Stability of Supported Amine Adsorbents to SO2 and NOx in

Article pubs.acs.org/IECR

Stability of Supported Amine Adsorbents to SO2 and NOx in Postcombustion CO2 Capture. 2. Multicomponent Adsorption Fateme Rezaei and Christopher W. Jones* School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, Georgia 30332, United States S Supporting Information *

ABSTRACT: Packed bed CO2 adsorption breakthrough experiments using both amine-impregnated and amine-grafted silica adsorbent materials in the presence of SO2, NO and NO2 impurities are reported. The effects of temperature, feed concentration and adsorbent amine loading on the dynamic adsorption capacity of the adsorbents are evaluated by performing dual component SO2/CO2, NO/CO2 and NO2/CO2 coadsorption experiments as well as three component SO2/NO/CO2 adsorption experiments. Although SO2 is found to significantly influence the dynamic CO2 capacity of aminosilica adsorbents, the obtained results confirm the long-term stability of the adsorbents during SO2/CO2 coadsorption runs when the bed is not allowed to fully saturate with SO2. On the other hand, little competitive effect of NO on CO2 adsorption is observed in any case. This is due to the decreased affinity of amine-based adsorbents toward NO as opposed to SO2. The more reactive nitrogen oxide, NO2, is shown to have a minimal impact on CO2 adsorption when it is present at low levels in the simulated flue gas. Among the adsorbents investigated, the results demonstrate that secondary amine containing adsorbents are more stable to SOx and NOx impurities in CO2 capture processes than those that contain primary amine groups.

1. INTRODUCTION

As an example from the zeolite literature, recently, Deng and co-workers2 evaluated the coadsorption of SO2, NO and CO2 on a series of ion-exchanged NaX zeolites to study the interactive effects of the gases in the simultaneous removal of these acidic gases from flue gas. On the basis of their results, the CO2 capacity of K-NaX dropped from 0.51 to 0.28 mmol/g in the presence of 2000 ppm of SO2 and 1000 ppm of NO and dropped even further to 0.13 when 5% O2 was present in the gas mixture. In another study,25 the coadsorption of SO2 and CO2 over tertiary amine-containing materials was performed under humid conditions to evaluate the suitability of these adsorbents as SO2 adsorbents. The authors reported a SO2 capacity of 2.19 mmol/g under dry conditions and a 3-fold increase when the moisture was present. In our previous paper,1 we evaluated the stability of supported amine adsorbents to SO2, NO and NO2 in postcombustion CO2 capture by performing cyclic, singlecomponent adsorption experiments. The degree of irreversible binding of SO2, NO, and NO2 to four supported amine adsorbents was evaluated to assess the SO2, NO, and NO2 adsorption capacities of the aminosilica adsorbents and their effects on the CO2 adsorption capacities by performing thermogravimetric studies. The materials tested in that work consisted of one class 1 aminosilica adsorbent26 (based on poly(ethylenimine)) and three class 2 materials26,27 made using three different silane coupling agents (based on a propyltrimethoxysilane linker) with primary, secondary and tertiary amines. The effects of temperature, concentration and amine

The deactivation of CO2 adsorbing materials in the presence of flue gas impurities such as SOx and NOx poses a significant challenge to the practical application and scale-up of the adsorption-based CO2 capture technologies. These impurities are particularly important, as the reaction between these species and many solid adsorbents is essentially irreversible in nature, reducing the adsorbent lifetime and making the capture process more costly. In that regard, recently, much effort has been put into evaluating the stability of CO2 adsorbent materials to SOx and NOx.1−8 The typical concentrations of SOx and NOx in coal-fired power plants (before sulfur scrubbing and/or selective catalytic reduction units) are approximately 0.2−0.25 and 0.15−0.2 vol %, respectively, whereas the approximate CO2 concentrations in similar power stations are 9−14 vol %.4 These elevated concentrations are often detrimental to amine adsorbents and solutions, and for this reason, their concentrations are reduced by sulfur scrubbing and/or selective catalytic reduction units to concentrations below ∼2 and ∼50 ppm, for SOx and NOx, respectively. Because of the importance of these impurity gases, there have been a number of investigations of the impact of SOx and NOx on CO2 adsorption capacity of zeolites9−13 and calcium-based adsorbents,5,14−18 as well as for solid-supported amine materials.4,19−22 However, the majority of the work in the literature has focused on single-component adsorption experiments and the synergy in coadsorbing of the SOx or NOx and CO2 has not been fully investigated. SOx and NOx impurities have been shown to bind irreversibly to most amine groups,4,19,20,23,24 therefore competitive, dynamic adsorption of SOx/NOx on amine adsorbents merits experimental investigation. © 2014 American Chemical Society

