CN104593803A - A solar-driven high-temperature electrolysis CO2/H2O synthesis gas system and its application - Google Patents

Abstract

The invention relates to a solar-driven high-temperature electrolysis CO ₂ /H ₂ O synthesis gas system. The system includes an electrolysis unit and a photothermal unit. The electrolysis unit is composed of a photoelectric unit, a cathode, an anode, an electrolytic cell and an electrolyte. Convert it into electrical energy to provide the required electrolysis voltage or current; the photothermal unit converts solar energy into heat energy, heats the solid electrolyte to reach a molten state, and heats the electrolytic cell to the electrolysis temperature; the electrolyte is a mixed molten electrolyte. The system utilizes the thermal/electrical synergistic coupling effect of the solar photo-thermal-electrochemical coupling process to form a perfect green solar energy conversion and storage system, which is clean, safe and sustainable, and provides comprehensive solutions for energy saving, emission reduction and solar resource integration. Utilization provides a new way, and at the same time realizes the co-electrolysis conversion of CO ₂ /H ₂ O under the conditions of low electrolysis voltage and relatively low temperature to produce synthesis gas, and realizes energy-saving and efficient resource utilization of CO ₂ .

Description

A solar-driven high-temperature electrolysis CO2/H2O synthesis gas system and its application

technical field

The invention relates to a new energy solar energy-driven CO ₂ /H ₂ O conversion synthesis gas system and its application, belonging to the fields of solar energy utilization, energy saving and emission reduction, and CO ₂ resource utilization.

Background technique

_CO2 is one of the most important greenhouse gases causing global climate change. The large amount of _CO2 emissions has become an international issue that has a major impact on the changes in the future world pattern. How to control _CO2 emissions has been listed as the primary topic of governments and United Nations meetings, and has become a strategic issue that needs to be solved urgently among many major global issues. , and carbon dioxide is a potential carbon resource, so it is of great strategic significance to develop corresponding carbon dioxide recovery and utilization technologies. At present, the recovery and conversion of carbon dioxide mainly focuses on catalytic activation to synthesize organic fuels or chemical raw materials, such as CH ₄ , CO+H ₂ , methanol, etc. A research team of Tokyo Institute of Technology in Japan developed a new type of composite photocatalyst in 2008, which can use sunlight to convert _CO2 into CO. This method is a photocatalytic method at room temperature, and the light conversion rate is extremely low; - Magnesium is used as a catalyst, which can mix carbon dioxide and hydrogen at a certain temperature and pressure to generate methane; Toshiba Corporation of Japan directly mixes the offgas with hydrogen-based acetylene, and uses electron beam or laser beam excitation to produce methanol and CO . However, these reactions can only be carried out under the conditions of high temperature and high pressure and the presence of a catalyst, and special reactors need to be equipped. The reaction process needs to consume a lot of energy and power. In addition, the performance of the catalyst is low and it is easy to deactivate at high temperature. There are still many difficulties in the large-scale conversion and utilization of carbon dioxide by this high-pressure catalytic hydrogenation method. Compared with chemical methods that require harsh conditions of high temperature and high pressure, in recent years, the electrochemical _CO2 fixation technology with milder reaction conditions and easy operation has become one of the research hotspots in the field of _CO2 resource utilization. The current research on electrochemical reduction of CO ₂ mainly involves dissolving CO ₂ in aqueous solvents and non-aqueous organic solvents, but this also limits its industrial application. In addition, CO ₂ is a gas molecule, and direct electrolytic reduction is very difficult. First, High energy consumption (high electrolysis voltage) is required, and the second is that the electrolysis reaction is very complicated, and the efficiency and selectivity are poor. Based on this, it is very important to develop a low-cost, simple and efficient method and device for resource utilization of CO ₂ in order to obtain better economic, social and environmental benefits.

Contents of the invention

The present invention provides a CO ₂ resource utilization method with simple system, energy saving, low cost and high efficiency, aiming at CO ₂ resource utilization and aiming at utilizing the synergistic effect of solar thermal/photoelectricity to combine CO ₂ /H ₂ O is electrolytically coupled and reduced to syngas under high-temperature molten salt conditions, and at the same time realizes the conversion and storage of solar energy to chemical energy. At the same time, under the conditions of low electrolysis voltage and relatively low temperature, the co-electrolysis conversion of CO ₂ /H ₂ O to produce synthesis gas is realized, and the electrolysis reaction is relatively simple and the reaction selectivity is good.

