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Article
Functionalized Fly ash basedalumino-silicates for capture of carbon dioxide
Vivek Kumar, Nitin K. Labhsetwar, Siddharth Meshram, and Sadhana Suresh RayaluEnergy Fuels, Just Accepted Manuscript • Publication Date (Web): 08 September 2011
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1
Functionalized Fly ash based alumino-silicates for capture of carbon 1
dioxide 2
Vivek Kumara, Nitin Labhsetwar
a, Siddharth Meshram
b and Sadhana Rayalu
a* 3
aNational Environmental Engineering Research Institute (NEERI),Nehru Marg, Nagpur, Maharashtra- 4
440020, India 5
bLaxminarayan Institute of Technology (LIT), Department of Chemistry, RTM Nagpur University, 6
Nagpur-440010, India 7
8
Abstract 9
Fly ash contains mainly alumina and silica as its main constituents. A novel method for 10
extraction of highly stable alumino-silicates from fly ash has been developed. The as-11
extracted alumino-silicate has been further functionalized with APTES (3-Aminopropyl 12
triethoxy silane), TRIS buffer (Tris hydroxymethyl aminomethane) and AMP (3-Amino 2- 13
methyl 1-Propanol) to impart basicity for carbon dioxide adsorption. A dynamic adsorption 14
capacity to the tune of 6.62 mg/g has been observed for FAS (Fly ash based alumino-silicate) 15
which has improved by a factor of 4.0 with adsorption capacity of 26.5 mg/g for AMP-16
functionalized FAS at 55 0C with 15% CO2 in N2. The positive influence of water was 17
observed with an improvement of adsorption capacity to 34.82 mg/g at 55 0C with 15% CO2, 18
82% N2 and 3% water vapor. The adsorbent is studied for adsorption capacity at varying 19
temperatures and the best performing adsorbent is characterized using X-ray diffraction 20
(XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) 21
spectroscopy, thermal analysis and elemental analysis to study the morphological properties 22
of the present adsorbent support. The excellent thermal stability of synthesized material 23
suggested the formation of promising alumino-silicate for CO2 adsorption. 24
25
26
*Corresponding author: 27
E-mail: s_rayalu@neeri.res.in; Telefax: +91-712-2247828 28
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1. INTRODUCTION 29
Fossil fuel combustion supplies more than 85% of energy for industrial activities, and 30
is thus the main source of greenhouse gases (GHG) in the form of CO2. This is expected to 31
remain almost unchanged over the next 25 years as world energy consumption doubles. Coal, 32
which has the highest carbon footprint per unit of energy, accounts for approximately 25% of 33
the world energy supply and 40% of the carbon emissions. 34
Over the next one hundred years, it has been projected that the combustion of fossil 35
fuels can add massive amounts of carbon dioxide into the atmosphere that can outsize the 36
uptake capacity of natural sinks1. The concentration of carbon dioxide in the Earth's 37
atmosphere was at a maximum of 391 ppm by volume as of April 20102. Annual mean 38
growth rate for Mauna Loa, Hawaii suggests an increase in the concentration by about 2 ppm 39
in 2009 with latest concentration of 393.69 ppm as of on June 20113. The continuing use of 40
fossil fuels and in turn the emission of carbon dioxide in the atmosphere has raised the 41
precondition for proficient capture, storage and sequestration methodologies4. Post 42
combustion carbon dioxide absorption has been applied on various occasions5-7
. The 43
significance of carbon dioxide absorption methodology suggests a non feasible solution 44
towards efficient carbon dioxide removal from power plants8, 9
. Research over the alternative 45
methodology selection such as pre combustion CO2 capture failed to provide expected 46
results10
. Adsorptive removal of emitted carbon dioxide from flue gas has provided efficient 47
methodology and amine modified mesoporous adsorbents have an edge over other classes of 48
adsorbents11, 12
. The use of microporous adsorbents such as activated carbon13
, nitrogen 49
