An evaluation of published kinetic models for vapor phase methanol

Subscriber access provided by Kaohsiung Medical University

Catalysis and Kinetics

An evaluation of published kinetic models for vapor phase methanol conversion to dimethyl ether over the H-ZSM-5 catalyst Ionut BANU, Rodica Ganea, Gabriel Vasilievici, Alin Anghel, Valentina Gogulancea, Gabriela Isopencu, and Grigore Bozga Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b01839 • Publication Date (Web): 18 Jul 2018 Downloaded from http://pubs.acs.org on July 21, 2018

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 30 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

An evaluation of published kinetic models for vapor phase methanol

2

conversion to dimethyl ether over the H-ZSM-5 catalyst

3

Ionut BANUa, Rodica GANEAb, Gabriel VASILIEVICIb, Alin ANGHELa, Valentina

4

GOGULANCEAa, Gabriela ISOPENCUa, Grigore BOZGAa*

5 6 7 8

a

9

The published kinetic models for methanol etherification over ZSM-5 zeolite were

10

evaluated against own experimental data. The process was investigated over a synthesized H-

11

ZSM-5 zeolite using a laboratory fixed bed reactor. The experiments were carried out at

12

atmospheric pressure, temperatures of 170-270 °C, methanol feed concentrations up to 15 mol %

13

and gas phase velocity (WHSV) values in the range 15-48 h-1. The results showed a decrease of

14

methanol conversion with respect to feed methanol concentration, the single reaction product

15

obtained in significant concentrations being dimethyl-ether (no secondary products were

16

observed in significant concentrations). The methanol conversion measurements were compared

17

with theoretical predictions based on the main kinetic models published for methanol

18

etherification over ZSM-5 zeolites with different acidities. As none of the published models

19

fitted satisfactorily our experimental data, we re-estimated the parameters of the tested models

20

and applied a discrimination procedure in order to identify the most suitable one. The best

21

quality of the fit was obtained by using a LH kinetic model based on the associative surface

22

reaction mechanism. The adequacy of this kinetic model was confirmed by statistical and

23

thermodynamic consistency criteria.

24

Keywords: catalysis, methanol etherification, kinetic model, H-ZSM-5 zeolite

University Politehnica of Bucharest, Faculty of Applied Chemistry and Material Science, Department of

Chemical and Biochemical Engineering, 1-7 Polizu Str., 011061, Bucharest, Romania b

National Research Institute for Chemistry and Petrochemistry, ICECHIM, 202 Spl. Independentei,

060021,Bucharest, Romania

25 26

Introduction

27

Dimethyl ether (DME) emerged in the last decades as a chemical product with potential

28

advantages in the clean energy supply, attracting a large research interest in academia and

29

industry. DME features outstanding fuel properties, exhibiting a high cetane number (55-60) and

30

excellent burning characteristics due to the low level of particulate products, low NOx emissions 1 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 30

31

and no release of sulfur compounds. These properties make DME a potential alterative to

32

petroleum diesel fuel, an interesting fuel for combustion cells and a largely applied LPG

33

substitute. LPG–DME blends have been suggested as fuels for use in cooking, heating and LPG-

34

fueled vehicles 1. It can be also used as an aerosol propellant and a liquid refrigerant suitable to

35

replace ozone destroying chlorofluorocarbons. DME is used as an intermediate for synthesis of

36

several oxygenated products such as methyl acetate, dimethyl sulfate etc. It is to be noted as well

37

that DME appears as an intermediate in the methanol conversion to hydrocarbons.

38

As the synthesis gas, the raw material for methanol synthesis, can be directly obtained

39

from biomass, DME has also the advantages of a renewable product 2-6. The economic aspects of

40

biomass utilization as raw material for production of syngas and its derivatives were analyzed in

41

an important number of published studies. As known, the bottlenecking step in the DME

42

production from syngas is the methanol synthesis (mainly due to its slower kinetics and higher

43

thermodynamic limitation, as compared with methanol etherification step). Therefore, the

44

economic viability of DME production from biomass is directly dependent on methanol

45

production viability. This issue was analyzed and demonstrated by several authors. Borgwardt 7,

46

estimated a cost of methanol production from biomass amounting to 0.42 USD/gal (~ 0.14

47

USD/kg). For a methanol plant using biomass as carbon source, with a capacity of 1085 million

48

gal/yr (~ 3.2 million t/yr), Li et al.

49

which could be compared to methanol price in the United States. On the European and North-

50

American markets the reported methanol price in July 2018 is around 0.49 USD/kg (~0.419

51

€/kg) ( https://www.methanex.com/our-business/pricing). Besides the economical viability, other

52

reasons for the utilization of the biomass for methanol production are that it permits to valorize

53

secondary feedstocks for industrial applications, decreasing, in the same time, the environment

54

impact of the process (Li et al. 9).

8

have reported a methanol production cost of 0.43 ($/gal)

55

DME can be produced at commercial scale by two technologies: (i) a technology using as

56

raw material the methanol previously synthesized in a different plant (two-step process or

57

indirect method) and (ii) a technology of DME fabrication directly from synthesis gas,

58

integrating the methanol synthesis and methanol dehydration in a single process unit (the one-

59

step process or the direct method). The latter is advantageous, particularly from the

60

thermodynamic point of view, as the methanol consumption is promoting the carbon oxides

61

hydrogenation to methanol. Furthermore, methanol etherification is less limited by the chemical 2 ACS Paragon Plus Environment

Page 3 of 30 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

62

equilibrium state as compared with the methanol synthesis. The one-step DME synthesis

63

involves the simultaneous use of two catalysts, the methanol synthesis catalyst (MSC) and

64

methanol etherification catalyst (MEC). These are used in the same catalytic reactor, in different

65

spatial distributions (individual grains of the two catalyst in different arrangements, or a bi-

66

functional catalyst prepared by combining the MSC and MEC in the same pellet 4).

67

Published studies have evaluated the catalytic performances of different acidic materials for 10, 11

68

methanol conversion to dimethyl ether (MEC component): alumina

69

mordenite or mordenite modified with metal oxides

70

ZSM-5 (MFI), zeolite, SAPO mesoporous materials or ion exchange resins 2, 14-16.

12, 13

, dealuminated H-

, ferrierite, Y zeolites, Beta-zeolite,

71

Review papers analyzing the methanol etherification catalysts, reaction mechanisms,

72

reaction kinetics and technologies were published by Spivey 17, Bozga et al. 4, Azizi et al. 5 and

73

Saravanan et al. 18.

74

In the DME synthesis by one-step technology, it is recommended to use MEC having

75

sufficiently high activity in the temperature window of the methanol synthesis reaction (usually

76

220- 280oC) in order to keep a limited rate of methanol synthesis catalyst deactivation

77

Although alumina is a cheap and widely available catalyst adequate for methanol etherification

78

in the two-step technology, its catalytic activity is too low to ensure a satisfactory methanol

79

conversion under the temperature conditions of methanol synthesis 20. Additionally, the presence

80

of water, which is a reaction product, deactivates alumina, presumably due to its blocking effect

81

on the acid sites

82

than alumina and more resistant to the presence of water are necessary. Published studies suggest

83

that a good candidate in this regard is the ZSM-5 zeolite, which is one of the most studied

84

zeolites and among the best catalysts reported for methanol etherification

85

catalytic activity and relatively low cost, it presents also the advantage of a tunable acidity and

86

superior resistance to water, as compared with other acidic zeolites

87

correlated the DME productivities of the H-ZSM5 zeolite, H-Y (Faujasite) and γ-alumina with

88

their Weitkamp hydrophobicity index (ratio of toluene adsorption by water adsorption). The best

89

productivities were obtained by using the H-ZSM-5 zeolites having relatively high Si/Al ratios,

90

i.e. increased hydrophobicity, these results evidencing that the acid sites concentration and

91

strength are not the only parameters to be adjusted, another important one being the catalyst

92

hydrophobicity. Published studies highlight that, if calcined at adequate temperatures, the

21

19

.

. Therefore, in the one-step technology etherification catalysts more active

22

23-25

. Besides its high

. Vanoye et al.

24

3 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 4 of 30

93

HZSM-5 zeolite is hydrothermally stable, a property that makes it usable in processes involving

94

reaction-regeneration cycles 26, 27.

95

An experimental study investigating the influence of the main process variables on methanol 28

96

dehydration over pure H-ZSM-5 zeolite was recently published by Ajami and Shariati

97

authors reported maximum methanol conversions (practically equilibrium levels) in the

98

temperature range 240–250°C. For temperatures over 270°C, the authors observed significant

99

amounts of byproducts (no details about their nature were provided).

