CN116393098A - CO adsorption modified by amine 2 Preparation method and application of acid-activated attapulgite material - Google Patents

Abstract

The invention belongs to the technical field of carbon dioxide capture and storage, and specifically discloses a preparation method of an acid-activated attapulgite material modified by amine to absorb _CO2 and its application in _CO2 capture in flue gas of a coal-fired power plant. The present invention uses attapulgite (ATP) as a raw material, and after acid activation, it is modified by impregnation with tetraethylenepentamine (TEPA) to obtain an acid-activated attapulgite material that absorbs _CO through amine modification . Introducing TEPA into the attapulgite material, compared with ordinary adsorbents, this material has excellent water resistance and cycle stability, and can maintain more outstanding carbon dioxide adsorption performance under different carbon dioxide concentrations, so the present invention It has practical significance for the research and development of carbon dioxide adsorbents that operate efficiently and stably for a long time.

Description

A preparation method and method of acid-activated attapulgite material modified by amine to absorb CO2 application

technical field

The invention belongs to the technical field of carbon dioxide capture and storage, and in particular relates to a preparation method of an acid-activated attapulgite material modified by amine to absorb _CO2 and its application in _CO2 capture in flue gas of a coal-fired power plant.

Background technique

CO ₂ is the most important greenhouse gas in the world, and the greenhouse effect brought about by the increase of CO ₂ concentration in the atmosphere has become one of the major environmental problems. Fossil fuel power plants are the largest source of carbon dioxide emissions. In order to control the emission of carbon dioxide, people have carried out a lot of research. Among them, carbon dioxide capture and storage (CCS) technology is a sustainable strategy to reduce short- and medium-term carbon dioxide emissions. The process aims to capture _CO2 emitted from large industrial facilities before it enters the atmosphere by different methods such as physical absorption method, chemical solvent method, cryogenic method and membrane system. Among these methods, liquid amine-based adsorption techniques have been extensively studied and also used industrially for decades. However, this method has disadvantages such as solvent loss, equipment corrosion, and high regeneration energy consumption. Therefore, to avoid these drawbacks, many studies have focused on CO2 capture on solid amine sorbents. Through chemical grafting and physical impregnation, amines are loaded on different solid substrates to absorb CO ₂ . Solid amine adsorbents have the advantages of high adsorption capacity, strong selectivity, good stability, and low energy consumption.

Among these solid amine adsorbents, different high specific surface area porous materials have been found for _CO2 capture, including molecular sieves, activated carbons, organic frameworks, and clays. Among them, clay minerals have attracted extensive attention due to their easy availability, low price, good adsorption properties, and good chemical and thermal stability. Some people use silane coupling agent to react with attapulgite to prepare _CO2 capture agent with good selectivity. Attapulgite clay is considered an ideal material because of its low cost and good performance, and its main source is attapulgite clay. Attapulgite clay is mainly composed of attapulgite (70% to 80%), and also contains a small amount of kaolinite, montmorillonite, quartz, sepiolite, hydromica and opal. The theoretical chemical formula of attapulgite is Mg ₅ Si ₈ O ₂₀ (OH) ₂ (OH ₂ ) ₄ 4H ₂ O. It is a chain-like hydrous magnesium aluminum silicate clay mineral and belongs to the 2:1 type clay mineral. . The chains aggregate in two dimensions to form semi-closed corridors, unlike other clay minerals. Due to this unique structure, attapulgite has a variety of special physical and chemical properties, mainly including adsorption, catalysis, ion exchange, rheology and plasticity. In terms of _CO2 adsorption, Li et al. used MEA-modified attapulgite to selectively adsorb _CO2 in simulated biogas, and its _CO2 adsorption capacity was greater than 2 mmol/g.

