Crystal dimension of ZSM-5 influences on para selective disproportionation of ethylbenzene

Article abstract of DOI:10.1166/jnn.2014.8532

Crystal size and crystal dimensions are vital role in shape selective feature. Para selective disproportionation of EthylBenzene (Dip-EB) was investigated over ZSM-5 synthesized in acidic medium. The catalysts were prepared by hydrothermal process with va

Full text of DOI:10.1166/jnn.2014.8532

Article
Journal of
Nanoscience and Nanotechnology
Vol. 14, 2493–2500, 2014
Copyright © 2014 American Scientific Publishers
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Printed in the United States of America
Crystal Dimension of ZSM-5 Influences on Para Selective
Disproportionation of Ethylbenzene
Srinivasan Hariharan1 and Muthaiahpillai Palanichamy2ꢀ∗
1Department of Chemistry, Anna University, Chennai 600025, India
2Department of Chemical Engineering, Hanseo University, Haemi-myun,
Seosan-si, Chungcheongnam-do, 356 706, South Korea
Crystal size and crystal dimensions are vital role in shape selective feature. Para selective dispro-
portionation of EthylBenzene (Dip-EB) was investigated over ZSM-5 synthesized in acidic medium.
The catalysts were prepared by hydrothermal process with various Si/Al ratios (50, 75 and 100)
using fluoride ion precursor. This fluoride ion precursor dissolves the ZSM-5 nutrients below it neu-
tral pH between 4 and 6. The synthesized material was subjected into various physico chemical
characterizations such as XRD, SEM, TGA and BET analyses. The XRD patterns showed high
crystalline nature and their resulting SEM images were also indicate thin prismatic crystals of large
dimension compared with alkaline medium synthesized one. The BET results earned good tex-
tural property. Catalytic activity of vapor phase Dip-EB was carried out between 523 and 673 K.
As their result, diethylbenzene (DEB) isomers were obtained, but para selective Diethylbenzene
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(p-DEB) was observed higher than others. The high selectivity towards p-DEB was due to large
IP: 219.141.127.176 On: Thu, 24 Mar 2016 15:19:46
crystal dimension of ZSM-5 catalysts synthesized in fluoride medium. Hence it is good commercial
Copyright: American Scientific Publishers
application for petrochemical feed stock production.
Keywords: ZSM-5, Large Crystals, Para Selective, Disproportionation, Diethyl Benzene.
1. INTRODUCTION
coke formation because of their free space availability.
This pore geometry evaluation has been already reported
in literature.12 Even the less coke form on such catalysts,
the activation of catalyst may be loss out their active cen-
ters by its free dispersion on large space index. Overcome
this problem, the choice of medium pore zeolites are bet-
ter perform to this catalytic activity by less strain of active
sties. In addition, the porous were obtained in the form
of nano spear, which is increased the surface area of syn-
thesized material. This high surface area of porous mate-
rials has also been reported for good catalytic behavior
of gas phase reaction.13 Here, the medium pore ZSM-5
zeolite one has been recommended for Dip-EB reaction,
because of it unique pore dimension around 5.4 Å, valu-
able to selective catalytic transformation.14ꢀ15 This high
silica ZSM-5 catalyst possess high thermal and hydrother-
mal stability resist it coke formation. The specific pore size
shape selective feature of this ZSM-5 catalyst has exten-
sively investigated for alkylation of benzene, acylation,
xylene isomerization and trans esterification reactions.16–18
Partial ion exchanged ZSM-5 also investigated for shape
Selective Dip of alkyl aromatics is one of the major
classes of petrochemical feed stock productions.1ꢀ2 The
selective EB conversion on this Dip reaction is yielded
valuable chemical products. Generally, it was obtained
as high conversion over heterogeneous solid acid cata-
lysts like zeolites.3ꢀ4 The active sites of Brönsted acid-
ity in zeolites is responsible for high diffusion rate of
EB conversion in EB-Dip reaction, however the selectiv-
ity is proportion to number of Lewis acid sites present
in it.5 Dip-EB reaction has been extensively reported over
dealuminated-Y and mordenite zeolites, because of its
super acidity nature.6–10 Over these catalysts, tuning Al
acidity by steaming/hydrothermal process generate more
