Composite absorbent for separating carbon dioxide in mixed gas

Abstract

The invention discloses a composite absorbent for separating carbon dioxide in mixed gas. According to the composite absorbent for separating the carbon dioxide in the mixed gas, the composite absorbent is composed of hydroxyethyl ethylenediamine, benzyl alcohol and water, the desorption temperature of the composite absorbent is smaller than 100 DEG C, and the composite absorbent can be applied to the scene with the desorption temperature smaller than 100 DEG C and shows good absorption and desorption effects on the CO2 in the mixed gas.

Description

Technical Field

[0001] The invention relates to the technical field of waste gas treatment, and in particular to a composite absorbent for separating carbon dioxide from mixed gas. Background Art

[0002] With the development of global industrialization and urbanization, carbon dioxide (CO2) emissions have risen sharply. CO2 is one of the main greenhouse gases, and its increased concentration in the atmosphere will lead to an intensified greenhouse effect. Therefore, how to reduce CO2 emissions and capture CO2 has become an urgent matter. Among the various technologies for reducing CO2 emissions, the environmentally friendly and efficient carbon capture, utilization and storage (CCUS) technology can separate CO2 from fixed carbon emission sources such as industrial processes and energy utilization or the atmosphere, and after capture and compression, transport it to a specific location for conversion and utilization or inject it into a reservoir for storage, thereby separating CO2 from the atmosphere for a long time, thereby achieving permanent emission reduction, and becoming the main means of reducing CO2 emissions in the global industry. Based on my country's energy characteristics of rich coal, lack of oil and less gas, coal-fired power generation is still the main means of my country's electricity source, but this method will produce a large amount of CO2, and CCUS technology can effectively achieve the normal supply of electricity and low-carbon operation of the entire process of coal-fired power plants.

[0003] In the CCUS system, chemical absorption refers to the process of using chemical solvents as absorbents and utilizing the chemical reaction between absorbents and CO2 to achieve directional removal of CO2. The absorbent is alkaline and CO2 is acidic, and the two undergo an acid-base neutralization reaction to generate salts. By changing the external conditions, the entire reaction can be reversed, thereby achieving the purpose of CO2 desorption and absorbent recycling. Physical absorption refers to using physical solvents as absorbents, and changing physical conditions such as pressure and temperature to make the physical solvent absorb and desorb CO2. During the entire process, the physical solvent will not react chemically with CO2, and has the advantages of fast desorption rate and low regeneration energy consumption.

[0004] A variety of additives are commonly added to current absorbents, but the absorption and desorption effects of the absorbents on CO2 are not significant. The introduction of a variety of additives makes the composition of the absorbent more complex, which greatly increases the possibility of reactions between the components within the absorbent, thereby further reducing the absorption and desorption effects on CO2. Summary of the invention

[0005] The present application provides a composite absorbent for separating carbon dioxide from a mixed gas, which can improve the absorption and desorption effects of CO2 on the basis of using fewer types of chemical components.

[0006] An embodiment of the present application provides a composite absorbent for separating carbon dioxide from a mixed gas, which is composed of hydroxyethylethylenediamine (AEEA), benzyl alcohol and water. The desorption temperature of the composite absorbent is less than 100°C.

[0007] In some embodiments, the mass of the hydroxyethylethylenediamine accounts for 30% of the total mass of the composite absorbent, calculated by mass percentage.

[0008] In some embodiments, the mass of the benzyl alcohol accounts for 30-50% of the total mass of the composite absorbent, calculated by mass percentage.

[0009] In some embodiments, the mass of the water accounts for 20-40% of the total mass of the composite absorbent, in terms of mass percentage.

[0010] In some embodiments, the composite absorbent is composed of 30% hydroxyethylethylenediamine, 50% benzyl alcohol and 20% water, by mass percentage.

[0011] In some embodiments, the average absorption rate of the composite absorbent in 120 min is between 2.68×10 -2 L / min to 3.68×10 -2 L / min.

[0012] In some embodiments, the average desorption rate of the composite absorbent in 120 min is between 2.23×10 -2 L / min to 2.47×10 -2 L / min.

[0013] In some embodiments, the desorption rate of the composite absorbent is not less than 80%.

