Organic modified nano-particle doped molten nitrate salt and preparation method thereof

Abstract

The invention discloses organically modified nanoparticle doped molten nitrate salt and a preparation method thereof, and belongs to the technical field of molten salt, the method comprises the following steps: uniformly mixing and stirring alcohol and nanoparticles, and carrying out solvothermal reaction, washing and primary drying to obtain organically modified nanoparticles; mixing the organic modified nano-particles with nitric acid molten salt, and performing secondary drying, heating reaction and grinding to obtain organic modified nano-particle doped nitric acid molten salt; the nanoparticles are silicon dioxide or titanium dioxide. The preparation method comprises the following steps: carrying out surface organic modification on nanoparticles through solvothermal reaction, and compounding the nanoparticles with nitric acid molten salt to obtain the organically modified nanoparticle doped nitric acid molten salt. By adding the organic modified nanoparticles, the heat transfer and storage performance of the molten salt can be effectively improved, and the obtained organic modified nanoparticle doped molten nitrate salt is stable in structure, simple in preparation process, low in melting point, low in production cost, simple and convenient in subsequent treatment, free of complex synthesis equipment and suitable for industrial large-scale production.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of molten salt, and particularly relates to an organic modified nanoparticle doped nitric acid molten salt and a preparation method thereof. BACKGROUND

[0002] The molten salt energy storage technology is not only suitable for heat transfer and heat storage process of the photo-thermal power station, but also is widely applied in multiple fields due to its high temperature working ability, wide use temperature range, excellent heat transfer ability, low system pressure and economy, etc. Whether it is the energy storage reconstruction of the thermal power plant, the reuse of industrial waste heat, or the industrial heating of valley electricity, the storage of photovoltaic and wind power generation, the molten salt energy storage shows its irreplaceable value. However, the molten salt energy storage technology has clear distinction from the operation parameters of the photo-thermal molten salt power generation system, so special requirements are put forward for the performance of the molten salt medium, especially the melting point control and the specific heat capacity. The commercialized molten salt products mainly concentrate on the eutectic nitrate, which has excellent high-temperature thermal stability, but the melting point is high, which is difficult to meet the requirements of the melting point of the thermal power-molten salt energy storage coupling technology, thereby limiting its application range in the photo-thermal power generation field. The existing molten salt materials are prone to the problem of agglomeration of the solid particles of the nanofluid composite molten salt in the long-term operation process, which leads to the solid / liquid separation and loses the heat transfer strengthening characteristics, thereby seriously reducing the strengthening effect on the molten salt and affecting the heat exchange efficiency of the heat exchanger. The mixed molten salt heat storage and heat transfer material improves the upper limit working temperature of the multi-component nitric acid molten salt through the addition of nano-oxides and the like, but the heat transfer performance still needs to be further improved, which is difficult to meet the actual application requirements. The dispersibility and stability of the nano-particles in the molten salt are poor, and the problem of uneven physical mixing distribution is prone to occur, which affects the overall performance and service life of the material.

[0003] The Chinese patent application with the publication number CN116656325A discloses a kind of nanofluid quaternary nitric acid molten salt heat storage medium and its preparation method and application. The patent application provides a kind of nanofluid quaternary nitric acid molten salt heat storage medium, including quaternary nitric acid molten salt system and functionalized modified nano-particles. The melting point of the nanofluid quaternary nitric acid molten salt is low, the specific heat capacity is large, the heat storage cycle thermal physical property is stable, and it is very suitable for thermal power-molten salt energy storage coupling system. However, the nanofluid modification method of the patent still needs to be further optimized. The Chinese patent application with the publication number CN116120900A discloses a kind of mixed molten salt heat storage and heat transfer material. The material includes 0.05~0.5wt% of nano-oxides, halogen molten salt, carbonic acid molten salt, nitric acid molten salt and the like. The mixed molten salt heat storage and heat transfer material maintains the low melting point of multi-component nitric acid molten salt, and simultaneously improves the upper limit working temperature of multi-component nitric acid molten salt, so that the use temperature of the molten salt is greatly widened. However, the patent application still has the problem that the heat transfer performance of the mixed molten salt needs to be further improved.

