Method of preparing a water-reactive sulfide material
A process for producing a low-cost water-reactive metal sulfide material includes dissolving a substantially anhydrous alkali metal salt and a substantially anhydrous sulfide compound in a substantially anhydrous polar solvent, providing differential solubility for a substantially high solubility alkali metal sulfide and a substantially low solubility by-product, and forming a mixture of the high solubility alkali metal sulfide and the low solubility by-product; separating the low solubility by-product from the mixture to isolate the supernatant including the alkali metal sulfide, and separating the polar solvent from the alkali metal sulfide to produce the alkali metal sulfide. The present invention provides a scalable process for production of a high purity alkali metal sulfide that is essentially free of undesired by-products.
1. A method for producing a water-reactive alkali metal sulfide compound comprising:
dissolving a substantially anhydrous alkali metal salt precursor and a substantially anhydrous sulfide precursor compound in one or more substantially anhydrous polar solvents, wherein the polar solvent provides differential solubility for a high solubility alkali metal sulfide and a low solubility by-product, and wherein the anhydrous sulfide precursor compound is a polysulfide;
forming a mixture comprising a supernatant of the high solubility alkali metal sulfide dissolved in the polar solvent, and a precipitate of the low solubility by-product;
separating the precipitate of the low solubility by-product from the supernatant;
evaporating the polar solvent from the supernatant; and
a heat treatment to isolate the water-reactive alkali metal sulfide.
2. The method of claim 1 , wherein the polysulfide comprises Na 2 S x , where x is greater than 1 but less than or equal to 10.
3. The method of claim 1 , wherein the substantially anhydrous alkali metal salt precursor is present in the dissolving step in a stoichiometric excess.
4. The method of claim 1 wherein the substantially anhydrous metal salt precursor is present in the dissolving step in an amount of 150% to 85% of stoichiometric.
5. The method of claim 1 , further comprising addition of a sulfur source at any point during the process to increase the purity of the final alkali metal sulfide product.
6. The method of claim 5 , the sulfur source comprising one or more of elemental sulfur and H 2 S.
7. The method of claim 6 , the sulfur source comprising elemental sulfur.
8. The method of claim 1 , wherein separating the low solubility by-product from the supernatant further comprises at least one of centrifuging, filtering, gravity settling, and cooling.
9. The method of claim 1 , further comprising adjusting the relative amounts of the alkali metal salt precursor and the sulfide precursor compound added to the solution to adjust the purity of the resultant alkali metal sulfide.
10. The method of claim 1 , wherein the alkali metal salt precursor is LiCl.
11. The method of claim 1 , wherein the alkali metal salt precursor and the sulfide precursor compound are independently dissolved in the polar solvent prior to forming of a combined mixture.
12. The method of claim 1 , wherein one of the alkali metal salt precursor and the sulfide precursor compound is dissolved in the polar solvent and the other is added to the solution in solid form.
13. The method of claim 1 , further comprising drying the resultant alkali metal sulfide.
14. The method of claim 1 , wherein separating the polar solvent from the supernatant further comprises at least one of evaporating the polar solvent, recrystallization, and heating under vacuum.
15. The method of claim 1 , further comprising introducing an anti-solvent compound to the supernatant of the high solubility alkali metal sulfide and the polar solvent, directly following the precipitation of the low solubility by-product.
16. The method of claim 15 , wherein the anti-solvent is selected from one or more of heptane and other non-polar solvents with substantial miscibility in the polar solvent and which increases the differential solubility of the alkali metal sulfide versus the by-products.
17. The method of claim 1 , wherein the substantially anhydrous polar solvent is at least one alcohol selected from the group consisting of ethanol, 1-propanol, 1-butanol, ethanol denaturing agents and mixtures thereof.
18. The method of claim 1 , wherein the alkali metal sulfide is Li 2 S.
19. The method of claim 1 , wherein the dissolving further comprises the addition of elemental sulfur to the one or more substantially anhydrous polar solvents.
20. A method for producing a water-reactive alkali metal sulfide compound comprising:
dissolving a substantially anhydrous alkali metal salt precursor and a substantially anhydrous sulfide precursor compound in one or more substantially anhydrous polar solvents, wherein the polar solvent provides differential solubility for a high solubility alkali metal sulfide and a low solubility by-product, and wherein the anhydrous sulfide precursor compound is Na 2 S x where x is greater than 1 but less than or equal to 10;
forming a mixture comprising a supernatant of the high solubility alkali metal sulfide dissolved in the polar solvent, and a precipitate of the low solubility by-product;
separating the precipitate of the low solubility by-product from the supernatant;
evaporating the polar solvent from the supernatant; and
a heat treatment to isolate the water-reactive alkali metal sulfide.