C&EN
FEATURE
Hydrogen Fluoride. . . . . . w h e r e it goes, h o w it's m a d e , w h y it's g r o w i n g Α . Η . STUEWE, Stauffer
Chemical
Co., New York, Ν. Y.
IF YOU were to ask the nonchemical man-in-the-street today what he knows about hydrofluoric acid, in most cases the reply would be, "It etches glass." While the passage of time has not changed this chemical phenomenon, it certainly has changed its relative im portance. What was once about the only use for the material now akes less th of total U. S. production. Successful commercial production and shipment of anhydrous acid, first achieved in 1931, opened a whole ar ray of new applications. From only a few thousand tons prior to World War II, consumption skyrocketed dur ing the war to a peak of nearly 50,000 tons for nonaluminnm uses alone. Anhydrous acid played a vital part in producing alkylate for high octane avia tion gasoline and in refining uranium for the atom bomb. The end of the war brought a temporary drop in re quirements. However, consumption has grown rapidly in the past ten years and should top 150,000 tons by 1960. At the present time there are five merchant producers of hydrofluoric acid in the U. S. In addition to these. D u Pont, Reynolds, and Alcoa produce large quantities for their own needs. Total production capacity for hydro fluoric acid ( excluding the primary alu minum industry) as reported by the U. S. Department of Commerce over the past decade has exceeded actual production by 15 to 20%. At the be
34
C&EN
D E C . 2 2, 1 9 5 8
ginning of 1958 total capacity was listed at 107,000 tons per year. While this is nowhere near the large over capacity that exists for many other chemicals at the present time, there has been no H F shortage in recent years. These companies are making HF: Company Blockson Divi sion of Olin Mathieson General Chemi cal Division of Allied Chemi cal
Plant Location Joliet, Ill.
Harshaw Chemi cal Nyotex Division of Stauffer Chemical Pennsalt Chemi cals Du Pont°
Cleveland, Ohio
Alcoa 0 Reynolds Metals* General Chemi cal00
North Claymont, Del. Baton Rouge, La. Nitro, W. Va.
Houston, Tex. Calvert City, Ky. Carney's Point, N. J. East St. Louis, Ill. Bauxite, Ark. Nichols, Calif.
°0 0 For captive use only. All production converted to AlF3 for West Coast aluminum industry consump tion. At the present time all commercial production of HF is by one route: the reaction of sulfuric acid with fluorspar.
Finely ground acid-grade fluorspar ( 9 7 to 98% CaFo) and a slight excess of strong sulfuric acid are fed continu ously into one end of a horizontal kiln like steel generator. External heat is applied, usually by direct fire, and the gaseous H F is liberated. The residue, primarily calcium sulfate, is discharged at the opposite end of the generator. Approximately five tons of spar and acid are required to produce o n e ton of HF, with about four tons of waste product being discarded. As it comes from the generator the hot gaseous stream has a composition of 95% H F , 1% impurities ( H 2 S 0 4 SiF 4 , H2O, CO2, and SO2), a n d 4% air. For converting to aluminum fluo ride, synthetic cryolite, and some other salts, the retort gas can be used directly. How ever, to make anhydrous and aque ous acid several subsequent purifying steps are needed. Cooling and scrubbing the gas as it leaves the generator removes some of the sulfuric acid, and some of t h e suspended dust particles. T h e gas stream is absorbed in weak "cycle" acid to produce a concentration of about 70% HF. It then passes through a dis tillation column to remove the high boiling impurities (water and sulfuric acid) and the product goes overhead. After cooling and condensing, a second fractional distillation takes out the low boiling impurities (SiF 4 , C O 2 , and SO 2 ) . The bottom fraction is anhy-
Fluorocarbons have meant a growing, market for hydrogen fluoride. General Chemical makes Gene-tron fluorocar· bons in this plant at Baston Rouge, La.
