CN101265588B - A method for producing aluminum by using ionic liquid low-temperature electrolytic alumina - Google Patents

Abstract

The invention relates to a method for producing aluminum by direct low-temperature electrolysis of aluminum oxide using ionic liquid, which is characterized in that aluminum oxide is dissolved in an ionic liquid of bisulfate (HSO ₄ ^- ) type anion as a low-temperature electrolyte, and direct current is directly used as raw material for aluminum oxide Solution, the cell voltage is higher than the decomposition voltage of alumina but lower than the electrochemical window of the ionic liquid, aluminum is precipitated at the cathode, and CO ₂ is produced at the anode. The ionic liquid adopted in the present invention has a wide range of sources, low price, good stability, high conductivity, wide electrochemical window, good thermal stability, environmental friendliness and can effectively dissolve alumina at low temperature. The ionic liquid is used to dissolve alumina as The low-temperature electrolyte greatly reduces the electrolysis temperature and cell voltage, has high energy utilization rate and greatly slows down the corrosion of equipment.

Description

A method for producing aluminum by using ionic liquid low-temperature electrolytic alumina

Technical field:

The invention belongs to the field of metal smelting, and specifically relates to a method for producing aluminum by using ionic liquid low-temperature electrolytic alumina.

Background technique:

The aluminum industry is the largest electrochemical industry in the world, and its output is second only to steel. Because of its light weight, good thermal and electrical conductivity, machinability and alloy composition, a large amount of aluminum is used in construction and structural materials, transportation devices, beverage cans, packaging materials, power transmission lines, daily necessities, machinery equipment etc.

The modern aluminum industry mainly uses the Hall-Héroult method to produce aluminum, that is, the cryolite-alumina molten salt electrolysis method. In this method, alumina is used as raw material, molten cryolite is used as electrolyte, direct current is passed into the electrolytic cell, and electrochemical reaction occurs at the cathode and _anode . and CO (20% to 25%). This method consumes 14000kW.h of electricity, 550-600kg of carbon anode, 30-50kg of fluorine salt, and 2 tons of alumina for every ton of aluminum produced by this method, and the electricity cost accounts for about 20%. However, the Hall-Héroult method has many disadvantages: the energy utilization rate is low, less than 50%; the electrolysis temperature is high, generally between 950°C and 970°C, which requires strict equipment and materials; the environment is seriously polluted, and a large amount of CO ₂ is produced. CO and harmful gases containing fluorine. And with energy shortages, rising electricity costs and global alumina prices continuing to rise, the electrolytic aluminum industry is moving towards a marginal profit industry. Reducing the cost of electrolytic aluminum is a top priority for the electrolytic aluminum industry.

Electrolysis of aluminum in low temperature electrolyte solution can effectively reduce the cell voltage. Each tank reduces the voltage by 0.1V, and 1 ton of aluminum will save electricity by 330kW.h; at the same time, the solubility of impurities in aluminum is reduced, and the corrosion of electrode materials and tank linings is also greatly slowed down. The current low-temperature aluminum electrolysis technology is still based on the Hall-Héroult method, using alumina as the raw material for aluminum smelting, with inert cathodes, inert anodes and insulating side walls, but the electrolysis temperature is still above 800 °C.

Chinese patent (CN1664170A) discloses a method for low-temperature production of aluminum and aluminum alloys, using AlCl ₃ type ionic liquid as a low-temperature electrolyte. They use alumina or aluminum-containing silicate minerals including bauxite, coal gangue, kaolin or kaolinite, kyanite, andalusite and sillimanite as raw materials to obtain anhydrous aluminum chloride by chlorination and further processing to obtain AlCl Type ₃ ionic liquid. Although the electrolysis temperature is effectively reduced, due to the harsh synthesis conditions of the AlCl ₃ -type ionic liquid, the properties are extremely unstable, sensitive to moisture in the air, and easily hydrolyzed to form HCl fumes, which need to be prepared and used in a vacuum or an inert atmosphere. Equipment can cause severe corrosion and pollute the environment. In addition, the existence of trace protons and oxide impurities will have a great impact on the properties of ionic liquids, greatly reducing the current efficiency and the purity of electrolytic aluminum. Throughout the whole process, it belongs to indirect electrolytic alumina, which has a long process, many side reactions, and many processes involved. The chlorination process is dangerous and pollutes the environment seriously, so it is not suitable for large-scale industrial production.

Invention content:

The purpose of the present invention is to overcome the defects of high electrolysis temperature, high energy consumption, high cost, and environmental pollution in the current electrolytic aluminum industry, and provide a method for producing aluminum by direct low-temperature electrolysis of alumina using ionic liquids, which has simple process flow and high electrolysis temperature. It has the characteristics of low, no fluoride emission and low production cost, and can be used in the method of industrial electrolytic aluminum.

