High-moisture-resistance amine-grafted solid adsorbent for directly capturing carbon dioxide from air as well as preparation method and application of high-moisture-resistance amine-grafted solid adsorbent

Abstract

The invention provides a high-moisture-resistance amine-grafted solid adsorbent for directly capturing carbon dioxide from air as well as a preparation method and application of the high-moisture-resistance amine-grafted solid adsorbent. The preparation method comprises the following steps: (1) providing an amino-functionalized porous silicon dioxide carrier, and (2) carrying out protective modification on a primary amine group on the surface of the carrier by utilizing di-tert-butyl dicarbonate ester to form an RNH-Boc structure, and constructing a compact hydrophobic layer on the surface layer of the adsorbent. The hydrophobic layer constructed by the invention effectively inhibits permeation and diffusion of water molecules through a steric hindrance effect, and stabilizes carbamate bonds generated in the adsorption process to resist hydrolysis. Under the condition of 30% relative humidity, the water absorption capacity of the adsorbent is only 22.5 wt% of that of BHG before modification, after 10 times of adsorption / desorption cycles, the CO2 adsorption capacity is improved by 69.2%, the problems of amine loss and performance degradation of an amine functionalized adsorbent in wet cycles are effectively solved, and the adsorbent is suitable for direct capture of carbon dioxide under wet conditions such as the atmospheric environment.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide capture technology, specifically relating to an amine-functionalized solid adsorbent with excellent moisture resistance and cycle stability prepared by hydrophobic group chemical modification technology, and its application in direct air capture of carbon dioxide. Background Technology

[0002] Direct air capture (DAC), as a key negative emission technology, has received widespread attention from academia and industry. Unlike capturing CO2 from high-concentration point sources (such as coal-fired power plants), DAC treats ambient air with extremely low concentrations (approximately 420 ppm) and complex compositions (containing O2, water vapor, etc.), which places extremely stringent requirements on the performance of capture materials. Among numerous CO2 capture materials, amine-functionalized porous solid adsorbents, especially those using mesoporous silica (such as SBA-15, MCM-41) as a carrier and chemically grafting organic amines (such as aminosilanes), have shown great potential in CO2 capture due to their high selectivity, low energy consumption, and non-corrosiveness.

[0003] However, the application of such adsorbents in real atmospheric environments (typically containing 0-100% relative humidity) faces severe challenges. Water vapor is the primary environmental factor leading to their failure, and moisture has a dual effect on amine adsorbents: under moderate humidity, moisture may slightly increase adsorption capacity by promoting bicarbonate formation; however, during cycling, especially in the temperature-induced desorption stage, water molecules compete with amine groups for adsorption, inducing oxidative degradation and hydrolytic loss of amine groups, as well as damage to the support structure, leading to rapid degradation of adsorbent performance. Therefore, improving the chemical stability and cycle life of amine-based solid adsorbents in humid environments has become a core technical bottleneck that must be overcome to promote the large-scale application of DAC technology.

[0004] Currently, amino-functionalized solid adsorption is a gas separation technology based on the principle of selective and reversible CO2 adsorption by adsorbents, capable of efficiently removing CO2 from flue gas. Compared to traditional liquid amine chemical absorption, this technology significantly reduces energy consumption by eliminating the need for large amounts of aqueous solutions. Although current technical bottlenecks include limited processing capacity and sensitivity to impurity gases, it exhibits unique advantages in treating low-concentration CO2 flue gas: it possesses abundant amino active sites, significantly increasing CO2 adsorption capacity; it has low regeneration energy consumption; it is less corrosive to equipment; and it has strong adaptability to changes in flue gas conditions. These characteristics make it highly advantageous for CO2 capture from stationary emission sources such as coal-fired power plants, and it is widely recognized as one of the most promising carbon capture technologies. Current research focuses on developing novel adsorbents with high capacity and high selectivity, as well as optimizing adsorption-desorption process parameters to further improve techno-economic efficiency. However, the CO2 adsorption capacity of traditional unprotected amino-grafted silica adsorbents can decrease by more than 70% after 10 cycles at 30% relative humidity, severely limiting its industrial application. To overcome these shortcomings, existing technologies have undergone some improvements. Some researchers have used cross-linking agents to prepare powdered adsorbents into particles, and then loaded organic amines onto calcined precursors using impregnation or chemical grafting methods to form immobilized amine adsorbents. This increases mechanical strength, reduces amine loss, and improves the stability and cyclicability of the adsorbent. However, this method still has significant limitations: it does not fundamentally prevent water molecule contact, but only delays water vapor-induced amine loss and structural collapse. Its water resistance test, involving immersion in water for ten minutes, is an extreme static test, and its performance will inevitably degrade significantly in real humid flue gas. In humid environments, water molecules need to desorb first before CO2 can contact the amine sites, prolonging the adsorption equilibrium time and reducing collection efficiency. Furthermore, acidic gases in real industrial flue gas may undergo irreversible reactions with the amines. Finally, its resistance to moisture and stability in long-term real humid flue gas still needs improvement.

