Capturing CO2 with Amine-Impregnated Titanium Oxides - Energy

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Capturing CO2 with Amine-impregnated Titanium Oxides Lina Ma, Ruizhu Bai, Gengshen Hu, Ru Chen, Xin Hu, Wei Dai, Herbert F.M. DaCosta, and Maohong Fan Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/ef401230q • Publication Date (Web): 01 Aug 2013 Downloaded from http://pubs.acs.org on August 2, 2013

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Capturing CO2 with Amine-impregnated Titanium Oxides Lina Maa, §, Ruizhu Bai a, §, Gengshen Hub, Ru Chena, Xin Hu*,a, Wei Daia, Herbert F. M. Dacostac, Maohong Fan*,d a

College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, PR China

b

Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces, Institute of Physical

Chemistry, Zhejiang Normal University, Jinhua 321004, PR China c

Chem-Innovations, P.O. Box 3665, Peoria, IL 61612, USA

d

Department of Chemical and Petroleum Engineering, University of Wyoming, Laramie,

Wyoming 82071, USA *

Corresponding author’s e-mail: [email protected]; phone: 86-151-0579-0257; fax: 86-579-8228-

8269 (X.H.) or e-mail: [email protected]; phone: 1-307-766-5633; fax: 1-307-766-6777(M.F.). §

Both authors contributed equally to this work.

.

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ACS Paragon Plus Environment

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Abstract

A series of porous titanium oxides was synthesized using different alkylamines and modified by amines including diethylenetriamine (DETA), triethylenetetramine (TETA) and tetraethylenepentamine (TEPA) for CO2 capture. These new composite CO2 sorbents were characterized by powder X-ray diffraction, transmission electron microscopy, nitrogen adsorption, Fourier transform infrared spectroscopy and thermogravimetric analysis. Their CO2 capture performances were evaluated in a fixed-bed reactor equipped with an on-line mass spectroscopy. Experimental results revealed that CO2 uptake capacities of the titania composite sorbents increase with amine loading but decrease with the size of impregnated amines. The highest CO2 sorption capacity achieved with the sorbents is 2.64 mmol/g. It is also found that besides the surface area and pore volume, the pore size of the support also plays an important role in determining the CO2 uptake capacity of the composite sorbents. In addition to their high CO2 adsorption capacities, the amine-impregnated titanias exhibit good stability and regenerability.

Key words: CO2 capture, Titanium oxide, Amines, Flue gas, Adsorption

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Introduction

Emission of CO2 has attracted worldwide attention, as CO2 is generally accepted to be a greenhouse gas with potentially significant contribution to climate change.1 Carbon capture and sequestration is considered as one of the most promising solutions to mitigate the CO2 emissions.2 Post-combustion capture of CO2 from coal-fired power plants is likely to be done with amine scrubbing,3 which is based on CO2 absorption using aqueous amine solutions or chilled ammonia. However, this method suffers from relatively low energy efficiency and issues associated with the use of liquid amine solvents such as equipment corrosion, solvent loss, and toxicity. To overcome these challenges, adsorption via solid sorbent has been proposed as an alternative.

4, 5

In recent years, intensive research has been focused on the development of new

sorbents. Examples of CO2-philic sorbent materials are carbons,6-9 zeolites,10, 11 silicas,12 and metal-organic frameworks.13-15 To increase the CO2 capture capacity under the condition of flue gas, a number of solid CO2 sorbents synthesized with amines and porous solids have been developed. The interaction between the CO2 and –NH2 moiety of these sorbents increased greatly, which resulted in considerable improvements in capacity and selectivity of CO2 sorption, and reversibility of these sorbents. Of all kinds of the reported solid supports, mesoporous silicas are considered as the most promising supports for amine immobilization due to their large surface area and pore volume, tunable pore structure, and high thermal stability. To date, different types of silica including MCM-41,2, 16, 17 MCM-48,18, 19 SBA-15,2, 20 SBA-16,21, 22 HMS,23 KIT-6,24and silica foam25-27 have been used as support materials for preparations of amine/oxide composite adsorbents. These silica-based amine sorbents show promising CO2 sorption capacity under the simulated flue gas condition. However, the CO2 uptake capacity of silica-based sorbents still

