Synthesis of novel polymer as solid acid-base catalyst for styrene from toluene

Article abstract of DOI:10.1134/S1070427214090316

A novel solid acid-base catalyst Cat-NH₂C₂H₄NH₂ with aluminum and nitrogen was prepared from phenol and formaldehyde by using triblock copolymer Pluronic F127 as a template and resol as a catalyst precursor via

Full text of DOI:10.1134/S1070427214090316

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2014, Vol. 87, No. 9, pp. 1371−1376. © Pleiades Publishing, Ltd., 2014.
BRIEF
COMMUNICATIONS
Synthesis of Novel Polymer as Solid Acid-Base
*
Catalyst for Styrene from Toluene
a,b
b
b
Yueli Wen , Bin Wang , and Wei Huang
a
College of Environmental Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, Shanxi, China
b
Key Laboratory of Coal Science and Technology of Ministry of Education and Shanxi Province,
Taiyuan University of Technology, Taiyuan 030024, Shanxi, China
e-mail: huangwei@tyut.edu.cn
Received September 10, 2014
Abstract—A novel solid acid-base catalyst Cat-NH C H NH with aluminum and nitrogen was prepared from
2
2
4
2
phenol and formaldehyde by using triblock copolymer Pluronic F127 as a template and resol as a catalyst
precursor via evaporation induced organic–organic assembly method. The catalyst was characterized by Fourier
transform infrared spectroscopy (FTIR) and X-ray photoelectron spectra (XPS). The acid-base properties of the
catalyst were determined by temperature programmed desorption (TPD) using CO and NH as probe molecules.
2
3
The side chain alkylation of toluene with methanol over the catalysts had been studied. The results showed that
Cat-NH C H NH has demonstrated the higher activity and selectivity than the conventional alkali exchanged
2
2
4
2
zeolites. This may be because that the weak or middle acid-base pairs on the catalyst are favored to bimolecular
side-chain alkylation reaction.
DOI: 10.1134/S1070427214090316
A novel solid acid-base catalyst Cat-NH C H NH
2
molecule is industrially produced by two subsequent
reactions: the alkylation of benzene with ethylene
to produce ethylbenzene and its dehydrogenation to
styrene. There is a potentially interesting alternative
route for production of styrene, which involves the
direct side-chain alkylation of toluene with methanol.
The side-chain alkylation of toluene with methanol over
base catalysts has been known for several decades [1].
Although base catalysts such as MgO and CaO were
successfully used for side-chain alkylation [2], alkali-
exchanged zeolites have demonstrated the highest
activities [(ethylbenzene + styrene) yield is about 20%]
and selectivities (styrene selectivity is about 10%) for
side-chain alkylation of toluene with methanol [3–5].
More specifically, basic zeolites such as Cs–X, Rb–X and
Cs–Y give side-chain alkylation [1], and the selectivity
to styrene can be improved by adding B, P, Cu or Ag to
the basic zeolite [6–8]. Also, small quantities of alkali-
hydroxide particles entrapped within the alfa cavities of
faujasite, strongly increase the alkylation in the side-chain
of alkyl aromatics [9–11].
2
2
4
with aluminum and nitrogen was prepared from phenol
and formaldehyde by using triblock copolymer Pluronic
F127 as a template and resol as a catalyst precursor via
evaporation induced organic–organic assembly method.
The catalyst was characterized by Fourier transform
infrared spectroscopy (FTIR) and X-ray photoelectron
spectra (XPS). The acid-base properties of the catalyst
were determined by temperature programmed desorption
(
TPD) using CO and NH as probe molecules. The
2 3
side chain alkylation of toluene with methanol over
the catalysts had been studied. The results showed that
Cat-NH C H NH has demonstrated the higher activity
2
2
4
2
and selectivity than the conventional alkali exchanged
zeolites. This may be because that the weak or middle
acid-base pairs on the catalyst are favored to bimolecular
side-chain alkylation reaction.
INTRODUCTION
Styrene is an industrially important chemical that
is used for production of plastics and rubbers. This
The side-chain alkylation of toluene with methanol
over base catalysts has been known for several decades
*
The text was submitted by the authors in English.
[
12]. Acid sites catalyze preferentially ring alkylation
1
371

