Title of Invention

"A PROCESS OF MANUFACTURING LITHIUM ALUMINATE (LiALO2) POWDER"

Abstract

The present invention relates to a process of manufacturing lithium aluminate (LiAlO2) powders from water-based sols and gels with homogeneous distribution of Li+ and A13+ ions by in-situ polymerization with a water soluble Lewis base. The gel powder after calcination at 200°C produces single phase LiAlO2 phase. The novelty of the present invention primarily resides in providing a process which is economical, environment friendly, energy efficient, high yielding and time saving which makes the process suitable for industrial manufacture. The main application of these LiAlO2 powders are in the molten carbonate fuel cell industries. The electrolyte tile in molten carbonate fuel cells is known to be composed of the lithium carbonate/potassium carbonate electrolyte supported on lithium aluminate.

Full Text

The present invention relates to a process of manufacturing lithium aluminate (LiAlO2) powder. This invention particularly relates to a process for manufacturing lithium aluminate powders from water-based sols and gels. The main application of these LiAlO2 powders are in the molten carbonate fuel cell industries. The electrolyte tile in molten carbonate fuel cells is known to be composed of the lithium carbonate/potassium carbonate electrolyte supported on lithium aluminate. Early methods of LiAlO2 powder preparation are mainly based on the solid state reactions. Reference may be made to K. Kinoshita, J. W. Sim and J. P. Alkerman in "Mater. Res. Bull., 13 (1978) pp. 445-455" wherein LiAlO2 was prepared by reaction of γ-alumina with mixtures of alkali carbonate or with alkali hydroxides. The samples containing γ-Al2O3, Li2C03 and K2C03 were physically mixed by ball milling and subsequently heated at 600° - 700°C in CO2 when a- LiAlO2 powder was formed. The samples containing Al2O3and LiOH or Al2O3 and LiOH plus KOH were prepared by impregnation technique wherein a slurry of A1203 powder was prepared in water under stirring. The hydroxides after dissolving in water was added to the Al2O3 slurry, followed by heating on a hot plate or in an oven to evaporate the water. The dried mass was heated at 450°C to produce LiAlO3 powder. The main drawbacks of the above process are (i) There is lack in homogeneity in the final product, (ii) Crystallization temperature of LiAlO2 powder formation is quite high, (iii) The method involves long processing time. Reference may also be made to T. C. Frianaza-Kullberg, D. P. McDoland and K. Jeff Davis, in "Ceram. Trans, Vol. 12, Ceramic Powder Science III, Eds. G. L. Messing, S. Hirano and H. Hausner, The American Ceramic Society Inc., Westerville, Ohio, pp. 147-154, (1990)" wherein, lithium salts such as lithium formate, lithium acetate, lithium benzoate, lithium carbonate or lithium hydroxide was mixed with alumina in stoichiometric quantity, dry ball-milled using zirconia balls overnight to ensure intimate mixing. The mixture was then placed on on alumina tray and heated in a stepwise manner from 200° to 700° - 900°C, ground and sieved. The method suffers from the following disadvantages : (i) There is lack in homogeneity in the final product, (ii) Crystallization temperature of LiAlO2powder formation is quite high, (iii) The method involves long processing time. The present day methods of preparing LiAlO2 powders mainly consists of solution phase reaction. Reference may be made to S.