Synthesis, characterization and evaluation of activated spherical carbon materials for CO2 capture

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Synthesis, characterization and evaluation of activated spherical carbon materials for CO2 capture

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Nannan Sun a,b, Chenggong Sun a,⇑, Hao Liu a,⇑, Jingjing Liu a, Lee Stevens a, Trevor Drage a, Colin E. Snape a, Kaixi Li c, Wei Wei b, Yuhan Sun d a

Energy and Sustainability Division, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, PR China Key Laboratory of Carbon Materials, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, PR China d Low Carbon Conversion Center, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, PR China b c

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h i g h l i g h t s

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 Spherical activated carbons with uniform diameters were prepared for CO2 capture.

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 Different methodologies were examined to enhance the surface affinity towards CO2.

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 The carbons showed high CO2 uptakes and favourable kinetics at elevated pressures.

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 A structure-performance relationship of the spherical carbons was established.

 The spherical carbons exhibited excellent promise as pre-combustion CO2 adsorbents.

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a r t i c l e 2 3 6 8 27 28 29 30 31

i n f o

Article history: Received 11 October 2012 Received in revised form 15 March 2013 Accepted 19 March 2013 Available online xxxx

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Keywords: Activated carbon Spherical carbon beads CO2 capture Adsorption

a b s t r a c t Activated carbon (AC) beads with desirable spherical forms were prepared from phenolic resins using a novel hydrothermal process coupled with a range of post-preparation treatments, and different strategies were employed to dope N-containing functionalities into the AC beads. Texture properties of the samples were characterized by N2 physisorption and scanning electron microscope (SEM), and the CO2 adsorption behavior was evaluated at both ambient and elevated pressures by using either thermal gravimetric or high pressure volumetric analysis method. By relate the CO2 uptakes of different samples with their texture properties and surface affinity, a structure-performance relationship was established. It was found that AC beads are a suitable option for realistic CO2 capture, especially in pre-combustion capture where CO2 partial pressure is relatively higher. Ó 2013 Elsevier Ltd. All rights reserved.

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1. Introduction Increased public awareness of global climate change has led to major concerns over the ever growing increase in climate-forcing CO2 emissions of which the largest single source arise from fossil fuel fired electric power generation [1,2]. Carbon capture and storage (CCS), coupled with other effective measures for improved energy efficiency, has widely been regarded as being a strategy in combating climate change by mitigating carbon emissions from fossil energy utilization without compromising energy security [3–5]. However, the state-of-the-art amine scrubbing technology for carbon capture from fossil fuel fired power plants incurs substantial energy penalty which can reach up to 37% in the case

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⇑ Corresponding authors. Tel.: +44 115 8468661; fax: +44 115 9514115. E-mail addresses: [email protected] (C. Sun), liu.hao@nottin gham.ac.uk (H. Liu).

of coal-fired power plants [6–10]. Consequently, alternative cost-effective capture technologies have to be developed. Solid adsorbents looping technology is widely recognized as having the potential to be a viable next generation capture technology compared to the aqueous amine scrubbing process, offering potentially significantly improved capture efficiency at reduced energy penalty, lower capital and operational costs and smaller plant footprints. However, the success of the low temperature solids looping technology is largely determined by the successful development of superior adsorbents materials. Among various materials currently under development, zeolites, activated carbon materials (AC), supported amines, metal oxides, metal carbonates, metal–organic frameworks (MOFs) are the most studied solid adsorbents for CO2 capture [11–27], and each type has their featured pros and cons, e.g. zeolites usually have high CO2 uptake but suffer from a performance decay under humid flue gas environment while supported amines are susceptible to thermal and oxi-

0016-2361/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.fuel.2013.03.047

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Table 1 Synthesis and nomination of the AC samples.

