Low-temperature molten salt, preparation method thereof and application method of low-temperature molten salt in electrolytic aluminum

Abstract

The invention provides low-temperature molten salt, a preparation method thereof and an application method of the low-temperature molten salt in electrolytic aluminum. The low-temperature molten salt is prepared by mixing and reacting one of an imidazole compound, a pyrazole compound, an oxazole compound, an isoxazole compound, an oxadiazole compound, a triazole compound, a thiophene compound, a thiazole compound, an isothiazole compound, a pyrrolidine compound and a piperidine compound with aluminum halide. The reaction can be completed in one step, operation is easy and convenient, and system stability is good. On the basis, electrolytic preparation of aluminum under an inert anode can be realized by adopting the low-temperature molten salt. The electrolysis process is low in temperature, low in energy consumption, high in aluminum product purity, high in current efficiency and free of carbon dioxide emission, and an electrolyte system can be recycled.

Description

Technical Field

[0001] The present invention belongs to the field of nonferrous metal smelting, and specifically relates to a low-temperature molten salt and a preparation method thereof and an application method thereof in electrolytic aluminum. Background Art

[0002] Aluminum is an important non-ferrous metal with the advantages of light weight, strong conductivity, good ductility and low cost. It is widely used in social life, industrial production, scientific research and other fields. For a long time, cryolite, alumina and other materials have been used as raw materials at home and abroad. First, electrolysis reaction is carried out in a high-temperature molten state, and then the generated aluminum liquid is extracted, purified and cast, and finally industrial-grade aluminum ingots are obtained (the mass purity is usually about 99.5%). The electrolysis temperature of this process is generally 930-970℃, and the production energy consumption per kilogram of aluminum is about 13.5kWh, while a large amount of carbon dioxide is emitted. In 2023, the annual electricity consumption and net carbon dioxide emissions of my country's electrolytic aluminum industry accounted for about 7% and 4% of the whole society respectively. Therefore, the traditional electrolytic aluminum process has the problems of high energy consumption, high temperature and heavy emissions.

[0003] In recent years, my country's electrolytic aluminum industry has generally faced an unfavorable situation of overcapacity, low efficiency, high energy consumption and heavy pollution. At the same time, in order to comply with the trend of sustainable development and energy conservation and emission reduction, it is necessary to significantly reduce reaction energy consumption and carbon dioxide emissions. On the other hand, with the rapid development of science and technology, economy and society, people have higher requirements for the quality and performance of aluminum. Among them, when the mass purity is greater than 99.9%, the conductivity, light reflection and antioxidant capacity of aluminum can be significantly improved, and it can be applied to cutting-edge industries such as electronic materials, new energy vehicles, optical devices and aerospace. Against the above background, it is necessary to strengthen the reform and innovation of electrolytic aluminum production technology and the upgrading of product quality.

[0004] Studies have shown that the key to solving the above problems lies in completing the electrolytic preparation of aluminum under low temperature conditions. So far, related work at home and abroad has mainly focused on the improvement of traditional high-temperature molten salt systems. Although there is a certain cooling space in the high-temperature molten salt system, the degree of cooling is relatively limited, and most reaction temperatures are still above 800°C. Among them, about half of the reaction energy consumption is used to maintain a high reaction temperature. The production energy consumption per kilogram of aluminum is still higher than 10kWh, and the current efficiency is generally lower than 95%. At the same time, carbon dioxide emissions are not significantly reduced. It can be said that these problems are mainly attributed to the inherent defects of the high-temperature molten salt system, which is difficult to completely solve through its own improvements. If this situation is to be completely changed, a new type of low-temperature electrolyte must be developed to reduce the reaction temperature and energy consumption from the source and avoid carbon dioxide emissions.

[0005] Low-temperature molten salts are a special class of electrolytes (also called ionic liquids). Unlike traditional high-temperature molten salts, this system is usually composed of organic cations and conventional anions, and the melting point can be below 100°C, many of which are close to room temperature. Studies have shown that some low-temperature molten salts can be used for the electrodeposition of aluminum. Among them, the most common are low-temperature molten salts containing imidazole, pyridine and quaternary ammonium cations. Compared with traditional high-temperature molten salts, the electrolysis temperature in low-temperature molten salts is as low as below 100°C, and the production energy consumption per kilogram of aluminum is lower than that of traditional high-temperature molten salt electrolysis. Therefore, low-temperature molten salts are expected to replace traditional high-temperature molten salt systems and realize the low-temperature electrolysis process of aluminum, thereby solving the inherent defects of traditional processes.