[0005] Therefore, developing a method for preparing amine-based solid adsorbents that can maintain high adsorption capacity and excellent cycling stability in humid environments has become a key factor in promoting the development of direct air capture technology. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for developing a hydrophobically modified amine solid adsorbent with high moisture resistance and cycling stability. This method utilizes a triple synergistic mechanism: the steric hindrance effect of tert-butyl forming a hydrophobic film on the pore surface, the promotion of the urethane hydrolysis desorption process, and the weakening of competition between water molecules and CO2 for active sites by a dense hydrophobic secondary amine layer. This effectively suppresses the negative impact of humidity on the amine adsorbent.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A highly moisture-resistant amine-grafted solid adsorbent for direct air capture of carbon dioxide comprises the following steps:

[0009] (1) The grafting agent was added to the aqueous solution of the carrier and mixed evenly. Then, the mixture was heated and refluxed under continuous stirring. After the reaction was completed, the mixture was filtered, washed and dried to obtain the precursor of amine grafting defects.

[0010] (2) The precursor carbonate obtained in step (1) and toluene solution are sealed, mixed thoroughly, and reacted in an oil bath. After the reaction is completed, the mixture is separated, washed, and dried to obtain ditert-butyl dicarbonate (Boc) protected amine graft solid adsorbent (BHG-Boc-100%).

[0011] According to a preferred embodiment of the present invention, the carrier in step (1) is boron-doped ultrasonically extracted hierarchical mesoporous silicon (B-HMS-U).

[0012] According to a preferred embodiment of the present invention, the aqueous solution in step (1) is toluene.

[0013] According to a preferred embodiment of the present invention, the mixing step in step (1) is as follows: 3g of B-HMS-U is added to 300mL of toluene, sealed and packaged, and stirred for 60min.

[0014] According to a preferred embodiment of the present invention, the heating temperature in step (1) is 85 °C and the reflux time is 16 h.

[0015] According to a preferred embodiment of the present invention, the washing step in step (1) is as follows: the filtered product is washed three times with toluene and ethanol respectively.

[0016] According to a preferred embodiment of the present invention, the percentage of hydroxyl groups protected by the hydrophobic group in step (2) is 50-100%. The hydrophobic protecting group is Boc.

[0017] According to a preferred embodiment of the present invention, the oil bath reaction in step (2) is carried out at 50°C for 24 h.

[0018] According to a preferred embodiment of the present invention, the washing step in step (2) is: washing with toluene and n-hexane three times.

[0019] According to a preferred embodiment of the present invention, the drying step in step (2) is: drying at 60°C for 12 hours in a vacuum drying oven.

[0020] The technical features and beneficial effects of this invention are as follows:

[0021] (1) By constructing a moisture-resistant hydrophobic layer directly at the molecular level through a Boc protection strategy, the problem of chemical degradation and loss of amine groups in humid environments is fundamentally solved. This hydrophobic layer physically blocks water molecule penetration through the huge steric hindrance effect of the tert-butyl group and resists hydrolysis by utilizing stable carbamate bonds, creating a "molecular armor" effect. This invention endows amines with high stability from a molecular structure perspective.

[0022] (2) Excellent stability against moisture cycling and low energy consumption characteristics, especially suitable for direct air capture in real atmospheric environments with complex composition. Under harsh conditions of 25°C, 420 ppm CO2 and 30% relative humidity, the adsorbent of this invention retains more than 90% of its CO2 adsorption capacity after 10 adsorption / desorption cycles, and the performance decay rate is less than 10%, which is far superior to the comparative patent, which has a capacity retention rate of about 80% after 100 cycles due to amine loss.

[0023] (3) The entire process does not require the use of inorganic crosslinking agents for high-temperature calcination and molding, and the process conditions are mild, avoiding the risk of collapse of the carrier pores and decomposition of amine groups at high temperatures. This invention, while maintaining the original high specific surface area and hierarchical pore structure of the carrier, achieves improved stability through liquid-phase chemical modification, ensuring that the adsorbent possesses both high amine loading, high dispersibility, and rapid adsorption kinetics. In contrast, the high-temperature calcination and molding process of the comparative patent may lead to pore shrinkage and a decrease in specific surface area, which is the fundamental reason for its "molding loss".

[0024] (4) By flexibly adjusting the proportion of Boc protection and the early design of the carrier (such as boron doping and silanol nest construction), the present invention can precisely optimize the hydrophobic properties, amine loading and CO2 diffusion rate of the adsorbent, making it suitable not only for direct air capture, but also for various low-concentration CO2 capture scenarios such as humid industrial tail gas and biogas purification, meeting the diverse carbon capture needs under different humidity and concentration conditions.