Received: Revised: Accepted: Published: 12103

May 17, 2014 July 3, 2014 July 8, 2014 July 8, 2014 dx.doi.org/10.1021/ie502024z | Ind. Eng. Chem. Res. 2014, 53, 12103−12110

Industrial & Engineering Chemistry Research

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Table 1. Amine Materials Used to Prepare Aminosilica Adsorbents amine

amine types

sample name

poly(ethylenimine) 3-aminopropyltrimethoxysilane (N-methylaminopropyl)trimethoxysilane (N,N-dimethylaminopropyl)trimethoxysilane

primary, secondary, tertiaryPEI primaryAPS secondaryMAPS tertiaryDMAPS

PD-PEI_2 PD-APS_2 PD-MAPS_2 PD-DMAPS_2

loading on the adsorption capacity of aminosilica adsorbents were then evaluated accordingly. It was shown that the materials were stable in the presence of NO and retained their full CO2 capacities after exposure to this gas. In contrast, all materials treated with NO2 exhibited a dramatic decrease in CO2 capacity as a result of deactivation of amine groups due to the irreversible binding of NO2. In the current study, we extend our previous work and continue evaluating the stability of amine adsorbents to SO2 and NOx in postcombustion CO2 capture by performing dynamic, multicomponent adsorption experiments in a fixed bed.

2. EXPERIMENTAL SECTION 2.1. Materials Synthesis. A detailed description of materials synthesis can be found in our previous paper.1 Here we briefly discuss the materials used in this study. A commercial silica support (PD09024 from PQ Corporation) was used to synthesize four different aminosilica adsorbents; one class 1 (PEI-impregnated material) and three class 2 adsorbent materials (aminosilane-based materials). Adsorbents with similar amine loadings were prepared for each material type. Table 1 summarizes the materials used to synthesize supported amine adsorbents with their corresponding nomenclature. For packed bed experiments, pellets were pressed under a pressure of 3000 psi and sieved between 400 and 500 μm. The sample codes in Table 1 start with the letters PD for the silica support, followed by the amine type and a number indicating the approximate amine loading for each sample. 2.2. Materials Characterization. Nitrogen physisorption measurements were carried out on a Micromeritics TRISTAR II at 77 K. Surface areas and pore volumes were calculated from the collected isotherm data. Surface areas were calculated using the Brunauer−Emmett−Teller (BET) method and pore volumes and pore diameters were calculated using the Frenkel−Halsey−Hill (BdB-FHH) method.36 A Netzsch STA409PG thermogravimetric analyzer (TGA) was used to determine the organic loading of the materials. The equilibrium adsorption capacity of materials was also measured using a Q500 thermogravimetric analyzer (TA Instruments). 2.3. Packed Bed Multicomponent Adsorption Measurements. Coadsorption breakthrough measurements were carried out in a packed bed column as schematically shown in Figure 1. A 7.0 cm long Pyrex tube with the diameter of 1.0 cm equipped with a fine-sized frit was loaded with 1.0 g of adsorbent pellets for each experiment. A heating tape was used to heat up the column during the desorption step and a thermocouple was used to probe the column temperature. The outlet gas concentrations were measured by a mass spectrometer (Pfeiffer Vacuum Omnistar, QMG 220). The breakthrough experiments were performed at 1 atm total pressure. First, nitrogen was flowed through the bed at 100 mL/min while the bed temperature was raised to 110 °C for 30 min, after which it was lowered back to room temperature and

