Remediation of Petroleum-Contaminated Soil and Simultaneous

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Remediation and Control Technologies

Remediation of Petroleum-Contaminated Soil and Simultaneous Recovery of Oil by Fast Pyrolysis De-Chang Li, Wan-Fei Xu, Yang Mu, Han-Qing Yu, Hong Jiang, and John C. Crittenden Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b03899 • Publication Date (Web): 16 Apr 2018 Downloaded from http://pubs.acs.org on April 16, 2018

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Environmental Science & Technology

Remediation of Petroleum-Contaminated Soil and Simultaneous Recovery of Oil by Fast Pyrolysis

De-Chang Li, † Wan-Fei Xu, † Yang Mu, † Han-Qing Yu, † Hong Jiang †,* and John C. Crittenden ‡

†

CAS Key Laboratory of Urban Pollutants Conversion, Department of Chemistry,

University of Science and Technology of China, Hefei 230026, China. ‡

School of Civil and Environmental Engineering and the Brook Byers Institute for

Sustainable Systems, Georgia Institute of Technology, Atlanta, Georgia 30332-0595, United States. * Corresponding Authors E-mail Address: [email protected]

ACS Paragon Plus Environment


ABSTRACT 1

Petroleum-contaminated soil (PCS) caused by the accidental release of crude oil into

2

the environment, which occurs frequently during oil exploitation worldwide, needs

3

efficient and cost-effective remediation. In this study, a fast pyrolysis technology was

4

implemented to remediate the PCS and concurrently recover the oil. The remediation

5

effect related to pyrolytic parameters, the recovery rate of oil and its possible

6

formation pathway, and the physicochemical properties of the remediated PCS and its

7

suitability for planting were systematically investigated. The results show that 50.9%

8

carbon was recovered in oil, whose quality even exceeds that of crude oil. Both

9

extractable total petroleum hydrocarbon (TPH) and water soluble organic matter

10

(SOM) in PCS were completely removed at 500 oC within 30 min. The remaining

11

carbon in remediated PCS was determined to be in a stable and innocuous state,

12

which has no adverse effect on wheat growth. Based on the systematically

13

characterizations of initial PCS and pyrolytic products, a possible thermochemical

14

mechanism was proposed which involves evaporation, cracking and polymerization.

15

In addition, the energy comsumption analysis and remediation effect of various PCSs

16

indicate that fast pyrolysis is a viable and cost-effective method for PCS remediation.

17 18


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19

TOC Art

20 21



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22 23

INTRODUCTION

24

Petroleum-contaminated soil (PCS) caused by the accidental release of crude oil into

25

the environment, which occurs frequently during oil exploitation worldwide.1,2 The

26

petroleum contaminants in the soil are harmful to the environment in three ways.3, 4

27

First, the majority of the petroleum components remain in the soil pore space in their

28

original liquid oil state, stunting the growth of soil microbes, plants and animals.

29

Second, a fraction of the petroleum hydrocarbons, including benzene, toluene,

30

ethylbenzene and xylene, dissolve in the soil moisture or groundwater, polluting the

31

groundwater and directly affecting human health.5,6 Finally, some evaporable

32

hydrocarbons volatilize into the atmosphere.7

33

Most petroleum contaminants are biodegradable over time, and many researchers

34

have reported the feasibility of PCS bioremediation with microbes or plants.8,9 The

35

major challenge for PCS bioremediation is the poor bioavailability and long

36

degradation period due to the inefficient air permeability of PCS and mass transfer

37

efficiency.10 Additionally, the existence of some components that are biologically

38

recalcitrant and seriously toxic, such as polycyclic aromatic hydrocarbons, decrease

39

the bioremediation efficiency.11,12 To reduce the remediation time, a series of

40

physicochemical

41

extraction,16,17 and chemical oxidation,18,19 have been developed for soil remediation.

42

Despite the efficiency of these methods, the pollution problems are not fully

43

addressed because the pollutants are merely transferred and post-treatments are still

44

necessary. In addition, the reagents used in most of these methods are expensive or

techniques,

such

as

thermal


desorption,13

washing,14,15

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45

remain in the soil for a long time.

46

Thermochemical remediations including incineration and pyrolysis can decompose

47

large organic molecules and may completely remove the contaminants from PCS.