The present invention is realized through the following technical steps:

(1) Synthesis of ionic liquid:

The present invention mainly adopts [emim]HSO ₄ and [bmim]HSO ₄ type ([Rmim]HSO ₄ ) ionic liquids as low-temperature electrolytes, and its synthesis reaction formula is as follows:

[mim]+RX=[Rmim]X (R=C ₂ H ₅ , C ₄ H ₇ , X=Br, Cl...)

[Rmim]X+NaHSO ₄ ＝[Rmim]HSO ₄ +NaX

[emim]X+NaHSO ₄ ＝[emim]HSO ₄ +NaX

[bmim]X+NaHSO ₄ =[bmim]HSO ₄ +NaX;

where mim is N-methylimidazole, [emim] ⁺ is N-ethyl-N'-methyl-imidazolium cation, [bmim] ⁺ is N-butyl-N'-methyl-imidazolium cation, [Rmim] ⁺ is the N-alkyl-N'-methyl-imidazolium cation.

The ionic liquid precursor [Rmim]X obtained by mixing and reacting N-methylimidazole and halogenated alkanes at a molar ratio of 1:1 was stirred at 50° C. for 24 hours. Then add a metered ratio of sodium bisulfate solid and a certain amount of acetone to it, and stir for 24 hours. The obtained ionic liquid was filtered with a sand core funnel, and the filtrate was extracted with CH ₂ Cl ₂ . Then, the CH ₂ Cl ₂ and acetone in the filtrate were removed by vacuum distillation and vacuum drying to finally obtain the product ionic liquid.

(2) Alumina electrolysis:

The ionic liquid and alumina are evenly mixed, and DC electrolysis is adopted; high-purity solid carbon is used as the anode and cathode respectively. The anode and cathode of the electrolytic cell are perpendicular to the cell surface, the distance between them is 3-3.5cm, the cell voltage is 2.0-2.5V, the anode current density is 0.65-0.70A/cm ² , and the electrolysis temperature is 100-200°C. The electrolytic cells are connected in series to form a series of electrolytic cells. The anode generates CO ₂ , the cathode obtains aluminum, and the current efficiency is greater than 95%. DC power consumption is 8-10KWh/kgAl.

Features of the present invention:

1. The present invention adopts ionic liquid to dissolve alumina as electrolyte to produce aluminum. As an electrolyte, ionic liquids are stable in nature, non-toxic and harmless, high in electrical conductivity, wide in electrochemical windows, good in thermal stability, stable in water vapor, easy to recycle and separate, and environmentally friendly.

2. The present invention greatly reduces the electrolysis temperature from 950°C to 970°C to 100°C to 200°C, effectively reduces the voltage of the electrolytic cell, improves the current efficiency, reduces energy consumption, and delays the corrosion of equipment at the same time.

Detailed ways:

Example 1

Using N-methylimidazole to react with C ₂ H ₅ Br, the two raw materials were mixed according to the molar ratio of 1:1, and stirred at 50°C for 24 hours to obtain [emim]Br. Then add solid sodium bisulfate in an equimolar ratio (based on the amount of N-methylimidazole) and a certain amount of acetone, and stir for 24 hours. The obtained ionic liquid was filtered with a sand core funnel, the filtrate was extracted with CH ₂ Cl ₂ , and CH ₂ Cl ₂ and acetone in the filtrate were removed by vacuum distillation and vacuum drying to obtain the product ionic liquid [emim]HSO ₄ .

The obtained ionic liquid is mixed evenly with industrial alumina, and direct current electrolysis is adopted. Use high-purity solid carbon as the anode and cathode. The anode and cathode of the electrolytic cell are perpendicular to the cell surface, the distance between them is 3.2cm, the cell voltage is 2.0V, the anode current density is 0.65A/cm ² , and the electrolysis temperature is 100°C. The electrolytic cells are connected in series to form a series of electrolytic cells. The anode generates CO ₂ , and the cathode obtains aluminum, with a current efficiency of 98%. The DC power consumption is 8KWh/kg·Al.

Example 2

[bmim]Br was obtained by mixing N-methylimidazole and C ₄ H ₉ Br in a molar ratio of 1:1.2 and stirring at 50°C for 48 hours. Then add solid sodium bisulfate and a certain amount of acetone at a molar ratio of 1:1.2 (based on the amount of N-methylimidazole) and stir at 50° C. for 12 hours. The obtained ionic liquid was filtered with a sand core funnel, and the filtrate was extracted with CH ₂ Cl ₂ . Then CH ₂ Cl ₂ and acetone in the filtrate were removed by vacuum distillation and vacuum drying to obtain the product ionic liquid [bmim]HSO ₄ .

Mix the ionic liquid and industrial alumina evenly, and conduct DC electrolysis. Use high-purity solid carbon as the anode and cathode. The anode and cathode of the electrolytic cell are perpendicular to the cell surface, and the distance between them is 3cm. The cell voltage is 2.1V, the anode current density is 0.70A/cm ² , and the electrolysis temperature is 120°C. The electrolytic cells are connected in series to form a series of electrolytic cells. The anode generates CO ₂ , and the cathode obtains aluminum, with a current efficiency of 95%. The DC power consumption is 9KW/kg·Al.