100 101

. The

A number of published studies evidenced better catalytic performances of H-ZSM-5 in the methanol etherification, as compared with γ-alumina 31

24, 29

; ferrierite zeolite

102

(Vanoye et al., 2013), and different mordenites

103

performances of ferrierite zeolites in the DME synthesis (see Frusteri et al.

104

therein).

30

, HY zeolite

. Recent studies have highlighted also good 32

and references

105

An inconvenience of the H-ZSM-5, as a catalyst for methanol etherification, is the occurrence

106

of the secondary reaction of DME conversion to hydrocarbons over its stronger acid sites; this

107

transformation is significant particularly at temperatures over 270oC

108

this, the strength and surface density of acid sites can be varied to a certain extent in order to

109

improve the zeolite’s catalytic properties

110

aim: partial neutralization of strong acid sites with alkaline metals

111

matrix of alumina (which is diluting the density of strong acid centers) 16, reducing the acidity by

112

increasing the Si/Al ratio

24, 33, 34

17

28

. Nevertheless, to avoid

. Different technical solutions were proposed in this 16, 31

, H-ZSM-5 binding in a

, decreasing the zeolite crystal size by appropriate synthesis

113

techniques , selection of special organic compounds as templates in the zeolite synthesis 36, an

114

alkaline treatment at the synthesis step combined with partial activation 37, working in presence

115

of air 38, and lastly modification of HZSM-5 with a small amount of antimony oxide 39.

116

35

Several studies

24, 34

observed an increase of reaction rate (methanol conversion) with an

117

increase in the Si/Al ratio. Migliori et al. 34 found also that the activation energy of the methanol

118

etherification reaction over H-ZSM-5 zeolite decreased with an increase of the Si/Al ratio,

119

indicating that the temperature sensitivity of the catalytic process is higher when using low Si/Al

120

ratio (high acidity) zeolites. However, it seems that in the hybrid catalyst for direct DME

121

synthesis, (CuZnAl/ZSM-5) the conclusions (regarding the HZSM-5 properties) obtained in

122

methanol etherification experiments do not confirm entirely 40, 41.


Page 5 of 30 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

123

Energy & Fuels

Bonura et al

20, 42

demonstrated experimentally a good performance of H-ZSM-5 zeolite as

124

etherification catalyst in the process of direct DME synthesis from carbon dioxide (3.0 MPa and

125

513 K), using Cu–ZnO–ZrO2 as methanol synthesis catalyst, in a fixed bed containing individual

126

pellets of the two catalysts. In the latter study, the authors found that the catalytic beds obtained

127

by mechanical mixing of individual pellets ensure superior performances as compared with the

128

bifunctional catalyst pellets.

129

Mechanism and kinetics of methanol etherification on the ZSM-5 zeolite

130

The design of the DME synthesis processes requires reliable kinetic models, constructed in

131

accord with the real mechanism of catalyst surface reaction. The methanol dehydration reaction

132

is described by the global equation:  cat → CH 3 − O − CH 3 + H 2 O 2CH 3 OH ←

133

(1)

134

The mechanism of methanol etherification on zeolite catalysts was investigated in a

135

significant number of published studies, by comparing theoretical predictions (i.e. density

136

functional theory) with experimental observations. The general conclusion is that the

137

etherification mechanism is dependent on the acidic sites strength and their density on the

138

surface. It is largely accepted the hypothesis that in the formation of DME are involved the

139

medium strength acid sites, whereas the strong acid sites are responsible for methanol conversion

140

to hydrocarbons 31.

141

The majority of published studies are hypothesizing that, in the etherification process over the

142

zeolite catalysts, there are involved Bronsted acid – Lewis base pairs of zeolite surface. Two

143

classes of mechanisms were proposed to explain the methanol etherification on the surface of

144

solid acidic catalysts of this type: dissociative (sequential) and associative (non-dissociative or

145

direct). Both of these involve a first step of methanol adsorption (protonation) on the Bronsted

146

acid groups (HX) by a hydrogen bond to the non-participant electrons of the alcoholic oxygen

147

atom to form a methoxonium cation (X-H---HO-CH3), as shown in Fig. 1 43.

148


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

149 150

Page 6 of 30

Fig. 1. Structure of the intermediary species appearing in methanol dehydration mechanisms 43

151

In the dissociative mechanism, the adsorbed methoxonium cation (protonated methanol)

152

eliminates water transforming into a methoxy intermediate, this being generally supposed as the

153

rate determining step. In a final step the methoxy intermediate reacts with a methanol molecule

154

forming DME. In the associative mechanism, the adsorbed methoxonium cation reacts with a

155

non-adsorbed methanol molecule to form a protonated methanol dimer ((X-CH3OH-H+)2 shown

156

in Fig. 1). Furthermore, this dimer reorganizes internally to form transition states which finally

157

dehydrate to DME. Different variants of these two mechanisms were adopted by different

158

authors to explain the methanol etherification on zeolite catalysts. Kubelková et al.

159

investigated the mechanism of DME synthesis from methanol over H-Y and H-ZSM-5 catalysts

160

using FT-IR spectroscopy, temperature-programmed desorption of methanol and mass

161

spectrometry. The authors adopted a dissociative mechanism, evidencing the apparition of

162

methoxonium cations ([CH3OH2]+) on the zeolite surface. These were assumed to dehydrate,

163

forming methoxy species, which react with gaseous methanol molecules giving DME (a Rideal -

164

Eley scheme).

165

Bandiera and Naccache

45

44

investigated the reaction over a highly dealuminated H-mordenite

166

zeolite and postulated that the surface reaction occurs by a dissociative, dual site mechanism.

167

According to this mechanism, a molecule of methanol is protonated on a Brønsted acid site,

168

generating adsorbed [CH3OH2]+ (methoxonium) cations. A second methanol molecule interacts

169

with an adjacent Lewis basic site (oxygen atom), losing a proton and generating an anion

170

[CH3O]−. Finally, the two ions combine forming DME and water.

171

Lu et al. 14 investigated the kinetics of the direct DME synthesis from syngas over a Cu–ZnO–

172

Al2O3/HZSM-5 catalyst in a fluidized bed reactor. The authors adopted a dissociative mechanism

173

for methanol dehydration over HZSM-5 zeolite, where the second step is the reaction between


Page 7 of 30 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

174

the methoxy cation and an adsorbed methanol molecule, leading to DME and adsorbed water

175

molecules.

176

Moses and Nørskov

46

analyzed both the dissociative and associative mechanisms for

177

methanol dehydration on a ZSM-22 catalyst, based on density functional theory (DFT)

178

calculations. The authors concluded that the dissociative route is faster compared with the

179

associative one. They also found that the dissociative and associative mechanisms have similar

180

dependencies on catalyst acidity and consequently the dissociative mechanism will also

181

dominate for weaker acids.

182

Blaszkowski and Santen

47

investigated theoretically, using DFT, the methanol

183

etherification over acidic zeolites. Three alternative surface mechanisms were analyzed,

184

involving the methanol interactions with the Brønsted acid and Lewis base sites of acid zeolite

185

catalysts. The most probable mechanism was found to be an associative one, involving the

186

simultaneous adsorption and reaction of two methanol molecules.

187

Ha et al.

48

adopted a version of an associative mechanism, including splitting steps, in a

188

kinetic study of methanol etherification over alkali metals (Na and K) modified ZSM-5 zeolite.

189

According to this study, the protonated methanol dimer, appearing in the associative mechanism,

190

rearranges itself to split either into the methyl carboxonium ion and carbenium ion at the same

191

time, or split into two methyl carboxonium ions. The resulting ions combine in the final steps to

192

form DME. From the results of experimental data fitting, the authors concluded that the rate

193

controlling step should be the decomposition of protonated methanol dimer. The mechanism

194

proposed by Ha was used by Tavan et al. [16] for methanol etherification over H-ZSM-5

195

catalyst.

196

The associative mechanism of methanol etherification over acid zeolites was also confirmed 43, 49

197

by the studies of Iglesia’s group

198

polyoxometalate clusters and zeolite H-BEA zeolite, they proposed, based on experimental

199

observations correlated with DFT calculations, a direct (associative) mechanism 43

. In a first study of methanol dehydration on Keggin 49

. In a

200

following study

201

functional theory(DFT), that on MFI (ZSM-5) catalysts the associative mechanism prevails in

202

typical conditions for methanol dehydration.

it was shown, by IR spectra and theoretical analysis based on density

203

In a ‘van der Waals corrected DFT’ study of the methanol-to-DME reaction on H-ZSM-5

204

zeolite, Ghorbanpour et al. 50 found that the associative route is preferred at lower temperatures, 7 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 8 of 30

205

but a transition in the mechanism from associative to dissociative is predicted at higher

206

temperatures, resulting in a temperature interval over which the etherification occurs by both

207

mechanisms. In particular, for H-ZSM-5 zeolite, the authors estimated a temperature limit of 700

208

K, below which the mechanism is associative.

