COMMODITY S EUMES
E D W I N M . O T T , Pennsylvania Salt Mfg. Co, Philadelphia,
Pa.
Fluorine N e w fluorspar deposits, nevf methods for recovering fluorides from phosphate rock, new markets—all these point to a bright future for fluorine chemicals
OK one side of the fabulous fluorine family is a material so dynamic that it will attack anything except the inert gases and chemicals that are already completely fluorinated; on the other, compounds so passive that they are largely impervious to a n y chemical or physical attack. The fluorine family includes the most active as w e l l as the most inert compounds. Much has been said about the unusual properties of fluorine chemicals. The re activity of fluorine—the gas that will b u m even water or asbestos; the inertness of fluorinated plastics like Teflon and Kel-F; the ability of hydrofluoric acid to dissolve glass; the great stability of the fluorocarbons. These and other unique accom plishments have attracted wide popular interest to fluorine compounds. While these extreme characteristics of fluorides have resulted in the development of materials for remarkable uses, most of the major commercial fluorine chemicals are employed because of properties that are m u c h more prosaic. They are sound chemical tools used in the manufacture of a w i d e variety of products that are essen tial t o our comfort and security. Fluorspar—The Primary S o u r c e of Fluoride Ion Fluorspar (calcium fluoride*) is the primary source of commercial fluoride ion. It is a major raw material for the chemi cal industry and is also used in the steel, aluminum, glass, enamel, and other proc ess industries. Most of the IT. S. domestic production comes from the Illinois-Ken t u c k y deposits, but it is also mined in Colorado, N e w Mexico, Utah, Nevada, Texas, Arizona, and Montana. In 1950, U. S. consumption of spar was 426,000 short tons, of which about 29 % came from foreign sources. F o r u s e in the chemical industry, fluor spar is refined to a ininimiim of 9 8 % cal c i u m fluoride and a maximum of 1 % silicon dioxide. This is called acid grade spar. 1626
GROWTH OF FLUORINE CHEMISTR1
The consumption of spar by the chemical industry is a good index of the rising im portance of the fluorine chemicals. In the absence of published inforraation it would be difficult to compile a n accept able and authoritative end ixse pattern for fluorine chemicals. T h e following table therefore is offered only as a general indi cation of hydrofluoric acid uses by con suming industries. Consumption of HF (Pennsalt Estimate) Industry Chemicals Aluminum Steel Petroleum Glass Miscellaneous Total
130
Ρ u.
% 42 42 6 6 2 2 100
Natural cryolite is another source of fluorine. Containing 54.4% fluorine, it has the highest fluorine content of any natural material of commercial significance. The Danish mine at Ivigtut, Greenland, is the only known commercial cryolite deposit in the world. Because of its tiigher cost and limited supply, cryolite is consumed as such by the metallurgical, glass, and ceramics industries and is not used in the production of fluorine cnemicals. The Pennsylvania Salt Manufacturing C o . im ports crude natural cryolite £rom Greenland and refines it at its Natrona, Pa., works. Phosphate rock could prove to "be an important source of fluorine in the future. The rock contains about 3-5% fluorine; in die production of superpHospHate about one third of this can b e recovered. At the current superphosphate production, rate, the amount of by-product fluorine i n com bined form is equivalent, in terms of fluorine content, t o more than half the total U . S. spar consumption and exceeds present requirements for acid grade spar. T h e Tennessee Valley Authority has developed a method of recovering the C H E M I C A L
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2Na*AlF« (cryolite) + 12H^O T h e inorganic fluorides have a w i d e range of industrial applications. The m o r e important of this group are the fluorides of aluminum, sodium, ammonium, p o t a s sium, barium, zinc, magnesium, chromium, and antimony. T h e principal use for aluminum fluo ride (AlF 3 ) is in the manufacture of alu minum, where it is a d d e d to the m o l t e n cryolite b a t h as an electrolyte component. It also has less important applications i n the ceramics industry. T h e Aluminum C o . of America, t h e largest U. S. producer, makes a l u m i n u m fluoride b y t h e reaction of alumina a n d H F : Al 2 Os 3 H 2 0 + 6 H F - > 2 AlFa -f 6 H 2 0 T h e sodium salt has b e e n much p u b licized in recent years in connection w i t h its use by municipalities for addition t o water supplies to reduce the incidence of dental caries. It is also a d d e d to m o l t e n steel ingots in the production of r i m m e d steel and is used in insecticide, fungicide, and preservative compositions. While there are m a n y and varied applications for the other simple fluorides, few of t h e m consume tonnage quantities. Synthetic cryolite is b y far t h e most i m portant of t h e double salts. Sodium anti mony fluoride is used as a mordant in dyes and in the synthesis of organic fluorides. Potassium titanium fluoride is used in t h e manufacture of high strength aluminum. T h e sodium, potassium, a n d ammonium fluoborates find application as sand agents in t h e casting of aluminum and m a g n e sium, in electrochemical processes, a n d in chemical research. T h e important acid fluorides, s o d i u m , potassium, a n d ammonium bifluoride, a r e used as laundry sours, w e l d i n g fluxes, a n d as components of glass frosting compounds. Potassium bifluoride is t h e electrolyte in the p r e p a r a t i o n of elemental fluorine. Dramatically elevated to a position of extreme importance during t h e final stages of W o r l d W a r II, a fluoride was instru mental in harnessing t h e power of atomic energy. I n t h e development of n u c l e a r reaction it b e c a m e necessary to s e p a r a t e and concentrate certain isotopes of u r a nium. For this purpose, a uranium c o m p o u n d that is thermally stable a n d h a s 1628
