76
P.A. Gushchin et al. / Journal of Catalysis 352 (2017) 75–82
alkylation of benzene with ethylene over the H-TMP-16 zeolite at
200–260 °C reaches 99% [17,18].
These data are comparable with those obtained by using the
aluminum chloride catalytic complex from the industrial alkyla-
tion installations.
The advantages of the alkylation process of benzene with ethy-
lene in the presence of DMDCS are:
An interesting study on the alkylation of benzene with ethylene
in the presence of MCM-49 zeolites was also carried out [19]. The
mesoporous zeolites are more active (2–10 wt%) in the alkylation
of benzene with ethylene in the liquid phase and more selective
towards ETB (90–97%), compared to conventional zeolites [20–
22,16].
A catalyst based on MCM-22 was used in technology, and
named as EBMaxTM by Mobil–Raytheon. In this application, the
alkylation is performed in the liquid phase. The first industrial
application was realized in 1997 [23,24].
In different studies [18–22,16], the mechanism of the alkylation
of benzene with ethylene was explained by the presence of {AlO4-
ꢀSiO4} tetrahedral ensembles in the lattice of zeolites [25–27]. The
reaction over the aluminosilicate catalyst surface occurs at the cen-
ters of the {AlO4ꢀSiO4} tetrahedral ensembles [28–31]. The ensem-
bles of {AlO6ꢀSiO4} are catalytically inactive. The basic
understanding of the catalysis over zeolites is presented in the the-
ory of catalysis by polyhedra [29–33].
– complete DMDCS solubilization in aromatic hydrocarbons with
the formation of a true thermodynamically stable solution;
– the alkylation takes place in a homogeneous mixture;
– the catalyst is non-toxic and the products of its hydrolysis are
environmentally friendly;
– the boiling points of benzene and DMDCS are very close, thus
these components can be distilled together out of the reaction
mixture for their subsequent circulation through the alkylation
unit;
– DMDCS is stable in the reaction mixture in the absence of mois-
ture, and its high activity and selectivity remain unchanged.
In view of this, the DMDCS catalyst favorably differs from the
aluminum chloride complex used with polyalkylbenzene.
The objective of this work is to develop a new catalyst that is
non-toxic, completely soluble in liquid aromatic hydrocarbons,
easily separated from the alkylation products during its circulation
in the system, and capable of forming environmentally friendly
products of hydrolysis.
3.2. Calculation of the equilibrium output
The process of benzene alkylation with ethylene generally
occurs at temperatures up to 573 K and atmospheric pressure,
and with a molar ratio of benzene to ethylene equal to 3:1. The
experiments described in this study were carried out at tempera-
tures ranging from 353 to 573 K, and the thermodynamic parame-
ters were calculated for this range. The standard Gibbs free energy
change was obtained according to the equation:
2. Experimental methods
Experiments involving the alkylation of benzene with ethylene
were carried out in an autoclave at elevated pressure (up to
10 atm) and temperatures up to 573 K. The ethylene used in the
experiments was of 98.88 wt% purity, while benzene was of chem-
ical purity grade. DMDCS was used as catalyst.
Pre-estimated amounts of benzene and DMDCS were loaded
into the autoclave, and ethylene was then injected under pressure.
Benzene was purified by shaking with concentrated H2SO4 to
remove thiophene, then washed with distilled water, and dried
in a desiccator over concentrated H2SO4.
DrGꢁ ¼ DrHꢁ ꢂ T ꢀ DrSꢁ ;
T
T
T
where DrGꢁ is the standard Gibbs free energy change for the ben-
T
zene alkylation reaction with ethylene, DrHꢁ is the enthalpy of the
T
reaction, and DrSꢁ is the entropy change of this reaction. These ther-
T
modynamic characteristics of the reaction were calculated using the
data from the standard heat of formation of benzene, ETB, and ethy-
lene and their standard entropies [34]. The resulting equation is:
The reaction mixture was analyzed chromatographically. The
mixture of benzene and DMDCS was distilled from the reaction
mixture on a distillation column to be reused in further alkylation
experiments.
D
GꢁT ¼ ꢂ103818 þ 142:687 ꢀ T;
in Joules.
The following values of the Gibbs free energy change were
obtained:
T = 353 R,
D
D
D
Gꢁ353 = ꢂ53449 J/mol;
Gꢁ453 = ꢂ39180 J/mol;
Gꢁ573 = ꢂ22058 J/mol.
3. Results and discussion
T = 453 R,
T = 573 R,
3.1. Effect of the DMDCS concentration on the yield of the alkylation
products
The calculated equilibrium constants were obtained according
to the equation:
The study of the alkylation of benzene with ethylene was car-
ried out in an autoclave by varying the DMDCS concentration
(10, 20, and 24 wt%) in the reaction mixture and according to the
ꢁ
ꢂDG
RT
T
KP ¼ e
:
nC6
H
The numerical values of the equilibrium constants at T = 353,
453, and 573 R were equal to: KP,353 = 1.23ꢀ108, KP,453 = 32,960,
and KP,573 = 102.53.
Therefore, the equilibrium yield of ethylbenzene is 0.999 mol
fraction at these temperatures. Consequently, the thermodynamic
conditions do not limit the kinetics of the alkylation of benzene
with ethylene, and the kinetics of the process reflect the occurring
of a kinetically irreversible reaction.
6
following experimental parameters: T = 513 R,
c
¼
¼ 3:1, con-
nC2
H
4
tact time
s
from 0.5 to 5 h, and initial pressure of 10 atm. Ethylene
was fed into the autoclave from a cylinder where it was enclosed
under a pressure of 50 atm. The results of these experiments are
presented in Table 1.
The composition of the products in the reaction mixture was
determined chromatographically. Hexene was formed as a result
of the ethylene polymerization reaction (trimerization).
According to Table 1, an increase in the yield of ethyl benzene
occurs with increasing DMDCS concentrations in the reaction mix-
ture under the initial pressure of 10 atm and temperature of 513 K.
3.3. Kinetics of the alkylation process
The kinetics of the benzene alkylation with ethylene in the
presence of DMDCS at the initial pressure of 10 atm, T = 513 K,
and molar ratio of benzene to ethylene of 3:1 were studied at
nC6
H
6
The highest yield of ethyl benzene of 28.78 wt% at
c
¼
¼ 3 : 1
nC2
H
4
was obtained at a concentration of DMDCS of 24 wt% and
s = 5 h.