209

Kinetic models for methanol etherification over ZSM-5 zeolites

210

The main kinetic models formulated for the methanol etherification, in accord with the

211

mechanisms described above, are presented in Tables 1 and 2.

212

Based on the associative adsorption mechanism presented above, there were deduced, by

213

different authors, the rate expressions (2) and (3) (Table 1). Also, by adopting the dissociative

214

type mechanisms, Lu et al. [11] proposed the rate expression (4) whereas Carr et al. 49, proposed

215

the rate expression (5).

216

The goal of our study was to investigate experimentally the vapor phase etherification of

217

methanol over a home synthesized alumina-binded H-ZSM-5 catalyst and to test the predictive

218

capabilities of the published kinetic models to fit the experimental data over the whole practical

219

domain of methanol conversions. As the quality of the fit was unsatisfactory for all the tested

220

models, a discrimination study was performed, and a kinetic model was selected appearing as the

221

most appropriate to describe the experimental data.

222 223

Catalyst synthesis and characterization

224

Synthesis of the H-ZSM-5 zeolite

225

A ZSM-5 zeolite has been prepared using hexamethylenediamine (HAD, Aldrich) as a structure

226

directing agent (template). The synthesis process included two main steps as described elsewhere

227

51

228

heating rate of 2°C/min to remove the organic compound occluded in the zeolite framework

229

during the crystallization step. The calcined Na-ZSM-5 sample was converted to the ammonium

230

form by ion exchange with a NH4NO3 solution (1M), at 80oC for 2 h, using a liquid/solid ratio of

231

20 mL/g. The resulting NH4-ZSM-5 powder was used to prepare the formulated catalyst by

232

extrusion.

. The as-synthesized Na-ZSM-5 zeolite powder was calcined in air at 580oC for 8 h, at a

233 8 ACS Paragon Plus Environment

Page 9 of 30 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

Energy & Fuels

234 235

Table 1. The proposed mechanisms for methanol etherification Associative mechanism, Ha et al. 52

Associative mechanism, Tavan et al. 29

Dissociative mechanism, Lu et al. 14

Dissociative mechanism, Carr et al. 49

 →( X −CH3 − OH − H + ) ( a ) + L ( H1) 2H3C − OH ( a ) + 2HX ←  2

 → HXCH 3OH CH 3OH ( a ) + HX ← 

( L1)  → CH X + H 2 O ( a ) HXCH 3OH ← ( L2)   → HXCH 3OHCH 3+ ( L3) CH 3+ X − + HXCH 3OH ←   → HXCH 3OH + CH 3 HXCH 3OHCH 3+ ← ( L4)  + +  → HXCH 3OH CH 3 ←  HXCH 3OCH 3 + H ( L5 )  → CH 3OCH 3 + HX HXCH 3OCH 3 ← ( L6 )  + −  → HX H + X ← ( L7 ) 

 → H3C − OH − H + ( a ) + ( X −CH3 − OH − H + ) ( a ) + L ←  2

+CH3+ X − + H2O ( a ) + X −

+ 3

( H 2)

 → H3C − OH − CH3+ ( a ) + H3C − OH − H + ( a ) + CH3+ X − ←  + HX

H3C − OH − CH

+ 3

 → H3C − O − CH3 + H ( a ) ← 

+

+L

 → HX H + X ←  +

−

( H 3) ( H 4) ( H 5)

−

 → HXCH3OH CH3OH ( a ) + HX ←   →CH X + H2O ( a ) HXCH3OH ←  + 3

−

 → DME − HX CH3OH ( g ) + CH3+ X − ←   → DME ( g ) + HX DME − HX ← 

( G1) ( G2 ) ( G3) ( G4 )

L-active site





1 pD pW  2  1 k KM  pM −  2  k K M  pM − p D pW  K p pM     K p   rM = rM = 1+ K M p M + KW pW 2 (1+ K M p M + K W pW ) (3) (2) The rate controlling step (RCS) is surface reaction (H3) RCS is surface reaction (H2)

 p2M 1  rM = k  − pD  p   W Kp  (4)

 p2  1 k KM  M − pD   pW K p    rM = p 1+ K M M pW (5)

RCS is surface reaction (L3)

RCS is the surface reaction (G3)

236 237


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

238 239

Page 10 of 30

Table 2. Published kinetic models for methanol dehydration to DME

N0 Reference 1

Ha et al. 52

Catalyst

Rate expression

Kinetic parameters

(K or Na) ZSM-5

 p p  kK  p 2M − D W   K p   r= 2 (1+ K M p M + KW pW ) 2 M

k = 1051⋅ e

−6278.6 T

K M = 7796 ⋅ e KW = 1825 ⋅ e

2

Tavan et al. 29 H-ZSM-5 Pure methanol

 p p  kK M  p M − D W   pM K p   r= (1+ K M p M + KW pW )

3

Lu et al. 14

4

Tavan and HZSM-5 Hasanvandian Pure methanol 53

 p2M pD  r =k  −  p K  p   W

HZSM-5

 p p r =k  p2M − D W  Kp 

mol kgcat s

11954.5 T

12064 T

k = 3812.11⋅ e

K M = 67.42 ⋅ e KW = 2.17 ⋅ e

,

, bar −1

−8345.4 T

13003.2 T

10804.5 T

k = 8.2894 ⋅10 4 ⋅ e

  

k = 525.32 ⋅ e

, bar −1

−10896 T

,

mol kgcat s

, bar −1

, bar −1 −6367.6 T

,

,

mol g cat s

mol kg cat s

240 241 242

H-ZSM-5-alumina catalyst formulation

243

The catalyst preparation was carried out by the extrusion of NH4-ZSM-5 powder using hydrated

244

alumina of pseudoboehmite type (65 % Al2O3) as binder and aqueous nitric acid (12 wt. % HNO3,

245

Aldrich) as peptizing agent. Further, the dry catalyst extrudates (diameter 2 mm) were calcined in air

246

at 550oC for 6 hours. The final calcination step involved the transformation of ZSM-5 zeolite from

247

ammonium to protonic form and the formation of γ-Al2O3 active phase. The final calcined catalyst

248

designated as H-ZSM-5/γ-Al2O3 (Ex) has the following composition: 60 wt.% of H-ZSM-5 zeolite

249

and 40 wt. % of γ-Al2O3 (matrix).


Page 11 of 30 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

250

Catalyst characterization

251

X-ray diffraction (XRD) of the as-synthesized zeolite sample was recorded on a computer-controlled

252

DRON DART UM2 diffractometer in the range of 2θ = 4-50o.

253

The nitrogen adsorption/desorption isotherms were recorded at 77 K in the relative pressure range

254

p/po=0.005-1.0 using a Quantachrome NOVA 2200e Gas Sorption Analyzer. Prior to adsorption

255

measurements, the samples were degassed at 300 °C under vacuum. Data processing was performed

256

using NovaWin version 11.03 software.

257

The specific surface area was determined by the standard Brunauer-Emmett-Teller (BET) equation

258

applied to the linear part of the adsorption isotherm. The total pore volume was estimated by the

259

volume adsorbed at a relative pressure p/po close to unity. The mesopores volume and mesopores

260

size distribution were estimated from desorption branch of the isotherm by applying the Barrett-

261

Joyner-Halenda (BJH) model. The Horwath-Kawazoe (HK) method was used for the calculation of

262

the micropores size. The t-plot method was used to estimate micropores volume, micropores surface

263

area and external surface area.

264

The acid strength distribution of zeolite samples was determined by the thermal desorption of

265

diethylamine (DEA). The weight loss in the temperature range of 160-600 °C was recorded using

266

DuPont Instrument ″Thermal Analyst 2000/2100″. The weight loss was used to estimate the

267

concentration of acid sites assuming that each mole of amine corresponds to one mole of proton of

268

zeolite framework.

269

Catalyst testing

270

Liquid methanol of 99.5 % (wt) purity from Sigma Aldrich was used in the etherification 2

271

experiments. According to the study published by Pop et al.

272

with alumina, the influence of the internal diffusion on the global kinetics is avoided for catalyst

273

particle size below 1.5 mm. Ha et al. 52 studied the methanol dehydration over Na modified HZSM-5

274

zeolite (pure state) and found that the influence of internal diffusion on the process kinetics is

for a SAPO-34 catalyst formulated

275

insignificant for zeolite pellets with the diameter below 840 µm (20-40 mesh). Similarly, Kim et al.

