JP2013516531A - Alkali metal polysulfide mixture - Google Patents

Abstract

  The present invention relates to mixtures of alkali metal polysulfides and mixtures of alkali metal polysulfides and alkali metal thiocyanates, processes for their preparation, their use as heat transfer fluids or heat storage fluids, and mixtures of alkali metal polysulfides or alkali metal polysulfides and The present invention relates to a heat transfer fluid or a heat storage fluid containing a mixture of alkali metal thiocyanate.

Description

  The present invention relates to mixtures of alkali metal polysulfides and mixtures of alkali metal polysulfides and alkali metal thiocyanates, processes for their preparation, their use as heat transfer fluids or heat storage fluids, and mixtures of alkali metal polysulfides or alkali metal polysulfides and The present invention relates to a heat transfer fluid or a heat storage fluid containing a mixture of alkali metal thiocyanate.

  Fluids for transferring thermal energy are used in various fields of technology. In internal combustion engines, a mixture of water and ethylene glycol carries the residual heat of combustion to a cooling device. A similar mixture carries the heat from the solar collector on the roof to the heat storage device. In the chemical industry, they carry heat from a heating device heated by electricity or fossil fuel to or from a chemical reactor.

  Depending on the field of use, the profile of the requirements for heat transfer fluids or heat storage fluids can vary greatly, so that in practice a large number of fluids are used. The fluid should be liquid at room temperature or even lower and have a low viscosity. At higher service temperatures, water is no longer considered and its vapor pressure becomes too high. Therefore, hydrocarbon-based mineral oils are used up to about 320 ° C., and oils containing synthetic aromatic compounds or silicone oils are used up to temperatures up to 400 ° C. (VDI Waermeatlas, VDI-Gesellschaff Verhenchtechnique undenieurwesen, Springer Berlin Heidelberg 2006).

  A new challenge for heat transfer fluids is solar power plants that generate electrical energy on a large scale (Butscher, R., Bird der Wissenshaft 2009, 3, pp. 84-92). To date, power plants with such a capacity of several hundred MW have been built, and more power plants are planned, especially in Spain, but also in North Africa and the United States. Sunlight irradiation is focused on the focal line of the mirror via, for example, a parabolic trough mirror. There is a metal tube in the glass tube to prevent heat loss, and the space between the concentric tubes is evacuated. A heat transfer fluid flows through the metal tube. Currently, mixtures of diphenyl ether and diphenyl are used here. A steam boiler is operated in which the heat medium is heated up to 400 ° C., whereby water is evaporated inside. This steam moves the turbine, which also moves the generator in the same way as a conventional power plant. Thus, a maximum peak efficiency of about 30 percent relative to the energy content of sunlight exposure is obtained. The efficiency of the steam turbine is about 37 percent at the inlet temperature.

  Both components of the mixture consisting of diphenyl ether and diphenyl used as the heating medium boil at about 256 ° C. under standard pressure. The melting point of diphenyl is 68-72 ° C, and the melting point of diphenyl ether is 26-39 ° C. When the two materials are mixed, the melting point drops to 12 ° C. The mixture of the two substances can be used up to 400 ° C. and decomposition occurs at higher temperatures. The vapor pressure is about 10 bar at that temperature and is still acceptable in industrial technology.

  Higher steam inlet temperatures are essential to achieve turbine efficiencies higher than 37 percent. Steam turbine efficiency increases with turbine inlet temperature. Modern fossil fuel power plants operate with steam inlet temperatures up to 650 ° C., and the efficiency thereby reaches approximately 45%. It would be technically possible to heat the heat transfer fluid at the focal point of the mirror to a temperature of approximately 650 ° C., thereby achieving a similarly high efficiency, but there is a limit to the heat transfer fluid currently used. The temperature resistance that has been made prevents this.