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cannot fully satisfy the needs of practical applications. In addition, the CO2 adsorption mechanism of these types of sorbents is not clear. Research on sorbents with different pore structure and surface chemistry properties can help better understand the CO2 sorption mechanism for amine/oxide composite adsorbents, which is beneficial to design solid supported amine sorbents with higher CO2 uptake capacities. On this theme, recently, people are increasingly interested in developing sorbents with amines and other oxides such as alumina,28-32 titania,33 or composite oxides, such as aluminosilicates34 or titanosilicates.35 For example, we previously investigated the CO2 uptake capacity of diethylenetriamine (DETA) impregnated microporous titania composite sorbents.36 It has been found that with a moderate DETA loading, the titania based sorbent exhibited a higher CO2 adsorption capacity than analogue DETA impregnated SBA-15,36 the recently reported DETA-impregnated activated carbon,37 and aluminum oxide materials.28 However, compared to silica-based amine sorbents, titania based sorbent development lags behind. Therefore, this study was designed to further understand the characteristics of titania based CO2 sorbents synthesized with titanium oxides possessing various porous

textures

and

amines

including

DETA,

triethylenetetramine

(TETA)

and

tetraethylenepentamine (TEPA) in order to give more insights in CO2 adsorption mechanism for the amine-impregnated oxide composite sorbents.

2. Experimental

Titanium(IV) isopropoxide was obtained from Aldrich. Hexylamine, octylamine, dodecylamine, octadecylamine were used as the templates and purchased from J&K Scientific. The organic amines used in this study include DETA, TETA, and TEPA, which were ordered

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from J&K Scientific. Table S1 shows the molecular structures and boiling points of these amines. Methanol and diethyl ether were supplied by Sinopharm Chemical Reagent Co., Ltd. Hydrochloric acid (HCl) was obtained from Quzhou reagent Juhua Co., LTD. Distilled water was used in all experiments. All the chemicals were used as they were received without any further purification.

2.1 Preparation of supporting materials-porous titanium oxides A series of four porous TiO2 materials was synthesized as described38, 39 previously from C6, C8, C12, and C18 amine templates. The detailed preparation procedure can be found in the Supporting Information. To facilitate the research, sorbents prepared in this research were labeled as Cx-Ti in which x represents the number of carbon in the amine template, accordingly, the four samples were C6-Ti, C8-Ti, C12-Ti and C18-Ti.

2.2 Synthesis of sorbents Amine functionalized TiO2 was prepared by wet impregnation. The typical preparation starts with dissolving the desired amount of amine (DETA, TETA or TEPA) into 10.0 g ethanol, stirring for 30 min, and adding 1 g Cx-Ti. The resulting slurry was stirred and refluxed at 80°C for 2 h, and then dried at 80°C until complete volatilization of ethanol was achieved. The obtained samples were denoted as n-amine/Cx-Ti in which n represents the weight percentage of amine in the composites. For instance, 50-TEPA/C6-Ti means the adsorbent contains 50 wt% TEPA and 50 wt% C6-Ti support.

2.3 Characterization

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The pore characteristics of the freshly made porous TiO2 were determined by nitrogen adsorption at -196°C using Quantachrome NOVA 4000e analyzers. The freshly made supports were degassed at 150°C under vacuum at 1 x10-3 Torr for a period of at least 12 h. The surface area was calculated using the multipoint Brunauer-Emmett-Teller (BET) method. The total pore volume (Vtotal) was determined as the volume of liquid nitrogen adsorbed at a relative pressure of 0.98. Transmission electron microscopy (TEM) was carried out using a JEOL-2100F transmission electron microscope operated at 200 KV. Thermogravimetric Analysis (TGA) was fulfilled with a NETZSCH STA 449C thermal graphic analyzer with a heating rate of 5 K/min in N2. Attenuated Total Reflection Infrared (ATR-IR) spectrum of TEPA was acquired on a Nicolet 670 FTIR spectrometer equipped with an ATR-IR accessory. Fresh support and TEPAimpregnated sorbents were also characterized by transmission infrared spectroscopy in the form of pellets. The X-ray diffraction (XRD) patterns of titanias were obtained on a Philips PW3040/60 automatic powder diffractometer using Cu Kα (λ=0.1542 nm) radiation.