The introduction of amine is also an important part of the preparation of solid amine adsorbents, and the modification methods are mainly divided into impregnation method and grafting method. The impregnation method refers to soaking the porous material in an organic amine solution, and loading the organic amine onto the surface and pores of the material, thereby improving the adsorption selectivity and adsorption capacity of the adsorbent for _CO2 . Commonly used impregnation organic amines mainly include ethanolamine (MEA), diethanolamine (DEA), tetraethylenepentamine (TEPA), polyethyleneimine (PEI), n-methyldiethanolamine (MDEA) and the like. Khail et al. used the impregnation method to load MEA on activated carbon, and found that many active sites were formed on the surface of impregnated activated carbon, which improved the _CO2 adsorption capacity and selectivity. Ardhyarini et al. found that when MDEA was impregnated on the mesoporous carbon surface with a loading of 43wt%, the _CO2 adsorption capacity increased from 1.60mmol/g to 2.63mmol/g, while when the MDEA loading was 50wt%, the _CO2 adsorption dropped to 1.76mmol/g. This is due to the excessive loading of organic amines, which leads to severe blockage of the pore structure of the material, which is not conducive to _CO2 adsorption. Therefore, it is necessary to reasonably control the loading of organic amines. The grafting method is to connect nitrogen-containing functional groups to the surface of the adsorption material through chemical bonds. This method can effectively reduce the volatilization of organic amines, but the steps are more complicated. Bamdad et al. grafted aminopropyltriethyloxysilane (APTES) to the surface of oxidized biomass activated carbon, and found that the content of N in the grafted activated carbon increased from 0.15 (%) to 3.90 (%), and the CO The maximum adsorption capacity of ₂ was 3.70mmol/g.

Contents of the invention

In view of the deficiencies in the above-mentioned prior art, the object of the present invention is to provide a preparation method and application of an acid-activated attapulgite material modified by amines to absorb CO ₂ . The present invention has prepared a highly efficient, stable, low-cost, and recyclable _CO2 adsorption material, using attapulgite (ATP), a material with low cost, as a raw material, and after acid activation, tetraethylenepentamine ( TEPA) impregnation method to modify it to obtain good _CO2 adsorption capacity and stability in flue gas.

In order to achieve the above object, the present invention takes the following technical solutions:

A kind of preparation method of the acid-activated attapulgite material that absorbs _CO through amine modification, comprises the following steps:

(1) preparing acid-activated attapulgite: activating attapulgite with acid to obtain acid-activated attapulgite;

(2) Amine modification: The acid-activated attapulgite obtained in step (2) was impregnated with tetraethylenepentamine, and after drying, the acid-activated attapulgite material modified by amine to absorb _CO2 was obtained.

Preferably, in step (1), the attapulgite is passed through a 50-mesh sieve, preferably, through a 50-200 mesh sieve, more preferably, through a 50-100 mesh sieve; the attapulgite is carried out before acid activation Washing with deionized water and pre-filtering to remove water-soluble impurities.

Further, in step (1), the concentration of the acid is 1-5mol/L, wherein the solid-liquid ratio, that is, the ratio of the mass of attapulgite to the volume of the acid is 1:10 to 1:20, g/mL, Described acid is any one in hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, is preferably hydrochloric acid, more preferably 2mol/L hydrochloric acid.

Further, in step (2), the acid-activated attapulgite obtained in step (2) is used after dissolving the tetraethylenepentamine in an organic solvent, and the ratio of the tetraethylenepentamine to the organic solvent is ( 0.6-1.2) g: (8-15) mL, preferably (0.6-1.2) g: 10 mL, the organic solvent is methanol.

Further, in step (2), the ratio of the mass of tetraethylenepentamine to the mass of acid-activated attapulgite is 20%-40%, preferably 25%-35%, more preferably 30%.

Further, in step (2), the soaking time is 10-15h, preferably 12h.

Application of the acid-activated attapulgite material modified by the above method to absorb _CO2 in the capture of _CO2 in flue gas.

Further, the flue gas is flue gas from a coal-fired power plant.

Further, the CO ₂ capture temperature is 40°C to 70°C, preferably 50°C to 60°C, more preferably 60°C.

Further, the CO ₂ concentration in the flue gas ranges from 10vol% to 20vol%.

Further, the adsorption mechanism of the acid-activated attapulgite material modified by amines to absorb CO ₂ in flue _gas under dry conditions is: 1 mol CO ₂ reacts with 2 mol amine groups to form a stable carbamate. The acid-activated attapulgite material modified by amines to adsorb _CO2 changes its adsorption mechanism for _CO2 when water vapor exists in the flue gas, and _CO2 reacts with amine groups 1:1 to form bicarbonate, which increases the The utilization rate of the adsorbent helps to improve the adsorption capacity of the adsorbent; on the other hand, in the presence of water, carbamate can also react with carbon dioxide and water to form bicarbonate, which promotes the adsorption of _CO2 . Therefore, preferably, the flue gas is under humid conditions or contains water vapor in the flue gas.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

(1) Change the attapulgite structure by acid activation, increase the specific surface area and the number of active sites;

(2) TEPA modification can significantly improve the _CO2 adsorption capacity of HATP and provide more active sites;

(3) This material has excellent water resistance and cycle stability;

(4) It can maintain more outstanding carbon dioxide adsorption performance under different carbon dioxide concentrations.

