Composition of hydrophobic ionic liquids for heat storage and thermal management applications

Abstract

Composition for heat storage, comprising at least one hydrophobic ionic liquid containing an organic cation and a tetrafluoroborate anion, wherein the cation is selected from the group of heterocyclic, nitrogen-containing cations with alkyl substituents, whose chain lengths lie between two and eight carbon atoms, and wherein the composition has a specific heat capacity of more than 0.9 joules per gram and kelvin within a temperature range of seventy-five to six hundred kelvin.

Description

AREA OF INVENTION

[0001] The present invention relates to a composition of hydrophobic ionic liquids designed for use as a heat storage and heat transfer medium. The invention belongs to the fields of physical chemistry and materials science, in particular to the development of ionic liquids with defined specific heat capacities and thermal stability properties suitable for industrial energy management systems. BACKGROUND OF THE INVENTION

[0002] Conventional heat transfer and heat storage materials such as mineral oils and synthetic organic compounds have limited thermal stability and can degrade at moderate temperatures, thus limiting their operational lifespan.

[0003] Ionic liquids – salts that consist entirely of ions – represent a superior alternative due to their negligible vapor pressure, high thermal and chemical stability, non-flammability, and adaptable molecular structure.

[0004] Hydrophobic ionic liquids containing long-chain organic cations and weakly coordinating anions remain stable even at elevated temperatures and are able to store and release large amounts of heat energy.

[0005] However, existing formulations of ionic liquids do not have reproducible data on specific heat capacity and often show inconsistent performance during repeated heating and cooling cycles.

[0006] The present invention provides a composition with controlled molecular structure, defined hydrophobicity and verified thermal behavior, which can be used as a reliable heat storage medium. SUMMARY OF THE INVENTION

[0007] The present invention relates to a composition of hydrophobic ionic liquids containing an organic cation selected from heterocyclic nitrogenous compounds, and an anion selected from tetrafluoroborate or an equivalent weakly coordinating anion.

[0008] The composition has the following properties: • specific heat capacity values ​​of more than 0.9 joules per gram and Kelvin over a temperature range of seventy-five to six hundred Kelvin; • negligible vapor pressure under standard atmospheric conditions; • Thermal stability above 500 Kelvin without measurable decomposition; and • Reversible heat absorption and heat release properties that enable long-term operation in closed heat storage cycles.

[0009] The molecular design ensures balanced electrostatic and dispersive interactions, resulting in superior energy uptake and minimal degradation during thermal cycles. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention relates to a composition of hydrophobic ionic liquids containing an organic cation and a weakly coordinating anion selected from the groups of tetrafluoroborate, hexafluorophosphate or bissulfonylimide compounds.

[0011] The composition exhibits high thermal stability, negligible vapor pressure, and reproducible specific heat capacity values ​​of more than 0.9 joules per gram and Kelvin over an extended temperature range. It serves as an efficient and durable heat transfer and energy storage medium for industrial and renewable energy applications.

[0012] The composition consists of the following components: Organic cation component: A heterocyclic, nitrogen-containing ring system, substituted with one or more linear or branched alkyl groups with two to eight carbon atoms. Anionic component: A weakly coordinating anion, selected from tetrafluoroborate, hexafluorophosphate or bissulfonylimide derivatives, which imparts hydrophobic properties and thermal stability to the composition.

[0013] The cation and the anion are combined in equimolar amounts to produce an ionic liquid at room temperature that has the desired physicochemical profile. synthesis

[0014] The present composition is prepared by a direct quaternization reaction between a nitrogen-containing base and an alkyl halide in a molten salt medium under inert conditions. The reaction mixture is held at a controlled temperature until a viscous phase of the ionic liquid has formed.

[0015] After completion of the reaction, the product is separated, repeatedly washed with non-reactive organic solvents to remove unreacted substances, and then dried under reduced pressure until constant mass is achieved. The resulting ionic liquid is clear, hydrophobic, and thermally stable.

[0016] Anion exchange, if required, is carried out by reacting the halide-containing ionic liquid with an aqueous solution of an alkali metal tetrafluoroborate. The reaction mixture is stirred until phase separation occurs. The ionic liquid layer is separated, washed with deionized water to remove soluble salts, and then dried in a vacuum environment. characterization

[0017] The structure and purity of the composition are confirmed by infrared spectroscopy, nuclear magnetic resonance spectroscopy, and elemental analysis. The absence of halide impurities is verified by a precipitation test with silver ion solutions. Thermal properties

[0018] The thermal properties are determined using calibrated thermal analysis equipment.

[0019] The data on specific heat capacity are recorded over a defined temperature range under inert conditions to ensure an accurate determination of the heat storage potential.

[0020] The measured profiles show stable and reproducible values ​​that are consistent with the structural design of the composition. Functional properties

[0021] The hydrophobic ionic liquid composition exhibits the following properties: • a stable liquid state over a wide temperature range, • negligible volatility and non-flammability, • Resistance to oxidative or hydrolytic decomposition, • constant heat capacity values ​​during repeated heating and cooling cycles as well as • a rapid restoration of thermal performance after prolonged operation.

[0022] These properties make the composition suitable for continuous use in thermal management systems operating under high-temperature and reliability conditions. Industrial applications

[0023] The composition acts effectively as: • Heat transfer medium in industrial reactors and heat exchange systems, • Phase change material in heat storage modules, • Coolant for electronic and electrochemical equipment as well as • Stabilizing medium in energy conversion processes such as solar thermal or waste heat recovery systems.

[0024] The combination of thermal stability, safety and reproducibility gives the composition a competitive advantage over conventional liquids and solid phase change materials.

Claims

[1] Composition for heat storage, comprising at least one hydrophobic ionic liquid containing an organic cation and a tetrafluoroborate anion, wherein the cation is selected from the group of heterocyclic, nitrogen-containing cations with alkyl substituents, whose chain lengths lie between two and eight carbon atoms, and wherein the composition has a specific heat capacity of more than 0.9 joules per gram and kelvin within a temperature range of seventy-five to six hundred kelvin. [2] Composition according to claim 1, wherein the ionic liquid comprises a pyridinium or imidazolium cation and the tetrafluoroborate anion imparts hydrophobic properties and increased thermal stability to the composition, thereby achieving uniform heat capacity behavior over the entire operating temperature range. [3] Composition according to claim 1, wherein the ionic liquid has a negligible vapor pressure, a high thermal stability of more than five hundred Kelvin and resistance to decomposition during repeated heating and cooling cycles, thereby serving as a stable heat transfer and energy storage medium. [4] Composition according to claim 1, wherein the ratio of cation to anion is in the molar ratio one to one, thereby ensuring complete ion pair formation and uniform physicochemical behavior.