NaY structure for the

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Materials and Interfaces

Core-shell zeolite composite with silicalite-1/NaY structure for the adsorption desulfurization of dimethyl disulfide from methyl tert-butyl ether Chao Yang, Xuan Meng, Dezhi Yi, Zhiming Ma, Naiwang Liu, and Li Shi Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b04733 • Publication Date (Web): 09 Nov 2018 Downloaded from http://pubs.acs.org on November 18, 2018

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Industrial & Engineering Chemistry Research

1

Core-shell zeolite composite with silicalite-1/NaY structure for the

2

adsorption desulfurization of dimethyl disulfide from

3

methyl tert-butyl ether

4

Chao Yang, Xuan Meng, Dezhi Yi, Zhiming Ma, Naiwang Liu, Li Shi*

5

State Key Laboratory of Chemical Engineering,

6

East China University of Science and Technology, Shanghai 200237, China

7

E- mail: [email protected]

8

Abstract: Desulfurization of dimethyl disulfide (DMDS) from methyl tert-butyl

9

ether (MTBE) has been studied on the silicalite-1/NaY core-shell composites. By

10

changing the mass ratio of tetraethyl orthosilicate (TEOS)/ NaY, the silicalite-1 shell

11

synthesis condition was conducted at the mass ratio of TEOS/ tetrapropylammonium

12

hydroxide (TPAOH)/ ethanol (EtOH)/ H2O=(10, 15, 20, 25, 30 g):19 g:17 g:87 g

13

((0.048, 0.072, 0.096, 0.12, 0.144): 0.0234: 0.369: 4.8293 in molar ratio, where the

14

mass of NaY zeolite was quantified to 5g) by a hydrothermal synthesis at 180 °C for

15

24 h. Results showed that when the mass ratio of TEOS/ TPAOH/ EtOH/ H2O/

16

NaY=20 g:19 g:17 g:87 g:5 g, the silicalite-1 coating could be dispersed and covered

17

on the surface of NaY well (the thickness of silicalite-1 shell ranged from 100-400 nm)

18

with the best sulfur adsorption capacity to be 20.711 mgs/gadsorbent. The shape selective

19

adsorption mechanism of desulfurizing DMDS from MTBE on these core-shell

20

composites was also elaborated.

21

Key words: Adsorptive desulfurization; Dimethyl disulfide; Methyl tert-butyl ether;

22

silicalite-1/NaY core-shell composites

23

1. Introduction

24

Since the Methyl tert-butyl ether (MTBE) was first synthesized in 1904, it had

25

been applied to numerous chemical reactions.1 However, the most importance of

26

MTBE was still based primarily on its good octane-enhancing property when used as

27

a gasoline additive agent.2,3 In fact, more than 95 % of MTBE produced were used in

28

this way. Industrially, MTBE was produced by the reaction of isobutene, contained in

29

C4-fractions, and methanol. As was known that the C4 stream contained various kinds

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Industrial & Engineering Chemistry Research 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

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of sulfur compounds including DMS (dimethyl sulfide), DMDS (dimethyl disulfide),

31

and so forth.4 When this C4 stream was used to produce MTBE, the content of DMDS

32

would reach more than 45 ppm.5 DMDS was a volatile organic compound containing

33

sulfur and produced mainly from petroleum refining processes, the wood-pulping

34

industry, and enemy-related activities.5 DMDS could cause toxic effects when inhaled

35

or absorbed by skin. Also, burning of fuel with DMDS would release SOx emissions,

36

leading to a negative environmental or healthy effect.6

37

In 2009, the European Union had clearly defined that the sulfur content of

38

gasoline must be less than 10 ppmw, then followed by Beijing in 2012.7 At present,

39

the industrial desulfurization methods for MTBE products could be classified into

40

three

41

hydrodesulfurization process required a harsh operational condition with high

42

temperature and high pressure, which was bound to reduce the octane number;

43

meanwhile, the huge energy consumption was unacceptable, and always accompanied

44

with the loss of MTBE. Whereas, adsorption desulfurization could be carried out at

45

atmospheric temperature and pressure, which was simple in operation and low energy

46

consumption. However, when desulfurizing DMDS from MTBE by adsorption, a

47

strong competitive adsorption between MTBE and DMDS on π-complex adsorbents

48

would occur,9,10 owing to the fact that the oxygen atom in MTBE was more

49

electronegative than sulfur atom in DMDS. Yang and co-workers12,13 found that the

50

sulfur adsorption capacity of the π-complex adsorbents would sharply decrease in the

51

presence of MTBE and even completely lost within large amounts of MTBE.

categories:

hydrodesulfurization,

distillation,

and

adsorption.8-11

The

52

Desulfurization on various adsorbents such as the activated carbons (ACs),14

53

modified composite oxide,15 and zeolite,16 had already been studied in depth. But the

54

key challenge was to find a kind of adsorbent that could selectively adsorb DMDS

55

from MTBE. Researches suggested that Y zeolite and its modified one had been

56

proved promising materials to meet this requirement because of its high solid acidity,

57

three-dimensional (3D) pore structure.17 Wakita et al.18 had investigated the removal

58

of dimethyl sulfide and t-butylmercaptan in the city gas using NaY, NaX, Hβ zeolite,

59

and found that the adsorption site of NaY was the Na+ in the supercage with a


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60

maximum sulfur capacity to be 1.1 mmols/gadsorbents of DMS on NaY. Lee et al.19 used

61

ion-exchanged zeolites to remove DMDS from C4 hydrocarbon mixture and claimed

62

that ion-exchanged zeolites were favorable adsorbents with high capacity in removal

63

of DMDS from gas hydrocarbon mixture at ambient conditions; and the best sulfur

64

capacity was 8.70 mgs/gadsorbents, when β zeolite with a SiO2/Al2O3 ratio to be 25

65

contented 10 wt% of Cu(I). Lv et al.20 studied the adsorptive separation of DMDS

66

from liquefied petroleum gas by different zeolites, and concluded that 5 wt%

67

Ag2O/NaY showed the highest breakthrough sulfur capacity reaching up to

68

87.86 mgs/gadsorbents, and the direct S-Ag(I) interaction played an important role in the

69

evidently improved adsorption ability and selectivity. Zhao et al.21 aimed at the

70

removal of DMDS from MTBE by using ZSM-5 zeolite; investigation showed that

71

both the pore structure and acidity play important roles in determining the sulfide

72

adsorption process and CLD-modified ZSM-5 zeolite exhibited an optimal DMDS

73

adsorption capacity to be 8.24 mgs/gadsorbents. Our research group also tried many

74

efforts in desulfurizing DMDS. Yi et al.5,22 used silver-modified bentonite and

75

liquid-phase ion exchanged NaY with Cu2+, Ni2+, Co2+ and Ce3+ to remove DMDS

76

from n-octane solution and concluded that multilayer intermolecular forces and S-M

77

bonds played important roles in desulfurization process.