Description of drawings

Figure 1: XRD patterns of ATP, HATP and TEPA/HATP adsorbents with different ratios of TEPA.

Figure 2: IR spectra of ATP, HATP and TEPA/HATP adsorbents with different ratios of TEPA.

Figure 3: SEM spectra of ATP, HATP and TEPA/HATP adsorbents with different ratios of TEPA, where: (a) is ATP, (b) is HATP, (c) is 20TEPA/HATP, (d) is 30TEPA /HATP, (e) is 40TEPA/HATP.

Figure 4: Thermogravimetric spectra of ATP, HATP and TEPA/HATP adsorbents with different ratios of TEPA.

Figure 5: _N adsorption-desorption curves and pore size distribution curves of ATP, HATP, and TEPA/HATP adsorbents with different ratios of TEPA.

Figure 6: Breakthrough curves and _CO adsorption capacity of ATP, HATP, and TEPA/HATP with different TEPA ratios.

Figure 7: Effect of reaction temperature on _CO2 adsorption performance of 30TEPA/HATP adsorbent.

Figure 8: Effect of _CO2 concentration on _CO2 adsorption performance of 30TEPA/HATP adsorbent.

Figure 9: Effect of water vapor on _CO adsorption performance of HATP and 30TEPA/HATP adsorbents.

Figure 10: 10 _CO adsorption cycle stability of 30TEPA/HATP adsorbent at 60 °C.

Detailed ways

The following is the applicant's further description of the technical solution of the present invention in combination with specific embodiments and accompanying drawings, but the scope of protection claimed by the claims of the present invention is not limited to the embodiments.

Raw materials used in the following examples: attapulgite (ATP) was purchased from Yixiang New Material Co., Ltd., and all attapulgite was pulverized by a pulverizer to pass through a 50-mesh sieve and reserved for future use. The original attapulgite was tested by X-ray fluorescence spectrometer (XRF), and it was found that attapulgite contained a large amount of SiO ₂ and other various metal oxides, wherein the contents of O and Si elements were 45.50% and 26.39%, respectively, Ca The four metal elements, Fe, Al and Mg accounted for more than other metal elements, accounting for 9.32%, 6.27%, 5.62% and 4.20% respectively.

Embodiment 1: A kind of preparation method of the acid-activated attapulgite material that absorbs _CO through amine modification, the steps are as follows:

(1) Pretreatment of ATP: take 20g of attapulgite crushed to pass through a 50 mesh sieve, wash and filter with deionized water, and repeat 3 times; take another 5g of attapulgite crushed to pass through a 50 mesh sieve with deionized After washing with water and filtering for 3 times, it was directly placed in an oven at 105°C to dry for 12 hours. The sample was labeled as ATP. After testing, its specific surface area was 91.06m ² g ^-1 , and its pore volume was 0.233cm ³ g ^-1 .

(2) Acid activation of ATP: Take ATP that has not been dried after being washed with deionized water and filtered in (1), and add 300mL2mol/L hydrochloric acid to it, wherein: the ratio of solid to liquid is 1:15, and the ratio of solid to liquid refers to uneven The ratio of the mass (g) of the rod clay to the volume (mL) of hydrochloric acid was magnetically stirred at 70° C. for 4 hours, and the stirring speed was 1200 rpm. After stirring, filter, wash with water until neutral, and dry in an oven at 105°C for 12 hours to obtain acid-activated ATP, marked as HATP. After testing: its specific surface area is 179.96m ² g ^-1 , and its pore volume is 0.293cm ³ g ^-1 .

(3) TEPA modification: Dissolve 0.6g, 0.9g, and 1.2g of tetraethylenepentamine (TEPA) in 10mL of methanol, and then add 3g of the acid-activated ATP in (2) to tetraethylenepentamine methanol solution , magnetically stirred at room temperature for 12 hours, and the stirring speed was 1200rpm. After the stirring was completed, it was directly placed in an oven at 75°C to dry for 6 hours to obtain acid-activated attapulgite materials modified by amines to adsorb CO ₂ . The samples were marked as 20TEPA /HATP, 30TEPA/HATP and 40TEPA/HATP adsorbents, the specific surface area and pore volume data are shown in Table 1.