Example 3

[bmim]Cl was obtained by mixing N-methylimidazole and C ₄ H ₉ Cl in a molar ratio of 1:1.3, stirring at 50°C for 24 hours. Then add solid sodium bisulfate and a certain amount of acetone at a molar ratio of 1:1.3 (based on the amount of N-methylimidazole) to it, and stir at 50° C. for 24 hours. The obtained ionic liquid was filtered with a sand core funnel, and the filtrate was extracted with CH ₂ Cl ₂ . Then CH ₂ Cl ₂ and acetone in the filtrate were removed by vacuum distillation and vacuum drying to obtain the product ionic liquid [bmim]HSO ₄ .

Mix the ionic liquid and industrial alumina evenly, and conduct DC electrolysis. Use high-purity solid carbon as the anode and cathode. The anode and cathode of the electrolytic cell are perpendicular to the cell surface, the distance between them is 3.5cm, the cell voltage is 2.2V, the anode current density is 0.68A/cm ² , and the electrolysis temperature is 130°C. The electrolytic cells are connected in series to form a series of electrolytic cells. The anode generates CO ₂ , and the cathode obtains aluminum, with a current efficiency of 97%. The DC power consumption is 9.2KW/kg·Al.

Example 4

[emim]Cl was obtained by mixing N-methylimidazole and C ₂ H ₅ Cl at a molar ratio of 1:1.4, stirring at 50°C for 48 hours. Then add solid sodium bisulfate and a certain amount of acetone at a molar ratio of 1:1.4 (based on the amount of N-methylimidazole) therein, and stir at 50° C. for 12 hours. The obtained ionic liquid was filtered with a sand core funnel, and the filtrate was extracted with CH ₂ Cl ₂ . Then CH ₂ Cl ₂ and acetone in the filtrate were removed by vacuum distillation and vacuum drying to obtain the product ionic liquid [emim]HSO ₄ .

Mix the ionic liquid and industrial alumina evenly, and conduct DC electrolysis. Use high-purity solid carbon as the anode and cathode. The anode and cathode of the electrolytic cell are perpendicular to the cell surface, the distance between them is 3.4cm, the cell voltage is 2.4V, the anode current density is 0.70A/cm ² , and the electrolysis temperature is 150°C. The electrolytic cells are connected in series to form a series of electrolytic cells. The anode generates CO ₂ , and the cathode obtains aluminum, with a current efficiency of 96%. The DC power consumption is 9.6KW/kg·Al.

Example 5

The ionic liquid precursor obtained by mixing and reacting N-methylimidazole and [emim]Br at a molar ratio of 1:1.5 and stirring at 50° C. for 24 h. Then add solid sodium bisulfate and a certain amount of acetone at a molar ratio of 1:1.5 (based on the amount of N-methylimidazole) therein, and stir at 50° C. for 24 hours. The obtained ionic liquid was filtered with a sand core funnel, and the filtrate was extracted with CH ₂ Cl ₂ . Then CH ₂ Cl ₂ and acetone in the filtrate were removed by vacuum distillation and vacuum drying to obtain the product ionic liquid [emim]HSO ₄ .

Mix the ionic liquid and industrial alumina evenly, and conduct DC electrolysis. Use high-purity solid carbon as the anode and cathode. The anode and cathode of the electrolytic cell are perpendicular to the cell surface, the distance between them is 3.5cm, the cell voltage is 2.5V, the anode current density is 0.66A/cm ² , and the electrolysis temperature is 200°C. The electrolytic cells are connected in series to form a series of electrolytic cells. The anode generates CO ₂ , and the cathode obtains aluminum, with a current efficiency of 97%. DC power consumption is 10KWh/kg·Al.

Claims (2)

1, a kind of method adopting ionic liquid low-temperature electrolytic aluminum oxide to produce aluminum is characterized in that directly taking aluminum oxide as electrolytic raw material, cation is the imidazole class cation that alkyl replaces, anion is that the ionic liquid of bisulfate ion is electrolyte; The ionic liquid is evenly mixed with industrial alumina, and direct current electrolysis is adopted. During electrolysis, the cell voltage is higher than the decomposition voltage of alumina but lower than the electrochemical window of the ionic liquid; CO ₂ is generated at the anode, and aluminum is obtained at the cathode. 2. A method for producing aluminum by using ionic liquid low-temperature electrolytic alumina as claimed in claim 1, characterized in that it directly uses industrial-grade alumina as raw material, and high-purity solid carbon as the anode and cathode; the current density is 0.65 to 0.70 A/cm ² , the cell voltage is 2.0-2.5V, the pole distance is 3-3.5cm, and the electrolysis temperature is 100-200°C.