1372
YUELI WEN et al.
reactions, but surface acidity is also necessary to catalyze
side-chain alkylation via combined acid–base pathways.
Abase site activates the methyl group of toluene, whereas
the acid site interacts with the aromatic ring. Thus, it has
been suggested that the side-chain alkylation of toluene
with methanol requires a cooperative action of acid/base
pairs for efficiently promoting the rate-limiting step in the
reaction mechanism [13–15].
a dropping funnel and a thermometer. 10 mL of forma-
lin (37 wt % formaldehyde) and 8 mL of concentrated
hydrochloric acid were added, following the addition of
6.8 g of the powders calcined under stirring condition.
The temperature was risen to 65°C.After the reaction run
for 9 h, the reaction was ended and finally dried under
vacuum at 100°C for 5 h.
Amination reaction. The chloromethylated powders
In an attempt to improve activities and selectivities
of catalyst for the alkylation of toluene with methanol,
a novel solid acid-base catalyst with aluminum and
nitrogen is prepared from phenol and formaldehyde by
using triblock copolymer Pluronic F127 as a template
and resol as a carbon precursor via evaporation induced
organic–organic assembly method.
were mixed with 30 mL of ethanol under stirring, then
5
2
8
mL of 1,2-diaminoethane was added dropwise below
5°C. The mixture was heated with stirring at 45°C for
h, followed by heating in an oven at 100°C for 3 h.The
final product was designated as Cat-NH C H NH and
2
2
4
2
shown in Fig. 1.
Catalyst Characterization
EXPERIMENTAL
Catalysts Preparation
The FTIR spectra are obtained on a Bio-Rad FTS-
0A spectrometer with KBr dispersion method. X-ray
6
Synthesis of resol. Resol was prepared from phenol
and formaldehyde in a base-catalyzed process. 6.1 g of
phenol was melted at 40°C in a flask and mixed with 20 mL
of ethanol under stirring.After 10 min, 10.5 mLof formalin
37 wt % formaldehyde) was added dropwise below 50°C.
Upon further stirring for 2 h at 75°C, the mixture was
cooled to room temperature. The pH was adjusted with
photoelectron spectra were acquired on an ESCALAB
50 spectrometer (VG ScientificLtd.,UK) equippedwi-
than AlK (hν =1486.6 eV). NH -TPD and CO -TPD
2
α
3
2
experiment were performed on a TP-5000 instrument.
The catalysts adsorbed NH or CO at 323 K until satu-
(
3
2
ration and purged with helium for 30 min to remove the
physisorbed NH or CO . The TPD data were collected
3
2
0
.6 M HCl solution until it reached a value of 7.0.
in flow helium from 323 to 1073 K at a heating rate of
Synthesis of Aluminum Phenolic Resinate. Alu-
–1
1
0 K min .
minum phenolic resinate was prepared from aluminum
and resol. 6.1 g of phenol was melted at 40°C in a three
necked flask and mixed with 250 mL of polydimethylsi-
loxane under stirring. Then 5.8 g of aluminum and 44 g of
prepared resol were added. The mixture was heated with
stirring at 180°C for 3 h. After the mixture was cooled
and filtered, the filter cake was collected.
Catalytic Test
The gas phase alkylation of toluene with methanol was
carried out in a fixed-bed tubular reactor at 1 atm. Cata-
lysts were sieved to retain particles with 0.35–0.42 mm
diameter for catalytic measurements and treated under
nitrogen at 450°C for 2 h before reaction in order to
remove H O, hydrocarbons, and CO . A liquid mixture
Organic–organic assembly. After filtering the sol-
ids obtained were crushed into powders. 1.0 g of F127
was dissolved in 20.0 mL methanol. The solid powders
prepared were added. After stirring for 2 h, the mixture
was poured into dishes to evaporate methanol at room
temperature for 10 h, followed by heating in an oven at
2
2
of toluene and methanol having a 5 : 1 molar ratio was
–1
pumped at a rate of 1.0–2.0 mL h and vaporized into a
flowing nitrogen stream that bypassed the reactor. After
flow rates and temperatures were stabilized, the reactant
stream of nitrogen and organics (5 : 1 molar ratio of N to
1
00°C for 5 h.
2
Calcination. Calcination was carried out in a tubular
organics) was fed to the reactor. The reaction was carried
out at 400°C, employing a space velocity (WHSV) of 2
h . The reaction products (toluene, methanol, styrene,
3
–1
furnace under a nitrogen with a flow rate of 30 cm min
–
1
at 600°C. The heating rate was 1°C min .
–1
Chloromethylation reaction. The chloromethylation
reaction was carried out in a fournecked flask of 250 mL
of equipped with a mechanical stirrer, a reflux condenser,
and ethylbenzene) were analyzed by on-line gas chro-
matography using a 0.53 mm × 50 m capillary column
HP-FFAPconnected to a flame ionization detector (FID).
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 9 2014

SYNTHESIS OF NOVEL POLYMER
1373
n
*
OH
HO
*
*
Al
HCHO
*
n
n
O
*
O
Al
O
*
*
*
n
n
*
n
n
Cl
Cl
*
F127
HCHO, HCl
O
O
Al
O
*
Assembly
Calcination
Chloromethylation
*
*
n
n
*
n
Cl
n
*
NH2
H
N
NH
H N
*
2
NH C H NH
2
2
2
4
O
O
Al
O
*
Amination
*
*
n
n
*
n
HN
NH2
Fig. 1. Scheme for the preparation of Cat-NH C H NH .
2
2
4
2
A Porapak Q (80/100 mesh) mesh, 10 ft, stainless steel
packed column connected to a thermal conductivity de-
tector (TCD) was used to analyze for carbon monoxide
and carbon dioxide. Reaction was maintained during 8 h
RESULTS AND DISCUSSION
Catalyst Characterization
(
time on stream). Catalytic results are calculated with
IR. The IR spectra of resol, aluminum phenolic resin-
ate, calcination, chloromethylation and amination (Cat-
NH C H NH ) are shown in Fig. 2. The aromatic ring
the products analysis obtained after reaching catalyst
stabilization.
2
2
4
2
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 9 2014