Higher temperatures than in trough solar power plants can be obtained in solar tower power plants, where one tower is surrounded by mirrors, and those mirrors collect sunlight into a receiver at the top of the tower. it can. A heat medium is heated in the receiver, and the heat medium is then used for steam generation and turbine operation via a heat exchanger. In the tower type power plant (Solar II, California), a mixture (60:40) consisting of sodium nitrate (NaNO ₃ ) and potassium nitrate (KNO ₃ ) was already used as the heat medium. The mixture can be used without problems up to 550 ° C, but has a very high melting point of 240 ° C.

  No organic substance has been known so far that is an organic substance that will last permanently without decomposing to temperatures above 400 ° C. Some of the dimethyl silicone-based or diphenyl silicone-based oils can also be used at temperatures up to 400 ° C., or rather somewhat higher. However, its very high cost is disadvantageous for use in solar power plants.

  Another possibility is the use known from nuclear technology with liquid sodium or sodium potassium alloy as the heating medium. However, the production of these metals is very expensive, and it is a safety technical issue to generate hydrogen gas by reacting with a small amount of water.

  Furthermore, low melting solders such as wood alloys (Bi—Pb—Cd—Sn alloys, melting point about 75 ° C.) are known. However, its very high specific gravity is disadvantageous for use as a heat transfer fluid.

  Further possible high-temperature heating media have been proposed on the basis of sulfur used, for example, in the form of mixtures with smaller amounts of selenium and / or tellurium (WO 2005/071037). Since liquid sulfur has a high viscosity in the range of 150 to 200 ° C. and cannot be pumped thereby, it is a problem as a heat medium. The viscosity is certainly lowered by the addition of bromine or iodine (US 4335578), but these are highly corrosive.

  It is technically possible to use water under a correspondingly high pressure. However, extremely high vapor pressures of over 270 bar at temperatures above 500 ° C. would prevent this and make the kilometers of pipelines of solar power plants expensive. Vapor itself has a relatively low thermal conductivity and a low heat capacity per volume, and therefore is not suitable as a heat medium compared to liquid.

  Another possibility is to use an inorganic molten salt as the heat transfer fluid. Such molten salts are state of the art for processes carried out at high temperatures. A eutectic mixture consisting of potassium nitrate, sodium nitrate and sodium nitrite has a melting point of 146 ° C. and is commercially available. However, when the temperature exceeds 450 ° C., nitrite is significantly decomposed into nitrite gas, alkali metal oxide and elemental nitrogen, so the upper limit of the application temperature is limited to 450 ° C. A eutectic mixture of sodium nitrate and potassium nitrate can be used up to a temperature of 600 ° C. However, the use of the mixture as a heat transfer fluid in a solar power plant is problematic because of its high melting point of about 220 ° C. A decrease in temperature below the melting point, such as at night or during periods of low sun exposure, may result in salt coagulation in the conduit. This must be prevented because local stresses occur during remelting that result in equipment damage. Freezing protection in the form of trace heating may also be possible, but at the high temperatures mentioned above, it is very difficult to achieve technically and more expensive. The melting point of a mixture consisting of sodium nitrate and potassium nitrate can be lowered by the addition of lithium nitrate or calcium nitrate (Bradshaw, RW, Meeker, DE, Solar Energy Materials 1990, Vol. 21, 51-60). page). However, while the mixture containing lithium nitrate is expensive and uneconomical, the presence of calcium promotes the decomposition of nitrate to nitrite and oxygen, thereby increasing the upper limit of application temperature to increase the calcium content. Along with that, it goes down.

  Furthermore, it seems possible to use metal halides as heat transfer fluids. In this case, the problem arises that halogen-containing liquids often cause corrosion in metal materials that can be used, especially at elevated temperatures.