enriched carbon14
, silica gel15
, advanced membranes16, 17
and amine incorporated zeolites18
50
have been reported in the recent time. There is need to develop low cost materials with 51
reasonably good capacity for carbon capture. In this connection, fly ash a waste material of 52
thermal power industry is proposed to be used. Fly ash is estimated to be generated in India to 53
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the tune of about 175 million tonnes by the year 2012. From about 83 existing thermal power 54
plants and1800 selected industrial units which had captive thermal power plants of >1MW, it 55
is expected to amplify to 200 MTPA in another decade. 56
Fly ash can cause serious environmental hazardous. Additionally, the land 57
requirement envisaged for disposal of fly ash is about 50,000 acre, with an annual 58
expenditure of about Rs 500 million for transportation. These problems undoubtedly make 59
obvious the fact that utilization of fly ash is absolutely essential. Technologies have been 60
developed for gainful utilization of fly ash. The utilization ranges from low to high value-61
added applications. Utilization of fly ash in India records a very low percentage of 2–3% as 62
compared to a corresponding figure of 30–80% for developed countries. This requires 63
development of some innovative technologies to promote fly ash utilization. 64
The possibility of synthesizing high value-added products such as zeolites from fly 65
ash was explored19-23
. Over 250 species of naturally occurring and synthetic zeolitic 66
compositions are available. In general, crystalline zeolites are alumino-silicates that consist of 67
AlO4 and SiO4 tetrahedra connected by mutual sharing of oxygen atoms and characterized by 68
pore openings of uniform dimension. Zeolites show remarkable ion-exchange capacity; they 69
are capable of reversibly desorbing adsorbed phases that are dispersed throughout the voids 70
of the crystal without displacing any atoms, which make up the permanent crystal structure. 71
The use of such zeolitic alumino-silicate adsorbents for carbon dioxide adsorption is 72
extensively reported in literature24-33
. In general, the zeolite-synthesizing process from fly ash 73
involves alkaline treatment, using caustic soda at higher temperatures (80–100 0C). Most 74
preceding studies evaluated the conversion of fly ash to zeolite-like materials under ambient 75
pressure conditions. There are reports available for usage of flash based adsorbents for 76
capture of carbon dioxide34- 37
. 77
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Related studies are reported wherein seawater has been used for precipitation of calcite 78
and aragonite from varying salinity samples38
. With this background, efforts have been made 79
to develop low cost adsorbents by avoiding a hydrothermal crystallization step, which is one 80
of the most energy intensive steps. This has been achieved by precipitating alumino-silicate 81
using double salt effect. Based on this, it has been attempted to synthesize low cost alumino-82
silcates as an alternate to zeolites for capture of carbon dioxide. This paper thus addresses 83
the synthesis of alumino-silcates from fly ash by varying conditions within feasible 84
parametric ranges for optimization of conditions along with characterization of fly ash-based 85
alumino-silcates (FAS). 86
87
2. MATERIALS AND METHODS 88
2.1. Materials 89
Fly ash sample was collected from the hopper of an electrostatic precipitator at Koradi 90
Thermal Power Plant, Nagpur. The raw fly ash samples were first screened through a Nonaka 91
Rikaki testing sieve of 100 micron mesh size to eliminate the larger particles. TRIS buffer 92
(Tris hydroxymethyl aminomethane) was procured from M/s.Calbiochem, Germany. 2-93
amino-2-methyl-1-propanol (AMP) and Aminopropyl triethoxysilane (APTES) were 94
procured from E-Merck, India and were used as such without any further purification. 95
Commercially available sea salt was procured from M/S Sigma Life Sciences, India. 96