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

A solar-driven high-temperature electrolysis CO ₂ /H ₂ O synthesis gas system, the system includes an electrolysis unit and a photothermal unit, the electrolysis unit is composed of a photoelectric unit, a cathode, an anode, an electrolytic cell and an electrolyte, and is characterized in that: the electrolytic The photoelectric unit of the unit converts solar energy into electrical energy and provides the required electrolysis voltage or current; the photothermal unit converts solar energy into thermal energy, heats the solid electrolyte to reach a molten state, and heats the electrolytic cell to the electrolysis temperature; The electrolyte is a mixture of molten carbonate and molten hydroxide, or a mixture of molten carbonate and molten oxide, or a mixture of molten carbonate, molten hydroxide and molten oxide, in electrolysis, in ( 0A-3A), the temperature of the electrolytic cell is above 600°C, and the electrolyte absorbs CO ₂ /H ₂ O in the air to be regenerated; preferably, the electrolytic current is 1A-2A, and the temperature of the electrolytic cell is 600°C-800°C; When the electrolyte is a mixture of molten carbonate and molten hydroxide, the molar ratio is carbonate:hydroxide=1:0.5～1; when the electrolyte is a mixture of molten carbonate and molten oxide, the molar ratio is Carbonate: oxide = 1:0.5 ~ 1; when the electrolyte is a mixture of molten carbonate, molten hydroxide and molten oxide, the molar ratio is carbonate: (hydroxide + oxide) = 1 :0.5～1. ;

Further, the photoelectric unit adopts one of silicon solar cell panels, multi-band gap solar cells, solar cells made of functional polymer materials, nanocrystalline solar cells, dye-sensitive solar cells, and concentrating solar cells, or the above-mentioned A series or parallel combination of two or more types of solar cells; silicon solar panels can use monocrystalline silicon, polycrystalline silicon, and amorphous silicon, and multi-bandgap solar cells can use gallium arsenide III-V compounds, cadmium sulfide, and copper indium Multiple compounds such as selenium are used as materials;

Further, the photothermal unit adopts one or a combination of Fresnel lenses, reflective concentrators, refracting concentrators, small trough line focusing systems, dish systems or tower systems , adjust the heating temperature by adjusting the spot size or concentration ratio;

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;

Further, 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 a high-purity corundum crucible or a high-temperature corrosion-resistant reactor;

Further, the carbonate is Li ₂ CO ₃ , Na ₂ CO ₃ , K 2 CO ₃ , Rb ₂ CO ₃ , MgCO _{3 ,} CaCO 3 , SrCO ₃ , BaCO _{3 ,} ZnCO ₃ , Li ₂ SiO ₃ , Na ₂ SiO _3. One or more mixtures of K ₂ SiO ₃ , Rb ₂ SiO ₃ ; the hydroxides are LiOH, NaOH, KOH, RbOH, Mg(OH) ₂ , Ca(OH) ₂ , Sr(OH) _2. Ba(OH) ₂ , Zn(OH) ₂ or a mixture of two or more; the oxides are Li ₂ O, Na ₂ O, K ₂ O, Rb ₂ O, MgO, CaO, SrO, BaO , ZnO, SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ or a mixture of two or more.

The method for producing synthesis gas by high-temperature electrolysis of CO ₂ /H ₂ O based on the above solar-driven high-temperature electrolysis CO ₂ /H ₂ O synthesis gas system is characterized in that the method includes the following steps:

(1) Construct an electrolytic unit composed of a photoelectric unit, cathode, anode, electrolytic cell and electrolyte;

(2) Heating the solid electrolyte in the electrolysis through the photothermal unit to form a molten electrolyte;

(3) Control the temperature of the electrolytic cell to be constant at 600°C-800°C;