[0004] In order to solve the problem of high melting point and insufficient specific heat capacity of commercial molten salt, it is urgent to find an organic modified nanoparticle doped nitric acid molten salt and its preparation method. By doping the organic modified nanoparticle into the nitric acid molten salt, the melting point is reduced and the heat storage and transfer performance is optimized to meet the parameter requirements of the molten salt energy storage technology. SUMMARY

[0005] In order to overcome the above-mentioned defects of the prior art, the purpose of the present application is to provide an organic modified nanoparticle doped nitric acid molten salt and its preparation method, so as to solve the technical problems that the melting point and specific heat capacity of the existing commercial molten salt heat do not meet the requirements of the molten salt energy storage technology, and the nanoparticles are easy to agglomerate in the molten salt and have poor dispersibility.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: The application discloses a preparation method of an organic modified nanoparticle doped nitric acid molten salt, which comprises the following steps: The alcohol and the nanoparticles are uniformly mixed and stirred, and then subjected to a solvothermal reaction, washing, and primary drying to obtain organic modified nanoparticles; the organic modified nanoparticles are mixed with the nitric acid molten salt, and then subjected to secondary drying, heating reaction, and grinding to obtain the organic modified nanoparticle doped nitric acid molten salt. The nanoparticles are silicon dioxide or titanium dioxide.

[0007] Preferably, the alcohol and the nanoparticles are used in a ratio of 10 mL: (1-2) g.

[0008] Preferably, the alcohol is n-butanol, tert-butanol or methanol.

[0009] Preferably, the temperature of the solvothermal reaction is 230-280 DEG C, and the holding time is 2-6 h.

[0010] Preferably, anhydrous ethanol is used for washing during the washing; and the temperature of the primary drying is 60-80 DEG C.

[0011] Preferably, the mass ratio of the organic modified nanoparticles to the nitric acid molten salt is (0.1%-0.2%):(99.8%-99.9%). The nitric acid molten salt is prepared by mixing KNO3 in an amount of 40%-60%, NaNO2 in an amount of 30%-45% and NaNO3 in an amount of 5%-15% according to the mass percentage.

[0012] Preferably, the conditions of the secondary drying are as follows: drying at 60-80 DEG C until completely dry.

[0013] Preferably, the conditions of the heating reaction are as follows: heating reaction at 300-450 DEG C for 12-24 h.

[0014] The application further discloses a preparation method of the organic-modified nanoparticle-doped nitric acid molten salt.

[0015] Preferably, the organic-modified nanoparticle-doped nitric acid molten salt comprises 0.1%-0.2% of the organic-modified nanoparticles and 99.8%-99.9% of the nitric acid molten salt in percentage by mass; The nitric acid molten salt comprises 40%-60% of KNO3, 30%-45% of NaNO2 and 5%-15% of NaNO3 in percentage by mass.

[0016] Compared with the prior art, the application has the following beneficial effects: The application discloses a preparation method of an organic-modified nanoparticle-doped nitric acid molten salt. The esterification reaction between alcohol and the surface hydroxyl group of nanoparticles is carried out at high temperature and high pressure through a solvothermal reaction to form an organic modification layer, which can significantly improve the dispersibility of the nanoparticles in the molten salt, reduce the agglomeration and avoid the uneven distribution problem caused by physical mixing. The two kinds of nanoparticles, namely, silicon dioxide and titanium dioxide, are widely available and low in cost, and the surface hydroxyl group is easy to be grafted with organic groups through the esterification reaction. After modification, the heat storage and heat transfer performance of the molten salt can be improved. The nanoparticles are modified first and then compounded with the molten salt, so that the organic modification layer is uniformly coated and the particle deposition caused by direct mixing is avoided, thereby improving the heat stability and heat storage consistency of the composite molten salt. In the application, the alcohol is grafted to the surface of the nanoparticles. At a relatively high temperature, the esterification reaction between the alcohol and the surface of the nanoparticles can improve the dispersibility of the nanoparticles and reduce the agglomeration of the nanoparticles in the molten salt.

[0017] Further, the ratio of the amount of alcohol to the amount of nanoparticles is 10 mL: (1-2) g, that is, 10 mL of alcohol corresponds to 1-2 g of nanoparticles, so that the surface hydroxyl group of the nanoparticles can fully react with the alcohol, and the modification layer is not too thick or insufficient due to the excessive alcohol. At the ratio, the degree of esterification is moderate, which can effectively improve the dispersibility of the particles and avoid the influence of too many organic groups on the heat stability of the molten salt.