Lewis acidity on extra framework of alumiunium active
sites.11 Those acidities are payable attention to this cat-
alytic activity of Dip reactions. However, the free reac-
tion occurs at active sites of large porous zeolites have
enhanced the catalytic conversion, but they retain high
∗Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2014, Vol. 14, No. 3
1533-4880/2014/14/2493/008
doi:10.1166/jnn.2014.8532
2493

Crystal Dimension of ZSM-5 Influences on Para Selective Disproportionation of Ethylbenzene
Hariharan and Palanichamy
selective oxidation and Dip reactions. The mono valent
In3+ ion exchanged zeolites creates more Lewis acid-
ity on the external framework has been reported for
toluene-cumene trans alkylation and Dip-EB reactions.19ꢀ20
Kaeding and coworkers (1985) reported ethylation and
Dip-EB to obtained p-DEB over modified metal oxides
of HZSM-5 zeolite.21 The high selectivity of p-DEB over
HZSM-5 also been reported by csicsery and coworkers.22
All these reports are target to improve the Lewis acid-
ity for such catalytic reactions. The high catalytic con-
version of dehydrogenation reaction was obtained over Ni
based nano material, because of their high surface area
concern.23 Hence, our present approaches can also key
point to the nanostructure of medium pore ZSM-5 zeolite
is expected more catalytic conversion for future investi-
gation. In addition, there are many investigation has been
attempted to enhance the shape selectivity over ZSM-5
zeolite. Fine tuning of pore opening by chemical and liq-
uid vapor depositions (CVD and LVD) was reported for
Dip-EB reaction.24–26 Though the evolution of hydrogen
bonding with silicon in high silica material was attributed
by CVD,27 but this chemical treatment contributes more
strain on the porous wall of zeolites. While the catalytic
activity of this ZSM-5 pore was tuned by CVD or LVD
techniques, the conversion of EB was decreased drastically
due to its diffusion problem. In addition, during this reac-
tion, the high selectivity to p-DEB with low EB conver-
sion does not appear as good for industrial convenience,
selective property of the catalyst. This large crystal was
developed through slow nucleation process involved by
fluoride ion precursor usage. In addition, fluoride ion pre-
cursor dissolves more nutrients to attain high crystalline
nature of this ZSM-5 catalyst. Hence the choice of ZSM-5
zeolite synthesized in acidic medium more active for selec-
tive catalytic transformation.
For this characteristics of ZSM-5 synthesized in fluo-
ride medium, the present study is investigate shape selec-
tive feature on vapour phase Dip-EB over ZSM-5 catalyst.
In this reaction, though the three isomers were formed,
the high selectivity towards p-DEB with good EB con-
version was observed. This p-DEB is a good de-sorbent
for the separation of p-xylene from C8 aromatic mixture.31
It is also precursor for 1,4 divinylbenzene used in the
production of cross-linked polystyrene. For this commer-
cial significance, the high selectivity towards p-DEB over
ZSM-5 catalyst was aimed. This fluoride medium syn-
thesized ZSM-5 showed better catalytic activity for para
selective transformation. The high selectivity of p-DEB
due to large crystals suppress it further isomers and
enhanced their molecular diffusion was observed in the
present investigation. Hence fluoride medium synthesized
ZSM-5 catalyst could be better performance to para selec-
tive transformation in Dip reactions.
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2. EXPERIMENTAL DETAILS
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2.1. Chemicals and Reagents
though recycling could solve this problem. It can be a good
approach, if the conversion is kept high in a single run
without compromising the selectivity of DEB product. For
this process, the chosen ZSM-5 catalyst should have high
activity and shape selectivity.
Copyright: American Scientific Publishers
The ZSM-5 zeolite synthesized in acid medium was
achieved by using Tetraethyl ortho silicate (TEOS),
(Al2SO4ꢂ23−, phosphoric acid (H3PO4ꢂ reagents were
purchased from Merck brand. NH4F and Tetrapropy
ammonium bromide (TPABr) were used as precursor and
structural directing agent for this synthesis. Double time
de-ionized distilled water was used for material prepara-
tion. Diluted ammonia and H2SO4 were also used to adjust
the pH of synthesis condition.
