Isotherm and Thermodynamic Studies on the Removal of Sulfur from

Subscriber access provided by Iowa State University | Library

Fossil Fuels

Isotherm and thermodynamic studies on the removal of sulfur from diesel fuel by mixing-assisted oxidative - adsorptive desulfurization technology Marvin L. Samaniego, Mark Daniel Garrido de Luna, Dennis C. Ong, Meng-Wei Wan, and Ming-Chun Lu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b04242 • Publication Date (Web): 17 Jan 2019 Downloaded from http://pubs.acs.org on January 17, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 32 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

Energy & Fuels

1

1

Isotherm and thermodynamic studies on the removal of sulfur from diesel fuel by mixing-

2

assisted oxidative - adsorptive desulfurization technology

3 4

Marvin L. Samaniegoa, Mark Daniel G. de Lunaa,b, Dennis C. Ongc, Meng-Wei Wand, Ming-

5

Chun Lud,*

6 7

a

8 9

Environmental Engineering Program, National Graduate School of Engineering, University of the Philippines, 1101 Diliman, Quezon City, Philippines

b

10

Department of Chemical Engineering, University of the Philippines, 1101 Diliman, Quezon City, Philippines

11

c

School of Technology, University of the Philippines Visayas, Miagao, Iloilo 5023, Philippines

12

d

Department of Environmental Resources Management, Chia-Nan University of Pharmacy and

13

Science, Tainan 71710, Taiwan, E-mail: [email protected]

14 15

* Corresponding author

16 17 18 19 20 21 22 23

ACS Paragon Plus Environment

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 2 of 32

2

24

Graphical Abstract

25 26

Highlights

27



PAC and alumina had homogeneous and heterogenous adsorption sites, respectively

28



Adsorption activation energy implied sulfur chemisorption on powdered alumina

29



Chemical reaction and diffusion processes controlled the sulfur-PAC adsorption

30



Adsorption process for both PAC and powdered alumina was endothermic

31



High and low temperature favored sulfur-PAC and -alumina adsorption, respectively

32 33 34 35 36 37 38 39 40


Page 3 of 32 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

Energy & Fuels

3

41

Abstract

42

In recent years, fuel modifications, such as the production of ultra-low sulfur diesel

43

(ULSD), have been mandated by international agencies to limit gaseous sulfur emissions and

44

reduce atmospheric pollution. In this study, raw diesel fuel was subjected to sequential (1) high

45

shear mixing-assisted oxidative desulfurization and (2) adsorptive desulfurization. A detailed

46

study on the isotherm and thermodynamics of sulfur removal was carried out using powdered

47

activated carbon (PAC) and powdered alumina in batch adsorption experiments. Results showed

48

that sulfur adsorption by PAC and powdered alumina followed the Langmuir (R2 = 0.9020) and

49

the Freundlich (R2 = 0.8626) isotherm models, respectively. Adsorption of sulfur by powdered

50

alumina was controlled solely by chemisorption, while adsorption by PAC was controlled by a

51

combination of a chemical reaction and diffusion processes. For both powdered alumina and

52

PAC, the positive values of the enthalpy of activation (ΔH) indicate that the adsorption process

53

was endothermic. Negative ΔS and increasing ΔG values with increase in temperature indicates

54

that lower temperatures favored sulfur adsorption by powdered alumina, while positive ΔS and

55

decreasing ΔG values with increase in temperature indicate that sulfur adsorption by PAC was

56

more favorable at high temperature.

57 58

Keywords: Adsorption; desulfurization; diesel; high-shear mixing; isotherm; thermodynamics

59 60 61 62 63


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 4 of 32

4

64

1. Introduction

65

Oxidative desulfurization (ODS) is considered the most effective alternative and/or post-

66

treatment method in removing sulfur from fossil fuels. Its advantage over other sulfur removal

67

technologies, such as selective adsorption, extractive separation, and biodegradation, include its

68

ability to produce low sulfur fuels at near ambient temperature and pressure1. These alternative

69

methods have been developed in order to address the problems encountered in current sulfur

70

removal methods, such as hydrodesulfurization, which has been the standard industrial-scale

71

desulfurization

72

hydrodesulfurization technology include higher sulfur content feedstock, arising from the

73

declining supply of crude oil and more stringent guidelines set by the United States

74

Environmental Protection Agency (U.S. EPA) which limit sulfur levels in diesel fuels to 15 ppm

75

from the previous 400 to 500 ppm2. At the onset, conventional hydrodesulfurization technology

76

already suffers from non-selective hydrogenation of olefins and aromatics, especially

77

dibenzothiophene (DBT) and its derivatives3,4. With the growing demand for ultra-low sulfur

78

fuels, this technology will have to operate at higher temperatures and pressures and will have to

79

involve

80

hydrodesulfurization is no longer adequate and cost-effective especially when large amounts of

81

refractory sulfur compounds are to be removed6,7.

larger

technology

reactors

for

with

decades.

volumes

Pressing

5-15

issues

times

the

with

this

present

energy-intensive

capacity5.

Thus,

82

ODS takes advantage of the fact that sulfur compounds in fuels are more prone to

83

oxidation compared to other hydrocarbon components. In ODS, sulfur compounds are converted

84

to highly polar sulfoxides and sulfones that can be readily removed by a suitable technology8.

85

Hereafter, the main challenge is to selectively separate the sulfur species with low polarity from

86

the non-polar liquid phase9. In the past decade, selective sulfur removal from fuels has been


Page 5 of 32 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

Energy & Fuels

5

87

accomplished using various adsorbents, including activated carbon10, alumina11, and silica12.

88

Activated carbon (AC) is a versatile and widely used adsorbent primarily for removal of

89

undesirable chemical species in liquids or gases. AC is produced from carbonaceous materials

90

such as wood, coconut shells, sugar, coal, and lignin. Its high surface area, well-developed

91

microporosity, and wide spectrum of surface functional groups make AC an ideal adsorbent13.