97
2.2. FAS synthesis 98
The elemental content of flyash was as follows: SiO2: 62.27; Al2O3: 30.96; Fe2O3: 99
1.25; TiO2: 1.67: CaO: 3.02; Na2O: 0.12; K2O: 0.41; and LOI: 0.29. In the present 100
investigation, fly ash based alumino-silicate (FAS) was synthesized by reacting fly ash with 101
caustic soda. The methodology used was the following: 102
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2.2.1. Fusion method 103
The FAS sample was synthesized by fusing fly ash with sodium hydroxide. A 104
homogenous fusion mixture was primed by proper grinding and mixing of fly ash and caustic 105
soda in 1:1.2 ratio. This mixture was heated at 550 0C for 2 h. The resultant fused mass was 106
cooled, milled and mixed thoroughly in distilled water (200 ml). The decant obtained after 107
filtration of the solid mass was mixed with 200 ml of artificial sea water containing 10 g of 108
sea salt. A white precipitate which was termed FAS was recovered by filtration. This was 109
vacuum-dried at 50 0C overnight to obtain granules of alumino-silicate. 110
111
2.3 Functionalization of alumino-silicate 112
In-situ functionalization of FAS was done using APTES (3-Aminopropyl triethoxy 113
silane), TRIS buffer (Tris hydroxymethyl aminomethane) and AMP (3-Amino-2- methyl 1-114
Propanol) by adding the functional molecule to fly ash decant solution during precipitation 115
The as-synthesized adsorbent was named FAS-APTES, FAS-TRIS and FAS-AMP was 116
pelletized and sieved to obtain granules of size 2-6 mm, suitable for breakthrough curve CO2 117
adsorption analysis. 118
119
2.4 Evaluation of materials for CO2 adsorption 120
Among several solutions of post combustion CO2 capture, fluidized bed adsorption 121
processes are considered to have high potential option for capturing CO2 gas from bulk flue 122
gas. The bed was filled with sorbent to adsorb gases. Initial screening for selection of best 123
functionalization molecule has been performed at 55 0C followed by evaluation at 30 and 75 124
0C. As flue gas comprises of CO2 mixed mainly with N2, CO, water vapors and particulate 125
matter; we restricted our evaluations with 15% CO2 balanced with N2 and introduction of 3% 126
water vapour for selected adsorbent-conditions. 127
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2.5 Breakthrough adsorption studies in flow through system 128
In this method, the gas stream to be treated is passed over a fixed bed of adsorbent. 129
An unsteady state condition prevails, in that the adsorbent bed continues to take up increasing 130
amounts of adsorbate gases. The composition of the gas stream at the outlet of the bed is 131
monitored continuously. Then the amount of a particular gas is followed as the fraction of the 132
concentration of that gas in the effluent gas from the adsorption column Ce over that of the 133
gas concentration in the feed gas, C0. This method matches practical (actual end use) 134
conditions like flow conditions, temperatures and multi-component streams and we can 135
calculate the dynamic adsorption capacities of the materials. 136
The gas manifold system consisted of Four lines fitted with mass flow controllers from 137
Aalborg (USA) with flows ranging between 1 and 200 ml/min. The controllers had an 138
accuracy of 1% full scale and a repeatability of 0.1% full scale. One of the lines was used to 139
feed in an inert gas, He, in order to dry the sample before each experiment. The other three 140
lines fed in CO2, N2 and water vapor; so that different gas mixtures akin to the concentrations 141
representative of different post-combustion capture gas streams could be prepared. Water was 142
being introduced using a peristaltic pump capable of releasing the minimum flow to the range 143
of 1-5 ml/min. The gases flowing through the different lines were mixed in a helicoidal 144
dispenser that ensured perfect mixing of the feed gas before it entered the bed. 145
A K-type thermocouple, located at a height of 50 mm above the porous plate (exit end 146