78

Silicalite-1 contained ten-membered rings with a basic structural unit made up of

79

eight five-membered rings; and the maximum aperture was less than 0.6 nm. When

80

coating Y zeolite with silicalite-1, the ordered silica shell with regular arranged pore

81

channels will not only enhance the stability and maintain the reactive activity of core

82

particles17 but provide a shape selectivity to allow DMDS (0.37 nm) to pass by only.

83

In the present study, considering that NaY zeolite had a high sulfur adsorption

84

capacity in simulated solution but low in MTBE solution; and silicalite-1 owned a

85

higher shape selectivity. Instead of directly selecting NaY zeolite as the adsorbent, we

86

coated NaY with an silicalite-1 shell (pure silica crystal) to form the silicalite-1/NaY

87

core-shell composites, expecting that the silicalite-1 coating could hinder MTBE from

88

diffusing into the NaY core. Many literatures had reported coating silicalite-1 on

89

ZSM-5,23-25 β zeolite26,27 or amorphous silica alumina (ASA)28. Zhao et al.17 also



90

reported a core-shell structured composite molecular sieves comprising mono-

91

dispersed nano-sized zeolite single-crystals (nano-zeolite Y) as cores and ordered

92

mesoporous silica as shells. Nevertheless, as a whole, coating silicalite-1 on NaY

93

zeolites and applying these core-shell composites to selectively adsorb DMDS from

94

MTBE were rarely investigated. In this paper, different silicalite-1/NaY core-shell

95

composites with various mass ratios of TEOS/NaY were synthesized. Moreover, the

96

adsorbents were characterized by scanning electron microscopy (SEM), transmission

97

electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared

98

spectra (FT-IR) and N2 adsorption-desorption experiment. The adsorption mechanism

99

of silicalite-1/NaY core-shell composites was also discussed based on these

100

experimental data and characterization analysis.

101

2. Experimental

102

2.1. Chemicals

103

Analytical pure ethanol (EtOH), tetraethyl orthosilicate (TEOS) and 25%

104

tetrapropylammonium hydroxide (TPAOH) solution were purchased from Shanghai

105

Tansoole Company. Industrial grade NaY (Si/Al = 2.4) was provided by Wenzhou

106

Catalyst Factory. Deionized water was used in all experiments.

107

2.2. Synthesis of silicalite-1 and core-shell composite molecular sieves

108

The silicalite-1/NaY core-shell structured composite molecular sieves were

109

synthesized through a sol-gel coating process by using TPAOH as the template,29

110

which was typically prepared as following:

111

Silicalite-1 shell precursor solution was a sol for the synthesis of silicalite-1

112

coatings consisting of TEOS as the silica source, TPAOH as the structure-directing

113

agent and ethanol, as well as deionized water at the mass ratio of TEOS/ TPAOH/

114

EtOH/ H2O=(10, 15, 20, 25, 30 g):19 g:17 g:87 g ((0.048, 0.072, 0.096, 0.12, 0.144):

115

0.0234: 0.369: 4.8293 in molar ratio). In order to make the TEOS hydrolyzed

116

sufficiently in water, TEOS was added dropwise and stirred for 2 h at room

117

temperature. To explore the synthesis condition of silicalite-1 shell, the mass ratio of

118

TEOS/NaY were ranged from 2 to 6 (including 2, 3, 4, 5 and 6, where the mass of

119

NaY zeolite was quantified to 5g). After a hydrothermal synthesis being carried out in


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120

an autoclave at 180 °C for 24 h, the as-made core-shell structured composites were

121

collected by two methods: vacuum filtration (maximum pore size of filter paper to be

122

15-20 μm) and centrifugation (6000 r/min for 30 min), respectively, washed with

123

enough deionized water, dried at 120 °C overnight, and then calcined in air at 550 °C

124

for 5 h.30,31 In this research, the core-shell composites by filtration were studied.

125

Silicalite-1 was prepared at the mass ratio of TEOS/ TPAOH/ EtOH/ H2O= 20

126

g:19 g:17 g:87 g (0.096: 0.0234: 0.369: 4.8293 in molar ratio) by the same synthetic

127

method only without adding NaY.

128

2.3. DMDS adsorption experiments

129

2.3.1. Static tests

130

To evaluate the sulfur adsorption capacity of the adsorbents, Static tests were

131

carried out by adding 0.2 g adsorbent into a 20 mL MTBE solvent mixed with DMDS

132

as the solute (sulfur content: 275.51 mg/L) within an 30 ml airtight container standing

133

at room temperature for 24 h. A TS-3000 fluorescence sulfur tester was used to

134

analyze the concentration of sulfur before and after the static tests.5,22 The sulfur

135

adsorption capacity of the adsorbent would be calculated as follow:

136

Sulfur adsorption capacity(mgs/gadsorbent) = (275.51- Ct)×20/0.2

137

where the Ct (mg/L) was the sulfur concentration of MTBE solution after static tests.

138

2.3.2. Dynamic tests

139

The adsorbents was put into a fixed bed flow reactor at atmosphere pressure (0.1

140

MPa) and room temperature (25 °C) with a weight hourly space velocity (WHSV) of

141

5 h-1 to evaluate their adsorption desulfurization performance. About 0.89 g of

142

adsorbent samples were fixed in the middle of a quartz column (length: 250 mm;

143

internal diameter: 6 mm); the spare spaces up and down were filled with quartz sand

144

(20-40 mesh). MTBE solution (sulfur content: 171.51 mg/L) was pumped into the

145

fixed-bed flow reactor at a flow rate of 6 ml/h. The export sulfur content was analyzed

146

by TS-3000 fluorescence sulfur tester periodically at a time interval of 30 min.

147

2.4. Characterization

148

2.4.1. Scanning electron microscopy and transmission electron microscope

149

Scanning electron microscopy (SEM) images were recorded on a Hitachi S-3400



150 151

microscope working at 15 KV acceleration voltage with a magnification of 16K. Transmission electron microscope (TEM) images were conducted on a

152

JEM-2100 working at 200 KV with a magnification of 1500 K.

153

2.4.2. N2 adsorption-desorption

154

In order to obtain the surface area, pore volume and other texture properties of

155

the adsorbents, a JW-BK200C instrument was used by adsorbing nitrogen at -196 °C

156

on about 150 mg samples, which should be previously degassed at 300 °C for at lest 2

157

h under high vacuum atmosphere. The total surface area (St), total pore volume (Vt),

158

micropore volume (Vmic), average pore size (Da) and micropore pore size (Dmic) could

159

be calculated by nitrogen isotherms.

160

2.4.3. X-ray diffraction

161

A X-ray Diffraction (XRD) was applied to analyze these silicalite-1/NaY

162

core-shell composites in the powder state. XRD was performed by a D8 Advance

163

polycrystalline diffractometer equiped with Cu Kα radiation (40 KV, 100 mA) over

164

the range from 10° to 75° in a step of 0.02°.