[0018] Further, the alcohol is n-butanol, tert-butanol or methanol. The molecular chains of n-butanol and tert-butanol are relatively long, the organic layer formed after grafting has large steric hindrance, can more effectively inhibit the agglomeration of the nanoparticles and improve the dispersibility in the molten salt, and the specific heat capacity reaches 1.431 J / (g·K). The molecular chain of methanol is short and the reactivity is high, so that the methanol can quickly react with the surface hydroxyl group of the nanoparticles, is suitable for a scene requiring efficient modification, and the methanol is easy to volatilize, has less residue in the washing and drying process, and has excellent melting point and specific heat capacity.

[0019] Further, the temperature of the solvothermal reaction is 230-280℃, and the holding time is 2-6h; 230-280℃ is the best temperature range for the esterification reaction of alcohol and the hydroxyl group on the surface of the nanoparticles. If the temperature is lower than 230℃, the reaction rate is slow, and the modification layer is incomplete; if the temperature is higher than 280℃, the alcohol may be decomposed or the structure of the nanoparticles may be damaged. The temperature range ensures that the esterification reaction is fully carried out, and a stable organic modification layer is formed. The holding time of 2-6h matches the temperature, ensures that the reaction is complete, and ensures that different alcohols can achieve the ideal modification effect.

[0020] Further, anhydrous ethanol is used for washing. Ethanol can effectively dissolve unreacted alcohol and byproducts, and is miscible with water, so that the residual impurities on the surface of the nanoparticles can be removed. The anhydrous condition avoids the introduction of water, prevents the nanoparticles from reabsorbing water and agglomerating, and ensures the stability of the modification layer; the temperature for one-time drying is 60-80℃. Low-temperature drying at 60-80℃ avoids the decomposition of the organic modification layer on the surface of the nanoparticles due to high temperature, and at the same time ensures that the residual ethanol is fully volatilized, so that dry and pure organic modified nanoparticles are obtained, laying a foundation for subsequent mixing with molten salt.

[0021] Further, the mass ratio of the organic modified nanoparticles to the nitric acid molten salt is (0.1%-0.2%):(99.8%-99.9%); the proportion of 0.1%-0.2% of the nanoparticles can effectively improve the heat storage and transfer performance of the molten salt, and the specific heat capacity is increased to 1.402-1.459 J / (g·K), and at the same time, agglomeration is avoided due to too many particles, which affects the flowability and thermal stability of the molten salt. Under this proportion, the nanoparticles are uniformly dispersed, and a stable composite system is formed with the molten salt. According to the mass percentage, the nitric acid molten salt is prepared by mixing 40%-60% of KNO3, 30%-45% of NaNO2 and 5%-15% of NaNO3; 40%-60% of KNO3 reduces the melting point of the molten salt and improves the low-temperature flowability; 30%-45% of NaNO2 improves the thermal stability of the molten salt and reduces high-temperature decomposition; 5%-15% of NaNO3 adjusts the phase change temperature of the molten salt, and forms a eutectic system with KNO3 and NaNO2, further reducing the melting point and widening the temperature range for use.

[0022] Further, the conditions for secondary drying are: drying at 60-80℃ until completely dry; after mixing the nanoparticles with the nitric acid molten salt, drying can remove the residual water or volatile impurities in the system, avoid the deliquescence of the molten salt due to water, and prevent the generation of gas at high temperature, which affects the chemical stability of the molten salt. Low-temperature drying at 60-80℃ prevents the decomposition of the nitric acid molten salt due to high temperature, and at the same time ensures that the modification layer of the nanoparticles is not damaged, and the structural stability of the composite molten salt is maintained.

[0023] Further, the heating reaction conditions are: heating reaction at 300-450℃ for 12-24h; 300-450℃, nitric acid molten salt melting, fully contact with the organic modified nanoparticles, enhance the interface binding force through physical infiltration and chemical action, reduce the nanoparticles deposition. The temperature range is lower than the decomposition temperature of nitric acid molten salt, ensure that the molten salt does not decompose, while promoting the uniform dispersion of nanoparticles. The reaction time of 12-24h ensures that the molten salt and nanoparticles are fully mixed to form a uniform composite system, improving production efficiency while ensuring product consistency.