Mixtures of alkali metal polysulfides, especially sodium polysulfides and potassium polysulfides, have a theoretically low melting point and may be used at temperatures up to and above 500 ° C. The phase diagram for the sodium sulfide-potassium sulfide-sulfur ternary system is calculated according to the composition K _0.84 Na _0.26 S _3.61 (78 ° C.), K _0.77 Na _0.23 S _3.75 (73 ° C.) and K _0.79 Na _0.21 S _In the case of _3.95 (83 ° C.), it has a fixed point having a low melting temperature. (Lindberg, D., Backman, R., Hupa, M., Chartrand, P., J. Chem. Therm. 2006, 38, 900-915). There is no experimental data for the ternary system. In the potassium sulfide-sulfur system, the melting point can be lowered to about 120 ° C. (Sangster, J., Pelton, AD, J. Phase Equil. 1997, Vol. 18, page 82). The disadvantage of alkali metal polysulfides is their relatively high viscosity in the molten state, in particular the high viscosity of sodium polysulfides (Cleaver, B., Davis, AJ, Electrochimica Acta 1973, Vol. 18, 727-731. page).

  DE 3824517 describes the use of mixtures of alkali metal thiocyanates as heat transfer fluids, in particular potassium thiocyanate and sodium thiocyanate. Potassium thiocyanate melts at 173 ° C and sodium thiocyanate melts at 310 ° C. The eutectic mixture of the two salts having a ratio of 73 mole% potassium thiocyanate to 27 mole% sodium thiocyanate has a melting point of approximately 130 ° C. The melt has a low viscosity and can therefore be pumped without increasing energy consumption.

  The disadvantage of alkali metal thiocyanate is that it already begins to decompose at temperatures above 450 ° C. Sulfur is removed to form an alkali metal cyanide having a higher melting point (Gmelins Handbuch der Anorganischen Chemie 1938, Vol. 22, page 899).

  The melting point of the alkali metal thiocyanate can be further lowered by adding further salts. In particular, the mixing of nitrite or nitrate lowers the melting point. However, the addition of oxidizing nitrite or nitrate results in explosive decomposition at elevated temperatures, which can be further accelerated by traces of dissolved heavy metals. Thus, the use of such a mixture is eliminated for industrial use.

  A further problem arises from trying to operate solar power plants continuously. This is accomplished by storing heat that can be used for power generation after sunset or during periods of bad weather during periods of high sunlight exposure. The accumulation of heat takes place directly by storing the heated heat medium in a well insulated storage tank or indirectly by transferring the heat to another storage medium.

  The indirect method has been realized at a 50 MW Andasol I power plant in Almeria, where about 28,000 tonnes of sodium nitrate and potassium nitrate melt (60:40) are used. The melt is pumped from the cooler tank (about 280 ° C.) through the oil salt heat exchanger to the hotter tank during the sun exposure time, where it is heated to about 380 ° C. The power plant is a fully charged storage battery at low sunlight and at night, and can operate at full load for about 7.5 hours (www.solarmillenium.de/upload/Download/Technology/Andasol1-3deutsch. pdf). In this way, it is certainly advantageous to use the heat transfer fluid as the storage fluid, since a corresponding oil salt heat exchanger can be dispensed with. This has not been taken into account so far because the vapor pressure of the oil is high and the costs are high compared to nitrates.

  The object of the present invention is to provide improved heat transfer fluids and heat storage fluids that are well available. It is desirable that the fluid can be used at temperatures above 400 ° C, preferably above 500 ° C. At the same time, the melting point should be as low as possible, preferably less than 200 ° C. In addition, it is desirable for the fluid to have a technically controllable vapor pressure as low as possible, preferably below 10 bar.

  The object is solved according to the invention by a mixture of alkali metal polysulfides.

Accordingly, the subject of the present invention is the general formula (M ¹ _x M ² _(1-x) ) ₂ S _y
[Wherein M ¹ and M ² represent Li, Na, K, Rb and Cs, M ¹ is not the same as M ² , and 0.05 ≦ x ≦ 0.95 and 2.0 ≦ y ≦ 6. .0]
Is a mixture of alkali metal polysulfides.

In a preferred embodiment of the invention, M ¹ is K and M ² is Na.

