Melamine derivative absorbent and application thereof in CO2 capture

Abstract

The invention discloses a melamine derivative absorbent and application thereof in CO2 capture, the melamine derivative absorbent has the following structural formula: # imgabs0 #, n1, n2 and n3 are saturated or unsaturated alkanes with 1-4 carbon atoms, n1, n2 and n3 can be the same or different, and groups R1, R2 and R3 are independently selected from one of hydrogen atom (H), methyl (-CH3), primary amine (-NH2), secondary amine (-NH-) and tertiary amine (-N-). The CO2 trapping solution based on the melamine derivative absorbent comprises the melamine derivative absorbent, water and / or a physical solvent. The melamine derivative absorbent is used for capturing CO2, and shows relatively high CO2 absorption rate and absorption capacity and relatively low desorption temperature. The melamine derivative absorbent not only has the characteristics of high absorption rate and high trapping capacity of a compound absorbent and a phase change absorbent, but also avoids the complexity and inconvenience of the existing mixed amine absorbent in the active amine screening and compounding process.

Description

Technical Field

[0001] The present invention belongs to the field of CO2 capture, and specifically relates to the development of a new chemical absorbent based on melamine derivatives and a method for applying the same to CO2 capture. Background Art

[0002] At present, the most widely studied and most mature carbon capture technology is the chemical absorption method based on alkaline absorbents. The essence is to use alkaline absorbents to react with CO2 in a low temperature environment (40°C) to form unstable salts to complete CO2 capture; then heat to 110-140°C to decompose the salts to release CO2, achieving CO2 enrichment and alcohol amine regeneration. However, since more than 50% of the heat energy is consumed in the heating and evaporation of the solvent during the desorption process, the desorption energy consumption is as high as 3.6-4.0GJ / tCO2, accounting for 80% of the total capture energy consumption, which greatly limits the large-scale promotion and application of chemical absorption. In order to promote the industrialization of chemical absorption, the development of new absorbents that can significantly reduce the energy consumption of CO2 capture has become a research focus and hotspot in the field of carbon capture.

[0003] Mixed amines are an important direction for the development of new absorbents in recent years. They combine different types of organic amines to integrate the absorption characteristics and advantages of different amines. Therefore, compared with single organic amines, mixed amines show faster CO2 absorption rate, higher CO2 absorption capacity and lower regeneration energy consumption. Lu et al. (Lu Shijian, Liu Jianwu, Yu Jianliang, etc. Capture of carbon dioxide in EOR output gas based on MDEA composite absorbent. Natural Gas Chemical Industry-C1 Chemistry and Chemical Engineering, 2019, 44, 79-85) took N-methyldiethanolamine as the main body, and added ethanolamine (MEA), diethanolamine (EDA), piperazine (PZ), 2-amino-2-methyl-1-propanol (AMP) and other activators. The results showed that the CO2 saturated absorption, CO2 regeneration rate and regeneration rate of this type of mixed amine absorbent were significantly improved compared with single N-methyldiethanolamine. Zhang et al. (R. Zhang, X. W. Zhang, Q. Yang, H. Yu, Z. W. Liang, X. Luo. Analysis of the reduction of energy cost by using MEA-MDEA-PZ solvent for post-combustion carbon dioxide capture (PCC), Appl. Energy 2017, 205, 1002-1011) studied the carbon capture energy consumption of MEA / MDEA / PZ mixed amine absorbents with different composition ratios and found that the energy consumption can be reduced by 15.22% to 49.22% depending on the ratio. Nwaoha et al. (C. Nwaoha, C. Saiwan, T. Supap, R. Idem, P. Tontiwachwuthikul, W. Rongwong, MJ Al-Marri, Abdelbaki Benamor. Carbon dioxide (CO2) capture performance of aqueous tri-solvent blends containing 2-amino-2-methyl-1-propanol (AMP) and methyldiethanolamine (MDEA) promoted by diethylenetriamine (DETA). Int. J. Greenhouse Gas Control 2016, 53, 292-304) compared the characteristics of a ternary mixed amine absorbent composed of AMP, MDEA and DETA and a MEA absorbent. Compared with the MEA absorbent, the cycle load and cycle capacity of the ternary mixed amine absorbent were increased by more than 100%, and the regeneration energy consumption was reduced by more than 50%.