2.4 CO2 adsorption and desorption The CO2 capture capacity of the adsorbent was determined with a fixed-bed reactor system as shown in Figure S1. The adsorption process was operated at atmospheric pressure and the outlet gases were analyzed by an online Mass Spectroscopy (MS) (OminiStar 200). 0.5 g of dried adsorbent was packed into the middle of the quartz-tube reactor (6 mm inner diameter) with its temperatures being controlled by heating tapes. Prior to each adsorption measurement, the adsorbent was activated by heating it to 100°C and keeping it at the same temperature for 1 h in He stream with a flow rate of 20 mL/min. After the sorbent was cooled to the desired adsorption temperature (e.g. 75°C), 10% CO2 balanced with N2 stream at a total flow rate of 20 mL/min was

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introduced and passed through the adsorbent bed until adsorption saturation was reached. The CO2 breakthrough capacity on an adsorbent was calculated by integration of breakthrough curve. Multiple cycle adsorption-desorption tests were used to evaluate the regenerability of the chosen sorbent. After the adsorption measurement, the sorbent regeneration was carried out by passing He (20 mL/min) through the bed at 100°C for 1 h. The same sorption-desorption procedure was conducted for 6 cycles to test the stability and adsorptive repeatability of the titania supported amines.

3 Results and discussion 3.1 Characteristics of sorbents The XRD patterns of this series of porous freshly prepared titanias are shown in Figure S2. There are no diffraction peaks, which imply that these materials do not possess any significant long-range order which is confirmed with the TEM image of C6-Ti presented in Figure S3. Figure S3 shows the amorphous and disordered wormhole pore structure of C6-Ti. Nitrogen adsorption/desorption isotherms of this series of freshly prepared titanias are shown in Figure 1. All the isotherms exhibit typical type I isotherms, indicating the microporous nature of these materials. While the isotherms show an almost flat sorption characteristic at P/P0>0.4, a low slope of the plateau indicates multilayer adsorption on the external surface revealing some mesoporosity. Table 1 presents a summary of the corresponding textural properties of the freshly prepared titanias prepared in this work, of which the surface area and pore volume decrease in the order of C8-Ti >C6-Ti>C12-Ti>C18-Ti. In order to confirm that amine has been impregnated into the supports, the ATR-IR spectrum of TEPA and FT-IR spectra of C6-Ti and composite sorbent 50-TEPA/C6-Ti are

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recorded and shown in Figure 2. As expected, the composite sorbent shows some characteristic peaks of TEPA indicating that it has been impregnated onto the support surface or into the internal channel of the supporting material. In the spectrum of TEPA (Figure 2a), a peak due to N-H stretching is observed at 3,268 cm−1, however, the peak is not clearly observed with 50TEPA/C6-Ti, possibly because it is overlapped with the broad band for surface O-H group and/or molecular adsorbed water (3,000-3,600 cm−1). The band at 1,590 cm-1 in TEPA corresponds to N-H bending vibration; whereas this band shifts to 1,576 cm-1 in 50-TEPA/C6-Ti, a revelation of the interaction between TEPA and titania. In the infrared spectrum of TEPA, peaks at 2,945, 2,802 and 1,447 cm-1 can be due to C-H stretching and bending vibrations, respectively. The similar peaks appear in the spectrum of 50-TEPA/C6-Ti. The amount of amine present in titania can be estimated from the weight loss of the materials determined by TGA. Figure S4 shows the TGA curves of C6-Ti and n-TEPA/C6-Ti (n=10, 30, 50). C6-Ti has about 10% weight loss before 400°C, which could be ascribed to the release of physically adsorbed atmospheric moisture and structural water. After 400°C, the thermogravimetric curve shows a nearly flat characteristic, which is consistent with what was reported with previous research.40, 41 Excluding the mass loss of C6-Ti, the whole mass drop of n-TEPA/C6-Ti is almost equivalent to the designed TEPA impregnation amounts.

3.2 CO2 capture capacities of sorbents C6-Ti based sorbents CO2 breakthrough curves of C6-Ti with various DETA, TETA and TEPA loading levels are recorded and shown at Figure 3. Since it has been reported previously that 75°C is the optimum adsorption temperature for most amine-functionalized sorbents, 2, 42-44 75°C was used to conduct

