Selective synthesis of p-ethylphenol by gas-phase alkylation of phenol with ethanol

Article abstract of DOI:10.1016/j.apcata.2014.08.016

The selective synthesis of p-ethylphenol from gas-phase alkylation of phenol with ethanol was studied on zeolites HZSM5 and HMCM22 at 523 K. Phenol reacted directly with ethanol to form ethylphenylether by O-alkylation, and p- and o-ethylphenol isomers by C-alkylation; secondary products were m-ethylphenol and dialkylated compounds. Both zeolites presented similar activity and formed low amounts of ethylphenylether and dialkylated products, but exhibited different ethylphenol isomers distribution. In fact, for a contact time of 99.3gh/mol the selectivity to p-ethylphenol was 51.4% on HMCM22 and only 14.2% on HZSM5. The superior performance of zeolite HMCM22 for selectively producing p-ethylphenol was due to its narrower pore channels that suppressed the formation of dialkylated products and hampered by diffusional constraints the formation of o-ethylphenol. The maximum p-ethylphenol yield obtained on HMCM22 was 41% at a contact time of 250gh/mol; for higher contact times, p-ethylphenol was increasingly converted to m-ethylphenol. All the samples deactivated on stream because of coke formation. The carbon amount built on HMCM22 diminished when contact time was increased thereby indicating that coke was mainly formed from the reactants. Additional catalytic runs showed that phenol was the main responsible of catalyst deactivation, probably because of its strong adsorption on surface active sites.

Full text of DOI:10.1016/j.apcata.2014.08.016

Applied Catalysis A: General 486 (2014) 77–84
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Selective synthesis of p-ethylphenol by gas-phase alkylation of phenol
with ethanol
∗
M.E. Sad, H.A. Duarte, C.L. Padró, C.R. Apesteguía
Catalysis Science and Engineering Research Group (GICIC), INCAPE – (UNL-CONICET), Santiago del Estero 2654, 3000 Santa Fe, Argentina
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 May 2014
Received in revised form 12 August 2014
Accepted 18 August 2014
Available online 29 August 2014
The selective synthesis of p-ethylphenol from gas-phase alkylation of phenol with ethanol was studied on
zeolites HZSM5 and HMCM22 at 523 K. Phenol reacted directly with ethanol to form ethylphenylether by
O-alkylation, and p- and o-ethylphenol isomers by C-alkylation; secondary products were m-ethylphenol
and dialkylated compounds. Both zeolites presented similar activity and formed low amounts of
ethylphenylether and dialkylated products, but exhibited different ethylphenol isomers distribution. In
fact, for a contact time of 99.3 g h/mol the selectivity to p-ethylphenol was 51.4% on HMCM22 and only
Keywords:
1
4.2% on HZSM5. The superior performance of zeolite HMCM22 for selectively producing p-ethylphenol
p-Ethylphenol
Ethylphenols
Alkylation
Phenol
was due to its narrower pore channels that suppressed the formation of dialkylated products and ham-
pered by diffusional constraints the formation of o-ethylphenol. The maximum p-ethylphenol yield
obtained on HMCM22 was 41% at a contact time of 250 g h/mol; for higher contact times, p-ethylphenol
was increasingly converted to m-ethylphenol. All the samples deactivated on stream because of coke
formation. The carbon amount built on HMCM22 diminished when contact time was increased thereby
indicating that coke was mainly formed from the reactants. Additional catalytic runs showed that phenol
was the main responsible of catalyst deactivation, probably because of its strong adsorption on surface
active sites.
Acid zeolites
©
2014 Elsevier B.V. All rights reserved.
1
. Introduction
distillation. The development of a novel technology using solid cat-
alysts able to selectively promote the formation of p-EP is therefore
highly desirable.
Ethylphenols are used in the production of phenolic resins,
antioxidants and in the varnish industry. ortho-Ethylphenol (o-EP)
and meta-ethylphenol (m-EP) are starting materials for photo-
chemicals while para-ethylphenol (p-EP) is employed for obtaining
Few studies about ethylation of phenol on solid catalysts are
found in literature and most of them deal with the synthesis of o-
EP. Aluminum orthophosphate-alumina and BPO4 catalysts were
tested in alkylation of phenol with ethanol at 573–733 K and a mix-
ture of O-alkylation and C-alkylation products was obtained [3,4].