  In a further preferred embodiment of the invention, 0.20 ≦ x ≦ 0.95. In a particularly preferred embodiment of the invention, 0.50 ≦ x ≦ 0.90.

  In a further preferred embodiment of the invention, 3.0 ≦ y ≦ 6.0. In particularly preferred embodiments of the invention, y is 4.0, 5.0 or 6.0.

In a particularly preferred embodiment of the invention, M ¹ is K, M ² is Na, 0.20 ≦ x ≦ 0.95 and 3.0 ≦ y ≦ 6.0.

In a particularly preferred embodiment of the invention, M ¹ is K, M ² is Na, 0.50 ≦ x ≦ 0.90 and y is 4.0, 5.0 or 6.0. is there.

A further embodiment is the composition (K _(1-x) Na _x ) ₂ S _z , wherein x is 0 to 1 and z is 2.3 to 3.5, preferably x is 0 0.5 to 0.7 and z is 2.4 to 2.9].

A further embodiment relates to an alkali metal polysulfide having an alkali metal polysulfide (Na _0.5-0.65 K _0.5-0.35 ) ₂ S _2.4-2.8 or composition (Na _0.6 K _0.4 ) ₂ S _2.6 .

  The mixtures according to the invention are distinguished by a particularly low melting point. In a preferred embodiment of the invention, the melting point of the mixture according to the invention is less than 200 ° C., in a particularly preferred embodiment less than 160 ° C.

  The mixture according to the invention has a high temperature stability. In a preferred embodiment of the invention, the mixture according to the invention is stable up to a temperature of 450 ° C., in a particularly preferred embodiment up to a temperature of 500 ° C. and in a particularly preferred embodiment even at temperatures above 500 ° C. doing.

  In a preferred embodiment of the invention, the mixture according to the invention has a vapor pressure of less than 5 bar at 500 ° C., particularly preferably less than 2 bar.

  The production of alkali metal polysulfides is known and can be carried out, for example, by reaction of alkali metal sulfides with sulfur. Another method is the direct reaction of alkali metals with sulfur as described for sodium in US4640832. The reaction of alkali metals with sulfur in liquid ammonia is also described. A further synthesis possibility is the reaction of alkali metal hydrogen sulfide or alkali metal sulfide with sulfur in an alcohol solution.

  A further subject of the present invention is a process for the preparation of a mixture of alkali metal polysulfides according to the invention, comprising a corresponding alkali metal sulfide with sulfur or a corresponding alkali metal polysulfide with or without sulfur and a protective gas. It is the said manufacturing method characterized by heating under or a vacuum.

  In a preferred embodiment of the process according to the invention, the starting material is heated to at least 400 ° C. for at least 0.5 hours.

  As the protective gas, a rare gas, preferably argon or nitrogen, is suitable.

  A further subject of the present invention is a process for the production of a mixture of alkali metal polysulfides according to the invention, characterized in that a solution of the corresponding alkali metal in liquid ammonia is reacted with sulfur under a protective gas. is there.

  A further subject of the present invention is the use of a mixture of alkali metal polysulfides according to the invention as a heat transfer fluid or a heat storage fluid.

  In a preferred embodiment of the invention, said use of the mixture of alkali metal polysulfides according to the invention eliminates air and moisture in order to prevent hydrolysis or oxidation of the heat transfer fluid or the heat storage fluid during operation, Preferably, it is carried out in a closed system, such as lines, pumps, regulators and containers.

  A further subject of the present invention is a heat transfer or heat storage fluid comprising a mixture of alkali metal polysulfides according to the present invention.

  The application range of the mixture of alkali metal polysulfides according to the invention can be further expanded when mixed with alkali metal thiocyanate.