92

The heteroatoms of porous carbon surface, mainly composed of oxygen, hydrogen, nitrogen, and

93

halogens bonded to the edges of the carbon layers, govern the AC surface chemistry14. Among

94

the heteroatoms, the oxygen-containing functional groups known as surface oxides, which are

95

most commonly formed on the AC surface, are responsible for the enhancement of the material’s

96

performance in catalytic reactions and adsorption processes15. On the other hand, aluminum

97

oxide, commonly known as alumina, is commercially produced by thermal dehydration of

98

aluminum trihydrate, Al(OH)3 or gibbsite16. When the trihydrate is heated to approximately 400

99

°C, it is converted to crystalline γ/η-alumina having small amounts of boehmite and surface area

100

of about 250 m2 g-1. However, when heated rapidly to 400-800 °C, gibbsite will become

101

amorphous in form, having a higher surface area of 300-350 m2 g-1. Alumina has good

102

mechanical properties and high surface area, which makes it a versatile sorbent for different

103

applications. It has been widely used to remove organic compounds from aqueous solutions17.

104

The performance of amorphous acidic alumina and crystalline boehmite in removing DBT was

105

evaluated in a published study18, where acidic alumina was identified as the adsorbent of choice

106

for the selective DBT removal via ultrasound-assisted oxidative desulfurization (UAOD)

107

process.

108

In this study, desulfurization of diesel fuel was carried out by sequential (1) high shear

109

mixing-assisted oxidative desulfurization and (2) adsorptive desulfurization using powdered


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 6 of 32

6

110

activated carbon and powdered alumina adsorbents. In addition, the isotherm and

111

thermodynamic parameters of both adsorbents were evaluated. This study was motivated by the

112

fact that sulfur removal from transportation fuels, such as diesel, is an urgent goal of clean fuel

113

research. The combustion of sulfur-containing fuels releases sulfur oxides (SOx) which are

114

precursors of acid rain and cause other adverse environmental effects19. These oxides also poison

115

automobile exhaust catalysts designed for nitrogen oxide (NOx) reduction20–23. Moreover, the

116

presence of SOx in the atmosphere poses health threats. Exposure to SOx in the ambient air has

117

been associated with the development of cancer, reduced lung function, increased incidence of

118

respiratory symptoms and diseases, irritation of the eyes, nose, and throat, and premature

119

mortality24,25.

120 121

2. Materials and methods

122

2.1 Chemicals and adsorbents

123

Commercial diesel was purchased from Taichin Company, Taiwan. Tetraoctylammonium

124

bromide ([CH3(CH2)7]4NBr, TOAB), phosphotungstic acid hydrate (H3PW12O40·20H2O, HPW),

125

and industrial grade hydrogen peroxide (50% purity) were purchased from Hung Yao

126

Instruments Company, Taiwan. Powdered alumina (activated Al2O3, Brockmann I, standard

127

grade, ~105 µm particle size, 7.285 nm pore size) was purchased from Aldrich Chemical Inc.

128

Powdered activated carbon (PAC) (~44 µm particle size, 2.222 nm pore size) was purchased

129

from Fluka Analytical. Previous work reported that PAC had a surface area of 846 m2 g-1 and

130

micropore area of 399 m2 g-1, while powdered alumina had lower surface area of 129 m2 g-1

131

which implies presence of mesopores (2-50 nm)21.

132


Page 7 of 32 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

Energy & Fuels

7

133

2.2 Analytical methods

134

The sulfur concentrations of all samples were analyzed as total sulfur using an X-ray

135

fluorescence sulfur-in-oil analyzer (SLFA-2100, Horiba Scientific). A calibration curve

136

established between sulfur concentration and a correlation factor became the basis for the direct

137

measurement of sulfur concentrations. Gas chromatography – sulfur chemiluminescence detector

138

(GC-SCD) (G6603A, Agilent Technologies) was used for the analysis of actual diesel fuel. The

139

GC-SCD identifies sulfur compounds in a liquid mixture and provides information on the

140

selectivity of the adsorption process to remove sulfur compounds. Adsorbent specific surface

141

area was analyzed using a Brunauer-Emmett-Teller (BET) analyzer (ASAP, Micromeritics).

142 143

The sulfur removal and the adsorption capacity for sulfur (qt) were computed using Eq. (1) and Eq. (2), respectively 𝑠𝑢𝑙𝑓𝑢𝑟 𝑟𝑒𝑚𝑜𝑣𝑎𝑙 (%) =

𝑞𝑡(𝑚𝑔/𝑔) =

(

𝐶0 ― 𝐶𝑒 𝐶0

)

⋅ 100

(𝐶0 ― 𝐶𝑡) ∙ 𝑉 𝑀

(1)

(2)

144 145

2.3 Desulfurization experiments

146

A mixture of 500 mL diesel fuel, containing 4 g phosphotungstic acid and an equal amount

147

of hydrogen peroxide with 2 g of TOAB, were added to a glass reactor and subjected to rapid

148

mixing at 353 K using a high shear mixer (T-25, Ultra-Turrax, China) at an agitation speed of

149

12,000 rpm for 35 min. The mixture was then allowed to cool and the organic phase was

150

decanted and subsequently used as the adsorbate during the adsorption experiments.

151

Sulfur removal from diesel after oxidative desulfurization was carried out in batch

152

experiments21 using an orbital water bath shaker (Gyromax 929, Amerex Instruments, Inc., USA)


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 8 of 32

8

153

set at a constant agitation speed of 120 rpm. A known amount of adsorbent was placed in a 250-

154

mL Erlenmeyer flask with 20 mL diesel fuel. The mixture was agitated at a pre-determined

155

temperature and contact time and filtered using a 0.2 µm polypropylene membrane prior to total

156

sulfur content analysis.

157

Pre-determined amounts of powdered alumina and PAC adsorbents (1, 3, 5, and 7 g) were

158

each added into separate 20 mL diesel fuel samples with initial sulfur concentration of 950 ppm

159

at 313 K. The adsorption capacities were measured at specified contact times, and the

160

equilibrium adsorption capacity was determined after 24 h of mixing. Sulfur adsorption by

161

powdered alumina and PAC adsorbents were also investigated at different temperatures (293,

162

298, and 313 K). All the computed adsorption capacities were used to fit various adsorption

163

isotherms and thermodynamics models.

