High specific heat quaternary sulfuric acid molten salt composite heat storage material and its preparation method and application

Abstract

The present invention discloses a high specific heat quaternary sulfuric acid molten salt composite heat storage material and its preparation method and application. The preparation comprises: mixing the sodium sulfate decahydrate, magnesium sulfate heptahydrate, potassium sulfate, and calcium sulfate and heating the mixture to a first dehydration temperature at a first heating rate for a first heat treatment, then heating the mixture to a second dehydration temperature at a second heating rate for a second heat treatment, and then heating the mixture to a melt blending temperature at a third heating rate for a third heat treatment to obtain a quaternary sulfuric acid molten salt; and stirring and ultrasonically mixing the quaternary sulfuric acid molten salt with a nano-inorganic material and melt blending the mixture to obtain a high specific heat quaternary sulfuric acid molten salt composite heat storage material. The present invention prepares the quaternary sulfuric acid molten salt in a one-step method through dehydration and coupling technology, which not only makes high-value utilization of the sodium, potassium, magnesium, and calcium resources of the salt lake, but also simplifies the process flow and reduces costs. At the same time, the addition of nanoparticles to the quaternary sulfuric acid molten salt increases the specific heat of the composite heat storage material.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat storage materials, and in particular relates to a high specific heat quaternary sulfuric acid molten salt composite heat storage material and a preparation method and application thereof. Background Art

[0002] Due to the continued use of fossil energy, it is gradually becoming depleted, and the resulting environmental and climate problems are becoming increasingly serious. Renewable energy plays a vital role in mitigating global warming and climate change. Solar energy, due to its pollution-free nature and abundant reserves, is considered one of the most promising alternative energy sources, and concentrated solar power (CSP) is a major method for utilizing solar energy. CSP technology can be divided into three generations based on the type and efficiency of the thermodynamic cycle. First- and second-generation CSP technologies both employ the Rankine cycle, with peak cycle temperatures below 550°C. They utilize solar salt (NaNO₃-KNO₃) for heat transfer and storage, achieving annual power generation efficiencies of 10-20%. Third-generation CSP technology further improves solar energy utilization efficiency by utilizing the Brayton cycle, with peak cycle temperatures exceeding 700°C. Currently, the most commonly used thermal storage materials in concentrated solar power plants are nitrates (Solar Salt) and nitrites (Hitec). However, their relatively low decomposition temperature (550°C) limits their application in third-generation CSP. Therefore, the design and development of molten salts that can operate stably at high temperatures is crucial for third-generation CSP.

[0003] Chlorides, carbonates, sulfates, and fluorides are considered to be potential candidate molten salts in the field of high-temperature heat transfer and have therefore been widely studied. Tian et al. prepared NaCl-CaCl2 eutectic salt. Wei et al. developed a ternary chloride molten salt composed of NaCl, CaCl2, and MgCl2. Patange et al. studied the CuCl-KCl-NaCl ternary molten salt. It can be seen that the existing molten salts are mostly nitrates, carbonates, and chlorides. At the same time, the raw materials prepared are mostly industrial-grade or molten salt-grade nitrates, carbonates, and chlorides. There are no reports on composite heat storage materials of high-specific-heat sodium sulfate-potassium sulfate-magnesium sulfate-calcium sulfate quaternary molten salts. Summary of the Invention

[0004] The main purpose of the present invention is to provide a high specific heat quaternary sulfuric acid molten salt composite heat storage material and its preparation method and application, so as to overcome the shortcomings of the existing technology.

[0005] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0006] An embodiment of the present invention provides a method for preparing a high specific heat quaternary sulfuric acid molten salt composite heat storage material, which comprises:

[0007] Sodium sulfate decahydrate, magnesium sulfate heptahydrate, potassium sulfate, and calcium sulfate are mixed and heated to a first dehydration temperature at a first heating rate for a first heat treatment, then heated to a second dehydration temperature at a second heating rate for a second heat treatment, and then heated to a melt blending temperature at a third heating rate for a third heat treatment to produce a quaternary sulfuric acid molten salt;

[0008] Furthermore, the quaternary sulfuric acid molten salt and the nano-inorganic material are stirred and ultrasonically mixed and melt-blended to prepare a high specific heat quaternary sulfuric acid molten salt composite heat storage material.

