Fractionation of Asphaltene by Adsorption onto Silica and Chemical

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Fractionation of Asphaltene by Adsorption onto Silica and Chemical Characterization by APPI(+)FT-ICR MS, ATR-FTIR and 1H-NMR Priscila T. H. Nascimento, Alexandre Ferreira Santos, Carlos Itsuo Yamamoto, Lilian V Tose, Eliane V. Barros, Gustavo R Gonçalves, Jair C. C. Freitas, Boniek G. Vaz, Wanderson Romão, and Agnes P. Scheer Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b00523 • Publication Date (Web): 14 Jun 2016 Downloaded from http://pubs.acs.org on June 15, 2016

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Scheme of fractionation of asphaltene by adsorption onto silica particles 288x194mm (150 x 150 DPI)

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Fractionation of Asphaltene by Adsorption onto Silica and

2

Chemical Characterization by APPI(+)FT-ICR MS, ATR-FTIR

3

and 1H-NMR

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4 5

Priscila T. H. Nascimento1†, Alexandre F. Santos1, Carlos I. Yamamoto1, Lilian

6

V. Tose,2 Eliane V. Barros,2 Gustavo R. Gonçalves,2,3 Jair C. C. Freitas,3

7

Boniek G. Vaz,4 Wanderson Romão,2,5‡ Agnes P. Scheer1.

8 9

1

Department of Chemical Engineering, Federal University of Parana, 81.531-

10

990, Curitiba, PR, Brazil

11

2

12

Federal University of Espírito Santo, 29075-910 Vitória, ES, Brazil

13

3

14

Federal University of Espírito Santo, 29075-910, Vitória, ES, Brazil

15

4

16

Brazil.

17 18

5

Petroleomic and Forensic Chemistry Laboratory, Department of Chemistry,

Laboratory of Carbon and Ceramic Materials, Department of Physics,

Chemistry Institute, Federal University of Goiás, 74001-970, Goiânia, GO,

Federal Institute of Espírito Santo, 29106-010 Vila Velha – ES, Brasil.

19 20

Corresponding author:

21

†

22

‡

[email protected] W. R [email protected] / Phone: + + 55-27-3149-0833

23 24

1 ACS Paragon Plus Environment

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Abstract

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Asphaltenes are defined as the petroleum fraction insoluble in n-

28

alkanes and soluble in aromatic solvents such as toluene. Such definition

29

implies that asphaltenes are not a homogeneous material but a mixture of

30

fractions. Asphaltenes represent one of major contributors to several

31

problematic issues for the petroleum industry. Destabilized asphaltenes can

32

cause arterial clogging within pipelines and wellbores, corrosion and fouling of

33

production equipment, reduction of catalyst activity in refining processes, and

34

others problems. This work describes an investigation of the separation of

35

asphaltenes into three different fractions by adsorption onto silica particles.

36

These fractions (two adsorbed and one non-adsorbed onto silica) were

37

characterized by elemental analysis (C, H and N), Fourier transform infrared

38

spectroscopy coupled to attenuated total reflectance (ATR-FTIR), 1H Nuclear

39

magnetic resonance (1H-NMR) spectroscopy and atmospheric pressure

40

photoionization Fourier transform ion cyclotron resonance mass spectrometry

41

(APPI-FT-ICR MS). APPI-FT-ICR MS and ATR-FTIR accessed chemical

42

information on a molecular level (molecular formula, carbon number, double

43

bond equivalent (DBE) distribution, and organic groups), whereas 1H-NMR

44

and elemental analysis provided the aromaticity degree and C/H atomic ratio

45

of the samples, respectively. The C/H atomic ratio decreases in the following

46

the order: non-adsorbed > whole asphaltene > adsorbed > irreversibly

47

adsorbed. Irreversible fraction adsorbed had the lowest percentage of

48

aromatic hydrogen compared to other fractions by 1H-NMR. There was a

49

good correlation between the results of NMR and elemental analysis. The


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efficiency of fractionation on silica particles was proven to be successful by

51

the low concentration of polyaromatic hydrocabons observed for two samples

52

adsorbed onto silica as well as by the increasing of aromaticity degree and

53

C/H ratio for non-adsorbed fraction. N2, N2O and NO compounds classes

54

were selectively separated from whole asphaltene and concentrated in polar

55

fractions (adsorbed fractions onto silica) having their carbon number and DBE

56

distribution reported. Therefore, this work demonstrated the selectivity of the

57

fractionation method onto silica to retain highly polar compounds and,

58

moreover, extends to the study of adsorbent surface and how the molecules

59

of the asphaltenes will behave against this change.

60 61 62

Key-words: fractionation; silica; asphaltene; APPI(+)-FT-ICR MS; NMR;

63 64 65 66 67 68 69 70 71 72 73 74


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1. Introduction

77

Asphaltenes are defined as the petroleum fraction insoluble in n-

78

alkanes such as n-pentane, n-hexane or n-heptane and soluble in aromatic

79

solvents such as toluene. 1 -5 The definition of this fraction implies that

80

asphaltenes are not a homogeneous material but a mixture of sub-fractions. It

81

is well recognized that asphaltenes comprise a major portion of surface-active

82

crude oil components and they are the largest, densest, most polar, and

83

aromatic components of crude oils, including polyaromatic compounds of

84

large molecular weight, ranging from 500 to 2000 g/mol. The molecules are

85

composed of fused aromatic rings linked with aliphatic chains and naphthenic

86

rings. They include a large variety of chemical species, containing sulphur,

87

nitrogen, metals and functional groups such as acids and bases.1

88

Asphaltenes are major contributors to several problematic issues in the

89

petroleum industry. Complications related to asphaltenes stability within the

90

supporting oil matrix affect the entire production chain, starting from the

91

reservoir where they can reduce oil recovery through changes in wettability of

92

mineral surfaces of reservoir, plugging of the wellbores,6 to asphaltene

93

deposition within wells. Destabilized asphaltenes can cause arterial clogging

94

within pipelines and wellbores,5 sedimentation and plugging during crude oil

95

storage, corrosion and fouling of production equipment, reduction of catalyst

96

activity in refining processes, and coke formation.1 On the other hand,

97

asphaltenes are suspected to hinder agglomeration between gas hydrate

98

particles in oil production pipelines, thus preventing the formation of solid


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99 100

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plugs, which would result in the blockage of the lines. Most of these effects are due to their surface-active properties.7