[0025] (5) The adsorbent prepared by the present invention still maintains high adsorption capacity under ultra-low CO2 partial pressure. Under DAC conditions of 25℃ and 420 ppm, the adsorption capacity can reach 2.3-2.5 mmol / g. At the same time, its core modifying reagent Boc has wide applications in organic synthesis and is cost-controllable. Moreover, the final adsorbent does not contain any precious metal components. It achieves an excellent balance between high efficiency, durability and economy, providing strong material support for the large-scale and commercialization of direct air capture technology. Attached Figure Description

[0026] Figure 1 Example 1 and Comparative Examples 1-3: Cyclic adsorption capacity at 25°C and 30% relative humidity. Detailed Implementation

[0027] An amine-functionalized solid adsorbent based on hydrophobic group chemical modification and its application in direct air CO2 capture. To make the advantages and technical solutions of the present invention clearer and more explicit, the present invention will be further described below with reference to specific embodiments.

[0028] Example 1

[0029] A method for preparing a hydrophobically modified amine-based solid adsorbent includes the following steps:

[0030] (1) 3 g of mesoporous silica support was vacuum dried at 100 °C for 3 h. The dried support was dispersed in 300 mL of anhydrous toluene and stirred for 60 min. Then, 6 mL of diethylenetriaminepropyltrimethoxysilane was added to the system, and the mixture was refluxed at 85 °C for 16 h. After the reaction was completed, the mixture was filtered and the solid product was washed repeatedly with toluene and anhydrous ethanol. Finally, the mixture was vacuum dried at 60 °C for 12 h to obtain the amino-functionalized support, denoted as BHG.

[0031] (2) Place 2.0 mmol of BHG carrier from step (1) into a 100 mL single-necked flask. In another container, dissolve 2.0 mmol of di-tert-butyl dicarbonate in 20 mL of toluene. Transfer this solution to the flask containing BHG. A mixed solution is obtained.

[0032] (3) Place the mixed solution from step (2) in an oil bath at 50°C and react for 24 hours. After the reaction is complete, filter to separate the solid powder and wash it three times each with toluene and n-hexane. Finally, dry it in a vacuum drying oven at 60°C for 12 hours to obtain the final product, denoted as BHG-Boc-100%.

[0033] Comparative Example 1

[0034] A method for preparing a hydrophobic group-modified amine solid adsorbent is the same as described in Example 1, except that no carbonate is added in step (2), and the resulting adsorbent is named BHG.

[0035] Comparative Example 2

[0036] A method for preparing a hydrophobic group-modified amine solid adsorbent is the same as described in Example 1, except that the carbonate added in step (2) is dimethyl carbonate, and the resulting adsorbent is named BHG-methyl-100.

[0037] Comparative Example 3

[0038] A method for preparing a hydrophobic group-modified amine solid adsorbent is the same as described in Example 1, except that the carbonate added in step (2) is dibutyl carbonate, and the resulting adsorbent is named BHG-buyl-100.

[0039] Experimental Example 1

[0040] The adsorbents prepared in Example 1 and Comparative Examples 1-3 were tested for their moisture resistance. The specific steps are as follows:

[0041] Moisture resistance and thermal stability are important parameters for direct air CO2 capture materials. We used thermogravimetric analysis (TGA) to test the water absorption of the adsorbents. The water absorption of the adsorbents was calculated by measuring the weight change of the adsorbents. The adsorbents were dehydrated at 100℃ for 10 min under nitrogen atmosphere. After cooling to 25℃, the airflow was switched to a nitrogen atmosphere with a relative humidity of 30% for 10 min. Finally, the temperature was raised to 80℃ and held for 10 min. The water absorption of each adsorbent was measured, and the calculated water absorption results are shown in Table 2.

[0042] Table 1. Water absorption and CO2 adsorption after 10 cycles in Example 1 and Comparative Examples 1-3

[0043] sample Water absorption (wt%) <![CDATA[CO2 adsorption capacity (mmol / g) after 10 cycles]]> Comparative Example 1 6.09 0.41 Comparative Example 2 3.57 1.48 Comparative Example 3 2.29 1.62 Example 1 1.37 2.12

[0044] Experimental Example 2

[0045] The adsorbents prepared in Example 1 and Comparative Examples 1-3 were tested for their cycling performance after 10 cycles. The specific steps are as follows:

[0046] Cyclic stability is a core indicator for the industrial application of adsorbents, directly determining system operating costs and sustainability. Therefore, 10 cycle performance tests were conducted at 25℃ and 30% relative humidity. The cyclic adsorption capacity of adsorbents protected by different types of hydrophobic groups was measured. Figure 1 As shown, the cyclic adsorption capacity of the adsorbents in Example 1 and Comparative Examples 1-3 is displayed.