[0024] The application also discloses an organic modified nanoparticle doped nitric acid molten salt prepared by the preparation method of the organic modified nanoparticle doped nitric acid molten salt.

[0025] Further, the organic modified nanoparticle doped nitric acid molten salt comprises 0.1%-0.2% of the organic modified nanoparticles and 99.8%-99.9% of the nitric acid molten salt in percentage by mass; the 0.1%-0.2% of the organic modified nanoparticles can improve the heat transfer efficiency of the molten salt through the interface effect, increase the specific heat capacity, and will not cause the viscosity of the molten salt to rise due to particle accumulation, ensuring the flow performance. The specific proportion of KNO3, NaNO2 and NaNO3 forms a eutectic system, reduces the melting point to 140℃, and utilizes the thermal stability of each component to make the composite molten salt remain chemically stable in high-temperature energy storage, and is not easy to produce gas or corrode equipment. The composite molten salt of the composition has low production cost, the nitric acid molten salt is widely available, the preparation process is simple, no complex equipment is needed, and the performance meets the requirements of low melting point, high heat storage and long service life of the energy storage system, and has the potential for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The preparation method flow chart of the organic modified nanoparticle doped nitric acid molten salt disclosed by the application is shown in the figure. DETAILED DESCRIPTION

[0027] The technical solutions of the application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the application.

[0028] In the present application, all the embodiments and preferred embodiments mentioned in the present application can be combined to form new technical solutions, if not otherwise specified.

[0029] In the present application, all the technical features and preferred features mentioned in the present application can be combined to form new technical solutions, if not otherwise specified.

[0030] In the present application, percentage (%) or part refers to the percentage by weight or weight parts of the composition, if not otherwise specified.

[0031] In the present application, each component or its preferred component involved can be combined to form new technical solutions, if not otherwise specified.

[0032] In the present application, unless otherwise specified, the numerical range "a-b" represents a shorthand for any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "6-22" represents that all the real numbers between "6-22" have been listed herein, and "6-22" is only a shorthand for these numerical combinations.

[0033] The lower limit and upper limit of the range disclosed in the present application can be one or more lower limits and one or more upper limits, respectively.

[0034] In the present application, the term "and / or" used herein means any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0035] In the present application, unless otherwise specified, each reaction or operation step can be carried out sequentially or according to the sequence. Preferably, the reaction method herein is carried out sequentially.

[0036] Unless otherwise specified, the professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the described content can also be applied in the present application.

[0037] In the first aspect, the present application provides an organic modified nanoparticle doped nitric acid molten salt, comprising, by mass percentage: 0.1%-0.2% organic modified nanoparticle and 99.8%-99.9% nitric acid molten salt.

[0038] In the preferred scheme of the present application, the nitric acid molten salt is a mixture composed of 40%-60% KNO3, 30%-45% NaNO2 and 5%-15% NaNO3 by mass fraction.

[0039] The nitric acid molten salt used in the application is a mixture of KNO3, Na(NO3)2 and NaNO3, and these nitric acid salts have high thermal stability, so that the composite molten salt can maintain stable chemical properties in a high temperature environment and is not easy to decompose or produce harmful gases.

[0040] The organic modified nanoparticle doped nitric acid molten salt comprises organic modified nanoparticles and nitric acid molten salt, and the nitric acid molten salt used in the application has wide sources, low price and small corrosion.

[0041] The currently used nanoparticles in molten salt are silicon dioxide or titanium dioxide, but the surface of the nanoparticles is rich in hydroxyl groups, which is easy to agglomerate, and the direct application effect is poor, so it is necessary to graft different organic groups on the surface of the nanoparticles to control the dispersibility and functionality of the nanoparticles.

[0042] In a second aspect, the application provides a preparation method of the organic modified nanoparticle doped nitric acid molten salt, comprising the following steps: The organic modified nanoparticle doped nitric acid molten salt is obtained by mixing the organic modified nanoparticles and the nitric acid molten salt, drying and heating, and then grinding.

[0043] In a preferred scheme of the application, the drying condition is drying at 60-80 DEG C until completely dry.

[0044] In a preferred scheme of the application, the heating reaction condition is heating at 300-450 DEG C for 12-24 h.

