EP2521692A1

EP2521692A1 - Mixtures of alkali polysulfides

Info

Publication number: EP2521692A1
Application number: EP10795730A
Authority: EP
Inventors: Fabian Seeler; Felix Major; Kerstin Schierle-Arndt; Jürgen WORTMANN; Martin GÄRTNER; Michael Lutz; Stephan Maurer; Otto Machhammer; Günther Huber; Hans-Josef Sterzel
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2010-01-05
Filing date: 2010-12-23
Publication date: 2012-11-14
Also published as: CN102712474A; IL220543A0; MA33949B1; MX2012007392A; TN2012000337A1; BR112012016656A2; WO2011083054A1; CA2785174A1; CL2012001795A1; AU2010340924A1; JP2013516531A; KR20120104423A

Abstract

The present invention relates to mixtures of alkali polysulfides and mixtures of alkali polysulfides and alkali thiocyanates, to a method for the production of same, to the use thereof as heat transfer media or heat storage media, and to heat transfer media or heat storage media comprising the mixtures of alkali polysulfides or the mixtures of alkali polysulfides and alkali thiocyanates.

Description

The present invention relates to mixtures of alkali metal polysulfides and mixtures of alkali metal polysulfides and alkali thiocyanates, processes for their preparation, their use as heat transfer or heat storage liquids and Wärmeträgero- or heat storage liquids containing the mixtures of Alkalipolysulfiden or the mixtures of Alkalipolysulfiden and Alkalithiocyanaten include.

Liquids for transferring heat energy are used in a variety of fields of technology. In internal combustion engines, mixtures of water and ethylene glycol carry the waste heat of combustion into the radiator. Similar mixtures transport the heat from solar roof collectors into heat storage. In the chemical industry, they move the heat from electric or fossil heated heating systems to or from chemical reactors to cooling devices.

Depending on the application, the requirement profile for heat transfer or heat storage liquids varies greatly, which is why in practice a variety of liquids is used. The liquids should be liquid at room temperature or even lower temperatures and have low viscosities. For higher operating temperatures, water is out of the question, its vapor pressure would be too high. Therefore, up to about 320 ° C hydrocarbon-based mineral oils and for temperatures up to 400 ° C synthetic aromatic-containing oils or silicone oils (VDI heat Atlas, VDI Society Process Engineering and Chemical Engineering, Springer Verlag Berlin Heidelberg 2006).

A new challenge for heat transfer fluids is thermal solar power plants, which generate large scale electrical energy (Butscher, R., Bild der Wissenschaft 2009, 3, pages 84 to 92). So far, such power plants were built with an installed capacity of a few hundred MW and many more are in Spain, but also in North Africa and the US in planning. The solar radiation is focused, for example via parabolic shaped mirror grooves in the focal line of the mirror. There is a metal tube, which is located in a glass tube to avoid heat losses, the space between the concentric tubes is evacuated. The metal tube is flowed through by a heat transfer fluid. At present, a mixture of diphenyl ether and diphenyl is used here. It heats the heat carrier to a maximum of 400 ° C and thus operates a steam generator in which water is evaporated. This steam drives a turbine, which in turn generates the generator just like in a conventional power plant. This results in peak efficiencies of around 30 percent relative to the energy content the sunlight. The efficiency of the steam turbine at this inlet temperature is approximately 37 percent.

Both components of the mixture of diphenyl ether and diphenyl used as a heat carrier boil under normal pressure at about 256 ° C. The melting point of the

Diphenyl is at 68-72 ° C, the diphenyl ether at 26-39 ° C. By mixing both substances, the melting point is lowered to 12 ° C. The mixture of both substances can be used up to a maximum of 400 ° C, at higher temperatures decomposition occurs. The vapor pressure at this temperature is about 10 bar, a pressure that is still tolerable in the art.

In order to obtain higher turbine efficiencies than 37 percent, higher steam inlet temperatures are necessary. The efficiency of a steam turbine increases with the turbine inlet temperature. Modern fossil-fueled power plants operate with steam inlet temperatures of up to 650 ° C and thus achieve efficiencies of 45%. It would be quite technically possible to heat the heat transfer fluid in the focal line of the mirror to temperatures around 650 ° C and thus also to achieve such high efficiencies; but this prohibits the limited temperature resistance of currently used heat transfer fluid.