Embodiment 2: performance characterization of adsorbent

Figure 1 shows the XRD patterns of ATP, HATP and TEPA/HATP adsorbents with different TEPA dosages, observing the crystal structure. It can be found that all materials can present the peak of attapulgite, which confirms that the addition of acid and TEPA did not change the crystal structure of ATP. In the ATP spectrum, the characteristic peaks of dolomite are 32.1°, 42.2°, 46.1° and 52.2°, respectively. After HCl treatment, the activated ATP (HATP) has no obvious dolomite peak. This phenomenon shows that 2mol/L HCl activation can remove impurity dolomite in attapulgite without destroying the crystal structure of ATP, thereby increasing the pore structure of ATP and releasing more active sites, which is beneficial to the addition of TEPA. At the same time, after acid treatment, a large amount of impurity ions such as Al ³⁺ , Ca ²⁺ , and Mg ²⁺ are dissolved, and the internal pore size and specific surface area of ATP increase, which is beneficial to the improvement of adsorption capacity. With the increase of the amount of TEPA modifier, the characteristic peak intensity of attapulgite increased significantly, indicating that TEPA promoted the crystallization of ATP. The increase in crystallinity can facilitate the adsorption of gas on the surface of the adsorbent, resulting in a better _CO2 removal rate.

In order to observe the functional groups of attapulgite and confirm the introduction of TEPA, FTIR experiments were carried out, and the curve is shown in Figure 2. From the untreated ATP spectrum, three peaks at 3606cm ^-1 , 3570cm ^-1 and 3516cm ^-1 can be detected, which are related to different hydroxyl groups. There is an obvious stretching vibration peak at 1288cm ^-1 for Mg-O, but this peak disappears after acid treatment. It shows that HCl activation can remove impurities in ATP and increase the number of active sites, which is consistent with the XRD results. In addition, the peak at 944 ^cm can be attributed to the stretching vibration of Si-O, and the peaks at 1599 ^cm and 744 ^cm are related to the surface hydroxyl groups. After TEPA impregnation, some new peaks appeared in the TEPA/HATP spectrum. Among them, 2890cm ^-1 , 1530cm ^-1 and 1420cm ^-1 are the stretching vibration peaks of CH, NH and CN respectively, indicating a large amount of loading of amine. Large amounts of TEPA may also lead to stronger peaks in the spectrum. Therefore, the FTIR results confirmed the successful introduction of TEPA, and the possible interactions are as follows:

Si-OH+RNH ₂ →Si-O ^- N ⁺ H ₃ R(1)

The surface morphology of ATP, HATP and TEPA/HATP adsorbents with different TEPA dosages was observed by SEM, and the results are shown in Figure 3, wherein: (a) is ATP, (b) is HATP, (c) For 20TEPA/HATP, (d) for 30TEPA/HATP, (e) for 40TEPA/HATP. It can be observed that the untreated ATP has a fibrous structure, and the fibers are densely aggregated together. After acid treatment, the fibers of HATP are more dispersed, indicating that acid modification can disperse the dense and orderly fibers in attapulgite, thereby increasing its specific surface area and enhancing the adsorption capacity of the adsorbent. After loading TEPA, agglomeration of some ATP fibers could be observed on attapulgite, indicating that amines were deposited on attapulgite. Interestingly, the addition of TEPA can reorder the fiber distribution. This can be attributed to the interaction of attapulgite with amines, as shown in formula (1). TEPA compounds can cover the surface of clay minerals to promote fiber agglomeration. This phenomenon leads to a decrease in the BET surface area of the ATP sample.

The thermal stability of original ATP and modified ATP was studied by TG, and the results are shown in Fig. 4. The weight loss process of the unmodified ATP material can be divided into three stages on the TG curve. The weight loss below 300°C (8.4%) can be explained by the removal of physically absorbed water and carbon dioxide, and the weight loss between 300°C and 550°C (4.1%) can be attributed to the spillage of chemically absorbed water. The final stage (9.5%) above 550 °C is the decomposition stage of impurities in the ATP sample. The TG curve of the HATP sample below 550 °C is similar to that of ATP, but when the temperature increases, the TG curve remains stable because the impurities have been removed by the acid. For TEPA-modified HATP materials, the weight loss is more obvious in the initial stage due to the excellent wet adsorption capacity of TEPA molecules. Above 120 °C, the weight loss of the TEPA/HATP curve is more significant, which is related to the volatilization and decomposition of amines. From 100°C to 250°C, the loss on the curve is most pronounced. The total weight loss rates of 20TEPA/HATP, 30TEPA/HATP and 40TEPA/HATP were 21.0%, 26.9% and 36.5%, respectively, indicating that the decrease in weight loss rate was related to the amount of modified TEPA.