drous, purr acid. containing about 99.95% HF. Although hydrofluoric- acid is a highly reactive. very hazardous chemical its handling has been perfected t o the point where shipping is almost as routine as with many other far loss dangerous chemicals. Since all H F production depends upon fluorspar, adequate supplies of this material are critical. In addition to its use to produce H F , fluorspar is widely used in the steel and ceramic industries. An estimated 645,000 tons were consumed in 1957, of which 51% 330.000 tons) were converted t o HF. 42% (270.000 tons used for steel manufacture, and 7% ( 45,000 tons) used for ceramics and other applications. Ten years ago domestic production of fluorspar supplied about three fourths of the U. S. requirements with imports supplying the remainder. By 1957 this situation had reversed. Acting on a split decision by the Tariff Commission. President Eisenhower three years ago decided the situation did not warrant invoking the escape clause against fluorspar imports. Domestic shipments in 1957 o f approximately 325,000 tons (of which an estimated 110.000 tons were stockpiled) declined 2% from 1956 and were only slightly greater than shipments in 1947. Over the same period imports have grown from 100.000 tons to over 600.000 tons. About 65% of current imports come from Mexico, 20% from Italy. 10% from Spain, with small amounts from Canada and West Germany. The domestic fluorspar producers, even captive producers, have found it increasingly difficult to remain competitive with importedTEMERATURE ACID However, there is another side to t h e picture. Current known U. S. fluorspar reserves
The End Is Not in Sight I
(HF consumption, short tons)
I
1957 HF Aluminum Buoride Fiuorocarbons Uranium production Synthetic cryolite Conversion to salts Stainless steel Petroleum alkyiatïon Special metals Etching and frosting Others
40,000 38,500 16,000* 13,000 7,500 7,000 6,000 3,000 2,000 2,000
Total I
135,000
29.6 28.5 11.8 9.6 5.6 5.2 4.5 2.2 1.5 1.5 100.0
HF
1963 Per cent of total
65,000 67,000 21,000° 25,000 S,400 8,100 9,000 6,000 2,200 3,300 215,000
° Net consumption.
Stauffer's h y d r o g e n C&EN
DEC.
fluoride 2 2,
I
30.2 31.2 9.8 11.6 3.9 3.8 4.2 2.8 1.0 1.5 100.0 I
(of h i g h e n o u g h quality to b e e c o nomically m i n e a b l e ) are definitely limited. A 1956 Bureau of Mines survey estimated reserves of 2 2 . 5 million tons of high grade ore and 1 2 million tons of lower grade ore. Estimates b y s o m e of the fluorspar industry indicated that the reserves may be s o m e w h a t higher. Because of t h e n a t u r e of the deposits, it is rather difficult to make an accurate estimate. B u t w i t h c o n s u m p t i o n rising steadily from the present rate of nearly 7 0 0 , 0 0 0 tons annually, i t w o u l d definitely b e p o s s i b l e t o exhaust the reserves within our lifetime if w e w e r e to rely o n domestic spar exclusively. T h e domestic fluorspar producers h a v e sufficient p r o d u c t i v e capacity to supply almost all of our current needs. A more ready m a r k e t for U . S. spar w o u l d give a n incentive for n e w exploration w h i c h u n d o u b t e d l y would a d d to our known reserves. B u t there are
36
Per cent of total
strong arguments for conserving our domestic d e p o s i t s of this strategic mineral as much a s possible. Conservation of our fluorspar reserves, while at the same t i m e e n c o u r a g i n g exploration for n e w d e p o s i t s and maintaining t h e domestic p r o d u c t i v e c a p a c i t y in a healthy condition, is a rather complex problem. It apparently has n o easy, inexpensive solution. G r o u p e d under four major categories, the markets for H F are: primary a l u m i n u m production, fluorocarbons (refrigerants, aerosols), uranium production ( A E C ) , and miscellaneous uses. T h e various silicofluorides also constitute a sizable market. However, since they are m a d e from silicon tetrafluoride, a by-product of fertilizer phosphate rock acidulation, they d o not represent an e c o n o m i c a l l y feasible market for H F . I n fact, in recent years silicofluorides h a v e b e e n replacing HF to
plant at H o u s t o n , Tex., u s e s large
1958
settling p o n d
some extent in making sodium fluoride, cryolite, a n d a l u m i n u m fluoride. Kaiser A l u m i n u m is currently recovering fluorine values from several fertilizer operations in Florida. Other c o m panies are also b e g i n n i n g to convert by-product fluorine values into cryolite and other inorganic fluorides. T h e potential fluorine value from acidulation in this country is quite large. As additional facilities are installed for its recovery and conversion to fluoride salts, this fluorine source could replace H F to a major extent in these uses. At present, it isn't e c o nomically possible to convert fluosilicic acid t o H F . If that problem is solved, it will h a v e a profound influence on the manufacture of H F as w e k n o w it today. T h e consumption figures for H F are substantial. H o w e v e r , most of the market is captive, and very little is available to a merchant producer. Uses are d i v i d e d into captive and nonc a p t i v e markets, and although these divisions are not perfect, they are close e n o u g h for our purposes. It should b e noted that the t w o areas w i t h the largest potential expansion are both basically c a p t i v e .