Higher temperatures than in parabolic trough power plants can be achieved in solar thermal tower power plants, where a tower is surrounded by mirrors, which focus the sunlight on a receiver in the upper part of the tower. In this receiver, a heat carrier is heated, which is then used via a heat exchanger for steam generation and operation of a turbine. In tower power plants (Solar II, California), a mixture of sodium nitrate (NaNO-3) and potassium nitrate (KNO3) (60:40) has been used as a heat transfer medium. This mixture can easily be used up to 550 ° C, but has a very high melting point of 240 ° C. Organic substances that permanently withstand temperatures above 400 ° C without decomposition are still unknown. Some dimethylsilicone- or diphenylsilicone-based oils can also be used up to temperatures of 400 ° C or even at slightly higher temperatures. However, their very high price speaks against their use in thermal solar power plants.

Another possibility is the use of liquid sodium or sodium-potassium alloy as heat carrier, which is known from nuclear technology. However, the production of these metals is very expensive and they govern with traces of water to hydrogen gas, which is a safety challenge. Furthermore, low-melting solders such as Wood's metal (Bi-Pb-Cd-Sn alloy, melting point about 75 ° C) are known. The very high specific gravity, however, argues against use as a heat transfer fluid. Further possible high-temperature heat carriers have been proposed on the basis of sulfur, which is used, for example, mixed with smaller amounts of selenium and / or tellurium (WO 2005/071037). Liquid sulfur is problematic as a heat carrier, since it is highly viscous in the range 150 to 200 ° C and thus not pumpable. Although the viscosity can be reduced by additives such as bromine or iodine

(US 4,335,578), but these are highly corrosive.

Technically, the use of water under a correspondingly high pressure is possible. However, this is counteracted by the extremely high vapor pressure of over 270 bar at temperatures of over 500 ° C, which would make the many kilometers of pipelines of a thermal solar power station uneconomically more expensive. The steam itself is disadvantageous as a heat transfer medium because of its comparatively low thermal conductivity and the low heat capacity per volume compared to a liquid.

Another possibility is the use of inorganic salt melts as a heat transfer fluid. Such molten salts are state of the art in processes that operate at high temperatures. The eutectic mixture of potassium nitrate, sodium nitrate and sodium nitrite has a melting point of 146 ° C and is commercially available. However, the upper application temperature is limited to 450 ° C, since above this temperature considerable decomposition of the nitrite to nitrous gases, alkali metal oxides and elemental nitrogen takes place. The eutectic mixture of sodium nitrate and potassium nitrate can be used up to temperatures of 600 ° C. However, the use of this mixture as a heat transfer fluid in solar power plants is problematic due to the high melting point of about 220 ° C. A decrease in the temperature below the melting point, z. For example, at night or during periods of low solar radiation, would result in a solidification of the salt in the pipes. This must be prevented, as re-melting would cause local stresses which would damage the plant. A Einfrierschutz in the form of a trace heating would be conceivable, but is technically very difficult to implement for such high temperatures and also expensive. Of the

Melting point of the mixture of sodium nitrate and potassium nitrate can be lowered by adding lithium nitrate or calcium nitrate (Bradshaw, RW, Meeker, DE, Solar Energy Materials 1990, Vol. 21, pages 51 to 60). However, mixtures with lithium nitrate are uneconomical because of the high price, while the presence of calcium promotes the decomposition of the nitrate to nitrite and oxygen and thus the upper application temperature is lowered with increasing calcium content. Furthermore, the use of metal halides as heat transfer fluid would be possible. This results in the problem that halogen-containing liquids, especially at elevated temperatures, often cause corrosion problems in the metallic materials to be used.

