Influence of n Si/n Al ratio of HY zeolite catalysts on alkylation of toluene with tert-butanol

Article abstract of DOI:10.1134/S0036024416130215

The highly selective synthesis of 4-tert-butyltoluene from toluene and tert-butanol over HY zeolites was performed in liquid phase. The effect of Si/Al ratio (6.3, 7.5, 11, 12) of HY zeolites on the alkylation performance was studied. The catalysts were characterized by SEM, XRD, FT-IR, and NH₃-TPD methods. With increase of Si/Al ratio, the conversion of toluene and the selectivity towards 4-tert-butyltoluene increased gradually. HY-12 was found to be more suitable for the tert-butylation of toluene. When the alkylation reaction was conducted at 180°C for 4 h using HY-12 catalyst, the conversion and the selectivity of 4-tertbutyltoluene reached 40.74 and 70.91%, respectively.

Full text of DOI:10.1134/S0036024416130215

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2016, Vol. 90, No. 13, pp. 2503–2507. © Pleiades Publishing, Ltd., 2016.
CHEMICAL KINETICS
AND CATALYSIS
Influence of nSi/nAl Ratio of HY Zeolite Catalysts on Alkylation
of Toluene with tert-Butanol1
Yuanyuan Wanga, Hua Songa,*, Xinglong Sunb, and HuaLin Songc
a College of Chemistry and Chemical Engineering, Northeast Petroleum University, Daqing 163318, Heilongjing, China
b Daqing Petrochemical Engineering Co., Ltd., Daqing 163714, Heilongjiang, China
c.Key Laboratory of Cancer Prevention and Treatment of Heilongjiang Province, Mudanjiang Medical University,
Mudanjiang 157011, China
*e-mail: songhua2004@sina.com, 349382397@qq.com
Received September 25, 2015
Abstract—The highly selective synthesis of 4-tert-butyltoluene from toluene and tert-butanol over HY zeolites
was performed in liquid phase. The effect of Si/Al ratio (6.3, 7.5, 11, 12) of HY zeolites on the alkylation per-
formance was studied. The catalysts were characterized by SEM, XRD, FT-IR, and NH3-TPD methods.
With increase of Si/Al ratio, the conversion of toluene and the selectivity towards 4-tert-butyltoluene
increased gradually. HY-12 was found to be more suitable for the tert-butylation of toluene. When the alkyla-
tion reaction was conducted at 180°C for 4 h using HY-12 catalyst, the conversion and the selectivity of 4-tert-
butyltoluene reached 40.74 and 70.91%, respectively.
Keywords: alkylation, Si/Al ratio, toluene, 4-tert-butyltoluene, HY zeolite
DOI: 10.1134/S0036024416130215
1. INTRODUCTION
et al. [12] studied three large-pore zeolites (HM, HY,
and Hβ) as catalysts in tert-butylation of toluene with
tert-butanol (TBA). HM (Si/Al = 17.5) showed the
best catalytic activity and the maximum para-selectiv-
ity (near 90%). Shivanand Pai et al. [13] investigated
vapor phase alkylation of toluene with TBA over the
large pore zeolites (Hβ, HY, and HMCM-22). HY
(Si/Al = 80) has strong acidity and lower acid site den-
sity, and also shows high activity in toluene conver-
sion. Sebastian et al. [14] investigated mordenite cata-
lysts with different Si/Al ratios (20, 45, 90) in
tert-butylation of toluene. HM (Si/Al = 90) with
strong acidity but lower acid site density, offered a high
toluene conversion and a better para-selectivity. Sel-
varaj et al. [15] studied highly selective synthesis of
PTBT over Al-MCM-41 with different Si/Al ratios
(21, 42, 62, 83, 104). The conversion of toluene
increased as Si/Al ratios decreased. Kostrab et al. [16]
reported that cerium-modified H-MOR (Si/Al =
10.5) catalyst was effective for tert-butylation of tolu-
ene in the liquid phase. Although cerium-modified H-
MOR decreased the conversion of toluene, an
enhanced and retained constant high para-selectivity
(near 90%) was obtained.
Alkylation is a process that can introduce an alkyl
group into a molecule by substitution or addition [1–
4]. It is very important in chemical production. The
4-tert-butyltoluene (PTBT) is an important interme-
diate for synthesis of 4-tert-butylbenzaldehyde and
4-tert-butylbenzoic acid, which are commercially used
in perfumery production and in the field of plastics
and resins. In industry, PTBT is often produced by
alkylation of toluene with isobutylene using Friedel–
Crafts alkylation catalysts, such as AlCl3, BF3, H2SO4,
HF, H3PO4, etc. [5]. However, these catalysts are dan-
gerous to handle and transport because of their high
toxicity and corrosivity. Therefore, the solid acid cata-
lysts have achieved considerable attention as “green”
and more convenient ones.
Zeolites are of great importance in a wide variety of
industrial catalytic processes. They have unique prop-
erties, such as low corrosivity, high porosity, easy sep-
aration, as well as uniform microporous structure cou-
pled with shape selectivity and thermal stability. Their
catalytic activity has been attributed mostly to the
presence of Brønsted acid sites. Zeolites, such as USY,
Beta, and mordenite, etc. have been used as catalysts
in the liquid phase alkylation process [6–11]. Mravec
In this paper, the alkylation of toluene with TBA is
discussed for the synthesis of PTBT over the HY zeo-
lite with various Si/Al ratios (6.3, 7.5, 11, and 12).
1
The article is published in the original.
2503