101

The adsorption of asphaltenes onto a surface is governed by both their

102

chemical and structural characteristics and the chemical and physical

103

properties of the sorbent.1 From studies of adsorption of asphaltenes, both

104

monolayer and multilayer adsorptions are reported, depending on the solvent

105

and source of asphaltenes.8,9,10a

106

Nordgard et al. synthesized model compounds with a molecular

107

structure similar to asphaltenes to simulate the behavior of adsorbent

108

surfaces. The model compounds consisting of a polyaromatic core (perylene-

109

based) with a fixed hydrophobic part on one side and branched alkyl chains of

110

varying end groups (acidic-end or aliphatic-end). The acid group prefers polar

111

systems and the polyaromatic cores stack normal to the surface. Although the

112

identification of asphaltene groups that effectively interact with the mineral

113

surface is not yet totally clear, an effective characterization technique should

114

be adopted aiming at a fine identification of such groups.10b

115

Padilla et al. searched the sorption properties and rheology of the

116

acidic polyaromatic compound (C5PeC11), which displays the type of surface

117

and interfacial tension activities according to pH. The adsorption interactions

118

compound C5PeC11 were evidenced by desorption experiment in the

119

oil/water interface.10c

120

In 2016, Subramanian et al. have developed a new fractionation

121

procedure based on adsorption of asphaltenes onto calcium carbonate. FTIR

122

analysis indicated that the sub-fractions obtained differed in the amount of

123

carbonyl, carboxylic acid or derivative groups present in them. The asphaltene


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fraction with highest concentration of carbonyl, carboxylic acid or derivative

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groups formed visco-elastic layers on stainless steel and also exhibited

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maximum adsorption (around 8 mg/m2) and the results obtained from QCM-D

127

measurement suggest that the interaction of the asphaltene sub-fractions tend

128

to prevent an adsorption of unfractionated asphaltenes onto stainless steel.10d

129

Dudásová et al.9 and Simon et al.8 reported the monolayer formation or

130

an “effective” monolayer, following a Langmuir behavior. This behavior is

131

similar to that suggested by Adams.4 Acevedo et al.6 and Behabahani et al.10a

132

on the other hand, reported multilayers formation. However, as discussed in

133

the literature, multilayer behavior can be only a manifestation of larger

134

aggregates.4

135

Although the identification of asphaltene groups that effectively interact

136

with the mineral surface is not yet totally clear, an effective characterization

137

technique should be adopted aiming at a fine identification of such groups.

138

Characterization techniques based on Fourier transform ion cyclotron

139

resonance mass spectrometry (FT-ICR MS) offer a reliable tool for the

140

resolution and elemental composition assignment of thousands of species in

141

petroleum-derived materials, enabling a molecular level analysis of complex

142

petroleum mixtures such as asphaltenes.11,12 Although elemental composition

143

does not by itself yield structural information, it provides visualization of

144

carbon number and aromaticity patterns within compositional heteroatom

145

“classes” (i.e., CcHhNnOoSs) and DBE (double bond equivalent), facilitating

146

material classification by heteroatom content and the degree of aromaticity.13-

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17


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In this work, the separation of asphaltenes into different fractions by

149

adsorption onto silica particles has been investigated. Besides, these fractions

150

were characterized by elemental analysis (C, H and N), Fourier transform

151

infrared spectroscopy coupled to attenuated total reflectance (ATR-FTIR), 1H

152

Nuclear magnetic resonance (1H-NMR) spectroscopy, and atmospheric

153

pressure photoionization Fourier transform ion cyclotron resonance mass

154

spectrometry (APPI-FT-ICR MS), to explore the interaction between the

155

different polar groups existing in asphaltene and the silica surface.

156 157

2. Experimental

158

2.1 Chemicals Asphaltene

159

extraction

from

crude

oil

was

done

using

160

n-hexane (Vetec PA). For asphaltene fractionation, silica Aerosil®200 (Evonil

161

Industries, Germany), toluene (VETEC 98 %), tetrahydrofuran (Neon 99.9 %),

162

Chloroform (Biotec 99%), Sodium hydroxide (Sigma-Aldrich > 99%).

