Mixed alkali liquor carbon dioxide trapping agent and trapping method thereof

Abstract

The invention discloses a mixed alkali liquor carbon dioxide trapping agent and a trapping method thereof. The trapping agent comprises the following components in percentage by mass: 22-38% of main absorbent sodium carbonate, 1-10% of auxiliary absorbent A organic amine, 2-7% of auxiliary absorbent B sodium phosphate and / or disodium hydrogen phosphate and the balance of water. When the carbon dioxide is captured, the gas containing the carbon dioxide is in full contact with the mixed alkali liquid carbon dioxide capturing agent, the capturing agent absorbs the carbon dioxide to generate sodium bicarbonate precipitate, and the separated sodium bicarbonate solid is heated and desorbed at the temperature of 100-180 DEG C to obtain sodium carbonate, the carbon dioxide and water; and finally, returning the analyzed sodium carbonate to the mixed alkali liquor for recycling, and dehydrating, drying and purifying the mixed gas of carbon dioxide and water to obtain carbon dioxide. The trapping agent has the advantages of low cost, high carbon dioxide absorption capacity, high absorption rate, low regeneration energy consumption, safety and no toxicity; the sodium carbonate saturated solution is activated by using organic amine, so that the carbon dioxide absorption efficiency is improved; the separated sodium bicarbonate is heated and decomposed to obtain carbon dioxide, so that the working energy consumption is greatly reduced.

Description

Technical Field

[0001] The invention relates to a mixed alkali solution carbon dioxide capture agent and a capture method thereof, belonging to the technical field of carbon dioxide capture. Background Art

[0002] The global climate problem caused by the greenhouse effect is related to the excessive emission of carbon dioxide into the atmosphere by human activities. Major countries in the world have launched scientific research and technological development related to carbon emission reduction. At present, the thermal power industry is the largest source of carbon dioxide emissions in various energy production processes. The carbon dioxide partial pressure in the flue gas produced is low (10~15%), but capturing this part of carbon dioxide is the most difficult and the most difficult task.

[0003] At present, the chemical absorption method is a relatively mature technology for capturing carbon dioxide in flue gas from thermal power plants. However, traditional absorption methods such as the alcohol amine method and the ammonia method have disadvantages such as high raw material costs, high energy consumption for absorbent regeneration, toxicity and serious corrosion of equipment; the chemical absorption method based on carbonate solution has the advantages of low regeneration energy consumption, low toxicity, no degradation, no volatilization of absorption alkali, simple process and low price of absorption alkali, and has a good application prospect in the field of flue gas carbon dioxide capture. Summary of the invention

[0004] The object of the present invention is to provide a mixed alkaline solution carbon dioxide capture agent and a capture method thereof. The absorbent is safe and non-toxic and can reduce the carbon dioxide capture cost and capture energy consumption.

[0005] In order to achieve the above objectives, the present invention provides the following technical solutions.

[0006] A mixed alkaline solution carbon dioxide capture agent, wherein the components and their mass percentages are as follows: 20-40% of a main absorbent sodium carbonate, 1-10% of an auxiliary absorbent A organic amine, 2-10% of an auxiliary absorbent B sodium phosphate and / or disodium hydrogen phosphate, and the remainder is water.

[0007] Preferably, the components and their mass percentages are: 23-35% sodium carbonate as the main absorbent, 1-6% organic amine as the auxiliary absorbent A, 2-8% sodium phosphate and / or disodium hydrogen phosphate as the auxiliary absorbent B, and the rest is water.

[0008] More preferably, the components and their mass percentages are: main absorbent sodium carbonate 25-32%, auxiliary absorbent A organic amine 1-5%, auxiliary absorbent B sodium phosphate and / or disodium hydrogen phosphate 2-6%, and the rest is water.

[0009] Most preferably, the components and their mass percentages are: main absorbent sodium carbonate 25-32%, auxiliary absorbent A organic amine 2-4%, auxiliary absorbent B sodium phosphate and / or disodium hydrogen phosphate 2-4%, and the rest is water.