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the sorption tests in this research. All the obtained CO2 capture capacities for the composite sorbents in this study are summarized in Table 2. The CO2 uptake capacity of C6-Ti is 0.30 mmol/g, after modified with different amounts of amines, the result samples show higher CO2 capacities ranging from 0.57 to 2.08 mmol/g indicating the occurrence of specific CO2-amine chemistry in these composite sorbents. In addition, the CO2 uptake capacities of the composite sorbents prepared with the same amine increase with the loading of amine. For example, with the increase of the DETA loadings from 10 to 50%, the CO2 sorption capacities of the sorbents increase from 0.76 to 2.08 mmol/g accordingly. This is consistent with previous reports that higher amine loading amounts result in higher CO2 capture capacity.2, 16, 17, 42 Furthermore, the sorption capacities of 50-DETA/C6-Ti, 50-TETA/C6-Ti and 50-TEPA/C6-Ti are in a descending order, which indicates that the composite sorbents modified by organic amines with smaller molecules have higher CO2 uptake capacities. Since C6-Ti is a microporous material, it is much easier for amine molecules with smaller sizes to enter into its pores and lead to better dispersion of NH2 functional group and thus more effective interaction with CO2. On the contrary, the large-size amines have low probabilities to enter the pores of the sorbents, and could deposit and conglomerate on the external surface of the support and consequently decreases the availability of active sites on sorbents for capture of CO2. On the other hand, the smaller size amine has higher N content per unit mass so when same amount of amines are used, the sorbent modified by amine with smaller size is equivalent to have higher amine loading level compared with that modified by amine with larger size and thus lead to the higher CO2 uptake capacity. C8-Ti based sorbents Figure 4 shows CO2 breakthrough curves for C8-Ti modified with various amounts of TETA and TEPA. The results for n-DETA/C8-Ti have been reported previously36 and the

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corresponding CO2 capture values are included in Table 2 for comparison. From the data, it is easily found that the CO2 uptake capacities of the composite sorbents increase with amine loading but decrease with the size of impregnated amines, which agrees with the above discussion. When comparing the effect of the support on CO2 uptake capacity, under the same amine and loading level, C8-Ti based sorbents show higher CO2 capture capacity than those of C6-Ti based samples with minor exceptions, e.g. 10% loading of TETA and TEPA. These results may be attributed to the higher surface area and pore volume of C8-Ti than those of C6-Ti. The high surface area of C8-Ti provides a large platform for dispersing amine molecules and maximizing exposure of its NH2 functional group for interaction with CO2. In the same time, the higher pore volume of C8-Ti may reduce the conglomerate of the impregnated amines within the pores, leading to better distribution of amine sites and thus higher CO2 uptake capacity. C12-Ti based sorbents CO2 breakthrough curves of C12-Ti with various DETA, TETA and TEPA loading levels are tested and shown at Figure 5. The corresponding CO2 capture values are summarized in Table 2. Same as the trend observed in C8-Ti and C6-Ti series sorbents, CO2 uptake capacities of the sorbents increase with amine loading and decrease with the size of impregnated amines. When further examine the effect of support on CO2 uptake capacity, it is found that under the identical conditions, C12-Ti based sorbents are inferior to those synthesized by C6-Ti and C8-Ti, which could be due to the smallest surface area and pore volume of C12-Ti among the three supports. C18-Ti based sorbents Figure 6 illustrates the CO2 breakthrough curve of C18-Ti modified with various amounts of DETA, TETA and TEPA, respectively. The corresponding calculated CO2 capture capacities

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are included in Table 2. For the C18-Ti series samples, effects of amine size and amine loading level on CO2 uptake capacity have the same trend with all the above discussed titania composite sorbents. However, when the CO2 capture data among sorbents prepared by different supports is compared, it is found that under the identical conditions, C18-Ti based sorbents have higher CO2 uptake capacity than those synthesized from C12-Ti with only exception of 10% DETA loading. This is contrary to the results from the above sections, since C12-Ti shows a higher surface area and pore volume than C18-Ti. This phenomenon can be explained by the higher average pore size of C18-Ti than C12-Ti (Table 1). The large pore size allows the bulky amine to enter the channels of the support more efficiently thus leading to superior CO2 capture capacity. Similar results have been reported for silica based sorbents.42 From these results, it can be proposed that besides the surface area and pore volume, the pore size of the support is also an important factor that determines the CO2 uptake capacity of amine-impregnated composite sorbents. This hypothesis can be further proved when the CO2 capture data of C18-Ti based sorbents is compared with those prepared with the C6-Ti support. For the sorbents modified by TETA and TEPA, the two series of samples show similar CO2 capture capacity. Considering the fact that C6-Ti has a pore volume of 0.50 cm3/g and surface area of 930 m2/g, almost twice larger than the pore volume and surface area of C18-Ti, which is only 0.31cm3/g and 448 m2/g, the larger pore size of C18-Ti compared with C6-Ti plays an important role in CO2 capture. On the other hand, for the DETA modified sorbents, C6-Ti based sorbents show higher CO2 uptake capacity than C18-Ti based samples, which is possibly due to the relatively smaller size of DETA, which can enter the pore channel of C6-Ti support more effectively than TETA and TEPA.