163 164

2.1.2 Particles – adsorbents The particles used for adsorption in this work were made of hydrophilic

165

silica,

Aerosil®200

166

fumed

(Evonil

Industries,

Germany),

and

their

167

physicochemical characteristics are summarized in Table 1. The specific

168

surface area was determined by N2 adsorption on Micromeritics TriStar 3000

169

instrument, and was calculated based on the BET (Brunauer-Emmet-Teller)

170

equation.26 The microporous volume was calculated by the t-plot method and

171

the pore size area distribution was obtained by Barret-Joyner-Halenda (BJH)


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analysis27

173

Instruments).

on

a

Quantachrome

NovaWin

analyzer

(Quantachrome

Table 1

174 175 176

2.2 Methods

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2.2.1 Asphaltene Extraction

178

Although several relevant papers used n-heptane as a solvent,18-25 and

179

different solvent oil ratio, the asphaltene extraction procedure was performed

180

in accordance to that described by Hannisdal et al., 200519 and Simon et al.,

181

2010.18 Brazilian asphaltene was extracted from a light crude oil. SARA

182

analysis of this crude oil was performed at Petrobras R & D Center, where a

183

standard chromatographic procedure has earlier been developed for the

184

semipreparative separation of crude oils and related materials into the four

185

SARA fractions: saturates, 62.9 wt %; aromatics, 18.4 wt %; resins, 17.9 wt

186

%; and asphaltenes, 0.71 wt %. Other physico-chemical properties of crude

187

oil are describes in Table 1S (supplementary material).

188

For obtaining the asphaltene fraction, the crude oil was initially heated

189

up to 60 °C, for at least one hour, and shaken to ensure homogeneity in the

190

sample. A 160 mL portion of n-hexane was added to 4 g of crude oil sample

191

and stirred for 24 h at room temperature. After mixing, the asphaltene fraction

192

was separated from the maltene using a 45 µm (Sartorius Stedium)

193

membrane filter. Other crude oil components were removed completely by

194

washing the asphaltene with n-hexane at 60 °C. Finally, the asphaltene was

195

dried in a desiccator until the sample mass remained constant.


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2.2.2 Determination of asphaltene adsorption by means of UV

198

spectrometry

199

The adsorption experiments were carried out at constant particle mass

200

(35 mg). Toluene was used as solvent in which solutions with initial

201

asphaltene concentrations in the range of 0.2 – 4.0 g/L were prepared. The

202

particles were shaken to be in contact with asphaltene solutions (10 mL per

203

sample) at 22 °C for 24 h to reach the saturation point. After that, the solids

204

were separated by centrifugation for 20 min at 4000 rpm. The amount of

205

adsorbed asphaltenes was calculated from the difference of asphaltene

206

solution concentrations before and after the adsorption. UV spectroscopy

207

(UV 1800, Shimadzu) was used to determine the concentration by evaluating

208

the absorbance at λ= 336 nm. 9,28,29 The amount of asphaltenes adsorbed on

209

the particles was calculated using the following equation: (1)

210

In this expression, C0 and C are the initial and supernatant concentrations

211

(g/mL), respectively, V is the solution volume (mL), m is the mass of particles

212

(g) and Asp is the particle specific surface area (m2/g).

213 214

2.2.3 Development of the separation technique

215

The procedure to separate the asphaltene surface active fraction from

216

the non-active fraction is based on adsorption of the surface active asphaltene

217

onto silica to provide three main fractions: non-adsorbed, adsorbed and

218

irreversibly adsorbed. First, the whole asphaltene is “putted” into silica; the

219

active fraction is adsorbed onto the polar surface while the non-active fraction 9 ACS Paragon Plus Environment

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is not adsorbed. The non-active fraction is simply recovered by centrifugation

221

and solvent evaporation. The active one is obtained by using THF to make the

222

asphaltene desorbed. The fractionation is finally obtained after THF

223

evaporation. The irreversible active fraction is obtained by using a mixture of

224

THF, CCl3 and NaOH 1M. The quantity of asphaltene was determined by UV

225

spectroscopy and by gravimetry. This procedure is summarized in Figure 1. Figure 1

226 227

2.2.4 Elemental analysis (C,H and N)

228

The contents of carbon (C), hydrogen (H), and nitrogen (N) were

229

analyzed using an elemental analyzer LECO CHNS 932.15 The analyzes were

230

conducted with use of helium and ultrapure oxygen (99.9999%) as carrier and

231

burning gases, respectively; and the oxidation temperature was 1100 °C. The

232

instrument was calibrated using acetanilide.14 The C, H, and N contents were

233

expressed in wt % and calculated from the average of measurements done in

234

triplicate.

235 236 237

2.2.5 1H Nuclear magnetic resonance (1H NMR) 1

H NMR spectra for asphaltene samples and its fractions (non-

238

adsorbed, adsorbed, and irreversibly adsorbed) were recorded on a Varian

239

VNMRS 400 spectrometer, operating at 9.4 T using 5 mm broadband 1H/X/D

240

probe. The experiments were performed at 25 °C, using 20 mg of asphaltene

241

diluted in 0.6 mL of deuterated chloroform. Tetramethylsilane (TMS) was used

242

to reference the chemical shifts. A spectral width of 6410.3 Hz was used with

243

a relaxation delay of 1.5 s and 512 scans were used. The relaxation agent

244

Cr(Acac)3 diluted in deuterated chloroform at 50 mM was also employed.14


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The degree of aromaticity (%) of asphaltene and its fractions were determined

246

through the integration of spectra from 9.0 to 6.0 ppm (for aromatic hydrogen)

247

and from 4.0 to 0.0 ppm (for aliphatic hydrogen). This procedure was

248

analogous to the one described by Oliveira et al.30

249

2.2.6 ATR-FTIR

250

For the FTIR studies, an ABB BOMEN IR (FTLA2000-102 model)

251

spectrometer coupled to a MIRacle attenuated total reflectance (ATR)

252

accessory was used. Whole asphaltene sample and its respective fractions

253

were placed under a single-reflection zinc selenide crystal plate, and a total of

254

15 scans were taken. The spectra were recorded from 4000 to 650 cm-1 in

255

transmission mode with a resolution of 4 cm-1. The background was

256

determined by experiments performed in air, which were conducted before

257

each sample was analyzed.31 The ATR-FTIR spectra were acquired using

258

GRAMS/AI software (Thermo Galactic).