276

16

277

840 to 1190 µm. (16-20 mesh). Considering these results, all the experiments reported in this study

278

were performed with catalyst pellets of H-ZSM-5 formulated with alumina (40 wt%) having a size

used Na modified HZSM-5 zeolite (formulated with alumina) as pellets having the size between


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 30

279

range 100-150 µm. The experimental set-up is presented in Fig. 2. The reaction was carried out

280

isothermally at atmospheric pressure in a quartz tube reactor (inner diameter 4 mm). A quantity of

281

catalyst (0.150 g) was loaded in the reactor between two layers of quartz beads to improve the gas

282

flow distribution across the catalyst bed. The reaction temperature was monitored at the center of the

283

catalyst bed with a Pt/Rh thermocouple having the accuracy of 0.1 oC, placed in a 1 mm external

284

diameter thermowell. A flow of nitrogen saturated with methanol at 30 °C was fed to the fixed-bed

285

reactor operated at atmospheric pressure. In order to get the desired methanol concentration in the

286

feed, the methanol-nitrogen stream was diluted in the right proportion with a stream of pure nitrogen.

287

The two flow rates of nitrogen were kept constant by using electronic mass flow controllers. The

288

pressure drop in the reactor was monitored by using a differential manometer. The concentrations in

289

the reactor effluent were measured on-line by gas chromatography, using a Varian CP-3800 GC

290

equipped with methanizer, FID and TCD detectors. A capillary column (Poraplot Q HT) was used to

291

separate methanol and DME products, using hydrogen as carrier gas. 7 3 MF C 1

4 9

MF C 2

8

10

5

11

2

6

Purge

1 Transfer line to cromatograph

292 293 294

Fig. 2. Experimental set-up (1- gas cylinder; 2, 3 – mass flow controllers; 4- methanol bubbler; 5-thermostated bath; 6-buffer vessel; 7pressure indicator; 8-furnace; 9-reactor; 10-catalyst bed; 11-innert bed)

295 296 297


Page 13 of 30

298

Results and discussions

299

Structural characterization

300

X-ray diffraction pattern of the synthesized zeolite (Na-ZSM-5 powder sample) in Fig. 4

301

shows the formation of a well-crystallized zeolite exhibiting the MFI type structure. As known, MFI

302

framework has a particular structure characterized by a void space of tridimensional interconnecting

303

channels of 10-rings, of 0.51x0.55 nm and 0.53x0.56 nm respectively.

304

The XRD analyses have evidenced characteristic diffraction peaks at 2θ values of 7.9o, 8.8o, 23.1o

305

and 23.9o, respectively, representing (011), (020), (051) and (033) planes of crystalline structure, in

306

accordance with reported data. The characteristic peaks in the ranges of 2θ=7-9o and 23-25o

307

respectively, were used to calculate the crystallinity of the zeolite sample 54, 55. The Si/Al ratio of the

308

ZSM-5 zeolite framework, evaluated by X-ray diffraction data, is around 40.

309

Hydrated alumina of pseudo-boehmite type structure was used as a conventional binder for the

310

extrusion of ZSM-5 zeolite. XRD - pattern in Fig. 3 illustrates the formation of γ -Al2O3 phase by

311

calcination of hydrated alumina precursor.

312

p -B - (2 31 ),(00 2)

γ-(400) γ-(311)

p-B (2 51 )

p-B - (05 1),(2 00 )

p-B - (0 31 )

p-B - (12 0)

p-B (02 0)

313

I (u.a.)

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

γ-(440) o

500 C

0

20

40

60

80

100

2θ CuKα

314 315

Fig. 3. XRD-pattern of hydrated alumina precursor and its calcined form


Energy & Fuels

γ−Al2O3(400)

111

151 133

051

200, 020

303

101, 011

501

H-ZSM-5 (P) H-ZSM-5/γ-Al2O3(Ex)

I (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 14 of 30

0

10

20

30

40

50

2θ CuKα

316 317

Fig. 4. X-ray diffraction pattern of synthesized ZSM-5 zeolite sample

318

As shown in Fig. 4 in the XRD – pattern of the catalyst extrudates, can be identified the

319

diffraction peaks characteristic for the MFI-type framework, as well as a diffraction peak at 2θ = 45o

320

(400) associated with the γ-Al2O3 phase. As the decrease of the diffraction peaks intensities is more

321

significant than the diminishing due to the dilution effect of zeolite phase, this can indicate a partial

322

amorphisation of the zeolite structure, during the catalyst preparation process. It is also worth to be

323

noted that the diffraction peaks at lower angles are affected, mainly due to their sensitivity to the

324

presence of some material in zeolite channels.

325

Textural characterization

326

The N2 adsorption/desorption isotherms and pore size distribution curves of ZSM-5 (P) and H-ZSM-

327

5/ γ -Al2O3 (Ex) samples are presented in Figs. 5 and 6.

328

The N2 sorption isotherm of ZSM-5 (P) sample is considered of type I, characteristic of

329

microporous materials displaying a significant hysteresis loop, which is an indicative of the

330

mesoporosity, as it was determined by the BJH-plot.


Page 15 of 30

0.0010

220

H-ZSM-5 (P)

H-ZSM-5/γ-Al2O3 (Ex)

0.0008

180 160

Dv(d) (cc/nm/g)

Volume adsorbed (cc/g)

200

140 120

adsorption desorption

100 80

0.0006

BJH-adsorption BJH-desorption 0.0004

0.0002

60 40

0.0000

20 0.0

0.2

331

0.4

0.6

0.8

0

1.0

2

4

6

332

8

10

12

14

16

18

20

Pore diameter (nm)

Relative pressure (p/po)

Fig. 5. N2 adsorption/desorption isotherm and BJH ads-des-pore size distributions of H-ZSM-5 (P) sample

333 334

The two pore size distribution (PSD) curves, derived from adsorption and desorption branches of the

335

isotherm, are quite similar in the lower pore size region. The presence of the inter-crystalline

336

mesopores of 3.8 nm diameter, observed on the BJH-desorption curve, can be associated with the

337

formation of zeolite particle aggregates. The step down characteristic in the desorption isotherm

338

reflect a “cavitation or tensile strength” effect associated with the spontaneous evaporation of

339

metastable pore liquid. This effect is evidenced by the presence of mesopores of 6.5 nm diameter. In

340

contrast, the pore size distribution derived from the adsorption isotherm does not reveal this

341

behavior.

0.0010 240


200 180

adsorption desorption

160


0.0008

BJHdes-Dv(d) (cc/nm/g)

220

Volume adsorbed (cc/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

Energy & Fuels

140 120 100

0.0006

0.0004

0.0002

80 0.0000 60 0.0

342 343 344

0.2

0.4

0.6

Relative pressure (p/po)

0.8

1.0

0

2

4

6

8

10

12

14

16

18

20

Pore diameter (nm)

Fig. 6. N2 adsorption/desorption isotherm and BJHdes-pore size distribution of H-ZSM-5/ γ -Al2O3 (Ex) sample


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 30

345

Textural properties of H-ZSM-5 (P) and H-ZSM-5/γ-Al2O3 catalyst extrudates (Ex) respectively are

346

summarized in Table 3.

347

Table 3. Textural properties of ZSM-5 samples

Sample

348 349 350

SBET

Sext

Sm

2

2

2

(cm /g)

(m /g)

(m /g) (m /g)

Vt 3

VM 3

Vm 3

(cm /g) (cm /g)

Dm

DM

(nm)

(nm)

H-ZSM-5 (P)

450

155

295

0.32

0.20

0.11

0.45

-


353

203

150

0.39

0.30

0.09

-

3.65

SBET = BET specific surface area; Sext = t-plot external surface area; Sm = t-plot micropores surface area; Vt = total pore volume; VM = BJH mesopores volume; Vm:= t-plot micropores volume; Dm= HK micropores diameter; DM =BJH mesopores diameter

351

The H-ZSM-5 (P) sample resulted from the zeolite synthesized as described above has a high

352

BET specific surface area (450 m2/g), which is in agreement with literature data obtained by using

353

nitrogen as standard adsorptive

354

2

micropores surface area (295 m /g) and a large pore volume (0.32 cm3/g). The relative large external

355

surface (155 m2/g) can be connected to the adsorption in the inter-crystalline space (textural porosity)

356

arising from the zeolite crystalline particle aggregation 56.

55

. The porous texture of this sample is characterized by a high

357

The formulation of the zeolite by extrusion is accompanied by a decrease in BET surface area

358

(from 450 to 353 m2/g), more significantly in micropores surface area (from 295 to 150 m2/g) and an

359

increase in total pore volume (from 0.32 to 0.39 cm3/g). The external surface area (203 m2/g) and

360

mesopores volume (0.3 cm3/g) of the catalyst extrudates are higher as compared with the

361

corresponding parent zeolite (Sext=155 m2/g; VM = 0.2 cm3/g), which is attributed to the contribution

362

of the alumina matrix. The mesoporosity generated during the formulation process, of the zeolite-

363

alumina composite, is characterized by a pore size distribution with a maximum value positioned at

364

3.65 nm.