The structural properties of different ATP adsorbents were characterized by _N2 adsorption-desorption experiments. The isotherm is shown in (a) in Figure 5, and the pore size distribution obtained by the BJH method is shown in (b) in Figure 5. The BET specific surface area and pore volume data for ATP, HATP and TEPA/HATP are summarized in Table 1. It can be seen from (a) in Figure 5 that both ATP and the modified material exhibit a typical type-iv isotherm, when the relative pressure P/P0 is greater than 0.4, the _N2 adsorption-desorption isotherm appears The obvious H3-type hysteresis loop indicates that a crack-type mesopore (mesoporous) structure appears in the ATP material. This crack-type mesoporous structure is considered to provide more active sites for TEPA molecules. The existence of hysteresis loops in mesoporous materials can be explained by capillary condensation. It can be found from Table 1 that after acid treatment, the specific surface area of ATP increased significantly from 91.06m ² /g to 179.96m ² /g, and the pore volume also increased from 0.233cm ³ /g to 0.293cm ³ /g. This can be explained that the acid treatment can remove impurities (Mg ²⁺ , Al ^{3+ ,} etc.) in the surface pores of the raw material ATP, thereby increasing the BET area and pore volume, which is beneficial to loading TEPA and absorbing CO ₂ . This conclusion is consistent with the results of XRD and SEM. However, the BET area and pore volume of the TEPA/ATP adsorbent decreased significantly after loading different amounts of TEPA, and the larger the added amount. The BET areas of 20TEPA/ATP and 30TEPA/ATP were 70.01m ² /g and 61.25m ² /g, respectively, while the BET area of 40TEPA/ATP dropped sharply to 39.17m ² /g. The possible reason is that the introduced amines occupy and fill the surface pores, leading to the pore blockage of ATP. From the pore size distribution of (b) in Figure 5, it can be seen that all samples have a peak centered at 28-29 nm, and there are multi-level pore sizes. After modified by TEPA, the peak intensity decreased obviously, confirming that the amine molecules entered the pores of ATP.

Table 1. BET specific surface area and pore volume results of ATP, HATP and TEPA/HATP

Embodiment 3: Adsorption performance experiment of adsorbent

Take 1g of adsorbent and put it in the middle of the quartz reaction tube, the length of the reaction tube is 0.4m, and the inner diameter is 20mm. First, pretreat the adsorbent with high-purity N ₂ (40mL/min) at 100°C for 1 h to remove CO ₂ and H ₂ O adsorbed on the surface of the adsorbent in the air; then lower the reactor temperature to a specific reaction temperature, and The gas was replaced with a simulated flue gas mixture of 15% CO ₂ /85% N ₂ (40 mL/min). The intake air flow is regulated by a mass flow controller. Measure the outlet _CO2 concentration with a _CO2 analyzer. The effect of water vapor on the performance of the adsorbent was realized by keeping the simulated flue gas flow pre-wetted at 60 °C in a water bath. The adsorption capacity of different ATP adsorbents for _{CO was} calculated according to the CO breakthrough curve as follows:

In the formula (2), Q is the _CO2 adsorption capacity (mmol/g), F is the gas flow rate (mL/min), M is the weight (g) of the ATP adsorbent, V is 22.4mL/mmol, and _C0 is the inlet CO ₂ concentration (vol.%), C is outlet CO ₂ concentration (vol.%).