A further subject of the present invention is the general formula ((M ¹ _x M ² _(1−x) ) ₂ S _y ) _m (M ³ _z M ⁴ _(1−z) SCN) _(1−m)
[Wherein M ¹ , M ² , M ³ , M ⁴ represent Li, Na, K, Rb, Cs, M ¹ is not identical to M ² , M ³ is not identical to M ⁴ , and 0 0.05 ≦ x ≦ 1, 0.05 ≦ z ≦ 1, 2.0 ≦ y ≦ 6.0, and the substance amount ratio m is 0.05 ≦ m ≦ 0.95]
A mixture of alkali metal polysulfide and alkali metal thiocyanate represented by

In a preferred embodiment of the invention, M ¹ and M ³ are K and M ² and M ⁴ are Na.

  In a further preferred embodiment of the invention, 0.20 ≦ x ≦ 1. In a particularly preferred embodiment of the invention, 0.50 ≦ x ≦ 1.

  In a further preferred embodiment of the invention, 3.0 ≦ y ≦ 6.0. In particularly preferred embodiments of the invention, y is 4.0, 5.0 or 6.0.

  In a further preferred embodiment of the invention, 0.20 ≦ z ≦ 1. In a particularly preferred embodiment of the invention, 0.50 ≦ z ≦ 1.

  In a further preferred embodiment of the invention, 0.20 ≦ m ≦ 0.80. In a particularly preferred embodiment of the invention, 0.33 ≦ m ≦ 0.80.

In a particularly preferred embodiment of the invention, M ¹ and M ³ are K, M ² and M ⁴ are Na, 0.20 ≦ x ≦ 1, 0.20 ≦ z ≦ 0.95,3. 0 ≦ y ≦ 6.0 and 0.20 ≦ m ≦ 0.95.
In a particularly preferred embodiment of the invention, M ¹ and M ³ are K, M ² and M ⁴ are Na, 0.50 ≦ x ≦ 1, 0.50 ≦ z ≦ 0.95, y Is 4.0, 5.0 or 6.0, and 0.33 ≦ m ≦ 0.80.

In a further particularly preferred embodiment of the invention, M ¹ and M ³ are K, x is 1, z is 1, y is 4.0, 5.0 or 6.0, and 0.33 ≦ m ≦ 0.80.

In a further particularly preferred embodiment of the invention, M ¹ and M ³ are K, x is 1, z is 1, y is 4 and m is 0.5.

In a further particularly preferred embodiment of the invention, M ¹ and M ³ are K, x is 1, z is 1, y is 5 and m is 0.5.

In a further particularly preferred embodiment of the invention, M ¹ and M ³ are K, x is 1, z is 1, y is 6 and m is 0.5.

  Surprisingly, it has been found that the alkali metal polysulfide and alkali metal thiocyanate mixtures according to the invention are more thermally stable than alkali metal thiocyanate alone. In addition, the viscosity of the alkali metal polysulfide and alkali metal thiocyanate mixture according to the present invention is lower than the viscosity of the alkali metal polysulfide mixture without alkali metal thiocyanate.

  The production of alkali metal thiocyanates is known and practiced on a large scale industrially.

  A further subject of the present invention is a process for producing a mixture of alkali metal polysulfides and alkali metal thiocyanates according to the invention by co-melting alkali metal polysulfides and alkali metal thiocyanates. The method can be carried out while stirring the melt.

  Mixtures of alkali metal polysulfides and alkali metal thiocyanates according to the present invention are generally suitable for high temperature applications requiring a heat medium having a wide fluid temperature range.

  A further subject of the present invention is the use of a mixture of alkali metal polysulfides and alkali metal thiocyanates according to the invention as heat transfer fluid or heat storage fluid.

  In a preferred embodiment of the present invention, said use of the alkali metal polysulfide and alkali metal thiocyanate mixture according to the present invention prevents air and moisture in the heat and fluid storage fluids from hydrolyzing or oxidizing during operation. This is preferably done in closed systems such as lines, pumps, regulators and containers.

  A further subject of the present invention is a heat transfer or heat storage fluid comprising a mixture of alkali metal polysulfides and alkali metal thiocyanates according to the invention.

