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Chemistry Letters Vol.33, No.3 (2004)
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Desulfurization of Thiophene in Alkaline Supercritical Water Studied by H and C NMR
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Shinya Yoshida, Koji Takewaki, Keiichi Miwa, Chihiro Wakai, and Masaru Nakahara
Environmental Process Development Department, Industrial Machine & Plant Development Center,
Ishikawajima-Harima Heavy Industries Co., Ltd., 1 Shinnakahara-cho, Isogo-ku, Yokohama 235-8501
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Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011
(Received November 5, 2003; CL-031053)
Thiophene, which is one of the major sulfur-containing
(as JIS K0101). The organic products in both the aqueous and or-
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compounds in crude oil as well as dibenzothiophene, was suc-
cessfully desulfurized by the heterolytic cleavage of the C–S–
C bond through the treatment with NaOH in supercritical water
ganic phases were characterized using H and C NMR spec-
troscopy (EX 270 Wide Bore, JEOL). The organic phase consist-
ed only of the remaining reactant with negligible organic
products.
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at 400 C. Thiophene was disintegrated into S and such car-
boxylic acids as formic, acetic, and succinic acids within 1 h.
First we examined how the desulfurization yield depended
on NaOH concentration. The decomposition yield in 20 min at
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00 C was 6.0, 33, 50, 58, and 57% at the NaOH concentrations
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Recently, super- and subcritical water has received much at-
tention as an alternative to hazardous organic solvents for a va-
of 1.0, 2.0, 3.0, 4.0, and 5.0 mol/dm , respectively. Thus the de-
sulfurization becomes efficient when NaOH is added in excess of
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riety of chemical processes.
In supercritical water, a number
thiophene. When the concentration is larger than 3 mol/dm , the
efficiency gets almost saturated. Hence we examined the reac-
of organic compounds can be decomposed to CO2 and H2O or
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transformed into some others.
Complete oxidation in super-
tion at 3 mol/dm of NaOH.
or subcritical water has been considered as a remarkable method
for the disposal of organic wastes. Used organic compounds are
originally synthesized from such fossil fuels as petroleum and
coal generated after a geologically long period, and they are still
organic resources, as long as the C–C and C–H bonds are re-
tained there. Instead of their burning or complete oxidation in
a very short time compared to the geological one, we should de-
velop a new method for converting them into useful organic
compounds by finding supercritical water reduction reac-
tions.8 Chemical recycles using hot water that is friendly to
the earth can be effective means of alleviating the resource short-
age in the future. For example, upgrading of crude oil is one of
the beneficial applications of this method. Crude oil contains sul-
fur as thiophene and dibenzothiophene that cause SOx during
combustion. Thus it is of great interest to develop the supercrit-
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ical water cracking of thiophene as in the case of rubber. To the
knowledge of the authors, there has been no report on the desul-
Time (min)
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Figure 1. Time dependence of the desulfurization yield at dif-
ferent amounts of Fe; 0 mol ( ), 0.01 mol ( ), 0.05 mol ( ),
and 0.1 mol ( ).
furization of thiophene in contrast to dibenzothiophene.
Autoclave used here was made of Hastelloy ‘‘C-276’’ as in a
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previous study. The reaction vessel was rolled up and down
with a rocking motion of the heater. Such reagents as thiophene,
NaOH, and iron powder (300 mesh) were supplied by Wako
Chemical Co., Ltd. We poured 0.01 mol of thiophene (the final
Figure 1 illustrates how the desulfurization yield determined
by monitoring S2 varies with time in the presence of Fe. The
initial increase of the yield is relatively large up to 20–30 min
and after that the increasing rate slightly decreases. The frag-
mentation reaction is catalyzed by Fe besides NaOH. However,
the reaction appears to proceed without Fe. In this case, the yield
is limited to 60% in 1 h. This suggests that the reaction is cata-
lyzed by the metal surface of the autoclave. In the gas phase,
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solution concentration being 0.5 mol/dm at ambient conditions)
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into 20 cm of aqueous NaOH solutions at different concentra-
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tions in the vessel (inner volume, 45 cm ), and replaced the air
in the autoclave with Ar. The reaction mixture was heated up
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to 400 C at the rate of 50 C/min with the induction heater.
At each reaction time, the autoclave was cooled down in a few
minutes with an electric fan to a temperature required for effec-
tive stopping of the reaction. To make the new reaction control-
lable, we need to identify the sulfur state and organic products by
chemical analyses. Before the product analysis, oxidized iron
precipitates were removed by filtration. A gaseous product,
CO2 was detected using FT-IR (WINSPEC-50, JEOL). The con-
CO and a small amount of gaseous thiophene were identified
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by FT-IR depending on the yield. Figures 2a and 2b illustrate
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the H and C NMR spectra, respectively. In Figure 2a, the
peaks at 1.9, 2.4, and 8.4 ppm are assigned to the CH of the ace-
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tate ion, the CH of the succinate, and the CH of the formate, re-
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spectively; cf., the chemical shifts of the CHs in thiophene are
7.1 and 7.3 ppm. Figure 2b shows the carboxyl groups, and that
the signals at 169, 182, and 183 ppm are assigned to the carbon-
centration of the only sulfur product, sulfide ion S2 in the aque-
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ous phase was determined by using methylene blue colorimetry
Copyright Ó 2004 The Chemical Society of Japan
Yoshida, Shinya