164 165

3. Results and discussion

166

3.1 Liquid fuel characteristics

167

The specifications of raw diesel fuel are shown in Table 1. The calculated initial sulfur

168

content of the raw diesel was 1,130 ppm. After oxidation, the amount of sulfur in diesel dropped

169

to 950 ppm. GC-SCD chromatograms of raw diesel fuel, diesel fuel after oxidative

170

desulfurization, and diesel fuel after adsorptive desulfurization are presented in Fig. 1. As shown

171

in the figure, thiophenic compounds, such as benzothiophene (BT) and dibenzothiophene (DBT),

172

were removed from raw diesel after oxidative desulfurization. In addition, the amount of sulfur

173

removed after oxidative desulfurization reached 15.9%, which is more than the 13.3% sulfur

174

removal from jet fuel obtained in a similar oxidative-adsorptive desulfurization study26.

175


Page 9 of 32 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

Energy & Fuels

9

176

3.2 Adsorption kinetics and thermodynamics

177

The effect of temperature on sulfur removal by powdered alumina and PAC adsorbents

178

was investigated in the temperature range of 293 to 313 K, below the flash point of the diesel

179

sample. The calculated adsorption capacities, qe, at different temperatures were obtained using

180

the pseudo-first order and pseudo-second order kinetic models. These models are useful in

181

determining the mechanism that governs the adsorption of adsorbate onto the adsorbent, as well

182

as the rate-determining step of the adsorption process27. The Lagergren pseudo-first order kinetic

183

model assumes that the rate-limiting mechanism of the adsorption process is physical

184

adsorption28. On the other hand, in the pseudo-second order kinetic model, chemisorption is

185

considered as the rate-limiting mechanism of the adsorption process29. A more detailed

186

discussion on the kinetics of sulfur removal using powdered alumina and PAC is presented

187

elsewhere21. Table 2 presents the calculated adsorption capacities, qe, at different temperatures as

188

fitted into the pseudo-first and pseudo-second order reaction kinetic models according to Eq. (3)

189

and Eq. (4), respectively: 𝑙𝑛(𝑞𝑒 ― 𝑞𝑡) = 𝑙𝑛𝑞𝑒 ― 𝑘1𝑡

(3)

𝑡 1 1 = + 𝑡 𝑞𝑡 𝑘2𝑞2𝑒 𝑞𝑒

(4)

190

where k1 is the rate constant of pseudo first-order adsorption (min-1), k2 (g mg-1 min-1) is rate

191

constant of pseudo second-order adsorption, qe and qt are the amount of metal ion adsorbed per

192

gram of sludge (mg g-1) at equilibrium and at any time, t, respectively.

193

The high coefficients of determination (R2>0.998) for the pseudo-second order kinetic

194

model, as presented in Table 2, imply that the rate-limiting step in the adsorption of sulfur

195

species on both PAC and powdered alumina was chemical adsorption. In addition, the adsorption

196

capacities for both adsorbents increased at higher adsorption temperatures.


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 10 of 32

10

197

The effects of temperature on the adsorption rate constants are better explained by the

198

adsorption activation energy, Ea30. The pseudo-second order rate constant, k2, can be expressed

199

as a function of temperature using the Arrhenius-type relationship, shown in Eq. (5): ln 𝑘2 = ln 𝐴 ―

𝐸𝑎 𝑅𝑇

(5)

200

where A is a constant called the frequency factor, R is the gas constant (8.314 J.mol-1 K-1), and T

201

is the temperature (K). The magnitude of the activation energy differentiates physical adsorption

202

from chemical adsorption. For physisorption, the activation energy is usually no more than 4.2 kJ

203

mol-1 since the forces involved are weak (van der Waals and electrostatic forces), and

204

equilibrium is rapidly attained and is reversible because of the small energy requirement.

205

Chemisorption, on the other hand, is specific and involves forces much stronger than in

206

physisorption. For activated chemisorption, the activation energy is between 8.4 and 83.7 kJ mol-

207

1,

208

very rapidly31. The activation energy of adsorption derived from the slope of the linear plot of ln

209

k2 versus 1/T (Fig. 2a) were 17.56 kJ mol-1 for powdered alumina (R2 = 0.9586) and -21.71 kJ

210

mol-1 for PAC (R2 = 0.9757). Thus, the rate-limiting step of sulfur adsorption onto powdered

211

alumina was chemisorption, involving exchange of electrons between the sulfur compounds and

212

the binding sites of powdered alumina32. The negative value of Ea for PAC suggests a multistep

213

mechanism wherein an increase in temperature shifts the equilibrium in favor of its endothermic

214

direction33. This means that adsorption of sulfur by PAC was not controlled by chemisorption

215

alone. To investigate this phenomenon, the activation energy of diffusion, E’, was calculated

216

using Eq. (6). In addition, the intraparticle diffusion coefficient, D, was determined using Eq. (7)

217

which was derived from Fick’s law:

while nonactivated chemisorption gives Ea values near zero because of the process occurring


Page 11 of 32 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

Energy & Fuels

11

ln 𝐷 = ln 𝐷0 ―

()

𝐸′ 1 𝑅 𝑇

ln [1 ― 𝐹(𝑡) ] = ― 2

𝜋2𝐷 𝑟2

(6)

𝑡

(7)

218

where D0 is the pre-exponential factor and r is the particle radius, assuming spherical geometry

219

(m). The value of D (m2 s-1) obtained for 3 g PAC adsorbent at different temperatures, using Eq

220

(7), was used to calculate the value of D0 and E’ from Eq. (6). The graph of ln D versus 1/T (Fig.

221

3) gave a D0 value close to zero and an E’ value of -24.095 kJ mol-1. Since the activation energy

222

for diffusion was less than the adsorption activation energy (E’ < Ea), the rate-limiting step of

223

sulfur adsorption onto PAC was a combination of both chemical reaction and diffusion

224

adsorption. Similar result on the comparison of activation energy and adsorption activation

225

energy was reported in another adsorption study34.

226

To further understand the thermodynamics of adsorption, the thermodynamic activation

227

parameters - enthalpy of activation (ΔH), entropy of activation (ΔS), and Gibbs free energy of

228

activation (ΔG) - were determined using Eq (8), Eq. (9) and Eq. (10) and summarized in Table 3: 𝐾=

𝑞𝑒 𝐶𝑒

―∆𝐺 = 𝑅𝑇𝑙𝑛𝐾 𝑙𝑛𝐾 =

∆𝑆 ∆𝐻 ― 𝑅 𝑅𝑇

(8) (9) ( 10 )

229

where K is the ratio of the concentration of adsorbate in adsorbent, qe, to the concentration of

230

adsorbate in solution, Ce16. The plot of ln K versus 1/T shown in Fig. 2b gave high coefficients of

231

determination for PAC (R2 = 0.9999) and powdered alumina (R2 = 0.9619). For both powdered

232

alumina and PAC, the positive value of ΔH indicates that the adsorption process was indeed

233

endothermic35. For PAC, a positive value of ΔS (79.380 J mol-1 K-1) reflects increased degrees of


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 12 of 32

12

234

freedom of the adsorbed sulfur compounds towards the selected adsorbents36. On the contrary,

235

the negative entropy for sulfur adsorption onto powdered alumina (-8.482 J mol-1 K-1) suggests a

236

decrease in randomness in the adsorption process and imply that the process may be reversible37.

