AM-TEPA Impregnated Disordered Mesoporous Silica as CO2

Oct 18, 2012 - ... was carried out in a thermostatted three-necked round-bottom flask equipped ...... Ian Harvey Arellano , Junhua Huang , Phillip Pen...
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AM-TEPA Impregnated Disordered Mesoporous Silica as CO2 Capture Adsorbent for Balanced Adsorption−Desorption Properties Xiaoyun Zhang, Xiuxin Zheng, Sisi Zhang, Bei Zhao, and Wei Wu* College of Science, China University of Petroleum (East China), Qingdao 266555, P. R. China S Supporting Information *

ABSTRACT: A disordered mesoporous silica was found to be a promising solid support for CO2 capture. It was prepared with a process similar to that for MCM-41. X-ray diffraction characterization (XRD) and transmission electron microscopy (TEM) confirmed its disordered structure. N2 adsorption−desorption tests indicated that its average pore size is significantly larger than that of MCM-41. On this support was deposited acrylamide (AM)-modified tetraethylenepentamine (TEPA), resulting in an adsorbent suitable for CO2 capture. This material exhibited well balanced adsorption and desorption properties. Substantially higher CO2 adsorption capacity (159.1 mg/g-adsorbent) was obtained with pure CO2 at 25 °C, and satisfactory stability during 12 adsorption−desorption turnovers was achieved.

1. INTRODUCTION Global climate change has become a worldwide issue1 because of significant and continuous increasing in atmospheric CO2 concentration by extensive utilization of fossil fuels. Thus various methods have been used to capture CO2 from the atmosphere, such as absorption, adsorption, membrane, and biotechnology.2 The most mature technology for large-scale CO2 capture utilizes aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), and methyldiethanolamine (MDEA)3 which selectively absorb CO2 around ambient conditions (40−65 °C, 1 atm). The concentrated CO2 is then recovered by heating the mixture to temperatures well above 100 °C (i.e., the desorption temperature of MEA is often at 100−150 °C).4 Though this technology is applied extensively today, it is highly energy-consuming for regeneration of solvents and is also plagued by corrosion problems.5 Therefore, there is a great need to develop viable and cost-effective technologies for CO2 capture. Solid amine technology integrates the advantages of absorption and adsorption and has been adopted as one of the promising methods in capturing atmospheric CO2.6 There are two main preparation methods to obtain solid amine adsorbents: (i) porous supports impregnated with liquid organic amines such as tetraethylenepentamine (TEPA) via a wet impregnation protocol7 and (ii) amines that could be covalently linked to a solid support via the use of silane chemistry.8 “Wet impregnation” was commonly used because of its simplicity in preparation. The supports often were normally structurally ordered materials with large pore size, high surface area, and a large number of highly dispersed active sites on the pore surface, which facilitated the distribution of amines throughout the pore space, such as activated carbons,9 carbon nanotubes,10 metal oxide,11 mesoporous molecular sieves.5,12−15 Yue et al. reported modified mesoporous silica SBA-15 and MCM-41 with tetraethylenepentamine (TEPA).16,17 A very high adsorption capacity (173 mg/g, 237 mg/g) was obtained. Prior to this work, we tested similar TEPA-modified adsorbents and found that this kind of material © 2012 American Chemical Society

was difficult to desorb completely. Moreover, the materials were unstable and liable to oxidation at a higher temperature, i.e. 100 °C. At that temperature, after 5-cycle runs, the sample gradually became yellow and lost most of its adsorption capacity (from initial 193.8 mg/g to 100.3 mg/g, retaining only 51.8% of its activity). Heydari-Gorji reported that PME-PEI (50) underwent a 14% loss after 120 cycles because of a combination of PEI evaporation and the formation of urea.18 It should be noted that the PEI they used had a low molecular weight (Mn ≈ 423) with about 20% tetraethylenepentamine (TEPA). The authors attributed the most weight loss to the release of TEPA. The relatively high volatility and liability to oxidation of primary amine were considered to be drawbacks for the sorbent stability; modification of primary amine to secondary amine has been adopted to solve the problem, since the latter is thermally and oxidatively more stable. Filburn et al. modified MEA with acrylonitrile (AN) to convert this primary amine to a secondary amine,19 and immobilized it within the pores of polymeric supports to provide a regenerable CO2 sorbent. These supported amines were used to remove low concentrations (7.6 mmHg) of CO2 and low-pressure vacuum was used to desorb the CO2 and regenerate the sorbent. The modified amines provided nearly a factor of 2 increase in CO2 removal capacity compared to the original primary amines and could potentially be used for CO2 capture in space life support systems and other confined spaces with low CO2 concentration. Nowadays in the preparation of CO2 adsorbents, the most used supports are structurally ordered materials. During our study of MCM-41, we found a structurally disordered mesoporous material by chance. It was prepared following the synthetic procedure of MCM-41 and could be used as the supports. In this work, acrylamide-modified tetraethylenepentamine (TM) was prepared and was impregnated to the Received: Revised: Accepted: Published: 15163