48

Particularly, compared to incineration that needs high temperature and aerobic

49

atmosphere which is not an energy-saving process,20,21 pyrolysis is operated at

50

relatively low temperature (~500 oC) and anoxic atmosphere, during which large

51

organic molecules can decompose into small molecules that can be more easily

52

removed. Although pyrolysis is a relatively efficient energy-saving process and

53

widely used in the production of renewable energy from biomass,22,23 there are few

54

applications reported in PCS remediation. Bulmău et al.24 and Vidonish et al.20

55

successfully

56

hydrocarbon-contaminated soil. Their experimental results showed that the total

57

petroleum hydrocarbon (TPH) concentration in PCS was considerably reduced by the

58

pyrolytic treatment. However, its flaw is that slow pyrolysis adopts a relatively low

59

heating rate of generally 3-20 oC/min, during which the functional groups in the

60

organic compounds are gradually split and form low-molecular-weight gases (CO,

61

CH4, CO2, etc.), resulting in a low oil recovery rate. In contrast, fast pyrolysis has a

62

high-heating rate of above 200 oC/s, during which the chemical bonds in organic

63

compounds are directly broken, mainly forming recoverable liquid oil.25-27

64

Accordingly, fast pyrolysis is a promising method for PCS remediation with

65

concurrent oil recovery.

66

employed

a

slow

pyrolysis

method

to

remediate

heavily

To the best of our knowledge, no study has explored the feasibility of PCS



67

remediation and oil recovery through fast pyrolysis, and a number of uncertainties

68

must be clarified. Like, through which pathway are the petroleum hydrocarbons

69

removed in the fast pyrolysis process? simple thermal desorption or thermochemical

70

decomposition? Also, can pyrolysis oil be recycled? Are there any changes in the

71

organic matter in the PCS? Finally, can the remediated soil be suitable for plant

72

growth?

73

To address these questions, and profiting from our ongoing research on

74

pyrolysis,28,29 we present herein a new study on PCS remediation and oil recovery

75

using fast pyrolysis technology. The aims of this study were to confirm the feasibility

76

of PCS remediation with fast pyrolysis in a short time, clarify the remediation

77

mechanism and investigate the effects of fast pyrolysis on organic matter present in

78

PCS. To these ends, we 1) studied the effect of the pyrolysis conditions on TPH and

79

soluble organic matter (SOM) removal; 2) evaluated the remediation effect by

80

analyzing the characteristics of the soil and conducting plant growth experiment; 3)

81

investigated the pyrolysis mechanism of petroleum in soil by analyzing the

82

components of the products in each phase.

83 84

MATERIALS AND METHODS

85 86

Materials. Uncontaminated soil was collected from the campus of the University

87

of Science and Technology of China (USTC). After the soil was dried, homogenized

88

and sieved to remove large particles, it was sterilized by autoclaving at 105 oC for 24


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89

h. Crude petroleum was obtained from the Shengli Oil Field in Shandong Province,

90

China, and its properties are shown in Table S1 of Supporting Information (SI). The

91

PCS used in the batch experiment was artificially prepared by uniformly blending the

92

crude petroleum with soil (at a mass ratio of 1:9) and drying in an oven at 105 oC. The

93

elemental composition of the obtained PCS is shown in Table S2 of SI. To verify the

94

universality of the fast pyrolysis method with actual PCS samples, we obtained two

95

kinds of actual PCS samples from the Shengli Oil Field in Shandong Province and the

96

Dagang Oil Field in Tianjin City, China. Dichloromethane was purchased from

97

Sinopharm Chemical Reagent Co. (Shanghai, China). Ultrapure water was used in all

98

the experiments.