165

2.4.4. FT-IR measurements

166

Fourier transform infrared spectra (FT-IR) was collected with a Magna-IR550

167

spectrometer (Nicolet Company) by mixing the adsorbent sample powder with the

168

dried KBr in an appropriate ratio (1:100 in mass). And the finely ground adsorbents

169

were pressed into a self-supporting wafer with a diameter of about 10 mm as the

170

scanning sample.

171

3. Results and discussion

172

3.1. Desulfurization performances of different core-shell NaY zeolites.

173

3.1.1. Static active data analysis


Page 6 of 28

mg/L

Raw material sulfur 286.43 concentration ： 275.51 mg/L

272.65

229.24

258.97

262.23

1.657

1.328

231.62 4.627

4.389

-1.092

A 174 175

mgs/gadsorbent

20.711

0.286 68.4

B

C

D

E

F

Sulfur adsorbtion capacity (mgs/gadsorbent)

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


Sulfur content after adsorption (mg/L)

Page 7 of 28

G

177

Figure 1. The sulfur content after adsorption and sulfur adsorption capacity for DMDS adsorption in MTBE of different absorbents: A. NaY, B. Silicalite-1, C. TEOS/NaY=2, D. TEOS/NaY=3, E. TEOS/NaY=4, F. TEOS/NaY=5, and G. TEOS/NaY=6

178

Static adsorption activity tests were carried out at room temperature to evaluate

179

the desulfurization performances of different adsorbents. And the sulfur content after

180

adsorption and sulfur adsorption capacity for DMDS adsorption in MTBE of these

181

absorbents were depicted in Figure 1. Results showed that compared with the raw

182

material sulfur concentration 275.51 mg/L, the sulfur content after adsorption of NaY

183

was increased, resulting in corresponding negative sulfur adsorption capacities to be

184

-1.092 mgs/gadsorbents, which suggested that MTBE could be adsorbed on NaY more

185

easily than DMDS. As a matter of fact, DMDS and MTBE were adsorbed on these

186

absorbents by π-complexation of matel-S and matel-O.10,32,33 Combined the structure

176

H3C

187

of DMDS

( H3C S S CH3 )

and MTBE (

H3C

O CH 3 CH3

), the methyl and tert butyl were both H3C H3C

188

electron donating groups, and the electron donating ability of tert butyl (

189

better than that of methyl ( CH3 ). By comparison, the electronegativity of O in

190

MTBE was weakened more than S in DMDS, leading to a smaller electronegativity

191

gap between S and O. When they formed matel-S and matel-O, It didn't make much

192

difference. In MTBE solution, owing to that the MTBE was much more than DMDS,

193

the contact probability between adsorbents and MTBE was absolutely much more

194

than that of DMDS. Thus, for DMDS, MTBE came into being a strong competitive


CH3

) was


195

adsorption on these π-complexation adsorbents,34 leading to a decrease in MTBE and

196

an increase in sulfur concentration, as well as a negative value of sulfur adsorption

197

capacity according to the calculation formula of sulfur adsorption capacity (section

198

2.3.1). However, when the NaY zeolite was coated by silicalite-1 to form the

199

core-shell structure with the mass ratio of TEOS/ NaY equaling 4, it performed the

200

best sulfur adsorption capacity to be 20.711 mgs/gadsorbents. It was worth mentioning

201

that the silicalite-1 alone as the adsorbent did not perform well either; the sulfur

202

adsorption capacity of silicalite-1 was only 0.286 mgs/gadsorbents. Compared with NaY

203

zeolite, silicalite-1 could adsorb a certain amounts of DMDS in MTBE solution with a

204

low sulfur adsorption capacity, indicating that silicalite-1 owned some selection

205

characteristics for DMDS in MTBE. However, there were almost no active adsorption

206

sites in silicalite-1 owing to its pure silicalite molecular sieve without aluminum

207

atoms in MFI skeleton structure; DMDS could only be adsorbed by a weak interaction

208

(van der Waals force) between silicalite-1 and DMDS. When coating NaY zeolite

209

with silicalite-1, the silicalite-1 coating would prevent MTBE from migrating into the

210

core-shell structure and the core NaY zeolite would adsorb DMDS, holding back

211

DMDS from migrating out of the core-shell structure. Thus, the core-shell composites

212

could obviously improve the sulfur adsorption capacity of both NaY and silicalite-1.

213

3.1.2. Dynamic active data analysis 100

Desulfurization rate of DMDS(%)

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 28

TEOS/NaY=2 TEOS/NaY=3 TEOS/NaY=4 TEOS/NaY=5 TEOS/NaY=6 NaY Silicalite-1

80 60 40 20 0 0

214 215 216 217

1

2

3

4

Time (h)

Figure 2. Breakthrough curves of NaY, silicalite-1, and silicalite-1/NaY core-shell structured composites adsorbing DMDS in MTBE solution

Dynamic adsorption activity tests were also carried out at room temperature to


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218

evaluate the desulfurization performances of different adsorbents. Figure 2 showed

219

the breakthrough curves for desulfurizing DMDS from MTBE on NaY, silicalite-1,

220

and silicalite-1/NaY core-shell structured composites. It could be seen from the curves

221

that with the elapse of time, the desulfurization performances of the adsorbents

222

overall showed a downward trend. Also, owing to the competitive adsorption, NaY

223

zeolite and silicalite-1 crystal still put up a poor performance in desulfurization, and

224

the desulfurization rate of NaY zeolite was even all along negative, indicating no

225

sulfur adsorption capacity at all. For the silicalite-1/NaY core-shell structured

226

composites, with the mass ratio of TEOS/NaY increasing, the sulfur adsorption

227

capacity did not follow this increasing step. when the the mass ratio of TEOS/ NaY

228

reached 4, more than 90% desulfurization rate could be achieved and kept for about

229

2.2 hours; as the mass ratio of TEOS/NaY further increased, the sulfur adsorption

230

capacity dropped instead.

231

3.2. SEM and TEM images of the core-shell NaY zeolites (a)

(b)

(c)

(f )

silicalite-1 coating

(e) silicalite-1 crystal

(d)

232 233 234

(g)

Figure 3. SEM images of NaY zeolite and silicalite-1/NaY composites:(a) NaY×7K, (b) NaY×16K, (c) TEOS/NaY=2×16K, (d) TEOS/NaY=3×16K, (e) TEOS/NaY=4×16K, (f) TEOS/NaY=5×16K, (g) TEOS/NaY=6×16K



(a)

(b)

(c)

(d) 100 nm

400 nm

235

Figure 4. TEM images of NaY (a), (b); and core-shell structure as TEOS/NaY=4 (c), (d).