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electron microscopy (TEM) measurements were taken on a JEOL JEM-2100F 200 kV. The Fourier transform infrared (FTIR) spectra were obtained using a Nicolet MAGNA 750 Spectrometer by measuring the absorbance of the KBr pellet containing 1−2 wt % of sample. Thermal, chemical, and physical properties of the M4 and M4-TM-50 were characterized by thermal gravimetric analysis (TGA) performed on a Perkin-Elmer-TGA7 analyzer. About 10 mg of the sample was heated at 10 °C/min to 800 °C in air (100 mL/min). Elemental analysis of the adsorbent for N was performed at elemental analysis section at China University of Petroleum using a Perkin-Elmer 2400 analyzer. 2.3. CO2 Sorption−Desorption Measurement. The adsorption and desorption performance of the adsorbent was performed in an apparatus assembled in our lab. The weight change of the adsorbent measured by a microbalance was monitored to determine the adsorption and the desorption performance of the materials. Before testing, the sample was heated to 100 °C for 1 h to eliminate the water and CO2. In a typical adsorption/desorption process, about 2 g of the adsorbent was placed in a sample column, heated to the designated temperature, and 99.8% bone-dry CO2 adsorbate was introduced at a flow rate of 80 mL/min. This process lasted for about 60 min. After adsorption, the sample was transferred to a vented oven at 100 °C for 2 h to regenerate the adsorbent. Adsorption capacity in mg-adsorbate/g-adsorbent and desorption capacity in percentage were used to evaluate the adsorbent and were calculated from the weight change of the sample in the adsorption/desorption process. The impacts of amine loading, adsorption temperature, and desorption ways on the adsorption and desorption performance of the adsorbent were also studied. Cyclical adsorption and desorption processes were performed to evaluate the stability of the adsorbent.

disordered mesoporous material. The solid amine adsorbent exhibited high adsorption and desorption performance. After 12 cycles, the adsorption capacity decreased from 128.8 to 127.8 mg/g, less than 1% of its initial capacity. Moreover, to our knowledge, this was the first time that AM-modified TEPA was impregnated to a structurally disordered mesoporous material for CO2 capture.

2. EXPERIMENTAL SECTION 2.1. Preparation of the Adsorbents. All chemicals were obtained from Sinopharm and used as received. Four mesoporous materials were prepared based on the hydrothermal method.20−23 Tetraethyl orthosilicate (TEOS) was used as silica source, cetyltrimethylammonium bromide (CTAB) was used as the surfactant template, and ethanediamine (EDA), NH3, or NaOH was used for pH adjustments. After reaction, the samples were aged for 48 h at 373 K. The white solids were recovered by filtration and washed with distilled water and ethanol. All materials were calcined in air under a thermal ramp of 2 °C/min to 550 °C, and then held at 550 °C in air for 5 h to remove the template. Samples with different molar ratios of starting materials were denoted as M1, M2, M3, M4, respectively, and the corresponding basis of each support is listed in Table S1 of the Supporting Information. Synthesis of modified tetraethylenepentamine (TEPA) was carried out in a thermostatted three-necked round-bottom flask equipped with a mechanic stirrer, a thermometer, and a dropping funnel. Acrylamide (2 equiv., 25% aqueous solution) was gradually dropped to TEPA at 35 °C. The mixture was heated up to 80 °C and kept for 1 h. Then water was eliminated from the mixture by vacuum. The TEPA-AM (TM) products were yellowish viscous liquids and totally water-soluble. The TM-modified materials were prepared by a wet impregnation method. In a typical preparation, the desired amount of TM was dissolved in 50 g of ethanol under stirring for about 30 min; 2 g of mesoporous material was then added to this solution. The resultant slurry was continuously stirred for about 2 h, and dried at 60 °C for 1 h under decreased pressure. This adsorbent was denoted as Mn-AM-X (n = 1, 2, 3, 4), where Mn represent the aforementioned silica support, AM means the amine, and X is the loading of amine as weight percentage in the sample. Three amines-modified M 4 adsorbents, M4-TEPA-50, M4-TM-50, and M4-DEA-50 were prepared for further investigations. 2.2. Characterization of the Adsorbents. The crystal structures of the mesoporous materials were investigated by Xray diffraction (XRD) on a Philips X’Pert PRO SUPER X-ray diffractometer with graphite-monochromated Cu Kα radiation (λ = 0.15418 nm). The unit cell parameter a was calculated from the (100) diffraction peak according to the equation a = 2 × d100/31/2. The N2 adsorption−desorption isotherms were collected at 77 K using a Micromeritics TriStar 3000 Porosimeter. The adsorbent was degassed prior to each measurement at 100 °C in a high vacuum for 3 h. The surface area was calculated using the BET method in the 0.05−0.35 relative pressure range, and pore diameter distributions were estimated from the desorption branch of isotherms based on the BJH (Barrett−Joyner−Halenda) model. The total pore volume was determined as the volume of liquid nitrogen adsorbed at a relative pressure of 0.99. The volume of pore size of each support was obtained using NLDFT methods from the adsorption branch as implemented in Micromeritics Instrument Corporation’s data software DFT plus V3.0. Transmission