[0014] In some embodiments, the desorption temperature of the composite absorbent is 95°C.

[0015] In some embodiments, the mixed gas includes flue gas from a coal-fired power plant.

[0016] It can be seen from the above technical solution that this specification provides a composite absorbent for separating carbon dioxide from a mixed gas. The composite absorbent is composed of three components: hydroxyethylethylenediamine, benzyl alcohol and water. It can be used in scenarios where the desorption temperature is less than 100°C, and exhibits good absorption and desorption effects on CO2 in the mixed gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of 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 work.

[0018] Figure 1 The diagram of the carbon dioxide absorption and desorption experimental device provided by the present application is shown;

[0019] Figure 2 A schematic diagram showing relevant test results of the composite absorbents provided in Example 1 and Comparative Examples 1-9 is shown;

[0020] Figure 3 A schematic diagram showing relevant test results of the composite absorbent provided in Examples 1-6 is shown. DETAILED DESCRIPTION

[0021] In order to facilitate the understanding of this specification, the specification will be described more fully below with reference to the relevant drawings. The preferred embodiments of this specification are given in the drawings. However, this specification can be implemented in many different forms without departing from the core spirit of this specification and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of this specification more thorough and comprehensive.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which this specification belongs. The terms used herein in this specification are only for the purpose of describing specific embodiments and are not intended to limit this specification. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0023] An embodiment of the present application provides a composite absorbent for separating carbon dioxide from a mixed gas. The composite absorbent is composed of hydroxyethylethylenediamine, benzyl alcohol and water. The desorption temperature of the composite absorbent is less than 100°C.

[0024] The composite absorbent provided in the embodiment of the present application is composed of three components: hydroxyethylethylenediamine, benzyl alcohol and water. The composite absorbent is applied to the process of separating CO2 in the mixed gas, which can include two stages, namely the absorption stage of CO2 and the desorption stage of CO2. Among them, in the absorption stage of CO2, for hydroxyethylethylenediamine, it can react with CO2 to generate carbamate, which can be hydrolyzed in water to generate free amine, and the generated free amine will continue to absorb CO2; for benzyl alcohol, it absorbs CO2 as a physical solvent and will not react with CO2. In the desorption stage of CO2, the carbamate generated by the reaction of hydroxyethylethylenediamine and CO2 is relatively stable and not easy to desorb, and as mentioned above, benzyl alcohol only physically absorbs CO2 and will not react with CO2, so the introduction of benzyl alcohol can improve the desorption effect; and, because the sensible heat required for benzyl alcohol to be heated to the desorption temperature is less than the sensible heat of water, and the latent heat taken away by the evaporation of water vapor is eliminated, most of the energy saved is used for the desorption reaction, so the introduction of benzyl alcohol can accelerate the process of solution desorption and improve the desorption rate.

[0025] The composite absorbent provided in the embodiment of the present application can complete desorption at a temperature below 100°C without raising the desorption temperature to above 100°C, and thus can absorb and separate CO2 from a mixed gas whose original temperature is below 100°C.

[0026] In some embodiments, by mass percentage, the mass of hydroxyethylethylenediamine accounts for 30% of the total mass of the composite absorbent, the mass of benzyl alcohol accounts for 30-50% of the total mass of the composite absorbent, and the mass of water accounts for 20-40% of the total mass of the composite absorbent.

[0027] After a large number of experiments, it was found that by controlling the amount of each component in the composite absorbent, the absorption and desorption rate of the composite absorbent for CO2 can be adjusted. Compared with composite additives under other addition ratios, when the mass percentage of hydroxyethylethylenediamine is controlled to be 30%, the mass percentage of benzyl alcohol is 30-50%, and the mass percentage of water is 20-40%, the resulting composite absorbent can comprehensively show a higher absorption rate, desorption rate and desorption rate.

[0028] In some embodiments, the composite absorbent is composed of 30% hydroxyethylethylenediamine, 50% benzyl alcohol and 20% water in terms of mass percentage. The inventors have found through experiments that if the mass percentage of hydroxyethylethylenediamine, the mass percentage of benzyl alcohol and the mass percentage of water in the composite absorbent are further controlled to be 30%, 50% and 20%, respectively, the composite absorbent has better comprehensive performance in terms of absorption rate, desorption rate and desorption ratio.