[0045] In a preferred scheme of the application, the grinding condition is grinding into powder.

[0046] In a preferred scheme of the application, the preparation method of the organic modified nanoparticles comprises the following steps: S1: mixing alcohol and nanoparticles and stirring uniformly; S2: transferring the mixed solution into a high-pressure reaction kettle and placing it in a drying box for solvent thermal reaction; S3: after the solvent thermal reaction, cleaning the solution with anhydrous ethanol; S4: The above solution is placed in a drying oven for drying.

[0047] In a preferred embodiment of the present application, in S1, the alcohol is n-butanol, t-butanol or methanol.

[0048] In a preferred embodiment of the present application, in S1, the nanoparticles are silica or titanium dioxide.

[0049] In a preferred embodiment of the present application, in S1, the ratio of alcohol to nanoparticles is 10 mL: (1-2) g.

[0050] In a preferred embodiment of the present application, in S2, the solvothermal reaction condition is 230-280℃ for 2-6h.

[0051] In a preferred embodiment of the present application, in S4, the drying temperature is 60-80℃.

[0052] The present application utilizes organic modified nanoparticles, which helps to ensure uniform distribution of nanoparticles in nitric acid molten salt, reduces deposition, thereby avoiding the problem of uneven distribution that may occur in subsequent physical mixing process, and improves the combination of nanoparticles and molten salt.

[0053] The present application provides an organic modified nanoparticle doped nitric acid molten salt and a preparation method thereof. Through solvothermal reaction, esterification reaction occurs between alcohol and the surface hydroxyl group of nanoparticles at high temperature and high pressure, forming an organic modification layer. This effectively improves the dispersibility of nanoparticles in molten salt, reduces agglomeration, avoids the problem of uneven distribution in physical mixing, and improves the stability and service life of the material. Silica or titanium dioxide is used as nanoparticles, which is widely available and low in cost. The surface hydroxyl group is easy to graft organic groups through esterification reaction, and after modification, the heat storage performance of molten salt can be improved. This effectively solves the problem of agglomeration of nano-fluid composite molten salt solid particles in the prior art, which leads to solid / liquid separation and loss of heat transfer enhancement characteristics. Through uniform coating of the organic modification layer, particle deposition caused by direct mixing is avoided, ensuring the thermal stability and heat storage consistency of the composite molten salt, and effectively improving the heat exchange efficiency of the heat exchanger. The prepared organic modified nanoparticle doped nitric acid molten salt has a low melting point and a high specific heat capacity, which not only meets the requirements of the power-thermal molten salt energy storage coupling technology for the melting point, but also significantly improves the heat storage performance of the material. The preparation method is simple and feasible, easy to operate, and easy to industrialize, and has good economic benefits and practical value.

[0054] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0055] Embodiment 1 A preparation method of organic modified nanoparticle doped nitric acid molten salt comprises the following steps: Step 1: 10 mL of n-butanol is mixed with 1 g of silica nanoparticles and stirred uniformly; the above mixed solution is transferred to a high-pressure reaction kettle, placed in a drying box, heated to 230℃, and kept for 6 h; after the solvothermal reaction, the solution is washed with anhydrous ethanol; after washing, it is placed in a drying box at 60℃ for drying, and organic modified nanoparticles are obtained.

[0056] Step 2: the above organic modified nanoparticles are mixed uniformly with 999 g of nitric acid molten salt, wherein the composition of the nitric acid molten salt is 53% KNO3+40% NaNO2+7% NaNO3; Step 3: the above composite molten salt is dried in a drying box at 60℃ until the mixture is completely dried; after drying, it is reacted in a high-temperature furnace at 300℃ for 24 h, ground into powder, and organic modified nanoparticle doped nitric acid molten salt is obtained.