of the column), was used to continuously monitor the column temperature with an accuracy 147
of ±1.5 ºC. The temperature was controlled by coupling the heating element coiled around the 148
reactor inside an insulated fabrication. The bed pressure was observed by means of a back-149
pressure regulator located in the outlet pipe with a repeatability of 0.5% full scale (0-40 bar). 150
The system was also equipped with a continuous gas analyzer, gas chromatograph (GC), 151
Claurus 500 from Perkin Elmer, fitted with a thermal conductive detector (TCD) in which He 152
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was used as the carrier gas. Feed gas and product stream were fed to auto sampler valve on 153
GC by using sample selector valve for selecting the desired stream. GC column used was 154
Porapak-Q with analysis conditions as follows; carrier gas = Nitrogen at 20 ml/min, 155
temperatures: oven = 60 °C, injector =110 °C, detector = 130 °C. 156
The TCD response was calibrated employing CO2/N2 mixtures of known composition. 157
The bed was packed with adsorbent in order to measure the dynamics of the CO2 in the 158
column. The feed gas inlet flow rate was kept constant (20 ml/min). The CO2 composition in 159
the column effluent gas was continuously monitored as a function of time (breakthrough 160
curve) until the composition approached the inlet gas composition value, i.e., until saturation 161
was reached. 162
Each sample was subjected to pretreatment for cleaning of the adsorbent surface. 163
Subsequently the adsorbent was exposed to feed gas flow and adsorption capacities were 164
estimated. About 5 g adsorbent was packed in a glass column having effective working 165
length 300 mm, internal diameter 10 mm, wall thickness 2 mm; and was heated from room 166
temperature to 110 °C for a period of 6 h in a flow of 20 ml He /min. The column was then 167
cooled to the predefined adsorption temperature. This was done to clean the adsorbent surface 168
and to remove any pre-adsorbed volatile matter in the adsorbent bed. A flow of CO2 was used 169
with circa 15 mol% balanced with N2 (Flow rates: CO2 = 3, N2 = 17 ml/min) for the 170
adsorption study. The total flow rate for adsorption was maintained at 20 ml/min. 171
Concentration of CO2 in exit gas stream was monitored continuously at an interval of 1 min 172
using TCD-GC and a pneumatically controlled sample injector. Experiments were continued 173
till saturation was reached and then CO2 flow was stopped (Figure 1). 174
175
2.6 Characterization 176
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All the prepared adsorbents were characterized using low and wide angle X-ray 177
diffraction (XRD) analyses to access the structural integrity of the adsorbent samples after 178
incorporation of the amines. The XRD patterns have been recorded using X-ray 179
diffractometer, Model (Phillips: PW-1830). The radiations of Cu-Kα were generated using X-180
ray generator of model (PW 1729) of same make and the β radiation were filtered using 181
monochromators. The Fourier Transform Infrared (FTIR) spectra of the synthesized materials 182
were recorded using a Perkin–Elmer spectrometer using the KBr pellet technique. The 183
samples were analyzed in the wavelength region 4000–400 cm-1
. This was done for 184
confirming the formation of the carbamate and bicarbonate groups, which are formed as the 185
adsorption product of CO2. 186
Scanning Electron Microscopy (SEM) analysis was carried out using JEOL, JSM 187
6380 A, analytical Scanning Electron Microscope. The elemental analysis of the samples was 188
determined by using a Thermo Flash Elemental analyser (EA) 1112 fitted with a MAS 200R 189
autosampler including instrument control. Data analysis was conducted with the help of 190
Eager Xperience software package. The standard method of Brunauer, Emmett and Teller 191
(BET) was used for measuring specific surface area of the adsorbent based on the physical 192
adsorption of a gas on the solid surface. Specific surface area of the catalysts was determined 193