259 260

2.2.7 APPI(+)FT–ICR MS

261

FT-ICR MS analysis was performed on a 9.4 T Q-FT-ICR MS hybrid

262

(Solarix, Bruker Daltonics, Bremen, Germany) instrument equipped with a

263

commercially available APPI14 source set to operate over a mass region of

264

m/z 200-1200. FT-ICR mass spectra of the whole the asphaltene and the

265

three fractions were acquired using positive ionization mode, APPI (+).

266

The whole asphaltene and its respective fractions were diluted to 0.5 mg

267

mL-1 in toluene. After, they were sonicated for 5 min and directly infused at a

268

flow rate of 10 µL min-1. The APPI(+) source conditions were as follows:

269

nebulizer gas pressure of 1.5 bar, capillary voltage of 3.5 kV, transfer capillary 11 ACS Paragon Plus Environment

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temperature of 250 °C and Krypton photoionization lamp. The ions were

271

accumulated in the hexapolar collision cell with time of 0.060 s followed by

272

transport to the analyzer cell (ICR) through the multipole ion guide system

273

(another hexapole). Each spectrum was acquired by accumulating 200 scans

274

of time-domain transient signals in 4 mega-point time domain data sets. The

275

front and back trapping voltages in the ICR cell were +0,80 V and +0,85 V. All

276

mass spectra were externally calibrated using a NaTFA solution 0.05 mg/mL

277

(m/z from 200 to 1200) after which they were internally recalibrated using a

278

set of the most abundant homologous alkylated compounds for each

279

sample.14,15 Mass spectra were acquired and processed using a custom

280

algorithm developed specifically for petroleum data processing, Composer

281

software (Sierra Analytics, Modesto, CA, USA). DBE versus carbon number,

282

DBE versus intensity and heteroatomic-containing compounds profile

283

diagrams were constructed to visualize and interpret the MS data.14,15 The

284

unsaturation level of each compound can be deduced directly from its DBE

285

value according to equation 2:

286

DBE = c – h/2 + n/2 + 1

(2)

287

Where c, h, and n are the number of carbon, hydrogen, and nitrogen atoms,

288

respectively, in the molecular formula.

289 290

3. Results and Discussion

291

3.1 Adsorption Isotherm

292

The adsorption isotherm was successfully fit to the Langmuir equation

293

R2 = 0.998, data not shown. The experiments, however, evidenced the


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294

occurrence of an “effective” monolayer adsorption regime; as discussed by

295

Adams, 2014.4

296

The maximum amount adsorbed on the particles (Γmax) is 2.9 mg/m²

297

and the affinity constant is 3.73 mL/mg. These results are consistent with the

298

reported, where values lower than 3.6 mg/m2 are expected for asphaltenes in

299

good solvents.

300

Table 2 shows the yield of different asphaltene fraction quantified both

301

by UV spectroscopy and gravimetry analyzes. The minor difference between

302

values obtained by the two methods can be attributed to the calibration curve

303

used for UV spectroscopy once this curve was done with unfractionated

304

asphaltenes and it is likely that the asphaltene fractions have a lightly different

305

response factor in UV.

306

Table 2.

307 308

3.2 Elemental analysis and 1H NMR

309

Whole asphaltene and its fractions (adsorbed, irreversibly adsorbed,

310

and non-adsorbed) were also characterized by elemental analysis and 1H

311

NMR spectroscopy; and the results are described in Tables 3 and 4,

312

respectively. Regarding the elemental contents, Table 3 shows that higher

313

carbon and hydrogen contents were observed for the whole asphaltene and

314

the non-adsorbed fraction (C = 80.0 and 81.0 wt. %, and H = 8.6 and 8.6

315

wt. %, respectively). Additionally, the C/H atomic ratio follows the order: non-

316

adsorbed > whole asphaltene > adsorbed > irreversibly adsorbed.

317

Table 3

318


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The aromaticity degree (%) or aromatic hydrogen content (Har, in at. %)

320

of whole asphaltene and its three fractions are shown in Table 4. Note that

321

the non-adsorbed fraction (Har = 9.5 at. %) is more aromatic than its original

322

asphaltene (Har = 6.3 at. %). In contrast, lower aromatic hydrogen content is

323

observed for the fraction irreversibly adsorbed onto silica (Har = 5.4 molar %).

324

This indicates that this fraction has a slightly higher aliphatic character

325

compared to remaining fractions. When confronting the 1H NMR data to the

326

results of elemental analysis, a good correlation is observed between Har

327

values and C/H atomic ratio,14 evidencing that the adsorption onto silica

328

particles is preferential for the less aromatic hydrogen asphaltene fractions.