Mixtures of alkali metal polysulfides, especially sodium and potassium polysulfides, should theoretically have low melting points and could be used at temperatures up to and above 500 ° C. The phase diagram for the ternary system sodium sulfide-potassium sulfide-sulfur is calculated to use invariant points with low melting temperatures for the compositions K0.84Na0.26S3.6i (78 ° C),

K0.77Na0.23S3.75 (73 ° C) and K0.79Na0.21S3.95 (83 ° C). (Lindberg, D., Backman, R., Hupa, M., Chartrand, P., J. Chem. Therm. 2006, Vol. 38, pages 900-915). Experimental data for this ternary system are not available In the potassium sulfide-sulfur system, the melting point can be lowered to about 120 ° C

(Sangster, J., Pelton, A.D., J. Phase Equil., 1997, vol. 18, page 82). A disadvantage of the alkali metal polysulfides is their relatively high viscosity in the molten state, especially that of sodium polysulfides (Cleaver, B., Davis, A.J., Electrochimica Acta 1973, Vol. 18, pages 727 to 731). DE 3824517 describes the use of mixtures of alkali thiocyanates as heat transfer fluids, in particular of potassium thiocyanate and sodium thiocyanate. Potassium thiocyanate melts at 173 ° C, sodium thiocyanate at 310 ° C. The eutectic mixture of the two salts with a ratio of 73 mol% of potassium thiocyanate to 27 mol% of sodium thiocyanate has a melting point of about 130 ° C. The melt is low viscosity and thus pumpable without increased energy consumption.

A disadvantage of the alkali thiocyanates is that they begin to decompose at temperatures above 450 ° C already. Excluding sulfur, the higher-melting alkali cyanides are formed (Gmelin's Handbook of Anorganic Chemistry 1938, Vol. 22, page 899).

The melting point of the alkali thiocyanates can be lowered further by admixing further salts. In particular, the admixture of nitrites or nitrates lowers the melting point. However, the addition of the oxidizing nitrites or nitrates causes an explosive decomposition at elevated temperatures, which can be additionally accelerated by possibly dissolved heavy metal traces. Thus, the use of such mixtures for technical use is excluded.

Another problem arises from the fact that the aim is to operate a solar thermal power plant continuously. This can be achieved by storing heat during periods of high solar radiation that can be used for power production after sunset or during periods of bad weather. storage Heat can be generated directly by storing the heated heat transfer medium in well-insulated storage tanks, or indirectly by transferring the heat to another storage medium. The indirect method is implemented in the 50 MW Andasol I power plant in Almeria, where approximately 28,000 t of a melt of sodium nitrate and potassium nitrate (60:40) are used. The melt is pumped from a colder tank (about 280 ° C) through an oil-salt heat exchanger into a hotter tank during the solar irradiation times while being heated to about 380 ° C. During periods of low solar radiation and at night, the power plant can be run at full load for approximately 7.5 hours under full load

(www.solarmillennium.de/upload/Download/Technologie/Andasol1 -3deutsch.pdf). However, it would be advantageous to use the heat transfer fluid as a storage fluid, since so the corresponding oil-salt heat exchanger could be saved. This is not considered because of the high vapor pressure of the oil and the higher price compared to the nitrate salts.

The object of the invention is to provide a readily available, improved heat transfer and heat storage liquid. The liquid should be able to be used at temperatures higher than 400 ° C, preferably above 500 ° C. At the same time, the melting point should be as low as possible, preferably below 200 ° C. The liquid should also have a technically controllable, the lowest possible vapor pressure, preferably lower than 10 bar. The object is achieved by mixtures of alkali metal polysulfides.

An object of the invention are thus mixtures of alkali metal polysulfides according to the general formula where M ¹ , M ² = Li, Na, K, Rb, Cs and M ^{1 is} not equal to M ² and 0.05 <x <0.95 and 2.0 <y <6.0. In a preferred embodiment of the invention, M ¹ = K and M ² = 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 another preferred embodiment of the invention, 3.0 <y <6.0. In a particularly preferred embodiment of the invention y = 4.0, 5.0 or 6.0. In a particularly preferred embodiment of the invention, M ¹ = K, M ² = Na, 0.20 <x <0.95 and 3.0 <y <6.0.

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

Another embodiment relates to alkali metal polysulfides of the composition

(K ₍ i_ _x) Na _x ) ₂ S _z , where x = 0 to 1 and z = 2.3 to 3.5, preferably x = 0.5 to 0.7 and z = 2.4 to 2.9 ,

Another embodiment relates to alkali metal polysulfides (Na ₀₅ to o, 65K ₀ , ₅ to 0.35) 282.4 u * 2,%. or those having the composition (Na ₀ , 6K ₀ , ₄ ) 2S ₂ , e.