using Micromeritics Gemini 2375 gas adsorption system. The samples were degassed at 105 194
°C. This temperature range was chosen keeping in mind the boiling point of TEPA used in 195
the present study. Isothermal analysis of adsorbents was performed using thermogravimetric 196
analysis (TGA) on a Perkin Elmer TGA. The combustion activities of the different adsorbents 197
were assessed using isothermal TGA from 25 to 700 0C. The adsorbents were heated at a rate 198
of 10 0C min
-1 from 25 °C to 700
0C under nitrogen with a flow rate of 20 ml/min (STP) to 199
check the thermal stability. 200
201
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3 RESULTS AND DISCUSSION 202
3.1 Selection of functionalization molecule 203
Bare FAS was functionalized and evaluated at 55 0C and 15% CO2 concentration with 204
10, 25 and 50 wt % of APTES, TRIS buffer and AMP. The dynamic CO2 adsorption capacity 205
of bare FAS was 6.62 mg/g at 55 0C which improved to 7.4 mg/g after 10 wt% APTES 206
loading. The adsorption capacity improved marginally to 10.8 mg/g after further increased 207
loading of 25 wt% and remained constant as the loading was increased to 50 wt%. TRIS 208
buffer provided the maximum adsorption capacity of 11.1 mg/g with 10 wt % loading and 209
failed to provide any further improvement after increased loading of 25 and 50 wt%. 210
Encouraging CO2 adsorption capacity was observed when FAS was loaded with AMP 211
solution. The adsorption capacity increased from 10.8 mg/g to 24.2 mg/g when AMP loading 212
was increased from 10 to 25 wt%. The small increase of 5% in loading provided increased 213
adsorption capacity to 26.5 mg/g suggested further increase in AMP loading. Though, the 214
adsorption capacity followed a decreasing trend when loading was increased from 30 to 40, 215
50, 80 and 100 wt % AMP signifying the selection of FAS-AMP-30 as the best performing 216
adsorbent (Table 2). 217
218
3.2 Effect of temperature on adsorption of CO2 219
The selected adsorbent FAS-AMP-30 was subjected to adsorption performance 220
studies at 30 and 75 0C with 15% CO2. The Breakthrough Curve (BTC) CO2 adsorption 221
capacity of adsorbent did not show any improvement at the selected temperatures when 222
compared to the performance at 55 0C (Figure 2). The optimal performance of FAS-AMP-30 223
was achieved at 55 0C with 15% CO2 and 20 ml/min flow rate. The decrease in adsorption 224
capacity at 75 0C also suggests the possibility of coupled physiosorption and chemisorption 225
analogous to the conventional adsorbents like zeolites and activated carbons (Table 3). 226
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3.3 Effect of moisture on adsorption of CO2 227
An improved adsorption performance of selected adsorbent FAS-AMP-30 has been 228
observed when water is being introduced at 55 0C with 15% CO2, 82% N2 and 3% water 229
vapor, maintaining 20 ml/min flow rate. The adsorption capacity of FAS-AMP-30 increased 230
to 34.82 mg/g reflecting the positive influence of water vapor towards adsorption 231
performance. 232
233
3.4 XRD 234
Wide angle XRD of FAS bare compared with FAS-AMP-30 suggests the amorphous 235
unordered morphology and pure adsorbent formation including the decrease in intensity after 236
AMP incorporation (Figure 3). The JCPDS card description # 46-1045 suggests Potassium 237
Aluminium Silicate (Microline) formation confirmed by 100% intense peak at 2� position 238
31.800. The use of sea salt as precipitating agent resulted in to the formation of calcium 239
Sodium Aluminate at 2� position 45.560. The formation of charoite (Potassium calcium 240
Silicate hydroxide hydrate) gets confirmed with the intense peak at 2� position 31.7 (JCPDS 241
card description # 42-1402) with cell parameters: a 19.61, b 32.12 and c 7.20. An intense 242
peak at 2� position 27.4 suggests the formation of tarasovite (Potassium Sodium Aluminium 243
Silicate hydroxide hydrate) with cell parameters: a 5.13 and c 44.01. 244
245