[0006] Although some research progress has been made in low-temperature molten salt aluminum electrolysis at home and abroad, there are still many problems, mainly as follows:

[0007] 1) The preparation process of imidazole-type, pyridine-type and quaternary ammonium-type low-temperature molten salts is relatively complicated, and generally requires at least two preparation steps. The first step is to react imidazole compounds, pyridine compounds or amine compounds with alkyl halides or hydrogen halides through nucleophilic reactions to obtain onium salt precursors, such as imidazolium chloride salts, etc.; the second step is to mix the onium salt precursors with aluminum chloride to obtain low-temperature molten salts for low-temperature aluminum electrolysis. The process uses relatively complex materials and has a long reaction time. Many onium salt precursors are easy to absorb water, which is not conducive to the preparation of low-temperature electrolyte systems, increases the difficulty of operation and purification, and brings high production costs, hindering the industrial application of technology. At the same time, low-temperature molten salts based on ethylene carbonate, dimethyl sulfone, urea, etc. and aluminum chloride and the electrodeposition process of aluminum have also been explored at home and abroad. It is worth noting that these substances still have some defects. For example, dimethyl sulfone, urea, and ethylene carbonate are solids at room temperature, and their high melting points are not conducive to low-temperature mixing with aluminum chloride, which prolongs the preparation time of the molten salt system. Secondly, the moisture in raw materials such as urea and their easy water absorption properties are also not conducive to the preparation of electrolytes and the electrodeposition of aluminum.

[0008] 2) To date, most of the work has used aluminum or aluminum alloys as soluble anodes for aluminum electrodeposition reactions. There is a lack of systematic research on the electrolysis of aluminum under inert anodes, making it difficult to achieve the production goal of preparing metallic aluminum from the electrolysis of aluminum compounds.

[0009] 3) The product purity of the traditional electrolytic aluminum process is relatively limited, and usually requires further refining and purification to obtain aluminum products with a purity greater than 99.9% (also known as high-purity aluminum or refined aluminum).

[0010] Therefore, it is necessary to further develop low-cost, easy-to-mix raw materials, simplify the preparation process of low-temperature molten salts, improve the physical and chemical properties of the electrolyte system, and establish a process for low-temperature electrolysis of aluminum under an inert anode, so as to obtain aluminum products with higher purity. Summary of the invention

[0011] Based on the above technical status and development trends, the present invention proposes a new low-temperature molten salt and a preparation method thereof, and also proposes an application method of the low-temperature molten salt in electrolytic aluminum, aiming to further simplify the reaction operation, reduce production energy consumption and side reactions, and improve the purity and current efficiency of aluminum products.

[0012] The invention discloses a method for preparing a low-temperature molten salt, which is prepared by mixing one of imidazole compounds, pyrazole compounds, oxazole compounds, isoxazole compounds, oxadiazole compounds, triazole compounds, thiophene compounds, thiazole compounds, isothiazole compounds, pyrrolidine compounds and piperidine compounds with aluminum halide at a molar ratio of 1:0.55-1.95 under an inert atmosphere at 10-30°C and 101-101.6 kPa for 0.5-3 hours.

[0013] Furthermore, the chemical structural formula of the imidazole compound is The chemical structural formula of the pyrazole compound is The chemical structural formula of the oxazole compound is The chemical structural formula of the isoxazole compound is The chemical structural formula of the oxadiazole compound is or The chemical structural formula of the triazole compound is or The chemical structural formula of the thiophene compound is The chemical structural formula of the thiazole compound is The chemical structural formula of the isothiazole compound is The chemical structural formula of the pyrrolidine compound is The chemical structural formula of the piperidine compound is Among them, R1~R 11 represents a C1-C6 alkyl group or a hydrogen atom.

[0014] Furthermore, the aluminum halide is one of aluminum trichloride, aluminum tribromide, aluminum triiodide, alkylaluminum dichloride, dialkylaluminum chloride, alkylaluminum dibromide, dialkylaluminum bromide, alkylaluminum diiodide, and dialkylaluminum iodide. The chemical structural formula of the alkylaluminum dichloride is The chemical structural formula of the dialkylaluminum chloride is The chemical structural formula of the alkylaluminum dibromide is The chemical structural formula of the dialkylaluminum bromide is The chemical structural formula of the alkyl aluminum diiodide is The chemical structural formula of the dialkylaluminum iodide is Among them, R, R1, and R2 in all chemical structural formulas represent methyl or ethyl.

[0015] Furthermore, the inert atmosphere is composed of one of helium, neon, argon, krypton, xenon and nitrogen with a mass content higher than 99.9%.

[0016] Another object of the present invention is to provide a low-temperature molten salt, which is prepared by the above preparation method.

[0017] The mass purity and ionic structure of the above-mentioned low-temperature molten salt are characterized by infrared absorption spectroscopy and nuclear magnetic resonance spectroscopy.

[0018] Another object of the present invention is to provide a method for using the above-mentioned low-temperature molten salt in electrolytic aluminum.

[0019] The method for applying the low-temperature molten salt in electrolytic aluminum comprises the following specific steps:

[0020] 1) Using low-temperature molten salt as electrolyte, using one of platinum, palladium, ruthenium, titanium, graphite, and glassy carbon as inert anode, using one of graphite, glassy carbon, aluminum, and platinum as cathode, and using constant voltage electrolysis method to prepare aluminum at low temperature under inert atmosphere. The electrolysis temperature is 30-80°C, the electrolysis voltage is 2.3-3.8V, the gas pressure is 101-101.6kPa, and the reaction time is 0.5-3h.

[0021] 2) After the electrolysis is completed, the cathode is removed from the electrolyte under an inert atmosphere and left to stand for 0.5 h, then rinsed with anhydrous ethanol and dried to obtain a metallic aluminum product.

[0022] Furthermore, in the above reaction step, the inert atmosphere is composed of one of helium, neon, argon, krypton, xenon and nitrogen with a mass content higher than 99.9%.