[0009] The embodiment of the present invention also provides a high specific heat quaternary sulfuric acid molten salt composite heat storage material prepared by the above preparation method, wherein the specific heat of the high specific heat quaternary sulfuric acid molten salt composite heat storage material is 1.42~1.70 J·g -1 ℃ -1 .

[0010] An embodiment of the present invention further provides an energy storage material, which at least includes the aforementioned high specific heat quaternary sulfuric acid molten salt composite heat storage material.

[0011] Compared with the prior art, the present invention has the following beneficial effects: the present invention uses sodium sulfate decahydrate, magnesium sulfate heptahydrate, potassium sulfate and calcium sulfate, which are abundant in salt lakes, as raw materials, and produces quaternary sulfuric acid molten salt through a one-step dehydration and coupling technology, which not only makes high-value utilization of salt lake sodium, potassium and magnesium resources, but also reduces the energy consumption of first dehydrating and then high-temperature blending to prepare sulfate in a one-step method, simplifies the process flow and reduces costs; at the same time, the addition of nanoparticles to the quaternary sulfuric acid molten salt increases the specific heat of the composite heat storage material. DETAILED DESCRIPTION

[0012] In view of the shortcomings of the prior art, the inventors of this case, after long-term research and extensive practice, have proposed the technical solution of the present invention. The technical solution of the present invention will be clearly and completely described below. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making any creative effort shall fall within the scope of protection of the present invention.

[0013] Specifically, as one aspect of the technical solution of the present invention, a method for preparing a high specific heat quaternary sulfuric acid molten salt composite heat storage material involves:

[0014] Sodium sulfate decahydrate, magnesium sulfate heptahydrate, potassium sulfate, and calcium sulfate are mixed and heated to a first dehydration temperature at a first heating rate for a first heat treatment, then heated to a second dehydration temperature at a second heating rate for a second heat treatment, and then heated to a melt blending temperature at a third heating rate for a third heat treatment to produce a quaternary sulfuric acid molten salt;

[0015] Furthermore, the quaternary sulfuric acid molten salt and the nano-inorganic material are stirred and ultrasonically mixed and melt-blended to prepare a high specific heat quaternary sulfuric acid molten salt composite heat storage material.

[0016] In some preferred embodiments, the preparation method specifically includes: mixing sodium sulfate decahydrate, magnesium sulfate heptahydrate, potassium sulfate and calcium sulfate uniformly and heating the mixture to 50-100°C at a first heating rate of 1-10°C / min for a first heat treatment, then heating the mixture to 250-350°C at a second heating rate of 1-10°C / min for a second heat treatment, then heating the mixture to 750-850°C at a third heating rate of 10-20°C / min for a third heat treatment, and finally cooling the mixture to room temperature to obtain the quaternary sulfuric acid molten salt heat storage material.

[0017] In some preferred embodiments, the mass ratio of the sodium sulfate decahydrate, magnesium sulfate heptahydrate, potassium sulfate and calcium sulfate is 57.6-61.6:25-28:4.4:1-10.

[0018] In some preferred embodiments, the mass ratio of the tetrabasic sulfuric acid molten salt to the nano-inorganic material is 100:0.3~2.0.

[0019] In some preferred embodiments, the nano-inorganic material includes any one or more combinations of nano-aluminum oxide, silicon dioxide, silicon carbide, and boron nitride, but is not limited thereto.

[0020] In some preferred embodiments, the melting point of the tetrabasic sulfuric acid molten salt is 680-700°C, and the decomposition temperature is 1005-1100°C.

[0021] In some preferred embodiments, the first heat treatment lasts for 1 to 4 hours.

[0022] In some preferred embodiments, the second heat treatment lasts for 1 to 4 hours.

[0023] In some preferred embodiments, the third heat treatment lasts for 3 to 6 hours.

