PROMISING PROCESS FOR SYNTHESIS
435
space velocity of 0.5 h–1, although the total content of
aromatic hydrocarbons is fairly high. At 750°ë and an IP
space velocity of 0.25 h−1, the main products of isophor-
one transformations are mesitylene (35.80%), xylenes
(22.50%), toluene (20.31%), benzene (6.55%), whereas
the amount of 3,5-xylenol is ~5%.
EXPERIMENTAL
Isophorone transformations were carried out in the
vapor phase at atmospheric pressure in a glass flow
reactor unit with a fixed catalyst bed. The reactor was a
quartz tube 650 mm in length and 18 mm in diameter
with two inner ports for thermocouples placed in the
evaporation and reaction zones. The isophorone vapor-
ization zone situated at the top of the reactor was filled
with ceramic packing. The bottom part—reaction
zone—was loaded with 10 cm3 of a catalyst. Isophor-
one was fed into the evaporator by a dosing pump; the
products were condensed and collected in a receiver.
Uncondensed vapors and gases were additionally
cooled in a vertical condenser and discharged into
atmosphere through a gas meter. At the end of the run,
the unit was purged with nitrogen.
The results of testing the chosen catalysts, Mg, Al,
and Si oxides, under conditions that ensure the maxi-
mum yield of 3,5-xylenol are given in Table 2.
It was found that all catalysts in question accelerate
the transformation of isophorone into 3,5-xylenol and
make it possible to conduct the reaction at lower tem-
peratures in comparison with the thermal version. Iso-
phorone transformations take place at a lower tempera-
ture if magnesium oxide is used as a catalyst: the IP
conversion was 77.7 wt % at 500°ë and reached
93.25% at 600°ë. Under these conditions, the selectiv-
The products were identified by instrumental meth-
ods, including GC–MS analysis on a Finnigan instru-
ment. Quantitative analysis of the reaction mixtures ity for 3,5-xylenol was high and reached 68.74 and
was carried out chromatographically on a Chrom-5 and 69.68%, respectively.
LKhM-8 MD instruments with a quartz capillary col-
On the basis of published data and the results
obtained in this work, we suppose that isophorone
undergoes dehydrogenation, dealkylation, and hydride
shift reactions during catalytic conversion, thus result-
ing in the desired product 3,5-dimethylphenol.
umn (50 m × 0.25 mm) coated with Carbowax-20M as
a stationary phase at temperature programmed from
50°ë to 180°C at a rate of 6°C/min. The carrier gas was
3
helium (1–1.5 cm /min).
Magnesia (GOST (State Standard) 4526-75), γ-alu-
mina (GOST 81-36-76) silica (GOST 3959), hydro-
thermal silica, and iron oxide-promoted silica were
used as catalysts for IP transformation into 3,5-xylenol.
The most active and selective 3,5-xylenol formation
catalysts are those exhibiting the highest dehydrogenat-
ing ability and having a surface with preferably basic
properties. Along with the strength and concentration
of acid and base sites, structural peculiarities of the
chosen catalysts also play a certain role. For example,
commercial beaded silicon dioxide catalyzes the trans-
formation of isophorone to 3,5-xylenol at 550°ë and a
feed space velocity of 0.5 h–1. Under these conditions,
the isophorone conversion was 79.21%, and the selec-
tivity for 3,5-xylenol was 61.63%. The hydrothermal
treatment of silica at 220–240°ë and a pressure of
3 atm for 6 h results in an increase in the isophorone
conversion under the same conditions up to 94.81% and
in the 3,5-xylenol selectivity to 79.33% (Table 2, entry 8).
Studying the catalytic properties of a commercial
γ-Al2O3 specimen calcined at 600°ë in isophorone
decomposition showed that the best results for isophor-
one conversion and 3,5-xylenol yield (79.2 and
61.63%, respectively) can be reached at a temperature
of 550°ë and feedstock space velocity of 0.5 h–1. X-ray
data for the γ-Al2O3 specimens thermally treated at
600°ë shows that their structure contains mainly the
crystalline γ phase and catalytically active sites in these
specimens have minimum acidity. From the data pre-
sented in Table 2, it follows that the most promising
catalyst for selective isophorone transformation to
3,5-xylenol is hydrothermal silica promoted with 2%
The results obtained during the thermal (500–700°ë)
and catalytic transformations of IP are given in Tables
1 and 2, respectively.
RESUTS AND DISCUSSION
The products of isophorone conversion under ther-
mal and thermocatalytic conditions are isomeric xyle-
nols, xylenes, cresols, mesitylene, toluene, and ben-
zene. The yield and ratio of the products depend on
temperature and contact time of isophorone, as well as
on the nature of the catalyst used.
Experimental data on influence of temperature on the
yield and composition of the IP transformation products
are listed in Table 1. As it is seen, the IP conversion con-
siderably increases with an increase in temperature to
500°ë; at 700°ë, the amount of the reactant isophorone
in the reaction mixture does not exceed 2.2%. The main
products in the temperature range of 600–650°ë are
3,5-xylenol and mesitylene. Along with these, the result-
ant mixture contains benzene, isomeric cresols, xylenols,
and trimethylphenols, which are probably formed as a
result of isomerization, disproportionation, and dealkyla-
tion reactions of mesitylene and xylenols, as well as
reduction of alkylphenols to alkylbenzenes. At 700°ë,
the yield of 3,5-xylenol decreases to 29.3% at a feed iron oxide. At 550°ë and an isophorone space velocity
PETROLEUM CHEMISTRY Vol. 46 No. 6 2006