Figure 1. Schematic of packed bed setup for multicomponent adsorption experiments.

allowed to equilibrate at that temperature for 30 min. The flow was then switched from nitrogen to the CO2 and/or SO2/NOx containing gas stream (dry) while continuously monitoring the outlet gas concentration and bed temperature. Before the start of the experiments, the mass spectrometer was calibrated with a dry gas stream containing known concentrations of CO2, SO2, NO and NO2. To assess any synergies in coadsorption of SOx or NOx and CO2 gases, two gas mixtures comprising 200 ppm of NO, 10% CO2 (balance nitrogen) and 200 ppm of SO2, 10% CO2 (balance nitrogen) were used in addition to singlecomponent adsorption gases. The multicomponent adsorption experiments were performed for binary (CO2/SO2 or CO2/NO or CO2/NO2) and ternary (CO2/SO2/NO) gas components at 35, 55 and 75 °C. In this method, the materials were simultaneously exposed to CO2 and SO2 or CO2 and NO and thereby their CO2 uptake was measured at two different temperatures similar to single-component tests done via TGA in our previous study.1 The dynamic adsorption capacity (qd) of the materials was calculated from the breakthrough profiles using the following equation:

qd =

Q FC0tS w

(1)

In the above equation, QF is the feed molar flow rate, C0 is the concentration of the adsorbate in the feed stream, w is the weight of the adsorbent materials loaded in the column and tS is the stoichiometric time, which can be estimated from breakthrough curves using the equation below:

tS =

∫0

∞⎛

C ⎞ ⎜1 − A ⎟∂t C0 ⎠ ⎝

(2)

where CA is the adsorbate concentration at the column outlet. 12104

dx.doi.org/10.1021/ie502024z | Ind. Eng. Chem. Res. 2014, 53, 12103−12110


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3.2. Packed Bed Multicomponent Adsorption Measurements. 3.2.1. SO2/CO2 Coadsorption. In our previous paper,1 we measured and compared the CO2 capacity of aminosilica materials before and after exposure to SO2 with various concentrations (i.e., 20, 100 and 200 ppm) at different temperatures (i.e., 35, 55 and 75 °C). In this investigation, the adsorbent materials were exposed to CO2 and SO2 simultaneously to assess the synergetic effects in coadsorption of SO2 and CO2. Figure 2a shows the CO2 and SO2 breakthrough profiles for the PD-MAPS_2 material when exposed to a gas mixture containing 200 ppm of SO2 and 10% CO2 at 35 °C. As can be observed, the CO2 breaks through the bed very quickly, whereas it takes much longer for SO2 to break through, mainly due to the low concentration of SO2 relative to that of CO2. The corresponding breakthrough times for CO2 and SO2 are 2 and 90 min, respectively. Figure 2b displays the SO 2 concentration curves for aminosilica adsorbents with similar amine loadings. Furthermore, the working capacities, calculated from eq 1, and breakthrough times corresponding to each material are listed in Table S1 (Supporting Information). In agreement with the single-component adsorption experiments,1 PD-MAPS_2, containing secondary amine moieties, exhibits the highest SO2 adsorption capacity, characterized by the longest breakthrough time, whereas PD-DMAPS_2 shows the fastest SO2 breakthrough, indicating that this adsorbent has the lowest adsorption capacity compared to other materials. To investigate the impact of the presence of SO2 on CO2 adsorption capacities, two approaches were employed. In the first approach, the coadsorption experiments were carried out until the CO2 appeared in the bed outlet gas stream and the runs were stopped right after the bed was saturated with CO2, akin to a real adsorption cycle; whereas in the second approach, the adsorption runs were continued until the bed was saturated with SO2. Analyzing the experimental results shown in Figure 3a−c, it can be inferred that for all materials, the CO2 capacity decreased significantly after five cycles when the bed was allowed to become saturated with SO2 during each cycle, whereas capacities remained almost unchanged (only slightly decreased) when the SO2 saturation did not occur in the bed during each cycle. Thus, the deactivation by SO2 can be suppressed by using short adsorption−desorption cycles during CO2 capture. The trend of the breakthrough curves in Figure 2

