ARTICLE pubs.acs.org/EF
Functionalized Fly Ash Based Alumino-Silicates for Capture of Carbon Dioxide Vivek Kumar,† Nitin Labhsetwar,† Siddharth Meshram,‡ and Sadhana Rayalu†,* † ‡
National Environmental Engineering Research Institute (NEERI), Nehru Marg, Nagpur, Maharashtra-440020, India Department of Chemistry, Laxminarayan Institute of Technology (LIT), RTM Nagpur University, Nagpur-440010, India ABSTRACT: Fly ash contains mainly alumina and silica as its main constituents. A novel method for the extraction of highly stable alumino-silicates from fly ash has been developed. The as-extracted alumino-silicate has been further functionalized with APTES ((3-aminopropyl)triethoxysilane), TRIS buffer (tris(hydroxymethyl)aminomethane), and AMP (3-amino-2-methyl-1-propanol) to impart basicity for carbon dioxide adsorption. A dynamic adsorption capacity of 6.62 mg/g has been observed for FAS (fly ash based alumino-silicate) and has improved by a factor of 4.0, with an adsorption capacity of 26.5 mg/g for AMP-functionalized FAS at 55 °C with 15% CO2 in N2. The positive influence of water was observed with an improvement of adsorption capacity to 34.82 mg/g at 55 °C with 15% CO2, 82% N2, and 3% water vapor. The adsorbent is studied for adsorption capacity at varying temperatures, and the best performing adsorbent is characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, thermal analysis, and elemental analysis to study the morphological properties of the present adsorbent support. The excellent thermal stability of synthesized material suggested the formation of promising aluminosilicate for CO2 adsorption.
1. INTRODUCTION Fossil fuel combustion supplies more than 85% of energy for industrial activities and is, thus, the main source of greenhouse gases (GHG) in the form of CO2. This is expected to remain almost unchanged over the next 25 years, as world energy consumption doubles. Coal, which has the highest carbon footprint per unit of energy, accounts for approximately 25% of the world energy supply and 40% of the carbon emissions. Over the next 100 years, it has been projected that the combustion of fossil fuels can add massive amounts of carbon dioxide into the atmosphere that can outsize the uptake capacity of natural sinks.1 The concentration of carbon dioxide in the Earth’s atmosphere was at a maximum of 391 ppm by volume as of April 2010.2 The annual mean growth rate for Mauna Loa, Hawaii, suggests an increase in concentration by about 2 ppm in 2009, with a concentration of 393.69 ppm as of June 2011.3 The continuing use of fossil fuels and, in turn, the continuing emission of carbon dioxide in the atmosphere have raised the precondition for proficient capture, storage, and sequestration methodologies.4 Postcombustion carbon dioxide absorption has been applied on various occasions.5 7 The significance of a carbon dioxide absorption methodology suggests a nonfeasible solution toward efficient carbon dioxide removal from power plants.8,9 Research of the alternative methodology selection, such as precombustion CO2 capture, failed to provide expected results.10 Adsorptive removal of emitted carbon dioxide from flue gas has provided an efficient methodology, and amine modified mesoporous adsorbents have an edge over other classes of adsorbents.11,12 The use of microporous adsorbents such as activated carbon,13 nitrogen enriched carbon,14 silica gel,15 advanced membranes,16,17 and amine incorporated zeolites18 has been reported. There is a need to develop low cost materials with a reasonably good capacity for carbon capture. Making this connection, fly ash, a waste material of the r 2011 American Chemical Society