[0024] In some preferred embodiments, the preparation method specifically comprises:

[0025] The quaternary sulfuric acid molten salt and the nano-inorganic material are stirred and ultrasonically mixed to form a mixture; wherein the stirring speed is 50-200 rpm, the ultrasonic frequency is 10-50 kHz, and the ultrasonic power is 100-500 W;

[0026] Furthermore, the obtained mixture is heated to 750-850°C at a heating rate of 10-20°C / min, melt-blended for 3-6 hours, and then cooled to room temperature to obtain a high specific heat quaternary sulfuric acid molten salt composite heat storage material.

[0027] In some preferred embodiments, the preparation method further comprises:

[0028] The first sulfate-type salt lake raw brine is subjected to freezing treatment to obtain a crude sodium sulfate decahydrate product; wherein the first sulfate-type salt lake raw brine has a sodium ion concentration of 10.0-11.0 wt%, a potassium ion concentration of 0.45-0.51 wt%, a magnesium ion concentration of 0.25-0.35 wt%, a chloride ion concentration of 14.5-15.2 wt%, and a sulfate ion concentration of 3.3-4.0 wt%;

[0029] and performing recrystallization on the crude sodium sulfate decahydrate product to obtain sodium sulfate decahydrate.

[0030] Furthermore, the freezing treatment temperature is -20~5°C and the time is 4~10 hours.

[0031] Furthermore, the heating temperature used in the recrystallization treatment is 40-80°C.

[0032] Furthermore, the cooling temperature used during the recrystallization treatment is -20~5°C.

[0033] Furthermore, the purity of the crude sodium sulfate decahydrate product is 85% to 95%.

[0034] Furthermore, the purity of the sodium sulfate decahydrate is greater than 99.0%.

[0035] In some preferred embodiments, the preparation method further comprises:

[0036] The raw brine from the second sulfate-type salt lake is subjected to evaporation and crystallization treatment to obtain a crude magnesium sulfate heptahydrate product; wherein the raw brine from the second sulfate-type salt lake has a sodium ion concentration of 6.0-8.0 wt%, a potassium ion concentration of 0.70-0.8 wt%, a magnesium ion concentration of 2.0-2.5 wt%, a chloride ion concentration of 14.5-16.0 wt%, and a sulfate ion concentration of 3.3-5.0 wt%;

[0037] and recrystallizing the crude magnesium sulfate heptahydrate product to obtain magnesium sulfate heptahydrate.

[0038] Furthermore, the temperature of the evaporation crystallization treatment is 20-35° C., and the time is 6-12 hours.

[0039] Furthermore, the heating temperature used in the recrystallization treatment is 40-80°C.

[0040] Furthermore, the cooling temperature used during the recrystallization treatment is 5-15°C.

[0041] Furthermore, the purity of the crude magnesium sulfate heptahydrate product is 80% to 95%.

[0042] Furthermore, the purity of the magnesium sulfate heptahydrate is greater than 99.0%.

[0043] In some more specific embodiments, the method for preparing the high specific heat quaternary sulfuric acid molten salt composite heat storage material comprises the following steps:

[0044] (1) Using raw brine from a sulfate-type salt lake as a raw material, freezing at a certain temperature to obtain a crude sodium sulfate decahydrate product, and recrystallizing the crude sodium sulfate decahydrate product to obtain sodium sulfate decahydrate with a grade of 99.0%. The raw brine from the sulfate-type salt lake has a sodium ion concentration of 10.0% to 11.0%, a potassium ion concentration of 0.45% to 0.51%, a magnesium ion concentration of 0.25% to 0.35%, a chloride ion concentration of 14.5% to 15.2%, and a sulfate ion concentration of 3.3% to 4.0%. The freezing temperature is -20°C to 5°C; the purity of the crude sodium sulfate decahydrate product is 85% to 95%; the recrystallization heating temperature is 40°C to 80°C, and the recrystallization cooling temperature is -20°C to 5°C; the purity of the sodium sulfate decahydrate product is greater than 99.0%.

