KR20120104423A - Mixtures of alkali polysulfides - Google Patents

Abstract

The present invention relates to mixtures of alkali metal polysulfides and mixtures of alkali metal polysulfides with alkali metal thiocyanates, methods for their preparation, their use as heat transfer or heat storage fluids, and mixtures of alkali metal polysulfides or alkali metals. A heat transfer or heat storage fluid comprising a mixture of sulfides and alkali metal thiocyanates.

Description

Mixture of alkali metal polysulfides {MIXTURES OF ALKALI POLYSULFIDES}

The present invention relates to mixtures of alkali metal polysulfides and mixtures of alkali metal polysulfides with alkali metal thiocyanates, methods for their preparation, their use as heat transfer or heat storage fluids, and mixtures of alkali metal polysulfides or alkali metals. A heat transfer or heat storage fluid comprising a mixture of sulfides and alkali metal thiocyanates.

Fluids that transfer thermal energy are used in many industries. In an internal combustion engine, a mixture of water and ethylene glycol transfers combustion waste heat to the radiator. A similar mixture transfers heat from the solar roof collector to the regenerator. In the chemical industry, this transfers heat from an electrical or fossil fuel heating device to a chemical reactor or transfers heat from a chemical reactor to a cooling device.

Depending on the field of use, the requirements profile of the heat transfer or heat storage fluid varies greatly, and therefore many fluids are actually used. These fluids should be liquid at room temperature or even at low temperatures and should be low in viscosity. At higher service temperatures water cannot be used; This is because the vapor pressure of water becomes too high. Thus, hydrocarbon-based mineral oils are used at temperatures below about 320 ° C. and synthetic aromatic containing oils or silicone oils are used at temperatures below 400 ° C. (VDI Waermeatlas, VDI-Gesellschaft Verfahrenstechnik und Chemieingenieurwesen, Springer Verlag Berlin Heidelberg 2006).

A new challenge for heat transfer fluids is solar thermal power plants that produce large amounts of electrical energy (Butscher, R., Bild der Wissenschaft 2009, 3, p. 84-92). To date, these plants have been built with a few hundred megawatts of installed power, and many others are planned, especially in Spain, and in North Africa and the United States. Solar radiation is focused at the focal line of the mirror, for example by parabolic mirror grooves. Metal tubes are placed in the glass tubes to prevent heat loss at the focal line, and the spaces between these concentric tubes are evacuated. The heat transfer fluid flows through the metal tube. Currently, a mixture of diphenyl ether and diphenyl is used here. The heat transfer medium is heated up to 400 ° C. and used to operate a steam generator that evaporates water. This steam drives the turbine, which runs the generator as in a conventional power plant. Thus, a maximum efficiency of about 30% is achieved based on the energy content of solar radiation. The efficiency of the steam turbine at this inlet temperature is about 37%.

The two components of the mixture of diphenyl ether and diphenyl used as heat transfer medium boil at about 256 ° C. under standard pressure. Melting | fusing point of diphenyl is 68-72 degreeC, and melting | fusing point of diphenyl ether is 26-39 degreeC. Mixing the two materials lowers the melting point to 12 ° C. Mixtures of both materials can be used up to 400 ° C; At higher temperatures decomposition occurs. The vapor pressure at this temperature is about 10 bar, which is still acceptable in industry.

To achieve turbine efficiency higher than 37%, higher steam inlet temperatures are required. The efficiency of the steam turbine increases with the turbine inlet temperature. Modern fossil fuel fired power plants operate at steam inlet temperatures below 650 ° C., thus achieving an efficiency of about 45%. It is technically entirely possible to achieve such high efficiency by heating the heat transfer fluid to a temperature of about 650 ° C. at the focal line of the mirror, but this is blocked by the limited heat resistance of the heat transfer fluids currently used.

Higher temperatures can be achieved in tower solar power plants than in parabolic trough power plants, where a tower is surrounded by a mirror that focuses sunlight into the receiver at the top of the tower. In this receiver the heat transfer fluid is heated, which is used by the heat exchanger to generate steam and to run the turbine. In tower power plants (Solar II, California), a mixture of sodium nitrate (NaNO ₃ ) and potassium nitrate (KNO ₃ ) (60:40) has already been used as the heat transfer medium. This mixture can be used without problems up to 550 ° C., but has a very high melting point of 240 ° C.