3.3 Regenerability of 50-TEPA/C8-Ti

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The stability and regenerability of the amine-impregnated titania sorbent are investigated. The 50-TEPA/C8-Ti was selected to study its cyclic CO2 sorption capacity due to its largest adsorption capacity among all the TEPA modified sorbents and the highest boiling point of TEPA among all the amines in this study. Figure 7 shows the cyclic CO2 adsorption capacities of 50-TEPA/C8-Ti in 6 consecutive runs. Full CO2 adsorption capacity of 1.75 mmol/g is achieved in the first cycle, while the adsorption capacity of the cycle 2 is 1.63 mmol/g decreased by 7% with respect to cycle 1. Further cyclic results show that the CO2 capture capacity decrease to 1.56 and 1.50 mmol/g in cycle 3 and 4, respectively. This capacity loss during the cyclic tests could be due to the continuous volatilization of the impregnated amines25, 43 or the formation of urea groups45 during the CO2 desorption process, which are ineffective towards CO2. Starting from the fourth cycle, 50-TEPA/C8-Ti shows virtually stable adsorption-desorption performance during the remaining consecutive runs. This may be explained by a strong interaction between TEPA and the titania support, as it has been proposed that the Ti sites can interact with amines by acting as Lewis acid sites.35 The volatilization of TEPA is limited due to this strong interaction between amine and titania and thus the amount of impregnated amine is constant after several cyclic tests, which lead to the stable performance of CO2 capture in the following cyclic runs. These results indicate that 50-TEPA/C8-Ti displays good stability and regenerability in multiple cyclic operations.

4 Conclusion In summary, porous titanias with different surface area, pore volume and pore size were synthesized using the alkylamines with different carbon chain lengths as templates. Amineimpregnated titania composite sorbents were prepared by wet impregnated method using various

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amounts of DETA, TETA and TEPA. From the CO2 uptake results, it is found that, when modified by the same amine, CO2 uptake capacities of the composite sorbents increase with amine loading. While, under the same amine loading, the CO2 capture capacity decreases with the size of the impregnated amines. It is also found that in addition to surface area and pore volume, pore size of the support also plays an important role in determining CO2 uptake capacity of the composite sorbents. These results indicate that to obtain composite sorbents with better performance, further optimization of sorbent preparation method is needed. The ideal support would have large surface area and pore volume together with relatively large and uniform pore size. In addition to excellent CO2 adsorption capacity, the amine-impregnated titanias exhibit good stability and regenerability.

Acknowledgments Financial support from the National Natural Science Foundation of China (21106136), National Undergraduate Training Programs for Innovation and Entrepreneurship of China and Wyoming Clean Coal Program is greatly appreciated.

Supporting Information Available Additional information includes details about sample preparation, 1 table and 4 figures. This material is available free of charge via the Internet at http://pubs.acs.org. References 1. Dutcher, B.; Fan, M.; Leonard, B.; Dyar, M. D.; Tang, J.; Speicher, E. A.; Liu, P.; Zhang, Y., J. Phys. Chem. C 2011, 115, (31), 15532-15544. 2. Ma, X.; Wang, X.; Song, C., J. Am. Chem. Soc. 2009, 131 (16), 5777-5783. 3. Rochelle, G. T., Science 2009, 325 (5948), 1652-1654. 4. Bae, Y. S.; Snurr, R. Q., Angew. Chem. Int. Ed. 2011, 50 (49), 11586-11596. 5. D'Alessandro, D. M.; Smit, B.; Long, J. R., Angew. Chem. Int. Ed. 2010, 49 (35), 60586082.