3. RESULTS AND DISCUSSION 3.1. Physical Properties of Materials. The physical characteristics of the bare silica support and amine-functionalized silica adsorbent pellets used in this study are summarized in Table 2 along with the amine loading of the materials, as Table 2. Physical Properties of Amine-Functionalized Silica Adsorbent Pellets material silica-bare silica with PEI, low loading silica with APS, medium loading silica with MAPS, high loading silica with DMAPS, high loading

amine loading (mmolN/g)

SBET (m2/g)

Vpore (cm3/g)

average pore size (nm)

PD PD−PEI_2

1.9

294 213

1.04 0.54

10 7

PD-APS_2

1.8

188

0.37

9

PD-MAPS_2

2.0

138

0.35

7

PD-DMAPS_2

1.8

163

0.33

6

abbreviation

determined by combustion in a TGA. To make direct comparisons between adsorption characteristics of the samples, materials were synthesized with similar amine loadings. As can be seen in the table, incorporating amines into the pores of the silica supports reduces the surface areas as well pore volumes and diameters, as expected. The amine loadings of the assynthesized materials are also listed in Table 2. It should also be noted here that upon pelletizing the powder samples, porosity decreased and therefore the pellets exhibited less porosity than the virgin powders. This was most likely a result of pore collapse that occurred under pressure. As a result, all pellet samples showed decreased CO2 uptake as compared to their powder counterparts. Comparing the data in Table 2 and those published in our previous paper1 confirms the drop in porosity. For example, the surface area and pore volume dropped from 150 m2/g and 0.5 cm3/g to 138 m2/g and 0.35 cm3/g, respectively, in the case of the PD-MAPS_2 material. Although this change is a minor one, it is consistent across all samples and is significant enough to warrant noting.

Figure 2. (a) Coadsorption breakthrough profiles for CO2 and SO2 on PD-MAPS_2 at 75 °C and (b) SO2 breakthrough profiles during coadsorption experiments on PEI, APS, MAPS and DMAPS adsorbents at 35 °C after exposure to 200 ppm of SO2/10% CO2. 12105



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Figure 3. CO2 working capacity with and without SO2 breakthrough on (a) PEI, (b) APS and (c) MAPS adsorbents after exposure to 200 ppm of SO2/10% CO2 at 35 °C.

Figure 4. SO2 concentration profiles (a) at different temperatures and (b) SO2 feed concentrations.

and the analysis of the adsorption capacities in Figure 3 show that the cyclic adsorption capacity decreases on passing from the first to the second adsorption cycle, whereas it remains almost constant throughout successive adsorption−desorption cycles. This sharp capacity loss can be attributed to the strong

and irreversible binding of SO2 on some amine sites and as a result, only a small fraction of adsorbed SO2 is desorbed while regenerating the adsorbent and therefore SO2 has a negative effect on CO2 adsorption. The plateau capacity after successive cycles might be explained by considering the weak interaction 12106



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ppm of NO and 10% CO2 at 35 °C, and the corresponding NO and CO2 concentration profiles over PD-MAPS_2 are displayed in Figure 5. On the basis of our single-component

