In deep hydrodesulfurization (HDS) of polyaromatic sulfur-containing compounds in light gas oil catalyzed by Co-Mo/Al2O3, the behavior of methyl-substituted benzothiophenes, monomethyldibenzothiophenes (Cl-DBTs) and dimethyldibenzothiophenes (C2-DBTs) was traced under the following conditions: temperature: 290-390°C, LHSV: 4h-1, Gas/Oil: 120Nl/l. Three kinds of trimethylbenzothiophenes were detected at 290°C and one of them was detected even at 310°C. This compound could be 2, 3, 7-trimethylbenzothiophene. The conversions of Cl-DBTs other than 4-methyldibenzothiophene (4-MDBT) were very close to the conversion of nonsubstituted DBT. The behavior of three kinds of C2-DBTs other than 4, 6-dimethyldibenzothiophene (4, 6-DMDBT) was very similar to that of 4-MDBT. These C2-DBTs were deduced to be DBT substituted with a methyl group at 4-position. These results suggest that substitution only at 4- and 6-positions retards the HDS rate of DBT in light gas oil.
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Kabe et al. (1993) studied this question.