Bal and Sivasanker [5] used different alkali-loaded fumed silicas
with the aim of selectively producing O-alkylation products; they
reported 100% of selectivity to ethylphenylether (EPE) for phenol
4
-vinylphenol, an intermediate in the synthesis of pharmaceuticals,
dyes, and various antioxidants that are used in the manufacture
of rubbers and polymers [1,2]. In particular, p-EP is convention-
ally prepared by sulfonation of ethylbenzene and subsequent alkali
fusion of the p-ethylbenzene sulfonic acid obtained [2]. However
this multistep process presents serious environmental concerns
because of the use of strong liquid acids and sodium hydroxide at
high temperatures, which cause corrosion of equipment, formation
of significant amounts of sodium sulfite as byproduct and waste
disposal problems. Furthermore, the boiling points of ethylphe-
nol isomers are so close that it is impractical to separate them by
conversions ranged from 10 to 63%. Iron catalysts such as Fe O4
3
showed a very high selectivity to o-EP (97–99%) for phenol con-
version of 86% at 653 K [6] whereas on CoAl-MCM-41 the o-EP
selectivity was 80% for 40% phenol conversion at the same tem-
perature [7]. Bezouhanova et al. [8] studied the phenol ethylation
reaction on zeolites HZSM5 and Ti-HZSM5 and reported that the
formation of o-EP was predominant at 573 K but at higher temper-
atures (623–723 K) the ethylphenols mixture contained mainly p-
and m-EP isomers. Das and Halgeri [9] investigated the alkylation
of phenol with ethanol on zeolites ZSM5 of different Si/Al ratios
at 673 K with the aim of promoting the selective formation of p-
EP; however, in all the cases, the p-EP yield was lower than 10%.
∗ Corresponding author. Tel.: +54 3424555279.
E-mail addresses: capesteg@fiq.unl.edu.ar, capesteg@gmail.com
(
C.R. Apesteguía).
URL: http://www.fiq.unl.edu.ar/gicic (C.R. Apesteguía).
http://dx.doi.org/10.1016/j.apcata.2014.08.016
926-860X/© 2014 Elsevier B.V. All rights reserved.
0

7
8
M.E. Sad et al. / Applied Catalysis A: General 486 (2014) 77–84
Yamagishi et al. [10] disclaimed another approach to selectively
produce p-EP on crystalline aluminosilicates by using ethylene and
phenol as reactants but the highest p-EP yield obtained was 8.5%
for temperatures between 573 and 873 K.
products. Samples (30–50 mg) were heated at 10 K/min from 298 K
to 1073 K. The evolved CO was converted into methane in a fixed
2
bed reactor containing a methanation catalyst (Ni/kieselguhr) at
673 K. Then, methane was analyzed using a flame ionization detec-
tor (gas chromatograph: SRI 8610C).
In this paper we studied the gas-phase ethylation of phenol at
5
23 K over zeolites HZSM5 and HMCM22 with the aim of improv-
ing the selective synthesis of p-EP. We selected these two zeolites
for performing our studies because in previous works on phe-
nol methylation over acid zeolites we observed that HZSM5 and
HMCM22 are potentially effective for promoting by shape selec-
tivity the formation of the para-isomer [11,12]. Also, we decided
to carry out our catalytic runs at a mild temperature taken into
account that the production of m-EP, the most thermodynamically
stable isomer, is favored at higher temperatures. Results will show
that at 523 K and contact time of 250 g mol/h, the p-EP yield on
zeolite HMCM22 was 41% that is significantly higher than the best
values reported in literature.
2
.3. Catalyst testing
The alkylation of phenol (Merck, >99%) with ethanol (Merck,
9.8%) in gas phase was carried out in a fixed bed tubular reac-
9
tor at 523 K and 101.3 kPa in continuous flow of N . Samples
2
(particles with 0.35–0.42 mm diameter) were pretreated in situ,
3
at 723 K in air flow (90 cm /min) for 2 h before reaction. Liquid
reactants (ethanol (E) and phenol (P), E/P = 1:1 molar) were fed
using a syringe pump and vaporized at 473 K in N2 (75 cm /min).
Catalytic experiments were performed at different contact times
3
0
P
(W/F ), between 24.8 and 300 g h/mol. Samples were collected
every 20 min during 3 h. Reactant and product concentrations
were measured by gas chromatography using an Agilent 6850
chromatograph equipped with a 30-m HP-Chiral capillary column
2
. Experimental
(
inner diameter: 0.32 mm, film thickness: 0.5 ␮m) connected to
2
.1. Catalyst preparation
a flame ionization detector. Phenol (XP) and ethanol (XE) conver-
sions were calculated as: XP,E = (Y
Y
0
− YP,E)/Y0 where YP and
0
Commercial zeolite HZSM5 (Zeocat Pentasil PZ-2/54, Si/Al = 20,
.43% Na) was calcined at 723 K in dry air flow (60 cm /min)
P,E
P,E
3
0
E
0
are the molar fractions of phenol and ethanol at the entrance
during 3 h before use. Zeolite HMCM22 was synthesized accord-
ing to [13], by using sodium aluminate (Alfa Aesar, Technical
Grade), silica (Aerosil Degussa 380), sodium hydroxide (Merck,
of the reactor while YP and YE are the molar fractions of phenol
and ethanol at the exit. Main products of the phenol ethylation
reaction were p-EP, m-EP, o-EP and EPE; two other minor chro-
matographic peaks were also detected, probably corresponding to
dialkylated ethylphenols that are named here as DAP. In order to
perform carbon balance calculations, we used as chromatographic
response factor for these two compounds the average response
factor determined experimentally for 2,4 and 2,6 xylenols in a pre-
vious work [12]. The selectivity to product i formed from phenol
>99%), hexamethyleneimine (Aldrich, 99%) and deionized water
as reagents. The molar composition of the synthesis gel was
SiO /Al O = 30, OH/SiO = 0.18, hexamethyleneimine/SiO = 0.35
2
2
3
2
2
and H O/SiO = 45. The gel was stirred at 423 K in a Teflon lined
2
2
stainless steel autoclave. After crystallization, the solid was recov-
ered by centrifugation, washed thoroughly with distilled water,
3
dried at 373 K and finally calcined at 773 K in dry air (60 cm /min).
