Selective synthesis of linear alkylbenzene by alkylation of benzene with 1-dodecene over desilicated zeolites

Article abstract of DOI:10.1016/j.cattod.2013.10.015

The alkylation of benzene with 1-dodecene to linear alkylbenzenes (LAB) was investigated over 12-ring zeolites MOR, BEA, and FAU with varying framework topologies and Si/Al ratios. The reaction was carried out under a high-pressure, 20 bar, in a fixed-bed flow reactor at 140 C, using WHSV 4 h^-1, benzene/1-dodecene molar ratio of 6.0 and time-on-stream of 6.0 h. In contrast to MOR and BEA zeolites, FAU exhibited the lowest selectivity (24%) to the desired 2-phenyl dodecane (2-LAB) due to its large cavities. The MOR and BEA with different Si/Al ratios were further desilicated using alkali-metal treatments (0.2 M and 0.05 M NaOH) to create hierarchical porous structure. The desilication of both zeolites improved the conversion of 1-dodecene and the selectivity to 2-LAB. The excellent stability resulting from desilication is attributed to a better diffusivity of the LAB isomers, shortening of real contact time, due to the enhanced mesporous structure in both zeolites and the higher Lewis acidity. The selectivity to 2-LAB increased to 70% over desilicated MOR (Si/Al ratio = 20) compared with a selectivity of 35% over desilicated BEA (Si/Al ratio = 24).

Full text of DOI:10.1016/j.cattod.2013.10.015

Catalysis Today 227 (2014) 187–197
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Selective synthesis of linear alkylbenzene by alkylation of benzene
with 1-dodecene over desilicated zeolites
a
a
a
a
Waqas Aslam , M. Abdul Bari Siddiqui , B. Rabindran Jermy , Abdullah Aitani ,
a,b
a,∗
ˇ
Ji rˇ í Cejka , Sulaiman Al-Khattaf
Center of Research Excellence in Petroleum Refining & Petrochemicals, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia
J. Heyrovsk y´ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Dolej sˇ kova 3, 182 23 Prague 8, Czech Republic
a
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 June 2013
Received in revised form
The alkylation of benzene with 1-dodecene to linear alkylbenzenes (LAB) was investigated over 12-ring
zeolites MOR, BEA, and FAU with varying framework topologies and Si/Al ratios. The reaction was carried
◦
−1
out under a high-pressure, 20 bar, in a fixed-bed flow reactor at 140 C, using WHSV 4 h , benzene/1-
dodecene molar ratio of 6.0 and time-on-stream of 6.0 h. In contrast to MOR and BEA zeolites, FAU
exhibited the lowest selectivity (24%) to the desired 2-phenyl dodecane (2-LAB) due to its large cavities.
The MOR and BEA with different Si/Al ratios were further desilicated using alkali-metal treatments (0.2 M
and 0.05 M NaOH) to create hierarchical porous structure. The desilication of both zeolites improved the
conversion of 1-dodecene and the selectivity to 2-LAB. The excellent stability resulting from desilication
is attributed to a better diffusivity of the LAB isomers, shortening of real contact time, due to the enhanced
mesporous structure in both zeolites and the higher Lewis acidity. The selectivity to 2-LAB increased to
70% over desilicated MOR (Si/Al ratio = 20) compared with a selectivity of 35% over desilicated BEA (Si/Al
ratio = 24).
3
0 September 2013
Accepted 3 October 2013
Available online 29 October 2013
Keywords:
Zeolites
Benzene alkylation
Long-chain olefin
MOR
BEA
Desilication
©
2013 Elsevier B.V. All rights reserved.
1
. Introduction
dealkylation, olefin isomerization and oligomerization reactions
that co-produce heavy alkenes and other undesired coke precur-
sor products. The oligomerization of 1-olefins, although usually
insignificant, occurs simultaneously with the main alkylation reac-
tion. Depending on the type of catalyst and olefin used, the reaction
Linear alkylbenzenes (LAB) with appropriate chain length are
predominantly used as synthetic detergent intermediates for the
manufacture of LAB sulfonate (LAS), which replaced dodecylben-
zenes in the 1960s. LAS is a synthetic surfactant that quickly and
completely biodegrades and does not cause any environmental
problems. Among six LAB isomers, 2-phenyl dodecane (2-LAB) is
the most desirable product for the detergent industry [1]. Cur-
rently, most of the 3.6 million tons/year of LABs is produced
using homogenous liquid phase catalysts such as hydrofluoric
◦
is conducted at temperatures less than 150 C to minimize skeletal
isomerization of olefins and to maintain high product linearity [3].
There are ongoing efforts to develop more active and stable
solid acid catalysts for LAB synthesis with major emphasis on
zeolites using either batch or flow reactors [4,5]. However, solid
acids have significantly lower activities than homogeneous ones,
although they provide improved reaction selectivity. The product
selectivity to 2-LAB over non-zeolite acid catalysts does not exceed
50% and catalysts are subjected to fast deactivation and difficult
regeneration. Zeolites with relatively small channels such as MFI
showed a low activity for benzene alkylation and poor selectivity
to LAB isomers because they easily deactivate by coking [2]. Among
large-pore zeolites investigated, zeolites with three-dimensional
topology such as FAU, MOR and BEA received the most attention
[6–11]. The difference in the selectivity to LAB isomers over vari-
ous zeolites was attributed to the product shape selectivity due to
the zeolite pore structures and the relative rate constant of isomer-
ization vs. alkylation of 1-dodecene [5]. The open pore structure of
the dealuminated FAU appears suitable for the production of LAB
isomers but it is not selective to 2-LAB.
acid (HF) or aluminum chloride (AlCl ) [2]. Unfortunately, these
3
catalysts have major disadvantages related to environmental pol-
lution, equipment corrosion, and separation problems. To avoid
these drawbacks, the detergent industry looks for environmentally
friendly processes, in particular utilizing solid acid catalysts. UOP
and Cepsa developed the DETAL process for solid bed alkylation
commercialized in 1995 [1,2].