99

PCS Remediation by Fast Pyrolysis. The PCS was heated with the fast pyrolysis

100

device depicted in Figure S1 of SI. In a typical run, a nitrogen flow of 0.8 L/min was

101

used and maintained over 20 min to remove air from the pyrolysis reactor while the

102

reactor was being heated to the target temperature (250-600 oC). Then, 10.0 g of the

103

sample was added into the quartz tubular reactor and held there for a given time at the

104

pyrolysis temperature with a nitrogen flow of 0.2 L/min. The reactor was cooled

105

naturally to the ambient temperature when pyrolysis was complete, and the solid

106

residue was harvested and weighed. The liquid condensate was gathered with the

107

assistance of an ethanol bath at a temperature of -20 oC. The pyrolysis gas was

108

collected with an air collection bag and measured by gas chromatography. The yield

109

of gaseous products was calculated by difference. The solid and liquid pyrolysis

110

products were denoted as PCS-Fx and Oil-Fx, respectively, where F indicates fast



111

pyrolysis and x stands for the pyrolysis temperature (x=250~600 oC).

112

TPH Extraction and Measurement. The TPH in the PCS sample was extracted

113

using the USA EPA Method 3550 and quantified with a weighing method,30 which is

114

described in Text S1 of SI. The determination of TPH in each sample was performed

115

in duplicate with a relative error below 3%. The composition and content of TPH

116

were characterized by gas chromatography-mass spectrometry (GC-MS) and and gas

117

chromatography/ flame ionization detector (GC/FID).

118

Pyrolysis Oil Collection and Determination. The liquid products of fast pyrolysis

119

were collected with the assistance of an ethanol bath at -20 oC. After the temperature

120

of the fast pyrolysis device dropped to room temperature, the oil yield was calculated

121

by measuring the weight difference of the collecting tube before and after pyrolysis.

122

To analyze the property of the pyrolysis oil obtained at 500 oC, the oil was centrifuged

123

at 8,000 rpm to separate oil and water. Then, the oil was stored in a 4 oC refrigerator

124

for further tests.

125

Extraction and Determination of Water Soluble Organic Matter (SOM). The

126

SOM in soil was extracted by adding 15 mL of water to 2.0 g soil in a 50 mL glass

127

conical flask. The operation process is described in Text S2.

128

Characterizations. Fourier transform infrared (FTIR) spectroscopy, elemental

129

analysis, fluorescence microscopy analysis, X-ray photoelectron spectroscopy (XPS)

130

analysis, Raman spectroscopy analysis, high resolution transmission electron

131

microscopy (HRTEM) analysis and gas chromatography-mass spectrometry

132

(GC-MS)analysis can be found in Text S3.


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133 134

RESULTS

135 136

PCS Remediation by Fast Pyrolysis. Effect of Pyrolysis Temperature. The pyrolysis

137

temperature, an important factor influencing the remediation effect of PCS and oil

138

recovery, was first investigated at the range of 250 to 600 oC for 30 min according to

139

the properties of crude oil.31 As an important index for PCS remediation, the

140

extractable amount of TPH was determined.32 The initial TPH of the PCS used in this

141

study was found to be 49.5 mg/g. After the pyrolysis treatment, the residual TPH in

142

the solid products was extracted with dichloromethane and quantified. As shown in

143

Figure 1a, the color of the dichloromethane solution became lighter as the pyrolysis

144

temperature increased and turned transparent at above 400 oC. Consistent with the

145

color changes, the removal rate of extractable TPH from PCS-F250 was 69.6%, and

146

became larger with the increased of the pyrolysis temperature. When the temperature

147

was above 400 oC, the TPH removal rate reached over 99%. Compared with other

148

thermal treatment methods for PCS remediation, including incineration and slow

149

pyrolysis, the fast pyrolysis method shows great advantages in saving energy

150

consumption due to both low temperature and short cycle.

151

Although most of the TPH in PCS can be removed at above 400 oC, some SOM

152

may be fixed by the soil particles even at high temperature, due to the abundant pores

153

and polar groups.33 SOM may pollute groundwater and cause aesthetic concerns, such

154

as taste, color and odor, and form complexation with metals that impacts plant



155

growth.2,5 Thus, it is necessary to characterize the remaining SOM in the remediated

156

soil, and ensure that most of them are removed. The concentration of SOM in an

157

aqueous solution was expressed as the total organic carbon (TOC) quantification, and

158

the TOC concentrations of the remediated PCS at different pyrolytic temperature are

159

shown in Figure 1b. The results indicate that the TOC concentration was reduced as

160

the pyrolysis temperature increased from 250 to 600 °C. The TOC concentrations of

161

the PCS pyrolyzed at 250-300 °C were higher than that of untreated PCS (35.2 mg/L),

162

which is mainly due to the generation of new soluble compounds during fast

163

pyrolysis.34 Notably, the TOC concentration of the PCS-F500 extract was only 2.94

164

mg/L (0.022 mg/g PCS-F500) with a removal rate of 91.6%, which is even lower than

165

that of the unpolluted soil (8.91 mg/L, 0.067 mg/g soil). Thus, considering both the

166

TPH and SOM removal, as well as the energy demand, 500 oC is a suitable pyrolysis

167

temperature for PCS remediation.