[0023] The electrolysis process is carried out in a diaphragm electrolytic cell, where the cathode and anode reaction areas are separated by a semipermeable membrane. After the electrolysis reaction is completed, metallic aluminum and halogen products can be obtained from the cathode and anode respectively.

[0024] After separation and purification, the purity of the final aluminum metal product is characterized by X-ray energy spectrum and atomic absorption spectrum, and the mass purity of aluminum is calculated based on the characteristic spectral line intensity, peak area and absorbance of aluminum element. The electrical energy and thermal energy of the electrolysis process are calculated based on the measurement results of the electricity meter, constant voltage DC power supply and calorimeter, and the electrolysis energy consumption is obtained after merging. The current efficiency is based on Faraday's law and is obtained by the ratio of the actual output of aluminum metal to the theoretical output.

[0025] The results of theoretical and experimental studies show that in the preparation process of the above-mentioned low-temperature molten salts, the nitrogen atoms, oxygen atoms, and sulfur atoms in imidazole compounds, pyrazole compounds, oxazole compounds, isoxazole compounds, oxadiazole compounds, triazole compounds, thiophene compounds, thiazole compounds, isothiazole compounds, pyrrolidine compounds, and piperidine compounds can respectively react with the aluminum atoms in the corresponding aluminum halides to generate corresponding cations and anions. In the reaction process of aluminum electrolysis, the anions of the above-mentioned low-temperature molten salts are the main electrochemically active substances participating in the electrode reaction, and can generate metallic aluminum and the corresponding halogen elements at the cathode and anode, respectively. For example, the anion [Al2Cl7] - At the cathode, it reacts to form metallic aluminum and anions [AlCl4] - , anion [AlCl4] - Reacts at the anode to generate anions [Al2Cl7] - and chlorine, the overall reaction formula is as follows:

[0026] 2[Al2Cl7] - →2[AlCl4] - +2Al+3Cl2.

[0027] Compared with the existing methods, the technical advantages of the present invention are as follows:

[0028] 1) The low-temperature molten salt of the present invention is obtained by direct reaction of one of imidazole compounds, pyrazole compounds, oxazole compounds, isoxazole compounds, oxadiazole compounds, triazole compounds, thiophene compounds, thiazole compounds, isothiazole compounds, pyrrolidine compounds, piperidine compounds and aluminum halide. The method can complete the preparation of low-temperature electrolytes through a one-step reaction without the aid of onium salt precursors, overcoming the problems of cumbersome preparation process and complicated operation of traditional low-temperature molten salts.

[0029] 2) Compared with the raw materials used in the prior art such as ethylene carbonate, dimethyl sulfone, urea, etc., the imidazole compounds, pyrazole compounds, oxazole compounds, isoxazole compounds, oxadiazole compounds, triazole compounds, thiophene compounds, thiazole compounds, isothiazole compounds, pyrrolidine compounds, and piperidine compounds described in the present invention generally have lower melting points and are not easy to absorb moisture in the environment. For example, 1-n-butylimidazole, pyrrolidine, 4-methylpyrazole, isothiazole, etc. are liquid at room temperature and are not easy to absorb water, which is convenient for direct mixing reaction with aluminum halide, shortening the preparation time of low-temperature molten salt, reducing reaction energy consumption, side reactions and by-products, simplifying the operation process, and enhancing the stability of the system.

[0030] 3) Based on the above-mentioned low-temperature molten salt, the present invention uses one of platinum, palladium, ruthenium, titanium, graphite, and glassy carbon as an inert anode, and one of graphite, glassy carbon, aluminum, and platinum as a cathode, so as to achieve the production purpose of preparing metallic aluminum from aluminum compounds under low temperature conditions by electrolysis. Using the method for preparing electrolytic aluminum described in the present invention, the electrolysis temperature does not exceed 80°C, and the electrolysis voltage is lower than 4V. Due to the higher stability of low-temperature molten salts and the lower electrolysis temperature and voltage, the use of a diaphragm electrolytic cell can further reduce reaction energy consumption, side reactions, and by-products, thereby improving the mass purity and current efficiency of metallic aluminum. The energy consumption for preparing each kilogram of aluminum is less than 8.5kWh, the mass purity of aluminum is higher than 99.9%, and the current efficiency can reach more than 98%. At the same time, there is no emission of carbon dioxide during the electrolysis process, and the electrolyte system can be recycled.