thermal power industry, is proposed to be used. About 175 million tonne of fly ash is estimated to be generated in India by the year 2012. From about 83 existing thermal power plants and 1800 selected industrial units that had captive thermal power plants of >1 MW, it is expected to amplify to 200 MTPA in another decade. Fly ash can cause serious environmental hazards. Additionally, the land requirement envisaged for the disposal of fly ash is about 50,000 acre, with an annual expenditure of about Rs 500 million for transportation. These problems undoubtedly make obvious the fact that the utilization of fly ash is absolutely essential. Technologies have been developed for gainful utilization of fly ash. The utilization ranges from low to high value-added applications. The utilization of fly ash in India records a very low percentage of 2 3%, as compared to a corresponding figure of 30 80% for developed countries. This requires the development of some innovative technologies to promote fly ash utilization. The possibility of synthesizing high value-added products such as zeolites from fly ash was explored.19 23 Over 250 species of naturally occurring and synthetic zeolitic compositions are available. In general, crystalline zeolites are alumino-silicates that consist of AlO4 and SiO4 tetrahedra connected by mutual sharing of oxygen atoms and characterized by pore openings of uniform dimension. Zeolites show remarkable ion-exchange capacity; they are capable of reversibly desorbing adsorbed phases that are dispersed throughout the voids of the crystal without displacing any of the atoms that make up the permanent crystal structure. The use of zeolitic alumino-silicate adsorbents for carbon dioxide adsorption is extensively reported in the literature.24 33 In general, the zeolite-synthesizing process from fly ash involves alkaline Received: August 9, 2011 Revised: September 8, 2011 Published: September 08, 2011 4854
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Table 1. CO2 Adsorption Capacities of Different Alumino-Silicate Adsorbents under Various Experimental Conditions samp. no. 1
2
type of alumino-silicate
adsorption temp and expt conditions
NaX
304.4 K, 214.38 Torra
205.7
NaX
305.8 K, 213.87 Torra
203.2
Na-ZSM-5
297.1 K, 235.14 Torra
63.2
H-ZSM-5
296.9 K, 230.47 Torra
48.8
H-ZSM-5
295.5 K, 140.95 Torra
38.3
4A
60 °C TPD procedure
42.3
5A
22.73
13X NaY
32.03 3.75
USY
134 78.2
30 to 150 °C GC method for 0.5 MPA
29.66
Rb-ZSM-5
29.66
13X
FTIR, 22 °C
6
13X
0 °Cb
140.8 (20.35 kPa)
20 °Cb
114.9 (20.43 kPa)
40 °Cb 60 °Cb
95 (23.66 kPa) 74.4 (27.00 kPa)
13X
13.6
184.8
40 °Cc
202.4
50 °Cc
228.8 290
5A
MRI technique at 2 atm and by adsorption of 13CO2, 25 °C
9
4A
TPD studies at 120 °C
30.8
5A 13X
16.7 22
APG-II
26.4
WE-G 592
11
ref 28 ref 29
58.1 (23.85 kPa)
30 °Cc
8
10
ref 27
7.908
5
80 °Cb
a
35.59 35.59
K-ZSM-5 Cs-ZSM-5
7
ref 26
84.2
ZN-19(clinoptilolite) Li-ZSM-5 Na -ZSM-5
ref 25
1.779 17 °C, volumetric system
ZNT(modernite) 4
ref 24
62.86
H-modernite ZAPS(erionite)
ref
0
Na-modernite 3
adsorption capacity (mg/g)
ref 30
ref 31 ref 32
16.7
13X
30 °Cd
55
13X
75 °Cd
15
FAS-bare
55 °Cd
FAS-AMP-30
30 °Cd
10.8
FAS-AMP-30 FAS-AMP-30
55 °Cd 75 °Cd
26.5 22.6
6.62
ref 33 present study
Volumetric method. b Static volumetric method. c PSA. d Breakthrough studies.
treatment, using caustic soda at higher temperatures (80 100 °C). Most of the preceding studies evaluated the conversion of fly ash to zeolite-like materials under ambient pressure conditions. There are reports available for the usage of flash based adsorbents for the capture of carbon dioxide.34 37 Related studies are reported wherein seawater has been used for the precipitation of calcite and aragonite from varying salinity samples.38 With this background, efforts have been made to develop low cost adsorbents by avoiding a hydrothermal crystallization step, which is one of the most energy intensive steps. This has been achieved by precipitating alumino-silicate using the double salt effect. On basis of this, the synthesis of low cost
alumino-silcates, as an alternative to zeolites for capture of carbon dioxide, has been attempted. This paper thus addresses the synthesis of alumino-silcates from fly ash by varying conditions within feasible parametric ranges for the optimization of conditions, along with the characterization of fly ash based aluminosilcates (FAS).