(S , mol of product i/mol of phenol reacted) was determined as:
i
S = [Y /ꢁY ] where Y is the molar fraction of products formed from
i
i
i
i
phenol. Diethylether and ethylene formed from ethanol were also
detected. Selectivities to these products (mol of diethylether or
2.2. Catalyst characterization
ethylene/mol of ethanol reacted) were determined as: S
=
diethylether
The crystal structure of HMCM22 was determined by pow-
der X-ray diffraction methods (XRD) using a Shimadzu XD-D1
Ydiethylether ∗ 2/(Y E0 − YE) and S
= Yethylene/(YE − YE) where
0
ethylene
Ydiethylether and Y
are the molar fractions of both products
ethylene
diffractometer and Ni-filtered CuK␣ radiation. XRD patterns were
◦
◦
at the exit of the reactor.
recorded in the 2ꢀ range from 2 to 45 . Total surface areas (SBET)
and sample porosities were measured by N2 physisorption at its
normal boiling point in an Autosorb Quantochrome Instrument
3. Results and discussion
1
-C sorptometer. The zeolite micropore volumes were deter-
mined using the adsorption branch of nitrogen isotherms by both
Dubinin–Radushkevich [14] and t-plot [15] methods. The t-plot was
obtained by using de Harkins–Jura Eq. [16]. The external surface
areas (Se), were obtained from the slopes of the t-plot lines. Before
adsorption, samples were treated under vacuum at 623 K for 8 h.
The nature, density and strength of surface acid sites were deter-
mined by infrared spectroscopy (IR) in a Shimadzu FTIR Prestige-21
spectrophotometer using pyridine as probe molecule. Samples
were ground to a fine powder and pressed into wafers (10–30 mg).
The discs were mounted in a quartz sample holder and transferred
to an inverted T-shaped Pyrex cell equipped with CaF2 windows.
Samples were initially outgassed in vacuum at 723 K during 2 h and
then a background spectrum was recorded after being cooled down
to room temperature. Spectra were recorded at room temperature,
after admission of pyridine, and sequential evacuation at 298, 423,
and 573 K.
3.1. Catalyst characterization
The physical and textural properties of the samples are pre-
sented in Table 1. BET surface areas of HZSM5 and HMCM22
2
were similar (350–400 m /g) as well as the corresponding exter-
2
nal surface areas (about 70 m /g). The zeolite micropore volumes
(<20 A˚ ) were determined analyzing the adsorption branch of nitro-
gen isotherms by both Dubinin–Radushkevich and t-plot methods.
Although the values obtained by Dubinin–Radushkevich method
were slightly higher than those determined from t-plots (Table 1),
both methods revealed that the micropore volume of HMCM22
was higher than that of HZSM5. In the case of zeolite HMCM22,
it was observed two linear ranges in t-plot (not shown here). The
first linear range did not pass by the origin which indicated the
presence of ultramicropores (<6 A˚ ), most likely the zeolite micropo-
res (4.0 × 5.5 A˚ and 4.0 × 5.0 A˚ ). Therefore, we also determined the
3
Coke formed on the catalysts during reaction was measured by
temperature programmed oxidation (TPO) using a 2% O /N molar
ultramicropore volume of HMCM22 (0.10 cm /g). The pore volume
determined here for HMCM22 is consistent with values reported
in literature. For example, the micropore volumes determined by
Rigoreau et al. [17] and by Juttu and Lobo [18] using t-plots were
2
2
stream. After reaction, the samples were maintained at the reaction
temperature in N flow 1 h before to perform the TPO experiment,
2
3
in order to eliminate weakly adsorbed molecules of reactants or
0.193 and 0.2 cm /g, respectively. In particular, the micropore and

M.E. Sad et al. / Applied Catalysis A: General 486 (2014) 77–84
79
Table 1
Textural properties of the catalysts.
2
˚
Catalysts
SBET (m /g)
Pore size (A)
t-Plot method
Dubinin–Radushkevich
method
3
Micropore volumen (cm /g)
Ultramicropore
volume (cm /g)
External surface
area, Se (m /g)
Micropore
volumen (cm /g)
3
2
3
HZSM5
HMCM22
350
400
5.1 × 5.5; 5.3 × 5.6
4.0 × 5.5; 4.1 × 5.1
0.155
0.169
–
0.10
73
68
0.18
0.21
OCH CH3
2
HMCM22-573K
10
OH
n
Ethylphenylether
tio
la
(EPE)
OH
ky
al
O-
HMCM22-423K
OH
C-
Phenol (P)
+
alky
CH CH
2 3
HZSM5-573K
HZSM5-423K
la
tio
n
Dialkylated
products
(DAP)
CH CH OH
3
2
Ethanol (E)
p-Ethylphenol
p-EP)
o-Ethylphenol
(o-EP)
(
CH CH3
2
1
700
1650
1600
1550
1500
1450
1400
OH
Wavenumber (cm-1
)
m-Ethylphenol
m-EP)
Fig. 1. FTIR spectra of pyridine adsorbed at 298 K and evacuated at 423 K and 573 K
on zeolites HMCM22 and HZSM5.