The mixtures according to the invention are characterized by particularly low

Melting points off. In a preferred embodiment of the invention is the

Melting point of the mixture according to the invention below 200 ° C, in a particularly preferred embodiment below 160 ° C.

The mixtures according to the invention have a high thermal stability. In a preferred embodiment of the invention, the mixtures according to the invention are stable up to a temperature of 450 ° C., in a particularly preferred embodiment up to a temperature of 500 ° C., in a very particularly preferred embodiment also at temperatures above 500 ° C. In a preferred embodiment of the invention, the mixtures according to the invention have a vapor pressure of less than 5 bar, more preferably less than 2 bar, at 500 ° C.

The preparation of alkali metal polysulfides is known and can be carried out, for example, by reacting alkali metal sulfides with sulfur. An alternative is the direct reaction of alkali metals with sulfur, as described in US 4,640,832 for sodium. The reaction of alkali metals in liquid ammonia with sulfur is also described. Another possibility for synthesis is the reaction of alkali hydrogen sulfides or alkali metal sulfides with sulfur in alcoholic solution.

Another object of the invention is a process for preparing the mixtures of alkali metal polysulfides according to the invention, characterized in that corresponding alkali metal sulfides are heated with sulfur or corresponding alkali metal polysulfides with or without sulfur under inert gas or in vacuo.

In a preferred embodiment of the process according to the invention, the starting materials are heated to at least 400 ° C. for at least 0.5 hours. Suitable inert gases are noble gases, preferably argon, or nitrogen.

Another object of the invention is a process for preparing the mixtures according to the invention of alkali metal polysulfides, characterized in that a solution of corresponding alkali metals in liquid ammonia is reacted with sulfur under inert gas.

Another object of the invention is the use of the mixtures according to the invention of alkali metal polysulfides as heat transfer or heat storage liquids.

In a preferred embodiment of the invention, the use of the mixtures according to the invention of alkali metal polysulfides with the exclusion of air and moisture, preferably in a closed system of, for example, pipelines, pumps, control elements and containers to hydrolytic reactions during operation or the oxidation of the heat transfer or To avoid heat storage fluid.

Another object of the invention are heat transfer or heat storage liquids, which comprise the inventive mixtures of alkali metal polysulfides sen.

The field of application of the mixtures of alkali metal polysulfides according to the invention can be further expanded if they are mixed with alkali thiocyanates. Another object of the invention are mixtures of alkali metal polysulfides and alkali metal thiocyanates according to the general formula

((M _x M ² _{(i_} _X)) ₂ S _y) _m (M ³ ZMV _Z) SCN) _{(i_} _m) where M ^1, M ^2, M ^3, M ⁴ = Li, Na, K, Rb, Cs and 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 mole fraction with 0.05 <m <0.95.

In a preferred embodiment of the invention, M ¹ and M ³ = K and M ² and M ⁴ = 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 another preferred embodiment of the invention, 3.0 <y <6.0. In a particularly preferred embodiment of the invention y = 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 = K, M ² and M ⁴ = Na, 0.20 <x <1, 0.20 <z <0.95, 3.0 <y <6.0 and 0.20 <m <0.95.

In a very particularly preferred embodiment of the invention, M ¹ and M ³ = K, M ² and M ⁴ = Na, 0.50 <x <1, 0.50 <z <0.95, y = 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 = K, x = 1, z = 1, y = 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 = K, x = 1, z = 1, y = 4 and m = 0.5.

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

In a further particularly preferred embodiment of the invention, M ¹ and M ³ = K, x = 1, z = 1, y = 6 and m = 0.5. It has surprisingly been found that the mixtures according to the invention of alkali metal polysulfides and alkali metal thiocyanates are more thermally stable than the alkali metal thiocyanates alone. In addition, the viscosity of the mixtures according to the invention of alkali metal polysulfides and alkali metal thiocyanates is lower than that of the alkali metal polysulfide mixtures without alkyl lithiocanates.

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

Another object of the invention is a process for the preparation of the inventive mixtures of alkali metal polysulfides and alkali thiocyanates by co-melting of alkali metal polysulfides and alkali thiocyanates. The process can also be carried out while stirring the melt.

