United States Patent Office Patented Feb
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3,428,422 United States Patent Office Patented Feb. 18, 1969 2 3,428,422 tent, the volatile P-material consists of approximately 5 PREPARATION OF PHOSPHORYL FLUORDE AND parts POF and 1 part HPO.F. DFLUOROPHOSPHORIC ACD In the practice of my process, it is merely necessary Robert A. Wiesboeck, Atlanta, Ga., assignor, by mesne as to heat a mixture of the phosphate source and fluoro signments, to USS Agri-Chemicals, Inc., Pittsburgh, Sulfonic acid to 150-400° C., preferably 350° C., to pro Pa., a corporation of Delaware duce phosphoryl fluoride and difluorophosphoric acid. No Drawing. Filed Nov. 14, 1967, Ser. No. 682,971 Sulfuric acid, which has a boiling point of 330° C. may U.S. C. 23-139 8 Claims be recovered as a by-product by heating the mixture to Int, Cl, C01b 25/10, 25/16, 33/08 400° C. The preferred procedure is to pass the vapor of fluorosulfonic acid through a hot bed of the phosphate 0. Source and collect the volatile product by fractionated condensation. The reaction begins at 150° C.; however, it ABSTRACT OF THE DISCLOSURE is advantageous to maintain the entire reactor at 350° C. Phosphoryl fluoride and difluorophosphoric acid are and, if desired, through 400° C. in order to remove the prepared directly from fluorosulfonic acid and a phos sulfuric acid. phate source, such as phosphate rock, phosphoric acid, a The reactant ratio is not critical; however, it is desir metal orthophosphate or metal polyphosphate, by heating able to use a 20-30% excess of the phosphate in order the mixture at a temperature of about 150-400° C. and to avoid the presence of unreacted fluorosulfonic acid in recovering the vapors as product. The evolved phosphoryl the product. fluoride and difluorophosphoric acid may be recovered 20 Employing phosphate rock containing 34.7% POs, a separately by the use of cold traps or other means. ratio of 2 parts rock to 3 parts fluorosulfonic acid cor responds to stoichiometric proportions. Silica in the rock is converted to SiF and the reactant ratio has to be BACKGROUND AND SUMMARY adjusted accordingly. The stoichiometric requirement of 25 fluorosulfonic acid to silica is 6.7:1. Conventional methods for the manufacture of phos The volatile product is passed through a series of traps phoryl fluoride are based on halogen transfer reactions of maintained at 100, -20, -100 and -196° C., whereby phosphoryl chloride with hydrogen fluoride or a fluoride by-product sulfuric acid, difluorophosphoric acid, phos Salt. Another method consists of heating phosphorus pent phoryl fluoride and silicon tetrafluoride are obtained in the oxide with calcium fluoride to 500-1000° C. Fluorophos 30 given order. phoric acids, on the other hand, are produced by reacting When phosphoric acid is the phosphate source reacted phosphorus pentoxide with hydrogen fluoride. All of the with fluorosulfonic acid, the following equation repre foregoing fluorophosphorus compounds are derived from sents the reaction with 100% HPO: phosphorus pentoxide which is accessible only through the electric furnace method. 35 I have discovered that phosphoryl fluoride and difluoro Ranges of phosphoric acids from 50% POs up to and phosphoric acid can be produced from phosphorus-con including POs itself are preferred. taining sources, such as phosphate rock, phosphoric acid, Specific examples illustrative of the invention may be a metal orthophosphate or a metal polyphosphate through set out as follows: the use of fluorosulfonic acid in a simple one-step opera 40 EXAMPLE tion. In the process, the phosphorus-bearing source is mixed with fluorosulfonic acid and the mixture heated to A 20.1-g. sample of pulverized phosphate rock was about 150-400° C. and the evolved vapors of phosphoryl placed on a screen in a vertical aluminum pipe and heated fluoride and difluorophosphoric acid may be recovered to 350° C. The phosphate rock had the following com while at the same time sulfuric acid is recovered as a by 45 position: 34.7% PO, 47.5% CaO, 5.57% SiO, 3.51% product. F, 1.36% Fe2O3, 0.70% AlO3. Fluorosulfonic acid vapor was introduced through the bottom inlet of the reactor DETALED DESCRIPTION pipe from an acid reservoir which was maintained at Phosphoryl fluoride (POF) and difluorophosphoric 200° C. acid (HPOF) can be prepared directly from phosphate The off-gas was passed through a series of traps main rock and fluorosulfonic acid. Other phosphate sources 50 tained at 100, -20, -100 and -196° C., collecting sul such as iron and aluminum phosphates or condensed furic acid, difluorophosphoric acid, phosphoryl fluoride