329

Table 4 shows also the Hγ, Hβ and Hα contents, which allow the

330

prediction about the asphaltene structural model (islands or continental).30

331

The high aliphatic hydrogen content, Halk, (in all cases higher than 90 at.) and

332

the low percentage of hydrogens in α position, Hα, in relation to quantities of

333

hydrogen atoms in the positions β and γ, Hβ and Hγ, suggest a large number

334

of condensed aromatic rings, greatly reducing the relative amount of aromatic

335

hydrogens per ring. Therefore, these results are consistent with the

336

continental structure.30,32,33 Table 4

337 338 339 340

3.3 ATR-FTIR

341

Figure 2a-d shows ATR-FTIR spectra of whole asphaltene and its

342

fractions. The main bands identified in the ATR-FTIR spectrum of whole

343

asphaltene are at 3367, 2955, 2918, 2850, 1629, 1458, 1375, 868, 808 and

344

720 cm-1. Table 2S (supplementary material) shows the band assignments for


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345

the ATR-FTIR spectra of whole asphaltene and its fractions.34-36 Methylene

346

and methyl groups (CH2 and CH3) can be identified at 2955, 2912 and 2850

347

cm-1 (asymmetric and symmetric stretching) and also at 1458 and 1375 cm-1

348

(bending). At 1629 cm-1 and 950-700 cm-1 regions, bands from stretching and

349

out of plane bending for N-H and C-H aromatic bonds are observed,

350

respectively. The band at ∼868 cm-1 suggests the presence of aromatic rings

351

with one isolated hydrogen, i.e., penta-substituted rings. The band with a

352

maximum at 808 cm-1 may be attributed to systems containing two or three

353

adjacent aromatic hydrogens, i.e., tri- and tetra-substituted rings. Finally, a

354

sharp band associated with rocking frequency of the chains with more than

355

three contiguous methylene groups is detected at 720 cm-1, Figure 2a. A

356

suitable analysis of this region can provide important conclusions about

357

condensation of aromatic rings in asphaltenes.36

358

For adsorbed and irreversibly adsorbed fractions, which, as discussed

359

above, presented lower C/H atomic ratios, new bands at 1744-1733, 1258,

360

1092-1088 and 1021-1014 cm-1 are clearly detected corresponding to polar

361

groups. Bands in the region around 1740 cm-1 and 1258 cm-1 are attributed to

362

C=O and -(C-O-C)ar- stretchings, respectively, whereas that bands in 1092-

363

1088 cm-1 and 1021-1014 cm-1 regions are attributed to C-N and S-O

364

stretchings, respectively, Figure 2b-c. Therefore, these fractions can be

365

considered to be the most polar fractions. Additionally, a strong band at 798

366

cm-1 is also detected, corresponding to aromatic system.34 Similar to whole

367

asphaltene, the O-H stretching37 is also identified at ≈ 3300 cm-1 for the

368

irreversibly adsorbed fraction, as well as N-H stretching in region of 3646 cm-

369

1

. It is expected that the high polarity surface of silica, due mostly to the


Page 17 of 37

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Energy & Fuels

370

presence of silanol groups, and additional hydrated silanols (or SiOH−OH2

371

complexes),38-40 interact strongly with molecules containing basic nitrogen,

372

carbonyl carbons, fused aromatic rings, oxygen functionalities (carboxylic

373

acids, ketones), and metal complexes (such as vanadyl porphyrins).40-42

374

Finally, the ATR-FTIR spectrum of the non-adsorbed sample, Figure

375

2d, is quite similar to the other fractions, except in the regions around 3300

376

and 1740 cm-1, which correspond to hydroxyl and carbonyl groups, where no

377

absorption bands were observed. Additionally, the higher C/H ratio and

378

aromaticity degree of this sample can be directly linked with the intensity of

379

the bands in the 720-700 cm-1 region. Figure 2

380 381 382

3.4 APPI(+)FT-ICR MS

383

Figure 3a-d displays the APPI(+) FT ICR mass spectra of whole

384

asphaltene, Figure 3a, and its fractions (non-adsorbed, Figure 3b, adsorbed,

385

Figure 3c, and irreversibly adsorbed, Figure 3d). The FT ICR mass spectra

386

show broadband profiles from m/z 200-700 with an average molar mass

387

distribution (Mw) centered at approximately m/z 466, 509, 447 and 426 for the

388

whole asphaltene and the non-adsorbed, adsorbed and irreversibly adsorbed

389

fractions. Note that a higher Mw value is observed for the highly aromatic

390

fraction (non-adsorbed, Figure 3b), whereas lower Mw values correspond to

391

highly polar fractions (adsorbed, 3c, and irreversibly adsorbed onto silica).

392

Figure 3

393


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 37

394

Figure 4 presents the polar and nonpolar compounds class distribution

395

according to counts of assigned molecular formulas from APPI(+)FT ICR MS

396

data. APPI(+) promoted ionization via two mechanisms: protonation and

397

electron transfer, producing [M+H]+ and M•+ ions. Consequently, the classes

398

observed were identified as protonated, CLASS[H], and radical, CLASS•+.13-15

399

APPI(+) evaluated selectively the nonpolar compounds such as hydrocarbons

400

(HC and HC[H] classes), basic nitrogen compounds (N and N[H] classes), as

401

well as multi-heteroatomic compounds (N2, N2[H], N2O, N2O[H], NO and

402

NO[H] classes). A higher abundance of aromatic hydrocarbons and low

403

polarity compounds (HC, HC[H], N, and N[H] classes) is observed for whole

404

asphaltene and non-adsorbed fraction. On other hand, for fractions adsorbed

405

onto silica (adsorbed and irreversibly adsorbed), highly polar compounds (N2

406

N2[H], N2O, N2O[H], NO classes) were selectively retained and concentrated

407

on these fractions as shown in Figure 4.

408

Figure 4

409 410

Figure 5a-d displays the DBE abundance distributions of HC, HC[H],

411

Figure 5a, N, N[H], Figure 5b, N2, N2[H], Figure 5c, NO and NO[H], Figure

412

5d, classes of whole asphaltene and its three fractions. For HC/HC[H]

413

classes, Figure 5a, DBE distributions expose that polycyclic aromatic

414

hydrocarbons (PAHs) are more abundant in the whole asphaltene and in the

415

non-adsorbed fraction, with the abundance maximum centered on average at

416

DBE = 26-27. Similar behavior is also observed for N and N[H] classes,

417

Figure 5b, with an abundance maximum of DBE centered at 24-25 for the

418

whole asphaltene and the non-adsorbed fraction. For high polarity species


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Energy & Fuels

419

(N2/N2[H] classes), Figure 5c, a higher abundance and distribution of

420

compounds (DBE from 12 to 32) are detected in fractions adsorbed and

421

irreversibility adsorbed onto silica with a maximum DBE distribution at 24-25.

