FORM -2
THE PATENTS ACT, 1970
(39 OF 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. Title of the Invention : THE METHOD OF PREPARATION OF POTASSIUM
FLUOROBORATE (KBF4)
2. Applicant(s)
Name, Nationality & Address :
THE SECRETARY, DEPARTMENT OF ATOMIC ENERGY, O.Y.C. Building, Chartrapathi Shivaji Maharaj Marg, Mumbai 400 001, Maharashtra, India, an Indian Institute
3. Preamble to the description :
COMPLETE : The following specification particularly describes the invention and the manner in which is to be performed.

FIELD OF INVENTION:
This invention relates to the method of preparation of potassium fluoroborate (KBF4).
BACKGROUND OF THE INVENTION:
Boron and its compounds such as potassium fluoroborate (KBF4), boron carbide (B4C) etc., find extensive applications in various industries. KBF4 is a key ingredient in a) welding, brazing and soldering fluxes, b) grain refining salts (flux) in the manufacture of aluminium and c) in refractories that are formed into complex shapes for non-ferrous casting industry. It is also used as a cleansing flux for non-ferrous metals such as magnesium and aluminium. In addition, KBF4 is a binder in abrasive products. KBF4 is extensively used in steel industries for 'boronizing' steels.
Pure elemental boron, which finds extensive applications in various industries ranging from agriculture to semiconductor industries, could be produced by a high temperature molten salt electrolytic process.
In the known method of preparation of KBF4, the boric acid is first converted to hydrofluroboric acid using aqueous hydrofluoric acid (40 %) from which KBF4 is precipitated using aqueous potassium hydroxide. Large amounts of HF and KOH are required for the said process (1.8 L of 40 % HF and 600 g of KOH per kg of KBF4). This process requires special equipment to handle highly corrosive HF that makes this process expensive. The commercially available HF contains significant quantities of silicon that precipitates along with KBF4. The other impurities present in the chemicals are also carried into the KBF4 precipitate, thus making the KBF4 impure. Generally KBF4 produced by this method is about 98% pure and its purity depends on the purity of starting chemicals. The boron obtained using this KBF4 is 92-95% pure and is usually contaminated with silica and other impurities.

Boron trifluoride forms stable addition compound with ethyl ether. Presently BF3-diethylether is converted to boric acid by reacting with water. This boric acid is subsequently converted to KBF4 using HF and KOH.
Large amounts of HF and KOH are required in the conventional process. The said process requires special equipment to handle highly corrosive HF that makes this process expensive. The commercially available HF contains high silica content which precipitates along with KBF4 (0.4 to 2.5%). The other impurities present in the chemicals are also carried into the KBF4 precipitate, thus making the product impure. The precipitate is washed several times in order to remove the excess fluoride and other water soluble impurities. Thus this process generates a large volume of aqueous fluoride waste. Even though the solubility of KBF4 is only 4 mg/mL at room temperature, due to the large amount of waste generated, the loss of enriched KBF4, a high value chemical, is very significant. Thus, the present method is for producing highly pure potassium fluoroborate directly from BF3-diethylether and potassium fluoride.
OBJECTS OF THE INVENTION:
An object of this invention is to propose a method of preparation of Potassium fluoroborate (KBF4);
Another object of this invention is to propose a simple and cost effective method for the preparation of KBF4;
Further object of this invention is to propose a method for the preparation of highly pure KBF4 from BF3-diethylether and KF;

Still farther object of this invention is to propose a method for the preparation of potassium fluoroborate with very little loss of boron and minimum waste generation;
Yet another object of this invention is to propose the use of the highly pure KBF4 of the present invention to produce high purity elemental boron by the electrowinning process.
BRIEF DESCRIPTION OF THE INVENTION:
According to this invention there is provided a method of preparation of potassium
fluoroborate (KBF4) comprising:
heating the round bottom flask in a silicon oil bath;
transferring BF3-diethylether solution into the RB flask;
adding anhydrous KF to the BF3-diethylether solution;
subjecting the mixture to the step of stirring;
refluxing the mixture for 24 firs;
cooling the reaction products to the room temperature;
mixing the reaction products with acetone;
subjecting the reaction products to the step of filtration to remove excess KF;
and drying the final product.
DETAILED DESCRIPTION OF THE INVENTION:
Preparation of high purity KBF4 from the solution of BF3-diethylether by two methods.
Reacting highly pure KF solid suspended in the BF3-diethylether solution at a high temperature to give solid KBF4 and then separating the solid KBF4.

