72
KOVAL’ et al.
Table 1. Results of synthesis of MTBE from BBF isobutyl-
ene and methanol. T = 80 C, P = 1 MPa, and w = 1 h
As was shown previously [6] and in this work, the
catalyst activity depends on many factors, in par-
ticular, on its structural characteristics. The studied
sulfonic cation exchangers are wide-porous (16/60)
and narrow-porous (30/100). The equivalent pore
diameters dominating in the samples are presented in
Table 3. The experimental data show that the sample
of cation exchanger with wider pores, KU-23-16/60
(d > 15 nm), exhibits the highest activity in produc-
tion of MTBE from BBF and methanol under the
same conditions. For the narrow-porous sample,
KU-23-30/100 (d = 1 mn), a significant increase in the
yield of product and conversion of isobutylene is ob-
served with increase in pressure by a factor of 1.5.
Under the selected conditions of MTBE synthesis,
the H-HSZ narrow-porous sample of the ZSM-5 type
exhibits low catalytic activity as well. It is evident
that in the case of sulfonic cation exchanger KU-23-
16/60 the system of wide transition pores facilitates
mass transfer in the catalyst granules, which, in turn,
increases the yield of the target product and the degree
of conversion of isobutylene.
1
Selectivity, wt %
Conversion
of isobutyl-
ene, wt %
Catalyst
MTBE
DB*
TB*
KU-23-16/60
KU-23-30/100
H-HSZ-50
96
85
68
0.2
13
3.8
2
32
84
61
17
* (DB) Diisobutylene and (TB) tert-butanol.
Table 2. Optimal conditions for synthesis of MTBE from
BBF isobutylene and methanol. Space velocity of raw
1
materials 1 h
S*
K*
Catalyst
T,
C
P, MPa
wt %
KU-23-16/60
KU-23-30/100
H-HSZ-50
80
100
150
1
1.5
1
96
98
83
84
85
25
The difference in the catalytic activity of the sam-
ples is also related to their acid base characteristics
* (S) Selectivity with respect to MTBE and (C) conversion.
caused by the acidic groups SO OH in the styrene
2
anol 1 : 1], the degree of conversion of isobutylene
does not exceed 84% and the maximal selectivity with
respect to MTBE reaches 96%. The degree of conver-
sion and the selectivity of formation of MTBE on
high-silica zeolite are 17 and 70%, respectively. As a
by-product only tert-butanol, formed owing to the
presence of moisture in raw materials, was detected.
At a low metanol:isobutylene ratio and higher tem-
perature isobutylene dimerizes. With increasing tem-
divinylbenzene matrix of ion-exchange resins or
Lewis or Brønsted acid centers in the case of H-HSZ.
The measurement of the total acidity of the samples
and differentiation of acid centers with respect to their
strength (Table 3) showed that on the surface of the
samples there are several types of acid centers dif-
ferent in the strength and that the strong acid centers
corresponding to the pK of the indicator transition
2.5 prevail. The KU-23-16/60 sample with increased
7
2
perature, at a certain concentration of reactants, inter- concentration of acid centers (151.7 10 mol m )
molecular dehydration of methanol, hydration of iso-
butylene, and formation of methyl sec-butyl and meta-
butylene ethers take place.
exhibits a high catalytic activity, and for low-efficient
catalyst in synthesis of MTBE (KU-23-30/100 sam-
ple) the concentration of acid groups is two orders of
7
2
magnitute lower (1.7 10 mol m ). The feature of
distribution of acid centers on the surface of the zeo-
lite catalyst with respect to strength is the same as in
the case of sulfonic cation exchanger 30/100, and their
The dependences of the selectivity and degree of
conversion of raw materials (isobutylene of BBF) on
the temperature and pressure pass through maxima.
The optimal parameters of synthesis ensuring the
maximal catalytic activity and selectivity of the
studied samples are presented in Table 2. For the
KU-23-30/100 sample, the pressure has a positive ef-
fect on the selectivity (increase from 85 to 98%) and
catalytic activity (the degree of conversion of iso-
butylene increases from 60 to 85%). For the KU-23-
16/60 sample, the similar results are observed under
mild conditions of synthesis (P = 1 MPa and T =
80 C). The reaction of methanol with isobutylene on
H-HSZ proceeds at 150 C and is characterized by low
conversion of isobutylene.
7
2
concentration is approximately 0.4 10 mol m .
The difference in the catalytic characteristics of these
two samples can be apparently caused by severe dif-
fusion deceleration in the H-HSZ sample, which
makes difficult mass transfer along the narrow zeolite
pores.
CONCLUSIONS
(1) The KU-23 sulfonic cation exchanger with
coarse pores and maximal concentration of acid cen-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 1 2001