Benzene alkylation with linear C10–C13 olefins to LAB, which is
a mixture of C10–C13 alkylbenzenes, is performed at a high ben-
zene/olefin ratio to suppress side reactions such as polyalkylation,
∗ Corresponding author. Tel.: +966 13 860 1429.
E-mail addresses: skhattaf@kfupm.edu.sa, cejka@jh-inst.cas.cz (S. Al-Khattaf).
0
920-5861/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.cattod.2013.10.015

1
88
W. Aslam et al. / Catalysis Today 227 (2014) 187–197
Table 1
List of parent and desilicated zeolites used in LAB alkylation reaction.
Zeolite sample
Pore structure
Sample code
Descriptiona
Si/Al molar ratio
Ultra-stable Y
Beta
3D, 7.4 A˚
3D, 7.3 × 6.5 and 5.6 × 5.6 A˚
FAU
BEA-24
DBEA-24
BEA-40
DBEA-40
MOR-18
DMOR-18
MOR-40
DMOR-40
MOR-180
Parent zeolite from Tosoh
Parent BEA from Tosoh
Desilicated BEA-24, treated with 0.05 M NaOH solution for 1 h at 100 C
Parent BEA from Tricat
Desilicated BEA-40, treated with 0.2 M NaOH solution for 0.5 h at 60 C
Parent MOR from Tosoh
Desilicated MOR-18, treated with 0.2 M NaOH solution for 0.5 h at 60 C
Parent MOR from J. Heyrovsk y´ Institute of Physical Chemistry
Desilicated MOR-40 treated with 0.2 M NaOH solution for 0.5 h at 60 C
Parent MOR from Tosoh
8
29
26
38
29
19
18
40
◦
◦
Mordenite
2D, 7 × 6.5 and 5.7 × 2.6 A˚
◦
◦
36
180
a
◦
◦
All zeolites were calcined at 650 C for 3 h (3 C/min).
HF-modified MOR [12] and steam-treated MOR [13] have
been investigated with varying successes. The improved behav-
ior of the steam-treated MOR was attributed to its lower acid
site concentration and less hydrophilic surface [13]. Tsai et al.
showed that LAB production over MOR is an exothermic reac-
tion, in which thermodynamic equilibrium was favorable at low
temperature, approaching 100% conversion at 227 C [14]. Using
a steam-pretreated MOR, the selectivity to 2-LAB exceeded the
thermodynamic equilibrium composition being higher than over
2. Experimental
2.1. Chemicals and catalysts
The parent zeolites used in this study included commercially
available zeolites with varying Si/Al molar ratio: two NH4-BEA
(BEA-24, BEA-40), two H-MOR (MOR-18, MOR-40, MOR-180) and
one USY zeolite (Si/Al = 8). The H-BEA was obtained by calcination
◦
◦
of NH4-BEA at 650 C for 3 h. Table 1 presents descriptions of the
catalysts such as zeolite FAU and AlCl . Compared with FAU zeo-
parent zeolites, their pre-treatment procedures and Si/Al ratio.
GC grade LAB isomers (used for quantitative analysis) and
laboratory grade benzene and 1-dodecene (used as feeds) were
purchased from Sigma–Aldrich.
3
lite, dealuminated MOR exhibited the selectivity to 2-LAB above
◦
7
0% at the reaction temperature of 200 C and at benzene/1-
hexadecene molar ratio equal to 8.6 [11]. Desilication of MOR
was found to improve catalytic stability in kinetic test up to 80 h
as compared with dealumination or metal impregnation for an
octadiene containing dodecene feed [15]. An optimum alkylation
catalyst was obtained by the desilication of MOR under mild con-
ditions (0.4 M NaOH) affording 100% conversion of 1-dodecene and
selectivity of 98% to LAB of which 2-LAB isomer selectivity was
around 78%.
2.2. Desilication procedures
The parent BEA and MOR zeolites were desilicated to prepare
mesoporous zeolites. Table 1 presents a description of the desili-
cated zeolites and their treatment procedures. The desilicated BEA
(DBEA-40) and desilicated MOR (DMOR-18, DMOR-40) were pre-
pared by treating the parent zeolites with a NaOH solution of 0.2 M
Zeolite BEA showed lower conversion and selectivity to 2-LAB
compared with MOR [17–19]. The lifetime of fluorinated BEA cat-
alysts depended on the specific surface area and pore volume
rather than strong Lewis acidity. At a fluorine content of 0.5%,
the lifetime of BEA zeolite increased from 23 to 32 h at maximum
BET area and pore volume [17]. Higher 1-dodecene conversion
◦
at 60 C for 0.5 h. The solid was then further ion exchanged with a
◦
0.1 M NH4Cl solution at 60 C for 4 h. The desilicated BEA (DBEA-
24) was prepared by slurrying the zeolite sample (5 g) in 350 ml
◦
of 0.05 M NaOH solution at 60 C for 1 h. The zeolite/alkali slurry
was immediately quenched in ice bath to stop further reaction, fil-
tered, dried and ion exchanged. All the ion-exchanged zeolites were
◦
was reported at 180 C for zeolite BEA with the lowest Si/Al ratio
12.5) [19]. At a higher Si/Al ratio, a greater portion of Lewis
◦
◦
(
calcined at 650 C for 3 h at a heating rate of 3 C/min.
acid sites initialized undesired side reactions like dimerization
or oligomerization of 1-olefins resulting in catalyst deactivation.