168

The Retention Time. One of the main advantages of fast pyrolysis over slow

169

pyrolysis is its short retention time. Thus, the effect of the retention time on the PCS

170

remediation was investigated by varying the retention time from 30 sec to 30 min ,

171

while keeping other conditions unchanged. The results shown in Figure 1c reveal that,

172

67.3% of the TPH in PCS could be removed in 30 seconds, and about 100% of the

173

TPH was removed in 5 min. However, the TOC concentration of the PCS pyrolyzed

174

at 500 oC for 5 min was still 16.0 mg/L, suggesting that the SOM cannot be

175

completely removed under these conditions. For the retention time of 30 min, both the

176

TPH and SOM were almost completely removed.


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177

The above-mentioned results demonstrated that PCS can be completely remediated

178

by fast pyrolysis at 500 oC in 30 min even if the SOM was considered. The retention

179

time is much shorter than that of slow pyrolysis, and the temperature is lower than

180

that of incineration, which can significantly reduce the energy consumption of the

181

PCS remediation.20

182

Oil Recovery during the PCS Remediation. The most prominent advantage of

183

fast pyrolysis is the oil recovery during the PCS remediation process. The yield of oil,

184

water, gas and solid after the fast pyrolysis of PCS at 500 oC are shown in Figure 2a.

185

Based on the yield of the products in each phase and elemental analysis results

186

(Tables S1 and S2), the contents of carbon and hydrogen in each phase were

187

calculated by the method as described in Text S4, which summarizes the fates of the

188

main petroleum components at 500 oC. As shown in Figure 2b, 50.9% of the C and

189

31.7% of the H in the initial PCS were recovered as pyrolysis oil by fast pyrolysis at

190

500 oC; , while 32.1% of the C and 22.0% of the H were kept in soil, and 17.0% of the

191

C and 46.1% of the H were converted into gaseous products.

192

The components of the pyrolysis oil were analyzed by GC-MS, and the results

193

shown in Figure 2c reveal a series of peaks that emerged for the pyrolysis oil

194

harvested at 500 oC, which are mainly attributed to alkanes and 1-alkenes with the

195

number of carbon atoms varying from 8 to 30. The detailed components are listed in

196

Table S3. Compared with the TPH extracted from PCS, these new peaks in the

197

pyrolysis oil indicated that the pyrogenic decomposition reactions of large molecules

198

into smaller ones occurred during the fast pyrolysis process. Additionally, the linear



with

carbon

atoms

ranging

from

8

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199

hydrocarbons

to

20

(C8-C20)

was

200

semi-quantitatively determined by GC/FID, using biphenyl as the reference

201

compound. As shown in Figure S2, when the pyrolysis temperature increased from

202

250 to 500 oC, the peak intensities of the C8-C20 hydrocarbons became larger, and then

203

decreased at 600 oC.

204

The elemental analysis of pyrolysis oil revealed that it mainly contains C, H, S, O

205

and N. According to the Dulong’s formula,35 the energy density can be calculated on

206

the basis of the elemental composition as in Eq.1.

207

Energy density (kJ/kg) ＝337C+1419(H-1/8 O)+93S+23.26N

(1)

208

The results reveal that the energy density of pyrolysis oil is 46.02 MJ/kg, which is

209

larger than that of crude petroleum (43.96 MJ/kg). The sulfur content is an important

210

index for evaluating petroleum products.36 Compared with the crude petroleum

211

(2.92%), the pyrolysis oil has lower sulfur content (2.03%), contributing to a better oil

212

quality. This finding indicates that a portion of sulfur was held in the soil or in the gas

213

after the pyrolysis process.