(
CH CH3
2
Scheme 1. Reaction network for the alkylation of phenol with ethanol.
ultramicropore volumes reported by Meloni et al. [19] for a zeolite
3
HMCM22 were 0.195 and 0.137 cm /g, respectively.
The nature and strength of surface acid sites were determined
from the IR spectra of adsorbed pyridine after admission at 298 K
and sequential evacuation at 423 and 573 K (Fig. 1). The relative
contributions of Lewis (L) and Brønsted (B) acid sites were obtained
by deconvolution and integration of pyridine absorption bands at
3.2. Catalytic tests
3.2.1. Alkylation of phenol with ethanol: catalyst activity
The gas-phase phenol ethylation was carried out on HZSM5 and
HMCM22 at 523 K using an equimolar reactant ratio and identi-
cal contact time. Fig. 2 shows the evolution of phenol and ethanol
−1
−1
−1
around 1540 cm and between 1440 cm and 1460 cm , respec-
tively [20–23]; results are presented in Table 2. Fig. 1 shows that the
conversions (XP, XE) and selectivities (S ) as a function of time on
i
−1
1
440–1460 cm band in the IR spectrum obtained on HZSM5 after
stream. Main products from phenol ethylation were ortho, meta and
para ethylphenols (EP) formed by C-alkylation of phenol, EPE (O-
alkylation of phenol) and dialkylated products (diethyphenols and
ethyl–ethylphenyl ether). Diethylether, ethylene and C3+ alkenes
formed from ethanol conversion reactions were also detected.
Results obtained in previous works [12,24] for phenol methyla-
tion allow us to propose the reaction network of Scheme 1 for
the ethylation of phenol on solid acids. Phenol can initially react
with ethanol via two parallel alkylation reactions to form primary
products: by O-alkylation phenol is transformed to EPE and by C-
alkylation yields directly o-EP and p-EP. Then EPE may be converted
to ethylphenols while isomerization of o-EP and p-EP leads to the
formation of m-EP. Finally, ethylphenols can react with ethanol to
produce dialkylated products.
evacuation at 423 K was split in two overlapping peaks correspond-
−1
−1
ing to pyridine adsorbed on Al (1455 cm ) and Na (1445 cm )
Lewis acid sites. The total amount of surface acid sites determined
on HZSM5 after evacuation at 423 K was similar to that on HMCM22
(Table 2). Nevertheless, the acid site distribution was different; in
fact, the B/L ratio on HMCM22 was three times higher than on
HZSM5. In order to evaluate the acid site strength, we compared
the amounts of pyridine remaining on the catalyst surface following
evacuations at 423 and 573 K. From data of Table 2 we determined
that the Py-573 K/Py-423 K ratio (i.e. the ratio of total amounts
of pyridine remaining on the sample after evacuation at 573 K
and 423 K) was 0.77 and 0.65 on HMCM22 and HZSM5, respec-
tively. These results showing that significant amounts of pyridine
remain adsorbed on the catalyst surface after evacuation at 573 K,
revealed that both zeolites contain strong acid sites. On the other
hand, the B/L ratio determined on HZSM5 after evacuation at 423 K
Fig. 2 shows that the initial phenol and ethanol conversions
were similar on HZSM5 and HMCM22 (X P0 = 40%, X = 100%). As
∼
0
E
expected, ethanol conversion was higher than phenol conversion
because ethanol not only reacts with phenol but also is consumed
in parallel dehydration/condensation reactions. Both XP and XE
diminished with time-on-stream reflecting the in situ sample deac-
tivation. Initially, the reaction formed on both zeolites essentially
ethylphenols and dialkylated products and minor amounts of EPE,
but with the progress of the reaction the EPE selectivity increased
at the expense of EP and DAP. After 3 h reaction the EPE selectivity
on HZSM5 increased up to 36% while SEP decreased from 92% to
(
B/L = 1.0) increased up to 1.8 following evacuation at 523 K, which
suggests that Brønsted sites present stronger acidity than Lewis
sites. Furthermore, comparison of IR spectra obtained on HZSM5
after evacuation at 423 K and 573 K allows inferring that Na Lewis
−1
acid sites (peak at 1445 cm ) are weaker than Al Lewis acid sites
−1
(
peak at 1455 cm ). On HMCM22 the B/L ratio also increased with
the evacuation temperature, from 3.2 (evacuation at 423 K) to 3.7
evacuation at 573 K).
(

8
0
M.E. Sad et al. / Applied Catalysis A: General 486 (2014) 77–84
Table 2
Characterization of catalyst acidity by FTIR of pyridine.
Catalysts
Evacuation temperaturea
T = 423 K
T = 573 K
Lewis sites (L), area/g
Brønsted sites (B), area/g
B/L
Lewis sites (L), area/g
Brønsted sites (B), area/g
B/L
HZSM5
HMCM22
341
176
337
560
1.0
3.2
155
120
287
444
1.8
3.7
a
Pyridine preadsorbed at 298 K.