Captive and Noncaptive Uses of H F in 1957 (In short t o n s ) Captive Noncaptive Aluminum All others 3 6 , 0 0 0 industry 53,000 Fiuorocarbons 38,500 Salts 7,500 Total 99,000 T h e fact that almost 7 5 % of the present market is c a p t i v e d o e s not make H F any less important as a
to h a n d l e
by-product
gypsum
slurry
chemical, but it definitely limits the demand reaching a merchant producer and makes it less interesting to a potential new producer.
Here's Where Inorganic Fluorides G o (short tons, excludes A I F 3 and Na3AlFe) as 100 % HF
Aluminum Industry Aluminum fluoride and synthetic cryolite are made almost entirely by the aluminum producers themselves for use as a flux and electrolyte in the production of primary aluminum. Although aluminum production has bogged down along with other phases of our current economy, its future is still considered favorable. As aluminum production grows so will the need for aluminum fluoride and cryolite. Considerable quantities of cryolite have been imported for some time, In the past few- years total imports have been in the range of 20.000 to 30,000 short tons per year, about equally divided between natural and synthetic. There is some indication that imports, at least of natural cryolite, will remain at the same general level. This means that in the future, domestic synthetic cryolite will make up a larger portion of the increasing needs. As previously mentioned, fluorides for aluminum production are being made to a limited extent from byproduct silicofluorides. If this trend continues, and there are indications that it will, the HF requirements for these applications may decline or possibly hold constant, with increases coming from the silicofluoride route. Fluorocarbons You do not have to be a chemist or a market research man to appreciate the growing market for fluorocarbons when you know that every time you turn around "they've put something else in one of those aerosol cans" or that one of your lucky neighbors has just completely air-conditioned his house. Some of the new uses aren't quite as well known, but they indicate a promising future. The fluorocarbons were first produced commercially by Du Pont in the early 1930's. Their consumption growth has been steady and rapid and probably exceeds 200 million pounds per year at the present time. It is estimated that the propellant and refrigerant industries each consume about 45% of the total production. Plastics and other miscellaneous products are small compared to these uses and, combined, are estimated at 10% of the total production.
Sodium fluoride Boron trifluoride Sodium bifluoride Ammonium bifluoride Fluoboric acid and its metal salts Potassium bifluoride Others Total
as Salt 6,000 2,000 2,500 2,000 9O0 300 800 14,500
1,900* 1,700 1,650 1,400 450 150 250° 7,500
° Sodium fluoride, potassium titanium fluoride, and others made in part from silicofluorides
Because of the extreme reactivity of fluorine, a fluoride of almost every element probably exists (except, perhaps, of the inert gases). But only a limited number have become commercial chemicals. Sodium Fluoride. The major uses of sodium fluoride are in the manufacture of rimmed steel, water fluoridation, and chemical cleaning. Examination of the uses of sodium fluoride does not point to much of a change from the very small growth in the past. Boron Trifluoride. Boron trifluoride as a catalyst is the subject of some several hundred patents. However, its commercial applications to date have not approached that level. The foremost uses are in producing coal tar and petroleum resins, and lube oil additives. Indications are that use of boron trifluoride will continue to grow on a modest scale along with growth of the end products of the reactions it catalyzes. Sodium Bifluoride. Principal uses for this chemical are in the horizontal acid line process for electrotinning steel for the well known "tin" can, and as a laundry sour. The future of sodium bifluoride is not overly encouraging. The annual rate of increase in the production of tin plate has diminished from almost 20% in 1952 to less than 10% in 1957. Ammonium Bifluoride. Ammonium bifluoride is one inorganic fluoride that has shown some growth in the past few years. It owes most of its use to the fact that it provides a method of using HF without some of the problems associated with handling HF. Ammonium bifluoride is used in industrial chemical cleaning and in acidizing oil wells when there are siliceous materials to be dissolved. Ammonium