214

Notably, the kinematic viscosity of pyrolysis oil is 27.6 mm2/s, which is

215

considerably smaller than that of crude petroleum (5815.8 mm2/s). Thus, the

216

recovered pyrolysis oil is easier to transport and use. The pyrolysis oil has a smaller

217

density (0.937 g/mL) than that of crude petroleum (0.997 g/mL). Moreover, the

218

carbon residue content and ash content of the recovered pyrolysis oil are lower than

219

that of crude petroleum, which produce less damage to the devices used in the

220

refining and burning processes. According to the above-mentioned test results, it can


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221

be concluded that the quality of the oil recovered from PCS is better than that of the

222

crude oil.

223

The components of the pyrolysis gas obtained at 500 oC were analyzed by GC

224

analysis, and the results are shown in Figure S3. As mentioned above, despite the

225

gaseous products accounting for only a small mass portion, they covered 17.0% of the

226

C and 46.2% of the H in the initial PCS.

227

Characterizations of Remediated PCS. Fluorescence Microscopy Analysis. Crude

228

oil can be detected with fluorescence techniques due to the presence of highly

229

fluorescent components like polycyclic aromatic hydrocarbons with various ring sizes

230

and compounds with conjugated π bonds.37,38 Accordingly, we employed fluorescence

231

microscopy to examine the petroleum residues to provide intuitive evidence of the

232

PCS remediation. The results presented in Figure 3 reveal that the uncontaminated

233

soil can only be observed under visible light, and nothing can be seen under light in

234

the non-visible spectrum. This indicated that no apparent fluorescence was emitted

235

from the pure soil, despite the presence of fluorescent substances like humic

236

substances. On the other hand, the PCS emitted distinct fluorescence under green,

237

blue, ultraviolet, and full-wave band light irradiations (Figure S4), especially under

238

the green light, where a clear orange red fluorescence was emitted (Figure 3e). Thus,

239

this confirmed that petroleum in the PCS can fluoresce despite the occurrence of light

240

attenuation, self-absorption, energy transfer and collisional quenching.39 However,

241

after the pyrolysis treatment, the PCS-F500 did not radiate distinguishable

242

fluorescence under different lights excitations. Crude oil is composed of saturated



243

hydrocarbons, aromatic hydrocarbons, non-hydrocarbons, colloids and asphaltenes,

244

among which the aromatic hydrocarbons and partial non-hydrocarbons are fluorescent

245

and difficult to biodegrade.37,40 Accordingly, the fluorescence analysis results

246

demonstrate that the fluorescence-emitting compounds which are intractable and

247

harmful can be easily removed from PCS by fast pyrolysis.

248

FTIR spectroscopy and Elemental Analysis. To further verify the performance of

249

fast pyrolysis in PCS remediation, FTIR spectroscopy was used to determine the

250

functional groups of the PCS samples, and the results are shown in Figure 4a.

251

Compared with uncontaminated soil, two new peaks, at 2853 cm–1 and 2924 cm–1,

252

arise in the FTIR curve of PCS, which are respectively ascribed to the symmetric and

253

asymmetric C-H stretching vibrations of petroleum hydrocarbons.41 After fast

254

pyrolysis at 250 oC, these two peaks were still present but became weaker. Then, they

255

almost disappeared in the PCS-F500, implying a drastic removal of petroleum

256

hydrocarbons.

257

The elemental compositions of the solid residues were also determined and are

258

shown in Figure 4b. The initial C and H contents were 6.68% and 1.49% respectively,

259

and they were both constantly decreased along with the increase of the pyrolysis

260

temperature. As mentioned above, 32.14% of the C and 22.03% of the H still

261

remained in the remediated soil in the form of carbon residue, which is thermally

262

stable and insoluble in dichloromethane or water. Consequently, it is considered to be

263

innocuous to the environment.