The mixtures of alkali polysulfides and alkali thiocyanates according to the invention are generally suitable for high-temperature applications which require a heat transfer medium with a wide liquid temperature range. Another object of the invention is the use of the mixtures according to the invention of alkali metal polysulfides and alkali thiocyanates as heat transfer or heat storage liquids. In a preferred embodiment of the invention, the use of the mixtures according to the invention of alkali metal polysulfides and alkali thiocyanates with the exclusion of air and moisture, preferably in a closed system of, for example, pipelines, pumps, control devices and containers, to hydrolytic reactions or the oxidation of the heat transfer or Heat storage fluid to avoid.

Another object of the invention are heat transfer or heat storage liquids comprising the novel mixtures of alkali metal polysulfides and alkali metal thiocyanates.

Examples:

1 . Synthesis of potassium sodium polysulfides (K _x Nai- _x ) 2S _y a) By melting mixtures of alkali polysulfides and sulfur

The starting materials K2S3 and Na2S ₄ were prepared by literature methods. Synthesis of Nao.464K1.536S3.745

3.51 g of K2S3, 0.43 g of sulfur and 1.06 g of Na2S4 were heated in a closed, evacuated quartz glass ampoule for 30 minutes at 400 ° C and then the melt cooled to room temperature. The ampoule was opened in an argon glovebox and the red to reddish yellow solid was pulverized by mortars (yield quantitative). The solid melts in the range of 151-157 ° C.

Synthesis of Nao.42K1.5eS3.80

3.65 g of K2S3, 0.49 g of sulfur and 0.95 g of Na2S4 were heated in a closed, evacuated quartz glass ampoule for 30 minutes at 400 ° C and the melt was then cooled to room temperature. The ampoule was opened in an argon glovebox and the red to reddish yellow solid was pulverized by mortars (yield quantitative). The solid melts in the range of 158-167 ° C.

Synthesis of Nao.325K1.675S3.6i 3.87 g K2S3, 0.38g sulfur, and 0.75 g Na 2 S ₄ were heated in a closed, evacuated quartz vial for 30 minutes at 400 ° C and then the melt is cooled to room temperature. The ampoule was opened in an argon glovebox and the red to reddish yellow solid was pulverized by mortars (yield quantitative). The solid melts in the range of 157-163 ° C.

b) By reaction of alkali metals with sulfur in liquid ammonia Synthesis of Nao. ₄ 6Ki. ₅₄ S3.75

The synthesis was carried out under argon atmosphere using Schlenk and glove box techniques. 63.6 g (1.98 mol) of sulfur were initially charged in liquid ammonia at -30 ° C in a glass flask. Subsequently, a blue solution of 5.50 g (0.24 mol) of sodium and 32.0 g (0.81 mol) of potassium metal in about 800 ml of liquid ammonia (-30 ° C) were added dropwise with stirring. The resulting mixture was warmed to room temperature and stirred until the ammonia had evaporated. The resulting orange solid was then freed at 150 ° C and vacuum (about 1 mbar) of ammonia residues. The solid melts in the range of 166-169 ° C.

Synthesis of Nao.23K1.77S3.75

The synthesis was carried out under argon atmosphere using Schlenk and glove box techniques. 43.0 g (1 .34 mol) of sulfur were placed in liquid ammonia at -30 ° C in a glass flask. Subsequently, a blue solution of 1.82 g (0.079 mol) of sodium and 24.9 g (0.63 mol) of potassium metal in about 800 ml of liquid ammonia (-30 ° C) were added dropwise with stirring. The resulting mixture was warmed to room temperature and stirred until the ammonia had evaporated. The resulting orange solid was then freed at 150 ° C and vacuum (about 1 mbar) of ammonia residues. The solid melts in the range of 165-166 ° C.

2. Synthesis and Properties of Mixtures of (K _x Nai- _x ) 2S _y with Alkali Diisocyanates a) Synthesis

Method 1: Corresponding amounts of potassium polysulfide (K ₂ S _X ) or potassium sodium polysulfide ((K _x Nai-x) 2Sy) and potassium thiocyanate (KSCN) were heated in a closed, evacuated quartz glass ampoule for 30 minutes at 400 ° C and then the melt to room temperature cooled. The vial was opened in an argon glovebox and the enamel was pulverized by mortars. Orange solids were obtained, the melting ranges of which are shown in Tab.