[0029] In some embodiments, the average absorption rate of the composite absorbent in 120 min is between 2.68×10-2 L / min to 3.68×10 -2 L / min. For example, the average absorption rate of the composite absorbent in 120 min can be 2.68×10 -2 L / min, 2.80×10 -2 L / min, 3.00×10 -2 L / min, 3.24×10 -2 L / min, 3.40×10 -2 L / min, 3.60×10 -2 L / min, 3.68×10 -2 L / min or any value between any two of the above absorption rates.

[0030] In some embodiments, the average desorption rate of the composite absorbent in 120 min is between 2.23×10 -2 L / min to 2.47×10 -2 L / min. For example, the average desorption rate of the composite absorbent in 120 min can be 2.23×10 -2 L / min, 2.29×10 -2 L / min, 2.32×10 -2 L / min, 2.35×10 -2 L / min, 2.40×10 -2 L / min, 2.45×10 -2 L / min, 2.47×10 -2 L / min or any value between any two of the above desorption rates.

[0031] In some embodiments, the desorption rate of the composite absorbent is not less than 80%. After a large number of experiments, it is found that the composite absorbent provided in the embodiments of the present application, when used in the process of separating carbon dioxide from the mixed gas, exhibits a high desorption rate, which can reach more than 80%, for example, the desorption rate can be 80%, 80.1%, 85.9% or other values ​​greater than 80%.

[0032] In some embodiments, the desorption temperature of the composite absorbent is 95° C. The desorption temperature of the absorbent in the field of waste technology treatment of coal-fired power plants is generally 90-110° C. (normal pressure), but due to the presence of a certain mass of water in the solution system, if the desorption temperature exceeds 100° C. (exceeding the boiling point of water), a large amount of water will volatilize during the entire desorption process, which is not conducive to desorption. The industrial application field of this technology particularly values ​​desorption under normal pressure. Therefore, considering the actual desorption temperature range in industrial applications and the volatility characteristics of water, the suitable desorption temperature of the composite absorbent provided in the embodiment of the present application is below 100° C. For example, the desorption temperature can be 95° C.

[0033] In some embodiments, the mixed gas includes flue gas from a coal-fired power plant.

[0034] The following are specific preparation examples involved in the above content of the present disclosure. It should be clear that the following examples are only for illustrating the composite absorbent for separating carbon dioxide from mixed gas disclosed above, and the specific implementation methods and parameters used therein are only one or several methods in accordance with the numerous processes and methods described above. Those skilled in the art can use other parameters according to the content introduced in this specification and prepare the composite absorbent for separating carbon dioxide from mixed gas according to the above method without deviating from the core spirit disclosed in the application.

[0035] The examples and comparative examples of the present application use the following method to test the separation effect of the composite absorbent on carbon dioxide in the mixed gas. Figure 1 The following is a diagram of a carbon dioxide absorption and desorption experimental device provided in an embodiment of the present application. Figure 1 As shown, the device may include a simulated coal-fired power plant flue gas unit A, an absorption and desorption unit B and a carbon dioxide detection unit C.

[0036] The simulated coal-fired power plant flue gas unit A includes a nitrogen gas cylinder 1 and a carbon dioxide and nitrogen mixed gas cylinder 2. The carbon dioxide partial pressure in the carbon dioxide and nitrogen mixed gas cylinder 2 is 15%, and the nitrogen partial pressure is 85%. The simulated coal-fired power plant flue gas unit A is connected to the absorption and desorption unit B through a pressure reducing valve 3, a pressure reducing valve 4, a three-way valve 5, a three-way valve 6 and a flow meter 7. The absorption and desorption unit B includes a heating and stirring component 9, a temperature detection component 10 and a condensation reflux component 8. The absorption and desorption unit B is connected to the carbon dioxide detection unit C through a drying component 11. The carbon dioxide detection unit C includes a carbon dioxide infrared analyzer 12 and a computer 13. The carbon dioxide infrared analyzer 12 can monitor the concentration of carbon dioxide at the outlet in real time.