Zeolite MTW [5,20] showed low activity while MWW modified
with 0.5 wt% phosphorus showed improved selectivity to 2-LAB
2.3. Catalyst characterization
The elemental analysis for Si and Al was measured using ICP
Optical Emission Spectrometer, Ultima 2, Horiba Scientific. 50 mg
catalyst sample was fused with 300 mg of Lithium metaborate in
(
52%) and increased catalytic stability for more than 33 h of
T-O-S [21].
Introducing mesopores into zeolites by alkaline treatment
desilication) can improve zeolite stability against coking by
enhancing the diffusivity of products and oligomer by-products
22,23]. Groen et al. demonstrated the effectiveness of desilication
◦
a muffle furnace at 950 C for 15 min. The fused product was dis-
(
solved in 20 ml of 4% HNO . The solution was further diluted with
3
deionized water to make a total volume of 50 ml. The X-ray powder
diffraction (XRD) was recorded on a Rigaku Miniflex II X-ray diffrac-
tomer using nickel filtered Cu K␣ radiation at 40 kV and 30 mA.
SEM images were taken on a Nova NanoSEM FEI with an accel-
erating voltage of 30 kV.
[
in making hierarchically structured micro-mesoporous MOR and
BEA zeolites for improved transport properties of feed and product
in benzene alkylation with ethylene [24,25]. Tsai and co-workers
reported improved catalytic activity and diffusion properties of
modified MOR for the LAB alkylation reaction and the transalky-
lation of heavy alkylbenzenes [15,26]. Similar results were also
reported for mesoporous MFI zeolites prepared using carbon black
pearls with microwave synthesis [27].
The surface area of the catalysts was measured using a Quanta-
chrome NOVA 1200 gas sorption analyzer by the adsorption of
◦
nitrogen at −196 C according to ASTM D3663 standard method.
Prior to nitrogen adsorption, the catalyst was evacuated for 2 h
◦
at 350 C. Micropore volume, Vmicro, was determined using t-plot
Nevertheless, there are no systematic studies of the stabilization
effect of mesoporous structure of zeolites on benzene alkylation
with long-chain olefins. Therefore, in this study, zeolites BEA and
MOR with different Si/Al ratios are modified by desilication aim-
ing to improve their catalytic performance in alkylation of benzene
with 1-dodecene.
method. The mesopore volume, Vmeso was estimated by subtracting
micropore volume, Vmicro, from the total pore volume, Vtot.
The acidic properties of the zeolites were measured using a
Nicolet 6700 FTIR spectrophotometer (Thermo Scientific) equipped
with a high temperature vacuum chamber using pyridine as a
probe. The zeolite sample (50 mg) was pressed and placed in a

W. Aslam et al. / Catalysis Today 227 (2014) 187–197
189
◦
sample holder for pretreatment at 550 C under vacuum for 1 h. The
◦
sample was then cooled to 100 C and the spectrum was recorded.
The physically adsorbed pyridine was removed by heating the sam-
◦
−5
ple at 150 C under vacuum (10 mbar) for 40 min. The removed
material was cooled to room temperature and then the spectrum
was recorded again. The concentrations of Brønsted and Lewis acid
sites were determined using the extinction coefficients from Ref.
[
28].
Temperature-programmed desorption (TPD) of ammonia was
performed in BEL-CAT-A-200, chemisorption apparatus consisting
of a gas mixing unit allowing both continuous and pulsed reactant
dosing, U-tube quartz micro-reactor with a thermocouple placed
inside the sample, and a thermal conductivity detector (TCD). The
◦
sample (50 mg) was pretreated in a flow of He (50 mL/min) at 500 C
for 1 h. Then the sample was exposed to He/NH mixture (95/5 vol%)
3
at room temperature for 30 min. TPD was performed in He flow
◦
(
50 mL/min) at a heating rate of 10 C/min, and the desorbed NH3
was monitored by a TCD detector.
2.4. Catalytic reaction
Fig. 1. LAB isomers formation in the alkylation of benzene with 1-dodecene [29].
Benzene alkylation reaction with 1-dodecene was performed
using a continuous flow fixed bed BTRS-Jr Laboratory Reactor Sys-
tem (Autoclave Engineers). A stainless steel reactor tube of 30 cm
length and 10 mm ID was operated in a down flow mode and
its effluents were passed through a gas-liquid separator. Catalyst
powder was pressed into a tablet, crushed and sieved to obtain
uniform size of particles in the range of 16–20 mesh. One gram
of catalyst was placed at the center of the reactor tube supported
by alumina spheres and glass wool. The reactor was pressurized
DBEA-40
up to 20 bar with N and heated in N2 flow of 50 ml/min up to
2
BEA-40
◦
◦
1
40 C at a rate of 10 C per minute. The feed mixture consisted
of benzene and 1-dodecene at a molar ratio of 6:1 with feed pre-
heaters kept at 140 C (reactant to catalyst weight ratio 10:1). The
◦
DBEA-24
BEA-24
reaction was performed for 6 h time-on-stream (T-O-S) and liq-
uid samples were collected at intervals of 0.5 to 1 h. An off-line gas
chromatograph-mass spectrometer (GS-MS Agilent 5890) was used
to identify the components of the reaction products. Quantitative
analysis of products was done in a GC (Agilent 7890A) equipped
with a flame ionization detector. A 30 m capillary column (Agilent
HP-5) with 0.32 mm ID was used to separate the product compo-
nents. Helium was used as carrier gas and the injector was operated
in split mode with a split ratio of 100:1. The main reaction prod-
ucts of benzene alkylation with 1-dodecene are 2–6 LAB (Fig. 1) and
dodecene isomers [29]. 1-LAB isomer was not detected due to its
very low equilibrium concentration [30].