[0045] (2) Using a sulfate-type salt lake brine as a raw material, evaporation and crystallization are performed at a certain temperature to obtain a crude magnesium sulfate heptahydrate product, and the crude magnesium sulfate heptahydrate product is recrystallized to obtain 99.0% magnesium sulfate heptahydrate. The sodium ion concentration of the sulfate-type salt lake brine is 6.0% to 8%, the potassium ion concentration is 0.70% to 0.8%, the magnesium ion concentration is 2.0% to 2.5%, the chloride ion concentration is 14.5% to 16%, and the sulfate ion concentration is 3.3% to 5.0%. The evaporation temperature is 20°C to 35°C; the purity of the crude magnesium sulfate heptahydrate product is 80% to 95%; the recrystallization heating temperature is 40°C to 80°C, and the recrystallization cooling temperature is 5°C to 15°C; the purity of the magnesium sulfate heptahydrate product is greater than 99.0%.

[0046] (3) According to a certain proportion, 20 g of sodium sulfate decahydrate, magnesium sulfate heptahydrate, potassium sulfate and calcium sulfate, which are abundant in the salt lake, are weighed in sequence, put into a crucible and mixed evenly. The crucible of the mixture is placed in a muffle furnace, and the temperature is increased to the first dehydration temperature at a certain heating rate and kept constant at the temperature for a certain time. The temperature is then increased to the second dehydration temperature at a certain heating rate and kept constant at the temperature for a certain time. The temperature is then increased to the melting and blending temperature at a certain heating rate and kept constant at the temperature for a certain time. The mixture is then cooled to room temperature to obtain a quaternary sulfate molten salt. The mixture comprises the following components: sodium sulfate decahydrate with a mass fraction of 57.6% to 61.6%, magnesium sulfate heptahydrate with a mass fraction of 25% to 28%, potassium sulfate with a mass fraction of 4.4%, and calcium sulfate with a mass fraction of 1% to 10%. The first stage heating rate is 1 to 10°C / min, the first dehydration temperature is 50 to 100°C, and the temperature is maintained constant for 1 to 4 hours. The second stage heating rate is 1 to 10°C / min, the first dehydration temperature is 250 to 350°C, and the temperature is maintained constant for 1 to 4 hours. The third stage heating rate is 10 to 20°C / min, the melt blending temperature is 750 to 850°C, and the temperature is maintained constant for 3 to 6 hours. The sodium sulfate-potassium sulfate-magnesium sulfate-calcium sulfate quaternary molten salt has a melting point of 680 to 700°C and a decomposition temperature of 1005 to 1100°C.

[0047] (4) Weigh 10 g of quaternary sulfate molten salt and nano-inorganic material in a certain proportion, place them in a reactor with stirring and ultrasound, heat to a certain temperature under a certain speed and ultrasound conditions, melt and blend for a certain time, and cool to room temperature to obtain a high specific heat quaternary sulfate molten salt composite heat storage material. The nano-inorganic material is one or two of nano-aluminum oxide, silicon dioxide, silicon carbide and boron nitride, and the amount of nano-material added is 0.3%-2.0% of the quaternary sulfate molten salt material; the stirring speed is 50-200 rpm; the ultrasonic frequency is 10-50 kHz, and the ultrasonic power is 100-500 W; the heating rate is 10-20 ° C / min, the melt blending temperature is 750-850 ° C, and the temperature is kept constant for 3-6 hours.

[0048] Another aspect of the present invention provides a high specific heat quaternary sulfuric acid molten salt composite heat storage material prepared by the above-mentioned preparation method, wherein the specific heat of the high specific heat quaternary sulfuric acid molten salt composite heat storage material is 1.42~1.70 J·g -1 ℃ -1 .

[0049] Another aspect of the embodiments of the present invention further provides an energy storage material, which at least includes the aforementioned high specific heat quaternary sulfuric acid molten salt composite heat storage material.

[0050] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments. This embodiment is implemented on the premise of the technical solution of the invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0051] Unless otherwise specified, the experimental materials used in the following examples can be purchased from conventional biochemical reagent companies.