[0037] Among them, 15% CO2 and 85% N2 form a mixed gas to simulate flue gas, and the inlet flow rate of the mixed gas is controlled by the imported rotor flowmeter to determine the concentration reading of the imported CO2. The infrared gas analyzer 12 records the concentration reading of the outlet CO2 every 15 seconds. Because N2 will not participate in the reaction, the absorption capacity, absorption rate, desorption capacity, desorption rate and desorption rate of the absorbent for CO2 can be calculated through the flow rate of N2 and the change in the concentration of inlet and outlet CO2.

[0038] 1. The process of conducting the absorption experiment using the carbon dioxide absorption and desorption experimental device specifically includes the following steps:

[0039] (1) Preheating the infrared gas analyzer 12: Start the infrared gas analyzer 12 and start preheating for 15 minutes;

[0040] (2) Zeroing the infrared gas analyzer 12: After the infrared gas analyzer 12 is preheated, open the pressure reducing valve 3 and the nitrogen cylinder 1, place the three-way valve 5 in the infrared gas analyzer 12 passage, introduce nitrogen into the infrared gas analyzer 12 and start zeroing for 180 seconds;

[0041] (3) Preparation of absorbent: Prepare the required absorbent solution and transfer it into a three-necked flask;

[0042] (4) Install the absorption device: Place the three-necked flask and the serpentine condenser in a water bath and fix them on an iron stand. The condensed water flows in from the lower opening of the condenser and out from the upper opening. Insert the thermometer into the solution and connect the inlet pipe to the outlet pipe. The inlet pipe is placed below the liquid surface of the solution.

[0043] (5) Absorbent pretreatment: Turn on the water bath to heat, set the absorption temperature to 40°C, and the stirring speed to 200 rpm;

[0044] (6) Pipeline cleaning: Place three-way valve 5 in the reactor inlet passage, three-way valve 6 in the nitrogen passage, turn on the rotor flowmeter, and use nitrogen to exhaust the CO2 in the device and pipelines. Wait for the infrared gas analyzer 12 to return to zero, indicating that the CO2 in the device and pipelines has been exhausted.

[0045] (7) Start the absorption reaction: observe the thermometer reading to reach 40°C, close the pressure reducing valve 3 and the nitrogen cylinder 1, open the mixed gas cylinder 2 and the pressure reducing valve 4, place the three-way valve 5 in the reactor inlet passage, place the three-way valve 6 in the mixed gas passage, adjust the rotor flowmeter flow rate to 0.6 L / min, and the infrared gas analyzer 12 automatically counts every 3 seconds;

[0046] (8) End the absorption reaction: wait for the reading of the infrared gas analyzer 12 to stabilize at 15.00%, close the mixed gas cylinder 2 and the pressure reducing valve 4, open the nitrogen gas cylinder 1 and the pressure reducing valve 3, place the three-way valve 5 in the reactor inlet passage, and the three-way valve 6 in the nitrogen passage, wait for the reading of the infrared gas analyzer 12 to return to zero, indicating that the CO2 in the pipeline has been exhausted, turn off the water bath heating and stirring, disassemble the three-necked flask and the condenser, and turn off the infrared gas analyzer 12.

[0047] The data processing method corresponding to the CO2 absorption experiment is as follows:

[0048] (1) The absorption rate of CO2 by the absorbent at time t is:

[0049]

[0050] r abs (t)—the absorption rate of CO2 by the absorbent at time t, mol / min

[0051] Q abs,2 —The flow rate of CO2 at the inlet during the absorption experiment, L / min

[0052] Q abs,1 —N2 flow rate in absorption experiment, L / min

[0053] —Volume concentration of CO2 in the mixed gas at the outlet at time t

[0054] V m —Gas molar volume, 22.4L / mol

[0055] (2) The average absorption rate of CO2 by the absorbent at time 0-t is:

[0056]

[0057] —The average absorption rate of CO2 by the absorbent within time t

[0058] t-absorption time, min

[0059] (3) The CO2 absorption capacity of the absorbent during the time 0-t is:

[0060]

[0061]

[0062] R(t)—CO2 absorption capacity of the absorbent during the period from 0 to t, mol CO2 / kg solution

[0063] R'(t)—CO2 absorption capacity of the absorbent during the period from 0 to t, mol CO2 / mol amine

[0064] m—solution mass, kg

[0065] n—the amount of amine in the absorbent, mol.

