Competitive adsorptions between thiophenic compounds over a CoMoS/Al2O3 catalyst under deep HDS of FCC gasoline

Article abstract of DOI:10.1016/j.apcata.2018.11.032

The transformation of various model sulfur compounds (2-methylthiophene: 2MT, 3-methylthiophene: 3MT and benzothiophene: BT) representative of sulfur compounds in FCC gasoline was investigated over a CoMoS/Al2O3 catalyst. More specifically, a quantitative reactivity scale was established with BT being more reactive than 3MT and 2MT. In mixture, their reactivity was reduced due to the presence of the other sulfur compound, the scale of reactivity being preserved. BT strongly inhibits the transformation of 2MT. With a single kinetic model based on a Langmuir Hinshelwood formalism, kinetic and adsorption parameters were calculated and the results explained by mutual competitive adsorption between 2MT and BT with a higher adsorption constant for BT compared to that of 2MT.

Full text of DOI:10.1016/j.apcata.2018.11.032

AppliedCatalysisA,General570(2019)292–298
Contents lists available at ScienceDirect
Applied Catalysis A, General
journal homepage: www.elsevier.com/locate/apcata
Competitive adsorptions between thiophenic compounds over a CoMoS/
Al2O3 catalyst under deep HDS of FCC gasoline
⁎
Alan Silva dos Santosa, Etienne Girardb, Philibert Leflaiveb, Sylvette Bruneta,
a Université de Poitiers, Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP), UMR 7285 CNRS, 4 rue Michel Brunet, TSA 71106, 86073, Poitiers Cedex9,
France
b IFP Energies nouvelles, Rond-point de l’échangeur de Solaize, BP 3, 69360, Solaize, France
A R T I C L E I N F O
A B S T R A C T
Keywords:
The transformation of various model sulfur compounds (2-methylthiophene: 2MT, 3-methylthiophene: 3MT and
benzothiophene: BT) representative of sulfur compounds in FCC gasoline was investigated over a CoMoS/Al2O3
catalyst. More specifically, a quantitative reactivity scale was established with BT being more reactive than 3MT
and 2MT. In mixture, their reactivity was reduced due to the presence of the other sulfur compound, the scale of
reactivity being preserved. BT strongly inhibits the transformation of 2MT. With a single kinetic model based on
a Langmuir Hinshelwood formalism, kinetic and adsorption parameters were calculated and the results ex-
plained by mutual competitive adsorption between 2MT and BT with a higher adsorption constant for BT
compared to that of 2MT.
Hydrodesulfurization
FCC gasoline
2-methythiophene
3-methylthiophene
Benzothiophene
Kinetic modeling
1. Introduction
representative of sulfur contents in a FCC gasoline are thiophene [6], al-
kylthiophenes [2,7], benzothiophene and its alkylated derivatives [8,9].
Due to increasing environmental concerns, constraints relative to
exhaust gas compositions have been reinforced worldwide. China V and
US Tier 3 regulations have thus imposed a 10 ppm maximum of sulfur in
commercial gasoline since 2017 [1]. Commercial gasoline is blended
from gasoline streams mainly produced by isomerization, reforming and
fluid catalytic cracking (FCC) units in refineries. In particular, catalytic
cracked gasoline represents 40–80% of the total gasoline composition but
accounts for almost all of the total sulfur amount present in non-hydro-
desulfurized commercial gasoline [2,3]. Consequently, there is a strong
need for achieving ultra-deep HDS of FCC gasoline, which comes with
developing highly active HDS catalysts. Meanwhile, these catalysts
should also exhibit a high selectivity to minimize olefins hydrogenation
(HDO) and preserve high octane values.
However, a major drawback of such approach lies in a lack of re-
presentativeness of the reactivity of a real catalytically cracked gasoline
where relative reactivities of reactants and potential competitive adsorp-
tions between reactants and products dictate the overall feed reactivity.