365

Table 4 presents the acidic properties of the H-ZSM-5/γ-Al2O3 (Ex) including the acid

366

strength distributions (defined as the amount of DEA desorbed) corresponding to weak (160-300oC),

367

medium (300-440oC) and strong (440-580oC) acid sites, respectively.


Page 17 of 30 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

368

Energy & Fuels

Table 4. Acidic properties of H-ZSM-5/γ-Al2O3 catalyst

Acidic strength distribution (mmol DEA/g)


Total acidity

Weak

Medium

Strong

(mmol DEA/g)

0.36

0.21

0.14

0.71

369

The diethylamine (DEA) desorption at low temperature (below 300oC) can be associated with silanol

370

groups on the external surface or that can arise from zeolite lattice defects. The higher temperature

371

region (> 300oC), corresponding to medium and strong acid sites, can be assigned to acid sites

372

generated by substitution of Si4+ with Al3+ in zeolite lattice. The resulting negative charge is

373

compensated by a proton corresponding to the hydrogen form of the zeolite (H-ZSM-5).

374

The theoretical acidity of the H-ZSM-5 zeolite associated with the framework aluminum

375

corresponding to the Si/Al=40 is 0.82 mmol/g. Therefore, the concentration of acid sites of the H-

376

ZSM-5/γ-Al2O3 catalyst extrudates, mainly the concentration of acid sites associated with the

377

diethylamine desorbed at high temperature (> 300oC) should be around 0.5 mmol/g. It can be

378

observed that the catalyst extrudates have a significant concentration of weakly acid sites and a

379

considerably lower concentration of strong acid sites. This result, obtained by using the amine

380

adsorption/desorption measurements, could suggest that the used method underestimates the acidity

381

of the H-ZSM-5 based catalyst.

382

Etherification experiments

383

Before its use in etherification experiments, the catalyst was conditioned for 2 h under a

384

nitrogen stream at 300 oC, and finally under a methanol-nitrogen stream for approximately 24 h at

385

290 oC, with the aim of stabilizing the activity. The reproducibility of the measurements was checked

386

by repeating the methanol conversion measurements in identical operating conditions. The results

387

presented in Fig. 7 show good reproducibility of experiments.

388

Fig. 8 presents methanol conversion- temperature curves that emphasize the influence of feed

389

methanol concentration, at two different gas flow rates. As observed, the increase of methanol

390

concentration leads to a decrease of methanol conversion (methanol etherification rate).


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 30

0.9 0.8 0.7 0.6 0.5 0.4 0.3

Exp 1 Exp 2 Exp 3

0.2 0.1 180

391 392

200

220

240

260

280

300

o

Temperature, C

Fig. 7. Reproducibility test for methanol etherification (WHSV 24 hr-1, concentration 8 % mol) 0.7 0.6

0.6 Feed concentration 8 mol % Feed concentration 13.5 mol %

Feed concentration 14.7 mol % Feed concentration 8.8 mol %

0.5

0.5

0.4

0.4 0.3 0.3 0.2

0.2

0.1

0.1 0 180

393 394

A 200

220

240

B 260

0 180

o

200

220

240

260

o

Temperature, C

Temperature, C

Fig. 8. Feed methanol concentration influence. A – WHSV 24 hr-1; B- WHSV 34 hr-1.

395

The results presented in Fig. 9, measured at constant feed methanol concentration and variable

396

flowrate, show a decrease of methanol conversion with the increase of feed flow rate, due to the

397

decrease of the residence time inside the catalyst bed. In the same time, this result is suggesting that

398

external diffusion does not have a significant influence on the global process kinetics at the level of

399

catalyst pellet.


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

Methanol conversion

Page 19 of 30

400 401 402 403 404

Fig. 9. Feed flowrate influence (feed methanol concentration 14 mol %) The influence of internal diffusion on the overall kinetics at the level of the catalyst pellet was evaluated using Weisz-Prater criterion 57. WP =

rM ,exp ⋅ρ p R p2 Deff ⋅ C M

,

(6)

405

where: rM ,exp - reaction rate; ρp - catalyst pellet density; Rp – radius of the catalyst pellet; Deff –

406

effective diffusion coefficient; CM- methanol molar concentration in gas phase.

407 408

The experimental data allowed the evaluation of the average reaction rate inside the catalyst bed:

rM ,exp =

FM ,0 ⋅ X M

(7)

mcat

409

FM,0 – molar methanol feed rate; XM – methanol conversion; mcat – weight of the catalyst. Considering

410

an average value of the effective diffusion coefficient Deff = 5⋅10-7 m2 s-1

411

there were obtained values for WP criterion between 0.05 – 0.2, indicating a negligible influence of

412

the internal diffusion on the overall process kinetics.

58

and ρp = 1300 kg m-3,

413

The test of published kinetic models

414

In order to evaluate the suitability of the published kinetic models to our experimental data, a

415

set of methanol dehydration process simulations were carried out, based on these kinetic models. The 19 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 20 of 30

416

simulations were performed using a plug-flow pseudo-homogeneous reactor model, for a WHSV of

417

23 hr-1, temperatures in the range of 170-270 °C and a methanol feed concentration of 14 mol %. The

418

published values of the parameters involved in the considered kinetic models are given in Table 2.

419

The simulation results are presented in Fig. 10. The interphase concentration and temperature

420

gradients, estimated in preliminary calculations, from the mass and heat balance around the catalyst

421

pellet 53, proved to be negligible for the working conditions of this study (as suggested also from the

422

experimental results presented in Fig. 9).

423

As seen from Fig. 10, none of the published kinetic models predicts with sufficient accuracy our

424

experimental data. This result is explained by the differences among the zeolites used in the

425

construction of these models, combined with the strong dependency of the catalytic performances on

426

the synthesis conditions and acidity of respective zeolites. The kinetic models published by Tavan et

427

al.

428

conversion values whereas the model published by Ha et al.

429

lower methanol conversion values as compared with our experimental ones.

430

The differences between our results and those predicted by the kinetic model of Tavan and

431

Hasanvandian

432

matrix than the HZSM-5 activity in the pure (as synthesized) state

433

fact that this kinetic model was based on experimental data measured at constant feed composition

434

(pure methanol). Another kinetic model for the same catalyst was also published by Tavan et al. 29.

435

However, it seems that there are some inconsistencies in the published values of kinetic parameters

436

for this model. Finally, the kinetic model published by Lu et al.

437

data for DME synthesis in a fluidized bed reactor. As known, the flow and mixing phenomena in

438

fluidized bed reactors are very complex and different of those in the fixed bed, so the accuracy of this

439

kinetic model could be affected by the hydrodynamics description used in its deduction. In

440

conclusion, this comparison study is evidencing relatively large differences between the predictions

441

of the published kinetic models, even for catalysts having close properties.

29

(pure HZSM-5) and Ha et al.

53

52

(Na modified ZSM-5) are predicting higher methanol 52

(K modified ZSM-5) is predicting

could be explained by the lower activity of the HZSM-5 formulated in the alumina

14

16

. A second reason could be the

was deduced using experimental


Page 21 of 30

1 0.9 0.8

Methanol conversion

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

0.7 0.6 0.5

This work Ha et al [48] (NaZSM) Ha et al [48] (KZSM) Tavan et al [26]-HZSM Tavan and Hasanvandian [49]-HZSM Lu et al [11]

0.4 0.3 0.2 0.1 0 180

190

200

210

230

240

250

260

270

280

o

Temperature, C

442 443 444

220

Fig. 10. Methanol dehydration simulation results

Estimation of the kinetic parameters

445

Due to the poor predicting capabilities of the published kinetic models, we performed a

446

model discrimination study in order to identify the most suitable model to our experimental

447

measurements. In this aim, the parameters of all kinetic models were re-estimated.

448 449

The temperature dependencies of the adsorption equilibrium constants are defined by van’t Hoff expression:

450

 ∆H a,J  K J = K J0 exp   ; J= M, D, W  RT 

451

The preexponential factors, Kj0, appearing in the adsorption equilibrium constants are directly

452 453

(8)

dependent on the entropy variations in the adsorption process 59, 60:

 ∆Sa,J  K J0 = exp    R 

(9)


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

454

Page 22 of 30

The entropy variation ∆Sa,J is negative and smaller than the gas phase entropy of the adsorbate J 60, 61:

455 T

− ∆Sa,J < Sg,J ; S g , J (T ) = S g , J ,0 +

456

∫

C p , J (T )

298

T

dT

(10)

457

In order to compare the prediction quality of models with different number of parameters, we used a

458

model selection criterion (MSC) given by equation (11). A model with a higher value of MSC will be

459

more appropriate 61, 62: N

∑ (X 460

MSC=

M , j ,exp

-X M ,exp ) 2

j=1 N

∑ (X

M , j ,exp

-X M , j )

2

2p N

(11)

j=1

461

X M , j ,exp , X M , j - experimental and calculated values of methanol conversion; N-number of

462

experimental determinations; p-number of model parameters.

