Indole Hydrodenitrogenation over Alumina and SilicaâAlumina

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Indole hydrodenitrogenation over alumina and silica-alumina supported sulfide catalysts - Comparison with quinoline Minh-Tuan Nguyen, Gerhard D. Pirngruber, Fabien Chainet, Melaz Tayakout, and Christophe Geantet Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b02993 • Publication Date (Web): 08 Sep 2017 Downloaded from http://pubs.acs.org on September 11, 2017

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Industrial & Engineering Chemistry Research

1

Indole hydrodenitrogenation over alumina and silica-alumina supported

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sulfide catalysts - Comparison with quinoline

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Minh-Tuan Nguyen1, Gerhard D. Pirngruber1, Fabien Chainet 1, Melaz Tayakout-Fayolle2*,

4

Christophe Geantet3

5

1

6

2

7

Boulevard du 11 novembre 1918, F-69100, Villeurbanne, France

8

3

9

IRCELYON, UMR 5256-CNRS, 2 avenue Albert Einstein, F-69626 Villeurbanne, France

IFP-Energies nouvelles, Rond-point de l’échangeur de Solaize, BP 3, 69360 Solaize, France Université de Lyon, Université Claude Bernard Lyon 1, CNRS, LAGEP UMR 5007, 43

Université de Lyon, Institut de recherches sur la catalyse et l’environnement de Lyon,

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Email addresses of authors:

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1. Minh-Tuan Nguyen: [email protected]

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2. Melaz Tayakout-Fayolle : [email protected]

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3. Fabien Chainet : [email protected]

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4. Gerhard D. Pirngruber : [email protected]

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5. Christophe Geantet: [email protected]

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* Corresponding author: Prof. Melaz Tayakout-Fayolle

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Email: [email protected]

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1 ACS Paragon Plus Environment


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Abstract

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A detailed kinetic model was proposed to analyze experimental data obtained from indole

22

hydrodenitrogenation (HDN) over γ-Al2O3 and amorphous silica-alumina (ASA) supported NiMo

23

catalysts. The goal was to investigate the support acidity effects on indole HDN and compare

24

with a recent study on quinoline HDN. Similarly to quinoline HDN, indole HDN occurred via the

25

hydrogenation of aromatic ring, followed by N-ring opening and exocyclic C-N bond breaking.

26

The high support acidity of NiMo(P)/ASA exhibited a promoting effect for N-removal steps and

27

adsorption of nitrogen compounds. However, in contrast to quinoline HDN, it did not clearly

28

induce a positive effect for hydrogenation step. The acidic function of ASA also favored the

29

formation of by-products such as toluene, cyclohexane, dimer and trimer of indole. Catalytic

30

conversion of a quinoline and indole mixture revealed a strong inhibiting effect of quinoline on

31

indole HDN whereas the inhibiting effect of indole on quinoline HDN was weak. The inhibition

32

was weaker over NiMo(P)/Al2O3 than over NiMo(P)/ASA. This result is in agreement with a

33

relative ranking of apparent adsorption constants of quinoline, indole and their products on

34

NiMo(P)/Al2O3 and ASA.

35

Highlights

36

•

Kinetic modeling of indole HDN over NiMo-based sulfide supported catalysts.

37

•

Effects of support acidity on the indole HDN were compared with quinoline HDN.

38

•

Mutual inhibiting effects of quinoline and indole in HDN.

39

•

Ranking of adsorption constants of quinoline, indole and their products was established.

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Key words: Hydrodenitrogenation, indole, quinoline, NiMo(P) catalysts, support acidity, silica-

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alumina, adsorption constant

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Graphical abstract

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1. Introduction Organonitrogen compounds in oil fractions poison acid catalysts in downstream oil refining

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1–3

and strongly inhibit deep hydrodesulfurization and hydrodearomatization

3–7

47

processes

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implementation of a hydrotreating stage to remove nitrogen compounds from petroleum feeds,

49

via hydrodenitrogenation (HDN) reaction, before hydrocracking or catalytic cracking processes

50

prevents the poisoning of catalysts and thus improves the conversion process. These reactions are

51

generally utilized for the upgrading of petroleum cuts of poor quality, such as vacuum gas oil and

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coker gas oil. The improvement of hydrodenitrogenation catalysts in order to enhance nitrogen

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compounds removal was studied by using new catalytically active phases

54

support acidity of conventional sulfide catalysts

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HDN activity is still under debate. It might be explained by direct involvement of acid sites

56

located on the support in the cleavage of the C-N bond

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support acidity can induce the modification of electronic properties of coordinately unsaturated

58

sites (CUS) on the promoted MoS2 nanoparticles

59

20,21

12–16

8–11

. The

or modifying

. The effect of support acidity on catalytic

17–19

14

. An alternative explanation is that the

and/or enhance the acidity of –SH group

, thus increase HDN activity of catalysts.

60

A better understanding of support effects on the mechanism and the kinetics of HDN of

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model nitrogen containing compounds is required for the improvement of the HDN catalysts. In

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petroleum fractions, the majority of nitrogen compounds found falls into two groups: the six-

63

membered pyridinic ring (basic compounds) and the five-membered pyrrolic ring (non-basic

64

compounds) 22. Quinoline and indole are representative basic and non-basic model compounds in

65

gas oil. The quinoline HDN has called more attention than the indole HDN in literature. Similarly

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to the quinoline HDN, the reaction network of indole HDN includes numerous consecutive

67

elemental steps and parallel competing pathways (Figure 1). 4 ACS Paragon Plus Environment

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A detailed kinetic analysis of the indole HDN reaction allows the evaluation of the

69

catalyst’s activity as well as support effects in different mechanistic steps: hydrogenation of

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aromatic rings, ring opening and C-N bond cleavage. Under hydrotreating conditions, indole was

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proved to be in thermodynamic equilibrium with 2,3-dihydroindole 23. After the hydrogenation of

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indole into 2,3-dihydroindole (HIN), the indole HDN can proceed via two reaction pathways: (i)

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hydrogenation of 2,3-dihydroindole (HIN) to octahydroindole (OHIN) and (ii) ring opening of

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indoline to o-ethylaniline (OEA) which occurred above 300°C

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hydrogenation of HIN into OHIN might be considered as the main pathway of indole HDN.

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However, above 340°C, intermediate products including OHIN and ethylcyclohexylamine

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(ECHA) were not detected in the product stream

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breaking of fully hydrogenated compounds was very fast under these reaction conditions.

. The pathway proceeding via

. This was probably because the C-N bond

OEA

HIN

N H

24,25

23

N H

EB

NH2

Indole

ECHE

N H

NH2 ECHA

OHIN

79

ECH

80

Figure 1: Reaction scheme of indole hydrodenitrogenation 24,25

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In a complex matrix of different N-compounds, reactivity of model compounds changes

82

due to the competitive adsorption. For example, indole is more reactive in individual test but less

83

reactive than quinoline in a mixture 26,27. From the tests of individual compounds, under the same

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reaction conditions (4 MPa and 340oC), Rabarihoela-Rakotovao and co-workers


28

reported that


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acridine was completely converted into hydrogenated products whereas the conversion of 1,4-

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dimethylcarbazole was not complete, but the latter was more reactive than acridine towards

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HDN. In a mixture with acridine, carbazole was less reactive than acridine due to the inhibiting

88

effect of acridine 29. In our previous paper

89

30

, a kinetic model coupled with liquid-vapor mass transfer and

90

competitive adsorption of hydrogen and nitrogen compounds on the same catalytic sites allowed

91

determining precise kinetic constants for all elementary steps and adsorption constants for all

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nitrogen-containing compounds (including NH3) of quinoline HDN. This kinetic model was

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successfully used to investigate the support acidity effects of NiMo-based supported catalysts in

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each reaction step of quinoline HDN

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with catalysts characterization data was applied to study the case of indole HDN. In the last part

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of this work, the HDN reactivity as well as mutual inhibiting effect of mixtures of quinoline and

97

indole will be analyzed. Adsorption constants of quinoline, indole and theirs intermediate

98

products during the hydrodenitrogenation will be compared.