The reactivity of these different sulfur molecules have been ambiguously
reported in the literature with different rankings. This apparent contra-
diction may originate from different operating conditions. At their operating
conditions –100ppmS in toluene, 1.3 MPa, 150 °C, LHSV = 3.5 h−1–,
Hatanaka et al. [10,11] established the following reactivity scale: ben-
zothiophene > thiophene > 3-methylthiophene > 2-methylthiophene >
2-ethylthiophene > 2,5-dimethylthiophene. The reaction rate of ben-
zothiophene was approximatively twice that of thiophene. These results also
confirmed the relative reactivities of 3-methylthiophene and 2-methylthio-
phene over a CoMoS/Al2O3 catalyst, as reported by Desikan et al. [12] at
atmospheric pressure and temperatures of 305 and 414 °C. However, in a
review on hydrodesulfurization processes, Song et al [13] suggested a re-
verse reactivity order with thiophene being more reactive than benzothio-
phene. This assumption was based on results originally published by Nag
et al. [14] on the hydrodesulfurization of benzothiophene and thiophene at
7,1 MPa and 300 °C. In this study, the reactivity of thiophene was higher by
a factor of 1.7 as compared to benzothiophene.
The FCC gasoline is a complex blend of more than 400 compounds,
mainly including paraffins, olefins, naphtenes and aromatics. The sulfur
compounds in FCC gasoline are represented in various families: mercap-
tans, thiophenes, benzothiophenes and their alkyl derivatives. The re-
partition and the total amount of these sulfur compounds depend on the
origin of the feedstock and the operating conditions of the FCC unit. As
reported in literature [4,5], for a typical feedstock, C1-thiophenes –i.e.
methylthiophenes–, C2-thiophenes and benzothiophenes correspond to
more than 50% of total sulfur compounds present in the mixture (Table 1).
Therefore, the sulfur compounds selected in model feeds as single
In addition, the potential competitive adsorptions over the catalyst
surface between reactants and products in complex feeds such as a real
⁎ Corresponding author.
E-mail address: sylvette.brunet@univ-poitiers.fr (S. Brunet).
https://doi.org/10.1016/j.apcata.2018.11.032
Received 8 July 2018; Received in revised form 9 November 2018; Accepted 28 November 2018
Availableonline29November2018
0926-860X/©2018ElsevierB.V.Allrightsreserved.

A.S. dos Santos et al.
AppliedCatalysisA,General570(2019)292–298
Table 1
2.2. Reaction conditions
Amount of sulfur compounds present in a feed containing 1.05 wt% of sulfur
[4].
Catalytic activity measurements were carried out in a fixed bed
reactor at 250 °C under a total pressure of 2 MPa with a ratio H2/feed of
360 N L/L [16–18]. The sulfur model feed (0.3 wt%, 1000 ppmS), di-
luted in n-heptane was injected in the reactor by a HPLC Gilson pump
(307 series, pump's head volume: 5 cm3). The mass of catalyst used was
50 mg of CoMo/Al2O3 and the contact time varied from 0 to 30 s.
Different types of feeds were used to study the transformation of the
sulfur model molecules alone or in mixture:
Sulfur Compounds
Sulfur Compounds
ppmS
%
Mercaptans
34
4.5
Thiophene
37
4.9
C1-thiophenes
106
24
14.1
3.2
Tetrahydrothiophene
C2-thiophenes
118
76
15.6
10.1
11.0
36.6
100
C3-thiophenes/thiophenol
C4-thiophenes/C1-thiophenol
Benzothiophene
Total Sulfur
1) Single component feed including a sulfur model molecule alone
(corresponding to 1000 ppmS) (0.3 wt% of 2 M T or 3 M T or 0.42 wt
% of BT) in n-heptane.
83
276
754
2) Feed consisting of a mixture of two sulfur components including
0.3 wt% of 2 M T (1000 ppmS) and various amounts of BT (corre-
sponding to 500, 1000 and 1500 ppmS) in n-heptane.
catalytically cracked gasoline have never been thoroughly investigated.
Indeed, most relevant articles focused on the inhibiting effect of H2S on
the transformation of single sulfur compounds in model feeds. Thus,
Fontaine et al. [15] evidenced that the presence of H2S had a weak
impact on the transformation of 2-methylthiophene over an un-
supported CoMoS catalyst at 2 MPa and 250 °C A similar effect was
observed by Dos Santos et al. [7] during the hydrodesulfurization of 3-
methyl-thiophene over a CoMoS catalyst supported on alumina at
2 MPa and 185 °C A decrease in the kinetic apparent constants as a
function of H2S partial pressure was attributed to a competitive ad-
sorption of 3-methylthiophene and H2S on the active sites of the cata-
lyst. To develop highly efficient catalysts and bridge the gap between
model feed and real catalytically cracked gasoline reactivities, there is
consequently a strong need for a proper understanding of the reactivity
scale of sulfur compounds under selective HDS operating conditions as
well as their interplay in mixture.