(4) Introduce CO ₂ and H ₂ O into the electrolytic cell through the air duct, control the DC power supply current to be constant at 1A-2A, and react for 1h-2h. The main reaction produces the main products of syngas CO and H ₂ in one step. The main reaction is : CO ₂ +H ₂ O ＝ CO+H ₂ +O ₂ , the intermediate product carbon simple substance and hydrogen obtained by the side reaction, the side reaction is:

1) Generate simple carbon and reduce CO ₂ /H ₂ O to generate CO/H ₂ :

CO ₂ ＝C+O ₂

C+CO ₂ ＝2CO

C+ _H2O ＝ _H2 +CO

2) Water electrolysis generates H ₂ , and H ₂ reduces CO ₂ to generate CO

H ₂ O＝H ₂ +1/2O ₂

H ₂ +CO ₂ =CO+H ₂ O;

The electrolytic reaction mechanism is:

Anode: 2O ^2- -4e ^- ＝O ₂

Cathode: 2OH ^- +CO ₃ ^2- +4e ^- ＝CO+H ₂ +4O ^2-

2H ⁺ +CO ₃ ^2- +4e ^- =CO+H ₂ +2O ^2- .

Beneficial technical effect of the present invention is as follows:

1. The present invention uses new energy solar energy to convert CO ₂ /H ₂ O synergistically into syngas (H ₂ and CO). This method utilizes solar thermal electrochemical production (STEP for short) process Thermal/electrical synergistic coupling, synergistic coupling regulates solar light-thermal-electricity utilization efficiency and molecular photo-thermal-electrochemical reaction characteristics, and synergistically acts on the thermal energy and electric energy generated by the solar photothermal and photoelectric effects on the oxide , carbonate, hydroxide or their mixtures, carry out specific CO ₂ /H ₂ O chemical conversion to synthesis gas reaction, convert and store solar energy into chemical energy, and at the same time realize the effective utilization of CO ₂ resources .

2. During the electrolysis reaction process, the solar energy is converted into heat energy through the photothermal unit, the electrolyte is heated, and the heating temperature is adjusted according to the electrolyte; at the same time, the solar energy is used to provide electric energy, and the required electrolysis voltage or current is adjusted according to the type of electrolyte and the heating temperature. Through the electrolysis of CO ₂ /H ₂ O, H ₂ and CO are obtained at the cathode, and O ₂ is obtained at the anode, which realizes the conversion and storage of solar energy into chemical energy. During the electrolysis process, the electrolyte absorbs CO ₂ /H ₂ O in the air, making the electrolyte It can be regenerated, thereby realizing the recycling and resource utilization of CO ₂ .

3. Most of the previous high-temperature molten salt systems are single mixed molten carbonates, and the co-electrolysis temperature of CO ₂ /H ₂ O is above 800°C. However, the present invention innovatively adds a certain Proportions of hydroxides and/or oxides. Hydroxide can be used as a source of hydrogen, and at the same time lower the melting point of the entire mixed molten salt system, so that CO ₂ /H ₂ O can be electrolyzed at a lower temperature. After the oxide reaches the molten state, it can absorb CO ₂ and H ₂ O in the air and convert it into carbonate and hydroxide, which plays a similar role to the mixture of carbonate and hydroxide, and also makes CO ₂ /H ₂ O can be electrolyzed at a lower temperature, and realize the resource utilization of CO ₂ with high efficiency and energy saving. Take sodium salt as an example, as shown in Figure 1:

Absorption: Na ₂ O+CO ₂ =Na ₂ CO ₃

_Na2O + _H2O ＝2NaOH

Release: Na ₂ CO ₃ =Na ₂ O+CO ₂

2NaOH＝ _Na2O + _H2O

4. The present invention has the advantage of generating synthesis gas ( _H2 and CO) in one step. The main reaction is: _CO2 + _H2O =CO+ _H2 + _O2 . for:

1) Generate simple carbon and reduce CO ₂ /H ₂ O to generate CO/H ₂ :

CO ₂ ＝C+O ₂

C+CO ₂ ＝2CO

C+ _H2O ＝ _H2 +CO

2) Water electrolysis generates H ₂ , and H ₂ reduces CO ₂ to generate CO

H ₂ O＝H ₂ +1/2O ₂

H ₂ +CO ₂ =CO+H ₂ O;

5. The invention synergistically utilizes the photothermal/photoelectric coupling effect of solar energy and the secondary electrochemical effect to construct a highly efficient integrated coupling CO ₂ /H ₂ O conversion synthesis gas system, which can generate the main products H ₂ and CO and a small amount in one step The by-product is solid elemental carbon. The energy of this system comes entirely from solar energy, and the two parts of solar thermal and photovoltaic are used in a coordinated manner at the same time, forming a perfect green solar energy conversion and storage system, which is clean, safe and sustainable. Utilization provides new avenues.