422

An analogous behavior is observed for NO/NO[H] class, Figure 5d.

423

Chacon-Patino et al.42 have reported the use of high performance thin

424

layer chromatography silica plates and an elutropic series of solvents

425

(hexane, toluene and CH2Cl2/MeOH) to fractionate asphaltenes according to

426

their particular affinity with the mobile and stationary phases. They observed

427

that for the polar non-eluted compounds and highly retained by the silica

428

surface with Rf = 0, exhibit molecular compositions with NnOo (o = 1, 2, 3 and

429

n = 1, 2) classes compared to the other subfractions. This result is similar to

430

observed in this work for fractions adsorbed onto silica particles. For eluted

431

compounds in CH2Cl2:MeOH and toluene and recovered from the silica, with

432

Rf = 0.69 and 0.90, respectively, they had predominantly HC, N1, N3, N1O1,

433

N3O1, N3O2, O1S1, O1S2, S1, NnOoS1 and OoS1 compound classes. Figure 5

434 435 436

Figure 6 illustrates the DBE versus the carbon numbers (CN) plots for

437

the most abundant classes of protonated molecules: HC[H], 6a, N[H], 6b,

438

N2[H], 6c and NO[H] classes, 6d.

439

APPI(+) data revels a higher amount of PAHs compounds (HC[H]

440

class, Figure 6a) for whole asphaltene and non-adsorbed fraction, with

441

distribution of carbon number (CN) ranging from C20 to C50 and DBE from 14

442

to 36. A similar behavior is observed for N[H] classes, where CN and DBE

443

ranges from C20 to C60 and from 8 to 34, respectively. For highly polar


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 37

444

asphaltene fractions (adsorbed and irreversibly adsorbed onto silica), low Mw

445

compound species corresponding to N[H], N2[H] and NO[H] classes are

446

selectively concentrated from asphaltene to adsorbed and irreversibly

447

adsorbed fractions with CN distribution of C24-C45, C15-C48 and C18-C45,

448

respectively, Figure 6b-d. This phenomenon is clearly observed in the

449

highlighted regions on DBE vs CN plots of N2 class (CN= 10-30 and DBE = 8-

450

20). As a consequence of this extraction, species of high aromaticity are

451

concentrated in the non-adsorbed fraction, being now detected (see the long

452

alkyl chains compounds of DBE = 20-30 that are highlighted in the red square

453

in Figure 6d, for instance).

454

Using the concept of planar slope, which the chemical imaging provides

455

a 45° line between the axes CN and DBE, a line was generated by connecting

456

the maximum DBE values at a given CN in the DBE versus carbon number

457

plots, allowing to extract the aromaticity degree from APPI(+)FT-ICR MS data.

458

This degree was obtained from the slopes of the lines determined by

459

DBE/carbon number ratio.15 The slopes of these lines were calculated by

460

linear regression and the values for protonated classes are shown in Figures

461

6a-d. In all cases, the slope is higher for the whole asphaltene and the non-

462

adsorbed fraction, as compared to the fractions adsorbed onto silica. These

463

results are in good agreement with elemental analysis the 1H NMR data,15

464

Tables 2 and 3, respectively. Figure 6

465 466 467

4 Conclusion


Page 21 of 37

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Energy & Fuels

468

Fractions of asphaltene with different surface-activity were successfully

469

obtained through adsorption on silica particles. The results of analysis by

470

APPI(+)FT-ICR MS,

471

asphaltenes and its fractions showed good correlation between the

472

techniques which provide the chemical information on a molecular level

473

(molecular formula, carbon number and DBE distribution), aromaticity degree

474

and C/H atomic ratio. It is important to emphasize that the adsorption on silica

475

particles is preferred in asphaltene fractions with a lower percentage of

476

aromatic hydrogen. The irreversible adsorbed fraction has a slightly higher

477

aliphatic character the other fractions. N2, N2O and NO compounds classes

478

were also selectively extracted from whole asphaltene to adsorbed and

479

irreversibly adsorbed fractions, where their carbon number and DBE

480

distribution ranging from C15 to C48 and from 12 to 34, respectively, were

481

evidenced.

1

H-NMR, ATR-FTIR and elemental analysis for the

482

The efficiency of the fractionation on silica was proven by the low

483

concentration of PAHs observed for fractions adsorbed and irreversibly

484

adsorbed onto silica particles, as well as the increasing of aromaticity degree

485

and C/H ratio for the non-adsorbed fraction. This demonstrates the selectivity

486

of the method to retain highly polar compounds and, moreover, extends to the

487

study of adsorbent surface and how the molecules of the asphaltenes will

488

behave against this change.

489 490 491 492

Acknowledgments Portions of this work were carried out as a part of the Joint Industrial Programme (JIP) Asphaltenes consortium “Improved Mechanisms

of


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Page 22 of 37

493

Asphaltene Deposition and Precipitation to Minimize Irregularities in

494

Production and Transport – A Cost Effective and Friendly Approach”

495

sponsored by the Norwegian Research Council (234112/E30) and the

496

following industrial sponsors AkzoNobel, British Petroleum, Canada Natural

497

Resources, Nalco Champion, TOTAL E&P Norge AS, Petrobras and Statoil.

