SYNTHESIS OF ETBE FROM TBA AND EtOH CATALYZED BY -ZEOLITE
293
hydrocarbon, and a nonsignificant effect on NOx [3,4].
It may be a good alternative compared to lighter alco-
hols because of its lower blending Reid vapor pressure
(bRvp), low vaporization latent heat, very low solu-
bility in water and so on which account for its full
fungibility in the petroleum refining and distribution
system [5], and compared to other tert ethers such as
TAME and TAEE because of their high cost. ETBE is
also attractive from the viewpoint of environment, as
it is derived from EtOH which can be obtained from
renewable resources such as biomass [6,7]. It was ex-
pected that by 2005, 5% of fuel used for transportation
in France should be produced from renewable sources
[8]. ETBE outranks MTBE as an octane enhancer and
is more attractive than MTBE for low bRvp blends as
required (less than 55 kPa) in some hot places during
summer or in tropical countries because ETBE has low
bRvp (28 kPa)thanMTBE (55–69kPa) [5]. Inaddition,
because the water solubility of MTBE (43 kg/m3) is
about 4 times higher than that of ETBE (12 kg/m3), the
use of ETBE reduces the risk of water contamination.
Generally, ETBE can be produced by an exothermic
reversible reaction between EtOH and IB. However, the
supply of IB is mainly limited from refinery catalytic
cracking and steam cracking fractions. Hence, alterna-
tive routes for the synthesis of ETBE were currently
explored [9]. TBA, a major byproduct of propylene
oxide production from IB and propylene in the ARCO
process, can be employed instead of IB as a reactant
[10]. TBA was first investigated for the ETBE synthe-
sis about 60 years ago [11]. There are two methods to
produce ETBE from TBA, namely the indirect and the
direct methods. In the indirect method, TBA is first de-
hydrated to IB in a reactor and then the produced IB is
reacted with EtOH to produce ETBE in a second reac-
tor. In the direct method which is of our interest, ETBE
is produced directly from TBA and EtOH in only one
reactor. It is favorable because it shortens the process
itself [12]. However, selection of proper catalysts with
high activity and selectivity is a major concern for the
success of this process.
direct synthesis of ETBE from TBA and EtOH in reac-
tive distillation columns. NaHSO4 failed to synthesize
ETBE. The homogeneous catalyst KHSO4 was found
to be superior to H2SO4 and Amberlyst-15 which pro-
duced IB as a main product; however, a subsequent
catalyst separation unit was required. Recent research
compared three cation-exchange resins of S-54, D-72,
and Amberlyst-15 [14]. It was observed (at T = 338 K)
that S-54 showed improvements (compared to those of
Amberlyst-15) of activity and selectivity of 6 and 5%,
respectively, while D-72 showed improvements of 10
and 1%, respectively.
The purpose of this investigation was to compare
the performance of -zeolite catalyst with the com-
mercial Amberlyst-15, which is usually used for tert-
ethers synthesis, for the production of ETBE from TBA
and EtOH by the direct method. The zeolitic catalyst
was chosen as it showed promising properties, high
thermal stability and no acid fume emission against
conventional resin-based catalysts [15]. In this study,
the kinetic parameters based on an activity model of
-zeolite catalyst were determined. The obtained pa-
rameters were used for modeling the ETBE production
inareactivedistillationwithorwithoutacombinedper-
vaporation unit (as proposed in our earlier work [10])
and a pervaporative membrane reactor.
EXPERIMENTAL
Catalyst Preparation
Synthesis of -zeolite powder was carried out in an
autoclave at 408 K and 300 kPa. Colloid of SiO2 and
NaAlO2, which were the main reagents employed in
the zeolite synthesis, were used to obtain a Si/Al ratio
of 42. A compound of tetraethylammonium hydroxide
was used as a template for crystals. Sodium and potas-
sium ions, contained in NaCl, NaOH, and KCl were
used as seeds for the crystals, as well as to balance
the ionic charges in the crystals. All these components
when mixed together formed a gel. To avoid quick
solidification of the gel, HCl was added to keep pH at
low level. The gel was stirred thoroughly at room tem-
perature before transferring it to the autoclave. Then,
the mixture was stirred and heated for 40 h. In order
to remove the template from the catalyst precursor, the
catalyst was calcined at 813 K for 3.5 h. After this, the
catalyst in the Na+ form was ion exchanged twice with
the solution of 2 M NH4NO3 at 353 K for 1 h. Then, the
ion-exchanged crystals were dried in an oven at 383 K
A number of researches are investigating the ETBE
synthesis by the direct method using various catalysts
such as Amberlyst-15, heteropoly acid (HPA), KHSO4,
NaHSO4, and H2SO4. Yin and coworkers [12] com-
pared the performance of Amberlyst-15 and HPA by
performing the reactions in a semibatch reactor. The
conversion and selectivity of Amberlyst-15 (at 338 K
and 8 h reaction time) were 62% and 43%, respec-
tively. Heteropoly acid was found to yield superior
selectivity (79%); however, it was less attractive be-
cause it was significantly inhibited by the presence of
water. Matouq and coworkers [13] employed KHSO4,
NaHSO4, H2SO4, and Amberlyst-15 as catalysts for the
+
for at least 3 h. The resulting crystals were in the NH4
form. Finally, calcination of the catalyst at 773 K for 2+h
was necessary to dissociate the ammonium ion, NH4
into NH3 and protonated form of hydrogen, H+. NH3