Example:
1. Potassium sodium polysulfide _{(K x Na 1-x)} 2 S starting due to melting of a) Synthesis alkali metal polysulfide, and mixtures consisting of sulfur _y substance K ₂ S ₃ and Na ₂ S ₄ was prepared according to methods known from the literature.

_{Synthesis of} Na _0.464 K _1.536 S _{3.745 3.51} g of K ₂ S ₃ , 0.43 g of sulfur and 1.06 g of Na ₂ S ₄ were sealed in a quartz glass ampoule sealed and evacuated for 30 minutes to 400 ° C. Upon heating, the melt was subsequently cooled to room temperature. The ampoule was opened in an argon glove box, and a red or reddish yellow solid was pulverized with a mortar (quantitative yield). The solid melts in the range of 151-157 ° C.

Synthesis of Na _0.42 K _1.58 S _3.80 3.65 g of K ₂ S ₃ , 0.49 g of sulfur and 0.95 g of Na ₂ S ₄ were sealed in a vacuumed quartz glass ampoule for 30 minutes up to 400 ° C. Upon heating, the melt was subsequently cooled to room temperature. The ampoule was opened in an argon glove box, and a red or reddish yellow solid was pulverized with a mortar (quantitative yield). The solid melts in the range of 158-167 ° C.

Synthesis of Na _0.325 K _1.675 S _3.61 3.87 g of K ₂ S ₃ , 0.38 g of sulfur and 0.75 g of Na ₂ S ₄ in a sealed and evacuated quartz glass ampoule for 30 minutes up to 400 ° C. Upon heating, the melt was subsequently cooled to room temperature. The ampoule was opened in an argon glove box, and a red or reddish yellow solid was pulverized with a mortar (quantitative yield). The solid melts in the range of 157-163 ° C.

b) Synthesis of Na _0.46 K _1.54 S _3.75 by reaction of alkali metal and sulfur in liquid ammonia. The synthesis was carried out by Schlenk and glove box technology under argon atmosphere. 63.6 g (1.98 mol) of sulfur was added to liquid ammonium at −30 ° C. in a glass flask. Subsequently, a blue solution of 5.50 g (0.24 mol) sodium metal and 32.0 g (0.81 mol) potassium metal in about 800 ml liquid ammonium (−30 ° C.) was added dropwise with stirring. The resulting mixture was warmed to room temperature and stirred until ammonia had evaporated. Residual ammonia was subsequently removed from the resulting orange solid at 150 ° C. and vacuum (about 1 mbar). The solid melts in the range of 166-169 ° C.

Synthesis of Na _0.23 K _1.77 S _3.75 The synthesis was performed by Schlenk and glove box techniques under an argon atmosphere. 43.0 g (1.34 mol) of sulfur was added to liquid ammonia at −30 ° C. in a glass flask. Subsequently, a blue solution of 1.82 g (0.079 mol) of sodium metal and 24.9 g (0.63 mol) of potassium metal in about 800 ml of liquid ammonia (−30 ° C.) was added dropwise with stirring. The resulting mixture was warmed to room temperature and stirred until ammonia had evaporated. Residual ammonia was subsequently removed from the resulting orange solid at 150 ° C. and vacuum (about 1 mbar). The solid melts at 165-166 ° C.

2. Synthesis and properties of having an alkali metal thiocyanate (K _x Na _1-x) a mixture consisting of ₂ S _y a) Synthesis Method 1:
Corresponding amounts of potassium polysulfide (K ₂ S _x ) or potassium sodium polysulfide ((K _x Na _1-x ) ₂ S _y ) and potassium thiocyanate (KSCN) are placed in a sealed, evacuated quartz glass ampoule for 30 minutes. Heated to 400 ° C. for minutes and the melt was subsequently cooled to room temperature. The ampoule was opened in an argon glove box, and the melt was pulverized with a mortar. An orange solid is obtained, the melting range of which is shown in Table 1.

