Abstract:
The present invention provides a process for the preparation of lithium metaphosphate comprising reacting a lithium source and a phosphorous source in solid state to obtain lithium metaphosphate.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a novel process for the preparation of lithium metaphosphate (LiPO 3 ) by a solid state thermal reaction. This compound is useful as an intermediate for the preparation of lithium hexa fluorophosphates (LiPF 6 ). This salt is a good electrolyte in aqueous, non-aqueous, solid and selected polymer medium The present invention particularly relates to the preparation of lithium metaphosphate (LiPO 3 ) compound which is the basic chemical for the preparation of lithium hexafluorophosphates (LiPF 6 ) by a novel solid state method which is not hitherto attempted anywhere.  
         BACKGROUND OF THE INVENTION  
         [0002]    Prior art literature on lithium metaphosphate (LiPO 3 ) discloses the reaction of lithium salts with metaphosphoric acid, which is obtained by heating pyro-phosphoric acid or ortho-phosphoric acid. The reaction occurring for the above two thermal processes are as follows:  
           [0003]    1. H 4 P 2 O 7 →2HPO 3 +H 2 O  
           [0004]    2. H 3 PO 3 →HPO 3 +H 2 O  
           [0005]    HPO 3 +LiOH→LiPO 3 +H 2 O  
           [0006]    Reference:  
           [0007]    Advanced Inorganic Chemistry, S. Sathiya Prakash G. D. Tuli, S. K. Basu and R. D. Radan, S. Chand &amp; Co., New Delhi, p. 988 (1998).  
           [0008]    The above methods need controlled conditions for the preparation of lithium metaphosphate. The above methods for the preparation of lithium metaphosphate also suffer from the following disadvantages:  
           [0009]    1. More than one step is involved to prepare LiPO 3 .  
           [0010]    2. Needs crystallization procedure once the product is formed from aqueous solution.  
           [0011]    Objects of the Invention  
           [0012]    The main object of this present invention is to provide a simple novel process for the synthesis of lithium meta phosphate (LiPO 3 ) which obviates the draw back mentioned above.  
           [0013]    Another object of the present invention is to provide a complete solid state reaction procedure for the preparation of LiPO 3 .  
           [0014]    Another object of the invention is to provide a single step process to obtain LiPO 3 .  
           [0015]    Yet another object of the invention is to get high yield of the product LiPO 3  (&gt;90%).  
         SUMMARY OF THE INVENTION  
         [0016]    The above and other objects have been achieved by the solid state method for the preparation of lithium metaphosphate of the invention.  
           [0017]    Accordingly, the present invention provides a process for the preparation of lithium metaphosphate comprising reacting a lithium source and a phosphorous source in a ratio of 1:1-2 in solid state at a temperature in the range of 300 to 650° C. to obtain the desired lithium metaphosphate.  
           [0018]    In one embodiment of the invention, the lithium source is selected from the group consisting of Li 2 O, LiCO 3 , LiOH, LiNO 3  and any mixture thereof In another embodiment of the invention, the phosphorous source is selected from the group consisting of ammonium pyrophosphate, ammonium orthophosphate, diammonium hydrogen phosphate and ammonium dihydrogen phosphate and any mixture thereof.  
           [0019]    In another embodiment of the invention, the reaction is carried out in solid state in a single step.  
           [0020]    In yet another embodiment of the invention, the reaction is carried out at a temperature of 350° C. for a time period of 12 hours and the lithium source is selected from Li 2 O, LiOH and LiNO 3 .  
           [0021]    In another embodiment of the invention, the reactive materials are heated in a muffle or in an electric furnace.  
           [0022]    In yet another embodiment of the invention, Li 2 CO 3  is reacted with the phosphorous source at a temperature of 600° C.  
           [0023]    In another embodiment the lithium source and the phosphorous source are mixed and ground well before being heated.  
           [0024]    In another embodiment of the invention, the lithium source and the phosphorous source are mixed in an equimolar ratio. 
       
