CN105386076A - An improved method for producing carbon nanotube system by high-temperature electrolysis of CO2 - Google Patents

Abstract

The present invention relates to an improved method for the carbon nanotube system produced by high-temperature electrolysis of _CO2 . The system includes an electrolysis unit, an electric heating unit and an inert gas protection unit. The electric heating unit heats the electrolysis unit. The electrolysis unit consists of a DC power supply, a cathode, Composed of anode, electrolytic cell and electrolyte. The electrolyte is a mixture of molten carbonate and molten oxide. The electrolysis temperature is between 610 and 690°C. In the mixture, the molar ratio of oxide to carbonate is in the interval (0,0.2] Constant current electrolysis or constant voltage electrolysis can be used inside. When using constant current electrolysis, the current density of the DC power supply is controlled between 20 ~ 500mA/cm ² . When using constant voltage electrolysis, the voltage of the DC power supply is controlled at 2.2V ~ 3.2V During electrolysis, carbon nanotubes and CO are obtained at the cathode, O ₂ is obtained at the anode, and the electrolyte absorbs the replenished CO ₂ and reacts with CO ₂ to regenerate. This system generates carbon nanotubes in one step, with simple reactions and few by-products. Good performance, by introducing inert gas into the reaction system, delaying the corrosion rate of electrodes and electrolytic cells, thereby improving the corrosion resistance of the entire system, so that the system has the characteristics of cleanliness, energy saving, high efficiency, safety and sustainability Energy saving and emission reduction and _CO2 resource utilization provide new ways.

Description

An improved method for producing carbon nanotube system by high-temperature electrolysis of CO2

technical field

The invention relates to an improved method for producing a carbon nanotube system by high-temperature electrolysis of CO ₂ , and belongs to the fields of energy saving and emission reduction and resource utilization of CO ₂ .

Background technique

Since the industrial revolution, the overexploitation of fossil fuels (coal, oil, natural gas, etc.) has increased the concentration of CO ₂ in the atmosphere from 0.27‰ at the beginning of the last century to more than 0.4‰ now. According to statistics, the CO ₂ produced by fossil fuel combustion is as high as 6Gt in the world every year. As of 2013, fossil energy provided 90% of the world's total energy demand, which means that CO ₂ emissions will continue to increase in the future. However, as the final product of the combustion process of carbonaceous substances, CO ₂ is also the most abundant C1 resource in nature. Therefore, exploring the chemical conversion and utilization technology of CO ₂ is of great significance for both environmental protection and effective resource utilization.

At present, CO ₂ chemical conversion technology mainly focuses on catalytic activation to synthesize organic fuels or chemical raw materials, such as CH ₄ , CO+H ₂ , urea, methanol, etc. Cong Yu et al. used ultrafine Cu-ZnO-ZrO ₂ catalyst to convert carbon dioxide into methanol with a yield as high as 73.4g(k h) ^-1 , higher than the industrial CH ₃ OH catalyst Cu-ZnO-Al ₂ O ₃ ; Tomishige et al. An appropriate amount of 2,2-dimethoxypropane was mixed into the CeO ₂ -ZrO ₂ catalyst system, and the catalyst system was used to promote the formation of dimethyl carbonate from carbon dioxide and methanol; Choudhary et al. used NiO-CaO catalysts to convert CO ₂ to CH The conversion of ₄ reached 99%, and the selectivities of both CO and _H2 reached 100%. The above reactions all need to be carried out under relatively harsh conditions, such as high temperature, high pressure, catalyst, etc., so special reactors need to be equipped, which are expensive and have a short service life. In the reaction process, due to the low performance of the catalyst, it is easy to deactivate at high temperature, and it is also prone to danger in the production process. Therefore, there are still many challenges and difficulties in the use of high-pressure catalytic hydrogenation to realize the resource utilization of carbon dioxide.