[0010] The organic amine as the auxiliary absorbent A is selected from organic amines commonly used in the current liquid amine method for capturing carbon dioxide, monoethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, and diisopropanolamine.

[0011] The preparation method of the carbon dioxide capture agent is as follows: the main absorbent sodium carbonate and the auxiliary absorbent organic amine, sodium phosphate and / or sodium dihydrogen phosphate are uniformly mixed with water.

[0012] The above-mentioned mixed alkali liquid carbon dioxide capture agent capture method comprises the following steps: (1) The gas containing carbon dioxide is fully contacted with the mixed alkali solution carbon dioxide capture agent, and the capture agent absorbs carbon dioxide to generate sodium bicarbonate precipitation; (2) separating sodium bicarbonate from the mixed alkali solution to obtain a solid; (3) heating sodium bicarbonate at 100-180°C to desorb sodium carbonate, carbon dioxide and water; (4) The sodium carbonate obtained by the analysis is returned to the mixed alkali solution for recycling, and the mixed gas of carbon dioxide and water is purified by dehydration and drying to obtain carbon dioxide.

[0013] In the above step (1), the absorption temperature of the collector is 30-60°C.

[0014] In the above step (1), the absorption pressure of the collector is from normal pressure to 2 MPa.

[0015] In the above step (1), the carbon dioxide concentration in the carbon dioxide-containing gas is 10-15%.

[0016] In the collector of the present invention, the absorbent A organic amine continuously "shuttles" up and down in the solution, greatly increasing the contact probability of carbon dioxide with the main absorbent, thereby shortening the time for the absorbent to absorb carbon dioxide to reach equilibrium. In the system, sodium phosphate and / or disodium hydrogen phosphate can increase the sodium ion concentration in the solution, thereby increasing the amount of sodium bicarbonate precipitation.

[0017] The present invention fully contacts the gas containing carbon dioxide with the capture agent, so that the capture agent absorbs carbon dioxide to generate a large amount of sodium bicarbonate precipitate, separates the sodium bicarbonate precipitate in the absorbed alkali solution, and further heats and regenerates it to obtain sodium carbonate.

[0018] At present, in the chemical process, concentrated potassium carbonate solution is mostly used to remove carbon dioxide from high-pressure tail gas. Sodium carbonate is also an absorbent of carbon dioxide, and its price is less than half of potassium carbonate. Sodium carbonate generates sodium bicarbonate after absorbing carbon dioxide. It has low solubility in water and can be precipitated in large quantities from alkaline solution. If the sodium bicarbonate precipitate is separated and heated to regenerate sodium carbonate, there is no need to heat the entire absorption system, which can greatly reduce the regeneration energy consumption.

[0019] The present invention obtains a new carbon dioxide capture agent by dissolving the main absorbent sodium carbonate, the organic amine absorbent and the auxiliary absorbent sodium phosphate and / or disodium hydrogen phosphate in water. After the capture agent absorbs carbon dioxide, a large amount of sodium bicarbonate precipitation will be generated to form a solid-liquid two-phase. Among them, the liquid phase contains a small amount of sodium bicarbonate, and the solid phase is mainly sodium bicarbonate. After the solid sodium bicarbonate is heated to release carbon dioxide, it is regenerated into sodium carbonate, and then mixed with the liquid phase to circulate and capture carbon dioxide. Compared with the prior art, the technical solution provided by the present invention has the following beneficial technical effects: 1. Using sodium carbonate as the alkaline substance for absorbing carbon dioxide greatly reduces the cost. The price of the main absorbent sodium carbonate is much lower than that of other absorbents, such as ethanolamine, diethanolamine, potassium carbonate, and liquid ammonia. When capturing the same amount of carbon dioxide, the present invention uses less sodium carbonate, which further reduces the cost of the absorbent of the present invention.

