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United States Patent Office Patented May 7, 1974 3,809,762 United States Patent Office Patented May 7, 1974 borate has been lost due to decomposition during the 3,809,762 various separation steps; thus resulting in a low yield. SYNTHESIS OF SODIUM HYDROXYTRI- FLUOROBORATE SUMMARY OF THE INVENTION Louis O. Gilpatrick, Oak Ridge, Tenn., assignor to the It is thus an object of this invention to provide a process United States of America as represented by the United ° whereby sodium hydroxytrifluoroborate may be produced States Atomic Energy Commission without the production of impurity by-products. No Drawing. Filed Aug. 18, 1972, Ser. No. 281,664 Int. CI. CO lb 7/00, 35/00 It is a further object of this invention to provide a U.S. CI. 423—277 4 Claims process whereby sodium hydroxytrifluoroborate may be 10 produced with a high yield and without the necessity of subsequent separation steps. ABSTRACT OF THE DISCLOSURE These and other objects are accomplished by a process Sodium hydroxytrifluoroborate is synthesized by re- wherein bicarbonate of soda is reacted with boron tri- acting bicarbonate of soda with boron trifluoride. fluoride to produce sodium hydroxytrifluoroborate as a single product. 15 BACKGROUND OF THE INVENTION DETAILED DESCRIPTION This invention was made in the course of, or under, a According to this invention it has been found that contract with the United States Atomic Energy Commis- sodium hydroxytrifluoroborate can be prepared by react- sion. It relates generally to a process for producing sodium 20 ing bicarbonate of soda with boron trifluoride to produce hydroxytrifluoroborate. only the desired product. This is somewhat surprising since NaF and complex mixtures of fluoroboric acid or H3BO3 In the operation of a molten salt breeder reactor, a would, under some conditions, be the expected products. a carrier salt of LiF, BeF2, and ThF4 (approxi- mately 72, 16, and 12 mole percent, respectively) con- Preferably, the reaction according to this invention is carried out by first forming a saturated solution of taining a small amount of UF< and/or PuF3 is used as 25 a reactor fuel. As a consequence of neutron reactions NaHC03 in H20 at a temperature of —5 to —20° C. The with the lithium in the carrier salt, tritium is produced as amount of NaHCOa added to the water is not critical so an undesirable by-product in the operation of this par- long as the solution is saturated as will be evidenced by ticular reactor. About 98% of the tritium present in the an excess of NaHC03 powder forming a slurry. In gen- reactor is produced by the GLi(n,a)T and TLi(n,a)T re- 30 eral, it is preferred to add about 0.1 to 0.25 mole of actions. Tritium, when produced in the reactor core, has NaHC03 per mole of water. The NaHC03 preferably is the ability to diffuse through the alloy container and added to the water at room temperature and then cooled primary heat exchanger to the coolant salt. If nothing is to —5 to —20° C. BF3 gas is then bubbled through the done to impede the flow of tritium, it will diffuse in a slurry at a flow rate of about 0.25 to 1.0 mole/hour per similar manner from the coolant salt through the second- 35 mole of NaHCOa while maintaining the temperature with- ary heat exchanger to steam used for operating turbines. in the range of —5 to —20° C. At the beginning of the Tritium, if it progresses to the turbines, will be released BFy addition the pH of the slurry is about 6.5. As the to the atmosphere and because of this high activity and BF3 is dissolved the pH of the solution is gradually low- /3-emitting characteristics of tritium, its presence in the ered until a pH of 4 is obtained. A pH of 4 represents the atmosphere creates a threat to both man and his environ- 40 most favorable pH range for stability of the product as ment. well as substantially the correct stoichiometric ratio of NaHC03 and BF3 required for the desired reaction Fortunately, it has been found that if a hydrogen-con- taining compound is introduced into the coolant salt in NaHC03 +BF3-> NaBF30H+C02t- quantities much greater than that of the tritium, the tritium will be sorbed, basically by ion exchange, to pre- 45 The slurry should be stirred continuously during the vent further diffusion to the secondary steam coolant. BF3 addition. It is critical to the process that the tempera- ture be maintained below —5° C. or preferably within the One such hydrogen-containing compound is sodium range of —5 to —20° C. If the temperature is raised above hydroxytrifluoroborate (NaBF3OH) which can be used this range the product will be contaminated with with a coolant salt of sodium tetrafluoroborate. In actual operation, a 200 megawatt reactor releases