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Modification of HY zeolite by fluorine and its influence on olefin alkylation thiophenic sulfur in gasoline.

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ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING
Asia-Pac. J. Chem. Eng. 2008; 3: 503–508
Published online 29 July 2008 in Wiley InterScience
(www.interscience.wiley.com) DOI:10.1002/apj.175
Research Article
Modification of HY zeolite by fluorine and its influence on
olefin alkylation thiophenic sulfur in gasoline
Zekai Zhang,1,2 Xiujie Li,1,2 Ling Zhang,1,2 Xiangxue Zhu,1 Shenglin Liu1 and Longya Xu1 *
1
2
Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, P. R. China
Graduate University of Chinese Academy of Sciences, Beijing 100049, P. R. China
Received 10 October 2007; Accepted 28 November 2007
ABSTRACT: The catalytic performance of a series of HY zeolites, modified by HF for olefin alkylation thiophenic
sulfur (OATS) process, was evaluated. It was found that acid sites distribution could be controlled through the amount
of HF. Under the optimized condition, activity, and selectivity of thiophene alkylation reaction in OATS could be
greatly improved. At the same time, coking behavior was suppressed during the course.  2008 Curtin University of
Technology and John Wiley & Sons, Ltd.
KEYWORDS: desulfurization; alkylation; fluorine modification; HY
INTRODUCTION
Deep desulfurization of gasoline has been an important
research topic since the last decades, and many desulfurization methods were available to solve this problem including hydrodesulfurization (HDS), adsorptive
desulfurization (ADS), oxide desulfurization (ODS),
and biological desulfurization (BioDS).[1 – 7] At the same
time, olefin alkylation thiophenic sulfur (OATS) process
is attracting more and more attention,[8] which provides
a new route for the desulfurization task. An OATS process can alkalize the thiophenes over acidic catalysts,
heighten their boiling point, and separate the alkalized
heavy compounds from gasoline by distillation.
As shown by previous studies,[9] thiophenes alkylation could be easily achieved, although some side reactions, such as aromatics alkylation and alkene oligomerization, coexisted with it. Therefore, a good OATS catalyst should show high selectivity for thiophenes alkylation reaction and less side reactions will reduce the
octane number loss.[10 – 12]
Fluorine modification has been proved to be a useful method to control the acidity of zeolite.[13 – 16]
Through the condense reaction of HF with SiOH and
bridge hydroxyl on zeolite, proper acidity would be
obtained, which may be good for some acidic catalyzed
reactions.[17 – 19] On the basis of these reports, we studied
the fluorine modification effect on the OATS catalytic
*Correspondence to: Longya Xu, Dalian Institute of Chemical
Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning,
P. R. China. E-mail: lyxu@dicp.ac.cn
 2008 Curtin University of Technology and John Wiley & Sons, Ltd.
ability of Hβ zeolite and got a rather effective result.[20]
In this article, we exhibit the results related to the fluorine modification effect on HY zeolite and its OATS
catalytic ability. All catalytic reactions were carried out
in a model gasoline system containing thiophene, hexene, xylene, and methylcyclohexane.
EXPERIMENTAL
Raw materials
Zeolite Y was obtained from Wenzhou Huahua Co. Ltd
of China (Si/Al2 = 20). The reactants were purchased
from varied sources: thiophene (99%) was purchased
from Special Chemical Agent Research Center of North
China region, Tianjin; methylcyclohexane (98%) was
from a sub-company of Sinopharm, Shanghai; 1-hexene
(97%) from Acros Organics; and xylene was from
Shenyang Lianbang Agents.
Preparation of the fluorinated HY zeolites
Zeolite Y was converted into the H-form by ionexchange method. The fluorinated HY was obtained by
the impregnation method and the fluorinated samples
were labeled as HY/nF, where n is the weight percent
(wt%) of fluorine introduced.
Z. ZHANG ET AL.
Asia-Pacific Journal of Chemical Engineering
Physicochemical properties characterization of
the fluorinated HY zeolites
The powder X-ray diffraction (XRD) technique, ammonia temperature programmed desorption (NH3 -TPD)
technique, and the pyridine IR (Py-IR) were used to
determine the relative crystallinity, the acidity, and
the acid distribution of the samples. Then the xylenedesorption behavior of the samples was monitored in
a U-shaped quartz microreactor connected to an MS
detector (OminiStar, Pfeiffer Co. Ltd), also the coke
deposition of the used catalysts. Detailed description
could be seen elsewhere.[20]
f
e
Intensity (a.u.)