Method 2:

Corresponding amounts of potassium polysulfide (K2S _X) or potassium sodium polysulfide ((K _x Nai-x) 2SY) and potassium thiocyanate (KSCN) were mixed and heated in a glass flask under an argon atmosphere at 180 ° C. It was stirred until a homogeneous melt had formed and then cooled to room temperature. Orange solids were obtained, the melting ranges of which were identical to those of the method prepared according to Method 1 (see Table 1).

Tab. 1

Composition melting range

[° C]

(K ₂ S ₄ ) 0.67 (KSCN) 0.33 123-125

(K ₂ S ₄ ) o.5o (KSCN) o.5o 1 10-1 12

(K ₂ S ₄ ) o.33 (KSCN) o.67 128-130

(K ₂ S ₅ ) o.5o (KSCN) o.5o 150-158

(K ₂ S ₆ ) o.5o (KSCN) o.50 146-153

(Nao ₄ 6Kl ₅₄ S3.75) o.5o (KSCN) o.50 92-100

(Nao. ₄ 6Kl. ₅₄ S3.75) o. ₄ 5 (KSCN) o.55 94-1 10

(Nao.23 Cl.77S ₃ .75) o.67 (KSCN) ₀ .33 100-108

(Na 0.23 part 77 S ₃ .75) 0.53 (KSCN) 047 98-102

(Na0.23Kl .77S ₃ .75) 0.50 (KSCN) ₀ .50 82-96

(Nao. ₂ 3Kl.77S ₃ .75) o. ₄ 8 (KSCN) o.5 ₂ 80-90

(Na ₂ 3Kl.77S ₃ .75) 0.33 (KSCN) ₀ .67 80-96 b) viscosity

The viscosity of the melts was determined by rotational viscometry. Table 2

c) temperature stability

The temperature stability study was based on the blends

(K ₂ S ₄ ) o.5 (KSCN) o.5 (melting range 1 10-1 12 ° C), (K ₂ S ₅ ) o.5 (KSCN) o.5 (melting range 150-158 ° C) and (K ₂ S6) o. ₅ (KSCN) o.5 (melting range 146-153 ° C).

Stability at 400 ° C: 3 g of a mixture of the composition (K2S4) or (KSCN) o.5 were stored in an evacuated quartz glass ampoule at 400 ° C for 28 days. The melting range of the mixture was unchanged.

3 g of a mixture of the composition (K2S5) os (KSCN) o.5 were stored in an evacuated quartz glass ampoule at 400 ° C. for 28 days. The melting range of the mixture was unchanged. 3 g of a mixture of the composition (K2S6) o.5 (KSCN) o. ₅ were stored in an evacuated quartz glass ampule at 400 ° C for 28 days. The melting range of the mixture was unchanged.

Stability at 450 ° C:

3 g of a mixture of the composition (K2S4) o.5 (KSCN) o. ₅ were stored in an evacuated quartz glass ampule for 28 days at 450 ° C. The melting range of the mixture was unchanged.

3 g of a mixture of the composition (K2S5) o.5 (KSCN) o. ₅ were stored in an evacuated quartz glass ampule for 28 days at 450 ° C. The melting range of the mixture was unchanged.

3 g of a mixture of the composition (K2S6) o.5 (KSCN) o. ₅ were stored in an evacuated quartz glass ampule for 28 days at 450 ° C. The melting range of the mixture was unchanged. Stability at 500 ° C:

3 g of a mixture of the composition (K2S4) o.5 (KSCN) o. ₅ were stored in an evacuated quartz glass ampule for 28 days at 500 ° C. The melting range of the mixture was unchanged.

3 g of a mixture of the composition (K2S5) o.5 (KSCN) o. ₅ were stored in an evacuated quartz glass ampule for 28 days at 500 ° C. The melting range of the mixture was unchanged. 3 g of a mixture of the composition (K2S6) o.5 (KSCN) o. ₅ were stored in an evacuated quartz glass ampule for 28 days at 500 ° C. The melting range of the mixture was unchanged.

