that as much as 200 pounds of the gas can be stored in one container a t 30 pounds per square inch gage if proper precautions are taken. For maximum safety, only nickel or Monel of adequate thickness should be used in direct contact with fluorine under pressure, since it is difficult to fire these metals except under very unusual conditions. For this type of storage the containers should be isolated in concrete rooms, adequately ventilated and made largely inaccessible to the operators. All necessary joints should be of extra heavy construction, using ring-type copper or aluminum gaskets which should be renewed every time the joint is broken. In the case of portable containers with fluorine under pressure, limited experience has shown that fluorine can be stored with considerable freedom from hazard in clean, dry, steel cylinders similar
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1947
TABLE v. EFFECTSO F FLUORIXE O S MISCELLANEOUS MATERIALS 20% I'
llaterial Clean cotton hand towels (4-plyj Clean laundered cotton cloth and wool suiting material backed with cotton (simulating clothing) Same as 1, b u t contaminated with clear, lubricating oil Clean asbestos gloves Clean natural rubber gloves, smooth clean qurfare.., ...
Paper, pine, wood block, spruce wood blqcli, angle iron, granite, painted wood and iron a
Pure Ii (50 . L b . / S q . I n . Gage) 3/s-in. '/*-in. orifice orifice 6 in.u 3 in."
Tank pressure Ib./sq. in gage
{S1:o d a t a
'Is-in. orifice 0 in.Q Fired a t 0 in. No data
Variable, b u t generally burned under most conditions S o d a t a h-ot safe a t 3 in K Od a t a 1 in.
S o data
S o data
h-0 d a t a
S o data
S o data
Xo data
reaction except when surfaces were rough or contaminated, then fired a t 4 In.
S o data
h-o d a t a
6 in.
Xo
3 in.
Figures (inches) indicate niinimurn distance to prevent burning.
to those used for chlorine, except that the valve must be packed with Teflon or its equivalent. However, for maximum safety the cylinders also should be constructed of nickel or Monel. iiltliough storage in small vessels has been accomplished up to 400 pounds per square inch gage, this pressure level is not desirable because it requires much greater precautions and, further, because it offers no particular advantage except reduction in metal requirements if the number needed is large. The latter problem can generally be more than offset by the use of a storage tank. It appears unlikely, a t least for the near future, that economic considerations will favor high pressure applications. '
SAFETY PRECAUTIONS
I n conducting the operations of generation, conveying, compression, and storage, it is essential that the folloviing principal safety precautions be observed (pressure operation is considered to begin a t 5 pounds per square inch gage) :
1. Valves handling pure fluorine above 5 pounds gage pressure should, wherever possible, be manipulated by extension handles passing through metal, brick, or concrete barriers or shields. For operations a t lou- pressures or with dilute fluorine, this precaution is unnecessary. 2. -All pure fluorine containers under pressure should be stored behind a suitable barricade and should never be approached by operators unless completely closed and demonstrably not leaking. If the container leaks, it should he allowed t o vent after being taken to an open field or safe distance from site of use. 3. :\11 rooms or barricaded sections containing fluorine under pressure should be inspected t o determine the existence of leakage, and all leaks should be repaired a t once. Leaks can be found by squirting aqueous ammonia from a wash bottle a t suspected points. The formation of a fog, as in the case of ammonia and hydrogen chloride, indicates the location of the leak. The use of filter paper moistened with pota. i u m iodide also gives a n indication of fluorine in concentration as loiv as 25 parts per million. 111more difficult cases it may be necmsary to pressure test the equipment and soap the connections, or to evacuate and test for leaks. 4. ITherever equipment is to be used for for reactions in which fluorine is to be emp be introduced don-15- and under conditions tion, so that if impurities are present, they can be burned out without the simultaneous ignition of the containers or other materials. This precaution is one of the most important in handling fluorine. 5 . All equipment which has contained fluorine must be thoroughly purged with d r y inert gas prior to opening, and also evacuated, if possible, t o assure removal of residual fluorine gas. 6. T h e use of fine adjustment valves to throttle gas from a pressure container in stages is preferred to dependence on the cylinder valve for throttling. T h e latter operation can easily
2 85
lead t o excessive discharge of gas and possible firing of equipment, if the cylinder valve is not made of Monel or nickel. 7. All pressure containers should be thoroughly cleaned and degreased prior t o use. I n addition, piping and other equipment, even for atmospheric pressure use, should be thoroughly cleaned and dried before exposure t o pure fluorine. Final cleanup should be with dilute fluorine. 8. The size of the containers for fluorine under pressure should be kept as small as possible. For laboratory use, where direct handling of the cylinder is involved, the total weight of pure fluorine a t 50 pounds gage should not exceed about 1 pound of gas. -4pressure maximum of 50 pounds per square inch gage should be set if no barricade is used. 9. If welding or soldering is done, arrangements should be made to minimize the amount of flux which is allowed to remain in the pipe or vessel, and as much as possible should be removed prior t o use.