Compared with the above very harsh conversion methods, in recent years, the safe, clean and easy-to-operate electrochemical capture conversion CO ₂ technology has become one of the research hotspots in the field of CO ₂ resource utilization. At present, the research on the electrochemical reduction of _CO2 mainly focuses on the electrolysis of _CO2 in aqueous solvents or non-aqueous organic solvents. In addition, as a highly stable non-combustible molecule, _CO2 has excellent thermodynamic stability. Therefore, it is very difficult to directly perform electrolytic reduction on it, requiring high energy consumption (high electrolysis voltage), and at the same time, the electrolytic reaction is very complicated, and the efficiency and selectivity are poor. Based on this, it is necessary to develop a low-cost, simple and efficient method and device for resource utilization of CO ₂ to obtain better economic, social and environmental benefits.

Contents of the invention

The present invention provides a _CO2 resource utilization method with simple system, energy saving, low cost, high efficiency and corrosion resistance, and an improved method of high-temperature electrolysis of _CO2 to produce carbon nanotubes. The system can operate at low electrolysis voltage and relatively low temperature Under this circumstance, the resource utilization of _CO2 can be realized, and carbon nanotubes, which are very valuable in nanotechnology, electronics, optics and other fields of material science and technology, can be produced, and the electrolysis reaction is relatively simple, and carbon nanotubes can be generated in one step. Good corrosion resistance and few by-products. In addition, the system is protected by inert gas (He, Ar, Ne) to improve its corrosion resistance.

The purpose of the present invention is achieved through the following technical solutions:

An improved system for producing carbon nanotubes by high-temperature electrolysis of CO ₂ , the system includes an electrolysis unit and an electric heating unit, the electric heating unit heats the electrolysis unit, and the electrolysis unit is composed of a DC power supply, a cathode, an anode, an electrolytic cell and an electrolyte, It is characterized in that: the electrolyte is a mixture of molten carbonate and molten oxide, in the mixture, the molar ratio of oxide to carbonate is in the interval (0,0.2], the electrolysis temperature is between 610-690°C, Use constant current electrolysis or constant voltage electrolysis, when using constant current electrolysis, the current density of the DC power supply is controlled between 20 ~ 500mA/ ^cm2 , when using constant voltage electrolysis, the voltage of the DC power supply is controlled between 2.2V ~ 3.2V ; In electrolysis, carbon nanotubes and CO are obtained at the cathode, O ₂ is obtained at the anode, and the electrolyte and CO ₂ react to be regenerated; the system also includes an inert gas protection unit, which is used to feed inert gas into the electrolysis reaction system to delay electrode and the corrosion rate of the electrolytic cell, thereby improving the corrosion resistance of the entire system, the inert gas protection unit can adopt helium, argon or neon gas sealed in steel cylinders.

The electrolytic reaction mechanism is:

Anode reaction: 2O ^2- -4e ^- ＝O ₂

Cathode reaction: CO ₃ ^2- +4e ^- ＝C+3O ^2-

CO ₃ ^2- +2e ^- ＝CO+2O ^2-

CO ₃ ^2- +3e ^- ＝1/2CO+1/2C+5/2O ^2-

Wherein the carbon nanotubes are enriched in the elemental carbon produced at the cathode.

Further, the current density of the DC power supply is 20-500mA/cm ² , the temperature of the electrolytic cell is 610-690°C; the current density of the DC power supply is preferably 100-400mA/cm ^{2 , and the} temperature of the electrolytic cell is preferably 627-677°C .

Further, the carbonate is Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , Rb ₂ CO ₃ , Cs ₂ CO ₃ , Fr ₂ CO ₃ , MgCO ₃ , CaCO ₃ , SrCO ₃ , BaCO ₃ , ZnCO One or a mixture of two or more of ₃ ; the oxides are Li ₂ O, Na ₂ O, K ₂ O, Rb ₂ O, Cs ₂ O, Fr ₂ O, MgO, CaO, SrO, BaO, ZnO, SiO _2. One or a mixture of Al ₂ O ₃ , Fe ₂ O ₃ .

Further, when the electrolyte is in a solid state, the electric heating unit provides heat energy required for the electrolyte to reach a completely molten state.

Further, the electric heating unit adopts ceramic or other high-temperature electric heating jackets, and the heating temperature is regulated by adjusting the transformer load.

Further, the inert gas protection unit adopts helium, argon or neon sealed in steel cylinders.

