Cement concrete rapid carbonization method based on electrochemical comprehensive action

Abstract

The invention discloses a cement concrete rapid carbonization method based on electrochemical comprehensive action, and belongs to the technical field of highway bridge engineering test detection. The rapid carbonization method for the cement concrete based on the electrochemical comprehensive action comprises the following steps: placing the cement concrete in a closed electrolytic bath containing electrolyte, introducing CO2 into the electrolyte, and carrying out electrolytic carbonization. By adopting the method disclosed by the invention, the concrete can be quickly carbonized, and the durability of the concrete can be more accurately evaluated before the concrete is used. Instruments adopted in the method are simple, and the problem that instruments and equipment used in an existing carbonization acceleration method are expensive is solved.

Description

Technical Field

[0001] This invention relates to the field of highway bridge engineering testing and inspection technology, and in particular to a rapid carbonation method for cement concrete based on the combined effect of electrochemical processes. Background Technology

[0002] Carbonation of concrete components is a significant factor affecting the durability of bridge structures. When carbon dioxide and water enter the concrete, it reduces the alkalinity of the concrete, causing carbonation, which in turn damages the passivation film on the reinforcing steel, triggers corrosion and expansion, and ultimately weakens the structural safety.

[0003] Assessing the degree of concrete carbonation requires on-site testing using the phenolphthalein indicator method. This measurement method detects carbonation after it has already formed, allowing for an assessment of the current carbonation status. However, when evaluating concrete durability, it is often necessary to know the carbonation progress before the concrete structure is put into use. Currently, model prediction methods are commonly used, but these methods have a high error rate. There are also methods that use rapid carbonation testing equipment to accelerate concrete carbonation, but the equipment is relatively expensive. Summary of the Invention

[0004] The purpose of this invention is to provide a rapid carbonation method for cement concrete based on electrochemical synergy, so as to solve the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of this invention: a method for rapid carbonation of cement concrete based on electrochemical synergy, comprising the following steps:

[0007] Cement concrete is placed in a closed electrolytic cell containing electrolyte, and CO2 is introduced into the electrolyte for electrolytic carbonization.

[0008] Preferably, the electrolyte comprises a NaHCO3 solution with a concentration of 0.5 to 1.5 mol / L.

[0009] Preferably, the voltage for electrolytic carbonization is 10–30V, and the current density is 0.5–2.0 mA / cm². 2 .

[0010] Preferably, the method for rapid carbonation of cement concrete based on electrochemical synergy further includes the step of replacing the electrolyte when the pH value of the electrolyte changes by more than 1 to 2.

[0011] The second technical solution of the present invention: an electrochemical carbonization device for realizing the above-mentioned rapid carbonization method of cement concrete, wherein the electrochemical carbonization device includes a carbon dioxide cylinder and an electrolytic cell connected by a gas pipe;

[0012] The electrolytic cell is equipped with an anode, a cathode, a power source, and a support for supporting the cement concrete specimen.

[0013] The anode is placed on the top surface of the cement concrete specimen;

[0014] The cathode is located on one side of the cement concrete specimen, and the cathode is not in contact with the cement concrete specimen, with a spacing of 50mm to 100mm.

[0015] If the spacing is too long, the current is too low, and the carbonation rate is slow; if the spacing is too small, the current rate is too high, which will cause the surface carbonization rate of the cement concrete specimen to be too fast, affecting the degree of carbonization inside the cement concrete specimen.

[0016] Preferably, the anode is made of metal;

[0017] The cathode is made of graphite.

[0018] The third technical solution of the present invention: a method for rapidly carbonizing cement concrete using the above-mentioned electrochemical carbonization device, comprising the following steps:

[0019] Lay the cement concrete specimen flat and immerse it completely in the electrolyte for at least 48 hours to allow it to fully absorb water (so as to maintain the weak conductivity of the concrete specimen during the test). This will result in a moist cement concrete specimen. (In the subsequent carbonation process, if the surface of the specimen appears dry to the naked eye, the surface should be sprayed with electrolyte to keep the cement concrete specimen continuously moist.)