A number of normal safety precautions involved in the handling of any dangerous gas should be included in all safety programs. These include the following: 1. All equipment or containers handling fluorine should be identified by distinctive colors. 2 . Goggles of Lucite, Plexiglas, or Lumarith should be worn n-herever operators must approach equipment containing pure fluorine under presure. 3. Construction should be fireproof a t every point rvliere fluorine is to be used. 4. Containers of fluorine should not be heated. Mixing of fluorine and other gases is quite slow so that, to assure complete homogeneity, iL is necessary to allow them to stand for several days prior to use. 5 . I t is desirable that two people be present i n all fluorine work, but, a t some dlstance from each other, eo that one can render assistance to the other in an emergency. 6 . Only trained and competent personnel should be permitted t o handle fluorine, and frequent checks should be made of the operation. A l l personnel involved in the operation should be familiar with the potentialities of fluorine for harm as well as the fa$ involved in its safe handling. I . .Idequate ventilation at all points is essential. The ventilating system should be capable of producing ten air changes per hourinknclosed spaces. 8. Kherever critical valves are involved, it is desirable that they be locked into position either open or ciosed, and that, they be tagged in any case. 9. A suit,able alarm system should be provided a t convenient points to permit, clearing of the area if necessary, and testing of this equipment a t periodic intervals should be stipulated. DISPOSAL
I n operations where fluorine is not completely used up in the process, it is frequently necessary to provide for the disposal of excess fluorine. Despite the great reactivity of this gas, adequate means for its disposal are comparatively limited. The matter of disposal is important, from the standpoint not only of health but also of psychology. S o t only are the operators in the vicinity annoyed by low concentrations of gas, but winds can carry the gas for long distances and it affects fruit and other vegetation. For these reasons fluorine should not be vented to the atmosphere 1)ut should be disposed of completely. The following disposal methods have been tried a t various times and n-ith the degrees of success indicated:
1 t E . t c m x WITH SODICMCHLORIDE.Passage of fluorine over sodium chloric!e or calcium chloride gives chlorine which can then he absorbed by soda lime, lime slurry, etc. This system has the disadvantage of involving the handling of considerable quantities of chemicals but is convenient for small laboratory installations. RE.KTIOX WITH CACSTICSODASOLUTIOSS. Solutions of 5 t o 10% by weight caustic soda completely destroy fluorine gases, provided the contact time of gas with liquid exceeds 1 minute. The long contact, time is necessary because fluorine reacts with caustic solutions to form fluorine oxide, OF*, a t contact times of approximately a second. I t is recommended that the contact between gas and liquid be good-for example, by a spray or packed tower. Detailed operation of such a system will be discussed i n another paper ( 3 ) .
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INDUSTRIAL AND ENGINEERING CHEMISTRY
COMBUSTION. Fluorine can be burned in a flame employing hydrocarbon fuel under conditions such that fluorine provides some of the oxidation normally furnished by excess air. The products of reaction include hydrofluoric acid and carbon fluorides, the latter being inert gases with no odor. However, the hydrofluoric acid formed is objectionable and should be removed. Therefore, it is desirable, if any appreciable quantities of fluorine are to be vented, that the burner gases he scrubbed with water or alkaline solutions t o remove the hydrofluoric acid. This presents a n appreciable corrosion problem and equipment has to be constructed of carbon, lead, etc., to withstand dilute hydrofluoric acid solutions. This system has the disadvantages of requiring the combustion of some fuel a t all times and is particularly disadvantageous for widely varying loads. REACTION WITH l $ r . 4 ~ ~ T ~ h. e disposal of fluorine by water scrubbing is not satisfactory, because fluorine does not altvays rea c t with water, for reasons unknown. Explosions have been encountered in such a system under some circumstances but not in others. Since there is insufficient information on how to control the reaction, i t is not satisfactory for design a t the present stage of development. REACTION WITH CARBON.The reaction of fluorine with carbon evolves so much heat that it is difficult t o design safe equipment t o handle such a process. Furthermore, the existence of an explosive compound F C (6) rules this method out. ABSORPTION BY LIME. The use of a lime slurry to remove fluorine in a liquid system is successful if sufficient contact time IS provided. Because lime is a much more dilute alkali than caustic soda, the destruction of the intermediate compound, OFz, is more difficult than in the case of caustic soda. Insufficient experience has been accumulated to establish a satisfactory quantitative basis for design. Furthermore, difficulties attending the handling of slurries are involved. ABSORPTION BY FLUORIDES OF LOWERVALE~TE. When inorganic fluorides, such as silver, antimony, cobalt, etc., are treated in their lower valence state with fluorine, they are oxidized t o the higher valence state and the fluorine is absorbed. T h e compound of higher valence can then be reduced to its lower state by hydrogen, and the hydrofluoric acid formed can be condensed out in a refrigerated trap. This method is decidedly unsatisfactory for small installations and, for large installations, has the usual hazards of handling hydrogen as well as involving a series of operations.