463

The estimation calculations were performed by the ‘lsqcurvefit’ function of the Matlab

464

programming environment, using our experimental data. The model parameters thus estimated are

465

given in Table 6.

466

The numerical values for correlation coefficient (R2) and of the model selection criterion (MSC),

467

presented in Table 6, indicate that, among the tested kinetic models, the associative adsorption one

468

given by rate expression (2) (proposed by Ha et al.

469

comparison between the calculated values of methanol conversion (with the kinetic model so

470

selected) and the measured ones is presented in Fig. 11.

52

) provides a better quality of the fit. A

471

Average relative sensitivities of methanol conversion in respect with model parameters were

472

also calculated. These were obtained by averaging the methanol conversion sensitivities in the

473

experimental points, using a relation similar with the one published by Weijers and Vanrolleghem 63:

474

475

Si , X = Si

qi ,n XM

;

Si =

1 N

N

å

j= 1

¶XM,j ¶ qi

;

XM =

1 N

N

å

X M , j ,nom

(12)

j= 1

The derivative was calculated numerically by centered differences formula: 22 ACS Paragon Plus Environment

Page 23 of 30 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

¶XM,j

476

¶ qi

=

X M+ , j - X M- , j qi+ - qi-

; qi+ = (1 + ε)qi ,nom ; qi- = (1- e )qi ,nom

(13)

477

In the previous relations, ε is the relative perturbation. and θi are kinetic parameters. The subscript

478

‘nom’ indicates the values corresponding to the nominal values

479

whereas X M+ , j and X M- , j are the calculated values of XM corresponding to the perturbed values of

480

parameter θi ( qi+ and qi- ), the other parameters being kept at nominal values.

481

The sensitivity values presented in Table 5 are evidencing that all the parameters of the kinetic model

482

(2) have a significant influence on the methanol conversion, except the adsorption enthalpy of

483

methanol which is relatively less important. However, we kept this parameter, working with the

484

kinetic model structure, as proposed by his authors.

485

Table 5. Values of the sensitivities for the calculated parameters Sensitivity

θi Si , X ,relation (12)

of model parameters ( qi ,nom ),

k0

E

KM,0

dHa,M

KW,0

dHa,W

0.381

0.192

0.333

0.085

0.207

0.146

486 487

The estimated values of activation energy and adsorption enthalpies for methanol and water are

488

compared with several published values for H-ZSM-5 and similar catalysts, in Table 7. As can be

489

seen, the values of the three parameters are well fitted within the ranges of published data.

490

The adequacy of the estimated values for the kinetic model parameters can be also tested

491

based on thermodynamic reasons. At 298 K, the gas phase entropies are Sg,M,0=239.7 J/(mole K) for

492

methanol and Sg,W,0 = 188.84 J mol-1K-1 for water

493

values for preexponential factors KM,0 and KW,0 for the rate expression (2) (Table 6) one obtains a

494

methanol adsorption entropy of -79.4 J mol-1 K-1 and a water adsorption entropy of -234.8 J mol-1K-1.

495

So, the calculated values for adsorption entropy, based on the rate expression (2), fulfill the

496

thermodynamic criterion (10).

64

. Using the relation (10), and the numerical


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 30

497

Table 6. The estimated kinetic parameters for methanol etherification (for the rate expressions

498

presented in Table 1)

Parameter

Rate expression (2) Ha et al. 52

Rate expression (3), Tavan et al. 29

Rate expression (4), Lu et al. 14

Rate expression (5), Carr et al. 49

k0, kmol kg-1 s-1 E, J mol-1

1.209·108(1±0.100)

1.684·1014 (1±0.058)

9.753·10-4 (1±0.166)

2.435·105 (1±0.346)

1.038·105 (1±0.038)

1.614·105 (1±0.067)

3.279·104 (1±0.012)

7.147·104 (1±0.327)

KM,0, bar-1

7.113·10-5 (1±0.082)

1.154 ·10-11 (1±0.154)

3.093 ·10-3 (1±0.031)

4.162 ·10-5 (1±0.073)

dHa,M, J mol-1

-5.294·104 (1±0.157)

-1.113·105 (1±0.151)

-3.362·104 (1±0.663)

-1.12·104 (1±0.115)

KW,0, bar-1

5.392 ·10-13 (1±0.083)

2.873 ·10-9 (1±0.089)

2.317 ·10-13 (1±0.152)

dHa,W, J mol-1

-1.451·105 (1±0.116)

-1.162·105 (1±0.096)

-4.251 ·104 (1±0.337)

R2 = 0.962, MSC= 25.5

R2 = 0.956, MSC= 22.7

R2 = 0.91, MSC= 12.9

R2 = 0.91, MSC=13.35

499 500 501 1

0.8

0.6

0.4

0.2

0

502 503

0

0.2

0.4

0.6

0.8

1

Experimental methanol conversion

Fig. 11. Parity diagram for associative kinetic model

504 505 24 ACS Paragon Plus Environment

Page 25 of 30 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

506

Energy & Fuels

Table 7. Published values for activation energy and adsorption enthalpies for methanol and water

H-ZSM-5

E, kJ/mole 147.5

∆HaM, kJ/mole -65

∆HaW, kJ/mole -74

Ha et al. 52

(K,Na) H-ZSM-5

52.2 - 55

99 - 105

92-100

Tavan and Hasanvandian 53

H-ZSM-5

69.4

108.11

89.83

Pop et al. 2

H-SAPO34/γ-Al2O3

80.1

-63.89

-49.06

115

90

Authors

Catalyst

Blaszkowski and Santen 47

Lee et al.

65

H-ZSM-5

Bercic and Levec 10

γ-Al2O3

143.7

70.5

42.1

This work

H-ZSM-5/γ-Al2O3

103.8

-52.94

-145.1

507 508

According to Vannice et al.

59

, the adsorption entropy should be in the range

509

0 ( ∆H 0ads in cal mol-1 and ∆S0ads in cal mol-1 K-1). As it can be 10 ≤ - ∆S0ads ≤ 12.2 - 0.0014 ∆H ads

510

easily checked, these thermodynamic restrictions are also fulfilled, both for methanol and water

511

estimated adsorption entropies.

512

Conclusions

513

Due to its high catalytic activity and selectivity, as well as its good hydrothermal resistance, the

514

ZSM-5 zeolite is one of the most appreciated catalysts for methanol etherification. A review of the

515

published studies, approaching the surface mechanism and kinetics of this catalytic process,

516

illustrated that two proposed mechanisms are able to explain the experimental observations and

517

theoretical analyses: the dissociative mechanism which involves a first step of methanol dissociation

518

on the Bronsted acid sites and the associative mechanism, which is hypothesizing that two molecules

519

of methanol associates on the acidic sites form a protonated methanol dimer as an etherification

520

intermediate. The studies published in the last period indicate that the two mechanisms could occur

521

concurrently, but in the typical conditions for methanol etherification the associative mechanism is

522

prevailing, the dissociative mechanism being dominant only at high temperatures. Methanol

523

etherification experiments conducted in vapor phase over a synthesized H-ZSM-5/γ-Al2O3 catalyst,

524

in the ranges typical for the DME direct synthesis process, evidenced a negative influence of

525

methanol concentration on the reaction extent. Methanol conversions close to chemical equilibrium 25 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 26 of 30

526

have been attained at temperatures around 270 °C, with no significant concentrations of by-products

527

detected in the reactor effluent. The results confirmed the published data regarding the good activity

528

and DME selectivity of the H-ZSM-5 zeolite formulated in an alumina binder. The experimental data

529

so obtained were used to evaluate the prediction capabilities of the main published kinetic models

530

proposed for the vapor phase methanol etherification over ZSM-5 zeolites with different acidities.

531

The results evidenced a poor quality of the predictions and significant differences between the

532

predictions of kinetic models developed for same catalysts. This is an expected result due to the

533

strong dependency of catalytic performances of the zeolite, on the precise composition and synthesis

534

conditions, combined with the diversity of zeolites used in the deduction of these models. A model

535

discrimination study indicated that a kinetic model based on the associative mechanism is the most

536

appropriate to describe the dependencies observed in our experimental data. The parameter values

537

and model quality proved to be consistent with the usual thermodynamic and statistical criteria.