264

Analysis of Carbon Residue in PCS-F500. To clearly establish the structure of


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carbon residues in the PCS after remediation, FTIR, Raman spectra and XPS analysis

266

were employed to determine its chemical compositions. Before the analysis, the

267

PCS-F500 sample was treated with hydrofluoric acid (HF, 30%, v/v) and hydrochloric

268

acid (HCl, 30%, v/v) to remove the soil portion. The obtained carbon residue was then

269

washed to neutral pH with pure water and dried in a vacuum oven at 60 oC. The FTIR

270

spectroscopy result shown in Figure S5 reveals that only one peak appears, which is

271

attributed to the C=C vibration of aromatic components. Also, as shown in Figure 4c,

272

according to the Raman spectra, the carbon residue has a high degree of graphitization

273

with an IG/ID ratio of 1.34. Additionally, the XPS results shown in Figure S6 reveal

274

that the main elemental component of the carbon residue is C (91.50%) and, a few O

275

(5.87%). The C1s spectra shown in Figure 4d reveal that the peaks at 284.3, 284.8 and

276

285.2 eV belong to graphitic carbon (20.2%), C-CH2 (37.6%) and C-CH3 (42.1%),

277

respectively (Table S4).42

278

A HRTEM image was examined to determine the structure of the graphitic carbon

279

in the PCS pyrolyzed at 500 oC. An anfractuous and folded carbon layer can be

280

observed at the border of the composite in Figure 4e. A typical image in which the

281

specimen mainly exhibits continuous straight graphite stripes is shown in Figure 4f.

282

The spacing between neighboring parallel fringes was found to be about 0.34 nm,

283

which agrees well with the {002} lattice plane spacing of graphite.43 These results are

284

consistent with the Raman and XPS analysis results, indicating that the carbon residue

285

in remediated PCS mainly exists in the graphite state. Together with the results of the

286

TPH and SOM contents in PCS-F500, it can be concluded that the carbon residue in



287

PCS after remediation is very stable and insoluble, existing mainly in the form of

288

fused aromatic rings with a large formula weight. This indicates that the pyrolysis of

289

PCS at 500 oC should be nontoxic to the ecosystem.

290

Plant growth Test. To investigate if after fast pyrolysis the soil can be reused for

291

vegetation growth, we conducted an experiment involving wheat growth. Unpolluted

292

soil, PCS with two different oil contents (10 and 20%), and the remediated PCS at

293

500 oC were used for wheat cultivation. The experimental details can be found in the

294

SI. The results shown in Figure 5a indicate that the germination of wheat seeds was

295

seriously inhibited in the culture with PCS, and the germination rate became lower

296

along with the increase of the petroleum content. After the PCS was treated by fast

297

pyrolysis at 500 oC, the inhibition of wheat germination by PCS was eliminated, and

298

all the tested seeds successfully germinated. In the following days, the wheat germs in

299

PCS-10%-F500 and PCS-20%-F500 showed a good growth rate, even better than that

300

in unpolluted soil, as shown in Figure 5b and Figure S7. This finding indicates that

301

after the soil is treated by fast pyrolysis it can be reused for vegetation growth.

302

Cost-benefit Analysis. A comparison of the cost benefit analysis between fast and

303

slow pyrolysis was conducted by considering the heat loss in the heating stage and

304

pyrolysis stage, as well as the high heating value of the recovered oil. The calculation

305

method is described in Text S5. The results indicate that the total energy consumption

306

of the PCS treatment by fast pyrolysis is 4.88×105 kJ, which is close to that of slow

307

pyrolysis (4.44×105 kJ) (Table S5). However, about 1.84×106 kJ of energy can be

308

obtained from the recovered oil, demonstrating that the PCS remediation with fast


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309

pyrolysis has the great advantage of saving in energy consumption.

310

Possible Pathways of Petroleum components removal during Pyrolysis. On the

311

basis of the aforementioned analyses of the pyrolysis products, we proposed a

312

possible pathway of petroleum components removal during fast pyrolysis (Figure 6).

313

The main components of petroleum, i.e. saturated hydrocarbons, aromatic

314

hydrocarbons, colloids and asphaltenes, may undergo transformations through three

315

ways during the pyrolysis process, namely through cracking, polymerization, and

316

evaporation.31,44 The saturated hydrocarbons, especially linear alkanes, cracked into

317

alkanes and alkenes with low molecular weight during the pyrolysis, which was

318

demonstrated by the component analysis of the pyrolysis oil and gas. A portion of

319

these hydrocarbons condensed forming pyrolysis oil, while the other portion was

320

released in the form of pyrolysis gas. The aromatic hydrocarbons are relatively

321

thermally stable, so they were probably converted into the pyrolysis oil directly or

322

polymerized into larger structure in the carbon residue.45,46 The colloids and

323

asphaltenes consist of aromatics, cyclic hydrocarbons, long-chain hydrocarbons and

324

hetero atoms.47 Due to their complex structure and large molecular weight, all the

325

cracking, polymerization, and cracking-polymerization may occur for colloids and

326

asphaltenes,48 among which polymerization played the major role, forming the major

327

part of the carbon residue.