-I Hirano, T. Hayashi and T. Kageyama in "J. Am. Ceram. Soc. 70 (1987) pp 171-174" wherein lithium ethoxide and aluminium ethoxide weighed in stoichiometric amounts were dissolved in ethanol by refluxing in a flow of nitrogen gas. The optimum concentration of each alkoxide in ethanol was 0.1 mol/L. Hydrolysis of the mixed alkoxide was carried out using four times the amount of distilled and decarbonated water. The precipitate obtained after hydrolysis was aged for 24h under reflux followed by cooling to room temperature. The precipitate (ß-LiAlO2), after ultrafiltered under nitrogen gas pressure of 5 bar followed by drying, were fired at 750°C for 4h when γ-LiAlO2 was obtained. The main drawbacks of the above process are: (i) The Li(OC2H5) and A1(OC2H5)3 both being highly moisture sensitive, handling in glove box filled with dry nitrogen is necessary. (ii) The process is lengthy as long time refluxing is necessary both before and after precipitation, (ii) The precipitate is collected by ultrafiltration in nitrogen gas pressure of 500 kPa. Reference may also be made to M. A. Valenzuela, J. Jimenez-Bicerril, P. Bosch, S. Bulbulian and V. H. Lara in "J. Am. Ceram Soc. 79 (1996) pp 455-60" wherein aluminiuin. Yet another object of the present invention is to provide a process for the manufacture of LiAlO2 powder which uses precursor chemicals that are cost-effective, and can be handled without any specific precautions. Still another object of the present invention is to provide a process for the manufacture of LiA1O2 powder which crystallizes at a very low temperature thus making the process energy efficient. Another object of the present invention is to provide a process of manufacturing LiAlO2 powder which is very simple and cost-effective. Accordingly, the present invention provides a process for the manufacture of LiAlO2 powder which comprises preparing an aqueous solution of aluminum salt aluminum nitrate nonahydrate, Al(NO3)3 9H2O, aluminum chloride hexahydrate, AlCl3. 6H20 with A13+ concentration in the range of 1 -3 M, filtering, adding a water soluble Lewis base such as ammonia solution with a concentration in the range of 15-25 wt% under stirring at ambient temperature to obtain a solution of pH in the range of 3.0 - 4.5, heating the resulting solution at a temperature in the range of 70 - 90°C to a solution with pH in the range of 3.0 - 4.0 and viscosity in the range of 5-15 mPa s, adding further, ammonia solution drop by drop to the solution kept at a temperature in the range of 70 - 90°C thereby increasing the pH in the range of 3.5-4.5 and viscosity in the range of 20-35 mPa s, adding a water soluble salt of lithium such as lithium nitrate, LiNO3, lithium chloride, LiCl with Al : Li mole ratio in the range of 1:1 to 1:3, into the resulting alumina solution kept at a temperature in the range of 70 -90°C to obtain a alurnina-Lithia bi-component sol, further heating the resulting clear alumina-Lithia bi-component sol at a temperature in the range of 80 - 90°C till gel formation, continuous heating of the resulting gel at a temperature in the range of 85 - 95°C to obtain a gel powder, heating the gel powder at 200°C to obtain the product. The process comprises the following operations : 1. An aluminium metal salt solution was prepared by dissolving aluminium nitrate nonahydrate, A1(NO3)3.9H20, aluminium chloride hexahydrate, A1C13.6H2O in water with AL3+concentration in the range of 1-3 M, and the solution was filtered. 2. A water soluble Lewis base such as ammonia solution with a concentration in the range of 15-25 wt% was added to the aluminium metal salt solution under stirring at ambient temperature to obtain a solution of pH in the range of 3.0 - 4.5. 3. The resulting solution was heated at a temperature in the range of 70° - 90°C for polymerizing it to a sol with pH and viscosity in the ranges 3.0-4.0 and and 5-15 mPa s respectively. 4. Ammonia solution was further added drop by drop to the alumina sol kept at a temperature in the range of 70° - 90°C to accelerate further polymerization, thereby increasing the pH and viscosity in the range of 3.5-4.5 and 20-35 mPa s respectively. 5. A. water soluble salt of lithium such as lithium nitrate, LiNO3, lithium chloride, LiCl with Al : Li mole ratio in the range of 1:1 to 1:3, was added to the alumina sol kept at a temperature in the range of 70° - 90°C, thereby resulting in the formation of a clear bi- component alumina-lithia sol. 6. The resulting clear bi-component alumina-lithia sol was further heated at a temperature in the range of 80° - 90°C till gel formation. 