DMOR-40
MOR-40
DMOR-18
MOR-18
0
10
20
30
40
50
60
70
2
Theta
Conversion of 1-dodecene and LAB selectivity were determined
as follows:
Fig. 2. X-ray diffraction patterns of parent and desilicated MOR (MOR-18, MOR-40,
DMOR-18, DMOR-40) and BEA (BEA-24, BEA-40, DBEA-24, DBEA-40).
•
•
1-Dodecene conversion = (Nd0 − N )/N × 100, where Nd0 is
d
d0
number of moles of 1-dodecene before reaction, and N is number
d
of moles of 1-dodecene after reaction.
(BEA-24, BEA-40 DBEA-24, DBEA-40) are shown in Fig. 2. The XRD
LAB selectivity (SLAB) = N /N × 100, where N is number of moles
t
l
l
patterns remain unchanged as for the position of individual diffrac-
tion lines while the intensity of some of them decreased as a result
of desilication.
of LAB in the final products and Nt is sum of moles of all products
including all dodecene isomers (1–6-dodecenes) and LAB isomers
(
2–6-phenyldodecanes) [4].
Fig. 3 shows the nitrogen adsorption–desorption isotherms for
selected zeolite samples (as for textural characteristics, see Table 2).
The desilicated MOR (DMOR-40) and BEA (DBEA-40) showed a Type
IV isotherm with enhanced hysteresis loop compared with par-
ent samples. Desilicated samples exhibited an increase in the BET
area accompanied by a significant increase in the mesopore volume
(Table 2). This phenomenon can be attributed to the formation for
mesopores at the expense of micropores [31]. The BET area and total
pore volume results show that FAU zeolite has the highest BET area
3
. Results and discussion
3
.1. Characterization results
The results of ICP-OES chemical analyses (Si/Al ratio), BET areas
and concentrations of acid sites in parent and desilicated zeolites
are presented in Tables 1 and 2. The XRD patterns of the parent
and desilicated MOR (MOR-18, MOR-40, DMOR-18, DMOR-40), BEA
2
3
(533 m /g) and total pore volume (0.41 cm /g).

1
90
W. Aslam et al. / Catalysis Today 227 (2014) 187–197
Table 2
Chemical, physical and acidic properties of parent and desilicated zeolites.
Zeolite
N2 adsorption characteristics
Acidity, pyridine (mmol/g)
Acidity TPD NH3 (mmol/g)
0.33
2
SBET (m /g)
Vmeso (cc/g)
Vmicro (cc/g)
Vtot (cc/g)
B
–
L
B/L
–
USY
Beta
533
0.21
0.20
0.41
–
BEA-24
DBEA-24
BEA-40
DBEA-40
Mordenite
MOR-18
DMOR-18
MOR-40
428
470
436
441
0.20
0.24
–
0.15
0.14
0.18
0.06
0.35
0.38
0.18
0.34
0.29
0.20
0.24
0.19
0.06
0.48
0.11
0.14
4.83
0.47
0.57
0.34
0.36
0.42
2.18
1.36
0.28
264
350
302
362
514
0.04
0.11
0.07
0.29
0.05
0.15
0.11
0.14
0.12
0.24
0.19
0.22
0.21
0.41
0.29
0.93
0.20
0.26
0.18
0.05
0.07
0.14
0.13
0.28
0.22
13.28
1.43
2.00
0.64
0.23
0.54
0.38
0.21
0.14
0.04
DMOR-40
MOR-180
SBET: BET specific surface area; Vmicro: micropore volume; Vmeso: mesopore volume; Vtot: total pore volume.
L: Lewis acidity; B: Brønsted acidity.
Fig. 4A and B shows the IR absorption bands of hydroxyl stretch-
ing vibrations of both parent and desilicated zeolites MOR and
BEA under study recorded at room temperature after activation
at 400 C (A) and after adsorption of pyridine at 100 C (B). Parent
and desilicated MOR zeolites showed distinctly two characteristic
parent zeolites, the concentration of Lewis acid sites increased
whereas the concentration of Brønsted acid sites decreased after
alkaline-treatment (Table 2). Holm et al. reported that upon zeolite
treatment with NaOH strong Lewis acid sites are generated, pre-
sumably from dislodged framework aluminum [36]. It indicates the
increase in the concentration of Lewis acid sites after desilication,
which is further confirmed from the presence of absorption band
◦
◦
−
1
−1
absorption bands around 3740 cm and 3610 cm due to termi-
nal silanols (Si OH) and bridging hydroxyl group associated with
Brønsted acid sites, respectively [32]. For parent MOR (MOR-18),
−
1
in the region of Al OH group around ∼3673 cm (Fig. 4).