328

Environmental Implications. Fast pyrolysis has potential application to different

329

types of PCSs. Considering that the levels of oil in the PCS may vary, PCSs with an

330

initial petroleum content ranging from 5% to 20% were fast-pyrolyzed at 500 °C. The



331

results showed that after the fast pyrolysis, the TPH removal efficiencies of all PCSs

332

were close to 100% with a residual TPH of less than 0.4 mg/g, while the TOC

333

concentrations of the soil extracts were in the range of 1-3 mg/L, which is lower than

334

that of unpolluted soil (Figure 7a). For the PCSs with different soil compositions and

335

oil source (Table S6), similar remediation efficiencies can be achieved (Figure 7b and

336

7c). Besides the artificially prepared PCSs, two kinds of actual PCSs from different

337

places were fast-pyrolyzed under the same conditions. The results also demonstrated

338

that the TPH removal rates almost reached 100% and the SOM concentrations were

339

lower than that of unpolluted soil (Figure 7d and Figure S8). These results clearly

340

show that fast pyrolysis can be adopted to quickly and efficiently remediate PCS with

341

different petroleum concentrations, a task that cannot be achieved by other

342

remediation methods (Table S7).

343 344

ACKNOWLEDGEMENTS

345

This research has been supported by the Natural Science Foundation of China (Grant

346

No. 21677138). The authors also would like to acknowledge the support by the Brook

347

Byers Institute for Sustainable Systems, Hightower Chair, and the Georgia Research

348

Alliance at the Georgia Institute of Technology.

349 350

ASSOCIATED CONTENTS

351

Supporting Information Available. Texts S1-S5, Tables S1-S7 and Figures S1-S8

352

are provided in SI. This material is available free of charge via the Internet at


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http://pubs.acs.org.

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496

Figure Captions

497

Figure 1. a) TPH removal from PCS at different pyrolysis temperatures and an image

498

of the residual TPH in 10 mL dichloromethane solution; b) The TOC concentrations

499

of soil samples treated at different temperatures; c) Effect of retention time on the

500

PCS remediation;

501

Figure 2. a) The yield of products from the PCS pyrolyzed at 500 oC; b) The

502

distribution of C and H in different phases; c) GC-MS results of the analysis of

503

pyrolysis oil obtained at 500 oC.

504

Figure 3. Fluorescence microscopy images of different samples. a, d: uncontaminated

505

soil; b, e: PCS; c, f: PCS-F500. a, b, c are images under visible light irradiation; d, e,

506

f are images under green light irradiation).

507

Figure 4. a) FTIR spectra of different soil samples; b) Elemental analysis results of

508

the PCS samples treated at different temperature; c) Raman spectra, d) XPS C1s

509

spectra e, f) HRTEM images of carbon residue in PCS-F500.

510

Figure 5. a) Germination rates of wheat seeds in different soil samples; b) average

511

shoot lengths of wheat germs over time.

512

Figure 6. The proposed possible pathways of petroleum components removal during

513

the fast pyrolysis.

514

Figure 7. a) Results of the remediation results of PCS with different oil

515

concentrations (The black boxes denote TPH removal; the gray columns denote the

516

TOC concentration of the SOM in water extract; the orange columns denote the THP

517

concentration in the remediated PCS); the effects of the soil composition and oil type


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518

on b) TPH removal and c) TOC concentration at different temperatures; d) Results of

519

the remediation of actual PCSs using the fast pyrolysis at 500 oC.

520



521 522 523 524 525

526 527

Figure 1

528


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530 531

Figure 2

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534 535

Figure 3

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538 539

Figure 4

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Figure 5

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Figure 6

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Figure 7

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Remediation of Petroleum-Contaminated Soil and Simultaneous

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