1
00
A
XE
100
B
SEP
8
6
4
2
0
0
0
0
0
8
6
4
2
0
0
0
0
0
XE
SEP
XP
SEPE
XP
SEPE
SDAP
SDAP
0
50
100
150
200
0
50
100
150
200
Time (min)
Time (min)
Fig. 2. Conversions (Xi) and selectivities (Si) as a function of time on stream. A: HMCM22, B: HZSM5 [523 K, PT = 101.3 kPa, PP = PE = 1.1 kPa, W/FP = 99.3 g h/mol].
6
5%. In contrast, on HMCM22, SEPE was only 10% at the end of the
and HZSM5 present similar initial activity for phenol ethylation and
convert totally ethanol.
run and SEP decreased slightly from 90% to 83%.
The alkylation of aromatic compounds with ethanol on zeolites
occurs through an electrophilic substitution on the aromatic ring
by the alkylating agent formed from ethanol dehydration on zeo-
lite acid sites [25]. In our case, ethanol is dehydrated on zeolitic
OH groups forming surface-bound ethoxide species that can alky-
late phenol or produce ethylene (by intramolecular dehydration)
and diethylether (by dehydration/condensation). Based on previ-
ous works [26–29], we present in Scheme 2 the mechanisms of
ethanol conversion on BrØnsted acid sites to produce ethylphenols,
ethylene or diethylether via the formation of surface-bound ethox-
ide intermediates. The alkylating agent attacks the phenol ring by
electrophilic substitution in ortho and para positions because of
the electron donor effect of phenol OH group that increases the
electronic density of positions 2, 4, and 6 in the ring.
Previous studies have reported that the selectivity of ethanol
dehydration to ethylene and diethylether over zeolites depends
on the sample topology, acidity and reaction temperature [30–32].
Here we have carried out a brief study of ethanol conversion
reactions on HZSM5 and HMCM22 at 473 and 523 K. Results are pre-
sented in Table 3. At 473 K, the initial ethanol conversion was higher
3
.2.2. Alkylation of phenol with ethanol: catalyst selectivity
Table 4 presents the values of initial reactant conversions deter-
mined from Fig. 2 as well as of the initial selectivities to all the
products formed from phenol ethylation reaction. On both zeo-
lites the carbon balance was higher than 90%, the selectivity to
DAP lower than 9% and EPE formation negligible. In contrast, the
ethylphenol product distribution observed on HMCM22 was signif-
icantly different to that obtained on HZSM5. In fact, on HMCM22 the
main product was p-EP (S0 = 51.4%) giving a para/(ortho + meta)
p-EP
isomer ratio of 1.5 while HZSM5 formed mostly o-EP (S0 = 49.0%)
o-EP
so that the para/(ortho + meta) ratio was only 0.2. Based on these
results that show the superior performance of HMCM22 for selec-
tively promoting the formation of p-EP, we selected this zeolite to
perform additional catalytic runs with the aim of gaining insight
on the phenol ethylation mechanism and exploring the possibil-
ity of increasing the p-EP yield (the initial p-EP yield on HMCM22
as determined from data of Table 4 was about 22%, at 523 K and
W/FP = 99.3 g h/mol).
0
0
on HMCM22 (XE = 70%) than on HZSM5 (X = 56%); both zeolites
E
formed essentially diethylether. At 523 K, ethanol was totally con-
verted on HMCM22 and HZSM5, producing mainly ethylene. This
selectivity change with the reaction temperature is consistent with
previous studies reporting that the activation energy of the ethanol
dehydration to ethylene is higher than that of ethanol conversion
to diethylether [32]. Both zeolites produced significant amounts of
3.2.3. p-Ethylphenol synthesis
Additional catalytic runs were carried out on HMCM22 by vary-
ing the contact time between 24.8 and 250 g h/mol. The observed
catalyst deactivation, however, required that each data point be
obtained on fresh catalyst and that initial yields be obtained by
extrapolating to initial time on stream. Fig. 3 shows the evolution
of initial reactant conversions and yields as a function of con-
tact time. The local slopes of the yield curves in Fig. 3 give the
rate of formation of each product at a specific reactant conversion
and contact time. The nonzero initial slopes of p-EP, o-EP and EPE
0
∼
additional products at 573 K (Table 3, XOthers = 16%), probably C
3+
hydrocarbons formed from ethylene as reported in literature [33].
In summary, from the catalyst activity data obtained at 523 K
and presented in Fig. 2 and Table 3 we infer that zeolites HMCM22

M.E. Sad et al. / Applied Catalysis A: General 486 (2014) 77–84
81
Scheme 2. Ethanol conversion mechanisms via the formation of surface-bound ethoxide intermediate: phenol alkylation, dehydration to ethylene and dehydra-
tion/condensation to diethylether.
Table 3
Ethanol conversion reactions on zeolites HZSM5 and HMCM22.
Temperature (K)
HZSM5
HMCM22
0
E
0
0
0
0
E
0
0
0
X
(%)
S
(%)
S
(%)
S
(%)
X
(%)
S
(%)
S
(%)
S
(%)
ethylene
diethylether
others
ethylene
diethylether
others
4
5
73
23
56
100
11
80
87
3
2
17
70
100
6
80
91
4
3
16
Ethanol conversion and selectivities obtained at t = 0.