The results of ammonia TPD of parent and desilicated zeolites
are presented in Fig. 4C and Table 2. All samples showed two
−1
the peak at 3611 cm corresponding to Brønsted acid sites was
sharp and highly distinct compared with other zeolites. The impact
of desilication is clearly reflected on the desilicated MOR sam-
ples (DMOR-18 and DMOR-40), where absorption band of Brønsted
acid peak (3615 cm ) is almost disappeared. In addition, for both
catalysts, formation of extra-framework aluminum species was
◦
desorption peaks in the temperature range of 130–600 C corre-
sponding to the weakly adsorbed ammonia (mainly physisorption)
and ammonia adsorbed on strong acid sites. The amount of des-
orbed NH3 was calculated from the high-temperature peak. Tian
et al. concluded that the acidity of zeolites is not only affected
by the framework Si/Al ratio but it is also related to the coordi-
nation and distribution of framework Si and Al sites [37]. Some
decrease in the concentration of strong acid sites with tempera-
−1
−1
observed at 3673 cm [33]. In contrast with desilicated DMOR-18,
DMOR-40 showed an apparent increase in the intensity of silanol
bands indicating the formation of new isolated silanols groups asso-
ciated with the formation of mesopores [34]. In the case of zeolite
−
1
◦
BEA (Fig. 4B), the peak at 3620 cm was very weak and broader
compared with MOR zeolites. The presence of such broad peak
indicates a wide distribution of acid sites [35]. Apparently, the dif-
ference in the intensity of silanol groups after desilication clearly
indicates the formation of mesopores.
ture maximum around 400 C is observed for desilicated DMOR-18
and DMOR-40. The observed changes of the concentrations of acid
sites may be attributed to the occurrence of framework dealumi-
nation [38]. In the case of desilicated beta (DBEA-24 and DBEA-40),
only a little change in the concentration of strong acid sites was
observed. This trend shows the possibility of some non-framework
aluminum reinsertion into the framework upon desilication [39] or
that desilication did not proceed in so large extent as for MOR.
The results of field emission-scanning electron microscopy (FE-
SEM) images with energy-dispersive X-ray (EDX) spectroscopy
analysis of parent and desilicated zeolites are presented in Fig. 5. In
general, desilication of zeolites BEA and MOR originally with Si/Al
Pyridine FTIR adsorption was used to characterize acidity of
all zeolites studied. Fig. 4B shows the FTIR spectra of pyridine
adsorbed for parent and desilicated MOR measured after evacu-
◦
ation at 150 C. Adsorption of pyridine resulted in the formation
of new absorption bands at 1545 (Brønsted) and 1454 (Lewis
−
1
acid sites) cm , respectively. The B/L ratios calculated from the
IR absorbance intensities are shown in Table 2. Compared with
Fig. 3. Nitrogen adsorption (᭹, ꢀ) and desorption (ꢀ, ꢁ) isotherms of selected parent and desilicated samples: (a) BEA-40, (b) DBEA-40, (c) MOR-40, and (d) DMOR-40.

W. Aslam et al. / Catalysis Today 227 (2014) 187–197
191
SiOH
Brθnsted
Lewis
(
A)
(B)
(d) DBEA-24
Al-OH
(c) BEA-24
SiOHAl
(b) DMOR-18
(a) MOR-18
3900
3800
3700
3600
3500
3400 1650
1600
1550
1500
1450
1400
-1
-1
Wave number (cm )
Wave number (cm )
(
C)
(d)
(
c)
(b)
(a)
100
200
300
400
o
500
600
Temperature ( C)
Fig. 4. FTIR spectra of parent zeolites: (A) prior to pyridine adsorption, (B) after pyridine adsorption (a) MOR-18, (b) MOR-40, red line: spectra of activated samples, black
◦
line: spectra after 20 min desorption at 150 C. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
ratios in the range 20–50 retains the morphology of parent zeo-
lites. Similarly, in the present study, the morphological difference
between parent and desilicated samples is less apparent. How-
ever, an agglomeration among the desilicated samples is seen. The
observed characteristics are similar to those reported for desili-
cated BEA zeolite [24].
On the other hand, the performance of MOR-18 showed that
1-dodecene conversion and selectivity to LAB isomers were both
above 92% (Table 3). The selectivity to 2-LAB (68%) and the 2-
LAB/3–5 LAB ratio (2.7) were the highest compared with FAU and
BEA-24. At longer T-O-S, MOR-18 showed a gradual deactivation, as
shown in Fig. 6A, which is probably due to the smaller MOR-18 pore
diameter compared with BEA-24 and FAU (Table 1). During the 6 h
T-O-S, the selectivities to total LAB, 2-LAB, and dodecene isomers
for the three zeolites were constant regardless of any change in
3.2. Benzene alkylation over parent zeolites
1
-dodecene conversion.
Fig. 6 and Table 3 present the catalytic performances of the par-
Conversion of 1-dodecene over three parent zeolites decreased
ent FAU, BEA-24 and MOR-18 in terms of 1-dodecene conversion,
stability, and selectivity to LAB isomers.
in the order of: FAU > MOR-18 > BEA-24 with a constant selectiv-
ity to 2-LAB during 6 h of T-O-S. The difference in the selectivity
to 2-LAB over the three zeolites is influenced by the ability of
the individual zeolite active sites in promoting benzene alkyl-
ation versus isomerization of 1-dodecene (Table 3 and Fig. 6).