Description of drawings

Fig. 1 system schematic diagram of the present invention;

Fig. 2 schematic diagram of the system of the present invention;

In the figure: 1 anode; 2 electrolytic cell; 3 electrolyte; 4 cathode; ₅ air duct; 6 anode product O ₂ ; 7 reaction raw material CO ₂ /H ₂ O; plate; 11 wires; 12 concentrators.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing.

The present invention is based on the high-temperature electrolysis of CO ₂ /H ₂ O synthesis gas system. As shown in Figure 2, the system includes an electrolysis unit and a photothermal unit. The electrolysis unit is composed of a photoelectric unit, a cathode, an anode, an electrolytic cell and an electrolyte. The electrolysis unit The cathode and anode of the electrolytic cell are placed in the same electrolytic cell, and the photoelectric unit converts solar energy into electrical energy to provide the required electrolytic voltage or current; the photothermal unit heats the electrolyte in the electrolytic cell, and enters the CO ₂ and H ₂ O, and lead out the cathode products CO and H ₂ and the anode product O ₂ through their respective air ducts. The photothermal unit converts solar energy into heat energy, heats the solid electrolyte to reach a molten state, and heats the electrolytic cell to the electrolysis temperature, and regulates the heating temperature by adjusting the size of the spot or the concentration ratio; the electrolyte is molten carbon Mixtures of acid salts and molten hydroxides, or mixtures of molten carbonates and molten oxides, or mixtures of molten carbonates, molten hydroxides and molten oxides, in electrolysis, in the interval (0A-3A) , the temperature of the electrolytic cell is above 600°C, and the electrolyte absorbs CO ₂ /H ₂ O in the air to be regenerated; when the current is less than 1A, the yield is too low and the reaction is slow; when the current is greater than 2A, the reaction is severe and the electrode corrosion is serious and the output is low , so the current is preferably 1A-2A, preferably, the electrolysis current is 1A-2A, and the temperature of the electrolytic cell is 600°C-800°C; the adjustment of the product concentration is realized by adjusting the electrolysis current and electrolyte composition.

Example 1

Grind ^and mix 20g Li ₂ CO ₃ , 20g Na ₂ CO ₃ , 20g K ₂ CO ₃ and 45.09g KOH in a mortar, and transfer them into a corundum crucible; The iron wire is used as the anode and the cathode, and the reaction is not limited by the size of the electrode area, and the larger the area is, the better the reaction is; adjust the spot size of the Fresnel lens to keep the temperature constant at 650°C; adjust the rheostat of the solar panel circuit to keep the current constant at 2A. After reacting for 1 hour, the syngas content (volume percentage) in the generated gas was: 89.72% H ₂ , 6.857% CO.

Example 2

Grind and mix 20g Li ₂ CO ₃ , 20g Na ₂ CO ₃ , 20g K ₂ CO ₃ and 51.63g Ba(OH) ₂ in a mortar, and transfer them into a corundum crucible ^; The nickel-chromium alloy wire and iron wire are used as the anode and cathode; the concentration ratio of the reflective concentrator is adjusted to keep the temperature constant at 750°C; the rheostat of the solar panel circuit is adjusted to keep the current constant at 2A. After reacting for 1 hour, the synthesis gas content (volume percentage) in the generated gas was: 85.67% H ₂ , 6.03% CO.

Example 3

Grind and mix 30g Li ₂ CO ₃ , 30g Na ₂ CO ₃ , 30g BaCO ₃ , 10.18g LiOH and 33.91g ZnO in a mortar, transfer them into a ^high -purity nickel reactor; Nickel sheet and nickel wire are used as anode and cathode; adjust the spot size of the Fresnel lens to keep the temperature constant at 600°C; adjust the rheostat of the solar panel circuit to keep the current constant at 1.5A. After 2 hours of reaction, the synthesis gas content (volume percentage) in the generated gas is: 83.38% H ₂ , 5.81% CO.