species such as pyro- and other polyphosphates can also and silicon tetrafluoride in the given order. The reaction be used in place of phosphate rock. was terminated after approximately 20 g. of fluorosulfonic The reaction may be carried out in a suitable apparatus acid vapor had been passed into the reactor and a slow as, for example, a pressure reactor. If desired, fluoro 55 sweep of nitrogen was applied to move all volatile product sulfonic acid vapors may be passed through a hot bed of into the trapping system. A total of 0.9 g, of difluorophos pulverized phosphate rock or metal phosphate and the phoric acid and 4.5 g. of phosphoryl fluoride was obtained. volatile product collected in a series of cold traps or other means. EXAMPLE I The basic reaction principle can be expressed by the 60 Reacting 12.2 g. of aluminum phosphate and 25.0 g. following equation: of fluorosulfonic acid as described in Example I produced 7.3 g. of phosphoryl fluoride. EXAMPLE III Difluorophosphoric acid represents the hydrolysis product 65 of phosphoryl fluoride: Chemically pure calcium metaphosphate (19.8 g.) was heated together with 60.0 g. of fluorosulfonic acid in an POFs--HO->HPOF--HF autoclave to 200 C. The reaction was completed within Accordingly, the amount of difluorophosphoric acid one hour as indicated by pressure constants. The tempera formed is dependent on the moisture and hydroxyl con 70 ture was then reduced to 150° C. and volatile material tent of the phosphate source. was expanded into an evacuated steel cylinder. The col Employing phosphate rock of 1.0-1.5% moisture con lected product consisted of 12.9 g, of phosphoryl fluoride 3,428,422 3. 4. and a small amount of fluorosulfonic acid which was re the bed fluorosulfonic acid vapors to evolve phosphoryl moved by fractionation through a 0° C. trap. fluoride and difluorophosphoric acid vapors, and collect ing and recovering said vapors. EXAMPLE IV 6. The process of claim 5 in which sulfuric acid vapors A 25.0-g. batch of calcium pyrophosphate and 60.0 g. are also evolved and the sulfuric acid vapors condensed of fluorosulfonic acid was reacted as described in Example at a temperature of about 100° C. III. The produced volatile material contained 11.2 g. Of 7. The process of claim 5 in which said bed of phos phosphoryl fluoride. phate rock is maintained at a temperature of about 350 While in the foregoing specification I have set forth C. specific procedure in considerable detail for the purpose 8. The process of claim in which phosphate rock is of illustrating embodiments of the invention, it will be O the phosphate source and the evolved vapors, which con understood that such details may be varied widely by tain sulfuric acid, difluorophosphoric acid and silicon those skilled in the art without departing from the spirit tetrafluoride in addition to phosphoryl fluoride, are re of my invention. covered by passage through cold traps maintained at 100, I claim: -20, -100 and -196° C. 1. In a process for preparing phosphoryl fluoride from a 5 phosphate source selected from the group consisting of References Cited phosphate rock, phosphoric acid, and metal orthophos UNITED STATES PATENTS phates and polyphosphates selected from the group con 2,408,785 10/1946 Lange -------------- 23-139 sisting of iron and aluminum, ortho and polyphosphates, 20 2,423,895 7/1947 Lange et al. ---------- 23-139 the steps of heating said phosphate Suorce to about 150 2,488,298 11/1949 Lange et al. ---------- 23-39 400° C. in contact with fluorosulfonic acid to evolve phos 2,570,924 10/1951 Dupont ------------- 23-203 phoryl fluoride vapors, and collecting and recovering said 2,712,494 7/1955 Dupont ------------- 23-203 vapors. OTHER REFERENCES 2. The process of claim 1 in which said source con 25 tains moisture and difluorophosphoric acid also is evolved Berak, “Chemical Abstracts,” vol. 57, November 1962. and the vapors thereof collected. pp. 11910–11911. 3. The process of claim in which the phosphate source Hayek et al., “Chemical Abstracts,” vol. 50, 1956, p. is used in an excess of about 20-30%. 3133. 4. The process of claim 1 in which a phosphate source 30 Lange et al., “Chemical Abstracts,” vol. 41, 1947, p. is maintained as a hot bed and fluorosulfonic acid vapors 4397, are passed through the bed to produce the volatile prod Ct. OSCAR R. VERTIZ, Primary Examiner. 5. In a process for preparing phosphoryl fluoride and difluorophosphoric acid from phosphate rock, the steps HERBERT T. CARTER, Assistant Examiner. of heating phosphate rock to form a hot bed having a 35 U.S. C. XR. temperature of about 150-400° C. and passing through 23-203, 205, 167, 172 .