[0047] Chemical structure analysis of dimethyl carbonate, dibutyl carbonate, and di-tert-butyl dicarbonate revealed that Boc exhibits the weakest polarity and strongest hydrophobicity due to the combined influence of the methyl group and carbon chain length. Therefore, it demonstrates the best cycling stability, with an adsorption capacity of 2.12 mmol / g after 10 adsorption / desorption cycles. The wet cycling performance is 69.2% higher than Comparative Example 1, and only 9.4% lower than that of fresh Example 1. During cycling, it maintains relatively fast adsorption kinetics. This is because the dense secondary amine hydrophobic layer prevents water from forming a physical water film on the adsorbent surface and inhibits the degradation of the urethane layer, thus hindering the contact between CO2 and the amino active sites. This indicates that utilizing Boc to protect the amino group effectively improves the adsorbent's moisture resistance.

[0048] This invention successfully prepared a hydrophobic amine-based solid adsorbent using a "hydrophobic group chemical modification" technique. By introducing hydrophobic groups (such as Boc) onto the surface of the solid amine adsorbent for chemical modification, a triple synergistic mechanism is utilized: the steric hindrance effect of the tert-butyl group forming a hydrophobic film on the pore surface, the promotion of the urethane hydrolysis desorption process, and the weakening of competition between water molecules and CO2 for active sites by the dense hydrophobic secondary amine layer. This effectively suppresses the negative impact of humidity on the amine adsorbent. Furthermore, the adsorption capacity showed no significant decrease after 10 cycles of adsorption-desorption testing, demonstrating a good cost advantage.

[0049] For any parts not described in this invention, existing technologies can be used as a reference. The above embodiments are only for illustrating the technical concept and features of this invention, and are intended to enable those skilled in the art to understand the content of this invention and implement it accordingly. However, the scope of protection of this disclosure is not limited thereto. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A highly moisture-resistant amine-grafted solid adsorbent for direct air capture of carbon dioxide, comprising the following steps: (1) Provides an amino-functionalized porous silica support; (2) The amino-functionalized carrier obtained in step (1) is mixed with ditert-butyl dicarbonate (Boc) in an organic solvent and reacted at 50-80°C for 12-36 hours. After the reaction is completed, the solid product is separated, washed and dried to obtain the hydrophobic modified amino-based solid adsorbent.

2. The method for preparing a highly moisture-resistant amine-grafted solid adsorbent for direct air capture of carbon dioxide according to claim 1, characterized in that, The amine-functionalized porous silica support mentioned in step (1) is prepared by loading organic amine molecules containing primary amine groups onto the porous silica support by chemical grafting; the organic amine molecules are preferably diethylenetriaminepropyltrimethoxysilane.

3. A method for preparing a highly moisture-resistant amine-grafted solid adsorbent for direct air capture of carbon dioxide according to claim 1 or 2, characterized in that, The porous silica support in step (1) is a silicon material with a layered bimodal mesoporous structure; preferably, the support is a boron-doped silicon material with the template agent removed by ultrasonic extraction.

4. The method for preparing a highly moisture-resistant amine-grafted solid adsorbent for direct air capture of carbon dioxide according to claim 1, characterized in that, The amount of ditert-butyl dicarbonate used in step (2) is such that the protection ratio of the primary amine groups in the amine functionalized carrier reaches 50% to 100%.

5. The method for preparing a highly moisture-resistant amine-grafted solid adsorbent for direct air capture of carbon dioxide according to claim 1, characterized in that, The organic solvent mentioned in step (2) is toluene, dichloromethane or tetrahydrofuran.

6. The method for preparing a highly moisture-resistant amine-grafted solid adsorbent for direct air capture of carbon dioxide according to claim 1, characterized in that, The reaction described in step (2) is carried out under an inert atmosphere.

7. A highly moisture-resistant amine-grafted solid adsorbent for direct air capture of carbon dioxide, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 6.

8. A highly moisture-resistant amine-grafted solid adsorbent for direct air capture of carbon dioxide according to claim 7, characterized in that, The adsorbent surface has a hydrophobic layer composed of an RNH-Boc structure; preferably, the secondary amine content on the adsorbent surface is not less than 90%.

9. The application of a highly moisture-resistant amine-based solid adsorbent as described in claim 7 or 8 in the capture of carbon dioxide in a gas.

10. The application according to claim 9, characterized in that, The gas is ambient air or industrial exhaust gas containing moisture; preferably, the CO2 adsorption capacity of the adsorbent decreases by no more than 10% after 10 adsorption / desorption cycles under a relative humidity of 30%.

11. A method for preparing a highly moisture-resistant amine-grafted solid adsorbent for direct air CO2 capture, characterized in that, It was prepared using the preparation method described in claim 1.

Images