Method 2:
Potassium polysulfide (K ₂ S _x) or potassium sodium polysulfide _{((K x Na 1-x} ) 2 S y) and mixing the appropriate amount of potassium thiocyanate (KSCN), 180 under an argon atmosphere in a glass flask Heated at ° C. Stir until a homogeneous melt is formed and then cool to room temperature. An orange solid was obtained whose melting range was equal to the melting range of the solid produced according to Method 1 (see Table 1).

Table 1

b) Viscosity The viscosity of the melt was measured using a rotational viscometer.

Table 2

c) Temperature stability The temperature stability test was carried out using a mixture (K ₂ S ₄ ) _0.5 (KSCN) _0.5 (melting range 110-112 ° C.), (K ₂ S ₅ ) _0.5 (KSCN) _0.5 (melting range 150-158 ° C. ) And (K ₂ S ₆ ) _0.5 (KSCN) _0.5 (melting range 146-153 ° C.).

Stability at 400 ° C:
3 g of a mixture of composition (K ₂ S ₄ ) _0.5 (KSCN) _0.5 was stored at 400 ° C. for 28 days in an evacuated quartz glass ampoule. The melting range of the mixture was unchanged.

3 g of a mixture of composition (K ₂ S ₅ ) _0.5 (KSCN) _0.5 were stored at 400 ° C. in a quartz glass ampoule evacuated for 28 days. The melting range of the mixture was unchanged.

3 g of a mixture of composition (K ₂ S ₆ ) _0.5 (KSCN) _0.5 was stored at 400 ° C. for 28 days in an evacuated quartz glass ampoule. The melting range of the mixture was unchanged.

Stability at 450 ° C:
3 g of a mixture of composition (K ₂ S ₄ ) _0.5 (KSCN) _0.5 was stored at 450 ° C. in a quartz glass ampoule evacuated for 28 days. The melting range of the mixture was unchanged.

3 g of a mixture of composition (K ₂ S ₅ ) _0.5 (KSCN) _0.5 was stored at 450 ° C. in a quartz glass ampoule evacuated for 28 days. The melting range of the mixture was unchanged.

3 g of a mixture of composition (K ₂ S ₆ ) _0.5 (KSCN) _0.5 was stored at 450 ° C. for 28 days in an evacuated quartz glass ampoule. The melting range of the mixture was unchanged.

Stability at 500 ° C:
3 g of a mixture of composition (K ₂ S ₄ ) _0.5 (KSCN) _0.5 was stored at 500 ° C. in a quartz glass ampoule evacuated for 28 days. The melting range of the mixture was unchanged.

3 g of a mixture of composition (K ₂ S ₅ ) _0.5 (KSCN) _0.5 was stored at 500 ° C. for 28 days in an evacuated quartz glass ampoule. The melting range of the mixture was unchanged.

3 g of a mixture of composition (K ₂ S ₆ ) _0.5 (KSCN) _0.5 was stored at 500 ° C. for 28 days in an evacuated quartz glass ampoule. The melting range of the mixture was unchanged.

Stability at 600 ° C:
3 g of a mixture of composition (K ₂ S ₄ ) _0.5 (KSCN) _0.5 was stored at 600 ° C. in a quartz glass ampoule evacuated for 28 days. The melting range of the mixture was unchanged.

3 g of a mixture of composition (K ₂ S ₅ ) _0.5 (KSCN) _0.5 was stored in a quartz glass ampoule evacuated for 28 days at 600 ° C. The melting range of the mixture was unchanged.

3 g of a mixture of composition (K ₂ S ₆ ) _0.5 (KSCN) _0.5 was stored at 600 ° C. in a quartz glass ampoule evacuated for 28 days. The melting range of the mixture was unchanged.