01.3 kPa total pressure, PE = 1.1 kPa, W/FE = 99.3 g h/mol.
1
Table 4
Catalytic results for the alkylation of phenol with ethanol.
Catalyst
Initial conversions (%)
Initial selectivities (%)
C balance (%)
0
P
0
E
0
p-EP
0
o-EP
0
0
EPE
0
X
X
S
S
S
S
S
DAP
m-EP
HZSM5
HMCM22
40.2
42.6
100
99
14.2
51.4
49.0
15.9
22.8
15.2
1.0
1.1
7.1
8.3
94.1
91.9
5
23 K, 101.3 kPa total pressure, PP = PE = 1.1 kPa, W/FP = 99.3 g h/mol.
confirm that they are primary products formed directly by the
attack of ethanol to phenol as depicted in Scheme 1. In contrast,
the zero initial slopes obtained for m-EP and DAP yield curves
suggest that these compounds are secondary products. m-EP is
probably formed by isomerization of p-EP and o-EP while the con-
secutive alkylation of ethylphenols with another ethanol molecule
accounts for the production of dialkylated products. On the other
hand, Fig. 3 shows that the EPE yield curve reaches a maximum at
shape selectivity concept and taking into account the reaction path-
ways involved in Scheme 1. Zeolite HZSM5 has a tridimensional
structure with 10-MR straight channel (5.1 A˚ × 5.5 A˚ ) intercon-
nected to sinusoidal 10-MR channel (5.3 A˚ × 5.6 A˚ ). HMCM22 has
a particular pore structure with two independent pore systems.
One pore system is tridimensional and composed of 12-MR
supercages (18.2 A˚ × 7.12 A˚ × 7.1 A˚ ) connected by 10MR windows
(4.0 A˚ × 5.5 A˚ ); the second, bidimensional, is composed of inter-
∼
˚
˚
W/FP = 49.6 g h/mol, indicating that EPE is converted to secondary
connected sinusoidal 10MR channels (4.0 A × 5.0 A) and does not
contain any cages [34,35]. The narrower channels of zeolite
HMCM22 can change the product distribution of phenol ethylation
reaction according to the ease of diffusivity of product molecules.
Although HMCM22 contain 12-MR supercages, only molecules that
can diffuse through the 10-MR pores may reach the internal active
products, probably ethylphenols, with increasing contact time. All
these results are consistent with the phenol ethylation reaction
network proposed in Scheme 1.
The higher selectivity to p-EP obtained on HMCM22 in com-
parison to HZSM5 (Table 4) may now be analyzed in terms of the

8
2
M.E. Sad et al. / Applied Catalysis A: General 486 (2014) 77–84
1
0
0
0
0
0
0
.0
.9
.8
.7
.6
.5
.4
1
8
6
4
2
0
00
40
30
20
10
0
0
0
0
0
x5
0
40
80
120
160
200
Time (min)
0
50
100 150 200 250
W/F (g h/mol)
P
Fig. 5. Time evolution of the activity for phenol conversion (aP ) on HMCM22 for
different contact times. (ꢁ) 250.0 g h/mol; (᭹) 198.6 g h/mol; (ꢀ) 149.0 g h/mol;
(ꢄ) 99.3 g h/mol; (ꢅ) 49.6 g h/mol; (ꢆ) 24.8 g h/mol [523 K, PT = 101.3 kPa,
PP = PE = 1.1 kPa].
Fig. 3. Conversions and yields at t = 0 as a function of contact time on HMCM22.
Phenol (ꢀ), ethanol (ꢁ), p-EP (♦), o-EP (ꢂ), m-EP (ꢀ), EPE (ꢁ), DAP (ꢃ) [523 K,
PT = 101.3 kPa, PP = PE = 1.1 kPa].
then remained almost constant for higher W/FP values. Thus, the p-
EP/o-EP molar ratio increased up to about 4 at W/FP = 250 g h/mol,
thereby confirming that zeolite HMCM22 markedly improves the
selective formation of p-EP. Nevertheless, the m-EP yield con-
stantly increased with W/FP reflecting the m-EP formation from
isomerization of p- and o-EP isomers; ꢂ0
reached 14% for
m-EP
W/FP = 250 g h/mol. Production of DAP was very low over the entire
W/FP range and ꢂ0 did not exceed 6%. This late result indicates
DAP
that the narrow channels of HMCM22 hinder the formation of bulky
intermediates involved in the alkylation of ethylphenols to DAP.
The EPE yield was negligible (less than 1%) for W/FP higher than
9
9.3 g h/mol which reveals that this primary product of phenol
Fig. 4. Ethylphenol isomers dimensions.
ethylation is rapidly converted to secondary products.