99

2. Experimental

100

2.1.

31

. In the present work, a similar methodology combined

Catalysts

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The two catalysts NiMo-based supported on γ-Al2O3 and amorphous silica-alumina

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(ASA), which were previously used for quinoline HDN 30,31, were prepared by incipient wetness

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impregnation method. The catalysts were characterized by Transmission Electron Microscopy

104

(TEM), X-ray Photoelectron Spectroscopy (XPS), and Infra-Red (IR) Spectroscopy of CO. The

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method of preparation, sulfidation and characterizations were well described in our previous


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paper 31. Some important properties of the two catalysts were repeated and summarized in Table

107

1.

108

Table 1: Catalysts properties 31 NiMo(P)/Al2O3 % wt MoO3

18.6%

14.0%

% wt NiO

3.84%

2.97%

Surface BET area (m2/g)

201

180

Grain density, g/cm3

1.3

1.55

NiMoS phase content by X-ray Photoelectron Spectroscopy, mmol/cm3 catalyst

0.424

0.318

ν(CO) of NiMoS band by Infra-Red Spectroscopy, cm-1

2129

2134

22

88

Cyclohexane isomerization conversion, % 109

NiMo(P)/ASA

2.2. Catalytic tests of indole HDN

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Prior to catalytic tests, the two catalysts were first crushed, sieved (80-125µm) and then

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sulfided ex-situ with a mixture of H2 and H2S (15 vol% H2S, flow rate of 1.3 L/g of catalyst/h) at

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400°C and for 4 h. Indole was obtained from Sigma Aldrich with 99% of purity. Catalytic tests of

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indole HDN were performed in a batch reactor (volume of 300 ml) with the same reaction

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conditions as the quinoline HDN: 7 MPa total pressure, at three different temperatures (340, 350

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and 360°C) and 0.75 gram of sulfide catalyst

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with 20 µL dimethyldisulfide (DMDS) to maintain a partial pressure of H2S in reactor. Since in

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industrial practice catalysts are compared on a volume basis, the catalyst mass was later

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converted into catalyst volume by using the grain density (Table 1). The stirring rate (800 rpm)

119

and the size of catalyst particles (80-125 µm) were selected so that vapor-liquid and liquid-solid

120

mass transfer diffusion limitations were absent, respectively. In order to avoid the co-elution of

31

. For each catalytic test, the reactor was loaded



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m-xylene, which was the aromatic solvent in quinoline HDN, and ethylbenzene (product of

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indole HDN) on the gas chromatogram due to the close retention times of these compounds, we

123

substituted m-xylene by 1,3,5-trimethylbenzene. Thus, the solvent for indole HDN was a mixture

124

of 35 wt% of 1,3,5-trimethylbenzene (98% of purity) and 65 wt% of squalane (99% of purity)

125

from Sigma Aldrich. The initial concentration of indole for kinetic studies was set to 0.5, 0.75

126

and 1 wt%.

127

Catalytic tests of the indole - quinoline mixture were performed at 350°C and 7 MPa, in a

128

mixture of 65% squalane and 35% 1,3,5-trimethylbenzene. Quinoline was obtained from Sigma

129

Aldrich with 98% of purity. The feed was loaded by 0.5 wt% of indole and 0.25 wt% of

130

quinoline. The concentration of quinoline was chosen (0.25 wt%) to be a half of that of indole

131

(0.5 wt%) in order to reinforce the inhibiting effect of indole on the HDN of quinoline, and

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confirm the inhibiting effect of quinoline (basic compound) on indole HDN even at low

133

concentration. Additional tests of quinoline HDN were performed under the same reaction

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conditions, i.e. 0.25 wt% of quinoline, in the absence of indole, in order to compare with the

135

mixture test.

136

Hot liquid sampling was carried out at different reaction times. The liquid samples were

137

analyzed by Gas Chromatography coupled to a Flame Ionization Detector (GC-FID) in order to

138

determine all component concentrations. Some liquid samples were also analyzed by Gas

139

Chromatography coupled to Nitrogen Chemiluminescence detector (GC-NCD) (Agilent

140

Technology, France) to verify the formation of heavy nitrogen containing products during indole

141

HDN. The analysis conditions of GC-FID and GC-NCD are given in Supporting Information 1.

142

The spent catalysts were washed with hot heptane (at 90°C) in a Soxhlet system for 24 hours and


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then dried under vacuum at 100°C for 24 hours. Carbon and nitrogen content were measured by

144

combustion (Flash 2000 Thermo Scientific instrument).

145

3. Results of catalytic tests and kinetic modeling

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3.1. Nitrogen mass balance during indole HDN

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As shown in Figure 1, the indole HDN proceeds through two parallel reaction pathways.

148

Under our reaction conditions, octahydroindole (OHIN) and ethylcyclohexylamine (ECHA) were

149

not detected. 2,3-dihydroindole and o-ethylaniline were intermediate products, while

150

ethylbenzene, ethylcyclohexene and ethylcyclohexane were found as final products. The nitrogen

151

mass balance was evaluated from all detected nitrogen compounds, including NH3 (deduced from

152

the amount of HDN products). However, we found that the nitrogen mass balance was poor,

153

particularly over the NiMo(P)/ASA catalyst, due to: (i) the evaporation of light compounds at hot

154

conditions; (ii) the formation of light and heavy by-products and (iii) the formation of nitrogen-

155

containing coke.

156

Experimental data showed that the concentrations of light components, i.e. ECH, ECHE

157

and EB at hot samplings (or at reaction conditions), were always lower than their concentration at

158

cold samplings (at 20oC and 3.4 MPa). The ratio between concentrations of these components at

159

hot to cold conditions varied in the range of 0.78 to 0.8. Consequently, a liquid-vapor equilibrium

160

simulation was needed in order to calculate the concentration of components in vapor phase, so as

161

to take them into account nitrogen mass balance. Thanks to L-V equilibrium constants of indole

162

and its products at reaction conditions (Supporting Information 2), obtained from the liquid-vapor

163

equilibrium simulation by ProSim software using the Grayson-Streed thermodynamic model


32

,


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164

we calculated the concentration of each component in the gas phase (Equation 1), assuming the

165

thermodynamic equilibrium.

Ci , g = Ci ,liq .

166

P θi . total RT Cliq

(Equation 1)

167

θi is the equilibrium constant, C i , g is the concentration of component i in the gas phase at

168

thermodynamic equilibrium with the component i in the liquid phase; C i ,liq is experimentally

169

total determined concentration of component in liquid phase and C liq is total concentration of all

170

components (including solvents and hydrogen) in the liquid phase.

171

The nitrogen mass balance error was defined as the difference between the total molar

172

quantity of all identified nitrogen compounds in liquid and vapor phase and the amount of indole

173

introduced into the reactor at the beginning of catalytic tests (Equation 2). n

174

χ=

n

o ∑ C i ,liq.Vliq + ∑ C i, gV g −n INDOLE i

n

i o INDOLE

.100% (Equation 2)

175

o V liq and V g are the liquid and vapor volumes, respectively; n INDOLE is the initial molar quantity of

176

indole introduced into the reactor. We found that the loss in nitrogen mass balance was

177

acceptable (approximately 5%) for all tests over NiMo(P)/Al2O3, but reached up to 13% for the

178

tests with 1 wt% of indole over NiMo(P)/ASA (Supporting Information 3). The loss in nitrogen

179

mass balance decreased with the initial concentration of indole.

180

A study on the formation of by-products and the loss of nitrogen as coke on the catalyst

181

surface was therefore carried out in order to evidence the loss of nitrogen in the test over


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NiMo(P)/ASA. By GC-NCD (Supporting Information 4A), we observed some light nitrogen-

183

containing by-products (below 0.5 wt% as compared to initial indole quantity), which eluted

184

earlier than o-ethylaniline from the GC column. The semi-quantitative evolution showed that

185

these compounds were produced at low HDN conversion and disappeared at high HDN

186

conversion, thus they were intermediate products. These compounds were probably formed by C-

187

C bond breaking reactions and later on denitrogenated into hydrocarbons products such as

188

benzene, cyclohexane. However, the superposition of light products, which were produced from

189

1,3,5-trimethylbenzene conversion with light products of indole HDN did not allow quantifying

190

the light by-products of indole HDN. Schulz et al.