Further, the cathode material of the electrolysis unit is nickel, platinum, titanium, ruthenium, iridium, palladium, iron, tungsten, chromium, copper, gold, graphite or stainless steel, or an alloy formed of several of the above materials; The anode material of the electrolysis unit is nickel, platinum, titanium, ruthenium, iridium, palladium, iron, tungsten, chromium, copper, gold, graphite or stainless steel, or an alloy formed of several of the above materials.

Further, the electrolytic cell adopts high-purity corundum crucible, high-purity nickel or other high-temperature corrosion-resistant reactors.

Based on above-mentioned high-temperature electrolysis CO _The improved method of carbon nanotube system, comprises the following steps:

(1) Construct an electrolytic unit composed of a DC power supply, cathode, anode, electrolytic cell, electrolyte and an inert gas protection unit;

(2) heating the solid electrolyte by an electric heating unit to form a molten electrolyte;

(3) Control the temperature of the electrolytic cell to be constant at 610-690°C;

(4) Introduce CO ₂ into the electrolytic cell through the air duct. When using constant current electrolysis, control the current density of the DC power supply between 20 and 500mA/cm ² . When using constant voltage electrolysis, control the voltage of the DC power supply at 2.2 Between V and 3.2V, react for a certain period of time, the main product is simple carbon in one step in the main reaction, and carbon nanotubes are enriched in the simple carbon. The total reaction is:

CO ₂ =C+O _{2 ;}

CO ₂ =1/2O ₂ +CO;

CO ₂ =3/4O ₂ +1/2CO+1/2C;

The electrolytic reaction mechanism is:

Anode reaction: 2O ^2- -4e ^- ＝O ₂

Cathode reaction: CO ₃ ^2- +4e ^- ＝C+3O ^2-

CO ₃ ^2- +2e ^- ＝CO+2O ^2-

CO ₃ ^2- +3e ^- = 1/2CO+1/2C+5/2O ^2- .

Beneficial technical effects of the present invention are as follows:

1. During the electrolysis reaction process, the electric heating unit converts electric energy into heat energy, heats the electrolyte, and adjusts the heating temperature according to the different electrolytes; at the same time, it uses a DC power supply to provide electric energy, and adjusts the required electrolysis voltage or current according to the type of electrolyte and the heating temperature , through electrolysis of CO ₂ , carbon nanotubes and CO are obtained from the cathode, and O ₂ is obtained from the anode, which realizes the conversion and storage of electrical energy to chemical energy. During the electrolysis process, the electrolyte solution absorbs the replenished CO ₂ and reacts with CO ₂ to regenerate the electrolyte. Thereby realizing the recycling and resource utilization of _CO2 . .

2. The electrolytic mechanism of CO high _- temperature electrolysis of carbon nanotubes of the present invention is:

Anode reaction:

[1]2O ^{2- -4e-} ＝O ₂

Cathode reaction:

[2] Carbon formation: CO ₃ ^2- +4e ^- ＝C+3O ^2-

[3] Formation of carbon monoxide: CO ₃ ^2- +2e ^- ＝CO+2O ^2-

[4] Formation of carbon monoxide and carbon: CO ₃ ^2- +3e ^- ＝1/2CO+1/2C+5/2O ^2-

The addition of the negative and positive reactions results in the electrolytic reaction:

[5] M ₂ CO ₃ =C(s)+O ₂ +M ₂ O;

[6] M ₂ CO ₃ ＝CO+M ₂ O+1/2O ₂ ;

[7] M ₂ CO ₃ =1/2CO+1/2C+M ₂ O+3/4O ₂ ;

[8] Absorption reaction of CO ₂ : M ₂ O+CO ₂ =M ₂ CO ₃

Adding the electrolysis reactions [5], [6], [7] and the _CO2 absorption reaction [8], the total reaction of the electrolysis unit can be obtained:

[9] _CO2 ＝C+O2 _;

[10]CO ₂ =1/2O ₂ +CO;

[11]CO ₂ =3/4O ₂ +1/2CO+1/2C

The carbonate ions in the molten carbonate electrolyte are electrolyzed into solid carbon and CO (as shown in Equation [2] and Equation [3]), and simultaneously generate O ^2- . On the one hand, the released oxygen negative ions can react with CO ₂ in the atmosphere to regenerate carbonate (equation [8]), thereby realizing sustainable CO ₂ capture and electrochemical conversion, and can also migrate to the anode for oxidation to generate oxygen (equation [1]), forming a CO ₂ -CO ₃ ^2- -C+CO+O ₂ cycle system in which carbon nanotubes are rich in the elemental carbon generated at the cathode.