504
d
c
b
a
10
Experimental procedure of olefin alkylation
thiophenic sulfur tests
The OATS tests were carried out in a fixed-bed reactor
(9 mm id × 300 mm). The feed (thiophene: 1-hexene:
xylene 1: 2: 5 c/c) was fed into the reactor and the
catalysts were passed into it by a high-pressure liquid
pump (SZB-5, Beijing Weixing Co. Ltd), after the catalyst was activated for 2 h with pure nitrogen at 500 ◦ C.
A gas chromatography (GC) detector (Shimadzu-2010,
Shimadzu Co. Ltd) with a flame ionization detector
(FID) and flame photometric detector (FPD) was used
to analyze the products.
RESULTS AND DISCUSSION
XRD patterns of the fluorinated HY zeolites
XRD patterns of the HY/nF catalysts are shown in
Fig. 1. It can be seen that the resultant HY zeolite
has typical FAU structures and good crystallinity. After
introduction of fluorine, the structure of HY zeolite is
still retained, which indicates that the modification does
not affect the long-range ordering of the HY obviously.
NH3 -TPD profiles of the fluorinated HY zeolites
Acidity of the HY/nF catalysts was measured by NH3 TPD as shown in Fig. 2. On HY zeolite two desorption
peaks could be distinguished, one centered at 260 ◦ C
and the other at 420 ◦ C, which correspond to weak and
strong acid sites, respectively. When fluorine was added
to zeolites, the total acidity amount of catalysts changed
a lot. Quantitative analysis of the NH3 -TPD profiles is
listed in Table 1. Introduction of 0.15% F led to an
increase in total acid sites from 3.11 × 1020 /g to 3.20 ×
1020 /g. When the fluorine content was 0.25%, less acid
sites (e.g. 3.10 × 1020 /g) were preserved on HY zeolite.
 2008 Curtin University of Technology and John Wiley & Sons, Ltd.
20
30
40
2θ/°
Figure 1. XRD patterns of the HY/nF catalysts with different
F addition. (a) HY(0.0% F), (b) 0.15% F, (c) 0.25% F,
(d) 0.35% F, (e) 0.50% F, and (f) 0.75% F.
Table 1. Acid sites change of the HY zeolite after
fluorination.
Acid sites (×1020 /g)
Sample
Total
W
M+S
HY/0F
HY/0.15F
HY/0.25F
HY/0.35F
HY/0.50F
HY/0.75F
3.11
3.30
3.10
2.99
2.95
2.57
1.14
1.21
1.17
1.09
1.07
0.91
1.97
2.09
1.93
1.90
1.88
1.66
W, weak; M, medium; S, strong.
Further increasing the fluorine content would lead to the
decrease of total acid sites concentration.
Py-IR spectra of the fluorinated HY zeolites
In order to get more information about the Brønsted
and Lewis acid sites, Py-IR spectra of HY/nF catalysts
were performed. As our tests were all carried out below
100 ◦ C, weak acid sites on HY/nF catalysts were not
active in the catalytic process. Medium and strong
acid sites play a more important role in the thiophene
alkylation reaction as suggested by Sun et al .[21] So
the effects of fluorine modification on the medium
and strong acid sites on HY zeolite were emphatically
studied here by Py-IR spectra. In order to take away the
adsorbed pyridine on weak acid sites, all the samples
were desorbed at 350 ◦ C with a pressure below 10−2 Pa
for 0.5 h after saturating pyridine at room temperature.