[0066] 2. The process of conducting a desorption experiment using a carbon dioxide absorption and desorption experimental device specifically includes the following steps:

[0067] (1) Desorption reaction preparation: Turn on the water bath to heat, set the desorption temperature to 95°C, and the stirring speed to 200 rpm;

[0068] (2) Start the desorption reaction: When the absorbent solution reaches 95°C, open the nitrogen cylinder 1 and the pressure reducing valve 3, place the three-way valve 5 in the reactor inlet passage, place the three-way valve 6 in the nitrogen passage, adjust the rotor flowmeter flow rate to 0.6 L / min, and the infrared gas analyzer 12 automatically counts every 3 seconds;

[0069] (3) Ending the desorption reaction: Wait until the reading of the infrared gas analyzer 12 stabilizes at 1.00%, indicating that the desorption reaction is over, close the nitrogen cylinder 1 and the pressure reducing valve 3, turn off the heating and stirring of the water bath, disassemble the three-necked flask and the condenser, and turn off the infrared gas analyzer 12.

[0070] The data processing method corresponding to the CO2 desorption experiment is as follows:

[0071] (1) The desorption rate of CO2 by the absorbent at time t is:

[0072]

[0073] r des (t)—Desorption rate of CO2 by the absorbent at time t, mol / min

[0074] Q des —N2 flow rate in desorption experiment, L / min

[0075] —Volume concentration of CO2 in the mixed gas at the outlet at time t

[0076] V m —Gas molar volume, 22.4L / mol

[0077] (2) The average desorption rate of CO2 by the internal absorbent at time 0-t is:

[0078]

[0079] —Average desorption rate of CO2 by the absorbent during the time 0-t, mol / min

[0080] t—desorption time, min

[0081] (3) The CO2 desorption capacity of the absorbent during the time 0-t is:

[0082]

[0083]

[0084] L(t)—CO2 desorption capacity of the absorbent during the period from 0 to t, mol CO2 / kg solution

[0085] L'(t)—CO2 desorption capacity of the absorbent during the period from 0 to t, mol CO2 / mol amine

[0086] m—solution mass, kg

[0087] n—the amount of amine in the absorbent, mol

[0088] (4) The remaining amount of CO2 in the absorbent after one absorption and desorption experiment is:

[0089] C=RL

[0090] C'=R'-L'

[0091] C—Residual amount of CO2 in the absorbent, mol CO2 / kg solution

[0092] C'—residual amount of CO2 in the absorbent, mol CO2 / mol amine

[0093] (5) The CO2 desorption rate of the absorbent after the absorption and desorption experiment is:

[0094]

[0095] θ—CO2 desorption rate of absorbent, %.

[0096] Example 1

[0097] This embodiment provides a composite absorbent for separating carbon dioxide from a mixed gas. The composite absorbent is composed of 30% hydroxyethylethylenediamine, 30% benzyl alcohol and 40% water, calculated by mass percentage.

[0098] Comparative Examples 1-9

[0099] The composite absorbents provided in Comparative Examples 1-9 are substantially the same as those in Example 1, except that other solvents are used instead of benzyl alcohol in Comparative Examples 1-9.

[0100] The compositions of the composite absorbents provided in Example 1 and Comparative Examples 1-9 are shown in Table 1 below, where each component is expressed in percent by mass.