3. The system synthesizes carbon nanotubes by controlling the current density and electrolysis temperature. The electrolysis temperature is 610-690°C. Constant current electrolysis or constant voltage electrolysis is used. When constant current electrolysis is used, the current density of the DC power supply is controlled at 20-500mA /cm ² , when constant voltage electrolysis is used, the voltage of the DC power supply is controlled between 2.2V and 3.2V. After a certain period of electrolysis, the elemental carbon generated by the cathode contains a large amount of carbon nanotubes.

4. Compared with the existing technology, the system has the following outstanding features: first, the current density is greatly reduced, the current density is only 20-500mA/cm ² , and the electrolysis voltage is only 2.2V-3.2V; second: the use of A variety of carbonates and metal oxide mixtures are used as electrolytes, which not only lowers the melting point of the system, but also increases the ability of the electrolyte to capture carbon dioxide, greatly increasing the renewal speed of the electrolyte; third: the electrode material can be selected from cheap iron wire and nickel Chrome alloy wire, effectively reducing production costs.

5. The concrete has an inert gas protection unit, which slows down the corrosion rate of electrodes and electrolytic cells by passing inert gas into the reaction system, thereby improving the corrosion resistance of the entire system.

6. The present invention generates carbon nanotubes in one step, with simple reaction, few by-products, good selectivity and good corrosion resistance. At the same time, electric energy and electrochemical effects are used to construct a corrosion-resistant CO ₂ conversion carbon nanotube system, which constitutes a perfect energy conversion and storage system, which is clean, efficient, safe and sustainable, and contributes to energy saving and emission reduction and CO ₂ Resource utilization provides a new way.

Description of drawings

Fig. 1 system schematic diagram of the present invention

In the figure: 1 anode; ₂ electric heating mantle; ₃ electrolyte; 4 electrolytic cell; 5 cathode; 12 inert gas cylinders

detailed description

Comparative example: no inert gas protection unit is used in the system

Grind and mix 22gLi ₂ CO ₃ , 61gNa ₂ CO ₃ and 17gK ₂ CO ₃ in a mortar, and transfer them into a corundum crucible; respectively use nickel-chromium alloy wire and iron wire with a surface area of 50cm ² as anode and cathode ; Make the temperature constant at 610(±2)°C, and the current density constant at 20mA/cm ² . After 1 hour of reaction, the elemental carbon produced by the cathode contained a large number of carbon nanotubes. The anode nickel-chromium alloy wire is severely corroded, and only about 3.5cm ² remains.

Example 1

Grind, pulverize and mix 61gLi ₂ CO ₃ , 22gNa ₂ CO ₃ and 17gK ₂ CO ₃ in a mortar, transfer them into a corundum crucible; use nickel-chromium alloy wire and iron wire with a surface area of 10cm ² as anode and cathode respectively ; Make the temperature constant at 620(±2)°C, and the current density constant at 150mA/cm ² . After reacting for 1 hour, the elemental carbon produced by the cathode contained a large amount of carbon nanotubes, and the nickel-chromium alloy wire of the anode was almost unchanged, and its shape was complete.

Example 2

Grind and mix 61gLi ₂ CO ₃ , 22gNa ₂ CO ₃ , 17gK ₂ CO ₃ and 2.15gNa ₂ O in a mortar, and transfer them into a corundum crucible ^; The iron wire is used as anode and cathode; the temperature is kept constant at 630(±2)°C, and the current density is kept constant at 350mA/cm ² . After reacting for 0.8 hours, the elemental carbon produced by the cathode contained a large number of carbon nanotubes, and the nickel-chromium alloy wire of the anode was almost unchanged, and its shape was complete.