191

the indole HDN over NiW/Al2O3, at 350°C and proposed a mechanism to explain the formation

192

of these products.

23

found about 5 wt% of light by-products of

193

Many heavy nitrogen containing by-products were also observed on the GC-NCD

194

chromatogram. Semi-quantification revealed that they were produced at short residence time and

195

further converted into lighter products or more condensed products (deposed on the catalysts as

196

coke). The formation of the heavy by-products, mainly dimers and trimers of indole, was

197

explained by the random linking of intermediate products

198

Cyclotron Resonance Mass Spectrometry (FT/ICR-MS) (Electrospray Ionization mode), several

199

heavy nitrogen containing by-products with 16 carbon atoms in the raw formula were found in

200

liquid samples obtained from tests over NiMo(P)/ASA (Supporting Information 4B). They were

201

probably dimers of indole and condensation products of indole with an ethyl-cyclohexyl

202

fragment. Moreover, after catalytic tests at 360°C and 1 wt% of indole, the spent NiMo(P)/Al2O3

203

and NiMo(P)/ASA catalysts contain 1.0 and 1.4 wt% of nitrogen, which represent about 6% and

33,34


. By Fourier Transform Ion


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9% of the total amount of nitrogen, respectively. This also contributes to the deficit in the

205

nitrogen mass balance.

206

In conclusion, the investigations of the by-products formation and the spent catalysts

207

revealed the cracking of C-C or C-N bonds which produced light products such as benzene,

208

toluene and cyclohexane. Moreover, acid sites on the catalysts led to alkylation, isomerization

209

and oligomerization, which induced the formation of heavy by-products and coke. The formation

210

of these by-products explains the loss of nitrogen in the mass balance. Consequently, in the

211

reaction mechanism scheme, a specific pathway leading to by-products has been added.

212

3.2. Catalytic indole HDN activity and selectivity

213

It should be highlighted that the formation of coke on very active sites of the fresh catalyst

214

is one of the inconveniences of using a batch reactor for evaluating catalyst activity. The

215

evolution of conversion and yields with time may be influenced by this transient behavior of the

216

catalyst. The deactivation or stabilization of the catalysts depends on the presence of coke

217

precursors in the feedstock. However, coke deposition was already observed during the heating

218

step of the test. Half of the final coke content was deposited when reaction conditions were

219

reached, so called to point, i.e. 0.6 wt% of carbon on the spent NiMo(P)/Al2O3 catalysts at to point

220

and 1.2 wt% carbon on the same spent catalyst after 3 hours of reaction times. In order to check if

221

this deactivation is detrimental, we tested a used catalyst again after resulfidation. We found that

222

the activity of the catalysts was almost unchanged. The deactivation ratios, i.e. the ratio between

223

the pseudo-first rate constants of the conversion of indole and dihydroindole obtained from the

224

test with fresh catalyst to that obtained from the test with spent catalyst, were close to unity. The

225

NiMo(P)/ASA was slightly more deactivated than the NiMo(P)/Al2O3. 12 ACS Paragon Plus Environment

Page 13 of 43

226

Figure 2 shows the HDN conversion, calculated by Equation 3, as a function of the

227

product of reaction time and catalyst volume. At 0.5 wt% of indole, the NiMo(P)/ASA gave a

228

higher HDN conversion than the NiMo(P)/Al2O3. However, at higher indole concentration the

229

HDN conversion over the two catalysts became equivalent. On the contrary, the quinoline HDN

230

activity of NiMo(P)/ASA was lower than that of NiMo(P)/Al2O331. The hydrogenation conversion

231

was calculated by Equation 4.  n + n ECHE + n ECH HDN Conv =  EB o n INDOLE 

232

 .100 % (Equation 3)  

o nINDOLE − (nINDOLE + nHIN ) .100% (Equation 4) HYD Conversion = o nINDOLE

233

234

100

100

(a)

80

HDN Conversion, %

HDN 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


60 NiMo(P)/Al2O3

40

NiMo(P)/ASA

20 0 0.0

(b)

80 60 NiMo(P)/Al2O3 40

NiMo(P)/ASA

20

0.2

0.4

0.6 3

0.8

0 0.0

Time x Volume of catalyst, h.cm

0.5

1.0

1.5

3

2.0

Time x volume of catalyst, (h.cm )

235

Figure 2: HDN conversion of indole over NiMo(P)/Al2O3 and NiMo(P)/ASA, at 350°C, 7 MPa,

236

in the test of (a) 0.5 wt% and (b) 1 wt% of indole

237

In terms of the selectivity to products, the NiMo(P)/ASA slightly favored the formation of

238

ethylbenzene (EB) (Figure 3), which is product of the direct Csp2-N bond breaking of o13 ACS Paragon Plus Environment


239

ethylaniline. Ethylcyclohexane was usually the main final product of indole HDN over the two

240

catalysts. The NiMo(P)/Al2O3 favored the accumulation of o-ethylaniline as compared to the

241

NiMo(P)/ASA. This might be explained by the lower reactivity of OEA or the higher formation

242

rate of OEA from hydroindole over NiMo(P)/Al2O3. Both of the above-mentioned selectivity

243

trends between two catalysts had already been found in quinoline HDN. The kinetic modeling

244

will allow us to get further insights.

(a)

80

14

Indole

60

o-Ethylaniline NiMo(P)/Al2O3

(b)

12

NiMo(P)/ASA

Yield, % mol

Yield, % mol

NiMo(P)/Al2O3

40 20

NiMo(P)/ASA

10 8 6 4 2

0 0

10

20

30

40 50 60 70 HYD Conversion, %

80

90

0

100

0

10

20

30


80

90

100

6

(c) 5

Ethylbenzene

(d)

80

Ethylcyclohexane

NiMo(P)/Al2O3

NiMo(P)/Al2O3

NiMo(P)/ASA

4

60 Yield, % mol

Yield, % mol

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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3 2

NiMo(P)/ASA

40 20

1

0 0 0

10

20

30

40

50

60

70

80

90

100

0

HYD Conversion, %

10

20

30


80

90

100

245

Figure 3: Comparison of products selectivty of the two catalysts in the conversion of indole at

246

350°C, 7MPa and 1 wt% indole, (a) Indole, (b) o-ethylaniline, (c) ethylbenzene, (d)

247

ethylcyclohexane.

248

3.3. Results of indole HDN kinetic modeling


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249

The kinetic model, which takes into account the liquid-vapor mass transfer and

250

competitive adsorption of hydrogen and nitrogen compounds on the same catalytic sites, was

251

described in detail in our previous paper

252

preferred to use only a single adsorption site in the Langmuir-Hinshelwood expression. The

253

adsorption constants of hydrocarbons (EB, ECH, ECHE), H2 and H2S were neglected as

254

compared to nitrogen compounds. The kinetic model allowed the estimation of kinetic and

255

adsorption parameters of indole HDN. The reaction scheme shown in Figure 4 was used for

256

establishing the kinetic equations.

30

. For the reasons discussed by Nguyen et al.