between CO2 and the remaining surface amine sites after degradation. Chuang and co-workers28 explained this plateau capacity as being associated with isolated amine sites that arise after a majority of surface amine sites irreversibly bind SO2. It was suggested that these isolated amine sites are thermally reversible and exhibit very weak interactions with CO2. The effect may also be due to the interaction of CO2 with the free silanol groups (Si−OH) on the surface of the silica support, leading to the physisorption of CO2 via hydrogen bonding. Furthermore, capacity loss is lower in the case of PD-MAPS_2, containing secondary amine moieties, relative to the other adsorbents, suggesting that this material is more stable upon exposure to SO2 than primary and tertiary containing amine adsorbents. It should be pointed out that because all measurements were carried out under dry conditions and tertiary amines do not appreciably chemisorb CO2 under dry conditions, a similar analysis was not performed for the PDDMAPS_2 sample. These results clearly indicate that supported amine adsorbents are reasonably stable to flue gas impurities during cyclic adsorption operation, even at high SO2 concentrations, especially in fast cycles. It should also be noted that actual concentration of SO2 in flue gas streams after sulfur treatment is much lower than the concentration considered in this study (i.e., ∼2 ppm versus 200 ppm), suggesting that rapid cycling with low SO2 concentrations will allow for long-term, stable cycling. Next, we evaluated the effect of temperature and SO2 concentration on the dynamic adsorption profiles of the aminosilica adsorbents. Figure 4a shows the breakthrough profiles at 35, 55 and 75 °C for PD-MAPS_2 when exposed to 200 ppm of SO2/10% CO2. It is clear that performing coadsorption experiments at higher temperatures results in an earlier SO2 breakthrough time and a drop in the SO2 adsorption capacity. As shown in our previous paper, the single-component adsorption runs showed a decrease in equilibrium capacities with temperature, as expected for class 2 materials, due to the exothermic nature of adsorption. Depending on the source of fuel, the concentration of SO2 in flue gas varies to some extent and therefore, it is worth investigating its influence on adsorption capacity of aminebased materials. A comparison between SO2 breakthrough adsorption curves corresponding to 20 and 200 ppm feed gas concentrations at 35 °C over the PD-MAPS_2 is depicted in Figure 4b. As can be derived from the data shown, the decrease in SO2 concentration leads to a displacement of the SO2 breakthrough curve to longer adsorption times and also results in a reduction of the capacity of the adsorbent from about 1.6 to almost 0.6 mmol SO2/g in the simultaneous presence of SO2 and CO2. Correspondingly, adsorption breakthrough times are dramatically lengthened from about 5 to 18 h when concentration increases from 20 to 200 ppm. Assuming that SO2 diffusion in the adsorbent bed remains the same, this decrease in breakthrough time with concentration is expected, which could be attributed to the increase in SO2 capacity with concentration, as mentioned above. 3.3.2. NO/CO2 Coadsorption. For the solid CO2 adsorbent materials to be stable under real flue gas conditions, it is not only important to evaluate their stability in the presence of SO2 but also to NOx, as flue gas contains NOx impurities as well. We therefore performed NO/CO2 coadsorption experiments in a similar way as the SO2/CO2 runs, namely, the aminosilica adsorbents were exposed to a mixture of gas containing 200

Figure 5. Coadsorption breakthrough profiles for CO2 and NO on PD-MAPS_2 after exposure to 200 ppm of NO/10% CO2 at 35 °C.

adsorption measurements, NO is not expected to adversely affect CO2 capture by competitive adsorption on the aminebased adsorbents. Comparing the breakthrough curves in Figure 5, it follows that NO breaks through the bed almost immediately, indicating very little affinity of the amines toward NO and very trivial capacity. As a result, the CO2 capacity was not influenced when NO was present in the gas mixture. The same trend was observed for other materials (i.e., PEI, APS and DMAPS; breakthrough data not shown). Table S2 (Supporting Information) summarizes the dynamic CO2 and NO coadsorption characteristics obtained from breakthrough profiles for amine-functionalized materials with similar amine loadings. Our data show that for all materials, the CO2 capacity can be retained in the presence of NO. For a more realistic analysis of the effect of NO on CO2 adsorption performance of the aminosilica adsorbents, consecutive adsorption/desorption cycle experiments were performed and the corresponding CO2 working capacities before and after NO/CO2 exposure are displayed in Figure 6. As evident from this figure, no significant capacity loss was

Figure 6. CO2 working capacity of amine-functionalized materials before and after exposure to 200 ppm of NO/10% CO2 at 35 °C. 12107