about one 50 H3B03+NaF gram tritium per day. This particular reactor design has formed by the reaction of NaBF^OH with H20, i.e., about 200 tons of sodium tetrafluoroborate (NaBFt) coolant to which is added 100 p.p.m. to 0.1 wt. percent NaBF30H+2H20-»NaF+H3B03+2HF. sodium hydroxytrifluoroborate as a tritium sink. Tritium, If the temperature is below this range the system may which is trapped by the sodium hydroxytrifluoroborate, 55 freeze. can be removed from the coolant in a side stream by When the pH of the solution reaches 4, the addition of fluorinating with HF to convert the hydroxytrifluoroborate BF3 must be stopped or the pH will decrease to about 2 at to the tetrafluoroborate, thus releasing hydrogen and trit- which point the product becomes unstable and decom- ium as collectable water vapor for disposal. poses to NaBF4. At this point stirring is continued until a In the past, sodium hydroxytrifluoroborate has been 60 clear solution is achieved. This normally takes less than synthesized by reacting a saturated aqueous solution of 5 minutes from the time that the BF3 addition was dis- sodium bifluoride with boric acid. The reaction continued. A clear solution indicates that the reaction is 0°C. complete and that the product NaBF3OH is in aqueous 2NaFz -f II3BO3 NaBFjOH + NaF, solution. However, at the lower temperatures and the 65 lower H20 concentrations given the product solubility produces sodium fluoride as an undesirable by-product. may be exceeded and a slurry will result. The sodium fluoride thus produced must be separated At this point NaBF^OH is precipitated from the water from the solution in order to yield pure sodium hydroxy- solution. There are many ways in which the precipitation trifluoroborate. The product solution has as another con- step may be carried out. Preferably, NaBF3OH is pre- taminant NaBF4 which is produced in a side reaction. 70 cipitated by adding cold ethanol at a temperature below When all of the separation processes have been com- —5° C. to the solution, thus lowering the activity of H20 pleted, a large amount of the sodium hydroxytrifluoro- and causing precipitation of NaBF3OH. Approximately 5 3,8' )9,762 3 4 volumes of ethanol per volume of solution are required 95% ethanol at —10° C. was then added as before and to bring about precipitation, NaBF3OH may also be pre- allowed to stand for an hour before filtration. cipitated by adding other reagents such as methanol or What is claimed is: acetone and by lowering the solution temperature. The 1. A method for preparing sodium hydroxy!rifiuoro- precipitate is easily filtered to yield NaBF3OH of about r borate comprising the steps of forming a slurry of 95 + % purity. NaHC0 In order to better the understanding of the process ac- 3 cording to this invention, the following specific example in water, bubbling BF3 through said slurry at a tempera- is eiven. ture below —5° C. until the pH of said slurry is about 4, EXAMPLE continously stirring said slurry until a clear aqueous solu- tion or a sodium hydroxytrifiuoroborate slurry is achieved, A successful preparation was made using the following precipitating said sodium hydroxytrifiuoroborate from procedure and quantities: said aqueous solution and separating said sodium hy- A 450 ml. stainless steel beaker was immersed in an droxytrifiuoroborate from said solution. ice-brine bath to which 200 ml. of water was added. Two 2. The method according to claim 1 wherein said tem- moles of sodium bicarbonate (NaHC0 ) or 168 g. were 3 perature is within the range of —5 to —20° C. added to maintain an excess of solid while stirring vigor- 3. The method according to claim 1 wherein said step obsly. This reagent was added in small amounts during of precipitating comprises adding ethanol at a temperature the course of the preparation. Boron trifluoride (BF ) 3 below —5° C. to said solution. gas from a reagent cylinder was then introduced as a fine 4. The method according to claim 1 wherein said step stream beneath the solution surface while keeping the tem- 20 perature as low as possible but no higher than —5° C. of separating comprises filtering said sodium hydroxytri- fiuoroborate precipitate from said solution. Carbon dioxide gas was rapidly evolved from the solu- tion during the period of BF3 addition as well as heat. For References Cited this reason the BF3 addition was kept to about 11 liters per hour (Vi mole) so that the temperature could be 25 UNITED STATES PATENTS kept under control at all times. Carbon dioxide evolution 3,262,984 7/1966 Oemler et al. 423—287 stopped when the NaHCOs had been exhausted, the pH of the solution dropped until it had reached a value be- OTHER REFERENCES tween 4 and 5.
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