Claims (24)

A mixture of alkali metal polysulfides having the general formula (M ¹ _x M ² _(1-x) ) ₂ S _y
[Wherein M ¹ and M ² represent Li, Na, K, Rb and Cs, M ¹ is not the same as M ² , and 0.05 ≦ x ≦ 0.95 and 2.0 ≦ y ≦ 6.0]
The said mixture shown by. The mixture of claim 1, wherein M ¹ is K and M ² is Na.   The mixture according to claim 1, wherein 0.20 ≦ x ≦ 0.95.   4. The mixture according to claim 1, wherein 3.0 ≦ y ≦ 6.0. 5. A mixture according to any one of claims 1 to 4, wherein, M ¹ is a K, M ² is Na, 0.20 ≦ x ≦ 0.95, and 3.0 The above mixture wherein ≦ y ≦ 6.0. The mixture according to any one of claims 1 to 5, wherein M ¹ is K, M ² is Na, 0.50 ≦ x ≦ 0.90, and y is 4 Said mixture being 0.0, 5.0 or 6.0.   7. A process for producing a mixture as claimed in claim 1, wherein the corresponding alkali metal sulfide is combined with sulfur or the corresponding alkali metal polysulfide is combined with or without sulfur. Heating under or in vacuum.   7. A process for producing a mixture as claimed in any one of claims 1 to 6, characterized in that a corresponding alkali metal solution in liquid ammonia is reacted with sulfur under a protective gas.   Use using the mixture according to any one of claims 1 to 6 as a heat transfer fluid or a heat storage fluid.   A heat transfer fluid or a heat storage fluid comprising the mixture of any one of claims 1 to 6. A mixture of an alkali metal polysulfide and an alkali metal thiocyanate having the general formula ((M ¹ _x M ² _(1-x) ) ₂ S _y ) _m (M ³ _z M ⁴ _(1-z) SCN) _{(1 −m)}
[Wherein M ¹ , M ² , M ³ , M ⁴ represent Li, Na, K, Rb, Cs, M ¹ is not identical to M ² , M ³ is not identical to M ⁴ , and 0 .05 ≦ x ≦ 1, 0.05 ≦ z ≦ 1, 2.0 ≦ y ≦ 6.0, and the substance amount ratio m is 0.05 ≦ m ≦ 0.95]
The said mixture shown by. A mixture according to claim 11, wherein, M ¹ and M ³ are K, and the mixture M ² and M ⁴ are Na.   13. The mixture according to any one of claims 11 or 12, wherein 0.20≤x≤1.   14. The mixture according to any one of claims 11 to 13, wherein 3.0 ≦ y ≦ 6.0.   15. The mixture according to any one of claims 11 to 14, wherein 0.20≤z≤1.   The mixture according to any one of claims 11 to 15, wherein 0.20≤m≤0.80. A mixture according to any one of claims 11 to 15, wherein, M ¹ and M ³ are K, M ² and M ⁴ are Na, 0.20 ≦ x ≦ 1, Said mixture wherein 0.20 ≦ z ≦ 0.95, 3.0 ≦ y ≦ 6.0, and 0.20 ≦ m ≦ 0.95. A mixture according to any one of claims 11 to 16, wherein, M ¹ and M ³ are K, M ² and M ⁴ are Na, 0.50 ≦ x ≦ 1, 0.50 ≦ z ≦ 0.95, y is 4.0, 5.0 or 6.0, and 0.33 ≦ m ≦ 0.80.   The method for producing a mixture according to any one of claims 11 to 18, wherein the corresponding alkali metal polysulfide and alkali metal thiocyanate are co-melted.   Use of the mixture according to any one of claims 11 to 18 as a heat transfer fluid or a heat storage fluid.   A heat transfer fluid or a heat storage fluid comprising one mixture according to any one of claims 11 to 18. A mixture of alkali metal polysulfides having the composition (K _(1-x) Na _x ) ₂ S _z , wherein x is 0 to 1 and z is 2.3 to 3.5. blend.   Use of the mixture according to claim 22 as heat transfer fluid or heat storage fluid.   A heat transfer fluid or a heat storage fluid comprising the one mixture according to claim 22.