Vol. 39, No. 3
From the foregoing examples, it is clear that disposal of fluorine varies with the conditions involved, but the use of caustic, or of the salt-soda lime combination, represents the most convrnient method for many installations: ACKNOWLEDGMENT
The authors acknowledge with appreciation the contributions made by the Hooker Electrochemical Company, E. I. du Pont de Semours K. Company, Inc., The Harshaw Chemical Company, The Johns Hopkins Cniversity, Columbia University, the Army (’orps of Engineers, Nanhattan District, The Kellex Corporation, and the inany individuals in these organizations, to the develop nients described in this paper. The work reported in this paper \vas done at the Kellex Corporation under contract from the \ranhattan District. LITERATURE CITED
(I! Bichowsky. F. R.,and Rossini F. D., “Thermochemistry of Chemical Substances”, New York, lteinhold Pub. Corp., 1937. ( 2 ) Bockemueller, 0.. “Organische Fluorverbindungen”. Stuttgart,
F. Enke, 1936. (3) Landau, R., Kellex Corp., Research Paper E7, Manhattan District Volumes (1947). (41 Latimer, W. M., “Oxidation Potentials”, New York, PrenticeHall, 1938. (5) Moissan, H., Compt. rend., 102, 1543 (1886). (6) Ruff, 0..and Bretschneider, O., Z . anorg. allgem. Chem., 217, 1-18 ( 1 9 3 4 ) ; Simons, J. H., and Block, L. P., J . Am. Chem. Soc., 61, 2962-6 (1939). PREBEXTED before the Symposium on Fluorine Chemistry as paper 37, Division of Industrial and Engineering Chemistry, 110th Neeting of the AMERICANCHEMICAL SOCIETY, Chicago, 111. The work described in this paper is covered also in a comprehensive report of work with fluorine and fluorinated compounds undertaken in connection with the Manhattan Project. This report i3 soon t o be published as Volume I of Di\-ision VI1 of the Manhattan Project Technical Series.
ANALYSIS AND DISPOSAL OF FLUORINE S. G. Turnbull, ,4.F. Benning, G. W. Feldmann, -4.L. Linch, R . C. McHarness, and YI. IC. Richards E. I . DU PONT DE NEMOURS & COMPANY, INC., WILMINGTON, DEL.
A SAFE analytical method for industrial use has been developed for the analysis of high quality fluorine. This method is based upon the reaction of hydrogen fluoride with sodium fluoride, the conversion of fluorine to chlorine by reaction with sodium chloride, and analysis of the chlorine for oxygen and inert gases by standard methods. The over-all error in fluorine purity by this method is indicated to be less than 0.4%. A safe method for the disposal of waste fluorine on a large scale has been developed and satisfactorily operated. The waste fluorine is burned with hydrocarbon gases, and acid products formed are removed from nontoxic carbon fluorides by scrubbing with water and sodium hydroxide.
A
SAFE, routine method for analysis of fluorine present in low or high concentrations a t atmospheric or superatmospheric pressures was required for proper control of the quality of fluorine, ( a ) as produced directly by electrolytic cells and ( b ) when packaged in cylinders after purification and compression. An analytical method reported in the literature ( 1 ) consisted of absorbing fluorine by mercury in glass equipment. This was considered unsatisfactory for our purposes because it would be extremely hazardous for unskilled operators, did not include the
determination of the hydrogen fluoride present as an impurity, and could not be used when the latter was present. An attempt \vas first made to develop a completely gasometric method in which the highly toxic and reactive fluorine could be converted to the less toxic and more easily handled chlorine, and the hydrogen fluoride transformed to the easily analyzed hydrogen chloride by reaction with chlorides. The reaction of fluorine with chlorides of the folloFving bivalent elements was studied: calcium, barium, magnesium, cadmium, and mercury. Although these chlorides did react to yield chlorine and metallic fluorides, it ivas found that the hydrogen fluoride impurity \vas only partially converted to hydrogen chloride, and was for the most part adsorbed upon the metallic fluorides formed in the reaction. hlloreover, fluorine reacted with moisture and with oxides that wcre difficult to remove from these metallic chlorides. This led t o the formation of oxygen, fluorine oxide, and hydrogen fluoride, which gave inaccurate results. Howcver, three satisfactory analytical methods xwre developed and are more fully described here. SODIUAI FLUORIDE-SODIUM CHLORIDE JlETHOD
The sodium fluoride-chloride method was developed for fluorine
at concentrations above 50%. The hydrogen fluoride is first removed quantitatively in a copper or nickel tube by sodium flue