    
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING  
       [0025]    [0025]FIG. 1 shows the X-ray analysis of the product obtained by the process of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]    Preferably equimolar quantities of ammonium pyrophosphate/ammonium orthophosphate/diammonium hydrogen phosphate/ammonium dihydrogen phosphate is allowed to react with Li 2 O/LiCO 3 /LiOH/LiNO 3  at a temperature of 350° C. in a muffle furnace for a period of 12 hours to get lithium meta phosphate (LiPO 3 ) which was confirmed by X-ray analysis. The reaction occurring with lithium salts and ammonium salts of pyro and ortho phosphates are as follows:  
         [0027]    1. (NH 4 ) 4 P 2 O 7 +2LiOH→2LiPO 3 +4NH 3 +3H 2 O  
         [0028]    2. (NH 4 ) 3 PO 4 +LiOH→LiPO 3 +3NH 3 +2H 2 O  
         [0029]    3. (NH 4 ) 2 HP) 4 +LiOH→LiPO 3 +2NH 3 +2H 2 O  
         [0030]    4. (NH 4 )H 2 PO 4 +LiOH→LiPO 3 +NH 3 +2H 2 O  
         [0031]    A novel method for the preparation of LiPO 3  is developed wherein equimolar quantities of LiOH/Li 2 CO 3 /Li 2 O/LiNO 3 . This mixture is ground well and then transferred into a porcelain/silica crucible. In the mixture, the lithium salt content to the phosphorous content should be in the molar ratio of 1:1. The silica crucible containing the mixture is introduced into an electric furnace. The furnace was slowly heated to 350° C. and the heating was continued for 12 hours keeping the same temperature. When the reaction is over, the furnace was cooled and the product was ground well and then examined for its purity and identity.  
         [0032]    In the process of the invention for the synthesis of lithium meta phosphate lithium salt (LiOH/Li 2 CO 3 /Li 2 O/LiNO 3 ) is mixed with equimolar quantities of ammonium pyrophosphate or ammonium orthophosphae or diammonium hydrogen phosphate or ammonium dihydrogen phosphate and the mixture is ground well and then transferred the mixture into a silica crucible and then the crucible containing the mixture is heated to 350° C. continuously in an electric furnace to get LiPO 3 . The reactants are solid state materials and are heated in a muffle or in an electric furnace. Pure dry AR Li 2 O or Li 2 CO 3  or LiOH or LiNO 3  was mixed with any one of the salts of ammonium pyrophosphate or ammonium orthophosphate or diammonium hydrogen phosphate or ammonium dihydrogen phosphate in equimolar quantities. The Li and P content of the salt was kept in the ratio 1:1. The mixture of the lithium and the phosphate salts are ground well and then the grounded mixture was transferred into silica vessel. The vessel was then introduced into a electric furnace. The furnace was slowly heated to 350° C. continuously for 12 hours and then the resultant product was powdered well and then analyzed for its purity and identity.  
         [0033]    The following examples are given by way illustration and therefore should not be construed to limit the scope of the prevent invention.  
       EXAMPLE 1  
       [0034]    A mixture of dry AR Li 2 CO 3  and dry AR (NH 4 )  4 P 2 O 7  was taken in 1:2 molar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 600° C. for 12 hours continuously. The resultant product is LiPO 3 .  
                                                                                                                                                   Components   Composition                                        Li 2 CO 3     0.74   g           (NH 4 ) 4 P 2 O 7     4.72   g                Initial Temperature   100° C.                Time   1   hour                Final Temperature   600° C.                Time   12   hours                Nature of the product   Transparent                      
 
         [0035]    Efficiency of the process &gt;90%  
         [0036]    Particle size of the mixture 5-10 mμ.  
       EXAMPLE 2  
       [0037]    A mixture of dry AR Li 2 CO 3  and dry AR (NH 4 )  3 PO 4  was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 600° C. for 12 hours continuously. The resultant product is LiPO 3 . Particle size of the mixture 5-10 mμ.  
                                                                                                                   Components   Composition                                        Li 2 CO 3     0.74   g           (NH 4 ) 3 PO 4     1.67   g                Temperature   600° C.                Time   12   hours                Nature of the product   Transparent                      
 
