show the distribution equilibria for the sulfur contents in the
two-phase systems. Without DCA, the sulfur content was
reduced only slightly, since the light oil contains three-ring
aromatics which absorb visible light only weakly. The reduction
rate for the sulfur content was enhanced drastically however by
the addition of DCA. For an MeCN:light oil volume ratio of 3:1,
2
h of irradiation decreased the sulfur level to 0.05 wt%, and 10
h of irradiation decreased the value to 0.005 wt%, which is the
value presently strictly legislated in Sweden. Light oil contain-
ing such a low sulfur level has not been achieved so far by the
3
HDS method, even under severe operating conditions at 673 K.
Thus, the present method is applicable as an energy-saving deep
desulfurization process to meet with the newest regulation for
sulfur content in light oil, and requires only air bubbling and
irradiation with visible light, avoiding the use of hydrogen and
high pressure.
The present study thus describes a novel desulfurization
process for light oil, effected by the combination of electron-
transfer photooxygenation and liquid–liquid extraction using an
oil–MeCN two-phase system. This could be developed as a
desulfurization process utilizing solar irradiation as a light
source. Work is in progress to develop the overall process,
including a method for subsequent recovery of DCA from the
resulting solutions.
Fig. 3 Time-course variation of sulfur content in light oil for differing
solution volume ratios: MeCN:light oil = (2,5) 1:1, (8,-) 3:1 and (Ω,:)
7
:1; filled symbols = without DCA, open symbols = with DCA.
·
2
and O
2
). In alcoholic solvents, the oxygenation seems to be
·2
prevented, owing to the shorter lifetime for O
2
. Bacciochi
et al.10 have suggested the C–S cleavage mechanism for the
electron-transfer reaction of benzyl phenyl sulfide, but DBT
gave only the S oxidation product, as mentioned in the case of
diphenyl sulfide.11 This is attributable to a stabilization of the
C–S bond of DBT by thiophenic heterocycles. The rate of DBT
oxidation decreased with photoirradiation time, as shown in Fig.
The authors are grateful for financial support in the form of a
Grant-in-Aid for Scientific Research (No. 09555237) from the
Ministry of Education, Science, Sports and Culture, Japan, and
by The Foundation of Sanyo Broadcasting (for T. H.)
2
(a), since the DBT-O formed also quenches the DCA
9
21 21
fluorescence (kq, DBT-O = 7.37 3 10 L mol
s ) and
Notes and references
competitive electron-transfer occurs. This problem can be
1
2
B. Lee, J. Air Waste Manage. Assoc., 1990, 41, 16.
M. Houalla, D. H. Broderick, A. V. Sapre, N. K. Nag, V. H. J. De Beer,
B. C. Gates and H. Kwart, J. Catal., 1980, 61, 523.
solved by adding a larger quantity of DCA [Fig. 2(b)]. The two
2
photoproducts of DBT, DBT-O and DBT-O , are both highly
polarized and insoluble in non-polar light oil.12 Thus the
process has potential for the desulfurization of light oil.
The above photoprocess was applied to the desulfurization of
light oil containing ca. 0.18 wt% sulfur, which is below the
previous regulation in Japan (0.2 wt%). Light oil (50–200 ml)
and MeCN (200–350 ml) saturated with DCA were introduced
into the reaction vessel at MeCN:light oil volume ratios of 1:1,
3
4
T. Kabe, A. Ishihara and H. Tajima, Ind. Eng. Chem. Res., 1992, 31,
1
577.
A. Amorelli, Y. D. Amos, C. P. Halsig, J. J. Kosman, R. J. Jonker, M.
De Wind and J. Vrieling, Hydrocarbon Process., 1992, June, 93.
5 F. Berthou and V. Vignier, Int. J. Environ. Chem., 1986, 27, 81.
6 T. Hirai, K. Ogawa and I. Komasawa, Ind. Eng. Chem. Res., 1996, 35,
5
76.
7
8
9
T. Hirai, Y. Shiraishi, K. Ogawa and I. Komasawa, Ind. Eng. Chem.
Res., 1997, 36, 533.
Y. Shiraishi, T. Hirai and I. Komasawa, Ind. Eng. Chem. Res., 1998, 37,
3
:1 or 7:1 v/v. The solutions were photoirradiated using a high-
pressure mercury lamp with a 3 wt% NaNO solution filter,
2
combined with air bubbling at atmospheric pressure.
2
03.
J. G. Carbart and J. N. Pitts, Jr., Photochemistry, Wiley, New York,
968, p. 737.
Certain quantities of DBTs from the light oil in the light oil–
MeCN two-phase system transfer into the MeCN phase,
together with other aromatics. The photoirradiation of the two-
phase system thus causes the oxidation of the DBTs in the
MeCN, resulting in the successive removal of the DBTs from
1
10 E. Bacciochi, C. Crescenzi and O. Lanzalunga, Tetrahedron, 1997, 53,
4469.
11 J. Eriksen, C. S. Foote and T. L. Parker, J. Am. Chem. Soc., 1977, 99,
8
6455.
the light oil phase. Fig. 3 shows the effect of the addition of
1
2 J. Bundt, W. Herbel and H. Steinhart, J. High Resolut. Chromatogr.,
992, 15, 682.
DCA on the time-course variation of the sulfur content in the
light oil, with respect also to variations in the MeCN:light oil
volume ratio. The data points, at an irradiation time of zero,
1
Communication 8/06658B
2602
Chem. Commun., 1998, 2601–2602