In summary, results in Fig. 3 show that on HMCM22, at 523 K and
W/FP = 250 g h/mol, phenol conversion reaches 71% yielding 41% of
sites of this zeolite because the 12-MR supercages are connected to
the exterior through a 10-MR window. Catalytic results in Table 4
prove that phenol can go inside the channels of zeolites HZSM5
and HMCM22 and form ethylphenols. However, the initial selec-
p-EP. This ꢂ0
value is significantly higher than those reported
p-EP
in previous (few) papers that investigated the selective produc-
tion of p-EP by phenol ethylation [9,10]. The superior performance
of zeolite HMCM22 for selectively producing p-EP is due to its
narrow pore channels that not only suppresses the alkylation of
ethylphenols to dialkylated products but also hamper by diffusional
constraints the formation of o-EP. Nevertheless, the maximum p-EP
yield was obtained here at W/FP = 250 g h/mol; when W/FP higher
tivity to p-EP was clearly higher on HMCM22 (S0 = 51.4%) than
p-EP
on HZSM5 (S0
= 14.2%). This result probably reflects the fact
p-EP
that inside the HMCM22 pores the o-EP isomer would diffuse at
much smaller rates than p-EP because its bigger dimension (Fig. 4
shows the relative dimensions of ethylphenol isomers). There are
not specific data in literature about the diffusion coefficients of
ethylphenol isomers on HMCM22, but several authors have stud-
ied the gas-phase diffusion of xylene isomers on 10-member ring
zeolites. Roque-Malherbe et al. [36] determined that the intrinsic
diffusion coefficient of o-xylene at 300 K is about four orders of
magnitude lower on HMCM22 than on HBEA. On zeolite HZSM11,
it was reported that the p-xylene diffusion coefficient at 400–425 K
is 20–30 times higher than that of o-xylene [37], while on HZSM5
at 373 K the same comparison of diffusion coefficients reached a
difference of two orders of magnitude [38]. A similar qualitative dif-
ference of the transport rates of p-EP and o-EP into the 10-MR pores
of HMCM22 may explain the drastic para-selectivity improvement
observed in Table 4 for the ethylation of phenol on HMCM22 as
compared to HZSM5.
than 250 g h/mol were employed the ꢂ0
diminished because p-
p-EP
EP was increasingly converted to m-EP. The isomerization of p-EP
to m-EP is favored on HMCM22 because this zeolite contains a high
concentration of strong Brønsted acid sites (Table 2).
On the other hand, the activity decay on HMCM22 during the
progress of the reaction was considerable in all the catalytic tests
performed in this work (see Fig. 2), thereby suggesting that the
reactions forming coke intermediates were not suppressed to any
significant extent. In basis of this observation, and taking into
account that no previous studies exist regarding catalyst deacti-
vation during the phenol ethylation reaction, we decided to carry
out additional catalytic tests in order to gain insight on catalyst
activity decay and coke formation.
0
Fig. 3 shows that Xp increased with W/FP on HMCM22, reaching
3.2.4. Catalyst deactivation and coke formation
7
1% at W/FP = 250 g h/mol; ethanol was totally converted for contact
To obtain a better knowledge about the activity decay observed
on zeolite HMCM22 for phenol ethylation, we plotted in Fig. 5 the
times higher than 99.3 g h/mol. p-EP yield continuously increased
0
with contact time up to 41% (Sp-EP = 59%) for W/FP = 250 g h/mol.
evolution of the activity for the conversion of phenol (a ) as a func-
P
In contrast, o-EP yield reached about 10% at W/FP = 149 g h/mol and
tion of time for different contact times. The activity aP is defined

M.E. Sad et al. / Applied Catalysis A: General 486 (2014) 77–84
83
Table 5
According to Table 5, phenol conversion increases while initial
Deactivation results for phenol ethylation.
deactivation d and % coke diminish when contact time is increased.
0
Contact time, W/FP (g h/mol)
Phenol
Deactivation results
This result strongly suggests that deactivation of zeolite HMCM22
on stream is mainly related to the presence of the reactants, ethanol
and/or phenol. Therefore, we decide to investigate the formation
of coke over HMCM22 when only ethanol is feeding to the reactor
at the same operation conditions used for the phenol ethylation
reaction in Fig. 2 (523 K, W/FP = 99.3 g h/mol, PE = 1.1 kPa, reaction
length = 3 h). We analyzed the ethanol conversion products (the ini-
tial product composition is included in Table 3) and determined the
amount of carbon formed on HMCM22 at the end of the run by TPO
technique. Although ethanol conversion remained close to 100%
during the entire catalytic run, we observed the change of color of
zeolite HMCM22 after reaction which indicated the presence of sur-
face carbonaceous deposits. The TPO curve obtained for HMCM22
sample recovered after the 3-h ethanol conversion run consisted of
conversion, XP0
(
%)
d0 (h 1)a
−
C (%)b
24.8
49.6
99.3
11.0
21.0
42.6
55.1
66.7
71.0
0.69
0.63
0.50
0.47
0.29
0.19
7.2
6.5
4.8
3.6
1.7
1.1
149.0
198.6
250.0
HMCM22, 523 K, PT = 101.3 kPa, PP = PE = 1.1 kPa.
a
Initial deactivation, d0 = (da/dt)t=0.