2504
YUANYUAN WANG et al.
The desorption experiments were carried out in the
temperature range of 120–600°C at the heating rate of
10 K/min.
2.4. Alkylation Reactions
The alkylation of toluene was carried out in a
0.3 L laboratory autoclave. Toluene (0.1 mol) and
0.3 mol of TBA were mixed with 60 mL of cyclohex-
ane. HY zeolite (1.0 g, 0.01 g/cm3) was further
added to the mixture. The reaction system was
sealed and deaerated with continuous N2 purging
for 30 min. Then the mixture was heated to a
selected temperature. After a certain period of time,
the mixture was cooled down to room temperature,
and the catalyst was removed by filtration. The liq-
uid phase was analyzed on GC-14C gas chromato-
graph equipped with SE-30 capillary column
(0.25 mm × 50 m). The measurement was per-
formed at the initial temperature of 60°C for 3 min,
the ramping rate of 20°C/min, the final tempera-
ture of 220°C for 10 min, with nitrogen as carrier
gas. The conversion of toluene (CToluene) and selec-
tivity of PTBT (SPTBT) were defined as follows:
1 μm
Fig. 1. SEM image of as-prepared HY-12 sample.
SEM, XRD, FT-IR, and NH3-TPD were used to
characterize catalyst properties. The effects of reaction
conditions are investigated in a detail.
2. EXPERIMENTAL
2.1. Materials
NaY zeolites were received from Zeolyst Int. Other
reagents (all of analytical grade) were purchased from
Acros Organics.
CToluene, wt % = fraction of toluene
converted (wt %) × 100,
4-tert-butyltoluene in prod. (wt %)
2.2. Preparation of the Catalysts
SPTBT
=
tert-butyltoluenes (wt %)
× 100%.
∑
A series of HY zeolites with different Si/Al ratios
were prepared from NaY zeolites (Si/Al = 6.3, 7.5, 11,
12) via ion exchange technique. In each case, 1 g of
NaY zeolite was added into 10 mL of NH4NO3 aque-
ous solution (1 mol/L), followed by stirring at 90°C
for 2h. The obtained samples were further filtered,
then dried at 120°C for 12 h. After that, the zeolites
were calcinated at 550°C for another 6 h.
3. RESULTS AND DISCUSSION
3.1. Physiochemical Characterization
The SEM image of HY zeolites with Si/Al ratio of
12 is shown in Fig. 1. We can found that the HY-12
crystals are tiny round-like particles with a diameter of
about 600 nm and a smooth surface.
2.3. Characterization
The microstructures of the HY zeolites were char-
acterized by scanning electron microscopy (SEM,
JSM-6360LA, JEOL). The X-ray diffraction (XRD)
patterns of HY zeolites were recorded on a X-ray dif-
fractometer (D/MAX-III V, Rigaku Co.) equipped
with CuKα radiation in the range of 10° < 2θ < 80°.The
infrared spectra (IR) were measured on a Perkin-
Elmer instrument. Before measurements, the as-pre-
pared samples were degassed at 180°C for 1h. The
acidity of the catalysts was determined by ammonia
temperature programmed desorption (NH3-TPD)
(Chembet-3000 System, Quantachrome, USA). For
NH3-TPD studies, the catalyst was activated in helium
flow for 1h at 550°C. Then the sample was cooled to
Figure 2 shows the XRD patterns of HY zeolites
with different Si/Al ratios. The diffraction peaks of HY
zeolites at 2θ of 15.64°, 18.66°, 20.36°, 23.63°, 27.04°,
30.73°, 31.79°, and 34.05° are corresponding to the
(331), (511), (440), (533), (642), (660), (555), and
(664) planes of Y zeolites, respectively. The character-
istic peaks intensity is strong, indicating that the as-
prepared zeolite samples are highly crystalline.
Typical FT-IR spectra of HY with different Si/Al
ratios are shown in Fig. 3. The observed spectra are
very similar. The absorption bands are observed at
120°C before the adsorption of NH3. Then NH3 1174 cm–1 (external asymmetric symmetric stretching
(10 mL/min) was passed through the sample for 1 h. vibration), 1048 cm–1 (internal asymmetric stretching
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 90
No. 13
2016