[0101] Table 1. Composition of the composite absorbent provided in Example 1 and Comparative Examples 1-9

[0102] serial number composition Example 1 Hydroxyethylethylenediamine + Benzyl alcohol + Water Comparative Example 1 Hydroxyethylethylenediamine + water Comparative Example 2 Hydroxyethylethylenediamine + n-propanol + water Comparative Example 3 Hydroxyethylethylenediamine + isopropyl alcohol + water Comparative Example 4 Hydroxyethylethylenediamine + n-butanol + water Comparative Example 5 Hydroxyethylethylenediamine + isobutyl alcohol + water Comparative Example 6 Hydroxyethylethylenediamine + tert-butyl alcohol + water Comparative Example 7 Hydroxyethylethylenediamine + polyethylene glycol + water Comparative Example 8 Hydroxyethylethylenediamine + ethylene glycol + water Comparative Example 9 Hydroxyethylethylenediamine + triethylene glycol + water

[0103] The aforementioned test method was used to test the experimental data corresponding to the composite absorbents provided in Example 1 and Comparative Examples 1-9. Figure 2 The schematic diagram of the test results of the composite absorbents provided by Example 1 and Comparative Examples 1-9 is shown in Table 2. The specific experimental test data of Example 1 and Comparative Examples 1-9 are shown in Table 2.

[0104] Table 2. Test results of composite absorbents provided by Example 1 and Comparative Examples 1-9

[0105]

[0106]

[0107] Combination Figure 2 , Table 2 shows that compared with the comparative examples, the composite absorbent prepared by using benzyl alcohol in Example 1 shows good effects in both absorption and desorption stages, with an absorption capacity of 61.08 LCO2 / L solution, a desorption capacity of 48.90 L CO2 / L solution, a desorption rate of 80.05%, and an average absorption rate of 3.68×10 -2 L / min, the average desorption rate reached 2.23×10 -2 L / min.

[0108] It should be noted that the inventors considered introducing diethylene glycol into the composite absorbent system during the experimental stage (replacing benzyl alcohol with diethylene glycol, or adding diethylene glycol on the basis of Example 1). However, under the same conditions, the viscosity of diethylene glycol is much higher than that of benzyl alcohol, such as at 298K and 0.1MPa, the viscosity of benzyl alcohol is 5.037cp, and the viscosity of diethylene glycol is 30cp. If diethylene glycol is introduced as a physical solvent, the viscosity of the absorbent solution will increase significantly, resulting in a decrease in the amount of CO2 absorbed by the solution. The reason is that a high-viscosity physical solvent will reduce the formation of ions in the solution and the rate of CO2 absorption. Since the viscosity of diethylene glycol is higher than that of benzyl alcohol, in the process of absorbing CO2, for a solution containing diethylene glycol, the rate of ion formation and CO2 absorption will be lower than that of the composite absorbent solution containing only benzyl alcohol in Example 1. Moreover, since diethylene glycol includes COC groups, and the COC groups and the amino groups in amines will form imines during the absorption reaction, the increase in the concentration of imines will hinder the combination of free amines in the solution with CO2, thereby reducing the absorption rate and amount of CO2; while the nucleophilic attack of benzyl alcohol on carbamate will generate alkyl carbonates and free amines, and the generated free amines will continue to absorb CO2, thereby increasing the absorption rate and amount of CO2 by the absorbent solution. Therefore, the introduction of diethylene glycol into the composite absorbent system does not have an advantage.

[0109] Embodiment 2-6

[0110] Examples 2-6 continue to compare the absorption and desorption performances of the composite absorbents prepared by changing the addition amounts of different components based on Example 1.

[0111] The compositions of the composite absorbents provided in Examples 1-6 are shown in Table 3 below, where each component in Table 3 is expressed in percent by mass.

[0112] Table 3. Composition of the composite absorbent provided by Examples 1-6

[0113] serial number Hydroxyethylethylenediamine Benzyl alcohol water Example 2 30％ 10％ 60％ Example 3 30％ 20％ 50％ Example 1 30％ 30％ 40％ Example 4 30％ 40％ 30％ Example 5 30％ 50％ 20％ Example 6 30％ 60％ 10％

[0114] The aforementioned test method was used to test the experimental data corresponding to the composite absorbent provided in each of Example-6. Figure 3 The schematic diagram of the test results of the composite absorbent provided by Examples 1 to 6 is shown. The specific experimental test data of Examples 1 to 6 are shown in Table 4.

