FLUORINE CHEMI LOREN C. MOSIER AYD WAYNE E. WHITE Ozark-Mahoning Co., Tulsa, Okla.
application in t h e petroleum industry are still being guarded as confidential, but i t may be said that this application will possibly open up a market for a tremendous amount of the new fluorophosphoric acids. Large scale tests are planned to permit final evaluation of these acids for the particular application. The discovery a t the University of Rochester t h a t sodium monofluorophosphate, Na2P03F, is highly effective i n preventing carious teeth in test animals and further t h a t this salt is only about one seventh as toxic as sodium fluoride has led to much interest and activity in the field of dental hygienic preparations where these two properties are of particular significance.
T h e fluorine chemicals pilot plant was established to supply experimental quantities of fluorophosphoric acids and salts, compounds never before available. Methods have been evolved for making t h e three fluorophosphoric acids (monofluoro, &P03F; difluoro, HPOzF2; and hexafluoro, IIPF6) and salts of the mono and hexa acids. Hundreds of samples have been supplied to laboratories for investigational purposes. The two most significant developments up to the present time in this new field of fluorine chemicals are in the rather widely divergent industries of petroleum production and medicinal-dental products. Details of the
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BENOH
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Figure 1. Floor Plan of Quonset Pilot Plant
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S a major producer of fluorspar, the OzarkXahoning Company has a definite interest in the development of new compounds which might lead to increased usage of this mineral. Iiesearc~h in fluorine compounds has been carried on for a number of years. In the research program particular attention has been given to the fluophosphoric (FP) compounds. Early laboratory inveqtigations led to methods for the production of anhydrous mono- (HZl'OjF) and difluophosphoric (HP02F2)acids and a Loncentrated aqueous solution of hexafluophosphoiic acid (HPF6). Salts of the mono- and hexafluophosphoric acids have also been prepared and studied ( I ) . The development of uses for these new compounds has required collaboration with other laboratories, and a pilot plant was necessary for preparation of larger-than-laboratory quantities for supplying samples as well as the selection of satisfactory equipment and methods for I egular commercial production. The reactants, reactions, and products all presented problems which had to be considered when planning the pilot plant arid equipment. A 40 X 40-foot quonset 11as erected for the pilot plant. -kt the time of construction, 1947, this \vas the most readily available type building. It has been used without insulation. Tulsa wintei temperatures are such that a 200,000-B.t.u. space heater, suspended in one corner of the building, proved adequate except in the coldest weather. The general arrangement o l the building is shown in Figure 1. Kot indicated are the floor drains located in the centers of the four quarters with the floor sloping in each quarter into the drain.
January 1951
INDUSTRIAL AND E N G INEERING CHEMISTRY
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magnesium oxide is kept in the safety equipment cabinet for use in the form of a thin slurry on skin areas accidentally contacted b y hydrofluoric or fluophosphoric acids. Figure 2. Dry Compartment for Handling Phosphoric Anhydride and Other Hydrophilic Substances Bclow oom artment on left is %ox containing desiccant; behind box is blower for circulating air through desiccant and working compartment
Anhydrous hydrogen fluoride and other noxiously fuming liquids must be handled in the preparation of fluorine compounds. For fume removal a blower (Ilg BC25, 0.5 hp., 1750 r.p.m., 1960 cubic feet per minute) was mounted a t one end near the roof with a 13-inch aluminum duct extending 20 feet along t h a t side of the building. For spot ventilation, a 10-inch diameter, lightweight neoprene-coated, flexible tube may be attached to the duct at either of two places. The tube (American Ventilating Hose Company) is in 2.5-foot lengths, and consequently the length can be varied as needed to reach the area where fume collection is required. For emergency use an oxygen-demand type mask is available in the safety equipment cabinet near the door. A safety shower controlled by a magnetic valve and a microsiiitch is also installed near the door. A howler alarm is connected in parallel with the magnetic valve to summon aid in case of emergency. Complete neoprene suits are provided for protection from acids. A can of
FLUOPHOSPHORIC ACIDS
Phosphoric anhydride is usually employed in the preparation of the fluophosphoric acids. I n relatively small scale preparations, this oxide is weighed and transferred to the reaction vessel in a dry compartment (Figure 2). This dry hood is a n airtight compartment with Pittsburgh Plate Glass Allite CR 39 sheet plastic windows in wooden frames; the windows can be removed for access to the inside of the hood. Plastic is used rather than glass which would become clouded by fluoride fumes. The air is pulled through screen-bottomed trays of activated alumina by a small blower and circulated through the working compartment and hack down to the trays. Plastic sleeves are fastened in armholes in panels which can replace any of the plastic window frames. When the alumina is freshly activated, the phosphoric anhydride stags dry and powdery while heing handled inside the compartment. The dimensions of the dry compartment-40 inches wide, 58 inches long, 76 inches over-all height a t peak, and 44 inches maximum height within the compartment-are such t h a t an;\r spot in the working area can be reached by the operator from one or the other of the two or three armhole panels which are in place during the charging of the smaller reaction vessels. These smaller reactors are of two sizes-approximately 1-gallon and 6gallon capacities. Either size can be placed on a balance inside the dry-air compartment so t h a t the previously calculated desired amount of the phosphorus pentoxide can readily be charged into the vessel. The phosphoric anhydride is reacted with anhydrous hydrogen fluoride or with a concentrated aqueous solution to make the
Figure 3. Five-Gallon Reactor in Operating Position with Can of Hydrogen Fluoride in Position for Draining into Reactor ’
Figure 4.