OEA

HIN

N H

k2

k7

N H

Indole

NH2

k3

k6

k 11

k8 k5

By - products

ECHE

N H

k9

NH2 ECHA

OHIN

k 10

very fast

257 258 259 260

261

, we

EB

k4

k1

31

ECH

Figure 4: Reaction scheme of indole HDN for kinetic modeling The reaction rate of each elementary step (except for the by-products formation pathway) was expressed by a generalized Langmuir-Hinshelwood model 30:

rvsolid = ,i

k i K i Ci ,liq n   1 + ∑ K j C j ,liq    j =1  

2

(Equation 5)

262

where ki is the apparent rate constant (mmol.l-1.s-1), Ki is the apparent adsorption constant of

263

component i (l.mmol-1), which were calculated via Arrhenius law (Equation 6) and Van’t Hoff

264

equation (Equation 7), respectively: 15 ACS Paragon Plus Environment


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Page 16 of 43

265

ki = A. exp(− Ea / RT )

(Equation 6)

266

Ki = B. exp(− ∆H ads / RT )

(Equation 7)

267

OHIN and ECHA are part of the reaction scheme, but were not detected in the product

268

streams under our reaction conditions. In the kinetic model, this was handled by using the

269

stationary regime theory, i.e. the rate of disappearance of ECHA and OHIN is equal to the

270

formation rate of these two compounds (Supporting Information 5). As a consequence,

271

constraints are introduced on the parameters: k5 and adsorption constants of OHIN and ECHA

272

could not be estimated and only the ratio of k8/k10 could be determined.

273

The by-product formation pathway (i.e. light by-products, heavy by-products and coke),

274

as discussed in part 3.1, was included in the reaction scheme for kinetic modeling in order to

275

minimize the difference between modeling and experimental data and consequently to gain

276

accuracy in the determination of the kinetic parameters. The kinetics of this pathway was

277

modeled by a simple first-order rate equation. This reaction pathway was assumed to occur on

278

acidic sites of the support, therefore, the reaction rate was considered to be only proportional to

279

the indole concentration, and there was no the competitive adsorption with H2. The kinetic

280

equation of this pathway is given by Equation 8:

281

r = k11.CINDOLE

(Equation 8)

282

Mass balance of each component is given in Supporting Information 5. The concentration

283

evolutions are described by a set of 18 molar balance equations of all components (except for

284

H2). About 700 experimental concentration points obtained from the tests at 3 different

285

temperatures and 3 initial indole concentrations were used to estimate 33 parameters including

286

pre-exponential factors (A, B), activation energies (Ea), adsorption enthalpies (∆Hads) and L-V


Page 17 of 43

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287

mass transfer coefficient (kLa). Results of the kinetic modeling are shown in the next part. Figure

288

5 shows that the product distribution was quite well fitted by the chosen kinetic model.

289

Figure 5: Comparison of simulation results (continuous line) and experimental data (points) of 4

290

tests at 350°C, over NiMo(P)/Al2O3 (a, b), NiMo(P)/ASA (c, d), at 1 wt% (a, c) and 0.5 wt% (b,

291

d) of indole

292 293

3.3.1. Adsorption parameters of indole and its products

294

The adsorption enthalpies (∆Hads,) of indole and its products varied in the range of 29-58

295

kJ/mol. These parameters were obtained with high confidence (accuracy below 5%). The 17 ACS Paragon Plus Environment


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Page 18 of 43

296

adsorption enthalpy of NH3 obtained by indole HDN had the same value as in quinoline HDN 31.

297

Thanks to pre-exponential factors and adsorption enthalpies obtained from the kinetic modeling,

298

we calculated the adsorption constants of indole and its products (Table 2).

299

Table 2: Adsorption enthalpies and adsorption constants of indole and its products NiMo(P)/Al2O3 Families of Ncompounds

NiMo(P)/ASA

∆Hads,

Ki, 350°C

∆Hads,

Ki 350°C

(kJ/mol)

(L/mol)

(kJ/mol)

(L/mol)

Indole

-29.3 (± 1.2%)

0.6 ± 0.2

-36.5 (± 1.2 %)

1.8 ± 0.9

HIN / OEA

-42.9 (± 1.7%)

18 ± 8

-46.0 (± 1.0 %)

57 ± 25

NH3

-44.9 (± 1.9%)

32 ± 14

-49.4 (± 1.0 %)

58 ± 26

300

The relative order of adsorption constants of indole and its products was established. The

301

adsorption of indole was very weak. It is expected to represent a lower inhibition effect than its

302

intermediate products. Saturated amines, i.e. OHIN and ECHA, are expected to exhibit very high

303

adsorption constants; however, due to undetectable concentrations of these compounds, their

304

adsorption constants could not be determined. Aromatic amines (HIN and OEA) and NH3 showed

305

relatively high adsorption constants. The adsorption constant of OEA was 20-30 times higher

306

than that of indole, and this compound is the main N-containing intermediate at our reaction

307

conditions. As a consequence, OEA was the main inhibitor of indole HDN. Comparing the two

308

catalysts, we found that the adsorption constants of nitrogen compounds over NiMo(P)/ASA

309

were nearly three times higher than the corresponding values over NiMo(P)/Al2O3.

310

3.3.2. Reaction pathways of indole HDN

311

In non-catalytic experiments, in the range of 340-360oC, about 10-15 mol% of indole was

312

converted to 2,3-dihydroindole. Experimental data of catalytic tests also provided ratios of 18 ACS Paragon Plus Environment

Page 19 of 43

313

concentration of indole to 2,3-dihydroindole in the range of 8-15%, i.e. close to thermodynamic

314

equilibrium. The results of the kinetic modeling could reproduce this thermodynamic equilibrium

315

(Figure 6). The evolution of [HIN]/[IND] ratios showed that the indole - dihydroindole

316

equilibrium was rapidly established under the reaction conditions. 0.5

0.5 (b) NiMo(P)/ASA

(a) NiMo(P)/Al2O3 0.4

0.4

Simulation Experimental

Ratio [HIN]/[IND]

Ratio [HIN]/[IND]

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


0.3

0.2

0.1

Simulation Experimental

0.3

0.2

0.1

0.0 0.0

0.5

1.0

1.5 2.0 Reaction time, h

2.5

0.0 0.0

3.0

0.5

1.0

1.5 2.0 Reaction time, h

2.5

3.0

317

Figure 6: [HIN]/[IND] ratio at 350°C, 1 wt% indole over (a) NiMo(P)/Al2O3 and (b)

318

NiMo(P)/ASA, determined by experimental data (point) and kinetic modeling (continuous lines)

319

As discussed above, the indole HDN comprises two reaction pathways: the first goes

320

through the hydrogenation of HIN into OHIN and the second through the ring opening of HIN.

321

Table 3 summarizes some kinetic parameters including the apparent, effective rate constants and

322

activations energies of every elementary reaction, for the first and the second pathway. The ring

323

opening of OHIN into ECHA was extremely fast over both catalysts.

324



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Page 20 of 43

325

Table 3: Apparent and effective rate constants at 350°C, activation energies of certain elementary

326

steps of indole HDN

NiMo(P)/Al2O3 Reaction

NiMo(P)/ASA

ki at 350oC, ki.Ki at 350°C, (mmol.L-1.s-1) (s-1)

IND ↔ HIN

Ea (kJ/mol)

k2/k1 = 0.0024

ki at 350oC, ki.Ki at 350°C, (mmol.L-1.s-1) (s-1)

Ea (kJ/mol)

k2/k1 = 0.0011

HIN → OHIN

57.9 ± 2.5

1.05

110.9 ± 1.9

31.3 ± 0.2

1.79

103.0 ± 1.3

HIN → OEA

28.2 ± 1.6

0.51

135.2 ± 2.4

14.5 ± 0.4

0.83

137.5 ± 1.7

OEA → ECHA

6.3 ± 0.2

0.11

87.5 ± 2.0

5.2 ± 0.2

0.30

93.7 ± 1.3

OEA → EB

1.7 ± 0.1

0.03

181.8 ± 2.4

1.7 ± 0.0

0.10

181.0 ± 0.8

IND → By Prods

-

0.0110

113.7 ± 1.7

-

0.0194

112.5 ± 1.4

327

Table 4: Ratio of apparent rate constant of β-elimination to direct hydrogenolysis reaction of

328

ethylcyclohexylamine (k8/k10) NiMo(P)/Al2O3

NiMo(P)/ASA

Ratio

k8/k10

340oC

350oC

360oC

340oC

350oC

360oC

3.2 ± 0.2

3.3 ± 0.1

3.8 ± 0.1

4.3 ± 0.1

6.5 ± 0.2

7.6 ± 0.3

329

The activation energies obtained for most reaction steps of indole HDN are similar for the

330

two catalysts. In general, the hydrogenation reactions have lower activation energies than C-N

331

bond cleavage reactions. The activation energies of Csp2-N bond breaking are higher than those of

332

Csp3-N bond breaking. This is coherent with the difference in the bond dissociation energy of

333

Csp2-N (614 kJ/mol) and of Csp3-N (305 kJ/mol) 35.