237

Table 3 shows that positive values of ΔG were observed at all temperature levels when 1 g

238

and 3 g of PAC and 1 g of powdered alumina were used. These positive ΔG values suggest that

239

the adsorption process was not spontaneous36, and energy is required to overcome the activation

240

energy and/or to form an activated complex in order for the adsorption process to proceed38. For

241

both PAC and powdered alumina at 313 K, the value of ΔG became more negative as adsorbent

242

dosage increased from a range of 1 to 7 g (Table 3). This means that increasing the adsorbent

243

dosage, which consequently increases the number of active sites, leads to a more feasible and

244

spontaneous adsorption process at 313 K and, in effect, results in higher sulfur removal. As a

245

rule of thumb, if ΔG becomes more positive as temperature increases, as in the case for 1 g

246

powdered alumina in a temperature range of 293 – 313 K, then the lower temperature makes the

247

adsorption easier31. On the contrary, if ΔG becomes more negative with an increase in

248

temperature, as observed for 3 g PAC in a temperature range of 293 – 313 K, the adsorption

249

process becomes more favorable at high temperature35. This is consistent with the result obtained

250

for powdered alumina with negative ΔS and with PAC having positive ΔS.

251 252

3.3 Adsorption isotherms and performance comparison with previous studies

253

Adsorption isotherm models are useful in understanding the interactions between

254

adsorbate molecules and the active sites on the adsorbent surface, as well as determining the

255

amount of adsorbate that can be removed by a known quantity of adsorbent27. The Langmuir39

256

and Freundlich40 isotherm models have been widely used to analyze the equilibrium adsorption


Page 13 of 32 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

Energy & Fuels

13

257

data. The Langmuir isotherm assumes that monolayer adsorption occurs between the adsorbate

258

and finite number of adsorbent active sites41. Furthermore, it assumes homogenous distribution

259

of adsorbent active sites, and that no interactions occur between adsorbed molecules37. On the

260

other hand, the Freundlich isotherm describes adsorption on a heterogeneous surface42, with the

261

assumption that the stronger binding sites on a heterogeneous surface are occupied initially, and

262

that the binding strength falls with a rise in the degree of site occupation43. The linear form of the

263

Langmuir and Freundlich isotherm equations are given by Eq. (8) and Eq. (9), respectively. A

264

plot of 1/qe versus 1/Ce was used to determine the Langmuir constants, and a plot of log qe versus

265

log Ce for the Freundlich constants: 𝐶𝑒 1 1 = + 𝑞𝑒 𝑞𝑚 𝐾𝐿𝑞𝑚 log 𝑞𝑒 = log 𝑘𝑓 +

1 log 𝐶𝑒 𝑛

(8)

(9)

266

where qe (mg g-1) is the amount of sulfur compound adsorbed at equilibrium, Ce (mg L-1) is the

267

remaining concentration of the solution at equilibrium, kL is the Langmuir adsorption constant

268

related to the affinity of binding sites, kf is an indicator of the adsorption capacity, and n is

269

related to the magnitude of the adsorption driving force and to the distribution of the energy sites

270

on the adsorbent.

271

Shown in Fig. 4 are the Langmuir and Freundlich plots of sulfur adsorption onto PAC and

272

powdered alumina at 313 K, while the model parameters and statistical fits of the adsorption data

273

are summarized in Table 4. Sulfur adsorption onto powdered alumina followed the Freundlich

274

model, with correlation factor, R2, higher than that obtained from the Langmuir model. This

275

confirms that heterogeneous and multilayer adsorption occurred by formation of covalent bonds

276

through electron sharing or exchange between sulfur and the available binding sites, facilitated


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 14 of 32

14

277

by the mesopores present on the powdered alumina21. The calculated value of n (1.294) was

278

greater than unity, which suggests that adsorption of sulfur onto powdered alumina was

279

favorable44. Similar study reported that DBT adsorption onto alumina follows the Freundlich

280

isotherm45. In contrast, sulfur adsorption onto PAC followed the Langmuir isotherm, with

281

correlation factor, R2, higher than that obtained from the Freundlich model. This implies that the

282

adsorption process took place on homogeneous sites, within the macro- and mesopores of PAC21,

283

that are identical and energetically equivalent46. The n value of 0.782 derived using Freundlich

284

isotherm was less than 1, rendering this isotherm inappropriate for the sulfur-PAC system. The

285

suitability of the Langmuir isotherm for sulfur adsorption onto PAC is confirmed by the

286

separation factor constant, RL, calculated using Eq. (10): 𝑅𝐿 =

1 (1 + 𝑘𝐿𝐶0)

(10)

287

where C0 is the initial concentration (mg L-1). The value of RL is used to determine if the

288

adsorption is unfavorable (RL > 1), linear (RL = 1), favorable (0 < RL < 1), or irreversible (RL =

289

0) 37. In this study, RL (0.662) was between 0 and 1, indicating that the adsorption was favorable.

290

Using the Langmiur isotherm model, the maximum adsorption capacity of 6.31 mg g-1 for PAC

291

was obtained. Previous study reported that DBT adsorption onto synthesized mesoporous carbon

292

adsorbent and the multi-ring sulfur compound adsorption onto carbon materials both followed

293

the Langmuir isotherm47.

294

Table 5 presents the equilibrium adsorption capacity of the adsorbents used in this study

295

compared with other adsorbents used in related studies. As shown, the adsorption capacities of

296

the PAC and powdered alumina were higher than the reported values on sulfur removal using

297

various adsorbents. The higher adsorption capacity of powdered alumina was due to the presence

298

of mesopores which facilitated contact between sulfur molecules and the internal sites of the


Page 15 of 32 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

Energy & Fuels

15

299

adsorbent, while the lower adsorption capacity of the PAC as compared with powdered alumina

300

was due to hindered access to micropores caused by saturation of the macro- and mesopores of

301

PAC with sulfur compounds during the adsorption process21.