[0004] According to the current research progress of absorbents at home and abroad, mixed amine absorbents combine the advantages of multiple single absorbents, have higher absorption capacity and absorption rate, and lower regeneration energy consumption. The overall technology is relatively mature, but there are still technical difficulties such as complex preparation process, tedious absorbent screening and ratio optimization. In addition, since the mixed amine absorbent needs to pay attention to the ratio of each component during use, the operation complexity is increased. Therefore, it is necessary to overcome these shortcomings through continuous technological innovation and optimization to promote the widespread application and development of composite amine absorbents in the field of CO2 capture. Summary of the invention

[0005] The purpose of the present invention is to address the deficiencies of the prior art and develop a melamine derivative absorbent and its application in CO2 capture, so as to further improve the CO2 absorption rate and absorption capacity, reduce the desorption temperature and regeneration energy consumption, and reduce solvent loss, while simplifying the preparation and operation process.

[0006] The melamine derivative absorbent provided by the present invention has the following structural formula:

[0007]

[0008] In the structural formula, n1, n2, n3 are saturated or unsaturated alkanes having 1 to 4 carbon atoms, n1, n2, n3 may be the same or different, the groups R1, R2, R3 are independently selected from one of hydrogen atom (H), methyl (-CH3), primary amine (-NH2), secondary amine (-NH-), tertiary amine (-N-), pyridine group, pyrrole group, and R1, R2, R3 may be the same or different.

[0009] The CO2 capture solution based on the melamine derivative absorbent provided by the present invention comprises the above-mentioned melamine derivative absorbent, water and / or a physical solvent.

[0010] In the above CO2 capture solution, the physical solvent is one or more of dimethyl sulfoxide, N,N-dimethylamide, cyclopentane, diethylene glycol dimethyl ether, and N-methylpyrrolidone.

[0011] In the above CO2 capture solution, the mass percentage of the melamine derivative absorbent is 5% to 30%, the mass percentage of water is 95% to 45%, and the mass percentage of the physical solvent is 0% to 25%. In a preferred embodiment, the mass percentages of the melamine derivative absorbent, the physical solvent and the water are 10%, 0% and 90% respectively.

[0012] The present invention provides a method for preparing the above-mentioned melamine derivative absorbent, the steps of which are as follows:

[0013] Dissolve halogenated melamine in toluene, add organic amine dropwise at 0-5°C, raise the temperature to 70-90°C and react for 2-6 hours after the addition is completed, cool to room temperature after the reaction is completed, remove the solvent, then add NaOH and dichloromethane, continue to heat to 30-55°C, react for 2-4 hours, filter, dry the obtained filtrate and remove the solvent to obtain a crude melamine derivative, and then purify it by recrystallization to obtain a high-purity melamine derivative;

[0014] The molar ratios of the organic amine, the halogenated melamine and NaOH are (1.0-5.0):1:(1.0-5.0) respectively.

[0015] In the above method, the halogenated melamine is preferably at least one of trichloro-s-triazine and 2-chloro-4,6-diamino-1,3,5-triazine; the organic amine is preferably at least one of 2-dimethylaminoethylamine, 2-dimethylaminopropylamine, methylamine, 2-(2-aminoethyl)pyridine and 2-(2-aminopropyl)pyrrole.

[0016] The present invention also provides a method for preparing the above-mentioned CO2 capture solution based on the melamine derivative absorbent, comprising the following contents:

[0017] The melamine derivative absorbent is added into a mixed solution of water and a physical solvent and mixed thoroughly to obtain a CO2 capture solution based on the melamine derivative absorbent.

[0018] The present invention also provides the use of the above melamine derivative absorbent in CO2 capture. Specifically, the application is used for preparing a CO2 capture solution.

[0019] The present invention also provides the use of the above melamine derivative in CO2 capture. Specifically, the application is as a CO2 absorbent.

[0020] The present invention also provides a method for capturing CO2 using the above-mentioned CO2 capture solution, comprising the following steps:

[0021] Step 1: Use a pre-prepared CO2 capture solution to absorb CO2 to form a CO2-rich solution (solution with high CO2 loading).