By reacting BF3-diethylether with aqueous KF solution at low temperature to produce KBF4.
Preparation of KBF4 by the reaction of solid KF with BF3-diethylether solution
The invention establishes a simple, industrially adaptable, environment-friendly clean and safe method for the cost effective preparation of highly pure KBF4 from BF3-diethylether which can be used for the production of high purity boron by the electrowinning process and also for other applications.
The experimental set up consists of a clean dried round-bottom flask fitted with a condenser tube of 80 cm in length. The flask is cooled by a chilled-water circulator. The open end of the condenser tube is closed with a guard tube filled with CaCl2. The RB flask is heated in a silicon oil bath and the temperature is maintained at 343 K. The ether complex is pre-cooled to 283 K in a refrigerator before weighing. BF3-diethylether solution is quickly weighed and transferred into the RB flask. Anhydrous KF is weighed and gently transferred into the RB flask. Anhydrous KF is weighed and gently transferred into the RB flask. The mixing of the solution is carried out by means of a magnetic stirrer. The contents were refluxed for 24 h. Subsequently the bath is cooled to room temperature, the reaction products are mixed with acetone and stirred. The excess ether along with acetone is filtered using a Whatman filter paper no.44. The powder is weighed and again washed with distilled water. The excess KF is dissolved in water and the remaining precipitate is filtered, dried under an IR lamp for an hour to constant weight. The analysis of the product is carried out by using inductively coupled plasma mass spectrometer (ICP-MS) and X-ray diffraction (XRD).
Preparation of KBF4 with aqueous KF solution and BF3-dietb.yleth.er

A similar set up is established for carrying out the experiment that demonstrated the conversion of BF3-diethylether to KBF4 by using aqueous KF solution.
A reaction vessel and condenser similar to that described in the previous reaction is used. A capillary tube is introduced in to the RB flask for the addition of an aqueous solution of KF. Complete leak tightness of the apparatus is ensured in order to avoid BF3 loss. The condenser tube and the RB flask are cooled by using a chilled water circulator. Pre-cooled BF3-diethylether is weighed and transferred into the RB flask quickly and cooled. A saturated solution of KF is prepared by dissolving high pure KF in quartz distilled water. KF solution is added to the BF3-diethylether solution using a peristaltic pump. The contents are mixed by using a magnetic stirrer and the desired amount of KF solution is transferred into the RB flask until cessation of the precipitation. The precipitate is then transferred into a separating funnel and the ether phase and the aqueous phase are separated. The aqueous solution containing the precipitate is filtered using a Whatman no. 44 filter paper, dried and weighed. The analysis of the product is carried out by using ICP-MS and XRD.
Procedure for analysis of KBF4 and analysis results:
The chemical analysis of the KBF4 powder (product) is carried out by using ICP-MS and XRD. A known amount of the powder is dissolved in water, diluted suitably for ICP-MS analysis for the determination of trace impurities and boron content. KBF4 concentrations are calculated by using a BF4" ion-selective electrode and from the boron concentration obtained by ICP-MS analysis. The boron and BF4" values are converted into the corresponding amounts of KBF4 and the recoveries were calculated based on the theoretical values. XRD analysis confirms that the compound is pure KBF4. ICP-MS analysis shows that most of the impurities are present below the detection limits.

Table 1: Recovery of KBF4 prepared using solid and aqueous KF reacting with BF3-diethylether

S.No. Weigh of
BF3-
diethylether
(g) Weight of KF used (g) Theoretical value of KBF4 (g) Actual weight of KBF4(g) Yield (%)
1 100 43.5 (solid) 89 81.9 92
2 60 26 (solid) 53.4 51 96.2
3 50 24 (solid) 44.5 43.3 97.4
4 50 35 mLof 1 mg/mL 44.5 44.1 99
5 100 75mL of 0.7g/mL 89 88.4 99
6 100 75mL of 0.7g/mL 89 88.2 99
Table 2: Impurities present in KBF4 prepared using solid and aqueous KF reacting with BF3-diethylether

Elements *KBF4 (pg/g) #KBF4(|Jg/g) #KBF4 (|Jg/g) ICP-MS Analysis Detection
Limits(µg/g)
Fe <20 <20 <20 20
Mg <10 <10 <10 10
Ca <20 <20 <20 20
Mn <1 <1 <1 1
Co <1 <1 <1 1
Si <10 <10 <10 10
*KBF4 prepared using solid KF reacting with BF3-diethyl ether (ethoxy ethane) # KBF4 prepared using aqueous KF reacting with BF3-diethyl ether (ethoxy ethane)

Table 3: Comparison of impurities present in KBF4 prepared by conventional method and present method

Elements KBF4 from BF3-diethyl ether
(µg/g) KBF4 from HF+KOH precipitation route (Mg/g)
Fe <20 100
Mg <10 300
Ca <20 300
Mn <1 30
Co <1 20
Si <10 400
A new environment-friendly and simple process for the cost-effective preparation of KBF4 from BF3-diethylether has been developed by two processes. In the "direct reflux" route it is necessary to cool and condense the vapors to avoid the loss of BF3 by vaporization. The "aqueous extraction" route appears to be simpler and faster. The end product obtained in both these methods is highly pure KBF4 (>99.9% pure). In the "direct reflux" route, it is necessary to heat the solution for a longer time, whereas in the aqueous route, the reaction goes to completion relatively faster. Both these reactions could be carried out at room temperature. Since the aqueous reaction is exothermic, the contents have to be cooled below 283 K in order to avoid the losses of BF3 and the KBF4. The product obtained in the "direct reflux" route is coloured possibly due to the presence of organics and has to be cleaned with acetone and water. The KBF4 obtained through the aqueous route is colorless and requires only very little water for washing to remove the excess KF. This reduces the loss of KBF4 during washing. The "aqueous extraction" route is simpler and faster and more amenable for scale up and industrial production. Although boric acid is cheaper compared to BF3-diethylether, the synthesis of high purity KBF4 from boric acid involves complex equipment and expensive chemicals such as HF.