[0020] The moistened cement concrete specimen is placed upright on a support, and electrolyte is added so that the depth of the electrolyte is at least 20% of the height of the cement concrete. The electrolysis tank is then covered to form a sealed environment. Carbon dioxide from a carbon dioxide cylinder is introduced into the electrolyte through a gas tube, and the power is turned on to carry out electrolytic carbonization.

[0021] Preferably, the electrolyte comprises a NaHCO3 solution with a concentration of 0.5 to 1.5 mol / L.

[0022] Preferably, the soaking time in the electrolyte is ≥48h.

[0023] The role of electrolyte:

[0024] It participates in chemical reactions, simulating the carbonation environment. Concrete carbonation mainly involves the reaction of carbon dioxide with alkaline substances such as calcium hydroxide in cement, reducing the alkalinity of the concrete. Sodium bicarbonate (chemical formula NaHCO3) is an inorganic compound whose solution is weakly alkaline. During the carbonation process, sodium bicarbonate solution can, to some extent, simulate the chemical conditions of the surrounding environment during concrete carbonation, promoting carbonation-like chemical reactions within the concrete, thus facilitating rapid detection of carbonation depth.

[0025] Stabilizing solution pH. Sodium bicarbonate solution has excellent buffering properties, enabling it to stabilize the solution's pH. During electrochemical experiments, the solution's pH may fluctuate as the reaction proceeds. Sodium bicarbonate can adjust and stabilize the pH, ensuring the experiment is conducted in a relatively stable chemical environment, leading to more accurate and reliable results. This is crucial for accurately determining the carbonation depth of concrete, as pH fluctuations can affect the response of the detection electrode and the measurement results.

[0026] As an ionic conductor, sodium bicarbonate is required in electrochemical experiments to conduct ions and form a current circuit. In solution, sodium bicarbonate dissociates into sodium ions (Na+). + ) and bicarbonate ions (HCO3) - These ions can move under the influence of an electric field, thus achieving ion conduction. In this way, a stable current can be formed between the negative electrode and the concrete, and the flow of the current causes the concrete to carbonize rapidly.

[0027] Preferably, the method further includes the step of replacing the electrolyte when the pH value of the electrolyte changes by more than 1 to 2.

[0028] Preferably, the voltage for electrolytic carbonization is 10–36 V, and the current density is 0.5–2 mA / cm². 2 .

[0029] Preferably, the CO2 concentration in the electrolyzer (the CO2 concentration in the non-electrolyte) is 20–30 vol.%.

[0030] Injecting high-concentration CO2 (20–100 vol.%) into a closed environment can significantly increase the partial pressure of gaseous CO2, resulting in an exponential increase in the solubility and diffusion rate of CO2 in the capillary pores of concrete. The carbonation rate increases with the increase of CO2 concentration in the electrolytic cell; when the CO2 concentration in the electrolytic cell increases to 20%, the carbonation rate can increase by more than 30 times.

[0031] More preferably, the electrolytic carbonization is carried out at an ambient temperature of 20±2℃ and an ambient relative humidity of 50-75%.

[0032] More preferably, when it is necessary to further increase the carbonization rate, the ambient temperature can be increased to 40-60℃. At this temperature, molecular motion can be accelerated, and the activation energy of the reaction can be reduced from about 50 kJ / mol under natural conditions to below 30 kJ / mol, thereby increasing the reaction rate constant by 5-8 times.

[0033] By precisely controlling the relative humidity of the environment (50-75%), it is possible to ensure that a sufficient liquid water film is formed in the capillary pores of concrete as a CO2 dissolution medium, and to avoid complete saturation of the pores that would hinder gas diffusion; this humidity range allows the carbonation reaction rate to reach its peak.

[0034] The principle of electrochemical rapid carbonization:

[0035] The essence of rapid carbonation of concrete is the artificial strengthening of a gas-liquid-solid three-phase reaction system, with the core reaction being the neutralization reaction between calcium hydroxide (Ca(OH)2) and carbon dioxide (CO2). Under natural conditions, this reaction takes a long time (from several months to several years) due to the low diffusion rate of CO2 and the uncontrollable temperature and humidity.