a high vapor pressure near room tempera t u r e was needed. Uranium hexafluoride, U F e , was t h e only material meeting these requirements and thereby a fluorine chemical aided in unveiling a new vista of physical and chemical resources for t h e advancement of mankind. Uranium hexafluoride is representative of a group of fluorides t h a t require gas eous elemental fluorine in their synthesis. Others of this type are chlorine trifluoride (C1F 3 ), b r o m i n e trifluoride ( B r F s ) , cobalt trifluoride ( C o F 8 ) , m a n g a n e s e trifluoride ( M n F 3 ) , mercuric fluoride ( H g F 2 ) , silver difluoride ( A g F 2 ) , a n d «mlfur hexafluoride (SF·). These materials are characterized hy high prices, ranging from $ 2 per pound for sulfur hexafluoride t o $ 3 0 per pound for silver difluoride. L o w production vol u m e contributes to their high cost and de velopment of large commercial applica tions could effect significant price reduc tions. However, they would never become as low in cost as the wet process fluorides. Except for sulfur hexafluoride, all of these fluorides from fluorine are extremely reactive. T h e metallic polyfluorides are used in indirect fluorination where ele mental fluorine would he too violent. Chlorine trifluoride a n d bromine tri fluoride are used in d u a l halogenation under controlled conditions. On the other extreme, sulfur hexafluo ride is very inert. D u e to its high dielec tric strength it is used as a gaseous in sulator in x-ray e q u i p m e n t and the like w h e r e extremely high voltages are en countered. It is nontoxic, extremely stable, nonflammable, a n d quite heavy. Pennsalt has been selling elemental fluorine as a compressed gas in cylinders. T h e major uses which h a v e developed to date are in t h e fields of fluorine research and rocket propellants. Larger quantities of fluorine are consumed in captive p l a n t s in the production of u r a n i u m hexafluoride, chlorine trifluoride, sulfur hexafluoride, metallic polyfluorides, and other fluorine derivatives. Fluosulfonic acid, FSO3H, is used com mercially as a catalyst in organic reactions and as a reagent in chemical processes. It is produced by treating liquid or gaseous hydrogen fluoride with liquid or gaseous sulfur trioxide under anhydrous conditions. Boron trifluoride has b e e n finding in creasing application as a catalyst i n or ganic reactions. It is shipped as a gas at a pressure of 1800 pounds per square inch. Complexes of boron trifluoride with ether, alcohol, and other organics are frequently used for convenience in shipping and handling. Fluorocarbons—Newcomers To the Family M u c h publicity has b e e n given these newcomers to the fluorine chemicals family. By the novel technique of intro ducing the fluorine atom into the organic compound directly in the electrolytic cell ( a method developed by J. H. Simons and exploited commercially by Minnesota Min ing & Mfg. C o . ) , m a n y fluoroorganics can b e prepared. They can also b e made b y CHEMICAL
N a t u r a l cryolite (Na 3 AlFe) from Green land is purified to 9 9 % at Pennsalt's Natrona, Pa., plant. I n the flotation proc ess, impurities, chiefly granite, are floated off t h e b a t h the reaction of hydrocarbons or chlorohydrocarbons with metal polyfluorides. Some of the m o r e important products of this class are t h e fluorocarbons ( organic c o m p o u n d s composed of carbon and fluo rine, e.g., C2F0); perfluoroethers (e.g., CeFicO ) ; perfluoroamines ( e.g., ( C3F7 )»Ν ) ; a n d fluoroorganic acids ( e.g., C2F5COOH). T h e y have been proposed for use as di electric liquids, fire extinguishing agents, lubricants and lubricant additives, and other applications w h e r e their great sta bility a n d other u n i q u e properties could b e used t o advantage. New Markets for Products Make Future Bright After W o r l d W a r II there was concern about t h e adequacy of U. S. fluorspar re serves a n d it was feared that the develop ment of the fluorine chemicals industry might b e curtailed b y a lack of this ore. However, new deposits discovered in the U. S., Mexico, Africa, and elsewhere assure us of a plentiful supply of fluorides for many years. Also, recent technological d e velopments promise that in case of short age, fluorspar supplies will be supple m e n t e d b y fluorides recovered from phos phate rock. More recently t h e scarcity of sulfur has thrown a shadow across the hydrofluoric acid picture. W i t h o u t sulfuric acid, hydro fluoric acid cannot be produced cheaply and the industry w o u l d b e retarded. H o w ever, t h e sulfur outlook has improved and there is no fear t h a t its shortage will have any serious effect on the fluorides industry. W i t h the basic raw materials picture being bright, w e can expect the fluorine chemicals to continue their natural, rapid growth without restriction. Recent devel opments of the u s e of fluorides in atomic energy, water fluoridation, fluoroorganics. and metallurgy a r e expected to accelerate the r a t e of d e m a n d for fluorine chemicals. AND
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