[0020] 2. The use of organic amines to activate the saturated sodium carbonate solution greatly improves the efficiency of capturing carbon dioxide. Compared with other activators such as amino acid ionic liquids and biological enzymes, the activator used in the present invention is resistant to high temperatures, has large working condition flexibility and low cost, and the organic amine / sodium phosphate activator is more suitable for ultra-large-scale flue gas capture.

[0021] 3. The properties of each substance in the system are stable and will not produce volatilization and oxidative degradation during the absorption and desorption cycle. The loss of absorbent in the circulation process is extremely small.

[0022] 4. Sodium carbonate, sodium phosphate, sodium bicarbonate, and disodium hydrogen phosphate are non-toxic, and only a small amount of diethanolamine as an activator is added and will not escape from the circulation system. Therefore, the absorbent of the present invention is safe and non-toxic during operation and is environmentally friendly.

[0023] 5. Sodium carbonate has good absorption capacity for sulfur oxides and nitrogen oxides, which reduces the cost of tail gas desulfurization and denitrification. After a period of operation, the sulfates and nitrates accumulated in the system can be separated, providing additional economic benefits.

[0024] 6. The present invention heats and decomposes the sodium bicarbonate precipitate separately to replace the traditional absorbent heating of the entire liquid phase system, and determines the reasonable and efficient regeneration conditions through experiments. Since only the sodium bicarbonate precipitate is heated and decomposed, the waste heat of the power plant can be used to replace the energy input of additional heating, which greatly reduces the working energy consumption and has little impact on the power generation efficiency of the power plant.

[0025] In summary, the absorbent provided by the present invention has the characteristics of low cost, large carbon dioxide absorption capacity, fast absorption rate, low regeneration energy consumption, safety and non-toxicity, and low carbon dioxide concentration of the absorbed gas at normal pressure. The carbon dioxide capture method using the absorbent has the advantages of strong absorption capacity and low analysis cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the experimental device used in Experimental Example 1; Figure 2 Schematic diagram of the experimental device used in Experimental Examples 2 and 3; Figure 3 A comparison chart of carbon dioxide absorption efficiency of activated saturated sodium carbonate solutions with different diethanolamine ratios provided in Example 1 and Comparative Examples 1-4; Figure 4 A comparison chart of the amount of sodium bicarbonate precipitate obtained from the carbon dioxide absorption experiment of activated saturated sodium carbonate solution with different diethanolamine ratios provided in Example 1 and Comparative Examples 1-4; Figure 5 A comparison chart of the filtrate pH of the sufficient carbon dioxide absorption experiment of the activated saturated sodium carbonate solution with different diethanolamine ratios provided in Example 1 and Comparative Examples 1-3; Figure 6 This is a comparison chart of the amount of sodium bicarbonate precipitate obtained from the sufficient carbon dioxide absorption experiment of diethanolamine-activated saturated sodium carbonate solution with different sodium phosphate ratios provided in Comparative Example 2 and Comparative Examples 5-7. DETAILED DESCRIPTION

[0027] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical scheme of the present invention is now described in detail in conjunction with embodiments and comparative examples. The following should not be construed as limiting the applicable scope of the present invention. Example 1

[0028] 19.85 g of sodium carbonate was dissolved in 50 g of deionized water to obtain a carbon dioxide capture agent.

[0029] Comparative Example 1 19.85 g of sodium carbonate as a primary absorbent and 0.25 g of diethanolamine as an activator were dissolved in 49.75 g of deionized water to obtain a carbon dioxide capture agent.

[0030] Comparative Example 2 19.85 g of sodium carbonate as a primary absorbent and 0.5 g of diethanolamine as an activator were dissolved in 49.5 g of deionized water to obtain a carbon dioxide capture agent.

[0031] Comparative Example 3 19.85 g of sodium carbonate as a primary absorbent and 1 g of diethanolamine as an activator were dissolved in 49 g of deionized water to obtain a carbon dioxide capture agent.