[0052] Example 1

[0053] 1) Weigh 1 kg of raw brine from a sulfate lake, containing 10.0% sodium ion concentration, 0.45% potassium ion concentration, 0.25% magnesium ion concentration, 14.5% chloride ion concentration, and 3.3% sulfate ion concentration. Freeze the brine at -20°C for 4 hours to obtain crude sodium sulfate decahydrate with a purity of 85%. Dissolve the crude sodium sulfate decahydrate at 40°C and recrystallize it at -20°C to obtain sodium sulfate decahydrate with a purity of 99.2%.

[0054] 2) Weigh 1 kg of raw brine from a sulfate lake, containing 6% sodium ion concentration, 0.7% potassium ion concentration, 2.0% magnesium ion concentration, 14.5% chloride ion concentration, and 3.3% sulfate ion concentration. Evaporate and crystallize the brine at 20°C to obtain crude magnesium sulfate heptahydrate with a purity of 80%. Dissolve and evaporate the crude magnesium sulfate heptahydrate at 40°C for 6 hours, and crystallize it at 5°C to obtain magnesium sulfate heptahydrate with a purity of 99.0%.

[0055] 3) Weigh 20 g of the above raw materials in a ratio of 57.6% sodium sulfate decahydrate, 28% magnesium sulfate heptahydrate, 10% calcium sulfate, and 4.4% potassium sulfate, put them into a crucible and mix them evenly. Place the mixture crucible in a muffle furnace, heat it to 50°C at a heating rate of 1°C / min, hold it at that temperature for 1 hour, then heat it to 250°C at a heating rate of 1°C / min, hold it at that temperature for 1 hour, then heat it to 750°C at a heating rate of 10°C / min, hold it at that temperature for 3 hours, and obtain a sodium sulfate-potassium sulfate-magnesium sulfate-calcium sulfate quaternary molten salt with a melting point of 680°C and a decomposition temperature of 1005°C.

[0056] 4) Weigh a total of 10 g of quaternary sulfate molten salt and nano-alumina in a certain proportion, with the nanomaterial added at 0.3 wt% of the quaternary sulfate molten salt, and place them in a stirring and ultrasonic reactor. Heat the mixture to 750°C at a rate of 10°C / min under stirring at 50 rpm, an ultrasonic frequency of 10 kHz, and an ultrasonic power of 100 W. The mixture is kept constant at this temperature for 3 hours and cooled to room temperature to obtain a high-specific-heat quaternary sulfate molten salt composite thermal storage material. The composite material has a specific heat of 1.42 J·K. -1 •g -1 .

[0057] Example 2

[0058] 1) Weigh 1 kg of raw brine from a sulfate lake, containing 11.0% sodium ion concentration, 0.51% potassium ion concentration, 0.35% magnesium ion concentration, 15.2% chloride ion concentration, and 4.0% sulfate ion concentration. Freeze the brine at 5°C for 10 hours to obtain a crude sodium sulfate decahydrate product with a purity of 95%. Dissolve the crude sodium sulfate decahydrate at 80°C and recrystallize at 5°C to obtain a 99.0% pure sodium sulfate decahydrate.

[0059] 2) Weigh 1 kg of raw brine from a sulfate lake, containing 8% sodium ion concentration, 0.8% potassium ion concentration, 2.5% magnesium ion concentration, 16% chloride ion concentration, and 5.0% sulfate ion concentration. Evaporate and crystallize the brine at 35°C to obtain crude magnesium sulfate heptahydrate with a purity of 95%. Dissolve and evaporate the crude magnesium sulfate heptahydrate at 80°C for 12 hours, and crystallize it at 15°C to obtain magnesium sulfate heptahydrate with a purity of 99.3%.

[0060] 3) Weigh 20 g of the above raw materials in a ratio of 61.6% sodium sulfate decahydrate, 33% magnesium sulfate heptahydrate, 1% calcium sulfate, and 4.4% potassium sulfate, put them into a crucible and mix them evenly. Place the mixture crucible in a muffle furnace, heat it to 100°C at a heating rate of 10°C / min, hold it at that temperature for 4 hours, then heat it to 350°C at a heating rate of 10°C / min, hold it at that temperature for 4 hours, then heat it to 850°C at a heating rate of 20°C / min, hold it at that temperature for 6 hours, and then obtain a sodium sulfate-potassium sulfate-magnesium sulfate-calcium sulfate quaternary molten salt with a melting point of 700°C and a decomposition temperature of 1100°C.