302 303

4. Conclusions

304

In this study, the oxidative-adsorptive desulfurization of diesel fuel was conducted using

305

PAC and powdered alumina as adsorbents. The positive ΔH values for sulfur adsorption by PAC

306

and powdered alumina adsorbents confirmed the endothermic nature of adsorption. The negative

307

ΔS value, and increasing ΔG values with increase in temperature, for sulfur adsorption by

308

powdered alumina indicates that lower temperatures favor the adsorption process, and the rate-

309

controlling step for powdered alumina is apparently a chemical sorption process. The positive ΔS

310

value, and decreasing ΔG values with increase in temperature, for sulfur adsorption by PAC

311

indicates that the adsorption process is more favorable at high temperature. For PAC the rate-

312

controlling step is a combination of both chemisorption and intraparticle diffusion, showing that

313

the adsorption of sulfur onto PAC is a multistep process wherein an increase in temperature

314

shifts the equilibrium in favor of its endothermic direction. For significant adsorption to occur,

315

an increase in adsorbent dosage, both for powdered alumina and PAC, is necessary, as shown by

316

the more negative value of ΔG at higher adsorbent dosage. Sulfur adsorption onto powdered

317

alumina occurred through electron sharing or exchange between sulfur and the heterogeneous

318

binding sites on the powdered alumina, while adsorption onto PAC took place on homogeneous

319

sites.

320


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 16 of 32

16

321

Declarations of interest

322

The authors declare no competing financial interest.

323 324

Acknowledgements

325

The authors would like to thank the Ministry of Science and Technology, Taiwan (Contract No.

326

MOST 99-2221-E-041-012-MY3) and the Department of Science and Technology, Philippines

327

for providing financial support for this research undertaking.

328 329

References

330

(1)

Park, Y. K.; Kim, S. Y.; Kim, H. J.; Jung, K. Y.; Jeong, K. E.; Jeong, S. Y.; Jeon, J. K.

331

Removal of Sulfur Dioxide from Dibenzothiophene Sulfone over Mg-Based Oxide

332

Catalysts Prepared by Spray Pyrolysis. Korean J. Chem. Eng. 2010, 27 (2), 459–464.

333

https://doi.org/10.2478/s11814-010-0086-x.

334

(2)

Bu, J.; Loh, G.; Gwie, C. G.; Dewiyanti, S.; Tasrif, M.; Borgna, A. Desulfurization of

335

Diesel Fuels by Selective Adsorption on Activated Carbons: Competitive Adsorption of

336

Polycyclic Aromatic Sulfur Heterocycles and Polycyclic Aromatic Hydrocarbons. Chem.

337

Eng. J. 2011, 166 (1), 207–217. https://doi.org/10.1016/j.cej.2010.10.063.

338

(3)

Robertson, J.; Bandosz, T. J. Photooxidation of Dibenzothiophene on TiO2/Hectorite Thin

339

Films Layered Catalyst. J. Colloid Interface Sci. 2006, 299 (1), 125–135.

340

https://doi.org/10.1016/j.jcis.2006.02.011.

341

(4)

Tang, H.; Li, W.; Zhang, T.; Li, Q.; Xing, J.; Liu, H. Improvement in Diesel

342

Desulfurization Capacity by Equilibrium Isotherms Analysis. Sep. Purif. Technol. 2011,

343

78 (3), 352–356. https://doi.org/10.1016/j.seppur.2010.10.003.


Page 17 of 32 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

Energy & Fuels

17

344

(5)

Hernandez-Maldonado, a. .; Yang, R. . Desulfurization of Liquid Fuels by Selective

345

Adsorption via π Complexation with Cu (I)-Y Zeolite. Ind. Eng. Chem. Res. 2003, 42 (I),

346

3103–3110.

347

(6)

Hussain, A. H. M. S.; Tatarchuk, B. J. Adsorptive Desulfurization of Jet and Diesel Fuels

348

Using Ag/TiOx-Al2O3and Ag/TiOx-SiO2adsorbents. Fuel 2013, 107, 465–473.

349

https://doi.org/10.1016/j.fuel.2012.11.030.

350

(7)

Lorençon, E.; Alves, D. C. B.; Krambrock, K.; Ávila, E. S.; Resende, R. R.; Ferlauto, A.

351

S.; Lago, R. M. Oxidative Desulfurization of Dibenzothiophene over Titanate Nanotubes.

352

Fuel 2014, 132, 53–61. https://doi.org/10.1016/j.fuel.2014.04.020.

353

(8)

Lorençon, E.; Alves, D. C. B.; Krambrock, K.; Ávila, E. S.; Resende, R. R.; Ferlauto, A.

354

S.; Lago, R. M. Oxidative Desulfurization of Dibenzothiophene over Titanate Nanotubes.

355

Fuel 2014, 132, 53–61. https://doi.org/10.1016/j.fuel.2014.04.020.

356

(9)

Zhou, A.; Ma, X.; Song, C. Liquid-Phase Adsorption of Multi-Ring Thiophenic Sulfur

357

Compounds on Carbon Materials with Different Surface Properties. J. Phys. Chem. B

358

2006, 110 (10), 4699–4707. https://doi.org/10.1021/jp0550210.

359

(10)

Chaichanawong, J.; Yamamoto, T.; Ohmori, T.; Endo, A. Adsorptive Desulfurization of

360

Bioethanol Using Activated Carbon Loaded with Zinc Oxide. Chem. Eng. J. 2010, 165

361

(1), 218–224. https://doi.org/10.1016/j.cej.2010.09.020.

362

(11)

de Luna, M. D. G.; Futalan, C. M.; Dayrit, R. A.; Choi, A. E. S.; Wan, M. W. Evaluation

363

of Continuously Mixed Reactor Configurations in the Oxidative-Adsorptive

364

Desulfurization of Diesel Fuel: Optimization and Parametric Studies. J. Clean. Prod.

365

2018, 203, 664–673. https://doi.org/10.1016/j.jclepro.2018.08.287.