Example 3

Grind, pulverize and mix 20gMgCO ₃ , 42gSrCO ₃ , 30gBaCO ₃ and 3.17gK ₂ O in a mortar, transfer them into a corundum crucible ^; use nickel-chromium alloy wire and iron wire with a surface area of 5cm2 as anode and cathode respectively; The temperature was kept constant at 640(±2)°C, and the current density was kept constant at 450mA/cm ² . After reacting for 0.8 hours, the elemental carbon produced by the cathode contained a large number of carbon nanotubes, and the nickel-chromium alloy wire of the anode was almost unchanged, and its shape was complete.

Example 4

Grind and mix 61gLi ₂ CO ₃ , 22gNa ₂ CO ₃ , 17gK ₂ CO ₃ and 2.7gLi ₂ O in a mortar, and transfer them into a corundum crucible ^; The iron wire is used as anode and cathode; the temperature is kept constant at 650(±2)°C, and the current is kept constant at 500mA/cm ² . After reacting for 0.8 hours, the elemental carbon produced by the cathode contained a large number of carbon nanotubes, and the nickel-chromium alloy wire of the anode was almost unchanged, and its shape was complete.

Example 5

Grind and mix 46.5gLi ₂ CO ₃ , 16.5gNa ₂ CO ₃ , 12.75gK ₂ CO ₃ and 8.15gNa ₂ O in a mortar, transfer them into a corundum crucible ^; Alloy wire and iron wire are used as anode and cathode; the temperature is kept constant at 660 (±2)°C, and the voltage is kept constant at 2.2-2.5V. After reacting for 0.5 hours, the elemental carbon produced by the cathode contained a large amount of carbon nanotubes, and the nickel-chromium alloy wire of the anode had almost no change, and its shape was complete.

Example 6

Grind, pulverize and mix 20gMgCO ₃ , 42gSrCO ₃ , 30gBaCO ₃ and 1.1gLi ₂ O in a mortar, transfer them into a corundum crucible ^; use nickel-chromium alloy wire and iron wire with a surface area of 5cm2 as anode and cathode respectively; Keep the temperature constant at 670 (±2)°C, and the voltage constant at 2.5-3.2V. After reacting for 0.5 hours, the elemental carbon produced by the cathode contained a large amount of carbon nanotubes, and the nickel-chromium alloy wire of the anode had almost no change, and its shape was complete.

Example 7

Grind and mix 20gMgCO ₃ , 42gSrCO ₃ , 30gBaCO ₃ and 2gLi ₂ O in a mortar, and transfer them into a corundum crucible ^; use nickel-chromium alloy wire and iron wire with a surface area of 5cm2 as anode and cathode respectively; The temperature is constant at 680 (±2)°C, and the voltage is constant at 2.2-3.2V. After reacting for 0.5 hours, the elemental carbon produced by the cathode contained a large amount of carbon nanotubes, and the nickel-chromium alloy wire of the anode had almost no change, and its shape was complete.

Example 8

Grind, pulverize and mix 31gLi ₂ CO ₃ , 11gNa ₂ CO ₃ , 8.5gK ₂ CO ₃ and 3.5gLi ₂ O in a mortar, and transfer them into a corundum crucible ^; And iron wire as anode and cathode; keep the temperature constant at 690 (±2)°C, and the voltage constant at 2.5-3.2V. After reacting for 0.5 hours, the elemental carbon produced by the cathode contained a large amount of carbon nanotubes, and the nickel-chromium alloy wire of the anode had almost no change, and its shape was complete.