[0061] 4) Weigh a total of 10 g of quaternary sulfate molten salt and nano-silica in a certain proportion, with the nanomaterial added at 2.0 wt% of the quaternary sulfate molten salt, and place them in a stirring and ultrasonic reactor. Heat the mixture to 850°C at a rate of 20°C / min under stirring at 200 rpm, an ultrasonic frequency of 50 kHz, and an ultrasonic power of 500 W. Hold the temperature constant for 6 hours, and cool to room temperature to obtain a high-specific-heat quaternary sulfate molten salt composite thermal storage material. The composite material has a specific heat of 1.65 J·K -1 •g -1 .

[0062] Example 3

[0063] 1) Weigh 1 kg of raw brine from a sulfate lake, containing 10.05% sodium ion concentration, 0.48% potassium ion concentration, 0.30% magnesium ion concentration, 15.0% chloride ion concentration, and 3.5% sulfate ion concentration. Freeze the brine at -10°C for 6 hours to obtain a crude sodium sulfate decahydrate product with a purity of 90%. Dissolve the crude sodium sulfate decahydrate at 60°C and recrystallize at 0°C to obtain sodium sulfate decahydrate with a purity of 99.3%.

[0064] 2) Weigh 1 kg of raw brine from a sulfate lake, containing 7% sodium ion concentration, 0.75% potassium ion concentration, 2.2% magnesium ion concentration, 15% chloride ion concentration, and 4% sulfate ion concentration. Evaporate and crystallize the brine at 30°C to obtain crude magnesium sulfate heptahydrate with a purity of 90%. Dissolve and evaporate the crude magnesium sulfate heptahydrate at 60°C for 8 hours, and crystallize it at 10°C to obtain magnesium sulfate heptahydrate with a purity of 99.1%.

[0065] 3) Weigh 20 g of the above raw materials in a ratio of 59.67% sodium sulfate decahydrate, 30.93% magnesium sulfate heptahydrate, 5% calcium sulfate, and 4.4% potassium sulfate, put them into a crucible and mix them evenly. Place the mixture crucible in a muffle furnace, heat it to 80°C at a heating rate of 5°C / min, hold it at that temperature for 3 hours, then heat it to 300°C at a heating rate of 5°C / min, hold it at that temperature for 2 hours, and then heat it to 800°C at a heating rate of 15°C / min, hold it at that temperature for 5 hours, to obtain a sodium sulfate-potassium sulfate-magnesium sulfate-calcium sulfate quaternary molten salt with a melting point of 686.5°C and a decomposition temperature of 1045.79°C.

[0066] 4) Weigh 10 g of quaternary sulfate molten salt, nano-boron carbide, and silicon nitride in a certain proportion, with the nanomaterial added at 1.0 wt% of the quaternary sulfate molten salt, and place them in a stirring and ultrasonic reactor. Heat the mixture to 800°C at a rate of 15°C / min under stirring at 100 rpm, an ultrasonic frequency of 30 kHz, and an ultrasonic power of 200 W. Hold the temperature constant for 5 hours, and cool to room temperature to obtain a high-specific-heat quaternary sulfate molten salt composite thermal storage material. The composite material has a specific heat of 1.69 J·K -1 •g -1 .

[0067] Comparative Example 1

[0068] 1) Weigh 1 kg of raw brine from a sulfate lake, containing 10.05% sodium ion concentration, 0.48% potassium ion concentration, 0.30% magnesium ion concentration, 15.0% chloride ion concentration, and 3.5% sulfate ion concentration. Freeze the brine at -10°C to obtain a crude sodium sulfate decahydrate product with a purity of 90%. Dissolve the crude sodium sulfate decahydrate at 60°C and recrystallize it at 0°C to obtain a 99.3% pure sodium sulfate decahydrate.