Page 21 of 43

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334

A comparison of the effective rate constants kiKi of HIN to either OHIN or OEA confirms

335

that the hydrogenation pathway was the dominating route in indole HDN, as already suggested in

336

the literature

337

breaking of HIN into OEA. The intermediate ECHA product was not detected in product stream

338

under our reaction conditions because the Csp3-N bond cleavage of ECHA into denitrogenated

339

products was extremely fast. Thus alkyl-cyclohexylamines were very reactive under

340

hydrotreating conditions 37,38. The hydrogenation of HIN into OHIN was the rate limiting step of

341

the first reaction pathway.

36

. The hydrogenation of HIN into OHIN was 2 times faster than the C-N bond

342

On the other hand, the pathway taking place via the hydrogenolysis of HIN into OEA and

343

then hydrogenation of the latter molecule into ECHA was also a non-negligible pathway. It was

344

faster than the direct HDN of OEA into EB. The hydrogenation of this molecule was the rate

345

determining step of HDN in this reaction pathway. OEA was quite refractory under our reaction

346

conditions. The accumulation of OEA during indole HDN due to its low reactivity could inhibit

347

the overall indole HDN, as confirmed by the high adsorption constant value of OEA as compared

348

to indole. This evaluation was coherent with a previous study of Olivé et al. 39.

349

Concerning the final C-N bond cleavage in ECHA to denitrogenated products, β-

350

elimination of ECHA was faster than the direct hydrogenolysis (Table 4). The NiMo(P)/ASA

351

catalyst favored β-elimination as compared to NiMo(P)/Al2O3, especially at high temperature.

352

The results of the kinetic modeling presented above show many analogies to quinoline

353

HDN. In both cases, the HDN of organonitrogen compounds occurred preferentially via the

354

hydrogenation pathway, while OEA or ortho-propylaniline (OPA) was only minor products. A

355

main difference between quinoline and indole is that the fully hydrogenated product of quinoline



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Page 22 of 43

356

(decahydroquinoline) is a major intermediate, while the fully hydrogenated product of indole

357

(OHIN) is not detected at all due to its high reactivity. Further, with both reactants the selectivity

358

to the aromatic amine (OEA and OPA) was lower over NiMo(P)/ASA, because its hydrogenation

359

and hydrogenolysis were faster over NiMo(P)/ASA than over NiMo(P)/Al2O3.

360

3.4. HDN of a mixture of indole and quinoline

361

The mutual inhibiting effect of quinoline and indole in HDN was determined by the

362

comparison of the individual compound test with the mixture test. Figure 7 shows the HDN

363

conversion of indole, in the absence and the presence of quinoline, over NiMo(P)/Al2O3 (a) and

364

NiMo(P)/ASA (b). In both cases, we observed that quinoline has a strong inhibiting effect on

365

indole HDN although the concentration of quinoline is half of the concentration of indole. The

366

inhibiting effect of quinoline and its nitrogen-containing products on indole HDN depends on the

367

adsorption coverage of these components on the same catalytic site. Major intermediate products

368

of quinoline HDN had a strong competitive adsorption with indole, and hence led to inhibition.

369

We observed the same shape of the indole HDN conversion curves over both catalysts. This

370

suggested that the same inhibiting phenomenon was observed in both catalysts. Moreover, due to

371

the high concentration and hence the high surface coverage of quinoline and its products at the

372

beginning of reaction, the indole HDN was likely more inhibited at low conversions (first half

373

hour). This explained the concave shape of the HDN conversion curves in the mixture tests at the

374

first 30 minutes of reaction, over both catalysts.


Page 23 of 43

(a)

Without quinoline With quinoline

100

Indole HDN conversion, %

100

Indole HDN 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


80 60 40 20 0 0.00

0.25

0.50

0.75

1.00

1.25

1.50

(b)

80 60 40

Without quinoline With quinoline

20 0

1.75

0.0

0.5

Time, h

1.0

1.5

2.0

2.5

Time, h

375

Figure 7: HDN conversion of indole in the absence and the presence of quinoline, (a) over

376

NiMo(P)/Al2O3, (b) over NiMo(P)/ASA, at 350°C, 7 MPa

377

For a quantitative comparison of the inhibiting effect of quinoline on the indole HDN between

378

the two catalysts, we calculated the ratio of the pseudo-first-order rate constant of the conversion

379

of indole and 2,3-dihydroindole in the presence of quinoline to the one in the absence of

380

quinoline. The ratios obtained were 0.448 and 0.263 for NiMo(P)/Al2O3 and NiMo(P)/ASA,

381

respectively. This indicated that quinoline and its products had stronger inhibiting effects on

382

indole HDN over NiMo(P)/ASA than over NiMo(P)/Al2O3. However, it should be noted that the

383

yield distribution of intermediate products of quinoline HDN was different between the two

384

catalysts at the same conversion of quinoline 31. For example, at the same quinoline conversion,

385

the yield of decahydroquinoline (DHQ) over NiMo(P)/ASA was always higher than that over

386

NiMo(P)/Al2O3 31. Both the high adsorption constant and the high yield distribution of DHQ, over

387

NiMo(P)/ASA, caused the high competitive adsorption with indole over this catalyst.

388

Figure 8 shows the HDN conversion of quinoline in the individual test and in the mixture

389

test (in the presence of indole), over the two catalysts. Over NiMo(P)/Al2O3, in the presence of

390

indole, we found that the HDN of quinoline was almost unaffected at the low indole conversion 23 ACS Paragon Plus Environment


391

(below 45%). This indicated that indole had a negligible inhibiting effect on quinoline HDN.

392

Above 50% conversion of indole, indole showed a light inhibiting effect on quinoline HDN,

393

presumably because the intermediate products such as OEA and HIN had a stronger inhibiting

394

effect than indole. Over NiMo(P)/ASA, the inhibiting effect of indole and its products on

395

quinoline HDN was stronger than over NiMo(P)/Al2O3, even at a low indole conversion.

100

100

(a)

Quinoline HDN conversion, %

Quinoline HDN 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

Page 24 of 43

80 60

With indole Without indole

40 20 0 0.0

0.5

1.0

1.5

2.0

2.5

(b) 80 60 40

Without indole With indole

20 0 0.0

0.5

Time, h

1.0

1.5

2.0

Time, h

396

Figure 8: HDN conversion of quinoline in the absence and the presence of indole, (a) over

397


398

4. Discussion

399

4.1. How does the support acidity impact the intrinsic activity?

400

The apparent rate constants (ki) of the major reaction steps (HIN → OHIN, HIN → OEA)

401

were significantly lower over NiMo(P)/ASA than over NiMo(P)/Al2O3 (Table 3). However, note

402

that the concentration of NiMoS active phase of NiMo(P)/ASA was lower than that of

403

NiMo(P)/Al2O3. When normalizing the apparent rate constants (ki) by the concentration of

404

NiMoS sites (Table 5), the difference between the two catalysts becomes weak. In contrast to

405

quinoline HDN, we cannot provide evidence that the support acidity leads to an increase of the

406

intrinsic hydrogenation rate of indole. The higher support acidity implied the stronger adsorption


2.5

Page 25 of 43

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407

of nitrogen compounds and resulted in the higher effective rate constants on NiMo(P)/ASA, but it

408

did not probably affect the activation of molecules in hydrogenation reactions of indole.