[0031] Therefore, the electrolysis energy consumption and temperature of the present invention are significantly lower than those of the traditional high-temperature molten salt electrolysis method, the emission of carbon dioxide is avoided, and the purity of aluminum is further improved. At the same time, the defects of the existing low-temperature molten salt preparation process being cumbersome and complicated to operate are solved, the preparation time of the low-temperature molten salt is shortened, the energy consumption and side reactions of the reaction are reduced, the operation process is simplified, and the stability of the system is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the infrared absorption spectrum of the low-temperature molten salt prepared in Example 1 of the present invention. -1 The absorption peak in the wavenumber range mainly corresponds to the stretching vibration between aluminum atoms and chlorine atoms, which is located at 600-660 cm -1 The absorption peak in the wavenumber range mainly corresponds to the stretching vibration between aluminum atoms and nitrogen atoms, which is located at 670-670 cm -1 The absorption peak in the wavenumber range mainly corresponds to the deformation vibration in the methylene group, 792 cm -1 The absorption peak at the wave number 820-1045cm corresponds to the bending vibration between aluminum atoms and nitrogen atoms. -1 The absorption peaks in the wavenumber range of 1050-1190 cm-1 mainly correspond to the bending vibrations between carbon atoms and between carbon atoms and nitrogen atoms in the cations. -1 The absorption peaks in the wavenumber range mainly correspond to the stretching vibrations between carbon atoms and between carbon atoms and nitrogen atoms in n-butyl, 1200-1480 cm -1 The absorption peaks in the wavenumber range mainly correspond to the bending vibrations between carbon atoms and hydrogen atoms, 1490-1650cm -1 The absorption peaks in the wavenumber range mainly correspond to the skeleton vibration of the imidazole ring, 2800~3200cm -1 The absorption peaks in the wavenumber range mainly correspond to the stretching vibrations between carbon atoms or nitrogen atoms and hydrogen atoms.

[0033] Figure 2 This is the NMR aluminum spectrum of the low-temperature molten salt prepared in Example 1 of the present invention. The displacement peaks of cations and anions are indicated in the figure.

[0034] Figure 3 This is a scanning electron microscope image of the metallic aluminum product prepared in Example 1 of the present invention.

[0035] Figure 4 This is an X-ray energy spectrum diagram of the metal aluminum product prepared in Example 1 of the present invention. The energy spectrum peak of aluminum has been marked in the figure. DETAILED DESCRIPTION

[0036] In order to facilitate understanding of the purpose and technical features of the present invention, the following examples are used for specific description. It should be clear that the protection scope of the present invention is not limited to the following examples, and all implementation methods that meet the purpose and technical features belong to the protection scope of the present invention.

[0037] Example 1

[0038] A low-temperature molten salt is obtained by mixing 1-n-butylimidazole and aluminum chloride in a molar ratio of 1:1.5 at 20° C. and a nitrogen atmosphere of 101.3 kPa for 2 hours.

[0039] The chemical structural formula of the 1-n-butylimidazole is

[0040] After characterization by infrared absorption spectrum and nuclear magnetic resonance spectrum, the mass purity of the prepared low-temperature molten salt is 99.6%. Among them, the cation is [AlCl2(1-n-butylimidazole)2] + , the anion is [Al2Cl7] - .

[0041] The low-temperature molten salt prepared above is used for electrolysis preparation of aluminum under an inert anode, and the reaction steps are as follows:

[0042] 1) Using the above-mentioned low-temperature molten salt as electrolyte, platinum as inert anode, glassy carbon as cathode, and constant voltage electrolysis method, aluminum was prepared by low-temperature electrolysis in a nitrogen atmosphere, wherein the electrolysis temperature was 30°C, the electrolysis voltage was 3.3V, the gas pressure was 101.3kPa, and the reaction time was 3h.

[0043] 2) After the electrolysis is completed, the cathode is removed from the electrolyte under a nitrogen atmosphere and left to stand for 0.5 h, then rinsed with anhydrous ethanol and dried to obtain a metallic aluminum product.

[0044] Characterized by X-ray energy spectrum and atomic absorption spectrum, the mass purity of the metal aluminum product is 99.98%, the energy consumption for preparing each kilogram of aluminum is 7.8 kWh, and the current efficiency is 99.2%.

[0045] Example 2

[0046] A low-temperature molten salt is obtained by mixing 4-methylpyrazole and aluminum tribromide at a molar ratio of 1:1.2 at 15°C and an argon atmosphere of 101.5 kPa for 1.5 hours.

[0047] The chemical structural formula of the 4-methylpyrazole is

[0048] After characterization by infrared absorption spectrum and nuclear magnetic resonance spectrum, the mass purity of the prepared low-temperature molten salt is 99.5%. Among them, the cation is [AlBr2(4-methylpyrazole)2] + , the anion is [AlBr4] - and [Al2Br7] - .

[0049] The low-temperature molten salt prepared above is used for electrolysis preparation of aluminum under an inert anode, and the reaction steps are as follows:

[0050] 1) Using the above-mentioned low-temperature molten salt as electrolyte, glassy carbon as inert anode, graphite as cathode, and constant voltage electrolysis method, aluminum was prepared by low-temperature electrolysis under argon atmosphere, wherein the electrolysis temperature was 50°C, the electrolysis voltage was 3V, the gas pressure was 101.5kPa, and the reaction time was 1.5h.

[0051] 2) After the electrolysis is completed, the cathode is removed from the electrolyte under an argon atmosphere and left to stand for 0.5 h, then rinsed with anhydrous ethanol and dried to obtain a metallic aluminum product.

[0052] Characterized by X-ray energy spectrum and atomic absorption spectrum, the mass purity of the metal aluminum product is 99.94%, the energy consumption for preparing each kilogram of aluminum is 7.2 kWh, and the current efficiency is 98.5%.

[0053] Example 3

[0054] A low-temperature molten salt is obtained by mixing 2,4,5-trimethyloxazole and diethylaluminum bromide at a molar ratio of 1:0.6 at 25°C and a neon atmosphere of 101 kPa for 1 hour.