[0069] 2) Weigh 1 kg of raw brine from a sulfate lake, containing 7% sodium ion concentration, 0.75% potassium ion concentration, 2.2% magnesium ion concentration, 15% chloride ion concentration, and 4% sulfate ion concentration. Evaporate and crystallize the brine at 30°C to obtain crude magnesium sulfate heptahydrate with a purity of 90%. Dissolve and evaporate the crude magnesium sulfate heptahydrate at 60°C and crystallize at 10°C to obtain magnesium sulfate heptahydrate with a purity of 99.1%.

[0070] 3) A total of 20 g of the above raw materials were weighed in a ratio of 15% sodium sulfate decahydrate, 20% magnesium sulfate heptahydrate, 50% calcium sulfate, and 15% potassium sulfate, placed in a crucible and mixed evenly. The crucible of the mixture was placed in a muffle furnace, heated to 80°C at a heating rate of 5°C / min, held at this temperature for 3 hours, then heated to 300°C at a heating rate of 5°C / min, held at this temperature for 2 hours, and then heated to 650°C at a heating rate of 15°C / min, held at this temperature for 5 hours. No sodium sulfate-potassium sulfate-magnesium sulfate-calcium sulfate quaternary molten salt was formed.

[0071] Comparative Example 2

[0072] 1) Weigh 1 kg of raw brine from a sulfate lake, containing 10.05% sodium ion concentration, 0.48% potassium ion concentration, 0.30% magnesium ion concentration, 15.0% chloride ion concentration, and 3.5% sulfate ion concentration. Freeze the brine at -10°C to obtain a crude sodium sulfate decahydrate product with a purity of 90%. Dissolve the crude sodium sulfate decahydrate at 60°C and recrystallize it at 0°C to obtain a 99.3% pure sodium sulfate decahydrate.

[0073] 2) Weigh 1 kg of raw brine from a sulfate lake, containing 7% sodium ion concentration, 0.75% potassium ion concentration, 2.2% magnesium ion concentration, 15% chloride ion concentration, and 4% sulfate ion concentration. Evaporate and crystallize the brine at 30°C to obtain crude magnesium sulfate heptahydrate with a purity of 90%. Dissolve and evaporate the crude magnesium sulfate heptahydrate at 60°C and crystallize at 10°C to obtain magnesium sulfate heptahydrate with a purity of 99.1%.

[0074] 3) 20 g of the above raw materials were weighed in a ratio of 59.67% sodium sulfate decahydrate, 30.93% magnesium sulfate heptahydrate, 5% calcium sulfate, and 4.4% potassium sulfate. The mixture was placed in a crucible and mixed thoroughly. The crucible was placed in a muffle furnace and heated to 80°C at a heating rate of 5°C / min and held at this temperature for 3 hours. The temperature was then increased to 300°C at a heating rate of 5°C / min and held at this temperature for 2 hours. The temperature was then increased to 800°C at a heating rate of 15°C / min and held at this temperature for 5 hours. A quaternary molten salt of sodium sulfate, potassium sulfate, magnesium sulfate, and calcium sulfate was obtained. The melting point of the quaternary molten salt was 686.5°C, the decomposition temperature was 1045.79°C, and the specific heat of the quaternary molten salt of sodium sulfate, potassium sulfate, magnesium sulfate, and calcium sulfate was 1.32 J·K.-1 •g -1 .

[0075] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments using other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0076] It should be understood that the technical solution of the present invention is not limited to the above-mentioned specific implementation cases. Any technical variations made according to the technical solution of the present invention without departing from the scope of protection of the purpose of the present invention and the claims shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high specific heat quaternary sulfuric acid molten salt composite heat storage material, characterized in that: include: The sodium sulfate decahydrate, magnesium sulfate heptahydrate, potassium sulfate and calcium sulfate are uniformly mixed and heated to 50-100° C. at a first heating rate of 1-10° C. / min for a first heat treatment, then heated to 250-350° C. at a second heating rate of 1-10° C. / min for a second heat treatment, then heated to 750-850° C. at a third heating rate of 10-20° C. / min for a third heat treatment, and finally cooled to room temperature to obtain a quaternary sulfuric acid molten salt; wherein the mass ratio of the sodium sulfate decahydrate, magnesium sulfate heptahydrate, potassium sulfate and calcium sulfate is 57.6-61.6:25-28:4.4:1-10; Furthermore, the quaternary sulfuric acid molten salt is stirred and ultrasonically mixed with nano-inorganic materials and melt-blended to obtain a high specific heat quaternary sulfuric acid molten salt composite heat storage material; wherein the nano-inorganic material is selected from any one or more combinations of nano-aluminum oxide, silicon dioxide, silicon carbide, and boron nitride.

