FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
PROVISIONAL
(See section 10 and rule 13)
AN ECONOMICAL METHOD OF MANUFACTURING POTASSIUM FLUORIDE
ADITYA BIRLA SCIENCE & TECHNOLOGY LIMITED
an Indian Company
of Aditya Birla Center, S. K. Ahire Marg, Worli, Mumbai 400 025,
Maharashtra, India
THE FOLLOWING SPEC IFICATION DESCRIBES THE INVENTION.

Field of the Invention
This invention relates to an economical method of manufacturing Potassium Fluoride.
Background of the Prior Art
There are two known methods for manufacturing Potassium Fluoride.
In the first method, potassium hydroxide is reacted with hydrofluoric acid and the resulting salt can then be purified by recrystallization. In the second method potassium metal is reacted vigorously with a halogen to form potassium halide. But this method is not a normal route of preparation of potassium fluoride because of the cost.
Generally, Potassium fluoride is used as a source for fluorine for organic fluorinations. In Organic chemistry, Potassium fluoride is the preferred source of fluoride for the conversion of chlorocarbons to fluorocarbons. In recent times increasing attention has been paid to the utilization of fluorine containing raw materials used in the fertilizer industry.
GB1419393 and US3842161: Discloses a method for preparation of metal fluoride, comprising two stages. In the first stage, KOH solution is treated with solid potassium silica fluoride at molar ratio less than 4 to form potassium fluoride solution and then separating off the silica. In the second stage, the remaining KOH is reacted with potassium silica fluoride. The silica is separated by filtration and potassium fluoride solution is recovered as a product.


The method suffers from many disadvantages like high silica content, contamination with heavy metals because of alkaline pH, involves many stages of reaction and separation.
US2556064 and US283363:
This is method for the preparation of potassium fluorosilicate from aqueous solution of hydrofluorosilicic acid free from silica and with dilute aqueous solution of potassium chloride free from insoluble impurities.
Object of the Invention:
One of the objects of the present invention is to provide a method for preparation of potassium fluoride having low silica content and heavy metals.
Another object of the present invention is to provide an economical method for preparation of Potassium fluoride from potassium chloride containing potassium fluoride and other organic impurities.
Yet another object of the invention is to manufacture potassium fluoride by cheaply available hydrofluorosilicic acid (which is a by-product from the fertilizer industry).
Yet another object of the invention is to produce potassium fluoride in high yield and high purity.


Description;
It is known that potassium fluoride can be prepared by the following reaction.
H2SiF6 + 2KCI= K2SiF6 + 2HCI
+
2H2SiF6 + SiO2 + 6KF = 3K2SiF6 + 2H2O
3H2SiF6 + 2KCI + SiO2 + 6KF = 4K2SiF6 + 2HCI + 2H2O
In accordance with this invention there is provided an effective method of manufacturing potassium fluoride which comprises the following steps :-
1) Heating hydrofluorosilicic acid and adding silica cake and product of organic fluorination reaction with continuous stirring.
2) Cooling the mixture to room temperature and then filtering.
3) Isolating the product and washing with water to remove solubles including hydrochloric acid.
4) Obtaining white solid powder of Potassium fluorosilicate.
5) Drying the product inside oven at 130°C.
6) placing Potassium fluorosilicate, water in a reaction vessel and then adding potassium hydroxide slowly.
7) Heating the reaction mixture to 88 to 92°C for another 40 min.
8) Cooling the resultant mixture to room temperature and then filtering.
9) Washing silica cake residue having moisture with water.

10) Filtering to give residue containing mostly silica.
11) Drying the residue (mostly silica) at 110°C.
12) Adjusting the pH of the filtrate to 6.5-7.5 using aqueous solution of hydrofluoric acid.


13) Heating the filtrate for 30 min at 90-105°C.
14) Cooling the filtrate to room temperature and filtering.
15) Using the residue (having about 40% water) for preparation of potassium fluoro silicate.
16) Obtaining the filtrate (potassium fluoride solution) having about 29% by weight of Potassium fluoride.
17) Removing the water by heating to get solid Potassium fluoride.
Detailed Description:
The present invention relates to the process for the preparation of Potassium fluoride (KF) from cheaply available hydrofluorosilicic acid [H2SiF6] which is a by-product from the fertilizer industry and with silica [SiO2].
In accordance with this invention there is provided a process for effective manufacturing potassium fluoride in which the hydrofluorosilicic acid solution (18% w/w solution in water) is heated to 95-98°C in a vessel and silica cake (having 40% moisture) is added to it. The by-product of organic fluorination reaction containing (potassium fluoride 10%, potassium chloride (in slurry form or in solid form) 89.5% and other impurities 0.5%) is added with continuous stirring to the above mixture. The reaction is continued for 45 min. at 95-100°C. Insoluble potassium fluorosilicate and hydrochloric acid are formed. The resultant mixture is cooled to room temperature and then filtered. The isolated product is washed with water to remove hydrochloric acid.


The product is dried inside oven at 130 C for 3 hrs. to get white solid powder of Potassium fluorosilicate with more than 99% purity and isolated product yield.
The resultant Potassium fluorosilicate, (preferably in slurry form) is heated to 88 to 92°C and 45% KOH is added slowly within 20 min. The reaction is continued for 40 min. at 88 to 92°C.
Reaction mixture is cooled to room temperature and then it is filtered to remove silica. This silica cake residue having 40%) moisture is washed with water to remove any potassium fluoride and un-reacted potassium hydroxide and is reused to prepare potassium fluorosilicate.
The pH of the filtrate or mother liquor is more than 8 (generally 10) is adjusted to 6.5 -7.5 using 48% aqueous solution of hydrogen fluoride or hydrofluorosilicic acid. It is heated for 30 min. at 90 to 105°C and then cooled at room temperature and filtered. The residue containing potassium fluorosilicate, fluorosilicates and other heavy metals is filtered out. The residue is reused for next batch. The filtrate (potassium fluoride solution) is obtained having about 29% (by wt.) of potassium fluoride. Solid potassium fluoride is obtained by removing water by heating.
While considerable emphasis has been placed herein on the specific steps of the preferred process, it will be appreciated that many steps can be made and that many changes can be made in the preferred steps without departing from the principles of the invention. These and other


changes in the preferred steps of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.