[0022] Step 2: Heat the CO2 rich solution obtained in step 1 to 60-80°C to desorb CO2 and regenerate the melamine derivative absorbent. After desorption, a CO2 lean solution (a solution with a low CO2 load) is obtained to achieve the recycling of the melamine derivative absorbent.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The melamine derivative absorbent of the present invention has the advantages of cheap and readily available raw materials and simple and easy synthesis steps. Its molecular structure contains basic functional groups such as primary amine, secondary amine and tertiary amine. The primary amine and secondary amine groups capture CO2 through a "zwitterion" reaction mechanism, showing a faster CO2 absorption rate, and the tertiary amine group captures CO2 through a "base catalysis" mechanism, showing a higher CO2 absorption capacity and a lower desorption temperature. Therefore, the melamine derivative absorbent not only has the characteristics of fast absorption rate and high capture capacity of composite absorbents and phase change absorbents, but also avoids the complexity and inconvenience of existing mixed amine absorbents in the active amine screening and compounding process.

[0025] 2. During the CO2 capture process, the desorption temperature of the melamine derivative absorbent of the present invention can be maintained at 60-80°C, which is 40°C lower than the desorption temperature of traditional absorbents, significantly reducing the energy consumption of CO2 capture.

[0026] 3. The CO2 capture solution based on the melamine derivative absorbent described in the present invention can adjust the CO2 capture efficiency and energy consumption by changing the chemical structure of the melamine derivative, the ratio of solvent to water, the type of physical solvent, etc., so as to meet the decarbonization requirements of different application scenarios (such as flue gas, biogas, natural gas, synthesis gas and air). BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 YesN 2 ,N 4 ,N 6 -Tris(2-(dimethylamino)ethyl)-1,3,5-triazine-2,4,6-triamine 1 H NMR spectrum.

[0028] Figure 2 YesN 2 ,N 4 ,N 6 -CO2 load curve of tris(2-(dimethylamino)ethyl)-1,3,5-triazine-2,4,6-triamine for absorbing mixed gases with different CO2 concentrations.

[0029] Figure 3 YesN 2 ,N 4 ,N 6 -CO2 desorption rate of CO2 saturated solution of tris(2-(dimethylamino)ethyl)-1,3,5-triazine-2,4,6-triamine at 80°C.

[0030] Figure 4 YesN 2 ,N 4 ,N 6Mass spectrum of -tris(3-(dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine.

[0031] Figure 5 YesN 2 ,N 4 ,N 6 -Tris(3-(dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine absorption rate of 40% CO2 mixed gas and CO2 load curve.

[0032] Figure 6 YesN 2 ,N 4 ,N 6 -Desorption rate and desorption ratio of a saturated solution of tris(3-(dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine at 80 °C.

[0033] Figure 7 YesN 2 ,N 4 ,N 6 -Tris(2-(dimethylamino)ethyl)-1,3,5-triazine-2,4,6-loading curve for absorbing CO2 from air.

[0034] Figure 8 YesN 2 -(3-(dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine 1 H NMR spectrum.

[0035] Fig. 9 YesN 2 -(3-(dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine absorbs 40% CO2 mixed gas absorption rate and CO2 load curve.

[0036] Fig.10 YesN 2 -(3-(Dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine CO2 rich solution desorption rate and desorption ratio at 80 °C. DETAILED DESCRIPTION

[0037] The present invention is further described below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art may make some non-essential improvements and adjustments to the present invention according to the above-mentioned invention content and implement the invention specifically, which still falls within the scope of protection of the invention.

[0038] The concentrations and content percentages in the following examples are all by mass percentage.

[0039] Example 1

[0040] (1) 4.60 g (25 mmol) of trichloro-s-triazine was dissolved in 100 ml of toluene and added to a three-necked flask. The solution temperature was lowered to 0-5°C. Subsequently, 8.90 g (87.5 mmol) of 3-dimethylaminoethylamine was added dropwise to the trichloro-s-triazine toluene solution. After the addition was completed, the temperature was raised to 80°C and reacted for 2-6 hours. After the reaction was completed, the reaction solution was cooled to room temperature and the solvent was removed. Subsequently, 3.00 g (75 mmol) of NaOH and 150 mL of dichloromethane were added and the temperature was continued to be raised to 40°C. The reaction was continued for 2-4 hours and filtered. The obtained filtrate was dried by adding MgSO4 and then filtered. The obtained filtrate was filtered again to remove the solvent to obtain N 2 ,N 4 ,N 6 -tris(2-(dimethylamino)ethyl)-1,3,5-triazine-2,4,6-triamine crude product, and then washed with a mixed solvent of dichloromethane and toluene (1:5, V / V) to obtain high-purity N 2 ,N 4 ,N 6 -tris(2-(dimethylamino)ethyl)-1,3,5-triazine-2,4,6-triamine, the structural characterization of which is shown in 1 H NMR ( Figure 1 ), the chemical shift of each proton peak in the compound has been assigned in the spectrum, and the integral area ratio of each proton resonance peak is in good agreement with the theoretical value, indicating that the compound has been successfully synthesized.