498

Thanks are also due to CNPq and CAPES for their financial support.

499 500

5. References 1

Mullins, O. C. Annual Review Anal. Chem. 2011, 4, 393– 418.

2

Speight, J. G. The Chemistry and Technology of Petroleum. 4a ed. CRC

Press: Boca Raton, FL, 2007. 3

Akbarzadeh, K.; Hammami, A.; Kharrat, A.; Zhang, D.; Allenson, S.; Creek,

J.; Kabir, S.; Jamaluddin, A.; Marshall, A. G.; Rodgers, R. P.; Mullins, O. C.; Solbakken, T. Oilfield Review, 2007, 19, 22–43. 4

Adams, J. J. Energy Fuels, 2014, 28, 2831–2856.

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Sjöblom, J.; Aske, N.; Auflem, I.H.; Brandal, Ø.; Havre, T. E.; Sæther, Ø.;

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Simon, S.; Jestin, J.; Palermo, T.; Barré l. Energy Fuels 2009, 23, 306–313.

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Behbahani, T. J.; Behbahani, Z. J. Petroleum Coal 2014, 56, 459–466; 10b

Nordgard, Erland L.; Landsem, Eva; Sjöblom, Johan. Langmuir films of asphaltene model compounds and their fluorescent properties. Langmuir, 2008, v. 24, n. 16, p. 8742-8751;

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Pradilla, D.; Simon, S., Sjoblom; J.,

Samaniuk; J., Skrzypiec; M.; Vermant, J. . Sorption and interfacial rheology study of model asphaltene compounds. Langmuir, 2016;

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Simon, S.; Gao, B.; Sjöblom, J. Asphaltene fractionation based on adsorption onto calcium carbonate:Part 1. Characterization of sub-fractions and QCM-D 21 ACS Paragon Plus Environment

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Klein, G. C.; Kim, S.; Rodgers, R. P.; Marshall, A. G. Energy Fuels 2006,

20, 1973–1979. 12

Mullins, O.C.; Sheu, E. Y.; Hammami, A.; Marshall, A.G. Asphaltenes,

Heavy Oils, and Petroleomics, New York: Springer, 2007. 13

Cunico RL, Sheu EY, Mullins OC. Molecular weight measurement of UG8

asphaltene using APCI mass spectroscopy. Pet Sci Technol 2004, 22 (7- 8), 787–98. 14

Pereira, T. M. C.; Vanini, G.; Oliveira, E. C. S.; Cardoso, F. M. R.; Fleming,

F. P.; Neto, A. C.; Jr, V. L.; Castro, E. V. R.; Vaz, B. G.; Romão, W. Fuel 2014, 118, 348-357. 15

Tose, L. V.; Cardoso, F. M. R.; Fleming, F. P.; Vicente, M. A. ; Silva, S. R.

C.; Aquije, G. M. F. V.; Vaz, B. G.; Romão, W. Fuel 2015, 153, 346-354. 16

Dias, H. P.; Dixini, P. V.; Almeida, L.C.P.; Vanini, G.; Castro, E.V.R.;

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44, 1349-1357. 20

Ancheyta, J.; Centeno, G.; Trejo, F.; Marroquín, G.; García, A.; Tenorio, E.;

Torres, A. Energy Fuel 2002, 16, 1121-1127. 21

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Trejo, F.; Ancheyta, J.; Morgan, T. J.; Herod, A. A.; Kandiyoti, R. Energy

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Trejo, F.; Ancheyta, J.; Rana, M. S. Energy Fuel 2009, 23, 429-439.

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2011, 25, 3678–3686. 35

Chiaberge, S.; Guglielmetti, G.; Montanari, L.; Salvalaggio, M.; Santolini, L.;

Spera, S.; Cesti, P. Energy Fuels 2009, 23, 4486–4495. 36

Khvostichenko, D. S.; Andersen, S. I. Energy Fuels 2009, 23, 811–819.

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Shen, J.; Zettlemoyer, A.; Klier, K. J. Phys. Chem. 1980, 84, 1453−1459.

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Touchstone, J. C. Practice of thin layer chromatography; John Wiley &

Sons: New York, 1992. 41

Huo, C.; Zhang, H.; Zhang, H.; Zhang, H.; Yang, B.; Zhang, P.; Wang, Y.

Inorg. Chem. 2006, 45, 4735−4742. 42

Chacón-Patiño, M. L.; Blanco-Tirado, C.; Orrego-Ruiz, J. A.; Gómez-

Escudero, A.; Combariza, M. Y. Energy Fuels 2015, 29, 1323−1331. 10b

Nordgard, Erland L.; Landsem, Eva; Sjöblom, Johan. Langmuir films of

asphaltene model compounds and their fluorescent properties. Langmuir, 2008, v. 24, n. 16, p. 8742-8751.