2. MATERIALS AND METHODS 2.1. Materials. Fly ash samples were collected from the hopper of an electrostatic precipitator at Koradi Thermal Power Plant, Nagpur. The raw fly ash samples were first screened through a 4855
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Figure 2. Breakthrough curve for FAS-AMP-30 at different temperatures.
Table 3. BTC Results for FAS-AMP-30 with 15% CO2 feed flow
Figure 1. Experimental setup used for breakthrough adsorption studies.
Table 2. BTC Results for Fly Ash Based Alumino-Silicates with 15% CO2 feed flow rate
adsorption adsorption
capacity
material
(mL/min)
temp (°C)
(mg/g)
FAS-bare FAS-APTES-10
20 20
55 55
6.62 7.4
FAS-APTES-25
20
55
10.8
FAS-APTES-50
20
55
10.8
FAS-TRIS-10
20
55
11.1
FAS-TRIS-25
20
55
6.9
FAS-TRIS-50
20
55
6.9
FAS-AMP-10
20
55
10.8
FAS-AMP-25 FAS-AMP-30
20 20
55 55
24.2 26.5
FAS-AMP-40
20
55
22.6
FAS-AMP-50
20
55
22.6
FAS-AMP-80
20
55
19.2
FAS-AMP-100
20
55
14.7
Nonaka Rikaki 100 μm mesh testing sieve to eliminate the larger particles. TRIS buffer (tris(hydroxymethyl)aminomethane) was procured from Calbiochem, Germany. The 3-amino-2-methyl1-propanol (AMP) and (3-aminopropyl)triethoxysilane (APTES) were procured from E-Merck, India, and were used as received, without any further purification. Commercially available sea salt was procured from M/S Sigma Life Sciences, India. 2.2. FAS Synthesis. The elemental content of fly ash was as follows: SiO2, 62.27; Al2O3, 30.96; Fe2O3, 1.25; TiO2, 1.67; CaO, 3.02; Na2O, 0.12; K2O, 0.41; and LOI, 0.29. In the present investigation, fly ash based alumino-silicate (FAS) was synthesized by reacting fly ash with caustic soda. The methodology used was as follows in section 2.2.1. 2.2.1. Fusion Method. The FAS sample was synthesized by fusing fly ash with sodium hydroxide. A homogeneous fusion mixture was primed by proper grinding and mixing of fly ash and caustic soda in a 1:1.2 ratio. This mixture was heated at 550 °C for 2 h. The resultant fused mass was cooled, milled, and mixed thoroughly in distilled water (200 mL). The decant obtained
a
adsorption
rate
adsorption
capacity
material
(mL/min)
temp (°C)
(mg/g)
FAS-AMP-30
20
30
10.8
FAS-AMP-30 FAS-AMP-30
20 20
55 75
26.5 22.6
FAS-AMP-30
20
55
34.82a
In presence of 3% water vapor.
after the filtration of the solid mass was mixed with 200 mL of artificial seawater containing 10 g of sea salt. A white precipitate, which was termed FAS, was recovered by filtration. This precipitate was vacuum-dried at 50 °C overnight to obtain granules of alumino-silicate. 2.3. Functionalization of Alumino-Silicate. The in situ functionalizations of FAS were done using APTES ((3-aminopropyl)triethoxysilane), TRIS buffer (tris(hydroxymethyl)aminomethane), and AMP (3-amino-2-methyl-1-propanol) by adding the functional molecules to the fly ash decant solution during precipitation. The as-synthesized adsorbents were named FAS-APTES, FAS-TRIS, and FAS-AMP and were pelletized and sieved to obtain granules of size 2 6 mm, suitable for breakthrough curve CO2 adsorption analysis. 2.4. Evaluation of Materials for CO2 Adsorption. Among several solutions of postcombustion CO2 capture, fluidized bed adsorption processes are considered to have a high potential for capturing CO2 gas from bulk flue gas. The bed was filled with adsorbent to adsorb gases. Initial screening for the selection of the best functionalization molecule has been performed at 55 °C, followed by evaluation at 30 and 75 °C. Because flue gas is comprised of CO2 that is mixed mainly with N2, CO, water vapor, and particulate matter, we restricted our evaluations with 15% CO2 balanced with N2 and introduce 3% water vapor for selected adsorbent conditions. 2.5. Breakthrough Adsorption Studies in Flow through System. In this method, the gas stream to be treated is passed over a fixed bed of adsorbent. An unsteady state condition prevails, in that the adsorbent bed continues to take up increasing amounts of adsorbate gases. The composition of the gas stream at the outlet of the bed is monitored continuously. Then, the amount of a particular gas is followed as the fraction of the concentration of that gas in the effluent gas from the adsorption column, Ce, over that of the gas concentration in the feed gas, C0. This method matches practical (actual end use) conditions such as flow conditions, 4856
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Figure 3. XRD comparison of FAS-bare and FAS-AMP-30.