7. The resulting gel was continuously heated at a temperature in the range of 85° - 95°C to produce the corresponding gel powder. 8. The gel powder when heated at 200°C produced single-phase, crystalline LiAlO2 powder. The novelty of the present invention primarily resides in providing a process which is economical, environment friendly, energy efficient, high yielding and time saving which makes the process suitable for industrial manufacture and the non-obvious inventive steps lies in the preparation of water-based lithia-alumina sols and gels, with molecular level mixing of Li and Al, by in-situ polymerization with a water soluble Lewis base. This molecular level mixing of Li+ and A13+ ions in the sol finally produces LiAlO2 powder with homogeneous distribution of Li+ and A13+ ions. The invention is described herein in details in the following examples, which are cited by way of illustration and therefore should not be construed to limit the scope of the present invention. Example 1 56.8902 g of Al(NO3)3.9H2O was dissolved in 150 mL of deionized water to make A1(NO3)3 concentration of about 1 M. The solution was filtered to remove the undissolved impurities. To this solution, concentrated ammonia solution (25wt%, GR) was added under vigorous stirring until the pH of the solution becomes 3. The resulting solution was then heated at 75° ± 1°C for 2h for obtaining a sol by polymerization. The pH and viscosity of the sol thus obtained was 3.0 and 15 ± 1 mPa s respectively. The sol was further heated at 75° ± 1°C in which concentrated ammonia solution (25 wt%) was again added drop by drop for further polymerization, maintaining the pH of the sol at 3.5. The viscosity of the resulting clear sol was 20 ± 1 mPa s. To this alumina sol, 10.45 g of lithium nitrate (LiNO3) was added under stirring. The clear bi-component lithia-alumina sol was further heated at 80° ± 1°C until gel formation occurred. The resulting gel was continuously heated at 95° ± 1°C until dried gel powder is obtained. X-ray diffraction analysis confirmed LiAIO2 phase after heating the gel powder at 200°C. Example 2 46.3811 g of A1(NO3)3.9H2O was dissolved in 100 mL of deionized water to make A1(NO3)3 concentration of about 1.5 M. The solution was filtered to remove the undissolved impurities. To this solution, ammonia solution (10wt%, GR) was added under vigorous stirring until the pH of the solution becomes 3.5. The resulting solution was then heated at 80° ± 1°C for Ih for obtaining a sol by polymerization. The pH and viscosity of the sol thus obtained was 3.0 and 15 + 1 mPa s respectively.The sol was further heated at 80° + 1°C in which ammonia solution (20 wt%) was again added drop by drop for further polymerization, maintaining the pH of the sol at 3.8. The viscosity of the resulting clear sol was 25 ± 1 mPa s. To this alumina sol, 17.0494 g of lithium nitrate (LiNO3) was added under stirring. The clear bi-component lithia-alumina sol was further heated at 80° ± 1°C until gel formation occurred. The resulting gel was continuously heated at 95° ± 1°C until dried gel powder is obtained. X-ray diffraction analysis confirmed LiAlO2 phase after heating the gel powder at 200°C. Example 3 39.1491 g of A1(NO;5)3.9H2O was dissolved in 75 mL of deionized water to make Al(NO3)3 concentration of about 2 M. The solution was filtered to remove the undissolved impurities. To this solution, ammonia solution (20wt%, GR) was added under vigorous stirring until the pH of the solution becomes 4. The resulting solution was then heated at 75° + 1°C for 1.5h for obtaining a sol by polymerization. The pH and viscosity of the sol thus obtained was 3.5 and 20 ± 1 mPa s respectively.The sol was further heated at 85° + 1°C in which ammonia solution (15 wt%) was again added drop by drop for further polymerization, maintaining the pH of the sol at 4. The viscosity of the resulting clear sol was 30 + 1 mPa s. To this alumina sol, 21.5835 g of lithium nitrate (LiNO3) was added under stirring. The clear bi-component lithia-alurnina