Generally, ZSM-5 synthesized hydrothermally in alka-
line medium (pH at 10ꢁ5 0ꢁ3) posses strong acidity is
due to more defects on the effect of alkali addition.28
During the catalytic reaction, it can be formed water
clusters around the active sites is one of the common prob-
lem encountered in alkaline medium synthesis. Crystalline
nature of the material is also not good for ZSM-5 syn-
thesized in alkaline medium. Hence, the choice of acidic
medium synthesized ZSM-5 catalyst can be eliminates
those drawbacks on former one. This acid medium syn-
thesized has been done by fluoride ion precursor, as the
result of synthesized material persist medium and weak
acid sites instead of strong acidity was reported.29 These
acid sites do not promotes further de-alkylation in selective
catalytic transformations. Though the acid sites concern
for conversion, the crystal dimensions were also signif-
icant effect on product selectivity. The high crystalline
material provides fast diffusion rate of product selectiv-
ity without de-promote of it further isomers. The crystal-
lization behavior of silicon porous microstructures is also
well established in the previous literature.30 Here, ZSM-5
synthesized in fluoride medium is afforded large crystal
dimension with low crystal defects enhances the shape
2.2. Material Synthesis
ZSM-5 material was synthesized by using the follow-
ing gel composition of 0.07 C12H28NBr:1.0 SiO2:0.01
Al2O3:0.01 P2O5:1.6 NH4F:80 H2O.
For ZSM-5 (50) synthesis, 0.23 g of Al2(SO4ꢂ3 and
0.08 g of H3PO4 was added in 39 g of water. The solution
was kept under constant stirred for an h. About 0.66 g of
TPABr was added in the solution mixture and allowed to
stir for another 1 h. In order to adjust pH of 5ꢁ5 0ꢁ2 in the
synthesis condition was using 1:1 diluted NH4 and H2SO4
solutions. After the adjustment of pH, the precipitate was
settled down in the solution. The solution was kept stirred
for another 1 h. Thereafter 7.3 g of TEOS was added and
allowed the solution vigorous stirred for free distribution
of silica. It followed by 2.1 g of NH4 F was added into
the solution mixture. The white gel was obtained after
3 h vigorous stirred of the solution mixture. The resulting
2494
J. Nanosci. Nanotechnol. 14, 2493–2500, 2014

Hariharan and Palanichamy
Crystal Dimension of ZSM-5 Influences on Para Selective Disproportionation of Ethylbenzene
gel was transferred into 75 ml Teflon lined auto clave
for 3 days crystallization process at 443 K. The crys-
talline product was obtained through rapid quenching treat-
ment. The catalyst was recovered by filtration and washed
through double time distilled water. Crystalline material
was dried at 483 K for 12 h. Template was removed by
calcinations of the synthesized material at 823 K for 16 h.
The other ZSM-5 (75 and 100) catalysts were also syn-
thesized by the same procedure adopted with appropriate
quantities of Al addition in the gel composition.
assembled inside the thermostat reactor maintained at con-
stant temperature. Nickel crome wire sensor used to indi-
cate the reactor temperature in digital monitor. The EB
was taken in 20 ml syringe infusion pump and maintained
the fixed time constant flow rate. Water cool condenser
was connected with 50 ml double neck round bottom flask
receiver used to collect the products at bottom of the reac-
tor. The products were confirmed in GC-MS (Gas chromo-
tograph/Mass spectrometer) (Perkin-Elmer Clarus 500).
3. RESULTS AND DISCUSSION
3.1. XRD Analysis
2.3. Characterization
The crystalline XRD pattern of synthesized material was
obtained in X-ray Diffractometer (PANalytical X’pert Pro).