Reactor is fine silver and jacket i s double-walled for cooling or heating; a similar double-walled jacket for a smaller reactor is shown in background
Aluminum tank (175-gallon) with HF cylinder i n position to bo drained into evacuated tank; end of fume-collecting tube is visible
Equipment for Larger Scale Production of FP Acids ( r i g h t center)
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Vo1. 43, No, I
FLUOPHOSPFIORIC SALTS
Altliougb home of Ihe salts can be made most satisfactoril> IJ\ n~utralizationof the acid by the desired base, in other instance. an entirely different reaction is better. This requires fusion oi the reaction mixture. Silver or graphite is commonly used foi coristiuction of the reaction vessel, which should be coveictl during heating to prevent escape of vapors. Because the molten salt should be poured before it cools n mpanq of quick and WIG, handling muqt lie piovided
PUALIZING V A L V E
Figure
5. Arrangement for Carrying Out Fusion Reaction in Closed Silver Container
Pyrometer and leads to thermocouple are shown lower lefL
fluophosphoric acids. The lieat of reactiou is rather high, and cooling is required during the mixing of the reactants. The nieans of adding hydrogen fluoride, of mixing the reactants, : ~ n dof removing reaction heat are shown in Figure 3. In the foreground is the 5-gallon reactor in place in a double-vr.alled jacket through which cold brine or Tater may be circulated. Mixing is effected by a rocking motion obtained through use of the motor and speed reducer visible in the picture. The hydrogen fluoride is added from the long container which is held rigidly by its support so that it moves with the reactor. I n the background in Figure 3 there is a similar device for use with the I-gallon reactor. The 5-gallon and 1-gallon reactors and the hydrogen fluoride container are of fine silver. Silver,' copper, aluminum, or polyethylene tubing can be used to conduct the hydrogen fluoride to the reactor which is evacuated bei'oi,e beginning a reaction so that the hydrogen fluoride will be drawn in readily. Flare nut-on-tubing type connectors are preferred. In some inst.ances it is convenient t o use a closed 5-gallon, jackeked, 316 stainless steel vessel made by the Pfaudler Company. It has an anchor-type agitator driven by an explosionproof motor and speed reducer. Difluophosphoric acid may be distilled from t'his t.hrough a stainless steel condenser. I n gencral, however, stainless steel equipment is not, recommended for use with the fluorine acids. For larger scale acid preparation an aluminum reactor is available; t,his is pictured in Figure 4. It's capacity is about 175 gallons; 1300-pound batches of the fluophosphoric acids can be made in this. The 16-inch opening permits rapid charging of the phosphorus pentoxide directly from GO- or 400-pound drums, and when handled properly the amount of water absorbed from the air is inconsequential. The cover can be attached quickly and the vessel evacuated so that it is ready to receive hydrogen fluoride from the cylinder mounted in its detachable cradle above the manhole. Cooling is effected by a water spray from the piping around the top of the reactor, Mixing is produced by the rocking mechanism shown in the picture.
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Figure 6.
Spray Dryer of 316 Stainless Steel
The requirements for the fusion 'rvere niet by the arrangement shown in Figure 5 . The container, about 1-gallon capacity, is rotated slowly for uniform heating in a gas flame. A thermocouple inserted in a crevice on the side of the silver container gives good temperature indication. The leads of the thermocouple arc brought through the shaft to a pair of copper rollector rings. Silver alloy springs attached to the pyrometer romplete the circuit from t'he slip rings t,o the galvanometer-type pyrometer. Hooks were made to lift the reactor out of thc furnace; a set oi' handles is used for holding the reactor while pouring the molteii salt. The spray dryer (Figure 6) was built to recover from solution certain salts which are subject t o hydrolysis. The blower draws the hot gases from the gas burner tangentially into the body and down past a baffle. The solution is sprayed into the chamber, and the hot gases quickly vaporize the water from the spray. The solids are separated by the centrifugal motion and collected in a jar a t the bottom of the cone. The capacity of the dryer is regulated by the capacity of the spray nozzle nnd the volume and temperature of the hot gases. ACKNOWLEDGiMEYT
The authors n-ish to express their gratitude to Floyd B. Bedwell for assistance in designing the 175-gallon reactor and to Jack H. Phillips for the drawings used for Figures 1 and 6. LITERATURE CITED
(1) ISD. ENG.CHEM., 40,2 4 A
RECEIYED May 1 5 , 1950.
(Septeqiher 1948)