[0041]

[0042] (2) The obtained 6.78gN 2 ,N 4 ,N 6 -tris(2-(dimethylamino)ethyl)-1,3,5-triazine-2,4,6-triamine was added to 100 ml of deionized water and stirred at 25 °C until uniform to obtain N-based 2 ,N 4 ,N 6 -CO2 capture solution of tris(2-(dimethylamino)ethyl)-1,3,5-triazine-2,4,6-triamine absorbent.

[0043] The CO2 capture performance test was carried out using a laboratory-made CO2 absorption and desorption integrated device.

[0044] CO2 absorption performance: Mixed gases with different CO2 concentrations were introduced into 50g of the above 0.2mol / L CO2 capture solution. Figure 2 It can be seen that as the volume concentration of CO2 in the mixed gas increases, N 2,N 4 ,N 6 -tris (2- (dimethylamino) ethyl) -1,3,5-triazine-2,4,6-triamine absorbent solution CO2 loading also increased. This example proves that N 2 ,N 4 ,N 6 -Tris(2-(dimethylamino)ethyl)-1,3,5-triazine-2,4,6-triamine absorbent has the ability to absorb CO2 of different concentrations and can be used in different carbon capture scenarios.

[0045] CO2 desorption performance: The temperature is 80℃, and the desorption test is carried out on the above CO2 rich liquid. Figure 3 It can be seen that the higher the CO2 load, the greater the desorption rate. Taking 40% CO2 as an example, the CO2 desorption rate reaches a maximum value of 1.5mmol / s when desorbed for 2000 seconds at 80℃, while the CO2 desorption rate reaches a maximum value of 1.2mmol / s when desorbed for 3000 seconds at 40% CO2. After the reaction, the pH meter was used to measure N 2 ,N 4 ,N 6 The pH value of the tris(2-(dimethylamino)ethyl)-1,3,5-triazine-2,4,6-triamine absorbent solution was 9.88, confirming that it had been regenerated.

[0046] Example 2

[0047] The operation process of this embodiment is basically the same as that of embodiment 1, except that 3-dimethylaminoethylamine is replaced with 3-dimethylaminopropylamine during the synthesis process. 2 ,N 4 ,N 6 -Tris(3-(dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine, N 2 ,N 4 ,N 6 -Tris(3-(dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine structural characterization see mass spectrum ( Figure 4 ), the molecular weight of the compound is 382.3, which is consistent with the theoretical value, indicating that the compound has been successfully synthesized. At the same time, the solvent of the CO2 capture solution was changed from water to a mixed solvent of DMSO and water, N 2 ,N 4 ,N 6 The mass ratios of -tris(3-(dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine:DMSO:water are 10%:10%:80% respectively.

[0048]

[0049] The CO2 capture performance test was also carried out using a self-made CO2 absorption and desorption integrated device. The specific results are as follows: Figure 5-6 As shown, it is proved that N 2 ,N 4 ,N 6 -Tris(3-(dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine absorbent solution has the ability to capture CO2. This example proves that different types of melamine derivatives are suitable for CO2 capture.

[0050] Example 3

[0051] The operation process of this embodiment is basically the same as that of embodiment 2, except that the simulated flue gas in the CO2 absorption step is changed to air (CO2 concentration is 400ppm). During the entire air direct capture process, the MH-410D infrared CO2 gas sensor is used to monitor the CO2 concentration in the exhaust gas, and the experiment is stopped when the CO2 concentration at the outlet reaches 400ppm. Figure 7 As shown in the figure, on the first day, the CO2 concentration in the tail gas was only 200ppm, indicating that it has the ability to directly absorb CO2 from the air. On the fourth day, N 2 ,N 4 ,N 6 -Tris(3-(dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine absorbent reaches the upper limit of CO2 absorption.