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10c

J. .

Pradilla, D.; Simon, S., Sjoblom; J., Samaniuk; J., Skrzypiec; M.; Vermant, Sorption

and

interfacial

rheology

study

of

model

asphaltene

compounds. Langmuir, 2016. 10d

Subramanian, S.; Simon, S.; Gao, B.; Sjöblom, J. Asphaltene fractionation

based on adsorption onto calcium carbonate:Part 1. Characterization of subfractions and QCM-D measurements. Colloids and Surfaces A: Physicochem. Eng. Aspects, 2016, v. 495, p. 136–148 Figures and Tables Captions Figure 1. Scheme of fractionation of asphaltene by adsorption onto silica particles. Figure 2. Adsorption isotherm of asphaltene in toluene on the particles fitted with the Langmuir model with a coefficient of determination of R2= 0.998. Figure 3. ATR-FTIR spectra of (a) whole asphaltene and its fractions: (b) non-adsorbed; (c) adsorbed (d) and irreversibly adsorbed. Figure 4. APPI(+) FT ICR mass spectra of (a) whole asphaltene and its fractions: (b) non-adsorbed; (c) adsorbed (d) and irreversibly adsorbed. Figure 5. Class distribution for whole asphaltene and its fractions obtained from APPI(+) FT ICR MS data. Figure 6. Relative abundances for HC/HC[H] (a); N/N[H] (b); N2/N2[H] (c) and NO/NO[H] (d) compounds classes from APPI (+) FT ICR MS data of whole asphaltene and its fractions. Figure 7. DBE versus carbon number plots for HC[H] class (a); for N[H] class (b); for N2[H] class (c); for NO[H] class (d), generated from APPI(+)FT ICR MS data of whole asphaltene and its fractions. Table 1. Physicochemical characteristics of Aerosil®200. Table 2. Asphaltene fractionation yields.


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Page 26 of 37

Table 3. Elemental contents (in wt. %) for the whole asphaltene and its fractions (adsorbed, irreversibly adsorbed, and non-adsorbed). Table 4. Har, Halk, Hγ, Hβ and Hα contents (molar %) obtained from H1 NMR spectra of whole asphaltene and its fractions.

Figures

Figure 1


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Energy & Fuels

Figure 2


Energy & Fuels

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Page 28 of 37

C28H22N2O DBE = 19

C29H26N2 DBE = 18

C29H23NO DBE = 19

402.19528

a) Whole

402.20913

402.21168 402.22601 402.22161

402.19526 402.20913 402.21168

b) Non-adsorbed

402.22600 402.22161

402.19527

c) Adsorbed

402.20915

402.21168

402.22601

402.21168

402.22601

402.19528

c) Irreversibly Adsorbed 402.20913 402.17

402.19

402.21

402.23

402.25

Figure 3


Page 29 of 37

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Energy & Fuels

Figura 4


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a)

(b)

(c)

(d)

Page 30 of 37

Figura 5


Page 31 of 37

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Energy & Fuels

(a)

(b)

(c)

(d)

Figure 6


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 37

Tables

Table 1 Properties

Value

Specific surface area (m2/g)

193 ± 8

Mesoporous area (m2/g)

576

External surface area (m2/g)

154

Microporous surface area (m2/g)

223

Mesoporous volume (cc/g)

0.085

Microporous volume (cc/g)

0.013

Average mesoporous pore size (Å)

15.4

Average microporous pore size (Å)

9.7


Page 33 of 37

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Energy & Fuels

Table 2 Yields (%)

UV-VIS

Gravimetry

Non-adsorbed

47.3 ± 0.45

48.1 ± 1.1

Adsorbed

31.5 ± 1.4

32.1 ± 0.3

Irreversibly adsorbed

8.5 ± 0.7

10.2 ± 0.6

Total

87.3 ± 1.7

90.4 ± 0.6


Energy & Fuels

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Page 34 of 37

Table 3 Elemental

Whole

contents (wt. %)

Asphaltene

Carbon

80.0 ± 0.6

72.0 ± 0.1

75.3 ± 05

81.0 ± 0.1

Hydrogen

8.6 ± 0.4

8.0 ± 0.3

8.8 ± 0.2

8.6 ± 0.8

Nitrogen

1.74 ± 0.03

1.42 ± 0.01

1.25 ± 0.05

1.72 ± 0.06

C/H atomic ratio

0.78

0.76

0.72

0.79

Adsorbed

Irreversibly

Non-adsorbed

Adsorbed


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Energy & Fuels

Table 4 δ (ppm)

Whole asphaltene

Adsorbed

Irreversibly adsorbed

Non-adsorbed

HAr (6.0-9.0)

6.3

7.2

5.4

9.5

Halk (0.0-6.0)

93.8

92.8

94.6

90.5

Hγ (0.5-1.0)

17.3

17.2

15.1

16.9

Hβ (1.0-2.0)

55.5

60.9

68.8

57.0

Hα (2.0-4.0)

21.0

14.7

10.8

16.6


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Supplementary Material Table 1S. Physico-Chemical properties of crude oil Origin Saturates Aromatics Resins Asphaltenes Density Viscosity Viscosity (wt %) (wt %) (wt %) (wt %) (15 °C - (15 °C (60 °C g/cm³) mPas) mPas) Brazil 62.9 18.4 17.9 0.71 0.8899 133.62 21.26


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Energy & Fuels

Table 2S. Bands assignments for the ATR-FTIR spectra of whole asphaltene and its fractions.28-31 Wavenumbers (cm-1)

Assignment

3646

NH stretching

3367-3326

O-H stretching

2964-2955

R-CH3 asymmetric methyl stretching

2918-2914

R-CH2 asymmetric methylene stretching

2850

R-CH2 symmetric methylene stretching

1744-1733

C=O stretching

1629-1597

C=N or (C=C)ar stretching

1464-1456

RCH3 symmetric deformation bending

1375-1365

R-CH3 asymmetric deformation bending

1260-1258

-(C-O-C)ar- stretching

1092-1083

C-N stretching

1021-1014

(S-O) sulfoxide stretching

868-865 808-792 720

Car-H (1H) isolated hydrogen bending out of plane Car-H (2H or 3H) two or three adjacent hydrogens bending out of plane R(CH2)n-R rocking when n > 3


Fractionation of Asphaltene by Adsorption onto Silica and Chemical

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