1. Effect on CO ₂ adsorption capacity under dry conditions

The breakthrough curves and _CO adsorption capacities of ATP, HATP and TEPA/HATP with different TEPA ratios are shown in Fig. 6. It can be seen from Fig. 6 (a) that the acidic activation improves the breakthrough time of ATP, and the addition of TEPA further improves the breakthrough time of ATP. However, when the TEPA loading was increased to 40%, its breakthrough time decreased, but was still slightly higher than 20TEPA/HATP. (b) in Fig. 6 is the _CO2 adsorption capacity of different adsorbents calculated by the breakthrough curve. Among all the materials, the adsorption amount of _CO2 by raw material ATP was the lowest (1.07 mmol/g), while that of HATP reached 1.37 mmol/g. This may be due to the fact that the impurities in the ATP pores are removed by acid, and the specific surface area increases, which is conducive to the adsorption of carbon dioxide. In addition, the removal of impurities also facilitates the loading of TEPA on ATP. The adsorption capacity of 20TEPA/HATP and 30TEPA/HATP was significantly increased to 2.1mmol/g and 3.28mmol/g, respectively. The possible reason is that the supported amines can react with _CO to generate stable carbamates, thus providing more active sites on the material. The reaction equation is as follows:

CO ₂ +2RNH ₂ →RNH ₃ ⁺ +RNHCOO ^- (3)

CO ₂ +2R ₂ NH→R ₂ NH ₂ ⁺ +R ₂ NCOO ^- (4)

From formula (3) and formula (4), it can be inferred that loading TEPA is beneficial to promote carbon dioxide capture. In the samples with TEPA loading of 20% and 30%, the ability to adsorb _CO2 increased with the increase of amine amount. But when the amount of TEPA was further increased to 40%, the _CO2 capture capacity decreased to 2.58mmol/g, this phenomenon may be due to the blockage of excess amine, the pores of the ATP material were filled by TEPA, and there was less space for _CO2 adsorption. Therefore, in all samples, 30% TEPA is the most suitable amount of CO2 capture. In addition, Table 2 shows the comparison of the CO ₂ adsorption capacity of the amine-modified adsorbents in the previous literature and this study under dry conditions. It can be found that among the materials modified with different amines, 30TEPA/HATP has the best _CO2 capture performance.

Temperature plays a key role in carbon dioxide adsorption. During the adsorption process, the temperature will affect the equilibrium of the adsorption reaction and mass transfer. Higher temperature is good for mass transfer, but high temperature is not good for adsorption because the adsorption reaction is exothermic. In order to reveal the effect of temperature on the _CO2 adsorption performance of 30TEPA/HATP adsorbent, performance experiments were carried out at 40 °C, 50 °C, 60 °C and 70 °C, respectively, and the breakthrough curve and _CO2 adsorption capacity results are shown in Fig. 7. As shown in (a) of Fig. 7, the order of breakthrough time is 60 °C > 50 °C > 70 °C > 40 °C, indicating that the _CO2 adsorption capacity on 30TEPA/HATP increases first and then decreases with increasing temperature. According to calculation, the adsorption capacity of _CO2 at 40°C, 50°C, 60°C and 70°C is 2.05mmol/g, 2.86mmol/g, 3.28mmol/g, 2.27mmol/g respectively. 60°C was identified as the optimum temperature for _CO2 capture. This may be because an increase in temperature can not only increase the activity of TEPA, but also accelerate the movement rate of carbon dioxide molecules, thereby promoting the diffusion of carbon dioxide in the pores and increasing its chances of contacting the active sites of the adsorbent. Therefore, the amount of adsorption increases with increasing temperature. However, the adsorption process of _CO2 is exothermic. When the temperature further increased to 70 °C, the adsorption process was mainly controlled by thermodynamics rather than kinetics, the adsorption equilibrium shifted to the desorption direction, and the adsorption capacity decreased.

In actual flue gas, the concentration of _CO2 is not constant, but fluctuates within a certain range. In order to obtain better application value, the adsorbent is required to exhibit good _CO2 capture performance under different _CO2 contents (10vol%, 15vol%, 20vol%). The CO ₂ concentration on the CO ₂ adsorption performance of the 30TEPA/HATP sample breakthrough curve and CO ₂ adsorption results are shown in Figure 8, and the carbon dioxide concentration varies in the range of 10vol% to 20vol%. From Fig. 8(b), it can be seen that there is no significant difference in the _CO2 capture performance under the three conditions. When the _CO2 concentration was 10vol%, 15vol% and 20vol%, the _CO2 adsorption capacity was 3.18mmol/g, 3.28mmol/g and 3.39mmol/g, respectively. The increase in _CO2 concentration can only slightly increase the _CO2 adsorption capacity. Interestingly, the breakout curves of the two are significantly different. The breakthrough time was significantly shortened when the _CO concentration was increased from 10 vol% to 20 vol%. The possible reason is that for every 5vol% increase in _CO2 concentration, the _CO2 content per unit volume also increases. A higher _CO2 concentration allows more _CO2 molecules to react with the amine groups within a certain period of time, helping to shorten the breakthrough time. However, the content of amine groups in 30TEPA/HATP remained unchanged, and the final _CO2 adsorption capacity basically remained unchanged. It can be seen that the 30TEPA/HATP material has good and stable _CO2 adsorption capacity under different _CO2 concentrations, but higher _CO2 content is beneficial to shorten the adsorption time.