The samples were subjected into moisture free treatment
before it XRD analysis. Cu Kꢃ (ꢄ = 1ꢁ54 Å) was used as
the radiation source and germanium liquid cool nitrogen
solid state used as detector. The high angle spectrum was
record at 2 theta from 5 to 80ꢀ, at each point count was
1.2ꢀ per 10 sec.
The crystal morphology and particle size of synthesized
material were examined under scanning electron micro-
scope (SEM-S-3400 N HITACHI). Ion sputter gold coated
fine thickness of the samples was magnification between
20 and 50 ꢅm. The elemental composition of the material
was also estimated under EDX software installed in the
same instrument.
The XRD patterns of fluoride medium synthesized ZSM-5
(50, 75 and 100) catalysts are shown in Figure 1. All of
them showed high crystalline nature without amorphous
formation. The 2 theta index patterns at 7.95, 9.11, 23.32,
24.45 and 45.29 were confirms MFI structure of ZSM-5
with previous reported result.32 All patterns of ZSM-5 (50,
75 and 100) showed an equal Intensity established maxi-
mum crystallization of the material was reached in our lab
scale synthesis condition.
High intensity of the synthesized material is clearly
states that maximum energy attainment for complete crys-
tal growth. Their relative crystallinity of the material was
compared to ZSM-5 synthesized in alkaline medium, but
it has low crystalline nature (not shown). Hence, the high
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crystallinity was achieved by fluoride ion precursor usage
The major weight losses and thermal stability of the
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in the gel composition. This fluoride ion slowly dissolves
material were investigated in TGA coupled DTA instru-
ment (SDT Q600 V8). The thermal examination of the
material was achieved by slow heating rate at 293 K min−1
under inert nitrogen atmosphere.
Copyright: American Scientific Publishers
all the ingredients, which is good for high crystallization in
1600
ZSM-5 (100)
1400
Textural property of the synthesized material was inves-
tigated under volumetric N2 gas sorption of Brunauer–
Emmet–Teller (BET-Micromeritics ASAP 2010) isotherm.
The thermostat of adsorption condition was kept at 76 K
by liquid cool N2 and isopropyl alcohol mixture. The BJH
method T -plot used to calculate pore volume of synthe-
sized material.
1200
1000
800
600
400
200
1600
ZSM-5 (75)
1400
Na-ZSM-5 (50) also synthesized hydrothermally alka-
line medium for catalytic activity comparison. The syn-
thesized material was ion exchanged by 48 ml of 0.1M
ammonium nitrate solution reflux at 363 K. Ion exchanged
material was washed by double time de-ionized water and
dried in oven at 393 K. Finally the material was subjected
in calcinations at 913 K for catalytic study.
1200
1000
800
600
400
200
1600
ZSM-5 (50)
1400
1200
1000
800
600
400
200
0
2.4. Catalytic Reaction
The fluoride medium synthesized ZSM-5 catalyst was
investigated for vapour phase Dip-EB between 523 and
673 K. This reaction was carried out in fixed bed, verti-
cal flow type reactor. About 0.3 g of catalyst was packed
inside the glass tube rod. The packing was made by
15 counts of ceramic beads mixed in 0.3 g of catalyst
placed inside the glass rod. This catalyst was hold by
either side of fine glass wool supports. The whole set was
5
10
15
20
25
30
35
40
45
50
2 Theta (θ)
Figure 1. XRD patterns of ZSM-5.
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Crystal Dimension of ZSM-5 Influences on Para Selective Disproportionation of Ethylbenzene
Hariharan and Palanichamy
Hence, the usage of fluoride ion precursor better for crys-
tallization in hydrothermal process was confirmed.
100
90
3.2. TGA Analysis
The thermal stability of as-synthesized ZSM-5 (50, 75
and 100) catalyst was confirmed in TGA analysis and the
results are presented in Figure 2. All of them showed,
similar weight loss trend reflects in their resulting TGA
spectrums.
80
ZSM-5 (100)
100
95
The weight loss from 373 K to 473 K was due to elimi-
nation of moisture content in the synthesized material. The
petite amount of water loss illustrates even the same mate-
rial can be subjected into the streaming dealumination, less
amount of water cluster form around the active sites and it
is negligible to the catalytic deactivation. The major weight
loss across 673 K to 823 K was assigned for degradation
of template. In TGA results, residual % decreased in the
order of ZSM-5 50 to 100 is illustrates an equal proportion
of aluminium entry in the framework of ZSM-5 catalysts.