Example 4

Grind and pulverize 30g Li ₂ CO ₃ , 30g Na ₂ CO ₃ , 30g CaCO ₃ , 46.45g K ₂ O and 3g Na ₂ SiO ₃ in a mortar and mix them evenly, and transfer them into a high-purity nickel reactor; A 20cm ² nickel sheet and a nickel wire are used as the anode and cathode; the spot size of the Fresnel lens is adjusted to keep the temperature constant at 650°C; the rheostat of the solar panel circuit is adjusted to keep the current constant at 2A. After 1 hour of reaction, the synthesis gas content (volume percentage) in the generated gas was: 82.28% H ₂ , 6.11% CO.

Example 5

Grind and mix 30g Li ₂ CO ₃ , 30g Na ₂ CO ₃ , 16.8g CaO and 101.31g RbOH in a mortar, and transfer them into a ^high -purity nickel reactor; The wire is used as the anode and the cathode; the spot size of the Fresnel lens is adjusted to keep the temperature constant at 800°C; the rheostat of the solar panel circuit is adjusted to keep the current constant at 1A. After 2 hours of reaction, the synthesis gas content (volume percentage) in the generated gas is: 80.62% H ₂ , 6.07% CO.

Obviously, the above descriptions and records are only examples and not intended to limit the disclosed content, application or use of the present invention. Given the teachings of the embodiments of the invention, the scope of the invention is to include any embodiment falling within the foregoing description and appended claims.

Claims (9)

1. a Driven by Solar Energy high-temperature electrolysis CO ₂/ H ₂o preparing synthetic gas system, this system comprises electrolysis cells and photo-thermal unit, electrolysis cells is made up of photovoltaic element, negative electrode, anode, electrolyzer and ionogen, it is characterized in that: the photovoltaic element of described electrolysis cells converts solar energy into electrical energy, and provides required electrolysis voltage or electric current; Described photo-thermal unit converts solar energy into heat energy, carries out heating and makes it reach molten state, and heat electrolyzer to electrolysis temperature to solid state electrolyte; Described ionogen is the mixture of fused carbonate and fusible hydrate, or the mixture of fused carbonate and molten oxide, or the mixture of fused carbonate, fusible hydrate and molten oxide, in electrolysis, Faradaic current is in (0A-3A) interval, electrolyzer temperature is more than 600 DEG C, the CO in electrolyte absorption air ₂/ H ₂o is regenerated; When ionogen is the mixture of fused carbonate and fusible hydrate, mol ratio is carbonate: oxyhydroxide=1:0.5 ~ 1; When ionogen is the mixture of fused carbonate and molten oxide, mol ratio is carbonate: oxide compound=1:0.5 ~ 1; When ionogen is the mixture of fused carbonate, fusible hydrate and molten oxide, mol ratio is carbonate: (oxyhydroxide+oxide compound)=1:0.5 ~ 1.

2. Driven by Solar Energy high-temperature electrolysis CO according to claim 1 ₂/ H ₂o preparing synthetic gas system, is characterized in that, described high-temperature electrolysis CO ₂/ H ₂o preparing synthetic gas high-temperature electrolysis CO ₂/ H ₂the electrolytic reaction mechanism of O preparing synthetic gas is:

Anode: 2O ^2--4e ^-=O ₂

Negative electrode: 2OH ^-+ CO ₃ ^2-+ 4e ^-=CO+H ₂+ 4O ^2-

2H ⁺+CO ₃ ^2-+4e ^-＝CO+H ₂+2O ^2-。

3. Driven by Solar Energy high-temperature electrolysis CO according to claim 1 ₂/ H ₂o preparing synthetic gas system, is characterized in that, described Faradaic current is 1A-2A, and described electrolyzer temperature is 600 DEG C ~ 800 DEG C.