[0036] This invention achieves accelerated carbonization through the following mechanism:

[0037] By using an external electric field and current, CO2 and water are accelerated to diffuse into the concrete under the strong action of the electric field and current. This causes the carbon dioxide and water to react rapidly with the alkaline substances in the concrete, quickly reducing the alkalinity of the concrete and causing it to carbonize rapidly. This allows for the detection of the change in the carbonation depth of the concrete over time in a shorter period of time.

[0038] The present invention discloses the following technical effects:

[0039] The method of this invention enables rapid carbonation of concrete, allowing for more accurate assessment of concrete durability before use. Furthermore, the method employs simple equipment, overcoming the problem of expensive equipment used in existing accelerated carbonation methods. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 The diagram below shows the electrochemical carbonization apparatus in Example 1, where 1 is a carbon dioxide cylinder, 2 is a carbon dioxide pipe, 3 is a support, 4 is an anode, 5 is a cathode, 6 is an electrolyte, 7 is an electrolytic cell, 8 is the top cover of the electrolytic cell, and 9 is a power source.

[0042] Figure 2 This is a time series diagram of the rapid carbonization values ​​for three current densities in Example 1. Detailed Implementation

[0043] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0044] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0045] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0046] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0047] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0048] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0049] In the following examples, "parts" refers to "parts by weight".

[0050] In a specific embodiment of the present invention, the electrochemical carbonization device consists of a carbon dioxide cylinder and an electrolytic cell;

[0051] The carbon dioxide cylinder and the electrolyzer are connected by a carbon dioxide gas pipe.

[0052] An electrolytic cell consists of an anode, a cathode, a power source, an electrolytic cell cover, and a support structure for supporting cement concrete specimens.

[0053] The power supply should be equipped with an ammeter and a voltmeter to facilitate monitoring of voltage and current at any time;

[0054] The anode is connected to the power source and the cathode is connected to the power source by copper wires. The anode and cathode form a closed circuit through a cement concrete specimen and electrolyte. The connection points of each part are coated with conductive silver paste.

[0055] The anode is located on the top surface of the cement concrete specimen;

[0056] The cathode is located on one side of the cement concrete specimen and is not in contact with the cement concrete specimen.

[0057] In a specific embodiment of the present invention, the cement concrete specimen is a cubic specimen with dimensions of 100mm × 100mm × 300mm. After the specimen is formed, it is cured for 28 days to obtain a cement concrete specimen with a strength grade of C15. The surface of the specimen is ground smooth, and the surface laitance is removed with a brush to ensure the surface of the specimen is clean. The carbonation rate of this cement concrete specimen is significantly lower than that of the present invention under traditional rapid testing methods (under traditional rapid carbonation methods, it generally takes at least 7 to 10 days to initially measure carbonation, while the method of the present invention can generally measure preliminary carbonation in 48 hours).

[0058] In a specific embodiment of the present invention, the anode is made of metal (such as stainless steel), has a diameter of 70 mm, and a thickness of 5 mm;

[0059] The cathode is made of graphite, with a diameter of 50 mm and a thickness of 200 mm;

[0060] The distance between the cement concrete and the cathode is 50mm to 100mm.

[0061] In a specific embodiment of the present invention, the electrolytic cell is made of glass, with internal dimensions of 500mm × 200mm × 400mm (length × width × height). It has a top cover (sealing cover) with two holes, one large and one small. The small hole has a diameter of 3mm, and the large hole has a diameter of 6mm. The small hole is for the carbon dioxide gas passage, and the large hole is for the inlet and outlet of the positive and negative electrode wires. After inserting the gas pipe and wires, the three holes need to be sealed with sealant.