[0055] The chemical structural formula of the 2,4,5-trimethyloxazole is

[0056] After characterization by infrared absorption spectrum and nuclear magnetic resonance spectrum, the mass purity of the prepared low-temperature molten salt is 99.3%. Among them, the cation is [Al(C2H5)2(2,4,5-trimethyloxazole)4] + , the anion is [AlBr2(C2H5)2] - and [Al2Br3(C2H5)4] - .

[0057] The low-temperature molten salt prepared above is used for electrolysis preparation of aluminum under an inert anode, and the reaction steps are as follows:

[0058] 1) Using the above-mentioned low-temperature molten salt as electrolyte, graphite as inert anode, and aluminum as cathode, aluminum was prepared by low-temperature electrolysis in a neon atmosphere by constant voltage electrolysis, wherein the electrolysis temperature was 60°C, the electrolysis voltage was 2.8V, the gas pressure was 101kPa, and the reaction time was 2.5h.

[0059] 2) After the electrolysis is completed, the cathode is removed from the electrolyte under a neon atmosphere and left to stand for 0.5 h, then rinsed with anhydrous ethanol and dried to obtain a metallic aluminum product.

[0060] Characterized by X-ray energy spectrum and atomic absorption spectrum, the mass purity of the metal aluminum product is 99.95%, the energy consumption for preparing each kilogram of aluminum is 6.7 kWh, and the current efficiency is 99.3%.

[0061] Example 4

[0062] A low-temperature molten salt is obtained by mixing 3,5-dimethylisoxazole and ethylaluminum dichloride at a molar ratio of 1:0.75 at 25° C. and a nitrogen atmosphere of 101.4 kPa for 1.5 hours.

[0063] The chemical structural formula of the 3,5-dimethylisoxazole is

[0064] After characterization by infrared absorption spectrum and nuclear magnetic resonance spectrum, the mass purity of the prepared low-temperature molten salt is 99.4%. Among them, the cation is [Al(C2H5)2(3,5-dimethylisoxazole)4] + , the anion is [Al2Cl6C2H5] - .

[0065] The low-temperature molten salt prepared above is used for electrolysis preparation of aluminum under an inert anode, and the reaction steps are as follows:

[0066] 1) Using the above-mentioned low-temperature molten salt as electrolyte, ruthenium as inert anode, platinum as cathode, and constant voltage electrolysis method, aluminum was prepared by low-temperature electrolysis in a nitrogen atmosphere, wherein the electrolysis temperature was 55°C, the electrolysis voltage was 2.7V, the gas pressure was 101.4kPa, and the reaction time was 2h.

[0067] 2) After the electrolysis is completed, the cathode is removed from the electrolyte under a nitrogen atmosphere and left to stand for 0.5 h, then rinsed with anhydrous ethanol and dried to obtain a metallic aluminum product.

[0068] Characterized by X-ray energy spectrum and atomic absorption spectrum, the mass purity of the metal aluminum product is 99.93%. The energy consumption for preparing each kilogram of aluminum is 6.4 kWh, and the current efficiency is 98.8%.

[0069] Example 5

[0070] A low-temperature molten salt is obtained by mixing 2-n-hexyl-1,3,4-oxadiazole and ethylaluminum dibromide at a molar ratio of 1:0.72 at 20° C. and in a helium atmosphere of 101.3 kPa for 0.8 h.

[0071] The chemical structural formula of the 2-n-hexyl-1,3,4-oxadiazole is

[0072] After characterization by infrared absorption spectrum and nuclear magnetic resonance spectrum, the mass purity of the prepared low-temperature molten salt is 99.5%. Among them, the cation is [Al(C2H5)2(2-n-hexyl-1,3,4-oxadiazole)4] + , the anion is [AlBr4] - and [Al2Br6C2H5] - .

[0073] The low-temperature molten salt prepared above is used for electrolysis preparation of aluminum under an inert anode, and the reaction steps are as follows:

[0074] 1) Using the above-mentioned low-temperature molten salt as electrolyte, glassy carbon as inert anode, and aluminum as cathode, aluminum was prepared by low-temperature electrolysis in a helium atmosphere by constant voltage electrolysis, wherein the electrolysis temperature was 70°C, the electrolysis voltage was 3.1V, the gas pressure was 101.3kPa, and the reaction time was 1h.

[0075] 2) After the electrolysis is completed, the cathode is removed from the electrolyte under a helium atmosphere and left to stand for 0.5 h, then rinsed with anhydrous ethanol and dried to obtain a metallic aluminum product.

[0076] Characterized by X-ray energy spectrum and atomic absorption spectrum, the mass purity of the metal aluminum product is 99.92%, the energy consumption for preparing each kilogram of aluminum is 7.5 kWh, and the current efficiency is 98.4%.

[0077] Example 6

[0078] A low-temperature molten salt is obtained by mixing 3,4-dimethyl-1,2,5-oxadiazole and aluminum chloride in a molar ratio of 1:0.55 at 23°C and 101.1 kPa argon atmosphere for 0.5 h.

[0079] The chemical structural formula of the 3,4-dimethyl-1,2,5-oxadiazole is

[0080] After characterization by infrared absorption spectrum and nuclear magnetic resonance spectrum, the mass purity of the prepared low-temperature molten salt is 99.7%. Among them, the cation is [AlCl2(3,4-dimethyl-1,2,5-oxadiazole)4] + , the anion is [AlCl4] - and [Al2Cl7] - .