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Entry

Sample

Precursors

1 2 3 4 5 6 7 8 9

PFs PFs-Ox PFs-Ami PFs-Ox-Ami PFs-10Mel PFs-Y PFs-MMA-Y PFs-Ce PFs-MMA-Ce

Phenolic Phenolic Phenolic Phenolic Phenolic Phenolic Phenolic Phenolic Phenolic

resin resin resin resin resin + 10 wt.% Melamine resin + Y(NO3)3 resin + Methyl methacrylate + Y(NO3)3 resin + Ce(NO3)3 resin + Methyl methacrylate + Ce(NO3)3

dative degradation despite their superior CO2 adsorption capacity and selectivity [7]. Activated carbon materials have long been used as sorbents in a wide range of industrial applications, and its highly developed porosities, wide availability and low cost relative to other solid adsorbents (e.g. Zeolite 13X) make them the candidate adsorbent materials for both post-combustion and in particular, pre-combustion CO2 capture. CO2 adsorption performance of activated carbons is determined by their pore structures and surface chemistry properties [7,14]. Sjostrom and Krutka compared the working capacities and cyclic stabilities of different types of solid sorbents (aminebased, zeolites and ACs) capturing CO2 from a lignite coal-fired electric generating unit, and they concluded that ACs can be the viable adsorbents for realistic CO2 capture especially if their CO2 uptake can be further improved [28]. Indeed, developing novel functionalized carbon-based adsorbents for CO2 capture has become the focuses of many recent investigations [29–31]. Xia et al. [31] prepared a series of nitrogen-doped ACs via a zeolite templating method, which showed extremely high CO2 uptakes of up to 6.9 mmol/g (30.36 wt.%) at 0 °C and ambient pressure. ACs can be produced from a variety of widely available precursor materials, such as coal, wood and many other manufactured polymeric materials (e.g. phenolic resins). One superior advantage of using synthetic polymers is that the chemical composition, morphology and pore structures of the resulting carbon materials can be better controlled relative to the use of other feedstock (e.g. coal) [32]. For instance, investigations conducted by Lu’s group demonstrated the feasibility of using polymers to produce monolith AC adsorbents, and one of the prepared nitrogen-enriched carbon monolith shows a CO2 adsorption capacity as high as 3.13 mmol/ g (13.77 wt.%) at 25 °C and ambient pressure [33,34]. However, most of these carbon-based adsorbent materials are produced by using costly sophisticated processes, which may prove difficult and uneconomic to scale up. Further, they are often produced in fine powder forms, which are not ideal for use in solid looping processes where fluidized and/or moving bed reactors are most likely involved. In this study the feasibility of using a novel commercialized hydrothermal process to produce functioning spherical AC adsorbent materials for carbon capture has been investigated, and a number of AC adsorbents with different textural and chemical properties have been evaluated in terms of their CO2 adsorption performances at both ambient and elevated pressures. These AC adsorbents possess desirable spherical shape, high mechanical strength and low dusting properties, which are the ideal characteristics for fluidized bed looping applications.

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2. Experimental

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2.1. Preparation of spherical carbon adsorbents (AC beads)

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All the AC beads were produced from phenolic resins based on a novel hydrothermal process. Typically, novolac-type phenolic

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Post-treatment Mild oxidation before carbonization

Activation atmosphere

No Yes No Yes Yes No No No No

Steam Steam Steam + NH3 Steam + NH3 Steam Steam Steam Steam Steam

resins and hexamethylenetetramine were first dissolved in methanol, the resulted solution was mixed with an aqueous solution of polyvinyl alcohol (PVA) and sealed in an autoclave. The mixture was then heated to 130 °C at a rate of 5 °C/min with rigorous stirring (400 RPM) and kept at this temperature for 1 h, after which the reactor was cooled down and the formed resin beads were recovered and washed adequately with distilled water and dried at 110 °C for 24 h. The resin beads were then carbonized and activated by selectively using different methodologies as follows: (i) Mild oxidation at 300 °C in air for 2 h, (ii) carbonization at 830 °C in N2 for 1 h, (iii) activation at 830 °C in steam for 1 h, and (iv) activation at 830 °C in NH3-containing steam for 1 h. Details of the procedures and nomination of samples are listed in Table 1, entry 1–4. A sample with addition of 10 wt.% (based on the raw novolac-type phenolic resin) of melamine to the raw phenolic resin were prepared to investigate an alternative way of involving nitrogen (Table 1, entry 5). The obtained products based on the above procedures are AC beads with good spherical form and a diameter of up to 1.5 mm. For comparison purpose, phenolic resin-based mesoporous ACs in the form of powders prepared by a Ce or Y catalytic procedure were also incorporated in the present paper (Table 1, entry 6–9). The synthesis of these samples was detailed in a previous paper [35].