[0062] In a specific embodiment of the present invention, the power supply can provide stable direct current with a voltage of 10–36V and a current density of 0.5–2.0 mA / cm². 2The power supply should provide a corresponding current output based on the surface area of ​​the specimen and the set power density, and should have overcurrent protection. The power supply voltage accuracy should be ±0.1V, and the current accuracy should be ±0.1mA. The current density is the ratio of the current magnitude to the area of ​​the cathode graphite electrode being energized.

[0063] In a specific embodiment of the present invention, the support member is a hollow cylindrical tube made of polyester material, with a height of 50mm, an outer diameter of 110mm, and an inner hollow diameter of 80mm.

[0064] In a specific embodiment of the present invention, if the pH value of the electrolyte changes by more than 1 to 2 units (meaning a pH change of 1 to 2), the electrolyte needs to be replaced.

[0065] Example 1

[0066] A rapid carbonation method for cement concrete based on the combined effects of electrochemical processes:

[0067] (1) Preparation of cement concrete specimens: 280 kg of cement, 150 kg of water, 600 kg of sand, 1000 kg of crushed stone and 10 kg of admixture (polycarboxylate superplasticizer) (low grade concrete) were used to prepare cubic specimens with dimensions of 100 mm × 100 mm × 300 mm, and cured for 28 days under standard curing conditions.

[0068] The surface of the specimen was ground smooth and the laitance was removed with a brush to ensure that the surface of the specimen was clean, thus obtaining a cement concrete specimen (i.e., a concrete specimen) with a strength grade of C15.

[0069] (2) Immerse the cement concrete specimen completely in the electrolyte (the electrolyte is a NaHCO3 solution with a concentration of 0.5 mol / L) for no less than 48 hours to allow the cement concrete specimen to fully absorb water and obtain a moist cement concrete specimen (and during the entire subsequent carbonation process, if the surface of the cement concrete specimen is observed to be dry by the naked eye, the electrolyte should be sprayed on the surface of the cement concrete specimen to keep the cement concrete specimen continuously moist).

[0070] Place the concrete specimen (wet cement concrete specimen) on the support 3 of the electrolytic cell 7, and fix the anode 4 to the top surface of the concrete specimen with conductive silver paste, ensuring that the anode 4 is in close contact with the top surface of the concrete specimen and is firmly fixed.

[0071] Add electrolyte 6 to electrolytic cell 7 so that the electrolyte level is 60 mm above the bottom of the concrete specimen;

[0072] Anode 4, power supply 9 and cathode 5 are connected by copper wire (industrial copper wire with a diameter of 2.76 mm), and conductive silver paste is applied to the connection. Cathode 5 is placed in electrolyte 6, and power supply 9 is placed on the upper part of electrolytic cell cover 8. Electrolytic cell cover 8 is provided with a large hole (the diameter of the large hole is 6 mm) for copper wire to pass through. After the copper wire passes through, it is sealed with sealant.

[0073] The power supply 9 is equipped with an ammeter and a voltmeter;

[0074] Carbon dioxide cylinder 1 and electrolytic cell 7 are connected by carbon dioxide gas tube 2. Carbon dioxide gas tube 2 passes through a small hole (3mm in diameter) on the top cover 8 of the electrolytic cell into the electrolyte 6. The small hole is sealed with sealant. Carbon dioxide gas tube 2 is equipped with a carbon dioxide valve.

[0075] Among them, anode 4 is made of stainless steel, with a diameter of 70mm and a thickness of 5mm;

[0076] The cathode 5 is made of graphite, with a diameter of 50 mm and a thickness of 200 mm;

[0077] The distance between the cement concrete specimen and cathode 5 is 100 mm;

[0078] The electrolytic cell 7 is made of glass, and its internal dimensions are: length × width × height 500mm × 200mm × 400mm;

[0079] Power supply 9 can provide stable DC power and can provide corresponding current output according to the surface area of ​​the specimen and the set power density. It also has overcurrent protection function, and the power supply voltage accuracy is ±0.1V and the current accuracy is ±0.1mA.

[0080] Support 3 is a hollow cylindrical tube made of polyester material. The hollow cylindrical tube has a height of 50mm, an outer diameter of 110mm, and an inner hollow diameter of 80mm.