To date, there are no organic substances known to decompose and permanently withstand temperatures above 400 ° C. Oils based on some dimethylsilicone or diphenylsilicone may also be used up to a temperature of 400 ° C. or even higher. However, the very high cost of these oils prevents their use in solar power plants.

Another option is to use liquid sodium or sodium-potassium alloys known from nuclear technology as the heat transfer medium. However, the production cost of these metals is very high, and these metals react with trace amounts of water to generate hydrogen gas, causing safety problems.

In addition, low melting point solder metals are known, such as Wood's metal (Bi-Pb-Cd-Sn alloy, melting point about 75 ° C.). However, very high specific gravity prevents its use as heat transfer fluid.

Further possible high temperature heat transfer media based on sulfur have been proposed, which are used for example in mixtures containing small amounts of selenium and / or tellurium (WO 2005/071037). Liquid sulfur is problematic as a heat transfer medium because sulfur has a high viscosity in the range of 150-200 ° C. and cannot be pumped in this form. The viscosity can be reduced using additives such as bromine or iodine (US 4 335 578), but these additives are very corrosive.

Technically, it is also possible to use water under the corresponding high pressure. However, this is prevented by very high vapor pressures in excess of 270 bar at temperatures above 500 ° C., which makes the multi-kilometre pipeline of the solar power plant uneconomically expensive. Steam itself is disadvantageous as a heat transfer medium due to its relatively low thermal conductivity and low heat capacity per unit volume compared to liquids.

Another option is to use an inorganic salt melt as the heat transfer fluid. Such salt melts are a technique currently used in processes operated at high temperatures. Eutectic mixtures of potassium nitrate, sodium nitrate and sodium nitrite have a melting point of 146 ° C. and are commercially available. However, the upper limit of use temperature is limited to 450 ° C., because at this temperature a significant decomposition of nitrates into nitrogen gas, alkali metal oxides and elemental nitrogen occurs. Eutectic mixtures of sodium nitrate and potassium nitrate can be used up to a temperature of 600 ° C. However, the use of this mixture as heat transfer fluid in solar power plants can be problematic due to the high melting point of about 220 ° C. For example, at night or during periods of low solar radiation, lowering the temperature below the melting point results in solidification of the salt in the pipeline. This should be avoided because of local stresses in the remelting process that damage the plant. Anti-freeze protection in the form of hot wire may be considered, but this is technically very difficult to implement and more expensive at such high temperatures. The melting point of the mixture of sodium nitrate and potassium nitrate can be lowered by adding lithium nitrate or calcium nitrate (Bradshaw, R. W., Meeker, D. E., Solar Energy Materials 1990, Vol. 21, p. 51-60). However, mixtures containing lithium nitrate are uneconomical due to their high cost, and the presence of calcium promotes the decomposition of nitrates to nitrites and oxides, further lowering the upper limit of use temperature even with higher calcium content.

It is also possible to use metal halides as heat transfer fluids. At this time, the problem arises that halogenated fluids often cause corrosion problems in the metal materials used, especially at high temperatures.

Mixtures of alkali metal polysulfides, especially mixtures of sodium polysulfide and potassium polysulfide, in theory have a low melting point and can be used up to 500 ° C. and higher. According to the calculations, the phase diagrams of ternary sodium sulfide-potassium sulfide-sulfur are compositions 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 _3.95 (83 ° C.) Have a low melting point for (Lindberg, D., Backman, R., Hupa, M., Chartrand, P., J. Chem. Therm. 2006, vol. 38, p. 900-915) . There is no experimental data for this system. In potassium sulfide-sulfur systems, the melting point can be lowered to about 120 ° C. (Sangster, J., Pelton, AD, J. Phase Equil. 1997, vol. 18, p. 82). One disadvantage of alkali metal polysulfides is the relatively high viscosity in the molten state, especially for sodium polysulfide (Cleaver, B., Davis, AJ, Electrochimica Acta 1973, vol. 18, p. 727-731). .

DE 3824517 discloses a mixture of alkali metal thiocyanates as a heat transfer fluid, in particular a mixture of potassium thiocyanate and sodium thiocyanate. Potassium thiocyanate melts at 173 ° C, and sodium thiocyanate melts at 310 ° C. The eutectic mixture of two salts having a ratio of 73 mol% potassium thiocyanate to 27 mol% sodium thiocyanate has a melting point of about 130 ° C. This melt is low in viscosity and thus pumpable without increasing energy costs.

