HYDRODESULFURIZATION OF THIOPHENE OVER BIMETALLIC ...

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Hamid A. Al-Megren
Normally, the flow rate of hydrogen was 20 ml/min at atmospheric pressure. The activity of nickel–molybdenum
supported catalysts (MECH, IMPR, and OMXC), and thiosophene conversion were studied at a temperature of
350°C
Blank reactor runs were conducted as described above in the absence of catalysts. No significant conversions of
thiophenes were observed under the conditions of each experiment. Carbon mass balancing closed within 8%, most
within 5%.
2.2.1. Gas Chromatography
The analysis of the reaction mixture was carried out using, a Hewlett–Packard 5890 series II. The instrument
equipped with 1 × 1/8" O.D. stainless steel packed column (80 – 100 mesh range Porpak S); and flame ionization
detector (FI), and thermal conductivity detector (TCD).
The instrument was calibrated by external standardization method using standard mixture of (CH4, C2H6, C2H4,
C3H8, C3H6, C4H10, C4H8, and C4H8).
2.3. Catalyst Characterization
Electron probe micro-analyzer (EPMA) (JEOL JXA-8900R/RL) was used for identification of constituent
elements in the prepared samples and to study the elements distribution over the support. Analysis was performed
by illuminating the sample surface with a finely focused electron beam and measuring the wavelengths and
intensities of characteristic X-rays from the specimen and the quantities of secondary electrons and backscattered
electrons from it.
The X-ray diffraction (XRD) was carried out in Philips PW1710 diffractometer with CuKα radiation. The data
were collected at room temperature, in θ/θ reflection mode, scanning the specimen between 3º–70º in 2θ, using steps
of 0.05º, with a time per step of 1.25 s.
The structure of the samples was studied using laser Raman spectroscopy from a Jobin Yvon Labram
spectrometer with a 632.8 nm HeNe laser, run in a back-scattered confocal arrangement. The samples were pressed
in a microscope slide; the scanning time was set to 30s. Raman spectra were recorded in air at room temperature
with a resolution of 2 cm –1 and a scanning range of 100 to 2500 cm –1 .
2.3.1. Physisorption
Nitrogen adsorption–desorption isotherm of MECH, IMPR, and OMXC catalyst samples were measured on a
Micromeretics ASAP2010 system using nitrogen sorption at 77K. Prior to the experiments, approximately 0.2 g of
sample was degassed at 523K for 16h. The surface areas were calculated using a multipoint Brunauer–Emmett–
Teller (BET) model. The pore size distribution was obtained using BJH and BET models and the total pore volumes
were estimated at a relative pressure of 0.99 atm, assuming full surface saturation with nitrogen.
For characterization purpose, samples of the fresh and used catalyst were passivated at room temperature in flow
of 1% O2/He before they were exposed to air.
3. RESULTS AND DISCUSSION
The surface area measurements for the three prepared bimetallic catalyst samples (MECH, IMPR, and OMXC) in
oxide phase, before sulfurization, are shown in Table 1. The surface areas for the samples increase in following
order: MECH (125.5 m 2 /g) > OMXC (122.5 m 2 /g) > IMPR (119.3 m 2 /g); the differences are relatively small. The
highest surface area for the sample prepared by mechanical method could be attributed to less dispersion between the
active component and surface of the support. In Table 1, the average pore diameter and the total volume, measured
for the three samples, were the highest for the samples prepared by mechanical and the lowest for the sample
prepared by combustion method. The particle size distribution analysis shows that the samples prepared by IMPR
and OMXC have almost similar size (~60μm), much higher than the particle size for sample prepared by MECH
(~27μm).
Table 1. Physical Properties of NiMoOx Catalyst Prepared by Impregnation, Mechanical, and Organic Matrix
Methods
Preparation Surface
Method Area m 2 g -1
Total Pore Volume
Cm 3 g -1
Average Pore Particle Size
Diameter A º Distribution μm
IMPR 119.27 0.16529 55.436 59.81
OMXC 122.50 0.16420 53.617 63.53
MECH 125.51 0.18621 59.343 26.81
January 2009 The Arabian Journal for Science and Engineering, Volume 34, Number 1A