         [0038]    Efficiency of the process &gt;90%  
         [0039]    Particle size of the mixture 5-10 mμ.  
       EXAMPLE 3  
       [0040]    A mixture of dry AR Li 2 CO 3  and dry AR (NH 4 )  2 PO 4  was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 600° C. for 12 hours continuously. The resultant product is LiPO 3 .  
                                                                                                                                                   Components   Composition                                        Li 2 CO 3     0.74   g           (NH 4 ) 2 HPO 4     1.15   g                Initial Temperature   100° C.                Time   1   Hour                Final Temperature   600° C.                Time   12   hours                Nature of the product   Transparent                      
 
         [0041]    Efficiency of the process &gt;91%  
         [0042]    Particle size of the mixture 5-10 mμ.  
       EXAMPLE 4  
       [0043]    A mixture of dry AR Li 2 CO 3  and dry AR (NH 4 )HPO4 was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was heated initially slowly and finally to 600° C. for 12 hours continuously. The resultant product is LiPO 3 .  
                                                                                                                   Components   Composition                                        Li 2 CO 3     0.74   g           (NH 4 )HPO 4     1.32   g                Initial Temperature   100° C.           Final Temperature   600° C.                Time   12   hours                Nature of the product   Transparent                      
 
         [0044]    Efficiency of the process &gt;90%  
         [0045]    Particle size of the mixture 5-10 mμ.  
       EXAMPLE 5  
       [0046]    A mixture of dry AR LiOH and dry AR (NH 4 ) 4 P 2 O 7  was taken in 1:2 molar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO 3 .  
                                                                                                                                                   Components   Composition                                        LiOH   0.74   g           (NH 4 ) 4 P 2 O 7     4.72   g                Initial Temperature   100° C.                Time   1   Hour                Final Temperature   600° C.                Time   12   hours                Nature of the product   Transparent                      
 
         [0047]    Efficiency of the process &gt;90%  
         [0048]    Particle size of the mixture 5-10 mμ.  
       EXAMPLE 6  
       [0049]    A mixture of dry AR LiOH and dry AR (NH 4 )  3 PO 4  was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO 3 .  
                                                                                                                   Components   Composition                                        LiOH   0.74   g           (NH 4 ) 2 HPO 4     1.15   g                Temperature   350° C.                Time   12   hours                Nature of the product   Transparent                      
 
         [0050]    Efficiency of the process &gt;90%  
         [0051]    Particle size of the mixture 5-10 mμ.  
       EXAMPLE 7  
       [0052]    A mixture of dry AR LiOH and dry AR (NH 4 )  2 HPO 4  was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO 3 .  
                                                                                                                                                   Components   Composition                                        LiOH   0.24   g           (NH 4 ) 2 HPO 4     1.32   g                Initial Temperature   100° C.                Time   1   hour                Final Temperature   600° C.                Time   12   hours                Nature of the product   Transparent                      
 
         [0053]    Efficiency of the process &gt;90%  
         [0054]    Particle size of the mixture 5-10 mμ.  
       EXAMPLE 8  
       [0055]    A mixture of dry AR LiOH and dry AR (NH 4 ) 4 P 2 O 7  was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was heated initially slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO 3 .  
                                                                                                                                                   Components   Composition                                        LiOH   0.24   g           (NH 4 ) 4 P 2 O 7     4.92   g                Initial Temperature   100° C.                Time   1   hour                Final temperature   600° C.                Time   12   hours                Nature of product   Transparent                      
 
         [0056]    Efficiency of the process &gt;90%  
         [0057]    Particle size of the mixture 5-10 mμ.  
       EXAMPLE 9  
       [0058]    A mixture of dry AR LiNO 3  and dry AR (NH 4 ) 4 P 2 O 7  was taken in 1:2 molar ratio. The mixture was ground well so as to get particle size in the range of 5-10μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO 3 .  
                                                                                                                                                   Components   Composition                                        LiNO 3     0.69   g           (NH 4 ) 4 P 2 O 7     4.92   g                Initial Temperature   100° C.                Time   1   hour                Final Temperature   600° C.                Time   12   hours                Nature of the product   Transparent                      
 
