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PREPARATION OF HIGHꢀOCTANE OXYGENATE FUEL COMPONENTS
63
Table 2. Ketalization of glycerol at different acetone/glycerol
particle size was 15 times smaller than the diameter of
the reactor to minimize jet breakthrough. The zeolite
and Fꢀ4SF/SiO2 catalyst samples were tableted (comꢀ
paction pressure of 3 t/cm2), the tablets were ground,
and a 1–1.5 mm fraction of particles was taken. For
the Tseokarꢀ600 and Zeolyst ZD 04028 catalysts, such
a fraction for experiments was collected after grinding
the catalysts as purchased. A few experimental runs
were performed in the “structured reactor” designed
for this purpose [33].
The ketalization reaction of xylose and xylitol was
investigated in a thermostated glass reactor equipped
with a reflux condenser. In some experiments, a carꢀ
tridge packed with molecular sieves 4A preliminarily
dried in a vacuum was installed between the condenser
and the reactor.
ratios
Acetone/glycerol, mol/mol
Catalyst
2
6
KUꢀ2 (60
°
C)
55
32
62
85
64
85
Tseokarꢀ600 (40
°
C)
Zeolite beta Zeolyst
CP811Tl (35 C)
°
Zeolite beta Zeolyst
60
21
82
37
CP814E (35
°C)
The glycerol, xylose, and xylitol ketalization prodꢀ
ucts were analyzed on a Kristallyuks 4000 M chroꢀ
matograph equipped with a flame ionization detector.
Zeolite HY
The column dimensions were 30 m
stationary phase was SBꢀ5ꢀOctyl (Supelco). The temꢀ
perature was programmed from 60 to 220 . A caliꢀ
×
0.4 mm, and the
acid sites are unnecessary for the formation of acetals
and ketals; it is sufficient to have a combination of
medium and weak acid sites [35]. Therefore, as a glycꢀ
erol ketalization catalyst, systems containing zeolites
°
С
bration mixture with an exactly known ketal concenꢀ
tration was used for quantitative analysis.
with different pore sizes, such as zeolite beta (6.6
6.7 nm pores), mordenite (6.5 nm pores), and zeoꢀ
lite HY (7.4 7.4 nm pores), were selected, as well as
×
The progress of the reactions involving monosacꢀ
charides and the product composition were also monꢀ
itored using NMR spectroscopy. After the reaction,
acetone was distilled off in a vacuum, and the resulting
sample was dissolved in deuterated DMSO. Its spectra
were taken with an Advance Bruker instrument operꢀ
ating at a frequency of 400.13 MHz. The chemical
×
7
×
systems based on the Fꢀ4SF polymer (Russian anaꢀ
logue of Nafion). The activity of the catalysts was
compared with that of the KUꢀ2 sulfonated cation
exchanger in the H form, which is one of the most
common catalysts for this reaction studied under the
batch reactor conditions.
The results are shown in Table 2 and Figs. 1–6.
Note that the condensation of polyols generally leads
to the formation of fiveꢀmembered cycles, whereas the
formation of sixꢀmembered rings is less favorable
owing to the fact that one of the methyl groups in the
final product is in the axial position of the chair conꢀ
formation [36]. In all cases, the selectivity of the most
thermodynamically stable product 1,2ꢀdiketal was
quantitative in the presence of acid catalysts. Moreꢀ
over, the conversion of acetone into its condensation
products did not exceed 1% in all runs. As can be seen,
the activity of the zeoliteꢀbased catalysts is somewhat
lower than that of KUꢀ2 at an acetone/glycerol ratio of
2 (Figs. 1–3). The catalysts based on zeolite beta are
the best. The yield of ketal on these catalysts reached
shifts are given on the
(0.00 ppm). The standard was DSS (3ꢀ(trimethylsiꢀ
lyl)propanesulfonic acid, 0.015 ppm). In the case of
δ
scale (ppm) relative to TMS
δ
GLC analysis, the ketals of xylose and xylitol were
determined directly in the reaction mixture with the
use of an internal standard (toluene).
RESULTS AND DISCUSSION
The formation of ketals of polyols is an acidꢀcataꢀ
lyzed reaction, which proceeds according to the
mechanism shown below:
+
OH
R1
HO
R2
2R1
O
R2
R4
+
O
HO
R3
R4
HO
R3
62% at 35
was 68% at 70
°
С
, whereas the maximum yield over KUꢀ2
°
С. The lowest activity was observed for
+R1
O
R1
O
R1
O
R2
R2
R4
R2
R4
the system containing bare zeolite HY (Fig. 4). A comꢀ
parison of the yields of ketal per acid site shows that
the catalysts based on zeolites beta exhibit the maxiꢀ
mum specific activity (Fig. 5). Of these, the catalyst
with the largest silica ratio and the highest hydrophoꢀ
bicity (zeolite beta Zeolyst CP811Tl) turned out to
have the highest activity.
O
O
R3
HO
R3
+
H
R4
R3
The reaction suggests the protonation of the ketone
oxygen and requires the use of acid catalysts that have
a sufficient strength to mediate such protonation and
the formation of the oxocarbonium ion [34]. At the
Note that the rateꢀdetermining step in the formaꢀ
same time, it is known that catalysts with very strong tion of cyclic ketals from polyols is the oxocarbonium
PETROLEUM CHEMISTRY Vol. 51
No. 1
2011