sol was further heated at 85° ± 1°C until gel formation occurred. The resulting gel was continuously heated at 90° ± 1°C until dried gel powder is obtained. X-ray diffraction analysis confirmed LiAlO2 phase after heating the gel powder at 200°C. Example 4 56.8902 g of A1(NO3)3.9H20 was dissolved in 50 mL of deionized water to make A1(NO3)3 concentration of about 3 M. The solution was filtered to remove the undissolved impurities. To this solution, ammonia solution (15wt%, GR) was added under vigorous stirring until the pH of the solution becomes 4.5. The resulting solution was then heated at 90° + 1°C for Ih for obtaining a sol by polymerization. The pH and viscosity of the sol thus obtained was 4.0 and 20+1 mPa s respectively.The sol was further heated at 85° ± 1°C in which concentrated ammonia solution (25 wt%) was again added drop by drop for further polymerization, maintaining the pH of the sol at 4.5. The viscosity of the resulting clear sol was 20 ± 1 mPa s. To this alumina sol, 10.45 g of lithium nitrate (LiNO3) was added under stirring. The clear bi-component lithia-alumina sol was further heated at 90° ± 1°C until gel formation occurred. The resulting gel was continuously heated at 90° ± 1°C until dried gel powder is obtained. X-ray diffraction analysis confirmed LiAlOa phase after heating the gel powder at 200°C. The main advantages of the present invention are: (i) The process for the manufacture of LiAlO2 powders does not require any sophisticated instrument. (ii) The process requires low temperature (200°C) of crystallization, thus the process is energy efficient. (iv) It is a tailor-made process, as the particle size and size distribution can be varied according to the necessity by changing the process parameters, (v) The process is simple and cost-effective. (vi) It uses water-based sols and gels as the precursor materials which are not health-hazard and does not create any atmospheric pollution during heat-treatment of gel materials, thus the process is environment friendly. (vii) The process uses raw materials which can be handled without any specific precautions. (viii) The process produces LiAlO2 powder with homogeneous distribution of Li+ and Al3+ ions. We Claim: 1. A process for the manufacture of LiAlO2 powder which comprises preparing an aqueous solution of aluminum salt aluminum nitrate nonahydrate, A1(N03)3. 9H2O, aluminum chloride hexahydrate, AlCl3. 6H2O with A13+ concentration in the range of 1-3 M, filtering, adding a water soluble Lewis base such as ammonia solution with a concentration in the range of 15-25 wt% under stirring at ambient temperature to obtain a solution of pH in the range of 3.0 - 4.5, heating the resulting solution at a temperature in the range of 70 - 90°C to a solution with pH in the range of 3.0 - 4.0 and viscosity in the range of 5-15 mPa s, adding further, ammonia solution drop by drop to the solution kept at a temperature in the range of 70 - 90°C thereby increasing the pH in the range of 3.5-4.5 and viscosity in the range of 20-35 mPa s, adding a water soluble salt of lithium such as lithium nitrate, LiNO3, lithium chloride, LiCl with Al : Li mole ratio in the range of 1:1 to 1:3, into the resulting alumina solution kept at a temperature in the range of 70 - 90°C to obtain a alumina-Lithia bi-component sol, further heating the resulting clear alumina-Lithia bi-component sol at a temperature in the range of 80 - 90°C till gel formation, continuous heating of the resulting gel at a temperature in the range of 85 - 95°C to obtain a gel powder, heating the gel powder at 200°C to obtain the product. 2. A process for manufacture of lithium aluminate (LiAlO2) powder substantially as herein described with references to the examples.

Documents:

1268-del-2001-abstract.pdf

1268-del-2001-claims.pdf

1268-del-2001-correspondence-others.pdf

1268-del-2001-correspondence-po.pdf

1268-del-2001-description (complete).pdf

1268-del-2001-form-1.pdf

1268-del-2001-form-18.pdf

1268-del-2001-form-2.pdf

1268-del-2001-form-3.pdf