3) Feed consisting of a mixture of either 2 M T or BT (1000 ppmS) and
H2S (from 0.2 to 1.45 kPa) in n-heptane. These H2S partial pressures
correspond to the amount of H2S produced by the transformation of
BT (or 2 M T) in mixture with 2 M T (or BT). These latter experi-
ments were carried out in order to identify the real inhibitor of the
transformation of a given sulfur compound (the other sulfur mole-
cule present or the H2S produced by its transformation).
The different partial pressures of the reactants, H2S and, H2 in-
troduced are reported in Table 3 for the sulfur molecules alone and in
mixture, respectively. n-heptane was not converted under these ex-
perimental conditions. No catalyst deactivation was observed for all the
experiments.
2.3. Products analysis
This paper deals with the comparison of the reactivity of sulfur model
molecules representative of various families in FCC gasoline alone and in
mixture in order to determine the most refractory sulfur compounds and
to quantify their competitive adsorption. The transformations of 2-me-
thylthiophene (2 M T), 3-methylthiophene (3 M T) and benzothiophene
(BT), -the selected model molecules- over a supported CoMoS catalyst
under selective HDS conditions (250 °C and 2Mpa of total pressure) were
thus studied alone, and then in mixture. Following a combined experi-
The reaction products were injected on-line by means of an auto-
matic sampling valve into a Varian gas chromatograph equipped with a
PONA capillary column and a flame ionization detector as in previous
works [16–18]. Desulfurized products, resulting from the transforma-
tion of 2-methylthiophene, 3-methylthiophene and benzothiophene are
designated as HDS products. The contact time is defined as the ratio
between the total amount of feed and the mass of catalyst in the oxide
form. 2 M T, 3 M T and BT reactivities are defined as the number of
moles of HDS products formed per hour and per gram of catalyst and
were calculated at conversion lower than 30% in a differential regime.
mental and theoretical approach,
a kinetic modeling based on a
Langmuir-Hinshelwood formalism was then developed to explain these
experimental results and provide quantitative elements of reactivity of
sulfur compounds in selective HDS conditions in place of the more
qualitative information that is found in the available literature (Table 1).
2.4. Kinetic modeling
The obtained experimental results were confirmed by a theoretical
approach using the Langmuir-Hinshelwood model and the Arrhenius
equation. Kinetic and adsorption parameters were first set from single
2. Experimental part
2.1. Catalyst and chemicals
®
component experiments using ReactOp software and were then used to
fit binary experimental results without further adjustment.
3. Results
Table 2 reports the main characteristics of the CoMoS/Al2O3 cata-
lyst provided by IFPEN. The catalyst was crushed and sieved to size
range between 250 and 315 μm and then sulfided in situ under H2S/H2
flow (10 mol% H2S) for 10 h at 400 °C at atmospheric pressure. 2-me-
thylthiophene (98% purity), 3-methylthiophene (98% purity), ben-
zothiophene (95% purity) and n-heptane (> 99% purity) were pur-
chased from Sigma-Aldrich. They were used without further
purification. Hydrogen sulfide (1 vol% in mixture with H2) was pur-
chased from Air Liquide.
3.1. Transformation of single sulfur compounds
In order to draw an unambiguous reactivity ranking of 2 M T, 3 M T
and BT, the hydrodesulfurization of single sulfur compounds was first
studied. The conversion of 2 M T, 3 M T and BT measured separately are
reported in Fig. 1. The distribution of the products are reported in Fig. 2
for 2 M T, in Fig. 3 for 3 M T and in Fig. 4 for BT. For the three sulfur
compounds, a linear dependence of conversion with contact time was
observed for conversions lower than 60%, thus corresponding to a
differential regime. At equivalent contact time, the conversion of BT
was systematically higher than those of 2 M T and 3 M T, as reported in
Table 4. In other words, the reactivity order observed under these
Table 2
Characteristics of the CoMoS/Al2O3 catalyst.