Figure 3 shows the infrared spectra of adsorbed
pyridine on HY/nF catalysts. The characteristic infrared
Asia-Pac. J. Chem. Eng. 2008; 3: 503–508
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
FLUORINATION EFFECT ON HY AND ITS OATS CATALYTIC PERFORMANCE
1.2
e
f
e
Intensity (a.u.)
d
0.8
c
b
a
0.4
d
c
b
0.0
1600
1550
200
300
400
500
Temperature (°C)
600
Figure 2. NH3 -TPD profiles of the HY/nF catalysts with
different F additions. (a) HY, (b) 0.15% F, (c) 0.25% F,
(d) 0.35% F, (e) 0.50% F, and (f) 0.75% F.
bands near 1540 cm−1 are attributed to pyridinium
ions on Brønsted acid sites and those near 1450 cm−1
are corresponding to pyridine coordinately bonded to
Lewis acid centers.[22] As shown in Fig. 3, there are
both Brønsted and Lewis acid sites on the HY zeolite.
Increasing F content (0.15%) leads to the increase of
both Lewis and Bronstedacid sites on HY zeolites.
Table 2 demonstrates the integrated intensity of Py-IR
bands and obviously the number of Brønsted acid sites
reaches its maximum at 0.15% F. Then the amount
of Brønsted acid sites decreased upon fluorine loading.
The number of Lewis acid sites reached its maximum
with 0.35% F, which is different from the phenomena
on Hβ zeolite.[20] At the same time, the ratio of
B/L reached its maximum value of 4.38 at 0.15% F,
then sharply decreased to 3.54 at 0.25% F and then
stabilized at about 3.0 within 0.75% F. So proper
fluorine modification increased the strong acid sites of
HY zeolite and changed its distribution of Lewis and
Brønsted acid sites. According to previous studies,[23,24]
these variations in acid properties should originate from
the reaction of fluorine ions with the bridge Si–OH–Al
groups on HY zeolite.
Effect of fluorine modification on the catalytic
performance of HY zeolite
As several main reactions including thiophene alkylation, xylene alkylation, and hexene oligomerization,
coexisted during the OATS process, and their activities reached its maximum value synchronously at 2 h
on stream,[25] the conversions at that time were chosen
 2008 Curtin University of Technology and John Wiley & Sons, Ltd.
1500
1450
1400
ν/cm-1
a
Figure 3. Py-IR spectra of the HY/nF catalysts with different
F addition at 350 ◦ C. (a) HY (0.0% F); (b) 0.15% F; (c) 0.25%
F; (d) 0.35% F; (e) 0.75% F.
Table 2. Distribution of B/L acid sites of the HY/nF
catalysts.
Peak area (arb units)
Sample
HY/0F
HY/0.15F
HY/0.25F
HY/0.35F
HY/0.75F
B
L
B+L
B/L
2.88
3.65
2.76
3.53
3.25
1.04
1.25
1.17
1.77
1.50
3.92
4.9
3.93
5.3
4.75
4.15
4.38
3.54
2.99
3.25
B, Brønsted acid sites; L, Lewis acid sites.
B/L = (εL /εB )(AB /AL ), where (AB /AL ) is the absorbance ratio and
(εL /εB ) is the molar absorption coefficient ratio, which is taken as
1.5 for samples having Si/Al2 > 15.[22]
to exhibit the effect of the fluorine modification on the
catalytic ability of the HY zeolite.
The effect of fluorine modification on the catalytic
activity of the HY zeolite is shown in Fig. 4. For HY
zeolite, thiophene conversion was only 62%, introduction of 0.25% fluorine could lead thiophene alkylation
activity to its maximum (80%, curve a). When the F
loading was more than 0.25%, thiophene conversion
began to decrease gradually just as the acidity of the
HY/nF catalysts decreased. It is interesting to point out
that HY/0.15F catalyst shows poor thiophene alkylation
activity and thiophene conversion is only 31%.
Along with the promotion of the thiophene alkylation,
hexene oligomerization reaction also happened. Its
activity followed the same trend, and the amplitude of
hexene oligomerization conversion was bigger than that
of thiophene conversion (curve b). However, fluorine
modification did not give rise to HY zeolite catalytic
activity for xylene alkylation reaction. Conversion of
xylene was low over most of fluorinated HY zeolites
(curve c) compared with original HY zeolite. Although
Asia-Pac. J. Chem. Eng. 2008; 3: 503–508
DOI: 10.1002/apj
505
Z. ZHANG ET AL.
Asia-Pacific Journal of Chemical Engineering
40
a
30
60
c
20
40
10
20
hexene oligomerization/%
thiophene conversion/%
80
b
0
0
0.0
0.2
0.4
F content (%)
0.6
0.8
Figure 4. Effect of fluorine modification on the OATS
process activity of HY zeolite. (a) Thiophene alkylation;
(b) hexene oligomerization; and (c) xylene alkylation. Reaction conditions: temperature 60 ◦ C, pressure 1.5 MPa,
WHSV 3.0 h−1 , and TOS 2 h.