3. RESULTS AND DISCUSSION 3.1. Comparison of the Supports. Powder X-ray diffraction (XRD) and nitrogen adsorption at 77 K were used to determine the structural characteristics of the supports. Figure 1 shows the powder XRD pattern of the mesoporous

Figure 1. XRD pattern of mesoporous materials (a) M1, M2, M3, and (b) M4.

silica samples. For M1, M2, and M3 materials, the observation of 3−4 peaks in Figure 1a indicated that they could be attributed to typical MCM-41. Clearly, M2 material was less ordered than M1 and M3 in structure. In contrast the single peak with smaller intensity accompanied by line broadening and the absence of the long-range second and third peaks in Figure 1b indicated a 15164

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Table 1. Textural Parameters of Samples M1−M4

M1 M2 M3 M4

a (unit cell parameter)

BET surface area (m2/g)

total pore volume (cm3/g)

pore diameter (nm)

wall thickness (nm)

sorption capacity at 25 °C (mg/g adsorbent)

desorption time at 100 °C in air (min)

4.35 3.87 4.48

1027.2 863.8 1052.6 451.5

0.73 0.48 0.69 0.54

2.85 2.24 2.62 4.75

1.50 1.63 1.86

65.9 60.3 90.1 128.8

90 100 90 70

disordered structure for the M4 material. High-angle XRD (up to 60°) (Figure S1) indicated that M4 material consisted of amorphous silica without any impurity. TEM analysis (Figure S2a) confirmed the disordered structure of the M4 material, while the well ordered MCM-41 having hexagonal pores is shown in Figure S2b. The corresponding textural parameters obtained from the nitrogen adsorption isotherms (Figure S3) and the adsorption− desorption capacities at 25 °C are listed in Table 1 and Table 2, Table 2. Adsorption-Desorption Capacities for M1−M4Based Adsorbents Mn-TM-50

M1-TM50 M2-TM50 M3-TM50 M4-TM50

sorption capacity at 25 °C (mg/g adsorbent)

desorption time at 100 °C in air (min)

65.9

90

60.3

100

90.1

90

128.8

70

Figure 2. FTIR spectrum of M4, TM, and M4-TM-50 materials at room temperature.

in the amide group which could also be seen in the FTIR spectrum of TM (Figure 2). Two distinctly new bands appeared at 2928 and 2850 cm−1 were due to the CH2 stretching modes of the TM chains. The bands at 1562 and 1472 cm−1 could be attributed to the asymmetric and symmetric bending of primary amines (NH2), respectively.1 In Figure 2, the bands appearing at 3299 and 3187 cm−1 could be attributed to the amine N−H stretching vibrations.1 After TM modification, these peaks disappeared and formed a new broad band at 3428 cm−1 with O−H stretching vibrations of the hydrogen bonded silanol groups.28 Therefore, these FTIR observations confirmed that TM had been impregnated in the pore of M4 material. In addition, the bands at 1412 and 1340 cm−1 could be ascribed to NCOO skeletal vibration.28 This was probably due to the reaction between adsorbent and traces of CO2 in air. The reaction of CO2 with amines could be explained by the zwitterion mechanism.1 Amines could react directly with CO2 to produce carbamates under anhydrous conditions following these equations:1