There no further weight loss was observed in the spectrum
confirms the synthesized material stable up-to 1073 K.
90
85
ZSM-5 (75)
100
95
90
85
80
ZSM-5 (50)
300 400 500 600 700 800 900 1000 1100 1200
Temperature (K)
3.3. SEM Images
Crystal morphology of synthesized material was clearly
viewed under SEM analysis. The SEM pictures of ZSM-5
(50, 100 and 150) are shown in Figure 3. In this acidic
Figure 2. TGA spectrum of ZSM-5.
hydrothermal process. Though the Si/Al ratio variation in
the gel composition, all the material showed the equal pro-
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medium synthesized ZSM-5 crystal showed similar mor-
33
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portion of crystallization indicates the optimum synthesis
conditions were perfect fit to the crystal growth nucleation.
phological structure of alkaline medium synthesized one.
Copyright: American Scientific Publishers
But they were large crystal dimension with low crystal
Figure 3. SEM images (a) ZSM-5 (50); (b) ZSM-5 (75); (c) ZSM-5 (100); (d) Na-ZSM-5 (50).
J. Nanosci. Nanotechnol. 14, 2493–2500, 2014
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Hariharan and Palanichamy
Crystal Dimension of ZSM-5 Influences on Para Selective Disproportionation of Ethylbenzene
Table I. Textural property of ZSM-5 zeolite.
defects. SEM picture of ZSM-5 materials were seems like
prismatic crystals. Tiny crystals were also noted in all the
spectrums. However the tiny crystals were presence, but
their resulting XRD spectrum does not show any amor-
phous form. Hence this tiny crystal is also considered the
part of crystalline material. The particle dimension was
observed around 50 ꢅm higher than alkaline medium syn-
thesized material. Generally, the large crystal dimension
is major contributes to selective transformation in the cat-
alytic applications. This crystal dimension was enhanced
the fast rate of molecule diffusion, where they reaction
occurs at active sites. It is less significance in low crys-
tal dimension of alkaline medium synthesis. In alkaline
medium synthesized ZSM-5 possess crystal defects also
reduce the driving force of molecular diffusion. The ele-
mental composition of the material was roughly calcu-
lated in EDX (not shown) analysis in the same instrument.
It shows the presence of T (Si and Al) atoms which were
used in the gel composition except F− ion. This confirms
the fluoride ion only play as the part of precursor purpose.
Si/Al ratios Surface area (m2/g) Pore volume (cm3/g) Pore size (Å)
50
75
100
442
375
353
0.17
0.17
0.18
5.4
5.4
5.4
3.5. Catalytic Activity
Vapour phase Dip-EB was investigated over acidic
medium synthesized ZSM-5 catalysts. The EB conversion
and product selectivity were used to understand the shape
selectivity phenomenon on the large crystal dimension of
ZSM-5 zeolite.
3.5.1. Effect of Temperature
The Dip-EB over ZSM-5 zeolite (50, 75 and 100) was
investigated at 523, 573, 598, 623, 648 and 673 K at WHSV
2.88 h−1. The products were analyzed by GC-MS. The
major product was p-DEB and benzene. In addition minor
amount of m-diethyl benzene (m-DEB) and o-diethyl
benzene (o-DEB) were also obtained. The results of
EB conversion and products selectivity are presented in
Table II.
3.4. BET Analysis
The textural property of synthesized ZSM-5 (50, 75
and 100) material was investigated on N2 gas sorption
isotherm in BET analysis. N2 sorption isotherm spectrums
are shown in Figure 4. All the spectrums are illustrates
type 1 isotherm curve. There results of surface area, pore
volume pore size are presented in Table I. The surface area
was decreased with increases in Si/Al ratios and this com-
mon trend was also observed in reference ZSM-5 zeolite.34
The high surface area of 442 m2/g was established good
crystalline nature of synthesized material. However the
surface area was decreased with Si/Al ratios, the pore
volume and pore size were remains as same for ZSM-5
zeolite.