[0081] Electrolyte 6 is a 0.5 mol / L NaHCO3 solution.

[0082] (3) Open the carbon dioxide valve and charge the electrolyte 6 with gas. Adjust the carbon dioxide flow rate so that the gas escapes in the electrolyte 6 in a uniform and fine bubble state. Control the flow rate at about 0.5 L / min so that the carbon dioxide concentration in the entire closed electrolytic cell 7 (the concentration of CO2 in the non-electrolyte) can be increased and finally stabilized at 20-30 vol.%.

[0083] (4) Turn on power supply 9, adjust the current and voltage, set the initial voltage to 15V, and the current density to 0.5mA / cm². 2 1.0 mA / cm 2 Or 2.0 mA / cm 2Three cement concrete specimens of the same strength grade were subjected to tests with different current densities.

[0084] (5) Observe the changes in electrolyte 6. Tiny bubbles will be generated at the anode 4.

[0085] (6) During the test, electric shock should be prevented. At the same time, close attention should be paid to whether there is any leakage of electrolyte. If any leakage is found, it should be dealt with in time. The test environment temperature should be maintained at 20±2℃ and the relative humidity at 60~70%.

[0086] (7) Initial carbonation depth measurement: After 7 days of power-on, turn off power supply 9 and carbon dioxide valve, and carefully remove the cement concrete specimen. No drying is required. Select 3 measurement points on the side of the cement concrete specimen and spray phenolphthalein alcohol solution at the measurement points. When the surface color of the cement concrete turns purplish-red, use a carbonation depth measuring instrument to measure the depth of the uncolored part, and take the average value as the initial carbonation depth value of the specimen.

[0087] After measuring the carbonization depth, the specimen is placed back into the electrolytic cell 7, the power supply 9 is connected, and the carbon dioxide gas valve is opened to resume electrolysis.

[0088] Adjust the voltage according to the initial carbonization depth and test results. If the carbonization speed is slow (no carbonization occurs after 48 hours of energization), the voltage can be increased to 18V and electrolysis can continue for 7 days.

[0089] (8) Second electrolysis and subsequent carbonization depth measurement: After the second electrolysis for 7 days, repeat the above steps of removing the specimen and measuring the carbonization depth. Subsequent electrolysis and carbonization depth measurements are basically cyclical according to this process, with each electrolysis lasting 7 days. Based on the previous carbonization depth increase, adjust the voltage appropriately, with each adjustment controlled within 2-3V. If the previous carbonization depth increase is less than 0.2mm, the voltage needs to be adjusted, and in this case, the voltage should be increased by 2V-3V.

[0090] (9) Repeat the above operation 15 times, electrolyze for 7 days each time, and complete the entire experiment in a total of 105 days.

[0091] (10) The electrolyte needs to be replaced during the entire test cycle.

[0092] Observe the electrolyte condition within 20 days of the start of the test. If there are no obvious abnormalities in appearance, replacement is not necessary. If the electrolyte shows obvious color changes, becomes cloudy, or produces precipitation, it should be replaced.

[0093] After approximately 30 days of testing, the ion concentration in the electrolyte will change due to the electrolysis reaction, and should be checked every 5–7 days. If the pH value of the electrolyte changes by more than 1–2, the electrolyte needs to be replaced.

[0094] During the later 10-20 days of the experiment, as the carbonization of the specimens deepens, the consumption and changes in the electrolyte will accelerate. The electrolyte should be checked every 3-5 days. If a significant decrease in electrolyte conductivity or a substantial reduction in bubble production occurs, the electrolyte should be replaced.

[0095] See schematic diagram of electrochemical carbonization device Figure 1 .

[0096] Table 1 Electrolysis conditions for specimen 1

[0097]

[0098]

[0099] Table 2 Electrolysis conditions for specimen 2

[0100]

[0101] Table 3 Electrolysis conditions for specimen 3

[0102]

[0103] Record the carbonization depth of the specimens after 105 days of testing, and draw a specimen sequence diagram. Figure 2 .