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2.2. Characterization of the AC beads

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Textural properties of the AC beads were studied by N2 physisorption on an ASAP 2420 instrument with N2 at 196 °C. Prior to the test, samples were degased at 120 °C for 5 h. The apparent surface area (SBET) was calculated according to the method suggested by Parra et al. [36]. The cumulative pore volumes (Vtotal) were calculated from the amount of nitrogen adsorbed at P/P0 of ca. 0.99, and the average pore volume was calculated as 4Vtotal/SBET. The micropore volume and surface area were determined by the tplot method. The morphology of the AC beads was studied by use of a QUANTA 600 scanning electron microscope (SEM) instrument at 25 kV.

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2.3. CO2 uptake measurement

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The CO2 capture behaviors of the AC beads were measured by a TA Q500 thermal gravimetric analyzer (TGA) under ambient pressure as follows: 20–30 mg of the AC beads was loaded in a platinum pan, heated to 115 °C and held at this temperature in flowing N2 (100 mL/min) for 10 min to remove physisorbed moisture and CO2, the temperature was then decreased (10 °C/min) and equilibrated at 30 °C. Adsorption was started by switching the gas to pure CO2 or 15 vol.% CO2 in N2 (100 mL/min), and the temperature was maintained at 30 °C for 30 min, after which the sample was heated to 115 °C with a ramp of 0.5 °C/min under the same

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N. Sun et al. / Fuel xxx (2013) xxx–xxx Table 2 Texture properties of the samples.

*

Sample

SBET (m2/g)

Vtotal (cm3/g)

Average pore width (nm)

Smicro (m2/g)

Vmicro (cm3/g)

Micro% (%)*

PFs PFs-Ox PFs-Ami PFs-Ox-Ami PFs-10Mel PFs-Y PFs-MMA-Y PFs-Ce PFs-MMA-Ce

909 1280 961 978 672 840 472 388 333

0.39 0.91 0.55 0.41 0.30 0.91 0.35 0.45 0.32

1.72 2.84 2.29 1.68 1.79 4.33 2.97 4.64 3.84

871 1075 841 924 628 291 325 100 178

0.35 0.43 0.33 0.37 0.25 0.19 0.18 0.07 0.11

89.7 47.3 60.0 90.2 83.3 20.9 51.4 15. 6 34.4

Micro% = Vmicro/Vpore  100%.

Fig. 1. SEM of the AC beads: (a) A PFs-Ox bead, (b) a PFs-Ami bead, (c) surface of PFs-10Mel, (d) inner structure of a broken PFs-Ox-Ami bead, the insert shows the entire bead and selected area, (e) cross section of a PFs-10Mel bead, and (f) details of the inner framework of a PFs-10Mel bead.

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atmosphere during adsorption, such a slow ramp allows the adsorption to change with temperature in a quasi-equilibration way in order to obtain the equilibrated CO2 uptake at different

temperatures. The reversibility of the adsorption/desorption of CO2 was previously checked to make sure the as-obtained data is valid.

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High pressure CO2 adsorption tests were carried out by using a Particulate Systems High Pressure Volumetric Analyzer (HPVA100). With each of these tests, about 0.5 g sample was loaded and sealed into a 2 mL stainless steel sample cell. The sample cell was firstly evacuated at 120 °C overnight to remove the physisorbed moisture and CO2, then it was transferred to the analysis port of the instrument, and the high pressure adsorption was performed at 45 °C from ambient pressure up to 40 bar (100 vol.% CO2).

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3. Results and discussion

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3.1. Characterization of the AC samples