Over ZSM-5 (50), the conversion increased from 523
to 623 K, but decreased at 673 K. The decrease of con-
version at 673 K was due to coke formation. Formation
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of coke was physically verified after the reaction. Since
medium pore ZSM-5 zeolites cannot provide large space
for coke formation,35 the decrease in conversion at 673 K
was not high. It was also high compared to some mod-
ified ZSM-5 catalysts reported for Dip-EB conversion.36
The enhancement was due to free diffusion of EB into
the pores of present catalysts compared to the modified
ZSM-5 catalysts.
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Copyright: American Scientific Publishers
The selectivity of p-DEB increased with the increase
in temperature from 523 to 623 K. Though the conver-
sion of EB decreased at 673 K, the selectivity of p-DEB
was high. The enhanced selectivity of p-DEB at 673 K
was due to pore size reduction as a result of coke for-
mation. This observation was indirectly confirmed coke
formation inside the ZSM-5 pore. Such enhancement in
shape selectivity of ZSM-5 as a result of coke formation
was also reported.37 The Dip-EB reaction scheme is shown
in Scheme 1.
The EB diffuses through the zeolite pore, protonation
of it yields benzene and ethyl cation. The free ethyl
cation attacks selectively at the para position of another
EB to form p-DEB. Although p-DEB could isomerise in
the channel intersection to m-DEB and o-DEB, only the
p-DEB can diffused out as its kinetic diameter is less than
the pore size. The high rate diffusion of p-DEB compared
to m- and o-DEB was also reported in the literature.37
Though isomerization of p-DEB was reported faster than
Dip reaction in ZSM-5 zeolite,38 high crystallinity can
avoid isomerisation of p-DEB on the external surface of
0.0
0.2
0.4
0.6
0.8
Pressure (P/P0)
Figure 4. N2 adsorption isotherms of ZSM-5 (ꢀ) Si/Al = 50; (•)
Si/Al = 75; (ꢁ) Si/Al = 100.
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Crystal Dimension of ZSM-5 Influences on Para Selective Disproportionation of Ethylbenzene
Hariharan and Palanichamy
Table II. Effect of temperature on ethylbenzene conversion and products selectivity.
Product selectivity (%)
Catalysts
Temperature in (K)
EB conversion (%)
p-DEB
m-DEB
o-DEB
Benzene+others
ZSM-5 (50)
523
573
598
623
648
673
26
27
31
33
31
24
38
39
42
46
50
61
5
8
11
13
14
10
3
2
4
3
2
2
54
51
43
38
34
27
ZSM-5 (75)
523
573
598
623
648
673
18
20
23
27
23
16
41
43
45
47
49
53
3
5
9
11
12
8
2
0
1
1
2
0
54
52
45
41
37
39
ZSM-5 (100)
H-ZSM-5 (50)
523
573
598
623
648
673
9
45
47
51
55
60
69
0
0
2
0
0
0
1
0
3
1
1
1
54
53
44
44
39
30
11
13
17
19
11
523
573
598
623
648
673
31
33
35
39
30
28
31
33
36
40
45
47
5
8
9
7
5
7
5
4
4
5
5
5
59
55
51
48
45
41
Notes: Reaction conditions: Catalyst 0.3 g; WHSV: = 2ꢁ88 h−1
.
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ZSM-5 crystals. The large crystal size can also favor selec-
to ZSM-5 (50), but selectivity of p-DEB was not much
affected similar to ZSM-5 (50). Hence ZSM-50 was more
active than others. In order to further verify the statement
that Dip-EB is catalyst dependent, the reaction was studied
at 623 K in the absence of catalyst, but p-DEB was not
observed, thus supporting Dip is catalytic dependent at the
chosen temperature range. The reaction was also carried
out over H-ZSM-5 derived from Na-ZSM-5 synthesized in
alkaline medium. The results are also shown in the same
table. Although the EB conversion was high compared to
ZSM-5 (50) the selectivity to p-DEB was low. Hence com-
pared to ZSM-5 synthesized in alkaline medium, ZSM-5
synthesis in fluoride medium was conformed better for
Dip-EB reaction.