4. Driven by Solar Energy high-temperature electrolysis CO according to claim 1 ₂/ H ₂o preparing synthetic gas system, is characterized in that, carbonate is Li ₂cO ₃, Na ₂cO ₃, K ₂cO ₃, Rb ₂cO ₃, MgCO ₃, CaCO ₃, SrCO ₃, BaCO ₃, ZnCO ₃, Li ₂siO ₃, Na ₂siO ₃, K ₂siO ₃, Rb ₂siO ₃in one or more mixture; Oxyhydroxide is LiOH, NaOH, KOH, RbOH, Mg (OH) ₂, Ca (OH) ₂, Sr (OH) ₂, Ba (OH) ₂, Zn (OH) ₂in one or more mixture; Oxide compound is Li ₂o, Na ₂o, K ₂o, Rb ₂o, MgO, CaO, SrO, BaO, ZnO, SiO ₂, Al ₂o ₃, Fe ₂o ₃in one or more mixture.

5. Driven by Solar Energy high-temperature electrolysis CO according to claim 1 ₂/ H ₂o preparing synthetic gas system, it is characterized in that, one in solar cell, nano-crystalline solar battery, dye-sensitized solar battery and concentrating solar battery that described photovoltaic element adopts silicon solar cell plate, multi-band-gap solar cell, functional high molecule material to prepare, or the two or more serial or parallel connection combination in above-mentioned solar cell types.

6. Driven by Solar Energy high-temperature electrolysis CO according to claim 1 ₂/ H ₂o preparing synthetic gas system, it is characterized in that, described photo-thermal unit adopts one or more the combination in Fresnel Lenses, reflection-type beam condenser, refraction type light gathering device, small-sized groove type line-focusing system, dish-style system or tower system, regulates and controls Heating temperature by regulating spot size or focusing ratio.

7. Driven by Solar Energy high-temperature electrolysis CO according to claim 1 ₂/ H ₂o preparing synthetic gas system, is characterized in that, the cathode material of described electrolysis cells is nickel, platinum, titanium, ruthenium, iridium, palladium, iron, tungsten, chromium, copper, gold, graphite or stainless steel, or the alloy of several formation in above-mentioned materials; The anode material of described electrolysis cells is nickel, platinum, titanium, ruthenium, iridium, palladium, iron, tungsten, chromium, copper, gold, graphite or stainless steel, or the alloy of several formation in above-mentioned materials.

8. Driven by Solar Energy high-temperature electrolysis CO according to claim 1 ₂/ H ₂o preparing synthetic gas system, is characterized in that, described electrolyzer adopts high-purity corundum body crucible or high temperature corrosion-resisting type reactor.

9. based on the Driven by Solar Energy high-temperature electrolysis CO one of claim 1-8 Suo Shu ₂/ H ₂the high-temperature electrolysis CO of O preparing synthetic gas system ₂/ H ₂the method of O preparing synthetic gas, is characterized in that: the method comprises the steps:

(1) electrolysis cells be made up of photovoltaic element, negative electrode, anode, electrolyzer and ionogen is built;

(2) solid state electrolyte is added in thermal electrolysis to form molten state ionogen by photo-thermal unit;

(3) electrolyzer homo(io)thermism is controlled at 600 DEG C-800 DEG C;

(4) in electrolyzer, CO is passed into by airway ₂and H ₂o, controls direct supply current constant at 1A-2A, reaction 1h-2h, and main reaction one step generates primary product synthetic gas CO and H ₂, main reaction is: CO ₂+ H ₂o=CO+H ₂+ O ₂, side reaction obtains intermediate product carbon simple substance and hydrogen, and side reaction is:

1) Formed simple substance the CO that reduces ₂/ H ₂o generates CO/H ₂:

CO ₂＝C+O ₂

C+CO ₂＝2CO

C+H ₂O＝H ₂+CO

2) water electrolysis generates H ₂, H ₂reduction CO ₂generate CO

H ₂O＝H ₂+1/2O ₂

H ₂+CO ₂＝CO+H ₂O；

Its electrolytic reaction mechanism is:

Anode: 2O ^2--4e ^-=O ₂

Negative electrode: 2OH ^-+ CO ₃ ^2-+ 4e ^-=CO+H ₂+ 4O ^2-

2H ⁺+CO ₃ ^2-+4e ^-＝CO+H ₂+2O ^2-。