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N2 physical adsorption/desorption was carried out to study the texture properties of the samples, the results are summarized in Table 2. Sample PFs obtained by carbonization and steam activation of the resin beads, which was regarded as a benchmark in the present study, possesses a BET surface area of 909 m2/g, which is situated within the range of reported values for phenolic resinbased AC powder [18,19,32]. By use of mild oxidation of the resin beads at 300 °C before carbonization, namely sample PFs-Ox, the surface area was increased to 1280 m2/g (44.8% increasing). This effect can be explained by the formation of a dense layer on the surface of the resin beads during their ‘‘spherization’’ in the hydrothermal process, which hindered the carbonization of inner core and thus the development of the porous structure. The mild oxidation induced cracks and/or pores on the surface as can be seen in Fig. 1a due to shrinkage of the resin framework at elevated temperature. These surface defects facilitated the diffusion of activation agents deep into the resin beads, enhanced the activation, and therefore a well-developed pore system was observed in sample PFs-Ox. As for the sample PFs-Ami, which was activated in NH3containing steam, the surface area and pore volume were higher than those of PFs, indicating a higher degree of activation by free radicals such as NH2, NH, atomic H and N from the thermal decomposition of NH3 [14]. In contrast, when the ammonia activation was performed to the mild oxidized resin beads, the surface area and pore volume decreased from 1280 m2/g and 0.91 cm3/g for PFs-Ox to 978 m2/g and 0.41 cm3/g for PFs-Ox-Ami, respectively. This is mainly due to the over-activation of the preoxidized resin beads, suggesting again that mild oxidation plays an important role in enhancing the activation of resin beads. The melamine modified sample (PFs-10Mel) was found to have smaller surface area and pore volume than the benchmark sample (PFs). Based on the calculated micropore percentage listed in Table 2 as well as the N2 isotherms (Fig. 2), it can be concluded that the prepared AC beads, namely samples of PFs, PFs-Ami, PFs-Ox, PFsOx-Ami and PFs-10Mel are mainly microporous materials with a minor mesoporous feature. However, all the catalytic-derived powder samples were mesoporous with much lower surface areas and micropore percentages than the AC bead samples (Table 2), in accordance with the findings of the previous study [35]. Fig. 1 shows some selected SEM images of the AC beads, noting that all the samples exhibited similar morphologies. Large amounts of cracks and pores were formed on the surfaces of the AC beads (Fig. 1a–c). Fig. 1d shows an image of a broken bead, a hierarchical inter-connected porous framework inside the AC beads is observed, which is further verified by the images of the cross-section showed in Fig. 1e–f. The large pores promote a better diffusion of CO2 throughout the AC beads, resulting in fast adsorption/desorption kinetics, which is of great importance for large scale CO2 capture process [29].

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3.2. CO2 uptakes at ambient pressure

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CO2 adsorption capacities of the AC samples at ambient pressure were evaluated by a thermal gravimetric method under

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100 vol.% CO2 and 15 vol.% (N2 balance) with the CO2 uptakes being calculated by the measured sample weight changes. The results are tabulated in Table 3, and a comparison of the CO2 uptakes of different samples in pure CO2 stream at 30 °C and 75 °C is shown in Fig. 3. As can be expected from thermodynamics, the adsorption capacity diminishes with the increase of temperature and the decrease of CO2 partial pressure. The benchmark sample PFs showed a CO2 uptake of 8.07 wt.% in a pure CO2 stream at 30 °C and atmospheric pressure. By adding a mild oxidation procedure before carbonization, the CO2 uptake increased to 9.31 wt.% due to the better texture properties of PFs-Ox (Table 2). Furthermore, the CO2 uptake of PFs can be improved by nitrogen doping: as can be seen from Table 2, all the nitrogen doped samples possess higher CO2 uptakes compared to PFs, especially for the NH3 activated samples, with the highest uptake of 10.33 wt.% obtained with PFs-Ox-Ami at 30 °C. Generally speaking, the catalytic-derived samples showed lower CO2 capacities due to their low micropore volumes because only the pores with width of lower than 1.0 nm are effective for the adsorption of CO2 under ambient pressures [37]. This can be further proved if one compares the MMA-involved samples with the MMA-free counterparts. Both of the two MMA-involved samples showed higher CO2 uptakes as well as micropore volumes in spite of lower surface areas and total pore volumes (Table 2). Fig. 4 shows the correlations of the CO2 uptakes (30 °C, pure CO2) with several texture factors. The adsorption capacities can be largely related to the microporous relative parameters but not the total pore volume. They decrease with the increasing of average pore width, indicating again the importance of micropores for adsorption of CO2. Surface chemistry is another important factor for adsorption investigated in the present study. As can be seen from Fig. 3 and Table 3, sample PFs-10Mel showed the lowest CO2 uptake at 30 °C in a pure CO2 stream among all the N-doped samples. However, with the increasing of temperature, the difference becomes very small. Taking the substantially lower surface area (Table 2) of PFs-10Mel into account, it can be concluded that the surface affinity was enhanced by nitrogen involving, particularly for PFs10Mel. Furthermore, the surface affinity towards CO2 can be compared more clearly from the CO2 uptakes at 15 vol.% CO2 as the contribution of surface chemistry becomes more important at lower CO2 partial pressures. In this case, the adsorption capacity of PFs-10Mel outperformed the other N-doped samples (Table 3). It is interesting to note that sample PFs-MMA-Y exhibited a high CO2 capacities at 75 °C in 15 vol.% CO2/N2 although its micropore volume is lower than the N-doped AC beads. This indicates a strong CO2 affinity for this sample. We believe that MMA involving could change the surface electrostatic field due to the induction of polar O-containing functionalities, and thus enhance the CO2 affinity via the interaction with the quadrupole of CO2 molecular [38,39]. Unfortunately, it is very difficult and challenging to synthesis these MMA-involved samples in spherical forms and larger surface areas, but the related work is currently ongoing. To have a quantitative comparison of the surface CO2 affinity of the different samples, their CO2 uptakes at 75 °C in 15 vol.% CO2 were normalized by their surface area as shown in Fig. 5. Medium CO2 affinity was observed for the benchmark sample PFs and a decreasing of affinity was registered for the mild oxidized sample PFs-Ox, probably because some surface and/or structure impurities which serve as highly energetic adsorption sites were removed during the mild oxidation procedure. N-doped samples showed a more significant surface affinity indicating an involvement of basic functionalities. For the catalytic-derived samples, both the MMAinvolved samples showed very high surface affinity due to the above mentioned possible surface electrostatic field enhancement,