CoO (wt%)
MoO3 (wt%)
Co/Mo (at./at.)
SBET (m2/g)
122
3
10
0.57
293

A.S. dos Santos et al.
AppliedCatalysisA,General570(2019)292–298
Table 3
Partial pressures (kPa) of the different compounds for the sulfidation step and the transformation of the different feeds.
Feed
A
B
C
D
E
F
Pressure (kPa)
Sulfidation
3 M T/2 M T
BT
2 M T + BT
2 M T + H2S
BT + H2S
P
H2S
10
0
0
0
0
0.8 – 1.45
0.2 – 0.37
P2MT or P3MT
PBT
2
0
2
2
–
0
0
2
1-3
0
2
PH2
90
0
1360
638
2000
1360
638
2000
1360
633-635
2000
1360
1360
PnC7
637.2-636.55
2000
637.8-637.63
2000
PTOT
100
(T = 250 °C, P = 2 MPa, CoMoS/Al2O3, H2/feed = 360 N L/L).
Fig. 3. Transformation of 3 M T. Distribution of products as a function of 3 M T
conversion. (T = 250 °C, P = 2 MPa, CoMoS/Al2O3, H2/feed = 360 N L/L).
2MB2N: 2-methylbut-2-ene, 2MB1N: 2-methylbut-1-ene, iC5: isopentane,
3MB1N: 3-methylbut-1-ene.
Fig. 1. Conversion of 2 M T, 3 M T and BT as a function of contact time.
(T = 250 °C, P = 2 MPa, H2/feed = 360 N L/L, CoMoS/Al2O3).
Fig. 2. Transformation of 2 M T. Distribution of the products as a function of
2 M T conversion (T = 250 °C, P = 2 MPa, CoMoS/Al2O3, H2/feed = 360 N L/
L). t-P2N: trans-pent-2-ene, c-P2N: cis-pent-2-ene, P1N: pent-1-ene, nC5: n-
pentane.
Fig. 4. Transformation of BT. Distribution of products as a function of BT
conversion. (T = 250 °C, P = 2 MPa, CoMoS/Al2O3, H2/feed = 360 N L/L). EB:
ethylbenzene, DHBT: dihydrobenzothiophene.
operating conditions is in agreement with the results previously ob-
tained by Hatanaka et al. [10,11] who reported that 2-methylthiophene
was less reactive than 3 M T and BT at a total pressure of 1.3 MPa and
temperatures ranging between 130 and 170 °C.
Table 4
Transformation of sulfur compounds. Comparison of the activity.
2 M T
3 M T
BT
Regarding the product distribution of the transformation of 2-MT,
the main products observed are pent-1-ene, cis-pent-2-ene and trans-
pent-2-ene as primary products and n-pentane as a secondary product
(Fig. 2). In agreement with the reaction scheme proposed previously
(Scheme 1) [2], there are two main potential pathways: direct de-
sulfurization (DDS) -leading to the formation of cis and trans-pent-2-
ene- and the hydrogenation (HYD) pathway -leading to the formation of
pent-1-ene- which both end up into the hydrogenation product (n-
pentane). However, the intermediates proposed in the reaction scheme
for 2 M T were not observed under selective HDS operating conditions.
Similar to 2 M T, the transformation of 3 M T also leads to the for-
mation of alkenes (i.e. 2-methylbut-1-ene, 2-methylbut-2-ene and 3-
methylbut-1-ene) as primary products and to the formation of
Conversion (%)
28.2
23.1
33.4
Activity (mol. h−1. g−1
)
0.376
0.597
0.833
(iso-conversion around 30% from feed B or C) (T = 250 °C, P = 2 MPa, CoMoS/
Al2O3, H2/feed = 360 N L/L).
isopentane as secondary product resulting from the hydrogenation of
alkenes (Fig. 3 according to the proposed reaction scheme in the lit-
erature (Scheme 2)) [7]
The transformation of BT leads to dihydrobenzothiophene (DHBT)
–resulting from the hydrogenation of the thiophenic ring– which ap-
pears as a primary product. The formation of ethylbenzene (EB) is also
observed as an apparent secondary product although it can be also
294

A.S. dos Santos et al.