Table 2 Comparison of _CO2 adsorption capacity of amine-modified absorbents under dry conditions

references:

[1] Gómez-Pozuelo, G.; Sanz-Pérez, ES; Arencibia, A.; Pizarro, P.; Sanz, R.; Serrano, DPCO ₂ adsorption on amine-functionalized clays. Microporous Mesoporous Mater. 47.

[2] Niu, M.; Yang, H.; Zhang, X.; Wang, Y.; Tang, A. Amine Impregnated Mesoporous Silica Nanotube as an Emerging Nanocomposite for CO ₂ Capture.ACSAppl.Mater.Interfaces 2016,8(27 ), 17312-17320.

[3] Wang, X.; Ma, X.; Song, C.; Locke, DR; Siefert, S.; Winans, RE; Mollmer, J.; Lange, M.; Moller, A.; Glaser, R. Molecular basket sorbents polyethyleneimine-SBA-15 for CO ₂ capture from flue gas: Characterization and sorption properties. Microporous Mesoporous Mater. 2013, 169, 103-111.

[4] Horri, N.; Sanz-Perez, E.S.; Arencibia, A.; Sanz, R.; Frini-Srasra, N.; Srasra, E. Amine grafting of acid-activated bentonite for carbon dioxide capture.Appl.Clay Sci .2019, 180, 105195.

[5] Yuan, M.; Gao, G.; Hu, X.; Luo, X.; Huang, _Y .; Jin, B.; Liang, Z. Ind. Eng. Chem. Res. 2018, 57(18), 6189-620

[6] Liu, L.; Chen, H.; Shiko, E.; Fan, X.; Zhou, Y.; Zhang, G.; Luo, X.; Hu, X. Low-cost DETA impregnation of acid- activated sepiolite for CO ₂ capture. Chem. Eng. J. 2018, 353, 940-948.

2. Effect on _CO2 adsorption capacity under humid conditions

Water vapor is an unavoidable component of actual flue gas. In order to simulate the actual flue gas, the 15% CO ₂ /85% N ₂ mixture is pre-wetted in a water bath at 60°C (with an evaporation device that takes out water vapor from N ₂ , the water vapor content is controlled by the temperature of the evaporation device, Then mix with CO ₂ through the gas mixing tank), and study the effect of water vapor on the CO ₂ adsorption performance of HATP and 30TEPA/HATP samples. It can be seen from Figure 9 that when water vapor is introduced into the simulated flue gas, the breakthrough time of _HATP is slightly shortened compared with that in dry flue gas; Medium is 1.13 mmol/g. The possible reason is that _H2O forms a water film on the adsorbent, blocks the pores, reduces the number of active sites, and finally leads to a decrease in the adsorption performance. It can be seen from Figure 9 that the breakthrough time of 30TEPA/HATP in wet flue gas is longer than that in dry flue gas, the breakthrough time is extended from 6 minutes to 7 minutes, and the total adsorption capacity rises from 3.28mmol/L to 3.82mol/L, indicating that water vapor enhances the adsorption capacity of 30TEPA/HATP on CO ₂ . In the presence of water, the _CO adsorption of the 30TEPA/HATP sample increased by 16.5%, indicating a significant facilitation by water vapor. This may be due to a change in the adsorption mechanism of the 30TEPA/HATP material in the presence of water vapor. Compared with the reaction of 1 mol CO ₂ and 2 mol amine groups under dry conditions [Formula (3) and Formula (4)], CO ₂ reacts with amine groups 1:1 to form bicarbonate, which improves the utilization of amine groups and contributes to Enhancement of adsorption capacity of the adsorbent [Equation (5) and Equation (6)]. In addition, the carbamates generated in formula (3) and formula (4) can also react with carbon dioxide and water to generate bicarbonate in the presence of water, which promotes the adsorption of _CO [formula (7) and formula ( 8)]. The reaction equation is as follows:

CO ₂ +RNH ₂ +H ₂ O→RNH ₃ ⁺ +HCO ₃ ^- (5)

CO ₂ +R ₂ NH+H ₂ O→R ₂ NH ₂ ⁺ +HCO ₃ ^- (6)

CO ₂ +R ₂ NCOO ^- +2H ₂ O→R ₂ NH ₂ ⁺ +2HCO ₃ ^- (7)

CO ₂ +RNHCOO ^- +2H ₂ O→RNH ₂ ⁺ +2HCO ₃ ^- (8)

Embodiment 4: the cyclic regeneration of adsorbent

In practical flue gas applications, the regenerative capacity of the adsorbent is important because it determines the service life and replacement frequency of the material, thereby affecting the cost of _CO2 capture. The spent TEPA/HATP adsorbent was regenerated at 100 °C under 40 mL/min N ₂ atmosphere after being adsorbed by CO ₂ . Figure 10 shows the adsorption capacity of 30TEPA/HATP adsorbent for 10 repeated cycles of carbon dioxide adsorption at 60 °C and desorption at 100 °C in _N2 atmosphere. The results showed that the adsorption amount of _CO2 was 3.28 mmol/g in the first cycle, and the adsorption amount decreased slightly as the number of cycles increased; this may be related to the degradation and volatilization of impregnated TEPA. After 10 cycles, the adsorption amount of TEPA was 3.04mmol/g, which only decreased by 7.0%, indicating that there was a strong chemical interaction between TEPA and acid-activated ATP. Overall, after 10 cycles of adsorption and desorption experiments, the 30TEPA/HATP adsorbent did not decrease significantly in _CO2 adsorption capacity, and still maintained a high adsorption performance, indicating that it has good cycle stability and has industrial application value.

Claims (10)

1. a kind of through amine modification adsorption _CO The preparation method of acid-activated attapulgite material is characterized in that, comprises the following steps: (1) prepare acid-activated attapulgite; (2) the acid-activated attapulgite obtained by impregnating step (2) with tetraethylenepentamine, after drying, obtains the acid-activated attapulgite material through amine modification adsorption _CO ; In step (2), the ratio of the mass of tetraethylenepentamine to the mass of acid-activated attapulgite is 20%-40%, preferably 25%-35%, more preferably 30%. 2. a kind of according to claim 1 through amine modification adsorption _CO The preparation method of acid-activated attapulgite material is characterized in that, in step (2), described tetraethylenepentamine is dissolved in organic solvent Then use the acid-activated attapulgite obtained in the impregnation step (2). 3. A method for preparing an acid-activated attapulgite material that absorbs _CO2 through amine modification according to claim 2, wherein the organic solvent is methanol. 4. A method for preparing an acid-activated attapulgite material that absorbs _CO2 through amine modification according to claim 2, characterized in that, in step (2), the immersion time is 10-15h. 5. a kind of according to claim ₂ through amine modification adsorption CO The preparation method of acid-activated attapulgite material is characterized in that, in step (1), attapulgite is activated with acid to obtain acid Activated attapulgite; the attapulgite is passed through a 50-mesh sieve; the attapulgite is washed with deionized water and pre-filtered before acid activation. 6. a kind of according to claim 5 through amine modification adsorption _CO The preparation method of acid-activated attapulgite material is characterized in that, in step (1), the concentration of described acid is 1-5mol/L , the ratio of the mass of the attapulgite to the volume of the acid is 1:10 to 1:20, g/mL. 7. a kind of according to claim 6 through amine modification adsorption _CO The preparation method of acid-activated attapulgite material is characterized in that, described acid is any in hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid . 8. Application of the acid-activated attapulgite material prepared by the method of any one of claims 1 to 7 through amine modification to absorb CO ₂ in the capture of CO ₂ in flue gas. 9. The application according to claim 8, characterized in that the _CO2 capture temperature is 40°C to 70°C, preferably 50°C to 60°C, more preferably 60°C. 10. The application according to claim 9, characterized in that the _CO2 concentration range in the flue gas is 10vol% to 20vol%; The application according to claim 9, characterized in that the flue gas contains water vapor under humid conditions or in the flue gas; The application according to claim 8, characterized in that the flue gas is flue gas from a coal-fired power plant.

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