One disadvantage of alkali metal thiocyanates is that they already begin to decompose at temperatures higher than 450 ° C. Excluding sulfur, higher melting alkali metal cyanide is formed (Gmelins Handbuch der Anorganischen Chemie 1938, vol. 22, p. 899).

The melting point of the alkali metal thiocyanate can be lowered by adding additional salts. In particular, the addition of nitrites or nitrates lowers the melting point. However, the addition of oxidative nitrites or nitrates at high temperatures causes explosive decomposition, which can be further facilitated by any traces of dissolved heavy metals. Therefore, the use of such mixtures for industrial use is ruled out.

Another problem arises from the fact that the goal is to run solar power plants continuously. This can be achieved by storing heat during periods of high solar radiation and using this heat in power plants after sunset or during bad weather. The heat may be stored directly by storing the heated heat storage medium in a suitable insulated storage tank or indirectly by transferring heat to another storage medium.

An indirect process is being carried out at the 50 MW Andasol I power plant in Spain, where 28,000 t of melt of sodium nitrate and potassium nitrate (60:40; wt%) is used. This melt is pumped from the colder tank (about 280 ° C.) to the hotter tank during the solar radiation period, during which the melt is heated to about 380 ° C. During periods of low solar radiation and at night, the plant can be run at full load in a fully charged storage state for about 7.5 h (www.solarmillennium.de/upload/Download/Technologie/Andasol1-3deutsch.pdf). However, it is advantageous to use a heat transfer fluid as a storage fluid, since this may eliminate the use of a corresponding oil-salt heat exchanger. This has not been considered until now due to the high vapor pressure and high cost of oil compared to nitrates.

It is an object of the present invention to provide readily available and improved delivery and heat storage fluids. The fluid should be able to be used at temperatures above 400 ° C., preferably at temperatures above 500 ° C. At the same time, the melting point should be lowest, preferably lower than 200 ° C. This liquid must also have a technically controllable minimum vapor pressure, preferably less than 10 bar.

According to the invention this object is achieved by a mixture of alkali metal polysulfides.

Accordingly, the present invention provides a mixture of alkali metal polysulfides of the general formula:

(M ¹ _x M ² _(1-x) ) ₂ S _y

Wherein M ¹ , M ² are Li, Na, K, Rb, Cs, M ¹ is not equal to M ² , 0.05 ≦ x ≦ 0.95, and 2.0 ≦ y ≦ 6.0.

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 a particularly preferred embodiment 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, 3.0 ≦ y ≦ 6.0.

In a very 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.

In another embodiment, (K _(1-x) Na _x ) ₂ S _z (where x is 0-1, z is 2.3-3.5, preferably x is 0.5-0.7, and z is 2.4-). 2.9), and an alkali metal polysulfide.

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

The mixtures of the present invention are particularly characterized by having a low melting point. In a preferred embodiment of the invention, the melting point of the mixtures of the invention is 200 ° C. or less, and in particularly preferred embodiments 160 ° C. or less.

The mixture of the present invention has high thermal stability. In a preferred embodiment of the invention, the mixtures of the invention are stable up to a temperature of 450 ° C., in a particularly preferred embodiment up to a temperature of 500 ° C., and in very particularly preferred embodiments, even at temperatures above 500 ° C.

In a preferred embodiment of the invention, the mixture of the invention at 500 ° C. has a vapor pressure of 5 bar or less, more preferably 2 bar or less.

The preparation of alkali metal polysulfides is known and can be carried out, for example, by reacting alkali metal sulfides with sulfur. One alternative method is the direct reaction of alkali metals with sulfur as described in US 4,640,832 for sodium. The reaction of alkali metals with sulfur in liquid ammonia has also been disclosed. Another method of synthesis is the reaction of alkali metal hydrides or alkali metal sulphides with sulfur in alcohol solutions.

The present invention provides a process for the preparation of a mixture of alkali metal polysulfides according to the invention, wherein under a protective gas or under reduced pressure, heating the corresponding alkali metal sulfides with sulfur or with the corresponding alkali metal polysulfides with or without sulfur It provides a manufacturing method comprising the step of.

