| Description |
In an attempt to better understand the fundamental chemistry of coal pyrolysis, the pyrolysis of model compounds containing structures similar to the prominent structures of bituminous coal has been studied. These compounds have been pyrolyzed in the temperature range 588 to 723 K (315 to 450°C) under isothermal constant volume batch reaction conditions. Experiments were conducted, depending on the temperature and model compound, at times from one to two-hundred forty minutes. Pyrolysis product mixtures were analyzed by gas chromatography and gas chromatography/mass spectrometry. The compounds successfully studied include 9-benzyl-l, 2, 3, 4-tetrahydrocarbazole (9BTHC), 1-benzyl-l, 2, 3, 4- tetrahydroisoquinoline-(1BTHIQ) and 4-benzylpiperidine(4BPP). The average material balances of 9BTHC and 1BTHIQ were 96.5% and 98.3%, respectively, with that of 4BPP being slightly lower (92.9%). The principal products observed during the pyrolysis of 9BTHC were 9-benzylcarbazole (9BC), 1, 2, 3, 4-tetrahydrocarbazole (THC), carbazole (CARB) and toluene (TOL). The pyrolysis of 1BTHIQ produced 1 - benzylisoquinoline (1BIQ), 1, 2, 3, 4-tetrahydroisoquinoline (THIQ), isoquinoline (ISOQ), and TOL. Observed as 4BPP pyrolyzed were 4-benzylpyridine (4BPY), pyridine (PYD), and TOL, with other minor products of varying amounts. The pyrolysis of 9BTHC and 1BTHIQ were conducted in the liquid phase at the lower temperatures, through a mixed phase region and completely in the vapor phase at the higher temperatures. The overall reaction order varied from about two to one as this progression from liquid to vapor phase occurred. No variation in product distributions occurred as the system varied, except that the conversion dramatically increased. The stabilization of the thermally produced radicals seems to preferentially occur by hydrogen abstraction from an unreacted or partially reacted model compound molecule, rather than intramolecular rearrangement. Mathematical models were developed i n an attempt to describe the pyrolysis of 9BTHC and 1BTHIQ utilizing the 'time-concentration' integral technique. Both compounds' pyrolyses are described most effectively with models consisting of all second order reactions. |