Compared with FAU, MOR-18 selectively formed 2-LAB (68.1%),
whereas the selectivity to 3–6 LAB isomers was 71.1% over FAU
due to its three-dimensional network of large cavities and open-
ings [5,40]. Moreover, the alkylation of benzene to LAB over zeolite
catalysts involves the interaction of 1-dodecene with strong acid
sites to form 2-dodecylcarbenium ion which undergoes a rapid
rearrangement followed by the attack of benzene ring by alkyl-
carbenium to form LAB isomers [26,41]. Both Brønsted and Lewis
acid sites are considered as active species in this reaction [42].
To further elucidate the performance of MOR-18 in a wide range
of 1-dodecene conversion, benzene alkylation experiments were
The FAU zeolite exhibited the highest 1-dodecene conversion
(
97%) and the highest selectivity to LAB isomers (97%) compared
with MOR-18 (93%) and BEA-24 (60%). Moreover, FAU was the most
stable catalyst with constant conversion and selectivity to LAB iso-
mers during the 6 h of time-on-stream (T-O-S), Fig. 6. Selectivity to
the desired 2-LAB over FAU zeolite was 26% and the 2-LAB/3–6 LAB
ratio was 0.4 (Table 3). High selectivity to 3–6 LAB isomers may be
attributed to FAU large pore opening of 7.4 A˚ permitting an easy
access and diffusion of dodecene into the super-cages of 12.4 A˚ .
Zeolite BEA-24 exhibited a rapid deactivation; 1-dodecene con-
version dropped from 73% to 45% at 6 h of T-O-S (Fig. 6). The
selectivity to 2-LAB was less than 24% and the 2-LAB/3–6 LAB iso-
mers ratio was 0.7. The selectivity to dodecene isomers was the
highest over BEA-24 (39%) as compared with FAU (2%) and MOR-
1
8 (6%). The drop in 1-dodecene conversion with T-O-S for BEA-24
is primarily due to its lower concentration of Brønsted acid sites
0.29 mmol/g), cf. Table 2.
◦
−1
performed at 100 C and WHSV between 5 and 40 h using dif-
ferent catalyst weights. Fig. 7 shows the increase in 1-dodecene
(

1
92
W. Aslam et al. / Catalysis Today 227 (2014) 187–197
Fig. 5. FE-SEM images of parent and desilicated samples: (a) BEA-24, (b) DBEA-24, (c) BEA-40, (d) DBEA-40, (e) MOR-18, (f) DMOR-18, (g) MOR-40, and (h) DMOR-40. All the
samples shown here are measured at 5 ␮m.
conversion from 25% to 86% with decreasing WHSV accompanied
by a significant decrease in the selectivity to 1-dodecene (from 80%
to 27%). As shown in Fig. 7, the selectivity to 2-LAB did not decrease
with increasing 1-dodecene conversion but kept constant at about
nearly constant over MOR-18 (90%) and MOR-180 (99%). After 1 h
of T-O-S, the selectivity to 2-LAB was 68% over MOR-18 compared
with 54% over MOR-180 and 34% over MOR-40. The selectivity to
dodecene isomers over MOR-40 (38%) was the highest, indicating
high isomerization activity compared with MOR-18 and MOR-180.
The behavior of MOR-18 and MOR-40 may be attributed to the
differences in the acidity characteristics of these two MOR sam-
ples (Table 2). MOR-18 exhibited higher concentration of Brønsted
acid sites compared with MOR-40, which may explain high selec-
tivity to dodecene isomers over MOR-40. However, diffusion of
bulky reactants and products could be easier for MOR with less
active sites [11,40]. With increasing Si/Al ratio in MOR zeolite, the
concentration of Lewis acid sites increased resulting in the sharp
decrease in the selectivity to LAB isomers for MOR-180 compared
8
6%.
3.3. Effect of Si/Al ratio
In the case of parent MOR samples with varying Si/Al ratios
(
MOR-18, MOR-40, MOR-180), the conversion of 1-dodecene and
the selectivities to LAB versus T-O-S are presented in Fig. 8. There
was no clear trend on the effect of Si/Al ratio on the behavior of
MOR samples. While the conversion of 1-dodecene over MOR-40
gradually decreased from 77% to 60% during the 6 h of T-O-S, it was
Table 3
◦
−1
Catalytic performance of parent zeolites for benzene alkylation at 140 C, 20 bar, WHSV = 4 h , benzene: 1-dodecene molar ratio = 6, 1 h T-O-S.
Parameter
Beta
Mordenite
USY
96.6
BEA-24
72.6
BEA-40
81.8
MOR-18
92.0
MOR-40
77.4
MOR-180
96.8
1
-Dodecene conversion (%)
Product selectivity (%)
Dodecene isomers
LAB isomers
2.0
96.7
1.3
39.2
59.7
1.1
25.4
74.6
0.0
5.7
93.4
0.9
37.9
58.5
3.6
1.6
19.2
28.0
>
C12 HC
LAB isomer selectivity (%)
2
3
2
-LAB
–6 LAB
-LAB/3–6 LAB
25.7
71.1
0.4
23.6
36.1
0.7
30.8
43.8
0.7
68.1
25.3
2.7
33.8
24.7
1.4
53.7
16.7
3.2

W. Aslam et al. / Catalysis Today 227 (2014) 187–197
193
1
00
100
8
6
4
2
0
0
0
0
0
80
60
40
20
(C)
0
(
A)
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
T-O-S, h
T-O-S, h
1
00
100
80
60
40
20
0
8
6
4
2
0
0
0
0
0
(
D)
(
B)
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
T-O-S, h
T-O-S, h
◦
Fig. 6. Catalytic performance of parent zeolites (
FAU, BEA-24, MOR-18) for 1-dodecene conversion and selectivities to LAB, 2-LAB and dodecene isomers at 140 C,
−1
2
0 bar, WHSV = 4 h , benzene: 1-dodecene molar ratio = 6.