[0057] Reference Figure 1 A preparation method flow chart of the organic modified nanoparticle doped nitric acid molten salt disclosed in the present application is shown in the figure. As can be seen from the figure, the preparation method of the organic modified nanoparticle doped nitric acid molten salt comprises the following steps: alcohol and nanoparticles (silicon dioxide or titanium dioxide) are mixed and stirred uniformly, solvothermal reaction, washing, one-time drying, and then organic modified nanoparticles are obtained; the organic modified nanoparticles are mixed with nitric acid molten salt, and after secondary drying, heating reaction, and grinding, organic modified nanoparticle doped nitric acid molten salt is obtained; the surface of the nanoparticles is organically modified through solvothermal reaction, and then the nanoparticles are compounded with nitric acid molten salt to obtain organic modified nanoparticle doped nitric acid molten salt. The addition of organic modified nanoparticles can effectively improve the heat storage and transfer performance of the molten salt, and the obtained organic modified nanoparticle doped nitric acid molten salt has stable structure, simple preparation process, low melting point, low production cost, simple subsequent treatment, and does not require complex synthesis equipment, and is suitable for industrial large-scale production.

[0058] Example 2 A preparation method of an organic modified nanoparticle doped nitric acid molten salt, comprising the following steps: Step 1: 10 mL of tert-butyl alcohol is mixed with 1 g of silica nanoparticles and stirred uniformly; the above mixed solution is transferred to a high-pressure reaction kettle, placed in a drying box, heated to 280°C, and kept for 2 h; after the solvothermal reaction, the solution is washed with anhydrous ethanol; after washing is completed, it is placed in a drying box at 80°C for drying, and an organic modified nanoparticle is obtained.

[0059] Step 2: the above organic modified nanoparticle is mixed uniformly with 999 g of nitric acid molten salt, wherein the composition of the nitric acid molten salt is 50% KNO3+40% NaNO2+10% NaNO3; Step 3: the above composite molten salt is dried in a drying box at 80°C until the mixture is completely dried; after drying, it is reacted in a high-temperature furnace at 450°C for 12 h, ground into powder, and an organic modified nanoparticle doped nitric acid molten salt is obtained.

[0060] Example 3 A preparation method of an organic modified nanoparticle doped nitric acid molten salt, comprising the following steps: Step 1: 10 mL of tert-butyl alcohol is mixed with 1 g of silica nanoparticles and stirred uniformly; the above mixed solution is transferred to a high-pressure reaction kettle, placed in a drying box, heated to 280°C, and kept for 2 h; after the solvothermal reaction, the solution is washed with anhydrous ethanol; after washing is completed, it is placed in a drying box at 80°C for drying, and an organic modified nanoparticle is obtained.

[0061] Step 2: the above organic modified nanoparticle is mixed uniformly with 999 g of nitric acid molten salt, wherein the composition of the nitric acid molten salt is 50% KNO3+40% NaNO2+10% NaNO3; Step 3: the above composite molten salt is dried in a drying box at 80°C until the mixture is completely dried; after drying, it is reacted in a high-temperature furnace at 450°C for 12 h, ground into powder, and an organic modified nanoparticle doped nitric acid molten salt is obtained.

[0062] Example 4 A preparation method of an organic modified nanoparticle doped nitric acid molten salt, comprising the following steps: Step 1: 10 mL of tert-butyl alcohol is mixed with 1 g of silica nanoparticles and stirred uniformly; the above mixed solution is transferred to a high-pressure reaction kettle, placed in a drying box, heated to 280°C, and kept for 2 h; after the solvothermal reaction, the solution is washed with anhydrous ethanol; after washing is completed, it is placed in a drying box at 80°C for drying, and an organic modified nanoparticle is obtained.

[0063] Step 2: mix the above organic modified nanoparticles with 999g nitric acid molten salt, wherein the composition of the nitric acid molten salt is 40% KNO3+45% NaNO2+15% NaNO3; Step 3: dry the above composite molten salt in a drying box at 70°C until the mixture is completely dry; after drying, react in a high-temperature furnace at 360°C for 20h, grind into powder, to obtain organic modified nanoparticles doped with nitric acid molten salt.

[0064] Example 5 A preparation method of organic modified nanoparticles doped with nitric acid molten salt, comprising the following steps: Step 1: mix 10mL methanol with 1.5g titanium dioxide nanoparticles, stir uniformly; transfer the above mixed solution to a high-pressure reaction kettle, put it into a drying box, heat to 260°C, and keep for 5h; after the solvothermal reaction, wash the solution with anhydrous ethanol; after washing, dry it in a drying box at 60°C, to obtain organic modified nanoparticles.