409

Table 5: Intrinsic apparent rate constants at 350oC (calculated per 1 mmol of NiMoS sites) of

410

indole HDN over both catalysts (mmol.L-1.s-1/mmol NiMoS) Reactions HIN → OHIN

NiMo(P)/Al2O3 NiMo(P)/ASA 237 ± 10 203 ± 1

Hydrogenation

HIN → OEA

Ring opening

115 ± 7

94 ± 3

OEA → ECHA

Hydrogenation

25.6 ± 0.9

33.9 ± 1.9

OEA → EB

Csp2-N bond breaking

7.0 ± 0.6

11.2 ± 0.1

411

For ring opening reactions, the difference between the ASA and the Al2O3-support was

412

small or absent, observed in both quinoline and indole HDN. Meanwhile, strong positive effects

413

of support acidity on the N-removal reactions, i.e. exocyclic C-N bond cleavage by

414

hydrogenolysis or β-elimination, were evidenced in both cases. The C-N bond breaking was

415

known to occur on acid sites of the support and –SH group

416

promoting effect of NiMo(P)/ASA on these reactions might be explained by the protonation of

417

the nitrogen atom by Brønsted acid sites located on the support or the modification of electronic

418

properties of CUS sites due to the higher acidity of ASA support.

419

4.2. What is the impact of support acidity on adsorption?

40,41

or on the CUS sites

12,42

. The

420

In both quinoline and indole HDN, nitrogen compounds (even indole, the neutral

421

compound) adsorbed more strongly over NiMo(P)/ASA than over NiMo(P)/Al2O3, which was in

422

line with studies in literature

423

nanoclusters, which exhibited Lewis acid character and could adsorb atoms with unpaired

424

electrons, were considered to be the active sites in sulfide catalysts

43,44

. Sulfur vacancies (CUS) located at the edges of MoS2


45

. The adsorption of sulfur


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 43

425

containing reactants during hydrodesulfurization reaction on CUS sites was evidenced by

426

theoretical calculations 46–48. The stronger adsorption of nitrogen compounds over NiMo(P)/ASA

427

might be related to the modification of electronic properties of CUS sites, i.e., the transfer of

428

electron from the CUS site into the support, inducing a deficiency of electron density on the

429

Lewis CUS sites. Moreover, nitrogen compounds could also adsorb on the –SH sites, albeit with

430

a lower adsorption energy, according to Density Functional Theory calculations

431

acidity of ASA support could imply a higher acidity of –SH sites, thus also favor the adsorption

432

of nitrogen compounds. We also do not exclude the adsorption of nitrogen compounds over the

433

acid sites of the support. These sites could be involved in the by-product formation or C-N bond

434

breaking reactions, but not in the hydrogenation or hydrogenolysis reactions.

435

4.3. Is there a self-inhibiting effect in indole HDN as in quinoline HDN?

49

. The higher

436

The kinetic modeling reproduced the difference in the HDN conversions between the two

437

catalysts, in the test of 1 wt% and 0.5 wt% of indole, as shown in Figure 2. In order to explain

438

the difference and compare with the quinoline HDN, competitive adsorption effects must be

439

n    considered. Figure 9 shows the adsorption term K i .Co ( Indole) / 1 + ∑ K j C j , liq  of the two rate j =1  

440

determining steps: HIN→OHIN (of the path 1) and OEA→ECHA (of the path 2) as function of

441

reaction time (at iso-volume of catalyst). Note that the adsorption constant of HIN and OEA had

442

the same value; therefore, these two rate determining steps would have the same value of the

443

adsorption term.

2


Page 27 of 43

2.0

2.0

(a)

(b) NiMo(P)/ASA NiMo(P)/Al2O3

1.5

2

1.5

KOEA.Co(Indole)/(1+ΣKjCj) (l/mmol)

NiMo(P)/ASA NiMo(P)/Al2O3

2

KOEA.Co(Indole)/(1+ΣKjCj) (l/mmol)

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


1.0

0.5

1.0

0.5

0.0

0.0 0.0

0.5

1.0

1.5

2.0

0.00

0.25

0.50

0.75

1.00 -1

Reaction time x Volume of catalyst (h.cm )

-1

Reaction time x Volume of catalyst (h.cm )

444

Figure 9: Plot of Ki/(1+∑KjCj,liq)2 values of the rate determining steps (HIN → OHIN and

445

OEA→ECHA) over both catalysts as function of reaction times, of the test at 1 wt% (a) and 0.5

446

wt% (b) of indole

447

In both tests of indole HDN, with either 1 wt% or 0.5 wt% of indole, the adsorption term

448

of these two rate limiting steps over NiMo(P)/ASA was higher than over NiMo(P)/Al2O3. This

449

means that the self-inhibiting effect due to the competitive adsorption of nitrogen compounds was

450

weaker on NiMo(P)/ASA than on NiMo(P)/Al2O3. This was different from the quinoline HDN, in

451

which the adsorption of intermediate products and NH3 became self-inhibiting and decreased the

452

overall activity of the ASA-supported catalyst 31. The absence of a self-inhibiting effect in indole

453

HDN was explained by the absence of saturated amines, i.e. OHIN and ECHA, which were very

454

rapidly converted. In contrast, the corresponding saturated amine in quinoline HDN, i.e.

455

decahydroquinoline (DHQ), was an abundant intermediate. These components had high

456

adsorption constants and hence strong adsorption on the catalytic site. Different aromatic amines

457

such as OEA and HIN produced during indole HDN had low concentration, thus this did not

458

result in a high self-inhibiting effect.

459



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

460

Page 28 of 43

4.4. Adsorption constants of quinoline, indole and their products

461

It should be recalled that the apparent adsorption constants of nitrogen compounds were

462

the relative values compared to the adsorption of solvents, thus they depended on the nature and

463

concentration of solvents. The HDN of quinoline and indole was studied in two different solvent

464

systems: 50 wt% of m-xylene + 50 wt% of squalane (S1) for quinoline HDN and 35 wt% of 1,3,5-

465

trimethylbenzene + 65 wt% of squalane (S2) for indole HDN. The nature and concentration of the

466

solvents played an important role via (i) competitive adsorption on the catalytic sites with

467

reactants and products and (ii) the relative volatility of nitrogen compound as compared to the

468

solvent. Consequently, the comparison of the apparent adsorption constants (Ki,) of indole and its

469

products with quinoline required an investigation on the solvent effects. For that, we performed

470

the HDN of indole in the two different solvents and calculated the initial disappearance rate of

471

indole and 2,3-dihydroindole. The initial reaction rate was compared between the two tests in the

472

two solvents in order to estimate the ratio of intrinsic adsorption constants between the two

473

solvents. This method is described in detail in Supporting Information 6. We can, thus,

474

recalculate the adsorption constants of indole and its intermediates relative to the solvent used for

475

quinoline. The corrected values are shown in Table 6.

476


Page 29 of 43

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


477

Table 6: Comparison of apparent adsorption constants of quinoline, indole and theirs products

478

relatively to the m-xylene+squalane solvent, at 350°C, over the two catalysts

Ki at 350°C (L/mol)

NiMo(P)/Al2O3

NiMo(P)/ASA

pKa

Indole

0.4

0.9

-3.6

14THQ / OPA

5.2

6.5

5.0 (14THQ)

Quinoline

6.0

9.5

4.9

HIN / OEA

10.6

28.2

5.0 (aniline)

NH3

18.9

28.7

9.25

DHQ / PCHA

22.1

31.1

11.2 (piperidine)

479

A ranking of adsorption constants of N-containing compounds was established in

480

correlation with their pKa values. This is expected to give insight information on the

481

quantification of inhibiting effects of nitrogen compounds on HDS and HDN reactions. The

482

adsorption of nitrogen compounds on the CUS sites depends not only on the electronic properties

483

of the sulfide active CUS sites, but also the electron density of the adsorbed molecule. The

484

saturated amines showed the highest adsorption constants, whereas indole, a neutral nitrogen

485

compound, showed the lowest adsorption constant. The former was explained by the high density

486

of electron on the nitrogen atom of the molecules; meanwhile the latter could be explained by

487

very weak basicity of indole, due to the conjugation of the free electron pair on nitrogen atom

488

with the aromatic ring. From Table 6, the adsorption constant ratio of indole to quinoline over

489

NiMo(P)/ASA was higher than over NiMo(P)/Al2O3. This was in line with the result obtained in

490

section 3.4, that indicated the stronger inhibiting effect of indole in quinoline HDN over

491

NiMo(P)/ASA than over NiMo(P)/Al2O3.