Table 4. Textural Properties of FAS Adsorbents Vtot (cm3/g)a
SBET (m2/g)b
DBJH (nm)c
FAS-bare
0.003262
0.5413
24.20
FAS-APTES-25 FAS-TRIS-25
0.007270 0.002883
2.07 1.4237
14.03 8.09
FAS-AMP-30
0.207041
91.3743
9.26
adsorbent
a
Total pore volumes calculated as the amount of N2 adsorbed at P/P0 = 0.99. b Brunauer Emmet Teller (BET) surface areas. c Pore diameter calculated by the Barett Joyner Halenda (BJH) method using the adsorption branches.
temperatures, and multicomponent streams, and we can calculate the dynamic adsorption capacities of the materials (Table 1). The gas manifold system consisted of four lines fitted with mass flow controllers from Aalborg (U.S.A.) with flows ranging between 1 and 200 mL/min. The controllers had an accuracy of 1% full scale and a repeatability of 0.1% full scale. One of the lines was used to feed in an inert gas, He, to dry the sample before each experiment. The other three lines fed in CO2, N2, and water vapor, so that different gas mixtures akin to the concentrations representative of different postcombustion capture gas streams could be prepared. Water was introduced using a peristaltic pump capable of releasing the minimum flow to the range 1 5 mL/min. The gases flowing through the different lines were mixed in a helicoidal dispenser that ensured perfect mixing of the feed gas before it entered the bed. A K-type thermocouple, located at a height of 50 mm above the porous plate (exit end of the column), was used to continuously monitor the column temperature with an accuracy of (1.5 °C. The temperature was controlled by coupling the heating element coiled around the reactor inside an insulated fabrication. The bed pressure was observed by means of a backpressure regulator located in the outlet pipe, with a repeatability of 0.5% full scale (0 40 bar). The system was also equipped with
Figure 4. N2 adsorption isotherm for FAS-bare.
a continuous gas analyzer and gas chromatograph (GC, Clarus 500 from Perkin-Elmer) fitted with a thermal conductive detector (TCD), in which He was used as the carrier gas. The feed gas and product streams were fed to an autosampler valve on the GC by using a sample selector valve for selecting the desired stream. The GC column used was a Porapak-Q column with analysis conditions as follows: carrier gas = nitrogen at 20 mL/min and temperature = 60 (oven), 110 (injector), and 130 °C (detector). The TCD response was calibrated employing CO2/N2 mixtures of known composition. The bed was packed with adsorbent in order to measure the dynamics of the CO2 in the column. The feed gas inlet flow rate was kept constant (20 mL/min). The CO2 4857
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Figure 7. Pore size distribution curve for FAS-AMP-30. Figure 5. N2 adsorption isotherm for FAS-AMP-30.
