76
MASHKINA, KHAIRULINA
case of thiophene. The results of comparison between
the catalyst activities at 300 C, = 3.1–3.5 s, and
(4–5) : 1 are given in Table 5. Under the conditions
examined, the reaction products contain no (methꢀ
ylthio)benzenes and only alkylation products form. At
100
20
1
3
°
τ
М =
2
180 and 300
only weak PS’s was inactive. At 180
having only strong PS’s (HSiW/SiO2) or weak PS’s
and strong Lꢀsites ( ꢀAl2O3) also exhibited no activity.
°
C
, the H3PO4/SiO2 catalyst containing
°C, the catalysts
γ
On the remaining catalysts, the benzene alkylation
proceeded (Table 6). In the presence of the catalyst
with strong PS’s and weak Lꢀsites (Cr/SiO2), xylenes
and tetramethylbenzene form in very low yield; with
the catalysts containing both strong PS’s and strong
Lꢀsites (AlSi, HNaY, HZSMꢀ5), the additional prodꢀ
ucts were toluene and trimethylbenzene. With increasꢀ
0
1
2
3
4
5
τ
, s
Fig. 1. Effect of the residence time on the conversion of
individual DMDS ( ) and DMDS in mixtures with
thiophene ( ) and benzene ( ) in the presence of HZSMꢀ5
1
2
3
catalyst,
T
= 250
°
C, and
M
= (4–5) : 1.
ing the temperature up to 300°C, the yields of all alkyꢀ
lation products increase. The catalyst activities
increase with an increasing acidity of their surface.
40
1
In the presence of zeolite HZSMꢀ5, the effect of
conditions on the reaction between DMDS and benꢀ
zene was studied. Individual benzene at 150–250
and = 1.2–5.1 s underwent no conversion, and at
300–350 the benzene conversion was no higher
than 1–2%. When mixed with benzene, DMDS reacts
in the same way as the individual disulfide. The
DMDS conversion increases with an increasing resiꢀ
dence time (Fig. 1). The (DMDS + benzene) converꢀ
sion at low temperatures was lower than that of the
°C
2
τ
°
C
20
3
5
4
individual disulfide. For example, at
τ
= 2.3 s and
М
=
0
20
40
4–5, the following data were obtained:
Thiophene conversion, %
Т
,
°
C
180 200 250 300 350
Fig. 2.
thio)thiophene, (
thiophene, and (
selectivities at different thiophene conversions over the
HZSMꢀ5 catalyst; = 180 C, = 4–5 : 1.
(
1
) 2,2ꢀ(Methylthio)thiophene, (
) 2ꢀmethylthiophene, (
) 2,3,4ꢀtrimethylthiophene formation
2
) 2,5ꢀdi(methylꢀ
3
5
4) 2,5ꢀdimethylꢀ
DMDS conversion, % 26
(DMDS + benzene)
conversion, %
50
14
80
68
98 100
3
92
98
T
°
M
In the presence of zeolite HZSMꢀ5 at
and
zene. At 180–200
lowꢀyield formation of its derivatives begin (0.3–
1.5 mol %). A noticeable conversion is observed at
Т
= 160
°
C
from 180 to 300
thiophene conversion. The yields of thioalkylatoin
products at 180 and different values of were
higher than those of alkylation products. The formaꢀ
tion selectivity of 2ꢀ(methylthio)thiophene at 180 is
about 1.2 times higher than that of 2,5ꢀdi(methylꢀ
thio)thiophene, and the formation selectivity of
2ꢀmethylthiophene is 1.3 and 8 times higher than
those of 1,2,3ꢀtrimethylthiophene and 2,5ꢀdimethꢀ
°C results in an increase in the
τ
= 1.3–26.1 s, DMDS does not react with benꢀ
°C
, the conversion of benzene and
°
C
М
°C
250–350
thioalkylation of benzene occurs, but only the alkylaꢀ
tion products (toluene and orthoꢀ, metaꢀ, and para
°C (Table 7). Under these conditions, no
ꢀ
xylenes in virtually equal amounts), 1,3,5ꢀtrimethylꢀ
benzene, and 1,2,4,5ꢀtetramethylbenzene form. A
ylthiophene, respectively. At 300°C and different М,
temperature rise at constant
the benzene conversion. With an increasing
τ
results in an increase in
, the
the formation selectivities of 2ꢀ(methylthio)ꢀ and
2,5ꢀdi(methylthio)thiophenes were almost equal; the
formation selectivity of 2ꢀmethylthiophene was ~1.5 and
6 times higher than those of 1,2,3ꢀtrimethylthiophene
τ
yields of all benzene derivatives increase. The yield of
toluene is <1 mol % and the yields of xylenes are
and 2,5ꢀdimethylthiophene, respectively. The total higher than those of triꢀ and tetramethylbenzenes. The
formation selectivity of thioalkylation products at
change in the benzene conversion at a constant temꢀ
perature virtually has no effect on the formation selecꢀ
tivities of benzene derivatives (see, e.g., Fig. 3). This
possibly suggests that the reaction proceeds via indeꢀ
180
350
°
°
C
C
is 67%, and that of alkylation products at
reaches ~97%.
The reaction between DMDS and benzene was
studied in the presence of the same catalyst as in the pendent pathways:
KINETICS AND CATALYSIS Vol. 57
No. 1
2016