492



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

493

Page 30 of 43

4.5. By-products

494

It should be recalled that the HDN conversion was calculated by the percentage of HDN

495

products (ECH, ECHE and EB). The lower HDN conversion obtained in the test of 1 wt% of

496

indole over NiMo(P)/ASA than Al2O3 supported catalyst might be attributed to the loss of indole

497

by the by-products formation. By the rate constant (k11) of the by-product formation path which

498

was higher over NiMo(P)/ASA than over NiMo(P)/Al2O3, the kinetic model reproduced a higher

499

conversion into by-products over NiMo(P)/ASA (Supporting Information 7). Analyses of spent

500

catalysts (elemental analysis and tests over spent catalyst) showed that NiMo(P)/ASA was

501

slightly more deactivated than NiMo(P)/Al2O3 due to the formation of heavy by-products and

502

coke deposition, in both quinoline and indole HDN.

503

5. Conclusions

504

The kinetic modeling of indole HDN over the two catalysts, NiMo(P)/Al2O3 and

505

NiMo(P)/ASA, allowed discriminating the support acidity effects on the reaction pathways and

506

the adsorption of nitrogen containing compounds on the catalytic sites. As in the case of

507

quinoline HDN, the indole HDN occurred via two reaction paths: the dominating path was

508

hydrogenation of 2,3-dihydroindole into octahydroindole and the minor path was the ring

509

opening of 2,3-dihydroindole into OEA. In both reaction paths, the hydrogenation of the aromatic

510

ring was the rate limiting step.

511

The support acidity effects of indole HDN was compared with the previous results of

512

quinoline HDN. From the kinetic modeling, we found that the NiMo(P)/ASA favored N-removal

513

steps, including Csp2-N bond breaking, β-elimination reaction and direct hydrogenolysis, which


Page 31 of 43

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


514

was in agreement with the quinoline HDN. However, in contrast to the quinoline HDN, the

515

support acidity effects on hydrogenation steps were not very significant in the case of indole.

516

A ranking of the apparent adsorption constants of quinoline, indole, their intermediate

517

products and NH3 was established. The ranking of adsorption constants of nitrogen compounds

518

was found to be relatively coherent with the ranking of pKa. The adsorption of N-containing

519

compounds depended not only on their basicity and but also on their size of molecules. Indole

520

had a negligible adsorption constant whereas saturated amines had highest adsorption constants.

521

Aromatic amines and NH3 showed also high adsorption constants. The adsorption constants of

522

nitrogen compounds were systematically higher over the ASA-supported catalyst than over the

523

Al2O3 counterpart. Further analysis of indole HDN kinetics showed the absence of the self-

524

inhibiting effects, which was otherwise observed in the case of quinoline HDN. The stronger

525

adsorption of nitrogen compounds over NiMo(P)/ASA increased the effective rate constants for

526

all elementary steps.

527

The HDN of indole was significantly inhibited by the presence of a basic nitrogen

528

compound, i.e. quinoline and its intermediate products, due to the competitive adsorption. The

529

inhibition was even stronger over the more acidic NiMo(P)/ASA catalyst. In the presence of

530

indole, the HDN of quinoline was almost unchanged over NiMo(P)/Al2O3, whereas it was

531

slightly inhibited over NiMo(P)/ASA. The results obtained during the mixture tests were in

532

agreement with the ranking of adsorption constants of quinoline, indole and theirs products. This

533

indicated that the HDN of neutral compounds, i.e. indole and carbazole, in the mixture or in the

534

real feed, would be strongly inhibited due to the competitive adsorption of basic nitrogen

535

compounds.

536 31 ACS Paragon Plus Environment


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Page 32 of 43

537

Acknowledgement

538

The authors are grateful for the financial support from IFP Energies Nouvelles and CNRS,

539

France. The authors would like to thank CAPUANO Jerome and ASSAM Lyes for their help in

540

GC-NCD and FT-ICR/MS analytical experiments.

541

Supporting Information

542

S1: GC-FID and GC-NCD analysis conditions of samples obtained from indole HDN;

543

S2: L-V equilibrium constants of indole and its products;

544

S3: Nitrogen mass balance of the test indole HDN;

545

S4A: GC-NCD analysis of indole HDN products;

546

S4B: FT-ICR/MS analyses of heavy by-products produced from indole HDN;

547

S5: Equations of reaction rates;

548

S6: Initial reaction rate method in order to compare adsorption constant of quinoline, indole and

549

their products.

550

S7: By-product formation of indole HDN calculated by the kinetic model;

551

S8: Output data obtained from the kinetic modeling

552

This material is available free of charge via the Internet at http://pubs.acs.org.

553 554

Corresponding author: Melaz Tayakout-Fayolle

555

Email: [email protected]

556

Notes: The authors declare no competing financial interest.

557


Page 33 of 43

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


558

Nomenclature

559

A, B: pre-exponential factors

560

ASA: amorphous silica alumina

561

C i ,liq : molar concentration of component i in liquid phase (mmol.L-1)

562

Ci , g : molar concentration of component i in gas phase (mmol.L-1)

563

total Cliq : total concentration of all components (including solvents and hydrogen) in liquid phase

564

P: pressure (bar)

565

T: temperature (K)

566

Vliq : volume of liquid phase in reactor (L)

567

V g : volume of gas phase in reactor (L)

568

o n INDOLE : initial molar quantity of indole introduced into the reactor (mmol)

569

θ i : Liquid-Vapor equilibrium constants of component i

570

C i*,liq : molar concentration of component i in liquid phase at equilibrium (mmol.L-1)

571

ki : apparent rate constant (mmol.L-1.s-1)

572

K i : equilibrium apparent adsorption constant of component i (L.mmol-1)

573

KSi: adsorption constant of the solvent i

574

kLa : coefficient of L-V transfer (s-1)

575

HDN: hydrodenitrogenation

576

CUS: coordinatively unsaturated sites

577

GC-FID: Gas Chromatography coupled to a Flame Ionization Detector

578

GC-NCD: Gas Chromatography coupled to Nitrogen Chemiluminescence detector



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

579

FT/ICR-MS: Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

580

HDN Conv: denitrogenation conversion of quinoline (%)

581

ni: molar quantity of component i (mmol)

582

ri ,solid : volumetric rate of formation of component i on the catalytic sites (mmol.L-1.s-1) v

583

SBET: specific surface area (m2.g-1)

584

to: initial point of reaction

585

Reactant, intermediates and products

586

IND: indole

587

HIN: dihydroindole

588

OHIN: octahydroindole

589

OEA: o-ethylaniline

590

ECHA: ethylcyclohexylamine

591

EB: ethylbenzene

592

ECH: ethylcyclohexane

593

ECHE: ethylcyclohexene

594

14THQ: 1,2,3,4-tetrahydroquinoline

595

58THQ: 5,6,7,8-tetrahydroquinoline

596

DHQ: decahydroquinoline

597

PCHA: propyl-cyclohexylamine

598

OPA: ortho-propylaniline

599

Greek letter

600

Ea: activation energy (kJ.mol-1)

601

∆Hads: adsorption enthalpy (kJ.mol-1)


Page 34 of 43

Page 35 of 43

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


602

References

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604

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605

8.

606

(2) Sau, M.; Basak, K.; Manna, U.; Santra, M.; Verma, R. P. Effects of organic nitrogen

607

compounds on hydrotreating and hydrocracking reactions. Catal. Today. 2005, 109, 112.

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(3) Kasztelan, S.; des Courières, T; Breysse, M. Hydrodenitrogenation of petroleum distillates :

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industrial aspects. Catal. Today. 1991, 10, 433.