AppliedCatalysisA,General570(2019)292–298
Scheme 1. Transformation of 2-methylthiophene (2 M T): 2-methyltetrahydrothiophene (2 M THT), pent-1,3-diene (P13DN), pent-1-ene (P1N), pent-2-ene (P2N), n-
pentane (nP).
Scheme 2. Transformation of 3-methylthiophene (3 M T), 3-methyltetrahydrothiophene (3 M THT), 2-methyl-but-1-ene (2MBN1), 2-methyl-but-2-ene (2MBN2),
3MBN1 (3-methyl-but-1-ene), isopentane (iC5).
formed directly from BT (Fig. 4). Consequently, the reaction scheme
established from these results can involve two pathways for the for-
mation of EB: a direct DDS pathway from BT involving a C–S bond
rupture and the hydrogenation pathway involving the formation of
DHBT and a subsequent C–S bond rupture (Scheme 3).
effect between 2 M T and BT was noticed. Moreover, the inhibition on
the transformation of 2 M T resulting from BT was higher (Fig. 5a) than
the opposite (Fig. 6a). At a contact time of 2 s, the decrease in con-
version for the transformation of 2 M T was equal to 54% while only
15% for the transformation of BT. This inhibiting effect is due to the
unconverted other sulfur compound (2 M T or BT) and not to the H2S
produced by its transformation. Indeed, if 2 M T or BT were substituted
by the amount of H2S produced by the conversion of both sulfur com-
pounds, the inhibiting effect observed was much lower in the trans-
formation of 2 M T (i.e. lower than 5%) (Table 5) and zero in the
In order to evaluate a mutual inhibiting effect between the different
sulfur compounds, the transformation of a feed containing 1000 ppmS
from 2 M T and different amounts of BT (from 500 to 1000 ppmS) was
studied. The contact time was varied in order to obtain a large range of
conversions (from 15 to 80%) of 2 M T and BT. A mutual inhibiting
Scheme 3. Transformation of benzothiophene (BT): Dihydrobenzothiophene (DHBT), Ethylbenzene (EB).
295

A.S. dos Santos et al.
AppliedCatalysisA,General570(2019)292–298
Fig. 5. Transformation of 2 M T: Comparison of simulation results (dotted lines) and experimental data (points) a) for the conversions of 2 M T alone and in presence
of BT and b) for the distribution of HDS products (pentane and pentenes). (T = 250 °C, P = 2 MPa, CoMoS/Al2O3, H2/feed = 360 N L/L).
transformation of BT (Table 6). Consequently, the decrease in the
conversion of 2 M T (around 60%) observed in mixture with BT corre-
sponds to an inhibition effect of the unconverted BT. Indeed, when BT is
present at high concentration (1500 ppm S) in the feed, its conversion is
low (i.e. 47%), which leads to an inhibition of the transformation of
2 M T around 66.5% (i.e. a conversion of 10.2% of 2 M T in the feed as
compared to a conversion of 28.2% in the absence of BT). In the op-
posite, for the conversion of BT, the presence of 2 M T leads to an in-
hibition of only around 15% whereas the concentration of unconverted
2 M T remains high due to its low conversion (maximum 17%) (see in
Table 5).
Table 5
Transformation of 2 M T. Effect of the amount of H2S or BT.
BT
BT Conv. (%) PH2S from BT
Inhibiting effect
(ppmS)
(kPa)
Total (%) By H2S
(%)
By BT (%)
500
80.0
60.3
47.0
0.80
1.20
1.45
63.1
68.3
70.3
1.7
2.8
3.8
61.4
65.5
66.5
1000
1500
(conversion of 2 M T of 42% from feed E and D, T = 250 °C, P = 2 MPa, H2/
feed = 360 N L/L, CoMoS/Al2O3).
Table 6
3.2. Kinetic modeling
Transformation of BT. Effect of the amount of H2S or 2 M T.
In order to understand and quantify the strong mutual inhibiting ef-
fects observed experimentally, a kinetic model was developed to de-
termine the kinetic and adsorption parameters of 2 M T, 3 M T and BT
transformations. As reported previously [17,18] the following assumptions
were made: a Langmuir-Hinshelwood model involving reactions between
adsorbed molecules, competitive adsorptions between sulfur compounds,
alkenes, alkanes and H2S, a unique type of site and an heterolytic dis-
sociation of H2 and H2S. The corresponding elementary steps were re-
ported previously under similar operating conditions [17,18].