236

The SEM images of the NaY zeolite and after the silicalite-1 coating were shown

237

in Figure 3. Finely scattered NaY zeolites could be observed in Figure 3 (a) and (b),

238

respectively. Figure 3 (c)-(g) showed the silicalite-1/NaY composites with different

239

mass ratio of TEOS/ NaY. When the mass ratio was low (TEOS/ NaY=2, TEOS/

240

NaY=3), randomly oriented silicalite-1 crystals were coated on the local external

241

surface of NaY zeolites. Figure 3 (e) showed the SEM images of the silicalite-1/NaY

242

composites when TEOS/NaY equaled 4, and the most outer surface of the NaY

243

zeolites was attached by silicalite-1 coating as shown in Figure 4 (c) and (d) against

244

with the smooth surface of NaY (Figure 4 a, b). And the thickness of the silicalite-1

245

shells was evaluated from 100 nm to 400 nm. However, when the mass ratio of

246

TEOS/ NaY reached 5 and 6, the chunk silicalite-1 crystals instead of scattered

247

silicalite-1 coatings were formed and embedded in the NaY zeolite particles rather

248

than coating NaY zeolites around. From Figure 3 (f) and (g), silicalite-1 overgrowth

249

could be easily observed.30,31

250

3.3. Mass gain of NaY zeolites after coating silicalite-1.

251

Figure 5 depicted the mass gain of NaY zeolites after coating silicalite-1. All in

252

all, The mass gain persistently increased with the increasing mass ratio of TEOS/NaY.

253

In this study, the NaY zeolite was fixed at 5 g. According to the mass ratio of

254

TEOS/NaY, the mass gain of NaY zeolite should be a straight line in theory as the

255

blue area or line. In order to investigate the actual yield of NaY zeolites after coating

256

silicalite-1, two different methods were tried to collect the silicalite-1/ NaY core-shell

257

structured composites: filtration and centrifugation, respectively.


Page 10 of 28

20

in theory after filtration after centrifugation

18 16

Mass gain (g)

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


200


175

mass gain (%)

mass gain (g)

150

14 12

125

10

100

8

75

6

50

4

25

2 0

Mass gain (%)

Page 11 of 28

1

2

3

4

5

6

7

0

TEOS/NaY (g/g) 258 259

Figure 5. Mass gain of NaY zeolites after coating silicalite-1

260

As shown in Figure 5, after centrifugation, In addition to some necessary losses,

261

the mass gain of NaY zeolites were similar and close to that in theory. However, the

262

red area or line showed that when the mass ratio of TEOS/ NaY was 2 and 3 (or 10:5

263

and 15:5) the mass gain increased slightly. While the mass ratio of TEOS/ NaY was 5

264

and 6 (or 25:5 and 30:5), there was not much difference in mass gain between

265

filtration and centrifugation. Combined with SEM patterns (Figure 3), we assumed

266

that when the mass ratio of TEOS/NaY was low (2 or 3), silicalite-1 crystals was

267

difficult to grow on the external surface of NaY zeolites, which meant a large amount

268

of silicalite-1 crystals with minimum size were formed through a homogeneous

269

nucleation in the solution, then filtered out the core-shell composites; and these

270

silicalite-1 crystals do not contribute to the external surface modification of NaY

271

zeolites;24 whereas, the mass ratio of TEOS/NaY was high (5 or 6), silicalite-1

272

crystals could easily form a large silica crystal, resulting in the fact that a large

273

amount of silicalite-1 would be held back together with NaY zeolites by the filter

274

paper. Actually, as shown in SEM and TEM patterns, the mass ratio of TEOS/ NaY to

275

be 4 (or 20:5) was the best choice for silicalite-1 crystals and NaY zeolites to form the

276

silicalite-1/NaY core-shell composite molecular sieves. Meanwhile, from the active

277

data in Figure 2, the mass ratio of TEOS/NaY equaling 4 performed the best

278

selectivity of DMDS and displayed the highest sulfur adsorption capacity.


mg/L


295

294.44

Raw material sulfur ： 284.53 mg/L

292.62

290

-0.809

285

mgs/gadsorbent

-0.587

291.64

-0.757

-0.711

-0.7

290.4

-0.8 -0.9 -1.0

a

0.0

-0.5 -0.6

292.1

-0.991

280


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 28

b

c

d

-1.1

e



-0.5 -1.0 a b c d e

-1.5 -2.0 -2.5 -3.0 -3.5

0

1

2

3

4

279

Time (h)

280

Figure 6. The sulfur content after adsorption; sulfur adsorption capacity for DMDS in MTBE solution, and breakthrough curves of different physical mixed absorbents: a. silicalite-1/NaY=0.1678, b. silicalite-1/NaY=0.3751, c. silicalite-1/NaY=0.8658, d. silicalite-1/NaY=1.2657, e. silicalite-1/NaY=1.5158.

281 282 283 284

In order to identify the advantage of core-shell structure in selective adsorption

285

DMDS from MTBE, the adsorption property over physical mixed NaY zeolites and

286

silicalite-1 was investigated (Figure 6). From the mass gain of NaY zeolites after

287

coating silicalite-1 shown in Figure 5, based on 5 g NaY zeolite, the mass gain of

288

NaY (or silicalite-1 coating) after filtration were 0.839 g, 1.8755 g, 4.329 g, 6.3285 g,

289

and 7.579 g (silicalite-1/NaY= 0.1648, 0.3751, 0.8658, 1.2657, and 1.5158 in mass),

290

respectively, according to different mass ratio of TEOS/NaY. Results showed the

291

adsorption property over physical mixed NaY zeolites and silicalite-1 exhibited no

292

selectivity in adsorption DMDS from MTBE. Compared to the core-shell structured

293

ones, these physical mixed adsorbents displayed a priority to adsorb MTBE in MTBE

294

solution, and performed only a compromised adsorption desulfurization between NaY

295

zeolites and silicalite-1. With the increase of silicalite-1 in physical mixed adsorbents,

296

the sulfur adsorption capacity for DMDS in MTBE calculated by the formula in

297

section 2.3.1 preferred an upward trend but still a negative value. Because NaY

298

zeolites completely lost its adsorption capacity for DMDS in the present of MTBE;

299

but silicalite-1 owned the selective adsorption property to a certain, which coincided


Page 13 of 28 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


300

with the static and dynamic active data analysis in section 3.1.1 and 3.1.2.

301

3.4. Textural properties of adsorbents.

302

Table. 1. Structural properties of NaY, silicalite-1 and core-shell structures. Adsorbents

*S

2/g)

t (m

*V

3 t (cm /g)

*D

a

(nm)

*V

mic

(cm3/g)

*D

mic

(nm)

NaY

793.325

0.406

1.709

0.29

0.8339

Silicalite-1

488.126

0.351

1.982

0.194

0.6554

*T/N=2

589.020

0.172

2.510

0.208

0.8529

T/N=3

624.385

0.308

2.141

0.213

0.8465

T/N=4

624.775

0.334

1.973

0.219

0.8463

T/N=5

559.097

0.281

2.008

0.181

0.8636

T/N=6

547.995

0.157

2.539

0.156

0.8987

304

mass ratio of TEOS/NaY; *St: total surface area; *Vt: total pore volume; *Da: average pore size; *Vmic: micropore pore volume; *Dmic: micropore pore size.