2. The preparation method according to claim 1, wherein: The mass ratio of the quaternary sulfuric acid molten salt to the nano-inorganic material is 100:0.3-2.0; And / or, the melting point of the tetrabasic sulfuric acid molten salt is 680-700°C, and the decomposition temperature is 1005-1100°C.

3. The preparation method according to claim 1, wherein: The first heat treatment time is 1 to 4 hours; And / or, the second heat treatment time is 1 to 4 hours; And / or, the third heat treatment is performed for 3 to 6 hours.

4. The preparation method according to claim 1, characterized in that Specifically include The quaternary sulfuric acid molten salt and the nano-inorganic material are stirred and ultrasonically mixed to form a mixture; wherein the stirring speed is 50-200 rpm, the ultrasonic frequency is 10-50 kHz, and the ultrasonic power is 100-500 W; Furthermore, the obtained mixture is heated to 750-850°C at a heating rate of 10-20°C / min, melt-blended for 3-6 hours, and then cooled to room temperature to obtain a high specific heat quaternary sulfuric acid molten salt composite heat storage material.

5. The preparation method according to claim 1, characterized in that Also includes: The first sulfate-type salt lake raw brine is subjected to freezing treatment to obtain a crude sodium sulfate decahydrate product; wherein the first sulfate-type salt lake raw brine has a sodium ion concentration of 10.0-11.0 wt%, a potassium ion concentration of 0.45-0.51 wt%, a magnesium ion concentration of 0.25-0.35 wt%, a chloride ion concentration of 14.5-15.2 wt%, and a sulfate ion concentration of 3.3-4.0 wt%; and performing recrystallization on the crude sodium sulfate decahydrate product to obtain sodium sulfate decahydrate.

6. The preparation method according to claim 5, characterized in that: The freezing treatment temperature is -20~5°C and the time is 4~10h; And / or, the heating temperature used in the recrystallization treatment is 40-80° C.; And / or, the cooling temperature used during the recrystallization treatment is -20~5°C; And / or, the purity of the crude sodium sulfate decahydrate product is 85% to 95%; And / or, the purity of the sodium sulfate decahydrate is greater than 99.0%.

7. The preparation method according to claim 1, characterized in that Also includes: The raw brine from the second sulfate-type salt lake is subjected to evaporation and crystallization treatment to obtain a crude magnesium sulfate heptahydrate product; wherein the raw brine from the second sulfate-type salt lake has a sodium ion concentration of 6.0-8.0 wt%, a potassium ion concentration of 0.70-0.8 wt%, a magnesium ion concentration of 2.0-2.5 wt%, a chloride ion concentration of 14.5-16.0 wt%, and a sulfate ion concentration of 3.3-5.0 wt%; and recrystallizing the crude magnesium sulfate heptahydrate product to obtain magnesium sulfate heptahydrate.

8. The preparation method according to claim 7, characterized in that: The evaporation crystallization treatment is performed at a temperature of 20 to 35° C. for 6 to 12 hours. And / or, the heating temperature used in the recrystallization treatment is 40-80° C.; And / or, the cooling temperature used during the recrystallization treatment is 5-15°C; And / or, the purity of the crude magnesium sulfate heptahydrate product is 80% to 95%; And / or, the purity of the magnesium sulfate heptahydrate is greater than 99.0%.

9. A high specific heat quaternary sulfuric acid molten salt composite heat storage material prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The specific heat of the high specific heat quaternary sulfuric acid molten salt composite heat storage material is 1.42-1.70 J·g -1 ℃ -1 .

10. An energy storage material, characterized in that At least includes the high specific heat quaternary sulfuric acid molten salt composite heat storage material according to claim 9.