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.

Suitable protective gases are rare gases, preferably argon or nitrogen.

The present invention provides a process for the preparation of a mixture of alkali metal polysulfides according to the invention, which comprises reacting a solution of a corresponding alkali metal sulfide in liquid ammonia with sulfur under a protective gas.

The invention further provides for the use of the mixture of alkali metal polysulfides according to the invention as heat transfer or heat storage fluid.

In a preferred embodiment of the invention, the mixture of alkali metal polysulfides according to the invention is preferably in a state of excluding air and moisture, in order to prevent hydrolysis or oxidation of the heat transfer or heat storage fluid during operation. Is used, for example, in closed systems of pipelines, pumps, regulating units and vessels.

The invention further provides a heat transfer or heat storage fluid comprising a mixture of alkali metal polysulfides according to the invention.

The field of application of the mixtures of alkali metal polysulfides according to the invention can be further extended when they are used with alkali metal thiocyanates.

The invention further provides a mixture of alkali metal polysulfides and alkali metal thiocyanates of 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 are Li, Na, K, Rb, Cs, M ¹ is not equal to M ² , M ³ is not equal to M ^4, and 0.05 ≦ x ≦ 1, 0.05 ≦ z ≦ 1, 2.0 ≦ y ≦ 6.0, and m is a molar ratio where 0.05 ≦ m ≦ 0.95.

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 a particularly preferred embodiment 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, 0.20 ≦ m ≦ 0.95.

In a very 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 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 mixtures of alkali metal polysulfides and alkali metal thiocyanates according to the invention have greater thermal stability than alkali metal thiocyanate alone. In addition, the viscosity of the mixture of alkali metal polysulfide and alkali metal thiocyanate according to the invention is lower than that of the alkali metal polysulfide mixture containing no alkali metal thiocyanate.

The preparation of alkali metal thiocyanates is known and is carried out on an industrial scale.

The present invention further provides a process for producing a mixture of an alkali metal polysulfide and an alkali metal thiocyanate according to the present invention by co-melting an alkali metal polysulfide and an alkali metal thiocyanate. This method can also be carried out while stirring the melt.

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

The invention further provides the use of a mixture of alkali metal polysulfides and alkali metal thiocyanates according to the invention as heat transfer or heat storage fluids.

In a preferred embodiment of the invention, the mixture of alkali metal polysulfides and alkali metal thiocyanates according to the invention excludes air and moisture to prevent heat transfer or hydrolysis reaction or oxidation of the heat storage fluid during operation. In a controlled state, it is preferably used, for example, in closed systems of pipelines, pumps, regulating units and vessels.

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

[Example]

1.Sodium-potassium polysulfide (K _x Na _1-x ) ₂ S _y Synthesis of

a) method of melting a mixture of alkali metal polysulfides and sulfur

K ₂ S ₃ and Na ₂ S ₄ starting materials were prepared according to the methods in the literature.

Na _0.464 K _1.536 S _3.745 Synthesis of

In a closed vacuum quartz glass ampoule 3.51 g of K ₂ S ₃ , 0.43 g of sulfur and 1.06 g of Na ₂ S ₄ were heated to 400 ° C. for 30 minutes, after which the melt was cooled to room temperature. The ampoules were opened in an argon glovebox and the red to red yellow solid was ground with a pestle (quantitative yield). The melting range of a solid is 151-157 degreeC.

Na _0.42 K _1.58 S _3.80 Synthesis of

3.65 g of K ₂ S ₃ , 0.49 g of sulfur and 0.95 g of Na ₂ S ₄ were heated to 400 ° C. for 30 minutes in a closed vacuum quartz glass ampoule, after which the melt was cooled to room temperature. The ampoules were opened in an argon glovebox and the red to red yellow solid was ground with a pestle (quantitative yield). The melting range of a solid is 158-167 degreeC.