2 M T Conv. (%) PH2S from 2 M T (bar) Inhibiting effect
Total (%) By H2S (%) By 2 M T(%)
10.0
15.4
18.9
0.2
17.2
15.5
14.2
0
0
0
17.2
15.5
14.2
0.31
0.37
(conversion of BT of 30% from Feed D and F, T = 250 °C, P = 2 MPa, H2/
feed = 360 N L/L, CoMoS/Al2O3).
For the transformation of 2 M T and 3 M T, different reactions were
Fig. 6. Transformation of BT: Comparison of simulation results (dotted lines) and experimental data (points) a) for the conversion of BT alone and in mixture with
2 M T and b) for the distribution of HDS products (Ethylbenzene: EB and Dihydrobenzothiophene : DHBT). (T = 250 °C, P = 2 MPa, CoMoS/Al2O3, H2/
feed = 360 N L/L).
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A.S. dos Santos et al.
AppliedCatalysisA,General570(2019)292–298
P
H
2
S
taken into account, respectively named R1 or R3 for the formation of
olefin intermediates and R2 and R4 for the formation of alkanes from
olefins.
KBT PBT KH S PH
S
2
2
K
P
H
2
Ea
S
r = k5. e RT
2
P
H
P
H
2
S
S
2
K
P
H
2
H
2
K
P
P
S
H
P
S
H
2
H S
2
2
1 + KBT PBT
+
+
+
KH S PH
S
2 2
K
K
P
S H
2 2
K
P
H
2
S
H
S
(R1)
P
H
P
H
2
S
2
KDHBT PDHBT KH S PH
S
2
2
K
Ea
S
r = k6. e RT
2
P
H
S
2
P
H
2
S
K
P
H
2
H
2
K
P
P
S
H
P
S
H
2
H
P
S
H
2
2
2
1 + KDHBT PDHBT
+
+
+
KH S PH
S
2 2
K
K
P
H S H
2 2
K
S
S
(R2)
The rate equations are as follows:
(R3)
(R4)
r = k1(3)
.
P
H
P
H
2
S
2
K2MT (3MT)P2MT (3MT) KH S PH
S
2
2
K
Ea
S
r = k7.
e
RT
2
P
H
S
2
P
H
2
P
H
P
S
K
P
2
H
2
H
2
KBT PBT KH S PH S
K
P
P
S
H
P
S
H
2
2
2
H S
2
2
K
Ea
S
H
2
1 + K2MT (3MT)P2MT (3MT)
+
+
+
KH S PH
S
2 2
K
K
P
H S
2
K
P
H
2
S
H
2
S
e
RT
S
2
P
H
P
H
2
S
2
K
P
H
2
H
2
K
P
S
P
H
P
S
H
P
S
2
2
1 + KBT PBT
+
+
+
KH S PH S
2 2
K
K
P
H
2
K
S
H
2
H
2
S
S
S
H
2
r = k2(4)
.
P
H
P
H
2
S
2
KPN PPN KH S PH
S
2
2
K
Ea
RT
S
To explain the order of reactivity observed experimentally as well as
the mutual inhibition of sulfur compounds, a kinetic modeling of the sulfur
compounds alone initially and then in a mixture was carried out. The
kinetic parameters (for the hydrodesulfurization and hydrogenation re-
actions) and the adsorption constants calculated from single component
experiments are reported in Table 7. A good fit of the transformation of
2 M T, 3 M T and BT is obtained. The modeling (dashed curve) and the
experimental results (points) for the conversion of 2 M T, BT and 3 M T
alone and their product distribution are respectively reported in Figs. 5–7.
It can be seen that the rate constants of the desulfurization step
(olefin formation) (k = 2.8 1012 h−1 and 5.5 1012 h−1 for 2 M T and
e
2
P
H
P
H
2
S
2
K
P
H
2
H
2
K
P
K
S
P
H
S
H
P
H
2
S
2
2
1 + KPN PPN
+
+
+
KH S PH S
2 2
P
K
P
H
2
K
S
H
2
H
2
S
S
S
Regarding the transformation of BT, the proposed reaction scheme
includes two pathways for its transformation: HYD of BT into dihy-
drobenzothiophene (DHBT) and then HDS of DHBT into ethylbenzene
(EB). The second pathway corresponds to the formation of ethylben-
zene directly from BT. Therefore, the consecutive reactions proposed to
model the transformation of BT are given below:
Table 7
Kinetic parameters and adsorption parameters for the reaction of sulfur com-
pounds, H2S and H2 (HDS: Hydrodesulfurization, HYD: Hydrogenation).