1
00
100
80
60
40
20
0
with the other zeolite catalysts (Table 3). This was associated with
increased amount of heavier hydrocarbons (>C12 HC) due to the
dimerization–polymerization reaction [19].
The effect of Si/Al ratio on the benzene alkylation was studied
using zeolites BEA-24, BEA-40, MOR-18, MOR-40, and MOR-180
as a function of T-O-S (Table 3 and Fig. 8). The conversion of
80
60
40
20
0
1
-dodecene and the selectivities to LAB and 2-LAB for both BEA cat-
alysts (BEA-24, BEA-40) decreased sharply with T-O-S. After 1.0 h
of T-O-S, 1-dodecene conversion was 73% for BEA-24 compared
with 82% for BEA-40. The selectivity to LAB was 60% over BEA-24
compared with 75% over BEA-40 and the selectivity to 2-LAB was
2
4% and 31%, respectively. The selectivity to undesired dodecene
isomers decreased from 39.2% over BEA-24 to 25.4% over BEA-40.
Although BEA-40 possesses a lower concentration of Brønsted acid
sites compared with BEA-24 (Table 2), the number of its Lewis
acid sites was higher than for BEA-24. As such, the selectivity to
dodecene isomers over BEA-40 was lower (25.4%) compared with
BEA-24 (39.2%) resulting in higher selectivity to LAB isomers over
BEA-40.
0
20
40
60
80
100
1
-Dodecene conversion, %
Fig. 7. Selectivity to 2-LAB and 1-dodecene versus 1-dodecene conversion for MOR-
◦
−1
1
O-S.
8 at 100 C, 20 bar, WHSV = 5–40 h , benzene: 1-dodecene molar ratio = 6, 1 h T-

1
94
W. Aslam et al. / Catalysis Today 227 (2014) 187–197
1
00
1
00
8
0
8
6
4
2
0
0
0
0
0
60
40
20
0
(
A)
(
B)
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
T-O-S, h
T-O-S, h
1
00
100
8
6
4
2
0
0
0
0
0
8
6
4
2
0
0
0
0
0
(
D)
(
C)
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
T-O-S, h
T-O-S, h
Fig. 8. Catalytic performance of parent MOR with different Si/Al ratios ( MOR-18; MOR-40;
dodecene isomers at 140 C, 20 bar, WHSV = 4 h , benzene: 1-dodecene molar ratio = 6.
MOR-180) for 1-dodecene conversion and selectivities to LAB, 2-LAB and
◦
−1
3
.4. Effect of zeolite desilication
activity. Desilicated DBEA-24 showed a remarkable increase in the
selectivity to 2-LAB from 24% (parent BEA-24) to 35% associated
with a sharp drop in the selectivity to dodecene isomers (from
39% to 2%). This increase in 1-dodecene conversion and decrease in
the selectivity to dodecene isomers over desilicated DBEA-24 may
be attributed to the presence of a higher amount of mesopores in
DBEA-24. Similar trend of improved 1-dodecene conversion and
selectivity to LAB was observed for BEA-40. The improvement of 1-
dodecene conversion and LAB selectivity with T-O-S for desilicated
DBEA-40 was more pronounced than the improvement of BEA-24
as shown in Fig. 9. This improvement may be attributed to the pres-
ence of mesopores decreasing the real contact time, suppressing as
the result the formation of coke precursors and subsequent catalyst
deactivation.
Desilication of MOR-18 and MOR-40 resulted in the increase
in the 1-dodecene conversion and 2-LAB selectivity, accompanied
by significant decrease in the deactivation of MOR-40. 1-Dodecene
conversion for both DMOR-18 and DMOR-40 was around 99%
after 6 h of T-O-S (Fig. 10). Desilicated DMOR-40 showed a sig-
nificant increase in the selectivity to 2-LAB from 34% (parent
The conversion of 1-dodecene and product selectivity charac-
teristics of parent and desilicated BEA (BEA-24, BEA-40, DBEA-24,
DBEA-40) and MOR (MOR-18, MOR-40, DMOR-18, DMOR-40) as a
function of T-O-S are presented in Figs. 9 and 10 and Table 4. As
discussed earlier, alkali-treatment increased the concentration of
Lewis acid sites whereas the concentration of Brønsted acid sites
decreased (Table 2).
As alkylation is catalyzed by moderate acid sites, higher LAB
selectivity in desilicated BEA and MOR zeolites may be attributed to
the inhibition of 1-dodecene isomerization. Table 2 shows that the
desilication of BEA zeolites resulted in an increase in the concentra-
tion of Lewis acid sites and mesopore volume with a corresponding
decrease in both the amount of Brønsted acid sites and micropore
volume [24]. The conversion of 1-dodecene over parent zeolite
BEA-24 (73%) increased significantly to 98% after desilication to
DBEA-24. Selectivity to LABs for BEA-24 increased from 60% to 97%
for DBEA-24 while the selectivity to dodecene isomers decreased
from 39% to 2% indicating a significant drop in isomerization

W. Aslam et al. / Catalysis Today 227 (2014) 187–197
195
1
00
100
8
6
4
2
0
0
0
0
0
80
60
40
20
(
A)
(B)
0
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
T-O-S, h
T-O-S, h
5
4
3
2
1
0
0
0
0
0
0
5
4
3
2
1
0
0
0
0
0
0
(D)
(
C)
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
T-O-S, h
T-O-S, h
Fig. 9. Catalytic performance of parent and desilicated BEA ( BEA-24; DBEA-24; BEA-40; DBEA-40) for 1-dodecene conversion and selectivities to LAB, 2-LAB and
◦
−1
dodecene isomers at 140 C, 20 bar, WHSV = 4 h , benzene: 1-dodecene molar ratio = 6.
