DEVELOPMENT OF A MICROREACTOR SYSTEM FOR UNSTEADY-STATE FISCHER-TROPSCH SYNTHESIS (VIBROFLUIDIZATION, FLUIDIZED BED, VIBRATION, TRANSIENT).

摘要

Vibrofluidized microreactor systems have been developed for studies of unsteady-state Fischer-Tropsch synthesis. This development is aimed at preventing carbon deposition on a fused-iron catalyst in a novel reactor called the "heat-tray." This reactor involves a supernatant gas flowing over a shallow fluidized bed of catalyst particles. Three systems were built: (1) a vibrofluidized-bed microreactor system for obtaining baseline carbon deposition information under industrially important reaction conditions; (2) a sliding-plug vibrofluidized-bed microreactor system for rapid switching of feed gases in the F-T synthesis; and (3) a cold-flow microreactor model for studying the gas mixing characteristics of the sliding-plug vibrofluidized-bed microreactor.; The results show that catalyst defluidization occurred under steady-state synthesis conditions below 395(DEGREES)C using a feed gas of H(,2)/CO ratio of 2:1 or less. Above 395(DEGREES)C, the probability of hydrocarbon chain growth ((alpha)) on the fused-iron catalyst was low enough ((alpha) < 0.50) to prevent accumulation of high-molecular-weight species that cause defluidization. Carbon deposition was rapid above 395(DEGREES)C when a feed gas of H(,2)/CO ratio of 2:1 or less was used.; Spent catalyst fractions in the form of free-flowing catalyst and "bugdust" were quantitatively analyzed for carbon and iron. Mossbauer spectroscopic analysis of free-flowing catalyst showed mainly Hagg carbide (x-Fe(,5)C(,2)) and magnetite (Fe(,3)O(,4)) with a smaller fraction present as (alpha)-Fe. Scanning electron microscopic analysis of the bugdust revealed a mass of highly porous, fine particles with a high carbon content (18.30 wt%).; Cold-flow microreactor model studies show that rapid (on the order of seconds), quantitative switching of feed gases over a vibrofluidized-bed of catalyst could be achieved. Vibrofluidization of the catalyst bed induced little backmixing of feed gas over the investigated flow-rate range of 417 to 1650 actual mm('3)/s. Further, cold-flow microreactor model studies showed intense solid mixing when a -150 + 300 (mu) bed of fused-iron catalyst was vibrofluidized at 24 cycles per second with a peak-to-peak amplitude of 4 mm.; The development of this microreactor system has provided an easy way of accurately determining integral fluid-bed kinetics in a laboratory reactor. Further, the unique ability of the microreactor system to rapidly switch feed gases over an intensely-mixed solid has important applications in chemical kinetics and reaction engineering.