respectively. All of the materials had mesoporous pores (2−5 nm), a larger surface area, and a certain wall thickness which indicated good thermal and hydrothermal stabilities. Although M4 had a disordered structure, after amine-modification it exhibited the largest sorption capacity (128.8 mg/g) compared with M1, M2, and M3 materials (65.9, 60.3, 90.1 mg/g, respectively) and the adsorption curves are shown in Figure S4. This was probably due to its larger pore diameter (4.75 nm). It was approximately two times larger than that of M1, M2, and M3 materials. With a larger pore diameter, more amine molecules could be loaded, and dispersed better, and CO2 mass-transfer would be easier with lower diffusion resistance, resulting in a larger sorption capacity. To test this hypothesis, we made M3TM-30 and M4-TM-30. With this low TM loading, diffusion resistance in the two materials could be ignored. As expected, M3-TM-30 showed a similar adsorption capacity (90.2 mg/g) compared with M4-TM-30 (96.3 mg/g). This further confirmed the advantage of M4 with larger pore size as an adsorbent support. This observation is in good accordance with that previously reported by Chen.24 Larger pore size and the presence of textural mesoporosity25 all made the M4 a desirable support material for amine impregnation. Thereby, M4 material was selected as the support for the later experiments. 3.2. Characterizations of TM-Modified Sorbent. Figure 2 shows the FTIR spectra of M4, TM, and TM-modified material samples. In Figure 2, the sharp peak at 3436 cm−1 on the M4 material was attributed to the O−H stretching vibrations of the hydrogen bonded silanol groups and adsorbed water molecules.26,27 The peak located at 1634 cm−1 could be assigned to adsorbed water. In the FTIR spectrum of M4-TM50, some additional peaks could be observed compared with M4 material. The sharp peak at 1668 cm−1 is assigned to carbonyl

CO2 + 2RNH 2 → RNHCOO− + RNH3+

(1)

CO2 + 2R 2NH → R 2NCOO− + R 2NH 2+

(2)

CO2 + R 2NH + R′NH 2 → R 2NCOO− + R′NH3+

(3)

The reaction between amine and CO2 yields ammonium bicarbonate through the following steps in the presence of water.1 CO2 + H 2O + RNH 2 → HCO3− + RNH3+

(4)

where R represents the alkyl groups. Thermal gravimetric analysis (TGA) was used for further confirmation of TM impregnation. Figure 3 showed weight loss by TGA and differential thermal analysis (DTA) profile of the M4-TM-50 sample. From the DTA curve, two main exothermic peaks and one endothermic peak could be seen, which correspond to four weight loss regions in the TG curves. The first step of thermal decomposition occurred at about 100 °C. 15165

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Figure 3. TG (a) and DTA (b) profiles of TM impregnated M4 samples.

Figure 4. Adsorption and desorption mass curves of amines-modified M4 absorbents: (a) adsorption mass curves and (b) desorption mass curves.

This could be attributed to desorption of moisture and CO2. In the temperature range of 140−550 °C, two exothermic peaks appeared at about 200 and 350 °C. These could be primarily ascribed to the combustion of the organic materials. The total weight loss of M4-TM-50 was 56.3%. If the adsorbed moisture and CO2 (approximately 9%) were excluded from the total weight loss, the real loading of TM was about 50%. This was quite close to the data obtained from the elemental analysis (48.92%). This is reasonable considering that the loading amount of TM on the support is about 50 wt %. 3.3. Adsorption and Desorption Properties of M4-TM. Figure 4 showed the adsorption mass uptake curves obtained with pure CO2 at 25 °C and the adsorption mass uptakes obtained at 100 °C for M4-TEPA-50, M4-TM-50, and M4-DEA50. The three materials showed similar favorable adsorption kinetics since 95% of the equilibrium capacity was reached within 5 min of exposure to pure CO2 (Figure 4a). The adsorption capacity is in the following order: M4-TEPA-50 (193.8 mg/g) > M4-TM-50 (128.8 mg/g) > M4-DEA-50 (109.0 mg/g). As shown in Figure 4b, upon rapid heating to 100 °C in air, the three amine-impregnated materials desorbed all the CO2 within 2 h, but with different desorption rates. Table 3 shows the elemental composition, adsorption efficiencies (mmol CO2/mmol N at 25 °C) and desorption properties at 100 °C. Although the adsorption efficiency of M4-TM-50 (0.22 mmol CO2/mmol N) was lower than that of M4-DEA-50 (0.50) and M4-TEPA-50 (0.33), but to DEA, it had a low molecular weight (105.14 g/mol) and thus it was more volatile than TM. Moreover, the adsorption capacity was also lower than TM. For M4-TEPA-50, the desorption time of M4-TM-50 material was 70 min, a little bit longer than that of M4-DEA-50 material (60 min), but much shorter than that of M4-TEPA-50

