CLIAMS:1. A method for preparation of hygroscopic homogenous salt mixture, the method comprising the steps of:
a) contacting at least one alkali metal salt with a metal salt having water of crystallization to form a heterogeneous mixture;
b) subjecting said heterogeneous mixture to a temperature of 140 to 180 °C in a closed system to obtain a homogenous mixture; and
c) removing water from the homogeneous mixture to obtain a hygroscopic homogenous salt mixture.
2. The method as claimed in claim 1, wherein the at least one alkali metal salt is selected from the group consisting of lithium salt of inorganic anions, sodium salt of inorganic anions, potassium salt of inorganic anions, and combinations thereof.
3. The method as claimed in claim 1, wherein the at least one alkali metal salt is selected from the group consisting of lithium metal salt, potassium metal salt, and combinations thereof.
4. The method as claimed in claim 1, wherein the at least one alkali metal salt weight ratio in the heterogeneous mixture is in the range of 65 to 90%.
5. The method as claimed in claim 1, wherein the at least one alkali metal salt is a combination of lithium and potassium nitrate.
6. The method as claimed in claim 5, wherein potassium nitrate weight ratio in the heterogeneous mixture is in the range of 60 to 70% and lithium nitrate weight ratio in the heterogeneous mixture is in the range of 5 to 20%.
7. The method as claimed in claim 1, wherein the at least one alkali metal salt is dried at a temperature in the range of 80 to 120 °C under reduced pressure before carrying out step (a).
8. The method as claimed in claim 1, wherein the metal salt having water of crystallization is selected from the group consisting of alkali metal salt, alkaline earth metal salt, and transitional metal salt.
9. The method as claimed in claim 1, wherein the metal salt having water of crystallization has melting point in the range 40 to 120 °C.
10. The method as claimed in claim 1, wherein the metal salt having water of crystallization has melting point in the range 40 to 80 °C.
11. The method as claimed in claim 1, wherein the metal salt having water of crystallization weight ratio in the heterogeneous mixture is in the range of 10 to 35%.
12. The method as claimed in claim 1, wherein the heterogeneous mixture has moisture content in the range 3 to 13 wt %.
13. The method as claimed in claim 1, wherein the heterogeneous mixture is subjected to a temperature of 140 to 180 °C for 0.5 to 1.5 h.
14. The method as claimed in claim 1, wherein the heterogeneous mixture is subjected to a temperature of 140 to 180 °C at a pressure in the range of 1.3 to 3 bars.
15. The method as claimed in claim 1, wherein the hygroscopic homogenous salt mixture has a melting temperature in the range of 100 to 150 °C.
16. A method for preparation of hygroscopic homogenous salt mixture, the method comprising the steps of:
a) contacting 60 to 70 wt % potassium nitrate and 5 to 20 wt % lithium nitrate with 10 to 35 wt % of a metal salt having water of crystallization to form a heterogeneous mixture;
b) subjecting said heterogeneous mixture to a temperature of 140 to 180 °C in a pressure tube for 0.5 to 1.5 h to obtain a homogenous mixture; and
c) removing water from the homogeneous mixture to obtain a hygroscopic homogenous salt mixture with a melting temperature in the range of 100 to 150 °C .
17. A hygroscopic homogenous salt mixture comprising: (a) at least one alkali metal salt; and (b) a metal salt having water of crystallization, wherein the hygroscopic homogenous salt mixture has a melting temperature in the range of 100 to 150 °C.
18. The salt mixture as claimed in claim 17, wherein the at least one alkali metal salt is a combination of lithium and potassium nitrate.
19. The salt mixture as claimed in claim 18, wherein potassium nitrate weight ratio in the homogenous mixture is in the range of 60 to 70% and lithium nitrate weight ratio in the homogenous mixture is in the range of 5 to 20%.
20. The salt mixture as claimed in claim 18, wherein the metal salt having water of crystallization is selected from the group consisting of alkali metal salt, alkaline earth metal salt, and transitional metal salt and the weight ratio in the homogeneous mixture is in the range of 10 to 35%.
21. The salt mixture as claimed in Claim 17 for use as solar thermal energy storage.
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