[0081] The low-temperature molten salt prepared above is used for electrolysis preparation of aluminum under an inert anode, and the reaction steps are as follows:

[0082] 1) Using the above-mentioned low-temperature molten salt as electrolyte, palladium as inert anode, graphite as cathode, and constant voltage electrolysis method under argon atmosphere, aluminum was prepared by low-temperature electrolysis. The electrolysis temperature was 40°C, the electrolysis voltage was 3.5V, the gas pressure was 101.1kPa, and the reaction time was 2.5h.

[0083] 2) After the electrolysis is completed, the cathode is removed from the electrolyte under an argon atmosphere and left to stand for 0.5 h, then rinsed with anhydrous ethanol and dried to obtain a metallic aluminum product.

[0084] According to the characterization of X-ray energy spectrum and atomic absorption spectrum, the mass purity of the metal aluminum product is 99.96%. The energy consumption for preparing each kilogram of aluminum is 8 kWh, and the current efficiency is 99.1%.

[0085] Example 7

[0086] A low-temperature molten salt is obtained by mixing 1-n-propyl-1,2,4-triazole and aluminum triiodide at a molar ratio of 1:1.4 at 18°C ​​and 101.6 kPa krypton atmosphere for 1 hour. Characterized by infrared absorption spectrum and nuclear magnetic resonance spectrum, the mass purity of the prepared low-temperature molten salt is 99.3%. The cation is [AlI2(1-n-propyl-1,2,4-triazole)2] + , the anion is [AlI4] - and [Al2I7] - .

[0087] The chemical structural formula of the 1-n-propyl-1,2,4-triazole is

[0088] The low-temperature molten salt prepared above is used for electrolysis preparation of aluminum under an inert anode, and the reaction steps are as follows:

[0089] 1) Using the above-mentioned low-temperature molten salt as electrolyte, titanium as inert anode, glassy carbon as cathode, and constant voltage electrolysis method in krypton atmosphere, aluminum was prepared by low-temperature electrolysis. The electrolysis temperature was 35°C, the electrolysis voltage was 3.8V, the gas pressure was 101.6kPa, and the reaction time was 2h.

[0090] 2) After the electrolysis is completed, the cathode is removed from the electrolyte under a krypton atmosphere and left to stand for 0.5 h, then rinsed with anhydrous ethanol and dried to obtain a metallic aluminum product.

[0091] Characterized by X-ray energy spectrum and atomic absorption spectrum, the mass purity of the metal aluminum product is 99.94%, the energy consumption for preparing each kilogram of aluminum is 8.3 kWh, and the current efficiency is 99.2%.

[0092] Example 8

[0093] A low-temperature molten salt is obtained by mixing 4-ethyl-1,2,4-triazole and aluminum tribromide at a molar ratio of 1:1.9 under a helium atmosphere of 10°C and 101.3 kPa for 3 hours.

[0094] The chemical structural formula of the 4-ethyl-1,2,4-triazole is

[0095] After characterization by infrared absorption spectrum and nuclear magnetic resonance spectrum, the mass purity of the prepared low-temperature molten salt is 99.5%. Among them, the cation is [AlBr2(4-ethyl-1,2,4-triazole)2] + , the anion is [Al2Br7] - and [Al3Br 10 ] - .

[0096] The low-temperature molten salt prepared above is used for electrolysis preparation of aluminum under an inert anode, and the reaction steps are as follows:

[0097] 1) Using the above-mentioned low-temperature molten salt as electrolyte, glassy carbon as inert anode, and graphite as cathode, aluminum was prepared by low-temperature electrolysis in a helium atmosphere by constant voltage electrolysis, wherein the electrolysis temperature was 65°C, the electrolysis voltage was 3.3V, the gas pressure was 101.3kPa, and the reaction time was 1.5h.

[0098] 2) After the electrolysis is completed, the cathode is removed from the electrolyte under a helium atmosphere and left to stand for 0.5 h, then rinsed with anhydrous ethanol and dried to obtain a metallic aluminum product.

[0099] Characterized by X-ray energy spectrum and atomic absorption spectrum, the mass purity of the metal aluminum product is 99.92%, the energy consumption for preparing each kilogram of aluminum is 7.9 kWh, and the current efficiency is 98.4%.

[0100] Example 9

[0101] A low-temperature molten salt is obtained by mixing 2-n-pentylthiophene and aluminum triiodide at a molar ratio of 1:1.8 at 26°C and a krypton atmosphere of 101.6 kPa for 2.5 hours.

[0102] The chemical structural formula of the 2-n-pentylthiophene is

[0103] After characterization by infrared absorption spectrum and nuclear magnetic resonance spectrum, the mass purity of the prepared low-temperature molten salt is 99.5%. Among them, the cation is [AlI2(2-n-pentylthiophene)2] + , the anion is [Al2I7] - and [Al3I 10 ] - .