305

Table.1 showed the structural properties of NaY, silicalite-1 and core-shell

306

structures. The total surface area (St) of NaY was 793.325 m2/g more than that of

307

silicalite-1. Meanwhile, NaY was also provided with larger total pore volume (Vt) and

308

microporous pore volume (Vmic). As the core zeolite, NaY with a larger Vt could

309

provide the core-shell structure more active adsorption centers. Compared the

310

microporous pore size (Dmic) of NaY and silicalite-1, silicalite-1 possessed a smaller

311

microporous channel with a Dmic of 0.6554 nm (Table.1 and Figure 7), making it clear

312

that when silicalite-1 was uniformly coated on NaY, it could hold back the adsorbates

313

with large size molecules from spreading into the core zeolites. And this constituted

314

the foundation of silicalite-1/NaY core-shell composites for selective adsorption of

315

DMDS from MTBE.

303

*T/N:

316

After NaY being coated by silicalite-1, the St was evidently decreased. However,

317

with the increase of TEOS/NaY (T/N), the St was not straight-in penetration; as the

318

T/N equaled 4, the St, Vt and Vmic of core-shell structures were maintained at a high

319

value, ensuring the core-shell structures a good adsorption and accommodation

320

capacity for the adsorbates. In this table, the inexplicable question was that the

321

average pore size (Da) of NaY zeolites was smaller than that of silicalite-1, as well as

322

why silicalite-1/NaY core-shell composites displayed firstly increased then decreased

323

Vmic when TEOS/NaY mass ratios ranged from 2 to 6. Explanation would be



324

presented in N2 adsorption-desorption isotherms. 0.8

0.035

NaY Silicalite-1 TEOS/NaY=2 TEOS/NaY=3 TEOS/NaY=4 TEOS/NaY=5 TEOS/NaY=6

0.030

3 -1 -1 dV/dD (cm g nm )

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

0.025

0.6

0.020 0.015

0.4 0.010 0.005

0.2

0.0 325 326

Page 14 of 28

0.000

0

1

2

3

2

4

4

6

5

8

6

10

7

12

8

14

9

10

Pore width (nm) Figure 7 BJH pore size distributions of different adsorbents

327

As shown in Figure 8, because of no obvious hysteresis loop and notable

328

plateau at high relative pressure being observed, the N2 adsorption-desorption

329

isotherms of NaY and core-shell structures were considered belonging to type-I,

330

suggesting the microporous property of these adsorbents.35 While the N2

331

adsorption-desorption isotherms of silicalite-1 was situated between type-I and

332

type-Ⅳ, indicating that silicalite-1 owned both microporous and mesoporous

333

properties. Obviously, owing to the presence of mesopores, the average pore size (Da)

334

of silicalite-1 was larger than that of NaY. However, the selective adsorption of

335

zeolite was only based on the micropores not the mesopores; the smaller the

336

micropore size was, the better the shape selecting function would be. Thus, Combined

337

with NaY zeolite, the silicalite-1 owned remarkable advantages in shape selection of

338

DMDS from MTBE.

339

As the results showed in Table. 1, the Vmic of NaY and silicalite-1 were 0.29 and

340

0.194 cm3/g, respectively. When NaY zeolite was coated by silicalite-1, Vmic of the

341

silicalite-1/NaY core-shell composites would obviously compromised compared with

342

NaY zeolite and silicalite-1(such as T/N=2, Vmic = 0.208 cm3/g). As the T/N

343

increased, more silicalite-1 crystal was covered on the surface of NaY zeolite; the

344

Vmic of the core-shell composites should be continuously reduced. However,


Page 15 of 28

345

combined with the TEM images of core-shell structure (Figure 4), the silicalite-1

346

crystal coating was not tightly arranged, but stacked together; and these stacking void

347

would absolutely affected the Vmic, leading to an increased Vmic from 0.208 to 0.219

348

cm3/g. 350


300

3

Volume adsorbed (cm /g )

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


250 200 150 100 50 0

349 350

0.0

0.2

0.4

0.6

0.8

1.0

Relative Pressure (P/P0) Figure 8. N2 adsorption-desorption isotherms of NaY, silicalite-1 and core-shell structures.

351

When T/N=5 and 6, owing to a larger concentration of TEOS, silicalite-1

352

crystals could easily form a large silica crystal, resulting in the fact that a large

353

amount of silicalite-1 would be held back together with NaY zeolites by the filter

354

paper (maximum pore size of filter paper to be 15-20 μm). The Vmic of silicalite-1 was

355

less than that of NaY; more silicalite-1 crystals doped in NaY meant greater decline in

356

Vmic of the core-shell composites. In addition, a larger concentration of TEOS also

357

meant that more nana-scaled silicalite-1 crystals were generated, which would

358

blocked the surface channel of NaY zeolite, leading to a sharp decrease in the Vmic of

359

the silicalite-1/NaY core-shell composites from 0.219 to 0.156 cm3/g.

360

3.5. XRD patterns of adsorbents.

361

X-ray diffraction analysis in Figure 9 depicted the mineralogical and core-shell

362

structures of the NaY zeolite, silicalite-1 crystal and NaY with silicalite-1 shell

363

(TEOS/ NaY=2, 3, 4, 5, and 6). From the X-ray diffraction patterns, the diffraction

364

peaks at 2θ=15.640 and 23.640 were considered the feature peaks of NaY zeolite.22

365

And after coating silicalite-1, the XRD patterns of the silicalite-1/NaY core-shell



366

structures showed the same diffraction peaks, suggesting that the crystalline zeolite

367

framework was retained during the coating process.17 Along with the increase mass

368

ratio of TEOS/NaY, the intensity of NaY zeolite feature peaks slightly decreased,

369

which might mostly ascribe to the coating process of diluted zeolites as the

370

mesoporous shell and the weak shielding effects of mesoporous shells on X-rays.17

371

Compared with the X-ray diffraction patterns of NaY and silicalite-1 crystal, a great

372

distinction was observed in the XRD patterns of NaY with silicalite-1 shell, but the

373

same feature peaks of the both were preserved. The most intense peaks of MFI-type

374

material, especially between 2θ=22-25 indicated that the silicalite-1 shell was

375

successfully coated on the surface of NaY zeolites.36

(7) (6)

Intensity (a.u.)