(R5)
(R6)
k x 1012 (h−1
)
Kads (bar−1
)
2 M T
3 M T
BT
R1 (HDS)
R2 (HYD)
R3 (HDS)
R4 (HYD)
R5 (HYD)
R6 (HDS)
R7 (HDS)
–
2.8
6.9
5.1
5.8
12
0.1
0.3
0.2
0.3
0.6
0.9
7.1
0.3
0.5
0.6
10.6
12.4
19
3.4 10−3 2 10-4
H2
–
–
1.8 10−7 9.0 10-9
H2S
–
0.5
0.02
(R7)
(T = 250 °C, P = 2 MPa, H2/feed = 360 N L/L, CoMoS/Al2O3).
The corresponding equation rate are as follows:
297

A.S. dos Santos et al.
AppliedCatalysisA,General570(2019)292–298
Fig. 7. Transformation of 3 M T: Comparison of simulation results (dotted lines) and experimental data (points) a) for the conversion of 3 M T and b) for the
distribution of products (C5 alkenes and isopentane iC5). (T = 250 °C, P = 2 MPa, CoMoS/Al2O3, H2/feed = 360 N L/L).
3 M T respectively) are lower than those of the corresponding saturated
hydrocarbon formation (k = 6.9 1012 h-1 and 5.8 1012 h-1 for 2 M T and
3 M T respectively) (Schemes 1 and 2). In addition, modeling confirmed
that the direct formation of ethylbenzene from BT was a minor pathway
in selective HDS operating conditions. Indeed, the rate constant is much
lower (k = 3.8 108 h-1) than that via the formation of DHBT (k = 12
1012 h-1) (Scheme 3). Moreover, the scale of reactivity of the three model
sulfur molecules was confirmed from the rate constants of the desulfur-
ization steps where those of BT is higher than those of 3 M T and 2 M T.
Similarly, the BT adsorption constant is higher than those of 3 M T and
2 M T (KBT = 12.4 bar-1, K3MT = 10.6 bar-1, K2MT = 7.1 bar-1).
adsorption constant was 40% higher than that of 2 M T, thus explaining
the stronger adsorption of BT on the catalytic sites. This also allowed us
to identify the most refractory sulfur compounds that are present in FCC
gasoline feed under deep HDS operating conditions. Notably, the
transformations of sulfur model compounds alone and in mixture could
be fitted from a single kinetic model based on a Langmuir-Hinshelwood
formalism. This clearly validated our combined experimental and the-
oretical approach and also demonstrated that inhibition phenomena
observed experimentally between sulfur molecules were due to com-
petitive adsorption on the catalyst surface.
To further narrow the representativeness gap between model mo-
lecules feeds and real catalytically cracked gasoline and get a deeper
understanding of complex feed reactivities, a similar approach will be
applied to understand the mutual influence of sulfur compounds and
olefins on their reactivity.
In addition, when components are in mixture, the experimental
results are also well modeled considering the same model without
further adjustments of the parameters fitted on single component ex-
periments. Indeed, the same parameters (kinetic and adsorption con-
stants) determined with the single sulfur compounds were used for the
modeling in mixture. The very good fit obtained confirms the validity
and the robustness of the chosen model and evidences the soundness of
the obtained adsorption and kinetic parameters. The mutual inhibiting
effect observed when 2 M T and BT were in mixture is well represented.
Indeed, the BT adsorption constant was higher (Kads = 12.4 bar−1) than
that of 2 M T (7.1 bar−1). The transformation of 2 M T (Fig. 5) was thus
impacted by the presence of unconverted BT, whereas conversely BT
was little impacted by 2 M T (Fig. 6). This confirmed competitive ad-
sorptions of the sulfur model molecules on the catalyst surface.
Acknowledgements
A. Silva dos Santos thanks CNPq - Brasil for a PhD grant and IFPEN
Lyon for the fruitful discussions.
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