[0032] Comparative Example 4 19.85 g of sodium carbonate as a primary absorbent and 2.5 g of diethanolamine as an activator were dissolved in 47.5 g of deionized water to obtain a carbon dioxide capture agent.

[0033] Comparative Example 5 19.85 g of sodium carbonate as a primary absorbent, 2.5 g of diethanolamine as an activator and 1.985 g of sodium phosphate as an auxiliary absorbent were dissolved in 47.5 g of deionized water to obtain a carbon dioxide capture agent.

[0034] Comparative Example 6 19.85 g of sodium carbonate as a primary absorbent, 2.5 g of diethanolamine as an activator and 3.97 g of sodium phosphate as an auxiliary absorbent were dissolved in 47.5 g of deionized water to obtain a carbon dioxide capture agent.

[0035] Comparative Example 7 19.85 g of sodium carbonate as a primary absorbent, 2.5 g of diethanolamine as an activator and 5.955 g of sodium phosphate as an auxiliary absorbent were dissolved in 47.5 g of deionized water to obtain a carbon dioxide capture agent.

[0036] Experimental Example 1 The purpose of this experimental example is to determine the optimal mass fraction of diethanolamine in water when diethanolamine is used to activate saturated sodium carbonate solution to absorb carbon dioxide at low cost and high efficiency.

[0037] The carbon dioxide capture absorbent provided in Example 1 and Comparative Examples 1-4 is evenly stirred to obtain a completely clear solution without turbidity.

[0038] The schematic diagram of the experimental device used in Experimental Example 1 is as follows Figure 1 The methods of capturing carbon dioxide using five absorbents in this experimental example are as follows: Adjust the temperature of the heating stirrer to 30°C and set the magnetic stirring rate to 1200 rpm, prepare five kinds of collector solutions in Example 1 and Comparative Examples 1-4, weigh them after stirring evenly, record the weights as, the weights of anhydrous calcium chloride drying bottles 1 and 2 as, and the weight of the potassium hydroxide tail gas absorption bottle as. Open the gas cylinder outlet valve, use a soap film flowmeter to measure the gas flow rate, adjust the gas flow rate to 70 mL / min, connect the whole set of experimental equipment, and start timing after observing that the bubbler is emitting gas stably. During the process, a soap film flowmeter is used to measure the flow rate every 10 minutes to prevent the flow rate change caused by unstable air pressure from affecting the experimental results. After 30 minutes, the ventilation is stopped, and the absorption bottle, anhydrous calcium chloride drying bottle 1, anhydrous calcium chloride drying bottle 2 and potassium hydroxide tail gas absorption bottle are weighed, and the masses are recorded as,, and respectively.

[0039] This experimental example uses mass analysis to solve the problem, and uses the average absorption efficiency in the first 30 minutes of absorption to characterize the absorption capacity of the absorbent in the early stage of absorption. The calculation formula is as follows:

[0040] In the formula α is the average absorption efficiency of the collector in 30 minutes; m3 is the initial mass of the absorption bottle in the experiment, g; m 4 is the mass of the initial anhydrous calcium chloride drying bottle 1, g; m 5 is the mass of the initial anhydrous calcium chloride drying bottle 2, g; m 6 is the mass of the potassium hydroxide tail gas absorption bottle at the beginning of the experiment, g; m 3 ’ The mass of the absorption bottle at the end of the experiment, g; m 4 ’ To end the experiment, the mass of anhydrous calcium chloride drying bottle 1, grams; m 5 ’ To end the experiment, the mass of the anhydrous calcium chloride drying bottle 2, grams; m 6 ’ is the mass of the potassium hydroxide tail gas absorption bottle at the beginning of the experiment, g; See Example 1 and Comparative Examples 1 to 4 for a comparison of the absorption efficiency of the capture agent for a mixed gas containing 10% carbon dioxide (10% carbon dioxide, 90% nitrogen). Figure 3 .