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32. Cai, W.; Yu, J.; Jaroniec, M., J. Mater. Chem. 2011, 21 (25), 9066-9072. 33. Knofel, C.; Martin, C.; Hornebecq, V.; Llewellyn, P. L., J. Phys. Chem. C 2009, 113 (52), 21726-21734. 34. Bellussi, G.; Broccia, P.; Carati, A.; Millini, R.; Pollesel, P.; Rizzo, C.; Tagliabue, M., Microporous Mesoporous Mater. 2011, 146 (1-3), 134-140. 35. Young, P. D.; Notestein, J. M., ChemSusChem 2011, 4 (11), 1671-1678. 36. Zhao, X.; Hu, X.; Hu, G.; Bai, R.; Dai, W.; Fan, M.; Luo, M., J. Mater. Chem. A 2013, 1 (20), 6208-6215. 37. Plaza, M. G.; Pevida, C.; Arenillas, A.; Rubiera, F.; Pis, J. J., Fuel 2007, 86 (14), 22042212. 38. Hu, X.; Skadtchenko, B. O.; Trudeau, M.; Antonelli, D. M., J. Am. Chem. Soc. 2006, 128 (36), 11740-11741. 39. Hu, X.; Trudeau, M.; Antonelli, D. M., Chem. Mater. 2007, 19 (6), 1388-1395. 40. Hague, D. C.; Mayo, M. J., J. Am. Ceram. Soc. 1994, 77 (7), 1957-1960. 41. Yan, J. H.; Zhu, Y.-R.; Tang, Y. G.; Zheng, S. Q., J. Alloys Compd. 2009, 472 (1-2), 429433. 42. Son, W. J.; Choi, J. S.; Ahn, W. S., Microporous Mesoporous Mater. 2008, 113 (1-3), 3140. 43. Qi, G.; Wang, Y.; Estevez, L.; Duan, X.; Anako, N.; Park, A. H. A.; Li, W.; Jones, C. W.; Giannelis, E. P., Energy Environ. Sci. 2011, 4 (2), 444-452. 44. Heydari-Gorji, A.; Belmabkhout, Y.; Sayari, A., Langmuir 2011, 27 (20), 12411-12416. 45. Sayari, A.; Belmabkhout, Y., J. Am. Chem. Soc. 2010, 132 (18), 6312-6314.

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Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 24

Table 1. Textural characteristics of titania supports Surface area, SBET a

Pore volume, Vtotalb

Pore diameter, dpc

(m2/g)

(cm3/g)b

(nm)

C6-Ti

930

0.50

2.16

C8-Ti

1037

0.62

2.38

C12-Ti

722

0.44

2.43

Sample

C18-Ti 448 0.31 Surface area was calculated using the BET method at P/P0=0.05-0.2. b Values at P/P0=0.98. c Average pore size, calculated by 4Vtotal/SBET a

16


2.72

Page 17 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Energy & Fuels

Table 2: CO2 adsorption capacity of TiO2 based composite sorbents at 75°C, 10 %(v/v) of CO2 in N2 and 1 atm. . Sample n%-DETA/ C6-Ti 10 30 50 n%-TETA/ C6-Ti 10 30 50 n%-TEPA/ C6-Ti 10 30 50 a From Ref. 36

CO2 adsorption capacities （mmol/g）

0.76 1.58 2.08

0.73 1.37 1.80

0.57 0.93 1.38

Sample n%-DETA/ C8-Ti 10 30 50 n%-TETA/ C8-Ti 10 30 50 n%-TEPA/ C8-Ti 10 30 50


0.78a 2.30a 2.64a

0.59 1.80 2.24

0.44 1.53 1.75

Sample


n%-DETA/ C12-Ti 10 30 50 n%-TETA/ C12-Ti 10 30 50 n%-TEPA/ C12-Ti 10 30 50

17


0.75 1.10 1.54

0.56 1.04 1.47

0.43 0.77 1.34

Sample n%-DETA/ C18-Ti 10 30 50 n%-TETA/ C18-Ti 10 30 50 n%-TEPA/ C18-Ti 10 30 50


