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US 4,908,043 AGranted
Method of producing crystals of anhydrous sodium sulfide
AssigneeSankyo Kasei Kabushiki Kaisha
InventorsKannosuke Maeda, Toshio Aoyama
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AssigneeSankyo Kasei Kabushiki Kaisha
InventorsKannosuke Maeda, Toshio Aoyama
Estimating the term…
Disclosed are single crystals of anhydrous sodium sulfide, and a method of producing single crystals of anhydrous sodium sulfide, characterized in that the method comprises concentrating an aqueous solution of sodium sulfide at a temperature of 97.degree. C. or higher, the solution containing about 2 to about 15% by weight of NaOH based on the aqueous solution to precipitate single crystals of anhydrous sodium sulfide from the aqueous solution.
A method of producing anhydrous sodium sulfide in the form of hexagonal isometric crystals having a purity of 97.6% or more, which comprises maintaining an aqueous solution of sodium sulfide containing from about 2 to about 25% by weight of NaOH at a temperature of 97.degree. C. or higher for at least 1 hour, and then concentrating the solution at a temperature of 97.degree. C. or higher to precipitate the anhydrous sodium sulfide crystals from the solution.
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Alkali metal sulfides or polysulfides: purification
Sulfur; Compounds thereof: alkali metal sulfides or polysulfides
Single-crystal growth from solutions using solvents which are liquid at normal temperature
Inorganic compounds or compositions: sulfur-, selenium- or tellurium-containing compounds
Term ended 23 Jun 2008 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
In recent years, there is a demand for high-purity sodium sulfide which is useful as a material for production of engineering plastics or the like and which is easy to handle.
Conventional processes for preparing sodium sulfides include those in which Na.sub.2 S crystals are precipitated from a Na.sub.2 S aqueous solution. This crystallization from the aqueous solution gives hydrates of Na.sub.2 S such as Na.sub.2 S.9H.sub.2 O, Na.sub.2 S.6H.sub.2 O, Na.sub.2 S 5.5H.sub.2 O, Na.sub.2 S.5H.sub.2 O, Na.sub.2 S.H.sub.2 O and the like (Mellors, Comprehensive Treatise on Inorganic and Theoretical Chemistry, Vol. II, part I, pp. 621 to 629; Mellors, Comprehensive Treatise on Inorganic and Theoretical Chemistry, Supplement II, part I, pp. 980 to 989; Seidel, Solubilities, Inorganic and Metal-Organic Compounds Vol. II, pp. 1113; Japanese Examined Patent Publication No. 3760/1975; etc.).
However, the hydrates of Na.sub.2 S as shown above are difficult to handle because they are significantly deliquescent and easily oxidizable in air. The foregoing crystallization has the further problem that NaSH or hydrogen sulfide is produced in the precipitation of Na.sub.2 S crystals, whereby a complex salt, ion pair and the like are formed, consequently leading to production of Na.sub.2 S with a low purity.
FIG. 1 is a curve showing the solubility of hydrates of Na.sub.2 S. As seen from FIG. 1, anhydrous sodium sulfide crystals are precipitated from the aqueous solution of Na.sub.2 S at or above 97.degree. C. This shows that Na.sub.2 S is separated out as an anhydrous crystal by concentrating the Na.sub.2 S aqueous solution to supersaturation while retaining the aqueous solution at 97.degree. C. or higher. This phenomenon was discovered for the first time by the present inventors.
In the Na.sub.2 S aqueous solution, Na.sub.2 S is in equilibrium with NaSH and NaOH according to the formula (1) given below and NaSH is in equilibrium with NaOH and H.sub.2 S as illustrated below according to the formula (2).
NaSH+NaOH.revreaction.Na.sub.2 S+H.sub.2 O (1)