Table 5. Chemical Analysis of FAS Adsorbents adsorbent
Figure 6. Pore size distribution curve for FAS-bare.
composition in the column effluent gas was continuously monitored as a function of time (breakthrough curve) until the composition approached the inlet gas composition value, that is, until saturation was reached. Each sample was subjected to pretreatment for the cleaning of the adsorbent surface. Subsequently, the adsorbent was exposed to the feed gas flow, and the adsorption capacities were estimated. About 5 g of adsorbent was packed in a glass column having an effective working length of 300 mm, an internal diameter of 10 mm, and a wall thickness of 2 mm; it was heated from room temperature to 110 °C for a period of 6 h in a flow of 20 mL He/min. The column was then cooled to the predefined adsorption temperature. This was done to clean the adsorbent surface and to remove any preadsorbed volatile matter in the adsorbent bed. A flow of CO2 was used with ca. 15 mol % balanced with N2 (flow rates: CO2 = 3 and N2 = 17 mL/min) for the
N mol %
C mol %
H mol %
N/C
FAS-bare
0.01
0.66
2.08
0.01
FAS-APTES-10
0.65
4.22
4.15
0.15
FAS-APTES-25
2.05
5.11
4.51
0.40
FAS-APTES-50
3.41
6.32
5.14
0.53
FAS-TRIS-10
4.21
5.11
4.14
0.82
FAS-TRIS-25
11.65
4.15
7.11
2.80
FAS-TRIS-50
14.21
7.54
8.14
1.88
FAS-AMP-10 FAS-AMP-25
0.87 2.78
5.11 6.44
1.24 4.54
0.17 0.43
FAS-AMP-30
4.21
8.15
7.45
0.51
FAS-AMP-40
5.12
7.15
4.84
0.71
FAS-AMP-50
5.89
7.81
5.12
0.75
FAS-AMP-80
7.45
7.42
4.18
1.00
FAS-AMP-100
11.84
12.45
7.84
0.95
adsorption study. The total flow rate for adsorption was maintained at 20 mL/min. Concentration of CO2 in the exit gas stream was monitored continuously at an interval of 1 min, using TCD-GC and a pneumatically controlled sample injector. The experiments were continued until saturation was reached, and then, the CO2 flow was stopped (Figure 1). 2.6. Characterization. All the prepared adsorbents were characterized using low- and wide-angle X-ray diffraction (XRD) analyses to access the structural integrity of the adsorbent samples after the incorporation of the amines. The XRD patterns have been recorded using an X-ray diffractometer (Phillips, model PW-1830). The radiations of Cu Kα were generated using an X-ray generator (Phillips, model PW 1729), and the β radiation was filtered using monochromators. The Fourier transform infrared (FTIR) spectra of the synthesized materials were recorded using a PerkinElmer spectrometer, using the KBr pellet technique. The samples were analyzed in the wavelength region 4000 400 cm 1. This was done to confirm the formation of carbamate and bicarbonate groups, which are formed as the adsorption product of CO2. 4858
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Energy & Fuels Scanning electron microscopy (SEM) analysis was carried out using a JEOL, JSM 6380 A, analytical scanning electron microscope. The elemental analysis of the samples was determined by using a Thermo flash elemental analyzer (EA) 1112 fitted with a MAS 200R autosampler including instrument control. Data analysis was conducted with the help of the Eager Xperience software package. The standard method of Brunauer, Emmett, and Teller (BET) was used for measuring the specific surface area of the adsorbent based on the physical adsorption of a gas on the solid surface. The specific surface area of the catalysts was determined using the Micromeritics Gemini 2375 gas adsorption system. The samples were degassed at 105 °C. This temperature range was chosen with the boiling point of the TEPA used in the present study in mind. The isothermal analysis of the adsorbents was performed using thermogravimetric analysis (TGA) on a Perkin-Elmer TGA instrument. The combustion activities of the different adsorbents were assessed using isothermal TGA from 25 to 700 °C. The adsorbents were heated at a rate of 10 °C min 1 from 25 to 700 °C under nitrogen, with a flow rate of 20 mL/min (STP), to check the thermal stability.
3. RESULTS AND DISCUSSION 3.1. Selection of Functionalization Molecule. Bare FAS was functionalized and evaluated at 55 °C and 15% CO2 concentration with 10, 25, and 50 wt % of APTES, TRIS buffer, and AMP. The dynamic CO2 adsorption capacity of bare FAS was 6.62 mg/g at 55 °C, which improved to 7.4 mg/g after the 10 wt % APTES loading. The adsorption capacity improved marginally to 10.8 mg/g
Figure 8. Thermal stability of FAS-bare and FAS-AMP-30 adsorbents.