[0041] According to the mass fraction of diethanolamine in water, the doping amount of diethanolamine will be screened from 0.5%, 1.0% and 2.0%. Figure 3 The average absorption efficiency in the middle 30 minutes was distributed in three sections: 0.0%~0.5%, and 2.0%~5.0%. With the increase of the amount of diethanolamine added, the absorption efficiency increased significantly. When the diethanolamine doping amount increased from 0.0% to 0.5%, the absorption efficiency increased from 20.0% to 38.0%, almost doubling, and the activation effect was the best. It can be seen that adding a small amount of diethanolamine to the system can greatly improve the absorption efficiency of saturated sodium carbonate solution for carbon dioxide. When the doping amount of diethanolamine was 0.5%~2.0%, the increase in the absorption efficiency of carbon dioxide slowed down significantly. When the doping amount of diethanolamine increased from 2.0% to 5.0%, its absorption efficiency tended to be flat, indicating that the addition of diethanolamine above 2.0% had limited effect on improving the absorption efficiency. In addition, the phenomenon of organic matter precipitation was observed at the end of the absorption of the 5.0% diethanolamine doping experimental group. Therefore, the mass fraction of diethanolamine in water is 1~4% is a suitable addition amount.

[0042] Experimental Example 2 The purpose of Experimental Example 2 is to determine the optimal mass fraction of diethanolamine in water when diethanolamine activates a saturated sodium carbonate solution to efficiently produce a precipitate of sodium bicarbonate.

[0043] The collectors of Example 1 and Comparative Examples 1-3 were prepared and stirred evenly to obtain completely clear solutions without turbidity.

[0044] The schematic diagram of the experimental device used in Experimental Example 2 is as follows Figure 2 The method for capturing carbon dioxide using the four capture agents of Example 1 and Comparative Examples 1 to 3 in this experimental example is as follows: Adjust the heating stirrer to keep the water bath at a constant temperature of 30°C, adjust the stirring speed to 1200 rpm, adjust the gas flow rate through the pressure gauge flowmeter, and use the soap film flowmeter to measure the mixed gas flow rate to be 200 mL / min. The total time for absorbing carbon dioxide is set to 11 hours. Measure the flow rate every 30 minutes to ensure that the total amount of carbon dioxide introduced within 11 hours of each experiment is the same. After the experiment, filter and separate the sodium bicarbonate precipitate, then place it in a petri dish to air dry naturally, and use a pH tester to determine the pH of the filtrate.

[0045] The comparison of the sodium bicarbonate precipitation obtained by the four collectors is as follows Figure 4 At the end of the carbon dioxide capture experiment, the filtrate pH was Figure 5 shown.

[0046] The mass fraction of diethanolamine in water increased from 0.0% to 0.5%, and the air-dried precipitate increased from 5.0 grams to 10.2 grams, an increase of 104%. The corresponding filtrate pH dropped from 10.8 to 10.3, with an obvious promoting effect, proving that a small amount of diethanolamine doping not only has a promoting effect in the early stage of carbon dioxide absorption, but also works in the middle and late stages of absorption. The mass fraction of diethanolamine in water increased to 1.0%, and the air-dried precipitate continued to increase, increasing by 132% compared with the undoped diethanolamine experimental group, and the pH remained at 10.3. Finally, the mass fraction of diethanolamine in water was increased to 2.0%, and its air-dried precipitate increased further, increasing by 176% compared with the undoped diethanolamine experimental group. At the end of the experiment, the filtrate pH dropped to 10.1. Figure 4 It can be seen that the mass of sodium bicarbonate precipitate obtained in the experiment is distributed in two stages: 0.0%-0.5% and 0.5%-2.0%, which proves that the addition of diethanolamine in the second stage also plays a role in accelerating the production of sodium bicarbonate precipitation.