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 28

(5) (4) (3) (2) (1)

10 376 377 378 379 380

20

30

40

50

60

70

2-Theta (degrees) Figure 9. X-ray diffraction patterns of NaY zeolite, silicalite-1 crystal and NaY with silicalite-1 shell: (1) NaY, (2) silicalite-1, (3) TEOS/ NaY=2, (4) TEOS/NaY=3, (5) TEOS/NaY=4, (6) TEOS/NaY=5, (7) TEOS/NaY=6

3.6. In situ FTIR spectra of adsorbents.

381

Figure 10 displayed the FT-IR spectra recorded after the adsorption of DMDS in

382

MTBE on different zeolites. The bands located at 2978 cm-1 which belonged to the

383

region of 3000-2800 cm-1 were considered as the aliphatic νC-H modes.37 Whereas,

384

owing to the fact that the adsorbents were immersed into the mixed solution of both

385

DMDS and MTBE, the bands observed at 2978 cm-1 of νC-H could not be conformed

386

belonging to DMDS or MTBE. As could be seen, there was no band on NaY zeolites

387

locating at 1226 cm-1, which was determined as the stretching vibration of C-S


Page 17 of 28 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


388

(belonging to the region of 1300~1000 cm-1), indicating that for the sake of the fierce

389

competitive adsorption between MTBE and DMDS, almost no DMDS was detected

390

on NaY zeolite. While via physical intermolecular force and other interactions, the

391

stretching vibration of C-S was catched on (2) silicalite-1 crystal and (3)-(7)

392

core-shell zeolites, suggesting that DMDS was actually absorbed on these core-shell

393

zeolites from MTBE solution and that silicalite-1 crystal or silicalite-1 coating owned

394

a shape-selection characteristic of molecular scale between DMDS and MTBE. The

395

bounds observed at 1011 and 1105 cm-1 belonged to the stretching vibration of C-O-C

396

which located at 1250~1000 cm-1 in theory; because when the core-shell zeolites were

397

used as adsorbents, the microporous or mesoporous hole could also adsorb and store

398

some MTBE. Therefore, the stretching vibration of C-O-C bond were detected by

399

FT-IR measurement. Actually, the MTBE did not penetrate into the NaY zeolite core

400

but just stayed on the surface of the core-shell zeolites. And the bands at 1622 cm-1

401

could be assigned to the hydroxide radical vibrations of water adsorbed in the NaY. 1226 1105

(1) (2) (3) (4) (5) (6) (7) 2978

3000 402 403

1622

2500

2000

1500

Wavenumbers (cm -1)

1011

1000

500

405

Figure 10. FT-IR spectra recorded after the adsorption of DMDS in MTBE on different NaY zeolites: (1) NaY, (2) silicalite-1 crystal, (3) TEOS/NaY=2, (4) TEOS/NaY=3, (5) TEOS/NaY=4, (6) TEOS/NaY=5, and (7) TEOS/NaY=6

406

3.7. Mechanism analysis

404

407

Figure 11 displayed the geometrical structures of NaY and NaY with silicalite-1

408

coating. The unit cell of NaY zeolite consisted of 18 four-membered rings, 4

409

six-membered rings and 4 twelve-membered rings. The diameter of the main channel



Page 18 of 28

410

entrance with twelve-membered ring was about 0.74 nm.17,38 The maximum diameter

411

of the main hole (or super cage) was about 1.25 nm with a volume of 0.850 nm3,

412

which provided NaY a possibility for the storage of DMDS.

413 414

0.74nm

415 MTBE

416 417

O

H3C

CH3

CH3

0.37nm

419

H3C

420 422

H3C

0.66nm

418

421

0.66nm

NaY

NaY+ silicalite-1 coating


monolayer

multilayer

DMDS

S S

CH3

425

Figure 11. The geometrical structures of NaY and NaY with silicalite-1 coating of both monolayer and multilayer, as well as the DMDS adsorption mechanism of silicalite-1/NaY core-shell structured composite in MTBE.

426

Silicalite-1 contained ten-membered rings with a basic structural unit made up of

427

eight five-membered rings; and the maximum aperture was less than 0.6 nm, which

428

provided silicalite-1 a shape selectivity to allow DMDS to pass by only. When NaY

429

was coated by silicalite-1, molecules with a size over 0.6 nm could be blocked outside

430

the channel. Accordingly, the silicalite-1/NaY core-shell structured composites

431

reflected good shape selectivity and appreciable sulfur adsorption capacity. As a

432

matter of fact, DMDS molecules were much smaller than that of MTBE, because of

433

no branched chains and large-size atoms in DMDS. As shown in Figure 8, the

434

maximum molecule size of MTBE was 0.74 nm and DMDS was 0.37 nm.39,40 DMDS

435

could diffuse rapidly in the microporous channels of silicalite-1 coating. However,

436

owing to the larger size and the branched structure, the diffusion of MTBE would be

437

inevitably limited, leading to the enrichment of DMDS on the core NaY zeolite and

438

the decreasing concentration of DMDS in MTBE solution.

423 424

439

In general, the silicalite-1 coating guaranteed the silicalite-1/NaY core-shell

440

structured composites a shape selectivity of these core-shell composites to prevent

441

MTBE from going into the NaY core and allow DMDS to pass by only. Accordingly,

442

the silicalite-1/NaY core-shell structured composites reflected good shape selectivity

443

and appreciable sulfur adsorption capacity. And this was how the silicalite-1/NaY


Page 19 of 28 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


444

core-shell structured composites performed in desulfurizing DMDS from MTBE.

445

4. Conclusion

446

NaY zeolite with numerous super cages provided it itself a possibility to store

447

DMDS, and silicalite-1 with a maximum aperture less than 0.6 nm made it itself

448

blocking MTBE from going inside. By shape selective adsorption, the silicalite-1/

449

NaY core-shell structured composites could desulfurize DMDS from MTBE well,

450

ignoring the strong competitive adsorption between MTBE and DMDS. When the

451

mass ratio of TEOS/ TPAOH/ EtOH/ H2O/ NaY=20 g:19 g:17 g:87 g:5 g, the

452

silicalite-1 coating could be dispersed and covered on the surface of NaY zeolites well

453

with the best sulfur adsorption capacity to be 20.711 mgs/gadsorbents; and more than

454

90% desulfurization rate could be achieved and kept for about 2.2 hours. In the next

455

work, a promising direction for deep desulfurizing DMDS from MTBE is to modified

456

the core NaY with some transition metal ions to improve the new core-shell structured

457

composites with a higher sulfur adsorption capacity.

458

Acknowledgments

459

Project financially supported by the National Science Foundation for Young

460

Scientists of China (No. 21706065); the Open Project of State Key Laboratory of

461

Chemical Engineering (SKL-ChE-18C02); China Postdoctoral Science Foundation

462

(NO.2017M621389), Shanghai Sailing Program (NO.18YF1406300), and Explore

463

and Research Foundation for Youth Scholars of Ministry of Education of China (NO.

464

222201814011).