[0052] Example 4

[0053] The operation process of this embodiment is basically the same as that of embodiment 1, except that in the synthesis process, trichloro-s-triazine is replaced by 2-chloro-4,6-diamino-1,3,5-triazine, N 2 -(3-(dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine structural characterization see 1 H NMR ( Figure 8 ), the chemical shift of each proton peak in the compound has been assigned in the spectrum, and the integral area ratio of each proton resonance peak is in good agreement with the theoretical value, indicating that the compound has been successfully synthesized. The ratio of CO2 capture solution is, N 2 The mass ratio of -(3-(dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine:water is 20%:80%.

[0054] The CO2 cycle absorption-desorption test was also carried out using a self-made CO2 absorption and desorption integrated device. The specific results are as follows Figure 9-10 As shown, it is proved that N 2 ,N 4 ,N 6-Tris(3-(dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine absorbent solution has the ability to capture CO2. This example proves that different types of melamine derivatives are suitable for CO2 capture.

[0055]

Claims

1. A melamine derivative absorbent, characterized in that: Its structural formula is as follows: In the structural formula, n1, n2, n3 are saturated or unsaturated alkanes having 1 to 4 carbon atoms, n1, n2, n3 may be the same or different, the groups R1, R2, R3 are independently selected from one of hydrogen atom (H), methyl (-CH3), primary amine (-NH2), secondary amine (-NH-), tertiary amine (-N-), pyridine group, pyrrole group, and R1, R2, R3 may be the same or different.

2. A CO2 capture solution based on the melamine derivative absorbent according to claim 1, characterized in that: The method comprises the melamine derivative absorbent according to claim 1, water and / or a physical solvent.

3. The CO2 capture solution according to claim 2, characterized in that: The physical solvent is one or more of dimethyl sulfoxide, N,N-dimethylamide, cyclopentane, diethylene glycol dimethyl ether, ethanol, isopropanol, and N-methylpyrrolidone.

4. The CO2 capture solution according to claim 2, characterized in that: The mass percentage of the melamine derivative absorbent is 5% to 30%, the mass percentage of water is 95% to 45%, and the mass percentage of the physical solvent is 0% to 25%.

5. The method for preparing the melamine derivative absorbent according to claim 1, characterized in that: Here are the steps: Dissolve halogenated melamine in toluene, add organic amine dropwise at 0-5°C, raise the temperature to 70-90°C and react for 2-6 hours after the addition is completed, cool to room temperature after the reaction is completed, remove the solvent, then add NaOH and dichloromethane, continue to heat to 30-55°C, react for 2-4 hours, filter, dry the obtained filtrate and remove the solvent to obtain a crude melamine derivative, and then purify it by recrystallization to obtain a high-purity melamine derivative; The molar ratios of the organic amine, the halogenated melamine and NaOH are (1.0-5.0):1:(1.0-5.0) respectively.

6. The method for preparing the melamine derivative absorbent according to claim 1, characterized in that: The halogenated melamine is preferably at least one of trichloro-s-triazine and 2-chloro-4,6-diamino-1,3,5-triazine; the organic amine is at least one of 2-dimethylaminoethylamine, 2-dimethylaminopropylamine, methylamine, 2-(2-aminoethyl)pyridine and 2-(2-aminopropyl)pyrrole.

7. The method for preparing a CO2 capture solution based on a melamine derivative absorbent according to claim 2, characterized in that: Includes the following: The melamine derivative absorbent is added into a mixed solution of water and a physical solvent and mixed thoroughly to obtain a CO2 capture solution based on the melamine derivative absorbent.

8. Use of the melamine derivative absorbent according to claim 1 in CO2 capture.

9. The use according to claim 8, characterized in that: The application is as a chemical absorbent for preparing CO2 capture solution.

10. A method for capturing CO2 using the CO2 capture solution according to claim 2, characterized in that: The following steps are involved: Step 1: Absorb CO2 with a pre-prepared CO2 capture solution to form a CO2-rich solution; Step 2: The CO2 rich liquid obtained in step 1 is heated to 60-80°C to desorb CO2 and regenerate the melamine derivative absorbent. After desorption, a CO2 lean liquid is obtained to achieve recycling of the melamine derivative absorbent.

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