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after the loading was further increased to 25 wt %, and it remained constant as the loading was increased to 50 wt %. TRIS buffer provided the maximum adsorption capacity of 11.1 mg/g with 10 wt % loading and failed to provide any further improvement after increased loading of 25 and 50 wt %. An encouraging CO2 adsorption capacity was observed when FAS was loaded with the AMP solution. The adsorption capacity increased from 10.8 to 24.2 mg/g when AMP loading was increased from 10 to 25 wt %. A small increase of 5% in loading provided an increased adsorption capacity of 26.5 mg/g, which prompted further increases in AMP loading. However, the adsorption capacity followed a decreasing trend when the loading was increased from 30 to 40, 50, 80, and 100 wt % AMP, signifying the selection of FAS-AMP-30 as the best performing adsorbent (Table 2). 3.2. Effect of Temperature on Adsorption of CO2. The selected adsorbent, FAS-AMP-30, was subjected to adsorption performance studies at 30 and 75 °C with 15% CO2. The breakthrough curve (BTC) CO2 adsorption capacity of the adsorbent did not show any improvement at the selected temperatures when compared to the performance at 55 °C (Figure 2). The optimal performance of FAS-AMP-30 was achieved at 55 °C with 15% CO2 at a 20 mL/min flow rate. The decrease in the adsorption capacity at 75 °C also suggests the possibility of coupled physiosorption and chemisorption analogous to the case of the conventional adsorbents, such as zeolites and activated carbons (Table 3). 3.3. Effect of Moisture on Adsorption of CO2. An improved adsorption performance of selected adsorbent FAS-AMP-30 has been observed when water is introduced at 55 °C with 15% CO2, 82% N2, and 3% water vapor, maintaining a 20 mL/min flow rate. The adsorption capacity of FAS-AMP-30 increased to 34.82 mg/g, reflecting the positive influence of water vapor toward adsorption performance. 3.4. XRD. Wide-angle XRD of FAS-bare compared with FASAMP-30 suggests the amorphous, unordered morphology and pure adsorbent formation, including the decrease in intensity after AMP incorporation (Figure 3). The JCPDS card description no. 46-1045 suggests potassium aluminum silicate (microline) formation, confirmed by a 100% intense peak at the 2θ position 31.800. The use of sea salt as a precipitating agent resulted in the formation of calcium sodium aluminate at the 2θ position 45.560. The formation of charoite (potassium calcium silicate hydroxide hydrate) is confirmed by the intense peak at the 2θ position 31.7 (JCPDS card description no. 42-1402) with the following cell parameters: a = 19.61, b = 32.12, and c = 7.20. An intense peak at the 2θ position 27.4 suggests the formation of tarasovite (potassium sodium aluminum silicate hydroxide hydrate) with the following cell parameters: a = 5.13 and c = 44.01.
Figure 9. SEM image of (A) FAS-bare and (B) FAS-AMP-30. 4859
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Figure 10. Comparative FTIR of FAS-bare and FAS-AMP-30.
