CATALYTIC ACTIVITY OF HꢀFORMS OF ZEOLITES IN THE ISOMERIZATION
737
Catalytic Experiments and Analysis
of the Reaction Products
Physicochemical Studies of HꢀMordenite Samples
The amount of acid sites was determined by the
n
ꢀPentane was isomerized under supercritical conꢀ temperatureꢀprogrammed desorption of ammonia
ditions at 260°C and 130 atm in the absence of hydroꢀ
NH3 TPD). Measurements were performed on a
gen or additional solvents in a laboratoryꢀscale flow semiautomated setup using a calibrated IR spectromꢀ
reactor. The pressure in the system was created by
(
n
ꢀ
eter as the NH3 detector. Before measurements, the
pentane supply using a highꢀpressure piston liquid catalyst was blown with N2 at 500°C for 1 h. Ammonia
pump and was controlled using a membrane valve. The was adsorbed at room temperature (5% NH3 in N2).
3
3
LHSV of the substrate (Vl, cm /(h cm Cat)), defined The amount of adsorbed ammonia was measured
as the ratio of the flow rate of the reactant in the liquid under linear heating of the sample in a nitrogen flow in
3
state at 20°C to the catalyst volume (0.2 cm ), was the temperature range from 100 to 600°C
.
–1
3
0 h . Heating the system to the reaction temperature
The degree of crystallinity and the modulus of
mordenite samples were determined by Xꢀray diffracꢀ
was carried out in a hydrocarbon flow at the preset
pressure.
The reaction products were analyzed by GLC using
a capillary column (100 m) packed with the OVꢀ101
phase with online sampling. The quantitative compoꢀ
sition of the conversion products was determined by
the internal normalization method. The conversion of
tion on a DRONꢀ2 diffractometer (Cu
К radiation,
α
goniometer angular velocity of 2 deg/min,
). CeO2 powder was used as the internal standard,
whose amount was 10% of the zeolite weight.
2
θ
= 15°–
30°
The adsorption of benzene vapor on Hꢀmordenꢀ
ite(5) and Hꢀmordenite(11) was studied uisng a graviꢀ
metric adsorption setup equipped with a McBain balꢀ
ance. Before measurements, the samples were
pumped at 400°C to constant weight. The residual
the initial
tivity were calculated using the formulas
100%
nꢀalkane and the ith reaction product selecꢀ
K
= (сin
–
сfin)/сin
×
–4
and
pressure was 10 Torr. Benzene adsorption was meaꢀ
sured at room temperature.
Si = (сfin, i – сin, i)/(сin
–
сfin
)
×
100%,
respectively, where cin and cfin are the initial and final
concentrations of
weight concentrations of component
hydrocarbon and in the reaction products.
n
ꢀpentane and сin, and сfin, are the
i
i
RESULTS AND DISCUSSION
i
in the initial
Conversion of nꢀPentane on the HꢀForms of Zeolites
The catalytic experiments under supercritical conꢀ
ditions were described in greater detail in a previous and 33.3 atm, and those of isopentane are 187.4°C and
publication [5].
The critical parameters of nꢀpentane are 196.6°C
33.4 atm. Thus, at temperatures above 200°C and
pressures higher than 40 atm, the reaction system is in
the supercritical state at any conversion of
The results of ꢀpentane isomerization under the
supercritical conditions on the Hꢀforms of zeolites at
60°C and 130 atm are given in Table 1. These results
show that the Hꢀform of mordenite (Si/Al = 11) is the
most active unpromoted zeolite catalyst, and zeolite Y
is the least active. Sixty minutes after the catalyst was
heated to the reaction temperature, the conversion of
nꢀpentane.
IR Spectroscopy
n
The acidic properties of the Hꢀforms of the zeolites
mordenite, Beta, Y, and ZSMꢀ5 were studied by difꢀ
fuse reflectance IR spectroscopy using nꢀpentane as
2
the probe molecule. IR spectra were recorded using a
thinꢀwall quartz tube with a gluedꢀin CaF2 window.
Before IR measurements, the samples were activated
using a glass vacuum setup. The residual pressure
n
ꢀpentane on Hꢀmordenite(11) is 30% at 87% isopenꢀ
–4
under pumping was 10 Torr. The presynthesized Hꢀ
form of a zeolite was heated in vacuo at 100°C for 1 h,
tane selectivity. Along with isopentane, C3 C4, and
,
C6+ hydrocarbons resulted from the process, indicatꢀ
ing that secondary disproportionation, oligomerizaꢀ
tion, and cracking reactions occur, but to a lesser
extent than on the other zeolites. It is noteworthy that
then the temperature was slowly increased to 450°C
and the sample was pumped for 2 h. ꢀPentane
adsorption of was carried out at room temperature.
,
n
IR spectra were recorded on a Nicolet Impact 410 the conversions of
nꢀpentane on Hꢀmordenite(5) and
FTIR spectrometer with a diffuse reflectance attachꢀ Hꢀmordenite(11) differ by one order of magnitude. In
–
1
ment at room temperature in the 6000–2000 cm
the series of mordenites with Si/Al = 6.5, 20, and 36,
–1
range with 4ꢀcm resolution. The spectra were conꢀ the conversion decreases with an increase in the
verted to the Kubelka–Munk units using the OMNIC degree of dealumination. There is a substantial differꢀ
program under the assumption that the reflectance of ence between Hꢀmordenite(11) and HꢀZSMꢀ5 in
–1
the zeolite at 5000 cm is 0.9. Overlapped absorption activity and selectivity in nꢀpentane conversion. As
bands were decomposed into their components under follows from the data presented, the isopentane selecꢀ
the assumption that separate bands are Gaussianꢀ tivity of pentasil ZSMꢀ5 is only 30% at 5% conversion.
shapes. Computer processing also included spectrum Light hydrocarbons, C and C , forming with 47%
3
4
smoothening and the subtraction of the background.
selectivity, dominate the reaction product.
KINETICS AND CATALYSIS Vol. 51
No. 5
2010