| Hydrodesulfurization of dibenzothiophene catalyzed by presulfided CoO-MoO(,3)/(gamma)-Al(,2)O(,3) was studied at 300(DEGREES)C and 70 atm hydrogen partial pressure in a batch reactor and in a unique high-pressure flow microreactor. Under these conditions, dibenzothiophene is simultaneously hydrodesulfurized to give biphenyl and hydrogenated to give a mixture of cyclohexylbenzene and two highly reactive dibenzothiophenes, 1,2,3,4-tetrahydrodibenzothiophene and 1,2,3,4,10,11-hexahydrodibenzothiophene.; Reaction rates were determined for both reactions from differential conversion data obtained with a catalyst of constant activity over wide ranges of reactant and product concentrations and three temperatures (275, 300, and 325(DEGREES)C). Selectivity was found to be a strong function of temperature and hydrogen sulfide concentration. At 275(DEGREES)C in the presence of 0.07 gmole of hydrogen sulfide/liter, the rates of hydrogenolysis and hydrogenation were 4.67 x 10('-9) and 14.9 x 10('-9) gmole/(g of catalyst(.)sec), respectively. In contrast, at 325(DEGREES)C and in the presence of 0.0015 gmole of hydrogen sulfide/liter, the rates of hydrogenolysis and hydrogenation were 460 x 10('-9) and 104 x 10('-9) gmole/(g of catalyst(.)sec), respectively.; The rate of hydrogenation of dibenzothiophene is represented by a Langmuir dependence on dibenzothiophene concentration and a first-order dependence on hydrogen concentration. Striking evidence for a near total lack of inhibition of the hydrogenation reaction by hydrogen sulfide was found. To explain the lack of inhibition by hydrogen sulfide, a "sandwich" model is proposed in which dibenzothiophene must intercalate between MoS(,2) layers in order for hydrogenation of the benzenoid rings to occur.; The rate of hydrogenolysis of dibenzothiophene is represented by a Langmuir form of rate equation nearly identical to those proposed in the literature for hydrogenolysis of other thiophenic compounds. A Langmuir dependence on hydrogen concentration at high concentrations was observed. Hydrogenolysis reactions are strongly inhibited by hydrogen sulfide and occur on active sites different from those active for hydrogenation. |