0.64 1.45 1.90

0.61 1.38 1.85

0.58 1.00 1.56

Energy & Fuels

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Page 18 of 24

Figure captions Figure 1. Nitrogen adsorption-desorption isotherms of C6-Ti, C8-Ti, C12-Ti and C18-Ti. Filled and empty symbols represent adsorption and desorption branches, respectively Figure 2. ATR-IR spectrum of (a) raw TEPA and FT-IR spectra of (b) 50-TEPA/C6-Ti and (c) C6-Ti Figure 3. Breakthrough curves of C6-Ti modified with various amount of (a) DETA, (b) TETA and (C) TEPA (adsorption at 75°C, gas flow rate: 20 cm3/min, inlet CO2 concentration: 10 vol.%) Figure 4. Breakthrough curves of C8-Ti modified with various amount of (a) TETA and (b) TEPA (adsorption at 75°C, gas flow rate: 20 cm3/min, inlet CO2 concentration: 10 vol.%) Figure 5. Breakthrough curves of C12-Ti modified with various amount of (a) DETA, (b) TETA and (C) TEPA (adsorption at 75°C, gas flow rate: 20 cm3/min, inlet CO2 concentration: 10 vol.%) Figure 6. Breakthrough curves of C18-Ti modified with various amount of (a) DETA, (b) TETA and (C) TEPA (adsorption at 75°C, gas flow rate: 20 cm3/min, inlet CO2 concentration: 10 vol.%) Figure 7. Cyclic adsorption-desorption of 50-TEPA/C8-Ti under 10 % CO2/N2 at 75°C

18


Page 19 of 24

3

Volume adsorbed (cm /g, STP)

500

C6-Ti C8-Ti C12-Ti C18-Ti

400

300

200

100

0 0.0

0.2

0.4

0.6

0.8

1.0

Relative pressure (P/P0)

N-H 3268

C-H 1447 N-H 1590

C-H 2802 C-H 2945

Figure 1. Nitrogen adsorption-desorption isotherms of C6-Ti, C8-Ti, C12-Ti and C18-Ti. Filled and empty symbols represent adsorption and desorption branches, respectively

Transmittance (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(a)

(b)

(c)

500

1000

1500

2000

2500

3000

3500

-1

Wavenumber (cm )

Figure 2. ATR-IR spectrum of (a) raw TEPA and FT-IR spectra of (b) 50-TEPA/C6-Ti and (c) C6-Ti

19


Energy & Fuels

(a) 1.0

0.8

10-DETA/C6-Ti 30-DETA/C6-Ti 50-DETA/C6-Ti

C/C0

0.6

0.4

0.2

0.0 0

10

20

30

40

50

60

Time (min)

(b) 1.0

0.8

10-TETA/C6-Ti 30-TETA/C6-Ti 50-TETA/C6-Ti

C/C0

0.6

0.4

0.2

0.0 0

10

20

30

40

50

60

Time (min)

(c) 1.0

0.8

10-TEPA/C6-Ti 30-TEPA/C6-Ti 50-TEPA/C6-Ti

0.6

C/C0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 24

0.4

0.2

0.0 0

10

20

30

40

50

60

Time (min)

Figure 3. Breakthrough curves of C6-Ti modified with various amount of (a) DETA, (b) TETA and (C) TEPA (adsorption at 75°C, gas flow rate: 20 cm3/min, inlet CO2 concentration: 10 vol.%)

20


Page 21 of 24

(a) 1.0

0.8


C/C0

0.6

0.4

0.2

0.0 0

10

20

30

40

50

60

Time (min)

(b) 1.0

0.8


0.6

C/C0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.4

0.2

0.0 0

10

20

30

40

50

60

Time (min)

Figure 4. Breakthrough curves of C8-Ti modified with various amount of (a) TETA and (b) TEPA (adsorption at 75°C, gas flow rate: 20 cm3/min, inlet CO2 concentration: 10 vol.%)

21


Energy & Fuels

(a) 1.0

0.8


C/C0

0.6

0.4

0.2

0.0 0

10

20

30

40

50

60

Time (min)

(b) 1.0

0.8


C/C0

0.6

0.4

0.2

0.0 0

10

20

30

40

50

60

Time (min)

(c) 1.0

0.8


0.6

C/C0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 24

0.4

0.2

0.0 0

10

20

30

40

50

60

Time (min)


22


Page 23 of 24

(a) 1.0

0.8


C/C0

0.6

0.4

0.2

0.0 0

10

20

30

40

50

60

Time (min)

(b) 1.0

0.8


C/C0

0.6

0.4

0.2

0.0 0

10

20

30

40

50

60

Time (min)

(c) 1.0

0.8


0.6

C/C0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.4

0.2

0.0 0

10

20

30

40

50

60

Time (min)


23


Energy & Fuels

2.0

1.75 1.63

1.56

1.50

1.49

1.50

4

5

6

1.5

CO2 uptake (mmol/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 24

1.0

0.5

0.0 0

1

2

3

7

Numbers of cycles

Figure 7. Cyclic adsorption-desorption of 50-TEPA/C8-Ti under 10 % CO2/N2 at 75°C

24


Capturing CO2 with Amine-Impregnated Titanium Oxides - Energy

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