material (110 min). For an industrial consideration, adsorbents with a favorable adsorption capacity and a shorter desorption time are highly desirable because of the lower operational costs and process scale-up. Therefore, M4-TM showed satisfactory adsorption and desorption properties, especially in terms of well-balanced adsorption and desorption performance for CO2 capture. The effect of amine loading on CO2 adsorption capacity was examined. M4-TM samples with amine loadings ranging from 40 to 70 wt % were tested using pure CO2 at 25 °C and the adsorption curves are shown in Figure S5. As shown in Figure 5, M4-TM-60 (60% amine loading) showed the highest capacity (159.1 mg/g) of the four samples. It was worth noting that M4TM-70, the sample with higher amine loading, exhibited relatively lower CO2 adsorption capacity (120.4 mg/g). This was probably due to the dispersion of TM on the support. When the TM loading was low, TM could be dispersed on the support quite well. Thus film diffusion resistance could be ignored, and CO2 adsorption capacity increased with the increasing of TM loading. This consideration was well supported by the data obtained from the N2−BET test (Figure S6). Following TM loading (from 40% to 60%), the BET surface area and total pore volume decreased from 451.5 m2/g, 0.54 cm3/g to 4.9436 m2/g, 0.0375 cm3/g respectively. This was also supported by observations of the texture of the impregnated materials, which changed gradually from a freeflowing powder to an agglomerated powder as the amine loading exceeded pore saturation. Further increasing the TM loading to some extent, the additional TM deposited on the adsorbent external surface after pore saturation. With large excesses of TM, film diffusion resistance became a limiting 15166

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Table 3. Elemental Composition, Adsorption, and Desorption Capacities of Adsorbents material

elemental analysis N (wt %)

organic loading (wt %)

mmol N/g adsorbent

molecules (amines)/nm2

mmol CO2/g adsorbent

mmol CO2/ mmol N

desorption time at 100 °C in air (min)

M1-TM-50 M2-TM-50 M3-TM-50 M4-TM-50 M4-DEA-50 M4-TEPA-50

14.50 14.09 14.34 14.48 6.88 18.40

48.97 47.59 48.43 48.92 51.63 49.68

10.36 10.06 10.24 10.35 4.92 13.14

1.97 1.92 1.95 1.97 6.55 3.50

1.50 1.37 2.05 2.87 2.48 4.40

0.14 0.11 0.16 0.22 0.50 0.33

90 100 90 70 60 100

adsorption capacity increased with the temperature. But at the higher temperature stage, the desorption process became the major reaction of the equilibrium, causing the decrease in adsorption capacity. To verify the above hypothesis, we designed the experiment as Xu reported.29 M4-TM-50 was tested at 55 and 25 °C in a CO2 flow for 120 min. If the adsorption capacity at 25 °C was similar to that at 55 °C, we could conclude that the low adsorption capacity at low temperature was caused by kinetic limitation. Otherwise, it may be caused by other reasons. The results showed that the M4-TM-50 adsorbent had a similar adsorption capacity at 55 and 25 °C. The adsorption capacity at 55 °C was 134.7 mg/g, and at 25 °C was 134.1 mg/g, which meant that the adsorption process at low temperature was kinetically controlled. The low adsorption capacity at low temperature was mainly caused by the low diffusion rate. Thus the adsorption mechanism would probably be suitable for the adsorbent we made. The stability of the sorbent is also a major concern for CO2 capture materials. An industrially useful adsorbent should possess excellent regenerability and stability with many adsorption−desorption cycles. To test the stability of M4-TM absorbents, 12 cycles of sorption−desorption were carried out. M4-TEPA materials were also tested for comparison. The adsorption process was operated in pure CO2 at 25 °C. Desorption was performed in a vented oven at 100 °C for 2 h. As shown in Figure 7, sample M4-TM-50 was fairly stable, with