538 539

Acknowledgment

540

This work has been funded by University Politehnica of Bucharest, through the “Excellence

541

Research Grants” Program, UPB – GEX. Identifier: UPB–EXCELENȚĂ–2016, The synthesis of

542

dimethyl ether from methanol over a H-ZSM-5 based catalysts, Contract number 400.

543 544

References

545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560

1. Arya, P. K.; Tupkari, S.; Satish, K.; Thakre, G. D.; Shukla, B. M., DME blended LPG as a cooking fuel option for Indian household: A review. Renew Sust Energ Rev 2016, 53, 1591-1601. 2. Pop, G.; Bozga, G.; Ganea, R.; Natu, N., Methanol Conversion to Dimethyl Ether over HSAPO-34 Catalyst. Ind. Eng. Chem. Res. 2009, 48, 7065-7071. 3. Tang, Q.; Xu, H.; Zheng, Y.; Wang, J.; Li, H.; Zhang, J., Catalytic dehydration of methanol to dimethyl ether over micro–mesoporous ZSM-5/MCM-41 composite molecular sieves. Applied Catalysis A: General 2012, 413-414, 36-42. 4. Bozga, G.; Apan, I. T.; Bozga, R. E., Dimethyl Ether Synthesis Catalysts, Processes and Reactors. Recent Patents on Catalysis 2013, 2, (1), 68-81. 5. Azizi, Z.; Rezaeimanesh, M.; Tohidian, T.; Rahimpour, M. R., Dimethyl ether: A review of technologies and production challenges. Chemical Engineering and Processing: Process Intensification 2014, 82, 150-172. 6. Li, Q.; Wen, X.; Wu, G.; Chung, H. T.; Gao, R.; Zelenay, P., High-Activity PtRuPd/C Catalyst for Direct Dimethyl Ether Fuel Cells. Angewandte Chemie International Edition 2015, 54, (26), 7524-7528. 7. Borgwardt, R. H. Hynol Process Evaluation; EPA/600/SR-97/153, 1998. 26 ACS Paragon Plus Environment

Page 27 of 30 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

561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604

Energy & Fuels

8. Li, Z.; Han, C.; Gu, T., Economics of biomass gasification: A review of the current status. Energy Sources, Part B: Economics, Planning, and Policy 2018, 13, (2), 137-140. 9. Li, D.-X.; Liu, J.-B.; Farahani, M. R.; Gao, W.; Huo, Y., Techno-economic analysis of biomass-to-biomethanol (BtS) via low-temperature steam gasification. Energy Sources, Part B: Economics, Planning, and Policy 2018, 13, (2), 91-95. 10. Bercic, G.; Levec, J., Catalytic Dehydration of Methanol to Dimethyl Ether. Kinetic Investigation and Reactor Simulation. Ind. Eng. Chem. Res. 1993, 32, 2478-2484. 11. Bercic, G.; Levec, J., Intrinsic and global reaction rate of methanol dehydration over alumina pellets. Industrial & Engineering Chemistry Research 1992, 31, (4), 1035-1040. 12. Khandan, N.; Kazemeini, M.; Aghaziarati, M., Determining an optimum catalyst for liquidphase dehydration of methanol to dimethyl ether. Appl Catal a-Gen 2008, 349, (1-2), 6-12. 13. Khandan, N.; Kazemeini, M.; Aghaziarati, M., Synthesis of Dimethyl Ether over Modified HMordenite Zeolites and Bifunctional Catalysts Composed of Cu/ZnO/ZrO2 and Modified HMordenite Zeolite in Slurry Phase. Catalysis Letters 2009, 129, (1-2), 111-118. 14. Lu, W.-Z.; Teng, L.-H.; Xiao, W.-D., Simulation and experiment study of dimethyl ether synthesis from syngas in a fluidized-bed reactor. Chemical Engineering Science 2004, 59, (22-23), 5455-5464. 15. Jiang, S.; Hwang, J. S.; Jin, T. H.; Cai, T. X.; Cho, W.; Baek, Y. S.; Park, S. E., Dehydration of methanol to dimethyl ether over ZSM-5 zeolite. B Korean Chem Soc 2004, 25, (2), 185-189. 16. Kim, S. D.; Baek, S. C.; Lee, Y.-J.; Jun, K.-W.; Kim, M. J.; Yoo, I. S., Effect of γ-alumina content on catalytic performance of modified ZSM-5 for dehydration of crude methanol to dimethyl ether. Applied Catalysis A: General 2006, 309, (1), 139-143. 17. Spivey, J. J., Dehydration Catalysts for the Methanol Dimethyl Ether Reaction. Chem Eng Commun 1991, 110, 123-142. 18. Saravanan, K.; Ham, H.; Tsubaki, N.; Bae, J. W., Recent progress for direct synthesis of dimethyl ether from syngas on the heterogeneous bifunctional hybrid catalysts. Appl Catal B-Environ 2017, 217, 494-522. 19. Bartholomew, C. H.; Farrauto, R. J., Fundamentals of industrial catalytic processes. 2nd ed.; Wiley: Hoboken, N.J., 2006; p xxiii, 966 p. 20. Bonura, G.; Cordaro, M.; Spadaro, L.; Cannilla, C.; Arena, F.; Frusteri, F., Hybrid Cu–ZnO– ZrO2/H-ZSM5 system for the direct synthesis of DME by CO2 hydrogenation. Applied Catalysis B: Environmental 2013, 140-141, 16-24. 21. Catizzone, E.; Aloise, A.; Migliori, M.; Giordano, G., Dimethyl ether synthesis via methanol dehydration: Effect of zeolite structure. Appl Catal a-Gen 2015, 502, 215-220. 22. Masih, D.; Rohani, S.; Kondo, J. N.; Tatsumi, T., Low-temperature methanol dehydration to dimethyl ether over various small-pore zeolites. Appl Catal B-Environ 2017, 217, 247-255. 23. Nakamoto, H.; Takahashi, H., Hydrophobic Natures of Zeolite-Zsm-5. Zeolites 1982, 2, (2), 67-68. 24. Vanoye, L.; Favre-Reguillon, A.; Rodriguez, M. F.; Dupuy, S.; Pallier, S.; Pitault, I.; De Bellefon, C., Methanol dehydration over commercially available zeolites: Effect of hydrophobicity. Catalysis Today 2013, 215, 239-242. 25. Han, X. L.; Wang, L.; Li, J. D.; Zhan, X.; Chen, J.; Yang, J. C., Tuning the hydrophobicity of ZSM-5 zeolites by surface silanization using alkyltrichlorosilane. Applied Surface Science 2011, 257, (22), 9525-9531.


