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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

318

319

320

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326

REFERENCES 327

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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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derived carbon materials, Fuel, 2005, 84, 2204–2210. 426

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capture from high carbon fly ashes, Waste Management, 2008, 28, 2320–2328. 428

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solutions of various salinities: Precipitation rates and overgrowth compositions, 430

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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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