3.5 BET Surface area and pore analysis 246
The pore characteristics and surface area variation of APTES, TRIS buffer and AMP 247
immobilized FAS were compared with bare FAS in Table 4. An unusual increase in surface 248
area of FAS-AMP-30 has been observed compared to bare and APTES/TRIS buffer 249
immobilized FAS (Table 4). The BET surface area has increased from 0.5413 to 91.3743 250
m2/g after AMP impregnation (Figure 4 and 5). Also substantial increase in pore volume 251
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from 0.003262 to 0.207041 cm3/g has been observed. These improved characteristics have 252
resulted in improved CO2 adsorption capacity by a factor of 4 (Table 2). The reason behind 253
the increase in surface area could be due to enhanced surface characteristics improvement by 254
AMP over the FAS surface. Also the possibility of leaching of surface metal ions from FAS 255
due to mixing of AMP or the role of AMP as a template for surface modification cannot be 256
ruled out which was not functional in case of APTES or TRIS immobilized FAS. The pore 257
size distribution curves (Figure 6 and 7) also support this possibility. 258
259
3.6 Elemental analysis of adsorbents 260
Elemental analysis data significantly provided information regarding the varying 261
amount of nitrogen functionality affecting the overall CO2 adsorption properties. 262
Theoretically, the high N/C ratio shall facilitate enhanced CO2 adsorption capacity. The trend 263
did not follow the said hypothesis and 50% loading of APTES, TRIS buffer and AMP failed 264
to provide the increased adsorption capacity practically (Table 5). The elemental content of 265
FAS was as follows: SiO2: 44.85; Al2O3: 25.71; Fe2O3: 0.41; TiO2: 0.11: CaO: 13.86; Na2O: 266
0.35; K2O: 10.93, other 2.10; and LOI: 0.32. The increase in calcium and potassium content 267
may be attributed to the addition of sea salt for precipitation of alumino-silicate. 268
269
3.7 Thermal stability 270
Bare FAS and FAS-AMP-30 were subjected to thermal treatment under nitrogen from 271
ambient to 700 0C. The excellent stability of bare FAS was observed with almost no weight 272
loss during the entire thermal treatment. An inconsequential weight loss similar to bare FAS 273
was observed for FAS-AMP-30 up to 200 0C which sharply started degradation after further 274
increase in temperature. Almost 20 % weight loss was recorded between 200-700 0C and this 275
could be due to the presence of AMP loading over FAS. The thermogravimetric temperature 276
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effect is provided in Figure 8. The complete crystallization of FAS-bare below 100 0C is 277
evident from almost no weight loss after increased temperature. 278
279
3.8 SEM 280
A distinct variation in surface morphology is observed through SEM images (Figure 9 281
A and B). The as-synthesized FAS bare has a smooth surface where a change in surface 282
morphology is evident for FAS-AMP-30. AMP has probably provided roughness to the FAS 283
surface thus providing sites for CO2 adsorption, as suggested by the BET results. 284
285
3.9 FTIR 286
The presence of a peak at a frequency of about 3400 cm-1
was observed in the FT-IR 287
spectra of the AMP modified FAS sample (Figure 10). This may be attributed to the N-H 288
stretching vibration. Figure 11 represents the FTIR spectrum of the aminated FAS-AMP-30 289
which was evaluated for adsorption of CO2. Further loading of amine on FAS was confirmed 290
by FTIR studies. In case of CO2 exposed sample, a peak at a frequency of 3300 cm-1
was also 291
observed, which may be attributed to the N-H stretch of carbamate species (-NHCOO-), 292
possibly formed by the interaction of the amine molecule with carbon dioxide (Figure 11) 18
. 293
This further substantiates the CO2 adsorption through interaction of CO2 with functional 294
groups of the adsorbent. 295
296
4. CONCLUSION 297
A novel method for extraction of highly stable alumino-silicates from fly ash has been 298