         [0059]    Efficiency of the process &gt;91%  
         [0060]    Particle size of the mixture 5-10 mμ.  
       EXAMPLE 10  
       [0061]    A mixture of dry AR LiNO 3  and dry AR (NH 4 )  2 HPO 4  was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO 3 .  
                                                                                                                                                   Components   Composition                                        LiNO 3     0.69   g           (NH 4 ) 2 HPO 4     1.32   g                Initial Temperature   100° C.                Time   1   hour                Final Temperature   600° C.                Time   12   hours                Nature of the product   Transparent                      
 
         [0062]    Efficiency of the process &gt;90%  
         [0063]    Particle size of the mixture 5-10 mμ.  
       EXAMPLE 11  
       [0064]    A mixture of dry AR LiNO 3  and dry AR (NH 4 )HPO 4  was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was heated initially slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO 3 .  
                                                                                                                                                   Components   Composition                                        LiNO 3     0.69   g           (NH 4 )HPO 4     1.15   g                Initial Temperature   100° C.                Time   1   hour                Final Temperature   600° C.                Time   12   hours                Nature of the product   Transparent                      
 
         [0065]    Efficiency of the process &gt;90%  
         [0066]    Particle size of the mixture 5-10 mμ.  
       EXAMPLE 12  
       [0067]    A mixture of dry AR Li 2 O and dry AR (NH 4 ) 4 P 2 O 7  was taken 1:2 molar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO 3 .  
                                                                                                                                                   Components   Composition                                        Li 2 O   0.30   g           (NH 4 ) 2 P 2 O 7     4.92   g                Initial Temperature   100° C.                Time   1   hour                Final Temperature   600° C.                Time   12   hours                Nature of the product   Transparent                      
 
         [0068]    Efficiency of the process &gt;91%  
         [0069]    Particle size of the mixture 5-10mμ.  
       EXAMPLE 13  
       [0070]    A mixture of dry AR Li 2 O and dry AR (NH 4 ) 2 HPO 4  was taken in equimolar ratio. The mixture was ground well as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO 3 .  
                                                                                                                                                   Components   Composition                                        Li 2 O   0.30   g           (NH 4 ) 2 HPO 4     1.32   g                Initial Temperature   100° C.                Time   1   hour                Final Temperature   600° C.                Time   12   hours                Nature of the product   Transparent                      
 
         [0071]    Efficiency of the process &gt;90%  
         [0072]    Particle size of the mixture 5-10 mμ.  
       EXAMPLE 14  
       [0073]    A mixture of dry AR Li 2 O and dry AR (NH 4 )HPO 4  was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was heated initially slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO 3 .  
                                                                                                                                                   Components   Composition                                        Li 2 O   0.30   g           (NH 4 )HPO 4     1.15   g                Initial Temperature   100° C.                Time   1   Hour                Final Temperature   600° C.                Time   12   hours                Nature of the product   Transparent                      
 
         [0074]    Efficiency of the process &gt;91%  
         [0075]    Particle size of the mixture 5-10 mμ.  
         [0076]    Conclusions  
         [0077]    Ammonium pyrophosphate or ammonium orthophosphate or diammonium hydrogen phosphate or ammonium dihydrogen phosphate reacts with Li salts like LiOH/Li 2 O/Li 2 CO 3 /LiNO 3  such that Li salt and P salt mixture combinations are in equimolar proportion (1:1) to form LiPO 3 , when the temperature of heating is maintained at about 350° C. for 12 hrs continuously. In the absence of Li 2 CO 3  in any of the above reaction mixture with ammonium pyrophosphate or ammonium orthophosphate or diammonium hydrogen phosphate or ammonium dihydrogen phosphate the temperature is 350° C. The colour of the product is white and the particle size can be brought to any decided level. X-ray analysis confirms the LiPO 3  formation.  
         [0078]    The Main Advantages of the Present Invention are:  
         [0079]    1. It is a single step, thermal procedure for the preparation of LiPO 3    
         [0080]    2. It is a solid state thermal procedure.  
         [0081]    3. Any of the lithium salts like LiOH/Li 2 CO 3 /Li 2 O/LiNO 3  is mixed with ammonium pyrophosphate or ammonium orthophosphate or diammonium hydrogen phosphate or ammonium dihydrogen phosphate to give LiPO 3 .  
         [0082]    4. This is a base material for the preparation of LiPF 6 .