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of the Hydrogenation and Hydrodesulfurization Reactions by Nitrogen Compounds over

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NiMo/Al2O3. Catal. Lett. 2008, 123, 181.

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NiMo/γ-Al2O3. J. Catal. 2004, 224, 278.

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619

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hydrodesulfurization of alkyldibenzothiophenes. Appl. Catal. Gen. 2002, 231, 253.

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623

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629

supported molybdenum carbide. Fuel Process. Technol. 2002, 77–78, 261.

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Witold, P.; Grzegorz, A.; Andrzej, K.; Zbigniew, S.; Sayag, C.; G. Djéga-Mariadassou.

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Gutiérrez, O. Y.; Singh, S.; Schachtl, E.; Kim, J.; Kondratieva, E.; Hein, J.; Lercher, J. A.

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Effects of the Support on the Performance and Promotion of (Ni)MoS2 Catalysts for

635

Simultaneous Hydrodenitrogenation and Hydrodesulfurization. ACS Catal. 2014, 4, 1487.

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Hydrotreating Catalyst Deactivation by Coke Deposition. Pet. Sci. Technol. 2001, 19, 697.

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Rocha, A. S.; Faro, A. C.; Oliviero, L.; Lélias, M. A.; Arnaud, T.; Gestel, J.; Maugé F.

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catalysts supported on Al2O3, Nb2O5 and Nb2O5/Al2O3. Catal. Lett. 2006, 111, 27.

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catalysts as a way to understand the electronic effects of the support Brønsted acidity on

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HDN activity. J. Catal. 2016, 339, 135.

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C. New benchmark for basic and neutral nitrogen compounds speciation in middle distillates

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using comprehensive two-dimensional gas chromatography. J. Chromatogr. A 2007, 1148,

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Kim, S. C.; Massoth, F. E. Kinetics of the Hydrodenitrogenation of Indole. Ind. Eng.

Chem. Res. 2000, 39, 1705. (25)

Zhang, L.; Ozkan, U. S. Hydrodenitrogenation of indole over NiMo sulfide catalysts.

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Nonbasic Nitrogen Compounds Present in Oil Sands Derived Heavy Gas Oil. Energy Fuels

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2001, 15, 377.

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Transformation

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Refractory

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Dimethyldibenzothiophene Over a NiMoP/Al2O3 Catalyst. Catal. Lett. 2008, 129, 50.

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and Nonbasic Nitrogen Species in a Trickle Bed Reactor Using Commercial NiMo/Al2O3

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Catalyst. Energy Fuels 2003, 17, 164.

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Modeling of Quinoline Hydrodenitrogenation over a NiMo(P)/Al2O3 Catalyst in a Batch

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Reactor. Ind. Eng. Chem. Res. 2015, 54, 9278.

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kinetic modeling for investigating support acidity effects of NiMo sulfide catalysts on

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quinoline hydrodenitrogenation. Appl. Catal. Gen. 2017, 530, 132.

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Rocha Aguilera, G.; Gupta, V. G.; Yang, S.; Kuznicki, S. M.; McCaffrey, W. C. Pyrrolic

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Ring Opening and Nitrogen Removal from Solution without Hydrogenation: Natural

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Indoles. J. Catal. 2000, 189, 70.

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methylcyclohexylamine over sulphided NiMo/γ-Al2O3 and Mo(P)/γ-Al2O3 catalysts. in Stud.

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(38) Rota, F.; Prins, R. Mechanism of the hydrodenitrogenation of o-toluidine and methylcyclohexylamine over NiMo/γ-Al2O3. Top. Catal. 2000, 11-12, 327. (39) Olivé, J.-L.; Biyoko, S.; Moulinas, C.; Geneste, P. Hydroprocessing of indole and o-ethyl aniline over sulfided CoMo, NiMo and NiW catalysts. Appl. Catal. 1985, 19, 165.

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Al2O3. J. Catal. 2012, 295, 155.

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(41) Akgerman, A.; Sanghvi, B. S. Quinoline denitrogenation on zeolite-based catalysts. Fuel Process. Technol. 1984, 9, 279.

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activity of hydrotreating CoMo/Al2O3 catalysts: a batch reactor study. Catal. Today 2004, 98,

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(43) Miller, J. T.; Hineman, M. F. Non-first-order hydrodenitrogenation kinetics of quinoline. J. Catal. 1984, 85, 117. (44) Qu, L.; Flechsenhar, M.; Prins, R. Kinetics of the hydrodenitrogenation of o-toluidine over fluorinated NiMoS/Al2O3 and NiMoS/ASA catalysts. J. Catal. 2003, 217, 284.



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(46) Harris, S.; Chianelli, R. R. Chapter 6: Theoretical Studies of Transition Metal Sulfide

719

Hydrodesulfurization Catalysts, Theoretical Aspects of Heterogeneous Catalysis. Theoretical

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Aspects of Heterogeneous Catalysis, Springer Netherlands, 1990, 206.

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(47) Zonnevylle, M. C.; Hoffmann, R.; Harris, S. Thiophene hydrodesulfurization on MoS2 : Theoretical aspects. Surf. Sci. 1988, 199, 320. (48) Joffre, J.; Lerner, D. A.; Geneste, P. Quantum Chemical Studies of the Adsorption of Thiophene on MoS2 Hydroprocessing Sites. Bull. Sociétés Chim. Belg. 1984, 93, 831.

725

(49) Humbert, S.; Izzet, G.; Raybaud, P. Competitive adsorption of nitrogen and sulphur

726

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727

333,78.

728 729


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730

Figure caption

731

Figure 1: Reaction scheme of indole hydrodenitrogenation 24,25

732

Figure 2: HDN conversion of indole over NiMo(P)/Al2O3 and NiMo(P)/ASA, at 350°C, 7 MPa,

733

in the test of (a) 0.5 wt% and (b) 1 wt% of indole

734

Figure 3: Comparison of products selectivty of the two catalysts in the conversion of indole at

735

350°C, 7MPa and 1 wt% indole, (a) Indole, (b) o-ethylaniline, (c) ethylbenzene, (d)

736

ethylcyclohexane

737

Figure 4: Reaction scheme of indole HDN for kinetic modeling

738

Figure 5: Comparison of simulation results (continuous line) and experimental data (points) of 4

739

tests at 350°C, over NiMo(P)/Al2O3 (a, b), NiMo(P)/ASA (c, d), at 1 wt% (a, c) and 0.5 wt% (b,

740

d) of indole

741

Figure 6: [HIN]/[IND] ratio at 350°C, 1 wt% indole

742

NiMo(P)/ASA, determined by experimental data (point) and kinetic modeling (continuous lines)

743

Figure 7: HDN conversion of indole in the absence and the presence of quinoline, (a) over

744


745

Figure 8: HDN conversion of quinoline in the absence and the presence of indole, (a) over

746


747

Figure 9: Plot of Ki/(1+∑KjCj,liq)2 values of the rate determining steps (HIN → OHIN and

748

OEA→ECHA) over both catalysts as function of reaction times, of the test at 1 wt% (a) and 0.5

749

wt% (b) of indole

over (a) NiMo(P)/Al2O3 and (b)

750



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 42 of 43

751

Table caption

752

Table 1: Catalysts properties 31

753

Table 2: Adsorption enthalpies and adsorption constants of indole and its products

754

Table 3: Apparent and effective rate constants at 350°C, activation energies of certain elementary

755

steps of indole HDN

756

Table 4: Ratio of apparent rate constant of β-elimination to direct hydrogenolysis reaction of

757

ethylcyclohexylamine (k8/k10)

758

Table 5: Intrinsic apparent rate constants at 350oC (calculated per 1 mmol of NiMoS sites) of

759

indole HDN over both catalysts (mmol.L-1.s-1/mmol NiMoS)

760

Table 6: Comparison of apparent adsorption constants of quinoline, indole and theirs products

761

relatively to the m-xylene+squalane solvent, at 350°C, over the two catalysts


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