465

Reference

466

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[6] Huang Huan; Salissou M. Nour; Yi Dezhi; Meng Xuan; Shi Li. Study on Reactive Adsorption Desulfurization of Model Gasoline on Ni/ZnO-HY Adsorbent. China Petroleum Processing and Petrochemical Technology. 2013, 15, 57-64. [7] Li, D. Crucial Technologies Supporting Future Development of Petroleum Refining Industry. Chin. J. Catal. 2013, 34, 48-60. [8] Hernández-Maldonado, A. J., and Yang, R. T. Desulfurization of Transportation Fuels by Adsorption. Catal. Rev. 2004, 46, 111-150. [9] Hernández-Maldonado, Arturo J., and Ralph T. Yang. Desulfurization of Commercial Liquid Fuels by Selective Adsorption via π-Complexation with Cu (I)-Y Zeolite. Industrial & engineering chemistry research. 2003, 42, 3103-3110. [10] Hernández-Maldonado, and Arturo J.. Desulfurization of transportation fuels by π-complexation sorbents: Cu(I)-, Ni(II)-, and Zn(II)-zeolites. Applied Catalysis B: Environmental. 2005, 56, 111-126. [11] Meng, X., Huang, H., Weng, H., and Shi, L.. Ni/ZnO-based Adsorbents Supported on Al2O3, SiO2, TiO2, ZrO2: A Comparison for Desulfurization of Model Gasoline by Reactive Adsorption. Bulletin of the Korean Chemical Society. 2012, 33, 3213-3217. [12] Hernández-Maldonado A. J., and Yang R. T.. New sorbents for desulfurization of diesel fuels via π-complexation. AIChE J. 2004, 50, 791-801. [13] Hernández-Maldonado A. J., and Yang R.T.. Desulfurization of transportation fuels by adsorption. Catal Rev. 2004, 46, 111-150. [14] Tang, X. L., Qian, W., Hu, A., Zhao, Y. M., Fei, N. N., and Shi, L.. Adsorption of thiophene on Pt/Ag-supported activated carbons prepared by ultrasonic-assisted impregnation. Industrial & Engineering Chemistry Research. 2011, 50, 9363-9367. [15] Ryzhikov, Andrey, Igor Bezverkhyy, and Jean-Pierre Bellat. Reactive adsorption of thiophene on Ni/ZnO: Role of hydrogen pretreatment and nature of the rate determining step. Applied Catalysis B: Environmental. 2008, 84, 766-772. [16] Sentorun-Shalaby, C., Saha, S. K., Ma, X., and Song, C.. Mesoporous-molecular-sievesupported nickel sorbents for adsorptive desulfurization of commercial ultra-low-sulfur diesel fuel. Applied Catalysis B: Environmental. 2011, 101, 718-726. [17] Lv, Y., Qian, X., Tu, B. and Zhao, D. Generalized synthesis of core–shell structured nano-zeolite@ordered mesoporous silica composites. Catalysis Today. 2013, 204, 2-7. [18] Wakita, H., Tachibana, Y., and Hosaka, M. Removal of Dimethyl Sulfide and t-Butylmercaptan from City Gas by Adsorption on Zeolites. Microporous Mesoporous Mater. 2001, 46, 237-247. [19] Lee, J., Beum, H. T., Ko, C. H., Park, S. Y., Park, J. H., Kim, J. N., Chun, B. H., and Kim, S. Y. Adsorptive Removal of Dimethyl Disulfide in Olefin Rich C4 with Ion-Exchanged Zeolites. Ind. Eng. Chem. Res. 2011, 50, 6382-6390. [20] Lidan Lv, Jie Zhang, Chongpin Huang, Zhigang Lei, and Biaohua Chen. Adsorptive separation of dimethyl disulfide from liquefied petroleum gas by different zeolites and selectivity study via FT-IR. Separation and Purification Technology. 2014, 125, 247-255. [21] Ya-wei Zhao, Ben-xian Shen, and Hui Sun. Chemical Liquid Deposition Modified ZSM-5 Zeolite for Adsorption Removal of Dimethyl Disulfide. Ind. Eng. Chem. Res. 2016, 55, 6475-6480. [22] Dezhi Yi, Huan Huang, Xuan Meng, and Li Shi. Adsorption-desorption behavior and


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mechanism of dimethyl disulfide in liquid hydrocarbon streams on modified Y zeolites. Applied Catalysis B: Environmental. 2014, 148, 377-386. [23] Zhonghao Jin, Su Liu, Lei Qin, Zhicheng Liu, Yangdong Wang, Zailcu Xie, and Xingyi Wang. Methane dehydroaromatization by Mo-supported MFI-type zeolite with core-shell structure. Applied Catalysis A: General. 2013, 453, 295-301. [24] Dung Van Vu, Manabu Miyamoto, Norikazu Nishiyama, Satoshi Ichikawa Yasuyuki Egashira, and Korekazu Ueyama. Catalytic activities and structures of silicalite-1/H-ZSM-5 zeolite composites. Microporous and Mesoporous Materials. 2008, 115, 106-112. [25] Meng Pan, Peng Li, Jiajun Zheng, Yujian Liu, Qinglan Kong, and Huiping Tian. Zeolite-zeolite composite composed of Y zeolite and single-crystal-like ZSM-5 zeolite: fabricated by a process like “big fish swallowing little one”. Materials Chemistry & physics. 2017, 194, 49-54. [26] Gerhard D. Pirngruber，Catherine Laroche, Michelle Maricar-Pichon，Loic Rouleau，Younes Bouizi, and Valentin Valtchev. Core-shell zeolite composite with enhanced selectivity for the separation of branched paraffin isomers. Microporous and Mesoporous Materials. 2013, 169, 212-217. [27] Zhao, Q., Qin, B., Zheng, J., Du, Y., Sun, W., and Ling, F. Core–shell structured zeolite–zeolite composites comprising Y zeolite cores and nano-β zeolite shells: synthesis and application in hydrocracking of VGO oil. Chemical Engineering Journal. 2014, 257, 262-272. [28] Yin, Y., Qin, L., Wang, X., Wang, G., Zhao, J., and Liu, B. Preparation of a core-shell structured Y@ASA composite material and its catalytic performance for hydrocracking of n-decane. Rsc Advances. 2016, 6, 111291-111298. [29] X. F. Qian, B. Li, Y.Y. Hu, G.X. Niu, D.Y.H. Zhang, R.C. Che, Y. Tang, D. S. Su, A. M. Asiri, and D.Y. Zhao. Exploring Meso-/Microporous Composite Molecular Sieves with Core-Shell Structures. Chemistry-A European Journal. 2012, 18, 931-939. [30] Miyake, K., Hirota, Y., Ono, K., Uchida, Y., Tanaka, S., and Nishiyama, N.. Direct and selective conversion of methanol to para-xylene over Zn ion doped ZSM-5/silicalite-1 core-shell zeolite catalyst. Journal of Catalysis. 2016, 342, 63-66. [31] Miyake, K., Hirota, Y., Ono, K., Uchida, Y., and Nishiyama, N.. Selective production of benzene, toluene and p-xylene (btpx) from various C1-3 feedstocks over ZSM-5/silicalite-1 core-shell zeolite catalyst. Chemistryselect. 2016, 1, 967-969. [32] A. J. Hernández-Maldonado, F. H. Yang, G. S. Qi, and R. T. Yang. Sulfur and nitrogen removal from transportation fuels by π-complexation. Journal of China Industrial Chemical Engineerings. 2006, 37, 9-16. [33] Y. Li, F. H. Yang, G. Qi, and R. T. Yang. Effects of oxygenates and moisture on adsorptive desulfurization of liquid fuels with Cu(I)Y zeolite. Catalysis Today. 2006, 116, 512-518. [34] Chen, H., Wang, Y., Yang, F. H., and Yang, R. T.. Desulfurization of high-sulfur jet fuel by mesoporous π-complexation adsorbents. Chemical Engineering Science. 2009, 64, 5240-5246. [35] Groen J. C., Peffer L. A. A., and Moulijn J. A.. On the introduction of intracrystalline mesoporosity in zeolites upon desilication in alkaline medium. Microporous & Mesoporous Materials. 2004, 69, 29-34. [36] By Younes Bouizi, Isabel Diaz, Loic Rouleau, and Valentin P. Valtchev. Core-Shell Zeolite