1374
YUELI WEN et al.
e
d
c
b
a
Wavelength, cm–1
Fig. 2. Infrared spectra of samples. (a) resol; (b) aluminum phenolic resinate; (c) calcination; (d) chloromethylation; (e) amination.
stretching absorptions (C=C) can be seen at 1388, 1464
formation of the Al–O–C complex [16, 17]. The binding
energy of Cat-NH C H NH depressed from 74.63 to
–1
and 1620 cm . The asymmetric and symmetric stretches
2
2
4
2
–1
in these curves are observed at about 2872 and 2959 cm ,
respectively. The C–O (phenol) stretch is observed at
74.43 eV, which indicates the complexation between
phenolic groups and Al. That is, the forms of aluminum
in Cat-NH C H NH molecules are Al–(O–Ph) .
–1
about 1035 cm . The Al–O stretch due to aromatic ring
2
2
4
2
3
–
1
appears at about 670 and 1050 cm . The absorptions at
The peaks located at 398.50 and 400.51 eV corre-
sponding to different nitrogen species are observed from
XPS spectra of Cat-NH C H NH (Fig. 4). The peaks at
–
1
1
120~1185 cm show O–H stretch. The peak at 935~905
–
1
cm correspond to C–Cl (benzyl) stretch.
2
2
4
2
XPS. The binding energies of Al 2p and N 1s in Cat-
398.50 eV most likely correspond to the formation of
NH C H NH are shown in Figs. 3 and 4, respectively.
primary amine (–NH ) [18]. The peaks at about 400.51 eV
2
2
4
2
2
The major peak (Fig. 3) component at the binding energy
of Cat-NH C H NH 74.63 eV has been assigned to the
is distributed to attributed to secondary amine (–NH–)
nitrogen [19–23].
2
2
4
2
Binding energy, eV
Binding energy, eV
Fig. 3. XPS of Al 2p of Cat-NH C H NH .
Fig. 4. XPS of N 1s of Cat-NH C H NH .
2
2
4
2
2
2
4
2
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 9 2014

SYNTHESIS OF NOVEL POLYMER
1375
a
b
a
b
Fig. 5. NH -TPD of Cat-NH C H NH . (a) after reaction;
Fig. 6. CO -TPD of Cat-NH C H NH . (a) after reaction;
3
2
2
4
2
2
2
2
4
2
(b) before reaction.
(b) before reaction.
Catalytic Reaction
Figure 6 shows the CO -TPD of Cat-NH C H NH
2 2 2 4 2
before and after reactions. It is very similar to the NH3-
TPD, so it can be concluded that the weak or middle
(< 500°C) acid and base sites are required for side-chain
alkylation of toluene with methanol.
The table summarizes the reactivity results for
the reference zeolite-based catalyst in [3] and Cat-
NH C H NH . The results show clearly that the styrene
2
2
4
2
selectivity of Cat-NH C H NH is much higher than the
2
2
4
2
reference zeolite-based catalyst.
CONCLUSIONS
The acidities of the catalystsbe before and after
reactions are shown in Fig. 5 by the NH -TPD profiles.
The novel solid acid-base catalyst Cat-NH2C2H4NH2
could be synthesized successfully, and characterized
by FTIR and XPS. The styrene selectivity of Cat-
3
The density of weak and middle (< 500°C) acid sites on
the catalysts decreases and that of strong acid sites (about
50°C) increases, which leading to the decrease of the
NH C H NH is much higher than the conventional
6
2
2
4
2
zeolite-based catalyst. From the activity and selectivity
of Cat-NH C H NH , CO , and NH -TPD, it can be
reactivity and styrene selectivity of Cat-NH C H NH .
2
2
4
2
That is the weak or middle (< 500°C) acid sites are
beneficial to side-chain alkylation of toluene with
methanol.
2
2
4
2
2
3
concluded the weak or middle (< 500°C) acid and base
sites are required for side-chain alkylation of toluene
with methanol.
Catalytic performance comparing the reference zeolite-based
a
catalyst and the catalysts
ACKNOWLEDGMENTS
Catalytic
performances
Reference,
%
Cat-NHC H NH ,
2 4 2
The authors gratefully acknowledge the financial
support of this study by the Qualified Personal Foundation
of Tayuan University of Technology (No. tyutr c-201338a
and 201359a), and the Youth Foundation of Tayuan
University of Technology (no. 2013Z023).
%
Reaction time, h
MET conversion
TOL conversion
EB selectivity
1
8
70.8
23.2
80.2
8.8
73.4
21.3
8.9
71.2
19.1
9.1
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81.2
26.4
80.9
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a
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