HY/0.15F catalyst possessed the maximal acidity in all
samples, the conversion of thiophene alkylation, xylene
alkylation, and hexene oligomerization all decreased
greatly. We will discuss the phenomenon in detail later.
The effect of fluorine modification on the selectivity of the HY zeolite is demonstrated in Fig. 5 and
the selectivity is defined as the ratio of one reaction
consumed hexene content to the total consumed hexene during the OATS process. It is clear that the fluorine modification promotes the selectivity of thiophene
alkylation over HY/0.25F catalysts. Loading of more
75
thiophene alkylation
F content leads to the decrease of thiophene alkylation selectivity. From the above results, we can deduce
that proper F addition on HY zeolite could improve
the activity and selectivity of thiophene alkylation more
desirably than those of the xylene alkylation and hexene
oligomerization.
Though the F addition promoted the activity and the
selectivity of HY zeolite, unfortunately, the fluorination
did not improve the stability of thiophene alkylation
over HY/nF catalysts clearly. As shown in Fig. 6(A),
with the proceeding of the reactions, the thiophene
conversions over different HY/nF catalysts were all
decreased clearly. At the same time, the effects of
fluorination on the stability of xylene alkylation and
hexene oligomerization were not evident too, and as
exhibited in Fig. 6(B) and (C), all of their conversions
have decreased to a rather low level within 8 h on
stream. Therefore, the fluorination of the HY zeolite
could not promote the stability of thiophene alkylation
under the reaction conditions.
TPO studies of the used HY/nF catalysts
In order to get the information about the catalyst
deactivation behavior of the HY/nF catalysts during
the OATS process, coke deposition of the HY/nF
catalysts was measured by Temperature Programmed
Oxidation (TPO) as shown in Fig. 7. Two peaks could
be distinguished on the HY catalyst: one at 380 ◦ C and
the other at 580 ◦ C. After introduction of fluorine, areas
of the two TPO peaks decreased upon the increase of
the F addition. At the same time two peaks shifted to
lower temperature after fluorine loading. That is to say,
fluorine modification of the HY zeolite may prohibit
the coke deposition to some degree during the OATS
process.
DISCUSSION
50
Selectivity/%
506
xylene alkylation
25
hexene oligomerization
0
0.0
0.2
0.4
F content (%)
0.6
0.8
Figure 5. Effect of fluorine modification on the OATS
process selectivity of HY zeolite. Reaction conditions:
temperature 60 ◦ C, pressure 1.5 MPa, WHSV 3.0 h−1 , and
TOS 2 h.
 2008 Curtin University of Technology and John Wiley & Sons, Ltd.
As mentioned in the introduction, we have obtained
a rather good effect of fluorine modification on the
catalytic performance of Hβ zeolite, and in this article,
we have attempted to study the effects on HY zeolite.
The results demonstrated that fluorine modification of
the HY zeolite improved its physicochemical properties
as well as its catalytic activity. At the same time some
interesting phenomena, especially the relation between
the acidity and activity of catalysts, were observed.
When compared to the results of Hβ zeolite, it was
clear that the total acidity was not the only factor to
determine the catalytic ability of HY zeolite. HY/0.15F
catalyst occupied more acid sites than HY although
it showed the worst catalytic activity. When the F
loadings are 0.25 and 0.35%, HY/nF catalysts exhibit
Asia-Pac. J. Chem. Eng. 2008; 3: 503–508
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
FLUORINATION EFFECT ON HY AND ITS OATS CATALYTIC PERFORMANCE
(A)
80
Thiophene conversion/%
0.00F
0.15F
60
b
0.25F
c
0.35F
0.50F
0.75F
40
a
d
20
0
2
3
4
5
TOS/h
6
7
8
200
hexene oligomerization/%
(B) 5
600
800
T/°C
4
Figure 7. TPO profiles of the used HY/nF catalysts within
8 h on stream.