Carbon formed after the 3 h runs.
b
a broad band with several peaks of CO evolved between 350 and
2
a
9
80 K (Fig. 6, curve A). Thus, ethanol conversion via dehydration,
6
4
2
0
0
0
0
dehydrogenation and condensation reactions proceeding mainly
on Brønsted acid sites (Scheme 2) forms also surface carbonaceous
deposits on HMCM22. Nevertheless, Fig. 6 shows that the profile of
curve A was completely different as compared to those obtained
from samples recovered after phenol ethylation runs (TPO pro-
files a–f). Furthermore, the %C determined by integration of TPO
curve A was 2.1%, significantly lower than the amount of carbon
obtained on HMCM22 sample recovered after the phenol ethyla-
tion run carried out under the same operation conditions (4.8%,
Table 5). All these results strongly suggested that phenol is the
main responsible for coke formation in phenol ethylation, either
because of its strong adsorption on catalyst active sites or by form-
ing coke precursors via secondary reactions with ethanol-derived
species. In a previous work on phenol methylation [40] we char-
acterized by infrared spectroscopy the nature of coke formed on
stream and detected the presence of phenolate, aromatic and pol-
yaromatic species adsorbed mainly on Lewis acid sites. Taking into
account that phenol is adsorbed preferentially on Lewis acid cen-
ters, predominantly in vertical orientation [41,42], formation of
coke intermediates on Lewis acid sites would suppress the active
sites required to promote phenol ethylation and may explain the
catalyst activity decay on stream observed in this work.
b
c
d
e
f
A
4
00
600
800
1000
Temperature (K)
Fig. 6. TPO profiles of HMCM22 samples recovered after using in 3-h phe-
nol ethylation runs at different contact times: (a) 24.8 g h/mol; (b) 49.6 g h/mol;
c) 99.3 g h/mol; (d) 149.0 g h/mol; (e) 198.6 g h/mol; (f) 250.0 g h/mol [523 K,
PT = 101.3 kPa, PP = PE = 1.1 kPa]. TPO profile A: HMCM22 sample recovered after
using in 3-h ethanol conversion run [523 K, 99.3 g h/mol, PT = 101.3 kPa, PE = 1.1 kPa].
(
0
P
0
P
as aP = rP/r , where r and rP are the phenol conversion rates at
t = 0 and t = t, respectively. Fig. 5 shows that the catalyst activity
decay clearly diminished when W/FP was increased. In order to
4. Conclusions
quantitatively evaluate the effect that varying contact time W/FP
0
(
and consequently X ) has on phenol conversion rate decay, we
Zeolites HZSM5 and HMCM22 promote efficiently the gas-phase
ethylation of phenol producing mainly ethylphenols and lower
amounts of ethylphenylether and diethylphenols. Zeolite HMCM22
is particularly suitable to selectively produce p-ethylphenol
because its sinusoidal 10-member ring channel structure hinders
by shape selectivity the formation of o-ethylphenol and blocks
the production of dialkylated products. At 523 K and 71% of phe-
nol conversion, the HMCM22 zeolite yields 41% of p-ethylphenol;
for higher phenol conversion values the p-ethylphenol yield
diminishes because p-ethylphenol is increasingly converted to m-
ethylphenol.
The activity of zeolite HMCM22 for phenol ethylation declines
with time on stream due to coking and the deactivation rate
increases proportionally to the amount of carbon deposited on
the solid. Formation of carbon decreases with phenol conversion
because coke is formed essentially from ethanol/phenol reactants.
Ethanol forms surface carbonaceous deposits on HMCM22 conver-
sion via dehydration, dehydrogenation and condensation reactions.
Nevertheless, phenol is the main responsible for coke formation
in phenol ethylation, either because of its strong adsorption on
catalyst active sites or by forming coke precursors via secondary
reactions with ethanol-derived species.
P
determined from the aP vs t curves of Fig. 5 the parameter d0
[daP/dt] accounting for initial deactivation rate [39]. Results
given in Table 5 show that d diminished from 0.69 h to 0.19 h
when W/FP was increased from 24.8 g h/mol to 250 g h/mol.
=
−
t=0
−
1
−1
0
The observed sample deactivation on stream could be attributed
to the formation of carbonaceous deposits from consecutive or par-
allel reactions of reactants and products on surface active sites.
We characterized the carbon deposited on the samples recovered
from the catalytic experiments showed in Fig. 5 by temperature-
programmed oxidation technique. Before the TPO characterization,
samples were treated at 523 K in N2 during 60 min. The obtained
TPO curves are presented in Fig. 6. The shapes of TPO curves were
similar for all the samples, presenting a single combustion peak
with a maximum at about 570 K. Carbon contents were determined
from the areas under the curves of Fig. 6 and are included in Table 5.
The formation of coke on HMCM22 diminished from 7.2% C (for
W/FP = 24.8 g h/mol) to 1.1% C (for W/FP = 250.0 g h/mol). Data in
Table 5 show that initial deactivation rate d increased proportion-
0
ally with the %C deposited on the samples, thereby suggesting that
coke formation was responsible for the activity decay observed in
Fig. 5 by blocking the surface active sites.

8
4
M.E. Sad et al. / Applied Catalysis A: General 486 (2014) 77–84
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and the Consejo Nacional de Investigaciones Científicas y Técni-
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