Stability at 600 ° C:

3 g of a mixture of the composition (K2S4) o.5 (KSCN) o. ₅ were stored in an evacuated quartz glass ampule at 600 ° C for 28 days. The melting range of the mixture was unchanged. 3 g of a mixture of the composition (K2S5) o.5 (KSCN) o. ₅ were stored in an evacuated quartz glass ampule at 600 ° C for 28 days. The melting range of the mixture was unchanged. 3 g of a mixture of the composition (K2S6) o.5 (KSCN) o. ₅ were stored in an evacuated quartz glass ampule at 600 ° C for 28 days. The melting range of the mixture was unchanged.

Claims

claims

1 . Mixtures of alkali metal polysulfides according to the general formula where M ¹ , M ² = Li, Na, K, Rb, Cs and M ^{1 is} not equal to M ² and 0.05 <x <0.95 and 2.0 <y <6.0.

2. Mixtures according to claim 1, wherein M ¹ = K and M ² = Na.

3. Mixtures according to one of claims 1 or 2, wherein 0.20 <x <0.95.

4. Mixtures according to one of claims 1 to 3, wherein 3.0 <y <6.0.

5. Mixtures according to one of claims 1 to 4, wherein M ¹ = K, M ² = Na, 0.20 <x <0.95 and 3.0 <y <6.0.

6. Mixtures according to one of claims 1 to 5, wherein M ¹ = K, M ² = Na, 0.50 <x <0.90 and y = 4.0, 5.0 or 6.0.

7. A process for the preparation of the mixtures according to any one of claims 1 to 6, characterized in that corresponding alkali metal sulfides are heated with sulfur or corresponding alkali metal polysulfides with or without sulfur under inert gas or in vacuum.

8. A process for the preparation of the mixtures according to any one of claims 1 to 6, characterized in that a solution of corresponding alkali metals in liquid ammonia is reacted with sulfur under protective gas.

9. Use of the mixtures according to one of claims 1 to 6 as heat transfer or heat storage liquids.

10. heat transfer or heat storage fluid, which comprises a mixture according to any one of claims 1 to 6.

1 1. Mixtures of alkali metal polysulfides, and alkali metal thiocyanates of the general formula ((M ¹ _x M ² _{(i_} _X)) ₂ S _y) _m (M ³ _z MV _Z) SCN) (i_ _m) where M ¹ , M ² , M ³ , M ⁴ = Li, Na, K, Rb, Cs and 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 mole fraction with 0.05 <m <0.95.

12. Mixtures according to claim 1 1, wherein M ¹ and M ³ = K and M ² and M ⁴ = Na.

13. A mixture according to any one of claims 1 1 or 12, wherein 0.20 <x <1.

14. Mixtures according to one of claims 1 1 to 13, wherein 3.0 <y <6.0.

15. Mixtures according to one of claims 1 1 to 14, wherein 0.20 <z <1.

16. Mixtures according to one of claims 1 1 to 15, wherein 0.20 <m <0.80.

17. Mixtures according to one of claims 1 1 to 15, wherein M ¹ and M ³ = K, M ² and M ⁴ = Na, 0.20 <x <1, 0.20 <z <0.95, 3.0 <y <6.0 and 0.20 <m <0.95.

18. Mixtures according to one of claims 1 1 to 16, wherein M ¹ and M ³ = K, M ² and

M ⁴ = Na, 0.50 <x <1, 0.50 <z <0.95, y = 4.0, 5.0 or 6.0 and 0.33 <m <0.80.

19. A process for the preparation of mixtures according to any one of claims 1 1 to 18, characterized in that corresponding alkali metal polysulfides and alkali metal thiocyanates are melted together.

20. Use of the mixtures according to any one of claims 1 1 to 18 as heat transfer or heat storage liquids.

21. Heat transfer or heat storage fluid, which comprises a mixture according to one of claims 1 1 to 18.

22. Mixtures of alkali polysulfides of the composition (K ₍ i_ _x) Na _x ) ₂ S _z

with x = 0 to 1 and z = 2.3 to 3.5.

23. Use of the mixtures according to claim 22 as heat transfer or heat storage liquids.

24. Heat transfer or heat storage fluid, which comprises a mixture according to claim 22.