bifluoride also plays an important part in producing beryllium metal. Fluoboric Acid and Its Salts. Fluoboric acid is used in electropolishing aluminum and in cleaning and pickling items to be plated in a fluoborate bath. Potassium fluoborate is used as a filler and grinding aid in making resinoid grinding wheels. Because of somewhat higher costs, fluoborates have been limited to specialty applications. Growth in the past has been steady but rather slow, perhaps in the range of 5 to 10% per year, and will probably continue at this rate. Potassium Bifluoride. Potassium bifluoride is used as an electrolyte in making fluorine. The fluorine production is primarily by AEC contractors for making uranium hexafluoride. Others. There are many fluorides which are sold only in very small quantities. Some of these are important enough, or appear to have future possibilities promising enough, to warrant at least a brief mention. Although sold in fair quantities for the grain refining of aluminum, a large part of the potassium titanium fluoride and potassium zirconium fluoride is made from silicofluorides. Thus as a market for HF they are not too large. Owing to its high dielectric strength, sulfur hexafluoride is being used on a limited scale as a gaseous insulator for electrical equipment. Perchloryl fluoride is a rather interesting new chemical with some very unusual properties. Its primary use at the present time is as a rocket fuel oxidizer. Chlorine trifluoride is finding use in oil well drilling operations. Although it is well publicized, consumption of stannous chloride is actually very small—on the order of 25 tons per year.
DEC.
2 2,
1958
C&EN
37
General Chemical and Pennsalt also produce these chemicals, and Union Carbide Chemical is coming on stream now. This brings total U S. capacity to about 450 million pounds per year. This should he enough to meet requirements for the next four to six years. Although it does not manufacture the conventional propellant-refrigerant type of fluorocarbon, Minnesota Mining and Manufacturing produces Kel-F ( polychlorotrifluoroethylene) and various unusual perfluorocarbons. The principal commercial fluorocarbons are trichlorofluoromethane— CCl :l F (fluorocarbon 11), dichlorodifluorornethane—CCL2F2 ( fluorocarbon 12), difluorochloromethane— HCClF2 ( fluorocarbon 22 ). Fluorocarbons 1 1 and 12 are used in various combinations, sometimes with other chemicals, such as methylene chloride, for aerosol propellants. They also find wide use as refrigerants. Fluorocarbon 22 is also finding increased use as a refrigerant. The fluorinated plastics Teflon and Kel-F are becoming increasingly important, also. In addition to its use as a refrigerant, fluorocarbon 22 serves as the raw material for tetrafluoroethylene, the monomer for Teflon. Fluorocarbon 113 is dechlorinated to produce trifluorochloroethylene, the monomer for Kel-F. Fluorocarbon 12 probably accounts for over half of the total production of the fluorocarbons with fluorocarbons 11 and 22 making u p most of the balance.
Atomic Energy Anhydrous H F has played a vital part in the production of uranium. It is used to produce U F 4 from the oxide and also is converted to elemental fluorine to produce UF6 from UF 4 . In 1957 approximately 27,000 tons of anhydrous H F were purchased and 16,000 consumed. The remainder was returned as 70% aqueous acid and used for applications which require it, such as pickling, metal cleaning, and frosting glass. In fact, most of the aqueous acid consumed last year came from this source. The future of the AEC's program is naturally not public information. But there is some indication that H F requirements for atomic energy are leveling off. Fusion may be more important than fission in the future. In addition, some decreases in the gross consumption are indicated from now on as the AEC returns a smaller percentage of the intake as spent aqueous acid. 38
C&EN
DEC.
2 2,
1958
Aqueous hydrofluoric acid is widely used in mixtures with other acids, such as nitric, for pickling stainless steel. Production of stainless and other heat resisting steels has increased significantly but not phenomenally over t h e past several years and. relative to total steel production, will probably continue to grow. However, there are many new products and techniques which are competing with it and will tend to take some of this growth. A modest amount of hydrofluoric acid is used in metal cleaning operations of various types, primarily to remove silica from castings.