developed. The in-situ incorporation of AMP resulted in an adsorbent with significantly 299
improved characteristics to adsorb carbon dioxide at lower temperature and its performance is 300
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analyzed using a conventional carbon dioxide capture methodology. The adsorbent is 301
characterized for surface morphology using XRD, SEM, FTIR, Elemental and thermal 302
analyses. XRD of the synthesized FAS revealed the formation of amorphous mesoporous 303
alumino-silicates. It is observed that the presence of nitrogen functionality does not facilitate 304
better adsorption of CO2. The optimized loading of functionalized molecule along with the 305
availability of adsorption pores (sites) facilitates the CO2 adsorption process. 306
307
ACKNOWLEDGEMENT 308
The authors acknowledge the support extended by Director, NEERI for his 309
encouragement. They also acknowledge the support extended by Dr. Wadodkar, JNARDDC, 310
Nagpur and Dr. Peshwe and Miss Gauri Deshmukh from VNIT, Nagpur for providing 311
characterization results. They acknowledge the facilities provided by Dr. Trevor Drage, 312
Associate Professor at Department of Chemical and Environmental Engineering and Dr. Lee 313
Stevans, University of Nottingham, UK. One of the authors Mr. Vivek Kumar would also 314
like to kindly acknowledge the Council of Scientific and Industrial Research (CSIR), India 315
for granting Senior Research Fellowship to him. 316
317
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326
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18. Chatti, Ravikrishna; Bansiwal, Amit K.; Thote, Jayashri A.; Kumar, Vivek; Jadhav, 376
Pravin; Lokhande, Satish K.; Biniwale, Rajesh B.; Labhsetwar, Nitin K.; Rayalu, 377
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35. Gray , M.L. ; Soong, Y. ; Champagne, K.J. ; Baltrus, John ; Stevens, R.W. ; Jr 422
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capture from high carbon fly ashes, Waste Management, 2008, 28, 2320–2328. 428
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432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
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List of tables: 447
Table 1: CO2 adsorption capacities of different alumino-silicate adsorbents under various 448
experimental conditions 449
Table 2: BTC results for Fly ash based alumino-silicates with 15% CO2 450
Table 3: BTC results for FAS-AMP-30 with 15% CO2 451
Table 4: Textural properties of FAS-bare and FAS-AMP-30 adsorbents 452
Table 5: Chemical analysis of FAS adsorbents 453
454
List of figures: 455
Figure 1: Experimental setup used for breakthrough adsorption studies 456
Figure 2: Breakthrough curve for FAS-AMP-30 at different temperature 457
Figure 3: XRD comparison of FAS-bare and FAS-AMP-30 458
Figure 4: N2 adsorption isotherm for FAS-bare 459
Figure 5: N2 adsorption isotherm for FAS-AMP-30 460
Figure 6: Pore size distribution curve for FAS-bare 461
Figure 7: Pore size distribution curve for FAS-AMP-30 462
Figure 8: Thermal stability of FAS-bare and FAS-AMP-30 adsorbents 463
Figure 9: SEM image of A) FAS bare and B) FAS-AMP-30 464
Figure 10: Comparative FTIR of FAS bare and FAS-AMP-30 465
Figure 11: FTIR of CO2 adsorbed FAS-AMP-30 466
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Table 1: CO2 adsorption capacities of different alumino-silicate adsorbents under various experimental conditions
S.No. Type of alumino-
silicate
Adsorption temperature and experimental
conditions
Adsorption capacity
(mg/g) Reference
1
NaX
NaX
Na-ZSM-5
H-ZSM-5
H-ZSM-5
Volumetric method
304.4 K,214.38 Torr
305.8 K,213.87 Torr
297.1 K,235.14 Torr
296.9 K,230.47 Torr
295.5 K, 140.95 Torr
205.7 mg/g
203.2 mg/g
63.2 mg/g
48.8 mg/g
38.3 mg/g
Dunne et al.(1996)
(Ref.24)
2
4A
5A
13X
NaY
USY
Na-Modernite
H- Modernite
60°C
TPD procedure
42.3 mg/g
22.73 mg/g
32.03 mg/g
3.75 mg/g
0 mg/g
62.86 mg/g
1.779 mg/g
Wang et al.(1998)
(Ref.25)
3
ZAPS(erionite)
ZNT(modernite)
ZN-19(clinoptilolite)
17°C ,
Volumetric system
134 mg/g
84.2 mg/g
78.2 mg/g g
Hernandez-Huesca et al.