[0104] The low-temperature molten salt prepared above is used for electrolysis preparation of aluminum under an inert anode, and the reaction steps are as follows:

[0105] 1) Using the above-mentioned low-temperature molten salt as electrolyte, graphite as inert anode, glassy carbon as cathode, and constant voltage electrolysis method in krypton atmosphere, aluminum was prepared by low-temperature electrolysis. The electrolysis temperature was 45°C, the electrolysis voltage was 3.4V, the gas pressure was 101.6kPa, and the reaction time was 2.3h.

[0106] 2) After the electrolysis is completed, the cathode is removed from the electrolyte under a krypton atmosphere and left to stand for 0.5 h, then rinsed with anhydrous ethanol and dried to obtain a metallic aluminum product.

[0107] Characterized by X-ray energy spectrum and atomic absorption spectrum, the mass purity of the metal aluminum product is 99.92%, the energy consumption for preparing each kilogram of aluminum is 8.2 kWh, and the current efficiency is 99.3%.

[0108] Example 10

[0109] A low-temperature molten salt is obtained by mixing 4-methylthiazole and dimethylaluminum chloride in a molar ratio of 1:0.7 at 30° C. and in a xenon atmosphere of 101.2 kPa for 1.2 hours.

[0110] The chemical structural formula of the 4-methylthiazole is

[0111] After characterization by infrared absorption spectrum and nuclear magnetic resonance spectrum, the mass purity of the prepared low-temperature molten salt is 99.4%. Among them, the cation is [Al(CH3)2(4-methylthiazole)4] + , the anion is [AlCl2(CH3)2] - and [Al2Cl3(CH3)4] - .

[0112] The low-temperature molten salt prepared above is used for electrolysis preparation of aluminum under an inert anode, and the reaction steps are as follows:

[0113] 1) Using the above-mentioned low-temperature molten salt as electrolyte, platinum as inert anode, and aluminum as cathode, aluminum was prepared by low-temperature electrolysis in a xenon atmosphere by constant voltage electrolysis, wherein the electrolysis temperature was 75°C, the electrolysis voltage was 2.6V, the gas pressure was 101.3kPa, and the reaction time was 1.5h.

[0114] 2) After the electrolysis is completed, the cathode is removed from the electrolyte under a xenon atmosphere and left to stand for 0.5 h, then rinsed with anhydrous ethanol and dried to obtain a metallic aluminum product.

[0115] Characterized by X-ray energy spectrum and atomic absorption spectrum, the mass purity of the metal aluminum product is 99.96%, the energy consumption for preparing each kilogram of aluminum is 6.2 kWh, and the current efficiency is 98.7%.

[0116] Embodiment 11

[0117] A low-temperature molten salt is obtained by mixing isothiazole and methyl aluminum diiodide at a molar ratio of 1:0.8 at 22° C. and in a xenon atmosphere of 101.5 kPa for 1.5 hours.

[0118] The chemical structural formula of the isothiazole is

[0119] After characterization by infrared absorption spectrum and nuclear magnetic resonance spectrum, the mass purity of the prepared low-temperature molten salt is 99.6%. Among them, the cation is [Al(CH3)2(isothiazole)4] + , the anion is [Al2I6CH3] - and [Al3I8(CH3)2] - .

[0120] The low-temperature molten salt prepared above is used for electrolysis preparation of aluminum under an inert anode, and the reaction steps are as follows:

[0121] 1) Using the above-mentioned low-temperature molten salt as electrolyte, titanium as inert anode, platinum as cathode, and constant voltage electrolysis method in a xenon atmosphere, aluminum was prepared by low-temperature electrolysis. The electrolysis temperature was 50°C, the electrolysis voltage was 3.2V, the gas pressure was 101.5kPa, and the reaction time was 2.6h.

[0122] 2) After the electrolysis is completed, the cathode is removed from the electrolyte under a xenon atmosphere and left to stand for 0.5 h, then rinsed with anhydrous ethanol and dried to obtain a metallic aluminum product.

[0123] Characterized by X-ray energy spectrum and atomic absorption spectrum, the mass purity of the metal aluminum product is 99.93%. The energy consumption for preparing each kilogram of aluminum is 7.6 kWh, and the current efficiency is 98.6%.

[0124] Example 12

[0125] A low-temperature molten salt is obtained by mixing pyrrolidine and aluminum chloride in a molar ratio of 1:1.95 at 28°C and a nitrogen atmosphere of 101 kPa for 2.6 hours.

[0126] The chemical structural formula of the pyrrolidine is

[0127] After characterization by infrared absorption spectrum and nuclear magnetic resonance spectrum, the mass purity of the prepared low-temperature molten salt is 99.8%. Among them, the cation is [AlCl2(pyrrolidine)2] + , the anion is [Al2Cl7] - and [Al3Cl 10 ] - .

[0128] The low-temperature molten salt prepared above is used for electrolysis preparation of aluminum under an inert anode, and the reaction steps are as follows:

[0129] 1) Using the above-mentioned low-temperature molten salt as electrolyte, palladium as inert anode, platinum as cathode, and constant voltage electrolysis method, aluminum was prepared by low-temperature electrolysis in a nitrogen atmosphere, wherein the electrolysis temperature was 80°C, the electrolysis voltage was 2.3V, the gas pressure was 101kPa, and the reaction time was 0.5h.

[0130] 2) After the electrolysis is completed, the cathode is removed from the electrolyte under a nitrogen atmosphere and left to stand for 0.5 h, then rinsed with anhydrous ethanol and dried to obtain a metallic aluminum product.