[0047] The sufficient carbon dioxide absorption experiment proved that diethanolamine still had a good promoting effect in the middle and late stages of carbon dioxide absorption. Among all experimental groups, the 2.0% diethanolamine doping group showed the best performance. Considering the experimental results of the absorption efficiency of Experimental Example 1, the mass fraction of diethanolamine in water was 1-4%, which had the best comprehensive efficiency in improving the time and cost of carbon dioxide absorption by the system.

[0048] Experimental Example 3 The purpose of Experimental Example 3 is to determine the optimal mass fraction of sodium phosphate in sodium carbonate in a saturated sodium carbonate solution activated by diethanolamine in order to further increase the amount of sodium bicarbonate precipitation and maintain a benign circulation operation of the absorbent.

[0049] The collectors of Comparative Examples 3, 5, 6 and 7 were prepared and used in the carbon dioxide absorption experiment of Experimental Example 3 after being stirred evenly.

[0050] The schematic diagram of the experimental device used in Experimental Example 3 is as follows Figure 2 , the method of capturing carbon dioxide is as follows: Adjust the heating stirrer to make the water bath reach 30°C, the stirring speed is 1200 rpm, use the soap film flowmeter to measure the gas flow, and adjust the mixed gas flow to 200mL / min. Measure the flow rate every 30 minutes, and stop the aeration when the system pH is 10.0. After the experiment, filter and separate the sodium bicarbonate precipitate, then place it in a petri dish to air dry, and measure the pH of the filtrate.

[0051] The comparison of the amount of sodium bicarbonate precipitate obtained by capturing carbon dioxide using four capture agents in this experimental example is as follows: Figure 6 shown.

[0052] Compared with the experimental group in which no sodium phosphate (0.0%) was added to the absorbent, the amount of sodium bicarbonate precipitate obtained in the absorption experiment increased significantly after adding sodium phosphate. In terms of the mass fraction of sodium phosphate to sodium carbonate, the air-dried precipitate obtained by the 10.0%, 15.0%, 20.0% and 30.0% sodium phosphate doped experimental groups increased by 25.4%, 26.8%, 26.8% and 58.5%, respectively. Among them, the 30% sodium phosphate doped experimental group had the largest increase, but because its slurry was too viscous, it was not practical to have the operability of cyclic capture in reality, so it was not suitable to add 30% sodium phosphate by mass of sodium carbonate. There was little difference in the effect of increasing the amount of sodium bicarbonate precipitate in the 10.0%, 15.0% and 20.0% doped experimental groups. Therefore, considering the cost and the effect of cyclic operation, it is better to add 10-20% sodium phosphate by mass of sodium carbonate to the system, and the best addition amount is 10%.

[0053] In summary, the optimal composition of the absorbent for capturing carbon dioxide in flue gas determined in Experimental Examples 1-3 of the present invention is to add 2% of diethanolamine by weight of water to a saturated sodium carbonate solution at 30°C, and to add 10% of sodium phosphate by weight of sodium carbonate. At a temperature of 30°C, diethanolamine can increase the initial carbon dioxide absorption rate of a saturated sodium carbonate solution by 2.5 times, and the carbon dioxide absorption within 11 hours by 3.2 times. The addition of 10% sodium phosphate can further increase the amount of sodium bicarbonate precipitation by about 25% on the basis of the promotion of diethanolamine. Example 2

[0054] 200 grams of sodium carbonate as a main absorbent, 20 grams of triethanolamine as an activator, 15 grams of diethanolamine as an activator and 20 grams of sodium phosphate as an auxiliary absorbent were dissolved in 500 grams of deionized water to obtain a carbon dioxide capture agent. Example 3

[0055] 200 grams of main absorbent sodium carbonate, 40 grams of activator N-methyldiethanolamine, 30 grams of auxiliary absorbent sodium phosphate, and 10 grams of disodium hydrogen phosphate were dissolved in 500 grams of deionized water to obtain a carbon dioxide capture agent. Example 4

[0056] 200 grams of sodium carbonate as a main absorbent, 50 grams of diisopropanolamine as an activator and 40 grams of disodium hydrogen phosphate as an auxiliary absorbent were dissolved in 500 grams of deionized water to obtain a carbon dioxide capture agent. Example 5