INFLUENCE OF nSi/nAl RATIO OF HY ZEOLITE CATALYSTS ON ALKYLATION
2505
vibration), 814 cm–1 (external symmetric stretching
vibration), 591 cm–1 (double six-member ring vibra-
tion), which are characteristic of HY zeolites.
HY-12
HY-11
HY-7.5
HY-6.3
3.2. Acid Сharacterization
The NH3-TPD studies provide valuable informa-
tion on relative acid strength, number and distribu-
tion of acid sites. Figure 4 shows the NH3-TPD pat-
tern of HY zeolites with different Si/Al ratios. All
the catalysts show two desorption peaks. The low
temperature peak is assigned to desorption of
ammonia from weak acid sites, while the high tem-
perature peak corresponds to desorption of ammo-
nia from strong acid sites. The total acidity of zeo-
lites gradually decreases as the Si/Al ratio grows.
This effect is more prominent for the low tempera-
ture peak.
10
15
20
25
30
35
40
45
2θ, deg
50
Fig. 2. XRD patters of HY with different Si/Al ratios.
Si/Al = 12
Si/Al = 11
Si/Al = 7.5
Si/Al = 6.3
3.3. Catalytic Activity Test
3.3.1. Comparison of HY with different Si/Al ratio.
The catalytic performance of HY zeolites with differ-
ent Si/Al ratios in the alkylation of toluene was shown
in Table. The main products were PTBT and 3-tert-
butyltoluene (MTBT). The 2-tert-butyltoluene
(OTBT) was not detected in the final products. This
can be explained by the steric hindrance of methyl
group and the shape-selectivity of specific structure of
HY zeolite. The toluene conversion increased gradu-
ally with the increasing of Si/Al ratio, and the order
was HY-12 > HY-11 > HY-7.5 > HY-6.3 which could
be explained by the change of acidic properties of the
catalysts. Based on the results of NH3-TPD, the acid
amount order was HY-6.3 > HY-7.5 > HY-11 > HY-12.
The stronger acidity of the catalyst promoted the
isomerization and dealkylation reaction, and these
side reactions were the main reason for zeolite deacti-
vation. The similar phenomenon was reported by
Shivanand Pai et al. [13].
591
814
1174
1048
500 1000 1500 2000 2500 3000 3500 4000
ν, cm−1
Fig. 3. FT-IR spectra of catalysts with different Si/Al
ratios.
Intensity, a.u.
12
3.3.2. Effect of catalyst load on alkylation. The
effect of the catalyst load was investigated in the range
from 0.005 to 0.015 g/cm3 using HY-12 catalyst, as
shown in Fig. 5. The conversion of toluene increased
gradually with the increase of catalyst amount at first,
which mainly resulted from the increasing of the
amount of acidic sites. However, when the catalyst
load increased beyond 0.01 g/cm3, more acidic sites on
the surface would accelerate the side reactions.
HY-6.3
10
HY-7.5
8
HY-11
HY-12
6
4
2
0
3.3.3. Effect of TBA/toluene molar ratio on alkyla-
tion. The influence of TBA/toluene molar ratio on
alkylation was shown in Fig. 6. It was found that the
maximum conversion of toluene was obtained at the
TBA/toluene molar ratio of 3 : 1. The excess of TBA
had negative effect on toluene conversion because it
400 500 600 700 800 900 1000
T, K
Fig. 4. NH -TPD patterns of HY catalysts with different
3
Si/Al ratios.
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 90 No. 13 2016