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observed, indicating that the presence of NO did not influence the CO2 capacity of the adsorbents, in close agreement with previous findings.1,19 These results clearly suggest that there is no negative synergy in the coadsorption of NO and CO2. 3.2.3. NO2/CO2 Coadsorption. Aminosilica adsorbents are reported to have some preferred affinity toward NO2.1,8,19,20,22 In our earlier investigation, we used a 200 ppm of NO2 gas concentration for single-adsorption experiments and investigated the impact of this concentration on the adsorbent’s CO2 adsorption capacity. This concentration is, however, far higher than the actual concentration of NO2 in flue gas streams coming from NOx removal units. Therefore, to have a more realistic analysis, we used a feed gas stream with 20 ppm of NO2/10% CO2 composition for coadsorption experiments. As can be observed from the data in Figure 7, for the PD-MAPS_2

has a less detrimental impact on the CO2 adsorption capacity under these conditions. However, in our previous study1 that used 200 ppm exposure levels, NO2 led to a more significant capacity loss than SO2. Thus, the relative importance of each gas in impacting CO2 capacities will depend on the exposure level, though both gases should be viewed as harmful to amine sites. To further address the long-term stability of the aminosilica adsorbents for CO2 capture, cyclic adsorption/desorption experiments were carried out at 35 °C. Figure 8 illustrates

Figure 8. CO2 working capacity of amine-functionalized materials before and after exposure to 20 ppm of NO2/10% CO2 at 35 °C.

the CO2 working capacities of PD-MAPS_2 before and after NO2/CO2 exposure for five consecutive cycles. According to this figure, the presence of a low concentration of NO2 does not impact the stability of the adsorbents significantly, and the CO2 capacity only slightly dropped after a few cycles. In our previous paper,1 we showed that NO2 could have a significant negative impact on the stability of aminosilica adsorbents when it is present at very high concentrations, whereas, as these results indicate, the materials retain their CO2 capacities in the presence of lower levels of NO2. 3.2.4. SO2/NO/CO2 Multiadsorption. Finally, to investigate any synergetic effect during the simultaneous adsorption of SOx and NO, a simulated flue gas stream with 200 ppm of SO2/200 ppm of NO/10% CO2 (balance nitrogen) was used for adsorption experiments. Figure 9 shows the comparison of the CO2, SO2 and NO breakthrough profiles for the PD-MAPS_2 adsorbent. Comparing the concentration profiles in this figure, it can be observed that NO and CO2 quickly breakthrough the fixed bed while SO2 is trapped in the bed. NO exhibits the fastest breakthrough, which can be attributed to its minimal dynamic adsorption capacity. The cyclic adsorption capacities obtained from the multiadsorption fixed bed runs suggest that the CO2 adsorption is influenced primarily by SO2 coadsorption and the CO2 capacity loss was dictated by SO2 and not NO, as would be inferred from the dual component adsorption experiments. Additionally, the presence of NO changes neither the CO2 nor SO2 adsorption characteristics, suggesting no synergistic interactions of NO and SO2.

Figure 7. Coadsorption breakthrough profiles for CO2 and NO2 on PD-MAPS_2 after exposure to 20 ppm of NO2/10% CO2 at 35 °C.

adsorbent, the NO2 breakthrough occurs at the same time as the CO2 breakthrough and the material exhibits a working capacity of 0.30 mmol NO2/g (at 20 ppm of NO2 in 10% CO2 at 35 °C). It should be noted that the other materials show similar behavior, also exhibiting nearly the same breakthrough time for CO2 and NO2. The high affinity of the adsorbent toward very low concentrations of NO2 can be attributed to the higher polarity and adsorption strength of NO2 than NO and CO2, and as a result, this gas will have a more adverse effect on CO2 adsorption than NO. It will also have a more adverse effect than SO2 on CO2 adsorption when its concentration is comparable to SO2, as our previous results demonstrated.1 The corresponding CO2 working capacities for each material were estimated from breakthrough curves and the results are listed in Table S3 (Supporting Information) along with the breakthrough times for both NO2 and CO2. From these data, it can be observed that for all amine-based adsorbents, the NO2 capacities are relatively high compared to those for NO under the experimental conditions studied here, even though its concentration was lower than that of NO in the breakthrough experiments. This is consistent with our past work focusing on single component measurements.1 Of the two gases that are more harmful to the CO2 capacity, NO2 and SO2, it is noteworthy that their relative impact on CO2 capacity depends on the exposure level. At identical 20 ppm feed concentrations, which might be in the range expected after flue gas desulfurization and NOx removal treatments, the NO2 working capacity is lower than the SO2 working capacity, and thus NO2