Petroleum Alkylation Another use for H F is in petroleum alkylation. High octane blending components for gasoline are produced by the anhydrous H F or sulfuric acid catalyzed alkylation of isobutane with butylène or other olefins. The H F process was introduced during World War 11 and has grown considerably since that time. Because of the larger volumes of sulfuric acid consumed and sludge waste acid produced per barrel of alkylate. H F is usually used when the proposed site is a considerable distance from a sulfuric plant or sludge regeneration unit. While sulfuric still dominates alkylate production in the U. S., H F is increasing its share of the total capacity. Considering the future of alkylation as a whole, it should be looked upon
A. H O W A R D S T U E W E received a B.S. in chemistry from the University of Cincinnati in 1 9 4 8 a n d an M.S. in 1949. After graduating, h e worked for Nopco Chemical at its control, development, and technical service laboratories in Harrison, N. J. In 1956, Stuewe joined Stauffer Chemical's market development department in New York City. Here he has studied the production and sale of hydrogen fluoride and its derivatives.
is being used at various stages of ore treating and refining of several "special metals." Most important among these special elements are niobium, tantalum, béryllium, and the rare earths. Because of their association in many cases with the defense effort, production has mushroomed recently, with a corresponding increase in the need for HF. Although the future of this group of materials is currently spotty—some of them are suffering along with the rest of the metals market—most producers are optimistic about the future development of industrial as well as military applica-
HG. takes Hold is Alkyfation
TEMERATURE ACID
r Source: The Oil and Gas:JournalTEMERATURE ACID only as one method of making high powered components for gasoline. T h e automobile makers' boosting of engine horsepower every year will be reflected in increased demands for high quality gasoline. Conversion of the commercial airline fleets to jets, burning JP-4, will tend to slow down growth of high octane gasoline consumption. Turbine engines for automobiles appear to b e a little too far from commercial use to consider now. acid, primarily aqueous, Hydrofluoric
tions. Production of special metals may prove to b e one of the largest nongovernment, noncaptive markets for H F . Although important, the historical use of H F for etching and frosting glass consumes only a very small portion of the H F produced today. Most of the 2000 tons is used by the large light bulb manufacturers to make the common frosted bulb. The use of electric lights will prob(Continued
on page
57)
Elemental Fluorine
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FEATURE (Continf.ed
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ably continue to grow at a rate faster than the general population increase. However, the rising use of fluorescent lights and the more recent advent of the ceramic coated bulbs may hold down growth of the frosted bulb. Miscellaneous There are several minor applications for H F which are not listed elsewhere. Uranium is being recovered from phosphate rock fertilizer operations in Florida. At the present time, this use is estimated to consume 300 tons of HF annually. And under certain conditions H F and/or some of its salts are used in chemical milling to remove selectively undesired areas from aircraft and other metal parts. This use is new and currently a small consumer of HF.
No discussion of H F would be complete without mention of elemental fluorine. Since it is made from anhydrous HF, it can be considered as a derivative of it. although that probably isn't the way we usually look at it. A considerable amount of fluorine is generated for making uranium hexafluoride. In addition, commercial quantities of fluorine are available for other uses. However. it is believed that these are still under development. There has been considerable discussion of the use of fluorine as an oxidizer in military rockets and interplanetary commuter vehicles. Because of its extreme reactivity many problems will have to be solxed. If at zero minus two seconds the control officer decides not to fire a Vanguard or Jupiter rocket, the liquid oxygen can be bubbled into the air with some beneficial effects. Things would not be so simple with fluorine. Nevertheless, ingenuity has solved tough problems before; and because» of the tremendous power that fluorine can unlock, some day its use may be considered as easy as the once dificult-to-handle anhydrous hydrofluoric acid is today. Recent announce-
ments by Bell Aircraft inu.. ate that progress is being made in this application. Also Allied's General Chemical is now shipping tonnage quantities of liquid fluorine in tanks surrounded by liquid nitrogen.