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Fig. 2. N2 adsorption isotherms of the samples.

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however, these materials have lower surface areas, which limited better adsorption capacities. Apart from a high equilibrium CO2 uptake, another decisive requirement for an adsorbent that can be used in realistic CO2 capture applications such as pre- and/or post-combustion, is fast adsorption kinetics [7]. For most AC-based materials, physical adsorption takes a major part in the total adsorption capacities, and thus reasonably fast adsorption/desorption kinetics can be expected. In the present study, however, AC beads with diameters of ca. 1 ± 0.5 mm being used, it is therefore worth to take the kinetic issue into consideration to elucidate if there is a diffusion problem.

To this end, a typical TGA curve during an entire purge–adsorption–desorption experiment is shown in Fig. 6 as all the AC beads exhibited similar trends. It is clearly shown that adsorption took place immediately after the gas was switched from N2 to CO2 with the equilibrium capacity being achieved in about 10 min, indicating acceptable adsorption kinetics of our AC beads.

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3.3. CO2 adsorption at elevated pressures

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By using a high pressure volumetric analysis (HPVA) method, high pressure CO2 adsorption tests were carried out with four AC

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Fig. 2. (continued)

Table 3 CO2 uptakes at different atmosphere and temperature. Sample

CO2 uptake-15% CO2 (wt.% on dry basis)

PFs PFs-Ox PFs-Ami PFs-Ox-Ami PFs-10Mel PFs-Y PFs-MMA-Y PFs-Ce PFs-MMA-Ce

CO2 uptake-100% CO2 (wt.% on dry basis)

30 °C

45 °C

60 °C

75 °C

30 °C

45 °C

60 °C

75 °C

2.18 2.21 2.74 2.93 2.98 1.63 2.14 1.26 1.87

1.25 1.25 1.60 1.72 1.80 1.02 1.53 0.85 1.31

0.63 0.60 0.81 0.88 0.97 0.54 0.99 0.42 0.75

0.21 0.17 0.28 0.31 0.39 0.18 0.56 0.03 0.30

8.07 9.31 9.80 10.33 9.20 5.61 6.26 3.98 5.39

5.59 6.40 7.01 7.36 6.83 4.15 4.96 3.20 4.36

3.88 4.42 5.00 5.23 4.99 3.01 3.78 2.38 3.32

2.61 2.98 3.44 3.57 3.51 2.08 2.75 1.60 2.40

Fig. 3. CO2 uptake comparison under pure CO2 stream.