4. CONCLUSIONS Multicomponent adsorption experiments were carried out to investigate the impact of SOx/NOx impurities on the CO2 12108



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(2) Deng, H.; Yi, H.; Tang, X.; Liu, H.; Zhou, X. Interactive Effect for Simultaneous Removal of SO2, NO, and CO2 in Flue Gas on Ion Exchanged Zeolites. Ind. Eng. Chem. Res. 2013, 52, 6778−6784. (3) Zhou, X.; Yi, H.; Tang, X.; Deng, H.; Liu, H. Thermodynamics for the Adsorption of SO2, NO and CO2 from Flue Gas on Activated Carbon Fiber. Chem. Eng. J. 2012, 200−202, 399−404. (4) Khatri, R. A.; Chuang, S. S. C.; Soong, Y.; Gray, M. Thermal and Chemical Stability of Regenerable Solid Amine Sorbent for CO2 Capture. Energy Fuels 2006, 20, 1514−1520. (5) Ridha, F. N.; Manovic, V.; Macchi, A.; Anthony, E. J. The Effect of SO2 on CO2 Capture by CaO-Based Pellets Prepared with a Kaolin Derived Al(OH)3 Binder. Appl. Energy 2012, 92, 415−420. (6) Lu, H.; Smirniotis, P. G. Calcium Oxide Doped Sorbents for CO2 Uptake in the Presence of SO2 at High Temperatures. Ind. Eng. Chem. Res. 2009, 48, 5454−5459. (7) Levasseur, B.; Ebrahim, A. M.; Bandosz, T. J. Interactions of NO2 with Amine-Functionalized SBA-15: Effects of Synthesis Route. Langmuir 2012, 28, 5703−5714. (8) Xu, X.; Song, C.; Miller, B. G.; Scaroni, A. W. Adsorption Separation of Carbon Dioxide from Flue Gas of Natural Gas-Fired Boiler by a Novel Nanoporous “Molecular Basket” Adsorbent. Fuel Process. Technol. 2005, 86, 1457−1472. (9) Zhang, J.; Xiao, P.; Li, G.; Webley, P. A. Effect of Flue Gas Impurities on CO2 Capture Performance from Flue Gas at Coal-Fired Power Stations by Vacuum Swing Adsorption. Energy Procedia 2009, 1, 1115−1122. (10) Adeyemo, A.; Kumar, R.; Linga, P.; Ripmeester, J.; Englezos, P. Capture of Carbon Dioxide from Flue or Fuel Gas Mixtures by Clathrate Crystallization in a Silica Gel Column. Int. J. Greenhouse Gas Control 2010, 4, 478−485. (11) Beeskow-Strauch, B.; Schicks, J. M.; Spangenberg, E.; Erzinger, J. The Influence of SO2 and NO2 Impurities on CO2 Gas Hydrate Formation and Stability. Chemistry 2011, 17, 4376−4384. (12) Daraboina, N.; Ripmeester, J.; Englezos, P. The Impact of SO2 on Post Combustion Carbon Dioxide Capture in Bed of Silica sand through Hydrate Formation. Int. J. Greenhouse Gas Control 2013, 15, 97−103. (13) Yi, H.; Deng, H.; Tang, X.; Yu, Q.; Zhou, X.; Liu, H. Adsorption Equilibrium and Kinetics for SO2, NO, CO2 on Zeolites FAU and LTA. J. Hazard. Mater. 2012, 203−204, 111−117. (14) Reddy, M. K. R.; Xu, Z. P.; Lu, G. Q. M.; Costa, J. C. D. Effect of SOx Adsorption on Layered Double Hydroxides for CO2 Capture. Ind. Eng. Chem. Res. 2008, 47, 7357−7360. (15) Czyżewski, A.; Kapica, J.; Moszyński, D.; Pietrzak, R.; Przepiórski, J. On Competitive Uptake of SO2 and CO2 from Air by Porous Carbon Containing CaO and MgO. Chem. Eng. J. 2013, 226, 348−356. (16) Li, Y.; Buchi, S.; Grace, J. R.; Lim, C. J. SO2 Removal and CO2 Capture by Limestone Resulting from Calcination/Sulfation/Carbonation Cycles. Energy Fuels 2005, 19, 1927−1934. (17) Arias, B.; Cordero, J. M.; Alonso, M.; Diego, M. E.; Abanades, J. C. Investigation of SO2 Capture in a Circulating Fluidized Bed Carbonator of a Ca Looping Cycle. Ind. Eng. Chem. Res. 2013, 52, 2700−2706. (18) Manovic, V.; Anthony, E. J. Sequential SO2/CO2 Capture Enhanced by Steam Reactivation of a CaO-Based Sorbent. Fuel 2008, 87, 1564−1573. (19) Diaf, A.; Garcia, J. L.; Beckman, E. J. Thermally Reversible Polymeric Sorbents for Acid Gases: CO2, SO2, and NOx. J. Appl. Polym. Sci. 1994, 53, 857−875. (20) Diaf, A.; Beckman, E. J. Thermally Reversible Polymeric Sorbents for Acid Gases, IV. Affinity Tuning for the Selective Dry Sorption of NOx. React. polym. 1995, 25, 89−96. (21) Belmabkhout, Y.; Sayari, A. Isothermal versus Non-isothermal Adsorption-Desorption Cycling of Triamine-Grafted Pore-Expanded MCM-41 Mesoporous Silica for CO2 Capture from Flue Gas. Energy Fuels 2010, 24, 5273−5280. (22) Liu, Y.; Ye, Q.; Shen, M.; Shi, J.; Chen, J.; Pan, H.; Shi, Y. Carbon Dioxide Capture by Functionalized Solid Amine Sorbents with