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

605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650

Page 28 of 30

26. Gayubo, A. G.; Aguayo, A. T.; Atutxa, A.; Prieto, R.; Bilbao, J., Role of reaction-medium water on the acidity deterioration of a HZSM-5 zeolite. Industrial & Engineering Chemistry Research 2004, 43, (17), 5042-5048. 27. Gayubo, A. G.; Aguayo, A. T.; Castilla, M.; Moran, A. L.; Bilbao, J., Role of water in the kinetic modeling of methanol transformation into hydrocarbons on HZSM-5 zeolite. Chem Eng Commun 2004, 191, (7), 944-967. 28. Ajami, H.; Shariati, A., Effect of acidic H-ZSM-5 catalyst in conversion of methanol to dimethyl ether. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects 2016, 38, (19), 2845-2853. 29. Tavan, Y.; Hosseini, S. H.; Ghavipour, M.; Khosravi Nikou, M. R.; Shariati, A., From laboratory experiments to simulation studies of methanol dehydration to produce dimethyl ether— Part I: Reaction kinetic study. Chemical Engineering and Processing: Process Intensification 2013, 73, 144-150. 30. Huang, M. H.; Lee, H. M.; Liang, K. C.; Tzeng, C. C.; Chen, W. H., An experimental study on single-step dimethyl ether (DME) synthesis from hydrogen and carbon monoxide under various catalysts. International Journal of Hydrogen Energy 2015, 40, (39), 13583-13593. 31. Hassanpour, S.; Yaripour, F.; Taghizadeh, M., Performance of modified H-ZSM-5 zeolite for dehydration of methanol to dimethyl ether. Fuel Processing Technology 2010, 91, (10), 1212-1221. 32. Frusteri, F.; Migliori, M.; Cannilla, C.; Frusteri, L.; Catizzone, E.; Aloise, A.; Giordano, G.; Bonura, G., Direct CO2-to-DME hydrogenation reaction: New evidences of a superior behaviour of FER-based hybrid systems to obtain high DME yield. J Co2 Util 2017, 18, 353-361. 33. Migliori, M.; Aloise, A.; Catizzone, E.; Giordano, G., Kinetic Analysis of Methanol to Dimethyl Ether Reaction over HMFI Catalyst. Ind. Eng. Chem. Res. 2014, 53, (38), 14885–14891. 34. Migliori, M.; Aloise, A.; Giordano, G., Methanol to dimethylether on H-MFI catalyst: The influence of the Si/Al ratio on kinetic parameters. Catalysis Today 2014, 227, 138-143. 35. Rownaghi, A. A.; Rezaei, F.; Stante, M.; Hedlund, J., Selective dehydration of methanol to dimethyl ether on ZSM-5 nanocrystals. Applied Catalysis B: Environmental 2012, 119-120, 56-61. 36. Yang, Q.; Zhang, H. T.; Kong, M.; Bao, X. X.; Fei, J. H.; Zheng, X. M., Hierarchical mesoporous ZSM-5 for the dehydration of methanol to dimethyl ether. Chinese Journal of Catalysis 2013, 34, (8), 1576-1582. 37. Wei, Y.; de Jongh, P. E.; Bonati, M. L. M.; Law, D. J.; Sunley, G. J.; de Jong, K. P., Enhanced catalytic performance of zeolite ZSM-5 for conversion of methanol to dimethyl ether by combining alkaline treatment and partial activation. Appl Catal a-Gen 2015, 504, 211-219. 38. Laugel, G.; Nitsch, X.; Ocampo, F.; Louis, B., Methanol dehydration into dimethylether over ZSM-5 type zeolites: Raise in the operational temperature range. Appl Catal a-Gen 2011, 402, (1-2), 139-145. 39. Mao, D.; Xia, J.; Zhang, B.; Lu, G., Highly efficient synthesis of dimethyl ether from syngas over the admixed catalyst of CuO–ZnO–Al2O3 and antimony oxide modified HZSM-5 zeolite. Energy Conversion and Management 2010, 51, (6), 1134-1139. 40. García-Trenco, A.; Vidal-Moya, A.; Martínez, A., Study of the interaction between components in hybrid CuZnAl/HZSM-5 catalysts and its impact in the syngas-to-DME reaction. Catalysis today 2012, 179, (1), 43-51. 41. Ordomsky, V. V.; Cai, M.; Sushkevich, V.; Moldovan, S.; Ersen, O.; Lancelot, C.; Valtchev, V.; Khodakov, A. Y., The role of external acid sites of ZSM-5 in deactivation of hybrid CuZnAl/ZSM-5 catalyst for direct dimethyl ether synthesis from syngas. Appl Catal a-Gen 2014, 486, 266-275. 28 ACS Paragon Plus Environment

Page 29 of 30 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

651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695

Energy & Fuels

42. Bonura, G.; Cordaro, M.; Cannilla, C.; Mezzapica, A.; Spadaro, L.; Arena, F.; Frusteri, F., Catalytic behaviour of a bifunctional system for the one step synthesis of DME by CO2 hydrogenation. Catalysis Today 2014, 228, 51-57. 43. Jones, A. J.; Iglesia, E., Kinetic, Spectroscopic, and Theoretical Assessment of Associative and Dissociative Methanol Dehydration Routes in Zeolites. Angew Chem Int Edit 2014, 53, (45), 12177-12181. 44. Kubelková, L.; Nováková, J.; Nedomová, K., Reactivity of surface species on zeolites in methanol conversion. Journal of Catalysis 1990, 124, (2), 441-450. 45. Bandiera, J.; Naccache, C., Kinetics of methanol dehydration on dealuminated H-mordenite: Model with acid and basic active centres. Applied Catalysis 1991, 69, (1), 139-148. 46. Moses, P. G.; Nørskov, J. K., Methanol to Dimethyl Ether over ZSM-22: A Periodic Density Functional Theory Study. ACS Catalysis 2013, 3, (4), 735-745. 47. Blaszkowski, S. R.; Santen, R. A. v., Theoretical Study of the Mechanism of Surface Methoxy and Dimethyl Ether Formation from Methanol Catalyzed by Zeolitic Protons. J. Phys. Chem. B 1997, 101, 2292-2305. 48. Ha, K. S.; Lee, Y. J.; Bae, J. W.; Kim, Y. W.; Woo, M. H.; Kim, H. S.; Park, M. J.; Jun, K. W., New reaction pathways and kinetic parameter estimation for methanol dehydration over modified ZSM-5 catalysts. Appl Catal a-Gen 2011, 395, (1-2), 95-106. 49. Carr, R. T.; Neurock, M.; Iglesia, E., Catalytic consequences of acid strength in the conversion of methanol to dimethyl ether. Journal of Catalysis 2011, 278, (1), 78-93. 50. Ghorbanpour, A.; Rimer, J. D.; Grabow, L. C., Computational Assessment of the Dominant Factors Governing the Mechanism of Methanol Dehydration over H-ZSM-5 with Heterogeneous Aluminum Distribution. ACS Catalysis 2016, 6, (4), 2287-2298. 51. Proscanu, R.; Cursaru, R. G. D.; Matei, V.; Vasilievici, G., Effect of Introduction of Lanthanum Cations in ZSM-5 Crystallization Step on Ethanol Conversion to Hydrocarbons. Revista de Chimie (Bucharest) 2014, 65, (12), 1517-1520. 52. Ha, K.-S.; Lee, Y.-J.; Bae, J. W.; Kim, Y. W.; Woo, M. H.; Kim, H.-S.; Park, M.-J.; Jun, K.W., New reaction pathways and kinetic parameter estimation for methanol dehydration over modified ZSM-5 catalysts. Applied Catalysis A: General 2011, 395, (1), 95-106. 53. Tavan, Y.; Hasanvandian, R., Two practical equations for methanol dehydration reaction over HZSM-5 catalyst – Part I: Second order rate equation. Fuel 2015, 142, (Supplement C), 208-214. 54. Baerlocher, C.; McCusker, L. B.; Olson, D.; Meier, W. M., Atlas of zeolite framework types. 6th ed.; Elsevier: Amsterdam, 2007; p vi, 398 p. 55. Kim, W. J.; Lee, M. C.; Hayhurst, D. T., Synthesis of ZSM-5 at low temperature and atmospheric pressure in a pilot-scale batch reactor. Microporous and Mesoporous Materials 1998, 26, (1), 133-141. 56. Mostafa, M. M. M.; Rao, K. N.; Harun, H. S.; Basahel, S. N.; El-Maksod, I. H. A., Synthesis and characterization of partially crystalline nanosized ZSM-5 zeolites. Ceramics International 2013, 39, (1), 683-689. 57. Froment, G. F.; Bischoff, K. B., Chemical reactor analysis and design. Second ed.; Wiley: New York, 1990; p XXXIV, 664 S. 58. Hinderer, J.; Keil, F. J., Diffusion and Reaction in Composite Catalysts. Hung J Ind Chem 1995, 23, (3), 207-213. 59. Vannice, M. A.; Hyun, S. H.; Kalpakci, B.; Liauh, W. C., Entropies of adsorption in heterogeneous catalytic reactions. Journal of Catalysis 1979, 56, (3), 358-362.


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

696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711

Page 30 of 30

60. Vannice, M. A., Kinetics of Catalytic Reactions. Springer Science-Business Media, Inc.: New York, 2005. 61. Banu, I.; Bercaru, G.; Bozga, G.; Danciu, T., Kinetic Study of Methyl Isobutyl Ketone Combustion over a Commercial Pt/Alumina Catalyst. Chemical Engineering & Technology 2016, 39, (4), 758–766 62. Picasso Escobar, G.; Quintilla Beroy, A.; Pina Iritia, M. P.; Herguido Huerta, J., Kinetic study of the combustion of methyl-ethyl ketone over α-hematite catalyst. Chemical Engineering Journal 2004, 102, (2), 107-117. 63. Weijers, S. R.; Vanrolleghem, P. A., A procedure for selecting best identifiable parameters in calibrating activated sludge model no. 1 to full-scale plant data. Water Sci Technol 1997, 36, (5), 6979. 64. Yaws, C. L., Chemical properties handbook : physical, thermodynamic, environmental, transport, safety, and health related properties for organic and inorganic chemicals. McGraw-Hill: New York, 1999; p vii, 779 p. 65. Lee, C. C.; Gorte, R. J.; Farneth, W. E., Calorimetric Study of Alcohol and Nitrile Adsorption Complexes in H-ZSM-5. The Journal of Physical Chemistry B 1997, 101, (19), 3811-3817.


An evaluation of published kinetic models for vapor phase methanol

Recommend Documents