3.5. BET Surface Area and Pore Analysis. The pore characteristics and surface area variations of APTES, TRIS buffer, and AMP immobilized FAS are compared with bare FAS in Table 4. An unusual increase in the surface area of FAS-AMP-30 has been observed compared to those of bare and APTES or TRIS buffer immobilized FAS (Table 4). The BET surface area has increased from 0.5413 to 91.3743 m2/g after AMP impregnation (Figures 4 and 5). Also, a substantial increase in pore volume from 0.003262 to 0.207041 cm3/g has been observed. These improved characteristics have resulted in an improved CO2 adsorption capacity by a factor of 4 (Table 2). The reason behind the increase in surface area could be a result of the enhanced surface characteristics improvement by AMP over the FAS surface. Also, the possibility of the leaching of surface metal ions from FAS, as a result of the mixing of AMP or the role of AMP as a template for surface modification, cannot be ruled out, which was not functional in the case of APTES or TRIS immobilized FAS. The pore size distribution curves (Figures 6 and 7) also support this possibility. 3.6. Elemental Analysis of Adsorbents. The elemental analysis data significantly provided information regarding the varying amount of nitrogen functionality affecting the overall CO2 adsorption properties. Theoretically, the high N/C ratio will facilitate enhanced CO2 adsorption capacity. The trend did not follow the said hypothesis, and the 50% loading of APTES, TRIS buffer, and AMP failed to provide the increased adsorption capacity practically (Table 5). The elemental content of FAS was as follows: SiO2, 44.85; Al2O3, 25.71; Fe2O3, 0.41; TiO2, 0.11: CaO, 13.86; Na2O, 0.35; K2O, 10.93; other, 2.10; and LOI, 0.32. The increase in calcium and potassium content may be attributed to the addition of sea salt for precipitation of alumino-silicate. 3.7. Thermal Stability. Bare FAS and FAS-AMP-30 were subjected to thermal treatment under nitrogen from ambient to 700 °C. The excellent stability of bare FAS was observed, with almost no weight loss during the entire thermal treatment. An inconsequential weight loss similar to that of bare FAS was observed for FASAMP-30 up to 200 °C, but it sharply started degradation after further increases in temperature. Almost 20% weight loss was recorded between 200 and 700 °C, and this could be due to the presence of AMP loading over FAS. The thermogravimetric temperature effect is provided in Figure 8. The complete crystallization of FAS-bare below
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Figure 11. FTIR of CO2 adsorbed FAS-AMP-30.
100 °C is evident from the nearly zero weight loss after increased temperature. 3.8. SEM. A distinct variation in surface morphology is observed through the SEM images (Figure 9). The as-synthesized FAS-bare has a smooth surface, whereas a change in surface morphology is evident for FAS-AMP-30. AMP has probably provided roughness to the FAS surface, thus providing sites for CO2 adsorption, as suggested by the BET results. 3.9. FTIR. The presence of a peak at a frequency of about 3400 cm 1 was observed in the FTIR spectra of the AMP modified FAS sample (Figure 10). This may be attributed to the N H stretching vibration. Figure 11 represents the FTIR spectrum of the aminated FAS-AMP-30 that was evaluated for adsorption of CO2. Further loading of amine on FAS was confirmed by FTIR studies. In the case of the CO2 exposed sample, a peak at a frequency of 3300 cm 1 was also observed, which may be attributed to the N H stretch of carbamate species ( NHCOO ), possibly formed by the interaction of the amine molecule with carbon dioxide (Figure 11).18 This further substantiates the CO2 adsorption through interaction of CO2 with functional groups of the adsorbent.
4. CONCLUSION A novel method for the extraction of highly stable aluminosilicates from fly ash has been developed. The in situ incorporation of AMP resulted in an adsorbent with significantly improved characteristics to adsorb carbon dioxide at lower temperatures, and its performance was analyzed using a conventional carbon dioxide capture methodology. The adsorbent is characterized for surface morphology using XRD, SEM, FTIR, elemental analysis, and thermal analysis. The XRD of the synthesized FAS revealed the formation of amorphous mesoporous alumino-silicates. It is observed that the presence of nitrogen functionality does not facilitate better adsorption of CO2. The optimized loading of the functionalized molecule, along with the availability of adsorption pores (sites), facilitates the CO2 adsorption process. ’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected]. Telefax: +91-712-2247828. 4860