[0131] Characterized by X-ray energy spectrum and atomic absorption spectrum, the mass purity of the metal aluminum product is 99.97%, the energy consumption for preparing each kilogram of aluminum is 5.5 kWh, and the current efficiency is 99.2%.

[0132] Example 13

[0133] A low-temperature molten salt is obtained by mixing 3,5-dimethylpiperidine and diethylaluminum iodide at a molar ratio of 1:0.65 at 16°C and 101.4 kPa neon atmosphere for 2 hours.

[0134] The chemical structural formula of the 3,5-dimethylpiperidine is

[0135] After characterization by infrared absorption spectrum and nuclear magnetic resonance spectrum, the mass purity of the prepared low-temperature molten salt is 99.2%. Among them, the cation is [Al(C2H5)2(3,5-dimethylpiperidinium)4] + , the anion is [AlI2(C2H5)2] - and [Al2I3(C2H5)4] - .

[0136] The low-temperature molten salt prepared above is used for electrolysis preparation of aluminum under an inert anode, and the reaction steps are as follows:

[0137] 1) Using the above-mentioned low-temperature molten salt as electrolyte, ruthenium as inert anode, and aluminum as cathode, aluminum was prepared by low-temperature electrolysis in a neon atmosphere by constant voltage electrolysis, wherein the electrolysis temperature was 70°C, the electrolysis voltage was 2.9V, the gas pressure was 101.4kPa, and the reaction time was 0.8h.

[0138] 2) After the electrolysis is completed, the cathode is removed from the electrolyte under a neon atmosphere and left to stand for 0.5 h, then rinsed with anhydrous ethanol and dried to obtain a metallic aluminum product.

[0139] Characterized by X-ray energy spectrum and atomic absorption spectrum, the mass purity of the metal aluminum product is 99.91%, the energy consumption for preparing each kilogram of aluminum is 6.9 kWh, and the current efficiency is 99.1%.

Claims

1. A method for preparing a low-temperature molten salt, characterized in that: The invention is prepared by mixing one of imidazole compounds, pyrazole compounds, oxazole compounds, isoxazole compounds, oxadiazole compounds, triazole compounds, thiophene compounds, thiazole compounds, isothiazole compounds, pyrrolidine compounds and piperidine compounds with aluminum halide in a molar ratio of 1:0.55-1.95 under an inert atmosphere of 10-30°C and 101-101.6 kPa for 0.5-3 hours.

2. The method for preparing a low-temperature molten salt according to claim 1, characterized in that: The chemical structural formula of the imidazole compound is The chemical structural formula of the pyrazole compound is The chemical structural formula of the oxazole compound is The chemical structural formula of the isoxazole compound is The chemical structural formula of the oxadiazole compound is The chemical structural formula of the triazole compound is or The chemical structural formula of the thiophene compound is The chemical structural formula of the thiazole compound is The chemical structural formula of the isothiazole compound is The chemical structural formula of the pyrrolidine compound is The chemical structural formula of the piperidine compound is Among them, R1~R 11 represents a C1-C6 alkyl group or a hydrogen atom.

3. The method for preparing a low-temperature molten salt according to claim 1, characterized in that: The aluminum halide is one of aluminum trichloride, aluminum tribromide, aluminum triiodide, alkylaluminum dichloride, dialkylaluminum chloride, alkylaluminum dibromide, dialkylaluminum bromide, alkylaluminum diiodide, and dialkylaluminum iodide. The chemical structural formula of the alkylaluminum dichloride is The chemical structural formula of the dialkylaluminum chloride is The chemical structural formula of the alkylaluminum dibromide is The chemical structural formula of the dialkylaluminum bromide is The chemical structural formula of the alkyl aluminum diiodide is The chemical structural formula of the dialkylaluminum iodide is Among them, R, R1, and R2 in all chemical structural formulas represent methyl or ethyl.

4. The method for preparing a low-temperature molten salt according to claim 1, characterized in that: The inert atmosphere is composed of one of helium, neon, argon, krypton, xenon and nitrogen with a mass content higher than 99.9%.

5. A low-temperature molten salt prepared by the method for preparing a low-temperature molten salt according to any one of claims 1 to 4.

6. The method for using low-temperature molten salt in electrolytic aluminum according to claim 5, characterized in that: The following steps are involved: 1) Using low-temperature molten salt as electrolyte, using one of platinum, palladium, ruthenium, titanium, graphite, and glassy carbon as inert anode, using one of graphite, glassy carbon, aluminum, and platinum as cathode, and using constant voltage electrolysis method to prepare aluminum at low temperature under inert atmosphere; wherein, the electrolysis temperature is 30-80° C., the electrolysis voltage is 2.3-3.8V, the gas pressure is 101-101.6kPa, and the reaction time is 0.5-3h; 2) After the electrolysis is completed, the cathode is removed from the electrolyte under an inert atmosphere and left to stand for 0.5 h, then rinsed with anhydrous ethanol and dried to obtain a metallic aluminum product.

7. The method for using low-temperature molten salt in electrolytic aluminum according to claim 5, characterized in that: The inert atmosphere is composed of one of helium, neon, argon, krypton, xenon and nitrogen with a mass content higher than 99.9%.

Images