- 上一篇：塑料注塑模具英文文献和翻译
- 下一篇：代理问题和企业理论英文文献和翻译
10
Isobutane Dehydrogenation Activity Measure-
ments. The isobutane dehydrogenation activity of the
13.5CrAl catalyst was measured in a continuous flow
reaction system consisting of a fixed-bed microreactor
along with a Fourier transform infrared (FTIR) gas
analyzer and a gas chromatograph (GC) for on-line
product analysis. The activity measurements were car-
ried out at 580 °C under atmospheric pressure. The
catalyst was heated to the reaction temperature under
5% O2/N2 (AGA, air 99.99%, N2 99.999%). Nitrogen used
in the experiments was purified with Oxisorb (Messer
Griesheim GmbH).
In the dehydrogenation experiments aimed to com-
pare the behavior of calcined and prereduced chromia/
alumina, the reduction of the catalyst (0.2 g) was
accomplished either during the first minutes on isobu-
tane stream or during a 30 min prereduction with 10%
H2/N2 (H2, AGA 99.999%) or 5% CO/N2 (CO, Messer
Griesheim GmbH, 99.997%). Dehydrogenation was car-
ried out for 15 min using isobutane feed (AGA 99.95%)
with a weight hourly space velocity (WHSV) of 5 h 1
and diluted with nitrogen at a molar ratio of 1:9. After
the dehydrogenation, the catalyst was flushed with
nitrogen and regenerated with diluted air. The reduc-
tion and regeneration productsscarbon oxides and
waterswere measured by FTIR. The dehydrogenation
products were monitored by FTIR for the first 6 min on
stream, a GC sample was taken after 10 min, and the
FTIR analysis was then continued. In selected measure-
ments the catalyst was regenerated directly after the
prereduction without implementing the dehydrogena-
tion stage.
The amount of coke as a function of time on isobutane
stream was measured for a hydrogen-prereduced cata-
lyst (0.1 g, 15-min prereduction with 10% H2/N2). The
isobutane flow with a WHSV of 30 h 1 was diluted with
nitrogen at a molar ratio of 1:1. Dehydrogenation was
carried out for 2, 5, 10, or 15 min and was followed with
the FTIR. The amount of coke deposited on the catalyst
during dehydrogenation was calculated from the amounts
of carbon oxides measured by FTIR during regeneration.
The gaseous products were analyzed on-line with a
Gasmet FTIR gas analyzer (Temet Instruments Ltd.)
equipped with a Peltier-cooled mercury cadmium
telluride detector and with an HP 6890 gas chromato-
graph equipped with an HP PLOT/Al2O3 “M” column
and a flame ionization detector. The FTIR spectra were
recorded in the wavenumber range of 4000 850 cm 1
with a resolution of 8 cm 1 and a scanning rate of 10
scans/s. The analysis cuvette (9 cm3) was maintained
at constant temperature (180 °C) and pressure (103
kPa). The spectra were measured every 2 s during the
first 2 min on stream, every 5 s during the next 2 min,
and thereafter every 30 or 60 s. Further details of the
FTIR gas analysis method and of the determination of
the product distribution based on the measured spectra
can be found elsewhere.
9,17 The conversions, selectivi-
ties, and yields were calculated on a molar basis.
In Situ DRIFTS-MSMeasurements. The formation
of hydroxyl and carbon-containing species during cata-
lyst reduction and isobutane dehydrogenation was
studied by in situ DRIFTS combined with MS. The
DRIFTS measurements were performed using a Nicolet
Nexus FTIR spectrometer and a Spectra-Tech high-
temperature/high-pressure reaction chamber. Gaseous
products were monitored on-line by a Pfeiffer Vacuum
OmniStar mass spectrometer. Nitrogen used in the
measurements was purified with Oxisorb (Messer-
Griesheim GmbH).
Isobutane dehydrogenation was investigated as a
function of time on stream at 580 °C for the three