b
3
c
2
a
d
1
0
2
3
4
5
TOS/h
6
7
8
6
7
8
(C)
20
xylene conversion/%
400
15
b
c
10
a
d
5
0
2
3
4
5
TOS/h
Figure 6. Effect of fluorine modification on OATS process
stability of HY/nF zeolite. (a) HY (0.0% F); (b) 0.25% F;
(c) 0.35% F; (d) 0.75% F. Reaction conditions: temperature
60 ◦ C, pressure 1.5 Mpa, and WHSV 3.0 h−1 .
a better performance than HY though their total acidity
is less than that of HY. Combining the Py-IR listed in
Table 2, it could be found that both HY and HY/0.15F
had bigger B/L ratio and poor thiophene alkylation
activity, although the HY/0.25F and HY/0.35F were
 2008 Curtin University of Technology and John Wiley & Sons, Ltd.
on the other side. It indicated that the distribution of
Brønsted and Lewis acid sites over HY/nF catalysts
could influence its catalytic activity and a lower B/L
ratio is good for the thiophene alkylation. This is
interesting, for it is well known that the alkylation
of mononuclear aromatics occurs following Rideal
mechanism, i.e. a carbenium ion attacks π electrons
of the ring, forms the alkylated product and releases
a proton.[26] Under this mechanism, the Brønsted acid
sites were favorable for the formation of carbenium
ions, which are always favorable for the alkylation
reaction, whereas the Lewis acid sites were somewhat
less useful during the course. A probable reason was the
synergetic effect between the Brønsted and Lewis acid
sites, i.e. when the B/L ratio was suitable, carbonium
ions could be formed on the Brønsted acid sites, and
the Lewis acid sites could adsorb a proper number
of thiophene molecules and let them react with the
carbonium ions, which enhanced the activity of the
catalyst. When the B/L ratio was not suitable (bigger or
smaller), the excessive carbonium ions or the captured
thiophene molecules would be produced, which would
decrease the efficiency of the catalyst. A proof for the
adsorption effect of the fluorinated HY zeolite could be
seen in the relationship between the xylene alkylation
activity and xylene adsorbability of the HY/nF catalysts.
It was mentioned before that the xylene alkylation
was restrained over most of the HY/nF catalysts,
although the acidity promotion of fluorinated HY zeolite
should result in higher activity of xylene alkylation.
According to the profiles of the xylene adsorption
behavior on the HY/nF catalysts, as shown in Fig. 8,
fluorine modification enhanced the xylene adsorbability
of the HY/nF catalysts, which suggested that the xylene
adsorption behavior change of HY/nF catalysts might
Asia-Pac. J. Chem. Eng. 2008; 3: 503–508
DOI: 10.1002/apj
507
Z. ZHANG ET AL.
Asia-Pacific Journal of Chemical Engineering
REFERENCES
xylene signal
508
f
e
d
c
b
a
50
100
150
200
250
300
T/°C
Figure 8. Xylene-TPD profiles of HY/nF catalysts with
different F additions. (a) HY (0.0% F), (b) 0.15% F, (c) 0.25%
F, (d). 0.35% F, (e) 0.50% F, and (f) 0.75% F.
have influenced its catalytic activity of the xylene
alkylation as well as the thiophene alkylation.
CONCLUSIONS
Thiophene alkylation catalytic activity was highly
enhanced on the HY zeolite through fluorine modification method. Characterization of the HY/nF catalysts
and the catalytic performance demonstrated the promotion of the fluorine modification to the physicochemical
properties and catalytic activity of HY zeolite. The promoted effect could reach its maximum at 0.25% F,
whereas the activity and selectivity of thiophene alkylation reached about 80 and 70% respectively. Such promotion should have originated from the redistribution
of B/L ratio on HY zeolite as evidenced by NH3 -TPD
and Py-IR results.
Acknowledgements
This project was supported by the National Basic
Research Program of China (2005CB221403) and
the Knowledge Innovation Program of the Chinese
Academy of Sciences (DICP K2007D3).
 2008 Curtin University of Technology and John Wiley & Sons, Ltd.
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DOI: 10.1002/apj
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