2506
YUANYUAN WANG et al.
The effect of Si/Al ratio of HY on toluene conversion and
product selectivity
3.3.4. Effect of reaction temperature on alkylation.
Figure 7 illustrates the influence of reaction tempera-
ture on conversion and selectivity over HY-12 catalyst.
We could find that the increasing of the temperature
promoted the conversion of toluene and led to a high
selectivity towards PTBT. When the temperature was
180°C, both the conversion of toluene and PTBT
selectivity reached the maximum. Further increase of
the temperature to 200°C resulted in a significant
decrease of conversion and PTBT selectivity. It was
because a higher temperature favored the secondary
reactions.
Si/Al ratio
Products
6.3
7.5
11
12
MTBT
PTBT
Other
5.23
14.15
1.15
6.49
16.85
1.11
7.24
19.68
0.95
7.37
20.09
0.92
Toluene
conversion
SPTBT, %
STBT, %
20.53
24.45
27.87
28.38
68.93
94.40
68.92
95.46
70.61
96.5
70.79
96.76
3.3.5. Effect of reaction time on alkylation. The
effect of reaction time on the tert-butylation of toluene
was shown in Fig. 8. It could be seen that with increas-
ing of the reaction time, the conversion of toluene
increased gradually. However, when the reaction time
facilitated the secondary reactions (oligomerization of
isobutylene), which resulted in the zeolite catalysts
deactivation.
Toluene conv./PTBT sel. (wt %)
100
Toluene conv./PTBT sel. (wt %)
100
90
80
70
90
80
70
PTBT selectivity
60
PTBT selectivity
60
50
40
30
20
10
0
50
40
30
Toluene convension
Toluene convension
20
10
0
0.006
0.009
0.012
0.015
1
2
3
4
5
Catalyst load, g/cm3
n(TBA)/n(toluene)
Fig. 5. The effect of the loading of catalyst on alkylation
over HY-12 catalyst.
Fig. 6. The effect of TBA/toluene molar ratio on alkylation
over HY-12 catalyst.
Toluene conv./PTBT sel. (wt %)
100
90
80
70
Toluene conv./PTBT sel. (wt %)
100
90
80
70
60
50
40
30
20
10
0
60
50
40
30
20
10
0
PTBT selectivity
PTBT selectivity
Toluene convension
Toluene convension
160
170
180
190
200
T, °C
2
3
4
5
6
Reaction time, h
Fig. 7. The effect of temperature on alkylation over HY-12
catalyst.
Fig. 8. The effect of time on alkylation over HY-12 catalyst.
Vol. 90 No. 13 2016
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A

INFLUENCE OF nSi/nAl RATIO OF HY ZEOLITE CATALYSTS ON ALKYLATION
2507
4. J. Jiang, G. Z. Lu, C. X. Miao, X. Wu, W. H. Wu, and
Q. Sun, Microporous Mesoporous Mater. 167, 213
(2013).
was longer than 4 h, the conversion declined. The
same tendency can be found for the PTBT selectivity.
This is mainly because the secondary reactions would
be promoted at longer reaction time.
5. S. Ostrowski and J. C. Dobrowolski, J. Mol. Catal. A:
Chem. 293, 86 (2008).
6. Y. Liu, L. Xu, B. B. Xu, Z. K. Li, L. P. Jia, and
W. H. Guo, J. Mol. Catal. A: Chem. 297, 86(2009).
4. CONCLUSION
7. A. Llanos, L. Melo, F. Avendano, A. Montes, and
The alkylation of toluene with TBA was studied
over HY zeolites with various of Si/Al ratios. The
physical properties of the catalysts were characterized
through SEM, XRD, and FT-IR, and their acidity was
characterized by NH3-TPD. By investigation of the
catalytic performance of HY catalysts, we found that
the catalyst with Si/Al ratio of 12 offered the best cat-
alytic activity. When the alkylation reaction was con-
ducted at 180°C for 4 h using HY-12 as catalyst, the
conversion of toluene and PTBT selectivity reached
40.74 and 70.91%, respectively.
J. L. Brito, Catal. Today 133, 20 (2008).
8. B. Xue, Y. X. Li, and L. J. Deng, Catal. Commun. 10,
1609 (2009).
9. S. Al-Khattaf, S. Rabiu, N. M. Tukur, and R. Alnaizy,
Chem. Eng. J. 139, 622 (2008).
10. W. Alabi, L. Atanda, R. Jermy, and S. Al-Khattaf,
Chem. Eng. J. 195, 276 (2012).
11. K. F. Liu, S. J. Xie, G. L. Xu, Y. N. Li, S. L. Liu, and
L. Y. Xu, Appl. Catal. A: Gen. 383, 102 (2010).
12. D. Mravec, P. Zavadan, and A. Kaszonyi, Appl. Catal.
A: Gen. 257, 49 (2004).
13. S. Pai, U. Gupta, and S. Chilukuri, Appl. Catal. A:
Gen. 265, 109 (2007)
REFERENCES
14. C. P. Sebastian, S. Pai, N. Sharanappa, and
C. V. V. Satyanarayana, Appl. Catal. A: Gen. 223, 305
(2004)
1. X. Z. Liang, Chem. Eng. J. 264, 251 (2015).
2. M. J. Gracia, E. Losada, R. Luque, J. M. Campelo,
D. Luna, J. M. Marinas, and A. A. Romero, Appl.
Catal. A: Gen. 349, 148 (2008).
15. M. Selvaraj, S. H. Jeon, J. Han, P. K. Sinha, and
T. G. Lee, Appl. Catal. A: Gen. 286, 44 (2005).
16. G. Kostrab, D. Mravec, M, Bajus, I. Janotka, Y. Sugi,
S. J. Cho, and J. H. Kim, Appl. Catal. A: Gen. 299, 122
(2006).
3. L. L. Song, Z. R. Li, R. Z. Zhang, L. F. Zhao, and
W. Li, Catal. Commun. 19, 90 (2012).
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 90 No. 13 2016