(1999)
(Ref.26)
4
Li-ZSM-5
Na -ZSM-5
K-ZSM-5
Rb-ZSM-5
Cs-ZSM-5
30°C
to 150°C
GC method For 0.5 MPA
35.59 mg/g
35.59 mg/g
29.66 mg/g
29.66 mg/g
7.908 mg/g
Katoh et al.(2000)
(Ref.27)
5
13 X
FTIR , 22°C
13.6 mg/g
Rege & Yang (2001)
(Ref.28)
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6
13 X
Static volumetric method
0°C
20°C
40°C
60°C
80°C
140.8 mg/g
(20.35kPa)
114.9 mg/g
(20.43 kPa)
95 mg/g
(23.66kPa)
74.4 mg/g
(27.00kPa)
58.1 mg/g
(23.85 kPa)
Lee et al.(2002)
(Ref.29)
7
13 X
PSA
30°C
40°C
50°C
184.8 mg/g
202.4mg/g
228.8 mg/g
Ko et al.(2003)
(Ref.30)
8
5A
MRI technique at 2 atm and by adsorption of 13
CO2, 25°C
290 mg/g
Cheng et al.(2005)
(Ref.31)
9
4A
5A
13X
APG-II
WE-G 592
TPD studies at 120°C
30.8 mg/g
16.7 mg/g
22 mg/g
26.4 mg/g
16.7 mg/g
Siriwardane et al.(2005)
(Ref.32)
10
13X
13X
Breakthrough studies
30°C
75°C
55 mg/g
15 mg/g
Rayalu et al.(2007)
(Ref.33)
11
FAS-bare
FAS-AMP-30
FAS-AMP-30
FAS-AMP-30
Breakthrough studies
55°C
30°C
55°C
75°C
6.62 mg/g
10.8 mg/g
26.5 mg/g
22.6 mg/g
Present study
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Table 2: BTC results for Fly-ash based alumino-silicates with 15% CO2
Material Feed flow rate
(ml/min)
Adsorption
temperature (0C)
Adsorption capacity
(mg/g)
FAS- bare 20 55 6.62
FAS-APTES-10 20 55 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 20 55 24.2
FAS-AMP-30 20 55 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
Table 3: BTC results for FAS-AMP-30 with 15% CO2
Material Feed flow rate
(ml/min)
Adsorption
temperature (0C)
Adsorption capacity
(mg/g)
FAS-AMP-30 20 30 10.8
FAS-AMP-30 20 55 26.5
FAS-AMP-30 20 75 22.6
FAS-AMP-30 20 55 34.82*
* In presence of 3% water vapor
Table 4: Textural properties of FAS-bare and FAS-AMP-30 adsorbents
Adsorbent Vtot (cm3/g)
b SBET (m
2/g)
c DBJH (nm)
d
FAS- bare 0.003262 0.5413 24.20
FAS-APTES-25 0.007270 2.07 14.03
FAS-TRIS-25 0.002883 1.4237 8.09
FAS -AMP-30 0.207041 91.3743 9.26
a Nitrogen, Carbon and Hydrogen content measured by elemental analysis
b Total pore volumes calculated as the amount of N2 adsorbed at P/Po = 0.99
c Brunauer-Emmet-Teller (BET) surface areas
d Pore diameter calculated by Barett-Joyner-Halenda (BJH) method using the adsorption
branches
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Temperature
Controller
To TCD-GC
Sample
Selector
MFC
MFC MFC
CO2
N2
Mixer
Tubular
Furnace
Auto-sampler
valve on GC
Stream for
feed Analysis
Table 5: Chemical analysis of FAS adsorbents
Adsorbent 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 0.87 5.11 1.24 0.17
FAS -AMP-25 2.78 6.44 4.54 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
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Fig 1: Experimental setup used for breakthrough adsorption studies
Fig 2: Breakthrough curve for FAS-AMP-30 at different temperature
Calcium
Sodium
Aluminate
Charoite
Tarasovite
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Fig 3: XRD comparison of FAS-bare and FAS-AMP-30
Figure 4: N2 adsorption isotherm for FAS-bare
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Figure 5: N2 adsorption isotherm for FAS-AMP-30
Figure 6: Pore size distribution curve for FAS-bare
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Figure 7: Pore size distribution curve for FAS-AMP-30
Fig 8: Thermal stability of FAS-bare and FAS-AMP-30 adsorbents
Fig 9: SEM image of A) FAS bare and B) FAS-AMP-30
A B
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4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 450.0
cm-1
%T
FAS BARE
FAS AMP
Fig 10: Comparative FTIR of FAS bare and FAS-AMP-30
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 450.0
cm-1
%T
3960.80
3746.02
3283.58
2947.54
2886.61
2825.68
1647.74
1577.00
1558.96
1551.32
1476.83
1407.04
1379.48
1307.50
1087.39
812.89
651.06
631.11
616.87
595.17
588.94
575.33
518.59
488.18
482.86
474.81
468.12
456.04
Fig 11: FTIR of CO2 adsorbed FAS-AMP-30
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