Hydrogenation-dehydrogenation of pyrenes catalysed by sulphided cobalt-molybdate at coal liquefaction conditions

Abstract

The hydrogenation and dehydrogenation kinetics of pyrene and hydropyrenes were studied in batch microreactors, both with and without catalyst, as a function of time, temperature, pressure and catalyst concentration. Under catalytic conditions at 648 K and 7.2 MPa, 4,5-dihydropyrene and pyrene reached equilibrium in 3 min with a molar ratio of 0.41. The heat of the hydrogenation reaction was —10 ± 1 kcal mol−1 compared with -12 kcal mol−1 for the hydrogenation of phenanthrene to 9,10-dihydrophenanthrene. The hydrogenation and dehydrogenation rates were negligible without catalyst. At 648 K with catalyst, 70% of the hydropyrenes reverted to pyrene in 5 min under nitrogen. The rapid pyrene—4.5-dihydropyrene equilibration implies that the equilibrium constant may be of more importance than the hydrogenation rate constant for predicting the amount of hydrogen available for donation by pyrene-like components in coal liquefaction solvents.