366

(12)

Teymouri, M.; Samadi-Maybodi, A.; Vahid, A.; Miranbeigi, A. Adsorptive


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 32

18

367

Desulfurization of Low Sulfur Diesel Fuel Using Palladium Containing Mesoporous Silica

368

Synthesized via a Novel In-Situ Approach. Fuel Process. Technol. 2013, 116, 257–264.

369

https://doi.org/10.1016/j.fuproc.2013.07.009.

370

(13)

Rivera-Utrilla, J.; Sánchez-Polo, M.; Gómez-Serrano, V.; Álvarez, P. M.; Alvim-Ferraz,

371

M. C. M.; Dias, J. M. Activated Carbon Modifications to Enhance Its Water Treatment

372

Applications. An Overview. J. Hazard. Mater. 2011, 187 (1–3), 1–23.

373

https://doi.org/10.1016/j.jhazmat.2011.01.033.

374

(14)

El-Sayed, Y.; Bandosz, T. J. Adsorption of Valeric Acid from Aqueous Solution onto

375

Activated Carbons: Role of Surface Basic Sites. J. Colloid Interface Sci. 2004, 273 (1),

376

64–72. https://doi.org/10.1016/j.jcis.2003.10.006.

377

(15)

Li, Y. H.; Lee, C. W.; Gullett, B. K. The Effect of Activated Carbon Surface Moisture on

378

Low Temperature Mercury Adsorption. Carbon N. Y. 2002, 40 (1), 65–72.

379

https://doi.org/10.1016/S0008-6223(01)00085-9.

380

(16)

381 382

Yang, R. T. Adsorbents : Fundamentals and Applications; John Wiley & Sons, Inc: Hoboken, New Jersey, 2003.

(17)

Bajpai, A. K.; Rajpoot, M.; Mishra, D. D. Studies on the Adsorption of Sulfapyridine at

383

the Solution-Alumina Interface. J. Colloid Interface Sci. 1997, 187 (1), 96–104.

384

https://doi.org/10.1006/jcis.1996.4655.

385

(18)

Etemadi, O.; Yen, T. F. Aspects of Selective Adsorption among Oxidized Sulfur

386

Compounds in Fossil Fuels. Energy and Fuels 2007, 21 (3), 1622–1627.

387

https://doi.org/10.1021/ef070016b.

388 389

(19)

de Luna, M. D. G.; Wan, M.-W.; Golosinda, L. R.; Futalan, C. M.; Lu, M.-C. Kinetics of Mixing-Assisted Oxidative Desulfurization of Dibenzothiophene in Toluene Using a


Page 19 of 32 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

Energy & Fuels

19

390

Phosphotungstic Acid/Hydrogen Peroxide System: Effects of Operating Conditions.

391

Energy & Fuels 2017, 31 (9), 9923–9929.

392

https://doi.org/10.1021/acs.energyfuels.7b01773.

393

(20)

Babich, I. V.; Moulijn, J. A. Science and Technology of Novel Processes for Deep

394

Desulfurization of Oil Refinery Streams: A Review. Fuel 2003, 82 (6), 607–631.

395

https://doi.org/10.1016/S0016-2361(02)00324-1.

396

(21)

de Luna, M. D. G.; Samaniego, M. L.; Ong, D. C.; Wan, M. W.; Lu, M. C. Kinetics of

397

Sulfur Removal in High Shear Mixing-Assisted Oxidative-Adsorptive Desulfurization of

398

Diesel. J. Clean. Prod. 2018, 178, 468–475. https://doi.org/10.1016/j.jclepro.2018.01.049.

399

(22)

Rodrigues, A. K. O.; Ramos, J. E. T.; Cavalcante, C. L.; Rodríguez-Castellón, E.;

400

Azevedo, D. C. S. Pd-Loaded Mesoporous Silica as a Robust Adsorbent in

401

Adsorption/Desorption Desulfurization Cycles. Fuel 2014, 126, 96–103.

402


403

(23)

Yu, G.; Lu, S.; Chen, H.; Zhu, Z. Diesel Fuel Desulfurization with Hydrogen Peroxide

404

Promoted by Formic Acid and Catalyzed by Activated Carbon. Carbon N. Y. 2005, 43

405

(11), 2285–2294. https://doi.org/10.1016/j.carbon.2005.04.008.

406

(24)

407 408

The World Bank Group. Sulfur Oxides. In Pollution Prevention and Abatement Handbook 1998; 1999; pp 231–234. https://doi.org/10.1016/B978-0-12-398499-9.00001-2.

(25)

Lloyd, A. C.; Cackette, T. A. Diesel Engines: Environmental Impact and Control. J. Air

409

Waste Manage. Assoc. 2001, 51 (6), 809–847.

410

https://doi.org/10.1080/10473289.2001.10464315.

411 412

(26)

Ma, X.; Zhou, A.; Song, C. A Novel Method for Oxidative Desulfurization of Liquid Hydrocarbon Fuels Based on Catalytic Oxidation Using Molecular Oxygen Coupled with


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 32

20

413

Selective Adsorption. Catal. Today 2007, 123 (1–4), 276–284.

414

https://doi.org/10.1016/j.cattod.2007.02.036.

415

(27)

Ong, D. C.; Pingul-Ong, S. M. B.; Kan, C. C.; de Luna, M. D. G. Removal of Nickel Ions

416

from Aqueous Solutions by Manganese Dioxide Derived from Groundwater Treatment

417

Sludge. J. Clean. Prod. 2018, 190, 443–451.

418

https://doi.org/10.1016/j.jclepro.2018.04.175.

419

(28)

Lagergren, S. Zur Theorie Der Sogenannten Adsorption Geloster Stoffe (About the

420

Theory of so-Called Adsorption of Soluble Substances). K. Sven.

421

Vetenskapsakademiens.Handlingar 1898, 24 (4), 1–39.

422

(29)

Ho, Y. S.; Mckay, G. A Comparison of Chemisorption Kinetic Models Applied to

423

Pollutant Removal on Various Sorbents. Process Saf. Environ. Prot. 1998, 76

424

(November), 332–340. https://doi.org/https://doi.org/10.1205/095758298529696.

425

(30)

Wen, J.; Han, X.; Lin, H.; Zheng, Y.; Chu, W. A Critical Study on the Adsorption of

426

Heterocyclic Sulfur and Nitrogen Compounds by Activated Carbon: Equilibrium, Kinetics

427

and Thermodynamics. Chem. Eng. J. 2010, 164 (1), 29–36.