Na _0.325 K _1.675 S _3.61 Synthesis of

3.87 g of K ₂ S ₃ , 0.38 g of sulfur and 0.75 g of Na ₂ S ₄ in a closed vacuum quartz glass ampoule were heated to 400 ° C. for 30 minutes, after which the melt was cooled to room temperature. The ampoules were opened in an argon glovebox and the red to red yellow solid was ground with a pestle (quantitative yield). The melting range of a solid is 157-163 degreeC.

b) the reaction of alkali metals with sulfur in liquid ammonia

Na _0.46 K _1.54 S _3.75 Synthesis of

Synthesis was performed under argon atmosphere using Schlenk and glovebox technology. First, 63.6 g (1.98 mol) of sulfur were added to liquid ammonia at −30 ° C. in a glass flask. Thereafter, a blue mixture of 5.50 g (0.24 mol) of sodium metal and 32.0 g (0.81 mol) of potassium metal in about 800 ml of liquid ammonia (-30 ° C) was added dropwise while stirring. The resulting mixture was warmed to room temperature and stirred until ammonia evaporated. Thereafter, the ammonia residue was removed from the orange solid formed under reduced pressure at 150 ° C. (about 1 mbar). The melting range of a solid is 166-169 degreeC.

Na _0.23 K _1.77 S _3.75 Synthesis of

Synthesis was performed under argon atmosphere using Schlenk and glovebox technology. First, 43.0 g (1.34 mol) of sulfur were added to liquid ammonia at −30 ° C. in a glass flask. Thereafter, a blue mixture 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 while stirring. The resulting mixture was warmed to room temperature and stirred until ammonia evaporated. Thereafter, the ammonia residue was removed from the orange solid formed under reduced pressure at 150 ° C. (about 1 mbar). The melting range of a solid is 165-166 degreeC.

2. (K _x Na _1-x ) ₂ S _y Synthesis and Characterization of Mixtures of Alkali Metal Thiocyanates with

a) synthetic

Method 1:

In a closed vacuum quartz ampoule, the 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) were brought to 400 ° C. After heating for 30 minutes, the melt was cooled to room temperature. The ampoules were opened in an argon glovebox and the fusion product was ground with a pestle. This gave an orange solid, the melting range of which is shown in Table 1.

Method 2:

In a glass flask under argon atmosphere, a corresponding amount of potassium polysulfide (K ₂ S _x ) or potassium sodium polysulfide ((K _x Na _1-x ) ₂ S _y ) and potassium thiocyanate (KSCN) was mixed and 180 Heated to ° C. The mixture was stirred until a homogeneous melt was formed and then cooled to room temperature. This gave an orange solid, the melting range of which was the same as that of the solid prepared according to Method 1 (see Table 1).

b) viscosity

The viscosity of the melt was measured using a rotary viscometer.

c) thermal stability

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 ) Thermal stability was investigated using _0.5 (melting range 146-153 ° C.).

Stability at 400 ° C:

3 g of a mixture having a composition of (K ₂ S ₄ ) _0.5 (KSCN) _0.5 were stored at 400 ° C. for 28 days in a vacuum quartz glass ampoule. The melting range of this mixture did not change.

3 g of a mixture having a composition of (K ₂ S ₅ ) _0.5 (KSCN) _0.5 were stored at 400 ° C. for 28 days in a vacuum quartz glass ampoule. The melting range of this mixture did not change.

3 g of a mixture having a composition of (K ₂ S ₆ ) _0.5 (KSCN) _0.5 were stored at 400 ° C. for 28 days in a vacuum quartz glass ampoule. The melting range of this mixture did not change.

Stability at 450 ° C:

3 g of a mixture having a composition of (K ₂ S ₄ ) _0.5 (KSCN) _0.5 were stored at 450 ° C. for 28 days in a vacuum quartz glass ampoule. The melting range of this mixture did not change.

3 g of a mixture having a composition of (K ₂ S ₅ ) _0.5 (KSCN) _0.5 were stored at 450 ° C. for 28 days in a vacuum quartz glass ampoule. The melting range of this mixture did not change.

3 g of a mixture having a composition of (K ₂ S ₆ ) _0.5 (KSCN) _0.5 were stored at 450 ° C. for 28 days in a vacuum quartz glass ampoule. The melting range of this mixture did not change.

Stability at 500 ° C:

3 g of a mixture having a composition of (K ₂ S ₄ ) _0.5 (KSCN) _0.5 were stored at 500 ° C. for 28 days in a vacuum quartz glass ampoule. The melting range of this mixture did not change.

3 g of a mixture having a composition of (K ₂ S ₅ ) _0.5 (KSCN) _0.5 were stored at 500 ° C. for 28 days in a vacuum quartz glass ampoule. The melting range of this mixture did not change.