Figure 9. Multiadsorption breakthrough profiles for CO2, SO2 and NO2 on PD-MAPS_2 after exposure to 200 ppm of SO2/200 ppm of NO/10% CO2 at 35 °C.

adsorption capacity of an array of aminosilica adsorbents. The coadsorption breakthrough profiles of SO2, NO and NO2 were evaluated in conjunction with CO2 concentration profiles. On the basis of our experimental results, it was found that the presence of NOx impurities at low concentrations do not significantly influence the CO2 adsorption capacity of aminosilica materials, with NO having no significant impact even at high concentrations of 200 ppm and NO2 having a minimal impact at more typical concentrations of 20 ppm. In addition, although high concentrations of SO2 in the simulated flue gas stream would result in CO2 capacity loss over many cycles, the adsorbents retained their CO2 capacities over many cycles when exposed to a low-concentration SO2 gas stream, suggesting that amine-based solid adsorbents are reasonably stable under dry flue gas conditions with realistic concentrations of impurity gases.

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ASSOCIATED CONTENT

S Supporting Information *

Tables S1−S3 show, respectively, SO2/CO2, NO/CO2 and NO2/CO2 coadsorption characteristics over aminosilica adsorbents at 35 °C using 200 ppm of SO2 or 200 ppm of NO or 20 ppm of NO2/10% CO2. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*C. W. Jones. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by DOE-NETL through grant number DE-FE0007804. However, any opinions, findings, conclusions or recommendations expressed herein are those of the author(s) and do not necessarily reflect the views of the DOE.

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REFERENCES

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