428

https://doi.org/10.1016/j.cej.2010.07.068.

429

(31)

430 431

Saha, P.; Chowdhury, S. Insight Into Adsorption Thermodynamics. In Thermodynamics Mizutani Tadashi, IntechOpen; InTech, 2011; pp 349–365. https://doi.org/10.5772/13474.

(32)

Saleh, T. A.; Sulaiman, K. O.; AL-Hammadi, S. A.; Dafalla, H.; Danmaliki, G. I.

432

Adsorptive Desulfurization of Thiophene, Benzothiophene and Dibenzothiophene over

433

Activated Carbon Manganese Oxide Nanocomposite: With Column System Evaluation. J.

434

Clean. Prod. 2017, 154, 401–412. https://doi.org/10.1016/j.jclepro.2017.03.169.

435

(33)

Revell, L. E.; Williamson, B. E. Why Are Some Reactions Slower at Higher


Page 21 of 32 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

Energy & Fuels

21

436

Temperatures? J. Chem. Educ. 2013, 90 (8), 1024–1027.

437

https://doi.org/10.1021/ed400086w.

438

(34)

Al-Ghouti, M.; Khraisheh, M. A. M.; Ahmad, M. N. M.; Allen, S. Thermodynamic

439

Behaviour and the Effect of Temperature on the Removal of Dyes from Aqueous Solution

440

Using Modified Diatomite: A Kinetic Study. J. Colloid Interface Sci. 2005, 287 (1), 6–13.

441

https://doi.org/10.1016/j.jcis.2005.02.002.

442

(35)

Choi, A. E. S.; Roces, S.; Dugos, N.; Arcega, A.; Wan, M. W. Adsorptive Removal of

443

Dibenzothiophene Sulfone from Fuel Oil Using Clay Material Adsorbents. J. Clean. Prod.

444

2017, 161, 267–276. https://doi.org/10.1016/j.jclepro.2017.05.072.

445

(36)

Choi, A. E. S.; Roces, S.; Dugos, N.; Wan, M. W. Adsorption of Benzothiophene Sulfone

446

over Clay Mineral Adsorbents in the Frame of Oxidative Desulfurization. Fuel 2017, 205,

447

153–160. https://doi.org/10.1016/j.fuel.2017.05.070.

448

(37)

De Castro, M. L. F. A.; Abad, M. L. B.; Sumalinog, D. A. G.; Abarca, R. R. M.;

449

Paoprasert, P.; de Luna, M. D. G. Adsorption of Methylene Blue Dye and Cu(II) Ions on

450

EDTA-Modified Bentonite: Isotherm, Kinetic and Thermodynamic Studies. Sustain.

451

Environ. Res. 2018. https://doi.org/10.1016/J.SERJ.2018.04.001.

452

(38)

Kan, C.-C.; Ibe, A. H.; Rivera, K. K. P.; Arazo, R. O.; de Luna, M. D. G. Hexavalent

453

Chromium Removal from Aqueous Solution by Adsorbents Synthesized from

454

Groundwater Treatment Residuals. Sustain. Environ. Res. 2017, 27 (4), 163–171.

455

https://doi.org/10.1016/J.SERJ.2017.04.001.

456

(39)

457 458

Langmuir, I. The Adsorption of Gases on Plane Surfaces of Glass, Mica and Platinum. J. Am. Chem. Soc. 1918, 40 (9), 1361–1403. https://doi.org/10.1021/ja02242a004.

(40)

Freundlich, H. Über Die Adsorption in Lösungen. Zeitschrift für Phys. Chemie 1906, 57


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 22 of 32

22

459 460

(1), 385–470. (41)

Kan, C.-C.; Sumalinog, M. J. R.; Rivera, K. K. P.; Arazo, R. O.; de Luna, M. D. G.

461

Ultrasound-Assisted Synthesis of Adsorbents from Groundwater Treatment Residuals for

462

Hexavalent Chromium Removal from Aqueous Solutions. Groundw. Sustain. Dev. 2017,

463

5, 253–260. https://doi.org/10.1016/J.GSD.2017.07.004.

464

(42)

Ong, D. C.; Kan, C.-C.; Pingul-Ong, S. M. B.; de Luna, M. D. G. Utilization of

465

Groundwater Treatment Plant (GWTP) Sludge for Nickel Removal from Aqueous

466

Solutions: Isotherm and Kinetic Studies. J. Environ. Chem. Eng. 2017, 5 (6), 5746–5753.

467

https://doi.org/10.1016/J.JECE.2017.10.046.

468

(43)

de Luna, M. D. G.; Flores, E. D.; Cenia, M. C. B.; Lu, M.-C. Removal of Copper Ions

469

from Aqueous Solution by Adlai Shell (Coix Lacryma-Jobi L.) Adsorbents. Bioresour.

470

Technol. 2015, 192, 841–844. https://doi.org/10.1016/J.BIORTECH.2015.06.018.

471

(44)

Danmaliki, G. I.; Saleh, T. A. Effects of Bimetallic Ce/Fe Nanoparticles on the

472

Desulfurization of Thiophenes Using Activated Carbon. Chem. Eng. J. 2017, 307, 914–

473

927. https://doi.org/10.1016/j.cej.2016.08.143.

474

(45)

Srivastav, A.; Srivastava, V. C. Adsorptive Desulfurization by Activated Alumina. J.

475

Hazard. Mater. 2009, 170 (2–3), 1133–1140.

476


477

(46)

Shah, S. S.; Ahmad, I.; Ahmad, W. Adsorptive Desulphurization Study of Liquid Fuels

478

Using Tin (Sn) Impregnated Activated Charcoal. J. Hazard. Mater. 2016, 304, 205–213.

479


480 481

(47)

Anbia, M.; Parvin, Z. Desulfurization of Fuels by Means of a Nanoporous Carbon Adsorbent. Chem. Eng. Res. Des. 2011, 89 (6), 641–647.


Page 23 of 32 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

Energy & Fuels

23

482 483

https://doi.org/10.1016/j.cherd.2010.09.014. (48)

Nanoti, A.; Dasgupta, S.; Goswami, A. N.; Nautiyal, B. R.; Rao, T. V.; Sain, B.; Sharma,

484

Y. K.; Nanoti, S. M.; Garg, M. O.; Gupta, P. Mesoporous Silica as Selective Sorbents for

485

Removal of Sulfones from Oxidized Diesel Fuel. Microporous Mesoporous Mater. 2009,

486

124 (1–3), 94–99. https://doi.org/10.1016/j.micromeso.2009.04.040.