Figure 5. Relationship between the TM loading of the M4 and CO2 adsorption capacity.

factor for the kinetics of CO2 uptake, causing the decreasing of CO2 adsorption capacity.12 The adsorption performance of the M4-TM-50 was measured at different temperatures in a pure CO2 atmosphere and the results are shown in Figure 6. With increasing temperature, the

Figure 6. Relationship between the adsorption temperature and CO2 capture capacity for M4-TM-50.

adsorption capacity of the M4-TM-50 became larger and reached its maximum value of 134.7 mg/g at 55 °C. When the temperature increased to 85 °C, the adsorption capacity sharply decreased to 97.8 mg/g. This behavior was probably related to its adsorption mechanism. The adsorption of CO2 into the M4TM material is an exothermic process. At the lower temperature stage, TM exists in the channels of M4 material, in a form just like nanosized particles. Only the CO2 affinity sites on the surface of the particles could readily react with CO2. The affinity sites inside the particles could only react with CO2 when CO2 was diffused into the particles29 and this is a kinetically controlled process. In this stage, the diffusion resistance decreased with increasing temperature. Thus the

Figure 7. Recycle adsorption/desorption runs of M4-TM-50 and M4TEPA-50 (adsorption at 25 °C; desorption at 100 °C).

only a minor decrease in adsorption capacity (1 mg/gadsorbent, i.e. less than 1% of initial capacity) after 12 adsorption−desorption cycles. In the case of M4-TEPA-50, although its initial adsorption capacity was quite high (193.8 mg/g), the capacity sharply decreased after 5 cycles. After 5 cycles, the sample gradually became yellow and lost most of its adsorption capacity. The first and last adsorption curves of each adsorbent are shown in Figure S7. Obviously, the difference 15167

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M4. This information is available free of charge via the Internet at http://pubs.acs.org.

between M4-TM-50 and M4-TEPA-50 is mainly due to the molecular structure of loaded amines. TEPA has more primary amine groups than TM. Although primary amine has a larger adsorption capacity, it also has poor resistance to oxidation and volatility.18 When reacted with AM, the primary amino groups in TEPA were mostly converted to secondary amino groups through Michael addition reaction. Thus the obtained TM materials showed better thermal and chemical stabilities than TEPA in amine-modified adsorbents. Stabilities of M4-TM and the other adsorbents are listed in Table 4. Zeolite 13X showed a high capacity for CO2 removal

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Corresponding Author

*Tel.: 86 532 86981571. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We thank the National Natural Science Foundation of China (Project 21172264), the Natural Science Foundation of Shandong Province in China (ZR2011BM012), and the Fundamental Research Funds for the Central Universities in China (11CX05012A) for financial support.

Table 4. Stabilities of M4-TM and Other Adsorbents adsorbent Zeolite 13X SBA-15-6/PEI M4-TM-50 SBA-15-PEI-60

cycling times adsorption capacity loss (%) 11 12 12 10

48.7 13.5 0.8 4.8

ref 30 1 this study 24

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REFERENCES

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at low temperature; however, its useful capacity decreased to 51.3% after 11cycles.30 Compared with the SBA-15/PEI adsorbents,1,18,24 M4-TM-50 material exhibited more stable sorption−desorption performance. One mg/g adsorption capacity loss (less than 1% of initial capacity) after 12 adsorption−desorption cycles was gained. Therefore, the M4TM material showed well balanced adsorption−desorption properties in terms of the CO2 capture capability, fast desorption performance, and regenerability. To our knowledge, this is the first time that AM-modified TEPA was impregnated to a structurally disordered mesoporous material for CO2 capture.

4. CONCLUSIONS AM-modified TEPA (TM) was deposited on four porous supports resulting in adsorbents suitable for removing CO2 from gas streams. The most promising support was found to be M4 with a disordered structure and larger pore size. Results indicated that the CO2 adsorption capacity was dependent on the amine loadings, adsorption temperature, and pore size of the support, and not on the structural order. Samples with low amine loading showed an increase in CO2 adsorption capacity which decreased with amine loading greater than 60%. At low temperature (