[0065] Step 2: mix the above organic modified nanoparticles with 998.5g nitric acid molten salt, wherein the composition of the nitric acid molten salt is 60% KNO3+35% NaNO2+5% NaNO3; Step 3: dry the above composite molten salt in a drying box at 70°C until the mixture is completely dry; after drying, react in a high-temperature furnace at 350°C for 18h, grind into powder, to obtain organic modified nanoparticles doped with nitric acid molten salt.

[0066] Example 6 A preparation method of organic modified nanoparticles doped with nitric acid molten salt, comprising the following steps: Step 1: mix 10mL n-butanol with 1g titanium dioxide nanoparticles, stir uniformly; transfer the above mixed solution to a high-pressure reaction kettle, put it into a drying box, heat to 240°C, and keep for 5.5h; after the solvothermal reaction, wash the solution with anhydrous ethanol; after washing, dry it in a drying box at 70°C, to obtain organic modified nanoparticles.

[0067] Step 2: mix the above organic modified nanoparticles with 999g nitric acid molten salt, wherein the composition of the nitric acid molten salt is 55% KNO3+45% NaNO2+10% NaNO3; Step 3: dry the above composite molten salt in a drying box at 65°C until the mixture is completely dry; after drying, react in a high-temperature furnace at 400°C for 16h, grind into powder, to obtain organic modified nanoparticles doped with nitric acid molten salt.

[0068] Example 7 A preparation method of organic modified nanoparticles doped with nitric acid molten salt, comprising the following steps: Step 1: 10 mL of n-butanol was mixed with 1 g of titanium dioxide nanoparticles and stirred uniformly; the above mixed solution was transferred to a high-pressure reaction kettle, placed in a drying box, heated to 270°C, and kept for 4 h; after the solvothermal reaction, the solution was washed with anhydrous ethanol; after washing, it was placed in a drying box at 65°C for drying, and organic modified nanoparticles were obtained.

[0069] Step 2: The above organic modified nanoparticles were mixed with 999 g of nitric acid molten salt, and the composition of the nitric acid molten salt was 52% KNO3+40% NaNO2+8% NaNO3. Step 3: The above composite molten salt was dried in a drying box at 75°C until the mixture was completely dried; after drying, it was reacted in a high-temperature furnace at 320°C for 22 h, ground into powder, and organic modified nanoparticles doped with nitric acid molten salt were obtained.

[0070] Example 8 A preparation method of organic modified nanoparticles doped with nitric acid molten salt, comprising the following steps: Step 1: 10 mL of n-butanol was mixed with 1 g of titanium dioxide nanoparticles and stirred uniformly; the above mixed solution was transferred to a high-pressure reaction kettle, placed in a drying box, heated to 250°C, and kept for 5 h; after the solvothermal reaction, the solution was washed with anhydrous ethanol; after washing, it was placed in a drying box at 75°C for drying, and organic modified nanoparticles were obtained.

[0071] Step 2: The above organic modified nanoparticles were mixed with 999 g of nitric acid molten salt, and the composition of the nitric acid molten salt was 45% KNO3+45% NaNO2+10% NaNO3. Step 3: The above composite molten salt was dried in a drying box at 70°C until the mixture was completely dried; after drying, it was reacted in a high-temperature furnace at 360°C for 20 h, ground into powder, and organic modified nanoparticles doped with nitric acid molten salt were obtained.

[0072] Table 1 Thermal physical property data of organic modified nanoparticles doped with nitric acid molten salt in Examples 1-5

[0073] Referring to Table 1, the thermophysical property data of the organic modified nanoparticle doped nitric acid molten salt in Examples 1-5 of the present application, including melting point and specific heat capacity, are analyzed, and it is found that the melting point of the obtained organic modified nanoparticle doped nitric acid molten salt is 140-146℃, and the lowest melting point is 140℃; the lower melting point is conducive to reducing the starting temperature of the molten salt in the energy storage system and reducing energy loss; and the relatively stable melting point indicates that the preparation process of the composite molten salt has certain controllability. The specific heat capacity of the obtained organic modified nanoparticle doped nitric acid molten salt is 1.402-1.459 J / (g·K), and the highest specific heat capacity is 1.459 J / (g·K); the higher value means that the organic modified nanoparticle doped nitric acid molten salt can store more heat per unit mass and temperature change, proving that the addition of the organic modified nanoparticle in the application can improve the heat transfer and storage performance of the molten salt. The melting point of the organic modified nanoparticle doped nitric acid molten salt is relatively low and stable, and the specific heat capacity is relatively high and has small fluctuations, indicating that it has good heat storage capacity and process controllability, and meets the demand for low melting point and high heat storage of materials in the field of molten salt energy storage.

