China Petroleum Processing and Petrochemical Technology, 2012, Vol. 14,
No. 3, pp 33-38
Reactive Adsorption of Thiophene on
ZnNi/Diatomite-Pseudo-Boehmite Adsorbents
Meng Xuan; Weng Huixin; Shi Li
(The State Key Laboratory of Chemical Engineering, East China University of
Science and Technology,
Shanghai 200237)
Abstract
The thiophene removal ability of the synthesized
ZnNi/diatomite-pseudo-boehmite adsorbent was tested in a labscale fixed-bed
reaction system. X-ray diffractograms (XRD) were used to characterize the
adsorbent samples. The effects of Zn/Ni molar ratio, various model fuels and
regeneration patterns on the RADS tests were studied. The adsorption mechanism
was investigated by XRD and MS analyses. The results indicted that thiophene in
the model fuel was first decomposed on the surface Ni of the adsorbent to form
Ni3S2 while the hydrocarbon portion of the molecule was released back into the
process stream, followed by reduction of Ni3S2 to form H2S in the presence of
H2, and then H2S is stored in the adsorbent accompanied by the conversion of
ZnO into ZnS.
Sulfur compounds existing in the fuels can lead
to SOx-related air pollution generated by vehicle engines. In order to minimize
the negative health and environmental effects of automotive exhaust emissions,
the sulfur level in motor fuels should be minimized. In fact, the zero-emission
and, as a consequence, zero levels of S compounds are called for worldwide in
the forthcoming 5–10 years. Such ultra low-sulfur fuels requirements will have
great impact on the oil refining processes. Efficiency of the desulfurization
technologies becomes a key issue. The conventional hydrodesulfurization (HDS)
process is highly efficient in removing thiols, sulfides, and disulfides, but
is less effective for treating aromatic thiophenes and thiophene derivatives
(especially benzothiophene, dibenzothiophene, and their alkylated derivatives). The efficiency of HDS decreases
substantially when it is used to produce ultralowsulfur (ULS) transportation
fuels.
Several non-HDS-based desulfurization technologies such as adsorptive
desulfurization, charge-transfer complex formation, extraction using ionic
liquids, and biocatalytic treatment, have been proposed recently for the
desulfurization of liquid fuels[2-4]. Among them, the reactive adsorption desulfurization
(RADS) is considered to be a promising approach for deep desulfurization of
liquid fuels because it combines the advantages of both catalytic HDS
technology and adsorptive desulfurization process[5]. The S Zorb process based
on reactive adsorption is the first real commercial process of importance. The
S Zorb process is carried out in the presence of hydrogen and zinc oxide with a
metal or metal oxide serving as a promoter on a carrier. Sulfur from the sulfur
compounds is transformed to hydrogen sulfide, which is by chemisorption bound
with zinc oxide to form zinc sulfide. Although there have been many patents and
patent applications in the field of desulfurization by the S Zorb process, but
only a few reports with articles are available about the effect of adsorbent
components and reaction conditions on the reactive adsorption of the sulfur
compounds.
In the present work, a systematic study to understand the effects of Zn/Ni
molar ratio, various model fuels and regeneration times on the performance of
the ZnNi/ diatomite-pseudo-boehmite adsorbent was conducted, and the results of
this study were discussed in this paper. In addition, we also tried to explore
the reactive adsorption mechanism.
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