MOR-40) to 60% associated with a drop in the selectivity to
dodecene isomers (from 38% to <2%). The significant increase in
Positive effect of desilication over both BEA and MOR sam-
ples as for conversion and selectivity in benzene alkylation
with 1-dodecene can be related to the changes of particu-
larly textural properties of desilicated zeolites. The increase
in both conversion and selectivity can be related to the
increase in the mesopore volume and expectedly in the external
surface area. We expect that alkylation can proceed at a higher
1
-dodecene conversion and decrease in the selectivity to dodecene
isomers over desilicated DMOR-40 may be attributed to a short-
ening of the real contact time due to desilication, which is
3
related to higher mesopore volume of DMOR-40 being 0.29 cm /g)
[
15,16].
Table 4
◦
−1
Catalytic performance of parent and desilicated zeolites for benzene alkylation at 140 C, 20 bar, WHSV = 4 h , benzene: 1-dodecene molar ratio = 6, 1 h T-O-S.
Parameter
Beta
Mordenite
BEA-24
72.6
DBEA-24
98.4
BEA-40
81.8
DBEA-40
98.3
MOR-18
92.0
DMOR-18
98.9
MOR-40
77.4
DMOR-40
98.8
1
-Dodecene conversion (%)
Product selectivity (%)
Dodecene isomers
LAB isomers
39.2
59.7
1.1
2.1
97.1
0.8
25.4
74.6
0.0
2.9
97.1
0.0
5.7
93.4
0.9
0.0
97.8
2.2
37.9
58.5
3.6
1.8
88.2
10.0
>
C12 HC
LAB isomer selectivity (%)
2
3
2
-LAB
–6 LAB
-LAB/3–6 LAB
23.6
36.1
0.7
35.2
61.9
0.6
30.8
43.8
0.7
39.3
57.8
0.7
68.1
25.3
2.7
70.0
27.8
2.5
33.8
24.7
1.4
59.6
28.6
2.1

1
96
W. Aslam et al. / Catalysis Today 227 (2014) 187–197
1
00
100
8
6
4
2
0
0
0
0
0
80
60
40
20
(
A)
(B)
0
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
T-O-S, h
T-O-S,, h
1
00
100
8
6
4
2
0
0
0
0
0
80
60
40
20
0
(D)
(
C)
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
T-O-S,, h
T-O-S,, h
Fig. 10. Catalytic performance of parent and desilicated MOR ( MOR-18; DMOR-18; MOR-40; DMOR-40) for 1-dodecene conversion and selectivities to LAB, 2-LAB
◦
−1
and dodecene isomers at 140 C, 20 bar, WHSV = 4 h , benzene: 1-dodecene molar ratio = 6.
reaction rate on the external surface of desilicated zeolites, increas-
ing thus the rate of the reaction. With respect to the selectivity to
to dodecene isomers and MOR favored the formation of
2-LAB.
2
-dodecyl benzene, the real contact time is decreased, as a result
2. The effect of varying Si/Al ratio revealed that catalytic per-
formance is improved (higher 1-dodecene conversion and
selectivity to LAB) with increasing Si/Al ratios for BEA-40 while
for MOR, a better performance was observed with decreasing
Si/Al ratio (MOR-18).
the primary alkylation product is not transformed to other iso-
mers. In addition, the alkylation reactions proceeds now mainly
on the external surface, limiting the accessibility of 1-dodecene
to be adsorbed and isomerized (note that benzene to 1-dodecene
ratio = 6:1).
3. The desilication of BEA and MOR zeolites by alkali treatment
improved activity and selectivity to 2-LAB due higher con-
centration of Lewis acid centers and diffusion behavior in the
micro-meso hierarchical structure. The selectivity to dodecene
isomers significantly dropped down in all desilicated zeolites
indicating a lower isomerization activity. Desilicated DMOR-18
exhibited the highest 1-dodecene conversion compared with the
other desilicated zeolites. Selectivity to LAB was almost 100%,
and the selectivity to 2-LAB was 70% at 99% 1-dodecene conver-
sion. However, the enhancement in the catalytic performance
of desilicated BEA was higher than that of desilicated MOR in
terms of 1-dodecene conversion and 2-LAB selectivity. This may
be attributed to the difference in mesoporosity between these
zeolites.
4
. Conclusions
The main conclusions of the study can be summarized as fol-
lows:
1
. Conversion of 1-dodecene and the selectivities to 2-LAB over
zeolites FAU, BEA, MOR and their desilicated analogs are con-
trolled by zeolite pore structure. FAU zeolite exhibited the
highest conversion, simultaneously with the lowest selectiv-
ity to 2-LAB due to its three-dimensional channel system
with large cavities. Zeolite BEA showed the highest selectivity

W. Aslam et al. / Catalysis Today 227 (2014) 187–197
197
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