487

(49)

Lim, S. M.; Kim, J. N.; Park, J.; Han, S. S.; Park, J. H.; Jung, T. S.; Yoon, H. C.; Kim, S.

488

H.; Ko, C. H. Energy-Efficient Sulfone Separation Process for the Production of Ultralow

489

Sulfur Diesel by Two-Step Adsorption. Energy and Fuels 2012, 26 (4), 2168–2174.

490

https://doi.org/10.1021/ef201964v.

491

(50)

Sarda, K. K.; Bhandari, A.; Pant, K. K.; Jain, S. Deep Desulfurization of Diesel Fuel by

492

Selective Adsorption over Ni/Al2O3and Ni/ZSM-5 Extrudates. Fuel 2012, 93, 86–91.

493


494 495 496 497 498 499 500 501 502 503 504


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 24 of 32

24

505 506 507 508 509 510 511 512 513

(a)

(b)


Page 25 of 32 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

Energy & Fuels

25

(c)

514

Fig. 1. GC-SCD chromatograms of diesel in various stages (a) raw, (b) after oxidative

515

desulfurization, and (c) after adsorptive desulfurization

516 517

Fig. 2. (a) Arrhenius plot of the pseudo-second order kinetic model and (b) plot of ln K versus

518

1/T for sulfur adsorption by PAC and powdered alumina

519 520 521 522 523


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 26 of 32

26

524 525 526 527 528 529 530 531

532 533

Fig. 3. Plot of ln D versus 1/T

534 535 536 537 538


Page 27 of 32 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

Energy & Fuels

27

539 540 541 542 543 544 545 546

547

Fig. 4. (a) Langmuir and (b) Freundlich plots of sulfur adsorption by PAC and powdered

548

alumina

549 550 551 552 553 554 555 556


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 28 of 32

28

557 558 559 560 561 562 563 564

Table 1. Physical and chemical properties of actual diesel fuel (supplied by TaiChin Company,

565

Taiwan) Property Cetane index Polycyclic aromatic carbon (%, m m-1) Flash point (°C) Water content (mg kg-1) Total contamination (mg kg-1) Kinematic viscosity at 40 °C (mm2 s-1)

Standard method ASTM D976 EN12916 ASTM D93 ISO12937 EN12662 ASTM D445

566 567 568 569 570 571 572 573 574 575 576


Value 48 11 55 200 22 2.0-4.5

Page 29 of 32 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

Energy & Fuels

29

577 578 579 580 581 582 583 584

Table 2. Equilibrium adsorption capacities of PAC and powdered alumina adsorbents at

585

different temperatures fitted into the pseudo-first and pseudo-second order reaction kinetics. Temperature (K)

Pseudo-first order k1 (min-1) qe (mg g-1) R2

Pseudo-second order k2 (g mg-1 min-1) qe (mg g-1)

R2

PAC 293

0.0135

0.9682

0.9433

0.0621

2.0214

0.9980

298

0.0144

1.0608

0.9212

0.0428

2.5393

0.9983

313

0.0168

1.2526

0.9135

0.0352

3.0057

0.9944

293

0.0794

2.355

0.9196

0.1149

4.722

0.9995

298

0.0655

2.429

0.9417

0.1178

4.726

0.9974

313

0.0835

1.829

0.9114

1.1774

4.758

0.9997

Powdered alumina

586 587 588 589 590 591 592


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 30 of 32

30

593 594 595 596 597 598 599 600

Table 3. Thermodynamic parameters of sulfur adsorption by PAC and powdered alumina Adsorbent (g) PAC 1

Temperature (K)

Keq

313 293 303 313 313 313

0.264 0.452 0.640 0.875 1.074 1.426

293 298 313 313 313 313

0.287 0.287 0.291 1.162 1.983 2.017

3 5 7 Powdered alumina 1 3 5 7

ΔH (kJ mol-1) ΔS (J mol-1 K-1) -

-

25.187

79.380

-

-

0.558

-8.482

-

-

601 602 603 604 605 606 607


ΔG (kJ mol-1) 3.466 1.934 1.123 0.348 -0.185 -0.923 3.041 3.090 3.214 -0.391 -1.781 -1.826

Page 31 of 32 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

Energy & Fuels

31

608 609 610 611 612 613 614 615

Table 4. Isotherm parameters for sulfur adsorption by PAC and powdered alumina Isotherm model Langmuir qmax (mg g-1) kL (L mg-1) R2 Freundlich kf (mg g-1)/(mg L-1) n R2

PAC

Powdered alumina

6.31 5.381 x 10-4 0.9020

27.03 2.828 x 10-4 0.8345

8.373 x 10-4 0.782 0.8948

0.027 1.294 0.8626

616 617 618 619 620 621 622 623 624 625 626


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 32

32

627 628 629 630 631 632 633 634

Table 5. Adsorption capacities for sulfur by various adsorbents Adsorbent Alumina, acidic Alumina, basic Alumina, neutral Zinc oxide Zeolite 13X Polymeric resin XAD-16 Polymeric resin XAD-4 Alumina basic (Alcoa) Alumina neutral (Alcoa) Activated carbon (Calgon F-300) Activated carbon (Calgon F-400) Silica gel (6-20 mesh) Silica Activated carbon (Calgon) CMS-4K(AC molecular sieve 4K) CMS-4K-5h (CMS-4K activated at 1173K for 5 h) Activated alumina ZSM-5 (Si/Al = 20) PAC Powdered alumina

Adsorbate DBTO in toluene (500 ppm sulfur)

commercial diesel fuel (473 ppm sulfur)

commercial diesel fuel (150 ppm sulfur)

qe(mg g-1) 5.7 5.5 4.3 0 0.6 0.6 0.8 0.9 1.4 4.1 4.4 5.1 1.1 0.5

Reference

0.3

49

18

48

0.05 commercial diesel fuel (325 ppm sulfur) commercial diesel fuel (950 ppm sulfur)

635


0.38 0.32 6.31 27.03

50

This study

Isotherm and Thermodynamic Studies on the Removal of Sulfur from

Recommend Documents