3 g of a mixture having a composition of (K ₂ S ₆ ) _0.5 (KSCN) _0.5 were stored at 500 ° C. for 28 days in a vacuum quartz glass ampoule. The melting range of this mixture did not change.

Stability at 600 ° C:

3 g of a mixture having a composition of (K ₂ S ₄ ) _0.5 (KSCN) _0.5 were stored at 600 ° C. for 28 days in a vacuum quartz glass ampoule. The melting range of this mixture did not change.

3 g of a mixture having a composition of (K ₂ S ₅ ) _0.5 (KSCN) _0.5 were stored at 600 ° C. for 28 days in a vacuum quartz glass ampoule. The melting range of this mixture did not change.

3 g of a mixture having a composition of (K ₂ S ₆ ) _0.5 (KSCN) _0.5 were stored at 600 ° C. for 28 days in a vacuum quartz glass ampoule. The melting range of this mixture did not change.

Claims (24)

Mixtures of alkali metal polysulfides of the general formula:
(M ¹ _x M ² _(1-x) ) ₂ S _y
Wherein M ¹ , M ² are Li, Na, K, Rb, Cs, M ¹ is not equal to M ² , 0.05 ≦ x ≦ 0.95, and 2.0 ≦ y ≦ 6.0. The mixture of claim 1 wherein M ¹ is K and M ² is Na. The mixture according to claim 1 or 2, wherein 0.20 ≦ x ≦ 0.95. The mixture according to any one of claims 1 to 3, wherein 3.0 ≦ y ≦ 6.0. The mixture according to any one of claims 1 to 4, wherein M ¹ is K, M ² is Na, 0.20 ≦ x ≦ 0.95, and 3.0 ≦ y ≦ 6.0. 6. The mixture of claim ¹ wherein M ¹ is K, M ² is Na, 0.50 ≦ x ≦ 0.90 and y is 4.0, 5.0 or 6.0. A process for the preparation of the mixture according to any one of claims 1 to 6, wherein the corresponding alkali metal sulfide is heated with sulfur or the corresponding alkali metal polysulfide with or without sulfur under a protective gas or under reduced pressure. The manufacturing method which includes doing it. A process for preparing a mixture according to any one of claims 1 to 6, comprising reacting a solution of the corresponding alkali metal in liquid ammonia with sulfur under a protective gas. Use of the mixture according to any one of claims 1 to 6 as heat transfer or heat storage fluid. A heat transfer or heat storage fluid comprising the mixture according to any one of claims 1 to 6. Mixtures of alkali metal polysulfides and alkali metal thiocyanates of 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 are Li, Na, K, Rb, Cs, M ¹ is not equal to M ² , M ³ is not equal to M ^4, and 0.05 ≦ x ≦ 1, 0.05 ≦ z ≦ 1, 2.0 ≦ y ≦ 6.0, and m is the molar ratio, where 0.05 ≦ m ≦ 0.95. The mixture of claim 11 wherein M ¹ and M ³ are K and M ² and M ⁴ are Na. The mixture according to claim 11 or 12, wherein 0.20 ≦ x ≦ 1. The mixture according to claim 11, wherein 3.0 ≦ y ≦ 6.0. The mixture according to claim 11, wherein 0.20 ≦ z ≦ 1. The mixture according to claim 11, wherein 0.20 ≦ m ≦ 0.80. The method 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, 0.20 ≦ z ≦ 0.95, 3.0 ≦ y ≦ 6.0 and 0.20 ≦ m ≦ 0.95. The compound of any one of claims 11-16 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. 19. A process for the preparation of the mixture according to any one of claims 11 to 18, which comprises eutectic the corresponding alkali metal polysulfide and alkali metal thiocyanate. Use of the mixture according to any one of claims 11 to 18 as a heat transfer or heat storage fluid. A heat transfer or heat storage fluid comprising the mixture according to any one of claims 11 to 18. A mixture of alkali metal polysulfides having a composition of (K _(1-x) Na _x ) ₂ S _z , where x is 0-1 and z is 2.3-3.5. Use of the mixture according to claim 22 as a heat transfer or heat storage fluid. A heat transfer or heat storage fluid comprising the mixture according to claim 22.