Copyright: American Scientific Publishers
tive diffusion of only p-DEB. Although the external acid
sites were not proved, very low selectivity to p-DEB con-
firmed their very low content. It also necessitated Dip to
occur within the zeolite pore confirmed by increase in tem-
perature the selectivity of m-DEB was slightly affected.
Hence, based on EB conversion and p-DEB selectivity it
was established that hydrothermal synthesis of ZSM-5 in
fluoride medium could be a better method than pore size
reduction.
The results of EB conversion, product selectivity over
ZSM-5 (75 and 100) are also presented in the same table
and compared. The conversion decreased in both compared
+
HO
3.5.2. Effect of WHSV
The effect of WHSV on Dip-EB was studied at 623 K.
The WHSV was varied as 2.89, 5.78 and 8.69 h−1 and the
H
Al–
+
+
+ H2C CH3
Si
+
ZSM-5
Table III. Effect of WHSV on ethylbenzene conversion and products
selectivity.
Product selectivity (%)
WHSV
(h−1
EB
ꢂ
conversion (%) p-DEB m-DEB o-DEB Benzene+others
2.88
5.77
8.66
33
30
23
46
49
53
13
9
7
3
2
0
38
40
40
C2H5
Note: Reaction conditions: Catalyst-H ZSM-5 (50); Catalyst 0.3 g; Temp = 623 K.
Scheme 1. Disproportionation of ethylbenzene.
2498
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Hariharan and Palanichamy
Crystal Dimension of ZSM-5 Influences on Para Selective Disproportionation of Ethylbenzene
Table IV. Effect of time on stream on ethylbenzene conversion and
products selectivity.
high crystalline nature, large crystal dimension and high
surface area by the aid of fluoride ion precursor. This
large crystal size and high crystalline nature of the mate-
rial cause high yield to p-DEB selectivity. Previously there
were many investigation has reported for Dip-EB over
modified ZSM-5, but the present study was carried out in
the concern of crystal behaviors such as high crystallanity,
crystal size and it acid strengths for high para selectivity.
On their resulting observation, p-DEB was obtained bet-
ter catalytic yield except others. This high yield of p-DEB
was due to fast diffused on high crystalline material and
well defined crystals of low external acidity. Hence this
acid medium synthesized ZSM-5 could be applied to the
study of toluene-Dip and other alkyl aromatics.
Product selectivity (%)
Time on
stream (h−1
EB
Benzene+
ꢂ
conversion (%) p-DEB m-DEB o-DEB
others
1
2
3
4
5
6
33
33
30
29
30
27
46
46
49
51
55
58
13
13
12
12
10
9
3
2
1
2
3
2
38
38
38
35
32
31
Note: Reaction conditions: Catalyst-ZSM-5 (50); Catalyst 0.3 g; WHSV: 5.77 h−1
Temp = 628 K.
;
results are presented in Table III. The conversion decreased
with increase in WHSV. The selectivity to p-DEB is
showed a slight increase whereas that of m-DEB decreased.
Hence m-DEB was verified to occur by isomerisation of
p-DEB. Isomerization of p-DEB to m-DEB can readily
occur on the external surface acid sites, but m-DEB to
o-DEB might not be favored. It can be formed in the
channel intersections via direct electrophilic reaction of
ethyl cation with EB, but it cannot be diffused out. So,
its formation might occur certainly on the external acid
sites by electrophilic substitution. The low selectivity was
due to high probability for isomerization of p-DEB com-
pared to electrophilic substitution of EB was reported.36
Acknowledgments: The authors acknowledge to Uni-
versity Grants Commissions (UGC) for financial aid to
carry out this work and DST-FIST for instrumentation
facility.
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3.5.3. Effect of Time on Stream
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Received: 2 January 2013. Accepted: 26 January 2013.
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Copyright: American Scientific Publishers
2500
J. Nanosci. Nanotechnol. 14, 2493–2500, 2014