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[38]

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[39]

573 574 575 576

[40]

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577 578 579 580 581

TOC graphic

582 583 0.74nm

584 585

NaY

586

MTBE

0.66nm

H3C

O

H3C

CH3

587

0.66nm

588

0.37nm

589

DMDS

590 591 592

monolayer silicalite-1 coating

593 594 multilayer silicalite-1 coating


H3C

S S

CH3

CH3

mgs/gadsorbent

20.711

Raw material sulfur concentration：275.51 mg/L

294.53

272.65

229.24

258.97

262.23

1.657

1.328

231.62 4.389

4.627

0.286

-1.902

68.4

B

A

C

E

D

F


mg/L

G

Fig. 1. Sulfur content after adsorption and sulfur adsorption capacity for DMDS adsorption in MTBE of different absorbents: A. NaY, B. Silicalite-1, C. TEOS/NaY=2, D. TEOS/NaY=3, E. TEOS/NaY=4, F. TEOS/NaY=5, and G. TEOS/NaY=6

100


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 23 of 28

TEOS/NaY=2 TEOS/NaY=3 TEOS/NaY=4 TEOS/NaY=5 TEOS/NaY=6 NaY Silicalite-1

80 60 40 20 0 0

1

2

Time (h)

3

4

Fig. 2. Breakthrough curves of NaY, silicalite-1, and silicalite-1/NaY core-shell structured composites adsorbing DMDS in MTBE solution



Page 24 of 28

(a)

(b)

(c)

(f )

silicalite-1 coating

(e) silicalite-1 crystal

(d)

(g)

Fig. 3. SEM images of NaY zeolite and silicalite-1/NaY composites:(a) NaY×7K, (b) NaY×16K, (c) TEOS/ NaY=2×16K, (d) TEOS/NaY=3×16K, (e) TEOS/NaY=4×16K, (f) TEOS/NaY=5×16K, (g) TEOS/NaY=6×16K

(a)

(b)

(c)

(d)

Fig. 4. TEM images of NaY (a), (b); and core-shell structure as TEOS/NaY=4 (c), (d).


20


18

Mass gain (g)

16

mass gain (g)

14

200


175

mass gain (%)

150

12

125

10

100

8

75

6

50

4

25

2 0

1

2

3

4

5

6

7

0

TEOS/NaY (g/g)

mg/L


295

294.44

Raw material sulfur：284.53 mg/L

292.62

290

-0.809

285

292.1 -0.757

mgs/gadsorbent

-0.587

291.64 -0.711

-0.6 -0.7

290.4

-0.8 -0.9 -1.0

-0.991

280

a

0.0

-0.5

b

c

d

-1.1

e


Fig. 5 Mass gain of NaY zeolites after coating silicalite-1


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


Mass gain (%)

Page 25 of 28

-0.5 -1.0 a b c d e

-1.5 -2.0 -2.5 -3.0 -3.5

0

1

2

Time (h)

3

4

Fig. 6. The sulfur content after adsorption; sulfur adsorption capacity for DMDS in MTBE solution, and breakthrough curves of different physical mixed absorbents: a. silicalite-1/NaY=0.1678, b. silicalite-1/NaY=0.3751, c. silicalite-1/NaY=0.8658, d. silicalite-1/NaY=1.2657, e. silicalite-1/NaY=1.5158.



0.8

0.035


3 -1 -1 dV/dD (cm g nm )

0.030

0.6

0.025 0.020 0.015

0.4

0.010 0.005

0.2

0.0

0.000

0

1

2

3

2

4

4

6

5

8

6

Pore width (nm)

10

7

12

8

14

9

10

Fig. 7 BJH pore size distributions of different adsorbents

350


300

3

Volume adsorbed (cm /g)

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 28

250 200 150 100 50 0

0.0

0.2

0.4

0.6

Relative Pressure (P/P0)

0.8

1.0

Fig. 8. N2 adsorption-desorption isotherms of NaY, silicalite-1 and core-shell structures.


Page 27 of 28

(7) (6)

Intensity (a.u.)

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


(5) (4) (3) (2) (1)

10

20

30

40

50

60

2-Theta (degrees)

70

Fig. 9. X-ray diffraction patterns of NaY zeolite, silicalite-1 crystal and NaY with silicalite-1 shell: (1) NaY, (2) silicalite-1, (3) TEOS/ NaY=2, (4) TEOS/NaY=3, (5) TEOS/NaY=4, (6) TEOS/NaY=5, (7) TEOS/NaY=6

1226 1105

(1) (2) (3) (4) (5) (6) 2978

3000

(7) 1622

2500

2000

1500

Wavenumbers (cm-1)

1011

1000

500

Fig. 10. FT-IR spectra recorded after the adsorption of DMDS in MTBE on different NaY zeolite: (1) NaY, (2) silicalite-1 crystal, (3) TEOS/NaY=2, (4) TEOS/NaY=3, (5) TEOS/NaY=4, (6) TEOS/NaY=5, and (7) TEOS/NaY=6



Page 28 of 28

MTBE

NaY



monolayer

multilayer

DMDS

Fig. 11. The geometrical structures of NaY and NaY with silicalite-1 coating of both monolayer and multilayer, as well as the DMDS adsorption mechanism of silicalite-1/NaY core-shell structured composite in MTBE.

Table. 1. Structural properties of NaY, silicalite-1 and core-shell structures. Adsorbents

St (m2/g)

*

Vt (cm3/g)

*

Da (nm)

*

*

Vmic (cm3/g)

Dmic (nm)

*

NaY

793.325

0.406

1.709

0.29

0.8339

Silicalite-1

488.126

0.351

1.982

0.194

0.6554

*T/N=2

589.020

0.172

2.510

0.208

0.8529

T/N=3

624.385

0.308

2.141

0.213

0.8465

T/N=4

624.775

0.334

1.973

0.219

0.8463

T/N=5

559.097

0.281

2.008

0.181

0.8636

T/N=6

547.995

0.157

2.539

0.156

0.8987

*T/N:

mass ratio of TEOS/NaY; *St: total surface area; *Vt: total pore volume; *Da: average pore size; *Vmic: micropore pore volume; *Dmic: micropore pore size.


NaY structure for the

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