KINETICS OF PROPYLENE EPOXIDATION WITH HYDROGEN PEROXIDE
467
In addition, oxygen was detected among the reaction ple wells were provided. A pressure of 5–7 atm was
products, which results from the reaction
maintained throughout the system. The feed flow rate
was controlled through electronic control of the
pump. After passage of a certain reaction mixture vol-
ume required for reaching the steady-state conditions,
the reaction mixture was sampled at the outlet of the
reactor.
The reaction mixture was analyzed on a Khromos
GKh-1000 gas chromatorgaph (Khromos, Russia)
equipped with a flame ionization detector and a metal
column (2 m × 3 mm) packed with 15 wt % Carbowax
6000 supported on Chromaton-N-AW. The flow rate
of the carrier gas (nitrogen) in the column was
50 mL/min. The injecvtion port and oven tempera-
tures were maintained around 180 and 130°C, respec-
tively. The detector temperature was 200°C. The com-
position of the reaction mixture was determined by
absolute calibration. The hydrogen peroxide content
was measured by iodometric titration.
The IR spectra of the catalyst samples in the spec-
tral range from 400 to 4000 s–1 were recorded as KBr
pellets in air on an IRAffinity-1 FT-IR spectrometer
(Shimadzu, Japan) at room temperature. The analysis
showed the complete coincidence between the posi-
tions of characteristic bands for the powdered and
granular titanium silicalite samples in the region of
540 and 960 cm–1.
The XRD patterns of samples prior to and after
molding were recorded on a Shimadzu LAB XRD-
6000 diffractometer (CuKα radiation, nickel filter,
scintillation counter, voltage of 30 kV, current of
30 mA) in the 2θ range from 10° to 80°; the scan rate
was 2 deg/min, and the step size was 0.02°. The reflec-
tions of both samples in the characteristic region 2θ =
23°–25° almost coincide. The intensities of peaks in
the XRD pattern of the granular catalyst were slightly
lower, which is likely due to the decrease in the
amount of the main component, titanium-containing
zeolite, as a result of addition of the binder. In addi-
tion, the intensities of the reflections at 31.12° and
32.66° in the XRD pattern of the granular sample
slightly increased; according to card no. 09-0440 from
the JCPDS database, these reflections belong to alu-
minum oxide.
(V)
2H2O2 → 2H2O+O2.
In recent years, there emerged quite a lot of publi-
cations concerning this method of propylene oxide
preparation, which studied different catalytic systems
[10], the physicochemical regularities [11, 12], and the
kinetics of the process [13]. However, the reaction was
performed most often on a fine crystalline heteroge-
neous catalyst dispersed in the reaction mass, while,
under industrial conditions, it is preferable to use
molded catalysts capable of functioning in the fixed
bed, which excludes the need for their subsequent sep-
aration from the reaction mixture.
The aim of the present work was to study the kinet-
ics and to develop a mathematical model for the liq-
uid-phase Pr epoxidation with a solution of HP in an
organic solvent in the presence of extruded titanium
silicalite as a heterogeneous catalyst.
EXPERIMENTAL
Methanol (analytical grade, Russian Standard
GOST 2222–95), propylene oxide (pure grade,
GOST 23001–88), 33–34% hydrogen peroxide (high-
purity grade, Specifications TU 2611-069-05807977–
2006), propylene (GOST 25043–87), tetrabutoxytita-
nium (Specifications TU 6-09-2738–89), tetraethox-
ysilane (Specifications TU 2435-419-05763441–2003),
and tetrapropylammonium hydroxide obtained by
passing tetrapropylammonium bromide (98%, Acros)
through an anion-exchange column were used in this
work.
Extruded titanium silicalite in the form of cylindri-
cal granules with a diameter of 2 mm and a length of
5 mm was prepared according to a procedure devel-
oped by us [14] and was used as a heterogeneous cata-
lyst. A powdered titanium silicalite with a mean parti-
cle size of 200–300 nm obtained as described in
[15, 16] was subjected to extrusion. The binder was
aluminum 5,6-oxynitrate.
The resulting powdered and granular catalyst sam-
ples were characterized by X-ray powder diffraction
and IR spectroscopy.
The morphology of the powdered catalyst samples
was evaluated by the analysis of photomicrographs
recorded on a Hitachi S-2500 scanning electron
microscope (Japan) equipped with a JNCA energy-
dispersive X-ray microanalysis attachment (Oxford
Instruments, United Kingdom). Based on the data
obtained, particle size distribution histograms for the
powdered catalyst (more than 250 particles) were plot-
ted. The statistical processing showed that the mean
particle size is 255 nm at a distribution width of 25 nm.
The morphology of samples was studied by scan-
ning electronmicroscopy and low-temperature nitro-
gen adsorption.
The process kinetics was studied in a laboratory-
scale continuous flow fixed-bed reactor. A tube-in-
tube reactor with an inner diameter of 15 mm and a
height of 250 mm filled with the granular titanium sil-
icalite was made of stainless steel. To ensure a uniform
input flow distribution over the reactor cross section,
the reactor bottom was filled with Fenske glass helices.
The reactor temperature was controlled using a liquid
The specific surface area, total pore volume, and
ultathermostat. To control the temperature profile pore size distribution in the powdered and granular
throughout the height of the catalyst bed, thermocou- samples (Table 1) were measured on a TriStar 3020
KINETICS AND CATALYSIS Vol. 57 No. 4 2016