[0074] In summary, the organic modified nanoparticle doped nitric acid molten salt and the preparation method thereof according to the present application include 0.1%-0.2% organic modified nanoparticles and 99.8%-99.9% nitric acid molten salt by mass percentage; the nitric acid molten salt used in the present application has wide sources, low price and small corrosion; and due to the high thermal stability of each nitrate, the composite molten salt is chemically stable at high temperature and is not easy to decompose or produce harmful gases; the addition of the organic modified nanoparticles (such as silica and titanium dioxide modified by alcohol such as n-butanol) can effectively improve the heat transfer and storage performance of the molten salt; the esterification reaction on the surface of the alcohol grafted particles can improve the dispersibility of the nanoparticles and reduce the agglomeration in the molten salt. The organic modified nanoparticles are combined with the nitric acid molten salt to obtain the organic modified nanoparticle doped nitric acid molten salt, which is mixed with the nitric acid molten salt after the nanoparticles are modified by solvothermal reaction, dried, heated and ground, and prepared, and the preparation process is simple, does not require complex equipment, has low melting point and production cost, is easy to handle, and is suitable for large-scale industrial production; and the organic modification ensures the uniform distribution of the nanoparticles in the molten salt, reduces deposition, avoids the problem of uneven distribution of physical mixing, improves the combination with the molten salt, and can be applied to the field of molten salt energy storage.

[0075] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing organic modified nanoparticles doped with nitrate molten salt, characterized in that: include: The alcohol and the nanoparticles are mixed and stirred uniformly, subjected to solvent thermal reaction, washed, and dried once to obtain organically modified nanoparticles; the organically modified nanoparticles are mixed with molten nitrate, subjected to secondary drying, heated reaction, and ground to obtain organically modified nanoparticles doped with molten nitrate; The nanoparticles are silicon dioxide or titanium dioxide.

2. The method for preparing organic modified nanoparticles doped with nitrate molten salt according to claim 1, characterized in that: The usage ratio of the alcohol and the nanoparticles is 10 mL: (1-2) g.

3. The method for preparing organic modified nanoparticles doped with nitrate molten salt according to claim 1, characterized in that: The alcohol is n-butanol, tert-butanol or methanol.

4. The method for preparing organic modified nanoparticles doped with nitrate molten salt according to claim 1, characterized in that: The temperature of the solvent thermal reaction is 230-280° C., and the insulation time is 2-6 hours.

5. The method for preparing organic modified nanoparticles doped with nitrate molten salt according to claim 1, characterized in that: Anhydrous ethanol is used for washing; the temperature of the primary drying is 60-80°C.

6. The method for preparing organic modified nanoparticles doped with nitrate molten salt according to claim 1, characterized in that: The mass ratio of the organic modified nanoparticles to the nitrate molten salt is (0.1%-0.2%): (99.8%-99.9%); The nitrate molten salt is prepared by mixing 40%-60% of KNO3, 30%-45% of NaNO2 and 5%-15% of NaNO3 by mass percentage.

7. The method for preparing organic modified nanoparticles doped with nitrate molten salt according to claim 1, characterized in that: The secondary drying condition is: drying at 60-80° C. until completely dried.

8. The method for preparing organic modified nanoparticles doped with nitrate molten salt according to claim 1, characterized in that: The heating reaction conditions are: heating the reaction at 300-450° C. for 12-24 hours.

9. An organic modified nanoparticle doped nitrate molten salt, characterized in that: The nanoparticles are prepared by the method for preparing organically modified nanoparticles doped with nitrate molten salt according to any one of claims 1 to 8.

10. The organic modified nanoparticle doped nitrate molten salt according to claim 9, characterized in that: The organic modified nanoparticles doped with nitrate molten salt comprise, by mass percentage, 0.1%-0.2% of the organic modified nanoparticles and 99.8%-99.9% of the nitrate molten salt; Calculated by mass percentage, the nitrate molten salt includes: 40%-60% KNO3, 30%-45% NaNO2 and 5%-15% NaNO3.

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