In addition, a large volume of aqueous fluoride waste is generated and the cost of treatment and disposal of this waste is high. Hence the synthesis of high purity KBF4 from BF.i-diethylether is cost-effective. This method can be used for the preparation of other fluoroborate like UBF4 and NaBF4 with high purity.
EXAMPLES:
Preparation of KBF4 by equilibration of solid KF with BF3-diethyIether
lOOg of BF3-diethylether was weighed and quickly transferred in an RB flask. 43.5 g KF (AR Anhydrous) weighed and added to the BF3-diemylether solution. The flask was closed with the condenser tube and CaCl2 guard tube. Mixing was carried out by using magnetic' stirrer. The solution was heated to 343 K by using a silicon oil bath for 24 h. The flask and the contents were then cooled and the excess organic was removed by acetone washing. Excess KF was removed by washing with water. The powder was dried and weighed. The final weight of the KBF4 powder was found to be 81.9 g corresponding to a yield of 92%.
24 g of anhydrous KF was weighed and transferred in to an RB flask. 50 g of BF3-diethylether was weighed and quickly transferred to this RB flask. The flask was closed with a condenser and a CaCl2 guard tube. The contents of the flask were mixed by using a magnetic stirrer. The content was heated by using a silicon oil bath for 24 h at 393 K, the excess organic was then removed by acetone washing. The product thus obtained was washed in order to remove the excess KF, dried and weighed. The final weight of the KBF4 was found to be 43.3 g corresponding to a yield of 97%.

Preparation of KBF4 from an aqueous solution of KF and BF3-diethylether
50 g of BF3-diethylether was transferred into an RB flask that fitted with a condenser tube and a guard tube containing CaCl2- A capillary tube was introduced into the RB flask in order to facilitate the addition of the aqueous solution. After ensuring that the apparatus is leak tight, the RB flask was immersed in to a cold water bath and maintained at a low temperature below 283 K. An aqueous solution of KF was prepared by dissolving 50 g of pure KF in 50 mL of quartz distilled water. This solution was then added to the BF3-diethyl ether solution using a peristaltic pump. The solution was mixed with a magnetic stirrer. The precipitate was transferred into a separating funnel and the ether phase was separated and collected separately. The aqueous solution containing the precipitate was filtered by using a Whatman No. 44 filter paper dried and weighed. The final weight of the KBF4 powder was found to be 44. 1 g corresponding to an yield of 99%.
100 g of BF3-diethylether was transferred into an RB flask fitted with a condenser tube and a guard tube containing CaCl2. A capillary tube was introduced into the RB flask in order to facilitate the addition of aqueous solution. After ensuring the leak tightness of apparatus, the RB flask was immersed in to a cold water bath and cooled the content to a temperature below 283 K. An aqueous solution of KF was prepared by dissolving 100 g pure KF in 150 mL of quartz distilled water. This KF solution was added to the BF3-diethyl ether solution by using a peristaltic pump. The solution was mixed by using a magnetic stirrer. The aqueous phase containing the precipitate was separated from the ether by using a separating funnel. The aqueous solution containing the precipitate was filtered by using Whatman No. 44 filter paper and dried and weighed. The final weight of the KBF4 powder was found to be 88 g corresponding to a recovery of 99%.

WE CLAIM:
1. A method of preparation of potassium fluoroborate (KBF4) comprising:
heating the round bottom flask in a silicon oil bath;
transferring BF3-diethylether solution into the RB flask;
adding anhydrous KF to the BF3-diethylether solution;
subjecting the mixture to the step of stirring;
refluxing the mixture for 24 hrs;
cooling the reaction products to the room temperature;
mixing the reaction products with acetone;
subjecting the reaction products to the step of filtration to remove excess KF;
and drying the final product.
2. The method as claimed in claim 1, wherein the RB flask is heated in a silicon bath and the temperature is maintained at 343K.
3. The method as claimed in claim 1, wherein the ether complex is precooled to 283K in a refrigerator before weighing and introducing to the RB flask.
4. The method as claimed in claim 1, wherein the said final product is washed with distilled water and then dried under an IR lamp for an hour to obtain a constant weight.
5. The method as claimed in claim 1, wherein instead of solid KF even aqueous solution of KF can be used.

6. The method as claimed in claim 5, wherein the RB flask is cooled by using a chilled water circulator and pre cooled Bp3-diethylether is transferred into the cool RB flask, a saturated solution of KF is added to the BF3-diethylether solution using a pump, the contents of the flask is then mixed and finally the precipitate funnel is filtered.
7. The method as claimed in claim 6, wherein the saturated solution of KF is prepared by dissolving high pure KF in quartz distilled water.
8. The method as claimed in claim 6 wherein the pump used is peristaltic pump.