dx.doi.org/10.1021/ef201212h |Energy Fuels 2011, 25, 4854–4861
Energy & Fuels
’ ACKNOWLEDGMENT The authors acknowledge the support extended by Director, NEERI, for his encouragement. They also acknowledge the support extended by Dr. Wadodkar, JNARDDC, Nagpur, and Dr. Peshwe and Miss Gauri Deshmukh from VNIT, Nagpur, for providing characterization results. They acknowledge the facilities provided by Dr. Trevor Drage, Associate Professor, Department of Chemical and Environmental Engineering and Dr. Lee Stevans, University of Nottingham, U.K. V.K. would also like to kindly acknowledge the Council of Scientific and Industrial Research (CSIR), India, for granting a Senior Research Fellowship to him. ’ REFERENCES (1) Falkowski, P.; Scholes, R. J.; Boyle, E.; Canadell, J.; Canfield, D.; Elser, J.; Gruber, N.; Hibbard, K.; Hogberg, P.; Linder, S.; Mackenzie, F. T.; Moore, B., III; Pederson, T.; Rosenthal, Y.; Seitzinger, S.; Smetacek, V.; Steffen, W. The global carbon cycle: a test of knowledge of Earth as a system. Science 2000, 290, 291–296. (2) Mauna Loa CO2 annual mean data; NOAA: 2011. Available online: ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_mm_mlo.txt.Trend data was used. (3) Annual Mean Growth Rate for Mauna Loa, Hawaii, Trends in Atmospheric Carbon Dioxide; NOAA Earth System Research Laboratory: Retrieved 28 April 2010; http://www.esrl.noaa.gov/gmd/ccgg/trends/ #mlo_growth. (4) Pires, J. C. M.; Martins, F. G.; Alvim-Ferraz, M. C. M.; Sim~oes, M. Recent developments on carbon capture and storage: an overview. Chem. Eng. Res. Des. 2011, 89, 1446–1460. (5) Wanga, M.; Lawala, A.; Stephenson, P.; Sidders, J.; Ramshawa, C. Post-combustion CO2 capture with chemical absorption: a state-of-theart review. Chem. Eng. Res. Des. 2011, 89, 1609–1624. (6) Lawal, A.; Wang, M.; Stephenson, P.; Yeung, H. Dynamic modelling of CO2 absorption for postcombustion capture in coal-fired power plants. Fuel 2009, 88, 2455–2462. (7) Ogawa, T.; Ohashi, Y.; Yamanaka, S.; Miyaike, K. Development of carbon dioxide removal system from the flue gas of coal fired power plant. Energy Procedia 2009, 1, 721–724. (8) Kemper, J.; Ewert, G.; Gr€unewald, M. Absorption and regeneration performance of novel reactive amine solvents for post-combustion CO2 capture. Energy Procedia 2011, 4, 232–239. (9) Zhu, D.; Fang, M.; Zhong, L.; Zhang, C.; Luo, Z. Semi-batch experimental study on CO2 absorption characteristic of aqueous ammonia. Energy Procedia 2011, 4, 156–163. (10) García, S.; Gil, M. V.; Martín, C. F.; Pis, J. J.; Rubiera, F.; Pevida, C. Breakthrough adsorption study of a commercial activated carbon for pre-combustion CO2 capture. Chem. Eng. J. 2011, 171, 549–556. (11) Sayari, A.; Belmabkhout, Y.; Serna-Guerrero, R. Flue gas treatment via CO2 adsorption. Chem. Eng. J. 2011, 171, 760–774. (12) Zhao, G.; Aziz, B.; Hedin, N. Carbon dioxide adsorption on mesoporous silica surfaces containing amine-like motifs. Appl. Energy 2010, 87, 2907–2913. (13) Drage, T. C.; Blackman, J. M.; Pevida, C.; Snape, C. E. Evaluation of activated carbon adsorbents for CO2 capture in gasification. Energy Fuels 2009, 23, 2790–2796. (14) Thote, J. A.; Iyer, K. S.; Chatti, R.; Labhsetwar, N. K.; Biniwale, R. B.; Rayalu, S. S. In situ nitrogen enriched carbon for carbon dioxide capture. Carbon 2010, 48, 369–402. (15) Leal, O.; Bolivar, C.; Ovalles, C.; Garcia, J. J.; Espidel, Y. Reversible adsorption of carbon dioxide on amine surface-bonded silica gel. Inorg. Chim. Acta 1995, 240, 183–189. (16) Du, N.; Park, H. B.; Robertson, G. P.; Dal-Cin, M. M.; Visser, T.; Scoles, L.; Guiver, M. D. Polymer nanosieve membranes for CO2 capture applications. Nat. Mater. 2011, 10, 372–375.
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dx.doi.org/10.1021/ef201212h |Energy Fuels 2011, 25, 4854–4861