The Future Predicting the future of anything is usually difficult, and in addition it is rather risky when you realize that five years from now someone might check up on you But since it is expected, and better men have plunged off the deep end in the past, i have offered a few projections. There are two basic assumptions in the estimates of future HP consumption. First, that the aluminum industry will recover from its current slowdown and follow its historicsteady rise; and second, that air-conditioning, aerosol packaging, and fluorinated plastics will continue their rapid expansion. New organic fluorine compounds will most probably add to the conventional fluorocarbons. In addition, it is assumed that by-product silicofluondes will not replace significant amounts of HF in producing the salts. •
AG CHEMICALS AND FOREIGN POLICY To: Walter J . Murphy. E d i t o r i a l D i r e c t o r ACS A p p l i e d P u b l i c a t i o n s AG AND FOOD'S December f e a t u r e a r t i c l e s h o u l d appeal t o a l l who s h a r e your i n t e n s e i n t e r e s t i n t h e i n t e r n a t i o n a l aspects of chemistry. I n " A g r i c u l t u r a l C h e m i c a l s in the World Market," E. T. C o l l i n s w o r t h , J r . ( p r e s i d e n t of V e l s i c o l Chemical C o r p . ) , p r e s e n t s a l u c i d a n a l y s i s of the p a r t t h a t f e r t i l i z e r s and p e s t i c i d e s can p l a y , and d o u b t l e s s w i l l p l a y , i n d e c i d i n g some of the w o r l d ' s t o u g h e s t p o l i t i c o economic q u e s t i o n s . Mr. C o l l i n s w o r t h ' s c o n c l u s i o n s , and h i s recommendations f o r i n t e l l i g e n t , forward—looking action on the p a r t o f i n d u s t r y — e s p e c i a l l y the p r o d u c e r s of p h a r m a c e u t i c a l s and a g r i c u l t u r a l c h e m i c a l s - - a r e food f o r s e r i o u s thought. It seems t o me t h e y j i b e w e l l w i t h your r e p e a t e d u r g i n g s that the chemical process i n d u s t r i e s shoulder greater r e s p o n s i b i l i t y i n p r o m o t i n g t h e cause of freedom throughout the w o r l d . Mr. C o i l i n s w o r t h ' s data a r e on f e r t i l i z e r s and p e s t i c i d e s , but h i s a r t i c l e c a r r i e s important i m p l i c a t i o n s f o r a l l . c h e m i c a l p r o c e s s i n g i n d u s t r i e s — a n d o t h e r i n d u s t r i e s as w e l l . B e s i d e s t h i s e x c e l l e n t f e a t u r e , t h e December i s s u e o f f e r s AG AND FOOD'S u s u a l w e l l - b a l a n c e d menu o f s t a f f - w r i t t e n i n t e r p r e t i v e r e p o r t s , b u s i n e s s and r e s e a r c h n e w s l e t t e r s , c o n t r i b u t e d r e p o r t s of s c i e n t i f i c p r o g r e s s , and news of p r o d u c t s , p r o c e s s e s , equipment, l i t e r a t u r e , and p e o p l e . And s p e a k i n g of p e o p l e , I s h o u l d l i k e t o c a l l speciala t t e n t i o n to our "Personal P r o f i l e " o f Dr. H. L. H a l l e r o f t h e USDA. One f r e q u e n t l y h e a r s c r i t i c i s m o f t h e huge and growing F e d e r a l Government, or of t h e " b u r e a u c r a t s " with which i t i s o f t e n a l l e g e d t o b e s t a f f e d . A l l too few p e o p l e know o f t h e immense c o n t r i b u t i o n s t h a t d e d i c a t e d government s c i e n t i s t s l i k e Dr. H a l l e r have made t o the well—being and p r o g r e s s o f t h i s n a t i o n . In c a l l i n g a t t e n t i o n t o t h e c a r e e r o f Dr. H a l l e r , and i n d i r e c t l y t o the work o f o t h e r s l i k e him, we have su r e l y brought more honor t o o u r s e l v e s than we c o u l d p o s s i b l y b r i n g t o them.
R. N . H a d e r , E d i t o r J o u r n a l of A g r i c u l t u r a l a n d F o o d
D E. C 2 2,
Chemlstry
1958
C&EN
57