[0104] from Figure 2 It can be seen that when the gas concentration and electrolyte concentration remain constant, the carbonization rate increases with the increase of current density.

[0105] Comparative Example 1

[0106] The following technical parameters will cause a slowdown in the carbonization rate:

[0107] (1) Compared with Example 1, under the condition that other conditions remain unchanged, the carbonization rate will be slower when the voltage is less than 15V;

[0108] (2) Compared with Example 1, under the same conditions, the current density is less than 0.1 mA / cm². 2 At that time, the carbonization rate will slow down significantly;

[0109] (3) Compared with Example 1, the lower the conductivity of the wire, the slower the carbonization rate will be;

[0110] (4) Compared with Example 1, when the concentration of carbon dioxide is less than 5 vol.%, the carbonization rate will be significantly slower;

[0111] (5) Compared with Example 1, the carbonization rate will slow down when the concentration of electrolyte decreases. For example, when the concentration of electrolyte decreases to 0.05 mol / L, the carbonization rate will slow down significantly.

[0112] (6) Compared with Example 1, the strength of the concrete specimens increased and the carbonation rate slowed down;

[0113] (7) Compared with Example 1, the connection between nodes in the closed loop is not good, and the carbonization speed will be slowed down.

[0114] (8) Compared with Example 1, the greater the distance between the cathode and the cement concrete specimen, the slower the carbonation rate will be.

[0115] (9) Compared with Example 1, the lower ambient temperature will slow down the carbonization rate.

[0116] (10) Compared with Example 1, the reduced ambient humidity will slow down the carbonization rate.

[0117] Comparative Example 2

[0118] Table 4. Similarities and differences between this invention and other rapid carbonization methods

[0119]

[0120]

[0121] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for rapid carbonation of cement concrete based on electrochemical synergy, characterized in that, Includes the following steps: Cement concrete is placed in a closed electrolytic cell containing electrolyte, and CO2 is introduced into the electrolyte for electrolytic carbonization.

2. An electrochemical carbonization apparatus for implementing the rapid carbonization method for cement concrete as described in claim 1, characterized in that, The electrochemical carbonization device includes a carbon dioxide cylinder and an electrolytic cell connected by a gas pipe; The electrolytic cell is equipped with an anode, a cathode, a power source, and a support for supporting the cement concrete specimen. The anode is placed on the top surface of the cement concrete specimen; The cathode is located on one side of the cement concrete specimen and is not in contact with the cement concrete specimen.

3. The electrochemical carbonization apparatus according to claim 2, characterized in that, The anode is made of metal; And / or, the cathode is made of graphite; And / or, the distance between the cement concrete specimen and the cathode is 50mm to 100mm.

4. A method for rapidly carbonizing cement concrete using the electrochemical carbonization apparatus according to any one of claims 2 to 3, characterized in that, Includes the following steps: Lay the cement concrete specimen flat and immerse it completely in the electrolyte for at least 48 hours to allow it to fully absorb water and obtain a moist cement concrete specimen. The moistened cement concrete specimen is placed upright on a support, and electrolyte is added so that the depth of the electrolyte is at least 20% of the height of the cement concrete specimen. The top cover of the electrolysis tank is then covered to form a sealed environment. Carbon dioxide from a carbon dioxide cylinder is introduced into the electrolyte through a gas tube, and the power is turned on to carry out electrolytic carbonization.

5. The method according to claim 4, characterized in that, The electrolyte comprises a NaHCO3 solution with a concentration of 0.5–1.5 mol / L.

6. The method according to claim 5, characterized in that, It also includes the step of replacing the electrolyte when the pH value of the electrolyte changes by more than 1 to 2.

7. The method according to claim 4, characterized in that, The electrolytic carbonization voltage is 10–36 V, and the current density is 0.5–2.0 mA / cm². 2 .

8. The method according to claim 4, characterized in that, The CO2 concentration in the electrolyzer is 20–30 vol.%.

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