[0057] 200 grams of sodium carbonate as a main absorbent, 30 grams of triethanolamine as an activator and 20 grams of sodium phosphate as an auxiliary absorbent were dissolved in 500 grams of deionized water to obtain a carbon dioxide capture agent. Example 6

[0058] 200 grams of main absorbent sodium carbonate, 30 grams of activator monoethanolamine, 20 grams of auxiliary absorbent sodium phosphate, and 10 grams of disodium hydrogen phosphate are dissolved in 500 grams of deionized water to obtain a carbon dioxide capture agent.

[0059] The present invention further increases the amount of the capture agent, prepares the carbon dioxide capture agents described in Examples 2-6, and further verifies the capture effect thereof, and obtains experimental results similar to those of Comparative Example 5. In particular, in terms of organic amine absorbents, various substituted organic amines and ionic liquids can also be used.

Claims

1. A mixed alkali solution carbon dioxide capture agent, characterized in that The components and their mass percentages are as follows: main absorbent sodium carbonate 22-38%, auxiliary absorbent A organic amine 1-10%, auxiliary absorbent B sodium phosphate and / or disodium hydrogen phosphate 2-10%, and the rest is water.

2. The mixed alkali solution carbon dioxide capture agent according to claim 1, characterized in that The components and their mass percentages are as follows: main absorbent sodium carbonate 23-35%, auxiliary absorbent A organic amine 1-6%, auxiliary absorbent B sodium phosphate and / or disodium hydrogen phosphate 2-8%, and the rest is water.

3. The mixed alkali solution carbon dioxide capture agent according to claim 2, characterized in that The components and their mass percentages are as follows: main absorbent sodium carbonate 25-32%, auxiliary absorbent A organic amine 1-5%, auxiliary absorbent B sodium phosphate and / or disodium hydrogen phosphate 2-6%, and the rest is water.

4. The mixed alkali solution carbon dioxide capture agent according to claim 3, characterized in that The components and their mass percentages are as follows: main absorbent sodium carbonate 25-32%, auxiliary absorbent A organic amine 2-4%, auxiliary absorbent B sodium phosphate and / or disodium hydrogen phosphate 2-4%, and the rest is water.

5. The mixed alkali solution carbon dioxide capture agent according to any one of claims 1 to 4, characterized in that: The organic amine of the auxiliary absorbent A is selected from monoethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine and diisopropanolamine.

6. The mixed alkali solution carbon dioxide capture agent according to claim 1, characterized in that: The sodium phosphate and disodium hydrogen phosphate are added in any proportion.

7. The method for preparing the carbon dioxide capture agent according to claim 1, characterized in that: The main absorbent sodium carbonate and the auxiliary absorbent organic amine, sodium phosphate and / or sodium dihydrogen phosphate are uniformly mixed with water.

8. The method for capturing carbon dioxide using a capture agent according to claim 1, characterized in that The steps include: (1) The gas containing carbon dioxide is fully contacted with the mixed alkali solution carbon dioxide capture agent, and the capture agent absorbs carbon dioxide to generate sodium bicarbonate precipitation; (2) separating sodium bicarbonate from the mixed alkali solution to obtain a solid; (3) heating sodium bicarbonate at 100-180°C to desorb sodium carbonate, carbon dioxide and water; (4) The sodium carbonate obtained by the analysis is returned to the mixed alkali solution for recycling, and the mixed gas of carbon dioxide and water is purified by dehydration and drying to obtain carbon dioxide.

9. The capture method according to claim 8, characterized in that: In the above step (1), the absorption temperature of the collector is 30-60°C, and the absorption pressure is from normal pressure to 2 MPa.

10. The capture method according to claim 8, characterized in that: In the above step (1), the carbon dioxide concentration in the carbon dioxide-containing gas is 10-15%.

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