[0115] Table 4. Test results of composite absorbents provided by Examples 1-6

[0116]

[0117]

[0118] Combination Figure 3 , Table 4 shows that, when the total amine concentration is 30wt%, with the increase of benzyl alcohol content and the decrease of water content, the absorption amount of hydroxyethylethylenediamine+benzyl alcohol+water gradually decreases, and the average absorption rate also gradually decreases. Among them, the absorption amount of 30wt% hydroxyethylethylenediamine+10wt% benzyl alcohol+60wt% water is the largest, reaching 62.27L CO2 / L solution. This is mainly because the carbamate generated by the reaction of hydroxyethylethylenediamine and CO2 will undergo hydrolysis reaction in the water system to generate free amines. The generated free amines will continue to absorb CO2, thereby increasing the absorption amount. Therefore, the addition of water is conducive to the increase of the absorption amount and the increase of the average absorption rate.

[0119] The desorption amount increases first and then decreases, wherein the desorption amount of 30wt% hydroxyethylethylenediamine+50wt% benzyl alcohol+20wt% water is the largest, reaching 51.85L CO2 / L solution. The desorption rate increases gradually, wherein the desorption rate of 30wt% hydroxyethylethylenediamine+60wt% benzyl alcohol+10wt% water is the largest, reaching 93.5%, and the average desorption rate increases gradually, mainly because the carbamate generated by the reaction of hydroxyethylethylenediamine and CO2 is relatively stable and difficult to desorb, and benzyl alcohol, as a physical solvent, only physically absorbs CO2 and does not react chemically with CO2, so the higher the benzyl alcohol content, the higher the desorption rate, and since the sensible heat required when benzyl alcohol is heated to the regeneration temperature is less than the sensible heat of water, the latent heat taken away by the evaporation of water vapor is eliminated, and most of the energy saved is used for the desorption reaction, thereby accelerating the process of solution desorption and improving the average desorption rate.

[0120] By comparing the absorption amount, desorption amount and desorption rate corresponding to the above 6 groups of composite absorbents with different proportions, it can be concluded that the comprehensive absorption-desorption effect of the ratio of 30wt% organic amine liquid + 50wt% benzyl alcohol + 20wt% water is the best.

[0121] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0122] The above-described embodiments only express several embodiments of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided by the present invention are all within the protection scope of the claims attached to the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims, and the description and drawings may be used to interpret the contents of the claims.

Claims

1. A composite absorbent for separating carbon dioxide from a mixed gas, characterized in that: The composite absorbent consists of hydroxyethylethylenediamine, benzyl alcohol and water, and the desorption temperature of the composite absorbent is less than 100°C.

2. The composite absorbent for separating carbon dioxide from mixed gas according to claim 1, characterized in that: Calculated by mass percentage, the mass of the hydroxyethylethylenediamine accounts for 30% of the total mass of the composite absorbent.

3. The composite absorbent for separating carbon dioxide from mixed gas according to claim 1, characterized in that: Calculated by mass percentage, the mass of the benzyl alcohol accounts for 30-50% of the total mass of the composite absorbent.

4. The composite absorbent for separating carbon dioxide from mixed gas according to claim 1, characterized in that: Calculated by mass percentage, the mass of the water accounts for 20-40% of the total mass of the composite absorbent.

5. The composite absorbent for separating carbon dioxide from mixed gas according to claim 1, characterized in that: According to mass percentage, the composite absorbent consists of 30% hydroxyethylethylenediamine, 50% benzyl alcohol and 20% water.

6. The composite absorbent for separating carbon dioxide from mixed gas according to claim 1, characterized in that: The average absorption rate of the composite absorbent in 120 min is between 2.68×10 -2 L / min to 3.68×10 -2 L / min.

7. The composite absorbent for separating carbon dioxide from mixed gas according to claim 1, characterized in that: The average desorption rate of the composite absorbent in 120 min is between 2.23×10 -2 L / min to 2.47×10 -2 L / min.

8. The composite absorbent for separating carbon dioxide from mixed gas according to claim 6 or 7, characterized in that: The desorption rate of the composite absorbent is not less than 80%.

9. The composite absorbent for separating carbon dioxide from mixed gas according to claim 1, characterized in that: The desorption temperature of the composite absorbent is 95°C.

10. The composite absorbent for separating carbon dioxide from mixed gas according to claim 1, characterized in that: The mixed gas includes flue gas from a coal-fired power plant.

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