beads, namely PFs-Ox, PFs-Ami, PFs-Ox-Ami and PFs-10Mel at 45 °C. The obtained results are shown in Fig. 7. From the isotherms showed in Fig. 7a–d, a rapid increasing of CO2 uptake from the beginning of the experiment up to ca. 10 bar is observed, indicating the narrow pore filling by CO2. After this stage, the increasing becomes slower with the increasing of CO2 pressure. Besides, the overlap between adsorption and desorption branches of the isotherms suggests almost reversible adsorption behaviors of the samples. Fig. 7e compares the CO2 uptake at 10, 20 and 40 bar of the tested samples. Very high CO2 uptakes of ca. 20–45 wt.% at 40 bar were obtained indicating the great potential of these AC beads to be used in pre-combustion capture applications such as Integrated Gasification Combined Cycle (IGCC)based power plants where the CO2 pressure is relatively higher.

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Fig. 4. Relationships between CO2 uptake and texture properties: (a) Total pore volume, (b) micropore volume, (c) micropore surface area and (d) average pore width.

Fig. 5. Comparison of surface affinity towards CO2.

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It is worth mentioning that the sample PFs-Ox outperformed the other samples at elevated pressure in contrast to its relative lower capacity at 1 bar (Fig. 7e). This can be explained by the classical pore-filling adsorption model, in which condensation of gas molecule in pores is determined by temperature, pressure and pore width. At a given temperature (45 °C at the present study), narrow pores will be rapidly filled up at low pressure as is observed in Fig. 7a–d. With the increasing of pressure, wider pores will be filled gradually results in higher adsorption capacities. Based on this model and the observation in Fig. 7e, we can conclude that comparing with the adsorption at ambient pressure, not only microp-

Fig. 6. A typical weight change curve during TGA experiment.

ores as concluded from Fig. 4, but also the total pore system will contribute to the CO2 uptake at elevated pressures. In addition, at high pressures, physical adsorption related to texture properties rather than chemical adsorption related to surface affinity will play far more important role in determining adsorption capacity. Therefore, sample PFs-Ox with the highest total pore volume (0.91 cm3/ g) was found to be the most effective sample at higher pressures. To further verify the above conclusion, the CO2 uptakes of different samples at 40 bar were correlated with both the total pore volume

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Fig. 7. CO2 adsorption behavior at 45 °C and elevated pressures: (a) Isotherm of PFs-Ox, (b) isotherm of PFs-Ami, (c) isotherm of PFs-Ox-Ami, (d) isotherm of PFs-10Mel, (e) comparison of CO2 uptake at different pressures, and (f) relationships between high pressure CO2 uptake and total/micro pore volume.

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and the micropore volume (Fig. 7f), a better correlation between the adsorption capacities and the total pore volume was found.

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4. Conclusions

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AC beads were prepared by carbonization and activation of phenolic-based resins beads with their surface affinity to CO2 being promoted by nitrogen incorporation. The texture properties of the AC beads were characterized by N2 physisorption and scanning electron microscope (SEM), and the CO2 capture capacities were evaluated at both ambient and elevated pressures by using either thermal gravimetric or high pressure volumetric analysis method. It has been found that the well-developed porous system is important to obtain a higher CO2 capture capacity, which can be related to microporosity at ambient pressure, whereas at elevated pressure, larger pores are also involved in the adsorption of CO2 via a pore filling process. The AC beads developed by the present study exhibited good CO2 uptakes and fast adsorption kinetics. Consider-

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ing their excellent CO2 adsorption capacities at elevated pressures and good spherical form, these AC beads have great potential for CO2 capture applications with pre-combustion CO2 capture such as in IGCC-based power plants where the CO2 pressure is high.

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Acknowledgments

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The authors wish to acknowledge the assistance of Dr. Miguel Castro Diaz with the characterization of some of the AC beads, and the financial support of the UK EPSRC Grants (EP/I010955/1, EP/G063176/1), and the National Natural Science Foundation of China (51061130536, 51172251 and 21203230).

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References

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Please cite this article in press as: Sun N et al. Synthesis, characterization and evaluation of activated spherical carbon materials for CO2 capture. Fuel (2013), http://dx.doi.org/10.1016/j.fuel.2013.03.047