Claims (8)

1. A kind of high-temperature electrolysis CO _The improved method of making carbon nanotube system, this system comprises electrolysis unit and electric heating unit, and electric heating unit heats electrolysis unit, and electrolysis unit is made of DC power supply, negative electrode, anode, electrolytic cell and electrolyte Composition, characterized in that: the electrolyte is a mixture of molten carbonate and molten oxide, in the mixture, the molar ratio of oxide to carbonate is in the interval (0,0.2], and the electrolysis temperature is between 610-690°C When using constant current electrolysis or constant voltage electrolysis, when using constant current electrolysis, the current density of the DC power supply is controlled between 20 ~ 500mA/ ^cm2 , when using constant voltage electrolysis, the voltage of the DC power supply is controlled at 2.2V ~ 3.2V During electrolysis, carbon nanotubes and CO are obtained at the cathode, O ₂ is obtained at the anode, and the electrolyte is regenerated by reacting with CO ₂ ; the system also includes an inert gas protection unit for introducing inert gas into the electrolysis reaction system. 2. The improved method for producing carbon nanotubes by high-temperature electrolysis of CO ₂ according to claim 1, characterized in that the current density of the DC power supply is 100-400 mA/cm ² , and the temperature of the electrolytic cell is 627-677°C. 3. The improved method of high-temperature electrolysis _CO2 system for carbon nanotubes according to claim 1, characterized in that, when the electrolyte is in a solid state, the electric heating unit provides the heat energy required for the electrolyte to reach a completely molten state. 4. high-temperature electrolysis CO according to claim ₁ The improved method of carbon nanotube system is characterized in that, described electric heating unit adopts pottery or other high-temperature type electric heating mantle, regulates heating temperature by adjusting transformer load, The inert gas protection unit adopts helium, argon or neon sealed in steel cylinders. 5. The improved method for producing carbon nanotubes by high-temperature electrolysis of CO ₂ according to claim 1, characterized in that the carbonates are Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , Rb ₂ CO ₃ , Cs ₂ CO ₃ , Fr ₂ CO ₃ , MgCO ₃ , CaCO ₃ , SrCO ₃ , BaCO ₃ , ZnCO ₃ or a mixture of two or more; oxides are Li ₂ O, Na ₂ O, K ₂ O, One or a mixture of two or more of Rb ₂ O, Cs ₂ O, Fr ₂ O, MgO, CaO, SrO, BaO, ZnO, SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ . 6. high-temperature electrolysis CO according to claim ₁ The improved method of carbon nanotube system is characterized in that, the cathode material of described electrolysis unit is nickel, platinum, titanium, ruthenium, iridium, palladium, iron, tungsten, Chromium, copper, gold, graphite or stainless steel, or an alloy formed of several of the above materials; the anode material of the electrolysis unit is nickel, platinum, titanium, ruthenium, iridium, palladium, iron, tungsten, chromium, copper, gold , graphite or stainless steel, or an alloy formed of several of the above materials. 7. The improved method of high-temperature electrolysis _CO2 system for carbon nanotubes according to claim 1, characterized in that, the electrolytic cell adopts a high-purity corundum crucible, high-purity nickel or other high-temperature corrosion-resistant reactors. 8. based on the high temperature electrolysis CO described in claim ₁ , 3, 4, 5, 6 or 7 The improved method of carbon nanotube system comprising the steps: (1) Construct an electrolytic unit composed of a DC power supply, cathode, anode, electrolytic cell, electrolyte and an inert gas protection unit; (2) heating the solid electrolyte by an electric heating unit to form a molten electrolyte; (3) Control the temperature of the electrolytic cell to be constant at 610-690°C; (4) Introduce CO ₂ into the electrolytic cell through the air duct. When using constant current electrolysis, control the current density of the DC power supply between 20 and 500mA/cm ² . When using constant voltage electrolysis, control the voltage of the DC power supply at 2.2 Between V and 3.2V, react for a certain period of time, the main product is simple carbon in one step in the main reaction, and carbon nanotubes are enriched in the simple carbon. The total reaction is: CO ₂ =C+O _{2 ;} CO ₂ =1/2O ₂ +CO; CO ₂ =3/4O ₂ +1/2CO+1/2C; The electrolytic reaction mechanism is: Anode reaction: 2O ^2- -4e ^- ＝O ₂ Cathode reaction: CO ₃ ^2- +4e ^- ＝C+3O ^2- CO ₃ ^2- +2e ^- ＝CO+2O ^2- CO ₃ ^2- +3e ^- = 1/2CO+1/2C+5/2O ² .