HYDRODESULFURIZATION OF THIOPHENE OVER BIMETALLIC ...

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Hamid A. Al-Megren
Figure 6 shows the ratios of butane and butenes (C4/C4 = ), which are produced from HDS of thiophene reaction.
The OMXC catalyst yielded the highest content of olefins, as compared to the IMPR catalyst. Products distribution
data provide some insight into the possible pathway of thiophene desulfurization, which is difficult to extract from
similar catalysts in which products are substantially altered by high rates of hydrogenation and isomerization
reactions.
More important are the differences between the three catalysts (IMPR, MECH, and OMXC) when we consider
the product distributions. GC analysis showed the formation of mainly C4 and C4 = fractions, but it has not showed
the formation of tetrahydrothiophene and butadiene. However many authors have argued for the preferential direct
desulfurization route, by the absence of tetrahydrothiophene [50].
Therefore our result shows that the pathway of reaction is the direct hydrodesulfurization route with successive
hydrogenation, as shown in Scheme 1.
S
HDS
HD
S
HD
HDS
HD
HDS
Scheme 1
With the three catalysts, the ratio of C4 to C4 = is around 2.5.
This suggests butane generation by hydrogenation of C4 compounds. These compounds are produced through the
hydrogenolysis of thiophene and probably from β-H elimination from intermediate hydrogenated thiophenes [55].
Table 2 shows the chemical analysis for the three samples analyzed before and after HDS reaction for more than
seven hours. The sulfur content for the three samples increased after the HDS reaction. This sulfur content increase
could be attributed to formation of sulfur species during the HDS reaction by the oxide phases that remain in the
sample. The sample prepared by OMXC method shows more chemical stability compared to the samples prepared
by other methods. The reaction rate was calculated for the HDS reaction over the three different catalysts. The
catalyst prepared using OMXC method a shows higher reaction rate than IMPR and MECH.
Table 2. Chemical Analysis for NiMoS Catalyst before and after HDS of Thiophene Reaction at 350ºC and
Atmospheric Pressure
Methods Before Reaction % After Reaction % Reaction rate
Al Mo Ni S Al Mo Ni S μmol (g min) -1
IMPR 47.28 24.49 7.41 20.81 41.61 24.36 5.61 28.42 58.16
OMXC 46.63 18.60 9.68 25.10 42.46 19.31 9.50 28.74 73.80
MECH 45.34 18.64 11.35 24.67 36.52 19.74 12.45 31.29 26.05
The structure stability after the HDS reaction for the three samples was analyzed by X-ray and Raman
spectroscopy. The X-ray patterns (Figure 7) for all the samples show higher structure stability after the HDS
reaction. The remaining peaks of MoO3 over the MECH sample after sulfurization reaction were converted to the
sulfide phase.
Raman spectra for the three samples after HDS reaction are shown in Figure 8. It is shown that all bands for
Mo=O and Mo–O–Mo vibrations at 995 cm –1 and 830 cm –1 on the IMPR sample are eliminated during the HDS
reaction. There is also a reduction in band 965 cm –1 for the MECH sample.
January 2009 The Arabian Journal for Science and Engineering, Volume 34, Number 1A
HD